JP2003055010A - Pretreating method for raw material in manufacture of cement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing a volatile metal component such as mercury contained in a raw material used for the manufacture of cement. SOLUTION: This method for manufacturing cement is characterized in that the concentration of the volatile metal component in the raw material is reduced by introducing the raw material used for the manufacture of cement to a heating furnace to gasify the volatile metal component contained in the raw material, introducing this high temperature gas to a cooling section, cooling the gas down to a temperature below the deposition temperature of the volatile metal component and liquefying or solidifying the metal component to separate the metal component from the gas and the resultant raw material is introduced to a cement manufacturing stage to calcine cement clinker.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw material pretreatment method for efficiently removing volatile metal components such as mercury in raw materials used for cement production to reduce the concentration thereof.

[0002]

2. Description of the Related Art In cement production, there are increasing opportunities to use various sludges, incinerator ash and other waste materials as raw materials and fuels. However, these wastes contain some heavy metals, which may increase the amount of heavy metals brought into the cement manufacturing process. Of the heavy metals contained in these wastes, mercury, zinc, selenium, etc., which have relatively high volatility, and these compounds volatilize in the high temperature part of the cement manufacturing process and are contained in the gas. Then, as the temperature of the gas decreases, these heavy metals are deposited on the surface of the dust contained in the gas,
Alternatively, they become fine particles of heavy metals or their compounds themselves. These dusts and particles are collected by the flue gas electrostatic precipitator (EP) and removed from the exhaust gas. Part of mercury, which has a particularly high volatility, remains in a gaseous state and is discharged while being contained in the flue gas.

[0003]

The dust collected by the electric dust collector (dust collecting dust) is mixed with the newly crushed raw material in the cement manufacturing process and becomes a part of the raw material, which is included in the dust collecting dust. Most of the volatile heavy metals contained in the clinker are volatilized again in the preheater part or the high temperature part of the rotary kiln, but they are contained in the gas and led to the exhaust gas system again to circulate in the cement manufacturing process. is doing. For this reason, unless measures are provided to reduce the carry-on of volatile heavy metals from the raw materials used in the cement manufacturing process, as the amount of volatile heavy metals brought in from the raw materials increases, the amount of circulation in the cement process increases and There is a problem that the amount of volatile heavy metals discharged to the outside increases.

[0004]

The present invention efficiently removes volatile metals such as mercury, which is a raw material used in such a cement manufacturing process, and reduces the amount of volatile heavy metals in exhaust gas discharged outside the system. Provide a way. In the treatment method of the present invention, by heating the raw material, the volatile metal is gasified and separated from the raw material, and this gas is cooled to separate and recover the volatile components to prevent the volatile metal from flowing into the cement firing system. Is the way.

That is, the present invention relates to a method for reducing volatile components of raw materials in cement production having the following constitution. (1) The raw material used for cement production is introduced into a heating furnace, the volatile metal component contained in the raw material is gasified, and this high-temperature gas is introduced into a cooling section to be cooled to a temperature below the precipitation temperature of the volatile metal component. A method for producing cement, which comprises liquefying or solidifying and separating from gas to reduce the concentration of volatile metal components in the raw material, guiding the raw material to the cement production process, and firing the cement clinker. (2) The cement manufacturing method according to (1), wherein the heating furnace is heated by the heat exhaust gas discharged in the cement manufacturing process.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below based on embodiments. The treatment method of the present invention introduces a raw material used for cement production to a heating furnace, gasifies the volatile metal component by heating it to a temperature equal to or higher than the volatilization temperature of the volatile metal component contained in the raw material, and cools this high temperature gas to a cooling part. The method for producing cement, characterized by cooling to below the precipitation temperature of the volatile metal component, liquefying or solidifying it and separating it from the gas, and introducing the raw material to the cement production process and firing the cement clinker. Is.

The outline of the processing method according to the present invention is shown in FIG. As shown in the figure, the treatment system of the present invention includes a heating furnace 30, a heating furnace 3 for receiving the raw material 10 of the cement manufacturing process.
A cooling unit 31 for cooling the high-temperature gas discharged from 0 and a suction fan 32 for sending the cooling gas discharged from the cooling unit 31 are provided.

In the manufacturing process of cement burning kiln, etc.,
The raw material 10 is introduced into the crusher 20 and crushed to a predetermined particle size. The raw material to be the subject of the present invention may be any raw material used in the cement manufacturing process, in particular, volatile metals such as mercury, selenium, cadmium and zinc, or volatile metal compounds such as chlorides thereof (volatilizing these compounds). The raw material contained in the (abbreviated as a metallic component) is preferentially treated. These raw materials are introduced into the heating furnace 30. It is preferable that the heating furnace 30 has, for example, a screw feeder 30a therein. The raw material fed from one end of the furnace 30 is heated above the volatilization temperature of the volatile metal component while being transported in the furnace, and the volatile metal component is gasified. Specifically, about 300 to 5
Heating to 00 ° C is preferred. Incidentally temperature which the vapor pressure of 1mmHg the mercury about 126 ° C., selenium, arsenic, cadmium about 356～ about 394 ° C., respectively, of zinc is about 487 ° C., and in the chloride, antimony chloride (SbCl ₃₎ is About 49 ° C, about 136 ° C for mercury chloride, about 316 ° C for tin chloride (SbCl ₂ ), zinc chloride (ZnCl ₂ ).
Is about 428 ° C. Therefore, these are mostly volatilized under heating at 300 to 500 ° C. However, as long as the restrictions on the equipment permit, there is no problem in gasification of volatile metals even at higher temperatures. In addition, if the treatment time in the heating furnace can be extended, the treatment may be performed at a temperature lower than 300 ° C. (a temperature at which the target metal is volatilized).

As the heat source, heat exhaust gas discharged from the cement manufacturing process such as a cement burning kiln may be used. The raw material after the volatile metal component is gasified is taken out from the outlet of the heating furnace 30.

The high temperature gas discharged from the heating furnace is cooled by the cooling unit 3.
Introduced in 1. As the cooling unit 31, for example, one having a structure in which a cooling jacket 31a is provided on the outer periphery and an inclined plate 31b is provided on the lower portion, or the like is used. The cooling unit 31 is cooled to a temperature not higher than the deposition temperature of the volatile metal component by the cooling jacket 31a. Specifically, it is cooled to, for example, 50 ° C. or lower. By this cooling, a volatile metal component in the gas, for example, mercury is liquefied and deposited on the surface of the inclined plate, and selenium, cadmium and the like are solidified and deposited as fine particles on the bottom of the cooling unit 31. Even if the temperature of the cooling unit 31 is higher than 50 ° C., mercury can be removed from the gas, but when the temperature is high, the amount of mercury remaining in the gas is large, and mercury is efficiently removed from the gas. Since it is not possible, it is appropriate that the cooling temperature be 50 ° C. or lower, and the lower the better, the better. Further, if the gas flow rate of the suction fan 32 is too large, the difference between the concentration of the volatile metal in the gas and the saturation concentration of the volatile metal in the cooling section becomes small, and it becomes impossible to efficiently remove it. The gas flow rate may be adjusted depending on the content of the volatile metal.

Mercury and the like accumulated on the bottom of the cooling unit are periodically taken out. On the other hand, the gas discharged from the cooling unit is guided to the outside of the system through the suction fan 32. The concentration of volatile metal components in this cooling gas is greatly reduced, and for example, mercury is 30%.
mg / m ³ N or less, zinc is 0.050mg / m ³ N or less,
Cadmium is 0.001 mg / m ³ N or less. This cooling gas is preferably returned as air introduced into the heater and circulated. In this way, the exhaust gas is circulated from the heating furnace 30 to the air introduced into the heater through the cooling unit 31, so that volatile metal components such as mercury contained in the exhaust gas are not directly discharged to the outside.

The cement raw material that has been subjected to the above heat treatment is
It is guided to the crusher 20 and thereafter subjected to the cement firing process. By the above heat treatment, the volatile components such as mercury contained in the cement raw material are reduced, and as a result, the volatile components circulating in the cement manufacturing process are also reduced, and the volatile components contained in the exhaust gas are also reduced. To be done.

[0013]

Example 1 10 kg of coal ash derived from a thermal power generation certificate used as a raw material in a cement manufacturing plant was filled in the center of a pipe (80 mmφ × 1000 mm) having open ends,
It heated at 200-500 degreeC for 30 minutes. At this time, 100 ml / min of air was introduced from one side opening of the test tube, and the gas discharged from the other end was introduced into a cooling tube and cooled to room temperature. Table 1 shows the content of mercury contained in the raw materials and the treatment effect.

[0014]

[Table 1]

[0015]

[Embodiment 2] Using the treatment system shown in FIG. 1, a part of the raw material of the cement manufacturing process is supplied to a heating furnace and heated to a predetermined temperature, and the heating gas is introduced into a cooling section to remove mercury in the cooling gas. separated. The cooled gas was returned to the heater again through a suction fan. The results of this treatment are shown in Table 2.

[0016]

[Table 2]

When the result of Example 2 is expanded to a treatment system of 10 t / hr, if the same performance is shown, the mercury concentration in the exhaust gas can be reduced by about 0.05 mg / m ³ N. It can be estimated that it is possible.

[0018]

Most of the volatile metal components such as mercury discharged from the cement manufacturing process are brought in from the waste raw material. Therefore, according to the treatment method of the present invention, the cement manufacturing process is performed by treating this raw material. It is possible to efficiently remove volatile components such as mercury that are brought into the room. As a result, the volatile components circulating in the cement manufacturing process are reduced, and the volatile components discharged to the outside of the system can be reduced. Further, since the method of the present invention mainly treats the raw material containing the volatile metal component, it does not require large-scale equipment,
It can be easily implemented by simply attaching it to the existing raw material charging process.

[Brief description of drawings]

FIG. 1 is a flow chart showing the processing steps of the present invention.

[Explanation of symbols]

10-raw material, 20-crusher, 30-heating furnace, 31-cooling unit, 32-cooling fan

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Claims (2)

[Claims] 1. A raw material used for cement production is introduced into a heating furnace, the volatile metal component contained in the raw material is gasified, and this high temperature gas is introduced into a cooling section to be cooled to a temperature below the precipitation temperature of the volatile metal component, By liquefying or solidifying this and separating it from the gas, the concentration of the volatile metal component in the raw material is reduced, and the raw material is introduced into the cement manufacturing process to burn the cement clinker, and the cement manufacturing method is characterized. . 2. The cement manufacturing method according to claim 1, wherein the heating furnace is heated by the hot exhaust gas discharged in the cement manufacturing process.