The raw meal is continuously fed into the rotary kiln via cyclone pre-heaters and feed hoppers. The material is transported towards the burner from the inlet to the outlet side utilising a slight incline and rotation. At temperatures of 1250°C to 1450°C in the rotary kiln, the raw meal is fired to cement clinker and cooled with air in the clinker cooler on the outlet side. The heated cooling air is then supplied to the rotary kiln as secondary air. Meanwhile the combustion exhaust gases flow counter current towards the inlet of the rotary kiln and are used in the calciner (cyclone preheater) for drying and calcination. Optionally, some of the heated cooling air is also used for the burners in the pre-calciner as tertiary air. The heat in the rotary tube is generated by the direct energy input from a multi-fuel burner. Various fuels can be fired at the same time.