JPH08215537A - Method for reducing nitrogen oxide in cement kiln exhaust gas and device therefore - Google Patents

Abstract

PURPOSE: To simply and surely reduce a NOX value. CONSTITUTION: A variable throttle device 5 is installed on a rising flue part 3 connecting a kiln oven end 2 of a kiln having a suspension preheater with a mixing room, and a throttling quantity of a throttle valve 6 of the variable throttling device 5 is adjusted and a flow rate of kiln exhaust gas is controlled and also a denitrification additive is jetted from a nozzle opening at a tip surface of the throttle valve to be mixed with the kiln exhaust gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for reducing NOx in exhaust gas of a cement kiln generated in a cement burning facility.

[0002]

2. Description of the Related Art In an NSP kiln with a calcination furnace, fuel is blown and burned in a rotary kiln and a calcination furnace. (See Japanese Patent Publication No. 51-30865, Japanese Patent Publication No. 60-18029, Japanese Patent Publication No. 2-55096)

When cement is produced in this kiln, NOx is mainly produced by combustion of fuel on the rotary kiln side. It is necessary to heat and sinter the raw material until it is semi-molten at the rotary kiln burning point, and the flame is required to have a high temperature so as to generate sufficient radiative heat transfer. Therefore, NOx is not generated in the rotary kiln. It is inevitable.

Further, the combustion of fuel on the calciner side is usually 800 ° C.
Since it is in the low temperature region of up to 1000 ° C, the generation of NOx is very small.

Therefore, as a method of reducing NOx, NOx generated on the rotary kiln side is suppressed, or
It is necessary to reduce it.

As a method of reducing this NOx, a denitration additive such as fuel, ammonia or urea is blown into the kiln exhaust gas flowing through the rising flue portion connecting the rotary kiln and the suspension preheater to remove the kiln exhaust gas and the fuel. A method for reducing NOx by mixing the same has been adopted (JP-A-53-1221, JP-B-56-2958).
0).

[0007]

In the conventional example, the denitration efficiency is poor, and the NOx value does not drop so much. Therefore, efforts have been made to reduce the NOx value to a desired value by increasing the addition amount of the denitration additive blown into the rising flue portion or changing the blowing method.

In view of the above circumstances, the present invention is simple and
The purpose is to surely reduce the NOx value.

[0009]

The present inventor has found that the NOx value may not decrease even if the addition amount of the denitration additive is large, and that the NOx value changes depending on the addition place, addition position, addition method, etc. As a result, I realized that the reason why the denitration effect was bad was that the kiln exhaust gas and the additive were not mixed uniformly, that is, the mixing effect was bad. Therefore, the present inventor intends to achieve the above object by configuring the present invention as follows in order to improve the mixing effect.

A variable throttle device is provided in the rising flue portion connecting the kiln kiln bottom of the suspension preheater kiln and the mixing chamber, and the flow rate of the kiln exhaust gas is controlled by adjusting the throttle amount of the throttle valve of the variable throttle device. A step; a step of ejecting a denitration additive from a nozzle opening at the tip surface of the throttle valve to mix with the kiln exhaust gas; a NOx content value in the exhaust gas at the uppermost cyclone outlet is detected, and based on the detected value A step of adjusting the throttle amount of the variable throttle device and the supply amount of the denitration additive, and the NOx.
Reduction method.

[0011]

The kiln exhaust gas flowing in the rising flue portion is throttled by the throttle valve of the variable throttle device to change its flow velocity, and the kiln exhaust gas colliding with the throttle valve is disturbed in the flow and swirled into the mixing chamber. Pour in. At this time, the denitration additive is ejected from the opening of the front end surface of the throttle valve, and the additive is mixed with the kiln exhaust gas while traversing the flow of the kiln exhaust gas.

When the NOx detection value of the NOx detecting means is not a desired value, the throttle amount of the throttle valve of the variable throttle device and the additive amount of the additive are adjusted so that the kiln exhaust gas and the additive are uniformly mixed. To do.

[0013]

Embodiments of the present invention will be described with reference to the accompanying drawings. In a rotary kiln with a suspension preheater equipped with a calcination furnace (hereinafter referred to as NSP kiln), a kiln kiln bottom 2 of a rotary kiln 1 is connected to a mixing chamber 4 via a rising flue portion 3.

The rising flue portion 3 is narrowed down to form a so-called contraction portion, and the flue portion cross-sectional area AS, that is, the flow passage cross-sectional area of the kiln exhaust gas is changed in the flue portion 3. A variable diaphragm device 5 is provided.

As shown in FIGS. 3 and 4, the variable throttle device 5 is provided with four throttle valves 6 that move in and out of the flue section 3. The throttle valve 6 slides independently of each other by a hydraulic cylinder 7.

The throttle valve 6 is made of a heat-resistant metal, and a denitration additive supply nozzle 8 is provided inside the throttle valve 6. The nozzle opening 8a at the tip of the nozzle is the tip surface 6 of the throttle valve.
A denitration additive pressure-feeding means 10 having a pump or the like is connected to the rear end of the opening a.

The shape, type and the like of the nozzle 8 are appropriately selected according to need, and for example, a spray nozzle or a blowing nozzle is used.

As denitration additives, carbon and hydrocarbon fuels such as pulverized coal, heavy oil, light oil, kerosene, LP
A single agent consisting of one kind of G and LNG or a mixture consisting of a plurality of kinds is used, but the present invention is not necessarily limited to this, and is appropriately selected as necessary. For example, ammonia gas, ammonia water, an aqueous solution of urea or an ammonia salt, or the like may be used as the denitration additive.

In the figure, SB is a calciner burner,
D is a cooler, KB is a kiln burner, arrow A1 is the exhaust gas flow direction, arrow A2 is the cement raw material flow direction, A3 is the fuel combustion air flow direction, and A4 is the denitration additive 30 flow direction. C1 to C4 are cyclones,
20 is provided at the exit 20a of the uppermost cyclone C1,
The NOx detector which measures the NOx value in a preheater exhaust gas is shown, respectively.

The operation of this embodiment will be described. First, the overall operation of the NSP kiln used for cement firing will be described. The cement raw material of 50 to 100 ° C., which is fed into the kiln exhaust gas duct KD1 from a raw material hopper (not shown), passes through the uppermost cyclone C1 and the cyclone C2,
It is thrown into the kiln exhaust gas ducts KD2 and KD3, respectively.

The kiln exhaust gas entering the kiln exhaust gas duct KD3 separates the raw material heated to 600 to 750 ° C. The separated raw material is an air blowing pipe 2 communicating with the cooler D.
7 is suspended and suspended in hot air of 300 to 700 ° C. and blown into the calcining furnace S.

The cement raw material in the calcining furnace S is 1000 to
After being mixed and stirred with a high temperature combustion gas of 1300 ° C. and exchanging heat with the kiln exhaust gas of approximately 900 to 1200 ° C. in the mixing chamber 4, heat is exchanged again and uniformly mixed at 830 to 950 ° C., and then the lowermost cyclone. Enter C4 and enter 820-9
It is fed into the rotary kiln 1 through the kiln kiln butt 2 as a cement raw material at 00 ° C.

The exhaust gas A generated in the rotary kiln 1
In No. 1 of the rising flue unit 3, the flow rate is adjusted by the variable throttle device 5 to control the flow velocity, and the denitration additive 30 is sprayed from the nozzle 8 and mixed into the mixing chamber 4. Then, it is mixed with the combustion gas generated in the calcining furnace S, but in the calcining furnace S, because of low temperature combustion, this combustion gas contains almost no NOx. Therefore, NOx of the kiln exhaust gas is mixed with NOx generated in the calcining furnace S in the mixing chamber 4 and diluted.

The variable throttle device 5 changes the size of the flue cross-section area AS by sliding the throttle valve 6 with a hydraulic cylinder to change the so-called throttle amount. When displacing the throttle valves 6, all the throttle valves 6 have the same protrusion amount as shown by the solid lines in FIGS. 3 and 4, or one opposing throttle valve as shown by the chain lines in FIG. The protrusion amount of 6 may be larger than that of the other. The shape and control method of the throttle valve 6 are appropriately selected as needed.

The exhaust gas A1 passing through the rising flue portion 3 is sprayed with the denitration additive 30 while the flow velocity is regulated by the throttle valve 6. At this time, the exhaust gas A1 collides with the throttle valve 6 and flows. Since it is disturbed, the denitration additive 30 blown out from the front end surface 6a of the throttle valve 6 enters the central portion of the flow of the exhaust gas and is well mixed.

Further, the exhaust gas A1 is the tip surface 6a of the throttle valve 6.
Since it rises while washing, the nozzle opening 8a of the denitration additive supply nozzle 8 that is open to the tip surface 6a does not get clogged.

Further, as the throttle valve 6 is further narrowed down, the nozzle 8 comes closer to the central portion of the flue portion 3, so that the exhaust gas A
Even if the flow rate of 1 becomes high, the additive can be sufficiently mixed.

During operation, the NOx detector 20 detects the NOx value in the uppermost cyclone C1 outlet exhaust gas A1, and the throttle amount of the variable throttle device 5 and the supply amount of the denitration additive 30 are adjusted so as to obtain a desired NOx value. Is adjusted. Desired NOx
When the value is higher than the value, the throttle amount is increased to reduce the flue section cross-sectional area AS to increase the flow velocity, and in the opposite case, the throttle amount is reduced to increase the flue section cross-sectional area AS to increase the flow rate. To reduce. The flow velocity to be adjusted at this time is appropriately selected as necessary. For example, the flow velocity of the kiln exhaust gas is 20 m /
It is selected within the range of S to 40 m / S.

In the above embodiment, the kiln with suspension preheater with calcination furnace was described, but it is needless to say that NOx can be reduced in the same manner in a kiln with suspension preheater without calcination.

[0030]

Since the present invention is configured as described above, it has the following remarkable effects. (1) Since the variable squeezing device is provided in the rising flue part, the flow rate of the kiln exhaust gas can be adjusted by changing the squeezing amount to uniformly mix the denitration additive. Therefore, NOx can be reduced without disturbing the operation of the rotary kiln, with almost no increase in the amount of heat.

(2) Since the denitration additive supply nozzle which is open at the tip surface of the throttle valve of the variable throttle device is provided, the kiln exhaust gas flows while washing the nozzle port of the nozzle. Therefore, it is possible to prevent clogging of the nozzle. or,
As compared with the case where the nozzle is fixed to the inner wall surface of the flue portion, the denitration additive can be supplied to the central portion side of the flow of the kiln exhaust gas, so that a better mixing effect can be obtained.

The NOx value in the exhaust gas from the uppermost cyclone outlet was measured and adjusted by changing the blowing amount of the denitration additive 30, and the results shown in Table 1 were obtained. However, the conditions in this experiment were as follows: fuel firing ratio, that is, fuel amount of rotary kiln / fuel amount of calcination furnace = 40/60, NOx in kiln kiln exhaust gas = 1000 ppm, (O2 = 10% standard),
Is. Note that fm is the ratio (%) of the denitration additive (fuel) to the kiln fuel, and NOx is NOx ppm (10% O2 conversion value) in the exhaust gas discharged from the uppermost cyclone outlet.

[0033]

[Table 1]

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is an enlarged view of a main part of FIG. 2;

FIG. 4 is a sectional view taken along line IV-IV in FIG. 3;

[Explanation of symbols]

 1 rotary kiln 2 kiln kiln 3 rising flue 4 mixing chamber 5 variable throttle device 6 throttle valve 7 hydraulic cylinder 8 denitration additive supply nozzle

Claims (9)

[Claims] 1. A variable throttling device is provided in a rising flue portion connecting a kiln kiln bottom of a suspension preheater kiln and a mixing chamber, and the throttling amount of the throttling valve of the variable throttling device is adjusted to control the flow rate of the kiln exhaust gas. A method of reducing NOx in the exhaust gas of a cement kiln, comprising: a step of controlling; and a step of ejecting a denitration additive from a nozzle opening at a tip surface of the throttle valve and mixing the additive with the exhaust gas of the kiln. 2. A variable throttling device is provided in a rising flue portion connecting a kiln kiln bottom of a suspension preheater kiln and a mixing chamber, and the throttling amount of the throttling valve of the variable throttling device is adjusted to change the flow rate of the kiln exhaust gas. A step of controlling; a step of ejecting a denitration additive from a nozzle opening at the tip surface of the throttle valve to mix with the exhaust gas from the kiln; a NOx content value in the exhaust gas from the uppermost cyclone outlet is detected, and the detected value is detected. A step of adjusting the throttle amount of the variable throttle device and the supply amount of the denitration additive based on the above; 3. The method for reducing NOx in the exhaust gas of a cement kiln according to claim 1 or 2, wherein the denitration additive is a carbon- or hydrocarbon-based fuel. 4. The carbon- and hydrocarbon-based fuel is a single additive composed of one of pulverized coal, heavy oil, kerosene, LPG and LNG, or a mixed additive composed of a plurality of kinds. NO in the cement kiln exhaust gas according to claim 3.
x reduction method. 5. The method for reducing NOx in the exhaust gas of a cement kiln according to claim 1 or 2, wherein the denitration additive is ammonia gas, ammonia water, an aqueous urea solution, or an aqueous solution of an ammonia salt. . 6. A rising flue portion connecting a suspension preheater and a rotary kiln; a variable throttle device provided in the rising flue portion and having a throttle valve; opening at a front end surface of the throttle valve, An apparatus for reducing NOx in exhaust gas of a cement kiln, comprising: a nozzle for ejecting a denitration additive. 7. A rising flue part connecting a calcination furnace of a suspension preheater and a kiln kiln of a rotary kiln;
A variable throttle device provided in the rising flue portion and having a throttle valve; a nozzle that opens at the tip end surface of the throttle valve and can eject the denitration additive; and the NOx value in the exhaust gas from the uppermost cyclone outlet. An NOx detector for detecting NOx in exhaust gas of a cement kiln. 8. A rising flue portion connecting a calcination furnace of a suspension preheater and a kiln kiln of a rotary kiln;
A variable throttle device provided in the rising flue section and having a throttle valve; a nozzle that opens at the tip end surface of the throttle valve and ejects the denitration additive supply; NOx value in the exhaust gas from the uppermost cyclone outlet A NOx detector for detecting NOx;
A NOx reduction device in the exhaust gas of a cement kiln, comprising: mixing control means for adjusting the throttling amount of the variable throttling device and the supply amount of the denitration additive based on the detection value of the detector. 9. The throttle valve comprises a plurality of valve members that slide independently of each other.
8. A device for reducing NOx in exhaust gas of a cement kiln according to 8.