Hydrodynamics of the continuously filtering slurry reactor — Influence of load of solids and particle size distribution

Abstract

Abstract--lnternal filtration in slurry bubble columns offers a possible solution to the filtration problems related to this reactor type. The applicability of the concept has already been demonstrated at full-scale for waste water treatment. Theoretical description of internal filtration is lacking, however.In previous work it was derived on basis of two different models, that in three-phase filtration solids concentration in the vicinity of the filter should uniquely depend on a single dimensionless number, i.e.The validity of the so-called cake build-up number was demonstrated by determining filter cake resistance as an indirect measure of solids concentration for a system in batch operation with respect to solids.In the present work the force balance model is extended to include the effect of particle size distribution. It is demonstrated that particle polydispersity can explain trends observed upon variation of load of solids, which cannot be understood assuming the particles to be monodispersed. Based on a simplified version of the model including particle polydispersity, a novel diameter characteristic to filtration behaviour of polydisperse solids is derived. Using this novel diameter in the cake build-up number, experimental results for four different size distributions can bc reasonably well described by a single master curve. ~ 1997

A two-dimensional hydrodynamic model of a slurry system with immersed filters

“…This kind of situation requires a drastically more complex model. From the good reproducibility of the experiments by Huizenga et al (1997) it, however, follows that cake resistance is not strongly dependent on the history of their experimental system. For comparison with their experiments, the assumption of a stratiÿed cake, therefore, seems to be justiÿed.…”

“…2). For a more detailed description the interested reader is referred to earlier publications (Huizenga et al, 1997(Huizenga et al, , 1998.…”

“…Following Huizenga et al (1997), a stratiÿed cake is assumed with particle size increasing with distance to the ÿlter (Fig. 4).…”

“…It was demonstrated by Huizenga et al (1997) that the so-called resistance diameter plays an important role in the interpretation of experimental results. This diameter is deÿned as the cut-o diameter at which the resistance of a uniform stratiÿed cake attains half of its maximum value: For a certain distribution of cake on the ÿlter and a certain value of solids concentration at the bottom of the ÿlter zone ( s; 0 ), axial dependencies of the relevant quantities in the ÿlter zone (solids concentration, pressure drop, liquid velocity and permeate ux) can be calculated.…”

“…1) cake build-up needs to be prevented, because it leads to a less e ective utilisation of the slurry bulk. Hydrodynamic models aimed at predicting whether a cake of solids will deposit on the ÿlter surface were published previously by the present authors (Huizenga, Kuipers, & van Swaaij, 1997, 1998. In the present article, these models are extended to include axial variations at the height of the ÿlter, which enables predicting the e ect of ÿlter length.…”