A blowdown stack is a chimney or vertical stack that is used to vent the pressure of components of a chemical, refinery or other process if there is a process problem or emergency. A blowdown stack can be used to complement a flare stack or as an alternative. The purpose is to prevent 'loss of containment' of volatile liquids and gases.
The failure of the blowdown stack to contain hydrocarbons vented from a raffinate splitter led to a catastrophic explosion at the Texas City Refinery (BP) in 2005.
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Blowdown stack Wikipedia(Text) CC BY-SA