A system and method for blending biomass fuel in a lignite medium-speed mill boiler

Abstract

The application discloses a system and method for blending and burning biomass fuel in a lignite medium-speed mill boiler, and belongs to the technical field of thermal power generation, and comprises a high-temperature and low-temperature molten salt tank, two-stage heat exchangers, multiple groups of induced draft fans, a lignite and biomass medium-speed mill, corresponding combustion nozzles, an air preheater, a dust collector and a boiler body. The surplus new energy and the redundant electric energy of the unit are used to heat the low-temperature molten salt, and the low-temperature molten salt is stored in the high-temperature molten salt tank; when the energy is released, the high-temperature molten salt is used to heat the low-temperature flue gas after dust removal, and the heat-exchanged and cooled molten salt flows back to the low-temperature molten salt tank. The flue gas after dust removal is divided into two paths, one path is mixed with the other path of original flue gas after being heated by the molten salt heat exchanger, the mixed high-temperature flue gas is divided into two groups and sent into two coal mills to dry the fuel; the waste flue gas after being milled is collected and exhausted into a flue. The biomass nozzle is arranged above the lignite nozzle, and the lignite heat source is used to guarantee the full combustion of the biomass, part of the flue gas after the air preheater is led out for heat exchange, and the remaining flue gas is externally discharged after dust removal.

Description

Technical Field

[0001] This invention belongs to the field of thermal power generation technology, specifically relating to a system and method for co-firing biomass fuel in a lignite medium-speed mill boiler. Background Technology

[0002] With the advancement of low-carbon retrofit technologies, co-firing biomass power generation with coal-fired units has become an important direction. Among these, using a medium-speed coal mill direct-fired pulverizing system to co-fire biomass is widely recognized as a highly economical retrofit solution due to its minimal equipment modification workload and ability to directly process relatively homogeneous shaped biomass materials (such as briquettes or pelletized straw and sawdust). However, when implementing this type of retrofit on lignite boilers, the insufficient drying capacity of the pulverizing system is a particularly prominent issue.

[0003] Lignite itself has a high total moisture content, which means that medium-speed mills already face a significant drying burden when grinding alone. According to the heat balance principle of the pulverizing system, the heat consumption from the evaporation of moisture in the raw coal accounts for the majority of the total heat consumption of the pulverizing system. When the amount of dryer at the pulverizer inlet and its temperature are constant, the drying output often becomes the main factor limiting the pulverizing output. Insufficient drying output will lead to obstructed pulverized coal output, coarser pulverized coal fineness, and a decrease in pulverizer outlet temperature. In severe cases, it may even cause abnormal discharge of coke or pulverizer blockage.

[0004] Against this backdrop, the introduction of biomass fuel for co-firing further exacerbates the burden on the drying system. Although briquetted biomass is easy to transport and meter, its moisture content and unique microstructure alter its grinding and flow characteristics within the medium-speed mill. The incorporation of biomass changes the overall physical properties of the fuel entering the furnace, increasing the ventilation resistance of the pulverizing system and the consumption of drying media. Under the original drying output margin designed for lignite, simultaneously drying two high-moisture or difficult-to-dry fuels easily leads to persistently low mill outlet temperatures, air-coal ratio imbalance, and severely weakens the system's drying capacity. Therefore, how to overcome the problem of insufficient drying output caused by the superposition of these two factors, while retaining the advantages of minimal modification to the medium-speed mill system and adaptability to briquetted biomass, has become a critical issue that urgently needs to be addressed in current coal-fired power generation technology coupled with biomass. Summary of the Invention

[0005] This invention provides a system and method for co-firing biomass fuel in a lignite medium-speed mill boiler, aiming to overcome the problem of insufficient drying output of the pulverizing system when such modifications are made to lignite boilers.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A system for co-firing biomass fuel in a lignite medium-speed mill boiler includes a high-temperature molten salt tank, a molten salt heat exchanger, a low-temperature molten salt tank, a flue gas mixing heat exchanger, a third induced draft fan, a biomass medium-speed mill, a lignite medium-speed mill, a fourth induced draft fan, a lignite burner nozzle, a biomass burner nozzle, an air preheater, a second induced draft fan, a dust collector, a first induced draft fan, and the boiler body. The lignite burner nozzles and biomass burner nozzles are arranged sequentially from bottom to top in the main combustion zone of the boiler body; the outlet of the low-temperature molten salt tank is connected to the inlet of the high-temperature molten salt tank, and the outlet of the high-temperature molten salt tank is connected to the inlet of the high-temperature molten salt tank through a molten salt heat exchanger. The second induced draft fan is used to extract a portion of the low-temperature flue gas after the dust collector is treated and divide it into two streams. One stream is fed into the molten salt heat exchanger for heating, and the other stream is fed into the flue gas mixing heat exchanger to mix and exchange heat with the high-temperature flue gas at the outlet of the molten salt heat exchanger. The mixed high-temperature flue gas obtained by the flue gas mixing heat exchanger is partly fed into the biomass medium-speed mill and partly fed into the lignite medium-speed mill. The flue gas generated by the combustion of the boiler body first passes through the air preheater. After part of it is drawn out by the second induced draft fan for heat exchange, the remaining flue gas can be dusted in the dust collector. The third induced draft fan is used to introduce part of the dust-removed flue gas into the molten salt heat exchanger for heat exchange, and then pass it into the flue gas mixing heat exchanger. The other part is directly passed into the flue gas mixing heat exchanger.

[0007] A further improvement of this invention is that the redundant power generation from new energy power generation and coal power is fed into a low-temperature molten salt tank and heated to high-temperature molten salt by electric heating.

[0008] A further improvement of the present invention is that the mixed high-temperature flue gas obtained by the flue gas mixing heat exchanger is diverted through a valve.

[0009] A further improvement of the present invention is that it further includes: the mixed low-temperature flue gas is introduced into the flue gas duct in front of the chimney by the fourth induced draft fan and then discharged.

[0010] A further improvement of the present invention is that the temperature of the molten salt in the high-temperature molten salt tank is in the range of 300℃ to 600℃.

[0011] A further improvement of the present invention is that the temperature range of the molten salt in the low-temperature molten salt tank is 250℃~400℃.

[0012] A further improvement of the present invention is that, after the remaining flue gas is purged in the dust collector, it is discharged into the air through the first induced draft fan and the chimney.

[0013] A method for co-firing biomass fuel in a lignite medium-speed mill boiler, the method being based on the aforementioned system for co-firing biomass fuel in a lignite medium-speed mill boiler, comprising: Redundant power generated by new energy sources and coal-fired power plants is fed into a low-temperature molten salt tank, where it is electrically heated to a high-temperature molten salt and then stored in the high-temperature molten salt tank. When energy needs to be released from the high-temperature molten salt, it is passed through a molten salt heat exchanger to heat the low-temperature flue gas, and the resulting low-temperature molten salt is then stored in the low-temperature molten salt tank. A second induced draft fan extracts a portion of the low-temperature flue gas after it has been treated by the dust collector and divides it into two streams. One stream is fed into the molten salt heat exchanger for heating, and the other stream is fed into a flue gas mixing heat exchanger to mix and exchange heat with the high-temperature flue gas at the outlet of the molten salt heat exchanger. The mixed high-temperature flue gas is diverted through valves, with one part going into the biomass medium-speed mill and the other into the lignite medium-speed mill. After increasing the drying output of biomass and lignite, the resulting mixed low-temperature flue gas is introduced into the flue gas duct in front of the chimney by the fourth induced draft fan and then discharged into the atmosphere. Inside the furnace, the biomass burner nozzles are arranged above the lignite burner nozzles to fully assist the combustion of biomass fuel with the heat generated by the combustion of lignite, ensuring the complete combustion of cellulose in the biomass. The flue gas generated by combustion first passes through an air preheater. After a portion is drawn out by the second induced draft fan for heat exchange, the remaining flue gas can be dusted in a dust collector.

[0014] Compared with the prior art, the present invention has at least the following beneficial technical effects: This invention provides a system and method for co-firing biomass fuel in a lignite medium-speed mill boiler. By coupling molten salt thermal storage with flue gas temperature regulation and employing a layered furnace nozzle arrangement, it effectively addresses the shortcomings of high-moisture-content biomass and lignite co-firing, such as difficulties in drying, poor biomass burnout, and the inability to utilize surplus renewable energy locally. This invention utilizes surplus electricity to electrically heat the molten salt thermal storage, achieving sequential storage of electrical energy into thermal energy. This provides a stable heat source for the pulverizing system on demand, eliminating the constraint of relying on instantaneous boiler exhaust for drying hot air. By leveraging flue gas diversion and mixing heat exchange, the inlet air temperature of the coal mill is flexibly controlled, significantly improving the pulverizing and drying output of lignite and biomass, and increasing the biomass co-firing ratio. The layout of the lignite combustion nozzles positioned below and the biomass nozzles positioned above relies on the high-temperature heat source of lignite to aid biomass combustion, ensuring complete combustion of cellulose and reducing incomplete combustion losses. At the same time, the system makes resource-efficient use of the low-temperature flue gas after boiler dust removal, and the coal mill exhaust gas is centrally incorporated into the flue gas pipeline, thereby improving the utilization rate of waste heat, reducing the unit's coal consumption and carbon emissions, and facilitating the implementation and application of biomass low-carbon retrofitting of coal-fired units. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the system of the present invention.

[0017] Explanation of reference numerals in the attached figures: 1-High-temperature molten salt tank, 2-Molten salt heat exchanger, 3-Low-temperature molten salt tank, 4-Flue gas mixing heat exchanger, 5-Third induced draft fan, 6-Valve, 7-Biomass medium-speed mill, 8-Lignite medium-speed mill, 9-Fourth induced draft fan, 10-Lignite burner nozzle, 11-Biomass burner nozzle, 12-Air preheater, 13-Second induced draft fan, 14-Dust collector, 15-First induced draft fan, 16-Chimney, 17-Boiler body. Detailed Implementation

[0018] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0019] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] 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 indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0021] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0023] It should be understood that, when used in this specification and the appended claims, 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.

[0024] 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.

[0025] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0026] 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.

[0027] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] Example 1 like Figure 1As shown, the present invention provides a system for co-firing biomass fuel in a lignite medium-speed mill boiler, comprising a high-temperature molten salt tank 1, a molten salt heat exchanger 2, a low-temperature molten salt tank 3, a flue gas mixing heat exchanger 4, a third induced draft fan 5, a valve 6, a biomass medium-speed mill 7, a lignite medium-speed mill 8, a fourth induced draft fan 9, a lignite burner nozzle 10, a biomass burner nozzle 11, an air preheater 12, a second induced draft fan 13, a dust collector 14, a first induced draft fan 15, a chimney 16, and a boiler body 17.

[0029] The system for co-firing biomass fuel in a lignite medium-speed mill boiler according to the present invention has the following connection method: Redundant power generated by new energy power generation and coal power is fed into a low-temperature molten salt tank 3, where it is electrically heated to high-temperature molten salt and then stored in a high-temperature molten salt tank 1. When energy needs to be released from the high-temperature molten salt, it is fed into a molten salt heat exchanger 2 to heat the low-temperature flue gas, and the resulting low-temperature molten salt is then stored in the low-temperature molten salt tank 3. A portion of the low-temperature flue gas treated by the dust collector 14 is extracted by the second induced draft fan 13 and divided into two streams. One stream is fed into the molten salt heat exchanger 2 for heating, and the other stream is fed into the flue gas mixing heat exchanger 4 to mix and exchange heat with the high-temperature flue gas at the outlet of the molten salt heat exchanger 2. The mixed high-temperature flue gas obtained from the flue gas mixing heat exchanger 4 is then diverted through a valve 6, with one portion fed into a biomass medium-speed mill 7 and the other into a lignite medium-speed mill 8. After increasing the drying output of the biomass and lignite, the resulting mixed low-temperature flue gas is introduced into the flue gas duct before the chimney 16 by the fourth induced draft fan 9 and then vented. Inside the furnace, the biomass burner nozzle 11 is positioned above the lignite burner nozzle 10, utilizing the heat generated by the combustion of lignite to fully aid the combustion of biomass fuel, ensuring the complete combustion of cellulose and other components in the biomass. The flue gas generated by combustion first passes through the air preheater 12. After a portion is drawn out by the second induced draft fan 13 for heat exchange, the remaining flue gas is dedusted in the dust collector 14 before being discharged through the first induced draft fan 15 and the chimney 16.

[0030] Example 2 like Figure 1 As shown, the present invention provides a system for co-firing biomass fuel in a lignite medium-speed mill boiler, comprising a high-temperature molten salt tank 1, a molten salt heat exchanger 2, a low-temperature molten salt tank 3, a flue gas mixing heat exchanger 4, a third induced draft fan 5, a biomass medium-speed mill 7, a lignite medium-speed mill 8, a fourth induced draft fan 9, a lignite burner nozzle 10, a biomass burner nozzle 11, an air preheater 12, a second induced draft fan 13, a dust collector 14, a first induced draft fan 15, and a boiler body 17.

[0031] The lignite burner nozzle 10 and the biomass burner nozzle 11 are arranged sequentially from bottom to top in the main combustion zone of the boiler body 17; the outlet of the low-temperature molten salt tank 3 is connected to the inlet of the high-temperature molten salt tank 1, and the outlet of the high-temperature molten salt tank 1 is connected to the inlet of the boiler body 17 via the molten salt heat exchanger 2; the second induced draft fan 13 is used to extract a portion of the low-temperature flue gas treated by the dust collector 14 and divide it into two streams, one of which is fed into the molten salt heat exchanger 2 for heating, and the other is fed into the flue gas mixing heat exchanger 4 to mix with the high-temperature flue gas at the outlet of the molten salt heat exchanger 2. The high-temperature mixed flue gas obtained by the flue gas mixing heat exchanger 4 is partially fed into the biomass medium-speed mill 7 and the other part into the lignite medium-speed mill 8. The flue gas generated by the combustion of the boiler body 17 first passes through the air preheater 12. After part of it is drawn out by the second induced draft fan 13 for heat exchange, the remaining flue gas can be dusted in the dust collector 14. The third induced draft fan 5 is used to introduce part of the dust-removed flue gas into the molten salt heat exchanger 2 for heat exchange, and then into the flue gas mixing heat exchanger 4; the other part is directly fed into the flue gas mixing heat exchanger 4. This plays a role in the proportion distribution of flue gas, which can regulate the temperature of the mixed flue gas in the flue gas mixing heat exchanger 4.

[0032] In this embodiment, the redundant power generation from new energy power generation and coal power is fed into the low-temperature molten salt tank 3 and heated to high-temperature molten salt by electric heating.

[0033] In this embodiment, the mixed high-temperature flue gas obtained by the flue gas mixing heat exchanger 4 is diverted through valve 6.

[0034] In this embodiment, the mixture of low-temperature flue gas is introduced into the flue gas duct before the chimney 16 by the fourth induced draft fan 9 and then discharged.

[0035] In this embodiment, the temperature of the molten salt in the high-temperature molten salt tank 1 ranges from 300℃ to 600℃.

[0036] In this embodiment, the temperature range of the molten salt in the low-temperature molten salt tank 3 is 250℃~400℃.

[0037] In this embodiment, the remaining flue gas is purged in the dust collector 14 and then discharged through the first induced draft fan 15 and the chimney 16.

[0038] Example 3 like Figure 1 As shown, the present invention provides a method for co-firing biomass fuel in a lignite medium-speed mill boiler, comprising: Redundant power generation from new energy sources and coal-fired power plants is fed into a low-temperature molten salt tank 3, where it is electrically heated to a high-temperature molten salt and then stored in a high-temperature molten salt tank 1. When energy needs to be released from the high-temperature molten salt, it is fed into a molten salt heat exchanger 2 to heat the low-temperature flue gas, and the resulting low-temperature molten salt is then stored in the low-temperature molten salt tank 3. A portion of the low-temperature flue gas treated by the dust collector 14 is extracted by the second induced draft fan 13 and divided into two streams. One stream is fed into the molten salt heat exchanger 2 for heating, and the other stream is fed into the flue gas mixing heat exchanger 4 to mix and exchange heat with the high-temperature flue gas at the outlet of the molten salt heat exchanger 2. The flue gas mixing heat exchanger 4 mixes... The resulting mixed high-temperature flue gas is diverted through valve 6, with one part going into the biomass medium-speed mill 7 and the other part going into the lignite medium-speed mill 8. After increasing the drying output of biomass and lignite, the resulting mixed low-temperature flue gas is introduced into the flue gas duct before the chimney 16 by the fourth induced draft fan 9 and then discharged. Inside the furnace, the biomass burner nozzle 11 is arranged above the lignite burner nozzle 10, utilizing the heat generated by the combustion of lignite to fully assist the combustion of biomass fuel and ensure the complete combustion of cellulose in biomass. The flue gas generated by combustion first passes through the air preheater 12. After part of it is drawn out by the second induced draft fan 13 for heat exchange, the remaining flue gas can be dusted in the dust collector 14.

[0039] The key points of this invention are as follows: A system and method for co-firing biomass fuel in a lignite medium-speed mill boiler includes a high-temperature molten salt tank, a molten salt heat exchanger, a low-temperature molten salt tank, a flue gas mixing heat exchanger, a third induced draft fan, valves, a biomass medium-speed mill, a lignite medium-speed mill, a fourth induced draft fan, a lignite burner nozzle, a biomass burner nozzle, an air preheater, a second induced draft fan, a dust collector, a first induced draft fan, a chimney, and a boiler body.

[0040] The key point of this invention is that it utilizes a high-temperature molten salt thermal storage system to convert the redundant power generation during the deep adjustment of new energy and coal-fired power into heat for storage, and uses flue gas for heat exchange when heat exchange is needed, thereby improving the drying output of lignite and biomass fuels and thus improving the power generation efficiency of lignite units.

[0041] The key point of this invention is that the high-temperature flue gas drawn out by the second induced draft fan is divided into two parts. One part is used to transfer the heat stored in the molten salt system, and the other part is used for mixing and temperature regulation. This system can dynamically adjust the flue gas volume and flue gas temperature according to the needs of the coal mill system, thereby fully improving the heat utilization efficiency of the molten salt thermal storage system.

[0042] The key point of this invention is that by using valves to divert the mixed high-temperature flue gas, the flue gas flow rate can be reasonably allocated according to the needs of the biomass and lignite pulverizing systems, and the drying output of the two pulverizing systems can be dynamically adjusted to improve the efficiency.

[0043] The key point of this invention is that by arranging the biomass burner nozzle on the lignite burner nozzle, the heat generated by the combustion of lignite can be used to fully assist the combustion of biomass fuel, promote the combustion of refractory substances such as cellulose in biomass, and reduce the pressure on subsequent environmental protection systems such as desulfurization.

[0044] The key point of this invention is that the heat stored in the molten salt thermal storage system is only used for flue gas heat exchange. The system is simple, and the implementation of this system can further reduce the operating load of lignite units and achieve deep peak shaving.

[0045] The key point of this invention is that a portion of the heat stored in the molten salt thermal storage system comes from the redundant power generation of new energy sources, thereby helping lignite-fired units to generate electricity efficiently and energy-savingly and to co-fire biomass fuels, which helps reduce carbon emissions.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0047] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A system for co-firing biomass fuel in a lignite medium-speed mill boiler, characterized in that, It includes a high-temperature molten salt tank, a molten salt heat exchanger, a low-temperature molten salt tank, a flue gas mixing heat exchanger, a third induced draft fan, a biomass medium-speed mill, a lignite medium-speed mill, a fourth induced draft fan, a lignite burner nozzle, a biomass burner nozzle, an air preheater, a second induced draft fan, a dust collector, a first induced draft fan, and the boiler body. The lignite burner nozzles and biomass burner nozzles are arranged sequentially from bottom to top in the main combustion zone of the boiler body; the outlet of the low-temperature molten salt tank is connected to the inlet of the high-temperature molten salt tank, and the outlet of the high-temperature molten salt tank is connected to the inlet of the high-temperature molten salt tank through a molten salt heat exchanger. The second induced draft fan is used to extract a portion of the low-temperature flue gas after the dust collector is treated and divide it into two streams. One stream is fed into the molten salt heat exchanger for heating, and the other stream is fed into the flue gas mixing heat exchanger to mix and exchange heat with the high-temperature flue gas at the outlet of the molten salt heat exchanger. The mixed high-temperature flue gas obtained by the flue gas mixing heat exchanger is partly fed into the biomass medium-speed mill and partly fed into the lignite medium-speed mill. The flue gas generated by the combustion of the boiler body first passes through the air preheater. After part of it is drawn out by the second induced draft fan for heat exchange, the remaining flue gas can be dusted in the dust collector. The third induced draft fan is used to introduce part of the dust-removed flue gas into the molten salt heat exchanger for heat exchange, and then pass it into the flue gas mixing heat exchanger. The other part is directly passed into the flue gas mixing heat exchanger.

2. The system for co-firing biomass fuel in a lignite medium-speed mill boiler according to claim 1, characterized in that, The redundant power generated by new energy power generation and coal power is fed into a low-temperature molten salt tank and heated to high-temperature molten salt using electric heating.

3. The system for co-firing biomass fuel in a lignite medium-speed mill boiler according to claim 1, characterized in that, The mixed high-temperature flue gas obtained by the flue gas mixing heat exchanger is then diverted through valves.

4. The system for co-firing biomass fuel in a lignite medium-speed mill boiler according to claim 1, characterized in that, Also includes: The mixed low-temperature flue gas is introduced into the flue gas duct in front of the chimney by the fourth induced draft fan and then discharged into the air.

5. A system for co-firing biomass fuel in a lignite medium-speed mill boiler according to claim 1, characterized in that, The temperature range of the molten salt in the high-temperature molten salt tank is 300℃~600℃.

6. The system for co-firing biomass fuel in a lignite medium-speed mill boiler according to claim 1, characterized in that, The temperature range of the molten salt in the low-temperature molten salt tank is 250℃~400℃.

7. A system for co-firing biomass fuel in a lignite medium-speed mill boiler according to claim 1, characterized in that, The remaining flue gas is purged through a dust collector and then discharged through the first induced draft fan and the chimney.

8. A method for co-firing biomass fuel in a lignite medium-speed mill boiler, characterized in that, This method, based on the lignite medium-speed mill boiler co-firing biomass fuel system of claim 1, includes: Redundant power generated by new energy sources and coal-fired power plants is fed into a low-temperature molten salt tank, where it is electrically heated to a high-temperature molten salt and then stored in the high-temperature molten salt tank. When energy needs to be released from the high-temperature molten salt, it is passed through a molten salt heat exchanger to heat the low-temperature flue gas, and the resulting low-temperature molten salt is then stored in the low-temperature molten salt tank. A second induced draft fan extracts a portion of the low-temperature flue gas after it has been treated by the dust collector and divides it into two streams. One stream is fed into the molten salt heat exchanger for heating, and the other stream is fed into a flue gas mixing heat exchanger to mix and exchange heat with the high-temperature flue gas at the outlet of the molten salt heat exchanger. The mixed high-temperature flue gas is diverted through valves, with one part going into the biomass medium-speed mill and the other into the lignite medium-speed mill. After increasing the drying output of biomass and lignite, the resulting mixed low-temperature flue gas is introduced into the flue gas duct in front of the chimney by the fourth induced draft fan and then discharged into the atmosphere. Inside the furnace, the biomass burner nozzles are arranged above the lignite burner nozzles to fully assist the combustion of biomass fuel with the heat generated by the combustion of lignite, ensuring the complete combustion of cellulose in the biomass. The flue gas generated by combustion first passes through an air preheater. After a portion is drawn out by the second induced draft fan for heat exchange, the remaining flue gas can be dusted in a dust collector.

9. A method for co-firing biomass fuel in a lignite medium-speed mill boiler according to claim 8, characterized in that, The temperature range of the molten salt in the high-temperature molten salt tank is 300℃~600℃.

10. A method for co-firing biomass fuel in a lignite medium-speed mill boiler according to claim 8, characterized in that, The temperature range of the molten salt in the low-temperature molten salt tank is 250℃~400℃.

Images