Experimental studies of gas holdup in a slurry bubble column at high gas temperature of a helium−water−alumina system

A Slurry bubble column with a high gas temperature has many advantages that motivates doing more detailed studies with this type of columns. Among these advantages; simple and cheap construction that requires less floor space, higher values of effective interfacial areas, high heat transfer rates per unit volume of the column, better temperature control, and lower pressure drop.

In the design of slurry bubble column systems, gas holdup which is a dimensionless parameter, plays an important role in the hydrodynamic analysis of such systems. It represents the volume of the gas phase (bubbles) relative to the total volume of slurry and gas inside the column.

There are many different factors that affect the behavior of the gas holdup, such as; the physical properties of the gas/liquid/solid phase, reactor size, gas distributor design, and the operating variables, i.e., pressure, superficial gas velocity, temperature, and solid loading. However, due to the complex interaction among the various phases, the flow field and hydrodynamics of the slurry bubble column have not yet been well understood.

In spite of the different systems and parameters that were investigated in the studies of the gas holdup, most of these studies, as well as empirical correlations for predicting gas holdup, were limited to ambient conditions and to air/aqueous solutions, and did not consider the effect of gas/liquid nature.

In the literature, no study has been found regarding detailed gas holdup investigations of slurry bubble column with high temperature helium gas. Therefore, this lack motivates the present work, which seeks to fill this gap by investigating experimentally the slurry bubble column using alumina-water slurry at 22^oC and helium gas at 90^oC.

In the experiments of this work, a high temperature helium gas (90^oC) is injected through a slurry of water and alumina solid particles at 22^oC. The importance of using helium gas lies in being a perfect fluid for transferring heat because of its high specific heat as well as being inert and safe to use.

The other significance of this work with respect to the existing literature, is the new form of the empirical equation of the gas holdup that depends only on the design parameters of the bubble column, such as the reactor dimensions, superficial gas velocity, and solid concentration. The existing empirical equations of the gas holdup were mainly formulated in terms of thermo physical properties of the gas and slurry.