Automatic closed safety water cutting method for liquefied hydrocarbon storage tank with two-stage isolation, two-stage water seal, saturated vapor pressure driving and flash function

Abstract

This invention relates to an automatic sealing and safety water cut-off method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function, for safe oil-water distribution. Each pressure tank in the liquefied hydrocarbon storage tank area is connected in series with its respective automatic water cut-off unit, and then the entire system is connected in series with a wastewater collection unit under the control of an intelligent controller. Under the control of the intelligent controller, the automatic sealing and safety water cut-off of the liquefied hydrocarbon storage tank with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function is performed. Alternatively, under the first-stage isolation water seal, the water cut-off is driven by saturated vapor pressure, and under the second-stage isolation water seal, liquefied hydrocarbons are flash-discharged from the wastewater tank to a safe release pipeline. After discharge, the wastewater is pressurized through a nitrogen pressurization valve pipeline and discharged to the boundary level detection sensor for water level monitoring. The method has the advantage that the final discharged wastewater will not contain or carry liquefied hydrocarbons that pose a fire hazard, ensuring the safe operation of the liquefied hydrocarbon storage tank area.

Description

Technical Field

[0001] This invention relates to a method for cutting water from a liquefied hydrocarbon storage tank, and more particularly to an automatic and safe water-cutting method for a liquefied hydrocarbon storage tank with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function. Background Technology

[0002] The applicant's patent document, CN214580436U, describes a system where each tank in a liquefied hydrocarbon storage tank group has an automatic water-cutting tank connected to an upstream standby drain valve and a piping valve via an outlet pipe. Each tank's water-cutting tank is then connected to an upstream wastewater tank, also under nitrogen protection, via its own check valve. The wastewater tank is led to a drain outlet via a pipe valve. Both the water-cutting tank and the wastewater tank are equipped with high, medium, and low temperature interface detection sensors that are connected to an intelligent controller. The outlet pipe of the storage tank is connected to the top of the water-cutting tank through a branch inlet pipe valve equipped with a branch inlet control valve. The bottom of the water-cutting tank is connected to the bottom or middle of the sewage tank through a branch drain pipe valve equipped with a branch drain control valve and a main inlet pipe valve equipped with a main inlet control valve. The bottom of the sewage tank is connected to the main drain pipe valve equipped with a main drain control valve leading to the sewage outlet. The high, medium and low interface detection sensors are electrically connected to the branch inlet control valve, the branch drain control valve, the main inlet control valve and the main drain control valve through an intelligent controller. The check valve is installed on the outlet side of the branch drain control valve.

[0003] The water inlet pipe between the water inlet control valve and the water cut-off tank is connected to the nitrogen pressurization control valve of the intelligent controller via a nitrogen injection tee and a nitrogen injection pipe; the top of the sewage tank is connected to the nitrogen pressurization control valve of the intelligent controller via a nitrogen injection pipe; the nitrogen injection port of the nitrogen pressurization control valve is connected to the pressure nitrogen source via a nitrogen supply pipe equipped with a check valve; the top and bottom of the water cut-off tank and the sewage tank are respectively connected to the side-mounted liquid level display pipes via pipe valves; the lower end of the side-mounted liquid level display pipe of the water cut-off tank is connected to the branch drain pipe via a liquid level drain valve; the lower end of the side-mounted liquid level display pipe of the sewage tank is connected to the main drain pipe via a liquid level drain valve. The water inlet pipe connected to the top of the water tank and the drain pipe connected to the bottom are connected to side-mounted level display pipes via upper and lower level valves. The nitrogen injection pipe connected to the top of the sewage tank and the main drain pipe connected to the bottom are connected to side-mounted level display pipes via upper and lower level valves. The water inlet pipes and nitrogen injection pipes before and after the nitrogen injection tee are connected to front and rear pressure relief valves via lower vent valves. The front and rear pressure relief valves are connected to the main vent pipe or main vent valve extending to the flare via upper vent valves. The upper level pipe connected to the top of the sewage tank and the nitrogen injection pipe are connected to front and rear pressure relief valves via lower vent valves. The front and rear pressure relief valves are connected to the main vent valve or main vent valve extending to the flare via upper vent valves. The nitrogen injection pipe and the main vent pipe of the water tank are connected to manual vent valves. The nitrogen injection pipe or upper level pipe of the sewage tank is connected to the main vent pipe via manual vent valves. The manual venting valve of the water-cutting tank consists of a manual venting valve section connecting the self-injecting nitrogen pipe to the main venting pipe, a nitrogen bypass control valve electrically connected to the intelligent controller and closed after venting at the end of water cutting, and the manual venting valve section. The nitrogen source side section of the nitrogen injection pipe of the water-cutting tank consists of a nitrogen pressurization control valve electrically connected to the intelligent controller and opened during water cutting, and manual nitrogen injection pipe valve sections on both sides. Throttling plates are installed on the nitrogen injection pipes of both the water-cutting tank and the sewage tank. The nitrogen pressurization control valve is a three-way valve for both water and nitrogen. The water inlet of the three-way valve is connected to a pressurized water source through a water supply pipe equipped with a check valve, and the nitrogen inlet of the three-way valve is connected to a pressurized nitrogen source through a nitrogen supply pipe equipped with a check valve.

[0004] Both the water-cutting tank and the sewage tank have backup drain valves at their bottoms, leading downwards to the sewage outlet. The medium and low interface detection sensors are respectively connected to the backup water-cutting limit signal input port and the normal water-cutting limit signal input port of the intelligent controller. The tops of both the water-cutting tank and the sewage tank are connected upwards to pressure transmitters electrically connected to the intelligent controller via pipe valves. The tops of both the water-cutting tank and the sewage tank are also connected to safety valves with temperature sensor transmitters at their outlets via pipe valves. The temperature sensor transmitters are used to detect liquefied hydrocarbon leaks and are connected to the safety valve leak signal input port of the intelligent controller. The medium, high, and low interface detection sensors are respectively located at the upper, middle, and lower parts of the water-cutting tank and the sewage tank. The sewage outlet is equipped with a combustible gas alarm electrically connected to the intelligent controller. However, when the sewage tank discharges sewage, the liquefied hydrocarbons dissolved in or carried by the sewage will not only pollute the environment but also pose a fire hazard. In particular, even if a combustible gas alarm is installed at the discharge outlet, the outlet is often located at the end of a long-distance pipeline far from the tank area. By the time the alarm is detected, the pipeline may already contain wastewater containing liquefied hydrocarbons, posing a fire hazard. Furthermore, when a backup discharge valve leading to the discharge outlet is installed at the bottom of the water cutter tank, the wastewater discharged from the water cutter tank, without undergoing secondary hydrocarbon-water separation in the wastewater tank, will contain more dissolved or entrained liquefied hydrocarbons than the wastewater discharged from the wastewater tank. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide an automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function. The wastewater discharged by this method will no longer contain or carry liquefied hydrocarbons that pose a fire hazard, ensuring the safe operation of the liquefied hydrocarbon storage tank area, automatic water-cutting unit, and wastewater collection unit.

[0006] To achieve the above objectives, this invention provides an automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks, featuring two-stage isolation, two-stage water sealing, saturated vapor pressure drive, and flash evaporation functions. Its key feature is that each pressure tank in the liquefied hydrocarbon storage tank area is connected in series with an automatic water-cutting unit, and then the units are connected in series with a wastewater collection unit under the control of an intelligent controller. The method further involves the pressure tanks being connected to a safety release pipeline via safety release valves at their tops for safe depressurization. The wastewater collection unit, equipped with a nitrogen pressurization valve pipeline and temperature, level, and pressure gauges, connects to the top of its wastewater tank, while the automatic water-cutting unit, equipped with either a temperature, level, and pressure gauge or a nitrogen pressurization valve pipeline and temperature, level, and pressure gauges, connects to its water-cutting tank. The top is connected to the safety release pipeline via a safety release valve and a bypass control valve. The water-cutting tank and the wastewater tank are each equipped with a boundary detection sensor to detect the water seal liquid level, and each is equipped with a water inlet control valve and a water-cutting control valve, and a second water inlet control valve and a drainage control valve. Under the control of the intelligent controller, the liquefied hydrocarbon storage tank with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation functions can automatically seal and safely cut off the water, or under the first-stage isolation water seal, drive the water-cutting tank with saturated vapor pressure to cut off the water, and under the second-stage isolation water seal, flash discharge liquefied hydrocarbons from the wastewater tank to the safety release pipeline via wastewater flash evaporation. After discharge, the wastewater in the wastewater tank is pressurized and discharged through a nitrogen pressurization valve to the boundary detection sensor to monitor the water level. The connecting pipeline between the automatic water-cutting unit and the liquefied hydrocarbon storage tank serves as a channel for hydrocarbon-water exchange through density difference. The inlet height of the automatic water-cutting unit should not be higher than the lowest point of the outlet connecting pipeline at the bottom of the liquefied hydrocarbon storage tank to ensure hydrocarbon-water exchange between the storage tank and the water-cutting tank. The present invention is equipped with a safety relief component on the upper part of the water tank and the sewage tank. When the pressure inside the water tank or the sewage tank exceeds the set pressure value, the excess pressure inside the tank is released through the safety relief component, thereby maximizing the operational safety.

[0007] Safety release valves are used to prevent overpressure in the corresponding equipment and ensure safe pressure operation. The saturated vapor pressure driven water cut-off under the primary isolation water seal is achieved by controlling the automatic water cut-off unit and the liquefied hydrocarbon storage tank in isolation through the reverse opening and closing of the inlet control valve and the outlet control valve, and the control of the hydrocarbon-water interface within the water cut-off tank, under the condition of the secondary inlet control valve being open. This ensures sufficient water seal for the wastewater in the water cut-off tank after the water cut-off. Flash evaporation occurs when wastewater accumulates to a certain level in the wastewater tank, and the wastewater is released through the closing and opening of the secondary inlet control valve and the bypass control valve. The wastewater tank of the collection unit is connected to the safety relief system via a bypass control valve and a safety release pipeline. This allows dissolved or entrained liquefied hydrocarbons in the wastewater to be flash-evaporated and separated before being discharged into the safety relief system under low pressure, reducing the amount of liquefied hydrocarbons carried in the wastewater. After flash evaporation, drainage is carried out under the secondary isolation water seal: with the secondary inlet control valve at the wastewater tank inlet of the wastewater collection unit closed, the drainage control valve and nitrogen pressurization valve pipeline are opened. Drainage is performed under the constraint of the water seal boundary within the wastewater tank and driven by pressurized nitrogen, ensuring that the discharged wastewater does not carry liquefied hydrocarbons that pose a fire hazard. This system ensures that the ultimately discharged wastewater will not contain or carry any liquefied hydrocarbons that pose a fire hazard, guaranteeing the safe operation of the liquefied hydrocarbon storage tank area, the automatic water cut-off unit, and the wastewater collection unit.

[0008] As an optimization, the saturated vapor pressure driven water cut-off under the primary isolation water seal is achieved by: with the secondary inlet control valve open, the reverse opening and closing control of the primary inlet control valve and the secondary outlet control valve of the automatic water cut-off unit's water cut-off tank, along with the control of the hydrocarbon-water interface within the water cut-off tank, to realize saturated vapor pressure driven water seal water cut-off in the isolated state between the automatic water cut-off unit and the liquefied hydrocarbon storage tank, ensuring sufficient water seal for the wastewater in the water cut-off tank after water cut-off; flash evaporation is achieved by: when the wastewater in the wastewater tank accumulates to a certain level, the secondary inlet control valve and the bypass control valve of the wastewater tank are closed and opened. The sewage tank of the sewage collection unit is connected to the safety relief system via a bypass control valve and a safety release pipeline. This allows dissolved or entrained liquefied hydrocarbons to be flash-evaporated and separated under low pressure before being discharged into the safety relief system, reducing the amount of liquefied hydrocarbons carried in the sewage. After flash evaporation, the drainage process is as follows: with the secondary inlet control valve at the sewage tank inlet of the sewage collection unit closed, the drainage control valve and nitrogen pressurization valve pipeline are opened. Drainage is carried out under the restriction of the water seal boundary in the sewage tank and driven by pressurized nitrogen, ensuring that the discharged sewage does not carry liquefied hydrocarbons that pose a fire hazard.

[0009] As an optimization, the safety release pipeline is connected via a safety release valve and a bypass control valve through parallel or parallel connections of safety release valves and bypass control valves, as well as a common check valve, to prevent backflow during safety release and venting, or to prevent safety release and flash evaporation. The safety release pipeline is used for overpressure release. The bypass control valve is used for special release during equipment maintenance or for flash evaporation. The check valve is used to prevent the medium in the safety release pipeline from flowing back into the pressure storage tank, the water cut-off tank, and the wastewater tank. That is, the check valve ensures that the medium in the safety release system does not flow back into the pressure storage tank and the water cut-off tank, and the control valve ensures that the gas pressure in the water cut-off tank remains stable within a preset range. The check valve ensures that the medium in the safety release system does not flow back into the wastewater tank, and the control valve ensures that the gas pressure in the wastewater tank remains within a preset range. In other words, the safety release system for the water tank is formed by connecting the safety release valve and bypass control valve via parallel safety release valves and bypass control valves, along with a common check valve. Similarly, the safety release system for the wastewater tank is formed by connecting the safety release valve and bypass control valve via parallel safety release valves and bypass control valves, along with a common check valve. Compared to parallel connections, the vibration interference between the safety release valves and bypass control valves is significantly reduced.

[0010] The nitrogen pressurization valve pipeline uses a series combination of a check valve and a control valve to prevent backflow during nitrogen pressurization or purging. The check valve prevents media from the water cut-off tank and wastewater tank from accidentally entering the nitrogen pressurization valve pipeline, while the control valve is used to start and stop nitrogen charging. The automatic water cut-off unit and wastewater collection unit are connected to the nitrogen system via pipelines equipped with check valves and control valves. The check valve ensures that media from the water cut-off tank and wastewater tank do not flow back into the nitrogen system, while the control valve provides the driving force for the water cut-off and drainage of the water cut-off tank and wastewater tank by replenishing nitrogen.

[0011] As an optimization, the top of the water-cutting tank is equipped with a nitrogen pressure valve pipeline and water-cutting temperature, level, and pressure gauges to ensure water is cut to the water seal level. Furthermore, when needed, the nitrogen pressure valve pipeline, under the control of the intelligent controller, supplies nitrogen to the automatic water-cutting unit and the wastewater collection unit, replacing all other media with nitrogen. During maintenance, the nitrogen pressure valve pipeline, also under the control of the intelligent controller, purges the automatic water-cutting unit, the wastewater collection unit, and connecting pipelines by supplying nitrogen. This improves the safety of equipment operation and maintenance.

[0012] As an optimization, the water seal liquid level detected by the boundary detection sensor is located at the bottom of the water cutting tank and the sewage tank. While ensuring the water seal function, it does not retain too much water seal water, thereby ensuring the quality and efficiency of water cutting and drainage.

[0013] As an optimization, the top of the wastewater tank is connected to a safety release pipeline via a safety release valve, a bypass control valve, and a negative pressure transfer pump. The negative pressure generated by the pump powerfully removes residual liquefied hydrocarbons from the flash-evaporated wastewater. The negative pressure transfer pump is used to create negative pressure within the tank when needed, such as after normal flash evaporation. This negative pressure distillation removes liquefied hydrocarbons soluble in or entrained in the wastewater. After removal, nitrogen is added via a nitrogen pressurization valve, and the drain control valve discharges wastewater until the tank level reaches the water seal level. This further removes dissolved and entrained liquefied hydrocarbons from the wastewater, ensuring absolutely safe wastewater discharge and making the process more environmentally friendly.

[0014] As an optimization, the top of the wastewater tank is connected to the safety release pipeline via a safety release valve, a bypass control valve, and a shared check valve. The pipelines before and after the bypass control valve are respectively connected via tee bypasses to the negative pressure control valves of the series-connected negative pressure transfer pump, thus avoiding the adverse effects of the negative pressure transfer pump on the safety release and flash evaporation efficiency. The bypass valves connecting to the negative pressure transfer pump help avoid its influence on normal flash evaporation. The flash evaporation under the negative pressure transfer pump is a powerful flash evaporation.

[0015] As an optimization, the water cut-off control valve is installed on the water cut-off branch pipes leading out from each water cut-off tank, and the secondary water inlet control valve is installed on the main water inlet pipe connecting all the water cut-off branch pipes to the wastewater tank. This is a normally open main valve in the normal operating state of the automatic water cut-off unit in the liquefied hydrocarbon storage tank area, to meet the compatibility control requirements of single-path control by the water cut-off control valve and main-path control by the secondary water inlet control valve. The water cut-off control valve is used to control water cut-off when the secondary water inlet control valve is open. The secondary water inlet control valve is used for upstream isolation of the wastewater tank and is a normally open valve in the normal operating state of the automatic water cut-off unit.

[0016] As an optimization, the level gauge measures the highest liquid level in the water tank and sewage tank in real time. This data is used by the intelligent controller to compare the liquid level detected by the interface detection sensor, especially the water level, and to perform comprehensive interface control by combining the dynamic liquid level measured by the level gauge with the fixed height liquid level detected by the interface detection sensor. This facilitates accurate and precise control by the intelligent controller.

[0017] As an optimization, the interface detection sensor configured in the water-cutting tank includes a high-level probe for detecting the highest liquid level, a low-level probe for detecting the water seal surface, and a low-level probe for detecting the liquefied hydrocarbon interface immediately above the water seal surface; the interface detection sensor configured in the wastewater tank includes a high-level probe for detecting the highest liquid level, a low-level probe for detecting the water seal surface, and a low-level probe for detecting the gas phase interface immediately above the water seal surface; the high-level probe is used to detect and limit the highest water level in the water-cutting tank and the wastewater tank, and the low-level probe is used to compare the detection signal with the low-level probe to ensure that after water cutting or drainage, the water level at the low-level probe is water seal water and the water level at the low-level probe is non-aqueous medium. The height region between the bottom probe used to detect the water seal surface and a low probe used to detect the water seal surface immediately above the liquefied hydrocarbon interface, and the height region between the bottom probe used to detect the water seal surface and a low probe used to detect the water seal surface immediately above the gas phase interface, are intermediate turbid emulsified zones where water mixes with other media. The presence of turbid emulsified zones between the bottom and low probes is more conducive to ensuring that the bottom probe is located at the wastewater surface, thus ensuring the water seal function.

[0018] The primary isolation and water seal water cutting of the automatic water cutting unit of this invention is as follows: The water cutting tank of the automatic water cutting unit is connected to the bottom outlet of the liquefied hydrocarbon storage tank via a pipeline, eliminating the need for additional openings in the liquefied hydrocarbon storage tank. When water precipitates from the hydrocarbon medium in the liquefied hydrocarbon storage tank, due to the greater density of water than the hydrocarbon medium, the precipitated water continuously flows into the water cutting tank through the storage tank drainage pipeline (lower part of the pipeline) under the influence of gravity. Simultaneously, under the influence of buoyancy, hydrocarbon medium with the same volume as the water entering the water cutting tank automatically floats back to the liquefied hydrocarbon storage tank through the storage tank drainage pipeline (upper part of the pipeline), achieving automatic exchange of hydrocarbons and water. When the interface detection sensor configured in the water cutting tank detects that the hydrocarbon-water interface level in the water cutting tank has risen to a preset high position, the automatic water cutting unit meets the water cutting conditions, the inlet control valve located at the inlet of the automatic water cutting unit closes, and the connection between the automatic water cutting unit and the liquefied hydrocarbon storage tank changes from a direct connection to an isolated state. If all measured values ​​of the instruments are within the normal range, the automatic water-cutting unit's water-cutting control valve opens under control, and water cutting begins. Driven by the saturated vapor pressure of the hydrocarbon medium remaining in the water-cutting tank, the wastewater in the water-cutting tank is automatically discharged and discharged into the wastewater tank through a pipeline. When the interface detection sensor configured in the water-cutting tank detects that the hydrocarbon-water interface level in the water-cutting tank has dropped to a preset low position, the water-cutting control valve closes, and water cutting ends. After the water-cutting control valve closes, wastewater at the preset interface level is still retained at the bottom of the water-cutting tank, achieving water seal control during the water-cutting process. Through the reverse opening and closing control of the automatic water-cutting unit's inlet control valve and the water-cutting control valve, as well as the control of the hydrocarbon-water interface level in the water-cutting tank, the isolation and water seal of the wastewater discharge from the automatic water-cutting unit are achieved. The isolation and water seal of the automatic water-cutting unit constitute the first-level isolation and water seal of this invention.

[0019] The secondary isolation and water seal shut-off of the wastewater collection unit of this invention are as follows: The wastewater collection unit is connected to the shut-off control valve of the automatic shut-off unit via pipeline. During the wastewater collection unit's water intake process, the discharge valve (which can be an automatic or manual valve) on the pipeline connected to the safety relief system is closed, the nitrogen valve on the pipeline connected to the nitrogen system is closed, and the wastewater collection unit's drain control valve is closed. When the wastewater tank reaches a preset high level, the wastewater collection unit's inlet control valve closes, and the connection between the wastewater collection unit and the automatic shut-off unit changes from direct connection to isolation. After the wastewater collection unit's inlet control valve closes, the discharge valve on the pipeline connected to the safety relief system opens, allowing dissolved wastewater or entrained liquefied hydrocarbons to be discharged into the safety relief system under low pressure through flash evaporation and separation. During this process, the pressure inside the wastewater tank gradually decreases. When the pressure inside the wastewater tank reaches a preset pressure value, the discharge valve on the pipeline connected to the safety relief system closes, and the connection between the wastewater collection unit and the safety relief system changes from direct connection to isolation. At this time, all automatic water-cutting control valves are closed, as is the inlet control valve of the wastewater collection unit. There are two valves isolating the liquefied hydrocarbon storage tank from the wastewater collection unit. After the wastewater collection unit completes this isolation, if all instrument readings are within the normal range, under control, the nitrogen valve on the pipeline connecting the wastewater collection unit to the nitrogen system opens, the gas phase pressure in the wastewater tank rises, and the drain control valve of the wastewater collection unit opens, initiating drainage. Driven by the nitrogen pressure inside the wastewater tank, the wastewater is discharged into the wastewater system through the drain control valve and pipeline. When the boundary level inside the wastewater tank drops to the preset low position, the drain control valve of the wastewater collection unit closes, ending the drainage. After the drain control valve closes, wastewater at the preset boundary level remains at the bottom of the wastewater tank, achieving water seal control during the wastewater discharge process. Through the reverse opening and closing control of the inlet and drain control valves of the wastewater collection unit, and the control of the boundary level inside the wastewater tank, the isolation and water seal of wastewater discharge from the wastewater collection unit are achieved. The isolation and water seal of the sewage collection unit is the second-level isolation and water seal of the method described in this invention.

[0020] Furthermore, by controlling the opening and closing of relevant control valves, the sewage collection unit has the following two operating states: ① Slight positive pressure operating state: By controlling the nitrogen flow rate into the sewage tank, the gas pressure inside the sewage tank is made slightly higher than the opening pressure of the one-way valve connected to the safety relief system. When the sewage tank reaches the preset high position, the inlet control valve of the sewage collection unit closes, and the connection between the sewage collection unit and the automatic water cut-off unit changes from a direct connection to an isolated state. After the inlet control valve of the sewage collection unit closes, the discharge valve on the pipeline connected to the safety relief system opens, allowing dissolved sewage or entrained liquefied hydrocarbons to be discharged into the safety relief system under low pressure through flash evaporation and separation. ② When the pressure inside the sewage tank exceeds the set pressure limit, the gas inside the sewage tank enters the pipeline connected to the safety relief system through the control valve and the one-way valve. By controlling the opening degree of the control valve and the flow rate of supplementary nitrogen, the gas pressure inside the sewage tank is kept within the preset range. At this time, the drain control valve of the sewage collection unit opens, and the sewage in the sewage tank is discharged into the sewage system through the drain control valve under the pressure of continuously supplemented nitrogen. When the boundary level inside the sewage tank reaches the preset low position, the drainage control valve closes, and the drainage process of the sewage collection unit ends.

[0021] ② Closed-loop operation: In this operation mode, the control valve connected to the safety relief system is normally closed. The gaseous pressure inside the sewage tank is determined by the added nitrogen and the liquefied hydrocarbons that have flashed into gaseous form. When the sewage tank reaches the preset high level, the inlet control valve of the sewage collection unit closes, and the connection between the sewage collection unit and the automatic water cut-off unit changes from a direct connection to an isolated connection. After the inlet control valve of the sewage collection unit closes, the discharge valve on the pipeline connected to the safety relief system opens, allowing dissolved or entrained liquefied hydrocarbons to be flashed and separated and discharged into the safety relief system under low pressure. When the pressure inside the sewage tank exceeds the set upper pressure limit, the gas inside the sewage tank enters the pipeline connected to the safety relief system through the control valve and check valve, and the discharge valve on the pipeline connected to the safety relief system closes.

[0022] With the control valve connected to the safety relief system closed and the gas pressure inside the sewage tank within the set range, the drain control valve of the sewage collection unit opens. At this time, the minimum pressure inside the sewage tank must be greater than the pressure of the sewage system. Under the action of the gas pressure inside the tank, the sewage in the sewage tank is discharged into the sewage system through the drain control valve. As the sewage in the sewage tank is discharged, when the boundary level inside the sewage tank reaches the preset low position, the drain control valve closes, and the drainage process of the sewage collection unit ends. Compared with the slightly positive pressure working state, the closed working state can significantly reduce the amount of gaseous emissions and nitrogen replenishment.

[0023] The operating modes are as follows: 1. Initial state: The air in the water-cutting tank, sewage tank, and their connecting pipelines described in this invention is replaced with nitrogen, and the pressure is controlled to a predetermined pressure value. At this time, the initial state is entered. In this state, the inlet control valve on the pipeline connecting the water-cutting tank and the liquefied hydrocarbon storage tank is open, and the water-cutting control valve at the bottom of the water-cutting tank is closed; the second inlet control valve on the pipeline connecting the sewage tank and the water-cutting tank, the water-cutting control valve at the bottom of the sewage tank, the bypass control valve at the top of the sewage tank, and the nitrogen charging control valve on the nitrogen charging valve pipeline are closed. 2. Water Inlet Process of the Water Cut-off Tank: When water precipitates from the hydrocarbon medium in the liquefied hydrocarbon storage tank, due to the density and specific gravity of water being greater than that of the hydrocarbon medium, the precipitated water continuously flows into the water cut-off tank through the storage tank drain line (lower part of the pipeline) under the action of gravity. Since the density and specific gravity of hydrocarbons are less than that of water, under the action of buoyancy, hydrocarbon medium with the same volume as the water entering the water cut-off tank automatically floats back to the liquefied hydrocarbon storage tank through the storage tank drain line (upper part of the pipeline), achieving automatic exchange of hydrocarbons and water. When the hydrocarbon-water interface level detection instrument configured in the water cut-off tank detects that the interface level has reached the high limit, the detection signal of the hydrocarbon-water interface level detection instrument changes from "hydrocarbon" to "water". At this time, the first water inlet control valve automatically closes, and the water inlet process ends. 3. Water Cut-off Process of the Water Cut-off Tank: After the first water inlet control valve closes, the automatic water cut-off process begins. When the temperature and pressure detection signals at each detection point, the valve position signals of other control valves, the interface position, and the interface detection signal are all within normal values, the water cut-off control valve of the water cut-off tank automatically opens, and the secondary inlet control valve of the sewage tank opens. At this time, the water in the water cut-off tank is discharged into the sewage tank through the pipeline under the driving force of the saturated vapor pressure of the hydrocarbon medium, and the "hydrocarbon-water interface" in the water cut-off tank drops steadily. When the hydrocarbon-water interface detection instrument configured on the water cut-off tank detects that the interface position reaches the lower limit, the water cut-off control valve automatically closes, and the water cut-off process ends. 4. Sewage tank inlet process: When the water cut-off tank is cutting water, the secondary inlet control valve of the sewage tank remains open, and the sewage discharged from the water cut-off tank enters the sewage tank through the connecting pipeline, and the sewage tank enters the inlet process. When the interface detection instrument configured on the sewage tank detects that the interface position reaches the upper limit, the secondary inlet control valve on the connecting pipeline between the sewage tank and the water cut-off tank automatically closes, the interface position in the sewage tank stops rising, the inlet process ends, and the sewage tank enters the sewage discharge process. 5. Flash Evaporation Process of the Wastewater Tank: After the secondary inlet control valve is closed, the wastewater tank enters the flash evaporation process. The bypass control valve on the pipeline connected to the safety relief system opens, allowing dissolved wastewater or entrained liquefied hydrocarbons to be flashed, separated, and discharged into the safety relief system of the safety release pipeline under low pressure. During this process, the pressure inside the wastewater tank gradually decreases. When the pressure inside the wastewater tank reaches the preset pressure value, the bypass control valve on the pipeline connected to the safety relief system closes. 6. Water Cut-off Process of the Wastewater Tank: After the bypass control valve on the pipeline connected to the safety relief system closes, the wastewater tank enters the automatic water cut-off process.When the temperature and pressure signals at each detection point, the valve position signals of other control valves, and the boundary position and detection signals are all within normal values, the drain control valve of the sewage tank automatically opens. Sewage in the tank, under gas pressure (closed-loop operation) or continuous nitrogen replenishment pressure (slight positive pressure operation), is discharged into the tank area's sewage system via pipeline. At this time, the water level in the sewage tank steadily decreases. When the boundary position detection instrument installed in the sewage tank detects that the boundary position has reached the lower limit, the drain control valve automatically closes, and the sewage discharge process ends.

[0024] In summary, the automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks of the present invention, which features two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation functions, ensures that the final discharged wastewater will not contain or carry liquefied hydrocarbons that pose a fire hazard, thus ensuring the safe operation of the liquefied hydrocarbon storage tank area, the automatic water-cutting unit, and the wastewater collection unit. It also boasts the advantages of high reliability and strong safety. Attached Figure Description

[0025] Figure 1 This is an overall schematic diagram of the automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation functions according to the present invention. Figure 2 This is a single-line flow diagram of the automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation functions according to the present invention. Detailed Implementation

[0026] As shown in the figure, the automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks of the present invention, which features two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation functions, is carried out by connecting each pressure storage tank 10 of the liquefied hydrocarbon storage tank area 40 in series with each automatic water-cutting unit 20, and then connecting them in series with a sewage collection unit 30 under the control of an intelligent controller; the bottom of the pressure storage tank 10 is connected to the water-cutting tank 21 through a front connecting pipeline 11 with an inlet control valve 22A to safely release the pressure of the pressure storage tank 10. The top of the pressure storage tank 10 is connected to the safety release pipeline 9 of the safety relief system via safety release valves. The top of the sewage collection unit 30, equipped with sewage nitrogen pressurization valve pipeline 32D and sewage temperature, level and pressure gauge 33B, and the top of the automatic water-cutting unit 20, equipped with water-cutting nitrogen pressurization valve pipeline 22D and water-cutting temperature, level and pressure gauge 23B, are connected to the safety release pipeline 9 of the safety relief system via sewage safety release valve 32E, sewage bypass control valve 32C, water-cutting safety release valve 22E, and water-cutting bypass control valve 22C. The water-cutting tank 21 and the sewage tank 31 are respectively equipped with water-cutting interface detectors for detecting the water seal liquid level. The system includes a water level sensor 23A and a wastewater boundary detection sensor 33A, and is equipped with an inlet control valve 22A and a water cut-off control valve 22B, as well as a second inlet control valve 32A and a drainage control valve 32B. Under the control of the intelligent controller BPCS50, the system automatically seals and cuts off the liquefied hydrocarbon pressure storage tank, which features two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation functions. Alternatively, it performs water cut-off from the water cut-off tank 21 under the first-stage isolation water seal and saturated vapor pressure drive, and flash discharge of liquefied hydrocarbons from the wastewater tank 31 to the safety release pipeline 9 under the second-stage isolation water seal. After discharge, the wastewater in the wastewater tank 31 is pressurized and discharged through the nitrogen pressurization valve pipeline to the boundary detection sensor to monitor the water level. The connecting pipeline between the automatic water cut-off unit 20 and the liquefied hydrocarbon pressure storage tank 10 serves as a channel for the exchange of hydrocarbon and water media through density difference. The height of the inlet of the automatic water cut-off unit 20 should not be higher than the height of the lowest point of the bottom outlet connecting pipeline of the liquefied hydrocarbon pressure storage tank 10. Figure 2 The height of point b is not higher than the height of point a, ensuring that hydrocarbon-water exchange is achieved between the pressure storage tank 10 and the water-cutting tank 21. This invention includes safety relief components on the upper part of the water-cutting tank and the wastewater tank. When the pressure inside the water-cutting tank or the wastewater tank exceeds a set pressure value, the safety relief components release the excess pressure, maximizing operational safety.

[0027] Safety release valves are used to prevent overpressure in the corresponding equipment and ensure safe pressure operation. The primary isolation, water-sealed saturated vapor pressure driven water cut-off is achieved by controlling the reverse opening and closing of an inlet control valve at the inlet of the automatic water cut-off unit's water cut-off tank and a water cut-off control valve at the outlet, as well as controlling the hydrocarbon-water interface within the water cut-off tank. This ensures that the automatic water cut-off unit is isolated from the liquefied hydrocarbon pressure storage tank, and guarantees sufficient water seal in the wastewater within the water cut-off tank after water cut-off. This avoids disturbance to the stratification within the pressure storage tank during water cut-off, reduces the entrainment of liquefied hydrocarbons in the cut-off wastewater, and prevents excessive water cut-off from carrying away liquefied hydrocarbons or hydrocarbon gas, minimizing hydrocarbon flash loss. Flash evaporation involves opening and closing the two inlet control valves and the bypass control valve on the pipeline when the wastewater in the wastewater tank reaches a certain level. This connects the wastewater collection unit's tank to the safety relief system via pipeline, allowing dissolved or entrained liquefied hydrocarbons to be flash-evaporated and separated under low pressure before being discharged into the safety relief system, further reducing the amount of liquefied hydrocarbons carried in the wastewater. The secondary isolation water seal drainage after flash evaporation involves opening the outlet drainage control valve and controlling the water level in the wastewater tank while the two inlet control valves at the wastewater collection unit's inlet are closed. This achieves water seal drainage in an isolated state between the wastewater collection unit and the automatic water-cutting unit, ensuring that the discharged wastewater does not carry liquefied hydrocarbons that pose a fire hazard. This process ensures that the ultimately discharged wastewater will not contain or carry any liquefied hydrocarbons that pose a fire hazard, guaranteeing the safe operation of the liquefied hydrocarbon pressure storage tank area, the automatic water-cutting unit, and the wastewater collection unit.

[0028] Specifically, under the primary isolation water seal and saturated vapor pressure driven water cutting: with the secondary inlet control valve open, the automatic water cutting unit achieves saturated vapor pressure driven water seal cutting under the isolation state between the automatic water cutting unit and the liquefied hydrocarbon pressure storage tank through the reverse opening and closing control of the primary inlet control valve and the water cutting control valve at the outlet, as well as the control of the hydrocarbon-water interface in the water cutting tank, and ensures that the sewage in the water cutting tank has sufficient water seal after water cutting; flash evaporation: when the sewage in the sewage tank accumulates to a certain level, the secondary inlet control valve and the bypass control valve of the sewage tank are closed and opened. The sewage tank of the sewage collection unit is connected to the safety relief system via a bypass control valve and a safety release pipeline. This allows dissolved or entrained liquefied hydrocarbons to be flash-evaporated and separated under low pressure before being discharged into the safety relief system, reducing the amount of liquefied hydrocarbons carried in the sewage. After flash evaporation, the drainage process is as follows: with the secondary inlet control valve at the sewage tank inlet of the sewage collection unit closed, the drainage control valve and nitrogen pressurization valve pipeline are opened. Drainage is carried out under the restriction of the water seal boundary in the sewage tank and driven by pressurized nitrogen, ensuring that the discharged sewage does not carry liquefied hydrocarbons that pose a fire hazard.

[0029] Specifically, such as Figure 2As shown, the water cut-off tank 21 is connected to the safety release pipeline 9 via the water cut-off safety release valve 22E and the water cut-off bypass control valve 22C. The safety release pipeline 9 is connected in parallel with the water cut-off safety release valve 22E and the water cut-off bypass control valve 22C, and is also connected to a common check valve. This system prevents backflow and ensures safe release and venting, forming the water cut-off tank safety release system. The sewage tank 31 is connected to the safety release pipeline 9 via the sewage safety release valve 32E and the sewage bypass control valve 32C. This system prevents backflow and ensures safe release and flash evaporation, forming the sewage tank safety release system. Compared to parallel connection, parallel connection significantly reduces vibration interference between the safety release valves and the bypass control valves. The valves in the water cut-off nitrogen pressurization valve pipeline 22D and the sewage nitrogen pressurization valve pipeline 32D are a series combination of check valves and control valves for nitrogen pressurization or purging to prevent backflow. Furthermore, when needed, the nitrogen pressurization valve pipeline, under the control of the intelligent controller, inputs nitrogen into the automatic water-cutting unit and the sewage collection unit, replacing all other media with nitrogen; when needed, under the control of the intelligent controller, the nitrogen pressurization valve pipeline also purges the automatic water-cutting unit, the sewage collection unit, and the connecting pipelines by inputting nitrogen during maintenance.

[0030] Specifically, the water seal liquid levels of the water cut-off interface detection sensor 23A and the sewage interface detection sensor 33A are located at the bottom of the water cut-off tank 21 and the sewage tank 31, respectively. This ensures the water seal function without leaving too much water seal water, thereby guaranteeing the quality and efficiency of water cut-off and drainage.

[0031] Specifically, the top of the wastewater tank 31 is connected to the safety release pipeline 9 via a wastewater safety release valve 32E, a wastewater bypass control valve 32C, and a negative pressure transfer pump. The negative pressure generated by the negative pressure transfer pump powerfully removes residual liquefied hydrocarbons from the wastewater in the tank after flash evaporation. The negative pressure transfer pump is used to create negative pressure in the wastewater tank when needed, such as after normal flash evaporation, to powerfully remove liquefied hydrocarbons soluble in the wastewater or carried in the wastewater. After removal, nitrogen is replenished through the nitrogen pressurization valve pipeline, and the drain control valve discharges wastewater until the tank water level drops to the water seal level. The top of the wastewater tank is connected to the safety release pipeline via the safety release valve, the bypass control valve, and a connected one-way valve. The pipelines before and after the bypass control valve are respectively connected to the negative pressure control valve before and after the series negative pressure transfer pump via three-way bypasses, avoiding any adverse effects of the negative pressure transfer pump on the safety release and flash evaporation efficiency.

[0032] Specifically, the water-cutting control valve 22B is installed on the water-cutting branch pipe 22 leading out from each water-cutting tank 21, and the dual-inlet control valve 32A is installed on the main inlet pipe 32 connecting all the water-cutting branch pipes to the sewage tank 31. It is a normally open valve in the main line under the normal operation of the automatic water-cutting unit 20 in the liquefied hydrocarbon storage tank area 40, so as to meet the compatibility control requirements of single-line control of the water-cutting control valve and main line control of the dual-inlet control valve.

[0033] Specifically, the level gauge measures the highest liquid level in the water tank 21 and the sewage tank 31 in real time. This data is used by the intelligent controller BPCS50 to compare the liquid level detected by the interface detection sensor, especially the water level, and to perform comprehensive interface control by combining the dynamic liquid level measured by the level gauge with the fixed height liquid level detected by the interface detection sensor. This facilitates accurate and precise control by the intelligent controller.

[0034] Specifically, the water-cutting tank 21 is equipped with a water-cutting interface detection sensor 23A, which includes a high-level probe for detecting the highest liquid level, a low-level probe for detecting the water seal surface, and a low-level probe for detecting the liquefied hydrocarbon interface immediately above the water seal surface; the wastewater tank 31 is equipped with a wastewater interface detection sensor 33A, which includes a high-level probe for detecting the highest liquid level, a low-level probe for detecting the water seal surface, and a low-level probe for detecting the gas phase interface immediately above the water seal surface; the high-level probe is used to detect and limit the highest water level in the water-cutting tank and the wastewater tank, and the low-level probe is used to compare the detection signal with the low-level probe to ensure that after water cutting or drainage, the water seal surface at the low-level probe is water and the non-aqueous medium at the low-level probe is water. The height region between the bottom probe used to detect the water seal surface and a low probe used to detect the water seal surface immediately above the liquefied hydrocarbon interface, and the height region between the bottom probe used to detect the water seal surface and a low probe used to detect the water seal surface immediately above the gas phase interface, are intermediate turbid emulsified zones where water mixes with other media. The presence of turbid emulsified zones between the bottom and low probes is more conducive to ensuring that the bottom probe is located at the wastewater surface, thus ensuring the water seal function.

[0035] This invention relates to an automatic safety water shut-off and wastewater closed-loop transportation system that connects multiple liquefied hydrocarbon pressure storage tanks via pipelines.

[0036] The closed-loop operation of the sewage tank is as follows: When the automatic water-cutting unit 20 cuts water from its water-cutting tank 21, the first inlet control valve 22A closes; when the sewage collection unit 30 cuts water from its sewage tank 31, the second inlet control valve 32A closes, achieving two-stage physical isolation. Sewage in the water-cutting tank 21 is discharged using the saturated vapor pressure of the internally stored hydrocarbon medium as the driving force, while sewage in the sewage tank 31 is discharged using gaseous pressure as the driving force.

[0037] The working process of the wastewater tank under slight positive pressure is as follows: When the automatic water-cutting unit 20 cuts water from its water-cutting tank 21, the first inlet control valve 22A is closed; when the wastewater collection unit 30 cuts water from its wastewater tank 31, the second inlet control valve 32A is closed, achieving two-stage physical isolation. Wastewater in the water-cutting tank 21 is discharged from the water-cutting tank 21 by the driving force provided by the saturated vapor pressure of the hydrocarbon medium stored inside, and wastewater in the wastewater tank 31 is discharged from the wastewater tank 31 by the driving force provided by the continuous replenishment of nitrogen.

[0038] The saturated vapor pressure drive occurs when the water-cutting interface detection sensor 23A in the water-cutting tank 21 detects that the hydrocarbon-water interface level in the water-cutting tank 21 has risen to a preset high level. At this point, the automatic water-cutting unit 20 is ready to cut water, and the inlet control valve 22A at the inlet of the automatic water-cutting unit 20 closes, switching the connection between the automatic water-cutting unit 20 and the liquefied hydrocarbon pressure storage tank 10 from a direct connection to an isolated state. If all measured values ​​are within the normal range, under control, the water-cutting control valve 22B of the automatic water-cutting unit 20 opens, and water cutting begins. Driven by the saturated vapor pressure of the liquefied hydrocarbons remaining in the water-cutting tank 21, the wastewater in the water-cutting tank 21 is automatically discharged and piped into the wastewater tank 31. When the water-cutting interface detection sensor 23A in the water-cutting tank 21 detects that the hydrocarbon-water interface level in the water-cutting tank 21 has fallen to a preset low level, the water-cutting control valve 22B closes, and water cutting ends. The flash evaporation function is that after the second inlet control valve 32A of the sewage collection unit 30 is closed, the sewage bypass control valve 32C on the pipeline connected to the safety release system is opened, so that the liquefied hydrocarbons dissolved in the sewage or entrained are discharged into the safety release pipeline 9 of the safety release system under low pressure through flash evaporation and separation.

[0039] In summary, the automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks of the present invention, which features two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation functions, ensures that the final discharged wastewater will not contain or carry liquefied hydrocarbons that pose a fire hazard, thus ensuring the safe operation of the liquefied hydrocarbon storage tank area, the automatic water-cutting unit, and the wastewater collection unit. It also boasts the advantages of high reliability and strong safety.

Claims

1. An automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function, wherein each pressure storage tank in the liquefied hydrocarbon storage tank area is connected in series with each automatic water-cutting unit, and then the units are connected in series with a wastewater collection unit under the control of an intelligent controller; characterized in that... The tops of the pressure storage tanks are connected to safety release pipelines via safety release valves for safe depressurization. The tops of the wastewater collection unit's wastewater tank (equipped with nitrogen pressurization valves and temperature / level / pressure gauges) and the tops of the automatic water-cutting unit's water-cutting tank (equipped with either temperature / level / pressure gauges or nitrogen pressurization valves and temperature / level / pressure gauges) are connected to safety release pipelines via safety release valves and bypass control valves, respectively. Both the water-cutting tank and the wastewater tank are equipped with interface detection sensors for detecting the water seal liquid level. The water-cutting tank is equipped with one inlet control valve and one water-cutting control valve, while the sewage tank is equipped with two inlet control valves and one drain control valve. Under the control of the intelligent controller, the liquefied hydrocarbon storage tank with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function can automatically and safely shut off the water, or under the first-stage isolation water seal, the saturated vapor pressure drive can drive the water-cutting tank to cut off the water, and under the second-stage isolation water seal, the sewage in the sewage tank can be flashed out to the safe release pipeline to discharge liquefied hydrocarbons. After discharge, the sewage in the sewage tank can be pressurized through the nitrogen pressurization valve pipeline to the boundary detection sensor to monitor the water level. Under the primary isolation water seal and saturated vapor pressure driven water cutting: with the secondary inlet control valve open, the automatic water cutting unit achieves saturated vapor pressure driven water seal cutting in an isolated state from the liquefied hydrocarbon storage tank through the reverse opening and closing control of the primary inlet control valve and the water cutting control valve at the outlet of the water cutting tank, as well as the control of the hydrocarbon-water interface in the water cutting tank, ensuring sufficient water seal for the wastewater in the water cutting tank after water cutting; flash evaporation: when the wastewater in the wastewater tank accumulates to a certain level, the secondary inlet control valve and the bypass control valve of the wastewater tank are closed and opened. The sewage tank of the sewage collection unit is connected to the safety relief system through a bypass control valve and a safety release pipeline. This allows dissolved or entrained liquefied hydrocarbons in the sewage to be flash-evaporated and separated before being discharged into the safety relief system under low pressure, reducing the amount of liquefied hydrocarbons entrained in the sewage. After flash evaporation, the drainage process is as follows: with the secondary inlet control valve at the sewage tank inlet of the sewage collection unit closed, the drainage control valve and nitrogen pressurization valve pipeline are opened. Drainage is carried out under the restriction of the water seal boundary in the sewage tank and driven by pressurized nitrogen, ensuring that the discharged sewage does not carry liquefied hydrocarbons.

2. The automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function as described in claim 1, characterized in that... The safety release pipeline is connected by a safety release valve and a bypass control valve. This connection is achieved by using parallel or parallel safety release valves and bypass control valves, as well as a common check valve, to prevent backflow during safety release and venting or during safety release and flash evaporation. The nitrogen pressurization valve pipeline uses a series combination of a check valve and a control valve to prevent backflow during nitrogen pressurization or purging.

3. The automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function as described in claim 1, characterized in that... The top of the water tank is equipped with a nitrogen pressurization valve pipeline and temperature, liquid level and pressure gauges. When needed, the nitrogen pressurization valve pipeline, under the control of the intelligent controller, inputs nitrogen into the automatic water-cutting unit and the sewage collection unit, replacing all other media with nitrogen. When needed, the nitrogen pressurization valve pipeline, under the control of the intelligent controller, also purges the automatic water-cutting unit, the sewage collection unit, and the connecting pipelines by inputting nitrogen during maintenance.

4. The automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function as described in claim 1, characterized in that... The water seal level detected by the boundary detection sensor is located at the bottom of the water cutting tank and the sewage tank, ensuring the water seal function without leaving too much water seal water.

5. The automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function as described in claim 1, characterized in that... The top of the sewage tank is connected to a safety release pipeline via a safety release valve, a bypass control valve, and a negative pressure transfer pump. The negative pressure generated by the negative pressure transfer pump is used to forcefully remove residual liquefied hydrocarbons from the sewage in the flash-evaporated sewage tank.

6. The automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function as described in claim 5, characterized in that... The top of the sewage tank is connected to the safety release pipeline via a safety release valve, a bypass control valve, and a common check valve; the pipelines before and after the bypass control valve are respectively connected to the negative pressure control front valve and negative pressure control rear valve of the series negative pressure transfer pump via a three-way bypass, so as to avoid the adverse effects of the negative pressure transfer pump on the safety release and flash evaporation efficiency.

7. The automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function as described in claim 1, characterized in that... The water-cutting control valve is installed on the water-cutting branch pipes leading out from each water-cutting tank, and the secondary water-inlet control valve is installed on the main water-inlet pipe connecting all the water-cutting branch pipes to the sewage tank. It is a normally open valve in the main line under normal operation of the automatic water-cutting unit in the liquefied hydrocarbon storage tank area, so as to meet the compatibility control requirements of single-path control of the water-cutting control valve and main-path control of the secondary water-inlet control valve.

8. The automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function as described in claim 1, characterized in that... The liquid level and pressure gauge in the temperature, liquid level and pressure gauge consists of a liquid level gauge and a pressure gauge. The liquid level gauge measures the highest liquid level in the water tank and sewage tank in real time, which is used by the intelligent controller to compare the liquid level detected by the interface detection sensor, and to perform comprehensive interface control by combining the dynamic liquid level measured by the liquid level gauge and the fixed height liquid level detected by the interface detection sensor.

9. The automatic sealing and safety water-cutting method for liquefied hydrocarbon storage tanks with two-stage isolation, two-stage water seal, saturated vapor pressure drive, and flash evaporation function as described in claim 1, characterized in that... The interface detection sensor configured in the water-cutting tank includes a high-level probe for detecting the highest liquid level, a low-level probe for detecting the water seal surface, and a low-level probe for detecting the liquefied hydrocarbon interface immediately above the water seal surface. The interface detection sensor configured in the wastewater tank includes a high-level probe for detecting the highest liquid level, a low-level probe for detecting the water seal surface, and a low-level probe for detecting the gas phase interface immediately above the water seal surface. The high-level probe is used to detect and limit the highest water level in the water-cutting tank and the wastewater tank. The low-level probe is used to compare the detection signal with the low-level probe to ensure that after water cutting or drainage, the water level at the low-level probe is water seal water and the water level at the low-level probe is non-aqueous medium.

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