An LNG gas supply system for dual-fuel ships

Abstract

The present invention provides an LNG gas supply system for a dual-fuel vessel, comprising a fuel tank, and a first pipeline and a second pipeline respectively connected to the fuel tank, wherein the first pipeline is used to transport LNG, and the second pipeline is used to transport BOG. The LNG gas supply system provided by the present invention utilizes direct steam heating and direct fresh water cooling to heat and cool LNG and BOG, resulting in a fast temperature regulation response without any lag, and can supply gas to gas-consuming equipment such as dual-fuel main engines, generators, and boilers. Furthermore, the outlet temperature of the forced evaporator, gas heater, and preheater is controlled by flow control, fully utilizing the energy of the gas. The system is simple to operate, has a wide adjustment range, and a fast response, without the need for additional equipment. Finally, the gas supply system features a simple design, minimal equipment, low investment costs, and minimal onboard space, significantly reducing the vessel's daily operating energy consumption and saving costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of shipbuilding, and in particular relates to an LNG gas supply system for a dual-fuel ship. Background Art

[0002] In existing liquefied natural gas (LNG) dual-fuel gas supply systems, indirect heating and cooling of the gas and boil-off gas is typically employed. This involves first using steam to heat or fresh water to cool a water-glycol mixture, which is then used as an intermediate medium to heat or cool the gas. Consequently, two water-glycol systems are typically required: a high-temperature water-glycol system for vaporizing liquid LNG and heating the gas, and a low-temperature water-glycol system for heating the boil-off gas (BOG) to the compressor's permissible temperature before entering the compressor, as well as cooling the BOG during operation.

[0003] The above method adds two water glycol circuits, which results in a complex system design, multiple equipment, high investment costs, and a large space occupied on board. In addition, due to the indirect regulation method, when the gas demand changes, the gas temperature must be controlled by adjusting the temperature of the water glycol, resulting in slow system response, delayed temperature regulation, and large fluctuations in gas temperature. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the present invention provides an LNG gas supply system for dual-fuel vessels, comprising a fuel tank and a first pipeline and a second pipeline respectively connected to the fuel tank, wherein the first pipeline is used to transport LNG and the second pipeline is used to transport BOG. The LNG gas supply system provided by the present invention utilizes direct steam heating and direct fresh water cooling to heat and cool LNG and BOG, resulting in a fast temperature regulation response without any lag, and can achieve gas supply to gas-consuming equipment such as dual-fuel main engines, generators, and boilers. In addition, the outlet temperature of the forced evaporator, gas heater, and preheater is controlled by flow control, fully utilizing the energy of the gas. The system is simple to operate, has a wide adjustment range, and a fast response, without the need for additional equipment. Finally, the gas supply system has a simple design, requires minimal equipment, has low investment costs, and occupies little space on board, significantly reducing the energy consumption of the vessel's daily operations and saving costs.

[0005] To achieve the above and other related objectives, the present invention provides an LNG gas supply system for a dual-fuel ship, comprising:

[0006] a fuel tank, and a first pipeline and a second pipeline respectively connected to the fuel tank, wherein the first pipeline is used to transport liquefied natural gas and the second pipeline is used to transport boil-off gas;

[0007] The first pipeline is provided with a forced evaporator, a spray cooling pipe, and a gas heater, which are connected in sequence. The forced evaporator is connected to the fuel tank, and the gas heater is connected to the gas-consuming equipment. In addition, the fuel tank is also connected to the spray cooling pipe via a third pipeline, the spray cooling pipe is also connected to the gas-consuming equipment via a fourth pipeline, and the forced evaporator is also connected to the gas heater via a fifth pipeline.

[0008] The second pipeline is provided with a preheater, a BOG compressor and an aftercooler which are connected in sequence. The preheater is connected to the fuel tank, and the aftercooler is connected to the gas-consuming equipment. In addition, the preheater is also connected to the aftercooler via a sixth pipeline. A three-way valve is provided between the BOG compressor and the aftercooler, and the three-way valve is connected to the preheater via a seventh pipeline.

[0009] Optionally, a first temperature sensor is provided at the outlet of the spray cooling pipe for detecting the temperature of the gas output by the spray cooling pipe and sending a first temperature signal.

[0010] Optionally, a first valve is provided on the third pipeline, and the first valve is communicatively connected to the first temperature sensor, for controlling the flow of the liquefied natural gas from the fuel tank into the spray cooling pipe according to the first temperature signal.

[0011] Optionally, a second temperature sensor is provided between the gas heater and the gas-consuming device, for detecting the temperature of the gas entering the gas-consuming device and sending a second temperature signal.

[0012] Optionally, a second valve is provided on the fourth pipeline, and the second valve is communicatively connected to the second temperature sensor, for controlling the flow of the gas entering the gas-consuming equipment from the spray cooling pipe according to the second temperature signal.

[0013] Optionally, the water vapor enters the forced evaporator through an eighth pipe, and a third valve is provided on the eighth pipe for controlling the flow of the water vapor entering the forced evaporator.

[0014] Optionally, a pressure sensor is provided between the third valve and the forced evaporator for detecting the pressure of the eighth pipeline and sending a pressure signal.

[0015] Optionally, the third valve is in communication with a pressure sensor, and the third valve controls the flow of the water vapor entering the forced evaporator according to the pressure signal.

[0016] Optionally, a steam trap group is provided on the fifth pipeline, and the water vapor heats the LNG in the forced evaporator and produces saturated condensate. The steam trap group is used to allow the saturated condensate to flow into the gas heater while blocking the uncondensed water vapor from entering the gas heater.

[0017] Optionally, a third temperature sensor is provided at the outlet of the preheater for detecting the temperature of the evaporated gas output by the preheater and sending a third temperature signal.

[0018] Optionally, the three-way valve is communicatively connected to the third temperature sensor, and is configured to control the flow rate of the boil-off gas from the BOG compressor into the preheater according to the third temperature signal.

[0019] The LNG gas supply system for dual-fuel ships provided by the present invention has at least the following beneficial effects:

[0020] 1. Utilizing direct steam heating and fresh water cooling, the system eliminates the traditional water-glycol intermediate loop, enabling complete heating and cooling of both LNG and BOG. Temperature regulation is responsive and hysteresis-free, enabling gas supply to dual-fuel main engines, generators, boilers, and other gas-consuming equipment. The system boasts a simple design, minimal equipment, low investment costs, and minimal onboard space, significantly reducing energy consumption and cost savings during daily vessel operations.

[0021] 2. The BOG preheater in this system uses high-temperature BOG gas compressed by the BOG compressor as a heat source and low-temperature BOG gas from the fuel tank as a cooling source. This fully utilizes both the thermal energy of the high-temperature BOG gas and the cooling energy carried by the low-temperature BOG gas. The BOG preheater requires no additional energy input and reduces the aftercooler's demand for liner water cooling.

[0022] 3. The outlet temperature of the forced evaporator, gas heater and preheater is controlled by adjusting the flow rate. It is simple to operate, has a large adjustment range, fast response, and does not require additional equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of an LNG gas supply system for a dual-fuel ship provided as an embodiment is shown.

[0024] Component number description

[0025] 11 First Pipeline

[0026] 12 Second Pipeline

[0027] 13 Third Pipeline

[0028] 14 The Fourth Pipeline

[0029] 15 The Fifth Pipe

[0030] 16 Sixth Pipeline

[0031] 17 Seventh Pipe

[0032] 18 The Eighth Pipe

[0033] 19 Ninth Pipe

[0034] 21 First temperature sensor

[0035] 22 Second temperature sensor

[0036] 23 Third temperature sensor

[0037] 30 pressure sensor

[0038] 41 First Valve

[0039] 42 Second Valve

[0040] 43 Third valve

[0041] 44 Three-way valve DETAILED DESCRIPTION

[0042] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0043] It should be noted that the illustrations provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Although the illustrations only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation, the form, quantity, positional relationship and proportion of each component in actual implementation can be changed at will under the premise of realizing the technical solution of this party, and the component layout form may also be more complicated.

[0044] Example

[0045] This embodiment provides an LNG gas supply system for dual-fuel ships, such as Figure 1As shown, it includes a fuel tank, and a first pipeline 11 and a second pipeline 12 respectively connected to the fuel tank, wherein the first pipeline 11 is used to transport liquefied natural gas (LNG), and is provided with a forced evaporator, a spray cooling pipe and a gas heater connected in sequence. The forced evaporator is connected to the fuel tank, and the gas heater is connected to the gas-consuming equipment; the second pipeline 12 is used to transport boil-off gas (BOG), and is provided with a preheater, a BOG compressor and an aftercooler connected in sequence. The preheater is connected to the fuel tank, and the aftercooler is connected to the gas-consuming equipment.

[0046] like Figure 1 As shown, the forced evaporator is connected to the fuel tank and the spray cooling pipe respectively through the first pipe 11. When the ship is sailing normally or in port, low-temperature (about -163°C) LNG is pumped from the fuel tank to the forced evaporator, heated and evaporated into gas in the forced evaporator, and then enters the spray cooling pipe for cooling.

[0047] like Figure 1 As shown, the fuel tank is also connected to the spray cooling pipe via a third pipe 13. This allows some low-temperature LNG (approximately -163°C) to enter the spray cooling pipe as a cooling medium through the third pipe 13 to spray-cool the gas, while simultaneously bringing the mixed gas temperature to approximately -20°C. A first temperature sensor 21 is provided at the outlet of the spray cooling pipe to detect the temperature of the mixed gas output from the spray cooling pipe and transmit a first temperature signal. A first valve 41 is provided on the third pipe 13 and is in communication with the first temperature sensor 21. The first valve 41 controls the flow of LNG from the fuel tank into the spray cooling pipe based on the first temperature signal.

[0048] As an example, when the temperature measured by the first temperature sensor 21 is higher than -20°C, a first temperature signal is sent to the first valve 41, and the opening of the first valve 41 increases, allowing more low-temperature (temperature of about -163°C) LNG to enter the spray cooling pipe through the third pipeline 13 to spray cool the gas, so that the temperature of the mixed gas reaches about -20°C.

[0049] like Figure 1As shown, water vapor enters the forced evaporator through the eighth pipe 18. A third valve 43 is provided on the eighth pipe 18 to control the flow of water vapor entering the forced evaporator. A pressure sensor 30 is provided between the third valve 43 and the forced evaporator to detect the pressure in the eighth pipe 18 and transmit a pressure signal. The third valve 43 is in communication with the pressure sensor 30 and controls the flow of water vapor entering the forced evaporator based on the pressure signal. The forced evaporator is also connected to the gas heater via the fifth pipe 15, which is equipped with a steam trap assembly.

[0050] For example, high-temperature, high-pressure (approximately 6.5 barg, approximately 165°C) steam from the boiler passes through third valve 43, where it is cooled and decompressed (approximately 1.2 barg, approximately 120°C) before entering the forced evaporator. This steam acts as a heat source, directly heating the LNG in the forced evaporator by releasing its latent heat of vaporization. The condensate is then condensed into saturated condensate. The saturated condensate then flows through the steam trap assembly into the gas heater, where it continues to serve as a heating medium for heating the gas. The steam trap assembly allows the saturated condensate to flow into the gas heater while preventing uncondensed water vapor from entering the heater. When the gas demand from the gas-consuming equipment decreases, the amount of saturated condensate decreases, and the pressure within the eighth pipeline 18 increases. When the pressure sensor 30 measures a line pressure greater than the set value (approximately 1.2 barg), it sends a pressure signal to the third valve 43, causing it to open more narrowly, thereby reducing the flow of water vapor into the forced evaporator.

[0051] like Figure 1 As shown, the gas heater is connected to the spray cooling pipe and the gas-consuming equipment respectively through a first pipe 11. The gas output from the spray cooling pipe (temperature of approximately -20°C) flows into the gas heater for continued heating until it meets the needs of the gas-consuming equipment and then flows into the gas-consuming equipment. A second temperature sensor 22 is provided between the gas heater and the gas-consuming equipment to detect the temperature of the gas entering the gas-consuming equipment and to transmit a second temperature signal. The spray cooling pipe is also connected to the gas-consuming equipment via a fourth pipe 14. A second valve 42 is provided on the fourth pipe 14, and the second valve 42 is in communication with the second temperature sensor 22 to control the flow of gas from the spray cooling pipe into the gas-consuming equipment based on the second temperature signal.

[0052] For example, when the gas temperature measured by second temperature sensor 22 exceeds 40°C, a second temperature signal is sent to second valve 42, causing the valve 42 to open wider. This allows more gas (at a temperature of approximately -20°C) not heated by the gas heater to serve as a cooling source. This gas, which flows through fourth conduit 14, cools the gas output from the gas heater until the final mixed gas reaches the required temperature before flowing into the gas-consuming device. In this embodiment, the required temperature of the gas-consuming device is approximately 40°C.

[0053] like Figure 1 As shown, the gas heater is connected to the forced evaporator through the fifth pipe 15. The steam trap group provided on the fifth pipe 15 allows the saturated condensate produced in the forced evaporator to flow into the gas heater. The saturated condensate (temperature of about 120°C) is used as a heating medium in the gas heater to directly heat the gas (temperature of about -20°C) output from the spray cooling pipe. The heated saturated condensate is output through the ninth pipe 19.

[0054] like Figure 1 As shown, the fuel tank, preheater, BOG compressor, aftercooler, and user equipment are sequentially connected via a second pipeline 12. Due to external heat intrusion and sloshing, excessive low-temperature BOG (-140°C) is generated in the fuel tank. The low-temperature BOG flows through the second pipeline 12 into the preheater for heating until it meets the input temperature requirement of the BOG compressor. It then flows through the second pipeline 12 into the BOG compressor for pressurization and temperature increase, then into the aftercooler for cooling, before finally flowing into the gas-consuming equipment. In this embodiment, the required input temperature of the BOG compressor is approximately -20°C.

[0055] like Figure 1 As shown, the preheater is also connected to the aftercooler via a sixth pipe 16. A three-way valve 44 is provided between the BOG compressor and the aftercooler. The three-way valve 44 is connected to the preheater via a seventh pipe 17. A third temperature sensor 23 is provided at the outlet of the preheater to detect the temperature of the BOG output from the preheater and generate a third temperature signal. The three-way valve 44 is communicatively connected to the third temperature sensor 23 to control the flow rate of BOG entering the preheater from the BOG compressor based on the third temperature signal.

[0056] For example, the temperature of BOG after being pressurized and heated by the BOG compressor is approximately 100°C, higher than the required temperature of the gas-consuming equipment and requiring cooling. Simultaneously, the low-temperature BOG in the preheater needs to be heated. Therefore, the high-temperature, high-pressure BOG output from the BOG compressor is split by a three-way valve 44, with one portion flowing to the aftercooler. The other portion flows through the seventh pipeline 17 as a heat source into the preheater, heating the low-temperature BOG in the preheater while cooling itself. The combined BOG flows out through the sixth pipeline 16, where it merges with the high-temperature, high-pressure BOG flowing to the aftercooler before flowing into the gas-consuming equipment. In this embodiment, a third temperature sensor 23 detects the temperature of the BOG output from the preheater and sends a third temperature signal to the three-way valve 44. The three-way valve 44 controls the flow of the high-temperature, high-pressure BOG into the seventh pipeline 17 based on the third temperature signal.

[0057] As an example, the aftercooler has a fresh water inlet and a fresh water outlet (not shown in the figure), and uses fresh water from the main engine cylinder jacket water circulation system as a cooling source.

[0058] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. An LNG gas supply system for dual-fuel ships, characterized in that: include: a fuel tank, and a first pipeline and a second pipeline respectively connected to the fuel tank, wherein the first pipeline is used to transport liquefied natural gas and the second pipeline is used to transport boil-off gas; The first pipeline is provided with a forced evaporator, a spray cooling pipe, and a gas heater, which are connected in sequence. The forced evaporator is connected to the fuel tank, and the gas heater is connected to the gas-consuming equipment. In addition, the fuel tank is also connected to the spray cooling pipe via a third pipeline, the spray cooling pipe is also connected to the gas-consuming equipment via a fourth pipeline, and the forced evaporator is also connected to the gas heater via a fifth pipeline. The fifth pipeline is provided with a steam trap group. The second pipeline is provided with a preheater, a BOG compressor and an aftercooler which are connected in sequence. The preheater is connected to the fuel tank, and the aftercooler is connected to the gas-consuming equipment. In addition, the preheater is also connected to the aftercooler via a sixth pipeline. A three-way valve is provided between the BOG compressor and the aftercooler, and the three-way valve is connected to the preheater via a seventh pipeline.

2. The LNG gas supply system for a dual-fuel ship according to claim 1, characterized in that: The outlet of the spray cooling pipe is provided with a first temperature sensor for detecting the temperature of the gas outputted by the spray cooling pipe and sending a first temperature signal.

3. The LNG gas supply system for a dual-fuel ship according to claim 2, characterized in that: The third pipeline is provided with a first valve, and the first valve is in communication with the first temperature sensor, and is used to control the flow of the liquefied natural gas from the fuel tank into the spray cooling pipe according to the first temperature signal.

4. The LNG gas supply system for a dual-fuel ship according to claim 1, characterized in that: A second temperature sensor is provided between the gas heater and the gas-consuming device, for detecting the temperature of the gas entering the gas-consuming device and sending a second temperature signal.

5. The LNG gas supply system for a dual-fuel ship according to claim 4, characterized in that: A second valve is provided on the fourth pipeline, and the second valve is in communication with the second temperature sensor, and is used to control the flow of the gas entering the gas-consuming equipment from the spray cooling pipe according to the second temperature signal.

6. The LNG gas supply system for a dual-fuel ship according to claim 1, characterized in that: The water vapor enters the forced evaporator through an eighth pipe. The eighth pipe is provided with a third valve for controlling the flow of the water vapor entering the forced evaporator.

7. The LNG gas supply system for a dual-fuel ship according to claim 6, characterized in that: A pressure sensor is provided between the third valve and the forced evaporator for detecting the pressure of the eighth pipeline and sending a pressure signal.

8. The LNG gas supply system for a dual-fuel ship according to claim 7, characterized in that: The third valve is in communication with the pressure sensor, and the third valve controls the flow of the water vapor entering the forced evaporator according to the pressure signal.

9. The LNG gas supply system for a dual-fuel ship according to claim 8, characterized in that The water vapor heats the LNG in the forced evaporator and generates saturated condensate. The steam trap assembly is used to allow the saturated condensate to flow into the gas heater while preventing the uncondensed water vapor from entering the gas heater.

10. The LNG gas supply system for a dual-fuel ship according to claim 1, characterized in that: A third temperature sensor is provided at the outlet of the preheater for detecting the temperature of the evaporated gas output by the preheater and sending a third temperature signal.

11. The LNG gas supply system for a dual-fuel ship according to claim 10, characterized in that: The three-way valve is in communication with the third temperature sensor and is configured to control a flow rate of the boil-off gas from the BOG compressor into the preheater according to the third temperature signal.

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