US2957318A - Control for refrigerating system - Google Patents

Description

Oct. 25, 1960 w. L. MORRISON 001mm. FOR REFRIGERATING SYSTEM Filed June 13, 1956 4 4 4 4 a z M a J2 |)l I-IrI4fl 2 V 7 6 ,7 6 n. 2 H 2 2 r 2 W W V V 7 7 0 7 a V ,1 M V MM WVEVJ 7 3 V ,1 M J 3 3 a 2 n". M. 9 7 V a I a v MM 3 0 7 3 H v v M m 4 w 4 J a 9 I a t 2 3 3 w 9 u u m M T: $2 55 2 Pg;\ E UH 7 62 M x 3 in! i 7 INVENTOR. WILLARD LMORRISON BY PARKER 8. CARTER ATTORNEYS Unite States Patent C) CONTROL FOR REFRIGERATING SYSTEM Willard L. Morrison, Lake Forest, Iil., assignor, by mesne assignments, to Liquefreeze Company, Inc., New York, N.Y., a corporation of New York Filed June 13, 1956, Ser. No. 591,153

.5 Claims. (Cl. 62-196) My invention relates to method of operating and controlling a refrigerating system and is especially useful with a system wherein a large number of separate chill boxes, for. example, separate insulated truck bodies must be suppliedwithliquid nitrogen atapproximately atmospheric pressure as a coolant to chill the load already placed in the chill box or truck body. Perhaps only one truck body needs to receive the liquid coolant. At another time, perhaps all of them need to receive the liquid coolant simultaneously and at other times as material comes and goes and shipments have to be made, the number of chill boxes or truck bodies receiving the coolant will vary widely.

I propose to supply the liquid nitrogen coolantbya system where the liquid is discharged into the coldbox, comes into intimate contact with the material being chilled, is boiled or vaporized by the heat of such material and the resultant gas is returned to the system for reliquefaction with a minimum of temperature rise.

The liquefaction capacity of the system must be sufiicient to supply liquid at a suitable rate of flow to. the maximum number of truck bodies which will at any one time need simultaneous chilling, perhaps thirty of them. Change in the number of chill boxes requiring nitrogen may be almost instantaneous. An apparatus of the type well adapted to my purpose does not lend itself too easily to change in capacity, does not lend itself well to OE and on operation such as is characteristic of the household refrigerator or freezer.

My control'is therefore especially intended to'prevent changein the mechanical operation of the compressors which form a part of the liquefaction systemso that those compressors will run constantly, independent of the amount of liquid being usedand the amount of gas being returned for liquefaction.

I have illustrated my invention in a multi-stage compressor which receives and compresses the gas returned from the truck bodies where it was vaporized, builds the pressure up to the desired point. Then the gas under compression, being also cooled to a desired low point will be discharged through a Joule-Thomson VZIVB'IO a receiver which holds the liquid and from which the liquid is supplied to the cold boxes or truck bodies to be chilled.

As long as the liquid is discharged from the receiver for use as a coolant, the heat of the material being cooled will continue to vaporize the liquid at substantially a constant rate so there will be a constant uniform supply of gas to the compressor system to be compressed and reliquefied.

But when the flow of liquid from the receiver stops and liquid no longer reaches the cold box for vaporization, the supply of gas to the compressor ceases and I propose, therefore, automatically to bypass each stage of compression when the supply of gas falls below a predetermined point.

If, for example, I have five stages of compression each stage will receive gas at relatively low pressure, will compress and heat it. The heat of compression will be removed and the compressed gas from the first stage will be discharged to the intake side of the second stage for another stage of compression.

However, when the supply of gas stops, I propose to short circuit each stage of compression separately so that the exhaust from each stage will return to the intake side thereof. Under these circumstances, the machinery keeps on operating but the only work done will be represented by mechanical friction and the friction of gas flow from exhaust back to intake. No work of compression will be done on the gas. This will continue until such time as supply of gas for compression and reliquefaction is resumed.

The system to which my invention is applied, therefore, includes multi-stage compression, one or more cooling stations where the compressed gas is cooled by any suitable heat exchange means, a reservoir into which the cooled compressed gas is discharged through a Joule- Thomson valve to liquefy at least part of the gas and maintain a supplyof liquid nitrogen available as a coolant anda cold box or boxes where liquid nitrogen from the liquid supply reservoir is brought into direct contact with the material to be chilled so that that material may furnish the heat to vaporize the gas, which gas is then returned'to the intake side ofthe' multi-stage compression apparatus.

My invention is illustrated diagrammatically in the accompanying flow sheet wherein like parts are indicated by like characters throughout the specification and drawing.

1 indicates a cold box or cooling station adapted to be connected or disconnected from the system. I have shown a plurality of them and there may be one or more. 2 indicates a liquid supply duct controlled by a valve 3 through which coolant, for example, liquid nitrogen is supplied to the box 1. The duct 2 is one of the branches of a manifold 4 which receives liquid nitrogen through a duct 5, from a liquid receiver 6. Leading from each cold box is a gas discharge duct 7 which leads to a gas discharge manifold 8. 9 is a diaphragm controlled electric switch, there being one connected to each discharge branch 7. Each switch 9 is electrically connected to the liquid control valve 3 so that when ever the pressure of the gas evolved in the box it exceeds a predetermined point, the valve 3 will shut off the flow of liquid, thus preventing the build up of excess pressure in the cold box. Each cold box may be connected or disconnected from the system by connection or disconnection of the ducts 2 and 7 associated therewith. The manually operated valves 10 and 11 will close the ducts 2 and 7 associated with each separate box or truck body when it is to be disconnected, thus making it possible to separate any of the boxes from the system without interfering with the refrigeration supply to the other boxes.

12 indicates a duct leading from the manifold 8 to a heat exchange passage 13 immersed in the liquid 14 in of compression. may direct the exhaust from the cylinder back to the the receiver 16 and serving as a superheat suppressor for the gas. 17 is a duct leading from the heat exchanger 13 to heat exchange element 18 in a heat exchanger 19. 20 is a duct leading from the heat exchange element 18 to heat exchange element 21 in the heat exchanger 22. 23 is a duct leading from 21 to the intake side of the compressor system.

I have for simplicity illustrated the compressor system diagrammatically by five identical cylinders each with a piston and ducts so that=the exhaust from each cylinder normally leads to the intake side of the next stage Similar valves, one for each cylinder,

intake side thereof instead of permitting it to pass on to the next stage. All the valves are simultaneously and uniformly actuated so that the gas always goes through all the stages of compression or thedischarge from each stage is by passed and returned to the intake side of that stage.

Identical figures are appliedto each stage. 24 is a compressor cylinder and piston. 25 is an exhaust duct leading from 24. 26 is an after cooler to remove heat of compression, 27 a supply duct leading to each stage of compression, 28 a two way valve, one foreach stage of compression which in one position directs gas from 25 through 26 to the next stage of compression but in another position directs gas from 25 back to 27 of the same stage through duct 29, when it is desired to by pass each stage of compression.

Motor 30 by drive member 31 simultaneously positions all valves.. Diaphragm switch 32 responsive to pres sure in duct 23 controls motor 30 to direct gas through the stages of compression when pressure in 23 is up and to by pass gas in each stage when gas supply in 23 fails. If, for example, a single box is to be cooled, the

valves 10 and 11 controlling supply to and discharge from that box will be open. All the other valves 10 and 11 in the system will be closed and the entire flow of liquid from the source of supply and gas return to the reliquefier will be associated with that single box. other boxes are also to be cooled at the same time, when the connections have been completed, the valves 10 and 11 associated with them will be open and flow will normally be generally uniform, subject only to the control of valve 3 responsive to excess pressure developed in any box. If it is desired to appreciably vary the relative supply of liquid to any box or boxes, one or more of the valves 10 may be manipulated to change the supply of liquid to the particular box or boxes in question. Under ordinary circumstances no adjustment of the valve 11 will be needed for this purpose. If there is differential adjustment of any one or more of the valves 10, that will result in a variation in the amount of liquid fed to the box in question and such variation will automatical- 'ly result in a variation in the gas discharged but this liquid discharged to the boxes and gas returned from the boxes to reliquefaction because it is important that the compression, liquefaction cycle be continuous, uninterrupted and substantially unvaried.

33 is a gas discharge duct leading from the last stage of compression through an oil separator 33a to heat exchanger 22. 34 leads from heat exchanger 22 to heat exchanger 35. Duct 36 leads from heat exchanger 35 to heat exchanger 19 and duct 37 leads from 19 to discharge through Joule-Thomson expansion valve 38 to receiver 6 so that some of the high pressure cold gas liquefies to continuously replenish and replace the liquid drawn off through duct 5.

In heat exchangers 19 and 22 the high pressure gas is cooled by heat exchange with the gas on its way from' the cold box or boxes to compression. In heat exchanger 35 the gas is cooled by an outside coolant from any suitable refrigeration source which enters through ducts 39, heat exchange element 40 and returns through duct 41, the details of the refrigeration means forming no part of the invention and not here illustrated.

The expansion through the Joule-Thomson valve 38 will not result in liquefying all the gas. The nitrogen not liquefied accumulates in the gas dome 42 above the liquid 14 and is discharged through a duct 43 controlled by a pressure relief valve 44 to mix with the gas traveling from the cold box in duct 17 on its way to compression. Some of the gas in duct 36 after having left heat exchanger 35 is conducted through gas duct 45 to expansion engine 46 where it does work and loses heat, thence to oil separator 47 through duct 48 controlled by check valve 49 to join with the gas in heat exchange element 18 on its way to the compressor.

Check valves 44 and 49 are set to prevent backward flow of the gas but open to permit flow of gas toward the compressor.

Thus whenever discharge of liquid from the receiver to the cooling station or stations stops, boiling of liquid and evolution of gas stops so no gas is available for compression. Under ordinary circumstances that will result in an immediate by passing or idling of each stage of compression while the machinery still runs. However, since we are dealing with a very cold material and since no insulation is one hundred percent perfect, it can happen that inflow of heat will vaporize enough of the liquid in the receiver 6 to raise the pressure in duct 23 to a point sufiicient to cause the valves 28 to again connect the various stages of compression. Under these circumstances, the compressor will operate and do useful work until the pressure again drops for lack of gas when the compressors will again do useless Work until liquid is actually withdrawn from the receiver to be used as a coolant.

Being designed for a maximum hourly capacity, the compressor cooler expansion system, when operating will produce the designed quantity of liquid nitrogen and as long as that quantity of liquid nitrogen is being used as a coolant, operation continues. The arrangement is intended to take care of a multiplicity of cold boxes or truck bodies or cooling stations. If only one is active, either the machine must stop, its capacity must change or the entire supply must be used at one station.

Experience has taught that'of the three alternatives the last is preferable. That is why it but a single cold box is on the line, valves 10 and 11 will be adjusted to permit the entire supply of liquid to enter the single box and the entire supply of gas will be generated in it and operation of the compressor and liquefaction will not be disturbed.

I have illustrated my invention with manifolds limited to four chill boxes. There might obviously be many more. Each box is connected by a detachable conduit to the liquid supply manifold 4 to the gas return or discharge manifold 8 and each of those conduits may be closed by the liquid valve 10 and the gas valve 11 so that when any box or boxes are disconnected, operation with respect to the remainder may continue.

Normally each valve 10 will be wide o'pen and the supply of liquid will be distributed or proportioned by the manifold to the various boxes. No adjustment between open and shut of the gas valve 11 is necessary because there will. always be enough gas boiled off from the liquid to produce a continuous flow for return of gas. If it is desired to vary the relative amounts of liquid supplied to the various boxes, that adjustment may be made with the valves 10 but does not need to be reflected in the valves 11. The valve 3 controlled in response to the pressure of the box has for its sole purpo'se to limit liquid flow to prevent the generation of excessive pressure in any box.

If it should happen that the entire supply of liquid supplied to one of the boxes would be vaporized rapidly enough to increase pressure in the box to the danger point, then as above indicated,the valve 3 would automatica lly shut ofi the .flowuntil thepressure iinlthez box had dropped to thepredetermined; safety point. This would not result in afailureof the supply of gas, .to the compressor because ifthe pressure in the boxwastoo high, that would .be becausethere was too much'gas and the gas would flow out under pressure, continuing supply to the compressor until the pressurein the boxdropped to the safety point,.at whichliquid would agaimflow. During such time theamount of liquid'in the-reservoir 6 would be increased becauseliquefaction would .be-continuing while. no dischargeitookplac'e and that; is the reason why it is important to have a substantial reservoir of the liquid to take care of such or any other variations.

I have illustrated my invention by reference to a Joule-Thomson expansion valve and by reference to nitrogen, by a diagrammatic illustration of a series of reciprocating compressors and other mechanical details which are shown most diagrammatically.

Other cold boiling liquids could be used as coolants. Air, oxygen, helium or perhaps other gases which can be safely used and handled and which can be brought into contact with foodstuffs without deleterious effect thereon may be used as a substitute for nitrogen but from my point of view, nitrogen is the preferable cold boiling liquid and I prefer to do the cooling at substantially atmospheric pressure. If the pressure in the cooled boxes or truck bodies for example were below atmospheric, there would be the danger that warm moisture laden atmospheric air might leak into the system, thus causing excessive heat losses and prematurely contaminating the refrigerant. On the other hand if the pressure in the cooling boxes were substantially above atmospheric the boxes would have to be designed :and built at substantially increased expense for construction, maintenance and shipment so as to carry excessive pressure.

Therefore, I prefer to build the boxes, designing them from a point of view of structural strength without reference to gas pressure either inward or outward. As a matter of fact pressure in the boxes might be in the order of a few inches of water per square foot so that it is at least very slightly above atmospheric and thus able to prevent entrance of warm ambient air.

Other means than the Joule-Thomson valve might be used to liquefy some or even all of the compressed gas. In either event, an important thing is that the various stages of compression desirable to build the pressure up from atmospheric to a point at which satisfactory liquefaction may occur should during the time that the liquid is not being discharged as a coolant and so no gas is available for compression, be able to operate, remain in operation and be ready to instantly resume the sup ply of gas under pressure when cold gas from the refrigeration stations is received. Thus when the various by-pass valves are moved to the position to conduct gas from one stage to another, each stage at that instant will be found to be handling gas at or substantially at the desired pressure for that stage and gas flow under pressure can commence almost if not actually instantaneously.

Since there is always likely to be a certain measure of loss of nitrogen from the system, the valve and duct associated or leading to the lower part of the receiver 6 is provided so that make up nitrogen may be added when needed.

I claim:

1. A gas liquefaction system including a compressor, a Joule-Thomson expander valve, a liquid gas receiver adapted to receive liquefied gas from the expander, a circuit including them, a plurality of chilling stations adapted to be selectively connected and disconnected in the circuit, to receive liquid from the receiver and return resultant gas to the compressor, means for maintaining the compressor in continuous uniform mechanical operation said means comprising means operative in response to failure -of -gassuppl-y to causethe exhaustfrorn the compressor to return to the intake side thereof, means for distributing and proportioning the entire'liquid discharge from the-receiver to any selected number of chilling stations and means for returning the resultant gas from all the chilling stations receiving the liquid to the compressor.

2. A refrigeration system, including a reservoir adapted to contain at all times a substantial quantity of cold boiling liquid such asnitrogen, meansincludingajloule- Thomson expander valve for reliquefying gaseo'us nitrogen and supplying it to the reservoir, a supply mani fold adapted to receive liquid from the reservoir, a discharge manifold adapted to conduct gas to the liquefying means, a plurality of cooling chambers, each separately and removably connected in parallel between the manifolds, a valve controlling each connection between each chamber and each manifold, the valves being adapted to close the connections to the manifolds when the chamber associated with the valves is disconnected, and means separately associated with each chamber adapted to stop liquid supply when the pressure in the chamber exceeds a predetermined point.

3. A refrigeration system, including a reservoir adapted to contain at all times a substantial quantity of cold boiling liquid such as nitrogen, means including a Joule- Thomson expander valve for reliquefying gaseous nitrogen and supplying it to the reservoir, a supply manifold adapted to receive liquid from the reservoir, a discharge manifold adapted to conduct gas to the liquefying means, a cooling chamber removably connected to both manifolds, valves adapted to close said connections when the chamber is removed and a separate valve adapted to prevent flow of liquid to the chamber when the pressure therein exceeds a predetermined point.

4. In a refrigeration system, a compressor, a reservoir adapted to contain a cold boiling liquid such as nitrogen, connections between the compressor and the reservoir including heat exchangers and a Joule-Thomson expander valve whereby compressed cooled gas is expanded into the reservoir with resultant liquefaction of some of the gas, a cooling chamber adapted to receive liquid from the reservoir and be vaporized by heat exchange therein, means for conducting the resultant gas back to the compressor for recycling and reliquefaction, said means including a coil in heat exchange relationship with the liquid in the reservoir, means for mixing the gas from the reservoir which failed to be liquefield with the gas from the cooling chamber and returning them together to the compressor, the gas on its way to the compressor being in heat exchange relationship with the compressed gas.

5. In a refrigeration system, a compressor, a reservoir adapted to contain a cold boiling liquid such as nitrogen, connections between the compressor and the reservoir including heat exchangers and an expander whereby compressed cooled gas is expanded into the reservoir with resultant liquefaction of some of the gas, a cooling chamber adapted to receive liquid from the reservoir and be vaporized by heat exchange therein, means for conducting the resultant gas back to the compressor for recycling and reliquefaction, said means including a coil in heat exchange relationship with the liquid in the reservoir, means for mixing the gas from the reservoir which failed to be liquefield with the gas from the cooling chamber and returning them together to the compressor, the gas on its way to the compressor being in heat exchange relationship with the compressed gas, the gas on its way from the compressor to the liquefier being in heat exchange relationship with the outside source of coolant and means for expanding some of the gas and causing it to do work for further cooling before it is compressed.

(References on following page) I Refer ences Cited in the file of this patent: UNITED STATES PATENTS Williams Jan. 21, 1913 Wolf Aug. 26, 1919 5 Jones Aug. 23, 1932 Sullivan Ian. 10, 1933 Zieber May 29, 1934 Edwards Jan. 29,1935 Gilmore Oct. 8, 193510 Frankl Feb. 11, 1936 8 Kan Aug. 25,1936 Kramer Jan. 14, 1941 Hanson June 16, 1942 Newton Mar. 9, 1943 Waterfill Nov. 21, .1944 Dodson -Jan. 11, 1949 Patterson Apr. 4, 1950 Van Nuys ..,Feb. 12,1952 Di ckieson Feb. 14, 1956 Gerteis July 24, 1956 Stiles Nov. 6, 1956

Images