A properly sized pressure relief vent is just one step in mitigating the consequences from a process upset such as a runaway chemical reaction, fire exposure, or other scenario. Safety and environmental concerns motivate appropriate design of downstream effluent handling equipment, be it a catch tank, separator, quench tank, or other system. Aspects to consider are the extent of two phase flow in the discharge, reaction forces on discharge piping, chemical compatibility with possible quench or scrubbing fluids. Fauske & Associates has the experience to support emergency relief system (ERS) design from start to finish, from hazard identification and calorimetry testing all the way through vent sizing and effluent handling.
In sizing pressure relief devices for reactive chemicals, knockout tanks may not be sized correctly to accommodate effluent handling. Quantifying reaction rates and the resulting flow regime from an upset scenario is the first step. Then, relief devices and piping can be sized. Then knockout tanks (used to separate liquid from vapor in a two-phase relief situation) are important and we notice that some customers use inadequately sized tanks for upset conditions - either by habit, assumptions or equipment limitation. (A knockout tank that is the same size as a reactor or storage tank is often incapable of effectively serving its purpose. As a rule of thumb for reactive upset scenarios, knockout tanks typically need to be 2 to 4 times the volume of the process vessel that is expected to relieve into it.) These are just some examples.
