Mitigation of the ammonium salts corrosion in overhead condensing system of crude tower

Key words:  ammonium salt  NH₄Cl deposition point  deliquesce point  water dew point

Abstract:

The overhead condensing systems of crude tower was taken as the research object. And the thermodynamic simulation of the oil and gas in the overhead was conducted using Aspen Plus, through which the deposition and deliquescence temperatures of NH₄Cl salt were predicted, and the conditions of NH₄Cl corrosion were determined. The vapor pressures of the saturated NH₄Cl solution were calculated by Aspen Plus, and the calculated values were modified with the vapor pressure data of NH₄Cl solution derived from literatures, through which a relationship between the deliquesce relative humidity (f_DRH) of NH₄Cl and temperature (T)was obtained. It is found that there is a linear correlation between f_DRH and T, which is f_DRH=-0.200 07T+82.708. The calculated salt point, deliquesce point and water dew point in the overhead condensing systems of crude tower are 116℃, 104℃ and 96℃, respectively. The sensitive area of NH₄Cl deposition temperature is from 104℃ to 116℃. The sensitive area of NH₄Cl under-deposit corrosion is between 104℃ and 96℃. When the concentration of NH₃ is higher than 5 mg/L, the tower overhead system has NH₄Cl salt deliquescence risk. The controlling of HCl and NH₃ pressure reduces NH₄Cl salts corrosion failures.