5. Conclusions
The CBG, methanol and DME-scenarios resulted in the highest specific fuel yields (5.2, 5.0 and 5.0 MJ primary energy/Nm3 biogas, respec- tively) among the scenarios studied, while FTD resulted in the lowest specific fuel yield (2.3 MJ PE/Nm3 biogas). However, when increasing the fuel distribution distance from 100 km to 1000 km, the DME, meth anol and LBG scenarios showed the best specific fuel yield performance. The methanol, FTD and DME-scenarios resulted in a total GWP (includ- ing fuel conversion from upgrading to combustion in bus engines) of
219, 244 and 253 g CO2-eq./Nm3 biogas, respectively, which was approximately half of the GWP from the LBG and CBG-scenarios. However,the choice of electricity mix (Base NORDEL, hard coal NORDEL and Swedish electricity mix) had a large impact on the total GWP perfor- mance. Overall, taking the energy efficiency and GWP into account, DME showed the best performance of the fuel conversion scenarios studied.
Acknowledgment
The authors would like to thank the Swedish Farmers' Foundation for Agricultural Research (SLF) for funding the study. Elham Ahmadi Moghaddam would like to thank Amir Sattari for comments that greatly improved the manuscript.