CN114321907B - Natural gas burner with low NOx emission - Google Patents

Abstract

The invention relates to a natural gas burner with low _NOx emission, which comprises a gas pipe, a primary air pipe and a secondary air pipe; the front end of the gas pipe has a plurality of fuel injection holes, and its rear end has a feed port; Coaxially sleeved on the outside of the gas pipe, a primary air passage is formed between the primary air pipe and the gas pipe, and the primary air passage has a primary air outlet near the fuel injection hole; the secondary air pipe is coaxially sleeved on the outside of the primary air pipe , a secondary air passage is formed between the secondary air pipe and the primary air pipe, and the secondary air passage has a secondary air outlet near the fuel injection hole; it arranges a plurality of fuel injection holes, as well as the primary air pipe and the secondary air pipe The setting realizes the staged supply of air, so that the flame shape and combustion reaction can produce a combustion state with a smaller temperature gradient in the entire combustion space, greatly improving the temperature uniformity of the entire combustion area, making the fuel fully combustible and reducing _NOx emissions.

Description

A Natural Gas Burner with Low NOx Emission

technical field

The invention relates to the technical field of gas industrial furnace combustion, in particular to a natural gas burner with low _NOx emission.

Background technique

Even though natural gas is an economical and clean fossil fuel, the nitrogen oxides produced during the combustion process cannot be ignored. Nitrogen oxides (NOx) are one of the main pollutants in the atmosphere, mainly in the form of NO and _NO2 . It can not only form acid rain or acid fog, which is harmful to human body and environment, but also an important precursor of PM _2.5 secondary particles, which can cause smog. On July 1, 2015, Beijing issued a new "Boiler Air Pollutant Emission Standard" (DB11/139-2015), which stipulates that from April 1, 2017, the NOx emission limit of newly built boilers is 30 mg/cubic rice. In view of the many adverse effects of NOx on the atmospheric environment and the NOx emissions gradually approaching the world's environmental protection standards, NOx has become the key target of pollution reduction in my country. In recent years, natural gas has been widely used in both industrial and civil fields, and the resulting pollutant emissions have attracted widespread attention. Therefore, this problem needs to be solved urgently.

As the core equipment for reducing nitrogen oxides (NOx) and affecting combustion thermal efficiency, gas burners have attracted extensive research by researchers at home and abroad. For a long time, researchers in our country have done a lot of research on coal-fired burners, but there are relatively few studies on gas-fired industrial furnace burners. Since some developed countries have restricted NOx emissions in the 1960s, and our country has paid attention to NOx emissions relatively late, resulting in the current low-nitrogen combustion technology in my country is not mature enough, and low-nitrogen gas burners rely too much on foreign imports.

Thermal NOx is mainly produced during the combustion process of natural gas. According to the formation mechanism of thermal NOx, effective ways to reduce NOx emissions include lowering the combustion temperature, controlling the oxygen concentration during combustion, and shortening the residence time of reactants in high-temperature areas, etc. . At present, the low-nitrogen combustion technologies for gas burners mainly include: air/fuel staged combustion technology, flue gas recirculation combustion technology, lean-burn premixed combustion technology, MILD combustion technology and catalytic combustion technology. Among them, air/fuel staged combustion technology, flue gas recirculation and other technologies have been widely used in engineering practice.

Contents of the invention

Based on the above statement, the present invention provides a natural gas burner with low NO _x emissions, to solve the problem of nitrogen oxidation in the exhaust caused by excessive combustion temperature and excessive residence time of the atmosphere and reactants in the high temperature area in the existing burner Technical problems with high substance content.

The technical scheme that the present invention solves the problems of the technologies described above is as follows:

A natural gas burner with low _NOx emission, comprising a gas pipe, a primary air pipe and a secondary air pipe;

The front end of the gas pipe has a plurality of fuel injection holes, and the rear end has a feed port;

The primary air pipe is coaxially sleeved on the outside of the gas pipe, and a primary air passage is formed between the primary air pipe and the gas pipe, and the primary air passage has a primary air outlet near the fuel injection hole ;

The secondary air pipe is coaxially sleeved on the outside of the primary air pipe, and a secondary air passage is formed between the secondary air pipe and the primary air pipe, and the secondary air passage is close to the fuel The orifice has a secondary air outlet.

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

The natural gas burner provided by this application realizes the staged supply of air by arranging multiple fuel injection holes and the arrangement of primary air pipes and secondary air pipes, so that the flame shape and combustion reaction produce a smaller temperature gradient in the entire combustion space. In the combustion state, the temperature uniformity of the entire combustion area is greatly improved, the fuel is fully burned, and the emission of NO _x is reduced.

On the basis of the above technical solutions, the present invention can also be improved as follows.

Further, it also includes a plurality of swirl blades, the plurality of swirl blades are installed in the secondary air passage near the secondary air outlet and are evenly distributed along the circumference of the gas pipe, the swirl blades An included angle β is formed with the central axis of the gas pipe, and the included angle β ranges from 20° to 45°.

Further, the angle range of the included angle β is 25°-40°.

Further, a combustion stabilization cover is also included, the combustion stabilization cover is coaxially connected to the front end of the secondary air pipe, and the opening of the combustion stabilization cover gradually expands from the rear end to the front end.

Further, the combustion stabilization hood forms an outward expansion angle γ with the central axis of the gas pipe, and the expansion angle is not greater than 40°.

Further, the expansion angle ranges from 15° to 40°.

Further, it also includes a premixing piece, which has a premixing chamber inside, and the premixing chamber is connected to the feed inlet through a mixing pipe, and the premixing piece is externally connected with the The water vapor pipeline, carbon monoxide pipeline and fuel pipeline connected by the premix chamber.

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

Further, it also includes a flue gas circulation pipe and a baffle, the flue gas circulation pipe is installed in the secondary air passage and arranged along the front-to-back direction, and the baffle is installed in the primary air passage and arranged along the front-to-back direction It is provided that the baffle is installed in the primary air channel and is divided into a front cavity and a rear cavity which are not communicated with each other, and the primary air inlet pipe is located at the front side of the baffle and connected to the The front cavity is communicated, and the primary air pipe is also connected to a smoke inlet pipe, which is located at the rear side of the baffle and communicated with the rear cavity. The end passes through the baffle and communicates with the rear cavity, and the front end of the flue gas circulation pipe extends to the primary air outlet and is fixed on the outside of the gas pipe through a fixing ring.

Further, the fuel injection hole is circular or elliptical, the front end of the gas pipe is formed with a hemispherical curved surface protruding forward, a plurality of the fuel injection holes are located on the hemispherical curved surface, and the The fuel injection holes are distributed in three rings at equal intervals, and the flow velocity of the fuel ranges from 10m/s to 20m/s.

Description of drawings

Fig. 1 is the structural representation of a kind of low _NOx emission natural gas burner that an embodiment of the present invention provides;

Figure 2. Schematic diagram of the front-end perspective of Figure 1;

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

Fig. 4 is a schematic structural view of a natural gas burner in another embodiment of the present invention.

Detailed ways

In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the application are given in the drawings. However, the present application can be embodied in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of this application more thorough and comprehensive.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used herein in the specification of the application are only for the purpose of describing specific embodiments, and are not intended to limit the application.

It will be appreciated that spatially relative terms such as "under", "beneath", "below", "under", "on", "above" etc., may be used herein to describe the relationship between one element or feature and other elements or features shown in the drawings. It will be understood that the spatially relative terms encompass different orientations of the device in use and 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" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary terms "below" and "beneath" can encompass both an orientation of above and below. In addition, the device may be otherwise oriented (eg, rotated 90 degrees or at other orientations) and the spatial descriptors used herein interpreted accordingly.

It should be noted that when an element is considered to be "connected" to another element, it may be directly connected to the other element, or connected to the other element through an intervening element. "Connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if the connected circuits, modules, units, etc. have the transmission of electric signals or data between each other.

When used herein, the singular forms "a", "an" and "the/the" may also include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprising/comprising" or "having" etc. specify the presence of stated features, integers, steps, operations, components, parts or combinations thereof, but do not exclude the presence or addition of one or more The possibility of 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 emission natural gas burner, which includes a gas pipe 1 , a primary air pipe 2 and a secondary air pipe 3 .

The gas pipe 1 is used to transport fuel (ie natural gas), wherein the front end of the gas pipe 1 has a plurality of fuel injection holes 1a, and its rear end has a feed port 1b.

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

The fuel injection hole 1a adopts multi-layer annular distribution, or multiple types of injection hole structure design with different hole sizes, and is located on the hemispherical curved surface 11 . It helps to reduce the jet rigidity of the fuel and increase the residence time of the fuel in the combustion chamber; it helps the fuel to diffuse to the hemispherical area, so that the air and the fuel can be fully mixed, so that the combustion reaction area is wider and the temperature uniformity is better.

The primary air pipe 2 is coaxially sleeved on the outside of the gas pipe 1. Specifically, the rear end of the primary air pipe 2 is welded to the gas pipe, and the front end is opened. A primary air pipe 2 and the gas pipe 1 are formed with a primary air pipe 2. An air passage 2a, the primary air passage 2a has a primary air outlet 2b close to the fuel injection hole 1a.

The secondary air pipe 3 is coaxially sleeved on the outside of the primary air pipe 2. Similarly, the rear end of the secondary air pipe 3 is welded to the primary air pipe 2, and the front end is open. The secondary air pipe A secondary air channel 3a is formed between 3 and the primary air pipe 2, and the secondary air channel 3a has a secondary air outlet 3b near the fuel injection hole 1a.

Preferably, the primary air pipe 2 is connected with a primary air inlet pipe 21 communicated with the primary air passage 2a, and the secondary air pipe 3 is connected with a secondary air pipe 21 communicated with the secondary air passage 3a. The inlet pipe 31, the primary air inlet pipe 21 and the secondary air inlet pipe 31 are all installed with a flow regulating valve (not shown in the figure); it can be understood that the flow regulating valve can be a manual regulating valve It can also be an automatic regulating valve, whichever is better in actual use, 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 secondary air The air flow at channel 3a is 3/4 of the total air flow; the air velocity in the primary air channel ranges from 10m/s to 20m/s, and the air velocity in the secondary air channel ranges from 20m/s to 40m/s.

When the above-mentioned natural gas burner is in use, the natural gas fuel is input into the gas pipe 1 from the feed port and sprayed out from the fuel injection hole 1a, and then the air is delivered to the fuel injection hole 1a from the primary air pipe 2 and the secondary air pipe 3 respectively. Mixed combustion with natural gas realizes the staged delivery of air, making the flame shape and combustion reaction produce a combustion state with a smaller temperature gradient in the entire combustion space, greatly improving the temperature uniformity of the entire combustion area, making the fuel fully combustible and reducing NO _x emissions.

Further, in order to enhance the mixing degree of the gas and the combustion-supporting gas, and make the gas stay in the combustion chamber for a longer time. The natural gas burner provided in this embodiment also includes a plurality of swirl vanes 4, and a plurality of swirl vanes 4 are installed in the secondary air channel 3a near the secondary air outlet 3b and along the gas pipe 1. Evenly distributed in the circumferential direction, the angle β between the swirl vanes 4 and the central axis of the gas pipe 1 ranges from 20° to 45°.

The swirl vane 4 can make the flame form a flow field with a certain swirl strength, and generate a central recirculation zone and an outer recirculation zone at the center and near the inner wall of the gas pipe respectively, which accelerates the mixing of fuel and air. The generated recirculation zone can entrain combustion products or combustion smoke, and then mix and burn with fuel again, thereby improving combustion efficiency and enhancing combustion intensity; this kind of burner with swirl vane 4 is different from traditional burners. The flow field characteristics effectively reduce the rigidity of the gas injection and increase the swirl characteristics, which can increase the residence time of the flue gas in the combustion chamber and improve the uniformity of the temperature in the combustion area. According to theoretical analysis and practical application proof, it can be further greatly improved Reduce _NOx emissions

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

In order to ensure the stability of flame combustion, the distance between the ignition point and the front end of the burner is reduced. This embodiment also includes a combustion stabilization cover 5, which is coaxially connected to the front end of the secondary air pipe 3, and the opening of the combustion stabilization cover 5 gradually expands from the rear end to the front end. Under the combined action of the combustion stabilization hood and the swirl blades, a recirculation area can be generated at the front end of the burner, entraining high-temperature flue gas for reburning.

Preferably, the expansion angle γ formed between the combustion stabilization cover 5 and the central axis of the gas pipe 1 is not greater than 40°.

More preferably, the expansion angle γ ranges from 15° to 40°.

In order to reduce the combustion temperature and reduce the oxygen concentration in the combustion process and suppress the formation of thermal NOx, this embodiment also includes a flue gas circulation pipe 6 and a baffle 61, and the flue gas circulation pipe 61 is installed in the primary air passage 2a The baffle plate 61 is installed in the primary air channel 2a and is divided into a front cavity and a rear cavity that are not connected to each other. Specifically, the baffle plate 61 is connected to the primary air channel 2a The channel 2a has a matching ring structure, the inner end of the baffle plate 61 is welded to the outer surface of the gas pipe 1, and the outer end of the baffle plate 61 is welded to the inner surface of the primary air pipe 2, thereby realizing the front cavity and the rear cavity There is no air flow between them.

The primary air inlet pipe 21 is located at the front side of the baffle plate 61 and communicated with the front cavity of the primary air passage 2a. The primary air pipe 2 is also connected with a smoke inlet pipe 22, and the smoke inlet pipe 22 is located at The rear side of the baffle 61 is arranged in communication with the rear cavity of the primary air passage 2a, and the rear end of the flue gas circulation pipe 6 passes through the baffle 61 and communicates with the rear cavity of the primary air passage 2a, The front end of the flue gas circulation pipe 6 extends to the primary air outlet 2b and is fixed on the outside of the gas pipe 1 by a fixing ring 62 .

Part of the flue gas generated by the combustion of fuel at the front end of the burner can be led to the smoke inlet pipe 22 through pipes and enter the burner again to form recirculated flue gas. The main components of flue gas are water vapor, carbon dioxide, nitrogen and a small amount of oxygen and nitrogen oxides. Adding recirculated flue gas during the combustion process can increase the initial temperature to reduce the combustion temperature, and at the same time dilute the concentration of oxygen, which will weaken the process of generating thermal _NOx from oxygen and nitrogen, and further reduce the formation of _NOx .

In this embodiment, in order to further reduce the emission of NOx, in another embodiment of the present application, the natural gas burner further includes a premixing element 7, and the premixing element 7 has a premixing chamber 7a inside, so The premixing chamber 7a is connected to the feed port 1b through a mixing pipe 71, and the premixing part 7 is externally connected with a water vapor pipeline 72, a carbon monoxide pipeline 73 and a fuel pipeline communicated with the premixing chamber 7a. 74.

Wherein, fuel pipeline 74 is used for the input of natural gas fuel, and water vapor pipeline 72 and carbon monoxide pipeline 73 are used for input water vapor and CO respectively, and CO is as a kind of reducing combustible gas, and adding CO in natural gas will affect the reaction temperature. and NO emissions. From the perspective of thermal properties, water vapor, as a diluent with high specific heat capacity, can absorb heat in the combustion chamber to lower the temperature; from the perspective of chemical properties, H ₂ O molecules are chemically active and can participate in many intermediate combustion reactions, changing the NO _x The formation pathway affects the concentration distribution of combustion intermediate products H, O, and OH, so that the formation of NO _x can be effectively suppressed.

Therefore, the natural gas burner provided by the present invention fully mixes the air and fuel through the specially designed and arranged porous fuel nozzles, and the staged supply of air, so that the flame shape and combustion reaction can be achieved in the entire furnace area or combustion space. A combustion state with a small temperature gradient can be generated, which can greatly improve the temperature uniformity of the entire heating area and minimize _NOx emissions. In addition, by adding CO to the natural gas burner, the oxygen concentration in the high-temperature combustion area can be reduced, so that the maximum temperature of the furnace area or the combustion space can be reduced, thereby reducing the emission of _NOx ; by adding water vapor to the natural gas burner, adding water vapor It can increase the concentration of OH free radicals, reduce the concentration of O and H atoms, thereby inhibiting the formation of _NOx , which can further effectively reduce the emission of _NOx .

In general, the natural gas burner makes the air and fuel mix more fully from the physical aspect, and can entrain high-temperature flue gas in the internal and external recirculation zones formed in the combustion chamber, which greatly improves the temperature uniformity of the entire combustion area , to reduce _NOx emissions; from the chemical aspect, adding diluent changes the chemical pathway of combustion reaction, which can reduce the precursors that produce _NOx and inhibit the formation of _NOx .

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (9)

1. A natural gas burner of low NOx emission, is characterized in that, comprises gas pipe, primary air pipe and secondary air pipe; The front end of the gas pipe has a plurality of fuel injection holes, and the rear end has a feed port; The primary air pipe is coaxially sleeved on the outside of the gas pipe, and a primary air passage is formed between the primary air pipe and the gas pipe, and the primary air passage has a primary air outlet near the fuel injection hole ; The secondary air pipe is coaxially sleeved on the outside of the primary air pipe, and a secondary air passage is formed between the secondary air pipe and the primary air pipe, and the secondary air passage is close to the fuel The nozzle hole has a secondary air outlet; It also includes a flue gas circulation pipe and a baffle, the flue gas circulation pipe is installed in the primary air passage and arranged along the front and rear directions, the baffle is installed in the primary air passage and separates them into non-communicating The front cavity and the rear cavity, the primary air inlet pipe is located on the front side of the baffle and communicated with the front cavity, the primary air pipe is also connected with a smoke inlet pipe, the inlet The smoke pipe is located on the rear side of the baffle and communicated with the rear cavity. The rear end of the smoke circulation pipe passes through the baffle and communicates with the rear cavity. The smoke circulation pipe The front end of the tube extends to the primary air outlet and is fixed on the outside of the gas pipe through a fixing ring. 2. The natural gas burner of low NOx emission according to claim 1, further comprising a plurality of swirl blades, a plurality of said swirl blades are installed in the secondary air channel near the secondary air outlet positions and are uniformly distributed along the circumference of the gas pipe, the swirl blades form an included angle β with the central axis of the gas pipe, and the angle range of the included angle β is 20°-45°. 3. The low NOx emission natural gas burner according to claim 2, characterized in that, the range of the included angle β is 25°-40°. 4. The natural gas burner with low NOx emission according to claim 1, characterized in that, it also comprises a stable combustion cover, and the stable combustion cover is coaxially connected to the front end of the secondary air pipe, and the stable combustion cover The opening of the cover gradually expands from the rear end to the front end. 5. The natural gas burner with low NOx emission according to claim 4, characterized in that, the combustion stabilization cover and the central axis of the gas pipe form an outward expansion angle γ, and the angle of the expansion angle γ is not greater than 40° °. 6. The natural gas burner with low NOx emission according to claim 5, characterized in that, the angle range of the expansion angle γ is 15°-40°. 7. The natural gas burner with low NOx emission according to claim 1, characterized in that, it also comprises a premixing part, the premixing part has a premixing chamber inside, and the gap between the premixing chamber and the feed inlet is The room is connected by a mixing pipe, and the premixing unit is externally connected with water vapor pipelines, carbon monoxide pipelines and fuel pipelines communicating with the premixing chamber. 8. The natural gas burner with low NOx emission according to claim 1, characterized in that, said primary air pipe is connected with a primary air inlet pipe communicated with said primary air passage, and said secondary air pipe is connected with There is a secondary air inlet pipe communicated with the secondary air passage, and a flow regulating valve is installed in the primary air inlet pipe and the secondary air inlet pipe; the air flow at the primary air passage is the total air flow 1/4 of the flow rate, the air flow at the secondary air passage is 3/4 of the total air flow; the air velocity in the primary air passage ranges from 10m/s to 20m/s, and the secondary air passage The range of air flow velocity inside is 20m/s～40m/s. 9. The natural gas burner with low NOx emission according to claim 1, wherein the fuel injection hole is circular or elliptical, and the front end of the gas pipe is formed with a hemispherical curved surface protruding forward, A plurality of the fuel injection holes are located on the hemispherical curved surface, and the fuel injection holes are distributed in a three-layer ring at equal intervals, and the fuel flow velocity ranges from 10m/s to 20m/s.

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