[sushibowl]

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.

[deepsun]

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.

[nayuki]

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

[deepsun]

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

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

[beerandt]

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.

[pfdietz]

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.

[pfdietz]

> 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.