Co-utilisation of Coal and Other Fuels in Cement Kilns
AUTHOR: Irene Smith
DATE: September 2003
Processes and fuels used to produce cement clinker are characterised prior to a summary of regional trends in cement production. Coal, fuel oil, natural gas, and petroleum cokes are used as main fuels. Secondary or alternative fuels include scrap tyres, various solid and liquid wastes, plastics and many biomass fuels, such as wood waste, sewage sludge, animal meal and fat. Handling practices for these fuels, including metering and feeding, are discussed. Processes within the kiln system are investigated, including operating conditions required to maintain stability when using different fuels. A general background is provided on legislation and control technology for greenhouse gas, NOx, SO2, particulate, trace element and organic emissions in the cement industry. Any effects attributable to co-utilisation of coal with other or alternative fuels are then reviewed. There are no technical constraints to substituting coal by an appropriate mix of alternative fuels as long as permits are obtained. The process ensures the necessary conditions for mineralisation of the clinker and product quality is not affected. Waste derived fuels reduce CO2 and NOx emissions in most cases. Their use has not increased emissions of hazardous air pollutants and the content of these substances in the fuel may be reduced by an appropriate balance of raw materials.