渣油加氢空气冷却器NH_(4)Cl结晶影响因素分析及沉积特性预测研究

渣油加氢装置因原料劣化腐蚀性强,设备长期处于极端运行工况下,导致冷换设备铵盐腐蚀性风险大。以沸腾床渣油加氢系统空气冷却器(简称空冷器)为研究对象,采用NRTL-RK模型构建多组分体系下反应流出物系统化学离子-平衡模型,并通过工艺过程关联分析和数值模拟分析相结合的方式,对系统内铵盐结晶腐蚀风险进行评估。计算结果表明,空冷器存在NH 4Cl腐蚀风险,结晶温度为169~187℃,且铵盐结晶速率随着温度降低不断增加,极限工况下为0.22 kg h。空冷器对流换热模型通过组分运输方程和冷凝模型构建,数值模拟结果表明,随着流动的持续,最大的传质系数(1.52×10^(-4)m s)和腐蚀速率(0.43 mm a)出现在出口集合管底部。

Simulation of Gas Oil Hydrotreater Heat Exchange Tube and Crystallization Prediction of NH_(4)Cl by Thermodynamic Equilibrium

The hydrotreater system heat exchanger is one of the main pieces of heat exchange equipment in petrochemical enterprises.In recent years,oil resources have shown a deterioration trend of high sulfur and high acid content,with corrosion risk being prominent in oil processing.Taking the multi-medium flow corrosion risk of the hydrotreater heat exchanger pipeline in a petrochemical enterprise as the research object,based on the parameter characteristics of corrosive NH_(3) and HCl media under a high-temperature and high-pressure environment,the ammonium salt crystallization and deposition mechanism under multi-phase flow is revealed.The thermodynamic equilibrium curve is modified based on the thermodynamic principle and fugacity coefficient variation,and the prediction model of ammonium chloride crystallization in hydrotreater heat exchanger under high temperature and high pressure is constructed according to the modification.This study uses the mixture model,the flow-thermal coupling method,and the discrete phase model method to carry out the numerical simulation of multiphase flow and the numerical prediction of particle distribution characteristics in the heat exchanger pipeline of the hydrotreater heat exchange equipment,so as to realize the quantitative prediction of the particle crystallization deposition distribution in the pipeline.The results show that with the decrease of temperature,the crystallization occurs first on both sides of the center of the tube bundle,and more crystallization occurs in the lower half of the U-shaped tube,which may seriously lead to problems such as pipe blockage and under-deposit corrosion.

Experimental and Numerical Investigation on Erosion Corrosion of the Air Cooler Tube Bundle in a Residue Hydrotreating Unit

Corrosion leakage occurred in the 14th tube bundle in the first row of a residual oil hydrotreating air cooler after operating for two years.The failure location was 0.5 m from the outlet header box.In this paper,the erosion corrosion of the air cooler tube bundle was investigated by experimental and numerical methods.Visual inspection,scanning electron microscopy(SEM),and X-ray diffraction(XRD)experiments were performed,and the failure morphology and material composition confirmed that the damage was caused by erosion corrosion.The shear stress transport k–ωturbulence model(SST-k–ω)was then used to investigate the flow and erosion corrosion characteristics,combined with mass transfer,corrosion rate,and ionization equilibrium models.The numerical simulation results revealed that the water phase volume fraction increased with flow and heat transfer in the fluid,which increased the mass flow rate and concentration of hydrogen sulfide.The mass transfer coefficient and corrosion rate were proposed as important parameters to characterize erosion corrosion.Moreover,the local concentration of wall shear stress was found to increase the risk of erosion corrosion.The predicted high-risk area was consistent with the actual failure area,which verified that this failure incident was attributable to erosion corrosion by the water phase.