Hybrid cycle for the production of liquefied natural gas

Abstract

refrigeration process for gas liquefaction which utilizes one or more vaporizing refrigerant cycles to provide refrigeration below about −40° C. and a gas expander cycle to provide refrigeration below about −100° C. Each of these two types of refrigerant systems is utilized in an optimum temperature range which maximizes the efficiency of the particular system. A significant fraction of the total refrigeration power required to liquefy the feed gas (typically more than 5% and often more than 10% of the total) can be consumed by the vaporizing refrigerant cycles. The invention can be implemented in the design of a new liquefaction plant or can be utilized as a retrofit or expansion of an existing plant by adding gas expander refrigeration circuit to the existing plant refrigeration system. Method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range, and a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream. Compressed refrigerant in the first refrigeration system may be cooled by refrigeration provided by a third refrigeration system. Compressed refrigerant in the second refrigeration system may be cooled by refrigeration provided by a third refrigeration system. At least a portion of the pressurized gaseous refrigerant stream, prior to work expansion, may be entirely cooled separately from cooling of the feed gas.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The production of liquefied natural gas (LNG) is achieved by cooling and condensing a feed gas stream against multiple refrigerant streams provided by recirculating refrigeration systems. Cooling of the natural gas feed is accomplished by various cooling process cycles such as the well-known cascade cycle in which refrigeration is provided by three different refrigerant loops. One such cascade cycle uses methane, ethylene and propane cycles in sequence to produce refrigeration at three different temperature levels. Another well-known refrigeration cycle uses a propane pre-cooled, mixed refrigerant cycle in which a multicomponent refrigerant mixture generates refrigeration over a selected temperature range. The mixed refrigerant can contain hydrocarbons such as methane, ethane, propane, and other light hydrocarbons, and also may contain nitrogen. Versions of this efficient refrigeration system are used in many operating LNG plants around the world.

Another type of refrigeration process for natural gas liquefaction involves the use of a nitrogen expander cycle in which nitrogen gas is first compressed and cooled to ambient conditions with air or water cooling and then is further cooled by counter-current exchange with cold low-pressure nitrogen gas. The cooled nitrogen stream is then work expanded through a turbo-expander to produce a cold low pressure stream. The cold nitrogen gas is used to cool the natural gas feed and the high pressure nitrogen stream. The work produced by the nitrogen expansion can be used to drive a nitrogen booster compressor connected to the shaft of the expander. In this process, the cold expanded nitrogen is used to liquefy the natural gas and also to cool the compressed nitrogen gas in the same heat exchanger. The cooled pressurized nitrogen is further cooled in the work expansion step to provide the cold nitrogen refrigerant.

Refrigeration systems utilizing the expansion of nitrogen-containing refrigerant gas streams have been utilized for small liquefied natural gas (LNG) facilities typically used for peak shaving. Such systems are described in papers by K. Müller et al entitled “Natural Gas Liquefaction by an Expansion Turbine Mixture Cycle” in Chemical Economy & Engineering Review, Vol. 8, No. 10 (No. 99), October 1976 and “The Liquefaction of Natural Gas in the Refrigeration Cycle with Expansion Turbine” in Erdöl und Kohie—Erdgas—Petrochemie Brennst-Chem Vol. 27, No. 7, 379-380 (July 1974). Another such system is described in an article entitled “SDG&E: Experience Pays Off for Peak Shaving Pioneer” in Cryogenics & Industrial Gases, September/October 1971, pp. 25-28.

U.S. Pat. No. 3,511,058 describes a LNG production system using a closed loop nitrogen refrigerator with a gas expander or reverse Brayton type cycle. In this process, liquid nitrogen is produced by means of a nitrogen refrigeration loop utilizing two turbo-expanders. The liquid nitrogen produced is further cooled by a dense fluid expander. The natural gas undergoes final cooling by boiling the liquid nitrogen produced from the nitrogen liquefier. Initial cooling of the natural gas is provided by a portion of the cold gaseous nitrogen discharged from the warmer of the two expanders in order to better match cooling curves in the warm end of the heat exchanger. This process is applicable to natural gas streams at sub-critical pressures since the gas is liquefied in a free-draining condenser attached to a phase separator drum.

U.S. Pat. No. 5,768,912 (equivalent to International Patent Publication WO 95/27179) discloses a natural gas liquefaction process which uses nitrogen in a closed loop Brayton type refrigeration cycle. The feed and the high pressure nitrogen can be pre-cooled using a small conventional refrigeration package employing propane, freon, or ammonia absorption cycles. This pre-cooling refrigeration system utilizes about 4% of total power consumed by the nitrogen refrigeration system. The natural gas is then liquefied and sub-cooled to −149° C. using a reverse Brayton or turbo-expander cycle employing two or three expanders arranged in series relative to the cooling natural gas.

A mixed refrigerant system for natural gas liquefaction is described in International Patent Publication WO 96/11370 in which the mixed refrigerant is compressed, partially condensed by an external cooling fluid, and separated into liquid and vapor phases. The resulting vapor is work expanded to provide refrigeration to the cold end of the process and the liquid is sub-cooled and vaporized to provide additional refrigeration.

International Patent Publication WO 97/13109 discloses a discloses a natural gas liquefaction process which uses nitrogen in a closed loop reverse Brayton-type refrigeration cycle. The natural gas at supercritical pressure is cooled against the nitrogen refrigerant, expanded isentropically, and stripped in a fractionating column to remove light components.

The liquefaction of natural gas is very energy-intensive. Improved efficiency of gas liquefaction processes is highly desirable and is the prime objective of new cycles being developed in the gas liquefaction art. The objective of the present invention, as described below and defined by the claims which follow, is to improve liquefaction efficiency by providing two integrated refrigeration systems wherein one of the systems utilizes one or more vaporizing refrigerant cycles to provide refrigeration down to about −100° C. and utilizes a gas expander cycle to provide refrigeration below about −100° C. Various embodiments are described for the application of this improved refrigeration system which enhance the improvements to liquefaction efficiency.

BRIEF SUMMARY OF THE INVENTION

The invention relates to a method for the liquefaction of a feed gassteam stream 100 enters heat exchanger 106, is cooled to a typical intermediate temperature of approximately −30° C., and cooled stream 102 flows into scrub column 108. The cooling in heat exchanger 106 is effected by the warming of mixed refrigerant stream 125 in the interior 109 of heat exchanger 106. The mixed refrigerant typically contains one or more hydrocarbons selected from methane, ethane, propane, i-butane, butane, and possibly i-pentane. Additionally, the refrigerant may contain other components such as nitrogen. In scrub column 108, the heavier components of the natural gas feed, for example pentane and heavier components, are removed. In the present examples the scrub column is shown with only a stripping section. In other instances a rectifying section with a condenser can be employed for removal of heavy contaminants such as benzene to very low levels. When very low levels of heavy components are required in the final LNG product, any suitable modification to scrub column 110 108 can be made. For example, a heavier component such as butane may be used as the wash liquid.

Bottoms product 110 of the scrub column then enters fractionation section 112 where the heavy components are recovered as stream 114. The propane and lighter components in stream 118 pass through heat exchanger 106, where the stream is cooled to about −30° C., and recombined with the overhead product of the scrub column to form purified feed stream 120. Stream 120 is then further cooled in heat exchanger 122 106 to a typical temperature of about −100° C. by warming mixed refrigerant stream 124 125. The resulting cooled stream 126 is then further cooled to a temperature of about −166° C. in heat exchanger 128. Refrigeration for cooling in heat exchanger 128 is provided by cold refrigerant fluid stream 130 from turbo-expander 166. This fluid, preferably nitrogen, is predominantly vapor containing less than 20% liquid and is at a typical pressure of about 11 bara (all pressures herein are absolute pressures) and a typical temperature of about −168° C. Further cooled stream 132 can be flashed adiabatically to a pressure of about 1.05 bara across throttling valve 134. Alternatively, pressure of further cooled stream 132 could be reduced across a work expander. The liquefied gas then flows into separator or storage tank 136 and the final LNG product is withdrawn as stream 142. In some cases, depending on the natural gas composition and the temperature exiting heat exchanger 128, a significant quantity of light gas is evolved as stream 138 after the flash across valve 134. This gas can be warmed in heat exchangers 128 and 150 and compressed to a pressure sufficient for use as fuel gas in the LNG facility.

Refrigeration to cool the natural gas from ambient temperature to a temperature of about −100° C. is provided by a mufti multi-component refrigeration loop as mentioned above. Stream 146 is the high pressure mixed refrigerant which enters heat exchanger 106 at ambient temperature and a typical pressure of about 38 bara. The refrigerant is cooled to a temperature of about −100° C. in heat exchangers exchanger 106 and 122 , exiting as stream 148. Stream 148 is divided into two portions in this embodiment. A smaller portion, typically about 4%, is reduced in pressure adiabatically to about 10 bara and is introduced as stream 149 into heat exchanger 150 to provide supplemental refrigeration as described below. The major portion of the refrigerant as stream 124 125 is also reduced in pressure adiabatically to a typical pressure of about 10 bara and is introduced to the cold end of heat exchanger 106. The refrigerant flows downward and vaporizes in interior 109 of heat exchanger 106 and leaves at slightly below ambient temperature as stream 152. Stream 152 is then re-combined with minor stream 154 which was vaporized and warmed to near ambient temperature in heat exchanger 150. The combined low pressure stream 156 is then compressed in multi-stage intercooled compressor 158 back to the final pressure of about 38 bara. Liquid can be formed in the intercooler of the compressor, and this liquid is separated and recombined with the main stream 160 exiting final stage of compression. The combined stream is then cooled back to ambient temperature to yield stream 146.

Final cooling of the natural gas from about −100° C. to about −166° C. is accomplished using a gas expander cycle employing nitrogen as the working fluid. High pressure nitrogen stream 162 enters heat exchanger 150 typically at ambient temperature and a pressure of about 67 bara, and is then cooled to a temperature of about −100° C. in heat exchanger 150. Cooled vapor stream 164 is substantially isentropically work expanded in turbo-expander 132, typically exiting at a pressure of about 11 bara and a temperature of about −168° C. Ideally the exit pressure is at or slightly below the dewpoint pressure of the nitrogen at a temperature cold enough to effect the cooling of the LNG to the desired temperature. Expanded nitrogen stream 130 is then warmed to near ambient temperature in heat exchangers 128 and 150. Supplemental refrigeration is provided to heat exchanger 150 by a small steam 149 of the mixed refrigerant, as described earlier, and this is done to reduce the irreversibility in the process by causing the cooling curves heat exchanger 150 to be more closely aligned. From heat exchanger 150, warmed low pressure nitrogen stream 170 is compressed in multistage compressor 168 back to a high pressure of about 67 bara.

As mentioned above, this gas expander cycle can be implemented as a retrofit or expansion of an existing mixed refrigerant LNG plant.

An alternative embodiment of the invention is illustrated in FIG. 2. Instead of the wound coil heat exchangers 106 and 128 shown in FIG. 1, this alternative utilizes plate and fin heat exchangers 206, 222, and 228 along with plate and fin heat exchanger 250. In this embodiment, the irreversibility in the warm nitrogen heat exchanger 250 is reduced by decreasing the flow of the cooling streams rather than by increasing the flow of warming streams. In either case the effect is similar and the cooling curves heat exchanger 250 become more closely aligned. In the embodiment of FIG. 2, a small portion of the warm high pressure nitrogen as stream 262 is cooled in heat exchangers 206 and 222 to a temperature of about −100° C., exiting as stream 202. Stream 202 is then re-combined with the main high pressure nitrogen flow and expanded in work expander 232.

FIG. 3 illustrates another alternate embodiment of the invention. In this embodiment, the working fluid for the gas expander refrigeration loop is a hydrocarbon-nitrogen mixture from the light vapor stream 300 evolved by flashing the liquefied gas from heat exchanger 128 across valve 134. This vapor is then combined with the fluid exiting turbo-expander 132, warmed in heat exchangers 128 and 150, and compressed in compressor 368. The gas exiting compressor 368 is then cooled in heat exchanger 308. The bulk of the gas exiting 308 is passed into heat exchanger 150 and small portion 304, equal in flow to the flow of flash gas stream 300, is withdrawn from the circuit for as fuel gas for the LNG facility. In this embodiment, the functions of fuel gas compressor 140 and recycle compressor 168 of FIG. 1 are combined in compressor 368. It is also possible to withdraw stream 304 from an interstage location of recycle compressor 368.

An alternate embodiment is illustrated in FIG. 4 in which another refrigerant (for example propane) is used to pre-cool the feed, nitrogen, and mixed refrigerant streams in heat exchangers 402, 401, and 400 respectively before introduction into heat exchangers 106 and 150. In this embodiment, three levels of pre-cooling are used in heat exchangers 402, 401, and 400, although any number of levels can be used as required. In this case, returning refrigerant fluids 156 and 170 are compressed cold, at an inlet temperature slightly below that provided by the pre-cooling refrigerant. This arrangement could be implemented as a retrofit or expansion of an existing propane pre-cooled mixed refrigerant LNG plant.

FIG. 5 shows another embodiment of the invention in which high pressure mixed refrigerant stream 146 is separated into liquid and vapor sub-streams 500 and 501. Vapor stream 501 is cooled to about −100° C., substantially liquefied, reduced to a low pressure of about 3 bars, and used as stream 503 to provide refrigeration. Liquid stream 500 is cooled to about −30° C., is reduced to an intermediate pressure of about 9 bara, and used as stream 502 to provide refrigeration. A minor portion of cooled vapor stream 505 is used as stream 504 to provide supplemental refrigeration to heat exchangers 150 as earlier described.

The two vaporized low pressure mixed refrigerant return streams are combined to form stream 506, which is then compressed cold at a temperature of about −30° C. to an intermediate pressure of about 9 bara and combined with vaporized intermediate pressure stream 507. The resulting mixture is then further compressed to a final pressure of about 50 bara. In this embodiment, liquid is formed in the intercooler of the compressor, and this liquid is recombined with the main flow 160 exiting the final compression stage.

Optionally, compressed nitrogen stream 510 could be cooled before entering heat exchanger 150 by utilizing subcooled refrigerant liquid stream 511 (not shown). A portion of stream 511 could be reduced in pressure and vaporized to cool stream 510 by indirect heat exchange, and the resulting vapor would be returned to the refrigerant compressor. Alternatively, stream 510 could be cooled with other process streams in the heat exchanger cooled by vaporizing refrigerant stream 502.

Another embodiment is shown in FIG. 6 in which heat exchangers 122, 106 and 150 of FIG. 1 are combined functionally into heat exchangers 600 and 601 to yield an equipment simplification. Note that a balancing stream such as stream 168 of FIG. 1 is no longer required. In this embodiment, the vaporizing mixed refrigerant circuit and the gas expander refrigeration circuit provide in heat exchanger 601 a portion of the total refrigeration required to liquefy the feed gas. These two refrigeration circuits also provide in heat exchanger 600 another portion of the total refrigeration required to liquefy the feed gas. The remainder of the total refrigeration required to liquefy the feed gas is provided in heat exchanger 128.

FIG. 7 presents an embodiment of the invention in which two separate mixed refrigerant loops are employed before final cooling by the gas expander refrigeration loop. The first refrigeration loop employing compressor 701 and pressure reduction device 703 provides primary cooling to a temperature of about −30° C. A second refrigeration loop employing compressor 702 and expansion devices 704 and 705 is used to provide further cooling to a temperature of about −100° C. This arrangement could be implemented as a retrofit or expansion of an existing dual mixed refrigerant LNG plant.

FIG. 8 presents an embodiment of the invention in which a two-fluid cascade cycle is used to provide precooling prior to final cooling by the gas expander refrigeration cycle.

FIG. 9 illustrates the use of expander 800 to drive the final compressor stage of the compressor for the gas expander refrigeration circuit. Alternatively, work generated by expander 800 can be used to compress other process streams. For example, a portion or all of this work could be used to compress the feed gas in line 900. In another option, a portion or all of the work from expander 800 could be used for a portion of the work required by mixed refrigerant compressor 958.

The invention described above in the embodiments illustrated by FIGS. 1-9 can utilize any of a wide variety of heat exchange devices in the refrigeration circuits including wound coil, plate-fin, shell and tube, and kettle type heat exchangers. Combinations of these types of heat exchangers can be used depending upon specific applications. For example in FIG. 2, all four heat exchangers 106 206, 122 222, 128 228, and 150 250 can be wound coil exchangers. Alternatively, heat exchangers 106 206, 122 222, 128 and 228 can be wound coil exchangers and heat exchanger 150 250 can be a plate and fin type exchanger as utilized in FIG. 1.

In the preferred embodiment of the invention, the majority of the refrigeration in the temperature range of about −40° C. to about −100° C. is provided by indirect heat exchange with at least one vaporizing refrigerant in a recirculating refrigeration circuit. Some of the refrigeration in this temperature range also can be provided by the work expansion of a pressurized gaseous refrigerant.

EXAMPLE

Referring to FIG. 1, natural gas is cleaned and dried in pretreatment section 172 for the removal of acid gases such as CO₂ and H₂S along with other contaminants such as mercury. Pretreated feed gas 100 has a flow rate of 24,431 kg-mole/hr, a pressure of 66.5 bara, and a temperature of 32° C. The molar composition of the stream is as follows:

TABLE 1

Feed Gas Composition
Component Mole Fraction

Nitrogen  0.009
Methane   0.9378
Ethane    0.031
Propane   0.013
i-Butane  0.003
Butane    0.004
i-Pentane 0.0008
Pentane   0.0005
Hexane    0.001
Heptane   0.0006

Pre-treated gas 100 enter enters first heat exchanger 106 and is cooled to a temperature of −31° C. before entering scrub column 108 as stream 102. The cooling is effected by the warming of mixed refrigerant stream 109 125, which has a flow of 554,425 kg-mole/hr and the following composition:

TABLE 2

Mixed Refrigerant Composition
Component Mole Fraction

Nitrogen  0.014
Methane   0.343
Ethane    0.395
Propane   0.006
i-Butane  0.090
Butane    0.151

In scrub column 108, pentane and heavier components of the feed are removed. Bottoms product 110 of the scrub column enters fractionation section 112 where the heavy components are recovered as stream 114 and the propane and lighter components in stream 118 are recycled to heat exchanger 106, cooled to −31° C., and recombined with the overhead product of the scrub column to form stream 120. The flow rate of stream 120 is 24,339 kg-mole/hr.

Stream 120 is further cooled in heat exchanger 122 106 to a temperature of −102.4° C. by warming mixed refrigerant stream 124 125 which enters heat exchanger 122 106 at a temperature of −104.0° C. The resulting stream 128 126 is then further cooled to a temperature of −165.7° C. in heat exchanger 128. Refrigeration for cooling in heat exchanger 128 is provided by pure nitrogen stream 130 exiting turbo-expander 166 at −168.0° C. with a liquid fraction of 2.0%. The resulting LNG stream 132 is then flashed adiabatically to its bubble point pressure of 1.05 bara across valve 134. The LNG then enters separator 136 with the final LNG product exiting as stream 142. In this example, no light gas 138 is evolved after the flash across valve 134, and flash gas recovery compressor 140 is not required.

Refrigeration to cool the natural gas from ambient temperature to a temperature of −102.4° C. is provided by a multi-component refrigeration loop as mentioned above. Stream 146 is the high pressure mixed refrigerant which enters heat exchanger 106 at a temperature of 32° C. and a pressure of 38.6 bara. It is then cooled to a temperature of −102.4° C. in heat exchangers exchanger 106 and 122 , exiting as stream 148 at a pressure of 34.5 bara. Stream 148 is then divided into two portions. A smaller portion, 4.1%, is reduced in pressure adiabatically to 9.8 bara and introduced as stream 149 into heat exchanger 150 to provide supplemental refrigeration. The major portion 124 of the mixed refrigerant is also flashed adiabatically to a pressure of 9.8 bara and introduced as stream 124 125 into the cold end of heat exchanger 122 106. Stream 124 125 is warmed and vaporized in heat exchangers 122 and exchanger 106, finally exiting heat exchanger 106 at 29° C. and 9.3 bara as stream 152. Stream 152 is then recombined with the minor portion of the mixed refrigerant as stream 154 which has been vaporized and warmed to 29° C. in heat exchanger 150. The combined low pressure stream 156 is then compressed in 2-stage intercooled compressor 158 to the final pressure of 34.5 bara. Liquid is formed in the intercooler of the compressor, and this liquid is recombined with the main flow 160 exiting the final compressor stage. The liquid flow is 4440 kg-mole/hr.

Final cooling of the natural gas from −102.4° C. to −165.7° C. is accomplished using a closed loop gas expander type cycle employing nitrogen as the working fluid. The high pressure nitrogen stream 162 enters heat exchanger 150 at 32° C. and a pressure of about 67.1 bara and a flow rate of 40,352 kg-mole/hr, and is then cooled to a temperature of −102.4° C. in heat exchanger 150. The vapor stream 164 is substantially isentropically work-expanded in turbo-expander 166, exiting at −168.0° C. with a liquid fraction of 2.0%. The expanded nitrogen is then warmed to 29° C. in heat exchangers 128 and 150. Supplemental refrigeration is provided to heat exchanger 150 by stream 149. From heat exchanger 150, the warmed low pressure nitrogen is compressed in three-stage centrifugal compressor 168 from 10.5 bara back to 67.1 bara. In this illustrative Example, 65% of the total refrigeration power required to liquefy pretreated feed gas 100 is consumed by the recirculating refrigeration circuit in which refrigerant stream 146 is vaporized in heat exchangers 106 and 150 and the resulting vaporized refrigerant stream 156 is compressed in compressor 158.

Thus the present invention offers an improved refrigeration process for gas liquefaction which utilizes one or more vaporizing refrigerant cycles to provide refrigeration below about −40° C. and down to about −100° C., and utilizes a gas expander cycle to provide refrigeration below about −100° C. The gas expander cycle also may provide some of the refrigeration in the range of about −40° C. to about −100° C. Each of these two types of refrigerant systems is utilized in an optimum temperature range which maximizes the efficiency of the particular system. Typically, a significant fraction of the total refrigeration power required to liquefy the feed gas (more than 5% and usually more than 10% of the total) can be consumed by the vaporizing refrigerant cycle or cycles. The invention can be implemented in the design of a new liquefaction plant or can be utilized as a retrofit or expansion of an existing plant by adding gas expander refrigeration circuit to the existing plant refrigeration system.

The essential characteristics of the present invention are described completely in the foregoing disclosure. One skilled in the art can understand the invention and make various modifications without departing from the basic spirit of the invention, and without deviating from the scope and equivalents of the claims which follow.

Claims

1. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing

(a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and

(b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;

2. The method of claim 1 wherein the third recirculating refrigeration circuit system utilizes a single component refrigerant.

3. The method of claim 1 wherein the third recirculating refrigeration circuit system utilizes a mixed refrigerant comprising two or more components.

4. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing

(a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and

(b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;

5. The method of claim 4 wherein the third recirculating refrigeration circuit system utilizes a single component refrigerant.

6. The method of claim 4 wherein the third recirculating refrigeration circuit system utilizes a mixed refrigerant which comprises two or more components.

7. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing

(a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and

(b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;

8. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing

(a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and

(b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;

9. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing

(a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and

(b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;

10. The method of claim 9 wherein all of the pressurized gaseous refrigerant is cooled separately from cooling of the feed gas.

11. The method of claim 9 wherein a portion of the pressurized gaseous refrigerant is cooled by indirect heat exchange with the at least one recirculating refrigeration circuit of (a).

12. The method of claim 9 wherein the first refrigeration system comprises a mixed component, pure component, and/or a cascaded vapor recompression refrigeration system.

13. An apparatus for the liquefaction of a feed gas comprising

(a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range, wherein at least a portion of the first temperature range is between −40° C. and −100° C.; and

(b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream, wherein at least a portion of the second temperature range is below −100° C.;

14. The apparatus of claim 13, wherein the second refrigeration system comprises

(6) compression means for compressing a second gaseous refrigerant to provide the pressurized gaseous refrigerant;

(7) heat exchange means for cooling the pressurized gaseous refrigerant to yield a cooled gaseous refrigerant;

(8) expansion means for work expanding the cooled gaseous refrigerant to provide the cold refrigerant;

(9) heat exchange means for warming the cold refrigerant to provide refrigeration in the second temperature range; and

(10) means for recirculating the resulting warmed refrigerant to provide the second gaseous refrigerant of (6).

15. The apparatus of claim 14, wherein at least one of the heat exchange means in the first and second refrigeration systems comprises a wound coil heat exchanger.

16. An apparatus for the liquefaction of a feed gas comprising

(a) a first refrigeration system comprising at least one recirculating refrigeration circuit utilizing two or more refrigerant components and providing refrigeration in a first temperature range; and

(b) a second refrigeration system which provides refrigeration in a second temperature range having a lowest temperature less than the lowest temperature in the first temperature range;

17. The apparatus of claim 16 wherein the heat exchange means of (2) cools all of the pressurized gaseous refrigerant separately from cooling of the feed gas.

18. The apparatus of claim 16 wherein the first refrigeration system comprises

(A) compression means for compressing the first gaseous refrigerant;

(B) heat exchange means for cooling and at least partially condensing the resulting compressed refrigerant;

(C) pressure reducing means for reducing the pressure of the resulting at least partially condensed compressed refrigerant;

(D) heat exchange means for vaporizing the resulting reduced-pressure refrigerant to provide refrigeration in the first temperature range and yield the vaporized refrigerant; and

(E) means for recirculating the vaporized refrigerant to provide the first gaseous refrigerant of (A).

19. The apparatus of claim 16 wherein at least a portion of the cooling in the heat exchanger of (2) is provided by indirect heat exchange by warming the cold refrigerant in (4).

20. The apparatus of claim 18 wherein at least one of the heat exchange means of the first and second refrigeration systems comprises a wound coil heat exchanger.