Device for mixing powders by cryogenic fluid and generating vibrations

Abstract

A device for mixing powders by a cryogenic fluid, characterised in that it comprises: a chamber for mixing the powders, comprising a cryogenic fluid, provided with means for forming a fluidised powder bed; a chamber for supplying powders in order to allow the powders to be introduced into the mixing chamber; a chamber for supplying cryogenic fluid in order to allow the cryogenic fluid to be introduced into the mixing chamber; a system for generating vibrations in the fluidised powder bed; and a system for controlling the system for generating vibrations.

Claims

1. Device for mixing powders by a cryogenic fluid, comprising: a chamber for mixing the powders, comprising a cryogenic fluid, provided with means for forming a fluidised powder bed, a chamber for supplying powders in order to allow the powders to be introduced into the mixing chamber, a chamber for supplying cryogenic fluid in order to allow the cryogenic fluid to be introduced into the mixing chamber, a system for generating vibrations in the fluidised powder bed, a system for controlling the system for generating vibrations.

2. Device according to claim 1, wherein the powders to be mixed are actinide powders.

3. Device according to claim 1, wherein the cryogenic fluid comprises a slightly hydrogenated liquid, which is a liquid comprising at most one hydrogen atom per molecule of liquid, having a boiling temperature less than that of water.

4. Device according to claim 1, wherein it further comprises a system for analysing the concentration of the suspension of powders and of the cryogenic fluid in the mixing chamber, of which the operation is in particular controlled by the controlling system.

5. Device as claimed in claim 1, wherein the mixing chamber is configured in such a way that the introduction of cryogenic fluid into the latter allows for a fluidisation of the powders to be mixed by percolation of the cryogenic fluid through the powder bed fluidised as such.

6. Device as claimed in claim 1, wherein the mixing chamber comprises a distribution system, in particular a grille or a sintered part, of the cryogenic fluid through the fluidised bed of powders in order to allow for a homogeneous distribution of the cryogenic fluid in the fluidised bed.

7. Device as claimed in claim 1, wherein the system for generating vibrations is at least partially located in the fluidised bed of powders.

8. Device according to claim 7, wherein the system for generating vibrations comprises sonotrodes introduced into the fluidised bed of powders.

9. Device according to claim 8, wherein the sonotrodes are controlled independently by the controlling system in order to induce a periodic phase shift of the phases between the sonotrodes in order to introduce unsteady interferences that improve the mixture within the fluidised bed powders.

10. Device according to claim 7, wherein the sonotrodes are configured to generate pseudo-chaotic oscillations of the Van der Pol type.

11. Device as claimed in claim 1, wherein it further comprises means for agitation in the mixing chamber so as to allow the mixing of the powders placed in suspension in the cryogenic fluid.

12. Device as claimed in claim 1, wherein it comprises a system of electrostatic charge of the powders intended to be introduced into the mixing chamber.

13. Device according to claim 12, wherein a portion of the powders is put into contact with a portion of the electrostatic charge system in order to be positively electrostatically charged and wherein the other portion of the powders is put into contact with the other portion of the electrostatic charge system in order to be negatively electrostatically charged, in order to allow for a differentiated local agglomeration.

14. Device as claimed in claim 1, wherein the cryogenic fluid is liquefied nitrogen.

15. Method for mixing powders by a cryogenic fluid, implemented by means of a device as claimed in claim 1, comprising the following steps: a) introduction of powders intended to be mixed into the mixing chamber through the chamber for supplying powders, b) introduction of cryogenic fluid intended to allow for the fluidisation of the fluidised bed of powders into the mixing chamber through the chamber for supplying cryogenic fluid, c) setting into vibration of the suspension of powders and of cryogenic fluid in the mixing chamber through the system for generating vibrations, d) obtaining of a mixture formed from powders after evaporation of the cryogenic fluid.

16. Method according to claim 15, wherein during the first step a), the powders are electrostatically charged differently in order to favour differentiated local agglomeration.

17. Method according to claim 15, wherein it also comprises the step of controlling the system for generating vibrations through the controlling system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention can be better understood when reading the following detailed description, of non-limiting embodiments of the latter, as well as examining the figures, diagrammatical and partial, of the annexed drawing, wherein:

(2) FIG. 1 shows a diagram illustrating the general principle of a device for mixing powders by a cryogenic fluid in accordance with the invention,

(3) FIG. 2 partially shows an example of the device in accordance with the invention,

(4) FIG. 3 shows a representation of lines of interferences induced by two vibrational sources that two vibratory sources that have the same pulse frequency,

(5) FIGS. 4A and 4B show the generation of stable oscillations induced by an oscillator of the Van der Pol type after convergence, and FIGS. 5A and 5B show the generation of quasi-chaotic oscillations of an oscillator of the Van der Pol type when its control parameters are adapted, and

(6) FIGS. 6, 7 and 8 respectively show photographs of a first type of powders before mixing, of a second type of powders before mixing, and of the mixture obtained from the first and second types of powders after mixing through a device and a method in accordance with the invention.

(7) In all of these figures, identical references can designate identical or similar elements.

(8) In addition, the various portions shown in the figures are not necessarily shown according to a uniform scale, in order to render the figures more legible.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(9) Note that in the embodiments described hereinafter, the powders P considered are actinide powders that allow for the manufacture of pellets of nuclear fuel. In addition, the cryogenic fluid considered here is liquefied nitrogen. However, the invention is not limited to these choices.

(10) In reference to FIG. 1, a diagram is shown illustrating the general principle of a device 1 for mixing powders P by a cryogenic fluid according to the invention.

(11) According to this principle, the device 1 comprises a mixing chamber E1, preferably thermally insulated, of powders P provided with means for forming a fluidised powder bed Lf, which can be seen in FIG. 2 described in what follows.

(12) In addition, the device 1 comprises a chamber A1 for supplying powders P in order to allow for the introduction of powders P into the mixing chamber E1, and a chamber B1 for supplying cryogenic fluid FC in order to allow for the introduction of the cryogenic fluid FC into the mixing chamber E1. In this way, it is possible to obtain a suspension of powders P and of the cryogenic fluid FC in the mixing chamber E1 forming a fluidised bed Lf.

(13) The chamber B1 for supplying cryogenic fluid FC can correspond to a chamber for distributing or a chamber for recirculating cryogenic fluid FC. This chamber B1 for supplying can allow for the distribution and/or the recycling of cryogenic fluid FC. It can in particular for a portion rely on a pressurising of a reservoir for the supply of liquefied gas.

(14) Moreover, advantageously, the device 1 also comprises a system for generating vibrations Vb in the fluidised powder bed Lf, a system Sp for controlling this system for generating vibrations Vb, and a system for analysing the concentration Ac of the suspension of powders P and of cryogenic fluid FC in the mixing chamber E1, of which the operation is controlled by the controlling system Sp.

(15) The controlling system Sp can in particular allow for the controlling of the operation of the device 1 and the processing of data, in particular in terms of conditions for supplying with powders P, with cryogenic fluid FC and/or in terms of amplitude of the vibrations.

(16) Advantageously, as it will appear more clearly in reference to FIG. 2, the mixing chamber E1 is configured in such a way that the introduction of cryogenic fluid FC into the latter will allow for a placing in fluidisation of the powders P to be mixed by percolation of the cryogenic fluid FC through the powder bed fluidised as such Lf.

(17) In reference to FIG. 2 indeed, an example of the mixing device is partially and diagrammatically shown 1 in accordance with the invention.

(18) This mixing device 1 comprises a mixing chamber E1 forming a reservoir with a main vertical axis having advantageously a symmetry of revolution, in particular in the shape of a cylinder, and being advantageously thermally insulated in order to minimise heat losses as its vocation is to receive a circulating liquefied gas phase.

(19) Advantageously, the cryogenic fluid FC (liquefied gas) is introduced into the bottom portion of the mixing chamber E1, at the inlet of the fluidised bed Lf of powders P, through a distribution system Sd, in particular in the form of a grille or sintered part, making it possible to distribute the cryogenic fluid FC homogeneously over the section of the passage of the fluidised bed Lf.

(20) Moreover, the mixing chamber E1 can be provided with a diverging zone in order to disengage the smallest particles of powders P and allow them to remain in the zone of the fluidised bed Lf.

(21) Furthermore, a system for analysing the concentration Ac of the suspension of powders P and of cryogenic fluid FC in the mixing chamber E1 is also provided, with this system Ac comprising in particular an optical sensor Co making it possible to observe the fluidised bed Lf of powders P through a viewing porthole H. The system Ac is as such interfaced through the fluidised bed Lf.

(22) The system for analysing the concentration Ac, provided with the optical sensor Co, can make it possible to analyse the concentration of the powders P, and even also analyse the granulometry of the granular medium formed in the mixing chamber E1.

(23) The system for analysing the concentration Ac can comprise an optical fibre of the emitting type (source of light illuminating the fluidised bed Lf) and receiving (sensor) type. It can further comprise a camera. Note then that the concentration of the particles depends on the distance between the emitting fibre and the receiving fibre, on the granulometric distribution of the particles, in the refractive index of the granular medium, and on the wavelength of the incident beam in the dispersion medium.

(24) Moreover, the device 1 comprises the system for generating vibrations Vb. This system advantageously comprises sonotrodes So.

(25) As can be seen in FIG. 2, the system for generating vibrations Vb is introduced in line with the fluidised bed Lf as close as possible to the introduction of the cryogenic fluid FC. In particular, the sonotrodes So can plunge within the fluidised bed Lf.

(26) The sonotrodes So can be controlled independently by the controlling system Sp (not shown in FIG. 2) in order to induce a periodic phase shift of the phases between the sources of vibrations in order to introduce unsteady interferences, in such a way as to improve the mixture within the fluidised bed Lf of powders P. In this respect, FIG. 3 shows a representation of the interference lines induced by two vibratory sources S1 and S2 having the same pulse frequency.

(27) Moreover, advantageously, the controlling of the vibrations through the controlling system Sp can induce quasi-chaotic vibratory signals. This can be achieved by controlling the sonotrodes So as as many oscillators of the Van der Pol type having unsteady adjustment parameters. In this respect, FIGS. 4A-4B and 5A-5B show the forms of interference within the suspension of powders P induced by two sources that have the same pulse phase, with these phases being constant. More precisely, FIGS. 4A and 4B show the generation of stable oscillations after convergence (parameters of the oscillator chosen: a=2.16, b=2.28 and w.sub.0=3 for an equation of motion of the type x+ax.Math.(x.sup.2/b.sup.21)+w.sub.0.sup.2.Math.x=0), while FIGS. 5A and 5B show the generation of quasi-chaotic oscillations of an oscillator of the Van der Pol type, of an equation of the type x+ax.Math.(x.sup.2/b.sup.21)+w.sub.0.sup.2.Math.x=0, by time variation of the pulse w.sub.0.

(28) Note that, by varying the phases of the sources of vibrations, the interferences can travel by a distance equivalent to the magnitude of the wavelength of the vibrations injected within the fluidised bed Lf. This thus allows for an addition degree of mixture.

(29) The application of vibrations according to complex oscillations, in particular quasi chaotic, contributes to a practically ideal mixture effect.

(30) Moreover, it is also to be noted that the chamber A1 for supplying powders P (not shown in FIG. 2) can allow for a supply via gravity, or even by a device of the endless screw type, or further even through a vibrating bed, for example.

(31) In addition, advantageously, the powders P can be electrostatically charged with opposite charges in order to make it possible during the placing in suspension to obtain a differentiated reagglomeration.

(32) The table 1 hereinafter moreover gives an example of the dimensioning of a device 1 in accordance with the invention.

(33) TABLE-US-00001 TABLE 1 Characteristics of the device 1 Values Useful diameter of the mixing chamber E1 15 cm Useful height of the mixing chamber E1 40 cm Circulation flow rate of the cryogenic fluid FC 0.5 m.sup.3/h Useful load of powders P 2 kg Mixing time about 5 min

(34) The effectiveness of the mixture that can be achieved through this invention can be characterised by the homogeneity of the granular medium obtained after mixing. As such, FIGS. 6, 7 and 8 respectively show photographs of a first type of powders before mixing, of a second type of powders before mixing, and of the mixture obtained from the first and second types of powders after mixing through a device 1 and a method in accordance with the invention.

(35) More precisely, FIG. 6 shows aggregates of cerium dioxide powders CeO.sub.2, FIG. 7 shows aggregates of alumina powders Al.sub.2O.sub.3, and FIG. 8 shows the mixture of these powders obtained with a mixing time of about 30 seconds.

(36) Good homogeneity of the granular medium after mixing is as such observed (of two powders implemented with equivalent masses). Indeed, in FIG. 8, it can be observed that for a scale of a few dozen microns, the aggregates of the two powders are present in a relatively equally distributed manner and the size of the aggregates has hardly varied (close to that of the initial powders to be mixed, here with a dimension close to 5 m).

(37) The invention as such makes use of various technical effects that make it possible in particular to achieve the desired level of homogenisation, such as those described hereinafter: the improved deagglomeration, at least partial, of the powders P when the latter are placed in suspension in the cryogenic liquid FC, the improvement of the wettability of the powders P by using the liquefied gas constituted by the cryogenic fluid FC, which is a liquid with a low surface tension, compared to water, with the latter able to be used advantageously without using any additive that is difficult to eliminate, the agitation close to the regime of a perfectly agitated reactor implemented by the movement of the means for agitation, able or not able to use the placing in vibration of the suspension as described in what follows, with these vibrations then being advantageously unsteady in order to limit the heterogeneous zones.

(38) Of course, the invention is not limited to the embodiments that have just been described. Various modifications can be made thereto by those skilled in the art.