Abstract:
A freezer apparatus for treating a product with cryogen includes a source of cryogen liquid and a source of cryogen gas; a first conduit for delivering a first amount of the cryogen liquid; a second conduit in fluid communication with the first conduit for delivering a second amount of the cryogen gas into the cryogen fluid for being mixed therewith to provide a cryogen mixture having a ratio selected of cryogen gas:cryogen liquid; and a delivery apparatus in fluid communication with the first conduit downstream of the second conduit, the delivery apparatus including at least one outlet through which the cryogen mixture passes for contacting a surface of the product. A related method is also provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present embodiments relate to apparatus and methods for controlling heat flux at a surface of, for example, a food product to kill campylobacter thereon. 
         [0002]    Campylobacter (meaning “twisted bacteria” due to its corkscrew appearance) is a bacteria recognized as one of the main causes of bacterial food borne disease in many developed countries. Transmission of the bacteria commonly occurs during ingestion of contaminated food or water, and the eating of raw meat. Campylobacter is frequently found in raw chicken products, although other food products have exhibited signs of this bacteria. 
         [0003]    During freezing applications of, for example, food products in industrial settings, it is understood that a direct spray of a cryogen such as for example liquid nitrogen (LIN) onto the product will increase overall heat transfer to the product, i.e. the cooling rate of the product. However, it is not known how to efficiently control the heat transfer rate of the product under spray nozzles which administer the liquid nitrogen, nor is there a known process that is economically beneficial to efficiently improve the heat transfer rates. That is, known apparatus and methods do not permit an industrial plant to adjust or fine tune a heat transfer profile within a cryogenic freezing process of food or other products. In particular, and using a poultry carcass as an example, an area of surface treatment of the carcass with a cryogen such as liquid nitrogen requires a specific heat flux at the surface of the product to kill campylobacter. In view of the cost of the cryogen used, if a heat flux is adjusted to be in excess of or not sufficient for the process, the resulting thermal shock will not be sufficient to kill the campylobacter at the surface of the carcass and will also result in an inefficient, wasteful and ineffective use of the cryogen. 
         [0004]    In order to be able to efficiently and optimally use LIN as the cryogen, the spraying of such should be with same having a consistency of atomized particles of LIN in an amount sufficient to destroy the campylobacter, but not to waste the LIN or freeze the product. Such an apparatus and method will therefore have to be able to provide the LIN in a spray with atomized particles being of just the right dimensions to both kill the campylobacter, but not waste the LIN or freeze the product. 
       SUMMARY OF THE INVENTION 
       [0005]    There is therefore provided an apparatus and method embodiments, wherein LIN sprays to be administered to animal carcasses and/or food products have a ratio of LIN gas:LIN liquid so that a consistent, uniform droplet size of the atomized LIN always be used to provide uniform heat transfer at the surface of the carcass and/or product. 
         [0006]    The present embodiments provide an optimum droplet size of liquid nitrogen (LIN) in order to produce a heat transfer coefficient at a surface of a carcass or specific food product in order to destroy the campylobacter bacteria, such as for example destruction of same on a poultry carcass. A resulting heat transfer at the surface of the carcass which produces a thermal shock in a temperature range which decreases at 600° C./min provides the necessary application of destructive shock to this bacteria, without freezing the product or carcass. 
         [0007]    The present embodiments can be applied during carcass treatment applications for disinfection of the carcasses, such as for example with respect to killing campylobacter, and also during cryogenic tunnel freezing applications where high heat transfer coefficients are used. 
         [0008]    There is therefore provided a freezer apparatus for treating a product with cryogen to kill bacteria on the product, apparatus which includes a source of cryogen liquid and a source of cryogen gas; a first conduit for delivering a first amount of the cryogen liquid; a second conduit in fluid communication with the first conduit for delivering a second amount of the cryogen gas into the cryogen fluid for being mixed therewith to provide a cryogen mixture having a ratio selected of gas:liquid; and a delivery apparatus in fluid communication with the first conduit downstream of the second conduit, the delivery apparatus including at least one outlet through which the cryogen mixture passes for contacting a surface of the product 
         [0009]    There is also provided a method of treating a product with cryogen to kill bacteria on the product, which method includes providing a source of cryogen liquid and a source of cryogen gas; providing a first amount of the cryogen liquid; providing a second amount of the cryogen gas into the cryogen liquid; mixing the first amount of the cryogen liquid and the second amount of the cryogen gas for providing a cryogen mixture having a ratio selected of gas:liquid; and applying said cryogen mixture to a surface of the product in an amount sufficient to destroy bacteria at said surface but not freeze the product. 
         [0010]    A cryogen mixture may be selected having a ratio of for example 10% cryogen gas to 90% cryogen liquid to be used to kill the bacteria, while a cryogen mixture may be selected having a ratio of 80% cryogen gas to 20% cryogen liquid which is cost-effective for destroying bacterial such as campylobacter. The cryogen gas can be gaseous nitrogen, and the cryogen liquid can be liquid nitrogen (LIN). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0011]    For a more complete understanding of the present embodiments, reference may be had to the following description taken in conjunction with the drawing FIGURE, of which: 
           [0012]    The FIGURE shows an apparatus for also providing a method to treat a food product with a cryogen to destroy campylobacter, according to the present embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring to the drawing FIGURE, an apparatus is shown generally at  10  which can be used with for example a tunnel freezer  12  for food products  14  and a spray tunnel  16  for providing a cryogenic spray for heat transfer/heat flux to implement a thermal shock to a carcass  18 , such as a carcass of a chicken, or for providing controlled heat transfer to, for example hamburger patties or any other food product. The apparatus  10  can be retrofit to existing freezer and tunnel assemblies and systems. The embodiment shown by way of example only can be used to provide a direct spray of liquid nitrogen (LIN) on poultry carcasses for treatment of campylobacter and similarly to provide liquid nitrogen sprays in the tunnel freezer  12  for application to the food product  14  as shown. The quality of the LIN selected for use will have a direct affect on droplet size and spray distribution of the nitrogen being discharged for use in the freezer  12  and the tunnel  16 . The “quality of the LIN” as used herein means the percentage of gas and the percentage of liquid that make up the fluid being introduced into the tunnel freezer  12  and the spray tunnel  16  to contact the food products  14  and the carcasses  18 . Accordingly, the apparatus  10  of the present embodiments can be adjusted and fine tuned until an optimum heat flux can be provided to both the food products  14  and/or the carcasses  18  to destroy campylobacter, without freezing the products and carcasses. 
         [0014]    The apparatus  10  includes a phase separator  20  for receiving liquid nitrogen (LIN) from an inlet pipe  22  in communication therewith, the inlet pipe in fluid communication with a bulk tank source (not shown) of the cryogen liquid. The tank may be a nitrogen bulk tank, by way of example only. The phase separator  20  consists of a tank or vessel  24  to hold the cryogen liquid  26  (the LIN). A bottom of the vessel  24  is provided with an outlet  28  from which the liquid  26  can be removed from the vessel. A vent  30  is in communication with a gas space  32  present above a surface of the cryogenic liquid  26 . 
         [0015]    A stream of the cryogenic liquid  26  is drawn out of the vessel  24  through a side stream pipe  34 . The pipe  34  extends upward to return the liquid  26  removed to an upper portion of the vessel  24 , whereupon the pipe is coiled at  36  in a direction downward into the vessel  24  from where it again reverses direction and extends upward to exit from the vessel as shown at  38  in the FIGURE. The sidestream pipe  34  is provided with a control valve  40  to regulate an amount of the cryogen liquid  26  being removed from the vessel  24 . 
         [0016]    A pipe main  42  or main has a proximate end connected to the outlet  28  of the vessel  24 . The main  42  is provided with a flowmeter  44  and a control valve  46 . The flowmeter  44  is disposed for communication with the main  42  for metering or measuring a first amount of the cryogen liquid upstream of a gas inlet pipe  58  or conduit. A distal end of the main  42  is provided with or connected to a manifold  48  or plenum which may have at least one nozzle  50  or perhaps a plurality of the nozzles disposed for use within a chamber  15  of the tunnel freezer  12  to provide at least one cryogen spray  51  for the chamber  15 . The main  42  extends through a sidewall  17  of the freezer  12 . A conveyor apparatus  52  transports the food products  14  through the chamber  15  of the tunnel freezer  12 . 
         [0017]    The manifold  48  may also be in fluid communication with a spray apparatus  54  of the spray tunnel  16 . The spray apparatus  54  may also include at least one nozzle  56  and for most applications a plurality of the nozzles to direct a cryogen spray  57  onto the carcass  18 . 
         [0018]    It should be understood that the tunnel freezer  12  and the spray tunnel  16  are shown by a way of example only with respect to their operable association with each other. That is, it is not necessary that the spray tunnel  16  is actually mounted to or formed integral with the tunnel freezer  12 . Rather, the distal end of the main  42  can be branched off to provide the manifold  48  and the spray apparatus  54  which can be constructed as separate assemblies in relatively close proximity to each other, but in different housings as required by the particular processing application. 
         [0019]    The spray apparatus  54  may also be formed with a plurality of conduits, such as a pair of conduits  55 , 59  spaced apart from each other for providing a channel  53  therebetween through which the product  18  (such as for example a food product) or carcass may pass. The conduits  55 ,  59  may each include at least one nozzle  56  for providing the cryogen spray  57 . 
         [0020]    The apparatus  10  also includes a gas inlet pipe  58  which has one end in fluid communication with a nitrogen gas tank (not shown) and an opposite or distal end in fluid communication with the main  42  as shown at  60  in the FIGURE. The gas from the gas tank flows through the pipe  58 , which also includes a flowmeter  62  and a control valve  64 . 
         [0021]    A controller  66  is in communication with the flowmeter  44 , the flowmeter  62  and the control valve  64  as shown respectively by the broken lines  68 ,  70 ,  72  (collectively referred to as  68 - 72 ). The communication lines  68 - 72  can operate wirelessly if necessary. Control valve  46  can be operated on a separate proportional-integral-derivative (PID) loop and is controlled based on liquid nitrogen (LIN) demand of the tunnel freezer  12  and flow through the main  42  (a temperature for the tunnel freezer process will determine to what extent the valve  46  is actuated to control the flow of the LIN to the tunnel freezer). 
         [0022]    In operation of the apparatus  10 , and as shown in the FIGURE, liquid nitrogen (LIN) from the bulk storage tank (not shown) is fed at pressure P 1 , temperature T 1  as a saturated liquid into the phase separator  20 . Any vapor created in the inlet pipe  22  is vented to atmosphere through the phase separator vent  30 . A small side stream of liquid nitrogen is taken from the vessel  24  in pipe  34  and passed through the control valve  40  or cryogenic regulator to reduce P 1  and T 1  to a pressure P 2  and a temperature T 2 , respectively. The side stream pipe  34  and control valve  40  function as a subcooler to provide the pressure P 2  and the temperature T 2 . This now colder side stream  34  is returned to the vessel  24  where it passes through the heat exchanger coil  36  submerged in the liquid nitrogen  26 . The colder side stream  34  subcools the liquid nitrogen  26  to the pressure P 1  and the temperature T 2 . The now pure subcooled liquid (all vapor removed) is passed through the main  42  across the flowmeter  44  and through the control valve  46 . The control valve  46  regulates the flow of liquid nitrogen into the process. Upon discharge from the control valve  46 , the liquid nitrogen experiences a pressure drop to a pressure P 3  and a temperature drop to a temperature T 3 . At this point in the main  42  the nitrogen is still subcooled with no vapor. Also at this point in the main  42 , a nitrogen vapor is introduced into the liquid stream through the gas inlet pipe  58 . A distal end of the pipe  58  may be connected to a head space of the nitrogen bulk storage tank (not shown) or a vaporizer, depending on the required flow rates. Such an arrangement provides for vapor in the head space of the bulk storage tank not to be wasted, but rather to be used as the cryogen vapor provided through the gas inlet pipe  58 . The control valve  64  in the pipe  58  controls the amount of nitrogen gas being discharged into the liquid stream. A portion of the cryogen mixture may be directed to the tunnel freezer  12  and the spray tunnel  16  for use therewith. 
         [0023]    The apparatus  10  permits an operator of same to control and regulate a droplet size of cryogen to be administered to the food products  14  and/or the carcasses  18 . It is the droplet size of the cryogen which will control and provide an effective heat transfer rate of the food product and the carcass. That is, in order to obtain the optimum size of the droplets emitted from the nozzles  50 , 56 , the nitrogen gas has to be injected into the liquid moving through the main  42  below the control valve  46  to provide the desired percentage ratio of gas to liquid. The present apparatus  10  provides for a uniform and consistent droplet size of the cryogen being administered to the food product  14  and/or the carcass  18 . It has therefore been determined herein that the quality of the LIN may be in a ratio of 80% gas:20% liquid to effectively destroy the campylobacter bacteria but not freeze the product. This also provides for an efficient and cost-effective use of the LIN. 
         [0024]    Both liquid and gaseous flow meters  44 ,  62 , respectively, are installed in respective pipelines to monitor flow rates. The flow meter  44  is disposed for metering the cryogen liquid upstream of the gas inlet pipe  58 , A desired liquid quality i.e. specific ratio of gas to liquid, can be entered into the controller  66 . The controller  66  monitors and regulates the output from the control valves  46 , 64  so that the desired quality of gaseous fluid is reached upon entrance of the two phase flow into the cryogenic freezing system. Accordingly, the quality of the LIN downstream of where the gas inlet pipe  58  is in communication with the main  42  is shown generally at  61  where mixing of the fluid and gas results in the cryogen droplets sized to provide an effective and efficient heat transfer at the products  14  and the carcasses  18 . 
         [0025]    The consistency of the droplet size upon mixing  61  does not change in any appreciable manner when the sprays  51 ,  57  are emitted from their respective nozzles  50 ,  56 . 
         [0026]    An embodiment of the apparatus  10  can be used with direct spray of atomized liquid nitrogen onto the food products  14  and the poultry carcasses  18  for treatment of Campylobacter. The quality of liquid has a direct effect on both droplet size and spray distribution of nitrogen being discharged from the nozzles  50 , 56 . The system can therefore be fine tuned until the optimum heat flux is reached for the process. 
         [0027]    It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.