Based On Fluent Software Simulate The Thermal Process In Cement Pre-calciner

The new dry cement production technology is the most advanced technology ofcement industry, and pre-calciner is one of the key equipments in this productiontechnology. This paper adopted Fluent software to simulate the new three spoutingpre-calciner of5000t/d cement production line, and directly showed the gas flow field,temprature field, species concentrations and solid particle trajectory, and discussed thethermal process of materialdispersion, heat transfer, fuel combustion and calcium carbonatedecomposition. The research could not only reasonably and scientifically optimize thethermal regulation of pre-calciner, and could provide powerful scientific reference fordesign and development of pre-calciner. These have important meaning to guide cementproduction, save energy, improve quality and decrease the cost of production. Main workand results are as follows:1. Use Gambit software to built geometrical model of new three spouting pre-calcinerin5000t/d cement production line. This pre-calciner includes combustion chamber, middlemixing chamber, up mixing chamber three parts, and then meshing by block mesh scheme.The optimal grid number is483261, and providing the powerful calculation condition fornumber calculation.2. The mathematical model of pre-calciner gas flow is builded according to fluid flowcharacteristics in pre-calciner. Turbulence model is standard k-ε model, and using SIMPLEalgorithm and sub-relaxation method to solve. The results show that: Look from whole, theflow field has good symmetrical patterns compared with the axis, which indicate flow fieldis stable in pre-calciner. The cold swirl flow effect is marked, upward spiral clockwise,existing many eddies.3. On the basis of air flow field simulation, together with actual thermal condition,applying multiphase flow theory, using DPM dispersed phase model and considering thegas-solid couple effects to simulate the cold flow field that add solid particles. The resultsshow that solid particles upward in the rotational flow and spouting double effects,dispersion degree is higher and fill the whole pre-calciner. The residence time is10.8s. Thecentrifugation of rotational flow makes the solid particles near the wall, forming the center concentration rarefaction, which not only beneficial for contacting fully of gas andpulverized coal, but also prolonging the service life of equipments.4. The combustion characteristic and dynamic characteristic of pulverized coal inpre-calciner is studied by thermal analysis. Based on the kinetic parameters and coldsimulation, using nonpremixed combustion model to simulate the pulverized coal flow,heat transfer, combustion in pre-calciner. The hot-state flow, temperature field,concentration field of the gas compositions and trajectories of particles in pre-calciner aregiven. The results show that influenced by the thermal current, hot state speed gradientdecreases and distribution of flow field is more uniform in pre-calciner. The highesttemperature area of temperature field in combustion chamber, close to1800K. As thepre-calciner height increase, it will gradually reduce and finally tend to distribute uniformly.The rotational flow and spouting effect of hot gas in pre-calciner improve the degree ofmaterial dispersing and turbulence, with the backmixing near the combustion chamber wall,which promotes full combustion of pulverized coal and the pyrolysis and evolution ofvolatile are more quickly. The concentration distribution of CO₂, O₂, CO in pre-calciner isreasonable. CO₂concentration is lower at pulverized coal inlet, but CO concentration ishigher. CO₂concentration is higher and CO concentration is close to zero to the outlet.5. The limestone that used by pre-calciner is studied by means of thermal analysis, andidentify the decomposition mechanism and kinetic parameters of calcium carbonate. Todiscuss the combustion and decomposition coupling field under different decompositionrate of raw meal base on the the numerical simulation of pulverized coal combustion. Theresults show that CO₂concentration distribution tends to become the same. Distributioncloud with good symmetrical patterns. The mass fractions are20.1%,21.03%,22.27%under the decomposition rate85%,88%,92%. High-temperature area after coupling still inthe combustion chamber and uniform distribution, which indacate that the pre-calciner isrunning steadily.