| Cement industry is an industry of high pollution and high energy consumption in ourcountry. It is very important on environmental protection, energy saving and consumptionreducing for economic cycle by improving the pulverized coal combustion performance.There are many problems in mostly cement enterprise after burning blended coal. Such as hesize of the secondary air temperature, air velocity can not be good match coal combustion,appeared pulverized coal difficult ignition, flame stability, low combustion efficiency, highenergy consumption, heavy pollution and other issues. So it has a great significance on thecement rotary kiln furnace gas flow field distribution, the mixed coal combustionperformance and the optimization of burner thermal parameters.The cement rotary kiln of the Sinoma cement of Xiangtan as the research object, throughthermal test on-site, CFD numerical simulation and thermal weight (TG)-differentialcalorimeter (DSC) experiments, carried out the following work:(1) The cement rotary kiln with size Φ4.8m×70m of the Sinoma cement of Xiangtanas the object, selecting the standard k~turbulent simulation model, pulverized coalcombustion model and other mathematical models, according to mapping on-site and thermaltest results to determine initial calculation conditions, using FLUENT software, a simulationstudy of turbulence motion law of the cold jet in the front of the rotary kiln, analyzing theimpact of the center wind to the kiln flow field, especially recirculation zone, and for the latterpart of the mixed coal combustion characteristics experimental study provides a good basis.(2) On the basis of the Cold Model, we have analyzed the operating parameters of theFour Channel Coal Burner, such as the inner to outer ratio of the air volume, the excessive aircoefficient, the secondary air temperature. And we studied these operating parameters impacton the coal combustion and NO_xformation in a rotary kiln. Finally, the operating parameterswere optimized. The appropriate working conditions were like this: the coal ratio ofbituminous coal to anthracite is one to one, the excess air coefficient is1.10, and thepulverized coal particle diameter is88meters. In terms of the kinds of rotary kiln andfour-channel pulverized coal burner, the optimal inner to outer ratio of the air volume is0.8,the optimal secondary air temperature is1255K.In this case, coal is just full combustionwith12meters kiln burning zone length and2200K flame temperature. It can meet therequirements of cement clinker calcinations. The mass concentration of NO_xin the rotarykiln is390.91mg/Nm~3.It meets the national NO_xemission standards because it’s less than400mg/Nm~3. (3) The thermogravimetry (TG)-differential scanning calorimetric(DSC) jointexperimental methods are used to analysis the ignition and burnout characteristics of mixedcoal in different proportions. Under steady heating rate the thermogravimetry analysis areused to measure the decrease of the coal sample weight as the temperature increases, whichwill obtain the TG curve and the DSC curves of the coal samples. Through the analysis of thebasic parameters of the coal such as the exothermic onset temperature Tstart, the exothermicend temperature Tend, the continuous combustion time t, the exothermal q, the weight loss ratedTg/dt etc, the combustion performance indicators of a variety of mixed coal in differentproportions are obtained: the combustion intensity I, the average heating intensity Z, thecombustion behavior S. The comprehensive evaluation about the combustion properties ofcement coal is carried out by the above indicators, which provides guidance for the evaluationabout the performance of the cement coal, the proper proportion of mixed coal, theelectrotype of the claimer, the thermal debugging of cement rotary kiln. |
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