Sustainable Energy from Biogas Reforming in a Microwave Discharge Reactor

Abstract

© 2015 The Authors. Published by Elsevier Ltd. Biogas is one of the most important renewable energy sources in modern societies. Generated from livestock manure and industrial wastewater, it can provide considerable savings in energy costs and reducing environmental impacts. Thailand is reported to have the potential to produce over one billion m3 of biogas a year. The biogas is generally utilized for heating, mechanical shaft works, and electricity generation. If pipeline networks or purification and compression facilities are not available, use of biogas is normally limited to only within and around farm areas. Alternatively, biogas may be converted via reforming reactions into synthetic gas. Because of presence of sulphur compounds in biogas, a catalytic reformer may face serious poisoning problem. In this work, non-catalytic, plasma assisted reforming of biogas was carried out at atmospheric pressure and room temperature in an 800 W, laboratory microwave discharge reactor. Effects of CH4/CO2 ratio (1, 2.33, 9), feed flow rate (8.33 - 50 cm3/s), and oxygen addition in terms of CH4/O2 ratio (1, 1.5, 2) on reactor performance (yield, selectivity, conversion, H2/CO and energy consumption) was investigated. It was found that biogas was successfully reformed into synthetic gas by a microwave plasma reactor under room temperature and non-catalytic conditions. For dry reforming of biogas, high H2 and CO yields were obtained at low energy consumption. Presence of oxygen enabled partial oxidation reforming that produced higher CH4 conversion, compared to purely dry reforming process. By varying CH4/CO2 as well as CH4/O2 ratios, synthetic gas with a wide range of H2/CO ratios can be generated. From the findings, it was suggested that the microwave plasma reactor may be practically used to reform biogas to produce more valuable intermediates or products such as synthetic gas.