Device for granulating powders by cryogenic atomisation

Abstract

A device for granulating powders by cryogenic atomisation, characterised in that it comprises: a device for mixing powders by cryogenic fluid, comprising at least one chamber for mixing powders, comprising a cryogenic fluid; and a device for atomising a suspension of powders mixed by the device for mixing powders in order to allow a granulation of the powders, comprising a way of fractionating the suspension of powders making it possible to adjust the size of the droplets of powders to be atomised, and a method for adjusting the moisture of the mixed powders and/or the moisture of the atomisation atmosphere.

Claims

1. A device for granulating powders by cryogenic atomisation, comprising: a device for mixing powders by a cryogenic fluid, comprising at least one chamber for mixing powders, comprising the cryogenic fluid, wherein the cryogenic fluid is a liquified gas and chemically inert; and a device for atomising a suspension of powders mixed by the device for mixing powders in order to allow for a granulation of the powders, wherein the device fractionates the suspension of powders making it possible to adjust the size of droplets of the powders and adjusts the moisture of the mixed powders and/or moisture of the atomisation atmosphere and wherein for fractionating the suspension of powders, the device is configured to allow for the adjusting of the diameter of the droplets of powders to be atomised, in such a way that the diameter of the droplets of powders is defined according to the following relationship: $\frac{d_o}{D}=G\left\{\frac{\mathrm{fD}}{v},\frac{1}{\mathrm{We}},\frac{1}{\mathrm{Re}},\frac{A}{D}\right\}$ with We=ρν.sup.2.Math.(d.sub.o)/σ and Re=ρd.sub.oν/μ, where: f represents the vibration frequency of the device for atomising, ν represents the speed of the suspension of powders, ρ represents the density of the suspension of powders to be fractionated, μ represents the viscosity of the suspension of powders to be fractionated, σ represents the surface tension of the suspension of powders to be fractionated, A represents the oscillation amplitude of an atomisation nozzle of the device for atomising, d.sub.0 represents the diameter of the droplets, and D represents the diameter of an atomisation nozzle of the device for atomising.

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

3. The 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, and wherein the cryogenic fluid is a gas at room temperature and a liquid at a temperature lower than room temperature.

4. The device as claimed in claim 1, wherein the device for mixing further comprises: a chamber for supplying powders in order to allow the powders to be introduced into the at least one chamber for mixing, means for agitation in the mixing chamber so as to allow the mixing of the powders placed in suspension in the cryogenic fluid.

5. The device according to claim 4, wherein the device for mixing comprises means for mixing of the at least one chamber for mixing according to a gyroscopic movement.

6. The device according to claim 4, wherein the device for mixing comprises: a plurality of mixing chambers of the powders, arranged successively in series one after the other, the chamber for supplying powders allowing for the introduction of powders into at least the first mixing chamber, a plurality of systems for restricting passage of the powders, with each system for restricting the passage being located between two successive mixing chamber, in order to constrain the distribution of powders from one mixing chamber to the next, with each mixing chamber comprising the cryogenic fluid and means for agitation so as to allow the mixing of the powders placed in suspension in the cryogenic fluid.

7. The device according to claim 6, wherein the systems for restricting the passage comprise screens and/or diaphragms.

8. The device according to claim 4, wherein the means for agitation comprise mobile mixing devices.

9. The device according to claim 4, wherein the means for agitation comprise means for generating vibrations.

10. The device according to claim 4, wherein the device for mixing comprises a system of electrostatic charge of the powders intended to be introduced into the mixing chamber or chambers.

11. The device according to claim 10, 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.

12. The device as claimed in claim 1, wherein the cryogenic fluid is liquefied nitrogen.

13. Method for granulating powders by cryogenic atomisation using the device claim 1, and comprising the following steps: a) introducing powders and cryogenic fluid into at least one chamber of the device for mixing powders by a cryogenic fluid in order to obtain a suspension of powders and of cryogenic fluid, b) atomising of the suspension of powders and of cryogenic fluid through the device for atomising in order to allow for a granulation of the powders, wherein the suspension of powders are fractionated making it possible to adjust the size of droplets of the powders and adjusts the moisture of the mixed powders and/or moisture of the atomisation atmosphere and wherein the diameter of the droplets of powders to be atomised are adjustable in such a way that the diameter of the droplets of powders is defined according to the following relationship: $\frac{d_o}{D}=G\left\{\frac{\mathrm{fD}}{v},\frac{1}{\mathrm{We}},\frac{1}{\mathrm{Re}},\frac{A}{D}\right\}$ with We=ρν.sup.2.Math.(d.sub.o)/σ and Re=ρd.sub.oν/μ, where: f represents the vibration frequency of the device for atomising, ν represents the speed of the suspension of powders, ρ represents the density of the suspension of powders to be fractionated, μ represents the viscosity of the suspension of powders to be fractionated, α represents the surface tension of the suspension of powders to be fractionated, A represents the oscillation amplitude of an atomisation nozzle of the device for atomising, d.sub.0 represents the diameter of the droplets, and D represents the diameter of an atomisation nozzle of the device for atomising, and c) obtaining of granules formed from powders.

14. Method according to claim 13, wherein during the first step a), the powders are oppositely electrostatically charged in order to favour differentiated local agglomeration.

15. A device for granulating powders by cryogenic atomisation, comprising: a device for mixing powders by a cryogenic fluid, comprising at least one chamber for mixing powders, comprising the cryogenic fluid, wherein the cryogenic fluid is a liquified gas and chemically inert; and a device for atomising a suspension of powders mixed by the device for mixing powders in order to allow for a granulation of the powders, wherein the device fractionates the suspension of powders making it possible to adjust the size of droplets of the powders and adjusts the moisture of the mixed powders and/or moisture of the atomisation atmosphere and wherein for fractionating the suspension of powders, the device is configured to allow for the adjusting of the diameter of the droplets of powders to be atomised by modulation according to a reduction factor of the diameter between the diameter of the droplets of powders to be atomised and the diameter of the granules obtained after atomisation of the suspension of mixed powders and evaporation of the cryogenic fluid, in such a way that: $\frac{d_0}{d_s}=R=\sqrt[3]{\frac{{\left[U\right]}_f}{{\left[U\right]}_i}}$ where: d.sub.0 represents the diameter of the droplets, d.sub.s represents the diameter of the granules, [U].sub.f represents the volume occupancy rate of powders in the agglomerate of granules formed after granulation, and [U].sub.i represents the concentration in powders of the suspension of powders to be atomised.

16. A device for granulating powders by cryogenic atomisation, comprising: a device for mixing powders by a cryogenic fluid, comprising at least one chamber for mixing powders, comprising the cryogenic fluid, wherein the cryogenic fluid is a liquified gas and chemically inert; and a device for atomising a suspension of powders mixed by the device for mixing powders in order to allow for a granulation of the powders, wherein the device fractionates the suspension of powders making it possible to adjust the size of droplets of the powders and adjusts the moisture of the mixed powders and/or moisture of the atomisation atmosphere and wherein the device for mixing further comprises: the at least one chamber for mixing the powders, comprising the 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 the 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.

17. The device according to claim 16, wherein the device for mixing further comprises a system for analysing the concentration of the suspension of powders and of the cryogenic fluid in the at least one chamber for mixing.

18. The device according to claim 16, wherein the at least one chamber for mixing comprises a distribution system 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.

19. The device according to claim 16, wherein the system for generating vibrations is at least partially located in the fluidised bed of powders.

20. The device according to claim 19, wherein the system for generating vibrations comprises sonotrodes introduced into the fluidised bed of powders.

21. The device according to claim 20, 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 of powders.

22. The device according to claim 20, the sonotrodes are configured to generate pseudo-chaotic oscillations of the Van der Pol type.

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 granulating powders by cryogenic atomisation in accordance with the invention,

(3) FIG. 2 diagrammatically shows the phases undergone by the suspension of atomised powders in order to obtain granules of powders,

(4) FIG. 3 shows a diagram illustrating the general principle of an example of a device for mixing powders of a device for granulating powders by cryogenic atomisation in accordance with the invention,

(5) FIG. 4 diagrammatically shows the agglomeration of particles of powders charged oppositely prior to the introduction thereof into mixing chambers of a device for mixing powders in accordance with the principle of the FIG. 3,

(6) FIGS. 5 and 6 respectively show two examples of devices for mixing in accordance with the general principle of FIG. 3 for a device for granulating in accordance with the invention,

(7) FIGS. 7A, 7B and 7C diagrammatically show alternative embodiments of the mobile mixing facilities of the device for mixing of FIGS. 5 and 6,

(8) FIG. 8 shows a diagram illustrating another example of a device for mixing powders of a device for granulating powders by cryogenic atomisation in accordance with the invention,

(9) FIG. 9 shows a diagram illustrating the general principle of another device for mixing powders by a cryogenic fluid pour a device for granulating powders by cryogenic atomisation in accordance with the invention,

(10) FIG. 10 partially shown another example of a device for mixing for a device for granulating powders by cryogenic atomisation in accordance with the invention,

(11) FIG. 11 shows a representation of lines of interferences induced by two vibrational sources having two vibratory sources that have the same pulse frequency, and

(12) FIGS. 12A and 12B show the generation of stable oscillations after convergence, and FIGS. 13A and 13B show the generation of quasi-chaotic oscillations of an oscillator of the Van der Pol type.

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

(14) 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

(15) 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.

(16) In reference to FIG. 1, a diagram illustrating the general principle of a device 20 for granulating powders P by cryogenic atomisation in accordance with the invention is shown.

(17) According to this principle, the device 20 for granulating powders P by cryogenic atomisation comprises a device 1 for mixing powders P by a cryogenic fluid FC and a device 10 for atomising a suspension of powders P mixed by the device 1 for mixing powders P in order to allow for a granulation of the powders P.

(18) The device 1 for mixing powders P comprises a mixing chamber E1 of powders P, wherein are introduced the cryogenic fluid FC and the powders P coming from a device A1 for supplying.

(19) The device 10 for atomising is coupled to the device 1 for mixing powders P, and comprises an atomisation nozzle 11 of droplets Go of powders P. Advantageously, the device 10 for atomising comprises a sonotrode.

(20) Advantageously, the device 10 for atomising of the suspension of powders P mixed by the device 1 for mixing powders P comprises means for fractionating the suspension of powders P making it possible to adjust the size of the droplets Go of powders P to be atomised. In addition, this device 10 also comprises means for adjusting the humidity of the mixed powders P and/or the moisture of the atomisation atmosphere.

(21) The adjusting of the humidity of the powders P to be mixed and to be atomised, or the adjusting of the humidity of the atmosphere within which is carried out the atomising of the powders, can make it possible to adjust the cohesion of the agglomerates, or granules Gs, resulting from the atomisation, through the creation of liquid bridges between aggregates Gs, as described hereinafter in reference to FIG. 2.

(22) The controlling of the size of the droplets Go of the suspension of mixed powders P can be carried out through diverse relationships such as described hereinafter.

(23) Indeed, the means for fractionating the suspension of powders P are advantageously configured to allow for the adjusting of the diameter d.sub.o of the droplets Go of powders P to be atomised, in such a way that the diameter d.sub.o of the droplets Go of powders P is defined according to the following relationship:

(24) $\frac{d_o}{D}=G\left\{\frac{\mathrm{fD}}{v},\frac{1}{\mathrm{We}},\frac{1}{\mathrm{Re}},\frac{A}{D}\right\}$
with We=ρν.sup.2.Math.(d.sub.o)/σ and Re=ρd.sub.oν/μ,
where:
f represents the vibration frequency of the device 10 for atomising,
ν represents the speed of the suspension of powders P,
ρ represents the density of the suspension of powders P to be fractionated,
μ represents the viscosity of the suspension of powders P to be fractionated,
σ represents the surface tension of the suspension of powders P to be fractionated,
A represents the oscillation amplitude of the atomisation nozzle 11 of the device 10 for atomising,
d.sub.o represents the diameter of the droplets Go, and
D represents the diameter of the atomisation nozzle 11 of the device 10 for atomising.

(25) Moreover, the content in powders in the suspension of mixed powders P to be atomised can advantageously be modulated in order to control the reduction factor R of the diameter between the diameter d.sub.o of the droplets Go of powders P to be atomised and the diameter d.sub.s of the granules Gs, or agglomerates, obtained after atomisation of the suspension of mixed powders P and evaporation of the cryogenic fluid FG.

(26) As such, the reduction factor R can be approached via the following formula:

(27) $\frac{d_0}{d_s}=R=\sqrt[3]{\frac{{\left[U\right]}_f}{{\left[U\right]}_i}}$
where:
d.sub.o represents the diameter of the droplets Go,
d.sub.s represents the diameter of the granules Gs,
[U].sub.f represents the volume occupancy rate of powders P in the agglomerate of granules Gs formed after granulation, and
[U].sub.i represents the concentration in powders P of the suspension of powders P to be atomised.

(28) Beyond controlling the diameter d.sub.o of the droplets Go of the suspension of powders P through one or several of the aforementioned parameters, adjusting the humidity of the powders P makes it possible to procure an increased cohesion of the granules Gs, or agglomerates. This adjustment in the humidity can be done during the introduction of the powders P into the mixing chamber E1 with the liquefied gas FG, or during the evaporation of the liquefied gas FG at the outlet of the atomisation nozzle 11, as shown in FIG. 2 described hereinafter.

(29) As such, in reference to FIG. 2, the phases undergone by the suspension of atomised powders P in order to obtain granules Gs of powders have been diagrammatically shown.

(30) In the phase a, the droplets Go of the powders P resulting from the atomisation are found of the suspension of powders P. These droplets Go comprise the liquefied gas FG and the powders P.

(31) During the phase b, the liquefied gas FG evaporates. The adjusting of the rate of humidity R.sub.Hu can be carried out at this level, as shown.

(32) Then, in the phase c, the agglomeration of the powders is obtained P in order to obtain the spherical granules Gs formed from particles of powders P between which are found liquid bridges of liquefied gas FG that is not evaporated.

(33) Now in reference to FIG. 3, a diagram is shown illustrating the general principle of an example of the device 1 for mixing powders P by a cryogenic fluid for a device 20 for granulating powders P by cryogenic atomisation in accordance with the invention, such as for example described hereinabove in reference to FIG. 1.

(34) According to this principle, the device for mixing 1 comprises a number n of mixing chambers E1, . . . , En of the powders P, arranged successively in series one after the other according to the same vertical direction in such a way that the powders can circulate through the mixing chambers E1, . . . , En under the effect of the force of gravity.

(35) Moreover, the device 1 comprises a number n−1 of systems for restricting the passage R1, . . . , Rn−1 of the powders P, with each system for restricting the passage R1, . . . , Rn−1 being located between two successive mixing chambers E1, . . . , En, in order to constrain the distribution of powders P from one mixing chamber E1, . . . , En to the next. Examples of such systems for restricting the passage R1, . . . , Rn−1 are shown in what follows in reference in particular to FIGS. 5 and 6.

(36) Furthermore, the systems for restricting the passage can comprise screens. The systems for restricting the passage can further comprise diaphragms.

(37) The systems for restricting the passage can be adjusted and configured so that their section of passage is decreasing according to the flow of the powders through the plurality of mixing chambers, the section of passage of an (n−1)th system for restricting the passage being as such greater than the section of passage of an nth system of restricting the passage by following the flow of the powders.

(38) In addition, the section of passage of the systems for restricting the passage can be less than the natural section of flow of the powders in such a way that these powders are necessarily deagglomerated when they pass from one mixing chamber to the other. As such, the residence time of the particles to be mixed is intrinsically sufficient to allow for deagglomeration.

(39) In addition, the device 1 also comprises two chambers A1 and A2 for supplying powders P, provided in particular for distributing powders of different types.

(40) The two chambers A1 and A2 for supplying powders P allows for the introduction of the powders P into the first mixing chamber E1 in contact with the cryogenic fluid FC of the first chamber E1. Then the powders P successively pass through the systems for restricting the passage R1, . . . , Rn−1 and the mixing chambers E2, . . . , En, with each mixing chamber comprising a cryogenic fluid FC.

(41) In addition, each mixing chamber E1, . . . , En comprises means for agitation 2 allowing for the mixing of powders P placed in suspension in the cryogenic fluid FC. Examples of such means of agitation 2 are provided in what follows in reference in particular to FIGS. 5 and 6.

(42) The two chamber for supplying A1 and A2 comprise for example hoppers with adjustable supply, using for example an endless screw, and/or systems of the metering type, in particular vibrating plates or tunnels.

(43) Furthermore, advantageously, the device 1 further comprises an electrostatic charge system C+, C− of the powders P introduced into the mixing chambers E1, . . . , En.

(44) In particular, the portion of the powders P contained in the first chamber for supplying A1 is put into contact with the positive portion C+ of the electrostatic charge system in order to be positively electrostatically charged, while the portion of the powders P contained in the second chamber for supplying A2 is put into contact with the negative portion C− of the electrostatic charge system in order to be negatively electrostatically charged.

(45) In this way, it is possible to allow for a differentiated local agglomeration, in other words prevent self-agglomeration. As shown in FIG. 4, which diagrammatically shows the agglomeration of particles of powders P charged oppositely prior to the introduction thereof into the mixing chambers E1, . . . , En, with the particles of the two powders P to be mixed being of an opposite electrostatic charge, a possible reagglomeration will occur mostly through the interposing of powders with a nature, and therefore charge, that are different. This as such makes it possible to favour mixing on the scale of the particles that comprise the powders P to be mixed.

(46) 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, the latter being advantageously used without the use of additives which are 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.

(47) In reference now to FIGS. 5 and 6, two examples of devices 1 for mixing for a device 20 for granulating powders P by cryogenic atomisation in accordance with the invention are diagrammatically shown, of which the principles have been described hereinabove in reference to FIG. 3.

(48) In each one of these two examples, the device for mixing 1 comprises, in addition to the elements described hereinabove in reference to FIG. 3, an agitation motor 5 able to drive in rotation first means of agitation 2a having the form of mobile mixing facilities 2a in the mixing chambers E1, . . . , En.

(49) These mobile mixing facilities 2a can comprise mobile grinding facilities. These mobile mixing facilities 2a can further comprise blades, mobile facilities with a duvet effect, turbines and/or blades, with these types of mobile facilities being respectively shown in the FIGS. 7A, 7B and 7C. In the embodiments of FIGS. 5 and 6, the mobile mixing facilities 2a comprise turbines.

(50) Moreover, in each one of these two examples, the device 1 further comprises second means of agitation 2b in the form of means for generating ultrasonic vibrations comprising sonotrodes 2b.

(51) In addition, the two embodiments shown in the FIGS. 5 and 6 are differentiated by the nature of the systems for restricting the passage R1, . . . , Rn−1 used.

(52) As such, in the embodiment of FIG. 5, the systems for restricting the passage R1, . . . , Rn−1 comprise diaphragms.

(53) In the embodiment of FIG. 6, the systems for restricting the passage R1, . . . , Rn−1 comprise screens, more precisely meshes of screens.

(54) In these two examples, the systems for restricting the passage R1, . . . , Rn−1 have a section of passage that can be adjusted and as such arranged in such a way that their sections of passage are ranked from the largest to the finest in the descending direction of the flow of powders P. Advantageously also, the sections of passage of these systems for restricting the passage R1, . . . , Rn−1 are less than the section of natural flow of the powders P in order to force the deagglomeration before the passage through these sections.

(55) In reference to FIG. 8, a diagram illustrating another example of the device 1 for mixing powders P for a device 20 for granulating powders P by cryogenic atomisation in accordance with the invention is furthermore shown.

(56) In this example, the device 1 comprises a single mixing chamber E1 and means for mixing MG of this mixing chamber E1 according to a gyroscopic movement.

(57) More precisely, these means for mixing MG according to a gyroscopic movement allow for the rotation of the mixing chamber E1 according to the three axes X1, X2 and X3 of three-dimensional metrology. This type of agitation by gyroscopic movement favours the mixture of powders P when they have high densities compared to the density of the fluid phase of the cryogenic fluid FC located in the mixing chamber E1.

(58) In addition, the mixing chamber E1 comprises means for agitation 2a, for example in the form of turbines.

(59) Now in reference to FIG. 9, a diagram illustrating the general principle of another example of the device 1 for mixing powders P by a cryogenic fluid for a device for granulating 20 in accordance with the invention is shown.

(60) According to this principle, the device for mixing 1 comprises a mixing chamber E1, thermally insulated, of powders P provided with means for forming a fluidised powder bed Lf, which can be seen in FIG. 10 described in what follows.

(61) In addition, the device for mixing 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.

(62) 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.

(63) Moreover, advantageously, the device for mixing 1 comprises also 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.

(64) 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.

(65) Advantageously, as it will appear more clearly in reference to FIG. 10, 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.

(66) In reference to FIG. 10 indeed, an example of the mixing device is partially and diagrammatically shown 1 for a device for granulating 20 in accordance with the invention.

(67) This mixing device 1 comprises a mixing chamber E1 forming a reservoir with a main vertical axis having 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.

(68) 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.

(69) 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.

(70) 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.

(71) 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.

(72) 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.

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

(74) As can be seen in FIG. 10, 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. The sonotrodes So can be controlled independently by the controlling system

(75) Sp (not shown in FIG. 10) 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. 11 shows a representation of the interference lines induced by two vibratory sources S1 and S2 having the same pulse frequency.

(76) Moreover, advantageously, the controlling of the vibrations through the controlling system Sp can induce chaotic vibratory signals. This can be achieved by controlling the sonotrodes So as as many oscillators of the Van der Pol type. In this respect, FIGS. 12A-12B and 13A-13B 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. 12A and 12B show the generation of stable oscillations after convergence (a=2.16, b=2.28 and w.sub.0=3), while FIGS. 13A and 13B 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.2−1)+w.sub.0.sup.2.Math.x=0, by time variation of the pulse w.sub.0.

(77) 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.

(78) The application of vibrations according to complex oscillations, in particular quasi chaotic, contribute to a practically perfect mixing effect.

(79) Moreover, it is also to be noted that the chamber A1 for supplying powders P (not shown in FIG. 10) 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.

(80) 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.

(81) 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.