Behavior of Rising Bubbles in a Gas-Fluidized Bed at Elevated Temperature

Abstract

Bubble size and the rise velocity of bubbles in fluidized beds at high temperature were measured by the electric capacitance method using an injection tube and a sintered-plate distributor. The bubble frequency increased with rise in temperature and the bubble size was rearranged as a function of bubble frequency and gas flow rate. The rise velocity of bubbles in swarms was divided into two terms, i.e., the rise velocity of isolated bubbles and the accelerated quantity due to bubble coalescence. The latter was correlated as a function of the ratio of distance between two successive bubbles to bubble radius. A model of bubble shape was proposed and effectively used to estimate the empirical coefficients included in the correlation for bubble size and rise velocity of bubbles. Intro ductionInformation on behavior of bubble motion is required to predict the performance of a fluidized catalytic reactor and to formulate an adequate model for design.Models of gas behavior in fluidized beds have been presented by many investigators4'6'8'11}, and theoretical and experimental evidence has shown that the coalescence of bubbles in swarms in a freely bubbling bed changes the bubble size, the rise velocity, the exchange of gas between bubble phase and dense In this study, measurements of bubble frequency, bubble size and rise velocity at high temperature in a fluidized bed were made by the electric capacitance method. Bubble size was correlated with bubble frequency and the rise velocity of isolated single bubbles was rearranged with the bubble size. Furthermore, the rise velocity of bubbles in swarms was correlated with the sum of the rise velocity of single bubbles and the term contributed to rise velocity by bubble coalescence. To explain the change in bubble size of coalesced bubbles, a new model for bubble shape is proposed. The relation between rise velocity and bubble size is discussed by considering the distance between the two successive bubbles and the change in bubble shape.

Analysis of Pressure Fluctuations in Fluidized Beds

“…This result agrees with several other researchers who used optical or capacitive probes to measure the bubble frequency over the same temperature range. [33][34][35] However, Fan et al 36 observed a more complex dependence between the dominant frequency and temperature than that reported by Svoboda et al 32 2.2.5. Multiple-Peak Phenomena.…”

Study of char gasification by carbon dioxide. 2. Continuous gasification in fluidized bed

“…A typical signal from the electroresistivity probe is given in Figure 5. Otake et al (1975) proposed the evaluation method for the rise velocity of bubbles and the height of bubbles by analyzing similar signals observed in this study. The procedure was expressed by eq 1 and 2 by use of the time delay between rise velocity of bubbles ub = 1 /a widths, b and b', were defined as half-widths of the two signals from one identical bubble.…”

Review of experimental methods for studying the hydrodynamics of gas-solid fluidized beds

“…1. provides data on instantaneous fluctuations of local heattransfer coefficients 2. can provide rise velocity by cross-correlation of two sensor signals 1. potential instrument for simultaneously studying freeboard and bed heattransfer characteristics 2. cross-correlation of twosensor response could provide data on rise velocity and pierced length Park et al, 1969Rigby et al, 1970Burgess and Calderbank, 1975Calderbank et al, 1976Mii et al, 1973Otake et al, 1975Whittmann et al, 1978Yoshida et al, 1982Cranfield, 1972Linneweber and Blass, 1983Yoshida et al, 1982Bashakov et al, 1973Bernis et al, 1973 Goose ns and Hellinck, 1973Wen et al, 1978Dils and Techenor, 1984 ering any portion of the photographic plate. The exposure for the portion of the plate onto which the image of a particle is focused is…”