Sound-assisted fluidized bed combustion of fine particles

The sound-assisted fluidized bed combustion of powders of tyre derived fuel (TDF) and of a biomass (Robinia Pseudoacacia) has been studied to assess t he benefits deriving from the application of an acoustic field on the perfo rmance of the combustor. Experiments consisted of steady combustion, either ordinary or sound-assisted, of TDF and Robinia fine particles. High intens ity acoustic fields of 120Hz reduce carbon elutriation rates by a factor of about 1.5, increasing the fixed carbon conversion efficiency by 5-8% and 2 -3% for TDF and Robinia respectively. Sound frequencies either lower or hig her than 120Hz reduce the effectiveness of sound, approaching the performan ces of ordinary fluidized bed combustors. Results have been analyzed assuming that fine particles are present in the bed either freely moving in the interstices of the bed (free fines) or atta ched onto coarse inert bed particles (attached fines). Accordingly the inve ntory of carbon under steady state conditions in the bed depends on the com petition between the following processes: elutriation of free fines, adhesi on of fines onto bed material, attrition of fine-coarse aggregates and comb ustion of fine particles. In this framework, acoustic fields have the prope rty of enhancing the formation of fine-coarse aggregates.