Carbon dioxide re-liquefaction

Abstract

Carbon dioxide re-liquefaction may be provided by a system capable of receiving a vented boiled off gas stream from a storage vessel at a first compressor; compressing the vented BOG stream at the first compressor into a first compressed BOG stream at a first pressure and a second compressed BOG stream at a second pressure, greater than the first pressure; cooling the first compressed BOG stream in a heat exchanger to produce a liquid stream by: cooling, via a refrigerant unit, the second compressed BOG stream to produce a first cold stream, of a temperature less than that of the first compressed BOG stream; exchanging heat from the first compressed BOG stream against tire first cold stream; and returning the liquid stream to the storage vessel.

Description

Attorney Docket No.: 6015645.00037TITLE CARBON DIOXIDE RE-LIQUEFACTIONCROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The present disclosure claims the benefit and priority of US Provisional Patent Application No.: 63 / 725,342, which was filed on 2025-11-26 and titled CARBON DIOXIDE RE-LIQUEFACTION, and, to the extent permitted by law, the entirety of which is incorporated herein by reference.BACKGROUND

[0002] Liquefaction is a process where the boiled off gas (BOG) from a storage tank is chilled and converted back to the liquid phase in order to control the pressure in the storage tanks and reduce / eliminate release of the BOG into the atmosphere from the tank. In various systems, re-liquefacation is performed by an external mechanical refrigerator or by a multistage BOG compression / expansion systems, but conventional systems are often energy intensive to operate or result in BOG release. Tire energy intensive nature of such systems run counter to the objectives of using these systems in a carbon-capture setting, as the additional production of energy to maintain the captured gas in a liquid state may result in additional greenhouse gases being released to generate the energy needed or as the efficiency of the initial capturing operation is reduced by releasing some of the initially captured gas as BOG.SUMMARY

[0003] The present disclosure provides an improved carbon dioxide (CO2) re-liquefaction system. The presently described system uses a refrigerant closed loop unit and feeds the boiled off gas (BOG) at the second stage compressor together with the first stage BOG compressor to increase the overall pressure of the BOG. Tire BOG is then split at the second stage BOG compressor discharge, liquefied through a series of heat exchangers, and returned to the storage tank as a liquid. When the BOG is CO2, CO2 may also be used as the refrigerant for the system, thereby allowing for closed-loop refrigeration.

[0004] Additional features and advantages of the disclosed method and apparatus are described in, and will be apparent from, the following Detailed Description and the Figures. The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the figures and description. Moreover, it should be noted that the language used in the11400583405.1Attorney Docket No.: 6015645.00037specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 illustrates an example deployment scenarios for storage vessels that may be used in conjunction with the described gas re-liquefaction system, according to embodiments of the present disclosure.

[0006] Figure 2 illustrates views of a CO?, re-liquefaction system, according to embodiments of the present disclosure.

[0007] Figure 3 is a flowchart for an example method of CO? re -liquefaction, according to embodiments of the present disclosure.

[0008] Figure 4 is a flowchart for an example method of producing re-liquefaction system, according to embodiments of the present disclosure.

[0009] Figure 5 illustrates a computing device, according to embodiments of the present disclosure.DETAILED DESCRIPTION

[0010] The present disclosure provides an improved gas re-liquefaction system. Tire presently described system uses a refrigerant closed loop unit and feeds the boiled off gas (BOG) at the second stage compressor together with the first stage BOG compressor to increase the overall pressure of the BOG. The BOG is then split at the second stage BOG compressor discharge, liquefied through a series of heat exchangers, and returned to the storage tank as a liquid. When the BOG is Carbon Dioxide (CO?), CO2 may also be used as the refrigerant for the system, thereby allowing for closed-loop refrigeration.

[0011] Figure 1 illustrates example deployment scenarios for storage vessels IlOa-f (generally or collectively, storage vessels) that may be used in conjunction with the described gas re-liquefaction system, according to embodiments of the presentdisclosure. Several storage vessels 110 may be deployed at different locations as part of a carbon-capture and sequestration chain, and more or fewer storage vessels 110 may be used in various scenarios in addition to the example scenario shown in Figure 1, which may operate with a one-to-one, a many-to-one, a one-to-many, or a many-to-many ratio to a gas re -liquefaction system (200, described with respect to Figure 2).

[0012] The storage vessels 110 may be of various sizes, shapes, and materials, that one of ordinary skill in the relevant art will be able to select based on localized engineering 21400583405.1Attorney Docket No.: 6015645.00037considerations. The storage vessels 110 are designed and configured to store and transport a liquefied gas, such as CO2. Various valves, thermal insulation, pressure and temperature sensors, and piping may be integrated in, or understood as being used with, the storage vessels 110 to accept inputs of liquids / gases, provided outputs of liquids / gases, allow for release or venting of BOG, permit return of re-liquefied BOG, monitor the temperature and pressure of the stored liquid / gas, etc.

[0013] Although generally discussed with respect to storage vessels 110a that hold liquid CO?, and that produce a boiled off gas (BOG) of gaseous CO?., the present disclosure contemplates that the presently described re-liquefaction system (200) may be deployed at any facility for the re-capture and liquefaction of any gas being stored as a liquid in a corresponding storage vessel 110 (e.g., liquid air, mixtures of substantially CO?, with traces of other compounds, liquid Nitrogen (LN?), liquid Oxygen (LOX), etc.). Additionally, the present disclosure contemplates that the liquid CO2 may include various impurities, and still be referred to as liquid CO?, such as, for example, between 0-10%, more preferably between 0-5%, and even more preferably between 0-0.5% by weight of one or more of water (H? O), oxygen (O?.), sulfur trioxide (SO3), hydrogen sulfide (H2S), nitrous oxide (NO), ammonia (NH3), carbon monoxide (CO), methane (CFL), hydrogen (H2), Argon (Ar), and nitrogen (N2), separately or in combination.

[0014] For example, a first storage vessel 110a may deployed on land, at a capture site 120 (e.g., to capture flue gases from a power generations station), while a second storage vessel 110b may be deployed on land at (or connected to) a sequestration site 130, such as a reservoir 170a (generally or collectively, reservoir 170) that the captured CO2 will be injected into for sequestration. In various embodiments, the reservoirs 170 may be various terrestrial or sub-sea geological structures from which hydrocarbons or salts were previously extracted, from which water was previously extracted (e.g., aquifers), or naturally forming sub-surface caves.

[0015] In one example, a near-shore loading site 140 may include a third storage vessel 110c (on land or a barge, jety, dock, platform, or the like) that receives the liquefied gas that is provided from a capture site 120 prior to being transported to a ship 150a (generally or collectively ship 150) for injection at an off-shore site 190 into an off-shore reservoir 170b via a well-head 180 or offload to an offshore platform 160 for injection into the off-shore reservoir 170b. The ships 150a-b may respectively include a fourth storage vessel HOd and a fifth storage vessel I lOe, and the offshore platforms 160a-b (generally or collectively, platforms 160) includes a sixth storage vessel llOf. In various embodiments, a first ship 150a may transfer the liquid from an associated storage vessel 1 lOd to the storage vessel 1 lOe of a second 31400583405.1Attorney Docket No.: 6015645.00037ship 150b. acting as a floating platform 160b, or to the storage vessel 11 Of of an anchored platform 160a (e.g., anchored to the sea floor), which includes pumping facilities to move the liquid into the reservoir 170. In some embodiments, a first ship 150a may include pumping facilities to move the liquid into the reservoir 170, and may be loaded from the near-shore loading site 140 with the liquid / gas from the third storage vessel 110c into a fourth storage vessel llOd and directly inject the liquid / gas from the fourth storage vessel 1 lOd into the reservoir 170 after traveling to the reservoir 170 (and mating with a well-head 180). In various embodiments, the ships 150 may include self-propelled watercraft, a barges that are propelled via other watercraft, and combinations thereof.

[0016] Accordingly, in a carbon-capture and sequestration chain, CO2 gas captured at a capture site 120 (which may be generated by an on-site CO? source, or captured from the atmosphere) may initially be stored in a first storage vessel 110a before being transferred to one or more of a second storage vessel 110b (e.g., for injection into a reservoir 170) or a third storage vessel 110c (e.g., for eventual transfer to a reservoir 170 outside of the range of the third storage vessel 110c). In a subsea or marine sequestration chain, the CO2 is transferred to fourth / fifth storage vessel 11 Od-e for one or more of direct delivery to a reservoir 170 or indirect delivery’ to a reservoir 170 (via another storage vessel l lOe / HOf, which may be held via a floating or anchored platform 160).

[0017] Regardless of where the storage vessels 110 are deployed, and despite the storage vessels 110 including insulation and cooling means to maintain the CO2 as a liquid (rather than a gas), to maintain the pressure in the storage vessels 110, some of the stored liquid may boil off as a gas and be vented as BOG, which should be recaptured and returned to the storage vessel 110. However, while working in marine environments, where energy may be at a premium due to limited power production capacity of the ships 150 or platforms 160, limited space on tire ships 150 or platforms 160, stricter requirements on component weight due to the ships 150 needing to remain buoyant, the effects of wave motion on the ships 150 and platforms 160 (and systems earned therein), and the presence of higher concentrations of salt in the air than terrestrial environments, the designs of systems to capture and return the BOG to the storage vessel 110 may require additional consideration compared to terrestrial-only systems. Accordingly, one of skill in tire art ’ill recognize that conventionally terrestrial re-liquefaction systems may not be generally applied in marine environments, and that special consideration must be taken when designing, fabricating, and using a re-liquefaction system 200 in a marine environment.41400583405.1Attorney Docket No.: 6015645.00037

[0018] Additionally, prior to injecting the CO2 into a reservoir 170, the temperature and pressure of the liquid CO2 may be adjusted to be substantially around or above the critical point, so that the liquid is transported from the storage vessel 110 to the reservoir 170 as a supercritical fluid. Accordingly, BOG may be produced as part of the injection process to a reservoir 170 or transfer process between two (or more) storage vessels 110, and the systems used to capture and return the BOG to the storage vessel 110 should be operable to contemporaneously receive an input liquid into the storage vessel and / or output a stored liquid from the storage vessel 110 to a reservoir 170 or another storage vessel 110 while cycling the BOG with respect to the storage vessel 110.

[0019] Figure 2 illustrates views of a CO2 re-liquefaction system 200, according to embodiments of the present disclosure. The present disclosure contemplates that the example re-liquefaction system 200 may be used in conjunction with any storage vessel 110, whether in a marine or terrestrial environment and whether in a mobile or static deployment.

[0020] The described re-liquefaction system 200 uses process-to-process cooling, using the BOG itself as a refrigerant by increasing the pressure in a multistage compression sy stem to achieves transcritical conditions before pressure letdown (e.g... stream expansion), thereby creating a Joule-Thomson (JT) effect and further cooling under subcritical conditions. For CO2 gas, the phase envelope from gas to liquid shift is approximately 30 degrees Celsius (C) before pressure let down. By manipulating the phase in the various streams, lower temperatures can be achieved in the streams.

[0021] As will be appreciated, a re-liquefaction system 200 may operate in a continuous flow, or in discrete batches, depending at least partially on the amount of BOG released from the storage vessel 110. Accordingly, various liquids or gasses may be transported as streams between the various elements of the re-liquefaction system 200, which may be continuously or discontinuously delivered to different elements via appropriate piping or ducting. Therefore, the present disclosure contemplates that the person of ordinary skill in the art will understand that various valves, splitters, collection tanks 210a-b (generally or collectively, collection tanks 210), and other flow-control elements may be used to selectively configure the pipes and ducts of the re -liquefaction system 200 to deliver different amounts of inputs and outputs at different times.

[0022] When discussing the various streams, the present disclosure contemplates that all or a portion of a described stream can be delivered between a first element and a second element. Accordingly, as used herein when discussing that an identified stream is directed51400583405.1Attorney Docket No.: 6015645.00037between a first element and a second element, the present disclosure contemplates that at least a portion of the identified stream is being directed as described.

[0023] For example, component A that produces stream A may direct stream A exclusively to component B at a first time and exclusively to component C at a second time, and component A may be understood as being configured to direct stream A to component B and component C (e.g., as time-based first / second portions) regardless of which component is currently receiving stream A. Similarly, component D that produces stream D may simultaneously direct stream D to component E and to component F, and may be understood as being configured to direct stream D to component E and to component F (e.g., as flow-based first / second portions) regardless of what portion of stream D is provided to component E or component F at a given time. Similarly, component G that produces and directs stream G only to component H, but may be throttled to provide any portion between 0-100% of a rated flow for stream G over a given time, may be understood as being configured to direct stream G to component H, regardless of what the flow rate is at any given time. Each of these examples shall be understood to describe a first component configured to direct a stream to a second component, regardless of whether the first component is also configured to direct that stream to a third component (at the same or different times) and regardless of what portion of the stream is so directed to any component.

[0024] Accordingly, a reference to the delivery, direction, receipt, or other action performed in relation to a stream shall be understood to refer to that action in relation to some or all of the identified stream. Additionally, discussion of an action performed in relation to a stream shall be understood as occurring at a given time, and that same action may be performed continuously across several times or discontinuously (e.g., not performed or performed differently at a second time). For example, a stream may be described as being directed to element A, while a second portion of that stream is directed to element B (either contemporaneously or at a different time), and that same stream may be directed to element A from time Ti to time T2, but not directed to element A from time T2 to time T3.

[0025] Various components of the presently described re-liquefaction system 200 may be in fluid communication with one another, such as through piping or ducting. The terms “■piping,” “pipes,” “pipework,” “ducts,” “ducting,” “ductwork,” “hoses”, “tubing”, and “plumbing” are used interchangeably herein to refer to elements used to transport various gases and liquids (generally, fluids) throughout the described re-liquefaction system 200 between or through other names elements, and may include (or omit) insulation to maintain the temperature (or allow the change of temperature) of fluids carried therein. One of ordinary skill 61400583405.1Attorney Docket No.: 6015645.00037in the relevant art will be able to select the materials and gauges of the piping or ducting based on the fluid flow requirements (e.g., flow rate, temperature, pressure, chemical composition) between two elements. Additionally, based on the positions of the various elements in the described re -liquefaction system 200 and desired flowrates among the various points in the re¬ liquefaction system 200, one of ordinary skill in the relevant art is expected to be able to route the various pipes and fluids carried therein (e.g,, via valve states) to achieve fluid communication among the various components as described herein. Accordingly, tire piping may be arranged to selectively configure two or more components to be in communication with one another to direct, send, receive, etc. various inputs and outputs. Two components in fluid communication with one another may be in direct fluid communication (e.g., piping or ducting directly connects the two components without intermediate components other than valves or collectors) or may have intermediate components for processing a fluid betw-een the two components, such as filters, pumps, heaters, coolers, condensers, vaporizers, in-line sensors (for temperature, pressure, flowrate, etc.), insulation, etc.

[0026] Figure 2 illustrates the re-liquefaction system 200 in a closed-loop configuration, in which the BOG is also used as tire refrigerant. Because the re-liquefaction system 200 may start and stop based on the amount of BOG gas produced at any given time, to ensure that sufficient refrigerant is available for use or for compression, various tanks 210a-b (generally or collectively, tanks 210, such as a collection tank 210 or buffer tank 210b) may be disposed throughout the system. In some embodiments, an operator may pre-charge the collection tanks 210 with agas (e.g., CO2) prior to initial operation of the re-liquefaction system 200 so that as BOG is received by the re-liquefaction system 200 sufficient gas supplies exist throughout the piping to allow for immediate operation of the re-liquefaction system 200. In some embodiments, the collection tanks 210 may be initially charged with the BOG as the BOG is received, thereby delaying complete operation of the re-liquefaction system 200 until sufficient BOG is collected in the various collection tanks 210 to pennit operation of the various subsystems that use the collected gases,

[0027] As BOG is released from a vent opening of the storage vessel 110 as a vented BOG stream, a first compressor 220a (generally or collectively, compressors 220) receives the vented BOG stream. In various embodiments, the first compressor 220a may impart suction to the vent to draw out the vented BOG stream. The first compressor 220a may also receive a stored BOG stream from the second collection tank 210b. Using these inputs, the first compressor 220a is configured to generate a first compressed BOG stream and a second compressed BOG stream. The first compressed BOG stream is generated a first pressure (e.g., 10 to 31 barg), which is 71400583405.1Attorney Docket No.: 6015645.00037greater than a pressure that the BOG stream is received from the storage vessel 110 (e.g., a received pressure of 5 to 7 barg), whereas the second compressed BOG stream is generated at a second pressure (e.g., 80 to 95 barg), which is greater than the first pressure. In various embodiments, the first compressor 220a may output both the first and second compressed BOG streams at the same time, or may alternate which compressed BOG stream is output at any given time.

[0028] The first compressed BOG stream is directed from tire first compressor 220a to a heat exchanger 230 (which may be understood as a re-liquefaction means), which includes a plurality of heat exchange lines 232a-c (generally or collectively, heat exchange lines 232), to cool the first compressed BOG stream into a liquid stream, and return the liquid stream to the storage vessel 110 via a return port. In various embodiments, one or more cold streams are passed through corresponding heat exchange lines 232 to cool and condense the first compressed BOG stream by removing heat from the first compressed BOG stream. In various embodiments, some or all of the heat exchange lines 232 may be active at any given time. Similarly, although referred to as a first, second, third, etc. heat exchange line 232, the present disclosure contemplates that the first compressed BOG stream may interact with the heat exchange lines 232 in any order and via different numbers of heat exchange lines 232 at any given time.

[0029] The second compressed BOG stream is directed from the first compressor 220a to a refrigerant unit 240 (which may be understood as a refrigerating means or a refrigerator), to cool the second compressed BOG stream into a first cold stream CS1 for use in the first heat exchange line 232a of the first heat exchange unit 230a. In some embodiments, the refrigerant unit 240 includes a heat exchange line 242 that uses the refrigerant stream returned from the heat exchanger 230 after re-liquefaction of the first compressed BOG stream into the liquid stream to act as a cold stream (e.g., a fourth cold stream CS4) of a lower temperature than the second compressed BOG stream to remove heat from the second compressed BOG stream to produce the first cold stream CS1. In various embodiments, the refrigerant unit 240 receives the return refrigerant stream from the heat exchanger 230 and includes an expansion valve or other volume expander or flow restrictor that allows the returned refrigerant stream to be further cooled to accept additional heat from the second BOG stream to thereby produce the first cold stream CSI, In various embodiments, the refrigerant unit 240 includes an expansion valve or other volume expander or flow restrictor that allows the second compressed BOG stream to be further cooled via the JT effect when producing the first cold stream CSI.81400583405.1Attorney Docket No.: 6015645.00037

[0030] In some embodiments, the second compressed BOG stream, after being cooled for use as the first cold stream CS1, is later expanded to produce one or more of a second cold stream CS2 and a third cold stream CS3. In some embodiments, the refrigerant stream returned from the heat exchanger 230 to the refrigerant unit 240 to cool the second compressed BOG stream includes one or more of a spent second cold stream CS2, a spent third cold stream CS3, a bypassed expanded BOG stream, a bypassed second cold stream CS2, and a bypassed third cold stream CS3. Depending on the operating mode of the system 200, the first cold stream CSI may have a temperature lower than the second compressed BOG stream with a temperature in the range of 24 to -48 degrees C.

[0031] The refrigerant stream, once spent in the refrigerant unit 240, is directed from the refrigerant unit 240 to the second compressor 220b, w'hich generates a recycle BOG stream that is directed to the buffer tank 210b to store as a stored BOG stream. The buffer tank 210b selectively provides the stored BOG stream to the first compressor 220a to output in combination with the vented BOG stream (either contemporaneously or in a time division to ensure continued operation of the system 200) as the first compressed BOG stream or the second compressed BOG stream.

[0032] The first cold stream CSI is passed through the first heat exchange line 232a to remove heat from the first compressed BOG stream, and is directed from an output end of the first heat exchange line 232a to a JT device 250. The IT device 250 produces an expanded BOG stream, which may be stored in a first collection tank 210a prior to being supplied as a second cold stream CS2 or a third cold stream CS3 carried by a second heat exchange line 232b and a third heat exchange line 232c, respectively, to remove heat from the first compressed BOG stream. In various embodiments, the JT device 250 is a turbo expander or other expansion device or expansion means, which produces an expanded BOG stream at a lower pressure than the first cold stream CSI (e.g., 5 to 10 barg), thereby producing the second cold stream CS2 and the third cold stream CS3 with temperatures in the range of -35 to -55 degrees C.

[0033] In various embodiments, the second cold stream CS2 and the third cold stream CS3, once spent in the heat exchanger 230, are received by a return line 260. The return line 260 mixes or combines the second cold stream CS2 and the third cold stream CS3, and produces a fourth cold stream CS4 that is routed to a fourth heat exchange line 242 in the refrigerant unit 240 to remove heat from the second compressed BOG stream. The fourth cold stream CS4, after being spent in the refrigerant unit 240, is then recycled back to the first compressor 220a as the recycle BOG stream.91400583405.1Attorney Docket No.: 6015645.00037

[0034] The JT device 250 controls the temperature of the second cold stream CS2 (and the third cold stream CS3, which is substantially equal to the second cold stream CS2) to be at or below the liquefaction temperature of the BOG stream. In various embodiments, one or both of the second cold stream CS2 and the third cold stream CS3 are provided at any given time to chill the first compressed BOG stream into the liquid stream in the heat exchanger 230, depending on the temperature, pressure, flowrate, and purity of the first compressed BOG stream on entry to the heat exchanger 230 (or after being chilled via the first heat exchange line 232a). In various embodiments, the heat exchange lines 232b-c may offer the same or different flow rates for the respective cold streams. Accordingly, an operator may control the outflow from the collection tank 210a via one or more cold streams according to the timing and temperature gradient needed to cool the gaseous first compressed BOG stream back into a liquid. Although illustrated with two heat exchange lines 232b-c to provide two cold streams with temperatures controlled by the operation of the JT device 250, the present disclosure contemplates that more than two temperature-controlled heat exchange lines 232 may be provided for selectively applying up to a corresponding number of cold streams to the first compressed BOG stream.

[0035] Additional benefits of using two or more temperature-controlled heat exchange lines 232b-c (e.g., rather than a single temperature-controlled heat exchange line 232) may include a more consistent cooling profile of the first compressed BOG stream, better heat transfer as single phase is more predictive compared to multiphase fluid., reduced energy consumption to operate the liquefaction system 200, more favorable pressure profiles for the various streams (e.g., improved safety), and other benefits.

[0036] In contrast to the temperature of the second cold stream CS2 and the third cold stream CS3, which are consistently controlled to ensure liquefaction of the BOG for return to the storage vessel 110 regardless of the operation mode of the system 200, the temperature of the first cold stream CS1 and the fourth cold stream CS4 are not controlled according to the temperature for liquefaction. Instead, each of the first cold stream CS1 and the fourth cold stream CS4 offer a ‘‘best-effort’’ for cooling the respective streams in the given operation mode so as to conserve energy in the system and reduce strain on the JT device 250 and the second / third exchange lines 232. Accordingly, the temperature of the first cold stream CS 1 and the fourth cold stream CS4 may van,' in different operational modes,

[0037] Figure 3 is a flowchart for an example method 300 of CO2 re-liquefaction, according to embodiments of the present disclosure. As will be appreciated, the re-liquefaction system 200 is configured for continuous operation, and although Figure 3 illustrates a sequence,101400583405.1Attorney Docket No.: 6015645.00037the present disclosure contemplates that the various operations described in relation to Figure 3 may be performed in parallel, as a continuous process, or in different orders than the order shown in Figure 3. The designation of the operations is therefore provided for the convenience of the reader, and is not intended to specify a preferred order.

[0038] Additionally, some or all of method 300 may be performed contemporaneously to receiving an input liquid in the storage vessel 110, transferring liquid between storage vessels 110 (e.g., between storage vessels on a single ship 150 or platform 160, or between different ships 150 or platforms 160), or outputting a stored liquid to a reservoir 170.

[0039] At block 310, the liquefaction system 200 receives a vented BOG stream from a storage vessel 110 at a first compressor 220a.

[0040] At block 320, the first compressor 220a compresses one or both of the vented BOG stream and / or a stored recycle BOG stream into a first compressed BOG stream at a first pressure and a second compressed BOG stream at a second pressure, greater than the first pressure.

[0041] At block 335, a heat exchanger 230 of the liquefaction system 200 cools the first compressed BOG stream to produce a liquid stream by exchanging heat from the first compressed BOG stream to one or more of a plurality of available cold streams carried by various heat exchange lines 232 in the heat exchanger 230.

[0042] At block 345, after the first compressed BOG stream has been cooled from a gas to a liquid, the heat exchanger returns a liquid stream to the liquid storage vessel 110.

[0043] At block 330, a refrigerant unit 240 of the liquefaction system 200 cools the second compressed BOG stream to produce a first cold stream CS 1 for use in a first heat exchange line 232a of the heat exchanger 230 to cool the first compressed BOG stream. Accordingly, the second compressed BOG stream is cooled to have a temperature less than that of the first compressed BOG stream before entry into the heat exchanger 230. In various embodiments, the refrigerant unit 240 includes a fourth heat exchange line 242, which receives a fourth cold stream CS4 from the output of one or more of the second cold stream CS2 and the third cold stream CS3 from the heat exchanger 230.

[0044] At block 340, the first heat exchange line 232a exchanges heat from the first compressed BOG stream against the first cold stream CS1 (e.g., as part of block 335 to cool the first compressed BOG stream).

[0045] At block 350, a JT device 250 receives the spent first cold stream CS 1 from the first heat exchange line 232a and expands the first cold stream CS1 into an expanded BOG stream. The expanded BOG stream has a lower temperature than the spent first cold stream CS 1 due 111400583405.1Attorney Docket No.: 6015645.00037to the JT effect, and may be used, per block 360, as one or more of a second cold stream CS2 in a second heat exchange line 232b or a third cold stream CS3 in a third heat exchange line 232c (e.g., as part of block 335 to cool the first compressed BOG stream). In various embodiments, the expanded BOG stream may be stored in a collection tank 210a prior to use as one or more of the second cold stream CS2 and the third cold stream CS3.

[0046] At block 370, the expanded BOG stream, once spent as the second cold stream CS2 or the third cold stream CS3 per block 360 may be returned as a fourth cold stream CS4 via a return line 260 for use in the refrigerant unit 240 to produce the first cold stream CS1 (e.g., as part of block 330 to cool the second compressed BOG stream). In various embodiments, depending on whether one or more valves in the system 200 have been configured in a bypass mode, the return refrigerant stream can include one or more of the spent first cold stream CS1, an expanded BOG stream from the JT device 250, a stored expanded BOG stream from the first collection tank 210a, a spent second cold stream CS2 from the return line 260, a spent third cold stream CS3 from the return line 260, and combinations thereof.

[0047] At block 380, the refrigerant unit 240 directs the refrigerant stream (after being spent per block 330 to cool the second compressed BOG stream into the first cold stream CS 1) to the second compressor 220b, which compresses the refrigerant stream into a recycle BOG stream. This recycle BOG stream may be directed from the second compressor 220b indirectly to the first compressor 220a via a buffer tank 210b or directly to the first compressor 220a for use with or alternatively to the vented BOG stream to produce the first compressed BOG stream and the second compressed BOG stream (e.g., per block 320).

[0048] Method 300 may continue, operating in a closed loop, until stopped by an operator or until the volume and pressure in the liquid storage vessel 110 no longer produces a vented BOG stream of sufficient volume to warrant re-liquefaction.

[0049] Figure 4 is a flowchart for an example method 400 of producing re-liquefaction system 200, according to embodiments of the present disclosure.

[0050] At block 410, a fabricator installs a liquid storage vessel 110. In various embodiments, the liquid storage vessel 110 is installed at a capture site 120, a terrestrial sequestration site 130, a near-shore loading site 140 (either on shore or on a structure or ship 150 near or within 5 kilometers (km) from a shore), on a ship 150 (including barges and self- powered watercraft), or on an off-shore platform 160 (located more than 5 km from shore),

[0051] At block 420, a fabricator installs tire components of a re-liquefaction system 200 in conjunction with the liquid storage vessel 110. In various embodiments, the components include a first compressor 220a; a second compressor 220b; a heat exchanger 230, including:121400583405.1Attorney Docket No.: 6015645.00037a first heat exchange line 232a; a second heat exchange line 232b; and a third heat exchange line 232c; a refrigerant unit 240; a JT device 250; and a return line 260.

[0052] In various embodiments, the fabricator may repeat one or both of block 410 and block 420 to install multiple instances of storage vessels 110 and re-liquefaction systems 200 for use with each other.

[0053] At block 430, the fabricator installs piping between the components of the reliquefaction system 200 and the storage vessel 110. The piping places the various components in fluid communication with one another, but may also selectively or temporarily block communication or establish bypass or alternative communications by various flow splitting or controlling devices. In various embodiments, the fabricator may include a plurali ty of valves and different locations with respect to the piping to selectively control the operation and flow between the various components and storage vessel 110. These valves may include manually actuated valves as well as motorized valves, pressure or temperature driven valves, safety release valves, and the like. Similarly, the fabricator may include various sensors for monitoring the temperature, pressure, flowrate, level, analyzer or the like in the various components or the piping between the various components.

[0054] When connected, the piping is configured to selectively direct streams of liquid or gas between the various components or bypass one or more of the components. For example, the piping may direct one or more of a vented boiled off gas (BOG) stream from the liquid storage vessel to the first compressor, a first compressed BOG stream from the first compressor to an input end of the heat exchanger, a second compressed BOG stream from the first compressor to a first input end of the refrigerant unit 240, a first cold stream (CS1) from a first output end the refrigerant unit 240 to an input end of the first heat exchange line, the first cold stream from an output end of the first heat exchange line to an input end of the expander, an expanded BOG stream from tire expander to input ends of one or both of the second heat exchange line and the third heat exchange line, one or both of a second cold stream (CS2) and a third cold stream (CS3) from output ends of one or both of the second heat exchange line and the third heat exchange line to the re turn line to an input end of the second heat exchange line, a return refrigerant stream from an output end of the second heat exchange line to a second input end of the refrigerant unit 240, a spent refrigerant stream from a second output end of the refrigerant unit 240 to the second compressor 220b, a recycle BOG stream from the second compressor 220b to the first compressor 220a; and a liquid stream from an output end of the heat exchanger 230 to the liquid storage vessel 110.131400583405.1Attorney Docket No.: 6015645.00037

[0055] At block 440, the fabricator connects a computing device (such as computing device 500 described with respect to Figure 5) to the various sensors, motors, and electrical interfaces of the liquid storage vessel 110 and the re -liquefaction system 200 to selectively control the combined system via stored instructions and user inputs, such as according to method 300 discussed in relation to Figure 3.

[0056] Figure 5 illustrates a computing device 500, as may be used in the control and operation of a CO2 re-liquefaction system 200, according to embodiments of the present disclosure. For example, the CO2 re-liquefaction system 200 may be controlled to perform the operations described with respect to method 300. The computing device 500 may include at least one processor 510, a memory 520, and a communication interface 530,

[0057] The processor 510 may be any processing unit capable of performing the operations and procedures described in the present disclosure (e.g., method 300). In various embodiments, the processor 510 can represent a single processor, multiple processors, a processor with multiple cores, and combinations thereof.

[0058] The memory 520 is an apparatus that may be either volatile or non-volatile memory and may include RAM, flash, cache, disk drives, and other computer readable memory storage devices. Although shown as a single entity, the memory 520 may be divided into different memory storage elements such as RAM and one or more hard disk drives. As used herein, the memory 520 is an example of a device that includes computer-readable storage media, and is not to be interpreted as transmission media or signals per se.

[0059] As shown, the memory 520 includes various instructions that are executable by the processor 510 to provide an operating system 522 to manage various features of the computing device 500 and one or more programs 524 to provide various functionalities to users of the computing device 500, which include one or more of the features and functionalities described in the present disclosure (e.g., method 300). One of ordinary skill in the relevant art will recognize that different approaches can be taken in selecting or designing a program 524 to perform the operations described herein, including choice of programming language, the operating system 522 used by the computing device 500, and the architecture of the processor 510 and memory 520. Accordingly, the person of ordinary skill in the relevant art will be able to select or design an appropriate program 524 based on the details provided in the present disclosure.

[0060] The communication interface 530 facilitates communications between the computing device 500 and other devices, including sensors, motors, pumps, heaters, etc. of the CO2 re-liquefaction system 200, which may also be computing devices as described in relation 141400583405.1Attorney Docket No.: 6015645.00037to Figure 5. In various embodiments, the communication interface 530 includes antennas for wireless communications and various wired communication ports. The computing device 500 may also include or be in communication, via the communication interface 530, one or more input devices (e.g., a keyboard, mouse, pen, touch input device, etc.) and one or more output devices (e.g., a display, speakers, a printer, etc.).

[0061] Although not explicitly shown in Figure 5, it should be recognized that the computing device 500 may be connected to one or more public and / or private networks via appropriate network connections via the communication interface 530. It will also be recognized that software instructions may also be loaded into a non-transitory computer readable medium, such as the memory 520, from an appropriate storage medium or via wired or wireless means.

[0062] Accordingly, the computing device 500 is an example of a system that includes a processor 510 and a memory 520 that includes instructions that (when executed by the processor 510) perform various embodiments of the present disclosure. Similarly, the memory 520 is an apparatus that includes instructions that, when executed by a processor 510, perform various embodiments of the present disclosure.

[0063] In addition to the embodiments described above, many examples of specific combinations are within the scope of the disclosure, some of which are detailed below:

[0064] Clause 1: A liquefaction system (200) for use with a liquid storage vessel (110), the system comprising: a refrigerant unit (240); a first compressor (220a) and a second compressor (220b), wherein the first compressor is configured to: receive a boiled off gas (BOG) stream from the liquid storage vessel at an input pressure; receive a recycle BOG stream from the second compressor; and produce, from a combined stream of one or both of the BOG stream and the recycle BOG stream, a first compressed BOG stream at a first pressure that is greater than the input pressure and a second compressed BOG stream at a second pressure that is greater than the first pressure; a heat exchanger (230), including a first heat exchange line (232a), a second heat exchange line (232b), and a third heat exchange line (232c), the heat exchanger configured to: receive the first compressed BOG stream from the first compressor to produce therefrom a liquid stream by exchanging heat from the first compressed BOG stream against a plurality of cold streams which include the second compressed BOG stream as a first cold stream carried by the first heat exchange line; and return the liquid stream to the liquid storage vessel; a JT device (250) in communication with the second compressor, configured to: receive the second compressed BOG stream after being spent as a first cold stream of the plurality of cold streams in the first heat exchange line; and produce an expanded BOG stream,11400583405.1Attorney Docket No.: 6015645.00037wherein the expanded BOG stream is provided to the heat exchanger as at least one cold stream of the plurality of cold streams; and wherein the second heat exchange line (232b) and the third heat exchange lines (232c) included in the heat exchanger (230) are each configured to: exchange heat between the expanded BOG stream and the first compressed BOG stream; and provide the expanded BOG stream to the refrigerant unit as a refrigerant stream after exchanging heat with the first compressed BOG stream.

[0065] Clause 2: The liquefaction system of any of clauses 1 or 3-10, wherein a refrigerant used comprises Carbon Dioxide (CO2) supplied from the liquid storage vessel.

[0066] Clause 3: The liquefaction system of any of clauses 1-2 or 4-10, wherein the BOG stream consists substantially of (CO2).

[0067] Clause 4: The liquefaction system of any of clauses 1-3 or 5-10, wherein the liquid stream is returned to the liquid storage vessel contemporaneously with a liquid being input to the liquid storage vessel,

[0068] Clause 5: The liquefaction system of any of clauses 1-4 or 6-10, wherein the liquid stream is returned to the liquid storage vessel contemporaneously with a liquid being output from the liquid storage vessel to a subsea sequestration reservoir.

[0069] Clause 6: The liquefaction system of any of clauses 1-5 or 7-10, wherein the expanded BOG stream is stored in a collection tank (210a) prior to exchanging heat with the first compressed BOG stream.

[0070] Clause 7: The liquefaction system of any of clauses 1-6 or 8-10, wherein the collection tank is in communication with the second heat exchange line and the third heat exchange line of the heat exchanger that are configured to: selectively provide a flow of the expanded BOG stream to one or both of the second heat exchange line and the third heat exchange line,

[0071] Clause 8: The liquefaction system of any of clauses 1-7 or 9-10, wherein when the second cold stream when is provided contemporaneously with the third cold stream to chill the first compressed BOG stream, a flow rate of the second cold stream through the second heat exchanger is different than a flow rate of the third cold stream through the third heat exchanger.

[0072] Clause 9: The liquefaction system of any of clauses 1-8 or 10, wherein the refrigerant unit is in communication with the second compressor and the heat exchanger, and is configured to: cool the second compressed BOG stream via the refrigerant stream to produce the first cold stream of the plurality of cold streams and a spent refrigerant stream; direct tire spent refrigerant stream to the second compressor, wherein the recycle BOG stream is generated by the second compressor from the spent refrigerant stream.161400583405.1Attorney Docket No.: 6015645.00037

[0073] Clause 10: The liquefaction system of any of clauses 1-9, wherein the recycle BOG stream is stored in a buffer tank (210b) prior to provision to the first compressor.

[0074] Clause 11: A method (300), comprising: receiving (310) a vented boiled off gas (BOG) stream from a storage vessel (110) at a first compressor (220a); compressing (320) the vented BOG stream at the first compressor into a first compressed BOG stream at a first pressure and a second compressed BOG stream at a second pressure, greater than the first pressure; cooling (335) the first compressed BOG stream in a heat exchanger (230) to produce a liquid stream by: cooling (330), via a refrigerant unit (240), the second compressed BOG stream to produce a first cold stream (CS1), of a temperature less than that of the first compressed BOG stream; and exchanging (340) heat from the first compressed BOG stream against the first cold stream; and returning (345) the liquid stream to the storage vessel.

[0075] Clause 12: The method of any of clauses 11 or 13-17, further comprising: returning (370) a refrigerant stream to the refrigerant unit from the heat exchanger; compressing (380) the refrigerant stream to produce a recycle BOG stream; providing the recycle BOG stream to the first compressor; and compressing (320) tlie recycle BOG stream with the vented BOG stream into the first compressed BOG stream and the second compressed BOG stream.

[0076] Clause 13: The method of any of clauses 11-12 or 14-17, further comprising: expanding (350) the first cold stream after exchanging heat with the first compressed BOG stream via a Joule-Thomson (JT) device (250) to produce an expanded BOG stream for use as a second cold stream (CS2); and exchanging (360) heat from the first compressed BOG stream to the expanded BOG stream as the second cold stream to cool the first compressed BOG stream.

[0077] Clause 14: The method of any of clauses 11-13 or 15-17, further comprising: providing the expanded BOG stream to the heat exchanger as a third cold stream (CS3) to further cool the first compressed BOG stream in parallel to being cooled by the second cold stream; combining outputs of the second cold stream and the third cold stream after having respectively cooled the first compressed BOG stream to produce a fourth cold stream (CS4); providing the fourth cold stream as a return refrigerant stream to the refrigerant unit to cool the second compressed BOG stream into the first cold stream.

[0078] Clause 15: The method of any of clauses 11-14 or 16-17, further comprising: receiving an input liquid in the storage vessel while returning the liquid stream to the storage vessel from the heat exchanger.171400583405.1Attorney Docket No.: 6015645.00037

[0079] Clause 16: The method of any of clauses 11-15 or 17, further comprising: outputting a stored liquid from the storage vessel to a subsea sequestration reservoir while returning the liquid stream to the storage vessel from the heat exchanger.

[0080] Clause 17: The method of any of clauses 11-16, wherein the vented BOG stream consists substantially of carbon dioxide (CO2).

[0081] Clause 18: A method (400), comprising: installing (410) a liquid storage vessel (110) on a ship (150); installing (420) a liquefaction system (200) on the ship, the liquefaction system having components including: a first compressor (220a); a second compressor (220b); a heat exchanger (230), including: a first heat exchange line (232a); a second heat exchange line (232b); and a third heat exchange line (232c); a refrigerant unit (240), including a fourth heat exchange line (242); a Joule-Thomson device (250); and a return line (260); and installing (430) piping on the ship, the piping configured to selectively direct: a vented boiled off gas (BOG) stream from the liquid storage vessel to the first compressor; a first compressed BOG stream from the first compressor to an input end of the heat exchanger; a second compressed BOG stream from the first compressor to a first input end of the refrigerant unit; a first cold stream (CS1) from a first output end the refrigerant unit to an input end of the first heat exchange line; the first cold stream from an output end of the first heat exchange line to an input end of the Joule-Thomson device; an expanded BOG stream from the Joule-Thomson device to input ends of one or both of the second heat exchange line and the third heat exchange line; one or both of a second cold stream (CS2) and a third cold stream (CS3) respectively from output ends of one or both of the second heat exchange line and the third heat exchange line to the return line; a return refrigerant stream from an output end of the return line to a second input end of the refrigerant unit; a spent refrigerant stream from a second output end of the refrigerant unit to the second compressor; a recycle BOG stream from the second compressor to the first compressor; and a liquid stream from an output end of the heat exchanger to the liquid storage vessel.

[0082] Clause 19: The method of clause 18, wherein the piping includes a plurality of valves disposed in connection with the piping, the method further comprising: connecting (440) a computing device (500) including a processor (510) and a memory (520) including instructions that, when executed by the processor, selectively control the plurality of valves to direct various streams among the components of the liquefaction system and the liquid storage vessel.

[0083] Clause 20: A ship, produced according the method of clause 18.181400583405.1Attorney Docket No.: 6015645.00037Clause 21: A liquefaction system (200) for use with a liquid storage vessel (110), the system comprising: a refrigerant unit (240); a first compressor (220a) and a second compressor (220b), wherein the first compressor is configured to: receive a boiled off gas (BOG) stream from the liquid storage vessel at an input pressure; receive a recycle BOG stream from the second compressor; and produce, from a combined stream of one or both of the BOG stream and the recycle BOG stream, a first compressed BOG stream at a first pressure that is greater than the input pressure and a second compressed BOG stream at a second pressure that is greater than the first pressure; a re-liquefaction means (230), including a first heat exchange line (232a), a second heat exchange line (232b), and a third heat exchange line (232c), the re-liquefaction means configured to: receive the first compressed BOG stream from the first compressor to produce therefrom a liquid stream by exchanging heat from the first compressed BOG stream against a plurality of cold streams which include the second compressed BOG stream as a first cold stream carried by the first heat exchange line; and return the liquid stream to the liquid storage vessel; a JT device (250) in communication with the second compressor, configured to: receive the second compressed BOG stream after being spent as a first cold stream of the plurality of cold streams in the first heat exchange line; and produce an expanded BOG stream, wherein the expanded BOG stream is provided to the heat exchanger as at least one cold stream of the plurality of cold streams; and wherein the second heat exchange line (232b) and the third heat exchange lines (232c) included in the re-liquefaction means (230) are each configured to: exchange heat between the expanded BOG stream and the first compressed BOG stream; and provide the expanded BOG stream to the refrigerant unit as a refrigerant stream after exchanging heat with the first compressed BOG stream.

[0084] Certain terms are used throughout the description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function.

[0085] As used herein, the term "‘optimize” and variations thereof, is used in a sense understood by data scientists to refer to actions taken for continual improvement of a system relative to a goal. An optimized value will be understood to represent “near-best” value for a given reward framework, which may oscillate around a local maximum or a global maximum for a “best” value or set of values, which may change as the goal changes or as input conditions change. Accordingly, an optimal solution for a first goal at a given time may be suboptimal for a second goal at that time or suboptimal for the first goal at a later time.191400583405.1Attorney Docket No.: 6015645.00037

[0086] As used herein, various chemical compounds are referred to by associated element abbreviations set by the International Union of Pure and Applied Chemistry (IUPAC), which one of ordinary skill in the relevant art will be familiar with. Similarly, various units of measure may be used herein, which are referred to by associated short forms as set by the International System of Units (SI), which one of ordinary skill in the relevant art will be familiar with.

[0087] As used herein, “about,” “approximately” and “substantially” are understood to refer to numbers in a range of the referenced number, for example the range of -10% to +10% of the referenced number, preferably -5% to +5% of the referenced number, more preferably -1% to +1% of the referenced number, most preferably -0.1% to +0.1% of the referenced number.

[0088] Furthermore, all numerical ranges herein should be understood to include all integers, whole numbers, or fractions, within the range. Moreover, these numerical ranges should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a disclosure of “from 1 to 10” should be construed as supporting a range of from 1 to 8, from 3 to 7, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, and so forth.

[0089] As used herein, the terms “upstream” and “downstream” are used in the sense of relative directions of a flow path, with elements referred as “upstream” being closer to a source than elements referred to as “downstream”, and elements referred as “downstream” being closer to a destination than elements referred to as “upstream”. Consider the example where element A provides output to element B, and element B provides output to element C. In the present example, both element A and element B may be referred to as “upstream” from element C, and both element B and element C may be referred to as “downstream” from element A, but relative to element B, element A (and not element C) would be considered “upstream” from element B and element C (and not element A) would be considered “downstream” from element B.

[0090] As used in the present disclosure, a phrase referring to “at least one of’ a list of items refers to any set of those items, including sets with a single member, and every potential combination thereof. For example, when referencing “at least one of A, B, or C” or “at least one of A, B, and C”, the phrase is intended to cover the sets of: A, B, C, A-B, B-C, A-C, and A-B-C, where the sets may include one or multiple instances of a given member (e.g., A-A, A-A-A, A-A-B, A-A-B-B-C-C-C, etc.) and any ordering thereof. For avoidance of doubt, the phrase “at least one of A, B, and C” shall not be interpreted to mean “at least one of A, at least one of B, and at least one of C”.201400583405.1Attorney Docket No.: 6015645.00037

[0091] As used in the present disclosure, the term “determining” encompasses a variety of actions that may include calculating, computing, processing, deriving, investigating, looking up (e.g., via a table, database, or other data structure), ascertaining, receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), retrieving, resolving, selecting, choosing, establishing, and the like.

[0092] Without further elaboration, it is believed that one skilled in the art can use the preceding description to use the claimed inventions to their fullest extent. The examples and aspects disclosed herein are to be construed as merely illustrative and not a limitation of the scope of the present disclosure in any way. It will be apparent to those having skill in the art that changes may be made to the details of the above-described examples without departing from the underlying principles discussed. In other words, various modifications and improvements of the examples specifically disclosed in the description above are within the scope of the appended claims. For instance, any suitable combination of features of the various examples described is contemplated.

[0093] Within the claims, reference to an element in the singular is not intended to mean “one and only one” unless specifically stated as such, but rather as “one or more” or “at least one”. Unless specifically stated otherwise, the term “some” refers to one or more. No claim element is to be construed under the provision of 35 U. S. C. § 112(f) in the United States or similar provisions in other jurisdictions unless the element is expressly recited using the phrase “means for” or “step for”. All structural and functional equivalents to the elements of the various embodiments described in the present disclosure that are known or come later to be known to those of ordinary skill in the relevant art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed in the present disclosure is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.211400583405.1

Claims

Attorney Docket No.: 6015645.00037CLAIMSThe invention is claimed as follows:

1. A liquefaction system (200) for use with a liquid storage vessel (110), the system comprising:a refrigerant unit (240);a first compressor (220a) and a second compressor (220b), wherein the first compressor is configured to:receive a boiled off gas (BOG) stream from the liquid storage vessel at an input pressure;receive a recycle BOG stream from the second compressor; and produce, from a combined stream of one or both of the BOG stream and the recycle BOG stream, a first compressed BOG stream at a first pressure that is greater than the input pressure and a second compressed BOG stream at a second pressure that is greater than the first pressure;a heat exchanger (230), including a first heat exchange line (232a), a second heat exchange line (232b), and a third heat exchange line (232c), the heat exchanger configured to:receive the first compressed BOG stream from the first compressor to produce therefrom a liquid stream by exchanging heat from the first compressed BOG stream against a plurality of cold streams which include the second compressed BOG stream as a first cold stream carried by the first heat exchange line; andreturn the liquid stream to the liquid storage vessel;a JT device (250) in communication with the second compressor, configured to: receive the second compressed BOG stream after being spent as a first cold stream of the plurality of cold streams in the first heat exchange line; and221400583405.1Attorney Docket No.: 6015645.00037produce an expanded BOG stream, wherein the expanded BOG stream is provided to the heat exchanger as at least one cold stream of the plurality of cold streams; andwherein the second heat exchange line (232b) and the third heat exchange lines (232c) included in the heat exchanger (230) are each configured to:exchange heat between the expanded BOG stream and the first compressed BOG stream; andprovide the expanded BOG stream to the refrigerant unit as a refrigerant stream after exchanging heat with the first compressed BOG stream.

2. The liquefaction system of claim 1, wherein a refrigerant used comprises Carbon Dioxide (CO2) supplied from the liquid storage vessel.

3. The liquefaction system of claim 1, wherein the BOG stream consists substantially of (CO₂).

4. The liquefaction system of claim 1, wherein the liquid stream is returned to the liquid storage vessel contemporaneously with a liquid being input to the liquid storage vessel.

5. The liquefaction system of claim 1, wherein the liquid stream is returned to the liquid storage vessel contemporaneously with a liquid being output from the liquid storage vessel to a subsea sequestration reservoir.

6. The liquefaction system of claim 1, where in the expanded BOG stream is stored in a collection tank (210a) prior to exchanging heat with the first compressed BOG stream.231400583405.1Attorney Docket No.: 6015645.000377. The liquefaction system of claim 6, wherein the collection tank is in communication with the second heat exchange line and the third heat exchange line of the heat exchanger that are configured to:selectively provide a flow of the expanded BOG stream to one or both of the second heat exchange line and the third heat exchange line.

8. The liquefaction system of claim 7, wherein when the second cold stream when is provided contemporaneously with the third cold stream to chill the first compressed BOG stream, a flow rate of the second cold stream through the second heat exchanger is different than a flow rate of the third cold stream through the third heat exchanger.

9. The liquefaction system of claim 1, wherein the refrigerant unit is in communication with the second compressor and the heat exchanger, and is configured to:cool the second compressed BOG stream via the refrigerant stream to produce the first cold stream of the plurality of cold streams and a spent refrigerant stream;direct the spent refrigerant stream to the second compressor, wherein the recycle BOG stream is generated by the second compressor from the spent refrigerant stream.

10. The liquefaction system of claim 1, wherein the recycle BOG stream is stored in a buffer tank (210b) prior to provision to the first compressor.

11. A method (300), comprising:receiving (310) a vented boiled off gas (BOG) stream from a storage vessel (110) at a first compressor (220a);241400583405.1Attorney Docket No.: 6015645.00037compressing (320) the vented BOG stream at the first compressor into a first compressed BOG stream at a first pressure and a second compressed BOG stream at a second pressure, greater than the first pressure;cooling (335) the first compressed BOG stream in a heat exchanger (230) to produce a liquid stream by:cooling (330), via a refrigerant unit (240), the second compressed BOG stream to produce a first cold stream (CS1), of a temperature less than that of the first compressed BOG stream; andexchanging (340) heat from the first compressed BOG stream against the first cold stream; andreturning (345) the liquid stream to the storage vessel.12, The method of claim 11, further comprising:returning (370) a refrigerant stream to the refrigerant unit from the heat exchanger; compressing (380) the refrigerant stream to produce a recycle BOG stream; providing the recycle BOG stream to the first compressor; andcompressing (320) the recycle BOG stream with the vented BOG stream into the first compressed BOG stream and the second compressed BOG stream.13, The method of claim 11, further comprising:expanding (350) the first cold stream after exchanging heat with the first compressed BOG stream via a Joule-Thomson (JT) device (250) to produce an expanded BOG stream for use as a second cold stream (CS2); andexchanging (360) heat from the first compressed BOG stream to the expanded BOG stream as the second cold stream to cool the first compressed BOG stream.251400583405.1Attorney Docket No.: 6015645.0003714. The method of claim 13, further comprising:providing the expanded BOG stream to the heat exchanger as a third cold stream (CS3) to further cool the first compressed BOG stream in parallel to being cooled by the second cold stream;combining outputs of the second cold stream and the third cold stream after having respectively cooled the first compressed BOG stream to produce a fourth cold stream (CS4);providing the fourth cold stream as a return refrigerant stream to the refrigerant unit to cool the second compressed BOG stream into the first cold stream.

15. The method of claim 11, further comprising:receiving an input liquid in the storage vessel while returning the liquid stream to the storage vessel from the heat exchanger.

16. The method of claim 11, further comprising:outputting a stored liquid from the storage vessel to a subsea sequestration reservoir while returning the liquid stream to the storage vessel from the heat exchanger.

17. The method of claim 11, wherein the vented BOG stream consists substantially of carbon dioxide (CO2).

18. A method (400), comprising:installing (410) a liquid storage vessel (110) on a ship (150);installing (420) a liquefaction system (200) on the ship, the liquefaction system having components including:261400583405.1Attorney Docket No.: 6015645.00037a first compressor (220a);a second compressor (220b);a heat exchanger (230), including:a first heat exchange line (232a);a second heat exchange line (232b); anda third heat exchange line (232c);a refrigerant unit (240), including a fourth heat exchange line (242);a Joule-Thomson device (250); anda return line (260); andinstalling (430) piping on the ship, the piping configured to selectively direct:a vented boiled off gas (BOG) stream from the liquid storage vessel to the first compressor;a first compressed BOG stream from the first compressor to an input end of the heat exchanger;a second compressed BOG stream from the first compressor to a first input end of the refrigerant unit;a first cold stream (CS1) from a first output end the refrigerant unit to an input end of the first heat exchange line;the first cold stream from an output end of the first heat exchange line to an input end of the Joule-Thomson device;an expanded BOG stream from the Joule-Thomson device to input ends of one or both of the second heat exchange line and the third heat exchange line;one or both of a second cold stream (CS2) and a third cold stream (CS3) respectively from output ends of one or both of the second heat exchange line and the third heat exchange line to the return line;271400583405.1Attorney Docket No.: 6015645.00037a return refrigerant stream from an output end of the return line to a second input end of the refrigerant unit;a spent refrigerant stream from a second output end of the refrigerant unit to the second compressor;a recycle BOG stream from the second compressor to the first compressor; anda liquid stream from an output end of the heat exchanger to the liquid storage vessel.

19. The method of claim 18, wherein the piping includes a plurality of valves disposed in connection with the piping, the method further comprising:connecting (440) a computing device (500) including a processor (510) and a memory (520) including instructions that, when executed by the processor, selectively control the plurality of valves to direct various streams among the components of the liquefaction system and the liquid storage vessel.

20. A ship, produced according the method of claim 18.1400583405.1

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