That could be some poor soul’s retirement grease.
You can heat your home with used cooking oil or used motor oil.
A wood burning furnace can be hooked up with an oil dripper that doesn't burn the wood unless the oil drip stops, the wood works as a wick as long as the oil is dripping on it.
I know of several auto repair shops that use them for heat.
They have a “Recycle your used oil here” sign out front, but the only recycling that get done is them burning it for heat in winter.