FR2754729A1 - Nozzle for in situ cleaning of falling film evaporators - Google Patents

Abstract

A cleaning nozzle for cleaning falling film evaporators is housed in a cylindrical body (2) which fits into a tube of the evaporator. Cleaning fluid is fed in through an opening (4) in the base (3) of the body and is distributed through the nozzle head (5). The head itself moves up in use (as shown) and down when not in use, to be more or less flush with the end (46) of the casing. An intermediate piece (23,24) allows the nozzle to rise-and-fall by a certain extent by the path of a lug in a slot (28). When the cleaning nozzle is in position in the top of a vertical bundle of tubes it can be used to clean the liquid feed chamber above and the liquid distribution grill.

Description

Device for dispensing a fluid, such as a washing liquid, and evaporator for a falling flow liquid comprising such a device
The present invention relates to a fluid distribution device, such as a washing liquid, of the type comprising a nozzle body provided with an inlet for a fluid, a fluid distribution nozzle comprising a distribution head displaceable in translation in said body between a closed position in which the distribution of the fluid is interrupted and an open position in which the distribution of the fluid is ensured, and means for mounting said nozzle in said nozzle body; it also relates to a falling-stream evaporator equipped with such a device.

 It is customary in the industry, especially in the food industry, to periodically clean the interior of a wide variety of facilities. This is particularly the case in the field of the concentration by evaporation of liquid food products such as sugary juices or milk. The normal cleaning procedure is cleaning in place, that is to say without dismantling the installation, the washing liquids being sent into circulation in the installation in place of the liquid product to be concentrated. There are however internal elements of the installation which cannot be satisfactorily cleaned by this procedure; this is particularly the case of the lower surface of the distribution grid of the product to be concentrated, arranged in the supply chamber of the falling-stream evaporators.

 The object of the present invention is therefore to propose a device as defined in the first paragraph of this description, this device being characterized in that said mounting means comprise a member for connecting the nozzle to the nozzle body and complementary means shaped to allow the movement of said connecting member between a locking position of this member relative to the nozzle body and an unlocking position of this member relative to the nozzle body.

 By the very structure of the mounting means, this device can be easily disassembled for cleaning. It can also be achieved with a minimum footprint, which allows it to be permanently installed inside an installation even of small volume. In particular it can, as will be seen in more detail below in the case of a falling-stream evaporator, be simply inserted into one of the tubes of the tube bundle, under the distribution grid.

 Depending on the application for which this device is intended, it may be advantageous to provide sealing means between the nozzle body and the nozzle, to avoid any introduction of external material (solid or liquid) into the nozzle body, which could be detrimental to the proper functioning of said device.

 The aforementioned complementary means are preferably shaped to pass from the locking position to the unlocking position and vice versa, by a simple movement in translation, in rotation then again in translation of said connecting member relative to the nozzle body.

 Thus, these complementary means may for example comprise at least two lugs provided on the internal face of the wall of the nozzle body or on the external face of the connecting member and able to be engaged and each held in a corresponding notch provided respectively on the connecting member or on the nozzle body.

Preferably, each notch is provided on the connecting member and comprises a first longitudinal section originating on the edge of the connecting member, opposite the dispensing head, a second section parallel to the first section, shorter than this. last and directed towards the edge of the connecting member, opposite said dispensing head, and a third section connecting the first and second sections.

 It will be added that each notch can in particular be a through notch provided on the connecting member.

 Furthermore, the mounting means preferably further comprise a first elastic element for holding said lugs in the bottom of the second section of the corresponding notch, this elastic element being disposed compressed between the edge of the connecting member, opposite to the dispensing head and an internal support area of the nozzle body. It is for example a helical spring, one end of which bears on said edge of the connecting member and the other end on said bearing zone of the nozzle body. In this case, it is advantageous for the lugs to be offset longitudinally by a distance corresponding to half the pitch of the helical spring, the notch corresponding to the lug closest to the dispensing head then having a first longer section. than the first section of the other notch. Thanks to this system, it is possible to introduce the spring into the nozzle body at will (or to extract it at will) simply by engaging the lower (or upper) turn in the pins and by "screwing" ( or by "unscrewing it".

 In the case where the dispensing head is in a manner known per se extended by an elongated element terminated by a means forming a stop, the connecting member is advantageously shaped so that said elongated member extends right through this member. connection, a second pre-stressed elastic element being disposed between this member and said stop means. The role of this elastic element is to maintain the dispensing head in the closed position as long as a sufficient force does not oppose this element to bring the head in the open position.

 This second element can for example be constituted by a helical spring.

 It will be added that the connecting member of the device according to the invention may advantageously include means for adjusting the amplitude of the translational movement of said dispensing head, these adjusting means comprising a hollow cylindrical element extending axially around said elongated element and secured by its upper end to the edge of the connecting member, opposite the dispensing head.

 The mounting means of the device according to the invention may further comprise complementary means for securing in rotation the connecting member to the elongate element extending the dispensing head. In this way, by imposing a rotational movement on the dispensing head, and therefore on said elongated element, this movement is transmitted by these complementary means to the connecting member which can therefore be brought into the unlocking or locking position. relative to the nozzle body.

 It will be noted that said complementary securing means may in particular comprise at least one longitudinal groove provided in the connecting member and a pin carried by the elongate element and in engagement with said groove.

 According to one embodiment, this longitudinal groove is through and the pin is removable.

 The present invention further relates to the particular application of the above device in a falling-stream evaporator.

 More specifically, it also relates to a liquid evaporator of the falling flow type, comprising in a manner known per se a bundle of tubes disposed in a heating body, said bundle being surmounted by a liquid supply chamber to be evaporated. , this evaporator being characterized in that it comprises at least one device as defined above, arranged in such a way that in the open position, the dispensing head of said device emerges above the bundle of tubes, means of sealing being provided to prevent any introduction of liquid from the supply chamber into the nozzle body of said device.

 Thus, this device can be placed in the heating body, suspended from the tubular plate which will have been provided with a hole allowing the reception of this device. It could alternatively be placed in at least one tube of the tube bundle, sealing means then being provided to prevent any introduction of liquid from the supply chamber into said tube.

 In order to avoid the presence of the dispensing device being at the origin of any zone of stagnation or retention of liquid, source of risk of microbial development detrimental to the quality of the product concentrated in the evaporator, this will preferably be positioned so that in the closed position of the dispensing head, the upper end of the latter is substantially at the level of the upper end of the bundle of tubes.

 It will be noted that when a grid for distributing the liquid to be evaporated is arranged above the bundle of tubes in the supply chamber, the location of the device described above will advantageously be chosen to distribute a washing liquid over the entire lower surface of this grid.

 When the dispensing device is placed in a tube, the washing liquid will advantageously be introduced through the base of this tube; the lower end of the latter may, in this case, be provided with a washing liquid inlet.

 It will be added that in the case where the dispensing device is placed in a tube of the bundle, this tube will advantageously be provided with a hole located below said device, so that this tube is then in communication with the inside the heating body.

 Indeed, thanks to this arrangement, the interior of the device will always be slightly overpressure relative to the supply chamber, which will prevent any introduction of liquid into the device from the supply chamber in case the means seal provided between the nozzle body and the nozzle would fail.

 Since there is a clearance between the internal surface of the tube and the external surface of the nozzle body, it is advantageous to introduce the distribution device into the upper part of a bundle tube without difficulty. invention of providing on the nozzle body means allowing, when the nozzle dispensing head is in the open position, a circulation of liquid between the interior of the nozzle body and the volume defined by said clearance.

 It should be noted that these means may for example comprise one or more through holes provided in the lower part of the nozzle body and one or more through holes provided in the upper part of this body and not closed by the dispensing head in the open position. .

 Thanks to these means, it will indeed be possible to prevent corrosive washing liquid (acid or base) permanently stagnating between the tube and the nozzle body and to allow this same corrosive washing liquid to be removed during the last wash (wash with water).

An embodiment of the invention is described below by way of example, with reference to the accompanying drawings in which
FIG. 1 is a partial longitudinal section of the device according to the invention, only part of the dispensing head having been shown in section and this head being in the closed position,
FIG. 2 is a partial longitudinal section of the device in FIG. 1, the latter being shown offset by an angle of 90 "relative to FIG. 1 and the head being in the open position,
FIG. 3 is a section along line III-III of FIG. 1,
FIG. 4 is a section along the line IV-IV of FIG. 1, and
FIG. 5 is a partial diagrammatic representation in section of the upper part of a falling-stream evaporator equipped with the device according to FIGS. 1 to 4.

 As shown in Figures 1 to 4, the device according to the invention comprises a nozzle body constituted by a hollow cylinder 1 having a side wall 2 and a bottom 3, the latter being provided with a fluid inlet 4, for example washing liquid.

 This device further comprises a fluid distribution nozzle comprising a distribution head 5 extended at its lower part by a cylindrical rod 6 terminated by a removable element forming a stop, for example a flange 7 which can be fixed to the lower end of the element 6, the total length of this nozzle not being greater than the interior length of the nozzle body.

 In the embodiment shown, the rod 6 is extended at its upper end by a first cylindrical section 8 having substantially the same diameter as the rod 6, this cylindrical section 8 itself being extended by a second cylindrical section 9 having a diameter higher than in the first section 8.

 The second section 9 flares at its upper end to end with a circular section member 10 whose diameter is very slightly less than the internal diameter of the cylinder 1. This member 10 is provided with a peripheral groove 11 in which is housed an O-ring 12 bearing on the internal face of the side wall 2 when the dispensing head 5 is in the closed position.

 On the section 9 is mounted for rotation a ring 13 provided with at least two orifices 14 extending tangentially between the internal face 15 of the ring and its external face 16. These orifices 14, when supplied with fluid, cause the rotation of the ring 13. This ring is further provided with non-tangential holes 17 whose arrangement and orientation are chosen to ensure a distribution of fluid in determined directions.

 Furthermore, on the first cylindrical section 8 is fitted a support member 18 of circular section retained by a circlip 19 inserted in a groove provided between the rod 6 and the section 8.

 This support member 18 is provided with a circular groove 20 receiving an O-ring 21. This member 18 further comprises vertical passages 22 extending into the internal space of the ring 13.

 Elements 8 to 22 define the above-mentioned dispensing head 5.

 It should be noted that this head 5 is movable in translation (longitudinally) in the cylinder 1 between a closed position and an open position.

 In the closed position (see FIG. 1), the upper surface of the head 5 is at the level of the upper edge of the cylinder 1, the O-ring 12 ensuring the seal between the wall 2 and the head 5; in addition, all the orifices 14, 17 are closed by the wall 2 and the distribution of fluid is thereby interrupted.

 In the open position (Figure 2), part of the head 5 emerges above the upper end of the cylinder 1; this emerging part is constituted by the elements 9 to 17 and the seal between the wall 2 and the head is ensured by the O-ring 21; in addition, all the orifices 14, 17 are cleared and the distribution of fluid is therefore possible.

 The device thus described also comprises means for mounting the nozzle in the nozzle body.

 According to the invention, these mounting means comprise a member for connecting the nozzle to the nozzle body, this member being constituted by a hollow cylinder comprising a side wall 23 and a bottom 24 whose internal face is inclined downward. This bottom 24 is provided with a central circular opening 25 in which the rod 6 can slide freely; vertical holes 26 are further provided distributed around the central opening 25.

 These mounting means further comprise complementary means for moving said connecting member between a locking position and an unlocking position of this member relative to the nozzle body.

 According to a preferred embodiment, these complementary means more specifically comprise, on the one hand at least two lugs 27 (two in the embodiment shown) mounted on the internal face of the side wall 2 and located in the same vertical plane, and on the other hand a corresponding number of through slots 28 (two in the embodiment shown) provided on the side wall 23.

 Each notch 28 consists of three sections, namely a vertical section 29 originating on the lower edge of the side wall 23 and extended by a horizontal section 30 which is itself extended by a vertical section 31 directed downwards.

 In the locked position, each lug 27 is held at the bottom of the section 31 of the corresponding notch. This maintenance can be ensured by a helical spring 32 disposed compressed between the bottom 3 of the nozzle body and the bottom 24 of the connecting member, a spring which pushes this member upwards.

 In the unlocked position, each lug 27 is arranged in the section 29 of the corresponding notch.

 It will be added that to facilitate the positioning of the helical spring 32, the pins 27 are offset longitudinally by a distance corresponding to half the pitch of the spring; the positioning of the latter is then carried out by inserting the highest lug in the first lower turn of the spring and by communicating to the latter a rotational movement around its longitudinal axis (screwing). It should be noted that in this case, the section 29 of the notch associated with the lug in the highest position, is longer (by a distance corresponding to that separating the two offset notches) than the section 29 of the '' other notch associated with the lug in the lowest position.

 The device thus described also comprises means for adjusting the amplitude of the longitudinal displacement of the dispensing head in the nozzle body. These means comprise a hollow cylindrical element 33 extending axially around the rod 6 and secured by its upper end to the bottom 24.

 It will be understood that the amplitude of the displacement will thus be defined by the distance separating the lower edge of the element 33 from the collar 7.

 The device is finally completed by a pin 34 inserted in an orifice passing radially through the rod 6, this pin being also engaged at each of its ends with a longitudinal transverse groove 35 formed in the side wall 23. In this way, any movement of rotation communicated to the rod 6 is transmitted, by means of this pin and of the grooves, to the connecting member with a view to securing (or detaching) the latter to the nozzle body.

 In the embodiment described above, the longitudinal displacement of the nozzle inside the nozzle body is ensured by the pressure of the fluid which can be supplied by the inlet 4. To keep the dispensing head closed, when the distribution of fluid is not desired, a prestressed helical spring 36 is interposed between the connecting member and the flange 7, the upper end of this spring resting on the bottom 24 and the lower end of this same spring taking support on said collar. This spring must of course be stiff enough to maintain the head in the closed position and at the same time soft enough to allow itself to be compressed by the fluid supply pressure.

 The device thus described operates in the following manner.

 No fluid being introduced into the nozzle body and the dispensing head then being maintained in the closed position under the effect of the spring 36, this head is brought into the open position by supplying the nozzle body via the inlet 4 with fluid , this fluid being at a pressure sufficient to compress the spring 36 until the flange 7 abuts on the lower edge of the cylindrical element 33. The members 9 to 13 are therefore moved above the level from the upper edge of the nozzle body 1. It follows that the orifices 14, 17 are released and the fluid is then able to flow under pressure, on the one hand through the tangential orifices 14, which causes the setting in rotation of the ring 13, and on the other hand by the orifices 17 in the form of pressurized jets.

 It should be noted that the seal between the nozzle body and the nozzle remains ensured by the O-ring 21.

 By interrupting the supply of fluid, the nozzle returns to its initial position under the return effect of the spring 36.

 The device according to the invention has the advantage of being able to be completely dismantled for cleaning.

 To facilitate this dismantling, the upper face of the member 10 is provided with a diametrical rib 37.

 However, disassembly is carried out in the following manner.

 An assembly / disassembly key comprising a gripping means terminated by a circular member provided with a groove capable of receiving the rib 37, this circular member also having the same diameter as the circular member 10, is positioned vertically of said member 10, the rib 37 being introduced into this groove. This key is then pushed down, which allows the nozzle to be pushed in until the pins 27 come into abutment in the bottom of the second section 30 of each groove 28.

 At this time, the mounting key communicates a rotational movement to the nozzle until each lug abuts in the bottom of the first section 29 of the corresponding notch.

 The pressure exerted is then released by means of the key.

 Under the effect of the helical spring 32, the connecting member, and leaving the nozzle, is pushed upward enough to be able to manually remove said nozzle.

 It is also possible to continue disassembly by removing the flange 7 and removing the pin 34, which allows the nozzle to be separated from the connecting member.

 Note that it is also possible to extract the coil spring 32 by engaging the last turn located at the upper end in the pins 27 and "unscrewing" the spring.

 The reassembly of the device is carried out by repeating the above steps, but in reverse, it being specified that during the introduction of the lugs into the corresponding notches, the entry of the notch having the first longest section is brought in line with the highest pin.

 It will have been noted that the complete assembly / disassembly of the device according to the invention is very simple and that it can be carried out by only one of its ends, this is completely original compared to the prior devices and greatly enlarges its scope.

 One of the applications of the device which has just been described is illustrated by FIG. 5. This FIG. 5 is a partial longitudinal section (upper part) of a falling-stream evaporator whose structure and operating principle are well known of the skilled person.

 An evaporator of this type comprises in particular a bundle of parallel tubes 38 held together at their upper end by an upper tube plate 39 and at their lower end by a lower tube plate (not shown).

This tube bundle is placed in a closed enclosure 40 supplied with steam (source of calories necessary for evaporation), this enclosure being called a heating body.

Above the tubular plate 39 is arranged a supply chamber 41 for the liquid product to be concentrated. In this supply chamber 41 is disposed, at a certain distance from the tubular plate 39, a distribution grid 42 which is substantially parallel to said plate 39 and has substantially the same surface as the latter. On its periphery, this grid carries a vertical side wall 43.

Above the grid 42 and substantially in the central part thereof, is arranged a vertical tubular inlet 44 of liquid to be evaporated supplying the grid 42. From the latter, the liquid flows on the tubular plate 39 , and then inside the tubes of the tube bundle 38 where it undergoes evaporation.

 During the concentration by evaporation, a deposit of dry matter is formed in the long run on the lower surface of the distribution grid 42.

 Such a deposit risks damaging the quality of the concentrated product, especially if this product is a food product. It is therefore essential to regularly clean the lower surface of this grid.

 This can be achieved by the present invention by implementing the above-mentioned liquid distribution device.

 More specifically, this device is placed in the upper part of at least one of the tubes 38 of the tube bundle.

 It will be added that sealing means are provided to prevent any introduction of the liquid to be concentrated from the supply chamber 41 into the tube equipped with said device. These sealing means can be constituted by a simple continuous weld bead produced between the upper edge of the hollow cylinder 1 and the tubular plate 39. This weld bead is represented by the reference 45 in FIGS. 1 and 2.

 It will be added that the upper end of the cylinder 1 is provided with a rim 46 to allow the dispensing device to be inserted into the tube while being supported by this rim on the tubular plate 39.

 As shown in Figure 5, the dispensing device is positioned in the tube so that in the closed position of the dispensing head, the upper end of the latter is substantially located at the upper end of said tube.

 The tube which is equipped with the dispensing device is chosen so as to be able to clean the entire lower surface of the grid 42 by means of the jets of pressurized washing liquid coming from the dispensing head in the open position. It should be noted that several tubes can be equipped with said device depending on the configuration of the evaporation installation.

 After a certain number of hours of operation of the evaporator, the supply of liquid product to be concentrated is interrupted. The evaporator is then washed by circulating, instead of the liquid to be concentrated, a washing liquid, or several successive washing liquids (generally acid, base, water).

 The next step is to wash (or simultaneously) the underside of the grid 42 and the orifices of the latter. To do this, the dispensing device is supplied with a washing liquid; this can be achieved by providing an inlet for pressurized washing liquid 47 at the lower end of the tube fitted with the dispensing device, this inlet being itself connected to a source of washing liquid.

 Under the effect of this supply, the dispensing head of the device is brought into the open position, that is to say it will position itself slightly above the tubular plate 39 and the jets of washing liquid under pressure from this head will strike the underside of the distribution grid 42 and thus clean the latter.

This cleaning will be carried out regularly thanks to the rotation of the ring 13.

 It is of course possible to use several detergents in which case the device will be successively supplied with these different detergents.

 When this cleaning operation is finished, the supply of washing product is interrupted, and the dispensing head then returns to its closed position.

 It will be added that in order to avoid any untimely introduction of liquid to be evaporated into the dispensing device as a result of a sealing problem which could arise at the joints 12 and 21, it is advantageous to provide a through hole (not shown) on the side wall of the tube fitted with said device, this hole being located below the bottom of the latter. The vapor pressure prevailing in the heating body, in operation, is generally very slightly higher than the pressure prevailing in the supply chamber. It will therefore be understood that if in the closed position of the dispensing head, there is no longer complete sealing, there will be passage of steam from the heating body to the supply chamber and not the reverse.

The presence of this through hole in the wall of the tube therefore ensures maximum security from a bacteriological point of view; in fact, a leak of liquid from the supply chamber into the device could present risks of bacterial development due to the dead zone thus formed.

 In addition, the pressure inside the tube fitted with said device then being perfectly known (that prevailing in the heating body), the spring 36 can be chosen as best as possible and ensure in the best conditions its return effect of the head of distribution in closed position.

 In order to easily position the dispensing device in one of the tubes 38 of the tube bundle, it is essential to provide a slight clearance between the internal surface of the tube and the external surface of the nozzle body of the device. Under these conditions, washing liquid is likely to stagnate in the volume defined by this play, which can be detrimental.

 To avoid this stagnation problem, the hollow cylinder 1 is provided with one or more through holes 48 at its lower part and at its upper part, in order to create a circulation between the interior of the nozzle body and the volume defined by the aforementioned game.

In the embodiment shown, these holes 48 are three in number at the bottom, arranged at 1200 in the same horizontal plane, and they are three in number at the top, arranged at 1200 in the same horizontal plane and offset by 60 relative to the holes in the lower part.

 n has been described above an application of the dispensing device according to the invention by placing it in a tube of an existing evaporator. Note however that this same device can also be implemented during the manufacture of an evaporator. In this case, it will not be positioned in a bundle tube, but preferably suspended directly in the heating body so that its rim 46 bears on the upper tubular plate 39. Of course, the holes 48 will then be nonexistent.

Claims (19)

REVENI) ICATTONS  1. Fluid distribution device, such as a washing liquid, comprising a nozzle body (1) provided with an inlet (4) for a fluid, a fluid distribution nozzle comprising a distribution head (5) displaceable in translation in said body between a closed position in which the distribution of the fluid is interrupted and an open position in which the distribution of the fluid is ensured, possible means for sealing between the nozzle and the nozzle body and means for mounting said nozzle in said nozzle body, characterized in that said mounting means comprise a connecting member (23, 24) from the nozzle to the nozzle body and complementary means (27, 28) shaped to allow movement of said connecting member between a position for locking this member with respect to the nozzle body and a position for unlocking this member with respect to the nozzle body.  2. Device according to claim 1, characterized in that said complementary means are shaped to pass from the locking position to the unlocking position and vice versa, by a translational movement, in rotation and then again in translation of said connecting member by relation to the nozzle body.  3. Device according to claim 2, characterized in that said complementary means comprise at least two lugs (27) provided on the internal face of the wall (2) of the nozzle body (1) or on the external face of the member link (23) and adapted to be engaged and maintained each in a corresponding notch (23) provided respectively on the link member or on the nozzle body.  4. Device according to claim 3, wherein each notch (28) is disposed on the connecting member and comprises a first longitudinal section (29) originating on the edge of the connecting member, opposite the dispensing head , a second section (31) parallel to the first section (29) and directed towards the edge opposite to the dispensing head, and a third section (30) connecting the first and second sections.  5. Device according to claim 2, 3 or 4, characterized in that said mounting means further comprises a first elastic element (32) for holding said lugs (27) in the bottom of the second section (31) of the notch corresponding, this elastic element being disposed compressed between the edge of the connecting member, opposite the dispensing head and an internal support area (3) of the nozzle body.  6. Device according to claim 5, characterized in that said first elastic element is a helical spring, one end of which bears on said connecting member and the other end on said internal bearing zone of the nozzle body and in that the lugs (27) are longitudinally offset by a distance corresponding to half the pitch of the helical spring, the notch corresponding to the lug closest to the dispensing head having a longer first section (29) than that of the other notch.  7. Device according to one of the preceding claims, wherein the dispensing head is extended by an elongated element (6) terminated by means (7) forming a stop, characterized in that the connecting member is shaped so that said elongated element (6) extends right through this connecting member, a second prestressed elastic element (36) being disposed between this member and said stop means.  8. Device according to claim 7, characterized in that said connecting member comprises means for adjusting the amplitude of the displacement in translation of said dispensing head, these means comprising a hollow cylindrical element (33) extending axially around of the elongated element (6) and secured by its upper end to the edge of the connecting member, opposite the dispensing head.  9. Device according to claim 7 or 8, characterized in that said second elastic element (36) is a helical spring.  10. Device according to claim 7, 8 or 9, characterized in that said mounting means further comprise complementary means (34, 35) for securing in rotation the connecting member to the elongated element (6) of the dispensing nozzle.  11. Device according to claim 10, characterized in that said complementary securing means comprise at least one longitudinal groove (35) provided in the connecting member and a pin (34) carried by the elongate element (6) and in taken with said groove.  12. Liquid evaporator of the falling flow type, comprising a bundle of tubes (38) disposed in a heating body (40), said bundle being surmounted by a supply chamber (41) for liquid to be evaporated, characterized in that it comprises at least one device according to any one of the preceding claims, arranged in such a way that in the open position, the dispensing head of said device emerges above the bundle of tubes, sealing means (12 , 21) being provided to prevent any introduction of liquid from the supply chamber (41) into the nozzle body of said device.  13. An evaporator according to claim 12, characterized in that said device is provided in at least one of the tubes (38) of the bundle, sealing means (45) being provided to prevent any introduction of liquid from the chamber d feed (41) in said tube (38).  14. Liquid evaporator according to claim 12 or 13, characterized in that in the closed position of the dispensing head, the upper end of the latter is located substantially at the level of the upper end of the bundle of tubes (38) .  15. Liquid evaporator according to claim 12, 13 or 14, further comprising a distribution grid (42) of the liquid to be evaporated disposed above the bundle of tubes in the supply chamber (41), characterized in that the location of said device is chosen to distribute a washing liquid on the lower surface of said grid.  16. Liquid evaporator according to any one of claims 13 to 15, in which a device is provided in at least one tube (38), characterized in that the lower end of this tube is provided with an inlet (47 ) washing liquid.  17. Evaporator according to one of claims 13 to 16, characterized in that the tube equipped with said device is provided with a hole located below said device, so that this tube is in communication with the interior of the body heating.  18. Liquid evaporator according to one of claims 13 to 17, in which a device is provided in at least one tube (38) and the nozzle body (1) of said device is dimensioned to leave a clearance between the internal surface of the tube (38) and the external surface of the nozzle body, characterized in that means (48) are provided on the nozzle body to allow, when the nozzle dispensing head is in the open position, a circulation of liquid of washing between the inside of the nozzle body and the volume defined by said clearance.  19. Liquid evaporator according to claim 18, characterized in that said means for allowing a circulation of the washing liquid comprise one or more through holes provided in the lower part and one or more through holes provided in the upper part of the nozzle body and not closed by the dispensing head in the open position.