Applied Mathematical Sciences Vol. 8, 2014, no. 131, 6565 - 6576
HIKARI Ltd, www.m-hikari.com http://dx.doi.org/10.12988/ams.2014.46450
A Techno-Economic Feasibility Assessment
on Small-Scale Forest Biomass Gasification
at a Regional Level
Daniele Dell’Antonia
Department of Agriculture and Environmental Sciences (DISA)
University of Udine, Via delle Scienze 208, Udine, Italy
Sirio R. S. Cividino
Department of Agriculture and Environmental Sciences (DISA)
University of Udine, Via delle Scienze 208, Udine, Italy
Olga Malev
Department of Agriculture and Environmental Sciences (DISA)
University of Udine, Via delle Scienze 208, Udine, Italy
Gianfranco Pergher
Department of Agriculture and Environmental Sciences (DISA)
University of Udine, Via delle Scienze 208, Udine, Italy
Rino Gubiani
Department of Agriculture and Environmental Sciences (DISA)
University of Udine, Via delle Scienze 208, Udine, Italy
Copyright © 2014 Daniele Dell’Antonia et al. This is an open access article distributed under the
Creative Commons Attribution License, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Abstract
In recent years public and political awareness to environmental issues and
energetic aspects have led to the development of alternative energy resources. The
6566 Daniele Dell’Antonia et al.
use of woody biomass from forest management presents a renewable, low-carbon
feedstock which can implement alternative sources for energy production. For
example, biomass gasification is a prominent conversion route for producing a
renewable clean feedstock used for power generation.
In 2012, the "burden-sharing" Decree 28/2012 of the Italian Ministry of Economic
Development introduced regional targets for Friuli Venezia Giulia region with an
increase of 257 ktoe produced from renewable energy equal to 12,7% of the
regional consumption. The present work was focused on overall mountain area of
this region in the North-East of Italy. The study showed technical and economic
aspects of forest combined heat and power (CHP) biomass system with two
different types of gasification plants: (i) gasification with combustion engine and
(ii) gasification with a Stirling engine. The technical and economic characteristics
of small-scale gasification technology was determined using the methodology of
Net Present Value (NPV) in order to identify the best technological solution for
the construction of a gas plant in a company that processes timber:
From the technical point of view the gasification plant with Stirling engines is a
more reliable energy system which is not subjected to strains due to the use of
synthesized gas during its normal activity. However, the investment costs are
significantly higher (€ 7,429/kWe) when compared to the costs necessary for a
gasifier with internal combustion engine (€ 4,040/kWe). The techno-economic
feasibility assessment has shown no substantial difference in the remuneration
time for both type of gasification plant being in the range of 4-5 year period.
Additional studies are necessary to elucidate both technical and economic aspects
and to suggest which type of technology is more suitable on small-scale forest
biomass gasification at a regional level.
Keywords: forest, wood biomass, gasification, economic analysis
1 Introduction
Forests play a key role in the overall socio-economic development providing
different material, environmental or occupational benefits and for that reason
increasing resources should be dedicated to forest sustainable management and
conservation. One potentially valuable by-product from conventional forestry
systems which produce wood for constructions and pulp or paper is biomass for
energy [Richardson, 2007]. Today biomass provides about 10% of the global
energy supply, amounting to around 14 PWh per year, of which the main part
(over 80%) originates from wood or shrubs, in form of trees, branches and
residues [Chum, 2011; IEA, 2011]. Woody biomass is regardedas as a “CO2
neutral” solid fuel and a promising alternative to decreasing resources of fossil
fuels [Zhou, 2006]. Biomass gasification is a prominent conversion route for
producing a renewable clean feedstock used for power generation [Wongchanapai,
2012]. Furthermore, use of biomass in district energy creates jobs and promotes
social and economic development in local communities [Openshaw, 2010; Yagi,
2011].
Techno-economic feasibility assessment 6567
In 2011 the energy consumption in Italy was of 168 Mtoe (million tons of oil
equivalent), where all renewable energy resources, including hydropower and
biomass, accounted for 20.2 Mtoe (about 12%) [Eurostat, 2013]. At the moment,
no published data exist on the relative contribution of biomass alone, but some
recent estimation report a total potential contribution of 24-30 Mtoe (about 13.6%)
[ITABIA, 2008]. The use of agro-forestry biomass can contribute to increased use
of renewable sources for energy production considering the latest directives of the
European Union (EU) Energy and Environment Policy that established a new
framework for renewable sources (Directive EC 28/2009; European Commission,
2009).
The Italian Energy Action Plan of 2010 set a target of at least 17% of total
energy generated from renewable sources by 2020 [European Commission, 2009].
In 2012, the "burden-sharing" Decree 28/2012 of the Italian Ministry of Economic
Development introduced regional obligations to ensure the accomplishment of
national 2020 targets. Regional targets for Friuli Venezia Giulia region are
particularly demanding for renewable energy, with a projected increase of 257
tonnes of oil equivalent (12,7% of the regional consumption): +138% in 2020
relative to 2005 [Ministry of Economic Development, 2012].
In relation to targets set both on national and regional level, the quantitative
analyses of strategies for utilizing woody biomass energy sources should be
performed both evaluating the potential resources of bioenergy in different
regions (e.g. forest-rich or with agricultural-land surplus) and identifying the
woody biomass demand within forestry industries, and other possible territorial
complications. In Friuli Venezia Giulia region the presence of highly
discontinuous agricultural activities and issues related to mountain regions make
somewhat difficult the exploitation of biomass for the simultaneous production of
electricity and heat (cogeneration). This problem is in part related to the use of
established technologies that have high power (> 1 MW) requiring significant
amounts of biomass (i.e. steam turbines or Organic Rankine Cycle) and it is in
part related to the lack of utilities with continuous use of heat throughout the year.
In north Italy is active a constant research of new technologies to make highly
applicable small to medium size plants (100-250 kWe) for biomass utilization and
more efficient energy conversion. Two different technologies may be usually
applied for biomass power generation: (i) gasification with internal combustion
engine and (ii) gasification with a Stirling engine. In this way agro-forestry
companies could diversify their income rendering it more stable by taking
advantages of state incentives for electricity production from biomass. In specific,
state incentives and municipal support are higher if the electricity production
derives entirely from forestry and agricultural by-products [Ministry of Economic
Development, 2012]. These technologies for energy generation allow also the
production of biochar, a form of charcoal produced through pyrolysis of
carbon-rich biomass. When this material is applied to agricultural lands it
increases soil water and nutrient retention as well as enhances its fertility while
sequestering carbon [Laird, 2008; Lehmann et al., 2007].
This study was focused on the mountain area of Friuli Venezia Giulia region
6568 Daniele Dell’Antonia et al.
(North-East Italy). We showed technical and economic aspects of CHP biomass
system with a small-scale gasification equipment. The biomass fuel considered in
this evaluation was represented by residues of wood processing and wood chips
from forest management procedures. The objective of this research was to find out
the economic feasibility of CHP system on small-scale level in mountain areas in
Italy comparing two different technologies for biomass power generation
2 Materials and methods
2.1 Study site
The study area is located in the Friuli Venezia Giulia region (North-East Italy)
and has a total surface area of 785,648 ha. According to the data of the National
Forests Inventory, the regional forests cover an area of 357,224 ha with an
average wood withdrawal of 170,000 m3 which is the 5% of raw material
requirements in woodworking industries [INFC, 2012]. The regional supply of
raw material is dependent on import from foreign countries with a yearly amount
of 3,000,000 m3 year distributed as follows: 70% panels (wood pulp), 11% chair
industry; 10% furniture; 2% floors and windows and 7% for energy or other uses
[Wood Services, 2010].
2.2 Gasification plants
The feasibility study has considered two different types of gasification plants
in order to identify the best technological solution for the construction of a gas
plant in a company that processes timber (Table 1).
In the first case study was identified a system with nominal power output of
140 kWe formed as follows:
• an updraft gasifier which produces fuel gas from wood chips: in this way it
is possible to avoid the use of filtering systems and use biomass with higher
moisture content;
• four heat generators for gas burning process (to note: direct contact with the
heads of Stirling engines);
• four Stirling engines with electric power unit of 35 kWe each;
• a heat accumulator that acts as a thermal stabilizer and allows the
accumulation of hot water.
The functioning of the system is fully automatized; biomass is loaded from
inside the reactor and subjected to high temperature with a limited oxygen supply
which allows the gasification of introduced materials. The syngas is extracted in
the upper part of the reactor and used to move Stirling engines. Besides electricity
this engine produces also heat used for warming of water contained within the
accumulator.
The second case study has a system with a nominal electric power of 250
kWe and is formed of:
Techno-economic feasibility assessment 6569
• a downdraft gasifier system with electrostatic filtering system of the syngas;
• a dryer for biomass moisture reduction localized in the inlet of the reactor
that uses the heat of the internal combustion engine;
• two sets of diesel engines with nominal power unit of 125 kWe.
In this system the syngas product is extracted at the bottom of the reactor and
passed through a series of scrubbers and electrostatic filters that allow the removal
of impurities. Consequently, the gas is injected with a small amount of diesel fuel
inside the combustion chamber of an internal combustion engine at the end of the
piston compression phase. The amount of added diesel fuel allows the ignition of
the mixture and starting the engine.
Energy
Gasifier with internal combustion
engine
Gasifier with
Stirling engine
Power
generation
efficiency
(%)
Power
(kW)
Energy (1)
(MWh/year)
Power
generation
efficiency
(%)
Power
(kW)
Energy (1)
(MWh/year)
Electricity 24 250 1,750 17.5 140 980
Thermal energy 45 480 3,360 70 560 3,920
Dispersions 31 295 2,065 12.5 100 700
Total 100 1,025 7,175 100 800 5,600
(1) 7.000 hours/year of energy plant activity
Table 1 – Technical characteristics of gasification plants.
2.3 A techno-economic feasibility assessment
Through the analysis of data on the thermal and electrical power efficiency of
the plant and overall activity hours (7,000 hours/year) it was possible to estimate
the total amount of produced energy by the gasifiers. Total electricity produced in
this way was directly transferred and used by the electrical network, while the
remaining thermal component could be used to meet the energy needs of the
company.
In the case of combined gasifier with internal combustion engine part of the
produced heat is used to dry the introduced biomass (10-15 % final humidity
content). On the contrary, for the system with Stirling engine there are no
particular requirements in relation to the humidity of applied fuel and all heat can
be re-used in the company for other purposes. In our feasibility assessment was
also evaluated the possibility of equipping sawmill with a dryer to allow the
re-use of thermal energy. In this way, a part of company's products could be dried
directly in situ thus avoiding and reducing the costs associated with use of
third-party companies for drying processes.
The technical and economic aspects of small-scale gasification technology
was determined using the methodology of Net Present Value (NPV). Profits from
6570 Daniele Dell’Antonia et al.
the sale of produced electricity have been calculated considering the base rate of
the Ministry of Economic Development in 2012, for the production of electricity
from renewable sources (229 €/MWh) added with the incentive for use of heat (40
€/MWh). The used thermal energy has been accounted as non-retrieved costs for
the drying of panels by third-party companies (30 €/t). After determining cost and
profit items it was calculated the expected cash flow for a 20-year investment
period during which remains valid the price for sale of electricity. In addition,
profits form electricity sale are not affected by inflation while remaining incomes
are subjected to these variations. For a more detailed analysis these incomes,
subjected to inflation, were calculated for each year in the whole considered
period. The calculated values were presented as incomes less costs deferred in
time using an interest rate equal to average of inflation adjustments indexes for
the period 1992-2012 (2.7%) [ISTAT, 2014]; using the following function:
CF = Ie − [It ∙ (1 + i)t] − [C ∙ (1 + i)t] (1)
Where:
CF, in €, is the annual cash flow;
Ie, in €, is the incomes from the sale of electricity energy;
It, in €, is the incomes from the re-use of thermal energy;
C, in €, is the cost for the management of the plants;
i, in %, is the interest equal to average of inflation;
t, is the time of the cash flow.
Afterwards, we calculated the cash flows, discounted to present value using
an interest rate equal to 4% and was determined the net present value (NPV) of
the two selected types of plants as follows:
∑ =nt=0
CF
(1+r)t (2)
Where:
CF, in €, is the annual cash flow;
r, in %, is the discount rate;
t, is the time of the cash flow;
n, is the year of the investment period.
3 Results
The first phase of the economic analysis was focused on the evaluation of
individual costs and incomes related to purchase and management of small-scale
gasification plants. The total investment cost for purchase and installation of the
gasification plant with four Stirling engines was equal to 1,040 M €, while the
cost of the gasification plant with internal combustion engines was of 1,010 M €
(Table 2).
Techno-economic feasibility assessment 6571
Plant Gasifier with internal combustion
engine Gasifier with Stirling engine
Gasifier 875,000 850,000
Dryer 55,000 110,000
Wood chipper 40,000 40,000
Connection to electrical network
10,000 10,000
Expenditures for civil
engineering works 30,000 30,000
Total 1,010,000 1,040,000
Gasifier costs (€/kWe) 4,040 7,429
Table 2 – Investment costs for the construction of gasification plants and associated dryers.
In Table 3 are presented economic accounts relative to costs and incomes of the
annual management of gasification plants. Maintenance costs and necessary
employment for the plant with Stirling engines account for an annual charge of €
31.900, compared to the gasifier with internal combustion engines where the planned
expenses are € 86.580. The relevant difference is due to the high demanding
maintenance of internal combustion engine powered with syngas. Due to this issue it
is considered the cost of 45 €/MWh produced for full-service maintenance provided
by the company which constructs gasification plants with internal combustion engine.
In Table 4, based on the availability of by-products (1100 tons/year) we
calculated the amount and the cost of necessary biomass for the operation of gasifiers
(40 % humidity): 829 tons/ year and 1,817 tons/year for the plant with the Stirling
engine and for the plant with internal combustion engine, respectively. In relation to
the re-use of thermal energy process of gasification plants, it is possible to dry a total
of 1,600 t/year of plates (13% of the processed products) for systems with Stirling
engine and about 700 tons/year of plates (6% of processed products) for gasifiers with
internal combustion engine.
Gasifier
Incomes (€/year) Costs (€/year)
Profit
(€/year)
Electricity Thermal
energy Total Biomass Managment Total
Gasifier with
internal combustion
engine
470,750 21,000 491,750 130,742 86,580 217,322 274,428
Gasifier with
Stirling engine 263,620 48,000 311,620 72,450 31,900 104,350 207,270
Table 3 – Profits and annual costs for the management of gasification plants.
6572 Daniele Dell’Antonia et al.
Biomass Prices
(€/t)
Gasifier with internal
combustion engine Gasifier with Stirling engine
Quantity
(t)
Total costs
(€)
Quantity
(t)
Total costs
(t)
Wood saw dust 20 700 14,000 700 14,000
Bark (cortex) and residues 40 300 12,000 300 12,000
Unmarketable wood 50 100 5,000 100 5,000
Chips to be integrated 50 1,817 90,850 829 41,450
Diesel fuel 1235 7.2 8,892 - -
Total - 2,924 130,742 1,929 72,450
Table 4 – Costs of used biomass for each gasification plant.
At the end of the techno-economic feasibility assessment we concluded that
the remuneration and compensation time for the gasification plant with four
Stirling engines is of 5 years, after which the NPV starts to have a positive value
up to the amount of approximately 1.5 M €. For gasification plants with internal
combustion engines the recovery time is equal to 4 years and the NPV value after
20 years results in the range of 1.9 M €.
In case of no re-use of thermal energy the investment would be reimbursed
after 7 and 13 years for the plant with internal combustion engine and the one
with Stirling engines, respectively. This economic situation is caused by a
decrease in profits; the incomes due to the drying of wood panels were not
accounted and also due to a lower price of marketed electricity (Figure 1).
4 Conclusions
From the technical point of view the gasification plant with Stirling engines is
a more reliable energy system which is not subjected to strains due to the use of
syngas during its normal activity. On the other hand, the internal combustion
engine is significantly affected by the quality of applied fuel and all uncertainties
associated with revision times of these engines are still elevated. Moreover, the
re-use of thermal energy for drying processes of the plates could implement the
energy efficiency of the simultaneous production of electricity and heat in
small-scale plants, compared to the large cogeneration system where most part of
heat is dissipated.
Techno-economic feasibility assessment 6573
Figure 1 – Cash flows of gasification plants in relation to profits from sale of electricity and
the re-use of thermal energy.
The analysis presented in this study could indicate that the investment costs in
both analyzed cases are extremely expensive for single companies. The
investment cost related to installed power units is greater in case of gasification
plant with four Stirling engines (€ 7,429/kWe) than that of gasifier with internal
combustion engine (€ 4,040/kWe). The economic analysis of the NPV
demonstrated that the installation of gasification plants with internal combustion
engine allows reimbursment of investment costs in shorter time compared to
gasifier with a Stirling engine. Nevertheless, the use of biomass gasification plants
for production of energy could reduce emission of carbon dioxide into the
atmosphere and implement carbon sequestration by distributing produced biochar
on agricultural land. Many issues must still be explored in terms of
techno-economic feasibility, local energy production policies and incentives based
on renewable sources as well as development of technologies that improve
efficiency of energy systems and the reduction of possible environmental impact.
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Received: June 1, 2014