Greenhouse gas emissions from peat and biomass-derived fuels, electricity and heat — Estimation of various production chains by using LCA methodology

摘要

More discussion is required on how and which types of biomass should be used toachieve a significant reduction in the carbon load released into the atmosphere in theshort term. The energy sector is one of the largest greenhouse gas (GHG) emitters andthus its role in climate change mitigation is important. Replacing fossil fuels with biomasshas been a simple way to reduce carbon emissions because the carbon bonded tobiomass is considered as carbon neutral. With this in mind, this thesis has the followingobjectives: (1) to study the significance of the different GHG emission sources relatedto energy production from peat and biomass, (2) to explore opportunities to developmore climate friendly biomass energy options and (3) to discuss the importance of biogenicemissions of biomass systems. The discussion on biogenic carbon and other GHGemissions comprises four case studies of which two consider peat utilization, one forestbiomass and one cultivated biomasses. Various different biomass types (peat, pine logsand forest residues, palm oil, rapeseed oil and jatropha oil) are used as examples todemonstrate the importance of biogenic carbon to life cycle GHG emissions. The biogeniccarbon emissions of biomass are defined as the difference in the carbon stock betweenthe utilization and the non-utilization scenarios of biomass. Forestry-drainedpeatlands were studied by using the high emission values of the peatland types in questionto discuss the emission reduction potential of the peatlands. The results are presentedin terms of global warming potential (GWP) values. Based on the results, the climateimpact of the peat production can be reduced by selecting high-emission-level peatlands for peat production. The comparison of the two different types of forest biomass in integratedethanol production in pulp mill shows that the type of forest biomass impacts thebiogenic carbon emissions of biofuel production. The assessment of cultivated biomassesdemonstrates that several selections made in the production chain significantly affectthe GHG emissions of biofuels. The emissions caused by biofuel can exceed the emissionsfrom fossil-based fuels in the short term if biomass is in part consumed in the processitself and does not end up in the final product. Including biogenic carbon and otherland use carbon emissions into the carbon footprint calculations of biofuel reveals theimportance of the time frame and of the efficiency of biomass carbon content utilization.As regards the climate impact of biomass energy use, the net impact on carbon stocks(in organic matter of soils and biomass), compared to the impact of the replaced energysource, is the key issue. Promoting renewable biomass regardless of biogenic GHGemissions can increase GHG emissions in the short term and also possibly in the longterm.