A dual-temperature-zone cascade heat accumulation power generation system and a safe and efficient operation method thereof in all working conditions

Abstract

The application discloses a dual-temperature-zone cascade heat storage power generation system and a safe and efficient operation method thereof in all working conditions, and the system constructs a cascade heat storage and dual-stage reheat injection coupling architecture of flue gas-electric heating synergy. The method is characterized in that full-condition safety monitoring and heat mass compensation are implemented. The system monitors the wall temperature margin of the heating surface in real time, especially under wide load fluctuation or low load, and the mass flow rate in the steam physical riser is matched by injection parameters to forcibly suppress the rapid rise of the wall temperature to ensure the safety of the heating surface. On this basis, the reference energy level heat mass compensation is implemented on the primary reheat side to improve the cycle efficiency, and the high-level energy injection is implemented on the secondary reheat side to actively shift the expansion process line and cooperatively suppress the end-stage water erosion. Through dynamic decoupling and accurate energy and mass supply, the irreversible exergy loss is effectively reduced, and the safety and thermal economy of the unit under full load, especially under deep regulation working conditions, are simultaneously optimized.

Description

Technical Field

[0001] This invention belongs to the field of coal-fired power generation and energy storage technology, specifically relating to a dual-temperature zone cascaded thermal storage power generation system and its safe and efficient operation method under all operating conditions. Background Technology

[0002] Against the backdrop of new power system construction and unit flexibility transformation, the operating mode of double reheat units has shifted from rated operating conditions to dynamic regulation across the entire load range. While double reheat technology improves unit thermal efficiency, its complex process presents challenges to both safety and economic efficiency. Especially under wide load fluctuations or low load conditions, a physical coupling contradiction exists between the safety margin of the heated surface tube wall temperature and the turbine stage efficiency. Coordinated regulation of core parameters such as heated surface metal temperature, reheat steam temperature, and the safety of the last-stage blades becomes crucial for maintaining long-term stable operation. Currently, unit regulation mainly relies on conventional methods such as flue gas dampers, burner tilt angle, and feedwater fine-tuning. These passive regulation methods are limited by thermal inertia and cannot adapt to the rapid response requirements under all operating conditions. Specifically, existing methods cannot proactively overcome the heat transfer degradation caused by reduced working fluid velocity due to load decreases without sacrificing efficiency. They also lack the ability to proactively reconstruct the expansion process line, leading to a regulatory dilemma where, when the unit deviates from its design operating conditions, prioritizing safety at the expense of efficiency, or prioritizing efficiency at the expense of approaching the safety boundary.

[0003] Therefore, there is an urgent need to introduce a new approach based on active external energy injection and orderly utilization of energy levels. By constructing a flue gas-electric-thermal synergistic cascade thermal storage architecture and utilizing precise thermo-mass replenishment to achieve dynamic decoupling of reheat system flow and energy, it has significant engineering value for removing strong parameter coupling constraints and achieving synergistic optimization of intrinsic safety and thermal economy across the entire load range. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a dual-temperature zone cascaded thermal storage power generation system and its safe and efficient operation method under all operating conditions. Addressing the coupled contradiction between safety and thermal economy faced by reheat units across the entire operating range, particularly the risk of lag response to wide load fluctuations and deterioration of heat transfer at low load steady state, the present invention constructs a dual-temperature zone cascaded thermal storage architecture including electric heating components. This system actively increases the plant load using the electrothermal conversion effect to assist the coal-fired power generation system in rapidly shaving and filling peak loads during wide load fluctuations. Furthermore, by constructing a cascaded thermal energy reserve with a mix of high and low loads, it provides a flexible source of thermal and mass compensation for all operating conditions. Based on this, the present invention proposes a global dynamic control strategy based on hard constraints on the heating surface wall temperature and multivariate energy efficiency optimization. Through the coordinated adjustment of forced mass flow compensation and active shifting of the expansion process line, the safe and efficient operation of the coal-fired power generation system under all operating conditions, from rated load to deep peak-shaving limit, is achieved.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A dual-temperature zone cascaded thermal storage power generation system includes: a coal-fired power generation system 1, a high-temperature molten salt thermal storage subsystem 20, a low-temperature molten salt thermal storage subsystem 32, a PID controller 44, and a power grid dispatch center 45. The coal-fired power generation system 1 is a double reheat unit. The high-temperature molten salt thermal storage subsystem 20 is coupled to the reheat steam side of the coal-fired power generation system 1. The low-temperature molten salt thermal storage subsystem 32 is coupled to the flue gas side and the feedwater side of the coal-fired power generation system 1. The working fluid outlet of the low-temperature molten salt thermal storage subsystem 32 is connected to the working fluid inlet of the high-temperature molten salt thermal storage subsystem 20, so that the steam generated by heating on the low-temperature side enters the high-temperature side for cascade heating, thereby forming a cascaded coupling relationship. This dual-temperature zone cascaded thermal storage architecture strictly follows the principle of energy cascade utilization. Through the orderly matching of high- and low-grade heat sources, it effectively reduces the irreversible heat transfer losses caused by large temperature differences in single heat source thermal storage, thereby significantly improving the overall thermodynamic perfection and comprehensive cycle energy efficiency of the system in the energy storage and release process.

[0006] The coal-fired power generation system 1 includes: an ultra-high pressure cylinder 2, a high pressure cylinder 3, a medium pressure cylinder 4, a low pressure cylinder 5, a generator 6, a condenser 7, a condensate pump 8, a shaft seal heater 9, a first low pressure heater 10, a second low pressure heater 11, a third low pressure heater 12, a deaerator 13, a feedwater pump 14, a first high pressure heater 15, a second high pressure heater 16, a third high pressure heater 17, a boiler 18, and a small steam turbine 19. In the coal-fired power generation system 1: the boiler 18 is connected to the inlet of the ultra-high pressure cylinder 2 via a main steam pipe; the ultra-high pressure cylinder 2 is connected to a high-pressure reheat extraction steam pipe and an exhaust steam pipe, wherein branches of the exhaust steam pipe are respectively connected to a primary cold reheat steam pipe, a small steam turbine 19 inlet steam pipe, and the extraction steam inlet of the second high-pressure heater 16; the third high-pressure heater 17 is connected to the extraction steam port of the ultra-high pressure cylinder 2 via the high-pressure reheat extraction steam pipe; the primary reheat steam inlet of the boiler 18 is connected to the primary cold reheat steam pipe, and its outlet is connected to the inlet of the high-pressure cylinder 3 via the primary reheat steam pipe; the outlet of the high-pressure cylinder 3 returns to the boiler 18 via a secondary cold reheat steam pipe, and the boiler 18 is then connected to the inlet of the intermediate pressure cylinder 4 via a secondary reheat steam pipe, and the exhaust steam pipe of the intermediate pressure cylinder 4 is connected to the inlet of the low-pressure cylinder 5; The ultra-high pressure cylinder 2, high pressure cylinder 3, medium pressure cylinder 4, and low pressure cylinder 5 are coaxially connected to the generator 6; the outlet of the low pressure cylinder 5 is connected to the inlet of the condenser 7, the outlet of the condenser 7 is connected to the inlet of the shaft seal heater 9, and the condensate pump 8 is located between the condenser 7 and the shaft seal heater 9. The extraction ports of the first low-pressure heater 10 and the second low-pressure heater 11 are respectively connected to the low-pressure extraction steam pipe of the low-pressure cylinder 5; the deaerator 13 and the first high-pressure heater 15 are respectively connected to the extraction steam pipe of the small steam turbine 19, and the exhaust steam pipe of the small steam turbine 19 is connected to the extraction steam inlet of the third low-pressure heater 12; the feedwater outlet of the third low-pressure heater 12 is connected to the water inlet of the deaerator 13, and the water outlet of the deaerator 13 is sequentially connected to the inlets of the first high-pressure heater 15, the second high-pressure heater 16, and the third high-pressure heater 17, and the... The feedwater pump 14 is located between the deaerator 13 and the first high-pressure heater 15; the outlet of the third high-pressure heater 17 is connected to the boiler 18 through a feedwater pipeline; wherein, a feedwater extraction branch is provided on the outlet side of the feedwater pump 14, which directly utilizes the original high-pressure feedwater of the coal-fired power generation system 1 to provide water for the steam compensation process of the steam compensation branch of the low-temperature molten salt thermal storage subsystem 32, eliminating the equipment investment and operating energy consumption of independently configured high-pressure water pumps. At the same time, the heat carried by the feedwater itself reduces the sensible heat consumption required for subsequent heating, greatly improving the thermal economy of the coal-fired power generation system 1.

[0007] The high-temperature molten salt thermal storage subsystem 20 includes: a secondary recompensation steam pressure matching device 21, a primary recompensation steam pressure matching device 22, a high-temperature side electric heater 23, a high-temperature molten salt first regulating valve 24, a high-temperature molten salt first pump 25, a high-temperature molten salt cold salt storage tank 26, a first high-temperature heat exchanger 27, a steam distribution valve 28, a high-temperature molten salt second regulating valve 29, a high-temperature molten salt second pump 30, and a high-temperature molten salt hot salt storage tank 31; The heat storage path is as follows: the first high-temperature molten salt pump 25 drives cold salt through the first high-temperature molten salt regulating valve 24 and the high-temperature side electric heater 23 into the high-temperature molten salt hot salt storage tank 31 to absorb electrical energy; the heat release path is as follows: the molten salt in the high-temperature molten salt hot salt storage tank 31 enters the first high-temperature heat exchanger 27 through the second high-temperature molten salt pump 30 and the second high-temperature molten salt regulating valve 29 to release heat energy and then returns to the high-temperature molten salt cold salt storage tank 26; considering the significant difference in energy level demand and flow gap faced by the primary and secondary reheat heating surfaces of the boiler 18 in the coal-fired power generation system 1, the steam distribution valve 28 is provided with a first outlet and a second outlet to construct an independent steam injection path, wherein the first outlet... The first outlet is directly connected to the primary reheat steam pressure matching device 22, aiming to directly inject steam that meets the lower energy level requirements of primary reheat, avoiding the degradation and consumption of high-grade thermal energy, and achieving cascade matching of energy flow. The second outlet is connected to the working fluid inlet of the first high-temperature heat exchanger 27, aiming to utilize the high-grade thermal energy released by the high-temperature hot salt to specifically undertake the secondary cascade superheating task. The outlet of the working fluid heated by the first high-temperature heat exchanger 27 is connected to the secondary reheat steam pressure matching device 21. The outlets of the secondary reheat steam pressure matching device 21 and the primary reheat steam pressure matching device 22 are respectively connected to the secondary cold reheat pipeline and the primary cold reheat pipeline of the coal-fired power generation system 1. The above-mentioned thermal storage process achieves precise matching of thermal energy grade with steam parameters of different energy levels, ensuring the flexibility and high quality of two-stage steam injection.

[0008] The low-temperature molten salt thermal storage subsystem 32 includes: a flue gas regulating valve 33, a first low-temperature molten salt pump 34, a first low-temperature molten salt regulating valve 35, a first low-temperature heat exchanger 36, a low-temperature side electric heater 37, a low-temperature molten salt hot salt storage tank 38, a second low-temperature molten salt pump 39, a second low-temperature molten salt regulating valve 40, a water supply bypass regulating valve 41, a second low-temperature heat exchanger 42, and a low-temperature molten salt cold salt storage tank 43; The heat storage path is as follows: the first low-temperature molten salt pump 34 drives the cold salt to capture the waste heat of the flue gas via the first low-temperature heat exchanger 36, fully recovering the waste heat at the tail end of the boiler to provide the basic latent heat of vaporization of the working fluid water. Then, the cold salt absorbs electrical energy through the low-temperature side electric heater 37, and the molten salt after absorbing heat finally collects in the low-temperature molten salt hot salt storage tank 38. This design, based on heat exchange between flue gas and feedwater and combined with low-temperature side electric heating reinforcement, can reduce the consumption of high-grade electrical energy in the initial heating stage and improve the overall thermal efficiency of the boiler 18. It realizes the efficient utilization of multi-energy coupling; the heat release path is as follows: the low-temperature molten salt second pump 39 drives the molten salt in the low-temperature molten salt hot salt storage tank 38 to enter the second low-temperature heat exchanger 42 through the low-temperature molten salt second regulating valve 40, and after exchanging heat with the feed water from the feed water bypass regulating valve 41 connected to the feed water pump 14 of the coal-fired power generation system 1, it returns to the low-temperature molten salt cold salt storage tank 43; the working fluid outlet of the second low-temperature heat exchanger 42 is connected to the working fluid inlet of the steam distribution valve 28 of the high-temperature molten salt thermal storage subsystem 20.

[0009] To comprehensively capture the thermal, mechanical, and electrical multidimensional characteristics of the system under unsteady-state conditions and provide sufficient data support for subsequent optimization algorithms, the input terminals of the PID controller 44 are connected to temperature and pressure sensors on the primary and secondary reheat steam pipelines of boiler 18 in the coal-fired power generation system 1, wall temperature sensors on the heating surfaces of the primary and secondary reheaters, humidity monitoring devices and pressure sensors on the exhaust pipeline of low-pressure cylinder 5, the real-time power signal terminal of generator 6, the temperature sensor on the molten salt pipeline at the outlet of the first low-temperature heat exchanger 36 in the low-temperature molten salt thermal storage subsystem 32, and the power grid dispatch center 45. This allows for real-time reception of steam temperature and pressure status, wall temperature safety indicators, exhaust humidity and back pressure feedback signals, real-time power of the coal-fired power generation system 1, and power grid load commands. The output terminal of the controller 44 is connected to the control terminals of the following devices in the high-temperature molten salt thermal storage subsystem 20: high-temperature side electric heater 23, high-temperature molten salt first regulating valve 24, high-temperature molten salt first pump 25, steam distribution valve 28, high-temperature molten salt second regulating valve 29, and high-temperature molten salt second pump 30. The output of the PID controller 44 is connected to the control terminals of the following devices in the cryogenic molten salt thermal storage subsystem 32: flue gas regulating valve 33, cryogenic molten salt first pump 34, cryogenic molten salt first regulating valve 35, cryogenic side electric heater 37, cryogenic molten salt second pump 39, cryogenic molten salt second regulating valve 40, and feedwater bypass regulating valve 41. By unifying the above key actuators with the PID controller 44, the lag caused by the decentralized control of underlying devices is overcome, and bidirectional precise synchronous control is achieved.

[0010] The number of high-pressure heaters and low-pressure heaters can be adjusted according to the specific configuration; the molten salt medium used in the high-temperature molten salt thermal storage subsystem 20 and the low-temperature molten salt thermal storage subsystem 32 is selected according to the thermal properties requirements within the operating temperature range of the high and low temperature zones.

[0011] The method for safe and efficient operation of a dual-temperature zone cascaded thermal storage power generation system under all operating conditions includes the following steps: Step 1: When the coal-fired power generation system 1 is under rated load or steady-state operation, it is in normal operation. The high-temperature molten salt thermal storage subsystem 20 and the steam compensation branch are kept in standby shutdown state. At this time, the feedwater bypass regulating valve 41, steam distribution valve 28, and the secondary compensation steam pressure matching device 21 and the primary compensation steam pressure matching device 22 are all in the closed position. The low-temperature molten salt thermal storage subsystem 32 executes the normal operation logic: the flue gas regulating valve 33 is opened to guide the flue gas at the tail end of the boiler 18. The molten salt from the low-temperature cold salt storage tank 43 is initially heated in the first low-temperature heat exchanger 36 and then stored in the low-temperature hot salt storage tank 38. This step avoids disturbing the working fluid flow and work process of the coal-fired power generation system 1 when it is in steady-state operation by isolating the high-temperature molten salt heat storage subsystem and the steam compensation branch. At the same time, only the flue gas heat exchange path on the low-temperature side is kept unobstructed, so as to achieve continuous recovery and energy storage of the waste heat of the low-grade flue gas at the tail of the boiler 18 without compromising the basic power generation efficiency. Step 2: Dual-temperature zone cascaded thermal storage: When the coal-fired power generation system 1 performs load reduction and peak shaving, the PID controller 44 activates a graded energy storage strategy: prioritizing the increase of the power of the low-temperature side electric heater 37; after the low-temperature side energy level meets the requirements, the PID controller 44 dynamically allocates the redundant plant power regulation margin to the high-temperature molten salt thermal storage subsystem 20, and actively increases the plant power load by significantly increasing the power of the high-temperature side electric heater 23 to quickly reduce the net grid output, and uses the electrothermal conversion effect to heat the high-temperature side molten salt and store it in the high-temperature hot salt storage tank 31, simultaneously completing the unit's deep peak shaving and high-grade thermal energy storage; this step greatly improves the response rate of the coal-fired power generation system 1 to grid commands, and converts the electrical energy that cannot be connected to the grid into high- and low-grade thermal energy reserves for storage.

[0012] Step 3: Steam production calorific value compensation and dynamic performance optimization under all operating conditions: When the system enters the steam production calorific value compensation stage, the PID controller 44 opens the feedwater bypass regulating valve 41 to draw out high-pressure feedwater, which first flows through the second low-temperature heat exchanger 42. The low-temperature hot salt released from the low-temperature molten salt hot salt storage tank 38 is used to quickly vaporize the high-pressure feedwater and heat it to a superheated state that matches the parameters of the first reheat cold section. The generated steam then flows into the steam distribution valve 28. Subsequently, the PID controller 44 executes the safety control logic based on the temperature margin of the heated surface tube wall in real time to allocate compensation steam: the steam allocated to the primary reheat side is directly injected into the coal-fired power generation system 1 through the primary reheat compensation steam pressure matcher 22; while the steam allocated to the secondary reheat side is guided to flow through the first high temperature heat exchanger 27, and uses the high-temperature molten salt hot salt storage tank 31 to perform cascade secondary superheating, and then injects into the coal-fired power generation system 1 through the secondary reheat compensation steam pressure matcher 21. Under the premise of confirming safety, the PID controller 44 executes the performance optimization logic based on heat rate and exhaust humidity. By dynamically adjusting the distribution ratio of the steam distribution valve 28 and the opening of the secondary reheat compensation steam pressure matcher 21 and the primary reheat compensation steam pressure matcher 22, it precisely controls the steam flow rate directly injected into the primary reheat side and the steam flow rate injected into the secondary reheat side after secondary heating in the first high temperature heat exchanger 27. This achieves a deep decoupling between the safety baseline and the operating efficiency, which not only physically suppresses the pipe wall overheating, but also actively reconstructs the expansion work process line, ensuring the maximization of the overall system benefits.

[0013] The typical operating conditions that trigger step 3 for steam generation heat and mass compensation are defined as wide load fluctuation or low load conditions. The specific operating modes include: Wide load fluctuation response mode: When the main steam flow decreases, i.e., when the coal-fired power generation system 1 experiences a large load change, the PID controller 44 actively absorbs the plant load by adjusting the electric heating power to assist in reducing the unit's net output and simultaneously builds cascaded energy level reserves; Low load limit maintenance mode: When the coal-fired power generation system 1 enters the boiler dry-wet state conversion range, the recirculation mode is activated, or when the working fluid mass flow rate drops to 35% or below the rated design value, inducing the risk of heat transfer deterioration, the PID controller 44 controls the high-temperature molten salt thermal storage subsystem 20 and the low-temperature molten salt thermal storage subsystem 32 to use the stored thermal energy to perform dual heat and mass compensation based on the heating surface safety constraints and working fluid quality feedback, so as to maintain a constant reheat steam temperature and eliminate the risk of water erosion of the last stage blades.

[0014] During the execution of steam generation calorific value compensation and dynamic performance optimization under all operating conditions in step 3, the PID controller 44 internally runs a safety constraint control algorithm based on multivariable decoupling, specifically including: setting the target load deviation of the coal-fired power generation system 1 as Δ P The temperature deviation of the reheat steam is Δ T rh1 The temperature deviation of the secondary reheat steam is Δ T rh2 Define the temperature margin vector of the heated surface tube wall. G = [ g 1, g2, ..., g n ], g i = T limit - T wall,i ,in, T limit This refers to the maximum allowable temperature of the metal tube wall material of the heated surface. T wall,i For real-time monitoring of the wall temperature of the heated surface; The PID controller 44 first performs a safety scan, and if the conditions are met... ,in If the preset safety warning threshold is reached, the algorithm immediately skips the performance optimization stage and enters the mass flow forced compensation mode. At this time, the feedwater bypass regulating valve 41 and the steam distribution valve 28 are instructed to increase the high-parameter steam injection flow of the corresponding heating surface. By instantaneously increasing the compensation steam injection flow, the working fluid mass flow rate in the reheater of boiler 18 is forcibly increased, thereby achieving rapid suppression of the metal wall temperature. In ensuring Under the premise that the PID controller 44 calculates the real-time heat rate deviation ,in, For the real-time heat rate of the coal-fired power generation system, The target optimal heat rate under the current load command, if it satisfies ,in The threshold for allowing fluctuations indicates that the current energy efficiency of the coal-fired power generation system is close to the theoretical optimum, and the algorithm reverts to the standby monitoring state; only when... At that time, the PID controller 44 performs multivariate optimization calculations to construct dynamic benefit weights for the primary reheat loop and the secondary reheat loop, respectively. , ,in, Represents the heat consumption rate of a coal-fired power generation system; This indicates the excessive deviation value of the humidity of the exhaust steam from cylinder 5 in the low-pressure cylinder; To characterize the proportional correlation constant that causes a 1% change in humidity to a change in stage efficiency, This characterizes the mechanical efficiency gain resulting from eliminating moisture loss. For unit step function, For reheat steam temperature, This refers to the secondary reheat steam temperature; when the coal-fired power generation system 1 is under deep peak-shaving wet conditions, the steam is very likely to cross the saturation line and enter the wet steam zone, causing water erosion. Additional compensation item for excessive exhaust steam humidity. Effective and significantly improved The numerical values ​​cause the algorithm to favor prioritizing compensation for the secondary reheat side; based on the dynamic benefit weights of the primary and secondary reheat loops, the PID controller 44 uses the total net system benefit... J Using maximization as the criterion, solve for the optimal heat and mass compensation flow vector. : in, These are the consumption costs of low-temperature molten salt level and high-temperature molten salt level, respectively, converted to unit mass compensation steam. This is a cost adjustment factor; These represent the compensating steam mass flow rates injected into the primary reheat side and the secondary reheat side, respectively, during the optimization calculation process. These represent the optimal target compensation steam mass flow rates for the primary reheat side and the secondary reheat side, respectively, obtained after solving the objective function maximization problem. Finally, the optimized heat and mass demand flow rate is transformed into the execution variable, namely the valve opening comprehensive control vector U, through the decoupling matrix D: in, This is a comprehensive control vector for valve opening that includes the execution commands for compensation on each reheat side; These are the execution variables for heat and mass compensation on the primary reheat side and the secondary reheat side, respectively, used to control the corresponding flow rates injected into the primary and secondary cold reheat pipelines. The valve target opening command; Decoupling matrix The inverse matrix; The decoupling matrix The parameters are corrected in real time according to the energy conservation equation of the cascade heat exchange process to eliminate the coupling interference on the pressure of the primary reheat side caused by steam injection into the secondary reheat side, and to ensure that the flow distribution and energy level matching of the whole system are accurately executed.

[0015] Advantages of this invention: (1) This invention constructs a cascaded thermal energy storage architecture with flue gas-electric-thermal synergy. On the low-temperature side, electrothermal reinforcement enables the working fluid to reach the primary cold regeneration energy level, while on the high-temperature side, it undertakes the secondary cascaded superheating task. This design utilizes cascaded temperature difference heat transfer to reduce irreversible energy loss during the energy conversion process, solves the energy level mismatch problem existing in traditional single heat source thermal energy storage, and improves the overall energy efficiency of the system during deep peak shaving cycles.

[0016] (2) This invention utilizes a two-stage reheat cold section steam injection mechanism to directly increase the working fluid mass flow rate within the heating surface tubes under low load conditions. The increased flow rate improves the convective heat transfer coefficient on the working fluid side and physically suppresses the tendency of wall temperature to rise due to decreased flow rate. This mechanism decouples the cooling demand of the heating surface from the load characteristics of the coal-fired power generation system, alleviates the parameter lag caused by the thermal inertia of the reheat system, and expands the safe operating range of the coal-fired power generation system.

[0017] (3) This invention achieves decoupling of energy efficiency and safety under all operating conditions. This invention does not pursue efficiency or safety in isolation, but establishes a dual-response logic based on priority. This invention implements a dual closed-loop control strategy with the wall temperature of the heated surface as a hard constraint and the heat rate and exhaust humidity as optimization objectives. Under the premise of prioritizing metal safety, it dynamically adjusts the steam injection parameters through multivariate decoupling operations and actively reconstructs the thermodynamic cycle expansion process line. This strategy not only maintains a constant reheat steam temperature, but also effectively prevents the risk of water erosion of the last-stage blades caused by the exhaust steam from the low-pressure cylinder entering the wet steam zone at the end of deep peak shaving, thus achieving the synergy between the inherent safety and thermal economy of the coal-fired power generation system under all operating conditions. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a dual-temperature zone cascaded thermal storage power generation system and its safe and efficient operation method under all operating conditions, according to the present invention.

[0019] Figure 2 This is a schematic diagram of the control flow of a dual-temperature zone cascaded thermal storage power generation system and its safe and efficient operation method under all operating conditions, according to the present invention.

[0020] The components in the attached diagram are labeled as follows: 1. Coal-fired power generation system; 2. Ultra-high pressure cylinder; 3. High pressure cylinder; 4. Intermediate pressure cylinder; 5. Low pressure cylinder; 6. Generator; 7. Condenser; 8. Condensate pump; 9. Shaft seal heater; 10. First low pressure heater; 11. Second low pressure heater; 12. Third low pressure heater; 13. Deaerator; 14. Feedwater pump; 15. First high pressure heater; 16. Second high pressure heater; 17. Third high pressure heater; 18. Boiler; 19. Small steam turbine; 20. High-temperature molten salt thermal storage subsystem; 21. Secondary recompensation steam pressure matching device; 22. Primary recompensation steam pressure matching device; 23. High-temperature side electric heater. 24. High-temperature molten salt regulating valve; 25. Pump; 26. High-temperature molten salt cold salt storage tank; 27. Second high-temperature heat exchanger; 28. Steam distribution valve; 29. ​​High-temperature molten salt regulating valve; 30. Pump; 31. High-temperature molten salt hot salt storage tank; 32. Low-temperature molten salt thermal storage subsystem; 33. Flue gas regulating valve; 34. Pump; 35. Low-temperature molten salt regulating valve; 36. First low-temperature heat exchanger; 37. Low-temperature side electric heater; 38. Low-temperature molten salt hot salt storage tank; 39. Pump; 40. Low-temperature molten salt regulating valve; 41. Feedwater bypass regulating valve; 42. Second low-temperature heat exchanger; 43. Low-temperature molten salt cold salt storage tank; 44. PID controller; 45. Power grid dispatch center. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0022] This invention discloses a dual-temperature zone cascaded thermal storage power generation system and its safe and efficient operation method under all operating conditions. By constructing a dual-temperature zone cascaded architecture with high and low temperatures, it utilizes plant power consumption and flue gas waste heat capture for cascaded thermal storage, and generates high-parameter compensation steam to provide dual "heat-mass" compensation for the primary and secondary reheat loops of the coal-fired power generation system.

[0023] like Figure 1 As shown, a dual-temperature zone cascaded thermal storage power generation system includes: a coal-fired power generation system 1, a high-temperature molten salt thermal storage subsystem 20, a low-temperature molten salt thermal storage subsystem 32, a PID controller 44, and a power grid dispatch center 45. The coal-fired power generation system 1 is a double reheat unit. The high-temperature molten salt thermal storage subsystem 20 is coupled to the reheat steam side of the coal-fired power generation system 1. The low-temperature molten salt thermal storage subsystem 32 is coupled to the flue gas side and the feedwater side of the coal-fired power generation system 1. The working fluid outlet of the low-temperature molten salt thermal storage subsystem 32 is connected to the working fluid inlet of the high-temperature molten salt thermal storage subsystem 20, so that the steam generated by heating on the low-temperature side enters the high-temperature side for cascade heating, thereby forming a cascaded coupling relationship. The low-temperature molten salt thermal storage subsystem 32 uses electric heating and waste heat from flue gas to initially heat the working fluid to the energy level required for reheating. Then, the high-temperature molten salt thermal storage subsystem 20 performs stepwise heating to meet the secondary superheating requirements. This graded extraction and matching of high- and low-grade heat sources avoids the huge heat transfer temperature difference caused by high-grade heat sources heating cold water, significantly reducing irreversible energy losses at the thermodynamic system level and improving cycle energy efficiency.

[0024] The coal-fired power generation system 1 includes: an ultra-high pressure cylinder 2, a high pressure cylinder 3, a medium pressure cylinder 4, a low pressure cylinder 5, a generator 6, a condenser 7, a condensate pump 8, a shaft seal heater 9, a first low pressure heater 10, a second low pressure heater 11, a third low pressure heater 12, a deaerator 13, a feedwater pump 14, a first high pressure heater 15, a second high pressure heater 16, a third high pressure heater 17, a boiler 18, and a small steam turbine 19. In the coal-fired power generation system 1: the boiler 18 is connected to the inlet of the ultra-high pressure cylinder 2 via a main steam pipe; the ultra-high pressure cylinder 2 is connected to a high-pressure reheat extraction steam pipe and an exhaust steam pipe, wherein branches of the exhaust steam pipe are respectively connected to a primary cold reheat steam pipe, a small steam turbine 19 inlet steam pipe, and the extraction steam inlet of the second high-pressure heater 16; the third high-pressure heater 17 is connected to the extraction steam port of the ultra-high pressure cylinder 2 via the high-pressure reheat extraction steam pipe; the primary reheat steam inlet of the boiler 18 is connected to the primary cold reheat steam pipe, and its outlet is connected to the inlet of the high-pressure cylinder 3 via the primary reheat steam pipe; the outlet of the high-pressure cylinder 3 returns to the boiler 18 via a secondary cold reheat steam pipe, and the boiler 18 is then connected to the inlet of the intermediate pressure cylinder 4 via a secondary reheat steam pipe, and the exhaust steam pipe of the intermediate pressure cylinder 4 is connected to the inlet of the low-pressure cylinder 5; The ultra-high pressure cylinder 2, high pressure cylinder 3, medium pressure cylinder 4, and low pressure cylinder 5 are coaxially connected to the generator 6; the outlet of the low pressure cylinder 5 is connected to the inlet of the condenser 7, the outlet of the condenser 7 is connected to the inlet of the shaft seal heater 9, and the condensate pump 8 is located between the condenser 7 and the shaft seal heater 9. The extraction ports of the first low-pressure heater 10 and the second low-pressure heater 11 are respectively connected to the low-pressure extraction steam pipe of the low-pressure cylinder 5; the deaerator 13 and the first high-pressure heater 15 are respectively connected to the extraction steam pipe of the small steam turbine 19, and the exhaust steam pipe of the small steam turbine 19 is connected to the extraction steam inlet of the third low-pressure heater 12; the feedwater outlet of the third low-pressure heater 12 is connected to the water inlet of the deaerator 13, and the water outlet of the deaerator 13 is connected to the inlets of the first high-pressure heater 15, the second high-pressure heater 16 and the third high-pressure heater 17 in sequence, and the feedwater pump 14 is located between the deaerator 13 and the first high-pressure heater 15; the outlet of the third high-pressure heater 17 is connected to the boiler 18 through the feedwater pipe; wherein, a feedwater extraction branch is provided on the outlet side of the feedwater pump 14, which directly utilizes the original high-pressure feedwater of the coal-fired power generation system 1 to provide water for the steam compensation process of the steam compensation branch of the low-temperature molten salt thermal storage subsystem 32. The advantage of this design is that it eliminates the equipment investment and additional operating energy consumption of a separate high-pressure booster pump. At the same time, the heat carried by the original feed water itself reduces the sensible heat consumption required for subsequent vaporization heating, which greatly improves the overall thermal economy of the coal-fired power generation system 1.

[0025] The high-temperature molten salt thermal storage subsystem 20 includes: a secondary recompensation steam pressure matching device 21, a primary recompensation steam pressure matching device 22, a high-temperature side electric heater 23, a high-temperature molten salt first regulating valve 24, a high-temperature molten salt first pump 25, a high-temperature molten salt cold salt storage tank 26, a first high-temperature heat exchanger 27, a steam distribution valve 28, a high-temperature molten salt second regulating valve 29, a high-temperature molten salt second pump 30, and a high-temperature molten salt hot salt storage tank 31; The heat storage path is as follows: the first high-temperature molten salt pump 25 drives cold salt through the first high-temperature molten salt regulating valve 24 and the high-temperature side electric heater 23 into the high-temperature molten salt hot salt storage tank 31 to absorb electrical energy; the heat release path is as follows: the molten salt in the high-temperature molten salt hot salt storage tank 31 enters the first high-temperature heat exchanger 27 through the second high-temperature molten salt pump 30 and the second high-temperature molten salt regulating valve 29 to release heat energy and then returns to the high-temperature molten salt cold salt storage tank 26; considering the significant differences in energy level requirements and flow gaps between the primary reheat heating surface and the secondary reheat heating surface of the boiler 18 in the coal-fired power generation system 1, the steam distribution valve 28 is provided with a first outlet and a second outlet to construct an independent cascade steam injection path, wherein the first outlet... The first outlet is directly connected to the primary reheat steam pressure matching device 22; this is designed to directly inject steam that meets the lower energy level requirements of primary reheat, avoiding the degradation and consumption of high-grade thermal energy, and achieving cascade matching of energy flow. The second outlet is connected to the working fluid inlet of the first high-temperature heat exchanger 27, aiming to utilize the high-grade thermal energy released by the high-temperature hot salt to specifically undertake the secondary cascade superheating task. The outlet of the working fluid heated by the first high-temperature heat exchanger 27 is connected to the secondary reheat steam pressure matching device 21. The outlets of the secondary reheat steam pressure matching device 21 and the primary reheat steam pressure matching device 22 are respectively connected to the secondary cold reheat pipeline and the primary cold reheat pipeline of the coal-fired power generation system 1. The above-mentioned cascade heat exchange and steam injection process achieves precise matching of thermal energy grade and steam parameters of different energy levels, ensuring the flexibility and high quality of two-stage steam injection.

[0026] The low-temperature molten salt thermal storage subsystem 32 includes: a flue gas regulating valve 33, a first low-temperature molten salt pump 34, a first low-temperature molten salt regulating valve 35, a first low-temperature heat exchanger 36, a low-temperature side electric heater 37, a low-temperature molten salt hot salt storage tank 38, a second low-temperature molten salt pump 39, a second low-temperature molten salt regulating valve 40, a water supply bypass regulating valve 41, a second low-temperature heat exchanger 42, and a low-temperature molten salt cold salt storage tank 43; The heat storage path is as follows: the first low-temperature molten salt pump 34 drives cold salt to capture waste heat from the flue gas via the first low-temperature heat exchanger 36. Then, the cold salt absorbs electrical energy through the low-temperature side electric heater 37. The molten salt, after absorbing heat, finally collects in the low-temperature molten salt hot salt storage tank 38. This heat storage path is based on the design of heat exchange between flue gas and feedwater combined with low-temperature side electric heating reinforcement, which greatly reduces the consumption of high-grade electrical energy in the initial heating stage, while improving the overall thermal efficiency of boiler 18 and realizing the efficient utilization of multi-energy coupling. The heat release path is as follows: the second low-temperature molten salt pump 39 drives the molten salt in the low-temperature molten salt hot salt storage tank 38 to enter the second low-temperature heat exchanger 42 through the second low-temperature molten salt regulating valve 40, and after exchanging heat with the feedwater from the feedwater bypass regulating valve 41 connected to the feedwater pump 14 of the coal-fired power generation system 1, it returns to the low-temperature molten salt cold salt storage tank 43. The working fluid outlet of the second low-temperature heat exchanger 42 is connected to the working fluid inlet of the steam distribution valve 28 of the high-temperature molten salt heat storage subsystem 20.

[0027] To comprehensively capture the thermal, mechanical, and electrical multidimensional characteristics of the entire system under unsteady and complex operating conditions, thereby providing sufficient high-precision data support for subsequent optimization algorithms, the PID controller 44 constructs a complete measurement and control feedback network: PID The signal input terminals of the controller 44 are respectively connected to the temperature and pressure sensors on the primary and secondary reheat steam pipelines of the boiler 18 in the coal-fired power generation system 1, the wall temperature sensors on the heating surfaces of the primary and secondary reheaters, the humidity monitoring device and pressure sensor on the exhaust pipeline of the low-pressure cylinder 5, the real-time power signal terminal of the generator 6, the temperature sensor on the molten salt pipeline at the outlet of the first low-temperature heat exchanger 36 in the low-temperature molten salt thermal storage subsystem 32, and the power grid dispatch center 45; used to receive real-time steam temperature and pressure status, wall temperature safety indicators, exhaust humidity and back pressure feedback signals, real-time power of the coal-fired power generation system 1, and power grid load commands; the high-temperature zone control output terminal of the PID controller 44 is respectively connected to the control terminals of the following equipment in the high-temperature molten salt thermal storage subsystem 20: high-temperature side electric heater 23, high-temperature molten salt first regulating valve 24, high-temperature molten salt first pump 25, steam distribution valve 28, high-temperature molten salt second regulating valve 29, and high-temperature molten salt second pump 30. The low-temperature zone control output terminal of the PID controller 44 is connected to the control terminals of the following devices in the low-temperature molten salt thermal storage subsystem 32: flue gas regulating valve 33, low-temperature molten salt first pump 34, low-temperature molten salt first regulating valve 35, low-temperature side electric heater 37, low-temperature molten salt second pump 39, low-temperature molten salt second regulating valve 40, and water supply bypass regulating valve 41.

[0028] By integrating the aforementioned key actuators into the central PID controller 44, the lag caused by the decentralized control of underlying devices is overcome, and bidirectional precise synchronous control is achieved.

[0029] The number of high-pressure heaters and low-pressure heaters can be adjusted according to the specific configuration; the molten salt medium used in the high-temperature molten salt thermal storage subsystem 20 and the low-temperature molten salt thermal storage subsystem 32 is selected according to the thermal properties requirements within the operating temperature range of the high and low temperature zones.

[0030] The specific implementation steps of the method for safe and efficient operation of a dual-temperature zone cascaded thermal storage power generation system under all operating conditions are as follows: Step 1: When the coal-fired power generation system 1 is under rated load or steady-state operation, the coal-fired power generation system 1 is in normal operation. The high-temperature molten salt thermal storage subsystem 20 and the steam production compensation branch are kept in standby shutdown state. At this time, the feedwater bypass regulating valve 41, the steam distribution valve 28, the secondary compensation steam pressure matching device 21 and the primary compensation steam pressure matching device 22 are all in the closed state. During this period, the low-temperature molten salt thermal storage subsystem 32 performs routine waste heat capture: the flue gas regulating valve 33 is opened, guiding the flue gas from the tail of boiler 18 into the first low-temperature heat exchanger 36, initially heating the molten salt from the low-temperature cold salt storage tank 43; this step effectively avoids aerodynamic disturbances caused by the working fluid flow and expansion work process during the steady-state operation of the coal-fired power generation system 1 by physically isolating the high-temperature molten salt thermal storage subsystem 20 and the steam compensation branch; at the same time, only the flue gas heat exchange path of the low-temperature molten salt thermal storage subsystem 32 is kept unobstructed, so as to achieve continuous recovery and basic energy storage of the waste heat of the low-grade flue gas at the tail of boiler 18 under the premise of ensuring that the basic power generation efficiency of the coal-fired power generation system 1 is not damaged, and to reserve initial heat for subsequent peak-shaving operations.

[0031] Step 2: When the coal-fired power generation system 1 enters a load reduction mode, the PID controller 44 executes a staged thermal storage strategy. It prioritizes reducing net output by increasing the plant power load of the low-temperature side electric heater 37 in the low-temperature molten salt subsystem 32, heating the cold salt in the low-temperature molten salt subsystem, and ensuring that the low-temperature side energy level meets the requirements. Then, the PID controller... The controller 44 distributes redundant plant power to the high-temperature side electric heater 23 of the high-temperature molten salt thermal storage subsystem 20. It uses the electrothermal conversion effect to heat the high-temperature side molten salt and store it in the high-temperature molten salt thermal storage tank 31. This process, without interfering with boiler combustion, rapidly reduces the unit's net output by increasing the plant load, and simultaneously builds high and low grade thermal energy reserves. This arrangement changes the traditional thermal power unit's lagging adjustment mode of simply reducing boiler combustion to lower the load. Under the premise of maintaining the basic combustion stability of boiler 18, it actively increases the plant power load to rapidly reduce the net grid output of the coal-fired power generation system 1, which greatly improves the response rate of the coal-fired power generation system 1 to the grid's deep peak shaving command, and converts the electrical energy that cannot be connected to the grid into high and low grade thermal energy reserves for storage. It simultaneously realizes the system's flexible deep peak shaving and the efficient conversion of high-quality thermal energy.

[0032] Step 3: The typical operating condition that triggers this step for steam generation heat and mass compensation is defined as the coal-fired power generation system 1 being in a wide load fluctuation or low load condition. Its operating modes specifically include: Wide load fluctuation response mode: When the main steam flow decreases, i.e., when the coal-fired power generation system 1 experiences a large load change, the PID controller 44 actively absorbs the plant load by adjusting the electric heating power to assist in reducing the unit's net output and simultaneously builds cascaded energy level reserves; Low load limit maintenance mode: When the coal-fired power generation system 1 enters the boiler dry-wet state transition range, the recirculation mode is activated, or when the working fluid mass flow rate drops to 35% or below the rated design value, inducing the risk of heat transfer deterioration, the PID controller 44 controls the high-temperature molten salt thermal storage subsystem 20 and the low-temperature molten salt thermal storage subsystem 32 to use the stored thermal energy to perform dual heat and mass compensation based on the heating surface safety constraints and working fluid quality feedback, so as to maintain a constant reheat steam temperature and eliminate the risk of water erosion of the last stage blades.

[0033] At this stage, the PID controller 44 opens the feedwater bypass regulating valve 41 to draw out high-pressure feedwater, which first flows through the second low-temperature heat exchanger 42. The high-pressure feedwater is rapidly vaporized and heated to a superheated state that matches the parameters of the first reheat cold section by the low-temperature molten salt hot salt storage tank 38. The generated steam then flows into the steam distribution valve 28.

[0034] During the aforementioned compensation and full-condition dynamic performance optimization process, the PID controller 44 internally runs a safety constraint control algorithm based on multivariable decoupling in real time, such as... Figure 2 As shown, the specific calculation and execution logic is as follows: The target load deviation of the coal-fired power generation system 1 is set as Δ. P The temperature deviation of the reheat steam is Δ T rh1 The temperature deviation of the secondary reheat steam is Δ T rh2 Define the temperature margin vector of the heated surface tube wall. G = [ g 1, g2, ..., g n ], g i = T limit - T wall,i ,in, T limit This refers to the maximum allowable temperature of the metal tube wall material of the heated surface. T wall,i For real-time monitoring of the wall temperature of the heated surface; First, the PID controller 44 performs a safety scan based on the temperature margin of the heated surface tube wall. If the condition is met... ,in If the preset safety warning threshold is reached, the algorithm immediately skips the performance optimization stage and enters the mass flow forced compensation mode. At this time, the feedwater bypass regulating valve 41 and the steam distribution valve 28 are instructed to increase the high-parameter steam injection flow of the corresponding heating surface. By instantaneously increasing the compensation steam injection flow, the working fluid mass flow rate in the reheater of boiler 18 is forcibly increased, thereby achieving rapid suppression of the metal wall temperature. In ensuring Under the premise that the heated surface is safe, the PID controller 44 further executes performance optimization logic based on heat rate and exhaust humidity to calculate the real-time heat rate deviation. ,in, For the real-time heat rate of the coal-fired power generation system, The target optimal heat rate under the current load command, if it satisfies ,in The threshold for allowing fluctuations indicates that the current energy efficiency of the coal-fired power generation system is close to the theoretical optimum, and the algorithm reverts to the standby monitoring state; only when... At that time, the PID controller 44 performs multivariate optimization calculations to construct dynamic benefit weights for the primary reheat loop and the secondary reheat loop, respectively. , ,in, Represents the heat consumption rate of a coal-fired power generation system; This indicates the excessive deviation value of the humidity of the exhaust steam from cylinder 5 in the low-pressure cylinder; To characterize the proportional correlation constant that causes a 1% change in humidity to a change in stage efficiency, This characterizes the mechanical efficiency gain resulting from eliminating moisture loss. For unit step function, For reheat steam temperature, This refers to the secondary reheat steam temperature; when the coal-fired power generation system 1 is under deep peak-shaving wet conditions, the steam is very likely to cross the saturation line and enter the wet steam zone, causing water erosion. Additional compensation item for excessive exhaust steam humidity. Effective and significantly improved The value of the value makes the algorithm biased towards prioritizing compensation on the secondary reheat side; Based on the dynamic benefit weights of the primary and secondary reheat loops, the PID controller 44 uses the total net system benefit... J Using maximization as the criterion, solve for the optimal heat and mass compensation flow vector. : in, These are the consumption costs of low-temperature molten salt level and high-temperature molten salt level, respectively, converted to unit mass compensation steam. This is a cost adjustment factor; These represent the compensating steam mass flow rates injected into the primary reheat side and the secondary reheat side, respectively, during the optimization calculation process. These represent the optimal target compensation steam mass flow rates for the primary reheat side and the secondary reheat side, respectively, obtained after solving the objective function maximization problem. Finally, the optimized heat and mass demand flow rate is transformed into an execution variable, namely, the valve opening comprehensive control vector U containing the execution commands for each reheat side compensation, through the decoupling matrix D: in, These are the execution variables for heat and mass compensation on the primary reheat side and the secondary reheat side, respectively, used to control the corresponding flow rates injected into the primary and secondary cold reheat pipelines. The valve target opening command; Decoupling matrix The inverse matrix; The decoupling matrix The parameters are corrected in real time according to the energy conservation equation of the cascade heat exchange process to eliminate the coupling interference on the pressure of the primary reheat side caused by steam injection into the secondary reheat side.

[0035] Based on the output of the aforementioned control vector U, the PID controller 44 precisely controls the two-stage steam injection flow rate by dynamically adjusting the distribution ratio of the steam distribution valve 28 and the opening of the secondary reheat compensation steam pressure matcher 21 and the primary reheat compensation steam pressure matcher 22. Specifically, the steam allocated to the primary reheat side is directly injected into the coal-fired power generation system 1 via the primary reheat compensation steam pressure matcher 22, while the steam allocated to the secondary reheat side is guided through the first high-temperature heat exchanger 27, where it undergoes cascade secondary superheating using the high-temperature molten salt hot salt storage tank 31 to achieve high parameter matching, before being injected into the coal-fired power generation system 1 via the secondary reheat compensation steam pressure matcher 21.

[0036] This step, through rigorous algorithm optimization and precise calorific value allocation, achieves accurate execution of flow distribution and energy level matching for the entire system, thus resolving the physical coupling contradiction between ensuring safety and efficiency when the coal-fired power generation system 1 deviates from its design operating conditions.

Claims

1. A dual-temperature zone cascaded thermal storage power generation system, characterized in that, The system includes: a coal-fired power generation system (1), a high-temperature molten salt thermal storage subsystem (20), a low-temperature molten salt thermal storage subsystem (32), a PID controller (44), and a power grid dispatch center (45); the coal-fired power generation system (1) is a secondary reheat unit; the high-temperature molten salt thermal storage subsystem (20) is coupled to the reheat steam side of the coal-fired power generation system (1); the low-temperature molten salt thermal storage subsystem (32) is coupled to the flue gas side and the feedwater side of the coal-fired power generation system (1); the working fluid outlet of the low-temperature molten salt thermal storage subsystem (32) is connected to the working fluid inlet of the high-temperature molten salt thermal storage subsystem (20) so that the steam generated by heating on the low-temperature side enters the high-temperature side for cascade heating, thereby forming a cascaded coupling relationship.

2. The dual-temperature zone cascaded thermal storage power generation system according to claim 1, characterized in that, The coal-fired power generation system (1) includes: an ultra-high pressure cylinder (2), a high pressure cylinder (3), a medium pressure cylinder (4), a low pressure cylinder (5), a generator (6), a condenser (7), a condensate pump (8), a shaft seal heater (9), a first low pressure heater (10), a second low pressure heater (11), a third low pressure heater (12), a deaerator (13), a feed water pump (14), a first high pressure heater (15), a second high pressure heater (16), a third high pressure heater (17), a boiler (18), and a small steam turbine (19). In the coal-fired power generation system (1): the boiler (18) is connected to the inlet of the ultra-high pressure cylinder (2) through the main steam pipe; the ultra-high pressure cylinder (2) is connected to a high-pressure reheat extraction pipe and an exhaust pipe, wherein the branches of the exhaust pipe are respectively connected to the primary cold reheat steam pipe, the steam inlet pipe of the small steam turbine (19) and the extraction inlet of the second high-pressure heater (16); the third high-pressure heater (17) is connected to the extraction port of the ultra-high pressure cylinder (2) through the high-pressure reheat extraction pipe; the primary reheat steam inlet of the boiler (18) is connected to the primary cold reheat steam pipe, and its outlet is connected to the inlet of the high-pressure cylinder (3) through the primary reheat steam pipe; the outlet of the high-pressure cylinder (3) returns to the boiler (18) through the secondary cold reheat steam pipe, and the boiler (18) is then connected to the inlet of the intermediate pressure cylinder (4) through the secondary reheat steam pipe, and the exhaust pipe of the intermediate pressure cylinder (4) is connected to the inlet of the low-pressure cylinder (5); The ultra-high pressure cylinder (2), high pressure cylinder (3), medium pressure cylinder (4), and low pressure cylinder (5) are coaxially connected to the generator (6); the outlet of the low pressure cylinder (5) is connected to the inlet of the condenser (7), the outlet of the condenser (7) is connected to the inlet of the shaft seal heater (9), and the condensate pump (8) is located between the condenser (7) and the shaft seal heater (9); The extraction ports of the first low-pressure heater (10) and the second low-pressure heater (11) are respectively connected to the low-pressure extraction pipe of the low-pressure cylinder (5); the deaerator (13) and the first high-pressure heater (15) are respectively connected to the extraction pipe of the small steam turbine (19), and the exhaust pipe of the small steam turbine (19) is connected to the extraction inlet of the third low-pressure heater (12); the feedwater outlet of the third low-pressure heater (12) is connected to the water inlet of the deaerator (13), and the water outlet of the deaerator (13) is connected to the water outlet of the deaerator (13). The feedwater pump (14) is connected to the inlet of the first high-pressure heater (15), the second high-pressure heater (16) and the third high-pressure heater (17) in sequence, and is located between the deaerator (13) and the first high-pressure heater (15); the outlet of the third high-pressure heater (17) is connected to the boiler (18) through a feedwater pipe; wherein, a feedwater extraction branch is provided on the outlet side of the feedwater pump (14) to provide water source for the steam compensation process of the steam compensation branch of the low-temperature molten salt thermal storage subsystem (32).

3. The dual-temperature zone cascaded thermal storage power generation system according to claim 1, characterized in that, The high-temperature molten salt thermal storage subsystem (20) includes: a secondary compensation steam pressure matching device (21), a primary compensation steam pressure matching device (22), a high-temperature side electric heater (23), a high-temperature molten salt first regulating valve (24), a high-temperature molten salt first pump (25), a high-temperature molten salt cold salt storage tank (26), a first high-temperature heat exchanger (27), a steam distribution valve (28), a high-temperature molten salt second regulating valve (29), a high-temperature molten salt second pump (30), and a high-temperature molten salt hot salt storage tank (31). The heat storage path is as follows: the first high-temperature molten salt pump (25) drives the cold salt through the first high-temperature molten salt regulating valve (24) and the high-temperature side electric heater (23) into the high-temperature molten salt hot salt storage tank (31) to absorb electrical energy; the heat release path is as follows: the molten salt in the high-temperature molten salt hot salt storage tank (31) enters the first high-temperature heat exchanger (27) through the second high-temperature molten salt pump (30) and the second high-temperature molten salt regulating valve (29) to release heat energy and then return to the high-temperature molten salt cold salt storage tank (26); the steam distribution valve (28) is provided with a first outlet and The second outlet is directly connected to the first recompensating steam pressure matching device (22); the second outlet is connected to the working fluid inlet of the first high-temperature heat exchanger (27), and the working fluid outlet heated by the first high-temperature heat exchanger (27) is connected to the second recompensating steam pressure matching device (21). The outlets of the second recompensating steam pressure matching device (21) and the first recompensating steam pressure matching device (22) are respectively connected to the secondary cold resteam pipeline and the primary cold resteam pipeline of the coal-fired power generation system (1).

4. The dual-temperature zone cascaded thermal storage power generation system according to claim 1, characterized in that, The low-temperature molten salt thermal storage subsystem (32) includes: a flue gas regulating valve (33), a low-temperature molten salt first pump (34), a low-temperature molten salt first regulating valve (35), a first low-temperature heat exchanger (36), a low-temperature side electric heater (37), a low-temperature molten salt hot salt storage tank (38), a low-temperature molten salt second pump (39), a low-temperature molten salt second regulating valve (40), a water supply bypass regulating valve (41), a second low-temperature heat exchanger (42), and a low-temperature molten salt cold salt storage tank (43); The heat storage path is as follows: the first low-temperature molten salt pump (34) drives the cold salt to capture the waste heat of the flue gas through the first low-temperature heat exchanger (36), and then the cold salt absorbs the electrical energy through the low-temperature side electric heater (37). The molten salt after absorbing heat is finally collected in the low-temperature molten salt hot salt storage tank (38). The heat release path is as follows: the second low-temperature molten salt pump (39) drives the molten salt in the low-temperature molten salt hot salt storage tank (38) to enter the second low-temperature heat exchanger (42) through the second low-temperature molten salt regulating valve (40), and after exchanging heat with the feed water from the feed water bypass regulating valve (41) connected to the feed water pump (14) of the coal-fired power generation system (1), it returns to the low-temperature molten salt cold salt storage tank (43). The working fluid outlet of the second low-temperature heat exchanger (42) is connected to the working fluid inlet of the steam distribution valve (28) of the high-temperature molten salt heat storage subsystem (20).

5. A dual-temperature zone cascaded thermal storage power generation system according to claim 1, characterized in that, The input terminals of the PID controller (44) are respectively connected to the temperature and pressure sensors on the primary and secondary reheat steam pipelines of the boiler (18) in the coal-fired power generation system (1), the wall temperature sensors on the heating surfaces of the primary and secondary reheaters, the humidity monitoring device and pressure sensor on the exhaust pipeline of the low-pressure cylinder (5), the real-time power signal terminal of the generator (6), the temperature sensor on the molten salt pipeline at the outlet of the first low-temperature heat exchanger (36) in the low-temperature molten salt thermal storage subsystem (32), and the power grid dispatch center (45); to receive real-time steam temperature and pressure status, wall temperature safety indicators, exhaust humidity and back pressure feedback signals, real-time power of the coal-fired power generation system (1), and power grid load commands; the PID controller (44) is connected to the temperature and pressure sensors on the primary and secondary reheat steam pipelines of the boiler (18) in the coal-fired power generation system (1), the wall temperature sensors on the heating surfaces of the primary and secondary reheaters, ... secondary reheaters, the The output of the controller (44) is connected to the control terminals of the following devices in the high-temperature molten salt thermal storage subsystem (20): high-temperature side electric heater (23), high-temperature molten salt first regulating valve (24), high-temperature molten salt first pump (25), steam distribution valve (28), high-temperature molten salt second regulating valve (29) and high-temperature molten salt second pump (30). The output of the PID controller (44) is connected to the control terminals of the following devices in the low-temperature molten salt thermal storage subsystem (32): flue gas regulating valve (33), low-temperature molten salt first pump (34), low-temperature molten salt first regulating valve (35), low-temperature side electric heater (37), low-temperature molten salt second pump (39), low-temperature molten salt second regulating valve (40), and water supply bypass regulating valve (41).

6. The dual-temperature zone cascaded thermal storage power generation system according to claim 1, characterized in that, The number of high-pressure heaters and low-pressure heaters can be adjusted according to the specific configuration; the molten salt medium used in the high-temperature molten salt thermal storage subsystem (20) and the low-temperature molten salt thermal storage subsystem (32) is selected according to the thermal properties requirements within the working temperature range of the high and low temperature zones.

7. A method for safe and efficient operation of a dual-temperature zone cascaded thermal storage power generation system under all operating conditions, as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: When the coal-fired power generation system (1) is in the rated load or steady-state operation stage, the coal-fired power generation system (1) is in normal operation. The high-temperature molten salt thermal storage subsystem (20) and the steam production compensation branch are in standby shutdown state. At this time, the feedwater bypass regulating valve (41), steam distribution valve (28), and the secondary compensation steam pressure matching device (21) and the primary compensation steam pressure matching device (22) are all in the closed position. The low-temperature molten salt thermal storage subsystem (32) executes the normal operation logic: the flue gas regulating valve (33) is opened to guide the flue gas at the tail of the boiler (18) into the first low-temperature heat exchanger (36) to preheat the molten salt delivered from the low-temperature cold salt storage tank (43) and then store it in the low-temperature hot salt storage tank (38). Step 2: Dual-temperature zone cascaded thermal storage: When the coal-fired power generation system (1) performs load reduction and peak shaving, the PID controller (44) starts the graded energy storage strategy: prioritizes increasing the power of the low-temperature side electric heater (37); after the low-temperature side energy level meets the requirements, the PID controller (44) dynamically allocates the redundant plant power regulation margin to the high-temperature molten salt thermal storage subsystem (20), actively increases the plant power load by significantly increasing the power of the high-temperature side electric heater (23) to quickly reduce the net grid output, and uses the electrothermal conversion effect to heat the high-temperature side molten salt and store it in the high-temperature hot salt storage tank (31), simultaneously completing the unit's deep peak shaving and high-grade thermal energy storage; Step 3: Steam production heat and mass compensation and dynamic performance optimization under all operating conditions: When the system enters the steam production heat and mass compensation stage, the PID controller (44) opens the feedwater bypass regulating valve (41) to draw out high-pressure feedwater, which first flows through the second low-temperature heat exchanger (42). The low-temperature hot salt released from the low-temperature molten salt hot salt storage tank (38) rapidly vaporizes the high-pressure feedwater and heats it to a superheated state that matches the parameters of the first reheat cold section. The generated steam then flows into the steam distribution valve (28). Subsequently, the PID controller (44) executes the safety control logic based on the temperature margin of the heated surface tube wall in real time to allocate compensation steam: the steam allocated to the primary reheat side is directly injected into the coal-fired power generation system (1) through the primary reheat compensation steam pressure matcher (22); while the steam allocated to the secondary reheat side is guided to flow through the first high temperature heat exchanger (27), and uses the high-temperature molten salt hot salt storage tank (31) to perform cascade secondary superheating, and then injects into the coal-fired power generation system (1) through the secondary reheat compensation steam pressure matcher (21). Under the premise of confirming safety, the PID controller (44) executes the performance optimization logic based on heat rate and exhaust humidity. By dynamically adjusting the distribution ratio of the steam distribution valve (28) and the opening of the secondary reheat steam pressure matching device (21) and the primary reheat steam pressure matching device (22), the controller precisely controls the steam flow rate directly injected into the primary reheat side and the steam flow rate injected into the secondary reheat side after secondary heating in the first high temperature heat exchanger (27).

8. The method according to claim 7, characterized in that: The typical operating conditions that trigger the steam generation heat and quality compensation in step 3 are defined as wide load fluctuation or low load conditions. The specific operating modes include: wide load fluctuation response mode: when the main steam flow decreases, i.e., the coal-fired power generation system (1) experiences a large load change, the PID controller (44) actively absorbs the plant load by adjusting the electric heating power to assist in reducing the unit's net output and simultaneously builds cascaded energy level reserves; low load limit maintenance mode: when the coal-fired power generation system (1) enters the boiler dry-wet state conversion range, the recirculation mode is started, or when the working fluid mass flow rate drops to 35% or below the rated design value, inducing the risk of heat transfer deterioration, the PID controller (44) controls the high-temperature molten salt thermal storage subsystem (20) and the low-temperature molten salt thermal storage subsystem (32) to use the stored thermal energy to perform dual heat and quality compensation based on the safety constraints of the heating surface and the working fluid quality feedback, so as to maintain the constant reheat steam temperature and eliminate the risk of water erosion of the last stage blades.

9. The method for safe and efficient operation under all working conditions according to claim 7, characterized in that, During the execution of steam generation calorific value compensation and dynamic performance optimization under all operating conditions in step 3, the PID controller (44) internally runs a safety constraint control algorithm based on multivariable decoupling, specifically including: setting the target load deviation of the coal-fired power generation system (1) as Δ P The temperature deviation of the reheat steam is Δ T rh1 The temperature deviation of the secondary reheat steam is Δ T rh2 Define the temperature margin vector of the heated surface tube wall. G = [ g 1, g2,..., g n ], g i = T limit - T wall,i ,in, T limit This refers to the maximum allowable temperature of the metal tube wall material of the heated surface. T wall,i For real-time monitoring of the wall temperature of the heated surface; The PID controller (44) first performs a safety scan, and if the conditions are met... ,in If the preset safety warning threshold is used, the algorithm will immediately skip the performance optimization stage and enter the mass flow forced compensation mode. At this time, the water bypass regulating valve (41) and steam distribution valve (28) are instructed to increase the high parameter steam injection flow of the corresponding heating surface. By instantaneously increasing the compensation steam injection flow, the working fluid mass flow rate in the reheater of the boiler (18) is forcibly increased, thereby achieving rapid suppression of the metal wall temperature. In ensuring Under the premise that the PID controller (44) calculates the real-time heat rate deviation. ,in, Real-time heat rate of coal-fired power generation system (1), The target optimal heat rate under the current load command, if it satisfies ,in The threshold for allowing fluctuations indicates that the current energy efficiency of the coal-fired power generation system (1) is close to the theoretical optimum, and the algorithm reverts to the standby monitoring state; only when At that time, the PID controller (44) performs multivariate optimization calculation to construct the dynamic benefit weights of the primary reheat loop and the secondary reheat loop respectively. , ,in, (1) Heat consumption rate of a coal-fired power generation system; This indicates the excessive deviation value of the exhaust humidity of the low-pressure cylinder (5); To characterize the proportional correlation constant that causes a 1% change in humidity to a change in stage efficiency, This characterizes the mechanical efficiency gain resulting from eliminating moisture loss. For unit step function, For reheat steam temperature, The secondary reheat steam temperature; when the coal-fired power generation system (1) is in deep peak shaving wet condition, the exhaust steam humidity exceeds the limit compensation item. Effective and significantly improved The numerical values ​​make the algorithm biased towards prioritizing compensation for the secondary reheat side; based on the dynamic benefit weights of the primary and secondary reheat loops, the PID controller (44) uses the total net benefit of the system. J Using maximization as the criterion, solve for the optimal heat and mass compensation flow vector. : in, These are the consumption costs of low-temperature molten salt level and high-temperature molten salt level, respectively, converted to unit mass compensation steam. This is a cost adjustment factor; These represent the compensating steam mass flow rates injected into the primary reheat side and the secondary reheat side, respectively, during the optimization calculation process. These represent the optimal target compensation steam mass flow rates for the primary reheat side and the secondary reheat side, respectively, obtained after solving the objective function maximization problem. Finally, the optimized heat and mass demand flow rate is transformed into the execution variable, namely the valve opening comprehensive control vector U, through the decoupling matrix D: in, This is a comprehensive control vector for valve opening that includes the execution commands for compensation on each reheat side; These are the execution variables for heat and mass compensation on the primary reheat side and the secondary reheat side, respectively, used to control the corresponding flow rates injected into the primary and secondary cold reheat pipelines. The valve target opening command; Decoupling matrix The inverse matrix; The decoupling matrix The parameters are corrected in real time according to the energy conservation equation of the cascade heat exchange process to eliminate the coupling interference on the pressure of the primary reheat side caused by steam injection into the secondary reheat side, and to ensure that the flow distribution and energy level matching of the whole system are accurately executed.

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