JPS5951508B2 - Cement firing method and device that reduce NOx in kiln exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for firing cement using a kiln and a suspension preheater, in which NOx in the kiln exhaust gas is reduced. Preheated cement raw materials, fuel, and air are mixed and burned in a calciner to generate reducing gases such as H2, CO5C05C (hydrocarbons), and this reducing gas is combined with kiln exhaust gas flowing from the kiln to the suspension preheater. By mixing these, NOx in the kiln exhaust gas (usually a value of 800 pIIn or more in a conventional kiln with a suspension preheater) is reduced, and air is supplied from the downstream of the outlet of the NOx removal section to reduce NOx in the kiln exhaust gas after NOx removal. In the cement firing method, which completes the combustion of excess reducing gas, de-N
A temperature detection end is attached to the Ox section to detect the temperature and control the amount of raw material supplied to the calciner accordingly, and the remaining preheater raw material is supplied downstream from the combustion air supply port for surplus reducing gas. The present invention relates to a cement firing method and apparatus for efficiently reducing NOx in a cement firing apparatus and completing combustion of surplus reducing gas.

The present invention is also patented (Japanese Patent Publication No. 53-11011 and Japanese Patent Application No. 49-106674 (Japanese Unexamined Patent Publication No. 51-34232)).
The present invention overcomes the drawbacks of ) and provides an improved cement firing method and apparatus, which can be applied not only to firing various types of cement but also to firing magnesia, dolomite, and other furnace materials.

There are various types of suspension preheaters with calcining furnaces for firing cement (Special Publication No. 47-26410).
Publication: Method and apparatus for calcining and decarboxylating cement raw material powder, Japanese Patent Publication No. 47-30404; Method and apparatus for preheating or calcining granular materials, Japanese Patent Publication No. 47-3040
Publication No. 5; Method and Apparatus for Preheating or Calcining Granular Materials, etc.), all of which involve burning fuel to provide the amount of heat required for calcining in a calcining furnace when calcining cement raw materials supplied from a preheater. Since it is necessary to supply a sufficient amount of air for heating, there is an inconvenience that the volume of the calcining furnace must be increased and the pressure of the supplied air must be increased.

Although this method is effective for calcining raw materials, it cannot reduce the absolute amount of NOx in the kiln exhaust gas.

The present inventors considered using the above calciner as a denitrification device, and installed a calciner that operates as a reducing gas generating furnace between the suspension preheater and the kiln of the cement firing equipment, and preheated with the preheater. The first method is to reduce NOx in the exhaust gas from the cement kiln by mixing the generated reducing gas with the kiln exhaust gas, supplying additional air if desired, and combusting it. proposed.

(Japanese Patent Publication No. 53-11011; Cement Calcining Furnace Equipped with Nitrogen Oxide Reduction Device, Japanese Patent Application No. 49-10667)
(No. 4: Ability to reduce NOx in exhaust gas from cement firing equipment) However, as a result of subsequent prototype experiments, in order to improve its effectiveness, it was necessary to supply it to a calciner that operates as a reducing gas generator. It has been found that it is necessary to adjust the amount of the raw material and to supply the remaining preheater raw material from the downstream of the air supply port, which mixes the reducing gas with the kiln exhaust gas and supplies it as desired.

The invention of the present application was made based on such experimental studies, and the first invention is a suspension preheater for preheating cement raw materials, and a method for reducing by mixing and burning the preheated raw materials, fuel, and air. A cement firing apparatus is used, which has a calcining furnace that generates a reactive gas, and a deNOx section that mixes the reducing gas with the kiln exhaust gas flowing from the kiln to the suspension preheater in order to reduce NOx in the kiln exhaust gas; In a cement firing method in which NOx is reduced by supplying air to the downstream side of the gas flow of the NOx removal section and burning excess reducing gas flowing out from the NOx removal section, detecting the temperature of the NOx removal section, Accordingly, among the preheated raw materials flowing out from the suspension preheater, the amount to be supplied to the calciner is adjusted, and what is not supplied to the calciner is transferred to the downstream side of the gas flow of the NOx removal section. This is a cement firing method in which NOx in kiln exhaust gas is reduced, characterized in that NOx is supplied downstream of the gas flow from an air supply device.

The second invention also provides a suspension preheater for preheating cement raw materials, a calciner for mixing and burning the preheated raw materials, fuel, and air to generate reducing gas, and a method for producing nitrogen in kiln exhaust gas.
a NOx removal section that mixes the reducing gas with the kiln exhaust gas flowing from the kiln to the suspension preheater in order to reduce Ox; and the NOx removal section that supplies air to burn excess reducing gas flowing out from the NOx removal section. In a cement firing apparatus having a conduit opening on the downstream side of the gas flow of the NOx section, the temperature of the NOx removing section is detected, and the preheated raw material flowing out from the suspension preheater is supplied to the calcining furnace in accordance with the temperature. A raw material separation damper that adjusts the amount of
and a chute for supplying preheated raw materials flowing out from the suspension preheater that are not supplied to the calciner by the raw material separation damper downstream of the gas flow at the opening of the conduit. A cement firing apparatus characterized by reducing NOx in kiln exhaust gas.

The invention of this application is patented (Japanese Patent Publication No. 53-11011 mentioned above)
In order to reduce the absolute amount of NOx in the kiln exhaust gas and completely burn out the excess reducing gas, the raw material from the preheater is transferred to the calciner and the excess reducing gas is combusted. (1) Detect the temperature of the section that mixes the reducing gas generated in the calciner with the kiln exhaust gas to reduce NOx in the kiln exhaust gas; (2) The remaining preheater raw material is supplied downstream from the combustion air supply port for excess reducing gas.

In the present invention, the above-mentioned NOx removal section is
A temperature of 800 to 1100°C suitable for carrying out the x reaction,
Preferably, the temperature is 900 to 1000°C to remove NOx.
Preferably, the temperature of the section is detected and the amount of feedstock to the calciner is controlled accordingly.

Next, embodiments of the present invention will be specifically described in detail with reference to FIGS. 1 and 2.

FIG. 1 shows a case where a fluidized calcination furnace is used as the calcination furnace, and FIG. 2 shows a case where an airflow calcination furnace is used as the calcination furnace.

Note that in FIGS. 1 and 2, the same reference numerals indicate the same parts, but the kiln main body and clinker cooler are omitted in FIG.

The present invention uses a conventional calciner 1 (Fig. 1) or 2 (Fig. 2), feeds fuel into the burner 7 for the calciner, and absorbs the sensible heat etc. of the cement raw material discharged from the cyclone 12. It is used to decompose solid fuels or liquid fuels into reducing gases.

Note that the arrow in the figure represents the shoot of high-temperature cement raw material.

The cement raw material is supplied to the cyclone 16 from a supply port (not shown) connected to the conduit 15. 14. 12. 10 suspensions are introduced into the preheater.

The cement raw material from the cyclone 10 is guided to the inlet of the kiln 3 by a chute.

The cement raw material from the cyclone 12 is led to the calciner 1 through a chute 25, but a portion is regulated by a damper 23, led to a conduit 9 through a chute 24, and returned to the cyclone 10 by a gas flow.

At this time, a small amount of primary air (amount less than the theoretical combustion air amount required to burn the supplied fuel) is pumped into the lower part 19 of the burner 7 for the calciner.
(Fig. 1) or from the surrounding area 19 (Fig. 2) and partially burns it to generate reducing gas, so almost no NOx is generated.

The reducing gas thus generated is introduced through the duct 20 into the NOx removal chamber 8 directly connected to the kiln outlet.

On the other hand, the exhaust gas from the kiln combusted by the kiln burner 5 for cement firing in the cement firing kiln 3 is at a high temperature and contains excess air, so when it is mixed with the reducing gas from the calciner, it is desorbed along with combustion. A NOx reaction occurs and reduces the NOx generated within the kiln.

N2. It contains CO5C05C and uses Cab, Al2O3, SiO2, etc. in cement raw materials as catalysts to reduce high concentration NOx to N2.

As shown in Figures 1 and 2, de-N from the clinker cooler 4.
A ventilation pipe 6 with a ventilation adjustment damper 21 is provided up to the outlet of the Ox chamber 8, and by introducing high-temperature surplus air of approximately 700 to 800°C from the cooler 4, the air flow from the exit of the NOx chamber 8 to the bottom cyclone 10 of the breheater is The combustion of the excess reducing gas after NOx removal is completed in the conduit 9.

As described above, highly concentrated NOx in the exhaust gas of the kiln 3 is efficiently reduced to <N2 in the NOx removal chamber 8, and after NOx is removed in the conduit 9 from the outlet of the NOx removal chamber 8 to the preheater lowest stage cyclone 10. In order to complete the combustion of the excess reducing gas, in the present invention, a thermometer 22 is attached to the NOx removal chamber 8 to measure the temperature inside the NOx removal chamber 8. The attached raw material separation damper 23 is operated to adjust the amount of raw material supplied from the raw material chute 25 to the calciner 1 or 2, and the remaining raw material is supplied from the raw material chute 24 to the downstream of the vent pipe 6. .

Note that the raw material chute 24 is connected to the conduit 9 at a position 0.3 times or more downstream, preferably at least twice the direct diameter of the conduit 9.

To explain its operation method, when the thermometer 22 detects a temperature higher than the temperature suitable for carrying out the NOx removal reaction in the NOx removal chamber 8, the raw material separation damper 23 is activated according to the instruction. , a large amount of raw material is supplied from the cyclone 12 to the calciner 1 or 2, and the raw material chute 24
The amount of raw material supplied into the conduit 9 is reduced.

Further, when the thermometer 22 detects a temperature lower than this, the amount of raw material supplied to the calciner 1 or 2 is reduced, and the amount of raw material supplied into the conduit 9 is increased.

In this way, NOx is removed in the NOx removing chamber 8.
The reaction is carried out efficiently and a high NOx removal effect can be obtained.

Furthermore, by supplying the raw material into the conduit 9 from downstream of the vent pipe 6 as described above, the excess reducing gas at the outlet of the deNOx chamber 8 can be effectively combusted by the air introduced from the vent pipe 6. I can do it.

(In order to burn the surplus reducing gas, a temperature of 750°C or higher, preferably 800°C or higher is suitable, and for this purpose it is better to supply the raw material from the downstream of the vent pipe 6.) 11, 13, and 15 are conduits connecting between the cyclones, 18 is an exhaust fan, 17 is a conduit connecting the uppermost cyclone and the exhaust fan 18, and 4' and 4'' are air and exhaust conduits for Tallinn force cooling.

FIG. 3 shows, for reference, a graph showing an example of the correlation between the reduction rate of NOx in the kiln combustion gas in the NOx removal chamber 8, temperature, and reaction time.

Example 3 500t/d cement firing equipment (average amount of fuel in the kiln 7200kg (heavy oil) 4300k per 7 hours)
g (Heavy oil) A 7-hour calciner was installed, and air was supplied to the calciner so that the CO gas concentration in the calciner outlet gas was 3 to 4%. NOx removal
Attach a thermometer (at the outlet of the chamber) and check the temperature at 93°C.
As a result of controlling the amount of raw material supplied to the calciner so that the temperature ranged from 0 to 950°C, 1100 pIlr was generated such as kill'/-h1.
It is possible to reduce the amount of NOx from about As a result of introducing an amount corresponding to an air-fuel ratio of 1.15 to the amount of fuel, and supplying the remaining preheater raw material to the calciner approximately 2.5 m downstream from this air supply port,
The combustion of the excess reducing gas at the outlet of the NOx removal chamber could be completed within the preheater.

At this time, if the amount of raw material supplied to the calciner increases and the NO
x The low temperature inside the chamber helps remove NOx.
When the temperature is detected by the thermometer attached to the chamber, the opening of the raw material separation damper attached to the raw material shoe I of the second cyclone from the bottom of the preheater is adjusted to determine the amount of raw material supplied to the calciner. Conversely, if it is detected that the temperature inside the deNOx chamber is high, the raw material separation damper is operated to increase the amount of raw material supplied to the calciner. By doing so, the amount of NOx in the kiln exhaust gas was constantly reduced.

In the example, the method shown in FIG. 4 was used as means for controlling the amount of raw material supplied to the calciner based on the instructions from the thermometer in the NOx removal chamber.

That is, a chromel-alumel thermoelectric lamp is used as the thermometer 22, the detected voltage is connected to a voltage/current converter 26 to convert it into a current, which is connected from an indicating controller 27 to a potential manipulator 28, The raw material separation damper 23 was operated by a potential controller.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an embodiment of the present invention using a fluidized calciner as a reducing gas generating furnace, and Fig. 2 is a schematic diagram of an embodiment of the present invention using an airflow calcining furnace as a reducing gas generating furnace. 3 is a graph showing an example of the correlation between the NOx reduction rate in the kiln combustion gas and temperature according to the present invention, and FIG. FIG. 2 is a block diagram of a control system used to control the amount. 10, 12. 14...Cyclone (suspension preheater), 1...Calcination furnace, 8.
... NOx removal section, 6 ... conduit,
23...Damper, 24...Shoe 1-
13...Kiln.

Claims (1)

[Scope of Claims] 1. A suspension preheater for preheating cement raw materials, a calciner that mixes and burns the preheated raw materials, fuel, and air to generate reducing gas, and reduces NOx in kiln exhaust gas. Therefore, a cement firing apparatus having a NOx removal section that mixes the reducing gas and the kiln exhaust gas flowing from the kiln to the suspension preheater is used, and air is supplied to the downstream side of the gas flow of the NOx removal section. In a cement firing method for reducing NOx in which excess reducing gas flowing out from a NOx removal section is combusted, the temperature of the NOx removal section is detected, and the preheated raw material flowing out from the suspension preheater in accordance with the temperature of the NOx removal section is detected. The amount supplied to the calciner is adjusted, and the air not supplied to the calciner is supplied downstream of the gas flow from an air supply position on the downstream side of the gas flow in the NOx removal section. A cement I firing method that reduces NOx in kiln exhaust gas. 2. Cement I: a suspension preheater for preheating the raw material, a calciner that mixes and burns the preheated raw material, fuel, and air to generate reducing gas, and a reducing furnace for reducing NOx in the kiln exhaust gas. a NOx removal section that mixes the gas with kiln exhaust gas flowing from the kiln to the suspension preheater; and a downstream stream of the gas flow of the NOx removal section that supplies air for burning excess reducing gas flowing out from the NOx removal section. In a cement firing apparatus having a conduit opened on the side, a raw material separation system that detects the temperature of the NOx removal section and adjusts the amount of preheated raw material flowing out of the suspension preheater to be supplied to the calciner accordingly. a damper, and a chute for supplying preheated raw material flowing out from the suspension preheater that is not supplied to the calciner by the raw material separation damper downstream of the gas flow of the opening of the conduit. A cement firing method characterized by reducing NOx in kiln exhaust gas.