NUMERICAL SIMULATION ANALYSIS OF FLOW CHARACTERISTICS OF DESCENDING FILM EVAPORATION OF SALT-CONTAINING WASTEWATER IN COAL CHEMICAL INDUSTRY
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摘要: 在黄河流域煤化工高盐废水处理中,降膜蒸发技术由于具有传热系数高、物料停留时间短及处理效率高等优点而被广泛应用,但蒸发过程因流动特性差异而导致蒸发传热效果不佳,成为煤化工"近零排放"处理的关键技术要点之一。通过数值模拟研究3% NaCl在不同入口速度下的降膜流动特性差异,并对比分析了3%、5%和7% NaCl降膜流动特性的轴向与径向变化。结果表明:在不同入口速度下,含盐污水(3% NaCl)液膜温度和液体体积分数变化影响更为明显,入口速度越小,温度升高和液体体积分数减小更为迅速。同一入口速度下,3%、5%和7% NaCl轴向与径向温度、轴向湍流强度、轴向与径向液体体积均相差不大,而浓度高的含盐污水相较于其他组分液体流动轴向速度和径向速度略大,径向湍流强度则相反。Abstract: In the treatment of high salt wastewater emitted from the coal chemical industry in the Yellow River basin, the falling film evaporation technology was widely used, due to its advantages of high heat transfer coefficient, short material residence time and high treatment efficiency, but the evaporation process was not effective due to the difference of flow characteristics, which became one of the keys to the near zero discharge treatment of coal chemical industry. In this paper, the differences in falling film flow characteristics of 3% NaCl at different inlet velocities were studied by numerical simulation, and the axial and radial changes of the falling film flow characteristics of 3%, 5% and 7% NaCl were compared. The results showed that the effect of the change in liquid film temperature and liquid volume fraction of saline wastewater (3% NaCl) was more obvious at different inlet velocities, and the smaller the inlet velocity, the more rapid the temperature increased and the liquid volume fraction decreased. At the same inlet velocity, the difference between axial and radial temperature, axial turbulence intensity and axial and radial liquid volume of 3%, 5% and 7% NaCl was not significant, while the axial velocity and radial velocity of saline effluent with high concentration were slightly higher than other components, while the radial turbulence intensity was the opposite.
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