Hi there,
You have a few options at this stage of the game:
- burn spoilage in your furnaces
- turn your spoilage into carbon (moderately more effecient than burning spoilage)
To obtain coal, you'll need to process it from carbon, which requires the Coal Synthesis tech. So one way or another, you'll need that carbon production. While in principle you could burn this coal, the process is net negative in energy production, so I don't recommend it. The coal you will be producing is also far better used in military science and explosive production instead.
Hope that helps
thanks
Jack