Method and device for recovering, from suspensions containing explosive charges, said explosive charges, dry

Abstract

A method for obtaining the explosive charge in dry granular form as well as a device suitable for implementing the method. The method includes: filtering the suspension, by passing same through a static filter in order to obtain a cake containing the granular explosive charge agglomerated by residual liquid; dewatering the cake by subjecting the cake to pressurized gas; splitting the dewatered cake and obtaining a fluidized bed of the desired explosive charge by exposing the dewatered cake to at least one stream of gas; at least one stream of gas being injected, under the dewatered cake to impinge said dewatered cake, according to two consecutive modes and the gas having a humidity height below that of the dewatered cake and a dew point temperature higher than the injection temperature thereof; and stopping at least one stream of gas and recovering the explosive charge in dry, granular form.

Claims

1. A process for obtaining, from a suspension of an explosive charge in a liquid, said explosive charge in dry and granular form, comprising: a) filtering, by passage through a static filter, said suspension, in order to obtain a cake, on said filter, including said explosive charge agglomerated by residual liquid; b) dewatering said cake by placing it under gas pressure; c) disintegrating the dewatered cake and obtaining a fluidized bed of the desired explosive charge, in dry and granular form, by the action, on said dewatered cake, of at least one gas jet, said at least one gas jet being injected, under said dewatered cake, in order to impact said dewatered cake, according to two successive sets of conditions: at first, at pressure p and at flow rate f, in order to create, in the dewatered cake, channels emerging in the upper part of said dewatered cake and also a fluidized bed above said dewatered cake; then subsequently, at pressure p and at flow rate F, F>f, in order to put the dewatered cake, traversed by said channels, under lift and to complete its disintegration; and said gas exhibiting a lower moisture content than that of the dewatered cake and a dew point greater than its injection temperature; and d) stopping said at least one gas jet and recovering said explosive charge in dry and granular form.

2. The process as claimed in claim 1, wherein the explosive charge is recovered in granular form and containing less than 1% by weight of liquid.

3. The process as claimed in claim 1, wherein said suspension exhibits a liquid/explosive charge ratio by weight of between 5 and 20.

4. The process as claimed in claim 1, wherein said cake exhibits a liquid/explosive charge ratio by weight of between 1 and 8.

5. The process as claimed in claim 1, wherein dewatering is carried out under a gas pressure between 210.sup.5 and 310.sup.5 Pa absolute (2 and 3 bar absolute).

6. The process as claimed in claim 1, wherein, on conclusion of step b), said dewatered cake exhibits a thickness of a maximum of 10 cm.

7. The process as claimed in claim 1, wherein said dewatered cake exhibits a liquid/explosive charge ratio by weight of between 0.5 and 2.

8. The process as claimed in claim 1, wherein said pressure p and said flow rates f and F are increasing.

9. The process as claimed in claim 1, wherein said gas is injected in the form of at least two jets.

10. The process as claimed in claim 1, wherein said injected gas exhibits a moisture content of less than 2% by weight and a temperature of between 20 and 70 C.

11. The process as claimed in claim 1, wherein said explosive charge is chosen from 3-nitro-1,2,4-triazol-5-one (ONTA), ammonium dinitramide (ADN), 2,4,6-triamino-1,3,5-trinitrobenzene (TATB) and trinitrotoluene (TNT) charges.

12. The process as claimed in claim 1, wherein said liquid is chosen from water, acidic aqueous solutions and organic solvents.

13. The process as claimed in claim 1, wherein the explosive charge is recovered in granular form and containing less than 0.1% by weight of liquid.

14. The process as claimed in claim 1, wherein said injected gas exhibits a moisture content of less than 2% by weight and a temperature of between 50 and 70 C.

15. The process as claimed in claim 1, wherein said liquid is chosen from aliphatic hydrocarbons, halogenated aliphatic hydrocarbons, aromatic hydrocarbons and nonflammable hydrofluoroethers.

16. The process of claim 1, wherein in the filtering step, a substantially cylindrical enclosure comprises, in its volume, in its bottom part, a filter capable of filtering a suspension and retaining a solid phase of the suspension; wherein the suspension is fed to the enclosure with a feeder, the feeder being arranged above the filter, and a liquid is discharged from the enclosure by a liquid discharger, the liquid discharger being arranged below the filter; wherein the enclosure is pressurized to create the pressure p with a pressurizer, the pressurizer being arranged above said filter; wherein the at least one gas jet is injected with a gas-injector, the gas-injector being arranged below the filter and being capable of delivering the gas in the form of at least one upward jet intended to impact the face of the retained solid phase resting on the filter; and wherein the gas is discharged from the enclosure with a gas discharger, the gas discharger being arranged above the filter.

17. The process of claim 16, wherein the pressurizer comprises a deflector.

18. The process of claim 16, wherein the gas-discharger comprises a particle filter.

19. The process of claim 16, wherein the cylindrical enclosure is connected, in its entirety, to earth.

Description

FIGURES

(1) FIGS. 1A to 4 diagrammatically show a device of the invention at different steps of the process of the invention.

(2) FIGS. 1A and 1B illustrate the filtration step (respectively at the start and end of said filtration).

(3) FIGS. 2A and 2B illustrate the step of dewatering the cake (respectively at the start and end of said dewatering).

(4) FIGS. 3A, 3B and 3C illustrate the progression of the disintegration of the dewatered cake until obtaining the fluidized bed (FIG. 3C).

(5) FIG. 4 illustrates the virtually final phase of the process (the dry charge is deposited on the filter, immediately before it is recovered).

(6) The intention is first of all to describe the device of the invention represented in said figures (represented in the course of operation).

(7) The constituent components of said device are described, more specifically with reference to the figures diagrammatically representing process phases during which they are or were directly involved.

(8) In each of the figures, a device 100 comprising an enclosure 10 of substantially cylindrical shape has been shown. In the volume of said enclosure 10, in the bottom part of the volume, the filter 1 is found. Said device 100 additionally comprises:

(9) means 13 for feeding said enclosure 10 with the suspension S to be filtered. These means are arranged in the top part of said enclosure 10, above said filter 1. These means 13 for feeding the suspension S are described more specifically below with reference to FIG. 1A. They comprise, according to the alternative form represented, a pipeline 13a for supplying said suspension S, a valve 13b for control of the supplying of said suspension S and an opening 13c arranged in the wall of said enclosure 10;

(10) means 11 for discharge of the liquid L from said enclosure 10. Said means 11 are obviously arranged in the bottom part of said enclosure 10, under the filter 1. These discharge means are described more precisely below with reference to FIG. 1A. They comprise, according to the alternative form represented, an opening 11a arranged in the bottom of the enclosure 10, a drain 11c and a valve 11b. Said drain 11b is suitable for discharging the liquid L of the suspension S into a receptacle 12;

(11) means 15 for pressurizing said enclosure 10. These means are obviously arranged above the filter 1. They are described more precisely below with reference to FIG. 2A. They are suitable for delivering the pressurizing gas G. They comprise upstream a supply of pressurized gas G or a compressor (means not represented) and then a pipeline 15a for supplying said pressurized gas G, a valve 15b for controlling the delivery of said pressurized gas G and an appropriate opening 15c made in the wall of the enclosure 10 (for the delivery, at the wall, of said pressurized gas G or the passage of said pipeline 15a providing the delivery of said gas G downstream of said opening 15c into the volume above the filter 1). A deflector 16 associated with said pressurizing means 15 has been shown in the figures. The intervention of such a deflector is appropriate for distributing the impact of the (dewatering) gas G over the maximum surface area of the cake 2 to be dewatered;

(12) means 14 for injecting gas G (it has been seen that advantageously G=G), in order to direct jets 4 of said gas G for action on the solid phase retained on said filter 1, for (direct) impact on (the lower face of) said solid phase. Said means 14 are, according to the alternative form represented, arranged (partially under said enclosure 10, completely under said filter 1) in order to deliver jets 4 of gas G under said filter 1 (four vertical upward jets 4). These injection means 14 are described more precisely below with reference to FIG. 3A. They comprise a pipeline 14a for supplying said gas G, a valve 14b for control of the delivery of said gas G, branch pipelines 14a oriented for delivery of jets 4 of gas G through nozzles 14d (provided at their ends) and openings 14c made in the wall (the bottom) of the enclosure 10 for the passage of said branch pipelines 14a. According to another alternative form, not represented, a pipeline equipped with a valve might correspond to each opening (14c);

(13) means 17 for discharge of gas (of the gas G and of the residual liquid L in the gaseous state) from said enclosure 10. These means are obviously arranged above said filter 1, in the top part of the enclosure 10. They are advantageously positioned as shown in the figures, directly above the filter 1, at the maximum distance from the injection of said gas G. Said means 17 are described more precisely below with reference to FIG. 3A. They comprise an orifice 17c made in the wall of the enclosure 10, a pipeline 17a for discharge of gas and a valve 17b. Said pipeline 17a emerges in the volume of the enclosure 10, according to the alternative form represented. A particle filter 18, capable of retaining the smallest particles generated by the disintegration of the dewatered cake 2, is associated with it. This filter might, according to another alternative form, be inserted in the wall, the pipeline not penetrating into the housing.

(14) An opening of the enclosure 10 has been represented at 20, which opening makes possible the recovery of the dried charge, dry, at the end of the process.

(15) It has also been shown, in each of the figures, that, according to the alternative form represented, the device 100 is electrically connected to earth, with continuous monitoring (Q) of the electrical continuity.

(16) It is now intended to describe the process of the invention with reference to the appended figures.

(17) As already indicated, FIG. 1A illustrates the start of the implementation of the filtration. The suspension S, including the explosive charge C in the liquid L, is delivered via the pipeline 13a of the feed means 13. The liquid L passes through the filter 1 and is recovered, via the means for discharge of liquid 11, in the receptacle 12. The valves 13b and 11b are obviously open and the valves 15b and 14b are for their part closed.

(18) All the suspension S having been poured onto the filter 1, a filtration cake 2 is formed on said filter 1. This cake 2 matches the shape of the enclosure 10, over a portion of its height, by thus being placed on the filter 1. It is shown in FIG. 1B, illustrating the end of the filtration step. The liquid L of the suspension S retained in said cake is henceforth referenced L. This cake 2 exhibits a thickness generally of between 5 and 20 cm (see above). Its upper surface has the reference 3 and its lower surface, resting on the filter 1, has the reference 3. On conclusion of this filtration step, the valve 13b is closed.

(19) Dewatering the cake 2 is represented diagrammatically in FIG. 2A. A portion of the liquid L (liquid L trapped in the cake 2) is extracted from said cake 2 (and is recovered in the receptacle 12) under the action of the pressurizing gas G. The valves 13b and 17b being closed, the pressurizing gas G is delivered via the pressurizing means 15. It has been seen that the deflector 16 appropriately provides for the distribution of said gas G at the upper surface 3 of the cake 2. The same references 3 and 3 have been retained for, respectively, the upper and lower surfaces of the cake at the beginning of dewatering (FIG. 2A), during dewatering, at the end of dewatering (FIG. 2B) and in the first phase of disintegration (FIG. 3A).

(20) On conclusion of this step of dewatering the cake 2, feeding with the pressurizing gas G is stopped (the valve 15b is closed) and a dewatered cake 2 is thus found on the filter 1. This cake 2, with a thickness lower than that of the cake 2 (not dewatered), generally of less than 10 cm (see above), is represented in FIG. 2B.

(21) The third step of the process of the invention (two-fold mechanical (in two steps) and thermal action of the gas G) is then carried out on said dewatered cake 2. In the alternative form represented diagrammatically, the disintegration and drying gas G is injected in the form of (four) jets 4 under the filter 1 (it thus (directly) impacts the dewatered cake 2 on its lower face 3 which rests on said filter 1) according to two successive sets of conditions (of pressure p and flowrates: f then F (see above)). The injection and its effect according to the first set of conditions have been represented diagrammatically in FIG. 3A and the injection and its effect according to the second set of conditions have been represented diagrammatically in FIG. 3B.

(22) In said FIG. 3A, the attack on the integrity of the dewatered cake 2 (direct attack by jets of gas, the gas being injected according to the first set of conditions), i.e. the appearance and the growth of channels 6a in the thickness of said dewatered cake 2, which growth of said channels 6a converts the latter into emerging channels 6 (or chimneys 6), has been represented diagrammatically. The eroded material which circulates in said channels 6a and 6 participates in the expansion of the erosion, very particularly at the upper surface 3 of the (disintegrating) dewatered cake 2, once it has exited from said channels 6. The charges thus extracted from said cake 2, which are more or less dry, are suspended above said cake 2. They constitute there an expanding fluidized bed 5a.

(23) In said FIG. 3B, the continuation of the attack on the integrity of the dewatered cake 2 (already partially disintegrated) has been represented diagrammatically. This attack, under the action of more powerful jets 4 (under the direct impact of said jets 4), detaches, from the filter 1, the disintegrating dewatered cake 2, which is then traversed by (wider) channels 6. This leads to a fluidized bed 5b (still expanding) which tends to occupy all the free volume of the enclosure 10.

(24) In FIG. 3C, the dewatered cake 2 has been completely disintegrated and the charge C, as a fluidized bed 5, occupies the entire free volume of the enclosure 10.

(25) In said FIGS. 3A, 3B and 3C, it is understood that the valve 17b is opened for the discharge of a portion of the injected gas G and moreover of the liquid L (in the gaseous state and possibly in the form of droplets) still present in the dewatered cake 2 at the end of the pressurizing step (the valves 13b, 15b and 11b obviously being closed). The charges C having smaller sizes (<30 m) are not discharged; they remain trapped in the particle filter 18.

(26) A description has in particular been given above of the mechanical action of the gas G insofar as it is easily displayed with regard to the physical state of the dewatered cake 2. It has very obviously been understood that said gas G also provides for the drying of the charge C, this drying being better and better as the disintegration of said dewatered cake 2 goes along, the residual liquid L present in said dewatered cake 2 being entrained (in the gaseous state and possibly in the form of droplets).

(27) On conclusion of the implementation of step c of the process, the feed of gas G is stopped (the valve 14b is closed and the jets 4 are cancelled). The fluidized bed 5 disappears and the charge C, in dry and granular form, is deposited on the filter 1. It can be recovered there via the opening 20 of the enclosure 10. This opening 20 has obviously been provided at an appropriate height. The recovery of the dry charge C can be carried out via an airlock, a glove box, arranged on said opening 20. FIG. 4 shows the charge C on the filter 1 and the opened opening 20 with an arrow to symbolize the step of recovery of said charge C in dry and granular form.

EXAMPLE

(28) The process of the invention has been carried out, in a device (enclosure of substantially cylindrical shape (H (height)=40 cm, D (diameter)=40 cm)) as represented diagrammatically in the appended figures, to recover, dry, an ONTA charge from a suspension including 10 kg of ONTA in water (75 liters).

(29) The ONTA crystals of the suspension exhibited a monomodal particle size distribution with a median diameter (D.sub.50) of 200 m. The suspension concerned exhibited a water/ONTA ratio by weight of 7.5.

(30) Step a (Filtration)

(31) The filter, arranged in the bottom part of the volume of the enclosure, was a filter made of stainless steel which exhibited a porosity graded at 150 m.

(32) The suspension was introduced into the enclosure above the filter. Its passage through said filter generated, on the latter, a cake (h (height)=20 cm, D (diameter)=40 cm). This cake exhibited a water/ONTA ratio by weight of approximately 5. The liquid was discharged in the bottom part of the enclosure.

(33) Step b (Dewatering)

(34) The upper part of the enclosure was subsequently pressurized from 210.sup.5 Pa absolute (2 bar absolute) to 310.sup.5 Pa absolute (3 bar absolute) for the purposes of dewatering the cake.

(35) The pressurizing gas (air) injected in the top part of the enclosure was dry gas (1% (by weight) of moisture).

(36) The pressure was maintained for 1 h.

(37) On conclusion of this pressurizing, the dewatered cake (h (height)<10 cm, D (diameter)=40 cm) was obtained in the enclosure, resting on the filter, which cake exhibited a water/ONTA ratio by weight of approximately 1.

(38) During this pressurizing, dewatering liquid was discharged.

(39) Step c (Obtaining a Fluidized Bed of Dry ONTA Grains)

(40) Step c1 (Creation of Channels (Chimneys) in the Dewatered Cake)

(41) Dry air (1% moisture) was then injected via the bottom of the enclosure (by 2 injectors) at a temperature of approximately 60 C. for 0.5 h. Said dry air thus (directly) impacted the face of the dewatered cake resting on the filter.

(42) Said dry air was injected at a flow rate of 20 to 50 Nm.sup.3/h and at a pressure varying (+0.16 bar/min) along a pressure gradient from 5 bar to 7 bar (from 510.sup.5 to 710.sup.5 Pa).

(43) The means provided in the top part of the chamber for the discharge of the drying gas (dry air charged with the liquid from the dewatered cake) were equipped with a particle filter.

(44) Step c2 (Lift of the Dewatered Cake with Channels+Erosion at the Surface and in the Volume of the Cake=Fluidized Bed)

(45) The same injection means were used to inject the same dry air (1% moisture) at the same temperature for a further 0.5 h, at a flow rate of 100 to 200 Nm.sup.3/h and along a pressure gradient from 5 bar to 7 bar (from 510.sup.5 to 710.sup.5 Pa).

(46) The cake, on conclusion of this 0.5 h, had entirely disintegrated. The grains of the explosive charge were dry, under lift. They constituted, with the dry air injected, a fluidized bed.

(47) Step d

(48) Once the injection of air was stopped, the dry grains settled on the filter and were recovered there.

(49) Approximately 9.5 kg of grains were recovered; the remainder of the 10 kg present in the initial suspension were lost in the filtration (smaller crystals) or were found trapped in the particle filter.

(50) The water/ONTA ratio by weight of the dry charge recovered was 0.1%.