A hierarchical operation system and method of a solar energy auxiliary coal-fired power generation system integrated with molten salt heat storage

Abstract

This application provides a tiered operation system and method for an integrated molten salt thermal energy storage solar-assisted coal-fired power generation system, belonging to the technical field of solar-assisted coal-fired power generation systems. The system provided includes a coal-fired power plant subsystem, a solar field subsystem, and a processing system. It adjusts the heat transfer oil flow rate of the PTC collector field and the molten salt flow rate of the molten salt thermal energy storage system according to the actual solar thermal energy input. It calculates the mass flow rate and pressure of each stage of extraction steam in each high-pressure heater in the high-pressure heater group based on the matrix heat balance equation and the Stodola formula. It switches the connection relationship between the salt-water heat exchanger and each high-pressure heater in the high-pressure heater group according to the load level and the actual solar thermal energy input, realizing tiered steam extraction substitution. The tiered operation system and method for an integrated molten salt thermal energy storage solar-assisted coal-fired power generation system provided in this application are used to achieve dynamic switching of extraction steam levels under different loads and solar irradiance conditions.

Description

Technical Field

[0001] This application relates to the field of solar-assisted coal-fired power generation systems, and in particular to a graded operation system and method for a solar-assisted coal-fired power generation system with integrated molten salt thermal storage. Background Technology

[0002] In existing technologies, the mainstream integrated solar-assisted coal-fired power generation scheme combines a parabolic trough solar collector system with a coal-fired unit. This involves replacing part of the steam extraction from the high-pressure heater via an oil-water heat exchanger, while simultaneously configuring a molten salt thermal storage system to recover surplus solar energy. This system mainly consists of a parabolic trough collector field, an oil-water heat exchanger, a molten salt tank, and an oil-salt heat exchanger. After heating the heat transfer oil, the parabolic trough collector field operates in parallel with the high-pressure heater via the oil-water heat exchanger, achieving a single-level steam extraction replacement. In terms of operational strategy, this scheme adopts a fixed steam extraction level replacement mode. The thermal storage system only recovers waste heat during periods of full unit load and high solar irradiance, without dynamically adjusting the operating logic based on actual changes in unit load and solar irradiance. Regarding performance optimization, related research mainly focuses on parameter optimization under steady-state conditions, such as matching the collector field area and thermal storage capacity, lacking dynamic performance optimization for wide-load, off-design conditions at 50% to 100% of rated operating conditions.

[0003] Existing technical solutions have several significant drawbacks. First, they suffer from poor load adaptability. The fixed extraction steam replacement mode leads to a substantial decrease in the work capacity of the extracted steam under partial load conditions, especially below 50% of the rated operating rate, resulting in insufficient utilization of solar energy and a significant reduction in the system's net solar power generation efficiency. Second, they lack sufficient fluctuation mitigation capabilities. The absence of a dynamic adjustment strategy to match solar irradiance fluctuations results in energy surplus and waste during periods of high solar irradiance at midday, and insufficient energy supply and large fluctuations in system efficiency during periods of low irradiance, leading to poor overall operational stability. Third, the thermal energy storage efficiency is low. Molten salt thermal energy storage systems can only recover waste heat in a simple manner and are not designed in conjunction with multi-stage extraction steam replacement. This prevents the adjustment of the temperature and flow rate of the thermal energy storage medium according to changes in unit load, limiting waste heat recovery capabilities. Furthermore, the systems lack dynamic performance support. Most research focuses on static design and steady-state analysis, failing to reveal the dynamic thermodynamic characteristics under wide-load off-design conditions, thus offering limited guidance for practical engineering applications. Furthermore, the steam extraction substitution lacks flexibility and strategies for tiered switching of extraction levels. It cannot dynamically match the extraction substitution energy level according to changes in solar irradiance and unit load, thus significantly limiting the conversion efficiency of solar energy to electricity. Summary of the Invention

[0004] In view of this, this application provides a graded operation system and method for a solar-assisted coal-fired power generation system with integrated molten salt thermal storage, which can realize the dynamic switching of extraction steam levels under different loads and solar irradiation conditions, and improve the adaptability of the solar-assisted coal-fired power generation system over a wide load range.

[0005] Specifically, this application is implemented through the following technical solution:

[0006] The first aspect of this application provides a tiered operation system for a solar-assisted coal-fired power generation system with integrated molten salt thermal energy storage, the system comprising:

[0007] A coal-fired power plant subsystem, comprising a generator, a condenser, a low-pressure heater group, a deaerator, and a high-pressure heater group, wherein the high-pressure heater group comprises a first high-pressure heater, a second high-pressure heater, and a third high-pressure heater;

[0008] The solar field subsystem includes a PTC collector field, a heat transfer oil pipeline, a molten salt thermal storage system, an oil-salt heat exchanger, an oil-water heat exchanger, and a salt-water heat exchanger.

[0009] The processing system is used to calculate the actual solar thermal energy input under the current operating conditions based on meteorological parameters, adjust the heat transfer oil flow rate of the PTC collector field and the molten salt flow rate of the molten salt storage system based on the actual solar thermal energy input, calculate the mass flow rate and pressure of each stage of extraction steam in the high-pressure heater group according to the matrix heat balance equation and the Stodola formula, determine the load under the current operating conditions, classify the load, and switch the connection relationship between the salt-water heat exchanger and each high-pressure heater in the high-pressure heater group according to the load level and the actual solar thermal energy input to achieve staged extraction steam substitution.

[0010] A second aspect of this application provides a method for the graded operation of a solar-assisted coal-fired power generation system with integrated molten salt thermal energy storage, the method comprising:

[0011] Real-time solar direct normal irradiance, ambient temperature, and wind speed are collected as meteorological parameters. These meteorological parameters are then input into the PTC collector field model to calculate the actual solar thermal energy input under the current operating conditions.

[0012] The flow rate of the heat transfer oil in the PTC collector field and the flow rate of the molten salt in the molten salt storage system are adjusted according to the actual input of solar thermal energy.

[0013] The feedwater heat exchange parameters and turbine flow characteristics parameters of the coal-fired power plant subsystem under the current operating conditions are obtained. Based on the matrix heat balance equation and the Stodola formula, the mass flow rate and pressure of the steam extracted from each stage of the first high-pressure heater, the second high-pressure heater, and the third high-pressure heater are calculated.

[0014] Based on the unit load level under the current operating conditions and the actual solar thermal energy input, and according to the mass flow rate and pressure of the steam extracted from each stage of the first high-pressure heater, the second high-pressure heater, and the third high-pressure heater, the connection relationship between the salt-water heat exchanger and the second and third high-pressure heaters is switched to achieve staged steam extraction substitution.

[0015] This application provides a graded operation system and method for a solar-assisted coal-fired power generation system with integrated molten salt thermal energy storage. Addressing the technical problems of existing solar-assisted coal-fired power generation systems, such as insufficient solar energy utilization under wide load conditions, unstable system efficiency due to irradiance fluctuations, lack of dynamic matching for steam extraction substitution, poor synergy between molten salt thermal energy storage and multi-stage steam extraction, and insufficient research on dynamic performance under off-design conditions, the key idea is to implement graded steam extraction substitution based on load and solar thermal energy input as the core control criteria. This is achieved by setting up a coal-fired power plant subsystem including a three-stage high-pressure heater, a solar field subsystem integrating a PTC collector field, multiple types of heat exchangers, and a molten salt thermal energy storage system, and combining it with a processing system capable of meteorological parameter analysis, dynamic adjustment of medium flow rate, calculation of steam extraction parameters, load grading, and switching of the connection relationship between heat exchangers and high-pressure heaters. The processing system first... Meteorological parameters are used to calculate the actual solar thermal energy input. The flow rates of heat transfer oil and molten salt are simultaneously adjusted to maintain the system's thermodynamic balance. Then, extraction parameters at each stage are calculated using professional formulas to complete load classification. Finally, the connection relationship between the salt-water heat exchanger and each high-pressure heater is dynamically switched according to the load level and solar thermal energy input. This achieves synergistic substitution of molten salt thermal storage and multi-stage extraction, as well as dynamic switching of extraction substitution levels. This effectively improves the solar energy utilization rate and net solar power generation efficiency over a wide load range, smooths system efficiency fluctuations caused by solar irradiance fluctuations, enhances the flexibility of extraction substitution and system operational stability, and fully leverages the waste heat recovery and fluctuation smoothing effects of molten salt thermal storage. It accurately matches the thermodynamic parameters of each system component, reveals the system's dynamic thermodynamic performance under non-design conditions, and provides effective technical support for the dynamic operation of actual engineering projects. Attached Figure Description

[0016] Figure 1 A schematic diagram of the structure of a first embodiment of the tiered operation system of the solar-assisted coal-fired power generation system with integrated molten salt thermal storage provided in this application;

[0017] Figure 2 A schematic diagram of the structure of a coal-fired power plant subsystem and a solar field subsystem shown as exemplary embodiments of this application;

[0018] Figure 3 The flowchart is a second embodiment of the graded operation method of the solar-assisted coal-fired power generation system with integrated molten salt thermal storage provided in this application.

[0019] Explanation of reference numerals in the attached figures:

[0020] 1: Coal-fired power plant subsystem;

[0021] 2: Solar energy field subsystem;

[0022] 11: Low-pressure heater assembly;

[0023] 12: High-pressure heater assembly;

[0024] HP1: First high-pressure heater;

[0025] HP2: Second high-pressure heater;

[0026] HP3: Third high-pressure heater;

[0027] Ex1: Oil-water heat exchanger;

[0028] Ex2: Oil-salt heat exchanger;

[0029] Ex3: Salt-water heat exchanger;

[0030] PTC: PTC thermal field. Detailed Implementation

[0031] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0032] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used herein are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0033] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information.

[0034] The following specific embodiments are given to illustrate the technical solution of this application in detail.

[0035] Figure 1 This is a schematic diagram of the first embodiment of the tiered operation system of the integrated molten salt thermal storage solar-assisted coal-fired power generation system provided in this application. Please refer to... Figure 1The system provided in this embodiment includes:

[0036] The coal-fired power plant subsystem 1 includes a generator, a condenser, a low-pressure heater group 11, a deaerator EDA, and a high-pressure heater group 12. The high-pressure heater group includes a first high-pressure heater HP1, a second high-pressure heater HP2, and a third high-pressure heater HP3.

[0037] Solar field subsystem 2, which includes PTC collector field PTC, heat transfer oil pipeline, molten salt thermal storage system, oil-salt heat exchanger Ex2, oil-water heat exchanger Ex1 and salt-water heat exchanger Ex3;

[0038] The processing system is used to calculate the actual solar thermal energy input under the current operating conditions based on meteorological parameters, adjust the heat transfer oil flow rate of the PTC collector field and the molten salt flow rate of the molten salt storage system based on the actual solar thermal energy input, calculate the mass flow rate and pressure of each stage of extraction steam in the high-pressure heater group according to the matrix heat balance equation and the Stodola formula, determine the load under the current operating conditions, classify the load, and switch the connection relationship between the salt-water heat exchanger and each high-pressure heater in the high-pressure heater group according to the load level and the actual solar thermal energy input to achieve staged extraction steam substitution.

[0039] Specifically, Figure 2 The schematic diagrams of the coal-fired power plant subsystem and the solar field subsystem shown in this exemplary embodiment are provided in the appendix. Figure 1 and Figure 2 The system consists of three core parts: a coal-fired power plant subsystem, a solar energy field subsystem, and a processing system. These three systems work together in a coordinated manner. The coal-fired power plant subsystem is the basic power generation unit, the solar energy field subsystem is the auxiliary heat collection and storage unit, and the processing system is the core control unit. Through the precise connection and functional coordination of each component, the system achieves efficient coupling between solar energy and coal-fired power generation, as well as staged steam extraction substitution based on load and solar irradiance.

[0040] Furthermore, the coal-fired power plant subsystem includes a generator, condenser, low-pressure heater group, deaerator, and high-pressure heater group, along with conventional coal-fired power generation equipment such as a steam turbine, boiler, and economizer. Internally, it follows the classic thermodynamic cycle connection logic of coal-fired power generation. The high-temperature and high-pressure steam generated by the boiler enters the steam turbine for expansion and work. The steam turbine drives the generator to complete the conversion of mechanical energy into electrical energy. The exhaust steam after the steam turbine has done work is discharged into the condenser for cooling into condensate. The condensate then enters the low-pressure heater group for initial heating. The heated water then enters the deaerator to remove dissolved oxygen, ensuring corrosion-free operation of subsequent equipment. The deaerated feedwater enters the high-pressure heater group. The first, second, and third high-pressure heaters in the high-pressure heater group are connected in series and heated to the set temperature by different levels of steam extraction from the steam turbine. Finally, the water enters the economizer and boiler to complete the water circulation, forming a closed-loop thermodynamic power generation cycle.

[0041] Furthermore, the coal-fired power plant subsystem uses a steam turbine and generator as its core power source. The exhaust steam from the low-pressure cylinder enters the condenser and condenses into water. After being heated by the low-pressure heater group, it is sent to the deaerator for deoxygenation. Then, the feedwater pump pressurizes the water and heats it by the high-pressure heater group before finally sending it to the boiler to form main steam that drives the steam turbine to do work. The steam extracted by the steam turbine provides heat sources for the low-pressure heater group, the deaerator, and the high-pressure heater group, forming a complete thermodynamic cycle and energy conversion system.

[0042] Furthermore, the high-pressure heater group heats the feedwater by extracting steam from the steam turbine, and is the direct target for the extraction steam replacement of the solar field subsystem. The three-stage high-pressure heater corresponds to the extraction steam of different energy levels of the steam turbine, providing an energy level matching basis for staged extraction steam replacement.

[0043] Furthermore, the solar field subsystem is the core unit of solar-assisted systems, including PTC collector fields, heat transfer oil pipelines, molten salt thermal storage systems, oil-salt heat exchangers (OSHE), oil-water heat exchangers (OWHE), and salt-water heat exchangers (SWHE). It forms a parallel coupling relationship with the coal-fired power plant subsystem, and the internal components also follow the logic of heat collection → heat exchange / heat storage → re-heat exchange in series / parallel.

[0044] Furthermore, the PTC collector field is connected to the OWHE and OSHE via heat transfer oil pipelines. The heat transfer oil, as the heat transfer medium, is heated by solar energy in the PTC collector field. Part of it directly enters the OWHE for heat exchange, while the other part enters the OSHE to exchange heat with molten salt. The molten salt thermal storage system is connected to the OSHE and SWHE. The low-temperature molten salt in the cold tank enters the OSHE to absorb the heat from the heat transfer oil and becomes high-temperature molten salt, which is then stored in the hot tank. The high-temperature molten salt in the hot tank enters the SWHE for heat exchange as needed. After heat exchange, the cooled molten salt flows back to the cold tank, forming a closed-loop molten salt thermal storage cycle. The heat transfer oil pipeline serves as the heat transfer medium transportation channel for the entire solar field subsystem, ensuring the circulation of heat transfer oil between the PTC collector field, OWHE, and OSHE.

[0045] Furthermore, the solar energy subsystem uses a PTC collector as its heat source. Heat transfer oil flows through the oil pipeline into the PTC collector to absorb solar heat and reach the set outlet temperature. It then flows into an oil-water heat exchanger to exchange heat with the feedwater. Excess heat is transferred to the molten salt storage system via an oil-salt heat exchanger. The hot salt then heats the feedwater in the salt-water heat exchanger to reach the temperature required for the original high-pressure heater outlet. As an external heat source for the coal-fired power plant system, the solar energy subsystem bypasses the feedwater that originally entered the high-pressure feedwater heater and heats it to reach the economizer inlet feedwater temperature, thus replacing the original extraction steam heating method. This is achieved by connecting the oil-water heat exchanger in parallel with the first-stage high-pressure feedwater heater and the salt-water heat exchanger in parallel with the second and third-stage high-pressure feedwater heaters.

[0046] Furthermore, the solar energy subsystem and the coal-fired power plant subsystem are coupled in parallel via the feedwater side, including:

[0047] The oil-water heat exchanger and the brine-water heat exchanger are connected in parallel with the high-pressure heater group; the solar energy subsystem serves as the external heat source for the coal-fired power plant subsystem. It bypasses the feedwater branch of the corresponding high-pressure heater through the oil-water heat exchanger and the brine-water heat exchanger, using solar thermal energy to replace the steam extracted from the turbine to heat the feedwater, so that the feedwater temperature matches the feedwater temperature at the economizer inlet.

[0048] Specifically, the solar energy collected by the parabolic trough solar collector is converted into high-temperature heat energy in the heat transfer oil. Part of this heat is directly used to heat the bypass feedwater via an oil-water heat exchanger, while the other part is stored in molten salt and used to heat the bypass feedwater via a salt-water heat exchanger as needed. This connection method saves the steam that would otherwise have been extracted from the turbine to heat the feedwater. The replaced extracted steam can continue to expand and do work within the turbine, thereby increasing the generator's output power. During this process, by precisely controlling the heat exchanger outlet parameters, the feedwater temperature after parallel mixing is ensured to be strictly consistent with the economizer inlet temperature when heated only by the high-pressure heater. This achieves efficient and seamless conversion of solar energy into electrical energy without interfering with the boiler and turbine's main operating boundary conditions.

[0049] On the one hand, by using a parallel structure on the feedwater side, the solar thermal utilization process is deeply coupled yet physically isolated from the thermal cycle of the coal-fired unit. Solar energy serves only as an external alternative heat source to preheat the feedwater, without requiring modifications to the coal-fired boiler and turbine structure, resulting in low modification costs and high operational safety. On the other hand, by replacing high-pressure steam extraction, the steam's work capacity is directly improved, allowing the solar energy conversion efficiency to break through the Rankine cycle limitations of traditional solar thermal power generation. Instead, higher thermal-to-power efficiency is achieved through the high-efficiency turbines of large-capacity coal-fired units. Without reducing the safety margin and peak-shaving capacity of the original units, the coal consumption and carbon emissions of the coal-fired units are effectively reduced, and the capacity for renewable energy absorption is enhanced.

[0050] Furthermore, the processing system is an intelligent control unit without physical pipeline connections. It establishes data connections with the coal-fired power plant subsystem (high-pressure heater group, steam turbine, load detection module) and the solar field subsystem (PTC collector field, molten salt thermal storage system, OWHE, SWHE) through various sensors and data transmission modules. At the same time, it controls the operating parameters and component connection relationships of the two major subsystems through actuators (flow regulating valve, heat exchanger bypass regulating valve, valve switch, etc.).

[0051] Furthermore, meteorological parameters such as direct solar irradiance, ambient temperature, and wind speed are collected. Based on the heat collection efficiency model of the PTC collector field, the actual solar thermal energy input under the current operating conditions is calculated, providing a basic data basis for all subsequent control operations. According to the calculated actual solar thermal energy input, the flow rate of the heat transfer oil in the PTC collector field is proportionally adjusted through the flow regulating valve to maintain a constant outlet temperature of the heat transfer oil in the PTC collector field, ensuring the heat exchange efficiency of the OWHE. At the same time, the molten salt flow rate of the molten salt thermal storage system is adjusted synchronously to match the flow rate of the heat transfer oil, ensuring the heat exchange efficiency of the oil-salt heat exchanger and maintaining the thermodynamic balance of the heat collection, heat exchange, and thermal storage systems. The matrix heat balance equation and Stodola formula are called, combined with the current unit operating parameters, to calculate in real time the corresponding high-pressure heaters in the high-pressure heater group. The system collects the mass flow rate and pressure of each extraction steam level to clarify the current working capacity of each extraction steam level, providing data support for energy level matching of extraction steam substitution; it collects parameters such as turbine output and generator power of the coal-fired power plant subsystem in real time to determine the actual operating load of the unit and classifies the load according to preset standards to clarify the current load conditions; based on the load level and the actual input of solar thermal energy, it dynamically switches the connection relationship between SWHE and the second and third high-pressure heaters (connected in parallel with the second high-pressure heater HP2 alone / connected in parallel with the third high-pressure heater HP3 alone / connected in parallel with both the second and third high-pressure heaters HP2 and HP3 simultaneously) by opening and closing the heat exchanger bypass regulating valve, while maintaining the stable parallel connection between OWHE and the first high-pressure heater, thus achieving flexible switching of extraction steam substitution levels.

[0052] Furthermore, the coal-fired power plant subsystem serves as the foundation, maintaining the thermodynamic cycle of conventional coal-fired power generation and providing a ready-made thermodynamic architecture and coupling nodes for solar assisted generation. The solar field subsystem collects solar energy through a PTC collector field, achieving direct steam extraction substitution via OWHE, and indirect steam extraction substitution via molten salt thermal storage system and SWHE, maximizing the utilization of solar energy. The processing system, as the core of regulation, integrates and analyzes multi-dimensional data such as meteorological parameters, solar thermal energy, unit load, and steam extraction parameters. By dynamically adjusting the medium flow rate and switching the heat exchanger connection relationship, it ensures that the steam extraction substitution of the solar field subsystem is always adapted to the operating conditions of the coal-fired power plant subsystem. Ultimately, this solves the problems of insufficient solar energy utilization, lack of flexibility in steam extraction substitution, and the impact of irradiance fluctuations on system stability in traditional systems, achieving efficient and coordinated operation over a wide load range.

[0053] Optionally, the connection structure between the brine-water heat exchanger and the high-pressure heater group includes a first parallel branch and a second parallel branch. The first parallel branch connects the water outlet of the brine-water heat exchanger to the water inlet of the second high-pressure heater, and a first switching valve group is provided on the first parallel branch. The second parallel branch connects the water outlet of the brine-water heat exchanger to the water inlet of the third high-pressure heater, and a second switching valve group is provided on the second parallel branch.

[0054] Specifically, the brine-water heat exchanger, as a key heat exchange device in the molten salt thermal storage system for releasing heat to the feedwater of the coal-fired unit, does not have its feedwater outlet directly connected to a single feedwater header. Instead, it is divided into two independent parallel branches. The first parallel branch starts at the feedwater outlet of the brine-water heat exchanger and ends at the feedwater inlet of the second high-pressure heater. A first switching valve assembly is installed on this branch to control its opening and closing. The second parallel branch also starts at the feedwater outlet of the brine-water heat exchanger, but ends at the feedwater inlet of the third high-pressure heater. A second switching valve assembly is installed on this branch to independently control its on / off state.

[0055] With the above arrangement, the solar-heated feedwater can be guided to different inlet locations depending on the opening and closing combinations of the first and second switching valve groups. When only the second switching valve group is open, the feedwater heated by the brine-water heat exchanger flows directly into the feedwater inlet of the third high-pressure heater, merging with the existing feedwater that has not been bypassed, thus introducing solar heat into the heating stage corresponding to the third-stage extraction steam. When only the first switching valve group is open, the heated feedwater bypasses the third high-pressure heater and is directly sent to the feedwater inlet of the second high-pressure heater, introducing solar heat into the heating stage corresponding to the second-stage extraction steam. When both switching valve groups are open, the heated feedwater is simultaneously delivered to the feedwater inlets of both the second and third high-pressure heaters, achieving coordinated sharing of the heating tasks for the two-stage extraction steam. This dual-branch structure with independent valve groups provides a flexible distribution path for the flow of heat at the brine-water heat exchanger outlet, enabling the same heat exchange equipment to serve the inlets of high-pressure heaters of different pressure levels.

[0056] Optionally, the molten salt outlet of the oil-salt heat exchanger is connected to the inlet of the hot tank of the molten salt thermal storage system, the outlet of the hot tank of the molten salt thermal storage system is connected to the molten salt side inlet of the salt-water heat exchanger, the feedwater side inlet and outlet of the salt-water heat exchanger are respectively connected to the feedwater bypass of the high-pressure heater group, and the stepwise increase in the outlet molten salt temperature of the oil-salt heat exchanger matches the feedwater inlet temperature range of the second high-pressure heater and the third high-pressure heater.

[0057] Specifically, on the heat input side of the molten salt, the oil-salt heat exchanger transfers the solar thermal energy carried by the heat transfer oil to the molten salt. Its molten salt outlet is directly connected to the inlet of the heat tank in the molten salt thermal storage system, allowing the molten salt, heated by the oil-salt heat exchanger, to flow into the heat tank for storage immediately. This stores the collected solar energy in the form of high-temperature sensible heat from the molten salt within the thermal storage system. On the heat release side of the molten salt, the outlet of the heat tank in the molten salt thermal storage system is connected to the molten salt side inlet of the salt-water heat exchanger. When the system needs to utilize the stored heat, high-temperature molten salt is drawn from the heat tank and pumped into the molten salt side flow channel of the salt-water heat exchanger as a heat source for heating the feedwater. The salt-water heat exchanger is a partitioned heat exchange structure, with its molten salt side and feedwater side independent of each other. Heat is transferred from the molten salt to the feedwater through the heat exchange walls.

[0058] Furthermore, the feedwater inlet and outlet of the brine-water heat exchanger are connected to the feedwater bypass of the high-pressure heater group. Specifically, a portion of the feedwater is drawn from the main feedwater path into the feedwater inlet of the brine-water heat exchanger, where it absorbs the heat released by the molten salt, causing its temperature to rise. The water then returns from the feedwater outlet to the corresponding feedwater inlet of the high-pressure heater group. This connection method allows the brine-water heat exchanger to operate in parallel with the existing high-pressure heater. The bypass feedwater heated by solar energy mixes with the feedwater flowing through the high-pressure heater at the corresponding heater inlet, jointly maintaining the feedwater temperature of the subsequent heated surfaces.

[0059] Furthermore, when the system operates under conditions requiring the intervention of a second high-pressure heater, the outlet molten salt temperature of the oil-salt heat exchanger is raised to a level compatible with the feedwater inlet temperature of the second high-pressure heater; when the system operates under conditions requiring the intervention of a third high-pressure heater, the outlet molten salt temperature is at a lower level coordinated with the feedwater inlet temperature of the third high-pressure heater; and when both stages of heaters are required to work together, the outlet molten salt temperature is set to an intermediate value. This correspondence between the temperature gradient and the heater temperature range ensures that the temperature of the molten salt flowing out of the hot tank is always reasonably matched in terms of energy level to the feedwater temperature requirement of the high-pressure heater connected in parallel with the salt-water heat exchanger, avoiding energy loss or redundant heat exchange area due to excessively large or small heat transfer temperature differences.

[0060] Furthermore, the steps for calculating the actual solar thermal energy input under the current operating conditions based on meteorological parameters include:

[0061] (1) Collect solar direct normal irradiance, ambient temperature and wind speed as meteorological parameters and input them into the PTC collector field model;

[0062] Specifically, the target parameters for collection are determined to be direct solar normal irradiance, ambient temperature, and wind speed. Each parameter is collected in real time through corresponding monitoring equipment, and the collected meteorological parameters are input into the preset parabolic trough solar collector model according to the preset data format.

[0063] Furthermore, the core meteorological parameters required for this system are identified as direct solar irradiance, ambient temperature, and wind speed. These three parameters are key meteorological factors affecting the heat collection efficiency and thermal energy conversion of the parabolic trough solar collector, providing fundamental data support for subsequent thermodynamic calculations. Parameters are collected using specialized monitoring equipment deployed around the parabolic trough solar collector and within the collector area. A solar radiation monitor is used to collect real-time direct solar irradiance, an ambient temperature sensor is used to collect real-time ambient temperature around the collector area, and a wind speed sensor is used to collect real-time wind speed in the collector area. All monitoring equipment continuously collects data at a preset frequency to ensure the real-time nature and accuracy of the parameters. The collected real-time data on direct solar irradiance, ambient temperature, and wind speed are processed and converted according to the preset digital format and data transmission protocol of the parabolic trough solar collector model. The processed meteorological parameters are then completely input into the model through the data transmission module, ensuring that the model can directly access this data for subsequent calculations.

[0064] (2) Based on the fixed design parameters of the PTC collector field, the actual solar thermal energy input converted by the PTC collector field under the current operating conditions is obtained by combining the thermodynamic calculation model with the meteorological parameters.

[0065] Specifically, the fixed design parameters of the parabolic trough solar collector are retrieved, a thermodynamic calculation model adapted to the collector is built, meteorological parameters are substituted into the thermodynamic calculation model, and thermodynamic iterative calculations are performed through the model in combination with the fixed design parameters to obtain the actual solar thermal energy input converted by the parabolic trough solar collector under the current operating conditions.

[0066] Furthermore, the fixed design parameters of the parabolic trough solar collector are retrieved. These parameters are inherent parameters determined during the design phase and do not change with operating conditions. Specifically, they include core design parameters such as the collector aperture area, the arrangement of the solar collector, the type of heat transfer fluid, the inlet design temperature of the heat transfer fluid, the collector's heat collection efficiency design coefficient, and the heat loss coefficient of the solar collector's pipes. All parameters are completely retrieved from the system database and verified to ensure accuracy. Next, a thermodynamic calculation model adapted to the parabolic trough solar collector is built. This model is based on the fundamental laws of heat transfer and thermodynamics, fully integrating the heat collection characteristics of the parabolic trough solar collector, the heat transfer characteristics of the heat transfer medium, and the heat loss characteristics of the solar collector. It can accurately reflect the quantitative relationship between meteorological parameters, fixed design parameters, and solar thermal energy conversion. Then, the meteorological parameters are simultaneously substituted into the model. In the completed thermodynamic calculation model, the calculation data was fully imported. The model, combined with the imported real-time meteorological parameters and the retrieved fixed design parameters, carried out multi-dimensional thermodynamic iterative calculations. During the calculation process, the influence of direct solar irradiance on the heat collection intensity, the influence of ambient temperature on the heat dissipation of the heat collection field, and the influence of wind speed on the convective heat loss of the heat collection field were fully considered. At the same time, the effective heat collection area was calculated by combining the collector aperture area, and the actual heat absorption of the heat transfer medium was calculated by combining the inlet temperature of the heat transfer fluid. Various heat losses, such as heat loss in the heat collection field pipelines and heat loss in the collector, were deducted. Through multiple iterative calculations, accurate calculation results were obtained. The calculation results are the actual solar thermal energy input obtained by the parabolic trough heat collection field through solar thermal conversion under the current actual operating conditions, which can be actually input into the subsequent heat exchange and thermal storage system. This provides the core quantitative basis for the subsequent flow adjustment and steam extraction substitution control of the system.

[0067] By collecting meteorological parameters in real time and inputting them into the parabolic trough solar collector model, and combining them with the inherent fixed design parameters of the solar collector, targeted solutions can be obtained based on the thermodynamic calculation model. This allows for accurate and real-time determination of the actual solar thermal energy input converted by the solar collector under the current operating conditions. It fully considers the actual impact of meteorological conditions on the solar collector process, and the design characteristics of the solar collector itself ensure the consistency and accuracy of the calculation results. This provides accurate and reliable basic data support for the subsequent system to dynamically adjust the flow rate of heat transfer oil and molten salt and match the extraction steam substitution level according to the actual solar energy input. It effectively avoids the problem of inaccurate system control caused by the deviation in the calculation of solar energy input, and ensures the efficient and accurate implementation of the hierarchical operation strategy of the solar-assisted coal-fired power generation system from the data source.

[0068] Furthermore, the steps for adjusting the flow rate of the heat transfer oil in the PTC collector field based on the actual solar thermal energy input include:

[0069] (1) Determine the real-time fluctuation of direct solar irradiance based on the actual solar thermal energy input;

[0070] Specifically, a quantitative correlation is established between the actual solar thermal energy input and the direct normal solar irradiance. The actual solar thermal energy input obtained in real time is substituted into the correlation, and the real-time fluctuation trend and fluctuation amplitude of the direct normal solar irradiance are determined through data comparison and analysis.

[0071] Furthermore, based on the fixed design parameters and thermodynamic calculation model of the PTC collector field, a quantitative correlation between the actual solar thermal energy input and the direct normal solar irradiance is established in advance. This correlation eliminates the interference of other meteorological parameters such as ambient temperature and wind speed, and clarifies the impact of a single change in direct normal solar irradiance on the actual solar thermal energy input, providing a quantitative basis for irradiance fluctuation judgment. The actual solar thermal energy input under the current operating conditions is substituted into the preset quantitative correlation, and historical data on the actual solar thermal energy input over continuous periods are retrieved to form a data sequence. By comparing and analyzing the difference and rate of change between the real-time actual solar thermal energy input and historical data, and by reverse derivation using the quantitative correlation, the real-time fluctuation trend of direct normal solar irradiance is accurately determined, i.e., whether the irradiance is increasing, decreasing, or stable. At the same time, the specific fluctuation amplitude is calculated, clearly understanding the dynamic changes in irradiance, and providing a clear direction and amplitude reference for subsequent flow rate adjustments.

[0072] (2) Adjust the flow rate of the heat transfer oil proportionally according to the real-time fluctuation to maintain the temperature of the heat transfer oil at the outlet of the PTC collector field at a preset value.

[0073] Specifically, a target temperature value for the heat transfer oil at the outlet of the PTC collector field is preset, a direct proportional control relationship is established between the fluctuation range of direct solar irradiance and the adjustment amount of heat transfer oil flow rate, the actual circulation flow rate of heat transfer oil is adjusted according to the real-time fluctuation of irradiance, and the outlet heat transfer oil temperature is monitored in real time and fine-tuned to keep the temperature stable at the preset value.

[0074] Furthermore, based on the design standards of the PTC collector field and the temperature matching requirements of subsequent heat exchange components, a fixed target temperature value for the heat transfer oil at the PTC collector field outlet is preset. This preset value is the optimal temperature to ensure efficient heat exchange in subsequent oil-water and oil-salt heat exchangers, and is the core objective of flow control. Combining the heat collection characteristics of the PTC collector field and the heat transfer characteristics of the heat transfer oil, a direct proportional control relationship is established between the fluctuation amplitude of direct solar irradiance and the adjustment amount of heat transfer oil flow rate. That is, the greater the irradiance fluctuation amplitude, the proportional increase in the adjustment amount of heat transfer oil flow rate ensures the accuracy and adaptability of flow rate adjustment. Based on the real-time fluctuation trend and amplitude of direct solar irradiance, and according to this direct proportional control relationship, the flow rate is adjusted through the flow regulating valve. The actual circulation flow rate of the heat transfer oil in the PTC collector field is adjusted accordingly. If the irradiation is enhanced, the heat transfer oil flow rate is increased proportionally to accelerate the circulation speed of the heat transfer medium and prevent the heat transfer oil from overheating due to excessive heat absorption. If the irradiation is weakened, the heat transfer oil flow rate is reduced proportionally to decrease the circulation speed of the heat transfer medium and ensure that the heat transfer oil can fully absorb solar energy to reach the target temperature. If the irradiation is stable, the heat transfer oil flow rate is kept constant. Finally, the temperature of the heat transfer oil at the outlet of the PTC collector field is monitored in real time by a temperature sensor. The monitored value is compared with the preset value. If there is a slight deviation, the heat transfer oil flow rate is slightly adjusted to achieve precise temperature control and ensure that the outlet heat transfer oil temperature is always kept stable at the preset value, thus ensuring the stable operation of subsequent heat exchange links.

[0075] By back-calculating the real-time fluctuations of direct solar irradiance from the actual solar thermal energy input, and adjusting the heat transfer oil flow rate proportionally to these fluctuations, the dynamic changes in solar irradiance can be precisely matched. This ensures that the heat transfer oil temperature at the PTC collector outlet remains stable at a preset value, avoiding both overheating issues caused by enhanced irradiance and insufficient temperature due to weakened irradiance. This guarantees the parameter stability of the collector's output heat energy, providing a constant heat source foundation for the efficient heat exchange of subsequent oil-water and oil-salt heat exchangers. By controlling the balance of system thermodynamic parameters at the collector stage, problems such as reduced efficiency of subsequent steam extraction replacement and mismatch between heat storage and heat exchange caused by fluctuations in heat transfer oil temperature are avoided, thus laying a solid parameter foundation for the stable implementation of staged steam extraction replacement.

[0076] Furthermore, the steps for adjusting the molten salt flow rate of the molten salt thermal storage system based on the actual solar thermal energy input include:

[0077] (1) Determine the fluctuation state of direct solar irradiance and load conditions based on the actual solar thermal energy input, and determine the preset temperature value of the molten salt at the outlet of the oil-salt heat exchanger;

[0078] Specifically, based on the actual solar thermal energy input, the fluctuation state of direct solar irradiance is derived, the current load condition of the unit is determined, and the adaptability requirements of irradiance fluctuation state and load condition are combined with the preset molten salt temperature gradient standard to determine the target preset temperature value of the molten salt at the outlet of the oil-salt heat exchanger.

[0079] Furthermore, by combining the quantitative correlation between the actual solar thermal energy input and the direct normal solar irradiance, the real-time fluctuation state of irradiance is derived, clarifying whether the irradiance is increasing, decreasing, stable, or in a high irradiance surplus or low irradiance deficiency stage. Simultaneously, based on the linkage between the actual solar thermal energy input and the unit load, combined with operating parameters such as unit output and power generation, the specific load condition of the current unit is accurately determined, clarifying whether it is a full load, medium load, or low load condition. Secondly, the system has pre-established corresponding molten salt temperature gradient standards based on the feedwater heating requirements of the coal-fired power plant subsystems under different load conditions and the solar energy utilization requirements under different irradiance fluctuation states. These standards clarify the temperature range that the molten salt at the oil-salt heat exchanger outlet must reach under various load conditions and irradiance fluctuation states, ensuring energy level matching for subsequent molten salt thermal storage and multi-stage steam extraction substitution. The determined irradiance fluctuation state is combined and matched with the load conditions. By comparing with the preset molten salt temperature gradient standard, a unique target molten salt temperature value at the outlet of the oil-salt heat exchanger is selected as the core control indicator for subsequent molten salt flow adjustment, ensuring that the molten salt temperature is highly adapted to the current system operating conditions.

[0080] (2) Based on the logic of matching the molten salt flow rate with the heat transfer oil flow rate, adjust the molten salt flow rate to ensure that the molten salt temperature at the outlet of the oil-salt heat exchanger reaches the preset value.

[0081] Specifically, a dynamic matching logic is established between the molten salt flow rate and the heat transfer oil flow rate. The actual flow rate of the adjusted heat transfer oil is obtained in real time. The theoretical adjustment value of the molten salt flow rate is calculated based on the matching logic. The molten salt circulation flow rate is adjusted according to the theoretical adjustment value. The molten salt temperature at the outlet of the oil-salt heat exchanger is monitored in real time and closed-loop fine-tuning is performed to ensure that the temperature reaches the preset value.

[0082] Furthermore, based on fundamental laws of heat transfer and considering the heat transfer area, heat transfer coefficient, and heat transfer characteristics of the oil-salt heat exchanger, as well as the molten salt and heat transfer oil flow rates, the system establishes a dynamic matching logic for molten salt and heat transfer oil flow rates. This dynamic matching logic clarifies the corresponding molten salt flow rate required to achieve specific heat exchange effects under different heat transfer oil flow rates. The core principle is to match the heat absorption of the molten salt with the heat release of the heat transfer oil, ensuring thermodynamic balance in the heat exchange process. The system acquires the actual circulating flow rate of the heat transfer oil in real time, adjusted according to irradiation fluctuations. This actual circulating flow rate is then substituted into the preset dynamic matching logic for molten salt and heat transfer oil flow rates. Through thermodynamic calculations, the theoretical adjustment value of the molten salt flow rate required to reach the preset temperature at the outlet of the oil-salt heat exchanger under the current operating conditions is obtained. The flow regulating valve of the molten salt thermal storage system is used to adjust the actual circulation flow rate of the molten salt according to the calculated theoretical adjustment value. If the heat transfer oil flow rate increases, the molten salt flow rate is increased proportionally to enhance the heat absorption of the molten salt; if the heat transfer oil flow rate decreases, the molten salt flow rate is decreased proportionally to avoid insufficient or excessive heat absorption by the molten salt. The molten salt temperature at the outlet of the oil-salt heat exchanger is monitored in real time by a temperature sensor. The monitored actual temperature is compared with the preset temperature value in real time. If there is a deviation, the molten salt flow rate is finely adjusted in a closed loop based on the above matching logic until the outlet molten salt temperature accurately reaches the preset value. This ensures that the heat quality of the molten salt thermal storage matches the heat exchange requirements of the subsequent salt-water heat exchanger, providing a stable molten salt heat source for multi-stage steam extraction replacement.

[0083] By combining the actual solar thermal energy input to determine the fluctuation state of direct normal solar irradiance and the unit load conditions, and based on this, the preset temperature value of the molten salt at the oil-salt heat exchanger outlet is precisely set. Relying on the logic of matching the molten salt flow rate with the heat transfer oil flow rate, the molten salt temperature can be highly adapted to the current irradiance conditions and load requirements of the system. This accurately ensures that the molten salt temperature at the oil-salt heat exchanger outlet reaches the preset value, achieving a balance in heat exchange between the heat transfer oil and the molten salt. It not only fully absorbs the surplus solar heat, but also provides a stable molten salt heat source with temperature matching for subsequent molten salt thermal storage and salt-water heat exchange according to different operating conditions. This ensures the synergy between molten salt thermal storage and multi-stage steam extraction replacement, avoiding problems such as insufficient waste heat recovery and mismatch of steam extraction replacement energy levels caused by molten salt temperature deviations. It further improves the system's adaptability to irradiance fluctuations and load changes, providing stable thermal storage end temperature support for the efficient implementation of staged steam extraction replacement.

[0084] Furthermore, the steps for calculating the mass flow rate and pressure of each stage of steam extraction in the high-pressure heater group based on the matrix heat balance equation and the Stodola formula include:

[0085] (1) Obtain the feedwater flow rate, feedwater temperature and heat exchange parameters of the high-pressure heater group of the coal-fired power plant subsystem under the current operating conditions, and establish the matrix heat balance equation of the high-pressure heater group based on the feedwater flow rate, feedwater temperature and heat exchange parameters;

[0086] Specifically, the feedwater flow rate and temperature of the coal-fired power plant subsystem, as well as the heat exchange parameters of the high-pressure heater group, are collected in real time under the current operating conditions. Data verification and standardization are performed on various collected parameters. Based on the basic laws of thermodynamic heat balance, a matrix heat balance equation adapted to the high-pressure heater group is constructed by combining the processed parameters.

[0087] Furthermore, core operating parameters are acquired in real time through flow sensors, temperature sensors, and heat exchange parameter monitoring modules within the coal-fired power plant subsystem. Feedwater flow rate refers to the actual circulating flow rate of feedwater entering the high-pressure heater group; feedwater temperature includes the real-time temperatures of feedwater entering and exiting each stage of the high-pressure heater; and heat exchange parameters of the high-pressure heater group cover inherent and condition-specific heat exchange indices such as heat exchange area, heat transfer coefficient, terminal temperature difference, and heat dissipation coefficient of each stage of the high-pressure heater. All parameters are collected at a preset system frequency to ensure data real-time performance and completeness. All collected parameters undergo data verification and standardization, eliminating outliers and filling in missing values. Simultaneously, parameters from different units of measurement and data formats are uniformly converted to a standard format for thermodynamic calculations, ensuring that the parameters can be directly used for equation construction and avoiding the impact of data errors on equation accuracy. According to the fundamental law of thermodynamic heat balance, in a high-pressure heater group, the heat released by the steam extracted from the turbine and the heat absorbed by the feedwater remain in balance after deducting heat dissipation losses. Combining the series heat exchange structure of the high-pressure heater group, feedwater flow rate and feedwater temperature are used as variables in the heat balance equation, and heat exchange parameters are used as fixed coefficients in the equation. A matrix heat balance equation for the high-pressure heater group is constructed. This equation accurately reflects the quantitative relationship between the heat released by the steam extracted from each stage of the high-pressure heater, the heat absorbed by the feedwater, and various parameters in matrix form, and can intuitively reflect the heat balance relationship of the entire high-pressure heater group.

[0088] Furthermore, in the constructed hybrid system, integrating solar thermal energy into the CFPP inevitably leads to changes in the mass flow rate and thermal parameters of the steam extracted from each stage of the original turbine. To analyze and calculate this change, a matrix thermal balance equation method was employed:

[0089] ;

[0090] in, yes ( The steam turbine extraction mass flow rate (kg / s) of the feedwater heater; yes The enthalpy increment (kJ / kg) of 1 kg of feedwater in the feedwater heater; express The heat released by 1 kg of steam extracted from the turbine in the feedwater heater (kJ / kg); express Enthalpy drop (kJ / kg) of 1 kg of wastewater in a water heater.

[0091] , and The following formula can be used for calculation:

[0092] ;

[0093] ;

[0094] ;

[0095] in, and They represent Enthalpy (kJ / kg) of 1 kg of feedwater at the outlet and inlet of the feedwater heater; for The enthalpy (kJ / kg) of steam extracted from the turbine in the feedwater heater; and Represent The enthalpy (kJ / kg) of 1 kg of wastewater discharged from the outlet and inlet of the water heater.

[0096] (2) The Stodola formula is introduced by combining the flow characteristics parameters of the steam turbine unit, and the matrix heat balance equation is solved to obtain the mass flow rate and pressure of each stage of steam extraction in each high-pressure heater.

[0097] Specifically, the flow characteristic parameters of the steam turbine unit are retrieved and substituted into the Stodola formula to complete the formula adaptation. The adapted Stodola formula is then combined with the matrix heat balance equation. The combined equations are iteratively solved using numerical calculation methods to finally obtain the mass flow rate and pressure of each stage of steam extraction for each high-pressure heater.

[0098] Furthermore, the Stodola formula (Stodola's conic law) is the core formula for calculating steam turbines under non-design conditions (variable load, variable radiation adaptation conditions). It is also often referred to as the elliptic law. It is a classic formula describing the flow characteristics of multi-stage steam turbines. It is specifically used to calculate the highly nonlinear relationship between extraction pressure and steam flow rate under unblocked turbine nozzle conditions. It is also a key basis for calculating extraction parameters of steam turbines under partial load and variable operating conditions.

[0099] By combining the matrix heat balance equations and the Stodola formula, a simulation model of the SACPG system was completed in EBSILON® Professional 13.2, and the feedwater flow rate, feedwater temperature, and heat exchange parameters of the high-pressure heater group under various load conditions of the coal-fired power plant subsystem were obtained.

[0100] Furthermore, the flow characteristic parameters of the turbine unit are retrieved from the system database. These parameters are core inherent parameters of the turbine unit, including the flow area, enthalpy drop, efficiency, and reaction degree of each stage of the turbine. They directly reflect the steam flow and work characteristics of the turbine and are a key foundation for the application of the Stodola formula. Next, the retrieved flow characteristic parameters are substituted into the Stodola formula to adapt it to the currently operating turbine unit. The adapted Stodola formula can accurately describe the dynamic relationship between steam flow rate, pressure, and enthalpy drop inside the turbine, and can reflect the influence of pressure changes in each stage of turbine extraction on the extraction steam mass flow rate under different load conditions. Next, the adapted Stodola formula was combined with the constructed matrix heat balance equation of the high-pressure heater group to form a system of simultaneous equations containing two unknowns: extraction steam mass flow rate and extraction steam pressure. The matrix heat balance equation defines the heat balance relationship between extraction steam parameters and feedwater parameters from the heat exchange end, while the Stodola formula defines the intrinsic correlation of extraction steam parameters from the turbine flow path end. The combination of these two equations provides comprehensive constraints on the extraction steam parameters. Numerical calculation methods were used to iteratively solve the simultaneous equations. During the solution process, the calculation results were repeatedly corrected based on the actual operating conditions of the current unit, such as load conditions and solar thermal energy input, until the calculation results of the equations converged to the preset accuracy. Finally, precise values ​​of the mass flow rate and pressure of each stage of extraction steam for each high-pressure heater were obtained, highly matching the current operating conditions and fully reflecting the actual energy level and work capacity of each stage of extraction steam.

[0101] By establishing a matrix heat balance equation by combining real-time feedwater flow rate, feedwater temperature, and high-pressure heater group heat exchange parameters of the coal-fired power plant subsystem, and then incorporating the turbine flow characteristics parameters to introduce the Stodola formula and solve the equations simultaneously, the mass flow rate and pressure of the extraction steam corresponding to each stage of the high-pressure heater can be accurately calculated. This approach relies on the matrix heat balance equation to fit the actual heat exchange thermodynamic laws of the high-pressure heater group, and uses the Stodola formula to match the flow work characteristics of the turbine group. This ensures that the calculated extraction steam parameters are highly consistent with the actual operating conditions of the unit, accurately reflecting the actual work capacity and energy level of the extraction steam at each stage under different loads and irradiation conditions. This provides a precise basis for the extraction steam parameters to dynamically switch the connection relationship between the brine heat exchanger and each high-pressure heater according to the operating conditions and to achieve staged extraction steam substitution. From a theoretical calculation perspective, this ensures the matching of the extraction steam substitution energy level with the actual operating state of the unit, avoiding problems such as unreasonable extraction steam substitution and low solar energy utilization efficiency caused by deviations in extraction steam parameter calculations. This lays a solid foundation for parameter calculation for the scientific implementation of the staged operation strategy.

[0102] Furthermore, by switching the connection relationship between the salt-water heat exchanger and each high-pressure heater in the high-pressure heater group based on the current load and the actual solar thermal energy input, the steps to achieve staged steam extraction substitution include:

[0103] (1) Determine the load level of the unit and the solar irradiance state corresponding to the actual solar thermal energy input under the current operating conditions, and retrieve the mass flow rate and pressure data of each extraction steam level calculated by the matrix heat balance equation and the Stodola formula.

[0104] Specifically, the system determines the current unit load level and the solar irradiance status corresponding to the actual solar thermal energy input in real time. It retrieves the extraction steam mass flow rate and pressure data at each level from the system database, obtained by solving the matrix heat balance equation and the Stodola formula simultaneously. This integrates the operating condition information and extraction steam parameters, providing a complete basis for subsequent extraction steam substitution mode switching.

[0105] Furthermore, based on the actual solar thermal energy input obtained in the previous steps, combined with operating parameters such as unit output and power generation, the current load level of the unit is accurately determined, specifying whether it is full load, 75% partial load, or 50% partial load. Simultaneously, based on the magnitude and trend of the actual solar thermal energy input, the corresponding solar irradiance state is determined, specifying whether the irradiance is sufficient, stable, insufficient, or surplus, thus understanding the actual solar energy supply capacity. Through the system's data retrieval module, the extraction steam mass flow rate and pressure data corresponding to each stage of the high-pressure heater, previously obtained by simultaneously solving the matrix heat balance equation and the Stodola formula, are completely extracted from the database. This data accurately reflects the actual work capacity and energy level of the extraction steam at each stage of the turbine under the current operating conditions. The determined load level, irradiance state, and retrieved extraction steam parameters are integrated and correlated to form a complete operating condition-parameter system. This ensures that subsequent switching of extraction steam replacement modes is highly matched with the current actual operating status of the unit and the solar energy supply capacity, avoiding a disconnect between the replacement strategy and the actual operating conditions.

[0106] (2) If it is a full-load condition, control the salt-water heat exchanger to be connected in parallel with the first high-pressure heater separately to achieve partial replacement of the third-stage extraction steam;

[0107] Specifically, after determining that the operating condition is full load, the on / off state of the valve is controlled to keep the brine-water heat exchanger connected in parallel only with the first high-pressure heater. At the same time, based on the extraction steam parameter data, the heat exchange load of the brine-water heat exchanger is adjusted to partially replace the third-stage extraction steam.

[0108] Furthermore, when the system determines that the current unit is under full load, considering the characteristics of the turbine extraction steam power generation capacity and the main use of solar auxiliary demand for supplementary utilization under this condition, the corresponding full load extraction steam substitution control logic is activated; by controlling the opening and closing of the bypass regulating valve and connecting valve of the heat exchanger between the coal-fired power plant subsystem and the solar field subsystem, the connecting valves between the brine-water heat exchanger and the second and third high-pressure heaters are closed, while the parallel connection valve between the brine-water heat exchanger and the first high-pressure heater is kept open, ensuring that the brine-water heat exchanger only forms a parallel heat exchange structure with the first high-pressure heater, and the bypass part enters the feedwater of the first high-pressure heater. Finally, based on the retrieved mass flow rate and pressure data of the third-stage extraction steam, and combined with the molten salt heat source parameters provided by the molten salt thermal storage system, the molten salt flow rate and feedwater bypass flow rate of the salt-water heat exchanger are precisely controlled. This allows the feedwater heated by the salt-water heat exchanger to partially replace the heating function of the third-stage extraction steam, thus achieving partial replacement of the third-stage extraction steam. This fully utilizes solar energy while avoiding excessive replacement that could affect the normal operation of the turbine under full-load conditions, ensuring the stability of the unit's full-load power generation.

[0109] (3) If it is a 75% partial load condition, control the salt-water heat exchanger and the second high-pressure heater to be connected in parallel separately to realize the replacement of the second stage steam extraction;

[0110] Specifically, after determining that the unit is operating at 75% partial load, the brine-water heat exchanger is connected in parallel with the second high-pressure heater by controlling the valve opening and closing. The heat exchange load is adjusted in combination with the extraction steam parameters to achieve complete replacement of the second-stage extraction steam.

[0111] Furthermore, when the system determines that the unit is operating at 75% partial load, considering the changes in the turbine extraction steam energy level and the increased demand for solar auxiliary power under this condition, the dedicated extraction steam substitution control logic for 75% partial load is activated. By adjusting the opening and closing of various connecting valves and bypass regulating valves, the connecting valves between the brine-water heat exchanger and the first and third high-pressure heaters are closed, while the parallel connecting valve between the brine-water heat exchanger and the second high-pressure heater is opened. This ensures that the brine-water heat exchanger forms a separate parallel heat exchange structure only with the second high-pressure heater, and all feedwater bypasses into the second high-pressure heater. Based on the retrieved mass flow rate and pressure data of the second-stage extraction steam, the system matches the molten salt heat source parameters of the molten salt thermal storage system, precisely controlling the molten salt flow rate and feedwater flow rate of the salt-water heat exchanger. This ensures that the feedwater temperature after being heated by the salt-water heat exchanger reaches the design outlet temperature of the second high-pressure heater, completely replacing the heating function of the second-stage extraction steam, reducing the amount of extraction steam in this stage, promoting further expansion of the extraction steam to do work, improving the utilization efficiency of solar energy, and adapting to the thermal cycle requirements of the unit under 75% partial load.

[0112] (4) If it is a 50% partial load condition, control the salt-water heat exchanger to be connected in parallel with the second high-pressure heater and the third high-pressure heater to achieve the coordinated substitution of the second and third stage extraction steam.

[0113] Specifically, after determining that the unit is operating at 50% partial load, the salt-water heat exchanger is connected in parallel with the second and third high-pressure heaters through valve on / off control. Combined with the extraction steam parameters, the heat exchange load is coordinated and adjusted to achieve coordinated substitution of the second and third stage extraction steam.

[0114] Furthermore, when the system determines that the unit is operating at 50% partial load, considering the reduced steam extraction capacity of the turbine under this condition and the core means of improving system efficiency through solar energy assistance, the system initiates a dedicated 50% partial load extraction steam substitution control logic. This condition represents the optimal state for solar energy utilization, and the multi-stage extraction steam substitution effect needs to be maximized. The system controls valve opening and closing, shutting off the connection valve between the brine-water heat exchanger and the first high-pressure heater, while simultaneously opening the parallel connection valves between the brine-water heat exchanger and the second and third high-pressure heaters. This creates a synchronous parallel heat exchange structure between the brine-water heat exchanger and the two-stage high-pressure heaters, allowing all feedwater to bypass the second and third-stage high-pressure heaters. Based on the retrieved mass flow rate and pressure data of the second and third-stage extraction steam, and considering the maximum heating capacity of the molten salt thermal storage system, the system precisely and collaboratively controls the molten salt flow rate delivered by the brine-water heat exchanger to the two-stage high-pressure heaters and the feedwater bypass flow rate. This ensures that the feedwater heated by the brine-water heat exchanger reaches the design outlet temperature of the second and third-stage high-pressure heaters, achieving a coordinated and complete substitution of the second and third-stage extraction steam. This method significantly reduces the amount of steam extracted from the turbine, maximizes the utilization of solar energy converted into heat, significantly improves the net solar power generation efficiency under 50% partial load conditions, and ensures the stability of the unit's thermodynamic cycle parameters under low load conditions.

[0115] First, the current unit load level and solar irradiance status are integrated and determined. At the same time, the core parameters of each extraction steam level are retrieved through precise calculation using professional formulas. Then, for three operating conditions—full load, 75% partial load, and 50% partial load—the salt-water heat exchanger and different high-pressure heaters are controlled to achieve single parallel or dual-unit parallel operation. This corresponds to the completion of third-stage extraction steam partial replacement, second-stage extraction steam replacement, and second- and third-stage extraction steam coordinated replacement. This achieves precise dynamic matching between the extraction steam replacement level and the unit load and solar irradiance status, making the heat utilization of the molten salt thermal storage system highly compatible with the extraction steam energy level at each stage. This maximizes the auxiliary role of solar energy under different load conditions, avoiding excessive extraction steam replacement under full load that affects the stable operation of the unit, and making full use of solar energy through multi-stage coordinated replacement under medium and low partial loads. This significantly improves the solar energy utilization rate and extraction steam replacement efficiency over a wide load range. At the same time, relying on precise extraction steam parameter data, the switching of staged extraction steam replacement is more scientific and more in line with the actual operating characteristics of the unit, effectively enhancing the operational stability and adaptability of the entire system under different operating conditions.

[0116] Furthermore, under full-load conditions, the molten salt is heated to a set temperature by the heat transfer oil in the oil-water heat exchanger and then enters the third-stage heater of the system, namely the salt-water heat exchanger, to heat a portion of the feedwater bypassed by the third-stage high-pressure feedwater heater to the temperature before it entered the second-stage high-pressure feedwater heater. This cuts off part of the turbine extraction steam entering the third-stage high-pressure feedwater heater, allowing it to enter the Rankine cycle together with the completely cut-off first-stage extraction steam to increase power generation.

[0117] If it is a 75% partial load condition, the outlet temperature of the heat transfer oil of the oil-water heat exchanger is higher than that of 100% THA, and the molten salt can be heated to a higher temperature to replace the second stage extraction steam with a stronger function. The salt-water heat exchanger is used to heat a portion of the feedwater at the inlet of the second stage high-pressure feedwater heater so that it reaches the original temperature before entering the first stage high-pressure feedwater heater.

[0118] Under a 50% partial load condition, the brine-water heat exchanger is connected in parallel with both the second and third high-pressure heaters to achieve coordinated replacement of the second and third stage extraction steam. In this condition, there is excessive surplus solar energy, and replacing a single high-pressure heater inevitably results in heat loss. Increasing the feedwater temperature difference between the inlet and outlet of the brine-water heat exchanger allows for the utilization of more solar energy. Therefore, simultaneously replacing the second and third stage extraction steam entering both the second and third stage high-pressure feedwater heaters, along with the originally disconnected first stage extraction steam, results in a 50% THA (Through Temperature Registry) condition, which is the optimal operating condition for optimizing solar energy utilization in the TES (Transmission System).

[0119] This embodiment provides an integrated molten salt thermal energy storage solar-assisted coal-fired power generation system. By constructing three collaborative subsystems—a coal-fired power plant, a solar field, and a processing system—it accurately calculates the actual solar thermal energy input based on meteorological parameters, dynamically adjusts the flow rates of heat transfer oil and molten salt to maintain system thermodynamic balance, and precisely solves for extraction parameters at each stage using matrix heat balance equations and the Stodola formula. Based on different load levels (full load, 75% partial load, 50% partial load) and solar irradiance conditions, it utilizes OSHE and SWHE temperature matching design to allow molten salt to selectively replace second and third-stage extraction steam under different load conditions, maximizing waste heat recovery. Dynamically switching the parallel connection relationship between the salt-water heat exchanger and each high-pressure heater achieves staged extraction steam replacement, effectively solving the problems of insufficient solar energy utilization under wide load conditions, unstable system efficiency due to irradiance fluctuations, and lack of extraction steam replacement in existing solar-assisted coal-fired power generation systems. Technical issues such as poor dynamic matching, poor coordination between molten salt thermal storage and multi-stage steam extraction, and insufficient research on dynamic performance under off-design conditions have been addressed. This approach significantly improves solar energy utilization and net solar power generation efficiency over a wide load range, significantly mitigates system efficiency fluctuations caused by solar irradiance fluctuations, enhances the flexibility of steam extraction substitution and system operational stability, fully leverages the waste heat recovery and fluctuation mitigation functions of molten salt thermal storage, accurately matches the thermodynamic parameters of various system components, reveals the system's dynamic thermodynamic performance under off-design conditions, and, based on the fact that retrofitting existing units does not require significant modifications to the original equipment, resulting in low retrofitting costs and short cycles. This approach not only enables flexible low-carbon transformation of existing coal-fired power units, reducing carbon emissions and improving the capacity for new energy absorption, but also provides precise and reliable technical support for the dynamic operation of actual projects, allowing solar-assisted coal-fired power generation systems to achieve efficient and stable adaptive operation within a 50%-100% rated load range.

[0120] Corresponding to the aforementioned embodiment of a graded operation system for a solar-assisted coal-fired power generation system with integrated molten salt thermal energy storage, this application also provides an embodiment of a graded operation method for a solar-assisted coal-fired power generation system with integrated molten salt thermal energy storage.

[0121] Figure 3 This is a flowchart of Embodiment 2 of the staged operation method for the solar-assisted coal-fired power generation system with integrated molten salt thermal storage provided in this application. Please refer to... Figure 3 The method provided in this embodiment includes:

[0122] S101. Real-time collection of solar direct normal irradiance, ambient temperature, and wind speed as meteorological parameters, inputting the meteorological parameters into the PTC collector field model, and calculating the actual solar thermal energy input under the current operating conditions.

[0123] S102. Adjust the flow rate of the heat transfer oil in the PTC collector field and the flow rate of the molten salt in the molten salt storage system according to the actual input of solar thermal energy.

[0124] S103. Obtain the feedwater heat exchange parameters and turbine flow characteristic parameters of the coal-fired power plant subsystem under the current operating conditions. Calculate the mass flow rate and pressure of the steam extracted from each stage of the first high-pressure heater, the second high-pressure heater, and the third high-pressure heater based on the matrix heat balance equation and the Stodola formula.

[0125] S104. Combining the unit load level under the current operating conditions and the actual solar thermal energy input, the connection relationship between the salt-water heat exchanger and the second and third high-pressure heaters is switched according to the mass flow rate and pressure of the steam extracted at each stage of the first high-pressure heater, the second high-pressure heater, and the third high-pressure heater, so as to realize the staged steam extraction substitution.

[0126] The method in this embodiment can be used to execute Figure 1 The steps of the system embodiment shown are similar in principle and process, and will not be repeated here.

[0127] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A tiered operation system for a solar-assisted coal-fired power generation system integrating molten salt thermal energy storage, characterized in that, The system includes: A coal-fired power plant subsystem, comprising a generator, a condenser, a low-pressure heater group, a deaerator, and a high-pressure heater group, wherein the high-pressure heater group comprises a first high-pressure heater, a second high-pressure heater, and a third high-pressure heater; The solar field subsystem includes a PTC collector field, a heat transfer oil pipeline, a molten salt thermal storage system, an oil-salt heat exchanger, an oil-water heat exchanger, and a salt-water heat exchanger. The processing system is used to calculate the actual solar thermal energy input under the current operating conditions based on meteorological parameters, adjust the heat transfer oil flow rate of the PTC collector field and the molten salt flow rate of the molten salt storage system based on the actual solar thermal energy input, calculate the mass flow rate and pressure of each stage of extraction steam in the high-pressure heater group according to the matrix heat balance equation and the Stodola formula, determine the load under the current operating conditions, classify the load, and switch the connection relationship between the salt-water heat exchanger and each high-pressure heater in the high-pressure heater group according to the load level and the actual solar thermal energy input to achieve staged extraction steam substitution.

2. The system according to claim 1, characterized in that, The solar energy field subsystem and the coal-fired power plant subsystem are coupled in parallel on the feedwater side, including: The oil-water heat exchanger and the brine-water heat exchanger are connected in parallel with the high-pressure heater group; the solar energy subsystem serves as the external heat source for the coal-fired power plant subsystem. It bypasses the feedwater branch of the corresponding high-pressure heater through the oil-water heat exchanger and the brine-water heat exchanger, using solar thermal energy to replace the steam extracted from the turbine to heat the feedwater, so that the feedwater temperature matches the feedwater temperature at the economizer inlet.

3. The system according to claim 1, characterized in that, The calculation of the actual solar thermal energy input under the current operating conditions based on meteorological parameters includes: The direct normal solar irradiance, ambient temperature, and wind speed are collected as meteorological parameters and input into the PTC collector field model. Based on the fixed design parameters of the PTC collector field, the actual solar thermal energy input converted by the PTC collector field under the current operating conditions is obtained by solving the thermodynamic calculation model in combination with the meteorological parameters.

4. The system according to claim 1, characterized in that, The adjustment of the heat transfer oil flow rate of the PTC collector field according to the actual solar thermal energy input includes: The real-time fluctuation of direct solar irradiance is determined by the actual solar thermal energy input. The flow rate of the heat transfer oil is adjusted proportionally to the real-time fluctuations to maintain the temperature of the heat transfer oil at the outlet of the PTC collector field at a preset value.

5. The system according to claim 1, characterized in that, The step of adjusting the molten salt flow rate of the molten salt thermal storage system according to the actual input of solar thermal energy includes: Based on the actual solar thermal energy input, determine the fluctuation state of direct normal solar irradiance and load conditions, and determine the preset temperature value of the molten salt at the outlet of the oil-salt heat exchanger. Based on the logic of matching the molten salt flow rate with the heat transfer oil flow rate, the molten salt flow rate is adjusted to ensure that the molten salt temperature at the outlet of the oil-salt heat exchanger reaches the preset value.

6. The system according to claim 1, characterized in that, The calculation of the mass flow rate and pressure of the extracted steam at each stage of each high-pressure heater in the high-pressure heater group based on the matrix heat balance equation and the Stodola formula includes: Obtain the feedwater flow rate, feedwater temperature, and heat exchange parameters of the high-pressure heater group of the coal-fired power plant subsystem under the current operating conditions, and establish the matrix heat balance equation of the high-pressure heater group based on the feedwater flow rate, feedwater temperature, and heat exchange parameters; By incorporating the flow characteristics parameters of the steam turbine unit and introducing the Stodola formula, the matrix heat balance equations are solved simultaneously to obtain the mass flow rate and pressure of the steam extracted at each stage of each high-pressure heater.

7. The system according to claim 1, characterized in that, The step of switching the connection relationship between the salt-water heat exchanger and each high-pressure heater in the high-pressure heater group according to the load level and the actual solar thermal energy input to achieve staged steam extraction substitution includes: Determine the load level of the unit and the solar irradiance state corresponding to the actual solar thermal energy input under the current operating conditions, and retrieve the mass flow rate and pressure data of each stage of extraction steam obtained by matrix heat balance equation and Stodola formula; If it is under full load, the salt-water heat exchanger is controlled to be connected in parallel with the first high-pressure heater to achieve partial replacement of the third-stage steam extraction. If the operating condition is 75% partial load, the salt-water heat exchanger is controlled to be connected in parallel with the second high-pressure heater to replace the second stage steam extraction. If the operating condition is 50% partial load, the salt-water heat exchanger is controlled to be connected in parallel with the second high-pressure heater and the third high-pressure heater to achieve coordinated replacement of the second and third stage extraction steam.

8. The system according to claim 1, characterized in that, The connection structure between the salt-water heat exchanger and the high-pressure heater group includes a first parallel branch and a second parallel branch. The first parallel branch connects the water outlet of the salt-water heat exchanger to the water inlet of the second high-pressure heater, and a first switching valve group is provided on the first parallel branch. The second parallel branch connects the water outlet of the salt-water heat exchanger to the water inlet of the third high-pressure heater, and a second switching valve group is provided on the second parallel branch.

9. The system according to claim 1, characterized in that, The molten salt outlet of the oil-salt heat exchanger is connected to the inlet of the hot tank of the molten salt thermal storage system. The outlet of the hot tank of the molten salt thermal storage system is connected to the molten salt side inlet of the salt-water heat exchanger. The feedwater side inlet and outlet of the salt-water heat exchanger are respectively connected to the feedwater bypass of the high-pressure heater group. The stepwise increase in the outlet molten salt temperature of the oil-salt heat exchanger matches the feedwater inlet temperature range of the second high-pressure heater and the third high-pressure heater.

10. A method for the graded operation of a solar-assisted coal-fired power generation system with integrated molten salt thermal energy storage, characterized in that, The method is implemented based on the system according to any one of claims 1-9, and the method includes: Real-time solar direct normal irradiance, ambient temperature, and wind speed are collected as meteorological parameters. These meteorological parameters are then input into the PTC collector field model to calculate the actual solar thermal energy input under the current operating conditions. The flow rate of the heat transfer oil in the PTC collector field and the flow rate of the molten salt in the molten salt storage system are adjusted according to the actual input of solar thermal energy. The feedwater heat exchange parameters and turbine flow characteristics parameters of the coal-fired power plant subsystem under the current operating conditions are obtained. Based on the matrix heat balance equation and the Stodola formula, the mass flow rate and pressure of the steam extracted from each stage of the first high-pressure heater, the second high-pressure heater, and the third high-pressure heater are calculated. Based on the unit load level under the current operating conditions and the actual solar thermal energy input, and according to the mass flow rate and pressure of the steam extracted from each stage of the first high-pressure heater, the second high-pressure heater, and the third high-pressure heater, the connection relationship between the salt-water heat exchanger and the second and third high-pressure heaters is switched to achieve staged steam extraction substitution.

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