JP7202467B2 - Method for denitration of cement kiln exhaust gas - Google Patents

Description

The present invention relates to a technology for reducing the concentration of nitrogen oxides (hereinafter referred to as "NOx") in combustion gas discharged from a cement kiln.

Exhaust gas from a cement kiln contains NOx resulting from the high-temperature region of the calcining zone. When the concentration of NOx is high, it can be removed by adding a denitration agent such as urea or ammonia, or by the reduction action of combustion in the calciner. NOx concentration is reduced. However, in the method of using urea as a denitration agent, urea is expensive, so the operating cost rises. In addition, if only urea is added, the denitrification efficiency is low, and there is a risk that surplus ammonia that has not reacted with NOx will be discharged out of the system as it is.

Therefore, the present applicant provided a denitrification burner that blows fuel and combustion air into the kiln bottom of the cement kiln to reduce NOx in the cement kiln exhaust gas in a low-oxygen region in the kiln bottom and burn the fuel. The decarboxylation efficiency of cement raw materials can also be improved, and a technique has been proposed for efficiently reducing the NOx concentration in cement kiln exhaust gas while maintaining a good firing state regardless of the type of calcining furnace (Patent Document 1). reference).

Japanese Patent No. 6476165

Based on the method described in Patent Document 1, conventionally, one denitration burner is installed at the bottom of the kiln, and 25 to 30% of the calciner fuel is blown from the denitration burner to reduce NOx in the cement kiln exhaust gas. , the NOx concentration was reduced, but only a reduction of 70 to 100 ppm (O ₂ = 10%) was obtained. .

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to further reduce the concentration of NOx in cement kiln exhaust gas.

In order to achieve the above object, the method for denitration of cement kiln exhaust gas of the present invention comprises a plurality of denitrification burners installed at the kiln bottom of the cement kiln, into the kiln bottom, and the cement kiln as a whole with the plurality of denitrification burners. A fuel of 50% or more and 100% or less of the fuel to be burned in the attached calciner and a small amount of air for pressure feeding are blown in, and the fuel is partially burned and gasified in a low oxygen concentration atmosphere. do. According to the present invention, the amount of reducing agent is increased, and since O2 is consumed, the influence of O2 at the bottom of the kiln is almost eliminated, so the NOx concentration in the cement kiln exhaust gas can be further reduced. In addition, by reducing the injection amount per burner for denitrification, adhesion of coating and collision between fuels are prevented, and the injected fuel mixes with the kiln exhaust gas flowing at the bottom of the kiln and collides with NOx in the kiln exhaust gas. You can increase your odds.

In addition, a part of the raw material discharged from the cyclone attached to the cement kiln is fractionated and fed to a position between 1000 mm above and 1000 mm below the installation site of the denitrification burner, thereby reducing Fe in the raw material. It can be used as a reducing agent for reducing ₂ O ₃ and denitrifying NOx.

As described above, according to the present invention, the NOx concentration in cement kiln exhaust gas can be further reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing one embodiment of a cement burning apparatus for carrying out a method for denitration of cement kiln exhaust gas according to the present invention; 1. It is the schematic which shows arrangement|positioning of the burner for denitrification in the kiln bottom of the cement baking apparatus of FIG. 1, (a) is a front view, (b) is a top view.

1 and 2 show an embodiment of a cement calcining apparatus for carrying out a cement kiln exhaust gas denitrification method according to the present invention. This cement calcining apparatus 1 is a cement raw material (hereinafter referred to as "raw material"). a preheater 2 for preheating R; A cement kiln 5 for firing the raw material R2 from the cyclone 2a with the fuel F1 blown from the main burner 15, a clinker cooler 6 for cooling the cement clinker fired in the cement kiln 5, and installed at the kiln bottom 4 of the cement kiln 5. It is composed of four denitrification burners 14 (14A to 14D) and the like. The structures of the preheater 2, the calciner 3, the cement kiln 5, the clinker cooler 6, etc., except for the denitrification burner 14, are the same as those of the conventional one.

The denitration burners 14 (14A to 14D) are arranged on the same horizontal plane as the bottom of the kiln 4, as shown in FIG. Further, at the tip of each denitrification burner 14, it is preferable to provide 6 to 10 swirl vanes with a swirl angle of 10 to 50 degrees, as in the cement burning apparatus described in Patent Document 1.

Next, the method for denitration of cement kiln exhaust gas according to the present invention will be described with reference to FIGS. 1 and 2. FIG.

The preheater 2 of the cement burning apparatus 1 preheats the raw material R using the exhaust gas G from the cement kiln 5 , and the calcining furnace 3 calcines the raw material R1 from the cyclone 2 b of the preheater 2 . At this time, the tertiary air G1 from the clinker cooler 6 is blown in together with the fuel F2 from the calciner burner 13 to burn the fuel F2. Pulverized coal, heavy oil, or the like is used for the fuel F2, and combustible waste may be used for part or all of the fuel F2.

Four denitration burners 14 (14A to 14D) installed at the kiln bottom 4 of the cement kiln 5 also blow the fuel F3 together with a small amount of air for pressure feeding to partially combust the fuel F3. The total amount of the fuel F3 injected from the four denitration burners 14 is 50% or more and 100% or less of the amount of the fuel F2 for the calciner 3 . Pulverized coal, heavy oil, and combustible waste can be used for the fuel F3 in the same manner as the fuel F2 for the calciner 3, and any one or more of these may be used at the same time.

By blowing in the fuel F3 from the denitrification burner 14, the NOx contained in the combustion gas G of the cement kiln 5 can be reduced in the low-oxygen region inside the kiln bottom. In addition, by gasifying the fuel F3 by partial combustion using a small amount of air for pumping, the raw materials R2 and R3 can be decarboxylated, and the decarboxylation efficiency of the cement calcining apparatus 1 as a whole can be improved. At this time, the mixed flow of the fuel F3 and the combustion air is swirled by the swirl vanes provided on the denitrification burner 14 and blown into the bottom of the kiln 4, so that the combustion efficiency of the fuel F3 is improved.

In addition, by increasing the amount of fuel F3 blown from the entire denitrification burner 14 to 50% or more and 100% or less of the amount of fuel F2 for the calcining furnace 3, the amount of reducing agent increases and the amount of O ₂ at the bottom of the kiln increases. Since there is almost no influence, the reduction effect does not decrease when the concentration of O ₂ at the bottom of the kiln is high as in the conventional case, and the concentration of NOx in the cement kiln exhaust gas can be effectively reduced.

Furthermore, when there is only one denitration burner 14, the fuel blown from the denitration burner 14 immediately moves upward. NOx on the side opposite to the denitrification burner 14 is difficult to be reduced, and the effect of reducing NOx is small. Therefore, in the present invention, by providing four denitration burners 14, the amount of blowing per denitration burner 14 is reduced, adhesion of coating and collision between fuels are prevented, and kiln exhaust gas flowing at the bottom of the kiln is prevented. and the collision probability with NOx in the kiln exhaust gas can be increased.

Further, by installing the denitration burner 14 on the same horizontal plane, it is possible to further increase the probability of collision with NOx in the kiln exhaust gas, which is preferable.

Furthermore, by generating 2% to 5% or more of CO at the bottom of the kiln 4, the Fe ₂ O ₃ in the raw material for cement becomes FeO, thereby exhibiting a greater NOx reduction effect.

Next, the fuel F1 such as pulverized coal is blown from the main burner 15 of the cement kiln 5, the raw material R2 from the cyclone 2a of the preheater 2 is fired, and the obtained clinker is cooled by the clinker cooler 6 to produce the cement clinker CL. obtain.

By using the cement burning apparatus 1 having the above configuration, a NOx reduction effect of 110 ppm (O ₂ =10%) or more was obtained.

In addition, although illustration is omitted, since the cement raw material coating adheres to the location where the denitrification burner 14 is installed, a portion of the raw material discharged from the cyclone of the preheater 2 is separated and removed from the location where the denitration burner 14 is installed. Delivery between 1000 mm above and 1000 mm below is preferred. In addition, it can be used as a reducing agent for denitrifying NOx by reducing Fe ₂ O ₃ in the raw material.

Although four denitration burners 14 are installed in the above-described embodiment, the number of denitration burners 14 is not limited to four, and the above effects can be obtained by installing a plurality of denitration burners 14 . When five or more denitrification burners 14 are installed, they may be arranged over two stages in the vertical direction instead of on the same horizontal plane.

Also, although the case where the cement burning apparatus 1 is of the SF type has been exemplified, the present invention can also be applied to other types of cement burning apparatuses.

1 Cement firing device 2 Preheater 2a Bottom cyclone 2b Third cyclone from top 3 Calcination furnace 4 Kiln bottom 5 Cement kiln 6 Clinker cooler 13 Calcination furnace burner 14 (14A to 14D) Denitration burner 15 Main burner

Claims (2)

50% or more and 100% or less of the fuel to be burned in the calcination furnace attached to the cement kiln from the plurality of denitration burners installed at the kiln bottom of the cement kiln into the kiln bottom. A method for denitrification of exhaust gas from a cement kiln, characterized by blowing in a sufficient amount of fuel and air for pumping, and partially combusting the fuel in a low oxygen concentration atmosphere. A portion of the raw material discharged from a cyclone attached to the cement kiln is fractionated and fed into a space between 1000 mm above and 1000 mm below the installation site of the burner for denitration. A method for denitration of a cement kiln exhaust gas as described.

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