Reforming of biogas using a non-thermal, gliding-arc, plasma in reverse vortex flow and fate of hydrogen sulfide contaminants

Abstract

Biogas is being produced everyday around the world due to land filling of organic wastes. Reforming of biogas to hydrogen rich gas offers a green source of energy. This work demonstrates reforming biogas into hydrogen rich gas via a non-thermal gliding arc plasma stabilized in a reverse vortex flow with very low and competitive specific energy requirement. Parametric tests determined the individual effects of power input (140-300 W), steam to carbon ratio (0.0–3.0), and equivalence ratio (0.1–0.7) on reformer performance. Factorial tests identified optimal operating condition based on minimizing the specific energy requirement, determined to be 184 kJ/mol H2 or 1.91 eV/H2 molecule, significantly below the value for conventional steam reforming of methane, 3.37 eV/H2 molecule produced. The optimum operating conditions were found at an equivalence ratio of 0.11, a steam to carbon ratio of 0.14, and an input plasma power of 160 W, resulting in methane conversion of 48.8%, hydrogen yield of 23.4%, hydrogen selectivity of 47.8%, and an efficiency of 25.3%. Hydrogen sulfide as a common contaminant in landfill gas has detrimental effects on downstream facilities. The reactor was also evaluated on synthetic biogas containing hydrogen sulfide at low concentration (21 ppm). About 5.7% of the sulfur input to the system was partitioned to the dry outlet reformate stream with the remainder captured as sulfate in a downstream impinger or recovered as a solid of unknown molecular structure deposited on tubing surfaces between the reformer and the impinger. This reforming technology offers potential to be deployed as a lightweight compact portable system for on-site applications such as landfills, and depending on available fuels, in mobile applications such as ships.