It is not common to have a depressurization system on the Coker gas plant. For systems that are in refineries that are close to residential communities, the possibility of a high-pressure leak with high concentrations of H2S could result in a toxic vapor cloud exposing off-site personnel to H2S at high concentrations. In a case such as this, it might be necessary to install a rapid depressurization system. Decreasing the pressure to ambient within 15 minutes would be a reasonable design parameter. The trays in the towers would have to be checked to make sure the depressurization rate did not exceed the maximum uplift the trays can withstand. The normal tray design as an uplift resistance of roughly 0.5 to 0.7 psi. Standard trays can be designed to provide an uplift resistance of 1 psi. These are somewhat dependent on the tower diameter. I think all the other internals in the gas plant should be able to withstand the rapid reduction in pressure without incident.
