A secondary air supply system for a CFB boiler

Abstract

A secondary air supply system for a CFB boiler includes a secondary air supply piping system and a secondary air supply nozzle layout structure. The second secondary air supply piping system has a U-shaped structure, surrounding the furnace body, with its connecting transition section arranged parallel to the furnace body rear wall. The first secondary air supply piping system has a T-shaped structure, with its transverse pipe section sealed at both ends, and is arranged parallel to the furnace body front wall. The sum of the cross-sectional areas of the two ends of the second secondary air supply piping is the same as the cross-sectional area of the longitudinal pipe section of the first secondary air supply piping, and the piping system is connected in parallel to the outlet end of the air preheater. The nozzle layout structure includes a first group of nozzles arranged on the front wall and a second group of nozzles arranged on the rear wall, which are symmetrically distributed along the front-to-back direction of the furnace body. Each nozzle of the first group of nozzles is connected in parallel to the transverse pipe section, and each nozzle of the second group of nozzles is connected in parallel to the transition connection section. The present invention has a simple structure and low maintenance costs, and can fundamentally solve the wear problem caused by dust scouring the furnace.

Description

Technical Field

[0001] The present invention relates to the field of chemical industry, and in particular to a secondary air supply system of a CFB boiler. Background Art

[0002] CFB boiler is a biomass circulating fluidized bed boiler. It has gradually attracted the attention of various countries due to its unique advantages that other combustion technologies cannot match in terms of fuel replacement, waste treatment and environmental protection.

[0003] The front and rear walls of the CFB boiler furnace are equipped with multiple nozzles to provide preheated secondary air into the furnace. Figure 1 At present, the secondary air duct passing through the air preheater is surrounded on the rear wall of the furnace to provide preheated secondary air to each nozzle on the rear wall, and a pipe is connected in parallel to the secondary air duct to surround the front wall of the furnace to provide preheated secondary air to each nozzle on the front wall.

[0004] This structure of the air supply pipe leads to unbalanced outlet pressure and flow of the nozzles on the front and rear walls, causing the dust generated in the furnace to flush the front or rear wall of the furnace for a long time, causing wear on the inner wall of the furnace and seriously reducing the service life of the CFB boiler.

[0005] Currently, complex calculations are usually performed based on the outlet pressure and flow rate of different nozzles, and these nozzles are arranged in an irregular staggered manner on the front wall or rear wall. This leads to complex design of CFB boilers, high maintenance costs, and difficulty in fundamentally solving the problem of wear on the inner wall of the furnace due to erosion.

[0006] Therefore, how to design a scientific and reasonable secondary air supply system is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0007] The purpose of the present invention is to address the deficiencies of the existing technology and provide a secondary air supply system for a CFB boiler, which has a simple structure and low maintenance cost. On the basis of providing stable and uniform secondary air, it can stabilize the flue gas flow field, reduce turbulence, and fundamentally solve the wear problem caused by dust scouring the furnace.

[0008] The technical solution of the present invention is: a secondary air supply system of a CFB boiler, including a secondary air supply pipeline system and a secondary air supply nozzle layout structure, the secondary air supply pipeline system includes a first secondary air supply pipeline and a second secondary air supply pipeline that are independent of each other, the second secondary air supply pipeline is in a U-shaped structure, the second secondary air supply pipeline in the U-shaped structure semi-surrounds the furnace body, the connecting transition section of the second secondary air supply pipeline in the U-shaped structure is arranged in parallel with the rear wall of the furnace body, the first secondary air supply pipeline is in a T-shaped structure, the transverse pipe section of the first secondary air supply pipeline in the T-shaped structure is sealed at both ends, and is arranged in parallel with the front wall of the furnace body, the sum of the cross-sectional areas at both ends of the second secondary air supply pipeline is the same as the cross-sectional area of the longitudinal pipe section of the first secondary air supply pipeline, and the second secondary air supply pipeline is in a T-shaped structure. Both ends of the air supply duct and the longitudinal pipe sections of the first and secondary air supply ducts are connected in parallel at the outlet end of the air preheater. The secondary air supply nozzle layout structure includes a first group of nozzles arranged on the front wall of the furnace body and a second group of nozzles arranged on the rear wall of the furnace body. The number of nozzles in the first group of nozzles is the same as the number of nozzles in the second group of nozzles, and they are symmetrically distributed along the front and rear directions of the furnace body. The nozzles of the first group of nozzles are arranged in at least one row and are symmetrically distributed along the left and right directions of the furnace body. The air outlet ends of the nozzles of the first group of nozzles are tilted downward toward the rear wall of the furnace body, and the inclination angle is 19-21°. The air inlet ends of the nozzles of the first group of nozzles are connected in parallel to the horizontal pipe section of the first and secondary air supply ducts, and the air inlet ends of the nozzles of the second group of nozzles are connected in parallel to the transition connection section of the second and secondary air supply ducts.

[0009] The horizontal pipe section of the first secondary air supply duct is fixed on the front wall of the furnace body by a plurality of first fixing parts and has a spacing space, and the connecting transition section of the second secondary air supply duct is fixed on the rear wall of the furnace body by a plurality of second fixing parts and has a spacing space.

[0010] The sum of the cross-sectional area of the longitudinal pipe section of the first and second air supply pipelines and the cross-sectional area of both ends of the second secondary air supply pipeline is adapted to the outlet end area of the air preheater.

[0011] The two ends of the second secondary air supply pipeline are respectively connected to both sides of the outlet end of the air preheater, and the longitudinal pipe section of the first secondary air supply pipeline is connected to the middle of the outlet end of the air preheater and is located between the two ends of the second secondary air supply pipeline.

[0012] The air outlet ends of the first group of nozzles and the second group of nozzles are all of reduced diameter and flush with the front wall or the rear wall of the furnace body.

[0013] The distribution density of the first group of nozzles and the second group of nozzles gradually decreases from the symmetrical center in the left-right direction of the furnace body to both sides.

[0014] The above technical solution has the following beneficial effects:

[0015] 1. The secondary air supply system of the CFB boiler includes a secondary air supply pipeline system and a secondary air supply nozzle layout structure, wherein the secondary air supply pipeline system is used to provide secondary air with a stable flow rate and a stable flow rate to the secondary air supply nozzle layout structure, and the secondary air supply nozzle layout structure is used to evenly distribute the secondary air delivered by the secondary air supply pipeline system. The secondary air supply pipeline system includes a first secondary air supply pipeline and a second secondary air supply pipeline that are independent of each other, which independently provide secondary air to the nozzles on the front wall of the furnace body and the nozzles on the rear wall of the furnace body. The second secondary air supply pipeline is a U-shaped structure, and the second secondary air supply pipeline with a U-shaped structure semi-surrounds the furnace body. The connecting transition section of the second secondary air supply pipeline with a U-shaped structure is arranged in parallel with the rear wall of the furnace body. The second secondary air supply pipeline of this structure can be regarded as two L-shaped air supply pipelines connected face to face. The first and second air supply ducts are in a T-shaped structure. The transverse pipe sections of the first and second air supply ducts in the T-shaped structure are sealed at both ends and are arranged in parallel with the front wall of the furnace body. The first and second air supply ducts of this structure can be regarded as two L-shaped air supply ducts connected back to back. The sum of the cross-sectional areas of the two ends of the second secondary air supply duct is the same as the cross-sectional area of the longitudinal pipe section of the first secondary air supply duct. The two ends of the second secondary air supply duct and the longitudinal pipe section of the first secondary air supply duct are connected in parallel at the outlet end of the air preheater. That is, the secondary air volume received by the starting end (longitudinal pipe section) of the first secondary air supply duct is the same as the secondary air volume received by the starting end (the sum of the two ends) of the second secondary air supply duct, and the number and angle of the bending sections of the two are the same, and the wind resistance formed is also similar, which can effectively ensure that the secondary air flow rate and flow velocity at the transverse pipe section of the first secondary air supply duct are the same as the secondary air flow rate and flow velocity of the connecting transition section of the second secondary air supply duct. The secondary air supply nozzle layout structure includes a first group of nozzles located on the front wall of the furnace body and a second group of nozzles located on the rear wall of the furnace body. The number of nozzles in the first group of nozzles is the same as the number of nozzles in the second group of nozzles, and they are symmetrically distributed along the front-to-back direction of the furnace body. That is, each nozzle of the first group of nozzles located on the front wall corresponds to the second group of nozzles located on the rear wall. The nozzles of the first group of nozzles are arranged in at least one row and are symmetrically distributed along the left and right directions of the furnace body to avoid uneven distribution of secondary air along the left and right directions of the furnace body. The air outlet ends of each nozzle of the first group of nozzles are tilted downward toward the rear wall of the furnace body, and the tilt angle is 19-21 degrees.The air inlet ends of each nozzle of the first group of nozzles are connected in parallel to the horizontal pipe section of the first secondary air supply pipeline, and the air inlet ends of each nozzle of the second group of nozzles are connected in parallel to the transition connection section of the second secondary air supply pipeline. This design makes the flow rate and flow velocity of the secondary air delivered by each nozzle of the first group of nozzles and each nozzle of the second group of nozzles the same. These secondary air with the same flow rate and flow velocity but opposite directions are mixed in the middle of the CFB boiler furnace body, and the momentum is offset, which can effectively stabilize the flue gas flow field and reduce turbulence, and eliminate the rotating airflow of the secondary air at the center of the furnace body. On the basis of providing secondary air to the fuel in the furnace body, the problem of the secondary air delivered to the furnace driving the dust to wash the front wall or the rear wall of the furnace body and causing wear is fundamentally solved.

[0016] 2. The horizontal pipe section of the first secondary air supply duct is fixed on the front wall of the furnace body by a number of first fixing parts, and has a spacing space. The connecting transition section of the second secondary air supply duct is fixed on the rear wall of the furnace body by a number of second fixing parts, and has a spacing space, so as to ensure that the two independent secondary air supply ducts stably provide secondary air to the corresponding secondary air nozzles, reduce the influence of the furnace body on the independent secondary air supply ducts, and ensure that the secondary air speed of each secondary air nozzle is uniform.

[0017] 3. The air outlet ends of the first and second groups of nozzles are of reduced diameter and flush with the front or rear wall of the furnace body, which can effectively improve the penetration ability of the secondary air delivered to the furnace, so that the secondary air can be quickly distributed throughout the furnace, ensuring the combustion efficiency of the fuel in the furnace.

[0018] 4. The distribution density of the first and second groups of nozzles gradually decreases from the symmetrical center of the furnace body to both sides, so that the amount of secondary air delivered to the center of the furnace is larger, meeting the demand for higher combustion temperature in the center of the furnace.

[0019] The following is a further description with reference to the accompanying drawings and specific implementations. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the present invention;

[0021] Figure 2 A schematic diagram of the layout structure of the secondary air supply nozzles of the present invention;

[0022] Figure 3 This is a schematic diagram of the distribution of the secondary air supply nozzle layout structure on the rear wall of the furnace body of the present invention.

[0023] In the accompanying drawings, 1 is the secondary air supply pipeline system, 2 is the secondary air supply nozzle layout structure, 3 is the first secondary air supply pipeline, 31 is the horizontal pipe section, 32 is the longitudinal pipe section, 4 is the second secondary air supply pipeline, 41 is the connecting transition section, 5 is the first group of nozzles, 6 is the second group of nozzles, 7 is the first fixing member, and 8 is the second fixing member. DETAILED DESCRIPTION

[0024] In the present invention, the pipelines and parts are manufactured in accordance with the requirements of "Technical Specification for Design of Smoke, Air and Pulverized Coal Pipelines in Thermal Power Plants" DL / T5121-2000.

[0025] See also Figures 1 to 3, which is a specific embodiment of the secondary air supply system of a CFB boiler. The secondary air supply system of the CFB boiler includes a secondary air supply pipeline system 1 and a secondary air supply nozzle layout structure 2. The secondary air supply pipeline system 1 includes a first secondary air supply pipeline 3 and a second secondary air supply pipeline 4, which are independent of each other. The second secondary air supply pipeline 4 is a U-shaped structure, and the second secondary air supply pipeline 4 with a U-shaped structure semi-surrounds the furnace body. The connecting transition section 41 of the second secondary air supply pipeline with a U-shaped structure is arranged in parallel with the rear wall of the furnace body. Specifically, the connecting transition section 41 of the second secondary air supply pipeline is fixed on the rear wall of the furnace body by a plurality of second fixing members 8, and has a spacing space, and the length of the connecting transition section is adapted to the width of the rear wall of the furnace body. The first and second air supply ducts 3 have a T-shaped structure, and the two ends of the transverse pipe section 31 of the T-shaped first and second air supply ducts are sealed and arranged parallel to the front wall of the furnace body. Specifically, the transverse pipe section 31 of the first and second air supply ducts is fixed on the front wall of the furnace body by a plurality of first fixing members 7, and has an interval space, and the length of the transverse pipe section is adapted to the width of the front wall of the furnace body. The sum of the cross-sectional areas at both ends of the second secondary air supply duct is the same as the cross-sectional area of the longitudinal pipe section 32 of the first secondary air supply duct. The two ends of the second secondary air supply duct and the longitudinal pipe section of the first secondary air supply duct are connected in parallel at the outlet end of the air preheater. In this embodiment, the cross-sectional area of the longitudinal pipe section 32 of the first secondary air supply duct and the sum of the cross-sectional areas at both ends of the second secondary air supply duct are consistent with the outlet end area of the air preheater. The two ends of the second secondary air supply duct are respectively connected to the two sides of the outlet end of the air preheater. The longitudinal pipe section of the first secondary air supply duct is connected to the middle of the outlet end of the air preheater and is located between the two ends of the second secondary air supply duct. Specifically, the outlet size of the air preheater is 8368*1455*6mm, the cross-sectional size of the longitudinal pipe section of the first secondary air supply duct is 4184*1455*6mm, and the cross-sectional size of one end of the second secondary air supply duct is 2092*1445*6mm. The secondary air supply nozzle layout structure 2 includes a first group of nozzles 5 arranged on the front wall of the furnace body and a second group of nozzles 6 arranged on the rear wall of the furnace body.The number of nozzles in the first group of nozzles is the same as the number of nozzles in the second group of nozzles, and they are symmetrically distributed along the front-to-back direction of the furnace body. The nozzles of the first group of nozzles are arranged in at least one row and are symmetrically distributed along the left-to-right direction of the furnace body. The air outlet ends of the nozzles of the first group of nozzles are tilted downward toward the rear wall of the furnace body, and the tilt angle is 19-21 degrees. In this embodiment, the number of nozzles in the first group of nozzles is eleven, arranged in two rows, of which the number of nozzles in the upper row is eight, and the number of nozzles in the lower row is three, and these nozzles are arranged in a distribution manner in which the distribution density gradually decreases from the center of symmetry in the left-to-right direction of the CFB boiler furnace body to both sides. Specifically, among the nozzles in the upper row, the ones closest to the center of symmetry are The distance between the first two nozzles is 600*2mm, the distance between the next two nozzles is 1880*2mm, the distance between the next two nozzles is 2760*2mm, and the distance between the two nozzles closest to the edge is 4440*2mm. The air outlet ends of each nozzle of the first group of nozzles are tilted downward toward the rear wall of the CFB boiler furnace body, and the tilt angle is 19-21°. Specifically, the tilt angle is 20°. In order to improve the penetration of the secondary air entering the furnace, the air outlet ends of each nozzle of the first and second groups of nozzles are reduced in diameter and flush with the front wall 1 or the rear wall 2 of the CFB boiler furnace body. Obviously, the arrangement and distribution of the second group of nozzles are the same as those of the first group of nozzles. The air inlet ends of each nozzle of the first group of nozzles are connected in parallel to the horizontal pipe section 31 of the first secondary air supply pipeline, and the air inlet ends of each nozzle of the second group of nozzles are connected in parallel to the transition connection section 41 of the second secondary air supply pipeline.

[0026] The working principle of the present invention is as follows: preheated secondary air is discharged from the outlet of the air preheater and divided into two parts. The two parts then enter the first secondary air supply duct through the longitudinal section of the first secondary air supply duct and the second secondary air supply duct through both ends of the second secondary air supply duct. After passing through the same number of bends and the same bending angle, the flow rate and velocity of the secondary air in the transverse section of the first secondary air supply duct are equal to the flow rate and velocity of the secondary air in the connecting transition section of the second secondary air supply duct, and the air flow rate and flow rate of each nozzle are guaranteed to be the same. These secondary air with the same flow rate and velocity but opposite direction are mixed in the middle of the CFB boiler furnace body, and their momentum is offset, stabilizing the flue gas flow field and reducing turbulence. The swirling air flow of the secondary air is eliminated in the center of the furnace body. On the basis of providing secondary air for the fuel in the furnace body, the problem of secondary air sent to the furnace driving dust to scour the front or rear wall of the furnace body and causing wear is fundamentally solved.

[0027] The applicant has verified that the application is in the CFB boiler of the combined heat and power plant to measure the flow rate of the secondary air to the furnace mouth. The data of each furnace nozzle are shown in Table 1.

[0028] Table 1

[0029]

[0030]

[0031] As can be seen from Table 1, the wind speed of each secondary air nozzle in the furnace is uniform, with an error of no more than ±1m / s, and the combustion efficiency of the CFB boiler is improved by 0.5%.

Claims

1. A secondary air supply system for a CFB boiler, characterized by: It includes a secondary air supply pipeline system (1), a secondary air supply nozzle layout structure (2), The secondary air supply pipeline system (1) comprises a first secondary air supply pipeline (3) and a second secondary air supply pipeline (4) which are independent of each other. The second secondary air supply pipeline (4) is in a U-shaped structure. The second secondary air supply pipeline (4) in the U-shaped structure semi-encloses the furnace body. The connecting transition section (41) of the second secondary air supply pipeline in the U-shaped structure is arranged in parallel with the rear wall of the furnace body. The first secondary air supply pipeline (3) is in a T-shaped structure. The transverse pipe section (31) of the first secondary air supply pipeline in the T-shaped structure is sealed at both ends and is arranged in parallel with the front wall of the furnace body. The sum of the cross-sectional areas of the two ends of the second secondary air supply pipeline is the same as the cross-sectional area of the longitudinal pipe section (32) of the first secondary air supply pipeline. The two ends of the second secondary air supply pipeline and the longitudinal pipe section of the first secondary air supply pipeline are connected in parallel at the outlet end of the air preheater. The secondary air supply nozzle layout structure (2) comprises a first group of nozzles (5) arranged on the front wall of the furnace body and a second group of nozzles (6) arranged on the rear wall of the furnace body. The number of nozzles in the first group of nozzles is the same as the number of nozzles in the second group of nozzles, and they are symmetrically distributed along the front-to-back direction of the furnace body. The nozzles of the first group of nozzles are arranged in at least one row and are symmetrically distributed along the left-to-right direction of the furnace body. The air outlet ends of the nozzles of the first group of nozzles are tilted downward toward the rear wall of the furnace body, and the tilt angle is 19-21 degrees. The air inlet ends of the nozzles of the first group of nozzles are connected in parallel to the transverse pipe section (31) of the first secondary air supply pipeline, and the air inlet ends of the nozzles of the second group of nozzles are connected in parallel to the transition connection section (41) of the second secondary air supply pipeline.

2. The secondary air supply system of a CFB boiler according to claim 1, characterized in that: The transverse pipe section (31) of the first secondary air supply pipeline is fixedly arranged on the front wall of the furnace body through a plurality of first fixing members (7) and has a spacing space, and the connecting transition section (41) of the second secondary air supply pipeline is fixedly arranged on the rear wall of the furnace body through a plurality of second fixing members (8) and has a spacing space.

3. The secondary air supply system of a CFB boiler according to claim 1, characterized in that: The sum of the cross-sectional area of the longitudinal pipe section (32) of the first secondary air supply pipeline and the cross-sectional area of both ends of the second secondary air supply pipeline is adapted to the outlet end area of the air preheater.

4. The secondary air supply system for a CFB boiler according to claim 3, characterized in that: The two ends of the second secondary air supply pipeline are respectively connected to both sides of the outlet end of the air preheater, and the longitudinal pipe section of the first secondary air supply pipeline is connected to the middle of the outlet end of the air preheater and is located between the two ends of the second secondary air supply pipeline.

5. The secondary air supply system of a CFB boiler according to claim 1, characterized in that: The air outlet ends of the first group of nozzles (5) and the second group of nozzles (6) are all of reduced diameter and flush with the front wall or the rear wall of the furnace body.

6. The secondary air supply system for a CFB boiler according to claim 1, characterized in that: The distribution density of the first group of nozzles (5) and the second group of nozzles (6) gradually decreases from the symmetrical center in the left and right directions of the furnace body to both sides.

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