Patent Application
20240230220
The present invention relates to a system and method for liquefaction of a gaseous oxygen stream for use as an oxidant for a space vehicle, and more particularly, to a system and method for both liquefaction of a gaseous oxygen stream and the densification of the resulting liquid oxygen stream.
Space vehicle launches require large quantities of cryogenic 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 the liquids below their boiling points can create a denser fluid which requires smaller tanks to hold the same volume. The limit to the level of densification is solidification at the triple point of the material.
Supply of the liquid oxygen to a launch platform at a launch facility typically requires in excess of 40 trailers of liquid oxygen to be trucked into the launch facility where the liquid oxygen is then densified. Similarly, liquid propellants such as liquid methane are also trucked to the launch facility
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. Examples of cryogenic based liquid oxygen densification systems are shown and described in U.S. Pat. Nos. 10,808,967 and 11,293,671.
Another challenge in propellant and oxidant densification is that it typically is performed at the liquid storage location near the launch platform using liquid nitrogen as the densification refrigerant. 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 a consumable within the process.
However, to further improve launch operations and reduce operating costs, there is a need to reduce or eliminate the transport of liquid oxygen via trucks to the launch facility and improve the supply arrangements for liquid propellants and oxidants. Thus, there is a continuing need to develop improved refrigeration cycles for liquefaction of gaseous oxygen and the densification of the resulting liquid oxygen as well as densification of other liquid propellants at the launch facility for use in launching space vehicles.
The present invention may be characterized as a system for production of a densified, liquid oxygen stream from a low pressure gaseous oxygen stream. The present system comprises: (i) a first refrigeration stage configured to receive a first refrigerant and flow the first refrigerant through a first primary heat exchanger to cool the low pressure gaseous oxygen stream and liquefy the cooled low pressure gaseous oxygen stream to yield a liquid oxygen stream; and (ii) a second refrigeration stage configured to flow a second refrigerant through a second heat exchanger to subcool the liquid oxygen stream and yield a densified, liquid oxygen stream. The first refrigeration stage includes a first warm refrigeration circuit, a second cold refrigeration circuit, a residual refrigeration circuit, and one or more recycle circuits. The first refrigerant flowing through the first heat exchanger is split into at least three portions, namely 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. The first refrigeration stage also preferably includes 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; and an expansion valve for expanding the residual portion of the first refrigerant stream. The warm exhaust and the cold exhaust are recycled in the one or more recycle circuits via the first heat exchanger to cool the low pressure gaseous oxygen stream. The first refrigeration stage also includes a first subcooler that is configured to receive all or a part of the expanded residual portion of the first refrigerant stream and subcool the low pressure gaseous oxygen stream and then liquefy the resulting subcooled stream via indirect heat exchange between the two streams. The warmed first refrigerant stream is then recycled via the one or more recycle circuits, which include one or more first refrigerant recycle compressors configured to compress the recycled warm exhaust, the recycled cold exhaust, and the recycled warmed first refrigerant stream.
The low pressure gaseous oxygen is preferably at a pressure of between about 1.5 bar(a) and 3.0 bar(a) and is supplied to the launch facility via an oxygen pipeline from a nearby air separation unit. Optionally, the nitrogen refrigerant used in the first refrigeration stage may also be supplied via a nitrogen pipeline from the nearby air separation unit. The densified, liquid oxygen stream, together with any liquid nitrogen and any densified liquid propellant, such as liquid methane may be stored in a plurality of storage tanks at the launch facility.
The two-stage refrigeration system used to liquify and subsequently densify the oxygen is preferably a modular or moveable unit that is transported between different launch platforms at a given launch facility. The first refrigeration stage is preferably a reverse Brayton refrigeration cycle disposed at the launch facility and is configured to receive a nitrogen-based refrigerant, cool the gaseous oxygen and then liquefy the cooled gaseous oxygen stream via indirect heat exchange to yield the subcooled, liquid oxygen stream. The second refrigeration stage is configured to flow a second mixed refrigerant comprising helium refrigerant, 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.
In some preferred embodiments, the expanded residual portion of the first refrigerant stream is split into a first expanded residual portion and a second expanded residual portion. The first expanded residual portion is used to liquify the gaseous oxygen and subcool the liquid oxygen stream and then recycled as an intermediate pressure return stream (e.g. between about 5 bar(a) and 10 bar(a)) while the second expanded residual portion and the second expanded residual portion is further expanded and used to subcool the liquid nitrogen refrigerant stream and then recycled as a low pressure return stream. The low pressure return stream is then compressed first in a feed compressor to an intermediate pressure and then to the multi-stage recycle compressor to a final pressure, preferably greater than about 50 bar(a).
In other preferred embodiments of the present system and method, the second refrigeration stage further comprises an auxiliary heat exchanger configured to cool the second refrigerant via indirect heat exchange with a diverted portion of the cold exhaust and wherein the diverted portion of the cold exhaust is then recycled to the one or more first refrigerant recycle compressors. The second refrigeration stage is preferably 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.
In still other preferred embodiments of the present system and method, a third refrigeration stage comprising a third heat exchanger is configured to densify a stream of liquid methane via indirect heat exchange with a diverted portion of the first refrigerant stream to yield a densified, liquid methane stream.
Where possible, it would be advantageous to dispose the first refrigeration stage and the second refrigeration stage on moveable platforms that can be transported to a location proximate a space vehicle launch platform at a launch facility.
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
Various embodiments and components of the present system and method for the combined liquefaction of a gaseous oxygen stream and densification of the resulting liquid oxygen stream are schematically depicted in
Turning now to
The first refrigeration stage uses a high pressure nitrogen refrigerant stream 55 at a pressure of about 50 bar(a) that is cooled a first heat exchanger 50 that can be segmented into a plurality of heat exchange sections, E1, E2, E3. To cool the high pressure nitrogen refrigerant stream 55, the first heat exchanger 50 is configured to include a first warm refrigeration circuit 52, a second cold refrigeration circuit 54, a residual refrigeration circuit 56, and one or more recycle circuits 58,59.
The nitrogen refrigerant stream 55 is referred to as a first refrigerant stream and is preferably split into three portions as it traverses the first heat exchanger 50, namely a first warm portion 62 of the first refrigerant stream that traverses through the first warm refrigeration circuit 52, a second cold portion 64 of the first refrigerant stream that traverses through the second cold refrigeration circuit 54, and a residual portion 66 of the first refrigerant stream that traverses through the residual refrigeration circuit 56. 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 58, 59.
The first refrigeration stage also preferably includes a warm turbine 63 configured to expand the first warm portion 62 the first refrigerant stream to yield an intermediate pressure warm exhaust 72 at a pressure of about 6 bar(a) and a cold turbine 65 configured to expand the second cold portion 64 the first refrigerant stream to yield an intermediate pressure cold exhaust 74 also at a pressure of about 6 bar(a). The warm exhaust 72 and the cold exhaust 74 are recycled in the one or more recycle circuits 58 to cool the low pressure gaseous oxygen stream 30 and the nitrogen refrigerant stream 55.
More specifically, the intermediate pressure cold exhaust 74 is mixed with an intermediate pressure recycle stream 77 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 gaseous oxygen stream 30 and the nitrogen refrigeration stream 55. Similarly, the intermediate pressure warm exhaust 72 is also mixed with intermediate pressure recycle stream 78 before being fed into the cold end of exchanger section E2 where it also provides refrigeration for the cooling of the gaseous oxygen stream 30 and nitrogen refrigeration stream 55. The combined intermediate pressure recycle stream 79 (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 81, which is then compressed in one or more recycle compressors 88.
The residual portion 66 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 75. Prior to expansion, the residual portion 66 of the high pressure first refrigerant stream is at a temperature above its critical point, so that no phase transition occurs. However, once the residual portion 66 of the first refrigerant stream is expanded or ‘flashed’ to an intermediate pressure it may exist in the liquid phase. The pseudo-liquefaction is advantageous because it eliminates the constant temperature phase transition that can create a large ‘Delta-T’ in the first heat exchanger composite curve. A large ‘Delta-T’ represents an inefficiency and an increase in power consumption.
The intermediate pressure liquid nitrogen stream 76 is then subcooled in a nitrogen subcooler E4. A first portion 82 of the subcooled, intermediate pressure liquid nitrogen is further expanded or ‘flashed’ in expansion valve 85 to form a low pressure nitrogen refrigerant stream 83 at a pressure of about 1.5 bar(a) that is used to subcool the intermediate pressure liquid nitrogen 76 in the nitrogen subcooler E4. The now boiled, low pressure nitrogen refrigerant stream 83 is recycled via recycle circuit 59 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 86 is compressed in a multi-stage feed compressor 85 and mixed with the fully warmed, intermediate pressure nitrogen recycle stream 81. The combined recycle stream 87 is further compressed in a multi-stage recycle compressor 88 and cooled in aftercooler 94 to form the high pressure nitrogen refrigerant stream 55. Make up nitrogen 99, preferably from the nearby air separation unit, can be supplied at various points in the process depending on the pressure and phase of the nitrogen source.
The first refrigeration stage also includes a subcooler E5 that is configured to receive a second portion 84 of the subcooled, intermediate pressure liquid nitrogen which provides the refrigeration necessary to subcool and liquefy the cooled, low pressure gaseous oxygen stream 30 via indirect heat exchange between the two streams to yield the low pressure liquid oxygen stream 40. The warmed or boiled, intermediate pressure recycle stream 77 is then recycled via one or more recycle circuits 58 and further warmed in heat exchanger sections E3, E2, and E1.
The gaseous oxygen stream 30, preferably piped in from the nearby air separation unit, enters combined liquefaction and 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 76. In the current embodiments, the low pressure gaseous oxygen stream 30 is at a pressure of between 1.5 bar(a) and 3.0 bar(a), or higher, and more preferably at a pressure of about 2.3 bar(a). The low pressure gaseous oxygen stream 30 is then cooled to near its condensation temperature in heat exchanger sections E1, E2, and E3 of the first heat exchanger 50. The cooled, low pressure gaseous oxygen stream 35 is then liquefied and subcooled in subcooler E5 via indirect heat exchange against the subcooled, intermediate pressure liquid nitrogen stream 84. While the current drawings depict subcooler E5 as a single heat exchange vessel, the use of multiple heat exchange vessels could be considered in this approach such as a first vessel configured as an evaporator section and a second vessel configured as a sensible heat section. As indicated above, the resulting liquid oxygen stream 40 is at a temperature of about 81 Kelvin.
The subcooled liquid oxygen stream 35 is cooled even further, and thus densified, to a temperature of about 57 Kelvin in a densification heat exchanger E6. The cooling occurs against a second mixed refrigerant stream 95 comprising helium, neon, or combinations of helium and neon. The second mixed refrigerant stream 95 may also include small amounts of other gases such as nitrogen and oxygen.
The densification heat exchanger E6 and second mixed refrigerant stream 95 form part of the second refrigeration stage, which is preferably a closed loop refrigeration stage. As shown in the drawings, the second refrigeration stage is configured to flow the neon and/or helium containing second mixed refrigerant 95 through a second heat exchanger 90 and the densification heat exchanger E6. The second refrigeration stage also includes a second refrigerant recycle compressor 91 disposed downstream of the second heat exchanger 90 and configured to compress the second mixed refrigerant feed 92 to yield the compressed second mixed refrigerant 93 and an aftercooler 98 configured to cool the compressed second mixed refrigerant 93 to ambient temperature.
The second refrigeration stage also includes a second refrigerant turbine 96 disposed downstream of the second heat exchanger 90 and upstream of the densification heat exchanger E6. The second refrigerant turbine 96 is configured to expand the compressed second mixed refrigerant 93 to yield an exhaust stream 97 that provides the refrigeration for the densification heat exchanger E6 necessary to the further subcool the liquid oxygen stream 40 and yield a densified, liquid oxygen stream 45. The partially warmed second mixed refrigerant 95 exiting the densification heat exchanger E6 is further warmed in second heat exchanger 90 to create the second mixed refrigerant feed 92 to the second refrigerant recycle compressor 91. The partially warmed second mixed 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 91. 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.
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 88. 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 85 as a stand-alone multi-stage centrifugal machine.
In addition to the work supplied by the warm turbine and cold turbine, the external power required to drive the multi-stage compressors and/or the ‘bridge’ machine are preferably obtained from renewable energy sources, such as solar power sources, located or disposed at the launch facility. As the need for densified liquid oxygen at the launch facility is typically an intermittent requirement at or near a space vehicle launch window, the use of renewable power sources, such as solar power, for the present system and methods is ideal. Also, in some embodiments may optionally be configured to operate as a nitrogen liquefaction system that takes gaseous nitrogen via the pipeline from the nearby air separation unit and produces and stores liquid nitrogen for other uses at the launch facility or in the surrounding liquid nitrogen merchant markets or the liquid nitrogen can be stored and subsequently used as an alternate source of power via a Liquid Nitrogen Energy Storage (LNES) system . Whatever the use, the production of liquid nitrogen could make economic sense during periods when there are no scheduled space vehicle launches from the launch platforms at the launch facility and the requirement for densified liquid oxygen at the launch facility is reduced.
The process flow diagrams depicted in
In the embodiment depicted in
In the embodiment depicted in
In this embodiment, the first refrigeration stage also includes subcooler E5 that is configured to receive the second portion 84 of the subcooled, intermediate pressure liquid nitrogen and the expanded stream 384 which provides the refrigeration necessary to subcool the liquid oxygen product to a temperature of about 81 Kelvin via indirect heat exchange between the two streams to yield the low pressure liquid oxygen stream 40. The warmed intermediate pressure recycle stream 177 exiting subcooler E5 is then recycled via one or more recycle circuits 58 and further warmed in heat exchanger sections E3, E2, and E1 together with the other intermediate pressure recycle streams to ambient temperatures prior to re-compression in the recycle compressor 88.
The embodiment depicted in
In addition, the residual portion 66 of the high pressure first refrigerant stream is split into two fractions, including the first high pressure residual fraction 166 and the second high pressure residual fraction 266. Similar to the embodiment of
Subcooler E5 is configured to receive the second portion 84 of the subcooled, intermediate pressure liquid nitrogen and the expanded stream 384 which provides the refrigeration necessary to subcool the liquid oxygen and yield the low pressure liquid oxygen stream 40. The warmed intermediate pressure recycle stream 177 exiting subcooler E5 is then recycled via one or more recycle circuits 58 and further warmed in heat exchanger sections E3, E2, and E1 together with the other intermediate pressure recycle streams to ambient temperatures.
While the present systems and methods for combined or integrated liquefaction and densification of gaseous oxygen have been described with reference to one or more 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 methods as set forth in the appended claims.
This application claims the benefit of and priority to U.S. provisional patent application Ser. No. 63/478,547 filed on Jan. 5, 2023 the disclosure of which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63478547 | Jan 2023 | US |
