CN108592013B

CN108592013B - Boiler system and method of operating the same

Info

Publication number: CN108592013B
Application number: CN201810449783.XA
Authority: CN
Inventors: 柳朝晖; 刘毅; 罗威; 郭军军; 廖海燕; 李延兵; 吴海波; 王巧; 王慧芳; 黄晓宏; 郑楚光
Original assignee: Huazhong University of Science and Technology; China Shenhua Energy Co Ltd; Beijing Guohua Electric Power Co Ltd; Shenhua Guohua Beijing Electric Power Research Institute Co Ltd
Current assignee: Huazhong University of Science and Technology; China Shenhua Energy Co Ltd; Beijing Guohua Electric Power Co Ltd; Shenhua Guohua Beijing Electric Power Research Institute Co Ltd
Priority date: 2018-05-11
Filing date: 2018-05-11
Publication date: 2020-05-12
Anticipated expiration: 2038-05-11
Also published as: CN108592013A

Abstract

The invention discloses a boiler system and an operation method of the boiler system. The boiler system includes a boiler; an induced draft fan; a desulfurizing tower, a condenser and a chimney; the first pipeline is arranged between the induced draft fan and the desulfurizing tower, and the second pipeline is arranged between the condenser and the chimney; the first air return pipeline is provided with a primary air fan, a first air valve, a first circulating flue gas valve and a first oxygen injection valve, and the first air return pipeline is connected with the second pipeline and communicated with the primary air port; and a second air return pipeline provided with an overfire air fan, a second air valve, a second circulating flue gas valve and a second oxygen injection valve, wherein the second air return pipeline is connected with the first pipeline and the second pipeline and communicated with an overfire air port, and the smoke exhaust valve is positioned at the downstream of the first ends of the first air return pipeline and the second air return pipeline. The boiler system provided by the embodiment of the invention has the advantages of low operation cost, less carbon dioxide emission and the like, and can be safely and stably switched between the air combustion working condition and the oxygen-enriched combustion working condition.

Description

Boiler system and method of operating the same

Technical Field

The invention relates to the field of energy, in particular to a boiler system and an operation method of the boiler system.

Background

The problem of greenhouse gas emission is becoming more and more severe, with carbon dioxide emitted from coal-fired power generation being the primary source of greenhouse gases. The oxygen-enriched combustion technology adopts a flue gas recirculation mode, and uses pure oxygen obtained by air separation and a part of boiler exhaust gas to form mixed gas to replace air as an oxidant during combustion, so that high-concentration carbon dioxide is enriched in the combustion exhaust gas, and the carbon dioxide is collected at low cost. By virtue of its near zero emissions and good acceptance with conventional air-fired technology, it has become one of the most competitive developments in current carbon capture technologies.

Disclosure of Invention

The invention aims to overcome the problems in the prior art and provides a boiler system and an operation method of the boiler system.

To achieve the above object, a first aspect of the present invention provides a boiler system comprising: a boiler, the boiler comprising: the furnace comprises a furnace body, a plurality of first burners and a plurality of second burners; the furnace body is internally provided with a hearth; the first burners are arranged on the furnace body at intervals along the circumferential direction of the furnace body, each first burner is provided with a primary air nozzle, and the central line of jet flow of the primary air nozzles is tangent to a first circumference along one of the clockwise direction and the anticlockwise direction; the second burners are arranged on the furnace body at intervals along the circumferential direction of the furnace body, each second burner is provided with a secondary air nozzle, and the jet flow central line of the secondary air nozzles is tangent to a second circumference along the other one of the clockwise direction and the anticlockwise direction; the furnace body is provided with a primary air port, a secondary air port and a flue gas outlet;

the flue gas inlet of the induced draft fan is communicated with the flue gas outlet of the furnace body;

the device comprises a desulfurizing tower, a condenser and a chimney, wherein a flue gas inlet of the condenser is communicated with a flue gas outlet of the desulfurizing tower;

the first end of the first pipeline is connected with a flue gas outlet of the induced draft fan, the second end of the first pipeline is connected with a flue gas inlet of the desulfurizing tower, the first end of the second pipeline is connected with a flue gas outlet of the condenser, the second end of the second pipeline is connected with a flue gas inlet of the chimney, and a smoke exhaust valve is arranged on the second pipeline;

the first end of the first air return pipeline is connected with the second pipeline, the second end of the first air return pipeline is communicated with the primary air port, and a primary fan, a first air valve, a first circulating flue gas valve and a first oxygen injection valve are arranged on the first air return pipeline; and

and the first end of the second air return pipeline is connected with one of the first pipeline and the second pipeline, the second end of the second air return pipeline is communicated with the secondary air port, the second air return pipeline is provided with a secondary fan, a second air valve, a second circulating flue gas valve and a second oxygen injection valve, and the smoke exhaust valve is positioned at the first end of the first air return pipeline and at the downstream of the first end of the second air return pipeline.

The boiler system provided by the embodiment of the invention has the advantages of low operation cost and less carbon dioxide emission, and the combustion working condition of the boiler system can be safely and stably switched between the air combustion working condition and the oxygen-enriched combustion working condition.

Preferably, the second air return line includes: a first end of the dry flue gas section is connected with the first pipeline, and a second end of the dry flue gas section is communicated with a flue gas inlet of the secondary fan; a wet flue gas section, a first end of the wet flue gas section being connected to the second pipeline, a second end of the wet flue gas section being communicated with a flue gas inlet of the secondary air fan, wherein each of the dry flue gas section and the wet flue gas section is provided with the second circulating flue gas valve, the second air valve is provided on one of the dry flue gas section and the wet flue gas section, and the second air valve is located at a downstream of the corresponding second circulating flue gas valve; and the first end of the air return section is connected with a smoke outlet of the secondary fan, the second end of the air return section is communicated with the secondary air port, the second oxygen injection valve is arranged on one of the dry smoke section, the wet smoke section and the air return section, and the second oxygen injection valve is positioned at the downstream of the corresponding second circulating smoke valve.

Preferably, boiler system further includes the pre-heater, the pre-heater has inlet flue gas, exhanst gas outlet, overgrate air import and overgrate air export, the inlet flue gas of pre-heater with the exhanst gas outlet intercommunication of furnace body, the exhanst gas outlet of pre-heater with the inlet flue gas intercommunication of draught fan, the return air section includes first portion and second part, the first end of first portion with overgrate air fan's exhanst gas outlet links to each other, the second end of first portion with the overgrate air import links to each other, the first end of second portion with the overgrate air export links to each other, the second end of second portion with the overgrate air mouth intercommunication.

Preferably, the preheater further has a primary air inlet and a primary air outlet, and the first return air duct includes: the first end of the first pipe section is connected with the second pipeline, and the second end of the first pipe section is connected with the smoke inlet of the primary air fan; the first end of the second pipe section is connected with the smoke outlet of the primary air fan, and the second end of the second pipe section is connected with the primary air inlet; and the first end of the third pipe section is connected with the primary air outlet, and the second end of the third pipe section is communicated with the primary air port.

Preferably, the first air valve and the first circulating flue gas valve are arranged on the first pipe section, and the first oxygen injection valve is arranged on the third pipe section, wherein the first air valve is positioned at the downstream of the first circulating flue gas valve.

Preferably, the boiler system further comprises a bypass pipeline, a first end of the bypass pipeline is connected with the second pipe section, a second end of the bypass pipeline is connected with the third pipe section, and a bypass valve is arranged on the bypass pipeline.

Preferably, the boiler system further comprises a first exhaust pipe and a second exhaust pipe, the first end of the first exhaust pipe is connected with the bypass pipeline, and the first end of the second exhaust pipe is connected with the return air section.

Preferably, the boiler system further comprises a dust remover, wherein a flue gas inlet of the dust remover is communicated with a flue gas outlet of the furnace body, and a flue gas outlet of the dust remover is communicated with a flue gas inlet of the induced draft fan.

A second aspect of the present invention provides a method of operating a boiler system according to the first aspect of the present invention, the boiler of the boiler system having an air combustion condition and an oxyfuel combustion condition, the boiler system performing a dry flue gas cycle, the method comprising:

when the working condition of the boiler is switched from the air combustion working condition to the oxygen-enriched combustion working condition, firstly reducing the opening degree of a smoke exhaust valve, opening a second circulating smoke valve and a second oxygen injection valve, and closing a second air valve so as to complete the switching process of secondary air, and then opening a first circulating smoke valve and a first oxygen injection valve and closing a first air valve so as to complete the switching process of primary air;

when the working condition of the boiler is switched from the oxygen-enriched combustion working condition to the air combustion working condition, firstly increasing the opening degree of the smoke exhaust valve, closing the second circulating smoke valve and the second oxygen injection valve, and opening the second air valve so as to complete the switching process of secondary air, and then closing the first circulating smoke valve and the first oxygen injection valve and opening the first air valve so as to complete the switching process of primary air;

wherein, the primary air circulating flue gas and the secondary air circulating flue gas are dehydrated by a condenser;

preferably, the change rate of the flow rate of the primary air is less than or equal to 5%, the oxygen concentration of the flue gas discharged from the furnace body is greater than or equal to 2% and less than or equal to 5% in the process of switching the air combustion condition to the oxygen-enriched combustion condition and in the process of switching the oxygen-enriched combustion condition to the air combustion condition under the working condition of the boiler, and the oxygen concentration of the primary air is greater than or equal to 18% and less than or equal to 23%.

A third aspect of the present invention provides a method of operating a boiler system according to the first aspect of the present invention, the boiler system having an air combustion condition and an oxyfuel combustion condition, the boiler system performing wet flue gas recirculation, the method comprising:

when the working condition of the boiler is switched from the air combustion working condition to the oxygen-enriched combustion working condition, the opening degree of a smoke exhaust valve is reduced, a second circulating smoke valve and a second oxygen injection valve are opened, a second air valve is closed so as to complete the switching process of secondary air, and meanwhile, a first circulating smoke valve and a first oxygen injection valve are opened and a first air valve is closed so as to complete the switching process of primary air;

when the working condition of the boiler is switched from the oxygen-enriched combustion working condition to the air combustion working condition, the opening degree of the smoke exhaust valve is increased, the second circulating smoke valve and the second oxygen injection valve are closed, the second air valve is opened so as to complete the switching process of secondary air, and meanwhile, the first circulating smoke valve and the first oxygen injection valve are closed and the first air valve is opened so as to complete the switching process of primary air;

wherein, the primary air circulating flue gas is dehydrated by a condenser, and the secondary air circulating flue gas is not dehydrated by the condenser;

Preferably, when the boiler is in the air combustion working condition, the pressure of a hearth outlet of the furnace body is negative pressure; when the boiler is in the oxygen-enriched combustion working condition, the pressure of the hearth outlet of the furnace body is positive pressure.

Drawings

FIG. 1 is a schematic structural diagram of a boiler system according to an embodiment of the present invention;

FIG. 2 is a schematic view of a partial structure of a boiler according to an embodiment of the present invention;

FIG. 3 is a schematic view of a partial structure of a boiler according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a boiler according to an embodiment of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

A boiler system 10 according to an embodiment of the present invention is described below with reference to the drawings. As shown in fig. 1, a boiler system 10 according to an embodiment of the present invention includes a boiler 111, an induced draft fan 112, a desulfurization tower 113, a condenser 114, a stack 115, a first duct 121, a second duct 122, a first return duct 130, and a second return duct 150.

The boiler 111 comprises a boiler body 1110, the boiler body 1110 is provided with a primary air port, a secondary air port and a smoke outlet, a smoke inlet of the induced draft fan 112 is communicated with the smoke outlet of the boiler 111, and a smoke inlet of the condenser 114 is communicated with the smoke outlet of the desulfurizing tower 113. The first end of the first pipeline 121 is connected with the flue gas outlet of the induced draft fan 112, and the second end of the first pipeline 121 is connected with the flue gas inlet of the desulfurizing tower 113. The first end of the second pipeline 122 is connected to the flue gas outlet of the condenser 114, the second end of the second pipeline 122 is connected to the flue gas inlet of the chimney 115, and the second pipeline 122 is provided with a smoke exhaust valve 123.

The first end of the first air return pipeline 130 is connected to the second pipeline 122, and the second end of the first air return pipeline 130 is communicated with the primary air port, wherein the first air return pipeline 130 is provided with a primary air fan 141, a first air valve 142, a first circulating flue gas valve 143 and a first oxygen injection valve 144. A first end of the second return air duct 150 is connected to one of the first duct 121 and the second duct 122, and a second end of the second return air duct 150 is communicated with the secondary air port. The second return air pipe 150 is provided with an overfire air fan 161, a second air valve 162, a second circulating flue gas valve 163 and a second oxygen injection valve 164, and the smoke exhaust valve 123 is located at the first end of the first return air pipe 130 and downstream of the first end of the second return air pipe 150.

A method of operating a boiler system 10 according to an embodiment of the present invention is described below with reference to FIG. 1. The boiler 111 of the boiler system 10 according to an embodiment of the present invention has an air combustion condition and an oxyfuel combustion condition.

When the working condition of the boiler 111 needs to be switched from the air combustion working condition to the oxygen-enriched combustion working condition, the opening degree of the smoke exhaust valve 123 is firstly reduced, the second circulation smoke valve 163 and the second oxygen injection valve 164 are opened, the second air valve 162 is closed so as to complete the switching process of the secondary air, and then the first circulation smoke valve 143 and the first oxygen injection valve 144 are opened, and the first air valve 142 is closed so as to complete the switching process of the primary air.

When the working condition of the boiler 111 needs to be switched from the oxygen-enriched combustion working condition to the air combustion working condition, the opening degree of the smoke exhaust valve 123 is increased, the second circulation smoke valve 163 and the second oxygen injection valve 164 are closed, the second air valve 162 is opened so as to complete the switching process of the secondary air, and then the first circulation smoke valve 143 and the first oxygen injection valve 144 are closed, and the first air valve 142 is opened so as to complete the switching process of the primary air. Thereby, the combustion condition of the boiler 111 can be switched between the air combustion condition and the oxyfuel combustion condition.

The boiler system 10 according to the embodiment of the present invention is provided with the first return air pipe 130 and the second return air pipe 150, and the first return air pipe 130 and the second return air pipe 150 are provided with corresponding valves and fans, so that not only the boiler 111 can have an air combustion condition and an oxycombustion condition, but also the operating condition of the boiler 111 can be safely and smoothly switched between the air combustion condition and the oxycombustion condition.

Specifically, when the boiler system is in dry flue gas circulation, the operation method comprises the following steps:

wherein, the primary air circulating flue gas and the secondary air circulating flue gas are dehydrated by a condenser.

When the boiler system is in wet flue gas circulation, the operation method comprises the following steps: when the working condition of the boiler is switched from the air combustion working condition to the oxygen-enriched combustion working condition, the opening degree of a smoke exhaust valve is reduced, a second circulating smoke valve and a second oxygen injection valve are opened, a second air valve is closed so as to complete the switching process of secondary air, and meanwhile, a first circulating smoke valve and a first oxygen injection valve are opened and a first air valve is closed so as to complete the switching process of primary air;

when the working condition of the boiler is switched from the oxygen-enriched combustion working condition to the air combustion working condition, the opening degree of the smoke exhaust valve is increased, the second circulating smoke valve and the second oxygen injection valve are closed, the second air valve is opened so as to complete the switching process of secondary air, and meanwhile, the first circulating smoke valve and the first oxygen injection valve are closed and the first air valve is opened so as to complete the switching process of primary air; that is, the secondary air circulation and the primary air circulation are performed simultaneously;

wherein, the primary air circulating flue gas is dehydrated by a condenser, and the secondary air circulating flue gas is not dehydrated by the condenser.

Not only can the operating costs of the boiler system 10 be reduced, but a portion of the carbon dioxide can be better captured. That is, the operating cost of the boiler system 10 can be reduced when the boiler 111 is in the air combustion condition, and carbon dioxide can be captured better when the boiler 111 is in the oxygen-rich combustion condition.

Therefore, the boiler system 10 according to the embodiment of the present invention has the advantages of low operation cost, less carbon dioxide emission, etc., and the combustion condition of the boiler 111 of the boiler system 10 can be safely and smoothly switched between the air combustion condition and the oxyfuel combustion condition.

Preferably, the rate of change of the flow rate of the primary air is 0.05 or less, whereby the stability of the pulverized coal flame in the boiler 111 can be improved. The rate of change of the primary air flow is (the primary air flow under the air combustion condition-the primary air flow under the oxygen-enriched combustion condition)/the primary air flow under the air combustion condition.

Preferably, the oxygen concentration of the flue gas discharged from the furnace body 110 during the switching from the air combustion condition to the oxycombustion condition and during the switching from the oxycombustion condition to the air combustion condition of the operating condition of the boiler 111 may be greater than or equal to 2% and less than or equal to 5%, thereby enabling the combustion efficiency of the boiler 111 to be the highest.

The oxygen concentration of the primary air may be 18% or more and 23% or less. This can prevent the mixture of the primary air and the pulverized coal from exploding, and can make the pulverized coal more easily ignited, and can improve the combustion stability of the boiler 111.

Wherein, the oxygen concentration of the flue gas means the volume percentage of the oxygen in the flue gas in the volume of the flue gas, and the oxygen concentration of the primary air means the volume percentage of the oxygen in the primary air in the volume of the primary air.

As shown in FIG. 1, in some embodiments of the invention, the boiler system 10 may include a boiler 111, an induced draft fan 112, a desulfurization tower 113, a condenser 114, a stack 115, a preheater 116, a dust separator 117, a first duct 121, a second duct 122, a first return duct 130, and a second return duct 150.

The preheater 116 may have a flue gas inlet and a flue gas outlet, the flue gas inlet of the preheater 116 may be in communication with the flue gas outlet of the furnace 1110, and the flue gas outlet of the preheater 116 may be in communication with the flue gas inlet of the dust separator 117. The flue gas outlet of the dust separator 117 may be communicated with the flue gas inlet of the induced draft fan 112, and the flue gas inlet of the condenser 114 may be communicated with the flue gas outlet of the desulfurizing tower 113.

The first end of the first pipeline 121 may be connected to the flue gas outlet of the induced draft fan 112, and the second end of the first pipeline 121 may be connected to the flue gas inlet of the desulfurizing tower 113. A first end of the second pipe 122 may be connected to the flue gas outlet of the condenser 114, a second end of the second pipe 122 may be connected to the flue gas inlet of the chimney 115, and a smoke exhaust valve 123 may be disposed on the second pipe 122.

As shown in fig. 1, in one embodiment of the present invention, the second return air duct 150 may include a dry flue gas section 151, a wet flue gas section 152, and a return air section 153.

A first end of the dry flue gas section 151 may be connected to the first pipe 121 and a second end of the dry flue gas section 151 may be in communication with a flue gas inlet of the overfire air fan 161. A first end of the wet flue gas section 152 may be connected to the second pipe 122 and a second end of the wet flue gas section 152 may be in communication with a flue gas inlet of the overfire air fan 161. The first end of the return air section 153 may be connected to a flue gas outlet of the overfire air blower 161 and the second end of the return air section 153 may be in communication with the overfire air port.

Wherein, a second circulating flue gas valve 163 may be provided on each of the dry flue gas section 151 and the wet flue gas section 152, a second air valve 162 may be provided on one of the dry flue gas section 151 and the wet flue gas section 152, and the second air valve 162 may be located downstream of the corresponding second circulating flue gas valve 163. A second oxygen injection valve 164 may be provided in one of the dry flue gas section 151, wet flue gas section 152 and return flue gas section 153, the second oxygen injection valve 164 being located downstream of the corresponding second recycle flue gas valve 163. Whereby air can be injected through second air valve 162 and oxygen-enriched gas or oxygen can be injected through second oxygen injection valve 164 regardless of whether second recycle flue gas valve 163 is closed or not.

"the second air valve 162 may be located downstream of the corresponding second circulating flue gas valve 163" means that: when the second air valve 162 is provided on the dry flue gas section 151, the second air valve 162 is located downstream of the second circulating flue gas valve 163 provided on the dry flue gas section 151, and when the second air valve 162 is provided on the wet flue gas section 152, the second air valve 162 is located downstream of the second circulating flue gas valve 163 provided on the wet flue gas section 152. The meaning of the second oxygen injection valve 164 being located downstream of the corresponding second circulation flue gas valve 163 is the same as the meaning of the second air valve 162 may be located downstream of the corresponding second circulation flue gas valve 163, and will not be described in detail herein.

Under the working condition of wet flue gas circulation, one part of circulating flue gas circulates from the dry flue gas section 151 to the hearth (as primary air of a combustor), and the other part of circulating flue gas circulates from the wet flue gas section 152 to the hearth (as secondary air of the combustor), so in the wet circulation scheme, the dry flue gas section 151 and the wet flue gas section 152 need to be arranged at the same time; under the condition of dry flue gas circulation, all the circulating flue gas is circulated back to the furnace from the dry flue gas section 151, so the wet flue gas section 152 can be omitted or the second circulating flue gas valve 163 on the wet flue gas section 152 can be closed.

Therefore, the boiler system 10 according to the present embodiment can perform either dry flue gas circulation or wet flue gas circulation. The smoke evacuation valve 123 may be located downstream of the first end of the dry flue gas section 151, the first end of the wet flue gas section 152, and the first end of the first return air duct 130. In other words, the flue gas discharged from the furnace body 1110 may first pass through the first end of the dry flue gas section 151, the first end of the wet flue gas section 152, and the first end of the first return air duct 130, and then pass through the smoke discharge valve 123.

As shown in fig. 1, in some examples of the invention, the preheater 116 may also have a overfire air inlet, an overfire air outlet, a primary air inlet and a primary air outlet.

The return air section 153 may include a first portion 154 and a second portion 155, a first end of the first portion 154 may be connected to a flue gas outlet of an overfire air blower 161, a second end of the first portion 154 may be connected to the overfire air inlet, a first end of the second portion 155 may be connected to the overfire air outlet, and a second end of the second portion 155 may be in communication with the overfire air outlet. The gas blown out by the overfire air fan 161 can thereby be preheated by the preheater 116, and the preheated gas enters the furnace body 1110 through the overfire air port as overfire air.

The first return air line 130 may include a first pipe segment 131, a second pipe segment 132, and a third pipe segment 133. A first end of the first pipe segment 131 may be connected to the second pipe 122, and a second end of the first pipe segment 131 may be connected to a smoke inlet of the primary air fan 141. A first end of the second pipe section 132 may be connected to the flue gas outlet of the primary air fan 141 and a second end of the second pipe section 132 may be connected to the primary air inlet. A first end of the third pipe segment 133 may be connected to the primary air outlet, and a second end of the third pipe segment 133 may be in communication with the primary air opening. The gas blown out by the primary air fan 141 can be preheated by the preheater 116, and the preheated gas enters the furnace body 1110 through the primary air port as primary air.

As shown in fig. 1, preferably, a first air valve 142 and a first circulation flue gas valve 143 may be provided on the first pipe section 131, a first oxygen injection valve 144 may be provided on the third pipe section 133, and the first air valve 142 may be located downstream of the first circulation flue gas valve 143. Whereby air can be injected through the first air valve 142 regardless of whether the first circulation flue gas valve 143 is closed or not. Also, by providing the first oxygen injection valve 144 on the third pipe section 133, i.e. by providing the first oxygen injection valve 144 downstream of the primary air fan 141, the amount of gas delivered by the primary air fan 141 can be reduced.

A second air valve 162 and a second oxygen injection valve 164 may be provided on the dry flue gas section 151, i.e., the second air valve 162 and the second oxygen injection valve 164 may be located upstream of the overfire air fan 161. Therefore, the mixing of the oxygen-enriched gas or the oxygen and the flue gas can be promoted, and the oxygen-enriched gas or the oxygen and the flue gas are mixed more uniformly.

As shown in FIG. 1, in one example of the present invention, boiler system 10 may further include a bypass line 171, a first end of bypass line 171 may be connected to second tube section 132, a second end of bypass line 171 may be connected to third tube section 133, and a bypass valve 174 may be disposed on bypass line 171.

The gas (mixture of flue gas and air) in second pipe section 132 can thus be let into third pipe section 133 through bypass line 171 by opening bypass valve 174. The primary air entering the furnace body 1110 does not need to be preheated, so that the temperature in the furnace body 1110 can be better adjusted, and the furnace body 1110 has a larger operation range. It will be appreciated by those skilled in the art that a valve 177 (e.g., a shut-off valve) may be provided in appropriate locations on the second pipe segment 132 and/or the third pipe segment 133, and that the valve 177 may be closed when the bypass valve 174 is open.

As shown in FIG. 1, in one particular example of the present invention, the boiler system 10 may further include a first exhaust duct 172 and a second exhaust duct 173, a first end of the first exhaust duct 172 may be connected to the bypass line 171, and a first end of the second exhaust duct 173 may be connected to the return air section 153. The first exhaust duct 172 may be provided with a first exhaust valve 175, and the second exhaust duct 173 may be provided with a second exhaust valve 176.

Thus, when the primary air is too much, a part of the primary air can be discharged through the first exhaust duct 172 by opening the first exhaust valve 175; when the secondary air is excessive, a part of the secondary air may be discharged through the second exhaust duct 173 by opening the second exhaust valve 176. This makes it possible to maintain the boiler 111 at a desired combustion condition.

Preferably, when the boiler 111 is in the air combustion condition, the pressure at the furnace outlet of the furnace body 1110 can be negative pressure. When the boiler 111 is in the oxycombustion condition, the pressure at the furnace outlet of the furnace body 1110 may be positive pressure. Therefore, when the boiler 111 is in the oxygen-enriched combustion condition, air can be prevented from leaking into the hearth and the flue of the furnace body 1110, and the concentration of carbon dioxide in the flue gas can be prevented from being reduced. Further, the energy consumption of the compression and purification section of the boiler system 10 can be reduced and the efficiency of the compression and purification section can be improved.

Preferably, when the boiler 111 is in the air combustion condition, the pressure at the furnace outlet of the furnace body 1110 may be greater than or equal to minus 60pa and less than or equal to minus 40 pa. When the boiler 111 is in the oxygen-enriched combustion condition, the pressure at the furnace outlet of the furnace body 1110 may be greater than or equal to 50pa and less than or equal to 100 pa.

More preferably, the pressure at the furnace outlet of the furnace body 1110 can be greater than minus 50pa when the boiler 111 is in the air combustion condition. When the boiler 111 is in the oxygen-enriched combustion condition, the pressure at the furnace outlet of the furnace body 1110 may be greater than or equal to 70pa and less than or equal to 80 pa.

The boiler 111 according to an embodiment of the present invention is described below with reference to the accompanying drawings. As shown in fig. 2 to 4, the boiler 111 according to the embodiment of the present invention includes a furnace body 1110, a plurality of first burners 1120, and a plurality of second burners 1130.

The furnace body 1110 has a hearth 1111 therein. A plurality of first burners 1120 are provided on the furnace body 1110 at intervals in the circumferential direction of the furnace body 1110 (i.e., the circumferential direction of the furnace 1111), each first burner 1120 has a primary air jet, and a jet center line L1 of the plurality of primary air jets is tangent to the first circumference C1 in one of the clockwise direction and the counterclockwise direction. A plurality of second burners 1130 are provided on the furnace body 1110 at intervals in the circumferential direction of the furnace body 1110, each second burner 1130 having a secondary air nozzle, a jet center line L2 of the plurality of secondary air nozzles being tangent to the second circumference C2 in the other of the clockwise direction and the counterclockwise direction.

The boiler 111 according to the embodiment of the present invention makes the rotational direction of the primary air injected from the first burner 1120 and the rotational direction of the secondary air injected from the second burner 1130 opposite to each other under the oxygen-enriched combustion condition by making the jet center line L1 of the plurality of primary air jets tangent to the first circumference C1 in one of the clockwise direction and the counterclockwise direction and making the jet center line L2 of the plurality of secondary air jets tangent to the second circumference C2 in the other of the clockwise direction and the counterclockwise direction, so that the rotational strength of the air flow (body air flow) in the furnace 1111 can be reduced, and thus the residual rotation of the air flow at the outlet of the furnace 1111 can be eliminated. Therefore, the smoke speed deviation and the smoke temperature deviation existing in the horizontal flue of the boiler 111 can be eliminated, so that the heat transfer efficiency can be ensured, the operation cost of the boiler 111 can be greatly reduced, and the boiler 111 can be safely operated.

Moreover, the primary air and the secondary air can be opposite in rotating direction by making the rotating direction of the primary air and the rotating direction of the secondary air opposite, so that the fuel flow can be more intensively mixed in the middle of the hearth 1111, so as to facilitate the combustion and the burnout of the fuel. Whereby the fuel can be utilized more sufficiently and more efficiently, so that the operating cost of the boiler 111 can be further reduced.

Therefore, the boiler 111 according to the embodiment of the present invention has the advantages of high heat transfer efficiency, low operation cost, high safety, etc.

As shown in fig. 2 to 4, the boiler 111 according to an embodiment of the present invention may include a furnace body 1110, a plurality of first burners 1120, and a plurality of second burners 1130.

The furnace body 1110 may have a furnace 1111 therein. A plurality of first burners 1120 may be provided on the furnace body 1110 at intervals in the circumferential direction of the furnace body 1110, each first burner 1120 may have a primary air nozzle, a plurality of second burners 1130 may be provided on the furnace body 1110 at intervals in the circumferential direction of the furnace body 1110, and each second burner 1130 may have a secondary air nozzle. The boiler 111 may thus have a plurality of the primary air jets and a plurality of the secondary air jets.

The jet centerlines L1 of the primary air jets may be tangent to the first circumference C1 in one of a clockwise direction and a counter-clockwise direction, and the jet centerlines L2 of the secondary air jets may be tangent to the second circumference C2 in the other of the clockwise direction and the counter-clockwise direction.

As shown in fig. 2, in one embodiment of the present invention, the boiler 111 may further include at least one third burner 1140, the third burner 1140 may be provided on the furnace body 1110, and the third burner 1140 may have an overfire air nozzle. Each of the first burners 1120 may be movably provided on the furnace body 1110 between a tangential position and a reverse tangential position.

Wherein the jet center line L1 of the primary air jets of the first plurality of burners 1120 located at the tangential position may be tangent to the third circumference in the other of the clockwise direction and the counterclockwise direction, the jet center line L1 of the primary air jets of the first plurality of burners 1120 located at the anti-tangential position may be tangent to the first circumference C1 in the one of the clockwise direction and the counterclockwise direction, and the jet center line of the over-fired air jets may be tangent to the fourth circumference in the one of the clockwise direction and the counterclockwise direction.

Therefore, the oxygen-enriched combustion working condition can be implemented by using the boiler 111, the air combustion working condition can be implemented by using the boiler 111, the application range of the boiler 111 can be expanded, the operation cost can be further reduced, and part of carbon dioxide can be trapped more easily.

Specifically, when the boiler 111 is in the oxycombustion condition, the third burner 1140 is in the off state, each first burner 1120 is in the reverse-cut position, the first burner 1120 injects the primary air into the furnace 1111, and the second burner 1130 injects the secondary air into the furnace 1111, and the primary air rotates in the opposite direction to the secondary air, so as to eliminate the residual rotation of the air flow at the outlet of the furnace 1111.

When the boiler 111 is in the air combustion condition, each first burner 1120 is located at the tangential position, the first burner 1120 injects a primary air into the furnace 1111, and the second burner 1130 injects a secondary air into the furnace 1111, and the rotation direction of the primary air is the same as the rotation direction of the secondary air. The third burner 1140 is in an open state to inject the over-fire air, which rotates in a direction opposite to the rotation direction of the primary air and the rotation direction of the secondary air, so as to eliminate the residual rotation of the air flow at the outlet of the furnace 1111.

As shown in fig. 2, the third burner 1140 may be located above the first and

second burners

1120 and 1130. The third burner 1140 may be plural, the plural third burners 1140 may be provided on the furnace body 1110 at intervals in the circumferential direction of the furnace body 1110, and the jet center line of the overfire air nozzle of the plural third burners 1140 may be tangent to the fourth circumference in the one of the clockwise direction and the counterclockwise direction.

Preferably, the third burner 1140 may be located above the second burner 1130 (the uppermost second burner 1130), and the third burner 1140 may be located below the corner of the boiler 111. In other words, the third burner 1140 may be located between the second burner 1130 (the uppermost second burner 1130) and the flare angle of the boiler 111 in the up-down direction. More preferably, the distance between the third burner 1140 and the second burner 1130 positioned uppermost may be substantially equal to the distance between the third burner 1140 and the flare angle of the boiler 111.

As shown in fig. 3 and 4, in one example of the present invention, the center of the first circumference C1 and the center of the second circumference C2 may be located on the same vertical line. Preferably, the center of the first circumference C1 and the center of the second circumference C2 can be located on the vertical center line of the furnace 1111. The radius of the first circumference C1 may be less than the radius of the second circumference C2.

In some examples of the present invention, as shown in fig. 2 to 4, the plurality of first burners 1120 and the plurality of second burners 1130 may be opposed to each other in the up-down direction, and the angle α between the projection of the jet center line L2 of the second burners 1130 opposed to each other in the up-down direction and the jet center line L1 of the first burners 1120 located at the position of the tangency on the horizontal plane may be 5 degrees or more and 20 degrees or less, whereby the structure of the boiler 111 may be made more reasonable.

As shown in fig. 4, for example, the first burner 1120 is opposite to the first second burner 1130 in the up-down direction, and the first burner 1120 is located at the position of the undercut, wherein the projection of the jet center line L1 of the first burner 1120 on the horizontal plane is the first straight line L3, the projection of the jet center line L2 of the second first burner 1130 on the horizontal plane is the first straight line L4, and the included angle α between L3 and L4 may be greater than or equal to 5 degrees and less than or equal to 20 degrees.

Preferably, the included angle α between the jet center line L2 of the second burner 1130 and the projection of the jet center line L1 of the first burner 1120 located at the undercut position on the horizontal plane may be greater than or equal to 7 degrees and less than or equal to 15 degrees, thereby making the structure of the boiler 111 more reasonable.

As shown in fig. 2, the plurality of first burners 1120 may constitute a plurality of first burner groups, and the plurality of first burner groups may be spaced apart in the up-down direction. Each of the first burner groups may include a plurality of first burners 1120, and the plurality of first burners 1120 of each of the first burner groups may be provided on the furnace body 1110 at intervals in a circumferential direction of the furnace body 1110. The plurality of second burners 1130 may constitute a plurality of second burner groups, and the plurality of second burner groups may be spaced apart in the up-down direction. Each of the second burner groups may include a plurality of second burners 1130, and the plurality of second burners 1130 of each of the second burner groups may be provided on the furnace body 1110 at intervals in a circumferential direction of the furnace body 1110.

Preferably, as shown in fig. 2, a plurality of first burners 1120 of a plurality of the first burner groups and a plurality of second burners 1130 of a plurality of the second burner groups may be opposite to each other in an up-down direction to form a plurality of rows of burners. Whereby each column of burners may include a plurality of first burners 1120 and a plurality of third burners 1140.

More preferably, a plurality of the first burner groups and a plurality of the second burner groups are alternately arranged in the vertical direction, as shown in fig. 2. The lowermost one of the plurality of first burner groups and the plurality of second burner groups may be the second burner group, and the uppermost one of the plurality of first burner groups and the plurality of second burner groups may be the second burner group. In other words, the plurality of first burners 1120 and the plurality of third burners 1140 of each row of burners may be alternately arranged, the lowermost burner of each row of burners may be the second burner 1130, and the uppermost burner of each row of burners may be the second burner 1130.

The third burner 1140 may be plural, and the plural third burners 1140 may be provided on the furnace body 1110 at intervals in the circumferential direction of the furnace body 1110. Preferably, a plurality of the third burners 1140, a plurality of the first burners 1120 of the first burner group, and a plurality of the second burners 1130 of the second burner group may be opposite to each other in an up-down direction to form a multi-row burner. Whereby each column of burners may include one third burner 1140, a plurality of first burners 1120, and a plurality of second burners 1130.

As shown in fig. 3, in a specific example of the present invention, each of the first burner groups may include four first burners 1120, the four first burners 1120 of each of the first burner groups may be disposed at four corners of the furnace body 1110 in a one-to-one correspondence, each of the second burner groups may include four second burners 1130, and the four second burners 1130 of each of the second burner groups may be disposed at four corners of the furnace body 1110 in a one-to-one correspondence.

The invention provides an air distribution method of a boiler. The air distribution method of the boiler comprises the following steps: under the oxygen-enriched combustion working condition, primary air and secondary air are provided to a hearth of the boiler, the primary air rotates in one of a clockwise direction and a counterclockwise direction in the hearth, and the secondary air rotates in the other of the clockwise direction and the counterclockwise direction in the hearth. That is, under the condition of oxygen-enriched combustion, the rotation direction of the primary air is opposite to that of the secondary air.

According to the air distribution method of the boiler, the rotating direction of the primary air is opposite to the rotating direction of the secondary air under the oxygen-enriched combustion working condition, so that the rotating strength of airflow (main airflow) in a hearth of the boiler can be reduced, and further, the residual rotation of the airflow at an outlet of the hearth can be eliminated. Therefore, the smoke speed deviation and the smoke temperature deviation existing in the horizontal flue of the boiler can be eliminated, so that the heat transfer efficiency can be ensured, the operation cost of the boiler is greatly reduced, and the boiler can be safely operated.

Moreover, the primary air and the secondary air can be oppositely collided by enabling the rotating direction of the primary air to be opposite to that of the secondary air, and then the fuel flow can be more intensively mixed in the middle of the hearth, so that the combustion and the burnout of the fuel are facilitated. Thereby, the fuel can be utilized more sufficiently and more effectively, so that the operating cost of the boiler can be further reduced.

Therefore, by using the air distribution method of the boiler according to the embodiment of the invention, the heat transfer efficiency can be ensured, the operation cost of the boiler can be greatly reduced, and the boiler can be safely operated.

Preferably, in the oxycombustion condition, the air distribution method may further include stopping the supply of the over-fire air into the furnace. This ensures a volumetric flow of gas into the burner, which is advantageous for the organization of the flow field in the furnace chamber.

In one embodiment of the present invention, the air distribution method may further include the steps of: under an air combustion condition, primary air and secondary air are provided to a furnace of the boiler, the primary air rotates in the other one of the clockwise direction and the counterclockwise direction within the furnace, and the secondary air rotates in the other one of the clockwise direction and the counterclockwise direction within the furnace. In other words, the primary air rotates in the same direction as the secondary air during air combustion conditions.

Under the air combustion working condition, because the air quantity is sufficient, a part of the secondary air can be sprayed into the hearth in an over-fire air mode, the over-fire air can be reversely cut with the airflow in the hearth, namely, the rotation direction of the over-fire air is opposite to that of the airflow in the hearth, and therefore the residual rotation of the airflow at the outlet of the hearth can be eliminated.

Wherein, under the oxycombustion condition, the primary air may be tangent to the first circumference C1 in the one of the clockwise and counterclockwise directions, and the secondary air may be tangent to the second circumference C2 in the other of the clockwise and counterclockwise directions. The secondary air may be tangential to the second circumference C2 in the other of the clockwise and counterclockwise directions under air combustion conditions.

Oxygen-enriched gas (oxygen volume percent is more than or equal to 95%) separated from the air separation device is divided into two portions of VO1 and VO2, the recirculated flue gas is also divided into two portions of VRFG1 and VRFG2, VO1 is mixed with VRFG1 as the primary air, and VO2 is mixed with VRFG2 as the secondary air. The flue gas circulation rate can be adjusted to ensure that the partial pressure of oxygen entering the furnace and VO/(VO + VRFG) are between 0.23 and 0.30. An amount of oxygen may be premixed in the primary air by an oxygen injector so that VO1/(VO1+ VRFG1) is between 0.10-0.30. The recycling flue gas refers to flue gas recycled from a dust remover or a flue gas condenser, the flue gas recycling ratio refers to the ratio of the total volume flow of the recycling flue gas to the total volume flow of wet flue gas at the outlet of the hearth, and the partial pressure of oxygen entering the hearth refers to the sum of the volume of the recycling flue gas and the total volume of the oxygen.

The center of the first circle C1, the center of the second circle C2, and the center of the third circle may be located on the same vertical line. Preferably, the center of the first circumference C1, the center of the second circumference C2, and the center of the third circumference may be located on a vertical center line of the furnace of the boiler.

The momentum of the primary air under the oxycombustion condition may be equal to the momentum of the primary air under the air combustion condition, i.e., the momentum of the primary air may remain unchanged before and after the switching condition.

The ratio of the wind speed of the primary wind under the oxycombustion condition to the wind speed of the primary wind under the air combustion condition may be (0.8-0.9): 1. in other words, the velocity of the primary air at the oxycombustion condition may be reduced by 10% -20% compared to the velocity of the primary air at the air combustion condition.

Preferably, the primary air may be a plurality of strands, and the secondary air may be a plurality of strands, and a momentum of a lowermost one of the plurality of strands of the secondary air in the oxycombustion condition is equal to or greater than a momentum of the lowermost one of the plurality of strands of the secondary air in the air combustion condition. Therefore, the lifting effect of the secondary air positioned at the lowest part under the oxygen-enriched combustion working condition can be enhanced.

Specifically, a plurality of the primary winds may constitute a plurality of the primary winds, each of the primary winds may include a plurality of the primary winds, a plurality of the secondary winds may constitute a plurality of the secondary winds, and each of the secondary winds may include a plurality of the secondary winds. Wherein, the momentum of each secondary air of the layer which is positioned at the lowest in the plurality of layers of secondary air under the oxygen-enriched combustion working condition is more than or equal to the momentum of each secondary air of the layer which is positioned at the lowest in the plurality of layers of secondary air under the air combustion working condition.

Under the oxygen-enriched combustion working condition, the ratio of the momentum of the secondary air except the secondary air positioned at the lowest part to the momentum of the primary air is (1-5): 1, under the air combustion condition, the ratio of the momentum of the secondary air except the secondary air positioned at the lowest part to the momentum of the primary air is (1-5): 1. preferably, in the oxycombustion condition, the ratio of the momentum of the secondary air to the momentum of the primary air, except for the secondary air located lowermost, is (1.5-4.2): 1, under the air combustion condition, the ratio of the momentum of the secondary air except the secondary air positioned at the lowest part to the momentum of the primary air is (1.5-4.2): 1.

for example, when the fuel is anthracite or lean coal, under the oxygen-rich combustion condition and the air combustion condition, the ratio of the momentum of the secondary air to the momentum of the primary air, except for the secondary air positioned at the lowest part, is (3-4.2): 1; when the fuel is bituminous coal, under the oxygen-enriched combustion working condition and the air combustion working condition, the ratio of the momentum of the secondary air except the secondary air positioned at the lowest part to the momentum of the primary air is (1.5-3.5): 1; when the fuel is lignite, under the oxygen-enriched combustion working condition and the air combustion working condition, the ratio of the momentum of the secondary air except for the secondary air positioned at the lowest part to the momentum of the primary air is (2-3): 1.

preferably, the momentum of each of the primary winds is equal to each other in the oxycombustion condition and the air combustion condition.

Preferably, under the oxygen-enriched combustion condition, the ratio of the momentum moment of the primary air to the momentum moment of the secondary air is (0.6-0.9): 1. more preferably, the ratio of the moment of momentum of each of the primary winds to the moment of momentum of each of the secondary winds is (0.6-0.9): 1.

because the momentum moment of the primary air is smaller than the momentum moment of the secondary air, the rotation direction of the airflow in the hearth is dominated by the secondary air, namely the rotation direction of the airflow in the hearth is the same as the rotation direction of the secondary air. Moreover, the radius of the second circumference C2 is larger than that of the first circumference C1, namely, the secondary air is positioned between the primary air and the wall surface of the hearth, so that the effect of air-wrapped powder can be formed, and the ash and slag accumulation on the wall surface of the hearth can be greatly avoided, thereby being beneficial to combustion.

As shown in fig. 4, the included angle α between the jet center line of the primary wind and the jet center line of the secondary wind in the up-down direction may be greater than or equal to 5 degrees and less than or equal to 20 degrees, preferably, the included angle α between the jet center line of the primary wind and the jet center line of the secondary wind in the up-down direction is greater than or equal to 7 degrees and less than or equal to 15 degrees.

Specifically, the multiple strands of the primary air of the multiple layers of the primary air can be opposite to each other in the up-down direction, the multiple strands of the secondary air of the multiple layers of the secondary air can be opposite to each other in the up-down direction, and the multiple strands of the primary air of each layer of the primary air and the multiple strands of the secondary air of each layer of the secondary air can be opposite to each other in the up-down direction.

Under the oxygen-enriched combustion condition, the primary air can be tangent to a first circumference, the secondary air can be tangent to a second circumference, the circle center of the first circumference and the circle center of the second circumference can be located on the same vertical line, the included angle α can be calculated according to the formula (I),

wherein l is the width (meter) of the hearth, d is the depth (meter) of the hearth, and R₂Is the radius (m) of the second circumference₁For the mass flow (please provide unit) of the primary air, m₂For the mass flow (please provide unit) of the secondary air, v₁Is the velocity (m/s), v, of the primary wind₂The velocity (m/s) of the secondary air, and the MR is the ratio of the momentum moment of the primary air to the momentum moment of the secondary air under the oxygen-enriched combustion condition.

The included angle α may thus be calculated from the MR, specifically, each of the primary winds may be tangent to the first circumference and each of the secondary winds may be tangent to the second circumference.

Under the oxygen-enriched combustion condition, the peroxide coefficient of each of the primary air and the secondary air is greater than or equal to 1.05 and less than or equal to 1.5. Preferably, the peroxide coefficient of each of the primary air and the secondary air is greater than or equal to 1.1 and less than or equal to 1.3. Wherein the peroxide coefficient is a ratio of the amount of oxygen supplied converted to coal powder per unit weight to the amount of oxygen required for complete combustion of coal powder per unit weight.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; may be mechanically coupled, may be electrically coupled or may be in communication with each other; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A boiler system, comprising:

a boiler, the boiler comprising: the furnace comprises a furnace body, a plurality of first burners and a plurality of second burners; the furnace body is internally provided with a hearth; the first burners are arranged on the furnace body at intervals along the circumferential direction of the furnace body, the first burners can be movably arranged on the furnace body between a tangent position and a reverse tangent position, each first burner is provided with a primary air nozzle, and the jet flow central lines of the primary air nozzles are tangent to a first circumference along one of a clockwise direction and a counterclockwise direction; the second burners are arranged on the furnace body at intervals along the circumferential direction of the furnace body, each second burner is provided with a secondary air nozzle, and the jet flow central line of the secondary air nozzles is tangent to a second circumference along the other one of the clockwise direction and the anticlockwise direction; the furnace body is provided with a primary air port, a secondary air port and a flue gas outlet;

a second air return pipeline, a first end of the second air return pipeline is connected with one of the first pipeline and the second pipeline, a second end of the second air return pipeline is communicated with the secondary air inlet, wherein the second air return pipeline is provided with a secondary air fan, a second air valve, a second circulating flue gas valve and a second oxygen injection valve, and the smoke exhaust valve is positioned at the first end of the first air return pipeline and at the downstream of the first end of the second air return pipeline;

the boiler of the boiler system comprises an air combustion working condition and an oxygen-enriched combustion working condition, when the boiler is in the air combustion working condition, each first combustor is located at the tangent position, and when the boiler is in the oxygen-enriched combustion working condition, each first combustor is located at the reverse tangent position.

2. The boiler system according to claim 1, wherein the second return air line comprises:

a first end of the dry flue gas section is connected with the first pipeline, and a second end of the dry flue gas section is communicated with a flue gas inlet of the secondary fan;

a wet flue gas section, a first end of the wet flue gas section being connected to the second pipeline, a second end of the wet flue gas section being communicated with a flue gas inlet of the secondary air fan, wherein each of the dry flue gas section and the wet flue gas section is provided with the second circulating flue gas valve, the second air valve is provided on one of the dry flue gas section and the wet flue gas section, and the second air valve is located at a downstream of the corresponding second circulating flue gas valve; and

and the first end of the air return section is connected with a flue gas outlet of the secondary fan, the second end of the air return section is communicated with the secondary air port, the second oxygen injection valve is arranged on one of the dry flue gas section, the wet flue gas section and the air return section, and the second oxygen injection valve is positioned at the downstream of the corresponding second circulating flue gas valve.

3. The boiler system according to claim 2, further comprising a preheater, the preheater has a flue gas inlet, a flue gas outlet, an overfire air inlet and an overfire air outlet, the flue gas inlet of the preheater is communicated with the flue gas outlet of the furnace body, the flue gas outlet of the preheater is communicated with the flue gas inlet of the induced draft fan, the return air section comprises a first part and a second part, a first end of the first part is connected with the flue gas outlet of the overfire air fan, a second end of the first part is connected with the overfire air inlet, a first end of the second part is connected with the overfire air outlet, and a second end of the second part is communicated with the overfire air port.

4. The boiler system of claim 3, wherein the preheater further has a primary air inlet and a primary air outlet, the first return air duct comprising:

the first end of the first pipe section is connected with the second pipeline, and the second end of the first pipe section is connected with the smoke inlet of the primary air fan;

the first end of the second pipe section is connected with the smoke outlet of the primary air fan, and the second end of the second pipe section is connected with the primary air inlet; and

and the first end of the third pipe section is connected with the primary air outlet, and the second end of the third pipe section is communicated with the primary air port.

5. The boiler system according to claim 4, wherein the first air valve and the first circulating flue gas valve are provided on the first pipe section, and the first oxygen injection valve is provided on the third pipe section, wherein the first air valve is located downstream of the first circulating flue gas valve.

6. The boiler system according to claim 4, further comprising a bypass line, a first end of the bypass line being connected to the second section and a second end of the bypass line being connected to the third section, wherein a bypass valve is disposed on the bypass line.

7. The boiler system according to claim 6, further comprising a first exhaust duct and a second exhaust duct, wherein a first end of the first exhaust duct is connected to the bypass line, and a first end of the second exhaust duct is connected to the return air section.

8. The boiler system according to claim 1, further comprising a dust remover, wherein a flue gas inlet of the dust remover is communicated with a flue gas outlet of the furnace body, and a flue gas outlet of the dust remover is communicated with a flue gas inlet of the induced draft fan.

9. A method of operating a boiler system according to any one of claims 1 to 8, wherein the boiler of the boiler system has an air combustion condition and an oxyfuel combustion condition, the boiler system performing a dry flue gas cycle, the method of operating comprising:

the change rate of the flow of the primary air is less than or equal to 5%, the oxygen concentration of the flue gas discharged by the furnace body is greater than or equal to 2% and less than or equal to 5% in the process of switching the air combustion working condition to the oxygen-enriched combustion working condition and the process of switching the oxygen-enriched combustion working condition to the air combustion working condition under the working condition of the boiler, and the oxygen concentration of the primary air is greater than or equal to 18% and less than or equal to 23%.

10. A method of operating a boiler system according to any one of claims 1 to 8, wherein the boiler of the boiler system has an air combustion condition and an oxyfuel combustion condition, the boiler system performing wet flue gas recirculation, the method of operating comprising:

11. The method of operating a boiler system according to claim 10,

when the boiler is in the air combustion working condition, the pressure of the hearth outlet of the boiler body is negative pressure;

when the boiler is in the oxygen-enriched combustion working condition, the pressure of the hearth outlet of the furnace body is positive pressure.