JP3337584B2 - Heating furnace combustion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion method for a heating furnace, a heat treatment furnace or the like (hereinafter referred to as a heating furnace) for heating a material to be heated such as a slab, a billet or a strip to a predetermined target temperature by a high-temperature combustion burner. It is about.

[0002]

2. Description of the Related Art Conventionally, in order to save energy in a heating furnace of this kind, a method of installing an indirect heat exchanger in a flue to recover sensible heat of flue gas as preheated air and use it for fuel combustion. However, in this indirect heat exchange method, the upper limit temperature of the preheated air is 600
Because the temperature is limited to about ° C, it is not possible to expect a significant increase in the combustion flame temperature, that is, an increase in the amount of radiant heat transferred to the material to be heated. There was a problem.

On the other hand, a method has recently been put into practical use in which fuel is burned with high-temperature air or high-concentration oxygen supporting gas to generate a high-temperature flame, and the material to be heated is rapidly heated with the high-temperature flame. For example, in the former method using high-temperature air combustion, a pair of regenerative burners in which a burner and a regenerator are integrated are alternately burned to generate high-temperature air of 1000 ° C. or more, and the fuel is burned with the high-temperature air. The high-concentration oxygen combustion method uses a high-concentration oxygen combustion method to burn the fuel and high-concentration oxygen with an oxygen burner to reduce the amount of combustion gas. The high-temperature flame is generated by decreasing the temperature, and the material to be heated is rapidly heated.

[0004] As described above, in the method of generating high-temperature flame by burning fuel with high-temperature air or high-concentration oxygen supporting gas, the amount of radiant heat transfer from the high-temperature flame to the material to be heated increases. The heating time is shortened by rapid heating of the material to be heated, and the heating furnace can be made compact. On the other hand, the fuel is burned with high-temperature air or high-concentration oxygen supporting gas, which has a fast combustion reaction rate. Therefore, the combustion flame becomes a high-temperature short flame, and as a result, in addition to a large increase in NOx (nitrogen oxide) in the combustion gas, the furnace temperature distribution in the axial direction of the burner becomes non-uniform. There is a problem that the material to be heated cannot be heated uniformly.

On the other hand, for example, Japanese Unexamined Patent Publication No.
There is a low NOx burner for a high-temperature sintering furnace as disclosed in JP-A-6-82306. The feature of this burner is to suppress NOx in high-temperature combustion, and to achieve this, FIG.
As shown in the figure, the primary combustion chamber 9 and the secondary combustion chamber 10 are provided in the burner tile 8 with different diameter steps, and the fuel supplied from the fuel nozzle 11 is supplied to the primary air nozzle 12 and the secondary air nozzle 13.
Performs two-stage combustion with the combustion air supplied from.
That is, a primary combustion gas containing unburned components is generated in the primary combustion chamber 9, and the primary combustion gas is mixed with the primary combustion gas in the secondary combustion chamber 10.
Secondary combustion is performed using secondary air, and NOx in high-temperature combustion is suppressed by two-stage combustion in a burner.

[0006]

However, the burner of the above construction is effective for reducing NOx below the conventional preheated air temperature of 600 ° C., but the preheated air temperature which has recently been put to practical use is the ignition temperature of the fuel. In a high-temperature air burner or a high-concentration oxygen burner (for example, about 700 ° C. for coke oven gas) or higher, the combustion reaction rate between the fuel and the supporting gas is extremely high. When completed, the flame becomes a high-temperature short flame, so that there is a problem that it cannot be applied to a heating furnace that requires low NOx properties and uniform heating properties.

As a method of solving this problem, the inventor has already disclosed in Japanese Patent Application No. 6-269639 a plurality of furnace body upper and lower walls on an extension of the reduction combustion burner arranged on the furnace body side wall of the heating furnace. A heating furnace has been proposed in which the supporting gas supply device is distributed and the fuel is dispersed and burned by the reducing combustion burner and the supporting gas supply device.

The present invention has devised a more effective method as proposed above, and has as its object to heat a fuel by burning a fuel with high-temperature air or high-concentration oxygen supporting gas to rapidly heat a material to be heated. At the same time as suppressing NOx generation,
An object of the present invention is to provide a heating furnace combustion method which ensures a flat furnace temperature distribution necessary for uniform heating of a material to be heated.

[0009]

Means for Solving the Problems The present invention has the following features in order to solve the above problems. That is, in a combustion method of a heating furnace in which a fuel is dispersed and burned by a burner and an in-furnace blowing nozzle using high-temperature air or high-concentration oxygen supporting gas to heat a material to be heated, the in-furnace blowing is performed. A nozzle is disposed near the peak of the furnace temperature on the central axis of the burner, and 10 to 40% of the fuel or supporting gas required for combustion is supplied from the blower nozzle in the downstream direction of the burner. And the remaining combustion gas is supplied from a burner.

[0010]

[Function] Since the fuel is dispersed and burned by the burner and the in-furnace injection nozzle, the maximum temperature of the burner flame decreases, and NOx
Is reduced. Further, from the vicinity of the peak of the furnace temperature on the central axis of the burner, 10 to 40% of the fuel or supporting gas required for combustion is blown in the downstream direction of the burner by a blow nozzle in the furnace, so that the fuel is blown into the furnace. Since the distributed combustion is performed and the calorific value of the in-furnace distributed combustion and the calorific value released from the burner flame to the material to be heated are substantially the same, the temperature distribution in the furnace in the axial direction of the burner becomes uniform, The material to be heated can be heated uniformly. In addition, since high-temperature air or high-concentration oxygen having a high combustion reaction rate is used as the supporting gas, there is no flame misfire or soot, which is a problem in strong oxidation combustion or strong reduction combustion of an air burner.

[0011]

FIG. 1 is a plan view of one zone of a side burner type heating furnace showing an embodiment of the heating furnace combustion method of the present invention.
FIG. 2 is a vertical sectional view of the heating furnace of FIG. 1 taken along the line AA. As shown in FIGS. 1 and 2, the outer shell of zone 1 of the heating furnace is composed of a furnace body side wall 2 made of refractory material, a furnace body upper wall 3a and a furnace body lower wall 3b. Heated material 4 in direction
A plurality of burners 5 are arranged in the upper and lower portions of the furnace, and fuel and high-temperature air or high-concentration oxygen supporting gas are supplied to the burners 5 by piping to form a burner flame 6 in the zone 1 of the heating furnace.

Further, from the flame temperature at the center of the burner flame 6, that is, 10 to 40% of the fuel or the supporting gas required for combustion is supplied from the in-furnace nozzle 7 arranged near the peak point of the in-furnace temperature. The fuel is blown in the downstream direction of the burner to perform in-furnace combustion of fuel in zone 1 of the heating furnace,
The material 4 to be heated is heated by the burner flame 6 and the flame of the dispersed combustion.

That is, 10 to 40% of the fuel or supporting gas required for combustion is blown from the in-furnace blowing nozzle 7 in the downstream direction of the burner flame, and the remaining fuel and supporting gas are supplied from the burner 5. When the fuel is blown into the furnace, the burner flame 6 becomes a strong oxidizing combustion flame containing a large amount of excess oxygen, and when the supporting gas is blown into the furnace, it becomes a strong reducing combustion flame containing a large amount of unburned gas. The maximum temperature of the burner flame 6 decreases, and the generation of NOx is suppressed.

Further, from the vicinity of the peak of the furnace temperature on the central axis of the burner, 10-40% of the fuel or supporting gas required for combustion is blown in the downstream direction of the burner by the furnace blow nozzle. Since the calorific value of the in-furnace combustion is substantially the same as the calorific value of the burner flame to the material to be heated, the temperature distribution in the furnace in the axial direction of the burner is reduced. It becomes uniform, and the material to be heated can be heated uniformly.

Further, since high-temperature air or high-concentration oxygen having a high combustion reaction rate is used as the supporting gas, there is no flame misfire or soot which is a problem in the strong oxidation combustion or strong reduction combustion of the air burner. .

The heating furnace is usually constituted by connecting a plurality of zones 1 as shown in FIG. 1 in the furnace length direction of the heating furnace, and the material 4 to be heated is located at one end of the heating furnace in the furnace length direction. It is charged into the heating furnace from the loading door, heated to a predetermined temperature while moving in the zone 1 of the heating furnace by a transport device such as a walking beam, and extracted from the extraction door on the other end side.

Next, the effects of the present invention will be described with reference to experimental examples. The experiment was performed using a cylindrical combustion experimental furnace (inner diameter 0.8 x furnace length 4.0).
m), an oxygen burner 5 with a combustion amount of 250,000 kcal / h was attached to one end of the furnace, and the in-furnace blowing nozzle 7 was attached from the side wall measurement hole of the experimental furnace to the center of the furnace, that is, on the central axis of the burner. .

The fuel was COG (coke oven gas, true calorific value 4320 kcal / Nm ³ ), the supporting gas was pure oxygen (oxygen concentration of 99.9% or more), and the oxygen ratio ( Assuming that the ratio of the measured oxygen amount to the theoretical oxygen amount is 1.05, the furnace blowing conditions (the type and amount of the furnace blowing fluid,
The position and direction of the in-furnace blowing nozzle 7) were variously changed, and the optimum in-furnace blowing conditions in which the uniformity of the in-furnace temperature distribution and the low NOx property were compatible were investigated.

One example of the experimental results is shown in FIGS.
FIG. 3 shows an experimental example of the in-furnace blowing ratio and the in-furnace temperature deviation in the furnace length direction in the burner axial direction. The results of COG in-furnace blowing are shown in the upper part of FIG. The results are shown in the lower part of FIG.

As can be seen from these results, from the vicinity of the peak of the furnace temperature on the central axis of the burner (2.0 m from the burner in this experiment), 10 to 40% of COG or oxygen required for combustion is obtained. By blowing the gas in the downstream direction of the burner, the temperature deviation in the axial direction of the burner, that is, the temperature uniformity in the furnace temperature distribution was significantly improved.

FIG. 4 shows the relationship between the distance from the burner and the furnace temperature ratio under the optimum furnace blowing conditions (from the vicinity of the peak of the furnace temperature of 2.0 m from the burner to the downstream of the burner). This is an experimental example, in which a flat furnace temperature distribution required for uniform heating could be formed by setting the oxygen blowing ratio in the furnace to an appropriate ratio of 10 to 40%. The furnace temperature ratio on the vertical axis in FIG. 4 is obtained by dimensionlessly dividing the measured furnace temperature at each measurement point by the average furnace temperature in the furnace length direction.

FIG. 5 shows the blow ratio in the furnace and O ₂ 1 at the furnace bottom.
FIG. 5 shows an example of an experiment using 1% NOx (hereinafter abbreviated as NOx). FIG.
The upper part of FIG. 5 shows the result of oxygen blowing into the furnace in the lower part of FIG. As can be seen from this result, while the reduced NOx was about 300 ppm in the burner alone combustion without in-furnace injection, the COG in the downstream direction of the burner from near the peak point of the in-furnace temperature of 2.0 m from the burner. In this case, the reduced NOx could be reduced to about 250 ppm or less.

In the case where oxygen is blown by 20% or more in the downstream direction of the burner from near the peak point of the furnace temperature of 2.0 m from the burner, the reduced NOx can be reduced to 100 ppm or less. From this, the uniform heating property of the material to be heated and the low N
The optimum furnace injection conditions that allow compatibility of Ox properties include 10 to 40%, preferably 20 to 30% of the fuel or supporting gas required for combustion from near the peak of the furnace temperature on the central axis of the burner. Was blown in the downstream direction of the burner. It should be noted that the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the spirit of the present invention.

[0024]

According to the method for burning a heating furnace of the present invention,
(1) Since the fuel is dispersed and combusted by the burner and the in-furnace injection nozzle, the maximum flame temperature is suppressed, and the amount of NOx generated is reduced. (2) In addition, since the combustion ratio between the burner and the in-furnace blowing nozzle is appropriate and the position and direction of the in-furnace blowing are optimal, the furnace temperature distribution in the axial direction of the burner is uniformed and the furnace is heated. The material can be heated uniformly. (3) Since high-temperature air or high-concentration oxygen having a high combustion reaction rate is used as a supporting gas, there is no flame misfire or soot which is a problem in a normal air burner in strong oxidation combustion or strong reduction combustion. And the like.

[Brief description of the drawings]

FIG. 1 is a plan view of one zone of a side burner type heating furnace showing an embodiment of the heating furnace combustion method of the present invention.

FIG. 2 is a longitudinal sectional view in the furnace width direction showing an embodiment of the heating furnace combustion method of the present invention.

FIG. 3 is a table showing an experimental example of a furnace blowing ratio and a furnace temperature deviation.

FIG. 4 is a table showing an experimental example of a distance from a burner and a furnace temperature ratio.

FIG. 5 is a table showing an experimental example of the in-furnace blowing ratio and NO ₂ converted to 11% O ₂ .

FIG. 6 is a longitudinal sectional view of a low NOx burner for a high-temperature sintering furnace showing a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Zone 2 Furnace body side wall 3a, 3b Furnace body upper wall, furnace body lower wall 4 Heated material 5 Burner 6 Burner flame 7 Furnace blowing nozzle 8 Burner tile 9 Primary combustion chamber 10 Secondary combustion chamber 11 Fuel nozzle 12 1 Secondary combustion air nozzle 13 Secondary combustion air nozzle

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-97620 (JP, A) JP-A-54-33210 (JP, A) JP-A-3-188223 (JP, A) JP-A-7-97 118753 (JP, A) Japanese Utility Model Showa 52-30401 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 1/52

Claims (1)

(57) [Claims] 1. A heating furnace combustion method for heating a material to be heated by using high-temperature air or high-concentration oxygen-supporting gas and performing combustion in a distributed manner with a burner and an in-furnace blowing nozzle. An in-furnace injection nozzle is disposed near a peak of the in-furnace temperature on the central axis of the burner, and 10 to 40% of fuel or supporting gas required for combustion is supplied from the in-furnace injection nozzle downstream of the burner. Supply in the direction,
A method for burning a heating furnace, comprising supplying remaining fuel and supporting gas from a burner.