(478d) Can We Control the Hydrodynamics of Slurry Bubble Columns?

The structuring of the multiphase reactors introduces extra degrees of freedom allowing decoupling of conflicting design objectives, such as high mass transfer versus low pressure drop in a packed bed. In this way, structuring facilitates reaching goals such as process intensification and more sustainable operation. At Delft University of Technology, much effort has been put over the past years in the research and development of structured reactors, such as structured gas solid-fluidized beds, structured fixed bed reactors, and structured slurry bubble columns. In this contribution, we will focus on the latter category.

In the current study, we aim at structuring slurry bubble columns and reducing the back-mixing by manipulating the gas phase. We investigate the effect of a needle sparger on extending the homogeneous flow regime and increasing the gas phase residence time. We apply optical probes to measure the local gas fraction and bubble dynamics in the system. With uniform gas injection system we show that the homogeneous flow regime can be extended beyond a gas fraction of 30% [1]. Further, we study the effect of solids on the hydrodynamics of the system. Experimental results for air-water-glass beads show that an increase in solids volume fraction: (1) decreases the gas fraction for a given superficial gas velocity, (2) shifts the transition point from homogeneous to heterogeneous flow to a lower gas velocity, (3) increases the mean bubble velocity by 60-100% in the range of superficial gas velocities from 0.02 to 0.1 m/s, and (4) has only a limited effect on the bubble size distribution. We conclude that using needle spargers, giving a very uniform gas supply, a first step towards structuring the hydrodynamics of slurry bubble columns has been taken.

[1] Hooshyar, N.; Hamersma, P. J.; Mudde, R. F.; van Ommen, J. R., Intensified Operation of Slurry Bubble Columns Using Structured Gas Injection. The Canadian journal of Chemical Engineering 2010, in press.