I was in the Electric industry for 37 years and followed this technology.
It never was successful. And if they knew how it was done, the Greens wouldn't like it anyway.
The plastic must be burned with coal. It never worked when burned by itself. They also don't use much plastic, less than 5% of the fuel burned is plastic.
The EPA drastically changed the way coal power plants are designed and operated. The EPA has demanded basically stack emmisions that are nothing more that CO2, water vapor, NOX and low particulates (minimal ash or soot).
To get soot free low emissions stack gases the operator has to have a nearly uniform fuel mixture day after day.
Because plastic is made with long chained carbon and the formulas very widely from product to product that is impossible. With thousands of different plastics in the consumer market and millions of empty containers filling trash bins every day the make up of those bins vary widely.
Then there is the coal fired power plant's emissions control equipment vary a lot.
I met a very rich man about 30 years ago that had worked for the same company as me had been the company's emissions control expert.
After retiring (early) he started a company that blended coal for power plants to work specifically with their pollution control systems to minimize emissions. He would chose for them a mix of hard and soft coal and where it was from to get the lowest ash and NOX emissions and have the least impact on their systems.
He made millions.
The way that plastic burn is unpredictable because the mix can't be formulated.
Probably the biggest problem with burning plastic is the ash production which is obvious to anyone who has ever burned a plastic bottle in a fire. The thick black ash that is produced is obvious.
That ash in a power plant coat the tubes that boil the water in the plant to produce steam. The ash insulates the tubes making the plant inefficient.
The plants that burn plastic waste never make a profit and require frequent maintenance outages.
These trash burners never got past the prototype plant stage that I know of, due to high cost of operation and low availability. They also could never get the emissions to the point where an EPA permit was even a dream.
And if they knew how it was done, the Greens wouldn't like it anyway.
Guess who funds them? Hence the post to which you responded. My take on what you said here (and thank you for it as the details about coal I did not know) is that burning it is better than trying to recycle it. Nothing is perfect. BTW, are you telling me that burning it with natural gas was never attempted or that it was not as successful? From a technical perspective, I don't know why it would be, albeit it might cost more.