Raw Coal is supplied to a CHPP so this is tonnes of coal from...

Raw Coal is supplied to a CHPP so this is tonnes of coal from the "PIT" Once the coal is processed through the CHPP, the rocks, clay and impurities are separated from the "product Coal" The "waste" / Rejects is then dumped on site typically back in an old pit. This reject is measured as a percentage waste, so if 20% of the processed coal is rejects, this will produce a yield of product coal of 80% which is a very good result. The lower the yield, the higher the reject / waste. There is also a factor of CSN and ash content results of product coal. Customers overseas will specify the ash and CSN properties of the coal they require for their furnaces etc.
Thermal coal is typically higher in ash content.