A combined cargo hold and method for transporting liquid hydrogen and LNG on a liquid cargo ship

Abstract

The present invention discloses a combined cargo hold and method for transporting liquid hydrogen and LNG by a liquid cargo ship. The combined transportation of liquid hydrogen and LNG is realized by placing a liquid hydrogen tank in an LNG tank, thereby solving the influence of the free liquid surface of liquid hydrogen and LNG on the stability of the ship during transportation, increasing the effective tank capacity of the liquid cargo ship, and improving the transportation capacity of the combined cargo hold. In addition, through the ingenious combination of the liquid hydrogen tank and the LNG tank, on the one hand, the temperature difference between the liquid hydrogen and the ambient temperature is reduced, and the thickness of the insulation layer of the liquid hydrogen tank is reduced; on the other hand, the ship does not need to be pressurized when fully loaded, and the ship will not have an excessive draft, thereby reducing the transportation cost of liquid hydrogen and LNG. In addition, the present invention also reasonably designs the loading capacity of liquid hydrogen and LNG, so that when the ship is fully loaded, the gravity on the liquid hydrogen tank is equal to the buoyancy, so that the load-bearing frame is subjected to 0 force, and when it is unloaded, the load-bearing frame is subjected to very small force, thereby increasing the sustainable working time of the combined cargo hold, so the present invention has very good practical application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of ships, and in particular relates to a combined cargo hold and method for transporting liquid hydrogen and LNG in a liquid cargo ship. Background Art

[0002] With the increasing severity of environmental pollution and the continuous depletion of fossil energy, the demand for clean and pollution-free new energy sources has increased dramatically in countries around the world. As natural gas and hydrogen energy have the advantages of being pollution-free and having high combustion efficiency, their international trade volume is increasing.

[0003] In order to increase the amount of hydrogen and natural gas transported at sea, hydrogen and natural gas are stored and transported in liquid form (liquid hydrogen, LNG) on ships. The ships used to transport liquid hydrogen and LNG are called "liquid hydrogen ships" and "LNG ships" respectively. The temperature of liquid hydrogen is -253℃ and the density is 70kg / m 3 Since the mass of liquid hydrogen per unit volume is relatively small, liquid hydrogen ships are gradually developing towards large-scale development in order to increase the transport weight of liquid hydrogen. According to relevant literature, a 280,000m 3 The length of a liquid hydrogen ship is 370m, the width is 75m, and the draft is 9.2m when empty, but only 10.02m when fully loaded, which is less than 1m. The reason is that the density of liquid hydrogen is too small, so the mass of liquid hydrogen per unit volume is also very small, which results in the ship's load capacity being very small even when fully loaded, and the center of gravity being high. Ballast water must be injected into the ballast tank to improve the ship's stability. In addition, there is a temperature difference of nearly 300℃ between liquid hydrogen and the natural environment. In order to reduce the penetration heat between liquid hydrogen and the external environment and reduce the generation of liquid hydrogen evaporation gas, a thicker insulation layer needs to be installed outside the liquid cargo tank. Therefore, the cost of transporting liquid hydrogen is very high, and even if an insulation layer is installed, more liquid hydrogen evaporation gas is still generated due to the large temperature difference. Therefore, liquid hydrogen ships have obvious problems and shortcomings.

[0004] In addition, the density of LNG is 420kg / m 3 , which is about 6 times the density of liquid hydrogen. Therefore, LNG has a larger mass per unit volume than liquid hydrogen. 3 The length of an LNG ship is 299m, the width is 46m, and the draft is 12m when fully loaded. Such a large draft requires that the channel construction depth of the LNG ship leading to its receiving station (i.e., unloading port) is relatively deep. Due to safety considerations, the construction of LNG receiving stations is relatively remote and far away from dry bulk cargo terminals. Therefore, the channel leading to the offshore of the LNG receiving station is also separate, so the construction cost of the LNG receiving station is extremely high, and the draft of the ship directly affects the construction cost of the channel. If the draft of the LNG ship can be reduced, the construction depth of the port channel can be reduced, thereby greatly reducing the construction and maintenance costs of the channel.

[0005] In addition, since the filling rate of the cargo holds of liquid cargo ships is usually 95% - 98%, the liquid cargo holds are not completely filled with liquid. Therefore, the liquid in the liquid cargo holds will flow back and forth as the ship sways. The liquid surface that freely changes in the liquid cargo hold due to the ship's sway is called the free surface. When a liquid hydrogen ship or an LNG ship undergoes rolling motion, due to the existence of the free surface, the center of gravity of the ship will shift, exacerbating the amplitude of the ship's roll and greatly reducing the stability of the ship. To reduce the impact of the free surface on the ship's stability, large oil tankers and the like adopt the method of compartmentalization, that is, the liquid cargo hold is divided into small compartments by partitions to carry crude oil to reduce the free surface. However, due to the extremely low temperature of LNG and liquid hydrogen, there is a temperature difference of at least nearly 200 °C from the natural environment, which places extremely high requirements on the low-temperature resistance of the partitions, greatly increasing the initial investment cost of the ship. Therefore, liquid hydrogen ships or LNG ships will not adopt the method of compartmentalization.

[0006] A common method for liquid hydrogen ships and LNG ships to reduce the free surface is to design the upper part of the liquid cargo hold into a "narrowed - mouth type", that is, the width of the liquid cargo hold (observed from the cross - sectional view) is smaller closer to the deck above. Carrying liquid through the "narrowed - mouth type" liquid cargo hold can effectively reduce the free surface of the liquid and improve the stability of the ship. However, there are prominent problems: due to the "narrowed - mouth type" design of the liquid cargo hold, the upper space of the ship fails to be fully utilized for loading liquid cargo, that is, there is still a lot of unused space between the upper part of the liquid cargo hold and the ship's deck, resulting in a large waste of the internal space of the hull and greatly reducing the cargo capacity of the ship. Therefore, there are obvious deficiencies and drawbacks in adopting the "narrowed - mouth type" liquid cargo hold.

[0007] Since the physical and chemical properties of liquid hydrogen and LNG are similar, the loading ports of LNG and liquid hydrogen can be located at the same port or the same berth. Similarly, the receiving stations for LNG and liquid hydrogen can also be located at the same port or the same berth. For example, countries such as Australia are rich in natural gas resources, with large export volumes, and also produce hydrogen energy on a large scale, exporting both LNG and liquid hydrogen. Therefore, loading LNG and liquid hydrogen simultaneously at the same port and receiving them at the same receiving station can be achieved both technically and from a market perspective.

[0008] Chinese Patent No. CN113028269A discloses an LH 2 and LNG combined transportation system and method. The fundamental purpose of this patent is to reduce the evaporation rate of LNG and liquid hydrogen during storage and transportation. Although this patent mentions that it can be used for LNG and liquid hydrogen transport ships, the technical solutions proposed in it do not solve the problems of the free surface and draft.

[0009] Based on this, if a cargo tank that can achieve the combined transportation of liquid hydrogen and LNG can be proposed, which can not only solve the influence of free liquid surface on the ship's stability, increase the transportation volume, but also solve the problem of too small or too large draft of the ship when transporting liquid hydrogen or LNG alone, then such a cargo tank has very high practical application value. Summary of the Invention

[0010] In view of the above problems, the present invention proposes a combined cargo tank and method for a liquid cargo ship to transport liquid hydrogen and LNG, which solves the influence of the free liquid surface on the ship's stability, increases the transportation volume, and reduces the transportation cost of liquid hydrogen and LNG; by transporting liquid hydrogen and LNG through the combined cargo tank, the ship does not need to inject ballast water when fully loaded, and it will also reduce the draft of the ship, lower the requirements for the loading port and the receiving terminal channel, and thus reduce the construction cost of the port and the channel.

[0011] The first object of the present invention is to propose a combined cargo tank for a liquid cargo ship to transport liquid hydrogen and LNG.

[0012] The present invention mainly includes: LNG tank, liquid hydrogen tank, transfer pump, hydrogen compressor, natural gas compressor, booster pump, condenser, first heater, second heater, ship main engine, support beam, load-bearing frame, connecting rod.

[0013] The liquid hydrogen tank is installed inside the LNG tank. The distance between the outer wall of the liquid hydrogen tank and the inner wall of the LNG tank is 1 / 30 to 1 / 20 of the ship's width in the horizontal direction along the ship's length and width, and the distance between the outer wall of the liquid hydrogen tank and the upper part of the inner wall of the LNG tank is 1.5 m to 2 m in the vertical direction.

[0014] The tank volumes of the liquid hydrogen tank and the LNG tank are equal.

[0015] The transfer pump is installed inside the LNG tank, and the transfer pump, booster pump, condenser, first heater, and ship main engine are connected in sequence through pipelines.

[0016] The hydrogen compressor, second heater, and ship main engine are connected in sequence through pipelines.

[0017] The natural gas compressor, condenser, and first heater are connected in sequence through pipelines.

[0018] The support beam is arranged between the liquid hydrogen tank and the LNG tank to play a supporting role.

[0019] The load-bearing frame is arranged below the liquid hydrogen tank and connected to the LNG tank to play a load-bearing role.

[0020] The connecting rod is arranged above the liquid hydrogen tank and connected to the LNG tank.

[0021] Among them, the liquid hydrogen tank and the LNG tank in the present invention are called combined cargo tanks.

[0022] The mass calculation of the liquid hydrogen and LNG carried in the liquid hydrogen tank and LNG tank is as follows:

[0023] Assume that the height from the bottom of the inner tank of the liquid hydrogen tank to the free liquid surface of liquid hydrogen is H, the height from the bottom of the outer tank of the liquid hydrogen tank to the free liquid surface of LNG is h, and the bottom area of the liquid hydrogen tank is S 1 , and the area of the "frame" formed by the outer wall of the liquid hydrogen tank and the inner wall of the LNG tank in the top view is S 2 , the density of LNG is ρ LNG , and the density of liquid hydrogen is The mass of the liquid hydrogen tank is m,

[0024] When the ship is fully loaded, the gravity of the liquid hydrogen and the liquid hydrogen tank is equal to the buoyancy of the LNG they receive, that is, the formula is satisfied

[0025]

[0026] The second object of the present invention is to propose a method for loading and unloading a combined cargo tank for transporting liquid hydrogen and LNG on a liquid cargo ship.

[0027] Method of loading at the loading port: During the loading process of the ship, first load a certain amount of LNG into the LNG tank to make the gravity of the liquid hydrogen tank equal to the buoyancy it receives, and then load liquid hydrogen and LNG into the liquid hydrogen tank and LNG tank simultaneously at a loading speed of 6S 1 : S 2 .

[0028] Method of unloading at the receiving station: First unload liquid hydrogen and LNG into the receiving station simultaneously at a unloading speed of 6S 1 : S 2 until the liquid hydrogen is unloaded completely, and then unload the LNG completely.

[0029] During the ship's voyage, the evaporation gas generated by LNG is first pressurized by a natural gas compressor, and then enters the condenser through a pipeline. The LNG used as the ship's fuel in the LNG tank is pumped out from the LNG tank by a barge pump, and then the LNG in the pipeline is pressurized by a booster pump, and then enters the condenser through the pipeline to be mixed with the natural gas. The natural gas is liquefied by using the cold energy of LNG, and then the two flow through the first heater for heating and vaporization. The liquid hydrogen evaporation gas generated in the liquid hydrogen tank first enters the second heater through a hydrogen compressor for heating, and then is sent to the ship's main engine for combustion together with the natural gas.

[0030] Advantages of the present invention:

[0031] 1. The present invention ingeniously places the liquid hydrogen tank in the LNG tank to achieve the combined transportation of liquid hydrogen and LNG. It uses a combined cargo tank to replace the original "necked-in" liquid cargo tank. Even if there is a free surface in the liquid hydrogen tank, the impact on the ship's stability is minimal, thus solving the problem of the free surface. At the same time, it solves the problem of waste of the internal space of the hull caused by the original liquid cargo tank, increases the effective cargo capacity of the liquid cargo ship, and improves the transportation volume of liquid hydrogen and LNG.

[0032] 2. By transporting liquid hydrogen and LNG through the combined cargo tank, the present invention can reduce the draft of the ship, thereby reducing the water depth requirements for the loading ports, receiving stations of liquid hydrogen and LNG and their corresponding waterways, and greatly reducing the construction and maintenance costs of ports and waterways.

[0033] 3. By transporting liquid hydrogen and LNG through the combined cargo tank, the ship does not need to inject ballast water like a liquid hydrogen ship even when fully loaded to increase stability, avoiding the additional fuel consumption caused by loading ballast water during the transportation process and reducing the transportation costs of liquid hydrogen and LNG. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 System diagram of the present invention;

[0035] Figure 2 Cross-sectional view of the combined cargo tank;

[0036] Figure 3 Schematic diagram of the combined cargo tank under the A-A section;

[0037] Figure 4 Longitudinal sectional view of a single combined cargo tank;

[0038] Figure 5 Distribution schematic diagram of the combined cargo tank on the ship;

[0039] In the drawings: 1. LNG tank; 2. Liquid hydrogen tank; 3. Barge pump; 4. Hydrogen compressor; 5. Natural gas compressor; 6. Booster pump; 7. Condenser; 8. First heater; 9. Second heater; 10. Ship main engine; 11. Support beam; 12. Load-bearing frame; 13. Connecting rod. DETAILED DESCRIPTION OF THE INVENTION

[0040] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0041] A combined cargo tank for a liquid cargo ship to transport liquid hydrogen and LNG, as Figure 1As shown, the system includes: an LNG tank 1, a liquid hydrogen tank 2, a transfer pump 3, a hydrogen compressor 4, a natural gas compressor 5, a booster pump 6, a condenser 7, a first heater 8, a second heater 9, a ship main engine 10, a support beam 11, a load-bearing frame 12, and a connecting rod 13.

[0042] The liquid hydrogen tank 2 is installed in the LNG tank 1. The distance between the outer wall of the liquid hydrogen tank 2 and the inner wall of the LNG tank 1 in the horizontal direction along the length and width of the ship is 1 / 30 to 1 / 20 of the ship width. The distance between the outer wall of the liquid hydrogen tank 2 and the upper part of the inner wall of the LNG tank 1 in the vertical direction is 1.5m to 2m. The liquid hydrogen tank 2 is connected to the inner wall of the LNG tank 1 in the horizontal direction through the support beam 11, and is connected to the inner wall of the LNG tank 1 at the bottom through the load-bearing frame 12. The tank capacities of the liquid hydrogen tank 2 and the LNG tank 1 are equal.

[0043] The transfer pump 3 is installed in the LNG tank 1, and the transfer pump 3 is used to transfer the fuel in the LNG tank 1; the transfer pump 3, the booster pump 6, the condenser 7, the first heater 8 and the ship's main engine 10 are connected in sequence through pipelines, wherein the booster pump 6 is used to pressurize the LNG fuel in the pipeline, the condenser 7 is used to liquefy the natural gas produced by the LNG, and the first heater 8 is used to heat the LNG to 40°C for supplying the ship's main engine 10 with fuel.

[0044] The hydrogen compressor 4, the second heater 9 and the ship main engine 10 are connected in sequence through pipelines, wherein the hydrogen compressor 4 is used to pressurize the hydrogen.

[0045] The natural gas compressor 5, the condenser 7 and the first heater 8 are connected in sequence through pipelines, wherein the natural gas compressor 5 is used to pressurize the natural gas.

[0046] The support beam 11 is provided between the bulkhead of the liquid hydrogen tank 2 and the LNG tank 1 to play a supporting role, thereby preventing the liquid hydrogen tank 2 from shaking when the ship rolls, and preventing the load-bearing frame 12 from being subjected to shear force.

[0047] The load-bearing frame 12 is arranged below the liquid hydrogen tank 2 and connected to the bottom of the LNG tank 1 to bear the load. The connecting rod 13 is arranged above the liquid hydrogen tank 2 and connected to the top of the LNG tank 1.

[0048] When the ship is unloaded, the support beam 11, the load-bearing frame 12 and the connecting rod 13 jointly resist the gravity of the liquid hydrogen tank 2, and minimize the tension, pressure and shearing force on the support beam 11, the load-bearing frame 12 and the connecting rod 13.

[0049] The mass calculation of liquid hydrogen and LNG carried by liquid hydrogen tank 2 and LNG tank 1 is as follows:

[0050] like Figure 2 , Figure 3 and Figure 4As shown, assuming that the height of liquid hydrogen from the bottom of the liquid hydrogen tank 2 to the free liquid surface is H, the height of LNG from the free liquid surface to the bottom of the liquid hydrogen tank 2 is h, and the bottom area of ​​the liquid hydrogen tank 2 is S 1 ,like Figure 3 The area of ​​the "frame" formed by the outer wall of the liquid hydrogen tank 2 and the inner wall of the LNG tank 1 is S 2 , the density of LNG is ρ LNG , the density of liquid hydrogen is The mass of the liquid hydrogen tank 2 is m. When the ship is fully loaded, the gravity of the liquid hydrogen and the liquid hydrogen tank 2 is equal to the buoyancy of the LNG, that is, the formula is satisfied. Because the thickness of the insulation layer of the liquid hydrogen tank 2 is very small, it is assumed during calculation that the bottom area inside the liquid hydrogen tank 2 is approximately equal to the bottom area outside the tank, and the influence of the thickness of the insulation layer can be ignored.

[0051] Theoretically, when the ship is fully loaded, the pressure or tension on the load-bearing frame 12 is 0. Even if liquid hydrogen and LNG produce evaporation gas during actual navigation, resulting in a certain amount of loss, the load-bearing frame 12 will only be subjected to extremely small pressure or tension due to the short navigation time and small evaporation amount. When the ship is unloaded, the weight of the empty tank of the liquid hydrogen tank 2 is relatively light, and the force on the load-bearing frame 12 is also very small.

[0052] The support beam 11, the load-bearing frame 12, and the connecting rod 13 are arranged at positions as follows: Figure 3 and Figure 4 shown.

[0053] A method for loading and unloading a combined cargo hold of liquid hydrogen and LNG in a liquid cargo ship: during the loading process of the ship, a certain amount of LNG is first loaded into the LNG tank 1 so that the gravity of the liquid hydrogen tank 2 is equal to the buoyancy it receives, and then the liquid hydrogen and LNG are simultaneously loaded into the LNG tank 1 at a speed of 6S. 1 :S 2 The liquid hydrogen and LNG are loaded into the liquid hydrogen tank 2 and the LNG tank 1 at the same time at a loading speed of 6S, so that the gravity of the liquid hydrogen tank 2 and the liquid hydrogen is equal to the buoyancy it receives during the loading process; similarly, during the unloading process of the ship, the liquid hydrogen and LNG are first loaded at a loading speed of 6S 1 :S 2 The liquid hydrogen and LNG are unloaded into the receiving station at the same time at a high unloading speed until the liquid hydrogen is unloaded, and then the LNG is unloaded. By this method, the pressure or tension on the load-bearing frame 12 and the connecting rod 13 during loading can be reduced to the greatest extent, thereby increasing the continuous working time of the combined cargo hold.

[0054] In the present invention, the force acting on the support beam 11, the load-bearing frame 12, and the connecting rod 13 is reduced, which is beneficial to reducing the sizes of the support beam 11, the load-bearing frame 12, and the connecting rod 13, reducing the use of low-temperature resistant materials, thereby reducing the cost, and being beneficial to the construction of the combined cargo hold. Moreover, reducing the size is beneficial to reducing the thermal bridge, that is, reducing the heat transfer of the support beam 11, the load-bearing frame 12, and the connecting rod 13, and reducing the evaporation amount of liquid hydrogen and LNG.

[0055] The arrangement mode of the combined cargo hold on the ship is as Figure 5 shown.

[0056] During the ship navigation process, the evaporated gas generated by LNG is first pressurized by the natural gas compressor 5, and then enters the condenser 7 through the pipeline. The LNG used as the ship fuel in the LNG tank 1 is pumped out from the LNG tank 1 by the barge pump 3, and then the LNG in the pipeline is pressurized by the booster pump 6, and then enters the condenser 7 through the pipeline, mixes with the natural gas compressed by the natural gas compressor 5, liquefies the natural gas by using the cold energy of LNG, and then the two flow through the first heater 8 for heating and vaporization together. The evaporated gas of liquid hydrogen generated in the liquid hydrogen tank 2 first enters the second heater 9 through the hydrogen compressor 4 for heating, and then mixes with the natural gas heated by the first heater 8 and is jointly transported to the ship main engine 10 for combustion.

[0057] Furthermore, since the liquid hydrogen tank 2 is installed above the LNG tank 1, and the horizontal distance between the outer wall of the liquid hydrogen tank 2 and the inner wall of the LNG tank 1 is very small, the free liquid surface of LNG is very small when the ship is fully loaded, approaching 0, and the free liquid surface of LNG hardly affects the stability of the ship. In addition, because the density of liquid hydrogen is very small, about 1 / 6 of the density of LNG, and the tank volumes of the liquid hydrogen tank 2 and the LNG tank 1 are equal, the center of gravity of the entire combined cargo hold when the ship is fully loaded is located in the LNG below the liquid hydrogen tank 2, and the center of gravity of LNG determines the center of gravity of the entire combined cargo hold. When the ship undergoes rolling motion, even if the free liquid surface of liquid hydrogen shifts, due to the large density and heavy mass of LNG, the shift of the center of gravity of the entire combined cargo hold is extremely small, that is, the influence of the free liquid surface existing in the liquid hydrogen tank 2 on the ship stability is negligible. Therefore, by transporting liquid hydrogen and LNG through the combined cargo hold, the problem that the free liquid surface has a great influence on the ship stability is solved without the cargo hold being designed into a "constricted type".

[0058] Furthermore, by making the shape of the liquid hydrogen tank 2 into an "open type", as Figure 2 shown, that is, the cross-sectional (cross-sectional) shape of the liquid hydrogen tank 2 is rectangular. Compared with the LNG tank and the liquid hydrogen tank of the same size, the loading capacity is large, greatly increasing the total tank volume of the LNG tank 1 and the liquid hydrogen tank 2, reducing the waste of the internal space of the ship, and improving the transportation volume of the liquid cargo ship.

[0059] Furthermore, by placing the liquid hydrogen tank 2 in the LNG tank 1 and transporting liquid hydrogen and LNG through the combined cargo hold, the ship does not need to inject ballast water like a liquid hydrogen ship to increase stability when fully loaded, avoiding the additional fuel consumption caused by loading ballast water during the transportation process and reducing the transportation costs of liquid hydrogen and LNG. Moreover, through combined transportation, the draft of the ship can be reduced. The ship will not have an excessive draft like an LNG ship, reducing the water depth requirements for the loading ports, receiving stations of liquid hydrogen and LNG and their corresponding waterways, and greatly reducing the construction and maintenance costs of ports and waterways.

[0060] Furthermore, a small amount of evaporated gas generated by liquid hydrogen and LNG during transportation can be transported together to the ship's main engine 10 for combustion. The mixed combustion of hydrogen and natural gas can effectively reduce the emission of greenhouse gas CO 2 and meet the requirements of green ships.

[0061] The specific implementation manner of the present invention is introduced above by taking a combined cargo hold as an example. All cargo holds in liquid hydrogen and LNG transport ships can apply the cargo hold of the present invention, and the implementation manners are the same as those above.

[0062] The above are only the preferred implementation manners of the present invention. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A combined cargo hold for a liquid cargo ship to transport liquid hydrogen and LNG, Characterized in that: The combined cargo hold includes an LNG tank (1), a liquid hydrogen tank (2), a transfer pump (3), a hydrogen compressor (4), a natural gas compressor (5), a booster pump (6), a condenser (7), a first heater (8), a second heater (9), a ship's main engine (10), a support beam (11), a load-bearing frame (12), and a connecting rod (13). The liquid hydrogen tank (2) is installed inside the LNG tank (1). The distance between the outer wall of the liquid hydrogen tank (2) and the inner wall of the LNG tank (1) is 1 / 30 to 1 / 20 of the ship's width in the horizontal direction along the ship's length and width. The distance between the outer wall of the liquid hydrogen tank (2) and the inner wall of the LNG tank (1) above is 1.5 m to 2 m in the vertical direction. The tank volumes of the LNG tank (1) and the liquid hydrogen tank (2) are equal. The transfer pump (3) is installed inside the LNG tank (1). The transfer pump (3), the booster pump (6), the condenser (7), the first heater (8), and the ship's main engine (10) are connected in sequence through pipelines. The hydrogen compressor (4), the second heater (9), and the ship's main engine (10) are connected in sequence through pipelines. The natural gas compressor (5), the condenser (7), and the first heater (8) are connected in sequence through pipelines. The support beam (11) is horizontally arranged between the liquid hydrogen tank (2) and the LNG tank (1). The load-bearing frame (12) is arranged below the liquid hydrogen tank (2) and connected to the bottom of the LNG tank (1). The connecting rod (13) is arranged above the liquid hydrogen tank (2) and connected to the top of the LNG tank (1). Let the height from the bottom of the inner cabin of the liquid hydrogen tank (2) to the free liquid surface of the liquid hydrogen be H, the height from the free liquid surface of the LNG to the bottom of the outer cabin of the liquid hydrogen tank (2) be h, and the bottom area of the liquid hydrogen tank (2) be S 1 , and the area formed by the outer wall of the liquid hydrogen tank (2) and the inner wall of the LNG tank (1) is in the shape of a "frame" and is S 2 , the density of the LNG is ρ LNG , the density of the liquid hydrogen is ρ LH2 , and the mass of the liquid hydrogen tank (2) is m When the ship is fully loaded, the gravity of the liquid hydrogen and the liquid hydrogen tank (2) is equal to the buoyancy of the LNG it receives, that is, S 1 Hρ LH2 g + mg = S 1 hρ LNG g.

2. A method for loading and unloading a combined cargo hold for a liquid cargo ship to transport liquid hydrogen and LNG, using the combined cargo hold according to claim 1. Characterized in that: During the loading process at the loading port, a certain amount of LNG is first loaded into the LNG tank (1). When the gravity of the liquid hydrogen tank (2) is equal to the buoyancy it receives, then liquid hydrogen and LNG are simultaneously loaded into the liquid hydrogen tank (2) and the LNG tank (1) at a loading speed of 6S 1 :S 2 .

3. According to the method for loading and unloading a combined cargo hold for a liquid cargo ship to transport liquid hydrogen and LNG according to claim 2, Characterized in that: During the unloading process at the receiving station, first unload the liquid hydrogen and LNG in the liquid hydrogen tank (2) and the LNG tank (1) into the receiving station at the same unloading speed of 6S 1 :S 2 until the liquid hydrogen is completely unloaded, and then unload the remaining LNG in the LNG tank (1).

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