A ship-to-ship liquefied natural gas offloading safety control system and method

Abstract

The application provides a safety control system for ship-to-ship liquefied natural gas unloading, which comprises a liquefied transport ship, a floating storage ship, a dynamic control module and a land terminal processing mechanism; the land terminal processing mechanism comprises a gas discharge unit and a liquid storage unit; the dynamic control module is composed of an unloading regulation unit, a temperature regulation unit and a pressure regulation unit; the transport ship output end is connected with the floating storage ship through a first liquid channel; the floating storage ship connection output end is connected with the liquid storage unit through a second liquid channel; the floating storage ship is connected with the transport ship through a first gaseous circuit; and the floating storage ship is connected with the gas discharge unit through a second gaseous circuit; the dynamic control module controls the first liquid channel, the second liquid channel, the first gaseous circuit and the second gaseous circuit to work through a remote network respectively; and the application solves the safety hidden trouble caused by improper control of liquefied natural gas unloading rate, temperature difference overrun and insufficient pressure regulation in the prior art.

Description

Technical Field

[0001] This invention relates to the field of liquefied natural gas loading, unloading, storage and transportation technology, and in particular to a ship-to-ship liquefied natural gas unloading and safety dynamic control system and method. Background Technology

[0002] Liquefied natural gas (LNG), as a clean and efficient energy source, occupies an important position in the global energy structure. The transportation and storage of LNG typically require maintaining extremely low temperatures (-162°C) to preserve its liquid state, which places high technical demands on related loading, unloading, and storage equipment.

[0003] Ship-to-ship (STS) operations are an important method of LNG transshipment, widely used in offshore floating terminals, small receiving stations, and emergency gas supply scenarios. STS operations achieve LNG transshipment through hose connections between LNG carriers and FSUs or FSRUs. However, current technologies still present the following technical challenges in LNG unloading operations:

[0004] 1) Insufficient minimum unloading rate setting: If the flow rate is too low during the unloading process, it may lead to the generation of "piston flow", which will affect the stable flow of liquefied natural gas in the pipeline and cause unsafe operation of the unloading system.

[0005] 2) Limitations of maximum unloading rate: In existing technologies, the unloading rate is mostly determined by a single factor (such as pipeline flow limit or evaporative gas handling capacity), failing to comprehensively consider the dynamic adjustment of multiple factors, resulting in low system efficiency;

[0006] 3) Insufficient temperature difference control: If there is a large temperature difference between the cargo tanks of the transport ship and the floating storage ship, it may lead to excessive thermal stress on the pipelines and equipment, increasing the risk of failure. At the same time, the amount of boil-off gas (BOG) generated under high temperature difference will increase dramatically, increasing the burden on the system.

[0007] 4) Low operational adaptability: Existing liquefied natural gas unloading operations mostly use a single hose connection method, which has poor efficiency and stability in high flow scenarios and fails to fully utilize the advantages of the unloading arm in high-intensity, high-flow scenarios.

[0008] Current research on liquefied natural gas (LNG) unloading operations mainly focuses on optimizing single-operation equipment or static analysis of fluid characteristics, lacking dynamic control of unloading rates and multi-scenario adaptability design, thus failing to meet operational needs under varying conditions. Specifically:

[0009] Several invention patents have been granted to address the problems of insufficient temperature difference control, complex unloading rate calculation, and poor adaptability of connected devices in existing technologies. For example:

[0010] CN107514541A discloses a floating storage and regasification device for continuously supplying natural gas fuel to port natural gas users and power plants. The device includes at least one medium-pressure zone storage tank mounted on the hull, and a low-pressure zone buffer tank, a submersible pump box, and an LNG regasification unit sequentially connected to the medium-pressure zone storage tank. Limited by industry standards, the low-cost medium-pressure zone storage tank, with its outer layer made of carbon steel, has its outlet located at the top of the tank. Continuous LNG flow is achieved through the working gas pressure difference between the medium-pressure zone storage tank and the low-pressure zone buffer tank. However, this patent still has the issue of needing further optimization of the size and weight of the medium-pressure zone storage tank and the low-pressure zone buffer tank to improve storage and transportation efficiency.

[0011] CN102654239B discloses a gasification system for a liquefied natural gas (LNG) receiving terminal. The system includes a floating gasification vessel module and an onshore module. The floating gasification vessel module includes a floating gasification vessel, which is equipped with at least one storage tank containing a backfill pump and an in-tank pump. This system overcomes the limitations of conventional large-scale onshore LNG receiving terminals, such as long construction periods, significant susceptibility to constraints from the surrounding environment and land resources, and poor flexibility. However, this patent still has issues that require further optimization of the structure and layout of the floating gasification vessel module to improve the efficiency and reliability of the gasification facility.

[0012] Therefore, there is an urgent need for a ship-to-ship liquefied natural gas unloading and safety dynamic control method that can comprehensively and dynamically adjust the unloading rate, optimize temperature difference control, and adapt to various connection devices, so as to improve the safety, economy and efficiency of operation. Summary of the Invention

[0013] To address the technical problems existing in the prior art, this invention provides a ship-to-ship liquefied natural gas (LNG) unloading and safety dynamic control system and its implementation. This invention solves the problems of insufficient temperature difference control, complex unloading rate calculation, and poor adaptability of connecting equipment in the prior art through scientific and reasonable unloading rate control and parameter optimization. This invention improves the safety and efficiency of LNG unloading operations and is particularly suitable for LNG transfer operations between LNG carriers and floating storage facilities.

[0014] In order to solve the problems existing in the prior art, the present invention adopts the following technical solution:

[0015] A safety control system for ship-to-ship liquefied natural gas (LNG) unloading includes a LNG carrier, a floating LNG storage vessel, a dynamic control module, and a land-based terminal processing unit. The land-based terminal processing unit includes a gas emission unit and a liquid storage unit. The dynamic control module comprises an unloading control unit, a temperature control unit, and a pressure control unit. The output end of the carrier is connected to the floating LNG storage vessel via a first liquid channel. The output end of the floating LNG storage vessel is connected to the land-based liquid storage unit via a second liquid channel. The floating LNG storage vessel is connected to the carrier via a first gaseous loop and to the land-based gas emission unit via a second gaseous loop. The dynamic control module controls the operation of the first liquid channel, the second liquid channel, the first gaseous loop, and the second gaseous loop.

[0016] in:

[0017] The unloading control unit is used to determine whether the natural gas liquid unloading rate of the first liquid channel and the second liquid channel is within the safe unloading range. If the natural gas liquid unloading rate is less than the lower limit rate of the safe unloading range, the temperature control unit is activated to control the temperature difference between the floating storage vessel and the transport vessel and increase the unloading rate. If the natural gas liquid unloading rate is greater than the upper limit of the safe unloading range, the pressure control unit is activated to dynamically control the gaseous natural gas to be input into the transport vessel and the gas emission unit through the first gaseous circuit and the second gaseous circuit respectively and reduce the unloading rate.

[0018] Furthermore, the lower limit rate of the safe unloading zone is calculated according to the following steps:

[0019] The thermal resistance can be calculated using the following formula:

[0020]

[0021] Where, D o and D i , , are the outer diameter and inner diameter of the unloading channel, respectively, and k is the thermal conductivity.

[0022] The heat flow rate per unit length of the liquid channel can be calculated using the following formula:

[0023]

[0024] Among them, T ∞ For ambient temperature, T LNG The temperature of the transport ship is given by R, which is the thermal resistance value calculated based on the channel parameters.

[0025] The vaporization mass flow rate per unit length of the liquid channel is calculated using the following formula:

[0026]

[0027] Among them, L v The latent heat of vaporization of the transport ship is q, where q is the heat flow rate per unit length.

[0028] The following formula is used to obtain the lower limit rate of the unloading area:

[0029]

[0030] Where ρ is the density of liquefied natural gas, in kg / m³. 3 , where n is the safety factor.

[0031] Furthermore, the upper limit rate of the safe unloading zone is calculated according to the following formula:

[0032] Q max =3600·v max ·A

[0033] Among them, Q max Maximum unloading rate, in meters 3 / h;v max A: Maximum flow velocity in the channel, in m / s; A: Cross-sectional area of ​​the channel, in m³ / s. 2 3600: Time conversion factor, converting seconds to hours; where:

[0034] The formula for calculating the cross-sectional area of ​​a flexible hose is as follows:

[0035]

[0036] Where D: the inner diameter of the hose.

[0037] Furthermore, the temperature control unit uses a binary phase diagram method to adjust the temperature difference between the floating storage vessel and the transport vessel to within 2.5℃ to 3.5℃.

[0038] Furthermore, the pressure control unit regulates the pressure difference between the first gaseous circuit and the second gaseous circuit within the range of 1 to 10 kPa.

[0039] Furthermore, the first liquid channel, the second liquid channel, the first gaseous circuit, and the second gaseous circuit are all composed of metal hoses with connectors; the inner layer of the metal hose is made of low-temperature resistant stainless steel alloy; the outer layer of the metal hose is covered with flexible composite material; the metal hose connector is made of ultra-low temperature nickel alloy material; the diameter of the metal hose ranges from 6 to 10 inches, and the length of the metal hose ranges from 20 to 50 meters.

[0040] The present invention also adopts the following technical solution, including the following steps:

[0041] S1. The dynamic control module performs pre-cooling circulation on the first liquid channel and the second liquid channel; at the same time, the dynamic control module adjusts the unloading rate of the first liquid channel and the second liquid channel to the range of the highest unloading rate.

[0042] S2. The unloading control unit determines whether the natural gas liquid unloading rate of the first liquid channel and the second liquid channel is within the safe unloading range.

[0043] If the natural gas liquid unloading rate is less than the lower limit rate of the safe unloading zone; that is:

[0044]

[0045] Then the temperature control module is activated to control the temperature difference between the floating storage vessel and the transport vessel to be within 2.5℃ to 3.5℃;

[0046] If the natural gas liquid unloading rate is greater than the upper limit rate of the safe unloading zone; that is:

[0047] Q max =3600·v max

[0048] Then the pressure control module is activated to dynamically control the gaseous natural gas to be input into the transport ship and the gas emission unit through the first gaseous circuit and the second gaseous circuit respectively; and the pressure control module controls the pressure difference between the first gaseous circuit and the second gaseous circuit to be within the range of 1 to 10 kPa.

[0049] S3. After the unloading operation is completed, the dynamic control module closes the first liquid channel and the first gas channel.

[0050] Beneficial effects

[0051] 1. This invention avoids problems such as "piston flow," gas-liquid separation, and system overpressure by dynamically adjusting the minimum and maximum unloading rates. The minimum unloading rate is achieved by using the binary phase diagram principle of liquefied natural gas, combined with the pressure regulation function of the land terminal and the floating storage regasification unit or floating storage unit, to achieve precise control of the temperature difference. Preferably, the temperature difference is controlled within 3°C, thereby reducing the thermal stress of the equipment and the amount of evaporated gas generated during the unloading process, and improving the overall stability of the system.

[0052] 2. This invention improves the versatility and adaptability of various operational scenarios, such as ship-to-ship transfer of liquefied natural gas (LNG), receiving at land terminals, and pressure regulation, by employing both hose connection and unloading arm connection methods. This invention supports a multi-pipe parallel unloading mode to meet different flow rate requirements and enhance operational flexibility.

[0053] 3. This invention effectively reduces the occurrence rate of liquefied natural gas (LNG) rollover effect by dynamically adjusting the unloading rate, thereby reducing the amount of vaporized gas generated during unloading, preferably reducing BOG emissions by 10% to 15%, and improving the economy and safety of LNG transportation. Furthermore, it can prevent overpressure and gas-liquid separation problems in the cargo tank, ensuring the safety and stability of the entire unloading process. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the structure of a ship-to-ship liquefied natural gas unloading safety control system according to the present invention;

[0055] Figure 2 This is a schematic diagram of the channel connection in a ship-to-ship liquefied natural gas unloading safety control system according to the present invention;

[0056] Figure 3 This is a schematic diagram illustrating the division of safe unloading zones in a ship-to-ship liquefied natural gas unloading safety control system according to the present invention.

[0057] Explanation of reference numerals in the attached figures:

[0058] 100 - Transport ship; 101 - First liquid channel; 102 - First gaseous circuit;

[0059] 200 - Floating storage vessel; 201 - Second liquid channel; 202 - Second gaseous circuit;

[0060] 300-Dynamic Control Module; 301-Unloading Control Unit; 302-Temperature Control Unit; 303-Pressure Control Unit; 304-Safe Unloading Area

[0061] 400 - Land-based terminal processing unit; 401 - Gas emission unit; 402 - Liquid storage unit Detailed Implementation

[0062] The following is in conjunction with the appendix Figures 1-3 The present invention will be described in detail below:

[0063] like Figure 1As shown, this invention provides a safety control system for ship-to-ship liquefied natural gas (LNG) unloading. The system includes a LNG carrier 100, a floating storage vessel 200, a dynamic control module 300, and a land-based terminal processing unit 400. The land-based terminal processing unit 400 includes a gas emission unit 401 and a liquid storage unit 402. The dynamic control module 300 consists of an unloading control unit 301, a temperature control unit 302, and a pressure control unit 303. The output end of the carrier 100 is connected to the floating storage vessel 200 via a first liquid channel 101. The output end of the floating storage vessel 200 is connected to the liquid storage unit 400 via a second liquid channel 201. 02 Connection; The floating storage vessel 200 is connected to the transport vessel 100 via a first gaseous circuit 102; and the floating storage vessel 200 is connected to the gas emission unit 401 via a second gaseous circuit 202; In this invention, the first liquid channel 101, the second liquid channel 201, the first gaseous circuit 102, and the second gaseous circuit 202 are all composed of metal hoses with connectors; the inner layer of the metal hose is made of low-temperature resistant stainless steel alloy; the outer layer of the metal hose is covered with flexible composite material; the metal hose connector is made of ultra-low temperature nickel alloy material; the diameter of the metal hose ranges from 6 to 10 inches, and the length of the metal hose ranges from 20 to 50 meters. In this invention, the first liquid channel 101 and the second liquid channel 201 are both composed of three metal pipes, such as... Figure 2 As shown.

[0064] Wherein: the dynamic control module 300 controls the operation of the first liquid channel 101, the second liquid channel 201, the first gaseous circuit 102 and the second gaseous circuit 202 respectively through a remote network;

[0065] The unloading control unit 301 is used to determine whether the natural gas liquid unloading rate of the first liquid channel 101 and the second liquid channel 201 is within the safe unloading region 304. Figure 3 As shown;

[0066] The pressure control unit 303 is used to determine whether the natural gas liquid unloading rate of the first gas channel 102 and the second gas channel 202 is within the safe unloading region 304. Figure 3 As shown;

[0067] If the natural gas liquid unloading rate is less than the lower limit rate of the safe unloading zone, then the temperature control unit is activated to control the temperature difference between the floating storage vessel and the transport vessel; wherein the lower limit rate of the safe unloading zone is calculated according to the following steps:

[0068] The thermal resistance can be calculated using the following formula:

[0069]

[0070] Where, D o and D i Here, denoted as the outer diameter and inner diameter of the unloading hose, respectively, and k is the thermal conductivity of the hose material.

[0071] The heat flow per unit length can be calculated using the following formula:

[0072]

[0073] Among them, T ∞ For ambient temperature, T LNG The temperature of the LNG is R, which is the thermal resistance value calculated based on the hose parameters.

[0074] The gasification mass flow rate per unit length is calculated using the following formula:

[0075]

[0076] Among them, L v The latent heat of vaporization of LNG is q, where q is the heat flow rate per unit length.

[0077] The following formula is used to obtain the lower limit rate of the unloading area:

[0078]

[0079] Where ρ is the density of liquefied natural gas (LNG), in kg / m³. 3 , where n is the safety factor.

[0080] If the natural gas liquid unloading rate exceeds the upper limit of the safe unloading area, the pressure control unit is activated to dynamically control the gaseous natural gas to be input into the transport ship and the gas emission unit through the first gaseous circuit and the second gaseous circuit respectively, and to reduce the unloading rate, wherein:

[0081] The upper limit rate of the safe unloading zone is calculated using the following formula:

[0082] Q max =3600·v max ·A

[0083] Among them, Q max Maximum unloading rate, in meters 3 / h;v max A: Maximum flow velocity in the channel, in m / s; A: Cross-sectional area of ​​the channel, in m³ / s. 2 3600: Time conversion factor, converting seconds to hours; where:

[0084] The formula for calculating the cross-sectional area of ​​a flexible hose is as follows:

[0085]

[0086] Where D: the inner diameter of the hose.

[0087] This invention achieves safe unloading of liquefied natural gas from ship to ship using the following steps.

[0088] S1. The dynamic control module performs pre-cooling circulation on the first liquid channel and the second liquid channel; at the same time, the dynamic control module adjusts the unloading rate of the first liquid channel and the second liquid channel to the range of the highest unloading rate.

[0089] S2. The unloading control unit determines whether the natural gas liquid unloading rate of the first liquid channel and the second liquid channel is within the safe unloading range.

[0090] If the natural gas liquid unloading rate is less than the lower limit rate of the safe unloading zone; that is:

[0091]

[0092] Then the temperature control module is activated to control the temperature difference between the floating storage vessel and the transport vessel to be within 2.5℃ to 3.5℃;

[0093] If the natural gas liquid unloading rate is greater than the upper limit rate of the safe unloading zone; that is:

[0094] Q max =3600·v max ·

[0095] The pressure control module is then activated to dynamically control the gaseous natural gas to be input into the transport ship and the gas emission unit through the first gaseous circuit and the second gaseous circuit, respectively; and the pressure control module regulates the pressure difference between the first gaseous circuit and the second gaseous circuit to be within the range of 1 to 5 kPa.

[0096] S3. After the unloading operation is completed, the dynamic control module closes the first liquid channel and the first gas channel. Specific implementation method 1:

[0098] This embodiment applies to the scenario of unloading natural gas from a liquefied natural gas (LNG) carrier to a floating storage unit (FSU) or a floating storage and regasification unit (FSRU). The dynamic control module pre-cools the first and second liquid channels; simultaneously, it adjusts the unloading rates of the first and second liquid channels to the maximum unloading rate range, ensuring the safety and efficiency of the natural gas unloading operation. LNG is transferred from the carrier to the cargo tank of the floating storage unit via three 8-inch metal hoses (20 meters long); the floating storage unit also supplies LNG to the land terminal via three 8-inch metal hoses (20 meters long). The meteorological space of the carrier and the floating storage unit are connected by one hose, i.e., the first gaseous loop; the meteorological space of the floating storage unit and the gaseous processing at the land terminal are connected by one hose, i.e., the second gaseous loop. In this embodiment, the carrier is a spherical tank with a pressure range of 5 kPa. <P ship <30kPa; the cargo tanks of floating storage vessels are spherical tanks with a pressure of 5kPa. <P FSRU / FSU <25 kPa. The pressure control range of the gas-liquid cargo tanks is maintained within 10 kPa by dynamically balancing the pressure through the first and second gaseous loops during the unloading process, ensuring a pressure difference between the transport ship and the floating storage ship. Detailed Implementation Method 2

[0100] Because the floating storage vessel temporarily suspends its gas supply to the land terminal (e.g., during maintenance or repair), it is to ensure that the gas supply capacity is restored within 6 hours to meet the terminal's needs.

[0101] 1) Unloading conditions for transport ships and floating storage vessels: Transport ships are 28,000m 3 Spherical storage tank type; floating storage vessel with a capacity of 125,000m. 3 Spherical storage tank type; liquefaction tank pressure range of transport ship is 5 kPa ≤ P shiip ≤30kPa; FSU cargo tank pressure is 5kPa≤P FSU ≤25kPa;

[0102] 2) Land terminal conditions: Storage tank volume is 600m³ 3 The downstream demand requires a gasification rate of 100m³ / h. 3 / h.

[0103] 3) Uninstall the system:

[0104] The first liquid channel between the transport ship and the floating storage vessel is connected by three 8-inch metal hoses, each 20 meters long. The second liquid channel between the floating storage vessel and the land-based terminal processing facility is also connected by three 8-inch metal hoses, each 20 meters long. This includes the maximum unloading rate of a single hose and the total unloading rate of multiple hoses operating in parallel. For detailed calculations, please refer to the relevant description in Implementation Method 1, where:

[0105] The maximum unloading rate of a single hose is Qmax, pipe = 796.2m. 3 / h

[0106] The total unloading rate of the three parallel tubes is Qmax,tota l=2388.6m 3 / h

[0107] Assuming that the land-based terminal storage tanks can maintain gas supply for 6 hours, the floating storage vessel must store liquefied natural gas during this period to meet subsequent gas supply needs.

[0108] Total demand for land-based terminals:

[0109] V demand =Q demand ×T 供气 =100×6=600m 3

[0110] The amount of liquefied natural gas stored on a floating storage vessel:

[0111] Assuming the floating storage vessel needs to store 3,600 m³ of gas before resuming gas supply. 3 To meet the continuous demand of an onshore terminal for 36 hours using LNG, the required unloading time is:

[0112]

[0113] During unloading, the pressure and temperature difference between the transport ship and the floating storage vessel need to be dynamically adjusted. Specific measures are the same as in Implementation Method 1, including the following: the pressure in the transport ship's cargo tanks gradually decreases, while the pressure in the floating storage vessel gradually increases; in the initial stage, the pressure in the floating storage vessel is reduced (e.g., to 5 kPa) to bring the natural gas temperature close to that of the transport ship; and in conjunction with premixed circulation operations, the temperature difference is controlled within 3°C. The operational procedure of this implementation method is similar to that of Implementation Method 1.

Claims

1. A safety control system for ship-to-ship liquefied natural gas unloading, the system comprising a liquefied gas transport vessel, a floating liquefied gas storage vessel, a dynamic control module, and a land-based terminal processing unit; the land-based terminal processing unit comprising a gas emission unit and a liquid storage unit; characterized in that; The dynamic control module comprises an unloading control unit, a temperature control unit, and a pressure control unit; the output end of the transport ship is connected to the floating liquefied petroleum storage vessel via a first liquid channel; the output end of the floating liquefied petroleum storage vessel is connected to the liquid storage unit via a second liquid channel; the floating liquefied petroleum storage vessel is connected to the transport ship via a first gaseous circuit; and the floating liquefied petroleum storage vessel is connected to the gas emission unit via a second gaseous circuit; the dynamic control module controls the operation of the first liquid channel, the second liquid channel, the first gaseous circuit, and the second gaseous circuit respectively; wherein: The unloading control unit is used to determine whether the natural gas liquid unloading rate of the first liquid channel and the second liquid channel is within the safe unloading range. If the natural gas liquid unloading rate is less than the lower limit rate of the safe unloading range, the temperature control unit is activated to control the temperature difference between the floating storage liquefied gas vessel and the transport vessel and increase the unloading rate. If the natural gas liquid unloading rate is greater than the upper limit rate of the safe unloading range, the pressure control unit is activated to dynamically control the gaseous natural gas to be input into the transport vessel and the gas emission unit through the first gaseous circuit and the second gaseous circuit respectively and reduce the unloading rate.

2. The safety control system for ship-to-ship liquefied natural gas unloading according to claim 1, characterized in that: The lower limit rate of the safe unloading zone is calculated according to the following steps: The thermal resistance can be calculated using the following formula: ; in, and , , are the outer diameter and inner diameter of the unloading channel, respectively, and k is the thermal conductivity; The heat flow rate per unit length of the liquid channel can be calculated using the following formula: ; in, For ambient temperature, R represents the temperature of the transport ship, and R is the thermal resistance calculated based on the channel parameters. The vaporization mass flow rate per unit length of the liquid channel is calculated using the following formula: ； in, The latent heat of vaporization of the transport ship, the Heat flow per unit length; The following formula is used to obtain the lower limit rate of the safe unloading zone: n ; in, The density of liquefied natural gas is expressed in units of... , where n is the safety factor.

3. A safety control system for ship-to-ship liquefied natural gas unloading according to claim 1, characterized in that: The upper limit rate of the safe unloading zone is calculated using the following formula: A ; in, Maximum unloading rate, in meters 3 / h; A: Maximum flow velocity in the channel, in m / s; A: Cross-sectional area of ​​the hose, in m³ / s. 2 3600: Time conversion factor, converting seconds to hours; where: The formula for calculating the cross-sectional area of ​​a flexible hose is as follows: ; Where D: the inner diameter of the hose.

4. A safety control system for ship-to-ship liquefied natural gas unloading according to claim 1, characterized in that, The temperature control unit uses a binary phase diagram method to adjust the temperature difference between the floating storage liquefied petroleum vessel and the transport vessel to within 2.5℃~3.5℃.

5. A safety control system for ship-to-ship liquefied natural gas unloading according to claim 1, characterized in that, The pressure control unit regulates the pressure difference between the first gaseous circuit and the second gaseous circuit within the range of 1~10 kPa.

6. A safety control system for ship-to-ship liquefied natural gas unloading according to any one of claims 1-5, characterized in that, The first liquid channel, the second liquid channel, the first gaseous circuit, and the second gaseous circuit are all made of metal hoses with connectors; the inner layer of the metal hose is made of low-temperature resistant stainless steel alloy; the outer layer of the metal hose is covered with flexible composite material; the metal hose connector is made of ultra-low temperature nickel alloy material; the diameter of the metal hose ranges from 6 to 10 inches, and the length of the metal hose ranges from 20 to 50 meters.

7. A method for controlling ship-to-ship liquefied natural gas unloading using the system as described in claim 1, characterized in that, Includes the following steps: S1. The dynamic control module performs pre-cooling circulation on the first liquid channel and the second liquid channel; at the same time, the dynamic control module adjusts the unloading rate of the first liquid channel and the second liquid channel to the range of the highest unloading rate. S2. The unloading control unit determines whether the natural gas liquid unloading rate of the first liquid channel and the second liquid channel is within the safe unloading range. If the natural gas liquid unloading rate is less than the lower limit rate of the safe unloading zone; that is: n ; in, The density of liquefied natural gas is expressed in units of... n is the safety factor; m is the vaporization mass flow rate per unit length of the liquid channel; Then the temperature control module is activated to control the temperature difference between the floating storage liquefied petroleum vessel and the transport vessel to be within 2.5℃~3.5℃; If the natural gas liquid unloading rate is greater than the upper limit rate of the safe unloading zone; that is: ; in, Maximum unloading rate, in meters 3 / h; : Maximum flow velocity of the channel, in m / s; 3600: Time conversion factor, converting seconds to hours; The pressure control module is then activated to dynamically control the gaseous natural gas to be input into the transport ship and the gas emission unit through the first gaseous circuit and the second gaseous circuit, respectively; and the pressure control module regulates the pressure difference between the first gaseous circuit and the second gaseous circuit to be within the range of 1~10 kPa. S3. After the unloading operation is completed, the dynamic control module shuts down the first liquid channel and the first gaseous circuit.

Images