JPH06174207A - Combustion furnace and combustion method - Google Patents

Abstract

PURPOSE:To enable reducing to a low level the evolution of NOx at the time of the combustion of fuel relating to various kinds of combustion furnaces. CONSTITUTION:There are provided a fuel-feeding hole 4, a low-temperature-time air-feeding hole 7 in a manner of surrounding the fuel-feeding hole 4 with, and at least one air-feeding hole 3 on the outer side of and with some distance from the low-temperature-time air-feeding hole 7, all directly opening into the furnace, in a setup to eject air from the low-temperature-time air-feeding hole 7 for the combustion when the temperature is below the firing point of the fuel gas and to eject air from the air-feeding hole 3 at the periphery for the combustion subsequent to rise of the temperature above the firing point.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a nitrogen oxides suitable for iron and steel furnaces and metal melting furnaces Combustion furnaces and the combustion method for (hereinafter referred to as NO _X) suppressed.

[0002]

2. Description of the Related Art Recently, various combustion methods for reducing NO _x production have been developed for environmental purification.

FIG. 5 shows an example of such a burner described in US Pat. No. 4,357,134. In the figure, 1 is a furnace body and 2 is a furnace. The burner has a fuel port 4 at the center and a plurality of air ports 3 arranged around it. The air jet sucks and mixes the fuel to burn it in the combustion chamber 5 of the burner. At this time, the air jet simultaneously sucks the combustion gas in the furnace, so that the combustion becomes low in oxygen concentration and the generation of NO _X is suppressed. The arrangement of the air port, the inclination angle, the ejection speed, and the like for effectively performing this are the contents of the invention.

However, this combustion method is combustion in the combustion chamber 5, and the amount of combustion gas in the furnace 2 sucked by the air jet is limited by the size of the combustion chamber 5. Further, since the combustion is performed in the combustion chamber 5 made of a refractory heat insulating material, there is no heat radiation at the flame base, which is particularly important for the generation of NO _X , so the flame temperature rises and NO _X does not decrease so much. There is.

In order to remedy this drawback, the present applicant has proposed in Japanese Patent Application No. 1-300103 a furnace combustion method as shown in FIGS. 6 (a) and 6 (b).

In the figure, 1 is a furnace body and 2 is the inside of the furnace. A distance d ₁ between the air supply port 3 and the fuel supply port 4 in the furnace 2
Open separately. Further, the air supply port 3 and the furnace inner wall 6 are also separated by a distance d ₂ . With such a configuration, fuel and air are injected from the air supply port 3 and the fuel supply port 4 into the furnace 2 and are burned in the furnace 2 while forming a recirculation flow as indicated by an arrow in the figure.

[0007]

However, in consideration of burning natural gas, an air amount of 10 times or more of the gas amount is required to perform complete combustion. Is overwhelmingly larger. Therefore, in this combustion method, when the air is ejected from the air supply port 3 located in the center of the burner, the fuel on the outside is also sucked, mixed and burned due to the overwhelming kinetic energy of the air jet. put away, the amount of air and gas are mixed with each furnace gas is small, therefore, it does not decrease the flame temperature is too, there is a problem that nO _X concentration does not significantly decrease.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to suppress NO _X generated when burning fuel in various combustion furnaces to a low level as compared with the conventional combustion method.

[0009]

In order to achieve the above object, in the present invention, a fuel supply port is directly opened in the furnace without a burner combustion chamber, and the fuel supply port is surrounded by the fuel supply port at low temperature. The first air supply port and at least one second air supply port spaced apart from the low temperature air supply port are provided so as to be directly opened in the furnace.

[0010]

[Function] By opening the fuel supply port and the air supply port directly in the furnace, and further arranging the air supply port on the outer periphery of the fuel supply port, the jet flow of air and the fuel flows like the burner tile in the furnace combustion gas. Since there is nothing to limit the suction, each of them efficiently sucks a large amount of the surrounding combustion gas before the fuel and the air are mixed, burns with a low oxygen concentration, and forms a low temperature flame. Also, since the flame starts to be burnt in the furnace and is formed, radiative heat transfer to the object to be heated starts at the same time as the start of combustion, and there is no part that burns in an adiabatic space such as burner tile. In addition, the flame temperature is further reduced. By significantly reducing the flame temperature in this way, NO _X can be significantly reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is an axial sectional view of an embodiment of a combustion furnace according to the present invention, and FIG. 2 is an end view of the combustion furnace shown in FIG.

In the figure, 1 is a furnace body, 2 is a furnace,
In such a configuration, the air supply port 3 and the fuel supply port 4
Respectively, air and fuel gas are directly ejected into the furnace 2 to form a recirculation flow of the furnace combustion gas in the furnace 2 as shown by an arrow in the figure, and after each is mixed with the furnace combustion gas, It burns and forms a flame such as 10 away from the furnace wall. When the temperature inside the furnace 2 is lower than a temperature at which stable combustion is possible, for example, at a low temperature of 750 ° C. or lower, the switching valve 9 attached to the air inlet 8 to the air supply port 3 is set so that the air flows into the A _L side. Air is jetted from the low-temperature air supply port 7 surrounding the fuel supply port 4 by switching to burn the fuel, and the temperature in the furnace 2 is higher than a temperature at which stable combustion can be performed.
For example, when the temperature reaches 750 ° C or higher, the switching valve 9 is set to A _H.
The combustion is continued by switching the air flow to the side. As an example, the switching valve 9 is driven by an air cylinder (not shown) mounted on the combustion device.

Table 1 shows a comparison of NO _x concentration when the conventional combustion method and the combustion method according to the present invention use natural gas as a fuel. Table 1

According to this, the input heat quantity 90 × 10
⁴ kcal / h, 8 fuel gas supply ports are provided around the air supply port, fuel gas is ejected in the axial direction at a velocity of 49 m / s, one air supply port is provided in the center, and air is 117 m / s In the conventional example ejected at 1, NO _x is 55 ppm. On the other hand, one fuel gas supply port was provided at the center, and the fuel gas was similarly ejected only in the axial direction from there, and eight air supply ports were provided at the outer periphery, and the fuel gas and air were ejected at the same speed as before. In the case of the present invention, NO _x is reduced by about 16% to 46 ppm.

In the combustion furnace of this embodiment, six air supply ports 3 are provided on the same virtual circle around the fuel supply port 4 provided at the center, and the six air supply ports 3 are arranged. Assuming that the diameter of the imaginary circle (referred to as the pitch circle diameter) is φ (mm), the present inventors have conducted many experiments, and as a result, the relationship between the pitch circle diameter φ and the input heat quantity Ip × 10 ⁴ kcal / h. It was confirmed that the amount of NO _x produced can be suppressed when satisfies the following equation.

Φ ≧ 10 ^1.89217 × Ip ^0.33697 FIG. 3 shows NO _x when the pitch circle diameter φ is taken on the horizontal axis.
The generated amount is shown, and it can be seen that the larger the pitch circle diameter φ, that is, the farther the air supply port 3 is from the center of the fuel supply port 4, the smaller the NO _x generation amount.

Furthermore, the present inventors have found the following facts regarding the relationship between the direction in which fuel gas is ejected from the fuel supply port 4 and the amount of NO _x produced.

That is, the fuel gas is ejected in the axial direction of the combustion furnace, and in addition, a part of the fuel is ejected in the direction indicated by an arrow in FIG. 4 (hereinafter referred to as the radial direction). In that case, the arrangement as shown in FIG. 4A in which the ejection direction collides with the air jet ejected from the air supply port 3 and the arrangement as shown in FIG. 4B penetrating between the air jets are obtained. The table below shows the results of the experiment. Table 2 Input heat quantity Ip = 90 × 10 ⁴ kcal / h As can be seen from Table 2, in the arrangement of FIG. 4A in which the fuel gas collides with the air jet, mixing of the gas and air is promoted and 41 ppm of NO _x is discharged. On the other hand, in the arrangement of FIG. 4 (b) in which the gas is ejected so as to penetrate between the air jets, the mixture does not mix rapidly, so combustion becomes slower and the brightness of the flame increases, and NO _x is about 30%. It decreases to 30 ppm. Thus, by injecting a part of the gas in the radial direction and into the gap of the air supply port, NO _X can be further reduced.

Although the above-described embodiments have been mainly described with respect to an industrial combustion furnace, the present invention can be similarly applied to a commercial-use or household-use combustion furnace.

[0021]

As described above, in the combustion furnace according to the present invention, the fuel supply port is directly opened in the furnace, and the low temperature air supply port and the low temperature air supply port are provided so as to surround the fuel supply port. At least one air supply port is opened outside the air supply port and opened in the furnace, and when the temperature is lower than the fuel gas ignition temperature, air is jetted from the low temperature air supply port and burned to become higher than the ignition temperature. After that, since the air is ejected from the peripheral air supply port to perform combustion, the amount of NO _X generated can be suppressed even if high-temperature preheated air is used, and stable combustion can be ensured. .

Further, in addition to ejecting the fuel gas in the axial direction, a part of the gas is ejected in the radial direction so as to penetrate through the air jet flow, thereby increasing the brightness of the flame. Further, NO _X can be reduced.

[Brief description of drawings]

FIG. 1 is an axial sectional view of an embodiment of a combustion furnace according to the present invention.

FIG. 2 is an end view of the combustion furnace shown in FIG. 1 as seen in the direction of arrow A.

FIG. 3 is a graph showing the relationship between the pitch circle diameter and the NO _X generation amount in the present invention.

4 (a) and 4 (b) are diagrams showing different positional relationships between a jet direction of a fuel gas and an air jet flow.

FIG. 5 is an axial sectional view of an example of a conventional combustion burner.

6A is a sectional view of a main part of another example of a conventional combustion burner, and FIG. 6B is an end view of the combustion burner shown in FIG.

FIG. 7 is a cross-sectional view of a main part of another example of a conventional combustion burner.

[Explanation of symbols]

 1 Furnace Body 2 Furnace 3 Air Supply Port 4 Fuel Supply Port 5 Combustion Chamber 6 Furnace Inner Wall 7 Low Temperature Air Supply Port 8 Air Inlet 9 Switching Valve 10 Flame

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[Procedure amendment]

[Submission date] May 22, 1991

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3] ─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 22, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

In the figure, 1 is a furnace body, 2 is a furnace, and in such a structure, air and fuel gas are directly jetted into the furnace 2 from the air supply port 3 and the fuel supply port 4, respectively. In Fig. 2, the recirculation flow of the combustion gas in the furnace is formed as shown by the arrow in the figure, and each mixture is mixed with the combustion gas in the furnace and burned to form a flame at a position such as 10 away from the furnace wall. To do. When the temperature in the furnace 2 is lower than a temperature at which stable combustion is possible, for example, at a low temperature of 750 ° C. or lower, the switching valve 9 attached to the air inlet 8 to the air supply port 3 is switched so that air flows into the A _L side. When the temperature in the furnace 2 reaches or exceeds a temperature at which stable combustion can be performed, for example, 750 ° C. or more, a switching valve is ejected from a low temperature air supply port 7 surrounding the fuel supply port 4 to burn the air. 9 for A
Switching is performed so that air flows into the _H side, and combustion is continued. As an example, the switching valve 9 is driven by an air cylinder (not shown) mounted on the combustion device.

Claims (3)

[Claims] 1. A first fuel-cooling first opening for use at low temperature so as to directly open a fuel supply opening and surround the fuel supply opening.
And the at least one second air supply port spaced apart from the low temperature air supply port to the outside and directly opened. 2. The fuel supply port ejects the fuel in a direction in which a part of the fuel is substantially perpendicular to the axis of the fuel supply pipe and does not collide with an air jet supplied from the second air supply port. The combustion furnace according to claim 1, wherein the fuel is injected into the combustion furnace in parallel with the axial line. 3. The fuel is supplied from a fuel supply port opened directly into the furnace, and at a temperature below the ignition temperature of the fuel, air is supplied from a first air supply port provided so as to surround the fuel supply port and burns. When the temperature in the furnace reaches the ignition temperature of the fuel or higher, the supply of air from the first air supply port is stopped, and at least 1 is provided outside from the first air supply port. Combustion method, characterized in that air is supplied from two second air supply ports for combustion in the furnace.