Solar–gliding arc plasma reactor for carbon dioxide decomposition: Design and characterization

Abstract

The conversion of low-value feedstock such as carbon dioxide (CO2) into higher-value products using renewable energy, particularly solar, can help fulfill the increasing need for fuels and chemicals while mitigating environmental emissions. A direct solar receiver-reactor fitted with a gliding arc (glidarc) electrical discharge for potentially greater efficiency and continuous operation solar thermochemical synthesis is presented. The nonequilibrium plasma inside the reactor chamber leads to increased solar energy absorption by the gas-phase feedstock, potentially enhancing chemical conversion. Moreover, the reliance on electrical energy to sustain the plasma allows compensating for fluctuations in the solar radiation input. Two solar-glidarc reactor configurations are investigated and evaluated for the decomposition of CO2 at atmospheric pressure conditions, namely: axi-radial (AXR) and reverse-vortex (RVX) flow. The former provides greater control of residence time but presents limited solar-plasma interaction; whereas the latter allows for greater interaction, but requires higher flow rates to confine the plasma, lowering the residence time. Flow paths and residence times are evaluated via Computational Fluid Dynamics (CFD) models used to guide reactor design and operation. Evaluation of the plasma volume at different reactor orientations, aimed to mimic in-field operation, show that the AXR configuration leads to a larger plasma volume compared to that by the RVX design. Net-absorption tests, aimed to assess the extent of solar-plasma interaction, showed up to 18% net-absorption of solar radiation for the RVX configuration and 7% for the AXR one, compared to 0% in the absence of plasma. The AXR configuration, despite its lower absorption of solar energy, leads to greater CO2 homogeneous gas-phase decomposition (i.e. in the absence of any catalyst), of up to 4.5%, mainly due to its flexibility in operating with lower residence times. The results indicate solar-plasma direct-receiver reactors provide a compelling approach to solar thermochemical synthesis processes.