US20020148225A1

US20020148225A1 - Energy conversion system

Info

Publication number: US20020148225A1
Application number: US09/833,176
Authority: US
Inventors: Larry Lewis
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-04-11
Filing date: 2001-04-11
Publication date: 2002-10-17

Abstract

The invention provides a method and apparatus for recovering work from a gas turbine and providing a cooled inlet air, a refrigeration capacity and that may use a common working fluid in both systems . More importantly the system provides a working fluid for more efficient heat transfer by maintaining a supercritical working fluid in an energy recovery system, for example, recovery of waste heat from a gas turbine exhaust.

Description

TECHNICAL FIELD

This invention pertains to the field of energy conversion and specifically to the conversion of heat energy to mechanical energy.

BACKGROUND OF THE INVENTION

Energy conversion engines have long been employed to recover process heat and convert it to mechanical energy as in the familiar Rankine cycle. Typical systems are in a series of patents by Alexander Kalina and various coworkers such as U.S. Pat. Nos. 5,095,708; 5,029,444; 4,982,568; 4,899,545; 4,732,005; 4,604,867; 4,586,340; 4,548,043; and 4,489,563. Scharpf, U.S. Pat. No. 5,842,345 teaches the use of two component working fluids, preferring ammonia and water, in a heat recovery method. DeVault U.S. Pat. No. 5,555,738, teaches use of an ammonia water refrigeration system to cool the inlet air of a gas turbine for improved efficiency. Lewis et al U.S. Pat. No. 6,195,997 discloses an energy recovery system using a refrigeration loop to cool the inlet air for a gas turbine wherein the working fluid is split into 2 streams. Rosenblatt U.S. Pat. No. 5,421,157 discloses an organic Rankin cycle system with a recuperator. U.S. Pat. No. 4,442,675 discloses a thermodynamic cycle wherein the work expanded fluid is compressed isentropically to its original pressure then heated at constant pressure to its initial temperature.

The art has not heretofore recognized the unexpected advantage of using a working fluid at supercritical conditions as a heat transfer medium in a waste heat recovery organic Rankin cycle with the expander mechanically coupled to a refrigeration compressor in a refrigeration cycle wherein the inlet air to a turbine is cooled by heat exchange with a cold fluid supply from the refrigeration unit while power to drive the refrigeration compressor is supplied by waste heat recovery from the turbine exhaust in the heat recovery system; while also providing additional cooling capacity. Indeed certain prior art patents suggest that the critical condition is the upper limit for heat transfer conditions. See for example U.S. Pat. No. 4,089,175. Others teach use of high boiling working fluids in order to maintain sub-critical conditions. See for example U.S. Pat. No. 4,137,965. In Linde, 1981, Reports on Science and Technology Vol. 31 pages 38 to 46, Hans-Peter Corneille and Siegfred Haaf, “ Organic Rankin Cycles for the Conversion of Waste heat and Solar Heat to Mechanical Energy” the advantages of using the organic Rankin cycle is discussed and Rankin cycles converting waste heat to mechanical energy in a variety of systems are described generically, but a system wherein a coupled refrigeration system used to cool inlet air for a gas turbine was not recognized in the art reported therein.

SUMMARY OF THE INVENTION

The invention may be described in several ways as alternate embodiments of the same novel discovery.

A conventional Rankine cycle that can be used in an energy recovery system that comprises:

a. providing a first working fluid to a first pump;

b. feeding the first working fluid to a heat transfer zone to transfer heat to the first working fluid thereby heating the first working fluid to a higher temperature,

c. feeding the heated first working fluid to an expansion means;

d. expanding the heated first working fluid to a lower pressure;

e. feeding the expanded lower pressure first working fluid to a heat transfer zone where the first working fluid is cooled;

f. returning the first working fluid to the first pump and repeating the cycle as set out above.

In a preferred embodiment the invention provides:

g. in a coupled refrigeration system the steps of feeding a second working fluid. to a second heat exchanger and heating the second working fluid by extracting heat from a refrigeration source;

h. feeding the heated working fluid work to a compressor coupled to the expansion means of the energy recovery system

i. compressing the heated working fluid to a higher pressure

j. feeding the compressed heated working fluid to an expansion means and

k. expanding the working fluid to a lower pressure

l. returning the expanded working fluid to the inlet side of the second heat exchanger to remove energy from a refrigeration source

In a more preferred embodiment the invention further provides the steps of:

m. supplying from the coupled refrigeration system a cooled fluid stream to a heat exchange means in contact with an inlet air stream to a gas turbine and cooling the inlet air stream to the turbine and

n. feeding heated turbine exhaust to the first heat transfer zone.

In a preferred embodiment the method further comprises:

a. feeding the first and second working fluids through a plurality of coupled expander/compressor pairs to recover energy and provide cooling in stages. These expanders can be in series or in parallel and a single expander can drive multiple stages of compression with the use of a gear driven multi-stage compressor or similar device.

In an especially preferred embodiment the method further provides the same working fluid in both the heat recovery system and the refrigeration system eliminating the need for mechanical seals between the two fluids. The working fluid may be any hydrocarbon, or other refrigerant, pure or mixed having energy efficient properties to enable waste heat recovery in the system. Hydrocarbon working fluids are preferred and normal butane, Isobutane, isopentane, normal pentane, iso-hexane, or normal hexane are the best mode working fluids known to the inventor.

In an optional embodiment the method further comprises the steps of feeding a third working fluid to a heat exchange in the refrigeration loop after the expansion means and cooling the third working fluid. Preferably the third working fluid cools the inlet air coming to a gas turbine. In a preferred embodiment the third working fluid is water, aqueous ethylene glycol solution, alcohol brines, or other brines.

The first working fluid stream may also be fed back through multiple compressors or heat exchangers to further increase heat uptake and process efficiency and /or to produce a lower refrigerant temperature.

In an alternate embodiment, the invention is an energy recovery apparatus that comprises:

a. fluid conduit means and a working fluid the conduit means connecting all components listed below;

b. pumping means;

c. heat exchange means with a sufficient pressure rating to contain the working fluid at an operating temperature above its critical temperature;

d. an expansion means connected to the heat transfer means and configured to receive a heated working fluid and expand said working fluid to a lower pressure zone thereby extracting mechanical work from the working fluid;

e. and condensing means configured to condense the working fluid at a pressure in the working fluid above atmospheric pressure.

A preferred apparatus further provides:

f. a second working fluid contained in conduits in a refrigeration system;

g. a compressor coupled to the expansion means to compress the second working fluid in the refrigeration system , a condenser to reject heat while condensing the working fluid, a refrigeration expansion means and a heat exchange evaporation means in the refrigeration system;

An especially preferred apparatus provides:

h. a gas turbine having an inlet air stream and an exhaust stream;

i. a heat exchange means to receive a cooled working fluid from the refrigeration system and positioned to cool the inlet air to the gas turbine;

j. a heat exchange means positioned to recover heat from the turbine exhaust and supply heat to the first working fluid prior to the first working fluid entering the work expansion means and under conditions wherein the first working fluid is heated above its critical temperature.

In a preferred embodiment the invention further comprises

k. a second pump means for circulating a third working fluid between a heat exchange means downstream from the refrigeration expansion means and a second heat exchange means in contact with inlet air to the gas turbine and a separate fluid conduit containing a working fluid and linking the second pump with the two heat exchange means;

In a preferred embodiment the working fluid in the energy recovery apparatus and the refrigeration system is the same. Hydrocarbon working fluids are preferred and more preferably the working fluid in both systems is selected from the group consisting of isobutane, normal butane, propane, iso-propane, normal pentane, iso pentane, hexane or a two component mixture of any of the preceding with any other of the preceding or a three or more component mixture of any of the preceding with any others of the preceding. The working fluid in the optional third conduit system, can be any heat transfer fluid, but is preferably water, aqueous ethylene glycol solution, alcohol brines, or brines.

In an additional preferred embodiment the apparatus comprises a series of turbo-expanders coupled to multiple compressor and may also employ a flash economizer or multiple refrigeration expansions and multiple heat recovery stages to provide additional heat recovery or refrigeration capacity.

The invention in an alternative embodiment provides a method for increasing the efficiency of a gas pipeline that comprises:

a. providing a gas compression system having a gas turbine that compresses the pipeline gas and a heat recovery system having a first working fluid and a first pump;

b. feeding the first working fluid through the first pump to a first heat transfer zone to transfer heat to the working fluid stream thereby heating the stream to a higher temperature using heat from the gas turbine exhaust,

c. feeding the heated working fluid to an expansion means operative coupled to a refrigeration system compression means;

d. expanding the first working fluid to a lower temperature and pressure;

e. feeding the expanded lower temperature and pressure first working fluid to a second heat exchanger where the first working fluid is cooled by heat exchange while rejecting heat to an external medium;

f. returning the first working fluid to the first pump and repeating the cycle as set out above

g. and in a coupled refrigeration system feeding a second working fluid. to second heat exchanger and heating the second working fluid;

h. feeding the heated second working fluid work to a compressor

i. compressing the heated working fluid to a higher pressure

j. condensing the compressed working fluid by rejecting heat to an external medium

k. feeding the condensed working fluid to an expansion means and

l. expanding the working fluid to a lower pressure

m. returning the expanded working fluid to inlet side of a heat exchange means in contact with an inlet gas pipeline stream to the pipeline gas compressor and cooling the inlet gas pipeline stream to the compressor and

n. feeding the turbine exhaust to supply heat to the heat transfer zone in contact with the first working fluid, and preferably

o. feeding the first and second working fluids through a plurality of coupled expander/compressor pairs to recover additional energy.

In summary, the invention provides a system for energy recovery that combines mechanically coupled refrigeration capacity with an energy recovery system to provide cooled air to a gas turbine inlet and/or other refrigeration load. The system preferably is operated with a working fluid having a phase diagram wherein the curve passes through a maximum and wherein the working fluid absorbs heat energy above its critical temperature. For a given system, the quantity of energy, usually heat, available to be recovered, the desired product temperature in the refrigeration system and the available heat sink capacity for condensing the working fluid will define the requirements for the latent heat of vaporization, and the temperature and pressure conditions that must be met by the working fluid. The working fluid may be of any composition that will meet the required temperature, pressure and heat transfer requirements of the system. Alternatively, operating temperature and pressure ranges for the overall system may be defined by mechanical limitations of desired equipment, such as the maximum operational pressure of a preferred heat exchanger or the desired approach temperature for the product temperature against ambient conditions. When these additional considerations are imposed on the system, the working fluid composition will be adjusted to meet these preferred ranges. Preferred working fluids are those listed and discussed above. Hydrocarbon or refrigerants listed in ASHRAE, or mixtures of these working fluids are especially preferred. However, those skilled in the art will recognize that in many applications other working fluids may be used to practice the invention.

In another embodiment the invention may be viewed as an improvement in the method for designing an energy recovery system disclosed in U.S. Pat. No. 6,195,997 to provide enhanced energy recovery while at the same time providing a coupled refrigeration capacity. The improvement comprises the steps of defining a desired product temperature in the refrigeration system, defining an available heat sink, defining a quantity of energy to be recovered in an energy recovery system, defining a means for converting the quantity of energy to be recovered into a recovered energy output while also providing sufficient heat energy to provide a sufficient quantity of a volatile component of at least a portion of the working fluid which is work expanded in a system having coupled compressors which compress a separate working fluid to be expanded to provide cooling to the defined product temperature when evaporated and, defining a group of conditions to be meet by a working fluid, the working fluid in the energy recovery system being substantially vaporized by contacting the energy to be recovered thereafter driving the means for energy recovery while also providing the compression required to generate the desired cooling in the refrigeration loop and selecting a working fluid composition that permits meeting all design constraints.

The invention is illustrated by the specific examples set out below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of pressure vs. enthalpy at various temperatures. [0063]
FIG. 2 is a flow diagram of the basic process providing cooling of the inlet air to the gas turbine and an additional process refrigeration capability. [0064]
FIG. 3 is an alternative embodiment providing refrigeration for cooling the inlet gas to a pipeline compressor to reduce horsepower requirements to compress natural gas. [0065]
FIG. 4 is a prior art system for compression of pipeline gas.[0066]

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a method for recovering energy from the exhaust gas of a combustion or catalytic combustion powered gas turbine. The gas turbine and compressor may be in any service, such as a gas turbine used to compress natural gas feeding a pipeline. In Lewis et al., U.S. Pat. No. 6,195,997, a system is disclosed for cooling the inlet stream to a gas turbine. In the present system a simplification is achieved eliminating the need to divide the working fluid stream. In its preferred embodiments the invention employs working fluids having the pressure enthalpy curve shape illustrated in FIG. 1. It has been found that more efficient heat transfer can be achieved when the working fluid is maintained above its critical pressure during the heat transfer step of the Rankine cycle. [0067]
Although any heat transfer fluid having the general pressure enthalpy relationship shown in FIG. 1 can be used, hydrocarbon working fluids are preferred. Desirable properties for working fluids include chemical stability within the entire temperature and pressure range, compatibility with usual materials, low inflammability and/or high ignition temperature, and non-explosiveness when mixed with air. Desirable physical properties include a vapor-pressure curve that is so located in that no negative pressure prevails during condensation and no high pressure exists during evaporation . The freezing point should be below the minimum environmental and operating temperature, and the isentropic curve should be as parallel to the saturation line as possible. The working fluid should have good heat transfer properties, low viscosity and heat conductivity. Most preferably the working fluid will be non-toxic, easily available, low-priced and provide a high process efficiency and high volumetric expansion work. In addition to the working fluids set out above, fluorocarbons, fluorochlorocarbons, and fluorohydrocarbons, or any other refrigerant meeting the above criteria can be employed. In an especially preferred mode of the heat transfer step of the Rankine cycle is carried out above the critical pressure of the working fluid and the compression and expansion steps are both carried out above the dew point temperature as illustrated in FIG. 1. . [0068]
The invention may be employed to increase the operating efficiency of any gas turbine that produces a waste heat exhaust. However it is particularly advantageous in pressure compression stations for gas pipelines, or to supply additional refrigeration capacity in a plant such as a liquefied natural gas (LNG) plant or Liquefied Petroleum Gas(LPG) recovery from a natural gas plant having need of such refrigeration. [0069]
The invention also provides additional advantages within a plurality of expanders and coupled compressors are used in series to provide multiple stages of energy recovery or compressed gas to supply separate refrigeration/evaporation stages. The invention is illustrated by several examples set out below. These examples are provided to illustrate the invention and not to limit the concepts embodied therein. The invention is defined and limited by the claims set out below. The examples below were modeled using Design II for Windows by WinSim, Inc. of Houston, Tex. [0070]

EXAMPLE 1

Turning to FIG. 2, a gas turbine waste heat power recovery and inlet air thrust augmentation cooling system is illustrated. The working fluid having the characteristics discussed above, in this example isobutane, in [0071] line 1 is supplied to pump p-i at 74 psia and 100 degrees F. and pumped to 750 psia at 105.14° F. The pumped working fluid is carried by line 2 to a waste heat recovery exchanger X-1 and heated to 317.6° F., passed to the liquid separator F-1, and the vapor exits the top at line 4 and enters expander E-2 providing 467.5 hp and passing by line 5 to liquid separator F-2 and again exits as a vapor through line 6 to work expander E-1 where it provides an additional 1256 hp while expanding to a final pressure of 74 psia. The exiting vapor from E-1 at 129.17° F. enters condensing heat exchanger X-2 rejecting 23,486,000 BTU/hr to atmosphere thereby cooling the stream to 100° F. and exiting at 8 to return to line 1 to repeat the cycle. In the refrigerant loop a second working fluid, in the example also isobutane, is compressed in the first stage compressor C-2 requiring 467.4 hp. The compressed fluid is conveyed by line 12 to the flash economizer F-3 and the vapor leaves the top by line 15 at 40.864° F. and enters compressor C-1 and is further compressed requiring 1252 hp. The compressed vapor follows line 16 and is condensed in X-3 rejecting 20,650,000 Btu/hr to atmosphere. The condensed liquid is expanded through refrigeration valve V-11, which is preferably a Joules-Thompson valve and expanded gas liquid mixture is conveyed to flash economizer F-3 by line 18. The expanded gas/liquid mixture is separated and heat exchanged in F-3 to provide additional vapor exiting the top and joining the stream in line 15 described above while the liquid exits by line 13 to refrigeration valve 12 where it is further expanded and cooled to 10.73° F. and by line 14 to enter evaporator X-5 where it provides an additional 13,514,000 BTU/hr of process refrigeration, A third working fluid, in the example water, absorbs 2,771,200 BTU/hr at the internal heat exchanger XF-3, and follows line 26 to heat exchanger X-4 where it provides 2,760,000 BTU/hr cooling to the inlet air stream of the gas turbine which passes through line 20. The inlet air to the turbine in line 20 is cooled from 100° F. to 45.164° F. on exiting in line 21. The air and combustion gases is heated to 826° F. in the turbine and passes through line 22 to waste heat recovery exchanger X-1 where it is cooled to 155.62° F. exit temperature as line 23 and exhaust to atmosphere. After being heated at X-4, the third working fluid flows through line 28 to Pump P-2 where it is circulated to exchanger XF-3 by lines 27 and 25.
In this example isobutane is used as both the first and second working fluid. This preferred mode eliminates the need for expensive mechanical seals in the coupled expander/compressor units since there is no need to prevent mixing of the working fluids in each loop. [0072]

EXAMPLE 2

Turning now to FIG. 3 an alternative embodiment is illustrated, and a net of the same energy recovery configuration as example [0073] 1. Work expanders E.-2 and E-1 provide 845.3 and 878.7 hp, and the Expander exit temperature is 127.26° F. and exchanger X-2 rejects 23,516,000 BTU/hr , but otherwise the loop is substantially as described in Example 1. In the Refrigeration system, the mechanically coupled compressors C-2 and C-1 require 844.9 HP and 870.5 HP respectively and the exit temperature from flash economizer F-3 is 66.242° F. in line 15. Condensing heat exchanger X-3 rejects 25,633,000 BTU/hr to atmosphere to condense the stream to 100 F for the liquid stream in line 17. The liquid from F-3 enters refrigeration expansion valve V-12 and exits at 31.823° F. then is divided at D-5 to provide cooling to two loads, the Chill water loop at exchanger X-18 where refrigerant is vaporized to cool the chilled water, then the vaporized refrigerant is returned to mixing chamber M-20 by line 33. The chill water loop removes 2,802,100 BTU/hr while cooling turbine inlet air in Stream 20 from 100° F. to 44.601° F. At the same time Stream 34 leaves divider D-5 and is cross-exchanged with stream 40 in X-19, exiting by line 35 to join the stream from line 33 at M20 and provide the vaporized low pressure gas feed to compressor C-2 by line 11. Exchanger X19 cools 80° F. natural gas at 800 psia (644225 lb/hr or 353.31 MM SCFD) in Line 40 down to 34.354° F. before it enters compressor C-16 which requires 4642 hp to pressurize and transmit the gas at pressure through an 80 mile segment of 24 inch pipeline to arrive at the next stage 80 miles away at 800.2 psia.
FIG. 4 illustrates a conventional pipeline compression station with no inlet cooling of the pipeline gas. Inlet gas at 800 psia and 80° F. is compressed to 1153 psia at 150.3° F. requiring 7679 hp, then gas cooler X-[0074] 2 rejects 12,663,000 Btu/hr to atmosphere to yield 120° F. transmission temperature and the gas reaches the end of the 80 mile segment at 799.5 psia. Thus a compression station configured according to the invention allows use of a substantially smaller and less expensive compressor at the compression station. Because the compressed gas exits the compressor at around 76° F. in the illustrated system (FIG. 3), no heat rejection equipment is required before the gas enters the transmission line.

Claims

We claim:

1. A method of recovering energy that comprises:

a. providing an energy recovery system having a first working fluid and a first pump;

b. feeding the first working fluid through the first pump to a first heat transfer zone to transfer heat to the working fluid stream thereby heating the stream to a higher temperature,

d. expanding the first working fluid to a lower temperature and pressure;

g. and in a coupled refrigeration system feeding a second working fluid. to a second heat exchanger and heating the second working fluid;

h. feeding the heated second working fluid to a compressor

i. compressing the heated working fluid to a higher pressure

k. feeding the condensed working fluid to an expansion means and

l. expanding the working fluid to a lower temperature and pressure

m. returning the expanded working fluid to inlet side of a heat exchange means in contact with an inlet air stream to a gas turbine and cooling the inlet air stream to the turbine and

n. feeding the turbine exhaust to supply heat to a heat transfer zone in contact with the first working fluid.

2. The method of claim 1 further comprising:

feeding the first and second working fluids through a plurality of coupled expander/compressor pairs to recover additional energy.

3. The method of claim 1 wherein the first working fluid and the second working fluid have the same composition.

4. The method of claim 1 wherein the first working fluid and the second working fluid are not separated by mechanical seals in the coupled expander compressor.

5. The method of claim 1 wherein the first working fluid and the second working fluid are selected from the group consisting of hydrocarbons or refrigerants listed in ASHRAE, or mixtures of these working fluids.

6. The method of claim 1 wherein the first and the second working fluids are each isobutane.

7. The method of claim 1 that further comprises the steps of feeding a third working fluid to a heat exchange zone in the refrigeration loop positioned after the expansion means and cooling the third working fluid.

8. The method of claim 1 wherein the third working fluid cools the inlet air coming to a gas turbine.

9. The method of claim 7 wherein the third working fluid is selected from the group consisting of water, aqueous ethylene glycol solution, glycol brines, alcohol brines, or brines.

10. The method of claim 1 wherein a plurality of work expanders is provided.

11. The method of claim 1 where the working fluid has a pressure enthalpy curve as shown in FIG. 1 and the first working fluid is maintained at a supercritical condition in the waste heat recovery heat exchanger.

12. An energy recovery apparatus that comprises:

a. fluid conduit means and a working fluid contained therein, the conduit means connecting all components listed below

b. pumping means connected to a waste heat transfer means configured to recover waste heat from a gas turbine;

c. an expansion means connected to a heat transfer means and configured to receive a heated working fluid and expand said working fluid to a lower pressure zone, thereby lowering the pressure and temperature;

d. a working fluid in a refrigeration system a component of which is vaporized by heat available from energy to be recovered in sufficient quantity to provide the desired product temperature when expanded in the expansion means while the combined working fluid can be fully condensed by the available heat sink means at pressures acceptable in the heat sink means;

e. a compressor mechanically coupled to the work expander means to compress the working fluid in the refrigeration system , a refrigeration expansion means and a heat exchange means in the refrigeration system;

f. a gas turbine having an inlet air stream and an exhaust stream;

g. a heat exchange means to receive a cooled working fluid from the refrigeration system and positioned to cool the inlet air to the gas turbine;

h. a heat transfer means positioned to recover heat from the turbine exhaust and supply heat to a working fluid prior to the working fluid entering the work expansion means;

13. The apparatus of claim 12 further comprising a second pump means for circulating a third working fluid between a heat exchange means downstream from the refrigeration expansion means and a second heat exchange means in contact with inlet air to the gas turbine and a separate fluid conduit containing a working fluid and linking the second pump with the two heat exchange means.

14. The apparatus of claim 12 further comprising the same working fluid in the energy recovery apparatus and the refrigeration system.

15. The apparatus of claim 12 wherein a working fluid is a hydrocarbon, a mixture of hydrocarbons, or refrigerants listed in ASHRAE, or mixtures of these working fluids.

16. The apparatus of claim 12 wherein a working fluid is isobutane.

17. The apparatus of claim 13 wherein third working fluid is selected from the group consisting of water, aqueous ethylene glycol solution, glycol brines, alcohol brines, or brines.

18. The apparatus of claim 12 wherein the apparatus comprises a plurality of turbo-expanders each coupled to a compressor.

19. The apparatus of claim 12 further comprising a flash economizer.

20. The apparatus of claim 12 further comprising a plurality of refrigeration expansion means.

22. The apparatus of claim 12 further comprising multiple heat recovery stages to provide additional heat recovery

23. The apparatus of claim 12 wherein the working fluid has a pressure enthalpy curve with a shape as shown in FIG. 1 and the apparatus is configured to maintain a condition in excess of a critical pressure in the waste heat transfer means.

24. A method for designing an energy recovery system for increasing the efficiency of a gas turbine by providing an integrated refrigeration capacity comprising the steps of defining a desired product temperature in the refrigeration system, defining an available heat sink, defining a quantity of energy to be recovered in an energy recovery system, defining a means for converting the quantity of energy to be recovered into a recovered energy output while also providing sufficient heat energy to provide a sufficient quantity of a volatile component of at least a portion of the working fluid which is work expander in a system having coupled compressors which compress a working fluid to be expanded to provide cooling to the defined product temperature when evaporated and, defining a group of conditions to be meet by a working fluid, the working fluid in the energy recovery system being substantially vaporized by contacting the energy to be recovered thereafter driving the means for energy recovery while also providing the compression required to generate the desired cooling in the refrigeration loop and selecting a working fluid composition that permits meeting all design constraints.

25. A method for increasing the efficiency of a gas pipeline which comprises: providing a gas compression system having a gas turbine that provides waste heat in an exhaust and a compressor for pipeline gas and a heat recovery system having a first working fluid and a first pump; feeding the first working fluid through the first pump to a first heat transfer zone to transfer heat to the working fluid stream thereby heating the stream to a higher temperature using heat from the gas turbine exhaust, feeding the heated working fluid to an expansion means operative coupled to a refrigeration system compression means; expanding the first working fluid to a lower temperature and pressure; feeding the expanded lower temperature and pressure first working fluid to a second heat exchanger where the first working fluid is cooled by heat exchange while rejecting heat to an external stream ;returning the first working fluid to the first pump and repeating the cycle as set out above and in a coupled refrigeration system feeding a second working fluid. to a second heat exchanger which heats the second working fluid by providing refrigeration; feeding the heated second working fluid work to a compressor compressing the heated working fluid to a higher pressure feeding the compressed heated working fluid to a condenser rejecting heat to an outside medium and to an expansion means and expanding the working fluid to a lower pressure returning the expanded working fluid to inlet side of a heat exchange means in contact with an inlet gas pipeline stream to a pipeline gas compressor and cooling the inlet gas pipeline stream to the compressor and feeding a gas turbine exhaust to supply heat to the heat transfer zone in contact with the first working fluid.

26. The method of claim 25 further comprising:

feeding the first and second working fluids through a plurality of coupled expander/compressor pairs.