Thermoelectric decoupling fused salt heat storage and heat supply transformation method

Abstract

The invention discloses a thermoelectricity decoupling fused salt heat storage and heat supply transformation method, and aims to efficiently utilize waste heat generated by a traditional coal-fired or gas-fired generator set and realize thermoelectricity decoupling and improve the energy utilization efficiency through an integrated fused salt heat storage technology. The method comprises the steps that a traditional generator set is systematically transformed, a fused salt circulation loop is designed and installed, a fused salt heat exchanger and a fused salt storage tank are connected, and fused salt is used as a heat transfer medium to store and release heat energy; meanwhile, a high and medium pressure cylinder bypass heat supply technology is implemented, the steam acting process is optimized, and the steam acting efficiency and the heat energy utilization rate are improved by adopting an intermediate reheat cycle and incomplete low pressure cylinder cutting strategy; in addition, an intelligent control system is further integrated, the running state of the fused salt heat storage and supply system is monitored and adjusted in real time, on-demand heat supply and intelligent adjustment are achieved, energy consumption and environmental pollution can be remarkably reduced by applying the method, the energy utilization efficiency is improved, and energy resources are saved. And an efficient, reliable and economical solution is provided for the fields of thermoelectric decoupling and waste heat utilization.

Description

Technical Field

[0001] The present invention relates to the field of energy conversion and storage technology, and specifically to a comprehensive energy transformation method that combines thermoelectric decoupling technology, molten salt heat storage technology and a variety of waste heat and waste heat recycling technologies. Background Art

[0002] With the transformation of the global energy structure and the growing demand for sustainable development, thermal-electric decoupling technology has become an important means to improve energy efficiency and promote clean energy consumption. Traditional coal-fired or gas-fired generators generate a large amount of waste heat during the power generation process, which is usually directly discharged into the atmosphere, not only causing a huge waste of energy, but also exacerbating environmental pollution problems. Therefore, how to efficiently utilize this part of waste heat to achieve cogeneration and thermal-electric decoupling has become a research hotspot in the current energy field.

[0003] As a highly efficient thermal energy storage and conversion technology, molten salt thermal storage technology has great application potential in the fields of thermoelectric decoupling and waste heat utilization due to its advantages of high energy storage density, good thermal stability, and long-term storage. By using molten salt as a heat transfer medium, the waste heat generated by the generator set can be stored and released for heating when needed, thereby achieving thermoelectric decoupling and improving energy utilization efficiency.

[0004] However, the application of molten salt heat storage technology in thermal-electric decoupling and heating transformation still faces many technical challenges. First, it is necessary to systematically transform the traditional coal-fired or gas-fired power generation units and integrate the molten salt heat storage system, which includes the design of the molten salt circulation loop, the transformation of the thermal system, and the implementation of high- and medium-pressure cylinder bypass heating technology. Secondly, in order to achieve efficient and stable thermal-electric decoupling, it is also necessary to optimize the steam work process, such as adopting an intermediate reheat cycle and an incomplete removal of the low-pressure cylinder strategy. In addition, in order to further improve the energy efficiency and reliability of the system, it is also necessary to design and implement an intelligent control system to monitor and intelligently adjust the molten salt heat storage and heating system in real time.

[0005] Under the current technical background, although there have been some studies on thermoelectric decoupling and molten salt heat storage technology, these studies often focus on the development and application of a single technology or system, lacking systematic transformation solutions and comprehensive optimization strategies. Therefore, how to propose an efficient, reliable and economical thermoelectric decoupling molten salt heat storage and heating transformation method has become an urgent problem to be solved. Summary of the invention

[0006] The present invention aims to provide a thermoelectric decoupling molten salt heat storage and heating transformation method, which systematically transforms the traditional coal-fired or gas-fired generator set, integrates molten salt heat storage technology, and combines high and medium pressure cylinder bypass heating technology, intermediate reheat cycle, incomplete removal of low pressure cylinder strategy and intelligent control system, etc., to achieve efficient, stable and reliable thermoelectric decoupling and heating, improve energy utilization efficiency, reduce energy consumption and environmental pollution. The present invention is achieved through the following technical solutions.

[0007] A thermoelectric decoupled molten salt heat storage and heating transformation method comprises the following steps:

[0008] a) Systematically transform traditional coal-fired or gas-fired generators and integrate molten salt heat storage technology, including:

[0009] (1) Design and install the molten salt circulation loop, including molten salt pump, molten salt heat exchanger, molten salt storage tank, molten salt pipeline and its insulation layer, to ensure efficient and stable circulation of molten salt during energy storage and release;

[0010] (2) Transform the thermal system by connecting the molten salt heat exchanger between the waste heat discharge point of the generator set and the heat user, using molten salt as a heat transfer medium to achieve thermal and electrical decoupling;

[0011] b) Implement high and medium pressure cylinder bypass heating technology, the specific steps are:

[0012] (1) Install and debug the steam bypass pipeline and its related valves and control systems to connect the steam channel between the high-pressure cylinder outlet and the medium-pressure cylinder inlet;

[0013] (2) Add an adjustable steam bypass valve and bypass air pump to control the steam flow and pressure entering the thermal power station according to the needs of heat users and grid dispatch instructions;

[0014] (3) Modify the intermediate pressure cylinder steam inlet valve to an adjustable type to ensure that the steam pressure matches the reheater inlet pressure. At the same time, install pressure sensors and temperature sensors on the intermediate pressure cylinder steam inlet pipe to monitor the steam status in real time;

[0015] c) Combined with the intermediate reheat cycle, the steam power generation process is optimized, including:

[0016] (1) Design and install a reheater and its related control system to heat the steam after the high-pressure cylinder has done work and improve the steam work efficiency;

[0017] (2) Adjust the steam turbine control strategy to ensure that the pressure and temperature of steam are stable during the reheating process. At the same time, install temperature sensors and pressure sensors at the outlet of the intermediate pressure cylinder and the outlet of the reheater to monitor the steam status in real time;

[0018] d) Implement the strategy of incomplete removal of low-pressure cylinders, including:

[0019] (1) Install intelligent control valves and flow sensors on the steam pipeline between the medium-pressure cylinder and the low-pressure cylinder to adjust the steam flow according to the grid demand and heating demand to prevent cylinder deformation caused by too low steam flow;

[0020] (2) Monitor and adjust the steam intake of the low-pressure cylinder to ensure that the low-pressure cylinder operates within a safe range;

[0021] e) Establish a molten salt waste heat absorption and waste heat recycling system, including:

[0022] (1) Design and install a flue gas waste heat recovery subsystem, using direct contact preheating and tubular heat exchange technology to recover flue gas waste heat. At the same time, install temperature sensors and flow sensors on the flue gas duct to monitor the flue gas temperature and flow in real time;

[0023] (2) Design and install a waste steam heat recovery subsystem, using a high-efficiency plate heat exchanger to recover the heat energy in the exhaust steam. At the same time, install temperature sensors and pressure sensors at the inlet and outlet of the plate heat exchanger to monitor the heat exchange efficiency in real time;

[0024] (3) Design and install a waste heat recovery subsystem for equipment surface heat dissipation, using a heat collection layer made of high thermal conductivity material to collect equipment heat dissipation, and install a temperature sensor on the surface of the heat collection layer to monitor the equipment surface temperature in real time;

[0025] f) Integrate intelligent control systems into molten salt heat storage and heating systems, including:

[0026] (1) Install high-precision temperature sensors, pressure sensors, flow sensors and liquid level sensors to monitor the molten salt temperature, pressure, flow and tank liquid level in real time;

[0027] (2) Integrated safety monitoring and early warning subsystem, using technologies such as ultrasonic detection and infrared thermal imaging to monitor the system operation status, prevent leakage, blockage and other abnormal conditions, and install vibration sensors and noise sensors at key locations to monitor the equipment operation status in real time;

[0028] (3) Design and implement automated control strategies to automatically adjust heat output according to heat user demand, grid dispatch instructions, and molten salt energy storage status, while installing ELCV or other intelligent regulating valves at the user end to achieve on-demand heat supply;

[0029] g) Install ELCV valves or other intelligent regulating valves at the user end and connect them to the intelligent control system to automatically adjust the heating output according to the temperature or heat demand set by the user to achieve on-demand heating. At the same time, install temperature sensors and flow sensors at the user end to monitor the heating effect in real time;

[0030] h) Implement system debugging and optimization, including:

[0031] (1) Overall debugging of the molten salt heat storage and heating system to ensure coordinated operation among the subsystems;

[0032] (2) Optimize the system based on the debugging results to improve system efficiency and stability;

[0033] (3) Provide training and guidance to operators to ensure safe and stable operation of the system.

[0034] Furthermore, the molten salt circulation loop also includes the following components:

[0035] The molten salt filter is arranged at an appropriate position in the molten salt circulation loop to remove impurities and particulate matter that may exist in the molten salt, ensuring the cleanliness of the molten salt during the circulation process, thereby improving the heat transfer efficiency of the molten salt heat exchanger and the stability of the system operation;

[0036] Molten salt deaerator, which removes dissolved oxygen from molten salt by injecting inert gas into the molten salt or using other deoxygenation technologies, preventing the molten salt from deteriorating due to oxidation and extending the service life of the molten salt;

[0037] The molten salt heating / cooling device is arranged between the molten salt storage tanks or at an appropriate position in the molten salt circulation loop, and is used to heat or cool the molten salt during the molten salt energy storage and release process to meet different heating needs.

[0038] Furthermore, the exhaust waste heat recovery subsystem also includes the following components:

[0039] The gas-liquid separator is arranged in the smoke exhaust duct to separate the moisture in the smoke from the smoke, preventing the moisture from entering the molten salt heat exchanger and affecting the heat transfer efficiency and the quality of the molten salt;

[0040] The impurity filter is arranged after the gas-liquid separator to further remove solid impurities and particulate matter in the flue gas, ensuring that the flue gas entering the molten salt heat exchanger is clean and free of impurities;

[0041] The flue gas regulating valve is arranged at the inlet and outlet of the exhaust waste heat recovery subsystem to adjust the amount of flue gas entering the molten salt heat exchanger according to the flue gas temperature and flow rate, thereby optimizing the waste heat recovery efficiency.

[0042] Furthermore, the exhaust steam waste heat recovery subsystem also includes the following components:

[0043] The backwash system is located downstream of the plate heat exchanger and is used to regularly clean the surface of the plate heat exchanger to remove accumulated impurities and dirt and maintain the heat transfer efficiency of the plate heat exchanger;

[0044] The drain valve and sewage outlet are arranged downstream of the backwash system to discharge the sewage and impurities generated during the cleaning process to ensure the cleanliness and hygiene inside the system.

[0045] Furthermore, the intelligent control system also includes the following functions:

[0046] Remote monitoring and diagnosis function, which is connected to the remote monitoring center through network communication technology to achieve remote monitoring and fault diagnosis of the system, and improve the reliability and safety of the system;

[0047] Data analysis and optimization function, which uses big data analysis technology to process and analyze the system's operating data, put forward optimization suggestions, and reduce the system's operation and maintenance costs;

[0048] The alarm and early warning function sends out alarm and early warning signals according to the system's operating status and preset thresholds, reminding operators to deal with abnormal situations in a timely manner and prevent accidents.

[0049] Furthermore, the ELCV valve or other intelligent regulating valve at the user end is connected to the intelligent control system and has the following characteristics:

[0050] It can automatically adjust the heating output according to the temperature or heat demand set by the user, realize heating on demand, and improve the flexibility and response speed of the heating system;

[0051] Able to automatically adjust heating strategies according to outdoor temperature and weather forecast data, optimize heating effects and reduce energy consumption;

[0052] It has a fault self-diagnosis function, which can monitor the working status of the valve in real time, automatically alarm when a fault is found, and try to take emergency measures to ensure the stable operation of the heating system.

[0053] Furthermore, the system debugging and optimization step also includes the following steps:

[0054] Energy efficiency evaluation and performance testing, which uses professional testing equipment and testing methods to test and evaluate the energy efficiency and performance of molten salt heat storage and heating systems to ensure that the system meets the design requirements and achieves the expected energy-saving and environmental protection effects;

[0055] Operator training and guidance, through theoretical explanations and practical operation drills, provide systematic training and guidance to operators to ensure that operators can master the operation and maintenance methods of the system and improve the operating efficiency and safety of the system.

[0056] Beneficial effects of the present invention:

[0057] 1. Realize heat and electricity decoupling, improve energy utilization efficiency, and optimize the operation mode of the cogeneration system;

[0058] 2. Solve the key issues of peak load regulation and heat supply guarantee of the units, and improve the peak load regulation and heat supply capabilities of the units;

[0059] 3. Realize the reuse of various waste heat, reduce energy waste and reduce environmental pollution;

[0060] 4. Improve the safety and stability of the system, reduce failure rate and maintenance costs.

[0061] Instruction Manual

[0062] Figure 1 It is a schematic diagram of the overall process of the present invention;

[0063] Figure 2 Schematic diagram of bypass heating for high and medium pressure cylinders;

[0064] Figure 3 It is a schematic diagram of incomplete removal of the low-pressure cylinder;

[0065] Figure 4 It is a schematic diagram of a molten salt heat storage device;

[0066] Figure 5 Schematic diagram of the preparation of eutectic salt. DETAILED DESCRIPTION

[0067] The scheme of the present invention is described in more detail and completely below.

[0068] Principle of the present invention:

[0069] Thermal decoupling is an energy conversion and storage technology that separates the generation and utilization of thermal and electrical energy to improve overall energy efficiency and flexibility. In the traditional energy conversion process, thermal energy and electrical energy are usually tightly coupled. For example, in a thermal power plant, the heat energy generated by fuel combustion is directly used for power generation. The thermal efficiency and electrical energy conversion efficiency of this process are subject to certain limitations. Thermal decoupling improves the heat storage device and optimizes the operating mode of the cogeneration system, making the generation of thermal energy and electrical energy more independent and efficient. Specific embodiment:

[0071] This project uses a 300MW unit and molten salt heat storage technology, which is deeply integrated with the unit to solve the key problems of peak load regulation and heat supply guarantee of the unit, and optimize the combined heat and power (CHP) operation mode. On the basis of ensuring the heating capacity of the unit, it adopts high and medium pressure cylinder bypass heating, waste heat and waste heat recycling, and molten salt heat storage to weaken the inherent thermoelectric coupling characteristics of the unit and improve the thermoelectric decoupling capacity of the unit.

[0072] (I) Specific improvement plan:

[0073] 1. Bypass heating of high and medium pressure cylinders

[0074] High and medium pressure cylinder bypass heating technology, since the new steam pressure is between 15.69-17.65MPa (for subcritical pressure turbines), most of the main steam is between 520-540℃, so part of the main steam passing through the high-pressure cylinder and the intermediate-pressure cylinder needs to be cooled and decompressed when passing through the bypass vacuum pump and sent to the heat site, and the other part enters the high-pressure cylinder and the intermediate-pressure cylinder to do work. Part of the steam in the intermediate-pressure cylinder enters the low-pressure cylinder through the bypass, and part of it is cooled and decompressed by the vacuum pump and sent to the heat site. In theory, the main steam can ensure the heat supply when the heat load is large. Therefore, the main steam bypass heating scheme is one of the deep peak-shaving schemes with the strongest peak-shaving capability, which can achieve a peak-shaving range of 0-100%;

[0075] The bypass heating scheme for reheat steam cooling and pressure reduction is limited by the exhaust volume of the high-pressure cylinder, the extraction volume is limited, and the peak-shaving capacity is also limited. It is suitable for situations where the peak-shaving target load is high. In the bypass heating scheme, because the boiler load is significantly higher than the steam turbine load, there will be a mismatch between the exhaust steam pressure of the high-pressure cylinder and the inlet pressure of the reheater, and between the heating extraction steam pressure and the pressure of the heat network heater. In engineering practice, this can be solved by technical means such as transforming the medium-pressure steam inlet valve into an adjustable valve and adding a pressure matcher.

[0076] 2. Intermediate reheat cycle

[0077] As for the shortcomings of the above-mentioned re-steam temperature reduction and pressure reduction scheme, an intermediate reheat cycle is introduced in combination with bypass heating. The steam after work in the high-pressure cylinder passes through the circulation pipeline and is heated by the reheater before entering the medium-pressure cylinder to complete the work. The purpose is to reduce the final humidity. Due to the increase in the initial pressure of large units, the exhaust humidity increases, and the erosion of the last few stages of the turbine blades increases. Although increasing the initial temperature can reduce the final humidity, increasing the initial temperature is limited by the temperature resistance of metal materials (the maximum allowable temperature of the cylinder shall not exceed 600°C), so the improvement on the final humidity is small; the use of an intermediate reheat cycle is conducive to the improvement of the final humidity, so that the final humidity drops to the allowable range, reduces the erosion of wet steam on the blades, and improves the internal efficiency of the low-pressure part. The second purpose is to improve the thermal efficiency. After correctly selecting the reheat pressure, the efficiency is increased by 4%-5%, and the thermoelectric coupling is weakened.

[0078] 3. Incomplete removal of the low-pressure cylinder

[0079] The technology of cutting off the low-pressure cylinder refers to closing the zero-seal butterfly valve to reduce or completely prevent steam from entering the low-pressure cylinder. The low-pressure cylinder reduces the conversion of electrical energy into mechanical energy, generates more heat with less electricity, and increases the heating efficiency of the cogeneration unit. Since only a very small part of the exhaust steam from the intermediate-pressure cylinder enters the low-pressure cylinder for rotor cooling, it is easy to cause cylinder deformation, resulting in collision between the stator and the rotor during operation; due to insufficient cooling of the low-pressure cylinder, it is easy to reduce the allowable stress of the last three-stage blades at this temperature, and the secondary stress may exceed the standard, thus causing blade damage, etc.

[0080] This method adopts incomplete removal of the low-pressure cylinder, and sets MESV and MECV valves in the steam bypass pipe connecting the medium-pressure cylinder and the low-pressure cylinder. An intelligent control device is used to control the steam entering the low-pressure cylinder, and the amount of steam entering the low-pressure cylinder for work is not reduced. The cylinder deformation caused by insufficient exhaust steam is solved while ensuring normal power supply. Since this is a condensing and extraction steam turbine, the impact of the pressure caused by excessive steam on the last-stage blades will be pumped to the condenser by the condenser pump to exchange heat with condensed water. The condenser forms a vacuum zone at the turbine exhaust port, causing the steam to expand to within the subcritical pressure in the low-pressure cylinder, thereby increasing the available enthalpy drop of the steam.

[0081] 4. Molten salt absorption waste heat recycling system

[0082] The groundbreaking ceremony of the "Molten Salt Thermal Storage Coupling Coal-fired Power Unit Thermal Power Decoupling" project held by China Energy Group in Suzhou marked the launch of the first GWh-level project of its kind in China. This project aims to achieve thermal power decoupling of coal-fired power units through molten salt thermal storage technology, improve the peak load regulation and heating capacity of the units, and solve the problem of balancing electricity and heat supply. China Energy Group has conducted application research on such technologies in multiple locations, adopted customized strategies, and designed multiple technical routes to support the clean energy transition.

[0083] As a science and technology demonstration project, the Suzhou project is technically supported by the Institute of New Energy. It uses a double-tank molten salt energy storage system and uses the extraction steam of coal-fired units to heat molten salt to meet the needs of heating and deep peak regulation. This method uses this double-tank molten salt energy storage system, combined with the previous heating transformation technology, and uses surface contact condenser heat exchange. The temperature after heat exchange in the condenser is sent to the molten salt for preheating through a heat pump, and the remaining various waste heats are combined to heat the molten salt.

[0084] (1) Analysis of waste heat sources

[0085] The sources of waste heat from power plants are diverse, and their characteristics vary significantly. High-temperature flue gas waste heat, which is usually in the range of 150-300°C, has the characteristics of a higher energy level. However, the flue gas is mixed with impurities such as dust and sulfur oxides, which will threaten the subsequent heat transfer process and the purity of the molten salt; the temperature range of turbine exhaust steam waste heat is about 40-60°C. Its advantage is that the flow rate is large and has good stability, and it can continuously and stably supply a certain amount of heat; the temperature span of equipment surface heat dissipation waste heat is between 50-150°C. Although the heat distribution is relatively scattered, the total amount of energy accumulated is still valuable.

[0086] (2) Preparation of heating plan

[0087] Utilization of exhaust waste heat:

[0088] Direct contact preheating stage: Create a special exhaust waste heat recovery chamber and introduce the molten salt in a specific way, such as using a top spray system or a side wall film guide device to evenly distribute the molten salt; high-temperature flue gas enters from the bottom of the chamber and directly contacts and exchanges heat with the molten salt; in this way, the molten salt can quickly rise from the initial temperature of 20°C to 100-120°C; at the chamber outlet, install an advanced gas-liquid separation and impurity filtration system, and use a multi-stage metal fiber filter combined with an electrostatic adsorption device to effectively remove tiny impurity particles in the flue gas to ensure that the molten salt is not contaminated.

[0089] Tubular heat exchange heating stage: The molten salt that has been preheated is transported to the tubular heat exchanger; the heat exchange tubes are made of special materials, such as nickel-based alloy tubes with excellent temperature resistance and corrosion resistance, and the tube wall thickness is accurately calculated to ensure good thermal conductivity and structural strength; the high-temperature flue gas flows in a turbulent state outside the tube to enhance the heat transfer effect, and the molten salt moves forward at a stable flow rate in the tube; with the help of precise flow control devices and intelligent temperature control systems, the flow and flow rate of the flue gas and molten salt are adjusted according to real-time monitoring data to further heat the molten salt to 200-250℃.

[0090] Utilization of exhaust steam and waste heat:

[0091] High-efficiency plate heat exchangers are used for heat exchange. The plates of the plate heat exchanger are made of composite materials and coated with nano-ceramic coatings on the surface. They have super corrosion resistance and anti-scaling performance, and can improve heat transfer efficiency. The exhaust steam flows into the channel on one side of the heat exchanger in a specific distribution mode, forming a cross-flow heat exchange pattern with the molten salt on the other side. The advanced flow channel design and optimized plate spacing are used to fully tap the heat in the exhaust steam, so that the molten salt temperature continues to rise to 300-350℃. In order to prevent trace impurities in the exhaust steam from accumulating on the surface of the plate, an automatic backwashing system is equipped, which is started according to the preset pressure difference or time period, and the plates are cleaned with high-pressure water or steam pulses.

[0092] Utilization of waste heat from equipment surface:

[0093] Indirect heat conduction is used to dissipate waste heat from the surface of the equipment. A heat collection layer made of high thermal conductivity materials (such as graphite sheets or metal copper foil) is tightly attached to the surface of the equipment. The heat collection layer is wrapped with insulation materials to reduce heat loss, and is only open at the connection with the small molten salt heating container; the molten salt is continuously circulated in the container by a circulating pump to exchange heat with the heat collection layer; a turbulent device such as a spiral blade or a static mixer is set inside the container to enhance the turbulence of the molten salt and improve the heat transfer efficiency, so that the molten salt is finally heated to 380-400℃ to reach the working temperature.

[0094] (3) System control and monitoring

[0095] Temperature control subsystem:

[0096] High-precision thermocouples or thermistor temperature sensors are installed at key locations such as the exhaust waste heat recovery chamber, the inlet and outlet of each heat exchanger, and the molten salt storage tank to collect temperature data in real time. These data are transmitted to the central control system. The control system controls the flow of high-temperature exhaust gas, exhaust steam and other waste heat by adjusting the opening of the electric valve according to the preset temperature curve and heating process requirements. At the same time, the speed of the molten salt circulation pump is adjusted to control the molten salt flow rate to ensure that the molten salt temperature reaches the target range accurately and stably.

[0097] Safety monitoring and early warning subsystem:

[0098] Install pressure sensors to monitor the pressure of the molten salt system. Once the pressure exceeds the set safety threshold, an alarm signal is immediately triggered and the safety valve is activated to release the pressure to prevent accidents such as pipeline rupture or container explosion caused by excessive pressure. For heat exchangers, pipelines and other equipment, non-invasive ultrasonic detection or infrared thermal imaging technology is used to regularly monitor faults and detect abnormal conditions such as leaks and blockages. If an abnormality is found, an alarm is issued in a timely manner and information on the location and type of the fault is provided, so that operation and maintenance personnel can quickly take targeted maintenance measures to ensure the safe, stable and efficient operation of the entire waste heat heating molten salt system;

[0099] For off-site heating, this project uses ELCV valves, which are installed on the heating pipelines of the molten salt heat storage device and are used for regulation according to different user needs.

[0100] 2. Experimental analysis and data processing

[0101] 1. High and medium pressure bypass heating

[0102] According to the simulation calculation results of Thermflow software, for the comparison between the single low-pressure bypass heating and this project (300MW unit), this method only displays the calculation results that can intuitively reflect the advantages.

[0103] 1) Calculation of thermal and electrical decoupling capability

[0104] (1) Thermal-electric decoupling capability: For the high- and medium-pressure bypass heating scheme, assuming that the initial power generation of the unit is P1 (unit: MW) and the power generation after heating is P2 (unit: MW), the power generation change caused by thermal-electric decoupling is

[0105] △P=P1-P2,

[0106] After adopting high and medium pressure bypass heating

[0107] P1 = 300MW, P2 = 286.783MW, then △P = 300-286.783 = 13.217MW;

[0108] D=△P / P rated (where Prated is the rated power of the unit)

[0109] D = (13.217 / 300) × 100%, indicating that the high and medium pressure bypass heating solution increases the peak load depth of the unit by about 4.41%.

[0110] 2) Heating capacity

[0111] According to the energy conservation and steam properties, it is assumed that the high and medium pressure bypass heating steam flow rate is G hp (Unit: kg / s), steam enthalpy is h hp (Unit: kJ / kg), heating power is Q hp (Unit: MW),

[0112] Q hp =(G hp ×h hp ) / 1000=33.33kg / s

[0113] Separate low bypass heating steam flow G lp (Unit: kg / s), assuming that the steam flow rate of the low-pressure cylinder is G l (Unit: kg / s),

[0114] G lp = k × G l , k is the proportionality coefficient. Take 300mw unit k = 0.26, G lp =0.26×100=26kg / s. It can be seen that the heating capacity is increased by about 28.19%

[0115] 3) Heat rate calculation

[0116] (1) Calculation of heat consumption rate of high and medium pressure bypass heating

[0117] Heat rate q hp =Q in-hp / P2,Q in-hp is the heat input when the high and medium pressure bypass is used for heating, and P2 is the power generated after heating.

[0118] Q in-hp =1.2×109kJ / h, P2=286783kW, then q hp =Q in-hp / P2=4184.7kJ / kWh.

[0119] (2) Heat consumption rate of single low-side heating

[0120] Assume that the heat consumption rate of the single low bypass heating is q lp , assuming that the input heat is Q under the same heating power in-lp , the power generation is Plp ,

[0121] Q in-lp =1.0×109kJ / h, P lp =290000kW, then q lp =3448.3kJ / kWh. Heat rate increased by 21.35%

[0122] 2. Comparative simulation calculation of incomplete removal of low-pressure cylinder

[0123] The following table is obtained based on the simulation calculation of Thermflex software:

[0124] Table 1 Incomplete removal of low pressure cylinder

[0125]

[0126]

[0127] According to the above table, the thermoelectric decoupling capability of the incompletely cut low-pressure cylinder is stronger than that of the complete low-pressure cylinder and the cut low-pressure cylinder. The normal operating mode of the complete low-pressure cylinder is relatively fixed, and the thermoelectric decoupling adjustment flexibility is limited. Although the cut low-pressure cylinder changes the operating mode, due to the extreme nature of its operating state, the effective adjustment range and accuracy of the thermoelectric decoupling are not as good as those of the incompletely cut low-pressure cylinder. The incompletely cut low-pressure cylinder can achieve a relatively better thermoelectric decoupling adjustment effect while maintaining good power generation and operating performance.

[0128] 3. Analysis of molten salt heat storage waste heat reuse system

[0129] (1) Heating capacity analysis (comparison data with electric heating)

[0130] Most power plants using molten salt heat storage use electric heating, which has sufficient heating energy and fast heating. The efficiency of this project in providing heat once is not as good as electric heating, but electric heating can only provide heat during off-peak hours, and it also involves new environmental protection issues. Therefore, the following results are obtained by using STEP7 V5.6 software for calculation and analysis:

[0131]

[0132] From this data, it can be concluded that the temperature control accuracy of electric heating is better than that of waste heat utilization. This project controls the accuracy and gas flow of control valves by setting control valves, such as the MESV, MECV, and ELCV valves mentioned above. In terms of hourly heating, considering that waste heat can be continuously heated without time limit, the problem of insufficient heating can be compensated.

[0133] (2) Comparative data on molten salt heat storage capacity

[0134] Eutectic salt is prepared by eutectic reaction of industrial waste salt NaSO4-NaCl-K+. The preparation process is shown in the figure

[0135] At present, most thermal power plants use eutectic salts of KNO3 and NaNO3. The production process is similar and will not be shown in this application. The two eutectic salts are calculated and analyzed to obtain the following table:

[0136] Table 2 Comparison of eutectic salt capabilities

[0137]

[0138]

[0139] The data show that adding potassium ions to the eutectic salt of sodium sulfate and sodium chloride has many advantages. From the perspective of melting point, it is significantly reduced, which can broaden the applicable temperature range, reduce the temperature resistance requirements and energy consumption of equipment, and improve the energy efficiency and stability of the system. In terms of specific heat capacity, it increases, which can better regulate the temperature during heat transfer and reduce energy consumption. The improvement of thermal conductivity is conducive to the rapid transfer of heat, reduces losses, and improves the efficiency of heat utilization. In terms of phase stability, it helps to enhance the stability of the eutectic salt when the temperature and environment fluctuate, reduce the risk of system failure, extend the service life and reduce maintenance costs.

[0140] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0141] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A thermoelectric decoupled molten salt heat storage and heating transformation method, characterized in that: The following steps are involved: a) Systematically transform traditional coal-fired or gas-fired generators and integrate molten salt heat storage technology, including: (1) Design and install the molten salt circulation loop, including molten salt pump, molten salt heat exchanger, molten salt storage tank, molten salt pipeline and its insulation layer, to ensure efficient and stable circulation of molten salt during energy storage and release; (2) Transform the thermal system by connecting the molten salt heat exchanger between the waste heat discharge point of the generator set and the heat user, using molten salt as a heat transfer medium to achieve thermal and electrical decoupling; b) Implement high and medium pressure cylinder bypass heating technology, the specific steps are: (1) Install and debug the steam bypass pipeline and its related valves and control systems to connect the steam channel between the high-pressure cylinder outlet and the medium-pressure cylinder inlet; (2) Add an adjustable steam bypass valve and bypass air pump to control the steam flow and pressure entering the thermal power station according to the needs of heat users and grid dispatch instructions; (3) Modify the intermediate pressure cylinder steam inlet valve to an adjustable type to ensure that the steam pressure matches the reheater inlet pressure. At the same time, install pressure sensors and temperature sensors on the intermediate pressure cylinder steam inlet pipe to monitor the steam status in real time; c) Combined with the intermediate reheat cycle, the steam work process is optimized, including: (1) Design and install a reheater and its related control system to heat the steam after the high-pressure cylinder has done work and improve the steam work efficiency; (2) Adjust the steam turbine control strategy to ensure that the pressure and temperature of steam are stable during the reheating process. At the same time, install temperature sensors and pressure sensors at the outlet of the intermediate pressure cylinder and the outlet of the reheater to monitor the steam status in real time; d) Implement the strategy of incomplete removal of low-pressure cylinders, including: (1) Install intelligent control valves and flow sensors on the steam pipeline between the medium-pressure cylinder and the low-pressure cylinder to adjust the steam flow according to the grid demand and heating demand to prevent cylinder deformation caused by too low steam flow; (2) Monitor and adjust the steam intake of the low-pressure cylinder to ensure that the low-pressure cylinder operates within a safe range; e) Establish a molten salt waste heat absorption and waste heat recycling system, including: (1) Design and install a flue gas waste heat recovery subsystem, using direct contact preheating and tubular heat exchange technology to recover flue gas waste heat. At the same time, install temperature sensors and flow sensors on the flue gas duct to monitor the flue gas temperature and flow in real time; (2) Design and install a waste steam heat recovery subsystem, using a high-efficiency plate heat exchanger to recover the heat energy in the exhaust steam. At the same time, install temperature sensors and pressure sensors at the inlet and outlet of the plate heat exchanger to monitor the heat exchange efficiency in real time; (3) Design and install a waste heat recovery subsystem for equipment surface heat dissipation, using a heat collection layer made of high thermal conductivity material to collect equipment heat dissipation, and install a temperature sensor on the surface of the heat collection layer to monitor the equipment surface temperature in real time; f) Integrate intelligent control systems into molten salt heat storage and heating systems, including: (1) Install high-precision temperature sensors, pressure sensors, flow sensors and liquid level sensors to monitor the molten salt temperature, pressure, flow and tank liquid level in real time; (2) Integrated safety monitoring and early warning subsystem, using technologies such as ultrasonic detection and infrared thermal imaging to monitor the system operation status, prevent leakage, blockage and other abnormal conditions, and install vibration sensors and noise sensors at key locations to monitor the equipment operation status in real time; (3) Design and implement automated control strategies to automatically adjust heat output according to heat user demand, grid dispatch instructions, and molten salt energy storage status, while installing ELCV or other intelligent regulating valves at the user end to achieve on-demand heat supply; g) Install ELCV valves or other intelligent regulating valves at the user end and connect them to the intelligent control system to automatically adjust the heating output according to the temperature or heat demand set by the user to achieve on-demand heating. At the same time, install temperature sensors and flow sensors at the user end to monitor the heating effect in real time; h) Implement system debugging and optimization, including: (1) Overall debugging of the molten salt heat storage and heating system to ensure coordinated operation among the subsystems; (2) Optimize the system based on the debugging results to improve system efficiency and stability; (3) Provide training and guidance to operators to ensure safe and stable operation of the system.

2. A thermoelectric decoupled molten salt heat storage and heat supply transformation method according to claim 1, characterized in that: The molten salt circulation loop also includes the following components: The molten salt filter is arranged at an appropriate position in the molten salt circulation loop to remove impurities and particulate matter that may exist in the molten salt, ensuring the cleanliness of the molten salt during the circulation process, thereby improving the heat transfer efficiency of the molten salt heat exchanger and the stability of the system operation; Molten salt deaerator, which removes dissolved oxygen from molten salt by injecting inert gas into the molten salt or using other deoxygenation technologies, preventing the molten salt from deteriorating due to oxidation and extending the service life of the molten salt; The molten salt heating / cooling device is arranged between the molten salt storage tanks or at an appropriate position in the molten salt circulation loop, and is used to heat or cool the molten salt during the molten salt energy storage and release process to meet different heating needs.

3. A thermoelectric decoupled molten salt heat storage and heat supply transformation method according to claim 1, characterized in that: The exhaust waste heat recovery subsystem also includes the following components: The gas-liquid separator is arranged in the smoke exhaust duct to separate the moisture in the smoke from the smoke, preventing the moisture from entering the molten salt heat exchanger and affecting the heat transfer efficiency and the quality of the molten salt; The impurity filter is arranged after the gas-liquid separator to further remove solid impurities and particulate matter in the flue gas, ensuring that the flue gas entering the molten salt heat exchanger is clean and free of impurities; The flue gas regulating valve is arranged at the inlet and outlet of the exhaust waste heat recovery subsystem to adjust the amount of flue gas entering the molten salt heat exchanger according to the flue gas temperature and flow rate, thereby optimizing the waste heat recovery efficiency.

4. A thermoelectric decoupled molten salt heat storage and heating transformation method according to claim 1, characterized in that: The exhaust steam waste heat recovery subsystem also includes the following components: The backwash system is located downstream of the plate heat exchanger and is used to regularly clean the surface of the plate heat exchanger to remove accumulated impurities and dirt and maintain the heat transfer efficiency of the plate heat exchanger; The drain valve and sewage outlet are arranged downstream of the backwash system to discharge the sewage and impurities generated during the cleaning process to ensure the cleanliness and hygiene inside the system.

5. A thermoelectric decoupled molten salt heat storage and heat supply transformation method according to claim 1, characterized in that: The intelligent control system also includes the following functions: Remote monitoring and diagnosis function, which is connected to the remote monitoring center through network communication technology to achieve remote monitoring and fault diagnosis of the system, and improve the reliability and safety of the system; Data analysis and optimization function, which uses big data analysis technology to process and analyze the system's operating data, put forward optimization suggestions, and reduce the system's operation and maintenance costs; The alarm and early warning function sends out alarm and early warning signals according to the system's operating status and preset thresholds, reminding operators to deal with abnormal situations in a timely manner and prevent accidents.

6. A thermoelectric decoupled molten salt heat storage and heating transformation method according to claim 1, characterized in that: The ELCV valve or other intelligent regulating valve at the user end is connected to the intelligent control system and has the following characteristics: It can automatically adjust the heating output according to the temperature or heat demand set by the user, realize heating on demand, and improve the flexibility and response speed of the heating system; Able to automatically adjust heating strategies according to outdoor temperature and weather forecast data, optimize heating effects and reduce energy consumption; It has a fault self-diagnosis function, which can monitor the working status of the valve in real time, automatically alarm when a fault is found, and try to take emergency measures to ensure the stable operation of the heating system.

7. A thermoelectric decoupled molten salt heat storage and heat supply transformation method according to claim 1, characterized in that: The system debugging and optimization step also includes the following steps: Energy efficiency evaluation and performance testing, which uses professional testing equipment and testing methods to test and evaluate the energy efficiency and performance of molten salt heat storage and heating systems to ensure that the system meets the design requirements and achieves the expected energy-saving and environmental protection effects; Operator training and guidance, through theoretical explanations and practical operation drills, provide systematic training and guidance to operators to ensure that operators can master the operation and maintenance methods of the system and improve the operating efficiency and safety of the system.

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