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Corrosion study in the Ethane purification plant of the petrochemical complex El Tablazo Pequiven

Abstract:

Since 1997, frequent shutdowns have been forced in the amine unit of the ethane purification plant of Pequiven, in which diethanolamine (DEA) is used as solvent. The shutdowns were mainly caused by corrosion problems in the bank tubes of reboiler E-103. Financially, a production cancelled because of a 4-day shutdown to replace the bank tubes amounts higher than MMUS$ 1. After various laboratory and field studies, recurring perforations and leaks were detected in tubes of reboiler bank tubes, caused by tris-hidro-xi-etil-etilen-diamine (THEED) corrosion, corrosion-erosion and CO2 pittings generated from hot spot formation, preferential CO2 stripping, DEA formation and reaction, and its degradation products. Damages have been caused by unproper operational practice without analysis of degradation products, and flow hydraulic restriction to reboiler. Using process simulation tools, it has been determined that current gas sweetening conditions using DEA constitute a barrier to diminish corrosion in the amine unit, and an obstacle to improve the gas volume treatment capacity in plant. Several valid options were analyzed to improve service efficiency. Evaluation matrix applied included selection of new amine, criteria of technical-economic analysis, and weigh of variables in function of the maximum operating efficiency of plant. After the analysis, a MDEA-based amine was found to be the best option to guarantee minimum corrosion, and maximum capacity of gas treatment in the ethane purification plant.