JPS6018209B2 - Method for reducing nitrogen oxides in cement firing exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for reducing nitrogen oxides in cement firing exhaust gas, and in particular, a method for reducing and denitrating NQ generated in the kiln by 50% or more in a cement kiln equipped with a suspension preheater. This paper relates to a method for reducing nitrogen oxides in cement firing exhaust gas.

In general, cement clinker requires firing by heating the raw material until it is semi-molten at the boiling point of the kiln, and the flame is required to be at a high temperature to produce sufficient radiant heat transfer, so the NQ in the kiln is Its occurrence is inevitable.

However, in recent years, there has been a strong demand for reducing the generation of NQ in cement firing exhaust gas, and various methods and devices have been proposed.

For example, the method described in Sabu No. 51-10624 is general denitration using main combustion, reduction combustion, and oxidation combustion.
In addition, in the one described in Tokikan Sho 50-10422, an auxiliary furnace is provided in the suspension preheater, and the fuel is burned in an oxygen-deficient state in the auxiliary furnace, and the gas contains oxygen and N○x from the kiln. NQ is mixed with gas, and when the mixed gas is further combusted, NQ is reduced and denitrified, and then secondary air is replenished for complete combustion. This latter method also performs denitrification at a stoichiometric air ratio of 01 or less, and is in a parallel relationship with the former method. Furthermore, this latter method involves the unreasonable task of causing incomplete combustion in the auxiliary furnace, and also requires complicated means of replenishing air. The present inventors believe that the catalytic effect of cement raw materials is very strong, and that we have developed a denitrification method in which hydrocarbon fuel is newly sucked in and combusted at a stoichiometric air ratio of 1.1 or less, that is, without the need for air replenishment later. However, as a result of additional experiments, it was discovered that the denitrification rate was unstable only under the conditions of the invention.

As a result of research, it was found that if the cement raw material, the kiln outlet gas containing oxygen and NQ, and the additional injected fuel were combusted at high speed and in a sufficiently mixed state to promote denitrification, a denitrification rate of 50% or more could be reliably obtained. It was confirmed. That is, according to the present invention, in order to obtain a high-speed state, the lower part of the rising flue connected from the rotary kiln to the first cyclone of the suspension preheater is constricted to form a straight pipe part, that is, a straight pipe-like striped flow part with an initial flow rate of 2 or more. The upper end of the contraction part is suddenly expanded, and the upper end thereof is used as an enlarged part or a flue of standard thickness to blow fuel into the bran flow part, and drop cement raw material into the rising and expanded part. In addition, in the present invention, when the fuel is light oil, for example, the fuel is injected from near the upper expansion part of the straight tube-shaped striped flow, and when heavy oil is used, it is blown from the lower part of the contraction flow, and the fuel is blown into the expansion part. to increase the temperature.

The strong turbulence from expansion to expansion improves the combustion rate, and the relative velocity resulting from the combination of the downward-to-upward gas flow and the upward-to-downward feedstock velocity cooperates with the same turbulence effect. The cement raw material powder is suspended and diffused into the high-speed combustion section, and theoretical air 1 is
．． The ring element of NQ is carried out in a state of oxygen residual of 1 or less. The method for reducing nitrogen oxides in cement firing exhaust gas according to the present invention will be explained in detail below with reference to examples thereof.

Figure 1 is a schematic diagram of the main parts of an apparatus for carrying out the method of reducing nitrogen oxides in cement firing exhaust gas according to the present invention. The lower part of the continuous rising flue 3 is constricted to form a straight pipe-shaped constrictor part 4 with a constriction ratio of 2 or more, and the upper end of this constrictor part 4 is suddenly expanded to produce smoke of a standard thickness above it. An enlarged portion 5 as a road is formed.

Fuel is blown into the contraction section 4, and cement raw material is supplied to the rising expansion section 6. Therefore, the combustion exhaust gas from the rotary kiln 1 is rapidly combusted in the lower part of the enlarged part 5 by new fuel supplied from the fuel injection pipe 7 of the striped flow part 4, and is then supplied from the cement raw material drop pipe 8. Suspension mixing of the raw material and combustion gas is created. Such exhaust gas containing the raw material is led to the first cyclone 2 of the suspension preheater, where the raw material is separated from the exhaust gas, and is supplied to the enlarged portion of the rising flue 3 of the rotary kiln 1 and fired in the rotary kiln 1. Ru. In this way, the combustion exhaust gas from the rotary kiln 1 is used to temporarily preheat the raw material in the preheater section, and is also used in the condenser section 4.
Due to the rapid combustion of the fuel supplied at the lower part of the enlarged part 5, the N*x contained in the exhaust gas is reduced. Comparative data between Examples of the present invention and Comparative Examples is shown below.

However, the basic conditions in each example are the part that displays the change (
Except for those marked with *), they are common and are as follows. The gas flow rate in the rising flue expansion part is 9/S, the vertical flow 0 section cross-sectional area b/a = 3 (where a is the cross-sectional area of the vertical flow part and b is the area of the rising flue expansion part. Below, the rising smoke The ratio of the cross-sectional area of the enlarged part to the cross-sectional area of the contracted part of the path is called the contracting ratio), the gas flow rate of the contracted part 4 is 27/S, the gas temperature of the contracted part 4 is 90000,
The air ratio of the gas star entering the condenser section 4 is 1.21, the cement raw material is fed downward into the expansion section 6, the weight of C is added to the condenser section 4, and the ratio of the amount of added heavy oil to the amount of heavy oil blown into the rotary kiln is 15%. , Air ratio after fuel addition: 1.0f Also, the N○x leg was standardized to the 0210% conversion value.

Example 0 Example No. 1 and comparative example no. 2 and no. 3 shows changes in the NQ reduction rate by changing the position of the burner, which is a fuel injection pipe, and the position of the cement raw material drop pipe.

In other words, it's a shame as a comparative example. In Comparative Example No. 2, the burner, which is the fuel injection pipe 7, is located at a position 7' above the contraction section 4 and three times the diameter of the enlarged section. In No. 3, the cement raw material drop pipe 8 was positioned above the contracted flow section 4 at a position 8' three times the diameter of the enlarged section. However, *marks indicate changes from the basic conditions. As is clear from the above values, changing the selection of the fuel addition position and raw material feed position is of decisive importance as a measure against NQ.

Example B Example No. 1.No. 4.No. 5 and Comparative Example M.
6 shows the change in the N○x reduction rate due to the change in the degree of longitudinal flow, that is, the contraction rate.

The contraction ratio needs to be at least 2, and there is a problem in that when the contraction ratio is increased, the ventilation resistance increases with the square ratio of the gas velocity.

Example m Example No. 9, No. 1.No. 10 and Comparative Example N
o. 7.No. 8 shows the effect of air ratio after fuel addition.

As is clear from this example, the air ratio after fuel addition is 1.1.
If it is 0 or more, the N○x reduction rate is low. Moreover, comparative example No. 7
In this case, the air ratio in the rotary kiln becomes too large. Air ratio after addition: 1.
If it is less than 00, there is a risk of not only heat loss but also combustion instability. Figure 2 shows the above basic conditions when the ratio of the amount of added heavy oil to the heavy oil blown into the rotary kiln is changed, and the air ratio after fuel addition is 1.
2 is a graph showing the denitrification rate obtained by adjusting the air ratio before addition so that 0.05 was constant.

As is clear from the figure, when the fuel addition rate is less than 10%, the NOx removal rate suddenly decreases, and even when the fuel addition rate is over 20%, the NOx removal rate does not improve significantly and the air ratio before fuel addition becomes excessive. Becomes a delinquent. As is clear from the above, as in the present invention, a straight pipe-shaped constriction section is provided at the bottom of the rising flue connecting the suspension preheater and the rotary kiln, and a steep expansion section is provided following this, and cement is added at the exit of the constriction section. supply raw materials,
Inject fuel in the vertical flow section, make the amount of fuel injected into the condenser section the stoichiometric air ratio after injection of 1.10 or less, and make the amount of fuel injected into the condenser section 10% of the amount of fuel used in the rotary kiln. By setting the content to 20% or less, nitrogen oxides in the exhaust gas can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a part of an apparatus for carrying out the method of the present invention, and FIG. 2 is a graph showing the relationship between fuel ratio and denitrification rate. In the diagram, 1... rotary kiln, 3... rising flue,
4... Contraction part, 7... Fuel injection pipe, 8
・・・・・・Raw material drop pipe. Spirit! Figure 2

Claims (1)

[Scope of Claims] 1. A straight pipe-shaped constriction section with a constriction rate of 2 or more and a steep expansion section following the constriction section are provided at the bottom of the rising flue connecting the suspension preheater and the rotary kiln, and at the exit of the constriction section. A method for reducing nitrogen oxides in exhaust gas from cement firing, which is characterized by supplying cement raw materials at a velocity from above to below and injecting hydrocarbon fuel into a condenser section. 2. The amount of fuel injected into the contraction section is the theoretical air ratio after injection of 1.
10. A method for reducing nitrogen oxides in cement firing exhaust gas according to claim 1, wherein the amount of nitrogen oxides is 10 or less. 3. A method for reducing nitrogen oxides in cement firing exhaust gas according to either claim 1 or 2, wherein the amount of fuel blown into the condenser section is 10% or more of the amount of fuel used in the rotary kiln. .