We are already separating out the majority elements from air via ASU plants, so we should compare the abundance of helium in what is left from typical extraction. And that looks quite technically viable, if obviously uneconomic at present.
We are already separating out the majority elements from air via ASU plants, so we should compare the abundance of helium in what is left from typical extraction. And that looks quite technically viable, if obviously uneconomic at present.
This is a very good point.
Oxygen, nitrogen, CO2 and argon make up 99.94% of the atmosphere. The remaining 0.06% has 5ppm is nearly 1% helium. That's up 200x from the original concentration and is well above the 0.3% that is sometimes quoted as the limit for economic extraction of helium (and well below the 7% of some natural gas).
Furthermore, the leftover gas is also already cold. It is absolutely true that 85K isn't very close to the boiling point of helium, it is a lot closer than starting at the temperature of gas at the well head.
The gotcha is almost certainly going to be that an ASU probably doesn't liquify most of the gas it takes in. That means that the exhaust gas will only be slightly enhanced.