FR2498946A1 - Cooled injector for feeding corrosive substance into boiler - esp. where sulphur hexa:fluoride is injected into reactor contg. lithium at high temp. - Google Patents

Abstract

The substance becomes corrosive when it is heated, e.g. SF6 or its decompsn. prods.; and is injected into a boiler contg. another corrosive substance, e.g. Li. The injector consists of a tube fixed on the boiler wall and contg. an outlet hole. In the tube is a nozzle made of a material resisting corrosion and contg. an axial hole for injecting a substance, e.g. SF6 into the boiler. The nozzle contains a double ring channel along which a coolant is fed to cool the nozzle; and the tube contg. the nozzle is pref. a poor conductor of heat. Used esp. for a boiler or reactor fed with Li and SF6, where the injector resists corrosion at high temp.

Description

 The subject of the present invention is a boiler injector intended for the introduction of a first chemical product, which is corrosive when it is brought above a certain temperature, such as sulfur hexafluoride or its decomposition products, in a boiler containing a second chemical brought to high temperature, and also corrosive to this temperature, such as lithium.

 Boilers of the Li / SF6 type give rise to chemical reactions at high temperature and use a charge of reactive product consisting of lithium which is molten at the reaction temperature. The combustion control is carried out in this case by the injection of sulfur hexafluoride. However, the production of an SF6 injector capable of operating on such a boiler poses particularly delicate problems. Indeed, sulfur hexafluoride or its decomposition products become very corrosive at high temperature. Likewise, lithium is also very corrosive at high temperature. However, the materials which resist lithium the best, for example, at the temperatures envisaged, are unable to effectively resist the attack of sulfur hexafluoride or its reaction products. Conversely, materials having relatively good anticorrosion properties faced with sulfur hexafluoride or its decomposition products resist poorly the attack of lithium. The service life or the quality of operation of injectors of known type made of compromise materials are therefore particularly limited.

 The present invention aims to remedy the aforementioned drawbacks and to provide an injector for a boiler capable of operating satisfactorily even when the reactive products present are particularly aggressive at high temperature.

 These aims are achieved by means of a boiler injector intended for the introduction of a first chemical, which is corrosive when it is brought above a certain temperature, such as sulfur hexafluoride or its decomposition products, in a boiler containing a second chinese product brought to a high temperature, and also corrosive to this temperature, such as lithium, characterized in that it comprises on the one hand, an envelope in the form of a sheath which is made integral with the walls of the boiler, and the part of which exposed to the second chemical contained in the boiler is made of a material resistant to heat to this second product and to its products of reaction with the first product, and, on the other hand, inside of the envelope, a nozzle made of a material chemically resistant to the first product and to its decomposition products, and provided with an injection channel provided with at least one outlet opening opening near the face i internal of the envelope, itself provided with at least one perforation in the zone situated opposite each of said outlet orifices, and in that a thermal barrier system is interposed between said injection channel and the face external of the envelope exposed to the products contained in the boiler, to limit the temperature of the injection channel to a value below which corrosion of the nozzle by the first chemical is tolerable.

 The envelope is preferably made of a material which is a poor conductor of heat.

 Advantageously, the thermal barrier system can include recesses in which the products injected or contained in the boiler cannot penetrate.

 According to one embodiment of the invention, at least one of the recesses is formed between the casing and the nozzle, and sealing means are provided between the outlet orifice and the perforation of the casing for prevent chemicals from entering through the clearance between the nozzle and the casing.

 The sealing means may each comprise at least one annular part forming a compressed seal between the nozzle and the casing around and in extension of each orifice of the injection channel, and this annular part then bears on at least the nozzle or the face. internal envelope along a contact area of reduced area.

 The annular parts forming a seal are advantageously made of a material which is poor in heat conductivity.

According to a particular characteristic of the invention, at least one spring is provided to press the nozzle on the internal face of the envelope or on the annular parts forming a seal, thus guaranteeing the permanence of the seal between the recess and the boiler,
In the case where recesses are formed to contribute to the formation of the thermal barrier system, at least one of the recesses, preferably that located in the nozzle, can be traversed by a cooling fluid.

 The nozzle is advantageously made of a material which is a good conductor of heat.

 Thanks to these various measures, it is thus possible to effectively avoid the local creation of hot spots at the level of the nozzle channel.

Other characteristics and advantages of the invention will emerge from the description which follows, of particular embodiments, given only by way of non-limiting example, in reference to the appended drawings, in which
FIG. 1 is a view in axial section of an embodiment of an injector according to the invention,
FIG. 2 is an enlarged detail view showing an example of a junction piece between the nozzle and the casing of an injector according to the invention, and
- Figure 3 is an axial sectional view of another embodiment of the injector
Referring to Figure 1, we see, mounted on the wall 1 of a boiler, not shown, an injector 100 for the injection for example of gaseous sulfur hexafluoride into the enclosure of the boiler containing itself, for example lithium.

 The injector essentially consists of a casing 10 in the form of a sheath into which is inserted a nozzle 20 provided with an axial central injection channel 24. The casing 10 comprises a lateral part 11, for example cylindrical, and a downstream end 12 having an internal face 16. The casing 10 is made of a material resistant to the product contained in the enclosure of the boiler and to its reaction products.

In the case where the boiler contains lithium, the casing 10 can also, like the wall 1, made of stainless steel.

 The nozzle 20 is itself made of a material resistant to a certain temperature to attack by the injected product or its decomposition products. In the case of injection of sulfur hexafluoride, the nozzle 20 can for example be made of unalloyed copper such as electrolytic copper, nickel-plated copper or nickel.

 The body of the nozzle 20 is made integral with the casing 10 by connecting means such as bolts 60 screwed onto a flange formed at the rear part of the casing 10. In this case, guide surfaces 23 are provided on a part of the body of the nozzle engaged in the casing 10. An annular seal 40 is arranged in a groove close to the bearing surfaces 23 Spaces are provided between the external face 22 of the nozzle 20 and the internal wall 15 of the casing 10, with a view to reducing the heat exchange between casing 10 and nozzle body 20.

 The downstream front face 21 of the nozzle 20 does not bear directly against the internal face 16 of the downstream end 12 of the casing 10. On the contrary, an annular junction piece 30, is clamped between the front face 21 of the nozzle and the inner face 16 of the downstream end 12 of the casing 10. The tightening of the part 30 between the nozzle 20 and the casing 10 can be carried out very simply, for example using springs 61 cooperating with the bolts 60 to exert a axial force on the entire nozzle body 20.

 The part 30 has a central opening 31 of section greater than that of the orifice 25 of the injection channel 24 of the nozzle. The downstream end 12 of the casing 10 is provided with a perforation 13 which is itself of larger section than the opening 31 of the part 30. The perforation 13 of the casing lo comprises for example a first cylindrical portion and a second conical portion 14 which widens towards the free end of the sheath 10 by forming a divergent.

 The annular junction piece 30 is centered in the internal cylindrical cavity of the casing 10 in the vicinity of the face 16 in order to achieve alignment between the orifice 15, the opening 31 and the perforation 13. The piece 30 has contact areas with reduced area with the internal face 16 of the casing 10 and the front face 21 of the nozzle 20. In the example shown in FIG. 1, the part 30 is in the form of a circular washer and its downstream face 33 is conical, and carries on the inner face 16, substantially planar, of the casing 10 along a closed line of relatively short length consisting of the length of the perforation 13 The upstream face 32 of the washer 30 is planar and likewise carries on the slightly conical front face 21 of the nozzle 20, along a closed line of short length around the orifice 25 of the injection channel 24.

There are thus reduced contact surfaces between casing and junction clamp as well as between junction piece and nozzle, and the presence of at least one piece 30 makes it possible to have at least two thermal resistances in series which increase the efficiency of the thermal barrier between the casing 10 and the nozzle 20. The presence of several parts similar to part 30 mounted one behind the other is conceivable in order to reduce heat transfers more strongly than .. Furthermore, part 30 must be adapted to form a seal preventing any penetration of the second product present in the boiler, inside the spaces formed between nozzle and casing in order to maintain the character of thermal barrier
It suffices for this that the contact surfaces with the part 30 are defined by closed lines surrounding the orifice 31.

 The part 30 is advantageously made of stainless steel for example, as is the casing 10, when the second product present in the boiler is lithium. Indeed, the part 30 has a thermal role and the diameter of its opening 31 not being critical, it can be made of stainless steel, a favorable metal by its low thermal conductivity, as well as its hardness, although poorly resistant corrosion by SF6. On the contrary, the nozzle 20 is advantageously made of a material which, in addition to its resistance to attack by the first product (such as sulfur hexafluoride), has a high thermal conductivity. This makes it easier to avoid the creation of hot spots in the vicinity of the injection channel 24.

 FIG. 1 shows a face 21 of the conical nozzle cooperating with a plane face 32 of the part 30. Naturally, the part 30 can have two conical faces 32 and 33 and the front face 21 of the nozzle can in this case flat bure. Thus, in Figure 2, there is shown a junction piece 30 comprising two conical faces 32 and 33 cooperating respectively with the flat front face 21 of the nozzle 20 and the internal face 16 of the sleeve portion 12 so as to limit the areas of contact to short lines. The part 30 is pierced with a contral opening 31a, 31b which extends the channel 24 terminated by the orifice 25, and has a larger section than that of the orifice 25. The opening of the part 30 has for example a first cylindrical portion 31a and a second conical portion 31b forming a diverging portion.

The downstream end 12 of the casing 10 may include a perforation in the form of a cylindrical channel 13 of larger section than the largest section of the opening 31a, 31b of the part 30, this channel being able to enter between erodes without consequence. mower.

 As can be seen in FIG. 1, the thermal barrier system between the external faces of the casing 10 subjected to the heat released by the boiler and the central injection channel 24 of the nozzle comprises complementary means which are associated and if necessary could be substituted for the means constituted by the spacings between nozzle 20 and casing 10 and the joining piece 30. These complementary means comprise recesses 27 formed in the nozzle body itself and produced in the form of a cavity annular concentric with the central channel 24 and extending up to almost the downstream end of the nozzle. A part 50 constituting a part of the body of the nozzle 20 comprises a tubular extension 51 engaged in the cavity 27 to define a path for circulation of fluid cooling coolant such as water or nitrogen. The fluid. cooling system can for example be introduced via a pipe 52 into a portion of cavity 27 closest to the central channel 24 and discharged from the peripheral portion of cavity 27 through a pipe 53. Cavities and a cooling circuit could also be arranged in the envelope 10 in order to limit the heat transfers towards the internal face of the envelope 10.

 The various elements of the thermal barrier system shown in FIG. 1 guarantee good protection of the central channel since the sheath-like envelope 10 connected to the enclosure 1 of the boiler provides protection for the nozzle 20 including on its face. front, opposite the second product present in the boiler, and the thermal insulation elements such as the recesses or the annular junction piece 30 prevent the temperature of the injection channel 24 from rising to a value for which the first product injects becomes corrosive to the material of this channel.

 FIG. 3 represents a schematic view of another possible embodiment of the invention.

In this case, a space is always provided between the nozzle 20 and the casing 10 and the contacts are reduced, but the part 123 of the body of the nozzle serving as a guide is provided with a thread which makes it possible to secure the body of the nozzle. with the casing 10 in the form of a sheath, while exerting a clamping action on an annular junction piece 30 which limits the contacts and the heat transfers between the internal face 16 of the downstream part 12 of the casing 10, and the face 21 of the nozzle 20 proper.

When the nozzle body 20 is blocked directly on the casing 10, like for example using the thread 123 of the embodiment of the
Fig 3, the springs 61 of Fig 1 are deleted.

In this case, the annular junction piece 30 can itself be produced in the form of an elastic washer, for example of the Belleville type. A pair of conical elastic washers 30 ', 30 "can thus constitute the junction between the front face 21 of the nozzle 20 and the internal face 16 of the casing 10. The washers 30', 30" which, in FIG. 3 are mounted in the opposite direction, although this is not compulsory, each have an opening 31 ′, 31 ″, the diameter of which is intermediate between that of the orifice 25 of the channel 24 and that of the perforation 13 of the envelope 10.

In some cases it is also possible to use only one pre-compressed elastic washer.

 The various means defining the thermal barrier system described with reference to FIGS. 1 to 3 can naturally be combined with one another and undergo variant embodiments.

Thus, the nozzle body 20 can be solid and have only its central channel 24, without additional recess 27. In this case, the contacts between the nozzle and the casing must be as small as possible or insulation cavities must be provided in the casing 10. On the other hand, when for example the nozzle is provided with cavities 27 equipped with a cooling system such as 51, 52, 53, the contacts between the nozzle 20 and the casing 10 are less critical. definition of a well defined contact area limited to a closed line of short length around the opening 31 of the annular junction piece 30 is particularly important between the faces 33 of the piece 30 and 16 of the envelope 10 In on the other hand, the contact area between the actual nozzle 20 and the face 32 of the part 30 is less critical and may between more extensive. Different nozzles can be combined with the same type of casing. Finally, the machining of the annular junction piece 30 can be very simplified if this piece is produced in the form of a washer such as that shown in FIG. . 1.

 The characteristics of the injector depend solely on the nozzle 20, while the perforation of the downstream end 12 of the casing 10 can meet less stringent conditions. According to a particular example of an injector suitable for a Li / SF6 type boiler an orifice diameter 25 of injection channel 24 greater than or equal to approximately 1.8 mm and an opening diameter 31 of part 30 of approximately 2 mm have been found to allow correct operation with a higher SF6 pressure or equal to 3 bars absolute.

 Of course, various modifications and additions can be made by those skilled in the art to the devices described without departing from the scope of the invention.

Claims (10)

 1. Boiler injector intended for the introduction of a first chemical, which is corrosive when it is brought above a certain temperature, such as sulfur hexafluoride or its decomposition products, in a boiler containing a second chemical product brought to a high temperature, and also corrosive to this temperature, such as lithium, characterized in that it comprises on the one hand, a casing (10) in the form of a sheath which is made integral with the walls of the boiler (1), and the part of which exposed to the second chemical contained in the boiler is made of a material resistant to heat to this second product and to its products of reaction with the first product, and, on the other hand, to inside the enclosure, a nozzle (20) made of a material chemically resistant to the first product and to its decomposition products, and provided with an injection channel (24) provided with at least one outlet orifice (25) opening near the internal face e (16) of the envelope, itself provided with at least one perforation (13) in the zone situated opposite each of said outlet orifices (25), and in that a thermal barrier system (27 , 30) is interposed between said injection channel (24) and the external face of the envelope exposed to the products contained in the boiler, in order to limit the temperature of the injection channel to a value below which the corrosion of the sprinkler by the first chemical is tolerable.  2. Injector according to claim 1, characterized in that the envelope (10) is made of a material which is poor conductor of heat.  3. Injector according to claim 1 or claim 2, characterized in that the thermal barrier system comprises recesses (27) into which the products injected or contained in the boiler cannot penetrate.  4. Injector according to claim 3, characterized in that at least one of the recesses is formed between the casing (iO) and the nozzle (20) and in that sealing means (30) are provided between said outlet (25) and said perforation (13) to prevent said chemicals from entering through the clearance existing between the nozzle 1203 and the envelope (10).  5. Injector according to claim 4, ca characterized in that the sealing means each comprise at least one annular part (30) forming a compressed joint between the nozzle (20) and the casing (10) around and in extension of each orifice (25) of the injection channel, and this annular part (30) bears on at least the nozzle (20) or the internal face (16) of the envelope (10) along a contact surface of reduced area.  6. Injector according to claim 5, ca characterized in that the annular parts (30) forming a seal are made of a material which is poor conductor of heat.  7. Injector according to any one of claims 4 to 6, characterized in that at least one spring (61) is provided for pressing the nozzle (20j on the internal face (16) of the envelope (lo) or on the annular parts (30) forming a seal, thus guaranteeing the permanence of the seal between the recess and the boiler.  8. Injector according to claim 5 or claim 6, characterized in that the annular parts (30 ', 30 ", 31', 31") forming a seal, interposed between the nozzle (20) and the internal face of the envelope (10) are formed from a precompressed elastic material.  9. Injector according to claim 3, characterized in that one of the recesses (27) at least forming a thermal barrier is traversed by a coolant.  10. Injector according to any one of claims 1 to 9, characterized in that the nozzle (20) is made of a material which is a good conductor of heat.