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.