Coal-fired generator set low-load energy-saving efficiency-improving system based on thermodynamic system reconstruction

Abstract

The invention discloses a coal-fired generator set low-load energy-saving efficiency-improving system based on thermodynamic system reconstruction, which comprises a boiler, a main steam pipeline, a flue gas pipeline and a secondary air pipeline are connected to the boiler, and a branch pipeline is connected to the main steam pipeline; the steam turbine assembly comprises a high-pressure cylinder; the fan assembly comprises an induced draft fan and an air feeder; the heating assembly comprises a hot air heater, the hot air heater is arranged in the secondary air pipeline, part of the branch pipeline is arranged in the secondary air pipeline in a penetrating mode and penetrates through the hot air heater, in the first operation state, no steam passes through the branch pipeline, and in the second operation state, no steam passes through the branch pipeline. The steam flow direction of the part, located in the hot air heater, of the branch pipeline is opposite to the flow direction of secondary air in the secondary air pipeline. According to the coal-fired generator set low-load energy-saving efficiency-improving system based on thermodynamic system reconstruction, the combustion stability can be improved, the boiler efficiency can be improved, and the heat loss can be reduced.

Description

Technical Field

[0001] This invention relates to the field of thermal power generation technology, and in particular to a low-load energy-saving and efficiency-enhancing system for coal-fired power generating units based on thermal system reconfiguration. Background Technology

[0002] With the increasing installed capacity of new energy power generation, its power output is greatly affected by environmental factors, making it impossible to provide a continuous and stable supply of electricity. Therefore, coal-fired power generating units need to undertake more peak-shaving tasks to balance the grid load.

[0003] In existing technologies, under low-load operation, the furnace combustion temperature is low. To ensure combustion stability, it is often necessary to increase the secondary air volume, i.e., increase the operating oxygen content and improve the excess air coefficient. However, even with a significant increase in operating oxygen content, coal-fired boilers still suffer from low burnout rates, high carbon content in slag and fly ash, and increased incomplete heat loss. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a low-load energy-saving and efficiency-enhancing system for coal-fired power generating units based on thermal system reconfiguration. This system can increase the temperature of secondary air, improve combustion stability, enhance boiler efficiency, reduce heat loss, and protect the boiler, extending its service life.

[0005] According to an embodiment of the present invention, a low-load energy-saving and efficiency-enhancing system for a coal-fired power generating unit based on thermal system reconfiguration includes: a boiler, wherein a main steam pipe, a flue gas pipe, and a secondary air pipe are connected to the boiler, and a branch pipe is connected to the main steam pipe; a turbine assembly, wherein the turbine assembly includes a high-pressure cylinder, and the steam inlet of the high-pressure cylinder is connected to the end of the main steam pipe opposite to the boiler; and a fan assembly, wherein the fan assembly includes an induced draft fan and an expelled draft fan, wherein the induced draft fan is connected to the end of the flue gas pipe opposite to the boiler for extracting the combusted flue gas from the boiler, and the expelled draft fan is connected to the end of the secondary air pipe opposite to the boiler. One end is connected for supplying secondary air to the boiler; a heating assembly is located outside the boiler and includes a hot air heater, which is located inside the secondary air duct. A portion of the branch duct passes through the secondary air duct and through the hot air heater. The low-load energy-saving and efficiency-enhancing system for coal-fired power generation units based on thermal system reconfiguration has a first operating state and a second operating state. In the first operating state, no steam passes through the branch duct. In the second operating state, the steam flow direction of the portion of the branch duct located inside the hot air heater is opposite to the flow direction of the secondary air in the secondary air duct.

[0006] According to an embodiment of the present invention, a low-load energy-saving and efficiency-enhancing system for coal-fired power generating units based on thermal system reconfiguration is provided. By setting a branch pipe on the main steam pipe and installing a hot air heater in the secondary air pipe, and having the branch pipe pass through the hot air heater, the heat of the steam in the branch pipe can be used to heat the secondary air in the secondary air pipe under low-load operation, thereby increasing the temperature of the secondary air, improving the combustion stability of the boiler, reducing the number of flameouts, effectively solving the problems of high oxygen content and large flue gas loss when the boiler is operating under low load, improving boiler efficiency, reducing heat loss, protecting the boiler, and extending its service life.

[0007] In addition, the low-load energy-saving and efficiency-enhancing system for coal-fired power generating units based on thermal system reconfiguration according to the present invention may also have the following additional technical features: In some embodiments, the turbine assembly further includes a high-pressure heater and a deaerator, the steam outlet of the high-pressure cylinder and the end of the branch pipe opposite to the main steam pipe are both adapted to be connected to the steam inlet of the high-pressure heater, the drain outlet and feedwater inlet of the high-pressure heater are both connected to the deaerator, and the feedwater outlet of the high-pressure heater is connected to the boiler.

[0008] In some embodiments, there are multiple high-pressure heaters, and the feedwater inlet of one of two adjacent high-pressure heaters closer to the boiler is connected to the feedwater outlet of the other. The high-pressure heater closest to the boiler among the multiple high-pressure heaters is the No. 1 high-pressure heater. The steam inlet of the No. 1 high-pressure heater is connected to the end of the branch pipe opposite to the main steam pipe, or the steam inlet of the No. 1 high-pressure heater is connected to the steam outlet of the high-pressure cylinder.

[0009] In some embodiments, the end of the branch pipe opposite to the main steam pipe is connected to the heating pipe.

[0010] In some embodiments, the heating assembly further includes an air preheater, and both the flue gas duct and the secondary air duct are connected to the air preheater. Along the flow direction of the secondary air in the secondary air duct, the air preheater is located upstream of the hot air heater.

[0011] In some embodiments, the induced draft fan is a plurality of fans, including an A-side induced draft fan and a B-side induced draft fan. Both the A-side and B-side induced draft fans are adapted to communicate with the flue gas duct, and are spaced apart along the length of the flue gas duct. The forced draft fan is a plurality of fans, including an A-side forced draft fan and a B-side forced draft fan. Both the A-side and B-side forced draft fans are adapted to communicate with the secondary air duct, and are spaced apart along the length of the secondary air duct. In the first operating state, both the A-side and B-side induced draft fans are connected to the flue gas duct, and both the A-side and B-side forced draft fans are connected to the secondary air duct. In the second operating state, one of the A-side and B-side induced draft fans is connected to the flue gas duct, and the other is disconnected from the flue gas duct; and / or, one of the A-side and B-side forced draft fans is connected to the secondary air duct, and the other is disconnected from the secondary air duct.

[0012] In some embodiments, both the A-side induced draft fan and the B-side induced draft fan are connected to the flue gas duct through induced draft pipes. The induced draft pipes are equipped with flue gas baffles to control the opening and closing of the induced draft pipes. The two induced draft pipes are connected by a first connecting pipe, which is spaced apart from the flue gas duct and is located upstream of the flue gas baffle along the flow direction of the flue gas in the induced draft pipes.

[0013] In some embodiments, both the A-side air supply fan and the B-side air supply fan are connected to the secondary air duct through air supply ducts. The air supply duct is provided with a secondary air damper for controlling the opening and closing of the air supply duct. The two air supply ducts are connected by a second connecting pipe, which is spaced apart from the secondary air duct and is located downstream of the secondary air damper along the flow direction of the secondary air in the air supply duct.

[0014] In some embodiments, the low-load energy-saving and efficiency-enhancing system for coal-fired power generating units based on thermal system reconfiguration further includes: a burner assembly, the burner assembly being disposed on the boiler and connected to the secondary air duct; and a nozzle assembly, the nozzle assembly being disposed on the boiler and connected to the burner assembly, the nozzle assembly having a plurality of nozzles extending into the boiler, the plurality of nozzles being arranged vertically and spaced apart, in the first operating state, all of the plurality of nozzles being open, in the second operating state, the nozzle located at the upper end of the plurality of nozzles being open, and / or, in the radially inward direction of the boiler, the nozzle is inclined upward.

[0015] In some embodiments, the nozzle assemblies are a plurality of those spaced apart along the circumferential direction of the boiler.

[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of a low-load energy-saving and efficiency-enhancing system for coal-fired power generating units based on thermal system reconfiguration, according to an embodiment of the present invention.

[0018] Figure label: 100. Low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration; 1. Boiler; 11. Main steam pipe; 12. Flue gas pipe; 13. Secondary air pipe; 14. Branch pipe; 141. First valve; 142. Second valve; 143. Pressure reducing valve; 15. Reheat pipe; 2. Steam turbine components; 21. High-pressure cylinder; 211. Third valve; 22. Intermediate-pressure cylinder; 23. Low-pressure cylinder; 24. High-pressure heater; 241. No. 1 high-pressure heater; 25. Deaerator; 26. Low-pressure heater; 27. Condenser; 3. Fan assembly; 31. Exhaust fan; 311. A-side exhaust fan; 312. B-side exhaust fan; 32. Supply fan; 321. A-side supply fan; 322. B-side supply fan; 33. Exhaust duct; 331. Flue gas damper; 34. First connecting duct; 341. First connecting damper; 35. Supply duct; 351. Secondary damper; 36. Second connecting duct; 361. Second connecting damper; 4. Heating components; 41. Hot air heater; 42. Air preheater; 5. Nozzle assembly; 51. Nozzle; 6. Generator. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0022] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0023] The following description, with reference to the accompanying drawings, describes a low-load energy-saving and efficiency-enhancing system 100 for coal-fired power generating units based on thermal system reconfiguration according to an embodiment of the present invention.

[0024] like Figure 1 As shown, the low-load energy-saving and efficiency-enhancing system 100 for coal-fired power generating units based on thermal system reconfiguration according to an embodiment of the present invention includes a boiler 1, a steam turbine assembly 2, a fan assembly 3, and a heating assembly 4.

[0025] Specifically, see the attached document. Figure 1 As shown, the boiler 1 is connected to a main steam pipe 11, a flue gas pipe 12 and a secondary air pipe 13. The main steam pipe 11 is connected to a branch pipe 14. The turbine assembly 2 includes a high-pressure cylinder 21. The steam inlet of the high-pressure cylinder 21 is connected to the end of the main steam pipe 11 away from the boiler 1.

[0026] It is understandable that the turbine assembly 2 also includes an intermediate-pressure cylinder 22 and a low-pressure cylinder 23. The high-pressure cylinder 21, intermediate-pressure cylinder 22 and low-pressure cylinder 23 are connected in sequence. The coal-fired power generation unit low-load energy-saving and efficiency-improving system 100 based on thermal system reconfiguration also includes a generator 6. The generator 6 is connected to the low-pressure cylinder 23. The boiler 1 is used to convert the chemical energy of the fuel into thermal energy through combustion, heat water to generate high-temperature and high-pressure steam, and the high-temperature and high-pressure steam enters the high-pressure cylinder 21 through the main steam pipe 11. The steam passes through the high-pressure cylinder 21, intermediate-pressure cylinder 22 and low-pressure cylinder 23 in sequence, expanding and doing work step by step, converting the thermal energy of the steam into mechanical energy, driving the rotor to rotate. The generator 6 is used to convert the mechanical energy of the turbine assembly 2 into electrical energy.

[0027] Further, see attached document. Figure 1 As shown, the fan assembly 3 includes an induced draft fan 31 and an expelled draft fan 32. The induced draft fan 31 is connected to the end of the flue gas duct 12 away from the boiler 1, and is used to extract the flue gas after combustion from the boiler 1. The expelled draft fan 32 is connected to the end of the secondary air duct 13 away from the boiler 1, and is used to send secondary air into the boiler 1. The heating assembly 4 is located outside the boiler 1 and includes a hot air heater 41. The hot air heater 41 is located inside the secondary air duct 13. A portion of the branch duct 14 passes through the secondary air duct 13 and through the hot air heater 41. The low-load energy-saving and efficiency-enhancing system 100 for coal-fired power generation units based on thermal system reconfiguration has a first operating state and a second operating state. In the first operating state, no steam passes through the branch duct 14. In the second operating state, the steam flow direction of the portion of the branch duct 14 located inside the hot air heater 41 is opposite to the flow direction of the secondary air in the secondary air duct 13. It should be noted that the first operating state is the normal load operating state, and the second operating state is the low-load operating state.

[0028] It is understood that by setting a branch pipe 14 on the main steam pipe 11 and installing a hot air heater 41 in the secondary air pipe 13, and having the branch pipe 14 pass through the hot air heater 41, the present invention can use the heat of the steam in the branch pipe 14 to heat the secondary air in the secondary air pipe 13 under low load operation, thereby increasing the temperature of the secondary air, thus improving the combustion stability of the boiler 1, reducing the number of times the boiler shuts down, effectively solving the problem of high oxygen content and large flue gas loss when the boiler 1 is operating under low load, improving the efficiency of the boiler 1, reducing heat loss, protecting the boiler 1, and extending its service life.

[0029] Furthermore, in the second operating state, the steam flow direction of the portion of the branch pipe 14 located inside the hot air heater 41 is opposite to the flow direction of the secondary air in the secondary air pipe 13, which can further improve the heat exchange effect between the steam in the branch pipe 14 and the secondary air in the secondary air pipe 13, and further increase the temperature of the secondary air.

[0030] It is understandable that, such as Figure 1 As shown, a first valve 141 is provided on the branch pipe 14. The first valve 141 is located between the main steam pipe 11 and the hot air heater 41 and can be used to control the opening and closing of the branch pipe 14 to match the first operating state or the second operating state. In the first operating state, the first valve 141 is closed, no steam passes through the branch pipe 14, and the steam in the main steam pipe 11 flows directly along the main steam pipe 11 to the high-pressure cylinder 21; in the second operating state, the first valve 141 is open, some of the steam in the main steam pipe 11 flows directly to the high-pressure cylinder 21, and some steam flows along the branch pipe 14 to the hot air heater 41.

[0031] According to an embodiment of the present invention, the low-load energy-saving and efficiency-enhancing system 100 for coal-fired power generating units based on thermal system reconfiguration, by setting a branch pipe 14 on the main steam pipe 11 and installing a hot air heater 41 in the secondary air pipe 13, and having the branch pipe 14 pass through the hot air heater 41, the heat of the steam in the branch pipe 14 can be used to heat the secondary air in the secondary air pipe 13 under low-load operation, thereby increasing the temperature of the secondary air, thereby improving the combustion stability of the boiler 1, reducing the number of shutdowns, effectively solving the problems of high oxygen content and large flue gas loss when the boiler 1 is operating under low load, improving the efficiency of the boiler 1, reducing heat loss, protecting the boiler 1, and extending its service life.

[0032] In some embodiments of the present invention, reference is made to the appendix. Figure 1 As shown, the turbine assembly 2 also includes a high-pressure heater 24 and a deaerator 25. The steam outlet of the high-pressure cylinder 21 and the end of the branch pipe 14 away from the main steam pipe 11 are both adapted to be connected to the steam inlet of the high-pressure heater 24. The drain outlet and feedwater inlet of the high-pressure heater 24 are both connected to the deaerator 25. The feedwater outlet of the high-pressure heater 24 is connected to the boiler 1.

[0033] It is understandable that, such as Figure 1 As shown, the high-pressure heater 24 uses steam from the branch pipe 14 and / or the high-pressure cylinder 21 to heat the feedwater, increase the feedwater temperature, and reduce the temperature difference between the feedwater entering the boiler 1 and the furnace, thereby improving the unit efficiency. The deaerator 25 works on the principle of thermal deaeration, which can both remove dissolved gases (such as oxygen) from the feedwater and store a certain amount of feedwater to alleviate the imbalance between the flow of condensate and feedwater.

[0034] Further, see attached document. Figure 1As shown, the turbine assembly 2 also includes a low-pressure heater 26 and a condenser 27. The steam inlet of the low-pressure heater 26 is connected to the steam outlet of the low-pressure cylinder 23. The drain outlet and feedwater inlet of the low-pressure heater 26 are both connected to the condenser 27. The feedwater outlet of the low-pressure heater 26 is connected to the deaerator 25. The low-pressure heater 26 uses the relatively low-pressure steam from the low-pressure cylinder 23 to heat the feedwater and increase the feedwater temperature. The condenser 27 is used to condense the steam entering the condenser 27 into water, and then send the feedwater to the low-pressure heater 26 to be heated by the steam.

[0035] Understandably, feedwater enters boiler 1 and is heated to generate main steam. The main steam enters the high-pressure cylinder 21 through the main steam pipeline to do work. The exhaust steam after doing work returns to boiler 1 through the reheat pipeline 15 for reheating. The generated reheat steam enters the intermediate-pressure cylinder 22 to do work. The exhaust steam after doing work in the intermediate-pressure cylinder 22 continues to enter the low-pressure cylinder 23 to do work. The exhaust steam after doing work in the low-pressure cylinder 23 enters the condenser 27 for condensation. Then, the condensate pump transports the condensed condensate to the low-pressure heater 26 for heating. After heating, it is transported to the deaerator 25 for deoxygenation. After passing through the feedwater pump and the high-pressure heater 24, it enters boiler 1, completing one steam-water cycle.

[0036] In a further embodiment of the invention, reference is made to the appendix. Figure 1 As shown, there are multiple high-pressure heaters 24. The feedwater inlet of the one closer to the boiler 1 among two adjacent high-pressure heaters 24 is connected to the feedwater outlet of the other. The one closest to the boiler 1 among the multiple high-pressure heaters 24 is the No. 1 high-pressure heater 241. The steam inlet of the No. 1 high-pressure heater 241 is connected to the end of the branch pipe 14 away from the main steam pipe 11, or the steam inlet of the No. 1 high-pressure heater 241 is connected to the steam outlet of the high-pressure cylinder 21.

[0037] like Figure 1 As shown, a second valve 142 is also provided on the branch pipe 14. The second valve 142 is located between the hot air heater 41 and the first high-pressure heater 241 and can be used to control the opening and closing of the branch pipe 14. A third valve 211 is provided between the steam inlet of the first high-pressure heater 241 and the steam outlet of the high-pressure cylinder 21. The third valve 211 is used to control the opening and closing of the steam inlet of the first high-pressure heater 241 and the steam outlet of the high-pressure cylinder 21, so as to match the first operating state or the second operating state.

[0038] Understandably, when this application is applied to a condensing generator set, in the first operating state, the third valve 211 is open, the steam inlet of the first high-pressure heater 241 is connected to the steam outlet of the high-pressure cylinder 21, the first valve 141 and the second valve 142 are both closed, and no steam passes through the branch pipe 14, thus preventing the steam flowing out of the high-pressure cylinder 21 from flowing back to the main steam pipe 11 via the branch pipe 14; in the second operating state, the first valve 141 is open, and the steam in the main steam passage is introduced into the hot air heater 41 for heating. Secondary air is introduced, and the steam flow and pressure are controlled by pressure reducing valve 143. The second valve 142 is opened, and the steam inlet of the No. 1 high-pressure heater 241 is connected to the end of the branch pipeline 14 away from the main steam pipeline 11. The steam heated by the secondary air in the branch pipeline 14 is introduced into the No. 1 high-pressure heater 241. After heat exchange is completed in the No. 1 high-pressure heater 241, it flows into the deaerator 25 by gravity in stages. The third valve 211 is closed, and the steam heated by the secondary air in the branch pipeline 14 is used as the entire steam source for the No. 1 high-pressure heater 241.

[0039] As a result, the secondary air temperature and feedwater temperature can be significantly improved, and the temperatures on both the flue gas side and the steam-water side are comprehensively improved. Although some of the main steam cannot enter the turbine to do work, it can increase the temperature of the main steam and reheat steam at the boiler outlet.

[0040] In some embodiments of the present invention, the end of the branch pipe 14 away from the main steam pipe 11 is connected to the heating pipe. It is understood that when the present application is applied to a cogeneration unit, connecting the end of the branch pipe 14 away from the main steam pipe 11 to the heating pipe allows the steam heated by the secondary air in the branch pipe 14 to be introduced into the heating pipe in the second operating state to provide steam heating for users outside the plant. At the same time, the valve of the original heating pipe can be closed to reduce the steam flow. If the steam heated by the secondary air in the branch pipe 14 can fully meet the heating demand, the valve of the original heating pipe can be completely closed.

[0041] In some embodiments of the present invention, reference is made to the appendix. Figure 1 As shown, the heating assembly 4 also includes an air preheater 42. The flue gas duct 12 and the secondary air duct 13 are both connected to the air preheater 42. Along the flow direction of the secondary air in the secondary air duct 13, the air preheater 42 is located upstream of the hot air heater 41.

[0042] It is understandable that by providing an air preheater 42, flue gas and secondary air can be introduced into the air preheater 42, and then heat exchange is carried out by rotary heating. During the process of flue gas and secondary air passing through the air preheater, the waste heat of the flue gas at the tail end of boiler 1 is used to heat the secondary air, thereby increasing the temperature of the secondary air. This can improve the combustion stability of boiler 1, reduce the number of times the boiler shuts down, effectively solve the problem of high oxygen content and large flue gas loss when boiler 1 is operating under low load conditions, improve the efficiency of boiler 1, reduce heat loss, and protect boiler 1, extending its service life.

[0043] By limiting the flow direction of the secondary air along the secondary air duct 13, the air preheater 42 is located upstream of the hot air heater 41. Considering that the temperature of the flue gas in the flue gas duct 12 is lower than the temperature of the steam in the branch duct 14, the cold secondary air can first exchange heat with the relatively low-temperature flue gas, and after the temperature is increased to a certain extent, it can then exchange heat with the relatively high-temperature steam, becoming hot secondary air flowing into the boiler 1. This can make full use of the waste heat of the flue gas and the heat of the steam to heat the secondary air, avoid the waste heat of the flue gas, and maximize the temperature of the secondary air when it enters the boiler 1.

[0044] In some embodiments of the present invention, reference is made to the appendix. Figure 1 As shown, there are multiple induced draft fans 31, including an A-side induced draft fan 311 and a B-side induced draft fan 312. Both the A-side induced draft fan 311 and the B-side induced draft fan 312 are adapted to be connected to the flue gas duct 12, and the A-side induced draft fan 311 and the B-side induced draft fan 312 are spaced apart along the length of the flue gas duct 12. There are multiple forced draft fans 32, including an A-side forced draft fan 321 and a B-side forced draft fan 322. Both the A-side forced draft fan 321 and the B-side forced draft fan 322 are adapted to be connected to the secondary air duct 13, and the A-side forced draft fan 321 and the B-side forced draft fan 322 are spaced apart along the length of the secondary air duct 13.

[0045] In the first operating state, both the A-side induced draft fan 311 and the B-side induced draft fan 312 are connected to the flue gas duct 12, and both the A-side supply fan 321 and the B-side supply fan 322 are connected to the secondary air duct 13. In the second operating state, one of the A-side induced draft fan 311 and the B-side induced draft fan 312 is connected to the flue gas duct 12, and the other is disconnected from the flue gas duct 12, and / or, one of the A-side supply fan 321 and the B-side supply fan 322 is connected to the secondary air duct 13, and the other is disconnected from the secondary air duct 13.

[0046] It is understandable that by providing two induced draft fans 31 and two forced draft fans 32, a redundant design can be achieved. In the event of a sudden failure of one induced draft fan 31 or forced draft fan 32, the remaining induced draft fans 31 and forced draft fans 32 can continue to operate, preventing the boiler 1 from being forced to shut down due to insufficient air volume. This can improve the reliability of the low-load energy-saving and efficiency-enhancing system 100 for coal-fired power generation units based on thermal system reconfiguration.

[0047] In the first operating state, boiler 1 requires a large amount of secondary air and needs to discharge a large amount of flue gas. The A-side forced draft fan 321 and the B-side forced draft fan 322 can provide a larger air volume, and the A-side induced draft fan 311 and the B-side induced draft fan 312 can discharge a larger amount of flue gas to meet the large air volume requirement. In the second operating state, shutting down the A-side forced draft fan 321 or the B-side forced draft fan 322, and / or shutting down the A-side induced draft fan 311 or the B-side induced draft fan 312 can improve the fan operating efficiency, relatively reduce the fan power consumption while ensuring the same air volume, and can break through the lower limit of the minimum operating air volume of the two fans, providing conditions for further reducing the air volume. Thus, the number of forced draft fans 32 and induced draft fans 31 that are turned on can be adjusted according to different operating states to meet different usage requirements.

[0048] Optionally, in the second operating state, it is possible to shut down only the A-side induced draft fan 311 or the B-side induced draft fan 312, while the A-side supply fan 321 and the B-side supply fan 322 remain on; it is also possible to shut down only the A-side supply fan 321 or the B-side supply fan 322, while the A-side induced draft fan 311 and the B-side induced draft fan 312 remain on; or it is possible to have one of the A-side induced draft fans 311 and the B-side induced draft fan 312 on and the other off, and one of the A-side supply fan 321 and the B-side supply fan 322 on and the other off.

[0049] Preferably, in the second operating state, one of the A-side induced draft fan 311 and the B-side induced draft fan 312 is connected to the flue gas duct 12, while the other is disconnected from the flue gas duct 12. Similarly, one of the A-side supply fan 321 and the B-side supply fan 322 is connected to the secondary air duct 13, while the other is disconnected from the secondary air duct 13. This improves operating efficiency under the same airflow conditions and further lowers the minimum operating airflow limit, allowing for airflow reduction through frequency conversion adjustment instead of closing dampers. After this technology is put into operation, it avoids the risks of surge and stall at low airflow, increases the airflow adjustment range, improves fan operating efficiency, reduces fan power consumption, and reduces plant power consumption.

[0050] It should be noted that after the flue gas in flue gas duct 12 is heated and the steam in branch duct 14 is heated, the secondary air temperature increases. Within a certain range, reducing the volume of secondary air will not affect combustion stability. Therefore, this measure can reduce the excess air coefficient, reduce flue gas heat loss, and improve boiler efficiency while ensuring combustion stability.

[0051] In a further embodiment of the invention, reference is made to the appendix. Figure 1 As shown, both the A-side exhaust fan 311 and the B-side exhaust fan 312 are connected to the flue gas duct 12 through the exhaust duct 33. The exhaust duct 33 is equipped with a flue gas baffle 331 to control the opening and closing of the exhaust duct 33, so as to match different operating modes and meet different user needs.

[0052] In the first operating state, the flue gas dampers 331 on both induced draft ducts 33 are open, allowing both the A-side induced draft fan 311 and the B-side induced draft fan 312 to connect to the flue gas duct 12, ensuring that flue gas can be discharged from the A-side induced draft fan 311 and the B-side induced draft fan 312; in the second operating state, when the flue gas damper 331 on the induced draft duct 33 directly connected to the A-side induced draft fan 311 is closed, and the flue gas damper 331 on the induced draft duct 33 directly connected to the B-side induced draft fan 312 is closed... When plate 331 is opened, the A-side induced draft fan 311 is disconnected from the flue gas duct 12, while the B-side induced draft fan 312 remains connected to the flue gas duct 12. When the flue gas damper 331 on the induced draft duct 33 directly connected to the A-side induced draft fan 311 is opened and the flue gas damper 331 on the induced draft duct 33 directly connected to the B-side induced draft fan 312 is closed, the A-side induced draft fan 311 remains connected to the flue gas duct 12, while the B-side induced draft fan 312 is disconnected from the flue gas duct 12.

[0053] Further, see attached document. Figure 1 As shown, the two exhaust pipes 33 are connected by a first connecting pipe 34. The first connecting pipe 34 is spaced apart from the flue gas pipe 12. Along the flow direction of the flue gas in the exhaust pipe 33, the first connecting pipe 34 is located upstream of the flue gas baffle 331. Even when the flue gas baffle 331 on one of the two exhaust pipes 33 is closed, the first connecting pipe 34 can still connect the two exhaust pipes 33, thereby maintaining the pressure balance on both sides.

[0054] Furthermore, see the attached document. Figure 1 As shown, the first connecting pipe 34 is equipped with a first connecting damper 341, which is used to control the connection and disconnection between the two exhaust pipes 33, enabling flue gas path switching and flow distribution. For example, in the first operating state, both the A-side exhaust fan 311 and the B-side exhaust fan 312 are connected to the flue gas pipe 12, and the first connecting damper 341 is closed; in the second operating state, one of the A-side exhaust fan 311 and the B-side exhaust fan 312 is connected to the flue gas pipe 12, while the other is disconnected from the flue gas pipe 12. In this case, the first connecting damper 341 needs to be opened to connect the two exhaust pipes 33 and ensure pressure balance on both sides.

[0055] In a further embodiment of the present invention, both the A-side air supply fan 321 and the B-side air supply fan 322 are connected to the secondary air duct 13 through the air supply duct 35. The air supply duct 35 is provided with a secondary air damper 351 to control the opening and closing of the air supply duct 35, so as to match different operating modes and meet different user needs.

[0056] In the first operating state, the secondary air dampers 351 on both air supply ducts 35 are open, allowing both the A-side air supply fan 321 and the B-side air supply fan 322 to connect to the secondary air duct 13, ensuring that the secondary air drawn by both fans 321 and 322 is delivered into the secondary air duct 13. In the second operating state, when the secondary air damper 351 on the air supply duct 35 directly connected to the A-side air supply fan 321 is closed, and the secondary air damper 351 on the air supply duct 35 directly connected to the B-side air supply fan 322 is closed... When the secondary air damper 351 is opened, the A-side air supply fan 321 is disconnected from the secondary air duct 13, while the B-side air supply fan 322 remains connected to the secondary air duct 13. When the secondary air damper 351 on the air supply duct 35 directly connected to the A-side air supply fan 321 is opened and the secondary air damper 351 on the air supply duct 35 directly connected to the B-side air supply fan 322 is closed, the A-side air supply fan 321 remains connected to the secondary air duct 13, while the B-side air supply fan 322 is disconnected from the secondary air duct 13.

[0057] Further, see attached document. Figure 1 As shown, the two air supply ducts 35 are connected by a second connecting pipe 36. The second connecting pipe 36 is spaced apart from the secondary air duct 13. Along the flow direction of the secondary air in the air supply duct 35, the second connecting pipe 36 is located downstream of the secondary air damper 351. Even when the secondary air damper 351 on one of the two air supply ducts 35 is closed, the second connecting pipe 36 can still connect the two air supply ducts 35, thereby maintaining the pressure balance on both sides.

[0058] Furthermore, see the attached document. Figure 1 As shown, a second connecting damper 361 is provided on the second connecting pipe 36 to control the connection and disconnection between the two air supply pipes 35, enabling switching of secondary air paths and flow distribution. For example, in the first operating state, both the A-side air supply fan 321 and the B-side air supply fan 322 are connected to the secondary air pipe 13, and the second connecting damper 361 is closed; in the second operating state, one of the A-side air supply fan 321 and the B-side air supply fan 322 is connected to the secondary air pipe 13, while the other is disconnected from the secondary air pipe 13. In this case, the second connecting damper 361 needs to be opened to connect the two air supply pipes 35 and ensure pressure balance on both sides.

[0059] In some embodiments of the present invention, reference is made to the appendix. Figure 1As shown, the low-load energy-saving and efficiency-enhancing system 100 for coal-fired power generating units based on thermal system reconfiguration also includes a burner assembly and a nozzle assembly 5. The burner assembly is mounted on the boiler 1 and connected to the secondary air duct 13. The nozzle assembly 5 is mounted on the boiler 1 and connected to the burner assembly. The nozzle assembly 5 has multiple nozzles 51 extending into the boiler 1. The multiple nozzles 51 are arranged vertically and spaced apart. Hot secondary air flows into the burner assembly from the secondary air duct 13 and is injected into the furnace through the multiple nozzles 51 via the nozzle assembly 5. In the first operating state, all multiple nozzles 51 are open. In the second operating state, the upper nozzle 51 is open, and / or, in the radially inward direction of the boiler 1, the nozzle 51 is tilted upward.

[0060] Understandably, in the second operating state, the unit operates at low load. To ensure combustion stability, the relatively lower nozzle 51 is usually opened. However, this application increases the temperature of the secondary air by sequentially exchanging heat with the flue gas in the flue gas duct 12 and the steam in the branch duct 14, thereby ensuring combustion stability in the furnace. Furthermore, by selectively opening the relatively upper nozzle 51 or adjusting the burner angle upwards, the flame center can be moved upwards, increasing the flue gas temperature at the furnace outlet. This increases the heat exchange capacity between the main steam and reheat steam, and to some extent, reduces the turbine's thermal energy consumption.

[0061] In a further embodiment of the invention, reference is made to the appendix. Figure 1 As shown, the nozzle assembly 5 consists of multiple nozzles spaced apart along the circumferential direction of the boiler 1. This avoids excessively high or low local flow velocities caused by concentrated fuel / air injection, resulting in a more uniform flow field distribution, improved combustion efficiency, enhanced equipment adaptability and safety, and significantly improved overall performance of the boiler 1 system.

[0062] In a specific example, the low-load energy-saving and efficiency-enhancing system 100 based on thermal system reconfiguration for coal-fired power generating units is applied to a subcritical condensing coal-fired power generating unit. This unit employs a subcritical pressure single-stage intermediate reheat controlled circulating drum boiler 1, with a П-type layout, tangential combustion at the four corners, balanced ventilation, and negative pressure operation. The turbine is a subcritical parameter, single-stage intermediate reheat, single-shaft, four-cylinder, four-exhaust condensing turbine. The regenerative system includes a three-stage high-pressure heater 24, a first-stage deaerator 25, and a four-stage low-pressure heater 26.

[0063] In the second operating state, the first valve 141 on branch pipeline 14 is opened to introduce part of the main steam into the hot air heater 41 to heat the secondary air. The steam extraction flow and pressure are controlled by the pressure reducing valve 143. The second valve 142 on branch pipeline 14 is opened to introduce the steam after heat exchange with the secondary air into the No. 1 high-pressure heater 241. At the same time, the third valve 211 from the original high-pressure cylinder 21 to the No. 1 high-pressure heater 241 is closed, and the main steam after heating the secondary air is used as the entire steam source for the No. 1 high-pressure heater 241. After this technology is put into operation, the secondary air temperature and feedwater temperature can be significantly improved, and the temperatures on both the flue gas side and the steam-water side are comprehensively improved. Although some of the main steam cannot enter the turbine to do work, it can increase the temperature of the main steam and reheat steam at the boiler 1 outlet, improve the cycle efficiency of the turbine assembly 2, and reduce the heat consumption of the turbine assembly 2.

[0064] Furthermore, in the second operating state, the B-side forced draft fan 322 and its corresponding secondary damper 351 on the forced draft duct 35 are shut off, the B-side induced draft fan 312 and its corresponding flue gas damper 331 on the induced draft duct 33 are shut off, and the first connecting damper 341 and the second connecting damper 361 are opened to maintain pressure balance on both sides. The air preheater 42 maintains dual-row operation to maintain temperature balance on both sides. The secondary air volume and furnace negative pressure are regulated only by the A-side forced draft fan 321 and the A-side induced draft fan 311. After the dual-row fans are changed to a single-row fans, the operating efficiency is improved under the same air volume, and the lower limit of the minimum operating air volume is further reduced. The air volume can be reduced by frequency conversion adjustment instead of closing the dampers. After this technology is put into operation, the risk of surge and stall at low air volume is avoided, the air volume adjustment range is increased, and the fan operating efficiency is improved and the fan power consumption is reduced.

[0065] Before implementing this invention, at 20% load, the feedwater flow rate of boiler 1 and the main steam flow rate entering the high-pressure cylinder 21 were 105.1 kg / s, the feedwater temperature was 196℃, the hot secondary air temperature was 224℃, the main steam temperature was 502℃, the reheat steam flow rate was 90.5 kg / s, the reheat steam temperature was 508℃, the oxygen content of the flue gas at the air preheater outlet was 12.88%, and the total power consumption of the forced draft fan 32 and the induced draft fan 31 was approximately 4800 kW. The calculated coal consumption rate for power supply was 410.74 g / kWh.

[0066] After implementing this invention, at 20% load, the feedwater flow rate of boiler 1 is 113.4 kg / s, the main steam flow rate entering the hot air heater 41 is 15 kg / s, the main steam flow rate entering the high-pressure cylinder 21 is 98.4 kg / s, the feedwater temperature is 241.7℃, the hot secondary air temperature is 279.5℃, the main steam temperature is 538.5℃, the reheat steam flow rate is 89.0 kg / s, the reheat steam temperature is 540.3℃, the oxygen content of the flue gas at the air preheater outlet is 8.00%, and the total power consumption of the forced draft fan 32 and the induced draft fan 31 is approximately 3000 kW. Calculations show that the coal consumption rate for power supply is 399.56 g / kWh, a decrease of 11.18 g / kWh compared to before implementation.

[0067] Other components and operations of the low-load energy-saving and efficiency-enhancing system 100 for coal-fired power generating units based on thermal system reconfiguration according to embodiments of the present invention are known to those skilled in the art and will not be described in detail here.

[0068] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0069] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration, characterized in that, include: A boiler, wherein a main steam pipe, a flue gas pipe and a secondary air pipe are connected to the boiler, and a branch pipe is connected to the main steam pipe; A steam turbine assembly, the steam turbine assembly including a high-pressure cylinder, the steam inlet of the high-pressure cylinder being connected to the end of the main steam pipe opposite to the boiler; A fan assembly, comprising an induced draft fan and an expelled draft fan, wherein the induced draft fan is connected to the end of the flue gas duct away from the boiler and is used to extract the flue gas after combustion from the boiler, and the expelled draft fan is connected to the end of the secondary air duct away from the boiler and is used to deliver secondary air into the boiler. A heating assembly, located outside the boiler and including a hot air heater, is provided inside the secondary air duct. A portion of the branch duct passes through the secondary air duct and through the hot air heater. The coal-fired power generation unit low-load energy-saving and efficiency-improving system based on thermal system reconfiguration has a first operating state and a second operating state. In the first operating state, no steam passes through the branch pipe. In the second operating state, the steam flow direction of the portion of the branch pipe located inside the hot air heater is opposite to the flow direction of the secondary air in the secondary air pipe.

2. The low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration according to claim 1, characterized in that, The turbine assembly also includes a high-pressure heater and a deaerator. The steam outlet of the high-pressure cylinder and the end of the branch pipe opposite to the main steam pipe are both adapted to be connected to the steam inlet of the high-pressure heater. The drain outlet and feedwater inlet of the high-pressure heater are both connected to the deaerator. The feedwater outlet of the high-pressure heater is connected to the boiler.

3. The low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration according to claim 2, characterized in that, There are multiple high-pressure heaters. The feedwater inlet of the one closer to the boiler in two adjacent high-pressure heaters is connected to the feedwater outlet of the other. The one closest to the boiler among the multiple high-pressure heaters is the No. 1 high-pressure heater. The steam inlet of the No. 1 high-pressure heater is connected to the end of the branch pipeline away from the main steam pipeline, or the steam inlet of the No. 1 high-pressure heater is connected to the steam outlet of the high-pressure cylinder.

4. The low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration according to claim 1, characterized in that, The branch pipe is connected to the heating pipe at the end opposite to the main steam pipe.

5. The low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration according to claim 1, characterized in that, The heating assembly also includes an air preheater. The flue gas duct and the secondary air duct are both connected to the air preheater. Along the flow direction of the secondary air in the secondary air duct, the air preheater is located upstream of the hot air heater.

6. The low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration according to claim 1, characterized in that, The induced draft fan is a plurality of fans, including an A-side induced draft fan and a B-side induced draft fan. Both the A-side induced draft fan and the B-side induced draft fan are adapted to be connected to the flue gas duct, and the A-side induced draft fan and the B-side induced draft fan are spaced apart along the length of the flue gas duct. The air supply fan is a plurality of fans, including an A-side air supply fan and a B-side air supply fan. Both the A-side air supply fan and the B-side air supply fan are adapted to be connected to the secondary air duct, and the A-side air supply fan and the B-side air supply fan are spaced apart along the length of the secondary air duct. In the first operating state, both the A-side induced draft fan and the B-side induced draft fan are connected to the flue gas duct, and both the A-side supply fan and the B-side supply fan are connected to the secondary air duct; in the second operating state, one of the A-side induced draft fan and the B-side induced draft fan is connected to the flue gas duct, and the other is disconnected from the flue gas duct, and / or, one of the A-side supply fan and the B-side supply fan is connected to the secondary air duct, and the other is disconnected from the secondary air duct.

7. The low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration according to claim 6, characterized in that, Both the A-side induced draft fan and the B-side induced draft fan are connected to the flue gas duct via induced draft ducts. The induced draft duct is equipped with a flue gas baffle to control the on / off state of the induced draft duct. The two exhaust ducts are connected by a first connecting pipe, which is spaced apart from the flue gas duct. Along the flow direction of the flue gas in the exhaust duct, the first connecting pipe is located upstream of the flue gas baffle.

8. The low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration according to claim 6, characterized in that, Both the A-side air supply fan and the B-side air supply fan are connected to the secondary air duct via air supply pipes. The air supply pipes are equipped with secondary air dampers to control the on / off state of the air supply pipes. The two air supply ducts are connected by a second connecting pipe, which is spaced apart from the secondary air duct. Along the flow direction of the secondary air in the air supply duct, the second connecting pipe is located downstream of the secondary air damper.

9. The low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration according to claim 1, characterized in that, Also includes: A burner assembly, which is mounted on the boiler and connected to the secondary air duct; A nozzle assembly is disposed on the boiler and communicates with the burner assembly. The nozzle assembly has multiple nozzles that extend into the boiler. The multiple nozzles are arranged vertically and spaced apart. In a first operating state, all of the multiple nozzles are open. In a second operating state, the upper nozzle among the multiple nozzles is open, and / or, in the radially inward direction of the boiler, the nozzle is tilted upward.

10. The low-load energy-saving and efficiency-improving system for coal-fired power generating units based on thermal system reconfiguration according to claim 9, characterized in that, The nozzle assembly consists of multiple nozzles spaced apart along the circumferential direction of the boiler.

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