Extraction centrifugal contactors

Typical regions for application of contactors of different types are given in Table 13.2. The choice of a contactor for a particular application requires the consideration of several factors including chemical stability, the value of the products and the rate of phase separation. Occasionally, the extraction system may be chemically unstable and the contact time must then be kept to a minimum by using equipment such as a centrifugal contactor. 

It is a practical fact that most industrial solvent extractions are carried out under nonequilibrium conditions, however close the approach may be for example, centrifugal contactor-separators (Chapter 9) rarely operate at distribution equilibrium. An interesting possibility is to expand this into extractions further from equilibrium, if the kinetics of the desired and nondesired products are different. Such operations offer a real technlogical challenge. 

Often the products of nuclear reactions have very short half-lives. This is especially true for the heaviest elements obtained by bombardment of heavy targets with heavy ions. To identify and characterize such short-lived nuclides, fast separations are required solvent extraction techniques are well suited to provide the required fast separations. For example, the SISAK method [68] has been successfully used in conjunction with in-line gas jet separators at heavy ion accelerators to identify short half-life actinide isotopes produced by collision of heavy atoms. The Sisak method involves use of centrifugal contactors, with phase residence times as low as tenths of a second, in conjunction with in-line radiometric detection equipment. 

Jenkins, J.A., Mills, A.L., Thompson, P.J., Jubin, R.T. 1993. Performance of centrifugal contactors on uranium and plutonium active PUREX flowsheets. In Solvent Extraction in the Process Industries ISEC 93, York, UK, September 16-21. Logsdail, D.H., Slater, M.J. Eds. Elsevier Applied Science, London and New York. 

Modolo, G., Asp, H., Vijgen, H. et al. 2008. Demonstration of a TODGA-based continuous counter-current extraction process for the partitioning of actinides from a simulated PUREX raffinate, PartB Centrifugal contactor runs. Solvent Extr. Ion Exch. 26 (1) 62-76. 

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. 

Bilancia, G., Facchini, A., Ferrando, M. et al. 2005. Selective actinide extraction with a tri-synergistic mixture using a centrifugal contactor battery. Solvent Extr. Ion Exch. 23 (6) 773-780. 

Kinetics of phase transfer should be sufficiently fast, both at the extraction and stripping steps, to allow short-residence time contactors to be employed. In pulsed columns, the contacting time averages a few minutes, while in centrifugal contactors, this contacting time might shorten to only a few seconds. 

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%. 

Nakahara, M., Sano, Y., Koma, Y., Kamiya, M., Shibata, A., Koizumi, T., Koyama, T. 2007. Separation of actinide elements by solvent extraction using centrifugal contactors in the NEXT process. Journal of Nuclear Science and Technology 44(3) 373-381. 

Design Principles and Applications of Centrifugal Contactors for Solvent Extraction... 

In this chapter, Section 10.2 gives an overview of the operation of the Argonne centrifugal contactor. Section 10.3 focuses on the design principles for this contactor. Section 10.4 discusses the worldwide applications of this contactor to solvent-extraction processes of interest to the nuclear and other industries. Comparisons with other types of contactors are made throughout the text, and a separate section is devoted to them in Section 10.4. However, because of their widespread use and the author s particular experience with them, the ANL contactor and its variations remain the primary focus. 

A solvent-extraction flowsheet is broken down into sections such as extraction, scrub, and strip. For each section, one or more component in a process fluid must be moved from one phase to the other phase with a specified degree of completeness. The first design problem is to determine the number of stages for each section to accomplish the required component transfer. With the well-defined stages of the centrifugal contactor, the following extraction factor (E) can be used to estimate the number of stages required ... 

The centrifugal contactor was first used to reprocess spent nuclear fuel at the SRS in 1966 (Webster et al., 1969). For almost 40 years, this 18-stage 25-cm SRL contactor was used for the extraction and scrub sections (the A-bank) of the PUREX (plutonium-uranium extraction) process at the SRS. Contactor operation stopped when the facility in which they were housed was shut down in 2003. This 18-stage contactor replaced a 24-stage mixer-settler. Mixer-settlers continued to be used for the rest of the processing, as most of the radiation was removed in the A-bank. The ability to... 

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