水泥回转窑物料流动与传热特性数值模拟

Numerical simulation of material flow and heat transfer characteristics of cement rotary kiln

针对回转窑煤粉燃烧过程中物料运动和传热特性难以仿真分析的问题,将回转窑看作是由高温烟气流域和物料流域组成且相互耦合的计算域。在壁面传热的基础上,利用热传导方程描述不同区域物料经窑壁向外散热的热流密度,并提出一种带传热补偿的物料和高温烟气的换热模型。采用此模型数值模拟回转窑内的煤粉燃烧、物料流动和烧结等,研究不同工况下物料流动和温度分布情况。研究结果表明:所建模型可以较准确地反映物料在回转窑内的传热和运动情况;回转窑转速的升高会增大物料沿轴向运动的加速度;增加回转窑内物料流量会降低物料温度,并加剧物料表层和内部的温度差;物料填充率的增加会扩大外回流区的范围,升高冷却带的温度;当物料填充率达到12%时会引发康达效应,使回转窑火焰在靠近物料区域向物料方向发生偏移。

According to the analysis of material movement and heat transfer characteristics in the process of pulverized coal combustion, the rotary kiln was considered as a calculation field composed of high-temperature flue gas flow and material flow, which were coupled with each other. Based on heat transfer on the wall surface, heat flow equation was used to describe heat flux of the material through kiln wall. A heat transfer model with heat transfer compensation was proposed to describe the heat transfer between material and high-temperature flue gas. This model was used to simulate the combustion of pulverized coal, material flow and sintering in the rotary kiln. In addition, flow and temperature distribution of the material under different working conditions were studied. The results show that the heat transfer and movement of the material in the rotary kiln can be accurately reflected by the model. The increase of the rotational speed improves the axial acceleration of the material in the rotary kiln. The increase of material flow rate in the rotary kiln results in the decrease of the temperature of the material, but improves the temperature difference between surface material and internal material. The increase of the material filling rate enlarges the area of the outer recirculation zone and improves the temperature of cooling zone. When the material filling rate reaches 12%, Coanda effect will be induced,causing the rotary kiln flame shift toward material direction near the material area.