SYSTEM AND METHOD FOR DENSIFICATION OF LIQUID OXYGEN

Abstract

A system and method for the production and supply of a densified, liquid oxidant to a space vehicle launch facility is provided. A stream of liquid oxygen taken from a co-located, liquid producing air separation unit is densified in a two refrigeration stage, integrated densification system. The first refrigeration stage is a nitrogen based reverse Brayton cycle refrigeration cycle that provides refrigeration to the second refrigeration stage. The second refrigeration stage is a helium and/or neon comprising refrigerant loop that densifies the liquid oxygen to a temperature between about 70 Kelvin and 57 Kelvin. The integrated densification system may also be configured to densify liquid methane or other propellants used in space vehicle launches.

Claims

1. A system for production of a densified, liquid oxygen stream from a liquid oxygen stream, the system comprises: a first refrigeration stage configured to receive a first refrigerant and flow the first refrigerant through at least one first heat exchanger; and a second refrigeration stage configured to flow a second refrigerant through a second heat exchanger configured to cool the second refrigerant via indirect heat exchange with one or more streams of the first refrigerant and configured to flow the second refrigerant through a densification heat exchanger to subcool and densify the liquid oxygen stream via indirect heat exchange with the second refrigerant; wherein the first refrigeration stage further comprises: a first warm refrigeration circuit, a second cold refrigeration circuit, a residual refrigeration circuit, and one or more recycle circuits; wherein the first refrigerant flowing through the first heat exchanger is split into a first warm portion of the first refrigerant stream in the first warm refrigeration circuit, a second cold portion of the first refrigerant stream in the second cold refrigeration circuit, and a residual portion of the first refrigerant stream in the residual refrigeration circuit; a warm turbine configured to expand the first warm portion the first refrigerant stream to yield an intermediate pressure warm exhaust; a cold turbine configured to expand the second cold portion the first refrigerant stream to yield an intermediate pressure cold exhaust; an expansion valve for expanding the residual portion of the first refrigerant stream to yield an expanded residual stream; wherein the warm exhaust, the cold exhaust, and the expanded residual stream are recycled in the one or more recycle circuits to cool the first refrigerant stream; and one or more first refrigerant recycle compressors configured to compress the recycled warm exhaust, the recycled cold exhaust, and the recycled expanded residual stream.

2. The system for production of a densified, liquid oxygen stream of claim 1 wherein the first refrigerant comprises nitrogen and the second refrigerant comprises helium or neon or both helium and neon.

3. The system for production of a densified, liquid oxygen stream of claim 2 wherein the second refrigeration stage is a closed loop refrigeration stage and further comprises: a second refrigerant recycle compressor disposed downstream of the second heat exchanger and configured to compress the second refrigerant; and a second refrigerant turbine disposed upstream of the second heat exchanger and configured to expand the compressed second refrigerant.

4. The system for production of a densified, liquid oxygen stream of claim 1 wherein: the expanded residual stream is split into a first expanded residual stream and a second expanded residual stream; the first expanded residual stream is further expanded and then recycled via the first heat exchanger as a low pressure return stream to cool the first refrigerant stream; and the second expanded residual stream is one of the one or more streams of the first refrigerant flowing through the second heat exchanger to cool the second refrigerant.

5. The system for production of a densified, liquid oxygen stream of claim 4 wherein the warmed, low pressure return stream is compressed in the one or more of the first refrigerant recycle compressors.

6. The system for production of a densified, liquid oxygen stream of claim 4 wherein the warmed, second expanded residual stream is recycled to the one or more of the first refrigerant recycle compressors.

7. The system for production of a densified, liquid oxygen stream of claim 4 wherein the one or more streams of the first refrigerant flowing through the second heat exchanger further comprises a diverted portion of the cold exhaust.

8. The system for production of a densified, liquid oxygen stream of claim 7 wherein the warmed diverted portion of the cold exhaust is recycled to the one or more first refrigerant recycle compressors.

9. The system for production of a densified, liquid oxygen stream of claim 1 wherein the first refrigeration stage or the second refrigeration stage or both the first refrigeration stage and the second refrigeration stage are disposed on moveable platforms.

10. The system for production of a densified, liquid oxygen stream of claim 1 wherein the liquid oxygen stream is at a pressure between about 1.3 bar(a) and 3.0 bar(a).

11. The system for production of a densified, liquid oxygen stream of claim 1 wherein the one or more first refrigerant recycle compressors are configured to compress the recycled warm exhaust, the recycled cold exhaust, and the recycled first refrigerant return stream to a pressure greater than about 50 bar(a).

12. The system for production of a densified, liquid oxygen stream of claim 1 wherein the intermediate pressure warm exhaust and the intermediate pressure cold exhaust are at a pressure between about 5 bar(a) and 10 bar(a).

13. The system for production of a densified, liquid oxygen stream of claim 12 wherein the low pressure return stream is at a pressure below the pressure of the warm exhaust and the pressure of the cold exhaust.

14. The system for production of a densified, liquid oxygen stream of claim 1 further comprising a third refrigeration stage comprising a third heat exchanger configured to densify a stream of liquid methane via indirect heat exchange with a diverted portion of the expanded residual stream to yield a densified, liquid methane stream.

15. A method of supplying a densified, liquid oxygen stream for a space vehicle launch, the method comprising the steps of: (i) producing a liquid oxygen stream and nitrogen refrigerants from an air separation unit; (ii) cooling the nitrogen refrigerant in a first refrigeration stage comprising a first heat exchanger; (iii) cooling a helium or neon containing second refrigerant in a second heat exchanger in a second refrigeration stage via indirect heat exchange with one or more streams of the nitrogen refrigerant; (iv) subcooling and densifying the liquid oxygen stream in a densification heat exchanger in the second refrigeration stage via indirect heat exchange with the second refrigerant to yield a densified, liquid oxygen stream; (v) transporting the densified, liquid oxygen stream to one or more launch platforms disposed at the launch facility;

16. The method of claim 15, wherein the first refrigeration stage is a reverse Brayton cycle refrigeration stage and wherein step (ii) of the method further comprises the steps of: splitting the nitrogen refrigerant flowing through the first heat exchanger into a first warm portion of the nitrogen refrigerant stream, a second cold portion of the nitrogen refrigerant stream, and a residual portion of the nitrogen refrigerant stream; expanding the first warm portion the nitrogen refrigerant stream in a warm turbine to yield an intermediate pressure warm exhaust; expanding the second cold portion the nitrogen refrigerant stream in a cold turbine to yield an intermediate pressure cold exhaust; expanding the residual portion of the nitrogen refrigerant stream to yield an expanded residual stream; recycling the warm exhaust, the cold exhaust, and at least a portion of the expanded residual stream in one or more recycle circuits to cool the nitrogen refrigerant stream; compressing the recycled warm exhaust, the recycled cold exhaust, and the recycled expanded residual stream in one or more nitrogen refrigerant recycle compressors.

17. The method of claim 16, wherein the second refrigeration stage is a closed loop refrigeration stage and further comprises a second refrigerant recycle compressor disposed downstream of the second heat exchanger and configured to compress the second refrigerant; and a second refrigerant turbine disposed upstream of the second heat exchanger and configured to expand the compressed second refrigerant.

18. The method of claim 16, further comprising the steps of: splitting the expanded residual stream into a first expanded residual stream and a second expanded residual stream; further expanding the first expanded residual stream to yield a low pressure return stream; recycling the low pressure return stream via the first heat exchanger to cool the nitrogen refrigerant stream; wherein the second expanded residual stream is one of the one or more streams of the nitrogen refrigerant flowing through the second heat exchanger to cool the helium or neon containing second refrigerant.

19. The method of claim 18, wherein the warmed, low pressure return stream is compressed in the one or more of the nitrogen refrigerant recycle compressors.

20. The method of claim 18, wherein the warmed, second expanded residual stream is recycled to the one or more of the nitrogen refrigerant recycle compressors.

21. The method of claim 16, further comprising the step of diverting a portion of the cold exhaust to through the second heat exchanger as one of the one or more streams of the nitrogen refrigerant flowing through the second heat exchanger.

22. The method of claim 21, further comprising the step of recycling the warmed, diverted portion of the cold exhaust to the one or more of the nitrogen refrigerant recycle compressors.

Description

BRIEF DESCRIPTION OF DRAWING

[0014] It is believed that the claimed system and method will be better understood when taken in connection with the accompanying drawings in which FIG. 1 shows a schematic of an embodiment of a system and method for the densification of a liquid oxygen stream.

DETAILED DESCRIPTION

[0015] Turning to FIG. 1, the illustrated system 525 and associated methods provide for the densification of a liquid oxygen stream. The illustrated system and method utilize two refrigeration stages, including a first refrigeration stage and a second refrigeration stage. The first refrigeration stage is preferably a nitrogen based refrigerant arrangement, such as a reverse Brayton cycle refrigeration cycle, that provides refrigeration for the second refrigeration stage. The second refrigeration stage is a helium or neon containing refrigerant loop containing some combination of helium and/or neon refrigerants with maybe small amounts of other gases such as nitrogen and oxygen that is used to further subcool and densify a liquid oxygen stream 540 to yield a densified liquid oxygen stream 545 at a temperature of between about 70 Kelvin to 57 Kelvin. The stream of liquid oxygen 540 is preferably received from a liquid oxygen storage tank (not shown) associated with a liquid producing air separation unit (not shown) or can be taken directly from the liquid producing air separation unit.

[0016] The first refrigeration stage uses a high pressure nitrogen refrigerant stream 555 at a pressure of about 50 bar(a) that is cooled a first heat exchanger 550 that can be segmented into a plurality of heat exchange sections, E1, E2, E3. To cool the high pressure nitrogen refrigerant stream 555, the first heat exchanger 550 is configured to include a first warm refrigeration circuit 552, a second cold refrigeration circuit 554, a residual refrigeration circuit 56, and one or more recycle circuits 558,559.

[0017] The nitrogen refrigerant stream 555 is referred to as a first refrigerant stream and is preferably split into three portions as it traverses the first heat exchanger 550, namely a first warm portion 562 of the first refrigerant stream that traverses through the first warm refrigeration circuit 552, a second cold portion 564 of the first refrigerant stream that traverses through the second cold refrigeration circuit 554, and a residual portion 566 of the first refrigerant stream that traverses through the residual refrigeration circuit 556. Upon exiting the first warm refrigeration circuit, the second cold refrigeration circuit, or the residual refrigeration circuit, the respective portions of the first refrigerant stream are recycled in one or more recycle circuits 558, 559.

[0018] The first refrigeration stage also preferably includes a warm turbine 563 configured to expand the first warm portion 562 the first refrigerant stream to yield an intermediate pressure warm exhaust 572 at a pressure of about 6 bar(a) and a cold turbine 565 configured to expand the second cold portion 564 the first refrigerant stream to yield an intermediate pressure cold exhaust 574 also at a pressure of about 6 bar(a). The warm exhaust 572 and the cold exhaust 574 are recycled in the one or more recycle circuits 558 to cool the nitrogen refrigerant stream 555.

[0019] More specifically, the intermediate pressure cold exhaust 574 is mixed with an intermediate pressure recycle stream 577 before being fed into the cold end of exchanger section E3 where the mixed stream (with cold exhaust) is warmed to provide refrigeration for the cooling of the nitrogen refrigeration stream 555. Similarly, the intermediate pressure warm exhaust 572 is also mixed with intermediate pressure recycle stream 578 before being fed into the cold end of exchanger section E2 where it also provides refrigeration for the cooling of the nitrogen refrigeration stream 555. The combined intermediate pressure recycle stream 579 (including the cold exhaust and warm exhaust) is further warmed in heat exchange section E1 to yield a fully warmed, intermediate pressure nitrogen recycle stream 581, which is then compressed in one or more recycle compressors 695.

[0020] The residual portion 566 of the first refrigerant stream is further cooled in heat exchange section E3 of the first heat exchanger and then expanded preferably using one or more expansion valves, including a first expansion valve 575. Prior to expansion, the residual portion 566 of the high pressure first refrigerant stream is at a pressure above its critical point, so that little or no phase transition occurs. However, once the residual portion 566 of the first refrigerant stream is expanded or flashed to an intermediate pressure it may exist in the liquid phase or in a dual phase. As explained above, the pseudo-liquefaction is advantageous.

[0021] The intermediate pressure liquid nitrogen stream 576 is then subcooled in a nitrogen subcooler E4. A first portion 582 of the subcooled, intermediate pressure liquid nitrogen is further expanded or flashed in expansion valve 585 to form a low pressure nitrogen refrigerant stream 583 at a pressure of about 1.5 bar(a) that is used to subcool the intermediate pressure liquid nitrogen 576 in the nitrogen subcooler E4. The now boiled, low pressure nitrogen refrigerant stream 583 is recycled via recycle circuit 559 through heat exchanger sections E3, E2, and E1 where it is further warmed to about ambient temperatures. Upon exiting the heat exchanger sections, the warmed, low pressure return stream 586 is compressed in a multi-stage feed compressor 685 and mixed with the fully warmed, intermediate pressure nitrogen recycle stream 581. The combined recycle stream 587 is further compressed in a multi-stage recycle compressor 695 to form the high pressure nitrogen refrigerant stream 555. Make up nitrogen 599 can be supplied at various points in the process depending on the pressure and phase of the nitrogen source.

[0022] The liquid oxygen stream 540, preferably taken from a storage tank or directly from an air separation unit, enters densification system at a relatively low pressure that will allow its boiling point to match up well with the condensation of the intermediate pressure liquid nitrogen 576. In the current embodiments, the liquid oxygen stream 540 is at a pressure of between about 1.3 bar(a) and 25.0 bar(a), and more preferably between 1.3 bar(a) and about 3.0 bar(a) and still more preferably at a pressure of about 2.3 bar(a). The liquid oxygen stream 540 is likely at a temperature of around 81 Kelvin.

[0023] The liquid oxygen stream 540 is subcooled and thus densified, to a temperature of between about 70 Kelvin and 57 Kelvin in a densification heat exchanger E6. The cooling occurs against a second refrigerant stream 595 comprising helium, neon, or combinations of helium and neon. The second refrigerant stream 595 may also include small amounts of other gases such as nitrogen and oxygen.

[0024] The densification heat exchanger E6 and second refrigerant stream 595 form part of the second refrigeration stage. As shown in the drawings, the second refrigeration stage is configured to flow the neon and/or helium containing second refrigerant stream 595 through a second heat exchanger 590 and the densification heat exchanger E6. The second refrigeration stage also includes a second refrigerant recycle compressor 591 disposed downstream of the second heat exchanger 590 and configured to compress the second refrigerant feed 592 to yield the compressed second refrigerant 593 and an aftercooler 598 configured to cool the compressed second refrigerant 593 to ambient temperature.

[0025] The second refrigeration stage also includes a second refrigerant turbine 596 disposed downstream of the second heat exchanger 590 and upstream of the densification heat exchanger E6. The second refrigerant turbine 596 is configured to expand the compressed second refrigerant 593 to yield an exhaust stream 597 that provides the refrigeration for the densification heat exchanger E6 necessary to the further subcool the liquid oxygen stream 540 and yield a densified, liquid oxygen stream 545. The partially warmed second refrigerant stream 595 exiting the densification heat exchanger E6 is further warmed in second heat exchanger 590 to create the second refrigerant feed 592 to the second refrigerant recycle compressor 591. The partially warmed second refrigerant can be further warmed to ambient temperature or be left somewhat below ambient temperature to take advantage of the power savings from cold compression in the second refrigerant recycle compressor 591. The process would have a make-up system on site to account for potential refrigerant losses over time and/or utilize liquid nitrogen from a storage tank for liquid assist or backup densification.

[0026] The embodiment depicted in FIG. 1 also optionally includes an integrated configuration between the first refrigeration stage and the second refrigeration stage. As seen therein, the diverted portion 674 of the intermediate pressure cold exhaust 574 is directed to the auxiliary warming passage 692 in the second heat exchanger 590 where it further cools the compressed, helium or neon containing second refrigerant stream 595 via indirect heat exchange. In addition, a diverted portion 868 of intermediate pressure stream 668 is also directed to another auxiliary warming passage 892 in the second heat exchanger 590 where it also cools the compressed, helium or neon containing second refrigerant stream 595 via indirect heat exchange. The warmed diverted stream 876 is then mixed with the warmed diverted stream 676 and the combined stream 976 is recycled back to the recycle compressor 695 where it is recombined with the combined recycle stream 587 and further compressed in a multi-stage recycle compressor 695 to form the high pressure nitrogen refrigerant stream 555.

[0027] The embodiment depicted in FIG. 1 also optionally includes an integrated liquid methane densification system 400. When using the integrated liquid methane densification system 400, the residual portion 566 of the high pressure first refrigerant stream is preferably split into two fractions, including the first high pressure residual fraction 666 and the second high pressure residual fraction 766. The first high pressure residual fraction 666 is expanded or flashed in expansion valve 675 to a pressure of about 6.0 bar(a) while the second high pressure residual fraction 766 is flashed in a second expansion valve 775 to a pressure of about 15.0 bar(a). The resulting intermediate pressure stream 668 is directed to and received by the subcooler E4 where it is subcooled while the resulting moderate pressure stream 768 is diverted to the liquid methane densification system 400. The warmed, liquid nitrogen stream 770 exiting the methane subcooler E7 is further expanded or flashed in another expansion valve 875 to yield expanded stream 884 at a pressure about equal to the second portion 584 of the subcooled, intermediate pressure liquid nitrogen.

[0028] As indicated above, the embodiment of the present system and method shown in FIG. 1 is particularly useful in situations where there is a ready supply of liquid oxygen and/or a source of nitrogen. As such, the embodiment shown in FIG. 1 is preferably co-located with a liquid producing air separation unit.

[0029] Another aspect of the present system and method relates to the turbomachinery configuration in the described embodiments. The present system and method can be operated with a traditional configuration with the warm turbine and cold turbine each coupled directly to single stage boosters, preferably a single stage of the recycle compressor 695. The present system and method can also utilize a fully integrated bridge machine which allows the compressors to absorb the energy from the warm turbine and cold turbines while decoupling the speeds of the compressor and turbines. Linde Inc., a member of the Linde Group of Companies, has also developed a portfolio of integral gear machines or single machines that combine compression stages and high efficiency radial inflow expanders having up to four driven pinions in what is referred to as an integral gear bridge machine. Linde's bridge machines are conventionally used in air separation plants and typically come in different frame sizes, for example frame sizes supporting bull or drive gear sizes between about 90 mm and 180 mm in diameter. Design studies have examined applications of the Linde bridge machines to operatively couple a plurality of radially inflow turbines and centrifugal refrigeration compression stages in a liquefaction system. The Linde bridge machines come fully packaged or integrated with appropriate PLC controllers, control valves, safety valves, oil system, etc. and can be easily outfitted with intercoolers and/or aftercoolers. The hardware constraints and limitations of the Linde bridge machines are typically a function of bull gear and driver assembly size. Use of a bridge type machine provides for a very high efficiency system. When configuring the present system and method to utilize the bridge machine arrangement, it may be advantageous to configure the feed compressor 685 as a stand-alone multi-stage centrifugal machine.

[0030] While the present system and method for densification of a liquid oxygen stream has been described with reference to one preferred embodiments, it is understood that numerous additions, changes, and omissions can be made without departing from the spirit and scope of the present system and method as set forth in the appended claims.