Figure 32. The Himsley Continuous Fluid-Solid contactor.'881
The major disadvantage of the Higgins contactor is the lifetime of the resin. Estimates range from as high as 30% resin inventory replacement per year due to attrition and breakage of the resin as it passes through the valves.
In the Himsley type of contactor, the resin is moved from one compartment or stage to the next countercurrent to the feed solution flow on atimed basis that allows for the rate of equilibrium resin loading in each stage. Thus each compartment or tray is designed to accommodate specific feed compositions and effluent requirements. Equipment from different commercial suppliers differ in the manner of resin transfer.
Fluidized Column Operations. Column contactors, when operated with the feedstream in a downflow mode, are poorly suited to handle fermentation slurries because of the excellent filtration characteristics of packed resin beds. For such slurries it is preferable to use a fluidized bed of resin such as is shown in Fig. 33j92] While most of the commercial applications discussed in the literature pertain to slurries of uranium tailings and paper mill effluent, the equipment may be adapted for use in treating fermentation broths.
The shape of the fluidized bed is important in controlling the position of the resin in the column. The effluent from the column should pass over a vibrating screen, e.g., as SWECO, to retain entrained resin, but allow mycellia to pass through.
The Ashai contactor, shown in Fig. 34, uses conventional pressure vessels as the resin column. These vessels have a resin support grid at the base and a resin screen at the top. The feedstream is fed in up-flow through the packed bed. Periodically the liquid contents of the column are allowed to drain rapidly which causes the resin to flow from the bottom of the bed to a similar vessel for regeneration. At the same time, fresh resin is added to the top of the active column from a resin feed hopper. This hopper contains a ball valve which passes the resin in during downflow operation and seals itself during the up-flow portion of the adsorption cycle.
The Cloete-Street ion exchange equipment is a multistage fluidized bed containing perforated distributor plates (Fig. 35). The hole size in the plates is greater than the maximum resin particle. The countercurrent movement of resin occurs due to the controlled cycling of the feedstream. With each cycle, the entire amount of resin in one chamber is transferred to the next chamber. Equipment with 4.5 m diameter columns and eight stages for a total height of about 20 m are in commercial operation.
The USBM equipment, shown in Fig. 36, is very similar to the Cloete-Street system. The differences are in the plate design, the method of transferring solids and in the method of removing the resin. This system and the Cloete-Street system are able to handle slurry feeds with up to 15% by weight solids.
The advantage of these fluidized bed columns is the relatively low capital cost, low operating cost, small space requirement, simple instrumentation and control compactability with conventional solvent extraction equipment.1911 Only those systems that can accommodate slurries with suspended solids are commercially feasible for biotechnology and fermentation operations. Otherwise, the small volume of fermentation feedstreams which need to be processed are not the scale of operations necessary to make continuous ion exchange processes cost effective.
cone removal device for resin feedstream inlet loaded layer cone removal device for resin feedstream inlet
Figure 33. Fluid bed ion exchange column. t92]
High concentration on K>n-exchange 'enn
Concentrated liquor in
2 Stop flow and settle
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