LNG supercooling system based on natural gas hydrogen-doped engine gas supply system and LNG ship

Abstract

The invention discloses an LNG subcooling system based on a natural gas hydrogen-doped engine gas supply system and an LNG ship. The LNG subcooling system comprises an LNG storage tank, an LNG pump, an LNG subcooling valve, an LNG subcooler, a liquid hydrogen storage tank, a liquid hydrogen pump, an LNG subcooling pipeline, a hydrogen pipeline, a hydrogen pipeline branch, a liquid hydrogen pipeline and a liquid hydrogen branch, and the LNG subcooler conducts subcooling through hydrogen and / or liquid hydrogen. The LNG ship is provided with the natural gas hydrogen-doped engine gas supply system and the LNG supercooling system of the natural gas hydrogen-doped engine gas supply system. The hydrogen serves as a main cold source, the liquid hydrogen serves as a supplementary cold source, the hydrogen side cold source can be reasonably allocated under various working conditions, it is guaranteed that the LNG subcooler is always kept in the optimal cooling effect interval in the heat exchange process, and stability and energy efficiency improvement of the LNG subcooling process are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas hydrogen blending engine gas supply, and particularly relates to an LNG subcooling system based on a natural gas hydrogen blending engine gas supply system and an LNG ship. BACKGROUND

[0002] In the natural gas hydrogen blending engine gas supply system, LNG is usually stored in a low-temperature vacuum adiabatic storage tank (typical storage temperature is about -162 DEG C, and pressure is about 0.1-1.0 MPa). However, due to the physical limit of the current adiabatic technology, the continuous leakage of external environmental heat into the storage tank is inevitable, thereby causing part of the LNG in the tank to absorb heat and vaporize to generate flash gas (BOG). More importantly, during the system operation, the pump working for LNG delivery will convert part of mechanical energy into heat energy and introduce it into the liquid, which further aggravates the vaporization of LNG and becomes an important source of BOG.

[0003] The continuous generation of BOG causes the internal pressure of the storage tank to continuously rise, which directly threatens the safe operation of the storage tank. In order to ensure safety, the traditional method is often forced to directly discharge excess BOG to the atmosphere or treat it by burning through a flare. However, this method has obvious disadvantages: on the one hand, it causes direct waste of valuable energy and emission of environmental pollutants (such as unburned methane); on the other hand, it also limits the ability of the system to operate stably for a long time without external discharge.

[0004] In order to overcome the above problems, various BOG treatment schemes have been proposed in the prior art, but they all have their own limitations: Direct diffusion or burning method: this method is simple in device and quick in response, but it wastes a lot of energy and has safety and environmental hazards, which does not comply with the principles of green and efficient energy utilization; External refrigeration recondensation method: the BOG is condensed by an independent external refrigeration system and then returned to the storage tank, but this method has high energy consumption, and the system structure is complex and the dynamic response is slow, which is difficult to adapt to the working conditions of rapid pressure fluctuation of the storage tank, and the operation is not economical.

[0005] Throttling and reliquefaction coupling process: the throttling expansion refrigeration effect and multi-stage heat exchange are used to realize the reliquefaction of BOG, and the technical process is complex, which requires high system design and control, resulting in high debugging and maintenance costs, and poor applicability in small and medium-sized or mobile application scenarios.

[0006] Engine gas consumption method: the BOG is introduced into the engine as fuel for consumption. This method realizes energy recovery, but its consumption capacity completely depends on the working condition of the engine. When the engine is in low load operation or shutdown state, this method is invalid, and it cannot be used as an independent pressure maintaining means, and other pressure control measures are still needed, so the system reliability is insufficient. SUMMARY

[0007] In view of the defects in the prior art, the present application provides a LNG supercooling system based on a natural gas hydrogen blending engine gas supply system to solve the above technical problems.

[0008] In order to achieve the above-mentioned purposes, the technical solutions of the present application are as follows: The LNG supercooling system based on the natural gas hydrogen blending engine gas supply system comprises an LNG storage tank, an LNG pump, an LNG supercooling valve, an LNG supercooler, a liquid hydrogen storage tank, a liquid hydrogen pump, an LNG supercooling pipeline, a hydrogen pipeline, a hydrogen pipeline branch, a liquid hydrogen pipeline and a liquid hydrogen branch, and the LNG supercooler is supercooled by hydrogen and / or liquid hydrogen. The LNG supercooling pipeline is sequentially connected with the liquid phase outlet of the LNG storage tank, the LNG pump, the LNG supercooling valve, the LNG inlet of the LNG supercooler, the LNG outlet of the LNG supercooler and the liquid phase inlet of the LNG storage tank; the hydrogen outlet of the liquid hydrogen storage tank is communicated with the inlet of a hydrogen compression supply circuit in the natural gas hydrogen blending engine gas supply system through the hydrogen pipeline, a hydrogen branch is arranged on the hydrogen pipeline, the hydrogen branch is sequentially connected with the hydrogen outlet of the liquid hydrogen storage tank, the hydrogen inlet of the LNG supercooler, the hydrogen outlet of the LNG supercooler and the inlet of the hydrogen compression supply circuit, and the junction points of the hydrogen branch and the hydrogen pipeline are respectively between the hydrogen outlet of the liquid hydrogen storage tank and the hydrogen inlet of the LNG supercooler and between the hydrogen outlet of the LNG supercooler and the inlet of the hydrogen compression supply circuit; the liquid hydrogen pipeline is sequentially connected with the liquid outlet of the liquid hydrogen storage tank, the liquid hydrogen pump and the inlet of a hydrogen forced heat exchange supply circuit in the natural gas hydrogen blending engine gas supply system, a liquid hydrogen branch is arranged on the liquid hydrogen pipeline, and the liquid hydrogen branch is sequentially connected with the liquid hydrogen outlet of the liquid hydrogen storage tank, the liquid hydrogen inlet of the LNG supercooler, the liquid hydrogen outlet of the LNG supercooler and the inlet of the hydrogen forced heat exchange supply circuit, and the junction points of the liquid hydrogen branch and the liquid hydrogen pipeline are respectively between the liquid hydrogen outlet of the liquid hydrogen storage tank and the liquid hydrogen inlet of the LNG supercooler and between the liquid hydrogen outlet of the LNG supercooler and the inlet of the hydrogen forced heat exchange supply circuit.

[0009] In an embodiment, a pressure sensor for measuring the pressure in the tank is arranged in the LNG storage tank, and the pressure sensor is electrically connected with the LNG pump and the LNG supercooling valve; when the measured value of the pressure sensor is higher than a pressure setting value, the LNG pump and the LNG supercooling valve are opened; when the measured value of the pressure sensor is not higher than the pressure setting value, the LNG pump and the LNG supercooling valve are closed.

[0010] In an embodiment, the hydrogen pipeline is provided with a hydrogen gas phase valve, the hydrogen branch pipeline is provided with a hydrogen subcooling valve, the hydrogen subcooling valve is arranged between the hydrogen branch pipeline and the hydrogen pipeline at the junction point and the hydrogen inlet of the LNG subcooler; the liquid hydrogen pipeline is provided with a liquid hydrogen supply valve, the liquid hydrogen branch pipeline is provided with a liquid hydrogen subcooling valve, and the liquid hydrogen subcooling valve is arranged between the liquid hydrogen branch pipeline and the liquid hydrogen pipeline at the junction point and the liquid hydrogen inlet of the LNG subcooler.

[0011] In an embodiment, the LNG subcooling pipeline is provided with a temperature sensor for measuring the temperature of LNG at the LNG outlet of the LNG subcooler, the temperature sensor is arranged at the LNG outlet of the LNG subcooler, and the hydrogen gas phase valve, the hydrogen subcooling valve, the liquid hydrogen supply valve and the liquid hydrogen subcooling valve are electrically connected with the temperature sensor.

[0012] In an embodiment, when the temperature sensor measurement value is lower than the low temperature threshold value, the opening degrees of the hydrogen gas phase valve, the hydrogen subcooling valve, the liquid hydrogen supply valve and the liquid hydrogen subcooling valve are maintained; when the temperature sensor measurement value is between the low temperature threshold value and the high temperature threshold value, the opening degree of the hydrogen subcooling valve is adjusted to continuously change the gaseous hydrogen flow, the heat exchange intensity is finely controlled, and the LNG outlet temperature is stabilized in the set range; when the temperature sensor measurement value is higher than the high temperature threshold value, the opening degree of the liquid hydrogen subcooling valve is increased.

[0013] In an embodiment, the LNG subcooler is a multi-channel heat exchanger, the LNG subcooler is provided with an LNG channel, a hydrogen channel and a liquid hydrogen channel, the flow directions of the media in the hydrogen channel and the liquid hydrogen channel are consistent, and the flow direction of the medium in the LNG channel is opposite to that in the liquid hydrogen channel.

[0014] In an embodiment, the LNG channel is arranged between the hydrogen channel and the liquid hydrogen channel, and the LNG subcooler is a welded aluminum plate fin structure heat exchanger.

[0015] The application also provides an LNG ship provided with a natural gas hydrogen blending engine gas supply system and the LNG subcooling system based on the natural gas hydrogen blending engine gas supply system.

[0016] Compared with the prior art, the application has at least the following beneficial effects: Dual cold source high-efficiency heat exchange: the application introduces gaseous hydrogen in the liquid hydrogen storage tank and liquid hydrogen as dual low-temperature cold sources, combines a specially designed plate fin heat exchanger, and constructs a set of LNG subcooling system which can efficiently realize LNG subcooling. The LNG subcooler adopts a three-way countercurrent partition plate heat exchange structure, takes hydrogen as the main cold source and liquid hydrogen as the supplementary cold source, fully utilizes the low-temperature cold energy of the hydrogen side, flexibly switches between the "only hydrogen subcooling" mode and the "hydrogen + liquid hydrogen combined subcooling" mode under different operating conditions, meets the BOG liquefaction demand, and also considers system energy efficiency optimization.

[0017] Differential hierarchical control: LNG flow path implements on-off control based on tank pressure, starts and stops the subcooling cycle when the pressure reaches the set threshold, to quickly respond to tank pressure fluctuations, achieve BOG suppression and liquid return pressure reduction; the hydrogen cold source flow path is continuously proportionally adjusted according to the outlet temperature of the subcooler, by dynamically adjusting the hydrogen flow and introducing liquid hydrogen cold source when necessary, to ensure that the heat exchange process is always in the optimal cooling interval. By integrating pressure sensors and temperature sensors, the system establishes an integrated automatic control mechanism of "tank pressure triggering-temperature correction", which can reasonably allocate hydrogen side cold sources under various working conditions, ensure that the LNG subcooler always maintains in the optimal cooling effect interval during the heat exchange process, and guarantee the stability and energy efficiency improvement of the LNG subcooling process. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a structural schematic diagram of the LNG subcooling system based on the natural gas hydrogen blending engine gas supply system in the embodiments of the present application; Figure 2 is a schematic diagram of the LNG tank pressure control process in the embodiments of the present application; Figure 3 is a schematic diagram of the temperature control process of the LNG outlet temperature of the LNG subcooler in the embodiments of the present application.

[0019] Reference signs: 1, LNG tank; 2, LNG pump; 3, LNG subcooling valve; 4, LNG subcooler; 5, liquid hydrogen tank; 6, liquid hydrogen pump; 7, liquid hydrogen subcooling valve; 8, liquid hydrogen gas supply valve; 9, hydrogen gas subcooling valve; 10, hydrogen gas gas phase valve; 11, LNG subcooling pipeline; 12, hydrogen pipeline; 1201, hydrogen branch; 13, liquid hydrogen pipeline; 1301, liquid hydrogen branch; 14, pressure sensor; 15, temperature sensor. DETAILED DESCRIPTION

[0020] In order to make the objects, technical solutions, and advantages of the present application clearer, the following will describe the present application through specific embodiments shown in the drawings. However, it should be understood that these descriptions are only exemplary, and are not intended to limit the scope of the present application. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present application.

[0021] The terms used in the present disclosure are merely for the purpose of describing specific embodiments, and are not intended to limit the present disclosure. The singular forms "a", "said" and "the" used in the present 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" used herein means and includes any or all possible combinations of one or more associated listed items.

[0022] It should be understood that, although the terms first, second, third, etc. can be employed in this disclosure to describe various information, these information should not be limited to these terms, and should not be understood as indicating or implying relative importance. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the disclosure, the first information can also be referred to as the second information, and similarly, the second information can also be referred to as the first information. Depending on the context, the word "if" as used herein can be interpreted as "when" or "upon determination" or "in response to determining".

[0023] In the description of the present application, unless otherwise specified and limited, it should be understood that the terms "mounting", "connecting", "connecting" should be understood in a broad sense, for example, it can be mechanical connection, or the communication between the internal elements, or direct connection, or indirect connection through intermediate medium, and those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0024] In order to better understand the technical scheme of the present application, the present application will be described in detail below in combination with the drawings.

[0025] As Figure 1 described, the present application provides a LNG supercooling system based on a natural gas hydrogen blending engine gas supply system, comprising an LNG storage tank 1, an LNG pump 2, an LNG supercooling valve 3, an LNG supercooler 4, a liquid hydrogen storage tank 5, a liquid hydrogen pump 6, an LNG supercooling pipeline, a hydrogen pipeline 12, a hydrogen pipeline branch 1201, a liquid hydrogen pipeline 13 and a liquid hydrogen branch 1301, the LNG supercooler 4 uses hydrogen and / or liquid hydrogen to supercool the LNG.

[0026] The LNG subcooling pipeline 11 is sequentially connected to the liquid phase outlet of LNG storage tank 1, LNG pump 2, LNG subcooling valve 3, LNG inlet of LNG subcooler 4, LNG outlet of LNG subcooler 4, and liquid phase inlet of LNG storage tank 1. The hydrogen outlet of liquid hydrogen storage tank 5 is connected to the inlet of the hydrogen compression supply circuit in the natural gas blending engine supply system via hydrogen pipeline 12. Hydrogen pipeline 12 is equipped with a hydrogen branch 1201, which is sequentially connected to the hydrogen outlet of liquid hydrogen storage tank 5, hydrogen inlet of LNG subcooler 4, hydrogen outlet of LNG subcooler 4, and inlet of the hydrogen compression supply circuit. The junction of hydrogen branch 1201 and hydrogen pipeline 12 is located at the hydrogen outlet of liquid hydrogen storage tank 5 and the LNG subcooler 4, respectively. The liquid hydrogen pipeline 13 is connected between the hydrogen inlet of the liquid hydrogen storage tank 5, the liquid hydrogen pump 6, and the inlet of the forced heat exchange supply circuit in the natural gas blending engine supply system. A liquid hydrogen branch 1301 is provided on the liquid hydrogen pipeline 13. The liquid hydrogen branch 1301 is connected in sequence between the liquid hydrogen outlet of the liquid hydrogen storage tank 5, the liquid hydrogen inlet of the LNG subcooler 4, the liquid hydrogen outlet of the LNG subcooler 4, and the inlet of the forced heat exchange supply circuit. The junction of the liquid hydrogen branch 1301 and the liquid hydrogen pipeline 13 is located between the liquid hydrogen outlet of the liquid hydrogen storage tank 5 and the liquid hydrogen inlet of the LNG subcooler 4, and between the liquid hydrogen outlet of the LNG subcooler 4 and the inlet of the forced heat exchange supply circuit.

[0027] LNG storage tank 1 is equipped with a pressure sensor 14 for measuring the pressure inside the tank, such as Figure 2 As shown, pressure sensor 14 is electrically connected to LNG pump 2 and LNG subcooling valve 3. When the value measured by pressure sensor 14 is higher than the pressure set value, LNG pump 2 and LNG subcooling valve 3 are opened. LNG in LNG storage tank 1 flows through LNG pump 2 and LNG subcooling valve 3 in sequence along LNG subcooling pipeline 11, and is subcooled by LNG subcooler 4 before flowing into LNG storage tank 1. When the value measured by pressure sensor 14 is not higher than the pressure set value, LNG pump 2 and LNG subcooling valve 3 are closed.

[0028] A hydrogen gas phase valve 10 is installed on the hydrogen pipeline 12, and a hydrogen subcooling valve 9 is installed on the hydrogen branch 1201. The hydrogen subcooling valve 9 is located between the junction of the hydrogen branch 1201 and the hydrogen pipeline 12 and the hydrogen inlet of the LNG subcooler 4. A liquid hydrogen supply valve 8 is installed on the liquid hydrogen pipeline 13, and a liquid hydrogen subcooling valve 7 is installed on the liquid hydrogen branch 1301. The liquid hydrogen subcooling valve 7 is located between the junction of the liquid hydrogen branch 1301 and the liquid hydrogen pipeline 13 and the liquid hydrogen inlet of the LNG subcooler 4.

[0029] A temperature sensor 15 is installed on the LNG subcooling pipeline 11 to measure the LNG temperature at the LNG outlet of the LNG subcooler 4. The temperature sensor 15 is located at the LNG outlet of the LNG subcooler 4 and is electrically connected to the hydrogen vapor phase valve 10, the hydrogen subcooling valve 9, the liquid hydrogen supply valve 8, and the liquid hydrogen subcooling valve 7. This application uses the measured value of the temperature sensor 15 as an indicator of the adequacy of the cold source supply to adjust the hydrogen cold source supply method in stages. Figure 3 As shown, when the temperature sensor 15 measures a value below the low-temperature threshold, it indicates that the cooling capacity provided to the LNG in the LNG subcooler 4 is sufficient or even excessive, maintaining the opening of the hydrogen vapor phase valve 10, hydrogen subcooling valve 9, liquid hydrogen supply valve 8, and liquid hydrogen subcooling valve 7. When the temperature sensor 15 measures a value between the low-temperature threshold and the high-temperature threshold, it indicates that the cooling capacity provided to the LNG in the LNG subcooler 4 is initially insufficient but has not yet significantly deviated from the target. The opening of the hydrogen subcooling valve 9 is increased to continuously change the gaseous hydrogen flow rate, precisely controlling the heat exchange intensity and stabilizing the LNG outlet temperature within the set range. When the temperature sensor 15 measures a value above the high-temperature threshold, it indicates that the cooling capacity provided to the LNG in the LNG subcooler 4 is severely insufficient. The opening of the liquid hydrogen subcooling valve 7 is increased to increase the amount of liquid hydrogen entering the LNG subcooler 4 to participate in heat exchange. The latent heat of vaporization of the liquid hydrogen will quickly compensate for the cooling capacity shortfall, causing the outlet temperature of the LNG subcooler 4 to drop back below the target value. The temperature sensor 15 is a dual-sensor redundancy type to ensure measurement accuracy.

[0030] In this embodiment, the LNG subcooler 4 is a multi-channel heat exchanger with a welded aluminum plate-fin structure. The LNG subcooler 4 contains LNG, hydrogen, and liquid hydrogen channels. The flow direction of the media in the hydrogen and liquid hydrogen channels is the same, while the flow direction of the media in the LNG channel is opposite to that in the liquid hydrogen channel. The liquid in the LNG channel flows counter-currently to the cold hydrogen media in the adjacent hydrogen and liquid hydrogen channels, resulting in a temperature gradient distributed in opposite directions. This maximizes the utilization of the cold energy of the hydrogen medium to cool and subcool the LNG. The plate-fin structure increases the heat transfer area, while the high thermal conductivity of aluminum further improves the heat exchange efficiency, significantly reducing the temperature of the LNG as it flows through the LNG subcooler 4. The inlet and outlet pipes of the LNG subcooler 4 are equipped with cryogenic sealing joints and insulation layers to reduce cold loss and ensure system safety.

[0031] The working principle of the LNG subcooling system based on the natural gas-blended hydrogen engine gas supply system in this embodiment is as follows: LNG circuit: LNG pump 2 is used to extract part of the liquid natural gas in LNG storage tank 1 when subcooling is needed, LNG subcooling valve 3 is used to control the opening or blocking of LNG into LNG subcooler 4, LNG in LNG storage tank 1 is extracted from the liquid phase outlet through LNG pump 2, LNG subcooling valve 3, and then into LNG subcooler 4, when LNG subcooler 4 completes the deep cooling of LNG, the subcooled LNG returns to LNG storage tank 1 through LNG subcooling pipeline. When the pressure of LNG storage tank is too high, the subcooling cycle is started to allow part of the LNG to absorb the cold source and then return to flow, mix with the original liquid in the LNG storage tank, thereby reducing the temperature of the liquid, condensing BOG, and relieving the pressure rise.

[0032] Liquid hydrogen and hydrogen gas cold source circuit: liquid hydrogen storage tank 5 provides two forms of cold source output, one, the liquid hydrogen in liquid hydrogen storage tank 5 is pressurized by liquid hydrogen pump 6, and then introduced into the liquid hydrogen flow channel of LNG subcooler 4 through liquid hydrogen subcooling valve 7; the liquid hydrogen is vaporized in LNG subcooler 4 by absorbing heat, and then becomes low-temperature hydrogen gas after releasing a large amount of cold energy, and is discharged or introduced into the subsequent hydrogen utilization system. The second, the hydrogen gas in the gas phase space of liquid hydrogen storage tank 5 is introduced into the hydrogen gas flow channel of LNG subcooler 4 through hydrogen gas subcooling valve 9. The gaseous hydrogen exchanges heat with LNG in LNG subcooler 4 and transfers cold energy to LNG. Liquid hydrogen subcooling valve 7 and hydrogen gas subcooling valve 9 are respectively used to adjust the flow of liquid hydrogen and gaseous hydrogen into LNG subcooler 4; hydrogen gas phase valve 10 is used to control the opening and closing of the gas phase of liquid hydrogen storage tank 5 and stabilize the output pressure. Through the above double-circuit design, LNG subcooler 4 can introduce hydrogen or liquid hydrogen as needed to provide a staged cold source strength.

[0033] Control logic: when pressure sensor 14 detects that the pressure of LNG storage tank 1 exceeds the preset upper limit (for example, P1> high pressure threshold), it indicates that the accumulation of BOG in LNG storage tank 1 causes the pressure to rise, the system immediately starts LNG pump 2 and opens LNG subcooling valve 3, and a subcooling cycle process begins, liquid natural gas is extracted and deep-cooled through LNG subcooler 4, and then LNG returns to LNG storage tank 1 through the return valve after being subcooled to the target temperature, and is injected into the liquid phase of LNG storage tank 1 to absorb heat, condense BOG, and reduce the pressure of LNG storage tank 1; when the pressure of LNG storage tank 1 returns to below the safety value, P1 feedback triggers the closing of LNG subcooling valve 3 and the stopping of LNG pump 2, ending the subcooling cycle and keeping the system in standby state. Through the on-off control based on the pressure threshold, the BOG can be processed as soon as it is generated, avoiding pressure overshoot and safety valve discharge.

[0034] The supercooling system takes the LNG temperature out of the LNG supercooler as an index to measure the sufficiency of the cold source supply, and adjusts the supply mode of the hydrogen cold source in stages: when the LNG supercooler 4 outlet temperature is detected to be lower than the low temperature threshold value, it indicates that the current provided cold quantity is sufficient or even excessive, at this time, the supercooling demand can be met mainly by relying on the gaseous hydrogen cold source, without additional supply of liquid hydrogen; when the outlet temperature fluctuates in the high temperature threshold value-low temperature threshold value interval, it indicates that the cold quantity starts to be insufficient but has not yet deviated seriously from the target, at this time, the gaseous hydrogen flow is continuously changed by adjusting the opening degree of the hydrogen supercooling valve 9, the heat exchange intensity is finely controlled, and the outlet temperature is stabilized in the set range; when the outlet temperature rises above the low temperature threshold value, it means that the gaseous hydrogen cold source alone cannot provide sufficient cold quantity. At this time, the control system automatically opens the liquid hydrogen supercooling valve 7, and a certain amount of liquid hydrogen enters the LNG supercooler 4 to participate in heat exchange. The latent heat of vaporization of the liquid hydrogen will quickly make up for the cold quantity gap, and prompt the LNG supercooler 4 outlet temperature to drop below the target value again. After the outlet temperature recovers, the liquid hydrogen flow can be appropriately reduced or the liquid hydrogen supercooling valve 7 can be closed, and only the gaseous hydrogen is retained to continue to maintain the supercooling, so as to save the liquid hydrogen resources. Through the above temperature closed-loop control, the continuous proportional adjustment and staged switching of the hydrogen cold source supply are realized, which ensures the stable LNG supercooling effect while maximizing the potential of the low temperature cold source.

[0035] Under the coordination of the above control strategy, the LNG supercooler 4 system of the application can flexibly adopt the "hydrogen supercooling only" and "hydrogen + liquid hydrogen combined supercooling" modes under different operating conditions according to actual needs, which not only meets the BOG liquefaction requirements, but also considers energy efficiency optimization: 1. Hydrogen supercooling only condition: when the LNG storage tank 1 pressure is slightly higher than the set value and the BOG generation amount is relatively small, the system preferentially adopts gaseous hydrogen as the only cold source for supercooling. At this time, an appropriate amount of cold hydrogen gas flow is introduced through the hydrogen supercooling valve 9 to pass through the LNG supercooler 4 and exchange heat with the LNG. The gaseous hydrogen gradually warms up from extremely low temperature to ambient temperature in the heat exchange process, while the LNG is cooled to a lower temperature and then returns to the LNG storage tank 1. The liquid hydrogen supercooling valve 7 remains closed during the entire process, and the cold energy of the liquid hydrogen tank 5 is utilized in gaseous form. Since the gaseous hydrogen cold source is adjustable and does not require phase change heat absorption, it can smoothly maintain the LNG in a supercooled state under small load conditions. At the same time, the hydrogen gas itself becomes a normal temperature gas after heat exchange and can be directly supplied to the engine for combustion, realizing the combination of cold energy recovery and energy utilization. In this mode, the system has the lowest energy consumption and high control accuracy, and is suitable for daily small-scale BOG adjustment to keep the LNG storage tank 1 pressure stable for a long time.

[0036] 2. Hydrogen and liquid hydrogen combined subcooling condition: when the environmental heat load increases or the BOG accumulation rate in the LNG storage tank 1 is high, and pure gaseous hydrogen cold source cannot fully subcool the LNG, the system enters the hydrogen and liquid hydrogen combined cooling mode. In addition to maintaining the continuous supply of gaseous hydrogen, the control system opens the liquid hydrogen subcooling valve 7 according to the outlet temperature feedback, and a small amount of liquid hydrogen is metered into the LNG subcooler 4. The liquid hydrogen rapidly vaporizes and absorbs heat in the LNG subcooler 4, and together with the gaseous hydrogen, it provides strong cooling for the LNG, causing the temperature of the subcooled LNG to drop significantly and effectively liquefying a large amount of BOG. In the combined subcooling mode, the total cooling capacity of the hydrogen cold source is significantly improved, which can cope with sudden BOG peaks or rapid pressure reduction requirements. The hydrogen gas formed after the vaporization of the liquid hydrogen can also enter the engine gas supply system, realizing the integration of cold energy utilization and energy supply. When the pressure of the LNG storage tank 1 returns to normal and the outlet temperature drops below the target, the control system can gradually close the liquid hydrogen subcooling valve 7, and transition back to the hydrogen subcooling mode only, to avoid unnecessary consumption of liquid hydrogen. This combined cooling condition ensures that BOG can be quickly and safely liquefied and treated in extreme conditions, preventing overpressure of the LNG storage tank 1, while also considering the economic use of liquid hydrogen resources.

[0037] The LNG subcooler (4) based on the natural gas hydrogen-doped engine gas supply system provided by the present application realizes efficient subcooling of LNG and BOG re-liquefaction using a liquid hydrogen cold source through structural innovation and control optimization.

[0038] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application and not to limit them; although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that; the specific embodiments of the application can be modified or some technical features can be replaced by equivalent; without departing from the spirit of the technical solutions of the present application, they should be included in the technical solution range of the present application claimed.

Claims

1. An LNG subcooling system based on a natural gas-blended hydrogen engine gas supply system, characterized in that, It includes an LNG storage tank, an LNG pump, an LNG subcooling valve, an LNG subcooler, a liquid hydrogen storage tank, a liquid hydrogen pump, an LNG subcooling pipeline, a hydrogen pipeline, a hydrogen pipeline branch, a liquid hydrogen pipeline, and a liquid hydrogen branch, wherein the LNG subcooler uses hydrogen and / or liquid hydrogen for subcooling; The LNG subcooling pipeline is sequentially connected to the liquid phase outlet of the LNG storage tank, the LNG pump, the LNG subcooling valve, the LNG inlet of the LNG subcooler, the LNG outlet of the LNG subcooler, and the liquid phase inlet of the LNG storage tank. The hydrogen outlet of the liquid hydrogen storage tank is connected to the inlet of the hydrogen compression supply circuit in the natural gas blending engine supply system via a hydrogen pipeline. A hydrogen branch is provided on the hydrogen pipeline, which sequentially connects to the hydrogen outlet of the liquid hydrogen storage tank, the hydrogen inlet of the LNG subcooler, the hydrogen outlet of the LNG subcooler, and the inlet of the hydrogen compression supply circuit. The junction of the hydrogen branch and the hydrogen pipeline is located at the hydrogen outlet of the liquid hydrogen storage tank and the hydrogen inlet of the LNG subcooler, respectively. The liquid hydrogen pipeline is connected between the liquid hydrogen outlet of the liquid hydrogen storage tank, the liquid hydrogen pump, and the inlet of the forced heat exchange supply circuit in the natural gas blending engine supply system. A liquid hydrogen branch is provided on the liquid hydrogen pipeline, which is connected in sequence to the liquid hydrogen outlet of the liquid hydrogen storage tank, the liquid hydrogen inlet of the LNG subcooler, the liquid hydrogen outlet of the LNG subcooler, and the inlet of the forced heat exchange supply circuit. The junction points of the liquid hydrogen branch and the liquid hydrogen pipeline are respectively between the liquid hydrogen outlet of the liquid hydrogen storage tank and the liquid hydrogen inlet of the LNG subcooler, and between the liquid hydrogen outlet of the LNG subcooler and the inlet of the forced heat exchange supply circuit.

2. The LNG subcooling system according to claim 1, characterized in that, The LNG storage tank is equipped with a pressure sensor to measure the pressure inside the tank. The pressure sensor is electrically connected to the LNG pump and the LNG subcooling valve. When the value measured by the pressure sensor is higher than the pressure set value, the LNG pump and the LNG subcooling valve are opened. When the value measured by the pressure sensor is not higher than the pressure set value, the LNG pump and the LNG subcooling valve are closed.

3. The LNG subcooling system according to claim 2, characterized in that, A hydrogen gas phase valve is installed on the hydrogen pipeline, and a hydrogen subcooling valve is installed on the hydrogen branch. The hydrogen subcooling valve is located between the junction of the hydrogen branch and the hydrogen pipeline and the hydrogen inlet of the LNG subcooler. A liquid hydrogen supply valve is installed on the liquid hydrogen pipeline, and a liquid hydrogen subcooling valve is installed on the liquid hydrogen branch. The liquid hydrogen subcooling valve is located between the junction of the liquid hydrogen branch and the liquid hydrogen pipeline and the liquid hydrogen inlet of the LNG subcooler.

4. The LNG subcooling system according to claim 3, characterized in that, A temperature sensor is installed on the LNG subcooling pipeline. The temperature sensor is used to measure the temperature of LNG at the LNG outlet of the LNG subcooler. The temperature sensor is located at the LNG outlet of the LNG subcooler. The hydrogen gas phase valve, hydrogen subcooling valve, liquid hydrogen supply valve and liquid hydrogen subcooling valve are all electrically connected to the temperature sensor.

5. The LNG subcooling system according to claim 4, characterized in that, When the temperature sensor reading is below the low temperature threshold, maintain the opening of the hydrogen gas phase valve, hydrogen subcooling valve, liquid hydrogen supply valve, and liquid hydrogen subcooling valve; when the temperature sensor reading is between the low temperature threshold and the high temperature threshold, increase the opening of the hydrogen subcooling valve to continuously change the gaseous hydrogen flow rate, finely control the heat exchange intensity, and stabilize the LNG outlet temperature within the set range; when the temperature sensor reading is above the high temperature threshold, increase the opening of the liquid hydrogen subcooling valve.

6. The LNG subcooling system according to claim 1, characterized in that, The LNG subcooler is a multi-channel heat exchanger. The LNG subcooler is equipped with an LNG channel, a hydrogen channel, and a liquid hydrogen channel. The flow direction of the medium in the hydrogen channel and the liquid hydrogen channel is the same, while the flow direction of the medium in the LNG channel is opposite to that in the liquid hydrogen channel.

7. The LNG subcooling system according to claim 6, characterized in that, The LNG flow channel is located between the hydrogen flow channel and the liquid hydrogen flow channel, and the LNG subcooler is a welded aluminum plate fin structure heat exchanger.

8. An LNG carrier, characterized in that, The LNG ship is equipped with a natural gas-hydrogen-blended engine supply system and an LNG subcooling system based on the natural gas-hydrogen-blended engine supply system as described in any one of claims 1-7.

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