JPH0849812A - Combustion furnace and low-nox combustion method thereof - Google Patents

Abstract

PURPOSE:To provide a combustion furnace, reduced in the production of NOx, and a low-NOx combustion method thereof, in the combustion furnace into which high-temperature combustion air is supplied. CONSTITUTION:A combustion furnace and a low-NOx combustion method, employing a combustion furnace 10, in which a combustion air supplying port 1 is separated from a fuel supplying port 2 by a distance L in heat accumulating combustion while an injection angle alpha is provided between the air supplying port 1 and a fuel supplying port 2 so that the jet stream of air 5 and the jet stream of fuel 6 are ejected into different directions, high-temperature combustion air 5 of 700 deg.C or higher and the fuel 6 are injected into a furnace 10 so that respective jet streams may not be superposed in the main streams thereof to restrain the mixing of the fuel 6 and the air 5 and slow combustion condition due to the rolling of exhaust gas into a combustion area is maintained. The injecting speed of the fuel is preferably 60 m/sec or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low NOx combustion method for suppressing the production of nitrogen oxides (hereinafter referred to as NOx) accompanying the combustion of various industrial furnaces and boilers, and in particular to a heat storage material such as ceramics. 100 depending on the sensible heat recovery device used
The present invention relates to a low NOx combustion method in a combustion furnace which uses high temperature combustion air preheated to a high temperature of 0 ° C. or higher.

[0002]

2. Description of the Related Art Generation of a large amount of NOx in a combustion furnace is
It is largely due to the high oxygen concentration and rapid high temperature combustion. However, in conventional general combustion, the flame is shortened mainly from the viewpoint of improving the combustion efficiency, and in order to shorten the flame, the combustion air and the fuel are mixed early and uniformly. Therefore, it is necessary to make it burn rapidly. Under such rapid combustion, the flame temperature rises, the high temperature region in the furnace also widens, and in addition, the local oxygen concentration in the combustion zone increases. As a result, a large amount of NOx
Was generated, and there was a problem in that it suffered from a dilemma between both combustion efficiency and pollution.

Therefore, a low NOx combustion method as shown in FIG. 4 has been proposed. The combustion method shown in FIG.
-300103 publication. In FIG. 4A, the combustion air supply port 51 and the fuel supply port 52 are provided in the furnace wall 50 at a distance L2. Then, the combustion air supply port 51 and the surrounding furnace inner wall 5
0 is separated by a distance L3 sufficient to form a recirculation flow in the furnace.

In the combustion method in the combustion furnace 50 having such a structure, the air and fuel injected from the respective supply ports 51 and 52 into the furnace are poorly mixed, and after mixing with the high temperature exhaust gas in the furnace, Since it is mixed in D in 2, the combustion is performed in the field where the oxygen concentration is low, and NOx is reduced. Also,
A furnace recirculation flow is formed between the combustion air supply port 51 and the surrounding furnace inner wall 50 to burn the inside of the furnace.

On the other hand, in this combustion method, CO and soot are generated when the temperature of the combustion furnace is low, and the flame stability is poor.
Therefore, the temperature in the furnace 50 is the ignition temperature of the fuel, for example, 7
At a low temperature of 50 ° C. or lower, the fuel is jetted from the sub-fuel supply port 53 provided in the combustion air supply port 51 to quickly and uniformly mix the combustion air and the fuel to perform rapid combustion. When the ignition temperature of the fuel reaches, for example, 750 ° C. or higher, the fuel supply is switched to the fuel supply port 52.
In addition, FIG.4 (b) is BB sectional drawing.

Before being injected into the furnace, the combustion air is preheated by the exhaust gas sensible heat recovery device from the viewpoint of improving combustion efficiency. The conventional sensible heat recovery device is based on a heat exchanger or the like, and the preheating temperature thereof is at most about 400 ° C to 600 ° C when the furnace temperature is 1300 ° C. However, recent sensible heat recovery devices such as heat storage combustion (regenerative) burners that use ceramics or the like having good heat storage properties raise the preheated air temperature to 1000 ° C. or higher.

[0007]

Therefore, since the combustion air is already at a high temperature of 1000 ° C. or higher when it is injected into the furnace, the temperature inside the furnace does not decrease and the combustion efficiency does not decrease, but it is the same as in the conventional case. In the combustion method, when high temperature combustion air and fuel undergo a combustion reaction in the furnace, the temperature becomes even higher, and a large amount of NOx is generated. It is possible to further increase the distance L2 between the combustion air supply port 51 and the fuel supply port 52 to suppress the mixing, but the entire furnace becomes large. Further, in the combustion furnace shown in FIG. 4, since the fuel supply hole 52 is provided in the furnace wall, large-scale work is required.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to reduce the generation of NOx in heat storage combustion to which high temperature combustion air is supplied. It is intended to provide a combustion furnace and a low NOx combustion method thereof.

[0009]

In order to achieve the above object, the present invention separates a combustion air supply port and a fuel supply port for injecting high temperature combustion air and fuel into a furnace in heat storage combustion. At the same time, the combustion furnace has a jet angle between both supply ports so that the air jet axis and the fuel jet axis are injected in different directions.

Further, when injecting high temperature combustion air and fuel of 700 ° C. or higher into the furnace, the high temperature combustion air and fuel are injected into the furnace so that the main flow portions of the jets do not overlap with each other. This is a low NOx combustion method that maintains a slow combustion state by suppressing the mixture of air and air by the exhaust gas self-circulation in the furnace. The jet speed of the fuel is preferably 60 m / sec or more.

[0011]

With the improvement of the sensible heat recovery device, once the temperature inside the furnace rises to the fuel ignition temperature, it does not drop much due to the supply of combustion air, etc. . When there is injected into the furnace so that the main flow parts of the jets of high temperature combustion air and fuel do not overlap, the respective jets burn with a low oxygen concentration while entraining the exhaust gas in the furnace. This combustion is slower than the combustion in which the combustion air and the fuel are directly mixed and burns, and the temperature does not rise rapidly. And since the oxygen concentration is also low, NOx
Is less likely to occur.

The jet speed of the fuel is 60 m / s.
When it is ec or more, a luminous flame spreads in the furnace, and the heating rate by radiation also increases. The heating property in the furnace is also improved. The denitration reaction also progresses due to the reduction reaction due to the thermal decomposition of the fuel on the side opposite to the side with the air flow in the direction of fuel injection.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.
FIG. 1B is a schematic sectional view showing a specific example of the combustion furnace 10 used for combustion of the present invention. 1 (a) is shown in FIG.
It is the sectional view on the AA line of (b), and FIG. 2 is C of FIG. 1 (b).
It is a -C line sectional view.

In FIG. 1B, the burner tile 8 is
The combustion air supply port 1 and the fuel supply port 2 are separated by a distance L and provided integrally with each other, and this L is the minimum necessary for injecting the main flow of the air jet and the fuel jet so that they do not overlap in the vicinity of the burner. L / D = 1 ~ depending on the injection angle
2 is sufficient. Here, D is the diameter of the air injection port.
Further, the combustion air supply port 1 and the fuel supply port 2 of the burner tile 8 are flush with the inner wall of the furnace 10. this is,
The high-temperature exhaust gas in the furnace is entrained by the momentum of the jet flow, and the self-exhaust gas circulation to the combustion zone is effectively performed. The combustion air supply port 1 is horizontally straight, and the tip of the fuel supply port 2 is inclined from the horizontal by an angle α so that the combustion air 5 and the fuel 6 are injected into the furnace in different directions. The angle α is selected in the range of approximately 5 to 45 °. Most preferably, it is about 15 °.

Below the combustion air supply port 1 of the burner tile 8, a heat storage body 4 such as ceramics of a sensible heat recovery device is provided. The sensible heat recovery device absorbs heat from the high-temperature combustion exhaust gas by the heat storage body 4 and discharges it from the inlet / outlet 9, and supplies heat to the air supplied from the inlet / outlet 9. The air passing through the combustion air supply port 1 is 1000
The temperature is raised to ℃ or more. A sub-fuel supply port 3 is further provided on the left side of the center of the combustion air supply port 1 in the drawing, and when the temperature inside the furnace 10 is 400 ° C. or lower, fuel is jetted from a safety measure, This is for warming up the furnace for stable combustion by uniformly mixing combustion air and fuel at an early stage.

As shown in FIG. 1 (a), the combustion furnace 10 is provided with a pair of burner tiles 8 as described above, and an auxiliary flue 7 is provided in the center of the furnace wall on the side facing them. . The auxiliary flue 7 has a function of drawing the combustion exhaust gas of the air 5 and the fuel 6 supplied from the pair of burner tiles 8 to the opposite side so that the exhaust gas is spread throughout the furnace.
The pair of burner units 8 are operated in an alternating manner.

The operation of the combustion furnace 10 having such a structure will be described. When the temperature in the furnace at the start of operation is low at 400 ° C. or lower, the fuel is jetted from the sub fuel supply port 3 to quickly and uniformly mix the combustion air and the fuel to perform rapid combustion. Then, when the temperature reaches 400 ° C. or higher, the fuel from the fuel supply port 2 is also supplied. Subsequent fuel supply from the sub-fuel supply port 3 depends on the method of use of the furnace, but is used together up to a predetermined temperature, or the temperature inside the furnace falls below a predetermined temperature
It is supplied supplementarily only when it is necessary to raise the temperature in the furnace by performing rapid combustion.

In the low NOx combustion method of the combustion furnace 10 having such a structure, when the temperature in the furnace is 1300 ° C.,
The fuel 6 and the high-temperature combustion air 5 heated to 1000 ° C. or higher by the sensible heat recovery device are injected from the supply ports 1 and 2 into the furnace so that the main flow parts of the respective jets do not overlap. Then, the respective jets sequentially mix and burn while incorporating the exhaust gas in the furnace. The combustion is slower than the combustion in which the combustion air 5 and the fuel 6 are directly mixed and burned, and does not have a local high temperature portion. Since the oxygen concentration is also low, the generation of NOx is reduced. as a result,
NOx generation is sufficiently reduced in a combustion furnace with high combustion efficiency to which high-temperature combustion air is supplied.

At this time, the flow velocity ratio between the fuel and the combustion air is set to 0.
When it is set to 3 or more, especially about 0.5 to 2, mixing of fuel and combustion air is suppressed, and each jet promotes combustion while entraining in-reactor exhaust gas into each jet. Further, in order to improve the mixing of each jet flow with the exhaust gas in the furnace, it is preferable to inject at a jet speed of 60 m / sec or more so that the flame length becomes half the furnace diameter or more. If the ejection speed is too fast, combustion reaction does not occur easily even when mixed with the exhaust gas in the furnace, and flame holding cannot be performed.Therefore, a flame holding burner should be provided in the furnace to slightly ignite the flame so that it does not go out. It is necessary to leave.

The specific test results are shown below. Distance L / D between combustion air supply port 1 and fuel supply port 2 = 1.5, inclination α of fuel supply port 2 from the horizontal α = 15 °, fuel ejection speed 80 m / s, air ejection speed 30-40 m / s, and when the air was burned at a preheating temperature of about 1000 ° C., NOx of 1000 ppm was generated when injected from the sub fuel supply port 3, but could be reduced to 10 ppm when injected from the fuel supply port 2. At this time, the flame was a bright flame and was large, the heating rate by radiation was also large, and the heating property in the furnace was also improved. The denitration reaction due to the thermal decomposition of the fuel also proceeded on the side opposite to the side where the air flow was in the direction of fuel injection.

In the above embodiment, one combustion air supply port 1 and one fuel supply port 2 having an inclination α of a predetermined angle from the horizontal are provided on the burner tile 8 at a distance L. However, as shown in FIG. 3, a plurality of combustion air supply ports 1 may be provided on a concentric circle having a predetermined radius L centered on one fuel supply port 2 having an inclination of a predetermined angle from the horizontal. In this case, a fan shape having a central angle θ of 240 ° or less is formed on the side opposite to the inclination of the fuel supply port 1 in order to make the jet directions of the fuel and the combustion air injected into the furnace different from each other. Thus, it is necessary to arrange a plurality of combustion air supply ports 1. Further, it is important that the predetermined radius L is set sufficiently large so that the main flow portions of the jet flows do not overlap.

[0022]

As described above, according to the combustion furnace and the low NOx combustion method thereof of the present invention, the fuel supply port and the combustion air supply port are separated from each other, and the air jet axis and the fuel jet axis are injected in different directions. As described above, by injecting an injection angle between the two, and by injecting into the furnace so that the main flow parts of the high-temperature combustion air and fuel jets do not overlap, the respective jets and After sufficiently reacting, the combustion air and fuel are mixed and burned to realize a slow combustion in which the temperature does not rise rapidly and the oxygen concentration is low, and NOx generation is reduced in a combustion furnace to which high-temperature combustion air is supplied. To do.

As a result, the fuel supply port and the air supply port are integrated into a compact burner body structure, which facilitates modification. Further, in the heat storage combustion burner, since the high temperature combustion exhaust gas passes through the air supply port, if the fuel supply port is in the air supply port, there is a problem that fuel caulking or burnout of the fuel injection hole occurs. According to the present invention, since the fuel supply port and the air supply port are separated from each other, the problem can be solved completely. Also,
According to the present invention, it can be used even at a low temperature and has good operability.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a specific example of a combustion furnace used for combustion of the present invention.

FIG. 2 is a sectional view taken along the line CC of FIG.

FIG. 3 is a diagram showing a combustion air supply port and a fuel supply port in the combustion furnace of the present invention.

FIG. 4 is a schematic cross-sectional view showing a conventional combustion furnace used for combustion.

[Explanation of symbols]

 1 Combustion Air Supply Port 2 Fuel Supply Port 4 Ceramics, etc. (Sensible Heat Recovery Device) 5 Air 6 Fuel 7 Flue 8 Burner Section 10 Combustion Furnace α Slope L Distance between Supply Ports

Claims (3)

[Claims] 1. A combustion furnace for injecting high temperature combustion air and fuel into a furnace for combustion in heat storage combustion, wherein the fuel supply port and the combustion air supply port are separated from each other, and the air jet shaft is provided. Combustion furnace characterized by having a jet angle between the fuel injection axis and the fuel injection axis so that they are injected in different directions. 2. A low NOx combustion method for a combustion furnace in which high temperature combustion air and fuel at 700 ° C. or higher are injected into a furnace for combustion, and the high temperature combustion is performed so that main flow portions of respective jets do not overlap. A low NOx combustion method, characterized by injecting commercial air and fuel into a furnace, and maintaining a slow combustion state by suppressing exhaust gas self-recirculation in the furnace. 3. The low NOx combustion method according to claim 2, wherein the jet speed of the fuel is 60 m / sec or more.