Environmental burdens over the entire life cycle of a biomass CHP plant

ENVIRONMENTAL BURDENS OVER THE ENTIRE LIFE

CYCLE OF A BIOMASS CHP PLANT

G. JUNGMEIER*, G. RESCH$ and J. SPITZER*

*Joanneum Research, Elisabethstrasse 5, A-8010 Graz, Austria$Stattegerstrasse 83B, A-8045 Graz, Austria

AbstractÐTo increase the use of biomass for energy production it is important to know the possibleand signi®cant environmental e�ects. A life cycle inventory (LCI) was made on a 1.3 MWel biomassCHP plant located in Reuthe/Vorarlberg/Austria with the purpose of analysing the di�erent environ-mental burdens over the entire life cycle. The plant is ®red with coarse and small fuelwood (10,000 t/yr)from industrial waste and forest residues. The boiler for the steam process has a moving grate burnerand a mu�e burner. The annual production is 4700 MWh of electricity and 29,000 MWh of districtheat. The methodology of the analysis is orientated on the ISO Comittee Draft of the Series 13,600.The analysis was carried out for the di�erent sections of the biomass plant over their entire life cycle±construction (1 yr), operation (20 yrs) and dismantling (1 yr).

The plant in Reuthe, which is the ®rst cogeneration system of this kind in Austria, is a model forother similar projects. The results are shown as environmental burdens of one year and of the entirelife cycle. Some results of the life cycle inventory, like the mass and energy balances, selected emissionsto air, allocation results and e�ects on carbon storage pools are given. The results demonstrate thatdepending on the stage and the period of life, di�erent environmental burdens become signi®cant, i.e.CO2 emissions of fossil fuels during construction, NOx emission during operation, emissions to soilduring dismantling. The di�erent options for allocating the environmental burdens to electricity andheat show a wide range of possible results, depending on the choice of allocation parameters (energy,exergy, credits for heat or electricity, price) i.e. for the particles emissions: 161 mg/kWhel to minus566 mg/kWhel, 0 mg/kWhth to 118 mg/kWhth. With the results of the analysis it is thus possible forfuture similar projects to know when and where signi®cant environmental burdens might be furtherreduced, and what kind of reseach and developement work should be done for further improvements.

The work for this paper has been part of the Austrian case study of the European Commission'sExternE project on external costs of power production. # 1998 Elsevier Science Ltd. All rights reserved

KeywordsÐLife cycle inventory; biomass; bioenergy; methodology; greenhouse gases; ISO; carbon bal-ance; allocation options.

1. INTRODUCTION

The aim of the ExternE Project, carried outwithin the European Commission R&DProgrammes Joule II and Joule III, was todevelop and demonstrate a uni®ed method-ology for the quanti®cation of the externalitiesof di�erent power generation technologies.1,2

One of the major tasks of ExternE is theNational Implementation Project of which theobjective is to establish a comprehensive andcomparable set of data on externalities ofpower generation. The tasks include the appli-cation of the ExternE methodology to themost important fuel cycles for each country,the dissemination of results in the di�erentcountries and the creation of a network ofscienti®c institutes familiar with the ExternEmethodology, data, and their application. TheNational Implementation Project has gener-

ated a large set of comparable and validated

results, covering more than 60 cases for 15

countries and 11 fuel cycles. This paper

describes the results gained from the ExternE

National Implementation Project for Austria.3

The impact-pathway model used within the

ExternE methodology to calculate burdens

consists of four steps:

. the calculation of emissions;

. the assessment of dispersions;

. the estimation of impacts and

. the economic valuation for the costs of

these impacts.

This paper covers the ®rst step of the impact

pathway model, the calculation of emissions

by using the ISO draft 13 600 to evaluate the

environmental burdens over the entire life

cycle of a biomass CHP plant.3,5±8,11

Biomass and Bioenergy Vol. 15, Nos 4/5, pp. 311±323, 1998# 1998 Elsevier Science Ltd. All rights reserved

Printed in Great Britain0961-9534/98 $ - see front matterPII: S0961-9534(98)00039-7

311

2. CHARACTERISTICS OF THE CHP PLANTREUTHE

In this chapter the technical characteristicsof the 1.3 MWel CHP plant in Reuthe aredescribed.

2.1. Introduction

The biomass CHP plant in Reuthe was builtin 1995 and put into operation in 1996. It isdesigned to:4

. utilize the fuel with an optimal e�ciency;

. reach a signi®cant reduction of emissions incomparison with the previous system;

. ensure operation at reasonable costs;

. enable the combustion of waste wood withlittle need for processing and

. to cover the heat demand of the local dis-trict heating net and the process heatdemand of the local industry.

Table 1 represents the technical characteristicsof the CHP plant Reuthe.

In accordance with the general guidelinesgiven by ISO CD 13,600,5±8 the di�erentstages of the biomass fuel cycle on which theinventory focuses, are:

. fuel transformation in the power plant;

. fuel storage;

. fuel processing;

. wood transport and

. wood cultivation and harvesting.

In the next chapters there is a description ofthese stages. The total life cycleÐconstruction,operation and dismantlingÐof each stage willbe analysed.

Figure 1 shows the scheme of the relevantstages of the biomass fuel cycle. Figure 2depicts the same scheme of the analysed bio-mass fuel cycle in accordance with the ISOCD 13,600 for the life cycle inventory5±8 withits main input materials and products.

2.2. Fuel transformation

The Fuel Transformation in the power plantincludes the steam generation and cogenera-tion of electrictity and heat. The steam is pro-duced in a boiler consisting of twoautonomous burners, a moving grate burnerand a mu�e burner.

Small fuelwood is burned in the mu�e bur-ner. The power range of the mu�e burner is2±10 MW. The fuel air mixture is blown intangentially. The fuel stays in the combustionchamber 1.5 sec on average. Even for smallfuelwood the share of non-burned fuel in theash can be kept extremely low. Furthermore acombustion with relatively low excess air(n = 1.4) becomes possible which in turnreduces NOx emissions. This e�ect is re-inforced by a certain amount of recirculated¯ue gas, which reduces the combustionchamber temperature to about 10008C.Washing water containing glue as a wasteproduct of the cleaning of the production

Table 1. Technical characteristics of the CHP Plant Reuthe3,4

Annual production (normal year) District heat Approx. 29 GWhGrid electricity Approx. 4.7 GWh

Boiler Steam mass ¯ow 10 t/hSteam temperature 4458CSteam pressure 32 bar

Burner Fuel input Max. 10 MWRange of power at mu�e 2 to 10 MWRange of power at grate 2 to 4 MW

Fuel Composition No bark, but partially water with glueSmall fuelwood 5% wood powder, 30% sawdust

Coarse fuelwood 65% shavingswood chips

Moisture content 8 to 12% atroLower heating value 4.5 to 4.8 kWh/kgInput of small fuel-wood 2200 kg/hInput of coarse fuel-wood 1100 kg/hFuel for pilot ¯ame Fuel oil

Turbine Type Counterpressure turbineElectric power 1.265 MW

Heat exchanger Type CondenserHeat power 6.3 MW

Flue gas Particle separator Multicyclon with electrostatic ®lterFlue gas volume ¯ow 17,000 Nm3/h (13% O2)Flue gas temperature 1708C

G. JUNGMEIER et al.312

machines is injected into the combustionchamber. The tiny glue particles cause a slightdenox e�ect of the ¯ue gas. For cold start a pilot¯ame burning fuel oil ignites the mu�e burner.Coarse fuelwood is burned on a mechanicallyadjustable zone-feed grate. The power range onthe grate burner is 2±4 MW. The fuel supply ismanaged by a screw conveyor. The primary air(n = 1.7) is fed from below and the secondaryair from above the grate. Part of the ¯ue gas isrecirculated to the grate burner. Both burnerscan be operated together for the maximum fuelpower of 10 MW, but also separately. In case ofrunning in combination the grate burner justdelivers a base load while the power is controlledby the mu�e burner which is adjustable forgreater speed.

Both sets of ®ring equipment are surroundedby the same steam boiler. After passing a doublestage superheater above the cooling screen the¯ue gas enters the steam boiler. The economizeris placed in the ¯ue gas after the steam boiler.The particle separator consists of a precipitatorand an electrostatic ®lter. It reduces the particleconcentration from 2500 mg/Nm3 to 10±25 mg/Nm3.

Two feed pumps transport the water to thesteam boiler. The steam boiler consists of aneconomizer, a preheater, a steamdrum (10 t/h,32 bar, saturated steam) and a superheater(30 bar, 4458C). In a counterpressure turbine thesuperheated steam is expanded to 1.3 bar. Atnominal rate it has a steam mass ¯ow of 10 t/h.At the entry to the turbine the steam pressure is28 bar at a temperature of 4408C. The exhauststeam pressure is 1.3 bar at a temperature of1838C. The turbine runs at a speed of 8250 rpm,the generator at a speed of 1500 rpm, delivering1.265 kW. The remaining heat is transmitted tothe heating network through a district heatexchanger.

2.3. Fuel storage

There are three di�erent storage systems.Fuel storage I for the coarse fuelwood has acapacity of 250 m3. A conveyor belt feeds thecoarse fuelwood to the grate. Fuel storage IIfor the small fuelwood has a total capacity of5100 m3 clustering three individual storage fa-cilities, each having a volume of 1700 m3.Small fuelwood is drawn up by suctiondirectly from the woodworking machine.

Fig. 1. Scheme of the stages of the biomass fuel cycle at the CHP Plant Reuthe.11

Life cycle of a biomass CHP plant 313

Transport air feeds the small fuelwood to themu�e burner. Fuel storage III for the fuel oilhas a capacity of 5 m3.

2.4. Fuel processing

There are two di�erent types of fuel proces-sing. In fuel processing I about 30% of theindustrial waste is chipped to coarse fuelwood.All the industrial waste is obtained from alocal lumber production plant, where about100,000 tonnes of lumber are processed eachyear, most of it spruce. There is no bark inthe industrial waste, because only debarkedsawn wood is used. In fuel processing II chip-ping from biomass to fuelwood and drying ofthe coarse fuelwood (from 35 to 10% moisturecontent) take place.

2.5. Wood transport

Fuelwood is transported by a truck over adistance of 50 kilometres to the CHP plant.The maximum load capacity of the truck is 5

tonnes. The truck carries fuelwood to theCHP plant twice a day.

2.6. Wood cultivation and harvesting

Wood grows in the vicinity of the CHPplant (Bregenzerwald region) over an averagedistance of 50 kilometers. Wood cultivationand harvesting includes wood cutting and col-lecting. On average, 30% of the annual fuelneed of the CHP plant Reuthe is supplied bywood chips from forestry residues. This fuel-wood is made up of twigs and branches leftover from cutting spruce trees, both forestthinning or ®nal clear cutting. The fuelwood iscollected in the felling zone after the logs havebeen trimmed and removed.

3. METHODOLOGY

In this section the methodology is describedwhich is mainly based on the ISO Comittee

Fig. 2. Stages of the biomass fuel cycle according to the ISO CD 13,600Ðmain input materials andproducts only3,11 (signs and symbols see Fig. 3).

Fig. 3. Elementary I/O model box.


Draft of the Series 13,600,5±8 but for somedetails other sources are used.15,16

3.1. Model structure

Since the life cycle inventory is an attemptto work out the environmental burdens of thefuel cycle it is essential to determine the sys-tem boundaries. At least, all important extrac-tions from nature as well as emissions into theenvironment have to be considered in theModel Structure.

ISO CD 13,600 describes the technosphereconsisting of an energyware demand sectorand an energyware supply sector. Both sectorsare divided into several subsectors,7 which areconnected via transport subsectors. Becausethe life cycle inventory covers the entire lifecycle of the plant, the construction, operationand dismantling are under separate consider-ation. Construction and dismantling of the

CHP plant is mainly part of the energywaredemand sector, whereas the operation of theCHP is mainly part of the energyware supplysector, as shown in Fig. 5. The di�erent sub-sectors analysed are shown in Fig. 1 and Fig. 4respectively.

In the Model Structure of the life cycleinventory each subsector and each stage of theCHP plant are described by a model box.7 Toenable a uniform approach a formal input±output model box is used in the ModelStructure. Each stage of the biomass fuel cycleas well as the considered subsectors arebalanced in an Elementary I/O model box(Fig. 3).5 This Elementary I/O model box hasstandardized horizontal and vertical inputsand outputs.5 The in- and outputs of theElementary I/O model box are grouped eachunder the same headings as shown in Fig. 3.The horizontal in- and outputs are mainly

Fig. 4. Model structure of the life cycle inventory3,11 (signs and symbols see Fig. 3).

Fig. 5. Time dependence in model structure3,11 (signs and symbols see Fig. 3).


used for balancing the operation of the bio-mass fuel cycle (Fig. 1). The vertical inputs areused mainly for the construction of the bio-mass fuel cycle and the vertical outputs areused mainly for the dismantling of the biomassfuel cycle (Fig. 4). Figure 3 presents the funda-mental form of the Elementary I/O modelbox.

In the Model Structure di�erent elementsare used for the graphical representation ofthe ¯owcharts and model boxes:5±8,15

1. Boxes: the system boundary is a box withtriple line. A modular sub-system is a box

con®ned by double lines and the non-mod-ular sub-system is a box with a bold line.

2. Flows: the main input materials and ser-vices, products, inputs for manufacturingand construction, outputs from terminationand dismantling are represented by double-line arrows. The ancillary materials and ser-vices as well as by-products are representedby dotted double-line arrows. The otherinputs and releases are represented bysimple-line arrows.

Fig. 4 shows the model structure of the lifecycle inventory of the biomass fuel cycle, ofwhich only the main ¯ows (main input ma-terials and products) are described; any othermain ¯ow originates from other subsectors.

3.2. Time and geographic scale

The model boxes in the model structurehave di�erent time and geographic scales.3,11

The time scale of the entire life cycle isassumed to be 22 years (Construction: year0±1; Operation: year 1±21; Dismantling: year21±22), as shown in Fig. 5. This means thatthe operational lifetime of all stages and theirdi�erent parts of the biomass fuel cycle isassumed to be 20 years.

The di�erent model boxes of the fuel cycleare located in di�erent geographic positions.In particular ®ve di�erent geographic positionsare de®ned: Reuthe, Vorarlberg (a province ofAustria), Austria, Europe and Asia. The en-vironmental burdens are analysed for each lo-cation separately and in sum.

4. RESULTS

Some examples of the results of the lifecycle inventory are shown, the mass andenergy balances of operation, selected emis-sions to air, allocation results and e�ects oncarbon storage pools.3,11

4.1. Mass and energy balance of operation

In the energy balance of the operation ofthe CHP plant the total energy input is 48,200MWh/yr. The main input materials, biomassand industrial waste, cover 48,000 MWh/yr,ancillary materials and services 200 MWh/yr.Other inputs make no contribution. At theenergy output side 33,700 MWh/yr are gridelectricity and district heat, while 14,500MWh/yr are releases (Fig. 6).11

Fig. 6. Energy balance of the operation of the CHPplant.11


In the mass balance of the operation of theCHP plant the total mass input is about882,000 t/yr of which main input materials are13,000 t/yr, ancillary materials 460 t/yr andother inputs 868,000 t/yr. 781,000 t/yr are airfor drying the biomass at the fuel processingstage and 86,000 t/yr are air for the combus-tion at the fuel transformation stage. Themass output as releases is 882,000 t/yr(Fig. 7).11

4.2. Environmental burdens

The environmental burdens of the CHPplant analysed are emissions to air, emissionsto water and emissions to soil. Beside that,noise, risk of accident, risk of ®re, use ofroads as well as equipment and servicesneeded are analysed. The analysis of the en-vironmental burdens is made separately on allstages and the major subsectors of the CHPplant's life cycle. The environmental burdensof the entire life cycle are presented for oneyear and the entire life cycle. As an example,

Table 2 shows the environmental burdens ofthe fuel transformation in the power plant andof the total life cycle referring to 1 TJ of fuelinput (161.6 TJ/a) and the total life cycle. Oneof the major contributions of the environmen-tal burdens of the biomass fuel cycle that areanalysed in detail results from emissions to airduring operation of the fuel transformationand from emissions to soil during dismantling.

4.3. Emissions of greenhouse gases

Figure 8 shows the results of the life cycleinventory for the emission of greenhouse gasesover the entire life cycle of the CHP plant.For the calculation of the CO2-equivalents ofCH4 and N2O, CO2-equivalent factors for 100years of IPPC are used.12 The CO2 emissionsfrom power generation during operation comefrom fuel oil that is needed to ignite the mu�eburner.

Concerning carbon dioxide emisions fromfossil fuels, Fig. 8 points out that the construc-tion of the biomass fuel cycle is the main con-

Fig. 7. Mass balance of the operation of the CHP plant.11


tributor. Particularly in the year of construc-tion, CO2 emissions account for about 70% ofthe total, the twenty years of operation andthe year of dismantling together for 30%.Concerning methane emissions the construc-tion stage contributes about 78% to the total,while operation and dismantling togetheraccount for 22% only.

In other words, the contribution of green-house gases to the emission of the constructionstage is signi®cant. It is presented in moredetail in Fig. 9, in order to see where the CO2

emissions come from. The construction of the

CHP plant consists of the manufacturing and

the construction subsectors. In Fig. 9 the CO2

emissions from the production of materials

and machines in the manufacturing and of the

construction subsector are listed. The CO2

emissions of the manufacturing subsector are

about 6500 t, those of the construction subsec-

tor at the building site about 400 t. The main

contributor is the production of steel (up to

66%) and concrete (up to 24%), which

Fig. 8. GHG emissions over entire life cycle of the CHP plant.

Table 2. Environmental burdens of the fuel transformation in the power plant and the total life cycle3,11

Fuel transformation in power plant Total life cycle

Environmental burden TJfuel input Life cycle(a) TJfuel input Life cycle(b)

Emissions to air (t/TJfuel input, t/life cycle)SO2 9.9 32 12 44NOx 99 320 110 380particles 6.1 20 11 40CO 25 40 34 120CxHy 15 47 23 81CO2 13 42 3100 11,000CH4 4.8 15 9.2 32NMVOC 11 35 13 46N2O 0.87 2.8 1.1 3.9

Emissions to soil (t/TJfuel input, t/life cycle)Ash-sludge 1400 4600 ± ±Ash 900 2900 ± ±Solids 43 140 ± ±Total 2400 7600 5600(c) 20,000(c)

Emissions to water (t/TJfuel input, t/life cycle)Contamin. water 2200 7000 ± ±Liquids 1.4 4.5 ± ±Total 2200 7000 r2200(d) r8000(d)

Noise (dB) 65 ± ± ±Risk of accident (man-h/TJfuel input, man-h/life cycle)

74 240,000 r110(d) r390,000(d)

Risk of ®re (h/TJfuel input, h/life cycle) 54 175,000 54 190,000Use of roads (km/TJfuel input, km/life cycle) 0 0 r31(d) r110,000(d)

Equipment/ services need (man-h/TJfuel input,man-h/life cycle)

37 120,000 54 190,000

(a) Lifetime of operation of Fuel Transformation: 20 years.(b) Lifetime of total life cycle: 22 years.(c) 13,000 t/yr from dismantling of the CHP plant.(d) Partly quanti®ed


together account for nearly 90% of the totalCO2 emissions from construction.

Summing up, the signi®cant GHG emissionsin the life cycle inventory come from the pro-duction of steel and concrete during the con-struction of the CHP plant.

4.4. NOx, CO, SO2 and particles emissions

Figure 10 shows the results of the life cycleinventory for the emission of SO2, particlesand NOx, respectively over the entire life cycleof the CHP plant. Their development is quitedi�erent to carbon dioxide. The emissions ofthese gases from the operation of the plant(up to 80%) seem to be more signi®cant thanthose from construction and dismantling, es-pecially with regard to NOx emissions. TheSO2 emissions from the operation are quitelow, as compared to other biomass sources,because there is hardly any bark in the fuel-wood.

Figure 11 presents some details of NOx (16t/yr) and CO (4.0 t/yr) emissions concerningthe operation of the biomass fuel cycle. NOx

emissions are mainly caused by the fuel trans-formation in the power plant (up to 85%) andthe fuel transport (up to 10%). CO emissionsare caused mainly by the fuel transformation(up to 59%), the fuel transport (up to 21%)and the steel subsector (up to 12%). Quiteremarkable is that the production of replace-ment parts makes such a signi®cant contri-bution.

In sum, the signi®cant emissions of NOx

and CO in the life cycle inventory come fromthe fuel transformation and transportationand the production of replacement parts in the

steel subsector during the operation of theCHP plant.

4.5. E�ects on carbon storage pools

The wood chips used in the cogenerationplant (5400 t/yr of biomass with a water con-tent of 50%, corresponding to 1350 tons ofcarbon) are removed from the surroundingforests (Bregenzerwald) as logging residues(branches and tops) that would otherwise beleft in the forest, and as wood from pre-com-mercial forest thinning. In the order to ®ndout, whether and to which extent suchremovals alter the amount of carbon stored inthe forests, two scenarios have been analysed:

. Scenario 1: Reference case with forest oper-ation as usual;

. Scenario 2: Increased harvest to operate theCHP plant. The di�erence between the twoscenarios represents the e�ect of the CHPplant. The model GORCAM (Graz/OakRidge Carbon Accounting Model)13,14 isused to analyze the carbon balance of the

Fig. 9. CO2 emissions from the construction of the CHP plant.

Fig. 10. NOx, CO, SO2 and particles emissions over theentire life cycle.


forests.3 Although there are many input par-

ameters for this system which are poorly

known (e.g. the initial amount of carbon

stored in the various pools) and hence the

results of the two scenarios in absolute

®gures should be used and interpreted with

caution, it is believed that the model can

capture the di�erence between the two scen-

arios, because they rely on the same input

parameters. The only exception is a change

in the amount of residues from thinning and

clear cutting that is removed from the for-

est.

The model output indicates that the mean sto-

rage of carbon in forest soil and litter over

150 years is lower in Scenario 2 than in

Scenario 1 (by 17 t C/ha). This di�erence

would also be 17 t C/ha if averaged for the

®rst 100 years and 16 t C/ha for the ®rst 50

years. It is important to note that, in order to

provide a continuous supply of biomass for

the CHP plant, a one-hectare system of forest

is not su�cient,3 i.e. a parcel with age 51

would experience no change for almost 30

years until the ®nal clear cut at age = 80. For

simplicity, however, it is assumed, that the car-

bon-release function is linear for the whole

forest system, with a total of 16 t C/ha

released after 80 years (0.2 t C/ha and year)

and no further loss occurring after t = 80.

The amount of carbon that is additionally

removed in Scenario 2 is 16 t C/ha from thin-

ning and 30 t C/ha from ®nal clear cut over

one rotation, i.e. the average yield of biomass

for energy is (16 + 30)/80 = 0.58 t C/ha and

year or 1.15 dry t of biomass per hectare and

year. In order to provide a total of 1350 t ofcarbon annually, an area of 2350 ha is needed.

Figure 12 shows the cumulative amount ofcarbon removed from these 2350 ha and thenet release of carbon from the soil and litterpools on the same area. Until time = 80 thenet carbon release corresponds to 34% of car-bon in the harvested biomass for bioenergy.

The share of net carbon releases of 34% after80 years (compared to removals) could be inter-preted as follows: given that the CHP plant sub-stitutes for a coal power plant with equale�ciency and assuming equal CO2 emissionsfactors for coal and wood (100 t CO2/TJ), thereduction of CO2 emissions will be 66 % duringa period of 80 years.

Finally, it is important to note that therecould be circumstances where the carbon sto-rage in the forest is increased due to additionalbiomass removals. For example, additionalthinning can lead to increased forest growth,and if this increase is large enough to compen-sate for the biomass removed due to this extrathinning, the mean carbon storage in the livingbiomass might be enhanced. This is especiallytrue for thinning of very young dense stands.

International agreements for CO2 emission-reduction targets will not necessarily includeland-use related carbon emissions or sinks,because these are rather short-term e�ects(compared to the long-term problem of cli-mate change), and more di�cult to monitorthan carbon emissions from fossil fuel burn-ing.

4.6. Allocation of environmental burdens

Combined heat and power production o�ersa rise in fuel e�ciency, leading to a decrease

Fig. 11. NOx and CO emissions during operation of CHP plant.


of environmental burdens emitted per unit ofuseful energy. There are some options for theattribution of environmental burdens to eitherheat or electricity. To compare di�erent allo-cations between electricity and heat the follow-ing options are analysed.9

. Allocation based on operational character-istics (grid electricity only, district heat only,credits for grid electricity, credits for districtheat).

. Allocation based on thermodynamic par-ameters (energy content, exergy content).

. Allocation based on the ®nal products'prices.

A CHP plant is operated to primarily satisfy aprede®ned demand of electricity or heat, sothat the additional production of electricity orheat might be considered as a side-e�ect i.e.assuming that the operation of the CHP plantis oriented towards electricity production, dis-trict heat is considered as a side-e�ect. To cal-culate the environmental burdens per unit ofelectricity generated, on the one hand onlyelectricity is considered and on the other handcredits for the production of district heat istaken into account. The credits are determinedby the environmental burdens avoided by theCHP plant due to replacing other technol-ogies.

The other allocation options use the annualenergy content (electricity 14%, heat 86%)and annual exergy content (electricity 44%,heat 56%) as well as the product price basedon the annual income (electricity 24%, heat76%) from electricity and heat as a weightingfactor for the calculation of the environmental

burdens between electricity and heat. Theexergy content of electricity is 1 and of heat0.2.

For information and illustration, the com-parison of di�erent allocation options for elec-tricity and heat from the CHP plant in thecase of particles emission during operation isshown in Fig. 13, indicating the wide range ofpossible results. Corresponding to the situ-ation before the operation of the CHPplant,4,10 the credits for district heat are calcu-lated from a heavy oil-®red heating plant(thermal e�ciency = 80%; particles = 90 mg/Nm3),4 and for grid electricity a heavy oil-®redpower plant (electric e�ciency = 35%; parti-cles = 30 mg/Nm3).10 Depending on the allo-cation the particles emissions per unit ofelectricity di�er from 161 mg/kWhel to minus566 mg/kWhel and per unit of heat from 0 mg/kWhth to 118 mg/kWhth. The credit for heatshows that there is a signi®cant reduction ofparticles emissions by replacing the heavy-oil®red plant in giving the produced electricity anegative emission which indicates a reductionof particles emissions.

5. CONCLUSIONS

The aim of this life cycle inventory studywas to analyse the details of the environmentalburdens of a biomass CHP plant, based onthe mass and energy balances over the entirelife cycle. Its results were used as the startingpoint for the calculation of external costs ofthe plant.

Concerning environmental burdens there arethree major conclusions:

Fig. 12. E�ects on carbon storage pools.3


1. The results show that environmental bur-dens signi®cantly depend on stage of thebiomass fuel cycle and on period of life, i.e.whether construction, operation and dis-mantling of the plant is considered. All inall contributions of operation are the mainsource of the life cycle emissions to air es-pecially for NOx and CO originating fromthe Fuel Transformation in the powerplant. The main CO2 emissions originatefrom the construction of the plant causedby the production of steel and concrete.Dismantling has the least contribution toemissions to air but the biggest contri-bution to emissions to soil.

2. The di�erent allocation options for the en-vironmental burdens per unit of electricityand heat show a wide range of possibleresults which makes comparisons to otherfuel cycles more complex and di�cult. Butthe results of allocation show that theremight be a signi®cant reduction of emis-sions to air by replacing old fossil fuelledenergy systems with biomass systems.

3. In total, the results seem to be site-speci®c,but could nevertheless be relevant to anumber of similar future biomass projectsin Austria.

Even though the ISO CD 13,600 Standardsare not fully developed, they support a sys-tematic approach towards life cycle studiesand o�er an interesting methodology concern-ing life cycle inventories.

AcknowledgementsÐThe work for this paper was mainlycarried out within the ExternE National ImplementationProject as one of the Austrian case studies and within theInternational Energy Agency's RD&D Program onBioenergy (IEA Bioenergy Task XV ``Greenhouse GasBalances of Bioenergy System''). Therefore the work wasfunded by the European Commission, Austrian Federal(Ministries of Economics, Science and Environment) andState research funds, the Austrian Power Association(VEOE) and the Austrian oil and gas company (OMV).

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Environmental burdens over the entire life cycle of a biomass CHP plant

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