A stable material return device for a circulating fluidized bed

Abstract

The present invention discloses a stable return feeding device for a circulating fluidized bed, which includes a riser pipe, a feeding chamber, a return feeding chamber, a slag discharge pipe, an ash discharge pipe, a wind cap type air distribution plate, a purging air pipe, etc. The return feeding chamber is connected to a gasifier, the feeding chamber is connected to a gas-solid separator through the riser pipe, the bottom of the return feeding chamber and the feeding chamber are connected and communicated, a purging air pipe and a slag discharge pipe are respectively arranged at both ends of the communicating area, a continuous and inclined wind cap type air distribution plate is arranged below the return feeding chamber and the feeding chamber, the air distribution plate is respectively connected to a fluidizing air chamber and a loosening air chamber, a material supplement pipe is connected above the riser pipe, and a plurality of pressure measuring pipes are arranged on the walls of the riser pipe and the feeding chamber. The structure of the present invention is simple. By means of the method of combining ash and slag separation and discharge with appropriate material supplement, the risks of blockage and gas leakage at the return feeding position are reduced, the controllability and stability of the return feeding device are improved, and it can be applied to circulating fluidized beds using various raw materials such as inferior coal and biomass, and the continuous and stable operation ability of the return feeding device is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of circulating fluidized bed, and in particular to a stable return feeding device for a circulating fluidized bed. Background Art

[0002] Circulating fluidized bed gasification technology is a rapidly developing clean energy technology, which has the advantages of strong raw material adaptability (inferior coal, biomass, etc. can be used), high carbon conversion rate, low pollutant emissions, and good load regulation. Its operating characteristic is that the fuel circulates multiple times in the circulating fluidized bed, fully reacts and gasifies, realizing the efficient conversion of solid raw materials into combustible gases.

[0003] The return feeding device is one of the important components of the circulating fluidized bed gasification system. The return feeding device and the gas-solid separator are the key equipment for the dynamic balance and stable operation of the material balance of the entire circulating fluidized bed, and are crucial for the solid circulation, heat transfer, bed temperature, and gasification of the boiler. The material balance of common return feeding devices is mainly controlled by the air supply volume of the fluidizing air and the loosening air, as well as the separation efficiency of the gas-solid separator. Due to the large circulation ratio of the circulating fluidized bed and the relatively high temperature of the circulating material, a non-mechanical valve is generally used as the return feeding device, and the U-shaped valve is a commonly used return feeding device in the circulating fluidized bed.

[0004] Currently, the return feeding devices of circulating fluidized beds generally lack internal monitoring means, and operators cannot adjust the air volumes of the fluidizing air and the loosening air in a timely manner to balance the material quantity in the return feeding device. If the conveying rate of the return feeding device to the gasification furnace is too small, one possibility is that a large amount of circulating material retained in the return feeding device returns to the gasification furnace, causing bed pressure fluctuations or bed collapse, and another possibility is that the return feeding device is blocked and can only be shut down for treatment; if the conveying rate of the return feeding device to the gasification furnace is too large, since the stacking height of the circulating material in the return feeding device decreases, it is extremely easy to cause reverse gas flow to form a short circuit. The reverse gas flow carries the material in the gasification furnace and accumulates in the loop seal, where gasification, combustion and other reactions occur, and in severe cases, it causes overheating and coking of the return feeding device. When the return feeding device fails to work, the circulating material is no longer fed into the gasification furnace, and the internal reaction of the gasification furnace begins to be disordered, seriously affecting the normal operation of the circulating fluidized bed.

[0005] The setting of the intake parameters of the return feeding device and the adjustment during operation are a difficult point in the experimental and production processes. The design of the return feeding device mainly needs to consider the following two aspects. One is that the raw materials of the circulating fluidized bed gasification system mainly include coal and biomass. The components and particle sizes of different coal types and different biomass raw materials are different, and the material density and bulk density of the materials accumulated at the return feeding device after reaction are also different. The other is that according to different designed solid circulation rates, the gas flow velocities in the circulating fluidized bed are different, and the separation efficiency of the gas-solid separator will also be affected, and correspondingly, the material inlet rate at the return feeder will also be affected.

[0006] During the continuous operation of the circulating fluidized bed gasification system, the return device continuously receives the high-temperature carbon-containing materials separated by the separator. However, there are a large number of dead zones on the side walls and at the bottom of the U-valve. Therefore, slagging and coking are likely to occur in the dead zones of the U-valve during continuous operation, affecting the return rate of the return device. If not dealt with and cleared in time, blockages will form. For complex circulating fluidized beds with multiple return devices, there are systematic deviations in the pressure differences between each return device and the furnace due to different positions, resulting in a continuous slow increase or continuous slow decrease in the height of the material column in the riser connected to the return device, making the particle circulation flux unstable, and then phenomena such as blockages or gas leakage occur. Once these serious faults occur, in common return device designs, the circulating fluidized bed often needs to be frequently started and stopped, and the return device needs to be disassembled to clean the blockage or refill the material to achieve the ideal height of the material column accumulation. Summary of the Invention

[0007] The purpose of the present invention is to provide a return device for a circulating fluidized bed that operates continuously and stably, has a low failure rate, and is easy to maintain, aiming at the common problems of slagging, coking, blockage, and gas leakage in the return device of the circulating fluidized bed in the prior art and the lack of monitoring means for the material accumulation condition at the return device.

[0008] To solve the above technical problems, the present invention provides the following technical solutions:

[0009] A stable return device for a circulating fluidized bed, characterized in that it includes a feeding chamber, a return chamber, a fluidizing air chamber, a loosening air chamber, a slag discharge pipe, an ash discharge pipe, a wind cap type air distribution plate, and a purging air pipe;

[0010] The bottoms of the feeding chamber and the return chamber are interconnected at the bottom to form a U-shaped structure. The inlet end of the feeding chamber is connected to a gas-solid separator through a riser, and the outlet end of the return chamber is connected to a gasifier;

[0011] The loosening air chamber is connected to the bottom of the feeding chamber, the fluidizing air chamber is connected to the bottom of the return chamber, the wind cap type air distribution plate is disposed through between the fluidizing air chamber and the return chamber, and between the loosening air chamber and the feeding chamber. The fluidizing air chamber provides fluidizing air to the return chamber through the wind cap type air distribution plate, and the loosening air chamber provides loosening air to the feeding chamber through the wind cap type air distribution plate;

[0012] The slag discharge pipe is disposed at the bottom of the return chamber near the gasifier side, and the connection between the slag discharge pipe and the return chamber is close to the wind cap type air distribution plate, for discharging the coke slag in the device;

[0013] The ash discharge pipe includes a first ash discharge pipe and a second ash discharge pipe. The first ash discharge pipe is disposed at the bottom of the loosening air chamber, and the second ash discharge pipe is disposed at the bottom of the fluidizing air chamber, for discharging the ash in the device;

[0014] The purging air duct is arranged on the feeding chamber or the return feeding chamber and is used to purge the coke dregs in the device into the slag discharging pipe.

[0015] Furthermore, the air cap type air distribution plate includes a first air distribution area and a second air distribution area. The first air distribution area is located between the loosening air chamber and the feeding chamber, and the second air distribution area is located between the fluidization air chamber and the return feeding chamber. The area ratio of the first air distribution area to the second air distribution area is equal to the cross-sectional area ratio of the feeding chamber to the return feeding chamber.

[0016] Furthermore, the included angle between the air cap type air distribution plate and the horizontal plane is 5 - 10°, and the inclination direction is towards the slag discharging pipe.

[0017] Furthermore, air caps are arranged on the first air distribution area and the second air distribution area, and the air caps are arranged in in-line or staggered arrangement.

[0018] Furthermore, the purging air duct includes a plurality of first purging air ducts and second purging air ducts. The first purging air ducts are arranged on the wall surface of the feeding chamber on the side far from the return feeding chamber and are arranged parallel to the air cap type air distribution plate. The second purging air ducts are horizontally arranged at the side wall connection of the feeding chamber and the return feeding chamber.

[0019] Furthermore, at least two first purging air ducts are provided. The first purging air ducts on both sides are 1 - 5 cm away from the edge of the wall surface of the feeding chamber. The air outlets of the first purging air ducts and the second purging air ducts are 1 - 5 cm higher than the air cap type air distribution plate.

[0020] Furthermore, simple directional air caps are installed at the air outlets of the first purging air ducts and the second purging air ducts. The purging gas is nitrogen or carbon dioxide, and the purging wind speed is 30 - 50 m / s.

[0021] Furthermore, at least three groups of pressure measuring pipes are included. The pressure measuring pipes are uniformly distributed obliquely downward on the riser pipe and the wall surface of the feeding chamber on the side far from the return feeding chamber, and the included angle with the vertical direction is 30 - 60°. The pressure measuring pipe at the lowest position is 5 - 10 cm higher than the air cap type air distribution plate, and the pressure measuring pipe at the highest position is 5 - 10 cm higher than the designed material column height.

[0022] Furthermore, a material supplement pipe is included. The material supplement pipe is arranged on the riser pipe and is higher than the uppermost pressure measuring pipe.

[0023] Furthermore, an electric slag discharging valve is arranged on the slag discharging pipe, and an electric ash discharging valve is arranged on the ash discharging pipe.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. For the return device of a circulating fluidized bed, the material accumulation height in the feeding chamber and the riser affects the pressure drop between the bottom of the material column and the upper end of the riser. To calculate the accurate pressure drop, the currently mature methods mainly include the radioactive tracer particle method, the aeration method, the heat balance method, the pressure drop method, and the wall surface velocity observation method. However, to obtain accurate material column accumulation height, solid flow rate, and particle flow rate, it is often necessary to combine the above methods for comprehensive measurement and calculation, resulting in relatively high installation costs and complex installation methods. The method of closely arranged pressure measurement pipelines proposed in the present invention can, when the material flow rate of the return device is not too large, well and intuitively observe the interval where the material column height is located through the change in pressure drop. When there is a risk of blockage due to the continuous increase in the material column height or a risk of gas leakage due to the continuous decrease in the material column height, it can timely remind the staff to adjust the operating parameters, enabling the return device to operate continuously and stably.

[0026] 2. For the return device of a circulating fluidized bed, the traditional slag discharge device is usually installed in the center of the air distribution plate, and the slag discharge pipe is at a low point. Even with the installation of purging air, it is very difficult to completely blow the coke slag that is likely to cause blockage into the slag discharge pipeline. The present invention adopts a comprehensive solution of an inclined air distribution plate, directional purging air combined with a side wall slag discharge port. The slag discharge port is located at the center position of the wall surface. The inclined air distribution plate utilizes the gravitational potential energy to facilitate the concentration of coke slag at the slag discharge port. The two-stage arrangement of the purging air achieves full coverage of the areas where slagging and coking may occur, and the purging air directly blows the coke slag into the slag discharge port, greatly improving the slag discharge efficiency of the return device. The slag discharge pipe is arranged on the side of the return chamber close to the gasifier, and the flow direction of the coke slag is the same as that of the material flow, which is also conducive to the aggregation of coke slag near the slag discharge pipe orifice. At the same time, the air distribution plate no longer needs to leave space for the slag discharge port, and the air distribution efficiency will also be improved. In addition, after long-term operation, part of the ash flows into the air chamber through the air distribution plate, and the accumulation of ash in the air chamber will cause blockage of the air chamber. However, this situation is avoided by arranging regularly opened ash discharge pipes in the fluidizing air and the loosening air chamber. The above solutions can greatly reduce the blockage risk at the return device.

[0027] 3. For the return device of a circulating fluidized bed, in the case of using the traditional structure, once the risk of gas leakage occurs, it is very difficult for the unit to continue operating. It is necessary to stop the machine in time and open the return device to refill the material to achieve the ideal material column accumulation height. Otherwise, a violent chemical reaction will occur in the return device and damage the device. The present invention adopts the method of adding a material replenishment pipe to the riser and estimates the material column accumulation height in combination with the change in pressure drop. New materials can be replenished in time through the material replenishment pipe, and materials can be replenished in time before the material column continuously drops and gas leakage occurs, realizing the dynamic stability of the material column height. Even in extreme cases where the risk of gas leakage has occurred, materials can also be replenished in time through the material replenishment pipe to re-achieve the ideal material column accumulation height, balance the pressure drop, and cooperate with the timely adjustment of the fluidizing air to block the gas leakage phenomenon and protect the safety of the device.

[0028] 4. Circulating fluidized bed gasification devices are known for their good raw material adaptability. However, different coal types and different biomass raw materials have different compositions and particle sizes, and the material density and bulk density of the materials accumulated at the return device after the reaction are also different. Through the above technical solutions, a simple structure and operation strategy are used to propose a return device that can operate continuously and stably. By increasing the fine-tuning means of the return device, the adaptability of the return device to different raw materials is improved, the adaptability of the return device to complex fluidized bed structures is enhanced, the risk of blockage and gas leakage faults is reduced, and the operating cost of the return device is reduced. Brief Description of the Drawings

[0029] Figure 1 It is the front view of the structure of the embodiment of the present invention;

[0030] Figure 2 It is a partial schematic view of the air cap type air distribution plate of the embodiment of the present invention;

[0031] Figure 3 It is the top view of the structure of the embodiment of the present invention;

[0032] Figure 4 It is Figure 1 The partial enlarged view at A in

[0033] Figure 5 It is Figure 1 The partial enlarged left view at B in

[0034] Wherein: 1 - riser; 2 - feeding chamber; 3 - return chamber; 4 - second purge air duct; 5 - fluidizing air chamber inlet; 6 - fluidizing air chamber; 7 - slag discharge pipe; 8 - electric slag discharge valve; 9 - second ash discharge pipe; 10 - electric ash discharge valve; 11 - material supplement pipe; 12 - first ash discharge pipe; 13 - loosening air chamber; 14 - loosening air chamber inlet; 15 - air cap type air distribution plate; 16 - first purge air duct; 17 - pressure measuring pipeline; 18 - first air distribution area, 19 - second air distribution area, 20 - air cap. Detailed Embodiment

[0035] To deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with the drawings. This embodiment is only used to explain the present invention and does not constitute a limitation to the protection scope of the present invention.

[0036] Figure 1 A specific embodiment of a stable return device for a circulating fluidized bed is shown, including a riser 1, a feeding chamber 2, a return chamber 3, a fluidizing air chamber 6, a loosening air chamber 13, a slag discharge pipe 7, a first ash discharge pipe 12, a second ash discharge pipe 9, an air cap type air distribution plate 15, a material supplement pipe 11, a first purge air duct 16, a second purge air duct 4 and a pressure measuring pipeline 17.

[0037] The bottom between the feeding chamber 2 and the return material chamber 3 is interconnected to form a U-shaped structure. The outlet of the return material chamber 3 is connected to the gasifier. The inlet of the feeding chamber 2 is connected to the gas-solid separator through the riser 1. A continuous wind cap type air distribution plate 15 is arranged below the return material chamber 2 and the feeding chamber 3. The fluidization air chamber 6 provides fluidization air to the return material chamber 3 through the fluidization air chamber air inlet 5 and the wind cap type air distribution plate 15. The loosening air chamber 13 provides loosening air to the feeding chamber 2 through the loosening air chamber air inlet 14 and the wind cap type air distribution plate 15.

[0038] The slag discharge pipe 7 is arranged at the position where the wind cap type air distribution plate 15 is connected to the bottom of the wall of the return material chamber 3. The first ash discharge pipe 12 and the second ash discharge pipe 9 are respectively connected to the bottom of the loosening air chamber 13 and the fluidization air chamber 6.

[0039] The first purge air pipe 16 is arranged on the wall of the feeding chamber 2 on the side far from the return material chamber. The direction is parallel to the wind cap type air distribution plate 15 and faces the passage opening of the slag discharge pipe 7. The second purge air pipe 4 is horizontally arranged on the side wall at the connection of the return material chamber 3 and the feeding chamber 2.

[0040] Three groups of pressure measuring pipes 17 are uniformly distributed on the wall of the riser 1 and the feeding chamber 2 on the side far from the return material chamber 3 in an inclined downward direction, and the included angle with the vertical direction is 30 - 60°. The pressure measuring pipe 17 at the lowest position is 5 - 10 cm higher than the wind cap type air distribution plate 5, and the pressure measuring pipe 17 at the highest position is 5 - 10 cm higher than the designed material column height.

[0041] The material supplement pipe 11 is arranged on the riser 1 and is higher than the uppermost pressure measuring pipe 17.

[0042] As Figure 2 shown, the wind caps are arranged in-line or staggered on the wind cap type air distribution plate 15. The wind cap type air distribution plate 15 is divided into a first air distribution area 18 and a second air distribution area 19, which are respectively connected to the loosening air chamber 13 and the fluidization air chamber 6. The area ratio of the two areas is the same as the cross-sectional area ratio of the channels of the feeding chamber 2 and the return material chamber 3. The angle between the wind cap type air distribution plate 15 and the horizontal plane is 5 - 10°, and the inclined direction faces the slag discharge pipe 7. A certain angle of inclination helps the material to flow from the feeding chamber 2 to the return material chamber 3, and at the same time also helps the coke slag to gather towards the slag discharge pipe 7 under the action of the purge air.

[0043] The slag discharge pipe 7 is located at the bottom of the wall surface of the return chamber 3 near the gasifier side and is in the central position of the wall surface. The first ash discharge pipe 12 and the second ash discharge pipe 9 are respectively located at the exact center of the bottom of the loose air chamber 13 and the exact center of the bottom of the fluidized air chamber 6. An electric slag discharge valve 8 is provided on the slag discharge pipe, and electric ash discharge valves 10 are provided on the first ash discharge pipe 12 and the second ash discharge pipe 9. The electric slag discharge valve 8 is synchronously opened when the purging air is turned on, and periodically discharges the ash and slag carried out by the purging air to prevent the return device from being blocked. The electric ash discharge valve 10 is periodically opened to discharge the ash accumulated in the fluidized air chamber 6 and the loose air chamber 13, and the opening interval is determined by the amount of ash generated after the gasification of the fluidized bed gasification raw material and the amount of ash flowing into the fluidized air chamber 6 and the loose air chamber 13 through the air cap type air distribution plate 15 during actual operation.

[0044] As Figure 3 shown, there are two first purging air pipes 16, which are arranged on the wall surface of the feeding chamber 2 on the side far from the return chamber 3 and are arranged parallel to the air cap type air distribution plate 15; there are two second purging air pipes 4, which are symmetrically and horizontally arranged at the connection of the side walls of the feeding chamber 2 and the return chamber 3. Among them, the first purging air pipe 16 is 1-5 cm away from the edge of the wall surface of the feeding chamber 2, and the air outlets of the first purging air pipe 16 and the second purging air pipe 4 are about 1-5 cm higher than the air cap type air distribution plate 15. The direction of the purging air introduced into the first purging air pipe 16 is parallel to the air cap type air distribution plate 15, and the direction of the purging air introduced into the second purging air pipe 4 is horizontal. The air outlets of the first purging air pipe 16 and the second purging air pipe 4 are about 1-5 cm higher than the air caps 20 on the air cap type air distribution plate 15. According to needs, when the area of the air cap type air distribution plate 15 is large, after arranging two purging air outlets close to the edge, the first purging air pipe 16 can add evenly spaced purging air outlets in the horizontal direction with the same height to achieve full coverage of the possible coking and slagging positions in the return device; when the channel between the feeding chamber 2 and the return chamber 3 is long, evenly spaced second purging air pipes 4 can be added along the connection of the return chamber 3 and the feeding chamber 2 to achieve full coverage of the possible coking and slagging positions in the return device.

[0045] The first purging air pipe 16 and the second purging air pipe 4 are periodically opened, and the opening interval is determined by the slagging rate of the selected gasification raw material in the return device. The electric slag discharge valve 8 is synchronously opened with the purging air to smoothly discharge the coke slag accumulated by the purging air. The second condition for the first purging air pipe 16 and the second purging air pipe 4 to be opened is that the height of the material column in the feeding chamber 3 and the riser 2 exceeds the ideal material column height range and there is a risk of blockage. At this time, the purging air and the electric slag discharge valve 8 are opened to discharge the excess material, reduce the height of the material column, and avoid blockage. The third condition for the first purging air pipe 16 and the second purging air pipe 4 to be opened is that the return device has pulsating return or is blocked. At this time, the purging air and the electric slag discharge valve 8 are opened, and at the same time, the fluidization air volume of the fluidized air chamber 6 is increased, and the loose air volume of the loose air chamber 13 is reduced to avoid gas leakage at this time.

[0046] As shown Figure 3 , Figure 4 in the figure, simple directional air caps partially wrapping the blowing openings of the first blowing air duct 16 and the second blowing air duct 4 are installed, which can protect the first blowing air duct 16 and the second blowing air duct 4 from being scoured by the materials discharged from the return device, enabling them to operate continuously and stably. The blowing air gas introduced into the first blowing air duct 16 and the second blowing air duct 4 can be nitrogen or carbon dioxide gas, and the wind speed is 30 - 50 m / s.

[0047] As shown Figure 1 in the figure, at least three pressure measuring pipes 17 are densely arranged on the wall surfaces of the feeding chamber 2 and the riser 1 on the side far from the return chamber 3. They are all located on the central axis of the device wall surface, evenly distributed in the height direction, and the height of the lowest pressure measuring pipe 17 is about 5 - 10 cm higher than that of the air cap type air distribution plate 15, and the height of the highest pressure measuring pipe 17 is 5 - 10 cm higher than the designed and calculated height of the material column. In the case where the designed height of the material column is on the high side or there is a need for a more accurate estimation of the height of the material column, several pressure measuring pipes 17 with uniform intervals can be added on the wall surface within the height range of the material column. The included angle between the pressure measuring pipe 17 and the vertical direction is 30 - 60°, facing obliquely downward. The method for estimating the height of the material column is mainly based on the fact that the pressure drop within the height range of the material column is relatively large, while the pressure drop in the area without material column accumulation above the riser 1 is relatively small. By densely arranging pressure measuring pipes within the ideal height range of the material column, the height range where the material column is located is estimated through the change of the pressure drop. The method for estimating the height of the material column has good practical effects when the material flux at the return device is stable.

[0048] As shown Figure 1 in the figure, the material supplement pipe 11 is connected to the wall surface of the riser 1, and its height is higher than the highest pressure measuring pipe 17 on the wall surface. The first condition for opening the material supplement pipe 11 is that when the height of the material column accumulation in the feeding chamber 3 and the riser 2 continuously decreases and there is a risk of gas leakage, the material supplement pipe 11 is opened to increase the height of the material column, balance the pressure drop, and stabilize the return material cycle. The second condition for opening the material supplement pipe 11 is that after the first blowing air duct 16 and the second blowing air duct 4 are opened, when the height of the material column accumulation in the feeding chamber 3 and the riser 2 is lower than the ideal height of the material column accumulation, the material supplement pipe 11 is opened to increase the height of the material column, balance the pressure drop, and stabilize the return material cycle. The third condition for opening the material supplement pipe 11 is that when a gas leakage fault occurs, the material supplement pipe 11 is opened to re - accumulate materials in the feeding chamber 3 and the riser 2, block the gas leakage fault, and protect the safety of the device.

[0049] The specific operation process of the above embodiments is as follows: Before the return material device starts to operate, open the material supplement pipe 11 to fill the return material device; when the return material device starts to operate, open the fluidization air chamber 6 and the loosening air chamber 13 for ventilation; after the return material device operates continuously for a period of time, open the first purge air pipe 16, the second purge air pipe 4 and the electric slag discharge valve 7, close them after opening for a period of time, and open the material supplement pipe 11 to restore the stacking height of the material column. After the return material device operates continuously for a period of time, start the electric ash discharge valve 10 and close it after opening for a period of time; when a blockage occurs, open the first purge air pipe 16, the second purge air pipe 4 and the electric slag discharge valve 7, close them after opening for a period of time, and open the material supplement pipe 11 to restore the stacking height of the material column; when air leakage occurs, open the material supplement pipe 11 to restore the stacking height of the material column.

[0050] The above specific implementation manners are only for illustrating the technical concept and structural features of the present invention, aiming to enable those skilled in the art to implement it accordingly. However, the above content does not limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A stable return device for a circulating fluidized bed, characterized in that: It includes a feeding chamber (2), a return material chamber (3), a fluidizing air chamber (6), a loosening air chamber (13), a slag discharge pipe (7), an ash discharge pipe, a wind cap type air distribution plate (15), and a purging air pipe; The bottoms between the feeding chamber (2) and the return material chamber (3) are interconnected at the bottom to form a U-shaped structure. The inlet end of the feeding chamber (2) is connected to a gas-solid separator through a riser pipe (1), and the outlet end of the return material chamber (3) is connected to a gasifier; The loosening air chamber (13) is connected to the bottom of the feeding chamber (2), the fluidizing air chamber (6) is connected to the bottom of the return material chamber (3), the wind cap type air distribution plate (15) is disposed through between the fluidizing air chamber (6) and the return material chamber (3), and between the loosening air chamber (13) and the feeding chamber (2). The fluidizing air chamber (6) provides fluidizing air to the return material chamber (3) through the wind cap type air distribution plate (15), and the loosening air chamber (13) provides loosening air to the feeding chamber (2) through the wind cap type air distribution plate (15); The slag discharge pipe (7) is disposed at the bottom of the return material chamber (3) near the gasifier side, and the connection between the slag discharge pipe (7) and the return material chamber (3) is close to the wind cap type air distribution plate (15) for discharging the coke slag in the device; The ash discharge pipe includes a first ash discharge pipe (12) and a second ash discharge pipe (9). The first ash discharge pipe (12) is disposed at the bottom of the loosening air chamber (13), and the second ash discharge pipe (9) is disposed at the bottom of the fluidizing air chamber (6) for discharging the ash in the device; The purging air pipe is disposed on the feeding chamber (2) or the return material chamber (3) for purging the coke slag in the device into the slag discharge pipe (7); It further includes a material supplement pipe (11) and at least three groups of pressure measuring pipes (17). The pressure measuring pipes (17) are uniformly distributed obliquely downward on the riser pipe (1) and the wall surface of the feeding chamber (2) away from the return material chamber (3) side, and the included angle with the vertical direction is 30 - 60°. The pressure measuring pipe (17) at the lowest position is 5 - 10 cm higher than the wind cap type air distribution plate (15), and the pressure measuring pipe (17) at the highest position is 5 - 10 cm higher than the designed material column height. The material supplement pipe (11) is disposed on the riser pipe (1) and is higher than the uppermost pressure measuring pipe (17).

2. The stable return device for a circulating fluidized bed according to claim 1, wherein: The wind cap type air distribution plate (15) includes a first air distribution area (18) and a second air distribution area (19). The first air distribution area (18) is located between the loosening air chamber (13) and the feeding chamber (2), and the second air distribution area (19) is located between the fluidizing air chamber (6) and the return material chamber (3). The area ratio of the first air distribution area (18) to the second air distribution area (19) is equal to the cross-sectional area ratio of the feeding chamber (2) to the return material chamber (3).

3. The stable return device for a circulating fluidized bed according to claim 2, characterized in that: The included angle between the wind cap type air distribution plate (15) and the horizontal plane is 5 - 10°, and the inclined direction is towards the slag discharge pipe (7).

4. The stable return device for a circulating fluidized bed according to claim 2, wherein: Wind caps (20) are disposed on the first air distribution area (18) and the second air distribution area (19), and the wind caps (20) are arranged in a staggered or in-line pattern.

5. The stable return device for a circulating fluidized bed according to claim 1, characterized in that: The purging air duct includes a plurality of first purging air ducts (16) and second purging air ducts (4). The first purging air ducts (16) are arranged on the wall surface of the feeding chamber (2) on the side far from the return material chamber (3), and are arranged parallel to the air cap type air distribution plate (15). The second purging air ducts (4) are horizontally arranged at the side wall connection of the feeding chamber (2) and the return material chamber (3).

6. The stable return device for a circulating fluidized bed according to claim 5, characterized in that: There are at least two first purging air ducts (16). The first purging air ducts (16) on both sides are 1-5 cm away from the edge of the wall surface of the feeding chamber (2). The air outlets of the first purging air ducts (16) and the second purging air ducts (4) are 1-5 cm higher than the air cap type air distribution plate (15).

7. The stable return device for a circulating fluidized bed according to claim 5, characterized in that: Simple directional air caps are installed at the air outlets of the first purging air ducts (16) and the second purging air ducts (4). The purging gas is nitrogen or carbon dioxide, and the purging wind speed is 30-50 m / s.

8. The stable material return device for a circulating fluidized bed according to claim 1, characterized in that: An electric slag discharge valve (8) is arranged on the slag discharge pipe (7), and an electric ash discharge valve (10) is arranged on the ash discharge pipe.

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