Gas supply system for guaranteeing high-pressure steam supply under low load by utilizing steam heat storage and heat exchange

Abstract

The invention discloses a gas supply system for guaranteeing high-pressure steam supply under low load through steam heat storage and heat exchange. The gas supply system comprises a coal-fired unit and a fused salt heat storage high-pressure steam supply system coupled with the coal-fired unit. The coal-fired unit comprises a boiler, a steam turbine ultrahigh pressure cylinder, a steam turbine high pressure cylinder, a primary reheat steam outlet diverter valve and a primary reheat intermediate reheater. The fused salt heat storage high-pressure steam supply system comprises a heat regeneration system pipeline, a reheat steam diverter valve, a main steam diverter valve, a temperature and pressure reduction device, a fused salt heater, a low-temperature fused salt tank, a low-temperature fused salt pump and a high-temperature fused salt tank. According to the gas supply system for guaranteeing high-pressure steam supply under the low load through steam heat storage and heat exchange, in the energy storage stage, primary reheat outlet steam is adopted as a basic heat source, part of main steam is introduced to conduct secondary heating on the fused salt, the heat storage temperature of the fused salt is increased, and the energy storage efficiency of the fused salt is improved. And an energy foundation is laid for directly generating steam with higher pressure by heating feed water in an energy release stage.

Description

Technical Field

[0001] This invention relates to the field of thermal power generation technology, and in particular to a gas supply system that utilizes steam heat storage and heat exchange to ensure high-pressure steam supply under low load conditions. Background Technology

[0002] As the global energy structure transformation deepens, the installed capacity of renewable energy continues to grow. However, its power generation output exhibits significant fluctuations and intermittency, adversely affecting the grid's frequency stability and placing higher demands on the grid's peak-shaving capabilities. To adapt to the structural changes in the grid and ensure the safe and stable operation of the power system, traditional thermal power units, as the "ballast" for grid peak shaving, need to fully leverage their rapid response and flexible adjustment capabilities to enhance the units' ability to quickly change loads, start and stop rapidly, and perform deep peak shaving.

[0003] Traditional units adopt a "stationary-sliding-stationary" operation mode. Under low load, the turbine extraction steam pressure drops significantly, making it difficult to maintain the required high-pressure steam supply parameters. If the heating steam parameters are guaranteed, the unit often needs to operate at medium to high load. As a result, the unit has to sacrifice its deep peak-shaving capacity to ensure heating, resulting in "wind and solar curtailment" during the heating season.

[0004] Integrating molten salt thermal energy storage systems into coal-fired power units is an effective way to improve their operational flexibility. By synergistically utilizing steam grade and optimizing the heat storage and release process, some steam is extracted during high-load periods to heat the molten salt for thermal storage. During low-load periods, the high-temperature molten salt heats the feedwater into steam, converting the stored high-temperature thermal energy into qualified steam output, thereby improving the flexibility of unit load regulation while ensuring steam supply. However, significant shortcomings remain when dealing with wide load fluctuations and strict steam supply parameter requirements. On the one hand, if only main steam or reheat steam is used for thermal storage during the thermal storage stage, the thermal storage temperature may be insufficient, affecting the steam generation pressure during the energy release stage, and also causing an imbalance in the turbine's axial thrust. On the other hand, it is difficult to maintain a stable high-pressure steam supply under all operating conditions. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, one objective of this invention is to propose a steam supply system that utilizes steam thermal storage and heat exchange to ensure high-pressure steam supply under low load conditions. In the energy storage stage, not only is reheated outlet steam used as the basic heat source, but also a portion of higher-grade main steam is introduced to reheat the molten salt. This measure significantly increases the thermal storage temperature of the molten salt, laying the energy foundation for directly generating higher-pressure steam by heating feedwater in the energy release stage.

[0006] According to an embodiment of the present invention, a steam supply system utilizing steam thermal storage and heat exchange to ensure high-pressure steam supply under low load includes: a coal-fired power unit and a coupled molten salt thermal storage high-pressure steam supply system; the coal-fired power unit includes: a boiler, a turbine ultra-high pressure cylinder, a turbine high-pressure cylinder, a primary reheat steam outlet diversion valve, and a primary reheat intermediate reheater, wherein the primary reheat intermediate reheater is located inside the boiler, and the steam outlet of the primary reheat intermediate reheater is connected to the steam inlet of the back pressure turbine and the steam inlet of the turbine high-pressure cylinder respectively; the boiler has a main steam outlet, which is divided into two paths, one path connected to the steam inlet of the turbine ultra-high pressure cylinder, and the other path connected to the desuperheating and pressure reducing device via the main steam diversion valve; the steam outlet of the turbine ultra-high pressure cylinder is connected to the steam inlet of the primary reheat intermediate reheater; the molten salt thermal storage high-pressure steam supply system includes: a regenerative system pipeline, a reheat steam diversion valve, a main steam diversion valve, a desuperheating and pressure reducing device, and a molten salt heater. The system comprises a heater, a low-temperature molten salt tank, a low-temperature molten salt pump, and a high-temperature molten salt tank. The main steam diversion valve controls the connection between the main steam outlet and the steam inlet of the desuperheating and pressure-reducing device. The reheat steam diversion valve controls the connection between the steam outlet of the primary reheat intermediate reheater and the steam inlet of the desuperheating and pressure-reducing device. The molten salt heater has a first channel, with its two ends connected to the outlet of the low-temperature molten salt tank and the inlet of the high-temperature molten salt tank, respectively. The low-temperature molten salt pump is located between the low-temperature molten salt tank and the molten salt heater, driving the circulating flow of molten salt. A portion of the main steam diverted by the main steam diversion valve and a portion of the reheat steam diverted by the reheat steam diversion valve converge at the molten salt heater via the desuperheating and pressure-reducing device. The two ends of the first channel are connected to the outlet of the low-temperature molten salt tank and the inlet of the high-temperature molten salt tank, respectively, forming the energy storage circuit of the molten salt thermal storage high-pressure steam supply system.

[0007] According to embodiments of the present invention, the steam supply system for ensuring high-pressure steam supply under low load by utilizing steam thermal storage and heat exchange not only uses reheated outlet steam as the basic heat source during the energy storage stage, but also introduces a portion of higher-grade main steam to reheat the molten salt. This measure significantly increases the thermal storage temperature of the molten salt, laying the energy foundation for directly generating higher-pressure steam by heating feedwater during the energy release stage.

[0008] In addition, the gas supply system according to the present invention, which utilizes steam thermal storage and heat exchange to ensure high-pressure steam supply under low load, may also have the following additional technical features: In some embodiments of the present invention, the molten salt heater further has a second channel, which is connected to the cryogenic molten salt pump. The molten salt in the cryogenic molten salt tank is pumped to the second channel of the molten salt heater to exchange heat with the steam collected by the desuperheating and depressurization device. The water working fluid after heat exchange with the steam collected by the desuperheating and depressurization device goes to the reheat system through the reheat system pipeline.

[0009] In some embodiments of the present invention, the coal-fired power unit further includes a turbine intermediate-pressure cylinder, a turbine low-pressure cylinder, a condenser, a condensate pump, a low-pressure heater, a deaerator, a feedwater pump, and a high-pressure heater; the extraction steam outlet of the turbine ultra-high-pressure cylinder is connected to the steam inlet of the high-pressure heater; the steam outlet of the turbine high-pressure cylinder is connected to the steam inlet of the boiler's secondary reheater, and the steam outlet of the secondary reheater is connected to the steam inlet of the turbine intermediate-pressure cylinder; the steam outlet of the turbine intermediate-pressure cylinder is connected to the steam inlet of the turbine low-pressure cylinder, and the turbine low-pressure cylinder... The steam outlet is connected to the steam inlet of the condenser; the extraction steam outlet of the intermediate-pressure cylinder of the steam turbine is connected to the steam inlet of the deaerator, and the extraction steam outlet of the low-pressure cylinder of the steam turbine is connected to the steam inlet of the low-pressure heater; the condensate outlet of the condenser is connected to the inlet of the low-pressure heater through the condensate pump, the outlet of the low-pressure heater is connected to the inlet of the deaerator, the effluent from the deaerator is pressurized by the feedwater pump and then transported to the inlet of the high-pressure heater, and the outlet of the high-pressure heater is adapted to be connected to the feedwater inlet of the boiler.

[0010] In some embodiments of the present invention, the coal-fired power unit further includes: a generator, wherein the ultra-high pressure cylinder of the steam turbine, the high pressure cylinder of the steam turbine, the intermediate pressure cylinder of the steam turbine, and the low pressure cylinder of the steam turbine are connected by a rotating shaft and jointly drive the generator to generate electricity to output electrical power.

[0011] In some embodiments of the present invention, the molten salt thermal storage high-pressure steam supply system includes: a high-temperature molten salt pump, a feedwater-molten salt heat exchanger, a saturated steam-molten salt heat exchanger, a steam drum, a superheated steam-molten salt heat exchanger, a back pressure compressor, a steam supply header, a feedwater diversion valve, a feedwater bypass pump, and a back pressure compressor inlet pipe; the feedwater-molten salt heat exchanger is internally provided with a first flow path and a second flow path for heat exchange, the outlet end of the first flow path is connected to the inlet of the low-temperature molten salt tank, and the inlet end of the second flow path is connected to the water outlet of the deaerator; the feedwater bypass pump is used to drive water to flow from the outlet of the deaerator to the inlet end of the second flow path, the feedwater diversion valve is used to control the on / off connection between the water outlet of the deaerator and the inlet end of the second flow path, and the superheated steam-molten salt heat exchanger is internally provided with a third flow path and a fourth flow path for heat exchange, the third flow path... The inlet end of the fourth flow path is connected to the outlet of the high-temperature molten salt tank. The steam outlet end of the fourth flow path goes directly to the steam supply header for heating via a desuperheating and pressure reducing device. The saturated steam-molten salt heat exchanger is equipped with a fifth flow path and a sixth flow path for heat exchange. One end of the fifth flow path is connected to the outlet of the third flow path, and the other end is connected to the inlet of the first flow path. One end of the sixth flow path is connected to the outlet of the second flow path, and the other end is connected to the inlet of the fourth flow path. The inlet end of the steam drum is connected to the outlet end of the sixth flow path. The steam drum is used to separate saturated steam from water. The steam drum has a steam outlet and a liquid outlet. The steam outlet is connected to the inlet end of the fourth flow path, and the liquid outlet is connected to the inlet end of the second flow path. The high-temperature molten salt pump is located between the high-temperature molten salt tank and the superheated steam-molten salt heat exchanger and is used to drive the molten salt circulation.

[0012] In some embodiments of the present invention, the molten salt thermal storage high-pressure steam supply system further includes: a molten salt heating gas source diversion valve, wherein the steam outlet end of the fourth flow path is supplied to the steam supply header via the molten salt heating gas source diversion valve through a desuperheating and pressure reducing device.

[0013] In some embodiments of the present invention, the molten salt thermal storage high-pressure steam supply system further includes: a molten salt heating gas source diversion valve and a back pressure turbine inlet diversion valve. The steam outlet end of the fourth flow path is divided into two paths. One path leads to the inlet of the back pressure turbine via the back pressure turbine inlet diversion valve and the steam inlet pipe of the back pressure turbine. The other path leads directly to the steam supply header for heating via the molten salt heating gas source diversion valve and the desuperheating and pressure reducing device.

[0014] In some embodiments of the present invention, the feedwater-molten salt heat exchanger, the saturated steam-molten salt heat exchanger, and the superheated steam-molten salt heat exchanger are all indirect-wall water-molten salt heat exchangers.

[0015] In some embodiments of the present invention, the steam flow rate at the outlet of the main steam diversion valve does not exceed 21% of the steam flow rate at the main steam outlet.

[0016] In some embodiments of the present invention, the steam flow rate at the outlet of the reheat steam diversion valve does not exceed 23% of the steam flow rate at the steam outlet of the primary reheat intermediate reheater.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a system schematic diagram according to some embodiments of the present invention.

[0019] Figure label: 1. Boiler; 2. Ultra-high pressure cylinder of steam turbine; 3. High pressure cylinder of steam turbine; 4. Intermediate pressure cylinder of steam turbine; 5. Low pressure cylinder of steam turbine; 6. Generator; 7. Condenser; 8. Condensate pump; 9. Low pressure heater; 10. Deaerator; 11. Feedwater pump; 12. High pressure heater; 13. Primary reheat steam outlet diversion valve; 14. Primary reheat intermediate reheater; 15. Regenerative system piping; 16. Reheat steam diversion valve; 17. Main steam diversion valve; 18. Desuperheating and pressure reducing device; 19. Molten salt heater; 20. Low-temperature molten salt tank; 21. Low-temperature molten salt pump; 22. High-temperature molten salt tank; 23. High-temperature molten salt pump; 24. Feedwater-molten salt heat exchanger; 25. Saturated steam-molten salt heat exchanger; 26. Steam drum; 27. Superheated steam-molten salt heat exchanger; 28. Molten salt heating gas source diversion valve; 29. ​​Back pressure compressor inlet diversion valve; 30. Back pressure compressor; 31. Steam supply header; 32. Feedwater diversion valve; 33. Feedwater bypass pump; 34. Back pressure compressor steam inlet pipe. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] In traditional molten salt thermal energy storage systems, main steam or reheat steam is usually extracted separately for thermal storage, which significantly impacts the heat balance in the boiler. Furthermore, maintaining stable high-pressure steam supply under wide load fluctuations during energy release is also a challenge. Therefore, this invention proposes a system utilizing steam thermal energy storage and heat exchange to ensure high-pressure steam supply under low load conditions, aiming to address at least one of the problems existing in current related technologies. The steam thermal energy storage and heat exchange system can maintain a heating pressure of 4.3 MPa under all operating conditions, while reducing the unit's power consumption, effectively improving the round-trip efficiency of the unit's energy storage system, and maintaining a high peak-shaving capacity. Under high load, the system uses a combination of reheat outlet steam and main steam to heat molten salt for energy storage. Simultaneously, steam from the intermediate reheater outlet drives the back-pressure turbine, with exhaust steam from the back-pressure turbine used for heating. Under low load, high-temperature molten salt heats the feedwater, and the resulting steam is fed into the unit for energy release. At this time, steam generated by the molten salt also enters the back-pressure turbine's inlet pipe. The back-pressure turbine's inlet steam pressure is increased to ensure adequate steam supply parameters under low load. When the molten salt steam supply pressure is insufficient to drive the back-pressure turbine, the back-pressure turbine shuts down, and the molten salt steam supply is directly depressurized and depressurized for heating. The specific technical solution is as follows: like Figure 1 As shown in the figure, a gas supply system according to an embodiment of the present invention utilizes steam thermal storage and heat exchange to ensure high-pressure steam supply under low load conditions. It should be noted that... Figure 1 The medium- and high-pressure heater 12, the desuperheating and pressure-reducing device 18, the low-temperature molten salt tank 20, and the high-temperature molten salt tank 22 are all drawn as two units, but in this gas supply system, only one of each of the aforementioned devices is actually installed. This drawing method in the system diagram is only to simplify the layout of the drawing, avoid complicated wiring, and facilitate integration. Figure 1 Understand the technical concept of this solution.

[0023] A steam supply system that utilizes steam thermal storage and heat exchange to ensure high-pressure steam supply under low load conditions includes a coal-fired unit and a coupled molten salt thermal storage high-pressure steam supply system.

[0024] Specifically, the coal-fired unit includes: a boiler 1, a steam turbine ultra-high pressure cylinder 2, a steam turbine high pressure cylinder 3, a primary reheat steam outlet diversion valve 13, and a primary reheat intermediate reheater 14. The boiler 1 has a main steam outlet, which is divided into two paths: one path connects to the steam inlet of the steam turbine ultra-high pressure cylinder 2, and the other path passes through the main steam diversion valve 17 to the desuperheating and pressure reducing device 18 and then to the molten salt heater 19 in the energy storage circuit. The main steam outlet is connected to the steam inlet of the steam turbine ultra-high pressure cylinder 2, and the steam outlet of the steam turbine ultra-high pressure cylinder 2 is connected to the steam inlet of the primary reheat intermediate reheater 14. The steam outlet of the primary reheat intermediate reheater 14 is connected to the steam inlet of the steam turbine high pressure cylinder 3. The boiler 1 contains the primary reheat intermediate reheater 14, and the steam outlet of the steam turbine ultra-high pressure cylinder 2 is connected to the steam inlet of the primary reheat intermediate reheater 14. The steam outlet of the primary reheat intermediate reheater 14 is connected to the steam inlet of the back pressure compressor 30 and the steam inlet of the steam turbine high pressure cylinder 3, respectively. The high-pressure steam supply circuit of the molten salt thermal storage high-pressure steam supply system includes a molten salt heating gas source diversion valve 28, a back pressure turbine inlet diversion valve 29, a back pressure turbine 30, a steam supply header 31, and a back pressure turbine inlet steam pipe 34. The steam supply system uses the back pressure turbine 30 for exhaust steam supply. During normal operating load and high load periods, the primary reheat steam outlet diversion valve 13 is opened, and the outlet steam of the primary reheat intermediate reheater 14 drives the back pressure turbine 30. The exhaust steam from the back pressure turbine 30 is used for heating. The primary reheat steam outlet diversion valve 13 is used to control the connection and disconnection between the steam outlet of the primary reheat intermediate reheater 14 and the steam inlet of the back pressure turbine 30. Under low load conditions, the molten salt steam supply pressure can... When the back pressure compressor 30 is driven, the inlet diversion valve 29 of the back pressure compressor opens, and the steam generated by the molten salt enters the steam inlet pipe of the back pressure compressor 30. This steam, together with the outlet steam of the primary reheat intermediate reheater 14, drives the back pressure compressor 30. This increases the steam inlet pressure of the back pressure compressor 30, ensuring the steam supply parameters under low load. When the molten salt steam supply pressure is insufficient to drive the back pressure compressor 30, the inlet diversion valve 29 is closed, the back pressure compressor 30 is deactivated, and the molten salt heating gas source diversion valve 28 is opened, allowing the molten salt steam supply to directly reduce temperature and pressure for heating. This complementary heating measure between the molten salt and the back pressure compressor 30 improves the round-trip efficiency of the molten salt thermal storage high-pressure steam supply system, achieves cascaded energy utilization, and enhances energy efficiency. When the coal-fired unit is in a high-load range, the main steam diversion valve 17, the reheat steam diversion valve 16, the primary reheat steam outlet diversion valve 13, and the low-temperature molten salt pump 21 are opened, thus opening the molten salt thermal storage circuit. When the coal-fired unit is in its normal operating load range, the primary reheat steam outlet diversion valve 13 is opened, and the main steam diversion valve 17, reheat steam diversion valve 16, feedwater diversion valve 32, molten salt heating gas source diversion valve 28, and back pressure turbine inlet diversion valve 29 are closed. The steam from the outlet of the primary reheat intermediate reheater 14 enters the back pressure turbine 30 through the steam inlet pipe and performs work. The exhaust steam from the back pressure turbine 30 is used to supply heat to users.

[0025] The gas supply system that utilizes steam heat storage and heat exchange to ensure high-pressure steam supply under low load has three operating modes: normal operating load range, low load range, and high load range.

[0026] When the coal-fired unit is in the high-load range, the main steam diversion valve 17, reheat steam diversion valve 16, primary reheat steam outlet diversion valve 13, and cryogenic molten salt pump 21 are opened, thus opening the molten salt thermal storage circuit. The molten salt thermal storage circuit can be a molten salt energy storage system including the regenerative system pipeline 15, reheat steam diversion valve 16, main steam diversion valve 17, desuperheating and pressure reducing device 18, molten salt heater 19, cryogenic molten salt tank 20, cryogenic molten salt pump 21, and high-temperature molten salt tank 22, which will not be elaborated further here.

[0027] This invention couples a coal-fired power unit with a molten salt thermal storage high-pressure steam supply system, adopting a high-load energy storage and low-load energy release operation mode. Under medium and low loads, the thermal storage system enters the energy release mode, and molten salt steam is supplied to the back pressure compressor 30 to increase the steam inlet pressure of the back pressure compressor 30 to ensure the steam supply parameters under low load, avoiding the decrease in steam supply pressure due to the decrease in unit load, and achieving a high-pressure steam supply guarantee of 4.3 MPa under all operating conditions.

[0028] When the coal-fired unit is in the low-load range, the main steam diversion valve 17, reheat steam diversion valve 16, and molten salt heating gas source diversion valve 28 are closed, while the feedwater diversion valve 32 and high-temperature molten salt pump 23 are opened, thus opening the molten salt heat release circuit. The molten salt heat release circuit can be the following molten salt energy release system, including a low-temperature molten salt tank 20, a high-temperature molten salt tank 22, a high-temperature molten salt pump 23, a feedwater-molten salt heat exchanger 24, a saturated steam-molten salt heat exchanger 25, a steam drum 26, a superheated steam-molten salt heat exchanger 27, a feedwater diversion valve 32, and a feedwater bypass pump 33.

[0029] When the molten salt steam supply pressure is sufficient to drive the back pressure compressor 30, the back pressure compressor inlet diversion valve 29 is opened, and the steam generated by the molten salt enters the back pressure compressor inlet steam pipeline. Together with the outlet steam of the primary reheat intermediate reheater 14, it drives the back pressure compressor 30. By increasing the back pressure compressor inlet steam pressure, the steam supply parameters under low load are ensured. When the molten salt steam supply pressure is insufficient to drive the back pressure compressor 30, the back pressure compressor inlet diversion valve 29 and the primary reheat steam outlet diversion valve 13 are closed, the back pressure compressor 30 is shut down, the molten salt heating gas source diversion valve 28 is opened, and the molten salt steam supply is directly de-heated and depressurized for heating, and then delivered to the heat users to meet the heating demand.

[0030] In some embodiments of the present invention, such as Figure 1As shown, the molten salt thermal high-pressure steam supply system also includes a molten salt energy storage system. Molten salt circulates within the molten salt energy storage system. The molten salt energy storage system includes a reheat system pipeline 15, a reheat steam diversion valve 16, a main steam diversion valve 17, a desuperheating and pressure reducing device 18, a molten salt heater 19, a low-temperature molten salt tank 20, a low-temperature molten salt pump 21, and a high-temperature molten salt tank 22. The main steam diversion valve 17 is used to control the connection and disconnection between the main steam outlet and the steam inlet of the desuperheating and pressure reducing device 18. The reheat steam diversion valve 16 is used to control the connection and disconnection between the steam outlet of the primary reheat intermediate reheater 14 and the steam inlet of the desuperheating and pressure reducing device 18. A portion of the main steam diverted by the main steam diversion valve 17 and a portion of the reheat steam diverted by the reheat steam diversion valve 16 converge at the molten salt heater 19 via the desuperheating and pressure reducing device 18. The molten salt heater 19 has a first channel for heating the molten salt within it. The two ends of the first channel are connected to the outlet of the low-temperature molten salt tank 20 and the inlet of the high-temperature molten salt tank 22, respectively, forming an energy storage loop for the molten salt thermal storage high-pressure steam supply system. A low-temperature molten salt pump 21 is located between the low-temperature molten salt tank 20 and the molten salt heater 19, driving the circulating flow of the molten salt. The molten salt heater 19 also has a second channel. The molten salt in the low-temperature molten salt tank 20, after passing through the low-temperature molten salt pump 21, flows into the molten salt heater 19 and exchanges heat with the steam converged by the desuperheating and pressure reducing device 18. The resulting water medium then travels through the reheat system pipeline 15 to the reheat system. This process converts excess electrical energy into high-temperature thermal energy for storage, effectively improving the unit's peak-shaving capacity and achieving a synergistic improvement in system economy and flexibility.

[0031] The molten salt thermal storage high-pressure steam supply system also includes a molten salt energy release system, which includes a low-temperature molten salt tank 20, a high-temperature molten salt tank 22, a high-temperature molten salt pump 23, a feedwater-molten salt heat exchanger 24, a saturated steam-molten salt heat exchanger 25, a steam drum 26, a superheated steam-molten salt heat exchanger 27, a feedwater diversion valve 32, and a feedwater bypass pump 33. The feedwater-molten salt heat exchanger 24 is internally equipped with a first flow path and a second flow path for heat exchange. The outlet of the first flow path is connected to the inlet of the low-temperature molten salt tank 20, and the inlet of the second flow path is connected to the water outlet of the deaerator 10. The feedwater bypass pump 33 is used to drive water from the outlet of the deaerator 10 to the inlet of the second flow path, and the feedwater diversion valve 32 is used to control the connection and disconnection between the water outlet of the deaerator 10 and the inlet of the second flow path. The superheated steam-molten salt heat exchanger 27 has a third and a fourth flow path for heat exchange. The inlet of the third flow path is connected to the outlet of the high-temperature molten salt tank 22. The steam outlet of the fourth flow path is divided into two paths depending on the operating conditions: one path leads to the inlet of the back pressure compressor 30 via the back pressure compressor inlet valve 29 and the back pressure compressor inlet pipe 34; the other path leads directly to the steam supply header 31 via the molten salt heating gas source diversion valve 28 and the desuperheating and pressure reducing device 18 for heating. The saturated steam-molten salt heat exchanger 25 has a fifth and a sixth flow path for heat exchange. One end of the fifth flow path is connected to the outlet of the third flow path, and the other end is connected to the outlet of the first flow path. The sixth flow path is connected at one end to the outlet of the second flow path and at the other end to the inlet of the fourth flow path. The inlet of the steam drum 26 is connected to the outlet of the sixth flow path. The steam drum 26 is used to separate saturated steam from water. The steam drum has a steam outlet and a liquid outlet. The steam outlet is connected to the inlet of the fourth flow path, and the liquid outlet is connected to the inlet of the second flow path. The high-temperature molten salt pump 23 is located between the high-temperature molten salt tank 22 and the superheated steam-molten salt heat exchanger 27. It is used to drive the molten salt circulation. The high-temperature molten salt tank 22, the third flow path, the fifth flow path, the first flow path, and the low-temperature molten salt tank 20 form the energy release loop of the molten salt heat storage high-pressure steam supply system.

[0032] In some embodiments of the present invention, the feedwater-molten salt heat exchanger 24, the saturated steam-molten salt heat exchanger 25, and the superheated steam-molten salt heat exchanger 27 are all indirect-wall water-molten salt heat exchangers. By exchanging heat between molten salt and the water working medium in the coal-fired unit, the heat exchange effect between molten salt and water, saturated steam, and superheated steam can be guaranteed, the boiler combustion stability can be guaranteed, the heat release efficiency of the molten salt heat storage system can be guaranteed, and the renewable energy power consumption of the power grid can be promoted.

[0033] According to some embodiments of the present invention, the feedwater diversion valve 32 can control the opening and closing between the water outlet of the deaerator 10 and the inlet of the second flow path. When the molten salt thermal storage system needs to release energy, the feedwater diversion valve 32 is opened, and the feedwater bypass pump 33 can provide driving force for the water flow. The feedwater diverted by the feedwater diversion valve 32 is connected to the feedwater bypass pump 33. The pressurized bypass feedwater is heated by the feedwater-molten salt heat exchanger 24 and then enters the steam inlet of the saturated steam-molten salt heat exchanger 25. After heat exchange, it enters the steam drum 26. The steam drum 26 separates the saturated steam into water. The water returns to the feedwater-molten salt heat exchanger 24 for reheating. The steam enters the superheated steam-molten salt heat exchanger 27. After heat exchange, the steam enters the back pressure compressor 30 to do work or the desuperheating and pressure reducing device 18 directly goes to the steam supply header for heating.

[0034] The coal-fired unit also includes a steam turbine intermediate-pressure cylinder 4, a steam turbine low-pressure cylinder 5, a generator 6, a condenser 7, a condensate pump 8, a low-pressure heater 9, a deaerator 10, a feedwater pump 11, and a high-pressure heater 12; the extraction outlet of the steam turbine ultra-high-pressure cylinder 2 is connected to the steam inlet of the high-pressure heater 12; the steam outlet of the steam turbine high-pressure cylinder 3 is connected to the steam inlet of the secondary reheater of boiler 1, and the steam outlet of the secondary reheater is connected to the steam inlet of the steam turbine intermediate-pressure cylinder 4; the steam outlet of the steam turbine intermediate-pressure cylinder 4 is connected to the steam inlet of the steam turbine low-pressure cylinder 5, and the steam outlet of the steam turbine low-pressure cylinder 5 is connected to the steam inlet of the condenser 7; the extraction outlet of the steam turbine intermediate-pressure cylinder 4... The steam outlet is connected to the steam inlet of the deaerator 10, and the extraction steam outlet of the low-pressure cylinder 5 of the steam turbine is connected to the steam inlet of the low-pressure heater 9. The condensate outlet of the condenser 7 is connected to the inlet of the low-pressure heater 9 through the condensate pump 8. The outlet of the low-pressure heater 9 is connected to the inlet of the deaerator 10. The water outlet of the deaerator 10 is pressurized by the feed water pump 11 and then sent to the inlet of the high-pressure heater 12. The water outlet of the high-pressure heater 12 is finally connected to the feed water inlet of the boiler 1. The ultra-high pressure cylinder 2, the high pressure cylinder 3, the intermediate pressure cylinder 4, and the low pressure cylinder 5 of the steam turbine are connected by a rotating shaft and jointly drive the generator 6 to generate electricity to output power.

[0035] In some embodiments of the present invention, in order to ensure that the pipe temperature of the primary reheat intermediate reheater 14 is within the allowable range of the material, sufficient steam must be maintained in the pipe to absorb the heat of the flue gas, thereby cooling the primary reheat intermediate reheater 14 and controlling the pipe temperature below the allowable value. Therefore, the steam diversion flow of the reheat steam diversion valve 16 does not exceed 26% of the reheat steam outlet steam volume, and can also effectively reduce the minimum electrical load rate of the coal-fired unit.

[0036] The gas supply system proposed in this invention utilizes steam thermal storage and heat exchange to ensure high-pressure steam supply under low load conditions. It employs a combination of reheat outlet steam and main steam to heat molten salt for energy storage, integrating a dual-tank molten salt thermal storage system consisting of a high-temperature molten salt tank and a low-temperature molten salt tank. Under low load conditions that maintain the minimum stable combustion load of boiler 1, the feedwater is heated by high-temperature molten salt, and the generated steam is introduced into the coal-fired unit to release energy, thereby improving the coal-fired unit's ability to rapidly increase load.

[0037] In the embodiments of the present invention, the steam diversion flow rate of the reheat steam diversion valve 16 does not exceed 26% of the reheat steam outlet steam volume; the main steam diversion flow rate of the main steam diversion valve 17 is 80% to 90% of the reheat steam diverted by the reheat steam diversion valve 16; this can effectively reduce the minimum electrical load of the coal-fired unit and avoid problems such as turbine axial thrust imbalance; at the same time, it can also prevent excessive steam from being drawn from the outlet of the main steam diversion valve 17, ensuring sufficient steam flow in the pipeline of the primary reheat intermediate reheater 14, avoiding the inability to cool the pipeline to the allowable temperature range due to insufficient steam flow and insufficient heat absorption capacity, thereby preventing the reheater from overheating.

[0038] Based on the above analysis, this application proposes a steam supply system that utilizes steam thermal storage and heat exchange to ensure high-pressure steam supply under low load conditions. Under high load conditions, molten salt is heated by a combination of reheat outlet steam and main steam to complete energy storage. Under low load conditions, feedwater is heated by high-temperature molten salt, and the generated steam is introduced into the unit to release energy. Introducing main steam during the energy storage process can raise the molten salt temperature, thereby increasing the feedwater evaporation temperature during energy release and further increasing the steam pressure generated by the molten salt. Simultaneously, the molten salt and back-pressure turbine employ complementary heating. Under low load conditions, the outlet steam pressure of the intermediate reheater 14 decreases, at which point the steam generated by the molten salt enters the back-pressure turbine inlet pipe 34, increasing the back-pressure turbine inlet pressure to ensure steam supply parameters under low load conditions. When the molten salt steam supply pressure is insufficient to drive the back-pressure turbine 30, the back-pressure turbine 30 is deactivated, and the molten salt steam supply directly reduces temperature and pressure for heating. The energy storage system in this application has high round-trip efficiency and can guarantee a high-pressure steam supply of 4.3 MPa under all operating conditions.

[0039] The core innovation of this method is: 1. High-grade composite thermal storage and temperature enhancement technology: In the energy storage stage, not only is reheat outlet steam used as the basic heat source, but also some higher-grade main steam is introduced to reheat the molten salt. This increases the thermal storage temperature of the molten salt, laying the energy foundation for generating higher-pressure steam directly by heating feedwater in the energy release stage.

[0040] 2. Complementary Heating Mechanism between Molten Salt and Back Pressure Unit 30: To address the challenge of insufficient steam pressure from the original heating source under low load conditions, two flexible energy release and complementary modes are designed. When the molten salt steam production pressure is high, its steam can be injected into the back pressure unit's inlet pipe 34 to increase the inlet steam pressure and ensure a heating output parameter of 4.3 MPa. When the molten salt steam production pressure is insufficient, the system can switch to back pressure unit 30 being shut down, and the molten salt steam, after being de-cooled and depressurized, can be directly used for heating. This switching mechanism ensures adaptive and stable steam supply pressure under all operating conditions.

[0041] 3. System integration optimization and efficiency improvement: The energy storage process is combined with the original back pressure turbine 30 heating process of the unit. Reheated steam is used to drive the back pressure turbine 30 to complete part of the heating, realizing the efficient use of energy on-site and reducing the loss in the energy conversion process. Thus, while ensuring the safety and reliability of steam supply, a high system round-trip efficiency is obtained, and the economy of the transformation scheme is improved.

[0042] In the description of this specification, references to terms such as "some embodiments," "examples," or "some examples" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, 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.

[0043] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A gas supply system for ensuring high-pressure steam supply at low load by using steam heat storage and heat exchange, characterized by The application relates to a coal-fired unit and a molten salt heat storage high-pressure steam supply system coupled with the coal-fired unit. The coal-fired unit comprises a boiler (1), a steam turbine super-high-pressure cylinder (2), a steam turbine high-pressure cylinder (3), a primary reheat steam outlet shunt valve (13) and a primary reheat intermediate reheater (14), the primary reheat intermediate reheater (14) is arranged in the boiler (1), and steam outlets of the primary reheat intermediate reheater (14) are communicated with steam inlets of a back-pressure turbine (30) and a steam inlet of the steam turbine high-pressure cylinder (3) respectively. The boiler (1) has a main steam outlet, the main steam outlet is divided into two paths, one path is communicated with a steam inlet of the steam turbine super-high-pressure cylinder (2), and the other path is communicated with a desuperheating and pressure-reducing device (18) through a main steam shunt valve (17); a steam outlet of the steam turbine super-high-pressure cylinder (2) is communicated with a steam inlet of the primary reheat intermediate reheater (14). The molten salt heat storage high-pressure steam supply system comprises a regenerative system pipeline (15), a reheat steam shunt valve (16), a main steam shunt valve (17), the desuperheating and pressure-reducing device (18), a molten salt heater (19), a low-temperature molten salt tank (20), a low-temperature molten salt pump (21) and a high-temperature molten salt tank (22), the main steam shunt valve (17) is used for controlling the opening and closing between the main steam outlet and a steam inlet of the desuperheating and pressure-reducing device (18), the reheat steam shunt valve (16) is used for controlling the opening and closing between a steam outlet of the primary reheat intermediate reheater (14) and a steam inlet of the desuperheating and pressure-reducing device (18), the molten salt heater (19) has a first channel, two ends of the first channel are respectively connected with an outlet of the low-temperature molten salt tank (20) and an inlet of the high-temperature molten salt tank (22), and the low-temperature molten salt pump (21) is arranged between the low-temperature molten salt tank (20) and the molten salt heater (19) and is used for driving the circulating flow of molten salt. Part of the main steam shunted by the main steam shunt valve (17) and part of the reheat steam shunted by the reheat steam shunt valve (16) are converged to the molten salt heater (19) through the desuperheating and pressure-reducing device (18), and two ends of the first channel are respectively connected with the outlet of the low-temperature molten salt tank (20) and the inlet of the high-temperature molten salt tank (22) to form an energy storage loop of the molten salt heat storage high-pressure steam supply system. The molten salt heater (19) further has a second channel, the second channel is communicated with the low-temperature molten salt pump (21), molten salt in the low-temperature molten salt tank (20) is conveyed into the second channel of the molten salt heater (19) through the low-temperature molten salt pump (21) to exchange heat with steam converged by the desuperheating and pressure-reducing device (18), and the water working medium after heat exchange of the steam converged by the desuperheating and pressure-reducing device (18) is sent to a regenerative system through the regenerative system pipeline (15).

2. The gas supply system of claim 1, wherein, ​ 3. The steam supply system according to claim 1, wherein The coal-fired unit further comprises a steam turbine intermediate pressure cylinder (4), a steam turbine low pressure cylinder (5), a condenser (7), a condensate pump (8), a low pressure heater (9), a deaerator (10), a feed water pump (11), a high pressure heater (12); a steam extraction outlet of the steam turbine super-high pressure cylinder (2) is connected with a steam inlet of the high pressure heater (12); a steam outlet of the steam turbine high pressure cylinder (3) is connected with a steam inlet of a secondary reheater of the boiler (1), a steam outlet of the secondary reheater is connected with a steam inlet of the steam turbine intermediate pressure cylinder (4); a steam outlet of the steam turbine intermediate pressure cylinder (4) is connected with a steam inlet of the steam turbine low pressure cylinder (5), a steam outlet of the steam turbine low pressure cylinder (5) is connected with a steam inlet of the condenser (7); a steam extraction outlet of the steam turbine intermediate pressure cylinder (4) is connected with a steam inlet of the deaerator (10), a steam extraction outlet of the steam turbine low pressure cylinder (5) is connected with a steam inlet of the low pressure heater (9); a condensate outlet of the condenser (7) is connected with a water inlet of the low pressure heater (9) through the condensate pump (8), a water outlet of the low pressure heater (9) is connected with a water inlet of the deaerator (10), water from the deaerator (10) is pressurized by the feed water pump (11) and then delivered to a water inlet of the high pressure heater (12), and a water outlet of the high pressure heater (12) is adapted to be in communication with a feed water inlet of the boiler (1).

4. The steam supply system according to claim 3, wherein The coal-fired unit further comprises a generator (6), the steam turbine super-high pressure cylinder (2), the steam turbine high pressure cylinder (3), the steam turbine intermediate pressure cylinder (4) and the steam turbine low pressure cylinder (5) are connected through a rotating shaft and jointly drive the generator (6) to generate electricity and output electric power to the outside.

5. The steam supply system according to claim 3, wherein The molten salt heat storage high-pressure steam supply system comprises a high-temperature molten salt pump (23), a feedwater-molten salt heat exchanger (24), a saturated steam-molten salt heat exchanger (25), a steam drum (26), a superheated steam-molten salt heat exchanger (27), a back pressure turbine (30), a steam supply main pipe (31), a feedwater diversion valve (32), a feedwater bypass water pump (33), and a back pressure turbine steam inlet pipeline (34); the feedwater-molten salt heat exchanger (24) is internally provided with a first flow path and a second flow path capable of heat exchange, the outlet end of the first flow path is in communication with the inlet of the low-temperature molten salt tank (20), and the inlet end of the second flow path is in communication with the water working medium outlet of the deaerator (10); the feedwater bypass water pump (33) is used to drive water to flow from the water outlet of the deaerator (10) to the inlet end of the second flow path, and the feedwater diversion valve (32) is used to control the on-off between the water working medium outlet of the deaerator (10) and the inlet end of the second flow path; the superheated steam-molten salt heat exchanger (27) is internally provided with a third flow path and a fourth flow path capable of heat exchange, the inlet end of the third flow path is connected with the outlet of the high-temperature molten salt tank (22), and the steam outlet end of the fourth flow path directly goes to the steam supply main pipe (31) for heat supply through a desuperheating and pressure reducing device (18); the saturated steam-molten salt heat exchanger (25) is internally provided with a fifth flow path and a sixth flow path capable of heat exchange, one end of the fifth flow path is connected with the outlet of the third flow path, the other end is connected with the inlet of the first flow path, one end of the sixth flow path is connected with the outlet of the second flow path, and the other end is connected with the inlet of the fourth flow path; the inlet end of the steam drum (26) is in communication with the outlet end of the sixth flow path, the steam drum (26) is used to realize the steam-water separation of saturated steam and water, the steam drum (26) has a steam outlet and a liquid outlet, the steam outlet is in communication with the inlet end of the fourth flow path, and the liquid outlet is in communication with the inlet end of the second flow path; the high-temperature molten salt pump (23) is located between the high-temperature molten salt tank (22) and the superheated steam-molten salt heat exchanger (27) and is used to drive the circulation of molten salt.

6. The steam supply system according to claim 5, wherein The molten salt heat storage high-pressure steam supply system further comprises a molten salt heat supply gas source diversion valve (28), and the steam outlet end of the fourth flow path directly goes to the steam supply main pipe (31) for heat supply through a desuperheating and pressure reducing device (18) via the molten salt heat supply gas source diversion valve (28).

7. The steam supply system according to claim 5, wherein The molten salt heat storage high-pressure steam supply system further comprises a molten salt heat supply gas source diversion valve (28) and a back pressure turbine inlet diversion valve (29), and the steam outlet end of the fourth flow path is divided into two paths, one path enters the inlet of the back pressure turbine (30) via the back pressure turbine steam inlet pipeline (34) through the back pressure turbine inlet diversion valve (29), and the other path directly goes to the steam supply main pipe (31) for heat supply through a desuperheating and pressure reducing device (18) via the molten salt heat supply gas source diversion valve (28).

8. The steam supply system according to claim 5, wherein The feedwater-molten salt heat exchanger (24), the saturated steam-molten salt heat exchanger (25), and the superheated steam-molten salt heat exchanger (27) are all water-molten salt heat exchangers of the partition wall type.

9. The steam supply system according to claim 1, wherein The steam flow at the outlet end of the main steam split valve (17) is not more than 21% of the steam flow at the main steam outlet.

10. The steam supply system according to claim 1, wherein The steam flow at the outlet end of the reheat steam split valve (16) is not more than 23% of the steam flow at the steam outlet of the primary reheat intermediate reheater (14).

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