The Simulation Of SNCR Process In Cement Precalciner Based On Fluent Software

Precalciner, one of the key equipments in cement precalcining technology, bears the task of multiple complex chemical reactions such as pulverized coal combustion, carbonate decomposition and so on. As one of the main pollutants in cement industry waste gas, NOx has caused serious damage to the environment. This paper adopted Fluent software to simulate the DD precacliner in one of 5000t/d cement production line, analyzed the flow field information and the characteristics of NOx formation in precacliner, and using selective catalytic reduction (SNCR) to reduce the emission concentration of NOx by urea. In order to get reasonable denitration parameters and provide theoretical guidance for cement precaliner, the SNCR working parameters were optimized. In this paper, the following works are implemented:(1) The Gambit software is used to build DD precacliner model according to actual sizes, the Boolean Operation is adopted to split the model into several regular shapes and block mesh technology is applied to get high quality meshes.(2) To get the flow field information of precacliner, the mathematical model is built, the standard k-s model, species transport model and P-I radiation model is proposed to simulate the turbulent flow, pulverized coal combustion, chemical reaction and radiation heat transfer respectively. The simulation results show that, the velocity of gas flow has good symmetrical distribution along the axis center and forms several vortexes which would enlarge back-mixing. The pulverized coal combustion creates a massive of heat, and the highest temperature is about to 1800K in main chamber which would descend in a parabolic gradient to the exit. The concentration distribution of volatile, O2, CO and CO2 conform to the basic rules of burning, which shows that the pulverized coal is in good combustion condition and the air proportion is appropriate.(3) The NOx generation model is used to simulate NO generation in precacliner based on the combustion, and the basic NO distribution is obtained. The simulate results show that, NO mainly produces in main combustor, which is the result of pulverized coal combustion. Under the diffusion of fluid, the concentration of NO presents uniform feature in precacliner eventually. Without considering the NO from kiln, the concentration of Fuel NOx at exit is about 450ppm, otherwise, it is 850ppm.(4) The SNCR model is adopted to simulate SNCR denitration process in precacliner by injecting urea, and the results show that the injection of urea can reduce the concentration of NO in waste gas. In order to improve denitration efficiency and obtain the optimum denitration parameters, the further optimizations are carried out. The results show that, when the urea injection is at height of 26m by 60°downwards with the velocity of 25 m/s in precacliner, the ability to removal of NO is the best. To obtain better denitration effect and lower NH3 escape, the molar ratio of urea and NO should be less than 1.0, which is best between 0.8 and 0.95.