The performance of three-dimensional kiln chambers using recycled cement is studied using basic geometric and operational parameters. A comprehensive 3D-simulator is developed that includes separate yet coupled computational models for the bed and the freeboard regions. Complex swirling airflow is taken into account, considering solid phase combustion, gas-phase combustion of volatile fuel, and radiative heat transfer in the freeboard zone: Clinkerization reactions are included in the bed zone, assuming that the solid matter behaves as psendofluid. Appropriate terms are used to model CO2 transfer from the bed to the freeboard zone. Proper inclusion of an additional feed stream coming from mechanical separation of demolition waste matter is also considered. The predictions of the simulations are consistent with observations from literature data and industrial experience. The sensitivity of the clinker composition and temperature profiles to selected parameters is also studied, revealing significant effects of the inlet feed composition and the heat-transfer conditions.