This talks about low caloric coals with high moisture clogging blast furnaces, which is why they need more expensive coking coal with high caloric content. Power plants can operate on low quality coal with high moisture so one would think that it should not be a problem. One only needs to heat water into steam while the other needs to be as hot as the sun, which is why agglomeration occurs due to sudden high temperatures. Lower quality coal has higher plasticity which can make it form into clumps.
Lower price of steel is dragging down coal prices. There is no economic sense for met coal to cost more than thermal coal for any long period of time. Met coal burns, and it burns well, I am sure it can be used to bring some water to boil. If I am right, then it would mean thermal prices will follow met prices and bring things back into order. It seems that power plants have not clued onto this, or, they may be stuck in existing contracts (most coal bought is locked into 1 year contracts) and cant make the switch.
On the flip side, you do have a point. Met and thermal coal burn different and boilers will be optimized for the way thermal burns. To use coke in power plants they would need to install a spreader stoker capable of burning Anthracite at its much higher ignition temperature and then replace it again to use thermal coal. This would be expensive and highly uneconomical despite the gap between coking coal prices and thermal prices. Thermal coal leaves behind clinkers which are great in cement production. Thermal power stations may have contracts with local cement factories to provide them with clinkers after burning at a set price, this would also be an incentive to continue burning thermal coal.
I have found blacksmith videos that are excellent at explaining how the two burn different and the residue that they leave as a result.
An excellent quote in the second video is that "coke is to coal what charcoal is to wood" basically, coke is the broken down and refined version of coal where all the impurities have been burned off. This makes sense since coke is a high grade of Anthracite which is the highest grade because it is the oldest and has spent the longest amount of time subject to the earths heat and pressure. Coke, interestingly is also much lighter than coal just as coal is lighter than wood which would justify its usually higher price per ton than thermal coal.
Coal miners also have a system in place to make sure coking coal is 24-40mm in particle size which is the optimal size for blast furnaces in steel production. Thermal coal on the other hand is much smaller at 106–75 µm per particle which produces the best results in terms of efficiency for boilers. Whether coking coal could even be usable at this small size is arguable due to its more brittle nature. Even if it was, the change in mine operations to produce smaller coke particles would no doubt add some logistical issues. Another option is to install a boiler that can handle higher particle sizes which as, mentioned earlier. would add further challenges and reduce efficiency and add huge costs to power stations, making it uneconomical.
After thinking about both sides I don't see coke as an option for boilers without extensive investment to reconfigure the power plant. In the course of writing this post I thought that coke would surely be suitable as a replacement thermal but then after some research I have learnt that the opposite is true.
Here is a link that explains very well why coking coal (Anthracite) is not used for steam boilers in power plants, also know as spreader stokers.
(20min delay)