Centrifugal contactors

R. A. Leonard and co-workers. Development of a 25cmA.nnular Centrifugal Contactor, ANL-80-15, Argonne National Laboratory, Chicago, lU., June 1980. 

The emulsion is separated in the centrifugal contactor (POD), which produces a stream containing water-soluble impurities and a stream of washed solvent. 

POD system The POD system consists of a Baker-Perkins Model A-l Contactor (that is, a Podbielniak centrifugal contactor) fabricated in stainless 316. A variable speed drive is capable of rotating the unit at speeds up to 10,000 rpm. The normal operating speed is 8100 rpm. 

POD Baker-Perkins A-l centrifugal contactor,316SS maximum temperature, 250°F ... 

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. 

The types of equipment used, which range from stirred tanks and mixer-settlers to centrifugal contactors and various types of columns, affect both capital and operating costs [9]. In the decision to build a plant, the choice of the most suitable contactor for the specific situation is most important. In some systems, because of the chemistry and mass transfer rates involved, several alternative designs of contacting equipment are available. In the selection of a contactor, one must consider the capacity and stage requirements solvent type and residence time phase flow ratio physical properties direction of mass transfer phase dispersion and coalescence holdup kinetics equilibrium presence of solids overall performance and maintenance as a function of contactor complexity. This may appear very complicated, but with some experience, the choice is relatively simple. 

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. 

Several centrifugal contactors of proprietary nature are on the market. Their controls are invariably built in. 

Centrifugal Contactors. These devices have large capacities per unit, short residence times, and small holdup. They can handle systems that emulsify easily or have small density differences or large interfacial tensions or need large ratios of solvent to feed. Some types are employed as separators of mixtures made in other equipment, others as both mixers and settlers, and some as differential contactors. 

Develop the hardware (e.g., centrifugal contactors, sensors, and other devices) and accompanying equipment, such as waste-treatment systems. 

The reaction rate of AHA is large enough to use centrifugal contactors. Process experiments with real SNF in a series of centrifugal contactors have demonstrated a separation of highly pure U with a yield of >99.99% (126, 183-188). The UREX+ process also enables the effective separation of Tc (189). 

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. 

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. 

Okamura, N., Takeuchi, M., Ogino, H., Kase, T., Koizumi, T. 2007. Development of centrifugal contactor with high reliability. GLOBAL 2007, Boise, ID, September 9-13. 

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. 

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. 

Wood, D.J., Law, J.D., Todd, T.A. 1998. Demonstration of a SREX process for the treatment of actual high activity waste at the INEEL using centrifugal contactors. Science and Technology for Disposal of Radioactive Tank Waste, Schulx, W.W., Lombardo, NJ. Eds. Plenum, New York, pp. 255-268. 

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. 

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. 

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

As part of a process comparison campaign carried out at the ITU, a DIDPA flowsheet was implemented countercurrently in 24 miniature centrifugal contactors ... 

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