Enhancement of CO2 conversion by counterflow gas quenching of the post-discharge region in microwave plasma sustained by gyrotron radiation

A threefold increase in the CO2 conversion and energy efficiency due to the cooling of the post-discharge region by the counter gas flow has been achieved in the plasma of an atmospheric pressure discharge supported by microwave radiation of a gyrotron with a frequency of 24 GHz in a carbon dioxide gas flow. The role of convective heat transfer in the process of gas mixture cooling in the post-discharge region has been experimentally demonstrated. At nitrogen quench gas flow of 4.5 l/min, the CO2 conversion was 23.8 % and energy efficiency was 19.7 %. The possibility of using the flow of cooled gas mixture (CO2,CO,O2) taken from the reactor as quenching gas has been experimentally demonstrated, which made it possible to achieve a CO2 conversion degree of 23.4 % and to eliminate the problem of dilution of reaction products by third-party gases. Based on numerical modeling, it is shown that the increase in the conversion degree upon the destruction of the plasma torch structure is due to the increase in heat exchange with the surrounding gas, and the efficiency of this destruction is determined by the velocity and density of quenching gas.