A ship-to-ship bunkering method between LNG carriers

Abstract

The present application relates to the technical field of shipbuilding, and particularly relates to a ship-to-ship filling method between LNG transport ships. The ship-to-ship filling method between LNG transport ships is as follows: a first transport ship in a post-delivery inert state and a second transport ship completing an LNG loading test are docked at a wharf; then a raw material cargo hold of the second transport ship is controlled to deliver gaseous natural gas to a target cargo hold on the first transport ship to perform gas exchange; then the raw material cargo hold of the second transport ship is controlled to deliver LNG to the target cargo hold on the first transport ship, and the target cargo hold is cooled by a cargo hold spray head of the target cargo hold on the first transport ship; finally, the raw material cargo hold of the second transport ship is filled with LNG to the target cargo hold on the first transport ship to a liquid level meeting the requirements of a maiden voyage. Thus, the problem that the time cost and operation cost are high due to the long time consumption of the preparation work before the LNG transport ship is delivered to the ship owner and loaded is solved.

Description

Technical Field

[0001] This invention relates to the field of shipbuilding technology, and in particular to a ship-to-ship bunkering method between LNG carriers. Background Technology

[0002] LNG carriers are high-end equipment designed for transporting liquefied natural gas at -163°C, and their construction and delivery adhere to stringent requirements. The standard delivery process for LNG carriers is as follows: After the ship's construction phase, LNG is loaded into some of the cargo holds to meet testing requirements before the vessel embarks for gas testing voyages. After all tests are completed, the remaining LNG is emptied, and the relevant cargo holds are then inerted with inert gas and dry air. The vessel is then docked at the pier for delivery procedures. Once the shipowner's operating company approves the vessel, the shipbuilding company delivers the LNG carrier to the company. The crew then sails the vessel to an LNG terminal for cargo hold inerting, natural gas replacement, and cooling before refueling.

[0003] The entire process described above, from ship delivery to loading completion, takes approximately ten days. The ship's berthing fees and daily sailing costs exceed one million yuan. This not only increases time costs but also raises the shipowner's operating costs, thereby indirectly weakening the competitiveness of LNG ships in the offshore LNG industry chain market. Summary of the Invention

[0004] In view of this, the present invention provides a ship-to-ship bunkering method for LNG carriers to solve the problems of long delivery time, high time cost, and high operating cost of LNG carriers to ship owners and pre-loading preparation work in the prior art.

[0005] A ship-to-ship bunkering method for LNG carriers involves mooring a first carrier in an inertized state after delivery at a dock, and mooring a second carrier that has completed an LNG loading test alongside the first carrier. The LNG-loaded cargo tanks on the second carrier are connected to at least one cargo tank on the inertized first carrier via a bunkering apparatus. This cargo tank on the first carrier is designated as the target cargo tank, and the LNG-loaded cargo tank on the second carrier is designated as the raw material cargo tank. Next, the raw material cargo tank on the second carrier supplies natural gas (with a temperature range of 10°C to 30°C) to the target cargo tank on the first carrier for gas exchange until the natural gas concentration in the target cargo tank reaches a preset threshold. Then, the raw material cargo tank on the second carrier supplies LNG to the target cargo tank on the first carrier, and the target cargo tank is cooled by spray nozzles on the first carrier until the temperature reaches a preset temperature. Finally, the raw material cargo tank on the second carrier replenishes the target cargo tank on the first carrier with LNG to the level required for the maiden voyage.

[0006] Furthermore, while cooling the target cargo hold through the cargo hold spray heads on the first transport ship, the target cargo hold is connected to the adjacent cargo hold that is in an inert state.

[0007] Furthermore, when connecting the target cargo hold of the first transport ship to the raw material cargo hold of the second transport ship, the gas collection platforms of the first and second transport ships are kept connected to each other.

[0008] Furthermore, before refueling the target cargo hold of the first transport ship with natural gas, the gas composition in the target cargo hold is detected, and the oxygen content in the target cargo hold of the first transport ship is kept at 0 and the dew point is kept at -40°C.

[0009] Furthermore, before using the refueling equipment to connect the first and second transport vessels, the first and second transport vessels are brought together together using ropes or connecting tools.

[0010] Furthermore, a buffer target is set between the first and second transport ships before they are connected together.

[0011] Furthermore, when supplying natural gas with a temperature range of 10°C to 30°C to the target cargo hold of the first transport ship, it is done through a vaporizer on the first transport ship.

[0012] Furthermore, after cooling the target cargo hold is completed, liquefied natural gas is continued to be injected into the target cargo hold.

[0013] Furthermore, the LNG in the raw material cargo hold of the second transport vessel shall not be less than 4,000 m³.

[0014] Furthermore, after cooling the target cargo hold, and before removing the refueling equipment, the temporary pipelines of the gas gathering platform are purged with ambient temperature nitrogen. The equipment is then removed once the natural gas concentration is below the preset value.

[0015] The ship-to-ship bunkering method between LNG carriers in this invention has the following advantages: By selecting a first carrier in an inert state and a second carrier that has completed an LNG loading experiment to simultaneously dock at the pier, subsequent operations on both carriers can be carried out concurrently. By connecting the LNG-loaded cargo tanks on the first carrier to the LNG-requiring cargo tanks on the second carrier, and since the second carrier needs to discharge LNG while the first carrier needs to inject LNG, the second carrier, having completed its LNG loading experiment, can simultaneously supply gas to the first carrier, which is in an inert state. This allows for simultaneous venting of the second carrier and natural gas replacement and cooling of the first carrier, enabling simultaneous operations on both carriers within the same timeframe, saving time and LNG usage. Furthermore, by controlling the amount of LNG supplied from the second carrier to the first carrier, and... The delivery temperature can achieve different functions. Injecting natural gas at 10°C to 30°C facilitates the removal of inert gases and also removes any carbon dioxide that may be present in the gas, preventing the formation of dry ice due to the low temperature during subsequent LNG injection, which would affect usability. After the natural gas replacement is completed, the low-temperature LNG in the second transport ship is used to cool the target cargo tank, facilitating subsequent LNG refueling. That is, by using the second transport ship, which should be discharging gas, to refuel the first transport ship, which is in an inert state, it is possible to carry out operations on both the first and second transport ships simultaneously, thereby saving overall operation time. Furthermore, directly using the LNG in the second transport ship to inject into the first transport ship also facilitates the efficient use of LNG. This solves the problem of long delivery times and high time and operating costs associated with the delivery of LNG transport ships to shipowners and the pre-loading preparation work in existing technologies.

[0016] Furthermore, since a large amount of gaseous natural gas is generated when the target cargo hold is cooled down, connecting the target cargo hold to the adjacent cargo hold allows for simultaneous cooling of the target cargo hold and replacement of natural gas in the adjacent cargo hold, thus improving efficiency.

[0017] Furthermore, by using refueling fixtures to connect the gas gathering platforms of the two vessels, it is convenient to make the connection using the existing structure.

[0018] Furthermore, by maintaining the required oxygen content and dew point before refueling, potential safety hazards can be avoided during use.

[0019] Furthermore, connecting the first and second transport vessels together prevents damage to the refueling equipment during the refueling process due to pulling.

[0020] Furthermore, the use of buffer targets helps prevent damage to the ship hull from collisions.

[0021] Furthermore, when performing gas replacement, existing marine vaporizers can be used to avoid the increased costs associated with using additional equipment.

[0022] Furthermore, refueling continues after the target cargo hold has cooled down, which allows the second transport ship to carry out subsequent inerting and airing operations, while also enabling the first transport ship to load a certain amount of LNG.

[0023] Furthermore, using room-temperature nitrogen for purging avoids the safety risks posed by flammable gases and also heats up the pipeline. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a flowchart of Embodiment 1 of the ship-to-ship bunkering method between LNG carriers in this invention; Figure 2 This is a schematic diagram showing the connection between the first and second transport ships in Embodiment 1 of the ship-to-ship bunkering method between LNG transport ships in this invention. Figure 3 This is a schematic diagram of the pipeline connection for natural gas replacement of the first LNG carrier in Embodiment 1 of the ship-to-ship bunkering method of the present invention. Figure 4 This is a schematic diagram of the pipeline connection for cooling the target cargo hold of the first transport ship in Embodiment 1 of the ship-to-ship bunkering method between LNG transport ships in this invention. Figure 5 This is a schematic diagram of the pipeline connection for the first LNG carrier to continue refueling in Embodiment 1 of the ship-to-ship refueling method of the present invention.

[0026] The labels in the diagram represent: 1. First transport ship; 11. Target cargo hold; 12. Vaporizer; 13. Spray pipe; 2. Second transport ship; 21. Raw material cargo hold; 22. Tank sweeping pump; 3. Refueling equipment; 4. Buffer target; 5. Dock. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0028] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0029] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0030] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0031] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two components. They can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0032] In the following description, suffixes such as "module," "part," or "unit" used to denote elements are used only for the convenience of the description of the invention and have no specific meaning in themselves. Therefore, "module" and "part" can be used interchangeably.

[0033] To better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0034] In Embodiment 1 of the ship-to-ship bunkering method between LNG carriers in this invention (hereinafter referred to as the bunkering method): The refueling method in this embodiment involves simultaneously docking the first transport ship 1, which is in an inert state, and the second transport ship 2, which has completed the LNG loading experiment, at the dock 5, and supplying gas to the first transport ship 1 from the second transport ship 2. This allows for simultaneous gas replacement and cooling of the first transport ship 1 and LNG discharge from the second transport ship 2, thereby saving time and reducing costs.

[0035] For LNG carriers, there may be multiple cargo holds for loading LNG. This embodiment uses a longitudinally arranged LNG hull as an example. The cargo holds of this type are arranged sequentially from bow to stern, with the one at the bow designated as Cargo Hold 1, followed by Cargo Hold 2, 3, and 4. In typical testing, loading experiments are usually conducted in Cargo Hold 4; therefore, this embodiment describes the LNG loading scheme using Cargo Hold 4 as an example. Cargo Hold 4 of the first carrier 1 is in an inert state and requires ventilation and cooling; this is designated as the target cargo hold 11 of the first carrier 1. Cargo Hold 4 of the second carrier 2 contains LNG and needs to be discharged; this is designated as the raw material cargo hold 21. Specifically, the following procedures are followed during refueling: Step 1. The target cargo hold 11 of the first transport vessel 1 remains inert and is berthed at dock 5. After the gas trial is completed, the second transport vessel 2, with approximately 4000 m³ of LNG loaded into its raw material cargo hold 21, is berthed at the shipyard dock 5 along with the first transport vessel 1. At this time, the target cargo hold 11 of the first transport vessel 1 should be kept inert, with the oxygen content reduced to 0% and the dew point measured at -40°C. This is to avoid safety hazards after natural gas injection. It is worth noting that the 4000 m³ LNG loading capacity described in this invention is a simulated estimate to meet the fuel consumption and cargo hold operation requirements for the maiden voyage after delivery of the LNG vessel, and can be adjusted according to the actual maiden voyage route after delivery of different vessels.

[0036] Step 2. Connect the first transport vessel 1 and the second transport vessel 2 using the refueling fixture 3. Specifically, since the connection between the first transport vessel 1 and the second transport vessel 2 is carried out on the sea surface, they may rise and fall with the waves. To prevent collisions caused by wind and waves during the double berthing, a scientific and reasonable mooring scheme was formulated through comprehensive analysis of the vessel's hull structure, the strength requirements of the mooring system, and actual operational needs. During the scheme design process, the arrangement position, quantity, specifications, and strength of the fixing points of the mooring lines were calculated and verified in detail, taking into account the vessel's operating conditions and mooring conditions, to ensure that the double berthing method can meet the safety requirements of the vessels under different operating conditions. A buffer target 4 is added between the two vessels to strengthen the safety measures between them. Regarding the connection between the first transport vessel 1 and the second transport vessel 2, the refueling fixture 3 used in this embodiment can be a widely existing refueling fixture or a redesigned fixture based on the distance between the two vessels and their specific structure; details will not be elaborated here. It is worth noting that the processing fixture connects the gas collection platforms of the first transport vessel 1 and the second transport vessel 2.

[0037] Step 3. Perform inert gas replacement. Start the tank cleaning pump 22 in the raw material cargo hold 21 of the second transport vessel 2, supplying liquid to the tank cleaning spray manifold of the gas gathering platform of the first transport vessel 1 through the gas gathering platform. LNG enters the vaporizer 12 through the cleaning spray manifold, vaporizes into natural gas, and then enters the target cargo hold 11 of the first transport vessel 1 for gas replacement. After the refueling fixture 3 is installed and the temporary pipeline is checked for tightness, start the tank cleaning pump 22 of the second transport vessel 2 to supply liquid to the tank cleaning spray manifold of the gas gathering platform of the first transport vessel 1 through the refueling fixture 3. LNG is a cryogenic liquid at -163℃; during the refueling process, attention should be paid to the cold displacement of the temporary pipeline to prevent deformation of the fixture under stress. LNG enters the vaporizer 12 of the first transport vessel 1 through the cleaning spray manifold, vaporizes into natural gas with a temperature range of 10℃ to 30℃, and then enters the target cargo hold 11 of the first transport vessel 1 to replace the inert gas. Natural gas can be easily transported through the existing gas gathering platform and spray pipe 13 on the ship. The target cargo tank 11, which is in an inert state, is replaced with natural gas at room temperature to keep the target cargo tank 11 pure and avoid the liquefaction or solidification of gases such as carbon dioxide at low temperature, which would affect the normal operation of the LNG carrier.

[0038] Step 4. Detect the natural gas concentration in the target cargo hold 11 of the first transport ship 1. When the concentration at all sampling points in the cargo hold reaches 99% VOL, the gas replacement is completed.

[0039] Step 5. Cool the target cargo hold 11 of the first transport vessel 1. Continue to supply natural gas from the second transport vessel 2 to the first transport vessel 1. LNG enters the cargo hold spray head directly through the tank cleaning spray pipe 13 to begin cooling the target cargo hold 11 of the first transport vessel 1. When the average temperature inside the cargo hold reaches -100℃, the cooling of the cargo hold is complete. It is worth noting that during the cooling process, the liquefied natural gas in the target cargo hold 11 will absorb heat and turn into gas. In this embodiment, since the first transport vessel 1 has multiple liquefied cargo holds, in order to make reasonable use of all the volatile gases and avoid indiscriminately releasing natural gas into the atmosphere and causing environmental pollution, a large amount of natural gas volatilized from cargo hold 4 is used to replace the inert gas in cargo hold 3 during the cooling process. That is, the cooling of cargo hold 4 and the gas replacement of cargo hold 3 are carried out simultaneously, saving time.

[0040] Step 6. The remaining LNG of the second transport vessel 2 is directly fed into the target cargo hold 11 through the tank cleaning spray manifold for LNG refueling. The refueling level is increased to meet the fuel consumption and cargo hold operations of the LNG vessel's maiden voyage after delivery. The final refueling amount should be determined based on the nautical miles and specific route of the maiden voyage after delivery, until refueling is completed.

[0041] Finally, purge the temporary pipelines of the gas gathering platform with room temperature nitrogen until the natural gas concentration drops to 2% before disassembling and refueling tool 3 to avoid residual natural gas accumulation. If there is any hot work, it should be carried out only after the system has passed the explosion-proof test and has been checked with a portable methane detector to prevent the risk of combustion and explosion.

[0042] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for ship-to-ship bunkering between LNG carriers, characterized in that: The first transport vessel, in an inertized state after delivery, is moored at the dock, and the second transport vessel, having completed its LNG loading test, is moored alongside the first transport vessel. The LNG-loaded cargo tank on the second transport vessel is connected to at least one cargo tank on the first transport vessel (which is in an inertized state) via a refueling device. This cargo tank on the first transport vessel is designated as the target cargo tank, and the LNG-loaded cargo tank on the second transport vessel is designated as the raw material cargo tank. Then, natural gas with a temperature range of 10°C to 30°C is supplied from the raw material cargo tank of the second transport vessel to the target cargo tank on the first transport vessel for gas exchange until the natural gas concentration in the target cargo tank reaches a preset threshold. Next, LNG is supplied from the raw material cargo tank of the second transport vessel to the target cargo tank on the first transport vessel, and the target cargo tank is cooled using spray nozzles on the first transport vessel until the temperature inside the target cargo tank reaches a preset temperature. Finally, LNG is refueled from the raw material cargo tank of the second transport vessel to the target cargo tank on the first transport vessel to the required level for the maiden voyage.

2. The ship-to-ship bunkering method between LNG carriers according to claim 1, characterized in that: When cooling the target cargo hold through the cargo hold spray head on the first transport ship, the target cargo hold is connected to the adjacent cargo hold that is in an inert state.

3. The ship-to-ship bunkering method between LNG carriers according to claim 1 or 2, characterized in that: When connecting the target cargo hold of the first transport ship to the raw material cargo hold of the second transport ship, the gas collection platforms of the first and second transport ships should be kept connected to each other.

4. The ship-to-ship bunkering method between LNG carriers as described in claim 1 or 2, characterized in that: Before refueling the target cargo hold of the first transport ship with natural gas, the gas composition in the target cargo hold was tested, and the oxygen content in the target cargo hold of the first transport ship was kept at 0 and the dew point was kept at -40°C.

5. The ship-to-ship bunkering method between LNG carriers according to claim 1 or 2, characterized in that: Before using the refueling equipment to connect the first and second transport vessels, use a rope or connecting tool to bring the first and second transport vessels together.

6. The ship-to-ship bunkering method between LNG carriers according to claim 5, characterized in that: Before connecting the first and second transport ships together, a buffer target is set between the first and second transport ships.

7. The ship-to-ship bunkering method between LNG carriers according to claim 1 or 2, characterized in that: When delivering natural gas with a temperature range of 10°C to 30°C to the target cargo hold of the first transport ship, it is done through the vaporizer on the first transport ship.

8. The ship-to-ship bunkering method between LNG carriers according to claim 1 or 2, characterized in that: After the target cargo hold has been cooled, liquefied natural gas will continue to be injected into the target cargo hold.

9. The ship-to-ship bunkering method between LNG carriers according to claim 1 or 2, characterized in that: The LNG in the raw material cargo hold of the second transport vessel shall not be less than 4,000 m³.

10. The ship-to-ship bunkering method between LNG carriers as described in claim 1 or 2, characterized in that: After cooling the target cargo hold, and before removing the refueling equipment, purge the temporary pipelines of the gas gathering platform with ambient temperature nitrogen. Remove the equipment only after the natural gas concentration is below the preset value.

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