JP3461090B2 - Preheating method for chlorine-containing scrap iron - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preheating scrap iron containing chlorine, which suppresses the generation of environmentally harmful aromatic organic chlorine compounds in a melting furnace, particularly in an electric furnace.

[0002]

BACKGROUND ART Conventionally, scrap iron (iron scrap) is mainly used in electric furnaces,
Others are remelted in converters and recycled. At this time, in the electric furnace, in order to reduce the consumption of the melting power, it is usual to preheat the scrap iron with the high-temperature exhaust gas generated in the electric furnace and charge the scrap iron into the electric furnace.

FIG. 4 shows an example of recent electric furnace equipment. The exhaust gas from the electric furnace 100 is attracted by the exhaust fan 106, and the CO in the exhaust gas is burned by the air supplied from the air blowing port 116 in the combustion tower 102 to become a high temperature (600 to 800 ° C.) exhaust gas. The scrap iron charged into the electric furnace is preheated in the preheating furnace 103 by the high-temperature exhaust gas in advance and then charged into the electric furnace.

On the other hand, the exhaust gas from the preheating furnace is 200 to 40
Cooled to 0 ° C, gas cooler 105, exhaust fan 10
6. It passes through the bag filter 107 and is discharged to the atmosphere. In some cases, the exhaust gas of the electric furnace may be combined with the exhaust gas of the building dust collecting system around the electric furnace and dust may be removed by the dust collector 107.

When the scrap iron is melted or preheated in the scrap iron melting furnace or the preheating furnace, oils, paints, plastics, etc. are usually attached to the scrap iron. Hydrocarbon compounds are generated by thermal decomposition. At this time, these deposits usually contain chlorine, and therefore, a trace amount of toxic aromatic organic chlorine compounds is also generated.

The aromatic organochlorine compounds include chlorobenzenes (CBs), chlorophenols (CPs) and polychlorobiphenyls (PCBs) which are not desirable for the human body.
) Or an extremely small amount, but generally called dioxins, polychlorodibenzoparadioxins (PCDD
s) and polychlorodibenzofurans (PCDFs)
Is included.

When the scrap iron deposit contains a large amount of cutting oil or grinding oil to which an organochlorine compound is added, or an organochlorine compound such as vinyl chloride, chlorine gas is generated during the pyrolysis process of the deposit. It is known that a large amount of Cl ₂ and hydrogen chloride HCl are generated, and therefore the generation concentration of aromatic organic chlorine compounds tends to be high.

When the exhaust gas temperature is 800 ° C. or higher,
Under the condition of staying for a second or more and oxygen concentration of 5 vol% or more, these aromatic organochlorine compounds are completely burned to cause low molecular hydrocarbons or carbon dioxide (CO
₂ ) and water (H ₂ O) once decomposed.

However, in the process of cooling the exhaust gas,
When the oxygen concentration in the exhaust gas is 2 vol% or more,
Due to the catalytic action of heavy metals such as Cu and Fe in the dust contained in the exhaust gas, chlorobenzenes (CBs) and chlorophenols (CPs) are contained in the exhaust gas in the temperature range of 250 to 500 ° C, particularly 300 to 350 ° C. )
It is known that re-synthesis reaction of polychlorobiphenyls (PCBs), polychlorodibenzoparadioxins (PCDDs), polychlorodibenzofurans (PCDFs) and the like actively occurs.

The aromatic organochlorine compounds thus produced, particularly polychlorodibenzodioxins and polychlorodibenzofurans, are cooled to 200 ° C. or lower, preferably 100 ° C. or lower in the course of cooling the exhaust gas after the preheating furnace to form dust. Most of the exhaust gas can be removed by adsorbing it and collecting dust with a bag filter. However, these substances are present in the collected dust. Therefore, in the conventional scrap iron melting furnace, there is a potential problem that aromatic organic chlorine compounds and the like, which are unfavorable to the environment, are released to the environment while being adsorbed in the dust.

In view of this, in Japanese Unexamined Patent Publication No. 6-117780, a combustion device and a holding chamber for thermal decomposition are provided at the latter stage of the preheating furnace of an electric furnace to quench exhaust gas, pass through a bag filter, and dissipate into the atmosphere. A method is disclosed (prior art 1). Further, Japanese Patent Application Laid-Open No. 7-207328 discloses a method of blowing carbon material into a carbon material when the scrap is melted in the upper-bottom blowing converter and absorbing the gas containing the generated organic chlorine compound in the carbon material. Technology 2).

[0012]

In the above-mentioned prior art 1,
Aromatic organic chlorine compounds in the exhaust gas generated in the melting furnace or the preheating furnace are decomposed in the high temperature combustion device or the holding chamber, but they may be synthesized again in the exhaust gas cooling process,
Therefore, the exhaust gas is rapidly cooled in a cooling tower. At this time, the remaining aromatic organic chlorine compound is adsorbed by the dust, so the dust is captured by the bag filter. Therefore, as mentioned above, a combustion furnace and a holding chamber are required, and the equipment is complicated.

Further, in the prior art 2, although iron scrap is melted in the upper-bottom blowing converter, the converter is not a versatile equipment as a scrap iron melting furnace, and the technology cannot be applied to an electric furnace. There is a problem. Furthermore, in any case, dust with an aromatic organochlorine compound attached thereto is discharged, which is environmentally unfavorable.

Therefore, in the present invention, the generation itself of the aromatic organochlorine compound in the melting furnace, particularly the electric furnace and the preheating furnace attached thereto is effectively suppressed, and the exhaust gas emitted into the atmosphere and the dust discharged. The purpose is to reduce the concentration of aromatic organic chlorine compounds in the product to the extent that it does not pollute the environment.

[0015]

As a result of intensive studies on the above problems, the present inventors have found that the oxygen concentration in the exhaust gas from the electric furnace etc. is such that the aromatic organic chlorine compounds, especially chlorophenols (CPs), poly The inventors have found that there is a certain relation with the generation of oxygen-containing aromatic organochlorine compounds such as chlorodibenzoparadioxins (PCDDs) and polychlorodibenzofurans (PCDFs), and have made the following inventions.

A first aspect of the present invention is a method for preheating the scrap iron by introducing exhaust gas from a melting furnace for melting scrap iron into the scrap iron preheating device, wherein a predetermined amount of carbon material is mixed with the scrap iron containing scrap iron in the scrap iron preheating device. When preheating the scrap iron, the oxygen concentration in the exhaust gas of the preheating device is set to 2 vol% or less, which is a method of preheating chlorine-containing scrap iron.

Conventionally, in the melting or preheating of scrap iron, it is not possible to completely suppress the generation of aromatic organochlorine compounds due to the combustion of attached organic matter. However, according to the research conducted by the inventors, when scrap iron is heated with exhaust gas having an oxygen concentration of 2 vol% or less in the exhaust gas, an aromatic organic chlorine compound, particularly an oxygen-containing aromatic organic chlorine compound is produced as described later. Is suppressed.

The reason for this is that chlorophenols, polychlorodibenzoparadioxins and polychlorodibenzofurans contain oxygen atoms in their molecular structures, so that when oxygen gas is not present in the exhaust gas, these This is because the synthesis of the aromatic organochlorine compound containing oxygen is suppressed. Therefore, in order to keep the concentration of oxygen gas in the exhaust gas at 2 vol% or less, the carbon material is mixed when the scrap iron is preheated. Here, the melting furnace is usually an arc heating electric furnace, but the present invention can be applied to, for example, a converter as well as this electric furnace.

A second aspect of the present invention is the preheating of waste iron containing chlorine according to the first aspect of the present invention, characterized in that a predetermined amount of an alkaline agent is mixed and charged into the waste iron preheating device together with the carbon material to preheat the waste iron. Is the way. When a predetermined amount of an alkali agent is mixed and charged together with the carbonaceous material, chlorine gas and hydrogen chloride generated during the dissolution or preheating of scrap iron can be neutralized and the generation of aromatic organic chlorine compounds can be further suppressed.

In a third aspect based on the above aspect, the carbonaceous material is coke, coal, activated carbon or a mixture thereof, and the particle size of these is 50 μm to 10 mm.
It is a preheating method for chlorine-containing scrap iron, characterized in that Carbon materials such as coke, coal, and activated carbon can be obtained relatively easily, and when the particle size is 50 μm to 10 mm so that the organic chlorine compound is easily adsorbed, the aromatic organic chlorine compound in the exhaust gas can be surely reduced.

A fourth invention is characterized in that the above-mentioned alkaline agent is any one of slaked lime, quicklime, limestone, magnesium hydroxide, sodium hydroxide, magnesium carbonate having a particle size of 10 μm to 1 mm, or a mixture thereof. This is a preheating method for chlorine-containing scrap iron. Slaked lime, quick lime, limestone and magnesium hydroxide, sodium hydroxide, magnesium carbonate are readily available alkaline agents,
By setting the particle size within the above range, chlorine gas and the like in the exhaust gas can be efficiently neutralized, and the generation of aromatic organic chlorine compounds can be further suppressed.

A fifth invention is the above invention, wherein the carbon material and / or the alkaline agent is added in an amount of 0.1 per 1 ton of scrap iron.
It is a method for preheating chlorine-containing scrap iron, which is characterized by mixing and loading 10 kg. Although the amount of various organic compounds contained in scrap iron cannot be specified, it is empirical that carbon materials and / or
Or 0.1-10 kg of alkaline agent per 1 ton of scrap iron
By mixing and charging, the total value of aromatic organic chlorine compounds, such as PCDDs and PCDFs, in the exhaust gas is 3
It can be reduced to 0 ng / Nm ³ or less.

In a sixth aspect of the present invention, there is provided the chlorine-containing waste iron according to the above invention, characterized in that a cooling gas is introduced in the vicinity of the exhaust gas outlet of the waste iron preheating device and the exhaust gas temperature in the vicinity of the exhaust gas outlet is set to 100 ° C. or less. It is a preheating method.
Normally, the gas temperature near the exhaust gas outlet of the scrap iron preheating device is 20
Although it is about 0 to 400 ° C., when cooling gas such as air is introduced and the exhaust gas temperature in the vicinity of the exhaust gas outlet is set to 100 ° C. or less, the aromatic organic chlorine compound is regenerated even if the exhaust gas contains an organic compound. It is never synthesized.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION When an organic compound is burned, carbon dioxide (CO ₂ ) and water (H ₂ O) are used depending on the burning method.
It is difficult to completely decompose it, and generation of hydrocarbon occurs. At this time, if chlorine is present in the organic compound,
A slight amount is accompanied by the generation of aromatic organic chlorine compounds. Furthermore, even if a small amount of chlorine is contained in the organic compound,
Trace amounts of polychlorodibenzoparadioxins and polychlorodibenzofurans are generated.

It has been confirmed that hydrogen chloride is generated not only from the organic chlorine in the organic compound adhering to scrap iron, but also from the inorganic chlorine such as salt (NaCl), which serves as the chlorine source of the organic chlorine compound. It has been known.

Since it is impossible to completely remove the chlorine adhering to the scrap iron, it is impossible to completely suppress the generation of the aromatic organochlorine compound by burning the organic matter adhering to the scrap iron. However, studies by the inventors have found that when scrap iron is heated in an oxygen-free atmosphere, the production of aromatic organochlorine compounds, particularly aromatic organochlorine compounds containing oxygen, is suppressed.
Below, the experiment which acquired the said knowledge is described.

50 kg (size 20-50 mm) of automobile shredder scraps 3 are loaded into an induction heating furnace 2 shown in FIG.
Heat to various temperatures in between. From the introduction pipe at the bottom of the heating device, a gas of CO ₂ : 15 vol% and N ₂ : 85 vol% to which 0 to 20 vol% of oxygen gas (O ₂ ) was further added was introduced as an introduction gas 6, and the inside of the device was charged. Was exhausted by the exhaust fan 10 and the exhausted gas was analyzed. The heating time was about 30 minutes, during which gas sampling was continuously performed, and the exhaust gas composition as an average value during that period was determined.

In FIG. 2, in the state of being heated to 800 ° C.,
Oxygen concentration in exhaust gas and aromatic organic chlorine compounds (PCDD
s + PCDFs, CPs, CBs).
From this figure, it is clear that when the oxygen concentration in the exhaust gas exceeds about 2 vol%, the amount of the aromatic organochlorine compound increases. Therefore, in the preheating of scrap iron, the oxygen concentration is set to 2
It has been found that it is important to keep it to be not more than vol%.

Further, as a result of an experiment in which the temperature and the oxygen concentration were variously changed, FIG. 3 was obtained. This figure shows the following results. At about 900 ° C or higher, the aromatic organic chlorine compound is almost decomposed regardless of the oxygen concentration. In the range of 200 to 900 ° C, the oxygen concentration is about 2 vol.
When it is more than 0.1%, re-synthesis or decomposition re-synthesis of the aromatic organochlorine compound occurs and the exhaust gas contains the aromatic organochlorine compound. At 200 ° C or lower, no aromatic organic chlorine compound is generated. That is, it means that the organic compound contained in the scrap iron is not decomposed, and further, even if the aromatic organic compound is contained in the gas, the synthesis of the aromatic organic chlorine compound is not performed.

Therefore, in the scrap iron preheating apparatus in the temperature range of 200 to 900 ° C. , when the oxygen concentration is 2 vol% or less, the aromatic organic chlorine compound containing oxygen is not generated. However, since the exhaust gas of the electric furnace is usually burned in the combustion tower, the exhaust gas introduced into the preheating furnace has an oxygen concentration of 2 vo.
It becomes 1% or less.

Therefore, it is necessary to take measures to reduce the oxygen concentration to 2 vol% or less. Therefore, in the same experimental device as described above, coke powder (particle size 0.5 to 5 m) was used as the carbon material.
m, surface area 20 m ² / g) and / or 100 to 500 g of slaked lime (special grade) and / or slaked lime (special grade) were uniformly mixed with scrap iron to conduct an experiment. In this experiment, the oxygen concentration in the introduced gas was 5 vol% and the temperature was 800 ° C. The results are shown in Table 1. In addition, Table 1
In addition, the results when the carbon material and the alkaline agent are not mixed are shown together.

As a result, CO ₂ : 13 vol%, N ₂ : 8
When scrap iron is preheated at 800 ° C. through an introduced atmosphere gas of ₂ vol%, O ₂ : 5 vol%, when coke lumps and / or slaked lime are added, as compared with the case where these are not added, these aromatic organic chlorine compounds It was found that generation was suppressed. In the experiment, the O ₂ concentration of the introduced gas was 5
Even in vol%, if carbon material is charged, the oxygen in the exhaust gas is consumed by the addition of coke lumps, and 1.5 vol%
It is considered that the oxygen concentration decreased and the generation of oxygen-containing aromatic organic chlorine compounds was suppressed.

Here, the carbon material to be added has a function of consuming oxygen in the exhaust gas, and also a hydrocarbon having an exhaust gas temperature of 200 ° C. or lower, particularly a benzene ring having a boiling point of 200 ° C. or higher and having a benzene ring having a planar structure. It is well known that it has a property of adsorbing a group organic chlorine compound. Therefore, the carbon material added together with the scrap iron adsorbs the aromatic organic chlorine compound generated during preheating. For this reason, the carbon material to be added has a specific surface area of 10 to 1200 in order to enhance the adsorption ability.
It is preferably m ² / g.

For this purpose, lignite coke, activated carbon and the like are suitable in addition to coke. The smaller the particle size, the higher the efficiency of contact with the exhaust gas, but if it is too small, it will be discharged together with the exhaust gas, and there will be no hindrance to the adsorption of aromatic organochlorine compounds, but oxygen in the exhaust gas during preheating can be consumed. Disappear. Therefore, the particle size of the carbon material is 50 μm-1
It is 0 mm, preferably 0.5 to 10 mm. In addition, the addition amount is 0.1-0.1 in consideration of the compatibility with scrap iron.
10 kg / t scrap iron is suitable.

On the other hand, it was found that the addition of slaked lime (Ca (OH) ₂ ) was effective in suppressing the generation of aromatic organic chlorine compounds such as chlorobenzene (CBs) containing chlorine. It is considered that this is because slaked lime neutralized HCl generated from the attached organic chlorine compound by thermal decomposition, and suppressed generation of the aromatic organic chlorine compound. In addition, vinyl chloride is 25
It is well known that it decomposes at 0 to 300 ° C to generate HCl.

In order to neutralize the generated HCl, in addition to slaked lime, limestone (CaCO ₃ ), quick lime (CaO), magnesium hydroxide (Mg (OH) ₂ ), sodium hydroxide (NaOH), and magnesium carbonate ( MgCO ₃ )
Other alkaline agents such as The smaller the diameter of the alkali agent to be added, the more preferable it is from the viewpoint of reactivity, but if it is too fine, it will be entrained in the exhaust gas and scattered, so that it will not be effectively consumed for the neutralization reaction in the preheating furnace. Therefore, the particle size is 10 μm to 1 mm, preferably 100 to 5
00 μm is suitable.

The amount of addition is determined by the chlorine content in the organic matter adhering to the scrap iron, but the chlorine content in the scrap iron is about 0.2 wt% at most, and if all of this becomes HCl, it will be neutralized. The amount of Ca (OH) ₂ required is 4 kg /
It is scrap iron. From this, considering the compatibility with scrap iron, 0.1-10 kg / t scrap iron is suitable for the addition amount of the alkaline agent.

These added carbon materials are charged into a melting furnace together with scrap iron and used effectively as carbon materials. Further, the aromatic organic chlorine compound adsorbed on the carbon material or the alkaline agent becomes high in temperature in the preheating process, and is slightly released from the carbon material or the alkaline agent, but when charged into the melting furnace,
The remaining aromatic organochlorine compound is 120 in the melting furnace.
Since it is heated above 0 ° C, it decomposes almost completely. On the other hand, the added alkaline agent such as lime is effectively used as a basicity adjusting agent for slag in the melting furnace.

Further, from the above-mentioned experiment, a cooling gas such as air is introduced near the exit of the preheating furnace to reduce the exhaust gas to 20
It is also clear that cooling to 0 ° C. or lower can suppress the resynthesis of the aromatic organic chlorine compound in the subsequent stage.

[0040]

[Table 1]

[0041]

As described above, according to the present invention, when the waste iron is preheated by using the high temperature exhaust gas from the scrap iron melting furnace, hydrocarbons and aromatics are burned at the time of burning and pyrolyzing the organic matter adhering to the scrap iron. Suppressing the generation of organochlorine compounds, particularly aromatic organochlorine compounds such as chlorophenols (CPs), chlorobenzenes (CBs), polychlorodibenzoparadioxins (PCDDs) and polychlorodibenzofurans (PCDFs) it can.

That is, a carbon material is added to a scrap iron preheating furnace so that the oxygen concentration in the exhaust gas is 2 vol% or less, and further, HCl and Cl ₂ generated from the chlorine content adhering to the scrap iron by an alkaline agent such as lime. The neutralization has an effect of suppressing the generation of the above aromatic organic chlorine compound.

In addition, by heat exchange with scrap iron,
While recovering heat from the high-temperature exhaust gas to scrap iron, the temperature of the exhaust gas has dropped, and by adsorbing hydrocarbons and aromatic organic chlorine compounds on the added carbon material,
By suppressing the discharge of these compounds to the latter stage of the preheating furnace and adsorbing them to the collected dust in the dust collector installed in the final stage, the amount of these aromatic organic chlorine compounds was thoroughly checked. There is an effect of reducing. Therefore, the amount of dust collected in the environment can be suppressed as low as possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an experimental device for basic experiments for the present invention.

FIG. 2 is a diagram showing a relationship between oxygen concentration in exhaust gas and aromatic organic chlorine compound concentration.

FIG. 3 is a diagram showing a state of generation of an aromatic organochlorine compound in relation to a temperature of exhaust gas and an oxygen concentration.

FIG. 4 is a diagram showing a preheating and exhaust gas treatment device in a conventional scrap iron melting furnace.

[Explanation of symbols]

2 induction heating furnace 3 shredder waste 4 gas introduction pipes 6 Introduced gas 8 piping 10 exhaust fan 100 electric furnace 102 combustion tower 103 Preheating furnace 105 gas cooler 106 exhaust system 107 Dust collector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F27D 17/00 101 F27D 17/00 101G 104 104D (56) Reference JP-A-10-8118 (JP, A) JP-A-8 -42980 (JP, A) JP-A-6-109367 (JP, A) JP-A-8-269527 (JP, A) JP-A-7-146082 (JP, A) (58) Fields investigated (Int.Cl) . ^7, DB name) C21C 5/52 ZAB C21C 5/28 C22B 1/00 C22B 9/16 F27D 13/00 F27D 17/00 101 F27D 17/00 104

Claims (4)

(57) [Claims] 1. A method of preheating waste iron by introducing exhaust gas from a melting furnace for melting scrap iron into a scrap iron preheating device, wherein the scrap iron preheating device together with chlorine-containing scrap iron, coke.
Any one selected from coal, activated carbon,
Alternatively, it is a mixture of two or more kinds, and the particle size of these is 50 μm.
When mixing a predetermined amount of carbon material of m to 10 mm to preheat the scrap iron, the oxygen concentration in the exhaust gas of the preheating device is set to 2 vol.
% Or less, a method for preheating chlorine-containing scrap iron. 2. The scrap iron preheating device together with the carbon material,
Slaked lime, quick lime, limestone, magnesium hydroxide, hydroxide
Choose from sodium and magnesium carbonate
Either one or a mixture of two or more of these,
The method for preheating waste iron containing chlorine according to claim 1, wherein a predetermined amount of an alkaline agent having a particle diameter of 10 μm to 1 mm is mixed and charged to preheat the scrap iron. 3. Preheating of chlorine-containing waste iron according to claim 1 or 2, wherein the carbon material and / or the alkaline agent are mixed and charged in an amount of 0.1 to 10 kg per ton of the waste iron. Method. 4. The cooling gas is introduced in the vicinity of the exhaust gas outlet of the scrap iron preheating device, and the exhaust gas temperature in the vicinity of the exhaust gas outlet is set to 200 ° C. or lower.
The method for preheating chlorine-containing scrap iron according to any one of 1.