Cement plants are an essential part of Europe’s industrial landscape and are increasingly important partners in innovative waste management solutions, called co-processing. Co-processing waste in this way consists of using both the calorific potential to heat the kiln and the material component from the fuel ash as a raw material, thereby reducing our requirement for natural resources.
Many different types of industrial by-products, waste and biomass can be used as fuel in a cement kiln, including refused derived fuel, waste oil, waste wood, sewage sludge, waste tyres, plastics, bone meal, solvents and impregnated sawdust. Once the calorific potential of this waste has been recovered, what is left over (i.e. ashes) will be bound in the clinker during the burning process, and thus used as a raw material to produce cement. This cannot be done in an arbitrary way however, as the chemical composition of the fuel ash must fit the overall raw meal composition. Therefore a good knowledge of the calorific and chemical composition of any fuel used in cement production is mandatory.
The use of waste materials and by-products offers a win-win-win situation. The cement sector helps other industries or municipalities dispose of their waste and, in exchange, gains access to cost-effective fuel sources or raw materials. Moreover, co-processing decreases dependency on fossil fuels, reduces the need for quarrying, and prevents waste ending up in landfill. It also has a direct impact on lowering CO2 emissions, since it reduces the quantity of natural raw materials needed for clinker production.
Co-processing in Europe varies from country to country because of different national regulations and/or waste management practices or local markets specificities. Acceptance by local authorities and communities or the vested interests of other economic actors can reduce the uptake of waste materials by the cement industry. Use of alternative resources in certain European countries is low and there is a clear potential for increased co-processing to benefit the environment, industry and society.
Co-processing offers a solution to use both waste and industrial by-products in a way that maximises their potential, i.e. by extracting the energy potential and using what remains as a raw material. Co-processing is effective because it is based on sound principles.
Part of the clinker used in certain types of cement can be replaced with alternative materials. Two main examples are granulated blastfurnace slag, a by-product of the steel manufacturing process, and fly ash, one of the materials resulting from the combustion of coal in traditional coal fired power plants.
The use of these by-products in cement production is not new; it has been common practice for decades and has led to several innovative cement types sometimes with different and beneficial characteristics. By using these products in cement manufacturing, millions of tonnes of alternative raw materials are put to good use, do not end up in landfill sites, reduce the need for virgin raw materials and lower the CO2 content of the resulting cement
Cement manufacturing is a volume business and the volumes of waste and by-products used are important. In 2010, the European cement industry recovered or recycled:
Using waste or industrial by-products in cement plants also makes sense from a financial point of view for local or regional governments because these materials are recovered using existing infrastructure without the cost of building an incinerator.