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- 2016
塔式尿素造粒粒径分析
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Abstract:
塔式造粒是当前生产中小颗粒尿素的主流工艺。根据塔式尿素造粒的物理过程, 分析了形成液滴的液柱的受力情况, 建立了液柱临界长度、 最大液滴直径的计算模型。模型计算与实验数据吻合得较好, 可以用于工程计算。利用该模型, 分析了喷口直径和各种操作条件对液滴直径的影响, 发现喷孔直径和喷孔所在处切向旋转速度对最大液滴直径的影响明显, 而喷孔液流速度影响较弱。塔体通风气流速度在低于1.5 m·s-1时影响较小, 高于1.5 m·s-1时影响显著。在一定范围内, 可以通过调整喷孔直径和喷孔所在处切向旋转速度来提高液滴最大直径, 但是液滴在造粒塔中下落冷却固化过程中可能出现二次分裂, 根据临界Weber数发现塔式尿素造粒的最大直径约是4 mm。
Abstract：Urea is produced in a tower with falling liquid droplets to enhance the evaporation and drying of the urea particles. The physical process has a liquid column feeding an atomizer. This study analyzes the effect of the nozzle diameter, liquid velocity and air flow velocity on the urea maximum drop diameter. A model is developed to predict the critical heights of the liquid column and the maximum drop diameter. The model predictions agree well with the experimental data, indicating its ability to predict the maximum drop diameter. The atomizer nozzle diameter and the tangential velocity at the orifice strongly influence the drop size, while the liquid velocity at the orifice has little impact on the maximum drop diameter. The air flow velocity in the tower also affects the maximum drop diameter when the air flow velocity is greater than 1.5 m·s-1, but the effect is very small for the air flow velocity less than 1.5 m·s-1. Thus, the maximum drop diameter can be increased by increasing the atomizer nozzle diameter and the tangential velocity at the orifice. Secondary breakup will occur with large drops falling in the tower during cooling and solidification. The critical Weber number gives the maximum drop diameter of urea in the tower for granulation processing about 4 mm.
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