System for storing ammonia fuel by using isolation cabin of LNG (Liquefied Natural Gas) transport ship

Abstract

The invention belongs to the technical field of ships, and particularly relates to a system for an LNG transport ship to store ammonia fuel through an isolation cabin. The system comprises an isolation cabin, a lightering pump, a supply valve, a circulating pump, a temperature sensor, a seawater heat exchanger, a seawater pump and a control unit. The ammonia fuel is stored in the isolation cabin of the LNG transport ship, heat exchange is carried out between the ammonia fuel in the isolation cabin of the LNG transport ship and external seawater, the temperature of the ammonia fuel in the isolation cabin is kept between-40 DEG C and-34 DEG C, a proper low-temperature environment is provided for the ammonia fuel, and the storage space problem of the ammonia fuel on the LNG transport ship is solved; and meanwhile, consumption of a high-grade heat source of the ship is avoided, and good economical efficiency is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ships, and in particular relates to an LNG transport ship storing an ammonia fuel system using an isolation tank. Background Art

[0002] As the impact of global climate change intensifies, the International Maritime Organization's requirements for greenhouse gas emissions from ships are becoming increasingly stringent, and "zero carbon" emissions in the shipping industry have become an urgent need. At present, merchant ships mainly use traditional fuels to install decarbonization devices, or carbon-free fuels, to solve the problem of ship emissions. These two methods achieve zero carbon emissions from ships. LNG carriers are also a type of merchant ship and face the same problems. Therefore, in order to invest less cost to meet the industry's "zero carbon" emissions, it is an ideal method for LNG carriers to use ammonia as a power fuel in the future.

[0003] LNG carrier (LNG carrier for short) refers to a ship that is specially used to transport liquefied natural gas. The density of LNG is usually 430kg / m 3 ~470kg / m 3 Since the density of LNG is relatively small, the storage space required is relatively large. For a fixed-size LNG carrier, in order to ensure that more LNG can be loaded, the LNG carrier must make full use of the effective space of the ship as much as possible. If the LNG carrier uses ammonia as a power fuel, the storage space that the ship can provide becomes extremely limited. In addition, in order to enhance the ship's anti-sinking and tank damage stability, multiple liquid cargo tanks are generally set up on the ship, and an isolation tank is set up between two adjacent liquid cargo tanks. The isolation tank is generally a narrow empty tank with only one rib spacing. Among them, the isolation tank of the LNG carrier has two important functions: one is to separate the two adjacent liquid cargo tanks; the other is to facilitate the installation of a heating system in the tank to prevent the steel plate between the adjacent liquid cargo tanks from increasing in brittleness due to too low temperature. If there is no isolation tank, the temperature of the steel plate between the two adjacent liquid cargo tanks can be close to the temperature of the LNG in the liquid cargo tank, reaching about -160°C, so low-temperature resistant stainless steel plates must be used. Although stainless steel plates can withstand low temperatures, because all the inner hulls of LNG carriers must be made of stainless steel, this method makes the ship expensive to build, so it is not adopted.

[0004] LNG is usually stored in a liquid form at -163℃ in an LNG cargo tank, with a temperature difference of about 200℃ from the surrounding environment. Although the bulkhead of the LNG cargo tank is provided with an insulation layer, the LNG stored inside it will still exchange heat with the outside through the insulation layer and the inner hull. For the inner hull on the port or starboard side, heat can be exchanged through the air or ballast water in the ballast tank, and then the air or ballast water will exchange heat with the outer hull on the port or starboard side of the ship, and finally the outer hull on the port or starboard side of the ship will exchange heat with the outside air or seawater outside the ship, so the temperature of the inner hull on the port or starboard side is relatively high and does not need to be heated. The cofferdam is a closed space with no air flow, and the cofferdam has a relatively small contact area with the outside world on the port or starboard side of the ship. Although the cofferdam will exchange heat through the air or ballast water in the ballast tank, and then the air or ballast water will exchange heat with the outer hull on the port or starboard side of the ship, and finally the outer hull on the port or starboard side of the ship will exchange heat with the outside air or seawater, the cofferdam will rarely exchange heat through the bulkhead on the port or starboard side of the ship; and because the cofferdam has a large contact area with the LNG cargo tank, the temperature of the LNG cargo tank is extremely low, and the LNG in the LNG cargo tank continuously absorbs the heat of the cofferdam, resulting in a continuous decrease in the temperature of the cofferdam bulkhead. When the temperature of the cofferdam bulkhead is too low, the brittleness of the cofferdam bulkhead will increase, thereby reducing the strength of the bulkhead. According to the literature "Research on Process Control and Microstructure Performance of High-Performance FH36 Ship Plate Steel" and "Analysis of Impact Fracture Behavior and Tough-Brittish Transition Temperature Curve of Ship Low-Temperature Steel", some ordinary ship steel plates still have high strength at -60℃~0℃, so the bulkhead material of the cofferdam is a steel plate that can maintain strength between -60℃~0℃. Usually, in order to avoid the bulkhead temperature of the cofferdam being too low, a corresponding heating coil is installed in the cofferdam. The ethylene glycol aqueous solution is heated by the high-grade heat source of the ship, and the high-temperature ethylene glycol aqueous solution is used as the heating medium to enter the heating coil, thereby heating the cofferdam, so that the temperature of the cofferdam is within the tolerance range of the ship steel plate, but this method will increase the consumption of the high-grade heat source of the ship, and it requires a large economic cost.

[0005] Ammonia is a clean energy source. Its combustion products are only nitrogen and water. It can achieve zero greenhouse gas emissions from ships and further meet the needs of the International Maritime Organization. Therefore, ammonia has good application prospects as a fuel for LNG carriers. However, ammonia fuel is flammable, explosive and corrosive. Compared with fuel oil, its storage requirements are more stringent. It cannot be stored in the double bottom of the ship or in the "corners" of the ship like fuel oil. Therefore, the storage location requirements of ammonia fuel are relatively high, and ammonia fuel usually needs to be stored at a low temperature of -33.6℃ on ships. Compared with other storage methods, low-temperature storage is more conducive to saving space. Not only that, the calorific value of fuel oil is 42kJ / kg and the density is 980kg / m 3, while the calorific value of ammonia fuel is 18.6kJ / kg and the density is 617kg / m 3 , if the same calorific value is achieved, the volume of ammonia fuel required is about 3.67 times the volume of fuel oil. In addition, ammonia fuel is stored at low temperatures and requires an insulation layer, so the volume of the ammonia fuel tank is about 4 times the volume of the fuel oil tank. In addition, LNG carriers have a high speed (about 19 knots), and because fuel consumption is proportional to the cube of speed, the fuel consumption is large (more than 100t / day), and the required fuel tank volume is also larger. Because the volume of ammonia fuel tanks is about 4 times the volume of fuel oil tanks, ships using ammonia fuel in the future will face the problem of larger fuel storage space.

[0006] Based on the above problems, the present invention proposes a system for storing ammonia fuel in an isolation tank on an LNG carrier. Since the bulkhead of the isolation tank can still maintain a relatively high strength between -60°C and 0°C, and the storage temperature of ammonia fuel is -33.6°C, if the ammonia fuel is stored at a low temperature in the isolation tank of the LNG carrier, not only can the storage temperature conditions of the ammonia fuel be met and the stability of the ammonia fuel be ensured, but the isolation tank also provides sufficient storage space for the ammonia fuel, thereby solving the problem of difficulty in storing ammonia fuel space on LNG carriers. Summary of the invention

[0007] The first object of the present invention is to propose an LNG carrier storing ammonia fuel system using an isolation tank based on the above-mentioned problem. The system includes a fuel supply system and a temperature control system.

[0008] Among them, the fuel supply system includes: isolation cabin, transfer pump, supply valve, processing unit and main engine.

[0009] The temperature control system includes: isolation cabin, circulation pump, temperature sensor, control unit, seawater heat exchanger and seawater pump.

[0010] In the fuel supply system, a transfer pump is provided at the bottom of the isolation tank; the transfer pump is connected to the supply valve, the processing unit and the main engine in sequence through pipelines. The ammonia fuel in the isolation tank of the LNG carrier enters the processing unit through the transfer pump and the supply valve, and the ammonia fuel is processed in the processing unit to reach the main engine combustion temperature and pressure before being sent to the ship's main engine for combustion.

[0011] In the temperature control system, ammonia fuel is stored in the isolation cabin, and the storage temperature of the ammonia fuel is -33.6°C. The bulkhead material of the isolation cabin is a steel plate that can maintain strength between -60°C and 0°C. A circulating pump is provided at the bottom of the isolation cabin; the circulating pump is connected to the seawater heat exchanger through a pipeline; the seawater heat exchanger is connected to the isolation cabin through a pipeline; the seawater pump is connected to the seawater heat exchanger through a pipeline; the temperature sensor is connected to the control unit; one side of the control unit is connected to the circulating pump, and the other side is connected to the seawater pump.

[0012] During the voyage of LNG carriers, LNG is usually stored in the LNG cargo tank in liquid form at -163℃, with a temperature difference of about 200℃ from the surrounding environment. Although the bulkhead of the LNG cargo tank is equipped with an insulation layer, the LNG stored inside it will still exchange heat with the outside world through the insulation layer and the inner hull, and the cofferdam is a closed space with no air flow, and the contact area between the cofferdam and the LNG cargo tank is large. Because the temperature of the LNG cargo tank is extremely low, the LNG in the LNG cargo tank continuously absorbs the heat of the cofferdam, resulting in a continuous decrease in the temperature of the cofferdam bulkhead. In order to prevent the bulkhead temperature of the cofferdam from being too low, the temperature of the ammonia fuel in the cofferdam of the LNG carrier will be adjusted through a seawater heat exchanger. The seawater pump draws seawater from the side of the ship as a heat exchange medium and enters the seawater heat exchanger. At the same time, the ammonia fuel in the cofferdam enters the seawater heat exchanger with the help of a circulating pump. The ammonia fuel exchanges heat with seawater in the seawater heat exchanger. After the heat exchange, the temperature of the ammonia fuel rises and then returns to the cofferdam through a pipeline. When the temperature sensor detects that the temperature in the isolation cabin is lower than -40℃, the temperature sensor will transmit a signal to the control unit, and the control unit will send instructions to the circulation pump and seawater pump to start the circulation pump and seawater pump, and exchange heat between seawater and ammonia fuel to increase the temperature of the ammonia fuel; when the temperature sensor detects that the temperature in the isolation cabin reaches -34℃, the circulation pump and seawater pump stop running, thereby ensuring that the temperature of the ammonia fuel in the isolation cabin is maintained between -40℃ and -34℃.

[0013] Beneficial effects of the present invention:

[0014] 1. The present invention stores ammonia fuel in the isolation tank of the LNG carrier, which solves the problem of storage space difficulty of ammonia fuel on the LNG carrier. At the same time, this storage method avoids the generation of BOG by the ammonia fuel in the isolation tank.

[0015] 2. The present invention exchanges heat between the ammonia fuel in the isolation tank of the LNG carrier and the external seawater, so that the temperature of the ammonia fuel in the isolation tank is maintained between -40°C and -34°C, replacing the traditional method of using the high-grade heat source of the ship to heat the ethylene glycol aqueous solution and then indirectly heating the isolation tank, and has better economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a system diagram of the present invention;

[0017] Figure 2 is a diagram of the fuel supply system of the isolation cabin of the present invention;

[0018] Figure 3 It is a schematic diagram of the position of the isolation cabin in the present invention;

[0019] In the attached figure: 1. Isolation compartment; 2. Transfer pump; 3. Circulation pump; 4. Temperature sensor; 5. Supply valve; 6. Seawater heat exchanger; 7. Seawater pump; 8. Control unit. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0021] An LNG carrier uses an isolation tank to store ammonia fuel system, which includes a fuel supply system and a temperature control system. Figure 3 As shown, LNG carriers usually have isolation tanks 1. Figure 1 Only the system diagram of one of the isolation chambers 1 is shown.

[0022] The fuel supply system includes: an isolation cabin 1, a transfer pump 2, a supply valve 5, a processing unit, and a main engine.

[0023] The temperature control system includes: an isolation cabin 1, a circulation pump 3, a temperature sensor 4, a seawater heat exchanger 6, a seawater pump 7, and a control unit 8.

[0024] In the fuel supply system, a transfer pump 2 is provided at the bottom of the isolation tank 1; the transfer pump 2 is connected to the supply valve 5, the processing unit, and the main engine in sequence through pipelines. The ammonia fuel in the isolation tank 1 of the LNG carrier enters the processing unit through the transfer pump 2 and the supply valve 5, and the ammonia fuel is processed in the processing unit to reach the main engine combustion temperature and pressure before being sent to the ship's main engine for combustion.

[0025] In the temperature control system, ammonia fuel is stored in the isolation cabin 1, and the storage temperature of the ammonia fuel is -33.6°C. The bulkhead material of the isolation cabin 1 is a steel plate that can maintain strength between -60°C and 0°C. A circulating pump 3 is provided at the bottom of the isolation cabin 1; the circulating pump 3 is connected to the seawater heat exchanger 6 through a pipeline; the seawater heat exchanger 6 is connected to the isolation cabin 1 through a pipeline; the seawater pump 7 is connected to the seawater heat exchanger 6 through a pipeline; the temperature sensor 4 is connected to the control unit 8; one side of the control unit 8 is connected to the circulating pump 3, and the other side is connected to the seawater pump 7; the temperature sensor 4 is located inside the isolation cabin 1, and is used to detect the temperature of the ammonia fuel in the isolation cabin 1.

[0026] During the voyage of the LNG carrier, the LNG (-163°C) stored in the cargo tank of the ship will exchange heat with the cofferdam 1, and the cofferdam 1 will continuously absorb the coldness of the LNG in the LNG cargo tank, so that the cofferdam 1 is in a low temperature environment. In order to prevent the bulkhead temperature of the cofferdam 1 from being too low, the temperature of the ammonia fuel in the cofferdam 1 of the LNG carrier will be adjusted through the seawater heat exchanger 6, and the seawater pump 7 will draw external seawater as a heat exchange medium into the seawater heat exchanger 6. At the same time, the ammonia fuel in the cofferdam 1 will enter the seawater heat exchanger 6 with the help of the circulation pump 3, and the ammonia fuel will exchange heat with the seawater in the seawater heat exchanger 6. After the heat exchange, the temperature of the ammonia fuel will rise, and then it will return to the cofferdam 1 through the pipeline. When the temperature sensor 4 detects that the temperature in the isolation cabin 1 is lower than -40°C, the temperature sensor 4 will transmit a signal to the control unit 8, and the control unit 8 will send instructions to the circulation pump 3 and the seawater pump 7 to start the circulation pump 3 and the seawater pump 7, and heat exchange between seawater and ammonia fuel will be carried out to increase the temperature of the ammonia fuel; when the temperature sensor 4 detects that the temperature in the isolation cabin 1 reaches -34°C, the circulation pump 3 and the seawater pump 7 stop running to ensure that the temperature of the ammonia fuel in the isolation cabin 1 is maintained between -40°C and -34°C.

[0027] In addition, in order to improve the ship's anti-sinking and damage stability, LNG carriers will be equipped with multiple liquid cargo tanks, and a cofferdam 1 will be provided between each liquid cargo tank. According to the literature "Research on Process Control and Microstructure Performance of High-Performance FH36 Ship Plate Steel" and "Analysis of Impact Fracture Behavior and Tough-Brittle Transition Temperature Curve of Marine Low-Temperature Steel", some ordinary marine steel plates still have high strength at -60℃~0℃. Therefore, the bulkhead material of the cofferdam 1 can be selected from a steel plate that can maintain strength between -60℃~0℃. At a temperature of -40℃~-34℃, the hull strength will not change much, and it can still maintain a high strength. The present invention exchanges heat between the ammonia fuel in the cofferdam 1 of the LNG carrier and the external seawater, so that the temperature of the ammonia fuel in the cofferdam 1 is maintained between -40℃~-34℃. Compared with the traditional method of using a high-grade heat source of a ship to heat the ethylene glycol aqueous solution and then indirectly heating the cofferdam 1, the present invention does not need to consume the high-grade heat source of the ship and has better economy.

[0028] However, ammonia fuel has the characteristics of flammability, explosiveness and corrosiveness, and its storage conditions are relatively harsh. When ammonia is used as a power fuel for LNG carriers, a special storage space must be set up on the ship. In addition, ammonia fuel usually needs to be stored at low temperatures on ships, and its storage temperature is -33.6°C. Low-temperature storage can avoid the generation of ammonia fuel BOG. ​​Most importantly, the speed of LNG carriers is relatively high, and a large amount of fuel will be burned during navigation, and the volume of the ammonia fuel tank is about 4 times the volume of the fuel tank, so ammonia fuel faces the problem of requiring more storage space. Therefore, the present invention makes full use of the space of the isolation tank 1 of the LNG carrier, and stores the ammonia fuel in the isolation tank 1, which solves the problem of the large storage space required for ammonia fuel on the LNG carrier. At the same time, this storage method can avoid the generation of BOG by the ammonia fuel in the isolation tank 1.

[0029] Taking an LNG carrier with a carrying capacity of 174,000 cubic meters as an example, the total length of the ship is 299 meters, the width is 46.4 meters, the depth is 26.25 meters, and the rated power of the ship's main engine is approximately 25,800 kW. If ammonia fuel is stored in the isolation tank 1 as the power fuel of the LNG carrier, the amount of ammonia fuel that can be stored in each isolation tank 1 is approximately 2000m 3 ~2400m 3 Since the ship is equipped with 4 LNG cargo tanks, it has 5 independent isolation tanks1, which can store a total of 10,000m 3 ~12000m 3 The ammonia fuel is about 18.6 kJ / kg and the density is 617 kg / m 3 According to calculations, the amount of ammonia fuel consumed by the ship in one day is about 400m 3 The amount of ammonia fuel consumed in 20 days of sailing is about 8000m 3 Therefore, storing ammonia fuel in the isolation tank 1 can fully meet the amount of fuel required by the LNG carrier during navigation. If the ammonia fuel in the isolation tank 1 is placed in other areas other than the isolation tank, it will seriously occupy the effective space of the ship, thereby reducing the cargo capacity of the ship.

[0030] The above is only a preferred embodiment 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 pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. An LNG carrier uses an isolation tank to store ammonia fuel system, characterized in that: The system comprises an isolation cabin (1), a transfer pump (2), a circulation pump (3), a temperature sensor (4), a supply valve (5), a seawater heat exchanger (6), a seawater pump (7), and a control unit (8). The isolation cabin (1) is used to store ammonia fuel. A circulation pump (3) is provided at the bottom of the isolation cabin (1); the circulation pump (3) is connected to the seawater heat exchanger (6) through a pipeline; the seawater heat exchanger (6) is connected to the isolation cabin (1) through a pipeline; the seawater pump (7) is connected to the seawater heat exchanger (6) through a pipeline; the temperature sensor (4) is connected to the control unit (8); one side of the control unit (8) is connected to the circulation pump (3) and the other side is connected to the seawater pump (7). A transfer pump (2) is provided at the bottom of the isolation cabin (1); the transfer pump (2) is connected to the supply valve (5), the processing unit, and the main engine in sequence through pipelines.

2. The LNG carrier according to claim 1 uses an isolation tank to store ammonia fuel system, characterized in that: The temperature in the isolation cabin (1) is controlled between -40°C and -34°C.

3. The LNG carrier according to claim 1 uses an isolation tank to store ammonia fuel system, characterized in that: The ammonia fuel in the isolation chamber (1) enters the seawater heat exchanger (6) through the circulation pump (3), exchanges heat with seawater in the seawater heat exchanger (6), and then returns to the isolation chamber (1) through the pipeline; When the temperature sensor (4) detects that the temperature in the isolation cabin (1) is lower than -40°C, the temperature sensor (4) transmits a signal to the control unit (8), and the control unit (8) controls the circulation pump (3) and the seawater pump (7) to start, so that the temperature of the ammonia fuel is increased by heat exchange between the seawater and the ammonia fuel; when the temperature sensor (4) detects that the temperature in the isolation cabin (1) reaches -34°C, the circulation pump (3) and the seawater pump (7) stop running.

Images