Key aspects in the fluidized bed combustion of tyre derived fuel

In this work the main mechanistic aspects of the fluidized bed combustion of tyre derived fuel (TDF) are analyzed by means of experimental and theoretical investigations. The time-resolved rates of carbon fines elutriation during the fluidized bed combustion of TDF have been measured during batch experiments in a bench scale reactor operated at 850°C. Experiments have been carried out under inert and oxidizing conditions in order to discriminate the influence of the parallel particle combustion on the elutriation rate. The latter tests have been conducted under both integral and differential conditions with respect to inlet oxygen concentration. The influence of gas superficial velocity and of oxygen partial pressure on carbon elutriation rates have been characterized. Results demonstrate that both variables exert influence upon the overall fixed carbon combustion efficiency. The efficiency increases slightly with the oxygen concentration and significantly if the gas superficial velocity decreases. On the whole results indicate that the efficiency of the fluidized bed combustion of TDF is determined by the competition between combustion and elutriation of char fines generated by primary fragmentation in the early stage of fuel conversion. Experimental results are further analyzed in the framework of a recently proposed model of a fluidized bed combustor fueled with high-volatile solid fuels. The model takes into account phenomena that assume particular importance with this kind of fuels, namely fuel particle fragmentation in the bed and volatile matter segregation and postcombustion above the bed. The analysis highlights the relevance of these issues to the assessment of the optimal operating conditions for combustion of TDF.