Hydrogen Production via Synthetic Biogas Reforming in Atmospheric-Pressure Microwave (915 MHz) Plasma at High Gas-Flow Output

Abstract

This paper is a contribution to the development of microwave plasma-based technology for hydrogen (H2) production from a so-called synthetic biogas, considered as a mixture of methane (CH4) and carbon dioxide (CO2). The efficiency of hydrogen production via reforming of CH4 in the synthetic biogas flowing through a waveguide-supplied metal cylinder-based microwave plasma source (MPS) operating at atmospheric pressure was tested experimentally. The MPS operated at a frequency of 915 MHz. The working plasma-forming gas was a mixture of CH4:CO2 of volume ratios from 0 to 1. Its flow rate was varied from 3 to 12 m3/h. The microwave power absorbed by the plasma was up to 7.5 kW. The experiment showed that using this kind of MPS, the plasma processing of the synthetic biogas can be run stably at high flow rates (up to 12 m3/h). The optimal CH4:CO2 ratio in terms of high energy efficiency of the microwave plasma reforming of CH4 was found to be 40:60. The maximum achieved hydrogen production rate was 156 g(H2)/h at a microwave absorbed power of 7.5 kW (at a flow rate of 6 m3/h) with the energy efficiency of hydrogen production of 21 g(H2)/kWh. The maximum energy yield of hydrogen production of 24 g(H2)/kWh was achieved at 4.5 kW of the microwave absorbed power (the hydrogen production rate was 108 g(H2)/h in this condition). The maximum methane conversion degree and maximum hydrogen selectivity were 86.5% and 73.3%, respectively at an absorbed microwave power of 6.5 kW (at 3 m3/h).