Flexible peak regulation system and method for coal-fired power plant
By introducing phase change materials and molten salt thermal energy storage systems into coal-fired power plants, the energy conversion process is optimized, the problem of low system energy efficiency is solved, and efficient energy management and peak shaving capabilities are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-14
- Publication Date
- 2026-04-10
AI Technical Summary
The existing flexible retrofit schemes for coal-fired power plants have low system energy efficiency, especially the thermal energy storage technology, which is inefficient and cannot effectively utilize the volatility of renewable energy.
In coal-fired power plants, a first peak-shaving section and a second peak-shaving section are introduced. Phase change materials are used to store steam thermal energy, and electrical energy is converted into thermal energy through molten salt. The energy conversion process is optimized by combining the thermal energy storage and release of heat transfer oil and molten salt.
It improved the system's energy efficiency, achieved zero-output peak shaving for coal-fired power plants, significantly reduced investment costs, and improved thermodynamic performance.
Smart Images
Figure FT_1 
Figure FT_2 
Figure FT_3
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of coal-fired power plant peak shaving, and in particular to a coal-fired power plant flexible peak shaving system and method. BACKGROUND
[0002] Coal-fired power plants have been proven to be able to actively regulate renewable energy capacity in the power grid as flexible power sources, thereby solving the problem of renewable energy curtailment. The integration scheme of multi-energy form coupling of coal-fired power plants and energy storage systems can accommodate more renewable energy in the power system and significantly reduce the minimum output power of coal-fired power plants. With the increase of renewable energy installed capacity, the current research focus gradually shifts to more efficient and economic integration schemes to further improve the cycle efficiency and economic performance of the coupled system.
[0003] In related technologies, thermal energy storage technology has significant cost-effectiveness, scalability and safety advantages, and is suitable as an energy storage scheme for flexible modification of coal-fired power plants. Common heat sources include main steam, reheated steam, high-temperature flue gas and electric heating. The above types of flexible modification schemes usually use molten salt as a heat storage medium to exchange heat with molten salt or electrically heat molten salt to ultimately produce high-temperature steam. However, the system energy efficiency of this technology is not high.
[0004] Therefore, there is an urgent need for a coal-fired power plant flexible peak shaving system and method to solve the above problems. SUMMARY
[0005] The embodiments of the present application describe a coal-fired power plant flexible peak shaving system and method, which can improve the energy efficiency of the system.
[0006] In a first aspect, an embodiment of the present application provides a coal-fired power plant flexible peak shaving system, comprising: a main body part comprising a boiler, a high-pressure steam turbine, a medium-pressure steam turbine and a low-pressure steam turbine connected in sequence along the flow direction of the main steam, and a condenser, a plurality of low-pressure heaters, a deaerator and a plurality of high-pressure heaters connected in sequence along the flow direction of the feed water, the plurality of low-pressure heaters being connected to the low-pressure steam turbine, the plurality of high-pressure heaters being connected to the high-pressure steam turbine and the medium-pressure steam turbine, the output end of the low-pressure steam turbine being connected to a generator, the low-pressure steam turbine being connected to the condenser, and the last high-pressure heater being connected to the boiler; a first peak shaving part, the inlet end of which is connected to the high-pressure steam turbine, and the outlet end of which is connected to the condenser, the deaerator and a second peak shaving part, the first peak shaving part being used to store the heat energy of part of the main steam entering the high-pressure steam turbine in the phase change material during the energy storage stage, and to heat part of the feed water discharged by the condenser and the deaerator using the heat energy stored in the phase change material during the energy release stage; The second peak-shaving section is connected to the generator at the inlet and to the high-pressure steam turbine, the last high-pressure heater, and the first peak-shaving section at the outlet. The second peak-shaving section is used to convert the electrical energy generated by the generator into heat energy and store it in molten salt during the energy storage stage, and to use the heat energy stored in the molten salt to heat part of the feedwater discharged from the last high-pressure heater and the first peak-shaving section to generate high-temperature steam during the energy release stage. The other part of the feedwater discharged from the last high-pressure heater and the first peak-shaving section is used to be discharged to the boiler, and the generated high-temperature steam is used to be discharged to the high-pressure steam turbine.
[0007] Secondly, one embodiment of the present invention provides a flexible peak-shaving method for coal-fired power plants, based on the flexible peak-shaving system for coal-fired power plants described in the above embodiment, comprising: During the energy storage stage, part of the main steam entering the high-pressure turbine is discharged to the deaerator after being heated by the first heat exchanger. The heat transfer oil in the heat storage tank is returned to the heat storage tank after absorbing heat by the first heat exchanger, so as to store the absorbed heat energy in the medium ball. The electric motor uses the electrical energy generated by the generator to drive the compressor and expander to rotate. The air discharged from the compressor is discharged to the sixth heat exchanger after being heated by the fifth heat exchanger. The molten salt in the second molten salt tank is discharged to the first molten salt tank after absorbing heat by the fifth heat exchanger. During the energy release phase, the heat transfer oil in the heat storage tank passes through the second and third heat exchangers in sequence to release heat and then flows back into the heat storage tank. Part of the feedwater discharged from the condenser absorbs heat through the third heat exchanger and is then discharged to the deaerator. Part of the feedwater discharged from the deaerator absorbs heat through the second heat exchanger and mixes with the feedwater discharged from the last high-pressure heater. The mixed feedwater is then discharged to the fourth heat exchanger. The high-temperature molten salt in the first molten salt tank releases heat through the fourth heat exchanger and is then discharged to the second molten salt tank. The feedwater absorbs heat through the fourth heat exchanger to generate high-temperature steam and is then discharged to the high-pressure turbine.
[0008] According to the flexible peak-shaving system and method for coal-fired power plants provided in the embodiments of the present invention, by setting up a first peak-shaving section and a second peak-shaving section, the first peak-shaving section can store the thermal energy of a portion of the main steam entering the high-pressure turbine in a phase change material during the energy storage phase, and use the thermal energy stored in the phase change material to heat a portion of the feedwater discharged from the condenser and deaerator during the energy release phase. Similarly, the second peak-shaving section can convert the electrical energy generated by the generator into thermal energy and store it in molten salt during the energy storage phase, and use the thermal energy stored in the molten salt to heat a portion of the feedwater discharged from the last high-pressure heater and the first peak-shaving section during the energy release phase to generate high-temperature steam. Therefore, the above technical solution can not only realize phase change latent heat energy storage using the first peak-shaving section, but also realize zero-output peak shaving of the coal-fired power plant using the second peak-shaving section, thereby improving the system's energy efficiency. Attached Figure Description
[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0010] Figure 1 This diagram illustrates the structure of the flexible peak-shaving system for a coal-fired power plant during the energy storage phase, according to an embodiment of the present invention. Figure 2 This diagram illustrates the structure of a flexible peak-shaving system for a coal-fired power plant during the energy release phase, according to an embodiment of the present invention. Figure 3 A schematic diagram of the parameters of the first and fifth heat exchangers during the energy storage phase is shown, along with a temperature-output power relationship diagram of the first heat exchanger. Figure 4 The diagram shows the parameters of the second and third heat exchangers and the temperature-output power relationship during the energy release phase. Figure 5 A schematic diagram of the parameters of the fourth heat exchanger and a temperature-output power relationship diagram are shown during the energy release phase.
[0011] Figure label: 1-Main body; 11-Boiler; 12-High-pressure steam turbine; 13-Medium-pressure steam turbine; 14-Low-pressure steam turbine; 15-Condenser; 16 - Low-pressure heater; 17-Deaerator; 18-High-pressure heater; 19-Generator; 2-First peak-shaving section; 21-Heat storage tank; 22-First heat exchanger; 23-Second heat exchanger; 24 - Third heat exchanger; 3-Second peak shaving section; 31 - First molten salt vessel; 32 - Second molten salt vessel; 33-Fourth heat exchanger; 34 - Fifth heat exchanger; 35 - Sixth heat exchanger; 36 - Seventh heat exchanger; 37 - Electric motor; 38 - Compressor; 39-Expander. Detailed Implementation
[0012] The solution provided by the present invention will now be described with reference to the accompanying drawings.
[0013] like Figure 1 and Figure 2 As shown, this embodiment of the invention provides a flexible peak-shaving system for a coal-fired power plant. The system includes a main body 1, a first peak-shaving section 2, and a second peak-shaving section 3, wherein: The main body 1 includes a boiler 11, a high-pressure steam turbine 12, a medium-pressure steam turbine 13 and a low-pressure steam turbine 14 connected in sequence along the main steam flow direction, and a condenser 15, multiple low-pressure heaters 16, a deaerator 17 and multiple high-pressure heaters 18 connected in sequence along the feedwater flow direction. The multiple low-pressure heaters 16 are connected to the low-pressure steam turbine 14, the multiple high-pressure heaters 18 are connected to the high-pressure steam turbine 12 and the medium-pressure steam turbine 13, the output end of the low-pressure steam turbine 14 is connected to a generator 19, the low-pressure steam turbine 14 is connected to the condenser 15, and the last high-pressure heater 18 is connected to the boiler 11. The inlet end of the first peak shaving section 2 is connected to the high-pressure steam turbine 12, and the outlet end is connected to the condenser 15, the deaerator 17, and the second peak shaving section 3. The first peak shaving section 2 is used to store the thermal energy of part of the main steam entering the high-pressure steam turbine 12 in the phase change material during the energy storage stage, and to use the thermal energy stored in the phase change material to heat part of the feedwater discharged from the condenser 15 and the deaerator 17 during the energy release stage. The inlet end of the second peak shaving section 3 is connected to the generator 19, and the outlet end is connected to the high-pressure steam turbine 12, the last high-pressure heater 18, and the first peak shaving section 2. The second peak shaving section 3 is used to convert the electrical energy generated by the generator 19 into heat energy and store it in molten salt during the energy storage stage, and to use the heat energy stored in the molten salt to heat part of the feedwater discharged from the last high-pressure heater 18 and the first peak shaving section 2 to generate high-temperature steam during the energy release stage. The other part of the feedwater discharged from the last high-pressure heater 18 and the first peak shaving section 2 is used to be discharged to the boiler 11, and the generated high-temperature steam is used to be discharged to the high-pressure steam turbine 12.
[0014] In this embodiment, by setting up a first peak-shaving section 2 and a second peak-shaving section 3, the first peak-shaving section 2 can store the thermal energy of a portion of the main steam entering the high-pressure turbine 12 in the phase change material during the energy storage phase, and use the thermal energy stored in the phase change material to heat a portion of the feedwater discharged from the condenser 15 and deaerator 17 during the energy release phase. Similarly, the second peak-shaving section 3 can convert the electrical energy generated by the generator 19 into thermal energy and store it in molten salt during the energy storage phase, and use the thermal energy stored in the molten salt to heat a portion of the feedwater discharged from the last high-pressure heater 18 and the first peak-shaving section 2 during the energy release phase to generate high-temperature steam. Therefore, the above technical solution can not only utilize the first peak-shaving section 2 to achieve latent heat energy storage through phase change, but also utilize the second peak-shaving section 3 to achieve zero-output peak shaving for coal-fired power plants, thereby improving system energy efficiency.
[0015] As is understandable, phase change latent heat energy storage utilizes the thermal storage properties of phase change materials (PCMs) to store or release heat, thereby regulating the temperature of the surrounding environment. PCMs can absorb or release large amounts of energy during phase change processes, possessing extremely high latent heat of phase change. Latent heat storage is achieved through the phase change process of the material, and the application of phase change energy storage can improve energy efficiency and alter the spatiotemporal distribution of energy use.
[0016] In some implementations, the phase change material can be either organic or inorganic; the specific type of phase change material is not limited here.
[0017] In one embodiment of the present invention, the first peak-shaving section 2 includes a heat storage tank 21 and a first heat exchanger 22 connected to the heat storage tank 21. The heat storage tank 21 is provided with heat transfer oil and a plurality of medium balls made of phase change material. The first heat exchanger 22 is connected to the high-pressure steam turbine 12 and the deaerator 17 respectively. During the energy storage stage, part of the main steam entering the high-pressure turbine 12 is discharged to the deaerator 17 after being released by the first heat exchanger 22. The heat transfer oil in the heat storage tank 21 is returned to the heat storage tank 21 after absorbing heat through the first heat exchanger 22, so as to store the absorbed heat energy in the medium ball.
[0018] In this embodiment, by setting a first heat exchanger 22 and setting heat transfer oil and multiple medium spheres made of phase change material in the heat storage tank 21, the heat transfer oil and high-temperature steam can be exchanged using the first heat exchanger 22, and the heat transfer oil can store thermal energy to a greater extent in the high-energy-density medium spheres.
[0019] In one embodiment of the present invention, the first peak-shaving section 2 further includes a second heat exchanger 23 and a third heat exchanger 24 connected to the heat storage tank 21. The second heat exchanger 23 is connected to the deaerator 17 and the second peak-shaving section 3 respectively, and the third heat exchanger 24 is connected to the condenser 15 and the deaerator 17 respectively. During the energy release phase, the heat transfer oil in the heat storage tank 21 passes through the second heat exchanger 23 and the third heat exchanger 24 in sequence to release heat and then flows back into the heat storage tank 21. Part of the feedwater discharged from the condenser 15 absorbs heat through the third heat exchanger 24 and is then discharged to the deaerator 17. Part of the feedwater discharged from the deaerator 17 absorbs heat through the second heat exchanger 23 and is then mixed with the feedwater discharged from the last high-pressure heater 18. The mixed feedwater is then discharged to the second peak-shaving section 3, and the rest of the feedwater is discharged to the boiler 11.
[0020] In this embodiment, by setting up a second heat exchanger 23 and a third heat exchanger 24, the heat transfer oil in the heat storage tank 21 can heat part of the boiler's bypass feedwater during the energy release phase, thereby reducing turbine exhaust and increasing the power output of the coal-fired power plant.
[0021] When the system is running stably, the outlet temperature of the heat storage tank 21 will gradually decrease due to the thermocline effect. In order to avoid the impact of this fluctuation on the boiler, the water temperature entering the boiler must be kept constant. This decrease will lead to a decrease in the feedwater flow rate in the second heat exchanger 23 and the third heat exchanger 24, which will result in an increase in the extraction of steam from the turbine, and thus lead to unstable power generation of the system.
[0022] To solve this technical problem, in one embodiment of the present invention, the first peak-shaving section 2 further includes a first oil tank (not shown in the figure) and a second oil tank (not shown in the figure). The first oil tank is filled with cold oil, and the second oil tank is connected to the heat storage tank 21, the first oil tank and the second heat exchanger 23 respectively. When the outlet temperature of the heat storage tank 21 drops below a preset value, the first oil tank opens, allowing the heat transfer oil in the heat storage tank 21 and the cold oil in the first oil tank to mix and enter the second oil tank. The mixed oil is then discharged through the second oil tank to the second heat exchanger 23. The oil inlet of the second heat exchanger 23 is the same when the first oil tank is not opened as it is when the first oil tank is opened.
[0023] In this embodiment, when the outlet temperature of the heat storage tank 21 drops beyond a preset value, the first oil tank is opened, allowing the heat transfer oil in the heat storage tank 21 and the cold oil in the first oil tank to mix and enter the second oil tank. The mixed oil is then discharged through the second oil tank to the second heat exchanger 23, thereby reducing the temperature of the heat transfer oil entering the second heat exchanger 23 to a set value (this value depends on the next constant temperature value, which is usually consistent with the melting point of the phase change material). It is also necessary to ensure that the oil inlet flow rate of the second heat exchanger 23 when the first oil tank is not opened is the same as the oil inlet flow rate of the second heat exchanger 23 when the first oil tank is open, so as to minimize the adjustment frequency of the water supply flow rate in the second heat exchanger 23 and the third heat exchanger 24, thereby achieving stable operation of the heating water supply system.
[0024] It should be noted that during the energy release phase (i.e., the load increase phase), the hot water from the outlet of the second heat exchanger 23 and the hot water from the outlet of the last high-pressure heater 18 are mixed and further distributed. As the grid load gradually increases, the boiler's load increase response time is slow due to thermal inertia and other reasons, while the response time of the second peak-shaving section 3 is faster. Therefore, the flow rate to the second peak-shaving section 3 (specifically the fourth heat exchanger 33) can be increased to quickly meet the load increase requirements. As the boiler load increases, the flow rate allocated to the second peak-shaving section 3 (specifically the fourth heat exchanger 33) gradually decreases, ultimately achieving stable output.
[0025] In order to set the mass flow rate of the portion of the feedwater discharged to the second peak-shaving section 3, in one embodiment of the present invention, the mass flow rate of the portion of the feedwater discharged to the second peak-shaving section 3 is determined by the following formula:
[0026] In the formula, for The constant flow rate of water discharged to the second peak-shaving section 3 ; This is the reference mass flow rate discharged from boiler 11 to the second peak-shaving section 3 when boiler 11 is in a stable state. ; The time is calculated from the moment the load increase command is triggered. ; This is the input time constant for the second peak-shaving section 3. ; The specific heat capacity at constant pressure of molten salt. ; The difference between the set value and the temperature of the feedwater discharged to the second peak-shaving section 3. ; This is a correction factor; The target output power of boiler 11, ; Real-time feedback power contributed to boiler 11 ; This is the real-time feedback power of the second peak-shaving section 3 when boiler 11 is in a stable state. ; Let 11 be the thermal inertia constant of the boiler. .
[0027] In this embodiment, considering that the flow rate allocated to the second peak-shaving section 3 is a physical process transitioning from zero to steady state, the inventors introduced a time-dependent negative exponential function and mapped it to a gain coefficient not exceeding 1 to characterize the gradual evolution of the allocated flow rate. Furthermore, considering the significant thermal inertia of the boiler system, parameters such as the rate of change of the target output power and the real-time feedback power are used as enhancing factors for the allocated flow rate, ensuring that a jump increment sufficient to offset boiler sluggishness is generated at the moment the load increase command is triggered. Furthermore, considering the mapping relationship between the target output power and mass flow rate during energy conversion, which is negatively correlated with the specific heat capacity of the molten salt and the real-time temperature difference, their product is used as the denominator to accurately convert the power command into a flow command. Furthermore, considering that the boiler output gradually compensates for the lost power over time, a negative exponential function based on the boiler's thermal inertia constant is introduced into the dynamic part, causing the influence of this factor to decrease in a controlled manner over time. Finally, the influence of the above factors is corrected and integrated through a correction coefficient, resulting in a mass flow rate allocated to the second peak-shaving section 3 at each moment that better reflects actual operating conditions.
[0028] In one embodiment of the present invention, the second peak-shaving section 3 includes a first molten salt tank 31, a second molten salt tank 32 and a fourth heat exchanger 33. The fourth heat exchanger 33 is connected to the first molten salt tank 31, the second molten salt tank 32, the second heat exchanger 23, the last high-pressure heater 18 and the high-pressure steam turbine 12 respectively. The first molten salt tank 31 is provided with high-temperature molten salt and the second molten salt tank 32 is provided with low-temperature molten salt. During the energy release phase, the high-temperature molten salt in the first molten salt tank 31 is discharged to the second molten salt tank 32 after releasing heat through the fourth heat exchanger 33. The feedwater discharged from the last high-pressure heater 18 and the second heat exchanger 23 is heated by the fourth heat exchanger 33 to generate high-temperature steam and is discharged to the high-pressure steam turbine 12.
[0029] In this embodiment, by providing a fourth heat exchanger 33, the thermal energy stored in the high-temperature molten salt can be transferred to the feedwater discharged from the last high-pressure heater 18 and the second heat exchanger 23 during the energy release phase, and high-temperature steam for discharge to the high-pressure turbine 12 can be generated, thereby further improving the power output of the coal-fired power plant.
[0030] Due to turbine safety limitations, to further reduce output load, the second peak-shaving section 3 can be used to achieve zero-output peak shaving for coal-fired power plants. In related technologies, electric heating of molten salt is generally used directly. However, this method converts high-quality electrical energy into low-quality thermal energy to heat the molten salt and ultimately produce high-temperature steam. The electro-thermal conversion efficiency of this method is less than 1, and the quality difference between electrical and thermal energy causes considerable irreversible losses, ultimately resulting in low system round-trip efficiency.
[0031] To solve this technical problem, in one embodiment of the present invention, the second peak-shaving section 3 further includes a fifth heat exchanger 34, a sixth heat exchanger 35, a seventh heat exchanger 36, an electric motor 37, a compressor 38, and an expander 39. The fifth heat exchanger 34 is connected to the first molten salt tank 31, the second molten salt tank 32, the compressor 38, and the expander 39, respectively. The sixth heat exchanger 35 is connected to the fifth heat exchanger 34, the seventh heat exchanger 36, the compressor 38, and the expander 39, respectively. The seventh heat exchanger 36 is connected to the sixth heat exchanger 35, the expander 39, and an external low-temperature cooling water pipeline, respectively. Air flows back to the compressor 38 after passing through the compressor 38, the fifth heat exchanger 34, the sixth heat exchanger 35, the expander 39, the seventh heat exchanger 36, and the sixth heat exchanger 35 in sequence.
[0032] In this embodiment, by setting up a fifth heat exchanger 34, a sixth heat exchanger 35, a seventh heat exchanger 36, an electric motor 37, a compressor 38, and an expander 39, air sequentially passes through the compressor 38, the fifth heat exchanger 34, the sixth heat exchanger 35, the expander 39, the seventh heat exchanger 36, and the sixth heat exchanger 35 before returning to the compressor 38. In this way, heat can be extracted from the low-temperature cooling water pipeline, thereby achieving a transfer of more heat energy than the consumed electrical energy (COP>1), which can significantly improve the system's energy efficiency and reduce carbon emissions.
[0033] For example, the electrically driven compressor 38 compresses the working medium (i.e., air) from 300°C to 2.86 bar and 550°C; the working medium heats the molten salt from 305°C to 545°C through the fifth heat exchanger 34 and stores the heat in the first molten salt tank 31; the working medium entering the compressor 38 is cooled by the sixth heat exchanger 35 and then further expanded to atmospheric pressure in the expander 39 after being cooled to ambient temperature, with the temperature dropping to -44.75°C; the working medium absorbs heat from the low-temperature cooling water through the seventh heat exchanger 36 and returns to ambient temperature, and then enters the cycle again.
[0034] In one embodiment of the present invention, the electric motor 37, the compressor 38 and the expander 39 are arranged coaxially, so that the expansion work of the expander 39 can provide additional power to the coaxial compressor 38.
[0035] like Figure 1As shown, in one embodiment of the present invention, a low-temperature cooling water pipeline (i.e., NM) is connected to the condenser 15, so that the low-temperature cooling water pipeline can provide cooling to the condenser 15, thereby achieving full utilization of energy.
[0036] In summary, by coupling the first peak-shaving section 2 and the second peak-shaving section 3 to the main body 1 of a coal-fired power plant, the investment cost of the peak-shaving system can be significantly reduced by utilizing the first peak-shaving section 2, while the thermodynamic performance of the system can be significantly improved by utilizing the second peak-shaving section 3. Thus, the technical solution provided by the embodiments of the present invention can simultaneously take into account both excellent thermodynamic performance and economic performance.
[0037] The following section presents the heat exchanger parameters and temperature-output power relationship diagrams for the energy storage and release stages, using data as an example.
[0038] like Figure 3 As shown, taking a typical 600MW coal-fired power plant as an example, during the energy storage process, the main steam is discharged from port X to the first heat exchanger 22, where its temperature rises from 60℃ to 375℃. According to the temperature matching principle, the temperature of the extracted main steam decreases from 538℃ to 105℃ and then mixes with the water at the outlet of the last low-pressure heater 16 before entering the deaerator 17. The outlet temperature of the heat storage tank 21 remains constant at 60℃ to maintain the heat transfer stability of the heat exchanger. Due to the limitation of the turbine's final stage cooling flow rate, the maximum extracted steam rate is 80kg / s. The additional power reduction task is undertaken by the second peak-shaving section 3, where 106kg / s of molten salt is pumped through the fifth heat exchanger 34, raising its temperature from 305℃ to 545℃. The first peak-shaving section 2 and the second peak-shaving section 3 consume 98.535MW and 28.4004MW of electrical energy, respectively, reducing the power output from 180.00MW to 114.6116MW, a reduction of 21.15% of the rated power output.
[0039] like Figure 4 and 5As shown, during the energy release process, the 375°C heat transfer oil enters the second heat exchanger 23 and the third heat exchanger 24 to heat the bypass feedwater to reduce the turbine's extraction rate. After its temperature drops to 60°C, it enters the heat storage tank 21 for further heating. Through precise design, the water in the second heat exchanger 23 is heated from 178.93°C to 265°C. Due to the pressure difference in the heat exchangers, the water in the third heat exchanger 24 is heated from 54.04°C to 145°C and mixed with the water from the outlet of the last low-pressure heater 16 before entering the deaerator 17. The heat release time of the second peak-shaving section 3 is consistent with the heat release time of the bypass feedwater. According to the law of conservation of mass, the temperature of the molten salt flowing through the fourth heat exchanger 33 decreases from 545°C to 305°C. Its heat is used to further heat the feedwater, turning it into high-temperature steam at 538°C, which mixes with the main steam at the boiler outlet before entering the turbine for power generation. During the energy release process, the power plant's power output increased from 450MW to 518.7272MW, achieving an 11.45% increase in rated power.
[0040] Furthermore, embodiments of the present invention also provide a flexible peak-shaving method for coal-fired power plants. Based on the flexible peak-shaving system for coal-fired power plants mentioned in the above embodiments, the method includes: During the energy storage phase, a portion of the main steam entering the high-pressure turbine 12 is discharged to the deaerator 17 after being deheated by the first heat exchanger 22. The heat transfer oil in the heat storage tank 21 is returned to the heat storage tank 21 after absorbing heat by the first heat exchanger 22, so as to store the absorbed heat energy in the medium ball. The motor 37 uses the electrical energy generated by the generator 19 to drive the compressor 38 and the expander 39 to rotate. The air discharged from the compressor 38 is discharged to the sixth heat exchanger 35 after being deheated by the fifth heat exchanger 34. The molten salt in the second molten salt tank 32 is discharged to the first molten salt tank 31 after absorbing heat by the fifth heat exchanger 34. During the energy release phase, the heat transfer oil in the heat storage tank 21 passes through the second heat exchanger 23 and the third heat exchanger 24 in sequence to release heat and then flows back into the heat storage tank 21. Part of the feedwater discharged from the condenser 15 absorbs heat through the third heat exchanger 24 and is then discharged to the deaerator 17. Part of the feedwater discharged from the deaerator 17 absorbs heat through the second heat exchanger 23 and mixes with the feedwater discharged from the last high-pressure heater 18. The mixed feedwater is then discharged to the fourth heat exchanger 33. The high-temperature molten salt in the first molten salt tank 31 releases heat through the fourth heat exchanger 33 and is then discharged to the second molten salt tank 32. The feedwater absorbs heat through the fourth heat exchanger 33 to generate high-temperature steam and is then discharged to the high-pressure turbine 12.
[0041] It is understood that the flexible peak-shaving method for coal-fired power plants provided in this embodiment and the flexible peak-shaving system for coal-fired power plants provided in the above embodiments are based on the same inventive concept, and therefore have the same beneficial effects, which will not be elaborated here.
[0042] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.
[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A flexible peak-shaving system for a coal-fired power plant, characterized in that, include: The main body includes a boiler, a high-pressure steam turbine, a medium-pressure steam turbine, and a low-pressure steam turbine connected in sequence along the main steam flow direction, and a condenser, multiple low-pressure heaters, a deaerator, and multiple high-pressure heaters connected in sequence along the feedwater flow direction. The multiple low-pressure heaters are connected to the low-pressure steam turbine, the multiple high-pressure heaters are connected to the high-pressure steam turbine and the medium-pressure steam turbine, the output end of the low-pressure steam turbine is connected to a generator, the low-pressure steam turbine is connected to the condenser, and the last high-pressure heater is connected to the boiler. The first peak shaving section is connected to the high-pressure steam turbine at the inlet end and to the condenser, deaerator, and second peak shaving section at the outlet end. The first peak shaving section is used to store the thermal energy of part of the main steam entering the high-pressure steam turbine in the phase change material during the energy storage stage and to use the thermal energy stored in the phase change material to heat part of the feedwater discharged from the condenser and deaerator during the energy release stage. The second peak-shaving section is connected to the generator at the inlet and to the high-pressure steam turbine, the last high-pressure heater, and the first peak-shaving section at the outlet. The second peak-shaving section is used to convert the electrical energy generated by the generator into heat energy and store it in molten salt during the energy storage stage, and to use the heat energy stored in the molten salt to heat part of the feedwater discharged from the last high-pressure heater and the first peak-shaving section to generate high-temperature steam during the energy release stage. The other part of the feedwater discharged from the last high-pressure heater and the first peak-shaving section is used to be discharged to the boiler, and the generated high-temperature steam is used to be discharged to the high-pressure steam turbine.
2. The flexible peak-shaving system for coal-fired power plants according to claim 1, characterized in that, The first peak-shaving section includes a heat storage tank and a first heat exchanger connected to the heat storage tank. The heat storage tank is equipped with heat transfer oil and multiple medium balls made of phase change material. The first heat exchanger is connected to a high-pressure steam turbine and a deaerator, respectively. During the energy storage phase, part of the main steam entering the high-pressure turbine is discharged to the deaerator after being heated by the first heat exchanger. The heat transfer oil in the heat storage tank is returned to the heat storage tank after absorbing heat by the first heat exchanger, so as to store the absorbed heat energy in the medium ball.
3. The flexible peak-shaving system for coal-fired power plants according to claim 2, characterized in that, The first peak-shaving section also includes a second heat exchanger and a third heat exchanger connected to the heat storage tank. The second heat exchanger is connected to the deaerator and the second peak-shaving section, respectively, and the third heat exchanger is connected to the condenser and the deaerator, respectively. During the energy release phase, the heat transfer oil in the heat storage tank passes through the second and third heat exchangers in sequence to release heat and then flows back into the heat storage tank. Part of the feedwater discharged from the condenser absorbs heat through the third heat exchanger and is then discharged to the deaerator. Part of the feedwater discharged from the deaerator absorbs heat through the second heat exchanger and is then mixed with the feedwater discharged from the last high-pressure heater. Part of the mixed feedwater is then discharged to the second peak-shaving section, and the rest of the feedwater is discharged to the boiler.
4. The flexible peak-shaving system for coal-fired power plants according to claim 3, characterized in that, The first peak-shaving section also includes a first oil tank and a second oil tank. The first oil tank is filled with cold oil, and the second oil tank is connected to the heat storage tank, the first oil tank and the second heat exchanger respectively. When the outlet temperature of the heat storage tank drops below a preset value, the first oil tank opens to allow the heat transfer oil in the heat storage tank and the cold oil in the first oil tank to mix and enter the second oil tank. The mixed oil is then discharged through the second oil tank to the second heat exchanger. The oil inlet to the second heat exchanger is the same when the first oil tank is closed as when the first oil tank is open.
5. The flexible peak-shaving system for coal-fired power plants according to claim 3, characterized in that, The mass flow rate of the portion of the feedwater discharged to the second peak-shaving section is determined by the following formula: In the formula, for The constant flow rate of water discharged to the second peak-shaving section. ; This is the reference mass flow rate discharged to the second peak-shaving section when the boiler is in a stable state. ; The time is calculated from the moment the load increase command is triggered. ; This is the input time constant for the second peak-shaving portion. ; The specific heat capacity at constant pressure of molten salt. ; The difference between the setpoint and the temperature of the feedwater discharged to the second peak-shaving section. ; This is a correction factor; The target output power of the boiler, ; Real-time feedback power contributed to the boiler. ; This refers to the real-time feedback power of the second peak-shaving section when the boiler is in a stable state. ; Let be the boiler's thermal inertia constant. .
6. The flexible peak-shaving system for coal-fired power plants according to claim 3, characterized in that, The second peak-shaving section includes a first molten salt tank, a second molten salt tank, and a fourth heat exchanger. The fourth heat exchanger is connected to the first molten salt tank, the second molten salt tank, the second heat exchanger, the last high-pressure heater, and the high-pressure steam turbine. The first molten salt tank contains high-temperature molten salt, and the second molten salt tank contains low-temperature molten salt. During the energy release phase, the high-temperature molten salt in the first molten salt tank is discharged to the second molten salt tank after releasing heat through the fourth heat exchanger. The feedwater discharged from the last high-pressure heater and the second heat exchanger is heated by the fourth heat exchanger to generate high-temperature steam and is discharged to the high-pressure turbine.
7. The flexible peak-shaving system for coal-fired power plants according to claim 6, characterized in that, The second peak-shaving section also includes a fifth heat exchanger, a sixth heat exchanger, a seventh heat exchanger, an electric motor, a compressor, and an expander. The fifth heat exchanger is connected to the first molten salt tank, the second molten salt tank, the compressor, and the expander, respectively. The sixth heat exchanger is connected to the fifth heat exchanger, the seventh heat exchanger, the compressor, and the expander, respectively. The seventh heat exchanger is connected to the sixth heat exchanger, the expander, and an external low-temperature cooling water pipeline, respectively. Air flows back to the compressor after passing through the compressor, the fifth heat exchanger, the sixth heat exchanger, the expander, the seventh heat exchanger, and the sixth heat exchanger in sequence.
8. The flexible peak-shaving system for coal-fired power plants according to claim 7, characterized in that, The electric motor, compressor, and expander are arranged coaxially.
9. The flexible peak-shaving system for coal-fired power plants according to claim 7, characterized in that, Low-temperature cooling water pipeline and condenser connection.
10. A flexible peak-shaving method for coal-fired power plants, characterized in that, The flexible peak-shaving system for coal-fired power plants based on any one of claims 7-9 includes: During the energy storage stage, part of the main steam entering the high-pressure turbine is discharged to the deaerator after being heated by the first heat exchanger. The heat transfer oil in the heat storage tank is returned to the heat storage tank after absorbing heat by the first heat exchanger, so as to store the absorbed heat energy in the medium ball. The electric motor uses the electrical energy generated by the generator to drive the compressor and expander to rotate. The air discharged from the compressor is discharged to the sixth heat exchanger after being heated by the fifth heat exchanger. The molten salt in the second molten salt tank is discharged to the first molten salt tank after absorbing heat by the fifth heat exchanger. During the energy release phase, the heat transfer oil in the heat storage tank passes through the second and third heat exchangers in sequence to release heat and then flows back into the heat storage tank. Part of the feedwater discharged from the condenser absorbs heat through the third heat exchanger and is then discharged to the deaerator. Part of the feedwater discharged from the deaerator absorbs heat through the second heat exchanger and mixes with the feedwater discharged from the last high-pressure heater. The mixed feedwater is then discharged to the fourth heat exchanger. The high-temperature molten salt in the first molten salt tank releases heat through the fourth heat exchanger and is then discharged to the second molten salt tank. The feedwater absorbs heat through the fourth heat exchanger to generate high-temperature steam and is then discharged to the high-pressure turbine.