Busting process industry's myth no. 20: Ton for ton, toxic gases produce more fatalities than flammable gases or liquids

Abstract

Worst credible release cases were evaluated for a Loss of Process Containment situation in a Gas Oil Hydro-Treater Unit's (GOHTU's) recycle gas piping, just upstream of the amine absorber where lean amine would remove most of the H2S from the recycle gas.It was found that the mass flow rate of the release was greater than the design mass flow rate through the piping where the Loss of Process Containment occurred. This made, except for possibly a short transient condition, the release impossibly high. A relatively easy way of correcting the worst credible case was to use the centrifugal compressor's surge condition as sizing criterion for the worst credible release. As a general good practice one should closely examine releases from locations where the ratio of the release mass rate over the given process mass rate has a value of one or greater. This dimensionless number, m˙rel/m˙HMB≥1 (where HMB stands for Heat and Material Balance) can be used as an early screening criterion to find release scenarios that are candidates for refinement when needed. Because most hydrotreaters/crackers have a similar unit operations layout, the given example could be used as a generalized worst case limiting criterion for such units.