Patent Application
20240230218
The present invention relates to a system and method for liquefaction of a liquid oxygen stream for use as an oxidant for a space vehicle, and more particularly, to a two-stage, integrated densification system configured to densify liquid oxygen to a temperature down to between about 70 Kelvin and 57 Kelvin. The first refrigeration stage is a nitrogen based reverse Brayton cycle refrigeration cycle configured to provide refrigeration to a helium and/or neon based second refrigeration stage.
Space vehicle launches require large quantities of liquid fuels and liquid oxygen to create the propulsion necessary to get the vehicle to space. Minimizing the volume and weight of the fuel/oxygen tanks is critically important to the viability of a rocket design. It is desired to fit all the necessary fuel into as small a volume as possible. Typically, cryogenic liquids are produced and stored in tanks in equilibrium with vapor at the liquid's boiling point temperature. Subcooling liquids below its boiling points can create a denser fluid which requires smaller tanks to hold the same mass or equivalent volume. The limit to the level of densification is solidification at the triple point of the material.
Cryogenic refrigeration systems have been used for decades in many rocket or space applications for purposes such as propellant or oxidant densification. For propellant or oxidant densification, the removal of sensible heat from a liquid propellant or oxidant, such as liquid oxygen, increases the density of the liquid, which is solely dependent on temperature since liquids are generally considered incompressible. Challenges facing the space industry related to propellant densification include reducing the operational and capital cost of propellant densification as well as reducing the time it takes to achieve the desired temperatures.
Supply of the liquid oxygen to a launch platform at a launch facility can require in excess of 40 trailers of liquid oxygen to be trucked into the launch facility where the liquid oxygen is then densified and similar or even more truckloads of a nitrogen based refrigerant for such densification. Current oxidant densification typically require more trailers of liquid nitrogen to be trucked in from external sources than trailers of liquid oxygen are required to densify the liquid oxygen which increases the overall logistics burden of trucking in liquid cryogens to the launch facility. The liquid nitrogen densification refrigerant is used just for cooling and thus is treated a consumable within the process. Examples of cryogenic based liquid oxygen densification systems that start with a liquid oxygen stream are shown and described in U.S. Pat. Nos. 10,808,967 and 11,293,671.
Such existing systems require the production of liquid oxygen at an air separation unit and trucking the liquid oxygen to a launch facility. Similarly, gaseous nitrogen is liquified at the air separation unit and the resulting liquid nitrogen is also trucked to the launch facility. At the launch facility, the trucked in liquid oxygen is densified using, in part, the trucked in liquid nitrogen. The ratio of liquid nitrogen used at the launch site to the liquid oxygen to be densified is roughly 2:1. This supply arrangement suffers from two challenges, namely the logistic challenges in transporting the large volumes of liquid oxygen and even larger volumes of liquid nitrogen from the air separation unit to the launch facility and the resulting waste nitrogen used at the launched facility that is most likely vented to the atmosphere.
Alternatively, one may transport gaseous oxygen and gaseous nitrogen from the air separation unit to the launch facility where they are liquefied and the liquid oxygen is subsequently densified. Examples of liquid oxygen densification systems that start with a gaseous oxygen stream are disclosed in U.S. provisional patent application 63/478,547 filed on Jan. 5, 2023, the disclosure of which is incorporated by reference herein. While this supply arrangement represents an improvement over the conventional launch site supply arrangements, it also suffers from logistic challenges, namely the construction, maintenance and operation of the required pipelines.
However, to further improve launch operations and further reduce operating costs, there is a need to improve upon the existing supply models, and specifically to reduce or eliminate the transport of liquid nitrogen via trucks to the launch facility. Thus, there is also a continuing need to develop improved refrigeration cycles for densification of liquid oxygen at locations apart from the launch facility where ample supply of liquid nitrogen are available and then transport the densified liquid oxygen to the launch platforms at the launch facility.
The present invention may be characterized as a system for production of a densified, liquid oxygen stream from a liquid oxygen stream. The present system comprises: (i) a first refrigeration stage configured to receive flow a nitrogen refrigerant through at least one first heat exchanger; and (ii) a second refrigeration stage configured to flow a helium or neon containing second refrigerant through a second heat exchanger configured to cool the helium or neon containing second refrigerant via indirect heat exchange with one or more streams of the nitrogen refrigerant. The second refrigeration stage is also configured to flow the helium or neon containing second refrigerant through a densification heat exchanger to subcool and densify the liquid oxygen stream via indirect heat exchange with the cooled, helium or neon containing second refrigerant. The first refrigeration stage further comprises at least four circuits, such as a first warm refrigeration circuit, a second cold refrigeration circuit, a residual refrigeration circuit, and one or more recycle circuits. Within the first refrigeration stage, the nitrogen refrigerant flowing through the first heat exchanger is split into a first warm portion in the first warm refrigeration circuit, a second cold portion in the second cold refrigeration circuit, and a residual portion of the nitrogen refrigerant stream in the residual refrigeration circuit. Within the first warm refrigeration circuit there is a warm turbine configured to expand the first warm portion the nitrogen refrigerant stream to yield an intermediate pressure warm exhaust and within the second cold refrigeration circuit there is a cold turbine configured to expand the second cold portion the nitrogen refrigerant stream to yield an intermediate pressure cold exhaust. The residual portion of the nitrogen refrigerant stream is also expanded to yield an expanded residual stream. The warm exhaust, the cold exhaust, and at least a portion of the expanded residual stream are recycled via the heat exchanger in the one or more recycle circuits to cool the nitrogen refrigerant stream and the recycled streams are compressed in one or more nitrogen recycle compressors.
The present invention may also be characterized as 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 reverse Brayton refrigeration cycle and 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 second refrigerant to yield a densified, liquid oxygen stream; and (v) transporting the densified, liquid oxygen stream to one or more launch platforms disposed at a launch facility.
As indicated above, the first refrigeration stage is preferably a reverse Brayton cycle refrigeration stage and step (ii) of the above-described method further comprises the steps of: (a) splitting the nitrogen refrigerant into a first warm portion, a second cold portion, and a residual portion of the nitrogen refrigerant stream; (b) expanding the first warm portion the nitrogen refrigerant stream in a warm turbine to yield an intermediate pressure warm exhaust; (c) expanding the second cold portion the nitrogen refrigerant stream in a cold turbine to yield an intermediate pressure cold exhaust; (d) expanding the residual portion of the nitrogen refrigerant stream to yield an expanded residual stream; (e) 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; and (f) compressing the recycled warm exhaust, the recycled cold exhaust, and the recycled expanded residual stream in one or more nitrogen refrigerant recycle compressors. In many embodiments, one of the one or more streams of the nitrogen refrigerant flowing through the second heat exchanger comprises a diverted portion of the cold exhaust.
In the preferred embodiments, the second refrigerant comprises a helium refrigerant, a neon refrigerant or some combination of helium and neon refrigerants with maybe small amounts of other gases such as nitrogen and oxygen through a second heat exchanger to subcool the liquid oxygen stream and yield a densified, liquid oxygen stream. The present system and method may also include a third refrigeration stage comprising a third heat exchanger that is configured to densify a stream of liquid methane via indirect heat exchange with a diverted portion of the nitrogen refrigerant stream to yield a densified, liquid methane stream. Lastly, in the preferred system for production of a densified, liquid oxygen stream, the first refrigeration stage and/or the second refrigeration stage may be disposed on moveable platforms or skids and transported, as needed to support launches of space vehicles at different locations
In some other preferred embodiments, the expanded residual stream may be split into a first expanded residual stream and a second expanded residual stream. The first expanded residual stream is then further expanded and then recycled via the first heat exchanger as a low pressure return stream to cool the first refrigerant stream. In such embodiments, the second expanded residual stream is directed to the second refrigeration stage as 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. Both the warmed, low pressure return stream and the other warmed nitrogen refrigerant streams flowing through the second heat exchanger are returned to the first refrigeration stage and compressed in the one or more of the first refrigerant recycle compressors.
It is believed that the claimed system and method will be better understood when taken in connection with the accompanying drawings in which
Turning to
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The embodiment depicted in
The embodiment depicted in
As indicated above, the embodiment of the present system and method shown in
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.
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.
This application claims the benefit of and priority to U.S. provisional patent application Ser. Nos. 63/478,547 filed on Jan. 5, 2023 and 63/484,003 filed on Feb. 9, 2023 the disclosures of which are incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63484003 | Feb 2023 | US | |
| 63478547 | Jan 2023 | US |
