A coal-fired generating unit secondary air steam preheating coupled flue gas heat supplement system and method

Abstract

The application discloses a coal-fired generating unit secondary air steam preheating coupled flue gas heat supplement system and method, wherein a high-temperature steam pipeline is connected with one end of a bypass steam flow regulating valve, the other end of the bypass steam flow regulating valve is connected with a shell side inlet of a steam air heater, an air outlet of an air preheater is connected with an inlet of a secondary air bypass inlet shutoff door, an outlet of the secondary air bypass inlet shutoff door is connected with an inlet of a bypass secondary air quantity regulating door, an outlet of the bypass secondary air quantity regulating door is connected with a pipe side inlet of the steam air heater, a pipe side outlet of the steam air heater is connected with an inlet of a secondary air bypass outlet shutoff door, and an outlet of the secondary air bypass outlet shutoff door is connected with an inlet of an SCR denitration device in a tail flue of a boiler, so that the system and the method can realize uniform and controllable improvement of the denitration inlet flue gas temperature, and guarantee safe and effective operation of the denitration system.

Description

Technical Field

[0001] This invention belongs to the field of energy conservation and emission reduction technology, and relates to a secondary air steam preheating coupled flue gas supplementation system and method for coal-fired power generation units. Background Technology

[0002] As the unit load rate continues to decrease, the flue gas temperature at the economizer outlet drops significantly. The activity of the catalyst used in selective catalytic reduction (SCR) denitrification units is highly sensitive to temperature, with its continuous operating temperature window typically ranging from 300℃ to 420℃. When the denitrification inlet flue gas temperature falls below the catalyst's minimum continuous operating temperature, the denitrification efficiency drops sharply, potentially causing irreversible catalyst deactivation. This resulting contradiction of "low load operation - low denitrification inlet flue gas temperature - SCR system shutdown - NOx emission exceeding standards" has become a key technical bottleneck restricting the clean and flexible operation of coal-fired units.

[0003] Against this backdrop, some regions (such as Jiangsu Province) have already mandated grid-connected denitrification systems, signifying that ultra-low NO emission standards not only require high limits but also operational stability. Guangdong Province has begun implementing a price compensation mechanism for the commissioning of denitrification systems in generating units. In the long term, with increasingly stringent national environmental standards and more frequent peak-shaving by generating units, requiring the commissioning of denitrification systems is an inevitable trend. Therefore, research on denitrification inlet flue gas temperature enhancement technology for coal-fired generating units is of significant practical importance for improving energy efficiency and promoting sustainable development.

[0004] Currently, the main whole-process denitrification technologies in China are: Economizer staged technology. Based on the flue gas temperature requirements at the inlet of the SCR denitrification unit, the economizer is split into two stages. After splitting, part of the economizer remains in its original location, while the other part is moved after the SCR denitrification unit. This reduces the heat release of the flue gas in the original economizer area, thereby increasing the flue gas temperature entering the SCR reactor.

[0005] Composite hot water recirculation technology. A bypass pipeline and corresponding flow control device are installed at the economizer to reduce the cold water flow entering the economizer; at the same time, recirculation pipelines and corresponding control devices are installed from the separator downcomer and the economizer downcomer respectively to draw a certain amount of hot water back to the bypass pumping point and before the economizer inlet header (water is drawn from the separator downcomer in wet conditions and from the economizer outlet in dry conditions), thereby increasing the working fluid temperature entering the economizer.

[0006] High-temperature flue gas bypass technology. High-temperature flue gas bypass technology involves extracting a portion of high-temperature flue gas from a certain point in the flue before the economizer. This portion of flue gas does not flow through the economizer's heated surface tube assembly but instead mixes with the flue gas at the economizer outlet via a bypass, thereby increasing the temperature of the flue gas entering the SCR unit.

[0007] Flue gas afterburning technology. Flue gas afterburning technology involves installing a flue gas afterburner between the economizer outlet and the denitrification inlet. The afterburner can be an oil burner or a gas burner, thereby effectively increasing the flue gas temperature.

[0008] The main technical defects of existing technologies are as follows: 1) Economizer grading technology is a permanent modification that is "irreversible." After the modification, because the heat exchange area is not adjustable, it lacks the ability to dynamically regulate flue gas temperature and is not adaptable to changes in coal type or operating conditions; it cannot enable the SCR denitrification system to be put into operation immediately after unit grid connection. 2) Composite hot water recirculation technology involves a large amount of engineering work, a long construction period, and high investment; it cannot enable the SCR denitrification system to be put into operation before unit grid connection. 3) High-temperature flue gas bypass technology cannot guarantee the heat exchange efficiency of the economizer; flue gas baffles accumulate ash and become stuck; the baffle sealing performance deteriorates, affecting catalyst life; it cannot enable the SCR denitrification system to be put into operation immediately after unit grid connection. 4) Although flue gas combustion technology can enable the SCR denitrification system to be put into operation before unit grid connection, this technology has high operating costs (consuming high-priced fuel), high safety risks (combustion explosion, overheating), and complex technical implementation (requiring solutions for mixed flue gas uniformity and explosion-proof control). Therefore, power plants are cautious when choosing this technology. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a secondary air steam preheating coupled flue gas supplementation system and method for coal-fired power generation units. This system and method can achieve uniform and controllable increase in the temperature of the flue gas at the denitrification inlet, ensuring the safe and effective operation of the denitrification system.

[0010] To achieve the above objectives, this invention discloses a secondary air steam preheating coupled flue gas supplementary heating system for a coal-fired power generation unit, comprising a high-temperature steam pipeline, a bypass steam flow regulating valve, a steam air heater, an air preheater, a secondary air bypass inlet shut-off valve, a bypass secondary air volume regulating valve, a secondary air bypass outlet shut-off valve, and a boiler. The high-temperature steam pipeline is connected to one end of the bypass steam flow regulating valve, and the other end of the bypass steam flow regulating valve is connected to the shell-side inlet of the steam heater. The air outlet of the air preheater is connected to the inlet of the secondary air bypass inlet shut-off valve. The outlet of the secondary air bypass inlet shut-off valve is connected to the inlet of the bypass secondary air volume regulating valve. The outlet of the bypass secondary air volume regulating valve is connected to the pipe-side inlet of the steam heater. The pipe-side outlet of the steam heater is connected to the inlet of the secondary air bypass outlet shut-off valve. The outlet of the secondary air bypass outlet shut-off valve is connected to the inlet of the SCR denitrification device in the tail flue of the boiler.

[0011] Furthermore, it also includes a high-temperature superheater, with a high-temperature steam pipe connected to the outlet of the high-temperature superheater.

[0012] Furthermore, it also includes a high-pressure cylinder, a low-temperature reheater, and a condenser. The high-temperature steam pipeline is connected to the inlet of the high-pressure cylinder, the outlet of the high-pressure cylinder is connected to the inlet of the low-temperature reheater, the shell-side outlet of the steam heater is connected to the cold reheat valve via bypass steam and the inlet of the low-temperature reheater, and the shell-side outlet of the steam heater is connected to the condenser valve via bypass steam and the inlet of the condenser.

[0013] Furthermore, it also includes a high-temperature reheater, with a high-temperature steam pipeline connected to the outlet of the high-temperature reheater.

[0014] Furthermore, it also includes an intermediate-pressure cylinder, a high-pressure cylinder, a low-temperature reheater, a low-pressure cylinder, and a condenser. The outlet of the high-temperature steam pipeline is connected to the inlet of the intermediate-pressure cylinder, the outlet of the high-temperature superheater is connected to the inlet of the high-pressure cylinder, the outlet of the high-pressure cylinder is connected to the inlet of the low-temperature reheater, the shell-side outlet of the steam heater is connected to the exhaust valve of the intermediate-pressure cylinder via bypass steam and is connected to the inlet of the low-pressure cylinder, and the shell-side outlet of the steam heater is connected to the valve of the condenser via bypass steam and is connected to the inlet of the condenser.

[0015] Furthermore, the boiler's tail flue is sequentially equipped with a screen-type superheater, a high-temperature superheater, a high-temperature reheater, a low-temperature reheater, an economizer, and an SCR denitrification device along the flue gas flow direction. The boiler's tail flue outlet is connected to the dust removal system inlet via the flue gas side of the air preheater. The fan outlet is connected to the air inlet of the air preheater. The air outlet of the air preheater is connected to the secondary air inlet of the furnace. The high-temperature superheater outlet is connected to the high-pressure cylinder inlet. The intermediate-pressure cylinder outlet is connected to the low-pressure cylinder inlet. The low-pressure cylinder outlet is connected to the condenser inlet. The condenser outlet is connected to the condensate pump inlet. The condensate pump outlet is connected to the low-pressure heater's absorber side inlet. The low-pressure heater's absorber side outlet is connected to the deaerator inlet. The deaerator outlet is connected to the high-pressure heater's absorber side inlet via the feedwater pump. The high-pressure heater's absorber side outlet is connected to the boiler's feedwater inlet.

[0016] Furthermore, the steam extraction port of the high-pressure cylinder is connected to the heat release side of the high-pressure heater, the steam extraction port of the intermediate-pressure cylinder is connected to the steam inlet of the deaerator, and the steam extraction port of the low-pressure cylinder is connected to the heat release side of the low-pressure heater.

[0017] Furthermore, the high-pressure cylinder, intermediate-pressure cylinder, low-pressure cylinder, and generator are arranged coaxially.

[0018] This invention discloses a method for secondary air steam preheating coupled with flue gas reheating in coal-fired power generating units, based on a secondary air steam preheating coupled with flue gas reheating system for coal-fired power generating units, comprising the following steps: The low-temperature air output from the air preheater is heated by the steam heater and then enters the inlet of the SCR denitrification unit. After mixing with the flue gas, it enters the SCR denitrification unit. The high-temperature steam output from the boiler is de-cooled and then enters the steam heater through the bypass steam flow regulating valve for heat exchange. The steam after heat exchange enters the low-temperature reheater or is discharged to the condenser.

[0019] This invention discloses a method for secondary air steam preheating coupled with flue gas reheating in coal-fired power generating units, based on a secondary air steam preheating coupled with flue gas reheating system for coal-fired power generating units, comprising the following steps: The low-temperature air output from the air preheater is heated by the steam heater and then enters the inlet of the SCR denitrification unit. After mixing with the flue gas, it enters the SCR denitrification unit. The reheat steam output from the boiler is de-heated and then enters the steam heater through the bypass steam flow regulating valve for heat exchange. The steam after heat exchange enters the low-pressure cylinder to do work or is discharged to the condenser.

[0020] The present invention has the following beneficial effects: In specific operation, the secondary air steam preheating coupled flue gas supplementary heating system and method for coal-fired power generation units described in this invention draws a high-temperature steam from the boiler side and sends it into a steam air heater. At the same time, a steam line is drawn from the air preheated by the air preheater and sent into the steam air heater. The steam air heater further heats the preheated air and then sends it into the inlet section of the SCR denitrification device. This achieves a uniform and controllable increase in the temperature of the flue gas at the denitrification inlet, ensuring the safe and effective operation of the denitrification system. It is highly practical. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a structural diagram of the present invention; Figure 2 This is another structural diagram of the present invention; Figure 3 A flowchart of the valve opening control method for bypass steam flow regulating valve 94; Figure 4 This is a flowchart of the method for controlling the opening of the bypass secondary air volume regulating door 92.

[0023] Among them, 1 is the boiler, 21 is the high-pressure cylinder, 22 is the medium-pressure cylinder, 23 is the low-pressure cylinder, 3 is the condenser, 41 is the condensate pump, 42 is the feedwater pump, 5 is the low-pressure heater, 6 is the deaerator, 7 is the high-pressure heater, 8 is the air preheater, 91 is the secondary air bypass inlet shut-off valve, 92 is the bypass secondary air volume regulating valve, 93 is the secondary air bypass outlet shut-off valve, 94 is the bypass steam flow regulating valve, 95 is the bypass steam to condenser valve, 961 is the bypass steam to reheat valve, 962 is the bypass steam to medium-pressure cylinder exhaust valve, and 10 is the steam heater. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0026] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0027] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0028] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0029] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0031] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0032] refer to Figure 1 The secondary air steam preheating coupled flue gas supplementary heating system of the coal-fired power generation unit of the present invention includes a high-temperature steam pipeline, a boiler 1, a high-pressure cylinder 21, a medium-pressure cylinder 22, a low-pressure cylinder 23, a condenser 3, a condensate pump 41, a feed water pump 42, a low-pressure heater 5, a deaerator 6, a high-pressure heater 7, an air preheater 8, a secondary air bypass inlet shut-off valve 91, a bypass secondary air volume regulating valve 92, a secondary air bypass outlet shut-off valve 93, a bypass steam flow regulating valve 94, and a steam air heater 10. The high-temperature steam pipeline is connected to one end of the bypass steam flow regulating valve 94, and the other end of the bypass steam flow regulating valve 94 is connected to the shell-side inlet of the steam heater 10. The air outlet of the air preheater 8 is connected to the inlet of the secondary air bypass inlet shut-off valve 91. The outlet of the secondary air bypass inlet shut-off valve 91 is connected to the inlet of the bypass secondary air volume regulating valve 92. The outlet of the bypass secondary air volume regulating valve 92 is connected to the pipe-side inlet of the steam heater 10. The pipe-side outlet of the steam heater 10 is connected to the inlet of the secondary air bypass outlet shut-off valve 93. The outlet of the secondary air bypass outlet shut-off valve 93 is connected to the inlet of the SCR denitrification device in the tail flue of the boiler 1.

[0033] refer to Figure 1 The high-temperature steam pipeline is connected to the outlet of the high-temperature superheater, the high-temperature steam pipeline is connected to the inlet of the high-pressure cylinder 21, the outlet of the high-pressure cylinder 21 is connected to the inlet of the low-temperature reheater, the shell-side outlet of the steam heater 10 is connected to the inlet of the low-temperature reheater via bypass steam to the cold reheat valve 961, and the shell-side outlet of the steam heater 10 is connected to the inlet of the condenser 3 via bypass steam to the condenser valve 95.

[0034] During operation, the low-temperature air output from the air preheater 8 is heated by the steam heater 10 and then enters the inlet of the SCR denitrification device. After mixing with the flue gas, it enters the SCR denitrification device. The high-temperature steam output from the boiler is de-cooled and then enters the steam heater 10 through the bypass steam flow regulating valve 94 for heat exchange. The steam after heat exchange enters the low-temperature reheater or is discharged to the condenser 3.

[0035] refer to Figure 2 The high-temperature steam pipeline is connected to the outlet of the high-temperature reheater. The outlet of the high-temperature steam pipeline is connected to the inlet of the intermediate-pressure cylinder 22. The outlet of the high-temperature superheater is connected to the inlet of the high-pressure cylinder 21. The outlet of the high-pressure cylinder 21 is connected to the inlet of the low-temperature reheater. The shell-side outlet of the steam heater 10 is connected to the inlet of the low-pressure cylinder 23 via the bypass steam to the intermediate-pressure cylinder exhaust valve 962. The shell-side outlet of the steam heater 10 is connected to the inlet of the condenser 3 via the bypass steam to the condenser valve 95.

[0036] During operation, the low-temperature air output from the air preheater 8 is heated by the steam heater 10 and then enters the inlet of the SCR denitrification device. After mixing with the flue gas, it enters the SCR denitrification device. The reheat steam output from the boiler is de-heated and then enters the steam heater 10 through the bypass steam flow regulating valve 94 for heat exchange. The heat-exchanged steam enters the low-pressure cylinder 23 to do work or is discharged to the condenser 3.

[0037] In detail, during the operation of boiler 1, air output from air preheater 8 is first delivered to the steam heater 10 for heating and heat exchange. The preheated air, heated by the steam heater 10, is then delivered to the flue gas inlet pipe section of the SCR denitrification device, where it is fully mixed with the high-temperature flue gas discharged from boiler 1 before denitrification. This flue gas-heated air mixture is then sent into the SCR denitrification device to carry out the catalytic reduction denitrification reaction. Reheated steam or high-temperature steam extracted from boiler 1 is first subjected to a desuperheating device for temperature regulation, adjusting the steam parameters to the temperature range suitable for heat exchange in the steam heater 10. After desuperheating, the steam flow rate is precisely controlled by the bypass steam flow regulating valve 94 and delivered into the steam heater 10 as a heat source medium for indirect heat exchange with the low-temperature air on the pipe side.

[0038] This invention can rapidly increase the inlet flue gas temperature of the SCR denitrification device. The system takes hot secondary air from the outlet of the air preheater 8, which is further heated by the steam heater 10 and then mixed with the flue gas at the denitrification inlet, thereby increasing the inlet flue gas temperature of the SCR denitrification device. This method can quickly and flexibly replenish heat under low load conditions or even after the unit is connected to the grid, ensuring the flue gas temperature conditions required for the denitrification system to be put into operation.

[0039] In this embodiment, a screen-type superheater, a high-temperature superheater, a high-temperature reheater, a low-temperature reheater, an economizer, and an SCR denitrification device are sequentially arranged in the tail flue of boiler 1 along the flue gas flow direction. The outlet of the tail flue of boiler 1 is connected to the inlet of the dust removal system via the flue gas side of the air preheater 8. The outlet of the fan is connected to the air inlet of the air preheater 8. The air outlet of the air preheater 8 is connected to the secondary air inlet of the furnace. The outlet of the high-temperature superheater is connected to the inlet of the high-pressure cylinder 21. The medium-pressure... The outlet of cylinder 22 is connected to the inlet of low-pressure cylinder 23. The outlet of low-pressure cylinder 23 is connected to the inlet of condenser 3. The outlet of condenser 3 is connected to the inlet of condensate pump 41. The outlet of condensate pump 41 is connected to the heat absorption side inlet of low-pressure heater 5. The heat absorption side outlet of low-pressure heater 5 is connected to the inlet of deaerator 6. The outlet of deaerator 6 is connected to the heat absorption side inlet of high-pressure heater 7 via feedwater pump 42. The heat absorption side outlet of high-pressure heater 7 is connected to the feedwater inlet of boiler 1.

[0040] In this embodiment, the steam extraction port of the high-pressure cylinder 21 is connected to the heat release side of the high-pressure heater 7, the steam extraction port of the medium-pressure cylinder 22 is connected to the steam inlet of the deaerator 6, and the steam extraction port of the low-pressure cylinder 23 is connected to the heat release side of the low-pressure heater 5.

[0041] In this embodiment, the high-pressure cylinder 21, the medium-pressure cylinder 22, the low-pressure cylinder 23, and the generator are arranged coaxially.

[0042] The specific working process of this invention is as follows: When the system is running, in addition to controlling the conventional operating equipment of the unit, it mainly controls the bypass secondary air volume regulating valve 92 and the bypass steam flow regulating valve 94.

[0043] The opening degree of the bypass steam flow regulating valve 94 is controlled by following the temperature of the mixed flue gas. Specifically, the inlet flue gas temperature of the SCR denitrification device is set to be no less than 300℃. The bypass secondary air volume regulating valve 92 follows the total volume of hot secondary air at the outlet of the air preheater 8. The bypass secondary air volume is set to maintain a certain ratio range (22%-27%) with the total volume of hot secondary air at the outlet of the air preheater 8. If it exceeds this range, the opening degree of the bypass secondary air volume regulating valve 92 needs to be adjusted to avoid large fluctuations in the volume of secondary air entering the furnace of boiler 1 for combustion.

[0044] refer to Figure 3 The inlet flue gas temperature of the SCR denitrification unit adopts a combination of feedback and feedforward. The feedback control adopts a PID controller, and the PID setpoint is the sum of the flue gas temperature setpoint and threshold 1. The feedforward control includes feedforward of coal feed rate and feedforward of the opening of bypass secondary air volume regulating valve 92, which are obtained by multiplying the coal feed rate with feedforward coefficient 1 and the bypass secondary air volume regulating valve 92 with feedforward coefficient 2, respectively. The feedforward signal is superimposed on the output of the PID controller to obtain the opening command of bypass steam flow regulating valve 94.

[0045] refer to Figure 4 The bypass secondary air volume regulating valve 92 is controlled by feedback control. The bypass secondary air volume regulating valve 92 opens gradually and maintains the ratio of bypass secondary air volume to the total hot secondary air volume at the outlet of air preheater 8 within the set value range (22%-27%). If it exceeds this range, the opening degree of the bypass secondary air volume regulating valve 92 needs to be adjusted. The opening degree command of the bypass secondary air volume regulating valve 92 is obtained by the PID controller based on the deviation between the set value and the actual value.

[0046] It should be noted that the present invention has the following characteristics: This invention enables the unit to have the capability to put into operation an SCR denitrification system before grid connection and during operation at ultra-low load (below 20% Pe).

[0047] This invention further reduces the deep peak-shaving load of the unit while increasing the operating load of boiler 1. After the flue gas temperature rise system is put into operation, the operating load of the unit can be further reduced, supporting the unit's flexible peak-shaving; the operating load of boiler 1 is increased, the main parameters of boiler 1 are improved, which can enhance the safety of boiler 1 and turbine operating at ultra-low loads.

[0048] This invention improves the adaptability of auxiliary equipment for boiler 1 under low-load operation. Under ultra-low load operation of boiler 1, induced draft fans and forced draft fans generally suffer from problems such as insufficient output adjustment capacity and significant decrease in fan efficiency; after the flue gas temperature rise system is put into operation, the fan operating load can be significantly increased, the fan operating efficiency can be improved by 10%-15%, and the fan operating safety can be further improved.

[0049] This invention does not change the original design of the heat exchange surface structure and flue gas of boiler 1, but it lacks strong adaptability to changes in coal type and operating conditions.

[0050] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and disclosure of the invention. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0051] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

[0052] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A secondary air steam preheating coupled flue gas reheating system for a coal-fired power generation unit, characterized in that, Includes high-temperature steam pipeline, bypass steam flow regulating valve (94), steam air heater (10), air preheater (8), secondary air bypass inlet shut-off valve (91), bypass secondary air volume regulating valve (92), secondary air bypass outlet shut-off valve (93) and boiler (1); The high-temperature steam pipeline is connected to one end of the bypass steam flow regulating valve (94), and the other end of the bypass steam flow regulating valve (94) is connected to the shell-side inlet of the steam heater (10). The air outlet of the air preheater (8) is connected to the inlet of the secondary air bypass inlet shut-off valve (91). The outlet of the secondary air bypass inlet shut-off valve (91) is connected to the inlet of the bypass secondary air volume regulating valve (92). The outlet of the bypass secondary air volume regulating valve (92) is connected to the pipe-side inlet of the steam heater (10). The pipe-side outlet of the steam heater (10) is connected to the inlet of the secondary air bypass outlet shut-off valve (93). The outlet of the secondary air bypass outlet shut-off valve (93) is connected to the inlet of the SCR denitrification device in the tail flue of the boiler (1).

2. The secondary air steam preheating coupled flue gas reheating system for coal-fired power generating units according to claim 1, characterized in that, It also includes a high-temperature superheater, and the high-temperature steam pipeline is connected to the outlet of the high-temperature superheater.

3. The secondary air steam preheating coupled flue gas reheating system for coal-fired power generating units according to claim 2, characterized in that, It also includes a high-pressure cylinder (21), a low-temperature reheater and a condenser (3). The high-temperature steam pipeline is connected to the inlet of the high-pressure cylinder (21), the outlet of the high-pressure cylinder (21) is connected to the inlet of the low-temperature reheater, the shell-side outlet of the steam heater (10) is connected to the inlet of the low-temperature reheater via a bypass steam to the cold reheat valve (961), and the shell-side outlet of the steam heater (10) is connected to the inlet of the condenser (3) via a bypass steam to the condenser valve (95).

4. The secondary air steam preheating coupled flue gas reheating system for coal-fired power generating units according to claim 1, characterized in that, It also includes a high-temperature reheater, with a high-temperature steam pipeline connected to the outlet of the high-temperature reheater.

5. The secondary air steam preheating coupled flue gas reheating system for coal-fired power generating units according to claim 1, characterized in that, It also includes a medium-pressure cylinder (22), a high-pressure cylinder (21), a low-temperature reheater, a low-pressure cylinder (23), and a condenser (3). The outlet of the high-temperature steam pipe is connected to the inlet of the medium-pressure cylinder (22). The outlet of the high-temperature superheater is connected to the inlet of the high-pressure cylinder (21). The outlet of the high-pressure cylinder (21) is connected to the inlet of the low-temperature reheater. The shell-side outlet of the steam heater (10) is connected to the inlet of the low-pressure cylinder (23) via bypass steam through the steam exhaust valve (962) of the medium-pressure cylinder. The shell-side outlet of the steam heater (10) is connected to the inlet of the condenser (3) via the steam exhaust valve (95) of the condenser through bypass steam.

6. The secondary air steam preheating coupled flue gas reheating system for coal-fired power generating units according to claim 1, characterized in that, The tail flue of the boiler (1) is equipped with a screen-type superheater, a high-temperature superheater, a high-temperature reheater, a low-temperature reheater, an economizer, and an SCR denitrification device in sequence along the flue gas flow direction. The outlet of the tail flue of the boiler (1) is connected to the inlet of the dust removal system via the flue gas side of the air preheater (8). The outlet of the fan is connected to the air inlet of the air preheater (8). The air outlet of the air preheater (8) is connected to the secondary air inlet of the furnace. The outlet of the high-temperature superheater is connected to the inlet of the high-pressure cylinder (21). The outlet of the intermediate-pressure cylinder (22) is connected to the low-pressure cylinder. The inlet of (23) is connected, the outlet of the low-pressure cylinder (23) is connected to the inlet of the condenser (3), the outlet of the condenser (3) is connected to the inlet of the condensate pump (41), the outlet of the condensate pump (41) is connected to the heat absorption side inlet of the low-pressure heater (5), the heat absorption side outlet of the low-pressure heater (5) is connected to the inlet of the deaerator (6), the outlet of the deaerator (6) is connected to the heat absorption side inlet of the high-pressure heater (7) via the feed water pump (42), and the heat absorption side outlet of the high-pressure heater (7) is connected to the feed water inlet of the boiler (1).

7. The secondary air steam preheating coupled flue gas reheating system for coal-fired power generating units according to claim 6, characterized in that, The steam extraction port of the high-pressure cylinder (21) is connected to the heat release side of the high-pressure heater (7), the steam extraction port of the medium-pressure cylinder (22) is connected to the steam inlet of the deaerator (6), and the steam extraction port of the low-pressure cylinder (23) is connected to the heat release side of the low-pressure heater (5).

8. The secondary air steam preheating coupled flue gas reheating system for coal-fired power generating units according to claim 6, characterized in that, The high-pressure cylinder (21), medium-pressure cylinder (22), low-pressure cylinder (23) and generator are arranged coaxially.

9. A method for coupling secondary air steam preheating with flue gas reheating in a coal-fired power generation unit, characterized in that, The secondary air steam preheating coupled flue gas supplementary heating system for coal-fired power generating units according to claim 3 includes the following steps: The low-temperature air output from the air preheater (8) is heated by the steam heater (10) and enters the inlet of the SCR denitrification device. After mixing with the flue gas, it enters the SCR denitrification device. The high-temperature steam output from the boiler is de-cooled and enters the steam heater (10) through the bypass steam flow regulating valve (94) for heat exchange. The steam after heat exchange enters the low-temperature reheater or is discharged to the condenser (3).

10. A method for coupling secondary air steam preheating with flue gas reheating in a coal-fired power generating unit, characterized in that, The secondary air steam preheating coupled flue gas supplementary heating system for coal-fired power generating units according to claim 5 includes the following steps: The low-temperature air output from the air preheater (8) is heated by the steam heater (10) and enters the inlet of the SCR denitrification device. After mixing with the flue gas, it enters the SCR denitrification device. The reheat steam output from the boiler is de-heated and enters the steam heater (10) through the bypass steam flow regulating valve (94) for heat exchange. The steam after heat exchange enters the low-pressure cylinder (23) to do work or is discharged to the condenser (3).

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