Abstract: The phenomenon of ammonium salt scaling and corrosion of high-pressure heat exchanger in the reaction system of a diesel hydrofining unit and its influence on the operation of the unit were introduced, the crystallization temperature of ammonium chloride determined by detailed calculation coincided with the operation data of the high-pressure heat exchanger, and then the scheme and implementation effect of online water washing were introduced, which can be used as a reference for the analysis and treatment of the scaling of ammonium salt in hydrofining unit.

Key words: high pressure heat exchanger, NH₄Cl crystallization, analysis of causes, washing after shut down