Previously, I did not know about this thing called flash pyrolysis, which is what you get when MORE POWER is added.
This means, we can use an actual engine as the "reaction chamber."
First, swap out the starter motor for something designed for continuous operation.
Into the engine's intake manifold,
feed a carefully controlled mix of O2 and recirculated exhaust gas.
Wet mill the plastic with some recirculated pyrolysis oil, heat it if it's too viscous, and pump it through the engine's fuel injectors.
When the spark ignites it, just enough of the compressed gas burns to heat the liquid to a temperature of 1000C, which is hot enough for the plastic in the liquid to undergo "flash pyrolysis." Pyrolysis is an endothermic reaction, which cools down the gas, so less mechanical power is produced than if the plastic were absent.
Pass the stuff coming out the exhaust manifold through a cyclone to separate the gas from the liquid (oil). Some of that oil is used to wet mill the plastic, the rest is your main product. Some of that gas is recirculated into the intake, while the rest, a mix of valuable and valueless gasses, is your secondary product.
Both products need to be distilled, obviously.
Using air instead of O2 saves the cost of an O2 concentrator, but dilutes the output with worthless N2 and NOx.
As before, nothing prevents biomass from being used instead of plastic, except for the fact that the world has glut of plastic.
Soot needs to be removed from the generated liquid and gas, and possibly the cylinders. I'm hoping no halfbaker is silly enough to ruin a catalytic converter by not removing it.
Because flash pyrolysis is almost but not quite instant, the cyclone separator should be have enough volume to give the gas and liquid moving through it a dwell time of 0.2 seconds.
The throughput can be controlled by the speed of the electric motor we are using to spin the engine.