https://en.m.wikipedia.org/wiki/Gas_flare
These are used for a number of things, from burning off ‘waste’ gases to converting methane to CO2 thus significantly reducing environmental impact. The purpose and frequency of use are dependant on the process(es) they’re associated with, so the ones you’re looking at could have any number of purposes. Most likely, it’s to burn off excess natural gas or relieve pressure from another part of the process.
Source: Environmental stack tester in U.S.
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