Numerical Simulations Of Flow Field And SNCR Denitration Technology In Precalciners Of Cement Industry

With the development of joint prevention and control work of air pollution and the gradually severe NOx emission standards of cement industry in China, there is a growing attention and promotion about using SNCR technology in precalciner for its feasibility and effectiveness. As the flow field distribution in precalcinor is the basic of researching DeNOx process, this study uses CFD method to simulate the distribution of flow field, temperature, NO formation in a typical calciner. Then, for the SNCR in domestic cement industry is relatively weak, the influence on the SNCR technology of various factors is simulated and optimized on the basis of above results, which provides theoretical reference for promotion and applications of SNCR technology to effectively reduce NOx emissions of cement industry in China.The cold simulation of the calciner shows:The main airflow modes in this kind of calciner is double spout with eddies in some areas. Asymmetric structure with a single tertiary air inlet leads to uneven distribution of velocity field and poor material dispersion. According to the flow field problems, several improved schemes in structure are presented and simulated, then the improvement effect on the original flow field of each structure is analysed. For these three improved structures, spray and swirl effect coexist in calciner with a single peripheral tertiary air inlet; calciner with two symmetry offset tertiary air inlets has swirl effect; calciner with two symmetry central tertiary air inlets has spray effect. Scheme2is more conducive to the material dispersion in calciner.The thermal simulation of the original calciner shows:Temperature distribution in calciner is uneven with high and low temperature region. And distributions of all components are complex in throat, materials inlets and coal inlets while well distributed in upper of calciner. NO mainly distributes in the high temperature zone, and NO in rotary kiln has small effect on NO distribution trends while has contribution to NO concentration in calciner. The quality of outlet concentration increases with high import concentration. When the import NO concentration is800ppm, the outlet NO concentration of calciner is813ppm, which has a great agreement with the measurements.The simulation of SNCR DeNOx reaction shows:Factors of nozzle height, ratio of NH3/NOx, spray gun depth and number of nozzles have great influence in the rate of denitration. The suitable installation height for nozzles is in23-30m with small depth and NH3/NOx between1-1.4. And in the moderate range the number of nozzles can be increased to improve denitrification rate. Factors of jet velocity, spray angle, particle size have low effect on rate of denitration.