Schlussbericht
(Englisch)
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In order to improve the yield of biogas plants, operators often purchase or cultivate substrates with high energy content. With a life cycle assessment (LCA), the environmental impacts due to the digestions of these substrates can be analysed.
In this report life cycle inventory datasets of biogas production from the following substrates are investigated: maize silage, sugar beets, fodder beets, beet residues, molasses, and glycerine. Furthermore, biogas from a grass refinery is analysed. The life cycle inventory data required for such an LCA are collected according to the ecoinvent v2.0 quality guidelines. The life cycle inventories are based on literature data and a current survey of 16 biogas plant operators, which was conducted within another project of the BFE "Biomass Research Programme".
In addition to the new inventories of the biogas production, life cycle inventories of the provision of electricity and heat from burning biogas from the examined substrates in a biogas engine (cogeneration unit) are set up. Part of this electricity and heat is then used for the operation of the biogas plants. In the survey the biogas plant operators declare that 62 % of the electricity consumption is met with electricity from a cogeneration unit that is operated with biogas. About 38 % of the electricity consumption is covered with electricity from the grid. The heat consumption is completely covered by the cogeneration unit.
Life cycle inventory datasets are also prepared for three technologies of biogas purification with the purpose of supplying biomethane to the natural gas grid. The considered technologies are amino washing, glycol washing, and pressure swing adsorption
The setup of life cycle inventory datasets allows for a detailed assessment and comparison of the environmental impacts of using biogas from different substrates and products of biogas operated cogeneration units.
The total greenhouse gas (GHG) emissions of a transport service with biogas fuel from the new established inventories and an average load of 1.6 passenger amounts to between 95 gCO2-eq./pkm (biogas from grass refinery) and 163 gCO2-eq./pkm (beet residues). Even though these values are lower than the greenhouse gas emissions of using conventional fuels, most biogas types analysed in this study do not comply with the thresholds for a tax reduction (40 % less GHG emissions compared to using conventional fuels). Important for the GHG result are the methane emissions from the biogas production and purification, and the dinitrogen monoxide emissions from the plant cultivation. Those emissions can vary significantly between individual biogas plants and different energy crops.
If considering the total environmental impacts assessed with the ecological scarcity method (2006), driving with biogas from non-waste substrates has higher environmental impacts compared to driving with conventional natural gas.
Electricity produced from biogas generated from energy crops has considerably higher environmental compared to the average electricity from the Swiss grid, whereas electricity produced from biogas generated from waste substrates has lower environmental impacts and can be considered as green electricity.
At present, biogas in Switzerland is mainly produced from sewage sludge, slurry, and biowaste. If the codigestion with higher shares of substrates made from energy crops increases significantly in future, the produced biogas cannot comply with the thresholds for a fuel tax reduction anymore.
Auftragnehmer/Contractant/Contraente/Contractor:
ESU-Services Ltd., fair consulting in sustainability
Autorschaft/Auteurs/Autori/Authors:
Stucki,Matthias
Jungbluth,Niels
Leuenberger,Marianne
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