Optimization Of SCR Denitration System Based On Gas-Solid Field And The Control Method Of Spraying Ammonia

Along with the increasingly stringent controls on NOx emission of coal-fired power plant, selective catalytic reduction (SCR) technology with the high denitration efficiency and non-secondary-pollution is becoming more and more popular. In the practical engineering, the inhomogeneous distribution of the parameters before the first catalyst layer, such as flue gas velocity, ammonia-nitrogen-ratio, the concentration of fly ash, would greatly reduce the denitration efficiency. So, the paper researched a SCR denitration system of 330 MW tangentially coal-fired boiler and optimized the gas-solid two-phase field and the control method of ammonia injection with the help of numerical simulation software.First, the full-scale three-dimensional geometric model of the original SCR denitration system is built with a ratio of 1:1. Then, based on the more practical non-uniform boundary condition, the flow of flue gas accompanied with heat and mass transfer is simulated by choosing appropriate numerical model and solving method. The contrast of simulation result and test data shows a little error, which proves the validity of the numerical simulation. With a further analysis, the inhomogeneous speed deviation coefficient before the first catalyst layer of the original system could reach 18.03%, which exceed the design requirement. By optimizing the right angle structure of reactor entrance and installing the guide plate, the inhomogeneous speed deviation coefficient could be reduced to 12.35%.Secondly, the paper simulated the fly ash particle movement characteristics by coupling discrete phase model Numerical calculation results show that:the inhomogeneous concentration deviation coefficient of fly ash before the first catalyst layer of the original and optimized SCR denitration system were 53.26% and 46.86% respectively, that is to say, the optimization of system structure based on the gas phase field improve concentration distribution uniformity of fly ash. To further reduce the distribution inhomogeneity of fly ash concentration, this article try to install flow regulating internals of different numbers and shapes in the SCR reactor. It’s found the case that used five circular flow regulating internals can not only make concentration deviation coefficient of fly ash before the first catalyst layer dropped to 32.03%, also make speed deviation coefficient reduced to 8.652%.As the optimization of system structure based on gas-solid two-phase field was completed, the mixing process of the ammonia and flue gas was then simulated. It’s found that, for the original vortex plate spraying ammonia mixing device in the plant, kinds of control methods of ammonia injection can not guarantee a good uniform distribution of ammonia-nitrogen-ratio before the first catalyst layer. However, if a new ammonia injection grid (AIG) and the non-uniform control method of ammonia injection was adopted, the ammonia-nitrogen-ratio deviation coefficient before the first catalyst layer can be reduced to 4.72%, which well met the engineering requirements.