Equipment and method for storing liquefied gas
The refrigeration system with control valves and sensors addresses boil-off gas issues by cooling and transferring liquefied gas within methane tankers, reducing losses and costs through efficient boil-off gas management.
Patent Information
- Application Number
- JP2024538413
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-01-28
- Filing Date
- 2022-12-07
- Publication Date
- 2025-01-24
AI Technical Summary
Existing methods for storing liquefied natural gas on methane tankers generate boil-off gas during loading operations, leading to product loss or high costs due to the need for boil-off gas compressors.
A refrigeration system with control valves and sensors manages fluid circulation and reinjection to minimize boil-off gas by cooling and transferring it to full tanks, using a refrigeration device to subcool the fluid and reinject it into empty tanks.
Reduces boil-off gas generation by efficiently cooling and reusing the gas, minimizing product loss and reducing the need for costly compressors.
Smart Images
Figure 2025501915000001_ABST
Abstract
Description
[Technical field]
[0001] The present invention relates to an installation and method for storing liquefied gas, for example liquefied natural gas.
[0002] The invention particularly relates to the storage and transportation of liquefied natural gas, for example on board methane tankers.
[0003] The invention relates more particularly to a storage installation for liquefied gas, for example liquefied natural gas, in particular on a ship, comprising a number of separate storage tanks each designed to contain liquefied gas, each tank having a lower part intended to contain the liquefied gas in a liquid state and an upper part intended to contain vapour from the liquefied gas, the installation comprising a cooling circuit with a refrigeration device, the cooling circuit comprising a withdrawal line having a first end opening into the lower part of the first tank and a second end connected to an inlet of the refrigeration device, the cooling circuit comprising a number of first inlet lines respectively connecting the outlet of the refrigeration device to each tank, the refrigeration device designed to cool a fluid flow circulating between its inlet and its outlet.
[0004] The invention particularly relates to the cooling of methane tankers (comprising multiple storage tanks) during loading operations (filling) with liquefied natural gas. [Background technology]
[0005] See EP 3510317 A1.
[0006] The present invention aims to reduce or eliminate the generation of boil-off gas during this operation.
[0007] Known solutions involve injecting liquefied gas pumped from full or residual tanks into the empty tanks. However, this generates boil-off gases in the empty tanks which are cooled. These boil-off gases are either lost (vented out, used to propel the ship or burned in a flare) or must be transported to a liquefaction unit to be re-injected into one of the tanks.
[0008] The first solution results in product losses, while the second solution is costly, especially since it requires the installation of a boil-off gas compressor to re-liquefy the boil-off gas. Summary of the Invention [Problem to be solved by the invention]
[0009] One object of the present invention is to alleviate some or all of the above-mentioned shortcomings of the prior art. [Means for solving the problem]
[0010] To this end, the installation according to the invention, which otherwise corresponds to the general definition given in the preamble above, is essentially characterized in that each of the tanks comprises a degassing line comprising a first end connected to the top of the tank and a second end connected to at least one recovery zone, the degassing line of each tank other than the degassing line of the first tank comprising a third end connected to the top of the first tank, the installation comprises at least a set of control valves arranged in the cooling circuit and an electronic control member for said valves, the control member being configured to command the opening and closing of the valves in order to cool the fluid contained in the first tank via the cooling circuit by withdrawing liquid from the first tank, cooling this withdrawn liquid in a refrigeration device and reinjecting this liquid into the first tank, the control member being further configured to inject the liquid cooled in the refrigeration device via one or more first injection lines into at least one other empty tank and to transfer the boil-off gas generated in this or these other empty tanks to the first tank via one or more third ends of the degassing lines.
[0011] Furthermore, embodiments of the invention may include one or more of the following features: - each first inlet line has a first end connected to an outlet of the refrigeration device and a second end opening into an upper portion of the tank; - the cooling circuit comprises a second inlet line connecting the outlet of the refrigeration device to the lower part of the first tank, - a control member configured to command the opening and closing of the set of valves to cool the fluid contained in the first tank by reinjecting cooled liquid via the first inlet line and / or the second inlet line; the installation comprises a set of pressure sensors in the tank, the control member being configured to command the opening and closing of valves to distribute the flow of cooled liquid reinjected into the first tank between the first inlet line and the second inlet line depending on the pressure level measured by the set of pressure sensors, the installation comprises a set of temperature sensors for the fluid in the tank, the control member being configured to command the opening and closing of the valve depending on the temperature level measured by the set of temperature sensors;
[0012] The invention also relates to a method for cooling tanks in a liquefied gas storage installation comprising a number of separate storage tanks each designed to contain a liquefied gas, each tank comprising at least a lower part intended to contain the liquefied gas in liquid form and at least an upper part intended to contain vapour from the liquefied gas, the installation comprising a cooling circuit comprising a refrigeration device, the cooling circuit comprising a withdrawal line with a first end opening into the lower part of the first tank and a second end connected to the inlet of the refrigeration device, the cooling circuit comprising a number of first inlet lines respectively connecting the outlet of the refrigeration device to each of the tanks, the refrigeration device being designed to cool a fluid flow circulating between its inlet and outlet, each of the tanks comprising a first end connected to the upper part of the tank and a second end connected to at least one recovery zone. and a second end of the degassing line for each tank other than the first tank, the degassing line having a third end connected to the top of the first tank, the installation comprising at least a set of control valves arranged in a cooling circuit, the first tank containing liquid and at least one other tank being empty and containing essentially boil-off gas, i.e. containing little or no liquid, the method comprising: cooling the fluid contained in the first tank via the cooling circuit by withdrawing liquid from the first tank, cooling the liquid in a refrigeration device and re-injecting the liquid into the first tank; injecting the liquid cooled in the refrigeration device into the at least one other empty tank; and transferring boil-off gas generated in the other tank or tanks to the first tank.
[0013] According to possible specific features: - during a cooling step, the fluid contained in the first tank is cooled to a temperature below the saturation temperature of the fluid at the pressure in the tank; the step of transferring the boil-off gas to the first tank is carried out by pressure equalization and / or via a pumping element such as a compressor, - the step of injecting the cooled liquid into at least one other empty tank and the step of transferring the boil-off gas generated in the other tank or tanks into the first tank are performed at least partially simultaneously; - a step of injecting cooled liquid into at least one other empty tank is carried out until the fluid in the other tank or tanks reaches a given temperature, which may be a low temperature, for example below the saturation temperature of the fluid at the pressure in the tank, - the method comprises, after the step of injecting the cooled liquid into at least one other empty tank, a step of filling at least one of the other tanks with liquefied gas, - The fluid is liquefied natural gas.
[0014] The invention may also relate to any alternative device or method including any combination of the above or below features falling within the scope of the claims.
[0015] Other features and advantages will become apparent from the following description, given with reference to the drawings. [Brief description of the drawings]
[0016] [Figure 1] FIG. 1 is a schematic partial view showing a possible exemplary embodiment of the structure and operation of an installation according to the invention in a first operating configuration. [Diagram 2] FIG. 2 is a similar view of the installation in a second operating configuration. [Diagram 3] FIG. 3 is a similar view of the installation in a third operating configuration. [Figure 4] FIG. 4 is a similar view of the installation in a fourth operating configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] The liquefied gas storage facility 1 shown comprises a number of separate storage tanks 2, 3, 4, 5 (four in this non-limiting example) each designed to contain liquefied gas, in particular liquefied natural gas.
[0018] Each tank 2, 3, 4, 5 typically comprises a lower part intended to contain the liquefied gas in liquid form and an upper part intended to accommodate vapour from the liquefied gas.
[0019] The installation 1 further comprises a cooling circuit equipped with a refrigeration device 7. This cooling circuit comprises at least one withdrawal line 6 having a first end opening into the lower part of the first tank 2 and a second end connected to an inlet of the refrigeration device 7.
[0020] The withdrawal line 6 may in particular include a pump 26 intended to suck the liquid in the first tank 2 .
[0021] The cooling circuit comprises a cooling fluid inlet line 8 connecting the outlet of the refrigeration device 7 to each of the tanks 2, 3, 4, 5 respectively.
[0022] The refrigeration device 7 is designed to cool, and in particular, where applicable, subcool, a fluid flow circulating between its inlet and outlet.
[0023] For example, the refrigeration device 7 comprises a cryogenic refrigerator with a refrigeration cycle of a cycle gas in a working circuit. The cycle gas comprises, for example, a pure gas or a mixed gas (for example, nitrogen, neon, argon, helium, hydrogen or a mixture thereof). The working circuit of the refrigerator 7 comprises a cycle gas compression member (for example, one or more electric compressors), a cycle gas cooling member (for example, one or more cooling heat exchangers), a cycle gas expansion member (one or more turbines and / or expansion valves), and a cycle gas heating member (one or more heat exchangers). The work of at least one of the turbines is preferably transferred to the compressor via a common drive shaft. In particular, heating and cooling may be provided, at least in part, by one or more countercurrent exchangers in which two different parts of the cycle gas circulate under different thermodynamic conditions (in particular temperatures).
[0024] In other words, the working circuit of the refrigerator may be configured to subject a working gas to a thermodynamic cycle which generates a cooling capacity at one end of the working circuit which is transferred to a cooled fluid circuit via one or more heat exchangers. The refrigerator 7 may in particular be a "Turbo Brayton" device sold by the Applicant.
[0025] As shown, each of the tanks 2, 3, 4, 5 includes a degassing line 10 having a first end connected to the top of the tank and a second end connected to at least one collection zone 11 (e.g., a vent to the atmosphere and / or to the inlet of an engine or gas combustion component).
[0026] The degassing line 10 of each tank 3, 4, 5 other than the degassing line of the first tank 2 is also connected to the top of the first tank 2 (via a third end).
[0027] As shown, the degassing lines 10 of each tank 2, 3, 4, 5 can be connected in parallel via a common line to the recovery zone 11. This also provides a fluid link between the tops of all tanks 2, 3, 4, 5 via the degassing lines 10 (which allows for the transfer of boil-off gas from one tank to another, if required, as described below).
[0028] The installation 1 comprises at least a set of valves 16, 18, e.g. control valves, arranged in the cooling circuit, which set of valves is in particular configured to allow targeted cooling of the tanks 2, 3, 4. The set of valves is preferably controlled (opened and closed) by an electronic control member 12, which for example comprises a microprocessor.
[0029] The control member 12 may in particular be configured to command the opening and closing of valves in order to cool the fluid contained in the first tank 2 via a cooling circuit.
[0030] This cooling can be performed by withdrawing liquid from the first tank 2 via the withdrawal line 6, then cooling this withdrawn liquid by heat exchange with a cold part of a refrigerator 7, and then reinjecting this cooled liquid into the first tank 2 via an injection line 8. As shown, the injection line 8 comprises a first end connected to the outlet of the refrigerator 7 and a second end opening into the top of the tank 2, for example in the form of one or more nozzles opening into the top of the tank. In other words, the injection member injects the subcooled liquefied gas into the vapour phase, i.e. above the level of the liquefied gas in the liquid state.
[0031] Some or all of the other tanks 3 , 4 , 5 are preferably also provided with such an inlet line 8 connected to the outlet of the refrigeration device 7 and with a second end opening into the top of the tank 2 .
[0032] In the configuration shown in [Figure 1], the first tank 2 still contains liquid, while the other tanks 3, 4, 5 are empty and at a relatively high temperature (little or no liquid). In the case of liquefied natural gas, the temperature of the gas in these other empty tanks 3, 4, 5 may be higher than -130°C, for example between -130°C and +30°C. In each of these tanks 2, 3, 4, 5, the pressure is lower than the set pressure of a safety valve (not shown for simplicity). Typically, the pressure in each tank is maintained below a given value of about a few hundred millibars (gauge pressure) above atmospheric pressure or a few bars (depending on the nature of the tank).
[0033] In a first stage or step, the contents of the first tank 2 may be cooled or sub-cooled as described above.
[0034] Liquid can be pumped from the first tank 2 via the withdrawal line 6, then cooled by the refrigerator 7, and then re-injected into the first tank 2 via the injection line 8 (corresponding valves 16, 18 are open).
[0035] That is, preferably, the first tank 2, which still contains liquid, is completely cooled, preferably below the saturation temperature, before cooling of the other empty tanks 3, 4, 5 begins. For example, the refrigeration device 7 may be designed to cool the liquefied gas coming from the tank 2 to a temperature between 35K and 150K, for example 110K or 80K (for example 5m 3 / h~50m 3 / h flow rate).
[0036] During this step, in order to avoid or limit possible boil-off gas generation in the first tank 2, the flow of reinjected cooled (subcooled) liquid can be distributed between the upper and / or lower parts of the tank 2.
[0037] For this purpose, and as shown, the installation 1 may have (at least for the first tank 2) a second inlet line 9 connecting the outlet of the refrigeration device 7 to the interior of the first tank 2, for example opening into the lower part of the first tank 2. Furthermore, the set of valves comprises at least one valve configured to control the re-injection of cooled liquid via the first inlet line 8 and / or the second inlet line 9 (see FIG. 1 ).
[0038] It should be noted that the second inlet line 9 may be designed to allow for injecting cooled (or supercooled) liquid into this or these other tanks (i.e. one or more separate second inlet lines 9 may be provided).
[0039] If the pressure in the tank 2 rises too much (e.g. above a given level), the cooled liquid is reinjected (via the first inlet line 8) mainly or exclusively into the upper part of the tank 2 (see FIG. 2). On the other hand, if the pressure drops (e.g. above a given level), the cooled liquid is reinjected (via the second inlet line 9) mainly or exclusively into the lower part of the tank 2.
[0040] Preferably, at the start of this cooling phase of the first tank 2, about 10% of the cooled liquid flow is reinjected via the first injection line 8.
[0041] The detection of this pressure level and / or its variations can be achieved by at least one sensor 20 measuring the pressure in the tank 2, for example in the degassing line 10.
[0042] Once the first tank 2 is sufficiently cooled (below its saturation temperature), the cooled (subcooled) liquid contained within the first tank 2 can be poured into one or more other empty tanks to cool them (simultaneously or sequentially).
[0043] As shown in FIG. 3, the cooled liquid leaving the refrigeration device 7 can be injected simultaneously into the first tank 2 and some or all of the other tanks via respective second injection lines 8 (with corresponding valves 18 open).
[0044] In this way, the installation 1 allows the subcooled liquid withdrawn from the first tank 2, which is not empty, to be injected into the empty tanks 3, 4, 5. The boil-off gases that arise when the cold liquid is injected into the empty tank are sucked off and returned to the first tank, which, however, contains liquid and is subcooled. This solution offers the option of returning the subcooled liquid separately to each of the tanks 3, 4, 5. This can be done by using a distribution valve on each tank or by using any other suitable means.
[0045] Injection of cold liquid into the empty tanks 3, 4, 5 results in boil-off gases being generated in the tanks 3, 4, 5 at a relatively high temperature. These boil-off gases are returned to the first tank 2 at a low temperature via a degassing line 10 connected to the first tank 2. These boil-off gases are sucked (or forced, if necessary) by the first tank 2 due to the pressure difference. These boil-off gases are at least partially cooled and recondensed in the low temperature environment of the first tank 2.
[0046] The cooled liquid flows injected into the hot tanks 3, 4, 5 can be regulated as a function of the pressure of these tanks.
[0047] For example, if the pressure increases too much (e.g., above a given level), the injected liquid flow can be relatively decreased, and if the pressure is relatively low or decreasing, the injected liquid flow can be relatively increased.
[0048] This process of cooling tanks 3, 4, 5 can continue until the empty tanks to be cooled are at a sufficiently low temperature, for example below the saturation temperature, for example below -130°C.
[0049] The detection of this temperature level and / or its variations can be performed, for example in the degassing line 10, by at least one sensor 21 measuring the temperature in one or more tanks.
[0050] Once the empty tanks have cooled sufficiently, liquid will appear or increase in volume in these tanks by injecting additional liquid into them (see Figure 4).
[0051] Advantageously, this step of cooling the empty tanks 3 , 4 , 5 is carried out after the release of the liquefied gas and before the subsequent filling of one or more tanks of the installation 1 .
[0052] Some or all of the valves may be valves controlled by a control member 12 in response to signals from a pressure sensor 20 and / or a temperature sensor 21 within the facility.
[0053] The present invention can be applied to installations storing liquefied natural gas or other cryogenic gases, e.g. liquefied below -100°C, or suitable mixtures of gases, e.g. biomethane, nitrogen, oxygen, argon and mixtures thereof.
[0054] The invention also relates to a transport vehicle, for example a transport ship, for transporting liquefied gas, for example liquefied natural gas, comprising such an installation.
Claims
1. A storage installation, in particular on a ship, for a liquefied gas, for example liquefied natural gas, comprising a number of separate storage tanks (2, 3, 4, 5) each designed to contain said liquefied gas, each tank having a lower part intended to contain said liquefied gas in liquid form and an upper part intended to contain vapour from said liquefied gas, said installation (1) comprising a cooling circuit with a refrigeration device (7), said cooling circuit having a first end opening into the lower part of a first tank (2) and a second end connected to the inlet of said refrigeration device (7). The cooling circuit comprises a plurality of first inlet lines (8) respectively connecting the outlet of the refrigeration device (7) to each of the tanks (2, 3, 4, 5), each of the tanks (2, 3, 4, 5) comprising a degassing line (10) having a first end connected to the top of the tank and a second end connected to at least one recovery zone (11), each tank other than the degassing line of the first tank (2) being provided with a first inlet line (12) and a second inlet line (13) connected to the top of the tank (2). The degassing line (10) of the tank (3, 4, 5) has a third end connected to the top of the first tank (2), and the installation (1) comprises at least a set of control valves (16, 18) arranged in the cooling circuit and an electronic control member (12) for said valves, the control member (12) being adapted to transfer the fluid contained in the first tank (2) to the cooling circuit by withdrawing liquid from the first tank (2), cooling said withdrawn liquid in the refrigeration device (7) and re-injecting said liquid into the first tank (2). the control member (12) is further configured to inject this liquid withdrawn from the first tank and cooled in the refrigeration device (7) into at least one other empty tank (3, 4, 5) via the first inlet line(s) (8) and to transfer boil-off gas generated in this or these other empty tanks (3, 4, 5) to the first tank (2) via the third end(s) of the degassing line(s) (10).
2. 2. Installation according to claim 1, characterized in that each first inlet line (8) has a first end connected to the outlet of the refrigeration device (7) and a second end opening into the top of a tank (2, 3, 4, 5).
3. 3. Installation according to claim 1 or 2, characterized in that the cooling circuit comprises a second inlet line (9) connecting the outlet of the refrigeration device (7) to the lower part of the first tank (2).
4. 4. Installation according to claim 3, characterized in that the control member (12) is configured to command the opening and closing of the set of valves in order to cool the fluid contained in the first tank (2) by reinjecting cooled liquid via the first inlet line (8) and / or the second inlet line (9).
5. 5. Installation according to claim 4, characterized in that it comprises a set of pressure sensors (20) in the tank, and the control member (12) is configured to command the opening and closing of the valves for distributing the flow of cooled liquid reinjected into the first tank (2) between the first inlet line (8) and the second inlet line (9) depending on the pressure level measured by the set of pressure sensors.
6. Installation according to any one of claims 1 to 5, characterised in that it comprises a set of temperature sensors (21) for the fluid in the tank, and in that the control member (12) is configured to command the opening and closing of the valve depending on the temperature level measured by the set of temperature sensors (21).
7. A method for cooling tanks in a liquefied gas storage installation comprising a number of separate storage tanks (2, 3, 4, 5) each designed to contain a liquefied gas, each tank comprising at least a lower part intended to contain said liquefied gas in a liquid state and at least an upper part intended to contain vapor from said liquefied gas, said installation (1) comprising a cooling circuit comprising a refrigeration device (7), said cooling circuit comprising a withdrawal line (6) having a first end opening into said lower part of a first tank (2) and a second end connected to an inlet of said refrigeration device (7), said cooling circuit comprising a number of first inlet lines (8) connecting the outlet of said refrigeration device (7) to each of said tanks (2, 3, 4, 5), respectively, and said refrigeration device (7) comprising a first inlet line (8) and a second inlet line (8) connected to said outlet of said refrigeration device (7 ... is designed to cool a fluid stream circulating between its inlet and outlet, each of said tanks (2, 3, 4, 5) comprises a degassing line (10) with a first end connected to the top of said tank and a second end connected to at least one recovery zone (11), said degassing line (10) of each tank (3, 4, 5) other than the degassing line of said first tank (2) comprises a third end connected to the top of said first tank (2), said installation (1) comprises at least a set of control valves (16, 18) arranged in said cooling circuit, said first tank (2) contains liquid and at least one other tank (3, 4, 5) is empty and essentially contains boil-off gas, i.e. contains little or no liquid, - cooling the fluid contained in the first tank (2) via the cooling circuit by withdrawing liquid from the first tank (2), cooling it in the refrigeration device (7) and reinjecting this liquid into the first tank (2); - injecting the liquid cooled in said refrigeration device (7) into at least one other empty tank; - transferring the boil-off gas generated in one or more other tanks (3, 4, 5) to said first tank (2); The method includes:
8. 7. A method according to claim 6, characterized in that during the cooling step, the fluid contained in the first tank (2) is cooled to a temperature below the saturation temperature of said fluid at the pressure inside the tank.
9. 8. The method according to claim 6 or 7, characterized in that the step of transferring the boil-off gas to the first tank (2) is performed by pressure equalization and / or via a pumping element such as a compressor.
10. 10. The method according to any one of claims 6 to 9, characterized in that the steps of injecting cooled liquid into at least one other empty tank and of transferring boil-off gas generated in the other tank or tanks (3, 4, 5) to the first tank (2) are performed at least partly simultaneously.
11. Method according to any one of claims 6 to 10, characterized in that the step of injecting cooled liquid into at least one other empty tank is carried out until the fluid in the other tank or tanks (3, 4, 5) reaches a given temperature, which may for example be a low temperature below the saturation temperature of the fluid at the pressure in the tank.
12. A method according to any one of claims 6 to 11, characterized in that after the step of injecting cooled liquid into at least one other empty tank, it comprises the step of filling at least one of said other tanks with the liquefied gas.
13. A method according to any one of claims 6 to 12, characterised in that the fluid is liquefied natural gas.