Contactor tests

As organic and aqueous phases are macroscopically separated by the membrane, HFM offer several hydrodynamic advantages over other contactors, such as the absence of flooding and entrainment, or the reduction of feed consumption (160, 161). The flowsheets tested in HFM were similar to those developed for centrifugal contactor tests. Computer codes based on equilibrium (162) and kinetics data, diffusion coefficients (in both phases and in the membrane pores), and a hydrodynamic description of the module, were established to calculate transient and steady-state effluent concentrations. It was demonstrated that, by selecting appropriate flow rates (as mass transfer is mainly controlled by diffusion), very high DFs (DI A 11 = 20,000 and DFrm = 830) could be achieved. Am(III) and Cm(III) back-extraction efficiency was up to 99.87%. 

Laboratory Scale Contactor Tests. The feasibility of each part of the flow sheet was tested in small, commercially available mixer-settler units which had 12 or 16 stages with individual mixer and settler volumes of 15 mL and 49 mL, respectively. 

Similar calculations for a U-Pu separation using HAN as reductant and the flow ratios of our modified Thorex flow sheet indicate that about the same Pu loss behaviour should be expected. However, for flow conditions more appropriate to the Purex process, negligible Pu losses are predicted. Uranium losses are predicted to be neglible for both sets of conditions. These predictions were also confirmed in contactor tests. 

As stated above, the design of an RDC contactor usually involves the performance of pilot tests due to the large number of factors whicF can influence performance. These pilot plant data must then be scaled-up to Rill commercial size. The following procedure is recommended. 

Lucas and Porter (U.S. Patent 3,370,401, 1967) developed a fiber-bed scrubber in which the gas and scrubbing liquid flow vertically upward through a fiber bed (Fig. 17-55). The beds tested were composed of knitted structures made from fibers with diameters ranging From 89 to 406 [Lm. Lucas and Porter reported that the fiber-bed scrubber gave substantially higher efficiencies than did venturi-type scrubbers tested with the same dust at the same gas pressure drop. In similar experiments, Semrau (Semrau and Lunn, op. cit.) also found that a fiber-bed contactor made with random-packed steel-wool fibers gave higher efficiencies than an orifice contactor. However, there... 

Unfortunately, relatively little information has been made available for industrial gas-liquid contactors. Further data from industry could permit significant tests of the reliability of the present correlations and their applicability to scale-up. Steel and Maxon (SI 1) reported on the power requirements during novobiacin fermentation in 20- and 250-liter pilot-plant vessels and in 12,000- and 24,000-gal vessels. The comparative data are difficult to evaluate because of changes that occurred in viscosity and gas retention during the course of the fermentation. In addition, geometric similarity did not prevail... 

The design of two-phase contactors with heat transfer requires a firm understanding of two-phase hydrodynamics in order to model effectively the heat- and mass-transfer processes. In this chapter we have pointed out areas where further theoretical and experimental research is critically needed. It is hoped that design engineers will be motivated to test the procedures presented, in combination with their use of the details from the original references, in the solution of pragmatic problems. 

The time required for a system to reach equilibrium can be determined by shake-out tests, as described in earlier sections. Contact times are varied between about 0.5 and 15 min, at suitable intervals, and the extraction coefficient for each contact time plotted as a function of time. With this method, there is a lower practical limit on the contact time of about 0.25 min. These data will not be directly applicable to a continuous process because the rate of metal extraction is a function, in part, of the type and degree of agitation. However, a good idea of whether the extraction rate is sufficiently fast for the system to be suitable for use in a large contactor can be obtained. For example, if equilibrium is attained in less than 1 min, almost any type of contactor may be used. 

In-line mixers manufactured by, for example, Kenics, Lightning, and Sulzer are also applicable for continuous small-scale testing of a solvent extraction process, and 1 inch diameter models are available. This mixer system can be used either horizontally or vertically. However, few data are available for this type of contactor, although they would appear to offer many possibilities, not only for liquid-liquid systems, but also for use in... 

Because of the diversity of contacting equipment available, it is unlikely that all these contactors will be available in any one laboratory or pilot plant. Consequently, unless test work is carried out on similar contactors, the system may not be optimized. Since mixer-settlers are the easiest to construct, are simple to operate, and require little room and low-flow rates, these contactors are, in many cases, the only ones used to investigate a continuous solvent extraction process. This is by no means ideal and may result in abandonment of a process that, using another type of contactor, could be found to be entirely satisfactory. 

The qualifications tests consists of checking the transmission of the one-bit binary information sent by the controller to the contactors, relays, electrovalves, pilot lights, and other digital outputs of the system. 

Laboratory Extractors. Pilot-Scale Testing, and Scale-Up. Several laboratory units arc useful in analysis, process control, and process studies. The AKUFVE contactor incorporates a separate mixer and centrifugal separator. It is an efficient instrument for rapid and accurate measurement of partition coefficients, as well as for obtaining reaction kinetic data. Miniature mixer-settler assemblies set up as continuous, bench-scale, multistage, countercurrent, liquid-liquid contactors are particularly useful Tor the preliminary laboratory work associated with flow-sheet development and optimization because these give a known number of theoretical stages. 

Meikrantz, D.H., Law, J., Todd, T. 2007. Design attributes and scale up testing of annular centrifugal contactors. Chemical Engineering Division of the AIChE Spring National Meeting, April 10-14, 2005, Atlanta, GA. INL/CON-05-00088. 

Chen, J., Tian, G., Jiao, R., Zhu, Y. 2001. A hot test for separating americium from fission product lanthanides by purified Cyanex 301 extraction in centrifugal contactors. Actinides 2001, Hayama, Japan, November 4—9. 

Law, J.D., Wood, D.J., Herbst, R.S. 1997. Development and testing of SREX flowsheets for treatment of Idaho Chemical Processing Plant sodium-bearing waste using centrifugal contactors. Sep. Sci. Technol. 32 C1 —4) 223-240. 

A 72-hour inactive test was performed to validate the whole process scheme in five pulse columns and 24 stages of centrifugal contactors at the INET (92). Nd and Zr simulated Am and Pu, respectively. DFs (expressed as the ratios [M]feed4 feed/[M] raff raff where ( ) represents the flow-rate of solute M) greater than 3000, 500, and 1000 were obtained for U, Nd, and Zr, respectively, thus demonstrating the feasibility and reliability of the TRPO process scheme. 

Previous active countercurrent tests performed in compact contactors (10 mm in diameter, 4-5 mL holdup per stage) on highly saline waste (-380 g/L of Na, Al, Fe, Cr, and Ni) had demonstrated that 99.9% of the actinides could be recovered with the rare earth elements (REEs) in six stages (93). 

Several countercurrent pilot plant tests have been run in centrifugal contactors ... 

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