Prediction of ammonium salt deposition in hydroprocessing air cooler tubes

Corrosion by wet ammonium salt is one of the main causes to the failure of reactor effluent air cooler (REAC) tubes. Based on a failure case, this paper presents the dynamic process of ammonium chloride (NH4Cl) deposition. A finite element method was used for the numerical simulation of the flow field, temperature field and concentration field to analysis this deposition process. The effect of velocity on ammonium salt deposition was also analyzed by the simulation. Based on the study, we suggest that the process of ammonium salt deposition may be affected by multi-physical field coupling. Higher temperature gradient exists between the fluid and the wall surface. As velocity increases, the amount of deposited salt reduces while the distance of the position with max amount to REAC inlet increases. Compared with actual failure instances, this method can be used effectively in predicting the relative severity of ammonium salt corrosion in REAC tubes.

► The process of ammonium salt deposition is affected by multi-physical field coupling.
► The simulated result was in good agreement with the actual failure instance.
► Increasing stream velocity will decrease the maximum concentration of NH4Cl salt.
► The failure position of hydroprocessing air cooler tube could be predicted effectively.