The Numerical Simulation And Optimization Of SCR Application For A Coal-fired Power Plant

Based on the deNOx project of a 600MW coal-fired power plant, software FLUENT of CFD was used to carry out the numerical optimization of SCR reactors, which are the core equipments in the project.The standardκ-s turbulence model was used to simulate the flow field of the main part of the reactor and its connected stack under boiler maximum continue rate (BMCR) condition. Based on the results, the reactor with slant top was better than flat top, the high or low speed in local areas could be weakened by curved corner, the outlet with gradual change was more conducive to optimize flow field. At the same time, the velocity distribution of flue gas could be effectively controlled by improving the position, number and shape of the guide vanes.The design of the reactor met the demands:the speed differential value of the first catalyst surface was 3.0% and pressure loss was about 830 Pa.Good NH3/NOX mixing in SCR reactor depends on the reasonable structure of ammonia injection grids (AIG) and the right method of injecting ammonia. AIG were simplified as a number of the nozzles, which would be arrayed with some regularity across the stack section. The appropriate NH3/NOX molar ratio could be gotten by grouping nozzles and increasing the amount of injecting ammonia near the wall according to the distribution of NOx. Catalyst layers and relative catalytic reaction were simulated by porous media and laminar flow finite-rate model, respectively. The design reached the requirements:deNOx performance was about 80.7% and the ammonia slip was about 2.26×10-6 after catalytic reaction.Dispersed phase model (DPM) was used to simulate the track of ash and the particle concentration distribution within the reactor. The results showed that particles easily subsided on the left side of catalyst layers, which might make ash accumulated. Therefore, it was necessary to install the soot blowers above the left side of each catalyst layer. The wearing and plugging of the catalysts, caused by the large size ash particles, could be avoided or reduced by soot blowers purging regularly.Through the investigation of the velocity distribution and pressure loss in varying operating conditions, the reliability of the SCR system was confirmed. Besides, a kind of insert-batch economizer bypass was developed to enhance the capacity of the system of regulating temperature. By adjusting the economizer bypass, the surface temperature of the first catalyst layer could be rised over the minimum operating temperature and the difference of temperature could be controlled in 10K.