Abstract:
An improved freezer and plant gas system that harnesses the cooling properties of the plant gas evaporator to facilitate energy and cryogen savings, as well as the automation and optimization of a plant thermal processing system. The freezer preferably includes an internally mounted evaporator sized to meet the gas requirements of the plant processes requiring inert gas. By evaporating the plant gas in the freezer, the freezer can be remotely located from the liquid cryogen source while still making liquid cryogen available when called for during a cryogenic treatment process metal or other materials. In addition, by evaporating in the freezer the freezer is able to harness the cooling properties of the evaporator to pre-cool the freezer and material prior to use of liquid in the cooling cycle. Alternatively, a liquid load basket is adapted to economically thermally treat materials in a deep cryogenic treatment.

Description:
This application is a continuation of U.S. Ser. No. 09/605,770 filed Jun. 28, 2002, which is incorporated herein by reference, now U.S. Pat. No. 6,408,632. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to freezers for cryogenic treatment of metals and other materials and, more particularly, to a freezer and plant gas system that harnesses the cooling properties of the plant gas evaporator in a manner that facilitates energy and cryogen savings, as well as, thermal processing automation and optimization. 
     BACKGROUND OF THE INVENTION 
     Recently, substantial attention has been drawn to cryogenic treatment of metal parts and tools. The cryogenic treatment process tends to enhance a metal&#39;s mechanical properties such as wear resistance, hardness, and dimensional stability. Manufacturing companies, which replace thousands of worn out tools every year at a tremendous cost to the company and the consumer, are turning to cryogenic treatment processes in growing numbers in an effort to increase tool life and reduce costs. Use of the cryogenic treatment process has also found its way into high performance applications and consumer type products. For instance, cryogenic treatment processes are used to enhance the performance and durability of auto racing cars, the accuracy of firearms, the performance of baseball bats and golf clubs, the tonal quality of musical instruments, and the accuracy of aeronautical measuring devices. It also plays an integral part in the construction of satellites, interplanetary probes, and ground and space based telescopes. Other areas in which the cryogenic treatment process is being used include the fields of medicine, genetics, and semiconductors. 
     The cryogenic treatment process typically includes the use of liquid cryogen, such as nitrogen or some other inert gas, to significantly cool parts or specimens well below zero degrees Fahrenheit (F.); in some instances, all the way down to minus 320° F. The cooling is typically accomplished in a “cold box” or insulated freezer compartment supplied with a liquid cryogen from a liquid storage tank. 
     Most facilities with freezer installations also include plant processes, such as heat treating, that utilize inert gas. To supply gas to these processes, evaporators, which enables the liquid cryogen to expand to gas, are installed near the liquid storage tank, usually on the same pad and typically in “free air” to take advantage of maximum heat exchanging properties. A drawback to placing the evaporators in “free air” is that a significant amount of cooling energy is unnecessarily wasted. Harnessing this energy could prove to be advantageous to overall plant processes and economics. 
     Another drawback to established freezer installations is the location of the freezer. Typically, the freezer is installed in the immediate vicinity of the liquid storage tank to ensure liquid is available in a reasonable amount of time when called for in the cooling process. This location may be a significant distance from the location most beneficial to the overall process and economics of a plant. For example, in heat treatment facilities, it may be desirable to locate the freezer on the other side of the plant within an automated thermal processing line, which would allow an operator to include heat treatment and cryogenic treatment in the treatment “recipe” for a given part or tool. However, the farther the freezer is located away from the liquid storage tank, the less efficient the freezer system will operate. 
     The inefficiency of the freezer system is due to the expansion of the liquid cryogen to gas within the liquid supply conduit. Specifically, the liquid cryogen will expand into gas in the conduit in which it is transported until the conduit itself is cooled below the temperature at which the cryogen will liquefy or stay in liquid form. The farther the freezer is away from the liquid source, the more gas that will evaporate and expand in the conduit and be wasted in the freezer, until the conduit is cooled and liquid reaches the freezer. Because freezer use is intermittent in most freezer installations, the liquid cryogen will typically re-expand along the conduit as the freezer and conduit warm between cooling processes. As a result, significant quantities of gas will likely be wasted upon each use of the freezer. 
     One way to combat this waste is to locate the freezer in the immediate vicinity of the liquid storage tank. But as noted above, this requires locating the freezer remotely from the designed heat/cryogenic treatment process and, thus, creates excessive labor costs due to material handling and transportation to and from the balance of the process. Alternatively, a cryogenic pumping system could be used to provide constant pressure to prohibit expansion of the liquid cryogen to gas in the piping system. However, such systems tend to be very costly to purchase and install, as well as, operate and maintain. 
     Thus, it would be desirable to provide a freezer and plant gas system in which the freezer can be located remotely from the liquid storage tank, wherein liquid is supplied to the freezer on demand without excessive wasting of gas, and wherein the cooling energy of the plant gas evaporation process can be harnessed. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved freezer and plant gas system that harnesses the cooling properties of the plant gas evaporator to facilitate energy and cryogen savings, as well as the automation and optimization of a plant thermal processing system. In a particularly innovative aspect of the invention, the freezer includes an internally mounted evaporator sized to meet the gas requirements of the plant processes requiring inert gas. By evaporating the plant gas in the freezer, the freezer can be remotely located from the liquid cryogen source while making liquid cryogen available when called for during a cryogenic treatment process of metal and other materials. In addition, by evaporating in the freezer the freezer advantageously harnesses the cooling properties of the evaporator to pre-cool the freezer and material to be treated prior to any use of liquid cryogen in the cooling process; resulting in significant cryogen and energy savings. 
     In another innovative aspect of the invention, a liquid load basket is adapted to economically thermally treat materials in a deep cryogenic treatment process. 
     Other innovative aspects of the invention include the preceding aspects individually or in combination. 
     Other aspects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of the plant gas system of the present invention with an isometric view of a cryogenic freezer of the present invention. 
     FIG. 2 is a piping schematic of the plant gas system of the present invention shown if FIG.  1 . 
     FIG. 3 is a graph showing liquid cryogen use of the freezer of present invention plotted against the temperature in degrees F. reach inside the freezer. 
     FIG. 4 is an isometric view of a liquid load basket of the present invention for use in deep cryogenic treatment processes. 
     FIG. 5 is a piping schematic of a prior art freezer installation. 
     FIG. 6 is a piping schematic of an alternative embodiment of the plant gas system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a plant gas system  10  of the present invention is shown. The plant gas system  10  includes a liquid storage tank  20  filled with a liquid cryogen, such as nitrogen, argon, or other liquid cryogen, a freezer  30  with an internally mounted plant gas evaporator  40 , and a plant gas reservoir  50 . In operation, liquid cryogen flows from the storage tank  20  into the freezer  30  to be used in a cryogenic treatment process and separately flows through the evaporator  40  where it is evaporated or expanded into gas. The expanded gas flows into the reservoir  50  and from there it is supplied to plant processes that utilize inert gas. By evaporating inside the freezer  30 , the plant gas system  10  of the present invention advantageously captures the cooling energy of the evaporator  40  that is normally lost in established plant gas methods, and economically and efficiently transports liquid cryogen over long distances. 
     Although most thermal processing plants have a sizeable inert gas usage for vacuum furnaces, nitrating furnaces, hardening furnaces, etc., only nominal plant gas usage, such as the introduction of vaporized inert gas into the plant&#39;s pneumatic system, is needed to cause liquid cryogen to flow to the plant gas evaporator  40  within the freezer  30  where it is expanded into gas. As a result, liquid cryogen tends to be immediately available when called for in the cooling process. More particularly, liquid cryogen tends to be available without having to expel and, therefore, waste significant quantities of warmer gas as the conduit cools to temperatures necessary to liquefy the cryogen. In addition, the cooling properties of the evaporator  40  advantageously pre-cool the freezer  30  and material to be processed prior to the use of any liquid cryogen. Depending on a plant&#39;s gas usage, the freezer and material can be pre-cooled to temperatures ranging from about minus 80° F. to about minus 150° F., and possibly lower. Accordingly, there tends to be substantial savings in the amount of liquid cryogen used during the cooling process. The amount of energy in BTU&#39;s that it takes to cool the freezer components and material to a desired temperature illustrates that the pre-cooling process saves a significant amount of liquid cryogen. 
     For example, the amount of energy (Q) in BTUs that it takes to cool the a load of material can be calculated as follows: 
     
       
           Q=M×S ×DELTA-T 
       
     
     wherein, 
     Q=Heat removed in BTU&#39;s 
     M=Mass in pounds (#s) of material to be cooled 
     S=Specific heat of material in BTU&#39;s/#/° F. 
     DELTA-T=Temperature differential between ambient temperature, which in heat treating facilities is typically 20° F. higher than outside temperatures, and the temperature to which the internal evaporator will cool the freezer compartment, freezer components, and the material to be processed. 
     For this calculation, the material and components to be cooled include a 1,000 #load of steel (S=0.12), a stainless steel (S=0.12) freezer load basket with associated components weighing approximately 180 #s, and a stainless steel freezer inner wall assembly weighing approximately 350 #s. Assuming an ambient temperature of 80° F., and a pre-cooled temperature of minus 100° F., 
     Delta-T=180° F. 
     Q Load =M L ×S L ×Delta-T=1,000×0.12×180=21,600 BTU&#39;s 
     Q Basket =M B ×S B ×Delta-T=180×0.129×180=3,532 BTU&#39;s 
     Q Wall =M W ×S W ×Delta-T=350×0.129×180=6,867 BTU&#39;s 
     Q Total =31,999 BTU&#39;s 
     According to this example, pre-cooling would save the amount of liquid cryogen necessary to generate 32,000 BTU&#39;s of cooling energy. 
     In addition to these savings, evaporating within the freezer  30  allows the freezer  30  to be located anywhere within the plant and preferably where it would be most beneficial to the overall process. More particularly, the ability to locate the freezer in the area of the plant where the balance of the before- and after-freezing processes are performed, enables a system operator to include freezing in the “recipe” for automated and semi-automated systems. This tends to create considerably savings in time and labor cost due to material handling. For instance, locating the freezer within the balance of heat treating equipment allows the same alloy baskets to be used for the hardening furnace, the washer, the tempering furnace and the freezer. Substantial savings in time and labor cost result from not having to transfer material from one basket to another, and back again, and from not having to transport material from the heat treatment line to the freezer, and back again. 
     As noted above, by evaporating in the freezer compartment, liquid cryogen tends to be immediately available at the freezer location. This enables better and more stable control of the temperature in the freezer compartment compared to a system that would first produce warmer gas, then liquid, each time the process calls for cooling. Freezer controls normally include an analogue input temperature control system utilizing a PID (proportional-integral-derivative algorithm) loop to open and close a cryogenic solenoid valve or actuate a motor operated valve (MOV) to control the flow of liquid into the insulated freezer compartment. In previous systems, when the PID control calls for cooling it will first encounter warm gas, then liquid. In response, the PID control is likely to over-react as the higher temperature gas being expelled almost instantaneously turns to the considerably lower temperature liquid. By encountering liquid from the outset, a control system employed with the freezer  30  of the present invention will tend to perform more efficiently and be more stable as the system acquires and maintains a desired temperature set point. 
     Referring in detail to FIGS. 1 and 2, the freezer  30  and plant gas system  10  of the present invention comprises a liquid cryogen storage tank  20  having primary  21  and secondary  11  liquid conduit lines extending therefrom. The liquid storage tank  20  stores gases such as nitrogen, argon, oxygen, helium, or others, or combinations thereof, in liquid form. Cryogenic globe valves  12  and  22  are installed along the liquid conduit lines  11  and  21  adjacent the storage tank  20  to isolate the tank  20  while it is being filled, repaired, or replaced. Located adjacent the storage tank  20  along secondary line  11  is a tertiary or backup evaporator  13 , which is normally exposed to ambient conditions as in typical plant gas systems. A secondary plant gas supply line  14  extends from the tertiary evaporator  13  and joins a primary plant gas line  42 , which feeds into a gas reservoir  50 . A dual pressure switch  53  on the reservoir  50  causes a solenoid valve  15  in the secondary plant gas line  14  to open and close depending on the gas pressure in the reservoir  50 . Preferably the solenoid valve will open when the pressure in the reservoir  50  goes below 80 pounds and will close when the pressure in the reservoir  50  raises above 95 pounds. The solenoid valve  15  is preferably a normally open-type solenoid valve to ensure plant processes have sufficient gas in the event of a power outage. A pair of isolation ball valves  16   a  and  16   b  is located on either side of the solenoid valve  15  to isolate the solenoid valve  15  for repair or replacement. A check valve  19 , preferably a swing back type with a Teflon seat, is located along the secondary gas line  14  after the solenoid valve  15 . The check valve  19  prevents back flow of gas from the primary plant gas line  42  along the secondary the plant gas line  14  toward the liquid storage tank  20 . 
     A pressure by-pass line  14   a  branches around the solenoid valve  15  and includes a pressure actuated valve  18  and a pair of isolation ball valves  17   a  and  17   b  located on both sides of the pressure actuated valve  18 . As the gas pressure builds up in the liquid storage tank  20  from the evaporation of the liquid cryogen, a pressure relief valve (not shown) would typically vent the gas from the tank  20  into the atmosphere. The bypass line  14   a  and valve  18  combat this wasteful method by advantageously allowing the gas to be flow into the gas reservoir  50 . 
     The primary liquid cryogenic supply line  21  extends from the liquid storage tank  20  to a freezer  30  of the present invention. The freezer  30  preferably includes an enclosure  30   a  having a door  30   b  that is opened to insert material for cryogenic treatment, an internally mounted evaporator  40 , a series of sprayer nozzles  33 , a flapper vent  36  to exhaust gas during the cooling process, and a fan  35  to uniformly circulate the cool gas. The freezer enclosure  30   a , which is generally box-like, preferably includes an external steel plating weldment and an internal stainless steel plating weldment. A load rack formed of three inch stainless steel tubing and rollers is preferably included adjacent the base of the enclosure. A pressure actuated ball-type drain closure is located in the floor of the enclosure to allow liquid to drain after the cooling process. A hydraulic cylinder preferably drives the door  30   b  of the enclosure  30   a . Alternatively, the door  30   b  could be driven by a pneumatic cylinder or a chain and roller type assembly. The design of the load rack and internal mechanical roller assembly, along with the external features, esthetic, mechanical or otherwise, are such that they can be altered or customized to accommodate different manufacturers preferences and/or requirements. 
     Because liquid cryogen flows to the freezer&#39;s internal evaporator  40 , where it is evaporated into gas for plant processes, the liquid cryogen is economically and efficiently transported over long distances and still made available for immediate use when called for during the cooling process. As a result, the freezer  30  can advantageously be placed remotely at distances well over 400 feet away from the liquid storage tank  20 . Depending on the gas usage of plant, it may be possible to efficiently operate the freezer/plant gas system with minimal insulation around the liquid cryogenic supply line  21  and still maintain liquid flowing through the supply line  21  to the freezer  30 . However, it may be economically desirable to vacuum jacket the supply line  21  to ensure that the freezer  30  harnesses the maximum amount of available cooling energy. 
     The liquid supply line  21  branches off adjacent the freezer  30  to sprayer and evaporator feed lines  21   a  and  21   b . Prior to branching off to the separate feed lines  21   a  and  21   b , the liquid supply line  21  includes a cryogenic ball valve  24  to isolate the freezer  30  for maintenance, repairs, or replacement. A 350 psi pressure relief valve is preferably located along the liquid supply line  21  between isolation valves  22  and  24 . 
     Inside the freezer compartment  30   a , the sprayer feed line  21   a  branches into two sprayer feed arms  31  and  32 . A series of spiral cone type spray nozzles  33  are connected to the feed arms  31  and  32 . The feed arms  31  and  32  and sprayer nozzles  33  are mounted along with the fan  35  adjacent the ceiling of the freezer compartment  30   a . As liquid cryogen is sprayed from the nozzles  33 , the fan  35  is operated to uniformly circulate cool gas around the material being treated. Prior to entering the freezer compartment  30   a , the sprayer feed line  21   a  includes a cryogenic ball valve  25 , a pressure regulator  27 , which prevents the freezer compartment  30   a  from becoming over pressurized during the cooling process, a solenoid valve  29 , which controls the flow of liquid cryogen to the spray nozzles  33  located on feed arms  31  and  32 , and a pair of pressure (350 psi) relief valves  26  and  28  preferably located between the isolation valve  25 , the pressure regulator  27  and the solenoid valve  29 . The freezer  30  preferably includes an analogue input temperature control system with a PID loop that includes a temperature control switch  34 . The temperature control switch  34  actuates the solenoid valve  29  between open and closed positions to control the flow of liquid cryogen to the spray nozzles  33 . Alternatively, the controller may be programmed to utilize an analog output in order to variably control a MOV valve that could be used in place of solenoid valve  29  to control the flow of liquid to the spray nozzles  33 . 
     The evaporator feed line  21   b  includes a cryogenic ball valve  38  prior to entering the freeze compartment  30   a . Pressure (350 psi) relief valves  37  and  39  are preferably located between isolation valves  24 ,  25  and  38 , and between isolation valve  29  and the internal evaporator  40 . The internal evaporator  40  is preferably mounted on the back interior wall of the freezer compartment  30   a . Alternatively, the evaporator  40  could be mounted on either side wall or ceiling of the freezer compartment  30   a , or may comprise two (2) or more internal evaporators connected in series or parallel within the freezer compartment  30   a . The internal evaporator  40 , which operates as the primary plant gas evaporator for the plant gas system  10  of the present invention, is preferably connected in series to an externally mounted secondary evaporator  41 . Both evaporators are preferably sized at 125% of plant gas capacity. As the temperature within the interior of the freezer compartment  30   a  decreases, the primary/internal evaporator  40  becomes less and less efficient resulting in liquid cryogen flowing out of internal evaporator  40  into the external/secondary evaporator  41 . The secondary/external evaporator  41  is utilized to evaporate any liquid cryogen that exits the primary/internal evaporator  40 . 
     A primary gas line  42  extends from the external evaporator  41  to the gas reservoir  50 . Prior to the reservoir  50  and a junction with the secondary gas line  14 , the primary gas line  42  includes a pressure regulator  45 , a check valve  47 , an isolation ball valve  48 , and a pressure (350 psi) relief valve  46  preferably located between the pressure regulator  45  and the isolation valve  48 . The pressure regulator  45  preferably prevents liquid cryogen from being pumped into the reservoir  50 , while the check valve  47 , which is preferably a swing back type with a Teflon seat, preferably prevents back flow of gas from the secondary gas line  14 . Another isolation valve  49  is located along the primary gas line  42  after the junction with the secondary gas line  14  and prior to a gas inlet  51  on the reservoir  50 . The reservoir  50  includes a pressure relief valve  52  and a gas outlet  54 . Another isolation valve  55  is located on the plant gas line  56 , which feeds gas to the plant processes that utilize inert gas. 
     A blanket gas line  42   a  preferably extends from the primary gas line  42 , just after the external evaporator  41 , back into the freezer  30 . The blanket gas system is activated when the freezer door  30   b  is opened and creates a positive gas pressure in the freezer compartment  30   a . The positive gas pressure tends to prevent ambient air from entering the freezer  30  and causing the internal evaporator  40  and other components to ice up. The blanket gas line  42   a  includes an isolation ball valve  43  and a solenoid valve  44 , which is actuated by a blanket gas control switch that is triggered by the opening of the freezer door  30   b.    
     In operation, plant gas is drawn off of the reservoir  50  through the reservoir outlet  54  causing the cryogen to flow in gas form through the liquid supply line  21 , the primary and secondary evaporators  40  and  41 , and the primary gas line  42  into the gas reservoir  50 , until the liquid supply line  21  cools to a temperature at which the cryogen remains a liquid. Once cryogen is flowing in liquid form through the liquid supply line  21  to the freezer  30 , it will flow through the internal primary evaporator  40  where it will expand into gas for the plant processes. The cooling properties of the internal primary evaporator  40  are harnessed by the freezer  30  to pre-cool the freezer compartment  30   a  to approximately minus 100° F. As the interior of the freezer compartment  30   a  becomes too cold for the primary evaporator  40  to effectively evaporate the liquid to gas, the secondary external evaporator  41  performs the necessary evaporation. By evaporating remotely at the freezer  30 , liquid tends to be immediately available when called for during the cooling process. 
     To begin the cooling process, the door  30   b  of the freezer  30  is opened to insert the material to be treated. Opening the door  30   b  triggers the solenoid  44  in the blanket gas line  42   a  to open and feed blanket gas into the interior of the freezer compartment  30   a . The blanket gas creates a positive pressure within the freezer compartment  30   a  and, thus, prevents ambient air from entering the freezer compartment  30   b . A load of material to be processed is then manually loaded, or loaded as part of an automated or semi-automated thermal processing line, into the freezer  30 . Once loaded, the freezer door  30   b  is shut and the blanket gas solenoid  44  closes. 
     The material is then pre-cooled to a desired temperature or for a desired amount of time by using a pre-cool timer or a thermostat, which can be used to initiate the cooling cycle. Once the material has cooled to a desired temperature, such as minus 100° F., or for a desired period of time, a temperature set-point is read by or entered into the control system. The temperature control switch  34  actuates the sprayer solenoid valve  29  to enable liquid cryogen to flow to and out of the spray nozzles  33 . The circulation fan  35  is also activated to uniformly distribute the cool gas around the material. As the temperature within the freezer compartment approaches the set-point temperature, the temperature control switch  34  modulates the sprayer solenoid valve  29  to acquire and maintain the set-point temperature. The material will be cooled at the set-point temperature for an appropriate amount of time to obtain the desired mechanical properties for the material being treated. After the treatment process is completed, the freezer door  30   b  is opened and the blanket gas system activated. 
     The control system includes a purge mode that enables a person to safely enter the freezer  30  and work on its internal components. The purge system will only work when the freezer door  30   b  is open. When activated, the purge system disables the liquid cryogen supply to the spray nozzles  33  by closing the sprayer solenoid valve  29 , disables the blanket gas system by closing the blanket gas solenoid valve  44 , and activates the fan  35  to vent any residual gas left in the freezer compartment  30   a . The purge system preferably must be manually reset. 
     Turning to FIG. 3, a graph is shown in which use of liquid cryogen by the freezer  30  is plotted against the temperature acquired in the freezer compartment  30   a . As shown, the freezer  30  of the present invention does not use any liquid cryogen in a first or pre-cool temperature region (A) as the freezer  30  and material to be treated are cooled from an ambient temperature of approximately 80° F. to a pre-cooled temperature of approximately minus 100° F. In a second temperature region (B), which is between the pre-cooled temperature of approximately minus 100° F. and a transition temperature of approximately minus 225° F., liquid cryogen is sprayed from the nozzles  33  to further cool the freezer  30  and material. The freezer&#39;s  30  liquid cryogen use in this temperature region (B) appears to gradually increase as the temperature decreases. The increase in liquid cryogen usage per degree (F.) change in temperature in this region (B) is relatively small until the temperature within the freezer  30  nears the transition temperature of approximately minus 225° F. The transition temperature is the temperature at which the freezer  30  tends to begin to use excess liquid for each degree (F.) change in temperature. In the third temperature region (C), which includes temperatures at which deep cryogenic treatment is typically conducted, the freezer&#39;s liquid cryogen usage appears to increase exponentially for each degree (F.) change in temperature as the temperature decreases from the transition temperature to approximately 320° F. While attempting to acquire and maintain a set-point temperature in this region (C), the spray nozzles  33  tend to approach operating at 100% capacity at 100% of the time. 
     To more economically accommodate the need for deep cryogenic treatment and avoid wasting liquid cryogen, the freezer  30  of the present invention preferably includes a liquid load basket  70 . As shown in FIG. 4, the liquid load basket  70  includes a generally box-like enclosure  71  mounted on an alloy tray  76 . The enclosure  71  includes an opening  73  at its top to vent expanding gas. The top of the enclosure  71  includes a pair of hingedly connected doors  74  and  75 . Mounted within the enclosure  71  are a series of liquid cryogen level detecting thermocouples  77   a-b  corresponding to levels  1 - 4 , and a series of off-set level detecting thermocouples  78   a-d  corresponding to off set levels  1 - 4 . The basket  70  also includes a liquid feed line or connector  72  to fill the basket  70  with liquid cryogen. The feed line  72  includes a flexible hose with a twist lock type adapter for manual or semi-automatic systems, or a male or female quick disconnect spline-type coupler for fully automatic systems. Although the load basket feed line  72  is connectable to a liquid load connector  60  in the freezer  30 , and the liquid load basket  70  is preferably used in conjunction with the freezer  30 , it is also directly connectable to a source of liquid cryogen. 
     As shown in FIG. 2, the liquid load connector  60  is located at the end of a liquid load feed line  21   c , which branches off of the liquid supply line  21 . The liquid feed line  21   c  includes an isolation ball valve  57 , a solenoid valve  59 , and a pressure (350 psi) relief valve  58  positioned there between. 
     In operation, the material to be processed by deep cryogenic treatment is placed within the liquid load basket  70 . The operator determines at which level the material will be completely submerged in the liquid cryogen and programs the desired level into the control system. The freezer door  30   b  is opened and the blanket gas system is activated. The liquid load basket  70  is placed inside the freezer  30  and coupled to the connector  60  on the liquid load feed line  21   c  of the freezer  30 . Once the liquid load basket  70  is inside the freezer  30 , the door  30   b  closes and the blanket gas is shut off by closing the blanket gas solenoid valve  44 . The liquid load basket  70  is pre-cooled to a desired temperature or for a desired period of time in a manner discussed above. Once the pre-cool temperature is reached or the time runs out, a set point temperature, which preferably equals a temperature that is slightly higher than the transition temperature, is read by or entered into the control system. The temperature control switch  34  then actuates the sprayer solenoid valve  29  sending liquid cryogen to the spray nozzles  33  to acquire the desired set-point temperature within the freezer  30 . As described, the material advantageously goes through two (2) steps of pre-cooling prior to being immersed in the liquid cryogen. The liquid cryogen usage within the liquid load basket  70  will tend to be lower than established methods as a result. 
     When the set-point temperature is reached, a fill control switch actuates the sprayer solenoid valve  59  to fill the liquid load basket  70  to a desired level. Assuming for exemplary purposes the set-point level is set at level  2 , the control system will allow the basket  70  to fill with liquid until the level  2  off-set thermocouple  78   b , senses a temperature equivalent to the liquid temperature of the cryogen, which is minus 320° F. for nitrogen, indicating that the liquid has reached the level  2  off-set. The fill control switch closes the solenoid valve  59  when the off-set thermocouple  78   b  senses the liquid temperature. The control system will maintain the liquid cryogen in the liquid load basket  70  at or above level  2  during the deep cryogenic treatment process by replenishing the liquid as it evaporates. More particularly, when the set-point thermocouple  77   b  senses a temperature above the liquid temperature of the cryogen, e.g., minus 319° F. for nitrogen, indicating that the liquid level has fallen below the desired level, the fill control switch opens the solenoid  59  to fill the liquid load basket  70  with liquid cryogen until the off-set thermocouple  78   b  again senses the liquid temperature. After the treatment process is completed, the freezer door  30   b  can be opened to allow the liquid cryogen in the liquid load basket  70  to evaporate into the atmosphere. 
     Alternatively, the liquid load basket  70  may be completely enclosed and include an exhaust gas outlet  80  feeding a gas line  79 , which may advantageously be coupled to a pneumatic gas system reservoir (not shown). In addition, in an attempt to reduce waste, the liquid load basket  70  may advantageously be connected via appropriate piping and valves to a liquid load recycle reservoir (not shown). During the deep cryogenic treatment process, evaporated gas is allowed to freely vent through gas outlet  80  and gas line  79  into the pneumatic gas reservoir. Once the treatment process is completed, a solenoid operated valve (not shown) in the pneumatic gas supply line  79  is closed. As the liquid cryogen in the liquid load basket  70  evaporates into gas, the pressure increases within the basket  70  to a level sufficient to force the remaining liquid cryogen out of the liquid load basket and into the liquid load recycle reservoir. Another solenoid valve (not shown) can be actuated to shut off access to the recycle reservoir when the control system senses that the liquid cryogen has been evacuated from the liquid load basket  70 . The control system preferably includes programming logic that enables the liquid cryogen stored in the recycle reservoir to be used in a subsequent deep cryogenic treatment prior to drawing liquid from the liquid feed supply line  21   c.    
     Other alternative embodiments to the present invention include using one gas or combination, for example, oxygen or helium or both, in liquid form, for pre-cooling, i.e., passing the liquid through the freezer&#39;s internal evaporator  40  where it is expanded into gas for other uses, and then using another gas or combination, such as nitrogen or argon or both, in liquid form for the cooling process. 
     In another alternative embodiment, established freezer installations can be retrofitted to take advantage of the cooling properties of an evaporator and the liquid savings associated with evaporating inside the freezer. An established freezer installation  100 , as shown in FIG. 5, typically includes a liquid storage tank  120 , a supply conduit  121 , and a freezer  130  with spray nozzles  133 . An isolation valve  122  is located adjacent the tank  120  and a control valve  125  is installed in the supply line  121  prior to the freezer  130  to control the flow of liquid into the freezer  130 . To ensure liquid is available at the freezer  130 , a pressure actuated valve  124  is typically installed in the supply line  121  prior to the control valve  125 . The pressure actuated valve  124  is used to vent gas from the supply line  121  to atmosphere (A) until the line  121  is sufficiently cool for liquid to flow. The valve  124  closes when liquid reaches the valve  124  to enable liquid to flow to the freezer  130 . 
     Turning to FIG. 6, the pre-cooling benefits and some of the liquid savings of the present invention can easily be taken advantage of by retrofitting the existing installation of FIG.  5 . The existing installation  100  can be retrofitted by removing the pressure actuated valve  124  and vent line  124   a  and installing an evaporator or heat exchange  140  within the freezer  130 . An evaporator feed line  123  branches off of the supply line  121  and feeds liquid to the evaporator  140 . After the liquid passes through the evaporator  140 , the exiting gas can be vented to atmosphere (A) or to plant or pneumatic gas systems (P). A pressure regulator  126  can be used to vent gas around the evaporator  140  along a by-pass line  128  to exit side of the evaporator  140  until liquid flows through the supply line  121 . A check valve  127  can be installed to prevent the back flow of gas. 
     While the invention is susceptible to various modifications and alternative forms, a specific example thereof has been shown in the drawings and is herein described in detail. It should be understood, however, that the invention is not to be limited to the particular form disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims.