The pre-combustion chamber for secondary fuels development status of a new technology

Thermal utilization of alternative fuels in the cement burning process makes an important contribution to the conservation of fossil fuels. To be introduced through the conventional burning positions of a cement kiln system in significant quantities, those fuels which are originally available in lump form have to be comminuted in energy- and cost-intensive processes. When lumpy fuels have been fed into the kiln inlet of precalciner plants with separate tertiary air supply, fuel substitution rates have typically been limited to rather low ratios for a variety of process reasons. In the case of whole tires, for example, the fuel ratio has been limited to 10-15 % of the total energy consumption of the kiln. A new thermal process makes it possible to increase the specific amount of fuel significantly by generating intermediate products with enhanced burn-out properties, which are then introduced into the calciner firing system. The development of the process started in small-scale trials with shredded tires and wood, and was continued by carrying out pilot trials in a Swiss cement plant. In the same plant, an industrial-scale unit with a throughput of 3 t/h of tires was installed and has been in continuous operation since 2000. All guaranteed values regarding throughput and emission have been met. A second industrial unit in Germany with a nominal tire throughput of 5 t/h, an advanced reactor design, and a new residue handling system is in the final phase of commissioning. The expectations with regard to throughput, kiln operation and emissions have already been reached. The flexible design of the reactor opens possibilities for a variety of alternative fuels in the future as well as the potential connection to the main burner of cement kilns. The paper explains the basic idea, plots the main development steps, shows the arrangement of the precombustion chamber within a cement kiln line, and reports operational results.