Numerical Simulation Study On High Efficiency And Stability Of Coal Blends Combustion In Rotary Kiln

Rotary kiln is one of the key equipment of NSP cement production, efficient and stablecombustion of pulverized coal in the kiln plays an important role in improving the yield andquality of the clinker as well as saving energy and reducing consumption. In recent years, forsaving costs, many companies begin using coal blends to produce cements. However, when thecoal blends are used in the rotary kiln, the original thermal parameter, mix ratio of coal andparticle size may not match its combustion characteristic well, which will cause the problemssuch as low efficiency and poor steady combustion. Therefore, it’s necessary to research andanalyze mixed coal combustion characteristic, obtaining the optimized system’s thermalparameters, mix ratio, particle size of coal.In the paper, the cement rotary kiln with size Φ4.8m×70m in the the Sinoma cement ofXiangtan and the special domestic TJB-KP-14type of swirling four-channel coal burner aretreated as the research objects. We studied coal blends combustion in the kiln by combining thecombination of field test with numerical simulation. The main research work is as follows:(1) A rotary kiln burner system physical model is established with GAMBIT, andconstructed the corresponding mathematical models based on the software of FLUENT, such asthe basic conservation equation, turbulent flow model, pulverized coal combustion model,radiation model, etc. Simulation studies is carried out based on the actual working condition ofthe rotary kiln. By analyzing and comparing with field test data, the feasibility of the numericalmodel has been verified.(2) The cold flow field simulation is carried on for studying the velocity field andconcentration field in the rotary kiln, analyze the impact of the center wind velocity, swirl vaneangle, vortex wind velocity and axial wind velocity on the performance of backflow region. Thebest parameters are as follows: the center wind velocity is40m/s, swirl vane angle is25,vortex wind velocity is80m/s, axial wind velocity is100m/s, and it forms the center backflowregion and some external backflow region in the kiln, the pulverized coal in the backflowregion is effectively gathered, which maks a good foundation for combustion. Then, theinfluence of reflux area if the zoom ring is installed in the coal burner wind channel isresearched. The study indicartes that coal will be divided into two jet stream through the zoomring, passing into the kiln stove, it has been formed a reasonable center backflow zone andouter backflow region.(3) Based on the heat flow field simulation study, the impact of coal combustion on the secondary air temperature, mixing ratio of coal, particle size and swirl vane angle areresearched. It indicates that when the excess air coefficient is1.10, the ratio of the internal andexternal airflow is4:5, these parameters are optimized: the best secondary air temperature is1300K, coal blends ratio is2:3, the average particle size is60μm and the swirl vane angle is25. Now the firing zone is about12m long, its high temperature is about2000K. Thepulverized coal can be efficiently and stably burned, which is fit with the requirement of cementproduction. Finally, after optimization of the parameters calculated by the boundary conditionsfor each flow field distribution in the kiln coal combustion, analyze simulation results andcombine with field tests, the final optimizations are obtained.The results of the paper can provide important reference for choosing appropriate coalblends ratio, particle size and thermal parameters in the cement rotary kiln.