| The most advanced technology in modern cement industry so far is the precalcining technique in the world. Although China’s cement industry has achieved great development in recent years, there still exists a gap with the international most advanced level in heat consumption, power consumption, pollutants such as NOx emission etc. The optimization of cement precalcining system is one of the main approaches to realize energy saving, consumption reducing, and pollutant emission decreasing. As a result, research on the technology of energy saving and emission reduction of the precalcining system in cement industry and applying these technologies in practical projects are of practical significance for the cement industry to realize low-carbon economy and harmonious development with resources and environment.Based on the laboratory experiments, theoretical analysis, computer simulation and practical measurement in cement industry, environmentally-friendly cement precalcining system were studied thoroughly. Major contents include:(1) The dispersing performance of splash boxes with various structures, with dispersion plates with different angle and insertion depth and so on was carried out using the experimental platform of splash box. From the mathematical analysis results, the optimum dispersion can be obtained for the material when the dispersion plate has an angle measuring 5 degrees and the insertion depth of 200 mm. Engineering application confirms that preheater exit gas temperature is 15~20oC lower after the optimization of splash box.(2) The parameters for the turbulence model in the computational fluid dynamics were corrected with the data from cold condition test of cyclone. The flow field, heat exchange efficiency and separation efficiency of the six-stage preheater system developed by Tianjin Cement Industry Design and Research Institute Company Limited (TCDRI) before and after optimization were simulated and analyzed with Reynolds stress model (RSM) and discrete phase model (DPM). The computational results indicate that the pressure loss of the optimized six-stage preheater system drops by 13.8% when compared with that of the previous one, while the heat exchange efficiency decreases by 1.7%, indicating that the optimized six-stage preheater system exhibits a better energy-saving result.(3) Based on the theoretical analysis and derivation, a formula to calculate the pressure loss of a cyclone used for cement production has been put into forward. This paper presents concepts of effective energy and non-effective energy, dictating the energy utilization efficiency for cyclones. Both reducing the pressure loss and raising utilization efficiency of effective energy should be considered for the cyclone development.(4) The correlation between the combustion characteristics of fuel and the design of calciner was studied with the lab tests and CFD modeling. The requirement for a reasonable and efficient calciner is to guarantee the ignition and complete combustion for various fuels and a high burnout rate. Meanwhile low pressure loss, simple structure and high operation reliability should be compatibly considered for the calciner.(5) The kinetic study of NO reduction over coal chars was carried out and kinetic parameters obtained were introduced into the numerical simulation in the calciner. The NOx emission concentration for tri-spouted TTF calciner, introducing the staged tertiary air to reduce NOx emission, was simulated through the computer auxiliary test platform for calciner. The practical measuring data in cement plants show that the method of staged tertiary air can decrease NOx emission by 10~36%. |
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