System and Method for the Production and Supply of a Densified Liquid Oxygen Product

The present invention relates to a system and method for the production and supply of a densified liquid oxygen product for use in space vehicle applications, and more particularly, to a system and method for production of a densified, liquid oxygen stream from a high pressure gaseous oxygen stream at a space launch facility using high pressure air or synthetic air as the refrigerant.

Space vehicle launch applications require large quantities of liquid fuels and liquid oxygen to create the propulsion necessary to get the vehicle into space. The quantities of liquid oxygen are very large and often exceed 1000 mtpd and the liquid oxygen must be densified by deep sub-cooling to maximize the oxidant payload of the launch. Subcooling the liquid oxygen below its' boiling point creates a denser oxidant which then requires smaller tanks to hold the same volume. The limit to the level of densification is solidification at the triple point of the material. Minimizing the volume and weight of the fuel/oxygen tanks is critically important to the viability of a rocket design and it is desired to fit all the necessary fuel/oxygen into as small a volume as possible.

Challenges facing the space industry related to oxygen densification include reducing the operational costs, including the power costs as well as reducing the capital costs of oxygen densification. Depending on the size of the space vehicle, 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. The use of so many liquid trailers for the delivery of the liquid oxygen is problematic from both a logistical and safety prospective. Most current oxidant densification processes conducted at space vehicle launch facilities also typically require more trailers of liquid nitrogen required to densify the liquid oxygen to be trucked in from external sources than trailers of liquid oxygen. This further increases the overall logistics burden of trucking in numerous truckloads of liquid nitrogen or other cryogenic liquids to the launch facility.

To further improve launch operations and reduce operating costs, there is a clear need to reduce or eliminate the transport of liquid oxygen and liquid nitrogen via trucks to the launch facility. In addition, there is a continuing need to develop improved refrigeration cycles for the liquefaction and densification of the oxygen at the launch facility. Improved refrigeration cycles for liquefaction and densification of the oxygen should both enhance the densification of the liquid oxygen used as the oxidant in space vehicle launch applications as well as reduce the power costs associated with such liquefaction and densification, ideally to a point where the liquefaction and densification of the oxygen consumes negligible power. Current liquefaction and densification processes performed at space vehicle launch facilities can require delivery of the power often in excess of 30 MW, which depending on the location and configuration of the launch site may be impractical.

Examples of conventional liquid oxygen densification systems are shown and described in U.S. Pat. Nos. 10,808,967 and 11,293,671. These and numerous other processes have been developed which utilizes liquid nitrogen and/or rare gases to produce liquid oxygen via indirect heat exchange. See for example U.S. Patent Application Publication No. 2023/068126, which discloses a process whereby liquid nitrogen is vaporized and turbo-expanded for purposes of absorbing the energy necessary to convert gaseous oxygen into liquid oxygen. Alternatively, high pressure gaseous nitrogen has been proposed to the liquefaction and densification of oxygen for space vehicle launch applications on offshore platforms, as disclosed in U.S. Patent Application Publication No. 2022/099364.

The present invention may be characterized as a system for production of a densified, liquid oxygen stream from a high pressure gaseous oxygen stream comprising: (i) a heat exchanger arrangement comprising a first heat exchange device configured to liquefy the high pressure gaseous oxygen stream and at least one high pressure gaseous air stream having a pressure greater than or equal to about 10 bar (a) via indirect heat exchange with a refrigerant stream to yield a liquid oxygen stream and a liquid air stream and a second heat exchange device configured to densify the liquified oxygen stream via indirect heat exchange with the liquid air stream to yield a densified liquid oxygen stream and a cold vaporized air stream; and (ii) one or more turbines configured to expand a diverted portion of the at least one high pressure gaseous air stream to yield one or more exhaust streams. The refrigerant stream comprises a mixture of the one or more exhaust streams and the cold vaporized air stream. The present system is preferably disposed proximate a space vehicle launch platform at a launch facility. The high pressure gaseous oxygen stream and the at least one high pressure gaseous air stream are preferably supplied to the launch facility via a pipeline from an air separation unit located within about 2 kilometers of the launch facility.

Alternatively, the present invention may be characterized as a method for production of a densified, liquid oxygen stream from a high pressure gaseous oxygen stream comprising the steps of: (a) liquefying the high pressure gaseous oxygen stream and at least one high pressure gaseous air stream having a pressure greater than or equal to about 10 bar (a) via indirect heat exchange with a refrigerant stream in a heat exchanger arrangement to yield a liquid oxygen stream and a liquid air stream; (b) densifying the liquified oxygen stream via indirect heat exchange with the liquid air stream in the heat exchange arrangement to yield the densified liquid oxygen stream and a cold vaporized air stream; (c) expanding a diverted portion of the at least one high pressure gaseous air stream and in one or more turbines to yield one or more exhaust streams; and (d) mixing the one or more exhaust streams and the cold vaporized air stream to yield the refrigerant stream. The heat exchange arrangement preferably comprises a first heat exchange device or heat exchange core configured to liquefy the high pressure gaseous oxygen stream and at least one high pressure gaseous air stream as well as a second heat exchange device or heat exchange core configured to densify the liquified oxygen stream.

In various embodiments of the present system and method, there may be one or more auxiliary compressors configured to compress the high pressure air stream to a pressure greater than or equal to about 50.5 bar (a). Also, the one or more turbines further comprise a first turbine configured to expand a diverted portion of the at least one high pressure gaseous air stream to yield a first exhaust stream and a second turbine configured to further expand the first exhaust stream to yield a second exhaust stream, and wherein the refrigerant stream comprises a mixture of the second exhaust stream and the cold vaporized air stream. Optionally, the one or more turbines may also include a third turbine configured to expand a second diverted portion of the high pressure gaseous air stream to yield a third exhaust stream, and wherein the second turbine is further configured to further expand a mixture of the first exhaust stream and the third exhaust stream to yield the second exhaust stream. Preferably, the present system and method further comprises an integral gear machine operatively coupling the one or more turbines and the one or more auxiliary compressors. In such embodiments, the work provided by the one or more turbines is preferably equal to or greater than the work required by the one or more auxiliary compressors.

In most embodiments at least a portion of the high pressure air stream, and preferably the bulk of the high pressure air stream, is used for the liquefaction of the high pressure gaseous oxygen stream. A second portion of the high pressure air stream is liquefied and subsequently evaporated at a pressure equal to and preferably less than ambient/atmospheric pressure. Optionally, a portion of the liquid air could be stored in a storage tank at the launch facility for an additional degree of flexibility in the present refrigeration system and method. A significant advantage is also realized by recouping the sensible cold from the evaporated stream by way of a vacuum pump that is configured to pressurize the cold vaporized air stream and recycle the cold vaporized air stream as part of the refrigerant stream. Also, the high pressure air stream can be a traditional liquid air stream produced as part of the air separation cycle from the nearby air separation plant or the high pressure air stream may alternatively be a synthetic air stream comprising a mixture of oxygen and nitrogen from the air separation unit.

The present system and method for the production of the densified, liquid oxygen stream incorporates several innovative and/or advantageous features when compared to conventional oxygen densification systems and processes currently used in many space vehicle launch applications. The first advantageous feature involves piping high pressure gaseous oxygen stream and a stream of high pressure purified air from a nearby air separation unit to the liquefaction site, preferably at the launch facility. The high-pressure purified air serves to provide the necessary pressure energy to facilitate liquid oxygen production and densification. This refrigeration necessary for the oxygen liquefaction and densification is preferably generated by gas expansion refrigeration process using diverted portions of the high pressure purified air stream. A second innovative aspect of the present system and method employs the integration of the oxygen liquefaction process with the oxygen densification process. The use of a cryogenic liquefaction process using the high pressure purified air stream enables the direct on-site integration of the densification process.

Another innovative aspect of the present system and method involves the use of an integral gear combined expansion-compression device, such as a compander or bridge machine (i.e. BRIM) that actually consumes negligible power. Such a compander or bridge machine would serve to both recoup the energy or work from the gas-expansion of the high pressure purified air streams and as means to redistribute the power to associated compression of the high pressure purified air streams. In this way, little or no external power needs to be brought to the liquefaction site. Yet another innovative or advantageous aspect involves the use of multiple turbo-expanders, operatively coupled to the integral gear machine to facilitate a high efficiency liquefaction of the high pressure gaseous oxygen stream. It has been found that the use of three turbo-expanders in addition to one or more auxiliary feed air compressors operatively coupled in a three pinion compander or bridge machine enables oxygen liquefaction at high efficiency.

Turning now to, there is shown a highly simplified depiction of the general processing scheme for the production and supply of a densified, liquid oxidant to a launch facility for use in a space vehicle launch. As seen therein, a high pressure gaseous oxygen streamis produced by an air separation unitlocated in proximity to a space vehicle launch facility. The high pressure gaseous oxygen streamis delivered to the space vehicle launch facilityvia an oxygen pipeline. Optionally, a high pressure air streamor synthetic air stream, comprised of a mixture of oxygen and nitrogen from the air separation unit, may also be directed via a pipeline from the air separation unitto the space vehicle launch facility. The high pressure air streamis preferably delivered via pipeline to the launch facilityat a pressure equal to or greater than 10 bar (a) and preferably at a pressure greater than 20 bar (a). Preferably, the air separation unitis located within 2 kilometers of the launch facility. The high pressure gaseous oxygen streamand the high pressure air streamare directed to a combined liquefaction and densification systemwhere the high pressure gaseous oxygen streamis liquefied and the resulting liquid oxygen streamis densified as described in more detail below with reference to. Preferably, the high pressure gaseous oxygen streammay be further compressed at the launch facility and delivered to the liquefaction process in a supercritical state. The resulting product from the combined liquefaction and densification system/process is a densified liquid oxygen productmay be stored in a storage tankand used in rocket launch applications from one or more launch padslocated at the launch facility. A low pressure stream of waste airfrom the liquefaction and densification process/system may be vented to the atmosphere or optionally recycled back to the air separation unit or used in other applications for clean dry air.

The air separation unitshown inis equipped with the conventional warm-end processing equipmentand cold-end processing equipment. The warm-end processing equipmentwithin the air separation unittypically comprises a main feed air compression train and air pre-purification units configured to substantially compress and pre-purify an incoming feed air stream, together with one or more turbine air circuits and/or booster air circuits. A portion of the substantially compressed and pre-purified airis extracted as a high pressure purified air stream from the warm end processing equipmentwithin the air separation unit. The cold-end processing equipmentwithin the air separation unittypically comprises a main or primary heat exchanger arrangement and a distillation column system that are typically housed in one or more insulated cold boxes. The cold-end processing equipmentwithin the air separation unitis configured to cool a portion of the substantially compressed and purified airand then fractionally distill or separate the cooled air in the distillation column system to yield a plurality of products, including a high-pressure gaseous oxygen streamand perhaps liquid nitrogen, liquid oxygen or argon products.

In the arrangement depicted in, liquid storage tanks are also preferably located at the launch facilityto store the densified liquid oxygen and optionally any liquid air produced within the combined liquefaction and densification system or other liquid products such as liquid nitrogen or liquid fuels such as methane needed at the launch facility. Although not shown, the liquefaction and densification system and/or components thereof may be disposed on moveable platforms that can be aggregated at a central location within the launch facilityor can be readily moved to a location proximate a space vehicle launch pador platform within the launch facility.

Turning now to, the illustrated liquefaction and densification systemand associated method receives a stream of high pressure gaseous oxygenpreferably at a pressure greater than or equal to 40 bar (a) and more preferably at a pressure greater than about 60 bar (a). The high pressure gaseous oxygen streamis directed to a first heat exchanger deviceor heat exchanger core configured to cool and condense the high pressure gaseous oxygen streamvia indirect heat exchange with a refrigerant stream to yield a liquid oxygen stream. The liquid oxygen streamis then directed to a second heat exchange deviceconfigured to subcool or densify the resulting liquid oxygen streamvia indirect heat exchange with a liquid air streamto yield the densified liquid oxygen streamand a cold vaporized air stream.

The illustrated liquefaction and densification systemand associated methods also receives one or more streams of high pressure gaseous airhaving a pressure preferably greater than or equal to about 10 bar (a), more preferably at a pressure greater than about 20 bar (a), and most preferably at a pressure equal to or greater than about 25 bar (a). The high pressure gaseous air streammay be further compressed in one or more auxiliary compressorsto a pressure at or near the supercritical pressure. The further compressed high pressure air stream is aftercooled in aftercoolerand directed to the first heat exchanger deviceor heat exchanger core. A first fraction of the further compressed high pressure air streamis pre-cooled or partially cooled and then diverted as streamto a first turbineor warm turbo-expander. The first exhaust streamexiting this first turbinewill typically be near saturation at a pressure preferably in the range of 5 bar (a) to 10 bar (a). The first exhaust streamis partially warmed in the first heat exchange deviceand the warmed streamis directed to a second turbineor cold turbo-expander which serves to further expand the warmed first exhaust to a pressure marginally above ambient or preferably about 1.2 bar (a) to yield a second exhaust stream. The second exhaust streamis directed back to the first heat exchange deviceas part of the refrigeration stream.

Another fraction of the further compressed high pressure air stream is fully cooled to a point where it is substantially liquefied. The liquefied air streamis then depressurized via an expansion valveand/or liquid turbine to a sub-ambient pressure. The depressurized streamis then substantially vaporized in a vacuum within the second heat exchange deviceor second heat exchange core against the liquid oxygen stream. The resulting cold vaporized air streamis pulled through a vacuum pumpand repressurized to a pressure just above ambient pressure or preferably to a pressure of about 1.2 bar (a). The repressurized cold vaporized air streamis directed back to the first heat exchange deviceas part of the refrigeration stream. As such, the refrigeration stream used to liquefy the high pressure gaseous oxygen streamand liquefy a portion or fraction of the high pressure air streamcomprises a mixture of the one or more exhaust streamsand the cold vaporized air stream.

The work resulting from expansion of a portion of the high pressure air stream in the first and second turbines is preferably directed to an integral gear compression-expansion device so that this work may be recouped for use in the further compression of the incoming or feed high pressure air stream in the one or more auxiliary compressorsand/or the vacuum pump. Ideally, the further compression of the feed high pressure air stream in the one or more auxiliary compressorsand re-pressurization of the sub-ambient cold vaporization air stream will be defined such that an energy balance within the integral gear compression-expansion device may be established without the import or export of additional power. In practice, however, the work provided by the one or more turbines,should be greater than 90% of the work required by the one or more auxiliary compressorsand the vacuum pump.

The schematic and process flow diagram depicted inis very similar to the schematic and process flow diagram ofdescribed above and, for sake of brevity, much of the descriptions of the detailed arrangements will not be repeated. Rather, the following discussion will focus on the differences and additions depicted in the process flow diagram ofwhen compared to the process flow diagram depicted in.

In the embodiment of, the high pressure gaseous oxygen streampreferably at a pressure greater than or equal to 40 bar (a) and more preferably at a pressure greater than about 60 bar (a) is cooled and condensed within the first heat exchange device, and the resulting liquid oxygen streamis then subcooled in the second heat exchange devicevia indirect heat exchange with a liquid air streamto yield the densified liquid oxygen streamand a cold vaporized air stream.

The key difference between the embodiment ofand the embodiment ofis that the high pressure gaseous air streamis further compressed to a supercritical pressure and then split into three fractions. Similar to the embodiment of, a first fraction of the further compressed high pressure air streamis diverted to a first turbinewhere it is expanded to produce a first exhaust stream. A second fraction of the further compressed high pressure air stream is fully cooled in the first heat exchangedevice to a point where it is substantially liquefied. The liquefied air streamis then depressurized via an expansion valveand/or liquid turbine to a sub-ambient pressure. A third fraction of the further compressed high pressure air stream is cooled in the first heat exchange deviceand the cooled streamis diverted to a third turbinewhere it is expanded to produce a third exhaust stream.

The first exhaust streamand the third exhaust streamare both warmed in the first heat exchange devicepossibly in different warming passages within the first heat exchange deviceand then mixed. The resulting mixed exhaust streamis then directed to the second turbineor cold turbo-expander which serves to further expand the mixed exhaust stream to a pressure marginally above ambient or preferably about 1.2 bar (a) to yield the second exhaust stream. The second exhaust streamis then directed back to the cold end of the first heat exchange deviceas part of the refrigeration stream. Note that in this embodiment, the temperature of the third turbine exhaustis comparable to the temperature of the second turbine exhaust.

Similar to the embodiment of, the resulting cold vaporized air streamin the embodiment ofis pulled through the vacuum pumpand repressurized to a pressure of about 1.2 bar (a). The repressurized cold vaporized air streammay be combined with the low-pressure exhaust streamof the second turbineas the refrigeration stream. The combined refrigeration stream is then warmed to ambient temperature, with the resulting low pressure air streampreferably being either vented or recycled back to the air separation unit.

The most obvious technical advantage realized by the present system and method for production of a densified, liquid oxygen stream from a pipeline supplied high pressure gaseous oxygen stream using pipeline supplied high pressure air streams as the refrigerant would be the elimination of the need to truck liquid oxygen and/or liquid nitrogen to the launch facility. Furthermore, there would be no need to have an additional refrigeration system for densification of liquid oxygen. By integrating the oxygen densification with the liquefaction using high pressure air streams, the disposable use of liquid nitrogen in conventional oxygen densification processes will be substantially reduced, if not eliminated. The use of a compander or bridge machine to recoup gas expansion power from the turbine expansion of the high pressure air streams would enable both a high efficiency liquefaction process and would potentially eliminate the capital associated with building out the high voltage power supply at the launch facility for oxygen liquefaction and densification purposes.

In a space vehicle launch applications requiring 1000+ mtpd of liquid oxygen, the external liquid nitrogen supply is typically about 0.4 (LN2/LO2). It is anticipated that if this requirement of liquid nitrogen were to be eliminated, the potential power savings realized by the air separation unit is on the order of about 10 MW. The reduction of liquid nitrogen demand from the air separation unit will also substantially simplify the air separation unit and air separation cycle design necessary to supply the high-pressure oxygen without supply of liquid nitrogen. A true gas only air separation unit designed to produce mainly high pressure gaseous oxygen stream and high pressure air streams required by the present system and method will likely require only a single turbine and a booster air compressor. The capital cost savings in the sir separation unit will likely be several million dollars compared to a dedicated integrated air separation and liquefaction plant currently used to supply liquid oxygen and liquid nitrogen to space application customers.

While the present systems and methods for the production of a densified liquid oxygen product has been described with reference to one or more preferred embodiments, it is understood that numerous variations, additions, changes, and omissions can be made without departing from the spirit and scope of the present systems and methods as set forth in the appended claims.

For example, with respect the air compression, dedicated air compression for refrigeration production is possible. The main air compression and associated pre-purification may reside at either or both locations, namely the air separation unit or the launch facility. Also, the main air compression as well as the auxiliary compression may be arranged in a serial compression arrangements or a parallel compression arrangements depending on the flow and pressure requirements from the space application customer together with any secondary requirements such as supply of merchant liquid or the need for liquid air energy storage. The air pre-purification demands may also be partitioned between the air separation unit and the launch facility. For instance, high pressure gaseous air supplied to the launch facility via pipeline may initially be dehydrated via absorption at the air separation unit and then piped to the launch facility where it may be further dried to a cryogenic ready condition.

In order to increase the liquid air yield fraction, a liquid turbine or dense phase expander may be employed to reduce the subsequent flash loss of the liquid air. Such a machine may be configured in series with subsequent valving to fully reduce the liquid air pressure prior to entry into the second heat exchange device for densification.

Also, while the liquefaction of supercritical oxygen at pressures>50.5 bar (a) is thermodynamically preferred, it is possible to configure the above-described system and method for lower oxygen pressures. In addition, it is possible to further compress the oxygen at the ASU or at the Launch pad. Such compression could be integrated into the integral gear machine.

The process may be operated without integral liquid oxygen densification or the process could be operated with intermittent liquid oxygen densification in which case the non-densified, liquified oxygen is simply stored in one or more storage tanks at the launch facility for subsequent densification or use. It is also conceivable to add a supplemental or alternative densification means using a different densification refrigerant such as rare gases, argon, or even liquid nitrogen. It is also possible to incorporate methane densification along with oxygen densification into the densification process Alternatively, one may even design the current liquefaction process to also liquefy a small stream of gaseous nitrogen from the air separation unit in conjunction using the high pressure air stream as the refrigerant, with the resulting liquid nitrogen subsequently stored in storage tanks or employed for supplemental densification or densification of methane.

Although it is highly advantageous to integrate the subject gas expanders into a common, single BRIM type machine, this need not be the case. Alternatively, the subject turbines or turbo-expanders may be connected to high speed generators or the power can be dissipated to brake. It should be noted that the vacuum compressor could also be integrated into the BRIM type machine. If power is available, the BRIM could employ a motor (or a generator). It is also possible to configure the auxiliary compressors as a dedicated booster compressors and operatively couple one or more of the auxiliary compressors to one or more of the turbines.