A carnot cell energy storage system simultaneously coupling waste heat and liquefied natural gas cold energy

Abstract

This invention provides a Carnot battery energy storage system that simultaneously couples waste heat and liquefied natural gas (LNG) cold energy, belonging to the field of energy storage technology and cryogenic energy comprehensive utilization technology. It includes a heat pump cycle unit, a thermal storage unit, a dual-pressure evaporation Rankine cycle power generation unit, and an LNG combined cycle power generation unit. During the charging phase, the heat pump working fluid absorbs cryogenic waste heat and is compressed and heated, transferring the heat to the thermal storage medium, realizing the conversion of electrical energy into thermal energy. During the discharging phase, based on the heat exchange integration characteristics of the multi-stream heat exchanger, the waste heat is used to first heat the working fluid in the low-pressure stage, and then preheat the working fluid in the high-pressure stage. The thermal storage medium and the cryogenic waste heat jointly drive the dual-pressure evaporation Rankine cycle power generation. Simultaneously, LNG cold energy is introduced, achieving cold energy recovery and additional power generation through the combined cycle power generation. This invention achieves deep utilization of cryogenic waste heat throughout its entire life cycle and the coupled utilization of LNG cold energy with the Carnot battery system, improving the system's energy utilization efficiency.

Description

Technical Field

[0001] This invention belongs to the field of energy storage technology and low-temperature energy comprehensive utilization technology, and relates to a Carnot battery energy storage system that simultaneously couples waste heat and liquefied natural gas cold energy. Background Technology

[0002] To achieve carbon peaking and carbon neutrality goals and accelerate the construction of a clean, low-carbon, safe, and efficient energy system, renewable energy technologies have developed rapidly in recent years. With the continuous expansion of installed capacity of renewable energy sources such as wind and solar power, their proportion in the power system is constantly increasing, driving the accelerated transformation of my country's energy structure towards a low-carbon direction. However, renewable energy power generation is characterized by significant intermittency and volatility. Large-scale grid connection significantly increases the volatility and uncertainty of the power system, placing higher demands on its stability, security, and regulation capabilities. Therefore, to ensure the safe and stable operation of the power system, developing large-scale energy storage technology has become an important way to support the high proportion of renewable energy consumption. Energy storage systems can store excess energy during off-peak hours and release energy during peak hours, thereby achieving "peak shaving and valley filling" and effectively mitigating the impact of unstable renewable energy power generation on the power grid.

[0003] Currently, energy storage technologies mainly include mechanical energy storage, thermal energy storage, chemical energy storage, electrochemical energy storage, and other forms of energy storage. Among them, in the field of mechanical energy storage, pumped hydro storage and compressed air energy storage are currently the most representative commercially viable large-scale energy storage technologies. These two types of energy storage technologies have advantages such as long lifespan and relatively mature technology, but they are largely limited by geographical conditions and have long construction cycles, thus restricting their further promotion and widespread application. Against this backdrop, developing efficient, reliable, and large-scale applicable new energy storage technologies has become an important research direction in the current energy storage field.

[0004] Carnot batteries, a novel energy storage technology based on thermodynamic cycles, store and release energy through a "electrical energy-thermal energy-electrical energy" conversion process. Compared with traditional large-scale energy storage technologies, Carnot batteries are generally not limited by geographical conditions and have advantages such as flexible system structure, wide applicable capacity range, and suitability for large-scale energy storage. Therefore, they have received increasing attention in recent years and are considered to have good application prospects in renewable energy consumption and the construction of new power systems.

[0005] Existing Carnot battery systems typically consist of a heat pump cycle, a thermal storage unit, and an Organic Rankine Cycle (ORC) power generation unit. The heat pump converts electrical energy into thermal energy for storage, and during the discharge phase, the thermal cycle generates electricity to achieve energy recovery. However, existing Carnot battery systems still have certain shortcomings. First, regarding the utilization of low-temperature waste heat, most systems only utilize low-temperature waste heat resources through the heat pump cycle during the charging phase. Although some studies have attempted to utilize low-temperature waste heat resources during both the charging and discharging phases, the waste heat flow rate during the discharging phase is less than that during the charging phase, resulting in an uneven utilization of low-temperature waste heat resources throughout the entire operating cycle, making it difficult to achieve continuous and efficient utilization.

[0006] Meanwhile, liquefied natural gas (LNG) has been widely used in energy supply systems due to its cleanliness, efficiency, and ease of long-distance transportation. During LNG gasification, a large amount of cryogenic energy is released, typically at temperatures as low as -160°C, possessing high thermodynamic value. Existing research indicates that LNG cryogenic energy can be used for power generation, refrigeration, and combined energy supply (CESP). Coupling it with a thermodynamic cycle to achieve combined cycle power generation is one of the important directions for improving the utilization efficiency of LNG cryogenic energy. Although some studies have proposed independent power generation schemes for LNG cryogenic energy recovery, most have not been effectively coupled with energy storage systems, failing to form a unified energy utilization system.

[0007] Therefore, there is an urgent need to propose a new type of Carnot battery energy storage system that can realize continuous and in-depth utilization of low-temperature waste heat throughout the entire charging and discharging process and effectively couple LNG cold energy, so as to improve the system's energy utilization efficiency and comprehensive power generation performance. Summary of the Invention

[0008] To address the problems of discontinuous waste heat utilization during the charging and discharging phases and the difficulty in effectively coordinating LNG cold energy with the energy storage process in existing Carnot battery energy storage systems, this invention proposes a Carnot battery energy storage system capable of achieving electrical energy storage, continuous and in-depth utilization of low-temperature waste heat, and efficient recovery of LNG cold energy. This system aims to enhance the continuous utilization of low-temperature waste heat throughout its entire lifecycle by optimizing the thermodynamic cycle structure during the discharge process and utilizing a multi-flow heat exchanger to achieve dual-pressure heat absorption of the working fluid during the discharge phase. Furthermore, it effectively couples the low-temperature cold energy released during LNG vaporization with the system's discharge process, thereby improving the system's level of synergistic utilization of cold and heat energy.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A Carnot battery energy storage system that simultaneously couples waste heat and liquefied natural gas (LNG) cooling energy is disclosed. The Carnot battery energy storage system operates in a charging phase during off-peak electricity demand and in a discharging phase during peak electricity demand. It comprises four parts: a heat pump unit, a thermal storage system, a dual-pressure evaporation Rankine cycle unit, and an LNG-based power generation unit. During the charging phase, the system utilizes the heat pump system to convert electrical energy into thermal energy. During the discharging phase, the system employs a cascaded system structure that synergistically couples the dual-pressure evaporation Rankine cycle and the LNG-based power generation cycle. The heat pump unit is connected to the thermal storage system via condenser 3, and is used to transfer heat to the thermal storage medium during the charging phase, completing the conversion of electrical energy into thermal energy. The thermal storage system is connected to the dual-pressure evaporation Rankine cycle unit via a multi-flow heat exchanger, and is used to provide heat to the dual-pressure evaporation Rankine cycle unit during the discharge phase. The dual-pressure evaporation Rankine cycle unit and the LNG combined process power generation unit are connected via an evaporator-condenser. The evaporator-condenser acts as a condenser for the dual-pressure evaporation Rankine cycle unit and as an evaporator for the LNG combined process power generation unit, so as to realize cascaded heat exchange between the two power generation units.

[0010] Furthermore, the heat pump working fluid, the thermal storage medium, the dual-pressure evaporation Rankine cycle working fluid, and the LNG combined cycle power generation working fluid are all pre-charged into their respective loops. During system operation, the heat pump working fluid circulates in a closed loop within the heat pump unit, the dual-pressure evaporation Rankine cycle working fluid circulates in a closed loop within the dual-pressure evaporation Rankine cycle unit, the LNG combined cycle power generation working fluid circulates in a closed loop within the LNG combined cycle power generation unit, and the thermal storage medium circulates between the cold and hot storage tanks and the heat exchange loop. Low-temperature waste heat comes from an external heat source, enters the system as external heat flow, releases heat in the corresponding heat exchange equipment, and is then discharged. LNG comes from an external LNG supply source, and after system pressurization, heat exchange, heating, expansion, and reheating, it is output as NG.

[0011] The heat pump unit includes an evaporator 1, a compressor 2, a first condenser 3, and a throttling valve 4. The outlet of the evaporator 1 is connected to the inlet of the compressor 2, the outlet of the compressor 2 is connected to the inlet of the first condenser 3, the outlet of the first condenser 3 is connected to the inlet of the throttling valve 4, and the outlet of the throttling valve 4 is connected to the inlet of the evaporator 1, forming a heat pump refrigerant circulation loop. The first condenser 3 is also connected to a heat storage system to transfer the heat released by the heat pump refrigerant to the heat storage medium. The evaporator 1 is used to absorb low-temperature waste heat. The compressor is used to compress the refrigerant using externally input electrical energy during the charging phase to increase the refrigerant's pressure and temperature. The first condenser 3 is used to transfer heat to the heat storage medium. The throttling valve 4 is used to reduce the refrigerant pressure.

[0012] The thermal storage system includes a cold water storage tank 5 and a hot water storage tank 6. The outlet of the cold water storage tank 5 is connected to the inlet of the thermal storage medium of the first condenser 3, the outlet of the thermal storage medium of the first condenser 3 is connected to the inlet of the hot water storage tank 6, the outlet of the hot water storage tank 6 is connected to the inlet of the thermal storage medium of the multi-stream heat exchanger 10, and the outlet of the thermal storage medium of the multi-stream heat exchanger 10 is connected to the inlet of the cold water storage tank 5, forming a thermal storage medium circulation loop. The hot water storage tank 6 is used to store the high-temperature thermal storage medium after heat absorption; the cold water storage tank 5 is used to store the low-temperature thermal storage medium after heat release. During the charging phase, the thermal storage medium absorbs heat released by the heat pump unit through the first condenser 3 and flows from the cold water storage tank 5 into the hot water storage tank 6. During the discharging phase, the thermal storage medium releases heat to the dual-pressure evaporation Rankine cycle unit through the multi-stream heat exchanger 10 and flows back from the hot water storage tank 6 to the cold water storage tank 5, thereby achieving heat storage and release.

[0013] The dual-pressure evaporative Rankine cycle unit includes a first working fluid pump 7, a distributor 8, a second working fluid pump 9, a multi-stream heat exchanger 10, a first working fluid expander 11, a second working fluid expander 12, a mixer 13, and an evaporative condenser 14. The working fluid outlet of the evaporative condenser 14 is connected to the inlet of the first working fluid pump 7. The outlet of the first working fluid pump 7 is connected to the inlet of the distributor 8. The first outlet of the distributor 8 is connected to the low-pressure working fluid inlet of the multi-stream heat exchanger 10; the second outlet of the distributor 8 is connected to the inlet of the second working fluid pump 9, and the outlet of the second working fluid pump 9 is connected to the high-pressure working fluid inlet of the multi-stream heat exchanger 10. The low-pressure working fluid outlet of the multi-flow heat exchanger 10 is connected to the inlet of the first working fluid expander 11, and the high-pressure working fluid outlet of the multi-flow heat exchanger 10 is connected to the inlet of the second working fluid expander 12. The outlets of the first working fluid expander 11 and the second working fluid expander 12 are respectively connected to the two inlets of the mixer 13. The outlet of the mixer 13 is connected to the dual-pressure evaporation Rankine cycle working fluid inlet of the evaporator-condenser 14 to form a dual-pressure evaporation Rankine cycle loop. The system comprises the following components: the first working fluid pump 7, which delivers the condensed circulating working fluid to the distributor 8; the distributor 8, which divides the circulating working fluid into a low-pressure branch and a high-pressure branch; the second working fluid pump 9, which further pressurizes the working fluid in the high-pressure branch; the multi-stream heat exchanger 10, which enables the working fluids in the low-pressure and high-pressure branches to absorb heat released from the heat storage medium and low-temperature waste heat, thereby achieving dual-pressure evaporation; the first working fluid expander 11, which expands the working fluid in the low-pressure branch to perform work; and the second working fluid expander 12, which expands the working fluid in the high-pressure branch to perform work; the mixer 13, which mixes the exhaust steam after expansion from the two branches; and the evaporator-condenser 14, which condenses the mixed working fluid and performs cascade heat exchange with the LNG combined cycle power generation unit.

[0014] The LNG combined cycle power generation unit includes a seawater preheater 15, a third working fluid expander 16, a second condenser 17, a third working fluid pump 18, an LNG pump 19, a first seawater heater 20, an LNG expander 21, and a second seawater heater 22. The working fluid outlet of the second condenser 17 is connected to the inlet of the third working fluid pump 18, the outlet of the third working fluid pump 18 is connected to the working fluid inlet of the seawater preheater 15, the working fluid outlet of the seawater preheater 15 is connected to the working fluid inlet of the evaporator-condenser 14 corresponding to the LNG combined cycle power generation unit, the working fluid outlet of the evaporator-condenser 14 corresponding to the LNG combined cycle power generation unit is connected to the inlet of the third working fluid expander 16, and the outlet of the third working fluid expander 16 is connected to the working fluid inlet of the second condenser 17, thus forming a circulating working fluid loop for LNG combined cycle power generation. Further, the LNG flow path is as follows: the LNG inlet is connected to the inlet of LNG pump 19, the outlet of LNG pump 19 is connected to the LNG side inlet of the second condenser 17, the LNG side outlet of the second condenser 17 is connected to the inlet of the first seawater heater 20, the outlet of the first seawater heater 20 is connected to the inlet of the LNG expander 21, and the outlet of the LNG expander 21 is connected to the inlet of the second seawater heater 22, the outlet of the second seawater heater 22 being NG. The third working fluid pump 18 is used to pressurize the circulating working fluid condensed in the second condenser 17 and transport it to the seawater preheater 15; the seawater preheater 15 is used to preheat the circulating working fluid using seawater; the evaporative condenser 14 is used to allow the preheated circulating working fluid to absorb the heat released by the dual-pressure evaporative Rankine cycle unit and evaporate; the third working fluid expander 16 is used to expand the evaporated circulating working fluid to perform work; the second condenser 17 is used to condense the circulating working fluid expanded by the third working fluid expander 16 and exchange heat with LNG. The LNG pump 19 is used to pressurize the LNG; the first seawater heater 20 is used to further increase the temperature of the LNG; the LNG expander 21 is used to expand the heated LNG to do work; the second seawater heater 22 is used to further heat the natural gas after it has been expanded by the LNG expander 21 to meet the output requirements.

[0015] Furthermore, during periods of low electricity demand, the Carnot battery energy storage system is in a charging phase, during which a heat pump system converts electrical energy into heat energy. The working fluid in the heat pump unit is a closed-loop circulating fluid, flowing between the evaporator 1, compressor 2, first condenser 3, and expansion valve 4. After being depressurized by expansion valve 4, the heat pump working fluid enters the evaporator 1, absorbs low-temperature waste heat, and vaporizes into low-pressure superheated steam. It is then compressed by compressor 2 to form a high-temperature, high-pressure working fluid, which exchanges heat with the low-temperature heat storage medium from the cold tank 5 in the first condenser 3, condensing into a high-pressure subcooled liquid. Afterward, the high-pressure subcooled liquid is depressurized again by expansion valve 4 and enters the next cycle. The heat storage medium is the circulating medium in the heat storage loop, flowing between the cold water tank 5, first condenser 3, multi-flow heat exchanger 10, and hot water tank 6, used to store and release heat. After absorbing heat and heating up, the heat storage medium enters the hot water tank 6, realizing the conversion and storage of electrical energy into heat energy.

[0016] Furthermore, during peak electricity consumption periods, when the Carnot battery energy storage system enters the discharge phase, it adopts a cascaded system structure that coordinates the dual-pressure evaporation Rankine cycle and the LNG combined power generation cycle. The dual-pressure evaporation Rankine cycle and the LNG combined power generation cycle are cascaded, with the heat released by the former being transferred to the latter via an evaporator-condenser for further power generation. The working fluid in the dual-pressure evaporation Rankine cycle unit is a closed-loop working fluid that circulates during system operation. The liquid working fluid in the dual-pressure evaporation cycle is pressurized by the first working fluid pump 7 and then enters the distributor 8, where it is divided into two working fluid streams: a first working fluid and a second working fluid. The heat storage medium and low-temperature waste heat serve as the heat source for the dual-pressure evaporation cycle, supplying heat to the first and second working fluids through a multi-stream heat exchanger 10. The waste heat is used to first heat the working fluid in the low-pressure stage and then preheat the working fluid in the high-pressure stage, thereby achieving cascaded utilization and deep recovery of waste heat. Specifically, the first working fluid enters the multi-stream heat exchanger 10 under low pressure, absorbs heat, and vaporizes, driving the first working fluid expander 11 to perform work. The exhaust vapor after expansion and work is called the first exhaust vapor. The second working fluid is further pressurized by the second working fluid pump 9, completes the heat absorption process on the high-pressure side, and drives the second working fluid expander 12 to perform work. The exhaust vapor after expansion and work is called the second exhaust vapor. The first and second exhaust vapors merge in the mixer 13 and enter the evaporator-condenser 14, where they exchange heat with the working fluid of the LNG combined cycle and condense into liquid. Subsequently, they are pressurized by the first working fluid pump 7 and transported to the distributor 8 to enter the next cycle. The dual-pressure evaporator-condenser cycle is connected to the LNG combined cycle through the evaporator-condenser. In the LNG combined cycle power generation system, the working fluid is pressurized by the third working fluid pump 18, then passes through the preheater 15 and the evaporator-condenser 14 to absorb heat and increase its temperature. It then enters the third working fluid expander 16 to expand and perform work. The expanded exhaust vapor returns to the second condenser 17 to exchange heat with the LNG, and then returns to the third working fluid pump 18, thus completing the cycle. Simultaneously, the LNG is pressurized by the LNG pump 19 and enters the second condenser 17, serving as the cold-side medium to exchange heat with the expanded working fluid of the combined cycle power generation system, achieving cold energy recovery. Subsequently, the heated LNG enters the first seawater heater 20 and the LNG expander 21, where it expands and performs work to generate electricity. Finally, it is heated by the second seawater heater 22 to complete the gasification process.

[0017] The beneficial effects of this invention are: (1) This invention constructs an organic Rankine cycle power generation unit based on a novel dual-pressure evaporation cycle and combines it with an integrated heat exchange structure of a multi-stream heat exchanger, so that the low-temperature waste heat participates in the heating process of the low-pressure stage and the high-pressure stage working fluid respectively during the discharge stage, realizing the continuous utilization of low-temperature waste heat throughout the entire operating cycle of the system, and keeping the utilization amount consistent during the charging and discharging stages, thereby significantly improving the waste heat utilization efficiency.

[0018] (2) In addition, the present invention introduces an LNG combined power generation unit, which converts the cold energy released during the LNG gasification process into electrical energy through heat exchange and expansion processes, thereby achieving efficient recovery and utilization of cold energy, and forming a synergistic power generation mechanism with the dual-pressure evaporation Rankine cycle, further improving the discharge power of the system during the discharge phase.

[0019] In summary, this invention not only ensures that the utilization of low-temperature waste heat remains consistent during the charging and discharging phases, enhancing the continuous utilization capability of low-grade waste heat throughout the entire system operation cycle, but also achieves effective recovery and cascade utilization of LNG cooling capacity by introducing an LNG combined power generation cycle, thereby improving the overall power generation performance and comprehensive energy utilization level of the system. Attached Figure Description

[0020] Figure 1 A flowchart of the charging phase of a Carnot battery energy storage system that simultaneously couples waste heat and liquefied natural gas cold energy; Figure 2 A flowchart of the discharge stage of a Carnot battery energy storage system that simultaneously couples waste heat and liquefied natural gas cold energy; In the diagram: 1 Evaporator; 2 Compressor; 3 First condenser; 4 Throttling valve; 5 Cold water storage tank; 6 Hot water storage tank; 7 First working fluid pump; 8 Flow divider; 9 Second working fluid pump; 10 Multi-stream heat exchanger; 11 First working fluid expander; 12 Second working fluid expander; 13 Mixer; 14 Evaporator-condenser; 15 Seawater preheater; 16 Third working fluid expander; 17 Second condenser; 18 Third working fluid pump; 19 LNG pump; 20 First seawater heater; 21 LNG expander; 22 Second seawater heater. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, wherein Embodiment 1 is used to illustrate the charging process of the system, and Embodiment 2 is used to illustrate the discharging process of the system. However, the scope of protection of the present invention is not limited to the following embodiments, and all equivalent substitutions or modifications made using the concept of the present invention should fall within the scope of protection of the present invention. The present invention will further describe the system operation process below with reference to specific embodiments.

[0022] A Carnot battery energy storage system that simultaneously couples waste heat and liquefied natural gas (LNG) cooling energy is disclosed. The Carnot battery energy storage system operates in a charging phase during off-peak electricity demand and in a discharging phase during peak electricity demand. It comprises four parts: a heat pump unit, a thermal storage system, a dual-pressure evaporation Rankine cycle unit, and an LNG-based power generation unit. During the charging phase, the system utilizes the heat pump system to convert electrical energy into thermal energy. During the discharging phase, the system employs a cascaded system structure that synergistically couples the dual-pressure evaporation Rankine cycle and the LNG-based power generation cycle. The heat pump unit is connected to the thermal storage system via condenser 3, and is used to transfer heat to the thermal storage medium during the charging phase, completing the conversion of electrical energy into thermal energy. The thermal storage system is connected to the dual-pressure evaporation Rankine cycle unit via a multi-flow heat exchanger, and is used to provide heat to the dual-pressure evaporation Rankine cycle unit during the discharge phase. The dual-pressure evaporation Rankine cycle unit and the LNG combined process power generation unit are connected via an evaporator-condenser. The evaporator-condenser acts as a condenser for the dual-pressure evaporation Rankine cycle unit and as an evaporator for the LNG combined process power generation unit, so as to realize cascaded heat exchange between the two power generation units.

[0023] The heat pump unit includes an evaporator 1, a compressor 2, a first condenser 3, and a throttling valve 4. The outlet of the evaporator 1 is connected to the inlet of the compressor 2, the outlet of the compressor 2 is connected to the inlet of the first condenser 3, the outlet of the first condenser 3 is connected to the inlet of the throttling valve 4, and the outlet of the throttling valve 4 is connected to the inlet of the evaporator 1, forming a heat pump working fluid circulation loop. The first condenser 3 is used to transfer heat to the heat storage medium. The throttling valve 4 is used to reduce the working fluid pressure. The heat storage system includes a cold water storage tank 5 and a hot water storage tank 6. The outlet of the cold water storage tank 5 is connected to the heat storage medium inlet of the first condenser 3, the outlet of the first condenser 3 is connected to the inlet of the hot water storage tank 6, the outlet of the hot water storage tank 6 is connected to the heat storage medium inlet of a multi-stream heat exchanger 10, and the outlet of the multi-stream heat exchanger 10 is connected to the inlet of the cold water storage tank 5, forming a heat storage medium circulation loop. The dual-pressure evaporative Rankine cycle unit includes a first working fluid pump 7, a distributor 8, a second working fluid pump 9, a multi-stream heat exchanger 10, a first working fluid expander 11, a second working fluid expander 12, a mixer 13, and an evaporative condenser 14. The working fluid outlet of the evaporative condenser 14 is connected to the inlet of the first working fluid pump 7. The outlet of the first working fluid pump 7 is connected to the inlet of the distributor 8. The first outlet of the distributor 8 is connected to the low-pressure working fluid inlet of the multi-stream heat exchanger 10; the second outlet of the distributor 8 is connected to the inlet of the second working fluid pump 9, and the outlet of the second working fluid pump 9 is connected to the high-pressure working fluid inlet of the multi-stream heat exchanger 10. The low-pressure working fluid outlet of the multi-stream heat exchanger 10 is connected to the inlet of the first working fluid expander 11, and the high-pressure working fluid outlet of the multi-stream heat exchanger 10 is connected to the inlet of the second working fluid expander 12. The outlets of the first working fluid expander 11 and the second working fluid expander 12 are respectively connected to the two inlets of the mixer 13. The outlet of the mixer 13 is connected to the working fluid inlet of the dual-pressure evaporation Rankine cycle of the evaporator condenser 14 to form a dual-pressure evaporation Rankine cycle loop. The LNG combined process power generation unit includes a seawater preheater 15, a third working fluid expander 16, a second condenser 17, a third working fluid pump 18, an LNG pump 19, a first seawater heater 20, an LNG expander 21, and a second seawater heater 22. The working fluid outlet of the second condenser 17 is connected to the inlet of the third working fluid pump 18, the outlet of the third working fluid pump 18 is connected to the working fluid inlet of the seawater preheater 15, the working fluid outlet of the seawater preheater 15 is connected to the working fluid inlet of the evaporator condenser 14 corresponding to the LNG combined process power generation unit, the working fluid outlet of the evaporator condenser 14 corresponding to the LNG combined process power generation unit is connected to the inlet of the third working fluid expander 16, and the outlet of the third working fluid expander 16 is connected to the working fluid inlet of the second condenser 17, thereby forming a circulating working fluid loop for LNG combined process power generation.The LNG flow path is as follows: the LNG inlet is connected to the inlet of LNG pump 19, the outlet of LNG pump 19 is connected to the LNG side inlet of the second condenser 17, the LNG side outlet of the second condenser 17 is connected to the inlet of the first seawater heater 20, the outlet of the first seawater heater 20 is connected to the inlet of LNG expander 21, the outlet of the LNG expander 21 is connected to the inlet of the second seawater heater 22, and the outlet of the second seawater heater 22 is NG.

[0024] Example 1 In Example 1, the charging process of a Carnot battery energy storage system that simultaneously couples low-temperature waste heat and liquefied natural gas cold energy is described. During the charging phase, the system utilizes a heat pump unit to convert electrical energy into heat energy and stores the heat in the heat storage system.

[0025] In this embodiment, the waste heat pressure is 101.325 kPa, the inlet temperature is 80 ℃, the outlet temperature is 70 ℃, the flow rate is 50 kg / s, and its composition is water. The working fluid required for the heat pump cycle is R245fa. The heat storage medium is water.

[0026] During the charging phase, the heat pump circulating working fluid R245fa exchanges heat with the low-temperature waste heat in evaporator 1, forming low-pressure steam at 75 ℃ and 462.6 kPa, which then enters compressor 2. After compression, the temperature of R245fa rises to 146.5 ℃ and the pressure rises to 2829 kPa, during which the compressor consumes 958.37 kW of power. Subsequently, the high-temperature and high-pressure R245fa enters the first condenser 3, where it exchanges heat with the low-temperature heat storage medium. The low-temperature heat storage medium comes from the cold water storage tank 5, and its temperature upon entering the first condenser 3 is 120 ℃ and its pressure is 360 kPa. After heat exchange, R245fa is condensed into a working fluid at 125 ℃ and 2829 kPa, which then enters the throttling valve 4 to reduce its pressure. After throttling, the dryness fraction of R245fa is 0.5955, the temperature drops to 60 ℃, and the pressure drops to 462.6 kPa. It then returns to evaporator 1, completing the charging cycle. At the same time, the heat storage medium absorbs heat and its temperature rises to 130 ℃, while the pressure remains unchanged (360 kPa). It then flows into hot water storage tank 6 to complete the heat storage.

[0027] According to Aspen Hysys simulation software, the power consumption of the compressor in this embodiment is 958.37 kW.

[0028] Example 2 In Example 2, the discharge process of a Carnot battery energy storage system that simultaneously couples low-temperature waste heat and liquefied natural gas (LNG) cold energy is described. During the discharge phase, the system employs a cascaded system structure that coordinates a dual-pressure evaporation Rankine cycle unit with an LNG combined power generation unit to generate electricity.

[0029] In Example 2, the waste heat pressure is 101.325 kPa, the inlet temperature is 80 ℃, the outlet temperature is 70 ℃, and the flow rate is 50 kg / s. Its composition is water. The heat storage medium is water. The working fluid required for the dual-pressure evaporation Rankine cycle is R245fa, and the working fluid required for the LNG combined cycle is propane. The liquefied natural gas vaporization pressure is 7000 kPa, the temperature is -162 ℃, and its molar composition is: methane 91.33%, ethane 5.36%, propane 2.14%, n-butane 0.47%, isobutane 0.46%, n-pentane 0.01%, isopentane 0.01%, and nitrogen 0.22%.

[0030] Dual-pressure evaporative Rankine cycle: During the discharge phase, the high-temperature heat storage medium (temperature 130 ℃, pressure 360 ​​kPa) in the hot water storage tank 6 flows into the multi-stream heat exchanger 10. At the same time, the low-temperature waste heat fluid (80 ℃, 101.325 kPa) enters the multi-stream heat exchanger 10 through another channel. Both flow through different channels to supply heat to the working fluid of the dual-pressure evaporative Rankine cycle. R245fa is condensed by the evaporator condenser 14 and then pressurized to 532.3 kPa (temperature 20.18 ℃) by the first working fluid pump 7. After passing through the first working fluid pump 7, it enters the distributor 8, which divides it into two streams. One stream enters the multi-stream heat exchanger 10 directly, and the other stream is pressurized to 1566 kPa (temperature 20.61 ℃) by the second working fluid pump 9 before entering the multi-stream heat exchanger 10. Two working fluids absorb heat from the storage medium and low-temperature waste heat through different heat exchange paths in the multi-flow heat exchanger 10, and then enter their respective expansion branches for subsequent power generation. The first working fluid is heated to 65 ℃ (pressure remains constant, 532.3 kPa) and then enters the first working fluid expander 11. The second working fluid is heated to 125 ℃ (pressure remains constant, 1566 kPa) and then enters the second working fluid expander 12. The two working fluids expand and generate power in their respective expanders. The outlet temperature of the working fluid in the first working fluid expander 11 is 30.66 ℃ and the pressure is 122.7 kPa, which is the first exhaust steam. The outlet temperature of the working fluid in the second working fluid expander 12 is 60.39 ℃ and the pressure is 122.7 kPa, which is the second exhaust steam. The output power of the first working fluid expander 11 and the second working fluid expander 12 are 94.04 kW and 665.7 kW, respectively. Subsequently, the first and second exhaust steam streams enter mixer 13 from their respective inlets and mix therein. The working fluid temperature at the mixer outlet is 54.10℃, and the pressure is 122.7 kPa. The steam then enters the evaporator-condenser 14, where it releases heat and condenses. The condensed working fluid R245fa cools to 20℃ and reaches a pressure of 122.7 kPa before flowing back into the first working fluid pump 7 for the next cycle. The evaporator-condenser acts as a condenser for the dual-pressure evaporator-ranken cycle and an evaporator for the LNG combined cycle, enabling cascaded heat exchange between the two cycles.

[0031] LNG Combined Power Generation Cycle: Propane first absorbs heat released from the condensation of the working fluid in a dual-pressure evaporation Rankine cycle in evaporator-condenser 14 and evaporates. It leaves evaporator-condenser 14 at a temperature of 30 °C and a pressure of 731.5 kPa, then enters the third working fluid expander 16 to generate electricity. After expansion in the third working fluid expander 16, the propane temperature drops to -23.32 °C and the pressure drops to 137.2 kPa, then it enters the second condenser 17. In the second condenser 17, propane exchanges heat with LNG and is condensed, leaving the second condenser 17 at a temperature of -35 °C and a pressure of 137.2 kPa. The condensed propane then enters the third working fluid pump 18, where it is pressurized to a temperature of -34.7 °C and a pressure of 731.5 kPa, before entering the seawater preheater 15. In the seawater preheater 15, propane absorbs heat from the seawater, raising its temperature to -20°C while maintaining a pressure of 731.5 kPa. It then re-enters the evaporator-condenser 14 to begin the next cycle. Simultaneously, the LNG cold stream is first pressurized by the LNG pump 19. The LNG enters the pump at -162°C and 7000 kPa; after pressurization, its temperature rises to -157.9°C and its pressure to 10000 kPa. It then enters the second condenser 17, where it exchanges heat with the propane as a cold-side medium. Leaving the second condenser, the LNG temperature rises to -36.56°C while maintaining a pressure of 10000 kPa. Subsequently, the heated LNG enters the first seawater heater 20, where it exchanges heat with the seawater, raising its temperature from -36.56°C to -10°C while maintaining a constant pressure. It then enters the LNG expander 21 to generate electricity. After being expanded by the expander, the LNG temperature drops to -31.21 ℃ and the pressure drops to 7000 kPa. Then, the LNG is heated by seawater in the second seawater heater 22 to natural gas (NG) at 10 ℃, and finally fed into the pipeline network. In the LNG combined cycle power generation, the output power of the third working fluid expander and the LNG expander are 634.8 kW and 187.5 kW, respectively.

[0032] According to the Aspen Hysys simulation software, the net output power of this process is 1330 kW, the round-trip efficiency is 138.8%, the thermal efficiency is 20.39%, and the usable energy efficiency is 28.38%, which realizes the efficient utilization of low-temperature waste heat.

[0033] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A Carnot battery energy storage system that simultaneously couples waste heat and liquefied natural gas cold energy, characterized in that, The Carnot battery energy storage system includes a heat pump unit, a thermal storage system, a dual-pressure evaporation Rankine cycle unit, and an LNG combined power generation unit. It is in the charging stage during the off-peak electricity consumption period and enters the discharging stage during the peak electricity consumption period. The Carnot battery energy storage system utilizes a heat pump system to convert electrical energy into thermal energy during the charging phase. During the discharging phase, it employs a cascaded system structure that combines a dual-pressure evaporation Rankine cycle and an LNG combined power generation cycle. The heat pump unit is connected to the thermal storage system via a first condenser (3) to transfer heat to the thermal storage medium during the charging phase, thus completing the conversion of electrical energy into thermal energy. The thermal storage system is connected to the dual-pressure evaporation Rankine cycle unit via a multi-flow heat exchanger to provide heat to the dual-pressure evaporation Rankine cycle unit during the discharging phase. The dual-pressure evaporation Rankine cycle unit and the LNG combined power generation unit are connected via an evaporator-condenser. The evaporator-condenser acts as a condenser for the dual-pressure evaporation Rankine cycle unit and an evaporator for the LNG combined power generation unit, thereby achieving cascaded heat exchange between the two power generation units. During the operation of the Carnot battery energy storage system, the heat pump working fluid circulates in a closed loop within the heat pump unit, the dual-pressure evaporation Rankine cycle working fluid circulates in a closed loop within the dual-pressure evaporation Rankine cycle unit, and the LNG combined cycle working fluid circulates in a closed loop within the LNG combined cycle power generation unit. The heat storage medium circulates between the cold and hot storage tanks and the heat exchange loop. Low-temperature waste heat comes from an external heat source and enters the Carnot battery energy storage system as external heat flow, where it is released and discharged after being released in the corresponding heat exchange equipment. LNG comes from an external LNG supply source and is pressurized, heat exchanged, heated, expanded, and heated again by the Carnot battery energy storage system before being output as NG.

2. The Carnot battery energy storage system according to claim 1, which simultaneously couples waste heat and liquefied natural gas cold energy, is characterized in that, The heat pump working fluid, heat storage medium, dual-pressure evaporation Rankine cycle working fluid, and LNG combined power generation cycle working fluid are all working media that are pre-charged into the corresponding circuits.

3. The Carnot battery energy storage system according to claim 1, which simultaneously couples waste heat and liquefied natural gas cold energy, is characterized in that, The heat pump unit includes an evaporator (1), a compressor (2), a first condenser (3), and a throttle valve (4); specifically: The evaporator (1) is used to absorb low-temperature waste heat. Its outlet is connected to the inlet of the compressor (2). The outlet of the compressor (2) is connected to the working fluid inlet of the first condenser (3). The working fluid outlet of the first condenser (3) is connected to the inlet of the throttle valve (4). The outlet of the throttle valve (4) is connected to the inlet of the evaporator (1) to form a heat pump working fluid circulation loop. The first condenser (3) is also connected to the heat storage system to transfer the heat released by the heat pump working fluid to the heat storage medium.

4. The Carnot battery energy storage system according to claim 3, which simultaneously couples waste heat and liquefied natural gas cold energy, is characterized in that, The thermal storage system includes a cold water storage tank (5) and a hot water storage tank (6); specifically: The outlet of the cold water storage tank (5) is connected to the inlet of the heat storage medium of the first condenser (3), the outlet of the heat storage medium of the first condenser (3) is connected to the inlet of the hot water storage tank (6), the outlet of the hot water storage tank (6) is connected to the inlet of the heat storage medium of the multi-stream heat exchanger (10), and the outlet of the heat storage medium of the multi-stream heat exchanger (10) is connected to the inlet of the cold water storage tank (5), forming a heat storage medium circulation loop; The hot water storage tank (6) is used to store the high-temperature heat storage medium after heat absorption; the cold water storage tank (5) is used to store the low-temperature heat storage medium after heat release; during the charging stage, the heat storage medium absorbs the heat released by the heat pump unit through the first condenser (3) and flows into the hot water storage tank (6) from the cold water storage tank (5); during the discharge stage, it releases heat to the dual-pressure evaporation Rankine cycle unit through the multi-stream heat exchanger (10) and flows back to the cold water storage tank (5) from the hot water storage tank (6), thereby realizing the storage and release of heat.

5. The Carnot battery energy storage system according to claim 4, which simultaneously couples waste heat and liquefied natural gas cold energy, is characterized in that, The dual-pressure evaporation Rankine cycle unit includes a first working fluid pump (7), a distributor (8), a second working fluid pump (9), a multi-stream heat exchanger (10), a first working fluid expander (11), a second working fluid expander (12), a mixer (13), and an evaporator-condenser (14); specifically: The outlet of the dual-pressure evaporative Rankine cycle working fluid of the evaporator condenser (14) is connected to the inlet of the first working fluid pump (7); the outlet of the first working fluid pump (7) is connected to the inlet of the distributor (8); the first outlet of the distributor (8) is connected to the low-pressure working fluid inlet of the multi-stream heat exchanger (10); the second outlet of the distributor (8) is connected to the inlet of the second working fluid pump (9), and the outlet of the second working fluid pump (9) is connected to the high-pressure working fluid inlet of the multi-stream heat exchanger (10); the multi-stream heat exchanger... The low-pressure working fluid outlet of the heat exchanger (10) is connected to the inlet of the first working fluid expander (11), and the high-pressure working fluid outlet of the multi-flow heat exchanger (10) is connected to the inlet of the second working fluid expander (12); the outlets of the first working fluid expander (11) and the second working fluid expander (12) are respectively connected to the two inlets of the mixer (13); the outlet of the mixer (13) is connected to the dual-pressure evaporation Rankine cycle working fluid inlet of the evaporator condenser (14), forming a dual-pressure evaporation Rankine cycle loop; The first working fluid pump (7) is used to transport the condensed circulating working fluid to the distributor (8); the distributor (8) is used to divide the circulating working fluid into a low-pressure branch and a high-pressure branch; the second working fluid pump (9) is used to pressurize the working fluid in the high-pressure branch; the multi-stream heat exchanger (10) is used to enable the working fluid in the low-pressure branch and the working fluid in the high-pressure branch to absorb the heat released by the heat storage medium and the low-temperature waste heat, so as to realize dual-pressure evaporation; the first working fluid expander (11) is used to make the working fluid in the low-pressure branch expand and do work, and the second working fluid expander (12) is used to make the working fluid in the high-pressure branch expand and do work; the mixer (13) is used to mix the exhaust gas after the expansion of the two branches; the evaporator condenser (14) is used to condense the mixed working fluid and perform cascade heat exchange with the LNG combined process power generation unit.

6. The Carnot battery energy storage system according to claim 5, simultaneously coupling waste heat and liquefied natural gas cold energy, is characterized in that, The LNG combined cycle power generation unit includes a seawater preheater (15), a third working fluid expander (16), a second condenser (17), a third working fluid pump (18), an LNG pump (19), a first seawater heater (20), an LNG expander (21), and a second seawater heater (22); specifically: The working fluid outlet of the second condenser (17) is connected to the inlet of the third working fluid pump (18), the outlet of the third working fluid pump (18) is connected to the working fluid inlet of the seawater preheater (15), the working fluid outlet of the seawater preheater (15) is connected to the working fluid inlet of the evaporator condenser (14) corresponding to the LNG combined cycle power generation unit, the working fluid outlet of the evaporator condenser (14) corresponding to the LNG combined cycle power generation unit is connected to the inlet of the third working fluid expander (16), and the outlet of the third working fluid expander (16) is connected to the working fluid inlet of the second condenser (17) to form an LN The combined power generation cycle working fluid loop is as follows: the LNG inlet is connected to the inlet of the LNG pump (19), the outlet of the LNG pump (19) is connected to the LNG side inlet of the second condenser (17), the LNG side outlet of the second condenser (17) is connected to the inlet of the first seawater heater (20), the outlet of the first seawater heater (20) is connected to the inlet of the LNG expander (21), the outlet of the LNG expander (21) is connected to the inlet of the second seawater heater (22), and the outlet of the second seawater heater (22) is NG. The third working fluid pump (18) is used to pressurize the circulating working fluid condensed by the second condenser (17) and deliver it to the seawater preheater (15); the seawater preheater (15) is used to preheat the circulating working fluid using seawater; the evaporator condenser (14) is used to allow the preheated circulating working fluid to absorb the heat released by the dual-pressure evaporation Rankine cycle unit and evaporate; the third working fluid expander (16) is used to expand the evaporated circulating working fluid to do work; the second condenser (17) is used to condense the circulating working fluid expanded by the third working fluid expander (16) and exchange heat with LNG; the LNG pump (19) is used to pressurize LNG; the first seawater heater (20) is used to further increase the temperature of LNG; the LNG expander (21) is used to expand the heated LNG to do work; the second seawater heater (22) is used to further heat the natural gas expanded by the LNG expander (21) to meet the output requirements.

7. The Carnot battery energy storage system according to claim 6, simultaneously coupling waste heat and liquefied natural gas cold energy, is characterized in that, During periods of low electricity demand, the Carnot battery energy storage system is in the charging phase, during which a heat pump system is used to convert electrical energy into heat energy; specifically: The working fluid in the heat pump unit is a closed-loop working fluid that circulates between the evaporator (1), compressor (2), first condenser (3), and throttle valve (4). After the working fluid is depressurized by the throttle valve (4), it enters the evaporator (1), absorbs low-temperature waste heat, and vaporizes into low-pressure superheated steam. Subsequently, it is compressed by the compressor (2) to form a high-temperature and high-pressure working fluid, and exchanges heat with the low-temperature heat storage medium from the cold tank 5 in the first condenser (3), condensing into a high-pressure subcooled liquid. After that, the high-pressure subcooled liquid is depressurized again by the throttle valve (4) and enters the next cycle. The heat storage medium is the circulating medium in the heat storage loop, which circulates between the cold water tank (5), first condenser (3), multi-stream heat exchanger (10), and hot water tank (6) to store and release heat. After the heat storage medium absorbs heat and heats up, it enters the hot water tank (6) to realize the conversion and storage of electrical energy into thermal energy.

8. A Carnot battery energy storage system simultaneously coupling waste heat and liquefied natural gas cold energy according to claim 7, characterized in that, During peak electricity consumption periods, the Carnot battery energy storage system enters the discharge phase, adopting a cascaded system structure that coordinates the dual-pressure evaporation Rankine cycle and the LNG combined power generation cycle. The dual-pressure evaporation Rankine cycle and the LNG combined power generation cycle are in an upper-lower cascade relationship. The working fluid in the dual-pressure evaporation Rankine cycle unit is a closed-loop working fluid, which circulates during system operation. The liquid working fluid in the dual-pressure evaporation cycle is pressurized by the first working fluid pump (7) and then enters the distributor (8) to be divided into two working fluids, including the first working fluid and the second working fluid. The heat storage medium and the low-temperature waste heat are used as the heat source of the dual-pressure evaporation cycle. The first and second working fluids are heated through the multi-stream heat exchanger (10). The waste heat is used to heat the working fluid of the low-pressure stage first, and then preheat the working fluid of the high-pressure stage, thereby realizing the cascade utilization and deep recovery of waste heat.

9. A Carnot battery energy storage system simultaneously coupling waste heat and liquefied natural gas cold energy according to claim 8, characterized in that, When the Carnot battery energy storage system enters the discharge phase, specifically: The first working fluid enters the multi-stream heat exchanger (10) under low pressure to absorb heat and vaporize, driving the first working fluid expander (11) to do work. The exhaust vapor after expansion and work is the first exhaust vapor. The second working fluid is further pressurized by the second working fluid pump (9), completes the heat absorption process on the high-pressure side, and drives the second working fluid expander (12) to do work. The exhaust vapor after expansion and work is the second exhaust vapor. The first and second exhaust vapors merge in the mixer (13) and enter the evaporator-condenser (14), where they exchange heat with the working fluid of the LNG combined cycle and condense into liquid. Then, they are pressurized by the first working fluid pump (7) and transported to the distributor (8) to enter the next cycle. The dual-pressure evaporator-condenser cycle is connected to the LNG combined cycle through the evaporator-condenser. In the LNG combined cycle... In the cycle, the working fluid is pressurized by the third working fluid pump (18), and then passes through the preheater 15 and the evaporator-condenser (14) to absorb heat and increase its temperature. It then enters the third working fluid expander (16) to expand and do work. The expanded exhaust gas returns to the second condenser (17) to exchange heat with LNG, and then returns to the third working fluid pump (18) to complete the cycle. At the same time, LNG is pressurized by the LNG pump (19) and enters the second condenser (17) to exchange heat with the expanded combined power generation cycle working fluid as a cold side medium, thereby realizing cold energy recovery. Subsequently, the heated LNG enters the first seawater heater (20) and the LNG expander (21) in sequence. After further heating, it expands and does work to generate electricity. Finally, it is heated by the second seawater heater (22) to complete the gasification process.

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