Numerical Study Of 660MW Coal-Fired Powerplant Flue Gas SCR De-NO_x System

Taking a domestic 660MW coal-fired power plant selective catalytic reduction (SCR) denitration system of as the research object, the regulation of De-NOx of a single hole catalyst、the distribution of velocity field、the distribution of concentration、the distribution of fly ash particles in the reactor are studied by using Fluent software, the results show that:(1) On the basis of E-R reaction kinetics, at the same time, considering the influence of internal and external diffusion and the adsorption of ammonia, a three dimensional single channel model was established. The oxidation of NH3 and SO2,the heating effect of the reaction were also considered. The model was testified to be reliable by compared with experimental data. Through simulation, the reaction has a wide temperature window,280℃ ～380℃, Along the length direction of catalyst, temperature rising slightly, exothermic phenomenon does not obvious. With the increase of NH3/NO ratio, the De-NOx efficiency and ammonia slip increased while the conversion rate of SO2 decreased. High space velocity can reduce both the De-NOx efficiency and SO2 conversion rate. In addition, SO2 conversion rate increase linearly with wall thickness of catalyst. Due to the obvious diffusion phenomenon, the De-NOx efficiency reduced significantly with the increase of wall thickness of catalyst.(2) The 3-D SCR model was established, the flow field was simulated, the results show that:due to the existence of two cross station in the reactor, the distribution of flow field at Ammonia Injection Grid does not uniform, the relative deviation coefficient of velocity is 27.5%, showing the regulation of higher velocity at the middle zone and lower velocity at the side zone. Increasing the amount of splitters at uptake variable cross-section plate can be slightly improved the distribution of flow field, but the relative deviation coefficient of velocity is also higher than 20%. The relative deviation coefficient of velocity can be reduced to 14.3%, by adding a porous plate which opening is 50% before AIG sectional. The concentration of fly ash in the reactor was simulated, the results show that:the concentration of fly ash is higher at the front of reactor, the quality is larger. The results show agreement with sampling experiment. Add the numbers of the splitters at upper corner can improve the uniform of concentration of fly ash in the reactor.(3) The gas-solid heterogeneous reaction of SCR was simulated by using Fluent coupled with detailed reaction mechanism of SCR, by the mode, the effects of the non-uniform distribution of both velocity and NH3/NO mole concentration ratio, the non-uniform distribution of temperature on the reaction was simulated. The results show that, The uniform degree of inlet velocity and temperature of the first layer has a little influence on the reaction, while the uniform degree of NH3/NO mole concentration ratio has a great influence on the reaction. The velocity distribution and the components distribution of inlet and outlet are similar.10 area ammonia injection strategy and 30 area ammonia injection strategy were made according to the characteristics of the distribution of flow field of AIG. The effects of three ammonia injection strategies on the De-NOx reaction are compared under 660MW stress, and NH3/NO mole concentration ratio is 0.8:1. The results show that:when using linear ammonia injection strategy, the relative deviation coefficient of NH3 at the entrance of first catalytic layer is 25.3%, the De-NOx efficiency is 75.5%, the volume fraction of ammonia slip at the outlet is 18×10-6.when using 10 area ammonia injection, the relative deviation coefficient of NH3 at the entrance of first catalytic layer is 8.9%,30 area ammonia injection can reduce the relative deviation coefficient to 5.6%. The De-NOx efficiency is 79.38% and 79.45% respectively, the volume fraction of ammonia slip at the outlet is 2.5× 10-6 and 2.2×10-6 respectively. At last the effects of 10 area ammonia injection strategy and 30 area ammonia injection strategy on the De-NOx reaction are compared under 400MW stress, and NH3/NO mole concentration ratio is 0.8:1. The results show that:as the rich NH3 region of the first layer catalyst when using 10 area ammonia injection strategy is bigger than 30 area ammonia injection strategy. So 30 area ammonia injection strategy get a better results than 30 area ammonia injection strategy. The De-NOx efficiency is 95.35% and 92% respectively, the volume fraction of ammonia slip at the outlet is 9.3×10-6 and 1.6R10-5 respectively.