Design, development and testing of miniature Liquid-Liquid Extraction contactors for RandD studies in nuclear environment

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Design, development and testing of miniature

Liquid-Liquid Extraction contactors for RandD studies in nuclear environment

H. Roussel, S. Charton

To cite this version:

H. Roussel, S. Charton. Design, development and testing of miniature Liquid-Liquid Extraction contactors for RandD studies in nuclear environment. ATALANTE 2016 - Nuclear Chemistry for Sustainable Fuel Cycles, Jun 2016, Montpellier, France. ATALANTE 2016 - Nuclear Chemistry for Sustainable Fuel Cycles, 2016. �hal-02416336�

De

si

gn, development and testing of miniature Liquid-Liquid

Extraction contactors for R&D studies in nuclear environment

Hervé Roussel, Sophie Charton

CEA, DEN, DTEC, SGCS, F- 30207 Bagnols-sur-Cèze, France

An innovative miniature stage-wise contactor:

the "Next Generation" mixer-settler

Refe

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Need for small-size liquid-liquid contactors

A key step in the development of a liquid-liquid extraction process for used nuclear fuel consists in testing the extraction

flowsheet at laboratory scale on radioactive solutions. The contactors used for these pilot trials must: i) be as small as possible

(to reduce the quantities of radioactive materials needed), ii) be similar to the industrial contactors (to make easier a later

scaling-up of the process), iii) be operable in nuclear environment (glove boxes or hot cells).

As no commercially available contactors fulfill these requirements, CEA has been developing tailor-made apparatus for several

decades . It is not possible to design a small contactor by simple scale reduction of a larger model: dominating phenomena in

hydrodynamics are changing while reducing the size and capillary effects grow in importance. The development and

optimization of miniature contactors usually begin with the design of a first prototype and ends up with the testing in pilot plant.

The major steps are introduced below in the case of a stage-wise contactor and of a differential one.

Twelve 4-stages mixer-settler batteries in the CBP shielded cell (Atalante)

[1] Patent FR 2 831 075 A1, Extracteurs liquide-liquide montés en batterie, P. Rivalier, F. Gandi, G. Ferlay, CEA, 10/22/2001

[2] Experimental and numerical investigation on mixing and axial dispersion in Taylor–Couette flow patterns, Nemri, M., Climent, E., Charton, S., Lanoë, J.-Y., Ode, D. (2012), Chem. Eng. Res. Des. 91, pp.2346-2354

[3] Liquid-liquid extraction between rotating cylinders, Davis, M.W. and Weber, E.J. (1960), Ind. Eng. Chem., 52, pp.929-934

An innovative miniature differential contactor:

the Taylor-Couette column

 Overall design

 Detailed features

 Mass transfer efficiency

Test system: extraction of nitric acid by a monoamide-based solvent

Individual stages arranged on CEA-patented rails[1] constituting modular batteries, all settlers facing the same direction in order to facilitate interphase observation

Mixer volume : 6 mL Settler volume: 20 mL Flowrate (A + O): up to 500 mL/h

Four-stages battery Individual stage

Proper choice of mixing chamber materials for emulsion type control

(stainless steel for oil in water or Teflon for water in oil)

Optimized W-shaped aqueous weir (right) to achieve a smooth continuous flow over a

wide range of flowrates (20 mL – 500 mL) Micropump for

flowrate-controlled internal recycling at each stage (light or heavy

phase)

1 cm 1 cm

Miniature Rushton-type turbine for combined

pumping and emulsification in the mixing chamber This turbine provides high

pumping effect

The miniature mixer-settler must achieve the same functions as larger ones, but the design must be adapted to the tiny size (dominant role of wall effects)

1 cm

The stage efficiency is high (≈90% compared to a theoretical stage) and, as expected, growths with the residence time and the agitation speed

This mixer-settler meets the

major expectations and is

under optimisation to improve

its useability in high activity

environment

study for nuclearized miniature mixer-settlers

(F. Dutilh, CEA/MAR/DTEC/SDTC/LTAP)

 Further development

residence time (min.)

MD-NG, Mass transfer efficiency

1500 rpm 1100 rpm

Taylor-Couette column (75 cm) Pulsed columns are widely implemented for nuclear fuel treatment, but

their reduction to laboratory scale is extremely challenging: • diameters below 15 mm are not achievable

 lower limit for flowrates ≈ 1 L/h

• the pulsation generates high axial dispersion

 pilot columns must be nearly as high as industrial ones (≈ 8 m)

 Taylor-Couette flow

 Taylor-Couette extraction column

This particular flow occurs in the gap between two

concentric cylinders (the inner one rotating, the outer one being fixed). Above a critical speed, liquids move in contra-rotating vortices.

It creates high agitation while axial mixing remains very low[2].

When applied to a biphasic system, the Taylor-Couette flows creates the emulsification needed for mass transfer[3].

The Taylor-Couette column is suited for testings with radioactive solutions: • the gap between the cylinders is narrow (≈ 2 mm)

 small flowrates ≈ 100 mL/h

• HETS (height equivalent to a theoretical stage) is much lower as in pulsed column

 Taylor-Couette column is smaller as the equivalent pulsed column.

Rotor Taylor vortices Heavy phase outlet Light phase outlet Light phase inlet Heavy phase

inlet phase_inlet

emulsion in a Taylor-Couette column

 Mass transfer efficiency

Test system: extraction of nitric acid by a TBP-based solvent)

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 0 1 2 3 4 5 6 [HN O3]org (mol/ L) [HNO3]aq (mol/L) equilibrium operating line McCabe-Thiele feed solution raffinate

number of theoretical stages determination by the McCabe-Thiele method 0 2 4 6 8 10 12 14 600 800 1000 1200 1400 1600 1800 HETS (c m) rotation speed (rpm)

Height Equivalent to a Theoretical Stage vs rotation speed

optimum _excessive mixing sub-optimal

droplets generation

A Taylor-Couette column can achieve the same separation as a 10 times higher pulsed column, while working with 10 times lower flowrates.