JPH1157361A - Waste gas treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the emission of harmful materials in the air by adsorbing the harmful materials such as dioxin contained in waste gas from an electric melting furnace at high efficiency. SOLUTION: The harmful materials such as dioxin contained in the waste gas is adsorbed on activated carbon by providing a mixing column 16 in the midway of a duct 26 through which the waste gas discharged from the electric melting furnace 1 is introduced into a bag filter 17 and blowing the fine powdery activated carbon into the mixing column in the tangential direction of the outer periphery of the mixing column to rotate the waste gas in the mixing column.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents the discharge of harmful substances such as dioxin from exhaust gas from electric melting furnaces such as arc furnaces and waste incinerators in steel mills and waste melting facilities. The present invention relates to an exhaust gas treatment method.

[0002]

2. Description of the Related Art For example, in a steel mill equipped with an arc furnace, a direct exhaust system for directly sucking exhaust gas generated during the melting period from the furnace and guiding the dust to a bag filter dust collector to collect dust, and a scrap mounting device. 2. Description of the Related Art A building exhaust system has conventionally been provided in which exhaust gas discharged from the arc furnace into the building at the time of entering or tapping steel is sucked from a ceiling hood and led to a baghouse type dust collector. Since the exhaust gas of the direct exhaust system sucked directly from the furnace has a high temperature, the exhaust gas is cooled through a cooling tower and then collected through a bag filter to collect dust.

[0003]

However, in the above-mentioned conventional dust collecting apparatus, dioxin (generic term for isomers such as polychlorinated dibenzoparadioxin and polychlorinated dibenzofuran) which is a toxic chlorine compound contained in exhaust gas, There is a problem that harmful substances such as heavy metals cannot be sufficiently collected. Therefore, development of a technique for improving the removal efficiency has been awaited.

[0004]

SUMMARY OF THE INVENTION The exhaust gas treatment method of the present invention is to solve the above-mentioned problem. A mixing tower is provided in the middle of a duct for guiding exhaust gas containing dioxin to a bag filter, and fine powdered activated carbon is produced. By blowing into the mixing tower from the tangential direction of the outer periphery of the mixing tower and swirling the exhaust gas in the mixing tower, harmful substances such as dioxin contained in the exhaust gas are adsorbed on the activated carbon. Features. Further, in the exhaust gas treatment method of the present invention, fine powdered activated carbon is blown from a tangential direction of an outer periphery into a duct for guiding an exhaust gas containing dioxin to a bag filter, and harmful substances such as dioxin contained in the exhaust gas are removed from the activated carbon. It is characterized in that it is made to adsorb. Further, the present invention is characterized in that, in the above-mentioned exhaust gas treatment method, slaked lime is blown into the exhaust gas at least upstream from the blowing position of the activated carbon.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to FIG. 1 with respect to an arc type electric melting furnace for melting iron scrap. In the figure, reference numeral 1 denotes an arc type electric melting furnace in which an electrode 3 is suspended in a furnace body, 10 denotes an exhaust gas outlet from which exhaust gas generated in the electric melting furnace 1 is discharged, and 11 denotes an upper part of the electric melting furnace 1. It is a ceiling hood provided on the ceiling of the building. The exhaust gas outlet 10 is provided with a combustion tower 13, a cooling tower 14, a bag filter 15, a mixing tower 16, a bag filter 17, and a booster blower 18 in this order from the upstream, and a blower 19 through a duct 5 to the ceiling hood 11, and A bag filter 20 is provided downstream thereof.

[0006] The combustion tower 13 burns and decomposes unburned components such as CO in the exhaust gas while the exhaust gas discharged from the electric melting furnace 1 flows downward. 6 injects slaked lime powder into the combustion tower 13 to remove HCl in the exhaust gas.
A slaked lime charging device provided to neutralize lime, wherein the charging device 6 includes a hopper 7 in which powdered slaked lime is stored,
The blower 8 includes a blower 8 and a charging throat 9. The slaked lime in the hopper 7 is pressure-fed to the charging throat 9 by the blower 8 and can be blown into the combustion tower 13. By blowing slaked lime in this way, HCl, which is a precursor of dioxin, is reduced, and the concentration of generated dioxin can be reduced. The cooling tower 14 has a built-in radiator through which cooling water flows, and cools the temperature of the exhaust gas to 250 ° C. or lower, which is the heat-resistant temperature of the bag filter.

The bag filter 15 includes a plurality of bag houses 2.
5 and collects dust contained in the exhaust gas and removes dust adhering to the bag filter.
To be discharged. In addition, bag filter 17
Similarly, a plurality of bag houses 28 are configured to collect dust in exhaust gas, remove dust adhering to the bag filter, and discharge the dust to the dust transport conveyor 30.

The mixing tower 16 has a spiral guide vane 41 disposed inside a vertically suspended cylindrical tower body 40.
As shown in FIG.
An inflow port 42 is formed so that 6 are continuous. 43,
Reference numeral 44 denotes an activated carbon injection port provided on the outer periphery of the tower main body 40. The injection ports 43 and 44 are provided in the tangential direction similarly to the inlet 42. Reference numeral 45 denotes an outlet formed in the lower part of the tower main body 40, and reference numeral 46 denotes an outlet provided for discharging dust settled in the tower main body 40.

Further, numeral 47 denotes a duct 2 as shown in FIG.
An activated carbon injection device 50 comprising a blower 49 and a hopper 48 in which powdered activated carbon is stored in the blowing port 47 and the blowing ports 43 and 44 is an activated carbon blowing port provided so as to be connected in a tangential direction on the outer periphery of 6. Each is provided. Then, the activated carbon in the hopper 48 is pressure-fed to each of the blowing ports by the blower 49, and the activated carbon is blown into the duct 26 and the tower body 40 from each of the blowing ports. The addition amount of the activated carbon is, for example, 100 to 500 mg per 1 Nm ^{3 of} exhaust gas.

The activated carbon blown from the blow-in port 47 is swirled together with the exhaust gas in the duct 26 as shown in FIG. The activated carbon blown from the blowing ports 43 and 44 is supplied to the mixing tower 16 by the force at the time of blowing.
Inside, it descends while turning along with the exhaust gas along the guide vane 41. Therefore, the contact efficiency with the exhaust gas is good, and the adsorption efficiency of harmful substances such as dioxins and heavy metals in the exhaust gas is significantly improved. The activated carbon thus adsorbing the harmful substance can be collected by the bag filter 17.

A booster blower 18 is provided on the downstream side of the bag filter 17, and a flow path switching damper 34 is provided on the downstream side of the blower 18. One side of the downstream side of the damper is connected to a duct 5 of a building exhaust system. Is connected to the upstream side of the blower 19, and the exhaust gas is combined with the house exhaust system, and the other is connected to an exhaust duct 35 connected to a chimney (not shown).

The bag filter 20 includes a plurality of bag houses 3.
6 that collects dust in the exhaust gas and removes dust adhering to the bag filter.
7. The purified exhaust gas is discharged from the upper part of the bag filter 20 into the atmosphere.

Therefore, the exhaust gas of 800 to 1200 ° C. sucked from the electric melting furnace 1 by the operation of the blower 18 is
After passing through the combustion tower 13, CO combustion and the like, and neutralization of acid gases such as HCl and SO 4 by slaked lime injection, and further cooled to 250 ° C. or lower by passing through the cooling tower 14, the bag filter 15 Fine dust containing dioxins, heavy metals, etc. is collected. Then, the temperature of the exhaust gas downstream of the bag filter 15 becomes 150 ° C. or less.

When activated carbon is blown from the activated carbon charging device 50, harmful substances such as dioxins and heavy metals are adsorbed on the activated carbon, and the activated carbon can be collected by the bag filter 17 downstream thereof. As described above, by adding the activated carbon downstream of the bag filter 15, the amount of the activated carbon to be added can be smaller than that of adding the activated carbon upstream of the bag filter 15. Also, by adding the gas downstream of the bag filter 15, the temperature of the exhaust gas can be sufficiently lowered.
Since the fire filter is trapped by the bag filter 15, there is an advantage that the risk of dust explosion, fire and the like is reduced.

The booster blower 18 is supplied from the bag filter 17.
The exhaust gas discharged through the exhaust pipe 35 can be directly discharged to the atmosphere through an exhaust duct 35,
By switching the exhaust gas to the exhaust gas from the building exhaust system, the concentration can be greatly reduced, and at the same time, the temperature can be reduced to 60%.
Since the temperature drops to about ° C., the solidification of harmful substances such as dioxin further proceeds, and this can be reliably collected by the bag filter 20.

[0016]

As described above, in the method for treating exhaust gas of the electric melting furnace according to the present invention, the contact efficiency between the exhaust gas and the activated carbon is improved by turning the activated carbon together with the exhaust gas in the duct or the mixing tower. In addition, harmful substances such as dioxin contained in exhaust gas can be adsorbed with high efficiency, and air pollution can be prevented. In addition, the addition of slaked lime to neutralize the exhaust gas has a beneficial effect, such as suppressing the generation of chlorine compounds.

[Brief description of the drawings]

FIG. 1 is an exhaust gas system diagram showing an embodiment of an exhaust gas treatment method for an electric melting furnace according to the present invention.

FIG. 2 is a cross-sectional view of the mixing tower shown in FIG.

FIG. 3 is a cross-sectional view of the duct shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric melting furnace 6 Slaked lime injection device 10 Exhaust gas outlet 13 Combustion tower 14 Cooling tower 15 Bag filter 16 Mixing tower 17 Bag filter 20 Bag filter 26 Duct 41 Guide vane 42 Inflow port 43,44 Activated carbon injection port 47 Activated carbon injection port 50 Activated carbon injection apparatus

Claims (3)

[Claims] A mixing tower is provided in the middle of a duct for guiding exhaust gas containing dioxin to a bag filter, and fine powdered activated carbon is blown into the mixing tower from a tangential direction of the outer periphery of the mixing tower. A method for treating exhaust gas, characterized in that harmful substances such as dioxin contained in the exhaust gas are adsorbed on the activated carbon by swirling. 2. A method of introducing fine powdered activated carbon into a duct for guiding dioxin-containing exhaust gas to a bag filter from a tangential direction of an outer periphery thereof to adsorb harmful substances such as dioxin contained in the exhaust gas to the activated carbon. An exhaust gas treatment method, characterized in that: 3. The exhaust gas treatment method according to claim 1, wherein slaked lime is blown into the exhaust gas at least upstream of the activated carbon blowing position.