Complex sentence: Some thought has been to include municipal waste when being co-fired with other supporting fuel in cement kilns to provide extra BTUs but this has proved to be expensive due to pollution controls and process-equipment fouling.
Split into simpler sentences: Some thought has been to include municipal waste when being co-fired with other supporting fuel in cement kilns to provide extra BTUs. However, this has proved to be expensive, due to pollution controls and process-equipment fouling.