System and method for upgrading lignite by using flue gas of coal-fired power plant

Abstract

The invention provides a system and a method for upgrading lignite by using flue gas of a coal-fired power plant. The system for upgrading the lignite by using the flue gas of the coal-fired power plant comprises a lignite upgrading device which is provided with a wet coal inlet, a dry coal outlet, a first flue gas inlet, a first flue gas outlet and a first water vapor outlet; a flue gas outlet of the pulverized coal boiler is connected with the flue, the flue is provided with a first flue gas connector, and the first flue gas connector is connected with a first flue gas inlet of the lignite upgrading device through a first pipeline; an inlet of the separator is connected with a smoke outlet of the lignite upgrading device, a second smoke outlet of the separator is connected with an inlet of the booster fan, and an outlet of the booster fan is connected with a smoke exhaust connector of the flue through a second pipeline; provided is a dry lignite collecting device. Therefore, according to the system for upgrading the lignite by using the flue gas of the coal-fired power plant, the lignite can be conveniently upgraded, the energy waste is reduced, and the safety is high.

Description

Technical Field

[0001] This invention relates to the field of lignite upgrading technology, specifically to a system and method for upgrading lignite using flue gas from coal-fired power plants. Background Technology

[0002] Lignite, as the least coalified type of coal, suffers from high moisture content (30%-50%), low calorific value (11-17 MJ / kg), and poor thermal stability. Direct utilization of lignite faces bottlenecks such as high transportation and storage risks, low combustion efficiency, and poor environmental performance. Upgrading technologies, through physical drying and chemical pyrolysis, can significantly reduce moisture content to 9%-15%, increase calorific value by 51.6%, and reduce greenhouse gas emissions by 15%. Utilizing waste heat from coal-fired power plant flue gas for lignite drying has significant advantages: firstly, it achieves cascaded energy utilization without additional heating; secondly, the improved combustion efficiency of upgraded lignite reduces the load on power plant environmental protection equipment, combining economic benefits with low-carbon emissions. However, systems utilizing flue gas from coal-fired power plants for lignite upgrading are generally complex, pose safety risks, and generate secondary pollution such as wastewater and waste gas. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a system and method for upgrading lignite using flue gas from coal-fired power plants.

[0004] The present invention includes a lignite upgrading system utilizing flue gas from a coal-fired power plant, comprising: A lignite upgrading device is used to reduce the moisture content of lignite. The lignite upgrading device has a wet coal inlet, a dry coal outlet, a first flue gas inlet, a first flue gas outlet, and a first water vapor outlet. A pulverized coal boiler, wherein the flue gas outlet of the pulverized coal boiler is connected to a flue, and the flue is provided with a first flue gas interface, the first flue gas interface being connected to the first flue gas inlet of the lignite upgrading device through a first pipeline, so that flue gas can be introduced into the lignite upgrading device from the first pipeline. The separator has its inlet connected to the flue gas outlet of the lignite upgrading device, its second flue gas outlet connected to the inlet of a booster fan, and the outlet of the booster fan connected to the flue gas exhaust port of the flue through a second pipeline. The separator's second solid outlet is connected to the second pipeline so that the flue gas in the second pipeline can be introduced into the flue. A dry lignite collection device, wherein the inlet of the dry lignite collection device is connected to the dry coal outlet.

[0005] Therefore, the lignite upgrading system utilizing flue gas from coal-fired power plants according to embodiments of the present invention facilitates lignite upgrading, reduces energy waste, and is highly safe.

[0006] In some embodiments, the flue is provided with a second flue gas inlet, which is connected to the flue gas inlet of the dry lignite collection device via a third pipeline, so that flue gas can be introduced into the dry lignite collection device from the third pipeline.

[0007] In some embodiments, the first flue gas interface is located between the denitrification device and the air preheater within the flue in the extension direction of the flue; The second flue gas inlet and the flue gas exhaust inlet are located downstream of the air preheater in the extension direction of the flue. The temperature of the flue gas discharged from the second flue gas inlet is lower than the temperature of the flue gas discharged from the first flue gas inlet. The second flue gas inlet is located between the air preheater and the flue gas exhaust inlet in the extension direction of the flue. The first pipeline is equipped with a flue gas shut-off valve and a first flue gas regulating valve group, which is used to regulate the flue gas flow rate in the first pipeline. The third pipeline is equipped with a second flue gas regulating valve group, which is used to regulate the flue gas flow rate in the third pipeline.

[0008] In some embodiments, the temperature of the flue gas discharged from the first flue gas interface is greater than or equal to 280°C and less than or equal to 320°C. The temperature of the flue gas discharged from the second flue gas interface is greater than or equal to 110°C and less than or equal to 130°C; A second fan is installed on the third pipeline.

[0009] In some embodiments, the dry coal outlet of the lignite upgrading device is connected to the inlet of the dry lignite collecting device via a screw conveyor, wherein the screw conveyor is a closed conveyor.

[0010] In some embodiments, the first steam outlet is connected to the second pipeline via a fourth pipeline.

[0011] In some embodiments, the lignite upgrading device is provided with a hollow screw conveyor, which includes a spirally extending hollow screw conveying section. The hollow screw conveying section rotates to move the lignite on it toward the adjacent dry coal outlet. The wet coal inlet and the dry coal outlet are located on opposite sides of the lignite upgrading device, and the first flue gas inlet is located on the side of the lignite upgrading device adjacent to the wet coal inlet.

[0012] The lignite upgrading system utilizing flue gas from a coal-fired power plant, as described in this embodiment of the invention, further includes: Storage bins for storing lignite; A crushing device for crushing lignite; A conveying device for conveying lignite; The storage bin, the crushing device, the conveying device, and the wet coal inlet of the lignite upgrading device are connected in sequence.

[0013] This invention also proposes a method for upgrading lignite using flue gas from coal-fired power plants, comprising the following steps: S1. Pass the flue gas from the first flue gas inlet of the flue into the lignite upgrading device; S2. Turn on the booster fan so that the flue gas enters the lignite upgrading device and then passes into the separator; S3. Start the lignite upgrading device so that the lignite in the lignite upgrading device exchanges heat with the flue gas introduced into the lignite upgrading device during the process of moving from the wet coal inlet to the dry coal outlet; S4. The dried lignite discharged from the dry coal outlet of the lignite upgrading device is fed into the dried lignite collecting device for collection.

[0014] In some embodiments, in step S1, the flue gas flow rate in the first pipeline is adjusted, and the temperature of the flue gas discharged from the first flue gas interface is greater than or equal to 280°C and less than or equal to 320°C. In step S3, after the lignite upgrading device is preheated to above 250°C by flue gas, lignite is conveyed to the lignite upgrading device from the wet coal inlet and the lignite upgrading device is started. The temperature of the flue gas discharged from the first flue gas outlet of the lignite upgrading device is greater than or equal to 100°C and less than or equal to 200°C. In step S4, low-temperature inert flue gas with a temperature greater than or equal to 110°C and less than or equal to 130°C is introduced into the dry lignite collection device to prevent the dry lignite from spontaneously combusting upon contact with air within the device. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a lignite upgrading system utilizing flue gas from a coal-fired power plant, according to an embodiment of the present invention.

[0016] Reference numerals: 1. Storage bin; 2. Crushing device; 3. Conveying device; 4. Lignite upgrading device; 41. Wet coal inlet; 42. Dry coal outlet; 43. First flue gas inlet; 44. First flue gas outlet; 45. First steam outlet; 5. Separator; 51. Second flue gas outlet; 52. Second solids outlet; 6. Booster fan; 7. Fly ash inlet; 8. Flue gas exhaust inlet; 9. Steam inlet; 10. Check valve; 11. Pulverized coal boiler; 12. Denitrification device; 13. First flue gas inlet; 14. Flue gas shut-off valve; 15. First flue gas regulating valve group; 16. Screw conveyor; 17. Dry lignite collection device; 18. Second flue gas inlet; 19. Second flue gas regulating valve group; 20. Second fan; 101. First pipeline; 102. Second pipeline; 103. Third pipeline; 104. Fourth pipeline. Detailed Implementation

[0017] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0018] The following describes an embodiment of the present invention using flue gas from a coal-fired power plant to upgrade lignite, with reference to the accompanying drawings. For example... Figure 1 As shown, the lignite upgrading system utilizing flue gas from a coal-fired power plant according to an embodiment of the present invention includes a storage bin 1, a crushing device 2, a conveying device 3, a lignite upgrading device 4, a pulverized coal boiler 11, a separator 5, and a dry lignite collection device 17.

[0019] Storage bin 1 is used to store lignite. Crushing device 2 is used to crush lignite; conveying device 3 is used to convey lignite. Lignite upgrading device 4 is used to reduce the moisture content of lignite, and lignite upgrading device 4 has a wet coal inlet 41, a dry coal outlet 42, a first flue gas inlet 43, a first flue gas outlet 44, and a first steam outlet 45.

[0020] Storage bin 1, crushing device 2, conveying device 3, and the wet coal inlet 41 of lignite upgrading device 4 are connected in sequence. This allows the lignite in storage bin 1 to be crushed by crushing device 2 and then conveyed by conveying device 3 to the wet coal inlet 41 of lignite upgrading device 4. For example, lignite with a moisture content of 30%-60% is stored in lignite storage bin 1 after entering the plant.

[0021] The lignite upgrading device 4 is equipped with a hollow screw conveyor, which includes a spirally extending hollow screw conveying section. The hollow screw conveying section rotates to move the lignite on it towards the adjacent dry coal outlet 42. Specifically, the wet coal inlet 41 and the dry coal outlet 42 are located on opposite sides of the lignite upgrading device 4, and the first flue gas inlet 43 is located on the side of the lignite upgrading device 4 adjacent to the wet coal inlet 41. Drying flue gas enters the lignite upgrading device 4 through the first flue gas inlet 43 and exits through the first flue gas outlet 44. Moist lignite enters the lignite upgrading device 4 through the wet coal inlet 41 and is dried by the flue gas under the action of the hollow screw conveyor before exiting through the dry coal outlet 42. Water vapor from the lignite upgrading device 4 exits through the first water vapor outlet 45.

[0022] For example, in the lignite upgrading unit 4, the flue gas and material exchange heat indirectly to prevent impurities in the flue gas from affecting the quality of the finished lignite. A hollow screw conveyor is installed inside the lignite upgrading unit 4 for the flue gas to pass through. The rotation of the hollow screw conveyor drives the lignite on the outside towards the outlet. As the lignite moves towards the outlet, it releases water vapor under the drying effect of the flue gas. By controlling the rotation speed of the internal hollow screw, the residence time of the lignite in the unit is adjusted to ensure that the moisture content of the dried lignite at the outlet meets the requirements.

[0023] like Figure 1 As shown, the flue gas outlet of the pulverized coal boiler 11 is connected to the flue, and the flue is provided with a first flue gas interface 13. The first flue gas interface 13 is connected to the first flue gas inlet 43 of the lignite upgrading device 4 through the first pipeline 101, so that the flue gas can be introduced into the lignite upgrading device 4 from the first pipeline 101, thereby using the flue gas discharged from the flue to dry the lignite in the lignite upgrading device 4.

[0024] In some embodiments, the first flue gas inlet 13 is located between the denitrification device and the air preheater within the flue in the extending direction of the flue. Specifically, the flue gas temperature discharged from the first flue gas inlet 13 is greater than or equal to 280°C and less than or equal to 320°C. For example, the flue gas temperature discharged from the first flue gas inlet 13 is 300°C.

[0025] The first pipeline 101 is equipped with a flue gas shut-off valve 14 and a first flue gas regulating valve group 15, which is used to regulate the flue gas flow rate in the first pipeline 101. The flue gas shut-off valve 14 and the first flue gas regulating valve group 15 together satisfy the functions of flue gas connection, blockage and regulation, so that after the flue gas shut-off valve 14 is opened, the first flue gas regulating valve group 15 can regulate the flue gas flow rate entering the lignite upgrading device 4.

[0026] like Figure 1As shown, the inlet of separator 5 is connected to the flue gas outlet of lignite upgrading device 4, and the second flue gas outlet 51 of separator 5 is connected to the inlet of booster fan 6. The outlet of booster fan 6 is connected to the flue gas exhaust port 8 of the flue through the second pipeline 102. This allows booster fan 6 to adsorb the flue gas discharged from separator 5 and provide negative pressure, facilitating the entry of flue gas from lignite upgrading device 4 into separator 5. For example, separator 5 is a cyclone separator. The purpose of separator 5 is to perform gas-solid separation on the dust-laden flue gas before it enters booster fan 6. Clean gas enters booster fan 6, while solid particles are sent to the outlet of booster fan 6, reducing wear on the impeller of booster fan 6.

[0027] The second solid outlet 52 of separator 5 is connected to the second pipeline 102 so that the flue gas in the second pipeline 102 can enter the flue. The first steam outlet 45 is connected to the second pipeline 102 through the fourth pipeline 104. Specifically, the second pipeline 102 is provided with a fly ash inlet 7 and a steam inlet 9. The second solid outlet 52 of separator 5 is connected to the fly ash inlet 7 so that the fly ash separated by separator 5 enters the second pipeline 102. The first steam outlet 45 is connected to the steam inlet 9 of the second pipeline 102 through the fourth pipeline 104 so that the steam from lignite upgrading device 4 can enter the second pipeline 102 and enter the flue gas exhaust inlet 8 of the flue under the pressure of booster fan 6.

[0028] In some embodiments, a check valve 10 is provided on the fourth pipeline 104 to prevent water vapor from flowing back.

[0029] like Figure 1 As shown, the inlet of the dry lignite collecting device 17 is connected to the dry coal outlet 42. Specifically, an inert atmosphere is maintained inside the dry lignite collecting device 17 to prevent spontaneous combustion of the lignite. The dry coal outlet 42 of the lignite upgrading device 4 is connected to the inlet of the dry lignite collecting device 17 via a screw conveyor 16. The screw conveyor 16 is a closed conveyor and is heat-resistant. Therefore, it is convenient to transport the dry lignite into the dry lignite collecting device 17 in a completely closed manner via the screw conveyor 16.

[0030] In some embodiments, a second flue gas inlet 18 is provided on the flue, which is connected to the flue gas inlet of the dry lignite collection device 17 via a third pipe 103, so that inert flue gas can be introduced into the dry lignite collection device 17 from the third pipe 103, thereby preventing the dry lignite in the dry lignite collection device 17 from burning. Specifically, a second fan 20 is provided on the third pipe 103 to allow flue gas to enter the dry lignite collection device 17. A second flue gas regulating valve assembly 19 is provided on the third pipe 103 to regulate the flue gas flow rate in the third pipe 103. For example, the second flue gas regulating valve assembly 19 includes a manual shut-off valve, an electric shut-off valve, and an electric regulating valve, etc., to satisfy the functions of flue gas connection, blockage, and regulation.

[0031] In some embodiments, the flue gas temperature discharged from the second flue gas interface 18 is greater than or equal to 110°C and less than or equal to 130°C, thereby ensuring that the temperature of the inert flue gas entering the dry lignite collection device 17 is greater than or equal to 110°C and less than or equal to 130°C. For example, the flue gas temperature discharged from the second flue gas interface 18 is 120°C.

[0032] In some embodiments, the second flue gas inlet 18 and the flue gas exhaust inlet 8 are located downstream of the air preheater in the extension direction of the flue. The temperature of the flue gas discharged from the second flue gas inlet 18 is lower than the temperature of the flue gas discharged from the first flue gas inlet 13. The second flue gas inlet 18 is located between the air preheater and the flue gas exhaust inlet 8 in the extension direction of the flue. That is, the flue gas exhaust inlet 8 is located downstream of the second flue gas inlet 18 in the extension direction of the flue, thereby preventing the flue gas discharged from the second flue gas inlet 18 from containing water vapor. The flue gas exhaust after heat exchange is fully transported to the downstream flue of the air preheater by the booster fan 6, and then successively treated by environmental protection facilities such as dust collectors and desulfurization towers before being discharged in compliance with standards. The water vapor generated by lignite dehydration is combined with the flue gas exhaust pipe through the check valve 10 and uniformly sent into the downstream flue of the air preheater to ensure that the boiler efficiency is not affected.

[0033] This invention also proposes a method for upgrading lignite using flue gas from a coal-fired power plant, based on an embodiment of the invention. The method includes the following steps: S1. The flue gas from the first flue gas inlet 13 of the flue is introduced into the lignite upgrading device 4. In step S1, the flue gas flow rate in the first pipeline 101 is adjusted, and the temperature of the flue gas discharged from the first flue gas inlet 13 is greater than or equal to 280℃ and less than or equal to 320℃. Specifically, after the flue gas shut-off valve 14 is opened, the first flue gas regulating valve group 15 regulates the flue gas flow rate introduced into the lignite upgrading device 4 so that the flue gas preheats the lignite upgrading device 4.

[0034] S2. Turn on the booster fan 6 so that the flue gas enters the lignite upgrading device 4 and then passes into the separator 5. Specifically, turn on the booster fan 6 and adjust its frequency to generate sufficient air pressure to overcome the system resistance and draw the 280-320°C flue gas from the first flue gas interface 13 into the lignite upgrading device 44.

[0035] S3. Start the lignite upgrading device 4 so that the lignite in the lignite upgrading device 4 exchanges heat with the flue gas introduced into the lignite upgrading device 4 during the process of moving from the wet coal inlet 41 to the dry coal outlet 42. Specifically, in step S3, after the lignite upgrading device 4 is preheated to above 250°C by the flue gas, lignite is conveyed to the lignite upgrading device 4 from the wet coal inlet 41 and the lignite upgrading device 4 is started. The temperature of the flue gas discharged from the first flue gas outlet 44 of the lignite upgrading device 4 is greater than or equal to 100°C and less than or equal to 200°C.

[0036] Specifically, the lignite conveying device 3 and the lignite crushing device 2 are started. The conveying device 3 can reliably transport lignite, and its output can be adjusted according to the system's processing capacity by frequency conversion control. The crushing device 2 can coarsely crush the lignite into particles of suitable size, which are then sent to the lignite upgrading device 4 via the conveying device 3.

[0037] Start the lignite upgrading unit 4 to ensure uniform heating during flue gas preheating. The flue gas inside the hollow screw conveyor of the lignite upgrading unit 4 indirectly contacts the lignite outside, causing the lignite to dry and dehydrate. The rotation speed of the hollow screw conveyor is adjustable; by matching the inlet flue gas temperature with the feed rate and the rotation speed of the hollow screw conveyor, the outlet temperature of the lignite upgrading unit 4 can be controlled between 100-200℃. For example, the flue gas temperature discharged from the first flue gas outlet 44 of the lignite upgrading unit 4 can be 120℃, 140℃, 160℃, 180℃, or 190℃.

[0038] S4. The dried lignite discharged from the dry coal outlet 42 of the lignite upgrading device 4 is fed into the dried lignite collecting device 17 for collection. Specifically, in step S4, low-temperature inert flue gas with a temperature greater than or equal to 110°C and less than or equal to 130°C is introduced into the dried lignite collecting device 17 to prevent the dried lignite from spontaneously combusting upon contact with air inside the dried lignite collecting device 17.

[0039] According to an embodiment of the present invention, the lignite upgrading system utilizing flue gas from a coal-fired power plant utilizes flue gas resources after the SCR denitrification device 12 and before the air preheater in the coal-fired power plant to dry, dehydrate, and upgrade lignite through indirect contact, without affecting the quality of the upgraded lignite. The extracted flue gas has already undergone denitrification treatment, and the exhaust gas temperature after heat exchange is similar to the outlet temperature range of the air preheater in the coal-fired power plant. Therefore, it is sent to the exhaust gas after the air preheater and before the dust collector, which can further treat the exhaust gas in an environmentally friendly manner without affecting the boiler efficiency. The entire system operates under negative pressure and in a closed loop, with no wastewater discharge. The water vapor generated during the lignite dehydration and drying process is also sent to the downstream of the exhaust gas in the air preheater tail flue, and is discharged after being treated by the subsequent environmental protection facilities of the coal-fired power plant. The flue gas provides a heat source for lignite drying and keeps the entire system in an inert flue gas atmosphere, preventing spontaneous combustion and explosion of lignite and its volatiles, thus ensuring high safety.

[0040] Therefore, the lignite upgrading system utilizing flue gas from coal-fired power plants according to embodiments of the present invention facilitates lignite upgrading, reduces energy waste, and is highly safe.

[0041] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0042] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0043] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0044] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0045] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0046] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A lignite upgrading system with coal-fired power plant flue gas, characterized by, The system comprises: a lignite upgrading device for reducing the moisture in lignite, the lignite upgrading device having a wet coal inlet, a dry coal outlet, a first flue gas inlet, a first flue gas outlet and a first water vapor outlet; a pulverized coal boiler, a flue gas outlet of the pulverized coal boiler being connected to a flue, the flue being provided with a first flue gas interface, the first flue gas interface being connected to the first flue gas inlet of the lignite upgrading device through a first pipeline so that flue gas can be introduced from the first pipeline into the lignite upgrading device; a separator, an inlet of the separator being connected to the flue gas outlet of the lignite upgrading device, a second flue gas outlet of the separator being connected to an inlet of a booster fan, an outlet of the booster fan being connected to a flue gas exhaust interface of the flue through a second pipeline, a second solid outlet of the separator being connected to the second pipeline so that flue gas in the second pipeline can be introduced into the flue; a dry lignite collecting device, an inlet of the dry lignite collecting device being connected to the dry coal outlet.

2. The lignite upgrading system with coal-fired power plant flue gas according to claim 1, characterized in that, The flue is provided with a second flue gas interface, the second flue gas interface being connected to a flue gas inlet of the dry lignite collecting device through a third pipeline so that flue gas can be introduced from the third pipeline into the dry lignite collecting device.

3. The lignite upgrading system using flue gas of a coal-fired power plant according to claim 2, wherein: the first flue gas interface is located between a denitration device and an air preheater in the flue in the extension direction of the flue; the second flue gas interface and the flue gas exhaust interface are located downstream of the air preheater in the extension direction of the flue, the temperature of flue gas discharged from the second flue gas interface is lower than the temperature of flue gas discharged from the first flue gas interface, and the second flue gas interface is located between the air preheater and the flue gas exhaust interface in the extension direction of the flue; the first pipeline is provided with a flue gas shut-off valve and a first flue gas regulating valve group, the first flue gas regulating valve group being used to regulate the flow of flue gas in the first pipeline; the third pipeline is provided with a second flue gas regulating valve group, the second flue gas regulating valve group being used to regulate the flow of flue gas in the third pipeline.

4. The lignite upgrading system using flue gas of a coal-fired power plant according to claim 2, wherein: the temperature of flue gas discharged from the first flue gas interface is greater than or equal to 280℃ and less than or equal to 320℃; the temperature of flue gas discharged from the second flue gas interface is greater than or equal to 110℃ and less than or equal to 130℃; the third pipeline is provided with a second fan.

5. The lignite upgrading system with coal-fired power plant flue gas according to claim 4, characterized in that, The dry coal outlet of the lignite upgrading device is connected to the inlet of the dry lignite collecting device through a screw conveyor, and the screw conveyor is a closed conveying conveyor.

6. The lignite upgrading system with coal-fired power plant flue gas of claim 5, wherein, The first water vapor outlet is connected to the second pipeline through a fourth pipeline.

7. The lignite upgrading system using flue gas of a coal-fired power plant according to claim 1, wherein: the lignite upgrading device is provided with a hollow screw conveyor, the hollow screw conveyor comprising a hollow screw conveying portion extending in a helical manner, and the hollow screw conveying portion rotates to move lignite thereon in the direction adjacent to the dry coal outlet. The wet coal inlet and the dry coal outlet are located on both sides of the lignite upgrading device, and the first flue gas inlet is arranged on the side of the lignite upgrading device adjacent to the wet coal inlet.

8. The lignite upgrading system with flue gases of a coal-fired power plant of any of claims 1 - 7, characterized in that, Further comprising: a storage bin for storing lignite; a crushing device for crushing lignite; a conveying device for conveying lignite; The storage bin, the crushing device, the conveying device and the wet coal inlet of the lignite upgrading device are connected in sequence.

9. A lignite upgrading method with flue gas of coal-fired power plants using the lignite upgrading system with flue gas of coal-fired power plants according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: S1, passing the flue gas of the first flue gas interface of the flue into the lignite upgrading device; S2, starting the booster fan so that the flue gas enters the separator after passing through the lignite upgrading device; S3, starting the lignite upgrading device so that the lignite in the lignite upgrading device exchanges heat with the flue gas entering the lignite upgrading device during the movement of the lignite from the wet coal inlet to the dry coal outlet in the lignite upgrading device; S4, passing the dry lignite discharged from the dry coal outlet of the lignite upgrading device into the dry lignite collecting device for collection.

10. The method for upgrading lignite by using flue gas of a coal-fired power plant according to claim 9, wherein In the step S1, the flue gas flow in the first pipeline is adjusted, and the temperature of the flue gas discharged from the first flue gas interface is greater than or equal to 280℃ and less than or equal to 320℃; In the step S3, after the lignite upgrading device is preheated by the flue gas to above 250℃, lignite is conveyed to the lignite upgrading device from the wet coal inlet and the lignite upgrading device is started, and the temperature of the flue gas discharged from the first flue gas outlet of the lignite upgrading device is greater than or equal to 100℃ and less than or equal to 200℃; In the step S4, low-temperature inert flue gas with a temperature greater than or equal to 110℃ and less than or equal to 130℃ is introduced into the dry lignite collecting device to prevent the dry lignite from self-igniting in the dry lignite collecting device.

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