O’Donnell Consulting Engineers, Inc. performed a failure analysis, and design modifications of a contactor vessel. The vessel is part of a scrubber process used remove hydrogen sulfide from bio-gas and landfill gas. The vessel is fabricated from FRP (Fiber-Reinforced Plastic) designed to maximum internal pressure of 10 psig and maximum external pressure of 0.15 psig. The vessel had failed during startup and commissioning.
The Inlet Gas Scrubber is protected from over pressure by a relief valve (PRV). Since it appears that there are no isolation valves between the Inlet Gas Scrubber, Contactor and Outlet Gas Scrubber, all three vessels are somewhat protected by this single PRV. However, it is preferable for each vessel to have its own individual pressure relief valve vented directly to the atmosphere. According to the P&IDs reviewed, there was no vacuum relief device to protect the Contactor Vessel from excessive external pressure.
The contactor vessel failed as a result of excessive internal vacuum due to a process excursion.
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