The sound-assisted fluidized bed combustion of powders made of tyre derived fuel (TDF) and of a biomass (Robinia Pseudoacacia) has been studied to assess the benefits deriving from the application of acoustic fields of different frequency on the performance of the combustor. The parameters monitored were: the carbon elutriation rate, the carbon loading in the bed and the degree of fixed carbon conversion. Both fuels are characterized by strong propensity to generate fines during pyrolysis and/or combustion. Elutriable particles are mainly formed during devolatilization for TDF, during char burn-off for Robinia. Experiments consisted of steady combustion, either ordinary or sound-assisted, of TDF and Robinia fine particles. Acoustic fields of 150dB and frequency of 80, 120 and 240Hz were used in sound assisted experiments. High intensity acoustic fields of 120Hz reduce carbon elutriation rates by a factor of about 1.5, regardless of the fuel used. Correspondingly, fixed carbon conversion efficiency increases by 5-8% and 2-3% for TDF and Robinia respectively. Sound frequencies either lower or higher than 120Hz reduce the effectiveness of sound, approaching the performances of ordinary fluidized bed combustors. Results have been analyzed considering that fine particles are present in the bed either as fines freely moving in the interstices of the bed (free fines) or as fines attached onto coarse inert bed particles (attached fines). Accordingly the inventory of carbon present under steady state conditions in the bed depends on the competition between the following processes: elutriation of free fines, adhesion and/or cohesion of elutriable fines onto bed material, generation of elutriable fines by attrition of fine-coarse aggregates and combustion of fine particles. In this framework, acoustic fields have the property of enhancing the formation of fine-coarse aggregates.
Sound-assisted fluidized bed combustion of fine particles
R Chirone;S Russo;F Scala
1999
Abstract
The sound-assisted fluidized bed combustion of powders made of tyre derived fuel (TDF) and of a biomass (Robinia Pseudoacacia) has been studied to assess the benefits deriving from the application of acoustic fields of different frequency on the performance of the combustor. The parameters monitored were: the carbon elutriation rate, the carbon loading in the bed and the degree of fixed carbon conversion. Both fuels are characterized by strong propensity to generate fines during pyrolysis and/or combustion. Elutriable particles are mainly formed during devolatilization for TDF, during char burn-off for Robinia. Experiments consisted of steady combustion, either ordinary or sound-assisted, of TDF and Robinia fine particles. Acoustic fields of 150dB and frequency of 80, 120 and 240Hz were used in sound assisted experiments. High intensity acoustic fields of 120Hz reduce carbon elutriation rates by a factor of about 1.5, regardless of the fuel used. Correspondingly, fixed carbon conversion efficiency increases by 5-8% and 2-3% for TDF and Robinia respectively. Sound frequencies either lower or higher than 120Hz reduce the effectiveness of sound, approaching the performances of ordinary fluidized bed combustors. Results have been analyzed considering that fine particles are present in the bed either as fines freely moving in the interstices of the bed (free fines) or as fines attached onto coarse inert bed particles (attached fines). Accordingly the inventory of carbon present under steady state conditions in the bed depends on the competition between the following processes: elutriation of free fines, adhesion and/or cohesion of elutriable fines onto bed material, generation of elutriable fines by attrition of fine-coarse aggregates and combustion of fine particles. In this framework, acoustic fields have the property of enhancing the formation of fine-coarse aggregates.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.