A Study On CFB Boiler Fly Ash Triboelectrostatic Separation

With the increasing of total and unit capability of CFB boilers, more attention is paid to the disposal of fly ash from CFB boilers. The paper studied the feasibility of the triboelectrostatic separation method to separate the carbon in fly ash from CFB boilers, the influences of the operating conditions and equipment structure on the separating efficiency and the electrification characteristic of fly ash from the aerosol generator.The composition and component morphology in CFB boiler fly ash were found to be different from that of PC boilers by studying the evolution of the minerals in the coal in the middle temperature range in CFB boiler. The minerals in CFB boiler fly ashes keep the same crystal structure as that of the coals. The tracer elements usually adhere on the fly ash surface. The glass is rarely to be found in the fly ashes except for those coming from CFB boilers using limestone for desulphurization, and the galss and the crystle minerals combine together with obvious transition zone.The relative independent separating existence between carbon and the minerals in 10 CFB boiler fly ashes were studied with 3 different separating methods, i.e. the shaking screen, the gravity solution separation and the minimal fluidization separation. The carbon and the minerals in 8 fly ashes are proved to exist relative independently. So the triboelectrosatic carbon separation for most CFB boiler fly ashes is feasible. The separating device of CFB boiler fly ashes was designed and manufactured based on the achievement of the PC boiler fly ash triboelectrosatic separation technology. The 8 CFB boiler fly ashes, in which the carbon and minerals exist relative independently, were used to study the efficiency of the triboelectrosatic separation device.Experiment results show that the separating efficiency increases with theelectric field intensity increasing, feed air flow decreasing and the inlet width decreasing of the triboelectrosatic separation cell. The charge capacity distribution model, optimized with experiment data, for the mineral and carbon particles through a aerosol generator was presented, with which the multi-field in the separation cell was calculated. The comparisons of the calculation results and the experiment data proved that the model is reliable. At last, the influences of the air breakdown voltage, the coagulation of fly ash particles and relative independent separate degree between the minerals and carbon on separating efficiency of the triboelectrostatic separating process are discussed.The work in the paper shows that the triboelectrostatic separation is feasible, reliable and controllable method for disposal of fly ash from CFB boilers.