Blowdown is the controlled removal, safe flow and disposal of vapour from a pressure vessel.
It is also undertaken in a plant emergency situation to remove and dispose of hazardous material to mitigate the possibility of incident escalation.
A restriction orifice plate downstream of the BDV ensures the vessel is blowndown in an appropriate time period.
For refinery and associated oil and gas systems the requirement is to reduce the pressure to 100 psig (6.9 barg) in 15 minutes.
[2] The failure of the blowdown stack to contain hydrocarbons vented from a raffinate splitter led to the catastrophic Texas City refinery explosion in 2005.