High-Power Closed-Loop Pilot System for Nitric Acid Production Using Inductively Coupled Microwave Plasma

This work presents the characterization of a large-scale pilot plant for nitric acid production that employs atmospheric-pressure plasma in a closed-loop configuration. The primary objective here is to evaluate the scientific and practical feasibility of using high-power Cerawave™ plasma torch technology, manufactured by Radom Corporation, to enhance the rate of nitric acid production of plasma-assisted nitrogen fixation systems, while achieving specific energy consumption (SEC) comparable to that of smaller-scale setups reported in the literature. We provide a comprehensive overview of the components of the pilot plant, its operational strategy, and the analytical models underlying its processes. Preliminary system optimization results are discussed alongside the outcomes from a controlled batch run. After 30.9 h of operation at 50 kW plasma power, the system produced 198.9 L of nitric acid with a concentration of 28.6% by weight, corresponding to overall SEC of approximately 5.3 MJ/mol. This SEC could be improved to 3.7 MJ/mol using absorption columns with greater than 90% absorption efficiency. Additionally, around 60% of the plasma power was recovered as usable process heat via a heat exchanger. These results demonstrate that plasma-based nitrogen fixation is scientifically and technically viable at higher production scales while maintaining competitive specific energy consumption using microwave plasma.