Flue gas waste heat utilization system
By designing a multi-level, staged flue gas waste heat utilization system, and using the flue gas discharged from the boiler to heat the condensed water and cold air multiple times, the problem of insufficient recovery of waste heat in the existing technology is solved, and efficient Energy utilization and pollutants are reduced.
Patent Information
- Application Number
- CN202411503473.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-25
- Publication Date
- 2025-02-18
AI Technical Summary
The prior art has failed to fully recover waste heat from flue gas through multi-level and phased heat exchange processes, resulting in low energy utilization and poor heat exchange effect.
A flue gas waste heat utilization system is designed, including a first heat exchange assembly, a second heat exchange assembly and an air pre-device. Through a multi-layer and staged heat exchange process, the flue gas discharged from the boiler is used to carry out condensate water and cold air. Heat multiple times to fully recover the residual heat.
Through a multi-level and phased heat exchange process, energy utilization efficiency is improved, energy waste and pollutant emissions are reduced, energy consumption and operating costs are reduced, and equipment life is extended.
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Figure CN119468238A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of flue gas waste heat utilization, and in particular to a flue gas waste heat utilization system. Background Art
[0002] With the rapid development of industrialization, boilers, as important energy conversion equipment, are widely used in various fields. However, during the operation of boilers, a large amount of high-temperature flue gas is generated, which contains a large amount of heat energy. In existing technologies, this part of heat energy is often directly discharged into the atmosphere, resulting in a huge waste of energy. In addition, this practice also increases the energy consumption of boilers, increases operating costs, and pollutes the environment. The flue gas emitted contains pollutants such as carbon dioxide, nitrogen oxides and particulate matter, which have an adverse effect on the atmospheric environment.
[0003] At present, air preheaters (air preheaters) are installed to preheat the air entering the boiler to improve combustion efficiency and reduce fuel consumption. At the same time, heat exchangers are also installed to heat condensate or feed water to recover part of the heat. These measures have improved energy utilization efficiency, reduced fuel consumption, and reduced environmental impact to a certain extent.
[0004] However, the existing technology fails to fully recover the waste heat in the flue gas through a multi-level and staged heat exchange process, resulting in low energy utilization and poor heat exchange effect. Summary of the invention
[0005] The purpose of the embodiment of the present invention is to provide a flue gas waste heat utilization system to solve the above problems.
[0006] In order to achieve the above-mentioned purpose, an embodiment of the present invention provides a flue gas waste heat utilization system, comprising: a first heat exchange component, a second heat exchange component and an air preheater, the first heat exchange component is connected to the second heat exchange component, the air outlet end of the second heat exchange component is connected to the low-temperature medium input end of the air preheater, and the flue gas input end of the second heat exchange component is respectively connected to the high-temperature medium output end of the air preheater and the flue gas output end of the first heat exchange component; The first heat exchange component is used to heat the condensate delivered to the boiler by utilizing the flue gas discharged from the boiler; The second heat exchange component is used to heat the cold air delivered to the boiler by using the heated circulating feed water; wherein the heated circulating feed water is obtained by heating the circulating feed water with the flue gas and condensed water after heat exchange by the first heat exchange component and the flue gas output by the air preheater; The air preheater is used to utilize the flue gas discharged from the boiler to perform secondary heating on the cold air delivered to the boiler, and to deliver the cooled flue gas to the second heat exchange component.
[0007] Optionally, the flue gas waste heat utilization system further comprises: a boiler and a condenser; the first heat exchange component comprises: a feed water heat exchanger, a condensate heat exchanger and a condensate recycling device; The first water inlet of the condensate circulation device is connected to the condenser, the first water outlet of the condensate circulation device is connected to the water inlet of the boiler, the second water outlet and the third water outlet of the condensate circulation device are respectively connected to the low-temperature medium input of the condensate heat exchanger, the low-temperature medium output of the condensate heat exchanger is connected to the second water inlet of the condensate circulation device, the fourth water inlet of the condensate circulation device is connected to the low-temperature medium input of the feed water heat exchanger, the low-temperature medium output of the feed water heat exchanger is connected to the third water inlet of the condensate circulation device, the high-temperature medium input of the feed water heat exchanger and the high-temperature medium input of the air preheater are both connected to the exhaust gas end of the boiler, the high-temperature medium output of the feed water heat exchanger is connected to the high-temperature medium input of the condensate heat exchanger, the high-temperature medium output of the condensate heat exchanger and the high-temperature medium output of the air preheater are respectively connected to the flue gas input of the second heat exchange component, and the low-temperature medium input of the feed water heat exchanger is also connected to the second heat exchange component; boiler, for exhausting flue gases; Condenser, used to output condensed water; A condensate recycling device is used to heat the condensate at low pressure to obtain low-pressure heated condensate; The condensate heat exchanger is used to heat the condensate after low-pressure heating by using the flue gas output from the feedwater heat exchanger, so as to obtain the condensate after the primary heating and the flue gas after the primary cooling; The condensate recycling device is used to mix the condensate after the primary heating and the condensate after the low-pressure heating treatment, and then perform deoxygenation and pressure-raising treatment to obtain the deoxygenated and pressure-raised condensate; The feed water heat exchanger is used to use the flue gas to perform secondary heating on the condensed water after deoxygenation and pressurization treatment, obtain the secondary heated condensed water and the secondary cooled flue gas, and transport the secondary cooled flue gas to the condensed water heat exchanger; The condensate recycling device is also used to perform high-pressure heating on the condensate after deoxygenation and pressure-boosting treatment to obtain high-pressure heated condensate, and mix the secondary heated condensate with the high-pressure heated condensate and transport them to the boiler.
[0008] Optionally, the condensate recycling device includes: a first low-pressure heater, a second low-pressure heater, a third low-pressure heater, a fourth low-pressure heater, a fifth low-pressure heater, a deaerator, a booster pump, a first high-pressure heater, a second high-pressure heater and a third high-pressure heater; The input end of the first low-pressure heater is connected to the condenser, the output end of the first low-pressure heater is connected to the input end of the second low-pressure heater, the output end of the second low-pressure heater is respectively connected to the input end of the third low-pressure heater and the low-temperature medium input end of the condensate heat exchanger, the output end of the third low-pressure heater is connected to the input end of the fourth low-pressure heater, the output end of the fourth low-pressure heater is respectively connected to the input end of the fifth low-pressure heater and the low-temperature medium output end of the condensate heat exchanger, the output end of the fifth low-pressure heater is connected to the input end of the deaerator, the output end of the deaerator is connected to the input end of the booster pump, the output end of the booster pump is respectively connected to the input end of the first high-pressure heater, the low-temperature medium input end of the feed water heat exchanger and the second heat exchange component, the output end of the first high-pressure heater is connected to the input end of the second high-pressure heater, the output end of the second high-pressure heater is connected to the input end of the third high-pressure heater, and the output end of the third high-pressure heater is respectively connected to the low-temperature medium output end of the feed water heat exchanger and the water inlet end of the boiler.
[0009] Optionally, the flue gas waste heat utilization system further includes: a blower; the second heat exchange component includes: a cold air duct heat medium water heater, a plate and shell heat exchanger, a first low-temperature economizer, and a second low-temperature economizer; The low-temperature medium input end of the heat medium water heater in the cold air duct is connected with the air supply fan, the low-temperature medium output end of the heat medium water heater in the cold air duct is connected with the low-temperature medium input end of the air preheater, the high-temperature medium input end of the heat medium water heater in the cold air duct is connected with the low-temperature medium output end of the plate and shell heat exchanger, the low-temperature medium input end of the plate and shell heat exchanger is connected with the low-temperature medium output end of the first low-temperature economizer, the low-temperature medium input end of the first low-temperature economizer is connected with the low-temperature medium output end of the second low-temperature economizer, the low-temperature medium input end of the second low-temperature economizer is connected with the high-temperature medium output end of the heat medium water heater in the cold air duct, the high-temperature medium input end of the plate and shell heat exchanger is connected with the low-temperature medium input end of the condensate heat exchanger, the high-temperature medium output end of the plate and shell heat exchanger is connected with the low-temperature medium output end of the condensate heat exchanger, the high-temperature medium input end of the first low-temperature economizer is respectively connected with the high-temperature medium output end of the air preheater and the high-temperature medium output end of the condensate heat exchanger, and the high-temperature medium output end of the first low-temperature economizer is connected with the high-temperature medium input end of the second low-temperature economizer; A blower for generating cooling air; The first low-temperature economizer is used to heat the circulating feed water delivered by the second low-temperature economizer by using the flue gas output by the air preheater and the flue gas after primary cooling, so as to obtain the flue gas after thrice cooling and the circulating feed water after primary heating; The plate and shell heat exchanger is used to use the condensed water after low-pressure heating to perform secondary heating on the circulating feed water after primary heating, so as to obtain the cooled condensed water and the secondary heated circulating feed water, and to transport the cooled condensed water to the deaerator; The heat medium water heater in the cold air duct is used to heat the cold air delivered to the boiler once by using the circulating water after secondary heating, so as to obtain the cold air after primary heating and the circulating water after cooling, and deliver the cold air after primary heating to the air preheater; The second low-temperature economizer is used to use the flue gas that has been cooled thrice to heat the cooled circulating feed water thrice, to obtain the flue gas that has been cooled 4 times and the heated circulating feed water, and to transport the heated circulating feed water to the first low-temperature economizer.
[0010] Optionally, the flue gas waste heat utilization system further includes: a third low-temperature economizer, a medium-pressure cylinder and a drain expansion tank; The low-temperature medium input end of the third low-temperature economizer is connected to the low-temperature medium output end of the air preheater, the low-temperature medium output end of the third low-temperature economizer is connected to the air inlet end of the boiler, the high-temperature medium input end of the third low-temperature economizer is connected to the third extraction exhaust end of the medium-pressure cylinder, and the high-temperature medium output end of the third low-temperature economizer is connected to the drain expansion tank; The intermediate pressure cylinder is used to discharge the three-stage extraction steam of the intermediate pressure cylinder; The third low-temperature economizer is used to heat the cold air delivered to the boiler three times by using the three-stage extraction steam of the intermediate pressure cylinder, and deliver the cooled three-stage extraction steam of the intermediate pressure cylinder to the drain expansion tank; The drain expansion tank is used to reduce the pressure of the three-stage steam extraction from the intermediate pressure cylinder after the temperature has been reduced.
[0011] Optionally, the first heat exchange assembly further includes: a first frequency converter, a first return water regulating valve group, a second return water regulating valve group, a first regulating valve, a first condensate booster pump, a second regulating valve, a second condensate booster pump, a third return water regulating valve group, a first check valve, a second check valve, a third check valve and a fourth check valve; The first frequency converter is arranged between the high-temperature medium input end of the feedwater heat exchanger and the flue gas end of the boiler, the first return water regulating valve group is arranged between the low-temperature medium output end of the feedwater heat exchanger and the output end of the third high-pressure heater, the second return water regulating valve group and the second check valve are respectively arranged between the output end of the fifth low-pressure heater and the low-temperature medium output end of the condensate heat exchanger, the second check valve is arranged at one end close to the output end of the fifth low-pressure heater, the first regulating valve and the first condensate booster pump are arranged in parallel with the second regulating valve and the second condensate booster pump between the low-temperature medium input end of the condensate heat exchanger and the second low-pressure heater. The third return water regulating valve group is arranged between the output end of the third low-pressure heater and the input end of the fourth low-pressure heater, the first regulating valve and the second regulating valve are arranged at one end close to the condensate heat exchanger, the first check valve is arranged between the low-temperature medium output end of the feed water heat exchanger and the input end of the first high-pressure heater, the third check valve is arranged between the low-temperature medium input end of the condensate heat exchanger and the output end of the fourth low-pressure heater, and the fourth check valve is arranged between the low-temperature medium input end of the condensate heat exchanger and the output end of the second low-pressure heater.
[0012] Optionally, the second heat exchange assembly further includes: a first circulating water booster pump, a third regulating valve, a second circulating water booster pump, a fourth regulating valve and a circulating water regulating valve group; The first circulating water booster pump and the third regulating valve are arranged in parallel with the second circulating water booster pump and the fourth regulating valve between the high-temperature medium output end of the cold air duct heat medium water heater and the low-temperature medium input end of the second low-temperature economizer, and the circulating water regulating valve group is arranged between the low-temperature medium input end of the first low-temperature economizer and the low-temperature medium output end of the second low-temperature economizer.
[0013] Optionally, the flue gas waste heat utilization system further includes: a fifth check valve, a condensation valve and a second frequency converter; The fifth check valve is arranged between the three-stage steam extraction end of the medium pressure cylinder and the high-temperature medium input end of the third low-temperature economizer, the condensation valve is arranged between the hydrophobic expansion tank and the high-temperature medium output end of the third low-temperature economizer, and the second frequency converter is arranged at the high-temperature medium input end of the air preheater and connected with the exhaust gas end of the boiler.
[0014] Optionally, the flue gas waste heat utilization system further includes: a denitration system, an electrostatic precipitator and an induced draft fan; The input end of the denitrification system is connected to the exhaust gas end of the boiler, the output end of the denitrification system is respectively connected to the high-temperature medium input end of the air preheater and the high-temperature medium input end of the feed water heat exchanger, the input end of the electrostatic precipitator is connected to the high-temperature medium output end of the first low-temperature economizer, the output end of the electrostatic precipitator is connected to the input end of the induced draft fan, and the output end of the induced draft fan is connected to the high-temperature medium input end of the second low-temperature economizer.
[0015] Optionally, the flue gas waste heat utilization system also includes: a steam air heater; the input end of the air blower is connected to the steam air heater.
[0016] Beneficial effects of the present invention: (1) Improve energy efficiency: Through a multi-level and phased heat exchange process, fully recover and utilize the waste heat in the boiler exhaust gas, reduce energy waste, and improve the thermal efficiency of the entire boiler system.
[0017] (2) Reduce energy consumption: Using the flue gas discharged by the boiler to preheat condensate and cold air can reduce boiler fuel consumption and reduce operating costs.
[0018] (3) Reduction of pollutant emissions: As energy efficiency is improved and fuel consumption is relatively reduced, pollutants emitted by boilers, such as carbon dioxide, nitrogen oxides and particulate matter, can be reduced.
[0019] (4) Improve the environment: Reduce pollution to the atmospheric environment by reducing boiler flue gas emissions and lowering emission temperatures.
[0020] (5) Extending equipment life: Preheating condensate can reduce the temperature difference of the heat exchange surface inside the boiler, reduce thermal stress, and help extend the service life of the boiler and its related equipment.
[0021] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following specific implementations, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings: Figure 1 It is a structural schematic diagram of a flue gas waste heat utilization system provided in an embodiment of the present invention.
[0023] Description of Reference Numerals 1-air preheater; 2-boiler; 3-condenser; 4-feedwater heat exchanger; 5-condensate heat exchanger; 6-first low-pressure heater; 7-second low-pressure heater; 8-third low-pressure heater; 9-fourth low-pressure heater; 10-fifth low-pressure heater; 11-deaerator; 12-boosting pump; 13-first high-pressure heater; 14-second high-pressure heater; 15-third high-pressure heater; 16-air blower; 17-cold air duct heat medium water heater; 18-plate and shell heat exchanger; 19-first low-temperature economizer; 20-second low-temperature economizer; 21-third low-temperature economizer; 22-intermediate pressure cylinder; 23-drain expansion tank; 24-first frequency converter; 25-first return water regulating valve group; 26-second return water regulating valve group; 27-first regulating valve; 28-first condensate booster pump; 29-second regulating valve; 30-second condensate booster pump; 31-third return water regulating valve group; 32-first check valve; 33-second check valve; 34-third check valve; 35-fourth check valve; 36-first circulating water booster pump; 37-third regulating valve; 38-second circulating water booster pump; 39-fourth regulating valve; 40-circulating water regulating valve group; 41-fifth check valve; 42-condensation valve; 43-second frequency converter; 44-denitrification system; 45-electrostatic precipitator; 46-induced draft fan; 47-Steam heater. DETAILED DESCRIPTION
[0024] The specific implementation of the embodiment of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiment of the present invention, and is not used to limit the embodiment of the present invention.
[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application.
[0026] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.
[0027] Embodiment 1 Please refer to Figure 1 , Figure 1It is a structural schematic diagram of a flue gas waste heat utilization system provided in an embodiment of the present invention, the system comprising: a first heat exchange component, a second heat exchange component and an air preheater 1, the first heat exchange component is connected to the second heat exchange component, the air outlet end of the second heat exchange component is connected to the low-temperature medium input end of the air preheater 1, and the flue gas input end of the second heat exchange component is respectively connected to the high-temperature medium output end of the air preheater 1 and the flue gas output end of the first heat exchange component; the first heat exchange component is used to heat the condensate delivered to the boiler by using the flue gas exhausted by the boiler; the second heat exchange component is used to use the heated circulating feed water to heat the cold air delivered to the boiler once; wherein the heated circulating feed water is obtained by heating the circulating feed water by the flue gas and condensate after heat exchange by the first heat exchange component and the flue gas output by the air preheater 1; the air preheater 1 is used to use the flue gas exhausted by the boiler to perform secondary heating on the cold air delivered to the boiler, and deliver the cooled flue gas to the second heat exchange component.
[0028] Specifically, the high-temperature flue gas generated by the boiler 2 during the combustion process is first discharged and then enters the first heat exchange component. In the first heat exchange component, the high-temperature flue gas exchanges heat with the condensate delivered to the boiler, and the heat in the flue gas is absorbed by the condensate, so that the temperature of the condensate increases, and the condensate is preheated. After the heat exchange, the temperature of the flue gas decreases, and then the flue gas is discharged from the flue gas output end of the first heat exchange component, and the low-temperature flue gas discharged from the first heat exchange component enters the flue gas input end of the second heat exchange component. At the same time, the condensate heated by the first heat exchange component also enters the second heat exchange component. In the second heat exchange component, the condensate exchanges heat with the low-temperature flue gas, further absorbing the heat in the flue gas, so that the temperature of the condensate continues to increase. At the same time, the cold air delivered to the boiler enters the second heat exchange component and exchanges heat with the circulating feed water heated by the condensate heated by the flue gas, so as to achieve the primary heating of the cold air. Then, the cold air heated once by the second heat exchange component enters the low-temperature medium input end of the air preheater. In the air preheater, the cold air exchanges heat with the high-temperature flue gas discharged from the boiler for the second time. After the heat exchange, the temperature of the cold air is further increased to achieve the preheating effect, and then it is transported to the boiler as the air required for combustion. After the flue gas releases heat in the air preheater, the temperature is reduced and finally transported to the desulfurization tower.
[0029] In one embodiment, the flue gas waste heat utilization system further includes: a boiler 2 and a condenser 3; the first heat exchange component includes: a feed water heat exchanger 4, a condensate heat exchanger 5 and a condensate recycling device; the first water inlet end of the condensate recycling device is connected to the condenser 3, the first water outlet end of the condensate recycling device is connected to the water inlet end of the boiler 2, the second water outlet end and the third water outlet end of the condensate recycling device are respectively connected to the low-temperature medium input end of the condensate heat exchanger 5, and the low-temperature medium output end of the condensate heat exchanger 5 is connected to the second water inlet end of the condensate recycling device. The fourth water inlet of the condensate recycling device is connected with the low-temperature medium input end of the feed water heat exchanger 4, the low-temperature medium output end of the feed water heat exchanger 4 is connected with the third water inlet of the condensate recycling device, the high-temperature medium input end of the feed water heat exchanger 4 and the high-temperature medium input end of the air preheater 1 are both connected with the exhaust gas end of the boiler 2, the high-temperature medium output end of the feed water heat exchanger 4 is connected with the high-temperature medium input end of the condensate heat exchanger 5, and the high-temperature medium output end of the condensate heat exchanger 5 and the high-temperature medium output end of the air preheater 1 are respectively connected with the high-temperature medium input end of the second heat exchange component. The flue gas input end is connected, and the low-temperature medium input end of the feed water heat exchanger 4 is also connected to the second heat exchange component; the boiler 2 is used to discharge the flue gas; the condenser 3 is used to output the condensed water; the condensed water recycling device is used to heat the condensed water at low pressure to obtain the condensed water after low pressure heating; the condensed water heat exchanger 5 is used to use the flue gas output from the feed water heat exchanger 4 to heat the condensed water after low pressure heating once, so as to obtain the condensed water after the once heating and the flue gas after the once cooling; the condensed water recycling device is used to heat the condensed water after the once heating and the flue gas after the low pressure heating The condensate is mixed with the deoxygenated and pressurized water and then deoxygenated and pressurized to obtain the deoxygenated and pressurized condensate; the feed water heat exchanger 4 is used to use the flue gas to perform secondary heating on the deoxygenated and pressurized condensate to obtain the secondary heated condensate and the secondary cooled flue gas, and the secondary cooled flue gas is transported to the condensate heat exchanger 5; the condensate recycling device is also used to perform high-pressure heating on the deoxygenated and pressurized condensate to obtain the high-pressure heated condensate, and the secondary heated condensate and the high-pressure heated condensate are mixed and then transported to the boiler 2.
[0030] In this embodiment, the system heats the condensed water by utilizing the waste heat of the flue gas multiple times, which not only improves the utilization of the heat of the flue gas but also reduces the consumption of external energy.
[0031] In one embodiment, if Figure 1As shown, the condensate recycling device includes: a first low-pressure heater 6, a second low-pressure heater 7, a third low-pressure heater 8, a fourth low-pressure heater 9, a fifth low-pressure heater 10, a deaerator 11, a booster pump 12, a first high-pressure heater 13, a second high-pressure heater 14 and a third high-pressure heater 15; the input end of the first low-pressure heater 6 is connected to the condenser 3, the output end of the first low-pressure heater 6 is connected to the input end of the second low-pressure heater 7, the output end of the second low-pressure heater 7 is connected to the input end of the third low-pressure heater 8 and the low-temperature medium input end of the condensate heat exchanger 5 respectively, the output end of the third low-pressure heater 8 is connected to the input end of the fourth low-pressure heater 9, and the output end of the fourth low-pressure heater 9 is connected to the input end of the condensate heat exchanger 5. The output end is respectively connected to the input end of the fifth low-pressure heater 10 and the low-temperature medium output end of the condensate heat exchanger 5, the output end of the fifth low-pressure heater 10 is connected to the input end of the deaerator 11, the output end of the deaerator 11 is connected to the input end of the booster pump 12, the output end of the booster pump 12 is respectively connected to the input end of the first high-pressure heater 13, the low-temperature medium input end of the feed water heat exchanger 4 and the second heat exchange component, the output end of the first high-pressure heater 13 is connected to the input end of the second high-pressure heater 14, the output end of the second high-pressure heater 14 is connected to the input end of the third high-pressure heater 15, and the output end of the third high-pressure heater 15 is respectively connected to the low-temperature medium output end of the feed water heat exchanger 4 and the water inlet end of the boiler 2.
[0032] In one embodiment, if Figure 1As shown, the flue gas waste heat utilization system also includes: an air blower 16; the second heat exchange component includes: a cold air duct heat medium water heater 17, a plate and shell heat exchanger 18 and a first low-temperature economizer 19 and a second low-temperature economizer 20; the low-temperature medium input end of the cold air duct heat medium water heater 17 is connected to the air blower 16, the low-temperature medium output end of the cold air duct heat medium water heater 17 is connected to the low-temperature medium input end of the air preheater 1, the high-temperature medium input end of the cold air duct heat medium water heater 17 is connected to the low-temperature medium output end of the plate and shell heat exchanger 18, and the low-temperature medium input end of the plate and shell heat exchanger 18 is connected to the first low-temperature economizer 20. The low-temperature medium output end of the coal burner 19 is connected, the low-temperature medium input end of the first low-temperature economizer 19 is connected to the low-temperature medium output end of the second low-temperature economizer 20, the low-temperature medium input end of the second low-temperature economizer 20 is connected to the high-temperature medium output end of the cold air duct heat medium water heater 17, the high-temperature medium input end of the plate and shell heat exchanger 18 is connected to the low-temperature medium input end of the condensate heat exchanger 5, the high-temperature medium output end of the plate and shell heat exchanger 18 is connected to the low-temperature medium output end of the condensate heat exchanger 5, the high-temperature medium input end of the first low-temperature economizer 19 is connected to the high-temperature medium output end of the air preheater 1 respectively The high-temperature medium output end of the first low-temperature economizer 19 is connected to the high-temperature medium input end of the second low-temperature economizer 20; the blower 16 is used to generate cold air; the first low-temperature economizer 19 is used to use the flue gas output by the air preheater 1 and the flue gas after the first cooling to heat the circulating feed water delivered by the second low-temperature economizer 20, so as to obtain the flue gas after the third cooling and the circulating feed water after the first heating; the plate and shell heat exchanger 18 is used to use the condensed water after low-pressure heating to heat the circulating feed water after the first heating for the second time, so as to obtain the flue gas after the third cooling and the circulating feed water after the first heating; The condensed water and the circulating feed water after secondary heating are used to transport the cooled condensed water to the deaerator 11; the heat medium water heater 17 in the cold air duct is used to heat the cold air transported to the boiler 2 once by using the circulating feed water after secondary heating, so as to obtain the cold air after primary heating and the circulating feed water after cooling, and transport the cold air after primary heating to the air preheater 1; the second low-temperature economizer 20 is used to heat the circulating feed water after cooling three times by using the flue gas after thrice cooling, so as to obtain the flue gas after four times cooling and the circulating feed water after heating, and transport the heated circulating feed water to the first low-temperature economizer 19.
[0033] In one embodiment, in order to avoid wear of the first low-temperature economizer 19 and the second low-temperature economizer 20, the first low-temperature economizer 19 and the second low-temperature economizer 20 can adopt a double H-shaped fin structure, and 2 rows of the same type of heat exchange dummy tubes are added to the windward side, and the first 4 rows of tubes are sprayed.
[0034] In one embodiment, since the first low-temperature economizer 19 is located in the flue before the dust collector, the ash in the flue gas is an alkaline substance that can neutralize part of the condensed sulfuric acid. In order to reduce the corrosion of the low-temperature section of the heat exchanger tube wall, the low-temperature section heat exchange tube bundle of the first low-temperature economizer 19 is made of ND steel.
[0035] In one embodiment, in order to prevent corrosion of the second low-temperature economizer 20, the 4 rows of tubes in the low-temperature section of the second low-temperature economizer 20 adopt an enameled spiral fin tube structure.
[0036] Specifically, in summer, the circulating water bypasses the plate and shell heat exchanger 18, and the heat medium water and condensate water exchange heat in the plate and shell heat exchanger 18. After the heat exchange, the temperature of the heat medium water drops to 110°C and then enters the cold air duct heat medium water heater 17 to release heat, heat the cold air at the inlet of the air preheater 1, and the heat medium water after heat release returns to the inlet of the second low-temperature economizer 20, forming a closed circulation system. In winter, the plate and shell heat exchanger 18 absorbs part of the heat of the heat medium water to heat the condensate of the condensate heat exchanger 5. The condensate is taken from the inlet condensate pipe of the condensate heat exchanger 5. The heated condensate is returned to the outlet condensate pipe of the condensate heat exchanger 5, and is mixed with the outlet condensate of the condensate heat exchanger 5 and sent to the inlet of the deaerator 11, thereby further improving the working capacity of the steam turbine.
[0037] In this embodiment, if Figure 1 As shown in the figure, the combined effect of the cold air duct heat medium water heater and the third low-temperature economizer makes it difficult for moisture in the air to condense into acid liquid, thereby reducing the corrosion of chloride ions to the flue environment. At the same time, this measure directly utilizes the heat of the flue gas, avoids the need for additional water resources and antifreeze spraying, and achieves the purpose of saving water resources and reducing operating costs. On this basis, we changed the working medium of the low-temperature economizer from water to circulating water to form a closed circulation system. The circulating water is circulated in the system, which effectively reduces the contact with the corrosive components in the flue gas, thereby reducing the corrosion and leakage risks of the pipeline. In addition, the closed circulation system also solves the leakage problem that is difficult to find due to low water pressure and small leakage points, and improves the safety and stability of the system. Finally, by setting up a plate and shell heat exchanger, we can adjust the flue temperature and effectively reduce problems such as high-temperature acid corrosion. This series of measures work together not only to protect the equipment from corrosion, but also to ensure the long-term stable operation of the system, reduce maintenance costs, and improve overall economic benefits.
[0038] In one embodiment, if Figure 1As shown, the flue gas waste heat utilization system also includes: a third low-temperature economizer 21, an intermediate pressure cylinder 22 and a hydrophobic expansion tank 23; the low-temperature medium input end of the third low-temperature economizer 21 is connected to the low-temperature medium output end of the air preheater 1, the low-temperature medium output end of the third low-temperature economizer 21 is connected to the air inlet end of the boiler 2, the high-temperature medium input end of the third low-temperature economizer 21 is connected to the three-stage extraction exhaust end of the intermediate pressure cylinder, and the high-temperature medium output end of the third low-temperature economizer 21 is connected to the hydrophobic expansion tank 23; the intermediate pressure cylinder 22 is used to discharge the three-stage extraction steam of the intermediate pressure cylinder; the third low-temperature economizer 21 is used to use the three-stage extraction steam of the intermediate pressure cylinder to heat the cold air transported to the boiler 2 three times, and transport the cooled three-stage extraction steam of the intermediate pressure cylinder to the hydrophobic expansion tank 23; the hydrophobic expansion tank 23 is used to reduce the pressure of the cooled three-stage extraction steam of the intermediate pressure cylinder.
[0039] In this embodiment, by providing the third low-temperature economizer 21, it cooperates with the cold air duct heat medium water heater 17 to further prevent moisture in the air from condensing into acid liquid, thereby further reducing the corrosion of chloride ions to the flue environment.
[0040] In one embodiment, if Figure 1 As shown, the first heat exchange component also includes: a first frequency converter 24, a first return water regulating valve group 25, a second return water regulating valve group 26, a first regulating valve 27, a first condensate boost pump 28, a second regulating valve 29, a second condensate boost pump 30, a third return water regulating valve group 31, a first check valve 32, a second check valve 33, a third check valve 34 and a fourth check valve 35; the first frequency converter 24 is arranged between the high-temperature medium input end of the feed water heat exchanger 4 and the exhaust gas end of the boiler 2, the first return water regulating valve group 25 is arranged between the low-temperature medium output end of the feed water heat exchanger 4 and the output end of the third high-pressure heater 15, the second return water regulating valve group 26 and the second check valve 33 are respectively arranged between the output end of the fifth low-pressure heater 10 and the low-temperature medium output end of the condensate heat exchanger 5, and the second check valve 33 is arranged near the output end of the fifth low-pressure heater 10. one end of the condensate heat exchanger 5, the first regulating valve 27 and the first condensate boosting pump 28 and the second regulating valve 29 and the second condensate boosting pump 30 are arranged in parallel between the low-temperature medium input end of the condensate heat exchanger 5 and the output end of the second low-pressure heater 7 and the output end of the fourth low-pressure heater 9, the third return water regulating valve group 31 is arranged between the output end of the third low-pressure heater 8 and the input end of the fourth low-pressure heater 9, the first regulating valve 27 and the second regulating valve 29 are arranged at one end close to the condensate heat exchanger 5, the first check valve 32 is arranged between the low-temperature medium output end of the feed water heat exchanger 4 and the input end of the first high-pressure heater 13, the third check valve 34 is arranged between the low-temperature medium input end of the condensate heat exchanger 5 and the output end of the fourth low-pressure heater 9, and the fourth check valve 35 is arranged between the low-temperature medium input end of the condensate heat exchanger 5 and the output end of the second low-pressure heater 7.
[0041] In this embodiment, by setting up the first frequency converter 24, the amount of flue gas from the denitrification system 44 to the water feed heat exchanger 4 is controlled. The frequency converter can be combined with the boiler control system to accurately control the amount of flue gas to the water feed heat exchanger 4 to avoid excessive flue gas inflow and waste of flue gas waste heat.
[0042] In this embodiment, the first water return regulating valve group 25, the second water return regulating valve group 26 and the third water return regulating valve group 31 are mainly responsible for regulating the return water pressure and temperature of the system to ensure stable operation of the system and avoid low-temperature corrosion of downstream components.
[0043] In this embodiment, two condensate pumps are usually configured in the condensate system of the thermal power plant, one of which is used as a running pump and the other is a standby. The first condensate booster pump 28 and the second condensate booster pump 30 are responsible for sucking low-pressure condensate and increasing its pressure to meet system requirements. At the same time, the first regulating valve 27 and the second regulating valve 29 are used to adjust the condensate flow rate, and when any condensate pump fails, it can quickly switch to another pump to ensure the continuous and stable supply of pressure and flow rate of the system.
[0044] In this embodiment, the first check valve 32, the second check valve 33, the third check valve 34 and the fourth check valve 35 are automatic valves whose main function is to prevent the medium from flowing back. They rely on the power of the fluid itself to automatically open or close the valve, allowing the medium to flow in one direction to protect the safety of pipelines and equipment.
[0045] In one embodiment, if Figure 1 As shown, the second heat exchange component also includes: a first circulating water booster pump 36, a third regulating valve 37, a second circulating water booster pump 38, a fourth regulating valve 39 and a circulating water regulating valve group 40; the first circulating water booster pump 36 and the third regulating valve 37 are arranged in parallel with the second circulating water booster pump 38 and the fourth regulating valve 39 between the high-temperature medium output end of the cold air duct heat medium water heater 17 and the low-temperature medium input end of the second low-temperature economizer 20, and the circulating water regulating valve group 40 is arranged between the low-temperature medium input end of the first low-temperature economizer 19 and the low-temperature medium output end of the second low-temperature economizer 20.
[0046] In this embodiment, the first circulating water booster pump 36, the third regulating valve 37, the second circulating water booster pump 38, and the fourth regulating valve 39, the circulating water booster pumps 36 and 38 are mainly responsible for raising the circulating water to a certain pressure to meet the pressure requirement of the system during the circulation process, and the regulating valves 37 and 39 are mainly used to adjust the circulating water flow rate.
[0047] In this embodiment, the circulating water regulating valve group 40 is responsible for regulating the flow rate, pressure and other parameters of the circulating water to ensure the effective operation of the system and the cascade utilization of waste heat.
[0048] In one embodiment, if Figure 1 As shown, the flue gas waste heat utilization system also includes: a fifth check valve 41, a condensation valve 42 and a second frequency converter 43; the fifth check valve 41 is arranged between the three-stage steam extraction end of the medium pressure cylinder 22 and the high-temperature medium input end of the third low-temperature economizer 21, the condensation valve 42 is arranged between the hydrophobic expansion tank 23 and the high-temperature medium output end of the third low-temperature economizer 21, and the second frequency converter 43 is arranged at the high-temperature medium input end of the air preheater 1 and connected with the exhaust gas end of the boiler 2.
[0049] In this embodiment, the fifth check valve 41 is located between the third-stage steam extraction 22 and the first flue gas waste heat utilization device 22 to prevent part of the water vapor from absorbing heat and liquefying and the extracted steam from flowing back.
[0050] In this embodiment, the condensate valve 42 is an automatic valve used in the steam heating system, and usually works in conjunction with the drain expansion tank 23. Its main function is to discharge condensate in the steam system and possible mixed air and other non-condensable gases, while preventing steam leakage. By timely removing condensate, the thermal efficiency of the heating equipment is ensured to be maintained at the best state, avoiding the performance of the equipment being affected.
[0051] In this embodiment, the second frequency converter 43 cooperates with the boiler control system to control the amount of flue gas from the denitration system 44 to the air preheater 1, so as to avoid excessive exhaust gas flowing into the air preheater bypass and causing waste of flue gas waste heat.
[0052] In one embodiment, if Figure 1 As shown, the flue gas waste heat utilization system also includes: a denitrification system 44, an electrostatic precipitator 45 and an induced draft fan 46; the input end of the denitrification system 44 is connected to the exhaust gas end of the boiler 2, and the output end of the denitrification system 44 is respectively connected to the high-temperature medium input end of the air preheater 1 and the high-temperature medium input end of the feed water heat exchanger 4, the input end of the electrostatic precipitator 45 is connected to the high-temperature medium output end of the first low-temperature economizer 19, the output end of the electrostatic precipitator 45 is connected to the input end of the induced draft fan 46, and the output end of the induced draft fan 46 is connected to the high-temperature medium input end of the second low-temperature economizer 20.
[0053] In this embodiment, the use of the denitration system 44 and the electrostatic precipitator 45 reduces the emission of pollutants in the flue gas, which meets environmental protection standards. In addition, the use of the induced draft fan 46 ensures the normal operation of the flue gas treatment system and improves the purification effect of the flue gas.
[0054] In one embodiment, if Figure 1 As shown, the flue gas waste heat utilization system also includes: a steam heater 47; the input end of the blower 16 is connected to the steam heater 47.
[0055] Specifically, the steam heater 47 is used to heat the cold air generated by the blower 16 .
[0056] In this embodiment, by installing the steam heater 47, it is possible to ensure that the flue temperature is within a safe range in both summer and winter, thereby avoiding corrosion and equipment operation problems caused by low temperatures.
[0057] In order to better understand the technical solution of the present invention, the main parameters of the waste heat utilization solution are introduced as follows: Table 1 Rated load operating parameters of the first low temperature economizer
[0058] Table 2 Parameters of the first low temperature economizer at 50% load
[0059] Table 3 Rated load operating parameters of the second low temperature economizer
[0060] Table 4 Parameters of the second low temperature economizer at 50% load
[0061] Table 5 Rated load operating parameters of plate and shell heat exchanger
[0062] Table 6 Parameters of 50% load condition of plate and shell heat exchanger
[0063] Table 7 Rated load parameters of cold air duct heat medium water heater
[0064] Table 8 Parameters of 50% load condition of cold air duct heat medium water heater
[0065] Table 9 Rated load operating parameters of feedwater heat exchanger
[0066] Table 10 Parameters of feedwater heat exchanger under 50% load condition
[0067] Table 11 Rated load operating parameters of condensate heat exchanger
[0068] Table 12 Parameters of 50% load ratio of condensate heat exchanger
[0069] Table 13 Structural parameters of different heat exchangers
[0070] Beneficial effects of the present invention: (1) Improve energy efficiency: Through a multi-level and phased heat exchange process, fully recover and utilize the waste heat in the boiler exhaust gas, reduce energy waste, and improve the thermal efficiency of the entire boiler system.
[0071] (2) Reduce energy consumption: Using the flue gas discharged by the boiler to preheat condensate and cold air can reduce boiler fuel consumption and reduce operating costs.
[0072] (3) Reduction of pollutant emissions: As energy efficiency is improved and fuel consumption is relatively reduced, pollutants emitted by boilers, such as carbon dioxide, nitrogen oxides and particulate matter, can be reduced.
[0073] (4) Improve the environment: Reduce pollution to the atmospheric environment by reducing boiler flue gas emissions and lowering emission temperatures.
[0074] (5) Extending equipment life: Preheating condensate can reduce the temperature difference of the heat exchange surface inside the boiler, reduce thermal stress, and help extend the service life of the boiler and its related equipment.
[0075] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.
[0076] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.
Claims
1. A flue gas waste heat utilization system, characterized in that: include: A first heat exchange component, a second heat exchange component and an air preheater (1), the first heat exchange component being in communication with the second heat exchange component, an air outlet end of the second heat exchange component being in communication with a low-temperature medium input end of the air preheater (1), and a flue gas input end of the second heat exchange component being in communication with a high-temperature medium output end of the air preheater (1) and a flue gas output end of the first heat exchange component; The first heat exchange component is used to heat the condensate delivered to the boiler by utilizing the flue gas discharged from the boiler; The second heat exchange component is used to heat the cold air delivered to the boiler using the heated circulating feed water; wherein the heated circulating feed water is obtained by heating the circulating feed water with the flue gas and condensed water after heat exchange by the first heat exchange component and the flue gas output by the air preheater (1); The air preheater (1) is used to utilize the flue gas exhausted from the boiler to perform secondary heating on the cold air delivered to the boiler, and to deliver the cooled flue gas to the second heat exchange component.
2. The flue gas waste heat utilization system according to claim 1, characterized in that: The flue gas waste heat utilization system further comprises: a boiler (2) and a condenser (3); the first heat exchange component comprises: a feed water heat exchanger (4), a condensate heat exchanger (5) and a condensate circulation utilization device; The first water inlet of the condensate circulation device is connected to the condenser (3), the first water outlet of the condensate circulation device is connected to the water inlet of the boiler (2), the second water outlet and the third water outlet of the condensate circulation device are respectively connected to the low-temperature medium input of the condensate heat exchanger (5), the low-temperature medium output of the condensate heat exchanger (5) is connected to the second water inlet of the condensate circulation device, the fourth water inlet of the condensate circulation device is connected to the low-temperature medium input of the feed water heat exchanger (4), and the low-temperature medium of the feed water heat exchanger (4) is connected to the low-temperature medium of the feed water heat exchanger (4). The output end is connected to the third water inlet end of the condensate recycling device, the high temperature medium input end of the feed water heat exchanger (4) and the high temperature medium input end of the air preheater (1) are both connected to the exhaust gas end of the boiler (2), the high temperature medium output end of the feed water heat exchanger (4) is connected to the high temperature medium input end of the condensate heat exchanger (5), the high temperature medium output end of the condensate heat exchanger (5) and the high temperature medium output end of the air preheater (1) are respectively connected to the flue gas input end of the second heat exchange component, and the low temperature medium input end of the feed water heat exchanger (4) is also connected to the second heat exchange component; A boiler (2) for exhausting flue gas; A condenser (3), used for outputting condensed water; A condensate recycling device is used to heat the condensate at low pressure to obtain low-pressure heated condensate; The condensate heat exchanger (5) is used to heat the condensate after low-pressure heating using the flue gas output from the feed water heat exchanger (4), thereby obtaining the once-heated condensate and the once-cooled flue gas; The condensate recycling device is used to mix the condensate after the primary heating and the condensate after the low-pressure heating treatment, and then perform deoxygenation and pressure-raising treatment to obtain the deoxygenated and pressure-raised condensate; A feed water heat exchanger (4) is used to use the flue gas to perform secondary heating on the condensed water after deoxygenation and pressure-raising treatment, thereby obtaining secondary heated condensed water and secondary cooled flue gas, and conveying the secondary cooled flue gas to the condensed water heat exchanger (5); The condensate recycling device is also used to perform high-pressure heating on the condensate after deoxygenation and pressure-boosting treatment to obtain high-pressure heated condensate, and to mix the secondary heated condensate with the high-pressure heated condensate and transport them to the boiler (2).
3. The flue gas waste heat utilization system according to claim 2, characterized in that: The condensate recycling device comprises: a first low-pressure heater (6), a second low-pressure heater (7), a third low-pressure heater (8), a fourth low-pressure heater (9), a fifth low-pressure heater (10), a deaerator (11), a booster pump (12), a first high-pressure heater (13), a second high-pressure heater (14) and a third high-pressure heater (15); The input end of the first low-pressure heater (6) is connected to the condenser (3), the output end of the first low-pressure heater (6) is connected to the input end of the second low-pressure heater (7), the output end of the second low-pressure heater (7) is respectively connected to the input end of the third low-pressure heater (8) and the low-temperature medium input end of the condensate heat exchanger (5), the output end of the third low-pressure heater (8) is connected to the input end of the fourth low-pressure heater (9), the output end of the fourth low-pressure heater (9) is respectively connected to the input end of the fifth low-pressure heater (10) and the low-temperature medium output end of the condensate heat exchanger (5), and the output end of the fifth low-pressure heater (10) is connected to the The input end of the oxygenator (11) is connected, the output end of the deaerator (11) is connected to the input end of the booster pump (12), the output end of the booster pump (12) is respectively connected to the input end of the first high-pressure heater (13), the low-temperature medium input end of the feed water heat exchanger (4) and the second heat exchange component, the output end of the first high-pressure heater (13) is connected to the input end of the second high-pressure heater (14), the output end of the second high-pressure heater (14) is connected to the input end of the third high-pressure heater (15), and the output end of the third high-pressure heater (15) is respectively connected to the low-temperature medium output end of the feed water heat exchanger (4) and the water inlet end of the boiler (2).
4. The flue gas waste heat utilization system according to claim 2, characterized in that: The flue gas waste heat utilization system further comprises: a blower (16); the second heat exchange component comprises: a cold air duct heat medium water heater (17), a plate and shell heat exchanger (18), a first low-temperature economizer (19), and a second low-temperature economizer (20); The low-temperature medium input end of the cold air duct heat medium water heater (17) is connected to the air supply fan (16), the low-temperature medium output end of the cold air duct heat medium water heater (17) is connected to the low-temperature medium input end of the air preheater (1), the high-temperature medium input end of the cold air duct heat medium water heater (17) is connected to the low-temperature medium output end of the plate and shell heat exchanger (18), the low-temperature medium input end of the plate and shell heat exchanger (18) is connected to the low-temperature medium output end of the first low-temperature economizer (19), the low-temperature medium input end of the first low-temperature economizer (19) is connected to the low-temperature medium output end of the second low-temperature economizer (20), and the low-temperature medium input end of the second low-temperature economizer (20) is connected to the low-temperature medium output end of the plate and shell heat exchanger (18). The high-temperature medium input end is connected to the high-temperature medium output end of the cold air duct heat medium water heater (17), the high-temperature medium input end of the plate and shell heat exchanger (18) is connected to the low-temperature medium input end of the condensate heat exchanger (5), the high-temperature medium output end of the plate and shell heat exchanger (18) is connected to the low-temperature medium output end of the condensate heat exchanger (5), the high-temperature medium input end of the first low-temperature economizer (19) is connected to the high-temperature medium output end of the air preheater (1) and the high-temperature medium output end of the condensate heat exchanger (5), respectively, and the high-temperature medium output end of the first low-temperature economizer (19) is connected to the high-temperature medium input end of the second low-temperature economizer (20); A blower (16) for generating cold air; The first low-temperature economizer (19) is used to heat the circulating feed water delivered from the second low-temperature economizer (20) using the flue gas output from the air preheater (1) and the flue gas after primary cooling, thereby obtaining the flue gas after thrice cooling and the circulating feed water after primary heating; The plate and shell heat exchanger (18) is used to use the condensed water after low-pressure heating to perform secondary heating on the circulating feed water after primary heating, thereby obtaining cooled condensed water and secondary heated circulating feed water, and transporting the cooled condensed water to the deaerator (11); The cold air duct heat medium water heater (17) is used to heat the cold air delivered to the boiler (2) once using the circulating water after secondary heating, thereby obtaining the cold air after primary heating and the circulating water after cooling, and delivering the cold air after primary heating to the air preheater (1); The second low-temperature economizer (20) is used to use the flue gas that has been cooled thrice to heat the cooled circulating feed water thrice, thereby obtaining the flue gas that has been cooled thrice and the heated circulating feed water, and to transport the heated circulating feed water to the first low-temperature economizer (19).
5. The flue gas waste heat utilization system according to claim 1, characterized in that: The flue gas waste heat utilization system further includes: a third low-temperature economizer (21), a medium-pressure cylinder (22) and a drain expansion tank (23); The low-temperature medium input end of the third low-temperature economizer (21) is connected to the low-temperature medium output end of the air preheater (1), the low-temperature medium output end of the third low-temperature economizer (21) is connected to the air inlet end of the boiler (2), the high-temperature medium input end of the third low-temperature economizer (21) is connected to the third extraction exhaust end of the medium-pressure cylinder, and the high-temperature medium output end of the third low-temperature economizer (21) is connected to the drain expansion tank (23); The intermediate pressure cylinder (22) is used to discharge the three-stage extraction steam of the intermediate pressure cylinder; The third low-temperature economizer (21) is used to heat the cold air delivered to the boiler (2) three times by using the three-stage extraction steam of the intermediate pressure cylinder, and deliver the cooled three-stage extraction steam of the intermediate pressure cylinder to the drain expansion tank (23); The drain expansion tank (23) is used to reduce the pressure of the three-stage extraction steam from the intermediate pressure cylinder after the temperature has been reduced.
6. The flue gas waste heat utilization system according to claim 3, characterized in that: The first heat exchange assembly further comprises: a first frequency converter (24), a first return water regulating valve group (25), a second return water regulating valve group (26), a first regulating valve (27), a first condensate boosting pump (28), a second regulating valve (29), a second condensate boosting pump (30), a third return water regulating valve group (31), a first check valve (32), a second check valve (33), a third check valve (34) and a fourth check valve (35); The first frequency converter (24) is arranged between the high-temperature medium input end of the feedwater heat exchanger (4) and the flue gas end of the boiler (2), the first return water regulating valve group (25) is arranged between the low-temperature medium output end of the feedwater heat exchanger (4) and the output end of the third high-pressure heater (15), the second return water regulating valve group (26) and the second check valve (33) are respectively arranged between the output end of the fifth low-pressure heater (10) and the low-temperature medium output end of the condensate heat exchanger (5), the second check valve (33) is arranged at one end close to the output end of the fifth low-pressure heater (10), the first regulating valve (27) and the first condensate boosting pump (28) and the second regulating valve (29) and the second condensate boosting pump (30) are arranged in parallel between the low-temperature medium input end and the low-temperature medium output end of the condensate heat exchanger (5). The third return water regulating valve group (31) is arranged between the output end of the second low-pressure heater (7) and the output end of the fourth low-pressure heater (9), the first regulating valve (27) and the second regulating valve (29) are arranged at one end close to the condensate heat exchanger (5), the first check valve (32) is arranged between the low-temperature medium output end of the feed water heat exchanger (4) and the input end of the first high-pressure heater (13), the third check valve (34) is arranged between the low-temperature medium input end of the condensate heat exchanger (5) and the output end of the fourth low-pressure heater (9), and the fourth check valve (35) is arranged between the low-temperature medium input end of the condensate heat exchanger (5) and the output end of the second low-pressure heater (7).
7. The flue gas waste heat utilization system according to claim 4, characterized in that: The second heat exchange assembly further comprises: a first circulating water booster pump (36), a third regulating valve (37), a second circulating water booster pump (38), a fourth regulating valve (39) and a circulating water regulating valve group (40); The first circulating water booster pump (36) and the third regulating valve (37) are arranged in parallel with the second circulating water booster pump (38) and the fourth regulating valve (39) between the high-temperature medium output end of the cold air duct heat medium water heater (17) and the low-temperature medium input end of the second low-temperature economizer (20), and the circulating water regulating valve group (40) is arranged between the low-temperature medium input end of the first low-temperature economizer (19) and the low-temperature medium output end of the second low-temperature economizer (20).
8. The flue gas waste heat utilization system according to claim 5, characterized in that: The flue gas waste heat utilization system further includes: a fifth check valve (41), a condensation valve (42) and a second frequency converter (43); The fifth check valve (41) is arranged between the third-stage steam extraction end of the intermediate pressure cylinder (22) and the high-temperature medium input end of the third low-temperature economizer (21), the condensation valve (42) is arranged between the hydrophobic expansion tank (23) and the high-temperature medium output end of the third low-temperature economizer (21), and the second frequency converter (43) is arranged at the high-temperature medium input end of the air preheater (1) and is connected to the exhaust gas end of the boiler (2).
9. The flue gas waste heat utilization system according to claim 4, characterized in that: The flue gas waste heat utilization system further includes: a denitration system (44), an electrostatic precipitator (45) and an induced draft fan (46); The input end of the denitration system (44) is connected to the exhaust gas end of the boiler (2), the output end of the denitration system (44) is respectively connected to the high-temperature medium input end of the air preheater (1) and the high-temperature medium input end of the feedwater heat exchanger (4), the input end of the electrostatic precipitator (45) is connected to the high-temperature medium output end of the first low-temperature economizer (19), the output end of the electrostatic precipitator (45) is connected to the input end of the induced draft fan (46), and the output end of the induced draft fan (46) is connected to the high-temperature medium input end of the second low-temperature economizer (20).
10. The flue gas waste heat utilization system according to claim 4, characterized in that: The flue gas waste heat utilization system further comprises: a steam air heater (47); and an input end of the air blower (16) is connected to the steam air heater (47).