Abstract:
The injection device according to the invention, intended to be attached to the wall of the bottom of a container containing a product to be cooled in bulk, includes a hollow cylindrical body in which a valve forced by a spring is inserted, a throughchannel appreciably parallel to said valve intended to be fed by pressurized cryogenic fluid, one end of said through-channel being connected to the cryogenic fluid feed system and the opposite end opening into the seat of the valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a §371 of International PCT Application PCT/FR2007/051549, filed Jun. 28, 2007. 
     BACKGROUND 
     The present invention relates to a device for injecting a cryogenic fluid into a chamber, under a pressure that is higher than the pressure in the chamber. 
     It is known to cool the content of a mixer or a kneader by introducing liquid CO 2  or liquid nitrogen (LN2) at the base of the bowl of the mixer or kneader. The liquid CO 2 , introduced under pressure via an injection nozzle, is converted, upon its expansion, in the nozzle, to a solid (dry ice), and to a cold gas. The solid is mixed with the content of the mixer and cools it, but the cold gas also contributes to cooling by passing through the overall mass contained in the bowl. 
     A known device for implementing this method comprises a plurality of injection devices, disposed in the bottom of the bowl, and fed with liquid CO 2  via a set of pipes, this set being provided with a single common control valve. 
     When the valve is closed, the liquid CO 2  present in the pipes downstream of this valve cannot be removed very rapidly by the injection devices, and, when the pressure falls below about 5.18 bar in the pipes, it is converted to dry ice in these pipes, which are thereby clogged. It is therefore impossible to resume the injection as long as this dry ice has not disappeared by being converted to gas by heating. 
     It is possible to provide for the pipes connecting the valve to the injection devices to be flexible, thereby permitting dismantling, and in consequence, serving to accelerate the restart of the system. However, this dismantling is a relatively lengthy and arduous operation. 
     The same drawbacks subsist if, instead of a common valve for all the injection devices, a plurality of independent valves are provided, each connected to an injection device by a separate flexible pipe: in this case clogging occurs in the flexible pipe. 
     It has been found that the clogging occurs when the pressure of the liquid CO 2  falls below 14 bar, which occurs fairly frequently when storage containers called “super-insulated” containers are used, such containers often being preferred in order to limit the heat losses. 
     A device for injecting into a chamber a liquid liable to solidify by expansion is known from document EP-A-376 823. 
     Patent EP-744 578 describes an injection device that overcomes the problems caused by clogging incidents in normal operating conditions. This device is such that the connection between the shutoff valve and the injection nozzle is calculated so that any slug formed in said connection and said nozzle following a closure of the injection valve can be expelled into the chamber by the pressurized liquid when the injection valve is reopened. 
     Thus the device does not comprise means for preventing the formation of the slug, but it is possible to expel this slug upon restart, so that a fresh injection can be carried out at any time after the end of a prior injection period. However, it proves that this device can be clogged by the entry of the material to be cooled in the injection device, so that the use of this device is limited to the cooling of a solid product. 
     A real need therefore exists for a device for injecting cryogenic fluid, a device that does not have the drawbacks encountered with the devices of the prior art and which is suitable for cooling any type of product, regardless of its physical state. 
     SUMMARY OF THE INVENTION 
     Thus the present invention relates to an injection device intended to be fixed to the bottom part of a container containing a product to be cooled in bulk, said injection device comprising a hollow cylindrical body in which a valve forced by a spring is inserted, said injection device comprising a through channel substantially parallel to said valve intended to be fed with pressurized cryogenic fluid, one end of said through channel being connected to the cryogenic fluid feed system and the opposite end terminating at the seat of the valve. 
     The spring is loaded in such a way that the valve cannot slide without being subjected to a cryogenic fluid pressure at least equal to a threshold pressure. Thus, as soon as the cryogenic fluid pressure is lower than a predefined threshold, the pressure required to cause the valve to slide will no longer be reached and the valve seat is repositioned tightly against the support wall. 
     Thanks to the device according to the invention, it is impossible for the material contained in the chamber to enter the device and create obstructions requiring dismantling and cleaning, regardless of the physical state of this material. 
     The device according to the invention is therefore equally suitable for cooling a product in liquid, pasty, solid or granular form. 
     In the context of the present invention, “pasty product” means any product having a viscosity between liquid and solid. 
     The device can advantageously replace, by overhead cooling, devices of vessels containing liquid or powdery products for which the bottom cooling systems of the prior art were unsuitable. 
     The cryogenic fluid used is liquid nitrogen or liquid CO 2 , particularly when the product to be cooled is a food product. However, the device according to the invention can be implemented with any type of cryogenic fluid. 
     The choice of the spring and its loading obviously depend on the cryogenic fluid that is used. Thus for nitrogen, it must be able to be loaded typically between 0 and 7 bar and for CO 2  up to 25 bar. 
     In order to optimize the operation of the valve, the device may comprise a plurality of through channels of which one end terminates at the seat of the valve. Thus, according to an advantageous embodiment, the device comprises n through channels, where n is between 1 and 20, an even number, their number increasing as the service pressure of the cryogenic fluid decreases, said channels being disposed symmetrically about the longitudinal axis of the valve. According to a particularly advantageous embodiment, two channels are disposed symmetrically about the longitudinal axis of the valve. 
     The device according to the invention is subjected to very great differences in temperature. In fact, the chamber wall to which the device is fixed is generally at ambient temperature, whereas the opposite part of the device which receives the cryogenic fluid feed is at a temperature of −196° C. Icing of the outer surface of the chamber is therefore inevitable. This may cause the material to be cooled to adhere to the icy wall of the chamber. The icy points become bonding points of the product contained in the chamber. These points expend and ultimately obstruct the valve, preventing any further injection of cryogenic fluid. 
     To avoid icing, according to one advantageous embodiment, provision is made to place a thermal bridge, that is, to insert a part of insulating material between the element of the device directly connected with the cryogenic fluid inlet and the element of the device placed directly on the vessel wall, the component elements then being dissociable. 
     The thermal bridge can be prepared from any insulating material, particularly a polymer resin or any other insulating plastic. 
     According to one particular embodiment, the device according to the invention comprises:
         a bottom element, which, in the operating position, is furthest from the chamber wall, and which is connected to the cryogenic fluid feed system,   a central element whose lower end bears on the bottom element,   a valve placed slidingly in a through hole made axially in the central element, the seat of the valve bearing tightly against the upper beveled part of said through hole,   a thermal bridge surrounding the central element and whereof the lower end bears against the bottom element,   a wall element surrounding the thermal bridge whereof the lower end bears against the bottom edge of the thermal bridge and whereof the upper end is intended to be fixed to the chamber wall,       

     said bottom element comprising:
         at least one feed channel whereof one end is connected to the feed system and the other end is connected to one end of a through channel present in the central element, said through channel being substantially parallel to the valve axis, its other end terminating at the valve seat,   a blind central recess intended to accommodate the free end of the valve axis surrounded by a loading spring,
 
said through hole of the central part having a larger diameter at its lower end, so that in the assembled position, the loading spring is maintained against said shoulder in the central larger diameter hole and in the central recess of the bottom element.
       

     Advantageously, the various components are made from steel, preferably from stainless steel, with the exception of the thermal bridge, which is made from an insulating material. 
     Advantageously, the various components are held together by means of a quick release or screwed or bayonet or similar coupling. 
     It must be possible to dismantle the inventive device particularly for the loading of the spring forcing the valve, or for a cleaning which is mandatory in the case of food products and which may be necessitated by an abnormal operation or even by accidental pollution. 
     According to one advantageous embodiment, the device is connected to the cryogenic fluid feed via a flexible fluid pipe. This is designed to allow rapid dismantling. In fact, the flexible pipe does not need to be dismantled for cleaning. 
     According to a preferred embodiment, the cleaning is further facilitated by maintaining the various components together by means of a mechanical rapid holding system (“quick” coupling). 
     According to a preferred embodiment, the inventive device being intended for operation under pressure, means are provided so that only authorized personnel can dismantle the device. For this purpose, the components of the device are fixed together by means of pilfer-proof screws and an anti-backlash cable is fixed on the one hand to the flexible hose, and, on the other hand, on either side of the “quick” coupling, to the bottom part of the device and to the top part thereof. The anti-backlash cable can only be removed by a special wrench whose use is reserved exclusively for authorized persons. 
     The inventive device is fixed tangentially to the previously perforated wall of the chamber. In the case in which the chamber is a mixer, it is advantageous to place the devices at about 45° from the mixing arms in a segment between an angle of 0° (that is, vertical) to 50° with regard to an angle of 90° (that is, horizontal to the mixer arms) so that the cryogenic fluid is injected into the core of the material to be cooled. 
     Furthermore, contrary to the devices of the prior art, part of the cryogenic fluid is already converted to solid before entering into contact with the mass to be cooled. This is because the cryogenic solid is formed as soon as the fluid strikes the seat of the valve in the space lying between the seat and the support. Owing to the fact that it is the cryogenic solid that enters into contact with the material to be cooled, the cooling efficiency is therefore higher than that obtained with the devices of the prior art. 
     The product can obviously be in motion in the chamber, thereby favoring heat exchanges and hence the cooling of the content. 
     According to an advantageous embodiment, the device according to the invention is fixed to the bottom part of the mixing bowl. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention will now be described in greater detail by means of a practical example, illustrated with the drawings, in which: 
         FIG. 1  shows a cross section of an installation comprising a chamber and devices according to the invention, 
         FIG. 2  shows an elevation view of a device according to the invention, 
         FIG. 3  shows a cross section along III-III in  FIG. 2 , and 
         FIG. 4  shows a cross section along IV-IV in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the bottom part of a chamber  1  on the wall of which two cryogenic fluid injection devices  3  according to the invention are fixed, preferably by welding. The devices  3  are connected by a flexible hose  4  and a thermally insulated pipe  5  to a solenoid valve  6  for the opening and closing of the cryogenic fluid feed. 
       FIG. 2  shows an injection device  3  in greater detail, comprising an upper part  7  whereof the free end  8  is intended to be fixed to the outer wall of a chamber, and a bottom part  9 , the two parts being connected by a quick coupling  10 . A flexible hose  4  is connected to the bottom part  9  of said device  3 . An anti-backlash cable  11  connects the flexible hose  4 , the bottom part  9  and the upper part  7 . This cable is fixed by means of safety hooks  12  so that only authorized persons can release it, for dismantling for example. 
     The valve, whereof only the upper face  13  is visible, is housed inside the device  3 . 
     As is more clearly observable in  FIGS. 3 and 4 , the injection device  3  comprises a body consisting of two parts joined together, the bottom part  9  and the upper part  7 . The upper part itself consists of three elements, a substantially cylindrical outer wall  14  of stainless steel, whereof one end bears directly against the bottom part  9 , and whereof the other end is intended to be fixed to the chamber wall. 
     Inside this wall  14 , a part with a matching shape is placed, called thermal bridge, also hollow, insulating, inside which a third stainless steel element  16  is placed, traversed at its center by the valve  17  and by two through channels  18  opening onto the upper beveled part of the part  16  intended to accommodate the seat  13  of the valve  17 . 
     The central through opening of the part  16  comprises three zones, a central zone  19   a  having a diameter substantially equal to that of the valve, so that the valve can be placed slidingly in this zone, and a bottom zone  19   b  having a larger diameter, so that it can accommodate, around the axis of the valve, the spring  19  forcing said valve. This spring  19  is maintained by the shoulder  20  formed between the zones  19   a  and  19   b.    
     At the upper opposite end, the zone  19   c  has a beveled shape, with a larger diameter at its free end, the shape of the bevel being suitable for tightly accommodating the seat of the valve when the valve is forced by the spring. 
     The bottom part  9  consists of a single stainless steel element, having a generally cylindrical shape. This part comprises a blind central recess  21  which, when the device is mounted, coincides with the opening  19   b  of the upper part. This recess is intended to accommodate the end of the valve maintained by the spring  19  and the spring loading nut  22 . 
     It also comprises, on either side of the blind recess, two vertical channels  23 ,  24  which, in the assembled position, each terminate at one end at a through channel  18  and at the other end in a perpendicular channel  25  of which one of the ends terminates at the channel  23  and the other is intended to be connected to the cryogenic fluid feed system by means of the coupling  26 . 
     The bottom part  9  is fixed to the central part  16  by screws  27  and  28 . 
     The screw  28  is a removal-proof screw in compliance with the safety standards for pressurized devices. 
     The parts  14  and  15  are joined to the part  9  by the coupling  10  (shown in  FIG. 2 ). 
     The coupling  10  is a quick release coupling. It could also be of the screwed or bayonet or similar type. 
     In operation, the valve  6  is open, and the cryogenic fluid is sent via the pipes  5  and the hose  4  into the device  3 , through the channel  25 , and then through each of the channels  18 . The pressurized fluid then applies a pressure to the seat of the valve, a space is thereby formed between the part  19   c  and the valve seat. The cryogenic solid begins to form in this space by the impact between the fluid and the valve seat, and is forced into the chamber. When it becomes necessary to stop the cryogenic fluid feed, the valve  6  is closed. 
     It may be observed that the dismantling-reassembly operations of the injection system  3  are very easy. If the coupling  10  is removed, the various constituent parts are separated, thereby allowing their inspection and cleaning. 
     The invention also relates to the use of an injection device as previously described for cooling a product in bulk. 
     It also relates to a method for cooling a material in bulk contained in a chamber, whereby a cryogenic fluid is injected into the core of the material to be cooled by means of at least one injection device, preferably m injection devices symmetrically distributed in the bottom part of the chamber, where m is an integer between 2 and 20, preferably an even number. 
     Advantageously, the chamber is a mixer. 
     The method is particularly suitable for cooling any type of material regardless of its physical state, particularly for liquid, pasty, solid or powder products. 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.