System and method for large-scale blending of biomass in a pulverized coal furnace

Abstract

The application discloses a system and method for large-proportion mixed combustion of biomass in a pulverized coal furnace, and belongs to the technical field of fuel combustion. The boiler is divided into a lower main combustion zone, an upper main combustion zone, a reduction zone and a burnout zone. The lower main combustion zone is provided with a biomass burner, the upper main combustion zone is provided with a pulverized coal burner and a biomass burner, the reduction zone is provided with a biomass burner, and the burnout zone is provided with a burnout air nozzle, which is beneficial to stable and efficient mixed combustion of coal and biomass and reduces nitrogen oxide emission. The application utilizes high-temperature flue gas waste heat to relieve low-temperature corrosion, and utilizes high-temperature low-oxygen flue gas, low-temperature low-oxygen flue gas and preheated air to dry biomass, so as to control the temperature and oxygen concentration of the drying medium, avoid fire risk and improve the energy utilization efficiency of the system.

Description

Technical Field

[0001] This invention belongs to the field of fuel combustion technology, and specifically relates to a system and method for co-firing biomass in a pulverized coal furnace. Background Technology

[0002] Biomass energy is the fourth largest energy source after coal, oil, and natural gas. It is characterized by being green, low-carbon, and clean, making it an ideal alternative to fossil fuels and playing a crucial role in promoting carbon emission reduction in my country. However, direct combustion of biomass suffers from low calorific value and severe ash and slag corrosion, limiting its large-scale power generation applications. Blending biomass with coal has become an important way to effectively utilize biomass energy and achieve low-carbon development of coal-fired power, attracting widespread attention. However, due to significant differences in combustion characteristics between biomass and coal, achieving high-proportion blending still faces many challenges.

[0003] Biomass is highly fibrous, making it difficult to break into uniform fine particles; when co-firing biomass in large proportions, it is usually difficult to guarantee a single, stable source of biomass, and existing crushing equipment generally lacks material compatibility; biomass contains a lot of dust and is prone to premature release of volatiles, which can easily lead to spontaneous combustion or even explosion risks during storage, transportation, and pretreatment; its calorific value is low, which can easily lead to unstable combustion; its high content of alkali metals, chlorine, and sulfur can easily cause serious problems of ash slagging and corrosion on heated surfaces; the nitrogen content and occurrence state in biomass also differ from those in coal, making it more difficult to control nitrogen oxide emissions after co-firing. Summary of the Invention

[0004] The purpose of this invention is to provide a system and method for co-firing biomass in a large proportion of pulverized coal furnaces, so as to solve the problems of difficult crushing and pretreatment, high risk of spontaneous combustion and explosion, poor combustion stability, serious problems of ash slagging and corrosion on the heated surface, and difficulty in controlling pollutant emissions when co-firing biomass in a large proportion.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A system for co-firing biomass in a pulverized coal boiler includes a boiler body, a tail flue, a fuel pretreatment and conveying system, and a tail flue gas treatment system. The boiler body is provided with a lower main combustion zone, an upper main combustion zone, a reduction zone, and a burnout zone from bottom to top. A biomass burner is installed on the side wall of the lower main combustion zone, a biomass burner and a pulverized coal burner are installed on the side wall of the upper main combustion zone, a biomass burner is installed on the side wall of the reduction zone, and a burnout air nozzle is installed on the side wall of the burnout zone. A low-temperature economizer and an air preheater are arranged from top to bottom in the tail flue. The fuel pretreatment and conveying system is used to crush and screen the fuel for pretreatment, and then convey the pretreated fuel to the furnace. The tail gas treatment system is used to desulfurize and remove dust from the flue gas in the tail flue, and then discharge the treated clean flue gas.

[0006] A further improvement of the present invention is that the fuel pretreatment and conveying system includes a biomass bin, an additive storage bin, a crushing device, a drying device, a separation device, a dust removal device, a screening device, a coal hopper, and a coal mill. Biomass in the biomass bin and additives in the additive storage bin are mixed together and then enter the crushing device. The crushed biomass and additive mixture is dried by the drying device and then conveyed into the separation device. The separated fine particles and drying medium are sent from the biomass burner to the reduction zone after passing through the dust removal device. The separated biomass and additive mixture particles enter the screening device and are screened into three particle sizes: large, medium and small. The coal in the coal hopper is ground to a set particle size by a coal mill, and then transported to the upper main combustion zone by a pulverized coal burner; large-particle biomass and additive particles are sent to the lower main combustion zone by a biomass burner; small-particle biomass and additive particles are sent to the reduction zone by a biomass burner; and medium-particle biomass is sent to the upper main combustion zone by a biomass burner.

[0007] A further improvement of the present invention is that the additives include aluminosilicate additives, phosphorus-based additives, and calcium-magnesium-based additives.

[0008] A further improvement of the present invention is that the crushing device has a detachable screen.

[0009] A further improvement of the present invention is that the air preheated by the air preheater, the low-temperature and low-oxygen clean flue gas drawn out in front of the chimney, and the high-temperature and low-oxygen flue gas drawn out from the horizontal flue are mixed and sent into the drying device as a drying medium to dry biomass and additives; a portion of the mixed flue gas is also introduced from below the drying device as fluidizing air.

[0010] A further improvement of the present invention is that the drying device is equipped with temperature and oxygen concentration monitoring devices, and the proportions are controlled by controlling the flow valves on the three flue gas / air pipes.

[0011] A further improvement of the present invention is that it also includes a fan, wherein the air transported by the fan is preheated by an air preheater and then sent to the furnace and the drying device respectively.

[0012] A further improvement of the present invention is that the tail flue gas treatment system includes a desulfurization and dust removal device and a chimney. After the tail flue gas is treated by the desulfurization and dust removal device, it is discharged from the chimney. A stream of low-temperature and low-oxygen clean flue gas is drawn out from in front of the chimney and sent into the drying device. A stream of high-temperature, low-oxygen flue gas is drawn out from the horizontal flue in front of the tail flue and exchanges heat with the low-temperature economizer and the air preheater in sequence; the high-temperature, low-oxygen flue gas after heat exchange is sent into the drying device.

[0013] A further improvement of the present invention is that the boiler is a four-corner tangent-circle boiler or a front and rear wall opposed boiler; If it is a tangentially circular boiler, the pulverized coal burner and biomass burner in the upper main combustion zone are arranged alternately along the height of the furnace. For boilers with opposing front and rear walls, the pulverized coal burners and biomass burners in the upper main combustion zone are arranged alternately along the width of the furnace.

[0014] A method for co-firing biomass in a pulverized coal boiler at a large proportion, the method being based on the aforementioned system for co-firing biomass in a pulverized coal boiler at a large proportion, comprising: The additives are fed into the crushing device along with the biomass, and then after drying, separation and screening, they are fed into the furnace through the biomass burner; the coal is ground to the set particle size by the coal mill and then fed into the furnace. A biomass burner is installed on the side wall of the lower main combustion zone, and large-particle biomass is introduced. Pulverized coal burners and biomass burners are alternately installed on the side wall of the upper main combustion zone, and pulverized coal and medium-sized biomass are introduced. A biomass burner is installed in the reduction zone to introduce small-particle biomass. The dry medium separated by the separation device is sent to the reduction zone through a biomass burner after dust removal treatment. A stream of high-temperature flue gas is drawn from the horizontal flue to the upper part of the low-temperature economizer to reheat the low-temperature economizer and the air preheater; The air preheated by the air preheater, the low-temperature and low-oxygen clean flue gas drawn from the front of the chimney, and the high-temperature and low-oxygen flue gas drawn from the horizontal flue are mixed together. Part of the mixture is used as a drying medium to dry the biomass, and the other part is sent into the bottom of the drying device as fluidizing air.

[0015] Compared with the prior art, the present invention has at least the following beneficial technical effects: 1) The additives are pre-treated together with the biomass, such as by crushing, so that the additives and biomass are fully mixed and then fed into the furnace through the biomass burner to alleviate the problem of fouling and slagging. 2) The crushing device is equipped with a detachable screen, which can adapt to different types of biomass and improve its material compatibility; 3) Install biomass burners on the side wall of the lower main combustion zone, introduce large-particle biomass to prolong its residence time and improve the burnout rate; 4) Coal pulverizers and biomass burners are alternately installed on the side wall of the upper main combustion zone, which makes the combustion of coal and biomass more uniform and complete, and improves combustion efficiency and combustion stability. 5) A biomass burner is installed in the reduction zone, and small-particle biomass is introduced. Small-particle biomass is easy to burn out. Even if it is introduced from the reduction zone in the upper part of the furnace, a high burnout rate can be guaranteed. In addition, small-particle biomass can quickly release highly reactive volatiles to generate incomplete combustion products such as CO with strong reducing properties, so as to reduce the nitrogen oxides produced by combustion below. 6) The dry medium separated by the separation device has a low oxygen concentration and contains tiny biomass particles. It is fed into the furnace from the reduction zone, which helps to enhance the reducing atmosphere in the reduction zone. 7) A stream of high-temperature flue gas is drawn from the horizontal flue to the upper part of the low-temperature economizer to reheat the low-temperature economizer and air preheater, thus avoiding the low-temperature corrosion problem caused by chlorine in biomass; 8) A drying device is provided to reduce the moisture content of biomass and increase its calorific value. Air preheated by an air preheater, low-temperature, low-oxygen clean flue gas drawn from the desulfurization and dust removal unit, and high-temperature, low-oxygen flue gas drawn from the horizontal flue are mixed. Part of this mixture is used as a drying medium to dry the biomass, while the other part is sent as fluidizing air to the bottom of the drying device to prevent biomass caking and accumulation. Temperature and oxygen concentration monitoring devices in the drying device control the ratio of the three flue gas / air streams through flow control valves to ensure suitable temperature and oxygen concentration within the drying device, avoiding the risk of spontaneous combustion and explosion. Attached Figure Description

[0016] 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.

[0017] Figure 1 This is a schematic diagram of a system for co-firing biomass in a pulverized coal furnace according to the present invention.

[0018] Figure 2 This is a schematic diagram of the burner arrangement for a tangentially circular pulverized coal boiler.

[0019] Figure 3 This is a schematic diagram of the burner arrangement for a pulverized coal boiler with opposing front and rear walls.

[0020] Explanation of reference numerals in the attached figures: 1 is the boiler body; 1.1 is the lower main combustion zone; 1.2 is the upper main combustion zone; 1.3 is the reduction zone; 1.4 is the burnout zone; 2 is the tail flue; 2.1 is the low-temperature economizer; 2.2 is the air preheater; 3 is the biomass silo; 4 is the additive storage silo; 5 is the crushing device; 6 is the drying device; 7 is the temperature and oxygen concentration monitoring device; 8 is the separation device; 9 is the dust removal device; 10 is the screening device; 11 is the coal hopper; 12 is the coal mill; 13 is the desulfurization and dust removal device; 14 is the chimney; 15 is the flow valve; 16 is the fan; 17 is the biomass burner; 18 is the pulverized coal burner; 19 is the burnout air outlet; 20 is the secondary air outlet. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

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

[0027] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0028] 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.

[0029] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0030] Example 1 See Figures 1-3 The present invention provides a system for high-proportion co-firing of biomass in a pulverized coal boiler, comprising: a boiler body 1, a lower main combustion zone 1.1, an upper main combustion zone 1.2, a reduction zone 1.3, a burnout zone 1.4, a tail flue 2, a low-temperature economizer 2.1, an air preheater 2.2, a biomass silo 3, an additive storage silo 4, a crushing device 5, a drying device 6, a temperature and oxygen concentration monitoring device 7, a separation device 8, a dust removal device 9, a screening device 10, a coal hopper 11, a coal mill 12, a desulfurization and dust removal device 13, a chimney 14, a flow valve 15, a fan 16, a biomass burner 17, a pulverized coal burner 18, a burnout vent 19, and a secondary air vent 20.

[0031] Coal is ground to a set particle size by the coal mill 12 and then fed into the furnace 1. Biomass in the biomass bin 3 and additives in the additive storage bin 4 are mixed and then fed into the crushing device 5, ensuring thorough mixing and reducing fouling and slagging. The crushed biomass-additive mixture is dried by the drying device 6 and then conveyed to the separation device 8. The separated fine particles and drying medium are sent from the biomass burner 17 to the reduction zone 1.3 after passing through the dust removal device 9. The low oxygen concentration of the drying medium helps to enhance the reducing atmosphere in the reduction zone. The separated biomass-additive mixture particles then enter the screening device 10 and are screened into large, medium, and small particle sizes.

[0032] Furthermore, the crushing device 5 has a detachable screen, which improves its material compatibility.

[0033] Furthermore, a biomass burner 17 is installed on the side wall of the lower main combustion zone 1.1 to introduce large-particle biomass, prolonging its residence time and improving the burnout rate.

[0034] Furthermore, biomass burners 17 and pulverized coal burners 18 are alternately arranged on the sidewalls of the upper main combustion zone 1.2. Pulverized coal is fed into the upper main combustion zone 1.2 via pulverized coal burners 18, and medium-sized biomass is fed into the upper main combustion zone 1.2 via biomass burners 17. If it is a tangentially round boiler, the pulverized coal burners 18 and biomass burners 17 in the upper main combustion zone 1.2 are alternately arranged along the height of the furnace. If it is a boiler with opposing front and rear walls, the pulverized coal burners 18 and biomass burners 17 in the upper main combustion zone 1.2 are alternately arranged along the width of the furnace, so that the combustion of coal and biomass is more uniform and complete, and the combustion efficiency and combustion stability are improved.

[0035] Furthermore, a biomass burner 17 is provided on the side wall of the reduction zone 1.3. Small-diameter biomass is fed into the reduction zone 1.3 through the biomass burner 17 to ensure a high burnout rate. The small-diameter biomass can quickly release highly reactive volatiles to generate incomplete combustion products such as CO with strong reducing properties, thereby reducing the nitrogen oxides generated by combustion below.

[0036] Furthermore, a burnout air nozzle 19 is provided on the side wall of the burnout zone 1.4 to deliver burnout air. Air grading helps to reduce the excess air coefficient of the main combustion zone, enhance the reducing properties of the main combustion zone, and reduce the nitrogen oxide content.

[0037] Furthermore, the low-temperature economizer 2.1 and the air preheater 2.2 are arranged from top to bottom in the flue at the tail end of the boiler. A stream of high-temperature flue gas is drawn out at the horizontal flue to the upper part of the low-temperature economizer 2.1 to reheat the low-temperature economizer 2.1 and the air preheater 2.2, thus avoiding the low-temperature corrosion problem caused by chlorine in biomass.

[0038] Furthermore, the high-temperature, low-oxygen flue gas, after heat exchange by the low-temperature economizer 2.1 and the air preheater 2.2, is sent into the drying device 6.

[0039] Furthermore, the tail flue gas is treated by the desulfurization and dust removal device 13 and then discharged from the chimney 14.

[0040] Furthermore, a stream of clean, low-temperature, low-oxygen flue gas is drawn from the front of chimney 14 and sent into the drying device 6.

[0041] Furthermore, the air transported by the blower 16 is preheated by the air preheater 2.2 and then sent to the furnace 1 and the drying device 6 respectively.

[0042] Furthermore, the air preheated by the air preheater 2.2, the low-temperature and low-oxygen clean flue gas drawn from the front of the chimney 14, and the high-temperature and low-oxygen flue gas drawn from the horizontal flue are mixed together. Part of the mixture is used as a drying medium to dry the biomass, and the other part is sent as fluidizing air into the lower part of the drying device 6 to prevent the biomass from caking and accumulating.

[0043] Furthermore, the drying device 6 is equipped with a temperature and oxygen concentration monitoring device 7, which controls the ratio of different flue gas / air in the drying medium to ensure that the temperature and oxygen concentration in the drying device are suitable, thus avoiding the risk of spontaneous combustion and explosion.

[0044] Example 2 See Figures 1-3 The present invention provides a method for co-firing biomass in a large proportion in a pulverized coal furnace, comprising: (1) The additives and biomass are fed into the crushing device 5 together, and then after drying, separation and screening, they are fed into the furnace 1 through the biomass burner 17; the coal is ground to the set particle size by the coal mill 12 and then fed into the furnace 1. (2) A biomass burner 17 is installed on the side wall of the lower main combustion zone 1.1 to introduce large-particle biomass; (3) Pulverized coal burners 18 and biomass burners 17 are alternately installed on the side wall of the upper main combustion zone 1.5, and pulverized coal and medium-sized biomass are introduced. (4) A biomass burner 17 is installed in the reduction zone 1.3 to introduce small-particle biomass; (5) The dry medium separated by the separation device 8 is sent to the reduction zone 1.3 through the biomass burner 17 after dust removal treatment; (6) A stream of high-temperature flue gas is drawn out from the horizontal flue to the upper part of the low-temperature economizer 2.1 to reheat the low-temperature economizer 2.1 and the air preheater 2.2; (7) The air preheated by the air preheater 2.2, the low-temperature and low-oxygen clean flue gas drawn from the front of the chimney 14 and the high-temperature and low-oxygen flue gas drawn from the horizontal flue are mixed. Part of the mixture is used as a drying medium to dry the biomass, and the other part is sent as fluidizing air to the bottom of the drying device 6.

[0045] Example 3 The biomass blending ratio, i.e., the proportion of biomass in the total calorific value of the fuel, should generally be controlled below 40%. This invention can simultaneously and effectively reduce NO. x To reduce SO2 emissions and prevent furnace temperature from deviating from a reasonable range. Compared to pure coal-fired operation, NO... x SO2 emission concentrations (standard conditions, dry basis, 6% O2) can be reduced by 0-21% and 0-18%, respectively. To avoid exacerbating incomplete combustion in the main combustion zone and significantly increasing CO concentration, the biomass blending ratio should be controlled below 20%. Compared to the operating condition with a biomass blending ratio of 20%, the peak CO concentration in the main combustion zone increases by 63%-95% when the biomass blending ratio is 30-50%, and the degree of incomplete combustion in the main combustion zone will be significantly increased.

[0046] If the boiler is a front and rear wall opposed boiler, the biomass burner 17 in the upper main combustion zone 1.2 should be arranged alternately with the pulverized coal burner 18 along the width of the furnace; if the boiler is a corner tangential boiler, the biomass burner 17 in the upper main combustion zone should be arranged alternately with the pulverized coal burner 18 along the height of the furnace. Compared with the feeding method of centrally setting multiple layers of biomass burners 17 and centrally arranging biomass burners 17 in the middle or on both sides of the furnace width, arranging biomass burners 17 and pulverized coal burners 18 alternately along the height or width can effectively increase the furnace temperature by about 10°C, reduce SO2 emissions by about 4%, and reduce the peak CO concentration in the main combustion zone by 4% to 24%. At the same time, the uniformity of temperature distribution and component distribution in the furnace is significantly improved.

[0047] The drying device 6 preferably uses fluidized bed drying technology, which has strong material adaptability and high heat transfer efficiency, and is suitable for drying bulk materials.

[0048] The drying device 6 is equipped with a temperature and oxygen concentration monitoring device 7. By controlling the ratio of different flue gas / air in the drying medium, the temperature and oxygen concentration in the drying device 6 are controlled at 50~120℃ and 1%~12%, respectively. When the temperature is high, the oxygen concentration should be kept low to avoid oxidation reaction of biomass or explosion of dust in biomass.

[0049] A stream of high-temperature flue gas is drawn from the horizontal flue to the upper part of the low-temperature economizer 2.1 to reheat the low-temperature economizer 2.1 and the air preheater 2.2. The temperature of the low-temperature economizer 2.1 and the air preheater 2.2 should generally not be lower than 180℃, otherwise SO2 and Cl elements will cause low-temperature corrosion in this area.

[0050] 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.

[0051] 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 in a pulverized coal boiler, characterized in that, It includes a boiler body (1), a tail flue (2), a fuel pretreatment and conveying system, and a tail flue gas treatment system. The boiler body (1) is arranged from bottom to top as a lower main combustion zone (1.1), an upper main combustion zone (1.2), a reduction zone (1.3), and a burnout zone (1.4). A biomass burner (17) is installed on the side wall of the lower main combustion zone (1.1), a biomass burner (17) and a pulverized coal burner (18) are installed on the side wall of the upper main combustion zone (1.2), a biomass burner (17) is installed on the side wall of the reduction zone (1.3), and a burnout air nozzle (19) is installed on the side wall of the burnout zone (1.4). A low-temperature economizer (2.1) and an air preheater (2.2) are arranged from top to bottom in the tail flue (2). The fuel pretreatment and conveying system is used to pretreat the fuel by crushing and screening, and to convey the pretreated fuel to the furnace (1). The tail flue gas treatment system is used to desulfurize and remove dust from the flue gas in the tail flue (2) and discharge the treated clean flue gas.

2. The system for high-proportion co-firing of biomass in a pulverized coal boiler according to claim 1, characterized in that, The fuel pretreatment and conveying system includes a biomass bin (3), an additive storage bin (4), a crushing device (5), a drying device (6), a separation device (8), a dust removal device (9), a screening device (10), a coal hopper (11), and a coal mill (12). Biomass in biomass bin (3) and additives in additive storage bin (4) are mixed and then fed into crushing device (5). The crushed biomass and additive mixture is dried by drying device (6) and then conveyed into separation device (8). The separated fine particles and drying medium are sent from biomass burner (17) to reduction zone (1.3) after passing through dust removal device (9). The separated biomass and additive mixture particles are then fed into screening device (10) and screened into three particle sizes: large, medium and small. The coal in the coal hopper (11) is ground to a set particle size by the coal mill (12) and then transported to the upper main combustion zone (1.2) by the pulverized coal burner (18); large-particle-size biomass and additive particles are sent to the lower main combustion zone (1.1) by the biomass burner (17); small-particle-size biomass and additive particles are sent to the reduction zone (1.3) by the biomass burner (17); and medium-particle-size biomass is sent to the upper main combustion zone (1.2) by the biomass burner (17).

3. A system for high-proportion co-firing of biomass in a pulverized coal boiler according to claim 2, characterized in that, Additives include aluminosilicate additives, phosphorus-based additives, and calcium-magnesium-based additives.

4. A system for high-proportion co-firing of biomass in a pulverized coal boiler according to claim 2, characterized in that, The crushing device (5) has a detachable screen.

5. A system for high-proportion co-firing of biomass in a pulverized coal boiler according to claim 2, characterized in that, The air preheated by the air preheater (2.2), the low-temperature and low-oxygen clean flue gas drawn out in front of the chimney (14) and the high-temperature and low-oxygen flue gas drawn out from the horizontal flue are mixed and sent into the drying device (6) as a drying medium to dry biomass and additives; part of the mixed flue gas is also introduced from below the drying device (6) as fluidizing air.

6. A system for high-proportion co-firing of biomass in a pulverized coal boiler according to claim 5, characterized in that, The drying device (6) is equipped with a temperature and oxygen concentration monitoring device (7), and its ratio is controlled by controlling the flow valve (15) on the three flue gas / air pipes.

7. A system for high-proportion co-firing of biomass in a pulverized coal boiler according to claim 2, characterized in that, It also includes a blower (16), and the air transported by the blower (16) is preheated by the air preheater (2.2) and then sent to the furnace (1) and the drying device (6).

8. A system for high-proportion co-firing of biomass in a pulverized coal boiler according to claim 2, characterized in that, The tail flue gas treatment system includes a desulfurization and dust removal device (13) and a chimney (14). After the tail flue gas is treated by the desulfurization and dust removal device (13), it is discharged from the chimney (14). A stream of low-temperature and low-oxygen clean flue gas is drawn out from the front of the chimney (14) and sent into the drying device (6). A stream of high-temperature, low-oxygen flue gas is drawn out from the horizontal flue in front of the tail flue (2) and exchanged with the low-temperature economizer (2.1) and the air preheater (2.2) in sequence; the high-temperature, low-oxygen flue gas after heat exchange is sent into the drying device (6).

9. A system for high-proportion co-firing of biomass in a pulverized coal boiler according to claim 2, characterized in that, The boiler (1) is a four-corner tangent boiler or a front and rear wall opposed boiler; If it is a four-corner tangential boiler, the pulverized coal burner (18) and biomass burner (17) in the upper main combustion zone (1.2) are arranged alternately along the height of the furnace; If it is a boiler with opposing front and rear walls, the pulverized coal burner (18) and biomass burner (17) in the upper main combustion zone (1.2) are arranged alternately along the width of the furnace.

10. A method for co-firing biomass in a large proportion in a pulverized coal boiler, characterized in that, This method is based on a system for high-proportion co-firing of biomass in a pulverized coal boiler according to any one of claims 2 to 9, comprising: The additives are fed into the crushing device (5) along with the biomass, and then fed into the furnace (1) through the biomass burner (17) after drying, separation and screening. The coal is ground to the set particle size by the coal mill (12) and then fed into the furnace (1). A biomass burner (17) is installed on the side wall of the lower main combustion zone (1.1) to introduce large-particle biomass; Pulverized coal burners (18) and biomass burners (17) are alternately arranged on the side wall of the upper main combustion zone (1.2), and pulverized coal and medium-sized biomass are introduced. A biomass burner (17) is installed in the reduction zone (1.3) to introduce small-particle biomass; The dry medium separated by the separation device (8) is sent to the reduction zone (1.3) through the biomass burner (17) after dust removal treatment. A stream of high-temperature flue gas is drawn from the horizontal flue to the upper part of the low-temperature economizer (2.1) to reheat the low-temperature economizer (2.1) and the air preheater (2.2); The air preheated by the air preheater (2.2), the low-temperature and low-oxygen clean flue gas drawn from the front of the chimney (14) and the high-temperature and low-oxygen flue gas drawn from the horizontal flue are mixed. Part of the mixture is used as a drying medium to dry the biomass, and the other part is sent as fluidized air to the bottom of the drying device (6).

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