Abstract:
Systems and methods freeze food products. A system provides a storage tank of liquefied gas, a gas-liquid separation tank, and a crust freezer. The crust freezer provides plates chilled by flow of liquefied gas through conduits traversing an interior volume of the plates. The method includes recirculating liquefied gas to improve cooling efficiency while lowering operation costs. The system and method further provide for integrated measurement and control of the flow of liquefied gas through components of the system. Freezing of the food products occurs at a surface of the food products along where the food products and the plate interface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 11/763,005 filed on Jun. 14, 2007, and which claims benefit to provisional application No. 60/813,940, filed Jun. 15, 2006. The entire contents of each aforementioned application are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Various approaches exist for freezing food products. The food products often pass over some form of “crusting table” to freeze bottom surfaces of the food products such that the food products can subsequently travel on belts or conveyors through additional freezing equipment. Without freezing the bottom surfaces first, the food products with soft and/or wet outer surfaces supported by the belt may stick to the belt leaving remnants that must be removed prior to continued use of the belt. Further, the belt may leave undesirable marks on the food products if the bottom surfaces are not frozen before the food products are placed on the belt. 
       SUMMARY 
       [0003]    Embodiments of the invention relate to devices and methods for freezing food products. One embodiment provides a refrigeration liquid recirculation system for chilling the food products. The system includes a chilling plate that has a fluid passageway traversing an interior volume thereof between an inlet and an outlet of the fluid passageway and a food contact surface for thermally contacting the food products to freeze at least a surface of the food products thermally interfacing with the chilling plate. The system further includes a source of liquefied gas fluidly coupled to the inlet of the fluid passageway via a supply line and coupled to the outlet of the fluid passageway via a return line such that the food contact surface is temperature controlled by flowing the liquefied gas through the fluid passageway. 
         [0004]    In one embodiment, a refrigeration liquid recirculation system for chilling food products includes a chilling plate having an interior volume that defines a fluid passageway connecting an inlet into the plate and an outlet from the plate. The chilling plate includes a food support surface for thermally contacting the food products to freeze at least a surface of the food products that interfaces with the chilling plate. Further, the system includes a source of refrigeration liquid fluidly coupled to the inlet and the outlet to define a circulation loop. A pump of the system disposed along the circulation loop maintains temperature of the chilled plate below −129° C. based on flow of the refrigeration liquid. 
         [0005]    For one embodiment, a method of chilling food products includes circulating a liquefied gas through a circulation loop. The circulating includes flowing the liquefied gas from a source of the liquefied gas to an inlet of a chilling plate, flowing the liquefied gas through the chilling plate, whereby the chilling plate is cooled, removing the liquefied gas from an outlet of the chilling plate, and flowing the liquefied gas that is removed back to the source. The method additionally includes disposing the food products on the chilling plate, thereby freezing the food products at a surface of the food products along where the food products and the plate interface 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein: 
           [0007]      FIG. 1  illustrates schematic components of an exemplary recirculation system that enables freezing of food products, in accordance with embodiments of the invention; 
           [0008]      FIG. 2A  illustrates part of the system with first and second chilling plates between which the food products are conductively frozen and optionally reshaped by compressive forces applied by the plates, in accordance with embodiments of the invention; 
           [0009]      FIG. 2B  illustrates an alternative circuitous flow path for liquefied gas through one of the chilling plates, in accordance with embodiments of the invention; 
           [0010]      FIG. 3  illustrates both of the chilling plates in use freezing and flattening the food products, in accordance with embodiments of the invention; and 
           [0011]      FIG. 4  illustrates use of one of the chilling plates in combination with a finishing freezer of the system, in accordance with embodiments of the invention. 
           [0012]      FIG. 5  illustrates another system with a chilling plate and a shower assembly that has orifices facing a support surface of the chilling plate to direct chilled vapor toward the chilling plate within an enclosure, in accordance with embodiments of the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0013]    The time required for food products to be on a cooling surface (e.g., “crusting table”) and hence the length of the surface corresponds to how cold the surface is able to be maintained. The crusting tables may be chilled with refrigerants such as fluorocarbons, but such refrigerants may only provide chilling to about −40° C. Alternatively, systems may utilize expensive liquid nitrogen to achieve lower temperatures by introducing the liquid nitrogen through channels in a plate of the table. However, the liquid nitrogen may vaporize as it passes to an outlet for the channels, thereby reducing cooling efficiency, increasing the cost of operation of the system due to consumption of the nitrogen that exits the outlet as gas, and limiting a lowest temperature achievable. 
         [0014]    Embodiments of the invention provide devices and methods for freezing and optionally shaping food products and/or storing frozen food products. In such embodiments liquefied gas is recirculated. Conduction between the food products and plates in communication with the liquefied gas being circulated freezes at least an outer surface of the food products. 
         [0015]      FIG. 1  illustrates one embodiment of an exemplary liquefied gas recirculation system  100 . As depicted, the recirculation system provides a circuit for the flow of liquefied gas, whereby liquefied gas may be provided from a source, to a point of use and then recirculated back to the source. It should be appreciated that the recirculation system  100  may include any number of inlets and outlets, e.g., to provide improved performance. It should also be appreciated that a secondary refrigerant, such as d-limonene, could be used in place of or in conjunction with (either mixed with or isolated from) the recirculated liquefied gas. The secondary refrigerant may be mechanically or cryogenically chilled and may include any liquid that is capable of being chilled to below −73° C., for example. For improved cooling efficiency, any or all of the components of the liquefied gas recirculation system  100  may be insulated from external temperatures, such as through the use of vacuum jackets or urethane coatings. 
         [0016]    In one embodiment of the invention, a storage tank  110  may provide a reservoir of liquefied gas. It should be appreciated by those skilled in the art that any one of a number of liquefied gases could be selected, including gases such as nitrogen, helium, argon or carbon dioxide, depending on the target temperature requirements. For the purposes of illustration and without limitation, in this example, nitrogen is utilized as the recirculated liquefied gas. The rate of flow of a first liquid nitrogen stream  116  from the storage tank  110  may be controlled by a first flow control valve  115 . The first liquid nitrogen stream  116  may be introduced into a gas-liquid separation tank  120 . The amount of liquid nitrogen contained in the gas-liquid separation tank  120  may be measured by a load cell or other liquid content measurement device  121 . In one embodiment, the first flow control valve  115  and the liquid content measurement device  121  may communicate with a control device  160  to provide integrated measurement and control of the amount of liquid nitrogen introduced into the gas-liquid separation tank  120 . 
         [0017]    The gas-liquid separation tank  120  may serve as a reservoir of nitrogen vapor for a cryogenic storage or freezer unit such as a finishing freezer  130  that may be a spiral or tunnel type of freezer. The rate of flow of a nitrogen vapor stream  126  may be controlled by a second flow control valve  125 . The temperature of the finishing freezer  130  may be measured by a first temperature measurement device  131 . In one embodiment, the second flow control valve  125  and the first temperature measurement device  131  may communicate with the control device  160  to provide integrated measurement and control of the amount of nitrogen vapor introduced into the finishing freezer  130 . 
         [0018]    The gas-liquid separation tank  120  may also serve as a recirculation reservoir for a crust freezer  150 . A second liquid nitrogen stream  141  may be drawn from the gas-liquid separation tank  120  by a pump  140 . The second liquid nitrogen stream  141  may then traverse first and second freezing plates  151 ,  152 , thereby providing cryogenic convective-conductive cooling of the plates  151 ,  152 . The system  100  may include only the first freezing plate  151  without the second freezing plate  152  for some embodiments, such as shown in  FIG. 4 . While the nitrogen vapor stream  126  may be at −101° C., the second liquid nitrogen stream  141  that may be at −184° C. provides relatively more cooling ability according to one embodiment. The freezing plates  151 ,  152  may be made of a heat-conductive material, such as aluminum, carbon steel, or stainless steel. A resultant liquid nitrogen/nitrogen vapor stream  156  may be returned to the gas-liquid separation tank  120 . 
         [0019]    In some embodiments, the second liquid nitrogen stream  141  stays at least 50% in liquid phase while passing through the plates  151 ,  152  such that the resultant liquid nitrogen/nitrogen vapor stream  156  contains less than 50% vapor. The second liquid nitrogen stream  141 , due to the liquid phase within the plates  151 ,  152 , provides improved heat transfer with the plates  151 ,  152  relative to heat transfer with vapor. Rate of flow for the liquid nitrogen/nitrogen vapor stream  156  exiting the crust freezer  150  may be controlled by a third flow control valve  155 . Operation of the pump  140  and/or the third flow control valve  155  passes the second liquid nitrogen stream  141  sufficiently fast, as made feasible due to the recirculation, through the plates  151 ,  152  to achieve the second liquid nitrogen stream  141  staying at least 50% liquid upon exiting the plates  151 ,  152 . 
         [0020]    The temperature of the crust freezer  150  and/or food products may be monitored by a second temperature measurement device  170 . In one embodiment, the pump  140 , the third flow control valve  155 , and the second temperature measurement device  170 , may communicate with the control device  160  to provide integrated measurement and control of the residence time of nitrogen in the freezing plates  151 ,  152 , thereby controlling the temperature of the crust freezer  150 . It should be appreciated that the locations of the pump  140  and the third flow control valve  155  are interchangeable. Although  FIG. 1  shows the second temperature measurement device  170  directly connected to the second freezing plate  152 , it should be appreciated that a variety of other configurations would provide appropriate measurements of the temperature of the crust freezer  150 . In one embodiment, the temperature for the plates  151 ,  152  of the crust freezer  150  may be maintained within a range of −129° C. to −173° C. Throughput may increase per unit length of the plates  151 ,  152  as the temperature of the plates  151 ,  152  is lowered. 
         [0021]    Although the streams  116 ,  126 ,  141 ,  156  are illustrated as individual streams, it should be understood that portions of each stream may be removed for other purposes not shown in  FIG. 1 . For example, all or some of the nitrogen vapor stream  126  may be used to cool an atmosphere around the plates  151 ,  152 . For some embodiments, the finishing freezer  130  may be omitted such that the nitrogen vapor stream  126  may be vented or liquefied by cooling and compressing prior to returning to the storage tank  110 . At least the liquid nitrogen streams  116 ,  141 , the liquid nitrogen/nitrogen vapor stream  156  and passage through the crust freezer  150 , may together define a sealed or closed environment preventing loss of nitrogen. 
         [0022]    In one embodiment, the control device  160  continuously communicates with the flow control valves  115 ,  125 ,  155 , the liquid content measurement device  121 , the temperature measurement devices  131 ,  170 , and the pump  140  to provide integrated measurement and control of all aspects of the liquefied gas recirculation system  100 . In an alternative embodiment, the control device  160  communicates sequentially with the various components as necessitated by the production process. 
         [0023]      FIG. 2A  illustrates one example of the crust freezer  150 . The second liquid nitrogen stream  141  may enter the crust freezer  150  through flexible first and second input tubing  210 ,  212 , which may be connected respectively to the first and second freezing plates  151 ,  152  via first and second input manifolds  211 ,  213 , respectively. The second liquid nitrogen stream  141  may be divided into a plurality of streams by the input manifolds  211 ,  213  for respective introduction into first and second plurality of inlet holes  220 ,  221 . Liquid nitrogen may flow through the first and second plurality of inlet holes  220 ,  221  into respective first and second plurality of conduit passageways  230 ,  231 , which may traverse the volume of the freezing plates  151 ,  152 . Although  FIG. 2A  illustrates straight conduit passageways  230 ,  231 , it should be appreciated that the conduit passageways  230 ,  231  could follow curved trajectories to provide for longer path length, thereby greater residence time for any given flow rate. An example of a possible curved trajectory conduit path  232  is illustrated in  FIG. 2B . It should also be appreciated that while bore diameters may be constant across the length of the conduit passageways  230 ,  231 , the bore diameters may also vary across the length of the conduit passageways  230 ,  231  to permit flow concentration at certain locations. A mixture of liquid nitrogen and nitrogen vapor may exit the conduit passageways  230 ,  231  through respective first and second plurality of outlet holes  240 ,  241 . First and second output manifolds  250 ,  252  facilitate coalescing of exiting streams into the liquid nitrogen/nitrogen vapor stream  156 , which flows out of the crust freezer  150  through flexible first and second output tubing  251 ,  253  coupled respectively to the first and second output manifolds  250 ,  252 . 
         [0024]    Although  FIG. 2A  illustrates the first input manifold  211 , for example, as a single (unitary) structure, it should be appreciated that each of the first plurality of inlet holes  220  may be individually connected to flexible first input tubing  210  via a connection substructure of a manifold assembly. The individual connections may be CGA-295 cryogenic fittings, dissimilar metal bayonet connections or other cryogenic fittings commonly known in the art. Additionally, it should be appreciated that the tubing  210 ,  212 ,  251 ,  253  may be constructed from a variety of cryogenic hoses known in the art, including both flexible and fixed transfer hoses. 
         [0025]    While  FIG. 2A  shows each of the first plurality of inlet holes  220 , for example, breaching the perimeter of the first freezing plate  151  from only one side, it should be appreciated that the first plurality of inlet holes  220  may exist on multiple sides of the first freezing plate  151 . For example, in one embodiment, gas flows in opposite directions in adjacent ones of the first plurality of conduit passageways  230 , necessitating alternating the first plurality of inlet holes  220  and first plurality of outlet holes  240  on one side of the first freezing plate  151 . One skilled in the art will appreciate that the temperature at specified points on the first freezing plate  151  can be more precisely controlled by customizing the configuration of the first plurality of conduit passageways  230  and the direction of gas flow through each of the first plurality of conduit passageways  230 . Similar variations may occur in configuration and flow direction for the second plurality of conduit passageways  231  within the second freezing plate  152 . 
         [0026]      FIG. 3  shows one embodiment of the crust freezer  150  in use with food products  300  being inserted between the freezing plates  151 ,  152 , which may or may not enclose the food products  300 . Examples of the food products  300  include meats, fruits, vegetables, solid products and liquid products. An outer surface of the food products  300  freezes due to heat transfer with the plates  151 ,  152 . Instead of just being frozen at the outer surface, the food products  300  may freeze throughout while on the crust freezer  150 . Variables that may be adjusted to control to what extent the food products  300  freeze while on the crust freezer  150  include thermal contact time between the food products  300  and the freezing plates  151 ,  152 , temperature of the freezing plates  151 ,  152 , and/or percentage of the food products  300  in contact with the freezing plates  151 ,  152 . For example, an interval between when the food products  300  are disposed on the crust freezer  150  and subsequently removed from the crust freezer  150  may vary based on length of the freezing plates  151 ,  152  and/or speed in which the food products  300  are conveyed across the freezing plates  151 ,  152 . In addition, mold shapes within the plates  151 ,  152  for liquid forms of the food products  300  or shaping of the food products as discussed hereinafter may facilitate controlling what percentage of the food products  300  is frozen while on the crust freezer  150  since making the food products  300  thinner can increase thermally interfacing surface area relative to volume of the food products  300  and hence the extent of freezing of the food products  300 . 
         [0027]    Pressure may be applied to the freezing plates  151 ,  152  by a pressure source  280 , which creates the pressure by moving the plates with actuation or gravity relative to one another or holding the plates  151 ,  152  a fixed distance apart while the food products  300  larger than the fixed distance are forced between the plates  151 ,  152 . For example, the pressure source  280  in one embodiment defines a piston coupled to the second freezing plate  152  at one end and an actuator  380  at another end. The actuator  380  fixed relative to the first freezing plate  151  may be under operation of the control device  160 . The control device  160  may periodically raise and lower the second freezing plate  152  corresponding to when subsequent one or more of the food products  300  pass between the plates  151 ,  152  during use. For some embodiments, the actuator  380  enables adjustment and selection of the fixed distance that the plates  151 ,  152  are maintained apart during feeding of the food products  300  in between the plates  151 ,  152 . If gravity creates the pressure, the second freezing plate  152  may hang via the pressure source  280  in a free sliding relationship above the first freezing plate  151  such that weight of the second freezing plate  152  itself urges the second freezing plate  152  toward the first freezing plate  151 . 
         [0028]    This application of pressure may cause the food products  300  to be compressed and/or change shape against flat and parallel first and second thermally conductive surfaces  261 ,  262  (visible in  FIG. 2A ) of respectively the first and second freezing plates  151 ,  152 . For example, flattening of the food products  300  facilitates even freezing and cooking. Further, reshaping of the food products  300  to standard shapes may allocate portions or aid in portion control or packaging. Although shown with the pressure source  280  working directly on the second freezing plate  152 , it should be appreciated that pressure could be applied to either or both of the freezing plates  151 ,  152 . 
         [0029]    The freezing of the food products  300  occurs at least partially as a result of contact, either direct or indirect without intervening gas convection, of the food products  300  with the conductive surfaces  261 ,  262  of the freezing plates  151 ,  152 . For some embodiments, a consumable first film  302  covers the first freezing plate  151  with the food products  300  supported by the first freezing plate  151  being disposed on the first film  302 . In operation, the first film  302  unwinds off an input roll  306  across the first freezing plate  151  and is recovered by a take-up roll  308  that is driven such the first film  302  acts to move the food products  300  along the first freezing plate  151 . The second freezing plate  152  may utilize a consumable second film  304  in a similar manner. Suitable materials for the films  302 ,  304  include plastics such as polyethylene. It should be understood that the food products  300  may be initially placed on the table and/or subsequently removed by manual acts, robotics, or passage from/to other conveyors. For example, the food products  300  may drop off of the first freezing plate  151  into packaging such as boxes suitable for storage and transport. 
         [0030]      FIG. 4  illustrates use of the crust freezer  150  with the first freezing plate  151  in combination with the finishing freezer  130 . Bottom surfaces of the food products  300  are sufficiently chilled (e.g., frozen) while on the first freezing plate  151 . In operation, the food products  300  move across the first freezing plate  151  toward the finishing freezer  130 . While not repeated for conciseness, such conveyance of the food products  300  may utilize techniques such as already described herein with respect to  FIG. 3  and the first film  302 . Upon reaching an end of the first freezing plate  151  the food products  300  fall or transfer onto a belt  400  that passes through the finishing freezer  130 . As a result of the bottom surface being frozen, the food products  300  can travel on the belt  400  of the finishing freezer  130  without problems of sticking or marking of the food products  300 . The finishing freezer  130  completes freezing of the food products  300  that are carried into, through and out of the finishing freezer  130  via the belt  400 . Once exited from the finishing freezer  130 , the food products  300  may undergo packaging and/or be taken away for storage and transport. 
         [0031]      FIG. 5  shows a chilling plate  551  (e.g., analogous to the plate  151  described herein, according to one embodiment) disposed in a tunnel arrangement, for some embodiments. The arrangement may include an enclosure  550  housing the chilling plate  551  and a shower assembly  552  that has orifices  553  facing a support surface of the chilling plate  551 . The orifices  553  direct chilled fluid toward the chilling plate  551  such that flow of the chilled fluid is brought into proximity or contact with the food products supported on the chilling plate  551  to effect heat exchange between the food products and the chilled fluid sufficient to facilitate chilling or freezing of the food products. The enclosure  550  includes an exhaust  531  for discharge or recovery of the chilled fluid expelled from the orifices  553  and contained by the enclosure  550 . 
         [0032]    For some embodiments, a phase separator  520  contains liquefied gas, such as liquid nitrogen, and provides the chilling fluid in the form of vapor or gaseous nitrogen to the shower assembly  552  through a shower input conduit  526 . The shower assembly  552  forms a hollow housing that may extend over part or all of the chilling plate  551  to define a plenum in communication with the orifices  553  that extend through a wall of the housing. In some embodiments, the orifices  553  may be disposed 0.3 meters or less above the chilling plate  551 . The shower assembly  552  may include the orifices  553  dispersed over the chilling plate  551  since many small columns of gas provide better heat transfer than an undivided flow of the gas. In some embodiments, a density of the orifices  553  is selected such that there are at least 5 of the orifices  553  per square foot. The temperature of gas or gasses from the shower input conduit  526  may be at or below −129° C. 
         [0033]    A shower pump  525  pressurizes the chilling fluid in the shower assembly  552  providing a pressure differential with higher pressure inside the shower assembly  552  than out. The shower pump  525  receives input from the shower input conduit  526  and from an ambient intake  527  disposed within the enclosure  550  to in part recycle the chilled fluid back through the shower assembly  552 . Due to the ambient intake  527 , the shower pump  525  can create the pressure differential using vapor vented from the phase separator  520  with or without drawing additional vapor/liquid from the phase separator  520 . The pressure differential creates jetting through the orifices  553  that may be formed in nozzles that extend from the shower assembly  552  or flush apertures through the wall of the shower assembly  552 . A spray pattern from each of the orifices  553  may provide a cylindrical, linear, or conical pattern, for example, that may be separated or overlapped upon reaching the chilling plate  551  with spray from an adjacent one of the orifices  553 . In some embodiments, a diffuser at a base of the input conduit  526  that terminates in the interior volume of the shower assembly  552  may facilitate uniform distribution of gas in the interior volume. 
         [0034]    The chilling plate  551  couples to the phase separator  520  via a supply conduit  541  and a return conduit  556 . A plate pump  540  disposed along the supply conduit  541  passes liquid nitrogen (e.g., at or below −184° C.) from the phase separator  520  through passageways  530  in the chilling plate  551  prior to recirculation back to the phase separator  520  through the return conduit  556 . A film  502  stretches across the chilling plate  551  from a supply roll  506  of the film to a driven uptake roll  508  of the film. In operation, chilling of the food products supported on the chilled plate  551  and carried by movement of the film  502  occurs simultaneously from conductive contact with the chilled plate  551  and flow from the shower assembly  552  of the chilled fluid brought into proximity or contact with the food products. The food products may be completely frozen upon exiting the enclosure  550  at the uptake roll  508  such that the food products are ready for packaging or shipping. 
         [0035]    It will be understood that many additional changes in the details, materials, steps, and arrangement of parts, which have been herein described and illustrated 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 and/or the attached drawings.