| Numerical and optimization research on fluid flow, high temperature heat transfer and pulverized coal combustion in rotary kiln for bauxite sintering has great significance on enhancing the monitoring of kiln operation, selecting suitable pulverized coal burner, optimizing operation regulation and eventually reducing energy consumption. Based on major industrial project entitled "research on simulation and optimization of rotary kiln for bauxite sintering and burner" and "development of online simulation and intelligent control system of rotary kiln for bauxite sintering", this paper is aimed at solving the problems widely existing in practical operation of rotary kiln for bauxite sintering and whirl four-channel pulverized coal burner applied to this kiln. The flowing of gas and burden, heat transfer among gas, burden and wall, and pulverized coal combustion in rotary kiln for bauxite sintering are fully studied by thermal measurement, cold modeling experiment and numerical simulation through combing the knowledge of heat transfer, mass transfer, momentum transfer and chemical reactions. The main contents and conclusions of this research include:(1) Based on similarity theory, a cold modeling experimental equipment of cyclone four-channel pulverized coal combustor and rotary kiln system is developed, and the flow field in model kiln is measured and analyzed. Meanwhile, by combining advanced computational fluid dynamics software CFX4.3 and Fortran programming, the cold flow field in the model kiln under operating conditions is simulated by using standard k-εand RNG k-εturbulent model respectively. The simulation results agree well with measurements. The profile and tendency of velocity distribution of the simulation results and measurements are the same, and meet the precision requirement of engineering prediction. Moreover, computational results of two turbulent models under this condition are approximately the same.(2) A rotary kiln for bauxite sintering with the length of 90m and the diameter of 4.5m using whirl four-channel coal burner is investigated. A mathematical model of flowing process in the rotary kiln, whose boundary conditions are obtained from the measurement, is developed to study the turbulent jet in the kiln by using standard k-εgas phase turbulent model and combining simulation software CFX4.3 and Fortran programming. The influences of main parameters on the flow field in the kiln, especially on the backflow region, are analyzed, which can provide reference data for practical conditions.(3) By applying standard k-εgas phase turbulent model, random orbit particle transport model, k-ε-(?)-g gas combustion model, Monte Carlo radiation model, limited difference method, structural mesh and SIMPLEC arithmetic, the velocity field, pressure field, temperature field and heat releasing field in the rotary kiln are simulated simultaneously. The quantitative effect of various operation parameters on temperature profile in the kiln is investigated, and the suitable operation regulation and structural parameter for the burner and kiln system are determined. Computational results and thermal measurements have the same tendency.(4) A new empirical method is developed to calculate the heat flux and length in the bauxite sintering rotary kiln, and discrete parameters including the amount of burden, gas and heat exchange in different regions, the temperature of gas and burden on the boundary of each zone can obtained from this method. In addition, a one-dimension heat transfer mathematical model is developed, which takes into accounts many factors, such as the physical and chemical reactions between gas and burden, heat transfer among gas, burden and kiln wall. From this model, the temperature profiles of material, gas, kiln inner wall and kiln outer wall can be obtained. These two methods have their respective features and so can compensate each other.(5) A flexible mathematical model of the temperature inside kiln wall and refractory layer in sintering zone of rotary kiln is developed. The temperature distributions of kiln inner and outer wall, refractory lining and attached clinker layer are investigated under different thickness. By applying ejection drying model, simulation study on temperature profile of burden and gas and concentration profile of water vapor in the gas in drying region is conducted and the effects of different negative pressures in kiln terminal and diameter of raw slurry particle on the physical parameters of gas and slurry are analyzed. Main computational results approximately agree with thermal measurements. Finally, suitable thickness of attached clinker, negative pressure in kiln terminal and raw slurry particle diameter are proposed.The research results have been successfully applied in a rotary kiln for bauxite sintering in an alumina plant. The operation shows that the rotary kiln on-line simulation and intelligent control system can realize computer-aided design and automatic control, optimize operations, stabilize work conditions and reduce energy consumption. The system can also be applied to other kilns.
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