Round boiler hearth of reverse blowing type internal circulating fluidized bed

Abstract

The invention discloses a back-blowing type circular boiler hearth of an internal circulating fluidized bed, which solves the problems of high processing cost, difficulty in maintenance, easiness in blockage of an air cap and non-uniform fluidization of a bed layer in the operation of an existing fluidized bed boiler due to an air distribution plate and an air cap structure. Comprising a hearth body and a concentric pipeline, the concentric pipeline is composed of an inner pipe and an outer pipe which are coaxially arranged, the inner pipe is a primary air supply channel, and an annular space between the outer pipe and the inner pipe is a secondary air supply channel. The primary air supply channel is connected with a fuel feeding device through a spiral feeder and conveys fuel to the bottom of the hearth. And the hearth inner pipe section of the secondary air supply channel is a water cooling sleeve. A semicircular channel and a conical bluff body are arranged at the bottom of the hearth, and a vortex area is formed to achieve fluidized combustion. Water cooling walls are arranged on the periphery of the hearth and form a working medium circulation loop with the header system. The concentric pipeline structure is used for replacing a traditional air distribution plate and a traditional air cap, combustion efficiency is high, the structure is compact, maintenance is easy and convenient, and the burner is suitable for various fuel and industrial scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of fluidized bed boilers, and particularly relates to a reverse-blowing internal circulation fluidized bed circular boiler furnace. Background Art

[0002] As of 2017, China had more than 3,000 circulating fluidized bed (CFB) boilers, accounting for 60% of the total number of CFB boilers in the world. Among them, the total capacity of CFB boilers used for power generation had approached 100 million kilowatts, making China the country with the largest number and capacity of CFB boilers in the world. The air distribution plate and air cap technology is the main fluidization device currently used in fluidized bed boilers. Taking a 10 - 15t / h boiler as an example, there are up to about 1,000 - 1,200 air caps on the air distribution plate, and 5 - 8 air holes are processed on each air cap. That is, there are 5,000 - 10,000 air holes on the boiler air distribution plate. Air jets outwards at a high speed of 30 - 50m / s through the air holes of the air caps, driving the materials on the air distribution plate to perform fluidization movement.

[0003] The air distribution plate air cap technology originated in the last century. Since 1965, relevant patent literatures on fluidized bed air cap technology have emerged. With the development of science and technology in China, the fluidized bed air distribution plate technology has made great progress. From the beginning of this century to now, there have been no less than thousands of design patents for air caps, and a large number of patented technologies have been put into production and operation. Although the processing technology of air cap technology has matured, and its material can withstand the test of long-term high-temperature operation, the number of air caps is large, and the processing volume is huge. Therefore, the cost of the air distribution plate is relatively high. In addition, inevitable problems still occur during long-term operation.

[0004] Air cap blockage, coking of bed fuel combustion, resulting in insufficient and uneven fluidization of the boiling layer of the bubbling bed and the dense phase region of the external circulation fluidized bed, leading to phenomena such as channeling in local areas and uneven fluidization state of the bed material on the air distribution plate are relatively common. Moreover, the number of air caps is huge, and the maintenance workload of the air distribution plate is heavy, seriously affecting the long-term normal operation of the boiler. Summary of the Invention

[0005] The purpose of the present invention is to provide a reverse-blowing internal circulation fluidized bed circular boiler furnace to solve the technical problems of high processing cost, difficult maintenance, and easy occurrence of air cap blockage and uneven bed fluidization caused by the air distribution plate and air cap structure in existing fluidized bed boilers. The boiler capacity to which the technology of the present invention is applied is suitable for small biomass fluidized bed boilers with a capacity of 6 - 75t / h, and can also be used for coal-fired industrial boilers with a capacity of 10 - 140t / h.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] A reverse-blowing internal circulation fluidized bed circular boiler furnace provided by the present invention includes a furnace body with a circular cross-section and a concentric pipe. One end of the concentric pipe extends into the furnace body and is fixed at the center of the furnace body, and the other end extends out of the top of the furnace body and is connected to an external air supply device. The concentric pipe includes an inner pipe and an outer pipe arranged coaxially. The inner pipe is a primary air supply channel, and the annular space between the outer pipe and the inner pipe is a secondary air supply channel. Air flows through the secondary air supply channel and is sprayed downward into the furnace to supplement the required oxygen for internal combustion. The primary air supply channel is connected to a fuel feeding device through a screw feeder for transporting fuel to the bottom of the furnace. The inner pipe section of the secondary air supply channel in the furnace is a water-cooled sleeve with a sandwich for cooling the pipe and absorbing combustion heat. The bottom of the furnace is a semi-circular annular channel with a conical blunt body arranged inside to facilitate the formation of an eddy region at the bottom of the furnace and fluidize the combustion of fuel particles. Water-cooled walls are provided around the furnace body. The water-cooled walls are connected through an upper header, a middle header, and a lower header, and form a working medium circulation system with the secondary air and water-cooled sleeve.

[0008] Further, the screw feeder passes through the outer pipe and is connected to the inner pipe to input fuel into the inner pipe. The fuel inlet of the inner pipe is set as a converging-diverging throat structure to accelerate the air flow rate to form a local negative pressure, suck in fuel through the local negative pressure, and prevent air leakage.

[0009] Further, a plurality of ash discharge holes are uniformly arranged along the circumference at the bottom of the furnace, and each ash discharge hole is correspondingly connected to a slag discharge pipe for discharging the bottom slag generated by combustion.

[0010] Further, the air outlet of the outer pipe is located at the bottom of the furnace, and the air outlet of the inner pipe is located in the middle of the furnace. Air flows out from the outlet and is sprayed into the lower part of the furnace to enhance the disturbance between gas and solid fuel and supplement the required oxygen to strengthen combustion.

[0011] Further, the concentric structure of the outer pipe and the inner pipe is fixed by welding with a plurality of fixing brackets made of high-temperature resistant steel to maintain coaxiality.

[0012] Further, at the height position of the outlet of the inner pipe on the furnace wall around the furnace, a lower water-cooled wall and a lower header of the water-cooled wall are provided. At the height position of the outlet of the outer pipe on the furnace wall around the furnace, an upper water-cooled wall and a middle header are provided. The middle header and the water-cooled sleeve are connected by a middle header connecting pipe. An upper header is arranged at the working medium outlet at the upper part of the upper water-cooled wall. The upper header and the water-cooled sleeve are connected by an upper header connecting pipe. In addition to connecting the heating surface to realize the natural circulation flow of the working medium, the upper header connecting pipe and the middle header connecting pipe are also used to fixedly support the position of the concentric pipe in the furnace.

[0013] Further, the lower water-cooled wall is a smooth tube water-cooled wall or a membrane water-cooled wall for absorbing the heat in the furnace.

[0014] Furthermore, it also includes a flue gas outlet pipe. The furnace flue gas outlet pipe is arranged at the upper part of the furnace. After the fuel is burned out in the upper part of the furnace, fly ash is formed and flows out of the furnace through the flue gas outlet pipe. The boiler outlet is connected to a flue, and an evaporation heating surface and a superheater are arranged inside the flue to absorb the heat of the flue gas.

[0015] Based on the above technical solutions, the embodiments of the present invention can at least produce the following technical effects:

[0016] (1) The reverse-blowing internal circulation fluidized bed circular boiler furnace provided by the present invention has significant beneficial effects compared with traditional fluidized bed boilers. First of all, this design adopts a concentric pipe structure (the inner pipe is the primary air supply channel, and the annular space outside the pipe is the secondary air supply channel), replacing the complex structure of the traditional air distribution plate and air caps. The primary air duct and the secondary air duct control the combustion temperature in the furnace not to be too high by different air inlet speeds and air pressures, and achieve complete combustion, greatly reducing the processing cost, reducing the maintenance workload, and at the same time avoiding the problems of air cap blockage and uneven fluidization of the bed layer. Secondly, in addition, the primary air, furnace feed, and secondary air are integrated and arranged at the center of the furnace. The primary air sends in the fuel and realizes the fluidization of the fuel at the bottom of the furnace. The secondary air supplements the oxygen required for combustion and adjusts the combustion in the furnace by the ratio of the primary and secondary air volumes. For different fuels, by reasonably designing the ratio of the primary and secondary air, low-temperature stable combustion in the furnace can be completely achieved.

[0017] (2) The reverse-blowing internal circulation fluidized bed circular boiler furnace provided by the present invention combines the semi-circular annular channel at the bottom of the furnace with a conical blunt body to form a vortex area, enabling uniform fluidized combustion of fuel particles, improving the combustion efficiency, and reducing the risk of coking. In addition, the secondary air is ejected from the middle of the furnace, enhancing the disturbance between the gas and the fuel and further optimizing the combustion process. The design of the water-cooled sleeve not only cools the pipeline, extends the equipment life, but also absorbs the combustion heat and improves the thermal energy utilization rate. In terms of maintenance, the outlet size of the concentric pipes is large and the direction is vertically downward, with a low probability of blockage, and the cleaning work can be carried out outside the furnace, significantly improving the maintenance environment. The reasonable arrangement of the ash discharge hole and the slag discharge pipe ensures the stability of the bed material level. The water wall and the header system form an efficient working medium circulation loop, further improving the thermal efficiency of the boiler. The overall structure is compact, with strong adaptability, and can be applied to a variety of fuels and industrial scenarios, having broad application prospects. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0019] Figure 1 is a schematic structural diagram of an embodiment of the present invention;

[0020] Figure 2 is Figure 1 a schematic structural diagram of the A-A sectional view of

[0021] Figure 3 is a top view of an embodiment of the present invention;

[0022] Figure 4 is a schematic structural diagram of the concentric pipes of the present invention;

[0023] Figure 5 is a schematic structural diagram of the upper header of the present invention;

[0024] Figure 6 is a schematic structural diagram of the middle header of the present invention;

[0025] Figure 7 is a schematic structural diagram of the lower header of the present invention;

[0026] In the figure: 1, screw feeder; 2, upper header; 3, middle header; 4, lower header; 5, slag discharge pipe; 6, conical blunt body; 7, bottom of the furnace; 8, concentric pipes; 9, lower water-cooled wall; 10, upper water-cooled wall; 11, outer pipe; 12, water-cooled sleeve; 13, inner pipe; 14, fixed support; 15, lower header body; 16, upper header body; 17, upper header nozzle; 18, middle header body; 19, middle header nozzle. Detailed implementation manners

[0027] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of the technical solutions appears to be contradictory or unable to be implemented, it should be considered that such a combination of the technical solutions does not exist and is not within the protection scope required by the present invention.

[0028] Embodiment: As shown in the appendix Figures 1 - 7As shown, a back-blowing internal circulating fluidized bed circular boiler furnace comprises a furnace body with a circular cross section and a concentric pipe 8, one end of the concentric pipe 8 extends into the furnace body and is fixed at the center of the furnace body, and the other end extends out of the top of the furnace body and communicates with an external air supply device; the concentric pipe 8 comprises an inner pipe 13 and an outer pipe 11 arranged coaxially, wherein the inner pipe 13 is a primary air supply channel, and the annular space between the outer pipe 11 and the inner pipe 13 is a secondary air supply channel, and air flows through the secondary air supply channel and sprays downward into the furnace to supplement the oxygen required for its internal combustion; the inner pipe 13 is connected to a screw feeder 1 at the top of the boiler furnace, and the screw feeder 1 feeds fuel into the inner pipe In 13, the air flow flowing into the inner tube 13 carries the fuel downward along the pipeline, and sprays out of the inner tube 13 into the bottom of the fluidized bed furnace; the inner pipe section of the secondary air supply channel is a water-cooled jacket 12 with an interlayer, which is used to cool the pipeline and absorb the heat of combustion; the lower part of the furnace is a boiling layer, the lower part of the boiling layer is the furnace bottom 7, and the upper part of the boiling layer is composed of a combination of a cylindrical structure with an equal cross-section and a hollow truncated cone structure with a tapered cross-section; the furnace bottom 7 is a semicircular annular channel, and a conical blunt body 6 is arranged inside. The fuel is carried by the primary wind and sprayed into the furnace bottom 7, and flows radially from the axis to the surroundings along the conical surface and the annular channel, forming a vortex moving from the inside to the outside. Four ash dropping holes are evenly arranged along the circumference at the bottom, and four slag discharge pipes 5 are installed accordingly. The bottom slag produced during the combustion process is discharged by the slag discharge pipes 5 to ensure the stability of the bed material amount at the bottom 7 of the furnace. The furnace bottom 7 realizes the vortex flow of materials. Water-cooled walls are arranged around the furnace body, and the water-cooled walls are connected through an upper header 2, a middle header 3 and a lower header 4, and form a working medium circulation system with the secondary air water-cooling sleeve 12.

[0029] In this embodiment, the input end of the screw feeder 1 is connected to the hopper, and the output end is connected to the inner tube 13 through the outer tube 11. The fuel is transported to the inner tube 13 by the screw feeder 1, and the air flow flowing into the inner tube 13 carries the fuel downward along the pipeline, and sprays out of the pipe mouth of the inner tube 13 into the furnace bottom 7. The fuel feed port of the inner tube 13 is set as a zoom-type throat structure, in which the air flow rate is accelerated, the dynamic pressure is increased, and a local negative pressure is formed. The air in the tube will not leak out through the loose part of the feed port. At the same time, the material at the inlet is sucked into the tube by the negative pressure and sent downward to the bottom of the furnace along with the air flow.

[0030] In this embodiment, the air outlet of the outer tube 11 is located at the bottom 7 of the furnace, and the air outlet of the inner tube 13 is located in the middle of the furnace. The air flows out from the outlet and is sprayed to the lower part of the furnace, thereby enhancing the disturbance between the gas and the solid fuel, supplementing the required oxygen, and strengthening the combustion.

[0031] In this embodiment, the concentric structure of the outer pipe 11 and the inner pipe 13 is formed by welding a plurality of fixed brackets 14 made of high-temperature resistant steel at a certain interval to fix their positions relative to each other and maintain the concentric structure. The two air duct sleeves of the concentric structure can be fabricated in one piece and assembled on site.

[0032] In this embodiment, water-cooled walls 9 and water-cooled wall lower headers 4 are provided at the height position of the outlet of the inner pipe 13 on the furnace walls around the furnace. The water-cooled walls 9 are smooth tube water-cooled walls or membrane water-cooled walls, which absorb the heat in the furnace. Upper water-cooled walls 10 and intermediate headers 3 are provided at the height position of the outlet of the outer pipe 11 on the furnace walls around the furnace. The intermediate headers 3 are connected to the water-cooled sleeves 12 by intermediate header connecting pipes 19. At the upper working medium outlet of the upper water-cooled walls 10, upper headers 2 are arranged. The upper headers 2 are connected to the water-cooled sleeves 12 by upper header connecting pipes 17. In addition to connecting the heating surfaces to realize the natural circulation flow of the working medium, the upper header connecting pipes 17 and the intermediate header connecting pipes 19 are also used to fixedly support the position of the concentric pipes 8 in the furnace. The lower headers 4 include lower header bodies 15.

[0033] In this embodiment, it further includes a flue gas outlet pipe 3. The furnace flue gas outlet pipe 3 is arranged at the upper part of the furnace. After the fuel in the upper part of the furnace is burned out, fly ash flows out of the furnace through the flue gas outlet pipe 3. The boiler outlet is connected to a flue, and evaporation heating surfaces and superheaters are arranged inside the flue to absorb the heat of the flue gas.

[0034] In this embodiment, the air in the primary air duct in the furnace carries the fuel and blows it downward to the bottom of the furnace, forming a vortex at the bottom to make the fuel particles in a fluidized state and carry out ignition and combustion. The air in the secondary air duct flows into the furnace to supplement oxygen for the fuel combustion in the furnace and strengthen the air flow disturbance, enhancing the contact between oxygen and solid fuel. Although the part of the inner pipe exposed in the furnace is in the boiling layer combustion area, the primary air and fuel flowing in the pipe are at a relatively low temperature, which plays a role in cooling the inner pipe. Especially when burning biomass fuel, to reduce fuel coking, the combustion temperature in this area is controlled lower than that of coal combustion. Therefore, the pipe sections of the air ducts in this area are made of ZG40Cr26Ni4Mn3NRe heat-resistant steel, while other parts can use ordinary Q235 steel. The conical blunt body at the center is made of heat-resistant steel. The inner pipe section of the outer pipe in the furnace is a water-cooled sleeve, which is an evaporation heating surface and is made of 20g boiler steel. There is no need to use more expensive high-temperature resistant steel to reduce the material cost.

[0035] The operation process of the present invention:

[0036] The fuel particles are crushed into 0-15mm by the crusher, transported into the primary air duct by the feeding device composed of a screw feeder and a hopper, carried away by the flowing air inside the air duct, and flow downward through the lower outlet of the primary air duct into the fluidized boiling area composed of the furnace bottom of the semicircular annular channel and the conical blunt body at the bottom of the furnace, and vortex flow from the center to the surroundings, driving the fuel to fluidize in a vortex at the bottom of the furnace. The furnace walls around the bottom of the furnace can be appropriately arranged according to actual conditions. The buried pipe heating surface can absorb heat to appropriately reduce the combustion temperature of the boiling layer, reduce or avoid combustion coking, and only refractory materials and thermal insulation materials can be arranged to stabilize fuel combustion.

[0037] The outlet of the secondary air duct is located in the middle of the furnace. Air flows out from the outlet and sprays into the lower boiling layer, which enhances the disturbance between the gas and the solid fuel, and replenishes the required oxygen to strengthen the combustion. The pipe section of the secondary air duct in the furnace is exposed to the high-temperature flame and flue gas environment of the furnace. In order to ensure its long-term safe operation and avoid damage to the steel pipe under high temperature conditions, it is designed as a water-cooled sleeve. On the one hand, the cooling pipe is prevented from burning, and on the other hand, the heating surface of the working medium in the furnace is increased, the combustion heat is absorbed, and the temperature in the furnace is adjusted.

[0038] The larger particles move in a fluidized state under the action of the vortex airflow at the bottom of the furnace, undergoing intense heat transfer and combustion oxidation reactions with the high-temperature flue gas and primary air. Some smaller particles move upward with the airflow into the middle of the furnace, mix with the oxygen in the secondary air and continue to burn and burn out.

[0039] The fly ash formed after the fuel in the upper part of the furnace is burned out of the furnace with the flue gas. A flue is set at the furnace outlet to arrange the evaporation heating surface and superheater to absorb the heat of the flue gas.

[0040] Operation and maintenance: Once the hood is blocked during operation, it is necessary to check and dredge the air holes one by one, clean the residue inside the hood, and even replace the severely worn hood, which requires a large amount of maintenance and repair work. During the maintenance and repair process, the staff often need to enter the furnace for maintenance and cleaning. The materials accumulated in the furnace are prone to dust, the air quality is poor, and the working environment is harsh. The present invention adopts a circular tube airflow back-blowing fluidizing device. During the design process, wear-resistant and high-temperature resistant steel with a certain thickness is used. The outlet size of the primary and secondary air ports is larger than the air holes of the former hood, and the opening direction is vertically downward. The probability of material blockage is much smaller than that of the former air distribution plate hood. Even if material blockage occurs, the staff can dredge and clean it outside the furnace through the manhole door after the furnace is shut down, without having to drill into the furnace. The maintenance workload is much less than the former, and the working environment is also significantly improved compared to the former.

[0041] Conventional circulating fluidized beds mainly use air distribution plates + air caps technology. Air is ejected from the air holes on the air caps, driving the solid bed materials on the air distribution plates to fluidize. In terms of processing and manufacturing, thousands of air caps need to be installed on the air distribution plates, and each air cap has 5-8 air holes, which require special processing and a large amount of processing and assembly work.

[0042] The present invention adopts an airflow back-blowing fluidizing device, uses primary air to carry solid fuel to form a jet of a certain speed, sprays into the bottom of the furnace to form a vortex, and realizes the fluidization movement of the material. The core components that need to be processed - the concentric tubes in the furnace and the fixed brackets between the concentric tubes, only have two circular steel pipes with different diameters and a few fixed brackets, and the processing and assembly volume is much smaller than the former. The secondary air casing and the water-cooled wall header do not require high-temperature resistant steel or difficult-to-process high-temperature brickwork. The relatively cheap 20g boiler steel can meet the requirements, or even Q235 ordinary steel, and the material cost will not be higher than that of traditional fluidized bed boilers.

[0043] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of the present invention to be protected is defined by the attached claims and their equivalents.

Claims

1. A back-blowing internal circulating fluidized bed circular boiler furnace, characterized in that: The invention comprises a furnace body with a circular cross section and a concentric pipe (8), one end of the concentric pipe (8) extends into the furnace body and is fixed at the center of the furnace body, and the other end extends out of the top of the furnace body and is connected to an external air supply device; the concentric pipe (8) comprises an inner pipe (13) and an outer pipe (11) arranged coaxially, wherein the inner pipe (13) is a primary air supply channel, and the annular space between the outer pipe (11) and the inner pipe (13) is a secondary air supply channel, and air flows through the secondary air supply channel and sprays downward into the furnace to supplement the oxygen required for internal combustion; the primary air supply channel is connected to the furnace body through a screw feeder (1). The furnace bottom (7) is connected to a fuel feeding device and is used to transport fuel to the furnace bottom (7). The furnace inner pipe section of the secondary air supply channel is a water-cooled jacket (12) with an interlayer, which is used to cool the pipe and absorb combustion heat. The furnace bottom (7) is a semicircular annular channel, and a conical blunt body (6) is arranged inside to facilitate the formation of a vortex area at the furnace bottom (7) so that the fuel particles can be fluidized and burned. The furnace body is surrounded by water-cooled walls, which are connected through an upper header (2), a middle header (3) and a lower header (4), and form a working medium circulation system with the secondary air water-cooled jacket (12).

2. The back-blowing internal circulating fluidized bed circular boiler furnace according to claim 1, characterized in that: The screw feeder (1) passes through the outer tube (11) and is connected to the inner tube (13), and the fuel is fed into the inner tube. The fuel feed port of the inner tube (13) is provided with a zoom-shaped throat structure, which accelerates the air flow rate to form a local negative pressure, and the fuel is sucked in through the local negative pressure to prevent air leakage.

3. The back-blowing internal circulating fluidized bed circular boiler furnace according to claim 1, characterized in that: A plurality of ash discharge holes are evenly arranged along the circumference of the furnace bottom (7), and each ash discharge hole is connected to a corresponding slag discharge pipe (5) for discharging bottom slag produced by combustion.

4. The back-blowing internal circulating fluidized bed circular boiler furnace according to claim 1, characterized in that: The air outlet of the outer tube (11) is located at the bottom (7) of the furnace, and the air outlet of the inner tube (13) is located in the middle of the furnace. Air flows out from the outlet and is sprayed to the lower part of the furnace, thereby enhancing the disturbance between the gas and the solid fuel, supplementing the required oxygen, and strengthening the combustion.

5. The back-blowing internal circulating fluidized bed circular boiler furnace according to claim 4, characterized in that: The concentric structure of the outer tube (11) and the inner tube (13) is fixed by welding via a plurality of fixing brackets (14) made of high temperature resistant steel to maintain coaxiality.

6. The back-blowing internal circulating fluidized bed circular boiler furnace according to claim 5, characterized in that: The furnace wall around the furnace is provided with a lower water-cooled wall (9) and a lower water-cooled wall header (4) at a height position at the outlet of the inner tube (13); the furnace wall around the furnace is provided with an upper water-cooled wall (10) and a middle header (3) at a height position at the outlet of the outer tube (11); the middle header (3) and the water-cooled jacket (12) are connected by a middle header pipe (19); an upper header (2) is arranged at the outlet of the working medium at the upper part of the upper water-cooled wall (10); the upper header (2) and the water-cooled jacket (12) are connected by an upper header pipe (17); the upper header pipe (17) and the middle header pipe (19) not only connect the heating surface to realize the natural circulation flow of the working medium, but also are used to fix and support the position of the concentric pipe (8) in the furnace.

7. The back-blowing internal circulating fluidized bed circular boiler furnace according to claim 6, characterized in that: The lower water-cooled wall (9) is a light tube water-cooled wall or a membrane water-cooled wall, which absorbs the heat in the furnace.

8. The back-blowing internal circulating fluidized bed circular boiler furnace according to claim 1, characterized in that: It also comprises a flue gas outlet pipe (3), wherein the furnace flue gas outlet pipe (3) is arranged at the upper part of the furnace, and after the fuel at the upper part of the furnace is burned out, fly ash is formed and flows out of the furnace through the flue gas outlet pipe (3), and the boiler outlet is connected to the flue, and an evaporation heating surface and a superheater are arranged inside the flue to absorb the heat of the flue gas.

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