Corrosion in the desulfurization system! !

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The reboiler at the bottom of the regeneration tower in my plant’s desulfurization system has caused the desulfurization system to shut down on multiple occasions due to corrosion. Based on the multiple corrosion occurrences and related data analysis, a preliminary understanding of the corrosion of this equipment has been obtained. Here is a brief discussion on the issue of corrosion. Metal corrosion is classified by its mechanism into two types: chemical corrosion and electrochemical corrosion. Leakage at the bottom of the regeneration tower is a type of chemical corrosion, which results from a chemical reaction between the metal surface and the environmental medium. First: The amine liquid system at the bottom of the regeneration tower contains corrosive impurities such as H2S, CO2, dissolved oxygen, and chlorides. Secondly: it is caused by the operating temperature exceeding the decomposition temperature of the amine solution, which leads to the decomposition of the amine solution and the formation of acidic substances. There are 3 measures to control this corrosion: injecting a retardant ； Improve equipment material ； Improve equipment, structures, and construction methods. From the perspective of process adjustment, several measures should be taken: 1. The composition of the medium in the amine solution system should be analyzed regularly; simply replacing it through discharge is not sufficient. 2. Keep the ethanolamine concentration below 15%; an increase in decompression pressure leads to a rise in the temperature in the regeneration tower, which exacerbates corrosion. Therefore, a lower pressure range should be maintained, and the temperature of the fluid returning to the regeneration tower must be kept below 123°C. 3. After welding the equipment and pipelines of the desulfurization system, post-weld stress-relief heat treatment must be carried out. High-strength materials should be used with caution in those parts of the desulfurization system where pressure is concentrated. 4. Regularly analyze the iron ion concentration in the amine solution to enhance monitoring of the degree of corrosion progression. 5. In the acidic water system at the top of the regeneration tower, there is condensate water containing high concentrations of CL-. Although the pH value of this condensate water is above 9.0, there is a risk of stress corrosion cracking; therefore, stainless steel should be used with caution. It is best to use carbon steel with a retardant, or carbon steel lined with plastic material.