NO347928B1

NO347928B1 - A system for preventing pressure-driven liquid spillage

Info

Publication number: NO347928B1
Application number: NO20230400A
Authority: NO
Inventors: Stian Magnusson
Original assignee: Azane Fuel Solutions As
Priority date: 2023-04-12
Filing date: 2023-04-12
Publication date: 2024-05-13

Description

Technical Field

[0001] The present invention concerns the technical field of handling and storage of liquids. Specifically, the present invention concerns a system for preventing pressure-driven liquid spillage, for liquids such as liquefied gases.

Background

[0002] The storage of liquids in pressurized storage tanks is required across a large range of industries. One example arises in the storages of low-carbon emission fuels, such as ammonia, hydrogen, or natural gas. These fuels are usually in gaseous form at ambient temperatures and pressures. During handling and storage, however, these fuels are often kept at low temperatures, in liquefied form, thereby reducing storage volumes and increasing storage energy densities. This is especially advantageous when storage space is limited and/or expensive, such as on vessels or land-based facilities with a limited footprint.

[0003] Safety forms an important aspect of the handling and storage of certain liquids, such as liquefied fuels, due to the inherent risks that these liquids pose when spillage occurs.

Ammonia, for instance, has a significant toxicity to both humans and animals. Hydrogen, on the other hand, has a very high flammability, where ignition may occur in mixtures of hydrogen with air, for volumetric hydrogen concentration as low as 4%. Consequently, spillage of these liquids into the surrounding processing- and / or storage facility, or into the general environment, should be prevented.

[0004] A specific issue concerning the storage of these liquids arises when a storage tank is partially filled with a liquid and the remaining part of the tank is occupied by a pressurized gas. The gas may, for example, be a boil-off gas, originating from the liquid itself, or a gas originating from any other source . The tank is provided with a flow line, traversing the wall of the tank, and including a portion within the tank and a portion outside the tank. Should a failure, such as a rupture, occur in the flow line portion located outside the tank, the gas pressure in the tank may drive an uncontrolled spillage of the liquid through the ruptured flow line, and into the surrounding environment. This situation is described in more detail below. Given the abovementioned toxicity and / or flammability of certain liquids, such as liquefied gases, this pressure-driven spillage may have severe detrimental consequences to human health and to the environment, besides a clear negative economic impact due to liquid loss.

[0005] CN 114413164 A discloses a pressure-reducing leakproof liquid gas storage tank comprising a pressure-reducing valve for controlling the speed of inlet and outlet of liquid gas. The tank is connected below the valve, and one side of the valve is connected with a detector and display, for detecting the amount of inlet and outlet liquefied gas and the content of residual liquefied gas in the tank. The tank further includes a double-layer tank shell, a netshaped semicircular groove formed in the inner wall of the outer-layer tank shell, a piston plate in the inner-layer tank shell, and a pressure reducing mechanism and double-channel pipeline.

[0006] In order to avoid such negative consequences, there is a need to provide a system for preventing pressure-driven liquid spillage in case of an unintended flow line failure. The system should preferably be simple and robust, with passive components, thereby reducing the chance for system failure. Furthermore, the system should preferably be economical and easy to implement, or to retrofit into an existing facility.

Summary of the invention

[0007] The present invention concerns a system for preventing pressure-driven liquid spillage, the system includes a tank for storing a liquid and a flow line for feeding liquid to or extracting liquid from, the tank. The flow line includes an outside portion, extending outside the tank, and an inside portion, extending inside the tank. The system further includes a side branch, arranged inside the tank, the side branch having one open end and having one end coupled to the inside portion. The system further includes a non-return valve, arranged in the side branch and configured to allow a one-way flow through the side branch, from the open end towards the inside portion. The present invention also concerns the use of such a system for the storage of liquefied gases.

Figures

[0008] Fig.1 schematically shows a prior art situation where failure of a flow line on the outside of a tank results in a pressure-driven liquid spillage from the tank.

[0009] Fig.2A schematically shows the system according to the present invention.

[0010] Fig.2B schematically shows a detail of the system according to the present invention.

[0011] Fig.3A schematically shows liquid levels in the system according to the present invention prior to flow line failure.

[0012] Fig.3B schematically shows liquid levels in the system according to the present invention after flow line failure.

Detailed description

[0013] Hereinafter, exemplary embodiments of the present invention are described in detail with reference to the accompanying figures. Like components are denoted by like reference numerals throughout the description and figures.

[0014] Firstly, a prior-art situation is schematically shown, with reference to fig.1. A storage tank 1 is partially filled with a liquid 2, such as a liquefied gas. For safety reasons, in order to avoid over-filling of the tank, the tank may normally be filled with liquid to a maximum of around 90%, optionally 95%, further optionally 98%, of its volume. Preferably, the tank has a lower fill percentage below this maximum, for instance to allow for a certain volume of boil-of gas from a liquefied fuel. The remaining, upper part of the tank is occupied by a pressurized gas 3. The gas may be a boil-off gas, originating from the liquid itself, or a gas originating from any other source. At least one flow line 4 is provided, extending from the outside of the tank to within the tank. The flow line 4 preferably extends into the bottom half of the tank. The flow line 4 may be provided with a closure valve (not shown) on the outside of the tank, for opening or closing fluid access to the tank via the flow line. The flow line 4 further includes an aperture at the end of the flow line that extends into the tank.

[0015] As shown in fig.1, in case of a failure 4’ of the flow line 4 at its portion extending outside the tank 1, for instance due to an accidental rupture or breakage, a spillage of liquid into the surrounding environment may occur. The pressurized gas 3 within the tank 1 may drive the liquid 2 through the flow line 4, where the liquid exits through the rupture site, as indicated by the striped arrows in fig.1. This pressure-driven liquid spillage occurs when the gas pressure in the tank is larger than the hydrostatic head of the liquid in the flow line between the liquid surface and the rupture location. This is also referred to as pressure-driven pumping of the liquid. For liquefied gases and / or other hazardous liquids, which may, for instance, be cold, toxic, or highly flammable, such a pressure-driven liquid spillage forms a considerable risk to the health and safety of operators or other personnel in the vicinity of the tank. Additionally, the pressure-driven liquid spillage may lead to possible environmental damage and / or economic loss.

[0016] A system for preventing pressure-driven liquid spillage according to the invention is schematically shown in fig.2A. The system includes a tank 1, for the storage of a liquid 2. The tank 1 may, for instance, be an insulated storage tank for the storage of liquefied fuels at subzero temperatures. The tank 1 is preferably a closed tank. The tank 1 may be placed on a vessel, on a floating installation, on land, or on a vehicle (not shown). The tank 1 may include various components (not shown here), required for normal operation and safety, such as a safety pressure-release valve and / or a vent line. The tank has an internal height H, schematically indicated by the dotted arrow in fig.1.

[0017] The system further includes at least one flow line 4. As schematically shown by the dotted arrow in fig.2B, the flow line has a diameter Df. The flow line 4 extends from the outside of the tank to the inside of the tank. Preferably the flow line 4 extends vertically inside the tank, from the top towards the bottom of the tank (top to bottom in fig.2A). The flow line 4 therefore includes an outside portion 4a, located outside the tank, and an inside portion 4b, located inside the tank. The connected end of the inside portion 4b is connected to the outside portion 4a. The free end of the inside portion 4b extends towards the bottom of the tank 1. The flow line 4 may be a bottom feed line, for feeding liquid to the bottom part of the tank.

Alternatively, the flow line 4 may be a pump line, for pumping liquid from the tank. The pump line may include a pump, located inside the tank (not shown), or may be connected to a pump located outside the tank (not shown).

[0018] The inside portion 4b has a length Li, as indicated by the dash-dotted arrow in fig.2A. The length Li of the inside portion 4b may be less or equal to least half the internal tank height Li ≤ 0.5 H, preferably less or equal to three-quarters of the internal tank height, Li ≤ 0.75 H, more preferably less or equal to 95% of the internal tank height, Li ≤ 0.95 H. Height H is taken to be the internal height of the tank at the location of the flow line, including any optional tank sump or tank dome. The flow line 4 comprises at least one aperture for the uptake of liquid from the tank, or for the feeding of liquid to the tank. The aperture is located at the free end of the inside portion 4b. The aperture may be formed by an open end of the inside portion 4b. Alternatively, the aperture may be formed in the side wall of the free end of the inside portion 4b.

[0019] The system further includes at least one side branch 5, arranged inside the tank. The side branch 5 includes a coupled end, which is coupled to the inside portion 4b of the flow line 4, see fig.2A and 2B. The side branch 5 further includes at least one free end, extending outward from the flow line 4, into the tank 1. The free end of the side branch 5 includes an aperture for the flow of gas into the side branch. The side branch 5 preferably extends perpendicularly to the flow line 4. Alternatively, the side branch 5 may extend at an angle of less than 90° from the flow line 4. The side branch 5 may be branched at the free end, comprising two or more branches, each including an aperture.

[0020] The distance Ls between the coupling of the side branch 5 to inside portion 4b, and the connection of the inside portion 4a to the outside portion 4b (see fig.2B) may be less than one quarter of the length Li of the inside portion 4b, Ls ≤ 0.25 Li, preferably less than one tenth of the length Li of the inside portion 4b, Ls ≤ 0.1 Li , more preferably less than one twentieth of the length Li of the inside portion 4b, Ls ≤ 0.05 Li . Thereby, it is advantageously assured that the side branch is located in the part of the tank 1 occupied by the pressurized gas. Further advantageously, the side branch is thereby connected to a part of the inside portion with inherent structural stiffness.

[0021] The cross-sectional area As of the side branch 5 may be at least equal to the crosssectional flow area Af of the flow line, As ≥ Af. The cross-sectional flow area Af equals the unrestricted portion of the cross-section of the flow line, through which the liquid can flow. Where the flow line is restricted, for instance by a filter, an impeller, a piston, or another component, Af therefore equals the total cross sectional area of the flow line minus the area of the restriction. Preferably, the cross-sectional area As of the side branch is at least 1.5 times the cross-sectional flow area Af of the flow line, As ≥ 1.5 Af. More preferably, the crosssectional area As of the side branch is at least twice the cross-sectional flow area Af of the flow line, As ≥ 2 Af. Advantageously, it is thereby assured that pressurized gas may flow from the tank into the side branch at sufficiently large volume rates to effectively avoid pressure-driven pumping of the liquid through an unintentional failure site during a failure of the outside portion, as detailed hereinbelow.

Alternatively, the cross-sectional area As of the side branch may be smaller than the crosssectional flow area Af of the flow line, As < Af.

[0022] With further reference to fig.2, the system further includes at least one non-return valve 6. The non-return valve 6 is arranged in the side branch 5. The non-return valve 6 may be a ball check valve, a piston valve, a disc check valve, a nozzle check valve, a swing check valve, or any other suitable valve or device allowing flow in one direction only. The non-return valve 6 is configured to allow a one-way flow through the side branch 5, from the open end of the side branch 5 towards the flow line 4. Consequently, a flow through the side branch 5 from the flow line 4 into the tank 1 is blocked by the non-return valve 6. The non-return valve 6 is further configured to open when the gas pressure at the open end of the side branch is higher than the gas pressure at the coupled end of the side branch 5. For a side branch 5 with a branched configuration, one non-return valve 6 is provided in each branch.

[0023] The invention further concerns a facility comprising a system according to the invention, wherein the facility is a vessel-based facility, a land-based facility, a vehicle-based facility, or a floating structure-based facility

[0024] Next, the operation of the system according to the invention in case of a flow line failure are described, with reference to fig.3A - B. In fig.3A, which shows liquid levels under a typical normal operational scenario and before any failure of the flow line 4, the tank 1 is partially filled with a liquid 2, such as a liquefied gas. The liquefied gas may, for instance, include liquefied ammonia, liquefied hydrogen, a liquefied natural gas, or a liquefied petroleum gas. However, other liquids may be used, such as liquefied CO2, liquefied helium, or liquefied oxygen. The remaining part of the tank 1 is filled with a pressurized gas 3. The pressurized gas 3 is preferably in a gaseous state. The gas pressure in the tank is larger than atmospheric pressure. The gas pressure in the tank may be as high as 5 bar or more, or even 10 bar or more. Prior to any flow line failure, the pressure in the flow line is equalized with the pressure in the tank.

[0025] As indicated in fig.3B, an unintentional failure 4’ of the outside portion 4a of the flow line 4 may occur, such as a rupture and / or breakage. Thereby, a sudden pressure drop occurs within the flow line. For a prior art system, as previously shown in fig.1, the flow line failure leads to a pressure-driven rising of the liquid into the flow line. The liquid may thereby spill through the failure site, into the outside environment. In the system according to the invention, shown in fig.3B, the pressure drop causes a pressure difference across the nonreturn valve 6 in the side branch 5. Consequently, the non-return valve 6 opens, allowing pressurized gas 3 to flow through the side branch 5 and into the flow line 4, as indicated by the striped arrows in fig.3B. Thereby, pressurized gas is vented from the tank through the rupture site. Consequently, even though the liquid may rise to a limited extent into the flow line, the liquid will not rise to the level of the side branch and gas-driven pumping with the associated liquid spillage is prevented. In order to assure that a sufficient volume flow of pressurized gas is drawn into the side branch 5, so as to prevent pressure-driven pumping, the side branch should have a sufficiently large cross-sectional area As, as compared to the cross-sectional flow area Af of the flow line and / or compared to the cross-sectional area, or outflow area, of the unintentional failure 4’.

[0026] In another embodiment, the system includes a tank and a flow line, as described hereinabove. The tank is provided with at least one regular vent line, for venting of gas to the outside environment. The vent line includes a valve, configured to open when overpressure is detected within the tank. The system further includes at least one pressure sensor, mounted in the flow line, and a control unit. The control unit is configured to open the valve in the vent line when a sudden pressure loss is detected in the flow line. In operation, in the event of a failure of the first part of the flow line, as described hereinabove, the pressure sensor will register a sudden pressure loss. The control unit may then open the valve in the vent line, to exhaust pressurized gas from the tank. Thereby gas pressure in the tank is reduced and gas-pumping of liquid, leading to pressure-driven liquid spillage, may be reduced or prevented.

List of references

[0027]

1 tank

2 liquid

3 pressurized gas

4 flow line

4’ failure site

4a outside portion

4b inside portion

5 side branch

6 non-return valve

Claims

1. A system for preventing pressure-driven liquid spillage, the system comprising:

− a tank (1) for storing a liquid (2);

− a flow line (4) for feeding liquid to or extracting liquid from, the tank (1), the flow line (4) having an outside portion (4a) extending outside the tank (1), and an inside portion (4b) extending inside the tank (1);

− a side branch (5), arranged inside the tank (1), the side branch (5) having one end coupled to the inside portion (4b) and one open end; and

− a non-return valve (6), arranged in the side branch (5) and configured to allow a one-way flow through the side branch (5), from the open end towards the inside portion (4b).

2. The system of claim 1 or 2, wherein the side branch (5) is coupled to the flow line (4) at the upper half, preferably the upper third, more preferably the upper quarter, most preferably the upper tenth, of the inside portion (4b).

3. The system of any preceding claim, wherein the non-return valve (6) is a ball check valve, a piston valve, a disc check valve, a nozzle check valve, or a swing check valve.

4. The system of any preceding claim, wherein the flow line (4) is a bottom feed line, for feeding liquid (2) to the bottom part of the tank (1), or a pump line, for pumping liquid (2) from the tank (1).

5. The system of any preceding claim, wherein Ls and Li are related as Ls ≤ 0.25 Li , preferably Ls ≤ 0.1 Li , more preferably Ls ≤ 0.05 Li ,

and wherein Ls is the distance between the coupling of the side branch (5) to inside portion (4b) and the connection of the inside portion (4a) to the outside portion (4b), and wherein Li is the length of the inside portion (4b).

6. The system of any preceding claim, wherein the cross-sectional area of the side branch As is equal to or larger than the cross-sectional flow area of the flow line Af , As ≥ Af, preferably As ≥ 1.5 Af, more preferably As ≥ 2 Af, where the cross-sectional flow area Af equals the unrestricted portion of the cross-section of the flow line.

7. The system of any preceding claim, wherein the side branch (5) is branched at the open end thereof and wherein a non-return valve (6) is arranged in each branch.

8. The system of any preceding claim, wherein the tank (1) is an insulated tank, configured to store a liquefied gas, such as liquefied ammonia, liquefied hydrogen, liquefied natural gas, or liquefied petroleum gas.

9. A facility comprising a system according to any one of claims 1 – 8, wherein the facility is a vessel-based facility, a land-based facility, a vehicle-based facility, or a floating structure-based facility.

10. Use of a system according to claim 1 – 8, for the storage of a liquefied gas, wherein the liquefied gas may comprise liquefied hydrogen, liquefied ammonia, liquefied natural gas, or liquefied petroleum gas.