Abstract: The failure cases of the E-104 tube bundles was analyzed and preliminarily judged that the system had corrosion under the ammonium salt scale. Then a simulation model of the reaction effluent system was established through software simulation. The risk of ammonium salt crystallization in the tube side and shell side of the failed heat exchanger was calculated. It was found that there was no risk of NH₄HS salt formation in the studied system. The ammonium salt crystallization temperature of the system increased slightly with the increase of the content of corrosive elements. The crystallization temperature of NH₄Cl in the hot high gas separation system in the original working condition and under new conditions were 177 ℃ and 181 ℃ respectively，and the NH₄Cl salt formation temperature of the cold low oil separation system were 178 ℃ and 182 ℃ respectively，which showed that under the original operating conditions，there was a risk of NH₄Cl crystallization in both the tube and shell side of E-104. Furthermore，the order of the factors affecting the crystallization temperature of NH₄Cl was determined as follows：content of Cl>content ofN >system gas flow rate>system operating pressure through the design of orthogonal experiments.What’s more，athree-dimensional map to predict the content change pattern was obtained，which will greatly improve the prediction efficiency of the NH4Cl salt temperature.

Key words: ammonium salt, ammonium chloride, cold low pressure separator oil, crystallization Temperature, orthogonal experiment