Ammonia injection controller in SCR-DeNOx system for marine diesel engines based on ARMAX and MPC

To comply with more stringent nitrogen oxides (NOx) emission standard Tier III, which was issued by the International Maritime Organization (IMO), shipping industry has been exploring effective measures for NOx emission reduction. Selective catalyst reduction (SCR) is widely used for its simultaneously achieving high NOx conversion efficiency and low ammonia slip. In this paper, a SCR denitrification (SCR-DeNOx) system for a certain marine diesel engine (MAN6S50MC-C) is used as the research object. A mechanism model is established for the SCR-DeNOx system and then a model of the ammonia injection control sub-system is identified. Based on the identified model, an ammonia injection controller is proposed in this paper, where model predictive control (MPC) strategy is used with the aim of increasing the robustness and reducing secondary pollution of the system. Simulation results show that the denitrification rate of the proposed MPC is increased by 5.66% while the ammonia slip is decreased by 25.6204ppm, compared with the traditional PID controller. It is a certain theoretical guiding significance for energy conservation and pollution reduction in the actual SCR-DeNOx system.