JP2003073154A - Method of manufacturing cement clinker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a cement clinker, in which no harmful hexavalent chromium is eluted. SOLUTION: In a firing process of the cement clinker, a combustible matter is fed to granulating raw material grain or clinker grain which contains the sexivalent chrome (Cr<+6> ) to reduce it. The combustible matter is fed from clinker cooling side into a kiln, the grain diameter of which is 1 mm-4 mm, and larger than that of powdered coal, i.e., it is necessary that the grain diameter of the combustible matter is larger than that of the powdered coal.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cement clinker, and more particularly to a method for producing a cement clinker in which contained Cr ^{+ 6} becomes harmless chromium. is there. 2. Description of the Related Art Conventionally, cement clinker is produced by mixing raw materials such as limestone, clay, quartzite, pyrite slag and other iron oxide raw materials in a kiln and firing the mixture at a high temperature to form the clinker. Although manufactured, clinker obtained in this way, in order not to reduce the quality of cement, it is necessary to avoid containing unburned combustibles inside the raw material particles or clinker particles during granulation, For this reason, it has been the principle that the combustibles are completely burned as soon as possible after being put into the kiln. [0003] However, the clinker thus produced contains a chromium salt in the form of harmful hexavalent chromium (Cr ⁺⁶ ), so that cement is used. There is a problem that hexavalent chromium in clinker is easily eluted from a concrete structure or an improved soil. As the amount of hexavalent chromium in the clinker increases, the elution amount increases, and in recent years when environmental standards are strict, various reference values and regulation values are often exceeded. Therefore, there was a strong desire to reduce the content of hexavalent chromium in the clinker as much as possible. Therefore, the present inventors have proposed a method of stopping or reducing the use of chromium-containing raw materials,
Considering the high cost due to alternative raw materials, it is not preferable in that the cost of producing cement is significantly increased. Thus, the present inventors have further studied this point in various ways. As a result, the production cost of cement does not increase significantly, and no harmful hexavalent chromium is eluted by changing hexavalent chromium to harmless chromium. A method for producing cement clinker was found. Therefore, the problem to be solved by the present invention is:
An object of the present invention is to provide a method for producing a cement clinker which does not dissolve harmful hexavalent chromium. [0005] The object of the present invention is to provide a cement clinker baking process in which hexavalent chromium (Cr ⁺⁶ ) present inside raw material particles or clinker particles during granulation.
In the method for producing a cement clinker for supplying a combustible material so that Cr can be reduced, the condition for reducing Cr ⁺⁶ is that the particle size is 1 mm to 4 m in the kiln from the clinker cooler side.
m. A method for producing a cement clinker, characterized in that a combustible material having a particle size larger than that of pulverized coal is supplied. According to the method for producing a cement clinker of the present invention, Cr ⁺⁶ in the clinker is reduced to harmless chromium such as trivalent chromium, and is present.
An excellent effect is obtained in that a cement clinker or a cement product free of elution of r ⁺⁶ can be obtained . [0007] Embodiments of the present invention will be described below, but the present invention is not limited thereto. Further, in the present invention, "supplying a combustible material so that Cr ^{+ 6} can be reduced" means supplying a combustible material so that conditions for reducing Cr ^{+ 6} are formed. . In the present invention, the condition for reducing Cr ⁺⁶ is that unburned combustible material is incorporated into raw material particles or clinker particles during granulation at least instantaneously in the clinker firing step. Is that
In such a state, a reducing atmosphere is formed only around the combustibles taken into the particles, due to the oxidation of the carbon and carbon monoxide in the combustibles and the decrease in the oxygen partial pressure. Can be reduced or eliminated by reducing the hexavalent chromium to a harmless chromium salt. The present invention is the same as ordinary firing conditions in that the entire firing atmosphere outside the clinker particles itself is not reduced. The raw materials for producing the cement clinker used in the present invention may be those usually used in this technical field, and include limestone, clay, quartzite, pyrite slag and other iron oxide raw materials. Examples of the combustibles used as fuel include various solid fuels and combustible solid wastes, and are preferably coke, various types of coarse-grained coal, anthracite with low volatility, sub-lean blue coal, or levy blue. It is a solid fuel that is more flame-retardant than charcoal. The particle size of these combustibles is
It is sufficient that the particle size is larger than that of the pulverized coal, but the particle size is preferably 1 mm to 4 mm. Combustible particle size is 1mm
If it is less than 3, a sufficient reducing atmosphere cannot be formed. If the particle size exceeds 4 mm, unburned substances are apt to remain in the clinker after firing, which may undesirably deteriorate cement quality. In the present invention, when a large amount of unburned matter is taken into the inside of the raw material particles or clinker particles,
A strong reducing atmosphere is created around the unburned matter that has been taken in.
Iron is reduced to divalent and solid solution in alite, and alite is decomposed into belite and free lime, and free lime increases, so that the fluidity when concrete is deteriorated, Strength developability may be reduced. Therefore, in order to prevent this, it is possible to investigate the content of hexavalent chromium and the cement quality in the actual production clinker by a simple test for the types of combustibles, their supply amounts, firing conditions, etc. It is desirable to determine the content while confirming the hexavalent chromium content and the cement quality. [0011] In the present invention, conditions for reducing the Cr ⁺⁶ is may supply combustible materials in the kiln from the clinker cooler side, in this case, the existing main burner, installed separately from the new burner Or a combustible for reducing hexavalent chromium ions in the fuel for the main burner. According to the present invention, by supplying a combustible material so as to reduce Cr ⁺⁶ present in the raw material particles or clinker particles during granulation, the supplied combustible material is unburned. Since it is taken into the clinker in the state of a substance, only the surroundings of the taken-in unburned substance form a combustible carbon, oxidation of generated carbon monoxide, and a reducing atmosphere with a reduced oxygen partial pressure. Hexavalent chromium in the clinker is reduced by the reducing action of the atmosphere to form harmless chromium. The embodiments of the present invention will be described below in more detail with reference to examples of the present invention, but the present invention is not limited to these examples. Example 1 Flame-retardant fuel was blown for a long time into a kiln that was firing 100 tons of ordinary Portland cement clinker at the time of production, and the total amount of chromium and hexavalent chromium in the clinker were determined. As a comparative example,
In the same kiln, total chromium and hexavalent chromium in the clinker during normal operation were determined. [0015] In the method of the present invention is attached to the burner for oil coke in the center of the main burner 5 of the kiln before 7-mentioned rotary kiln 1 is shown in cross section in FIG. 1, the particle size in high pressure air 1500mmaq from here Flexi coke particles of 3 mm (manufactured by Toa Oil Co., Ltd.) were blown in at 7 kg / t · clinker. [Table 1] As is apparent from Table 1, in Example 1 of the present invention, the total chromium content in the clinker was substantially the same, whereas the content of hexavalent chromium was higher than that in the normal operation of the comparative example. It can be seen that is greatly reduced. At this time, the amount of the free lime of the clinker of Example 1 was 0.7%, which was not particularly larger than that of the ordinary product, and there was no problem with the quality of the cement produced using the clinker. According to the present invention, in the firing step of the cement clinker, hexavalent chromium (Cr ⁺⁶ ) present inside the raw material particles or clinker particles during granulation can be reduced so as to be combustible. In the method for manufacturing a cement clinker for supplying a material, the condition for reducing Cr ⁺⁶ is that a combustible having a particle size of 1 mm to 4 mm and a particle size larger than that of the pulverized coal is supplied into the kiln from the clinker cooler side. As a result, the Cr ⁺⁶ in the clinker is reduced to a harmless chromium salt and the Cr ⁺⁶
The cement clinker or the cement product without elution was obtained, and the cement using this clinker had no influence on the quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing a kiln used in the present invention. [Description of Signs] 1 Rotary kiln 2 Preheater 3 Cooler 4 Kiln bottom 5 Main burner 6 Kiln front

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Hisamaru Yamamoto             12 Mitsubishi Matsubara-cho, Kanda-cho, Kyoto-gun, Fukuoka             Terial Corporation Kyushu Factory F-term (reference) 4G012 KA02 KA08

Claims (1)

Claims: 1. A combustible material is supplied so as to reduce hexavalent chromium (Cr ⁺⁶ ) present in raw material particles or clinker particles during granulation in a cement clinker firing step. In the method for producing cement clinker, the condition for reducing Cr ⁺⁶ is to supply a combustible having a particle size of 1 mm to 4 mm and a particle size larger than that of the pulverized coal from the clinker cooler side into the kiln. Production method of cement clinker.