Molten salt heat storage system based on heat energy grading matching

Abstract

The invention relates to a fused salt heat storage system based on heat energy grading matching. The system comprises a first-stage heat exchange unit, a second-stage heat exchange unit, a third-stage heat exchange unit and a mixing unit, and the first-stage heat exchange unit comprises a first-stage fused salt heat storage loop and a first-stage heat exchange adjusting valve and is used for absorbing and storing high-grade heat of exhaust gas of an exhaust pipeline of a boiler furnace; the second-stage heat exchange unit comprises a second-stage fused salt heat storage loop and a second-stage heat exchange regulating valve and is used for absorbing and storing high-grade heat of main steam extraction of a main steam extraction pipeline of a high-pressure cylinder of the steam turbine; the third-stage heat exchange unit comprises a third-stage fused salt heat storage loop and a third-stage heat exchange regulating valve and is used for absorbing and storing low-grade heat of air exhaust of an intermediate-pressure cylinder of an air exhaust pipeline of the intermediate-pressure cylinder of the steam turbine; the mixing unit mixes the three kinds of exhaust heat and outputs working medium fluid meeting the target temperature so as to adapt to different preset operation working conditions of the thermal power generating unit. Therefore, heat energy can be stored and released in a gradient mode through the system, wide-temperature-range efficient utilization is achieved, and the flexibility and energy efficiency of the thermal power generating unit are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy and power engineering, and in particular to a molten salt heat storage system based on hierarchical matching of thermal energy. BACKGROUND

[0002] With the continuous growth of global energy demand and the increasing awareness of environmental protection, improving energy utilization efficiency and reducing environmental pollution have become important issues in the energy field. As one of the main power production methods, the operation efficiency and environmental performance of thermal power generating units directly affect the sustainable use of energy and the sustainable development of the environment. Therefore, how to improve the thermal efficiency of thermal power generating units through technological innovation while reducing their impact on the environment has become a problem that needs to be solved in the energy field.

[0003] In related technologies, molten salt heat storage technology uses molten salt as a thermal energy storage medium to absorb and store excess heat during high-load operation of thermal power generating units, and release this heat when needed to improve power generation efficiency or meet heating demand. However, the existing molten salt heat storage technology has problems such as insufficient temperature range coverage, mismatched heat quality, and lack of flexibility in thermal energy management in the flexibility transformation of thermal power generating units, which need to be solved. SUMMARY

[0004] The present application provides a molten salt heat storage system based on hierarchical matching of thermal energy to solve the problems of insufficient temperature range coverage, mismatched heat quality, and lack of flexibility in thermal energy management in the flexibility transformation of thermal power generating units in existing molten salt heat storage technology, and improve the flexibility and energy efficiency of thermal power generating units.

[0005] To achieve the above-mentioned purpose, the first aspect of the present application proposes a molten salt heat storage system based on hierarchical matching of thermal energy, comprising: a first heat exchange unit, a second heat exchange unit, a third heat exchange unit, and a mixing unit, wherein, The first heat exchange unit is coupled with a boiler furnace flue gas extraction pipeline, and the first heat exchange unit comprises a first molten salt heat storage circuit and a first heat exchange regulating valve, for absorbing and storing the heat of flue gas extraction in the boiler furnace extraction pipeline using the first molten salt heat storage circuit and the first heat exchange regulating valve; The second heat exchange unit is coupled with a steam turbine high-pressure cylinder main steam extraction pipeline, and the second heat exchange unit comprises a second molten salt heat storage circuit and a second heat exchange regulating valve, for absorbing and storing the heat of main steam extraction in the steam turbine high-pressure cylinder main steam extraction pipeline using the second molten salt heat storage circuit and the second heat exchange regulating valve; The third heat exchange unit is coupled with a steam turbine intermediate-pressure cylinder extraction pipeline, and the third heat exchange unit comprises a third molten salt heat storage circuit and a third heat exchange regulating valve, for absorbing and storing the heat of intermediate-pressure cylinder extraction in the steam turbine intermediate-pressure cylinder extraction pipeline using the third molten salt heat storage circuit and the third heat exchange regulating valve; The mixing unit is used for mixing heat of the flue gas extraction, heat of the main steam extraction and heat of the intermediate pressure cylinder extraction, and outputting working fluid meeting a target temperature to adapt to different preset operation conditions of the thermal power generating unit.

[0006] According to an embodiment of the present application, the primary molten salt heat storage circuit comprises a first primary molten salt heat exchanger, a second primary molten salt heat exchanger, a first primary molten salt circulating pump, a second primary molten salt circulating pump, a first primary molten salt storage tank and a second primary molten salt storage tank, wherein, The primary molten salt heat storage circuit is used for absorbing and storing heat of the flue gas extraction from the boiler flue gas extraction pipeline through a first molten salt medium, and transferring the heat of the flue gas extraction to a first working fluid for output.

[0007] According to an embodiment of the present application, the secondary molten salt heat storage circuit comprises a first secondary molten salt heat exchanger, a second secondary molten salt heat exchanger, a first secondary molten salt circulating pump, a second secondary molten salt circulating pump, a first secondary molten salt storage tank and a second secondary molten salt storage tank, wherein, The secondary molten salt heat storage circuit is used for absorbing and storing heat of the main steam extraction from the steam turbine high pressure cylinder main steam extraction pipeline through a second molten salt medium, and transferring the heat of the main steam extraction to a second working fluid for output.

[0008] According to an embodiment of the present application, the tertiary molten salt heat storage circuit comprises a first tertiary molten salt heat exchanger, a second tertiary molten salt heat exchanger, a first tertiary molten salt circulating pump, a second tertiary molten salt circulating pump, a first tertiary molten salt storage tank and a second tertiary molten salt storage tank, wherein, The tertiary molten salt heat storage circuit is used for absorbing and storing the intermediate pressure cylinder extraction from the steam turbine intermediate pressure cylinder extraction pipeline through a third molten salt medium, and transferring the intermediate pressure cylinder extraction to a third working fluid for output.

[0009] According to an embodiment of the present application, the heat of the main steam extraction enters the tertiary heat exchange unit for heat exchange after heat exchange in the secondary heat exchange unit.

[0010] According to an embodiment of the present application, the primary heat exchange regulating valve is used for regulating flow of the first working fluid entering the first secondary molten salt heat exchanger and output flow of the first working fluid after heat absorption; The secondary heat exchange regulating valve is used for regulating flow of the second working fluid entering the second secondary molten salt heat exchanger and output flow of the second working fluid after heat absorption; The tertiary heat exchange regulating valve is used for regulating flow of the third working fluid entering the second tertiary molten salt heat exchanger and output flow of the third working fluid after heat absorption.

[0011] According to one embodiment of the present application, the first molten salt medium is a fluorinated salt, the second molten salt medium is a binary molten salt, and the third molten salt medium is a ternary molten salt.

[0012] According to one embodiment of the present application, the fluorinated salt is a lithium fluoride-sodium fluoride-potassium fluoride system, the binary molten salt is a sodium nitrate-potassium nitrate mixture, and the ternary molten salt is a sodium nitrate-potassium nitrate-calcium nitrate mixture.

[0013] According to one embodiment of the present application, the molten salt heat storage system based on thermal energy hierarchical matching further comprises a temperature sensor, a flow sensor, and a control unit, wherein, The temperature sensor is used to monitor the real-time temperature of the molten salt and the temperature of the working fluid outlet; The flow sensor is used to monitor the flow of the working fluid of each molten salt heat exchanger; The control unit is used to determine the target opening of each heat exchange regulating valve based on the load prediction result of the thermal power generating unit and the preset heating demand, and to adjust the corresponding heat exchange regulating valve according to the target opening of each heat exchange regulating valve.

[0014] According to the molten salt heat storage system based on thermal energy hierarchical matching, the high-grade heat of the flue gas extraction pipeline of the boiler furnace is absorbed and stored by the first heat exchange unit; the high-grade heat of the main steam extraction pipeline of the high-pressure cylinder of the steam turbine is absorbed and stored by the second heat exchange unit; the low-grade heat of the intermediate-pressure cylinder extraction pipeline of the intermediate-pressure cylinder of the steam turbine is absorbed and stored by the third heat exchange unit; and the above three kinds of extraction heat are mixed by the mixing unit to output the working fluid that meets the target temperature, so as to adapt to different preset operating conditions of the thermal power generating unit. Therefore, the system can store and release heat energy in a gradient manner, realize efficient utilization in a wide temperature range, and solve the problems of insufficient temperature range coverage, mismatched heat grade, and lack of flexibility in heat energy management in the existing molten salt heat storage technology in the flexibility reconstruction of the thermal power generating unit, thereby improving the flexibility and energy efficiency of the thermal power generating unit.

[0015] To achieve the above-mentioned purpose, the second aspect embodiment of the present application proposes a thermal energy peak shaving method for a thermal power generating unit, which adopts the molten salt heat storage system based on thermal energy hierarchical matching of the first aspect embodiment, and the method comprises the following steps: When the thermal power generating unit is in a first preset operating condition, the heat of the flue gas extraction is absorbed and stored by the first heat exchange unit, the heat of the main steam extraction is absorbed and stored by the second heat exchange unit, and the heat of the intermediate-pressure cylinder extraction is absorbed and stored by the third heat exchange unit; In a case where the thermal power generating unit is in the second preset operation condition, the proportions of the output flow rates of the working fluid of the first heat exchange unit, the second heat exchange unit and the third heat exchange unit are adjusted, and working fluids of different grades are mixed through the mixing unit to output working fluid meeting the target temperature.

[0016] The thermal energy peak shaving method for the thermal power generating unit provided by the embodiment of the present application can realize gradient storage and release of thermal energy through the molten salt thermal storage system based on hierarchical matching of thermal energy, realize efficient utilization in a wide temperature range, and solve the problems of insufficient temperature range coverage, mismatch of heat grade and lack of flexibility in thermal energy management of the existing molten salt thermal storage technology in the flexibility reconstruction of the thermal power generating unit, thereby improving the flexibility and energy efficiency of the thermal power generating unit.

[0017] The additional aspects and advantages of the present application will be partially given in the following description, partially become obvious from the following description, or be understood by the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0018] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which: Figure 1 A block schematic diagram of a molten salt thermal storage system based on hierarchical matching of thermal energy provided according to an embodiment of the present application; Figure 2 A structural schematic diagram of a molten salt thermal storage system based on hierarchical matching of thermal energy according to an embodiment of the present application; Figure 3 A flowchart of a thermal energy peak shaving method for a thermal power generating unit provided according to an embodiment of the present application. DETAILED DESCRIPTION

[0019] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, in which the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0020] The molten salt thermal storage system based on hierarchical matching of thermal energy provided according to an embodiment of the present application is described below with reference to the accompanying drawings.

[0021] Figure 1 A block schematic diagram of a molten salt thermal storage system based on hierarchical matching of thermal energy according to an embodiment of the present application.

[0022] Before introducing the molten salt thermal storage system based on hierarchical matching of thermal energy provided by the embodiment of the present application, the related technical background is briefly introduced.

[0023] The molten salt thermal storage technology is considered as a key means to improve the flexibility of thermal power units due to its high energy density, good thermal stability and suitability for long-term energy storage. At present, this technology has achieved engineering application in the field of solar thermal power generation. For example, the binary nitrate salt (60% sodium nitrate + 40% potassium nitrate) system can cover the high temperature region of about 290-560℃, and the ternary molten salt (sodium nitrate-potassium nitrate-calcium nitrate) can be extended to the medium and low temperature region of 140-500℃. However, the existing single molten salt thermal storage system is difficult to meet the thermal energy storage requirements of thermal power units with wide temperature range and multiple extraction steam grades. On the one hand, binary salt performs well in high-temperature thermal storage, but has low efficiency in medium and low-temperature thermal energy recovery; on the other hand, ternary salt is suitable for low-temperature thermal storage, but cannot withstand the high-temperature heat load of main steam extraction, thereby causing a mismatch of thermal energy grade. In addition, when dealing with multiple extraction heat of thermal power units, the heat exchanger of single thermal storage medium needs to withstand a large temperature difference, which is easy to cause thermal stress and efficiency loss, increasing the complexity of system integration.

[0024] More importantly, the boiler tail and the furnace flue gas of thermal power units contain a large amount of high-temperature waste heat. This part of heat is usually discharged through temperature and pressure reduction, flue gas bypass and other ways during low-load operation or peak shaving operation, thereby causing problems of insufficient energy utilization and efficiency reduction. The traditional molten salt thermal storage system mainly focuses on the recovery of steam extraction waste heat, and fails to fully exploit the high-grade heat energy on the flue gas side. If the flue gas heat can be matched with high-temperature molten salt (for example, fluoride salt system, which can work at a temperature of 900-1200℃), not only the temperature range of molten salt thermal storage can be widened, but also the deep coupling between the boiler, steam turbine and thermal storage system can be realized, and the overall thermal energy utilization efficiency can be improved. Although there are some improvement schemes such as segmented heat exchange and multi-salt mixing, there are still problems such as insufficient temperature range coverage, mismatch of heat grade and lack of flexibility in thermal energy management.

[0025] Based on the above problems, the molten salt thermal storage system based on thermal energy hierarchical matching is proposed in the embodiments of the present application. By designing a three-stage molten salt thermal storage circuit, configuring a working fluid flow adjusting mechanism and a working fluid mixing output structure, the efficient recovery and wide temperature range adjustable output of flue gas waste heat and multi-grade extraction thermal energy of thermal power units are realized, and the deep peak shaving capacity and energy utilization efficiency of thermal power units are significantly improved.

[0026] The molten salt thermal storage system based on thermal energy hierarchical matching proposed in the embodiments of the present application will be described in detail below.

[0027] As Figure 1As shown, the molten salt heat storage system 1000 based on thermal energy hierarchical matching includes a first heat exchange unit 100, a second heat exchange unit 200, a third heat exchange unit 300, and a mixing unit 400, wherein the first heat exchange unit 100 is coupled with the boiler furnace flue gas extraction pipeline, the first heat exchange unit 100 includes a first molten salt heat storage loop 101 and a first heat exchange regulating valve 102, for absorbing and storing the heat of the flue gas extraction in the boiler furnace extraction pipeline by using the first molten salt heat storage loop 101 and the first heat exchange regulating valve 102; the second heat exchange unit 200 is coupled with the main steam extraction pipeline of the high-pressure cylinder of the steam turbine, the second heat exchange unit 200 includes a second molten salt heat storage loop 201 and a second heat exchange regulating valve 202, for absorbing and storing the heat of the main steam extraction in the main steam extraction pipeline of the high-pressure cylinder of the steam turbine by using the second molten salt heat storage loop 201 and the second heat exchange regulating valve 202; the third heat exchange unit 300 is coupled with the extraction pipeline of the intermediate-pressure cylinder of the steam turbine, the third heat exchange unit 300 includes a third molten salt heat storage loop 301 and a third heat exchange regulating valve 302, for absorbing and storing the heat of the intermediate-pressure cylinder extraction in the extraction pipeline of the intermediate-pressure cylinder of the steam turbine by using the third molten salt heat storage loop 301 and the third heat exchange regulating valve 302; the mixing unit 400 is used for mixing the heat of the flue gas extraction, the heat of the main steam extraction, and the heat of the intermediate-pressure cylinder extraction, and outputting the working fluid meeting the target temperature to adapt to different preset operating conditions of the thermal power generating unit.

[0028] It should be noted that the molten salt heat storage system 1000 based on thermal energy hierarchical matching also includes a boiler system, such as Figure 2 As shown, the boiler system mainly includes a boiler 1, a high-pressure cylinder 2 of a steam turbine, an intermediate-pressure cylinder 3, a low-pressure cylinder 4, a condenser 5, a condensate pump 6, a low-pressure heater 7, a deaerator 8, a feedwater pump 9, and a high-pressure heater 10, forming a conventional thermodynamic cycle of the thermal power generating unit.

[0029] To achieve efficient recovery and utilization of waste heat of thermal power units, embodiments of the present application can effectively recover and store waste heat generated by thermal power units in different operating stages through hierarchical matching. Specifically, the molten salt thermal storage system 1000 based on thermal energy hierarchical matching includes a first heat exchange unit 100, a second heat exchange unit 200, and a third heat exchange unit 300. Each heat exchange unit can recover and store waste heat in different temperature ranges. When needed, the stored heat can be released to meet the heating or power generation needs of the thermal power unit by adjusting the flow of the working fluid through the control valve. The first heat exchange unit 100 is configured with a first molten salt thermal storage circuit 101 and a first heat exchange regulating valve 102, which is coupled with the boiler 1 furnace flue gas extraction pipeline and is responsible for absorbing and storing the high-grade heat (referring to heat with higher temperature, larger energy density, and can be directly used for efficient energy conversion (such as power generation or driving mechanical equipment)) of the flue gas extraction in the boiler 1 furnace extraction pipeline; the second heat exchange unit 200 is configured with a second molten salt thermal storage circuit 201 and a second heat exchange regulating valve 202, which is coupled with the turbine high-pressure cylinder 2 main steam extraction pipeline and is responsible for absorbing and storing the high-grade heat of the main steam extraction in the turbine high-pressure cylinder 2 main steam extraction pipeline; the third heat exchange unit 300 is configured with a third molten salt thermal storage circuit 301 and a third heat exchange regulating valve 302, which is coupled with the turbine intermediate-pressure cylinder 3 extraction pipeline and is responsible for absorbing and storing the low-grade heat (referring to heat with lower temperature, smaller energy density, and difficult to be directly used for efficient energy conversion) of the intermediate-pressure cylinder extraction in the turbine intermediate-pressure cylinder 3 extraction pipeline.

[0030] The molten salt thermal storage system 1000 based on thermal energy hierarchical matching also includes a mixing unit 400 (i.e., a working fluid mixing interface) connected to the outlets of the working fluid of the first heat exchange unit 100, the second heat exchange unit 200, and the third heat exchange unit 300. The mixing unit 400 mixes heat of different temperature levels (i.e., heat of flue gas extraction, heat of main steam extraction, and heat of intermediate-pressure cylinder extraction) according to the actual operating conditions of the thermal power unit to output working fluid that meets specific requirements (i.e., target temperature, such as 140-560°C) for different application scenarios, such as boiler 1 feedwater heating and low-pressure cylinder 4 reheating. This design not only improves the utilization efficiency of waste heat, but also increases the flexibility and adaptability of the system. At the same time, the mixing unit 400 is designed with an anti-backflow structure to ensure the independence of the first heat exchange unit 100, the second heat exchange unit 200, and the third heat exchange unit 300 during the heat exchange process, avoiding fluid flow from affecting the stability of the system.

[0031] Optionally, in some embodiments, the primary molten salt heat storage circuit 101 includes: a first primary molten salt heat exchanger 11, a second primary molten salt heat exchanger 12, a first primary molten salt circulation pump 13, a second primary molten salt circulation pump 14, a first primary molten salt storage tank 15, and a second primary molten salt storage tank 16. The primary molten salt heat storage circuit 101 is used to absorb and store the heat of the flue gas extraction from the flue gas extraction pipeline of the boiler 1 through the first molten salt medium, and to transfer the heat of the flue gas extraction to the first working fluid for output.

[0032] Specifically, such as Figure 2 As shown, the primary molten salt heat storage circuit 101 mainly consists of a molten salt heat exchanger, a molten salt circulation pump, and a molten salt storage tank (i.e., the first-stage molten salt heat exchanger 11, the second-stage molten salt heat exchanger 12, the first-stage molten salt circulation pump 13, the second-stage molten salt circulation pump 14, the first-stage molten salt storage tank 15, and the second-stage molten salt storage tank 16). During the operation of the primary molten salt heat storage circuit 101, the high-grade heat from the flue gas extracted from the boiler furnace extraction pipeline can directly enter the primary molten salt heat exchanger 11. The primary molten salt circulation pump 13 can extract the low-temperature molten salt (first molten salt medium) from the primary molten salt storage tank 15 (cold salt tank) and transport it to the primary molten salt heat exchanger 11. Inside the primary molten salt heat exchanger 11, the high-temperature flue gas and the low-temperature molten salt (first molten salt medium) exchange heat (the flue gas transfers heat to the low-temperature molten salt (first molten salt medium) through the tube wall of the heat exchanger). After the first molten salt medium absorbs the heat from the flue gas, its temperature rises. The heated first molten salt medium is then transported to the secondary molten salt storage tank 16 (hot salt tank) by the secondary molten salt circulation pump 14 for heat storage, thereby realizing the heat absorption process. When heat release is required, the second-stage molten salt circulation pump 14 can extract the high-temperature molten salt (first molten salt medium) from the second-stage molten salt storage tank 16 (hot salt tank) and transport it to the second-stage molten salt heat exchanger 12. In the second-stage molten salt heat exchanger 12, the high-temperature molten salt (first molten salt medium) transfers heat to the first working fluid (such as water or steam), causing the temperature of the first working fluid to rise. The heated first working fluid can then be output to subsequent processes. At this point, the high-temperature molten salt (first molten salt medium) that has exchanged heat with the first working fluid becomes low-temperature molten salt (first molten salt medium), which can be transported to the first-stage molten salt storage tank 15 (cold salt tank) to await the next cycle of heating.

[0033] Optionally, in some embodiments, the secondary molten salt heat storage circuit 201 includes: a first secondary molten salt heat exchanger 21, a second secondary molten salt heat exchanger 22, a first secondary molten salt circulation pump 23, a second secondary molten salt circulation pump 24, a first secondary molten salt storage tank 25, and a second secondary molten salt storage tank 26. The secondary molten salt heat storage circuit 201 is used to absorb and store the heat of the main steam extraction from the main steam extraction pipeline of the high-pressure cylinder of the steam turbine through the second molten salt medium, and to transfer the heat of the main steam extraction to the second working fluid for output.

[0034] Specifically, such as Figure 2 As shown, the secondary molten salt heat storage circuit 201 is also composed of a molten salt heat exchanger, a molten salt circulation pump, and a molten salt storage tank (i.e., the first and second secondary molten salt heat exchanger 21, the second and second secondary molten salt heat exchanger 22, the first and second secondary molten salt circulation pump 23, the second and second secondary molten salt circulation pump 24, the first and second secondary molten salt storage tank 25, and the second and second secondary molten salt storage tank 26). During the operation of the secondary molten salt heat storage circuit 201, the high-grade heat from the main steam extraction in the main steam extraction pipeline of the high-pressure cylinder 2 of the steam turbine can directly enter the first and second secondary molten salt heat exchangers 21. The first and second secondary molten salt circulation pump 23 can extract the low-temperature molten salt (second molten salt medium) from the first and second secondary molten salt storage tank 25 (cold salt tank) and transport it to the first and second secondary molten salt heat exchangers 21. In the first and second secondary molten salt heat exchangers 21, the high-temperature flue gas and the low-temperature molten salt (second molten salt medium) exchange heat (the flue gas transfers heat to the low-temperature molten salt (second molten salt medium) through the tube wall of the heat exchanger). After the second molten salt medium absorbs the heat from the flue gas, its temperature rises. The heated second molten salt medium is transported to the second and second secondary molten salt storage tank 26 (hot salt tank) by the second and second secondary molten salt circulation pump 24 for heat storage, thereby realizing the heat absorption process. When heat release is required, the second-stage molten salt circulation pump 24 can extract the high-temperature molten salt (second molten salt medium) from the second-stage molten salt storage tank 26 (hot salt tank) and transport it to the second-stage molten salt heat exchanger 22. In the second-stage molten salt heat exchanger 22, the high-temperature molten salt (second molten salt medium) transfers heat to the second working fluid (such as water or steam), causing the temperature of the second working fluid to rise. The heated second working fluid can then be output to subsequent processes. At this point, the high-temperature molten salt (second molten salt medium) that has exchanged heat with the second working fluid becomes low-temperature molten salt (second molten salt medium), which can be transported to the first-stage molten salt storage tank 25 (cold salt tank) to await the next cycle of heating.

[0035] Optionally, in some embodiments, the three-stage molten salt heat storage circuit 301 includes: a first-stage molten salt heat exchanger 31, a second-stage molten salt heat exchanger 32, a first-stage molten salt circulation pump 33, a second-stage molten salt circulation pump 34, a first-stage molten salt storage tank 35, and a second-stage molten salt storage tank 36. The three-stage molten salt heat storage circuit 301 is used to absorb and store the intermediate-pressure cylinder exhaust gas from the turbine intermediate-pressure cylinder exhaust pipeline through the third molten salt medium, and to transfer the intermediate-pressure cylinder exhaust gas to the third working fluid for output.

[0036] Specifically, such as Figure 2 As shown, the three-stage molten salt heat storage circuit 301 is also composed of a molten salt heat exchanger, a molten salt circulation pump, and a molten salt storage tank (i.e., the first and third stage molten salt heat exchangers 31, the second and third stage molten salt heat exchangers 32, the first and third stage molten salt circulation pumps 33 and 34, the first and third stage molten salt storage tanks 35 and 36). During the operation of the three-stage molten salt heat storage circuit 301, the low-grade heat from the extraction of air from the intermediate-pressure cylinder 3 of the turbine can directly enter the first-third-stage molten salt heat exchanger 31. The first-third-stage molten salt circulation pump 33 can extract the low-temperature molten salt (third molten salt medium) from the first-third-stage molten salt storage tank 35 (cold salt tank) and transport it to the first-third-stage molten salt heat exchanger 31. Inside the first-third-stage molten salt heat exchanger 31, the high-temperature flue gas and the low-temperature molten salt (third molten salt medium) exchange heat (the flue gas transfers heat to the low-temperature molten salt (third molten salt medium) through the tube wall of the heat exchanger). After absorbing the heat from the flue gas, the temperature of the third molten salt medium rises. The heated third molten salt medium is then transported to the second-third-stage molten salt storage tank 36 (hot salt tank) by the second-third-stage molten salt circulation pump 34 for heat storage, thereby realizing the heat absorption process. When heat release is required, the second and third stage molten salt circulation pump 34 can extract the high-temperature molten salt (third molten salt medium) from the second and third stage molten salt storage tank 36 (hot salt tank) and transport it to the second and third stage molten salt heat exchanger 32. In the second and third stage molten salt heat exchanger 32, the high-temperature molten salt (third molten salt medium) transfers heat to the third working fluid (such as water or steam), causing the temperature of the third working fluid to rise. The heated third working fluid can then be output to subsequent processes. At this point, the high-temperature molten salt (third molten salt medium) that has exchanged heat with the third working fluid becomes low-temperature molten salt (third molten salt medium), which can be transported to the first and third stage molten salt storage tank 35 (cold salt tank) to await the next cycle of heating.

[0037] Therefore, the first-stage molten salt heat storage circuit 101, the second-stage molten salt heat storage circuit 201 and the third-stage molten salt heat storage circuit 301 have independent molten salt circulating pumps and molten salt storage tanks respectively, so that independent storage and release of heat can be realized to support hierarchical heat management. In addition, the three molten salt heat storage circuits can independently operate and can be flexibly switched by means of the heat storage inlet and outlet switch valves (i.e., heat exchange regulating valves) to achieve stable switching between the heat storage mode and the heat release mode.

[0038] For example, during high-load operation of the thermal power unit (i.e., the first preset working condition), the molten salt heat storage system 1000 based on hierarchical matching of thermal energy is in the heat storage mode, the furnace or the tail flue gas is exchanged with the fluorinated salt through the first-stage molten salt heat exchanger 11, the high-temperature waste heat is absorbed and stored in the second-stage molten salt storage tank 16; at the same time, the main steam extraction is exchanged with the binary molten salt through the second-stage molten salt heat exchanger 21, the heat is stored in the second-stage molten salt storage tank 26; the intermediate-pressure cylinder extraction is exchanged with the ternary molten salt through the third-stage molten salt heat exchanger 31, the medium and low-grade heat is stored in the second-stage molten salt storage tank 36. The first-stage heat exchange regulating valve 102, the second-stage heat exchange regulating valve 202 and the third-stage heat exchange regulating valve 302 cooperatively regulate the flow of the working fluid during operation to ensure optimal heat exchange efficiency and maintain stable molten salt temperature.

[0039] During low-load or peak-regulation operation of the thermal power unit (i.e., the second preset working condition), the molten salt heat storage system 1000 based on hierarchical matching of thermal energy is switched to the heat release mode, the first-stage molten salt heat storage circuit 101, the second-stage molten salt heat storage circuit 201 and the third-stage molten salt heat storage circuit 301 release the stored heat as needed, heat the corresponding working fluid through the corresponding molten salt heat exchanger, and the working fluids of different temperature levels are mixed at the mixing unit 400 in a set proportion, the flow ratio of the three working fluids is dynamically adjusted by adjusting the opening degree of each heat exchange regulating valve, and then the temperature of the working fluid output by the mixing unit 400 is accurately controlled.

[0040] Alternatively, in some embodiments, the heat of the main steam extraction is exchanged in the second-stage heat exchange unit 200 and then enters the third-stage heat exchange unit 300.

[0041] That is, after the heat of the main steam extraction is exchanged in the second-stage heat exchange unit 200, the heat energy carried thereby can be further transported to the third-stage heat exchange unit 300 for heat exchange through the connecting pipeline between the second-stage heat exchange unit 200 and the third-stage heat exchange unit 300 and the control and adjustment of the second-stage heat storage to third-stage heat storage switch valve 41. This multi-stage series heat exchange mode can realize gradient utilization of steam waste heat and significantly improve the waste heat recovery efficiency of the entire system, thereby maximizing energy utilization benefits.

[0042] The heat from the air extracted from the intermediate-pressure cylinder, after undergoing heat exchange in the three-stage heat exchange unit 300, can directly enter the condenser 5 in the boiler system. In the condenser 5, the remaining heat from the air extracted from the intermediate-pressure cylinder is released, condensed into water, and then sent back to the boiler 1 by the condensate pump 6 for reheating, completing one cycle.

[0043] Optionally, in some embodiments, the first-stage heat exchange regulating valve 102 is used to regulate the flow rate of the first working fluid entering the second-stage molten salt heat exchanger 12 and the output flow rate of the first working fluid after heat absorption; the second-stage heat exchange regulating valve 202 is used to regulate the flow rate of the second working fluid entering the second-stage molten salt heat exchanger 22 and the output flow rate of the second working fluid after heat absorption; and the third-stage heat exchange regulating valve 302 is used to regulate the flow rate of the third working fluid entering the second-stage molten salt heat exchanger 32 and the output flow rate of the third working fluid after heat absorption.

[0044] like Figure 2 As shown, the system is equipped with a primary heat exchange regulating valve 102, a secondary heat exchange regulating valve 202 and a tertiary heat exchange regulating valve 302 on the heat exchange working fluid side. These valves are used to precisely regulate the flow rate of the working fluid entering each molten salt heat exchanger and the output flow rate of the working fluid after heat absorption. By adjusting the ratio of the output flow rates of the three working fluids, dynamic mixing of the heat exchange working fluids can be achieved at the downstream mixing unit 400.

[0045] Specifically, the primary heat exchange regulating valve 102 can control the flow rate of the first working fluid entering the second-stage molten salt heat exchanger 12, which helps to control the heat exchange process between the first molten salt medium (high-temperature salt) and the first working fluid, ensuring that the first molten salt medium (high-temperature salt) can effectively transfer the absorbed heat to the first working fluid. The primary heat exchange regulating valve 102 can also regulate the output flow rate of the first working fluid after it has been heated by the second-stage molten salt heat exchanger 12. This can dynamically adjust the supply of the first working fluid according to the load demand of the thermal power unit or other process requirements. In addition, the primary heat exchange regulating valve 102 can also quickly cut off or reduce the flow rate of the first working fluid when abnormal conditions occur in the system (such as overheating, overpressure, etc.) to protect the second-stage molten salt heat exchanger 12 and other system equipment from damage.

[0046] Similarly, the secondary heat exchange regulating valve 202 can control the flow of the second working fluid into the second secondary molten salt heat exchanger 22, help control the heat exchange process between the second molten salt medium (high-temperature salt) and the second working fluid, and ensure that the second molten salt medium (high-temperature salt) can effectively transfer the absorbed heat to the second working fluid; the secondary heat exchange regulating valve 202 can also adjust the output flow of the second working fluid heated by the second secondary molten salt heat exchanger 22, which can dynamically adjust the supply amount of the second working fluid according to the load demand of the thermal power generating unit or other process requirements; the secondary heat exchange regulating valve 202 can also quickly cut off or reduce the flow of the second working fluid when abnormal conditions (such as overheating, overpressure, etc.) occur in the system, to protect the second secondary molten salt heat exchanger 22 and other system equipment from damage.

[0047] The tertiary heat exchange regulating valve 302 can control the flow of the third working fluid into the second tertiary molten salt heat exchanger 32, help control the heat exchange process between the third molten salt medium (high-temperature salt) and the third working fluid, and ensure that the third molten salt medium (high-temperature salt) can effectively transfer the absorbed heat to the third working fluid; the tertiary heat exchange regulating valve 302 can also adjust the output flow of the third working fluid heated by the second tertiary molten salt heat exchanger 32, which can dynamically adjust the supply amount of the third working fluid according to the load demand of the thermal power generating unit or other process requirements; the tertiary heat exchange regulating valve 302 can also quickly cut off or reduce the flow of the third working fluid when abnormal conditions (such as overheating, overpressure, etc.) occur in the system, to protect the second tertiary molten salt heat exchanger 32 and other system equipment from damage.

[0048] Optionally, in some embodiments, the first molten salt medium is a fluorinated salt, the second molten salt medium is a binary molten salt, and the third molten salt medium is a ternary molten salt.

[0049] Specifically, in the embodiments of the present application, the first molten salt medium used by the first molten salt heat storage circuit 101 is a fluorinated salt medium with a working temperature range of 900-1200 ℃, mainly used for recovering the high-temperature waste heat in the boiler 1 furnace flue gas extraction. The temperature of these flue gases is relatively high, and a high-temperature resistant molten salt medium can be used to absorb and store heat. The second molten salt medium used by the second molten salt heat storage circuit 201 is a binary molten salt medium with a working temperature range of 290-560 ℃, mainly used for recovering the medium-temperature heat energy in the main steam extraction of the high-pressure cylinder 2 of the steam turbine. The temperature of these extraction gases is relatively low, but still contains a large amount of usable heat energy. The third molten salt medium used by the third molten salt heat storage circuit 301 is a ternary molten salt medium with a working temperature range of 140-500 ℃, mainly used for recovering the low-temperature heat energy in the extraction of the intermediate-pressure cylinder 3 of the steam turbine. The temperature of these extraction gases is the lowest, but can still be effectively utilized.

[0050] By using molten salt media of different temperature ranges, the waste heat of the thermal power generating unit can be utilized in stages. The high-temperature waste heat is used to heat feed water or generate electricity, the medium-temperature thermal energy is used for industrial heating or heating, and the low-temperature thermal energy is used to preheat feed water or other low-temperature heat users. By matching the temperature range of the molten salt medium with the temperature of the heat source, the heat loss in the heat exchange process can be reduced, and the utilization efficiency of thermal energy can be improved.

[0051] Optionally, in some embodiments, the fluorinated salt is a lithium fluoride-sodium fluoride-potassium fluoride system, the binary molten salt is a sodium nitrate-potassium nitrate mixture, and the ternary molten salt is a sodium nitrate-potassium nitrate-calcium nitrate mixture.

[0052] Specifically, in the embodiments of the present application, the fluorinated salt is a lithium fluoride-sodium fluoride-potassium fluoride system, which is suitable for high-temperature environments and can remain stable at such high temperatures without decomposition or phase change; the binary molten salt is a sodium nitrate-potassium nitrate mixture, which is suitable for medium-temperature environments and has good thermal stability within this temperature range; and the ternary molten salt is a sodium nitrate-potassium nitrate-calcium nitrate mixture, which is suitable for low-temperature environments and is also stable within the corresponding temperature range.

[0053] As can be seen, by selecting the lithium fluoride-sodium fluoride-potassium fluoride system, the sodium nitrate-potassium nitrate mixture, and the sodium nitrate-potassium nitrate-calcium nitrate mixture as molten salt media of different temperature ranges, the molten salt thermal storage system can have optimal thermal stability, lower corrosiveness, good thermal conductivity, chemical compatibility, and safety within their respective working temperature ranges, thereby achieving efficient, reliable, and economical thermal energy storage and utilization.

[0054] Optionally, in some embodiments, the molten salt thermal storage system 10 based on thermal energy grading matching further comprises a temperature sensor, a flow sensor, and a control unit, wherein the temperature sensor is used to monitor the real-time temperature of the molten salt and the temperature of the working medium outlet; the flow sensor is used to monitor the flow of the working fluid of each molten salt heat exchanger; and the control unit is used to determine the target opening of each heat exchange regulating valve based on the thermal power generating unit load prediction result and the preset heating demand, and to adjust the corresponding heat exchange regulating valve according to the target opening of each heat exchange regulating valve.

[0055] Specifically, to achieve intelligent management of the molten salt thermal energy storage system 1000 based on graded matching of thermal energy, this embodiment of the application also includes temperature sensors, flow sensors, and control units. These are used to monitor in real time the temperature of the molten salt in the primary molten salt thermal energy storage loop 101, the mixing temperature at the working fluid outlet, and the flow rate of the working fluid in each molten salt heat exchanger. Combined with the control unit, based on the current load of the thermal power unit, predicted load dynamics, and preset heating demand, the flow rate ratio of the working fluid is calculated, and the opening degree of each heat exchange regulating valve is automatically adjusted to the target opening degree. This achieves control of the flow rate ratio on the working fluid side, realizing closed-loop control and dynamic thermal energy management. This control strategy not only improves the heat exchange efficiency of the system but also reduces the need for manual intervention, enhancing operational safety and economy.

[0056] In summary, the molten salt thermal storage system based on thermal energy gradation matching proposed in this application has at least the following beneficial effects: (1) Wide temperature range thermal energy adaptation: By using the graded combination of fluoride salt, binary molten salt and ternary molten salt, multi-grade heat storage can be achieved from high temperature flue gas (900-1200 ℃) to main steam extraction (290-560 ℃) and medium pressure cylinder extraction (140-500 ℃), covering a wider temperature range.

[0057] (2) Flexible heat management: By adjusting the flow rate ratio of the working fluid in the three-stage heat exchange unit, the dynamic distribution and mixed output of heat energy of different grades can be achieved to meet the flexible heating needs of thermal power units under different load conditions.

[0058] (3) Enhance peak shaving capacity: When the system is in a state of deep peak shaving and low load operation, it can release the stored multi-grade heat to assist the operation of the boiler and turbine, thereby improving the peak shaving depth and energy efficiency of the unit.

[0059] (4) Efficient utilization of flue gas waste heat: Effectively recover high-temperature waste heat in boiler flue gas, realize dual-channel coupling of flue gas side and turbine side of thermal power unit, and greatly improve energy utilization rate.

[0060] (5) Intelligent control: Equipped with temperature and flow monitoring and automatic control devices, supporting heat energy management based on load forecasting, realizing fully automatic operation and reducing the need for manual intervention.

[0061] (6) Applicable to newly built or renovated thermal power units, especially in the context of a power grid environment with a high proportion of new energy sources, it can effectively improve the flexibility of thermal power units, reduce carbon emissions and optimize the energy structure.

[0062] The molten salt thermal energy storage system based on graded matching of thermal energy proposed in this application uses a primary heat exchange unit to absorb and store high-grade heat from the flue gas extracted from the boiler furnace extraction pipeline; a secondary heat exchange unit to absorb and store high-grade heat from the main steam extraction pipeline of the turbine high-pressure cylinder; and a tertiary heat exchange unit to absorb and store low-grade heat from the intermediate-pressure cylinder extraction pipeline of the turbine. A mixing unit combines these three types of extracted heat to output a working fluid that meets the target temperature, adapting to different preset operating conditions of the thermal power unit. Therefore, this system enables graded storage and release of thermal energy, achieving efficient utilization over a wide temperature range. It solves the problems of insufficient temperature range coverage, mismatched heat grades, and lack of flexibility in thermal energy management inherent in existing molten salt thermal energy storage technologies for the flexible retrofitting of thermal power units, thereby improving the flexibility and energy efficiency of thermal power units.

[0063] Next, referring to the accompanying drawings, a thermal energy peak-shaving method for thermal power units according to embodiments of this application is described.

[0064] Figure 3 This is a flowchart of a thermal power unit heat energy peak shaving method according to an embodiment of this application.

[0065] like Figure 3 As shown, the thermal power unit's peak-shaving method adopts... Figure 1 The molten salt thermal energy storage system based on thermal energy grading matching in this embodiment includes the following steps: In step S301, when the thermal power unit is in the first preset operating condition, the heat of flue gas extraction is absorbed and stored through the first-stage heat exchange unit, the heat of main steam extraction is absorbed and stored through the second-stage heat exchange unit, and the heat of intermediate pressure cylinder extraction is absorbed and stored through the third-stage heat exchange unit.

[0066] In step S302, when the thermal power unit is in the second preset operating condition, the output flow rate ratio of the working fluid in the first-stage heat exchange unit, the second-stage heat exchange unit and the third-stage heat exchange unit is adjusted, and working fluids of different grades are mixed by the mixing unit to output working fluid that meets the target temperature.

[0067] According to the thermal energy peak shaving method for thermal power units proposed in the embodiments of this application, thermal energy can be stored and released in a gradient manner through a molten salt thermal energy storage system based on thermal energy grade matching, so as to achieve efficient utilization over a wide temperature range. This solves the problems of insufficient temperature range coverage, mismatch of heat quality and lack of flexibility in thermal energy management in the flexible transformation of thermal power units by existing molten salt thermal energy storage technology, thereby improving the flexibility and energy efficiency of thermal power units.

[0068] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0069] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0070] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A molten salt thermal storage system based on thermal energy stage matching, characterized in that, include: The system consists of a primary heat exchange unit, a secondary heat exchange unit, a tertiary heat exchange unit, and a mixing unit. The primary heat exchange unit is coupled to the flue gas extraction pipeline of the boiler furnace. The primary heat exchange unit includes a primary molten salt heat storage circuit and a primary heat exchange regulating valve, which are used to absorb and store the heat of the flue gas extracted from the boiler furnace using the primary molten salt heat storage circuit and the primary heat exchange regulating valve. The secondary heat exchange unit is coupled to the main steam extraction pipeline of the high-pressure cylinder of the steam turbine. The secondary heat exchange unit includes a secondary molten salt heat storage circuit and a secondary heat exchange regulating valve, which are used to absorb and store the heat of the main steam extraction in the main steam extraction pipeline of the high-pressure cylinder of the steam turbine. The three-stage heat exchange unit is coupled to the turbine intermediate pressure cylinder extraction pipeline. The three-stage heat exchange unit includes a three-stage molten salt heat storage circuit and a three-stage heat exchange regulating valve, which are used to absorb and store the heat of the intermediate pressure cylinder extraction in the turbine intermediate pressure cylinder extraction pipeline. The mixing unit is used to mix the heat from the flue gas extraction, the heat from the main steam extraction, and the heat from the intermediate pressure cylinder extraction, and outputs a working fluid that meets the target temperature to adapt to different preset operating conditions of the thermal power unit.

2. The system according to claim 1, characterized in that, The primary molten salt thermal storage circuit includes: a first-stage molten salt heat exchanger, a second-stage molten salt heat exchanger, a first-stage molten salt circulation pump, a second-stage molten salt circulation pump, a first-stage molten salt storage tank, and a second-stage molten salt storage tank, wherein... The primary molten salt heat storage circuit is used to absorb and store the heat of the flue gas extraction from the boiler furnace flue gas extraction pipeline through the first molten salt medium, and transfer the heat of the flue gas extraction to the first working fluid for output.

3. The system according to claim 2, characterized in that, The secondary molten salt thermal storage circuit includes: a first-stage molten salt heat exchanger, a second-stage molten salt heat exchanger, a first-stage molten salt circulation pump, a second-stage molten salt circulation pump, a first-stage molten salt storage tank, and a second-stage molten salt storage tank, wherein... The secondary molten salt heat storage circuit is used to absorb and store the heat of the main steam extraction from the main steam extraction pipeline of the high-pressure cylinder of the steam turbine through the second molten salt medium, and to transfer the heat of the main steam extraction to the second working fluid for output.

4. The system according to claim 3, characterized in that, The three-stage molten salt thermal storage circuit includes: a first-stage molten salt heat exchanger, a second-stage molten salt heat exchanger, a first-stage molten salt circulation pump, a second-stage molten salt circulation pump, a first-stage molten salt storage tank, and a second-stage molten salt storage tank. The three-stage molten salt thermal storage circuit is used to absorb and store the gas extracted from the intermediate pressure cylinder of the steam turbine through the third molten salt medium, and to transfer the gas extracted from the intermediate pressure cylinder to the third working fluid for output.

5. The system according to claim 1, characterized in that, The heat from the main steam extraction is exchanged in the secondary heat exchange unit and then enters the tertiary heat exchange unit for further heat exchange.

6. The system according to claim 4, characterized in that, The primary heat exchange regulating valve is used to regulate the flow rate of the first working fluid entering the second-stage molten salt heat exchanger and the output flow rate of the first working fluid after heat absorption. The secondary heat exchange regulating valve is used to regulate the flow rate of the second working fluid entering the second secondary molten salt heat exchanger and the output flow rate of the second working fluid after heat absorption. The three-stage heat exchange regulating valve is used to regulate the flow rate of the third working fluid entering the second and third stage molten salt heat exchangers and the output flow rate of the third working fluid after heat absorption.

7. The system according to claim 4, characterized in that, The first molten salt medium is a fluoride salt, the second molten salt medium is a binary molten salt, and the third molten salt medium is a ternary molten salt.

8. The system according to claim 7, characterized in that, The fluoride salt is a lithium fluoride-sodium fluoride-potassium fluoride system, the binary molten salt is a sodium nitrate-potassium nitrate mixture, and the ternary molten salt is a sodium nitrate-potassium nitrate-calcium nitrate mixture.

9. The system according to claim 1, characterized in that, Also includes: Temperature sensor, flow sensor and control unit, among which, The temperature sensor is used to monitor the real-time temperature of the molten salt and the temperature of the working fluid outlet; The flow sensor is used to monitor the flow rate of the working fluid in each molten salt heat exchanger; The control unit is used to determine the target opening degree of each heat exchange regulating valve based on the load prediction results of the thermal power unit and the preset heating demand, and to adjust the corresponding heat exchange regulating valve according to the target opening degree of each heat exchange regulating valve.

10. A method for peak shaving of thermal power units, characterized in that, The method employs the molten salt thermal storage system based on thermal energy gradation matching as described in any one of claims 1-9, wherein the method includes the following steps: When the thermal power unit is in the first preset operating condition, the heat of flue gas extraction is absorbed and stored through the first-stage heat exchange unit, the heat of main steam extraction is absorbed and stored through the second-stage heat exchange unit, and the heat of intermediate pressure cylinder extraction is absorbed and stored through the third-stage heat exchange unit. When the thermal power unit is in the second preset operating condition, the output flow rate ratio of the working fluid in the first-stage heat exchange unit, the second-stage heat exchange unit and the third-stage heat exchange unit is adjusted, and working fluids of different grades are mixed by the mixing unit to output working fluid that meets the target temperature.

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