关键词: 乙烯装置, 裂解气, 压缩机, 段间冷却器, 腐蚀, 硫化氢, 结焦, 相变

Abstract:

The outer walls of the E-3113 and E-3114 intercoolers in the compression unit of the ethylene plant had suffered severe corrosion, affecting the long-term and safe operation of the unit. Macroscopic corrosion inspection, chemical composition analysis, metallographic structure analysis, and corrosion product analysis were used to conduct corrosion monitoring and analysis on the interstage cooler tube bundle. The results showed that there was more coking at the inlet of the tube bundle, and local corrosion pits on the surface of the tube bundle were connected in sheets, resulting in corrosive thickness reductionof the tube bundle. The main reason for the corrosion of the interstage coolers tube bundle was acid corrosion, mainly caused by wet hydrogen sulfide. The partial pressure of the corrosive medium, surface coking of the tube bundle, and dew point corrosion in the phase change zone jointly promoted the corrosion of the tube bundle. A process anti-corrosion measure was taken by adding a neutralizing corrosion inhibitor before the inlet of the shell side of the first to fourth interstage coolers. The results showed that the average pH value of the condensate in the intercooler system increased from 5.23 before the measure was taken to 7.91 after the measure was taken, and remained stable at 7.0～9.0. The concentration of iron ions was less than 1.0 mg/L, and the acidic corrosive medium in the system was neutralized, slowing down corrosion. In addition, the eddy current inspection results of the tube bundle showed that 92% of the heat exchange tubes had no significant wall thickness reduction, and there has been no corrosion leakage of the tube bundle since it was put into use in 2019, indicating a good anti-corrosion effect of the system process.

Key words: ethylene plant, cracking gas, compressor, interstage cooler, corrosion, hydrogen sulfide, coking, phase transition