Potential for Greenhouse Gas Emission Reductions by Using Biomethane as a Road Transportation Fuel

摘要

The aim of this thesis is to study whether the use of biomethane as a transportation fuelis reasonable from climate change perspective. In order to identify potentials andchallenges for the reduction of greenhouse gas (GHG) emissions, this dissertationfocuses on GHG emission comparisons, on feasibility studies and on the effects ofvarious calculation methodologies. The GHG emissions calculations are carried out byusing life cycle assessment (LCA) methodologies. The aim of these LCA studies is tofigure out the key parameters affecting the GHG emission saving potential ofbiomethane production and use and to give recommendations related to methodologicalchoices. The feasibility studies are also carried out from the life cycle perspective bydividing the biomethane production chain for various operators along the life cycle ofbiomethane in order to recognize economic bottlenecks.Biomethane use in the transportation sector leads to GHG emission reductionscompared to fossil transportation fuels in most cases. In addition, electricity and heatproduction from landfill gas, biogas or biomethane leads to GHG reductions as well.Electricity production for electric vehicles is also a potential route to direct biogas orbiomethane energy to transportation sector. However, various factors along the lifecycle of biomethane affect the GHG reduction potentials. Furthermore, themethodological selections have significant effects on the results. From economicperspective, there are factors related to different operators along the life cycle ofbiomethane, which are not encouraging biomethane use in the transportation sector.To minimize the greenhouse gas emissions from the life cycle of biomethane, wastefeedstock should be preferred. In addition, energy consumption, methane leakages,digestate utilization and the current use of feedstock or biogas are also key factors. Toincrease the use of biomethane in the transportation sector, political steering is neededto improve the feasibility for the operators. From methodological perspective, it isimportant to recognize the aim of the life cycle assessment study. The life cycleassessment studies can be divided into two categories: 1.) To produce average GHGinformation of biomethane to evaluate the acceptability of biomethane use compared tofossil transportation fuels. 2.) To produce GHG information of biomethane related toactual decision-making situations. This helps to figure out the actual GHG emissionchanges in cases when feedstock, biogas or biomethane are already in other use. Forexample directing biogas from electricity production to transportation use does notnecessarily lead to additional GHG emission reductions. The use of biomethane seems to have a lot of potential for the reduction of greenhouse gas emissions as atransportation fuel. However, there are various aspects related to production processes,to the current use of feedstock or biogas and to the feasibility that have to be taken intoaccount.