Anti-condensation feedwater heating device of molten salt steam generation system of a solar thermal power station and control method

Abstract

The application discloses a kind of condensation-preventing feedwater heating devices and control methods for molten salt steam generation system of photo-thermal power station, and relates to the technical field of photo-thermal power station molten salt energy storage and steam generation system, the device includes three parallel feedwater pipelines, segmented steam water heater, U-shaped tube preheater with guide vane diffusion chamber, modular electric heater and control system, the segmented steam water heater adopts high-temperature countercurrent, low-temperature parallel flow structure, and the preheater molten salt inlet is provided with a diffusion chamber and a guide vane to eliminate the local low-temperature dead zone.The application uses a multi-parameter joint control algorithm, with molten salt temperature, feedwater temperature and unit load as input to realize intelligent distribution and seamless switching of electric heating and steam heating, with feedwater temperature fluctuation less than 5℃ during the switching process, and with molten salt solidification risk grading early warning and interlock protection, which can effectively prevent molten salt crystallization and blockage, improve heat exchange efficiency, reduce power consumption, and ensure safe and stable operation of the system under all operating conditions.

Description

Technical Field

[0001] This invention relates to the technical field of molten salt energy storage and steam generation systems for solar thermal power plants, specifically to an anti-condensation feedwater heating device and control method for a molten salt steam generation system in a solar thermal power plant. Background Technology

[0002] In tower solar thermal power plants and coal-fired thermal storage systems, the molten salt steam generation system is the core heat exchange component. The commonly used binary mixed molten salt typically has a physical freezing point of around 220℃. During system startup, low-load operation, or rapid load changes, if the preheater inlet feedwater temperature is too low, the temperature of the preheater heat exchanger tube wall will fall below the molten salt freezing point, potentially leading to molten salt crystallization on the tube wall or even blockage of the heat exchanger tubes.

[0003] In existing technologies, electric heaters are typically used to heat feedwater during the start-up phase, or complex heat storage medium circulation is used to maintain the temperature. However, single electric heating is energy-intensive and slow to respond, while existing steam heating solutions lack optimization for anti-condensation scenarios in their switching logic and structural design, making it difficult to guarantee the safety of the preheater cold end under all operating conditions. Therefore, developing an efficient and reliable anti-condensation feedwater heating device and control method is of great significance. Summary of the Invention

[0004] The purpose of this invention is to overcome or at least partially solve the above problems by providing an anti-condensation feedwater heating device and control method for a molten salt steam generation system in a solar thermal power plant.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a condensation-preventing feedwater heating device for a molten salt steam generation system in a solar thermal power plant, which is arranged on the feedwater pipeline of the preheater of the molten salt steam generation system. The feedwater pipeline adopts a three-way parallel structure, including a feedwater bypass, a steam heating bypass, and an electric heating bypass. A feedwater temperature monitoring point is set at the junction of the three bypasses.

[0006] The steam heating bypass is equipped with a segmented steam-water heater, which is divided into a high-temperature section and a low-temperature section. In the high-temperature section, the high-temperature steam flows in the opposite direction to the feed water flowing through the steam heating bypass, and performs countercurrent heat exchange. After heat exchange, the steam enters the low-temperature section and flows in the same direction as the feed water flowing through the steam heating bypass, and performs parallel flow heat exchange.

[0007] An electric heater is provided on the electric heating bypass for electric auxiliary heating of the feed water flowing through the electric heating bypass;

[0008] It is also equipped with a control system, which is electrically connected to the regulating valves of the three bypasses, the segmented steam water heater and the electric heater, and the feedwater temperature monitoring point. The control system is used to receive the temperature detection signal from the feedwater temperature monitoring point, adjust the opening of each bypass regulating valve and the working status of each heater, and control the feedwater mixing temperature of the three bypasses.

[0009] Preferably, the preheater is a U-tube heat exchanger, with molten salt flowing through the shell side and feedwater flowing through the tube side, and the molten salt inlet is provided with a gradually expanding diffusion cavity with a guide plate.

[0010] Preferably, the electric heater is modularly configured, consisting of multiple independent electric heating units connected in parallel.

[0011] Preferably, the guide plate has an inclination angle of 30 to 45 degrees, and the diffusion cavity volume is the residence time of molten salt flow rate for 5 seconds under rated operating conditions.

[0012] Preferably, the preheater shell is provided with staggered baffles to guide the molten salt to flow in a "Z" shape.

[0013] Preferably, the steam in the segmented steam-water heater enters from the upper inlet, and the feedwater enters from the lower inlet. The saturated steam undergoes countercurrent heat exchange in the high-temperature section, while the condensate undergoes cocurrent heat exchange in the low-temperature section.

[0014] A method for controlling the heating of feedwater to prevent condensation in a molten salt steam generation system of a solar thermal power plant includes the following steps:

[0015] A multi-parameter joint control algorithm is adopted, with molten salt inlet temperature, preheater inlet feedwater temperature and unit load as input parameters, and the target value of preheater inlet feedwater temperature is set to ≥240℃.

[0016] During the start-up phase, the modular electric heater is activated when the feed water temperature is below 240℃; when the evaporator pressure meets the heat exchange requirements, the steam heating bypass is activated and the electric heating power is linearly reduced to achieve seamless switching of the heat source.

[0017] During normal operation, the saturated steam at the evaporator outlet is used as the heat source. The opening of the steam inlet valve of the steam water heater is adjusted to maintain the feedwater temperature at 240-260℃.

[0018] The control system performs seamless switching interlock protection, over-temperature protection, and risk classification and early warning for molten salt solidification.

[0019] Preferably, during the switching process between the electric heater and the steam heater, the feedwater temperature fluctuation is kept below 5°C through preheating sequence control and linear power adjustment.

[0020] As a preferred approach, the risk classification and early warning system for molten salt solidification includes: a safe zone with a feedwater temperature ≥250℃; an early warning zone with a feedwater temperature <230℃ and <250℃, requiring the addition of steam heating or the activation of electric heating compensation; and a danger zone with a feedwater temperature ≤230℃, triggering interlock protection.

[0021] As a preferred option, the interlocking protection actions for the hazardous area include, but are not limited to, fully opening the heating source, cutting off the water supply pump or closing the water supply inlet valve, and initiating the molten salt emergency venting.

[0022] As a preferred option, a combined heating mode using a steam heater and an electric heater is adopted under low-load conditions.

[0023] Compared with existing technologies, this invention provides an anti-condensation feedwater heating device and control method for a molten salt steam generation system in a solar thermal power plant. Through multi-parameter joint control, segmented high-efficiency heat exchange, uniform molten salt distribution, seamless heat source switching, and graded prevention and control of molten salt solidification risks, it thoroughly solves the problem of molten salt crystallization and blockage in the molten salt steam generation system of a solar thermal power plant under startup, low-load, and variable-load conditions from both structural and control perspectives. The segmented steam-water heater adopts a combination of counter-current and parallel-current structures, which can fully utilize the latent heat of steam and the sensible heat of condensate, significantly improving heat exchange efficiency and recovering waste heat from the system. The preheater inlet diffuser chamber works in conjunction with the guide plate to achieve uniform distribution of molten salt, eliminating local low-temperature dead zones, while buffering fluid impact, reducing thermal stress, and extending equipment service life. Seamless switching and interlocking protection between electric heating and steam heating ensures that feedwater temperature fluctuations during switching are less than 5°C, ensuring undisturbed operation. It also prioritizes the use of steam heat sources generated by the evaporator, significantly reducing electric heating energy consumption. Multi-parameter coordinated adjustment and graded early warning interlocking mechanisms achieve precise temperature control and active safety protection under all operating conditions, greatly improving the reliability and safety of system operation and meeting the long-term, stable, and efficient operation requirements of solar thermal power plants. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall process of the anti-condensation water supply heating system of the present invention;

[0025] Figure 2 This is a schematic diagram of the internal structure of a segmented steam-water heater.

[0026] Figure 3 This is a diagram showing the layout of the molten salt inlet diffusion chamber and guide vanes in the preheater;

[0027] Figure 4 This is a schematic diagram of multiple parallel connections and flow distribution on the water supply side;

[0028] Figure 5 This is a block diagram of the multi-parameter coordinated adjustment logic of the control system.

[0029] Figure 6 This is a diagram showing the modular layout and switching sequence of the electric heater.

[0030] Figure 7 A flowchart for risk classification, early warning, and interlocking protection of molten salt solidification. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings.

[0032] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this description, those skilled in the art can make creative modifications to this embodiment as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

[0033] This invention provides an anti-condensation feedwater heating device and control method for a molten salt steam generation system in a solar thermal power plant, which solves the technical problems in the prior art. The overall concept is as follows:

[0034] Example 1

[0035] Please see Figures 1-7 A condensation-preventing feedwater heating device for a molten salt steam generation system in a solar thermal power plant includes a three-way parallel feedwater pipeline, a segmented steam-water heater internally divided into high-temperature and low-temperature sections, a preheater, a modular electric heater, and a control system.

[0036] Specifically, during startup, the control system monitors the preheater inlet feedwater temperature T_fw. If T_fw is below 240℃, the modular electric heater is activated as needed. Once the evaporator generates saturated steam at sufficient pressure, the steam-water heater bypass is activated for preheating.

[0037] Combination Figure 2 As shown, the segmented steam-water heater of this invention employs a unique internal structural design. The heater is internally divided into a high-temperature section and a low-temperature section by a partition plate. Saturated steam (hot fluid) from the evaporator enters from the upper inlet of the heater, where it exchanges heat with feedwater in a counter-current manner in the high-temperature section, utilizing the latent heat of the steam to rapidly raise the feedwater temperature. The high-temperature condensate formed after steam condensation enters the low-temperature section, where it exchanges heat with the lower-temperature feedwater that has just entered the heater in a parallel flow, fully utilizing the sensible heat of the condensate. Feedwater (cold fluid) enters from the lower part of the heater, flows sequentially through the low-temperature section and the high-temperature section, and then exits from the upper outlet. This segmented (counter-current + parallel flow) design ensures extremely high heat exchange efficiency while avoiding thermal stress concentration caused by excessive local temperature differences.

[0038] Specifically, the high-temperature section of the segmented steam-water heater utilizes the latent heat of saturated steam to heat the feedwater, while the low-temperature section utilizes the sensible heat of condensate. By adjusting the opening of the steam inlet valve, the bypass feedwater is heated to 280℃, and after mixing with the main feedwater, the preheater inlet temperature is ensured to remain stable at 240-260℃.

[0039] Combination Figure 3 As shown, the preheater of this invention preferably adopts a U-tube heat exchanger structure. To completely eliminate the risk of molten salt condensation at the cold end, the preheater adopts an arrangement where molten salt flows through the shell side and feedwater flows through the tube side. High-temperature molten salt (hot fluid) enters from the inlet on the upper side of the shell, while feedwater (cold fluid) enters from the inlet of the water chamber on the lower side and flows out from the outlet on the upper side. Specifically, a gradually expanding diffusion chamber is provided at the molten salt inlet on the upper side of the shell, and multiple guide plates are arranged inside the diffusion chamber, with the inclination angle of the guide plates set between 30 degrees and 45 degrees. After the high-temperature molten salt enters the diffusion chamber, it is uniformly dispersed under the forced guidance of the guide plates and then flows downwards through the U-shaped heat exchange tube bundle. Baffles are also arranged alternately inside the shell to guide the molten salt to flow in a "Z" shape. The combination of the diffuser and the guide plate effectively overcomes the drawback of uneven fluid distribution at the inlet of conventional heat exchangers, eliminates the "dead zone" of excessively slow flow velocity or low temperature, fundamentally prevents molten salt from crystallizing and solidifying locally on the tube wall, and buffers fluid impact, thus extending the equipment's lifespan.

[0040] Specifically, the preheater inlet diffuser chamber volume is designed to accommodate the residence time of molten salt flow for 5 seconds under rated operating conditions, and the guide plate angle is set to 40 degrees, which effectively reduces the impact of molten salt entering the tube bundle and eliminates thermal stress.

[0041] Combination Figure 4 As shown, the feedwater-side multi-path parallel and flow distribution system of this invention adopts a three-path parallel structure. Feedwater from the high-pressure heater is divided into three paths at the branching point: the first path is a feedwater bypass, equipped with a main regulating valve, used to directly deliver low-temperature feedwater; the second path is a steam-heated bypass, equipped with an inlet steam regulating valve and a steam-water heater, using saturated steam from the evaporator to heat the feedwater, producing high-temperature feedwater of approximately 280°C, with the condensate discharged from the condensate outlet after heat exchange; the third path is an electric-heated bypass, equipped with an electric-heated bypass regulating valve and an electric heater module, used for independent auxiliary heating of the feedwater under specific operating conditions (such as during system startup or when the steam heat source is insufficient). After the above three feedwater paths are mixed at the confluence point, the temperature (T_fw) of the mixed feedwater is measured at the temperature monitoring point (TE), and finally enters the preheater inlet. The control system adjusts the opening of the main regulating valve, the steam inlet regulating valve, and the electric heating bypass regulating valve to control the mixing ratio of feedwater at different temperatures, thereby accurately controlling the feedwater temperature at the preheater inlet within the target range of 240-260℃, effectively preventing molten salt condensation inside the preheater.

[0042] Combination Figure 5As shown, the control system of this invention employs multi-parameter collaborative adjustment logic. This logic uses the molten salt inlet temperature (T_ms), the preheater inlet feedwater temperature (T_fw), and the unit load command (Load_cmd) as input parameters, and achieves intelligent allocation between electric heating and steam heating through a collaborative allocation algorithm. During startup or extremely low load phases, the system primarily relies on the electric heating bypass, using a PID algorithm to adjust the electric heater power in real time, ensuring the feedwater temperature quickly reaches above 240℃. As the load increases, when the evaporator pressure meets the heat exchange requirements, the system activates the steam heating bypass and simultaneously linearly reduces the electric heating power, achieving seamless heat source switching and ensuring feedwater temperature fluctuations are less than 5℃. During normal operation, the system primarily uses steam heating, precisely maintaining the feedwater temperature between 240-260℃ by collaboratively adjusting the flow distribution ratio between the main regulating valve and the steam inlet regulating valve. This control logic features multi-parameter coupling, complementary heat sources, seamless switching, and safety priority, completely eliminating the risk of molten salt condensation at the preheater cold end from the control level.

[0043] Combination Figure 6 As shown, the electric heater of this invention adopts a modular design with multiple independent units connected in parallel and is equipped with precise switching timing control logic. Physically, the electric heater module consists of multiple independent electric heating units connected in parallel. The control system, based on the required heating power, adjusts the power of a single module by deploying different numbers of modules or regulating the power of individual modules, achieving precise heating through a combination of stepped and stepless regulation. This avoids the impact on the power grid caused by frequent start-ups and shutdowns of high-power electric heaters. Simultaneously, multiple modules serve as backups for each other, improving system reliability. Regarding the switching timing, when the system switches from electric heating-dominated to steam heating-dominated (at time t1), the control system executes cross-linear regulation logic: the steam inlet regulating valve slowly opens at a set slope, while the output power of the electric heater synchronously and linearly decreases at a matching slope. Through this "one increase, one decrease" power compensation timing, the total heat input to the feedwater remains constant during the switching transition period (t1 to t2), achieving a smooth and undisturbed switching between the two heat sources and ensuring feedwater temperature fluctuations are less than 5°C. Once the steam heat source meets the requirements, the system can quickly and smoothly shut down the high-energy-consuming electric heating, maximizing the utilization of the steam heat energy inside the system and achieving the goal of energy saving and consumption reduction.

[0044] Combination Figure 7As shown, the control system of this invention is also equipped with molten salt solidification risk classification early warning and interlocking protection logic. This logic establishes a complete safety defense line from active regulation to classification early warning and then to interlocking protection. The system monitors the preheater inlet feedwater temperature (T_fw) in real time and divides it into a safe zone, an early warning zone, and a danger zone. When T_fw ≥ 250℃, the system is in the safe zone and maintains the conventional multi-parameter coordinated regulation logic; when 230℃ < T_fw < 250℃, the system enters the early warning zone, triggering a first-level early warning, and the control system forcibly increases the opening of the steam inlet regulating valve. If the steam pressure is insufficient, the electric heating module is immediately activated for heat source compensation; when T_fw ≤ 230℃, the system determines that there is an immediate risk of molten salt solidification, enters the danger zone, and triggers a second-level high-risk alarm and interlocking protection action. Under interlocking protection, the system will fully open all heating sources. If the temperature continues to drop, the feedwater pump will be immediately cut off or the feedwater inlet valve will be closed, and the molten salt side emergency venting logic will be activated simultaneously. This tiered prevention and control mechanism features tiered response, maximized heat source utilization, and a safety bottom-line mentality. It avoids frequent false triggering of protection actions while ensuring that, even under extreme accident conditions, the risk of molten salt crystallization inside the preheater can be completely eliminated through physical isolation or venting. Under low-load conditions, a combined heating mode using steam heaters and electric heaters is employed.

[0045] The above description of the embodiments is provided to facilitate understanding and use of the present invention by those skilled in the art. It is obvious to those skilled in the art that various modifications can be made to the embodiments, and the general principles described herein can be applied to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A condensation-preventing feedwater heating device for a molten salt steam generation system in a solar thermal power plant, disposed on the feedwater pipeline of the preheater of the molten salt steam generation system, characterized in that, The water supply pipeline adopts a three-way parallel structure, including a water supply bypass, a steam heating bypass, and an electric heating bypass. A water supply temperature monitoring point is set at the junction of the three bypasses. The steam heating bypass is equipped with a segmented steam-water heater, which is divided into a high-temperature section and a low-temperature section. In the high-temperature section, the high-temperature steam flows in the opposite direction to the feed water flowing through the steam heating bypass, and performs countercurrent heat exchange. After heat exchange, the steam enters the low-temperature section and flows in the same direction as the feed water flowing through the steam heating bypass, and performs parallel flow heat exchange. An electric heater is provided on the electric heating bypass for electric auxiliary heating of the feed water flowing through the electric heating bypass; It is also equipped with a control system, which is electrically connected to the regulating valves of the three bypasses, the segmented steam water heater and the electric heater, and the feedwater temperature monitoring point. The control system is used to receive the temperature detection signal from the feedwater temperature monitoring point, adjust the opening of each bypass regulating valve and the working status of each heater, and control the feedwater mixing temperature of the three bypasses.

2. The anti-condensation feedwater heating device for a molten salt steam generation system in a solar thermal power plant according to claim 1, characterized in that: The guide plate has an inclination angle of 30 to 45 degrees, and the diffusion cavity volume is the residence time of molten salt flow rate for 5 seconds under rated operating conditions.

3. The anti-condensation feedwater heating device for a molten salt steam generation system in a solar thermal power plant according to claim 1, characterized in that: The preheater shell is equipped with staggered baffles to guide the molten salt to flow in a "Z" shape.

4. The anti-condensation feedwater heating device for a molten salt steam generation system in a solar thermal power plant according to claim 1, characterized in that: The segmented steam-water heater has steam entering from the upper inlet and feedwater entering from the lower inlet. Saturated steam undergoes countercurrent heat exchange in the high-temperature section, while condensate undergoes cocurrent heat exchange in the low-temperature section.

5. The anti-condensation feedwater heating device for a molten salt steam generation system in a solar thermal power plant according to claim 1, characterized in that: The feedwater temperature at the outlet of the steam heating bypass is 280℃, and the feedwater temperature at the inlet of the preheater after the three-way mixing is stable at 240-260℃.

6. A method for controlling the heating of feedwater to prevent condensation in a molten salt steam generation system of a solar thermal power plant, applied to the device described in any one of claims 1-5, characterized in that, Includes the following steps: A multi-parameter joint control algorithm is adopted, with molten salt inlet temperature, preheater inlet feedwater temperature and unit load as input parameters, and the target value of preheater inlet feedwater temperature is set to ≥240℃. During the start-up phase, the modular electric heater is activated when the feed water temperature is below 240℃; when the evaporator pressure meets the heat exchange requirements, the steam heating bypass is activated and the electric heating power is linearly reduced to achieve seamless switching of the heat source. During normal operation, the saturated steam at the evaporator outlet is used as the heat source. The opening of the steam inlet valve of the steam water heater is adjusted to maintain the feedwater temperature at 240-260℃. The control system performs seamless switching interlock protection, over-temperature protection, and risk classification and early warning for molten salt solidification.

7. The method for controlling the heating of feedwater to prevent condensation in a molten salt steam generation system of a solar thermal power plant according to claim 6, characterized in that: During the switching process between the electric heater and the steam heater, the feedwater temperature fluctuation is kept below 5°C through preheating sequence control and linear power regulation.

8. The method for controlling the heating of feedwater to prevent condensation in a molten salt steam generation system of a solar thermal power plant according to claim 6, characterized in that: The risk classification and early warning system for molten salt solidification includes: a safe zone with a feedwater temperature ≥250℃; an early warning zone with a feedwater temperature <230℃ and <250℃, requiring mandatory addition of steam heating or electric heating compensation; and a danger zone with a feedwater temperature ≤230℃, triggering interlock protection.

9. The method for controlling the heating of feedwater to prevent condensation in a molten salt steam generation system of a solar thermal power plant according to claim 8, characterized in that: Interlocking protection actions in hazardous areas include, but are not limited to, fully opening the heating source, cutting off the water supply pump or closing the water supply inlet valve, and initiating molten salt emergency venting.

10. The method for controlling the heating of feedwater to prevent condensation in a molten salt steam generation system of a solar thermal power plant according to claim 6, characterized in that: Under low-load conditions, a combined heating mode using a steam heater and an electric heater is adopted.

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