High-low pressure gas supply system using LNG cold energy and operation method

Abstract

The application provides a high-low pressure gas supply system and operation method using LNG cold energy. The high-low pressure gas supply system comprises a fuel tank. Liquid fuel in the fuel tank releases cold energy through a gas supply regenerator, enters a liquid heater to release cold energy again, and finally changes into high-pressure gas supply fuel, and transmits cold energy to heat exchange medium flowing through the liquid heater. Evaporated gas in the fuel tank is pressurized and heated by a compressor to change into high-pressure gaseous fuel and enter a gas heat exchanger. Heat exchange medium absorbing cold energy flows out from the liquid heater and passes through the gas heat exchanger, thereby exchanging heat with the high-pressure gaseous fuel to change the high-pressure gaseous fuel into low-pressure gaseous fuel. The low-pressure gaseous fuel can also flow back to the gas cooler and the gas supply regenerator to realize double cooling to achieve re-liquefaction. In the whole gas supply system, the cooling of the high-pressure gaseous fuel in the gas heat exchanger and the cooling in the re-liquefaction process are all from the cold energy of the liquid fuel itself, thereby realizing efficient use of energy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ship fuel transportation, in particular to a high-low pressure gas supply system utilizing LNG cold energy and a running method. BACKGROUND

[0002] In response to increasingly stringent environmental regulations, the current shipping industry is vigorously developing dual-fuel ships using liquefied natural gas (LNG) as clean fuel. Most existing dual-fuel ships use natural gas as clean fuel. Natural gas is always in the form of low-temperature liquid during transportation or storage. When LNG is delivered to the main engine or generator for use, it needs to be pressurized to a higher pressure and heated to a certain temperature to meet the user's usage conditions.

[0003] LNG has a low temperature and carries a lot of cold energy. When LNG is pumped out of the fuel tank and heated to the required temperature by steam or water glycol heat transfer medium, the cold energy of LNG is directly wasted. The boil-off gas (BOG) generated in the tank needs to be liquefied again to meet the demand for LNG due to the increase in tank pressure.

[0004] How to apply the cold energy of LNG to the refrigeration and liquefaction process of BOG has become a technical problem that needs to be solved by technical personnel. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a high-low pressure gas supply system utilizing LNG cold energy, which solves the problem that the cold energy of LNG is not utilized and the need to equip a reliquefaction device for BOG liquefaction recovery in the prior art.

[0006] To achieve the above object and other related objects, the present application provides a high and low pressure gas supply system using LNG cold energy, which comprises a fuel tank, a fuel tank fuel pump for pumping liquid fuel is placed in the fuel tank, the outlet of the fuel tank fuel pump is connected to the buffer tank outside the tank through a pipeline, the bottom of the buffer tank is connected to the fuel pump outside the tank through a pipeline, the outlet of the fuel pump outside the tank is connected to the liquid side inlet of the gas supply regenerator through a pipeline, the liquid fuel releases cold energy after being heated in the gas supply regenerator and flows out from the liquid side outlet of the gas supply regenerator, the liquid side outlet of the gas supply regenerator is connected to the LNG side inlet of the liquid heater, the heat exchange medium flowing into the liquid heater absorbs the cold energy of the liquid fuel entering the LNG side inlet of the liquid heater, so that the liquid fuel is gasified to form high pressure gas supply fuel; the evaporation gas in the fuel tank enters the inlet buffer tank through the pipeline on the top of the tank, the tank top of the inlet buffer tank is connected to the first stage compressor and the second stage compressor through a pipeline in sequence, the high pressure gaseous fuel flowing out of the outlet of the second stage compressor enters the LNG side inlet of the gas heat exchanger, the heat exchange medium absorbing cold energy flows out of the liquid heater and passes through the gas heat exchanger, the high pressure gaseous fuel entering the LNG side inlet of the gas heat exchanger is cooled and decompressed by heat exchange with the heat exchange medium, thereby being converted into low pressure gaseous fuel.

[0007] Optionally, the low pressure gaseous fuel flows out from the LNG side outlet of the gas heat exchanger, the low pressure gaseous fuel flowing out from the LNG side outlet of the gas heat exchanger is divided into two paths, one path is connected to the low pressure gas supply valve, the outlet of the low pressure gas supply valve is connected to the low pressure gas supply pipeline; the other path is connected to the back gas side inlet of the gas cooler, the flow distribution ratio of the two paths can be changed by adjusting the opening degree of the low pressure gas supply valve; the back gas side outlet of the gas cooler is connected to the gas side inlet of the gas supply regenerator, the low pressure gaseous fuel entering the back gas side inlet of the gas cooler is cooled by absorbing cold energy and then enters the gas side inlet of the gas supply regenerator; the low pressure gaseous fuel after cooling absorbs the cold energy of the liquid fuel flowing through the gas supply regenerator to realize re-liquefaction and then flows out from the gas side outlet of the gas supply regenerator and returns to the middle part of the gas-liquid separator through a pipeline.

[0008] Optionally, the top of the gas-liquid separator is connected to the inlet of the exhaust valve through a pipeline, the outlet of the exhaust valve is connected to the gas supply side inlet of the gas cooler; the gas supply side outlet of the gas cooler is connected to the low pressure gas supply pipeline of the outlet of the low pressure gas supply valve; the low temperature mixed gas from the top of the gas-liquid separator enters the gas supply side of the gas cooler and transfers cold energy to the low pressure gaseous fuel entering the back gas side of the gas cooler, so that the low temperature mixed gas is warmed and then discharged from the low pressure gas supply pipeline.

[0009] Optionally, the bottom of the gas-liquid separator is connected to the inlet of the liquid discharge valve through a pipeline, the outlet of the liquid discharge valve is connected to the pipeline between the outlet of the fuel tank fuel pump and the buffer tank, so that the liquid return fuel enters the buffer tank again.

[0010] Optionally, the tank top of the gas inlet buffer tank is connected to the low pressure side of the gas inlet regenerator through a pipeline; the low pressure side outlet of the gas inlet regenerator is connected to the first stage compressor; the outlet of the first stage compressor is connected to the inlet of the high pressure side of the gas inlet regenerator, and the high pressure gaseous fuel after being pressurized by the first stage compressor enters the high pressure side of the gas inlet regenerator to absorb the cold energy of the boil-off gas entering the low pressure side of the gas inlet regenerator to realize cooling, and the outlet of the high pressure side of the gas inlet regenerator is connected to the inlet of the second stage compressor.

[0011] Optionally, the heat exchange medium flows into the heat exchange inlet of the liquid heater from the pipeline; the heat exchange medium flowing out of the heat exchange outlet of the liquid heater is divided into two paths, one path is connected to the heat exchange inlet of the gas heat exchanger, and the other path is connected to the heat exchange medium regulating valve; the heat exchange outlet of the gas heat exchanger is combined and flowed with the outlet of the heat exchange medium regulating valve through a pipeline, so that the heat exchange medium finally flows out; by adjusting the opening degree of the heat exchange medium regulating valve, the flow distribution ratio of the two paths can be changed, and the flow of the heat exchange medium entering the gas heat exchanger can be changed.

[0012] Optionally, the heat exchange medium is water glycol.

[0013] The application also provides a running method of the high-low pressure gas supply system, which comprises the following steps: S1, high pressure gas supply mode, the running process comprising: the cabin fuel pump is operated to deliver liquid fuel from the fuel cabin to the buffer tank, the out-cabin fuel pump is operated to pump out the liquid fuel in the buffer tank and pressurize it to the required pressure of the high pressure user and send it to the liquid heater; in the liquid heater, the liquid fuel exchanges heat with the heat exchange medium, the liquid fuel is gasified and its temperature is within the required temperature range of the user, thereby supplying gas to the high pressure user.

[0014] Optionally, the method further comprises the following step: S2, low pressure gas supply mode, the running process comprising: the boil-off gas in the fuel cabin enters the gas inlet buffer tank from the pipeline at the cabin top, the boil-off gas in the gas inlet buffer tank is pumped out by the first stage compressor, is compressed by the second stage compressor, is then introduced into the gas heat exchanger, exchanges heat with the low temperature heat exchange medium after absorbing the cold energy by the liquid heater to achieve cooling to the required temperature of the user, and finally passes through the low pressure gas supply valve to supply gas to the low pressure user.

[0015] Optionally, the method further comprises a step S3: a cold energy recovery mode, and the operation process comprises: before supplying the low-pressure user with gas, the amount of low-pressure gaseous fuel flowing out of the LNG side outlet of the gas heat exchanger and flowing back to the gas cooler is correspondingly reduced or increased by increasing or reducing the opening of the low-pressure gas supply valve; the low-pressure gaseous fuel entering the gas side inlet of the gas cooler is cooled by absorbing cold energy and then enters the gas side inlet of the fuel supply heat exchanger; the cooled low-pressure gaseous fuel absorbs cold energy of the liquid fuel flowing through the fuel supply heat exchanger again and then flows out of the gas side outlet of the fuel supply heat exchanger and finally enters the gas-liquid separator; the liquid backflow fuel in the gas-liquid separator can enter the buffer tank again through the opening of the liquid discharge valve; the low-temperature mixed gas in the gas-liquid separator enters the gas supply side of the gas cooler through the gas discharge valve, thereby supplying the low-pressure gaseous fuel in the gas side of the gas cooler with cold energy, and finally being discharged from the low-pressure gas supply pipeline.

[0016] As described above, the application provides a high-low pressure gas supply system and an operation method using LNG cold energy. The high-low pressure gas supply system comprises a fuel tank. The liquid fuel in the fuel tank releases cold energy in the fuel supply heat exchanger and then enters the liquid heater. The liquid fuel entering the liquid heater releases cold energy again and then changes into high-pressure gas supply fuel. In the process, cold energy is transferred to the heat exchange medium flowing through the liquid heater. The boil-off gas in the fuel tank is pressurized and heated by the compressor and then changes into high-pressure gaseous fuel and enters the gas heat exchanger. The heat exchange medium absorbing cold energy flows out of the liquid heater and then passes through the gas heat exchanger. The high-pressure gaseous fuel is cooled and depressurized by heat exchange with the heat exchange medium, thereby changing into low-pressure gaseous fuel. The low-pressure gaseous fuel not only meets the use demand, but also can flow back to the gas cooler and the fuel supply heat exchanger for double cooling to achieve re-liquefaction. In the whole gas supply system, the cold energy of the high-pressure gaseous fuel in the gas heat exchanger and the cold energy of the low-pressure gaseous fuel in the re-liquefaction process all come from the cold energy of the liquid fuel itself. This design fully utilizes the cold energy, meets the user demand, realizes efficient use of energy, and therefore saves the additional re-liquefaction device and saves valuable space for the ship. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A connection diagram of components of the high-low pressure gas supply system in the application is shown.

[0018] Figure 2 A working process diagram of the high-low pressure gas supply system in the application for high-pressure gas supply is shown.

[0019] Figure 3 A working process diagram of the high-low pressure gas supply system in the application for high-pressure gas supply and low-pressure gas supply is shown.

[0020] Figure 4 A working process diagram of the high-low pressure gas supply system in the application for high-pressure gas supply, low-pressure gas supply, and cold energy recovery is shown.

[0021] Element No. Explanation Fuel tank 1, in-tank fuel pump 2, buffer tank 3, out-tank fuel pump 4, air supply heat exchanger 5, liquid heater 6, high-pressure air supply valve 7, air inlet buffer tank 8, air inlet heat exchanger 9, primary compressor 10, secondary compressor 11, gas heat exchanger 12, low-pressure air supply valve 13, gas cooler 14, gas-liquid separator 15, exhaust valve 16, liquid discharge valve 17, heat medium regulating valve 18. DETAILED DESCRIPTION

[0022] The present application is herein described, by way of example only, with the assistance of the accompanying drawings detailed description of which will become more apparent with the description in the following examples. Other advantages and benefits of the present application will become apparent from such description.

[0023] As will be realized, the application is capable of modifications in various obvious aspects, all without departing from the application. The application also is capable of other embodiments and of being practiced or being carried out in various ways. Examples of the application are described in detail herein, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the application and is intended to be as broad as possible and as being limited only by the broadest interpretation of the appended claims.

[0024] For purposes of the description hereinafter, the terms "upper", "lower", "right", "left", "vertical", "horizontal", and derivatives thereof shall relate to the application as it is oriented in use. Therein, the terminology "above" and "below" shall refer to the directions of the relative positions of the components as they are oriented in use. Terminology used herein for the purpose of describing particular embodiments or examples is not intended to be limiting of the application. For example, as used herein, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of the entities. It is also to be understood that the terms "comprising", "including", "containing" and "having" are intended to be open-ended terms. The use of the term "comprising" or "including" or "containing" or "having" to describe a feature, integer, step, or component of the application is not meant to be construed as implying that there are no additional features, integers, steps, or components that the application does not include. The use of the terms "comprising", "including", "containing" and "having" to describe a feature, integer, step, or component of the application is not meant to be construed as implying that there are no additional features, integers, steps, or components that the application does not include.

[0025] In the context of this application, a structure described as being "on" another structure can comprise an embodiment in which the first and second structures are formed in direct contact, or can comprise an embodiment in which additional structures are formed between the first and second structures, such that the first and second structures can not be in direct contact.

[0026] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. It is also possible in the prior art to use different terminologies to describe certain structures or methods.

[0027] As Figure 1As shown, the application provides a high and low pressure gas supply system using LNG cold energy, which comprises a fuel tank 1, an in-tank fuel pump 2, a buffer tank 3, an out-tank fuel pump 4, a gas supply regenerator 5, a liquid heater 6, a high pressure gas supply valve 7, an air inlet buffer tank 8, an air inlet regenerator 9, a primary compressor 10, a secondary compressor 11, a gas heat exchanger 12, a low pressure gas supply valve 13, a gas cooler 14, a gas-liquid separator 15, an exhaust valve 16, a liquid discharge valve 17, and a heat medium regulating valve 18.

[0028] The in-tank fuel pump 2 is arranged in the fuel tank 1 to pump out the liquid fuel in the fuel tank 1, and the outlet of the in-tank fuel pump 2 is connected to the buffer tank 3 outside the tank through a pipeline. The bottom of the buffer tank 3 is connected to the out-tank fuel pump 4 through a pipeline, and the outlet of the out-tank fuel pump 4 is connected to the liquid side inlet of the gas supply regenerator 5 through a pipeline. The liquid fuel releases cold energy in the gas supply regenerator 5 and then flows out from the liquid side outlet of the gas supply regenerator 5. The liquid side outlet of the gas supply regenerator 5 is connected to the LNG side inlet of the liquid heater 6, and the heat medium flowing into the liquid heater 6 absorbs the cold energy of the liquid fuel entering the LNG side inlet of the liquid heater 6, so that the liquid fuel is gasified to form high pressure gas supply fuel. The LNG side outlet of the liquid heater 6 is connected to the high pressure gas supply valve 7, and the outlet of the high pressure gas supply valve 7 is used for high pressure gas supply.

[0029] The BOG in the fuel tank 1 enters the air inlet buffer tank 8 through a pipeline on the top of the tank. The tank top of the air inlet buffer tank 8 is connected to the primary compressor 10 and the secondary compressor 11 through a pipeline in sequence, and the high pressure gaseous fuel flowing out of the outlet of the secondary compressor 11 enters the LNG side inlet of the gas heat exchanger 12. The heat medium absorbing cold energy flows out of the liquid heater 6 and passes through the gas heat exchanger 12. The high pressure gaseous fuel entering the LNG side inlet of the gas heat exchanger 12 is cooled and decompressed by heat exchange with the heat medium, thereby being converted into low pressure gaseous fuel. Since the temperature of the gas increases after being pressurized by the compressor, the heat medium absorbing cold energy in the liquid heater 6 is used to cool and decompress the high pressure gaseous fuel, that is, the cold energy contained in the liquid fuel is transferred to the cooling process of the high pressure gaseous fuel through the heat medium. It should be noted that the temperature of the BOG in the fuel tank 1 is relatively low and cannot be directly used for low pressure gas supply, so it needs to be pressurized and heated first, and then cooled and decompressed to reach the required normal temperature. The cold energy for cooling comes from the cold energy of LNG itself, and no additional cold energy supply is needed. The pressurization and heating are achieved by the compressor, and no external heating pipeline is needed. Moreover, the compressor can also be used to regulate the pressure of the gas flow.

[0030] More specifically, the tank top of the intake buffer tank 8 is connected to the low pressure side of the intake heat exchanger 9 through a pipeline; the low pressure side outlet of the intake heat exchanger 9 is connected to the first stage compressor 10; the outlet of the first stage compressor 10 is connected to the inlet of the high pressure side of the intake heat exchanger 9, and the high pressure gaseous fuel after being pressurized by the first stage compressor 10 enters the high pressure side of the intake heat exchanger 9 to absorb the cold energy of the boil-off gas entering the low pressure side of the intake heat exchanger 9 to achieve cooling. The outlet of the high pressure side of the intake heat exchanger 9 is connected to the inlet of the second stage compressor 11.

[0031] The low pressure gaseous fuel flows out from the LNG side outlet of the gas heat exchanger 12, and the low pressure gaseous fuel flowing out from the LNG side outlet of the gas heat exchanger 12 is divided into two paths, one of which is connected to the low pressure gas supply valve 13, and the outlet of the low pressure gas supply valve 13 is connected to the low pressure gas supply pipeline; the other of which is connected to the gas return side inlet of the gas cooler 14, and the flow distribution ratio of the two paths can be changed by adjusting the opening degree of the low pressure gas supply valve 13. The gas return side outlet of the gas cooler 14 is connected to the gas side inlet of the supply heat exchanger 5, and the low pressure gaseous fuel entering the gas return side inlet of the gas cooler 14 is cooled by absorbing cold energy and then enters the gas side inlet of the supply heat exchanger 5; the low pressure gaseous fuel after being cooled absorbs the cold energy of the liquid fuel flowing through the supply heat exchanger 5 to achieve re-liquefaction, and then flows out from the gas side outlet of the supply heat exchanger 5 and returns to the middle part of the gas-liquid separator 15 through a pipeline, and since the liquid side of the supply heat exchanger 5 is the first heat exchange module through which the liquid fuel flows, it still maintains a very low temperature, so it can liquefy the gaseous fuel.

[0032] The bottom of the gas-liquid separator 15 is connected to the inlet of the liquid discharge valve 17 through a pipeline, and the outlet of the liquid discharge valve 17 is connected to the pipeline between the outlet of the cabin fuel pump 2 and the buffer tank 3, so that the liquid return fuel enters the buffer tank 3 again. The buffer tank 3 is mixed with LNG discharged by the cabin fuel pump and LNG discharged from the bottom of the gas-liquid separator 15, so as to ensure that the fluid entering the out-of-cabin fuel pump is all liquid. It should be understood that when the low pressure demand of the low pressure gas supply pipeline decreases, the return flow of the low pressure gaseous fuel entering the gas cooler 14 can be increased so that it is re-liquefied and stored.

[0033] The top of the gas-liquid separator 15 is connected to the inlet of the exhaust valve 16 through a pipeline; the outlet of the exhaust valve 16 is connected to the gas supply side inlet of the gas cooler 14; the gas supply side outlet of the gas cooler 14 is connected to the low-pressure gas supply pipeline at the outlet of the low-pressure gas supply valve 13. The low-temperature mixed gas from the top of the gas-liquid separator 15 enters the gas supply side of the gas cooler 14 and transfers cold energy to the low-pressure gaseous fuel entering the return side of the gas cooler 14, so that the low-temperature mixed gas is warmed and discharged from the low-pressure gas supply pipeline. Here, the low-temperature mixed gas includes nitrogen and natural gas, and some nitrogen in the pipeline is difficult to be liquefied (the liquefaction temperature of nitrogen is lower than that of natural gas), so the gas-liquid separator 15 is used to separate part of the high-pressure nitrogen that cannot be liquefied, and the low-temperature mixed gas formed by the difficult-to-condense nitrogen and natural gas is discharged to the outside low-pressure gas supply pipeline through the exhaust valve.

[0034] The heat exchange medium (preferably water glycol) flows into the heat exchange inlet of the liquid heater 6 from the pipeline; the heat exchange medium flowing out of the heat exchange outlet of the liquid heater 6 is divided into two paths, one of which is connected to the heat exchange inlet of the gas heat exchanger 12, and the other of which is connected to the heat exchange medium regulating valve 18; the heat exchange outlet of the gas heat exchanger 12 is combined and flowed with the outlet of the heat exchange medium regulating valve 18 through a pipeline, so that the heat exchange medium finally flows out of the system. By adjusting the opening degree of the heat exchange medium regulating valve 18, the flow distribution ratio of the two paths can be changed, and the flow of the heat exchange medium into the gas heat exchanger 12 can be changed.

[0035] Based on the high-low pressure gas supply system utilizing LNG cold energy described above, the application also provides a corresponding operation method, which includes three operation modes, including a high-pressure gas supply mode, a high-pressure gas supply mode + low-pressure gas supply mode, and a high-pressure gas supply mode + low-pressure gas supply mode + cold energy recovery mode. The operation method includes the following steps S1 to S3, each step representing an operation mode.

[0036] S1: high-pressure gas supply mode, the operation process includes: the cabin fuel pump 2 operates to transport the liquid fuel from the fuel tank 1 to the buffer tank 3; the outboard fuel pump 4 operates to extract the liquid fuel in the buffer tank 3 and pressurize it to the required pressure of the high-pressure user, and send it to the liquid heater 6; in the liquid heater 6, the liquid fuel exchanges heat with the heat exchange medium, the liquid fuel is gasified and its temperature is within the user demand temperature range, the high-pressure gas supply valve 7 is opened, and the high-pressure user is supplied with gas. The working process is as shown in Figure 2 .

[0037] S2: low pressure gas supply mode, the operation process includes: the boil-off gas (BOG) in the fuel tank 1 enters the gas buffer tank 8 from the pipeline on the top of the tank, the boil-off gas in the gas buffer tank 8 is extracted by the primary compressor 10, enters the primary compressor 10 after passing through the low pressure side of the gas preheater 9, is compressed into high pressure gaseous fuel and enters the high pressure side of the gas preheater 9, and is heat exchanged with the boil-off gas on the low pressure side in the gas preheater 9. After heat exchange, it is compressed by the secondary compressor 11 to reach the required pressure of the user, and then enters the gas heat exchanger 12, is heat exchanged with the low temperature heat exchange medium after absorbing cold energy by the liquid heater 6, and is cooled to the required temperature of the user, and finally passes through the low pressure gas supply valve 13 to supply gas to the low pressure user. The amount of heat exchange medium entering the gas heat exchanger 12 can be controlled by adjusting the opening of the heat exchange medium regulating valve 18, so as to control the temperature of the gas flowing out of the low pressure gas supply pipeline. The working process is as shown in Figure 3

[0038] S3: cold energy recovery mode, the operation process includes: before supplying gas to the low pressure user, the amount of low pressure gaseous fuel flowing out of the LNG side outlet of the gas heat exchanger 12 is relatively reduced or increased by increasing or reducing the opening of the low pressure gas supply valve 13, so that the amount of gas flowing back to the gas cooler 14 is relatively reduced or increased; the low pressure gaseous fuel entering the gas side inlet of the gas cooler 14 is cooled by absorbing cold energy and then enters the gas side inlet of the gas supply preheater 5; the low pressure gaseous fuel after cooling absorbs the cold energy of the liquid fuel flowing through the gas supply preheater 5 and then flows out of the gas side outlet of the gas supply preheater 5, and finally enters the gas-liquid separator 15. The liquid reflux fuel in the gas-liquid separator 15 can enter the buffer tank 3 again by opening the liquid discharge valve 17. The low temperature mixed gas in the gas-liquid separator 15 enters the gas supply side of the gas cooler 14 through the gas discharge valve 16, so as to supply cold energy for the low pressure gaseous fuel on the gas return side of the gas cooler 14, and finally is discharged from the low pressure gas supply pipeline. The working process is as shown in Figure 4

[0039] ​​In summary, the application provides a high and low pressure gas supply system using LNG cold energy and an operating method. The high and low pressure gas supply system comprises a fuel tank. Liquid fuel in the fuel tank releases cold energy through a gas supply regenerator and enters a liquid heater. The liquid fuel entering the liquid heater releases cold energy again and is converted into high pressure gas supply fuel. In the process, cold energy is transferred to heat exchange medium flowing through the liquid heater. Evaporated gas in the fuel tank is pressurized and heated by a compressor and is converted into high pressure gaseous fuel and enters a gas heat exchanger. Heat exchange medium absorbing cold energy flows out of the liquid heater and passes through the gas heat exchanger. The high pressure gaseous fuel is cooled and depressurized by heat exchange with the heat exchange medium, thereby being converted into low pressure gaseous fuel. The low pressure gaseous fuel meets the use requirements and can also flow back to the gas cooler and the gas supply regenerator for double cooling to achieve reliquefaction. In the entire gas supply system, the cooling of the high pressure gaseous fuel in the gas heat exchanger and the cooling in the reliquefaction process are all from the cold energy contained in the liquid fuel. This design fully utilizes the cold energy, meets the user requirements, realizes efficient use of energy, and thus saves the additional reliquefaction device, saving valuable space for the ship.

[0040] The above embodiments only exemplarily illustrate the principles and effects of the application, and are not used to limit the application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the application should be covered by the claims of the application.

Claims

1. A high and low pressure gas supply system utilizing LNG cold energy, characterized by, The high-low pressure gas supply system comprises a fuel tank, a fuel tank fuel pump for pumping liquid fuel is placed in the fuel tank, the outlet of the fuel tank fuel pump is connected to the buffer tank outside the tank through a pipeline, the bottom of the buffer tank is connected to the fuel pump outside the tank through a pipeline, the outlet of the fuel pump outside the tank is connected to the liquid side inlet of the gas supply heat exchanger through a pipeline, the liquid fuel releases cold energy after being heated in the gas supply heat exchanger, and then flows out from the liquid side outlet of the gas supply heat exchanger, the liquid side outlet of the gas supply heat exchanger is connected to the LNG side inlet of the liquid heater, the heat exchange medium flowing into the liquid heater absorbs the cold energy of the liquid fuel entering the LNG side inlet of the liquid heater, so that the liquid fuel is gasified to form high-pressure gas fuel; The evaporation gas in the fuel tank enters the gas inlet buffer tank through a pipeline on the top of the tank, the tank top of the gas inlet buffer tank is connected to the first-stage compressor and the second-stage compressor through a pipeline in sequence, the high-pressure gaseous fuel flowing out of the outlet of the second-stage compressor enters the LNG side inlet of the gas heat exchanger, the heat exchange medium absorbing cold energy flows out of the liquid heater and passes through the gas heat exchanger, and the high-pressure gaseous fuel entering the LNG side inlet of the gas heat exchanger is cooled and depressurized by heat exchange with the heat exchange medium, thereby being converted into low-pressure gaseous fuel.

2. The high-low pressure gas supply system utilizing LNG cold energy according to claim 1, characterized in that: The low-pressure gaseous fuel flows out of the LNG side outlet of the gas heat exchanger, the low-pressure gaseous fuel flowing out of the LNG side outlet of the gas heat exchanger is divided into two paths, one path is connected to the low-pressure gas supply valve, and the outlet of the low-pressure gas supply valve is connected to the low-pressure gas supply pipeline; the other path is connected to the gas return side inlet of the gas cooler, and the flow distribution ratio of the two paths can be changed by adjusting the opening degree of the low-pressure gas supply valve; The gas return side outlet of the gas cooler is connected to the gas side inlet of the gas supply heat exchanger, the low-pressure gaseous fuel entering the gas return side inlet of the gas cooler is cooled by absorbing cold energy and then enters the gas side inlet of the gas supply heat exchanger; the low-pressure gaseous fuel after cooling absorbs the cold energy of the liquid fuel flowing through the gas supply heat exchanger to realize re-liquefaction, and then flows out from the gas side outlet of the gas supply heat exchanger and returns to the middle part of the gas-liquid separator through a pipeline.

3. The high-low pressure gas supply system utilizing LNG cold energy according to claim 2, characterized in that: The top of the gas-liquid separator is connected to the inlet of the exhaust valve through a pipeline, the outlet of the exhaust valve is connected to the gas supply side inlet of the gas cooler, the gas supply side outlet of the gas cooler is connected to the low-pressure gas supply pipeline of the outlet of the low-pressure gas supply valve; the low-temperature mixed gas from the top of the gas-liquid separator enters the gas supply side of the gas cooler and transfers cold energy to the low-pressure gaseous fuel entering the gas return side of the gas cooler, so that the low-temperature mixed gas is warmed and discharged from the low-pressure gas supply pipeline.

4. The high-low pressure gas supply system utilizing LNG cold energy according to claim 3, characterized in that: The bottom of the gas-liquid separator is connected to the inlet of the liquid discharge valve through a pipeline, and the outlet of the liquid discharge valve is connected to the pipeline between the outlet of the fuel tank fuel pump and the buffer tank, so that the liquid return fuel enters the buffer tank again.

5. The high-low pressure gas supply system utilizing LNG cold energy according to claim 4, characterized in that: The tank top of the gas inlet buffer tank is connected to the low-pressure side of the gas inlet heat exchanger through a pipeline; the outlet of the low-pressure side of the gas inlet heat exchanger is connected to the first-stage compressor; the outlet of the first-stage compressor is connected to the inlet of the high-pressure side of the gas inlet heat exchanger, the high-pressure gaseous fuel after being pressurized by the first-stage compressor enters the high-pressure side of the gas inlet heat exchanger to absorb the cold energy of the evaporation gas entering the low-pressure side of the gas inlet heat exchanger to realize cooling, and the outlet of the high-pressure side of the gas inlet heat exchanger is connected to the inlet of the second-stage compressor.

6. The high-low pressure gas supply system utilizing LNG cold energy according to claim 4, characterized in that: The heat exchange medium flows into the heat exchange inlet of the liquid heater from the pipeline; the heat exchange medium flowing out of the heat exchange outlet of the liquid heater is divided into two paths, one of which is connected to the heat exchange inlet of the gas heat exchanger, and the other is connected to the heat exchange medium regulating valve; the heat exchange outlet of the gas heat exchanger is merged with the outlet of the heat exchange medium regulating valve through the pipeline, so that the heat exchange medium finally flows out; by adjusting the opening degree of the heat exchange medium regulating valve, the flow distribution ratio of the two paths can be changed, and the flow of the heat exchange medium entering the gas heat exchanger can be changed.

7. The high-low pressure gas supply system utilizing LNG cold energy according to claim 4, characterized in that: The heat exchange medium is water glycol.

8. A method of operating a high-low pressure gas supply system as claimed in any one of claims 4-7, characterized in that The method comprises the following steps: S1: high-pressure gas supply mode, the operation process comprising: the fuel pump in the cabin operates to transport liquid fuel from the fuel cabin to the buffer tank, the fuel pump outside the cabin operates to extract the liquid fuel in the buffer tank and pressurize it to the required pressure of the high-pressure user, and deliver it to the liquid heater; in the liquid heater, the liquid fuel exchanges heat with the heat exchange medium, the liquid fuel is gasified and its temperature is within the required temperature range of the user, thereby supplying gas to the high-pressure user.

9. The method of operating a high-low pressure gas supply system of claim 8, wherein, Further comprising the following steps: S2: low-pressure gas supply mode, the operation process comprising: the boil-off gas in the fuel cabin enters the intake buffer tank from the pipeline at the top of the cabin, the boil-off gas in the intake buffer tank is extracted by the primary compressor, then compressed by the secondary compressor, then enters the gas heat exchanger, exchanges heat with the low-temperature heat exchange medium after absorbing cold energy by the liquid heater, and is cooled to the required temperature of the user, and finally passes through the low-pressure gas supply valve to supply gas to the low-pressure user.

10. The method of claim 9, wherein Further comprising the following steps: S3: cold energy recovery mode, the operation process comprising: before supplying gas to the low-pressure user, by increasing or decreasing the opening degree of the low-pressure gas supply valve, the low-pressure gaseous fuel flowing out of the LNG side outlet of the gas heat exchanger is returned to the gas cooler, and the amount of gas entering the return gas side inlet of the gas cooler is correspondingly reduced or increased; the low-pressure gaseous fuel entering the gas side inlet of the gas cooler is cooled by absorbing cold energy and then enters the gas side inlet of the gas supply heat exchanger; the cooled low-pressure gaseous fuel absorbs the cold energy of the liquid fuel flowing through the gas supply heat exchanger again and then flows out from the gas side outlet of the gas supply heat exchanger, and finally enters the gas-liquid separator; the liquid return fuel in the gas-liquid separator can enter the buffer tank again by opening the liquid discharge valve; the low-temperature mixed gas in the gas-liquid separator enters the gas supply side of the gas cooler through the gas discharge valve, thereby supplying cold energy to the low-pressure gaseous fuel of the return gas side of the gas cooler, and finally discharging from the low-pressure gas supply pipeline.

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