System and method for increasing temperature of reheated steam through low-load stable combustion of boiler

Abstract

The invention provides a system and method for increasing the temperature of reheated steam through low-load stable combustion of a boiler, and relates to the technical field of thermal power generation. The system comprises a primary air supply device used for conveying hot primary air to a primary air duct; the secondary air supply device is used for conveying hot secondary air to the secondary air duct; the air extraction pipeline is used for extracting high-temperature flue gas exhausted by the economizer and conveying the high-temperature flue gas to the primary air duct and the secondary air duct; the separating device is used for separating particulate matters in the high-temperature flue gas, and the high-temperature flue gas after particulate matter separation becomes preliminarily purified flue gas; the primary air branch is used for conveying the primarily purified flue gas to a primary air duct so as to increase the air temperature of the hot primary air; and the secondary air branch is used for conveying the primarily purified flue gas to a secondary air duct so as to increase the air temperature of the hot secondary air. According to the system and method for increasing the temperature of the reheated steam through low-load stable combustion of the boiler, the temperature of the reheated steam of the boiler is remarkably increased, the operation economy of the boiler is improved, and the problem that in the prior art, the low-load combustion stability of the boiler is poor is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal power generation, and in particular to a system for raising the temperature of reheated steam by stably burning a boiler at low load and a method for raising the temperature of reheated steam by stably burning a boiler at low load. Background Art

[0002] For coal-fired boilers, the main problems in low-load operation are: poor boiler combustion stability, reduced reheat steam temperature, and environmental protection parameters that are easily exceeded. The main reason for the poor boiler combustion stability is the reduction in primary and secondary hot air temperatures and the reduction in coal powder concentration. Compared with the required primary and secondary hot air temperatures, the temperature is reduced by about 50°C to 70°C. As the amount of coal burned decreases, the furnace is in an oxygen-rich combustion state as a whole, and the staged combustion state cannot be achieved, causing the boiler flame center to decrease, the reheat steam temperature to drop, and NO x Concentration emission exceeds the standard and other issues. At present, the transformations for low-load stable combustion and environmental protection compliance of boilers mainly include burner upgrades, fan adaptability modifications, and boiler reheater heating surface modifications. Most of these modifications involve the modification of the boiler body, and the modification cost is also high. While improving the low-load stable combustion of the boiler and increasing the reheat temperature, the modification also has an adverse effect on the operating economy of the boiler under high and medium loads.

[0003] Therefore, there is an urgent need for a device that can solve at least one of the above problems. Summary of the invention

[0004] The purpose of the embodiments of the present invention is to provide a system and method for increasing the reheat steam temperature by stably burning a boiler at low load, so as to solve the problem of poor combustion stability of the boiler at low load in the prior art.

[0005] In order to achieve the above object, the present invention provides a system for raising the temperature of reheated steam by stable combustion of a boiler at low load, the system comprising: A primary air supply device is used to deliver hot primary air to the primary air duct; A secondary air supply device for delivering hot secondary air to the secondary air duct; The exhaust duct has an exhaust air inlet and a pair of exhaust air outlets. The exhaust air inlet of the exhaust duct is connected to the air outlet of the economizer of the coal-fired unit. The pair of exhaust air outlets of the exhaust duct are respectively connected to the primary air branch and the secondary air branch. The exhaust duct is used to extract the high-temperature flue gas discharged from the economizer and transport the high-temperature flue gas to the primary air duct and the secondary air duct. The separation device is arranged on the pipe section of the exhaust pipe and is used to separate the particulate matter in the high-temperature flue gas. The high-temperature flue gas after the particulate matter is separated becomes the preliminary purified flue gas; The primary air branch is connected between the exhaust air outlet of the exhaust duct and the air inlet of the primary air duct, and is used to transport the preliminarily purified flue gas to the primary air duct to increase the wind temperature of the hot primary air; The secondary air branch is connected between another exhaust air outlet of the exhaust duct and the air inlet of the secondary air duct, and is used to transport the preliminarily purified flue gas to the secondary air duct to increase the wind temperature of the hot secondary air.

[0006] Specifically, the primary air supply device includes a primary fan and a primary air preheater; The air outlet of the primary fan is connected to the air inlet of the primary air preheater, the air outlet of the primary air preheater is connected to the air inlet of the primary air duct, the primary fan is used to deliver primary air to the primary air preheater, the primary air preheater is used to heat the primary air to become hot primary air, and the hot primary air is discharged from the air outlet of the primary air preheater to the primary air duct.

[0007] Specifically, the secondary air supply device includes a secondary air fan and a secondary air preheater; The air outlet of the secondary fan is connected to the air inlet of the secondary air preheater, the air outlet of the secondary air preheater is connected to the air inlet of the secondary air duct, the secondary fan is used to deliver secondary air to the secondary air preheater, the secondary air preheater is used to heat the secondary air to become hot secondary air, and the hot secondary air is discharged from the air outlet of the secondary air preheater to the secondary air duct.

[0008] Specifically, the separation device comprises a first cyclone separator and a second cyclone separator which are sequentially arranged on the pipeline section of the air extraction pipeline; The first cyclone separator is used to initially separate particulate matter from the high-temperature flue gas to form primary purified flue gas; The second cyclone separator is used for secondary separation of particulate matter in the primary purified flue gas discharged from the first cyclone separator to form preliminary purified flue gas; wherein the particle size of the particulate matter separated by the first cyclone separator is larger than the particle size of the particulate matter separated by the second cyclone separator. Specifically, the system further includes: a recirculation baffle assembly including a recirculation baffle and a baffle driver; The recirculation damper is rotatably arranged at the air outlet of the economizer, and the rotation of the recirculation damper can adjust the temperature of the high-temperature flue gas discharged from the air outlet of the economizer; The baffle driver is used to drive the recirculation baffle to rotate.

[0009] Specifically, the system further comprises: a recirculation fan, which is arranged on the pipe section of the exhaust pipe and is used to pump the preliminarily purified flue gas discharged from the separation device to the primary air duct and / or the secondary air duct.

[0010] Specifically, the system further comprises: a recirculation fan inlet baffle and a recirculation fan outlet baffle; The recirculation fan inlet baffle is arranged on the exhaust duct, located on one side of the recirculation fan air inlet, and is used to adjust the temperature of the initially purified flue gas entering the recirculation fan; The recirculation fan outlet baffle is arranged on the exhaust duct, located at one side of the recirculation fan outlet, and is used to adjust the temperature of the preliminarily purified flue gas pumped by the recirculation fan.

[0011] Specifically, the system further comprises: a secondary air branch baffle, which is arranged on the secondary air branch and is used to adjust the temperature of the preliminarily purified flue gas flowing through the secondary air branch.

[0012] Specifically, the system further comprises: a booster fan inlet baffle, a booster fan and a booster fan outlet baffle arranged on the primary air branch; The booster fan is used to increase the pressure of the preliminarily purified flue gas flowing through the primary air branch and pump the preliminarily purified flue gas to the primary air duct; The booster fan inlet baffle is arranged on the primary air branch, on the side of the booster fan air inlet, and is used to adjust the temperature of the initially purified flue gas entering the booster fan; The booster fan outlet baffle is arranged on the primary air branch, located on the side of the booster fan outlet, and is used to adjust the temperature of the initially purified flue gas entering the primary air duct.

[0013] Another aspect of the present invention provides a method for raising the reheat steam temperature by stably burning a boiler at low load, which is based on any of the above-mentioned systems for raising the reheat steam temperature by stably burning a boiler at low load, and the method for raising the reheat steam temperature by stably burning a boiler at low load comprises: delivering hot primary air to the primary air duct through the primary air supply device, and delivering hot secondary air to the secondary air duct through the secondary air supply device; Extract high-temperature flue gas from the economizer outlet of the coal-fired unit and separate the high-temperature flue gas into preliminary purified flue gas through a separation device; The preliminarily purified flue gas is sent into the primary air duct to increase the temperature of the hot primary air, and / or the preliminarily purified flue gas is sent into the secondary air duct to increase the temperature of the hot secondary air.

[0014] The system for raising the temperature of reheated steam in a boiler with low load and stable combustion provided by the present invention comprises a primary air supply device which delivers hot primary air to the primary air duct, and a secondary air supply device which delivers hot secondary air to the secondary air duct. When the wind temperatures of the hot primary air and the hot secondary air cannot reach the required wind temperatures, the high-temperature flue gas discharged from the economizer outlet is extracted through an exhaust pipe, and the high-temperature flue gas is separated and treated by a separation device to separate particulate matter in the high-temperature flue gas. After being treated by the separation device, the high-temperature flue gas becomes preliminarily purified flue gas, which enters the primary air duct through a primary air branch to raise the wind temperature of the hot primary air finally formed in the primary air duct through the preliminarily purified flue gas. The preliminarily purified flue gas can also enter the secondary air duct through the secondary air branch, and the wind temperature of the hot secondary air finally formed is raised through the preliminarily purified flue gas. At the same time, affected by the reduced oxygen concentration in the secondary air, the staged combustion effect in the boiler is obvious, the flame center of the furnace is raised, and under the effect of the increased combustion flue gas volume, the temperature of the boiler reheated steam can be significantly raised, the economic efficiency of the boiler operation is improved, and the problem of poor low-load combustion stability of the boiler in the prior art is solved.

[0015] 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

[0016] 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 schematic diagram of the layout of a system for increasing the reheat steam temperature by stable combustion of a boiler at low load provided by an embodiment of the present invention.

[0017] Description of Reference Numerals 1-secondary fan; 2-secondary air preheater; 3-boiler; 4-dry slag machine; 5-economizer; 6-low-temperature superheater; 7-low-temperature superheater flue gas adjustment damper; 8-recirculation damper; 9-first cyclone separator; 10-first air lock; 11-second cyclone separator; 12-second air lock; 13-recirculation fan inlet damper; 14-recirculation fan; 15-recirculation fan outlet damper; 16-secondary air branch damper; 17-boost fan inlet damper; 18-boost fan; 19-boost fan outlet damper; 20-pulverizer; 21-primary fan; 22-primary air preheater; 30-primary air supply device; 31-primary air duct; 40-secondary air supply device; 41-secondary air duct; 50-exhaust duct; 60-primary air branch; 70-secondary air branch. DETAILED DESCRIPTION

[0018] 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.

[0019] Figure 1 This is a schematic diagram of the layout of the system for increasing the reheat steam temperature by stably burning the boiler at low load. Figure 1 As shown, the present invention provides a system for increasing the reheat steam temperature by stably burning a boiler at low load, comprising: The primary air supply device 30 is used to deliver hot primary air to the primary air duct 31; A secondary air supply device 40 for delivering hot secondary air to the secondary air duct 41; The exhaust duct 50 has an exhaust air inlet and a pair of exhaust air outlets. The exhaust air inlet is connected to the air outlet of the economizer 5 of the coal-fired unit. The pair of exhaust air outlets are respectively connected to the primary air branch 60 and the secondary air branch 70. The exhaust duct 50 is used to extract the high-temperature flue gas discharged from the economizer 5 and transport the high-temperature flue gas to the primary air duct and the secondary air duct. The separation device is arranged on the pipe section of the exhaust pipe 50 and is used to separate particulate matter from the high-temperature flue gas. The separated high-temperature flue gas becomes the preliminary purified flue gas. The primary air branch 60 is connected between the exhaust air outlet of the exhaust duct 50 and the air inlet of the primary air duct, and is used to transport the preliminarily purified flue gas to the primary air duct to increase the wind temperature of the hot primary air; The secondary air branch 70 is connected between another exhaust air outlet of the exhaust duct 50 and the air inlet of the secondary air duct, and is used to transport the preliminarily purified flue gas to the secondary air duct to increase the air temperature of the hot secondary air.

[0020] The system for increasing the reheat steam temperature by stably burning a boiler at low load provided by the present invention is as follows: Figure 1As shown, the primary air supply device 30 delivers hot primary air to the primary air duct 31, and the hot primary air in the primary air duct 31 finally enters the coal mill 20. The secondary air supply device 40 delivers hot secondary air to the secondary air duct 41, and the hot secondary air finally enters the boiler 3. When the wind temperatures of the hot primary air and the hot secondary air cannot meet the high-efficiency operation of the unit, an exhaust duct 50 is provided to extract the high-temperature flue gas discharged from the air outlet of the economizer 5 of the coal-fired unit, and the high-temperature flue gas is separated and processed by a separation device to separate particulate matter in the high-temperature flue gas. The high-temperature flue gas separated by the separation device becomes preliminary purified flue gas, which is sent to the primary air duct 31 and mixed with the hot primary air in the primary air duct 31 to increase the overall temperature of the flue gas in the primary air duct 31, thereby increasing the temperature of the hot primary air in the primary air duct 31. The primary air is sent into the coal mill 20, and the preliminarily purified flue gas can also be sent into the hot secondary air duct 41. The preliminarily purified flue gas and the hot secondary air are mixed in the hot secondary air duct 41 to increase the temperature of the hot secondary air, which can increase the temperature of the hot secondary air from 270°C to 340°C, and the temperature is increased by about 60°C-70°C. The rigidity of the hot secondary air is also improved. The high-temperature flue gas of the economizer 5 is separated and sent into the primary air duct and the secondary air duct, which not only increases the temperature of the hot primary air and the temperature of the hot secondary air, but also, due to the reduction in oxygen concentration in the secondary air, the staged combustion effect in the boiler 3 is obvious, and the center of the furnace flame rises. With the increase in the amount of combustion flue gas, the temperature of the boiler reheat steam can be significantly increased, thereby improving the economy of the boiler operation and solving the problem of poor low-load combustion stability of the prior art boiler.

[0021] In one embodiment, Figure 1 As shown, the primary air supply device 30 includes a primary fan 21 and a primary air preheater 22; The air outlet of the primary fan 21 is connected to the air inlet of the primary air preheater 22, and the air outlet of the primary air preheater 22 is connected to the air inlet of the primary air duct 31. The primary fan 21 is used to convey primary air to the primary air preheater 22, and the primary air preheater 22 is used to heat the primary air to become hot primary air. The hot primary air is discharged from the air outlet of the primary air preheater 22 to the primary air duct 31.

[0022] The secondary air supply device 40 includes a secondary air fan 1 and a secondary air preheater 2; The air outlet of the secondary fan 1 is connected to the air inlet of the secondary air preheater 2, and the air outlet of the secondary air preheater 2 is connected to the air inlet of the secondary air duct. The secondary fan 12 is used to transport secondary air to the secondary air preheater 2. The secondary air preheater 2 is used to heat the secondary air to become hot secondary air. The hot secondary air is discharged from the air outlet of the secondary air preheater 2 to the secondary air duct 31.

[0023] The primary fan 21 of the primary air supply device 30 delivers primary air to the primary air preheater 22. The primary air enters the primary air preheater 22 and is heated to become hot primary air. The hot primary air is discharged from the primary air preheater 22 and enters the primary air duct 31 and the coal mill 20. The secondary fan 1 of the secondary air supply device 40 delivers secondary air to the secondary air preheater 2. The secondary air is heated in the secondary air preheater 2 and becomes hot secondary air. The hot secondary air enters the hot secondary air duct 41 and then enters the boiler 3 for combustion.

[0024] In order to send the high-temperature flue gas into the coal mill 20 or the boiler 3, the separation device includes a first cyclone separator 9 and a second cyclone separator 11 which are sequentially arranged on the pipe section of the exhaust pipe 50; The first cyclone separator 9 is used to initially separate particulate matter in the high-temperature flue gas into primary purified flue gas; The second cyclone separator 11 is used for secondary separation of particulate matter in the primary purified flue gas discharged from the first cyclone separator 9 to form preliminary purified flue gas; wherein the particle size of the particulate matter separated by the first cyclone separator 9 is larger than the particle size of the particulate matter separated by the second cyclone separator 11. The particulate matter in the high-temperature flue gas is separated by the first cyclone separator 9 and the second cyclone separator 11 to purify the high-temperature flue gas. The high-temperature flue gas treated by the first cyclone separator 9 and the second cyclone separator 11 becomes preliminarily purified flue gas.

[0025] In order to adjust the temperature of the high-temperature flue gas at the outlet of the economizer 5, the system further comprises: a recirculation damper assembly, comprising a recirculation damper 8 and a damper driver; The recirculation damper 8 is rotatably arranged at the air outlet of the economizer 5. The rotation of the recirculation damper 8 can adjust the temperature of the high-temperature flue gas discharged from the air outlet of the economizer 5; The baffle driver is used to drive the recirculation baffle 8 to rotate.

[0026] Specifically, the system further comprises: a recirculation fan 14, which is arranged on the pipe section of the exhaust pipe 50 and is used to pump the preliminarily purified flue gas discharged from the separation device to the primary air duct and / or the secondary air duct.

[0027] Specifically, the system further comprises: a recirculation fan inlet baffle 13 and a recirculation fan outlet baffle 15; The recirculation fan inlet baffle 13 is arranged on the exhaust duct 50, located at the air inlet side of the recirculation fan 14, and is used to adjust the temperature of the preliminarily purified flue gas entering the recirculation fan 14; The recirculation fan outlet baffle 15 is arranged on the exhaust duct 50 , located at one side of the air outlet of the recirculation fan 14 , and is used to adjust the temperature of the preliminarily purified flue gas pumped by the recirculation fan 14 .

[0028] Specifically, the system further includes: a secondary air branch baffle 16 , which is disposed on the secondary air branch 70 and is used to adjust the temperature of the preliminarily purified flue gas flowing through the secondary air branch 70 .

[0029] Specifically, the system further includes: a booster fan inlet baffle 17, a booster fan 18 and a booster fan outlet baffle 19 arranged on the primary air branch 60; The booster fan 18 is used to increase the pressure of the preliminarily purified flue gas flowing through the primary air branch 60 and pump the preliminarily purified flue gas to the primary air duct; The booster fan inlet baffle 17 is arranged on the primary air branch 60, located on the air inlet side of the booster fan 18, and is used to adjust the temperature of the initially purified flue gas entering the booster fan 18; The booster fan outlet baffle 19 is arranged on the primary air branch 60, located on the air outlet side of the booster fan 18, and is used to adjust the temperature of the preliminarily purified flue gas entering the primary air duct.

[0030] The high-temperature flue gas is discharged from the air outlet of the economizer 5 and enters the exhaust duct 50. The temperature of the discharged high-temperature flue gas is adjusted by the recirculation baffle 8 arranged at the air outlet of the economizer 5. The high-temperature flue gas flows in the exhaust duct 50 and enters the first cyclone separator 9 and the second cyclone separator 11 in sequence. After the high-temperature flue gas is separated by the first cyclone separator 9, the particles are separated and deposited on the bottom plate of the first cyclone separator 9. A first air lock 10 is arranged at the bottom of the first cyclone separator 9. The first air lock 10 prevents the particles deposited in the first cyclone separator 9 from flowing out at will, and also avoids The gas enters and exits the first cyclone separator 9 through the first air lock 10, and the first-stage purified flue gas enters the second cyclone separator 11 to continue to separate the particulate matter in the first-stage purified flue gas. A second air lock 12 is arranged at the bottom of the second cyclone separator 11. The second air lock 12 prevents the particulate matter deposited in the second cyclone separator 11 from flowing out at will. The high-temperature flue gas is treated through two stages of separation, and the crystallinity of the preliminarily purified flue gas is improved. A purge device can also be arranged on the air inlet side of the recycling baffle 8 to blow away the accumulated dust on the recycling baffle 8 through the purge device. The baffle driver is a compressed air driver.

[0031] After the preliminary purified flue gas is discharged from the air outlet of the second cyclone separator 11, it is sent into the primary air duct and the secondary air duct through the recirculation fan 14. The recirculation fan 14 is a high-temperature variable frequency centrifugal fan. The fan variable frequency output is adjusted in real time according to the change of wind pressure in the secondary air duct. The temperature of the preliminary purified flue gas entering the recirculation fan 14 is adjusted by the recirculation fan inlet baffle 13 arranged on the air inlet side of the recirculation fan 14. The recirculation fan outlet baffle 15 arranged on the air outlet side adjusts the wind temperature sent into the primary air duct 31 or the secondary air duct 41. The preliminarily purified flue gas flows through the primary air branch 60 and then enters the primary air duct 31. The primary air branch 60 is provided with a booster fan inlet baffle 17, a booster fan 18 and a booster fan outlet baffle 19. The booster fan 18 adjusts the pressure of the preliminarily purified flue gas entering the primary air duct 31. The booster fan inlet baffle 17 and the booster fan outlet baffle 19 respectively adjust the temperature of the preliminarily purified flue gas entering the booster fan 18 and the preliminarily purified flue gas and the temperature of the preliminarily purified flue gas entering the primary air duct.

[0032] Another aspect of the present invention provides a method for raising the reheat steam temperature by low-load stable combustion of a boiler, which is performed based on any of the above-mentioned systems for raising the reheat steam temperature by low-load stable combustion of a boiler, and the method for raising the reheat steam temperature by low-load stable combustion of a boiler comprises: delivering hot primary air to the primary air duct through the primary air supply device, and delivering hot secondary air to the secondary air duct through the secondary air supply device; Extract high-temperature flue gas from the economizer outlet of the coal-fired unit and separate the high-temperature flue gas into preliminary purified flue gas through a separation device; The preliminarily purified flue gas is sent into the primary air duct to increase the temperature of the hot primary air, and / or the preliminarily purified flue gas is sent into the secondary air duct to increase the temperature of the hot secondary air.

[0033] The system for raising the temperature of reheated steam in a boiler with low load and stable combustion provided by the present invention comprises a primary air supply device which delivers hot primary air to the primary air duct, and a secondary air supply device which delivers hot secondary air to the secondary air duct. When the wind temperatures of the hot primary air and the hot secondary air cannot reach the required wind temperatures, the high-temperature flue gas discharged from the economizer outlet is extracted through an exhaust pipe, and the high-temperature flue gas is separated and treated by a separation device to separate particulate matter in the high-temperature flue gas. After being treated by the separation device, the high-temperature flue gas becomes preliminarily purified flue gas, which enters the primary air duct through a primary air branch to raise the wind temperature of the hot primary air finally formed in the primary air duct through the preliminarily purified flue gas. The preliminarily purified flue gas can also enter the secondary air duct through the secondary air branch, and the wind temperature of the hot secondary air finally formed is raised through the preliminarily purified flue gas. At the same time, affected by the reduced oxygen concentration in the secondary air, the staged combustion effect in the boiler is obvious, the flame center of the furnace is raised, and under the effect of the increased combustion flue gas volume, the temperature of the boiler reheated steam can be significantly raised, the economic efficiency of the boiler operation is improved, and the problem of poor low-load combustion stability of the prior art boiler is solved.

[0034] The optional implementation modes of the embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above implementation modes. Within the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical scheme of the embodiments of the present invention, and these simple modifications all belong to the protection scope of the embodiments of the present invention.

[0035] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe various possible combinations.

[0036] In addition, various implementation modes of the embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the embodiments of the present invention, they should also be regarded as the contents disclosed by the embodiments of the present invention.

Claims

1. A system for increasing the temperature of reheated steam by stably burning a boiler at low load, characterized in that: The system for increasing the reheat steam temperature by stable combustion of the boiler at low load comprises: A primary air supply device (30) for delivering hot primary air to the primary air duct (31); A secondary air supply device (40) for supplying hot secondary air to the secondary air duct (41); An exhaust duct (50) has an exhaust air inlet and a pair of exhaust air outlets, the exhaust air inlet of the exhaust duct (50) is connected to the air outlet of the economizer (5) of the coal-fired unit, the pair of exhaust air outlets of the exhaust duct (50) are respectively connected to the primary air branch (60) and the secondary air branch (70), and the exhaust duct (50) is used to extract high-temperature flue gas discharged from the economizer (5) and transport the high-temperature flue gas to the primary air duct and the secondary air duct; A separation device is arranged on a pipe section of the exhaust pipe (50) and is used to separate particulate matter from the high-temperature flue gas, and the high-temperature flue gas after the particulate matter is separated becomes the preliminarily purified flue gas; The primary air branch (60) is connected between the exhaust air outlet of the exhaust pipe (50) and the air inlet of the primary air duct, and is used to transport the preliminarily purified flue gas to the primary air duct to increase the air temperature of the hot primary air; The secondary air branch (70) is connected between another exhaust air outlet of the exhaust duct (50) and the air inlet of the secondary air duct, and is used to transport the preliminarily purified flue gas to the secondary air duct to increase the air temperature of the hot secondary air.

2. The system for increasing the reheat steam temperature by low-load stable combustion of a boiler according to claim 1 is characterized in that: The primary air supply device (30) comprises a primary fan (21) and a primary air preheater (22); The air outlet of the primary fan (21) is connected to the air inlet of the primary air preheater (22), and the air outlet of the primary air preheater (22) is connected to the air inlet of the primary air duct (31). The primary fan (21) is used to transport primary air to the primary air preheater (22), and the primary air preheater (22) is used to heat the primary air to become hot primary air. The hot primary air is discharged from the air outlet of the primary air preheater (22) to the primary air duct (31).

3. The system for increasing the reheat steam temperature by low-load stable combustion of a boiler according to claim 2 is characterized in that: The secondary air supply device (40) comprises a secondary air fan (1) and a secondary air preheater (2); The air outlet of the secondary fan (1) is connected to the air inlet of the secondary air preheater (2), and the air outlet of the secondary air preheater (2) is connected to the air inlet of the secondary air duct (41). The secondary fan (1) is used to convey secondary air to the secondary air preheater (2), and the secondary air preheater (2) is used to heat the secondary air to form hot secondary air. The hot secondary air is discharged from the air outlet of the secondary air preheater (2) to the secondary air duct.

4. The system for increasing the reheat steam temperature by low-load stable combustion of a boiler according to claim 1 is characterized in that: The separation device comprises a first cyclone separator (9) and a second cyclone separator (11) which are sequentially arranged on a pipe section of an air extraction pipe (50); The first cyclone separator (9) is used to initially separate particulate matter from the high-temperature flue gas to produce primary purified flue gas; The second cyclone separator (11) is used for secondary separation of particulate matter in the primary purified flue gas discharged from the first cyclone separator (9) to form preliminary purified flue gas; wherein the particle size of the particulate matter separated by the first cyclone separator (9) is larger than the particle size of the particulate matter separated by the second cyclone separator (11).

5. The system for increasing the reheat steam temperature by low-load stable combustion of a boiler according to claim 1, characterized in that: The system further comprises: a recirculation baffle assembly comprising a recirculation baffle (8) and a baffle driver; The recirculation damper (8) is rotatably arranged at the air outlet of the economizer (5), and the rotation of the recirculation damper (8) can adjust the temperature of the high-temperature flue gas discharged from the air outlet of the economizer (5); The baffle driver is used to drive the recirculation baffle (8) to rotate.

6. The system for increasing the reheat steam temperature by low-load stable combustion of a boiler according to claim 1, characterized in that: The system further comprises: a recirculation fan (14), arranged on a pipe section of the exhaust pipe (50), and used for pumping the preliminarily purified flue gas discharged from the separation device to the primary air duct and / or the secondary air duct.

7. The system for increasing the reheat steam temperature by low-load stable combustion of a boiler according to claim 6, characterized in that: The system further comprises: a recirculation fan inlet baffle (13) and a recirculation fan outlet baffle (15); The recirculation fan inlet baffle (13) is arranged on the exhaust duct (50) and is located on one side of the air inlet of the recirculation fan (14), and is used to adjust the temperature of the preliminarily purified flue gas entering the recirculation fan (14); The recirculation fan outlet baffle (15) is arranged on the exhaust duct (50) and is located on one side of the air outlet of the recirculation fan (14), and is used to adjust the temperature of the preliminarily purified flue gas pumped by the recirculation fan (14).

8. The system for increasing the reheat steam temperature by low-load stable combustion of a boiler according to claim 1, characterized in that: The system further comprises: a secondary air branch baffle (16) arranged on the secondary air branch (70) and used for adjusting the temperature of the preliminarily purified flue gas flowing through the secondary air branch (70).

9. The system for increasing the reheat steam temperature by low-load stable combustion of a boiler according to claim 1, characterized in that: The system further comprises: a booster fan inlet baffle (17), a booster fan (18) and a booster fan outlet baffle (19) arranged on the primary air branch (60); The booster fan (18) is used to increase the pressure of the preliminarily purified flue gas flowing through the primary air branch (60) and pump the preliminarily purified flue gas to the primary air duct; The booster fan inlet baffle (17) is arranged on the primary air branch (60) and is located on the air inlet side of the booster fan (18), and is used to adjust the temperature of the initially purified flue gas entering the booster fan (18); The booster fan outlet baffle (19) is arranged on the primary air branch (60) and is located on one side of the air outlet of the booster fan (18), and is used to adjust the temperature of the preliminarily purified flue gas entering the primary air duct.

10. A method for increasing the reheat steam temperature by stable combustion of a boiler at low load, based on the system for increasing the reheat steam temperature by stable combustion of a boiler at low load according to any one of claims 1 to 9, characterized in that: The method for increasing the reheat steam temperature by stable combustion of a boiler at low load comprises: delivering hot primary air to the primary air duct through the primary air supply device, and delivering hot secondary air to the secondary air duct through the secondary air supply device; Extract high-temperature flue gas from the economizer outlet of the coal-fired unit and separate the high-temperature flue gas into preliminary purified flue gas through a separation device; The preliminarily purified flue gas is sent into the primary air duct to increase the temperature of the hot primary air, and / or the preliminarily purified flue gas is sent into the secondary air duct to increase the temperature of the hot secondary air.

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