阅读说明：本技术 一种分级回水层燃锅炉系统 (Graded water return grate firing boiler system ) 是由 郭强 于 2019-10-29 设计创作，主要内容包括：本发明涉及锅炉设备技术领域,公开了一种分级回水层燃锅炉系统,包括锅炉本体和尾部烟道,锅炉本体的内部设有对流受热面,尾部烟道上设有省煤器,省煤器的入口连接锅炉回水,对流受热面的入口同时与省煤器的出口和锅炉回水相连。本发明提供的一种分级回水层燃锅炉系统,设置管道直接连通锅炉回水和对流受热面,在锅炉负荷降低时,可控制部分锅炉回水直接进入对流受热面中,从而减少进入省煤器中的水量,进而减少与尾部烟气的对流换热,从而可提高尾部烟气的温度,便于控制烟气温度保持温度,避免由于降低锅炉负荷而导致烟温下降引起的受热面低温腐蚀的温度。(The invention relates to the technical field of boiler equipment, and discloses a graded return water layer combustion boiler system which comprises a boiler body and a tail flue, wherein a convection heating surface is arranged inside the boiler body, a coal economizer is arranged on the tail flue, an inlet of the coal economizer is connected with return water of a boiler, and an inlet of the convection heating surface is simultaneously connected with an outlet of the coal economizer and the return water of the boiler. According to the staged return water grate-firing boiler system, the pipeline is arranged to be directly communicated with the return water of the boiler and the convection heating surface, when the load of the boiler is reduced, part of the return water of the boiler can be controlled to directly enter the convection heating surface, so that the amount of water entering the economizer is reduced, the convection heat exchange with tail flue gas is further reduced, the temperature of the tail flue gas can be increased, the temperature of the flue gas can be conveniently controlled to be kept, and the temperature of low-temperature corrosion of the heating surface caused by reduction of the temperature of the flue gas due to reduction of the load of the boiler is avoided.)

1. The utility model provides a hierarchical return water grate-firing boiler system, includes boiler body and afterbody flue, its characterized in that, the inside of boiler body is equipped with convection heating surface, be equipped with the economizer on the afterbody flue, the boiler return water is connected to the entry of economizer, the entry of convection heating surface simultaneously with the export of economizer and boiler return water link to each other.

2. The staged return water grate-firing boiler system according to claim 1, wherein a first valve is arranged between the boiler return water and the inlet of the economizer, and a second valve is arranged between the boiler return water and the inlet of the convection heating surface.

3. The staged return water grate-firing boiler system according to claim 1, wherein the boiler body comprises a vertically installed main furnace, a secondary furnace and a convection channel are sequentially arranged at the rear part of the main furnace side by side, the top end of the main furnace is communicated with the top end of the secondary furnace, the bottom end of the secondary furnace is communicated with the bottom end of the convection channel, and the top end of the convection channel is communicated with a tail flue.

4. The staged return water grate-firing boiler system according to claim 3, wherein the sidewalls of the main furnace and the auxiliary furnace are respectively provided with a membrane water-cooling wall, the convection heating surface is arranged in the convection passage, and the outlet of the convection heating surface is connected with the inlet of the membrane water-cooling wall.

5. The staged return water grate-firing boiler system according to claim 3, wherein a grate is arranged at the bottom of the main furnace, the grate is covered at the bottom of the main furnace, the cross-sectional areas of the middle part and the top of the main furnace are smaller than that of the bottom of the main furnace, the auxiliary furnace is bent, and a transition part is arranged between the bottom end of the auxiliary furnace and the bottom end of the convection channel.

6. The staged water return grate-firing boiler system according to claim 3, further comprising: a flue gas recirculation device; the flue gas recirculation device is communicated with the interior of the main furnace and the tail end of the tail flue and used for introducing the flue gas at the tail end of the tail flue into the interior of the main furnace.

7. The staged return water grate-firing boiler system according to claim 6, wherein the flue gas recirculation device comprises a flue gas recirculation main air pipe, a flue gas taking port is arranged at the tail end of the tail flue, the flue gas taking port is connected with the flue gas recirculation main air pipe, and the flue gas recirculation main air pipe is arranged on one side, close to the tail, of the grate.

8. The staged water return grate-firing boiler system according to claim 7, wherein the flue gas recirculation main duct is arranged in parallel with the upper surface of the grate along the width direction of the grate, the flue gas recirculation main duct is vertically connected with a plurality of nozzles, and outlets of the nozzles are arranged downward.

9. The staged water return grate-fired boiler system according to claim 8, wherein a plurality of nozzles are uniformly arranged along the width direction of the grate; the smoke taking port is arranged behind the air preheater on the tail flue.

10. The staged return water grate-firing boiler system according to claim 8, wherein the flue gas recirculation main duct is disposed inside the auxiliary furnace, and the nozzles are inserted into the main furnace through a side wall of the auxiliary furnace; and two ends of the flue gas recirculation main air pipe respectively penetrate out of the hearth to be connected with the two smoke taking ports in a one-to-one correspondence manner.

Technical Field

The invention relates to the technical field of boiler equipment, in particular to a staged backwater grate firing boiler system.

Background

China is a developing country taking coal as a main energy source, and the coal resource accounts for about 75% of the total energy production and consumption of China. The boiler in China mainly uses fire coal as a main part, the boiler is used as a heat absorption device, the exhaust gas temperature of the boiler is greatly related to the thermal efficiency of the boiler, the exhaust gas temperature is high, the thermal efficiency of the boiler is low, the exhaust gas temperature is low, and the thermal efficiency of the boiler is high.

The boiler product in the current market adopts a single-stage water return mode, the exhaust gas temperature is about 150 ℃ under the rated working condition, and the thermal efficiency of the boiler is about 83 percent. However, when the load of the boiler varies, the exhaust gas temperature at the tail portion cannot be controlled well. Especially when the low-load operation is carried out, the tail exhaust gas temperature is too low, the low-temperature corrosion of the heating surface can be caused, the safety of materials cannot be guaranteed, and NO in the flue gas at the outlet of the boiler is caused_xThe initial emission concentration and the combustible content of the fly ash are increased, NO_xThe concentration is 400-500mg/Nm³Even higher, can not satisfy denitration technology (SCR and SNCR method) requirement, along with current environmental protection requirement stricter day by day, this cost that has greatly increased the later stage denitration is unfavorable for economic environmental protection target.

The coal-fired industrial boiler used at present generally has the problem that the tail exhaust gas temperature can not be controlled.

Disclosure of Invention

Technical problem to be solved

The invention aims to provide a graded return water grate-firing boiler system which is used for solving or partially solving the problem that the tail smoke discharge temperature can not be controlled generally in the existing coal-fired industrial boiler.

(II) technical scheme

In order to solve the technical problem, the invention provides a staged return water layer combustion boiler system which comprises a boiler body and a tail flue, wherein a convection heating surface is arranged inside the boiler body, a coal economizer is arranged on the tail flue, an inlet of the coal economizer is connected with return water of a boiler, and an inlet of the convection heating surface is simultaneously connected with an outlet of the coal economizer and the return water of the boiler.

On the basis of the scheme, a first valve is arranged between the boiler backwater and the inlet of the economizer, and a second valve is arranged between the boiler backwater and the inlet of the convection heating surface.

On the basis of the scheme, the boiler body comprises a vertically-installed main hearth, an auxiliary hearth and a convection channel are sequentially arranged at the rear part of the main hearth side by side, the top end of the main hearth is communicated with the top end of the auxiliary hearth, the bottom end of the auxiliary hearth is communicated with the bottom end of the convection channel, and the top end of the convection channel is communicated with a tail flue.

On the basis of the scheme, the side walls of the main hearth and the auxiliary hearth are respectively provided with a membrane water-cooled wall, the convection heating surface is arranged in the convection channel, and the outlet of the convection heating surface is connected with the inlet of the membrane water-cooled wall.

On the basis of the scheme, the fire grate is arranged at the bottom of the main hearth, the bottom of the main hearth covers the fire grate, the cross-sectional areas of the middle part and the top of the main hearth are smaller than that of the bottom of the main hearth, the auxiliary hearth is bent, and a switching part is arranged between the bottom end of the auxiliary hearth and the bottom end of the convection channel.

On the basis of the scheme, the method further comprises the following steps: a flue gas recirculation device; the flue gas recirculation device is communicated with the interior of the main furnace and the tail end of the tail flue and used for introducing the flue gas at the tail end of the tail flue into the interior of the main furnace.

On the basis of the scheme, the smoke recycling device comprises a smoke recycling main air pipe, the tail end of the tail flue is provided with a smoke taking port, the smoke taking port is connected with the smoke recycling main air pipe, and the smoke recycling main air pipe is arranged on one side, close to the tail, of the fire grate.

On the basis of the scheme, the flue gas recirculation main air pipe is arranged in parallel with the upper surface of the fire grate along the width direction of the fire grate, the flue gas recirculation main air pipe is vertically connected with a plurality of nozzles, and outlets of the nozzles are arranged downwards.

On the basis of the scheme, a plurality of nozzles are uniformly arranged along the width direction of the fire grate; the smoke taking port is arranged behind the air preheater on the tail flue.

On the basis of the scheme, the flue gas recirculation main air pipe is arranged inside the auxiliary hearth, and the nozzle penetrates through the side wall of the auxiliary hearth and is inserted into the main hearth; and two ends of the flue gas recirculation main air pipe respectively penetrate out of the hearth to be connected with the two smoke taking ports in a one-to-one correspondence manner.

(III) advantageous effects

According to the staged return water grate-firing boiler system, the pipeline is arranged to be directly communicated with the return water of the boiler and the convection heating surface, when the load of the boiler is reduced, part of the return water of the boiler can be controlled to directly enter the convection heating surface, so that the amount of water entering the economizer is reduced, the convection heat exchange with tail flue gas is further reduced, the temperature of the tail flue gas can be increased, the temperature of the flue gas can be conveniently controlled to be kept, and the temperature of low-temperature corrosion of the heating surface caused by reduction of the temperature of the flue gas due to reduction of the load of the boiler is avoided.

Drawings

FIG. 1 is an overall schematic view of a staged backwater grate-fired boiler system according to an embodiment of the invention;

FIG. 2 is an overall schematic view of a staged backwater chain boiler system according to an embodiment of the invention;

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

FIG. 4 is a schematic view of a flue gas recirculation ductwork in an embodiment of the present invention;

FIG. 5 is a schematic view of a nozzle in an embodiment of the invention.

Description of reference numerals:

1-a drum;	2-main furnace chamber;	3, a grate;
			4, an auxiliary hearth;	5-convection heating surface;	6-tail flue;
7-a coal economizer;	8-air preheater;	9 — a first valve;
			10-a second valve;	11-flue gas recirculation equipment;	12-a convection channel;
13-boiler water return;	14-a switching part;	15-a denitration module;
			111-flue gas recirculation main air duct;	112-nozzle.

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The embodiment of the invention provides a staged return water grate-firing boiler system, and referring to fig. 1, the boiler system comprises a boiler body and a tail flue 6, a convection heating surface 5 is arranged inside the boiler body, an economizer 7 is arranged on the tail flue 6, an inlet of the economizer 7 is connected with boiler return water 13, and an inlet of the convection heating surface 5 is simultaneously connected with an outlet of the economizer 7 and the boiler return water 13.

According to the staged return water layer combustion boiler system provided by the embodiment, the pipeline is arranged to be directly communicated with the boiler return water 13 and the convection heating surface 5, the boiler return water 13 can enter the economizer 7 to exchange heat with flue gas and then enter the convection heating surface 5, and the boiler return water 13 can also directly enter the convection heating surface 5.

When the load of the boiler is reduced, part of boiler return water 13 can be controlled to directly enter the convection heating surface 5, so that the water quantity entering the economizer 7 is reduced, the convection heat exchange with tail flue gas is reduced, the temperature of the tail flue gas can be increased, the temperature of the flue gas can be conveniently controlled to be kept, and the temperature of low-temperature corrosion of the heating surface caused by reduction of the load of the boiler due to reduction of the temperature of the flue gas is avoided.

Furthermore, when the tail flue 6 is connected with a dust remover, the temperature of the flue gas can be controlled to be above the dew point temperature of the dust remover by adjusting the boiler backwater 13, so that the low-temperature corrosion loss is reduced.

Further, a first valve 9 is arranged between the boiler return water 13 and the inlet of the economizer 7, and a second valve 10 is arranged between the boiler return water 13 and the inlet of the convection heating surface 5. The amount of the boiler return water is adjusted by adjusting the opening degree of the first valve 9 and the second valve 10.

Specifically, when the boiler load is reduced to below 70%, and when the boiler load is lower than 70% and is gradually reduced, according to the operation condition, the opening degree of the first valve 9 is gradually reduced, and the opening degree of the second valve 10 is gradually increased, so that the heat exchange amount of the economizer is reduced, and the exhaust gas temperature is ensured to be above the dew point temperature (about 120 ℃).

Further, the boiler body includes the main furnace 2 of vertical installation, and the rear portion of main furnace 2 is equipped with vice furnace 4 and convection current passageway 12 side by side in proper order, and the top of main furnace 2 is linked together with the top of vice furnace 4, and the bottom of vice furnace 4 is linked together with the bottom of convection current passageway 12, and the top of convection current passageway 12 is linked together with afterbody flue 6.

The rear part of the main hearth 2 is the rear side in the flow direction of the flue gas, i.e. the part to which the flue gas flows backwards. The auxiliary furnace 4 and the convection channel 12 are also vertically arranged and are connected with the main furnace 2 in sequence side by side. The layer combustion boiler is additionally provided with an auxiliary hearth 4 and a convection channel 12 at the rear side of a main hearth 2. Flue gas generated by combustion of fuel inside the main furnace 2 flows into the auxiliary furnace 4 through a top outlet, then flows from the top to the bottom of the auxiliary furnace 4 into the convection channel 12, and then flows into the tail flue 6.

According to the layer combustion boiler structure, the auxiliary hearth 4 and the convection channel 12 are sequentially arranged behind the main hearth 2 side by side, the top of the main hearth 2 is communicated with the auxiliary hearth 4, and the bottom of the auxiliary hearth 4 is communicated with the convection channel 12, so that the main hearth 2, the auxiliary hearth 4 and the convection channel 12 form an S-shaped three-return-stroke flue gas channel, the flow distance of flue gas can be effectively increased, the combustion time of fuel, namely pulverized coal, in a boiler is increased, and the combustion efficiency is improved; the products which are not fully combusted in the flue gas are reduced, the emission of sulfur oxides and nitrogen oxides is reduced, the environmental protection investment is reduced, and the economical efficiency is improved.

Furthermore, membrane type water-cooled walls are attached to the peripheral side walls of the main hearth 2 and the auxiliary hearth 4; the side wall of the convection channel 12 is also provided with a membrane water-cooling wall, and a convection heating surface 5 is arranged in the convection channel 12 to improve the use efficiency of heat. The membrane water-cooled wall is communicated with a downcomer which is connected with the boiler barrel 1.

Furthermore, the side walls of the main hearth 2 and the auxiliary hearth 4 are respectively provided with a membrane water-cooled wall, the convection heating surface 5 is arranged in the convection channel 12, and the outlet of the convection heating surface 5 is connected with the inlet of the membrane water-cooled wall.

When the boiler operates at normal load, the flow of boiler backwater is as follows: boiler return water 13 enters the economizer 7 through an economizer inlet header, then flows out of an economizer outlet header, enters a convection heating surface inlet header, and then flows out of a convection heating surface outlet header and enters a membrane water-cooled wall.

When the operation load of the boiler is reduced and the flue gas temperature is lower than the preset temperature, the flow of the boiler backwater 13 is as follows: the boiler return water 13 can partially flow into an economizer inlet header and partially directly flow into a convection heating surface inlet header; boiler return water 13 flowing into the economizer inlet header flows out of the economizer outlet header into the convection heating surface inlet header, and then flows out of the convection heating surface outlet header into the membrane water-cooled wall; boiler return water 13 flowing into the convection heating surface inlet header flows out of the convection heating surface outlet header into the membrane water-cooled wall.

On the basis of the above embodiment, further, the bottom of the main furnace 2 is provided with the fire grate 3, the bottom of the main furnace 2 covers the fire grate 3, the cross-sectional areas of the middle part and the top of the main furnace 2 are smaller than the cross-sectional area of the bottom, the auxiliary furnace 4 is bent, and the adapter part 14 is arranged between the bottom end of the auxiliary furnace 4 and the bottom end of the convection channel 12.

That is, the fire grate 3 is completely positioned in the main hearth 2, the fire grate 3 has an unchanged structure compared with the original single hearth, the cross sections of the middle part and the top part of the main hearth 2 are reduced so as to reduce the occupied width of the main hearth 2, and the auxiliary hearth 4 and the convection passage 12 are arranged side by side.

The auxiliary hearth 4 and the convection channel 12 are arranged side by side with the top and the middle of the main hearth 2, and the bottom of the auxiliary hearth 4 can be bent to enable the outlet to face one side above the fire grate 3; the convection channel 12 can be arranged with the auxiliary hearth 4 at the top and the middle part, and the bottom can be bent to enable the outlet to face to one side; the outlet at the bottom of the convection channel 12 can be located above the outlet at the bottom of the secondary hearth 4. In order to facilitate the communication between the bottom of the auxiliary hearth 4 and the bottom of the convection channel 12, a switching part can be arranged to be respectively communicated with the two, and the flue gas turns at the switching part 14 and flows into the convection channel 12.

The structure of the arrangement structure can reduce the structural change of the existing boiler grate 3, the auxiliary hearth 4 and the convection channel 12 can be additionally arranged on the basis of the arrangement of the existing grate 3, the combustion efficiency can be improved on the basis of the original fuel combustion amount, and the pollutant emission can be reduced.

Further, the bottom and middle of the main hearth 2 may be bent.

This layer natural boiler structure still includes: a flue gas recirculation device 11; the flue gas recirculation device 11 is communicated with the inside of the main hearth 2 and the tail end of the tail flue 6 and is used for introducing the flue gas at the tail end of the tail flue 6 into the main hearth 2. The starting end of the tail flue 6 is connected with the outlet of the hearth. The end of the back pass 6, i.e. the part through which the flue gas flows, is closer to the end of the back pass 6, the lower the temperature of the flue gas.

According to the boiler structure provided by the embodiment, part of flue gas is taken from the tail end of the tail flue 6 and is sent into the main hearth 2, so that the combustion temperature of a combustion area in the main hearth 2 can be reduced, and the generation of nitrogen oxides is reduced; the requirement of the emission of nitrogen oxides in environment protection is met, the investment of environment-friendly equipment and the operating cost of the environment-friendly equipment are reduced, and better economic benefit and social benefit are achieved; and the flue gas is introduced into the main hearth 2 again, thereby being beneficial to the full and complete combustion of the fuel, further improving the heat utilization rate and improving the heat efficiency.

On the basis of the above embodiment, further referring to fig. 3, the flue gas recirculation device 11 includes a flue gas recirculation main air duct 111, the end of the tail flue 6 is provided with a flue gas taking port, the flue gas taking port is connected to the flue gas recirculation main air duct 111, and the flue gas recirculation main air duct 111 is disposed on one side of the fire grate 3 close to the tail.

The smoke taking port can be arranged on the side wall at the tail end of the tail flue 6 and used for leading out smoke. The flue gas recirculation main air pipe 111 is used for guiding the flue gas taken out from the flue gas taking port to one side of the fire grate 3 close to the tail part. The flue gas can contact with the ash at the tail part of the fire grate 3, thereby reducing the temperature of the ash, reducing the heat loss of the ash and improving the boiler efficiency.

On the basis of the above embodiment, further, the flue gas recirculation main duct 111 is arranged in parallel with the upper surface of the grate 3 along the width direction of the grate 3. The main flue gas recirculation air pipe 111 is arranged along the width direction of the fire grate 3, so that the recirculated flue gas is distributed in the width direction of the fire grate 3, namely, the recirculated flue gas is positioned on one side of the fire grate 3 close to the tail part, and the temperature of ash slag at the tail part is convenient to reduce.

Referring to fig. 4 and 5, a plurality of nozzles 112 are vertically connected to the flue gas recirculation main duct 111, and outlets of the nozzles 112 are disposed downward. I.e. the nozzles 112 spray the recirculating flue gas towards the grate 3 above the grate 3. Further, the outlet of the nozzle 112 should be located in the main combustion zone inside the main furnace 2; so as to effectively reduce the combustion temperature and reduce the generation of nitrogen oxides.

On the basis of the above embodiment, further, a plurality of nozzles 112 are uniformly arranged along the width direction of the grate 3; the temperature of the main combustion area in the main hearth 2 and the temperature of the ash can be uniformly reduced, so that the denitration effect is improved, the heat loss of the ash is fully reduced, and the heat efficiency is improved. The distance between the flue gas recirculation main air pipe 111 and the tail part of the fire grate 3 is 450 mm and 550 mm. So that the flue gas recirculation main air pipe 111 corresponds to the position of ash on the fire grate 3. Further, the smoke taking port is arranged behind the air preheater 8 on the tail flue.

On the basis of the above embodiment, further, the flue gas recirculation main duct 111 is arranged inside the auxiliary furnace 4, and the nozzle 112 penetrates through the side wall of the auxiliary furnace 4 and is inserted into the main furnace 2; two ends of the flue gas recirculation main air pipe 111 respectively penetrate out of the hearth to be connected with the two smoke taking ports in a one-to-one correspondence manner. Because the main furnace 2 is bent, the sectional area of the middle part is smaller than that of the bottom part, so that the space of the main furnace 2 corresponding to the upper part of the tail part of the fire grate 3 is smaller, the flue gas recirculation main air pipe 111 can be arranged in the auxiliary furnace 4, and the nozzle 112 can penetrate through the membrane water-cooled wall between the main furnace 2 and the auxiliary furnace 4.

Smoke taking ports can be respectively arranged on two opposite sides of the tail end of the tail flue 6, so that two ends of the smoke recycling main air pipe 111 are connected with the two smoke taking ports in a one-to-one correspondence mode, the smoke recycling main air pipe 111 can be conveniently and fixedly installed, and the recycled smoke can be uniformly fed above the grate 3. Further, an induced draft fan can be arranged on a connecting pipeline between the flue gas recirculation main air pipe 111 and the flue gas taking port to provide conveying power for the recirculated flue gas.

In addition to the above embodiments, further, the convection heating surface 5 is provided inside the convection passage 12. The tail flue 6 is sequentially provided with an economizer 7 and an air preheater 8 along the flowing direction of flue gas, the tail flue 6 is arranged at the rear part of the air preheater 8 and is connected with an induced draft fan, and the induced draft fan can be sequentially connected with an economizer and a desulfurization device. The convection channel 12 can be further provided with a denitration module 15, and the denitration module 15 can be an SCR catalyst module to realize denitration in the furnace.

On the basis of the foregoing embodiments, further, the present embodiment provides a boiler denitration method based on the grate-fired boiler structure according to any one of the foregoing embodiments, including: drawing the recirculated flue gas from the end of the back pass 6; the recirculated flue gas is introduced into the main furnace 2 and above the rear part of the grate 3.

On the basis of the embodiment, the temperature of the extracted recirculation smoke is less than or equal to 150 ℃; the proportion of the recycled flue gas in the total flue gas is 15-25%; the flow velocity of the recirculated flue gas into the main furnace 2 is 25-35 m/s.

Specifically, a smoke outlet is arranged at the rear part of the air preheater 8, the temperature of smoke at the smoke outlet is lower than 150 ℃, and the smoke is taken to be sent to a smoke recycling device 11 above the rear part of the grate 3. The flue gas recirculation main air pipe 111 and the flue gas recirculation nozzle 112 are arranged at the tail part of the rear arch, are vertically arranged downwards and are about 500mm away from the tail part of the fire grate 3, and the cooling of slag is required to be ensured.

The maximum flue gas circulation amount is about 20 percent of the total flue gas amount. In actual operation, the frequency conversion fan can be used for adjusting the amount of the recycled flue gas so as to obtain the best effect. The size and the number of the inner openings of the flue gas recirculation nozzle 112 are selected according to the flue gas quantity, the flue gas velocity in the flue gas recirculation nozzle 112 is about 30m/s, and the rear arches are uniformly distributed as much as possible during arrangement. Welding is adopted between the flue gas recirculation main air pipe 111 and the flue gas recirculation nozzle 112, and flat steel of the membrane wall corresponding to the flue gas recirculation nozzle 112 is perforated according to the size of the flue gas recirculation nozzle 112.

According to the layer combustion boiler structure and the boiler denitration method, part of flue gas is taken from the tail part of the boiler and is sent to the rear part of the fire grate 3, so that the combustion temperature of a main combustion area on the fire grate 3 is reduced, and the generation of nitrogen oxides is reduced. The problems of low thermal efficiency and high emission of nitrogen oxides of the grate-fired industrial boiler are solved, and the treatment intensity of pollutants (nitrogen oxides) of the grate-fired boiler can be reduced; the ash temperature is reduced, the heat loss of ash is reduced, and the boiler efficiency is improved; the combustion temperature of flame in the hearth is reduced, and the generation of nitrogen oxides is reduced; the method meets the requirement of environment-friendly emission of nitrogen oxides, reduces the investment of environment-friendly equipment and the operating cost of the environment-friendly equipment, and has better economic benefit and social benefit.

On the basis of the above embodiments, further, referring to fig. 2, the boiler structure and the denitration method described in the above embodiments are also applicable to a chain boiler, and the specific structural arrangement and operation method of the chain boiler are similar to those of the above grate firing boiler, and are not described again.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.