System and method for blending combustion of multi-element clean fuel in coal-fired circulating fluidized bed

Abstract

The invention discloses a system and method for blending combustion of multi-element clean fuel in a coal-fired circulating fluidized bed, and belongs to the technical field of fuel combustion. Biomass is fed into the hearth from the coal feeding opening and the secondary air opening, the combustion uniformity and the combustion efficiency are improved, and the range of a reduction area is enlarged. Two layers of hydrogen feeding ports are formed in the side wall of the hearth, so that the combustion stability and uniformity are enhanced; and a hydrogen feeding port is formed in the horizontal flue, so that the temperature of tail flue gas is increased, and low-temperature corrosion is avoided. The tail flue gas recirculation is utilized to avoid overtemperature coking in a dense-phase region, and the generation of nitrogen oxides at high temperature is inhibited. Moisture in tail smoke is recycled and sent to the washing device, the moisture content in the smoke is reduced, and the problems of ash deposition, slag bonding and corrosion are solved.

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 multiple clean fuels in a coal-fired circulating fluidized bed. Background Technology

[0002] Fluidized bed boilers feature low-temperature combustion, stable combustion, strong load regulation capability, and high fuel adaptability, enabling them to adapt to the mixed combustion of different fuels. Fluidized bed boilers have become ideal equipment for co-firing multiple clean fuels. Coal-fired circulating fluidized bed boilers coupled with the combustion of multiple clean fuels show broad application prospects.

[0003] Biomass and hydrogen are common clean fuels. Biomass is widely available and is the fourth largest energy source after coal, oil, and natural gas. It is characterized by being green, low-carbon, and clean. Blending biomass with coal has become an important way to effectively utilize biomass energy and has been listed as a primary method for the low-carbon transformation of coal-fired power plants, attracting widespread attention. However, biomass is diverse in type, complex in composition, varies greatly in properties, and is scattered in distribution. Direct combustion of biomass also presents problems such as low calorific value, severe ash accumulation and corrosion, which place higher demands on coal-fired boilers and restrict their direct power generation applications. Meanwhile, hydrogen energy has been incorporated into new energy storage methods, and hydrogen production technology has been vigorously developed, but there is also the problem of overproduction. Hydrogen has significant advantages in terms of low calorific value, maximum laminar flame propagation speed, minimum ignition temperature, minimum ignition energy, and adiabatic flame temperature. It does not produce CO2 or NO during combustion. x It is a high-quality fuel that burns quickly, flexibly, and cleanly, and there is no fuel escape phenomenon. Using excess hydrogen for co-firing is beneficial to further reduce carbon emissions from thermal power plants.

[0004] The blending of coal, biomass, and hydrogen is beneficial for reducing carbon emissions, achieving resource synergy, and improving combustion characteristics. However, the fuel characteristics of coal, biomass, and hydrogen are quite different, and blending may lead to problems such as local overheating, unstable combustion, low combustion efficiency, difficulty in controlling nitrogen oxides, and severe ash and slagging. Summary of the Invention

[0005] The purpose of this invention is to provide a system and method for co-firing multiple clean fuels in a coal-fired circulating fluidized bed, in order to solve the problems of combustion stability, combustion efficiency, temperature control, nitrogen oxide control, and ash accumulation and slagging in the co-firing of coal, biomass and hydrogen mentioned in the background art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A system for co-firing multiple clean fuels in a coal-fired circulating fluidized bed includes a furnace, a cyclone separator, a return material device, a tail flue, a fuel storage and conveying system, and a tail flue gas treatment system. An air distribution plate is installed at the bottom of the furnace. A coal feed port is arranged on the front wall. Two secondary air ports are arranged on the front and rear walls respectively. They are located above the coal feed ports, and from bottom to top, they are the lower secondary air port and the upper secondary air port. A hydrogen feed port is set below the lower secondary air port on the rear wall of the furnace and above the secondary air port on the front wall. The return material device is used to transport the material captured by the cyclone separator back to the lower part of the circulating fluidized bed furnace and to prevent the high-temperature flue gas in the furnace from backflowing into the cyclone separator. The fuel storage and delivery system is used to store fuel and deliver it to the furnace. The tail gas treatment system is used to treat the flue gas in the tail flue.

[0007] A further improvement of the present invention is that a hydrogen feed port is provided in the horizontal flue between the outlet of the cyclone separator and the inlet of the tail flue.

[0008] A further improvement of the present invention is that the fuel storage and conveying system includes a coal hopper, a coal mill, a biomass silo, a crushing device, a washing device, a drying and forming device, a biomass hopper, a biomass conveying device, a Roots blower, and a diversion device. The coal in the coal hopper is ground into powder by a coal mill and then fed into the furnace through the coal feed port. After being crushed by the crushing device, the biomass in the biomass bin is sent to the washing device for washing. After washing and separation, the biomass is prepared into biomass pellets by the drying and forming device, and then sent into the furnace for combustion via the biomass hopper, conveying device and diversion device. The Roots blower is connected to the biomass conveying device to provide it with high-pressure airflow, ensuring the conveying of biomass; The diversion device is used to divert biomass into multiple streams in a proportional manner and deliver them to different feeding positions accordingly.

[0009] A further improvement of the present invention is that the diversion device divides the biomass into three streams. One part of the biomass is premixed with coal and fed into the furnace through the coal feed port, while the other two parts of the biomass are fed into the furnace through the lower secondary air inlets of the front and rear walls, respectively.

[0010] A further improvement of the present invention is that the tail gas treatment system includes a moisture recovery device, a dust removal device, and a chimney. The moisture recovery device is used to condense water vapor in the tail flue gas into liquid water for collection; Dust removal devices are used to separate solid particulate matter such as fly ash and unburned carbon from the tail flue gas; Chimneys are used to discharge flue gas that has been treated by moisture recovery and dust removal devices.

[0011] A further improvement of the present invention is that the moisture recovery device recovers moisture from the tail flue gas and sends it to the water washing device for biomass water washing pretreatment.

[0012] A further improvement of the present invention is that a stream of clean flue gas with low temperature and low oxygen is drawn out from the front of the chimney and sent into the furnace through the air distribution plate.

[0013] A method for co-firing multiple clean fuels in a coal-fired circulating fluidized bed, the method being based on the aforementioned coal-fired circulating fluidized bed system for co-firing multiple clean fuels, comprising: 1) Coal in the fuel storage and transportation system is ground and pulverized before being sent to the furnace for combustion; biomass is pre-treated by crushing, washing and separating, drying and shaping before being sent to different areas of the furnace for combustion. 2) A coal feed port is arranged on the front wall of the furnace to introduce premixed coal and biomass; 3) Two layers of secondary air inlets are arranged on the front and rear walls above the coal feed inlet. The lower secondary air inlet is used to introduce secondary air and biomass, while the upper secondary air inlet is used to introduce secondary air. 4) Two layers of hydrogen feed ports are provided on the side wall of the furnace, located below the secondary air inlet on the rear wall and above the secondary air inlet on the front wall, respectively. When the hydrogen co-firing ratio is low or the boiler load is low, hydrogen is mainly fed into the furnace from the hydrogen feed port below the secondary air inlet on the rear wall. When the hydrogen co-firing ratio is high, a portion of the hydrogen is fed into the furnace from the hydrogen feed port above the upper secondary air inlet.

[0014] A further improvement of the present invention is that it also includes: 5) the bottom of the furnace is an air distribution plate, through which primary air and low-temperature, low-oxygen clean flue gas that has been treated by a moisture recovery device and a dust removal device are introduced.

[0015] A further improvement of the present invention is that it also includes: 6) a moisture recovery device is arranged after the tail flue to recover moisture in the tail flue gas and send it to the water washing device for biomass water washing pretreatment.

[0016] Compared with the prior art, the present invention has at least the following beneficial technical effects: 1) A coal feed port is arranged on the front wall of the furnace to introduce premixed coal and biomass, thereby improving combustion uniformity and combustion efficiency; 2) Secondary air inlets are arranged on the front and rear walls of the furnace to introduce secondary air and biomass, which promotes complete combustion of biomass and expands the reduction zone. 3) Two layers of hydrogen feed ports are provided on the side wall of the furnace, located below the secondary air inlet on the rear wall and above the secondary air inlet on the front wall, respectively. When the hydrogen co-firing ratio is low or the boiler load is low, hydrogen is mainly fed into the furnace from the hydrogen feed port below the secondary air inlet on the rear wall. The temperature in this area is slightly lower than that of the front wall, but the oxygen concentration is higher, which is conducive to hydrogen combustion and improves the boiler's stable combustion capability at low load. When the hydrogen co-firing ratio is high, a portion of the hydrogen is fed into the furnace from the hydrogen feed port above the upper secondary air inlet to avoid excessively high temperature in the dense phase zone, appropriately increase the temperature in the dilute phase zone, and reduce the nitrogen oxides generated by combustion. 4) The bottom of the furnace is an air distribution plate, which introduces primary air and low-temperature, low-oxygen clean flue gas that has passed through the moisture recovery device and dust removal device. This avoids the problem of overheating and coking in the dense phase zone caused by the combustion of a large proportion of hydrogen, while strengthening the reducing atmosphere in the dense phase zone and inhibiting the generation of nitrogen oxides. 5) A hydrogen feed port is arranged at the horizontal flue, and a small amount of hydrogen is introduced to allow the hydrogen to burn and release heat before the inlet of the tail flue, thereby increasing the temperature of the flue gas entering the tail flue and avoiding the low-temperature corrosion problem caused by co-firing biomass. 6) A moisture recovery device is installed after the tail flue to recover the large amount of moisture generated by hydrogen combustion in the tail flue gas and send it to the water washing device for biomass water washing pretreatment to remove alkali metals, chlorine and other impurities, alleviate ash accumulation, slag formation and corrosion problems, and reduce the moisture content of the emitted flue gas to avoid affecting the reliability and life of dust removal devices and other equipment. Attached Figure Description

[0017] 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.

[0018] Figure 1 This is a schematic diagram of a coal-fired circulating fluidized bed system for co-firing multiple clean fuels, according to the present invention.

[0019] Explanation of reference numerals in the attached figures: 1 is the furnace, 1.1 is the air distribution plate, 1.2 is the coal feed port, 1.3 is the lower secondary air inlet, 1.4 is the upper secondary air inlet, 2 is the cyclone separator, 3 is the return material device, 4 is the tail flue, 5 is the hydrogen feed port, 6 is the coal hopper, 7 is the coal mill, 8 is the biomass silo, 9 is the crushing device, 10 is the water washing device, 11 is the drying and forming device, 12 is the biomass hopper, 13 is the biomass conveying device, 14 is the Roots blower, 15 is the diversion device, 16 is the moisture recovery device, 17 is the dust removal device, and 18 is the chimney. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0029] Example 1 See Figure 1 The present invention provides a coal-fired circulating fluidized bed system for co-firing multiple clean fuels, comprising: a furnace 1, an air distribution plate 1.1, a coal feed inlet 1.2, a lower secondary air inlet 1.3, an upper secondary air inlet 1.4, a cyclone separator 2, a return material device 3, a tail flue 4, a hydrogen feed inlet 5, a coal hopper 6, a coal mill 7, a biomass silo 8, a crushing device 9, a washing device 10, a drying and forming device 11, a biomass hopper 12, a biomass conveying device 13, a Roots blower 14, a diversion device 15, a moisture recovery device 16, a dust removal device 17, and a chimney 18.

[0030] The coal in the coal hopper 6 is ground into powder by the coal mill 7 and then fed into the furnace 1 through the coal feed port 1.2; the biomass in the biomass bin 8 is crushed by the crushing device 9 and then sent to the washing device 10 for washing treatment. The biomass after washing and separation is prepared into biomass pellets by the drying and forming device 11, and then sent to different areas of the furnace 1 for combustion via the biomass hopper 12, the conveying device 13 and the diversion device 15.

[0031] Before entering the furnace, the biomass is crushed and then washed with water. Washing effectively removes most of the alkali metals and chlorine from the biomass. The system uses a diversion device 15 to distribute the treated biomass particles into different areas of the furnace, which is crucial for optimizing gas-solid mixing. By adjusting the position of the biomass entering the furnace, the release point of volatiles can be controlled, avoiding excessively strong local reducing atmospheres, thereby suppressing thermal NO without sacrificing combustion efficiency. xThe generation of biomass pellets is as follows: When biomass supply is insufficient, more coal can be burned; when the power grid requires rapid response for peak shaving, hydrogen can be co-fired at the hydrogen feed port 5. Biomass is a zero-carbon fuel, and hydrogen is a zero-carbon energy source. Co-firing them can significantly reduce the carbon emission intensity of the entire system, which is in line with environmental protection policy guidelines. The "biomass pellets" prepared by the drying and molding device 11 have a higher energy density than loose biomass and are easier to transport and store. The settling characteristics of the pellets in the furnace are closer to those of coal particles, which prolongs their residence time in the furnace, which is conducive to complete combustion and reduces the carbon content of fly ash. Due to the co-firing of hydrogen, the water vapor content in the flue gas will be higher. The moisture recovery device can recover this condensate, realizing water conservation in the power plant.

[0032] Furthermore, the Roots blower 14 is connected to the biomass conveying device 13 to provide it with high-pressure airflow, ensuring stable and efficient conveying of biomass.

[0033] Furthermore, the diversion device 15 divides the biomass into three streams. One part of the biomass is premixed with coal and fed into the furnace 1 through the coal feed port 1.2. The other two parts of the biomass are fed into the furnace 1 through the lower secondary air inlets 1.3 on the front and rear walls, respectively.

[0034] Furthermore, a coal feed port 1.2 is arranged on the front wall of the furnace 1 to introduce premixed coal and biomass, thereby improving combustion uniformity and combustion efficiency.

[0035] Furthermore, secondary air inlets 1.3 are arranged on the front and rear walls of the furnace 1 to introduce secondary air and biomass, promote the complete combustion of biomass, and expand the reduction zone. Furthermore, secondary air inlets 1.4 are arranged on the front and rear walls of the furnace 1 to introduce secondary air, so that the incomplete combustion products are burned off and a reducing atmosphere is created in the dense phase zone.

[0036] Furthermore, a hydrogen feed port 5 is provided below the secondary air inlet 1.3 on the rear wall of the furnace 1 and above the secondary air inlet 1.4 on the front wall. When the hydrogen co-firing ratio is low or the boiler load is low, hydrogen is mainly fed into the furnace from the hydrogen feed port 5 below the secondary air inlet 1.3 on the rear wall. The temperature in this area is slightly lower than that of the front wall, but the oxygen concentration is higher, which is conducive to hydrogen combustion and improves the boiler's stable combustion capability at low load. When the hydrogen co-firing ratio is high, a portion of the hydrogen is fed into the furnace from the hydrogen feed port 5 above the upper secondary air inlet 1.4 to avoid excessively high temperatures in the dense phase zone, appropriately increase the temperature in the dilute phase zone, and reduce the nitrogen oxides generated by the secondary combustion at the upper secondary air inlet 1.4.

[0037] Furthermore, the bottom of the furnace 1 is an air distribution plate 1.1, through which primary air and low-temperature, low-oxygen clean flue gas that has passed through the moisture recovery device 16 and the dust removal device 17 are introduced, thereby reducing the temperature of the dense phase zone, strengthening the reducing atmosphere of the dense phase zone, and inhibiting the generation of nitrogen oxides.

[0038] Furthermore, a hydrogen feed port 5 is provided in the horizontal flue between the outlet of the cyclone separator 3 and the inlet of the tail flue 4. Hydrogen enters the horizontal flue from the hydrogen feed port 5 and burns and releases heat, increasing the temperature of the flue gas entering the tail flue 4 and avoiding the low-temperature corrosion problem caused by co-firing biomass.

[0039] Furthermore, the moisture recovery device 16 condenses the water vapor in the tail flue gas into liquid water for collection and sends it to the water washing device 10 for biomass water washing pretreatment, which alleviates the problems of ash accumulation, slag formation and corrosion, while reducing the moisture content of the emitted flue gas.

[0040] Furthermore, the dust removal device 17 separates solid particles such as fly ash and unburned carbon from the tail flue gas.

[0041] Example 2 See Figure 1 The present invention provides a method for co-firing multiple clean fuels in a coal-fired circulating fluidized bed, comprising: (1) The coal in the coal hopper 6 is ground into powder by the coal mill 7 and then sent to the furnace 1 for combustion; the biomass in the biomass bin 8 is pre-treated by crushing, water washing and separation, drying and molding, and then sent to different areas of the furnace 1 for combustion. (2) A coal inlet 1.2 is arranged on the front wall of furnace 1 to introduce premixed coal and biomass; (3) Two layers of secondary air inlets are arranged on the front and rear walls above the coal feed inlet 1.2. The lower secondary air inlet 1.3 is used to introduce secondary air and biomass, and the upper secondary air inlet 1.4 is used to introduce secondary air. (4) Two layers of hydrogen feed ports 5 are provided on the side wall of the furnace 3, respectively located below the secondary air inlet 1.3 on the rear wall of the furnace and above the secondary air inlet 1.4 on the front wall; when the hydrogen co-firing ratio is low or the boiler load is low, hydrogen is mainly fed into the furnace 1 from the hydrogen feed port 5 below the secondary air inlet 1.3 on the rear wall; when the hydrogen co-firing ratio is high, a portion of hydrogen is fed into the furnace 1 from the hydrogen feed port 5 above the upper secondary air inlet 1.4. Furthermore, the present invention also includes: (5) the bottom of the furnace 1 is an air distribution plate 1.1, through which primary air and low-temperature, low-oxygen clean flue gas that has passed through the moisture recovery device 16 and the dust removal device 17 are introduced; Furthermore, the present invention also includes: (7) a moisture recovery device 16 is arranged after the tail flue 4 to recover moisture in the tail flue gas and send it to the water washing device 10 for biomass water washing pretreatment.

[0042] 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.

[0043] 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 multiple clean fuels in a coal-fired circulating fluidized bed, characterized in that, It includes a furnace (1), a cyclone separator (2), a return material device (3), a tail flue (4), a fuel storage and conveying system, and a tail flue gas treatment system; An air distribution plate (1.1) is provided at the bottom of the furnace (1), a coal feed port (1.2) is arranged on the front wall, and two layers of secondary air are arranged on the front and rear walls respectively. They are located above the coal feed port (1.2), and from bottom to top are the lower secondary air port (1.3) and the upper secondary air port (1.4). A hydrogen feed port (5) is provided below the lower secondary air port (1.3) on the rear wall of the furnace and above the secondary air port (1.4) on the front wall. The return device (3) is used to transport the material captured by the cyclone separator back to the lower part of the circulating fluidized bed furnace (1) and prevent the high-temperature flue gas in the furnace (1) from backflowing into the cyclone separator (2). The fuel storage and delivery system is used to store fuel and deliver it to the furnace (1); The tail flue gas treatment system is used to treat the flue gas from the tail flue (4).

2. The system for co-firing multiple clean fuels in a coal-fired circulating fluidized bed according to claim 1, characterized in that, A hydrogen feed port (5) is provided in the horizontal flue between the outlet of the cyclone separator (2) and the inlet of the tail flue (4).

3. A system for co-firing multiple clean fuels in a coal-fired circulating fluidized bed according to claim 1, characterized in that, The fuel storage and conveying system includes a coal hopper (6), a coal mill (7), a biomass silo (8), a crushing device (9), a washing device (10), a drying and forming device (11), a biomass hopper (12), a biomass conveying device (13), a Roots blower (14), and a diversion device (15). The coal in the coal hopper (6) is ground into powder by the coal mill (7) and then fed into the furnace (1) through the coal feed port (1.2); The biomass in the biomass bin (8) is crushed by the crushing device (9) and then sent to the washing device (10) for washing. The biomass after washing and separation is prepared into biomass pellets by the drying and forming device (11), and then sent into the furnace (1) for combustion via the biomass hopper (12), the conveying device (13) and the diversion device (15). The Roots blower (14) is connected to the biomass conveying device (13) to provide it with high-pressure airflow to ensure the conveying of biomass; The diversion device (15) is used to divert biomass into multiple streams in proportion and deliver them to different feeding positions accordingly.

4. A system for co-firing multiple clean fuels in a coal-fired circulating fluidized bed according to claim 3, characterized in that, The diversion device (15) divides the biomass into three streams. One part of the biomass is premixed with coal and fed into the furnace (1) through the coal feed port (1.2). The other two parts of the biomass are fed into the furnace (1) through the lower secondary air inlets (1.3) on the front and rear walls, respectively.

5. A system for co-firing multiple clean fuels in a coal-fired circulating fluidized bed according to claim 1, characterized in that, The tail gas treatment system includes a moisture recovery device (16), a dust removal device (17), and a chimney (18). The moisture recovery device (16) is used to condense water vapor in the tail flue gas into liquid water for collection; The dust removal device (17) is used to separate solid particles such as fly ash and unburned carbon from the tail flue gas; Chimney (18) is used to discharge flue gas that has been treated by moisture recovery device (16) and dust removal device (17).

6. A system for co-firing multiple clean fuels in a coal-fired circulating fluidized bed according to claim 5, characterized in that, The moisture recovery device (16) recovers the moisture in the tail flue gas and sends it to the water washing device (10) for biomass water washing pretreatment.

7. A system for co-firing multiple clean fuels in a coal-fired circulating fluidized bed according to claim 5, characterized in that, A stream of clean flue gas with low temperature and low oxygen is drawn out from the front of the chimney (18) and sent into the furnace (1) through the air distribution plate (1.1).

8. A method for co-firing multiple clean fuels in a coal-fired circulating fluidized bed, characterized in that, This method, based on the coal-fired circulating fluidized bed system for co-firing multiple clean fuels as described in claim 5, includes: 1) Coal in the fuel storage and transportation system is ground and pulverized before being sent into the furnace (1) for combustion; biomass is pre-treated by crushing, washing and separation, drying and molding before being sent into different areas of the furnace (1) for combustion. 2) A coal inlet (1.2) is arranged on the front wall of the furnace (1) to introduce premixed coal and biomass; 3) Two layers of secondary air inlets are arranged on the front and back walls above the coal feed inlet (1.2). The lower secondary air inlet (1.3) introduces secondary air and biomass, and the upper secondary air inlet (1.4) introduces secondary air. 4) Two layers of hydrogen feed ports (5) are provided on the side wall of the furnace (3), which are respectively arranged below the secondary air inlet (1.3) on the rear wall of the furnace and above the secondary air inlet (1.4) on the front wall. When the hydrogen co-firing ratio is low or the boiler load is low, hydrogen is mainly fed into the furnace (1) from the hydrogen feed port (5) below the secondary air inlet (1.3) on the rear wall. When the hydrogen co-firing ratio is high, a portion of hydrogen is fed into the furnace (1) from the hydrogen feed port (5) above the upper secondary air inlet (1.4).

9. A method for co-firing multiple clean fuels in a coal-fired circulating fluidized bed according to claim 8, characterized in that, Also includes: 5) The bottom of the furnace (1) is an air distribution plate (1.1), through which primary air and low-temperature, low-oxygen clean flue gas that has been treated by the moisture recovery device (16) and the dust removal device (17) are introduced.

10. A method for co-firing multiple clean fuels in a coal-fired circulating fluidized bed according to claim 9, characterized in that, Also includes: 6) A moisture recovery device (16) is arranged after the tail flue (4) to recover the moisture in the tail flue gas and send it to the water washing device (10) for biomass water washing pretreatment.

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