Liquefied gas storage tank and liquefied gas storage tank gas handling method

Abstract

The present invention relates to a liquefied gas storage tank gas handling method, which comprises: an inert gas injection step of injecting inert gas through a replacement gas supply pipe disposed in a liquefied gas storage tank; a depressurizing step of discharging residual gas including the inert gas remaining in the liquefied gas storage tank to the outside through a residual gas discharge pipe disposed in the liquefied gas storage tank; a replacement gas injection step of injecting liquefied gas until a predetermined pressure is reached through a replacement gas supply pipe disposed in the liquefied gas storage tank in a state in which the residual gas discharge pipe is closed; and a final discharge step of additionally discharging the residual gas by opening the residual gas discharge pipe, wherein, during injection of a replacement gas, mixing with the residual gas can be prevented, thereby reducing the replacement time.

Description

Liquefied gas storage tank and liquefied gas storage tank gas treatment method

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0131742 filed September 27, 2024, and all contents disclosed in the document of said Korean Patent Application are incorporated herein as part of this specification.

[0003] Technology field

[0004] The present invention relates to a liquefied gas storage tank, and more specifically, to a liquefied gas storage tank comprising a replacement gas supply pipe at the top of the liquefied gas storage tank and a residual gas discharge pipe at the bottom of the liquefied gas storage tank.

[0005] In addition, the present invention relates to a gas treatment method for a liquefied gas storage tank, comprising a depressurization step for discharging residual gas containing inert gas to the outside before a replacement gas injection step within the liquefied gas storage tank, and a final discharge step for additionally discharging residual gas when a certain pressure is reached during replacement gas injection.

[0006] As environmental regulations are tightening worldwide, research on eco-friendly fuels that can replace conventional fossil fuels is steadily underway, and hydrogen is gaining attention as one of them.

[0007] Hydrogen can be transported in a liquefied state for transportation efficiency when moving from production facilities to demand centers, and liquefied hydrogen carriers can be used when transporting liquefied hydrogen by sea.

[0008] For vessels that use liquefied gas as fuel or transport it, a gas treatment process is performed within the liquefied gas storage tanks after construction, during sea trials, and during maintenance while in operation.

[0009] In the case of LNG (Liquefied Natural Gas), an inerting step is performed to inject inert gas into the air inside the liquefied gas storage tank, followed by a gas-up step to replace it with NG (Natural Gas), thereby removing moisture, carbon dioxide, and oxygen present inside the liquefied gas storage tank. During the replacement process of air and inert gas, the two gases undergo a mixing process; however, because the two gases do not mix well during the replacement process of inert gas and NG, a method is used in which lighter NG is injected into the upper part of the liquefied gas storage tank and nitrogen is removed from the lower part of the tank.

[0010] However, if the same gas treatment methods used for conventional liquefied gas storage tanks as those for LNG are applied to liquefied hydrogen storage tanks, the high permeability of hydrogen can easily lead to mixing between the inert gas and hydrogen. Consequently, this results in problems such as increased replacement time during the process of replacing the inert gas and hydrogen, as well as increased costs due to the increased amount of hydrogen required.

[0011] The present invention aims to provide a gas treatment method for a liquefied gas storage tank comprising a depressurization step for discharging residual gas containing inert gas to the outside before a replacement gas injection step, and a final discharge step for additionally discharging residual gas when a certain pressure is reached during replacement gas injection.

[0012] In addition, the present invention aims to provide a liquefied gas storage tank comprising a replacement gas supply pipe at the top of the liquefied gas storage tank and a residual gas discharge pipe at the bottom of the liquefied gas storage tank.

[0013] The present invention relates to a gas treatment method for a liquefied gas storage tank, and may include an inert gas injection step of injecting inert gas through a replacement gas supply pipe provided in the liquefied gas storage tank; a depressurization step of discharging residual gas containing inert gas remaining in the liquefied gas storage tank to the outside through a residual gas discharge pipe provided in the liquefied gas storage tank; a replacement gas injection step of injecting replacement gas through a replacement gas supply pipe provided in the liquefied gas storage tank until a certain pressure is reached while the residual gas discharge pipe is closed; and a final discharge step of opening the residual gas discharge pipe to additionally discharge residual gas.

[0014] In one example, the pressure reduction step can reduce the pressure inside the liquefied gas storage tank to a preset pressure using a vacuum pump.

[0015] In one example, the end of the depressurization step and the replacement gas injection step can be determined based on a value measured by a pressure sensor installed in the liquefied gas storage tank.

[0016] In one example, a stabilization phase of a certain period of time may be provided between the depressurization phase and the replacement gas injection phase.

[0017] In one example, a liquefied gas storage tank may include an inner wall portion for containing liquefied gas, an outer wall portion disposed outside the inner wall portion, an insulating space disposed between the inner wall portion and the outer wall portion, a replacement gas supply pipe communicating with the inner wall portion at the top of the liquefied gas storage tank, and a residual gas discharge pipe communicating with the inner wall portion at the bottom of the liquefied gas storage tank.

[0018] In one example, it may include a vacuum pump connected to an insulating space gas exhaust pipe communicating with the insulating space and a residual gas exhaust pipe.

[0019] In one example, a plurality of replacement gas concentration sensors may be included that are arranged vertically within the inner wall.

[0020] The present invention provides a gas treatment method for a liquefied gas storage tank comprising a pressure reduction step for discharging residual gas containing an inert gas before a replacement gas injection step, and a final discharge step for additionally discharging residual gas when a certain pressure is reached during replacement gas injection, thereby preventing mixing with residual gas during replacement gas injection and reducing replacement time.

[0021] In addition, the present invention can reduce the cost of gas replacement in a liquefied gas storage tank by using a vacuum pump to maintain a vacuum in the insulation space of the liquefied gas storage tank, thereby performing a pressure reduction step and a final discharge step.

[0022] FIG. 1 is a planar cross-section of a liquefied gas storage tank according to one embodiment of the present invention.

[0023] FIG. 2 is a flowchart of a gas treatment method for a liquefied gas storage tank according to one embodiment of the present invention.

[0024] FIG. 3 is a diagram showing the step of injecting inert gas into a liquefied gas storage tank through a replacement gas supply pipe according to one embodiment of the present invention.

[0025] FIG. 4 is a diagram showing the step of discharging residual gas through a residual gas discharge pipe in a liquefied gas storage tank according to one embodiment of the present invention.

[0026] FIG. 5 is a diagram showing the step of injecting liquefied gas into a liquefied gas storage tank through a replacement gas supply pipe according to one embodiment of the present invention.

[0027] FIG. 6 is a diagram showing a final discharge step in which liquefied gas is injected into a liquefied gas storage tank through a replacement gas supply pipe and residual gas is additionally discharged through a residual gas discharge pipe according to one embodiment of the present invention.

[0028] FIG. 7 is a graph showing the pressure of the inner wall of a liquefied gas storage tank according to a change in time during the gas treatment process of a liquefied gas storage tank according to one embodiment of the present invention.

[0029] FIG. 8 is a graph showing the gas volume ratio of the inner wall portion of a liquefied gas storage tank according to time change during the gas treatment process of a liquefied gas storage tank according to one embodiment of the present invention.

[0030] Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that in assigning reference numerals to the components of each drawing, the same components are given the same reference numeral whenever possible, even if they are shown in different drawings. Furthermore, in describing the embodiments of the present invention, if it is determined that a detailed description of related known components or functions would hinder understanding of the embodiments of the present invention, such detailed description is omitted.

[0031] In addition, terms such as first, second, A, B, (a), (b), etc., may be used when describing the components of the embodiments of the present invention. These terms are intended merely to distinguish the components from other components, and the essence, order, or sequence of the components is not limited by these terms. Where it is stated that a component is "connected," "combined," or "joined" to another component, it should be understood that the component may be directly connected or joined to the other component, but that another component may also be "connected," "combined," or "joined" between each component.

[0032]

[0033] Below, a method for treating gas in a liquefied gas storage tank (S1) and a liquefied gas storage tank (100) according to an embodiment of the present invention will be described.

[0034]

[0035] Liquefied gas storage tank

[0036] Referring to FIG. 1, the liquefied gas storage tank (100) may include an inner wall portion (110) that contains liquefied gas inside; an outer wall portion (120) disposed outside the inner wall portion; an insulating space (130) disposed between the inner wall portion and the outer wall portion; a replacement gas supply pipe (210) communicating with the inner wall portion (110) at the top of the liquefied gas storage tank (100); and a residual gas discharge pipe (220) communicating with the inner wall portion (110) at the bottom of the liquefied gas storage tank (100).

[0037] A liquefied gas carrier is a vessel capable of transporting liquefied gases such as liquefied ammonia and liquefied hydrogen. In this invention, liquefied hydrogen is used as an example, but the invention is not limited thereto.

[0038] The liquefied gas storage tank (100) may be provided as a pressure vessel-type C-Type tank having a cylindrical structure with a circular cross-section. The C-Type tank can store liquefied gases in a cryogenic state, such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), hydrogen, and ammonia, inside. However, there are no restrictions on the storage targets of the liquefied gas storage tank (100).

[0039] The inner wall portion (110) is the internal structure of the liquefied gas storage tank (100) for storing cryogenic liquid, and the outer wall portion (120) may be the outer structure of the liquefied gas storage tank (100) for storing cryogenic liquid. As the liquefied gas storage tank (100) is made of double walls, the thermal insulation performance may be improved.

[0040] The insulation space (130) refers to the space between the inner wall (110) and the outer wall (120), and the insulation space (130) can be filled with a filler and vacuum-treated.

[0041] The insulation space (130) can block heat transfer between the inner wall (110) and the outer wall (120). By making the insulation space (130) a vacuum, the insulation performance of the storage tank can be improved, and the effect of reducing the generation of evaporated gas of the liquefied gas can be achieved.

[0042] The vacuum pump (240) can be connected to an insulation space gas discharge pipe (230) connected within the insulation space (130). The vacuum pump (240) can create a vacuum by discharging internal gas from the insulation space (130) to the outside through the insulation space gas discharge pipe (230). Additionally, the vacuum pump (240) can discharge residual gas to the outside through a residual gas discharge pipe (220) connected within the inner wall (110). By discharging residual gas to the outside through the existing vacuum pump (240) without the need to install a separate vacuum pump (240), the gas replacement cost of the liquefied gas storage tank (100) can be reduced.

[0043] The replacement gas supply pipe (210) is positioned at the top of the liquefied gas storage tank (100) and can be connected to the inner wall (110) of the liquefied gas storage tank (100).

[0044] A replacement gas control valve (211) may be provided in a replacement gas supply pipe (210). The replacement gas control valve (211) may open when an inert gas or replacement gas is injected into the inner wall (110) of the liquefied gas storage tank (100).

[0045] Specifically, the inert gas can be nitrogen gas, and the replacement gas can be hydrogen.

[0046] The residual gas discharge pipe (220) may be positioned at the bottom of the liquefied gas storage tank (100). One end of the residual gas discharge pipe (220) may be connected to the inner wall portion (110) of the liquefied gas storage tank (100), and the other end of the residual gas discharge pipe (220) may be connected to the insulation space gas discharge pipe (230).

[0047] A residual gas control valve (221) may be provided in a residual gas discharge pipe (220). The residual gas control valve (221) may be opened to discharge residual gas present in the inner wall (110) of the liquefied gas storage tank (100) to the outside. Additionally, the residual gas control valve (221) may be closed when injecting replacement gas into the inner wall (110) of the liquefied gas storage tank (100).

[0048] The residual gas may include oxygen, water vapor, and inert gas present in the liquefied gas storage tank (100).

[0049] One end of the insulating space gas exhaust pipe (230) can be connected to the insulating space (130), and the other end of the insulating space gas exhaust pipe (230) can be connected to the vacuum pump (240).

[0050] The pressure sensor (310) may be placed within the inner wall portion (110) of the liquefied gas storage tank (100). Specifically, the pressure sensor (310) may be placed to communicate with the inner wall portion (110) of the liquefied gas storage tank (100). The pressure sensor (310) can measure the pressure of the inner wall portion (110) of the liquefied gas storage tank (100).

[0051] The concentration sensor (320) may be placed within the inner wall portion (110) of the liquefied gas storage tank (100). Specifically, the concentration sensor (320) may be placed so as to be in communication with the inner wall portion (110) of the liquefied gas storage tank (100). Additionally, a plurality of concentration sensors (320) may be placed vertically within the inner wall portion (110).

[0052]

[0053] Liquefied Gas Storage Tank Gas Treatment Method

[0054] Referring to FIG. 2, the present invention relates to a gas treatment method (S1) for a liquefied gas storage tank (100) according to one embodiment of the present invention, which may include: an inert gas injection step (S10) of injecting inert gas through a replacement gas supply pipe (210) provided within the liquefied gas storage tank (100); a pressure reduction step (S20) of discharging residual gas containing inert gas remaining within the liquefied gas storage tank (100) to the outside through a residual gas discharge pipe (220) provided within the liquefied gas storage tank (100); a replacement gas injection step (S30) of injecting replacement gas through a replacement gas supply pipe (210) provided within the liquefied gas storage tank (100) until a certain pressure is reached while the residual gas discharge pipe (220) is closed; and a final discharge step (S40) of opening the residual gas discharge pipe (220) to further discharge residual gas.

[0055] After the liquefied gas carrier or propulsion vessel is built in a dock, a sea trial is performed to check whether various facilities, such as the liquefied gas storage tank (100), are operating normally, and prior to that, a gas treatment method (S1) for the liquefied gas storage tank for the sea trial may be performed.

[0056] In the case of existing liquefied natural gas (LNG) storage tanks, moisture, carbon dioxide, and oxygen present inside the tank can be removed through the inerting and gasing-up stages.

[0057] The inerting step involves injecting inert gas to remove oxygen from the liquefied gas storage tank (100). The gasing step involves injecting liquefied gas to replace the inert gas with liquefied gas within the liquefied gas storage tank (100).

[0058] When applying a conventional gas treatment method for a liquefied gas storage tank (100), such as LNG, mixing occurs between a highly permeable gas, such as hydrogen, and an inert gas, thereby increasing the replacement time during the process of replacing the inert gas with the highly permeable gas. To solve this, the gas treatment method (S1) for a liquefied gas storage tank according to the present invention includes a pressure reduction step (S20) for discharging residual gas containing inert gas before the replacement gas injection step (S30), and a final discharge step (S40) for additionally discharging residual gas when a certain pressure is reached during replacement gas injection. Therefore, according to the present invention, mixing with residual gas during replacement gas injection can be prevented, thereby reducing the replacement time.

[0059] Referring to FIG. 3, an inert gas injection step (S10) is illustrated in which inert gas is injected through a replacement gas supply pipe (210) provided in a liquefied gas storage tank (100).

[0060] Before the inert gas injection step (S10), water vapor, oxygen, etc. may be present in the liquefied gas storage tank (100).

[0061] With the replacement gas control valve (211) and the residual gas control valve (221) open, inert gas can be injected into the liquefied gas storage tank (100) through the replacement gas supply pipe (210). Residual gas can be naturally discharged out of the liquefied gas storage tank (100) while the replacement gas is injected into the liquefied gas storage tank (100). Therefore, the pressure inside the liquefied gas storage tank (100) can be maintained at a constant level.

[0062] Referring to FIG. 4, a depressurization step (S20) for discharging residual gas containing inert gas provided in a liquefied gas storage tank (100) to the outside is illustrated.

[0063] Before the depressurization step (S20), inert gas, water vapor, oxygen, etc. may exist as residual gas in the liquefied gas storage tank (100).

[0064] With the residual gas control valve (221) open and the replacement gas control valve (211) closed, the vacuum pump (240) is operated so that the residual gas can be discharged to the outside of the liquefied gas storage tank (100) through the residual gas discharge pipe (220). At this time, the insulation space gas control valve (231) can also be opened to perform vacuuming within the insulation space (130).

[0065] In the pressure reduction step (S20), the pressure inside the liquefied gas storage tank (100) can be reduced to a preset pressure using a vacuum pump (240). The pressure sensor (310) measures the pressure of the inner wall (110) of the liquefied gas storage tank (100) to determine whether the pressure of the inner wall (110) of the liquefied gas storage tank (100) has been reduced to a preset pressure. More specifically, the pressure can be reduced until the pressure of the inner wall (110) of the liquefied gas storage tank (100) is, for example, 0.1 bar or 0.001 bar. However, 0.1 bar or 0.001 bar is exemplary and is not limited thereto. When the pressure of the inner wall (110) of the liquefied gas storage tank (100) is reduced to a preset pressure, the pressure reduction step (S20) is terminated.

[0066] FIG. 5 illustrates a replacement gas injection step (S30) in which liquefied gas is injected through a replacement gas supply pipe (210) provided within a liquefied gas storage tank (100).

[0067] With the replacement gas control valve (211) open and the residual gas control valve (221) closed, liquefied gas can be injected into the liquefied gas storage tank (100) through the replacement gas supply pipe (210).

[0068] In the replacement gas injection step (S30), the replacement gas control valve (211) of the inner wall (110) of the liquefied gas storage tank (100) can be opened gradually to control the flow rate of the replacement gas injected into the liquefied gas storage tank (100). The replacement gas injection step (S30) can be terminated when the pressure of the inner wall (110) of the liquefied gas storage tank (100) increases to a certain pressure, for example, atmospheric pressure. However, the fact that the certain pressure is up to atmospheric pressure is exemplary and is not limited thereto.

[0069] FIG. 6 illustrates a final discharge step (S40) in which replacement gas is injected through a replacement gas supply pipe provided in a liquefied gas storage tank (100), and at the same time, residual gas is additionally discharged through a residual gas discharge pipe (220).

[0070] With the replacement gas control valve (211) and the residual gas control valve (221) open, the replacement gas is injected through the replacement gas supply pipe (210), and at the same time, the remaining residual gas can be discharged outside the liquefied gas storage tank (100) through the residual gas discharge pipe (220).

[0071] FIG. 7 is a graph showing the pressure inside a liquefied gas storage tank (100) according to the change in time during the gas treatment process of a liquefied gas storage tank according to one embodiment of the present invention.

[0072] FIG. 8 is a graph showing the ratio of gas volume in a liquefied gas storage tank (100) according to the change in time during the gas treatment process of a liquefied gas storage tank according to one embodiment of the present invention.

[0073] The volume of the liquefied gas storage tank (100) is, for example, based on 1000L, and the state of the liquefied gas storage tank over time is shown.

[0074] Referring to FIG. 7, the pressure of the inner wall (110) of the liquefied gas storage tank (100) over time is shown as a graph.

[0075] The inert gas injection step (S10) may take about 20 minutes, and the pressure of the inner wall (110) of the liquefied gas storage tank (100) may be 1.0 bar.

[0076] The depressurization step (S20) may take about 30 minutes, and the pressure of the inner wall (110) of the liquefied gas storage tank (100) may be lowered to a preset pressure of 0.1 bar or 0.001 bar.

[0077] Between the depressurization step (S20) and the replacement gas injection step (S30), a stabilization step (S25) of a certain period of time may be provided. The stabilization step (S25) may take about 5 minutes, and the pressure of the inner wall (110) of the liquefied gas storage tank (100) may be maintained at a preset pressure of 0.1 bar or 0.001 bar.

[0078] During the stabilization stage (S25), flow may occur within the liquefied gas storage tank (100) while passing through the depressurization stage (S20). If the replacement gas injection stage (S30), in which replacement gas is injected immediately while flow is occurring within the liquefied gas storage tank (100), is performed, mixing may occur between the replacement gas and the residual gas. Therefore, the stabilization stage (S25) can suppress mixing between the replacement gas and the residual gas by stabilizing the flow within the liquefied gas storage tank (100).

[0079] The replacement gas injection step (S30) may take about 20 minutes, and the pressure of the inner wall (110) of the liquefied gas storage tank (100) may rise to 1.0 bar.

[0080] The final discharge step (S40) may take about 10 minutes, and the pressure of the inner wall (110) of the liquefied gas storage tank (100) may be maintained at 1.0 bar.

[0081] The time and pressure described in Fig. 7 are exemplary values ​​and are not limited thereto.

[0082] The end of the depressurization step (S20) and the replacement gas injection step (S30) can be determined based on the value measured by the pressure sensor (310) installed in the liquefied gas storage tank (100).

[0083] The pressure sensor (310) measures the inner wall portion (110) of the liquefied gas storage tank (100), and when the pressure of the inner wall portion (110) of the liquefied gas storage tank (100) reaches a preset value during the pressure reduction step (S20), the pressure reduction step (S20) may be terminated. For example, the preset pressure may be 0.1 bar or 0.001 bar.

[0084] Additionally, while the pressure sensor (310) measures the inner wall portion (110) of the liquefied gas storage tank (100), if the pressure of the inner wall portion (110) of the liquefied gas storage tank (100) reaches a preset value during the replacement gas injection step (S30), the replacement gas injection step (S30) may be terminated. For example, the preset pressure may be atmospheric pressure.

[0085] FIG. 8 is a graph showing the gas pressure ratio of the inner wall portion (110) of the liquefied gas storage tank (100) according to the change in time during the gas treatment process of the liquefied gas storage tank according to one embodiment of the present invention.

[0086] The volume ratio of residual gas in the depressurization step (S20) can be reduced as the depressurization progresses, because the residual gas is discharged along the residual gas discharge pipe (220).

[0087] The residual gas mass ratio of the replacement gas injection step (S30) can be maintained because the residual gas discharge pipe (220) is closed, and the liquefied gas volume ratio can increase from 0 because liquefied gas is injected through the replacement gas supply pipe (210).

[0088] The residual gas volume ratio of the final discharge stage (S40) can be reduced to 0 because the residual gas is discharged along the residual gas discharge pipe (220), and the liquefied gas volume ratio can be increased because the liquefied gas is continuously injected through the replacement gas supply pipe (210).

[0089] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by these embodiments. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

1. In a method for treating gas in a liquefied gas storage tank, An inert gas injection step of injecting inert gas through a replacement gas supply pipe provided within the above-mentioned liquefied gas storage tank; A depressurization step of discharging residual gas containing the inert gas remaining in the liquefied gas storage tank to the outside through a residual gas discharge pipe provided in the liquefied gas storage tank; A replacement gas injection step of injecting liquefied gas through the replacement gas supply pipe provided in the liquefied gas storage tank until a certain pressure is reached, while keeping the residual gas discharge pipe closed; and A gas treatment method for a liquefied gas storage tank comprising a final discharge step of opening the residual gas discharge pipe to additionally discharge residual gas.

2. In Claim 1, The above pressure reduction step is a method for treating liquefied gas storage tanks by reducing the internal pressure of the liquefied gas storage tank to a preset pressure using a vacuum pump.

3. In Claim 2, A method for treating gas in a liquefied gas storage tank, wherein the termination of the above-mentioned depressurization step and the above-mentioned replacement gas injection step is determined according to a value measured by a pressure sensor installed in the liquefied gas storage tank.

4. In Claim 1, A method for treating gas in a liquefied gas storage tank, wherein a stabilization phase of a certain period is provided between the above-mentioned pressure reduction step and the above-mentioned replacement gas injection step.

5. In a liquefied gas storage tank, An inner wall portion that accommodates liquefied gas inside; An outer wall portion disposed outside the inner wall portion above; An insulating space disposed between the inner wall and the outer wall; A replacement gas supply pipe communicating with the inner wall portion at the top of the liquefied gas storage tank; and A liquefied gas storage tank comprising a residual gas discharge pipe communicating with the inner wall portion at the bottom of the liquefied gas storage tank.

6. In Claim 5, A liquefied gas storage tank comprising an insulating space gas discharge pipe communicating with the insulating space and a vacuum pump connected to the residual gas discharge pipe.

7. In Claim 6, A liquefied gas storage tank comprising a plurality of replacement gas concentration sensors arranged vertically within the inner wall portion.

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