Bubble characteristics in an internally circulating fluidized bed.

Abstract

In an internally circulating fluidized bed, the bubble properties (bubble chord length, volume fraction, rising velocity and frequency) in the fluidized bed and the solids circulation rate from a fluidized bed to a moving bed were determined, along with the effects of gas velocity on solids circulation rate and bubble properties in the fluidized bed. The solids circulation rate increases with increase in gas velocity. The measured bubble chord length distribution in the fluidized bed is well represented by the logarithmic normal distribution. The measured bubble chord length, volume fraction and rising velocity increase with bed height and gas velocity to the fluidized bed. However, bubble chord length, volume fraction and local bubble frequency decrease with increasing gas velocity to the moving bed. The bubble chord length, volume fraction and rising velocity are lower in the bed wall region and exhibit a peak value at a dimensionless lateral distance of 0.5–0.8, and the peak moves to the center region of the bed with increasing bed height. The rate of increase in bubble rising velocity increases with bubble size up to about 0.07 m, at which the flow regime may lie between bubbly and slugging flows. The bubble properties in the internally circulating fluidized bed have been correlated with the solids circulation on the basis of theoretical equations in the literature.