JP2011084425A - Method for decreasing mercury component and organic chlorine compound in exhaust gas from cement production equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently decreasing the discharge of mercury components and organic chlorine compounds such as PCB and dioxins in an exhaust gas discharged from cement production equipment. <P>SOLUTION: In the method for decreasing the mercury components and the organic chlorine compounds in the exhaust gas from the cement production equipment, dust collected in the latter half of a dust collector in the cement production equipment is introduced into a heating furnace and heated to 300-600°C under the introduction of a carrier gas to volatilize the mercury components and the organic chlorine compounds in the collected dust and the exhaust gas discharged from the heating furnace is brought into contact with water in a mercury component removing apparatus to absorb the mercury component, and the exhaust gas discharged from the mercury component removing apparatus is introduced into a high temperature part of ≥800°C to decompose the organic chlorine compound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for efficiently reducing mercury components and organochlorine compounds in exhaust gas discharged from a cement production facility.

In recent years, recycling of waste has been an important social issue, and in cement manufacturing plants, wastes such as various sludges, incineration ash, and waste plastics are often used as cement raw materials and fuels.
These wastes often contain heavy metals, of which volatile heavy metal components such as mercury and its chlorides volatilize in the high temperature part of cement production facilities and are contained in the gas. The Thereafter, as the temperature of the gas decreases, these heavy metals or the like are deposited on the surface of dust contained in the gas, or become fine particles of the heavy metal or its compound itself. These dust and fine particles are collected by the electric dust collector in the flue and removed from the gas.
In cement production facilities, coal, wood chips, sludge, waste plastics, and other combustibles that are brought into cement production facilities as cement raw materials and fuel are brought in from unburned gas generated without complete combustion, and waste plastics. Chlorine reacts to synthesize organochlorine compounds such as PCBs and dioxins. These organochlorine compounds also volatilize in the high temperature part of the cement production facility, are contained in the gas, and are adsorbed to the dust in a lower temperature electrostatic precipitator.
All of heavy metals such as mercury, dioxins and organochlorine compounds such as PCB are partly discharged from the flue to the outside air, but most of them are circulated in the cement production facility.
For this reason, if there is no means for treating mercury or organochlorine compounds in the gas, the amount of heavy metals such as mercury, dioxins and PCB circulating in the cement production facility will increase, and as the gas temperature decreases Problems such as mercury depositing in the ducts, increasing mercury emissions in the exhaust gas discharged from the chimney of the cement manufacturing facility, and organic chlorine compound emissions increase.

Patent Document 1 considers that the chlorine content in cement raw materials is the cause of the generation of dioxins and PCBs in cement manufacturing facilities, and uses a preheater before putting the cement raw materials into the raw material mill. Preheat to separate the organic chlorine compound from the cement raw material, etc., and supply the heat treatment gas containing the generated organic chlorine compound to the high temperature part at 800 ° C or higher during normal operation in the cement production facility. A method for reducing organochlorine compounds in exhaust gas from a cement production facility is described.
However, preheating a large amount of cement raw material requires a large preheater and a large amount of heat, and is a large-scale treatment.
In Patent Document 2, the dust collected from the exhaust gas in the cement manufacturing process is guided to a heating furnace, and mercury or the like contained in the dust collected is heated to a vaporization temperature or higher to be gasified to be an acidic or oxidizing solution. A method for treating exhaust gas for cement production is described in which mercury is removed by a method of absorption and the like, and dust collection dust from which mercury or the like has been removed is used as part of the cement raw material.
However, Patent Document 2 does not consider any organic chlorine compounds in the cement manufacturing process. That is, if a system in which a chlorine compound and mercury coexist is heated, in order to absorb elemental mercury (metallic mercury) in Patent Document 2, although mercury chloride (HgCl ₂ ) is the main component, As the absorbing solution, an acidic solution or an oxidizing solution is used. Moreover, there is no description about the removal of organochlorine compounds in the cement manufacturing process.

Japanese Patent No. 4075909 Japanese Patent Laid-Open No. 2002-355531

  An object of the present invention is to provide a method capable of efficiently reducing the amount of mercury components and organochlorine compounds such as PCBs and dioxins in exhaust gas discharged from cement production facilities.

The present invention is a method for reducing mercury components and organochlorine compounds in exhaust gas from a cement production facility having the following configuration.
(1) Dust collected in the latter half of the dust collector of the cement production facility is guided to a heating furnace and heated to 300-600 ° C under the introduction of carrier gas to volatilize mercury components and chlorine compounds in the dust collection dust. The exhaust gas exiting the heating furnace is brought into contact with cleaning water in a mercury component removing device to absorb the mercury component, and the exhaust gas exiting the mercury component removing device is heated to a high temperature part in a cement production facility at 800 ° C. or higher. A method for reducing mercury components and organochlorine compounds in exhaust gas from a cement production facility, characterized in that the organochlorine compounds are decomposed by introducing them into the atmosphere.
(2) The method for reducing mercury components and organochlorine compounds in the exhaust gas from the cement production facility according to (1), wherein the carrier gas introduced into the heating furnace is a thermal exhaust gas discharged from the cement production facility.

  According to the present invention, a small-scale facility is added to an existing cement manufacturing facility, and a part of the dust collected in the latter half of the dust collector that adsorbs the mercury component and the organochlorine compound at a high concentration is heat-treated. The post-treatment removes some of the mercury components and organochlorine compounds that circulate in the cement production facility. As a result, mercury components and organic chlorine in the exhaust gas discharged from the cement production facility outside the system are removed. The amount of the compound discharged can be efficiently reduced.

It is an example of the cement manufacturing equipment (partial view) used for the method for reducing mercury components and organochlorine compounds according to the present invention.

Hereinafter, the present invention will be specifically described based on embodiments.
The present invention introduces dust collection dust collected in the latter half of the dust collector of the cement production facility to a heating furnace, heats it to 300 to 600 ° C., volatilizes mercury components and organochlorine compounds in the dust collection dust, The exhaust gas exiting the heating furnace is brought into contact with cleaning water in the mercury component removal device to absorb the mercury component, and the exhaust gas exiting the mercury component removal device is guided to a high temperature part in a cement manufacturing facility at 800 ° C. or higher. This is a method for reducing mercury components and organochlorine compounds in exhaust gas from a cement production facility that decomposes organochlorine compounds. In this specification, the mercury component refers to elemental mercury (metallic mercury) and mercuric chloride, and the organic chlorine compound refers to PCB (polychlorinated biphenyl), dioxins, and the like.

  An example of a cement production facility (partial view) used for the method for reducing mercury components and the like according to the present invention is shown in FIG. The cement manufacturing facility used in the present invention includes a heating furnace 30 for heating the dust collected by the electric dust collector 23 and a mercury component removal for removing mercury and the like from the exhaust gas of the heating furnace 30 in a normal cement manufacturing facility. The apparatus 40 is provided with a gas delivery pipe 50 through which the exhaust gas of the mercury component removing apparatus 40 can be introduced into the kiln bottom part (high temperature part of 800 ° C. or higher) of the rotary kiln 15. In addition, as a high temperature part of 800 degreeC or more which can throw in the exhaust gas which came out of the mercury component removal apparatus, the kiln front part of the rotary kiln 15, the calcining furnace 14, etc. are mentioned other than that, as mentioned later.

In the cement production facility used in the present invention, the cement raw material is processed in a normal cement production process.
That is, the cement raw material pulverized by the raw material mill 11 is temporarily stored in the storage silo 12, then the cement raw material in the storage silo 12 is preheated by the preheater 13 (four cyclones in the figure), and then the calcining furnace The temperature is raised until the limestone is decarboxylated at 14, and the heated cement raw material is heated in the rotary kiln 15 to fire the cement clinker. Thereafter, the cement clinker is put into a clinker cooler and cooled.

On the other hand, in the cement manufacturing facility used in the present invention, the gas flows as follows.
When the cement raw material is heated in the preheater 13, the calcining furnace 14, and the rotary kiln 15, the mercury component and the organic chlorine compound contained in the cement raw material are volatilized in the exhaust gas, and the gas is supplied to the preheater 13. The uppermost cyclone (the gas temperature at the outlet is about 400 ° C.) exits and is sent to the sedimentation chamber 21.
Dust having a large particle size is separated in the sedimentation chamber 21, and the exhaust gas whose gas temperature is adjusted by the stabilizer 22 is sent to the electric dust collector 23. The exhaust gas that has exited the sedimentation chamber 21 is also sent to the raw material mill 11, and the exhaust gas that has exited from the raw material mill 11 joins the exhaust gas sent to the electric dust collector 23.
The electric dust collector 23 collects dust having a small particle size contained in the gas.
Since the gas temperature in the electric dust collector 23 is about 80 to 150 ° C., most of the mercury component and the organic chlorine compound in the gas are adsorbed by the unburned material in the dust. The dust collected in the electrostatic precipitator 23 has a smaller particle diameter in the second half than in the first half, and a mercury component and an organic chlorine compound are adsorbed at a high concentration.
The collected dust collected in the first half of the electrostatic precipitator 23 is directly sent to the mixing silo / storage silo 12 of the raw material mixing / supply system, and the mercury component collected in the latter half of the electric precipitator 23 is further increased. The collected dust adsorbed to the concentration is sent to the heating furnace 30. A part of the exhaust gas in which the dust is collected by the electric dust collector 23 is discharged outside the system through the chimney 24. The other exhaust gas enters the mixing silo / storage silo 12 together with the dust, and then sent to the preheater 13 together with the cement raw material, thereby forming a gas circulation system in the cement manufacturing facility.

  Dust collection dust collected in the latter half of the electric dust collector sent to the heating furnace 30 and adsorbing a larger amount of mercury components, etc. is heated to 300-600 ° C. while being transported in the furnace, and the mercury components and organic matter are collected. The chlorine compound volatilizes and is discharged to the mercury component removing device 40 by the carrier gas. Here, as described above, the mercury component refers to elemental mercury (metal mercury) and mercuric chloride, and when dust collection dust in which a chlorine compound coexists is heated in the heating furnace 30, 50% of mercury atoms. The above is mercuric chloride.

The heating furnace 30 is a device attached outside the existing cement manufacturing facility, and its structure is not limited. For example, a heating screw type heater, a paddle type heater, a rotary type heater, or the like can be employed.
As the heat source of the heating furnace 30, electric heating, hot air heating, burner heating, or the like can be adopted.
As the carrier gas of the heating furnace 30, air, nitrogen gas or nitrogen-rich gas (nitrogen concentration is 90% or more) and exhaust gas and exhaust air of cement manufacturing equipment can be used. If exhaust gas of 300 ° C. or higher and exhaust air are used, the amount of heat necessary for the heat treatment of dust can be reduced.

The heating temperature of the dust collection dust in the heating furnace 30 is 300 to 600 ° C., but if it is less than 300 ° C., the separation of the mercury component and the organic chlorine compound from the dust collection dust becomes insufficient. The separation effect of mercury components, etc. remains the same, making it uneconomical.
The residence time of the dust collection dust in the heating furnace 30 is preferably about 30 to 120 minutes.

  The dust collection dust from which the mercury component and the organochlorine compound are separated in the heating furnace 30 is sent to the mixing silo / storage silo 12 of the raw material mixing / supplying system to be converted into the raw material.

The high-temperature carrier gas in which the mercury component and the organic chlorine compound in the dust collection dust are volatilized is led to the mercury component removing device 40 and brought into contact with cleaning water of 80 ° C. or less as the absorption liquid, thereby chlorinating the carrier gas. The second mercury is absorbed by the absorbing solution, and the metallic mercury is accumulated at the bottom of the mercury component removing device 40 as a precipitate.
The mercuric chloride absorption liquid is treated in the waste water treatment facility, and the metal mercury at the bottom of the mercury component removing device 40 is periodically taken out.

  Examples of the mercury component removing device 40 include a spray tower, a cyclone scrubber, and a leaky shelf tower.

The exhaust gas from the mercury component removal device 40 from which the mercury component has been removed and the organochlorine compound is contained passes through the gas delivery pipe 50 and is introduced into a high-temperature portion in the cement manufacturing facility at 800 ° C. or higher. Examples of the high temperature part in the cement manufacturing facility at 800 ° C. or higher include the lower stage part of the preheater 13, the calcining furnace 14, the kiln bottom part of the rotary kiln 15, the kiln front part of the rotary kiln 15, the high temperature part of the clinker cooler, and the like.
In the high temperature part, organic chlorine compounds such as PCBs and dioxins are decomposed.

In the cement production facility used in the present invention, as described above, a part of the dust collected in the latter half of the dust collector 23 is guided to the heating furnace 30 and subjected to heat treatment, so that mercury in the dust collected dust is collected. Components and organochlorine compounds are volatilized, and the exhaust gas exiting the heating furnace 30 is brought into contact with water in the mercury component removal device 40 to absorb the mercury component, and the exhaust gas exiting the mercury component removal device 40 is heated to 800 ° C. or higher. It leads to the high temperature part in the cement manufacturing facility and decomposes the organochlorine compound, and a part of the mercury component and organochlorine compound circulating in the cement manufacturing facility are removed.
That is, a part of the dust collection dust collected in the latter half of the dust collector 23 (1/20 to 1/3 of the entire dust collection dust) is heated to 300 to 600 ° C. in a heating furnace to perform the post-treatment described above. The amount of mercury components and organochlorine compounds removed by performing the following steps is the normal amount of mercury components brought into the cement production facility from the outside, the normal amount of organic chlorine compounds brought into the cement production facility from the outside, and It exceeds the amount produced in cement production facilities. As a result, the circulation amount of the mercury component and the organic chlorine compound in the cement manufacturing facility, and the mercury component and the organic chlorine compound in the exhaust gas discharged out of the system in equilibrium with the circulation amount (from the outlet of the electrostatic precipitator 23 through the chimney 24). The concentration is greatly reduced by continuous operation.

  Hereinafter, the present invention will be described more specifically by way of examples.

[Example 1]
Part of the dust collected by the electrostatic precipitator of the cement manufacturing facility is guided to the heating furnace (electric heating system) and heated under the introduction of carrier gas (air) to produce dust. The mercury component and PCB contained therein were volatilized in the carrier gas. This carrier gas is introduced into a mercury component removing device (spray system) and brought into contact with washing water, whereby the mercury component (78% mercuric chloride 78%) in the carrier gas is absorbed or separated into the absorption liquid, followed by mercury. The carrier gas exiting the component removal apparatus was blown into the kiln bottom of the rotary kiln 15 of the cement production apparatus. Table 1 shows the dust treatment conditions, the mercury concentration of the dust before and after the heat treatment, and the PCB concentration. Mercury component removal rate is 5.4 kg / day (removal rate by heat treatment 69%, first day of treatment), PCB removal rate is 475 g / day (removal rate by heat treatment 95%, first day of treatment) Is calculated. Table 1 shows the daily changes in the mercury component and PCB discharge concentrations in the outlet gas of the electrostatic precipitator (same as the gas discharged outside the system) when continuously operated under the dust treatment conditions. During this continuous operation, the amount of mercury components brought into the cement production facility from the outside is about 1.6 kg / day, and the amount of PCB brought in from the outside and the amount produced in the cement production facility is about 240 g / day. Met.

  As shown in Table 1, according to the method of the present invention, dust collected in the latter half of the dust collector is treated by separating mercury components and PCBs in a heating furnace and removed from the circulation system in the cement manufacturing facility. By doing so, the mercury component concentration and PCB concentration in the exhaust gas discharged out of the system from the cement production facility could be remarkably reduced.

11 Raw material mill 12 Raw material mixing / supply silo (mixed silo / storage silo)
13 Preheater 14 Calciner 15 Rotary kiln 21 Sedimentation chamber 22 Stabilizer 23 Electric dust collector 24 Chimney 30 Heating furnace 40 Mercury component removal device 50 Gas delivery pipe

Claims (2)

  The dust collected in the second half of the dust collector of the cement production facility is guided to a heating furnace and heated to 300 to 600 ° C. under the introduction of a carrier gas to volatilize mercury components and organochlorine compounds in the dust collection dust, The exhaust gas exiting the heating furnace is brought into contact with cleaning water in a mercury component removal device to absorb the mercury component, and the exhaust gas exiting the mercury component removal device is led to a high temperature part in a cement manufacturing facility at 800 ° C. or higher. A method for reducing mercury components and organochlorine compounds in exhaust gas from a cement production facility, characterized by decomposing organochlorine compounds.   The method for reducing mercury components and organochlorine compounds in exhaust gas from a cement production facility according to claim 1, wherein the carrier gas introduced into the heating furnace is thermal exhaust gas discharged from the cement production facility.

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