Effectiveness of Three Reactor Chemical Looping for ammonia production using Aspen Plus simulation

Abstract

This study uses Aspen Plus simulations to explore the performance of a new flowsheet for ammonia production using Three Reactor Chemical Looping (TRCL) technology. In TRCL, the solid Oxygen Carrier continuously circulates between a Fuel Reactor, a Steam Reactor and an Air Reactor. The Oxygen Carrier is reduced in the Fuel Reactor and oxidised in the Steam and Air Reactors. Hydrogen generated in the Steam Reactor and nitrogen produced from the Air Reactor form a synthesis gas that is converted to ammonia. This study compares the TRCL process with the conventional ammonia process and a pseudo-continuous Chemical Looping Reforming (CLR) process that uses packed beds. Energy and environmental indicators are evaluated for the three processes. It was found that the energy consumed in the TRCL process is higher than the other two processes because of higher steam consumption in the Steam Reactor for generating hydrogen. However, if conversion in the Steam Reactor of greater than 67.5% can be achieved, the energy performance indicators are comparable with the conventional and CLR processes. At 67.5% conversion, the specific energy consumption becomes 21.5 GJ/tNH3. It is also noted that the Specific Energy Consumption for Carbon dioxide Avoidance (SPECCA) is much better than the conventional ammonia process at a steam conversion higher than 67.5%. Although further development is needed, this study shows that TRCL holds promise for lower energy consumption and better environmental performance than other commercial ammonia production technologies.