Annealed coal

What if coal becomes particularly easy to molecularly shake apart if it is non-combustively heat treated, reverse cyogenically-hardened in a sense? You would get more joules/second out of lesser grades of coal, improving efficiency, or reducing combustion chamber size for higher output.

This is the opposite of cryogenically treating organic polymers (published are hardwood and bamboo [link]) to make them tougher; warming coal to noncombustion temperatures for 5-24 hours may make the coal particularly flammable. The possible % gain in joules/second is as far as I know unresearched, but if if coal becomes 9-27% "less tough" to combust then entirely new kinds of coal fueled power plants could be developed.

Also, they could do a stepwise examination of pollution produced by coal treated from -170C to +227, at 1 degree intervals to see if any of the temperature pre-treatments have a "least pollution" producing profile. It's possible that cryogenically treated coal is anthracite-ish even though it is a less carbonaceous coal.

Now, if warming coal (annealing) to +220-227 causes efficiency gains, it seems like just storing the coal next to the smokestack could produce this degree of warming. Although possibly otherwise at cogeneration applications, and thermoelectric electricity generation, which might be more efficient uses of the 220-227C warmth.

Solar thermal treatment of coal is also a possibility (cofocal mirrors on outdoor coal transport channels) at some weather pattern locations.

If, conversely, cryogenic treatment of coal is beneficial, either from an efficiency (imitation anthracite joules/second even with less carbon) or pollution perspective, the cheapest refrigeration I am aware of is ammonia freeezers. and a 2020 published value is -80 F.

The thing about freeze-treating coal is that, obviously shorter freezer durations are more energy efficient, but, then again, once it is only at -80F, perhaps you can leave it at that for 240 hours instead of 5-24 hours (established "give it a day" cryogenic treatment practice) but for 240 hours (an order of magnitude more freezer time to make up for the cheap, comparatively warmer -80F ammonia freezing).

It's unclear from the internet thing I read, but ammonia alone refrigeration may reach -120 C or better

And, just as an aside, treating coal with cryogenic freezing has a winter advantage; Even just doing it in Northern Hemisphere cold weather season could start the the refrigeration process at outdoor winter temperature of 0C. Freezing from that is cheaper than 28C summers.