Environmental Impact of different Power Production Techniques using Biomass

1. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
Environmental Impact of different Power Production
Techniques using Biomass
P.P.A.J. van Schijndel, J. Huisman, J.M.N. van Kasteren and F.J.J.G. Janssen
Eindhoven University of Technology
Faculty of Chemistry and Chemical Engineering
Centre for Environmental Technology
The Netherlands
Abstract
In this paper the results of a study concerning the technical, economical and
environmental aspects of the energy source biomass are presented. In the first part of
the study an techno-economical ranking was made of a number of possible biomass to
power technologies. The best available techniques were submitted to an environmental
Life Cycle Assessment to compare on environmental impact. Following biomass routes
the following were chosen for further LCA research: 1. Co-combustion of biomass in a
conventional powder coal power plant, 2. Stand alone biomass firing with steam cycle,
3. Stand-alone biomass gasification with combined cycle and 4. Combustion in a
domestic waste-incinerator.
The functional unit was chosen to be the combustion of biomass, according to a
calorific value of 966 TJ, combined with a production of 425 TJ electricity. This unit
equals the yearly power production of a moderate sized decentralised power plant. To
processes with less efficient electricity production, electricity was added supplied by
the grid in the Netherlands.
An environmental ranking was determined based on the Eco Indicator ’95 method.
Determining factor is the electricity production efficiency. Biomass co-combustion
scores better than stand alone gasification which is better than stand alone combustion
which is again better than waste incineration. Domestic waste incinerators have an
advanced gas-cleanup system but the low efficiency makes them less suitable for
making electricity. Uncertainties in the study were the choice of functional unit and the
lack of data on abiotic depletion of energy carriers. Surprisingly, variation of the
functional unit didn’t change the overall ranking of the different techniques.
Introduction
As a result of the global increase in energy use and the depletion of fossil fuel stocks,
world-wide much research is done in the area of cheap and sustainable energy sources.
This study focuses on the use of biomass as a source for sustainable energy
production. Since biomass is a renewable energy source it will not contribute to extra
CO2 emissions. Therefore biomass will not contribute to the global warming problem
as fossil fuels do.

2. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
Sources for biomass are:
q Wastes: e.g. paper sludge, organic sludge, garden wastes, thinning wood,
agricultural waste,
q Special energy crops: e.g. cultivated poplar wood, miscanthus and rapeseed.
This study focuses on the use of biomass waste in the Netherlands. In the Netherlands
the possible power production from biomass waste will be about 150 PJ (1 PJ=1015
J),
which is 4% of total power production. In 2020 the contribution of sustainable power
should be 270 PJ, this means that biomass waste could contribute around 50% of the
sustainable power production (Faaij, 1996).
It is important to use the optimal techniques to make electricity out of biomass. The
techniques should be both technically, economically and environmentally feasible. Next
chapters comprise with a first selection on basis of technology and economy.
Biomass conversion techniques
Many different biomass conversion routes exist currently. These routes can be divided
into thermal methods, like gasification, combustion and pyrolysis and into biological
methods, like composting, fermentation and digestion. Most important products of
biomass conversion are fuels, i.e. petrol and diesel, chemicals like methanol, ethanol or
other special products, electricity and heat, also see Figure 1.
Figure 1. Most important biomass conversion routes
The most important aspects on the process technology of the three conversion routes,
combustion, pyrolysis and gasification, will be explained first.
Combustion (Incineration)
One of the oldest known biomass conversion techniques is incineration. Burning dried
wood (waste) to cook is still common practise in many countries around the world.
Although wood is a renewable source there are many environmental problems related
to it’s use as there are deforestation, soil erosion, eutrophication and health problems.
State of the art incineration is highly efficient with emissions fulfilling all environmental
standards (Janssen, 1999). Electricity is made using a normal steam turbine cycle. If
biomass is incinerated together with coal or other fuels the term co-combustion is
used.
Fuel gas
Charcoal
Pyrolysis-oil
Heat
Synthesis
Gasturbine
Gas engine
Steam turbine
Slurry production
Upgrading
etc.
Primary product Process technology Secondary productConversion technology
Gasoline, diesel
Methanol
Electricity
Heat
Slurry-fuel
etc.
Gasification
Pyrolysis
Combustion

3. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
Gasification
If biomass is heated to high temperatures (above 700°C) with understochiometric
amount of oxygen and some moisture, small molecules are formed like CO, CO2, H2,
CH4 and water. The reaction is called gasification as a syngas is produced from a solid
or liquid. Main advantage is that either the syngas can be used for production of
chemicals or can be burned in a boiler (steam cycle) or even a gasturbine (combined
cycle). Another advantage is that the gas volume to be cleaned is much smaller when
compared to incineration because the gas clean up takes place before the actual
combustion (Schijndel, 1997).
Hydrothermal treatment, HTU
A new technique in this field is HTU. It consists of hydro treating biomass/water
mixtures at (near) critical conditions of 250-500°C degrees and 300 bars (Cuelenaere,
1999) followed by upgrading of the bio oil formed. If pyrolysis is used to make
electricity directly on site it is not competitive compared to the other techniques.
Pyrolysis
When biomass is heated with exclusion of any oxygen the process is called pyrolysis.
In pyrolysis three products are formed, namely solid carbons, oily liquid, called bio oil,
and a gas. Main reason for using pyrolysis in stead of burning or gasification is the
formation of products like the bio oil, which can be upgraded into gasoline or diesel or
specific chemicals.
Electricity production technologies
When a fuel is combusted, the hot gases can be used to make steam in a steam boiler.
The hot pressurised steam can pass an expander to drive a generator for making
electricity, see Figure 2. It is also possible to let the hot gases expand in a gas turbine
followed by a steam cycle, which is called combined cycle or Steam and Gas cycle, see
Figure 3. A combined cycle is known for higher efficiencies compared to single steam
cycles. Maximum efficiencies of 50% can be reached by combined cycle.
Figure 2. Layout of steam cycle technology
Fuel
Air
Pump
~
Condensor
Steamturbine
Exhaust gasses
Steam
Water
Boiler

4. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
Figure 3. Layout of combined cycle technology
Technical and economical ranking of different conversion techniques
A selection of these techniques was made using following criteria:
• Conversion technique must have been proven in a pilot plant, or a pilot plant must
be in start-up phase,
• Conversion technique should be economical feasible within 5 years,
• Conversion technique should be feasible in the Netherlands, for different biomass
waste types (including wood), on a 5-30 MWe scale.
The first two criteria are used only to compare conversion systems, which are feasible
to be implemented in the near future. The last criterion is chosen because due to
transport distances the use of biomass is restricted to relative small power units.
All pyrolysis routes and the pressurised gasification routes failed the selection criteria.
Table 1 shows the conversion techniques, which fulfils the criteria (Huisman, 1999).
Table 1. Biomass waste conversion routes fulfilling proposed criteria
General technique Specific system
Gasification Circulating Fluidised Bed reactor, cold gas clean up, Steam
and Gas Turbine
Co-combustion of gasifier gas in a gas or coal fired steam
cycle
Co-combustion of gasifier gas into gas fired combined cycle
plant (gas and steam turbine)
Incineration Co-combustion in Coal Powder Power plant with Steam
Cycle
Stand alone Circulating Fluidized Bed combustion with Steam
Cycle
Gasturbine
Fuel
Air
H
R
S
G
Stack
Pump
~
Condensor
Steamturbine
Hot gasses
Steam
Water

5. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
In order to determine the technical and economical feasibility of the selected
techniques, 5 ranking criteria were used, namely:
1. Price of final products
2. Developing stage of technique
3. Energetic (exergetic) efficiency
4. Flexibility towards different types of biomass feed
5. Feasibility of introducing the technique in the economy
The results of this final ranking can be found in Table 2. As can be seen most
techniques are combustion techniques. The reason for this is that the techniques are
proven and most can be combined with existing plants, which keeps investments low.
Gasifier techniques are very promising although there is less experience with such
systems. Stand-alone techniques are ranked lowest, because of higher investment costs
and lower efficiency.
Table 2. Final ranking of most promising biomass conversion techniques
Rank Technique / route Price electricity
NL ct / kWh
Electrical
Efficiency
1 Co-combustion in a powder coal power plant
with steam cycle
4 – 13 32 – 44 %
2 Co-combustion of gasifier gas in a normal
gas/coal power plant with steam cycle
9 – 18 30 %
3 Co-combustion of gasifier gas in a gas power
plant (STEG) Combined cycle
10 – 23 35 %
4 stand alone gasification (atmospheric) in
fluidised circulating bed with combined
cycle, cold gas cleanup, system
12 – 27 40 %
5 Stand alone combustion in a circulating
fluidised bed reactor with steam cycle
12 – 20 22 – 28 %
Table based on Huisman (1999). 100 NL ct = 1 NL Guilder = 2,20371 Euro
Environmental comparison using LCA
The techniques ranked 1, 4 and 5 in Table 2, were further investigated using LCA. For
the techniques 2 and 3 there is not yet sufficient data to perform an LCA. The
technique of environmental Life Cycle Assessment by means of SIMAPRO 4.0
software, with the Dutch Eco-indicator’95 values, was chosen, as it is an accepted tool
to carry out such a comparison. LCA were carried out according to the CML
methodology (Heijungs, 1992a,b). Environmental impact categories considered in this
method are: greenhouse effect (global warming), ozone depletion, acidification,
eutrophication, heavy metals, carcinogenics, winter and summer smog, pesticides,
energy use and emission of solids.

6. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
Important aspects of the LCA
The choice of a functional unit is crucial for the outcome of the LCA as all calculations
are related to this specific definition. In this study the goal is to make electricity out of
clean waste wood. Following functional unit has been chosen:
Thermal treatment of an amount of biomass equal to 966 TJ calorific value (LHV)
and joined production of 424,80 TJ electricity in one year (f1).
This functional unit can be translated for example to co-combustion of wood in a high
efficient coal power plant with 44% electrical efficiency as is shown in Table 3.
Table 3. Example of co-combustion of wood in a coal power plant
Value
Biomass input 60 kton
Dry mass fraction 92 %
Calorific value (LHV) 16,1 MJ/ton
Production hours per year 6500
Total calorific value 966 TJ
Net power conversion efficiency 44%
Net power production 424,8 TJe
Because the other techniques don’t have efficiencies as high as 44%, extra electricity
has to be produced. The environmental burden for this extra production is the average
environmental burden of the Dutch power sector divided by the amount of electricity.
The functional unit chosen has several advantages like same amounts of input of
biomass and coal, and a valid comparison of the different techniques. A second
functional unit was used in the LCA study for verification and sensibility check on the
results. This second functional unit was defined as the thermal treatment of biomass to
produce 1 MJ electricity (f2).
Other important aspects of performing a high quality LCA are the gathering of data
from reliable sources followed by a sensibility check of different parameters on the
outcome of the study (Huisman, 1999, Schijndel 1998, Nieuwlaar, 1994 and Mann,
1997).
In this LCA study gasification, combustion and co-combustion were compared to the
alternative treatment, which is co-combustion via a waste incinerator (efficiency 21%).
In this paper the most important results on the comparison between biomass co-
combustion, gasification and the waste incinerator will be shown.
Results and discussion
The techniques of biomass co-combustion, gasification, combustion have been
compared to waste incineration. A selection of the results is presented in this chapter.
The LCA outcome of the comparison between biomass co-combustion and biomass
waste incineration based upon functional units 1 and 2 can be seen in Figure 4. The
environmental impact for waste incineration is much higher compared to co-
combustion for most impact categories and both functional units.

7. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
AVI : waste incineration, CVB: Co-combustion, fe1: functional unit 1, fe2: unit 2, Y-axis : normalised environmental impact.
Figure 4. Co-combustion versus waste incineration of waste wood
In Figure 5 the results for the comparison of co-combustion of waste wood and stand-
alone gasification of two types of waste wood and poplar wood waste are shown.
Again co-combustion shows lower environmental impact on most categories except
eutrophication.
CVB:Co-combustion, VGA1:gasification poplar waste, VGA2 and 2b: gasification of waste wood, fe1/fe2; functional units 1,2.
Figure 5. Co-combustion of waste wood compared to gasification of poplar and waste wood

8. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
The comparison between co-combustion and stand-alone combustion of waste wood is
shown in figure 6. Again the same result is obtained, co-combustion scores better in
most environmental impact categories.
CVB2: co-combustion waste wood, CVB4: co-combustion clean waste wood, VBA4: stand-alone combustion of waste wood.
Figure 6. Co-combustion and stand-alone combustion of clean waste wood
The most important environmental impact categories for all LCA’s have been
greenhouse effect, acidification and heavy metal emissions. The efficiency of the
different techniques has a major influence on the outcome of the LCA study, which is
shown by the environmental ranking:
1. Co-combustion in a coal power plant,
2. Stand-alone gasification with combined cycle,
3. Stand-alone combustion with steam cycle and
4. Biomass co-combustion in waste incineration plant.
The choice of functional unit has a great influence on the outcome of the LCA studies,
however also with the use of an alternative unit the environmental ranking is the same.
Availability of data has been no problem in this study. Most data used was measured
and from reliable sources (Huisman, 1999) but some data was obtained from
simulations (Ree, 1996). Some chemical compounds do not have environmental effects
defined in the LCA software, like dioxins. It is not known how these missing data
effects the outcome of the study. Since most unknown components are emitted in very
low quantities the final effects on the outcome are expected to be negligible. The
influence of transport distance of the biomass was investigated but it did not have a
large influence on the study outcome. Abiotic depletion is an important environmental
impact category in the comparison of fossil fuels with biomass waste. However this
category has not been implemented yet in the LCA method although necessary data on
fossil fuel stocks are available.

9. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
Conclusions and Outlook
The LCA study showed following environmental ranking of biomass to power
techniques: Co-combustion scores better as stand-alone gasification, which scores
better then stand-alone combustion which is finally better as biomass combustion in a
municipal incinerator. Interesting outcome was the fact that the choice of functional
unit was very important but did not change the ranking order of the different systems.
The environmental impact category abiotic depletion has to be operationalised in the
next version of LCA. This study only focussed on power production and not on co-
generation. In future LCA studies on co-generation, exergy analysis will be used to
compare different systems.
References
P. Cuelenaere, Hydro thermal Biomass Conversion, MSc. Thesis, Centre for
Environmental Technology, Eindhoven University of Technology, The Netherlands (in
Dutch), 1999.
A. Faaij, Energy from Biomass and waste, PhD-Thesis, Utrecht University, The
Netherlands, 1996.
R. Heijungs, et. al., Environmental Life Cycle assessment of products, Part I: Manual,
Centrum voor Milieukunde Leiden, Leiden, October 1992.
R. Heijungs, et. al., Environmental Life Cycle assessment of products, Part II:
Backgrounds, Centrum voor Milieukunde Leiden, Leiden, October 1992.
J. Huisman, Environmental Life Cycle Assessment of thermal biomass conversion
techniques, MSc. Thesis, Centre for Environmental Technology, Eindhoven University
of Technology, The Netherlands (in Dutch), 1999.
F.J.J.G. Janssen and R.A. van Santen, Environmental Catalysis, Chapter 2 and 13,
Imperial Press, London, 1999.
M.K. Mann, P.L. Spath, Life cycle assessment of a Biomass Gasification Combined-
Cycle System, National Renewable Energy Laboratory, December, 1997.
E. Nieuwlaar, Using Life Cycle Assessments in the Analysis of Energy Systems,
University of Utrecht, the Netherlands, Vakgroep Natuurwetenschap en Samenleving.
Rapp.nr. 94025, December 1994.
R.v. Ree, A.B.J. Oudhuis, A. Faaij, A.P.W.M. Curvers, Modelling of a Biomass-
Integrated-Gasifier/ Combined-Cycle (BIG/CC) System with the flowsheet simulation
programme ASPENplus, ECN-C-95-041, Petten, June 1996.
P. van Schijndel, J. van Kasteren and F. Janssen, Biomass as a sustainable energy
source, a multi-disciplinary approach, Entrée ’97, Environmental Training in
Engineering Education, November 12-14, 1997, Sophia-Antipolis, France

10. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
P. van Schijndel, J. Huisman and F.J.J.G. Janssen, LCA of power production from
biomass, the comparison of coal-power with different biomass-power production
systems, 6th
LCA Case Studies Symposium, SETAC Europe, Brussels, 2 December
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Netherlands, 1998.

11. Presented at ENTRÉE’99, 10-13 November 1999, Tampere, Finland
Personalia
The author;
Patrick van Schijndel studied chemical engineering at the Eindhoven University of
Technology (TUE) and graduated in 1994. He got his teaching degree in chemistry at
TUE in 1995. Since 1996 he is doing his PhD on cleaner production at CMT, and
combines this with setting up a MSc. course in environmental technology for the
University of Dar Es Salaam in Tanzania.
The co-authors;
Jaco Huisman studied chemical engineering at TUE and graduated in the CMT group
in March 1999 on the subject of Technical, economical and environmental analysis of
thermal biomass conversion techniques. The outcome of his research, which was
carried out under supervision of Prof. Janssen en Patrick van Schijndel, is published in
this paper.
Han van Kasteren studied chemical engineering at TUE and in 1990 he received his
PhD degree. In 1990 he worked at the Inter-University Environmental Institute
Brabant (IMB). From 1991 he works as appointed lecturer at the TUE, in the field of
environmental technology. In 1996 he was appointed director of PRI at the TUE. At
PRI economic and technical feasibility studies of the recycling of wastes are carried
out.
Frans Janssen is head of the department responsible for gasification, combustion of
fossil fuels and chemical processes at KEMA in Arnhem, The Netherlands. At KEMA
he is working in the field of research and development of gas cleanup systems for
gasification of coal, heavy oils and biomass, pyrolysis of waste and biomass, energy
saving technologies and water purification.
At the TUE he is director of the Centre for Environmental Technology of the Faculty
of Chemical Engineering. CMT focuses on environmental education and environmental
research.
Address:
Centre for Environmental technology
Faculty of Chemistry and Chemical Engineering
Eindhoven University for Technology
Room STO 3.25
P.O. Box 513, 5600 MB Eindhoven
The Netherlands
Phone: +31 40 247 31 97
Fax: + 31 40 245 37 62
Email: p.p.a.j.v.schijndel@tue.nl
http://www.chem.tue.nl/cmt