JPH06317308A - Operating method of low nox burner - Google Patents

Abstract

PURPOSE: To reduce the NOx emission of a burner by providing a flame stabilizer adjacent to the burner, excessively increasing the ratio of air in an air/gas mixture and increasing the velocity of the air/gas mixture passing through the burner. CONSTITUTION: When a mixture type burner 64 is provided with one or comparatively few outlet ports, that is, discharge orifices, a black body (wide and flat object) 60 as an inner flame stabilizer is arranged inside the outlet, that is, discharge orifice 62 of the mixture type burner 64. The black body 64 is directed inside an outlet port 62 so that the flow of the air/gas mixture comes into contact with the convex surface of the black body. In addition, the air/gas mixture contains excessive air and its velocity is close to a velocity at which the air/gas mixture starts to 'lift off' from the end surface of the burner 64 defining the outlet port 62. As a result, the air/gas mixture generates a zone for maintaining combustion before it blows out from the black body into the outlet port of the burner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion device and, more particularly, to a combustion technique with a very low NOx generation rate.

[0002]

2. Description of the Related Art In recent years, interest in the problem of air pollution has been rapidly increasing. This problem is especially acute in urban areas. There are many sources of air pollution, such as internal combustion engines, chemical plants, and power plants. One of the most important pollutants is nitrogen oxides such as NO and NO ₂ which are generally called NOx, and NOx causes air pollution due to the creation of smog.

Fuel combustion facilities such as power plants have various sources of NOx emissions. One of the so-called “high temperature NO” sources of NOx emission is the nitrogen (N) of the combustion air.
₂ ) It is generated by the oxidation of components. Thermodynamically, in order to generate NO by the oxidation of nitrogen, 1538 ° C (280
A temperature of 0 ° F) is required. First, diatomic nitrogen (N ₂ ) dissociates into monoatomic nitrogen (N), and then NO is generated. Another NOx called "fuel NO"
Emission sources include many fuels such as ammonia (NH ₃ )
Originates from the fact that it contains monatomic nitrogen-containing substances such as. In this case, the conversion of fuel-bound (fuel-bound) N to NO occurs at temperatures well below 1538 ° C. (2800 ° F.) because the separation of N ₂ bonds is not a prerequisite for NO generation. . The conversion of fuel bound N to NO can occur even at temperatures as low as 704 ° C. (1300 ° F.).

Yet another NOx called "quick NO"
The source of emission results from the fast reaction. Generation of NO due to high-speed reaction in the flame front (flame front) is already known, and there is a problem that is currently being researched, and a widely accepted theory regarding its generation mechanism has not yet been established. In areas with strict air pollution regulations, such as Southern California, it is becoming difficult to meet NOx emission standards with existing burners and / or methods of operating them.

Various methods have been conventionally developed for reducing the amount of NOx produced, but the degree of reduction achieved is often insufficient to satisfy the strict air pollution regulations mentioned above. is there. Some conventional methods are based on the principle of reducing NOx by multi-stage combustion. For example, such multi-stage combustion burns the first fuel as a "lean mixture" in the first stage, and the combustion products generated thereby are mixed and burned with the second fuel in the second stage to burn NOx. It consists of creating an atmosphere that reduces the amount produced. Alternatively, the fuel and air may be introduced into the burner in two separate streams having different fuel / air ratios. One flow is an excess air flow and the other flow is
Overflow of fuel. One flow is ignited to perform the first-stage combustion, and the combustion ignites the other flow to perform the second-stage combustion. Further, the third stage of combustion is performed by mixing and burning excess air of one flow and excess fuel of the other flow. Yet another method for reducing the NOx generation amount is to connect a plurality of burners in series in the flow direction of the combustion air and burn the fuel having the low NOx generation characteristic at the last burner in the row. .

NO can also be achieved by lowering the combustion temperature.
The x generation amount can be reduced. The combustion temperature is either by injecting water into the combustion gas to cool the flame directly, or
It can be lowered by adding a cooling gas to an air / fuel gas mixture (also referred to as "air / fuel mixture", "air / gas mixture" or simply "mixture").
Also, the flame temperature can be lowered by using a radiant burner, which is essentially a surface burner, often using ceramic fibers, metal fibers or reticulated ceramic foam as the radiant surface. A major drawback of most surface combustors is the large volume of air / gas mixture that remains in the burner due to their large size.
Thus, if a flashback occurs (the probability is high), the resulting deflagration will be of a nature close to that of an explosion. Another drawback of surface combustors is that the burner surface temperature must be kept very high in order to obtain optimum radiant heat output (radiation efficiency) for a constant fuel input. The surface combustion temperature is very sensitive to the air / fuel ratio (hereinafter, also simply referred to as “air-fuel ratio”), the flow velocity of the air-fuel mixture, and the homogeneity of the air-fuel mixture. The radiant heat output of the burner decreases at the rate of the fourth power of the decrease in the surface temperature of the burner. Therefore, the flame temperature must be raised in order not to reduce the radiant heat output, and as a result, the NOx generation amount is increased.

NOx production can also be reduced by recirculating the exhaust gas into the combustion chamber. In that case, a part of the exhaust gas may be mixed with the combustion gas before combustion, or may be separately fed into the combustion zone. The recirculated exhaust gas functions as a diluent to lower the overall oxygen concentration and lower the flame temperature. Basically, the combustion air supply is impure, which reduces NOx emissions but increases carbon monoxide (CO) emissions.

Yet another way to reduce NOx emissions is to modify the composition of the air / gas mixture. For example, if a mixture of oxygen and an inert gas other than nitrogen (N ₂ ) is used as the combustion atmosphere, the amount of NOx generated will be reduced. Alternatively, the nitrogen reacts with the oxide of (N ₂₎ was introduced into the additive to the combustion chamber to the creation of a reducing agent to produce nitrogen (N _2), thereby reducing the generation of NOx .

As described above, there are many methods for reducing the NOx generation amount, but all of the above-mentioned methods have their own drawbacks in terms of cost, reliability, performance and the like.
For example, if the combustion temperature is lowered to reduce the amount of NOx generated, the radiant heat flux emitted by the burner is reduced. Multi-stage combustion requires large facilities and control devices, which all result in high costs. In addition, the exhaust gas recirculation method requires additional equipment and increases the amount of carbon monoxide (CO) generated. The method of adding additives to create the reducing agent increases operating costs. The fibrous materials used in the radiation method are expensive, often brittle, and prone to clogging by dust, thus necessitating filtration equipment and associated maintenance. Moreover, such an air filtration device cannot prevent the burner blockage problem that is inevitably associated with the combustion of many fuel gases containing contaminants such as tar.

The generation of high temperature NO is the main mechanism of NOx generation in the combustion of clean gas such as natural gas, and it has already been established that the mechanism of the Zeldovich chain reaction is applicable to the generation of high temperature NO. . Analytical models of chemical kinetics predict that NOx production will increase with increasing time and temperature. This is proved by the fact that in the actual combustion device, the peak (maximum) generation rate of NOx hardly occurs on the fuel lean side of the stoichiometric curve. N, obtained using an analytical model of the Zeldovich chain reaction
The predicted value (theoretical value) of the relative contribution of time and temperature to the generation of O is shown in FIG. The graph of FIG. 1 also shows the contribution of the "residence time" (the time during which the air-fuel mixture stays in the combustion zone, and thus the time it is exposed to the combustion reaction temperature) to the generation of NOx. That is, NO
It is shown that it takes a certain amount of time to generate x. Figure 1 shows the importance of "residence time" in NOx generation, calculated using the analytical model of the Zeldovich chain reaction. At a flame temperature of 1871 ° C. (3400 ° F.) at a residence time of 0.1 seconds, 0.7 seconds and 4.5 seconds, 100 ppm level, 1000 pp, respectively.
m-level and equilibrium levels of NOx are generated. All of these levels are above the NOx emission standard.

In some cases, the combustion reaction (flame) temperature can be lowered by using an excessive amount of combustion air, so that the amount of lever and NOx generated can be reduced. However, this effect can only be used to advantage in the case of homogeneous premixed combustion devices (in chemical terms, plug flow reactors). In plug flow mode, the peak (highest) concentration of fuel / air (peak concentration of fuel relative to air) is equal to the average concentration due to the premixing of fuel and air. As a result, the average flame temperature is equal to the peak flame temperature. The amount of NOx generated is proportional to this flame temperature level. In a mixed-in-nozzle type (a type in which fuel and air are mixed in a nozzle) burner (stirred reactor), mixing and combustion reaction are performed at substantially the same time, and the mixing of There is a large variation in air concentration. As a result, stratification occurs in the air-fuel mixture, and locally the fuel / air peak concentration significantly exceeds the average value. A high temperature is generated in the high-concentration portion, and therefore a high level of NOx generation rate is obtained.

The premixed combustion system also has an advantage that the heat release rate per unit combustion volume is higher than that of the in-nozzle mixed combustion system. However, in other respects, especially in terms of combustion stability limits, the premixed combustion system
Inferior to the mixed combustion method in the nozzle. That is, in the premixed combustion system, when the value of the air / fuel ratio exceeds a certain limit,
The combustion reaction leaves the burner and the flame disappears (so-called "extinguish" or "blown out"). Such a phenomenon is shown in FIG. As seen in Figure 2,
Premixed burners have a limited combustion or flame stability range in the lean fuel operating range that is more useful, ie, less polluting. Further, in any type of burner, the combustion efficiency is reduced before the extinction of the flame, that is, "blowout" occurs. A reduction in combustion efficiency produces a large amount of unburned, combustible pollutants (especially CO when burning natural gas).

In solving the NOx problem, NOx and C
Both O must be considered at the same time. This is because the reduction of one pollutant may simply be a compromise with the amount of the other pollutant generated. In most conventional burners, the amounts of CO and NOx produced are generally inversely proportional. Removal of carbonaceous pollutants, such as CO, can be achieved with relatively simple techniques, but generally accepted techniques are used for NOx and CO
There were various problems in controlling both of them simultaneously. First, it takes time and a relatively high temperature (generally 1371 ° C.) to oxidize CO to carbon dioxide (CO ₂ ). It is already known that temperatures above 1538 ° C (2800 ° F) lead to NOx generation. This can be understood by referring to the graph of FIG. The graph in Fig. 3 shows NO
3 is a graph of x vs. flammables (eg CO) showing the pollutant emission level acceptable range where the burner is believed to operate at acceptable pollutant emission levels.

In order to maintain clean (pollution-free) and efficient combustion, a stable combustion region must be created. Without it, the extinction or "blown out" of the flame occurs. Combustion efficiency and flame stability have a close correlation, and "blown out" is, of course, a state where combustion efficiency is zero. Flame stabilization can be achieved by placing a flame stabilizer such as a flame holder (flame holder) or bluff body (blunt, wide flat object) in the air / gas mixture stream. A typical flame stabilizer includes a wire mesh (screen), a rod and a flame insert. Such a flame stabilizer is
It has also been recognized that it also serves to reduce the amount of NOx produced. Further, the above-mentioned surface burner, that is, a radiation burner using a ceramic fiber, a metal fiber or the like as a radiation surface is also used for the same purpose. The rods and radiating surfaces provide a heat absorbing mechanism that allows the absorbed heat to be re-radiated to the absorbing surface beyond the flame region. By such means, the NOx generation amount can be reduced, and at the same time, the flame temperature can be reduced. The key to this method is
It depends on the radiant heat emitting surface being able to remove a significant portion of the heat generated, thereby controlling the flame temperature. According to the experimental results, it was found that the NOx generation amount increased as the heat flux to the radiant heat emission surface increased. This means that if the shape and size of the radiant heat emitting surface, that is, the surface area is constant, the amount of radiant heat from the reaction zone is substantially constant, which impedes the ability to control the reaction temperature at high heat flux. Because it is done. The surface burner has a heat flux (Kcal / cm ² /
Time) increases, the radiant heat operating mode changes to the blue flame operating mode. Generally, 39.06 Kcal / c
At heat fluxes above m ² / hr (1000 BTU / in ² / hr), typical surface burners "blown out".
And a large amount of CO is generated before that.

[0015]

In view of the above-mentioned drawbacks of the prior art, it is desired to provide a burner device which minimizes the amount of NOx produced and reduces the level of CO produced. Referring to FIG. 3, it is desirable to provide a burner device capable of operating within a pollutant emission level tolerance region, and yet, the emission of pollutants can range from low combustion rates to high combustion rates. It is desirable to maintain the emission level within the allowable range over the rate range. The present invention aims to satisfy such a demand.

[0016]

It is well known that the use of excess air in premixed burners reduces NOx emissions as the excess air lowers the combustion temperature. The present invention further reduces the "residence time" by increasing the velocity of the air / gas mixture,
It is based on the fact that it reduces the amount of NOx produced. However, increasing the velocity of the air / gas mixture causes the problem of flame "lift-off" (disengagement and thus extinguishing or blowing) from the burner. N
In order to minimize the amount of Ox produced and yet prevent "lift-off" of the flame, the present invention solves this problem by using a flame stabilizer or flame holder. The flame stabilizer may be made of a heat resistant material and formed into an arbitrary shape. Figures 4-6 and 8-10 show various types of premix burners that can utilize the system of the present invention. These burners are 195.3
~ 3,906 Kcal / cm ² / hour (5,000-10
It has been found to operate at port face loads in the range of 10,000 BTU / in ² / hr).

What was not recognized in the prior art is the involvement of "residence time" in the generation of NOx. By increasing the velocity of the air / gas mixture, the "residence time" exposed to the combustion reaction temperature is reduced. 195.3 to 3906 Kcal / cm ² / hour (5, 5
Port face loads in the range of 000 to 100,000 BTU / in ² / hour) correspond to a tenth to one-twentieth reduction in "residence time" compared to prior art burners. It is noted here that the "port face load" is a load based on the total area of the burner ports (nozzles), and not a load based on the open area or slot area forming the passage of the air / gas mixture. I want to.

Experiments were carried out at a high heat flux using a ribbon burner, a ceramic burner with a port, and a porous ceramic burner described later. Ceramic rod-type flame holders and wire mesh-type flame holders were also used. In both cases, both NOx and CO emissions were very low. The results of such an experiment are shown in FIG.

[0019]

EXAMPLE The amount of NOx produced is a function of the combustion temperature and the time required to complete the combustion. In addition to the various conventional methods described above for reducing NOx emissions, it is also possible to use excess air in the air / gas mixture.
It is known to contribute to the reduction of Ox generation amount. In this case, the decrease in the NOx generation amount is considered to be due to the decrease in the combustion temperature due to excess air. Further, in order to reduce the generation amount of NOx, a method of increasing the speed of the air / gas mixture can be used. Increasing the velocity of the air / gas mixture can be achieved by reducing the size of the orifice through which the air / gas mixture passes, or by increasing the port face load described above. By increasing the velocity of the air / gas mixture,
The "residence time" associated with flame creation is reduced. That is, the residence time of the combustion gas in the reaction zone of the flame is considerably shortened, thus reducing the generation of NOx. However, the increase in the velocity of the air / gas mixture must be limited to a level below which the flame begins to "lift off" from the burner. Increasing the velocity of the air / gas mixture above this level will result in flame blowout. In order to increase the velocity of the air / gas mixture above the rate at which the flame begins to "lift off" from the burner, a flame stabilizer or flame holder must be utilized.

FIG. 4 uses an external flame stabilizer and NO
1 illustrates one of a number of premix burner units 10 that can be operated using the method of the present invention to suppress x emissions to very low levels. Burner unit 10
Is provided with a plenum (high pressure chamber) 12 and a perforated distribution plate 14 extending across the upper surface of the plenum 12 and forming a nozzle of a burner. The perforated distribution plate 14 includes a plurality of through orifices or outlet ports (also simply referred to as "ports") 1
Have six. A flame retainer / distributor matrix 18 is disposed adjacent to the upper surface of the perforated distributor plate 14.

FIG. 5 shows another implementation of a premix burner unit, which also utilizes an external flame stabilizer and can be operated using the method of the present invention to suppress NOx emissions to very low levels. Here is an example: The burner unit 20 comprises a burner body 22 and a plurality of parallel flame holding / distributing ribbons 24 arranged adjacent to the top surface thereof. These flame hold down / dispensing ribbons 24 define ports 26 therebetween.

FIG. 6 shows that an external flame stabilizer is used and NO
Figure 6 shows yet another embodiment of a premix burner unit that can be operated using the method of the present invention to suppress x production to very low levels. This burner unit 30 has a plurality of ports 3 as shown in FIG.
4 is provided with a ceramic tile distribution plate 32. Each port 34 has a substantially constant diameter through section 3
If desired, a tapered section 38 having a diameter of 6 and an increasing diameter from the connection with the through section 38 to the outer surface 40 of the distributor plate 32 may be incorporated.

The burner units shown in FIGS. 4 to 7 are merely examples of burner units in which the method of the present invention can be used to suppress NOx generation to an extremely low level. The method can be carried out using various other types of burners, and there is no particular limitation on the size and shape of the burner, the configuration of the ports, the material of the burner, and the manufacturing method. Whatever type of burner is used, the plenum or burner body is connected to an air / gas source so that the air / gas source supplies a combustible air / gas mixture to the plenum or burner body. In any case, at least one flame stabilizer is placed slightly above the burner unit port used. The flame stabilizer shall consist of at least one ceramic flame rod, flame gauze or a combination thereof for stabilizing the flame created above the ports provided in the burner used. You can In addition to stabilizing the flame above the port, the flame stabilizer can release radiant heat that serves to suppress NOx generation.

According to experiments, the thickness is 2.34 mm (0.0
It has been found that flame gauze made of 92 in) nichrome or inconel wire can be suitably used as a flame stabilizer for various types of burners.
The optimum distance between the flame stabilizer and the top of the burner for minimizing NOx generation can be determined empirically or by experiment.

Alternatively, if the premix burner has only one outlet port or nozzle, or a relatively small number, then as shown in FIG.
A bluff body (a blunt, wide, flat object) 60 can be placed as an internal flame stabilizer in the outlet or injection port 62 of FIG. The bluff body 60 can be formed into various shapes such as a substantially hemispherical steel welding cap. By pressing the outer end of the set screw 66 through the screw hole formed in the bluff body with the inner wall of the burner 64, It can be retained in the outlet port 62.
The bluff body 60 is positioned in the outlet port 62 such that the flow of the air / gas mixture contacts the convex surface of the bluff body. Thus, the bluff body 60
It presents a particular shape of obstruction to the flow of the air / gas mixture. In the configuration of FIG. 8, a separate ignition tube (not shown) is used to ignite the air / gas mixture. air/
The velocity of the gas mixture is close to the velocity at which it begins to "lift off" from the end surface defining the outlet port 62 of the burner 64. The air / gas mixture flow impinges on the upstream or convex surface of the bluff body 60 and circulates in the zone downstream of the bluff body in the opposite direction to the air / gas mixture flow direction from the bluff body. Burner 6
4 to create a region where combustion is maintained before jetting out to the exit port 62.

FIG. 9 shows another embodiment of a premix burner incorporating an internal flame stabilizer. In this embodiment, the bluff body 70 is attached to the end of the ignition tube 72. Again, the bluff body 70 can be of various shapes such as a generally hemispherical steel weld cap. Alternatively, the ignition tube 72 and the bluff body 70 may be composed of a pipe and a reduced diameter connector. The ignition tube 72 and the bluff body 70 are connected to the outlet port 74 of the burner 76.
The inner end of the set screw 78, which is passed through a screw hole formed in the bluff body, can be held therein by being pressed against the inner wall of the burner 76. The ignition tube 72 and the bluff body 70 are arranged concentrically within the burner 76.
The air / gas mixture is supplied to the outer peripheral surface of the ignition tube 72 and the burner 7.
6 through the passage 80 to and from the inner wall surface of the bluff body 70, hitting the upstream or convex surface of the bluff body 70 and in the opposite direction to the flow direction of the air / gas mixture in the zone downstream of the bluff body. It creates a region that circulates and sustains combustion before ejecting from the bluff body to the exit port 74 of the burner 76. The air / gas mixture is ignited by the ignition flame (ignition) in the ignition tube 72, and the resulting combustion product gas is ejected from the outlet port 74 of the burner 76. As with the configuration of FIG. 8, the velocity of the air / gas mixture is close to the velocity at which it begins to “lift off” from the end surface defining the outlet port 74 of the burner 76. The bluff body of Figures 8 and 9 achieves flame stabilization,
It allows the velocity of the air / gas mixture to be increased to a velocity above which a flame "lift-off" would occur if the bluff body (flame stabilizer) were not used. Also, if you use such a bluff body,
It has also been found that it is not necessary to place a flame stabilizer outside the burner exit port.

FIG. 10 shows another embodiment of a premix burner incorporating an internal flame stabilizer. In this example,
A flame holder 90 that functions as a bluff body (flame stabilizer) as shown in FIGS. 8 and 9 is attached to the end of the ignition tube 92. The flame holder 90 can be cup-shaped. The ignition tube 92 is arranged in a concentric relationship within the pipe 94. The circumferential edge 96 of the pipe 94 has a tapered opening 1
Inner end surface 102 of refractory diffuser 98 having 00
Butt against. The diameter of the tapered opening 100 gradually increases from the diffuser inner end surface 102 to the outer end surface 104. The inner diameter of the pipe 94 is approximately equal to the diameter of the tapered opening 100 at the inner end surface 102 of the diffuser 98. Thus, the pipe 94 is aligned with the tapered opening 100 and the surface defining the inner diameter of the pipe 94 and the tapered opening 1
No discontinuity exists with the surface defining 00. Close to the outlet 108 of the flame holder 90, the flame holder 90 and the tapered opening 10 of the diffuser.
A swirl vane assembly 106 is interposed between the surface defining 0. The air and fuel gas flow through holes 110 and 112 formed in the wall of burner housing 114, respectively.
Through a plurality of mixing venturis 116 into chamber 118 and from there into pipe 94 through its inner end 120. The thus premixed air / gas mixture passes through the passage 122 between the inner peripheral surface of the pipe 94 and the outer peripheral surface of the ignition tube 92, the surface defining the tapered opening 100 of the diffuser and the flame holder 90.
Flows into the passage 124 between the outer peripheral surface of the. The air / gas mixture then circulates as it passes through the swirl vane assembly 106, in a zone downstream of the flame holder 90, opposite to the direction of flow of the air / gas mixture, to maintain combustion. To create. The air / gas mixture is ignited by an ignition flame (ignition) in the ignition tube 92, and the resulting combustion products gas is ejected from the burner outlet port 126. The velocity of the air / gas mixture is close to the velocity at which it begins to "lift off" from the end surface defining the outlet port 74 of the burner 76. As with the burner of FIGS. 8 and 9, the flame holder 90 achieves flame stabilization,
Allows the velocity of the air / gas mixture to be increased to a velocity above which flame "lift-off" would occur if the flame holder were not used.

Whether or not a flame stabilizer is used,
In accordance with the method of the present invention, the burner is operated with excess air to keep the combustion temperature just below that at which a large amount of NOx is produced, and the "residence time" associated with flame creation is minimized. It was thus confirmed that the emission amount of NOx can be suppressed to an acceptable level. In the method of the present invention, an appropriate ratio of excess air is supplied and a high heat flux (Kcal / cm ² /
It has been demonstrated that the use of a high velocity premixed air / gas mixture in combination with (time) can control the "residence time" and the combustion temperature, thereby minimizing NOx emissions. However, if you need a flame stabilizer in the form of a flame rod, flame gauze or bluff body to ensure that the flame does not "lift off" from the burner, as it will send excess air at a high velocity. There is. Use of a flame stabilizer increases the flame extinguishing or "blown out" maximum speed of the air / gas mixture. The flame stabilizer can also function as a heat radiator, thereby suppressing the temperature so that the combustion temperature does not exceed the temperature at which a large amount of NOx is generated.

However, the stabilization of the flame can be achieved by, for example, circulating the jet streams opposed to each other, or wake (wake).
can also be achieved by aerodynamic means such as inducing a flow) and with aerodynamic means it is not necessary to use a flame stabilizer as described above.

[0030]

According to the operating conditions of the present invention described above, approximately 195.3 to 3,906 Kcal / cm ² / hour (5,5).
It has been found that a very high heat flux of 000-100,000 BTU / in ² / h) can be obtained. 195.3K
A heat flux of cal / cm ² / hr is without the flame stabilizer and a heat flux of 3,906 Kcal / cm ² / hr is obtained with the flame stabilizer.

As is clear from the graph of FIG. 11, the NOx generation amount decreases as the proportion (%) of excess air increases. When 20% or more of excess air is used, the amount of NOx generated can be suppressed within the recently set regulation standard. Thus, according to the operating parameters described above, ie, combining a proper proportion of excess air with a nominal operating temperature of 1649 ° C. (3000 ° F.) and high heat flux, acceptable NOx.
Emission levels can be achieved. Furthermore, according to the above operating parameters, it was found that the NOx generation amount decreases as the heat flux increases, as long as the "residence time" is shortened as much as possible. This is in contrast to prior art burner systems in which as the heat flux increases, the amount of NOx produced increases proportionately. Such an advantage, that is, the advantage of the present invention that the amount of NOx generated decreases as the heat flux increases, has not been taught in the prior art.

Even in combustion applications at high oxygen concentrations with high flame temperatures leading to increased NOx production, increasing the velocity of the air / gas mixture reduces the "residence time", resulting in It was confirmed that the generation amount of NOx was reduced. Also in the case of combustion applications where the air / gas mixture is preheated (and thus has a high flame temperature), the preheating operation increases the velocity of the air / gas mixture, resulting in a "residence time". It was observed that the NOx was shortened and the amount of NOx generated was decreased.

Another advantage of the present invention is NOx and C.
The amount of O generated is kept within the "pollutant emission level allowable region" shown in FIG. As described above, in the conventional burner, in order to reduce CO to CO ₂ , both the time and the relatively high temperature leading to the generation of NOx are required. Therefore, the generation amount of NOx and CO Are inversely proportional to each other. The method of the invention, namely
According to the result of the experiment using the excess air of 20% or more at the high velocity, the extremely low level of NOx of about 20 ppmv.
Even when the generation rate was suppressed, it was found that the CO generation amount in that case did not become excessive and was within the "pollutant emission level allowable range". As described above, the method of the present invention suppresses the generation level of CO to a low level, and
Minimize the amount of Ox generated.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to the structures and forms of the embodiments illustrated herein, and deviates from the spirit and scope of the present invention. It should be understood that various embodiments are possible and that various changes and modifications can be made.

[Brief description of drawings]

FIG. 1 is a graph showing the theoretical concentration of NOx versus time and temperature calculated using an analytical model of the Zeldovic chain reaction.

FIG. 2 is a graph of air / fuel ratio versus flame “blown out” speed for in-nozzle and premix burners.

FIG. 3 is a graph of nitrogen oxides (NOx) versus combustibles (eg, CO), showing the pollutant emission level tolerance region where burners are believed to operate at acceptable contaminant emission levels.

FIG. 4 is a cross-sectional view of an example of a premix burner unit that utilizes an external flame stabilizer and can be operated using the method of the present invention.

FIG. 5 is a cross-sectional view of another type of premix burner unit that utilizes an external flame stabilizer and can be operated using the method of the present invention.

FIG. 6 is a cross-sectional view of yet another type of premix burner unit that utilizes an external flame stabilizer and can be operated using the method of the present invention.

7 is a partially enlarged sectional view of a ceramic tile distribution plate of the burner unit of FIG. 6.

FIG. 8 is a cross-sectional view of an example of a premix burner unit that utilizes an internal flame stabilizer and can be operated using the method of the present invention.

FIG. 9 is a cross-sectional view of another type of premix burner unit that utilizes an internal flame stabilizer and can be operated using the method of the present invention.

FIG. 10 is a cross-sectional view of yet another type of premix burner unit that utilizes an internal flame stabilizer and can be operated using the method of the present invention.

FIG. 11 is a graph of the ratio (%) of NOx generation amount to excess air.

[Explanation of symbols]

 10: Burner Unit 16: Orifice 18: Flame Holding / Distribution Matrix 20: Burner Unit 24: Flame Holding / Distribution Ribbon 26: Outlet Port 30: Burner Unit 32: Ceramic Tile Distributing Plate 34: Outlet Port 60: Bluff Body (Flame) 62: Outlet port 64: Burner 70: Bluff body (flame stabilizer) 72: Ignition tube 74: Outlet port 76: Burner 90: Flame holder (flame stabilizer) 92: Ignition tube 94: Pipe 98: Diffuser 100 : Taper opening 106: Vortex blade assembly 114: Burner housing 126: Outlet port

Claims (14)

[Claims] 1. A method of operating a burner in a manner to reduce the amount of NOx produced, wherein a flame stabilizer is disposed in the vicinity of the burner so that the ratio of air in the air / gas mixture becomes excessive. Premixing air and gas into an air / gas mixture, increasing the velocity of the air / gas mixture through the burner to reduce the time required for flame production, A method of operating a burner, characterized by igniting a gas mixture. 2. The method of operating a burner according to claim 1, wherein the flame stabilizer is arranged close to an outlet port of the burner. 3. The method of operating a burner according to claim 1, wherein the flame stabilizer is disposed in an outlet port of the burner. 4. The burner operating method according to claim 1, wherein the flame stabilizer is arranged outside an outlet port of the burner. 5. The method of operating a burner of claim 1, wherein the velocity of the air / gas mixture is increased by reducing the size of the orifice through the air / gas mixture in the burner. . 6. The method of operating a burner of claim 1, wherein the velocity of the air / gas mixture is increased by increasing the port face load of the burner. 7. The method of operating a burner of claim 1, wherein the velocity of the air / gas mixture is close to the velocity at which it begins “lifting off” from the burner's outlet port. 8. The method of operating a burner of claim 1, wherein the flame stabilizer is at least one flame rod. 9. The burner operating method according to claim 1, wherein the flame stabilizer is a flame wire mesh. 10. The method of operating a burner of claim 1, wherein the flame stabilizer is a combination of a flame gauze and at least one flame rod. 11. The method of operating a burner according to claim 1, wherein the flame stabilizer is a bluff body. 12. A method of operating a burner in a manner to reduce the amount of NOx produced, wherein air and gas are premixed so that the proportion of air in the air / gas mixture is excessive, and the air / gas mixture is mixed. And increasing the velocity of the air / gas mixture through the burner to reduce the time required to produce the flame and ignite the air / gas mixture to aerodynamically A method of operating a burner, characterized in that it is stabilized by means. 13. The method according to claim 12, wherein the aerodynamic means are jet flow circulations facing each other.
Burner operation method described in. 14. The method of operating a burner of claim 12, wherein the aerodynamic means is a wake.