JPH06294586A - Dioxin generation preventing method for scrap melting furnace and its pre-heating device, and dioxin generation preventing device - Google Patents

Abstract

PURPOSE:To prevent dioxin from generating by a method wherein an exhaust gas discharged from a scrap melting furnace (electric furnace) is burnt by a high combustion to eliminate carbon monoxide in the exhaust gas. CONSTITUTION:An exhaust gas discharged from a scrap melting furnace (electric furnace) 1 enters a combustion chamber 20 through a sliding pipe 19. Then, the exhaust gas discharged from the combustion chamber 20, e.g. passes through a bucket 25 for scrap preheating under a condition in which a switching valve 23 of a by-pass 22 is opened, and a switching valve 24 of the by-pass 22 is closed, and is introduced to a combustion tower 2 under a condition in which a switching valve 29 is opened. When the operation of the scrap melting furnace 1 starts, the quantity of carbon monoxide increases. However, for a few minutes from the start of power connection of the scrap melting furnace 1, the quantity of carbon monoxide is lower than the explosion limit, and carbon monoxide does not burn. For this reason, the inside of the combustion tower 2 is kept at a high temperature which is 800 deg.C or higher from the start of a power connection of the scrap melting furnace 1 to burn and make the exhaust gas stay for 2 seconds or longer, and thus, dioxin is prevented from generating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dioxin generation preventing method and a dioxin generation preventing device in an iron scrap melting furnace (electric furnace) and its preheating device.

[0002]

2. Description of the Related Art FIG. 5 shows a path of exhaust gas in a conventional iron scrap melting furnace (electric furnace) and its preheating device. Here, the exhaust gas discharged from the iron scrap melting furnace (electric furnace) 101 first passes through the sliding tube 102 and then enters the combustion chamber 10.
Enter 3. The exhaust gas that has passed through the combustion chamber 103 is
It is introduced into the iron scrap preheating bucket 105 with the bypass switching valve 106 open and 107 closed. Here, the raw iron scrap is preheated by the sensible heat of the exhaust gas, and enters the gas cooler chamber 110 with the switching valve 108 opened. The temperature of the exhaust gas gradually decreases, and the exhaust gas is sucked by the blower 111 and introduced into the dust collector 109.

[0003]

In such a conventional iron scrap melting furnace (electric furnace) and preheating apparatus, poisonous dioxins are generated in the process of heating and melting the iron scrap.

Dioxin is an abbreviation for polychlorodibenzodioxin (a chlorinated compound in which two benzene rings are linked by two oxygen atoms), and a large number of isomers depending on the number and position of chlorine atoms attached to the benzene ring. I have a body. Commonly known dioxin includes 2.
3.7.8-Tetrachlorodibenzodioxin (2.
3.7.8-TCDD), which is highly toxic, is highly carcinogenic and teratogenic to the fetus, and has a property of being hardly decomposed.

And polychlorobiphenyl (PCB)
Aromatic chlorine compounds such as and hexachlorobenzene
Dioxins are also generated in the iron scrap melting furnace (electric furnace) and its preheating device because they are oxidized during combustion to generate dioxins.

This dioxin is an iron scrap melting furnace (electric furnace)
Specific conditions that occur in or in the preheating device are: (1) Burning or residual heat at a low temperature of 800 degrees Celsius or less. (2) Organic chlorine compounds are present in the combustion products. (3) Carbon monoxide (CO) remains in the exhaust gas after combustion. If at least these three conditions are provided, dioxin is easily generated in the iron scrap melting furnace (electric furnace) and the like.

In the conventional iron scrap melting furnace (electric furnace) and its preheating apparatus shown in FIG. 5, first, the iron scrap melting furnace (electric furnace) 10 is used.
The exhaust gas from the combustion chamber 10 passes through the sliding pipe 102
Enter 3. This sliding tube 102 is an iron scrap melting furnace (electric furnace)
Iron scrap melting furnace (electric furnace) because 101 tilts when tapping
A suction pipe 102 a fixed to 101 and a sliding pipe 102 b fixed to the combustion chamber 103 are juxtaposed with a slight gap 104.

Exhaust gas emitted from the iron scrap melting furnace (electric furnace) 101 is ignited and burned in the combustion chamber 103. Initially, the exhaust gas does not contain carbon monoxide (CO) at all, but when the concentration thereof gradually increases and exceeds the explosion limit (containing 12.5%), the exhaust gas forms a phase with the air flowing through the gap 104 between the suction pipes 102a and 102b. In other words, it burns in the combustion chamber 103.

The concentration of carbon monoxide (CO) in the exhaust gas emitted from the iron scrap melting furnace (electric furnace) 101 varies depending on the operating conditions of the furnace, but is 0% to 1 for several minutes after the start of energization of the furnace.
The concentration is 3%, and thereafter, the concentration is approximately 14% to 22%.

Although the amount of air flowing from the gap 104 between the suction pipes 102a and 102b is constant, the concentration of carbon monoxide (CO) generated in the iron scrap melting furnace (electric furnace) 101 is constantly changing. Further, the combustion chamber 103 in which the exhaust gas enters is very small, and the heat load rate (kcal / m) of the combustion chamber 103 is small.
^{From the point of view of 3}・ h), it is difficult to completely burn, and incomplete combustion is inevitable. Therefore, incombustible carbon monoxide (CO) gas is released into the atmosphere. The amount of gas generated in the iron scrap melting furnace (electric furnace) 101 also changes every moment.

The high temperature exhaust gas from the combustion chamber 103 is introduced into the iron scrap preheating bucket 105 with the bypass switching valve 106 open and 107 closed. Here, the raw iron scrap is preheated by the sensible heat of the exhaust gas, and enters the gas cooler chamber 110 with the switching valve 108 opened. The temperature of exhaust gas gradually decreases,
It is sucked by the blower 111 and introduced into the dust collector 109.

The Dalai powder in the iron scraps uses cutting oil and grinding oil to improve the life and working efficiency of the tool when machined by a machine tool such as a lathe. An organic chlorine compound is used. In addition, vinyl chloride, plastic scraps, etc. are mixed in the iron scraps,
These also contain organic chlorine compounds.

The exhaust gas temperature when entering the iron scrap preheating bucket 105 is 700 to 900 degrees Celsius, and the exhaust gas temperature when exiting from the iron scrap preheating bucket 105 is 300 to 450 degrees Celsius, The iron scraps are steamed in the iron scrap preheating bucket 105.

This state is as follows: (1) Burning or residual heat at a low temperature of 800 degrees Celsius or less. (2) Organic chlorine compounds are present in the combustion products. (3) Carbon monoxide (CO) remains in the exhaust gas after combustion. The above-mentioned dioxin generating condition is provided.

On the other hand, the bypass switching valves 106 and 107 are closed.
In the open state, the high temperature exhaust gas that has left the combustion chamber 103 is directly introduced into the dust collector 109. The exhaust gas emitted from the iron scrap melting furnace (electric furnace) 101 gradually rises in temperature at room temperature at the start of energization of the furnace, and reaches about 1350 degrees Celsius at the time of final tapping.

Since vinyl chloride, plastic scraps and the like are mixed in the iron scrap, the iron scrap is melted from the start of energization of the iron scrap melting furnace (electric furnace) 101 to about 800 degrees Celsius. Iron scraps are steamed in the melting furnace (electric furnace) 101, and toxic dioxins are generated under the conditions (1), (2), and (3).

Also, when the temperature exceeds 800 degrees Celsius, incomplete combustion occurs due to the narrow combustion chamber 103 through which exhaust gas passes, and carbon monoxide (CO) remains in the exhaust gas, Similarly, toxic dioxins are generated under the conditions (1), (2), and (3).

Therefore, the present invention was created in order to solve the above-mentioned problems, and exhaust gas discharged from an iron scrap melting furnace (electric furnace) is introduced into a combustion tower and completely burned at a high temperature to generate dioxin. The present invention provides a method and a device for preventing generation of dioxin in an iron scrap melting furnace (electric furnace) and a preheating device therefor.

[0019]

In order to solve the above-mentioned technical problems, the present invention introduces exhaust gas discharged from an iron scrap melting furnace (electric furnace) into a combustion tower and burns it at a high temperature. Dioxin was prevented by eliminating carbon monoxide in the exhaust gas.

In addition, the exhaust gas is completely burned by generating eddy currents and turbulent flow in the combustion tower.

On the other hand, the dioxin generation preventing device was constructed by including an iron scrap melting furnace (electric furnace) and a combustion tower for burning exhaust gas discharged from the iron scrap melting furnace (electric furnace) at a high temperature.

In the above dioxin generation preventing device, an ignition burner is installed in the combustion tower, a first air blowing section for generating a vortex is installed above the ignition burner, and a turbulent flow is generated below the ignition burner. A second air blow section was installed.

[0023]

According to the present invention, the exhaust gas discharged from the iron scrap melting furnace (electric furnace) is introduced into a combustion tower and burned at a high temperature, and along with this combustion, carbon monoxide (CO) in the exhaust gas is eliminated to produce dioxins. Prevented the occurrence.

Further, eddy current / turbulent flow is generated in the combustion tower to mix the exhaust gas and oxygen to completely burn the exhaust gas.

In the combustion of the exhaust gas, a vortex flow is generated to mix the exhaust gas and oxygen and then ignited by an ignition burner, and a turbulent flow is generated in the exhaust gas in a combustion state.
It completely burns the exhaust gas.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

The method for preventing dioxin generation in the iron scrap melting furnace (electric furnace) and the preheating apparatus therefor according to the present invention is to introduce the exhaust gas from the iron scrap melting furnace (electric furnace) into a combustion tower for high temperature combustion. To prevent the generation of dioxins.

As an apparatus for realizing this method,
For example, as shown in FIG. 1, an iron scrap melting furnace (electric furnace) 1
And a combustion tower 2 for burning the exhaust gas from the iron scrap melting furnace (electric furnace) 1 at a high temperature.

As shown in FIG. 2, the combustion tower 2 is tubular and has a first air blowing section 3 and a second air blowing section 4 above it.
Is equipped with.

The first air blowing section 3 mixes the exhaust gas and oxygen introduced into the combustion tower 2 by the water cooling duct 5,
The structure is such that a vortex flow is generated in the combustion tower 2. Specifically, as shown in FIGS. 2 and 3, a plurality of air blowing pipes 6 and 7 arranged in the circumferential direction of the combustion tower 2 are provided in an appropriate number of stages (two stages in FIG. 2). . As shown in FIG. 3, each of the air-blowing pipes 6 and 7 made of heat-resistant steel is provided with a jet port on the right side of the tip end so as to generate a counterclockwise vortex flow in the combustion tower 2. There is. The vortex flow is not limited to the counterclockwise direction, and for example, a jet port may be formed on the left side of the tip end of each of the air blowing pipes 6 and 7 to generate a clockwise vortex flow in the combustion tower 2. .

The second air blowing section 4 has a structure for generating a turbulent flow in the combustion tower 2 in order to completely burn the exhaust gas ignited by the burner 8. Specifically, as shown in FIGS. 2 and 4, a plurality of air blowing pipes 9, 10, 11, and 12 made of heat-resistant steel are arranged in the circumferential direction of the combustion tower 2 in an appropriate number of stages (see FIG. It is provided on the 4th row in 2). As shown in FIG. 4, each of the air blowing pipes 9, 10, 11 and 12 has a jet opening at the tip end thereof so that the jetted air is directed toward the center of the combustion tower 2 and reaches almost the center. The outlet is made thin so that Further, the pressure at which the gas is ejected to the center of the combustion tower 2 against the flow of exhaust gas is selected.

The conditions such as the size of the combustion tower 2 thus constructed are not uniform depending on the capacity of the iron scrap melting furnace (electric furnace) 1, but at least the exhaust gas in the combustion tower 2 is 2 seconds or more. To stay. Be able to raise the temperature in the combustion tower 2 to 800 degrees Celsius or higher. The oxygen concentration in the exhaust gas should be 6% or more. Etc. must be provided.

Then, in order to set the oxygen concentration in the exhaust gas to 6% or more, the number of stages of each of the air blow pipes 6, 7, 9, 10, 11, 12 and one blow pipe are set by the measurement instruction of the gas analyzer 26. Controls the jetting / stopping of each air.

As shown in FIG. 2, the two combustion towers 2,
13 are connected by a water cooling duct 14, and this water cooling duct 1
The third air blowing section 15 and the burner 1 which generate a swirl in
When 6 is attached, exhaust gas can be combusted more completely and the generation of dioxins can be reliably prevented. Combustion tower 2
According to the amount of exhaust gas generated, for example, three or more combustion towers 2 may be installed in parallel, or one may be provided.

Next, the path of the exhaust gas in this device (FIG. 1) will be described.

First, the exhaust gas from the iron scrap melting furnace (electric furnace) 1 passes through the sliding tube 19 and enters the combustion chamber 20. The sliding tube 20 is a suction tube 19 fixed to the iron scrap melting furnace (electric furnace) 1 because the iron scrap melting furnace (electric furnace) 1 tilts during tapping.
Although a and the sliding tube 19b fixed to the combustion chamber 20 are juxtaposed with each other with a slight gap 21, the gap 21 is made small so that the amount of air entering from the gap 21 is reduced as much as possible. To do.

Then, the high-temperature exhaust gas leaving the combustion chamber 20 passes through the iron scrap preheating bucket 25 with the switching valve 23 of the bypass 22 open and closed 24, and is introduced into the combustion tower 2 with the switching valve 29 open. To be done. In addition, the switching valve 23 of the bypass 22
The hot exhaust gas that has left the combustion chamber 20 in the closed or 24-open state may be directly introduced into the combustion tower 2.

When the operation of the iron scrap melting furnace (electric furnace) 1 is started, the amount of carbon monoxide (CO) gradually increases from the state where it does not exist at all. However, since the explosion limit of carbon monoxide (CO) is 12.5%, the iron scrap melting furnace (electric furnace) 1
For a few minutes from the start of energization, the combustion temperature will fall below the explosion limit, and no combustion will occur no matter how much carbon monoxide (CO) and oxygen are mixed.

Therefore, when an organic chlorine compound such as vinyl chloride or plastic scrap is mixed in the iron scrap in the iron scrap melting furnace (electric furnace) 1, the iron scrap is from room temperature to about 600 degrees Celsius. Will be in a steamed state, and the conditions for generating dioxin will be provided.

Therefore, the present invention provides an iron scrap melting furnace (electric furnace).
Since the burner 8 of the combustion tower 2 raises the temperature in the combustion tower 2 to a high temperature of 800 degrees Celsius or more from the start of energization 1 of FIG.

When the content of carbon monoxide (CO) is 13% or more, the explosion limit is exceeded and carbon monoxide (CO) itself continues to burn, so the burner 8 of the combustion tower 2 triggers combustion. It should be used only for ignition.

Then, in the combustion tower 2, the exhaust gas and oxygen are mixed by the first air blowing section 3 to generate a swirl flow to promote combustion of the exhaust gas. Further, the second air blowing unit 4 generates a turbulent flow in the burning exhaust gas to completely burn the exhaust gas in a short time so that the carbon monoxide (CO) concentration in the exhaust gas is 100 ppm or less.

The first air blowing section 3 and the second air blowing section 4
The air ejected from the air contains about 21% oxygen (O2), but by increasing the oxygen (O2) content ratio or using pure oxygen, the combustion speed of the exhaust gas can be increased and the combustion tower 2 can be downsized. Can be planned.

As for the amount of air ejected from the first air blowing section 3 and the second air blowing section 4, the amount of oxygen (O2) in the exhaust gas is measured by the gas analyzer 26, and the amount of oxygen (O2) is about 6 %
Set to include the above.

As shown in FIG. 2, the exhaust gas that has passed through the combustion tower 2 enters the heat exchanger 17 to boil the water in the boiler tube 18 to secure electric energy, or make hot water for use. Then, it is sent to the dust collector 27.

[0046]

According to the present invention, the iron scrap melting furnace (electric furnace)
It is possible to prevent the generation of dioxins by introducing the exhaust gas emitted from No. 1 into the combustion tower 2 and burning it at high temperature.

That is, since the exhaust gas is burned in the combustion tower 2 at a high temperature of 800 degrees Celsius or higher, and the carbon monoxide (CO) concentration in the exhaust gas is reduced to 100 ppm or lower by this high temperature combustion, the iron waste is dissolved. Even if an organic chlorine compound is present in the furnace (electric furnace) 1, it is possible to prevent the generation of dioxins.

Further, in the combustion tower 2, since the exhaust gas is completely combusted by generating the eddy current / turbulent flow, it is possible to surely prevent the generation of dioxin.

On the other hand, the dioxin generation preventing device comprises an iron scrap melting furnace (electric furnace) 1 and a combustion tower 2 for burning exhaust gas discharged from the iron scrap melting furnace (electric furnace) 1 at a high temperature.
Since the structure is extremely simple, it has practically excellent effects such that the manufacturing cost of the device can be kept low.

Further, an ignition burner 8 is installed in the combustion tower 2, and a first air blow-in portion 3 is installed above the ignition burner 8 to generate a swirl flow. Therefore, exhaust gas and oxygen are mixed evenly before ignition. Exhaust gas can be burned by the burner 8.

Since the second air blowing section 4 is installed below the ignition burner 8 to generate a turbulent flow in the exhaust gas in a combustion state, the exhaust gas can be completely burned and dioxins can be surely prevented.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a distribution route of exhaust gas.

FIG. 2 is a side sectional view of a combustion tower.

FIG. 3 is a plan sectional view of a first air blowing section.

FIG. 4 is a plan sectional view of a second air blowing section.

FIG. 5 is a schematic view showing a distribution route of exhaust gas in a conventional device.

[Explanation of symbols]

1 Iron Scrap Melting Furnace (Electric Furnace) 2 Combustion Tower 3 First Air Blowing Part 4 Second Air Blowing Part 5 Water Cooling Duct 6 Air Blowing Pipe 7 Air Blowing Pipe 8 Burner 9 Air Blowing Pipe 10 Air Blowing Pipe 11 Air Blowing Pipe 12 Air blow pipe 13 Combustion tower 14 Water cooling duct 15 Third air blow part 16 Burner 17 Heat exchanger 18 Boiler pipe 19 Sliding pipe 20 Combustion chamber 2
0 19a Suction pipe 19b Sliding pipe 21 Gap 22 Bypass 23 Switching valve 24 Switching valve 25 Iron scrap preheating bucket 26 Gas analyzer 27 Dust collector 28 Blower 29 Switching valve 101 Iron scrap melting furnace (electric furnace) 102 Sliding pipe 102a Suction Pipe 102b Sliding pipe 103 Combustion chamber 104 Gap 105 Iron dust preheating bucket 106 Switching valve 107 Switching valve 108 Switching valve 109 Dust collector 110 Gas cooler chamber 111 Blower

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[Procedure amendment]

[Submission date] March 2, 1994

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Dioxin generation preventing method and dioxin generation preventing device in iron scrap melting furnace and preheating device thereof

Claims (4)

[Claims] 1. To prevent generation of dioxin by introducing exhaust gas discharged from an iron scrap melting furnace (electric furnace) into a combustion tower and burning it at a high temperature, and by eliminating carbon monoxide in the exhaust gas with this combustion. A method for preventing generation of dioxin in an iron scrap melting furnace (electric furnace) and its preheating device, characterized by the above. 2. A method for preventing dioxin generation in an iron scrap melting furnace (electric furnace) and its preheating apparatus according to claim 1, wherein a vortex flow / turbulent flow is generated in the combustion tower to completely burn the exhaust gas. 3. An iron scrap melting furnace (electric furnace), comprising an iron scrap melting furnace (electric furnace) and a combustion tower for burning exhaust gas discharged from the iron scrap melting furnace (electric furnace) at a high temperature. ) And a dioxin prevention device for the preheating device. 4. An ignition burner is installed in the combustion tower, a first air blowing section for generating a vortex is installed above the ignition burner, and a second air blowing section for generating a turbulent flow is installed below the ignition burner. The dioxin generation preventing device in the iron scrap melting furnace (electric furnace) and its preheating device according to claim 3.