METHOD AND APPARATUS FOR CONTACT REFRIGERATION IN CRYOGENIC SOLID BELT FREEZER
Methods and apparatus for contact freezing a food product. A conveyor belt or other support may have an active region that supports materials on an outer surface. Liquid cryogen may be provided in bulk contact with an inner surface of the active region via splashing, agitation, pumping, gravity feed, and the like.
Tunnel freezers are commonly used for the refrigeration of food products. A device of this type has, for example, been described in U.S. Pat. No. 4,589,264. In this device, products are transported through a tunnel freezer on a conveyor belt and sprayed from above with a cryogenic liquid. Another known configuration utilizes a mechanically or cryogenically refrigerated flat plate in a tunnel freezer arrangement in which a thin plastic sheet is drawn across the plate with products lying on top of the sheet. Another known configuration involves cooling the lower return portion of the conveyor belt by running it through a cryogen immersion bath. After the cold belt exits the underside return, it refrigerates products and moves products through a tunnel freezer. In another known configuration described in U.S. Pat. No. 4,858,445 and U.S. Pat. No. 6,725,686, product is held on an active region of a conveyor belt and is run directly through a liquid nitrogen bath.
SUMMARY OF INVENTIONThe inventors have appreciated that in some applications, it may be desirable to freeze food products or other materials in an energy and cost-effective arrangement that is different than conventional tunnel freezer systems. For example, tunnel freezer systems typically use metal mesh conveyor belts that have holes or other openings in the surface on which products are placed. Thus, in some cases, freezing products in a conventional tunnel freezer may result in forming belt marks on the product, loss of product shape, product damage, generation and loss of product fines and/or drip losses to the product.
One aspect of the invention relates to a cooling element that may include a cooling surface with an outer surface and an inner surface. The outer surface may support a material to be cooled, such as a food product. In some embodiments, the cooling element may be a static or a moving element, e.g., as part of a conveyor belt. The conveyor belt may have an active region that supports materials and a return region that may be a portion that moves to return back to the active region. A cryogen supply system may provide liquid cryogen directly to the inner surface of the cooling element. In some embodiments in which the cooling element is part of a conveyor belt, the cryogen supply system may provide liquid cryogen directly to the inner surface of the conveyor belt in the active region. In some embodiments, liquid cryogen may be provided in direct, bulk liquid contact to the inner surface of the cooling element or conveyor belt. In one embodiment, liquid cryogen may be splashed onto the inner surface by rotating agitators that are partially or completely submerged in a plenum of liquid cryogen. In another embodiment, a wave generator in a plenum of liquid cryogen may create waves of liquid cryogen that wet the inner surface from below. The waves may be moving or stationary. In yet another embodiment, a sparger fed with a suitable gas positioned within a plenum of liquid cryogen may create a multitude of gas bubbles which, upon rising through the liquid cryogen bath and bursting, may cause wetting of the inner surface. In yet another embodiment, the cryogen supply system may include an element that helps to evenly or otherwise distribute cryogen to the inner surface. For example, a conveyor belt with an active region may be positioned above a grooved distributor plate that is positioned above a plenum. Liquid cryogen may be provided by a prime mover into the plenum from a cryogen-holding container. The prime mover may consist of a pump, a gravity feed, an agitator, or any other suitable element. The liquid cryogen provided from the container to the plenum may enter the distributor plate from below and exit out the top of the distributor through grooves for contact with the inner surface of the conveyor belt. In some embodiments, liquid cryogen that contacts the conveyor belt may have nearly zero upward velocity. In some embodiments, the liquid cryogen may contact the inner surface of the belt at different locations along the belt, creating several discrete contact regions where the liquid cryogen is in contact with the inner surface.
In another aspect of the invention, the conveyor belt may include various components. In some embodiments, the conveyor belt may include a rod belt underlay combined with a solid belt overlay where the solid belt is supported and driven by the rod belt. The rod belt may provide a gap between the solid belt and the cryogen supply system. This gap may be useful for venting vaporized cryogen while allowing liquid cryogen to contact the inner surface of the solid belt. Alternately in an embodiment where a spacing mechanism is not integrated into the belt, a corrugated grooved distributor can be used where the corrugations provide escape routes for vaporized liquid cryogen and a passage for excess liquid cryogen.
Another aspect of the invention relates to a method of providing liquid cryogen directly to only the bottom of a cooling surface. The top of the cooling surface may be arranged to contact a material to be cooled, such as a food product. In some embodiments, the liquid cryogen may be provided from a plenum to the bottom of the surface. In some embodiments, the liquid cryogen may be moved from a liquid cryogen container to the bottom of the surface. In one embodiment, the cryogen may be evenly distributed across the bottom of the surface. In some embodiments, the bottom of the cooling surface may be wetted by liquid cryogen due to agitation of liquid cryogen, wave generation or sparging of liquid cryogen held below the cooling surface.
These and other aspects of the invention will be apparent from the following detailed description and claims.
Aspects of the invention are described with reference to illustrative embodiments and to the drawings in which like numerals reference like elements, and wherein:
The inventors have appreciated that the known configurations for the refrigeration of food products may, in some cases, have undesired outcomes or consequences. For example, tunnel freezer systems typically use metal mesh conveyor belts that have holes or other openings in the surface on which products are placed. Thus, in some cases, freezing products in a conventional tunnel freezer may result in forming belt marks on the product, loss of product shape, product damage, and drip and moisture losses to the product. In those systems mentioned above in which a plastic sheet is drawn across a refrigerated plate, the plastic sheeting may be a significant expense because it is typically only used once then discarded. In addition, immersion of the return portion of a conveyor belt may provide poor control of the belt surface temperatures, e.g., in regions where the belt surface supports the products as the regions move through the freezer. Additionally, immersion of the product with the active portion of a conveyor belt may result in decreased quality of the product due to excessive and/or non-uniform freezing and/or contamination of the cryogen due to contact with the product. In some embodiments that incorporate one or more aspects of the invention, a freezer system may avoid making belt marks on a product, may avoid the need for using a plastic sheet or other material interposed between the product to be frozen and a chilling conveyor belt and/or may provide for relatively tight control of freezing surface temperatures. However, as discussed in more detail below, some or all of these features need not be provided in all embodiments that incorporate one or more aspects of the invention.
Various aspects of the invention are described below and/or shown in the drawings. These aspects of the invention may be used alone and/or in any suitable combination with each other. Aspects of the invention are not limited in any way by the illustrative embodiments shown and described herein.
Materials 120 provided onto the cooled outer surface 2 may become frozen or otherwise chilled at the region of contact 121 with the cooled outer surface 2, as well as at other portions of the material 120, which may be cooled by thermal conduction, convection and/or radiation.
In some embodiments, the cooling element 6 can be an active region 4 of a conveyor belt 1, as shown in
The cryogen supply system 100 can provide cryogen to the inner surface 3 in a variety of arrangements, as discussed above and will be illustrated in more detail below. In several of the embodiments described, the active region 4 of the conveyor belt 1 may move material 120 through a tunnel freezer for cooling a product as well as other processes. It should be understood, however, that a tunnel freezer is neither a required nor a necessary feature. Instead, aspects of the invention may be used in any suitable environment and for any suitable purpose other than chilling a food product.
Previously known freezing arrangements, such as in U.S. Pat. Nos. 5,467,612 and 5,460,015, disclose the use of cryogen spray nozzles to spray liquid cryogen onto the underside of a conveyor belt. The non-vaporized liquid cryogen exits from these spray nozzles in a series of individual droplets. In contrast, in one aspect of the invention, liquid cryogen is provided in direct, bulk liquid contact with the inner surface 3 of the cooling element 6. The term bulk liquid contact is used to mean contact with the element using a contiguous volume of liquid, as opposed to distinct and separate liquid droplets. In some embodiments, volumes of liquid cryogen that are in bulk liquid contact with the cooling element 6 may be contiguous with a plenum holding a relatively large volume of liquid cryogen, e.g., of several gallons or more. In other embodiments, volumes of liquid cryogen that are in bulk liquid contact with the cooling element 6 may have a volume of about 10-15 ml or more.
Additionally, nozzle-type spray configurations like that in U.S. Pat. Nos. 5,467,612 and 5,460,015 require storage of liquid cryogen at pressures of around 20 psi or greater, and, during operation of the freezing process, delivery of liquid cryogen occurs through spray nozzles at pressures around 40-60 psi. The disadvantage of pressurizing liquid cryogen during storage and/or delivery to an object to be cooled is loss of refrigeration capacity of the cryogen. In one aspect of the invention, liquid cryogen can be stored and supplied to a support for cooling at pressures less than about 20 psi, thereby decreasing the loss of refrigeration capacity of the cryogen due to pressurization.
Also, spray nozzles generally output liquid cryogen with high kinetic energy. In contrast, in one aspect of the invention, liquid cryogen is provided in direct contact with the inner surface 3 of the cooling element 6 at nearly zero velocity. By nearly zero velocity, it is meant that the velocity of the liquid cryogen is very small when it contacts the inner surface 3 of the cooling element 6; much smaller than the velocity of liquid cryogen from a spray nozzle.
In some embodiments, liquid cryogen is provided to at least portions of the inner surface 3 in the active region 4 from a plenum. The plenum may be any vessel suitable for holding liquid cryogen and may be of various depths or other dimensions, shapes and/or volumes.
In the illustrative embodiment of
In another embodiment shown in
In another embodiment shown in
In yet another embodiment shown in
Liquid cryogen may be provided into the plenum 65 from a cryogen-holding container 50 by a prime mover, such as a pump 70. The prime mover may consist of a pump, a gravity feed, an agitator, or any other suitable element. The liquid cryogen provided from the container 50 to the plenum 65 may enter a grooved distributor plate 60 from below and exit out the top of the distributor plate 60 through grooves 61, as shown for example in
The distribution grooves 61 on the distributor plate 60 may allow cryogen to be evenly distributed along the inner surface 3 in the active region 4 as cryogen exits the distributor plate 60. In some embodiments, the grooves may be arranged to supply more cryogen to particular portions of the inner surface 3 and provide a non-even distribution along the inner surface 3. The spacing between grooves may also vary. The grooves 61 may be spaced closely together, far apart, uniformly spread out over the distributor plate 60, and/or without any regular pattern. The distribution of grooves 61 may also be arranged in a variety of configurations.
In some arrangements, the prime mover 70 may provide liquid cryogen through the distributor plate in direct, bulk liquid contact with the inner surface 3 of the active region 4. In some arrangements, a 0.5 to 1.0 inch throw of liquid cryogen above the distributor plate 70 is enabled by the prime mover 70, e.g., the liquid cryogen may move upwardly above the plate 70 about 0.5 to 1 inch before being stopped and moved downwardly away from the belt by gravity (unless the cryogen strikes the inner surface 3 prior to being stopped in upward movement by gravity). In some embodiments, the distance between the plate and the belt may be arranged to equal the throw distance of liquid cryogen above the plate, causing the cryogen to contact the belt at approximately the maximum trajectory height of the liquid cryogen, at which the velocity of the moving cryogen is nearly zero. In this arrangement, the liquid cryogen that contacts the inner surface 3 may have nearly zero velocity. The distributor plate 70 may create a plurality of discrete contact regions where the liquid cryogen is in bulk liquid contact with the inner surface 3.
As mentioned previously, the conveyor belt 1 may include various components. In one arrangement, the conveyor belt 1 may include a rod belt 10 underlay combined with a solid belt overlay 12, as shown in
As shown in
The inventor has appreciated that, in some embodiments, it is advantageous to store and deliver liquid cryogen at low pressures to decrease loss of refrigeration capacity of the cryogen due to pressurization. Liquid cryogen may be stored and delivered at low pressures less than about 20 psi, moved to a discharge location and delivered to cool or freeze products. Liquid cryogen may also be stored at medium pressures at about 20 to 50 psi. The discharge location may be at an elevation above the products or other object to be cooled and liquid cryogen may be delivered to the products/object via a gravity feed, rainfall, perforated plate, slits, weirs, overhead nozzle spray, or other suitable arrangement. Additionally, the discharge location may be positioned below the products/object to be cooled and the liquid cryogen may contact the products/object from below by any suitable means such as via a pump, mechanical agitation, wave generation, sparging, nozzle spray, direct immersion of products and/or belt into the liquid cryogen, or other suitable arrangement (e.g., including arrangements discussed above). The liquid cryogen may be delivered to any freezer or other cooling system, such as a solid belt freezer, open belt freezer, static non-moving freezer, or other suitable arrangement.
The cryogen supply system 100 in the above embodiments, including
In some embodiments, it may be desirable to provide a pump that operates to efficiently move liquid cryogen at relatively low pressure and at high volumes. The inventor has appreciated that relatively high pump efficiency can be important in some cryogenic applications, e.g., because an inefficient cryogenic pump will heat the cryogen, causing boiling and cavitation that may diminish the effectiveness of the pump, decrease the lifespan of the pump and/or cause excessive waste of liquid cryogen. Providing liquid cryogen at low pressure and high volumes is one way to efficiently move cryogen, e.g., while helping to minimize cryogen loss and maximize the cooling effect. As stated earlier, pressurizing liquid cryogen may decrease the refrigeration capacity of the cryogen. In some embodiments, an axial rotor pump, as shown in
In
A pump inlet 72 may be located near a bottom of the tubular space and a pump outlet 73 may be located above the bottom, or other suitable arrangement. The axis of the rotor 80 may be arranged along the longitudinal axis of the tubular space 86. The rotor 80 may be connected to a drive shaft 83 such that rotation of the drive shaft 83 causes rotation of the rotor 80. Pump vents 85 may be located on the side of the pump housing 71 near the top 76 to prevent the buildup of pressure at the top of the housing during operation of the pump. Since the axial pump 70 contains relatively few components, the pump may be easily disassembled and reassembled for inspection and cleaning.
In some embodiments, it may be desirable to support the drive shaft 83 with bearings. The inventors have appreciated that bearings are often problematic components of any cryogenic system since the system must operate at extremely low temperatures. A liquid lubricant may not remain in a liquid state at cryogenic temperatures. Thus, bearings utilizing dry lubricant may be desirable. For example, in
In some embodiments, it may be desirable to construct the pump 70 such that a seal is not required between the drive shaft 83 and the top 76 of the pump housing 71. Seals are often made of a supple material. The inventors have appreciated that, in a cryogenic system, a supple material may become brittle and crack during use. Of course, a seal may be used in the pump 70, and the invention is not limited in this regard. In one sealless embodiment, as shown in
As shown in
In another sealless embodiment, as shown in
In some embodiments, the pump may include shaft stays 96, as shown in
The axial rotor pump may be used for a variety of different applications and is not limited to the belt cooling configuration described above. In some embodiments, the axial rotor pump may be used to deliver liquid cryogen to an elevation above an active portion 3 of an outer surface 2 of a conveyor belt 1. The elevated liquid cryogen may then be used to contact and cool products from above using a waterfall or rain configuration. In another embodiment, the axial rotor pump may be used with any tunnel freezer system to recycle cryogen by moving non-vaporized cryogen back to a sump or cryogen reservoir. In short, the axial rotor pump may be used in any suitable application for moving liquid cryogen from one location to another, regardless of the purpose for movement of the cryogen.
The above and other aspects of the invention will be appreciated from the detailed description and claims. It should be understood that although aspects of the invention have been described with reference to illustrative embodiments, aspects of the invention are not limited to the embodiments described. Also, aspects of the invention may be used alone, or in any suitable combination with other aspects of the invention.
Claims
1. A material cooling system comprising:
- a conveyor belt having an inner surface and an outer surface, the conveyor belt having an active region in which the outer surface faces generally upwardly and is configured to support a material for cooling, and a return region in which the outer surface faces generally downwardly; and
- a cryogen supply system arranged to provide a liquid cryogen in direct, bulk liquid contact with only the inner surface of the conveyor belt in at least part of the active region.
2. The device of claim 1, further comprising a plenum constructed and arranged to contain the liquid cryogen.
3. The device of claim 2, wherein the cryogen supply system further comprises a pump arranged to move liquid cryogen from a container to the inner surface of the conveyor belt in the active region.
4. The device of claim 3, wherein the plenum is located below the inner surface of the conveyor belt in the active region, the plenum being constructed and arranged to receive a liquid cryogen from the pump.
5. The device of claim 4, wherein the cryogen supply system further comprises a plate having a plurality of grooves, the plate arranged to direct a flow of liquid cryogen from the grooves toward the inner surface of the conveyor belt in the active region.
6. The device of claim 1, further comprising a gap arranged to vent a gas between the cryogen supply system and the inner surface of the conveyor belt in the active region.
7. The device of claim 3, further comprising a cryogen return constructed and arranged to guide liquid cryogen from the inner surface of the belt in the active region into the container.
8. The device of claim 2, wherein the cryogen supply system further comprises at least one mechanical agitator in the plenum.
9. The device of claim 2, wherein the cryogen supply system further comprises a mechanical wave generator constructed and arranged to create at least one wave on a surface of the liquid cryogen in the plenum.
10. The device of claim 1, wherein the cryogen supply system is arranged to create a plurality of discrete contact regions where the liquid cryogen is in bulk liquid contact with at least a portion of the inner surface.
11. The device of claim 1, wherein the cryogen supply system is arranged to move the liquid cryogen upwardly toward the inner surface such that the liquid cryogen makes direct bulk liquid contact with at least a portion of the inner surface.
12. The device of claim 11, wherein the liquid cryogen is at nearly zero velocity during contact with at least a portion of the inner surface.
13. The device of claim 1, wherein the belt includes a solid belt and a rod belt, wherein the rod belt lies below the solid belt in the active region and above the solid belt in the return region.
14. The device of claim 1, further comprising providing liquid cryogen to the outer surface of the conveyor belt in at least part of the active region.
15. A method for cooling a material, comprising:
- providing a solid conveyor belt having a top surface that faces generally upwardly and a bottom surface that faces generally downwardly, wherein the top surface is configured to hold the materials to be cooled; and
- providing liquid cryogen in direct, bulk liquid contact with only the bottom surface of the solid conveyor belt by moving a liquid cryogen from a plenum to the bottom surface.
16. The method of claim 15, wherein the step of providing liquid cryogen includes causing the liquid cryogen to contact the bottom surface in bulk liquid form at a plurality of discrete regions.
17. The method of claim 15, wherein the step of providing liquid cryogen includes directing the liquid cryogen upwardly in bulk liquid form for contact with the bottom surface of the solid conveyor belt.
18. The method of claim 15, wherein the step of providing liquid cryogen includes generating a wave on a surface of the liquid cryogen in the plenum.
Type: Application
Filed: May 18, 2011
Publication Date: Nov 22, 2012
Inventors: Bryce M. Rampersad (Bloomingdale, IL), Theodore H. Gasteyer, III (Naperville, IL), Gary D. Lang (Naperville, IL)
Application Number: 13/110,368
International Classification: F25D 17/02 (20060101); F25D 25/04 (20060101);