alt Hacker NewsDid you ever try to burn plastic?
1) Plastic is not liquid, so you can't pipe it to a gas or oil power plant. You may argue that coal isn't liquid either, but continue reading...
2) Burning plastic generates toxic fumes.
3) Plastic ash is sticky and very difficult to clean.
You might like to read about https://en.wikipedia.org/wiki/Incineration and https://en.wikipedia.org/wiki/Waste-to-energy_plant
It's a fascinating topic. There's even more problems than the ones you bring up, but engineers are also pretty smart.