Optimization Simulation of Ammonia Injection in SCR DeNO_x System of Coal-Fired Power Plant

To improve the uniformity of NO_x mass concentration distribution at the outlet of SCR (selective catalytic reduction) denitration reactor of a 660 MW unit, this paper proposed an optimal ammonia injection strategy based on the kinetic model with the objective of minimizing the relative standard deviation of NO_x mass concentration distribution at the outlet of SCR. The on-site measured data was used as the inlet boundary condition, and CFD numerical simulation calculations were conducted by coupling turbulent flow, component transport, and chemical reactions in the reactor. The ammonia flow characteristics was visually analyzed, and the flow influence coefficient of the ammonia injection grid partition/nozzle was defined. The optimal controllable ammonia injection flow of different partitions or nozzles of the ammonia injection grid can be obtained by directly solving the optimization matrix equation, and combining the mathematical relationship between the outlet NO_x concentration distribution and the inlet NH₃ concentration, which is based on the SCR reaction kinetics model. The simulation results show that under the uniform ammonia injection mode, the mixing matching degree of ammonia nitrogen concentration in different zones is not high, the relative standard deviation of NO_x mass concentration at the outlet of SCR reactor reaches 40.1%, and the uniformity of NO_x mass concentration distribution at the outlet is poor. After the optimization of ammonia injection according to the method proposed in the paper, the relative standard deviation of NO_x mass concentration at the outlet decreases to 6.8%, and the uniformity of the outlet is greatly improved. This can not only realize the pressure line emission of NO_x to meet environmental requirements but also avoid areas with high and low denitrification efficiency. The flow field was visualized through numerical simulation in the article, and ammonia injection optimization was carried out by quantitatively solving the ammonia injection volume of each valve. This can provide theoretical reference for actual ammonia injection optimization debugging in power plants and reduce the blindness of adjustment.