A skid-mounted LNG cold energy and pressure energy recycling system and method

Abstract

The application discloses a kind of pry dress formula LNG cold energy, pressure energy recycling system and method, including LNG gas supply device, cold energy recovery power generation device and pressure energy recovery power generation device, can quickly realize LNG gas supply and power generation.LNG gas supply device includes LNG storage tank, cryogenic pump, heat exchanger, pressure energy recovery device, pressure sensor, temperature sensor, odorizing device, cold energy recovery power generation device includes two-stage nitrogen gas brayton cycle device, pressure energy recovery power generation device includes bypass valve, flow regulating valve, flow meter, coaxial two turbine expanders, permanent magnet generator, air temperature type vaporizer, pressure regulating valve.The application is used for tank car transportation LNG, user needed in emergency supply, and utilizes LNG cold energy, pressure energy and other energy power generation, can effectively recover the residual pressure of LNG, cold energy, and improve the comprehensive utilization efficiency of LNG energy, is conducive to the effect of energy saving and emission reduction.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of LNG energy recycling, and particularly relates to a pry-mounted LNG cold energy and pressure energy recycling system and method. BACKGROUND

[0002] Natural gas is one of the cleanest fossil fuels, has a high calorific value and low environmental pollution capacity, and is widely used in countries around the world. Natural gas trading needs long-distance transportation, and there are mainly three forms of transportation: pipeline transportation, compressed natural gas cylinder transportation and liquefied natural gas tank transportation. For places not connected to the natural gas pipeline network, liquefied natural gas (LNG) tank transportation is the primary choice. By compressing and cooling natural gas to its condensation point of -162℃, the storage capacity of natural gas can be reduced by 600 times. From 2015 to 2040, global LNG trade is expected to double, reaching 31 trillion cubic feet.

[0003] LNG is re-gasified to the ambient temperature in the process of going to the user, which releases cold energy of 840kJ / kg. This part of cold energy is often directly discharged through the vaporizer or air, causing a large amount of cold energy waste. The natural gas after gasification will waste pressure energy in the process of supplying users. After the LNG tank truck arrives at the use site and completes loading and unloading, there is often residual natural gas. People usually directly vent the residual natural gas. Methane, the main component in natural gas, is a greenhouse gas that not only pollutes the environment but also causes a large amount of waste energy. Therefore, it is necessary to recycle LNG cold energy, pressure energy and LNG tank truck residual pressure, which has the significance of energy saving and emission reduction and environmental protection. SUMMARY

[0004] The present application aims to provide a pry-mounted LNG cold energy and pressure energy recycling system to solve the problems in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a skid-mounted LNG cold energy and pressure energy recovery and utilization system, comprising an LNG tank truck, an LNG storage tank, a cryogenic pump, a cold energy recovery power generation device, a first vaporizer, a pressure energy recovery power generation device, a pressure sensor, a temperature sensor, and an odorization device, which are connected sequentially via pipelines; the cold energy recovery power generation device is a two-stage Brayton cycle device, consisting of a first heat exchanger, a second heat exchanger, a mixer, a working fluid pump, a regenerator, a second vaporizer, a first turboexpander, a first generator, and a separator connected via pipelines to form a two-stage Brayton cycle; the LNG tank truck's vapor phase pipe is connected to the inlet of the first heat exchanger, and the outlet of the second heat exchanger is connected to the inlet of the first vaporizer; the pressure energy recovery power generation device includes a bypass valve, a flow regulating valve, a flow meter, a pressure energy power generation device, a third vaporizer, and a pressure regulating valve; the pressure energy power generation device includes a second turboexpander, a first overrunning clutch, a second generator, a second overrunning clutch, and a third turboexpander; the inlet of the flow regulating valve is connected to the first vaporizer via a pipeline. The flow regulating valve, the flow meter, the second generator, the second turbine expander, the third vaporizer, and the pressure regulating valve are connected by pipelines to form a pressure energy recovery and power generation branch. The second turbine expander has a first inlet and a first outlet, and the third turbine expander has a second inlet and a second outlet. The first inlet is connected to the pipeline of the flow regulating valve, the first outlet is connected to the inlet of the third vaporizer through a pipeline, the outlet of the third vaporizer is connected to the second inlet through a pipeline, and the second outlet is connected to the pipeline of the pressure regulating valve. The second turbine expander and the third turbine expander are coaxially connected by the first overrunning clutch and the second overrunning clutch, respectively, with the second generator connected in the middle between the two overrunning clutches. The bypass valve is connected in parallel with the pressure energy recovery and power generation branch. The pipeline of the pressure regulating valve is equipped with the pressure sensor, the temperature sensor, and the odorization device. The working medium of the cryogenic pump is LNG, and the working medium of the working medium pump is nitrogen.

[0006] Preferably, the first heat exchanger and the second heat exchanger are connected by pipelines. The outlets of the first heat exchanger and the second heat exchanger are connected to the mixer, while their inlets are connected to the separator. The mixer is connected to the working fluid pump. The outlet of the working fluid pump is connected to the second nitrogen inlet of the regenerator. The second nitrogen outlet of the regenerator is connected to the inlet of the second vaporizer. The outlet of the second vaporizer is connected to the inlet of the first turbine expander. The first turbine expander is connected to the first generator. The outlet of the first turbine expander is connected to the first nitrogen inlet of the regenerator. The first nitrogen outlet of the regenerator is connected to the separator.

[0007] Preferably, both the first generator and the second generator are permanent magnet generators, and both the first overrunning clutch and the second overrunning clutch are ball-type overrunning clutches. The permanent magnet generator includes a rotating shaft, a stator, a rotor, an end cover, stator teeth, a stator winding, a permanent magnet, a rotor core, a first arc-shaped slot, a second arc-shaped slot, and a third arc-shaped slot. There is an air gap between the stator and the rotor core. Multiple stator slots are evenly spaced along the circumferential direction on the side surface of the air gap. The stator slots form equally spaced stator teeth on the side surface of the air gap. Each stator tooth is provided with a set of coils. All the coils constitute the stator winding. The end cover is located at both ends near the rotor core. Each stator tooth has the first arc-shaped slot, the second arc-shaped slot, and the third arc-shaped slot.

[0008] Preferably, the first vaporizer, the second vaporizer, and the third vaporizer are all ambient temperature vaporizers.

[0009] A skid-mounted LNG cold energy and pressure energy recovery and utilization method based on any of the above-mentioned systems includes: S1: When a user urgently needs to use natural gas and electricity, the LNG tanker transporting LNG and the skid-mounted LNG cold energy and pressure energy recovery and utilization system are quickly moved to the site.

[0010] S2: LNG transported by LNG tank trucks is first stored in LNG storage tanks. The vapor phase pipe of the LNG tank truck is directly connected to the inlet of the first heat exchanger. The LNG is pumped by a cryogenic pump and combined with the residual liquid in the vapor phase pipe into the first and second heat exchangers.

[0011] S3: Start the cold energy recovery power generation device. The nitrogen in the cycle absorbs heat and heats up through the second vaporizer, and then enters the first turbine expander to expand and do work, driving the first generator to generate electricity. The nitrogen after doing work enters the regenerator for reheating. The nitrogen coming out of the regenerator is separated into two gas streams by the separator and then cooled by LNG through the first heat exchanger and the second heat exchanger respectively. The cooled nitrogen enters the working fluid pump for pressurization after being merged by the mixer, and then enters the regenerator, where it is heated by the higher temperature nitrogen discharged from the first turbine expander. Finally, the nitrogen coming out of the regenerator enters the second vaporizer to absorb heat, completing the entire process of the two-stage nitrogen Brayton cycle and realizing the LNG cold energy recovery power generation function.

[0012] S4: LNG and the residual liquid in the gas phase pipe are heated in the first and second heat exchangers, releasing cold energy to raise the temperature, and then vaporized through the first vaporizer. The vaporized natural gas enters the pressure energy recovery power generation unit.

[0013] S5: The flow rate is adjusted by controlling the opening of the bypass valve, which changes the pressure of the natural gas passing through the bypass. The flow rate is controlled by the flow regulating valve to control the flow rate of the power generation branch. The flow meter is used to display the branch flow rate. LNG enters the second turbine expander from the first inlet to do work. After doing work, it is discharged from the first outlet and enters the third vaporizer to absorb heat. Then it enters the third turbine expander from the second inlet to do work. The third turbine expander and the second turbine expander are coaxially connected to the first overrunning clutch and the second overrunning clutch, respectively, to drive the permanent magnet generator to generate electricity. The natural gas discharged from the second outlet is discharged again through the pressure regulating valve.

[0014] S6: The gas is discharged to users through an odorization device, providing timely warnings in case of natural gas leaks and increasing system safety;

[0015] S7: The natural gas discharged from the pressure regulating valve is combined with the natural gas from the bypass valve and discharged to complete the LNG pressure energy recovery and utilization and pressure regulation;

[0016] S8: The pressure and temperature of the natural gas are fed back through pressure and temperature sensors to ensure that the output natural gas meets the user's requirements.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. The skid-mounted LNG cold energy and pressure energy recovery system of the present invention can be easily moved and quickly supplied to users who need natural gas and electricity.

[0019] 2. The LNG cold energy recovery device of the present invention uses a two-stage nitrogen Brayton cycle to recover the cold energy of LNG. The recovered cold energy drives a permanent magnet generator to generate electricity through a turbine expander. The pressure energy recovery device can recover the pressure energy of LNG and use two turbine expanders to drive a permanent magnet generator to generate electricity. It can simultaneously supply gas and electricity, realizing the comprehensive utilization of energy.

[0020] 3. The pressure energy recovery device of the present invention can adjust the outlet natural gas pressure while realizing pressure energy power generation, so that the temperature and pressure of the outlet natural gas meet the user's requirements. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0022] Figure 2 This is a schematic diagram of the cold energy recovery power generation device of the present invention;

[0023] Figure 3 This is a schematic diagram of the pressure energy power generation device of the present invention;

[0024] Figure 4 This is a schematic diagram of the permanent magnet generator structure of the present invention;

[0025] Figure 5 This is a schematic diagram of the workflow of the present invention.

[0026] In the diagram: 1. LNG tanker; 2. LNG storage tank; 3. Cryogenic pump; 4. First heat exchanger; 5. Second heat exchanger; 6. Cold energy recovery power generation unit; 601. Mixer; 602. Separator; 603. Working fluid pump; 604. Regenerator; 6041. First nitrogen inlet; 6042. First nitrogen outlet; 6043. Second nitrogen inlet; 6044. Second nitrogen outlet; 605. Second vaporizer; 606. First turbine expander; 607. First generator; 7. First vaporizer; 8. Pressure energy recovery power generation unit; 801. Flow regulating valve; 802. Flow meter; 803. Pressure energy power generation unit; 80 4. Pressure regulating valve; 805. Bypass valve; 806. Third vaporizer; 9. Pressure sensor; 10. Temperature sensor; 11. Odorization device; 12. First inlet; 13. First outlet; 14. Second turbine expander; 15. First overrunning clutch; 16. Stator; 17. Rotor; 18. Second overrunning clutch; 19. Third turbine expander; 20. Second inlet; 21. Second outlet; 22. Shaft; 23. Second generator; 24. End cover; 25. Stator teeth; 26. Stator winding; 27. Permanent magnet; 28. Rotor core; 29. ​​First arc-shaped slot; 30. Second arc-shaped slot; 31. Third arc-shaped slot. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] like Figure 1 , Figure 3 , Figure 5As shown, this invention provides a skid-mounted LNG cold energy and pressure energy recovery and utilization system, including an LNG tanker 1, an LNG storage tank 2, a cryogenic pump 3, a cold energy recovery and power generation device 6, a first vaporizer 7, a pressure energy recovery and power generation device 8, a pressure sensor 9, a temperature sensor 10, and an odorization device 11, which are connected sequentially by pipelines; the cold energy recovery and power generation device 6 is a two-stage Brayton cycle device, consisting of a first heat exchanger 4, a second heat exchanger 5, a mixer 601, a working fluid pump 603, a regenerator 604, a second vaporizer 605, a first turbine expander 606, a first generator 607, and a separator 602 connected by pipelines to form two stages. The system employs a Brayton cycle, with the LNG tanker 1's vapor phase pipe connected to the inlet of the first heat exchanger 4, and the outlet of the second heat exchanger 5 connected to the inlet of the first vaporizer 7. The pressure energy recovery power generation device 8 includes a bypass valve 805, a flow regulating valve 801, a flow meter 802, a pressure energy power generation device 803, a third vaporizer 806, and a pressure regulating valve 804. The pressure energy power generation device 803 includes a second turbine expander 14, a first overrunning clutch 15, a second generator 23, a second overrunning clutch 18, and a third turbine expander 19. The inlet of the flow regulating valve 801 is connected to the outlet of the first vaporizer 7 via a pipeline. The flow regulating valve 801, the flow meter 802, the second generator 23, the second turbine expander 14, the third vaporizer 806, the third turbine expander 19, and the pressure regulating valve 804 are connected by pipelines to form a pressure energy recovery and power generation branch. The second turbine expander 14 has a first inlet 12 and a first outlet 13, and the third turbine expander 19 has a second inlet 20 and a second outlet 21. The first inlet 12 is connected to the pipeline of the flow regulating valve 801, and the first outlet 13 is connected to the inlet of the third vaporizer 806 through a pipeline. The outlet of the third vaporizer 806 is connected to the pipeline of the flow regulating valve 801. The pipeline connects to the second inlet 20, and the second outlet 21 connects to the pipeline of the pressure regulating valve 804; the second turbine expander 14 and the third turbine expander 19 are coaxially connected via the first overrunning clutch 15 and the second overrunning clutch 18, respectively, with the second generator 23 connected in the middle between the two overrunning clutches; the bypass valve 805 is connected in parallel with the pressure energy recovery power generation branch; the pipeline of the pressure regulating valve 804 is equipped with the pressure sensor 9, the temperature sensor 10, and the odorization device 11; the working medium of the cryogenic pump 3 is LNG, and the working medium of the working medium pump 603 is nitrogen. The LNG tanker 1 transporting LNG and the skid-mounted LNG energy recovery and utilization system are quickly moved to the site for gas and power supply.On one hand, the LNG tanker truck 1 and the skid-mounted LNG energy recovery system arrive at the user's location. The LNG discharged from the LNG tanker truck 1 is first stored in the LNG storage tank 2. The vapor phase pipe of the LNG tanker truck 1 can be directly connected to the inlet of the first heat exchanger 4. The LNG pumped by the cryogenic pump 3 can merge with the residual liquid in the vapor phase pipe and go to the first heat exchanger 4 and the second heat exchanger 5 for heat absorption. Then it is vaporized by the first vaporizer 7. The vaporized natural gas enters the pressure energy recovery device 8 for pressure energy recovery and pressure regulation before being discharged. Finally, it is discharged to the user through the odorization device 11. The odorization device can provide timely warnings in case of natural gas leakage, increasing the safety of the system.

[0029] like Figure 2 As shown, the first heat exchanger 4 and the second heat exchanger 5 are connected by pipes. The outlets of the first heat exchanger 4 and the second heat exchanger 5 are connected to the mixer 601, while the inlets are connected to the separator 602. The mixer 601 is connected to the working fluid pump 603. The outlet of the working fluid pump 603 is connected to the second nitrogen inlet 6043 of the regenerator 604. The second nitrogen outlet 6044 of the regenerator 604 is connected to the inlet of the second vaporizer 605. The outlet of the second vaporizer 605 is connected to the inlet of the first turbine expander 606. The first turbine expander 606 is connected to the first generator 607. The outlet of the first turbine expander 606 is connected to the first nitrogen inlet 6041 of the regenerator 604. The first nitrogen outlet 6042 of the regenerator 604 is connected to the separator 602. In this embodiment, the circulating nitrogen passes through the second... The vaporizer 605 absorbs heat and heats up, then enters the first turboexpander 606 to expand and do work, driving the first generator 607 to generate electricity. The nitrogen gas after doing work enters the regenerator 604 from the first nitrogen inlet 6041 and exits from the first nitrogen outlet 6042 for reheating. The nitrogen gas exiting the regenerator is separated into two streams by the separator 602, which pass through the first heat exchanger 4 and the second heat exchanger 5 respectively, and is cooled by LNG. The cooled nitrogen gas is then merged by the mixer 601 and enters the working fluid pump 603 for pressurization, and then enters the regenerator 604. It enters from the second nitrogen inlet 6043 and exits from the second nitrogen outlet 6044, where it is heated by the higher-temperature nitrogen gas discharged from the first turboexpander 606. Finally, the nitrogen gas exiting from the second nitrogen outlet 6044 of the regenerator 604 enters the second vaporizer 605 to absorb heat, completing the entire process of the two-stage nitrogen Brayton cycle and realizing the LNG cold energy recovery and power generation function.

[0030] like Figures 3-4As shown, both the first generator 607 and the second generator 23 are permanent magnet generators. The first overrunning clutch 15 and the second overrunning clutch 18 are ball-type overrunning clutches. The permanent magnet generator includes a shaft 22, a stator 16, a rotor 17, an end cover 24, stator teeth 25, a stator winding 26, a permanent magnet 27, a rotor core 28, a first arc-shaped slot 29, a second arc-shaped slot 30, and a third arc-shaped slot 31. An air gap exists between the stator 16 and the rotor core 28. Multiple stator slots are evenly spaced along the circumferential direction on the surface of the air gap. These slots form evenly spaced stator teeth 25 on the surface of the air gap. Each stator tooth 25 has a set of coils, and all coils constitute the stator winding 26. The end cover... 24 is located at both ends near the rotor core 28, and each stator tooth has a first arc-shaped groove 29, a second arc-shaped groove 30, and a third arc-shaped groove 31. In this embodiment, the other ends of the first overrunning clutch 15 and the second overrunning clutch 18 are coaxially connected to the second turbine expander 14 and the third turbine expander 19, respectively. When high-pressure natural gas enters the two turbine expanders, it drives the rotating shaft 22 to do work, converting pressure energy into mechanical energy. This, in conjunction with the stator 16 and the rotor 17, drives the permanent magnet generator to cut magnetic lines of force to generate electricity, converting mechanical energy into electrical energy. The first arc-shaped groove 29, the second arc-shaped groove 30, and the third arc-shaped groove 31 on each stator tooth can effectively reduce cogging torque, reduce vibration and noise, and optimize the voltage waveform.

[0031] like Figure 3 As shown, the first vaporizer 7, the second vaporizer 605, and the third vaporizer 806 are all ambient air vaporizers; in this embodiment, the ambient air vaporizer has wide overall adaptability and high efficiency.

[0032] This invention provides a skid-mounted LNG cold energy and pressure energy recovery and utilization method based on any of the above-mentioned systems, comprising: S1: when a user urgently needs to use natural gas and electricity, the LNG tanker 1 transporting LNG and the skid-mounted LNG cold energy and pressure energy recovery and utilization system are quickly moved to the site;

[0033] S2: The LNG transported by the LNG tanker 1 is first stored in the LNG storage tank 2. The vapor phase pipe of the LNG tanker 1 is directly connected to the inlet of the first heat exchanger 4. The LNG is pumped by the cryogenic pump 3 and combined with the residual liquid in the vapor phase pipe into the first heat exchanger 4 and the second heat exchanger 5.

[0034] S3: Start the cold energy recovery power generation device 6. The nitrogen in the cycle absorbs heat and rises in temperature through the second vaporizer 605, and then enters the first turbine expander 606 to expand and do work, driving the first generator 607 to generate electricity. The nitrogen after doing work enters the regenerator 604 for reheating. The nitrogen coming out of the regenerator 604 is separated into two streams by the separator 602 and then passes through the first heat exchanger 4 and the second heat exchanger 5 respectively to be cooled by LNG. The cooled nitrogen is merged through the mixer 601 and then enters the working fluid pump 603 for pressurization, and then enters the regenerator 604, where it is heated by the higher temperature nitrogen discharged from the first turbine expander 606. Finally, the nitrogen coming out of the regenerator 604 enters the second vaporizer 605 to absorb heat, completing the entire process of the two-stage nitrogen Brayton cycle and realizing the LNG cold energy recovery power generation function.

[0035] S4: LNG and the residual liquid in the gas phase pipe are heated in the first heat exchanger 4 and the second heat exchanger 5 to release cold energy and increase temperature. Then, they are vaporized through the first vaporizer 7. The vaporized natural gas enters the pressure energy recovery power generation device 8.

[0036] S5: The flow rate is adjusted by controlling the opening of the bypass valve 805, changing the pressure of the natural gas passing through the bypass. The flow rate of the power generation branch is controlled by the flow regulating valve 801. The flow meter 802 is used to display the branch flow rate. LNG enters the second turbine expander 14 from the first inlet 12 to do work. After doing work, it is discharged from the first outlet 13 and enters the third vaporizer 806 to absorb heat. Then it enters the third turbine expander 19 through the second inlet 20 to do work. The third turbine expander 19 and the second turbine expander 14 are coaxially connected to the first overrunning clutch 15 and the second overrunning clutch 18, respectively, driving the permanent magnet generator to generate electricity. The natural gas discharged from the second outlet 21 is discharged again through the pressure regulating valve 804.

[0037] S6: Discharged to users through odorization device 11, providing timely warnings in case of natural gas leaks and increasing system safety;

[0038] S7: The natural gas discharged from the pressure regulating valve 804 is combined with the natural gas from the bypass valve 805 and discharged to complete the LNG pressure energy recovery and utilization and pressure regulation;

[0039] S8: The pressure and temperature of the natural gas are fed back through pressure sensor 9 and temperature sensor 10, so that the output natural gas meets the user's requirements. Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A skid-mounted LNG cold energy and pressure energy recovery and utilization system, characterized in that, It includes LNG tank trucks, LNG storage tanks, cryogenic pumps, cold energy recovery power generation devices, first vaporizers, pressure energy recovery power generation devices, pressure sensors, temperature sensors, and odorization devices, which are connected in sequence through pipelines; The cold energy recovery power generation device is a two-stage Brayton cycle device, consisting of a first heat exchanger, a second heat exchanger, a mixer, a working fluid pump, a regenerator, a second vaporizer, a first turboexpander, a first generator, and a separator connected by pipelines to form a two-stage Brayton cycle. The LNG tanker's vapor phase pipe is connected to the inlet of the first heat exchanger, and the outlet of the second heat exchanger is connected to the inlet of the first vaporizer. The pressure energy recovery power generation device includes a bypass valve, a flow regulating valve, a flow meter, a pressure energy power generation device, a third vaporizer, and a pressure regulating valve. The pressure energy power generation device includes a second turboexpander, a first overrunning clutch, a second generator, a second overrunning clutch, and a third turboexpander. The inlet of the flow regulating valve is connected to the outlet of the first vaporizer via a pipeline. The flow regulating valve, the flow meter, the second generator, the second turboexpander, the third vaporizer, and the pressure regulating valve are connected via pipelines to form a pressure energy recovery power generation branch. The second turboexpander has a first inlet and a first outlet, and the third turboexpander has a second inlet and a second outlet. The first inlet is connected to the pipeline of the flow regulating valve, the first outlet is connected to the inlet of the third vaporizer via a pipeline, the outlet of the third vaporizer is connected to the second inlet via a pipeline, and the second outlet is connected to the pipeline of the pressure regulating valve. The second turboexpander and the third turboexpander are coaxially connected via the first overrunning clutch and the second overrunning clutch, respectively, with the second generator connected between the two overrunning clutches. The bypass valve is connected in parallel with the pressure energy recovery power generation branch. The pressure regulating valve is equipped with the pressure sensor, the temperature sensor and the odorization device. The working medium of the cryogenic pump is LNG and the working medium of the working medium pump is nitrogen. The first heat exchanger and the second heat exchanger are connected by pipes. The outlets of the first heat exchanger and the second heat exchanger are connected to the mixer, while their inlets are connected to the separator. The mixer is connected to the working fluid pump. The outlet of the working fluid pump is connected to the second nitrogen inlet of the regenerator. The second nitrogen outlet of the regenerator is connected to the inlet of the second vaporizer. The outlet of the second vaporizer is connected to the inlet of the first turbine expander. The first turbine expander is connected to the first generator. The outlet of the first turbine expander is connected to the first nitrogen inlet of the regenerator. The first nitrogen outlet of the regenerator is connected to the separator.

2. The skid-mounted LNG cold energy and pressure energy recovery and utilization system according to claim 1, characterized in that, Both the first generator and the second generator are permanent magnet generators. The first overrunning clutch and the second overrunning clutch are both ball-type overrunning clutches. The permanent magnet generator includes a rotating shaft, a stator, a rotor, an end cover, stator teeth, a stator winding, a permanent magnet, a rotor core, a first arc-shaped slot, a second arc-shaped slot, and a third arc-shaped slot. There is an air gap between the stator and the rotor core. Multiple stator slots are evenly spaced along the circumferential direction on the side surface of the air gap. The stator slots form equally spaced stator teeth on the side surface of the air gap. Each stator tooth is provided with a set of coils. All the coils constitute the stator winding. The end cover is located at both ends near the rotor core. Each stator tooth has the first arc-shaped slot, the second arc-shaped slot, and the third arc-shaped slot.

3. The skid-mounted LNG cold energy and pressure energy recovery and utilization system according to claim 1, characterized in that, The first vaporizer, the second vaporizer, and the third vaporizer are all ambient temperature vaporizers.

4. A skid-mounted method for recovering and utilizing the cold and pressure energy of LNG based on the system described in any one of claims 1 to 3, comprising: S1: When users urgently need natural gas and electricity, the LNG tank trucks transporting LNG and the skid-mounted LNG cold energy and pressure energy recovery and utilization system will be quickly moved to the site. S2: LNG transported by LNG tank trucks is first stored in LNG storage tanks. The vapor phase pipe of the LNG tank truck is directly connected to the inlet of the first heat exchanger. The LNG is pumped by a cryogenic pump and combined with the residual liquid in the vapor phase pipe into the first and second heat exchangers. S3: Start the cold energy recovery power generation device. The nitrogen in the cycle absorbs heat and heats up through the second vaporizer, and then enters the first turbine expander to expand and do work, driving the first generator to generate electricity. The nitrogen after doing work enters the regenerator for reheating. The nitrogen coming out of the regenerator is separated into two gas streams by the separator and then cooled by LNG through the first heat exchanger and the second heat exchanger respectively. The cooled nitrogen enters the working fluid pump for pressurization after being merged by the mixer, and then enters the regenerator, where it is heated by the higher temperature nitrogen discharged from the first turbine expander. Finally, the nitrogen coming out of the regenerator enters the second vaporizer to absorb heat, completing the entire process of the two-stage nitrogen Brayton cycle and realizing the LNG cold energy recovery power generation function. S4: LNG and the residual liquid in the gas phase pipe are heated in the first and second heat exchangers, releasing cold energy to raise the temperature, and then vaporized through the first vaporizer. The vaporized natural gas enters the pressure energy recovery power generation unit. S5: The flow rate is adjusted by controlling the opening of the bypass valve, which changes the pressure of the natural gas passing through the bypass. The flow rate is controlled by the flow regulating valve to control the flow rate of the power generation branch. The flow meter is used to display the branch flow rate. LNG enters the second turbine expander from the first inlet to do work. After doing work, it is discharged from the first outlet and enters the third vaporizer to absorb heat. Then it enters the third turbine expander from the second inlet to do work. The third turbine expander and the second turbine expander are coaxially connected to the first overrunning clutch and the second overrunning clutch, respectively, to drive the permanent magnet generator to generate electricity. The natural gas discharged from the second outlet is discharged again through the pressure regulating valve. S6: The gas is discharged to users through an odorization device, providing timely warnings in case of natural gas leaks and increasing system safety; S7: The natural gas discharged from the pressure regulating valve is combined with the natural gas from the bypass valve and discharged to complete the LNG pressure energy recovery and utilization and pressure regulation; S8: The pressure and temperature of the natural gas are fed back through pressure and temperature sensors to ensure that the output natural gas meets the user's requirements.

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