JPH06109367A - Collection of dust in exhaust of electric arc furnace - Google Patents

Abstract

PURPOSE:To collect efficiently dust in exhaust gas from an electric arc furnace, so that harmful substance of chlorine compound is not be scattered outside an electric furnace system. CONSTITUTION:Exhaust gas from an electric furnace 1 is supplied to a burning tower 3, where the exhaust gas is heated to burn carbon compound it contains. In this instance, a burning device 4 is used as a subsidiary means. The exhaust gas exhausted from the burning tower is supplied to a primary dust collecting device 10 while it is kept at a temperature higher than 400 deg.C, so that the dust in the exhaust gas can undergo a first dust gathering operation and be collected at the temperature of 400 deg.C. Next, the exhaust gas after the first dust gathering operation is cooled by a cooling tower 14 down to a temperature below 70 deg.C. Then, the cooled exhaust gas is supplied to a dust catching and filtering device 16, where the dust in the exhaust gas undergoes a second dust gathering operation and is collected at the temperature of 70 deg.C. Next, the collected dust is blown into an electric furnace 1 in operation by a dust transfer device 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of recovering dust contained in exhaust gas of an arc arc electric furnace for carrying out metal melting and refining using raw materials mainly composed of steel scrap.

[0002]

2. Description of the Related Art An arc arc type electric furnace (hereinafter referred to as "electric furnace")
Is a raw material mainly composed of steel scrap, and the exhaust gas (hereinafter referred to as “exhaust gas”) inevitably generated in the process of melting the raw material and then refining is leaked to the outside of the process. It has a direct pulling dust collector (hereinafter, referred to as "dust collector") that performs processing without doing so. This dust collector is included in the electric furnace that is the exhaust gas source and the exhaust gas.
Combustion tower that burns CO gas, cooling tower that cools high-temperature gas (including equipment with a spray tower that directly sprays water if necessary), collection and filtration equipment that collects and filters dust contained in exhaust gas, and generated gas A fern that sucks in, a discharge tower that discharges the exhaust gas after collecting and filtering, a device that collectively discharges the collected dust, and a heat-retaining method, a water-cooling method, and a method for connecting each device without leaking the exhaust gas The duct is composed of one or a combination of two or more of the air cooling systems. The exhaust gas of the electric furnace is a high temperature gas,
It has been conventionally practiced to use the stored heat to preheat the steel waste to be inserted to recover waste heat and promote energy saving. (Hereinafter, a device that uses the retained heat of the exhaust gas from an electric furnace to preheat the inserted steel scrap and recover the exhaust heat)

In many of the current dust collectors of electric furnaces, a residual heat device is arranged in the process. However,
The original purpose of the dust collector of the electric furnace is to separate and collect the dust contained in the exhaust gas, and to make the dust concentration in the gas released into the atmosphere (hereinafter referred to as "release gas") below the environmental standard. is there. Current dust collectors have the ability to keep the dust concentration in the released gas below environmental standards.

The temperature of the exhaust gas passing through the dust collector depends on the structure of the residual heat device and the exhaust gas treatment method (for example, the total dust collector of the entire steel factory (hereinafter referred to as "building dust collector") for building dust collection. Depending on the difference in the mixing treatment method, etc.}, it is in the range of approximately 70 to 250 ° C due to the collection efficiency of the collection device, the heat resistance of the materials used and the cooling method.

Further, in the dust collected by the dust collector, valuable metals are often collected in the next process.

[0006]

In the exhaust gas generated from the electric furnace, in addition to the substances specified by the environmental standards, it is possible to mix it with the raw materials to be used, to perform high heat treatment of the electric furnace and to perform exhaust gas cooling treatment thereafter. Although it is a very small amount, it contains chlorine compound-based harmful substances by being synthesized by the synthetic reaction in.

The properties of this chlorine compound-based harmful substance are shown in FIG. As shown in Fig. 1, in the case of chlorine compound-based harmful substances, the decomposition reaction temperature range is 800 ℃ or higher, the synthesis temperature range is 300 ℃ to 700 ℃, and
It is said that it is in a stable state in the form of fine particles at temperatures below 200 ° C. In addition, we have found that chlorine compound-based harmful substances have a dust collection rate that changes depending on the exhaust gas temperature when passing through a dust collector, that is, when the exhaust gas temperature is high, the dust collection rate decreases and It has been found that the dust concentration is high, while the dust collection rate is high when the exhaust gas temperature is low.

In the future, when the designated substances of the current environmental standards are changed and the toxic substances of chlorine compounds are changed to designated substances, the present dust collectors contain toxic substances of chlorine compounds in the exhaust gas or dust. Therefore, even if the dust concentration in the exhaust gas is reduced and it is collected in the dust, it is necessary to treat the chlorine compound-based harmful substance in the next step.

There is also a method of reusing the generated dust in the electric furnace, but since the generated amount is large, the treatment cost is high and the economical efficiency is poor, and at least the treatment in the next step must be entrusted.

[0010] Further, in the municipal waste incinerator, development of technology aimed at reducing chlorine compound-based harmful substances is being carried out. However, the temperature fluctuation of the high temperature gas generated and the dust concentration in the exhaust gas are different from those of the electric furnace. Therefore, the method of reducing chlorine compound-based harmful substances is also different.

The present invention has been made to solve these problems, and an object thereof is to reduce chlorine compound harmful substances in the emission gas released to the atmosphere and to collect dust for recovery. By installing the collecting device in two stages, dust with little chlorine compound-based harmful substances and dust with a large amount are collected separately, and dust with little chlorine compound-based harmful substances is used for the next process treatment. The purpose is to construct a device that does not release chlorine compound-based harmful substances to the outside of the electric furnace system by returning a large amount of dust to the electric furnace and performing high-temperature treatment for decomposition. Another object is to reduce the amount of dust returned to the electric furnace so that the dust can be returned endlessly, have no effect on the next step, and can be economically processed at low cost.

[0012]

[Means for Solving the Problems] We have conducted extensive studies to solve the above problems. As a result, the following findings (1) and (2) were obtained. (1) The solution to the above-mentioned problems is to keep the exhaust gas generated from the electric furnace during operation of the electric furnace at 800 ° C or higher in the exhaust gas treatment process at all times, and to use chlorine compound-based hazardous substances mixed in the steel scrap to be used and the electric furnace. Decomposes chlorine compound-based harmful substances that are synthesized inside, and further in the exhaust gas treatment process dust by high temperature dust collection method (dust with low content of chlorine compound-based harmful substances) and dust by low temperature dust collection method (chlorine This can be achieved by collecting two types of dust containing a large amount of compound-based harmful substances) and reducing the content of chlorine-based compound-based harmful substances in the exhaust gas discharged into the atmosphere.

(2) Dust recovered by the high temperature dust collection method with a small content of chlorine compound-based harmful substances is provided for the next step treatment such as zinc recovery, while chlorine recovered by the low temperature dust collection method is used. Dust containing a large amount of compound-based harmful substances is returned to the electric furnace during operation and subjected to high-temperature treatment at a temperature of 800 ° C or higher to decompose chlorine compound-based harmful substances, and then in the electric furnace and exhaust gas treatment process. Can be processed.

The present invention was made based on the above findings. The present invention supplies exhaust gas discharged from an electric furnace to a combustion tower, heats the exhaust gas in the combustion tower to burn carbon compounds contained in the exhaust gas,
Then, the heated exhaust gas is cooled by a cooling device, and then the dust contained in the cooled exhaust gas is collected and filtered by a collecting and filtering device, and the exhaust gas after the dust collecting and filtering is discharged to the atmosphere. In the method of collecting dust in the exhaust gas of the arc arc type electric furnace, the primary dust collector is arranged downstream of the combustion tower, and the exhaust gas discharged from the combustion tower is maintained at a temperature of 400 ° C or higher. It is supplied to the primary dust collector, and the dust in the exhaust gas is collected by the primary dust collector at a temperature of 400 ° C. or higher and collected, and then the exhaust gas after the primary dust collection is cooled by the cooling. Cooling by the device, and then collecting and filtering the dust contained in the cooled exhaust gas by the collecting and filtering device, and discharging the exhaust gas after the dust collecting and filtering to the atmosphere. With a butterfly. Further, it is preferable that a combustion device is provided in the combustion tower and the exhaust gas in the combustion tower is heated by the combustion device. Further, the exhaust gas after primary dust collection by the above method is conducted by the cooling device.
After cooling to a temperature of 70 ° C. or lower, then the cooled exhaust gas is supplied to the collecting and filtering device, and the dust in the exhaust gas is secondarily collected by the collecting and filtering device at a temperature of 70 ° C. or less. It is characterized in that the dust that is secondarily collected and then collected is blown into an operating electric furnace by a dust carrying device provided in the collecting and filtering device.

In the present invention, a combustion device (flame heating device) is provided in the combustion tower, the temperature of the exhaust gas generated from the electric furnace is constantly kept at 800 ° C. or higher, and the chlorine compound-based harmful substances emitted from the electric furnace are removed from the combustion tower. Disassemble with.

A dust collector (primary dust collector) is installed in the combustion tower or at a place near the combustion tower, and the dust in the exhaust gas from which the chlorine compound harmful substance is decomposed in the combustion tower is collected by the primary collector. The primary dust is supplied to a dust device and does not contain chlorine compound-based harmful substances (low content) in a low temperature range for re-synthesis. Next, after collecting the primary dust, the exhaust gas that exits the primary dust collector is cooled by a cooling device such as a cooling by a cooling tower or a mixing treatment with the building dust of the building dust collector to control the exhaust gas temperature. After the temperature is kept below 70 ° C, a dust collection filter (secondary dust collector) with a homogeneous and dense filter cloth filter or adsorbent filter will collect dust containing fine particles (secondary dust collector). However, the chlorine compound-based harmful substance is collected as much as possible by this secondary dust collecting device, and the amount of the chlorine compound-based harmful substance and dust in the released gas is reduced.

Further, the dust containing a large amount of chlorine compound-based harmful substances collected by the secondary dust collector is directly or indirectly supplied to the electric furnace during high temperature operation, and the chlorine compound-based harmful substances contained in these dusts are collected. Decomposes substances.

The decomposed chlorine compound-based harmful substances are shown in FIG.
As shown in, after the electric furnace exhaust gas is cleaned by the primary dust collector, it is re-synthesized in the process of the dust collector where it reaches the temperature (200 ° C or less) at which it can be released to the atmosphere.

[0019]

[Function] The present invention focuses on the temperature fluctuation of the electric furnace exhaust gas obtained from the knowledge, and there is a time when the temperature of the electric furnace exhaust gas does not fall within the decomposition temperature range (800 ° C or higher) of chlorine compound-based harmful substances. A combustion device that can raise flames is installed in the combustion tower, which is a type of combustion device, and the exhaust gas temperature of the electric furnace is kept at the decomposition temperature (800 ° C or more) of the chlorine compound-based hazardous substance to keep chlorine compound-based hazardous substance It decomposes.

The chlorine compound-based harmful substance contained in the exhaust gas has a very small amount when mixed in dust particles at a high exhaust gas temperature of 300 ° C. or higher.
It collects 80% or more of electric furnace exhaust gas dust by primary dust collection at a temperature of 400 ° C or higher. Further, for the primary dust collection, a cyclone type device or the like which has been hardly used in the conventional electric furnace exhaust gas dust collection device can be used.

When the electric furnace exhaust gas is at a low temperature of 70 ° C. or lower, the amount of the chlorine compound-based harmful substance mixed in the dust particles increases, and the amount increases in the fine particles. By collecting the fine particles as much as possible, dust containing a large amount of chlorine compound-based harmful substances is collected. As a result, the exhaust gas emitted into the atmosphere becomes a clean gas containing less chlorine compound-based harmful substances.

When the collected dust is sent to the next process,
Like the exhaust gas emitted to the atmosphere, dust containing less chlorine compound-based harmful substances is desirable, so the dust collected by the primary dust collection is sent to the next process.

Dust containing a large amount of chlorine compound-based harmful substances collected by the secondary dust collection should be supplied to the electric furnace when the exhaust gas from the electric furnace reaches a high temperature (800 ° C or higher) and decomposed in the electric furnace and in the combustion tower. As a result, steelmaking melting and refining work using steel scrap can be carried out without taking out chlorine compound-based harmful substances to the outside of the electric furnace system.

[0024]

Embodiments of the present invention will now be described with reference to the drawings. 2 and 3 are system flow charts showing the overall configuration of the electric furnace and the electric furnace exhaust gas dust collecting apparatus according to the method of the present invention, and FIG. 2 is the apparatus of the first embodiment in which the treatment is performed only with the electric furnace exhaust gas, FIG. 3 shows an apparatus according to the second embodiment that processes the exhaust gas of the electric furnace and the dust collection of the building in common. 4 is a schematic explanatory view showing a combustion tower and a combustion device, FIG. 5 is a schematic explanatory view showing a primary dust collector, and FIG. 6 is a schematic explanatory view showing a secondary dust collector.

In FIGS. 2 and 3, reference numeral 1 is an electric furnace for metal melting and refining, which operates using electric arc energy and combustible oil or gas. Reference numeral 2 denotes an elbow and a smoke collecting duct (hereinafter referred to as "smoke collecting duct"), which has a function of sending gas generated from the electric furnace to the exhaust gas treating apparatus, and connects the electric furnace 1 and the combustion tower 3. The smoke collecting duct 2 is divided in the middle and has a structure with a gap, so that the electric furnace 1 can be driven arbitrarily and the outside air can be sucked.

The combustion tower 3 burns carbon monoxide contained in the exhaust gas of the electric furnace by the air sucked from the void of the smoke collecting duct 2. Reference numeral 4 is a combustion device (burner) that uses combustible oil or gas and is used when the temperature of the exhaust gas of the electric furnace is low, and maintains the exhaust gas temperature at 800 ° C or higher.

Reference numeral 5 denotes a residual heat duct, which is separated from the duct 9 and is connected to the residual heat device 6. The residual heat device 6 residual heats the raw material inserted into the electric furnace with the high-temperature exhaust gas emitted from the electric furnace 1. A residual heat blower 7 is a device for supplying exhaust gas to the residual heat device 6. The duct 9 connects the combustion tower 3 and the primary dust collector 10 to each other.

The primary dust collector 10 collects 80% or more of the dust contained in the exhaust gas. After collecting the dust, the exhaust gas passes through the duct 13 and enters the cooling tower 14. Reference numeral 11 denotes a conveyor, which is a transport device that sends the dust collected by the primary dust collector 10 to the dust processing device 12 in the next step. The cooling tower 14 controls the exhaust gas temperature.
It is a device that lowers the temperature below 70 ° C. 15 is a duct, cooling tower 14
And the secondary dust collector 16 are connected.

The secondary dust collector 16 is a device for collecting dust in the exhaust gas that could not be collected by the primary dust collector 10.
Reference numeral 17 denotes a conveyer, which is a conveying device that sends the dust collected by the secondary dust collecting device 16 to the dust conveying device 21. The dust transfer device 21 is a device that transfers and blows dust into the electric furnace 1. A duct 18 connects the secondary dust collector 16 and the blower 19. The blower 19 is a suction / exhaust device (fern) that sucks the exhaust gas from the electric furnace without leaking and sends it to the chimney 20.

2 and 3 show an example in which the blower 19 is arranged after exiting the secondary dust collector 16, but a method in which the blower 19 is arranged in front of the secondary dust collector 16 is also common. is there. The chimney 20 is an emission device (emission tower) that emits exhaust gas into the atmosphere after performing a predetermined function in each device.

In FIG. 3, reference numeral 22 indicates the building exhaust gas collected in the upper part of the building. Reference numeral 23 is a duct, which is a device for sending the building exhaust gas to the secondary dust collector 16 through the collecting duct 24. A collecting duct 24 is connected to the secondary dust collector 16.
The electric furnace exhaust gas sent from the duct 15 and the building exhaust gas sent from the duct 23 are mixed in the collecting duct 24 and supplied to the secondary dust collector 16.

As shown in FIG. 4, the electric furnace exhaust gas and the air sucked in the middle of the smoke collection duct 2 pass through the smoke collection duct 2 and enter the combustion tower 3. The residual heat exhaust gas enters the combustion tower 3 from the residual heat device 6 through the residual heat exhaust gas duct 8. The retained heat of the electric furnace exhaust gas is used as an ignition source, and the oxygen contained in the drawn air burns the carbon compounds contained in the electric furnace exhaust gas and the residual heat exhaust gas and the carbon compounds of carbon monoxide.

The combustion device 4 burns kerosene or a combustion gas using air, and heats the electric furnace exhaust gas by the combustion fire and the combustion gas generated to keep the temperature at 800 ° C. or more at all times. Further, the combustion device 4 is equipped with a mechanism for automatically performing combustion by a temperature detection device so that the temperature of the exhaust gas passing through the combustion tower 3 does not fall below 800 ° C.

As shown in FIG. 5, the exhaust gas 51 supplied from the combustion tower 3 enters along the circumference from the upper part of the primary dust collector 10 shown in FIG. It descends while rotating, then rises in the center of the main unit, and the exhaust duct 13
Pass through.

During the process in which the exhaust gas descends while spirally rotating in the main body 52, dust contained in the exhaust gas is separated,
Collect in the dust storage tank 53 at the bottom of the main body. Dust enters the conveyor 11 via the cut-out valve 54, and the dust processing device
Sent to 12. The blower 56 is a device that returns the gas accumulated in the storage tank 53 to the exhaust gas 51 via the exhaust duct 57.

As shown in FIG. 6, the exhaust gas 71 cooled in the cooling tower 14 shown in FIG. 2 passes through the flow dividing tank 72 of the secondary dust collector 16,
Enter a large number of filter cloths 73. The gas passes through the filter cloth 73, collects in the chamber 80, and is discharged to the blower 19 through the duct 18. The dust contained in the exhaust gas is filtered by the filter cloth 73 and collected in the storage tank 75. The dust adhering to the filter cloth 73 is periodically vibrated by a vibrating device 79 to be removed. Storage tank 75
The dust collected in (1) is cut out by the valve (76), enters the transfer conveyor (17) through the cutout port (77), and is sent to the dust transfer device (21).

In FIG. 6, a filter device with a filter cloth 73 is used as the secondary dust collector 16, but an adsorbent filter device for performing adsorption filtration with an adsorbent may be used instead.

[0038]

As described above, according to the present invention, the dust contained in the exhaust gas can be separated and recovered, and the dust concentration in the gas released into the atmosphere can be kept below the environmental standard. Dust containing almost no compound-based harmful substances and dust containing a large amount of chlorine-based compound harmful substances can be collected separately, and moreover, most of the dust can be collected without containing chlorine-based compound harmful substances. Yes, it can be treated by recovering valuable metals, etc. Furthermore, dust containing a large amount of toxic substances of chlorine compounds can be returned to the electric furnace endlessly, so there is no effect on the next process,
Moreover, since the amount of dust to be returned is small, it is economically advantageous, and thus an industrially useful effect is brought about.

[Brief description of drawings]

FIG. 1 is a graph showing the behavior of chlorine compound-based harmful substances with temperature.

FIG. 2 is a system process diagram showing the overall configuration of an electric furnace and an electric furnace exhaust gas dust collector according to the first embodiment of the present invention.

FIG. 3 is a system process diagram showing the overall configuration of an electric furnace and an electric furnace exhaust gas dust collector according to a second embodiment of the present invention.

FIG. 4 is a schematic explanatory view showing a combustion tower and a combustion device.

FIG. 5 is a schematic explanatory view showing a primary dust collector.

FIG. 6 is a schematic explanatory view showing a secondary dust collector.

[Explanation of symbols]

 1 Electric Furnace 2 Smoke Collection Duct 3 Combustion Tower 4 Combustion Device 5 Exhaust Heat Duct 6 Exhaust Heat Device 7 Exhaust Heat Blower 8 Exhaust Heat Exhaust Gas Duct 9 Duct 10 Primary Dust Collector 11 Conveyor 12 Dust Treatment Device 13 Duct 14 Cooling Tower 15 Duct 16 Secondary Dust collector 17 Conveyor 18 Duct 19 Blower 20 Chimney 21 Dust supply device 22 Building exhaust gas 23 Duct 24 Collecting duct 51 Exhaust gas 52 Main body 53 Storage tank 54 Cut-out valve 56 Blower 57 Discharge duct 71 Exhaust gas 72 Dividing tank 73 Filter cloth 75 Storage tank 76 Valve 77 Cut-out port 79 Vibration device 79 Dust supply device 80 Chamber.

Claims (3)

[Claims] 1. An exhaust gas discharged from an electric furnace is supplied to a combustion tower, the exhaust gas is heated in the combustion tower to burn a carbon compound contained in the exhaust gas, and then the heated exhaust gas is discharged. The gas is cooled by a cooling device, then
In a method of collecting dust in exhaust gas of an arc arc type electric furnace, which collects and collects dust contained in the cooled exhaust gas by a collecting and filtering device and releases the exhaust gas after collecting and filtering the dust to the atmosphere. A primary dust collector is disposed downstream of the combustion tower, and the exhaust gas discharged from the combustion tower is maintained at a temperature of 400 ° C. or higher and supplied to the primary dust collector, and the primary dust collector is used to Dust in the exhaust gas is collected by primary collection at a temperature of 400 ° C or higher, then the exhaust gas after primary collection is cooled by the cooling device, and then the dust contained in the cooled exhaust gas. A method for collecting dust in exhaust gas of an arc arc type electric furnace, wherein the exhaust gas after collecting and filtering the dust is discharged to the atmosphere, while collecting and collecting the gas by the collecting and filtering device. 2. The method for collecting dust in exhaust gas of an arc arc type electric furnace according to claim 1, wherein a combustion device is provided in the combustion tower, and the exhaust gas in the combustion tower is heated by the combustion device. 3. The exhaust gas after primary dust collection by the method according to claim 1 or 2, is cooled to a temperature of 70 ° C. or lower by the cooling device, and then the cooled exhaust gas is collected. The dust in the exhaust gas is supplied to a filtering device and secondarily collected by the collecting and filtering device in a temperature state of 70 ° C. or less, and then the second dust is collected and collected, A method for recovering dust in exhaust gas of an arc arc type electric furnace, characterized in that the dust is blown into an operating electric furnace by a dust conveying device provided in a collecting and filtering device.