Fixed Bed Chemical Looping beyond Gas Switching: Application to Dynamic Industrial Waste Gas Conversion

This article presents first-of-their-kind investigations on fixed bed chemical looping as a means of converting dynamic industrial process waste gases containing CO, H2, or hydrocarbons to a product suitable for delivery to a CO2 separation system, without dilution by excess combustion air or flaring outside of process lines. The electric arc furnace (EAF) is used as a case study for its extreme variability in composition and flow rates, and a sample process configuration is presented. Copper- and iron-based oxygen carrier (OC) materials are tested using batched synthetic CO-rich EAF off-gas at the bench scale in a fixed bed reactor to assess the operating limits of the materials with respect to temperature, flow rate, and OC conversion. Results show high OC utilization is possible before breakthrough, with potential for increases in higher-temperature reactors. External mass transfer resistances and possible flow channeling were observed in the bench-scale system and their elimination in pilot and full-scale reactors is discussed. Coke deposition occurred on the iron-based material and resulted in minor deactivation; however, pathways for elimination via temperature management and the use of a small supply of steam with feed gases are described. A selection of processes with dynamic product or waste streams that may benefit from fixed bed chemical looping as a waste treatment or emissions reduction system are introduced, highlighting the absence of treatment methods in use. A fixed bed chemical looping reactor configuration utilizing external heat removal is proposed for load balancing.