US3494145A

US3494145A - Integral turbo compressor-expander system for refrigeration

Info

Publication number: US3494145A
Application number: US735720A
Authority: US
Inventors: Hunt Davis; Malcolm L Land
Original assignee: Worthington Corp
Current assignee: Edison International Inc
Priority date: 1968-06-10
Filing date: 1968-06-10
Publication date: 1970-02-10
Anticipated expiration: 1987-02-10

Description

Feb. 10; 1970 H. DAVIS ETAL INTEGRAL TURBO C'OMPRESSOR-EXPANDER SYSTEM FOR REFRIGERATION Filed June 1;), 1968 2 Shets-Sheet l n mrea some: UU (s2) 27 25 22 F 37 m i INYGRCOOLER 3| 35 2 3O 23 FA z Z0 M! COMP\RESSION P flt DRIVE cvcu-z MEANS \3 23 V (I0) 4 m V L 1 1 4; W q; g" k A t W s AFTER- 4 I w f COOLER 2 ,55' INTERCOOLER (so) 7 d l (54-) 39 sq; J Q 57 5 1 45 L! J 40 f? f J HEATZELSESZER gi 1 1 Q44) 47 ficgd 1 REFZ ISEEEV I'ION fig LOAD HUNT DAVIS MALCOM L. LAND F] G I INVENTORS $MMM Feb. 10 1970 RO S m1. 4 3,494,145

INTEGRAL TURBO COMPRESSOR-EXPANDER SYSTEM FOR REFRIGERATION Filed June 10, 1968 2 Sheets-Sheet 2 EX A COMPRESSION 7 1 WITH WITH I'M-ER- (l-x FLOW RE-HEAT a coOLlNG 40o C b /1 um-r 4: w\ U 1 z t g 4 m 4 4 Z 8 III (I D.

ENTHALPY H F I G. 2

HUNT DAVIS MALCOM L. LAND INVENTORS BY BMJMM United States Patent 3,494,145 INTEGRAL TURBO COMPRESSOR-EXPANDER SYSTEM FOR REFRIGERATION Hunt Davis and Malcolm L. Land, Williamsville, N. assignors to Worthington Corporation, Harrison, N.J., a corporation of Delaware Filed June 10, 1968, Ser. No. 735,720 Int. Cl. F25b 9/00, 11/00 U.S. Cl. 62-402 14 Claims ABSTRACT OF THE DISCLOSURE A closed fluid loop system wherein fluid, to be used as a refrigerant, is alternately compressed and cooled in a multi-stage compressor system having intercoolers between its stages. A portion of the fluid after being alternately compressed and cooled is used as a heat transfer media in a series of heat exchangers with the balance of the fluid being alternately expanded and heated in a multi-stage expansion machine having reheat heat exchangers between its stages and the discharge of its last stage serially connected to the series of heat exchangers. The compressor and expansion machines are arranged to permit power recovery by the compressor from the expansion means.

Background of the invention This invention relates generally to compressor-expander systems and more particularly to such systems which are closed loops or circuits to condition fluid coolants to be used subsequently as a refrigerant.

While many and varied systems have been proposed and used to condition fluid coolants, each operating with a degree of efficiency, none of such systems provides the optimum degree of efficiency and reliability desired for refrigeration as is required for liquification of gases. It is acknowledged that rotating compressor and expander machinery has been extensively incorporated into fluid handling systems and that closed loops or circuits are not new in cooling systems. However, none of the systems heretofore devised combine the equipment and fluid concepts in the novel manner according to the present invention.

Summary of the invention.

The present invention contemplates a closed fluid loop system for conditioning a fluid coolant to be used subsequently to liquify gases by refrigeration, including multistage compressor means with intercoolers between the stages for alternately compressing and cooling the fluid coolant thereby cumulatively increasing the fluid coolant pressure while maintaining its temperature between predetermined minimum and maximum limits. After the last stage of compression the fluid coolant is cooled in an aftercooler and then passes to a first of a series of heat exchangers where it is further cooled.

A portion of the compressed fluid coolant after leaving the first heat exchanger enters a second heat exchanger where it is further cooled and then passes through an expansion device where it is reduced in pressure before entering a third heat exchanger where it is in non-contacting heat transfer relationship with and absorbs heat from the gas to be liquified.

That portion of the compressed fluid coolant after leaving the first heat exchanger which does not pass through the second heat exchanger is bypassed to the first stage of a multi-stage expander means having reheat heat exchangers between its stages for alternately expanding and heating the compressed fluid to cumulatively decrease the pressure of the coolant fluid while main- 3,494,145 Patented Feb. 10, 1970 ICC taining its temperature within predetermined minimum and maximum limits.

The reheat between expander stages and after the last stage of expansion takes place within the second of the series of heat exchangers mentioned above where the expanded coolant fluid absorbs heat from the compressed coolant fluid.

After the coolant fluid from the last stage of expansion leaves this second heat exchanger it flows through the first of the series of heat exchangers mentioned above and is in non-contacting heat transfer relationship with and absorbs heat from the compressed coolant fluid flowing therethrough as described above.

Similarly, the compressed coolant fluid after flowing through the third heat exchanger where it has absorbed heat from and liquified the gas, flows through the second of the series of heat exchangers in the same flow path as the coolant fluid from the last stage of expansion and then to the first heat exchanger where, joined with the flow of coolant fluid from the last expansion stage reheat, it absorbs heat from the compressed coolant fluid flowing therethrough.

To complete the closed loop, the coolant fluid after leaving the first heat exchanger where it has absorbed heat from the compressed coolant fluid, enters the first compressor stage for recirculation through the cycle.

A drive means having a double extended shaft is provided to effect eflicient power recovery within the system. One of the shaft extensions is drivingly connected to the compressor means and the other shaft extension is drivingly connected to the expander means such that the power recovered in the expander due to the expansion of the coolant fluid is used to drive the compressor.

Accordingly, an object of the present invention is to provide a closed loop or circuit with rotating machines for efficiently and reliably conditioning a fluid coolant.

Another object of the present invention is to provide the foregoing system which maintains the fluid coolant at instantaneous optimum conditions throughout its complete cycle of operation; specifically approaching isothermal expansion and compression processes, which minimize external power requirements.

Further objects and advantages of the invention will become apparent from a study of the following specification taken in conjunction with the accompanying drawings wherein,

In the drawings:

FIGURE 1 is a diagrammatic illustration of a system made in accordance with the present invention, and

FIGURE 2 is an illustrative pressure-enthalpy diagram for the system of FIGURE 1.

Referring now to the drawings and particularly to FIG- URE 1, a system in accordance with the present invention for conditioning a fluid coolant by controlled pressure and temperature changes is generally comprised of a drive or power means 10 which is drivingly connected to a compressor means 20 and an expander means 30 each with interstage heat transfer means providing multi-stage compression and expansion cycles, respectively. In addition to inter-stage heat transfer means, a primary heat transfer means 40 is provided for inter-cycle heat transfer and to provide a cold box or process load heat exchanger for refrigeration as may be used to liquify gases.

Rotating mechanical equipment Considering first the mechanical aspects of the system, the motor or drive means 10 is of a through shaft type construction providing shafts 11 and 12 which extend therefrom along the common center of rotation and in opposite directions from one another. A pair of

drive gears

13 and 14 are mounted on the ends of the shaft 11 and 12, respectively. To facilitate connection of the drive means 10, at least one of the shafts, in this instance shaft 11, may be divided and joined together by a drive coupling in accordance with any of the present day accepted machine assembly practices.

Rotating or turbo-machinery preferably is provided for the compression and expansion cycles, in each instance having more than one stage as may be desired or required by the system and its environment. One example of the general type of equipment suitable for embodiment herein is disclosed by the US. Patent 3,001,692 granted to O. Schierl wherein four rotating stages are mechanically connected in pairs on opposite sides of a drive center and are sequentially flow connected with inter-stage coolers or heat exchangers.

As is diagrammatically shown in FIGURE 1, the compressor means is provided with four

stages

21, 22, 23 and 24 mechanically connected in pairs by two shafts and 26 and has

intercoolers

52, 53 and 54 respectively between

stages

21 and 22, 22 and 23 and 23 and 24, and an aftercooler 50 at the discharge of the last compressor stage 24 all for purposes to be further described below.

The

shafts

25 and 26 are provided with driven gears or

pinions

27 and 28, respectively, which are in mesh with the drive gear 13. While the gear train of the machine 20 is herein disclosed as comprising the drive gear 13 and the driven

gears

27 and 28, this is for facility of description and no limitation is intended thereby. It should be understood that a more sophisticated gear train may be required for the motor means 10 to drive the compressor means 20 at its optimum speed. Although gear trains provide reliable and positive rotating drive connections, other types of drives well known in the art may be used in lieu thereof.

The expander means 30 similarly is provided with four

stages

31, 32, 33 and 34 mechanically connected in pairs by two shafts and 36 and has

reheat coils

56, 57 and 58 respectively between

stages

31 and 32, 32 and 33, and 33 and 34, and a reheat coil 46 at the discharge of the last expansion stage 34 all for purposes to be further described below.

The

shafts

35 and 36 are provided with gears or

pinions

37 and 38, respectively, which are in mesh with the gear 14. As before, the present three member gear train is to facilitate description herein and is not to be construed as defining any limitation of the present invention. The three member gear trains comprised of

gears

13, 27 and 28, and 14, 37 and 38, respectively, provide a positive rotating drive connection through the drive means 10 between the compressor and expander means 20 and 30 resulting in a driving-driven machine assembly which is unitary in character with multiple stages thereof all rotating at substantially optimum speeds during operation.

The starting torque or load on the drive means 10 will be initially high and will gradually reduce during run-up to a normal operating torque or load during normal operation. The starting and run-up torque can be reduced by absence of compression and expansion, and the various stages may be vented (not shown) for this purpose. After the vents are closed for operation, the additional torque output required from the driving means 10 will be determined primarily by the compression delivered by the compressor means 20 and the character of the fluid being compressed.

The expander means 30 acts as a fluid motor during operation and normally less or, in some instances, relatively little torque output will be required from the driving means 10 because forces of expansion in the

expander stages

31, 32, 33 and 34 will exert a driving torque on the

shafts

35 and 36, as will be familiar to those skilled in this art, and therefore, the specific starting torque, runup torque and operating torque required from the motor or drive means 10 will be determined by the design of the equipment, the amounts of compression and expansion delivered, and the nature of the fluid being conditioned. It should be realized, however, that by interlocking the expander means 30 to the drive means 10 and the compressor means 20 will result in a primary or input power savings.

Heat transfer equipment The primary heat transfer means generally designated at 40 consists of three separate heat exchange means serially connected and designated as preheat heat exchanger 41 reheat heat exchanger 44 and cold box heat exchanger 47, each having multiple non-contacting flow paths for fluid coolant to be further described below.

As previously mentioned in regard to compressor means 20 under Rotating Mechanical Equipment an intercooler 52 is provided between and is operatively associated with

stages

21 and 22 for receiving compressed fluid coolant from compressor stage 21 and cooling it at constant pressure before delivery to the compressor stage 22 where it is further compressed. Similarly, an intercooler 53 is provided between and is operatively associated with

stages

22 and 23 for receiving compressed fluid coolant from compressor stage 22 and cooling it at constant pressure before delivery to compressor stage 23 Where it is again compressed to a higher pressure. Further, an intercooler 54 is provided between and is operatively associated with

stages

23 and 24 for receiving compressed fluid coolant from compressor stage 23 and cooling it at constant pressure before delivery to the compressor stage 24 where it is once again compressed to an even higher pressure. In all the above mentioned intercoolers, 52, 53 and 54 the coolant fluid is in a non-contacting heat transfer relationship with and is cooled by an independent heat transfer medium flowing therethrough as will be familiar to those skilled in this art and will need no further explanation.

After being compressed in compressor stage 24, the high pressure fluid coolant flows through an aftercooler 50 operatively associated therewith as previously mentioned and is thereby cooled at constant pressure by being in a non-contacting heat transfer relationship with a heat transfer media flowing therethrough.

The high pressure coolant fluid next flows through coil 42, serially connected to aftercooler 50, and disposed within preheat heat exchanger 41, where it is in a noncontacting heat transfer relationship with and is cooled at a constant pressure by coolant fluid flowing in a coil 43 as will be further described.

After being cooled as constant pressure in preheat heat exchanger 41 a portion of the high pressure coolant fluid flows through a coil 45, serially connected to coil 42, and disposed within preheat heat exchanger 44, where it is in a non-contacting heat transfer relationship with and is further cooled at constant pressure by coolant fluid flowing in

coils

46, 56, 57 and 58 which function as reheat coils between the expansion stages and after the last stage of expansion as previously mentioned.

That portion of the high pressure coolant fluid which has now been cooled in reheat heat exchanger 44 is expanded and thereby cooled in a throttling valve 51 having an inlet operatively associated with coil and an outlet operatively associated with a coil 48 disposed within cold box heat exchanger 47 wherein the now expanded, low temperature coolant fluid is in a non-contacting heat transfer relationship with and cools a process load, such as a gas to be be liquified, circulating therethrough in a coil 49.

After absorbing heat from the process load in heat exchanger 47 and therefore experiencing a constant pressure temperature rise, the coolant fluid in coil 48 passes to coil 46, serially connected thereto and disposed within reheat heat exchanger 44, where it is in a non-contacting heat transfer relationship with and absorbs heat at constant pressure from coil 45 disposed therein as previously mentioned.

Finally, after flowing through coil 46, the coolant fluid flows through coil 43 serially connected thereto and disposed within preheat heat exchanger 41 where it is in a non-contacting heat transfer relationship with and absorbs heat at a constant pressure from high pressure fluid coolant in coil 42 disposed therein as mentioned above.

Having completed the cycle of compression, cooling, expansion and cooling, and reheat, the coolant fluid flows through a conduit 29 operatively associated at one end with coil 43 and at the other end to compressor stage 21 where the coolant fluid is again compressed and repeats the cycle.

As mentioned above, only a portion of the compressed fluid coolant after being cooled in heat exchanger 41 enters reheat heat exchanger 44 for further cooling. The balance of the fluid is bypassed to a conduit 39 operatively associated with coil 42 into the inlet of the first expansion stage 31 of expander means 30 where it is expanded to a lower pressure and temperature.

A reheat coil 56, disposed within reheat heat exchanger 44, is serially connected to the discharge of the expansion stage 31 for receiving the expanded fluid coolant and absorbing heat from the fluid coolant in coil 45 in non-contacting heat transfer relationship therewith thus increasing the temperature of the expanded coolant fluid at constant pressure.

Similarly, the inlet of the second expansion stage 32 is serially connected to coil 56 for receiving the fluid coolant, after reheat in coil 56 and expanding it to a still lower pressure before it passes to a second reheat coil 57 operatively associated therewith and also disposed within reheat heat exchanger 44.

As with coil 56, coil 57 is in a non-contacting heat transfer relationship with and receives heat from fluid coolant in coil 45 thus increasing the temperature of the expanded fluid coolant at constant pressure before it passes to the inlet of the third expansion stage 33 serially connected to coil 57 where the fluid coolant is again expanded to a lower pressure.

As with expansion stages 31 and 32, the discharge of expansion stage 33 is serially connected to a reheat coil, in this case coil 58, disposed within reheat heat exchanger 44 where it is in a non-contacting heat transfer relationship with and absorbs heat at constant pressure from the high pressure fluid coolant in coil 45.

To complete the expansion stage of the cycle, a fourth expansion stage 34 is serially connected to and receives fluid coolant from coil 58 for again expanding the fluid coolant to a still lower pressure after reheat in coil 58.

After the fluid coolant is expanded in expansion stage 34 it passes through a conduit 55 operatively associated at one end with the discharge of expansion stage 34 and at the other end with coil 46 disposed Within reheat heat exchanger 44 where this flow is joined by the discharge flow coil 48 as previously mentioned.

Thus, the combined flow in coil 46 is in non-contacting heat transfer relationship with and absorbs heat at a constant pressure from the compressed fluid coolant flowing in coil 45 before passing to coil 43 serially connected thereto and which as already mentioned is disposed within preheat heat exchanger 41 where the coolant fluid is in a non-contacting heat transfer relationship with and absorbs heat at constant pressure from the compressed coolant fluid flowing in coil 42 before it enters the first compression stage for recycling.

The changes in pressure and temperature that take place in the compression and expansion stages and the constant pressure heat transfer process occurring within the several heat exchangers as disclosed above are clearly shown by reference to a pressure-enthalpy diagram as will now be discussed.

Operation FIGURE 2 is a pressure-enthalpy diagram for an illustrative system such as shown in FIGURE 1, made in accordance with the present invention and which arbitrarily operates within a pressure range of from 50 to 400 pounds per square inch. Predetermined maximum and minimum temperatures of the fluid coolant being conditioned are shown by temperature curves T1 and T2, respectively, for the compression cycle and by temperature curves T3 and T4, respectively, for the expansion cycle. The inlet and outlet pressure and temperature conditions of the fluid coolant with respect to each of the system components are indicated by letters a-u and the locations in the system are similarly referenced in FIGURE 1.

As compressed fluid coolant flows through the coil 42 its heat loss Q, indicated by line (1-1), is absorbed, as indicated by line k-m, by the return flow of fluid coolant through the coil 43. At this point, flow from the coil 42 is apportioned wherein flow X is delivered to the expander means 30 and flow (1-X) is delivered to the reheat heat exchanger 44. As the fluid coolant is conditioned in the expansion cycle, a pressure drop will be realized at each stage which is indicated by lines bd, e-f, gh and i respectively, and is cumulative. Thus, the pressure from the inlet to the discharge of the expander means 30, drops from 400 to 50 pounds per square inch. Each drop in pressure is attended by a temperature drop but, unlike the pressure losses, these heat losses are not cumulative because of the inter-stage reheat as indicated by lines d-e, f-g and h-i as the fluid coolant flows through the

respective coils

56, 57 and 58. Discharge flow X from the expander means 30 has now reached the location in the system to be re-united with working flow (1X).

The working flow of fluid coolant through the coil 45 realizes a further heat loss Q, indicated by line b-c, which provides the reheat for the expansion cycle and is partially absorbed, as indicated by line 'k, by the return flow of fluid coolant through the coil 46. Discharging flow from the coil 45 passing through the throttling valve 51 realizes a sharp drop in pressure, indicated by line c-l, and the working flow (l-X) of fluid coolant is at its minimum pressure and temperature as it approaches the process load of cold box heat exchanger 47.

As the gas to be liquified by refrigeration flows through coil 49 it realizes a heat loss Q which is absorbed, as indicated by line l-- by the working flow (1-X) of fluid coolant through the coil 48. The discharging flow (l-X) now re-unites with the discharge flow X from the expander means 30 to provide a full return flow of fluid coolant.

The return flow of fluid coolant from the coil 43, which has absorbed heat from the high pressure fluid coolant, flow through the coil 42 as previously discussed, is delivered to the compressor means 20. The pressure of the fluid coolant is increased at each compression stage, as indicated by the lines m-n, 0-p, rs and t-u, respectively, which is cumulative. Therefore, the pressure of the fluid coolant, from the inlet to the discharge of the compressor means 20, rises from 50 to 400 pounds per square inch. Each pressure rise is attended by an increase in temperature which is not realized cumulatively because of the action of the

inter-coolers

52, 53 and 54 with the aftercooler 50, as indicated by lines n-o, p-r, s-t and u-a, respectively.

Accordingly, flow of fluid coolant through each of the compressor means 20 during the compression cycle and the expander means 30 during the expansion cycle realizes a. multi-step or multi-stage pressure change which is cumulative while the temperature varies between two predetermined limits because of temperature change from compression or expansion coupled with the action of the heat transfer means operatively associated with the various stages.

The main or primary heat transfer means 40, in effect, provides a multi-stage conditioning upon the fluid coolant. The preheat exchanger 41 acts as a compression cycle heat exchanger means wherein the transfer of heat is effected between the inlet and discharge flows to and from the compressor means 20. The reheat heat exchanger 44 accomplishes second stage heat transfer wherein the working flow of fluid coolant gives up heat both to the return flow of fluid coolant through the coil 46 and to provide the reheat for the expansion cycle. The third stage heat transfer or work output of the system is accomplished in the cold box or process load heat exchanger 47 wherein the process load or heat from the gas to be liquified flowing through the coil 49 is absorbed by the flow of fluid coolant through the coil 48.

By the foregoing, it should be readily understood that a system made in accordance with the present invention conditions a fluid coolant in a closed loop or circuit to accomplish a desired amount of Work efficiently and economically, maintains the fluid coolant in instantaneous optimum conditions through the complete system operating cycle and provides for power recovery by coupling the expander means 30 to the compressor means 20 through the drive means 10.

It will be understood that the invention is not to be limited to the specific construction or arrangement of parts shown but that they may be widely modified within the invention defined by the claims.

What is claimed is:

1. A system for conditioning a fluid coolant to liquify gases by refrigeration, comprising:

compressor means including cooling means for cumulatively increasing the pressure of the fluid coolant while maintaining its temperature within predetermined minimum and maximum levels, said compressor means having multi-stage expansion means integrally mounted on multiple power gears;

expander means including reheat means for cumulatively decreasing the pressure of the fluid coolant while maintaining its temperature within predetermined minimum and maximum levels, said expander means having multi-stage expansion means integrally mounted on multiple power gears;

primary heat transfer means flow connected to said compressor and expander means, and including a cold box heat exchanger for effecting a transfer of heat from the gases to be liquified to the fluid coolant; and

drive means connected to said compressor and expander means, and providing a driving connection therebetween thereby permitting power recovery in said system to be delivered directly from said expander means to said compressor means, said drive means being provided with a common shaft connecting said expander means to said compressor means through both said multiple power gears.

2. The system in accordance with claim 1, wherein:

said cooling means being a plurality of inter-stage coolers each flow connected between a different two of said multi-stage compressing means; and

said reheat means being a plurality of inter-stage flow paths disposed in said primary heat transfer means each flow connected between a different two of said multi-stage expansion means.

3. The system in accordance with claim 2, and

said cooling means further including an aftercooler connecting the discharge of the last multi-stage compressing means to said primary heat transfer means.

4. The system in accordance with claim 3, wherein:

said primary heat transfer means is provided with means for apportioning discharging flow of the fluid coolant from said compressor means for providing inlet flow of fluid coolant to said expander means and a working flow of fluid coolant to said cold box heat exchanger.

5. The system in accordance with claim 3, wherein:

said primary heat transfer means is provided with a first heat exchanger having a first flow path connected to said aftercooler to receive fluid coolant discharging therefrom, and a second flow path connected to the inlet of the first of said multi-stage compress ing means.

6. The system in accordance with claim wherein:

said primary heat transfer means is further provided with a reheat exchanger having a first flow path connected to said first flow path of said first heat exchanger, and a second flow path connected to said second flow path of said first heat exchanger;

said reheat flow paths being disposed in said reheat exchanger; and

said cold box heat exchanger having a flow path for fluid coolant flow connected between said first and second flow paths of said reheat exchanger.

7. The system in accordance with claim 6, and

said primary heat transfer means being provided with pressure reducing means connecting said first flow path of said reheat exchanger to said flow path of said cold box heat exchanger.

8. The system in accordance with claim 6, and

the first stage of said multi-stage expansion means having an inlet connected between said first flow paths of said first heat exchanger and reheat exchanger; and

the last stage of said multi-stage expansion means having a discharge connected between said second flow path of said reheat exchanger and said flow path of said cold box heat exchanger.

9. The system in accordance with claim 8, and

10. A system for conditioning a fluid coolant to be used as a refrigerant comprising:

multi-stage compressor means having cooling means between the stages for alternately compressing and cooling said fluid coolant;

an aftercooler means serially connected to the last of said compressor stages for receiving said compressed fluid coolant for cooling said compressed fluid coolant;

a first heat transfer means serially connected to said aftercooler means for further cooling said compressed fluid coolant in non-circulating heat transfer relationship with expanded fluid coolant flowing therethrough;

conduit means operatively associated with said first heat transfer means for receiving said expanded fluid coolant and transmitting it to the first of said compressor stages;

a second heat transfer means having a plurality of flow paths for said fluid coolant wherein the first of said flow paths is serially connected to said first heat transfer means for receiving a portion of said compressed fluid coolant flowing therethrough and further cooling it, and a second of said flow paths is serially connected to said first heat transfer means for delivering said expanded fluid coolant thereto;

throttling means serially connected to the said first flow path for receiving said compressed fluid coolant flowing therethrough and expanding it to a lower pressure and temperature;

a third heat transfer means serially connected to said throttling means for receiving said expanded fluid coolant wherein said fluid coolant acts as a refrigerant in non-contacting heat transfer relationship with a fluid to be cooled flowing therethrough;

conduit means serially connected to said third heat transfer means for receiving said fluid coolant and transmitting it to said second flow path in said second heat transfer means;

multi-stage expansion means having heating means between the stages for alternately expanding, and heating a portion of said fluid coolant;

conduit means operatively associated at one end with the first of said expansion stages and at the other end with said first heat transfer means for receiving a portion of said compressed fluid coolant flowing therethrough and transmitting it to said first expansion stage;

conduit means operatively associated at one end with the last of said expansion stages and at the other end with said second flow path in said second heat transfer means for receiving said expanded fluid coolant and transmitting it to said second flow path; and

drive means operatively associated with said multistage compressor means and said multi-stage expansion means.

11. The system as in claim 10 wherein said heating means between said expansion stages are disposed within said second heat transfer means and are in non-contacting heat transfer relationship with said compressed fluid coolant flowing in said first flow path.

12. The system as in claim 10 wherein said drive means has a common shaft connecting said expansion means to said compressor means through said drive means to permit said compressor means to use power recovered by said expansion means from the expansion of said fluid coolant.

13. The system as in claim 12 wherein said common shaft has rotatably disposed on each end a driving gear 10 in mesh with driven gears rotatably disposed on a shaft operatively associated with said compressor means and a shaft operatively associated with said expansion means respectively.

14. The system as in claim 13 wherein said heating means between said expansion stages are disposed within said second heat transfer means and are in non-contacting heat transfer relationship with said compressed fluid coolant flowing in said first flow path.

References Cited UNITED STATES PATENTS 3,300,991 1/1967 Carney 62-172 3,321,930 5/1967 La Fleur 6287 3,327,495 6/1967 Ergenc 6288 3,355,903 12/1967 La Fleur 62402 FOREIGN PATENTS 554,464 7/ 1932 Germany.

WILLIAM J. WYE, Primary Examiner US. Cl. X.R. 628 8