fuel supply handbook for biomass-fired power projects

China Biomass Cogeneration Development Project

Fuel Supply Handbookfor Biomass-Fired Power Projects

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China Biomass Cogeneration Development Project

Fuel Supply Handbook

for Biomass-Fired Power Projects

Fuel Supply Handbook for Biomass-Fired Power Projects

Prepared for World Bank/ESMAPColophonBTG Biomass Technology Group BVP.O. Box 8357500 AV EnschedeThe NetherlandsTel. +31-53-4861186Fax [email protected]

May 2010

Energy Sector Management Assistance Program (ESMAP) reports are published to communicate the results of ESMAP’s work to the development community with the least possible delay. Some sources cited in this paper may be informal documents that are not readily available.

The findings, interpretations, and conclusions expressed in this report are entirely those of the author(s) and should not be attributed in any manner to the World Bank, or its affiliated organizations, or to members of its board of executive directors for the countries they represent, or to ESMAP. The World Bank and ESMAP do not guarantee the accuracy of the data included in this publication and accepts no responsibility whatsoever for any consequence of their use. The boundaries, colors, denominations, other information shown on any map in this volume do not imply on the part of the World Bank Group any judgment on the legal status of any territory or the endorsement of acceptance of such boundaries.

iii

Contents

Acknowledgments ................................................................................................................................................................................ vii

Glossary ................................................................................................................................................................................................... viii

Acronyms and Abbreviations................................................................................................................................................................x

Executive Summary ............................................................................................................................................................................... xii

1 Introduction ....................................................................................................................................................................................... 1

2 Biomass as a Source of Energy ......................................................................................................................................................2

2.1 SourcesofBiomassFeedstock..............................................................................................................................................................................2

2.2 BiomassFeedstockCommonlyUsedinChina...............................................................................................................................................2

2.3 ThreeCategoriesofBiomassResidues..............................................................................................................................................................3

2.4 BiomassFuelCharacteristicsandFuelSelectionConsiderations...........................................................................................................32.4.1 BiomassConstituents.................................................................................................................................................................................42.4.2 ActualDensity,BulkDensity,andEnergyDensity..........................................................................................................................42.4.3 ParticleDimensionandParticleSizeDistribution..........................................................................................................................52.4.4 MoistureContent........................................................................................................................................................................................ 62.4.5 CalorificValue............................................................................................................................................................................................... 62.4.6 AshContentandQuality..........................................................................................................................................................................72.4.7 ChemicalComposition.............................................................................................................................................................................. 82.4.8 Contaminants............................................................................................................................................................................................... 10

2.5 Example:SomeExperienceswithBiomassFuel-FeedingSystems....................................................................................................... 10

2.6 ConclusionsandRecommendations................................................................................................................................................................ 102.6.1 Conclusions................................................................................................................................................................................................... 102.6.2 Recommendations...................................................................................................................................................................................... 11

3 Biomass Resource Assessment ................................................................................................................................................... 12

3.1 TypesofBiomassPotential................................................................................................................................................................................... 12

3.2 BasicApproachestoBiomassResourceAssessments.............................................................................................................................. 123.2.1 StatisticalAssessments............................................................................................................................................................................. 133.2.2 SpatiallyExplicitAssessments............................................................................................................................................................... 13

3.3 StepsinaBiomassResourceAssessment....................................................................................................................................................... 13

3.4 StrawResourceAssessmentsinChina............................................................................................................................................................. 14

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Contents

3.5 SpatiallyExplicitStrawResourceAssessments:AnExamplefromEurope....................................................................................... 153.5.1 StrawPotentialperRegion..................................................................................................................................................................... 153.5.2 StrawPotentialfor5x5kmGrids......................................................................................................................................................... 17

3.6 SizeoftheBiomassPowerPlant........................................................................................................................................................................ 18

3.7 ConclusionsandRecommendations................................................................................................................................................................ 183.7.1 Conclusions................................................................................................................................................................................................... 183.7.2 Recommendations..................................................................................................................................................................................... 19

4 Biomass Supply from Straw ......................................................................................................................................................... 21

4.1 Introduction................................................................................................................................................................................................................ 21

4.2 TheTechnologyandMethodsofStrawProduction................................................................................................................................. 214.2.1 Production,Raking,andCollectionofStraw.................................................................................................................................. 214.2.2 TransportingStrawtoStorage............................................................................................................................................................. 224.2.3 Long-TermStorage.................................................................................................................................................................................... 224.2.4 DeliveryfromLong-TermStoragetoPowerPlant....................................................................................................................... 224.2.5 HandlingattheBiomassPowerPlant............................................................................................................................................... 23

4.3 CurrentStatusofStrawSupplyinChina....................................................................................................................................................... 244.3.1 StrawAvailabilityinChina...................................................................................................................................................................... 244.3.2 StrawCollectionPracticesinChina................................................................................................................................................... 24

4.4 StrawSupplyinChina:CaseStudies................................................................................................................................................................ 25CaseStudyA: 30MWBiomassPowerPlantinShandongProvince.................................................................................................. 25CaseStudyB: 12MWBiomassPowerPlantinHenanProvince.......................................................................................................... 26CaseStudyC: 30MWBiomassPowerPlantinHenanProvince......................................................................................................... 26CaseStudyD: 24MWBiomassPowerPlantinJiangsuProvince........................................................................................................ 26

4.5 StrawSupplyinEurope:CaseStudies............................................................................................................................................................. 26CaseStudyE: 39.7MWBiomass-FiredPowerPlantinEnsted,Denmark........................................................................................ 26CaseStudyF: 38MWStraw-FiredPowerPlantinEly,UnitedKingdom......................................................................................... 26CaseStudyG:25MWStraw-FiredPowerPlantinSangüesa;Navarra,Spain................................................................................ 27

4.6 ConclusionsandRecommendations............................................................................................................................................................... 274.6.1 Conclusions.................................................................................................................................................................................................. 274.6.2 Recommendations.................................................................................................................................................................................... 28

5 Biomass Supply from Forestry Residues ................................................................................................................................. 29

5.1 Introduction............................................................................................................................................................................................................... 295.1.1 ForestryResiduesTypesandYields................................................................................................................................................... 295.1.2 ForestryResiduesProductionCostFactors.................................................................................................................................... 29

5.2 Harvesting(Extraction).......................................................................................................................................................................................... 305.2.1 ExtractioninConnectionwithFinalFelling.................................................................................................................................... 305.2.2 ExtractioninConnectionwithClearingandThinning................................................................................................................ 31

5.3 Comminution............................................................................................................................................................................................................. 315.3.1 ComminutionatLanding......................................................................................................................................................................... 315.3.2 ComminutionattheSource..................................................................................................................................................................335.3.3 ComminutionattheEnd-UseFacility............................................................................................................................................... 345.3.4 ComminutionataTerminal....................................................................................................................................................................37

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Contents

5.4 BiomassFuelStorage...............................................................................................................................................................................................375.4.1 StoringForestryResiduesatRoadside..............................................................................................................................................375.4.2 StoringForestryResiduesatBiomass-FiredPowerPlant.......................................................................................................... 38

5.5 BioenergyFuelChainCaseStudiesfromChina.......................................................................................................................................... 38

5.6 BioenergyFuelChainCaseStudiesfromEurope....................................................................................................................................... 38

5.7 Conclusions................................................................................................................................................................................................................ 39

6 Managing the Biomass Fuel Supply .......................................................................................................................................... 42

6.1 OrganizingtheBiomassFuelSupply................................................................................................................................................................ 42

6.2 BiomassFuelContracting..................................................................................................................................................................................... 426.2.1 BiomassFuelQuantity..............................................................................................................................................................................436.2.2 BiomassFuelQuality.................................................................................................................................................................................436.2.3 BiomassFuelPricing.................................................................................................................................................................................. 446.2.4 OtherSupplyContractConsiderations........................................................................................................................................... 44

6.3 BiomassFuelSupplyControl.............................................................................................................................................................................. 456.3.1 IntroductiontoFuelQualityControlMeasures........................................................................................................................... 456.3.2 QualityManagementforFuelSupplyControl..............................................................................................................................466.3.3 CaseStudy:QualityManagementofAgriculturalResiduesinDenmark........................................................................... 476.3.4 CaseStudy:QualityManagementofForestryResiduesinFinland...................................................................................... 47

6.4 MitigationStrategiesforManagingSupplyRisks.......................................................................................................................................48

6.5 ConclusionsandRecommendations...............................................................................................................................................................49

References and Other Resources ...................................................................................................................................................... 51

Annexes1 InternationalExperiencewithGrowingEnergyCrops........................................................................................................................................ 55

2 FuelStandardsandSpecifications............................................................................................................................................................................... 58

3 CalculationoftheNetCalorificValueatDifferentBasesandEnergyDensityasReceived—EN14961-1...................................... 61

4 TypesofBiomassPotential............................................................................................................................................................................................. 63

5 DeterminationofYieldfromAgriculturalCropsandResidues......................................................................................................................64

6 GuidelinesforPlanningaBiomassResourceSurvey............................................................................................................................................66

7 FinnishResearchintoReducingBiomassSupplyCosts....................................................................................................................................... 67

8 SampleBiomassFuelSupplyContract.......................................................................................................................................................................68

9 EnergyDensityofForestChips..................................................................................................................................................................................... 77

10 AlternativesforReflectingEnergyContentinBiofuelPrice............................................................................................................................80

11 ExampleoftheSamplingandHandlingProcessforWoodFuels....................................................................................................................81

12 QualityManagementSystemforSolidBiomassSupply.................................................................................................................................... 82

13 FuelSupplyRiskMatrix.....................................................................................................................................................................................................84

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Contents

Figures2.1 BiomassAppearancesandVolumes...............................................................................................................................................................................42.2 TheNetCalorificValue(NCV0=19MJ/kg)asaFunctionofWetDryBasisMoisture(Mandu)....................................................... 62.3 BottomAshStoredinaStorageTank(left),FlyAshIstheAshThatDerivesfromFlueGasCleaning(right)............................... 83.1 TheInfluenceofSustainabilityCriteriaonBiomassPotential......................................................................................................................... 133.2 StrawYieldasaFunctionofGrainYield.................................................................................................................................................................... 163.3 TotalStrawProductionperRegion(tons)................................................................................................................................................................. 163.4 StrawUsedperHeadofCattle...................................................................................................................................................................................... 173.5 AvailableStrawperRegion(tons).................................................................................................................................................................................. 173.6 AvailableStrawper5x5kmGridCell(tons).............................................................................................................................................................. 174.1 TurningandRakingofSwathsBeforeBaling............................................................................................................................................................ 214.2 TractorandBalerinOperation....................................................................................................................................................................................... 214.3 LoadingStrawintheField............................................................................................................................................................................................... 224.4 OutdoorStorageofStraw.............................................................................................................................................................................................. 234.5 PoleBarninCaliforniaforStorageofRiceStraw.................................................................................................................................................. 234.6 TruckforLong-DistanceStrawTransport................................................................................................................................................................. 234.7 Unloading12BalesinOneOperation......................................................................................................................................................................... 235.1 TypicalCostStructureofForestChipsinFinland—PricesatPlant,ExcludingVAT,2002.................................................................... 305.2 ForestChipsProductionChainBasedonChippingatRoadside(Landing).................................................................................................325.3 ChipperTruck........................................................................................................................................................................................................................335.4 ForestChipsProductionChainBasedonTerrainChipping............................................................................................................................... 345.5 ForestChipsProductionChainBasedonComminutionofLooseResiduesatanEnd-UseFacility............................................... 355.6 Timberjack1490DResidueBaler................................................................................................................................................................................... 355.7 LoadingCRLBundlesonaForwarder......................................................................................................................................................................... 365.9 ProductionChainBasedonCompositeResidueLogs........................................................................................................................................ 365.8 StorageofCRLBundles.................................................................................................................................................................................................... 365.10 AWoodChipsDeliverySystemIntegratingDifferentSupplyConcepts.................................................................................................... 395.11 AForestryResiduesSupplySystemBasedonBundledSlashDelivery........................................................................................................406.1 CostStructuresofDifferentForestryResiduesFuelsinFinland.................................................................................................................... 456.2 MethodologytoApplyandImplementQualityAssurance............................................................................................................................. 47A2.1 CEN/TC335WithintheBiomass-Biofuel-BioenergyField................................................................................................................................ 58A2.2 ExampleofClassificationBasedonOriginandSource,MajorTradedForm,andProperties............................................................ 59A2.3 ExampleofaFuelQualityDeclarationUsedforBulkDelivery.......................................................................................................................60A9.1 ExamplesoftheEnergyDensityofSelectedFuels,ShowingtheLoadVolumeRequiredfor1toe............................................... 78A12.1 DeterminationofCustomerRequirements............................................................................................................................................................. 82

Tables2.1 SummaryofTypicalPropertiesofPrimary,Secondary,andTertiaryResidues...........................................................................................32.2 CompositionofDifferentBiomassTypes(percentageofweight,moisturefree).....................................................................................42.3 BulkDensitiesofDifferentBiomassSources(indicativevalues)........................................................................................................................52.4 MethodologytoMeasuretheBulkDensityofForestChips..............................................................................................................................52.5 FuelDataatTypicallyOccurringMoistureContent...............................................................................................................................................72.6 GuidingValuesandGuidingRangesforElementsinBiomassAshesforUnproblematicThermalUtilization............................. 92.7 GuidingValuesandGuidingRangesforElementsinBiomassFuelsforUnproblematicThermalUtilization............................... 93.1 YieldofMainCropStrawsinChinaandTheirHeatingValues,2005............................................................................................................ 153.2 TypicalScaleofOperationforVariousSizesandTypesofBioenergyPlants............................................................................................ 195.1 ForestProductivityinFinland........................................................................................................................................................................................ 30A9.1 TheEnergyDensityofForestBiomassChipsandCrushedBarkinFinlandat40PercentMoistureContent............................. 77

vii

Investment Consulting & Management Co. Ltd, led by Ding Hang with the participation of Jia Xiaoli, Li Xiaozhen, and Wu Fan, prepared a background study report to analyze the current development status of the biomass power industry in China, and provided valuable input to this fuel supply handbook.

The World Bank team that supervised the consultants’ work and the preparation of the report consisted of Ximing Peng, task team leader, and Noureddine Ber-rah, energy advisor. The team would like to give spe-cial recognition to peer reviewers Xiaodong Wang, Senior Energy Specialist at the World Bank; Shiping Qin, Biomass Specialist at the Energy Research Insti-tute of the National Development Reform Commis-sion; and Huiyong Zhuang, Project Manager at the National Bio Energy Company of China. The team would like to also thank Defne Gencer, Energy Ana-lyst at the World Bank, editor Rebecca Kary, editor Sherrie Brown, graphic designer Gemma Drohm, and designer Laura Johnson for their efforts in producing the final publication.

The World Bank team also extends its gratitude to Ede Ijjasz, Sector Manager at the World Bank’s China and Mongolia Sustainable Development Unit, and Amarquaye Armar, Manager, ESMAP, who provided the resources and guidance to make this publication possible.

Acknowledgments

This publication is part of a technical assistance activity funded by the Energy Sector Management Assistance Program (ESMAP) for the promotion of biomass proj-ects in Inner Mongolia. This technical report was pre-pared with a view to identifying means for addressing fuel supply problems faced by biomass projects, not only in Inner Mongolia, but also in other provinces in China, as well as in many developing countries, where fuel supply problems have, in many cases, delayed, or even derailed, biomass projects.

This technical report was prepared by BTG Biomass Technology Group BV.1 The primary authors were John Vos and Lud Uitdewilligen of BTG. The report also benefited from the contributions of Eija Alakanga of the Technical Research Center of Finland (VTT), Patricia Thornley of the University of Manchester, and Alexandre Thébaud of BTG. Its dissemination is part of the World Bank’s efforts to share international expe-riences in renewable energy and to ensure the success of biomass projects in developing countries.

A team of experts from the China Energy Conser-vation Investment Corporation (CECIC) Blue-Sky

1. BTG Biomass Technology Group BV is a Dutch firm of bio-mass specialists. For more than 20 years, BTG has specialized in the process of conversion of biomass into useful fuels and energy.

The financial and technical support by the Energy Sector Management Assistance Program (ESMAP) is gratefully acknowledged. ESMAP—a global knowledge and technical assistance partnership administered by the World Bank and sponsored by official bilateral donors—assists low- and middle-income countries, its “clients,” to provide modern energy services for poverty reduction and environmentally sustainable economic development. ESMAP is governed and funded by a Consultative Group (CG) comprised of official bilateral donors and mul-tilateral institutions, representing Australia, Austria, Canada, Denmark, Finland, France, Germany, Iceland, the Netherlands, Norway, Sweden, the United Kingdom, and the World Bank Group.

viii

Glossary

Agricultural residues: Byproducts of agricultural prac-tice (cultivation of farms and harvesting activities), labeled as “primary” and byproducts of the process-ing of agricultural products, for example, for food or feed production, labeled as “secondary.” Straw of wheat and corn are examples of primary agricultural residues. Bagasse and rice husks are examples of sec-ondary agricultural residues.

Bioenergy: All types of energy derived from biofuels, including wood energy and agro-energy.

Biofuel: Any solid, liquid, or gaseous fuel produced from biomass.

Biomass: The organic matter generated by the photo-synthesis of plants. The source of biomass will depend to some extent upon the availability in the local area. Basically, five categories of raw materials are used for biomass fuel production: forestry residues, energy crops, agricultural residues, food waste, and industrial waste and coproducts.

Biomass-fired power generation: Biomass is burned in specially designed boilers to generate high-pressure steam to drive the turbine and transfer the power to the generator for electricity generation.

Biomass resource assessment: An assessment to deter-mine the availability of biomass for a power plant. The type of potential is a crucial criterion when dis-cussing biomass availability because it determines the approach and methodology and thereby the data requirements of the biomass resource assessment.

Bulk density: Mass of a portion of a solid fuel divided by the volume of the container that is filled by that portion under specific conditions.

Calorific value, heating value: Energy amount per unit mass or volume released on complete combustion.

Density: Ratio of mass to volume. It must always be stated whether the density refers to the density of individual particles or to the bulk density of the mate-rial and whether the mass of water in the material is included.

Dry basis: Condition in which the solid biofuel is free from moisture.

Dry matter: Material after removal of moisture under specific conditions.

Energy crops: Plants grown to produce biofuels, or directly exploited for their energy content. Commer-cial energy crops are typically densely planted, high-yielding crop species, such as Miscanthus, Salix L., or Populus L.

Feedstock: Any biomass destined for conversion to energy or biofuel. For example, corn is a feedstock for ethanol production, and soybean oil is a feedstock for biodiesel. Cellulosic biomass has the potential to become a significant feedstock source for biofuels.

Forestry residues: Both primary residues, that is, left-overs from cultivation and harvesting activities (such as twigs, branches, and precommercial thinning mate-rial) and secondary residues, that is, those resulting from any processing steps (such as sawdust, bark, and black liquor).

Fossil fuel: A nonrenewable energy source produced by the remains of living organisms that built up under-ground over geological periods in liquid (oil), solid (coal, peat), and gaseous (natural gas) forms.

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Glossary

Gray straw: Straw that has been lying in the field and that has been exposed to rain has a reduced content of the corrosive matter, chlorine and potassium. Contrary to “yellow” straw, this “gray” straw is less wearing on the boiler, since part of the matter that corrodes the boiler wall and tubes has been removed. Gray straw also has a somewhat higher calorific value than yellow straw.

Organic matter: Combustible fraction of dry matter.

Particle size distribution: Proportion of various particle sizes in a solid fuel.

Renewable energy: Energy produced from sources that can be renewed indefinitely, for example, hydro, solar, geothermal, and wind power, as well as sustainably produced biomass.

Roundwood: Wood in its natural state as felled, with or without bark.

Sawdust: Fine particles created when sawing wood.

Straw: Straw is an agricultural byproduct, the dry part of a cereal plant, after the grain or seed has been removed.

Quality management system: A tool to control the over-all supply chain to ensure fuel quality.

Volume: Amount of space that is enclosed within an object.

Wet basis: Condition in which the solid biofuel con-tains moisture.

Wood chips: Chipped woody biomass in the form of pieces with a defined particle size produced by mechanical treatment with sharp tools, such as knives. Wood chips have a subrectangular shape with a typi-cal length of 5–50 mm and a low thickness compared with other dimensions.

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Acronyms and Abbreviations

BEE Biomass Energy Europe

C Carbon

Ca Calcium

CCP Critical control point

Cd Cadmium

CEN European Committee for Standardization

CEN/TC European Committee for Standardization/Technical Committee

CHP Combined heat and power

Cl Chlorine

CRESP China Renewable Energy Scale-Up Program

CRI Crop residue index

CRL Composite residue log

d.b. Dry basis

DIN German Standardization Institute (Deutsches Institut für Normung)

ESMAP Energy Sector Management Assistance Program

EU European Union

Eurostat Statistical office of the European Union

GCV Gross calorific value (same as HHV)

GIS Geographical Information System

H Hydrogen

HCL Hydrochloric acid

HHV Higher heating value

K Potassium

LHV Lower heating value

MC Moisture content

N Nitrogen

NCV Net calorific value (same as LHV)

NOx Nitrogen oxides

NUTS Nomenclature of Territorial Units for Statistics, a geocode standard for referencing the administrative divisions of countries for statistical purposes (nomenclature d’unités territoriales statistiques)

O Oxygen

odt Oven dry ton

OECD Organisation for Economic Co-operation and Development

ONORM Austrian Standardization Institute (Österreichisches Normungsinstitut)

QA Quality assurance

QM Quality management

RE Renewable energy

RF Recoverability factor

RPF Residue-to-product factor

S Sulfur

SOx Sulfur oxides

SRWC Short-rotation woody crops

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Acronyms and Abbreivations

UK United Kingdom

VTT Technical Research Centre of Finland (Valtion Teknillinen Tutkimuskeskus)

w.b. Wet basis

wt% on d.b. Weight percent

Zn Zinc

UNITS OF MEASURE

cm Centimeter

GJ Gigajoule

GW Gigawatt

GWh Gigawatt-hour

ha Hectare

hr Hour

kg Kilogram

km Kilometer

km2 Square kilometer

kWth Kilowatt-thermal

kWh Kilowatt-hour

m Meter

m2 Square meter

m3 Cubic meter

MJ Megajoule

mu Chinese unit of area (1 ha = 15 mu)

MW Megawatt

MWe Megawatt electric

MWh Megawatt-hour

MWth Megawatt thermal

MWh/m3 Megawatt-hours per cubic meter

t Ton (metric)

tce Ton of coal equivalent

toe Ton of oil equivalent

TWh/a Terawatt-hours per year

yr Year

xii

Executive Summary

Biomass energy development in China is supported by the Energy Sector Management Assistance Program (ESMAP) project entitled China Biomass Cogenera-tion Development, Heating Network Development. Biomass Technology Group BV (BTG) was commis-sioned by ESMAP to write an operation-oriented handbook to provide new investors in the sector with guidance on managing their fuel supply risk during the planning and preparation stage of bioenergy projects. The handbook is divided into five chapters following the Introduction.

Biomass as a Source of Energy

The characteristics of the biomass used as fuel have a direct impact using biomass power plant design, oper-ation, and performance. They also have an impact on the best way to handle fuel (for example, collection, transport, pretreatment, and storage). Less homoge-neous and/or low-quality fuels need more sophisti-cated combustion systems. Similarly, appropriate fuel selection is vital in managing fuel supply risk. Fuel standards and specifications have been developed to support the matching of fuel supply and energy sys-tem. A plant design and environmental permits that allow as much fuel flexibility as possible are recom-mended in anticipation of possible changes in biomass fuel supply.

Biomass Resource Assessment

During the planning stage of the biomass-fired power plant project, a biomass resource assessment is required to determine the biomass availability in the selected area. It is better not to rely exclusively on any prior biomass resource assessment, if and where available, but to carry out a dedicated survey to collect, verify,

and/or validate biomass resource data. It is impor-tant to use a consistent biomass resource assessment methodology that not only applies theoretical crop-to-residue factors, but also considers the competitive uses of biomass, and material losses incurred during biomass collection, storage, and transport caused by climate, humidity, and other reasons. Furthermore, it is always necessary to involve an experienced pro-fessional (consultant organization) to support the resource assessment.

Biomass Supply from Straw

In the preparation stage of a bioenergy project, a good understanding and organization of the biomass supply chain are necessary to realize an optimal fuel supply to the power plant. When using straw for energy purposes, the supply chain logistical principles are basically no different than for traditional straw applications. However, the scale of operation is sig-nificantly larger, calling for some degree of mecha-nization and automation. The challenge for Chinese straw suppliers is to organize the highest throughput in straw collection at the lowest cost. Important les-sons can be learned from Denmark, where practical experience operating biomass power and combined heat and power (CHP) plants using wheat straw has been gained since the late 1980s. However, because of different local circumstances in China, the Danish experience cannot be copied directly.

Biomass Supply from Forestry Residues

For optimal management of fuel supply to the bio-mass-fired power plant, a good understanding and organization of the biomass supply chain is required. When using forestry residues for energy production,

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Executive Summary

it is crucial to consider harvesting (extraction), com-minution (chipping or crushing), transportation, and storage costs carefully. The selection of the forest fuel harvesting technology requires complex technical analysis, taking into account the annual need for for-est fuels and other fuels, annual availability of forest fuels, location of plant, size of plant yard, type of bio-mass energy plant, prevailing technology to produce chips, and the need for Geographical Information Sys-tem– (GIS-) based availability and cost analysis.

The production methods and cost breakdown for for-est chips vary considerably between countries and regions. Generally, the cost depends on how well the unit operations in the supply chain are organized and structured. Furthermore, the efficiency of a procure-ment system is highly dependent on the environment and infrastructure in which it operates. Economic, social, ecological, industrial, and educational factors, as well as local traditions, also have effects. Conse-quently, there is no single production system that can be seen as the optimal solution for all countries, or for all situations within a given country.

Managing the Biomass Fuel Supply

The aim of biomass contracting is to secure the long-term availability of biomass fuel for the right price; therefore, long-term contracts are preferred. At the plant planning stage, biomass should be contracted for before the biomass-fired power plant goes onstream, to have sufficient biomass fuel readily available before initial operation.

At the plant operational stage, it is important to ensure that biomass fuel delivered to the biomass power plant meets the contractual fuel standards and specifications. Biomass fuel not in compliance with the contractual standards and specifications can cause operational problems with the combustion process, or can decrease the equipment life span. Fuel quality con-trol is necessary throughout the whole supply chain, and it is recommended that investors apply some kind of quality management (QM) system. It is important to write practical procedures into a manual that can serve as a tool for each unit operation in the biomass supply chain, such that all the processes and interac-tions are fully under control. Finally, an instrument for assessing fuel supply risks and developing mitiga-tion strategies is described.

1

This handbook provides an overview of the main top-ics that need consideration when managing the sup-ply of biomass to large biomass power plants. It will help investors in China to develop, with assistance of local biomass supply experts, their own solutions. The focus is on biomass residues, in particular agricultural residues (mainly straw and stalks) and forestry resi-dues (mainly residues from forestry operations).

The handbook is intended to provide the reader a com-prehensive overview of the relevant issues to consider when planning and preparing an investment in a bio-mass power plant. Each chapter covers (a) a thorough introduction of the relevant topics; (b) best practices and case studies from China and from leading over-seas countries, showcasing international experience; and (c) lessons learned, practical tips, and sugges-tions for candidate investors in biomass energy plants. In particular, the report describes the experience of Scandinavian countries as an illustration of best prac-tices. Denmark is a world leader in large-scale energy production from straw, and Finland and Sweden are world leaders in large-scale energy production from forestry residues.

With regard to biomass supply, each biomass power plant needs its own solution based on local conditions and circumstances and, unlike in China, Scandinavia biomass production is highly mechanized. The expe-rience gained in Denmark, Finland, and Sweden is

included to give prospective Chinese investors a sense of the type of organization required, the levels of pro-ductivity achievable, and the current technological state of the art, so as to appreciate better the possi-bilities and challenges of arranging large-scale, highly mechanized biomass supplies. Solutions developed and applied in Scandinavia cannot be copied one-to-one in China, but the approach, technology, and logis-tics developed elsewhere in the world can give Chinese investors insight into and inspiration for setting up and optimizing biomass supply chains in China.

This handbook covers a wide range of topics related to biomass fuel supply risk in the planning and prepa-ration stages for a biomass-fired power plant. chapter 2 introduces the use of biomass as an energy source, including fuel selection considerations and the fuel standards and specifications required to match a par-ticular fuel supply to a power generation system. chap-ter 3 describes the use of biomass resource assessments at the project planning stage. chapters 4 and 5 give insight into the biomass supply from straw and for-estry residues, respectively. Fuel supply management is covered in chapter 6, which addresses the topics to be considered both at the plant planning stage and at the operational stage. It describes a methodological approach for fuel inspection and quality control, as well as an instrument for assessing fuel supply risks and developing mitigation strategies.

1. Introduction

2

2. Biomass as a Source of Energy

animal bedding, such as poultry litter; and organic material from excess production or insufficient market, such as grass silage.

• Food waste comes from food and drink manufac-ture, preparation, and processing, and includes post-consumer waste. Along the entire food sup-ply chain, huge quantities of waste are produced that are distinguishable as wet and dry waste. The majority consists of waste that has relatively high moisture content.

• Industrial waste and coproducts result from manu-facturing and industrial processes. During many industrial processes, residues, waste, or coproducts are produced that are further divided into woody and nonwoody materials (such as paper pulp and wastes, textiles, or sewage sludge).

2.2 Biomass Feedstock Commonly Used in China

In China, all the above-mentioned raw material cate-gories are available, in principle, for power generation and eligible for support under the Renewable Energy (RE) Law that entered into force on January 1, 2006. In practice, much of the power generation capacity expansion since has been based on agricultural resi-dues, that is, maize stalks, cotton stalks, wheat straw, rice stalks, and husks. A few projects also use forestry wastes, such as branches of fruit trees, tree bark, roots of fast-growing poplar, shrub stumps, and wood-pro-cessing wastes. The fuel used would seem to depend mainly on what biomass is available in sufficient quantities and at an affordable price. Although energy crops offer substantial potential, in particular in the medium to long term, the biomass quantities required and the current level of financial support available under the RE law for biomass-based power generation is insufficient to render energy crop–based power gen-eration economic. Generally speaking, the cultivation

This chapter introduces different categories of raw material that can be used as biomass feedstock (sec-tion 2.1), explains why this handbook will focus on the use of biomass residues as feedstock (section 2.2), and presents a classification of biomass residues (sec-tion 2.3).

Those topics are followed by a description of the most important fuel characteristics of agricultural and forestry biomass residues, and a discussion of the relevance of these characteristics for the design, opera-tion, and performance of biomass-fired power plants (section 2.4). Finally, some examples of operational experience with biomass fuel-feeding systems in North America are presented (section 2.5).

2.1 Sources of Biomass Feedstock

A wide variety of raw materials can be used to produce biomass fuels. The source of biomass will depend to some extent on the availability in the local area. Basi-cally, five categories of raw materials are used for bio-mass fuel production (Biomass Energy Centre 2009).

• Forestry residues result from forestry, cultivation and management of trees, or from wood processing activities. Wood fuel can be derived from conven-tional forestry practice and from tree management operations and the management of parks, gardens, and transport corridors.

• Energy crops are high-yield crops grown specifi-cally for energy applications. Energy crops can be categorized into short-rotation energy crops, grasses and agricultural energy crops, and aquatics (hydroponics).

• Agricultural residues are derived from agriculture harvesting or processing. Agricultural residues can be further differentiated into the arable crop resi-dues of straw or husk; animal manures and slurries;

3


of dedicated energy crops will only be a viable option for large-scale biomass production in the long term.2 For this reason, this handbook focuses on the biomass categories most widely used in the recently estab-lished Chinese biomass-fired power plants: biomass residues.

2.3 Three Categories of Biomass Residues

Biomass residues can be divided into primary, second-ary, and tertiary residues, released after harvest, dur-ing processing, or after end use, respectively.3 Table 2.1 sketches typical characteristics of the various resi-due categories.

Agricultural residues are the byproducts of agricul-tural practice (cultivation of farms and harvesting activities), labeled as “primary,” and byproducts of

2. Annex 1 discusses international experience with growing dif-ferent types of energy crops for solid biomass production.3. Until 2006, most of the biomass-fired generation capacity installed in China was based on secondary residues, in particu-lar on bagasse, the fibrous residue that remains after sugarcane or sorghum stalks are crushed to extract their juice. Second-ary residues are generally the most attractive feedstock for bioenergy production because they are released centrally and are relatively clean. Primary residues are the best alternative. Although collection costs are higher, their availability is gener-ally substantial.

the processing of agricultural products, for example, for food or feed production, labeled as “secondary.” Straw from wheat and corn are examples of primary agricultural residues. Bagasse and rice husks are exam-ples of secondary agricultural residues.

Forestry biomass refers to harvests from forests avail-able for wood supply. Forestry residues include both primary residues, that is, leftovers from cultivation and harvesting activities (such as twigs, branches, and precommercial thinning material), and secondary resi-dues, that is, those resulting from any processing steps (for example, sawdust, bark, and black liquor).

2.4 Biomass Fuel Characteristics and Fuel Selection Considerations

Because of the wide variety of raw materials, there is also considerable variation in fuel characteristics, even when limiting the assessment to forestry and agricul-tural residues. This section explores the main biomass fuel characteristics, such as biomass constituents, bulk and energy density, particle dimension and particle size distribution, moisture content, calorific value, ash content and quality, chemical composition, and contaminants.

Table 2.1 Summary of Typical Properties of Primary, Secondary, and Tertiary Residues

Characteristic Primary residues Secondary residues Tertiary residues

Origin Harvest residues Processing residues Residues after end use

Typical examples Stalks, straw, thinnings Bagasse, husks, sawdust Demolition wood, organic waste

Release During harvest season Part of the year, or

throughout the year

Throughout the year

Accessibility Distributed on land, during

harvest

High, typically released centrally

in factory, during processing

Centrally at waste collection site,

after end use

Collection costs High Low Low to moderate

Contamination Possibly sand, which can

lead to high ash content

Generally low Depends on use, increased risk of

foreign materials (other waste materials)

Alternative uses Mainly soil fertilization and

cattle feed and bedding

Cattle feed, factory energy

demand

Incineration with energy recovery

Source: BTG.

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These biomass fuel characteristics are relevant for the design, operation, and performance of the biomass-fired power plant. It is also important to take into account that the availability of a biomass fuel may change over time (as other opportunities arise or origi-nal fuel sources dry up). Appropriate fuel selection is an important aspect of managing fuel supply risks (see chapter 6).

Wiltsee (2000) argues that selecting a power plant design and applying for permits that allow maximum flexibility in the use of feedstock are the best strategy to deal with a potential change in fuel mix.

2.4.1 Biomass ConstituentsAt the molecular level, biomass consists of three mole-cule types: cellulose, hemi-cellulose, and lignin. Cellu-lose is the structural component of the primary cell wall of green plants. Cellulose is a straight, stiff molecule consisting of several thousands of glucose (C6-) units.

Hemi-cellulose molecules are polymers built of about 200 C5- and C6- sugars with a much smaller degree of polymerization, embedded in the cell walls of plants. Lignin, with an empirical formula of approximately CH1.5O0.6 , is a three-dimensional polymer composed of phenolic units. It serves as the “glue” between indi-vidual cells. Table 2.2 presents the composition of dif-ferent types of biomass.

2.4.2 Actual Density, Bulk Density, and Energy DensityThe actual density of different sources of biomass does not vary much. There is, however, a large range of different shapes and sizes of biomass (for exam-ple, wood is available as roundwood, stacked logs, chopped logs, or forest chips), as can be seen in figure 2.1, which influences biomass weight in relation to volume. Therefore, it is better to talk about the bio-mass bulk density. Table 2.3 shows bulk densities for straw, wood, and coal.

Table 2.2 Composition of Different Biomass Types (percentage of weight, moisture free)

Biomass type Cellulose Hemi-cellulose Lignin Extractives Ash

Softwood 41 24 28 2 0.4

Hardwood 39 35 20 3 0.3

Pine bark 34 16 34 14 2

Straw (wheat) 40 28 17 11 7

Rice husks 30 25 12 18 16

Peat 10 32 44 11 6

Source: Wagenaar, Prins, and Swaaij 1994.

Figure 2.1 Biomass Appearances and Volumes

Source: Francescato and others 2008.

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Because biomass has a lower bulk density and a lower energy density than coal or natural gas, larger quanti-ties are required to produce the same electrical output, and the boiler design needs to be different. Energy den-sity, the result of dividing the bulk density by the net calorific value, influences the fuel logistics (transport and storage), the fuel-feeding system, and the process control of the thermal conversion process (van Loo and Koppejan 2002). When the biomass-fired power plant is to run on a biomass fuel with a low bulk den-sity, densification of the raw material may be neces-sary, depending on the transport distance between the collection area for the raw material and the power plant.

A methodology to measure the bulk density of forest chips through sampling is described in table 2.4.

2.4.3 Particle Dimension and Particle Size DistributionDepending on the supply chain, biomass fuels arrive at the power plant as unit or bulk material. For agri-cultural residues such as straw, the material is usually delivered in bales (unit material). Wood is often deliv-ered chipped or pelletized (bulk material). The parti-cle dimension and particle size distribution need to be carefully matched with the applicable (a) fuel-feeding system and (b) combustion technology.

Biomass feeding systems impose limitations on the size and shape of feedstock. For example, oversized fuel particles can jam certain fuel-feeding systems. Some

feeding systems are capable of handling fuels with a broad range of particle sizes (such as walking floors and “ram stokers”), whereas others tolerate only a narrow range of particle sizes (for example, pellet burners). The variation in particle size, or particle size distribution, can be homogeneous (for example, pellets) or nonho-mogeneous (for example, untreated bark).

Depending on the type, size, shape, and quality of the biomass fuel, different combustion technologies are applied. Less homogeneous and lower-quality fuels need more sophisticated combustion systems. Low-quality biomass can only be combusted properly in medium- and large-scale systems.

Table 2.4 Methodology to Measure the Bulk Density of Forest Chips

1. Use a bucket of known volume (e.g., 13 liters) and a

pair of scales.

2. Take a representative sample from the truck

container, e.g., 3 buckets from a 40 m3 container

(ref. CEN/TS 14778-1), and fill the bucket without

compacting the chips.

3. Weigh the samples and divide their mean value (kg)

by the known volume (liters); e.g.,

(3.25 kg x 1,000 liters) 4 13 liters = 250 kg per measurement.


Table 2.3 Bulk Densities of Different Biomass Sources (indicative values)

Biomass shape Bulk density (kg/m3)

Straw (chopped) 50

Straw (big bales) 130

Straw pellets 600

Wood chips 250

Sawdust 200

Wood pellets 650

Coal 850


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Fuel standards have been introduced for biomass to become a commodity fuel with common definitions, common methods, and a clear classification system. In Europe, the European Committee for Standardiza-tion (CEN) established a technical committee (CEN/TC 335) to develop standards to describe all forms of solid biomass, including wood chips, wood pellets and briquettes, logs, sawdust, and straw bales. The CEN/TC 335 standards support the matching of the thermal conversion system with the fuel supply. More information on fuel standards and specifications is presented in annex 2.

2.4.4 Moisture ContentAn important biomass characteristic influencing com-bustion behavior, the adiabatic temperature of com-bustion, and the volume of flue gas produced per energy unit is the moisture content (water content). Fuels with higher moisture content will have a greater mass and, therefore, higher bulk densities. With a higher moisture content, the energy density will be lower, and the subsequent volume of fuel required for a given amount of heat will be larger. The moisture content of biomass fuel depends on such factors as the kind of material, the time of harvesting, the kind of pretreatment, and the method and duration of storage (van Loo and Koppejan 2002). The moisture content for straw varies between 10 and 25 percent. Wood from the forest has a moisture content that may vary from 15 to 60 percent, depending on the duration of open-air seasoning (Francescato and others 2008).

For optimal operation of the biomass boiler, keeping the moisture content as constant as possible is impor-tant. Firing a fuel with a higher moisture content than the design value can result in lower conversion efficiency, lower power output, and higher levels of harmful emissions (van Loo and Koppejan 2002). In practice, this means that most often only one type of biomass is used per boiler. Another possibility is to blend fuels into a homogeneous mixture or integrate a drying step into the biomass supply chain.

2.4.5 Calorific ValueThe calorific value refers to the heating potential of a fuel and is a measure of its energy content (MJ/kg). Depending on how water in the combustion products is

released, the calorific value is expressed either as gross calorific value (GCV) or net calorific value (NCV).4 In the first case, the water is released as a liquid; in the second case, the water is released as a vapor, and the thermal energy required for vaporization is deducted. When not explicitly specified in the literature, calorific value is generally assumed to be NCV.

For thermal conversion, a biomass fuel with low mois-ture content is preferred because its calorific value is higher. In figure 2.2, the effect of moisture content on calorific value (NCV) is shown for wood. In table 2.5, calorific value is shown for straw, wood, coal, and natural gas. According to van Loo and Koppe-jan (2008), the GCV of biomass fuels usually varies between 18 and 22 MJ/kg dry basis (d.b.) and can be calculated reasonably well by using the following empirical formula:

GCV = 0.3491 × XC + 1.1783 × XH + 0.1005 × XS – 0.0151 ×

XN – 0.1034 × XO – 0.0211 × Xash [MJ/kg, d.b.],

where Xi is the content of carbon (C), hydrogen (H), sulfur (S), nitrogen (N), oxygen (O), and ash in wt% (d.b.). A bomb calorimeter can be used for exact

4. Sometimes also referred to as higher heating value (HHV) and lower heating value (LHV), respectively.

Figure 2.2 The Net Calorific Value (NCV0 = 19 MJ/kg) as a Function of Wet Dry Basis Moisture (M and u)


40

35

30

25

20

15

10

5

0

calo

rific

val

ue (M

J/kg

)

moisture on w.b. (M%)

0 10 706050403020 80

0 1506725 400

moisture on d.b. (u%)

7


determination of the GCV according to standardized procedures. As van Loo and Koppejan (2008) men-tion, the content of C, H, and S contributes positively to the GCV, while N, O, and ash contribute negatively to the GCV.

The NCV can be calculated from the GCV, taking into account the moisture and hydrogen content of the fuel by applying the following equation:

NCV = GCVw

100

h

1001 – – 2,444 ×

w

100– 2,444 × × 8.936

w

1001 – [MJ/kg, w.b.],

where w is the moisture content of the fuel in wt% (w.b.), h is the concentration of hydrogen in wt% (d.b.), 2.444 is the enthalpy difference between gaseous and liquid water at 25°C and 8.936 is MH2O/MH2; that is, the molecular mass ratio between H2O and H2.

The European Standard EN 14961:2005 Solid Biofu-els—Fuel Specifications and Classes normalizes how to

calculate the NCV at dry base and as received. Details on the standard are provided in annex 3.

Drying biomass fuel increases its calorific value.

2.4.6 Ash Content and QualityAfter the thermal conversion of biomass, bottom ashes, fly ashes, and/or slags remain, depending on the fuel and technology used. Bottom ash is taken out at the bottom of the boiler (stored in a storage tank; see left panel of figure 2.3), and the remainder is whirled round in the boiler with the combustion air and removed by a flue gas cleaning system (fly ash; see right panel of figure 2.3). Fly ash can further be divided into cyclone light ash and fine particles from electrostatic and bag filters. Storage and sale can be considered as treatment options for the collected ashes. Ashes are often recycled and used as a constitu-ent of construction materials.

The amount and quality of ash are important char-acteristics when selecting a biomass fuel. Both are

Table 2.5 Fuel Data at Typically Occurring Moisture Content

Unit Yellow strawa Gray strawa Wood chips Hard coal Natural gas

Moisture content % 10–20 10–20 40 12 0

Volatile components % > 70 > 70 > 70 25 100

Ash % 4 3 0.6–1.5 12 0

Carbon (C) % 42 43 50 59 75

Hydrogen (H) % 5 5.2 6 3.5 24

Oxygen (O) % 37 38 43 7.3 0.9

Chloride (Cl) % 0.75 0.2 0.02 0.08 —

Nitrogen (N) % 0.35 0.41 0.3 1 0.9

Sulfur (S) % 0.16 0.13 0.05 0.8 0

Calorific value, water and ash-free MJ/kg 18.2 18.7 19.4 32 48

Calorific value, actual MJ/kg 14.4 15 10.4 25 48

Ash softening temperature °C 800–1,000 950–1,100 1,000–1,400 1,100–1,400 —

Source: Nikolaisen and others 1998.

Note: — = Not applicable.

a. Straw that has been lying in the field and that has been exposed to rain has less corrosive matter, chlorine and potassium. Contrary to “yellow” straw, this “gray” straw is less wearing on the boiler because part of the matter that corrodes the boiler wall and tubes has been removed. Gray straw also has a somewhat higher calorific value than yellow straw (Nikolaisen and others 1998).

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dependent on the biomass fuel that is used. Accord-ing to Francescato and others (2008), debarked wood is the lowest ash-containing biomass, whereas agri-cultural residues typically have a high ash content. The ash content of debarked wood is usually less than 1 percent, while the ash content of agricultural resi-dues is 5–10 percent—and as much as 20 percent for rice husk.

Besides the quantity of ash, the chemical composition of ash is important because it can influence the melt-ing behavior. Because the ash melting point of straw is lower than the ash melting point of wood, slag can be produced. According to Nikolaisen and others (1998), this is important, particularly for power plants where a high steam temperature is desired to achieve great effi-ciency. In table 2.6, some guiding values and guiding ranges for elements in biomass ashes are shown, includ-ing the problems that can occur and some techniques to reduce the values to within the guiding ranges.

2.4.7 Chemical CompositionBiomass contains low levels of minerals, salts, and other materials taken up from the soil or air dur-ing growth. Table 2.7 shows some fuel data and the chemical composition of wheat straw, wood, coal, and natural gas. According to Pastre (2002), the higher concentrations of the elements nitrogen (N), sulfur (S), and chlorine (Cl) in straw are a result of the use of pesticides and fertilizer.

For a wide range of biomass feedstocks, chemical and physical characteristics are included in the Phyllis database, accessible at www.ecn.nl/phyllis.

The presence of these salts, minerals, and other ele-ments partly determine the level of gaseous and par-ticulate emissions, ash, and slagging. Some guiding values and guiding ranges for elements in biomass are shown in table 2.7, including the problems that can occur and selected techniques to reduce the values to within the guiding ranges.

Biomass fuel characteristics, such as the area of origin, ash content, chemical content, and to some extent, moisture content, affect the level and composition of emissions into the air. When maintaining the local air quality is a crucial consideration in the planning, consent, and permitting processes, emissions have direct implications for the suitability of biomass fuel. In Europe, ever-stricter levels for the emissions of nitrogen oxides (thermal NO

x and fuel NOx) are set because of their harmful effects on the environment. To meet the NOx emission level values, it is important to work with temperatures as low as possible and with accurate control of the combustion air (Vos 2005a). Furthermore, it is important to consider the use of emissions-reduction equipment.

When using straw, which has a relatively high potas-sium content, fuel slagging can be a serious problem.

Figure 2.3 Bottom Ash Stored in a Storage Tank (left), Fly Ash Is the Ash That Derives from Flue Gas Cleaning (right)


9


Table 2.6 Guiding Values and Guiding Ranges for Elements in Biomass Ashes for Unproblematic Thermal Utilization

ElementGuiding concentration in the ash (wt% on d.b.) Limiting parameter

Elements that can cause problems outside of guiding concentration ranges

Techniques for reduction to guiding ranges

Ca 15–35 Ash-melting point Straw, cereals, grass Temperature control on the grate and in the furnace

K < 7.0 Ash-melting point, deposits, corrosion

Straw, cereals, grass To prevent corrosion: see Cl (table 2.7)

— Aerosol formation Straw, cereals, grass Efficient dust precipitation, fuel leaching

Zn < 0.08 Ash recycling Bark, wood chips, sawdust Fractioned heavy-metal separation

— Particulate emissions Bark, wood chips, sawdust Efficient dust precipitation, treatment of condensates

Cd < 0.0005 Ash recycling Bark, wood chips, sawdust See Zn

— Particulate emissions Bark, wood chips, sawdust See Zn

Source: van Loo and Koppejan 2002.

Note: d.b. = dry basis. Guiding values for ashes related to the biomass fuel ashes according to ISO 1171-1981 at 550˚C; analytical method recommended for ash analysis: pressurized acid digestion and inductively coupled plasma mass spectrometry (ICP) or flame atomic absorption spectrometry (AAS) detection.

Table 2.7 Guiding Values and Guiding Ranges for Elements in Biomass Fuels for Unproblematic Thermal Utilization

Element

Guiding concentration

in the fuel (wt% on d.b.) Limiting parameter

Outside guiding concentration ranges, problems can occur for

Techniques for reducing to within guiding ranges

N < 0.6 NOx emissions Straw, cereals, grass Primary measures (air staging, reduction zone)

< 2.5 Waste wood, fiber boards Secondary measures (SNCR or SCR process)

Cl < 0.1 Corrosion Straw, cereals, grass • Fuel leaching• Automatic heat exchanger cleaning• Coating of boiler tubes• Appropriate material selection

< 0.1 HCL emissions Straw, cereals, grass • Dry sorption• Scrubbers• Fuel leaching

< 0.3 PCDD/F emissions Straw, cereals, grass • Sorption with active carbon• Catalytic converters

S < 0.1 Corrosion Straw, cereals, grass See Cl

< 0.2 SOx emissions Grass, hay See HCL emissions

Source: van Loo and Koppejan 2002.

Note: d.b. = dry basis; SNCR = Selective non-catalytic reduction; SCR = Selective catalytic reduction; PCCD/F = Emissions of polychlorinated dibenzodioxin and dibenzofuran. N and S analysis recommended: combustion/gas chromatographic detection; Cl analysis recommended: bomb combustion/ion chromatographic detection.

10


Slagging refers to the fusing of bottom ash, which for straw occurs at temperatures of about 800–900°C (table 2.6). The presence of chlorine and alkali in straw is also problematic. These substances react to sodium chloride (NaCl) and potassium chloride (KCl) in the flue gas. The chlorides are extremely corrosive to the steel of the boiler, particularly at high temperatures5 (DTI 2007a).

2.4.8 ContaminantsBesides contaminants within the biomass itself, which can result in harmful emissions to air and soil if not treated properly, biomass feedstock can be contami-nated with materials such as soil or stones, metal, and plastics. These contaminants can jam fuel-feeding sys-tems. Sand can result in glass formation during com-bustion (Carbon Trust 2005a). To avoid this type of contamination, it is important to design a proper physical handling mechanism for transferring fuel from where it is stored to where it is combusted (Carbon Trust 2005a).

2.5 Example: Some Experiences with Biomass Fuel-Feeding Systems

Experience around the world shows that fuel-feeding systems in biomass power plants often cope with start-up problems. It is not uncommon that during the first couple of years of plant operation, significant amounts of time and money are spent to solve such problems as excessive equipment wear, fuel blockages, bottlenecks in the feed system, and tramp metal sepa-ration problems. Some examples from North America are the biomass power plant in Tacoma, Washington (United States, operational since 1991), where person-nel stressed the need to take extra care at the beginning of the project with the design of the fuel-feeding sys-tem; and the power plant at Stratton, Maine (United States, operational since 1989), where the original owners spent about US$1.8 million during the first year of operation to improve the operation of the fuel yard. The biomass-fired power plant in Williams Lake (British Columbia, Canada; operational since 1993) modified the fuel-handling system after start-up by

5. Many of the biomass power plants operating in China have high-temperature boilers and high-pressure grate furnaces in-stalled.

adding the ability to reverse the drag chains on the dumping hoppers (to make it possible to unplug fuel jams), and adding three more rolls to each disk screen to reduce the carryover of fine particles that tended to plug up the hog (Wiltsee 2000).

Teething problems with fuel-feeding systems at the newly established biomass-fired power plants in China are not yet well documented. However, such problems are reportedly not uncommon. For example, it is understood that the Henan province plant experi-enced such problems because of design inadequacy in the Chinese context.

2.6 Conclusions and Recommendations

2.6.1 ConclusionsThe characteristics of the biomass used as fuel have a direct impact on the biomass power plant design, operation, and performance, including the fuel-feed-ing system, boiler technology, and emissions control. In addition, they have an impact on the best way to handle fuel (collection, transportation, pretreatment, and storage). Less homogeneous and/or low-quality fuels need more sophisticated combustion systems. Some important fuel characteristics are as follows:

• The moisture content, and closely related to it, the calorific value. For thermal conversion, biomass fuel with a low moisture content is preferred.

• The bulk density has a great impact on supply logistics and transport costs. For low-density fuels (for example, chopped straw), densification prior to transportation may be necessary.

• It is important to have an appropriate match between the biomass particle dimension or parti-cle size distribution and the fuel-feeding system or combustion technology to avoid frequently occur-ring problems with the fuel-feeding system (for example, excessive wear, fuel hang-ups, and tramp metal separation problems). Fuel standards and specifications ensure a proper match between fuel supply and thermal conversion system.

• Ash quantity, quality, and composition are impor-tant issues when selecting a biomass fuel. Com-bustion of agricultural residues results in larger quantities of ash than combustion of forestry

11


residues. The composition of ash can influence its melting behavior, which can cause slagging prob-lems to occur, in particular for straw. In all cases, the proper treatment, storage, and sale of ashes should be given due consideration.

Emissions-reduction measures not only depend on the type of biomass used, but also on local requirements and the environmental regulations that are in force.

Appropriate fuel selection is vital in managing fuel supply risk.

2.6.2 Recommendations• Carefully determine which biomass type(s) will be

used in the power plant, and which fuel specifica-tions will apply (for example, particle size and dis-tribution, moisture content, and calorific value).

• Take advantage of available fuel standards and specifications to allow a good match between the fuel supply and the energy system.

• Try to make maximum use of secondary residues; these are usually the cheapest, and they are released centrally and relatively clean.

• Make sure that plant design and permits allow as much fuel flexibility as possible to anticipate poten-tial future changes in the availability of biomass fuel (fuels sometimes change significantly over the years as other opportunities arise or old fuel sources diminish).

• Keep the moisture content of the biomass fuel as constant as possible for optimal plant operation.

• Avoid contamination of the biomass fuel because this may lead to operational problems (such as jamming) and excessive emissions.

• Carefully select emissions-reduction equipment to meet relevant emissions limitation values, for example, for nitrogen oxides.

• Consider installing a dual-feeding system to allow the use of different types of biomass. The installa-tion of dedicated boilers for the different types of biomass is also an option.

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3. Biomass Resource Assessment

sustainability aspects in biomass resource assessments is within the scope of ongoing research.7

The implementation of sustainability standards in analyses of biomass potential mostly decreases the resulting potential by limiting either the area available (for example, by excluding areas designated for nature conservation) or the anticipated yields (for example, through less intensive management methods in sensi-tive areas). This approach is demonstrated in figure 3.1. Sometimes the application of sustainability cri-teria can increase the biomass potential, for example, if biomass from landscape conservation activities is included.

Depending on the intended objective, different types of biomass resource assessments are used. The aim may be to determine the theoretical potential to assist scenario development. Alternatively, the aim may be to determine the practical “implementation” potential to assist project developers and investors. In the latter case, such issues as alternative land uses, supply logis-tics, financial viability, and sustainability are explicitly taken into account. In this handbook the second aim is relevant.

3.2 Basic Approaches to Biomass Resource Assessments

Depending on whether the focus is primarily on bio-mass supply, biomass demand, or a combination of both, three basic approaches to biomass resource assessments can be identified:

7. The Biomass Energy Europe (BEE) project (http://www.eu-bee.com) is currently developing a standardized methodology for including sustainability aspects in biomass resource assess-ments. Relevant public results of the BEE project will become available in 2010.

3.1 Types of Biomass Potential

When discussing the availability of biomass, the type of potential is a crucial criterion, because it deter-mines to a large extent the approach and methodology and thereby also the data requirements of a biomass resource assessment. There are four distinct types of biomass potential6:

• Theoretical potential: Describes the ultimate resource potential based on calculation or mea-surement of the net primary productivity of the biomass.

• Technical potential: Limits the resource potential by accounting for terrain limitations, land use and environmental considerations, collection inefficien-cies, and a number of other technical and social constraints.

• Economic potential: Limits the resource potential by incorporating cost information, such as harvest, transportation, and processing costs.

• Implementation potential: Limits the economic potential by taking into account economic, institutional, and social constraints and policy incentives.

In theory, a fifth potential can be considered, the environmentally or ecologically sustainable poten-tial, defined as the fraction of the other potentials that meets certain environmental sustainability crite-ria. Around the world there is strong demand for the inclusion of sustainability aspects in resource assess-ments. The concept of sustainable biomass contains multiple environmental, economic, and social aspects, and measurement of these aspects—how to measure biodiversity or the impacts of energy crops on climate change—can be complex. The possibility of including

6. The different type of potentials are discussed in more detail in annex 4.

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• Resource-focused methods.• Demand-driven methods.• Integrated assessments.

Resource-focused methods are normally used to deter-mine the theoretical or technical potential, whereas demand-driven methods are used to determine the eco-nomic or implementation potential. Integrated assess-ments can be used to determine any of the four types of biomass potential. The general approach determines to a large extent the methodology that is used and, in turn, the methodology determines to a large extent the data that are used. For the purposes of this handbook, resource-focused assessments are the most relevant.

Resource-focused assessments investigate the bioen-ergy resource base and the competition between dif-ferent uses of the resources. That is, the focus is on the supply of biomass energy. Resource-focused assess-ments typically estimate the theoretical or technical potential to produce biomass for energy, thereby usu-ally taking into account the demand for land to be used for food production and biomass needed for the production of food and materials.

Resource-focused assessments can be further divided into statistical and spatially explicit assessments.

3.2.1 Statistical AssessmentsStatistical assessments make use of data from statis-tics on land use, crop yields, crop production, and forest inventories and literature. The statistical data are combined with conversion factors, such as yields per hectare and residue-to-crop factors. These factors are based on expert judgment, field studies, or litera-ture review. In addition, further assumptions are made about the fraction of biomass available for energy pro-duction, taking into account biomass or land needed for other purposes.

As illustrated in section 3.4, the statistical assessment method is widely used in biomass resource assess-ments in China.

3.2.2 Spatially Explicit AssessmentsThe most advanced resource-focused assessments include spatially explicit data on the availability and accessibility of land and forests in combination with calculations of the yields of energy crops and forests, based on growth models that use spatially explicit data on, for example, climate, soil type, vegetation type, and management. When statistics are available at a detailed level, results from statistical assessments can be presented in a spatially explicit way.

As illustrated in section 3.5, in recent years there have been various efforts in Europe to use spatially explicit assessments to determine straw availability in selected regions.

3.3 Steps in a Biomass Resource Assessment

A resource assessment normally includes the follow-ing steps:

• Data collection, which typically covers a large number, type, and scope of data sources (up to sat-ellite imagery, if available).

• Data analysis, which includes sorting out the most relevant data sources and applying residue-to-crop ratios.

• Data completion, which entails filling in the blank spots and mapping current biomass utilization processes.

Figure 3.1 The Influence of Sustainability Criteria on Biomass Potential

Sources: BTG; Drohm Design & Marketing.

Technical potentialland × yield

Society

Econ

omy

Environment

Sustainable potential

land and yield restrictions

14


The methods employed to assess biomass resources will vary, depending on the following:

• The purpose for which the data are required.• The level of detail required.• The information already available for the particu-

lar country, region, or local site.

The Biomass Assessment Handbook (Rosillo-Calle and others 2006) presents a step-by-step method for determining the availability of agricultural crops and residues (annex 5).

With regard to assessing biomass resources, two important observations can be made:

• Determination of conversion factors: In resource assessment, use is often made of residue-to-prod-uct factors (RPFs) and recoverability factors (RFs). Although much attention has been given to deter-mining RPFs, relatively little research seems to have been done on assessing RFs.

• Need for field surveys: Unless detailed studies from the area in question already exist, some detailed field research at chosen sample sites is desirable to validate and fine-tune the data. Supporting activi-ties, such as visiting government authorities, for-estry institutes, and large agro-industries, help to collect resource data and fill data gaps.

Independent of the application for which the removed biomass is to be used, it is important not to exploit and remove the maximum potential, for environmen-tal and biodiversity reasons (for example, soil fertility). In the Nordic countries (Finland and Sweden), the fol-lowing rules of thumb are applied to calculate poten-tial harvestable forestry residues (AEBIOM 2007):

• 75 percent of maximum potential of final fellings,• 45 percent of thinnings,• 20 percent of stumps from final fellings, and• 25 percent of the additional fellings (that is, fellings

of the unutilized increment or roundwood balance).

For agricultural residues, it is equally important not to exploit and remove the maximum potential. Soil

organic matter affects virtually all soil properties, for example, physical structure, ease of cultivation, ease of root growth, erosion, nutrients, and biodiversity. In general, more is better. An additional environmental benefit is that carbon from the atmosphere is being locked up.

3.4 Straw Resource Assessments in China

Long-term availability and the ability to contract for affordable straw are important for the effective opera-tion of a straw-fired power plant. To help ensure that sufficient amounts of straw can be acquired year by year, a plant owner-developer should be conservative in assessing the total implementation potential and the share of this potential that can be acquired. Bio-mass power companies do not like to be vulnerable to local farmers holding out for higher straw prices. It is therefore common practice to assume a reserve factor of 50–75 percent or more, as well as to reflect annual resource fluctuations caused by weather, land use changes, changes in crop mix, price developments, and other factors.

In line with the guidelines discussed in annex 6, typi-cal biomass resource assessments in China use sta-tistics on land use, crop yields, crop production, and forest inventory, and combine them with conversion factors, such as yields per hectare and RPFs. The latter are based on expert judgment, field studies, or litera-ture review. In addition, further assumptions are made about the fraction of biomass available for energy production.

Applying this method, Li and others (2009) estimate the annual availability of straw biomass for power gen-eration at more than 700 million tons (table 3.1).

A commonly expressed concern in China is the absence of a “standard” method for biomass resource assessment in general and straw resource assessment in particular. For example, the observation is explic-itly or implicitly made by ZERS (2008), NAU (2008), and CECIC (2009b). In an effort to address this issue, CECIC (2009b) proposed a Technical Regulation of Resource Assessment for Crop Straw Combustion

15


Power Generation Project, specifically for the assess-ment of straw.

Despite the expressed concern about lack of a standard, there is a general understanding in China about the proper resource assessment method to be adopted, and the CECIC Blue-Sky method mentioned above entails a suitable approach. The quality of the survey data and assumptions is of greater concern. Some efforts have been made to determine agro-ecological, region-specific RPFs, but as elsewhere in the world, in China much less attention has been paid to assessing RFs.

To increase the validity of the data and to assess the practical straw potential more accurately, expanding the scope and coverage of the survey may be consid-ered in the following ways:

• Carrying out actual field measurements of straw usage for all applications.

• Incorporating time series in the survey (for exam-ple, by repeating the survey in subsequent years).

• Incorporating questions related to structural changes in straw supply and demand, in particular the future demand of large users of straw, such as other biomass-fired power plants.

3.5 Spatially Explicit Straw Resource Assessments: An Example from Europe

In an effort to assess the technical potential of straw from wheat and barley, Edwards and others (2006) combined Europe-wide statistical data on wheat and cattle production per administrative region from Euro-stat with GIS data on land coverage and administra-tive boundaries. In addition, supporting information from straw-for-energy studies was also used.

The study is an interesting example of a spatially explicit resource assessment, and various other authors have replicated the approach. It is a useful method to determine the potential for large, straw-fired power plants. In principle, the method is appli-cable to any cereal crop, including maize straw and cotton straw, provided that a formula for the pertinent straw-to-grain ratio exists or can be developed. It can be applied anywhere in the world, including China, provided some basic GIS data are available.

3.5.1 Straw Potential per RegionThe Edwards and others (2006) assessment started by estimating the straw yield (straw, tons per hectare of arable land) as a function of the grain yield (grain, tons per hectare). Starting from literature values on

Table 3.1 Yield of Main Crop Straws in China and Their Heating Values, 2005

Main crops Yield of crops Coefficient

Yields of straws/

106 tons

High heat value/

106 J/Kg

Low heat value/

106 J/Kg

Rice 180.59 1 180.59 15.24 13.97

Wheat 97.45 1 97.45 16.67 15.36

Corn 139.37 0.5 278.73 16.90 15.54

Potato 36.48 1 36.48 15.61 14.23

Beans 21.58 0.67 32.37 17.59 16.15

Peanut 14.34 0.5 28.68 18.60 17.23

Rape 13.05 0.33 39.16 15.23 13.81

Fiber 6.82 0.33 20.46 17.37 15.99

Total 509.67 – 713.91 – –

Source: Li and others 2009.

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the empirical range of harvest indices (grain or above-ground biomass), Edwards and others (2006) deduced straw-to-grain ratios as a function of grain yield. This discontinuous relation was smoothed into a conve-nient function:

Straw = grain × 0.769 – 0.129 × arctan [(grain – 6.7)/1.5],

where grain is the grain yield in tons per hectare and arctan is the inverse of the tangent function.

The function (see figure 3.2) indicates that the straw-to-grain ratio falls from a maximum of 0.94 to a mini-mum of 0.62 as the grain yield increases. Although this formula is based on data for wheat, experts have con-firmed that it is also approximately correct for barley, which would be confined to the low-yield, high-straw ratio end of the curve.

The function was applied to European statistical data (Eurostat) for wheat and barley yields, area, and production, and was linked with GIS NUTS2 regions.8 The resulting estimate of straw potential from wheat and barley at the regional level is pre-sented in figure 3.3.

8. The Nomenclature of Territorial Units for Statistics (NUTS, for the French nomenclature d’unités territoriales statistiques) is a geocode standard for referencing the administrative divi-sions of countries for statistical purposes.

Not all produced straw is available for bioenergy. The first two constraints that need to be quantified are environmental limitations and competing uses for straw.

Environmental constraints prevent collection of straw from fields where there are unfavorable soil condi-tions: low organic matter content, risk of degradation processes, limited water resources, and extremes of climate. In these cases, plowing back the straw into the soil helps sustain soil fertility.

In Europe, the main competing use for straw is cattle bedding or litter. Significant amounts of straw are also used in horticulture and mushroom production, and for industrial processes. Exact amounts involved have proved hard to assess. The information published in various international, national, and regional studies is inconsistent, and often based on an expert guess lacking documentation of the methodology and termi-nology. There are also a few surveys, but comparison between them is limited for the same reasons.

It is generally accepted that cattle raising is the most important competitive use of straw. The amount of straw used per head of cattle depends on how long cattle stay indoors (which varies with climate and

Figure 3.2 Straw Yield as a Function of Grain Yield

Source: Edwards and others 2006.

1.0

0.9

0.8

0.7

0.6

0.5

0

stra

w/g

rain

inde

x

grain yield (tons/ha)0 1 865432 117 9 10

Figure 3.3 Total Straw Production per Region (tons)


17


geography), what types of shed are used, and the avail-ability of straw in the region. Based on the scattered data of available studies, Edwards and others (2006) estimated the straw used per head of cattle (SUPH, tons per head) from total straw produced per head of cattle in the region (SPPH, tons per head) by an empirical equation (see figure 3.4):

SUPH = 2 × [1– exp (– SPPH/2)],

where SUPH is the straw used per head of cattle in tons per head, exp is an exponential function, and SPPH is the total straw produced per head of cattle in the region in tons per head.

Using this equation, the estimated amount of straw used per head of cattle in different regions lies between 0.1 and 2.0 tons per year. Subtracting this estimate of competitive use results in a map of the net surplus of straw at the regional level (figure 3.5). Some regions show a net deficit.

3.5.2 Straw Potential for 5x5 km GridsThe Eurostat statistics used in the above calculations are available at a level of detail corresponding to the NUTS2 regions. Edwards and others (2006) consid-ered this level of detail insufficient, and used CORINE (Coordination of Information on the Environment)9 Land Cover data for 2000 (CLC 2000) to spatially dis-aggregate the information from the statistical regions onto a regular grid with a cell resolution of 5x5 km.

The area of wheat and barley was estimated for each 5x5 km grid cell, assuming that the area is distributed

9. CORINE Land Cover is a European database of biophysical soil use.

Figure 3.4 Straw Used per Head of Cattle


3.0

2.5

2.0

1.5

1.0

0.5

0

used

str

aw/h

ead

(ton

ne)

total straw per cattle head (tonne)0 1 865432 97

Figure 3.5 Available Straw per Region (tons)


Figure 3.6 Available Straw per 5x5 km Grid Cell (tons)


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uniformly on the fraction of the cell devoted to the CLC 2000 category 211 (arable land). Then straw production for each 5x5 grid was found by distrib-uting the net straw surplus for each NUTS2 region among its constituent grid cells in proportion to the areas of wheat and barley in each cell. This results in a more detailed map of net straw availability.

3.6 Size of the Biomass Power Plant

The optimal size of a biomass power plant depends on two competing cost factors. As size increases, spe-cific investment costs drop as a result of economies of scale, while transport costs increase as a result of longer biomass transportation distances. The compe-tition between these cost factors leads to an optimum size at which the cost of energy produced from bio-mass is minimized (Searcy and Flynn 2008).

Apart from the optimal size, many other factors need to be taken into consideration when planning a bio-mass-fired power plant. To keep transportation costs within limits, it is recommended that a biomass power plant be sited close to where the biomass becomes available. And it is always a good idea to locate a power plant on a railway or, even better, a waterway. Unless biomass is available at, or near, zero or even a negative cost, it is also generally recommended to generate power in a cogeneration mode to make effi-cient use of the available biomass, and therefore to locate the plant near one or more large heat users. It is understood that at many of the biomass power plants installed in China in 2006–08, these considerations were not taken into account.

When sufficient data are available, the crossover point at which further increasing the biomass-fired power plant size decreases its overall economics can be calcu-lated. Where this is not the case, a rule of thumb can be applied. A commonly accepted value for the maxi-mum distance that unprocessed biomass can still be economically transported is 50 km. Longer transpor-tation distances may still be acceptable if the biomass is first converted into a solid or liquid fuel with higher energy density, or if water transportation rather than road transportation is used.

The study by Sims (2007) presents an overview of the typical fuel requirements, number of vehicle move-ments, land area requirement, and supply radius for various sizes of bioenergy plants (see table 3.2). Table 3.2 illustrates that for bioenergy plants of the size commonly installed in China (20–30 MW

e), 2–5 per-cent of the agricultural land area within a radius of 50 km is needed. Li (2008) also proposed a maximum supply radius of 50 km for the collection of maize straw and stalk to feed a 24 MWe biomass CHP plant in Mongolia.

When other large biomass users operate, or plan to operate, in the same collection area, competition for resources can be high. This is what is actually happening in the case of biomass-fired power plants in Shandong and Jiangsu provinces. It is therefore recommended to use conservative estimates about the available land area and the associated biomass availability.


3.7.1 ConclusionsMany different types of biomass potential exist. For investors in Chinese biomass-fired power plants, implementation potential is the most relevant. It takes into account such topics as alternative land uses, sup-ply logistics, financial viability, and sustainability.

There are various ways of determining biomass avail-ability. A resource-focused assessment is the most relevant approach when investing in a biomass-fired power plant.

Steps in a biomass resource assessment include data collection, data analysis, and data completion. The better the quality of the data that is available, or can be collected, the more sophisticated the assessment method can be.

Applying detailed residue-to-crop factors may give a misleading sense of accuracy, in particular when information about alternative biomass uses is patchy or poor.

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In recent years, several efforts have been initiated around the world to improve biomass resource assess-ment methodologies. Examples of such initiatives include the work of the Joint Research Centre of the European Commission (Ispra, Italy) on the availability of straw in the member states of the European Union (EU); the EU-sponsored Biomass Energy Europe proj-ect that looks at the availability of all types of bio-mass residues and crops across Europe, with a special emphasis on Central and Eastern Europe; and the research and field work of Imperial College (Lon-don, United Kingdom) in, for example, Africa and the Pacific. In China, CECIC Blue-Sky has carried out rel-evant work on crop straw assessments. The methods developed and results obtained by the initiatives men-tioned can be useful for planning a biomass resource survey in China.

For the government of China, it may be worthwhile to support the development of a spatially explicit assessment methodology for the predominant bio-mass resources in China (such as rice straw and corn stalks).

3.7.2 RecommendationsUse a consistent biomass resource assessment method-ology that uses not only theoretical RCFs to calculate the available biomass amount, but that also considers the competitive uses of biomass and material losses incurred during biomass collection, storage, and trans-port caused by climate, humidity, and other reasons.

Carry out field surveys to verify and validate existing biomass resource assessment data. Particular atten-tion should be paid to the following:

• The type, amount, seasonality, and usage of local agricultural and forestry biomass resources.

• Conversion factors, including RPFs and RFs.• Time-series data.• The current status of local biomass-fired power

generation projects (in operation, under construc-tion, or awaiting approval) and their fuel demand.

Try to collect data covering a period of more than a single year so that seasonal patterns and a trend can be established.

Table 3.2 Typical Scale of Operation for Various Sizes and Types of Bioenergy Plants

Type of plant

Heat(th) or power(e)

capacity ranges, and

annual hours of operation

Biomass fuel

required (odt/yr)

Vehicle movements

for biomass

delivery to the plant

Land area required to

produce the biomass

(% of total within a given radius)

Small heat 100–250 kWth

2,000 hr

40–60 3–5/yr 1–3% within 1 km radius

Large heat 250 kWth

–1 MWth

3,000 hr

100–1,200 10–140/yr 5–10% within 2 km radius

Small CHP 500 kWe–2 MW

e

4,000 hr

1,000–5,000 150–500/yr 1–3% within 5 km radius

Medium CHP 5–10 MWe

5,000 hr

30,000–60,000 5–10/day 5–10% within 10 km radius

Large power plant 20–30 MWe

7,000 hr

90,000–150,000 25–50/day and night 2–5% within 50 km radius

Source: Sims 2007.

Note: odt = Oven dry ton. Transport and land use requirements to meet annual biomass demands when operating at various capacity factors. Biomass yields when produced from forest arisings, agricultural residues, or purpose-grown energy crops are assumed at about 5–10 odt/ha annually.

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When conducting interviews, consider expanding cov-erage by including the following:

• Actual field measurements of straw usage for all applications.

• Use of time series in the survey (for example, by repeating the survey in subsequent years).

• Questions related to structural changes in straw supply and demand.

When considering a resource survey, make use of handbooks published on this topic, for example, The Biomass Assessment Handbook (Rosillo-Calle and others 2006). These detailed handbooks present fur-ther useful and practical guidelines for planning and carrying out biomass resource surveys.

Do not mistake biomass availability for the ability to acquire it under contract. (Aspects of contracting for biomass are discussed in chapter 6.)

For environmental and biodiversity reasons (for example, soil fertility) do not exploit and remove the maximum potential from the sites identified for

collection and harvesting of agricultural or forestry residues.

Do not plan on using more than 25 percent of the biomass that is identified as available. Ideally, a bio-mass-fired power plant should not use more than 10–15 percent of the freely available biomass. Such large reserve factors are recommended to ensure that sufficient biomass residues can be acquired year by year for an affordable price. The large reserve fac-tors reflect the annual resource fluctuations caused by weather, land use changes, changes in crop mix, price developments, and other factors.

Do not carry out the survey on your own. Rather, involve an experienced professional consultant who, in an advisory capacity, can give recommendations on the survey methodology. The adviser can also be charged with the full organization of the survey in the form of interviews, questionnaires, and workshops to get first-hand information from local stakeholders, including key officials from local government agencies, agricultural experts, the owners of livestock and planting farms, grain processing factories, and rural households.

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4. Biomass Supply from Straw

4.1 Introduction

During grain harvesting, straw becomes available as a byproduct. This straw can be used as fuel. In Denmark, the national government adopted a straw-for-energy policy in 1986. During the last 20 years, extensive experience has been gained in Denmark with the use of straw for larger-scale CHP generation. Large-scale straw handling for energy purposes has developed into an independent discipline in agriculture in which par-ticularly large farms and machine pools make invest-ments. Most Danish farmers with straw contracts produce about 100 tons of straw annually. A few large farms and machine pools have developed large-scale handling of 10,000–30,000 tons of straw annu-ally. Straw-for-energy plants were set up elsewhere in Europe recently (for example, Poland, Spain, and the United Kingdom), but with a few exceptions, they were smaller scale and primarily meant to generate heat.

Section 4.2 discusses the state of the art in high-vol-ume biomass supply from straw. The section is mainly based on the experience gained in Denmark, which to date is the only country besides China where several large-scale, straw-fired CHP plants have been set up.

The supply chain model developed in Denmark can be replicated in other countries that have highly mecha-nized agricultural sectors. Section 4.3 introduces straw supply practice in China. Current straw-supply models can at best be qualified as semi-mechanized. Sections 4.4 and 4.5 present short case studies of the straw sup-ply arrangements set up at large-scale biomass power plants in China and Europe, respectively.

4.2 The Technology and Methods of Straw Production

4.2.1 Production, Raking, and Collection of StrawStraw is a byproduct of cereal grain production (such as wheat, rye, barley, triticale, and oats) by combine harvester. The combine harvester arranges straw in swaths.

When rainfall occurs, turning or raking of the swaths is important for the straw quality. This is done by a tractor equipped with a raker (see figure 4.1).

Once sufficiently dry, the straw can be baled using a tractor equipped with a baler and an accumulator (see figure 4.2). Balers come in several types and sizes: small baler, round baler, medium baler, and big baler.

Figure 4.1 Turning and Raking of Swaths Before Baling


Figure 4.2 Tractor and Baler in Operation


22


For Danish power plants, only large bales including so-called big bales and mid bales are accepted. Big bales have dimensions of 120 x 130 x 240 cm, a den-sity of 140–185 kg/m3, and a weight of 500–800 kg. A big baler has a capacity of 12–25 tons/hr. In recent years a midi bale was introduced (dimensions of 120 x 90 x 240 cm). The weight is 425–500 kg per bale. The advantage of the shorter bale is that the bale density is slightly higher and the tractor or truck can carry three layers of midi bales instead of two layers of big bales. The handling capacity of loading is also increased. The disadvantage is that the straw crane in the plant has to be modified.

4.2.2 Transporting Straw to StorageWhen transporting straw to storage, various tech-niques and methods are used depending on the local conditions. Big bales are loaded and unloaded by front-end loader, trencher, loader tractor, telescope loader, or the like. The telescope loader is suitable for unloading, because it can reach high up when storing the bales in stacks. The front-end loader is the most common. Depending on the front-end loader equip-ment and lifting capacity, the tractor load capacity and stability, and the local conditions, one or two bales are handled at a time (see figure 4.3). The capacity is high-est when handling two bales at a time, but this puts a severe load on the tractor’s front axle, and the stability of the tractor is decreased dramatically if no balancing weight is mounted on the back of the tractor. Modified trucks or truck trailers are widely used. The size of the

load varies from 6 to 18 bales. Over long distances, the tractor is often towing two trailers so that the size of the truckload is as much as 24 big bales.

4.2.3 Long-Term StorageStraw can be stored indoors or outdoors. Indoor stor-age keeps the moisture content stable and prevents mold, minimizing losses. Large storage spaces have a capacity of 1.5–2.5 tons/m2. Outdoor storage is cheap, but it is mainly suitable for short-term storage, and the straw needs to be covered with a tarpaulin.

Huisman, Jenkins, and Summers (2002) evaluated storage systems for rice straw bales and identified the following storage systems:

• Uncovered• Tarped stacks• Wrapped bales• Individual wrap• Tube wrap• Pole barns• Metal buildings• Greenhouse loading docks• Fabric buildings• Truss-arched tarp

There are substantial differences between stacking capacities, stacking arrangements, system lifetime, and system costs among the different storage systems. Huisman, Jenkins, and Summers (2005) conclude that in all cases, except for wrapping, costs decrease with the larger storage quantity. The differences between 800 tons and 4,000 tons are substantial, between 4,000 tons and 20,000 tons are small, and between 20,000 and 100,000 tons are very limited. Uncovered storage of big bales (figure 4.4) is only justifiable for short periods (maximum six months) when only the top layer might be lost. For rice straw, pole barns seem to be the cheapest solution (see figure 4.5). They have a roof only. Metal buildings are slightly more expen-sive, but are closed on all sides, so better protect the straw from rain from the side, animals, and arson.

4.2.4 Delivery from Long-Term Storage to Power PlantDepending on the distance to be covered, delivery to the power plant takes place by truck or tractor. When

Figure 4.3 Loading Straw in the Field


23


transporting by haulage contractor, the farmer or the haulage contractor loads the truck, and the haulage contractor travels to the plant where plant personnel unload by forklift truck, overhead traveling crane, or the like. When transporting by tractor, the speed of operation and consequently the capacity is con-siderably lower, with the differences increasing with increasing transport distance.

When transporting by truck, the cargo is almost always loaded 12 bales on the truck and 12 bales on the truck trailer distributed in two layers (see figure 4.6). This is also seen in tractor transport, but load sizes of 16 or 20 bales are also widely used, particularly for trans-port over short distances.

Unloading at the plants by crane often requires the bales to be arranged accurately on the transport vehicles. The bales should have a specified dimension and not exceed a certain weight. Unloading by crane requires the use of big bales, because the power plants are equipped for this size of bale (see figure 4.7).

4.2.5 Handling at the Biomass Power PlantAs a result of its low density, the storage of straw is space consuming. On average, Danish power plants have storage facilities for eight days of operation at full load. The straw supplier delivers the straw to the plant by truck or tractor-towed trailers. The plant takes care of unloading by forklift truck, overhead traveling crane, and the like.

Figure 4.4 Outdoor Storage of Straw


Figure 4.5 Pole Barn in California for Storage of Rice Straw


Figure 4.6 Truck for Long-Distance Straw Transport


Figure 4.7 Unloading 12 Bales in One Operation

Source: Danish Technological Institute/Lars Nikolaisen.

24


The bales are weighed on unloading, using either a weighbridge or platform scales. The weighbridge is the fastest because only two weighing operations are car-ried out (gross and tare of the truck). Platform scales are used when the truck drives onto the platform with the front wheels. The truck is weighed every time a bale is unloaded. A weighbridge is two to three times more expensive than platform scales, so the choice between the two options is a matter of increased investment against increased working time.

For the determination of the moisture content, a mea-suring instrument equipped with a spear for insertion into the straw bale is used. The resistance over two electrodes is measured and converted into water per-centage. Normally, three measurements are taken of each bale, and the average moisture content is calcu-lated. Depending on practice and the wording of the contract, either a few bales or the whole load may be rejected. Bales with moisture content of more than 20 percent are usually rejected because combustion would be too uneven, especially at part load.

All large power plants are equipped with an automatic crane that lifts the bales from storage to the straw table. The crane is programmed to pick up the bales in a certain order, so it is important for the truck or fork-lift driver to place the bales in marked sections when unloading. Chaff cutters, shredders, or straw dividers are used to pull apart the baled straw.

4.3 Current Status of Straw Supply in China

4.3.1 Straw Availability in ChinaIn China, straw resources are abundant. There are more than 200 kinds of crop straws that can potentially be used to generate energy. The main crops are rice, wheat, corn, cotton, beans, oil seed, and potatoes. According to the Statistical Yearbook of China, in 2006, the total area of crops sown was 155 million hectares, and the total output of the main crops was about 510 million tons. Applying relevant residue-to-crop factors, Li and others (2009) estimated the total straw output at more than 700 million tons. This straw comes mainly from the eastern region of China. Applying a similar method,

the NDRC (2008) estimated the amount of annual available agricultural residues at 681 million tons.

Some 80 percent of the agricultural residues are consid-ered recoverable for further use. Excluding the amount used as fertilizer, forage for livestock, and industrial materials (such as papermaking), the amount of agri-cultural residues available for energy use is more than 300 million tons. However, because about half of crop residues are consumed through direct combustion in rural life, the actual amount of agricultural residues available for centralized biomass-fired power genera-tion is on the order of about 150 million tons, or 75 million tons of coal equivalent.

4.3.2 Straw Collection Practices in ChinaChina has huge volumes of varied, dispersed, and seasonally available types of straw that could be used for power generation. However, relying on traditional collection technology and methods, it is difficult to achieve the high volumes needed to meet the indus-trial requirements for large-scale, standardized, and continuously available straw.

A recent study by CECIC Blue-Sky Investment (CECIC 2009a) discusses the methods used at Chinese bio-mass-fired power plants for collection, storage, and transportation of straw and stalks. There appears to be wide variety in the current biomass supply chain and thus little standardization, even in projects with the same investor, the same fuel type, and the same power generation capacity. The large variety in supply chain models is hardly surprising—on the one hand, the biomass fuel-supply market is relatively new, and on the other hand, each biomass-fired power plant has its unique setting and requires, at least to some extent, its own solution.

Modes for fuel supply include the following:

• Specialized biomass fuel purchasing stations, either established by the biomass power plant or operated by another investor jointly with the local govern-ment or other organizations.

• Cooperation with a professional broker in charge of biomass collection, pretreatment, and storage. A biomass fuel collection agreement will be reached

25


between the broker and the power plant. The agree-ment will at least cover fuel price formula, fuel amount, fuel quality, and method of transaction.

• Cooperation with a multitude (thousands) of var-ied fuel suppliers, including medium- and small-scale biomass fuel brokers and individual rural households.

• Combinations of the three modes mentioned above (CECIC 2009a).

Modes for fuel collection include the following:

• Rural households: Direct collection and storage of biomass fuel, and delivery directly to the purchas-ing stations owned by the plant or to the plant site.

• Fuel brokers: Purchase of biomass fuel in rural areas, either in the field or from rural households, and then delivery to the plant purchasing stations, or storage in their own fuel-storage sites.

• Power plant: Purchase of crop-reaping equipment; organization of a special team to help rural house-holds do crop harvesting work nearly free of charge; and then taking charge of biomass collection, stor-age, and transportation (CECIC 2009a).

Modes for fuel storage include the following:

• Cotton stalks and wood chips with high volumetric weight are usually stacked in the open air.

• Wheat, corn, and rice stalks are treated by scat-tering and bundling, then storing them in the fuel barn; it is less common to process these stalks into biomass briquettes (CECIC 2009a).

The four case studies in the next section illustrate the biomass procurement modes applied across China.

The current straw collection practice in China can at best be classified as “semi-mechanized,” and it involves the application of a traditional chaff cutter for cotton stalk shredding and hydraulic balers for bundling.

The experience gained to date shows that mecha-nized methods must be used to ensure the quality and quantity of the raw material. Furthermore, the collec-tion radius needs to be chosen wisely. If the collec-tion radius is too small, the demand for biomass fuel

cannot be met. If the collection radius is expanded, collection costs will increase as a result of the higher transportation distances and costs, and the need for suitable storage facilities (CECIC 2009a).

In response to the lack of suitable feedstock collec-tion technology, National Bio Energy Co. Ltd. (the owner of more than a dozen large-scale biomass energy plants in China) and the Chinese Academy of Agricultural Mechanization Sciences have proposed a research, development, and demonstration project to develop new equipment for collecting cotton stalks and corn straw. Starting from current technological research on straw collection, baling, and shredding, the research project aims at making a breakthrough in key technologies, including mechanical compression, automatic baling, cotton stalk collection, and efficient shredding. The proposal was submitted to the 2009 Competitive Grant Facility biomass tender organized by the China Renewable Energy Scale-Up Program, and is being considered for funding. The cotton stalk pickup combine harvester would have a production capacity of 10–14 mu/hr (equivalent to 0.67–0.93 ha/hr), and the corn straw large-square baler would have a production capacity of 9–12 mu/hr (0.6–0.8 ha/hr).

4.4 Straw Supply in China: Case Studies

In this section, short case studies are presented illus-trating straw supply arrangements at selected bio-mass-fired power plants in China. The information was obtained from CECIC (2009a).

Case Study A: 30 MW Biomass Power Plant in Shandong ProvinceThe annual fuel demand at the 30 MW Shandong plant is about 220,000 tons. To ensure biomass supply (cotton stalks and forestry residues, such as bark and wood chips), the plant built eight stations for biomass purchasing, storage, and transportation. Site selec-tion for the purchase stations was mainly based on biomass resource distribution, transportation, natural conditions, water resources, and power supply. The biomass supplied to the fuel station is mostly collected by local fuel brokers. Some fuel brokers have their own fuel storage places and pretreatment equipment. The project owner signs contracts with fuel brokers

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specifying fuel amount, quality, and price. The bio-mass fuel is pretreated by biomass purchase stations or fuel brokers, and there is no further pretreatment at the biomass power plant.

Case Study B: 12 MW Biomass Power Plant in Henan ProvinceThe primary biomass used here includes cotton stalks, wheat stalks, maize stalks, peanut husks, tree bark, and wood chips. The biomass fuel is mainly supplied by small-scale fuel brokers or even directly by local rural households. There is no contract between the plant and the fuel suppliers. To encourage the local rural households to transport biomass fuel to the power plant, all involved households received a permit that allows them to enter the tollgate free of charge. The biomass fuel is pretreated at the plant.

Case Study C: 30 MW Biomass Power Plant in Henan ProvinceBiomass fuels used here include straw (wheat, maize, and other), tree bark, and roots. Initially, several straw purchase stations were built by the biomass power plant. These were equipped with capital-intensive handling equipment, such as bundling machines. The fuel supply was not satisfactory. Therefore, instead of running its own purchase stations, the biomass power plant signed contracts with about 10 large-scale fuel brokers to ensure fuel supply. These fuel brokers have their own storage places and bundling machines, and can pretreat the fuel and then send it to the plant. In addition, about 100 small-scale fuel brokers and local rural households send biomass fuel to the fuel brokers for pretreatment.

Case Study D: 24 MW Biomass Power Plant in Jiangsu ProvinceThe annual fuel demand (mainly wheat stalk, rice straw, and other yellow straw) at this plant is about 300,000 tons. Fuel brokers and local rural households have their own storage places and bundling machines, and they can pretreat the fuel to ensure the fuel supply. Because of competition from seven biomass power plants within a 150 km radius, the regional avail-ability of fuel is limited and biomass fuel needs to be collected from up to 150 km distant. A second factor

complicating fuel supply is the occurrence of the rainy season in June and July. During this period, wheat stalks cannot dry naturally, and easily decay, resulting in low calorific value and high moisture content, and the effective fuel price will rise accordingly.

4.5 Straw Supply in Europe: Case Studies

In this section, case studies discuss straw supply arrangements at biomass-fired power plants in Europe. One example each is presented for Denmark, England, and Spain—the main European countries using straw to generate power.

Case Study E: 39.7 MW Biomass-Fired Power Plant in Ensted, DenmarkThe biomass-fired boiler plant at the Enstedværket (Denmark) consists of two boilers, a straw-fired boiler producing heat at 470°C, and a wood chip–fired boiler superheating the steam from the straw-fired boiler to 542°C. The superheated steam is led to the high-pressure steam system of the Enstedværket Unit 3. With an estimated annual consumption of 120,000 tons of straw and 30,000 tons of wood chips, the bio-mass-fired boiler produces 88 MW of thermal energy, including 39.7 MW of electrical power.

Straw is supplied to the plant by truck, with an average of 40 trucks per day, each containing 24 straw bales weighing, on average, 500 kg per bale. Five truckloads supply between 80 m3 and 100 m3 of wood chips to the plant every day.

Fuel feeding to the straw-fired boiler is fully automatic. The system includes automatic cranes and conveyors, which deliver the straw bales to four feeding lines. The straw is burned on a water-cooled vibrating grate.

Case Study F: 38 MW Straw-Fired Power Plant in Ely, United KingdomThe 38 MWe straw-fired power plant in Ely (United Kingdom) was the world’s largest at the time of its con-struction. It consumes 200,000 tons of straw per year and is also capable of burning a range of other biofuels and up to 10 percent natural gas. The main fuel of the plant is agricultural straw from the production of

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cereals, such as wheat, oat, barley, and rye. The straw is supplied to the plant in so-called Hesston bales weigh-ing approximately 500 kg each. The straw bales are stored at the plant in two separate barns, each contain-ing straw for approximately 24 hours of operation at full plant load. The handling of straw bales in the barns is performed by large dual-rail cranes. An automated conveying system transports the straw bales from stor-age to the firing system of the steam boiler.

Case Study G: 25 MW Straw-Fired Power Plant in Sangüesa; Navarra, SpainThe Sangüesa plant consumes approximately 160,000 tons of straw and corn stover per year. The straw is supplied by farmers growing crops within a radius of 75 km from the plant site. The bales of straw arrive at the plant on trucks. The trucks deliver the fuel to the straw barn storage area where the moisture content and weight of the bales are measured and the straw is stored. The data recovered from the moisture content and weight measurements are registered and form the basis for the purchaser in determining the price for the straw. The barn is divided into three sections, and it has a storage capacity of three days of operation.

The power plant is equipped with three automatic dual-rail cranes. These cranes unload the trucks and store the straw in piles according to a prearranged system. The cranes also feed the straw bales onto automatic conveyors that transport the straw from the straw barn to the boiler building. When the bales arrive at the feeding system, an automatic knife cuts the twines. The straw then enters a disintegrator where the straw bale is loosened before being fed into the boiler at the required, controlled flow rate.


4.6.1 ConclusionsWhen using straw for energy applications, the logisti-cal principles are basically the same as for traditional straw applications. However, the scale of operation is significantly larger, in particular related to storage and to ensuring the proper moisture content and year-round availability.

Currently, a wide variety of biomass collection, stor-age, and transportation modes are evident in China, even in projects with the same investor, the same fuel type, and the same power generation capacity. There seems to be little or no standardization. This is hardly surprising since, on the one hand, the supply market is relatively new and immature and, on the other hand, each biomass power plant has its unique setting and requires to some extent a different solution.

Transport logistics are crucial for economic power plant operation. For low-density straw, the collection area should be kept as small as possible. When the col-lection radius expands, collection costs increase as a result of the higher transport distances and costs, and the need for suitable storage facilities. Densification of straw in the form of pellets or briquettes may be con-sidered, depending on the transport distance.

Because of its seasonal availability, a large portion of the straw used at the power plant will need to be stored for several months. Given that there is only a two-month harvest window for straw, large volumes of storage are needed. The optimal storage size is dif-ficult to determine because of the various issues that need to be considered (such as fire risk and protection against rain). The storage at capacity at the power plant site is usually very limited (in the range of a few days) because of the daily volumes needed (500–1,000 tons per day). On average, Danish power plants have storage facilities for eight days’ operation at full load.

A biomass resource assessment that also considers current and future competing uses for raw materials is required to assess the long-term availability of straw. For example, the biomass power plant in Jiangsu province (section 4.4, case study D) had to cope with the limited regional availability of fuel because of competition with seven other biomass power plants within a 150 km radius. To tackle this supply bottle-neck, it is worth exploring the use of a broad biomass fuel mix so as to limit vulnerability to market change, short-term weather conditions, and long-term climate change. Long-term biomass contracting (see chapter 6) is a further instrument to help secure the power plant’s fuel supply.

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The challenge for Chinese straw suppliers is to orga-nize the highest throughput in straw collection at the lowest cost. Important lessons can be learned from Denmark, where practical experience operating bio-mass power and CHP plants on wheat straw has been gained since the late 1980s.

The Danish experience will not be replicated directly in China, because local conditions and practices in China must be taken into consideration. For example, China has more farmers, a lower degree of mechaniza-tion, different types of cereal crops, and different unit prices and price structures.

Although Chinese rural labor is cheap, the experience from Denmark suggests that highly mechanized meth-ods are required to ensure the quality and quantity of the straw supply. In China, as elsewhere, the straw-harvesting season lasts only two months. Therefore, a certain degree of mechanization and automation of the straw harvesting process may be warranted. This is recognized by China’s largest biomass-fired plant operator, National Bio Energy (NBE). Together with the Chinese Academy of Agricultural Mechanization Sciences, NBE has initiated the development of new equipment for collecting, baling, and shredding cotton stalks and corn straw.

To ensure economies of scale, Chinese power plant operators and fuel suppliers may unite their efforts to develop high-throughput straw-collecting equipment. The government of China should consider catalyzing such cooperation.

4.6.2 Recommendations• Make sure that the transport logistics of straw are

well managed because they make up a high share of the delivered fuel costs, and they impose a limit on the maximum plant size.

• For high-capacity power plants, use large rectangu-lar bales and a weighbridge.

• Obtain straw from at least a few different fuel sup-pliers (brokers) to prevent a single fuel supplier (broker) from controlling the fuel price (see section 4.4, case study B).

• Do not store straw outdoors for long (maximum six months). Indoor storage is more expensive, but it keeps the moisture content stable and prevents mold, thus minimizing losses).

• Depending on practice and the biomass contract, do not accept straw with a high moisture content (usually straw with more than 20 percent moisture content is rejected in Denmark). Fuel combustion would become too uneven, especially at part load operation.

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5. Biomass Supply from Forestry Residues

Extraction of forest fuel in conjunction with final fell-ing not only supplies a source of renewable energy but also provides higher revenues for forest owners, because regeneration is promoted through the removal of harvest residues from the final felled area. Branches and tops equal 20–30 percent of the biomass above the stumps. In the Finnish Wood Energy Technology Programme, the Technical Research Centre of Finland (VTT) investigated yields of biomass residues under a typical management regime of a southern Finnish forest stand (Hakkila 2004). The results are presented in table 5.1.

5.1.2 Forestry Residues Production Cost FactorsWhile fossil fuels occur in large deposits and can be produced at a constant cost, forest fuels are scattered and must be collected from a large number of loca-tions. The production costs of these residues depend on many steps within the logistics chain—such as harvesting (extraction), comminuting (chipping or crushing), and storage and transport—as well as the scale of operation, the biomass source, and the quality requirements placed upon the biomass (figure 5.1).

The largest fraction of the procurement costs consists of terrain and road transport. Therefore, the core of forest chip logistics is the control of transportation. Converting the biomass into transportable form with a chipper, crusher, or baler also is an essential part of the logistics system.

A significant gap exists between the cost of fuel from the early thinnings and that from final cuttings. The gap is caused by the high cost of cutting and bunch-ing small trees from thinnings; in the other phases of the procurement chain, cost differences are modest. If no stumpage is paid, the cost level under Finnish conditions stood at €12.8/MWh for whole-tree chips and €8.4/MWh for logging residue chips (2002 data).

5.1 Introduction

5.1.1 Forestry Residues Types and YieldsForestry residues consist of small trees, branches, tops, and unmerchantable wood left in the forest after the clearing, thinning, or final felling of forest stands. Worldwide, experience with the large-scale use of forestry residues for power production is limited. Actually, in most countries, forestry residues are not collected at all for this purpose. The main barriers to their use are high transportation, harvesting, and han-dling costs.

The heavily forested Nordic countries of Finland and Sweden may be the only countries where forestry residues are used for power production on a relevant scale. The two countries have promoted this applica-tion for some time by, among other things, support-ing the development and optimization of harvesting, handling, and transportation technology and logistics. Advanced technologies in the fuel supply and logistics chain have enhanced the use of forestry residues as a new raw material resource that is efficiently used in the form of wood chips. These technologies are still under development, and improvements are made continually.

Three main sources of forestry residues can be iden-tified: slash from final fellings, slash and small trees from thinnings and clearings of young stands, and unmerchantable wood. The forestry residues or “for-est slash” generated at final fellings include the waste left on the ground after the forestry operations have taken place (wood harvesting) and the excess pro-duction that has not been used. Forest slash mainly consists of the tops of trunks, stems, branches, leaves, stumps, and roots. In Sweden, slash from final fellings constitutes the largest share (over 71 percent in 1996 and even more in 2003).

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Annex 7 presents some of the main findings from the Finnish research into reducing biomass supply costs.

5.2 Harvesting (Extraction)

5.2.1 Extraction in Connection with Final FellingFelling adapted for forest fuel extraction is performed with conventional machinery, but according to a spe-cial method. When felling, the harvester operator works so that forest fuel, that is, branches and tops, is gathered into stacks. The trees are felled and tilted over forward, and the fuel is stacked 100–150 cm high and laid alongside the driving passage. After felling, the stacks are often left in the clearing to shed their crown foliage. Crown foliage contains high concen-trations of nutrients that should be left to benefit for-est soil. The crown foliage should preferably be spread evenly over the final felled area, but this is difficult to carry out in practice. The stacks are hauled out with a forwarder to a roadside landing, often in the summer after felling. The tractor should be equipped with an open gripper to avoid bringing up rocks and soil with the load. To take large loads, it should also have some kind of extended trailer, and loading should be done laterally and back to front. The machinery does not have to be otherwise modified for forest fuel extrac-tion. The fuel should be deposited in stacks at an open, dry place where it can continue to dry. Stacks can also be covered with paper and anchored by a few bun-dles of harvest residues. Chipping is carried out at the stacks, and forest fuel chips are transported onward

mainly by trucks with demountable body systems and containers (Emilsson 2006).

A number of different forest fuel extraction systems are applied after mechanical final felling. These systems have somewhat divergent sequences and techniques:

• The forest fuel can be transported directly to an energy plant or terminal from the temporary depot in the forest and be chipped or crushed at the plant or terminal. One problem with this system is that it is difficult to make the load sufficiently compact

Table 5.1 Forest Productivity in Finland

Yield of timber Biomass residues

Treatment Stand age (years) (m3/ha) m3/ha toe/ha GJ/ha

Precommercial thinning 10–20 — 15–50 3–9 125–375

1st commercial thinning 25–40 30–80 30–50 6–9 250–375

2nd commercial thinning 40–60 50–90 20–40 4–8 165–335

3rd commercial thinning 50–70 60–100 20–40 4–8 165–335

Final harvest 70–100 220–330 70–130 13–24 545–1005

Total during rotation n.a. 360–600 155–310 30–58 1,255–2,430

Source: Hakkila 2004.

Note: n.a. = Not applicable.

Figure 5.1 Typical Cost Structure of Forest Chips in Finland—Prices at Plant, Excluding VAT, 2002

Sources: BTG; Drohm Design & Marketing based on Hakkila 2004.

16

14

12

10

8

6

4

2

0

cost

, €/M

Wh

logging residue chips

whole-tree chips

overheadtruck transportchipping at landingoff-road transportcutting

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for transport to be financially viable. Technical refinements aimed at solving this problem are being developed.

• Chipping can be carried out in the felled area with a mobile chipper, which then dumps the forest fuel chips in containers parked at a forest roadside or in a shuttle transporter.

• The forest fuel is sometimes hauled out of the felled area to a forest road immediately after felling, with crown foliage still attached. This method may be preferable on severely acidified soil with a high nitrogen deposition, since crown foliage extraction reduces the nitrogen load. Here as well, chipping can be done at the roadside or after transport to a heating plant or terminal. When green forest fuel that has not shed its crown foliage is extracted, the need for ash recycling to compensate for the extraction increases.

• There are also techniques for bundling fresh forest fuel with the crown foliage still attached into log-like bundles that can essentially be handled like round timber. The main advantage of this technique is that standard timber trucks can be used, and further transport of timber and forest fuel can be coordi-nated. The method requires appropriately dimen-sioned crushers at the heating plant or terminal.

5.2.2 Extraction in Connection with Clearing and Thinning

Integrating forest fuel extraction with a forestry oper-ation, such as thinning or clearing, is a relatively new practice. Clearing entails a net expenditure for the forest owner and, as a result, is sometimes neglected, leading to large areas of young forest with high stem numbers that must be dealt with. These stands are ideal for extraction of forest fuel. For cost reasons, extraction is carried out mainly in conjunction with mechanical thinning or clearing. Since the extraction volume is less than in connection with final felling, the financial pressure is also greater. An accumulating multitree-handling harvester is often used, which cuts stems, accumulates them, and puts them in bundles alongside the skid road for hauling to a landing. This technique enhances performance considerably com-pared with single-tree handling by making hauling easier. The forest fuel can either be chipped at the stack or transported directly to a terminal or boiler plant

for processing. Here, as with extraction in conjunc-tion with final felling, there are a number of variants or combinations for the extraction (Emilsson 2006):

• Conventional thinning harvesters are used for thicker stands. The method is similar to that used for mechanical final felling.

• Chipping can be carried out in the stand, preferably along skid roads, after which the chips are dumped in containers.

• One interesting variant is “long tops,” a method of thinning in which the harvester cuts the tops at a diameter thicker than normal, and the forest fuel is extracted as long, untrimmed tops. This yields more forest fuel at the expense of pulpwood.

• Forest fuel can also be extracted in connection with restoration of meadowlands and pastures, visibility clearing, and so forth, using technical systems simi-lar to those used for extraction in conjunction with thinning and clearing.

5.3 Comminution

Comminution (sizing of the fuel) is the most impor-tant phase in the forest fuel production chain, since it has a crucial impact on system efficiency. Comminu-tion may take place at (a) the roadside or landing site, (b) the source, (c) the end-use facility, or (d) a fuel terminal.

A forest fuel production system is built around the comminution phase. The position of the chipper or crusher in the biomass procurement chain largely determines the state of biomass during transportation and, consequently, whether subsequent machines are dependent on each other. When there is such depen-dence, the production system is “hot,” and the chain is referred to as a hot chain. When there is no such dependence, the production system is “cool,” and the chain is referred to as a cool chain.

5.3.1 Comminution at LandingComminution at a landing or roadside is the tradi-tional option for forest chip production. The biomass is hauled by forwarders to the landing and bunched into 4–5 m high piles. The forwarder operates inde-pendently of the chipper. Comminution is performed

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at the landing using farm tractor–driven chippers in smaller operations and heavy truck-mounted chippers or crushers in large-scale operations (see figure 5.2).

Chips are blown directly into a 100–130 m3 trailer truck. The chip truck is typically equipped with either a bottom conveyor or a side tipper, and it weighs about 23 tons unloaded. This allows a maximum load of 37 tons of chips to be transported (when the allowable total mass is 60 tons, as in Finland). With very moist chips, overloads are possible, whereas with dry chip loads, total weight stays well under the upper limit.

When comminution takes place at the landing or roadside, the chipper and chip truck are dependent on each other. For that reason the system is hot and vulnerable to machines waiting on each other, which can result in reduced operational efficiency. Thus, the logistics between the chipper and the chip trucks is crucial to keeping the fuel supply economically viable. However, if the chipper and chip truck belong to dif-ferent contractors, optimization of the logistics may be difficult.

Another problem is that a wider landing area is required than in the alternative systems. This is because of the large roadside inventories of biomass and the simulta-neous presence of the chipper and the truck.

Landing chippers do not operate off-road and can there-fore be heavier, stronger, and more efficient than terrain chippers. They are reliable, their technical availability is high, and they have a long life span. They need to be highly efficient. To avoid peak stresses for the machin-ery because of sudden variations in the feeding rate, the chipper should have a long feeding table, facilitating a smooth raw material flow. Drum chippers are more suitable than disc chippers. Drum chippers produce more homogeneous, that is, even-quality chips (with fewer splinters) and are also not as sensitive to impuri-ties. If the biomass, such as stump and root wood, is contaminated by stones and soil, it is possible to use crushers that are more tolerant than chippers.

The productivity of roadside chipping is affected by the characteristics of the raw material, storage, and work-ing site arrangements, as well as the properties of the chipper. In general, productivity varies between 40 bulk m3 and 80 bulk m3 per effective working hour. It is nor-mally faster to process fresh forestry residues than dry raw material. An overly careful utilization of the bottom bundles of forestry residues is not profitable. Significant extra costs may be incurred because the impurities from the ground might damage the chipper knives.

To prevent the system from overheating, the truck-mounted chipper and chip truck can be replaced by a

Figure 5.2 Forest Chips Production Chain Based on Chipping at Roadside (Landing)

Source: VTT, Alakangas.

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single chipper truck (see figure 5.3). This truck blows the chips directly into a container and then hauls the load to the plant. Since the chipper truck is equipped with a chipping device and crane, load capacity suf-fers, and the radius of operations around the plant is reduced. Conversely, because only one single unit is needed, the chipper truck is suitable for small work sites and for delivering chips to smaller-scale plants.

5.3.2 Comminution at the SourceComminution in the terrain, or at the source, requires a highly mobile chipper suitable for cross-country operations that is equipped with a tippable 15–20 m3 chip container. Terrain chippers are typically built on a forwarder chassis. The chipper moves in the terrain on strip roads and transfers the biomass with its grap-ple loader to the feeder of the chipping device. The

load is hauled to the roadside and tipped into a truck container, which may be on the ground or on a truck trailer (see figure 5.4).

Because a single machine carries out both the com-minution of biomass and the off-road transport of chips, the cost of shifting machines from site to site is reduced, and smaller forestry sites become com-mercially viable. Moving the terrain chipper from one working site to another can be accomplished either on a low-bed trailer or, for short distances, by driving the terrain chipper on roads. The use of containers reduces the interdependence between the chipper and the truck, although it is not entirely removed, and the system remains somewhat hot. Large landing areas are not required, but a level and firm site is necessary for the truck containers.

Figure 5.3 Chipper Truck

Source: L&T Biowatti.

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For off-road operation, the chipper must be as light as possible, while still sufficiently strong and stable. Even so, terrain chippers tend to be too heavy for use on soft soils, while the use of crushing equipment in ter-rain is out of the question. A terrain chipper requires flat and level ground and, because of its small load size and slow speed, its range is less than 300–400 m. Snow causes problems in the winter and results in a higher moisture content unless the terrain chipper operates at a landing.

By using exchangeable chip containers for long-dis-tance transport of the wood chips, there is no danger of forming a hot chain, provided there are sufficient containers to be filled. Chip trucks use typically 30–50 bulk m3 chip containers, two or three of which can be transported at the same time, raising the total volume of the load to 80–100 m3.

The cost competitiveness of a terrain chipper is fairly weak for long forest haulage distances. When large volumes of forest fuels are produced, the terrain chip-ping system becomes difficult to control.

5.3.3 Comminution at the End-Use FacilityA third option for processing forestry residues is chip-ping or crushing at the end-use facility. In this system, chipping and trucking are fully independent of each

other, and hot chain problems are avoided. The tech-nical and operational availability of the equipment increases, which raises productivity and reduces costs. Furthermore, control of the procurement process is facilitated, demand for labor is decreased, and the control of fuel quality is improved. Mobile chippers can be replaced by heavy stationary crushers that are suitable for comminuting all kinds of biomass, includ-ing stump and root wood and recycled wood.

Under Finnish conditions, comminution at the end-use facility is the most economic processing option, provided the processed volumes are large (only large plants can afford a stationary crusher) and the trans-portation distance does not exceed 55 km. The larger the fuel flow, the more obvious the advantages become. Requirements include a heavy crane and a fairly large storage and processing space. Noise and dust emis-sions can be a problem, and they need attention.

The main challenges of this processing option are related to long-distance transport of forestry residues. Truck transportation of biomass traditionally takes place in the form of loose forestry residues, whole trees, or pieces of stump and root wood. The low bulk density of the biomass is the weak link in the system. Without compacting the forestry residues, truckloads remain very small.

Figure 5.4 Forest Chips Production Chain Based on Terrain Chipping


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The traditional approach to increasing the truckload is to compact the load or extend the load space, or both. A new approach is the baling of loose forestry residues into composite residue logs (CRLs). The baling takes place in the forest at the woodlot before transport. The two approaches are discussed below.

Comminution of Loose Forestry ResiduesThe principles of processing loose forestry residues at an end-use facility are presented in figure 5.5. Long-dis-tance transportation of forestry residues imposes sev-eral requirements on the transportation equipment:

• The load space of the truck should be built accord-ing to the maximum allowable dimensions.

• The load space must have a closed bottom and sides.

• The trucks should be equipped with special cranes suitable for loading and unloading residue, as well as for compacting the load.

• Special forestry residue grapples are more suitable for loading than are normal timber grapples.

The transportation density of forestry residues can be improved by using separate hydraulic compressing cylinders and bolster bars. The disadvantages of this system include extra costs and a fairly complicated equipment structure.

Comminution of Baled Forestry ResiduesBaling forestry residues is one way of compacting raw material to improve the productivity of long-distance

transportation. Building on a Fiberpac design, intro-duced earlier in Sweden, Timberjack (now part of and renamed John Deere) further developed the technol-ogy that resulted in the 1490D residue baler (see fig-ure 5.6).

In this system, forestry residues are compressed and tied into 0.7 m diameter, 3 m long bales or CRLs. A bale of green residues weighs 500–550 kg and has an energy content of about 1 MWh. Bales are trans-ported to the roadside using a conventional forwarder (figure 5.7) and are stored at the roadside for one to three months to dry (figure 5.8). The bales are trans-ported to the power plant using a conventional tim-ber truck. About 12 bales form one forwarder load, and 65 bales or 30 tons form one truckload (truck-

Figure 5.5 Forest Chips Production Chain Based on Comminution of Loose Residues at an End-Use Facility


Figure 5.6 Timberjack 1490D Residue Baler

Source: Drohm Design & Marketing/Deere & Company image gallery.

36


trailer combination). CRLs can also be transported to the end-use site together with commercial timber, for example, pulpwood. At some plants in Finland, long-distance transportation is done by rail.

Unloading the CRLs takes place at the end-use site with equipment similar to that for unloading pulpwood.

In the most efficient cases, the CRLs are unloaded directly from the truck to the feeding table of the crusher. The baled residues processing chain is illus-trated in figure 5.9.

The advantages of CRLs in large-scale operations become clear when considering not only the costs from separate work phases of the processing chain, but also logistics, operational availability, process control, reli-ability, scaling, and environmental impacts:

Figure 5.7 Loading CRL Bundles on a Forwarder

Source: Drohm Design & Marketing/Deere & Company image gallery.

Figure 5.8 Storage of CRL Bundles

Sources: BTG; Drohm Design & Marketing/Deere & Company image gallery.

Figure 5.9 Production Chain Based on Composite Residue Logs


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• Machines operate independently of each other.• Flexible integration in the procurement of indus-

trial wood.• Accurate real-time information about the inven-

tories.• Fewer problems with noise, dust, and litter.• Reduced space requirement; simple storage.• Reduced transport and overhead costs.• Improved control of fuel flow and reliable delivery.

The advantages must be weighed against the extra cost of baling. In Finland, the system based on CRLs and comminution at a plant quickly became popular. The organizations responsible for the procurement of raw material for the forest industries found the baling technology an attractive way to integrate fuel produc-tion into their operations. A range of other countries (Austria, the Czech Republic, France, Germany, Hun-gary, Italy, Portugal, Spain, Sweden, Switzerland, and the United States) have tested the John Deere (previ-ously Timberjack) residue baler, with some of them using it for commercial operations.

It may still be economical to transport forestry resi-dues over short distances to the plant as unprocessed loose material.

5.3.4 Comminution at a TerminalComminution at a terminal is a compromise between comminution at a landing and at the end-use facility. Biomass is hauled uncomminuted to the terminal for size reduction, and then transported to the plant as chips.

If the network of terminals is dense, the distance from the forestry site to the terminal remains short. The sys-tem does not differ much from the traditional option where comminution is carried out at a landing.

If a fuel producer operates only a few terminals—and they are located far from the biomass sources—off-road transport with a forwarder and on-road trans-port with a truck will be separate operations. The size of the terminal will be larger, and the system will not

differ greatly from comminution at plant. The termi-nal may be paved, and the use of a crusher will be possible.

A terminal is a tool for controlling the procurement process. Biomass can be stored at the terminal uncom-minuted and processed during the winter season when the demand for fuel is high and working conditions at the forest end are difficult. The arrangement makes it possible to apply baling technology to supply forest chips to smaller energy plants that do not have sta-tionary crushers.

5.4 Biomass Fuel Storage

According to Vares and others (2005), the amount of fuel stored at the boiler plant and thus the capacity of the fuel storage facility depends on several factors, including the type of agreement with the fuel supplier (see chapter 6). A minimum reserve is necessary to pro-vide continuous fuel supply, and a maximum reserve is required for providing fire safety. Furthermore, there is always a danger of breathing in the allergy dust or micro-organisms in woodchip storage. For that rea-son, it is important not to work alone in the storage facility, and important for the storage side to be well ventilated. Covering forestry residues prevents mold growth during extended storage.

The best way to store forestry residues is to lay them on a waterproof surface (cement or asphalt) protected by a cover located in a sunny and ventilated site (Fran-cescato and others 2008). However, depending on the management of the biomass supply chain and the availability of storage space beside the biomass-fired power plant, forestry residues are stored either at the roadside or at the power plant location. Short-term storage for one to several days of uninterrupted opera-tion is always required at the biomass power plant.

5.4.1 Storing Forestry Residues at RoadsideAccording to Savolainen and Berggren (2000), stor-age of forestry residues at a roadside landing needs to comply with the following:

38


• Planning must be done carefully because of the “hot chain,” for example, where the unavailability of one unit affects the whole chain.

• The landing must be spacious, level, and well bear-ing. No stumps, big rocks, or any other obstacles that could hinder movements should be at the site.

• The landing should not be close to electrical or tele-phone lines.

• The landing should be spacious enough for vehicles to turn and pass.

• The landing should have the necessary space for the piles of forestry residues—approximately 10 m in width for every 100 m3 of forestry residue if the pile is approximately 5 m tall and wide.

Some other important aspects concerning roadside storage are the following:

• Forestry residue storage piles should be as large as possible. In practice, the rear edge of the pile may be located at a maximum distance of 5–6 m from the edge of the road.

• Small piles get wet easily during storage.• A few bundles of whole trees (or tops) should be

placed transversely on the bottom of the pile to protect forestry residues from contamination and frost during the winter.

• Forestry residues should be placed in a roadside pile with the butts of the trees facing the road.

• Piling crosswise should be avoided.5.4.2 Storing Forestry Residues at Biomass-Fired

Power PlantAccording to Vares and others (2005), biomass stor-age at the power plant must meet the following basic requirements:

• Adequate protection of the fuel from the impacts of weather, and from surface and ground water.

• Mechanized storage and, for larger capacities, automation.

• Access for delivery vehicles to unload directly in the storage or mechanized reception unit.

The fuel storage at the biomass-fired power plant always consists of at least two parts:

• Interim storage with capacity for a few days of plant operation (typically between two and eight days).

• A terminal with an automated boiler fuel sup-ply, with capacity of up to 24 hours of plant operation.

These two types of storage are usually situated in the same building, although they may be located sepa-rately. At smaller power plants, a bulldozer fills the terminal and hauls forestry residues from the interim storage. At bigger power plants, an automatically operated crane is used for filling the terminal.

5.5 Bioenergy Fuel Chain Case Studies from China

Although it is understood that at least some of the Chinese biomass-fired power plants use forestry resi-dues as one of their feedstocks (for example, the 30 MW power plants in Shandong and Henan provinces, which mainly use bark and wood chips), few docu-ments on assessing forestry residues for this purpose seem to be publicly available in English.

5.6 Bioenergy Fuel Chain Case Studies from Europe

As discussed in section 5.1, Finland and Sweden have the most experience using forestry residues for power production. In the frame of the EUBIONET-2 project (www.eubionet.net), funded by the European Com-mission, more than 30 supply chain case studies were developed, describing biomass supply chains in use at bioenergy plants across Europe, including in Finland and Sweden.10

10. Case studies #2 Forest residue supply chain for CHP plants in Central Finland, and #7 Supply chain for wood chips from early thinning in Sweden. The case studies are available at eu-bionet2.ohoi.net.

39


Another valuable source of case studies is the 5EURES project, which was also funded by the European Commission.11

Figures 5.10 and 5.11 present graphical representa-tions of two sample forestry fuel supply systems, applied by the companies VAPO and UPM-Kymmene, respectively (Pöysti 2005). Earlier sections of this chapter, in particular sections 5.2–5.4, discuss the var-ious unit operations that make up the respective fuel supply chains. Note that each biomass fuel situation will require a customized supply system.

11. Study material from the project 5EURES—Bioenergy Pro-duction Know-How to Five European Regions is available at www.ncp.fi/koulutusohjelmat/metsa/5Eures/study_material_index2005.htm.

5.7 Conclusions

The challenge for Chinese forestry residue suppliers is to organize the highest throughput in fuel collection at the lowest cost. Important lessons can be learned from Finland and Sweden, where practical experience operating biomass district heating, CHP, and power plants on forest fuel has expanded considerably over the last few decades.

The Nordic experience with the large-scale supply of forest chips will not be replicated directly in China because the production methods and cost breakdown of forest chips vary considerably between countries and regions. Due consideration will be given to local conditions and practices in China. Generally, the cost depends on how well the unit operations in the sup-ply chain are organized and structured. Furthermore,

Figure 5.10 A Wood Chips Delivery System Integrating Different Supply Concepts

Sources: BTG; Drohm Design & Marketing based on Pöysti 2005.

Vapo Company—Organizing wood chip delivery

Collecting felling residue (harvester-forwarder) Purchasing ground wood to storages along roads

Transportation in forests—tractor trailer

Transportation in forests—forest tractor

Transporting chips semi rigid lorry Transporting chips—3 containers

Transportation lorryTerminal chipping—TT97

tractor chipperTerminal chipping—TT97

RMT lorry chipper

Transporting chips—articulated lorry

Toppila heat plant, 267–315 MW, fuel usage 3,800 GWh, forest chips 42 percent (equals 30,000 m3)

Terminal storageChipping—TT97 RMT

lorry chipperChipping—TT97tractor chipper

40


the efficiency of a procurement system is highly depen-dent on the environment and infrastructure in which it operates. Economic, social, ecological, industrial, and educational factors, as well as local traditions, also have an effect.

Selection of the forest fuel harvesting technology requires a complex technical analysis that takes into account

• Annual need for forest fuels and other fuels.• Annual availability of forest fuels.

• Fuel mix (residues, small trees, stumps).• Transport distances in the forest or the on-road

network.• Location of plant (center of a town or in the subur-

ban area).• Size of plant yard (storage).• Type of biomass energy plant (power only, heat

only, CHP).• Dominant technology to produce chips.• Need for GIS-based resource availability and cost

analysis.

Figure 5.11 A Forestry Residues Supply System Based on Bundled Slash Delivery

Sources: BTG; Drohm Design & Marketing based on Pöysti 2005.

UPM-Kymmene Corporation—Organizing bundled slash delivery

Piling felling residue with harvester-forwarder

Bundling slash (Timberjack/Fiberjack 370 slashbundler)

Transporting slash bundles in forest (Forest tractors)

Transporting slash bundles long distance (timber lorries)

Alholmens Kraft heat plant, 580 MW, fuel usage 3,500 GW forest chips 12 percent (equals 200,000 m3)

A forest fuel supply chain will be built around the chip-per or crusher, since comminution or sizing of the fuel is the most important phase in the production chain. To select the most-suitable comminution system, the following issues are important to consider:

• Hot chain versus cold chain: In roadside chipping the chipper and truck are dependent on each other (hot chain). As a consequence, the potential operat-ing time of the chipper or chip truck may be wasted by waiting, resulting in a low degree of capacity utilization and high chipping costs. Chipping at an end-use facility makes the chipper and truck inde-pendent of each other (cold chain) and makes it easier to ensure a high degree of capacity utiliza-tion and thus to achieve low chipping costs.

• Load volume: The low bulk density or load volume of unprocessed material is the weak link in the end-use facility chipping system. New technology (for example, the bundling of slash or the delimbing of small trees) helps to improve the bulk density and reduces transport costs.

• Investment costs: The costs of centralized commi-nution equipment are high, and an end-use facility chipping system is suitable only for large plants. The roadside landing chipping system is suitable for smaller energy plants.

The cost and productivity of the forest chip supply vary greatly between countries because of differences in forest resources, annual harvest, and cost structure of machinery. Often the costs depend on how well all the operations featured in the supply chain are inte-grated. In general, the production cost of forestry resi-dues largely depends on the following criteria:

• Comminution type.• Transportation distance.• Storage and drying.• Degree of mechanization.• Steepness of the terrain.• Type and size of the machines used.• Labor costs in the country.

When a number of harvesting sites for forestry res-idues are available, it is important to select the site

41


with the best characteristics from the perspective of biomass supply. Characteristics of a good harvesting site for forestry residues include the following:

• Many tree species with a large portion of foliage and branches, for example, spruce (Picea abies), which allows for a good recovery rate and productivity.

• Enough fertile soils.• A sufficiently large felling site or a concentration of

stands.• Easily traversed, well-bearing ground.• No undergrowth to hinder forestry.

• Short terrain transport distance.• A spacious roadside storage area for long distance

transport.

Hauling distances to the energy plant help determine which harvesting chain is the most economic. Hauling distances should be kept within reasonable limits. If distances become too long to provide sufficient bio-mass to a dedicated large-scale biomass energy plant, it may be wiser to opt for a smaller energy plant or aim at the cofiring of biomass.

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6. Managing the Biomass Fuel Supply

6.1 Organizing the Biomass Fuel Supply

A biomass-fired power plant needs biomass fuel. To operate continuously, and in particular at the time of initial plant start-up, the power plant will need a stock of biomass fuel. To replenish the stock, biomass fuel will need to be supplied to the plant regularly. For a large power plant, dozens of trucks or several train-loads may be needed on a daily basis.

To ensure the efficient operation of a biomass fuel sup-ply chain, the fuel supplies need to be well organized during the planning stage, as well as the operational stage of the power plant. Efficient organization is nec-essary to be able to procure biomass fuel at acceptable costs, so that the power plant can operate profitably. Furthermore, any entity providing investment capi-tal for a bioenergy plant will usually require that fuel supply contracts be in place before project funding is approved.

There is no standard recipe for how best to organize and structure the biomass fuel supply chain, given that it depends on many factors. However, it is possible to draw up an overview of important fuel supply con-siderations. This chapter will address some of these issue.

Section 6.2 presents the main aspects of biomass fuel contracting. These will need careful consideration at the planning stage. Section 6.3 discusses activities at the power station (for example, sampling, exclusion, and monitoring) aimed at ensuring that the biomass fuel received meets the supply contract requirements. These activities need attention at the operational stage. This section also describes a method for fuel inspec-tion and quality control.

For various reasons, the price, quantity, and specifica-tions of actual fuel supplies may not match what was contracted. It is therefore important for the biomass power plant to develop a strategy to mitigate fuel sup-ply irregularities and risks. Section 6.4 describes how a fuel supply risk matrix can be used to develop miti-gation strategies.

6.2 Biomass Fuel Contracting

At the plant planning stage, Chinese biomass-fired power plants should preferably sign long-term supply contracts to secure the large volumes of fuel required for plant operation. Biomass fuel contracting refers to all activities aimed at securing the supply of biomass fuel of the right quality, in the right way, in the right quantities, at the right time, and at the right price.

The main issues to cover in a biomass fuel supply con-tract are fuel quantity, fuel quality (including quality standards and specifications), fuel pricing, and fuel delivery. Other important terms usually covered in biomass fuel supply contracts are guarantees, sam-pling, payment conditions, an escape provision for conditions beyond the control of either buyer or seller, penalties for noncompliance, and other terms and conditions.

Depending on the biomass power plant’s preferences, it may seek to contract for feedstock from a single sup-plier, or a few or multiple suppliers. It is recommended to enter into contracts with at least a few different fuel suppliers to avoid temporary shutdown if the bio-mass supply from a dominant supplier is interrupted or becoming too expensive. For example, the 12 MW Henan province biomass power plant has chosen to work with many small-scale fuel brokers to prevent a

43


large fuel supplier or broker from controlling the fuel price.

If the power plant decides to deal with a few preferred suppliers, a thorough assessment of their capacity and reliability is warranted. Such assessments are less important (and probably not even feasible) when the power plant deals with a multitude of suppliers.

To meet the power plant’s preference to deal with a limited number of contract partners, individual fuel owners (land owners or crop growers) can band together in a cooperative and work through the coop-erative to contract with the power plant. Alternatively, a private fuel supplier can operate as an intermediary between landowners and growers on one side and the power plant on the other.

Annex 8 presents a sample biomass fuel supply con-tract with some guidance notes, developed by the Car-bon Trust (Carbon Trust 2005b).

6.2.1 Biomass Fuel QuantityThe amount of fuel a biomass power plant requires is directly linked to the plant’s capacity, the number of operational hours, the load factor, and the conversion efficiency. Other important factors include the type(s) of biomass used, its bulk and energy density, moisture content, and calorific value.12 Even for the same type of biomass (wood), there can be considerable fluctua-tions in these parameters.13

12. See chapter 2 for more details on relevant fuel character-istics.13. Although the energy content of wood by weight varies very little between different timber species, the density varies significantly. Therefore, if the end user is purchasing biomass by weight, the species of timber should not matter (although clearly the moisture content of the biomass will). However, if purchasing biomass by volume, the energy content will be de-pendent upon the timber species. For example, the typical calo-rific value of softwood chips at 30 percent moisture content is 0.70 MWh/m3, compared with 1.02 MWh/m3 for hardwood chips at 30 percent moisture content. In addition, the bulk den-sity will vary considerably, resulting in a highly variable volume expansion from 1 m3 of solid wood to anywhere between 2 and 5.5 times the original volume when chipped (Carbon Trust 2005a). See annex 9.

Thus, the first step is to determine which type(s) of biomass to fire in the power plants, and to assess the approximate amount of each biomass type needed per period of time (for example, daily, weekly, monthly, or annually). It is understood that Chinese power plants are usually designed to be sufficiently flexible, and they already have the required operational permits in place to allow a blend or mix of different types of bio-mass to be fired.

Which biomass fuel is actually contracted for does not depend so much on the availability of the biomass fuel alone, but on its availability at the right price. This concept is also known as contractability. Important factors that help determine the availability of a spe-cific type of biomass from a given supplier at a given time include the following:

• The supply radius considered.• Competing uses (applications).• Competition among suppliers.• Seasonal patterns (crop growing/harvesting seasons).• Terrain conditions (access may be restricted during

winter or rainy season).

To the extent that these factors are not covered in the biomass resource assessment, they should be taken into consideration before the power plant signs any contracts with its fuel suppliers.

6.2.2 Biomass Fuel QualityThe quality of the biomass feedstock has a large influ-ence on the performance of the combustion process and the equipment life span. Smaller plants especially require high-quality biomass fuel. For that reason, it is very important to include quality requirements in the biomass fuel supply contract.

To help the biomass power plants formulate quality requirements, it may be practical to use fuel standards. For example, solid biomass standards were introduced in Europe and in individual European countries for biomass fuel to become a commodity with common definitions, common methods, and a clear classifica-tion system. At the European level, the CEN devel-oped standards to describe all forms of solid biomass,

44


including wood chips, wood pellets and briquettes, logs, sawdust, and straw bales. More information on these CEN biomass fuel standards and specifications is presented in annex 2.

When supplied fuel is not in compliance with the speci-fications, it may be rejected by the buyer or reduced to a price that is agreeable to both buyer and seller.

6.2.3 Biomass Fuel PricingTo ensure that the biomass power plant is capable of operating economically in the long term, it is crucial that biomass fuel is always available at an acceptable price. Biomass power plants should put a high prior-ity on contracting for and securing low-cost feedstock. The price that a power plant needs to pay for biomass feedstock depends on many factors, including fuel type (species), quality, volumes from suppliers, reliability, local market conditions, availability (which depends on such factors as the season, the weather, and market competition), and transportation distances and costs. Because so many different factors influence the final biomass fuel price, it is recommended to determine benchmark prices and to carry out market surveys at regular intervals (data collection and analysis on avail-ability of residues and demand by current and future competitors).

The final price can consist of a fixed price negotiated with the fuel supplier or an initial price based on the full costs of supplying biomass to the power plant with a price index. The initial price then changes over time by periodically applying the agreed-on indexation (Carbon Trust 2005b).

To negotiate effectively, it is important for a biomass plant owner to understand the cost structure of the biomass fuel. In the highly developed Danish straw-for-energy market and the Finnish and Swedish wood-for-energy markets, cost structure surveys are done every few years. DTI (2007b) presents a cost structure for wheat straw (production of big bales) in Denmark that covers the value of wheat straw in the field (€5.00 per ton); turning or raking (€5.00 per ton); baling (€19.00 per ton); loading, transport, unloading (€6.00 per ton); and storing at the farm (€14.00 per ton) (DTI

2007a, 2007b). An example of cost structures for dif-ferent forestry residue fuels in Finland is shown in fig-ure 6.1.

For all biomass fuels, the moisture content is a very important quality specification. Dry biomass has a greater specific energy content than wet biomass. For that reason, it is recommended during biomass con-tracting to reflect moisture content in the biomass pricing wherever possible. Van Loo and Koppejan (2008) mention three different alternatives for pricing fuel based on the delivered energy content. Details are presented in annex 10.

The increased demand for, and use of, agricultural and forestry residues for energy generation (for example, as a result of a new bioenergy plant being built in the same collection area) can lead to higher feedstock prices, first, for the raw material itself, as a direct result of increased competition for its use, and second, for the transportation of the raw material, because it may need to be obtained from more difficult and distant stands. Two examples can illustrate this upward price trend. In Finland, the price for logging residue chips dropped in the 1980s and 1990s, but increased in the early years of this century, partly as a result of increased demand. In the Netherlands, highly competitive uses for wheat straw (soil conditioning, cattle breeding, horticulture, bedding material for tulip bulbs) forced the price up to more than €100 per ton. The development and implementation of new bioenergy technologies can further increase the mar-ket competition for agricultural and forestry residues. Examples include second-generation ethanol produc-tion or thermal “biomass-to-liquid” production.

6.2.4 Other Supply Contract ConsiderationsSeasonal RestrictionsSpecific fuels, such as agricultural and forestry residues, may only be available in specific periods or under cer-tain field conditions. In Scandinavia, forest operations come to a halt during part of the year as a result of limited terrain accessibility. For agricultural residues, the harvesting window is typically limited to approxi-mately two months. To address these seasonal restric-tions, it is important to construct biomass storage

45


capacity and to build up a sufficiently large fuel stock (at the biomass power plant or elsewhere in the supply chain). In addition, the biomass power plant may try, whenever possible, to arrange planting and collection schedules with growers and forest owners. This allows better planning of delivery dates and supply quantities. When high-quality straw, for example, is available at a certain time (even within a common straw harvesting window of two months), less straw has to be stored during the season, resulting in lower storage costs.

Initial Fuel Stock Build UpA special situation arises at initial plant start-up. The biomass fuel needed for initial operation needs to be contracted for and accumulated in the months before the power plant starts operating at full scale. This requires early fuel contracting and construction of effective fireproof and rainproof storage, as well as sufficient working capital to pay for these fuel sup-plies and facilities. To minimize the risk of temporary

shutdown in the event of possible biomass fuel supply interruptions, a biomass power plant should always maintain a fuel buffer stock.

Contract DurationBiomass-fired power plants generally prefer long-term contracts for biomass fuel supply because financing agencies demand security of income. However, farm-ers and landowners prefer a balance between security of income (long-term contract) and flexibility.

6.3 Biomass Fuel Supply Control

6.3.1 Introduction to Fuel Quality Control MeasuresAt the plant operational stage, many activities need to be carried out at the power station to ensure that the biomass fuel received meets the supply contract requirements. Such activities include transportation outside the plant; fuel inspection and quality control inside the plant; confirmation and determination of

Figure 6.1 Cost Structures of Different Forestry Residues Fuels in Finland

Source: Laitila 2005.

Note: RS = Roadside; PP = Power plant. A harwarder is a combination harvester and forwarder.

delivery cost

terminal cost

transport

chipping

in-woods chipping

harwarder logging

forwarding

bundling

felling and bunching

other cost

40

35

30

25

20

15

10

5

0

cost

at

the

plan

t, �

/m3 The cost gap =

felling cost

feller buncher

and chipping at RS. Whole

trees

fellerbuncher

and crushing atPP. Whole

trees

harwarderand

chipping at RS. Whole

trees

harwarderand

chipping atPP. Whole

trees

lumberjackand

chipping atRS. Whole

trees

lumberjackand

chipping atPP. Whole

trees

harvesterand

chipping at RS. Delimbed

trees

harvesterand

chipping at terminal. Delimbed

trees

chipping at

roadsidestorage

chippingin

terrain

looseloggingresidues

loggingresiduebundles

Logging residuesSmall trees from early thinnings

46


the fuel price upon arrival at the plant; management of the fuel loading, transportation, and storage inside the plant; and staff training and management. Each subsystem should coordinate well with the others to ensure fuel supply and reduce risks.

Relevant tasks include the following (CECIC 2009a):

• Fuel transportation system outside the plant: This mainly includes the construction and maintenance of roads outside the power plant, selection and improvement of loading systems and transporta-tion, and communication and coordination with the local transportation department. At present, the loading system and transportation are usually managed by biomass fuel suppliers themselves, and the power plant takes charge of road maintenance and coordination with the local transportation department.

• Inspection and quality control system inside the plant: Fuel quality control is the key step for a biomass-fired power generation plant. It is necessary to identify the method of fuel evaluation according to the requirements of the biomass boilers and other equipment, and then to ascertain the fuel purchase price. It is important to continually improve qual-ity control and evaluation-record management. An example of the sampling and handling process applied to wood fuels in Finland is presented in annex 11.

• Fuel price upon arrival at the plant: The price fluctu-ates according to fuel type, season, and quality, as well as the relationship between fuel demand and supply. It is necessary to establish a scientific and feasible price and fuel purchase method to encour-age rural households to collect and transport bio-mass fuel to the plant.

• Loading, transportation, and storage system inside the plant: A 25 MW biomass power generation project needs more than 500 tons of biomass fuel every day. It is very important to ensure sufficient fuel supply by effective fuel loading, and by selecting the suitable feeding system, fuel storage amount, and pattern. In addition, it is necessary to make sure that road layout and construction inside the plant, as well as the fire and water prevention sys-tems, are designed and constructed well.

• Staff training and management: At present, about 50 percent of the staff are involved in biomass fuel supply in biomass-fired power generation plants in China. They play an important role in the effi-ciency of fuel supply and cost control for power generation.

6.3.2 Quality Management for Fuel Supply ControlTo ensure that the delivered biomass complies with the quality standards and specifications in the bio-mass fuel supply contract, fuel inspection and quality control are necessary throughout the biomass sup-ply chain. All operators in the biomass supply chain should apply quality control measures. Especially at the gate of the biomass-fired power plant where the physical reception of the fuel takes place, sampling, exclusion, and monitoring of the fuel is required.

A possible tool for controlling fuel quality along the entire supply chain is a quality management (QM) sys-tem. Langheinrich and Kaltschmitt (2006) developed a six-step methodology for designing a QM system for solid biomass supply (see figure 6.2). They recommend setting out the practical implementation of the QM system in an operator manual, which will help keep all process steps and interactions under control. At a minimum, the manual should cover the following:

• Documentation of origin (traceability of raw material).

• Steps in the process chain, critical control points (CCPs), criteria and methods to ensure appropri-ate control at CCPs, and nonconforming products (production requirements).

• Description of transport, handling, and storage.• Quality declaration and labeling (final production

specification).

The methodology is described in more detail in annex 12.

Quality Assurance (QA) measures should (a) be sim-ple to operate, (b) not cause undue bureaucracy, and (c) offer savings in costs to both producers and users. The application of QA measures enables the reduc-tion of costly quality control measures and will lead to lower failure costs.

47


Quality Control (QC) includes the selection and appli-cation of appropriate sampling and sample-reduction techniques, as well as test methods. QC is important for assessing the properties of the fuel that is delivered, but it does not directly affect the quality of a product. The application of sample and test methods is expen-sive, so they should be used carefully and not as a mat-ter of routine (Langheinrich and Kaltschmitt 2006).

6.3.3 Case Study: Quality Management of Agricultural Residues in Denmark

In the highly developed Danish straw-for-energy market, the presence of mold in the straw is mostly ascertained by visual inspection. To measure weight, the larger power plants and CHPs use automatic mea-surement systems, while the smaller district heating plants measure manually by unloading. To determine the moisture content, a measuring spear is inserted in the straw bales. Typically, in one load (16–24 bales), the spear is inserted in at least four bales in differ-ent positions of the bale. The biomass price is deter-mined based on an average of the moisture content measurements.

If the average moisture content is more than 13 per-cent, the payable load is reduced by 2 percent for each percentage point over 13 percent. Thus, the price for the load is reduced. If the average moisture content is more than 23 percent for two bales, the load will be rejected. If the average moisture content is less than 13 percent, the payable load is increased by 2 percent for

each percentage point that the moisture content is less than 13 percent, but only to 10 percent. No further price adjustments are made if the moisture content is less than 10 percent (DTI 2007b).

6.3.4 Case Study: Quality Management of Forestry Residues in Finland

In the highly developed wood-for-energy market in central Finland, fuel is paid for on the basis of its energy content, and fuel inspection at cogeneration plants often focuses on just two aspects: moisture content and net calorific value. While unloading the forestry residues, the truck driver takes fuel samples manually, using special sample buckets. These buckets have a cylinder, with a diameter of about 15 cm, in the nose of an arm. According to the standard, 4–6 sam-ples should be taken from one truck-trailer load. In practice, sometimes just one sample is taken from the truck and another from the trailer. This causes inaccu-racy in determining single-load properties, but when the annual volume is large, occasional faults will even out over larger numbers of loads. Single fuel samples are combined and, from the combined sample, mois-ture content is determined daily for each supplier. Calorific value is tested less frequently, for instance, once a month. Particle size is determined only when new machines or raw materials are introduced or as a random control (DTI 2007a). To measure weight, weighbridges are used. Energy content is calculated according to the European Technical Standard CEN/TS 15234.

Figure 6.2 Methodology to Apply and Implement Quality Assurance

Sources: BTG; Drohm Design & Marketing based on Langheinrich and Kaltschmitt 2006.

Note: QA = Quality assurance.

1.Description of process chain

5.Selection ofappropriate

QA measures

Elaboration of a process (site)-specific manual

4.Identification

of CriticalControl Points

3.Analysis of

qualityinfluencing

factors

2.Determinationof customerrequirements

6.Routines for

non-conformingmaterials

48


6.4 Mitigation Strategies for Managing Supply Risks

In addition to organizing efficient fuel supply under normal conditions, the biomass power plant should also develop an emergency system to address potential disruptions in the fuel supply. Disruptions can result from different causes, and which of the large number of supply risks are most pertinent for a given biomass power plant is situation-specific. It is important for a biomass plant owner or operator to make plant-spe-cific risk assessments, that is, carefully examine what could cause disruptions in the biomass fuel supply and identify suitable mitigation measures, so that the focus can be placed on the risks that have the highest prob-ability, or the greatest impact, or both.

A biomass fuel supply risk matrix is a suitable tool to determine key risks and mitigation options. Develop-ing a risk matrix consists of the following steps:

• Cause: Identify the risks along the biomass fuel sup-ply chain that can cause supply disruptions. During the risk-identification process, identify all possible fuel supply risks, irrespective of their probability and impact. Risks are undesirable events that hin-der the achievement of project objectives.

• Potential impact (event): Identify the consequences to the biomass fuel supply if the event occurs.

• Risk probability classification:• Risk probability (low, moderate, high) is the

likelihood that a risk event occurs.• Risk impact (low, moderate, high) is the conse-

quences that the risk event will have on achiev-ing project objectives.

• Remedies: Develop solutions to minimize or elimi-nate the risks (mitigation strategies). Examples of mitigation strategies include biomass contracting, fuel inspection (sampling, exclusion, and monitor-ing), engineering design (dual feed system, buffer capacity, and storage), and the availability of alter-native biomass fuels.

To rank the risks, two possible approaches can be adopted:

• Cardinal scales identify the probability and impact on a numerical value, from .01 (very low) to 1.0 (certain).

• Ordinal scales identify and rank the risks from very high to very unlikely.

Each identified risk is fed into a matrix, which maps out the risk (cause and consequences), its probability, and its possible impact. The risks with higher prob-ability and impact are a more serious threat to the bio-mass power project than risks with lower impact and probability.

There are many potential sources of risk that can affect the continuous supply of affordable feedstock to the power plant (Thornley, personal communica-tion, 2009).14 A survey of the relevant literature and Thornley’s own long-term experience developing bio-energy projects around the world confirm that manag-ing fuel supply risks is a crucial factor for efficient and economic plant operation. Annex 13 gives an exam-ple. The matrix is only intended as an example, show-ing some common supply risks and mitigation factors. Without a detailed field study of the experience at sev-eral Chinese power plants, it is not possible to accu-rately identify and rank the most relevant supply risks. It is recommended that the power plant develop a fuel supply risk matrix at the project planning stage. With the assistance of a biomass supply expert, the supply risks and the most suitable mitigation strategies can be determined.

Experience around the world shows that Chinese bio-mass power plants are not unique in facing problems managing biomass fuel supply risks. For example, power utilities in the United States (Midwest, South-east, and Texas) that use woody biomass as a fuel for power generation are facing the gap between the supply needs of power utilities and the practices and capabilities of the existing woody biomass suppliers. As stated above, biomass fuel supply specialists can help identify key physical delivery risks and mitigation

14. Dr. Patricia Thornley, Tyndall Centre for Climate Change Research, University of Manchester. Throughout her academic career, Dr. Thornley has identified hundreds of risk factors for biomass power plants.

49


strategies, as well as assign prices to risk-management challenges and opportunities. These topics were cov-ered at a web seminar organized by Electric Utility Consultants Inc.15


It is recommended that power plants carefully select biomass fuel suppliers and develop long-term relation-ships and sign long-term supply contracts with the preferred suppliers.

Long-term contracts with few or multiple fuel sup-pliers (or brokers) help to reduce biomass supply risks. Farmers and landowners often consider a bal-ance between security of income (long-term contracts) and flexibility to be important, and they may prefer shorter-term contracts.

The practical involvement of a biomass-fired power plant itself in fuel supply starts at the power plant gate only if the fuel supply is fully contracted to a fuel bro-ker or other external entity.

The biomass power plant should have a fuel stock available at all times. For large-scale power plants, as in China, this will require several fuel deliveries per day. It is important to design a power plant with some fuel flexibility and to build enough storage capac-ity to allow for scheduled (for example, the Chinese New Year break) and unexpected interruptions in fuel supply.

To help ensure year-around availability of biomass at the plant, the power plant owner or operator can adopt several approaches. Options include arranging planting schemes with growers and forest owners, constructing sufficient storage capacity for continu-ous operation, and fixing schedules for biomass fuel deliveries.

Fuel quality standards and specifications should be included in the contract to match the fuel supply with

15. Web seminar entitled Managing Supply Risks of Woody Biomass for Power Generation, held October 16, 2009.

the installed energy system. Biomass fuel not in com-pliance with the specifications in the contract may be rejected or the fuel price may be reduced.

To negotiate for fuel supplies effectively, it is impor-tant for a biomass plant owner to understand the cost structure of the biomass fuel. It is recommended that the moisture content be reflected in the biomass price, because it is related to the calorific value of the fuel.

It is recommended to determine benchmark biomass fuel prices and to carry out market surveys at regu-lar intervals (data collection and analysis on residues availability and the demand of current and future competitors). The increased demand for, and use of, agricultural and forestry residues for energy genera-tion can lead to higher feedstock prices.

In addition to organizing efficient fuel supply under normal conditions, the biomass power plant should also develop an emergency system to address poten-tial disruptions in the fuel supply. Managing fuel sup-ply risks is a crucial factor for efficient and economic plant operation. To manage physical delivery risks, it is recommended not to depend on a single type of bio-mass fuel.

The power plant should assess fuel supply risks, that is, examine carefully what could cause disruptions in the biomass fuel supply and identify suitable mitiga-tion measures. Priority should be given to the risks that have the highest probability and/or the greatest impact.

A biomass fuel supply risk matrix is a suitable tool for determining key biomass fuel supply risks and mitiga-tion options. A biomass supply expert can help the power plant determine supply risks and the most suit-able mitigation strategies.

It is recommended that investors use a tool for manag-ing the biomass fuel supply, for example, a QM sys-tem, and to document practical implementation steps in the form of a manual that can serve as a tool for each operator active in the supply chain.

50


To manage price risks, an interesting option is to offer the preferred biomass supplier a financial stake in the power plant. The cost of biomass supply is an impor-tant parameter in the financial performance of the

power plant. When the biofuel supplier has a financial interest in the power plant’s performance, the chance of this supplier increasing fuel prices unreasonably will be reduced.

51

References and Other Resources

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———. 2008. “European Standards for Solid Biofuel. Fuel Specification and Classes, Multipart Standard.” Prepared for the PHYDADES project (www.phydades.info). VTT Energy, Jyväskylä, Finland.

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EUBIA (European Biomass Industry Association). 2005. “There are four main supply chains of forest residues.” http://www.eubia.org/191.98.html.

———. Case study 2, “Forest Residue Supply Chain for CHP Plants in Central Finland,” http://eubionet2.ohoi.net/GetItem.asp?item=file;4880; and case study 7, “Supply Chain for Wood Chips from Early Thinning in Sweden.” http://eubionet2.ohoi .net/GetItem.asp?item=file;4858.

Forestry Commission Scotland. 2009. Wood Energy Website: www.usewoodfuel.co.uk.

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Hakkila, P. 2004. Developing Technology for Large-Scale Production of Forest Chips. Wood Energy Technology Programme 1999–2003. Technology Programme Report 6/2004. Helsinki, Finland: TEKES. www.tekes.fi/julkaisut/ Wood_Energy_Final.pdf.

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———. 2005. “Storage Systems for Rice Straw in California.” University of California, Davis. http://www.fte.wur.nl/NR/rdonly res/3B4A9556-8AE9-44B3-97BD-D9317266E63F/40598/ StoragesystemsforricestrawinCalifornia1.pdf.

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Li, J. 2008. “Report on Maize Straw to Crop Ratio and Avail-ability in Ulanhot, Inner Mongolia.” Center for Science and Technology Development, Ministry of Education, Beijing, April.

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Pastre, O. 2002. “Analysis of the Technical Obstacles Related to the Production and Utilisation of Fuel Pellets Made from Agricultural Residues.” Report prepared by EUBIA for the ALTENER project Pellets for Europe.

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55

Annex 1: International Experience with

Growing Energy Crops

A steady supply of biomass of sufficient quality is critical to the economic viability of biomass power production. Where the availability of biomass from residues is limited, additional biomass can be obtained from the cultivation of dedicated energy crops. This annex briefly discusses the state of the cultivation of dedicated energy crops, referred to as “energy plan-tations,” and their contribution to biomass fuel sup-ply. Both short-rotation woody crops (SRWC), such as willows and poplars, and herbaceous energy crops, such as Miscanthus and switchgrass, are potential bio-mass sources.

The establishment of energy plantations in Europe in the 1990s was driven by the implementation of a com-prehensive support system for the agricultural sector. In some EU countries, energy crops were cultivated on demonstration fields, for example, in Greece (sor-ghum, eucalyptus), Germany (Miscanthus), and Fin-land (reed canary grass). In most of the then 15 EU member states, energy crop cultivation was limited to a few field trials. Commercial cultivation of woody energy crops developed only in Sweden, where com-mercial willow plantations covered 15,000–17,000 ha. The European experience is described in more detail below.

Worldwide, thousands of hectares of commercial plan-tations of SRWC, such as willow, poplar, eucalyptus, and southern pine, exist. These plantations provide valuable information about yields, propagation tech-niques, variety development, and best management practices. Recent research in the United States shows that the economics of SRWC biomass for bioenergy use are not yet favorable compared with non-energy uses, and that SRWC fuelwood is not competitive with coal for power production, the dominant fossil fuel in U.S. and Chinese electric power generation (Graham 1995).

Different approaches can be adopted to improve the relative competitiveness of SRWC and to stimulate its use:

• Experience from Sweden shows that, if located, designed, and managed wisely, energy crop planta-tions can, besides producing renewable energy, also generate local environmental benefits. Examples of such multifunctional bioenergy systems are Salix L. plantations leading to soil carbon accumulation, increased soil fertility, reduced nutrient leaching, and improved hunting potential, representing more general benefits. Another category of plantations is those designed for dedicated environmental ser-vices, such as shelter belts for the prevention of soil erosion, plantations for the removal of cadmium from contaminated arable land (phytoextraction), and vegetation filters for the treatment of nutri-ent-rich, polluted water (van Loo and Koppejan 2008).

• The market valuation of biomass feedstocks can internalize environmental benefits, such as carbon credits or reduced gas emissions.

The relative competitiveness of SRWC for biomass power production will still be dictated by local con-ditions and will likely vary from region to region. In the long term, yield improvements and more-efficient harvest technologies are likely to play a bigger role in reducing SRWC unit costs.

With regard to herbaceous (grassy) energy crops, experience gained to date is relatively limited. In the United States switchgrass and in Europe Miscanthus have been tested on a relatively large scale. Both basic and applied research is needed, not only on yield and management, but also on the conditions for their suc-cessful adoption. Besides profitability, other adoption factors include adaptability of energy crops to existing

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farming practices, machinery, time allocation, and farming know-how.

European Experience Growing Woody and Grassy Energy Crops

Luger (2002) presents an overview of energy cropping experience in Europe in the 1990s. His article covers woody crops, herbaceous crops, and oil seed crops. For the first two categories, discussed below, the area under cultivation since his overview was published may not have changed dramatically.

With regard to woody crops, willow (Salix sp.) is grown mainly in the northern parts of the EU. In Sweden, some 17,000 ha of willow are grown. The combined contribution of other EU willow-growing countries, in particular, Denmark, Finland, Ireland, the Netherlands, and the United Kingdom, was on the order of 1,000 ha. Poplar (Populus sp.) can be grown in warmer climates than willow. In some countries, such as Austria, Belgium, Ireland, Germany, and the United Kingdom, both willow and poplar are grown. In the Netherlands, about 32,000 ha of poplar have been established, but not for energy purposes. In France, about 350 ha have been established and used for pulp production. The largest European areas of Eucalypt (Eucalyptus sp.) in short rotation have been established in Portugal, where approximately 500,000 ha are grown for pulp production. In France, a total of about 500 ha of eucalypts are planted for pulp pro-duction, and in Greece and Italy, only small test plots of a few hectares for research have been established.

With regard to herbaceous crops, Miscanthus sp. was introduced to Europe as an ornamental plant. As a C4 perennial grass, it is better adapted to warmer climates.16 In Denmark about 30 ha are established, while in Germany there are about 100 ha, and in Aus-tria and France a few hectares. In Belgium, Greece, Ireland, Italy, Portugal, Spain, and the United King-dom, small research plots were established as part of

16. Agricultural experts make a distinction between C3 and C4 plants, depending on the length of the growing season. A C4 plant is a plant that produces the 4-carbon compound ox-alocethanoic (oxaloacetic) acid as the first stage of photosyn-thesis.

the European Miscanthus Network. Reed canary grass (RCG) is native to Sweden, as well as many other parts of northern Europe. Several thousand ha of RCG have been established in Sweden, although very little of the grass is used for energy. In Finland, about 50 ha have been established. Small research plots have been estab-lished in Denmark, Germany, Ireland, and the United Kingdom. Cardoon (Cynara cardunculus) is a peren-nial thistle-like plant that seems to be well adapted to dry Mediterranean conditions where most precipita-tion occurs during the winter season. In Spain, about 50 ha of experimental fields have been established. Within the Cynara network, green Cynara forage cut-tings were tested during winter in Greece, Italy, and Portugal. Sorghum (Sorghum bicolor) is an annual C4 crop of tropical origin. It is, therefore, mainly adapted to southern Europe. Both sweet sorghum and fiber sorghum have been tested for energy production. Bel-gium, France (about 15 ha), Greece, Italy, Portugal, and Spain grow sorghum. Hemp (Cannabis sativa) has a long tradition as a fiber crop, but the use of hemp for energy is a new idea. In the Netherlands, hemp is used for pulp production. Approximately 5 ha are grown for energy uses. An area of 1,000 ha is grown commercially for fiber use. In Austria, 160 ha of hemp were grown for seed and fiber use (Luger 2002).

Luger (2002) concludes that a few energy crops have exceeded the level of research, development, and dem-onstration, and have become commercialized. These examples exist because of the political and financial support given by some countries, and they have pro-vided valuable information on the future demands for the implementation of energy crops in European agriculture. The best-known example of large-scale commercial energy crop production for biomass heat and power generation is the cultivation of willow in Sweden.

Economic calculations show basic costs of production and delivery to a power plant to be in the range of €34–86/odt (caution: 1996 data). The Swedish calcu-lation of €59/odt for willow is the most well founded. These costs compare favorably with market prices pre-vailing at the time for biomass residues (such as forest wood chips), which were on the order of €32–68/odt in Sweden and about €80/odt in Denmark. The mean

57

Annex 1: International Experience with Growing Energy Crops

market price of straw in Denmark is about €70/odt. The market price of fossil fuels (in €/GJ) is lower than these biomass prices (Luger 2002).

The above cost ranges indicate that basic production costs of energy crops in some cases can compete with existing biomass based on market prices, and with fossil fuels, but only if land rentals and profits for the farmers are not included in the calculations.

Chinese Experience Growing Woody and Grassy Energy Crops

Wang and Xiao (2008) present a list of species suit-able for fuelwood production. In China, suitable spe-cies include the following:

• Eucalypt, Cassia siamea, birch, and sawtooth oak in the high mountainous regions of Sichuan and Yunnan provinces.

• Quercus acutissima, Quercus variabilis, alder, Cori-aria sinica, and acacia in the mountainous regions of Sichuan and Shaanxi.

• Sawtooth oak, eucalypt, Acacia mearnsii, Zenia insignis, and Schima superba in the low mountain-ous regions of south and central Yunnan.

• Sawtooth oak, Pinus massoniana, Platycarya stro-bilacea, acacia, Lespedeza, Choerospondias axillaris in the low mountainous and hilly regions of north-west Zhejiang, south Anhui, and northeast Jiangxi.

• Acacia dealbata, Castanopsis luminifera, Pinus massoniana, eucalypt, Zenia insignis, and Schima superba in the mountainous regions of south Jiangxi, southwest Hubei, southeast Guizhou, cen-tral and northern Guangdong, and Guangxi.

Wang and Xiao (2008) report that in northern China, 600,000 ha of fuelwood forests are planted annually. An estimated 100 million tons per year of woody mate-rial can be collected. According to the State Forestry Administration’s National Energy Forest Construc-tion Plan, more than 10 million mu of demonstration energy forests will be built up during the 11th Five-Year Plan period (2006–10). These forests will provide significant potential for future energy generation.

In 2005, total forested area in China stood at 175 mil-lion ha, of which 68 percent was natural forest (121 million ha) and 32 percent was planted forest (54 mil-lion ha). The forest stock is unevenly distributed and mostly concentrated in the five principal forest regions, which account for 90 percent of total forest stand vol-ume. Seventy percent of existing forest is in middle and young age.

Since the mid-1990s, China has pursued an active afforestation policy at all government levels. With an annual afforestation rate of approximately 3–4 mil-lion ha, the national forest coverage rate is expected to increase from 18.21 percent in 2005 to 20 percent in 2010. In addition to expansion of the coverage rate, China strives to improve the quality of its forests, enhance carbon fixation capacity per unit of forest area, moderately increase the usage and service life of forest lumber, and strengthen forest products’ carbon stock capacity.

Dr. Chunfeng Wang, Deputy Director General of the State Forestry Administration, envisages that by 2010, up to 300 million tons of forest biomass can be used as a substitute for coal for energy generation (Wang 2009).

58

Annex 2: Fuel Standards and Specifications

Fuel standards have been introduced so that biomass can become a commodity fuel with common defini-tions, common methods, and a clear classification system. It is important that the fuel is fit for purpose (proper match between fuel supply and energy system) and delivered according to a quality standard and specification. Fuel quality standards also encourage the uptake of biomass fuels through consumer confi-dence (Richards and Maunder 2008).

In Europe, the European Committee for Standardiza-tion (CEN) formed a technical committee (CEN/TC 335—Solid Biomass) to develop standards to describe all forms of solid biomass within the biomass-biofuel field (figure A2.1), including wood chips, wood pellets and briquettes, logs, sawdust, and straw bales. CEN/TC 335 allows all relevant properties of the fuel to be described, and includes both normative information (must be provided) and informative information (may

be provided). As well as the physical and chemical characteristics of the fuel, CEN/TC 335 also requires information on the source of the material.

The CEN/TC 335 standards are intended to be uni-versal standards. The European solid biofuel stan-dards build on national solid biofuel standards that were already in place in, for example, Austria, Ger-many, and Sweden (ÖNORM, DIN, and SS standards, respectively).

Standards

When investing in a biomass-fired power plant, it is important to know that most types of conversion equipment work effectively only with select types and forms of biomass fuel. As mentioned before, there are different sets of standards. Regardless of which set of standards is applied, it is important to work closely

Figure A2.1 CEN/TC 335 Within the Biomass-Biofuel-Bioenergy Field

Sources: BTG; Drohm Design & Marketing based on the work of CEN/TC 335.

CEN/TC 335

Liquid and gaseous biofuel

Non-fuels

Biofuel

Solid biofuel

Prod

uctio

n/pr

epar

atio

n

Biomass Bioenergy

Con

vers

ion

Con

vers

ion

59

Annex 2: Fuel Standards and Specifications

with both fuel supplier and system installer to ensure that the fuel purchased is suitable for the system, that the fuel supplier undertakes to deliver a consistent quality of fuel, and that the fuel can be stored and handled at the site correctly (Carbon Trust 2005a).

Specification and Classes

The classification of biomass is based on origin and source, major traded types, and properties. Classifi-cation is useful for boiler and burner manufacturers to select property classes for their products. The clas-sification can be marked on the product if packaged, and for bulk material, a fuel quality declaration can be used (CEN/TS 15234) (see figure A2.2).

According to Alakangas (2008), the minimum require-ments for a fuel quality declaration are as follows:

• Supplier (body or enterprise), including contact information.

• A reference stating compliance to the CEN/TS 15234.

• Origin and source (prEN 14961-1).• Traded form (prEN 14961-1 or other parts).• Normative properties.• Chemical treatment if chemically treated biomass

is traded.• Signature (authorized person), name, date, and

place.• The fuel quality declaration can be approved elec-

tronically (signature and date can be approved by signing the waybill or stamping the packages).

An example of a quality declaration according to Part 1–Bulk delivery is shown in figure A2.3.

Figure A2.2 Example of Classification Based on Origin and Source, Major Traded Form, and Properties

Sources: BTG; Drohm Design & Marketing based on Alakangas 2008.

Origin/source

Origin/source

Documentationof origin

(Table 1 in EN14961-1)

Fuelproduction

Conversion

Qualitydeclaration(prEN 15234)Fuel Quality Assurance

(prEN 15234 upgrading ongoing)

(Tables with property grades in prEN 14961-1)Traded form

(for example, pellet)

Biomass Solid biofuel Bioenergy use

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EN 14961—Part 1

Producer EAA Biofuels

Pellet factory Jyväskylä, Finland

Origin 1.2.1.2 (Sawdust, pine)

Traded form Pellets

Normative Dimensions D08

Moisture, w-% M 10

Ash, w-% dry A0.5

Mechanical durability, w-% pellets after DU97.5

Amount of fines, w-% (<3.15 mm) F1.0

Additives, w-% of pressing mass 0.5 w-% starch

Bulk density, kg/m3 BD 650

Net calorific value as received, kWh/kg Q4.7

Sulphur, w-% dry basis 0.05

Informative Nitrogen, w-% dry basis N0.3

Chlorine, w-% dry basis C10.03

Figure A2.3 Example of a Fuel Quality Declaration Used for Bulk Delivery

Sources: BTG; Drohm Design & Marketing based on Alakangas 2008.

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Annex 3: Calculation of the Net Calorific Value at Different Bases and Energy Density as Received—EN 14961-1

D.1 The net calorific value of dry basis

The net calorific value at a constant pressure for a dry sample (dry basis, in dry matter) is derived from the corresponding gross calorific value at a constant vol-ume according to Equation (EN 14918) (1)

qp,net,d = qv,gr,d – 212.2 × w(H)d – 0.8 × [w(O)d + w(N)d] (1)

where

qp,net,d is the net calorific value for dry matter at a con-stant pressure in joules per gram(J/g) or kilojoules per kilogram (kJ/kg);

qv,gr,d is the gross calorific value for dry matter in joules per gram(J/g) or kilojoules per kilogram (kJ/kg);

w(H)d is the hydrogen content, in percent-age by mass, of the moisture-free (dry) biofuel (including the hydrogen from the water of hydration of the mineral matter as well as the hydrogen in the biofuel substance);

w(O)d is the oxygen content, in percentage by mass, of the moisture-free biofuel;

w(N)d is the nitrogen content, in percentage by mass, of the moisture-free biofuel.

For the calculation of the net calorific value as received using Equation (2) in D.2, the result from Equation (1) in joules per gram(J/g) or kilojoules per kilogram (kJ/kg), shall be divided by 1 000 to get the result in megajoules per kilogram (MJ/kg).

Note: [w(O)d + w(N)d] can be derived by subtract-ing from 100 (w-%) the percentages of ash, carbon, hydrogen, and sulphur.

D.2 The net calorific value as received

a) Calculation from dry basisThe net calorific value (at constant pressure) on as received (the moist biofuel) can be calculated on the net calorific value of the dry basis according to Equa-tion (2).

qp,net,ar = qv,net,d × 100 – Mar

100– 0.024 43 × Mar (2)

where

qp,net,ar is the net calorific value (at constant pressure) as received in megajoules per kilogram (MJ/kg);

qp,net,d is the net calorific value (at constant pressure) in dry matter in megajoules per kilogram (MJ/kg);

Mar is the moisture content as received [w-%];

0.024 43 is the correction factor of the enthalpy of vaporization (constant pressure) for water (moisture) at 25°C (in megajoules per kilogram (MJ/kg) per 1 w-% of moisture).

b) Calculation from dry and ash-free basisThe net calorific value (at constant pressure) on as received (the moist biofuel) can be calculated from a net calorific value of the dry and ash-free basis accord-ing to Equation (3).

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qp,net,ar =

(3)100

qp,net,daf × (100 – Ad)×

100 – Mar

100– 0.024 43 × Mar

where

qp,net,ar is the net calorific value (at constant pressure) as received, in megajoules per kilogram (MJ/kg);

qp,net,daf is the net calorific value (at constant pressure) in dry and ash-free basis, in megajoules per kilogram (MJ/kg);

Mar is the moisture content as received (w-%);

qp,net,ar is the ash content in dry basis (w-%);

0,024 43 is the correction factor of the enthalpy of vaporization (constant pressure) for water (moisture) at 25 °C (in megajoules per kilogram (MJ/kg) per 1 w-% of moisture).

In both the above cases a) and b), the calorific value can be either determined for that particular lot or a typical value can be used.

• If the ash content of the fuel is low and rather con-stant, the calculation can be based on the dry basis equation with a typical value of qp,net, d;

• If the ash content varies quite a lot (or is high) for the specific biofuel then using the equation for dry and ash-free basis with a typical value of qp,net,daf is preferable.

The result shall be reported to the nearest 0.01 MJ/kg.

D.3 Energy density as received

The wood fuels for small-scale heating plants and households are traded usually on a volume basis and energy content (net calorific value) is informed often as megawatts hour (MWh) per bulk volume. Bulk den-sity and moisture content is measured or estimated.

The energy density as received can be calculated according to Equation (4).

Ear = (4)3600

1 × qp,net,ar × BDar

where

Ear is the energy density of the biofuel as received, in megawatts hour per cubic meter (MWh/m3) of bulk volume;

qp,net,ar is the net calorific value (at constant pressure) as received, in megajoules per kilogram (MJ/kg);

BDar is the bulk density, that is, volume weight of the biofuel as received, in kilograms per cubic meter (kg/m3) of bulk volume;

36001

is the conversion factor for the energy units (megajoules (MJ) to megawatts hour (MWh)).

The result shall be reported to the nearest 0.01 MWh/m3 of bulk volume.

The values of net calorific value and bulk density used in equations can be either measured or based on typi-cal values of biofuels. The typical net calorific values of solid biofuels are reported in Annex B of this Euro-pean Standard.

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Annex 4: Types of Biomass Potential

This annex is based on the work carried out by BTG in the frame of the European BEE project (publication forthcoming).

Theoretical Potential

The theoretical potential is the overall maximum amount of terrestrial biomass that can be considered theoretically available for bioenergy production within fundamental biophysical limits. The theoretical poten-tial is usually expressed in joules of primary energy, that is, the energy contained in the raw, unprocessed biomass. Primary energy is converted into secondary energy, such as electricity or liquid and gaseous fuels. For biomass from crops and forests, the theoretical potential represents the maximum productivity under theoretically optimal management taking into account limitations that result from temperature, solar radia-tion, and rainfall. The theoretical potential for residues and waste equals the total amount that is produced.

Technical Potential

The technical potential is the fraction of the theoreti-cal potential that is available under the anticipated techno-structural framework conditions and with the current technological possibilities, also taking into account spatial constraints from competition with other land uses (food, feed, and fiber production), as well as ecological (such as nature reserves) and other nontechnical constraints. The technical potential is

usually expressed in joules of primary energy, but sometimes also in secondary energy carriers.

Economic Potential

The economic potential is the share of the technical potential that meets criteria of economic profitability within the given framework conditions. The economic potential generally refers to secondary bioenergy car-riers, although sometimes primary bioenergy is also considered.

Implementation Potential

The implementation potential is the fraction of the economic potential that can be implemented within a certain time frame and under concrete sociopoliti-cal framework conditions, including economic, insti-tutional, and social constraints and policy incentives. Studies that focus on feasibility or the economic, envi-ronmental, or social impacts of bioenergy policies relate to implementation potential.

Classifying biomass potential helps the reader to understand the information presented. For instance, some biomass types show high technical potential, but their economic potential is limited because of the high costs of extraction and transport. Therefore, the type of potential must be explicitly mentioned in every bio-mass resource assessment.

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Annex 5: Determination of Yield from Agricultural Crops and Residues

The Biomass Assessment Handbook (Rosillo-Calle and others 2006) describes a survey methodology for determining the availability of agricultural crops and residues. The methodology is briefly presented below.

Accurate estimates of the availability of crop residues require good data on crop production by region or district. If these data are not available, a survey will be necessary. A survey should include information on all uses for crop residues besides fuel (such as burning in situ, mulching, animal feed, and house building), so that the amount available as fuel can be calculated.

An assessment of agricultural residues should include the following steps:

Define which types of biomass to include: It is important to consider data only on those agricultural crops and residues that are used for fuel rather than the total biomass production on any site.

Obtain data on yields and stocks: For agricultural crops, reliable information on yields and stocks, quantified accessibility, calorific values, and storage and/or con-version efficiencies must be accurately determined. A study of the sociocultural behaviors of the inhabitants of the project area will help to determine biomass use patterns and future trends.

Calculate technical potential: A method for estimating crop residues is to use the crop residue index. This is defined as the ratio of the dry weights of the residue produced to the total primary crop produced for a particular species or cultivar.

Technical potential = yearly crop production x RPF.

The crop residue index is determined in the field for each crop and crop variety, and for each agro-ecolog-ical region under consideration. It is very important to state clearly whether the crop is in the processed or unprocessed state, for example, for rice, whether the husk is included in the crop weight.

To obtain accurate estimates of residue production, it is thus important to have good estimates of crop production by country, region, or district. This may entail undertaking surveys, especially in the subsis-tence sector, to determine production of both crops and plant residues. If only general estimates of crop residues are required, crop production figures may be obtained from country statistics or UN bodies, such as the Food and Agriculture Organization of the United Nations (FAOSTAT). However, such statistics may be based on guesses when dealing with subsistence agri-cultural production, and hence, if accurate informa-tion is needed, field surveys may still be necessary.

Calculate economic and implementation potential: The quantity of biomass from crop residues that is available for fuel is only a fraction of the technical potential, because not all of it will be accessible at a reasonable cost. Accessibility of crop residues depends mainly on the location and the economic value of the residues. The location determines the collection costs. If these costs are higher than the economic value of the residues, they will not be used for fuel.

Not all residues are available for energy production. The use of agricultural residues for fuel must com-pete with alternative uses, particularly with the need to preserve soil fertility, retain moisture, and provide soil nutrients, as well as various other uses of which

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Annex 5: Determination of Yield from Agricultural Crops and Residues

fodder, fiber, and fuel are the most common. Thus, for environmental or financial reasons, part of the resi-dues is not available as biomass fuel.

To take into account the collection costs and the alternative uses, a recoverability factor (RF) is often defined.

Implementation potential = Technical potential x RF

The common method to assess RFs is by interview-ing prospective users of agricultural residues, such as

households and rural industries. The method is simple and straightforward, but it has a number of flaws, which may result in reliability issues and thus poor col-lected data. Users are unlikely to closely monitor their daily use (volume and/or weight) of freely available agricultural residues, let alone detect any usage pattern and long-term trends. At best, they can guess their cur-rent use. They may find it difficult to correctly recall any year-to-year straw usage fluctuations as a result of higher or lower availability. And they may also give socially desirable answers. It is clear that a proper bio-mass assessment cannot rely on just one interview.

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Annex 6: Guidelines for Planning a Biomass Resource Survey

experience. It may even be possible (or necessary) to interpolate figures from other regions and countries. Again, critical examination of the data is essential for adequate evaluation.

Convert existing data to standard units to allow easy comparison between localities whenever possible.

Consider demand and supply analysis: If data on bio-mass supply is initially too difficult to obtain, the use of demand analysis data may help to fill the informa-tion gaps.

Decide on the feasibility and scope of field surveys: Ideally, information should always be verified by spe-cific field research where feasible. Field surveys will provide the most accurate and up-to-date informa-tion, but they are difficult and expensive.

Aim to collect time-series data: Only data collected over a number of seasons, say five years, will show trends in use and allow for climatic variation (both annual and seasonal).

The Biomass Assessment Handbook (Rosillo-Calle and others 2006) presents useful guidelines for plan-ning a biomass resource survey:

Decide on the size of the survey and the degree of detail required: What is the reason for the assessment, what are the objectives, and what kind of action should fol-low? Decisions made at this stage will determine the type of questions asked, the survey methods used, and the funds and other resources required.

Determine what data already exist: A great deal of time and money can be saved if some of the informa-tion required already exists, or if it can be obtained from existing data. Useful sources could include national, regional, and local databases, and statistics produced by both government and nongovernmental organizations. Published tables, graphs, and conver-sion tables may provide estimates of stock and yield for forests and woodland.

Existing information should be carefully examined and interpreted by personnel with good judgment and

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The Finnish Wood Energy Technology Programme (1999–2003) aimed to drive down the cost of wood fuel supply, placing strong emphasis on researching the development and optimization of logistics. Some interesting findings from the program include the following:

• Moving comminution to an end-use facility or terminal was found to be an effective measure for enhancing the reliability of the procurement sys-tem. Residue bales help to smooth the logistics: the system becomes less vulnerable, waiting times between machines are eliminated, winter storage is facilitated, and the entire process becomes easier to control. Residue baling technology is only suitable for large-scale operations, and the availability of a crusher at the end-use facility is a precondition. The crusher makes it possible to receive stump and root wood as well, and the raw material base and fuel supply are consequently broadened. Large 150 m3 truck-and-trailer vehicles have been built to trans-port loose forestry residues, residue bales, unde-limbed tree sections, and stump and root wood to the plant, separately or mixed.

• It nevertheless remains more common that for-est fuels arrive at the end-use facility as chips. If the distance is short, the landing site crowded, or reception at a plant limited, the truck does not use a trailer. The maximum load volume is then 60 m3.

Otherwise, the truck is equipped with a trailer, and the load volume is typically 100–130 m3.

• Queuing of fuel trucks is an unnecessary cost factor that should be eliminated. Queuing may occur at large plants, especially in cold winter weather when the need for fuel is high. The peak time of arriv-als is typically in the morning. To avoid queuing, bottlenecks should be removed from the receiving system, and the arrivals should be scheduled.

• Unfortunately, little compatibility among machines has been achieved in the forest chips procurement chain. The lack of compatibility is because forestry conditions vary from the early uncommercial thin-ning of young stands to the final harvest of mature stands, and because the technology is still in its infancy. Several alternative production systems are in use, each employing special equipment that is not necessarily compatible with other systems. This diversity causes problems in practice. Contractors’ flexibility is restricted, and investments become risky when technology prevents changing from one sys-tem to another. Furthermore, machine markets are fragmented, manufacturing in series is not possible, and machine prices remain high. Therefore, when-ever possible, it is preferable to use conventional equipment for the harvesting and transportation of forest biomass. This philosophy is also recom-mended for China. However, special equipment remains a necessity in many phases of the chain.

Annex 7: Finnish Research into Reducing

Biomass Supply Costs

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Annex 8: Sample Biomass Fuel Supply Contract

SPECIMEN BIOMASS SUPPLY CONTRACT FOR (SITE)

Source: CarbonTrust(http://carbontrust.co.uk/technology/technologyaccelerator/biomass-online-resources.htm)

Contract between <SUPPLIER> and <END USER> for the supply of solid biomass to <SITE>.

Preamble:a. <SUPPLIER COMPANY NAME> is the private/public company, whose registered office is at <ADDRESS>,

Company Number XXXX, hereinafter referred to as “the supplier”;b. <END USER NAME> is the private/public company whose registered office is at <ADDRESS>, Company

Number XXXX, hereinafter referred to as “the end user”;c. <ADDRESS> is the site (owned and) operated by the end user where the delivery of biomass is required by

the end user, hereinafter referred to as “the site.”

1. Contract1.1. The supplier agrees to supply to the end user and the end user agrees to purchase from the supplier biomass

to the specifications, in the quantities, for the period, at the price, and on the terms and conditions set out below.

1.2 For the purpose of maintaining control over the necessary quality, the end user agrees neither to purchase nor use biomass from any other source or supplier except where the supplier is unable to provide deliveries or meet biomass specification requirements within three working days of the due date.

2. Biomass specification2.1 Moisture content. The target moisture content on a wet basis shall be XX% by weight based on the [rel-

evant standards] [see guidance notes] but in any event shall not exceed XX%.2.2 Contaminants such as soil or stones, metal and plastics should be less than 2% by weight of the total bio-

mass load.2.3 The biomass particle size shall comply with the [relevant standards].

3. Duration of contract3.1 This contract is for a period of <XX> and will commence on <DATE> and end on <DATE>, (with a formal

review after the first three months of the contract to assess the need for any adjustments to the contract). Any adjustments need to be agreed jointly between the end user and supplier. If the supplier or end user cannot agree or meet adjustments, each party should be able to terminate after 3 months if it wishes to.

3.2 This contract may be extended by agreement of both parties not less than three months before the end of the original contract period.

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3.3 In the event of either party failing to meet their contractual obligations under this agreement the other party has the right to terminate the contract at three months notice unless such breach of contract is rem-edied by the defaulting party to the reasonable satisfaction of the non-defaulting party. If any material breach is committed by either party which, in the reasonable opinion of the non-defaulting party, cannot be remedied within 10 working days the non-defaulting party may terminate this agreement immediately by way of written notice.

4. Quantity4.1 The minimum monthly quantity of biomass supplied during the defined contract will be XX cubic metres

OR XX tonnes (delete as appropriate) at the specification defined in Clause 3.4.2 The end user may order amounts in addition to that specified in 4.1 by requesting an additional delivery

from the supplier, specifying the quantity required, and the date and time by when the end user requires the delivery in accordance with Clause 7.4. If the supplier is able to satisfy the request, it shall notify the end user accordingly and deliver the amount requested as soon as is reasonably practicable. The supplier may charge the contract price for any additional delivery made in accordance with Clause 5. If the supplier cannot satisfy the request, it shall notify the end user of the reason why.

5. Price5.1 The price for biomass delivered into the fuel store of the end user will be based upon the following tariff

up until <DATE> (delete as appropriate): • £XX per m3 of biomass; OR: • £XX per tonne of biomass.5.2 Loads of different volumes/weights (delete as appropriate) will be charged on a pro rata basis in accor-

dance with the above rate.5.3 The price of the biomass will be upgraded annually [see guidance notes] and increased in <MONTH> of

each year in agreement with the end user.

6. Fuel sources6.1 The biomass will be derived from the following sources (delete as appropriate): • licensed harvested forestry timber; • sawmill residues; • arboricultural arisings; • short rotation coppice (SRC); •agricultural arisings (e.g. straw); •energy crops, such as miscanthus; •clean recycled wood, exempt from the Waste Incineration Directive. The parent source of the biomass is declared as being (insert as appropriate).

7. Delivery of biomass7.1 Biomass will be supplied in bagged/baled/loose form [delete as appropriate] and delivered to the end user

by a suitable vehicle for delivery into the end user’s fuel store.7.2 A risk assessment and method statement shall be prepared in advance by the supplier following an initial

site visit and discussion with the end user, to take account of the hazards on site and the risks posed to pedestrians, vehicles and property on the site during biomass delivery and offloading. This shall be for-mally reviewed annually, or whenever a change to the hazards and risks on site are identified.

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7.3 On the dispatch of any consignment of biomass, the supplier shall send a Delivery Note and a Fuel Qual-ity Declaration to the end user by electronic mail or facsimile. A paper copy of the Delivery Note shall be provided to the end user at the site(s) with the delivery of each consignment.

7.4 The notice period for requesting delivery of biomass from the end user will be a minimum of XX days.7.5 Responsibility for checking levels of biomass within the fuel store and informing the supplier of the need

for a fuel delivery rests with the end user.7.6 In the event of the requirement for a delivery at less than the notice period in clause 7.4 an additional fee

of £XX will be payable to cover the costs of an emergency delivery.7.7 Unless otherwise agreed in advance with the end user, deliveries shall be made between the hours of XX.00

and YY.00, or any other time agreed with the end user in advance between Monday and XXXday.7.8 If a delivery cannot be made within the hours specified in the contract and the whole or part of the deliv-

ery is not possible due to obstructions on the end user’s site that are beyond the control of the supplier, the supplier will be entitled to compensation to cover the cost of transport and payment of an additional surcharge of XX% of the value of the biomass ordered, unless the end user informs the supplier of said obstruction within the notice period specified in Clause 7.4 above.

7.9 Upon delivery of the biomass to the end user, visual checks shall be made by the end user to ensure confor-mity to the agreed specification.

7.10 If checks reveal that the biomass does not conform to the agreed specification as per Clause 2, the end user reserves the right to reject the load in full. In the event that it is not possible to visually check the fuel load until it is in the fuel silo, but the woodchip is subsequently found to not conform to the agreed specifica-tion within 24 hours of delivery, then the end user reserves the right to reject the fuel. Rejected fuel will be removed by, and at the expense of, the supplier. Any such dispute over the specification of the biomass will be resolved as per Clause 11.

7.11 The supplier shall be responsible for immediately clearing up any biomass spilt during offloading and shall provide suitable tools for this job.

7.12 The biomass shall remain at the risk of the supplier until delivery to the company is complete (that is, the biomass is offloaded into the end user’s store), when ownership of the biomass shall pass to the end user.

8. Sampling8.1 The end user may at any time send representative samples of biomass for evaluation, analysis, testing and

approval. All samples must meet the specification. Such tests are to be at the end user’s expense.8.2 The strategy for maintaining the original quality of the biomass once the supplier has delivered it on site is

the responsibility of the end user.

9. Terms of payment9.1 The supplier will invoice the end user on a monthly basis. This will be based upon the number of loads

recorded (by weight or volume) and will be assessed on the XX day of each month. The invoice amount will be the number of loads multiplied by the price per load adjusted for volume or weight as outlined in clause 5.1 plus the VAT rate in force at time of billing.

9.2 Terms are monthly payment at XX days from date of invoice.9.3 In the event that any payments are overdue the supplier has the right to refuse to make further supplies

until all outstanding overdue invoices have been settled.9.4 Interest shall be payable on amounts overdue at the daily published Bank of England base rate plus 2%.

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10. Other terms and conditions10.1 Boiler outage or operational problems that are a direct result of sub-standard maintenance, boiler misuse/

neglect or boiler defects are not the responsibility of the supplier. In this instance, any cost that is incurred by the supplier as a result of not being able to deliver fuel will be charged to the end user.

10.2 The supplier will indemnify the end user against the cost of repair to fuel handling and combustion equip-ment caused by the supplier or supply of biomass not in accordance with the specification set out in clause 2.1, 2.2 and 2.3, with the exception of consequential losses such as having to pay for heat supplied from other sources to a limit of £XXXX [see guidance notes].

10.3 The supplier will have public liability insurance of £5,000,000/10,000,000 [see guidance notes].10.4 The supplier’s liability under this Agreement (including under any indemnity) shall be limited to £XXXX

[see guidance notes].

11. In the event of a dispute11.1 Both parties shall attempt in good faith to negotiate a settlement to any dispute between them arising out

of or in connection with the contract within thirty days of either party notifying the other of the dispute. Initially the party who wishes to bring the dispute to the notice of the other will do so in writing. The other party will respond to this in writing within 5 working days of receiving the notification of a potential dispute. Where the potential dispute relates to on-site issues at either the end-user or supplier sites, a joint site meeting will normally take place within 8 working days of the potential dispute being brought to the other party’s attention.

11.2 Where a resolution has been agreed after one or more meetings, including a site meeting (if appropriate), this shall be communicated in writing and noted by both parties.

11.3 Where a resolution cannot be agreed after several attempts, the parties will attempt to settle it by media-tion in accordance with the Centre for Effective Dispute Resolution (CEDR) Model Mediation Procedure. Unless otherwise agreed between the parties, the mediator will be nominated by CEDR.

12. Force Majeure12.1 A party, provided that it has complied with the provisions of clause 12.3, shall not be in breach of this

agreement, nor liable for any failure or delay in performance of any obligations under this agreement (and, subject to clause 12.4, the time for performance of the obligations shall be extended accordingly) arising from or attributable to acts, events, omissions or accidents beyond its reasonable control (Force Majeure Event), including but not limited to any of the following:

(a) Acts of God, including but not limited to fire, flood, earthquake, windstorm or other natural disaster; (b) war, threat of or preparation for war, armed conflict, imposition of sanctions, embargo, breaking off of

diplomatic relations or similar actions; (e) compliance with any law; (f) fire, explosion or accidental damage; (h) extreme adverse weather conditions; (i) collapse of building structures, failure of plant machinery, machinery, computers or vehicles; (j) any labour dispute, including but not limited to strikes, industrial action or lockouts; (k) non-performance by suppliers or subcontractors (other than by companies in the same group as the

party seeking to rely on this clause); and (l) interruption or failure of utility service, including but not limited to electric power, gas or water.

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12.2 The corresponding obligations of the other party will be suspended to the same extent as those of the party first affected by the Force Majeure Event.

12.3 Any party that is subject to a Force Majeure Event shall not be in breach of this agreement provided that: (a) it promptly notifies the other parties in writing of the nature and extent of the Force Majeure Event

causing its failure or delay in performance; and (b) it could not have avoided the effect of the Force Majeure Event by taking precautions which, having

regard to all the matters known to it before the Force Majeure Event, it ought reasonably to have taken, but did not; and

(c) it has used all reasonable endeavours to mitigate the effect of the Force Majeure Event to carry out its obligations under this agreement in any way that is reasonably practicable and to resume the performance of its obligations as soon as reasonably possible.

12.4 If the Force Majeure Event prevails for a continuous period of more than six months, any party may termi-nate this agreement by giving 14 days’ written notice to all the other parties. On the expiry of this notice period, this agreement will terminate. Such termination shall be without prejudice to the rights of the par-ties in respect of any breach of this agreement occurring prior to such termination.

13. Third party rights A person who is not a party to this agreement shall not have any rights under or in connection with it.

14. Governing law and jurisdiction14.1 This agreement and any dispute or claim arising out of or in connection with it or its subject matter shall

be governed by and construed in accordance with the law of England and Wales.14.2 The parties irrevocably agree that the courts of England and Wales shall have exclusive jurisdiction to settle

any dispute or claim that arises out of or in connection with this agreement or its subject matter.

Agreed this <DATE>

Name ______________________________ Position ______________________________

(On behalf of <END USER>)

Name ______________________________ Position ______________________________

(On behalf of <SUPPLIER>)

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GUIDANCE NOTES FOR COMPLETION OF BIOMASS FUEL SUPPLY CONTRACT (WEIGHT OR VOLUME)

These guidance notes are intended to assist with the completion of the specimen supply contract for biomass by weight or volume. Neither the specimen contract nor the notes are intended to be prescriptive, and consideration must be given to site specific issues and the supplier/end user relationship. Both parties are advised to seek legal advice before entering into a legally binding contract. For additional background information on biomass fuels, storage, handling and a range of other relevant information the Carbon Trust’s guide to biomass heating is avail-able for download via the website: www.carbontrust.co.uk/biomass.

Preamble.This section is normally straightforward. However, the end users may not necessarily own the site or the instal-lation—they may be operating it on behalf of a client (the owner), in which case the owner of the site needs defining separately in this part of the contract.

1. ContractThe supplier and end user may mutually agree that clause 1.2 is overly restrictive—it may be necessary in terms of quality control, yet restricts the end user from sourcing alternatives should there be any doubt about the security of supply from a single supplier. Alternatively, the end user may choose a biomass co-operative (such as South West Wood Fuels) in which case, whilst only one supplier provides biomass to the end user, it will have been sourced from multiple suppliers earlier in the supply chain.

2. Biomass specificationThe appropriate biomass specification will depend on the fuel type (see Section 6), and to some extent on the performance specification of the boiler. Standards are vital for biomass to become a commodity fuel which end users can buy with confidence.

The European Committee for Standardization (CEN) formed a technical committee (CEN/TC 335–Solid Bio-mass) to develop standards to describe all forms of solid biomass within Europe, including wood chips, wood pellets and briquettes, logs, sawdust and straw bales. The standards allow all relevant properties of the fuel to be described, as well as the physical and chemical characteristics of the fuel, methodologies for sampling and assessment of moisture content, etc. Whilst some of these standards are still in draft form, they are becoming more widely used in the UK, and are readily available from several sources, including the Biomass Energy Centre (www.biomassenergycentre.org.uk).

Alternatively, the Austrian Standards Institute (Österreichisches Normungsinstitut, referred to as ONORM) Standard M7 133 or the German Institute for Standardization (Deutsches Institut für Normung) DIN 66 165 tend to be de facto across Europe and are widely used in the UK.

Ultimately, the end user should seek advice from the boiler manufacturer so as not to compromise any warran-ties, then select the most appropriate biomass specification in line with the manufacturer’s recommendations.

3. Duration of contractThe supplier and end user may agree an appropriate supply contract period of between 1 and 5 years. It is sug-gested that a sensible period of notice for either contract extension or termination would be three months, but this can be varied by agreement between the supplier and end user as required.

74


4. QuantityThis contract template allows for supply by either volume or weight subject to the end user and supplier agreeing their preferences.

Whilst the energy content of wood by weight varies very little between different timber species, the density varies significantly. Therefore, if the end user is purchasing biomass by weight, the species of timber should not mat-ter (although clearly the moisture content of the biomass will). However, if purchasing biomass by volume, the energy content will be dependent upon the timber species; for example, the typical calorific value of softwood chips at 30% moisture content is 0.70 MWh/m3, compared to 1.02 MWh/m3 for hardwood chip at 30% MC. In addition, the bulk density will vary considerably, resulting in a highly variable volume expansion from 1 m3 of solid wood to anywhere between 2 and 5.5 times the original volume when chipped.

Foresters tend to work in volume. Arguably though, purchase by weight is less problematic provided that the moisture content is specified and agreed in advance (based on the boiler specification), and that the supply com-plies with that agreed moisture content.

It is important from the supplier’s perspective that a prescribed quantity (by weight or volume) is agreed contrac-tually, whilst making provision for the end user to request additional biomass as required (but with reasonable notice).

5. PriceIt is generally accepted that fresh felled wood of most species weighs about 1 tonne per solid cubic metre, but as the wood becomes air dry it loses between one quarter and one half of its weight. Appendix 1 illustrates how this varies between species. However, the volume increases when wood is chipped. As a general rule of thumb, 1 tonne of woodchip will be equivalent to 4 cubic metres of chip. However, this conversion must be used with caution, as it does not take account of varying moisture content.

The final price (for either weight or volume) will depend on numerous factors, including the biomass quality, local market conditions, availability, and distance of travel. End users are recommended to appraise the local market to determine benchmark prices before negotiating the final price with the selected supplier.

The price should then be indexed by setting an initial price based upon the full costs of supplying the biomass to the site. The initial price then changes over time by periodically applying agreed indexation. However, the issue of an appropriate index for biomass is a complex one. Whilst it is important that biomass costs continue to be competitive vis-à-vis fossil fuel prices in order to maintain economic viability for the end user, biomass suppliers also need to be able to make a profit margin sufficient to maintain the economic viability of their business. The rising cost of fossil fuels will invariably have a knock-on effect to the price of biomass (i.e. with respect to har-vesting, processing and transportation costs, all of which are processes reliant upon fossil fuels).

There are a number of different forms of indexation which could be applied:

• A price index for a major fuel such as the index for a heavy fuel oil (or gas) for [medium] sized manufacturing companies produced by the Department for Business, Enterprise and Regulatory Reform as contained in the Quarterly Energy Prices (e.g. Table 3.1.1: Percentage price movements between Q2 2007 and Q2 2008 for heavy fuel oil (HFO), electricity and gas, by size of consumer, for manufacturing industry) which can be found at http://www.berr.gov.uk/files/file47741.pdf;

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• A general index as an agreed proportion of the Retail Price Index (RPI), except that if haulage costs (a critical cost factor for biomass fuel) increase by more than twice RPI in one 12 month period, the fuel supplier has the right to re-open discussions on prices;

• The price could simply increase at an agreed rate per annum e.g. 2% or 5%.

The most appropriate indexation should ultimately be mutually agreed between the supplier and the end user.

6. Fuel sourcesThe source of biomass will depend to some extent upon availability in the local area. The contract is designed to be able to support the supply of a wide range of biomass fuels, including straw, cord wood, wood chip, wood pellet, short rotation coppice (SRC) such as poplar and willow, grass and non-woody energy crops such as Mis-canthus (Miscanthus giganteus), Switchgrass (Panicum virgatum), Reed canary grass (Phalaris arundinacea), Rye (Secale cereale), Giant reed (Arundo donax), and Hemp (Cannabis sativa).

7. Delivery of biomassConditions for delivery of fuel will be site dependent, but need to fully take account of the health and safety risks to pedestrians, vehicles and property on the end user site. It is important that the supplier conducts a site survey well in advance, and identifies all risks and hazards on site before negotiating with the end user the most appropriate days and times of delivery. For example, if the installation is at a school, it may be considered more appropriate that delivery times to site are outside of normal school hours, in order to minimise the risk to pupils. Equally, the attendance during deliveries of an end user representative (e.g. Maintenance Operative, Site Supervi-sor) may be necessary for both health & safety and security reasons. Weekend deliveries may be acceptable or preferable at certain sites, depending on security policies and access arrangements.

7.4 In terms of notice periods for deliveries, the supplier may need 3–7 days in order to plan the delivery.

7.5 If the end user is remote and has no one on site, responsibility for determining fuel levels may be assigned by prior agreement to the supplier.

8. SamplingCurrent relevant standards for sampling include CEN Technical Specification 14778-1, Solid Biomass–Sampling–Part 1: Methods for Sampling and/or CEN Technical Specification 14778-2, Solid Biomass–Sam-pling–Part 2: Methods for sampling particulate mate-rial transported in lorries. Both specifications may be considered unnecessarily complex for certain sites, however. Part 2 is most relevant to a large capacity plant receiving multiple lorry deliveries per day.

Where moisture content is the critical factor, CEN Technical Specification 14774-2:2004 Solid bio-mass—Methods for the determination of moisture content—Oven dry method—Part 2: Total moisture—Simplified method may be considered the most appro-priate methodology.

Appendix 1: Relation between weight and volume of air dried wood

Air dried wood Weight kg/m3

Beech, oak 750

Ash, birch 716

Sycamore 662

Elm 581

Poplar 486

Pines 550

Spruces 465

Larch 560

Douglas fir 580

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9. Terms of paymentThe date of invoicing may depend upon the end user’s financial accounting periods, whilst payment terms will depend upon the supplier’s standard terms and conditions of sale. Both must be agreed in advance to avoid any dispute at a later date.

10. Other terms and conditionsThe level of the supplier’s public liability insurance may depend on the end user’s standard requirements.

This must be agreed in advance to avoid any dispute at a later date.

It is important that the limit on liability at Clause 10.2 and 10.4 is agreed at an appropriate figure. This should be representative of the end user’s possible total loss but market practice is typically that such a sum does not exceed the maximum value of the contract to the supplier (that is, the value of the total volume of fuel to be supplied over the course of the contract).

77

Annex 9: Energy Density of Forest Chips

Table A9.1 The Energy Density of Forest Biomass Chips and Crushed Bark in Finland at 40 Percent Moisture Content

Energy density

Source Basic density, kg/m3 MJ/m3 kWh/m3 toe/m3

Whole tree

Scots pine 395 7,100 1,970 0.169

Norway spruce 400 7,020 1,950 0.167

Birch 475 8,270 2,300 0.197

Bark

Scots pine 280 5,460 1,520 0.130

Norway spruce 360 7,090 1,970 0.169

Birch 550 12,490 3,470 0.297

Crown without foliage

Scots pine 405 7,780 2,160 0.185

Norway spruce 465 8,400 2,330 0.200

Birch 500 9,040 2,510 0.215

Crown with foliage

Scots pine 405 7,660 2,130 0.183

Norway spruce 425 7,730 2,150 0.184

Source: Richardson and others 2002.

Heating value is determined per unit mass of dry or fresh fuel. Since woody biomass is frequently bought and measured by volume, and transport and storage facilities are built by volume rather than mass, it is also important to know the effective heating value per unit volume. This is the energy density of a fuel. The basic density, that is, the oven dry mass per green vol-ume in kg/m3, serves as a conversion factor from mass to solid volume.

Variation in the basic density of tree species and bio-mass components is considerably greater than the variation in the effective heating value of dry mass.

Therefore, the differences are larger when calculations are made on a volume basis. Energy density is highest in chips from high-density species, such as oaks. In the Nordic forests, a solid cubic meter of birch bark has a heating value equal to 0.30 tons of oil equivalent (toe). The corresponding figure for Scots pine bark is only 0.13 toe (see table A9.1).

In forestry the primary unit of volume is cubic meters (m3) solid wood. For biomass chips, although m3 solid is a practical unit for comparison between tim-ber varieties with varying bulk density, m3 loose is a more commonly used (although less accurate) unit.

78


Therefore, the bulk density or solid content of chips, that is, the ratio of solid volume to loose volume of chips, must also be known. The solid content of chips is affected by the following factors:

• Particle shape: The greater the diagonal-to-thick-ness ratio in chip particles, the lower the solid content.

• Particle size distribution: Material with a heteroge-neous size distribution has smaller spaces between particles. Chipped fuel from whole trees or forestry residue contains more fine material than uniform chips from pulpwood logs and tends to have a higher solid content.

• Tree species: Fuel chips from brittle, low-density material contain more fine particles and have a higher solid content.

• Branch content: Fresh branches and pliable twigs tend to produce long particles that reduce the solid content of chips.

• Storage: Stored biomass tends to contain more fine material and fewer long particles than fresh mate-rial. The solid content is slightly higher than that of chips from fresh biomass.

• Season: Frozen biomass produces finer material during comminution because of brittleness. This results in a higher solid content.

• Loading method: Blowing chips through the dis-charge spout of a chipper into a truck increases the solid content per unit volume to a greater extent than freefall from a conveyor, tractor bin, loader, or silo. Blowing from above gives a higher solid content than lateral blowing. The stronger the fan pressure, the greater the compaction of the particles.

• Settling: The solid content of a chip load increases during transport because of vibration and settling. Factors contributing to settling are the initial solid content of the load, length of haul, evenness of the road, and possible freezing of the chips. Settling takes place rapidly at first, but slows down after the first 10–20 km of travel. From the standpoint of transport efficiency, the solid content before haulage is more important than the content after haulage.

The solid content of fuel chips varies between 38 per-cent and 44 percent, depending on the factors listed

Figure A9.1 Examples of the Energy Density of Selected Fuels, Showing the Load Volume Required for 1 toe

Sources: BTG; Drohm Design & Marketing based on Richardson and others 2002.

Note: HDW, MDW, LDW refer to high-, medium-, and low-density wood.

18

16

14

12

10

8

6

4

2

0

load

vol

ume

requ

ired

(m3 )

fuel oil coal wood chips, LDW

wood chips, MDW

milled peatwood chips, HDW

sod peatwood pellets

fuel type

79

Annex 9: Energy Density of Forest Chips

above. A commonly used conversion factor is 40 percent. A solid cubic meter of wood thus produces approximately 2.5 m3 loose of chips. Low energy den-sity is a problem associated with biomass chips. The space required for transporting and storing a given quantity of energy in biomass chips is 11–15 times greater than that needed for oil and 3–4 times that required for coal, resulting in higher costs. For this reason, fuelwood is traditionally and ideally used close to the source. If woody biomass is ground, dried, and pressed into pellets, its energy density is increased significantly (see figure A9.1).

As industrial demand for biomass chips increases, the average distance between utilization point and source will increase, as will the cost of transportation. In con-trast to fossil fuels, economy of scale becomes negative for wood-based fuels, although bulk transportation (train or ship) can make the operation less dependent on distance. To control the cost of fuel in large instal-lations, forest biomass chips are often cofired with bark, sawdust, peat, coal, or municipal waste.

80

Annex 10: Alternatives for Reflecting Energy Content in Biofuel Price

This annex is based on van Loo and Koppejan (2008).

Recommended method: The recommended method of reflecting energy content in the price of the biofuel is to calculate its energy content based on weight and net calorific value (NCV). A typical method is to weigh the load at a scale house and to measure the mois-ture content of samples from the load using a mois-ture meter that provides quick results. The NCV can be calculated using the gross calorific value (GCV) of the delivered fuel and the moisture content obtained from the measurements (see section 2.2). The GCV of each fuel source should be determined by chemical analysis prior to the first delivery. The energy content is calculated by multiplying the NCV by the weight of the biomass fuel, which then factors into the price of the delivered fuel.

Alternative 1: An alternative, but less accurate, assess-ment method, which can be used when no scale house is available, is based on a measurement of the delivered volume rather than weight. The volume can be con-verted to weight by using the average value of the bulk density of the specific biomass fuel. It is important for

the bulk densities of all delivered biomass fuels to be determined prior to the first delivery, to improve the accuracy of the assessment process. The uncertainty of this method is that (a) the estimation or measurement of the volume delivered is in most cases less precise than a weight measurement, and (b) the bulk density of biomass fuels varies.

Alternative 2: Another alternative is to calculate the fuel price based on the amount of heat produced from the plant according to heat meter measurements. The effi-ciency of the combustion plant should be taken into account, so that reasonable market prices for the fuel are achieved. An advantage is that there are no costs for mass, volume, or moisture content determinations, and calibrated heat meters are very accurate. A disadvan-tage is that it is quite difficult to allocate the produced heat to a specific fuel amount from a specific supplier if there are multiple fuel suppliers. Another disadvantage is the influence of operating conditions on plant effi-ciency, because this would reduce the fuel price (insuf-ficient boiler cleaning can decrease boiler efficiency). Finally, during storage, the energy content of the fuel can decrease, which would also reduce the fuel price.

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Annex 11: Example of the Sampling and

Handling Process for Wood Fuels

Sources: BTG; Drohm Design & Marketing based on Impola 1998.

Note:

a. In proportion to mass of dry matter.

b. In proportion to quantity of wood fuel.

Combined samples

Laboratory sample

Mixing and division

at least 2 liters

Reserve sample

Simple samples (increments)of at least 1 liter

• necessary number of samples• at 5 liters

Method 1 (about 0.5 litera)Method 2

(about 0.5 literb)

Airdrying

Crushing <25 mm (when needed)

• at least 0.5 liter• necessary number of duplicate samples

• <0.5 mm• at least 5 liters

Calorific value sample

Analysis samples

Duplicate laboratory samples

Moisture samples

2 samples of 0.3–1.0 liters

Grinding

Mixing and division

Mixing and division

Mixing and division

82

Annex 12: Quality Management System for Solid Biomass Supply

Langheinrich and Kaltschmitt (2006) developed a six-step methodology for designing a quality man-agement (QM) system for solid biomass supply. They recommend that the practical implementation of the QM system be set out in an operator manual. The six steps, fine-tuned where relevant to the supply of agricultural and forestry residues, are described briefly below.

1. Description of Process ChainThe operator manual starts with a complete descrip-tion, with a sufficient level of detail, of all individual steps (unit operations) of the supply chain, from col-lection of agricultural and forestry residues to deliv-ery at the biomass power plant. It is recommended

to use a flow diagram to describe all unit opera-tions and their links. chapters 4 and 5 of this hand-book describe the supply chain for agricultural and forestry residues, respectively. Describing the supply chain in this manner helps to struc-ture the unit operations logically, determine links, and identify process owners for the allocation of responsibilities.

2. Determination of Customer RequirementsNext, the customer requirements are determined (figure A12.1). These requirements depend on previous and subsequent unit operations. The product requirements at the unit operation level may be different from a product standard that

Figure A12.1 Determination of Customer Requirements

Sources: BTG; Drohm Design & Marketing based on Langheinrich and Kaltschmitt 2006.

Requirements to be demandedof a previous process

Requirements to be demandedof a subsequent process

Customer requirements from a previous process

Customer requirements from a subsequent process

Previousprocess

Subsequentprocess

Unit operation under consideration

83

Annex 12: Quality Management System for Solid Biomass Supply

would be applicable to the final product. However, the requirements of the next operator in the supply chain should always be met. Each operator should do the following:

• Ascertain that the feedstock from the previous pro-cess is in compliance with the relevant CEN/TS 1496117 standard.

• Take into account the likely variability of relevant properties of the feedstock and other factors.

• Take into consideration documentation and logisti-cal demands, since logistics are of great importance among qualitative properties.

3. Analysis of Quality-Influencing FactorsStep 3 involves an analysis of the factors that have the most influence on biomass fuel quality. Typical factors include the following:

• Effectiveness of preliminary inspections of fuel sources;

• Effectiveness of checking incoming loads;• Appropriateness of applied methods to handle,

store, and process materials;• Quality control measures adopted;• Company management and responsibility; and• Qualification and knowledge of staff.

4. Identification of Critical Control PointsCritical control points, that is, the interfaces between processes, should be identified with a view to minimiz-ing the costs of quality control and to laying the foun-dations for a traceability system. Data on the origin of the feedstock and on the processes that the feedstock has undergone are systematically collected and ana-lyzed. Critical control points include places at which relevant properties can be most readily assessed and places with the largest potential for quality improve-ment and/or cost-reduction interventions:

17. The European Technical Standards for solid biomass fuels.

• The point at which raw materials are collected or purchased;

• The point at which raw materials are preprocessed and loaded for delivery to the next point in the chain and within the premises of the final supplier;

• The points at which the condition of the material is (or can be) changed deliberately;

• The point at which the final product is loaded for delivery; and

• The point of delivery at the end users’ premises.

5. Selection of Appropriate Quality Assurance MeasuresDepending on the results from previous steps of the methodology, appropriate quality assurance mea-sures have to be identified and applied. The following aspects should be taken into account:

• Allocation of responsibilities,• Elaboration of work instructions,• Proper documentation of processes and test

results,• Training of staff,• System for complaint procedures,• Customer satisfaction and maintenance of the qual-

ity assurance system,• Preliminary inspection of raw material suppliers

and formulation of acceptance criteria,• Enforcement of quality assurance meetings, and• Failure mode and effect analysis.

6. Routines for Nonconforming MaterialsWhen visual inspection or test methods show that the raw material at the gate of the plant does not con-form, the load should be rejected (before tipping of the load). Appropriate procedures must be in place for dealing with varying degrees of nonconformity. When nonconformity is discovered, a nonconformity report must be generated, and handling agreed on with the end user.

84

Annex 13: Fuel Supply Risk Matrix

Cause (fuel supply risk examples)

Potential

consequences

(event) Probability Impact Mitigating factors

• Low availability of biomass

• Competing usage

• Fuel supplier controlling fuel supply

• Old fuel sources dry up

Price of biomass

fuel (raw material)

increases; future

escalation

High High • Determine benchmark prices

• Commission independent market

study

• Enter into long-term fuel supply

contracts

• Contract with multiple fuel suppliers

• Allow fuel flexibility and ensure availa-

bility of back-up fuel

• Lower harvest capacity as a result

of bad harvest conditions or limited

terrain accessibility

• No mechanized methods for

biomass collection, storage, and

transport

• Transportation distance increases

• Higher machinery expenses because

of breakdown or other unexpected

situations resulting in lower net

output

• Lack of practical experience

Procurement costs

of biomass fuel

increases (logistics

of supply)

High High • Commission biomass resource assess-

ment to ensure required land is availa-

ble within reasonable transportation

distance

• Enter into long-term fuel supply

contracts

• Control transportation

• Require densification of biomass to

reduce transport costs

• Make the fuel supplier financially

involved in plant operation

• Arrange planting schemes with

growers or forest owners

• Develop storage capacity for conti-

nuous operation

• Contract for fixed time schemes for

biomass fuel delivery

• Train staff; provide clear work instruc-

tions; allocate responsibilities

(continued)

85

Annex 13: Fuel Supply Risk Matrix

Cause (fuel supply risk examples)

Potential

consequences

(event) Probability Impact Mitigating factors

• Insufficient match between

biomass fuel and fuel feed system

(off spec)

• Lack of practical experience

Insufficient agri-

cultural or forestry

residues at the right

specification to

operate plant

Moderate High • Enter into supply contracts that

include standards and specifications

• Monitor fuel quality (QM system)

• Prove plant operation with variety of

fuel specifications

• Enter into contracts stating that

biomass fuel not in compliance with

specifications may be rejected or

reduced in price (incentives or penal-

ties to fuel suppliers and growers)

• Train staff; provide clear work

instructions; allocate responsibilities

• Increase of transport costs

• Higher ash content than foreseen

• Change in legislation

Higher prices for

ash removal

Moderate Moderate • Enter into long-term contracts for

ash removal

• Enter into contracts that include

standards for ash quantity and quality

• Absence of equipment to remove

foreign objects

• Problems with fuel feed system

Presence of foreign

objects interrupts

operation

Moderate Moderate • Use front-end screening to remove

foreign objects

• Ensure feeder redundancy and easy

maintenance access to dislodge

• Change in legislation Supplies halt

because of the

absence of required

permits

Low High Obtain permits that allow as much

fuel flexibility as possible

Source: Based on Thornley (not dated publication, and oral communication).

The Energy Sector Management Assistance Program

(ESMAP) is a global knowledge and technical assis-

tance trust fund program administered by the World

Bank and assists low- and middle-income countries

to increase know-how and institutional capability to

achieve environmentally sustainable energy solutions

for poverty reduction and economic growth.

fuel supply handbook for biomass-fired power projects

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