Numerical Simulation And Optimization Of Low Nitrogen Combustion Process In Cement Precalciner

The precalciner is one of the important thermal equipments in the cement industry,and it is also the focus of NOx emission reduction research.In recent years,the NOx emission standards in the cement industry are increasingly stringent.In order to save energy and reduce NOx emission,the optimization research of the structure and process parameters of the precalciner has become an urgent problem in the cement industry.The numerical simulation method is one of the main research methods because of its advantages of convenience,efficiency,resource saving and capital saving.In this dissertation,the 4,500 t·d^-1 three-spray precalciner of a cement plant in Hebei Province was taken as the research object.On the basis of simulating the flow field in the precalciner,the combustion process,decomposition process and NO generation in the furnace were simulated via the Fluent software.The effects of raw material angle,tertiary air velocity and tertiary air temperature on combustion process and NO generation were analyzed.Based on the response surface method,a second-order response model was established.The optimized conditions of low nitrogen combustion were explored.The main conclusions are as follows:1)Obvious three spray effects and reflux effects were generated in the precalciner.These characteristics of the gas phase flow field were compatible with the structure of the precalciner.The combustion of pulverized coal formed two high temperature zones,and the average temperature at the outlet was 1250 K.The total NO concentration at the outlet was 526 ppm,and the error was within an acceptable range compared to the actual operating conditions.2)From the single-factor study,it was known that the raw material angle mainly affected the position and rate of NO generation.With the increase of the tertiary air velocity from 22 m·s^-1 to 38 m·s^-1,the NO concentration at the outlet increased from 124ppm to 220 ppm.At the tertiary air temperature of 1123 K,the NO concentration was 211ppm,it was higher than that in other conditions.3)Based on the Box-Behnken Design?BBD?method,multiple regression analysis and binomial fitting were performed on the three factors and response values.A quadratic response surface model equation for the NO concentration at the outlet of the precalciner was obtained.A new response surface model was established by optimization.The optimum conditions for low nitrogen combustion of the process were 70°for the raw material angle,26 m·s^-1 for the tertiary air velocity,and 1280 K for the tertiary air temperature.The NO concentration at the outlet of the model was 131.9 ppm,and the simulated actual value was 142.4 ppm.The optimization model has a good fit and can be used for the preliminary analysis and prediction of NO concentration at the outlet of precalciner,providing reference for practical projects.