| As multifunctional production equipment, rotary kiln can undertake tasks of material conveying, heat transfer, combustion, and chemical reactions. Due to its good mixing performance, efficient heat transfer ability and flexibility to a variety of industrial processes, rotary kiln is widely used in cement, metallurgy, papermaking, chemical industry, building materials and other industrial fields. However, as a large heat exchange device, the heat exchange way, of "accumulation mode" between hot air flow and material in kiln, often causes adverse consequences, such as, high energy consumption, low heat utilization rate, waste of resource, etc. In recent years, through the field testing and numerical calculation, many scholars home and abroad have applied the fundamental theory of heat, mass and momentum transfer and chemical reaction, and carried on comprehensive research on processes of thermal flow, heat transfer and combustion in the rotary kiln, so as to improve the thermal efficiency and reduce energy consumption.Based on a bauxite sintering clinker kiln of04.5X90m, according to the features of physical and chemical processes in different areas of the rotary kiln, the kiln body is divided into seven belts along the transport direction of material. Based on heat exchange characteristics in each belt, one-dimensional axial heat transfer model was established. The model took into account of material exothermic reaction, radiation heat transfer of fuel combustion and indirect heat transfer way of kiln wall, etc. Using the calibration data as the initial thermal calculation parameters, by MATLAB software programming, the temperature distributions were obtained by model calculations, as well as the heat transfer between the gas, material and kiln wall. Results were consistent with the literature on thermal measurement value, which indicated that the calculation model had good prediction ability, and could provide certain guidance for the improvement and optimization of the actual operation process of rotary kiln production systems. Results showed that the radiation heat transfer played a dominant role in the process of heating materials in the calcining zone and the combustion zone; gas and kiln wall played nearly the same role on heating materials; while kiln wall acted as indirectly-heated media.Good performance of the burner could provide the best production system for rotary kiln thermal condition. The study and optimization of the structure and performance of the pulverized coal burner would be beneficial to reducing system energy consumption, improving the production ability of the rotary kiln, and meeting the needs of environmental protection. In the paper, according to the kiln and burner model available in cold jet experiment of the literature, using the software of FLUENT, a three-dimensional cold jet model of four channel swirl pulverized coal burner was set up. The model applied k-epsilon gas-phase turbulence model and multiple pieces of non-uniform grid technology. Through numerical calculation, the article comprehensively analyzed how the supply air parameters of each duct and the swirl angle of internal flow worked on axial, tangential and radial velocity field, and found out the change rules of the turbulent jet flow field under different working conditions. Results showed that central flow played an important role to forming reflow zones, which could accelerate pulverized coal ignition and stable combustion. Internal rotational flow and high-speed external flow formed jet with velocity difference, which made pulverized coal and air flow intensively mixed, and high temperature secondary air involved into flame region, which was helpful to accelerate the pulverized coal combustion and raise the utilization ratio of heat. In order to obtain suitable flame shape, wind speed and swirl vane angle should be selected reasonably. Moreover, raising the velocity of internal and external flow simultaneously would be beneficial to improve swirl intensity and entrainment capability of the turbulent jet. |
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