JPH11323344A - Process for reducing nox in coke oven combustion exhaust - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently reduce NOx in combustion exhaust in coke ovens. SOLUTION: In a coke oven heated by combustion of a rich gas, lean gas or mixture gas thereof, wherein fuel gas is supplied from the bottom part 13 of combustion chambers 1 and wherein air for combustion is supplied from the bottom part of the combustion chambers 1 or from multiple nozzles 2 placed in the height direction through ducts 3 created in the bottom part 13 of the combustion chambers 1 and in dividers 12 of the combustion chambers 1, a reductive gas containing hydrogen is blown in from a position from 1 to 2.5 m higher from gas feed openings 9 established at the bottom part 13 of the combustion chambers 1 with a blowing angle of from 90 to 60 deg. upward against the combustion exhaust flow. Since the optimal blowing position, blowing angle and blowing process of the reductive gas are determined, NOx in combustion exhaust is efficiently reduced, even in coke ovens with special forms.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for reducing NOx in flue gas in a coke oven.

[0002]

The nitrogen oxides generated by combustion in the Background of the Invention coke oven _{NO, NO 2, N 2 O} , there are N ₂ O _5, etc., are referred to as these are collectively NOx. This NOx is classified into thermal NOx, prompt NOx, and fuel NOx. In a coke oven, thermal NOx originating from nitrogen in combustion air occupies most of the NOx. And
The generation ratio is expressed by the following equation (1). From this equation (1), it can be seen that the generation of thermal NOx is affected by the flame temperature, the nitrogen concentration and the oxygen concentration.

[0003]

DNOx / dt = N ₂ × O ₂ ^1/2 × exp (-k / T) where k: constant T: flame temperature NOx, N ₂ , O ₂ : concentration of each composition

Means for reducing the NOx content in flue gas in a coke oven include a method of lowering the flame temperature by recirculating the flue gas and a method of reducing the oxygen and nitrogen concentrations by partially burning the flue gas. Methods for reducing are known.

[0005] Among them, the method of recirculating the combustion exhaust gas is practiced in a coke oven of a copper circulation type. In this case, the combustion exhaust gas is mixed into the combustion side flue through one or two openings provided at the bottom of the twin-type combustion chamber (twin flue) to lower the flame temperature, and to lower the oxygen concentration, thereby reducing NOx. The generation rate is suppressed.

In order to reduce the NOx content by partial combustion, a multi-stage coke oven is used. For example, JP-A-61-13328
No. 6 and JP-A-1-306494, the combination of in-system recirculation of flue gas and multi-stage combustion of air and gas,
In order to effectively reduce the NOx content, it is necessary to appropriately combine the in-system recirculation of the combustion exhaust gas, the discharge rate of the lower stage air, and the arrangement of the second combustion stage. In addition, Japanese Patent Application Laid-Open No. 4-501876 further states that the proper arrangement of gas / air dilution of the combustion exhaust gas outside the furnace, the circulation hole at the bottom of the combustion chamber, the rich gas nozzle, and the poor gas port is important.

[0007]

However, the above-mentioned conventional method is a combination of the reduction of the flame temperature due to the recirculation of the flue gas and the reduction of the oxygen and nitrogen concentrations due to the partial combustion, and the quantitative improvement. The amount of generation was limited.

Therefore, in the recirculation system of the combustion exhaust gas in the copper circulation method, the exhaust gas circulation amount cannot be arbitrarily changed. Also, in a large coke oven with a combustion chamber height of 6.5 m or more and a high operation rate operation with a carbonization time of 12 hours or less, the volume of exhaust gas increases and the cross-sectional area of the circulation port restricts the operation. There is a problem that the exhaust gas circulation rate cannot be increased to 20% or more.

The method of reducing NOx by partial combustion has been adopted in the form of "multi-stage combustion" in Carl still type coke ovens, Otto type coke ovens, and Nippon Steel M type coke ovens, and has been effective. In order to further reduce the generation of NOx in a coke oven, the structure of the combustion chamber itself is changed to suppress the generation of NOx, or
It is necessary to decompose the generated NOx.

As a method for decomposing NOx produced, it is known to reductively decompose NOx produced by combustion with a reducing gas. However, for adaptation to a coke oven, the combustion chamber is a bottom-fired type. In addition, the shape is very special with a length of 450 to 600 mm, a width of 800 to 1100 mm, and a height of 5000 to 7000 mm,
In addition, there is a problem with the blowing position and blowing angle of the reducing gas, and the blowing method, so that it has not been implemented yet.

On the other hand, the requirement for the prevention of environmental pollution is increasing year by year, and the regulation value of NOx emission of a new coke oven is considerably stricter than that of an existing coke oven in view of laws and regulations. It may even be impossible.

The present invention has been made in view of the above-mentioned conventional problems, and by optimally defining the blowing position and blowing angle of the reducing gas and the blowing method,
NOx in flue gas in specially shaped coke ovens
It is an object of the present invention to provide a method capable of effectively reducing the pressure.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention relates to a method for producing NOx in a flue gas of a coke oven according to the present invention.
The reduction method is 1 to 2.5 m from the gas supply port at the bottom of the combustion chamber.
At a height position, a reducing gas containing hydrogen is blown at an angle perpendicular to the flow of the combustion exhaust gas by 60 ° upward. And by doing this,
NOx generated in the combustion chamber is decomposed and reduced by a reduction reaction.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A method for reducing NOx in a flue gas of a coke oven according to the present invention is heated by burning rich gas or poor gas, or a mixed gas thereof, and the fuel gas is supplied from the bottom of the combustion chamber. The combustion air is supplied from a gas supply port at the bottom of the combustion chamber in a coke oven supplied from a plurality of supply ports in the height direction through a combustion chamber bottom or a duct provided in the combustion chamber bottom and the combustion chamber partition wall. ~ 2.5m
Is injected at an angle perpendicular to the flow of the combustion exhaust gas at an angle of up to 60 ° at a height position of the fuel gas. It is economical to use furnace gas.

That is, rich gas (coke oven gas) or poor gas (blast furnace gas) or a mixture of these gases and combustion air supplied from the bottom of the combustion chamber rises in the combustion chamber while diffusing and burning. Combustion in a narrowly limited space such as the combustion chamber of a coke oven has a wider combustion area in the height direction than combustion in an open space.

In the combustion in the combustion chamber of such a coke oven, although the maximum combustion point varies depending on the gas supply amount, the gas heat generation amount, or the air ratio, the present inventor has determined that the ambient temperature during the combustion and the internal combustion chamber are different. As a result of measuring the wall temperature, it was found that NOx
It was found to show a reduction effect.

That is, at a height of less than 1 m from the gas supply port where the combustion is not completed, even if a reducing gas containing hydrogen gas is blown, the reduction reaction of chemical formula 1
Since the effect of reducing NOx by decomposing Ox does not appear, in the present invention, the blowing position of the reducing gas is set at a height of 1.0 m or more from the gas supply port. On the other hand, when the reducing gas injection position exceeds 2.5 m, the temperature of the combustion exhaust gas decreases, and the reductive decomposition reaction of NOx is delayed.
In the present invention, the blowing position of the reducing gas is set to a height of less than 2.5 m from the gas supply port.

[0018]

## STR1 ## 2NO + H ₂ = N ₂ + 2OH

In order to mix the combustion gas with NOx-containing combustion gas more quickly, it is necessary to inject the reducing gas at a right angle to the flow of the combustion exhaust gas upward by 60 °. In an experiment conducted by the present inventor, when the injection angle was made parallel to the flow of the combustion exhaust gas, the effect of reducing NOx was not obtained. Incidentally, the shape of the reducing gas injection port when performing the method for reducing NOx in coke oven combustion exhaust gas according to the present invention is not particularly limited, but the width is widened and the height is suppressed. It is desirable to form a slit shape.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for reducing NOx in coke oven combustion exhaust gas according to the present invention will be described below with reference to an embodiment shown in FIGS. 1 is a double furnace capable of performing poor gas heating or rich gas heating, and a cross-sectional view taken along the line AA in FIG. 2 in which a NOx reducing gas supply device is laid in an air multi-stage combustion structure furnace;
2 is a horizontal sectional view taken along the line BB of FIG. 1, FIG. 3 is a horizontal sectional view taken along the line CC of FIG. 1, and FIG. 4 is a single furnace capable of heating only rich gas. FIG. 5 is a sectional view taken along the line DD of FIG. 5 in which the reducing gas supply device is laid, and FIG.
FIG. 6 is a horizontal sectional view taken along the line FF of FIG. 4, and FIG.
8 is a sectional view taken along the line GG of FIG. 8 using the reducing gas supply device of x, and FIG. 8 is a horizontal sectional view taken along the line HH of FIG. 7.

In the double furnace shown in FIGS. 1 to 3, in the case of poor gas combustion, fuel gas is supplied in a single stage from the poor gas supply port 9 through the poor gas supply duct 4 provided at the bottom 13 of the combustion chamber 1. It is supplied to the combustion chamber 1. Further, in the case of rich gas combustion, the fuel gas is supplied to the combustion chamber 1 in a single stage from the rich gas supply nozzle 6 also provided at the bottom 13 of the combustion chamber 1.

On the other hand, the combustion air is roughly classified into primary air and secondary air. The primary air is supplied from a primary air supply port 10 through a primary air supply duct 5 provided at the bottom 13 of the combustion chamber 1.
Further, the secondary air is supplied from the primary air supply port 10 through the secondary air supply duct 3 provided on the partition wall 12, for example, 2.5 mm.
The air is supplied to the combustion chamber 1 in multiple stages from secondary air supply nozzles 2 provided at two places at heights of m and 3.5 m.

Reference numeral 7 denotes a supply duct for, for example, coke oven gas containing hydrogen. The supply duct 7 is provided on a partition wall 11. The coke oven gas passes through the supply duct 7 and from the primary air supply port 10 through the reducing gas supply nozzle 8 installed at a height of, for example, 2 m, to the combustion chamber 1.
Supplied within. As shown in FIG. 3, for example, the reducing gas supply nozzle 8 is of a slit type having a wide width and a reduced height, and the blowing angle to the combustion chamber 1 is, for example, that of the combustion exhaust gas. At right angles to the flow. In addition, 14 in FIGS. 1-3 shows a furnace wall.

N in the coke oven combustion exhaust gas according to the present invention
The Ox reduction method is performed using, for example, a coke oven having the above-described configuration. The reducing gas supply nozzle 8 provided at a height of 2 m from the poor gas supply port 9 in the bottom portion 13 of the combustion chamber 1. Therefore, for example, a coke oven gas is blown as a reducing gas, for example, so as to be perpendicular to the flow of the combustion exhaust gas.

When the coke oven gas shown in FIGS. 1 to 3 is used and a coke oven gas of 20% of rich gas is blown from the reducing gas supply nozzle 8 at a right angle to the case parallel to the flow of the combustion exhaust gas. FIG. 9 shows the NOx distribution of the combustion chamber 1 in the height direction. From FIG. 9, it can be seen that when the coke oven gas is blown in parallel to the flow of the combustion exhaust gas, there is almost no change from the case where the coke oven gas is not blown, and there is no effect. On the other hand, when the coke oven gas is injected at right angles to the flow of the combustion exhaust gas, NOx is reduced by about 20% as compared with the case where the coke oven gas is not injected.

FIG. 10 shows the results obtained when the blowing angle of the reducing gas (coke oven gas) was changed under the same conditions as in FIG.
It shows an example of the Ox reduction effect. As is apparent from FIG. 10, when the blowing angle of the reducing gas (coke oven gas) is perpendicular to the flow of the combustion exhaust gas to 60 ° upward, there is an effect of reducing NOx.

FIG. 11 shows an example of the NOx reduction effect when the blowing height position of the reducing gas (coke oven gas) is changed under the same conditions as in FIG. This figure 1
As is clear from 1, reducing gas (coke oven gas)
Is the largest NOx around 1.5-2m
There is a reduction effect.

N in the coke oven combustion exhaust gas according to the present invention
The method for reducing Ox is not limited to the double furnace having the structure shown in FIGS. 1 to 3, and the single furnace capable of supplying only rich gas shown in FIGS. 4 to 6, and FIGS. 7 and 8. As shown, the present invention is also applicable to a coke oven of a recirculation type of combustion exhaust gas in which a circulation port 15 is provided in a combustion chamber.

FIG. 12 shows the effect of recirculation (circulation) of the combustion exhaust gas when rich gas (coke oven gas) is burned in a multistage combustion furnace, and the injection of reducing gas. The result of combining the effects of the cases is shown. It can also be seen that NOx is reduced by about 20% even when the flue gas is recirculated in the furnace.

[0030]

As described above, in the method for reducing NOx in flue gas of a coke oven according to the present invention, the position and angle of blowing the reducing gas and the blowing method are optimally specified. Even in a coke oven having an irregular shape, NOx in the combustion exhaust gas can be effectively reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view taken along the line AA in FIG. 2 in which a NOx reducing gas supply device is laid in a multi-stage combustion structure furnace in a double furnace capable of poor gas heating or rich gas heating. .

FIG. 2 is a BB horizontal sectional view of FIG.

FIG. 3 is a horizontal sectional view taken along the line CC of FIG. 1;

FIG. 4 is a sectional view taken along the line DD in FIG. 5 in which a NOx reducing gas supply device is laid in a single-stage furnace capable of heating only rich gas, and in a multi-stage air combustion type furnace.

FIG. 5 is an EE horizontal sectional view of FIG. 4;

FIG. 6 is a horizontal sectional view taken along line FF of FIG. 4;

FIG. 7 is a sectional view taken along the line GG of FIG. 8 in which a recirculation of combustion exhaust gas and a reducing gas supply device for NOx are used in combination with an air multistage combustion structure furnace.

8 is a horizontal sectional view taken along the line HH in FIG. 7;

FIG. 9 is a diagram showing an effect when a reducing gas is blown at 20% of a fuel gas when a rich gas is used as the fuel gas.

FIG. 10 is a diagram illustrating an effect when the blowing angle of the reducing gas is changed under the same conditions as in FIG. 9;

FIG. 11 is a diagram showing an effect when the position of the blowing height of the reducing gas is changed under the same conditions as in FIG. 9;

FIG. 12 shows the result of combining the effect of recirculating flue gas in the furnace and the effect of injecting reducing gas when burning rich gas in a multistage combustion furnace. It is.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Secondary air supply nozzle 3 Secondary air supply duct 7 Supply duct 8 Reducing gas supply nozzle 9 Poor gas supply port 10 Primary air supply port 11 Partition wall 12 Partition wall 13 Bottom part

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yutaka Suzuki 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd.

Claims (2)

[Claims] The fuel gas is heated by combustion of a rich gas or a poor gas, or a mixture thereof, and the fuel gas is supplied from a bottom of the combustion chamber, and combustion air is supplied to a bottom of the combustion chamber or a bottom of the combustion chamber and a partition wall of the combustion chamber. In a coke oven supplied from a plurality of supply ports in the height direction through a duct provided at a height of 1 to 2.5 m from the gas supply port at the bottom of the combustion chamber, a reducing gas containing hydrogen is supplied. A method for reducing NOx in coke oven combustion exhaust gas, wherein the gas is blown at an angle that is perpendicular to the flow of the exhaust gas at an angle of up to 60 °. 2. The method for reducing NOx in flue gas of a coke oven according to claim 1, wherein a coke oven gas is used as a reducing gas for reducing and decomposing NOx.