[jsilence]

The CO2 expelled from the Calcium Carbonate is quite pure compared to CO2 from combustion which usually contains nitrous oxides. This makes it suitable for capture and liquification and thn for example as a gasous fertilizer in greenhouses. A heat exchanger can recuperate a good chunk of the residual heat and pipe that to the air intake for the gas burners that are used to heat the furnaces.

Not saying every cement plant is doing this. But it is possible and makes sense.

Focussing solar power to the furnace would eliminate a sensible usage of the residual heat within the process itself.