Causes of hydrogen sulfide corrosion in the three-stage Claus process
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Three-stage Claus process, with flue gases sent for incineration. During the initial testing, a large-scale leak was detected in the heat exchanger. Upon opening the heat exchanger, it was observed that there was a yellow-brown layer on the surface of the tube sheet, which fell off in large quantities upon contact. These issues are most evident in three units: the first process gas heater, the second process gas heater, and the third process gas heater. In all three heat exchangers, steam flows in the shell side, while the process gas flows in the tube side. The shell side operating temperature is 271°C, while the tube side temperature ranges from 160°C to 250°C. The tube sheet is made of 16MnR, and the heat exchange tubes are made of 20. Water is generated in the process gas stream of the acid gas combustion furnace, and a large amount of water is produced as a result of the Claus reaction. I wonder whether, at lower temperatures, the presence of water combines with hydrogen sulfide, resulting in hydrogen erosion? Is it hydrogen sulfide that directly corrodes the material in humid environments? Is it H2S-H2O corrosion? Can corrosion be prevented by increasing the operating temperature?
It is likely caused by sulfide stress corrosion. First of all, the presence of condensed water in the equipment can be ruled out; if there is any water, it should be present in the sulfur condenser earlier in the process. The reason might lie in the excessive hardness of the tube sheet or improper heat treatment. When selecting materials, for heating with medium-pressure steam, a combination of 0Cr18Ni9 and 20G could be considered, while for sulfur condensers, a combination of 20R and seamless steel pipes of grade 20 would be appropriate.
Any other good suggestions? Was no sulfur recovery done?