JP2002172314A - Kiln flue gas treatment method by chlorine bypass and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a kiln to be operated safely and economically with a small heat loss and to enable a fine-particle dust to be treated in a simple way. SOLUTION: A part of a kiln flue gas G is extracted from a kiln 1 through a gas extraction duct 2 and instantaneously cooled to 600-700 deg.C or lower. Then, dust W in the cooled flue gas is classified with a classifier 8 into a coarse powder and a fine powder. The coarse powder separated is returned to the kiln 1, and the fine powder is discharged into a cement system. The duct 2 extracts more than 0% but not more than 5% of the flue gas, and the classification point of the classifier 8 is 5-7 μm.

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 treating kiln exhaust gas by chlorine bypass.

[0002]

2. Description of the Related Art Generally, a cement clinker is provided by an SP (suspension preheater) kiln or an NSP (new S).
P) When firing in a kiln, volatile components such as chlorine, alkali, and sulfur brought from the cement raw material and fuel are sequentially concentrated by circulating in a kiln preheater system.

[0003] However, this circulation reaches equilibrium in several hours, and the amount of volatile components brought into the system from the cement raw material and fuel becomes equal to the amount of volatile components taken out of the system by the cement clinker. It has been known.
In this case, if the amount of the volatile component brought into the raw material and the fuel is large, the amount of the volatile component in the clinker is also large, and these adversely affect the quality of the cement. Further, when the volatile component in the system increases, a low-melting point compound is formed, and the preheater is frequently clogged, resulting in impaired stable operation of the kiln. In recent years, especially when the effective use of industrial waste has been promoted, the situation has become inevitable to use those with a high chlorine content, and there are situations where efficient removal of volatile components is desired. Has become.

In order to reduce the amount of volatile components in the kiln / preheater system, a so-called alkali bypass method has been used. In this method, a kiln exhaust gas having a high volatile component concentration is extracted outside the system by an alkali bypass to remove alkali. Next, the alkali bypass will be briefly described.

[0005] Kiln exhaust gas of about 1100 ° C extracted from the kiln through an extraction duct is introduced into a cooling chamber, where it is mixed with cool air from a fan to reduce the gas temperature to 400 to 4 ° C.
Lower to 50 ° C. At this time, a compound of a volatile component is condensed on the surface of the dust due to a decrease in the gas temperature. Further, water is sprayed in the next spray tower to lower the temperature to about 150 ° C., and then the dust is collected by an electric dust collector, and the remaining gas is discharged to the atmosphere via a fan. The dust is collected by a spray tower and an electric dust collector, but is a dust in which volatile components are concentrated, and is discarded.

However, in the above method, the kiln exhaust gas of about 1100 ° C. extracted by the alkali bypass is discharged out of the system, and the heat loss is greatly increased. In addition, a large amount of dust is discharged out of the system and disposed of. However, disposal is becoming difficult year by year due to shortage of places and changes in consciousness of local residents in the treatment plant.

In order to reduce heat loss and the amount of waste dust, Japanese Patent No. 1835995 and Japanese Patent No. 1702995 have been proposed. In these patents, the cooling temperature of the gas is set to 600 to 700 ° C. in order to reduce the heat loss of the exhaust gas.
And collecting the gas with a dust collector, returning the exhaust gas to a preheater exhaust gas system and recovering heat with a waste heat boiler,
This is a method of cooling the extracted gas to 600 to 700 ° C., recovering heat with a dedicated boiler, collecting dust with a dust collector, and discharging the exhaust gas out of the system. Also, these patents are
The absolute amount of the processing dust is reduced by passing the extracted gas at -700 ° C. through a classifier and returning the dust of 10 μm or more to the kiln as it is.

The point of the patent is that, in short, the extracted gas is converted from the conventional 400-450 ° C. to 600-700 ° C.
It has been found that heat loss and equipment cost can be reduced. Another object is to find that the alkali is ubiquitous on the fine powder side, to separate 10 μm or more by a classifier and return it to the kiln, thereby reducing the amount of waste dust. That is, the present invention embodies the discovery by accurately grasping the condensation temperature of the volatile component and by discovering that the alkali is more distributed on the fine powder side of the dust.

[0009] The conventional example is mainly aimed at removing alkali components, and in order to achieve this purpose, it is necessary to extract a large amount of kiln exhaust gas. Even if the two patented inventions mentioned above are implemented, the heat loss of the kiln pre-heater system is 140 to 180 J / kg clinker in the SP kiln when 10% of the kiln exhaust gas is bled.
It becomes about 50-70 J / kg-clinker in NSP kiln. The greatest factor of this heat loss is the large amount of bled gas of the kiln exhaust gas. Further, since the amount of exhaust dust increases in proportion to the amount of the extracted air, the method of treating the exhaust dust also becomes a serious problem.

In view of the above circumstances, an object of the present invention is to make it possible to secure stable operation of a kiln economically with little heat loss. Another object is to facilitate the processing of fine dust.

[0011]

SUMMARY OF THE INVENTION The present invention provides a process for extracting a part of a kiln exhaust gas from a kiln, a process for cooling the extracted exhaust gas to a temperature equal to or lower than a melting point of a chlorine compound, and a process for classifying dust in the exhaust gas. A process for separating coarse powder and fine powder by a classifier, a process for returning the separated coarse powder to the kiln, and a step for sending the fine powder downstream of the classifier; 0%
And 5% or less.

The present invention provides a process for extracting a part of a kiln exhaust gas from a kiln, a process for cooling the extracted exhaust gas to a temperature equal to or lower than a melting point of a chlorine compound, and a method for separating dust in the exhaust gas by a classifier into coarse powder and fine powder. And a step of returning the separated coarse powder to the kiln and sending out the fine powder to the downstream side of the classifier, wherein the ratio of the extracted amount of the kiln exhaust gas is , More than 0% and 5% or less, and the separation particle size in the classifier is 5 μm to 7 μm.

According to the present invention, there is provided an extraction means for extracting a part of the kiln exhaust gas from the kiln, and
Cooling means for cooling to less than or equal to 700 degrees, a classifier for separating the dust in the cooled exhaust gas into coarse powder and fine powder,
A coarse and fine powder conveying means for returning the separated coarse powder to the kiln and sending the fine powder to a downstream side of the classifier; wherein the bleeding means comprises 0% of the bleed amount of the kiln flue gas. And air is extracted at a rate of 5% or less, and the classifier has a classification point of 5 μm to 7 μm.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted intensive studies on the problems of the conventional example, and firstly, to determine which of the volatile components which hinder stable operation of a kiln, which component hinders stable operation of a kiln. investigated. As a result, they found that chlorine most acutely affected the stable operation of the kiln. That is, chlorine is about 1 times less than alkali and sulfur in components in clinker.
Although the content is 1/0, it has been found that a slight change in the concentration sharply affects the formation of a coating in the preheater, and furthermore, the stable operation of the kiln.

Based on this finding, a method for effectively removing chlorine has been studied. As a result, as shown in FIG. 1, it was found that a large reduction rate was obtained with chlorine (curve A) at a lower bleed amount than alkali (curves B and C). In FIG. 1, the vertical axis indicates the concentration reduction rate (%) and the horizontal axis indicates the bypass rate (%), and the numerical values are expressed in logarithms.

That is, it was found that 98% or more of chlorine can be removed by extracting 10% of the kiln exhaust gas. In addition, the alkali removal rate at that time is about 10%, and it has been found that if this is used well, the amount of bled gas of kiln exhaust gas can be significantly reduced. In this experiment, the relationship between the kiln exhaust gas extraction rate α% and the chlorine reduction rate β% (chlorine reduction rate per 1% of kiln extraction rate) was 0%,
Β = 50% for <α <1%, β = for 1% <α <5%
At 8.5%, 5% <α <14%, β = 1.4%. Accordingly, the chlorine reduction rate reached 90% when the kiln exhaust gas extraction amount was about 5%. Considering economy and practicality, it was found that an extraction amount of 5% had a sufficient effect.

The inventor further produced a simple chlorine-alkali circulation model shown in FIG. 2 and investigated the chlorine-alkali bypass rate (%) and the removal rate (%). In this model, the cement raw material M passes through the preheater PH and kiln RK.
Some of the chlorine and alkali (sodium and potassium) in the raw material M are volatilized and circulate in the kiln together with the kiln exhaust gas, and the other is discharged out of the kiln together with the clinker CK.

Using this experimental apparatus, the volatilization rate ε ₁ of the chlorine and alkali in the raw material M and the circulating volatility ε 2, that is, the case where the material that has volatilized in the kiln during the circulation condenses and then volatilizes again were examined. As a result, chlorine ε1 = ε2 = 0.995 sodium ε ₁ = 0.2, ε ₂ = 0.8 potassium ε ₁ = 0.4, ε ₂ = 0.9.

That is, the volatility of chlorine ε ₁ = 99.5% is equal to the volatility of alkali ε ₁ (sodium 20%, potassium 40
%), The ratio of chlorine discharged outside the kiln is 0.5%, which is extremely small as compared with alkali. Since almost no chlorine is discharged to the outside of the kiln, the chlorine concentration in the kiln becomes extremely higher than that of the alkali, which causes the formation of coaching.

Next, a bypass BP is provided near the kiln inlet IN.
The kiln exhaust gas was extracted, and the extraction ratio (bypass rate) (%) and the removal rate (%) having the same meaning as the concentration reduction rate were measured. The result shown in FIG. 3 was obtained. In FIG. 3, curve A1 is chlorine, curve B1 is potassium, and curve C1.
Represents sodium, respectively. As is clear from FIG. 3, for the alkali (sodium C1, potassium B1), the bypass ratio and the removal ratio are almost directly proportional within the range of the bypass ratio of 0 to 10%.

However, the removal rate is as low as about 10 to 20% even when the bypass rate is 10%. On the other hand, for chlorine A1, 2
A high removal rate of 60% or more can be obtained even at a low bypass rate of not more than 5%, and a removal rate of 90% can be obtained at a bypass rate of 5%.

The relational expression between the chlorine-alkali removal rate X and the bypass rate v is: (ε ₁ + xε ₂ ) (1-v) = removal rate x removal rate x = ε ₁ (1-v) / _{{1-ε 2 (1-} v)} removal ratio _{x = 100 (ε 1 + xε} 2) v is known. From this relational expression, it can be seen that in order to obtain a constant removal rate x, the bypass rate v may be smaller as the volatility ε ₁ or ε ₂ is higher.

In this process, as shown in FIG. 4, it has been found that chlorine (curve D) is more ubiquitous in fine powder than alkali (curve E). Curve F shows the cumulative particle size distribution, the horizontal axis shows the particle size (μm), and the vertical axis shows the cumulative particle size distribution (%). As a result, it was found that a sufficient chlorine reduction rate can be obtained with about 5 to 7 μm instead of 10 μm as in the alkali bypass when passing through a classifier after cooling the extracted gas and focusing on removing chlorine only. did.

Based on this finding, compared to the alkali bypass,
The chlorine bypass made it possible to reduce the amount of waste dust. Therefore, the amount of waste dust is less than 0.1% of kiln production.

Conventionally, this waste dust was taken out of the system and buried or washed with water to remove alkali components, and then used as a part of a cement raw material. This is because, in the case of an alkali bypass, the amount of exhaust dust is large, and if it is returned to the cement system as it is, the quality of the cement is adversely affected.

The present inventor paid attention to this point, and studied how much chlorine bypass dust was added to cement to affect the quality. As a result, the result as shown in FIG. 5 was obtained. According to FIG. 5, when the chlorine bypass dust using the present invention is mixed in the cement in an amount exceeding 0.1%, the mortar 28-day compressive strength which is an important index for the quality of the cement may be extremely reduced. Understand. From this, it was found that the addition of chlorine bypass dust to the cement was possible without any problem if it was 0.1% or less. In FIG. 5, the vertical axis shows the mortar 28-day compressive strength ratio (-), and the horizontal axis shows the chlorine bypass dust addition rate (%).

The amount of clinker produced by a cement kiln and the amount of cement produced are usually proportional, and the dust discharged from the chlorine bypass according to the present invention is 0.1% of the clinker produced.
% Or less, and the cement quality does not deteriorate even if the entire amount is mixed with the cement. The conventional alkaline bypass generates a large amount of dust, and it is impossible to add the entire amount to the cement. This is a method that has become possible only by using the present invention.

A kiln exhaust gas treatment apparatus using a chlorine bypass according to a first embodiment of the present invention will be described with reference to FIG. When performing chlorine bypass, a rotary kiln (also called kiln) 1
The kiln exhaust gas G is extracted from the inlet of the furnace through the bleed duct 2 to a preheater (not shown). This extraction position is desirably as far as possible from the place where the raw material flows, for example,
The kiln riser is selected. This is because the bleeding duct 2 is less likely to be damaged farther from the raw material and the chlorine concentration is higher. The ratio of the amount of air extracted from the kiln exhaust gas should be more than 0% and 5% or less.

The high-temperature kiln exhaust gas G extracted from the extraction duct 2 is cooled by the cooler 3 at the melting point of the chlorine compound, that is, 600 to 70.
After instantaneously quenching to 0 ° C., the mixture is classified by a classifier 8, for example, a cyclone classifier. This cyclone classifier 8
Is, SP, when the akg clinker production of kiln per minute when the NSP kiln, the cross-sectional area of the cyclone body a × 7.55 × 10 ^-3 m ² or less, preferably, a × 5 × When the range is from 10 ⁻⁴ m ^{2 to} a × 5 × 10 ⁻³ m ² , the facility is well-balanced in economy and efficiency.

The classification point of this classifier is 5 to 7 μm, and the powder exceeding the classification point is returned to the kiln 1 as it is.
The gas G containing fine powder of 5 to 7 μm or less is heat-exchanged through the boiler 9 and then collected by the dust collector 5, and the gas G is released to the atmosphere. The dust W having a high chlorine content collected by the boiler 9 and the dust collector 5 is discharged out of the cement kiln system.

The dust W containing the discharged chlorine at a high concentration
A suitable vehicle 10, such as a truck, a pneumatic vehicle,
Pneumatic transport, transport by belt conveyor, chain conveyor, etc. to the cement finishing mill system. The transported dust W is mixed with the clinker in the clinker tank 18 baked out of the kiln 1 via the primary storage bin 11a, the measuring device 12a, and the transport means 13.

The dust w may be supplied to and mixed with the storage bin 11b containing the clinker or the cement 17 discharged from the finishing mill 20 and further from the finishing mill 20.

A second embodiment of the present invention will be described with reference to FIG. In this embodiment, the high-temperature kiln exhaust gas G extracted from the kiln exhaust gas extraction duct 2 is directly guided to a classifier 8, for example, a cyclone, and the melting point of the chlorine compound is 600 to 700 ° C.
Classifying while cooling.

In the cooling method, cooling air is instantaneously cooled by introducing cool air CL from the entrance of the cyclone 8 or the body portion 8a. Subsequent processing is the same as in the first embodiment.

A third embodiment of the present invention will be described with reference to FIG. This embodiment shows another exhaust gas treatment method in the above embodiment. A dust collector capable of treating the kiln exhaust gas G that has passed through the classifier 8 even at a high temperature, for example, a fine particle dust G having a high chlorine concentration is separated by a moving bed dust collector 22, and the exhaust gas is returned to the exhaust gas of the kiln preheater 23. The heat is recovered by the waste heat boiler 24 provided.

Incidentally, 25 is a calciner, 26 is a preheater,
27 is an induction fan, S is a cyclone of the preheater 26,
Are respectively shown.

A fourth embodiment of the present invention will be described with reference to FIGS. This embodiment shows still another exhaust gas treatment method in the above embodiment. After the coarse particles are separated by the classifier 8, it is necessary to separate the fine powder in the exhaust gas G. At this stage, the gas temperature is as high as about 400 to 500 ° C. Then, the exhaust gas can be returned to the kiln system and the calorie can be recovered by a waste heat boiler, but cannot be collected by a normal dust collector. Therefore, conventionally, the temperature was lowered by watering,
Alternatively, a method of attaching a small boiler to perform temperature reduction and heat recovery has been performed.

However, the method of lowering the temperature by watering cannot be used because it makes it difficult to use dust for cement. Therefore, a device for cooling using cold air, for example,
An indirect air cooling device for cooling indirectly or a cool air mixing type cooling device is used.

This indirect air cooling device will be described. As shown in FIG. 10, this device 28
The combination of the path 81 and the path 82 of the cold air CL reduces the temperature of the dust-containing gas G to 200 ° C. or less by the cool air CL.

Normally, in this type of indirect cooling, water is used as a refrigerant. However, when water is used in the present invention, dew condensation or humidity increases at the boundary surface, and a deliquescent chlorine compound adheres. As a result, a trouble occurs in which the cooler is blocked. Therefore, by using cold air as the refrigerant, it has become possible to lower the temperature of the dust-containing gas without causing the above-mentioned trouble.

A fifth embodiment of the present invention will be described with reference to FIG. The difference between this embodiment and the first embodiment is that the classifier 8
An air mixing type cooling device 93 similar to the cooler 3 is provided between the dust collector 6 and the dust collector 6.

The embodiment of the present invention is not limited to the above. For example, the cool air CL sent to the cooler 3 is sent more than the other embodiments and the temperature of the kiln
After the temperature is reduced to not more than 00 ° C., it may be introduced into the classifier 8.

[0043]

As is apparent from the above description, the present invention has the following remarkable effects. (1) Since the extraction rate of the kiln exhaust gas is set to more than 0% and 5% or less, chlorine is almost removed. Therefore, the rotary kiln can be operated stably, and chlorine can be effectively removed with minimum heat loss. (2) The chlorine bypass requires a smaller amount of bleed gas as compared with the conventional alkali bypass, so that the processing equipment is small, the space and equipment costs are both small, and the kiln can be operated stably economically.

(3) Compared with the conventional example, the amount of extracted dust of the kiln exhaust gas is small and the classifying point of the classifier is also small, so that the amount of exhaust dust is significantly reduced. Therefore, instead of completely discharging the dust out of the cement system, it is possible to reduce the dust to a level that does not affect the quality of the cement even if it is mixed into the cement by bypassing the kiln. can do. Further, since the amount of dust is extremely small as compared with the conventional example, even if landfilling, washing, and the like are performed, the amount of processing is small, which is economically advantageous.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a kiln exhaust gas bypass ratio (%) and a chlorine concentration reduction ratio (%) of the present invention.

FIG. 2 is a diagram showing an experimental apparatus.

FIG. 3 is a diagram showing experimental results.

FIG. 4 is a diagram showing the relationship between the dust particle size (μm) and the cumulative particle size distribution (%) of the present invention.

FIG. 5 is a graph showing the relationship between the chlorine bypass dust addition rate (%) of the present invention and the mortar 28-day compressive strength ratio (-).

FIG. 6 is a diagram showing a first embodiment of the present invention.

FIG. 7 is a diagram showing a second embodiment of the present invention.

FIG. 8 is a diagram showing a third embodiment of the present invention.

FIG. 9 is a diagram showing a fourth embodiment of the present invention.

FIG. 10 is an enlarged perspective view of the indirect air cooling device of FIG. 9;

FIG. 11 is a diagram showing a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rotary kiln 2 Extraction duct 3 Cooler 8 Classifier 5 Dust collector 6 Dust collector 10 Transportation means 17 Cement 18 Clinker tank 20 Finishing mill

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoki Ueno 5310 Sankeijiri, Kumagaya City, Saitama Prefecture Chichibu Onoda Kumagaya Plant F-term (reference) 4D002 AA18 AC05 BA13 BA14 CA13 EA02 GA01 GB03 GB07 HA06 HA08

Claims (3)

[Claims] A step of extracting a part of the kiln exhaust gas from the kiln; a step of cooling the extracted exhaust gas to a temperature lower than the melting point of the chlorine compound; and a step of classifying the dust in the exhaust gas into coarse powder and fine powder by a classifier. A kiln exhaust gas treatment method comprising: a separating step; and a step of returning the separated coarse powder to the kiln and sending the fine powder downstream of the classifier. % And not more than 5%. 2. A process for extracting a part of the kiln exhaust gas from the kiln, a process for cooling the extracted exhaust gas to a temperature lower than the melting point of the chlorine compound, and a process for separating dust in the exhaust gas into coarse powder and fine powder by a classifier. A kiln exhaust gas treatment method comprising: a separating step; and a step of returning the separated coarse powder to the kiln and sending the fine powder downstream of the classifier. % And not more than 5%, and the separation particle size in the classifier is 5 μm to 7 μm. 3. Extraction means for extracting a part of the kiln exhaust gas from the kiln, cooling means for cooling the extracted exhaust gas to 600 to 700 ° C. or less, and converting the cooled dust in the exhaust gas into coarse powder. A kiln exhaust gas treatment device comprising: a classifier that separates the fine powder into fine particles; and a coarse / fine powder conveying unit that returns the separated coarse powder to the kiln and sends the fine powder downstream of the classifier; The gas is extracted at a rate of more than 0% and 5% or less of the amount of the extracted gas of the kiln exhaust gas, and the classification point of the classifier is 5%.
A kiln exhaust gas treatment apparatus using a chlorine bypass, which has a diameter of from 7 μm to 7 μm.