Performance analysis of a 2.45 GHz microwave plasma torch for CO2 decomposition in gas swirl configuration

Abstract

Abstract Microwave plasmas are a promising technology for energy-efficient CO2 valorization via conversion of CO2 into CO and O2 using renewable energies. A 2.45 GHz microwave plasma torch with swirling CO2 gas flow is studied in a large pressure (20–1000 mbar) and flow (1–100 L min−1) range. Two different modes of the plasma torch, depending on the operating pressure and microwave input power, are described: at pressures below 120 mbar the plasma fills most of the plasma torch volume whereas at pressures of about 120 mbar an abrupt contraction of the plasma in the center of the resonator is observed along with an increase of the gas temperature from 3000 K to 6000 K. The CO outflow is generally found to be proportional to the plasma effective power and exhibits no significant dependence on the actual CO2 flow injected into the reactor but only on the input power at certain pressure. Thermal dissociation calculations show that, even at the lowest pressures of this study, the observed conversion and energy efficiency are compatible with a thermal dissociation mechanism.