Gasification heats the waste with little or no oxygen in order to produce a chemical reaction. The waste does not burn rather the chemical reaction produces synthetic gases.
These can be burned to turn a turbine, which spins a generator and creates electricity.
As yet gasification technologies have ‘to reach an acceptable (positive) gross electric efficiency. The high efficiency of converting syngas to electric power is counteracted by significant power consumption in the waste preprocessing, the consumption of large amounts of pure oxygen (which is often used as gasification agent), and gas cleaning.”
Plastic can be regasified (?) along with all sorts of other products.