Two-stage expansion interstage regenerative LNG (Liquefied Natural Gas) cold energy power generation system

Abstract

The invention relates to a two-stage expansion interstage regenerative LNG (Liquefied Natural Gas) cold energy power generation system, which is characterized in that a regenerator is arranged, interstage steam extraction is utilized to extract part of exhaust steam of a first-stage turbo expander, and circulating working medium fluid after a working medium booster pump is heated; therefore, the heat absorption average temperature of the circulating working medium is improved; moreover, by arranging the subcooler, interstage steam extraction heat is fully absorbed, the drainage temperature is reduced to about 15 DEG C below the saturation temperature, and the amount of flash steam entering the condenser is greatly reduced; therefore, pipeline vibration caused by flash evaporation is avoided, and meanwhile, the condensation load of unit mass exhaust steam is reduced; the working medium circulation amount of the system is increased, and the system generation power is obviously improved; as a cold energy power generation system with higher power generation efficiency, the system is beneficial to efficiently recycling LNG cold energy, and has important significance in improving the economy of an LNG cold energy power generation project, reducing energy consumption, reducing environmental influence and realizing high-quality development of an LNG industrial chain.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of LNG cold energy power generation, and particularly relates to a two-stage expansion inter-stage regenerative LNG cold energy power generation system. BACKGROUND

[0002] LNG (liquefied natural gas) needs to be endothermically gasified and warmed to above zero degrees before being exported to the natural gas pipeline network. A large amount of heat is absorbed during the gasification of LNG, and a large amount of cold energy is released. The cold energy released during the gasification of 1 ton of LNG is equivalent to about 240-260 kWh of electric energy. A large LNG receiving station with an annual processing capacity of 6 million tons releases about 1.5 billion degrees of electric energy in theory every year. However, this part of cold energy is usually not utilized but is taken away by seawater, and a large amount of energy is consumed to complete the gasification of LNG, which wastes the valuable cold energy contained in LNG and causes great waste of energy.

[0003] Under the dual-carbon target, improving the utilization efficiency of LNG cold energy is of great significance to promoting energy saving and carbon reduction of the LNG industry chain. LNG cold energy power generation, as an important way of cold energy utilization, has been demonstrated in some receiving stations. However, the current cold energy power generation unit mainly adopts a simple organic Rankine cycle, which is limited by insufficient cold energy utilization depth and low power generation efficiency. SUMMARY

[0004] In view of at least one problem in the prior art, the present application aims to provide a two-stage expansion inter-stage regenerative LNG cold energy power generation system, which solves the problems in the prior art that a large amount of cold energy released during the gasification of LNG is usually not utilized but is taken away by seawater, and a large amount of energy is consumed to complete the gasification of LNG, which wastes the valuable cold energy contained in LNG and causes great waste of energy, and the current cold energy power generation unit mainly adopts a simple organic Rankine cycle, which is limited by insufficient cold energy utilization depth and low power generation efficiency, so that it is helpful to efficiently recover and utilize LNG cold energy, and has important significance to improving the economic efficiency of LNG cold energy power generation projects, reducing energy consumption, reducing environmental impact and realizing high-quality development of the LNG industry chain.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A two-stage expansion inter-stage regenerative LNG cold energy power generation system, comprising a first-stage turbine expander, a second-stage turbine expander, an evaporator, a regenerator, a subcooler, a throttling valve, a working fluid booster pump, a condenser and a natural gas heater; The inlet of the first-stage turbine expander is connected with the shell side outlet of the evaporator; the outlet of the first-stage turbine expander is connected with the inlet of the second-stage turbine expander and the shell side inlet of the regenerator, respectively; The outlet of the second-stage turbine expander is connected to the shell-side inlet of the condenser; The shell-side outlet of the condenser is sequentially connected to the working fluid booster pump, the tube-side inlet of the subcooler, the tube-side inlet of the regenerator, and the shell-side inlet of the evaporator; the tube-side outlet of the condenser is connected to the shell-side inlet of the natural gas heater; the tube-side outlet of the natural gas heater is connected to the tube-side inlet of the evaporator. The throttling valve is installed on the pipe between the shell-side outlet of the subcooler and the shell-side inlet of the condenser.

[0006] Preferably, the shell-side outlet of the natural gas heater is connected to a natural gas export pipeline, and the pipe-side inlet of the natural gas heater can be vented to seawater.

[0007] Preferably, the working fluid booster pump is connected to an electric motor.

[0008] Preferably, the first-stage turbine expander and the second-stage turbine expander are coaxially connected, and the second-stage turbine expander is connected to the generator.

[0009] Preferably, the generator is configured as an explosion-proof brushless excitation synchronous generator, the motor is configured as an explosion-proof synchronous motor; the evaporator is configured as a shell-and-tube heat exchanger, the regenerator is configured as a shell-and-tube heat exchanger, the subcooler is configured as a shell-and-tube heat exchanger, the condenser is configured as a coiled tube heat exchanger, and the natural gas heater is configured as a shell-and-tube heat exchanger.

[0010] Preferably, the shell-side outlet of the regenerator is connected to the shell-side inlet of the subcooler.

[0011] Preferably, the condenser is arranged at a high position, and the evaporator and the natural gas heater are arranged longitudinally at a low position relative to the condenser. Preferably, the pipe-side inlet of the condenser is connected to the LNG pipeline. LNG enters the pipe-side inlet of the condenser and absorbs the heat of the low-pressure gaseous organic working fluid entering the shell side of the condenser, condensing it into a liquid state. The medium-low temperature LNG after absorbing heat and evaporating enters the shell side of the natural gas heater from the pipe-side outlet of the condenser for further heat absorption and temperature rise to above zero degrees Celsius before entering the natural gas export pipeline network. At room temperature seawater enters the pipe side of the natural gas heater to heat the medium-low temperature NG. Seawater from the pipe side outlet of the natural gas heater enters the pipe side of the evaporator to heat and evaporate the high-pressure organic working fluid in the shell side of the evaporator. The liquid medium-pressure organic working fluid at the shell-side outlet of the regenerator enters the shell-side inlet of the subcooler, and the liquid medium-pressure organic working fluid with a certain degree of subcooling at the shell-side outlet of the subcooler enters the throttling valve to expand and further reduce the temperature, thereby reducing the amount of flash steam entering the condenser.

[0012] Preferably, the seawater temperature at the pipe-side outlet of the evaporator is ~℃ lower than the ambient seawater temperature at the pipe-side inlet of the natural gas heater.

[0013] Preferably, an ultrasonic flow meter is installed on the pipe connecting the shell-side outlet of the evaporator and the inlet of the first-stage turbine expander.

[0014] The present invention has the following advantages due to the adoption of the above technical solutions: 1. The two-stage expansion stage regenerative LNG cold energy power generation system provided by this invention, by setting up a regenerator and utilizing interstage extraction steam to extract part of the exhaust steam from the first-stage turbine expander and heat the circulating working fluid after the working fluid booster pump, increases the average heat absorption temperature of the circulating working fluid, thereby improving the system's circulating thermal efficiency. Furthermore, by setting up a subcooler, the heat from the interstage extraction steam is fully absorbed, reducing the condensate temperature to approximately 15°C below the saturation temperature, significantly reducing the amount of flash steam entering the condenser. This avoids pipeline vibration caused by flash evaporation and reduces the condensation load per unit mass of exhaust steam, thereby increasing the system's working fluid circulation and significantly improving the system's power generation. When the condensate temperature is reduced below the saturation temperature, propane can be used as the working fluid for the system's circulation. Taking a cold energy generator set in an LNG receiving terminal as an example, the two-stage expansion stage regenerative LNG cold energy power generation system disclosed in this invention is used... The power system achieves a 13.3°C increase in working fluid endothermic temperature, a 7.5% increase in working fluid circulation volume, a 195.8kW increase in power generation, and a 0.644% increase in system power generation efficiency, representing a 4.779% improvement. This addresses existing technologies where a large amount of cold energy released during LNG vaporization is often not utilized and is instead carried away by seawater; the high energy consumption required for LNG vaporization wastes the valuable cold energy contained in LNG; and the low power generation efficiency of existing cold energy generators, which primarily use simple organic Rankine cycles and are limited by insufficient cold energy utilization. This system, with its higher power generation efficiency, facilitates the efficient recovery and utilization of LNG cold energy, significantly improving the economics of LNG cold energy power generation projects, reducing energy consumption, minimizing environmental impact, and achieving high-quality development of the LNG industry chain.

[0015] 2. The two-stage expansion stage regenerative LNG cold energy power generation system provided by this invention can reduce pipeline pressure loss and improve the work capacity of the circulating working fluid per unit mass by setting up an ultrasonic flow meter; it further facilitates the effective recovery and utilization of LNG cold energy, which can improve the economic efficiency of LNG cold energy power generation projects, reduce energy consumption, reduce environmental impact, and achieve high-quality development of the LNG industry chain. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the structure of a two-stage expansion stage regenerative LNG cold energy power generation system provided in an embodiment of the present invention.

[0017] Marked in the attached diagram: 1. First-stage turboexpander, 2. Second-stage turboexpander, 3. Generator, 4. Evaporator, 5. Regenerator, 6. Subcooler, 7. Throttling valve, 8. Electric motor, 9. Working fluid booster pump, 10. Condenser, 11. Natural gas heater. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0019] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the system or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. The arrow direction in the figure represents the direction of liquid flow.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "assembly," "setup," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] This invention provides a two-stage expansion stage regenerative LNG cold energy power generation system, which can extract part of the exhaust steam from the first-stage turbine expander to heat the high-pressure fluid medium at the outlet of the working fluid booster pump; thereby increasing the heat absorption temperature of the working fluid and thus improving the system's cycle thermal efficiency. The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] Example Please refer to Figure 1The two-stage expansion stage regenerative LNG cold energy power generation system provided in this embodiment includes a first-stage turbine expander 1, a second-stage turbine expander 2, an evaporator 4, a regenerator 5, a subcooler 6, a throttle valve 7, a working fluid booster pump 9, a condenser 10, and a natural gas heater 11. The inlet of the first-stage turbine expander 1 is connected to the shell-side outlet of the evaporator 4; the outlet of the first-stage turbine expander 1 is connected to the inlet of the second-stage turbine expander 2 and the shell-side inlet of the regenerator 5, respectively. The outlet of the second-stage turbine expander 2 is connected to the shell-side inlet of the condenser 10; The shell-side outlet of condenser 10 is connected in sequence to the working fluid booster pump 9, the tube-side inlet of subcooler 6, the tube-side inlet of regenerator 5, and the shell-side inlet of evaporator 4; the tube-side outlet of condenser 10 is connected to the shell-side inlet of natural gas heater 11; the tube-side outlet of natural gas heater 11 is connected to the tube-side inlet of evaporator 4. The throttle valve 7 is installed on the pipe between the shell-side outlet of the subcooler 6 and the shell-side inlet of the condenser 10.

[0023] In practical applications, the high-pressure gaseous organic working fluid from the shell-side outlet of evaporator 4 enters the inlet of the first-stage turbine expander 1. The medium-pressure gaseous organic working fluid from the outlet of the first-stage turbine expander 1 splits into two streams: one enters the inlet of the second-stage turbine expander 2, and the other enters the shell-side inlet of the regenerator 5 to act as a heat source to heat the working fluid. The low-pressure gaseous organic working fluid from the outlet of the second-stage turbine expander 2 merges with the low-pressure liquid organic working fluid throttled at the outlet of the throttling valve 7 and enters the shell-side inlet of condenser 10. The low-pressure liquid organic working fluid from the shell-side outlet of condenser 10 is pressurized by the working fluid booster pump 9 and then enters the tube-side inlet of subcooler 6. The preheated high-pressure organic working fluid from the tube-side outlet of subcooler 6 enters the tube-side inlet of regenerator 5 for further preheating. The high-pressure organic working fluid from the tube-side outlet of regenerator 5 enters the shell-side inlet of evaporator 4 to absorb heat and evaporate. The shell-side outlet of regenerator 5 is connected to the shell-side inlet of subcooler 6. The liquid medium-pressure organic working fluid from the shell-side outlet of regenerator 5 enters the shell-side inlet of subcooler 6. The liquid medium-pressure organic working fluid with a preset subcooling degree from the shell-side outlet of subcooler 6 enters the throttling valve 7 for throttling expansion, thereby further reducing the temperature and decreasing the amount of flash steam entering condenser 10. The LNG in the station enters the pipe-side inlet of condenser 10 and absorbs heat from the low-pressure gaseous organic working fluid on the shell side of condenser 10, causing the circulating working fluid to condense into a liquid state. At the same time, the medium-low temperature LNG after heat absorption and evaporation enters the shell-side inlet of natural gas heater 11 from the pipe-side outlet of condenser 10, and further absorbs heat to raise the temperature to above zero degrees before entering the natural gas export pipeline network. Specifically, the working fluid at the inlet of the first-stage turbine expander 1 is set to propane, and the fluid at the pipe-side inlet of the natural gas heater 11 is set to seawater.

[0024] The specific processes of the two-stage expansion stage regenerative LNG cold energy power generation system in this embodiment, including LNG circulation, working fluid circulation, and seawater circulation, are as follows: LNG cycle: LNG, pressurized by the high-pressure pump in the receiving terminal, enters the pipe-side inlet of condenser 10 and exchanges heat with the working fluid at the shell-side inlet of condenser 10. After being heated to a gaseous state in condenser 10, LNG enters the shell-side inlet of natural gas heater 11 and exchanges heat with seawater, which serves as a heat source. Finally, it is heated to above 0°C and transported to the plant's natural gas export pipeline.

[0025] Working fluid circulation: The high-pressure working fluid from the working fluid booster pump 9 enters the tube-side inlet of the subcooler 6 and exchanges heat with the working fluid at the shell-side inlet of the subcooler 6; then it enters the tube-side inlet of the regenerator 5 and exchanges heat with the interstage extraction steam entering the shell-side inlet of the regenerator 5, thereby further increasing the temperature; then it enters the shell-side inlet of the evaporator 4 and exchanges heat with the seawater heat source at the tube-side inlet of the evaporator 4, and is heated to a steam state with a preset superheat; then it enters the first-stage turbine expander 1 to expand and do work. The exhaust steam from the first-stage turboexpander 1 is divided into two streams: one stream enters the second-stage turboexpander 2 to continue expanding and doing work, and the exhaust steam from the second-stage turboexpander 2 after doing work enters the shell-side inlet of the condenser 10 and is condensed into liquid by the LNG in the tube-side inlet of the condenser 10; the other stream serves as the heat source for the regenerator 5 and enters the shell-side inlet of the regenerator 5, and then enters the shell-side inlet of the subcooler 6, where it further exchanges heat with the high-pressure working fluid after being pressurized by the working fluid booster pump 9 to cool down; the working fluid with a preset subcooling degree at the shell-side outlet of the subcooler 6 enters the throttle valve 7 for depressurization and then enters the shell-side inlet of the condenser 10; in the shell-side inlet of the condenser 10, it is condensed into liquid by the LNG in the tube-side inlet of the condenser 10; the liquid working fluid at the bottom of the shell-side outlet of the condenser 10 enters the working fluid booster pump 9 for pressurization, completing one cycle and starting the next cycle.

[0026] Seawater circulation: Seawater pressurized by the seawater pump in the receiving station enters the pipe-side inlet of the natural gas heater 11 and exchanges heat with the low-temperature natural gas at the shell-side inlet of the natural gas heater 11; then it enters the pipe-side inlet of the evaporator 4 and serves as a heat source to heat the working fluid at the shell-side inlet of the evaporator 4; finally, it enters the seawater drainage channel in the receiving station from the pipe-side outlet of the evaporator 4.

[0027] The heat source for the natural gas heater 11 and the evaporator 4 is seawater, which is usually below 35°C and is a low-grade heat source.

[0028] Specifically, the shell-side outlet of the natural gas heater 11 is connected to the natural gas export pipeline.

[0029] Specifically, the working fluid booster pump 9 is connected to the electric motor 8.

[0030] Furthermore, generator 3 is configured as an explosion-proof brushless excitation synchronous generator, and motor 8 is configured as an explosion-proof synchronous motor.

[0031] Specifically, the first-stage turbine expander 1 and the second-stage turbine expander 2 are coaxially connected, and the second-stage turbine expander 2 is connected to the generator 3.

[0032] Specifically, the condenser 10 is arranged at a high position, while the evaporator 4 and the natural gas heater 11 are arranged at a low position relative to the condenser 10.

[0033] By arranging the condenser 10 at a high position, sufficient net positive suction head is ensured when the saturated liquid working medium from the shell-side outlet of the condenser 10 enters the impeller inlet of the working medium booster pump 9, thus preventing cavitation. Combined with the longitudinal low-position arrangement of the evaporator 4 and the natural gas heater 11 relative to the condenser 10, space can be saved.

[0034] In addition, the first-stage turbine expander 1, the second-stage turbine expander 2 and the generator 3 are arranged inside the plant, while the working fluid booster pump 9 is arranged separately in a semi-underground location to further ensure sufficient net positive suction head and prevent cavitation.

[0035] Specifically, the evaporator 4 is a shell-and-tube heat exchanger, the regenerator 5 is a shell-and-tube heat exchanger, the subcooler 6 is a shell-and-tube heat exchanger, the condenser 10 is a coiled tube heat exchanger, and the natural gas heater 11 is a shell-and-tube heat exchanger.

[0036] At this time, ambient temperature seawater enters the pipe-side inlet of the natural gas heater 11 and heats the medium-low temperature NG. The seawater from the pipe-side outlet of the natural gas heater 11 enters the pipe-side inlet of the evaporator 4, heating and evaporating the high-pressure organic working fluid in the shell-side inlet of the evaporator 4.

[0037] Specifically, the temperature difference between the seawater temperature at the pipe-side inlet of the natural gas heater 11 and the seawater temperature at the pipe-side outlet of the evaporator 4 is ≤5℃, in order to prevent cold pollution to the surrounding sea area and protect the marine ecological environment.

[0038] For example, the seawater temperature at the pipe-side outlet of evaporator 4 is 3-5°C lower than the ambient seawater temperature at the pipe-side inlet of natural gas heater 11, thus better protecting the marine ecosystem.

[0039] In this embodiment, an ultrasonic flow meter is installed on the pipe connecting the shell-side outlet of the evaporator 4 and the inlet of the first-stage turbine expander 1 to reduce pressure loss and improve the work capacity of the circulating working fluid per unit mass.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A two-stage expansion stage regenerative LNG cold energy power generation system, characterized in that, It includes a first-stage turboexpander (1), a second-stage turboexpander (2), an evaporator (4), a regenerator (5), a subcooler (6), a throttle valve (7), a working fluid booster pump (9), a condenser (10), and a natural gas heater (11). The inlet of the first-stage turbine expander (1) is connected to the shell-side outlet of the evaporator (4); the outlet of the first-stage turbine expander (1) is connected to the inlet of the second-stage turbine expander (2) and the shell-side inlet of the regenerator (5), respectively. The outlet of the second-stage turbine expander (2) is connected to the shell-side inlet of the condenser (10); The shell-side outlet of the condenser (10) is sequentially connected to the working fluid booster pump (9), the tube-side inlet of the subcooler (6), the tube-side inlet of the regenerator (5), and the shell-side inlet of the evaporator (4); the tube-side outlet of the condenser (10) is connected to the shell-side inlet of the natural gas heater (11); the tube-side outlet of the natural gas heater (11) is connected to the tube-side inlet of the evaporator (4); The throttle valve (7) is installed on the pipe between the shell-side outlet of the subcooler (6) and the shell-side inlet of the condenser (10).

2. The two-stage expansion stage regenerative LNG cold energy power generation system according to claim 1, characterized in that, The shell-side outlet of the natural gas heater (11) is connected to a natural gas export pipeline, and the pipe-side inlet of the natural gas heater (11) can be vented to seawater.

3. The two-stage expansion stage regenerative LNG cold energy power generation system according to claim 1, characterized in that, The working fluid booster pump (9) is connected to the electric motor (8).

4. The two-stage expansion stage regenerative LNG cold energy power generation system according to claim 3, characterized in that, The first-stage turbine expander (1) and the second-stage turbine expander (2) are coaxially connected, and the second-stage turbine expander (2) is connected to the generator (3).

5. The two-stage expansion stage regenerative LNG cold energy power generation system according to claim 4, characterized in that, The generator (3) is configured as an explosion-proof brushless excitation synchronous generator, and the motor (8) is configured as an explosion-proof synchronous motor; the evaporator (4) is configured as a shell-and-tube heat exchanger, the regenerator (5) is configured as a shell-and-tube heat exchanger, the subcooler (6) is configured as a shell-and-tube heat exchanger, the condenser (10) is configured as a coiled tube heat exchanger, and the natural gas heater (11) is configured as a shell-and-tube heat exchanger.

6. The two-stage expansion stage regenerative LNG cold energy power generation system according to claim 1, characterized in that, The shell-side outlet of the regenerator (5) is connected to the shell-side inlet of the subcooler (6).

7. The two-stage expansion stage regenerative LNG cold energy power generation system according to claim 1, characterized in that, The condenser (10) is arranged at a high position, and the evaporator (4) and the natural gas heater (11) are arranged at a low position relative to the condenser (10).

8. The two-stage expansion stage regenerative LNG cold energy power generation system according to claim 1, characterized in that, The pipe-side inlet of the condenser (10) is connected to the LNG pipeline. LNG enters the pipe-side inlet of the condenser (10) and absorbs the heat of the low-pressure gaseous organic working fluid entering the shell side of the condenser (10) to condense it into liquid. After absorbing heat and evaporating, the medium-low temperature LNG enters the shell side of the natural gas heater (11) from the pipe-side outlet of the condenser (10) to further absorb heat and rise to above zero degrees before entering the natural gas export pipeline network. Ambient seawater enters the tube side of the natural gas heater (11) to heat the medium-low temperature NG. Seawater from the tube side outlet of the natural gas heater (11) enters the tube side of the evaporator (4) to heat and evaporate the high-pressure organic working fluid in the shell side of the evaporator (4). The liquid medium-pressure organic working fluid at the shell-side outlet of the regenerator (5) enters the shell-side inlet of the subcooler (6). The liquid medium-pressure organic working fluid with a certain degree of subcooling at the shell-side outlet of the subcooler (6) enters the throttle valve (7) for expansion to further reduce the temperature and reduce the amount of flash steam entering the condenser (10).

9. The two-stage expansion stage regenerative LNG cold energy power generation system according to claim 1, characterized in that, The seawater temperature at the pipe-side outlet of the evaporator (4) is 3-5°C lower than the ambient seawater temperature at the pipe-side inlet of the natural gas heater (11).

10. The two-stage expansion stage regenerative LNG cold power generation system according to any one of claims 1-9, characterized in that, An ultrasonic flow meter is installed on the pipe connecting the shell-side outlet of the evaporator (4) and the inlet of the first-stage turbine expander (1).

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