Simulation and optimization of water gas shift process in ammonia plant: Maximizing CO conversion and controlling methanol byproduct

Abstract

The water gas shift reaction is one of the most important reactions in ammonia production plants for purifying hydrogen streams from carbon monoxide. This reaction occurs in two consecutive reactors at high and low temperatures. In the current study, the simulation was first carried out for these two reactors in one of the ammonia production units, and then the process variables were optimized to maximize hydrogen production in three states: one that was relatively near-equilibrium, one that was far from equilibrium and one that was near the end of the run. Methanol formation as a byproduct was also identified during process evaluation as a crucial limitation. The optimization results in all three modes indicate that maximum carbon monoxide conversion could be achieved during the catalyst lifetime if the reactors operate at low temperature and pressure at the start-up. As the catalyst lifetime increases, the inlet temperature and pressure must be increased to keep the catalyst active.