Life cycle assessment of compressed biomethane gas as second generation biofuel in Thailand

Abstract

This study aims to conduct life cycle assessment (LCA) of compressed biomethane gas (CBG) in terms of both energy and environmental aspects. The system boundary was set to cover all processes throughout the entire life cycle of CBG including provision of feedstocks (pig manure and Napier grass), biogas production, upgrading, compression, transportation, and operation in a vehicle (combustion). This is called a well- to- wheel (WTW) analysis. Required data for the analysis were extracted from literature and were also collected at an actual CBG plant in Thailand (Mae Taeng, Chiangmai). The data were analyzed by using commercia LCA software, Sima Pro 7.1, based on functional units of 1 MJ of CBG. The resulting CBG from the processes was evaluated in terms of global warming potential (GWP) and net energy ratio (NER). The results were also compared with those of conventional fuels (CNG and gasohol 95). The energy analysis results showed that the NER of CBG was higher than one, implying a net energy gain for this CBG system. For the environmental aspect, the results indicated that the biogas production process had the highest GWP impact resulting from high methane loss and the energy consumption. Compared with conventional fuels, the GWP of CBG was higher than these of fossil-based CNG and gasohol 95 for the well-to-tank (WTT) phase. On the contrary, the comparative result of GWP in tank-to-wheel (TTW) phase was reversed. When combining WTT and TTW, the GWP of CBG in WTW phase was shown to be better than these of the conventional fuels.