LNG receiving station cold energy power generation system and method

Abstract

The invention provides an LNG receiving station cold energy power generation system and method. The method comprises the steps that a first heat exchanger conducts heat exchange on liquid-phase LNG and a gaseous working medium; the second heat exchanger is used for carrying out heat exchange on the first gas-phase LNG and a low-grade heat source; the working medium circulating pump pressurizes the liquid working medium to obtain the pressurized liquid working medium; the third heat exchanger performs heat exchange on the pressurized liquid working medium and the low-grade heat source subjected to primary heat exchange to obtain a pressurized gaseous working medium; the expansion generator set uses the pressurized gaseous working medium to generate power; and the liquid working medium is a hydrofluorocarbon refrigerant. In this way, cold energy power generation can be achieved through a single circulation system without a complex technological process, and cost is low; as the working medium does not contain alkane elements, a corresponding auxiliary gas treatment system does not need to be arranged, and the cost is reduced; due to the good thermodynamic property of the hydrofluorocarbon refrigerant, the power generation efficiency of each ton of LNG cold energy is improved by 10%, and the power generation efficiency is ensured.

Description

Technical Field

[0001] The present application relates to the technical field of cold energy power generation, and in particular to a cold energy power generation system and method for an LNG receiving station. Background Art

[0002] Liquefied natural gas (LNG) cold energy power generation has the characteristics of short industrial chain, mature technology, strong industrial independence, high utilization efficiency and strong feasibility. The efficient utilization of energy during its operation has become a research focus.

[0003] CN103075250A discloses a method for cascading liquefied natural gas cold energy power generation, which includes two parts: natural gas medium Rankine cycle and refrigerant medium Rankine cycle. It uses vaporized natural gas and another refrigerant as power generation working fluids, and realizes multiple cascade heat exchange with LNG by controlling the pressure of natural gas medium and refrigerant medium. On the one hand, it solves the problem of excessive effective energy loss in the process of refrigerant recovering LNG cold energy during Rankine cycle power generation, and on the other hand, through system integration, the cold energy carried by the pressurized liquefied refrigerant in the Rankine cycle is reused to improve the utilization efficiency of cold energy; at the same time, the invention uses heat medium water as the medium to use the flue gas waste heat discharged to the atmosphere after power generation of the gas-steam combined power plant near the receiving station as the low-temperature heat source for cold energy power generation, which can not only improve the power generation efficiency of the Rankine cycle, but also the waste heat utilization will not have an adverse effect on the power generation efficiency of the gas power plant, and can reduce the thermal pollution caused by the waste heat of the flue gas to the environment. The system can be understood as five cold energy recovery cycles. Although the cold energy recovery efficiency of the system is high, the process is too complicated and the cost is high.

[0004] CN104373165A discloses a system for generating electricity using liquefied natural gas cold energy, including a first LNG pump, a second LNG pump, a third LNG pump, a low-pressure natural gas condenser, a medium-pressure natural gas condenser, a low-pressure refrigerant condenser, a first liquid refrigerant pump, a second liquid refrigerant pump, a third liquid refrigerant pump, a refrigerant gasifier, a high-pressure natural gas heater, a high-pressure natural gas superheater, a refrigerant expander, a natural gas expander, a sub-medium-pressure refrigerant condenser, and a medium-pressure refrigerant condenser. The heat medium water after heat exchange with the flue gas of the power plant is used as a low-temperature heat source. The entire power generation process includes two parts: a natural gas medium Rankine cycle and a mixed refrigerant medium Rankine cycle. The effective energy loss in the LNG cold energy recovery process is reduced, and the cold amount of the entire temperature difference of LNG from -160°C to 0°C can be recovered, thereby improving the power generation efficiency of LNG cold energy. However, the process is also too complicated, with more equipment and higher cost.

[0005] CN103075250A discloses a method for cascaded utilization of liquefied natural gas cold energy for power generation, which is characterized by comprising two parts: a natural gas medium Rankine cycle and a refrigerant medium Rankine cycle. The method utilizes vaporized natural gas and another refrigerant as power generation working fluids, and realizes multiple cascade heat exchange with LNG by controlling the pressure of the natural gas medium and the refrigerant medium. On the one hand, the problem of excessive effective energy loss in the process of refrigerant recovery of LNG cold energy during Rankine cycle power generation is solved. On the other hand, the cold energy carried by the pressurized liquefied refrigerant in the Rankine cycle is reused through system integration to improve the utilization efficiency of cold energy. At the same time, the present invention uses heat medium water as a medium to utilize the flue gas waste heat discharged to the atmosphere after power generation from a gas-steam combined power plant near a receiving station as a low-temperature heat source for cold energy power generation, which can not only improve the power generation efficiency of the Rankine cycle, but also the waste heat utilization will not have an adverse effect on the power generation efficiency of the gas power plant, and can reduce the thermal pollution caused by the waste heat of the flue gas to the environment. Similarly, the process flow of the system is relatively complicated, and the acquisition of heat sources is often restricted by geographical regions. It cannot be applied to typical coastal port LNG receiving stations and is not universal.

[0006] It can be seen that the cold energy power generation system in the prior art requires a complex process flow of multiple cycles to ensure the power generation efficiency of the system, and for different types of low-grade heat sources, the corresponding process flow and process equipment need to be adjusted, resulting in increased costs. In other words, when using LNG cold energy for power generation in the prior art, it is impossible to take into account both power generation efficiency and power generation cost. Summary of the invention

[0007] In view of the problems existing in the prior art, an embodiment of the present invention provides a cold energy power generation system and method for an LNG receiving station to solve or partially solve the technical problem in the prior art that it is impossible to take into account both the power generation cost and the power generation efficiency when using LNG cold energy for power generation.

[0008] In a first aspect of the present invention, a cold energy power generation system for an LNG receiving station is provided, the system comprising: a first heat exchanger, a second heat exchanger, a third heat exchanger, a working fluid circulation pump and an expansion generator set; the first heat exchanger is connected to the second heat exchanger, the second heat exchanger is connected to the third heat exchanger, the working fluid circulation pump, the third heat exchanger, the expansion generator set and the first heat exchanger are connected; wherein,

[0009] The first heat exchanger is used to perform heat exchange between liquid-phase LNG and gaseous working medium; the gaseous working medium is converted into liquid working medium, and the liquid-phase LNG is converted into first gaseous-phase LNG;

[0010] The second heat exchanger is used to perform heat exchange between the first gas-phase LNG and the low-grade heat source to obtain the low-grade heat source and the second gas-phase LNG after one heat exchange;

[0011] The working medium circulation pump is used to pressurize the liquid working medium to obtain pressurized liquid working medium;

[0012] The third heat exchanger is used to perform heat exchange between the pressurized liquid working medium and the low-grade heat source after the primary heat exchange to obtain the pressurized gaseous working medium;

[0013] The expansion generator set is used to generate electricity using the pressurized gaseous working medium; wherein,

[0014] The liquid working fluid is a hydrofluorocarbon refrigerant.

[0015] In the above scheme, the system further includes:

[0016] An electric heater is installed between the third heat exchanger and the expansion generator set, and is used to heat the pressurized gaseous working medium.

[0017] In the above scheme, the first outlet of the first heat exchanger is connected to the first inlet of the second heat exchanger, the first inlet of the first heat exchanger is connected to the liquid LNG pipeline, and the first outlet of the second heat exchanger is connected to the natural gas pipeline network;

[0018] The second outlet of the second heat exchanger is connected to the first inlet of the third heat exchanger;

[0019] The second inlet of the third heat exchanger is connected to the outlet of the working medium circulation pump, and the first outlet of the third heat exchanger is connected to the inlet of the electric heater;

[0020] The inlet of the expansion generator set is connected to the outlet of the electric heater, and the outlet of the expansion generator set is connected to the second outlet of the first heat exchanger; the second outlet of the first heat exchanger is connected to the inlet of the working medium circulation pump.

[0021] In the above scheme, the system also includes: a high-pressure pump, which is connected to the first inlet of the first heat exchanger, and the high-pressure pump is used to pressurize the liquid LNG; the pressure of the pressurized liquid LNG is 65 to 95 barg, and the temperature is -140°C to -160°C.

[0022] In the above scheme, the low-grade heat source includes: at least one of seawater, power plant drainage, solar energy drainage and geothermal energy drainage.

[0023] A second aspect of the present invention provides a cold energy power generation method for an LNG receiving station, the method being applied to a power generation system as described in any one of the first aspects, the method comprising:

[0024] Using a first heat exchanger to perform heat exchange between liquid-phase LNG and gaseous working medium, the liquid-phase LNG is converted into first gas-phase LNG;

[0025] The gas-phase LNG and the low-grade heat source are heat exchanged by the second heat exchanger to obtain the low-grade heat source and the second gas-phase LNG after the first heat exchange;

[0026] Using a working medium circulation pump to pressurize the liquid working medium to obtain pressurized liquid working medium;

[0027] The pressurized liquid working medium is heat exchanged with the low-grade heat source after the primary heat exchange by using the third heat exchanger to obtain the pressurized gaseous working medium;

[0028] The expansion generator set is used to generate electricity based on the pressurized gaseous working medium; wherein,

[0029] The liquid working fluid is a hydrofluorocarbon refrigerant.

[0030] In the above scheme, after the pressurized liquid working medium is heat exchanged with the low-grade heat source after the primary heat exchange by the third heat exchanger to obtain the pressurized gaseous working medium, the method further includes:

[0031] The pressurized gaseous working medium is heated by an electric heater to increase the temperature of the pressurized gaseous working medium by 1 to 5°C.

[0032] In the above scheme, the temperature of the first gas phase LNG is 40°C to -60°C, the temperature of the second gas phase LNG is greater than 0°C, and the pressure of the second gas phase LNG is 64 to 94 barg.

[0033] In the above scheme, when the first heat exchanger is used to perform heat exchange between liquid LNG and gaseous working medium, the temperature of the gaseous working medium is -35°C to -40°C, the pressure of the gaseous working medium is 20 to 100 kpag; the temperature of the liquid LNG is -140°C to -160°C.

[0034] In the above scheme, the temperature of the pressurized liquid working medium is -40°C to -45°C, and the pressure of the pressurized liquid working medium is 500 to 700 kpag.

[0035] The present invention provides a cold energy power generation system and method for an LNG receiving station, the system comprising: a first heat exchanger, a second heat exchanger, a third heat exchanger, a working fluid circulation pump and an expansion generator set; the first heat exchanger is used to perform heat exchange between liquid-phase LNG and gaseous working fluid, the gaseous working fluid is converted into liquid working fluid, and the liquid-phase LNG is converted into first gas-phase LNG; the second heat exchanger is used to perform heat exchange between the first gas-phase LNG and a low-grade heat source, to obtain a low-grade heat source after a heat exchange and a second gas-phase LNG; the working fluid circulation pump is used to pressurize the liquid working fluid, to obtain a pressurized liquid working fluid; the third heat exchanger is used to perform heat exchange between the pressurized liquid working fluid and the low-grade heat source after a heat exchange, to obtain The pressurized gaseous working fluid; the expansion generator set is used to generate electricity using the pressurized gaseous working fluid; wherein the liquid working fluid is a hydrofluorocarbon refrigerant; thus, since the system has a simple structure and is a single-cycle system, cold energy power generation can be achieved without a complex process flow, so the cost is relatively low; and since the liquid working fluid is a hydrofluorocarbon refrigerant and does not contain alkane elements, there is no need to set up a corresponding auxiliary gas treatment system, thereby reducing the equipment investment of the system and further reducing the cost; in addition, the hydrofluorocarbon refrigerant has good thermodynamic properties, and compared with traditional alkane media such as propane, the power generation efficiency of each ton of LNG cold energy can be increased by 10%, while ensuring the power generation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] By reading the detailed description of the preferred embodiment below, various other advantages and benefits will become clear to those of ordinary skill in the art. The accompanying drawings are only used for the purpose of illustrating the preferred embodiment and are not considered to be limitations of the present invention. In addition, the same reference symbols are used to represent the same components throughout the accompanying drawings.

[0037] In the attached picture:

[0038] Figure 1 The overall structural schematic diagram of the cold energy power generation system of the LNG receiving station according to one embodiment of the present invention is shown;

[0039] Figure 2 A schematic flow chart of a cold energy power generation method for an LNG receiving station according to an embodiment of the present invention is shown.

[0040] Description of reference numerals:

[0041] 1-first heat exchanger, 2-second heat exchanger, 3-third heat exchanger, 4-working fluid circulation pump, 5-expansion generator set, 6-electric heater, 101-low-grade heat source, 102-low-grade heat source after primary heat exchange, 103-low-grade heat source after secondary heat exchange, 201-liquid working fluid after pressurization, 202-gaseous working fluid, 203-gaseous working fluid after temperature increase, 204-gaseous working fluid after decompression to normal pressure, 205-liquid working fluid before pressurization, 301-liquid phase LNG, 302-first gas phase LNG, 303-second gas phase LNG. DETAILED DESCRIPTION

[0042] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0043] The present invention provides a cold energy power generation system for an LNG receiving station. In order to better understand the technical solution of the present application, the following LNG cold energy and LNG receiving station are first introduced here.

[0044] LNG cold energy is a high-quality clean energy. Theoretically, one ton of LNG can release about 240kW·h of cold energy when it is gasified. As an important link in the LNG industry chain, the main function of the LNG receiving station is to receive LNG transported by ocean-going ships, store and gasify it to obtain gaseous natural gas (NG) products, and supply gas to urban residents and / or industrial users through the natural gas pipeline network.

[0045] Therefore, how the cold energy power generation system of the LNG receiving station can efficiently and reasonably (at a moderate cost) recycle and utilize LNG cold energy and make it applicable in most LNG receiving stations is an issue that needs to be focused on at present.

[0046] However, at present, most LNG cold energy power generation systems have the following main disadvantages:

[0047] First, the process is complicated and the cost is high; second, hydrocarbon substances (such as propane) are mostly used as intermediate circulating fluids, and the emissions of refrigerants cannot be safely discharged into the gas system of the LNG storage tank. The only way is to add corresponding flare treatment facilities, and smoke elimination facilities must also be considered. The investment and operation and maintenance costs of these auxiliary treatment facilities are even higher than the engineering investment of the cold energy power generation device, which directly increases the cost of the entire power generation system. In other words, the existing LNG cold energy power generation system only focuses on power generation efficiency, weakens the investment cost of the power generation system, and cannot take into account both power generation efficiency and investment cost.

[0048] Based on this, the present invention provides a cold energy power generation system for an LNG receiving station, such as Figure 1 As shown, the system includes: a first heat exchanger 1, a second heat exchanger 2, a third heat exchanger 3, a working fluid circulation pump 4 and an expansion generator set 5; the first heat exchanger 1 is connected to the second heat exchanger 2, the second heat exchanger 2 is connected to the third heat exchanger 3, and the working fluid circulation pump 4, the third heat exchanger 3, the expansion generator set 5 and the first heat exchanger 1 are connected;

[0049] The first heat exchanger 1 is used to perform heat exchange between the liquid-phase LNG and the gaseous working medium, converting the gaseous working medium into the liquid working medium, and converting the liquid-phase LNG into the first gas-phase LNG;

[0050] The second heat exchanger 2 is used to perform heat exchange between the first gas phase LNG and the low-grade heat source to obtain the low-grade heat source and the second gas phase LNG after one heat exchange;

[0051] The working medium circulation pump 4 is used to pressurize the liquid working medium to obtain pressurized liquid working medium;

[0052] The third heat exchanger 3 is used to perform heat exchange between the pressurized liquid working medium and the low-grade heat source after the primary heat exchange to obtain the pressurized gaseous working medium;

[0053] The expansion generator set 5 is used to generate electricity using the pressurized gaseous working medium; wherein,

[0054] The liquid working fluid is a refrigerant of the hydrofluorocarbon category, such as Freon, or a mixture of several hydrofluorocarbons.

[0055] Low-grade heat sources can be understood as heat sources with low thermal energy (for example, temperatures below 100°C), and low-grade heat sources can include at least one of seawater, power plant drainage, solar drainage, and geothermal drainage. Since the working fluid (liquid working fluid and gaseous working fluid) in this embodiment is a refrigerant of the hydrofluorocarbon category, and the liquid working fluid and gaseous working fluid in the present invention only contain fluorine and carbon non-alkane substances, which are non-flammable. Therefore, there is no need to set up an additional gas processing system.

[0056] Compared with alkane refrigerants (such as propane), since the gas emissions of alkane must meet certain emission standards and are not allowed to be directly discharged into the air, a flare treatment system needs to be set up separately. Therefore, the present invention uses hydrofluorocarbon refrigerants, which can also reduce the equipment investment corresponding to the flare treatment system.

[0057] Furthermore, the hydrofluorocarbon type working fluid in the present invention has good thermodynamic properties (specific heat capacity, etc.), and thus can also improve power generation efficiency. Compared with alkane-type refrigerants, the power generation efficiency per ton of LNG cold energy in the present invention can be increased by 10%.

[0058] Different types of expansion generators have different requirements for the superheat of the gas at the inlet. For example, turbine expansion generators require that the gas at the inlet cannot carry liquid, while the inlet of screw expansion generators can allow a certain amount of liquid. Therefore, in order to match different types of expansion generators, refer to Figure 1 , the system further comprises:

[0059] The electric heater 6 is installed between the third heat exchanger 3 and the expansion generator set 5, and is used to heat the pressurized gaseous working medium.

[0060] In this way, if the expander generator set 5 is of turbine type, the electric heater can be controlled to turn on; if the expander generator set 5 is of screw type, the electric heater can be turned on or off. However, if the power generation efficiency is taken into consideration, it is recommended to turn on the electric heater regardless of the type of expander generator set. When the electric heater 6 is turned on, the superheat of the gas at the inlet of the expander generator set 5 can be increased, thereby improving the power generation efficiency and operating stability of the expander generator set 5, increasing the adaptability of the power generation system under different environmental conditions, and improving the cold energy utilization rate and power generation per ton of product.

[0061] For example, when the low-grade heat source is seawater, the seawater temperature is too low in winter (5-7°C), but after turning on the electric heater 6, the power generation per ton of LNG can be around 20-25 kWh.

[0062] Due to the presence of the electric heater 6, the present invention can be applied to any of the above low-grade heat sources, so the cold energy power generation system of the LNG receiving station can select a suitable low-grade heat source according to local conditions, and when different types of heat sources are selected, the power generation system does not need to change the power generation process flow accordingly, which indirectly reduces the investment cost of the power generation system.

[0063] Continue to refer Figure 1 , the first outlet of the first heat exchanger 1 is connected to the first inlet of the second heat exchanger 2, the first inlet of the first heat exchanger 1 is connected to the liquid LNG pipeline, and the first outlet of the second heat exchanger 2 is connected to the natural gas pipeline network;

[0064] The second outlet of the second heat exchanger 2 is connected to the first inlet of the third heat exchanger 3;

[0065] The second inlet of the third heat exchanger 3 is connected to the outlet of the working medium circulation pump 4, and the first outlet of the third heat exchanger 3 is connected to the inlet of the electric heater;

[0066] The inlet of the expansion generator set 5 is connected to the outlet of the electric heater 6 , and the outlet of the expansion generator set 5 is connected to the second outlet of the first heat exchanger 1 ; the second outlet of the first heat exchanger 1 is connected to the inlet of the working medium circulation pump 4 .

[0067] Here, the system also includes: a high pressure pump ( Figure 1 The high-pressure pump is connected to the first inlet of the first heat exchanger 1, and is used to pressurize the liquid LNG. For example, the pressure of the liquid LNG after pressurization is 65 to 95 barg, and the temperature is -140°C to -160°C.

[0068] Specifically, continue to refer to Figure 1 When the cold energy power generation system is generating electricity, it is a single cycle power generation mode, which mainly includes three loops: the first loop is the liquid LNG loop (301, 302, 303); the second loop is the low-grade heat source loop (101, 102, 103), and the third loop is the working fluid circulation loop (201, 202, 203, 204 and 205).

[0069] In the first loop, the first inlet of the first heat exchanger 1 is mainly used to receive pressurized liquid-phase LNG 301. In the first heat exchanger 1, the gaseous working medium 204 and the pressurized liquid-phase LNG 301 undergo a heat exchange, and the liquid-phase LNG 301 becomes gas-phase LNG 302. After the gas-phase LNG 302 and the low-grade heat source 101 undergo heat exchange, the gas-phase LNG 302 is heated and converted into gas-phase LNG 303 for transportation to the external natural gas pipeline network.

[0070] In the second loop, the low-grade heat source 101 and the gas-phase LNG 302 exchange heat, and the low-grade heat source 102 after the primary heat exchange is output. The low-grade heat source after the primary heat exchange and the pressurized liquid working medium 201 undergo secondary heat exchange in the second heat exchanger 2, and the low-grade heat source after the secondary heat exchange is discharged from the second heat exchanger 2. This ensures that the inlet and outlet temperature difference of the low-grade heat source is no more than 5°C.

[0071] In the third loop, the liquid working medium is pressurized by the working medium circulation pump 4 to obtain the pressurized liquid working medium 201, the liquid working medium 201 and the low-grade heat source 102 after the first heat exchange are heat exchanged in the third heat exchanger 3, the liquid working medium 201 is converted into the gaseous working medium 202, and then the gaseous working medium 202 is heated by the electric heater 6 to increase the temperature of the gaseous working medium 202 by 1 to 5°C, and then the gaseous working medium 202 enters the expansion generator set 5 to generate electricity, and a part of the gaseous working medium 202 will enter the first heat exchanger 1 through the outlet of the expansion generator set 5, and then the gaseous working medium 202 and the pressurized liquid LNG 301 are heat exchanged in the first heat exchanger 1, and the gaseous working medium 202 is converted into the liquid working medium 205 and re-enters the working medium circulation pump 4 for recycling.

[0072] It is worth noting that for the first heat exchanger 1, high-efficiency heat exchange tubes are used to replace the bare tubes in the first heat exchanger 1. Since the high-efficiency heat exchange tubes have a fin structure, the heat transfer area is increased compared to the bare tubes, thereby effectively improving the heat transfer efficiency of the condensation side and the gasification side phases, which can increase the heat transfer efficiency by 30%. The heat exchange efficiency of the first heat exchanger 1 is 80-90%, which can effectively reduce the heat exchange temperature difference, improve the heat exchange efficiency of liquid LNG and gaseous working fluid, and the unit LNG power generation.

[0073] It can be seen that due to the simple structure of this system, which is a single cycle system, cold energy power generation can be achieved without complex process flow, so the cost is low; and because the liquid working medium is a hydrofluorocarbon refrigerant, which does not contain alkane elements, there is no need to set up a corresponding auxiliary gas treatment system, which reduces the equipment investment of the system and further reduces the cost; in addition, compared with traditional alkane propane and other media, hydrofluorocarbon refrigerants can increase the power generation efficiency of each ton of LNG cold energy by 10%, while ensuring the power generation efficiency. Further, by optimizing the structure of the first heat exchanger, the heat transfer efficiency of the first heat exchanger can be increased by 30%, effectively reducing the heat exchange temperature difference, thereby improving the heat exchange efficiency of liquid LNG and gaseous working medium and the unit LNG power generation. At the same time, an electric heater is set before the inlet of the expansion generator set to increase the temperature of the gaseous working medium at the inlet of the expansion generator set, thereby improving the utilization rate of cold energy and the power generation per ton of product.

[0074] Based on the same inventive concept as the above-mentioned embodiment, this embodiment also provides a cold energy power generation method for an LNG receiving station, which is applied to the cold energy power generation system for the LNG receiving station mentioned above. Figure 2 The method comprises the following steps:

[0075] S210, using a first heat exchanger to perform heat exchange between liquid-phase LNG and a gaseous working medium, and the liquid-phase LNG is converted into a first gas-phase LNG;

[0076] S211, using a second heat exchanger to perform heat exchange on the gas-phase LNG and the low-grade heat source to obtain the low-grade heat source and the second gas-phase LNG after the first heat exchange;

[0077] S212, pressurizing the liquid working medium by using a working medium circulation pump to obtain pressurized liquid working medium;

[0078] S213, using a third heat exchanger to perform heat exchange on the pressurized liquid working medium and the low-grade heat source after the primary heat exchange, to obtain a pressurized gaseous working medium;

[0079] S214, generating electricity based on the pressurized gaseous working medium using an expansion generator set.

[0080] Specifically, the first inlet of the first heat exchanger 1 is mainly used to receive the pressurized liquid LNG 301. In the first heat exchanger 1, the gaseous working medium 204 and the pressurized liquid LNG 301 undergo a heat exchange, and the liquid LNG 301 becomes gaseous LNG 302. After the gaseous LNG 302 and the low-grade heat source 101 undergo heat exchange, the gaseous LNG 302 is heated and converted into gaseous LNG 303 for transportation to the external natural gas pipeline network.

[0081] In the second loop, the low-grade heat source 101 and the gaseous LNG 302 are heat exchanged in the second heat exchanger 2, and the low-grade heat source 102 after the primary heat exchange is output. The low-grade heat source after the primary heat exchange and the pressurized liquid working medium 201 are heat exchanged for the second time in the third heat exchanger 3, and the low-grade heat source 103 after the secondary heat exchange is discharged from the third heat exchanger 3. In this way, the inlet and outlet temperature difference of the low-grade heat source is ensured to be no greater than 5°C.

[0082] In the third loop, the liquid working medium is pressurized by the working medium circulation pump 4 to obtain the pressurized liquid working medium 201, the liquid working medium 201 and the low-grade heat source after the first heat exchange are heat exchanged in the third heat exchanger 3, the liquid working medium 201 is converted into the gaseous working medium 202, and then the gaseous working medium 202 is heated by the electric heater 6 to increase the temperature of the gaseous working medium 202 by 1 to 5°C, and then the gaseous working medium 202 enters the expansion generator set 5 to generate electricity, and a part of the gaseous working medium 202 will enter the first heat exchanger 1 through the outlet of the expansion generator set 5, and then the gaseous working medium 202 and the pressurized liquid LNG 301 are heat exchanged in the first heat exchanger 1, and the gaseous working medium 202 is converted into the liquid working medium 205 and re-enters the working medium circulation pump 4 for recycling.

[0083] It is worth noting that for the first heat exchanger 1, high-efficiency heat exchange tubes are used to replace the bare tubes in the first heat exchanger 1, thereby effectively improving the heat transfer efficiency of the condensation side and the vaporization side phases, which can increase the heat transfer efficiency by 30%, effectively reduce the heat exchange temperature difference, and improve the heat exchange efficiency of liquid LNG and gaseous working fluid and the unit LNG power generation.

[0084] In practical applications, when the power generation system and method provided above are applied to a certain LNG receiving station, seawater is used as a low-grade heat source and LNG is used as a cold source; the implementation is as follows:

[0085] Continue to refer Figure 1After the liquid phase LNG 301 is pressurized by the high-pressure pump, the pressure of the pressurized liquid phase LNG is 65 to 95 barg and the temperature is -140°C to -160°C. Subsequently, the pressurized liquid phase LNG 301 enters the first heat exchanger 1, performs heat exchange with the gaseous working medium 204, and the liquid phase LNG 301 is converted into the first gas phase LNG 302, and the temperature of the first gas phase LNG 302 is 40°C to -60°C. Next, the first gas phase LNG 302 is transported to the second heat exchanger 2, the first gas phase LNG 302 is heat exchanged with the seawater 101, and the first gas phase LNG 302 is converted into the second gas phase LNG 303, the temperature of the second gas phase LNG 303 is greater than 0°C at this time, and the pressure is 64 to 94 barg, and the second gas phase LNG 303 is transported to the natural gas pipeline network.

[0086] The liquid working medium 201 passes through the third heat exchanger 3, is heated and vaporized by seawater, and the liquid working medium 201 is converted into a gaseous working medium 202, and the temperature of the gaseous working medium 202 is -12°C to 15°C. Subsequently, the gaseous working medium 202 passes through an electric heater, and the temperature is increased by 1 to 5°C to form a gaseous working medium 203, and the gaseous working medium 203 is sent to the inlet of the expansion generator set 5. At the outlet of the expansion generator set 5, the gaseous working medium 204 is decompressed to normal pressure, with a pressure of 20 to 100 kpag and a temperature of -35°C to -40°C. The gaseous working medium 204 enters the first heat exchanger 1 to exchange heat with the liquid LNG 301, and the gaseous working medium 204 is condensed to become a liquid working medium 205, and the temperature is -40°C to -45°C.

[0087] The liquid working medium 205 passes through the pipeline into the working medium circulation pump 4 and becomes the liquid working medium 201. The pressure is increased to 500-700 kPag, the temperature is -40°C--45°C, and it enters the third heat exchanger 3 again to complete the cycle.

[0088] The seawater 101 fluctuates with the seasons, with a temperature range of 5 to 30°C and a pressure of 2 barg. It passes through the second heat exchanger 2 and the third heat exchanger 3 in sequence. Finally, the temperature of the low-grade heat source 103 differs from that of the low-grade heat source 101 by no more than 5°C, and the pressure drop loss is 80 to 200 kPa.

[0089] Through one or more embodiments of the present invention, the present invention has the following beneficial effects or advantages:

[0090] The present invention provides a cold energy power generation system and method for an LNG receiving station, the system comprising: a first heat exchanger, a second heat exchanger, a third heat exchanger, a working fluid circulation pump and an expansion generator set; the first heat exchanger is used for performing heat exchange between liquid-phase LNG and gaseous working fluid, the gaseous working fluid is converted into liquid working fluid, and the liquid-phase LNG is converted into first gas-phase LNG; the second heat exchanger is used for performing heat exchange between the first gas-phase LNG and a low-grade heat source, to obtain a low-grade heat source after one heat exchange and a second gas-phase LNG; the working fluid circulation pump is used for pressurizing the liquid working fluid, to obtain a pressurized liquid working fluid; the third heat exchanger is used for performing heat exchange between the pressurized liquid working fluid and the low-grade heat source after one heat exchange, to obtain a pressurized gaseous working fluid; the expansion generator set is used for generating electricity using the pressurized gaseous working fluid; wherein the liquid working fluid is a refrigerant of the hydrofluorocarbon category. Thus, since the system has a simple structure and is a single-cycle system, it can realize cold energy power generation without complicated process flow, so the cost is relatively low; and since the liquid working fluid is a hydrofluorocarbon refrigerant and does not contain alkane elements, there is no need to set up a corresponding auxiliary gas treatment system, which reduces the equipment investment of the system and further reduces the cost; in addition, hydrofluorocarbon refrigerants have good thermodynamic properties. Compared with traditional alkane media such as propane, the power generation efficiency of each ton of LNG cold energy can be increased by 10%, while ensuring the power generation efficiency.

[0091] Furthermore, by optimizing the structure of the first heat exchanger, the heat transfer efficiency of the first heat exchanger can be increased by 30%, effectively reducing the heat exchange temperature difference, thereby improving the heat exchange efficiency of liquid LNG and gaseous working fluid and the unit LNG power generation. At the same time, an electric heater is set before the inlet of the expansion generator set to increase the temperature of the gaseous working fluid at the inlet of the expansion generator set, thereby improving the cold energy utilization rate and the power generation per ton of product.

[0092] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cold energy power generation system for an LNG receiving station, characterized in that: The system includes: a first heat exchanger, a second heat exchanger, a third heat exchanger, a working fluid circulation pump and an expansion generator set; the first heat exchanger is connected to the second heat exchanger, the second heat exchanger is connected to the third heat exchanger, the working fluid circulation pump, the third heat exchanger, the expansion generator set and the first heat exchanger are connected; wherein, The first heat exchanger is used to perform heat exchange between liquid-phase LNG and gaseous working medium; the gaseous working medium is converted into liquid working medium, and the liquid-phase LNG is converted into first gaseous-phase LNG; The second heat exchanger is used to perform heat exchange between the first gas-phase LNG and the low-grade heat source to obtain the low-grade heat source and the second gas-phase LNG after one heat exchange; The working medium circulation pump is used to pressurize the liquid working medium to obtain pressurized liquid working medium; The third heat exchanger is used to perform heat exchange between the pressurized liquid working medium and the low-grade heat source after the primary heat exchange to obtain the pressurized gaseous working medium; The expansion generator set is used to generate electricity using the pressurized gaseous working medium; wherein, The liquid working fluid is a hydrofluorocarbon refrigerant.

2. The system according to claim 1, characterized in that The system further comprises: An electric heater is installed between the third heat exchanger and the expansion generator set, and is used to heat the pressurized gaseous working medium.

3. The system according to claim 1, characterized in that The first outlet of the first heat exchanger is connected to the first inlet of the second heat exchanger, the first inlet of the first heat exchanger is connected to the liquid LNG pipeline, and the first outlet of the second heat exchanger is connected to the natural gas pipeline network; The second outlet of the second heat exchanger is connected to the first inlet of the third heat exchanger; The second inlet of the third heat exchanger is connected to the outlet of the working medium circulation pump, and the first outlet of the third heat exchanger is connected to the inlet of the electric heater; The inlet of the expansion generator set is connected to the outlet of the electric heater, and the outlet of the expansion generator set is connected to the second outlet of the first heat exchanger; the second outlet of the first heat exchanger is connected to the inlet of the working medium circulation pump.

4. The system according to claim 1, characterized in that The system further includes: a high-pressure pump connected to the first inlet of the first heat exchanger, and the high-pressure pump is used to pressurize the liquid-phase LNG; the pressure of the pressurized liquid-phase LNG is 65 to 95 barg, and the temperature is -140°C to -160°C.

5. The system according to claim 1, wherein: The low-grade heat source includes at least one of seawater, power plant drainage, solar energy drainage and geothermal energy drainage.

6. A cold energy power generation method for an LNG receiving station, characterized in that: The method is applied in the power generation system according to any one of claims 1 to 5, and the method comprises: Using a first heat exchanger to perform heat exchange between liquid-phase LNG and gaseous working medium, the liquid-phase LNG is converted into first gas-phase LNG; The gas-phase LNG and the low-grade heat source are heat exchanged by the second heat exchanger to obtain the low-grade heat source and the second gas-phase LNG after the first heat exchange; Using a working medium circulation pump to pressurize the liquid working medium to obtain pressurized liquid working medium; The pressurized liquid working medium is heat exchanged with the low-grade heat source after the primary heat exchange by using the third heat exchanger to obtain the pressurized gaseous working medium; The expansion generator set is used to generate electricity based on the pressurized gaseous working medium; wherein, The liquid working fluid is a hydrofluorocarbon refrigerant.

7. The method according to claim 6, characterized in that After the pressurized liquid working medium is heat exchanged with the low-grade heat source after the primary heat exchange by the third heat exchanger to obtain the pressurized gaseous working medium, the method further comprises: The pressurized gaseous working medium is heated by an electric heater to increase the temperature of the pressurized gaseous working medium by 1 to 5°C.

8. The method according to claim 6, characterized in that The temperature of the first gas phase LNG is 40° C. to −60° C., the temperature of the second gas phase LNG is greater than 0° C., and the pressure of the second gas phase LNG is 64 to 94 barg.

9. The method according to claim 6, characterized in that When the first heat exchanger is used to perform heat exchange between liquid LNG and gaseous working medium, the temperature of the gaseous working medium is -35°C to -40°C, the pressure of the gaseous working medium is 20 to 100 kpag; the temperature of the liquid LNG is -140°C to -160°C.

10. The method according to claim 6, characterized in that The temperature of the pressurized liquid working medium is -40°C to -45°C, and the pressure of the pressurized liquid working medium is 500 to 700 kPag.

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