Effects of an immersed tube in deep and shallow slugging fluidized beds

The effects of an immersed tube on slugging fluidization and particle behaviors in slugging fluidized beds were investigated using computational fluid dynamics. Both shallow and deep slugging fluidized beds with and without an immersed tube were simulated using the two-fluid model. The presence of an immersed tube gave rise to regions of high voidage below the tube and regions of low voidage above the tube. Formation of the high voidage region occurred by particle deflection away from the immersed tube, while that of the low voidage region resulted from particle vortices above the tube. The presence of an immersed tube was observed to facilitate bubble formation and bubble coalescence in both shallow and deep slugging fluidized beds. In shallow beds, an immersed tube regularized pressure fluctuations but increased the amplitude of fluctuations. In deep beds, an immersed tube reduced the frequency of pressure fluctuations by facilitating wall slug formation. Based on random sampling and statistical testing (Z-test) of mean slug lengths, it was concluded that mean slug lengths increased when U was increased from 0.90 m/s to 1.0 m/s in the deep free column (p-value = 0.0422). Based on an F-test of the slug length variance, it was concluded that there was larger variability of slug lengths for U of 1.0 m/s than for U of 0.90 m/s in the deep free column (p-value = 0.0202). However, the results of these statistical tests on mean slug lengths and slug length variance for the deep single tube column showed that U had no significant effect on mean slug length or slug length variance at the 5% significance level. Thus, one of the effects of an immersed tube in a deep slugging fluidized bed was regulation of the size of slugs formed and prevention of any significant increase in mean slug size or slug size variability.