A Comparative Assessment of Biogas Upgradation Techniques and Its Utilization as an Alternative Fuel in Internal Combustion Engines

Growing concern about the rapid depletion of fossil fuels, current environmental conditions, energy challenges and new environmental regulations has encouraged the researchers worldwide for new environmentally compatible alternatives from natural resources. In this context, biogas produced from anaerobic digestion of organic resources may be considered as a significant bioenergy with the potential to address these concerns. Biogas is a mixture of methane and carbon dioxide as the major constituents with other trace components like water vapor, hydrogen sulfide, ammonia, carbon monoxide and nitrogen. Uses of biogas can be seen in heating, cooking, lighting and power production. However, cleaning of biogas from its impurities, mainly CO2 and H2S, can extend its scope of applications. There are numerous physico-chemical (viz. cryogenic, adsorption, membrane separations and absorption) and biological (in situ and ex situ) technologies for biogas upgradation. These operations are aimed at enriching the methane content of biogas above 90% and thereby enhancing the calorific value up to 35.3 MJ/m3. The purpose behind such upgrading is generally focused to meet the fuel standards to be used in vehicles, for injection in the natural gas grid, and to be used as substrate for the production of chemicals or for fuel cell applications. Enriched biogas is compressed and stocked in gas cylinder and transported to the desired location for utilization. Additionally, use of enriched biogas reduces greenhouse gas emissions. This chapter aims at meticulously evaluating the existing and emerging biogas production and upgradation technologies and confers the outlook for overcoming the challenges associated with them.