A liquid tank safety valve system with emergency isolation function and its use method

Abstract

The present invention relates to a liquid tank safety valve system with an emergency isolation function and a method for using the same. The system includes a storage tank, an air duct, a safety valve, an emergency isolation device, an exhaust pipe, a vent mast, and an inert gas source. The top of the storage tank is a gaseous space formed by the accumulation of evaporated gas from the liquefied gas. The gaseous space is connected to the inlet of the safety valve via the air duct. The outlet of the safety valve is connected to the exhaust pipe and the vent mast in sequence. The vent mast is mounted on the deck of a ship. The emergency isolation device is mounted on the air duct, and the emergency isolation device is connected to the inert gas source. The liquid tank safety valve system with an emergency isolation function and a method for using the same have a simple system configuration. When the safety valve fails, the emergency isolation device is used to spray high-speed, inert gas into the air duct inlet of the safety valve, forming an inert gas curtain inside the air duct, thereby isolating the evaporated gas in the storage tank and preventing the evaporated gas from overflowing. The system is highly economical and reliable.

Description

Technical Field

[0001] The present invention relates to the technical field of ship engineering equipment, and in particular to a liquid tank safety valve system with an emergency isolation function and a use method thereof. Background Art

[0002] For liquefied gas tankers, when the pressure relief valve installed on the liquid tank fails, there should be an emergency isolation safety device. The function of the emergency isolation safety device is to urgently isolate the evaporated gas in the tank from the failed safety valve to prevent the evaporated gas in the tank from overflowing when the failed safety valve is disassembled and repaired.

[0003] There are two main emergency isolation measures currently in widespread use:

[0004] Measure 1: Install a manual valve on the safety valve inlet pipeline. In the event of a safety valve failure, this manual valve closes, severing the connection between the safety valve and the storage tank and providing emergency isolation. Because liquefied gas typically has a low temperature, this manual valve is a relatively expensive cryogenic valve, resulting in a high initial investment cost. Furthermore, the valve's actuator and sealing components, exposed to the harsh offshore environment for extended periods, pose a risk of seal failure, making it impossible to isolate the safety valve in the closed state. Furthermore, the valve could be misoperated, posing a significant risk to the tank's safety.

[0005] Measure 2: Install a branch pipe on the safety valve inlet pipeline, equipped with a full-pass ball valve. The ship is equipped with an inflatable airbag. In the event of a safety valve failure and isolation, the full-pass ball valve on the branch pipe is opened, and the airbag is inserted through the branch pipe into the safety valve inlet pipeline. The airbag is then inflated, and the expansion of the airbag blocks the safety valve inlet pipeline, thus achieving emergency isolation. During the airbag installation process, some evaporation of the gas in the cabin will inevitably occur. Furthermore, during operation, the airbag needs to be replaced regularly, which increases operating costs.

[0006] The prior art (CN111734860A) discloses a pilot-operated safety valve with an isolation air chamber, comprising a main valve, a pilot valve, a main valve inlet and a main valve outlet on the main valve, a main valve chamber inside the main valve, the pilot valve comprising a pilot valve body and a pilot valve cover, a medium chamber and an isolation air chamber inside the pilot valve body, a sliding column installed between the medium chamber and the isolation air chamber, a piston connected to the upper end of the sliding column, a spring assembly connected between the piston and the pilot valve cover, the piston adapted to be installed in the medium chamber, a pressure inlet pipe connected between the medium chamber and the main valve inlet, an air inlet nozzle connected to the pilot valve body, a follow-up valve assembly driven by the sliding column installed in the isolation air chamber, the follow-up valve assembly divides the isolation air chamber into an air intake chamber and an exhaust chamber, a pressure-releasing pipe is connected between the air intake chamber and the main valve chamber, and a pressure-exhaust pipe is connected between the exhaust chamber and the main valve outlet. This solution aims to solve the problem that the pilot-operated safety valve is prone to corrosion and blockage of the pilot valve pipeline during use, affecting the sealing of the pilot valve and main valve chambers and shortening the service life of the safety valve. However, it does not solve the problems of valve misoperation and overflow of evaporative gas. Summary of the Invention

[0007] To solve the technical problems existing in the prior art, the present invention provides a liquid tank safety valve system with an emergency isolation function and a method for using the same. When a safety valve fails, the emergency isolation device is used to spray high-speed, inert gas into the safety valve inlet air duct, forming an inert gas curtain inside the air duct, thereby isolating the evaporated gas in the storage tank and preventing the evaporated gas from overflowing.

[0008] To achieve the above object, the technical solutions of the present invention are as follows:

[0009] A liquid tank safety valve system with an emergency isolation function comprises a storage tank, an air duct, a safety valve, an emergency isolation device, an exhaust pipe, a vent mast, and an inert gas source. The top of the storage tank is a gas phase space formed by the accumulation of evaporated gas from the liquefied gas. The gas phase space is connected to the inlet of the safety valve through the air duct. The outlet of the safety valve is connected to the exhaust pipe and the vent mast in sequence. The vent mast is installed on the deck of the ship. The emergency isolation device is installed on the air duct, and the emergency isolation device is connected to the inert gas source.

[0010] As a preferred technical solution, the storage tank is provided with heat insulation facilities.

[0011] As an optimal technical solution, the air guide pipe is provided with a first branch pipe, a second branch pipe and a pressure gauge, the first branch pipe is installed with a first branch pipe valve, the second branch pipe is installed with a second branch pipe valve, and the pressure gauge is a pressure vacuum type.

[0012] As a preferred technical solution, one end of the first branch pipe is connected to the emergency isolation device, and the other end of the first branch pipe is connected to the inert gas source through the first branch pipe valve, and the inert gas provided by the inert gas source is nitrogen.

[0013] As a preferred technical solution, the second branch pipe is arranged on the air duct between the first branch pipe and the safety valve. The liquid tank safety valve system also includes a gas analyzer. The second branch pipe is connected to the gas analyzer through a second branch pipe valve.

[0014] As a preferred technical solution, the emergency isolation device includes a collecting pipe, a manifold and a gas nozzle. The collecting pipe is arranged outside the gas duct and is connected to the inert gas source through a first branch pipe. There are at least two manifolds, one end of the manifold is connected to the collecting pipe, and the other end of the manifold is fixedly connected to the gas nozzle. The gas nozzle is inserted into the gas duct and evenly distributed on the inner surface of the gas duct. The connection between the gas nozzle and the gas duct is fixed and sealed by welding.

[0015] As an optimal technical solution, the safety valve automatically opens when the pressure in the gas phase space of the storage tank reaches a set value, thereby discharging the evaporated gas accumulated in the gas phase space.

[0016] As a preferred technical solution, when a safety valve fails, a method for using a liquid tank safety valve system with an emergency isolation function includes the following steps:

[0017] The first step is to connect the inert gas source to the first branch valve. After confirming that the gas pressure provided by the inert gas source meets the requirements, open the first branch valve and connect to the emergency isolation device. The inert gas passes through the first branch pipe, the header pipe, the manifold, and is injected into the gas guide pipe through the gas nozzle.

[0018] The second step is to continuously inject inert gas through the emergency isolation device, connect the gas analyzer to the second branch valve, open the second branch valve, and sample and analyze the gas in the air pipe. As the inert gas is continuously injected, the content of evaporation gas detected by the gas analyzer gradually decreases until the content is less than the set value, and then close the second branch valve. At this time, the air pipe from the emergency isolation device to the safety valve inlet is in an inert state;

[0019] The third step is to remove and maintain the faulty safety valve after the inerting of the air duct is completed. During the removal of the safety valve, when the pressure gauge reading drops, the tightness of the connection between the safety valve and the air duct is damaged. At this time, the inert gas pressure is increased to about 6 bar. As the inert gas pressure increases, the inert gas flow rate entering the air duct also increases accordingly. The high-speed inert gas forms an air curtain in the circular area of ​​the gas nozzle distribution in the air duct, isolating the evaporated gas in the tank. After the safety valve is removed, the air duct is immediately sealed with a blind flange. During the installation of the blind flange, when the pressure gauge reading rises, the tightness of the connection between the blind flange and the air duct is restored. At this time, the first branch valve is closed to gradually cut off the supply of the inert gas source.

[0020] The fourth step is to open the first branch valve, inject inert gas into the air duct through the emergency isolation device, open the second branch valve, and use a gas analyzer to monitor the changes in the evaporative gas content in the air duct until the air duct is inerted. Then remove the blind flange and increase the inert gas pressure to about 6 bar according to the changes in the pressure gauge reading to form a gas curtain, isolate the evaporative gas in the storage tank, reinstall the safety valve, and gradually close the first branch valve according to the changes in the pressure gauge reading.

[0021] As a preferred technical solution, in step 1 and step 4, when the first branch valve is opened, the inert gas pressure is higher than the real-time pressure in the storage tank and lower than the design pressure of the storage tank.

[0022] As a preferred technical solution, in the second step, the set value is that the volume content of the evaporation gas in the sampled gas is less than 2%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The liquid tank safety valve system with emergency isolation function of the present invention utilizes an inert gas system (such as a nitrogen system) commonly equipped on liquefied gas ships or liquefied gas fuel ships, which reduces the initial investment of the entire system, does not require additional operating expenses, and has good economic efficiency;

[0025] (2) The emergency isolation device used in the liquid tank safety valve system with emergency isolation function of the present invention has a simple design structure, is less affected by environmental factors during operation, has good stability, has no moving parts, has low maintenance frequency, and has high working reliability;

[0026] (3) In the method for using a liquid tank safety valve system with an emergency isolation function of the present invention, an inert gas is used as the isolation medium. Even if the evaporated gas in the storage tank overflows, the ratio of the overflowed mixed gas (evaporated gas and inert gas) is always within a safe range under the dilution effect of the inert gas, and there is no risk of explosion, etc., which has higher safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the installation and application of a liquid tank safety valve system with an emergency isolation function on a ship according to the present invention;

[0028] Figure 2 This is a schematic diagram of the working state of a liquid tank safety valve system with an emergency isolation function according to the present invention;

[0029] Figure 3 It is a structural schematic diagram of an emergency isolation device in a liquid tank safety valve system with an emergency isolation function according to the present invention;

[0030] Figure 4 This is a schematic structural diagram of the emergency isolation device of Example 2.

[0031] In the figures, the reference numerals are described as follows:

[0032] 1. Storage tank; 2. Gas duct; 3. Emergency isolation device; 31. Manifold; 32. Manifold; 33. Gas nozzle; 4. Safety valve; 5. Exhaust pipe; 6. Vent mast; 7. First branch valve; 8. Second branch valve; 9. Inert gas source; 10. Gas analyzer; 11. First branch pipe; 12. Second branch pipe; 13. Pressure gauge; 14. Blind flange; 20. Vessel. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below in conjunction with specific embodiments:

[0034] Example 1, as Figure 1 As shown, a liquid tank safety valve 4 system with an emergency isolation function includes a storage tank 1, an air duct 2, a safety valve 4, an emergency isolation device 3, an exhaust pipe 5, a ventilation mast 6, and an inert gas source 9. The top of the storage tank 1 is a gas phase space formed by the accumulation of evaporated gas of the liquefied gas. The gas phase space is connected to the inlet of the safety valve 4 through the air duct 2. The outlet of the safety valve 4 is connected to the exhaust pipe 5 and the ventilation mast 6 in sequence. The ventilation mast 6 is installed on the deck of the ship, the emergency isolation device 3 is installed on the air duct 2, and the emergency isolation device 3 is connected to the inert gas source 9.

[0035] The storage tank 1 is used to store liquefied gas as cargo or fuel and can be any of the type A, type B, type C and membrane containment systems defined by the IMO (International Maritime Organization). The storage tank 1 is provided with insulation facilities and is arranged inside the ship structure or on the deck.

[0036] The air guide pipe 2 is provided with a first branch pipe 11, a second branch pipe 12 and a pressure gauge 13. The first branch pipe 11 is installed with a first branch pipe 11 valve 7, and the second branch pipe 12 is installed with a second branch pipe 12 valve 8. The branch pipe valve can be a stop valve or a ball valve, which is connected to the branch pipe by welding or flange. The pressure gauge 13 is a pressure vacuum type, and the installation method is fixed installation or quick installation.

[0037] One end of the first branch pipe 11 is connected to the emergency isolation device 3, and the other end of the first branch pipe 11 is connected to the inert gas source 9 through the first branch pipe 11 valve 7. The inert gas source 9 is an inert gas provided by the ship's inert gas system or a mobile gas cylinder. The boiling point of the inert gas should be lower than that of the liquefied gas stored in the storage tank 1. Considering economy and applicability, nitrogen is the best choice.

[0038] Second branch pipe 12 is installed on gas conduit 2 between first branch pipe 11 and safety valve 4, as close as possible to the inlet of safety valve 4. The liquid tank safety valve 4 system also includes a gas analyzer 10. Second branch pipe 12 is connected to gas analyzer 10 through second branch pipe 12 valve 8. Gas analyzer 10 is used to measure the volume content of evaporated gas. It can be suction-type, fixed, or portable, and its operating principle can be infrared, thermal conductivity, electrochemical, or catalytic.

[0039] like Figure 3 As shown, the emergency isolation device 3 includes a header 31, a manifold 32 and a gas nozzle 33. The header 31 is annular or polygonal and is arranged outside the gas duct 2. The header 31 is connected to the inert gas source 9 through the first branch pipe 11. There are at least two manifolds 32. One end of the manifold 32 is connected to the header 31, and the other end of the manifold 32 is fixedly connected to the gas nozzle 33 by threading or welding. The gas nozzle 33 is inserted into the gas duct 2 and is evenly distributed on the inner surface of the gas duct 2. The connection between the gas nozzle 33 and the gas duct 2 is fixed and sealed by welding.

[0040] like Figure 4 As shown, embodiment 2 provides another structure of the emergency isolation device 3, in which the manifold 31 is installed inside the gas duct 2, the manifold 32 is shorter, or even the manifold 32 is eliminated, and the gas nozzles 33 can be directly installed on the manifold 31 in a radial arrangement, and the number of the gas nozzles 33 is at least two.

[0041] In Example 1, one or more safety valves 4 can be provided, and the type can be pilot type, spring type or gravity type. The safety valve 4 automatically opens when the pressure in the gas phase space of the storage tank 1 reaches a set value, and discharges the evaporated gas accumulated in the gas phase space, preventing the storage tank 1 from continuously increasing in pressure, thereby ensuring the safety of the storage tank 1.

[0042] In Example 1, the vent mast 6 is connected to the outlet of the safety valve 4 through the exhaust pipe 5, so that the gas discharged from the safety valve 4 can be guided vertically upward for safe release.

[0043] When the safety valve 4 fails, a method for using the liquid tank safety valve 4 system with emergency isolation function includes the following steps:

[0044] The first step, such as Figure 2 As shown, the inert gas source 9 is connected to the valve 7 of the first branch pipe 11. After confirming that the gas pressure provided by the inert gas source 9 meets the requirements, that is, the inert gas pressure is higher than the real-time pressure in the storage tank 1 and lower than the design pressure of the storage tank 1, the valve 7 of the first branch pipe 11 is slowly opened to connect to the emergency isolation device 3. The inert gas passes through the first branch pipe 11, the header 31, the manifold 32 in sequence, and is injected into the gas guide pipe 2 through the gas nozzle 33.

[0045] The second step is to continuously inject inert gas through the emergency isolation device 3, connect the gas analyzer 10 to the valve 8 of the second branch pipe 12, slowly open the valve 8 of the second branch pipe 12, and sample and analyze the gas in the air duct 2. As the inert gas is continuously injected, the content of evaporation gas detected by the gas analyzer 10 gradually decreases until the content is less than the set value. The valve 8 of the second branch pipe 12 is closed. The set value is that the volume content of evaporation gas in the sampled gas is less than 2%. At this time, the air duct 2 from the emergency isolation device 3 to the inlet of the safety valve 4 is in an inert state;

[0046] In the third step, after the inerting of the air duct 2 is completed, the faulty safety valve 4 is removed and maintained. During the removal of the safety valve 4, when the pressure gauge 13 reading drops, it indicates that the tightness of the connection between the safety valve 4 and the air duct 2 is damaged. At this time, the inert gas pressure is increased to about 6 bar (the pressure is adjusted according to the diameter of the air duct 2). As the inert gas pressure increases, the flow rate of the inert gas entering the air duct 2 also increases accordingly. The high-speed inert gas forms a circular area in the air duct 2 where the gas nozzles 33 are distributed. Form an air curtain to isolate the evaporating gas in the storage tank 1. After the safety valve 4 is removed, immediately use the blind flange 14 to close the air duct 2. During the installation of the blind flange 14, when the reading of the pressure gauge 13 rises, it indicates that the tightness of the connection between the blind flange 14 and the air duct 2 has been restored. At this time, close the valve 7 of the first branch pipe 11 and gradually cut off the gas supply of the inert gas source 9. The closing speed of the valve 7 of the first branch pipe 11 should ensure that the reading of the pressure gauge 13 does not rise significantly during the installation of the blind flange 14, and the reading cannot exceed the design pressure of the storage tank 1;

[0047] In the fourth step, the installation process of the safety valve 4 is similar to the operations in the first to third steps. Specifically, under the premise that the pressure of the inert gas provided by the inert gas source 9 is slightly higher than the real-time pressure in the storage tank 1 and not higher than the design pressure of the storage tank 1, the valve 7 of the first branch pipe 11 is opened, and the inert gas is injected into the air duct 2 through the emergency isolation device 3. The valve 8 of the second branch pipe 12 is opened, and the changes in the evaporation gas content in the air duct 2 are monitored by the gas analyzer 10 until the air duct 2 is inerted. Then, the blind flange 14 is removed, and the inert gas pressure is increased to about 6 bar according to the changes in the pressure gauge 13 reading to form a gas curtain to isolate the evaporation gas in the storage tank 1, and the safety valve 4 is installed. According to the changes in the pressure gauge 13 reading, the valve 7 of the first branch pipe 11 is gradually closed to ensure that the pressure in the air duct 2 does not fluctuate greatly during the installation process.

[0048] This embodiment is only a further explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for using a liquid tank safety valve system with an emergency isolation function, characterized in that: The method for using a liquid tank safety valve system also relates to a liquid tank safety valve system with an emergency isolation function, the system comprising a storage tank, an air duct, a safety valve, an emergency isolation device, an exhaust pipe, a vent mast, and an inert gas source. The top of the storage tank is a gas phase space formed by the accumulation of evaporated gas of the liquefied gas. The gas phase space is connected to the inlet of the safety valve through the air duct. The outlet of the safety valve is connected to the exhaust pipe and the vent mast in sequence. The vent mast is installed on the deck of a ship. The emergency isolation device is installed on the air duct. The emergency isolation device is connected to the inert gas source. When a safety valve fails, the method of using the system includes the following steps: The first step is to connect the inert gas source to the first branch valve. After confirming that the gas pressure provided by the inert gas source meets the requirements, open the first branch valve and connect to the emergency isolation device. The inert gas passes through the first branch pipe, the header pipe, the manifold, and is injected into the gas guide pipe through the gas nozzle. The second step is to continuously inject inert gas through the emergency isolation device, connect the gas analyzer to the second branch valve, open the second branch valve, and sample and analyze the gas in the air pipe. As the inert gas is continuously injected, the content of evaporation gas detected by the gas analyzer gradually decreases until the content is less than the set value, and then close the second branch valve. At this time, the air pipe from the emergency isolation device to the safety valve inlet is in an inert state; The third step is to remove and maintain the faulty safety valve after the inerting of the air duct is completed. During the removal of the safety valve, when the pressure gauge reading drops, the tightness of the connection between the safety valve and the air duct is damaged. At this time, the inert gas pressure is increased to about 6 bar. As the inert gas pressure increases, the inert gas flow rate entering the air duct also increases accordingly. The high-speed inert gas forms an air curtain in the circular area of ​​the gas nozzle distribution in the air duct, isolating the evaporated gas in the tank. After the safety valve is removed, the air duct is immediately sealed with a blind flange. During the installation of the blind flange, when the pressure gauge reading rises, the tightness of the connection between the blind flange and the air duct is restored. At this time, the first branch valve is closed to gradually cut off the supply of the inert gas source. The fourth step is to open the first branch valve, inject inert gas into the air duct through the emergency isolation device, open the second branch valve, and use a gas analyzer to monitor the changes in the evaporative gas content in the air duct until the air duct is inerted. Then remove the blind flange and increase the inert gas pressure to about 6 bar according to the changes in the pressure gauge reading to form a gas curtain, isolate the evaporative gas in the storage tank, reinstall the safety valve, and gradually close the first branch valve according to the changes in the pressure gauge reading.

2. The method for using a liquid tank safety valve system with emergency isolation function according to claim 1, characterized in that: In the first and fourth steps, when the first branch valve is opened, the inert gas pressure is higher than the real-time pressure in the storage tank and lower than the design pressure of the storage tank.

3. The method for using a liquid tank safety valve system with emergency isolation function according to claim 1, characterized in that: In the second step, the set value is that the volume content of the evaporation gas in the sampled gas is less than 2%.

4. The method for using a liquid tank safety valve system with emergency isolation function according to claim 1, characterized in that: The storage tank is provided with heat insulation facilities.

5. The method for using a liquid tank safety valve system with emergency isolation function according to claim 1, characterized in that: The air guide pipe is provided with a first branch pipe, a second branch pipe and a pressure gauge. The first branch pipe is installed with a first branch pipe valve, the second branch pipe is installed with a second branch pipe valve, and the pressure gauge is a pressure vacuum type.

6. The method for using a liquid tank safety valve system with emergency isolation function according to claim 5, characterized in that: One end of the first branch pipe is connected to the emergency isolation device, and the other end of the first branch pipe is connected to an inert gas source through a first branch pipe valve. The inert gas provided by the inert gas source is nitrogen.

7. The method for using a liquid tank safety valve system with emergency isolation function according to claim 5, characterized in that: The second branch pipe is arranged on the air guide pipe between the first branch pipe and the safety valve. The liquid tank safety valve system also includes a gas analyzer. The second branch pipe is connected to the gas analyzer through a second branch pipe valve.

8. The method for using a liquid tank safety valve system with emergency isolation function according to claim 5, characterized in that: The emergency isolation device includes a header, a manifold and a gas nozzle. The header is arranged outside the gas duct and is connected to the inert gas source through a first branch pipe. There are at least two manifolds, one end of the manifold is connected to the header, and the other end of the manifold is fixedly connected to the gas nozzle. The gas nozzle is inserted into the gas duct and evenly distributed on the inner surface of the gas duct. The connection between the gas nozzle and the gas duct is fixed and sealed by welding.

9. The method for using a liquid tank safety valve system with emergency isolation function according to claim 1, characterized in that: The safety valve automatically opens when the pressure in the gas phase space of the storage tank reaches a set value, and discharges the evaporated gas accumulated in the gas phase space.

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