The mill I'm talking about actually burns straight wood products - mostly whole tree chips. Aside from a small amount of diesel used to get the fire in the boiler going when they startup, and a few additives like urea to tweak the emissions, it's all wood.
Black Liquor is interesting. Just down the road from my old plant, there is an International Paper mill that has been relying on that loophole for years to keep themselves afloat. All the mill's internal machinery is either steam-driven or runs on the electricity produced by their on-site plant. Lately they've been over-producing power and selling it back on the grid due to these credits, to the point that they have kept paper machines running at paper prices that would otherwise be unsustainable, just to keep a steady supply of black liquor for their power plant.
Black Liquor is interesting. Just down the road from my old plant, there is an International Paper mill that has been relying on that loophole for years to keep themselves afloat. All the mill's internal machinery is either steam-driven or runs on the electricity produced by their on-site plant. Lately they've been over-producing power and selling it back on the grid due to these credits, to the point that they have kept paper machines running at paper prices that would otherwise be unsustainable, just to keep a steady supply of black liquor for their power plant.