Fluidization characteristics of gas-fluidized beds: Air and glass beads system

Good gas-solids contacting and solids mixing are essential features, both for efficient coal combustion and desulfurization of coal in a fluidized-bed combustor. It will therefore be very useful if suitable procedures could be developed to characterize the quality of fluidization in gas-solid systems. Three different procedures are discussed in this article with reference to air and glass beads of four different average sizes: 1.(i) in one scheme, the bed voidage is measured at minimum fluidization and the variation of this quantity with Reynolds number at minimum fluidization is correlated with the powder classification scheme of Saxena and Ganzha and hence with the corresponding fluidization characteristics. A major effort is directed at substantiation and confirmation of this characterization scheme, which relates the fluidization behavior to the Reynolds number at incipient fluidization.2.(ii) The local heat-transfer coefficient of a probe element immersed in the bed is also measured as a function of the superficial fluidizing velocity and the nature of variation is taken as representing the quality of bed fluidization.3.(iii) A technique is developed to measure the time-history of the temperature fluctuation of a probe element and to relate this parameter to the bed-fluidization characteristics.