Abstract:
A freezer includes a housing having a space therein for receiving a cryogenic gas, and an inlet and an outlet in communication with the space; a conveyor belt having an outer edge and being arranged for movement through the space for transferring a product from the inlet through to the outlet; a solid longitudinal member disposed in the space adjacent the outer edge for segregating the space into an upper chamber and a lower chamber; and a transfer duct operatively associated with the housing and having a first opening in communication with the upper chamber for receiving the cryogenic gas from the upper chamber and a second opening in communication with the lower chamber for expelling the cryogenic gas into the lower chamber.

Description:
BACKGROUND 
       [0001]    The present embodiments relate to spiral freezers and related processes wherein a cryogen gas is introduced into the freezer for chilling or freezing of products such as for example food products. 
         [0002]    Exhaust gas from known cryogenic freezing systems is removed as waste and therefore typically 100% of the energy in the exhaust gas is wasted. Spiral freezing systems operate in an isothermal manner (at a constant temperature) and therefore, gas exhausted is usually at the operating temperature of the spiral freezer. This exhaust gas is usually at a temperature of −80° F. (−62.2° C.) to −120° F. (−84.4° C.). 
         [0003]    It would therefore be desirable to use the exhaust gas of a spiral freezer or other type of freezer to capture gas for additional refrigeration for more efficient use of the freezer. 
       SUMMARY OF THE INVENTION 
       [0004]    The present inventive embodiments described below include a precooler apparatus, which may be integrated with the existing spiral or other type of freezer, to utilize exhaust gas from the freezer to precool a product such as a food product, before entering the main or actual freezing chamber. Such construction and method provides efficiency gains for the freezer, e.g. less nitrogen (N 2 ) gas is used in the freezer without diminishing the freezer&#39;s capacity. 
         [0005]    The present inventive embodiments can be used with a cryogen such as for example liquid or gaseous carbon dioxide (CO 2 ) or nitrogen (N 2 ). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    For a more complete understanding of the present inventive embodiments, reference may be had to the following drawing FIGURE taken in conjunction with the description of the embodiments, of which: 
           [0007]    The FIGURE is a partial cross-sectional view of a spiral freezer having a precooler for the freezer of the present embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0008]    Referring to the FIGURE, a spiral freezer with precooler apparatus is shown generally at  10 . The freezer  10  includes a housing  12  with a chamber  14  arranged therein for receiving a drum  16  for rotational movement within the chamber. The drum  16  is rotated about an axle  18  to which it is mounted; the axle connected to a drive mechanism  20  (such as a motor) mounted external to the housing  12 . A conveyor belt  22  having an outer edge  23  or periphery is arranged for rotational movement in a spiral configuration about the drum  16 . The conveyor belt  22  may be of the continuous type as shown in the FIGURE. The housing  12  includes an inlet  24  at a  26  side of the housing, and an outlet  28  at another side  30  of the housing. The inlet  24  and outlet  28  may optionally be disposed at opposed sides of the housing. The conveyor belt  22  is constructed and arranged with respect to the chamber  14  to introduce products  32 , such as food products, through the inlet  24  in the direction of the arrows  34  into the chamber where the products are chilled or frozen for being removed from the chamber through the outlet  28 . 
         [0009]    A baffle  36  is disposed in the chamber  14  for segregating the chamber into an upper freezing zone  38  above the baffle, while the area below the baffle is a lower precooling zone  40 . The freezing zone  38  occupies approximately seventy percent (70%) of the chamber  14 , while the precooling zone occupies approximately thirty percent (30%) of the chamber, for example. 
         [0010]    A cryogen, such as a cryogenic liquid or gas, for example nitrogen (N 2 ) or carbon dioxide (CO 2 ), is provided to the chamber  14  through the pipes  42 , 44  as indicated by the arrows  46 , 48 , respectively. Each of the pipes  42 , 44  includes a respective valve  50 , 52  for controlling introduction of the cryogen into the chamber  14 . If a cryogen liquid  46 , 48  is used such liquid will usually change phase into a gaseous form upon introduction into the chamber  14 . By way of example only reference herein may be to a cryogenic gas, due to the phase change. 
         [0011]    The conveyor belt  22  can be a mesh or solid construction, and can be formed from plastic, metal or a combination of both. 
         [0012]    The housing  12  is provided with a precooling zone exhaust duct  54  constructed and arranged for example at the first side  26  proximate the inlet  24 , and a freezing zone exhaust duct  56  constructed and arranged for example at the other side  30  proximate the outlet  28 . 
         [0013]    A transfer duct  58  is constructed and arranged with respect to the housing  12  to transfer the cryogenic gas  46 , 48  in the freezing zone  38  to the precooling zone  40  by circumventing the baffle  36 . The baffle  36  is of solid construction, i.e. no cryogen gas is permitted to pass through the baffle. A fan  60  is disposed for rotational movement within the transfer duct  58  to draw the cryogenic gas  46 , 48  from the freezing zone  38  through the transfer duct into the precooling zone  40 . The transfer duct  58  may be a pipe mounted to the sidewall  30 , or may be integrally formed as part of the sidewall. 
         [0014]    The baffle  36  is arranged in the chamber  14  so as not to interfere with the rotational movement of the drum  16  and the conveyor belt  22 , and the continuous return arrangement of the belt between the zones  38 , 40 . 
         [0015]    A controller  62  is electronically connected as shown by the broken line  64  to the valves  50 , 52  and the fan  60 . This arrangement permits the controller  62  to signal for the necessary flow rate of the cryogenic gas  46 , 48  to be introduced into the freezing zone  38  of the chamber  14  by controlling the openings of the valves and the speed of the fan  60 . 
         [0016]    The apparatus  10  prevents air or atmosphere external to the housing  12  from entering the inlet  24  and the outlet  28  by injecting 100% of the total mass flow into the freezing zone  38  and then allowing only 90% of the total mass flow to enter the precooling zone  40 . There can always be a given flow rate of cryogen into the chamber  14 . The flow rate can be designated as “X” (not shown in the FIGURE). The controller  62  opens or closes valves  50 , 52  to a specific orifice diameter so that the flow rate of cryogen into the apparatus  10  maintains a setpoint temperature in the upper freezing zone  38 . Because the actual position of the control valves  50 , 52  is known, and the pressure and temperature of the cryogen  46 , 48  entering through the valves are known, the actually mass flow rate of the cryogen into the apparatus is also known. The controller  62  operates the fan  60  to draw a mass flow rate of 0.9×(90% of X). The fan  60  is operated by a variable speed motor (not shown), so varying the motor speed is directly proportional to the mass flow rate of gas drawn through the transfer duct  58  by the fan. Only 90% of the mass flow is drawn from the upper freezing zone  38  into the lower pre-cooling zone  40 , because 10% of the gas must be allowed to exit the system under pressure at the outlet  28  of the apparatus  10 . This is to prevent external warm air from entering the freezer apparatus. The remaining 90% of the mass flow, now in the lower precooling zone  40  below the baffle  36  is exhausted from the precooling zone exhaust duct  54  and/or a central exhaust port (not shown). A signal from the controller  62  which controls the variable speed fan  60  in conjunction with the valve  50 , 52  openings permits the apparatus  10  to maintain the necessary mass volume in the chamber  14 . A remaining 10% of the cryogenic gas introduced into the chamber  14  at the freezing zone  38  can be exhausted through the outlet  28 . 
         [0017]    As the fan  60  draws the cryogenic gas  46 , 48  from the freezing zone  38  through the transfer duct  58  into the precooling zone  40 , the gas comes in contact with the warmer product  32 , which has entered the precooling zone from the inlet  24 , to remove energy from the food product prior to it entering the freezing zone  38 . The cryogenic gas provided from the transfer duct  58  into the precooling zone  40  can now be exhausted at the precooling zone duct  54  at a significantly warmer temperature (approximately −20° F. (−28.8° C.)), thereby increasing the overall efficiency of the apparatus  10 . This is because the food product has been precooled in the precooling zone  40  such that a lesser amount of the cryogen gas  46 , 48  is necessary in the freezing zone  38  in order to reduce the temperature of the food product to that which is needed. 
         [0018]    In the Example where the cryogenic gas  46 , 48  is introduced into the chamber  14  through the pipes  42 , 44 , the gas is at −80° F. (−62.2° C.). There would therefore be a 9%-11% overall cryogen efficiency gained. If the upper freezing zone  38  was operated at −80° F. and the lower precooling zone  40  at −20° F., the following calculation is an Example comparing a conventional isothermal spiral freezer with the present embodiment, as an isothermal spiral freezer would operate and exhaust the gas at −80° F.(−80° F.−(−20° F.) is −60° F.). See the following Example. 
       Example 
     Conventional Isothermal Spiral Freezer Exhaust=−80° F.(−62.2° C.) 
     Dual Zone Precooler Spiral Freezer  10  Exhaust  54 =−20° F.(−28.8° C.) 
     LN 2  Efficiency of Conventional Isothermal Spiral Freezer: 
       [0019]    Assume liquid nitrogen @ 30 psig and at a saturated state entering the freezer. 
         [0020]    LN 2  heat of vaporization=78.8 Btu/lb., therefore 
         [0000]    total potential refrigeration=78.8 (Btu/lb)+0.24 (Btu/lb.*° F.)×ABS(−300−(−80)). 
         [0021]    (the delta T or ΔT is =ABS(−320°−(−80°))F 
         [0022]    ˜0.24 Btu/lb.*° F. (specific heat of nitrogen gas). 
         [0023]    ˜ΔT=ABS(−300−(−80)), where −300° F.=Temp. of liquid nitrogen entering freezer, and −80° F.=Exhaust temp of gas exiting freezer. 
         [0024]    78.8 Btu/lb.+0.24 (Btu/lb.*° F.)×(220)=131.6 Btu/lb. 
       LN 2  Efficiency of Dual Zone Precooler Spiral Freezer  10 : 
       [0025]    Assume liquid nitrogen @ 30 psig and at a saturated state entering the freezer. 
         [0026]    90% of exhaust gas leaves freezer through exhaust duct  54  of precooler zone  40  at a temperature of −20° F. 
         [0027]    10% of exhaust gas leaves freezer through exhaust duct  56  of freezing zone  38  at a temperature of −80° F. 
         [0000]    Therefore, total potential refrigeration is: 
         [0000]    
       
         
           
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         [0028]    The 9.8% represents the overall increase in the capacity of the cryogen used in the apparatus  10  to absorb heat. This is referred to as the cryogen efficiency. Therefore, for the same mass flow rate of cryogen used in a conventional isothermal spiral freezer and in the dual zone freezer apparatus  10 , the present apparatus  10  provides for the cryogenic gas  46 , 48  to remove 9.8% more heat from the apparatus. 
         [0029]    As more cryogen gas  46 , 48  is introduced into the upper freezing zone  38 , the controller  62  will increase the speed of the fan  60  which will increase the mass flow of cryogen into the lower precooling zone  40 . The fan  60  is controlled by the controller  62  to pull or draw the cryogenic gas at a higher volumetric flow rate. 
         [0030]    The baffle  36 , in conjunction with the transfer duct  58 , prevents the gas  46 , 48  in the freezing zone  38  from indiscriminately entering the precooling zone  40 , by directing the gas to and through the duct  58  in a controlled flow depending upon the temperature to be used in the precooling zone. 
         [0031]    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.