Opening en inerted vessel


Inert conditions inside process equipment can be lost quickly when the equipment is opened. For example, opening the manhole cover of nitrogen blanketed vessel containing methanol can lead to a relatively fast ingress of air, because nitrogen-methanol vapour mixture is usually slightly lighter than air (see video below). Similar ingress of air occurs when opening a manhole cover of a vessel containing heavy flammable vapour, if the vessel is equipped with a column above manhole level, for example.

 

CFD model of opening an inerted vessel containing liquid methanol (showing the area above liquid surface). The legend on the right is a colour representation of the percentage of oxygen at the inner surface of the vessel. The green surface swirling inside the vessel represents the area with limiting oxygen content for inerting of methanol. The magenta surface outside of the vessel represents the area with concentration of the methanol vapour at lower explosive limit. Therefore, the volume of actual explosive mixture expands between green and magenta surfaces. Note that explosive mixture forms immediately in the area of the manhole and gradually fills the entire free volume of the vessel. Naturally, much more complicated geometries can be used as models for realistic situations. Video is time lapsed.