The invention relates to a device for separating phases of a diphasic mixture and the application of this device to the determination of the physical and/or chemical parameters of a diphasic mixture, in particular a liquidxe2x80x94liquid diphasic mixture, preferably a liquidxe2x80x94liquid diphasic emulsion.
In particular, the invention enables the physical parameters of a diphasic mixture, such as a diphasic emulsion, to be determined by propagation of plane sound waves.
Within the scope of the present invention, diphasic mixture is generally understood to mean any emulsion or dispersion in which a first phase, for example a solution, is in the form of a continuous phase, and a second phase, for example a solid, liquid or gas phase, is in the form, for example, of droplets or particles dispersed in the continuous phase. The second phase is usually called xe2x80x9cdispersed phasexe2x80x9d.
This type of diphasic mixture is used in particular to separate chemical elements in solution. The separation process essentially consists in bringing into contact a first solution, for example an aqueous solution, containing chemical elements, with a second solution comprising, for example, an organic solvent, which plays the role of an extractant. This bringing into contact is intended to allow a transfer of material between the two solutions.
The transfer of material is favoured by the formation of a diphasic mixture in the form of an emulsion or dispersion with fine droplets, in such a way as to increase the interfacial exchange area between the phases present. Decantation then allows the liquids to be separated after the transfer of the material.
Different separation devices that operate according to the process mentioned above are known. Among these, mixer decanter type devices, centrifuge extractor type devices or pulsed column type devices may be cited.
In extraction columns, two liquid phases are made to circulate in counter-current, wherein the heavy phase is injected into the top of the body and the light phase is injected into the bottom of this body. By bringing these two phases into contact, the element to be separated is shared out between each of the phases according to the laws of chemical thermodynamics and, by playing on the affinity of an element for one of the phases, one can extract this element almost completely and separate it from other elements.
Thus, in particular, liquidxe2x80x94liquid extraction processes, used in reprocessing of used fuel operations, are carried out in contactors that, in their mixing zone, produce diphasic emulsions. The efficiency of the transfer of elements between phases is particularly linked to the local volume percent of the dispersed phase and the local interfacial exchange area, but one also seeks to determine other physical and chemical parameters of liquid phases present in the emulsion zone, such as elementary concentrations of elements (for example U, Pu), conductivity, acidity, density, etc.
These various parameters may be determined by several procedures. The first procedure consists in taking a sample, in other words a small volume of emulsion, and carrying out measurements on each phase after leaving them to decant.
However, this type of procedure has disadvantages. In fact, taking a sample of emulsion disrupts the hydraulic operation of the contactor.
Moreover, sampling is only possible if the separation device contains a sufficient volume of mixture. Furthermore, the sampled volume must be re-injected into the separation device or must be stored after each measurement. In addition, in the event where the diphasic mixture contains very radioactive substances, the sampling and the storage of measurement samples may be impracticable or very restricting.
A second procedure, intended in particular to establish the density of the continuous phase and the velocities or propagation times of the waves separately in each of the phases during processing, consists in installing, in the separation device, decantation chambers, near to a mixing zone. These xe2x80x9cin situxe2x80x9d decantation chambers are however likely to modify the hydraulic behaviour of the device and to locally modify the characteristics of the diphasic mixture.
More precisely, as regards more specifically the local retention rate, a method for measuring the local retention rate by ultrasound wave propagation has already been described in documents (1), (2) and (3).
It shows that this parameter xcex2 may be represented by:                     β        =                              t            -                          t              c                                                                          g                d                            ⁢                              t                d                                      -                                          g                c                            ⁢                              t                c                                                                        (        1        )            
wherein:
t, tc and td=time of flight of the ultrasonic wave in the emulsion, the continuous phase and the dispersed phase alone; and
gc and gd=correction factor for the acoustic path in the aqueous and organic phases.
When transfer of material between the phases occurs, an on-line calibration of the propagation velocities in each of the phases must be carried out under the same physical and chemical conditions as in the measurement in the emulsion.
A destructive method has been proposed in document (4) by sampling and decanting a volume of emulsion before measurement.
An acoustic microscopy method has also been described in document (5) and has the advantage of being neither destructive nor intrusive, but it only allows one to determine the calibration parameter in the continuous phase.
Similarly, as regards the interfacial exchange area, there are optical methods for analysing the average size and the average number of droplets allowing the local interfacial exchange area to be determined. However, these techniques, by light diffusion and diffraction, assume that the local retention rate on-line is known; it is, for example, the principle on which are based the devices of the FORULACTION(copyright) Company, sold under the name TURBISCAN(copyright).
The large amount of droplets does not allow simple determination, by analysis and image processing, to be conceived.
On-line determinations of other parameters are achieved through analyses on samples taken.
The measurement of the density of the continuous phase is achieved in document (5) by acoustic microscopy, but the method on its own does not allow the value in the dispersed phase to be determined.
The problem of determining the physical and chemical parameters is particularly acute in the devices presently used in new liquidxe2x80x94liquid extraction installations for the reprocessing of used nuclear fuels. In fact, in order to limit the volumes of nuclear material, the columns are very small.
In such devices, few samples may be taken on-line and the geometry of the extraction devices implies limiting, as much as possible, hydraulic disruptions by intrusion or local modification of the dimensions.
There is therefore a need for a device for separating and renewing the phases of a diphasic mixture, in particular a liquidxe2x80x94liquid diphasic mixture, for example a liquidxe2x80x94liquid diphasic emulsion, which does not modify the hydraulic behaviour of the device in which it is placed and which does not modify the characteristics of the diphasic mixture.
There is also a need for a device for separating and renewing the phases of a diphasic mixture, in particular a liquidxe2x80x94liquid diphasic mixture, which allows perfect, complete separation and renewal of the phases.
There is also a need for a device for measuring the physical and chemical parameters of a liquidxe2x80x94liquid diphasic emulsion, which allows these measurements to be made without taking samples, without intrusion, without inducing hydraulic disruptions and without modifying the characteristics of the diphasic mixture.
Finally, there is a need for a measurement device that allows such measurements to be made with a high degree of reliability and precision, whatever the nature and the volume of the emulsion.
The aim of the present invention is to provide a device for separating and renewing the phases of a diphasic mixture, for example a liquidxe2x80x94liquid diphasic emulsion, which meets, among others, the requirements cited above.
The aim of the present invention is also to provide a device for separating and renewing the phases of a diphasic mixture, for example a liquidxe2x80x94liquid diphasic emulsion, which does not have the drawbacks, limitations, defects and disadvantages of devices of the prior art and which solves the problems of the prior art.
This aim and others are attained, in accordance with the invention, by a device for separating and renewing the phases of a liquidxe2x80x94liquid diphasic mixture, comprising a first liquid phase and a second liquid phase circulating in counter-current in a liquidxe2x80x94liquid extraction device, wherein said separation device is in the form of a straight hollow cylinder, in which the principal generator is substantially perpendicular to the direction of movement of the liquid phases, and in which one of the bases comprises the wall of the extraction device or is positioned in contact with this wall, said cylinder comprising:
An input orifice for the phase that one wishes to trap, placed on the lateral wall of the cylinder, substantially in the axis of movement of said phase that one wishes to trap.
An output orifice for said phase that one wishes to trap, separated, relatively smaller than said input orifice and located on the other cylinder base.
A third orifice, for the other phase, of intermediate size between the size of the input orifice and the size of the output orifice, placed near to the input orifice.
The device for separating and renewing phases according to the invention, due to its specific geometry, the specific lay out of the phase input and output orifices and the relatively specific dimensions of these orifices, has the effect, among other things, of limiting hydraulic disruptions, not affecting the characteristics of the diphasic mixture, and allowing complete, total separation of the phases. As a result, the device according to the invention provides a solution to the problems posed by devices of the prior art and meets, in a satisfactory manner, all of the requirements indicated above.
Preferably, the diphasic mixture is a liquidxe2x80x94liquid diphasic emulsion (or dispersion).
Advantageously, the material making up the device according to the invention has a wettability that is more adapted to the phase that one wishes to trap.
The phase that one wishes to trap is generally either an organic phase or an aqueous phase.
Thus, if the phase that one wishes to trap is an organic phase, a material that is both organophilic and hydrophobic, such as TEFLON(copyright) (PTFE, polytetrafluoroethylene), PVDF (poly(vinylidene fluoride)) which better resists radiation), or polychlorotrifluoroethylene (KEL-F(copyright)) is preferably selected.
If the phase that one wishes to trap is an aqueous phase, then a hydrophilic material, such as stainless steel or polyethylene, is preferably selected.
Advantageously, the device according to the invention has a small size, and is thus perfectly adapted to the liquidxe2x80x94liquid extraction devices in installations for reprocessing used nuclear fuels.
Despite its small size, it perfectly fulfills its role of separator, while nevertheless retaining sufficient volume of separated phase to allow physical and chemical measurements and analyses to the carried out, for example, on-line.
The size and the dimensions of the device according to the invention are obviously a function of the size of the liquidxe2x80x94liquid extraction device, in which it will be placed.
The length and the diameter of the devices are adjusted in order to:
Maintain the local volume
Ensure a transparency of 20 to 30% (the separators then replace the column packing plates).
The length of the device thus remains generally less than or equal to 85% of the diameter of the body or the flange. The maximum diameter of the device is generally less than or equal to 90% of the diameter of the body or the flange of the extraction device.
It should also be pointed out that the intermediate flange does not necessarily have the same geometry as the body.
The minimum values are the minimum diameter and length values (separation volume) required to ensure separation and renewal.
According to our experience, the minimum length is close to 6 mm, for example (1minxe2x88x926 mm) and the minimum diameter is near to 10 mm, for example (Øminxe2x88x9210 mm).
But this also depends on the material used and the nature of the phase. In fact, the xe2x80x9ccouplingxe2x80x9d is more or less important on the internal walls depending on the affinity, viscosity, etc.
Thus, as an example, if the extraction device has a diameter (body diameter) of 50 mm, the device(s) according to the invention will be cylinders with diameter of 25 mm and length of 20 mm.
If the extraction device has a diameter of 27 mm, the device(s) according to the invention will be cylinders with diameter of 15 mm and length of 12 mm.
Finally, if the extraction device has a diameter of 15 mm, the device(s) according to the invention will be cylinders with diameter of 12 mm and length less than 10 mm (exterior 12 mm to 13 mm).
The separation device according to the invention may be fitted with one or several different sensors, to carry out measurements in the separated phase.
These measurements are particularly physical and/or chemical measurements, such as concentration, conductivity, temperature, pH, etc.
In addition, the invention concerns an intermediate instrumentation flange for a liquidxe2x80x94liquid extraction device comprising one or several devices for separating and renewing phases, as described above.
Advantageously, said flange is fitted with one or several sensor(s), for example from one to ten sensors that are sensors that carry out physical/chemical measurements, on-line, in the separated phase of each of the devices for separating and renewing the phases.
Advantageously, said flange is fitted, in addition, with one or several sensor(s), for example from one to ten sensors that are ultrasonic sensors for carrying out measurements within the diphasic mixture itself, for example the emulsion.
The sensor(s) (whether in the separators or independent of these in the flanges or independent of these) carry out physical, chemical, optical, acoustical measurements, selected particularly among density, concentration, acidity, temperature, pH, conductivity, diffusion, diffraction, light absorption and propagation and attenuation of sound wave measurements.
The flange may thus comprise one or several sensor(s) for carrying out reference measurements relating to one or several parameter(s) or order(s) of magnitude in the separated phase of the phase separation device(s) and one or several sensor(s) for carrying out measurements relating to the same parameter(s) or order(s) of magnitude within the emulsion.
The sensor(s) may in particular be ultrasonic sensors.
The flange may advantageously comprise three or four ultrasonic sensors and two phase separation devices.
Finally, the invention concerns an on-line measurement, instrumentation device for a liquidxe2x80x94liquid extraction device comprising one or several flange(s), as defined above.
Advantageously, said flanges are placed along the extraction device, in order to establish a measurement profile concerning one or several parameter(s) of the mixture.