转炉蒸发冷却器换热效率数值模拟
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摘要
基于国内某钢厂65 t转炉蒸发冷却器运行参数,采用CFD方法的离散相模型模拟了蒸发冷却器内雾化液滴与高温烟气间的换热效率,考察了单个液滴粒径、雾化液滴粒径分布对换热效率的影响。结果表明,模拟结果与实际运行参数吻合较好,计算的出口温度为468 K,实际为483 K,相对误差为3.1%,模型可靠。粒径小于300μm的雾滴均能在0.62 s内蒸发完全,不同粒径的雾滴完全蒸发所需时间最高相差20多倍。液滴与高温烟气的换热效率受粒径分布影响较大,中位粒径d50=340μm和d50=95μm的雾滴在同一截面的平均温度可相差70K。烟气温度下降先快后慢,最后趋于平稳,烟气主要降温区域为喷嘴下游3.5 m内。
In Lurgi-Thyssen dedusting system of steelmaking converter, the evaporative cooler represented a crucial operating unit, in which the hot dust-laden flue gas had to be cooled by saturation with water. The cooling process of the gas consisted of gas-liquid two phase flow and interphase heat and mass transfer. In this work, k-e standard equation and Lagrange discrete phase model were employed to describe the gas turbulent flow and the heat/mass transfer with droplet evaporation individually. The computational fluid dynamics(CFD) simulation for practical engineering project showed that the large-flux cooling gas was commonly constructed in a nonuniform flow caused by the sharp turnings at the inlet and outlet channels. The simulation results of the model were ingood agreement with the actual working condition parameters of the evaporative cooler. The relative error of flue gas outlet temperature was 3.1%, the simulation results were reliable. The smaller the size of atomized droplet was, the shorter the time was required to reach the critical evaporation temperature and complete evaporation. The droplet with a particle size of less than 300 μm could evaporate completely within 0.62 s. The main temperature drop of flue gas was within 3.5 m downstream of the nozzle. The heat transfer efficiency of droplet and high temperature flue gas was greatly affected by particle size distribution. The mean temperature of the same section corresponding of droplets with d50=340 μm and d50=95 μm can differ by 70 K. Using rosin-rammler distribution function to describe droplet size distribution, the effect of particle size distribution on the cooling efficiency of flue gas was studied. The droplet size should not be too large or too small. The particle size was too small to make a reasonable use of evaporative cooler space. The temperature of flue gas dropped unevenly and the droplet evaporation was incomplete due to the large particle size, resulting in wet bottom or wall hanging of the device.
In Lurgi-Thyssen dedusting system of steelmaking converter, the evaporative cooler represented a crucial operating unit, in which the hot dust-laden flue gas had to be cooled by saturation with water. The cooling process of the gas consisted of gas-liquid two phase flow and interphase heat and mass transfer. In this work, k-e standard equation and Lagrange discrete phase model were employed to describe the gas turbulent flow and the heat/mass transfer with droplet evaporation individually. The computational fluid dynamics(CFD) simulation for practical engineering project showed that the large-flux cooling gas was commonly constructed in a nonuniform flow caused by the sharp turnings at the inlet and outlet channels. The simulation results of the model were ingood agreement with the actual working condition parameters of the evaporative cooler. The relative error of flue gas outlet temperature was 3.1%, the simulation results were reliable. The smaller the size of atomized droplet was, the shorter the time was required to reach the critical evaporation temperature and complete evaporation. The droplet with a particle size of less than 300 μm could evaporate completely within 0.62 s. The main temperature drop of flue gas was within 3.5 m downstream of the nozzle. The heat transfer efficiency of droplet and high temperature flue gas was greatly affected by particle size distribution. The mean temperature of the same section corresponding of droplets with d50=340 μm and d50=95 μm can differ by 70 K. Using rosin-rammler distribution function to describe droplet size distribution, the effect of particle size distribution on the cooling efficiency of flue gas was studied. The droplet size should not be too large or too small. The particle size was too small to make a reasonable use of evaporative cooler space. The temperature of flue gas dropped unevenly and the droplet evaporation was incomplete due to the large particle size, resulting in wet bottom or wall hanging of the device.
引文
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[2]Wu J M,Huang X,Zhang H.Numerical investigation on the heat and mass transfer in a direct evaporative cooler[J].Applied Thermal Engineering,2009,29(1):195-201.
[3]冉景煜,张志荣.不同物性液滴在低温烟气中的蒸发特性数值研究[J].中国电机工程学报,2010,30(26):62-68.Ran J Y,Zhang Z R.Numerical study on evaporation characteristics of different substance droplet in low temperature flue gas[J].Proceedings of the CSEE,2010,30(26):62-68.
[4]黄小萍,钱付平,王来勇,等.转炉一次除尘新OG系统高效喷淋塔喷嘴雾化特性的数值模拟[J].过程工程学报,2018,18(3):461-468.Huang X P,Qian F P,Wang L Y,et al.Numerical simulation of atomization characteristics in high efficient spray tower nozzle of new OG system of the primary dedusting system for converter[J].The Chinese Journal of Process Engineering,2018,18(3):461-468.
[5]高继慧,陈国庆,高建民,等.半干法压力旋流式喷嘴雾化性能数值模拟[J].哈尔滨工业大学学报,2010,42(3):437-441.Gao J H,Chen G Q,Gao J M,et al.Numerical simulation on atomizing performance of pressure swirl nozzle for semi-drying FGD[J].Journal of Harbin Institute of Technology,2010,42(3):437-441.
[6]周正,吴畏,郑昕,等.喷嘴雾化特性及脱硫废水蒸发数值模拟[J].化工进展,2018,37(1):32-38.Zhou Z,Wu W,Zheng X,et al.Experimental research on spray characteristics of nozzle and numerical simulation of desulfurization wastewater evaporation[J].Chemical Industry and Engineering Progress,2018,37(1):32-38.
[7]Dushin V R,Kulchitskiy A V,Nerchenko V A,et al.Mathematical simulation for non-equilibrium droplet evaporation[J].Acta Astronautica,2008,63(11/12):1360-1371.
[8]辛娟娟,周致富,辛慧,等.单个液滴蒸发模型中不同质量传递公式的有效性分析[J].化工学报,2012,63(6):1704-1708.Xin J J,Zhou Z F,Xin H,et al.Validation analysis of different mass transfer formula in single droplet evaporation model[J].CIESCJournal,2012,63(6):1704-1708.
[9]Jiang Z Y,Chen P Y,Liu P,et al.Numerical simulation and structure optimization of converter gas evaporative cooler[C]//Proceedings of the ASME Heat Transfer Summer Conference.2013:V002T07A030.
[10]王聃.转炉煤气干法除尘喷淋系统实验研究[D].武汉:华中科技大学,2011:6-7.Wang R.Experimental study on converter dry dedusting cooler system[D].Wuhan:Huazhong University of Science and Technology,2011:6-7.
[11]袁文博,向晓东,石零,等.气液两相旋流喷嘴雾化特性[J].环境工程学报,2013,7(12):4891-4894.Yuan W B,Xiang X D,Shi L,et al.Atomization characteristics of gas-liquid two phase rotation flow spray nozzle[J].Chinese Journal of Environment Engineering,2013,7(12):4891-4894.
[12]Ochowiak M,Matuszak M,W?odarczak S,et al.The concept design and study of twin-fluid effervescent atomizer with air stone aerator[J].Chemical Engineering&Processing Process Intensification,2018,124:24-28.
[13]Ramamurthi K,Sarkar U K,Raghunandan B N.Performance characteristics of effervescent atomizer in different flow regimes[J].Atomization&Sprays,2009,19(1):41-56.
[14]Gadgil H P,Raghunandan B N.Some features of spray breakup in effervescent atomizers[J].Experiments in Fluids,2011,50(2):329-338.