Computational fluid dynamics applied to a cement precalciner

This paper describes a study of the use of computational fluid dynamics (CF D) to investigate the performance of a precalciner vessel at a cement works . In this vessel, limestone, held in suspension, is calcined to calcium oxi de and the endothermic reaction is supported by the combustion of coal. Results are presented from a CFD model that contains all the essential feat ures of the precalciner as operated when burning coal. The model fully repr esents the reactions and fluid dynamics of the precalciner. Previously unid entified features are illustrated. Certain key features at points in the pr ecalciner, where some limited measurements can be made, are compared with t he parameters indicated by the computational model. The measurements are co nsistent with the results calculated by the model indicating fair validatio n. The CFD data show the following: 1. The gases undergo distinct recirculation. 2. The coal particles entering at one inlet have significantly different tr ajectories and temperature histories from those entering at the second diam etrically opposed inlet. 3. There is 90 per cent completion of coal combustion at the exit. 4. 73 per cent limestone in the raw meal is calcined to calcium oxide at th e exit from the precalciner. 5. The highest reaction rate of the raw meal is closer to one side of the v essel due to interaction with the gas flows. Future work is proposed which, firstly, will provide further validation of the results so far attained by selective measurements on the precalciner an d, secondly, will model the combustion and aerodynamic behaviour of waste-d erived fuels in the precalciner vessel, commencing with shredded car tyre c hips.