system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't refineries reclaim their flare's energy to heat water or the distillation stack?
gpt
I worked at a refinery. And we did use hot exhaust from the refining process to fire a steam plant that powered a ~~10KW~~ 10MW co-generation plant that mostly powered the refinery with a small amount of sell-back to the power company.    
But that hot exhaust was a continuous part of the ongoing process, not temporary like a flare would be.   
As you may know, refineries are just big giant chemistry sets.    
One process feeds another process feeds another process and so on.   
If some part of the process fails, bad stuff can happen, vessels get over filled, or over pressurized, or under filled and under pressurized, or flammable and poisonous product gets spilled. The hard part about this is : a refinery + co-generation can't just start up and shut down with the push of a button. It takes days, sometimes weeks to do a proper start-up and days to do a shut down.   
So, what you have, for safety and efficiency, are those emergency flare stacks at various points in the process so that in the event of an "upset" in the process, the production flow has somewhere to go wile the process is either being fixed or shut down.   
The burn-off is so the material does not collect anywhere and form an explosive air/gas mixture.   
You can tell if a plant process is "upset" if you see flares when you drive by.    
It means something aint right up in there.   
Flares are supposed to be temporary in nature so there is no economic benefit to build co-generation for them.