Moving granular bed is one of the candidates of high temperature dust collectors. In the present work, influence of temperature on the collection performance of granular bed filter was experimentally investigated. When there is no temperature difference between aerosol and granules, the collection efficiency at a high temperature is estimated by the prediction equation obtained at room temperature with correction for the physical property of air due to the temperature rise. When the temperature gradient exists between aerosol and granules, the collection efficiency of submicron particles markedly iilcreased at a low filtration velocity as the temperature difference increased, because of thermophoretic force. Although the utilization of thermophoretic force leads to cooling of gas, thermophoretic force may be used to remove submicron particles effectively.

View full abstract

Size-selective collection of aerosol particles was performed by the collision to the liquid surface in Andersen Air Sampler composed of six nozzle plates, and then analysis of the liquid suspension for the particle size distribution and the particle concentration was conducted by Coulter Counter. Two types of aerosol particles, frittered glass powder (sphericity : 0.14) and flyash (1.0) , were employed. As a result, (1) agglomerates of the glass aerosol particles were found in the 1st and 2nd stages. In order to disintegrate the agglomerates into single particles, a plate having the same nozzle size as that of the 6th stage was attached upstream of the 1st stage. The disintegration effect of air turbulence was positive for glass powder, and negative for flyash. (2) From the data on the number of the collected particles in each stage, by using the “number balance calculation in multi-stage ” method previously developed, the partial collection efficiency curves and the particle size distributions simultaneously calculated were successfully obtained for each stage. The distributions calculated were found to be in good agreement with experimentally observed ones, The partial collection efficiency curve was expressed by a mathematical equation with two parameters. Though the particle size distributions for all the stages are broader than what has been understood as the characteristic for AAS, it could be attributed to the coagulation due to the high concentration of the aerosol used in this experiment. (3) The hollows on the liquid surface formed by jet flow from the nozzle slightly enhanced the partial collection efficiency, for both the frittered glass and the flyash particles. (4) As for the effect of the particle shape in inertial collection, as has been reported so far, the efficiency for spherical particle is higher than that of non-spherical one.

View full abstract