Comparative Analysis of Bio-Gas Electrification from Anaerobic Digesters in Nepal

This research paper presents minimum gas pressure and size of biogas digester required to run biogas generator in Nepal through comparative analysis of different biogas digesters and generators. Three underground concrete anaerobic biogas digesters of sizes; 7 m3, 10m3 and 75m3 were analysed with 0.4 kVA and 0.6 kVA biogas generators to test gas pressure required to run these generators. The tests were done in summer season with an average day temperature of 28oC. Meanwhile, the gas released from biogas digester was directly coupled with the generator. From the analysis, it was found that minimum gas pressure required to run 0.4 kVA and 0.6 kVA biogas generators were 7 kPa and 10 kPa respectively. Considering 75 W load, pressure drop of 5 kPa was noted for 1.5 hours average time loading condition. The generator efficiency was 30% which is lower than projected due to impurities in gas. The gas compositon had an average of 54% methane and 18% Carbon and 28% other gases. In order to remove potential impurity, H2S scrubber was used but it resulted in decrease of average 5 kPa output pressure. It was depicted that the power output increased with gas purification and gas storage with controlled release of gas. In the market of Nepal, with minimal of 1 kVA biogas generator availability, an anaerobic digester of minimum 15m3 size is suggested for biogas electrification.