EP0944802B1 - Method for dynamic separation into two zones with a screen of clean air - Google Patents

Abstract

An air curtain (14) is used to dynamically separate a zone (10) to be protected and a contaminating zone (12) communicating with each other through at least one separation zone (11), the air curtain being formed by simultaneously injecting at least two adjacent clean air jets into the same direction in the separation zone (11). More precisely, the air curtain (14) comprises a slow jet, in which the tongue (16) covers the entire separation zone (11) and a fast jet inserted between the slow jet and the zone (10) to be protected and for which the injection flow is such that it induces an air flow equal to approximately half the injection flow of the slow jet, on its surface in contact with the slow jet. Preferably, clean ventilation air is also injected into the zone (10) to be protected at a flow equal to at least the air flow induced by the surface of the air curtain in contact with the ventilation air, and in any case at a speed not less than 0.1 m/s.

Description

Technical area

The invention relates to a method for ensure the dynamic separation of a contaminating zone and an area to be protected, communicating between them by at least one separation zone, by means of a clean air curtain obtained by injecting into the separation area at least two clean air jets adjacent and in the same direction.

The method according to the invention can be used in many industrial sectors.

A first family of industries concerned by this process includes all industries (agrifood, medical, biotechnology, high technology, etc.), in which it is necessary prevent the atmosphere in a given work area either contaminated by ambient air, carrying a thermal, microbial, particulate contamination and / or gas.

Another family of industries concerned by the process according to the invention includes industries (nuclear, chemical, medical, etc.) in which man and his environment must be protected vis-à-vis toxic or dangerous products placed inside a containment.

State of the art

There are currently two types of solutions to ensure the dynamic separation of two zones communicating with each other by one or more separation zones in order, for example, to allow entry and exit of objects: protection by ventilation and air curtain protection.

Ventilation protection consists of artificially create a pressure difference between the two zones, so that the pressure in the area to be protected is greater than the prevailing pressure inside the contaminating zone. So in the case where the area to be protected contains a product susceptible to be contaminated by the ambient air, we inject into the zone to protect a laminar flow which blows towards outside through the separation zone. In the opposite case where it is a question of protecting the personnel and the environment located outside a space contaminated, dynamic containment is ensured by using exhaust ventilation in this contaminated space. In either case, a rule empirical imposes a minimum speed of ventilated air 0.5 m / s, in the plane of the separation zone by which the two zones communicate, in order to avoid the transfer of contamination to the area to be protected.

The effectiveness of this protection technique ventilation is not perfect, especially in a so-called "break-in" situation, that is to say when objects are transferred across the separation zone interposed between the two zones. Of more, this type of protection requires treating and check, as appropriate, the entire area suitable for protect from the outside atmosphere contaminant or the entire contaminated area. When the area to be treated and controlled is large dimensions, this entails a cost of equipment and particularly important functioning. Finally, this ventilation protection technique only provides one-way protection, that is, it does not act only when contamination transfers are not only possible in one direction.

The air curtain protection technique consists of injecting simultaneously, in the area of separation by which the two zones communicate, a or several jets of clean air, adjacent and likewise meaning, which form a fictitious gate between the area to protect and the contaminating area.

According to the theory of jet planes turbulent, it is recalled that a plane air jet is breaks down into two distinct zones: a transition zone (or heart zone) and a development zone.

The transition zone corresponds to the part jet center, supported on the nozzle, in which the velocity vector is constant. This area corresponds to the part of the jet in which no mixture enters the injected air and the air present on either side of the jet does not occur. In section along a perpendicular plane in terms of the separation zone, the width of the transition zone gradually decreases in moving away from the nozzle. For this reason, this area transition will be called "dart" in the rest of the text.

The jet development area is the part of the latter located outside the area of transition. In this jet development area, the outside air is entrained by the flow of the jet. This results in variations in the velocity vector and by air mixing. Air entrainment by the two faces of the jet, in this development zone, is called "induction". An induced air jet thus, on each of its faces, an air flow which depends in particular on the injection rate of the jet in question.

In JP-B-36 7228, it was proposed create an air curtain by simultaneously injecting in the separation zone three adjacent air jets and in the same sense. More specifically, an air jet relatively fast is injected between two air jets relatively slow. This arrangement is supposed to ensure more efficient containment than a single air jet, by the fact that the air entrained and stirred by the jet central is slightly contaminated air from relatively slow jets injected on both sides of this central air jet.

However, this document does not take into account or the length of the darts of each jet, or their injection rates, so that the efficiency of the confinement is very random.

In document FR-A-2 530 163, it is proposed to ensure the containment of a polluted room, having an opening, by injecting therein a air curtain formed by two adjacent clean air jets and in the same sense. More specifically, the separation dynamic is ensured by a relatively first draft slow (called "slow jet"), the sting of which covers in the whole opening. The second jet (called "jet fast "), relatively fast compared to the slow jet, is installed between the slow jet and the area to be protected. Its function is to stabilize the slow jet, by a suction effect which presses this slow jet against the jet fast.

In this document FR-A-2 530 163, it is clarified that the dart of the slow jet is long enough to cover the entire opening when the width of the injection nozzle of this slow jet is at least equal to 1 / 6th of the height of the opening to be protected. It is also indicated that the injection rates of the two air jets must be such that the induced air flow by the face of the rapid jet which is in contact with the slow jet is substantially equal to the injection rate of this last.

In document FR-A-2 652 520, it is offered to use an air curtain to protect a clean work area, with an opening, opposite contaminating external environment. The main characteristics of the air curtain are comparable to those described in document FR-A-2 530 163. It is further specified that the speed slow jet injection should be around 0.4 m / s or 0.5 m / s. It is also specified that the jets are emitted so that the outer face of the rapid jet arrives at the limit of the plane of the opening. Considering expansion angles of the jets, this results in a angle of approximately 12 ° between the median plane of the jets and the plan of the opening.

In document FR-A-2 652 520, it is also proposed to simultaneously inject clean air ventilation, at a temperature adapted to the needs, inside the work area to be protected. It is indicated that this clean ventilation air should be injected at a flow rate substantially equal to the induced flow rate by the face of the rapid jet which is in contact with air clean ventilation.

Furthermore, it is also indicated in the document FR-A-2 652 520 that the rework grid by which we recover the two jets is arranged outside from the opening, and below the workstation, so as to control the ventilation of the area contaminated. In addition, the two side walls which delimit the opening are extended outwards over a distance at least equal to the thickness of the curtain of air.

In document FR-A-2 659 782, it is proposed to add to the two clean air jets described in document FR-A-2 530 163 a third air jet clean relatively slow, so the fast air jet is located between two adjacent slow jets and Same direction.

In this arrangement, which incorporates the main characteristics of documents FR-A- 2 530 163 and FR-A-2 652 520, the injection rate of clean air ventilation inside the area to be protected is considerably decreased. In addition, dynamic containment is insured in both directions, which was not the case in previous documents.

Reducing the air injection rate clean ventilation inside the area to be protected follows from the fact that the induction in this zone is produced by the development area of one of the jets slow and no longer by the jet development zone fast as in the case of an air curtain with two jets.

Despite improvements to the air curtain technique by these different documents, experiments and simulations made by applicants have shown that the effectiveness of containment obtained with the air curtain devices described in documents FR-A-2 530 163, FR-A-2 652 520 and FR-A-2 659,782 remained very perfectible, especially in situation of break-ins.

Statement of the invention

The subject of the invention is precisely a process of dynamic separation of two communicating zones between them by at least one separation zone, using an air curtain, the principle of which is comparable to that described in the documents FR-A-2 530 163, FR-A-2 652 520 and FR-A-2 659 782, but whose containment efficiency is appreciably improved, especially in the event of break-ins.

• on injecte dans ladite zone de séparation, à un premier débit d'injection, un premier jet d'air propre relativement lent, comprenant un dard apte à recouvrir toute la zone de séparation ;
• on injecte simultanément dans la zone de séparation, à un deuxième débit d'injection, un deuxième jet d'air propre relativement rapide, adjacent au premier jet et de même sens que celui-ci, entre la zone à protéger et le premier jet ;

ce procédé étant caractérisé par le fait qu'on règle le deuxième débit d'injection, afin que le débit d'air induit par la face du deuxième jet en contact avec le premier jet, soit au plus sensiblement égal à la moitié du premier débit d'injection.In accordance with the invention, this result is obtained by means of a process for dynamic separation of a contaminating zone and a zone to be protected, communicating with one another by at least one separation zone, this method comprising the following steps:

• a relatively slow first jet of clean air is injected into said separation zone, at a first injection rate, comprising a dart capable of covering the entire separation zone;
• a relatively fast second jet of clean air is injected simultaneously into the separation zone, at a second injection rate, adjacent to the first jet and in the same direction as the latter, between the zone to be protected and the first jet;

this process being characterized by the fact that the second injection flow is adjusted, so that the air flow induced by the face of the second jet in contact with the first jet is at most substantially equal to half of the first flow injection.

The applicants have discovered and verified, by experience and by calculation, that all these characteristics are essential for obtaining a "barrier effect" between the two zones, ie so that the sting actually covers the entire area of seperation.

Indeed, if the induction of the face of the jet fast, created by the blowing rate thereof, is too important, we can consider that there is overconsumption of the slow jet sting and this has consequently a decrease in the length of the slow jet; therefore, the cover of the opening to be protected is imperfect (case of all art documents previous). On the other hand, if the speed of the fast jet is too weak, stabilization of the slow jet by induction of the face of the fast jet in contact with the slow jet is not maximum. Therefore, the applicants have established that it is essential that the induced air flow by the face of the second (fast) jet in contact with the first jet (slow) either lower or, preferably, substantially equal to half the injection rate of this first jet and not equal to the totality of this flow injection, as the documents teach FR-A-2 530 163, FR-A- 89 12861 and FR-A-2 659 782.

Air curtain can provide containment dynamic in either direction, if we add on the first two jets a third relatively slow. In this case, we inject into the separation, at a third injection rate, a third relatively slow clean air stream, adjacent on the second roll and in the same direction as the first and second jet, between the area to be protected and the second jet. The third jet includes a dart capable of covering the whole separation zone. We then set the third injection rate so that it is substantially equal to the first injection rate, so that the air flows induced by the faces of the second jet respectively in contact with the first and the third jets are at most substantially equal to the half of the first and third injection rates. Thanks to these features, the third jet effectively covers the entire separation zone.

Preferably, simultaneously injected clean ventilation air inside the area to be protect, at an injection rate at least equal to the rate air induced by the second or third jet (depending on that the air curtain includes two or three jets), on the face of it in contact with the clean air of ventilation. The plaintiffs have discovered that this characteristic allows to obtain a "purifying effect" in the area to be protected, especially in the event of break-ins through the air curtain.

In order to optimize the purifying effect and what whatever the number of jets forming the air curtain, we advantageously injects clean ventilation air to a speed such as the speed of this clean air of ventilation, related to the area plan surface separation, at least equal to 0.1 m / s.

In case internal ventilation is used, clean ventilation air is injected into the an entire rear or upper wall of the area to protect, towards the separation zone. The wall through which clean air is injected ventilation is therefore oriented parallel or substantially perpendicular to the plane of the area of separation.

If you also want to control the temperature inside the protected area, we inject clean ventilation air at a regulated temperature.

To further optimize the barrier effect provided by the air curtain, all clean air jets are preferably injected in directions substantially parallel to the plane of the area of separation. In addition, we advantageously recover all clean air jets through a return grille installed opposite the injection nozzles of these jets and located in a plane substantially perpendicular to the direction of clean air jets.

Optimization of the barrier effect provided by the air curtain can also be obtained by extending the side walls of the opening, located on both sides of the clean air jets, so that they extend to the contaminating area over a distance at least equal to the maximum thickness of the jets.

Brief description of the drawings

• la figure 1 est une vue en perspective, qui illustre de façon schématique la protection d'une zone de travail propre au moyen d'un rideau d'air formé de deux jets d'air adjacents, selon une première forme de mise en oeuvre du procédé de l'invention ; et
• la figure 2 est une vue en perspective comparable à la figure 1, qui illustre schématiquement la protection d'une zone de travail propre au moyen d'un rideau d'air formée de trois jets d'air adjacents, selon une deuxième forme de mise en oeuvre du procédé de l'invention.

Two forms of implementation of the invention will now be described, by way of nonlimiting examples, with reference to the appended drawings, in which:

• Figure 1 is a perspective view, which schematically illustrates the protection of a clean work area by means of an air curtain formed of two adjacent air jets, according to a first embodiment of the method of the invention; and
• Figure 2 is a perspective view comparable to Figure 1, which schematically illustrates the protection of a clean work area by means of an air curtain formed of three adjacent air jets, according to a second form of setting implementing the method of the invention.

Detailed description of two forms of implementation

In Figure 1, we have respectively designated by references 10 and 12 an area to be protected and a contaminating area.

In the embodiment shown, the zone 10 to be protected consists of the interior space clean of a work station and the contaminating area 12 is constituted by the space outside this workplace. This outdoor space is a source of thermal, particulate contamination, gaseous and / or microbial vis-à-vis the interior space of the work station.

The workstation that forms zone 10 to protect is delimited by watertight walls in all directions except to the right considering Figure 1. More specifically, the face of the workstation turned to the right in Figure 1 forms a separation zone, constituted by an opening 11, by which zone 10 to be protected communicates with the contaminating external zone 12. This opening 11 is intended, for example, to allow entry and exit of objects in zone 10 to be protected, as well as possible handling within this area, from the contaminating outdoor area 12. It is note that this illustration is only a example of implementation, in no way limiting, the zones 10 and 12 can communicate through one or more zones of separation of any orientations and which are not not necessarily materialized by openings, without departing from the scope of the invention.

In particular, in one embodiment not shown, according to which the area to be protected is a conveyor running along a line path, circular or even winding, the separation zone between the contaminating zone and the zone to be protected extends longitudinally along the path of said conveyor.

In order to preserve dynamic separation zones 10 and 12 despite the presence of the opening 11, an air curtain 14 is permanently formed in this opening when the installation is used. In the embodiment illustrated schematically in FIG. 1, this air curtain 14 is formed by injecting simultaneously in the opening two air jets own adjacent and the same direction.

More precisely, we inject into opening 11 a first jet of clean air, relatively slow, of which only the sting 16 is represented, and a second jet of clean air, relatively fast compared to on the first draft, of which only the sting 18 is represented. The second jet is injected between the first jet and zone 10 to be protected. To simplify, the first jet and the second jet are respectively called "jet slow "and" rapid jet "in the rest of the text.

Slow jet and fast jet injections in the opening 11 are made respectively by juxtaposed nozzles 20 and 22.

In the embodiment shown, in which the opening is rectangular and has two horizontal edges and two vertical edges, and without limitation, the injection nozzles 20 and 22 extend over the entire length of the top edge of the opening 11, so that the air curtain 14 is formed over the entire width thereof. Both jets forming the air curtain 14 are then recovered in all by a single rework grid 24 which extends along the bottom edge of the opening and over the entire length of this edge. The vertical edges of the opening 11, are materialized by two side walls 26, located on either side of the two jets forming the air curtain 14. These two side walls 26 extend into contaminating zone 12 over a distance at least equal to the maximum thickness of the jets.

As illustrated schematically in Figure 1, the slow jet, injected by the nozzle 20, is dimensioned so that its dart 16 covers the entire plane of the opening 11 to be protected. This result is obtained by ensuring that the range, or length, of the dart 16 is at least equal to the height of the opening 11. For this purpose, the width of the nozzle 20, parallel to the plane of FIG. 1, is at least 1/6 ^th and preferably 1/5 ^th of the height of the opening 11 to be protected. Thus, and only by way of example, for an opening 1 m high, the width of the nozzle 20 will be at least 0.20 m.

In addition, in order to avoid as much as possible turbulence and for economic reasons the speed of the slow jet emitted by the nozzle 20 is advantageously fixed at 0.5 m / s. Because the length of the stinger 16 of the slow jet is at least equal to the height of the opening to protect and that this jet is relatively slow, the air streams follow the outline of passing objects through the air curtain 14, without breaking the confinement.

The low speed of the slow jet injected by the nozzle 20, however, has the consequence that this jet, if it were alone, would risk being destabilized by the aeraulic or mechanical disturbances which can occur near the air curtain, thus causing the break in the confinement of the work station. This is why we add to the slow jet the fast jet injected by the nozzle 22 and whose higher speed allows to ensure the stability of the first jet and, consequently, to improve the efficiency of the confinement in situation of 'break-ins through the dynamic barrier formed by the air curtain 14. By way of nonlimiting example, the width of the nozzle 22 by which the rapid jet is injected can be equal to approximately 1/40 ^th of the width of the nozzle 20, which corresponds to 0.005 m in the example described.

In order to optimize the barrier effect guaranteed by the combination of the two jets, the applicants established that the injection rate of the fast jet, injected via nozzle 22, must be adjusted so that the air flow induced by the face of this rapid jet which is in contact with the slow jet, injected through nozzle 20, i.e. less than or preferably substantially equal to the half the injection rate of this slow jet. Of experiments and simulations have shown that this characteristic led to a noticeable improvement of the barrier effect compared to the prior art, in which the rapid jet flow is adjusted so that the air flow induced by the face of this rapid jet in contact with the slow jet, i.e. substantially equal to slow jet injection rate.

By way of illustration, which is in no way limitative, if the blowing rate of the slow jet injected through the nozzle 22 is 360 m ³ / h, the blowing rate of the fast jet injected through the nozzle 22 must be around 42 m ³ / h. This latter value is to be compared with the value of approximately 84 m ³ / h recommended in the prior art.

In order to ensure the recovery of everything the air blown by nozzles 20 and 22 and air driven by the air curtain 14, the return grille 24 communicates with suction means (not shown), designed for this purpose. In practice, the air recovered by the return grille 24 is advantageously purified by specific purification means (not shown) before being recycled to the nozzles 20 and 22. The excess air is then rejected outside after a second specific purification.

In the digital example given above, the air suction flow rate through the intake grille 24 is 825 m ³ / h.

The applicants also established that the barrier effect is further optimized when each of the two jets is injected in a substantially direction parallel to the vertical plane of the opening 11 and when the return grid 24 is perpendicular to this direction. In other words, it is desirable that the outlet openings of the nozzles 20 and 22 are located in the same horizontal plane and as the grid 24 is located below the nozzles 20 and 22 in another horizontal plane.

In addition, a purifying effect on the area 10 to be protected is obtained by ensuring ventilation internal of this zone and respecting a flow injection determined for this internal ventilation. This purifying effect, added to the barrier effect provided by air curtain 14, significantly improves efficiency containment, especially in the event of break-ins.

More specifically, in the form of embodiment of Figure 1 which relates to an air curtain 14 formed of two adjacent jets of the same direction, the injection rate of clean ventilation air at the interior of zone 10 to be protected is at least equal at the air flow induced by the rapid jet, injected by the nozzle 22, on the face of this rapid jet which is in contact with clean ventilation air, i.e. on the face of the rapid jet facing zone 10 to protect. In addition, clean ventilation air is injected at a speed such as the speed of this air, related to the surface of the plane of the opening 11 either at least equal to 0.1 m / s.

In the illustrated embodiment schematically in Figure 1, the injection of air clean ventilation inside zone 10 to protect is effected by a blast grille 28 which extends over the entire rear wall of the area to protect, i.e. over the entire wall of the area working facing opening 11 and oriented parallel to the vertical plane thereof. Grid supply air 28 through which clean air is injected ventilation is located on the left considering Figure 1.

In one embodiment (not already mentioned), according to which the area to protect is a moving conveyor following a given path, the wall through which air is injected clean ventilation forming the purifying flow, is the upper wall of the area to be protected. This wall is arranged opposite the conveyor and oriented then substantially perpendicular to the plane of the area of separation.

When the temperature in the zone 10 to be protected must be maintained at a value determined uniform, clean ventilation air is injected through the air outlet grille 28 at a temperature regulated. To this end, temperature regulation means, such as a heat exchanger (not shown), are placed in the ventilation circuit, upstream of the discharge grille 28.

In the nonlimiting example described above, the blowing rate of the internal ventilation is 360 m ³ / h.

Experiments and simulations have shown that compliance with the characteristics which have just been described guarantees confinement efficiencies 10 to 100 times better than those obtained according to the prior art. Thus, the confinement efficiency of a dynamic barrier being defined as the ratio of the concentration of pollutants, particulate or gaseous, in the contaminating zone to the concentration of the same pollutants in the zone to be protected, the characteristics described above make it possible to achieve containment efficiencies between 10 ⁴ and 10 ⁶ .

In Figure 2, a second illustrated form of implementation of the method according to the invention. This second form of implementation resumes, for the essentials, the characteristics described above referring to figure 1, adding a third relatively slow jet between the fast jet and the area to protect. For this reason, the elements of the installation illustrated in Figure 2 which are identical to those of the installation described above in se referring to figure 1 are designated by the same reference figures and no description will be given detailed.

Thus, we recognize in Figure 2 the area 10 to be protected, the contaminating zone 12, the opening 11, nozzles 20 and 22 through which are respectively injected the slow jet and the fast jet including the darts are shown in 16 and 18, the side walls 26 of the opening 11 and the air grille 28 ensuring internal ventilation of zone 10 to be protected.

The air curtain, designated in this case by the reference 14 ', further includes a third air jet clean, relatively slow compared to the fast jet, which is emitted by a nozzle 30 adjacent to the nozzle 22, between the fast jet and the zone 10 to be protected, so to be adjacent to the rapid jet and in the same direction as the other jets. The sting of this third jet is illustrated at 32 in Figure 2.

The dimensions of the nozzle 30 are chosen so that the dart 32 of the third jet covers the entire opening. For this purpose, the nozzle 30 extends, like the nozzles 20 and 22, over the entire length of the upper edge of the opening 11, and the width of this nozzle 30 is at least equal to 1/6 ^th and, from preferably, 1/5 ^th of the height of the opening 11. In practice, the widths of the nozzles 20 and 30 are the same and, for example, 0.20 m in the case of the digital illustration given above. , without limitation, with reference to FIG. 1.

In the second form of implementation of the method according to the invention, the injection rate is adjusted of the slow jet delivered by the nozzle 30, so that this flow rate is substantially equal to the injection flow rate of the slow jet delivered by the nozzle 20. Thus, the flow rates of air induced by the faces of the fast jet, emitted by the nozzle 22, respectively in contact with each of the jets slow, are lower or, preferably, substantially equal to half the injection rates of these jets slow.

As illustrated in Figure 2, it is note that the width of the return grille, designated in this case by the reference 24 ', is adapted to the width air curtain, so that all jets are recovered by this 24 'grid. More specifically, the grille 24 'for the return of the air curtain 14' formed of three jets, is wider than the rework grid 24 the air curtain 14, formed of two jets.

The use of a 14 'air curtain formed of three adjacent jets and in the same direction allows a effective dynamic separation of the two zones in one and the other direction.

In addition, in the second form of implementation work illustrated in Figure 2, the presence of a another slow jet, between the fast jet and zone 10 to protect, reduces the injection rate of the internal ventilation compared to the first form of Implementation. Indeed, the air injection rate clean ventilation through the supply grille 28 is then at least equal to the air flow induced by the jet slow emitted by nozzle 30, on the face of this third jet which is in contact with clean ventilation air.

In the digital example given above, the injection rate of each of the slow jets is 360 m ³ / h, the blowing rate of the internal ventilation is 360 m ³ / h and the suction rate of the grid 24 'recovery is 1185 m ³ / h.

As in the first form of implementation work of the invention, the three jets are preferably injected in directions parallel to the plane of opening 11 and the return grid is placed in below the injection nozzles 20, 22 and 30 and oriented perpendicular to this plane. By the way, the speed to which ventilation air is injected into the zone 10 to be protected is advantageously at least equal to 0.1 m / s.

The containment efficiencies obtained in the second embodiment of the invention, illustrated in Figure 2, are comparable to those that were given in the case of the first form of implementation, described previously with reference in Figure 1.

It should be noted that many modifications can be performed on facilities described, without departing from the scope of the invention.

These changes relate first place the applications, which are numerous and concern all cases in which it is necessary to ensure the thermal and dynamic separation of two atmospheres with gas concentrations, particulate and / or different bacteriological (a clean atmosphere and the other contaminated, as well as at a temperature be different), while allowing the passage repeated objects from one area to another, without the clean area does not become contaminated. Examples of these applications are the protection of workstations food, medical, biotechnology or high technologies, displays for the distribution of sensitive products, etc.

Possible modifications concern also the shape, orientation and number of areas of separation by which the two zones communicate, as well as the choice of the edges of the separation zone on which the injection nozzles are installed and the rework grid, which may be different from those that have been described.

Claims (14)

1. Process for dynamic separation of a contaminating zone (12) and a zone to be protected (10), communicating with each other through at least one separation zone (11), this process comprising the following steps:

   a first relatively slow clean air jet is injected into the said separation zone (11) at a first injection flow, comprising a tongue (16) capable of covering the entire separation zone;

   a second relatively fast clean air jet is injected at the same time into the separation zone (11) at a second injection flow, adjacent to and in the same direction as the first jet, between the zone to be protected (10) and the first jet;

   the said process being characterized by the fact that the second injection flow is adjusted so that the air flow induced by the surface of the second jet in contact with the first jet is not greater than about half of the first injection flow.
2. Process according to claim 1, in which the second injection flow is adjusted so that the air flow induced by the surface of the second jet in contact with the first jet is equal to approximately half of the first injection flow.
3. Process according to either of claims 1 and 2, in which clean ventilation air is injected simultaneously inside the zone to be protected (10) at an injection flow equal to at least the air flow induced by the second jet, the surface of which is in contact with clean ventilation air.
4. Process according to either of claims 1 and 2, in which a third relatively slow jet is injected into the separation zone (11) at a third injection rate, adjacent to the second jet and in the same direction as the first and second jets, between the zone to be protected (10) and the second jet, the third jet comprising a tongue (32) capable of covering the entire separation zone (11), and the third injection flow is adjusted so that it is approximately equal to the first injection flow, such that the air flows induced by the surfaces of the second jet in contact with the first and the third jets respectively, are not more than approximately half the first and third injection flows.
5. Process according to claim 4, in which the third injection flow is adjusted such that the air flows induced by the surfaces of the second jet in contact with the first and third jets respectively are equal to approximately half of the first and third injection flows.
6. Process according to either of claims 4 and 5, characterized in that clean ventilation air is injected simultaneously inside the zone to be protected (10), at an injection flow equal to at least the air flow induced by the third jet on the surface of the air flow in contact with the clean ventilation air.
7. Process according to any one of claims 3 and 6, characterized in that clean ventilation air is injected at a speed such that the speed of this clean ventilation air divided by the area of the plane of the separation zone (11) is equal to at least 0.1 m/s.
8. Process according to any one of claims 3, 6 and 7, characterized in that clean ventilation air is injected over the entire surface of a wall of the zone to be protected (10), in the direction of the separation zone (11).
9. Process according to claim 8, characterized in that the wall on which the clean ventilation air is injected is the rear wall of the zone to be protected (10), which is parallel to the plane of the separation zone (11).
10. Process according to claim 8, characterized in that the wall on which the clean ventilation air is injected is the top of the zone to be protected (10), laid out approximately perpendicular to the plane of the separation zone (11).
11. Process according to any one of claims 3 and 6 to 10, characterized in that the temperature of the clean ventilation air is regulated.
12. Process according to any one of the previous claims, characterized in that all clean air jets are injected in directions approximately parallel to the plane of the separation zone (11).
13. Process according to any one of the previous claims, characterized in that all clean air jets are recovered through an intake grille (24, 24') installed facing the injection nozzles (20, 22, 30) through which the said jets are injected and located in a plane approximately perpendicular to the direction of the clean air jets.
14. Process according to any one of the previous claims, characterized in that the separation zone (11) is bounded by side walls (26) located on each side of the clean air jets extending towards the contaminating zone (12) over a distance equal to at least the maximum thickness of the jets.

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