Energy costs and environmental standards encouraged cement manufacturers world-wide to evaluate to what extent conventional fuels can be replaced by alternative fuels, i.e., processed waste materials. Clinker burning is well suited for various alternative fuels. In order select a suitable alternative fuel, a commercial modelling tool (ASPEN PLUS (R)) is used to model the four-stage pre-heater kiln system of a full-scale cement plant (clinker production similar to2900 tons/day), using petcoke as fuel. The goal is to optimise process control and alternative fuel consumption, while maintaining clinker product quality. Calculations with varying amounts of different fuels are compared with a reference case. The dependence of process performance on the amount of combustion air is clearly demonstrated and the energy demand of the process could be predicted for varying fuel mixes. (C) 2003 Elsevier B.V. All rights reserved.