petroleum refining- what are those stacks with the flames at the top

[jz78817]

In the downriver Detroit metro area, there are several oil refineries which I drive past fairly regularly. There’s always at least several fairly tall and skinny chimneys/stacks which have flames burning at the top. What are they burning off? If it’s a combustible/flammable gas, wouldn’t it be something better captured and used rather than just making a giant metal candle?

[coremelt]

Gas flare

On oil production rigs, in refineries and chemical plants, its primary purpose is to act as a safety device to protect vessels or pipes from over-pressuring due to unplanned upsets.
Flare gas recovery systems are occasionally used to collect low flows of waste gas and return it to the Process Plant as opposed to burning the gas

[dzero]

Thanks. Bonus: I love learning new technical jargon.

[Sailboat]

Here’s the sort of thing that safety device is intended to prevent:

Texas City Refinery Explosion

Specifically:

@Wikipedia

The particular type of disposal system serving the raffinate tower was a blowdown drum with an atmospheric vent stack, rather than an inherently safer and more environmentally sound knock-out tank and flare system.

Note that BP itself was aware of the need to install a flare system:

During 2002 [the explosion occurred in 2005], BP’s Clean Streams project proposed converting the blowdown drum to a flare knock-out tank, and routing discharges to a flare. When it was found that a needed relief study of the ISOM system had not been completed due to budget constraints, the Clean Streams project proposed adding a wet/dry system to the ISOM instead.

15 people were killed and 170 injured in the explosion and subsequent fire.