​​What’s that Flame at the top of a Oil Refinery?

During the day-to-day operations of a working refinery, by-products created in the process are collected and routed to recovery tanks for further processing where they are converted into gasoline, diesel, jet fuel and other products. If abnormal conditions occur (such as a power failure, an equipment malfunction or a vessel overpressure), some gases are rerouted to the flare system to be safely combusted, instead of being emitted directly into the air.  
Refinery personnel are constantly monitoring the flare system from an on-site control room.
Rarely, you might see black smoke coming from the flare. That happens when there’s not enough steam available to burn all the hydrocarbons; after a short delay the site personnel adjust the steam as necessary to optimize the combustion process.
People may also notice a rumbling sound coming from the flare. The sound is created by the mixing of vapours, air and steam during the process.