US3374642A - Refrigeration method and apparatus for cyclical requirements - Google Patents

Description

March 26, 1968 R. E. M MINN 3,374,642

REFRIGEEATION METHOD AND APPARATUS FOR CYCLICAL REQUIREMENTS 2 Sheets-Sheet 1 Filed Aug. 18, 1966 I [VAPOR/170A I Jf/"A/PATOR V MMPREJJM WR 0 TRREE MN Q P cwmRw o fl lw w i W s L E ER f M mm fijgDH A m :m U/\.

M w W W a a w 5 m 5 0 ATTORNEY REFRIGERATION METHOD AND APPARATUS FOR CYCLICAL REQUIREMENTS Filed Aug. 18, 1966 2 Sheets-Sheet 2 76 L l T l T 70 72 lggt;j

INVENTOR. JAMES F WEILER BY PAUL. L- DEVEJZTERH DUDLE'f R-Doauz I J2.

United States Patent ABSTRACT OF THE DISCLOSURE The present invention is directed to an improvement in refrigeration units and more particularly an improvement in such units used to meet cyclical requirements. The present invention utilizes a portion of the substance cooled by the unit during minimum requirement periods to supercool the refrigerant in the unit; thereby giving this refrigerant sensible heat capacity or addiional sensible heat capacity, as the case may be, in addition to its latent heat capacity. The invention then utilizes this super-cooled refrigerant during periods of maximum requirement, the cooling capacity provided by the refrigeration unit alone being insufficient to cool the substance during these maximum requirement periods. The added sensible heat capacit however, provides the necessary additional cooling power.

In the normal application of a refrigeration system, the refrigeration required remains essentially constant. There are numerous situations, however, where refrigeration requirements are cyclical in nature. These last-mentioned situations have certain periods which require a peak or maximum amount of refrigeration and alternating intervals requiring a relatively low amount of refriegration. To handle such situations in the past, a refrigeration unit of a size sutficient to meet the maximum refrigeration was utilized. As is obvious, this results in an uneconomical arrangement due to the fact that the full capacity of the refrigeration unit is used only during periods of peak refrigeration requirement. During the remainder of the operation time, which is the major portion of the time, the unit is operating at less than capacity.

A further disadvantage in utilizing a refrigeration unit capable of handling maximum requirements is that the oversized refrigeration system is vastly underloaded at the low refrigeration requirement portion ofthe cycle. Due to the wide variation between the maximum and the minimum refrigeration requirement levels, the normal unloading features of the refrigeration unit is often not adequate to supply the necessary turndown. This may result in shutdowns caused by low suction pressures and by the freezing of the compressor in the refrigeration unit. Furthermore, the controls necessary to vary the operation of the refrigeration unit in accordance with the cyclical requirement are usually rather sophisticated and expensive, thus adding tothe cost.

The present invention seeks to overcome these disadvantages by utilizing a refrigeration unit which is capable of handling as a maximum load a refrigeration requirement lying between the maximum and minimum requirements of the system to be refrigerated. Obviously, the unit would be incapable of handling the maximum load requirements should the refrigeration unit be operated in the conventional manner. During the minimum requirement periods, however, the cooling capacity of the unit exceeds the amount required. Figuratively speaking, the present invention seeks to store this'excessive refrigeration capacity to be used during the peak periods. The present invention seeks to, in effect, supplement the cooling capacity of the unit by utilizing-a portionof the substance 3,374,642 Patented Mar. 26, 1968 that is cooled by the unit, to super-cool the refrigerant utilized in the refrigeration unit. In this manner, the refrigerant is cooled to a temperature substantially below the temperature obtainable by the use of the refrigeration unit alone, and gives to the refrigerant a sensible heat capacity to supplement its latent heat capacity. This sensible heat capacity imparted by the additional drop in temperature of the refrigerant allows the refrigeration unit to provide the additional refrigeration necessary during the period of maximum requirement.

More particularly, the present invention utilizes valve means which allows a portion of the process gas or substance cooled in the evaporator of the refrigeration unit to be diverted from its regular path of travel to a heat exchanger-accumulator through which the refrigerant passes. This diversion takes place during the periods of minimum refrigeration requirement when the refrigeration that may be supplied exceeds the demand. Since excessive cooling capacity exists refrigerant is allowed to accumulate in the accumulator, an amount of refrigerant less than that available being sufficient to cool the process gas. The cooled process gas is used by the heat exchangerto further cool this refrigerant in the accumulator. All during the period of minimum requirement, gas is diverted through the heat exchanger, continuously cooling the refrigerant accumulated therein to lower and lower temperatures. The refrigerant is, in effect, super-cooled. As the cycle reverses itself and the refrigeration load increases, the process gas is no longer diverted to the heat exchanger and the super-cooled refrigerant stored in the accumulator is supplied to the evaporator as needed. The additional cooling capacity provided to the refrigerant during the periods of minimum requirement, however, is sufficient to provide the additional cooling capacity needed for the maximum requirement periods.

it is, therefore, an object to provide a new and novel method and means by which cyclical refrigeration requirements may be met without providing the oversized unit necessary to meet the maximum requirement level and without the resultant cost of such an oversized unit.

It is a further object of the present invention to provide a method and means by which cyclical refrigeration requirements may be met by use of a refrigeration unit having a cooling capacity of less than the maximum required in the cycle.

A still further object of the present invention is to provide an economical and relatively simple method and means to meet cyclical refrigeration needs reliablyand with little possibility of a shutdown due to excessive underloading of the refrigeration unit during the minimum refrigeration requirement periods.

A still further object of the present invention is to provide a novel refrigeration system having means to determine the refrigeration requirement at any time and, during periods when the refrigeration supplied by the refrigeration system operating in a conventional manner exceeds the requirement, a portion of the substance cooled by the refrigeration system is used to further cool the refrigerant, whereby additional cooling capacity is acquired by the refrigerant for use during the maximumv periods when the refrigeration unit is unable to carry theload.

An additional object is to store refrigerant not needed during minimum requirement periods and to super-cool this stored refrigerant by use of a portion of the process gas which has been previously cooled, the stored supercooled refrigerant being used as required during periods when the cooling required exceeds the normal cooling capacity of the refrigeration unit.

Other and further objects, features, and advantages will be apparent from the following description of a presently preferred embodiment of the" invention, given for the purpose of disclosure, taken in conjunction with the accompanying drawings whereinlike character erences designate like parts throughout the several views and in which:

FIGURE 1 is a graph depicting cyclical refrigeration requirement of a system,

FIGURE 2 is a schematic diagram of a preferred embodiment of the refrigeration system utilizing the present' from the tower before it is capable of further operation.

This is performed by heating a portion of the previously dried process gas and passing it once again through the tower. This vaporizes the adsorbed material and carries it out of the unit. The desiccant unit must then be cooled before it is returned to operation.

In a three tower desiccant unit, for example, one tower is used to adsorb the water and hydrocarbons from the process gas, the second is in the heating phase and the third is in the cooling phase. This is illustrated in FIG- URE 3. The gas is fed through pipe 60 into the first tower 62 which, during this cycle, is adsorbing. A portion of the steam is diverted as shown at 68 to tower 66 for cooling purposes, tower 66 having been heated during the previous cycle. After cooling tower 66, this gas is heated by heater 70 and is then moved to tower 64 for the heating phase, tower 64 being the adsorbing tower during the previous cycle. The heated gas coming from the tower 64 carries with it the vaporized water and heavy components that had been adsorbed by tower 64 during the previous cycle. The heated gas is cooled somewhat by an ambient air cooler 72 and then passes through conduit to the refrigeration unit 74 which is the subject of the present invention.

The refrigeration unit 74 cools the heated process gas to a temperature at which it may be reintroduced into the stream 60 without unduly elevating the temperature of stream 60. The refrigeration unit must also condense and remove the water and the heavy components from the process, gas. After the operation of the refrigeration unit, the process gas flows through conduit 34 to stream 60 and is passed through the desiccant unit and out through stream 76 for consumption or further processing.

The purpose, therefore, of the refrigeration unit is to cool the gas and to condense the heavy components in the gas. When the cycle shown in FIGURE 3 begins, the tower 64 is cold and the gas coming to refrigeration unit 74 is also cold. As the tower heats up, the temperature and the heavy component content of the gas increases. Tower 64 is then switched to cooling, but the temperature and heavy component content of the gas will continue to rise until it reaches a' peak. It will then drop off to approximately the temperature of the cooling gas and the ngxt cycle will begin with tower 62 being in the heating p ase.

1 Turning now to FIGURE 1, a graph is set forth which depicts in line 70, the variations in the refrigeration requirements of a typical systeni or operation having a cyclical refrigeration requirement. In the example illustrated, the minimum requirement is approximately 6 tons and the maximum'or peak requirement is 25 tons. The minimums and the maximums alternate and the change from one to the other is gradual. For purposes of discus sion, it may be assumed that a 12 ton refrigeration unit will be sufficient to handle this cyclical load with the utilization of the present invention. The amount of refrigeration that will be supplied by this unit is shown by the line 72 on the graph.

When the requirement of the operation dips belQW 1.2

ref-

4; tons, an excessive amount of cooling capacity is available from the refrigeration unit since it functions at 'a constant rate as shown by line 72. This period of operation is illustrated by the portion of line 70 which lies below line 72 and, for purposes of this application, will be known as the period of minimum refrigeration requirement. The portion of the cycle lying above line 72 illustrates the period during which the demand exceeds the supply and will be called the period of maximum refrigeration requirement. 7

Turning now to FIGURE'Z, there is shown a schematic diagram of a system embodying the present invention. The process gas enters by the conduit 10 moving in the direction of the arrowhead. The process gas then enters an initialheat exchanger 12 which is a conventional gas to gas heat exchanger. The process gas then passes out of heat exchanger 12 by means of the conduit 14 and into the evaporator 16. The evaporator 16 is connected by means of conduit 18 to the separator 20. A first conduit 22 extends from the separator for conveying out of the system the water and hydrocarbons condensed in the evaporator and a second conduit 24 extends from the separator and is used to convey gas to the three-way valve 26, which has two outlet ports, 28 and 30. The outlet port 28 is connected to the conduit 32 which connects with the heat exchanger 12 for heat exchange with the process gas of the conduit 10. Conduit 34 extends out of the heat exchanger 12 and leads to the dry desiccant unit which is not shown, thereby providing means to convey the process gas to the desiccant unit for the drying of the gas.

The outlet port is connected to accumulator-heat exchanger by the conduit means 36, whereby process gas coming out of port 30 will be in heat exchange relation with the refrigerant as will be explained below. Extending out of the accumulator-heat exchanger 40 is conduit 38 which connects with the conduit 34.

A conventional compression-refrigeration system is utilized in the preferred embodiment and is comprised of a compressor 42 connected by means of conduit 44 to a condenser 46. The condenser 46 is connected by conduit 48 to the accumulator-heat exchanger 40. Conduit 50 leads out of the accumulator-heat exchanger 4t} and connects with the expansion valve 52 which, in turn, communicates with the evaporator 16, The refrigeration cycle is completed by the conduit 54 which leads from the evaporator to the compressor 42.

Liquid level control means 51 operates the expansion valve 52 in response to the level of the liquid refrigerant in the evaporator 16. As part of the control means 51, a float rides on the surface of the liquid refrigerant in evaporator 16, and as the refrigerant evaporates and the liquid level drops, the control means 51 opens expansion valve 52 to allow more refrigerant into the evaporator.

A back pressure valve 53 is located in the return conduit 54 to regulate the amount of vapor that is allowed to move from the evaporator in response to the action of compressor 42. Control means 55 operates the back pressure valve 53 in response to the vapor pressure in the evaporator. As the refrigerant evaporates, this pressure will increase causing the control means 55 to open valve 53, allowing the evaporated refrigerant to flow to the compressor 4 2,The compressor is also equipped with a suction pressure control 57 so that if the suction decreases to a predetermined level due to the closing of valve 53,-

the compressor will be shut off and no refrigerant will circulate.

The element 40 functions as an accumulator for the refrigeration system as well as a heat exchanger to subcool the refrigerant as will be explained. In its capacity as an accumulator, the refrigerant, which may be Freon or any other suitable substance, accumulates in the. vessel 40. Vapor space is provided in the vessel 40 to allow for possible expansion of the refrigerant and further functions as a surge vessel to insure that an adequatevolume er refrigerant is available in the system to respond to the varying load requirements.

A control means 60 is provided to control the threeway valve 26, thereby regulating the amount of gas that is allowed to flow out of port 38. The control means is operatively connected by element 58 to the temperature sensitive means 56 which is located within the flow of the process gas in conduit 18, the control means 60 opening and closing port 30 in response to temperature changes picked up by the element 56 as is setforth more fully below.

In operation, the process gas enters the cooling system by the conduit in a vapor state. Initial or precooling is provided by the heat exchanger 12, the cooling medium being previously cooled process gas which is conveyed to the heat exchanger 12 by the conduit 32. After this initial pre-cooling, the process gas moves through conduit 14 and into the evaporator 16. It is at this point that the process gas is cooled to the desired temperature. It then flows out of the evaporator 16 and into the separator 20 by means of the conduit 18. The cooling of the process gas in the evaporator will result in the condensation into a liquid of water and certain heavy components which were removed from the dry desiccant tower. The separator functions to remove this liquid from the process gas and may be a standard liquid-gas separating unit, the liquid being taken off by means of the outlet conduit 22. The cooled and dry gas exits from the separator by means of the conduit 24 and enters the three-way valve 26.

In a standard or prior art refrigeration system employed passes through the exchanger by means of conduit 32. It

is to be-understood that the added heat taken on in the precooling step by the process gas coolant does not raise the temperature of the process gas coolant in the stream 34 over that required for further processing or other use.

When the refrigeration requirement drops into a period of minimum requirement, the process gas that is passing through the evaporator is cooled to a temperature below the temperature it obtains during the maximum requirement period due to the fact that the temperature of the refrigerant in the evaporator remains approximately constant as will be explained. Therefore,

the cooling supplied exceeds that required. This drop in temperature of the process gas is noticed by the heat sensitive element 56 as the gas flows through the conduit 18. -Any drop in temperature is relayed by the temperature sensitive element 56 through element 58 to the control means 60. Upon the process gas reaching a preset temperature, control meansfit) begins to open the outlet port 30. Accordingly, a portion of the cooled process gas is diverted through the conduit 36 to the heat exchanger 40. As the refrigeration requirement of the evaporator continues to drop, the outlet port is opened to a greater extent, allowing more of the cooled process gas to pass to the heat exchanger 40. This, of course, decreases the amount of cooled process gas that flows through the conduit 32 to the heat exchanger 12, thereby decreasing the amount of precooling of the stream in the line 10. Since the refrigeration requirement is now in a minimum requirement period, the refrigeration supplied by the refrigeration unit alone is more than adequate to handle the load and the precooling is not necessary.

Turning now to the refrigeration unit itself, the refrigerant passes through the compressor 42 at a relatively high temperature. It then moves to the condenser 46 by means of conduit 44 where it is condensed into a liquid. It then passes through conduit 48 into the accumulatorheat exchanger 40. Except in periods of minimum refrigeration requirement, the refrigerant would then pass to the expansion valve 52 by means of conduit 50 with no additional cooling of it in the vessel 49. In passing through the expansion valve 52, the refrigerant is subjected to a lower pressure, whereby it is allowed to expand or evaporate in the evaporator 16 and absorb heat from the process gas due to this vaporization.

During periods of minimum requirement, the rate of evaporation of the liquid refrigerant in the evaporator 16 is decreased due to the decrease in cooling required. This results in a rise in the level of liquid refrigerant in the evaporator 16 which is sensed by the level control 51, which in turn, actuates the expansion valve 52 to restrict the flow of refrigerant into the evaporator. The restricted flow of the refrigerant allows it to accumulate in the vessel 40.

The decrease of the amount of refrigerant going into the evaporator 16 does not alter the temperature therein due to the effect of the back pressure valve 53 and its control means 55. As the rate of evaporation decreases, the vapor pressure will also decrease. This will be sensed by control 55 which Will act-uate valve 53 to restrict the outflow of evaporated refrigerant from the evaporator, thereby maintaining the pressure in the evaporator 16 constant. The operation of controls 51 and 55 tend, therefore, to maintain a constant temperature within the evaporator, regardless of the load on the evaporator.

As mentioned previously, the vessel 40 functions not only as an accumulator, but also as a common heat exchanger. Accordingly, when the cooled process gas is allowed to pass through the heat exchanger, the refrigerant in the accumulator is cooled to a temperature below that at which it exits from the condenser. Thus, the operation of the process gas in heat-exchanger 40 supercools the refrigerant. This super-cooling continues during the entire portion of the cycle in which there is a minimum refrigeration requirement.

When the refrigeration requirement reaches its minimum level and starts its upswing toward the peak requirement, the temperature of the process gas leaving the evaporator starts to rise. This is picked up :by the heat responsive element 56, and accordingly, the control means operates to lessen the amount of gas that is allowed to flow out of port 30. As the requirement, and, in turn, the temperature of the gas leaving the evaporator 16, increases, the control means 69 closes the outlet port 30 a proportionate amount. Upon the refrigeration requirement entering a period of maximum requirement, the outlet port 30 is completely closed and all of the process gas moves through the heat exchanger 12, whereby the, precooling of the entering process gas is at its maximum level, thus taking away as great a portion of the load on the evaporator as possible. At this point in the process, no cooled process gas passes through the heat exchanger 40. By this time, however, the refrigerant that has accumulated in the vessel 40 has been supercooled to a temperature sufliciently low enough for it to meet the peak refrigeration requirement when supplemented by the normal output from the refrigeration unit. By reducing the temperature of the refrigerant to a level below that at which it is normally maintained by the operation of the refrigeration unit alone, additional cooling capacity is furnished by this lower temperature level which is in addition to the refrigeration provided by the continued operation of the refrigeration unit, sufficient to maintain proper coolingof the process gas during the maximum requirement periods even though the capacity of the refrigeration system by itself is inadequate for such purposes.

Stated another way, the cooling capacity of the refrigerant without the super-cooling is restricted normally to its latent heat capacity. Although this may not always be the situation, for purposes of explanation, it will suffice. Upon evaporating, therefore, each pound of the nonsuper-cooled refrigerant will absorb its latent heat of vaporization and no more. By super-cooling the refrigerant, however, a sensible heat capacity has been imparted to the refrigerant due to the difference in the lowered temperature of the refrigerant as compared to the temperature of the process gas that is to be cooled. In other words, heat will be absorbed by the refrigerant due to its lowered temperature, as well as its latent heat of vaporization which will be absorbed as it evaporates. The total cooling capacity of the refrigeration system 7 during periods of maximum requirement is, therefore, the

latent heat capacity of the refrigerant plus the sensible heat capacity of the refrigerant received during the preceding minimum requirement period.

By way of example, an actual application of the present invention produced the following results. It was found that in analyzing the process refrigeration requirements in the situation in question, a minimum refrigeration tonnage of 5.25 tons existed at the beginning of the cycle period. The refrigeration requirement then increased to a maximum or peak of 23.25 tons at approximately halfway through the cycle. The requirement then gradually descended to a level of approximately 5.7 tons at the end of the cycle. By the application of the present invention, a 12-ton refrigeration unit Was found to be adequate to carry the load due to the super-cooling and accumulation of the excessive refrigeration during the minimum load requirements. In spite of the additional cost brought about by the additional equipment necessary to carry out the present invention the overall cost was reduced approximately 25% over the cost of a larger unit which was capable of carrying the peak load requirement in a conventional manner.

Accordingly, it is seen that the present invention achieves the objectives set forth at the outset and provides a novel and reliable method of meeting cyclic refrigeration demands. These objects are achieved by utilization of a relatively inexpensive arrangement of equipment. Furthermore, the present invention eliminates a troublesome operating problem in that the inability of the compressor to achieve an excessively high degree of turndown is obviated. A refrigeration system has been described herein which is reliable in its performance due to its relative simplicity. The large initial cost of the oversized refrigeration unit necessary to meet the peak requirements in a conventional manner is done away with, and the savings more than offsets the additional cost necessary for the added equipment required by the present invention.

The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned as well as others adherent therein. While a presently preferred embodiment of the invention has been given for the purpose of disclosure, numerous changes in the detail of the construction and the combination, size, shape and arrangement of parts and uses may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

What is claimed is:

1. A system for cooling a substance wherein the cooling requirements are cyclical, having periods of maximum and minimum requirement, including a refrigeration unit including a chiller through which said substance travels to be cooled.

said unit containing a refrigerant and having sufficient capacity to cool said substance to the temperature desired during periods of minimum requirement, said capacity being insuflicient to cool said substance to the desired temperature during periods of maximum requirement, and

additional cooling means for utilizing, during minimum requirement periods, a portion of said substance after it leaves the chiller to super-cool a portion of the refrigerant, thereby providing sufiicient additional cooling capacity to supply the necessary refrigeration required during periods of maximum requirement.

2. The invention of claim 1 wherein,

said additional cooling means is partially comprised of heat exchanger means through which the refrigerant flows, and further including,

valve means for diverting a portion of said substance after it leaves the chiller to said heat exchanger means, said heat exchanger means being so constructed that the cooled substance is placed in heat exchange relationship with the refrigerant to cool the portion of the refrigerant in the heat exchanger.

3. The invention of claim 2 wherein the refrigerant evaporates in the chiller to at least partially cool the substance, the rate of evaporation varying directly with the cooling requirements, i

inlet control means for maintaining the level of the liquid refrigerant in the chiller substantially constant, and outlet control means for maintaining the pressure in the chiller substantially constant, by regulating the exit of the evaporated refrigerant from the chiller,

said inlet and outlet control means cooperating to provide uniform cooling of the substance throughout the cyclical cooling requirements.

4. The invention of claim 3 wherein,

said heat exchange means is partially comprised of an.

accumulator vessel which is in heat exchange relationship with said cooled substance passing through the heat exchanger, and wherein,

said inlet control means is partially comprised of a valve which may be opened and closed in varying degrees, and which is regulated by the control means,

said control means closing said valve in increasing amounts as the rate of evaporation decreases, thereby decreasing the amount of refrigerant flowing into the chiller, the refrigerant that is prevented from flowing into the chiller accumulating in the vessel Where it is cooled to said second temperature, said accumulated refrigerant being the supercooled refrigerant to be used during maximum requirement periods,

said control means opening said valve in increasing amounts to increase the flow of refrigerant into the chiller as the rate of evaporation increases.

5. The invention of claim 4 wherein the level of liquid refrigerant in the chiller fluctuates as the rate of evaporation varies, and

said inlet control means is partially comprised of:

liquid level monitoring means positioned in the chiller to drnonitor the level of liquid refrigerant therein, an

inlet regulating means operatively connected to said momtoring means and to said valve to maintain the liquid level substantially constant in the chiller, by opening and closing said valve as necessary to compensate for the increase or decrease of refrigerant evaporated, and

said outlet control means includes:

a second valve that may be opened and closed in varying degrees to regulate the exit of the evaporated refrigerant,

pressure sensitive means responsive to vapor pressure changes in the chiller,

outlet regulating means operatively connected to the second valve and the pressure sensitive means to maintain the vapor pressure in the chiller at a substantially constant level by opening and closing the valve in varying degrees to compensate for increases and decreases in the pressure resulting from an increased or decreased rate of evaporization,

said inlet and outlet means coacting to maintain the pressure and the temperature within the chiller at an essentially constant level.

6. The invention of claim 5 and being further defined as,

said means to divert the portion of the substance to the heat exchanger means being partially comprised of,

a valve, having a first outlet for normal flow of said substance and a second outlet in fluid communication with said heat exchanger means, said second outlet being normally closed,

said invention further including:

temperature responsive means to determine when said refrigeration requirements is in a maximum or a minimum requirement period, and

control means operatively connected to said temperature responsive means and to said valve for opening the second outlet as the refrigeration requirement of the substance enters a period of minimum requirement.

7. The invention of claim 6 wherein the temperature responsive means is further defined as including,

a temperature sensitive element located in operative relation to said substance after the substance has been cooled, whereby any change in temperature of the substance will be noticed by the heat sensitive element and relayed to said last mentioned control means.

8. A system of refrigeration for cooling a substance to a desired temperature having cyclical cooling requirements with maximum and minimum requirement periods including,

a refrigeration unit including,

a refrigerant circulating through said unit,

an evaporator which evaporates said refrigerant to cool said substance, the evaporation of said refrigerant being more than suflicient to cool the substance to the desired temperature during periods of minimum requirement but being insufficient to cool the substance to the desired temperature during maximum requirement periods,

first conduit means to feed the refrigerant into the evaporator, and

second conduit means to remove the evaporated refrigerant from said evaporator,

a first heat exchanger through which said first conduit means passes, said heat exchanger being partially comprised of an accumulator vessel,

an expansion valve in said first conduit means between the first heat exchanger and the evaporator for regulating the flow of the refrigerant into the evaporator,

liquid level control means including,

fioat means for monitoring the level of the unevaporated refrigerant in the evaporator, and

regulating means operatively connected to the expansion valve and to the float means for maintaining the unevaporated refrigerant level constant by opening and closing the valve in response to level changes indicated by the float means, said refrigerant accumulating in the heatexchanger-aocumulator when the expansion valve decreases the flow to the evaporator,

a second'valve in said second conduit means for regulating the fiow'of the evaporated refrigerant,

pressure sensitive means for monitoring the pressure of the evaporated refrigerant in the evaporator,

second regulating means for monitoring said pressure constant by opening and closing said valve in response to pressure changes indicated by the pressure sensitive means,

substance inlet conveying means for introducing the substance into the evaporator for the cooling thereof,

substance outlet conveying means for the removal of the substance from the evaporator,

a valve in said outlet conveying means including,

a first outlet port for the normal travel of the cooled substance coming from the evaporator,

a second outlet port communicating with the heatexchanger-accumulator,

control means responsive to the temperature of the cooled substance moving through said outlet conveying means for opening the second outlet port upon decreases in the temperature of the cooled substance and for closing the second port upon increases in the temperature of the cooled substances,

The heat-exchanger-accumulator being so constructed as to place the portion of the refrigerant moving through the heat-exchanger-accumulator and the refrigerant accumulated therein in heat exchange relation with the cooled substance passing through the second outlet port whereby this portion of the refrigerant is supercooled,

a precooling heat exchanger for. utilizing the cooled substance passing through the first outlet port to precool the substance prior to its introduction into the evaporator, said precooling heat exchanger being located in the inlet conveying means being in communication with the first outlet port.

9. In a system of refrigeration for cooling a substance, wherein the cooling requirements are cyclical having maximum and minimum requirement periods and having varying requirements within said periods, said system including a refrigeration unit containing a refrigerant, means to circulate said refrigerant to and from a chiller Where the cooling of said substance takes place, said refrigeration unit having an output capable of cooling said refrigerant to a first temperature which is more than sufficient to cool said substance to the desired temperature during periods of minimum refrigeration requirement, but said first temperature being insufficient for the chiller to cool the substance to said predetermined temperature during periods of maximum refrigeration requirement, the combination with,

additional cooling means for cooling a portion of the refrigerant to a second temperature which is lower than said first temperature by use of a portion of the cooling substance, said additional cooling means including,

vheat exchanger means through which the refrigerant passes, and

means to divert a portion of said substance after it leaves thechiller to said heat exchange means, said diverted portion being placed in heat exchange relationship with the refrigerant in the heat exchanger to cool said refrigerant to said lower temperature, and further including,

inlet valve control means for decreasing the flow of refrigerant to the chiller as the refrigeration requirement decreases and for increasing the flow of the refrigerant as the requirement increases,

said heat exchanger means being partially comprised of an accumulator vessel for accumulating the refrigerant when its flow to the chiller is decreased, said accumulated refrigerant being in heat exchange relation with the cooled substance as it passes through the heat exchanger means, thus cooling the accumulated refrigerant to said lower temperature,

the refrigerant being defined as being in liquid form as it enters the chiller, the chiller evaporating the refrigerant to cool the substance, the rate of evaporation increasing as the cooling requirement increases and decreases as the requirement decreases, a predetermined level of the refrigerant being maintaincd in the chiller, said inlet valve control means further including,

' a float resting on the liquid refrigerant in said chiller and being responsive to the changes in the level of said refrigerant, said inlet valve control means regulating the flow of refrigerant into the chiller in response to the liquid refrigerant level changes as indicated by said float, and further including,

.outlet control means for maintaining a constant vapor pressure in the chiller, said outlet control means regulating the amount of evaporated refrigerant removed from the chiller, whereby a substantially constant pressure is maintained, said outlet control means being defined as including,

pressure sensitive means responsive to changes in vapor pressure in the chiller,

a valve to control the flow of evaporated refrigerant from the chiller and means responsive to pressure changes indicated by the pressure sensitive means for opening and closing the valve, thereby maintaining the pressure in the chiller constant, and

control means operatively connected to said diverting means for preventing any of said cooled substance from flowing into the heat exchanger means during periods of maximum refrigeration requirement and for controlling the amount of cooled substance diverted during periods of minimum requirement,

a temperature responsive element disposed in the flow of said cooled substance after it leaves the chiller to pick up any change in temperature of said cooled substance resulting from variations in the refrigeration requirement,

a valve including,

an inlet port for receiving said cool substance,

at first outlet port for exit of said cooled substance,

and

a second outlet port in fluid communication with said heat exchange means, and

means in said valve operated by said control means for closing said second outlet port during periods of maximum requirement and for opening the second outlet port in varying degrees during periods of minimum requirement in response to the increases and decreases in substance temperature picked up by said temperature responsive element, whereby the amount of cooled substance flowing to the heat exchanger means as controlled.

10. The invention of claim 9 and further including,

a precooling heat exchanger for precooling the substance prior to its entering the chiller thereby taking a part of the load off of the chiller, said precooling heat exchanger utilizing the cooled substance flowing out of the first outlet port as its cooling medium, the amount of precooling varying 'with the amount of said cooled substance flowing through said precooling heat exchanger, whereupon the amount of precooling is at a maximum during periods of maximum refrigerat-ion requirement and varies in direct proportion to the refrigeration requirement during periods of minimum requirement, whereby the temperature of the substance entering the chiller will increase due to lack of precooling as the refrigeration requirement decreases, thus preventing a sharp drop in cooled substance temperature due to the excessive refrigeration capacity during periods of minimum requirement.

11. A method for cooling a substance, wherein the cooling requirements are cyclical, having periods of maximum and minimum refrigeration requirement, including the steps of,

utilizing a refrigeration unit which employs a refrigerant and which has a cooling capacity of less than that required to cool the substance as desired during periods of maximum requirement but in excess of that required to cool a substance as desired during periods of minimum requirement,

passing said substance through said refrigeration unit wherebyit is cooled as desired during periods of minimum requirement by the action of said unit alone,

utilizing a portion of said cooled substance to cool at least a portion of the refrigerant to a temperature -lower than the temperature induced by the refrigeration unit alone, and

utilizing as needed the additional cooling power of this lower refrigerant temperature to supplement the cooling capacity of the refrigeration unit during periods of maximum refrigeration requirement, whereby suliicient capacity to cool the substance to the desired temperature is provided during said maximum periods.

12. The invention of claim 11 wherein the refrigeration unit is partially comprised of an evaporator which evaporates the refrigerant as needed to cool the substance, the rate of evaporization varying with the refrigeration requirement, and including the steps of,

accumulating a portion of the refrigerant during low refrigeration requirement periods when the rate of evaponization is low, and cooling only this accumulated refrigerant to said lower temperature,

flowing said accumulated refrigerant to the evaporator as needed to cool the substance as desired.

13. The invention of claim 12 including the following steps:

monitoring the level of unevaporated refrigerant in the evaporator,

maintaining this level at a predetermined level by the introduction of refrigerant as needed, monitoring the pressure of the evaporated refrigerant in the evaporator, and

maintaining this pressure substantially constant by removing evaporated refrigerant upon increases in said pressure, whereby the maintenance of a substantially constant refrigerant level and pressure produces a substantially constant temperature in the evaporator.

14. The invention of claim 13 wherein the refrigeration uni-t is partially comprised of heat exchanger means to bring the refrigerant and the substance into heat exchange relationship whereby the substance is cooled as desired, said substance passing from the heat exchanger means after it is cooled, and further including the steps of,

diverting a po-rtion'of said cooled substance after it leaves the heat exchanger means, and employing said diverted portion to cool the accumulated refrigerant to said lower temperature.

15. The invention of claim 14 wherein said maximum periods of refrigeration requirement have a maximum requirement and said minimum period-shave a minimum requirement, and further including the steps of,

increasing the amount of substance diverted as the refrigeration requirement approaches the minimum requirement, and

decreasing said amount diverted as the refrigeration requirement moves away from the minimum require ment, none of said substance being diverted, however, when the refrigeration requirement is in a period of maximum requirement.

16. The invention of claim 14 and further including the steps of,

monitoring the temperature of said substance as it leaves the heat exchanger means, diverting a portion of said substance leaving the heat exchanger means upon any drop in the temperature of the substance leaving the heat exchanger means, increasing the amount of substance diverted upon subsequent drops in the monitored temperature, and decreasing the amount diverted upon any increase in the monitored temperature. 17. The invention of claim 16 and further including the step of,

preventing any of said substance from being diverted during periods of maximum refrigeration requirement. 18. The invention of claim 17 and further including the steps of,

precooling said substance as it approaches the heat exchanger means, utilizing previously cooled substance for said precooling 13 14 and wherein the diverting of a portion of said subtaking P1366 y during peri s of minim m restance as it leaves the heat exchanger means is 'q fu th d fi d References Cited diverting said portion away from said precool ing step 5 UNITED STATES PATENTS 2,763,132 9/1956 Jue 62-95 X LLOYD L. KING, Primary Examiner.

whereby the precooling of said substance approaching the heat exchanger means is decreased, the divert- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,374,642 March 26, 1968 Robert E. McMinn It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, lines 10 and 28 and column 10, line 46, "heat exchanger", each occurrence, should read heat exchanger means Column 8, line 25 and column 11, line 30, "exchange, each occurrence, should read exchanger Signed and sealed this 31st day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

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