A hot air feed water flue gas steam coupling deep peak shaving system

Abstract

The present application relates to a kind of hot air feed water flue gas steam coupling deep peak shaving system applied to the field related to thermal power generation, by arranging back pressure machine, secondary air heater in machine furnace coupling regenerative system and the series connection of both with No.1 high pressure heater, new regenerative coupling system is formed;The system extracts steam of main steam system under low load, part is used to replace power-driven pump or fan, another part is used to heat secondary air, coupling of hot air and steam is formed, quality and efficiency are realized, while the temperature of main steam and reheat steam is improved, and the temperature of feed water entering boiler coal economizer is improved, and the inlet flue gas temperature of SCR denitration system is improved, the coupling of feed water flue gas and steam is formed, thereby the low load combustion stability of boiler is improved, the coal consumption rate of unit is reduced, the problem of industrial steam supply of unit and thermal decoupling is realized, while the load rate of dry-wet state conversion of thermal power unit is reduced, the operation economy of unit and the service life of unit are improved.

Description

Technical Field

[0001] The present invention relates to a peak-shaving system, and more particularly to a deep peak-shaving system with hot air feedwater flue gas steam coupling applied in the field of thermal power generation. Background Technology

[0002] In recent years, with the rapid growth of the proportion of new energy (wind power and photovoltaic) power generation in the country, the flexible operation capability of thermal power units as peak-shaving power sources urgently needs to be improved. The unit load needs to be frequently reduced to 15%-20% of the rated load or even lower for deep peak shaving. Under this condition, a series of technical challenges emerge: First, the unit's coal consumption for power generation increases significantly. For example, the coal consumption for power generation of a 1000MW unit under 20% THA conditions can be as high as 375g / kWh, far exceeding the 285g / kWh under THA conditions. Second, the boiler furnace temperature decreases, and the stable combustion capability deteriorates, often requiring oil injection for combustion assistance, increasing operating costs and posing safety hazards. Third, the economizer outlet flue gas temperature decreases accordingly, often below 280℃ under 30% rated load, failing to meet the normal operating temperature window of the SCR denitrification catalyst, resulting in decreased denitrification efficiency, increased ammonia slip rate, and potential air preheater blockage. In addition, the main steam and reheat steam temperatures deviate significantly from the design values ​​under low load, affecting the unit's thermal economy and turbine safety. Finally, the pressure of industrial heating extraction steam (usually from cold reheat steam) is also difficult to meet the heating parameter requirements under low load.

[0003] To address the aforementioned issues, existing technologies have proposed several improvement solutions. For example, Chinese patent CN108843412B discloses a turbine regenerative system, which employs a dual-turbine system consisting of a back-pressure turbine and a feedwater pump turbine. The exhaust steam from the back-pressure turbine is used for regenerative heating, aiming to improve cycle efficiency and simplify regulation and control. However, this system primarily optimizes the regenerative process and does not address utilizing steam energy to enhance boiler air temperature and combustion stability, nor does it solve the problems of excessively low SCR inlet flue gas temperature and industrial extraction steam parameter matching. Another example is Chinese patent CN111677568A, which discloses a combined large and small turbine back-pressure heating system and method. This system utilizes the surplus pressure head of the extracted steam from the back-pressure turbine to generate electricity for subsequent heating, achieving cascaded energy utilization. However, the core of this solution lies in improving heating economy; its application scenarios and functional design focus on external heating rather than addressing the inherent problems of the boiler and turbine itself under deep peak-shaving conditions, such as improving main / reheat steam temperature and enhancing boiler combustion stability.

[0004] Therefore, existing technologies lack a comprehensive technical solution that can systematically and holistically address the challenges of drastically increased coal consumption for power generation during deep peak shaving in thermal power units, difficulties in stable boiler combustion, excessively low SCR flue gas temperature, low main reheat steam temperature, high dry-wet state transition load rates, and industrial steam extraction assurance. It is necessary to develop a novel system that deeply couples hot air, feedwater, flue gas, and steam to achieve efficient cascaded energy utilization and safe, flexible operation. Summary of the Invention

[0005] In view of the above-mentioned prior art, the technical problem to be solved by the present invention is that the coal consumption for power generation increases significantly under low load of thermal power units, and the combustion of boilers is unstable, and the inlet flue gas temperature of SCR denitrification system is also difficult to meet the standard.

[0006] To address the aforementioned problems, this invention provides a deep peak-shaving system for hot air feedwater flue gas steam coupling, comprising a main steam pipeline connected to a thermal power unit, a peak-shaving unit connected to the middle of the main steam pipeline, a high-pressure turbine cylinder connected to the end of the main steam pipeline, and a high-pressure heater feedwater heating system. The high-pressure heater feedwater heating system includes a No. 1 high-pressure heater and a No. 2 high-pressure heater connected in series. The thermal power unit includes a boiler and, along the flue gas flow direction, a superheated steam system, a reheated steam system, an economizer, an SCR denitrification system, and an air preheater, arranged sequentially within the boiler. A combustion air supply is installed on each side of the boiler furnace. A section of extraction steam pipeline connects the steam turbine high-pressure cylinder and the No. 1 high-pressure heater. An extraction steam check valve is installed on the extraction steam pipeline. The exhaust end of the steam turbine high-pressure cylinder is also connected to two parallel extraction steam pipelines to the reheater and a second extraction steam pipeline. The ends of the second extraction steam pipeline to the reheater and the second extraction steam pipeline are respectively connected to the reheat steam system and the No. 2 high-pressure heater. A second extraction steam check valve is installed on the second extraction steam pipeline. The end of the No. 1 high-pressure heater is connected to the economizer via a main feedwater pipeline. The inlet end of the No. 2 high-pressure heater is connected to the high-pressure heater feedwater pipeline.

[0007] The peak-shaving unit includes a back-pressure turbine and a secondary air heater. The tube-side inlets of the back-pressure turbine and the secondary air heater are connected in series via the back-pressure turbine exhaust pipe. The inlet of the back-pressure turbine is fixedly connected to the middle of the main steam pipe via a superheated steam system extraction pipe. A superheated steam extraction isolation and regulating valve is installed on the superheated steam system extraction pipe. A pipe leading to the secondary air heater is connected between the shell-side inlet of the secondary air heater and the outlet of the air preheater. A pipe leading to the combustion air box is connected between the shell-side outlet of the secondary air heater and the combustion air box. A pipe leading to the secondary air heater exhaust pipe is connected to the tube-side outlet of the secondary air heater. At the end of the secondary air heater exhaust pipe, a pipe leading to the industrial extraction steam system and a steam pipe leading to the high-pressure heater are connected in parallel to the high-pressure heater feedwater heating system. Along the steam flow direction, an industrial extraction steam regulating isolation valve and an industrial extraction steam check valve are installed sequentially on the pipe leading to the industrial extraction steam system. A steam check valve leading to the high-pressure heater system and a regulating isolation valve leading to the high-pressure heater system are connected sequentially on the steam pipe leading to the high-pressure heater system.

[0008] In the aforementioned hot air feedwater flue gas steam coupling deep peak shaving system, under the low load operation condition of the unit, it not only improves the unit's stable combustion capability and reduces the unit's dry-wet state conversion load rate, but also matches industrial steam extraction sources to achieve energy cascade utilization and efficient industrial heating. At the same time, it effectively increases the inlet flue gas temperature of the SCR denitrification system, enabling the unit to better adapt to flexible retrofitting and operation.

[0009] As a further improvement to this application, the steam pipeline to the high-pressure heater is connected in parallel with the No. 1 high-pressure heater, and temperature sensors are installed at the inlets of the reheat steam system, economizer, and SCR denitrification system.

[0010] As a further improvement of this application, the back pressure machine directly drives the driven equipment, which is one or both of a pump or a fan.

[0011] As another improvement of this application, an overspeed protection system is installed on the back pressure unit. Three speed sensors are installed on the rotor of the back pressure unit. The three speed sensors are connected to the overspeed protection system. The overspeed protection system includes a calculation module, an alarm unit, a steam diversion module, a rapid emergency shut-off valve, a reverse braking module, and a control center installed on the back pressure unit. The rapid emergency shut-off valve is installed on the superheated steam system extraction pipe and is connected in series with the superheated steam extraction isolation regulating valve. The overspeed protection system also includes a flow meter and a pressure meter installed at the outlet of the driven equipment, as well as a recirculation valve installed on the driven equipment.

[0012] As a further improvement to this application, the steam diversion module includes a diversion pipe connected between the superheated steam system extraction pipe and the back compressor exhaust pipe, and a solenoid valve installed on the diversion pipe.

[0013] As a further improvement to this application, the overspeed protection system's protection steps are as follows:

[0014] S11. The rotational speed of the back pressure machine rotor is monitored in real time by a speed sensor, and the rate of change of the data obtained by each speed sensor is calculated in real time by a calculation module. When the rate of change of the data obtained by one speed sensor exceeds the preset safety value, it indicates that the rotor of the back pressure machine is accelerating.

[0015] S12. Monitor the flow and pressure changes at the outlet of the driven equipment in real time using flow meters and pressure gauges. When a sudden drop in flow or pressure occurs, it indicates that the load is about to disappear.

[0016] S13. When the rotor accelerates and the load is about to disappear at the same time, the alarm unit is triggered to sound an alarm and issue a corresponding warning. At the same time, the control center automatically controls the opening of the superheated steam extraction isolation regulating valve to reduce the power source in advance and suppress the upward trend of the speed.

[0017] S2. When the speed of the back pressure machine rotor continues to rise and exceeds the rated speed, the reverse braking module is triggered, causing the control center to control the recirculation valve on the driven equipment to open significantly, thereby instantly increasing the load on the back pressure machine, forcibly consuming its rotor kinetic energy, and forcing its speed to drop.

[0018] S3. If the rotor speed of the back pressure unit continues to increase after the first two protection steps, or if the speed is ≥110% of the rated speed, the control center will control the rapid emergency shut-off valve to close directly, thereby cutting off the steam source. At the same time, the steam diversion module will be triggered, so that the remaining steam in the pipeline will be diverted again and directly bypass the back pressure unit to reach the secondary air heater, thereby achieving rapid depressurization of the back pressure unit and effectively eliminating the expansion and work capacity of the residual steam.

[0019] S4. Finally, the control center shuts down the peak-shaving unit until the anomaly is repaired and then restarted.

[0020] As a further improvement to this application, the overspeed protection system also includes a data storage module. The data from the speed sensor, pressure gauge, and flow meter are all stored in the data storage module. The data storage module also has a separate abnormal dataset, which stores the abnormal data acquired by the speed sensor, pressure gauge, and flow meter, as well as the time nodes corresponding to the abnormal data.

[0021] In summary, by arranging a back-pressure turbine and a secondary air heater in the boiler-turbine coupled regenerative system and connecting them in series with the No. 1 high-pressure heater, a new regenerative coupling system is formed. An industrial steam extraction adjustment system is then installed in this new system and optimized to match the existing industrial steam extraction system, reducing the unit's coal consumption rate for power generation and achieving cascaded energy utilization and efficient industrial heating. Under low load, this system extracts steam from the main steam system, using part of it to replace electrically driven pumps or fans, reducing energy consumption, and the other part to heat the secondary air, thus coupling hot air and steam, achieving improved quality and efficiency. Simultaneously, it increases the temperature of the main steam, reheat steam, and feedwater entering the boiler economizer, as well as the inlet flue gas temperature of the SCR denitrification system, forming a coupling between feedwater, flue gas, and steam. This improves the boiler's low-load stable combustion capability, decoupling the unit's industrial steam supply from thermal power, while reducing the load rate during dry-wet state transitions in thermal power units, improving the unit's operating economy and lifespan. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the regenerative system of the deep peak-shaving technology for coupling hot air feedwater flue gas and steam in the first embodiment of this application.

[0023] Figure 2 This is a schematic diagram of a traditional regenerative system.

[0024] Figure 3 This is a system block diagram of an overspeed protection system installed on a back pressure machine according to the second embodiment of this application.

[0025] Figure 4 This is a schematic diagram of the rotational speed monitoring process according to the second embodiment of this application;

[0026] Figure 5 This is a schematic diagram of the steam diversion module according to the second embodiment of this application;

[0027] Figure 6 This is a schematic diagram of the steam diversion module being triggered according to the second embodiment of this application;

[0028] Figure 7 This is a schematic block diagram of the data storage module according to the second embodiment of this application;

[0029] Figure 8 This is a flowchart of the overspeed protection system according to the second embodiment of this application.

[0030] Explanation of the labels in the diagram:

[0031] 1. Boiler; 2. Superheated steam system; 3. Reheated steam system; 4. Economizer; 5. SCR denitrification system; 6. Air preheater; 7. Combustion air box; 8. High-pressure cylinder of steam turbine; 9. Back pressure compressor; 10. Secondary air heater; 11. No. 1 high-pressure heater; 12. No. 2 high-pressure heater; 13. Superheated steam extraction isolation regulating valve; 14. Industrial extraction steam non-return valve; 15. Industrial extraction steam regulating isolation valve; 16. First stage extraction steam non-return isolation valve; 17. Steam non-return valve to high-pressure heater system; 18. Regulating isolation valve to high-pressure heater system; 19. Second stage extraction steam non-return isolation valve.

[0032] a. Main steam pipeline; c. Main feedwater pipeline; d. First-stage extraction steam pipeline; e. Second-stage extraction steam pipeline to reheater; f. Second-stage extraction steam pipeline; g. Superheated steam system extraction steam pipeline; h. Back-compressor exhaust steam pipeline; j. Secondary air heater exhaust steam pipeline; k. Pipeline to industrial extraction steam system; l. Air pipeline to combustion air box; m. Air pipeline to secondary air heater; n. Steam pipeline to high-pressure heater; o. High-pressure heater feedwater pipeline. Detailed Implementation

[0033] The two embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0034] First implementation method:

[0035] Figure 1 This invention illustrates a deep peak-shaving system for hot air feedwater flue gas steam coupling, comprising a main steam pipe a connected to a thermal power unit, a peak-shaving unit connected to the middle of the main steam pipe a, a turbine high-pressure cylinder 8 connected to the end of the main steam pipe a, and a high-pressure heater feedwater heating system. The high-pressure heater feedwater heating system includes a first high-pressure heater 11 and a second high-pressure heater 12 connected in series. The thermal power unit includes a boiler 1 and, along the flue gas flow direction, a superheated steam system 2, a reheated steam system 3, an economizer 4, an SCR denitrification system 5, and an air preheater 6 within the boiler 1. A combustion air box 7 is installed on each side of the furnace of the boiler 1. The turbine high-pressure cylinder 8 and... A section of extraction steam pipe d is connected between the No. 1 high-pressure heater 11 and the No. 1 high-pressure heater 11. A section of extraction steam check valve 16 is installed on the extraction steam pipe d. The exhaust end of the turbine high-pressure cylinder 8 is also connected to two parallel extraction steam pipes e and f leading to the reheater. The ends of the two extraction steam pipes e and f are respectively connected to the reheat steam system 3 and the No. 2 high-pressure heater 12. A section of extraction steam check valve 19 is installed on the extraction steam pipe f. The end of the No. 1 high-pressure heater 11 is connected to the economizer 4 via the main feedwater pipe c. The inlet end of the No. 2 high-pressure heater 12 is connected to the high-pressure heater feedwater pipe o.

[0036] The peak-shaving unit includes a back-pressure turbine 9 and a secondary air heater 10. The back-pressure turbine 9 replaces the electric drive to directly drive the pump or fan. The back-pressure turbine 9 can also be a small back-pressure steam turbine. The tube-side inlet of the back-pressure turbine 9 and the secondary air heater 10 are connected in series via the back-pressure turbine exhaust pipe h. The inlet of the back-pressure turbine 9 is fixedly connected to the middle of the main steam pipe a via a superheated steam system extraction pipe g. A superheated steam extraction isolation regulating valve 13 is installed on the superheated steam system extraction pipe g. The shell-side inlet of the secondary air heater 10 is connected to the outlet of the air preheater 6 via a pipe m leading to the secondary air heater. The shell-side outlet of the secondary air heater 10 is connected to the combustion air box 7 via a pipe l leading to the combustion air box. The tube-side outlet of the secondary air heater 10 is connected to the secondary air heater exhaust pipe j. The end of the secondary air heater exhaust pipe j is connected in parallel with... The industrial extraction steam system is connected to the industrial extraction steam system pipeline k, and the high-pressure heater feedwater heating system is connected to the high-pressure heater steam pipeline n. The high-pressure heater steam pipeline n is connected in parallel with the No. 1 high-pressure heater 11. Along the steam flow direction, the industrial extraction steam regulating isolation valve 15 and the industrial extraction steam check valve 14 are installed sequentially on the industrial extraction steam system pipeline k. The high-pressure heater steam pipeline n is connected sequentially to the high-pressure heater system steam check valve 17 and the high-pressure heater system regulating isolation valve 18. In the above-mentioned hot air feedwater flue gas steam coupling deep peak shaving system, under the low load operation condition of the unit, it not only improves the unit's stable combustion capability, but also matches the industrial extraction steam source to achieve energy cascade utilization and efficient industrial heating. At the same time, it effectively increases the inlet flue gas temperature of the SCR denitrification system, making the unit better adaptable to flexible modification and operation.

[0037] When the unit is working, pressurized feedwater from the outlet of No. 2 high-pressure heater 12 enters No. 1 high-pressure heater 11. Part of the steam source of No. 1 high-pressure heater 11 is taken from the extraction steam of the high-pressure cylinder 8 of the steam turbine, and enters No. 1 high-pressure heater 11 through a section of extraction steam pipeline d. A section of extraction steam non-return isolation valve 16 arranged on the section of extraction steam pipeline d plays the role of isolation and preventing steam backflow.

[0038] Part of the steam on the main steam pipe a enters the back pressure turbine 9 through the superheated steam system extraction pipe g, and then heats the secondary air. The heated steam enters the No. 1 high-pressure heater 11 of the high-pressure heater feedwater heating system through the steam pipe n leading to the high-pressure heater, and heats the feedwater there. This part of the steam is another part of the steam source for the No. 1 high-pressure heater 11. The feedwater, the steam passing through the turbine high-pressure cylinder 8, and the steam that has been reheated by the back pressure turbine 9 and the secondary air heater 10 are all heated together in the No. 1 high-pressure heater 11 and then go to the economizer 4 through the main feedwater pipe c. This effectively increases the feedwater temperature at the inlet of the economizer 4, which in turn increases the outlet flue gas temperature, increases the heat load of the boiler water-cooled wall area, and indirectly improves the low-load stable combustion capability.

[0039] When the outlet flue gas temperature of economizer 4 is increased, it will directly enter the SCR denitrification system 5, which will increase the inlet flue gas temperature of SCR denitrification system 5, thus realizing flexible operation under deep peak shaving of the unit.

[0040] In addition, during the above process, the steam originally going to the high-pressure cylinder 8 of the turbine is partially diverted to the back compressor 9, which reduces the amount of steam entering the high-pressure cylinder 8 of the turbine. However, the heat absorption capacity of the reheat steam system 3 is not weakened, thereby passively increasing the temperature of the reheat steam that passes through the high-pressure cylinder 8 of the turbine and goes to the reheater pipe e after the second stage extraction, thus effectively reducing the coal consumption for power generation of the unit.

[0041] Meanwhile, the steam passing through the back pressure unit 9 will enter the secondary air heater 10 along the back pressure unit exhaust pipe h. The air returning from the air preheater 6 to the combustion air box 7 will first pass through the secondary air heater 10 and fully contact the heated steam to achieve heat exchange. This will significantly increase the temperature of the combustion air entering the boiler under low load conditions, enhance the boiler's low load stable combustion capability, reduce the carbon content of fly ash and slag, thereby improving the boiler's combustion efficiency and further reducing the unit's coal consumption rate for power supply. At the same time, it will increase the temperature of the main steam generated at the superheated steam system 2.

[0042] In addition, some of the steam that has been heated by the back pressure unit 9 and the secondary air heater 10 is split at the steam pipeline n leading to the high pressure heater and the pipeline k leading to the industrial extraction steam system. Part of the steam goes to the high pressure heater feedwater heating system, while the other part of the steam can go to the original unit's industrial extraction steam system for optimized matching along the pipeline k leading to the industrial extraction steam system. Furthermore, the back pressure unit 9 can drive a pump or fan according to the steam quality parameters, replacing electric drive, to improve the utilization rate of steam thermal energy and reduce energy consumption.

[0043] Temperature sensors are installed at the inlets of the reheat steam system 3, economizer 4, and SCR denitrification system 5. These sensors can effectively monitor the temperature of the steam or gas entering each unit during operation, allowing for timely adjustment of the back pressure compressor 9 based on temperature changes. This ensures stable operation of the peak-shaving system and enhances the generator set's combustion stability under low-load conditions.

[0044] In summary, by arranging a back-pressure turbine, a secondary air heater, and a No. 1 high-pressure heater 11 in parallel within the boiler-turbine coupled regenerative system, a new regenerative coupling system is formed. Simultaneously, an industrial steam extraction adjustment system is installed within the system, optimized and matched with the existing industrial steam extraction system, reducing the unit's coal consumption rate for power supply and achieving cascaded energy utilization and efficient industrial heating. This system extracts steam from the main steam system under low load, using part of it to replace electrically driven pumps or fans, reducing energy consumption, and the other part to heat the secondary air, forming a coupling between hot air and steam, thus improving quality and efficiency. It also increases the temperature of the main steam, reheat steam, and feedwater entering the boiler economizer, as well as the inlet flue gas temperature of the SCR denitrification system, forming a coupling between feedwater, flue gas, and steam. This improves the boiler's stable combustion capability under low load, decoupling the unit's industrial steam supply from thermal power, while reducing the load rate during dry-wet state transitions in thermal power units, improving the unit's operating economy and lifespan.

[0045] Second implementation method:

[0046] Since the improvement of this peak-shaving system mainly involves the setting of the back pressure unit 9, and the back pressure unit 9 is prone to overspeed abnormalities during actual use, when it becomes abnormal, it will not only affect the stable operation of the unit, but also cause the rotor blades to break, resulting in significant economic losses and safety hazards. Based on this problem, this embodiment adds an overspeed protection system for the back pressure unit 9 on the basis of the first embodiment, while the rest remains the same as the first embodiment.

[0047] Figure 3 As shown, an overspeed protection system is installed on the back pressure unit 9. Three speed sensors are installed on the rotor of the back pressure unit 9. For example, the three speed sensors can be evenly distributed around the rotor at 120° intervals. The three speed sensors are connected to the overspeed protection system. The overspeed protection system includes a calculation module, an alarm unit, a steam diversion module, a rapid emergency shut-off valve, a reverse braking module, and a control center installed on the back pressure unit 9. The rapid emergency shut-off valve is installed on the superheated steam system extraction pipe g and is connected in series with the superheated steam extraction isolation regulating valve 13. The overspeed protection system also includes a flow meter and a pressure gauge installed at the outlet of the driven equipment, as well as a recirculation valve installed on the driven equipment.

[0048] like Figure 5 The steam diversion module includes a diversion pipe connected between the superheated steam system extraction pipe g and the back pressure turbine exhaust pipe h, as well as a solenoid valve installed on the diversion pipe.

[0049] like Figure 8 The overspeed protection system's overspeed protection steps for the back pressure unit 9 are as follows:

[0050] S1. Early Warning and Prevention:

[0051] S11. The rotational speed of the back pressure unit 9 rotor is monitored in real time by a speed sensor, and the rate of change of the data acquired by each speed sensor is calculated in real time by a calculation module, such as... Figure 4 When the rate of change of data obtained by more than one speed sensor exceeds the preset safety value, it indicates that the rotor of the back pressure machine 9 is accelerating. The preset safety value here can be selected and set according to actual needs.

[0052] S12. Monitor the flow and pressure changes at the outlet of the driven equipment in real time using flow meters and pressure gauges. When a sudden drop in flow or pressure occurs, it indicates that the load is about to disappear.

[0053] S13. When the rotor accelerates and the load is about to disappear at the same time, the alarm unit is triggered to sound an alarm and issue a corresponding warning, such as alerting the staff to the abnormal situation of rotor acceleration or the load about to disappear through sound and light alarm or voice broadcast. At the same time, the control center automatically controls the opening of the superheated steam extraction isolation regulating valve 13 to reduce the power source in advance and suppress the upward trend of speed.

[0054] S2. When the speed of the back pressure machine rotor continues to rise and exceeds the rated speed, the reverse braking module is triggered, causing the control center to control the recirculation valve on the driven equipment to open significantly, thereby instantly increasing the load on the back pressure machine 9, forcibly consuming its rotor kinetic energy, and forcing its speed to drop.

[0055] S3. If, after the first two protective steps, the rotor speed of the back pressure unit 9 continues to increase, or the speed is ≥110% of the rated speed, the control center will directly close the rapid emergency shut-off valve to cut off the steam source. Figure 6 At the same time, the steam diversion module is triggered, that is, the solenoid valve opens, so that the remaining steam in the pipeline is diverted again, and some residual steam can flow into the diversion pipe, thereby directly bypassing the back pressure machine 9 and reaching the secondary air heater 10, realizing rapid depressurization of the back pressure machine 9 and effectively eliminating the expansion and work capacity of the residual steam.

[0056] S4. Finally, the control center shuts down the peak-shaving unit until the anomaly is repaired and then restarted.

[0057] like Figure 7 The overspeed protection system also includes a data storage module. Data from the speed sensor, pressure gauge, and flow meter are all stored in the data storage module. The data storage module also has a separate abnormal dataset, which stores the abnormal data acquired by the speed sensor, pressure gauge, and flow meter, as well as the corresponding time points. By recording the abnormal data, it is easier for staff to determine the time point of the abnormality and related abnormal data when maintaining the back pressure machine 9. This facilitates the development of relevant maintenance measures based on the data and reduces the difficulty of maintenance.

[0058] In light of current practical needs, the above-described embodiments adopted in this application are not limited to these. Any changes made within the scope of knowledge possessed by those skilled in the art without departing from the concept of this application still fall within the protection scope of this invention.

Claims

1. A deep peak-shaving system for hot air feedwater flue gas steam coupling, characterized in that: The system includes a main steam pipe (a) connected to the thermal power unit, a peak-shaving unit connected to the middle of the main steam pipe (a), a turbine high-pressure cylinder (8) connected to the end of the main steam pipe (a), and a high-pressure heater feedwater heating system. The high-pressure heater feedwater heating system includes a No. 1 high-pressure heater (11) and a No. 2 high-pressure heater (12) connected in series. The thermal power unit includes a boiler (1) and a superheated steam system (2), a reheated steam system (3), an economizer (4), an SCR denitrification system (5), and an air preheater (6) arranged sequentially along the flue gas flow direction. A combustion air box (7) is installed on each side of the furnace of the boiler (1). The turbine high-pressure cylinder (8) and the No. 1 high-pressure heater (11) are connected. A section of extraction steam pipe (d) is connected to the turbine. A section of extraction steam check valve (16) is installed on the extraction steam pipe (d). The exhaust end of the turbine high-pressure cylinder (8) is also connected to two parallel extraction steam pipes to the reheater (e) and two extraction steam pipes (f). The ends of the two extraction steam pipes to the reheater (e) and the two extraction steam pipes (f) are respectively connected to the reheat steam system (3) and the second high-pressure heater (12). A two-stage extraction steam check valve (19) is installed on the two extraction steam pipes (f). The end of the first high-pressure heater (11) is connected to the economizer (4) via a main feedwater pipe (c). The inlet end of the second high-pressure heater (12) is connected to the high-pressure heater feedwater pipe (o). The peak-shaving unit includes a back-pressure turbine (9) and a secondary air heater (10). The tube-side inlet of the back-pressure turbine (9) and the secondary air heater (10) are connected in series via a back-pressure turbine exhaust pipe (h). The inlet of the back-pressure turbine (9) is fixedly connected to the middle of the main steam pipe (a) via a superheated steam system extraction pipe (g). A superheated steam extraction isolation regulating valve (13) is installed on the superheated steam system extraction pipe (g). The shell-side inlet of the secondary air heater (10) is connected to the air preheater (6). A duct (m) leading to the secondary air heater is connected between the outlets. A duct (l) leading to the combustion air box is connected between the shell-side outlet of the secondary air heater (10) and the combustion air box (7). A steam exhaust duct (j) of the secondary air heater (10) is connected to the tube-side outlet of the secondary air heater (10). At the end of the steam exhaust duct (j) of the secondary air heater, a duct (k) leading to the industrial extraction steam system and a steam duct (n) leading to the high-pressure heater are connected in parallel to the industrial extraction steam system and the high-pressure heater feedwater heating system. Along the direction of steam flow, an industrial extraction steam regulating isolation valve (15) and an industrial extraction steam non-return valve (14) are installed sequentially on the pipeline (k) leading to the industrial extraction steam system, and a steam non-return valve (17) leading to the high-pressure heater system and an regulating isolation valve (18) leading to the high-pressure heater system are connected sequentially on the steam pipeline (n) leading to the high-pressure heater system. The back pressure machine (9) is equipped with an overspeed protection system. Three speed sensors are installed on the rotor of the back pressure machine (9). The three speed sensors are connected to the overspeed protection system. The overspeed protection system includes a calculation module, an alarm unit, a steam diversion module, a rapid emergency shut-off valve, a reverse braking module, and a control center installed on the back pressure machine (9). The rapid emergency shut-off valve is installed on the superheated steam system extraction pipe (g) and is connected in series with the superheated steam extraction isolation regulating valve (13). The overspeed protection system also includes a flow meter, a pressure meter installed at the outlet of the driven equipment, and a recirculation valve installed on the driven equipment. The steam diversion module includes a diversion pipe connected between the superheated steam system extraction pipe (g) and the back pressure turbine exhaust pipe (h) and a solenoid valve installed on the diversion pipe; The overspeed protection system's protection steps are as follows: S1. Early Warning and Prevention: S11. The rotational speed of the back pressure machine (9) rotor is monitored in real time by the speed sensor, and the change rate of the data obtained by each speed sensor is calculated in real time by the calculation module. When the change rate of the data obtained by one speed sensor exceeds the preset safety value, it indicates that the rotor of the back pressure machine (9) is accelerating. S12. Monitor the flow and pressure changes at the outlet of the driven equipment in real time using flow meters and pressure gauges. When a sudden drop in flow or pressure occurs, it indicates that the load is about to disappear. S13. When the rotor accelerates and the load is about to disappear at the same time, the alarm unit is triggered to issue an alarm and make a corresponding warning. At the same time, the control center automatically controls the opening of the superheated steam extraction isolation regulating valve (13) to decrease. S2. When the speed of the back pressure machine rotor continues to rise and exceeds the rated speed, the reverse braking module is triggered, causing the control center to control the recirculation valve on the driven equipment to open significantly, thereby instantly increasing the load of the back pressure machine (9), forcibly consuming its rotor kinetic energy, and forcing its speed to drop. S3. After the first two protection steps, if the rotor speed of the back pressure machine (9) continues to increase or the speed is ≥110% of the rated speed, the control center controls the rapid emergency shut-off valve to close directly, thereby cutting off the steam source. At the same time, the steam diversion module is triggered, so that the remaining steam in the pipeline is diverted again and directly crosses the back pressure machine (9) to reach the secondary air heater (10), thereby achieving rapid depressurization of the back pressure machine (9). S4. Finally, the control center shuts down the peak-shaving unit until the anomaly is repaired and then restarted.

2. The hot air feedwater flue gas steam coupling deep peak-shaving system according to claim 1, characterized in that: The steam pipeline (n) leading to the high-pressure heater is connected to the No. 1 high-pressure heater (11), and temperature sensors are installed at the inlets of the reheat steam system (3), economizer (4) and SCR denitrification system (5).

3. The hot air feedwater flue gas steam coupling deep peak-shaving system according to claim 1, characterized in that: The back pressure unit (9) directly drives the pump or fan instead of the electric drive, and the pump or fan is the driven device.

4. The hot air feedwater flue gas steam coupling deep peak-shaving system according to claim 1, characterized in that: The overspeed protection system also includes a data storage module, in which the data from the speed sensor, pressure gauge, and flow meter are all stored. The data storage module also has a separate abnormal dataset, which stores the abnormal data acquired by the speed sensor, pressure gauge, and flow meter, as well as the time nodes corresponding to the abnormal data.

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