Improved re-liquefier system

Abstract

A re-liquefier system 100 comprises a cryogenic storage tank 110 for containing a fluid; a separation tank 230 connected to the cryogenic storage tank 110; a cryocooler 201 connected to the separation tank 230; a second storage tank 150 located downstream of the cryogenic storage tank 110; a conduit network providing flow paths for the fluid comprising a reliquefying flow path 410 and a final storage flow path 420; a compressor 240; a liquid pump 120; and a surplus cooling heat exchanger 130 located between the reliquefying flow path 410 and the final storage flow path 420 configured to transfer heat between the fluid passing through the reliquefying flow path 410 and the final storage flow path 420.

Description

[0001] IMPROVED RE-LIQUEFIER SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a re-liquefier system. More particularly, but not exclusively, it relates to a re-liquefier system for use in recovering boil-off cryogenic gas from cryogenic storage tanks.

[0004] BACKGROUND OF THE INVENTION

[0005] Various substances used in industrial applications are gases at room temperature and have extremely low boiling points, such that in liquid form they must be stored in specially thermally insulated cryogenic tanks. For example, hydrogen has a boiling point of -252.9 °C (20 K) at atmospheric pressure, and liquid hydrogen is used in applications such as liquid rocket fuel and fuel cells. Storing such substances in liquid form is also more space efficient even when it is the gas form which is ultimately used.

[0006] Due to heat leakage into a cryogenic storage tank, it is typical for some portion of the stored liquid to be lost to boil-off over time, usually vented to atmosphere via a pressure relief valve. Typical losses for hydrogen may be around 1% per day, although this will depend on the insulation and the resulting rate of heat leakage. Additional heat leakage into a cryogenic storage tank can occur due to cryogen vapour leaking back into the tank when cryogen is pumped out of the tank, for example to re-fuel a vehicle. The cryogen may be stored in its liquid state in such a cryogenic liquid storage tank, then delivered to a second tank in the vehicle as a pressurised gas.

[0007] Instead of venting the boil-off gas to atmosphere and having it go to waste, it is possible to re-liquefy the boil-off and return it to the cryogenic tank. However, this requires hardware capable of both reaching sufficiently low temperatures and providing adequate cooling power. The most efficient systems typically used for industrial cryogenic liquefaction are large and expensive, and are impractical for use in merely re-liquefying boil-off from storage tanks. A smaller scale solution is needed which is suitable for use with individual cryogenic storage tanks. However, this has proved difficult to achieve without significant inefficiency and high levels of complexity, hence wasteful venting of boil-off to atmosphere remains dominant.

[0008] It is therefore desirable to develop re-liquefier systems which are more efficient and simpler, such that they are economical to adopt in the prevention of wasting stored cryogenicliquids. Further, it is desirable to improve cooling and re-liquefying capacity when cryogen is pumped out of the cryogenic storage tank to another location.

[0009] It is an object of the present invention to provide a re-liquefier system which overcomes or at least partially ameliorates some of the abovementioned disadvantages or which at least provides the public with a useful choice.

[0010] BRIEF DESCRIPTION OF THE INVENTION

[0011] According to a first aspect the invention broadly comprises a re-liquefier system comprising:

[0012] a cryogenic storage tank for containing a fluid;

[0013] a separation tank connected to the cryogenic storage tank, the separation tank configured to receive boil-off gas of the fluid from the cryogenic storage tank, and return the fluid in a liquid-form to the cryogenic storage tank;

[0014] a cryocooler connected to the separation tank configured to receive and cool the boil-off gas;

[0015] a second storage tank located downstream of the cryogenic storage tank; a conduit network providing flow paths for the fluid, the conduit network comprising:

[0016] a reliquefying flow path connected to the cryocooler;

[0017] a final storage flow path connecting the cryogenic storage tank to the second storage tank;

[0018] a compressor to drive circulation of the fluid through the re-liquefier system; a liquid pump located on the final storage flow path; and

[0019] a surplus cooling heat exchanger located between the reliquefying flow path and the final storage flow path configured to transfer heat between the fluid passing through the reliquefying flow path and the final storage flow path.

[0020] According to another aspect, further comprising a vaporiser located on the final storage flow path.

[0021] According to another aspect the vaporiser is located downstream from the liquid pump.

[0022] According to another aspect the vaporiser is located downstream from the surplus cooling heat exchanger.According to another aspect the vaporiser is an ambient vaporiser.

[0023] According to another aspect the liquid pump is located upstream from the surplus cooling heat exchanger.

[0024] According to another aspect heat is configured to transfer from the reliquefying flow path to the final storage flow path.

[0025] According to another aspect the second storage tank is a high pressure gas storage tank.

[0026] According to another aspect the second storage tank is a removable and mobile storage tank.

[0027] According to another aspect further comprising a controller to control a valve associated with the reliquefying flow path, the valve having an open condition to allow fluid to pass through the surplus cooling heat exchanger or a closed condition for fluid to bypass the surplus cooling heat exchanger.

[0028] According to another aspect further comprising a sensor to detect a condition in the system to determine if the valve is to be in an open condition or a closed condition.

[0029] According to another aspect the second storage tank is rated to store the fluid at a pressure higher than the cryogenic storage tank.

[0030] According to another aspect the second storage tank is rated to store the fluid at approximately 350 or 700 bar.

[0031] According to another aspect the second storage tank is rated to store the fluid greater than 1000 bar.

[0032] According to another aspect the cryogenic storage tank is rated to store the fluid at a pressure of approximately 10 bar.

[0033] According to another aspect the cryocooler comprises a plurality of heat exchangers connected in series and a plurality of cold heads in series to cool the boil-off gas by transferringheat from an outflowing flow of gas to the separation tank to an inflowing flow of gas from the separation tank.

[0034] According to another aspect the cryocooler comprises three cold heads.

[0035] According to another aspect the cryocooler comprises three or four heat exchangers.

[0036] According to another aspect three of the plurality of heat exchangers are mounted within a cryostat of the cryocooler.

[0037] According to another aspect one heat exchanger for re-liquefying is mounted outside a cryostat of the cryocooler and a remainder of the plurality of heat exchangers for reliquefying are mounted within the cryostat.

[0038] According to another aspect the plurality of cold heads and the plurality of heat exchangers are connected such that the outflowing flow of gas flows through the heat exchangers and the cold heads in an alternating fashion.

[0039] According to another aspect the plurality of heat exchangers are counterflow heat exchangers.

[0040] According to another aspect the fluid is hydrogen.

[0041] According to another aspect the invention broadly comprises a method of operating the re-liquefier system of any one of the preceding clauses, the method comprising:

[0042] connecting the separation tank to the cryogenic storage tank;

[0043] supplying boil-off gas from the cryogenic storage tank;

[0044] re-liquefying gas by running the compressor and the cryocooler to circulate gas through the re-liquefier system;

[0045] returning liquid from the separation tank to the cryogenic storage tank; pumping liquid from the cryogenic storage tank towards the second storage tank; and transferring heat from the final storage flow path to the re-liquefying flow path as fluid passes through the surplus cooling heat exchanger; and

[0046] receiving and storing fluid pumped from the cryogenic storage tank in the second storage tank.According to another aspect further comprising vaporising fluid as it passes through the vaporiser before passing the gas to the second storage tank.

[0047] According to another aspect further comprising pumping the liquid through the liquid pump such that the pressure of the gas received by the second storage tank is higher than the pressure of the liquid stored in the cryogenic storage tank.

[0048] According to another aspect the gas stored in the second storage tank is pressurised to approximately 350 or 700 bar.

[0049] According to another aspect the gas stored in the second storage tank is pressurised to over 1000 bar.

[0050] According to another aspect liquid stored in the cryogenic storage tank is approximately 10 bar.

[0051] According to another aspect the fluid passing through the vaporiser is heated by ambient air before being received by the second storage tank.

[0052] According to another aspect further comprising using surplus cooling from the final storage flow path to cool the reliquefying flow path.

[0053] According to another aspect further comprising opening and closing the pathway of the reliquefying flow path that passes through the surplus cooling heat exchanger via a valve.

[0054] According to another aspect additional cooling by passing the fluid in the reliquefying flow path through the surplus cooling heat exchanger occurs intermittently.

[0055] According to another aspect additional cooling by passing the fluid in the reliquefying flow path through the surplus cooling heat exchanger occurs continuously.

[0056] According to another aspect the compressor drives flow or more flow through the reliquefier system in a burst mode for additional cooling, and drives less or no flow during normal operation.

[0057] According to another aspect further comprising closing the pathway of the reliquefying flow path when there is no surplus cooling available in the final storage flow path.According to another aspect there is no surplus cooling available when the liquid pump is not operating.

[0058] According to another aspect the re-liquefier system controls the proportion of flow through the surplus cooling heat exchanger in response to temperature, pressure and / or flow sensors in the system, or a liquid pump operation status.

[0059] According to another aspect pumping liquid from the cryogenic storage tank towards the second storage tank pressurises the liquid.

[0060] Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings.

[0061] As used herein the term "and / or" means "and" or "or", or both.

[0062] As used herein "(s)" following a noun means the plural and / or singular forms of the noun.

[0063] The term "comprising" as used in this specification and claims means "consisting at least in part of". When interpreting statements in this specification and claims which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

[0064] In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present invention. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.

[0065] For the purpose of this specification, where method steps are described in sequence, the sequence does not necessarily mean that the steps are to be chronologically ordered in that sequence, unless there is no other logical manner of interpreting the sequence.BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The invention will now be described by way of example only and with reference to the drawings in which:

[0067] Figure 1 shows a schematic of a re-liquefier system.

[0068] Figure 2 shows a schematic of a re-liquefier system, with additional details of the reliquefaction system.

[0069] Figure 3 shows a schematic of a re-liquefier system with additional details of the cryocooler.

[0070] Figure 4 shows a schematic of a re-liquefier system with reference to the flow paths through the re-liquefier system.

[0071] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0072] According to various aspects of the various embodiments of the present invention as illustrated in Figures 1-4, there is provided a re-liquefier system 100 which will now be described.

[0073] The re-liquefier system 100 is for recovering boil-off gas from a cryogenic storage tank 110. It will be understood that the cryogenic storage tank 110 itself may not form part of the invention. The cryogenic storage tank may be of an entirely conventional type, and the reliquefier system 100 is external and connectable to the cryogenic storage tank 110. The invention is primarily directed towards liquid hydrogen storage. However, it may be equally applicable to other cryogenic liquids such as helium, for example. Thus, the generic terms "cryogen", "gas", "liquid" and "fluid" are used throughout the specification, but it will be understood that the invention is intended for use with substances having a boiling point low enough to necessitate cryogenic storage in liquid form. Further, it will be understood that the terms "fluid", "cryogen" and "hydrogen" may be used interchangeably.

[0074] As shown in Figure 1, the re-liquefier system 100 comprises a cryogenic storage tank 110. The cryogenic storage tank 110 is configured to contain a fluid which may be a cryogenic fluid such as hydrogen. In some configurations, downstream of the cryogenic storage tank 110 there is a second storage tank 150. In some applications, the cryogenic storage tank 110 may be used to fill or re-fill the second storage tank 150. The fluid stored in the second storage tank150 may then be used as a fuel. The second storage tank 150 may also be, or be referred to as, a high-pressure storage tank 150 or a high-pressure gas storage tank 150.

[0075] In some configurations, in order to transfer the fluid from the cryogenic storage tank 110 in its liquid state to the second storage tank 150 in its gaseous state, the fluid is pressurised and vaporised.

[0076] In some configurations, there is a cryogenic liquid pump 120 configured to pump the fluid in its liquid state out of the cryogenic storage tank 110 and increase the pressure of the fluid. The cryogenic liquid pump 120 may boost the pressure of the fluid to a target pressure higher than the pressure of the fluid in the cryogenic storage tank 110.

[0077] In some configurations, the fluid may be stored in the cryogenic storage tank 110 at 8-12 bar. In other configurations, the fluid may be stored in the cryogenic storage tank 110 at less than 10 bar.

[0078] In some configurations, the second storage tank 150 is rated to store the fluid at a pressure higher than the cryogenic storage tank 110. The fluid may be stored in the second storage tank 150 at a pressure of 350 bar or 700 bar. These two pressures are the standard charge pressure fortrucks and cars, respectively, for gaseous hydrogen. In other configurations, the second storage tank 150 may store gas at 1000 bar or more. The second storage tank 150 may be a mobile tank, such as a vehicle fuel tank, mobile refueller, or gas transporting tube trailer, or it may be a stationary tank that is subsequently used to refuel a mobile application. If the second storage tank 150 is a stationary tank, it should hold gas at high pressures, e.g. greater than 1000 bar.

[0079] The cryogenic liquid pump 120 is located downstream of the cryogenic storage tank 110.

[0080] In some configurations, as referenced in Figure 2, the fluid may then pass through a vaporiser 140 located downstream of the cryogenic liquid pump 120, which vaporises and warms the fluid. In some configurations, the vaporiser 140 may be an ambient vaporiser 140 that warms the fluid using ambient air.

[0081] The vaporiser 140 may be included in the re-liquefier system 100, where the system 100 intends to supply pressurised gas. In other configurations, the vaporiser 140 is not present, as shown in Figure 1. There are situations where it can be desirable to supply cold gas e.g. for fast re-fuelling of a vehicle, where there is a benefit for supplying gas at -40°C, or for refuellinga MOF tank (metal organic framework), where there is a need to charge at high pressure and cryogenic temperature.

[0082] In some configurations, the fluid may then be stored in a gaseous state at a high pressure in the second storage tank 150 located downstream of the vaporiser 140.

[0083] Additionally, the re-liquefier system 100 may comprise a first portion 200. This first portion 200 of the re-liquefier system 100 may be configured to receive gaseous fluid from the cryogenic storage tank 110, liquefy the fluid, and return liquid fluid to the cryogenic storage tank 110. There may be a re-liquefying flow path 410 through the first portion 200 of the reliquefier system 100.

[0084] As shown in Figure 4, the re-liquefier system 100 may comprise a conduit network which provides flow paths for the fluid. The conduit network may comprise two flow paths: a re-liquefying flow path 410, and a final storage flow path 420. The final storage flow path 420 may alternatively be a high-pressure flow path 420. Both flow paths may be in fluid communication with the cryogenic storage tank 110. The re-liquefying flow path 410 may be re-circulatory with respect to the cryogenic storage tank 110. The high-pressure flow path 420 may be in fluid communication with both the cryogenic storage tank 110 and the second storage tank 150. It will be understood that the cryogenic liquid pump 120, the vaporiser 140 and the second storage tank 150 may be located downstream of the cryogenic storage tank 110 along the final storage flow path 420, or may be in fluid communication with the final storage flow path 420. Components of the first portion 200 of the re-liquefier system 100, which are yet to be described in detail, shall be understood to be located along the reliquefying flow path 410, or in fluid communication with the re-liquefying flow path 410.

[0085] A heat exchanger 130 is provided, located along the final storage flow path 420 and downstream of the cryogenic storage tank 110. The heat exchanger 130 may be located between the cryogenic liquid pump 120 and the vaporiser 140, and therefore fluid flowing from the cryogenic storage tank 110 to the second storage tank 150 flows from the cryogenic storage tank 110, then through the cryogenic liquid pump 120, then through the heat exchanger 130, then through the vaporiser 140, then into the high-pressure storage tank 150. As such, the vaporiser 140 and the second storage tank 150 may be located downstream of the heat exchanger 130, and the cryogenic liquid pump 120 and cryogenic storage tank 110 may be located upstream of the heat exchanger 130. This heat exchanger 130 may be a surplus cooling heat exchanger 130.The surplus cooling heat exchanger 130 comprises two flow paths between which heat is exchanged. The first flow path through the surplus cooling heat exchanger 130 may be part of the final storage flow path 420, or in fluid communication with the final storage flow path 420. The second flow path though the surplus cooling heat exchanger 130 may be part of the re-liquefying flow path 410 through the first portion 200 of the re-liquefier system 100. The surplus cooling heat exchanger 130 is configured to transfer heat between the part of the final storage flow path 420 within the surplus cooling heat exchanger 130 and a part of the reliquefying flow path 410 through the first portion 200 of the re-liquefier system 100 within the surplus cooling heat exchanger 130. As such, the surplus cooling heat exchanger 130 is configured to transfer heat between the fluid in the re-liquefying flow path 410 and the fluid in the final storage flow path 420.

[0086] The surplus cooling heat exchanger 130 may be configured to improve the reliquefying performance of the re-liquefier system 100 by transferring heat from the fluid in the re-liquifying flow path 410 to the fluid in the final storage flow path 420. As this can reduce the temperature of the fluid in the re-liquefying flow path 410, the rate at which this fluid can be liquefied may be increased. This provides the advantage of improved re-liquefying performance. Further, the efficiency of the system may be improved by using the surplus cooling power available from the fluid in the final storage flow path 420.

[0087] In some configurations, the second storage tank 150 may be located on or in a vehicle. In some configurations, the second storage tank 150 may be disconnected from the re-liquefier system 100, and may be configured such that it may be connected to and disconnected from the cryogenic storage tank 110. The second storage tank 150 may be used to store hydrogen gas to be used as a fuel for a vehicle. In some configurations, the second storage tank 150 may be mobile. In some configurations, the second storage tank 150 may be located spaced apart from the rest of the re-liquefying system 100. In some configurations, the second storage tank 150 may be located a substantial distance from the rest of the reliquefying system 100.

[0088] There are some applications in which the improved performance of the re-liquefier system 100 is particularly advantageous. For example, some fluid may be vaporised by the cryogenic liquid pump 120, and this vaporised fluid may then be returned to the cryogenic storage tank 110. As such, the improved re-liquefying performance provided by the surpluscooling heat exchanger 130 may allow the increased amount of vaporised fluid created when the cryogenic liquid pump 120 is running to be re-liquefied effectively.

[0089] Further, the surplus cooling heat exchanger 130 can increase the effectiveness of the vaporiser 140, as the fluid is already increased in temperature by the surplus cooling heat exchanger 130 before reaching the vaporiser 140.

[0090] As shown in Figure 2, the re-liquefier system 100 may comprise a separation tank 230 in fluid communication with the cryogenic storage tank 110. The separation tank 230 receives gaseous fluid from the cryogenic storage tank 110, and returns liquid after the fluid is re-liquefied. Depending on the mode of operation of the re-liquefier system 100, the fluid travelling through the various pathways in the system may occur intermittently or continuously. Further, the connection to the cryogenic storage tank 110 may take various forms, as will subsequently be described in more detail.

[0091] To provide the necessary cooling, the re-liquefier system 100 further comprises a cryocooler 201. To provide the necessary pressure differential, the re-liquefier system 100 further comprises a compressor 240 connected to drive circulation of fluid through the reliquefier system 100 and raise the pressure within the reliquefying flow path 410.

[0092] The flow of vapor out of the cryogenic storage tank 110, towards the cryocooler 201 should be continuous. While the flow of liquid back to the cryogenic storage tank 110 may be intermittent.

[0093] The flow of fluid through the surplus cooling heat exchanger 130 is also controllable (e.g. by a valve 310) to be intermittent, so that a portion of the flow from the compressor 240 can be efficiently cooled in that heat exchanger 130 whenever there is surplus cooling available e.g. when the cryogenic liquid pump 120 is operating. Sensors 510 may be used to determine whether pathways should be opened or closed. The sensors 510 may be pressure or temperature sensors to detect when there may be advantage to directing flow through the surplus cooling heat exchanger 130.

[0094] The re-liquefier system 100 has a controller 520 to control the valve 310 associated with the reliquefying flow path 410, the valve 310 having an open condition to allow fluid to pass through the surplus cooling heat exchanger 130 or a closed condition for fluid to bypass the surplus cooling heat exchanger 130. One or more sensor(s) 510 may detect a condition in the system 100 to determine if the valve 310 is to be in an open condition ora closed condition.The gaseous fluid may be boil-off gas of the cryogenic fluid stored in the cryogenic storage tank 110.

[0095] The capacity of the separation tank 230 may be approximately 20 L, but could be adapted to the size of the cryogenic storage tank 110.

[0096] In some configurations, for example as shown in Figure 2, there may be valves 310 to control the flow of fluid through the re-liquefying flow path. In some configurations, there may be valves and instrumentation 310 to control the flow of fluid through the re-liquefying flow path 410 (referenced in Figure 4). This can allow the fluid to passthrough either the surplus cooling heat exchanger 130, the cryocooler 201, or both. The valving and instrumentation 310 may also be used to control the proportion of the fluid flow through the surplus cooling heat exchanger 130 and cryocooler 201. This can allow the surplus cooling heat exchanger 130 to be used in addition to the cryocooler 201 only when additional re-liquefying performance is needed. In some configurations, this can allow for a burst mode, in which the re-liquefication rate is increased temporarily. For example, burst mode may be activated whenever the cryogenic liquid pump 120 is being used to pressurise a flow to the second storage tank 150, as there will be surplus cold available and merit in directing flow to the surplus cooling heat exchanger 130. Flow to the surplus cooling heat exchanger 130 could also be determined based on temperatures in the re-liquefier circuit and / or in the path from the cryogenic liquid pump 120 to the vaporiser 140. There also may be benefit scheduling the operation of the cryogenic liquid pump 120 to optimise dual purposes of replenishing the second storage tank 150 and providing surplus cooling via the surplus cooling heat exchanger 130.

[0097] As shown in Figure 3, a plurality of cold heads 220 are mounted within the cryocooler 201. The cold heads 220 are part of the cryocooler 201 and may utilise any suitable cooling cycle, for example pulse tube or Stirling. Warming of the gas is provided by a plurality of heat exchangers 210, some or all of which may also be mounted within the cryocooler 201. In some configurations, the cryocooler 201 comprises three or four heat exchangers 210. In some configurations, three of the plurality of heat exchangers 210 are mounted within a cryostat (not shown) of the cryocooler 201. Optionally, one heat exchanger 210 for re-liquefying is mounted outside a cryostat of the cryocooler 201 and a remainder of the plurality of heat exchangers 210 for re-liquefying are mounted within the cryostat.

[0098] The heat exchangers 210 are connected in series to warm a first flow of gas coming from the separation tank 230 by transferring heat from a second flow of gas returning to theseparation tank 230. The compressor 240 is fed by the first flow of gas after the first flow of gas is warmed by the heat exchangers 210, such that the compressor 240 can operate at nearambient temperature and hence high efficiency. The compressor 240 raises the pressure and then returns the second flow of gas to flow through the cold heads 220, which are connected in series to actively cool the flow back down.

[0099] The compressor 240 can be situated outside of the cryocooler 201, since it is more efficiently operated at ambient temperature. By using cascaded heat exchangers 210 to warm the first flow of gas before it is fed to the compressor 240, instead of active heating or drawing in heat from the environment, less cooling power is required from the cold heads 220 to remove the added heat from the second flow of gas - this cooling power is instead provided by the first flow of gas itself. The use of the compressor 240 in the final stage of cooling helps to enable a more compact cryocooler 201 to be used for the re-liquefying system 100 while still maintaining high capacity.

[0100] The preferred connection arrangement is that in which the second flow of gas flows through the heat exchangers 210 and the cold heads 220 in an alternating fashion, which will in general be most thermally efficient. Use of counterflow heat exchangers will also improve efficiency. Figure 3 depicts a cryocooler 201 having three cold heads 220, such that between two to four heat exchangers 210 can be alternated with the cold heads 220. Preferably, the number of heat exchangers 210 is at least equal to the number of cold heads 220, to facilitate an alternating path.

[0101] There is also provided a method of operating the re-liquefier system 100 as herein described.

[0102] In some configurations, the method comprises connecting the cryogenic storage tank 110 to the separation tank 230, and supplying the separation tank 230 with boil-off cryogenic gas from the cryogenic storage tank 110.

[0103] The gas may then re-liquefied by running the compressor 240 and cryocooler 201 to circulate the gas through the re-liquefying flow path 410 through the re-liquefier system 100 and liquefy the gas. The liquid is then returned to the cryogenic storage tank 110.

[0104] In some configurations, the liquid can then be pumped from the cryogenic storage tank 110 towards the second storage tank 150 along the final storage flow path 420. The liquid is pressurised by the cryogenic liquid pump 120.In some configurations, as the fluid passes through the surplus cooling heat exchanger 130, heat is transferred between the fluid in the re-liquefying flow path 410 and the fluid in the final storage flow path 420. Heat may be transferred from the fluid in the reliquefying flow path 410 to the fluid in the final storage flow path 420. As such, the fluid in the re-liquefying flow path 410 may be cooled and the fluid in the final storage flow path 420 may be heated.

[0105] In some configurations, the fluid may then be vaporised as it passes through the vaporiser 140. The vaporiser 140 warms the liquid so that it is vaporised. The vaporiser may warm the fluid using the ambient air surrounding the vaporiser.

[0106] The fluid, (e.g. as a gas), may then be received and stored in the second storage tank 150.

[0107] In some configurations, the method of operating the re-liquefier system 100 comprises opening and closing the part of the re-liquefying flow path 410 that passes through the surplus cooling heat exchanger 130. This may be achieved using a valve 310.

[0108] In some configurations the compressor 240 may be configured to operate in a burst mode, and to drive flow or more flow through the re-liquefying flow path 410 in the burst mode. This may allow for additional cooling and reliquefying capacity. The compressor 240 drives less or no flow during normal operation.

[0109] The flow from the re-liquefier flow path to the surplus cooling heat exchanger 130 may be controlled so that it does not flow if there is no surplus cooling available in the final storage flow path 420 (e.g. when pump 120 is not operating).

[0110] In some configurations, the re-liquefier system 100 controls the proportion of flow through the surplus cooling heat exchanger 130 in response to temperature, pressure and / or flow sensors 510 in the system, or to a liquid pump operation status.

[0111] The re-liquefier system 100 of the present invention provides a number of key benefits over alternative re-liquefier systems.

[0112] Firstly, the re-liquefier system 100 of the present invention enables a large improvement in re-liquefying performance. This increase in performance may be utilised to increase the amount of fluid vapour that can be re-liquefied, or the rate at which fluid vapour can be re-liquefied. This increased performance may be utilised consistently, or only when a boost to the re-liquefying performance is needed. An improvement in re-liquefying performance may mean that less fluid is lost to boil-off and then venting. As hydrogen isexpensive, and recognised as a virtual greenhouse gas, recapturing boil-off hydrogen from a cryogenic storage tank 110 is highly desirable.

[0113] Secondly, the re-liquefier system 100 may allow a smaller cryocooler 201 to be used in the system. Alternatively or additionally, the arrangement of heat exchangers within the cryocooler 201 may be simplified. As a result, it may be possible to reduce the size and level of complexity of the entire re-liquefying system 100.

[0114] The present system supplies and stores high pressured gas located in a second storage tank 150. To achieve this a cryogenic liquid pump 120 is provided in the system. The cryogenic liquid pump 120 introduces a heat load to the system when operating, which can heat and vaporise some of the fluid, leading to fluid in a gaseous state being discharged back into the cryogenic storage tank 110.

[0115] Additionally, in some situations there can be heat loads introduced to the cryogenic storage tank 110 when it is re-filled with fluid. In this situation, the re-liquefying system 100 can help to re-liquefy fluid vaporised by these heat loads.

[0116] In both of these situations, there is a large amount of fluid vaporised, or vaporised fluid introduced to the cryogenic storage tank 110 in a short period of time. If the fluid cannot be re-liquefied at the same or close to the same rate it is vaporised, there will be a build-up of vaporised fluid, causing the pressure in the cryogenic storage tank 110 to increase, and the cryogenic storage tank 110 will need to vent to reduce the pressure. This requires a reliquefying system 100 that can quickly increase its re-liquefying capacity in these situations where fluid is vaporised at a higher rate. The surplus cooling heat exchanger 130 where the reliquefying flow path 410 and final storage flow storage flow path 420 pass through allows the re-liquefier system 100 to meet this need.

[0117] To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims.

[0118] This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which thisinvention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

Claims

CLAIMS1. A re-liquefier system comprising:a cryogenic storage tank for containing a fluid;a separation tank connected to the cryogenic storage tank, the separation tank configured to receive boil-off gas of the fluid from the cryogenic storage tank and return the fluid in a liquid-form to the cryogenic storage tank;a cryocooler connected to the separation tank configured to receive and cool the boil-off gas;a second storage tank located downstream of the cryogenic storage tank; a conduit network providing flow paths for the fluid, the conduit network comprising:a reliquefying flow path connected to the cryocooler;a final storage flow path connecting the cryogenic storage tank to the second storage tank;a compressor to drive circulation of the fluid through the re-liquefier system; a liquid pump located on the final storage flow path; anda surplus cooling heat exchanger located between the reliquefying flow path and the final storage flow path configured to transfer heat between the fluid passing through the reliquefying flow path and the final storage flow path.

2. The re-liquefier system of claim 1, further comprising a vaporiser located on the final storage flow path.

3. The re-liquefier system of claim 2, wherein the vaporiser is located downstream from the liquid pump.

4. The re-liquefier system of claim 2 or 3, wherein the vaporiser is located downstream from the surplus cooling heat exchanger.

5. The re-liquefier system of any one of claims 2 to 4, wherein the vaporiser is an ambient vaporiser.

6. The re-liquefier system of any one of the preceding claims, wherein the liquid pump is located upstream from the surplus cooling heat exchanger.

7. The re-liquefier system of any one of the preceding claims, wherein heat is configured to transfer from the reliquefying flow path to the final storage flow path.

8. The re-liquefier system of any one of the preceding claims, wherein the second storage tank is a high pressure gas storage tank.

9. The re-liquefier system of any one of the preceding claims, wherein the second storage tank is a removable and mobile storage tank.

10. The re-liquefier system of any one of the preceding claims, further comprising a controller to control a valve associated with the reliquefying flow path, the valve having an open condition to allow fluid to pass through the surplus cooling heat exchanger or a closed condition for fluid to bypass the surplus cooling heat exchanger.

11. The re-liquefier system of claim 10, further comprising a sensor to detect a condition in the system to determine if the valve is to be in an open condition or a closed condition.

12. The re-liquefier system of any one of the preceding claims, wherein the second storage tank is rated to store the fluid at a pressure higher than the cryogenic storage tank.

13. The re-liquefier system of any one of the preceding claims, wherein the second storage tank is rated to store the fluid at approximately 350 or 700 bar.

14. The re-liquefier system of any one of claims 1 to 12, wherein the second storage tank is rated to store the fluid at a pressure greater than 1000 bar.

15. The re-liquefier system of any one the preceding claims, wherein the cryogenic storage tank is rated to store the fluid at a pressure of approximately 10 bar.

16. The re-liquefier system of any one of the preceding claims, wherein the cryocooler comprises a plurality of heat exchangers connected in series and a plurality of cold heads in series to cool the boil-off gas by transferring heat from an outflowing flow of gas to the separation tank to an inflowing flow of gas from the separation tank.

17. The re-liquefier system of claim 16, wherein the cryocooler comprises three cold heads.

18. The re-liquefier system of any one of claims 16or 17, wherein the cryocooler comprises three or four heat exchangers.

19. The re-liquefier system of claim 18, wherein three of the plurality of heat exchangers are mounted within a cryostat of the cryocooler.

20. The re-liquefier system of any one of claims 16 to 19, wherein one heat exchanger for re-liquefying is mounted outside a cryostat of the cryocooler and a remainder of the plurality of heat exchangers for re-liquefying are mounted within the cryostat.

21. The re-liquefier system of any one of claims 16 to 20, wherein the plurality of cold heads and the plurality of heat exchangers are connected such that the outflowing flow of gas flows through the heat exchangers and the cold heads in an alternating fashion.

22. The re-liquefier system of any one of claims 16 to 21, wherein the plurality of heat exchangers are counterflow heat exchangers.

23. The re-liquefier system of any one of the preceding claims, wherein the fluid is hydrogen.

24. A method of operating the re-liquefier system of any one of the preceding claims, the method comprising:connecting the separation tank to the cryogenic storage tank;supplying boil-off gas from the cryogenic storage tank;re-liquefying gas by running the compressor and the cryocooler to circulate gas through the re-liquefier system;returning liquid from the separation tank to the cryogenic storage tank;pumping the liquid from the cryogenic storage tank towards the second storage tank; transferring heat from the final storage flow path to the re-liquefying flow path as fluid passes through the surplus cooling heat exchanger; andreceiving and storing fluid pumped from the cryogenic storage tank in the second storage tank.

25. The method of claim 24, when dependent on any one of claims 2 to 5, further comprising vaporising fluid as it passes through the vaporiser before passing the gas to the second storage tank.

26. The method of claim 24 or 25, further comprising pumping the liquid through the liquid pump such that the pressure of the gas received by the second storage tank is higher than the pressure of the liquid stored in the cryogenic storage tank.

27. The method of any one of claims 24 to 26, wherein the gas stored in the second storage tank is pressurised to approximately 350 or 700 bar.

28. The method of any one of claims 24 to 26, wherein the gas stored in the second storage tank is pressurised to over 1000 bar.

29. The method of any one of claims 24 to 28, wherein liquid stored in the cryogenic storage tank is approximately 10 bar.

30. The method of any one of claims 25 to 29, wherein the fluid passing through the vaporiser is heated by ambient air before being received by the second storage tank.

31. The method of any one of claims 24 to 30, further comprising using surplus cooling from the final storage flow path to cool the reliquefying flow path.

32. The method of any one of claims 24 to 31, further comprising opening and closing the pathway of the reliquefying flow path that passes through the surplus cooling heat exchanger via a valve.

33. The method of claim 30, wherein additional cooling by passing the fluid in the reliquefying flow path through the surplus cooling heat exchanger occurs intermittently.

34. The method of any one of claims 24 to 32, wherein additional cooling by passing the fluid in the reliquefying flow path through the surplus cooling heat exchanger occurs continuously.

35. The method of any one of claims 24 to 33, wherein the compressor drives flow or more flow through the re-liquefier system in a burst mode for additional cooling, and drives less or no flow during normal operation.

36. The method of any one of claims 24 to 35, further comprising closing the pathway of the reliquefying flow path when there is no surplus cooling available in the final storage flow path.

37. The method of claim 36, wherein there is no surplus cooling available when the liquid pump is not operating.

38. The method of any one of claims 24 to 37, wherein the re-liquefier system controls the proportion of flow through the surplus cooling heat exchanger in response to temperature, pressure and / or flow sensors in the system, or a liquid pump operation status.

39. The method of any one of claims 24 to 38, wherein pumping liquid from the cryogenic storage tank towards the second storage tank pressurises the liquid.

Images