Post-plasma carbon bed design for CO2 conversion: Does size and insulation matter?

Abstract

We present the performance of a post-plasma carbon bed for improving plasma-based CO₂ conversion, studying the effect of bed length and additional thermal bed insulation. The experiments were conducted using an atmospheric pressure gliding arc plasmatron in both high and low specific energy input (SEI) regimes. Each bed was equipped with a silo to enable continuous carbon feeding and operation for an order of 1 h, thus overcoming previous limitations in literature. Importantly, we derive an improved energy efficiency (EE) calculation with an accurate and unambiguous consideration of the key reaction contributions of both plasma and carbon bed. This derivation serves to highlight the inconsistencies that arise in determining EE in such a complex chemical system. We therefore advise and advocate for the use of energy cost (EC) as the key reported energy metric in systems using post-plasma carbon beds. The optimum conversion and energy metrics were obtained with the longest bed, reaching a conversion of 41%, an EE of 51% and an EC of 0.41 MJ/mol at high SEI. The design of the insulated bed and silo allow for previously unreported preheating of the carbon, which reduces oscillations observed in the conversion profiles of the short and long beds. Preheating of the external silo for the long bed also yields a near-complete removal of oscillations. Finally, when comparing our performance with results from literature for post-plasma carbon beds, our system clearly improves upon the state-of-the-art, both in absolute values of conversion and energy metrics at the same SEI, as well as by sustaining this improvement for extended periods of time.