US3507128A - Continuous cryogenic process combining liquid gas and mechanical refrigeration - Google Patents

Description

'T. H. Mummy ET AL 3,507,128

April 21. 1970 CONTINUOUS CRYOGENIC PROCESS COMBINING LIQUID GAS AND MECHANICAL REFRIGERATION 2 Sheets-Sheet 1 Filed Dec. 22; 1967 m @GQQR 1 vw m 8 mm mm m N N MkQQQ why and g r, Z/INXLENTORS 70/77 H. Mu 00/75. Z/ /re ATTORNEY Filed Dec. 22, 1967 vA i] 21, 1970 T. H. MURPHY ETAL CONTINUOUS CRYOGENIC PROCESS COMBINING LIQUID GAS 2 Sheets-Sheet 2 AND MECHANICAL REFRIGERATION 75m /7. Murphy 0/70 QWQNTORS ATTORNEY United. States Patent Oflice 3,507,128 Patented Apr. 21, 1970 3,507 128 CONTINUOUS CRYOGENIC PROCESS COM- BINING LIQUID GAS AND MECHANICAL REFRIGERATION Tom H. Murphy, N. 8616 Country Homes Blvd. 99208, and Don E. Tucker, E. 10515 Sinto Ave. 99206, both of Spokane, Wash.

Filed Dec. 22, 1967, Ser. No. 692,774 Int. Cl. F25d 3/10 U.S. C]. 62-63 5 Claims ABSTRACT OF THE DISCLOSURE A continuous cryogenic process for freezing food prodnets in an inert gas atmosphere by combined liquid gas and mechanical refrigeration including: the lowering of product temperature near its freezing point by mechanical refrigeration, rapid freezing of the product substantially by liquid gas refrigeration, and continued lowering of product temperature to the desired terminal point chiefly by mechanical refrigeration. The process is continuous and applies more expensive liquid gas refrigeration only at critical stages when its benefits are most pronounced, with more economical mechanical refrgeration removing heat at other times. The rapid freezing of product Without regelation and in an inert atmosphere reduces product deterioration by both physical and chemical causes to produce a resultant superior product.

BACKGROUND OF INVENTION Related applications There are no prior applications directly related hereto filed in this or any foreign country, though applicants have herefore filed applications on a similar static process.

Field of invention This invention relates generally to the field of cryogenics and more particularly to a continuous process combining freezing by mechanical refrigeration and liquid gas to obtain the benefits of each by limitation of gas freezing to its principal beneficial range.

Description of prior art Freezing of food products with both mechanical refrigeration and liquid gases, by various heat transfer means, has heretofore been known and practiced. Certain limitations, however, are associated with each type of freezing. Mechanical refrigeration causes deterioration of the product because of the nature of the process itself, which oftentimes allows regelation to continue over an extended period during the freezing operation to physically break down cell structure of cellulated products and thereby expose the cell contents directly to the atmosphere for relatively long periods of time to cause various chemical changes, especially of an oxidative nature. Both such physical and chemical changes effect the aesthetic properties of the food, if not its nutrative properties. Liquid gas freezing largely eliminates these problems, but has not proven commercially feasible because of its relatively high cost. Many processes for freezing with either mechanical or liquid gas refrigeration separately have hereto become known but none have combined the two freezing processes to create a new economically feasible process having the advantages of gas freezing.

The instant invention is distinguishable from the prior art in that it provides a using of liquid gas refrigeration only during a limited period-substantially the time of the actual freezing of the productto prevent excessive regelation so as to provide the greatest economy with sub stantially all the benefits of liquid gas freezing, while still allowing a continuous operation for greatest efiiciency and economy of use.

SUMMARY OF INVENTION The instant invention was conceived to provide a continuous cryogenic process combining liquid gas and mechanical refrigeration in such fashion as to gain the advantages of each and more particularly to such a process that provides liquid gas freezing during the relatively short period of solidification of product to prevent regelation and its resultants.

Our invention provides an enclosure insulated from its environs wherein our process operates. The enclosure may be chamberized, completely or partially, or otherwise configures to allow each of the steps of our process to operatively function. A conveyor or similar product moving meens is provided to cause transit of product through the enclosure.

The first step of our process transfers heat from the product substantially by mechanical refrigeration means until the product temperature is lowered to, or very near, its freezing point. Preferably, the mechanical refrigeration means are provided with an air circulating system that forces the refrigerated air with some force against the product being cooled to remove the air envelope thereabout and thereby aid freezing. An inert gas atmosphere may be maintained during this period.

.The second step of our process receives the product, cooled to or very nearly to, its freezing point, and coiltinues to remove heat from it, principally by liquid gas refrigeration until such time as the product is substantially frozen by vaporization of the liquid gas. In this step the gas is preferably sprayed in liquid form directly upon the product and, if necessary, auxiliary means of moving the gas are provided to intimately admix it with product to cause freezing in as short a time as possible. Preferably sufiicientof the gas of this step is provided to the first and third steps to maintain an inert gas atmosphere about the product for the entire process.

The third step of our process receives the frozen product from the second step and provides additional mechanical refrigeration to reduce the final temperature of the then frozen product to the desired terminal point.

Thereafter the product is removed from the freezing chamber for wrapping, packaging or other disposition as desired.

Specific apparatus for accomplishing the process is disclosed.

In providing such a process and apparatus it is:

A principal object of our invention to provide a continuous cryogenic process, combining the use of both mechanical refrigeration and liquid gas refrigeration, with the liquid gas cryogen used substantially during the actual time of freezing of the product.

A further object to provide such a process that may maintain an inert gas atmosphere about the product during the entire freezing period.

A further object to provide such a process that has the economic advantages of mechanical freezing while maintaining the quality and aesthetic advantages of liquid gas freezing.

A further object to provide apparatus for carrying out such a process.

A still further object of our invention to provide such apparatus and process of the nature aforesaid that are new and novel, and otherwise well adapted to the uses and purposes for which they are intended.

These and other objects of our invention will become apparent from consideration of the following specification and accompanying drawings. In carrying out the objects of our invention, however, it is to be understood that its essential features are susceptible of change in design, ordering and structural arrangement with only one preferred practical embodiment being illustrated, as required.

DESCRIPTION OF DRAWINGS In the accompanying drawings, wherein like numbers of reference refer to similar parts throughout:

FIGURE 1 is a semi-diagrammatic cross-sectional view of an elongated chamberized freezing enclosure wherein our process is carried out.

FIGURE 2 is a vertical cross-sectional view of the freezing chamber of FIGURE 1, showing its details and configuration from this aspect.

FIGURE 3 is a diagrammatic representation, in normal symbology, of a particular electrical control circuit that is embodied in our invention.

FIGURE 4 is an elongate semi-diagrammatic cross-sectional view of a species of elongate non-chamberized freezing enclosure.

FIGURE 5 is an elongated semi-diagrammatic crosssectional vi;ew of a species of freezing enclosure having vertically arranged compartments for each of the process steps.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularly to the drawings, and especially to that of FIGURE 1, it will there be seen that our invention generally includes elongated, insulated freezing enclosure having a first precooling area 10A with precooling mechanical refrigeration 11, second freezing area 10B with gas refrigeration 12, and a third, finish freezing area 10C with finish freezing mechanical refrigeration 13. Conveyor structure 14 is associated with the freezing chamber to carry product 15 therethrough to effect the freezing process.

Freezing chamber 10 is an elongate, rectilinear area defined by paired opposed sides 16 structurally joining bottom 17, top 18, input end 19 and output end 20. In the specie of FIGURE 1, vertical septums 21 are provided to divide the chamber into precooling portion 10A, freezing portion 10B, and post-cooling portion 10C. The various exterior walls of our invention serve as an insulating encasement and a rigid support for appertenant structures.

Appropriate orifices 22 are provided in the structure to allow product imput to the various areas and closing means 23 cooperate therein to provide at least partial closure thereof when not in use. The particular closing means illustrated are pivotably mounted doors, but other closing devices, especially as known in the gas freezing art, may well be used.

The eificiency of our process is related to a substantial degree to the thermal conductivity and resultant heat loss through the freezing chamber walls, so insulation 24 therein should be as great as reasonably possible. In some structures it may be possible to locate the freezing chamber 10 in a holding freezer room (not shown) so that the temperature about most of the outer peripheral surface of the chamber wall will be at that of the holding freezer, generally some several degrees below zero, and thus lesson heat transfer. The particular configuration of the chamber is not critical to our invention so long as it provide a sufficiently elongate course for product travel to accomplish the freezing purposes specified.

A second species of non-chamberized freezing enclosure is illustrated in FIGURE 4. This enclosure is quite similar to the specie of FIGURE 1 except it has somewhat more length and provides no septums dividin the various process areas. In this specie, obviously, the operative area of each process step is not distinctly defined though the area of principal operation of each step are in spaced unique areas. This specie has the advantage of readily supplying inert gas to all areas in which the process operates.

A third specie of vertically compartmentalized freezing enclosure is illustrated in FIGURE 5. Here the freezing chamber is divided into three vertically related, atmospherically communicating areas for each of the steps of our process by the horizontal septums 21a. Each compartment is provided with a conveyor structure 14 for product transit with gravity activated product transfer means 79 communicating from each higher conveyor to each lower conveyor to create a continuous product course through the structure. In this enclosure, product may enter either at the top or bottom, but in either event it is to be noted that the colder gases in the enclosure will be most dense and by action of gravity will tend to migrate downwardly to enhance the cooling in the lower levels, somewhat in the fashion of a recycling process.

Conveyor structure 14, providing product transit through the freezing enclosure, includes product belt 25 carried for motion extending complete length of the freezing enclosure. This conveyor is of ordinary structure with the product belt carried by at least one slave roller 26 and driven by driving roller 27 motivated by mechanical linkage 28 with prime mover 29. Such conveyor structures are well known and constitute no direct part of our invention.

Both precooling and post-cooling mechanical refrigeration stages 11, 12 are essentially the same except for their positioning. Each mechanical refrigeration system includes compressor 30 communicating by pressure lead 31 to expansion coil 32, thence to return to the compressor through vacuum lead 33 to complete the gas cycle. Compressors 30 are of ordinary commercial construction, preferably two-stage; one compressor, if of sufficient capacity, and provided with appropriate controls might be used for both refrigeration stages.

Expansion coil housing 34 is structurally carried by the inner wall of freezing chamber 10, by brackets 35, at a spaced distance from the wall. It is provided with fans 36 and deflection plates 37 to create an air flow over the expansion coils and direct the resultant air flow as directly as possible to product 15 with relatively great velocity to disturb any static air envelopes about the product that might retard freezing.

Gas refrigeration equipment 12 includes external pressurized liquid gas supply 38 communicating by inlet conduit 39 through control valve 40 and thence conduit 41 to divider 42 and through laterals 43 to spray heads 44. The spray heads are positioned preferably at spaced distances and above the product so as to direct a relatively fine spray of liquid gas presented therethrough into a maximum or substantial portion of the product to be frozen. Preferably additional fans 45 are provided in freezing area 10B to aid in intimately comingling the liquid gas with the product. Because of the extremely low temperature of the liquid gas relative its normal surroundings, the various gas containers outside the freezing chamber preferably are insulated to prevent excessive heat transfer therefrom.

If necessary to maintain an inert gas atmosphere in the pre-cooling and post-cooling areas 10A, 10C, additional gas distribution equipment (not shown) may be used, to distribute small quantities of gas into these areas at appropriate periods. Normally, however, with the species of enclosures shown and even with closing means 23 for orifices 22 sufficient gas passes from the freezing area into other areas to maintain an appropriate atmosphere Without any other provisions being made therefor.

With liquefied gas being passed into freezing area 10B and expanded therein, provision must be made by pressure activated outlet vent 46 to prevent excessive pressure of gas within the freezing enclosure. Such vents are well known in the art. Since the normal inert gases used in re frigeration processes are deleterious to humans, outlet vent 46 preferably exhausts to the atmosphere in a fashion that will not cause danger to humans.

One possible electrical circuit for control of our invention is shown in the diagrammatic illustrations of FIG- URE 3. It comprises an alternating current source having entrance leads 47, 48. IShunted between these leads is continuous three-track recording thermometer 49 having a thermocouple type sensing mechanism located in each of the three process areas. Lead 48 communicates through fuse 51 to master off-on switch 52. From this switch lead 51 thence communicates in series with mechanical refrigeration switches 53, 54 and thermostatic switches 55, 56 controlling respectively precooling area A and postcooling area 10C and thence by lead 58 in series through operation light 59 and thence by lead 60 to entrance lead 47. In series with lead 57 and in parallel with mechanical refrigeration switches 53, 55 and 54, 56 is push-button reset switch 61 which communicates by line 62 in series through door switch 63, emergency switch 64, and high pressure cutoff switch 65 and thence through lead 55 ultimately back to solenoid reset switch 67. Line 68 communicates from the line 58 in series through reset light 69 thence through line 70 to temperature control switch 71 and thence through line 72 to the coil of gas valve 74 and back to entrance lead 47. Gas operating light 73 is shunted between lines 70 and 72 to indicate when the gas valve 74 is operating to allow gas to flow into the freezing chamber. The coil of solenoid reset switch 67 is shunted between entrance lead 47 and lead 70 as illustrated.

A time-activated clock switch 75 is shunted between imput lead 48 and line 62, as indicated, to provide current for predetermined intervals through leads 76, 77 to the coil of gas valve 74 to maintain an inert gas atmosphere in the freezing chamber during the freezing process if gas be not required for freezing. It is to be noted that with this circuitry gas will not be supplied by the valve 74 unless all of the various safety switches 63, 64, 65 are inactive and in normally closed position to provide a fail safe safety circuitry.

In normal operation the door switch, emergency switch and high pressure cut-off switch are all in closed position, but should any of them activate by opening, the activation will cause a stoppage of the entire gas system and an activation of the solenoid reset switch coils. If this solenoid reset switch be activated, the system can then again be put into operation only by closing the appropriate safety switch and activating the push-button reset switch, after correcting the difliculty.

With this structure in mind the freezing process of our invention may be described and the operation of the various apparatus more fully understood.

Product to be frozen is established in particulated masses, on pallets 78 or individually, if desired, upon conveyor belt 25 so that major portions of the surface of each piece of product are exposed to the surrounding atmosphere. The product is then moved into precooling area 10A and mechanical refrigeration applied in the precooling step. In this initial cooling stage, the average gaseous temperature within cooling area 10A reaches approximately thirty degrees. The means temperature of the product is moved downwardly to, or very nearly to, the product freezing point, which with most food products will normally be slightly below the freezing point of water. Normally, this precooling to the freezing point will be done with mechanical refrigeration as it is most economical and few deleterious results occur in the product during this process. Substantially no freezing of the product occurs during this stage.

If the product does deteriorate during the precooling process because of the time required or because of the atmosphere is too chemically active, or the product too sensitive, inert gas may be maintained in the product atmosphere during this period; also in instances of failure of the mechanical refrigeration, cooling may be continued with liquid gas in the precooling stages by establishing gas dispersal apparatus (not shown) in the precooling chamber or allowing it to encroach upon this area from the freezing area.

With the mean product temperature at very nearly its freezing point, it is passed into central freezing area 10B where the liquid gas freezing system is brought into service to freeze the product very rapidly to a solid state. Liquified nitrogen is introduced into the chamber and allowed to expand to a gaseous state therein, thusly utilizing its heat vaporization to rapidly bring the product below its normal freezing point. Again, during this stage, mechanical refrigeration from additional source (not shown) or from encroachment of the existing facilities in the freezing area may be used to further speed the time of freezing, and in fact this is generally quite desirable, though the result of the mechanical refrigeration is not nearly so pronounced as that of the gas. The product is maintained in the central freezing area until it is substantially frozen nd at least at an average temperature as low as its freezing point and preferably somewhat below.

In this condition the frozen product is transferred to post-freezing area 10C where its temperature is further reduced, principally by mechanical refrigeration, to the desired terminal point. Very little product deterioration will occur after the product is solidified and this stage may therefore be carried out by the more economical mechanical refrigeration.

The product is then removed from the freezing chamber for further processing as desired.

It is to be noted from the foregoing that the liquid gas freezing of product is limited substantially to a period from the time the product is at its freezing point until it has completely frozen, and the mechanical refrigeration is used both before and after this period to lower the temperature of the product. The liquid gas freezing is found advantageous in rapidly transferring product to a solid state, so that no regelation is allowed to occur and formation of crystals, especially that might damage structure in cellulated material, is prevented or substantially lessened. Inert gas also displaces the partial pressure of oxygen circumjacent the product and provides a chemically inert atmosphere that prevents many chemical changes during the freezing process when cells may be ruptured and product not yet solidified.

The liquid gas freezing is a relatively expensive process and therefore is limited to the time of its greatest utility with the more economical mechanical refrigeration being used at such times as its economies are most advantageous. The inert gas atmosphere may, of course, be maintained at relatively little expense during the entire process to prevent oxidative or other changes brought about by atmospheric conditions about the product during this period.

It is desirable during the entire freezing process that an inert gas atmosphere be maintained in the freezing chamber to reduce partial pressure of water vapor therein and prevent frost formation on the refrigeration coils. The clock switch accomplishes this objective by providing short bursts of gas by activating the gas valve on a predetermined cycle, unless prevented by the safety switches.

The particular time of transit in the freezing chamber will vary with each particular product, but in general the size of each process area may be appropriately regulated to allow one speed of transit through the entire enclosure. If this be not the case, however, individual conveyors may be provided in each process area to operate at different speeds to give the appropriate period of transit required for that area. Individual conveyors, though, cause various problems in product timing and accumulation and therefore are not particularly desirable if not necessary.

It is further to be noted that our process could allow gas refrigeration to be applied to replace, at least partially, mechanical refrigeration either in the precooling or postcooling cycle, or both, in emergencies if the mechanical refrigeration should fail.

In carrying out our process, We presently prefer to use liquid nitrogen as an inert gas refrigerant. It is conveniently obtainable as a by-product of the oxygen industry and its low temperature of liquification, latent heat and inert nature admirably suit the purposes of our invention. Obviously, however, other gases having similar properties might well be used.

It is to be understood that the foregoing description is necessarily of a detailed nature so that a specific embodiment of our invention might be set forth as required, but it is to be understood that various modifications, changes, multiplication of parts and substitution in and ordering of processes may be resorted to Without departing from the spirit, essence, or scope of our invention.

Having thusly described our invention, what we desire to protect by Letters Patent, and

What we claim is:

1. The continuous process of combined mechanicalliquid gas freezing as aforesaid, comprising in combination:

cooling of product in the first processing area substantially to its freezing point substantially by mechanical refrigeration;

transport of the pre-cooled product to a second freezing area;

cooling the product rapidly by liquid gas refrigeration and mechanical refrigeration to substantially freeze the product, the liquid gas refrigeration being generated by spraying the liquid gas into the freezing area and allowing it to evaporate;

transport the frozen product to a third post-cooling freezing cooling area;

cooling of the frozen product to the desired terminal point substantially by mechanical refrigeration; and removal of the product.

2. The invention of claim 1 wherein the process is carried out in an enclosure with a turbulent low pressure inert gas atmosphere therein during the entire processing period.

3. As an article of manufacture, apparatus for the combined liquid gas-mechanical freezing of product as defined in claim 5, comprising:

a freezing enclosure, defined by insulated peripheral surfaces, and having means of moving product through first, second and third lineally adjacent processing areas; mechanical refrigeration means in at least said first and third processing areas, including heat transfer coils and means of circulating air thereacross and Within said areas and compressor and valve means associated with said coils to cause refrigeration therein;

inert gas freezings means in said second processing area. including at least one spray head adapted to disperse a liquid gas cryogen Within said second processing; chamber;

means of supplying liquid gas to the inert gas freezing means;

means of maintaining turbulence in the second process ing area;

means of maintaining relatively low pressure in the second processing area to allow evaporation of the liquid gas cryogen; and

control means adjustably regulating the temperature in each said processing area.

-4. The invention of claim 3 wherein the freezing enclosure is divided into three communicating horizontal chambers by vertical septums having orifices for ingress and egress of product.

5. The invention of claim 3 wherein the freezing enclosure is divided into three communicating vertically related chambers by horizontal septums.

References Cited UNITED STATES PATENTS 3,405,531 10/1968 Davis et al 6263 3,413,818 12/1968 Pelmulder 6263 2,059,970 11/1936 Robillard 6265 X 3,287,925 11/1966 Kane et a1. 62-64 X 3,294,553 12/1966 Benson 99-493 3,297,454 l/l967 Webster et a1. 62-64 X 3,345,828 10/1967 Klee et a1 6264 X 3,385,075 5/1968 Casale 62-63 WILLIAM E. WAYNER, Primary Examiner US. Cl. X.R. 62-332, 374

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