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.

Analysis and Prediction of Corrosion Risk in Atmospheric Distillation Tower Overhead System

In order to optimize the atmospheric tower overhead low-temperature system,the physical parameters,multiphase composition,aqueous dew point temperature,and ammonium salt crystallization temperature are simulated with process simulation software.The temperature distribution in overhead heat exchanger is calculated by heat transfer calculation.The special parts with elbows near the inlet and outlet of heat exchanger are studied by fluid field analysis.Results indicate that under current operating conditions,the aqueous dew point temperature and initial crystallization temperature of NH4Cl are 91°C and 128°C,respectively.Ammonium salt appears in the distillation tower and liquid water occurs in heat exchanger tubes,in which the dew point induced corrosion is the most direct factor for heat exchanger corrosion.In the heat exchanger,condensate water appearing in the area 2.7 meters away from the bundle inlet can give rise to corrosion risk under the moist NH4Cl and high concentration of acidic solution circumstance.For the pipes and elbows located near the inlet and the outlet of heat exchanger,the flow field presents an unsymmetrical distribution.High risk areas are mainly concentrated on the external bend of elbows where the liquid water concentration is higher.The coupling of simulation methods established thereby is approved as an effective way to evaluate the corrosion risk in the atmospheric column overhead system and can provide a scientific basis for corrosion control.