JPH1160297A - Flue gas treatment from cement kiln - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the channel of cement raw materials from being blocked in the pre-heater to increase the quality of the cement product and decrease the costs for installing the dust collector and the exhausting gas treatment system. SOLUTION: The exhaustion gas occurring when clinker is fired is extracted through the bypass 4 into the outside of the kiln. On the way of the bypass, the temperature of the gas is lowered down to 600-700 deg.C. The volatile components liquefied by the temperature fall stick to the dust. This dust is classified by means of a high-performance cyclone 5 and is removed out of the system. In the meantime, the remaining gas fraction is fed back to the pre-heater 2 having almost the same temperature of the gas temperature. As a result, the channel of the cement raw materials is prevented from being blocked by the volatile components wandering in the cement kiln. Thus, the cement product can be improved in its quality and in addition, the costs for installing the dust collector and the exhaust gas treatment system can be saved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas from a cement kiln, and more particularly, to a cement kiln in which a part of exhaust gas generated when a cement raw material is calcined in a cement kiln is extracted from a bypass to the outside and treated. And a method for treating exhaust gas.

[0002]

2. Description of the Related Art A cement kiln for sintering a cement raw material calcined by a preheater at about 1100 ° C. is provided in a facility for firing a cement raw material. In this kiln, a cement raw material calcined by a preheater is fired with heavy oil or pulverized coal as a fuel while rotating a horizontal cylindrical kiln shell to produce a cement clinker in the middle. Incidentally, volatile materials such as alkali elements (Na, K, etc.), Cl, S and their compounds are contained in cement raw materials and fuels. This volatile component is vaporized by the heat of sintering of the cement kiln and then circulated in a closed system of the cement kiln and the preheater, whereby it is gradually concentrated. Note that this concentration circulation becomes equilibrium in several hours. At this time, if the amount of the volatile component in the system is large, (1) the amount of the volatile component contained in the clinker after sintering naturally inevitably increases, and the quality of the cement deteriorates. (2) In addition, a low-melting point compound, which is a volatile component, is generated in the system, adheres to the inner wall surface of the preheater, and frequently blocks the flow path of the cement raw material, thereby hindering the kiln operation.

Therefore, as a conventional technique for solving this,
For example, a "method for treating cement kiln exhaust gas" described in Japanese Patent Publication No. 5-50458 is known. This one is
This is a technique for extracting kiln exhaust gas having a high alkali concentration to the outside of the system by an alkali bypass to reduce the amount of alkali in the system. More specifically, in this method, a part of the exhaust gas (around 1100 ° C.) in the cement kiln is cooled down to 600 to 700 ° C. below the melting point of the alkali compound on the way, and then classified externally from the alkali bypass. Lead to the container. Here, after classification according to the particle size of the dust, coarse particle dust having a particle size of 10 μm or more (the amount of alkali is relatively small) is returned to the cement kiln. On the other hand, high-temperature exhaust gas (having a large amount of alkali) containing fine dust having a particle size of less than 10 μm is first guided to a boiler to recover the heat of the exhaust gas, and then the fine dust is removed by a dust collector. Is the way. Thereby, high calorie heat retained by the exhaust gas derived from the alkaline bypass can be effectively recovered. In the case of fine dust having a particle size of less than 10 μm, usually, the total alkali amount carried by the dust is 80%.
It contains about%.

[0004]

According to the above-mentioned prior art, the dust in the exhaust gas discharged from the alkaline bypass to the outside of the kiln is converted into coarse dust classified by a classifier into a cement kiln. Will be returned. Volatile components are also attached to the surface of the coarse dust, although less than the fine dust having a particle size of less than 10 μm. As a result, by returning the heat of the coarse dust, there is an advantage that the fuel cost of the cement kiln can be slightly saved, but the concentration of volatile components in the kiln increases. Therefore, although the closing time is later than when the bypass is not installed, there is a problem that the volatile component gradually grows on the inner wall surface of the preheater and blocks the flow path of the cement raw material. In addition, there is another problem that the proportion of volatile components contained in the clinker as an intermediate product increases, and the cement quality deteriorates.

[0005] On the other hand, the classified fine dust is captured by a dust collector after heat recovery by a boiler. Before the gas is released to the atmosphere from the chimney, the volatile components are finally removed by the exhaust gas treatment equipment connected to this dust collector so that the trace gas in the gas afterwards does not cause air pollution by the trace volatile components in the gas. Had been removed. As a result,
There has been a problem that equipment costs for disposing exhaust gas treatment equipment in which various large-sized devices are arranged are increased.

Therefore, the present inventors lowered the volatile components contained in the exhaust gas to 600 to 700 ° C. below the melting point of the compound as a volatile component and caused the volatile components to adhere to the dust.
By removing this and returning the remaining exhaust gas to the temperature range of the preheater that is approximately equal to this gas temperature, the amount of volatile components in the cement kiln can be reduced and the blockage of the cement material flow path of the preheater can be prevented, and the product can be prevented. The present inventors have found that the quality of cement can be improved, and that the equipment cost for installing a dust collector and an exhaust gas treatment system is not required, thereby completing the present invention.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent clogging of a flow path of a cement raw material of a preheater, to improve the quality of a product cement, and to install a dust collector and an exhaust gas treatment system. An object of the present invention is to provide a method for treating exhaust gas from a cement kiln, which can reduce costs.

[0008]

According to the present invention, a cement material calcined by a preheater is calcined by a cement kiln, and a part of generated exhaust gas is bled to an outside through a bypass. A step of lowering the temperature of the exhaust gas extracted by the bypass to 600 to 700 ° C. below the melting point of the compound which is a volatile component contained in the exhaust gas, and after the temperature of the exhaust gas has dropped, the volatile component And removing the dust adhering to the gas and returning the remaining gas to a temperature range of the preheater substantially equal to the gas temperature.

[0009] Examples of the cement raw material here include general raw materials such as limestone, clay, quartzite and iron raw materials. The clay before the preheater is charged is dried by a clay dryer, and then crushed and mixed with other raw materials by a raw material mill. The calcining temperature of the cement raw material by the preheater is about 800 to 900 ° C. at the outlet temperature. Examples of volatile components (low melting point compounds) contained in the exhaust gas include NaBr (melting point 747 ° C.), KB
r (melting point 730 ° C), NaCl (melting point 801 ° C), KC
1 (melting point: 776 ° C.).

As an apparatus for lowering the exhaust gas temperature to 600 to 700 ° C., which is lower than the melting point of the compound as a volatile component, for example, an air-cooling apparatus that blows cold air directly onto the exhaust gas or various heat exchangers are used. Can be. As a classifier that removes dust in the extracted exhaust gas, for example, a high-performance cyclone that can capture dust having a particle size of 0.2 μm or more can be used. Here, the extraction means extracting gas components such as exhaust gas to the outside. In addition, by capturing dust having a particle size of 0.2 μm or more, usually, most of the volatile components in the exhaust gas can be removed. For example, a graph showing the relationship between the particle size of dust and the amount of alkali in the exhaust gas shown in FIG. In FIG. 3, a indicates the particle size distribution of dust by its cumulative value. b
Is a cumulative value indicating the ratio of the amount of alkali in the exhaust gas to the particle size of the dust.

The classification accuracy of the high-performance cyclone is determined, for example, by the wind speed of the exhaust gas sent from the bypass 4 to the high-performance cyclone 5 as shown in FIG. Numerical values such as the diameter D, the diameter d of the gas return pipe 8 inserted from the upper surface of the cyclone 5, the eccentric position of the gas return pipe 8, and the length L of the pipe 8 inserted into the cyclone 5 are appropriately changed. Thereby, it can be changed relatively easily.

[0012]

According to the present invention, when the cement raw material calcined by the preheater is fired in a cement kiln, exhaust gas containing volatile components is generated. The exhaust gas is bled to the outside through the bypass, and the temperature of the flue gas is reduced to 600 to 700 ° C. below the melting point of the compound that is a volatile component contained in the gas during the bled. As a result, the liquefied volatile component compound adheres to the surface of the dust, and then the dust is removed out of the system. Therefore, volatile components are also removed from the system together with the dust. On the other hand, the remaining gas is returned to a temperature range substantially equal to that of the preheater. As a result, it is possible to prevent the flow path of the cement raw material of the preheater from being blocked by a volatile component floating in the cement kiln. Moreover, the quality of the product cement can be improved. Furthermore, equipment costs for installing a dust collector and an exhaust gas treatment system can be reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a front view including a partial cross-sectional view of a cement burning facility to which a method for treating exhaust gas from a cement kiln according to an embodiment of the present invention is applied. In FIG.
Reference numeral 1 denotes a cement burning facility to which the exhaust gas treatment method for a cement kiln according to one embodiment is applied. The cement sintering facility 1 sinters a cement material calcined in a preheater 2 by a cement kiln 3 and bleeds a part of the generated exhaust gas to an external high-performance cyclone (classifier) 5 through a bypass 4. is there. The cement kiln 3 here produces cement clinker at 90 to 100 t / h.

The preheater 2 preheats a cement raw material pulverized by a raw material mill (not shown) to a predetermined temperature so as to be easily fired by a cement kiln 3 in a later step. The preheater 2 is provided with a large number of cyclones 2a mounted on a steel frame base of several stories. The cement kiln 3 has a horizontal cylindrical kiln shell 3a slightly inclined downward toward the downstream side. A refractory 3b is provided on the inner wall surface of the kiln shell 3a. Kiln shell 3a
While rotating in the circumferential direction (around the axis), the cement raw material from the preheater 2 is baked by burner heating using heavy oil or pulverized coal as fuel to produce cement clinker in the middle.

The end of the bypass 4 is connected to the kiln-side end of the preheater 2. In the middle of the bypass 4, the exhaust gas extracted from the cement kiln 3 is mixed with cold air from the fan 6 to reduce the exhaust gas temperature to 600 to 70.
A cooling chamber 7 for lowering the temperature to 0 ° C. is connected. FIG.
As shown in (1), the high-performance cyclone 5 has a body portion 5a whose lower part is gradually reduced in diameter. On the upper surface of the trunk 5a,
The tip of the pre-peater 2 shown in FIG.
The base of the gas distribution pipe 8 connected to the 0 ° C. region is inserted. The gas distribution pipe 8 is inserted into an eccentric position on the upper surface of the body 5a.

Next, a method of treating exhaust gas from a cement kiln using the cement firing equipment 1 will be described. As shown in FIG. 1, the cement raw materials are each cyclone 2 a of the preheater 2.
Is calcined while flowing down. Thereafter, the cement raw material flows into the kiln bottom of the cement kiln 3 and is generated in the cement clinker by firing in a kiln 3 with a burner. As described above, when the cement raw material calcined by the preheater 2 is fired in the cement kiln 3, exhaust gas containing volatile components is generated. This exhaust gas is extracted to the outside through the bypass 4. During the extraction, the exhaust gas passes through the cooling chamber 7, and is cooled by the cool air from the fan 6 to a temperature lower than the melting point of the compound that is a volatile component contained in the exhaust gas.
The temperature is reduced to 700 ° C. Thereby, the compound which is a volatile component adheres to the surface of the dust contained in the exhaust gas.

As shown in FIG. 2, the dust enters the high-performance cyclone 5, where it is centrifuged, and
Is removed from the system through a discharge pipe connected to the bottom of the system.
On the other hand, the remaining gas component is returned from the gas distribution pipe 8 to a temperature region (600 to 700 ° C.) substantially equal to that of the preheater 2. The high-performance cyclone 5 is a high-performance cyclone capable of capturing dust having a particle size of 0.2 μm or more. Thereby, for example, in terms of the alkali content of the volatile component, as shown in the graph of FIG. 3, it is possible to remove 95% or more of the alkali content captured in the entire dust.

As a result, the amount of the volatile component attached to the dust returned into the cement kiln 3 is extremely small, and it is possible to prevent the flow path of the cement material of the preheater 2 from being blocked by the volatile component. At the same time, the proportion of volatile components contained in the clinker can be reduced to improve the quality of the product cement. Moreover, the gas thus classified is returned into the preheater 2, so that
The processing equipment for the classified gas, which was required in the prior art, becomes unnecessary, and the equipment cost for that can be reduced. Further, since the portion of the preheater 2 where the gas content is returned is in the temperature range of the preheater 2 which is substantially equal to the gas temperature as described above, the gas content is smoothly reduced without lowering the calcining temperature of the preheater 2. Can be introduced into the preheater 2.

[0019]

According to the present invention, the exhaust gas generated at the time of baking the clinker is reduced to a gas temperature of 600 to 7 during the bypass.
The temperature was lowered to 00 ° C., and the air was extracted to the outside. The dust to which the compound, which is a volatile component liquefied at the temperature was lowered, was classified and removed, while the remaining gas was separated by a pre-heater substantially equivalent to the gas temperature. Since the temperature is returned to the temperature range, it is possible to prevent the flow path of the cement raw material of the preheater from being blocked by a volatile component floating in the cement kiln. Moreover, the quality of the product cement can be improved. Further, equipment costs for installing a dust collector and an exhaust gas treatment facility can be reduced.

[Brief description of the drawings]

FIG. 1 is a front view including a partial cross-sectional view of a cement burning facility to which a method for treating exhaust gas from a cement kiln according to an embodiment of the present invention is applied.

FIG. 2 is an explanatory diagram of a high-performance cyclone according to one embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a dust particle size and an alkali amount according to one embodiment of the present invention.

[Explanation of symbols]

 1 Cement firing equipment, 2 Preheater, 3 Cement kiln, 4 Bypass, 5 High performance cyclone.

Claims (1)

[Claims] 1. A process in which a cement raw material calcined by a preheater is calcined in a cement kiln, and a part of generated exhaust gas is bled to the outside through a bypass, and the temperature of the flue gas bled by the bypass is measured in the flue gas. And a step of lowering the temperature of the exhaust gas to 600 to 700 ° C. or lower, which is lower than the melting point of the compound that is a volatile component contained in the exhaust gas. Returning to a temperature range of the preheater substantially equal to the gas temperature.