CN112728527B

CN112728527B - Boiler combustion system

Info

Publication number: CN112728527B
Application number: CN202011628935.6A
Authority: CN
Inventors: 闫攀
Original assignee: Ningbo Mingzhou Thermal Power Co ltd
Current assignee: Ningbo Mingzhou Thermal Power Co ltd
Priority date: 2020-12-31
Filing date: 2020-12-31
Publication date: 2022-09-16
Anticipated expiration: 2040-12-31
Also published as: CN112728527A

Abstract

The application relates to a boiler combustion system, and belongs to the technical field of combustion equipment. The system comprises a boiler, a combustor for supplying heat to the boiler, a blower for supplying primary air to the combustor and a flue gas recirculation device; the flue gas recirculation device comprises a recirculation flue and a recirculation fan, one end of the recirculation flue is connected with the flue gas output end of the boiler, the other end of the recirculation flue is connected with the air outlet of the air blower, and the recirculation fan is connected with the recirculation flue and transmits the flue gas at the flue gas output end of the boiler to the air outlet of the air blower. After the boiler is combusted, the flue gas is discharged through the recirculation flue, and is conveyed to the air outlet of the air blower through the recirculation fan, and is mixed with the primary air inlet of the air blower to form secondary air inlet _x Thereby making NO discharged from the boiler _x The content is reduced.

Description

Boiler combustion system

Technical Field

The application relates to the technical field of combustion equipment, in particular to a boiler combustion system.

Background

A boiler is an energy conversion device that uses the thermal energy released by a fuel or other thermal energy to heat water or other fluid to certain parameters. The boiler can release a large amount of NO in the combustion process _x NO in the atmosphere _x Nitric acid rain can be generated after being dissolved in water, the acid rain can cause harm to the environment and cause huge economic loss, and in order to reduce NO of the boiler _x The boilers in the related art all adopt low-nitrogen combustion technology.

The related art low-nitrogen combustion technology is generally based on an air staged combustion method, and the basic principle is to perform the combustion process of fuel in stages. In the first stage, the amount of air supplied from the burner to the furnace of the boiler is reduced to 80% of the total air amount required for combustion, such that the fuel is first combusted under lean rich combustion conditions, wherein the excess air ratio a in the combustion zone is less than 1, thereby reducing the combustion speed and temperature level in the combustion zone, thereby not only delaying the combustion process, but also reducing the generation of NO _x Reaction rate of (3), inhibiting NO _x The amount of the product produced in this combustion.

However, the more incomplete combustion products are produced in the first stage, the more likely it is to cause slagging and corrosion inside the boiler, so that the boiler is easily damaged.

Disclosure of Invention

In order to make the boiler not fragile under the environment of low nitrogen burning, this application provides a boiler combustion system.

The application provides a boiler combustion system adopts following technical scheme:

a boiler combustion system comprises a boiler, a combustor for supplying heat to the boiler, an air blower for supplying primary air to the combustor and a flue gas recirculation device;

the flue gas recirculation device comprises a recirculation flue and a recirculation fan, one end of the recirculation flue is connected with the flue gas output end of the boiler, the other end of the recirculation flue is connected with the air outlet of the air blower, and the recirculation fan is connected with the recirculation flue and transmits flue gas of the flue gas output end of the boiler to the air outlet of the air blower.

By adopting the technical scheme, when the boiler burns, the air blower is started, primary air is provided for the combustor through the air blower, and the primary air provides oxygen required by combustion for the combustor, so that the combustor burns normally; after the boiler is combusted, the flue gas is discharged through the recirculation flue, and is conveyed to the air outlet of the air blower through the recirculation fan, and is mixed with the primary air inlet of the air blower to form secondary air inlet _x Thereby making NO discharged from the boiler _x The content is reduced, and the boiler is not easily damaged by a flue gas recirculation method.

Optionally, the boiler combustion system further comprises an economizer and a condenser which are connected with the flue gas output end of the boiler, one end of the economizer, which is far away from the boiler, is connected with the condenser, and one end of the recirculation flue is connected with a pipeline between the economizer and the condenser.

By adopting the technical scheme, in the related technology, the flue gas discharged by boiler combustion firstly enters the economizer and then enters the condenser, condensed water is separated out from the flue gas in the condenser, and the recirculation flue is arranged between the economizer and the condenser, so that part of the recirculation flue gas discharged from the economizer enters the recirculation flue, and the other part of the recirculation flue gas enters the condenser, the flue gas entering the condenser is reduced, and the separation of the condensed water in the condenser is reduced.

Optionally, boiler combustion system is still including locating the flue gas blender between air-blower and the combustor, the export of flue gas blender is connected with the air outlet of air-blower, the air outlet of flue gas blender and the entry linkage of combustor, the tip and the flue gas blender of recirculation flue are connected, the gas of recirculation flue and the gas of air-blower form mixed flue gas through mixing in the flue gas blender.

Through adopting above-mentioned technical scheme, the recirculation flue gas that comes out from the air-blower and come out from the boiler all gets into the flue gas mixer, through the homogeneous mixing of flue gas mixer, makes the mixed flue gas that gets into the boiler even. Experiments prove that the air mixing of the recirculated flue gas and primary air is very important, if two air flows can not be mixed uniformly, the oxygen distribution in a boiler hearth is uneven, a local high-temperature area appears, and the low-nitrogen combustion effect is influenced.

Optionally, the flue gas blender includes the casing and locates in the casing and use the axis of casing as the rotatory mixed piece of center pin pivoted, the circumference lateral wall of rotatory mixed piece is provided with a plurality of limit baffle, forms the flue gas passageway that supplies mixed flue gas to flow to the export of flue gas blender from the import of flue gas blender between two adjacent limit baffle.

Through adopting above-mentioned technical scheme, after spacing through limit baffle, form a plurality of flue gas passageways between rotatory mixing element and the casing, get into in the flue gas mixer primary air inlet and the recirculated flue gas gets into the flue gas passageway, primary air inlet and recirculated flue gas mix in the flue gas passageway, and flow out the flue gas mixer through the flue gas passageway, and simultaneously, rotatory mixing element uses the axis of casing as the center pin rotation, make the primary air inlet in the flue gas passageway together rotatory along with rotatory mixing element with the recirculated flue gas, and then make the primary air inlet in the flue gas passageway mix more evenly with the recirculated flue gas.

Optionally, the limit baffle is in the arc extension setting of rotatory mixing element, limit baffle's extending direction is opposite with the rotation direction of rotatory mixing element.

Through adopting above-mentioned technical scheme, limit baffle's extending direction is opposite with the direction of rotation of rotatory mixing element, and when rotatory mixing element rotated, gas in flue gas channel rotated together, and it is faster to make the gas in flue gas channel remove in rotatory mixing element.

Optionally, the side that rotatory mixing piece was kept away from to limit baffle is connected with the inside wall of casing, the circumference side of recirculation flue and flue gas mixer is connected to gas in the gas recirculation flue evenly flows into a plurality of flue gas passageways when making rotatory mixing piece rotate.

Through adopting above-mentioned technical scheme, when rotatory mixing element rotated in the casing, the relative rotation takes place for recirculation flue and rotatory mixing element, and the recirculated flue gas in the recirculation flue gets into a plurality of flue gas passageways in proper order, makes the volume of the recirculated flue gas in a plurality of flue gas passageways the same, makes recirculated flue gas and primary air inlet misce bene.

Optionally, the casing includes the shell and wears to locate the shell and with the shell rotates the inner shell of connecting, the inner shell lateral wall is provided with the gyro wheel, the inside wall of shell is provided with the confession the guide rail that the gyro wheel removed, the both ends and the shell of inner shell pass through the bearing and rotate and be connected.

Through adopting above-mentioned technical scheme, when rotatory mixing element rotated, rotatory mixing element drove the inner shell and together in the shell internal rotation to the gyro wheel is at the guide rail internal rotation, through the cooperation of gyro wheel and guide rail, makes the inner shell more smooth and easy and stable in the shell internal rotation.

Optionally, the inner shell is provided with an annular air inlet communicated with the plurality of flue gas channels, the end of the recirculation flue is rotatably connected with the inner shell, and the recirculation flue is communicated with the annular air inlet.

By adopting the technical scheme, the recirculation flue is communicated with the annular air inlet, and after the rotary mixing piece rotates in the shell, the recirculation flue gas of the recirculation flue enters the flue gas channel from the annular air inlet, and the recirculation flue gas in the recirculation flue uniformly enters the flue gas channel because the annular air inlet is an annular opening.

Optionally, the inner shell cover is equipped with the cover annular air inlet's annular seal ring, annular seal ring sets up the blow vent that is linked together with annular air inlet, the tip pressure of recirculation flue is in annular seal ring, and recirculation flue with the blow vent is linked together.

Through adopting above-mentioned technical scheme, through the setting of annular seal ring, make in the difficult entering shell of air in the inner shell to improve the leakproofness between inner shell and the shell, press on annular seal ring through the tip of recirculation flue, make the leakproofness between annular seal ring and the inner shell higher.

Optionally, the housing is provided with a retaining ring which limits movement of the annular sealing ring.

Through adopting above-mentioned technical scheme, ring type seal is located the retaining ring, and when the inner shell rotated, ring type seal took place relative rotation with the inner shell, through the effect of solid fixed ring, made ring type seal be difficult for taking place relative rotation on the inner shell.

In summary, the present application includes at least one of the following beneficial technical effects:

1. the flue gas discharged from the boiler enters the boiler again through the recirculation device, the combustion speed of fuel in the combustor is restrained, and the generation of NO from oxygen and nitrogen is reduced _x Thereby making NO discharged from the boiler _x The content is reduced;

2. the mixed flue gas entering the boiler is uniformly mixed by the flue gas mixer;

3. the recirculation flue is communicated with the annular air inlet, and after the rotary mixing part rotates in the shell, the recirculation flue gas of the recirculation flue enters the flue gas channel from the annular air inlet, so that the recirculation flue gas in the recirculation flue uniformly enters the flue gas channel.

Drawings

FIG. 1 is a schematic block diagram of a boiler combustion system according to an embodiment of the present application.

Fig. 2 is a schematic view of a blower according to an embodiment of the present application in a state in which the blower is connected to a flue gas mixer.

FIG. 3 is a cross-sectional view of a flue gas mixer of an embodiment of the present application.

Fig. 4 is a schematic structural diagram of a flue gas mixer according to an embodiment of the present application.

Fig. 5 is an exploded view of the outer shell and the inner shell according to an embodiment of the present application.

Fig. 6 is a schematic structural diagram of an inner shell according to an embodiment of the present application.

Fig. 7 is a schematic structural view of a rotating mixing element according to an embodiment of the present application.

Fig. 8 is a schematic structural diagram of the motor according to the embodiment of the present application after being connected to the flue gas mixer.

Fig. 9 is a schematic structural view illustrating an annular sealing ring hooped on an inner shell according to an embodiment of the present application.

Fig. 10 is a schematic structural view of an inner case of the embodiment of the present application.

Description of reference numerals: 1. a boiler; 2. a burner; 3. a blower; 4. a coal economizer; 5. a condenser; 6. a flue gas recirculation device; 61. a recirculation flue; 62. a recirculation fan; 7. a flue gas mixer; 71. a housing; 711. a housing; 712. an inner shell; 713. half shells; 7131. a fixing ring; 7132. a limiting groove; 714. connecting sheets; 715. a bearing; 716. an O-shaped sealing ring; 717. a guide rail; 718. a roller; 719. an annular air inlet; 72. rotating the mixing member; 73. a limit baffle; 74. a flue gas channel; 75. a motor; 76. an end cap; 77. a connecting pipe; 78. an annular seal ring; 781. a vent; 79. an accommodating chamber; 791. an inlet; 792. and (7) an outlet.

Detailed Description

The present application is described in further detail below with reference to figures 1-10.

The embodiment of the application discloses boiler combustion system.

Referring to fig. 1, the boiler combustion system includes a boiler 1, a burner 2, a blower 3, an economizer 4, a condenser 5, and a flue gas recirculation device 6, the burner 2 is connected to the boiler 1, the blower 3 is connected to an end of the burner 2 away from the boiler 1, the blower 3 inputs primary intake air to the burner 2 and provides oxygen required for combustion of the burner 2, and then the burner 2 provides heat for heating liquid to the boiler 1.

One end of the economizer 4 is connected with the flue gas output end of the boiler 1, one end of the economizer 4, which is far away from the boiler 1, is connected with the condenser 5, so that the flue gas discharged from the boiler 1 enters the economizer 4, passes through the economizer 4 and then enters the condenser 5, condensed water is sucked out of the condenser 5, and then the flue gas is discharged into the atmosphere.

The flue gas recirculation device 6 comprises a recirculation flue 61 and a recirculation fan 62, one end of the recirculation flue 61 is connected with a pipeline between the economizer 4 and the condenser 5, the other end of the recirculation flue is connected with a pipeline between the blower 3 and the combustor 2, the recirculation fan 62 is connected with the recirculation flue 61, gas which comes out of the economizer 4 and enters the recirculation flue 61 is recirculation flue gas, the recirculation flue gas is sucked into the recirculation flue gas through the recirculation fan 62 and flows out of one end of the recirculation flue, which is close to the blower 3, and is mixed with primary inlet air of the blower 3 to form secondary inlet air which enters the combustor 2, the secondary inlet air is defined as mixed flue gas, and the concentration of the mixed flue gas in the primary inlet air is lower than that of the mixed flue gas, so that the combustion speed in the combustor 2 is inhibited, and the generation of thermal NOx by oxygen and nitrogen is reduced.

Referring to fig. 1 and 2, related experiments prove that mixing of recirculated flue gas and primary air intake is very important, if the two air flows cannot be uniformly and effectively mixed, uneven distribution of oxygen in the combustor 2 is caused, so that local high temperature in the combustor 2 occurs, and further low-nitrogen combustion effect is influenced, and therefore, in order to enable the recirculated flue gas and the primary air intake to be more uniformly mixed, a flue gas mixer 7 is arranged between the air blower 3 and the combustor 2.

Referring to fig. 2 and 3, the flue gas mixer 7 has a receiving cavity 79 penetrating through both ends thereof, and the both ends of the flue gas mixer 7 are an inlet 791 and an outlet 792, respectively. The air outlet of the blower 3 is connected with the inlet 791 of the flue gas mixer 7, one end of the recirculation flue 61 is connected with the flue gas mixer 7 and communicated with the accommodating cavity 79, and the outlet 792 of the flue gas mixer 7 is connected with the inlet of the combustor 2, so that the recirculation flue gas and primary air are uniformly mixed by the mixer and then conveyed into the combustor 2.

To allow the gas in the flue gas mixer 7 to be more quickly transported from the inlet 791 to the outlet 792, the flue gas mixer 7 is positioned obliquely downward from the inlet 791 to the outlet 792.

The flue gas mixer 7 comprises a shell 71 and a rotary mixing element 72 arranged in the shell 71, wherein the shell 71 comprises an outer shell 711 and an inner shell 712 arranged in the outer shell 711, the inner shell 712 is rotatably connected with the outer shell 711, and the rotary mixing element 72 is connected with the inner side wall of the inner shell 712, so that the rotary mixing element 72 rotates in the outer shell 711.

Referring to fig. 3 and 4, the housing 711 is formed by splicing two half shells 713 with the same shape and structure through bolts, the two half shells 713 are arranged in central symmetry with respect to an axis of the housing 711, each half shell 713 extends outwards to form a connecting piece 714, when the two half shells 713 are connected, a concave surface of one half shell 713 faces a concave surface of the other half shell 713, the connecting pieces 714 of the two half shells 713 are attached to each other, and the bolts penetrate through the two attached connecting pieces 714 to connect the two attached connecting pieces 714, so that the two half shells 713 are connected.

The inner shell 712 is rotatably connected in the outer shell 711, and two ends of the inner shell 712 are in supporting connection with the outer shell 711 through bearings 715, in order to improve the sealing performance between the inner shell 712 and the outer shell 711, the two ends of the inner shell 712 are both provided with O-ring 716 clamped between the inner shell 712 and the outer shell 711, the O-ring 716 at each end is coaxial with the bearing 715 at the end, and the O-ring 716 is located on the side surface of the bearing 715 away from the other bearing 715, i.e., the outer side of the bearing 715, which is convenient for a worker to replace.

Referring to fig. 5 and 6, the concave surface of the half shell 713 is provided with an arc-shaped guide rail 717, after the two half shells 713 are spliced, the two guide rails 717 are spliced into a complete circular guide rail 717, the outer side wall of the inner shell 712 is convexly provided with at least one roller 718, the number of the rollers 718 may be two or three, but the number of the rollers is set to enable the inner shell 712 to be rotatably supported on the outer shell 711, and the rollers 718 are in rolling connection with the guide rail 717, so that the rollers 718 roll on the guide rail 717.

Referring to fig. 7, the rotary mixing member 72 is shuttle-shaped, a plurality of limit baffles 73 are provided on a circumferential side wall of the rotary mixing member 72, the limit baffles 73 are spaced apart from each other in a circumferential direction of the rotary mixing member 72, the limit baffles 73 arc-extend from one end to the other end of the rotary mixing member 72, and an extending direction of the limit baffles 73 is opposite to a rotating direction of the rotary mixing member 72 in the housing 711. The side of the limit baffle 73 far away from the rotating mixing piece 72 is fixedly connected with the inner side wall of the inner shell 712, so that the rotating mixing piece 72 is connected with the inner shell 712, and an arc-shaped flue gas channel 74 is formed between two adjacent limit baffles 73. Because the rotating mixing member 72 is shuttle-shaped, the width between two adjacent limit baffles 73 gradually decreases from the end near the inlet 791 to the end near the outlet 792, so that the width of the smoke passage 74 gradually narrows. When the mixed flue gas moves in the flue gas channel 74, along with the gradual narrowing of the flue gas channel 74, the moving speed of the mixed flue gas in the flue gas channel 74 is faster, so that the speed of the mixed flue gas entering the combustor 2 is faster, and when the speed of the mixed flue gas is fast, the mixing of the mixed flue gas and the fuel is promoted, and the generation of NOx is reduced.

It is noted that the opening of the end of the inner housing 712 near the blower 3 is larger than the maximum diameter of the rotating mixing element 72 plus the height of the limit stop 73, so that both the rotating mixing element 72 and the limit stop 73 can penetrate into the inner housing 712 from the end of the inner housing 712.

Referring to fig. 8, the rotating mixing member 72 is connected with a motor 75, the motor 75 is disposed at the outlet 792 end of the flue gas mixer 7, the motor 75 is connected with the wall or the boiler 1, the output shaft of the motor 75 extends into the accommodating cavity 79 from the outlet 792 of the flue gas mixer 7 and is fixedly connected with the rotating mixing member 72 coaxially, and the rotating mixing member 72 is driven by the motor 75 to rotate in the housing 711.

Flue gas mixer 7 is provided with the end cover 76 that covers export 792, and end cover 76 is connected with a plurality of connecting pipes 77 that are the annular setting around the output shaft of motor 75, and in the one end of connecting pipe 77 stretched into and held the chamber 79, the other end stretched into in combustor 2, made the mixed flue gas in the flue gas mixer 7 transmit to in combustor 2 through connecting pipe 77.

Referring to fig. 9 and 10, the end of the recirculation flue 61 extends into the outer housing 711 and is rotatably connected to the housing 71, the inner housing 712 is provided with an annular air inlet 719 communicated with the plurality of flue gas passages 74, the annular air inlet 719 is annular and is coaxially disposed with the inner housing 712, so that the inner housing 712 is divided into two parts by the annular air inlet 719, and the position of the inner housing 712 where the annular air inlet 719 is provided is connected to the limit baffle 73, so that the two parts of the inner housing 712 are connected by the plurality of limit baffles 73.

Inner shell 712 is equipped with annular seal ring 78 that covers annular air inlet 719, and annular seal ring 78 rotates with inner shell 712 and is connected, and the width of annular seal ring 78 is greater than the width of annular air inlet 719, makes annular seal ring 78 and inner shell 712 take place relative rotation. The annular sealing ring 78 is provided with an air vent 781 penetrating through one set of opposite side surfaces of the annular sealing ring 78, the air vent 781 is connected with the annular air inlet 719, and the end part of the recirculation flue 61 is pressed on the annular sealing ring 78 and covers the air vent 781, so that the recirculation flue gas of the recirculation flue 61 enters the annular air inlet 719 from the air vent 781 of the annular sealing ring 78.

In order to make the annular sealing ring 78 cover the annular air inlet 719 more firmly, the inner side wall of the outer shell 711 is provided with the fixing ring 7131, the fixing ring 7131 is provided with a limiting groove 7132 for the annular sealing ring 78 to be embedded, when the outer shell 711 is connected with the inner shell 712, the annular sealing ring 78 is embedded into the limiting groove 7132, so that the annular sealing ring 78 is not easy to move on the surface of the inner shell 712, and meanwhile, when the inner shell 712 rotates, the annular sealing ring 78 is kept fixed in the limiting groove 7132, so that the recirculation flue 61 and the annular sealing ring 78 are relatively fixed, and further, the recirculation flue in the recirculation flue 61 enters each flue gas channel 74.

The implementation principle of the boiler combustion system in the embodiment of the application is as follows: when mixed flue gas is required to be introduced into the combustor 2, the blower 3, the recirculation fan 62 and the motor 75 are started, primary air is blown into the flue gas channel 74 by the blower 3, the recirculation fan 62 introduces the recirculated flue gas into the flue gas channel 74, the rotary mixing piece 72 is driven by the motor 75 to rotate around the axis of the flue gas mixer 7 as a central shaft, and the mixed flue gas moves towards one side close to the combustor 2 in the flue gas channel 74 and enters the combustor 2.

The above embodiments are preferred embodiments of the present application, and the protection scope of the present application is not limited by the above embodiments, so: all equivalent changes made according to the structure, shape and principle of the present application shall be covered by the protection scope of the present application.

Claims

1. A boiler combustion system, characterized by: comprises a boiler (1), a burner (2) for supplying heat to the boiler (1), a blower (3) for supplying primary air to the burner (2) and a smoke recirculation device (6);

the flue gas recirculation device (6) comprises a recirculation flue (61) and a recirculation fan (62), one end of the recirculation flue (61) is connected with the flue gas output end of the boiler (1), the other end of the recirculation flue is connected with the air outlet of the air blower (3), and the recirculation fan (62) is connected with the recirculation flue (61) and transmits the flue gas at the flue gas output end of the boiler (1) to the air outlet of the air blower (3);

the boiler (1) combustion system further comprises a flue gas mixer (7) arranged between the blower (3) and the combustor (2), an inlet (791) of the flue gas mixer (7) is connected with an air outlet of the blower (3), an air outlet of the flue gas mixer (7) is connected with an inlet of the combustor (2), the end part of the recirculation flue (61) is connected with the flue gas mixer (7), and gas of the recirculation flue (61) and gas of the blower (3) are mixed in the flue gas mixer (7) to form mixed flue gas;

the flue gas mixer (7) comprises a shell (71) and a rotary mixing part (72) which is arranged in the shell (71) and rotates by taking the axis of the shell (71) as a central shaft, the circumferential side wall of the rotary mixing part (72) is provided with a plurality of limiting baffles (73), and a flue gas channel (74) for mixed flue gas to flow from an inlet of the flue gas mixer (7) to an outlet (792) of the flue gas mixer (7) is formed between every two adjacent limiting baffles (73); the width between two adjacent limit baffles (73) is gradually reduced from one end close to the inlet (791) to one end close to the outlet (792);

the limiting baffle (73) is arranged on the rotary mixing part (72) in an arc-shaped extending manner, and the extending direction of the limiting baffle (73) is opposite to the rotating direction of the rotary mixing part (72); the side that rotatory mixing element (72) was kept away from in limit baffle (73) is connected with the inside wall of casing (71), recirculation flue (61) is connected with the circumference side of flue gas blender (7) to gas in the recirculation flue (61) evenly flows into in a plurality of flue gas passageways (74) when making rotatory mixing element (72) rotate.

2. A boiler combustion system according to claim 1, characterized in that: boiler (1) combustion system still includes economizer (4) and condenser (5) be connected with the flue gas output end of boiler (1), the one end that boiler (1) was kept away from in economizer (4) is connected with condenser (5), the pipeline between economizer (4) and condenser (5) is connected to the one end of recirculation flue (61).

3. A boiler combustion system according to claim 1, characterized in that: the shell (71) comprises an outer shell (711) and an inner shell (712) which penetrates through the outer shell (711) and is rotatably connected with the outer shell (711), rollers (718) are arranged on the outer side wall of the inner shell (712), a guide rail (717) for the movement of the rollers (718) is arranged on the inner side wall of the outer shell (711), and two ends of the inner shell (712) are rotatably connected with the outer shell (711) through bearings (715).

4. A boiler combustion system according to claim 3, characterized in that: the inner shell (712) is provided with an annular air inlet (719) communicated with the plurality of smoke channels (74), the end part of the recirculation flue (61) is rotatably connected with the inner shell (712), and the recirculation flue (61) is communicated with the annular air inlet (719).

5. A boiler combustion system according to claim 4, characterized in that: inner shell (712) cover is equipped with and covers annular seal ring (78) of annular air inlet (719), vent (781) that are linked together with annular air inlet (719) are seted up to annular seal ring (78), the tip of recirculation flue (61) is pressed annular seal ring (78), and recirculation flue (61) with vent (781) are linked together.

6. A boiler combustion system according to claim 5, characterized in that: the housing (711) is provided with a fixing ring (7131) which limits the movement of the annular seal ring (78).