CFD Simulation Study In SCR-Denox System Of Coal-Fired Power Plant

In coal-fired power plants, NOx, mainly composed of NO and NO2, is the second largest pollutant followed SOx. Since 2004, DeNOx has become another important domain after the desulfurization in China.Since selective catalytic reduction (SCR) of NOx is wildly applied in DeNOx industry, this paper will focus upon the computational fluid dynamics (CFD) simulation of ammonia-flue gas mixing in SCR-DeNOx process. First, NOx control techniques are briefly reviewed. Then, SCR technique is described in detail, including the principle, the structure of SCR-DeNOx system, the arrangement of reactor, a few of main factors affecting the denitration efficiency of selective catalytic reduction, and so on. Case study is carried out to improve the DeNOx operation in 300MW Coal-fired Units, followed up by the conclusion and prospect of this paper.The main content in this thesis is CFD simulation for SCR-DeNOx system. The distribution of NOx/NH3 concentration and flow velocity before entering the catalyst layers is especially focused upon, with the aim of maximizing NOx reduction and minimizing ammonia slip. CFD , FLUENT 6.3, is used to simulate the flue duct of SCR system, through choosing proper numerical models and the parameters. Simulation shows that the grid-shaped mixer functions well to radial mixing and therefore provides homogenization of gas concentration. As a result, satisfactory uniform distribution of NH3 concentration is achieved before the mixed gas entering the catalyst layers. It is also demonstrated that the four groups of turning vanes in the position of turning duct decrease velocity maldistribution, while the pressure drop subjects to no increase caused by turning vanes. Furthermore, a new kind of mixer, turbine-shaped mixer, is studied for its mixing function. Finally, the shape of exit-duct of SCR system is optimized through CFD simulation.The CFD software FLUENT has the advantage that data of velocity, pressure and concentration for the whole flow field is obtained. After flow model test, the CFD simulation results may optimize the design of mixer and turning vanes, satisfy the demand of the uniformity for the distribution of NOx/NH3 concentration and flow velocity in SCR system.