Publisher Summary This chapter discusses a robust control system for the overall ammonia synthesis loop. The control system in object should be able to reject external disturbance on the main process variables and uncertainty on the adopted control settings. A complete dynamic analysis, including all heat and material recycles was performed to address the multistable behavior from one side and the controllability issue from the other. The model extension to the overall synthesis loop implies new equations related to a cascade of heat exchangers plus a two-stage flash where the ammonia is condensed and separated as a liquid product while the gas is recycled to the reaction stages. Two of the aforementioned heat exchangers are adopted for feed preheating so determining strong heat system integration. With this more complete layout, sustained oscillations can be induced by smaller disturbances than those pointed out by previous studies. A conventional control scheme is analyzed in terms of pairing and optimal control settings. The sensitivity analysis shows that errors on the control parameters due to a poor tuning can lead to sustained oscillations with respect to pressure disturbances even in presence of closed-loop conditions.
