system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 : why is there a tower with a burning flame at the top of it in every petrol plant ?
gpt
Usually when oil is extracted, there comes with it a crapload of water and natural gas. The fluids go into a vessel called a separator which, you guessed it, separates the oil, water and gas. 

The water is taken aside and usually pumped back into the ground or purified and used for other purposes. The oil heads to a fractional distillation column. The gas that is left behind is usually not pure enough to make it worth purifying, compressing and storing/selling. So what do you do with all this flammable-but-not-pure natural gas?

In some plants they use it to feed the boilers that power the plant itself or provide other functions. But sometimes they cant do this or the amount of gas produced is just so high that the boilers cant use it all. In those cases, the most economical thing to do is to just burn it. As pointed out before, the carbon dioxide has a lower impact on the environment than the methane otherwise would.