Biomass energy systems

Renewable energyfrom biomass direct burning

Agenda

• Biomass materials as a source of renewable energy• Biomass energy advantages• Financing/Funding of renewable energy systems• Plant configuration examples• Technology Summary• WTE for customers entering the renewable energy business

Biomass materials: introduction

• wastes from forestry and sawmill operations (bark, wood chips, sawdust, logging debris)

• urban wood wastes (shipping pallets, packing and leftover construction wood)

• agricultural wastes (crop residues, sugarcane, rice husks, coconut shells, cotton residues and palm oil residues)

• fast-growing trees and crops (“energy crops”) such as poplar, willow and switchgrass, grown specially for energy (electricity or liquid fuels)

• other natural resources (straw, peat) • organic wastes (animal manure, processing wastes) • organic portions of municipal solid waste (found in municipal

sewage and landfills)

Wood remains the world’s largest source of biomass, but the wide variety of biomass fuel sources also includes:

Biomass materials: moisture content and LHV

Moisture content

Lower heating valueThermal

powerElectric

Power

Biomass fuels(Wet basis -

%) MJ/kg

GJ/tonnekcal/kg

Mcal/tonnekWh/kg

MWh/tonnekWh/kg

MWh/tonne

Wood (wet, fresh cut) 40 10,40 2484 2,88 0,72

Wood (air dried, humid zone) 20 14,60 3487 4,04 1,01

Wood (air dried, dry zone) 15 15,60 3726 4,32 1,08

Wood (oven dry) 0 20,00 4777 5,54 1,39

Bagasse (wet) 50 8,20 1959 2,27 0,57

Bagasse (dry) 13 16,20 3869 4,49 1,12

Wheat straw 12 15,20 3630 4,21 1,05

Maize stalk 12 14,70 3511 4,07 1,02

Maize cobs 11 15,40 3678 4,27 1,07

Rice hulls (air dry) 9 14,40 3439 3,99 1,00

Cotton stalk 12 16,40 3917 4,54 1,14

Coconut husks 40 9,80 2341 2,71 0,68

Coconut shells 13 17,90 4275 4,96 1,24

Dung cake (dried) 12 12,00 2866 3,32 0,83Here yield in conversion from thermal to electric power is equal to 25%. More realistically, a 20-30% range should be considered.

Advantages of biomass energy

• Wide availability• A renewable resource (when sustainably used and managed)• Less waste being sent to landfills

– burning unusable waste materials such as bark, construction wastes and tree clippings helps to reduce the pressure to expand local landfill sites while generating useful energy

• Can help provide answers to the climate change issue– does not increase atmospheric levels of carbon dioxide, a primary

greenhouse gas, because of the cycles of regrowth for plants and trees– can decrease the amount of methane, another greenhouse gas, which is

emitted from decaying organic matter

• Can be converted into several forms of energy– Biomass can be converted in energy by direct burning – Recent tries to convert wood in gas – yet unreliable results– organic waste in landfills can produce methane– corn, wheat and other materials can be used to manufacture liquid fuel

ethanol

Financing biomass energy systems

• Renewable energies receive a considerable financial support, by national and transnational organizations:– National/EU investment subsidies schemes– Support mechanism for power production from renewable sources– Benefits from carbon trade (Clean Development Mechanism)– Worldwide financial institutions (IFC, WB, ADB,…)– Commercial banks providing “soft” loans for RE projects– Commercial fund facilities

• WTE can supports its customers in their approach to various national and international financial institutions and agencies

How is biomass energy used (I)

Possible ways to exploit the energy content of biomasses are:• Co-firing • Direct combustion in dedicated power or CHP (combined

heat and power) plants• Gasification• Anaerobic digestion/Landfill gas• Bio-refineries

How is biomass energy used: WTE focus (II)

• Direct Combustion– The simplest and oldest way– Biomass is burn in boilers to produce high pressure steam. Steam turns a turbine

connected to a generator. As the steam causes the turbine to rotate, the generator turns and electricity is produced.

– Most of the world’s biomass power plants use direct combustion.– In some cases, the steam from the plants is also used to heat water and buildings

(cogeneration or CHP “combined heat and power” facilities). – Limited thermal efficiency: electric energy obtained from a direct combustion

systems typically is around 20-30 % of total energy in biomass.– System efficiencies can be increased through cogeneration (up to 60-70% of

primary energy can be used as thermal + electric energy).• Co-firing

– Burning biomass, along with coal, in traditional power plant boilers.– Economic ways to produce electricity from biomass, because existing power plant

equipment can be used without major modifications. – Some coal-fired power plants in North America use this technology to help reduce

the use of coal and, thereby, lower emissions of carbon dioxide, possibly also sulphur dioxide and nitrogen oxides.

– Allows biomass to be converted to electricity at a higher thermal efficiency (33 - 37 %)

How is biomass energy used (III)

Conceptual scheme of a direct combustion biomass energy system

Biomass characteristics influencing system design

• Characteristics of biomass as fuel – to be considered for a proper design of the system (impacting: biomass handling, furnace design, air pollution control system configuration– Energy content (low heating value LHV) range– Moisture– Chemical composition (S, Cl, F, N, C, O, H content)– quantity and quality of ashes from combustion process

Technologies in detail: Adiabatic process

• adiabatic process A process in which no heat enters or leaves a system. An adiabatic change is usually accompanied by a rise or fall in the temperature of the system, accompanied by work extraction

• Furnace adiabaticity (y): a coefficient representing the ratio between the heat exchanged through the furnace walls and the total heat available (fuel combustion, preheated combustion air, fumes recirculation, etc.)– Refractory lined furnace: no heath exchange through the furnace walls,

coefficient y approximately equal to 0.95 (always consider some losses because of dissipation)

– Water wall furnace: heath exchange through the furnace walls, coefficient y can reach value as low as 0.65

Technologies in detail: adiabatic and non-adiabatic systems

• Furnace entirely lined with refractory

• Designed to process fuel characterized by low/medium value of energy content (LHV)

• Higher specific production of fumes – due to higher excess air quantities used to control furnace temperature

• Reduced energetic performances• Increased flexibility to changes in

fuel LHV• Increased flexibility to thermal

load

Fully adiabatic system (y = 0.95)

• Water wall furnace• Specifically designed to process

fuel having high energy content (LHV)

• Lower specific production of fumes

• Better energetic performances• Limited flexibility to changes in

fuel LHV• Limited flexibility to changes in

thermal load

Non adiabatic system (y = 0.65)

Adiabatic and non-adiabatic systems to process waste differing for LHV

WTE advantage

• WTE design furnaces based on the energy content of waste, combining various project options to reach the optimal value of adiabaticity for the system Possibility to go beyond the usual pattern, considering only the alternative between a fully refractory lined furnace (effective but scarcely efficient regarding energy recovery) and a water wall furnace (efficient but much less flexible to changes in fuel energy content and furnace load)

• Properly designed adiabatic (y = 0.95) systems can process fuel with energy content as low as 6000-6500 kJoule/kg (1433-1522 kCal/kg)

• An adiabatic furnace coupled with a fumes recirculation system can process fuel with high energy content (LHV), reaching the same energetic efficiency of a water wall furnace

Plant configuration examples (I)

Typical small biomass power plant, low/medium LHV biomass, including feeding system, furnace, boiler, air pollution control (APC) system

Plant configuration examples (III)

• Biomass energy system (wine production residues, wood chips)

• Suitable to process moist/low energy content biomasses: fully refractory lined furnace

• Flue gas recirculation to achieve better performances in energy recovery

Technical characteristics

Furnace suitable for biomass with low energy content (7.75 to 12.5 MJ/kg)

Plant configuration examples (II)

• Refractory lined furnace• “Water wall” post-combustion • Suitable for biomasses of medium

energy content• Easy to extract SH, EVA, ECO• Double SH with intermediate

desuperheater (to keep constant the steam temperature independently of fouling and thermal load

• Slag discharged in scraper (water bath)

• Refractory roof (suspended type)

Technical characteristics

Furnace suitable for biomass with medium energy content (8.8 to 16.7 MJ/kg)

Plant configuration examples (II)

• Tube walls to maximize heath absorption in combustion chamber

• Tube walls roof• Horizontal boiler convective section• Radiation channels in vertical

configuration• Easy to maintain – easy to access • Double SH with intermediate

desuperheater (steam temperature non influenced by fouling or changes in thermal load

• Slag discharge in scraper (water bath)

• Sodium bicarbonate reactor

Technical characteristics

Furnace suitable for biomass with medium energy content (9.8 to 16.7 MJ/kg)

Technology summary (I)

General parameters

Scale of applications Industrial, medium to large

Energy services Electricity and process heat/steam

Typical electrical capacity 1 to 50 MWel

Typical heat to power ratio 20-30%

Technical parameters of interest

Technology summary (II)

Technical parameters

Basic equipment Furnace, boiler, steam turbine and thermal cycle, APC

Typical steam conditions

20 to 80 bar, 380-500 °C

Biomass fuel Any (furnace and boiler design varies with fuel)

Typical biomass rate 1 to 2 dry kg/kWh; 7500 to 15000 dry tonnes/year per installed MWe

Key cost factors Capital investment (especially at smaller scale)Fuel cost and availability

Technical concerns Deposition on boiler tubes with high ash biomassAsh melting in the furnaceFluctuation in LHV of biomass

Technical parameters of interest

Assuming an availability of 7500 hours/year

Technology summary (III)

Environment & Organization

Environmental strengths Use of biomass more efficient with CHP or water desalinizerMultiple fuel capability

Environmental issues Particulate emissions, thermal pollution, ash disposal

Total direct jobs 20 (up to 10 MWe)

40 (from 10 to 30 MWe)1xMWe (starting from 30 MWe )

Labour: high/managerial skill level

20%

Labour: moderate skill level 65%

Labour: low skill level 15%

Environmental and organizational parameters

WTE philosophy: design for flexibility (I)

• Flexibility the system is capable to process different materials – differing for energy content, moisture, chemical composition, quantity/ characteristics of ashes

• The need for flexibility arise from financial/economic considerations:– Some biomasses can be more or less available of depending on the

period of the year (seasonal availability)• Possibility to buy when price is low, storing reserves for future production

– Important market price dynamics have to be expected• increase in demand of biomasses for energy applications can determine price

rise• Demand from energy generation systems can be in competition with other

business domains (i.e. wood residues demand from chipboard panels manufacturers)

WTE philosophy: design for flexibility (II)

• Technical options:– Furnace design based on the range of biomass energy content (Low

Heating Value – LHV). The most relevant design option concerns the quantity of heat exchanged through the furnace walls

– Air pre-heating: strongly suggested when in need to burn moist/low energy content biomasses. When seeking for highest performances, regenerative air pre-heating is required

– Flue gas recirculation: allowing a refractory lined furnace to reach the same level of efficiency in energy recovery of a water walls furnace

– Flue gas temperature control (boiler outlet) – to reduce corrosion risks (on economizer banks) and to guarantee the proper operability of air pollution control (APC) system

WTE in the biomass energy business domain

• Consolidated experience in design of direct burning biomass energy systems

• Project design depending on installed power, type(s) of biomass used, …..

• Concept and Feasibility studies• Base and Detailed Engineering• Full support to customer during procurement, construction,

commissioning and start-up • EPC to be discussed case by case

How to contact us

WTE – Waste to Energy s.r.l.Via San Michele, 1521052 Busto Arsizio (Varese)ItalyTel.: +39 – 0331 - 67 00 66Fax: +39 – 0331 - 32 02 96E-Mail: wte@wastetoenergy.it

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