Simulation Study On Heat Transfer In The Clinker Cooling Process Of Grate Cooler

Grate cooler is the key equipment in the cooling process of cement clinker,the heat transfer between clinker and cooling air in it has direct influence on the quality of cement and the energy consumption of the clinker burning system.However,at present,the clinker cooling process of grate cooler in China's cement industry often has the problem of "supercooling" or "undercooling",and the heat recovery efficiency of grate cooler still lags behind the advanced level in the world.In the paper,the NC42340 grate cooler is used as the research object and the simulation model is established to analyse the flow and heat transfer in the grate cooler.The influence of clinker particle diameter,porosity,clinker layer thickness,cooling air speed and grate speed on the cooling of clinker is mainly studied,at the same time,the waste heat utilization effects of two circulating air schemes under different air temperatures are discussed,so as to provide theoretical support for the actual operation of grate cooler.The specific research contents and conclusions are as follows:(1)On the basis of FLUENT porous media model and simulation program written by UDF to realize the thermal non-equilibrium heat transfer between cooling air and clinker and the influence of horizontal movement of clinker on heat transfer characteristics.The reliability of the model is verified by comparing the simulation results with the measured data,on the basis of this,the distribution rules of flow field,pressure field and temperature field in the grate cooler are analysed: there are two areas with velocity of 0 between the three air outlets,the pressure of the 1?9 air chambers decreases in turn and the pressure of clinker layer is decreased gradually along the thickness direction,both the temperature of cooling air and clinker decreases gradually along the length direction of the grate cooler and increases along the clinker layer thickness direction.(2)With the increase of clinker particle diameter,the temperature of secondary and tertiary air decreases linearly,the clinker discharge temperature,the temperatures of waste heat power generation air and low-temperature exhaust gas all increase,the effect of porosity on the cooling of clinker is relatively small,and the average temperature of the three air outlets is linearly negatively correlated with the porosity,the increase of cooling air speed is beneficial to reduce the temperature of clinker and the low-temperature exhaust gas,but at the same time,the temperature of the secondary and tertiary air and the waste heat power generation air is also decreased,the temperature of secondary and tertiary air,the waste heat power generation air and the clinker discharge temperature all increase with the increase of the clinker layer thickness and grate speed.Through comprehensive evaluation,as far as the thesis is concerned,the clinker particle diameter should be less than 25 mm,the porosity should be controlled between 0.3 and 0.45,the reasonable clinker layer thickness should be 600 mm?700 mm,the range of cooling air speed should be V3?V5(1.75 m/s?2.15 m/s),and the grate speed should be controlled between 0.007 m/s and 0.008 m/s.(3)According to the relevant process requirements of cement production,the optimal combination of each parameter is determined through the orthogonal analysis and the comprehensive balance analysis: the clinker particle diameter is 10 mm,porosity is 0.3,cooling air speed is 1.75 m/s(V3),the clinker layer thickness is 700 mm and the grate speed is 0.007 m/s.(4)The waste heat utilization effects of two circulating air schemes under different air temperatures are compared and analyzed,the results show that the total waste heat utilization by introducing the circulating air into the front air chamber(scheme 2)is always greater than that by introducing the circulating air into the middle air chamber(scheme 1),and the critical point of waste heat utilization of waste heat power generation is the circulating air temperature of 360 K,When the circulating air temperature is less than 360 K,the waste heat utilization of scheme 2 is greater than that of scheme 1,however when the circulating air temperature is more than 360 K,the waste heat utilization of scheme 1 is more than that of scheme 2.Combining the clinker discharge temperature under the two schemes,scheme 2 has better waste heat utilization effect.