JPH07146082A - Exhaust gas treating method for electric furnace - Google Patents

Abstract

PURPOSE:To fix chlorine, etc., generated at the time of preheating as chloride and to reduce generation of organic chlorine compound itself by adding salt of at least one type of element selected from alkalis to scrap when the scrap is preheated by exhaust gas of an electric furnace. CONSTITUTION:Exhaust gas from an electric furnace 1 is guided to a burnings tower 2 to burn unburnt components. In this case, since the gas has a high temperature and large energy, it is partly passed through a plurality of scrap preheaters 3 to preheat shredder scraps of a waste vehicle. The gas is sucked to a main blower 7, guided to a plurality of spraying towers 8 and cooled. Then, the gas is passed through a bag dust collector 9 to remove dusts and condensed organic components. In this case, salt of at least one element selected from alkalis and alkaline earth elements is added in the preheater 3. Thus, chlorine, etc., generated when vinyl chloride in the scrap is thermally decomposed is fixed as chloride.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric furnace exhaust gas treatment method, and more particularly to an exhaust gas treatment method capable of reducing the emission of organochlorine compounds out of the system when preheating scrap with exhaust gas.

[0002]

2. Description of the Related Art Exhaust gas generated from an electric furnace when a steelmaking raw material is charged into the electric furnace to be melted and refined is passed through a combustion tower to completely burn organic compounds and detoxify them. After that, it is cooled, dust-collected, etc., and discharged to the outside of the system. However, in order to partially recover the thermal energy of the high-temperature exhaust gas of the electric furnace, when the exhaust gas after passing through the combustion tower is passed through the scrap preheater, the vinyl chloride and extreme pressure additives contained in the scrap are There is a risk that processing oils and the like containing will come into contact with the exhaust gas and produce incompletely combusted organic chlorine compounds, and such organic compounds should be collected even if they occur. In a conventional electric furnace having a scrap preheating device, a method is adopted in which the temperature of the exhaust gas after passing through the scrap preheating device is lowered as much as possible, and is captured together with dust by a bag filter.

[0003]

Conventionally, it can be said that the generation of the organic chlorine compound in the scrap preheating device is allowed and the trapping efficiency after the generation is improved. However, when a large amount of dust containing vinyl chloride and processing oil containing extreme pressure additives are present in the raw material scrap, the generation of organochlorine compounds in the scrap preheating device will increase accordingly, and only the capture efficiency will be improved. May not be able to deal with it. An object of the present invention is to provide an electric furnace exhaust gas treatment method capable of reducing the generation itself of organic chlorine compounds in a scrap preheating device.

[0004]

In order to achieve the above object, an electric furnace exhaust gas treatment method according to the present invention comprises the following methods. At least a part of the exhaust gas from the electric furnace is passed through a scrap preheating device, then the exhaust gas is passed through a spray cooling tower, and then the exhaust gas is passed through a bag dust collector, in the scrap preheating device, alkali and alkaline earth An electric furnace exhaust gas treatment method, wherein a salt of at least one element selected from the group is added, and then the exhaust gas from the electric furnace is passed through the scrap preheating device.

[0005]

In the above method of the present invention, in the scrap preheating device, the processing oil containing vinyl chloride and the extreme pressure additive contained in the scrap is thermally decomposed by touching the high temperature exhaust gas from the electric furnace. Occasionally, chlorine is produced, but the chlorine chemically reacts with the added salt of alkali or alkaline earth to be fixed as chloride of alkali or alkaline earth, and is immobilized, and formation of organic chlorine compound is suppressed. Also, there is no problem in discharging organic chlorine compounds out of the system.

[0006]

EXAMPLE FIG. 1 shows an exhaust gas treatment apparatus for an electric furnace. A combustion tower 2 is connected to the electric furnace 1, and a parallel path of a scrap preheating device 3 and a gas cooler 4 is connected to the combustion tower 2. A blower 5 is provided downstream of the scrap preheating device 3. The parallel paths merge again, and the dust settling tower 6 is connected to the merged path. The settling tower 6 is connected to a main blower 7, and the main blower 7 is connected to a spray cooling tower 8. A bypass path is provided for the spray cooling tower 8. The path passing through the spray cooling tower 8 and the bypass path join again, and the bag dust collector 9 is connected to this joining path.

The exhaust gas from the electric furnace 1 is guided to the combustion tower 2 and the unburned components are completely burned. Since the exhaust gas has a large amount of heat energy at a high temperature, at least a part of the exhaust gas is passed through the scrap preheating device 3 in order to be used for preheating the scrap put into the electric furnace 1. Among the scraps, there is a machining oil such as a cutting oil containing vinyl chloride (a covering material for electric wires, etc.) and an extreme pressure additive from the shredder, like shredder scrap of an abandoned automobile. These are decomposed by the heat of exhaust gas to produce chlorine, usually in the form of HCl (hydrogen chloride) vapor. The exhaust gas passed through the scrap preheating device 3 preheats the scrap, and the temperature of the scrap itself is lowered by the scrap. The temperature of the exhaust gas passed through the gas cooler 4 side can be reduced by the gas cooler 4. Since the exhaust gas still contains a large amount of dust, the dust is separated from the gas and settled by utilizing the difference in specific gravity in the dust settling tower. Exhaust gas is further main blower 7
And is sent to a spray tower 8 where a water spray is applied to the exhaust gas to wash the exhaust gas and reduce the exhaust gas temperature. Organic components in exhaust gas are condensed and washed, or are adsorbed by dust and removed. Finally, the exhaust gas is passed through a bag dust collector 9 to remove remaining dust and condensed organic components by a bag filter, and then released to the atmosphere.

In the above, when the scrap preheating device 3 is opened and the steelmaking scrap is fed into the scrap preheating device 3, at least one or more elements selected from alkali and alkaline earth are contained in the scrap preheating device 3. Salt 10 is added. Then, the lid is closed and the exhaust gas from the electric furnace 1 is passed through the scrap preheating device 3.

Of the above, the alkali elements include, for example, Na and K, and the salts thereof are, for example, Na ₂ CO.
₃ , K ₂ CO _3, etc. Examples of alkaline earth elements include Ca and Mg, and salts thereof include CaO, Ca (OH) ₂ , CaCO ₃ , MgO and Mg.
(OH) ₂ , MgCO ₃ and the like. The salt addition method may be any of a method of mixing in scrap, a method of spreading the scrap under the preheating device, a method of spreading the scrap so as to cover the upper portion, and a method of alternately charging scrap and salt.

When chlorine is generated in the scrap through the exhaust gas as described above and floats in the form of Cl ₂ and HCl, these chlorine and hydrogen chloride react with the salts of the alkali, alkaline earth and the additives, NaCl, CaCl ₂ , MgC
It produces chloride with high stability such as l ₂ and immobilizes the chlorine component. Therefore, it is possible to prevent the chlorine component in the gas from recombining with the organic component to form an organic chlorine compound. That is, the chlorine component is more
Attempts to form a chlorine compound by chemically reacting with an alkali salt or an alkaline earth salt, so that the production of an organic chlorine compound is suppressed to that extent. Therefore, the amount of the organic chlorine compound discharged outside the system through the bag dust collector 9 also decreases.

The confirmation test of the immobilization of the chlorine component was carried out in each of the test by the desktop device in FIG. 2 and the test by the actual device in FIG. In the desk test of the apparatus of FIG. 2, the mixture shown in Table 1 of vinyl chloride (predetermined chlorine equivalent) and the immobilizing agent was put in a heatable tubular furnace 11 and various heating temperatures and mixing were changed. The test was conducted, and the exhaust gas from the tubular furnace 11 was sucked by the pump 12. The amount of chlorine fixed by the fixing agent was determined by taking out the mixture in the tubular furnace 11, dissolving it in water, and analyzing the components. Since it exists in the form of salt, it can be dissolved in water to measure the amount of residual soluble chlorine. On the other hand, the amount of volatile chlorine (present in the form of hydrogen chloride) that was not fixed by the fixing agent was set in the absorption bottle 13 in the path between the tubular furnace 11 and the pump 12 to capture hydrogen chloride. Since hydrogen chloride is easily dissolved in water, water is put in the absorption bottle 13 and the exhaust gas from the tubular furnace 11 is passed through it to analyze the hydrogen chloride-absorbed water or measure its PH to capture chlorine. The quantity was measured. The results are shown in Table 1.

[0012]

[Table 1]

It can be seen from Table 1 that the thermal decomposition of vinyl chloride is maximized at around 600 ° C, and 80% or more can be fixed around 600 ° C by the reaction with the salt of alkaline earth. In addition, alkaline earth salts are more effective than chlorine salts in fixing chlorine. Further, the more immobilization agent, the more the immobilization of chlorine is promoted.

In the actual machine test by the apparatus shown in FIG. 1, the scrap preheater is 50-2 for 70 tons of scrap.
00 Kg of Ca (OH) ₂ was added and operation was carried out. As a result of measuring chlorophenol and chlorobenzene immediately before the bag filter, the amount of scavenged chlorine was reduced to 1/10 or less as compared with the case where Ca (OH) ₂ was not added. Therefore, it was found that the amount of discharged chlorine was 1/10 or less.

[0015]

According to the present invention, a salt of at least one element selected from alkali and alkaline earth elements is added to the scrap preheating device so that the exhaust gas can pass therethrough. Chlorine and hydrogen chloride generated when vinyl chloride, etc. in scrap is thermally decomposed can be fixed as chloride by reacting with the above salts, suppressing the generation of organic chlorine compounds in the scrap preheater. It is possible to suppress the discharge to the outside of the system.

[Brief description of drawings]

FIG. 1 is a system diagram of an exhaust gas treatment device of an electric furnace.

FIG. 2 is a systematic diagram of an apparatus for carrying out a desk test of the method of the present invention.

[Explanation of symbols]

 1 Electric furnace 3 Scrap preheater

Claims (1)

[Claims] 1. An electric furnace exhaust gas treatment method in which at least a part of exhaust gas from an electric furnace is passed through a scrap preheater, then the exhaust gas is passed through a spray cooling tower, and then the exhaust gas is passed through a bag dust collector, in the scrap preheater. ,
An electric furnace exhaust gas treatment method comprising adding a salt of at least one element selected from alkali and alkaline earth and then passing the exhaust gas from the electric furnace through the scrap preheating device.