the way it was explained to me is if you see the flares then something is wrong. It may not be catastrophic or anything serious but something isn't going according to plan. Because you're right, why burn it off when you can sell it?

It generally means something is out of balance, which doesn't necessarily mean something is wrong. Usually not.

But if something is wrong, yea you can bet they will be burning off with big flares.

It's usually a small amount of waste, and handling gas is very different from distillate.

You'd need to either liquify that gas or collect it to a pipeline in order to make it useful. I remember reading that modern refineries make use of the gases instead of flaring them though I'm not sure how.

Usually, when refineries flare something like that it's because what they are burning is not suitable for use, and making it suitable would cost more than the product would sell for.

Often methane as a by-product of oil production is flared, because the amount is small enough that it's not worth setting up processing plants and supply chains for. Other times, the fluid is heavily contaminated by e.g. sulfur compounds, and would be costly to purify. Still other times the production of the fluid is unreliable or intermittent, and cannot sustain a continuous production process.

Although, flare gas recovery systems exist nowadays to make use of these waste gases, commonly for local power production for the refinery itself.

That's why plastic bags are so cheap -- ethanol is a byproduct, but you earn more if you discard it and sell only oil.

But the burned up ethanol would be perfectly suitable for products.

Nowadays there are some regulations to prevent that, so they may sell up ethanol at negative prices sometimes.

UPDATE: Ethene, not ethanol.

You wrote ethanol (C₂H₆O), but do you mean ethylene/ethene (C₂H₄)? Polyethylene (PE) is a very common plastic, such as HDPE, LDPE, PET.

You're right, sorry, I thought of ethene.

Like here is a good review https://youtu.be/325HdQe4WM4

Yea while $ viability is true, it's better to think of as

1) using some potentially useful products as fuel to burning off things you don't want and

2) the buffer to keep non-steady inflows in a suitable ready condition for steady-state processing. (When real world steady-state is less than ideal.)

Number 2 is really what dominates the equation, as shutting in gas sources or even just turning off pipelines is incredibly more complicated than just an 'off' switch.

And turning back on is even more complicated. In the case of wells, once you shut in, turning back on may never result in the same level of production as before.

There are large storage facilities for natural gas (underground, often in depleted gas fields or solution mined from salt formations) that buffer changes in consumption. These enable pipelines to operate efficiently even when demand is going up and down with the seasons.

> Although, flare gas recovery systems exist nowadays to make use of these waste gases, commonly for local power production for the refinery itself.

Cogeneration like that is huge. When PURPA was passed in 1978 requiring utilities to buy cogenerated power it was a major reason for the end of the first wave of nuclear power plant construction in the US.

They flare to quickly burn off excess gases as a safety mechanism rather than anything else. Venting gas into the air would be much worse.

Can't that burning be converted into energy like boiling water to turn a turbine to generate energy? Or not worth the payoff?

One place where gas is flared off is landfills. Methane is produced by anaerobic decay and must be burned to reduce its climate impact.

One unfortunate consequence of this is bird injury, particularly raptors. They like to perch on the flare stack, and when it flares to life... if they are lucky, only their feathers are damaged and they can be rehabbed. This can probably be ameliorated by design of the stack to avoid perching, but that isn't always done.

I know biogas digesters exist, but I am unfamiliar with the economics of such systems. It seems like a better way to deal with the methane than flaring it off, but cheap natural gas in the US might make it uneconomical to do so. I’d be curious if anyone has any insight into that.

People have looked at microturbines to burn landfill gas. It's not something one could just put into a natural gas pipeline as it's about 1/2 CO2. Even in microturbines it requires cleanup because of cosmetics. In a landfill, cosmetics decay to produce volatile organosilicon compounds, and when these burn they deposit silicon dioxide slag on turbine components.

Renewable natural gas / bio gas is alive and growing in the US. The economics are supported by California Low Carbon Fuel Standard credits.

Sources include captured landfill gas and bio digesters processing animal manure.

Captured bio gas is injected into adjacent natural gas transmission pipe lines and commingled with chemically identical fossil natural gas.

The CO2 has to be scrubbed out. This is not necessarily all negative, since if the CO2 is injected underground for sequestration it makes biogas carbon negative.