EP2171118A1

EP2171118A1 - Method and device for spraying a pulverulent material into a carrier gas

Info

Publication number: EP2171118A1
Application number: EP08761417A
Authority: EP
Inventors: Osvaldo Di Loreto
Original assignee: Fib-Services International Sa
Current assignee: FIB-SERVICES INTELLECTUAL S.A.
Priority date: 2007-07-05
Filing date: 2008-07-03
Publication date: 2010-04-07
Anticipated expiration: 2028-07-03
Also published as: EG25537A; PT2171118E; SI2171118T1; CA2692486A1; BRPI0813988B1; CN101755070A; CN101755070B; MX2010000186A; UA98340C2; TN2009000549A1; KR20100046175A; DK2171118T3; ATE503855T1; BE1017673A3; JP5124641B2; AU2008270262A1; CA2692486C; BRPI0813988A2; WO2009004053A1; EP2171118B1

Abstract

Method of spraying a pulverulent material into a carrier gas, comprising the acceleration of the carrier gas under pressure up to a sonic velocity before an expansion enabling the pulverulent material to be entrained, with formation of a constant stream of carrier gas entraining an adjustable predetermined amount of pulverulent material, and safety device for spraying pulverulent material into a carrier gas.

Description

"METHOD AND DEVICE FOR PROJECTING PULVERULENT MATERIAL INTO A CARRIER GAS"

The present invention relates to a method of spraying a powdery material into a carrier gas having an overall flow rate, said process comprising:

a flow of said carrier gas under pressure,

an acceleration of said pressurized carrier gas to a sonic speed,

an expansion of said pressurized carrier gas with the formation of a vacuum zone having a value less than said carrier gas flow pressure and a drive of a quantity of said powdery material by said relaxed carrier gas, and

a projection of said pulverulent material entrained by said carrier gas. Such a method is for example known from the document

US-6,402,050 which describes apparatus for dynamic spraying of powdery materials with gases in the field of application of the production of coatings for example anticorrosion or reflective for machined surfaces. This document describes the use of a sonic neck with a particular ratio of the cross-sectional areas between the sonic nozzle and the supply of pulverulent material, in order to maintain a pressure below atmospheric pressure to ensure the transport of the powder by a flow of air at atmospheric pressure. This document does not disclose that the sonic type nozzle makes it possible to obtain a constant flow of powdery material. However, in the field of furnace refractory wall repairs by flame projection, gunning, ceramic welding or reactive sputtering, the reproducibility of a pulverulent material spraying process and all related adjustments such as those of the quantity of pulverulent matter, the speed of projection, the force of the impact, & c. are directly influenced adversely by a non-reproducible variable carrier gas flow.

Of course, there are known devices that include a flowmeter which controls, via a regulator, a valve to obtain a constant gas flow, but such systems are complex to implement and require elements whose purchase prices and operation are a direct function of accuracy. Therefore, these systems are not very applicable, not to mention the fact that the final precision (probably due to the sequence of elements) often leaves something to be desired. In addition, certain methods known in the field of powdered material spray repair comprise an adjustment of the amount of pulverulent material driven by means of a worm or spinner, but the use of such devices drive requires the use of electric motors, which is incompatible with the use of a carrier gas and reactive (eg oxygen) with at least one element of said powdery material.

To be able to use these electric motors in a safe manner, it would be necessary to use an inert gas such as nitrogen, which is not compatible with the process according to the invention because the carrier gas must be reactive with an element of the material pulverulent and in any case requires an additional supply of nitrogen, which makes the process less flexible.

The invention therefore aims to overcome these disadvantages by providing a method in which the flow of pulverulent material is adjustable and reproducible without affecting the flow of the carrier gas. To this end, the method according to the invention is characterized in that it further comprises an adjustment of said lower pressure, which exists in the depression zone by derivation or not, before the expansion, of an adjustable quantity of said gas carrier having been accelerated to reintroduce said adjustable amount in the aforesaid depression zone without modifying said flow rate, in particular in its entirety.

The amount of instant powdered material entrained should be advantageously optimized from the point of view of the excellence of the coating but also from the point of view of the cost of consumption of the latter. Upstream of the cane or spraying lance, it is therefore important to intimately mix the pulverulent material with the carrier and reagent gas in an adjustable amount. Therefore, constraints also dictate the value of this last parameter.

The method according to the invention as described above has the desired flexibility compared to a conventional method using a venturi effect. Indeed, the projection method according to the invention comprising a step of adjusting said depression by shunting or not, before the expansion of an adjustable amount of carrier gas has been accelerated, allows, while not changing the flow rate of carrier gas outlet, to change the value of the lower pressure in the vacuum zone, which allows to adjust the amount of pulverulent material entrained.

If the amount of carrier and reactant gas withdrawn and reintroduced is large, the value of the pressure in the vacuum zone will be closer to the compression pressure and the amount of pulverulent material entrained will be reduced. On the other hand, if the quantity of carrier and reactive gas withdrawn and reintroduced is small, the value of the pressure in the depression zone will be considerably lower compared with the value of the aforesaid compression pressure and a quantity of substantial and close pulverulent material. its maximum value will also be driven. If the amount of carrier gas is zero, the value of the depression is maximum and has the value furthest away from the compression pressure that the process can achieve and the maximum amount of pulverulent material is entrained. Therefore, the amount of carrier gas and reactant derivative (that is to say, withdrawn and reintroduced) allows to adjust in a particularly clever way the amount of pulverulent material entrained.

The invention has thus made it possible to overcome at least part of the drawbacks of the state of the art by making it possible to adjust to a reproducible value the quantity of pulverulent material entrained while ensuring a flow of carrier gas which is constant, thereby guaranteeing a constant ejection speed. In fact, the final result, the reproducibility and the quality of the projection depend directly on this flow of pulverulent material entrained by the said carrier gas.

An optimal carrier gas flow ensures optimal transport of the material to be sprayed and since the projection is made by means of a cane or projection lance, having a well-defined projection section, the projection speed for a given temperature carrier gas will be conditioned by the flow of this carrier gas.

Thanks to the acceleration up to the sonic velocity, for example obtained by creating a shock wave in a venturi, the sonic blocking establishes a fixed flow rate which is not influenced by the variations in pressure drop in the downstream circuit. Therefore, the carrier gas flow has become constant and the projection speed conditioned by this constant flow is optimal. The optimal ejection speed thus obtained in the carrier gas greatly increases the reliability and reproducibility of the pulverulent material spraying method according to the invention.

In the field of repairing refractory walls of furnaces, glass treatment plants, coking plants, etc., the method according to the invention can be advantageously applied in a reactive projection repair process which consists in projecting medium of a carrier gas stream on a zone concerned, a pulverulent material (comprising for example a refractory filler and metal powder), finely pulverized.

Indeed, when a wall of refractory material has superficial or deep damage, the user must repair them as quickly as possible so as not to aggravate the damage given the intense operating conditions.

During the reactive projection repair operation, the quality of the coating obtained on the generally refractory wall, depends on several parameters including the substrate temperature and the projection speed.

In this type of process, the carrier gas can also be advantageously a reactive gas with at least one of the elements of the pulverulent material and, in contact with the hot wall, the mixture reacts spontaneously and a series of chemical reactions leads to the formation of a homogeneous, adherent refractory material whose characteristics are compatible with those of the treated support.

The projection speed is a preponderant element. Indeed, if the latter is too weak, there is a risk of backfire. If it is too important, the amount of material may not react (because not participating in the exothermic reaction) and bounce excessively on the wall at the expense of the quality of the magma formation generated by the reactive projection.

The method according to the invention therefore aims to provide an optimum weld quality by providing a projection quality and impact of said powdery material on the surface to be repaired constant over time. The method according to the invention makes it possible to obtain a flow of carrier and reactive gas directly dependent on the inlet pressure but independent of any pressure change resulting from the downstream circuit. The grains constituting the pulverulent material sprayed are driven by an optimized speed thanks to the carrier gas which conveys the pulverulent material pneumatically and their quantity is adjustable.

In this type of application of reactive sputtering repair, the carrier gas is also a reactive gas that not only serves as a transport fluid but actively participates in the exothermic physicochemical reaction. The final quality of the projected product depends mainly on the following factors:

the global enthalpy produced during the exothermic reaction and therefore the amount of carrier and reactive gas used as well as the temperature, the chemical composition or the formulation of the pulverulent material,

the quantity of powder sprayed, ie the mass flow rate of pulverulent material, the optimum flow rate of the carrier and reactive gas making it possible to obtain an optimal speed of ejection of the reagents for a given application.

Since the carrier gas flow according to the invention advantageously has a constant value at the outlet, free from any variation due to imperfections, the method according to the invention has an optimal speed of projection for a given application.

Advantageously, the method according to the invention further comprises a compression of said reactive carrier gas which has been accelerated prior to expansion, which improves the entrainment of the pulverulent material aforesaid. Other embodiments of the process according to the invention are mentioned in the appended claims.

The invention further relates to a device for spraying a powdery material in a carrier gas comprising:

a pressurized carrier gas inlet, a convergent-divergent nozzle with a sonic neck in communication with said inlet of said underpressure carrier gas,

a supply of pulverulent material communicating with a zone of depression; means for expansion of the carrier gas connected to said convergent-divergent sonic-neck type nozzle receiving the pressurized carrier gas and ending in said zone of depression, and

an outlet of said pulverulent material entrained by said carrier gas expanded out of the vacuum zone. Unfortunately, such a device does not allow, as mentioned above to obtain a projection of optimal pulverulent material, which affects on the one hand the reproducibility of the work done by this device and on the other hand the quality of the finished work, nor to adjust the amount of pulverulent material entrained. The aim of the invention is to overcome the drawbacks of the state of the art by providing a device making it possible to obtain an optimum projection speed for a mass flow rate of selected powder, increasing the reproducibility of the work performed by the user of the device according to the invention. invention and accuracy as well as the costs of pulverulent material. To solve this problem, there is provided according to the invention, a device as indicated above, characterized in that it further comprises a flow control device of said powder material in said carrier gas comprising a circuit of derivation of said carrier gas provided with a device for adjusting the amount of derivative carrier gas, said bypass circuit comprising a carrier gas sampling orifice disposed upstream of said vacuum zone of said carrier gas and a reintroduction orifice for said gas taken carrier located in said depression zone.

Said convergent-divergent type nozzle with a sonic collar makes it possible to maintain, downstream, a constant flow of carrier gas leading to a predetermined quantity of pulverulent material which is therefore adjustable by means of derivation.

In this way, the carrier gas that passes through the convergent-divergent nozzle sonic or also called Laval's son undergoes an acceleration to a sonic speed through a shock wave that was created in the venturi. The sonic lock thus obtained establishes a fixed flow rate that is not influenced by the pressure difference between the upstream and the downstream of the nozzle. In addition, the amount of adjustable powder material is also optimized. Therefore the flow rate of the mixture of pulverulent material in the carrier gas is optimal and the exothermic reaction also. The total projection is optimized and the yield is increased.

The carrier gas reintroduced into the vacuum zone causes a counterpressure that acts on the vacuum and at most the amount of carrier gas reintroduced into the vacuum zone is large, the more the amount of pulverulent material entrained is low. The opposite is also applicable. If the user wishes to drive the maximum quantity of powdery material, it is sufficient not to take carrier gas. The amount of carrier gas withdrawn and reintroduced is adjusted using the control organ.

Advantageously, the device according to the invention comprises an injector communicating on the one hand with said convergent-divergent sonic-neck type nozzle and on the other hand with said expansion means and said depression zone, said injector comprising at least a narrowing zone. The presence of the injector improves the entrainment of the pulverulent material in the zone of depression and the narrowing zone makes it possible to increase the pressure just before the relaxation. Therefore, the pressure difference will be greater and the effectiveness of training also. Preferably, said branch circuit control member is a needle valve. This makes it possible to obtain all the possible values between the maximum value of sampled gas and the minimum value, the needle valve operating by clamping and not by crenellations. Advantageously, said sampling orifice is disposed upstream of said narrowing zone of said injector. In this way, the carrier gas that is to be derived to regulate the amount of pulverulent material is removed prior to compression and represents a counterpressure to the pressure (lower pressure) prevailing in the vacuum zone, thereby permitting a more sensitive setting of the amount of pulverulent material sucked.

In an advantageous embodiment, the vacuum zone is connected to a diverging passage, preferably made of tungsten carbide, itself connected to said outlet orifice of said pulverulent material entrained by the carrier gas. The diverging passage is preferably made of an abrasion resistant material such as tungsten carbide and provides a similar operation to that of a nozzle.

In a particularly advantageous embodiment, said convergent-divergent sonic-neck type nozzle has a diameter smaller than the diameter of each element downstream of said convergent-divergent sonic-neck type nozzle.

Therefore, it is said convergent-divergent sonic neck nozzle that dictates the constant flow until the output of the device according to the invention.

In a preferred embodiment of the invention, the outlet of pulverulent material entrained by said carrier gas is a tubular orifice comprising the diverging passage, in which a first housing surrounds at least said tubular outlet orifice and in which a second housing surrounds a flexible pipe leading to a connected projection lance at said output, the two housings being connected together by conventional connection means. This makes it possible to obtain a pulverulent material spraying device in a compact and portable carrier gas which is sufficiently safe. In fact, the fragile elements confined inside are protected from the environment. The possible accidental exothermic reactions that may occur during the projection are also confined in the device according to the invention and in the second housing, which makes it possible to avoid injuring the user. The second housing is particularly suitable in case of flashback to prevent the user from being burned since generally the carrier and reactive gas is oxygen.

Preferably, a hot-melt wire connected on the one hand to a trigger which comprises an open position of carrier gas passage and a closed position of carrier gas lock and secondly in said second housing, said hot-melt wire being arranged to maintain said trigger in the open position. In this way, in case of backfire, the hot-melt wire breaks instantaneously and the trigger passes almost instantly to the closed position of the carrier gas (oxygen). This prevents the backward propagation of the flame front and thus the explosion or fire.

In a particularly safe embodiment, said first and second housings are connected to each other by biasing means having a predetermined restoring force, for example springs holding together conventional connection means. The setting of the springs is such that, during an overpressure due to a flashback in the tubular outlet orifice it separates from the divergent, thus directly allowing a return to atmospheric pressure. Therefore, these two elements deviate from each other a few very brief moments, which also avoids the explosion or fire. Advantageously, the second security box comprises two filtering devices that allow the evacuation of gases and dust while blocking a spread of flames during such an incident.

Other embodiments of the device according to the invention are indicated in the appended claims.

Other features, details and advantages of the invention will become apparent from the description given below, without limitation and with reference to the accompanying drawings.

Figure 1 is a sectional view of a pulverulent material spraying device in a carrier gas according to the invention.

Figure 2 is a sectional view of a complete assembly comprising the same device as that shown in Figure 1 where we can see the details of the hot-melt wire, the second housing and weighed springs according to the invention. FIG. 3 is a view from above of a variant of the device for spraying a powdery material in a carrier gas according to the invention.

Figure 4 is a sectional view of a complete assembly of a variant of the device shown in Figure 1. In the figures, identical or similar elements bear the same references.

FIG. 1 illustrates a pulverulent material projection device in a carrier gas for implementing the projection method according to the invention. As mentioned above, the principle consists in projecting by means of a carrier gas a pulverulent material finely pulverized on a zone concerned. The carrier gas is, for example, also reactive with an element of the pulverulent material. The reactive carrier gas is, for example, oxygen which participates in the exothermic reaction of the metal powder contained in the pulverulent material. The device according to the invention illustrated in FIG. 1 comprises an inlet 1 of gaseous oxygen under pressure coming either from a cylinder or from a compressed reservoir, for example at 200 bar. The pressure of the pressurized oxygen entering the device according to the invention was previously regulated by means of a pressure reducer 2 or several regulators 2 in series connected to the cylinder or the tank (not shown). A value of this pressure of oxygen under pressure given by way of example is 5.2 bar. The pulverulent material enters the device according to the invention via a feed hopper 18 made of pulverulent material. Gaseous oxygen under pressure enters the device according to the invention through the above-mentioned inlet 1 and reaches a nozzle 3 of the Laval type, that is to say of the convergent-divergent type, the dimensional factors of which are such that the nozzle 3 is considered sonic. The Laval type nozzle comprises a convergent section 4, a sonic neck 5 and a diverging section 6.

The nozzle 3 is followed in the illustrated embodiment of a recess 7. The recess 7 advantageously comprises at least one oxygen withdrawal for deriving a quantity of oxygen accelerated by said nozzle 3. Part of the carrier oxygen and reagent is derived by two orthogonal bores 8, 8 'connected to a needle valve 9 which adjusts the value of the amount of oxygen derived. It is also provided in the embodiment shown to measure the value of the static pressure of the oxygen accelerated by the nozzle 3 by means of two orthogonal bores 10, 10 'made in said recess 7. The measurement of this pressure static will be done for example using a pressure gauge 11.

The Laval-type or convergent-divergent type 3 sonic nozzle is secured to an injector 12 which will be supplied with carrier gas having been accelerated (oxygen) with a flow rate, a pressure and a speed dictated by the convergent-type nozzle. diverge 3 above. The injector 12 is preferably made of a material compatible with the passage of oxygen. The carrier and reactive oxygen with at least one element of the pulverulent material, which has passed through the injector under high pressure, then results in a vacuum zone 19, which is, in this embodiment, an enclosure having a volume much greater than that of the nozzle of the injector 12 and thus serving as expansion means. The expansion of the carrier gas creates a vacuum in the aforesaid enclosure which has the effect of driving the powdery material in the feed hopper 18. Advantageously, the enclosure is fed with pulverulent material by removing a shutter Controlled by control means, for example, pneumatically by means of a jack 21.

The expansion means may consist of any known expansion means, such as the chamber volume greater than that of the aforementioned injector, or the divergent portion of a venturi.

The position of the injector 12 is advantageously collinear with the outlet 22 of the pulverulent material entrained by the carrier and reactive oxygen. The outlet is equipped with a diverging assembly 22 made of an abrasion resistant material such as, for example, tungsten carbide.

The injector 12 has a narrowing zone allowing the accelerated carrier gas to be compressed before it reaches the depression zone 19.

In this illustrated embodiment, the Laval type nozzle 3 is secured to a preferably metallic assembly 13 which consists of three coaxial subassemblies 12, 14, 16. The preferably metallic subassembly 14 has on its outside diameter a throat

17 in which bores 15 made radially allow the passage of a portion of the flow of oxygen from the conduit connected to the needle valve 9. The sub-assembly 16 is a ring for the closing of the groove 17 of the subassembly 14. The ring 16 connects to the needle valve 9 through a bore in the ring 16 to the right of the groove 17 aforesaid.

The needle valve 9 is then connected to the bore 8 and / or the bore 8 'by a pipe 36 of a nature compatible with the passage of oxygen. The closing or opening of the needle valve 9 allows or not the bypass (withdrawal) in the branch circuit 36 of an amount of oxygen necessary for the working conditions. The oxygen thus withdrawn into the counterbore 7 (withdrawal orifice) through an opening of the needle valve 9 will then be reintroduced via the circuit 36 into the ring 17 (reintroduction orifice of the carrier gas), it will pass into the bore 15 and will then end in an annular space 25 existing between the metal sub-assembly 14 and the injector 12. In this way, at the outlet of the injector 12, the oxygen flow rate accelerated out of the convergent-type nozzle diverging at sonic neck 3 is recovered. The bypass circuit 36, the assembly constituted by the recess 7, the bores 8, 8 ', the needle valve 9, the reintroduction orifice 17, the bore 15 and the annular space 25 are called.

Indeed, the accelerated oxygen leaving the nozzle 3 has a flow rate d _L , a speed v _L and a pressure P _L. When a part _D of the accelerated oxygen flow rate _L is derived, the oxygen flow rate passing into the injector is d ,. The oxygen that passes into the injector is driven by a speed v, and has a pressure P ₁ . The oxygen of the portion of the flow derived from _D is also driven by a speed v _D and has a pressure P ₀ in the annular space 25.

At the outlet of the injector 12 and the annular space 25, the oxygen will have a resulting pressure P _R and a resulting speed v _R. These resulting pressures and velocities condition the amount of pulverulent material entrained. The opening or closing of the needle valve 9 will cause a variation of the flow rates d, and d _D , a variation of the pressures P ₁ and P _{0 as} well as speed changes v, and v _D. The resulting pressure P _R and the resulting velocity v _R will therefore be variables. The direct consequence is a variation in the amount of pulverulent material entrained, due to the variation of kinetic energy and the momentum. There will therefore be a change in the importance of the generated venturi effect.

However, the accelerated carrier gas flow values d _L at the outlet of the Laval nozzle 3 and the outgoing oxygen flow rate of the device according to the invention d _R are identical since the flow rate of the carrier gas remains constant during the crossing. of the device according to the invention. Therefore, by diverting or bypassing a portion of the flow rate _D , by opening the needle valve 9 in the bypass circuit 36, the flow rate that passes into the injector 12 d is reduced accordingly. . The characteristics such as pressure P ₁ , mass flow M ₁ , and speed v, out of the metal injector will be modified. If the needle valve 9 is fully open and allows a maximum oxygen flow rate corresponding to the maximum value that d _D (derived oxygen flow rate) can reach, the amount of pulverulent material entrained will be the amount of minimum pulverulent material which can be driven by the device according to the invention (instantaneous quantity). If the needle valve 9 is closed and does not allow bypass, then the amount of pulverulent material entrained is at its maximum value. The bypass is not always necessary, it is advisable to provide the possibility of closing the adjustment member and in this case the needle valve 9 (instantaneous quantity). In a variant, the groove 17 may be an integral part of the support body of the assembly 13. Similarly, the skilled person will readily understand that the geometric positions of the radial bores may be very different depending on the requirements of the bulk.

The bores 8 'and 10' are machined perpendicular to the two bores 8 and 10 themselves orthogonal to the formed plane by chambering 7, but those skilled in the art will readily understand that these geometric positions are dictated only by steric constraints and congestion. It goes without saying that a single bore 8, 10 could be sufficient to derive accelerated oxygen or to measure the value of the static pressure and that there is no need for positioning for variants according to the invention.

The dimensional factors of the Laval type nozzle are such that the static pressure of the oxygen passing through said nozzle 3 has a value equal to or less than the product of the pressure at the inlet of the nozzle (compression pressure) and a factor of 0.528. Under these conditions, the nozzle 3 is considered sonic and the operating conditions of the assembly depend only on the initial fluid pressure upstream, that is to say the pressure dictated by the pressure regulator 2, consisting for example of one or more regulators 2. The divergent tungsten carbide 22 can be positioned and fixed in a support block 23.

The dimensional factors of the injector assembly 12 and divergent 22 are such that the operating principle can also be likened to a venturi type nozzle. In a variant according to the invention, upstream of the convergent-divergent sonic-neck type nozzle 3, there is a non-return safety device 24 having a normally open gate valve and making it possible to prevent the gas from backing up into the device according to the invention. 'invention. Indeed, when it is hot oxygen or a backfire, it is advantageous to have a non-return safety that blocks the passage in case of heating or return slag.

FIG. 2 illustrates a more complete reactive spray repair assembly comprising the same device as that shown in FIG. 1. In this assembly, a hopper 18 'of greater capacity than the aforementioned feed hopper 18 is located at above this one. The A pulverulent material composed of refractory and metal powders used in the process according to the invention is therefore transferred from the hopper 18 'to the hopper 18 by natural flow and by gravity.

In the feed hopper 18 leading into the depression zone 19, a movable register 26 will advantageously be placed allowing a smooth flow in the mixing chamber of carrier gas (oxygen) and powder. In the case of a backfire and in the case of a gas return able to go up in the hopper 18, since the pulverulent material therein is reactive (at least one of the elements constituting it) with the carrier gas ( oxygen), the amount of pulverulent material liable to cause an explosion is reduced, and therefore the amount of pulverulent material lost.

The device illustrated in FIG. 2 also comprises, as previously mentioned, a support block 23 which is also referred to in the context of the present invention as the first housing 23 which surrounds the outlet 35 of pulverulent material entrained by the gas. carrier in the form of a tubular orifice with diverging passage 22 (for example, anti-abrasion tungsten carbide). The device according to the invention, in its preferred form illustrated here further comprises a second housing 27. The second housing 27 surrounds the lance 28 of reactive spraying of the pulverulent material entrained by said carrier gas and reagent.

The first housing 23 is connected to the second housing 27 by conventional connecting means 29 and 29 'such as a threaded projection and a thread, flanges and the like. The conventional connection means 29 and 29 'are held in place by the pressure exerted by a series of return means 30 having a predetermined restoring force. These return means 30 are, for example, calibrated springs. The predetermined return force or the setting of the springs is such that during an overpressure in the projection lance 28 following a flashback, the two conventional connection means separate. This allows an instantaneous return to atmospheric pressure in enclosures in which there was a pressure conducive to ignition and explosion.

As can also be seen, the device according to the invention also comprises an additional safety device. Indeed, in addition to the backstop safety 24, the movable register 26 in the feed hopper 18 aforesaid, first and second housings 23 and 27, return means 30, the device further has a hot-melt thread

31 judiciously positioned. The hot-melt wire 31 is in the path of the hot gas stream. During the separation of the conventional connection means 29 and 29 'under the effect of an overpressure incident or during a flashback occurring in said second housing 27, the hot gas stream immediately melts the hot melt 31 which is then almost instantly cut. Its break releases the voltage on the trigger 32 security. The sudden release of the trigger

32 interrupts the flow of oxygen and the gas passage is blocked.

In addition, the device according to the invention is equipped at the second housing 27 of filtering devices 33 and 34 for the cooled evacuation of gases and dusts during such an incident (flashback). In the variant of the device according to the invention illustrated in FIG. 3, the bypass circuit for adjusting the quantity of pulverulent material entrained by the carrier and reactive gas is arranged differently. The other elements shown function as in and are described by the detailed description of Figures 1 and 2 including all the alternatives explained.

The bypass circuit 36 is composed of an adjusting member 9 (needle valve) of the amount of carrier gas derived from a carrier gas sampling port 7 and a reintroduction port 25 of the derivative gas in the enclosure of the depression zone. The sampling or withdrawal orifice 7 is disposed at the outlet of the nozzle of Laval 3. Of course, this draw-off orifice can be disposed in many other places provided that the latter is disposed upstream of said expansion zone 19 of said carrier gas, the operation will be optimal.

Similarly, as an alternative, a hot-melt wire 31 is connected on the one hand to the trigger 32 and on the other hand to a point between said first 23 and said second housing 27. The wire (hot melt) 31 holds the trigger 32 in the open position as long as there is no flashback. If an incident should occur, the conventional connection means

29, 29 'would separate from each other and the end of the wire (hot melt) 31 would be released, which would have the effect of releasing the pressure on the trigger and block the supply of oxygen.

FIG. 4 illustrates a variant of the device illustrated in FIG. 1, in which the branch circuit is still arranged differently. The other elements function as in the embodiment illustrated in FIG.

The device according to the invention illustrated in FIG. 4 comprises an inlet 1 of gaseous oxygen under pressure. The pulverulent material enters the device according to the invention via a feed hopper 18 made of pulverulent material. Gaseous oxygen under pressure enters the device according to the invention by the aforesaid inlet 1 and reaches a nozzle 3 Laval type (sonic). The Laval type nozzle comprises a convergent section 4, a sonic neck 5 and a diverging section 6.

The nozzle 3 is followed in the illustrated embodiment of a recess 7. The recess 7 advantageously comprises at least one oxygen withdrawal allowing to derive a quantity of oxygen accelerated by said nozzle 3 by means of an orthogonal bore 8 connected to a needle valve 9 which adjusts the value of the amount of oxygen derived. It is also provided in the illustrated embodiment to measure the value of the static pressure of oxygen accelerated by the nozzle 3 through an orthogonal bore 10 made in said recess 7, for example using a manometer 11.

The chambering connected to the nozzle type Laval is secured to an injector 12 which will be supplied with accelerated carrier gas (oxygen) with a flow rate, a pressure and a speed dictated by the nozzle 3 aforesaid. The nozzle 3 has, for example, a diameter of 3.4 mm

The injector 12, for example having a diameter of 3.7 mm, therefore ends up in a depression zone 19, which is also, in this embodiment, an enclosure having a volume much greater than that of the nozzle of the injector 12 and thus serving as means of relaxation.

The expansion of the carrier gas creates a vacuum in the aforesaid enclosure which has the effect of driving the powdery material in the feed hopper 18. Advantageously, the enclosure is fed with pulverulent material by removing a shutter Controlled by control means, for example, pneumatically by means of a jack 21.

In this illustrated embodiment, the injector 12 is secured to the support block 23 which confines said depression zone 19 and the diverging passage 22 defining the outlet 35.

The support block 23 comprises on its outside diameter a groove 17 and an orthogonal bore 15 which allow the passage of a portion of the flow of oxygen from the conduit connected to the needle valve 9. The needle valve 9 is then connected to the bore 8 by a pipe 36 of a nature compatible with the passage of oxygen. The closing or opening of the needle valve 9 allows or not the bypass (withdrawal) in the branch circuit 36 of an amount of oxygen necessary for the working conditions. The oxygen thus withdrawn into the counterbore 7 (withdrawal orifice) through an opening of the needle valve 9 will then be reintroduced via the circuit 36 into the ring 17 (reintroduction orifice of the carrier gas), it will pass into the bore 15 and will then end in an annular space at the depression zone 19. In this way, at the outlet of the injector 12, the accelerated oxygen flow at the exit of the convergent-divergent sonic-neck type nozzle 3 is recovered. The bypass circuit 36 is called the assembly constituted by the recess 7, the bore 8, the needle valve 9, the reintroduction orifice 17, the bore 15.

The operation and the other elements are identical to what has been described for FIG.

EXAMPLE

A constant O ₂ flow enters the device according to the invention with a value of 30 Nm ³ / h and has a pressure at the outlet of the expander 2 of 5.2 bar. The maximum operating pressure at the inlet of the injector (static pressure) is 4.05 bar. The needle valve, initially closed, was gradually opened and the mass flow rate of pulverulent material was measured. The results are shown below in the table.

It is understood that the present invention is in no way limited to the embodiments described above and that many modifications can be made without departing from the scope of the appended claims.

Claims

A method of spraying a powdery material into a carrier gas having an overall flow rate, said method comprising

a flow of said pressurized carrier gas, an acceleration of said pressurized carrier gas to a sonic speed,

a projection of said pulverulent material entrained by said carrier gas, characterized in that the method furthermore comprises an adjustment of said lower pressure by derivation or not, before the expansion, of an adjustable quantity of said carrier gas which has been accelerated to reintroduce said adjustable amount in said vacuum zone without modification of said overall flow rate.

2. The method of claim 1, further comprising a compression of said accelerated carrier gas prior to expansion.

The process of claim 2, wherein said carrier gas is a reactive gas participating in an exothermic reaction with at least one element of said pulverulent material.

4. Apparatus for spraying a powdery material in a carrier gas comprising: - an inlet (1) of pressurized carrier gas

a convergent-divergent nozzle with a sonic neck (3) in communication with said inlet (1) of said pressurized carrier gas

a feed (18) of pulverulent material communicating with a depression zone (19), means for relaxing the carrier gas connected to said convergent-divergent sonic-neck type nozzle (3) receiving the pressurized carrier gas and ending in said depression zone (19) and

an outlet (35) of said pulverulent material entrained by said expanded carrier gas outside the vacuum zone (19), characterized in that it further comprises a flow control device (11, 7, 8, 15, 17, 36) of said pulverulent material in said carrier gas comprising a bypass circuit (36) of said carrier gas provided with an adjusting member (9) for the amount of derived carrier gas, said bypass circuit (36) comprising a carrier gas sampling port (7,8) disposed upstream of said vacuum zone (19) of said carrier gas and a reintroduction orifice (15,17) of said sampled carrier gas located in said vacuum zone (19), said sonic convergent-divergent type nozzle (3) being arranged to maintain, downstream, a constant flow of carrier gas causing a predetermined amount of pulverulent material.

5. Device according to claim 4, further comprising an injector (12) communicating on the one hand with said convergent-divergent sonic-neck type nozzle (3) and on the other hand with said detent means and said zone depression (19), said injector (12) comprising at least one narrowing zone.

Apparatus according to claim 4 or claim 5, wherein said sonic convergent-divergent type nozzle (3) has a diameter less than the diameter of each element downstream of said convergent-divergent sonic-neck type nozzle ( 3).

7. Device according to one of claims 4 to 6, wherein said adjustment member is a needle valve (9).

8. Device according to any one of claims 4 to 7, wherein said sampling port (7, 8) is disposed upstream of said narrowing zone of said injector (12).

9. Device according to any one of claims 4 to 8, wherein said depression zone (19) is connected to a diverging passage (22), for example tungsten carbide, itself connected to said outlet (35). said pulverulent material entrained by the carrier gas.

The device of claim 9, wherein said output

(35) of pulverulent material entrained by said carrier gas is a tubular orifice comprising the diverging passage (22), wherein a first housing (23) surrounds at least said tubular outlet port (35) and wherein a second housing (27) ) surrounds a flexible pipe leading to a projection lance (28) connected to said outlet (35), the two housings (23, 27) being connected together.

11. Device according to claim 10, further comprising a hot-melt wire (31) connected on the one hand to a trigger (32) which comprises an open position for passage of carrier gas and a closed position for blocking carrier gas and secondly in said second housing (27), said hot melt wire (31) being arranged to keep said trigger (32) in the open position.

12. Device according to claim 10 or claim 11, wherein said first and said second housing (23,27) are connected to each other by return means (30) having a predetermined restoring force.

13. Device according to claim 12 when dependent on claim 10, further comprising a wire (31) thermofusible connected on the one hand to a trigger (32) which comprises an open position of carrier gas passage and a closed position carrier gas blocking and secondly between said first and said second housing (23,27), said hot melt wire (31) being arranged to maintain said trigger (32) in the open position.