Thermal power generating unit deep peak shaving system and operation method thereof

Abstract

The invention provides a thermal power generating unit deep peak shaving system which comprises a thermal power generating unit system and a fused salt energy storage system, the thermal power generating unit system comprises a boiler, a steam turbine generator unit and a water supply unit, and the fused salt energy storage system comprises a fused salt heating unit, a high-temperature heat pump unit, a fused salt storage unit and a steam generator. And the fused salt heating unit comprises a superheated steam heater and a saturated steam heater which are communicated in sequence. The system has the advantages that the output of the thermal power generating unit can be effectively reduced, the grade of steam during heat release of the fused salt energy storage unit can be guaranteed while heat energy of boiler steam is completely utilized in a stepped mode, and the overall energy conversion and energy storage efficiency of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal power generation energy storage, and particularly to a deep peak shaving system for a thermal power unit and an operation method thereof. Background Art

[0002] China is a country lacking oil and gas, with relatively rich coal resources, and coal-fired power generation units are excellent peak shaving units. With the increase in the proportion of new energy installed capacity, the demand for deep peak shaving transformation of thermal power is increasing day by day.

[0003] The main purpose of the deep peak shaving transformation of thermal power is to reduce the unit load to below 30%, or even zero output. At present, the load of coal-fired power generation units can generally only be reduced to about 30%. Further reduction will lead to problems such as unstable combustion of the boiler and excessive pollutant emissions.

[0004] At present, using the external molten salt energy storage technology to assist in realizing the deep peak shaving of coal-fired power generation units below 30% load is one of the mainstream technologies, which generally includes three technical routes:

[0005] (1) Electric heating molten salt energy storage: The principle is to directly convert the electric power load below 30% of the coal-fired power generation unit into the heat energy of molten salt, so as to realize the deep peak shaving of the unit.

[0006] (2) Steam heating molten salt energy storage: Extract the main steam or reheated steam of the coal-fired power generation unit to heat the molten salt, thereby reducing the steam volume of the steam turbine and reducing the power generation of the unit.

[0007] (3) Flue gas heating molten salt: Extract the flue gas of the coal-fired boiler of the coal-fired power generation unit to heat the molten salt, thereby reducing the steam generation amount of the coal-fired boiler and further reducing the power generation of the unit.

[0008] In actual use, it is found that the energy storage efficiency of the first method is relatively low, because its thermoelectric efficiency does not exceed 50%, which will cause waste of energy; although the second method has a higher energy storage efficiency than the first method, since most of the steam energy exists in the latent heat of condensation, and the steam condensation temperature is generally not higher than 350 °C (the higher the pressure, the higher the condensation temperature), this also means that even if 550 °C steam is extracted, it is difficult to heat the molten salt temperature to above 400 °C, resulting in loss of energy quality; although the third method can heat the molten salt to a higher temperature, the heat transfer coefficient of the flue gas is small, and the equipment needs to be designed to be of a larger size, making it difficult to implement the transformation of existing units for utilization, with low practicability. Summary of the Invention

[0009] Aiming at the deficiencies in the prior art, the present invention provides a deep peak shaving system for a thermal power unit, which solves the problems of low energy storage efficiency, low quality of generated steam, and low overall exergy efficiency existing in the coupling of molten salt energy storage with thermal power units in the prior art.

[0010] The above technical object of the present invention is achieved by the following technical solutions:

[0011] A deep peak shaving system for a thermal power unit includes a thermal power unit system and a molten salt energy storage system. The thermal power unit system includes a boiler, a steam turbine generator set, and a feed water unit. The boiler is connected to the steam turbine generator set to supply main steam and reheated steam to the steam turbine generator set. The feed water unit is connected to the steam turbine generator set to liquefy the steam from the steam turbine generator set into feed water and is simultaneously connected to the boiler to supply the feed water to the boiler. The molten salt energy storage system includes a molten salt heating unit, a high-temperature heat pump unit, a molten salt storage unit, and a steam generator. The molten salt heating unit includes a superheated steam heater and a saturated steam heater connected in sequence.

[0012] The high-temperature side inlet of the superheated steam heater is connected to the thermal power unit system to flow in a part of the extracted main steam / or reheated steam. The high-temperature side outlet of the superheated steam heater is connected to the high-temperature side inlet of the saturated steam heater. The low-temperature side inlet and the low-temperature side outlet of the superheated steam heater are both connected to the molten salt storage unit to flow in low-temperature molten salt and flow out high-temperature molten salt. The superheated steam heater is used to exchange heat between the extracted main steam and / or reheated steam and the low-temperature molten salt.

[0013] The high-temperature side inlet of the saturated steam heater is connected to the high-temperature side outlet of the superheated steam heater to flow in the saturated steam from the superheated steam heater. The high-temperature side outlet of the saturated steam heater is connected to the feed water unit. The low-temperature side inlet and the low-temperature side outlet of the saturated steam heater are both connected to the high-temperature heat pump unit to flow in a low-temperature gas circulating medium and flow out a high-temperature gas circulating medium. The saturated steam heater is used to exchange heat between the saturated steam and the low-temperature gas circulating medium.

[0014] The high-temperature heat pump unit is respectively connected to the saturated steam heater and the molten salt storage unit. The high-temperature heat pump unit is used to heat the high-temperature gas circulating medium after heat exchange with the saturated steam to a predetermined temperature and make it exchange heat with the low-temperature molten salt. The gas circulating medium circulates in the circuit of the high-temperature heat pump unit.

[0015] The high-temperature side inlet and the high-temperature side outlet of the steam generator are both connected to the molten salt storage unit to flow in high-temperature molten salt and flow out low-temperature molten salt. The low-temperature side inlet of the steam generator is connected to the feed water unit to flow in the diverted feed water. The low-temperature side outlet of the steam generator is connected to the thermal power unit system to flow out superheated steam that can be confluent with the main steam and / or the reheater.

[0016] As a preferred embodiment of the present invention, the high-temperature heat pump unit includes a heat pump expander, a heat pump compressor, and a heat pump heater that are connected in sequence to form a loop. The heat pump expander is respectively connected to the low-temperature side inlet of the saturated steam heater and the high-temperature side outlet of the heat pump heater. The heat pump compressor is respectively connected to the low-temperature side outlet of the saturated steam heater and the high-temperature side inlet of the heat pump heater. The low-temperature side inlet and the low-temperature side outlet of the heat pump heater are both connected to the molten salt storage unit to flow in low-temperature molten salt and flow out high-temperature molten salt.

[0017] As a preferred embodiment of the present invention, the heat pump compressor and the heat pump expander are arranged coaxially.

[0018] As a preferred embodiment of the present invention, the molten salt storage unit includes a cold salt tank and a hot salt tank. The inlet of the cold salt tank is connected to the high-temperature side outlet of the steam generator. The outlet of the cold salt tank is respectively connected to the low-temperature side inlet of the superheated steam heater and the molten salt inlet of the high-temperature heat pump unit. The inlet of the hot salt tank is respectively connected to the low-temperature side outlet of the superheated steam heater and the molten salt outlet of the high-temperature heat pump unit. The outlet of the hot salt tank is connected to the high-temperature side inlet of the steam generator.

[0019] As a preferred embodiment of the present invention, it further includes a high-pressure water heat storage system. The high-pressure water heat storage system includes a high-pressure water heater and a water storage unit. The high-temperature side inlet of the high-pressure water heater is connected to the high-temperature side outlet of the saturated steam heater to flow in the subcooled water from the saturated steam heater. The high-temperature side outlet of the high-pressure water heater is connected to the feed water unit. The low-temperature side inlet and the low-temperature side outlet of the high-pressure water heater are connected to the water storage unit to flow in low-temperature high-pressure water and flow out high-temperature high-pressure water. The high-pressure water heater is used to complete the heat exchange between the subcooled water and the low-temperature high-pressure water.

[0020] As a preferred embodiment of the present invention, the high-pressure water heat storage system further includes a steam feed water preheater. The high-temperature side inlet and the high-temperature side outlet of the steam feed water preheater are both connected to the water storage unit to flow in high-temperature high-pressure water and flow out low-temperature high-pressure water. The low-temperature side inlet of the steam feed water preheater is connected to the feed water unit. The low-temperature side outlet of the steam feed water preheater is connected to the low-temperature side inlet of the steam generator.

[0021] As a preferred embodiment of the present invention, the water storage unit includes a single water storage tank. The low-temperature side inlet of the high-pressure water heater is communicated with the lower outlet of the single water storage tank, and the low-temperature side outlet of the high-pressure water heater is communicated with the upper inlet of the single water storage tank; or the water storage unit includes a cold water tank and a hot water tank. The low-temperature side inlet of the high-pressure water heater is communicated with the outlet of the cold water tank, and the low-temperature side outlet of the high-pressure water heater is communicated with the inlet of the hot water tank.

[0022] As a preferred embodiment of the present invention, the water storage unit includes a single water storage tank. The low-temperature side inlet of the high-pressure water heater is communicated with the lower outlet of the single water storage tank, and the low-temperature side outlet of the high-pressure water heater is communicated with the upper inlet of the single water storage tank. The high-temperature side inlet of the steam feed water preheater is communicated with the hot water outlet of the single water storage tank, and the high-temperature side outlet of the steam feed water preheater is communicated with the cold water inlet of the single water storage tank;

[0023] or the water storage unit includes a cold water tank and a hot water tank. The low-temperature side inlet of the high-pressure water heater is communicated with the outlet of the cold water tank, and the low-temperature side outlet of the high-pressure water heater is communicated with the inlet of the hot water tank. The high-temperature side inlet of the steam feed water preheater is communicated with the outlet of the hot water tank, and the high-temperature side outlet of the steam feed water preheater is communicated with the inlet of the cold water tank.

[0024] As a preferred embodiment of the present invention, the feed water unit includes a condenser, a low-pressure heater, a deaerator, and a high-pressure heater that are connected in sequence. The condenser is communicated with the steam turbine generator set, the high-pressure heater is communicated with the boiler, and the deaerator or the passage between the deaerator and the condenser is also used to introduce subcooled water from the molten salt heating unit and divert a part of the feed water to the steam generator.

[0025] Based on the same inventive concept, the present invention also provides an operation method of the thermal power unit deep peak shaving system as described above. The specific technical solution is as follows, including

[0026] Peak shaving stage: When the thermal power unit system is in peak shaving operation, the thermal power unit system maintains stable combustion and low load operation. The molten salt heating unit, the high-temperature heat pump unit, and the molten salt storage unit jointly participate in the operation. Part of the main steam and / or reheated steam is extracted as a heat source and first flows through the superheated steam heater to exchange heat with part of the low-temperature molten salt flowing through the superheated steam heater from the molten salt storage unit to complete molten salt energy storage;

[0027] The extracted main steam and / or reheated steam flows out of the superheated steam heater and cools down to become saturated steam, which then flows through the saturated steam heater and exchanges heat with the low-temperature gas circulating medium that comes from the high-temperature heat pump unit and flows through the saturated steam heater. The low-temperature gas circulating medium absorbs heat and is heated by the high-temperature heat pump unit to become a high-temperature gas circulating medium that can reach a predetermined temperature, and exchanges heat with a part of the low-temperature molten salt that comes from the molten salt storage unit and flows through the high-temperature heat pump unit to complete molten salt energy storage;

[0028] The saturated steam flows out of the saturated steam heater and cools down to become subcooled water. The subcooled water directly flows through the feed water unit for recycling and becomes boiler feed water, or the subcooled water exchanges its remaining heat to high-pressure water through a high-pressure water heater and then flows through the feed water unit for recycling and becomes boiler feed water. The high-pressure water after absorbing heat is used to provide heat energy to the external heat user end or preheat a part of the feed water diverted from the feed water unit through a steam feed water preheater during the peak stage;

[0029] Peak stage: When the thermal power unit system is operating at peak load, the molten salt heating unit and the high-temperature heat pump unit stop operating, and the molten salt storage unit and the steam generator participate in the operation. The high-temperature molten salt stored in the molten salt storage unit flows through the steam generator and exchanges heat with a part of the feed water diverted from the feed water unit. The generated superheated steam converges with the main steam and / or reheated steam of the thermal power unit system and enters the steam turbine generator set.

[0030] Working principle:

[0031] The present invention relates to a deep peak shaving system for a thermal power unit and its operation method, which mainly adopts the technology of cascaded utilization of heat. It can not only store energy during the peak shaving of the thermal power unit system and further reduce the load of the thermal power unit, but also provide steam energy for the thermal power unit system to help the thermal power unit system increase the load during the peak operation of the thermal power unit system.

[0032] The conventional operation process of the thermal power unit system is as follows: the main steam generated by the boiler's superheater heating the boiler feed water passes through the steam turbine generator set and then re-enters the boiler, and is heated by the reheater to become reheated steam. The reheated steam passes through the steam turbine generator set and is liquefied by the water supply unit to become boiler feed water, and then is transported to the boiler to complete the cycle. When the thermal power unit system is in peak operation, the thermal power unit system first relies on its own regulation ability to reduce the overall load to about 30%. When the load is further reduced, part of the superheated steam is extracted (main steam is extracted separately or reheated steam is extracted separately or main steam and reheated steam are extracted at the same time) and flows to the superheated steam heater. The superheated steam heater exchanges heat with the low-temperature molten salt flowing to the superheated steam heater through the molten salt energy storage unit, so that the sensible heat in the superheated steam is converted and stored in the molten salt. The temperature of the superheated steam is between 500 and 600°C, and the molten salt is heated to a maximum of about 600°C. The high-temperature molten salt after absorbing heat flows back into the molten salt storage unit for storage. The superheated steam passing through the superheated steam heater drops in temperature after releasing heat and becomes saturated steam. Because most of the heat of saturated steam is latent heat of condensation and the temperature is about 300°C to 400°C, it is no longer possible to heat the molten salt to the upper limit temperature of 400 to 600°C. At this time, the superheated steam is heated to a maximum temperature of about 600°C through the molten salt energy storage unit. The saturated steam heater exchanges heat between saturated steam and the low-temperature gas circulating medium in the high-temperature heat pump unit, so that the low-temperature gas circulating medium absorbs the heat of the saturated steam and is heated by the high-temperature heat pump unit to become a high-temperature gas circulating medium that can heat the molten salt to the upper limit temperature. The high-temperature gas circulating medium further exchanges heat with the low-temperature molten salt in the molten salt storage unit, so that the low-temperature molten salt reaches the upper limit use temperature. The high-temperature molten salt after absorbing heat flows back into the molten salt energy storage unit for storage; the saturated steam passing through the saturated steam heater becomes supercooled water after the latent heat is released, and the supercooled water flows through the water supply unit for recycling and becomes boiler feed water to complete the cycle, or the supercooled water exchanges the remaining heat to high-pressure water through the high-pressure water heater and then flows through the water supply unit for recycling and becomes boiler feed water. The high-pressure water after absorbing heat is used to provide heat energy to the external heat user end or to preheat part of the feed water diverted from the water supply unit during the peak stage through the steam feed water preheater.

[0033] When the thermal power unit system is operating at its peak, the molten salt heating unit and the high-temperature heat pump unit stop operating, and the high-temperature molten salt stored in the molten salt storage unit flows through the steam generator and exchanges heat with part of the feed water diverted from the feed water unit in the steam generator, and the superheated steam generated is simultaneously merged with the main steam or reheat steam or the main steam and reheat steam of the thermal power unit system and enters the steam turbine generator set.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The passing steam exchanges heat with molten salt through the provided superheated steam heater, and its thermal energy is converted and stored in the high-temperature molten salt. The saturated steam exchanges heat with the gas circulation medium through the provided saturated steam heater, and its thermal energy is converted and stored in the gas circulation medium. Then, the temperature of the gas circulation medium is further increased through the high-temperature heat pump unit, and the high-temperature gas circulation medium exchanges heat with the molten salt again, and its thermal energy is converted and stored in the high-temperature molten salt. In this way, the thermal energy of the boiler steam can be effectively utilized and stored to the greatest extent, and the energy storage efficiency is high.

[0036] Through the provided steam generator, the high-temperature molten salt exchanges heat with the feed water flowing in by diversion from the feed water unit. The diverted feed water absorbs the thermal energy of the high-temperature molten salt and becomes superheated steam, and flows into the steam turbine generator set together with the main steam and / or reheated steam through a pipeline, playing the role of quickly increasing the load during peak operation.

[0037] The present invention utilizes the molten salt heating unit and the high-temperature heat pump unit to not only convert and store the thermal energy of the superheated steam of the boiler, but also convert and store the thermal energy of the saturated steam after the superheated steam is cooled, that is, the thermal energy of the boiler steam is fully utilized in a stepped manner. Except that a small part of electric energy is consumed when the high-temperature heat pump unit raises the latent heat of condensation of the low-grade steam to the thermal energy of the gas circulation medium with a higher grade, the others are all conversions and storages from thermal energy to thermal energy, and the conversion efficiency can almost reach 100%. The overall energy storage efficiency of the system is relatively high, and the exergy efficiency is relatively high. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the first operation process of the present invention (where the water storage unit is a single water storage tank and is connected to the high-pressure water heater);

[0039] Figure 2 It is a schematic diagram of the second operation process of the present invention (where the water storage unit includes a cold water tank and a hot water tank and is connected to the high-pressure water heater);

[0040] Figure 3 It is a schematic diagram of the third operation process of the present invention (where the water storage unit is a single water storage tank and exchanges the heated high-pressure water with an external system or device);

[0041] Figure 4 It is a schematic diagram of the fourth operation process of the present invention (where the water storage unit includes a cold water tank and a hot water tank and exchanges the heated high-pressure water with an external system or device).

[0042] In the above-mentioned drawings: 1. Boiler; 2. Steam turbine generator set; 3. Condenser; 4. Condensate pump; 5. Low-pressure heater; 6. Deaerator; 7. No. 1 feed water pump; 8. High-pressure heater; 9. Superheated steam heater; 10. Saturated steam heater; 11. High-pressure water heater; 12. Heat pump compressor; 13. Heat pump expander; 14. Heat pump heater; 15. Hot salt tank; 16. Cold salt tank; 17. Water storage single tank; 171. Cold water tank; 172. Hot water tank; 18. Steam generator; 19. Steam feed water preheater; 20. No. 2 feed water pump. Detailed implementation manners

[0043] The technical solutions in the present invention will be further described below in conjunction with the drawings and embodiments.

[0044] Embodiment:

[0045] Referring to Figures 1 to 4 , it is a deep peak shaving system for a thermal power unit, including a thermal power unit system, a molten salt energy storage system, and a high-pressure water heat storage system. The thermal power unit system includes a boiler 1, a steam turbine generator set 2, and a feed water unit. The boiler 1 is connected to the steam turbine generator set 2 and conveys main steam and reheated steam to the steam turbine generator set 2. After passing through the steam turbine generator set 2, the main steam can re-enter the boiler 1 for heating and become reheated steam. After passing through the steam turbine generator set 2, the reheated steam will enter the feed water unit. The feed water unit includes a condenser 3, a low-pressure heater 5, a deaerator 6, and a high-pressure heater 8. The condenser 3 is connected to the steam turbine generator set 2 and is used to liquefy the steam discharged from the steam turbine generator set and pump the liquefied feed water into the low-pressure heater 5 through a condensate pump 4, and then further enter the deaerator 6 connected to the low-pressure heater 5 for deaeration treatment. After the treatment, the feed water will be pumped into the high-pressure heater 8 through a No. 1 feed water pump 7 and finally conveyed back to the boiler 1.

[0046] The molten salt energy storage system includes a molten salt heating unit, a high-temperature heat pump unit, a molten salt storage unit, and a steam generator 18. The molten salt heating unit includes a superheated steam heater 9 and a saturated steam heater 10 connected in sequence. The high-temperature side inlet of the superheated steam heater 9 is connected to the thermal power unit system. Specifically, a part of the main steam or reheated steam can be extracted therefrom through a pipeline, or the main steam and the reheated steam can be extracted simultaneously and enter the superheated steam heater 9. The molten salt storage unit includes a cold salt tank 16 and a hot salt tank 15. The inlet of the cold salt tank 16 is connected to the high-temperature side outlet of the steam generator 18 and receives and stores the low-temperature molten salt that has flowed through the heat exchange in the steam generator 18. The outlet of the cold salt tank 16 is connected to the low-temperature side inlet of the superheated steam heater 9 and transports the low-temperature molten salt to the superheated steam heater 9 for heat exchange. The inlet of the hot salt tank 15 is connected to the low-temperature side outlet of the superheated steam heater 9 and receives and stores the high-temperature molten salt that has absorbed the steam heat in the superheated steam heater 9. The outlet of the hot salt tank 15 is connected to the high-temperature side inlet of the steam generator 18 and can transport the high-temperature molten salt into the steam generator 18 for heat exchange. The low-temperature side inlet of the steam generator 18 is connected to the water outlet of the deaerator 6 and pumps the divided feed water through the No. 2 feed water pump 20. The low-temperature side outlet of the steam generator 18 is connected to the thermal power unit system and flows out the superheated steam that can be combined with the main steam or the reheater or the main steam and the reheater respectively, and enters the steam turbine generator set 2 together during the peak stage to play a role in quickly increasing the load. Since the temperature of the superheated steam entering the superheated steam heat exchanger is approximately 500 - 600 °C, the molten salt can be heated to approximately 500 - 600 °C at most. Such a setting can effectively utilize the steam entering the superheated steam heater 9 to heat the molten salt during the peak shaving stage, improve the utilization rate of thermal energy, increase the peak shaving depth of the unit, and achieve the purpose of energy storage and peak shaving. During the peak stage, the stored high-temperature molten salt is used to vaporize the feed water through the steam generator 18 and combine it with the thermal power unit system, releasing the thermal energy stored in the high-temperature molten salt and achieving the effect of energy release during the peak.

[0047] The high-temperature side outlet of the superheated steam heater 9 is connected to the high-temperature side inlet of the saturated steam heater 10, and saturated steam formed after heat exchange of superheated steam flows into the saturated steam heater 10. Most of the heat of this saturated steam is latent heat of condensation and the temperature is about 300°C to 400°C. However, the upper limit temperature requirement for the molten salt heat storage temperature is 400 to 600°C. Therefore, this saturated steam can no longer heat the low-temperature molten salt to the upper limit temperature. The present invention provides a high-temperature heat pump unit to solve this problem. The high-temperature heat pump unit includes a heat pump expander 13, a heat pump compressor 12, and a heat pump heater 14 that are connected in sequence to form a loop. The heat pump expander 13 is respectively connected to the high-temperature side outlet of the heat pump heater 14 and the low-temperature side inlet of the saturated steam heater 10. It receives the low-temperature gas cycle medium that has flowed out from the high-temperature side outlet of the heat pump heater 14 after heat exchange and transports the low-temperature gas cycle medium to the low-temperature side inlet of the saturated steam heater 10. The heat pump compressor 12 is respectively connected to the low-temperature side outlet of the saturated steam heater 10 and the high-temperature side inlet of the heat pump heater 14. It receives the high-temperature gas cycle medium that has flowed out from the low-temperature side outlet of the saturated steam heater 10 and performs further work on it to increase the temperature; and transports the further heated high-temperature gas cycle medium to the high-temperature side inlet of the heat pump heater 14. The gas cycle medium can be air, argon, nitrogen, helium, or carbon dioxide. It is worth mentioning that the heat pump compressor 12 and the heat pump expander 13 can be arranged in a coaxial connection. In this way, by consuming the compression energy of the gas cycle medium and recovering the energy for the compression of the heat pump compressor 12, the energy consumption of the heat pump compressor 12 is reduced. The low-temperature side inlet of the heat pump heater 14 is connected to the outlet of the cold salt tank 16 and receives the low-temperature molten salt flowing out from the cold salt tank 16. The low-temperature side outlet of the heat pump heater 14 is connected to the inlet of the hot salt tank 15 and transports the high-temperature molten salt after heat exchange with the high-temperature gas cycle medium to the hot salt tank 15. Such a setting can effectively utilize the latent heat of condensation contained in the saturated steam, transfer its energy to the gas cycle medium, and after the absorption of the gas cycle medium and the further work and temperature increase of the heat pump compressor 12 on it, it can heat the molten salt to the upper limit temperature and at the same time consume the electric energy generated by the steam turbine generator set 2, further increasing the peak shaving depth of the unit. Of course, the electric energy source of the high-temperature heat pump unit can also come from other external systems, such as other separate power supply systems, standby power generation systems, and abandoned photovoltaic and wind power energy, etc.

[0048] The high-temperature side outlet of the saturated steam heater 10 can be connected to the high-pressure water heat storage system. The saturated steam after passing through the saturated steam heater 10 will condense into subcooled water. At this time, the temperature of the subcooled water is about 200 - 350 °C. When connected to the high-pressure water heat storage system, the high-pressure water heat storage system can further utilize this part of the heat. The high-pressure water heat storage system includes a high-pressure water heater 11, a water storage unit, and a steam feed water preheater 19. The high-temperature side inlet of the high-pressure water heater 11 is connected to the high-temperature side outlet of the saturated steam heater 10 and receives the subcooled water flowing in from the saturated steam heater 10; the high-temperature side outlet of the high-pressure water heater 11 is connected to the deaerator 6 (it can also be connected to a certain pipeline node between the low-pressure heater 5 or the deaerator 6 and the condenser 3), and the subcooled water after consuming heat flows back into the boiler 1 after being treated by the feed water unit. The water storage unit can be a single water storage tank 17 or composed of a cold water tank 171 and a hot water tank 172. Figure 1 、 Figure 3 The connection example of the single water storage tank 17 is given. Figure 2 、 Figure 4 The connection examples of the cold water tank 171 and the hot water tank 172 are given. Figure 1 As shown, when the water storage unit is a single water storage tank 17, this single water storage tank 17 can store the high-temperature and high-pressure water after heat exchange. The low-temperature side inlet of the high-pressure water heater 11 is connected to the lower outlet of the single water storage tank 17 and receives the flowing low-temperature and high-pressure water; the low-temperature side outlet of the high-pressure water heater 11 is connected to the upper inlet of the single water storage tank 17 and conveys the high-temperature and high-pressure water after heat exchange. The high-temperature side inlet of the steam feed water preheater 19 is connected to the hot water outlet of the single water storage tank 17 and receives the high-temperature and high-pressure water flowing in from the single water storage tank 17. The high-temperature side outlet of the steam feed water preheater 19 is connected to the cold water inlet of the single water storage tank 17 and conveys the low-temperature and high-pressure water after releasing heat after heat exchange. The water temperature distribution in the entire single water storage tank 17 is an upper high-temperature and high-pressure water area, a middle thermocline area, and a lower low-temperature and high-pressure water area. Figure 2As shown, when the water storage units are the cold water tank 171 and the hot water tank 172, the low-temperature side inlet of the high-pressure water heater 11 is connected to the outlet of the cold water tank 171 and receives the inflowing low-temperature high-pressure water; the low-temperature side outlet of the high-pressure water heater 11 is connected to the inlet of the hot water tank 172 and conveys the high-temperature high-pressure water after heat exchange with the subcooled water to it. The high-temperature side inlet of the steam feed water preheater 19 is connected to the outlet of the hot water tank 172 and receives the high-temperature high-pressure water flowing in from the hot water tank 172. The high-temperature side outlet of the steam feed water preheater 19 is connected to the inlet of the cold water tank 171 and conveys the low-temperature high-pressure water after heat exchange and heat release. The low-temperature side inlet of the steam feed water preheater 19 is connected to the deaerator 6 in the feed water unit, and the shunted feed water is pumped in by the No. 2 feed water pump 20. The low-temperature side outlet of the steam feed water preheater 19 is connected to the low-temperature side inlet of the steam generator 18. Such a setting can, during peak operation, exchange heat between the high-temperature high-pressure water and the feed water flowing into the low-temperature side of the steam feed water preheater 19, so as to raise the water temperature of the feed water as much as possible when it flows into the steam generator 18, further effectively increasing the vaporization speed of the feed water, reducing the energy consumption for generating steam, and indirectly playing a role in quickly increasing the load. Of course, the high-temperature side outlet of the saturated steam heater 10 can also be directly connected to the deaerator 6 or the low-pressure heater 5 or the pipeline node between the deaerator 6 and the condenser 3. In addition, the water storage unit can also be connected to an external hot water user terminal to provide heated high-pressure water, such as Figure 3 , Figure 4 shown.

[0049] For the operation method of the above thermal power unit deep peak shaving system, the system mainly has two operation stages during operation,

[0050] Peak shaving stage: When the thermal power unit system is in peak shaving operation, the thermal power unit system maintains stable combustion and low load operation. The overall load of the thermal power unit system can be reduced to about 30% at the lowest. At this time, the molten salt heating unit, the high-temperature heat pump unit, the molten salt storage unit, and the high-pressure water heat storage system participate in the operation together. The steam generator 18 does not operate. By extracting part of the main steam or reheat steam or both the main steam and reheat steam as the heat source, it first flows through the superheated steam heater 9, exchanges heat with the low-temperature molten salt from the cold salt tank 16, and stores the high-temperature molten salt after heat absorption in the hot salt tank 15;

[0051] The extracted steam is cooled and flows out of the superheated steam heater 9 to become saturated steam and flows through the saturated steam heater 10. The saturated steam heater 10 exchanges heat with the low-temperature gas circulating medium from the heat pump expander 13. The high-temperature gas circulating medium after absorbing heat flows into the heat pump compressor 12 and is heated by the heat pump compressor 12 to become a high-temperature gas circulating medium that can reach a predetermined temperature (that is, it can match the temperature of the heated high-temperature molten salt or the temperature of the steam generated by the subsequent steam generator 18). The high-temperature molten salt flows into the heat pump heater 14 to exchange heat with the low-temperature molten salt from the cold salt tank 16. The high-temperature molten salt after heat exchange flows into the hot salt tank 15 for storage;

[0052] The saturated steam from the saturated steam heater 10 is cooled and flows out to become supercooled water, which is then exchanged with the low-temperature high-pressure water from the water storage tank 17 or the cold water tank 171 through the high-pressure water heater 11. The high-temperature high-pressure water that absorbs heat and flows out will be stored in the water storage tank 17 or the hot water tank 172. The supercooled water that passes through the high-pressure water heater 11 will eventually flow through the water supply unit for recycling and become the feed water for the boiler 1.

[0053] Peak stage: When the thermal power unit system is in peak operation, the molten salt heating unit and the high-temperature heat pump unit stop operating, and the molten salt storage unit, the steam generator 18, the water storage unit and the steam feed water preheater 19 participate in the operation. Part of the feed water diverted from the water supply unit first flows through the steam feed water preheater 19, and exchanges heat with the high-pressure hot water flowing into the steam feed water preheater 19 from the water storage tank 17 or the hot water tank 172, so that the feed water flowing through the steam feed water preheater 19 is preheated, and the feed water flowing out of the steam feed water preheater 19 flows into the steam generator 18 again, and the high-temperature molten salt stored in the hot salt tank 15 also flows through the steam generator 18, and the two exchange heat, the feed water absorbs heat and vaporizes, and the superheated steam generated is merged with the main steam or reheat steam or the main steam and reheat steam of the thermal power unit system through the pipeline and enters the steam turbine generator unit 2.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A deep peak shaving system for a thermal power unit, comprising a thermal power unit system and a molten salt energy storage system. The thermal power unit system includes a boiler (1), a steam turbine generator set (2) and a feed water unit. The boiler (1) is connected to the steam turbine generator set (2) for delivering main steam and reheated steam to the steam turbine generator set (2). The feed water unit is connected to the steam turbine generator set (2) for liquefying the steam from the steam turbine generator set (2) into feed water and is simultaneously connected to the boiler (1) for delivering the feed water to the boiler (1), characterized in that: The molten salt energy storage system includes a molten salt heating unit, a high-temperature heat pump unit, a molten salt storage unit, and a steam generator (18). The molten salt heating unit includes a superheated steam heater (9) and a saturated steam heater (10) that are connected in series. The high-temperature side inlet of the superheated steam heater (9) is connected to the thermal power unit system to flow in a part of the extracted main steam / or reheated steam. The high-temperature side outlet of the superheated steam heater (9) is connected to the high-temperature side inlet of the saturated steam heater (10). The low-temperature side inlet and the low-temperature side outlet of the superheated steam heater (9) are both connected to the molten salt storage unit to flow in low-temperature molten salt and flow out high-temperature molten salt. The superheated steam heater (9) is used to exchange heat between the extracted main steam and / or reheated steam and the low-temperature molten salt. The high-temperature side inlet of the saturated steam heater (10) is connected to the high-temperature side outlet of the superheated steam heater (9) to flow in the saturated steam from the superheated steam heater (9). The high-temperature side outlet of the saturated steam heater (10) is connected to the feed water unit. The low-temperature side inlet and the low-temperature side outlet of the saturated steam heater (10) are both connected to the high-temperature heat pump unit to flow in low-temperature gas circulation medium and flow out high-temperature gas circulation medium. The saturated steam heater (10) is used to exchange heat between the saturated steam and the low-temperature gas circulation medium. The high-temperature heat pump unit is respectively connected to the saturated steam heater (10) and the molten salt storage unit. The high-temperature heat pump unit is used to heat the high-temperature gas circulation medium after heat exchange with the saturated steam to a predetermined temperature and exchange heat with the low-temperature molten salt. The gas circulation medium circulates in the circuit of the high-temperature heat pump unit. The high-temperature side inlet and the high-temperature side outlet of the steam generator (18) are both connected to the molten salt storage unit to flow in high-temperature molten salt and flow out low-temperature molten salt. The low-temperature side inlet of the steam generator (18) is connected to the feed water unit to flow in the branched feed water. The low-temperature side outlet of the steam generator (18) is connected to the thermal power unit system to flow out the high-temperature steam participating in the output of the steam turbine generator set.

2. The deep peak shaving system for a thermal power unit according to claim 1, wherein: The high-temperature heat pump unit includes a heat pump expander (13), a heat pump compressor (12), and a heat pump heater (14) that are connected in series to form a circuit. The heat pump expander (13) is respectively connected to the low-temperature side inlet of the saturated steam heater (10) and the high-temperature side outlet of the heat pump heater (14). The heat pump compressor (12) is respectively connected to the low-temperature side outlet of the saturated steam heater (10) and the high-temperature side inlet of the heat pump heater (14). The low-temperature side inlet and the low-temperature side outlet of the heat pump heater (14) are both connected to the molten salt storage unit to flow in low-temperature molten salt and flow out high-temperature molten salt.

3. The deep peak shaving system for a thermal power unit according to claim 2, characterized in that: The heat pump compressor (12) and the heat pump expander (13) are arranged coaxially.

4. The deep peak shaving system for a thermal power unit according to claim 2, wherein: The gas circulation medium circulating in the high-temperature heat pump unit includes air, argon, nitrogen, helium, or carbon dioxide.

5. A deep peak shaving system for a thermal power unit according to claim 1 or 2, characterized in that: The molten salt storage unit includes a cold salt tank (16) and a hot salt tank (15). The inlet of the cold salt tank (16) is communicated with the high-temperature side outlet of the steam generator (18), and the outlet of the cold salt tank (16) is respectively communicated with the low-temperature side inlet of the superheated steam heater (9) and the molten salt inlet of the high-temperature heat pump unit; the inlet of the hot salt tank (15) is respectively communicated with the low-temperature side outlet of the superheated steam heater (9) and the molten salt outlet of the high-temperature heat pump unit, and the outlet of the hot salt tank (15) is communicated with the high-temperature side inlet of the steam generator (18).

6. The deep peak shaving system for a thermal power unit according to claim 1, wherein: It further includes a high-pressure water heat storage system, which includes a high-pressure water heater (11) and a water storage unit. The high-temperature side inlet of the high-pressure water heater (11) is communicated with the high-temperature side outlet of the saturated steam heater (10) to flow in the subcooled water from the saturated steam heater (10). The high-temperature side outlet of the high-pressure water heater (11) is communicated with the water supply unit. The low-temperature side inlet and the low-temperature side outlet of the high-pressure water heater (11) are communicated with the water storage unit to flow in low-temperature high-pressure water and flow out high-temperature high-pressure water. The high-pressure water heater (11) is used to complete the heat exchange between the subcooled water and the low-temperature high-pressure water.

7. The deep peak shaving system for a thermal power unit according to claim 6, characterized in that: The high-pressure water heat storage system further includes a steam feed water preheater (19). The high-temperature side inlet and the high-temperature side outlet of the steam feed water preheater (19) are both communicated with the water storage unit to flow in high-temperature high-pressure water and flow out low-temperature high-pressure water. The low-temperature side inlet of the steam feed water preheater (19) is communicated with the water supply unit, and the low-temperature side outlet of the steam feed water preheater (19) is communicated with the low-temperature side inlet of the steam generator (18).

8. The deep peak shaving system for a thermal power unit according to claim 6, characterized in that: The water storage unit includes a single water storage tank (17). The low-temperature side inlet of the high-pressure water heater (11) is communicated with the lower outlet of the single water storage tank (17), and the low-temperature side outlet of the high-pressure water heater (11) is communicated with the upper inlet of the single water storage tank (17); or the water storage unit includes a cold water tank (171) and a hot water tank (172). The low-temperature side inlet of the high-pressure water heater (11) is communicated with the outlet of the cold water tank (171), and the low-temperature side outlet of the high-pressure water heater (11) is communicated with the inlet of the hot water tank (172).

9. The deep peak shaving system for a thermal power unit according to claim 7, characterized in that: The water storage unit includes a single water storage tank (17). The low-temperature side inlet of the high-pressure water heater (11) is communicated with the lower outlet of the single water storage tank (17), and the low-temperature side outlet of the high-pressure water heater (11) is communicated with the upper inlet of the single water storage tank (17). The high-temperature side inlet of the steam feed water preheater (19) is communicated with the hot water outlet of the single water storage tank (17), and the high-temperature side outlet of the steam feed water preheater (19) is communicated with the cold water inlet of the single water storage tank (17). Alternatively, the water storage unit includes a cold water tank (171) and a hot water tank (172). The low-temperature side inlet of the high-pressure water heater (11) is communicated with the outlet of the cold water tank (171), the low-temperature side outlet of the high-pressure water heater (11) is communicated with the inlet of the hot water tank (172), the high-temperature side inlet of the steam feed water preheater (19) is communicated with the outlet of the hot water tank (172), and the high-temperature side outlet of the steam feed water preheater (19) is communicated with the inlet of the cold water tank (171).

10. A deep peak shaving system for a thermal power unit according to claim 1 or 6 or 7, characterized in that: The feed water unit includes a condenser (3), a low-pressure heater (5), a deaerator (6), and a high-pressure heater (8) that are connected in sequence. The condenser (3) is communicated with the steam turbine generator set (2), the high-pressure heater (8) is communicated with the boiler (1), and the deaerator (6) or the passage between the deaerator (6) and the condenser (3) is also used to introduce subcooled water from the molten salt heating unit and divert a part of the feed water to the steam generator (18).

11. A method for operating a deep peak shaving system of a thermal power unit according to any one of claims 1 to 10, characterized in that, including Peaking stage: When the thermal power unit system is in peaking operation, the thermal power unit system maintains stable combustion and low-load operation, and the molten salt heating unit, the high-temperature heat pump unit, and the molten salt storage unit participate in the operation together. Part of the main steam and / or reheat steam is extracted as a heat source and first flows through the superheated steam heater, and exchanges heat with part of the low-temperature molten salt flowing through the superheated steam heater in parallel from the molten salt storage unit to complete molten salt energy storage; The extracted main steam and / or reheat steam flows out of the superheated steam heater after cooling down and becomes saturated steam, and then flows through the saturated steam heater, and exchanges heat with the low-temperature gas cycle medium flowing through the saturated steam heater from the high-temperature heat pump unit. The low-temperature gas cycle medium absorbs heat and is heated by the high-temperature heat pump unit and then becomes a high-temperature gas cycle medium that can reach a predetermined temperature, and exchanges heat with part of the low-temperature molten salt flowing through the high-temperature heat pump unit from the molten salt storage unit to complete molten salt energy storage; The saturated steam flows out of the saturated steam heater after cooling down and becomes subcooled water. The subcooled water directly flows through the feed water unit for recycling and becomes boiler feed water, or the subcooled water exchanges its remaining heat to high-pressure water through the high-pressure water heater and then flows through the feed water unit for recycling and becomes boiler feed water. The high-pressure water after absorbing heat is used to provide heat energy to the external heat user end or preheat part of the feed water diverted from the feed water unit through the steam feed water preheater during the peak stage; Peak stage: When the thermal power unit system is in peak operation, the molten salt heating unit and the high-temperature heat pump unit stop operating, and the molten salt storage unit and the steam generator participate in the operation. The high-temperature molten salt stored in the molten salt storage unit flows through the steam generator and exchanges heat with part of the feed water diverted from the feed water unit. The generated superheated steam converges with the main steam and / or reheat steam of the thermal power unit system and enters the steam turbine generator set.

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