Potentials of AFR co-processing

Resources are becoming scarcer and more expensive worldwide driving a search for viable alternatives including the use of Alternative Fuels and Raw Materials (AFR). The cement industry began to use Residue Derived Fuels (RDF) after the oil crisis in the early 1980s. By 2010, their use had increased to about 10% replacement of the total thermal energy demand. Utilizing mainly used oil and tyres, RDF consists of different types of hazardous and non-hazardous waste from both industrial and municipal origin. This trend is expected to continue in the coming years due to economic benefits and the necessity to significantly cut the cement industry's CO
₂
emissions, which comprise nearly 5 % of the total man-made CO
₂
production worldwide. This paper focuses on the main aspects of pre-processing waste and co-processing RDF in cement kilns. It includes identification, waste management, pre-treatment and utilization in cement clinker production. Processing techniques range from simple procedures for single component streams to mechanical-biological treatment for mixed municipal solid waste. The complete clinker manufacturing process has to be considered with regard to both mechanical equipment and product quality. Pre-processing and handling concepts within the cement plant as well as the impact of RDF on the manufacturing process are emphasized. Of major importance in this context is RDF combustion at its point of introduction, as well as emissions and clinker quality. Based on these prerequisites, some particular techniques for RDF use in pre-calciners and rotary kiln main burners are presented, mainly featuring an intelligent fuel mix management, additional measures such as mechanical or thermal pre-treatment, and process-integrated measures such as modified main burners or process parameter adaptations in case of direct RDF feeding into the pre-calciner. In the following, concepts are introduced based on the mechanical, physical and thermal processing of alternative fuels.