Problem No. 46: CO₂ cooler failure

CO₂ coolers in the inter stages of CO₂ compressors typically cool down the CO₂ stream by means of cooling water. It is preferable for the cooling water through the tubes to have a minimum velocity to avoid fouling and corrosion issues. This is not a problem after the first and second stage when CO₂ pressures are still relatively low. However, after the third stage the CO₂ pressure is about 10 bar, too high (meaning too expensive) to have the CO₂ on the shell side. Vendors specify coolers with the cooling water on the shell side and the CO₂ through the tubes. This however introduces several failure mechanisms: As cooling water velocities cannot be guaranteed to be above a minimum value in the complete shell, fouling can occur. Also, chlorides accumulate (even when chloride levels are relatively low) and cause chloride stress corrosion cracking in austenitic stainless-steel tubes. In this type of cooler choosing duplex as the material of construction for the tubes is the best choice for a reliable heat exchanger.

Irfan Rashid, working in Operations at FFBL in Pakistan starts the discussion with the following question: Does anyone have experience of CO₂ cooler failure where failure occurs after the third stage of the CO₂ compressor?