CN114321907B

CN114321907B - Natural gas burner with low NOx emission

Info

Publication number: CN114321907B
Application number: CN202111444559.XA
Authority: CN
Inventors: 罗自学; 马燕熊; 程强
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2021-11-30
Filing date: 2021-11-30
Publication date: 2023-03-28
Anticipated expiration: 2041-11-30
Also published as: CN114321907A

Abstract

The invention relates to a low NO _x A discharged natural gas burner including a gas pipe, a primary air pipe, and a secondary air pipe; the front end of the gas pipe is provided with a plurality of fuel spray holes, and the rear end of the gas pipe is provided with a feed inlet; the primary air pipe is coaxially sleeved outside the fuel gas pipe, a primary air channel is formed between the primary air pipe and the fuel gas pipe, and a primary air outlet is formed in the primary air channel and close to the fuel spray hole; the secondary air pipe is coaxially sleeved outside the primary air pipe, a secondary air channel is formed between the secondary air pipe and the primary air pipe, and the secondary air channel is provided with a secondary air outlet close to the fuel spray hole; it realizes the hierarchical confession of air through arranging a plurality of fuel orifices to and setting up of primary air pipe and secondary air pipe, thereby makes flame shape, combustion reaction produce the combustion state that temperature gradient is littleer in whole combustion space, improves the temperature homogeneity in whole combustion area greatly, makes the fuel fully burn, reduces NO _x Is discharged.

Description

Low NO x Vented natural gas burner

Technical Field

The invention relates to the technical field of combustion of gas industrial furnaces, in particular to a low-NO furnace _x Vented natural gas burner.

Background

Even though natural gas is an economical, clean fossil fuel, the nitrogen oxides produced during combustion are not negligible. Nitrogen oxides (NOx) are one of the main pollutants of the atmosphere, mainly NO and NO ₂ Exist in the form of (1). It not only can form acid rain or acid mist to cause harm to human body and environment, but also is PM _2.5 Important precursors of secondary particles can cause haze. A new emission standard of boiler atmospheric pollutants (DB 11/139-2015) is released in Beijing City at 7/1 th in 2015, and the NOx emission limit of a newly-built boiler is 30 mg/cubic meter from 4/1 th in 2017. In view of the adverse effects of NOx on the atmospheric environment and the gradual approach of NOx emission to the environmental protection standard of the world, NOx has become a key object of pollution emission reduction in China. In recent years, natural gas has been widely used in industrial fields as well as civil fields, and the problem of emission of pollutants caused by the natural gas has attracted general attention. Therefore, this problem is urgently solved.

Gas burners have been widely studied by researchers at home and abroad as a core device for reducing nitrogen oxides (NOx) and affecting combustion heat efficiency. For a long time, researchers in China have studied a lot of coal-fired burners, and the research on burners of industrial gas-fired furnaces is relatively less. As the NOx emission is limited in some developed countries in the last 60 th century, and the attention degree of China to the NOx emission is relatively late, the low-nitrogen combustion technology in China is not mature enough at present, and the low-nitrogen gas burner is excessively dependent on foreign imports.

The combustion process of natural gas mainly generates thermal NOx, and aiming at the generation mechanism of the thermal NOx, the ways for effectively reducing the NOx emission comprise reducing the combustion temperature, controlling the oxygen concentration in the combustion process, shortening the retention time of reactants in a high-temperature area and the like. The low-nitrogen combustion technology of the gas burner mainly comprises the following steps: air/fuel staged combustion technology, flue gas recirculation combustion technology, lean premixed combustion technology, MILD combustion technology, and catalytic combustion technology. Among them, air/fuel staged combustion technology, flue gas recirculation, etc. have been widely used in engineering practice.

Disclosure of Invention

Based on the above expression, the present invention provides a low NO _x The discharged natural gas burner solves the technical problems that the content of nitrogen oxides in the discharged gas is high due to overhigh combustion temperature, atmosphere and overlong retention time of reactants in a high-temperature area in the conventional burner.

The technical scheme for solving the technical problems is as follows:

low NO _x The discharged natural gas burner comprises a gas pipe, a primary air pipe and a secondary air pipe;

the front end of the gas pipe is provided with a plurality of fuel spray holes, and the rear end of the gas pipe is provided with a feed inlet;

the primary air pipe is coaxially sleeved outside the fuel gas pipe, a primary air channel is formed between the primary air pipe and the fuel gas pipe, and the primary air channel is provided with a primary air outlet close to the fuel spray hole;

the secondary air pipe is coaxially sleeved on the outer side of the primary air pipe, a secondary air channel is formed between the secondary air pipe and the primary air pipe, and the secondary air channel is close to the fuel spray holes and is provided with a secondary air outlet.

Compared with the prior art, the technical scheme of the application has the following beneficial technical effects:

the application provides a natural gas combustor is through arranging a plurality of fuel orifices to and the hierarchical confession of air is realized in setting up of primary air pipe and secondary air pipe, thereby makes flame shape, combustion reaction produce the combustion state that temperature gradient is littleer in whole combustion space, improves the temperature homogeneity in whole combustion area greatly, makes the abundant burning of fuel, reduces NO _x And (4) discharging.

On the basis of the technical scheme, the invention can be further improved as follows.

The gas burner is characterized by further comprising a plurality of cyclone blades, wherein the plurality of cyclone blades are arranged at the position, close to the secondary air outlet, of the secondary air channel and are uniformly distributed along the circumferential direction of the gas pipe, included angles beta are formed between the cyclone blades and the central axis of the gas pipe, and the angle range of the included angles beta is 20-45 degrees.

Further, the angle range of the included angle beta is 25-40 degrees.

Further, still include surely fire the cover, surely fire cover coaxial coupling in with the front end of secondary air pipe, surely fire the opening of cover and expand from the rear end to the front end gradually.

Furthermore, an outward expansion angle gamma is formed between the stable combustion cover and the central axis of the gas pipe, and the angle of the expansion angle is not more than 40 degrees.

Further, the angle range of the divergence angle is 15-40 degrees.

Further, the premixing device comprises a premixing part, a premixing chamber is arranged in the premixing part, the premixing chamber is connected with the feeding hole through a mixing pipe, and a steam pipeline, a carbon monoxide pipeline and a fuel pipeline which are communicated with the premixing chamber are connected to the outside of the premixing part.

Further, a primary air inlet pipe communicated with the primary air channel is connected to the primary air pipe, a secondary air inlet pipe communicated with the secondary air channel is connected to the secondary air pipe, and the primary air inlet pipe and the secondary air inlet pipe are both provided with flow regulating valves; the air flow rate at the primary air channel is 1/4 of the total air flow rate, and the air flow rate at the secondary air channel is 3/4 of the total air flow rate; the air flow velocity range in the primary air channel is 10 m/s-20 m/s, and the air flow velocity range in the secondary air channel is 20 m/s-40 m/s.

Further, still include flue gas circulating pipe and baffle, the flue gas circulating pipe install in just set up along the fore-and-aft direction in the secondary air passageway, the baffle install in just set up along the fore-and-aft direction in the primary air passageway, the baffle install in the primary air passageway and separate it for anterior cavity and the rear cavity that do not communicate each other, the primary air advances to manage and is located the baffle front side and with anterior cavity intercommunication sets up, the primary air pipe still is connected with into the tobacco pipe, it is located to advance the tobacco pipe the baffle rear side and with rear cavity intercommunication sets up, the rear end of flue gas circulating pipe passes the baffle with rear cavity intercommunication, the front end of flue gas circulating pipe extends to the primary air export is fixed in through a solid fixed ring the gas pipe outside.

Furthermore, the fuel spray holes are circular or elliptical, a hemispherical curved surface protruding forwards is formed at the front end of the fuel gas pipe, the fuel spray holes are located on the hemispherical curved surface, the fuel spray holes are distributed in a three-layer annular shape at equal intervals, and the flow speed range of fuel is 10-20 m/s.

Drawings

FIG. 1 shows a low NO according to an embodiment of the present invention _x A schematic diagram of a vented natural gas combustor;

FIG. 2 is a schematic front end view of FIG. 1;

FIG. 3 is a partial cross-sectional view of the front end of FIG. 1;

fig. 4 is a schematic structural diagram of a natural gas burner according to another embodiment of the present invention.

Detailed Description

To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Embodiments of the present application are set forth in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

It will be understood that spatial relationship terms, such as "under", "below", "beneath", "below", "over", "above", and the like, may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements or features described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary terms "under" and "under" can encompass both an orientation of above and below. In addition, the device may also include additional orientations (e.g., rotated 90 degrees or other orientations) and the spatial descriptors used herein interpreted accordingly.

It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or be connected to the other element through intervening elements. The "connection" in the following embodiments is to be understood as "electrical connection", "communication connection", and the like if the connected circuits, modules, units, and the like have transmission of electrical signals or data therebetween.

As used herein, the singular forms "a", "an" and "the" may include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises/comprising," "includes" or "including," etc., specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof.

As shown in FIGS. 1 to 4, the present application provides a low NO _x Discharged natural gas burner, it includes gas pipe 1, primary air pipe 2 and secondary air pipe 3.

The gas pipe 1 is used for transporting fuel (i.e., natural gas), wherein the gas pipe 1 has a plurality of fuel injection holes 1a at a front end thereof and a feed port 1b at a rear end thereof.

Preferably, the fuel injection holes 1a are circular or elliptical, a hemispherical curved surface 11 protruding forward is formed at the front end of the gas pipe 1, the plurality of fuel injection holes 1a are located on the hemispherical curved surface 11, the fuel injection holes 1a are distributed in a three-layer ring shape at equal intervals, and the flow velocity range of the fuel when the burner is used is 10 m/s-20 m/s.

The fuel spray holes 1a are distributed in a multi-layer annular mode or are designed by adopting spray hole structures with different pore sizes and are positioned on the hemispherical curved surface 11. The jet rigidity of the fuel is reduced, and the residence time of the fuel in the combustion chamber is increased; the fuel is favorably diffused to the hemispherical area, so that the air and the fuel are fully mixed, the combustion reaction area is wider, and the temperature uniformity is better.

Primary air pipe 2 is coaxial to overlap and is located the outside of gas pipe 1, it is specific, primary air pipe 2's rear end and gas pipe welding, the uncovered setting of front end is formed with primary air channel 2a between primary air pipe 2 and the gas pipe 1, primary air channel 2a is close to fuel orifice 1a has primary air outlet 2b.

The coaxial cover of secondary air pipe 3 is located the outside of primary air pipe 2, similar, the rear end and the welding of primary air pipe 2 of secondary air pipe 3, the uncovered setting of front end, secondary air pipe 3 with be formed with secondary air passageway 3a between the primary air pipe 2, secondary air passageway 3a is close to fuel orifice 1a has secondary air outlet 3b.

Preferably, a primary air inlet pipe 21 communicated with the primary air passage 2a is connected to the primary air pipe 2, a secondary air inlet pipe 31 communicated with the secondary air passage 3a is connected to the secondary air pipe 3, and a flow rate adjusting valve (not shown in the figure) is installed in each of the primary air inlet pipe 21 and the secondary air inlet pipe 31; it can be understood that the flow regulating valve can be a manual regulating valve or an automatic regulating valve, so as to achieve better practical effects, wherein in order to ensure the uniformity of air mixing, the air flow at the primary air passage 2a is 1/4 of the total air flow, and the air flow at the secondary air passage 3a is 3/4 of the total air flow; the air flow velocity range in the primary air channel is 10-20 m/s, and the air flow velocity range in the secondary air channel is 20-40 m/s.

When the natural gas burner is used, natural gas fuel is input into the gas pipe 1 from the feed port and sprayed out from the fuel spray holes 1a, then air is respectively conveyed to the fuel spray holes 1a from the primary air pipe 2 and the secondary air pipe 3 to be mixed and combusted with the natural gas, so that the graded conveying of the air is realized, the flame shape and the combustion reaction generate a combustion state with smaller temperature gradient in the whole combustion space, the temperature uniformity of the whole combustion area is greatly improved, the fuel is fully combusted, and NO is reduced _x And (4) discharging.

Furthermore, in order to enhance the mixing degree of the fuel gas and the combustion-supporting gas, the fuel gas stays in the combustion chamber for a longer time. The natural gas burner provided by the embodiment further comprises a plurality of swirl blades 4, the swirl blades 4 are arranged at the position of the secondary air channel 3a close to the secondary air outlet 3b and are uniformly distributed along the circumferential direction of the gas pipe 1, and the angle range of the included angle beta between the swirl blades 4 and the central axis of the gas pipe 1 is 20-45 degrees.

The swirl vanes 4 can make the flame form a flow field with certain swirl strength, and are arranged in the center and close toA central reflux area and an outer reflux area are respectively generated near the inner wall of the gas pipe, so that the mixing of fuel and air is accelerated. The generated backflow area can absorb combustion products or combustion smoke and perform mixed combustion with fuel again, so that the combustion efficiency is improved, and the combustion intensity is enhanced; the burner with the swirl vanes 4 has obvious flow field characteristics different from the traditional burner, effectively reduces the gas injection rigidity, increases the swirl characteristics, can increase the residence time of flue gas in a combustion chamber, improves the uniformity of the temperature of a combustion area, and can further greatly reduce NO according to theoretical analysis and practical application verification _x Is discharged from

More preferably, the included angle β is preferably in the range of 25 ° to 40 °.

In order to ensure the stability of flame combustion, the distance of an ignition point from the front end of the burner is reduced. The secondary air pipe is characterized by further comprising a combustion stabilizing cover 5, wherein the combustion stabilizing cover 5 is coaxially connected with the front end of the secondary air pipe 3, and the opening of the combustion stabilizing cover 5 is gradually expanded from the rear end to the front end. The stable combustion cover and the swirl vanes can generate a backflow area at the front end of the combustor under the combined action, and the high-temperature smoke is sucked in an entrainment mode for reburning.

Preferably, the angle of divergence gamma formed between the stable combustion cover 5 and the central axis of the gas pipe 1 is not more than 40 degrees.

More preferably, the angle range of the divergence angle γ is 15 ° to 40 °.

In order to reduce the combustion temperature, reduce the oxygen concentration in the combustion process and inhibit the generation of thermal NOx, the embodiment further comprises a flue gas circulating pipe 6 and a baffle 61, wherein the flue gas circulating pipe 61 is installed in the primary air channel 2a and is arranged along the front-back direction, the baffle 61 is installed in the primary air channel 2a and divides the primary air channel 2a into a front cavity and a rear cavity which are not communicated with each other, specifically, the baffle 61 is of an annular structure matched with the primary air channel 2a in the direction, the inner end of the baffle 61 is welded with the outer surface of the gas pipe 1, the outer end of the baffle 61 is welded with the inner surface of the primary air pipe 2, and no air flow passes through the front cavity and the rear cavity.

The primary air inlet pipe 21 is located at the front side of the baffle 61 and is communicated with the front cavity of the primary air channel 2a, the primary air pipe 2 is further connected with a smoke inlet pipe 22, the smoke inlet pipe 22 is located at the rear side of the baffle 61 and is communicated with the rear cavity of the primary air channel 2a, the rear end of the smoke circulation pipe 6 penetrates through the rear cavity of the baffle 61 and the primary air channel 2a, and the front end of the smoke circulation pipe 6 extends to the primary air outlet 2b and is fixed on the outer side of the gas pipe 1 through a fixing ring 62.

Part of the flue gas generated by the combustion of the fuel at the front end of the burner can be guided to the smoke inlet pipe 22 by a pipeline and then enters the interior of the burner again to form recirculated flue gas. The main components of the flue gas are water vapor, carbon dioxide, nitrogen and a small amount of oxygen and nitrogen oxides. The addition of recirculated flue gas during combustion can increase the initial temperature and thereby reduce the combustion temperature, while diluting the oxygen concentration, which will reduce the formation of thermal NO from oxygen and nitrogen _x Further reducing NO _x And (4) generating.

In the present embodiment, in order to further reduce the amount of NOx emissions, in another embodiment of the present application, the natural gas burner further includes a premix 7, the premix 7 has a premix chamber 7a inside, the premix chamber 7a is connected to the feed port 1b through a mixture pipe 71, and a steam pipe 72, a carbon monoxide pipe 73 and a fuel pipe 74 which are communicated with the premix chamber 7a are connected to the outside of the premix 7.

The fuel line 74 is used for inputting natural gas fuel, the water vapor line 72 and the carbon monoxide line 73 are used for inputting water vapor and CO respectively, the CO is used as a reducing combustible gas, and the CO added into the natural gas has influence on the reaction temperature and NO emission. From the thermal property, the water vapor is used as a diluent with high specific heat capacity and can absorb heat in the combustion chamber so as to reduce the temperature; from the chemical properties aspect, H ₂ The O molecule is chemically active and can participate in many intermediate combustion reactions to alter NO _x Influence the concentration distribution of H, O and OH as combustion intermediate products, thereby effectively inhibiting NO _x And (4) generating.

Thus, it is possible to provideThe natural gas burner provided by the invention fully mixes air and fuel through the specially designed and arranged porous fuel spray holes and the graded feeding of the air, so that the flame shape and the combustion reaction generate a combustion state with smaller temperature gradient in the whole hearth region or combustion space, the temperature uniformity of the whole heating region can be greatly improved, and NO is reduced to the maximum extent _x And (4) discharging. In addition, by adding CO into the natural gas combustor, the oxygen concentration of a high-temperature combustion area can be reduced, so that the highest temperature of a hearth area or a combustion space is reduced, and NO is reduced _x Discharging of (3); the NO is inhibited by adding water vapor to the natural gas burner to increase the concentration of OH free radicals and reduce the concentration of O and H atoms _x Thus, NO can be further effectively reduced _x And (4) discharging.

In general, the natural gas burner enables air and fuel to be mixed more fully from the physical aspect, high-temperature smoke can be sucked in the internal and external backflow areas formed in the combustion chamber, the temperature uniformity of the whole combustion area is greatly improved, and NO is reduced _x Discharging of (3); chemically, the addition of diluents alters the chemical pathways of the combustion reaction, enabling the reduction of NO production _x Precursor of (2), inhibition of NO _x And (4) generating.

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.

Claims

1. The natural gas burner with low NOx emission is characterized by comprising a gas pipe, a primary air pipe and a secondary air pipe;

the secondary air pipe is coaxially sleeved on the outer side of the primary air pipe, a secondary air channel is formed between the secondary air pipe and the primary air pipe, and the secondary air channel is provided with a secondary air outlet close to the fuel spray hole;

still include flue-gas circulation pipe and baffle, the flue-gas circulation pipe install in just set up along the fore-and-aft direction in the primary air passageway, the baffle install in the primary air passageway and separate it for anterior cavity and the rear cavity that each other does not communicate, the primary air advances the pipe to be located the baffle front side and with anterior cavity intercommunication sets up, the primary air pipe still is connected with into tobacco pipe, it is located to advance the tobacco pipe the baffle rear side and with rear cavity intercommunication sets up, the rear end of flue-gas circulation pipe passes the baffle with rear cavity intercommunication, the front end of flue-gas circulation pipe extends to the primary air export is fixed in through a solid fixed ring the gas pipe outside.

2. The natural gas burner with low NOx emission according to claim 1, further comprising a plurality of swirl vanes installed at a position of the secondary air passage close to the secondary air outlet and uniformly distributed along a circumferential direction of the gas pipe, the swirl vanes forming an included angle β with a central axis of the gas pipe, the included angle β being in an angle range of 20 ° to 45 °.

3. The low NOx-emitting natural gas burner as claimed in claim 2, wherein said included angle β is in the range of 25 ° to 40 °.

4. The low NOx-emitting natural gas burner as claimed in claim 1, further comprising a combustion stabilizing cap coaxially connected to a front end of said secondary air pipe, an opening of said combustion stabilizing cap being gradually expanded from a rear end to a front end.

5. The natural gas burner with low NOx emission according to claim 4, wherein the combustion stabilizing cover forms an outward divergence angle γ with a central axis of the gas pipe, the divergence angle γ being not greater than 40 °.

6. The natural gas burner with low NOx emissions according to claim 5, characterized in that the divergence angle γ ranges from 15 ° to 40 °.

7. The natural gas burner with low NOx emission according to claim 1, further comprising a premixing piece, wherein a premixing chamber is arranged inside the premixing piece, the premixing chamber is connected with the feeding hole through a mixing pipe, and a water vapor pipeline, a carbon monoxide pipeline and a fuel pipeline which are communicated with the premixing chamber are connected to the outside of the premixing piece.

8. The natural gas burner with low NOx emission according to claim 1, wherein a primary air inlet pipe communicating with the primary air passage is connected to the primary air pipe, a secondary air inlet pipe communicating with the secondary air passage is connected to the secondary air pipe, and a flow rate adjusting valve is installed in each of the primary air inlet pipe and the secondary air inlet pipe; the air flow rate at the primary air passage is 1/4 of the total air flow rate, and the air flow rate at the secondary air passage is 3/4 of the total air flow rate; the air flow velocity range in the primary air channel is 10 m/s-20 m/s, and the air flow velocity range in the secondary air channel is 20 m/s-40 m/s.

9. The natural gas burner with low NOx emission according to claim 1, wherein the fuel injection holes are circular or elliptical, a hemispherical curved surface protruding forward is formed at the front end of the gas pipe, a plurality of the fuel injection holes are located on the hemispherical curved surface, and the fuel injection holes are arranged in a three-layer ring shape at equal intervals, and the flow rate of the fuel ranges from 10m/s to 20m/s.