Study on the corrosion mechanism of ammonium salt crystallization in waste heat boiler of a sulphur recovery unit
The waste heat boiler of a company's sulphur recovery unit encountered a wide range of crystallization phenomenon during operation,causing serious problems to the unit such as flow channel deposition blockage and equipment corrosion and leakage.This study focused on the corrosion mechanism of crystallization on equipment.The microstructure,elemental distribution and phase composition of the crystalline samples were determined using scanning electron microscope(SEM),energy spectrometry(EDS)and X-ray diffractometer(XRD),respectively.The results show that the microstructures of the crystalline samples exhibit both smooth and dense and rough and porous morphologies,with grain sizes in the range of 20~50 μm.The elements contained are mainly N,O,S,Fe and C,in which the Fe content on the bottom surface of the crystalline samples in the column tubes of the waste heat boiler reaches 35%,indicating that the deposited crystals have a strong corrosive effect on the equipment.The main phases of the crystallites are ammonium salts such as NH4HSO4,(NH4)2SO4 and(NH4)3H(SO4)2.The NH3 contained in the tail gas of sulphur production is the root cause for the formation of the crystallites.In addition,the corrosion processes in different regions were described in detail.It provides reference for the research and solution of similar problems in the device.