Computational Modeling of Co2 Decomposition by Concentrated Solar Energy – Enhanced Microwave Plasma

Abstract

The conversion of carbon dioxide (CO 2 ) into higher-value products using renewable energy can help fulfill the increasing need for fuels and chemicals and limit CO 2 emissions. Solar-Enhanced Microwave Plasma (SEMP) CO 2 conversion aims to combine the advantages of solar thermochemical methods (direct use of the most abundant form of renewable energy) and plasmachemical approaches (high efficiency, continuous operation). SEMP exploits the greater absorption of solar photons by CO 2 in Non-Local Thermodynamic-Equilibrium (NLTE) state compared to CO 2 in LTE 1 . A computational study of a SEMP reactor operating with an Ar-CO 2 (7:1) mixture at near atmospheric pressure is presented. The SEMP reactor receives 700 W of incident microwave power at 2.45 GHz and 525 W of incident solar radiation power. Three hierarchical models are investigated: (i) plasmachemical conversion neglecting radiative energy transport, (ii) plasmachemical conversion including radiative transport, and (iii) solar-plasmachemical conversion. The 2D models comprise, in completely-coupled approaches, fluid flow, heat transfer, energy conservation for electrons and heavy-species, radiative transport in participating media, and Ar-CO 2 chemical kinetics through the discharge tube; coupled to microwave electromagnetic field dynamics through the waveguide and the discharge tube. The results show that the plasma is localized near the location of incident microwave energy and that CO 2 decomposition is greatest at that location. The incident radiative flux leads to more uniform distributions of heavy-species and moderately greater temperatures throughout most of the discharge tube. Simulation results reveal that conversion efficiency increase from 4.4% to 9.8% with increasing solar input power from 0 to 525 W. An experimental setup was built, and the CO 2 conversion experimentally measured 2 . Good agreement is shown between the modeling and experimental results. The enhanced process performance appears to be consequence of the greater solar radiation absorption by microwave plasma.