加氢空冷器NH4Cl流动沉积特性数值模拟

摘要

针对失效频繁的加氢空冷系统,通过对NH4 Cl沉积过程的工艺关联分析,揭示了NH4 Cl颗粒的成因及沉积机理,基于Eulerian-Lagrange方法建立NH4 Cl沉积数理模型,模拟空冷器内多相流体系下NH4Cl颗粒沉积分布特性.结果表明:空冷器内气液相及平均流速分布波动较大,导致部分管束内NH4 Cl颗粒沉积加剧,颗粒沉积多集中在管箱两侧底部及两侧边缘管束入口附近;空冷器内铵盐沉积速率存在临界值,当多相流的流速大于3.0 m/s时,铵盐颗粒的沉积速率稳定在一个相对较低的范围内,而当其流速小于3.0 m/s时,颗粒的沉积速率将随着流速的降低而迅速升高;数值计算结果与失效案例的统计结果及红外测温仪的检测结果基本一致.%In a case study of air cooler system with frequent failures of a hydrogenation unit,the causes and deposition mechanisms of NH4Cl particles are revealed through the process correlation analysis of NH4Cl deposition.Based on Eulerian-Lagrange method,the mathematical model of flow deposition of NH4Cl particles is established,and the distribution nature of NH4Cl particles in multiphase flow is simulated in air cooler system.The results show that the distribution of gas-liquid phase and average flow velocity in the air cooler fluctuate greatly,which accelerates the deposition of NH4Cl particles in some tube bundles.The depositions of particles are concentrated near the bottom of the tube header and the inlet of the tube bundles on both sides.When the average flow velocity of the multiphase flow is higher than 3.0 m/s,the deposition rate of the NH4Cl particles is stable within a relatively low range,and when the flow velocity is lower than 3.0 m/s,the deposition rate of the particles will rapidly increase with the decreasing flow rate.The numerical calculation results are consistent with the statistical results of failure cases and infrared thermometer tests.