JPH11179131A - Method and apparatus for treating waste gas from electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat dioxins of a waste gas of an electric furnace by simple process while saving energy without requiring a secondary combustion apparatus for the waste gas nor leaking the waste gas out of the treatment system. SOLUTION: This method includes processes of leading a waste gas to a combustion chamber 2 and/or a duct to burn unburned gas components in the combustion chamber or the like, cooling the resultant high temperature waste gas 4a emitted out of the chamber by a cooling apparatus, and purifying the obtained gas by a dust collecting apparatus 12. In this case, if the temperature of the waste gas emitted out of the combustion chamber is 800 deg.C or higher, the waste gas is cooled by the cooling apparatus and then purification treatment is carried out by the dust collecting apparatus. On the other hand, if the temperature of the waste gas is lower than 800 deg.C, the waste gas is recovered in a gas holder 8 and when the temperature of the waste gas emitted out of the combustion chamber is 800 deg.C or higher, together with the waste gas emitted out of an electric furnace, the waste gas recovered in the gas holder 8 is burned in a combustion chamber while the flow rate of the recovered waste gas being so controlled as to keep the temperature of the waste gas emitted out of the combustion chamber at 800 deg.C or higher, and after that, the waste gas kept at 800 deg.C or higher is cooled and purified by a dust collecting apparatus 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for cooling and purifying exhaust gas generated from an electric furnace during the operation of a steelmaking electric furnace facility for producing steel by melting and refining iron scrap and the like. In particular, the present invention relates to a method for suppressing and removing toxic substances such as dioxins contained in the exhaust gas, and to a device for such a method.

[0002]

2. Description of the Related Art In an electric furnace for steelmaking, usually, iron scrap is mainly heated and melted by arc energy or high-frequency energy to perform oxidation refining and reduction refining.
The molten metal is tapped into a ladle, and alloy iron is added to adjust the components of the molten metal to produce molten steel. Thus, in a series of steps of heating and melting iron scrap in a steelmaking electric furnace, refining the resulting molten metal, tapping into a ladle, and discharging the slag, exhaust gas is generated from the electric furnace. . This exhaust gas contains toxic components other than gas components such as CO, CO ₂ , N ₂ , O ₂ , H ₂ and H ₂ O, iron oxide fine powder, and high vapor pressure metal elements such as Zn and Sn. Contains the substance dioxin. The source of dioxin is organic chlorine-based compounds caused by vinyl chloride, plastic paint, etc. attached to and mixed with iron scrap as the main raw material for dissolution.
They are formed when they burn under predetermined conditions. Exhaust gas generated from the electric furnace is cooled by a predetermined device, guided to a dust collector, dust is removed, a cleaning process is performed,
As a result, after the dust content rate and the concentration of harmful substance components in the exhaust gas have fallen below the specified values, they are released to the atmosphere. Therefore, in the operation of an electric furnace for steelmaking, it is desired to operate under conditions that do not generate dioxin.

FIG. 3 shows a schematic flow chart of an example of a conventional exhaust gas treatment apparatus for an electric furnace for steelmaking. In the figure, 1 is an electric furnace for steelmaking, 2 is a combustion chamber, 2 'is a secondary combustion device, 9 is a spray spray cooling tower, and 12 is a dust collector. The high-temperature exhaust gas 1a generated from the electric furnace 1 is led to the combustion chamber 2, where the combustible gas in the exhaust gas is burned and the secondary combustion device 2 'is further burned.
The exhaust gas is heated by a burner or the like, the temperature of the exhaust gas is raised, and dioxin in the exhaust gas is burned and decomposed. Next, the exhaust gas from which dioxin has been removed is passed through a water-cooled duct 3
Indirect cooling through a water spray spray tower 9
And cooled directly.

In this exhaust gas cooling, the temperature of the exhaust gas is rapidly cooled from 350 ° C. or higher to 250 ° C. or lower in order to prevent the resynthesis reaction of dioxin. If the quenching is insufficient, the exhaust gas is contaminated by the resynthesis of dioxin. The temperature of the exhaust gas at the inlet of the bag filter as the dust collector 12 is desirably lowered to 80 ° C. or less, so that dioxin is adsorbed on dust in the exhaust gas, and the dust adsorbed by dioxin is collected by the bag filter. Thus, the exhaust gas 14a from which dioxins and dust have been removed is emitted from the chimney 14 (hereinafter referred to as "prior art 1").

Further, as a technique for preventing the generation of dioxin in the operation of an electric furnace for steelmaking, for example, Japanese Patent No. 2596507 discloses the following method.
For low-temperature exhaust gas generated from an electric furnace during charging and tapping of raw materials, adsorbent is blown into the middle of the duct to adsorb dioxin in the exhaust gas, and exhaust gas containing adsorbent contaminated with dioxin is filtered. To separate the dust (hazardous dust) containing this dirty adsorbent from the exhaust gas,
The harmful dust is collected and blown into the electric furnace again. on the other hand,
For high-temperature exhaust gas generated from an electric furnace during melting and refining, the exhaust gas is burned while supplying energy from the outside to convert the dioxin into detoxified exhaust gas, and this exhaust gas is cooled through a water-cooled duct. The mixture is further cooled by mixing with another cold air containing no dioxin, and the mixture is passed through a filter to separate dust containing no dioxin (hereinafter referred to as "prior art 2").

[0006]

The above prior art has the following problems. According to Prior Art 1, dioxin in exhaust gas can be reliably decomposed by managing the operating conditions of the secondary combustion device. However, since the secondary combustion device is provided and secondary combustion of the dioxin in the exhaust gas is performed to decompose, the running cost of the secondary combustion device is increased, and extra energy is consumed, which is an economic problem. Remains.

In the prior art 2, a step of injecting the dust containing dioxin in the exhaust gas into the electric furnace again must be performed. However, it is desired to develop a method for performing this step safely and stably, and the problem remains. .

Accordingly, an object of the present invention is to provide dioxin in exhaust gas generated from an electric furnace by providing a secondary combustion device for the exhaust gas, without consuming extra energy, and by simply operating the electric furnace. It is an object of the present invention to develop a method and an apparatus for treating an exhaust gas of an electric furnace for steelmaking, which can treat the exhaust gas without leaving the system for exhaust gas treatment. And
An object of the present invention is to solve the above-mentioned problem by inexpensively and safely detoxifying dioxin mixed in electric furnace exhaust gas.

[0009]

SUMMARY OF THE INVENTION In view of the above, intensive studies have been made to develop an exhaust gas treatment method for an electric furnace for steelmaking. The present inventors have found that the concentration of dioxin in exhaust gas generated from an electric furnace for steelmaking has a strong correlation with the temperature of exhaust gas, and the concentration of dioxin is very high at the time of low exhaust gas temperature such as in the initial stage of dissolution. Is extremely low when the temperature exceeds 800 ° C. The present invention is based on the above findings, and does not treat relatively low temperature exhaust gas containing dioxin as it is, but once collects and stores it. Then, when the temperature of the electric furnace exhaust gas is sufficiently high in one heat cycle, the idea of treating the low-temperature stored exhaust gas by utilizing the excess sensible heat of the exhaust gas was conceived. In this specification, the exhaust gas refers to an exhaust gas generated from an electric furnace as a base material, in a subsequent exhaust gas treatment step, air is sucked into the exhaust gas, before or after combustion, dioxin,
Regardless of whether or not it contains dust, adsorbents, etc., it is referred to as exhaust gas.

According to a first aspect of the present invention, there is provided a method for treating exhaust gas from an electric furnace for steelmaking, wherein high-temperature exhaust gas generated from the electric furnace during the operation of the electric furnace for steelmaking is led to a combustion chamber and / or a duct, and the unburned exhaust gas in the exhaust gas is treated. Gas components are burned in a combustion chamber and / or a duct, high-temperature exhaust gas discharged from the combustion chamber and / or a duct is cooled by a cooling device, and then guided to a dust collector, and the exhaust gas is purified by the dust collector. When the temperature of the exhaust gas discharged from the combustion chamber and / or the duct is 800 ° C. or more, the exhaust gas is cooled by the cooling device and then purified by the dust collecting device. And
When the temperature of the exhaust gas discharged from the combustion chamber and / or the duct is lower than 800 ° C, the exhaust gas is collected in the gas holder, and then when the temperature of the exhaust gas discharged from the combustion chamber and / or the duct is 800 ° C or higher. The exhaust gas collected in the gas holder is burned together with the exhaust gas generated from the electric furnace in a combustion chamber and / or a duct, and the combustion chamber and / or
Alternatively, the flow rate of the recovered exhaust gas is adjusted so that the temperature of the exhaust gas discharged from the duct is maintained at 800 ° C. or higher, and the exhaust gas maintained at 800 ° C. or higher is cooled by a cooling device. It is characterized by performing the purification process.

An exhaust gas treatment apparatus for a steelmaking electric furnace according to a second aspect is characterized by having the following apparatus and mechanism. That is, a steelmaking electric furnace, a combustion chamber and / or a duct for burning unburned gas components in exhaust gas generated from the electric furnace, and a cooling device for cooling exhaust gas discharged from the combustion chamber and / or duct. A dust collector for purifying exhaust gas discharged from the cooling device, a blower for discharging exhaust gas from the dust collector, the electric furnace for steelmaking, a combustion chamber and / or a duct, a cooling device,
A mainstream duct connecting the dust collector and the exhaust fan, and an exhaust gas channel switching device for switching the exhaust gas discharged from the combustion chamber and / or the duct from the duct leading to the cooling device to another duct. And a recovery duct comprising: a gas holder for accommodating the exhaust gas led to the another duct by the exhaust gas flow switching device; and a duct for introducing the exhaust gas in the gas holder to the combustion chamber. And introducing the exhaust gas in the gas holder into the combustion chamber and / or the duct in accordance with the temperature of the exhaust gas at the exit of the combustion chamber and / or the duct, and setting the temperature of the exhaust gas at the exit of the combustion chamber and / or the duct to 800 ° C. or more. And an exhaust gas temperature / flow rate control mechanism for maintaining the exhaust gas temperature and flow rate.

[0012]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a schematic flow chart showing an example of an exhaust gas treatment apparatus for carrying out the method for treating exhaust gas of an electric furnace according to the present invention. This is the same as the flow chart of the conventional exhaust gas treatment apparatus for a steelmaking electric furnace shown in FIG. 3, but further provided with an exhaust gas flow switching device 5 in the water cooling duct 3 on the outlet side of the combustion chamber 2.
Then, a gas holder 8 is provided to collect and store the exhaust gas in the gas holder 8, and an appropriate amount of the exhaust gas 8 a is sent from the gas holder 8 in a timely manner according to the exhaust gas temperature and the flow rate on the exit side of the combustion chamber, and mixed with the exhaust gas 1 e. It is something to do. The method and the device according to the invention will be further described with reference to FIG.

The high-temperature exhaust gas 1a generated from the electric furnace 1 is sucked into the smoke collecting pipe 1d through the elbow pipe 1b and the sliding pipe 1c, then becomes the exhaust gas 1e, and enters the combustion tower 2.
The sliding pipe 1c is located between the elbow pipe 1b and the smoke collecting pipe 1d, and slides in the axial direction of the smoke collecting pipe 1d to suck outside air together with the exhaust gas 1a when the high temperature exhaust gas 1a is sucked into the smoke collecting pipe 1d. To form an appropriate gap in the conduit. In this way, the exhaust gas 1e containing the outside air becomes uncombusted gas components in the exhaust gas 1e in the combustion chamber 2, for example, CO or H
₂ is burned, resulting temperature of the exhaust gas 1e is increased. Then, the exhaust gas temperature instruction control device 4 installed on the outlet side of the combustion chamber 2 measures the temperature of the exhaust gas 4a and transmits the following signals according to the following cases (a) and (b), respectively: The exhaust gas flow path is changed by the exhaust gas flow path switching device 5 and the exhaust gas stored in the gas holder 8 is sent out by starting the blower 7. Then, as described in (b) below, control is performed so that the temperature of the exhaust gas 4a at the outlet of the combustion chamber 2 is maintained at 800 ° C. or higher.

(A) The exhaust gas temperature at the outlet of the combustion chamber is 8
During the middle, late, and refining stages of the melting period in the electric furnace, the temperature of the electric furnace exhaust gas 1a is high, so that the time when the exhaust gas temperature at the combustion chamber outlet becomes 800 ° C. or more continues for a long time. FIG.
FIG. 3 shows an example of the change over time of the exhaust gas temperature at the outlet of the combustion chamber 2 during one heat cycle under normal electric furnace operating conditions.

The exhaust gas temperature at the outlet of the combustion chamber 2 is 800
At a temperature of not less than ° C., even if dioxin is contained in the exhaust gas 1e, it is decomposed by combustion, so that the exhaust gas 4a hardly contains dioxin. Therefore, the exhaust gas 4a is guided to the cooling device 10 via the exhaust gas flow switching device 5 and cooled. The cooling of the exhaust gas 4 a by the cooling device 10 is performed, for example, by guiding the exhaust gas 4 a to the water cooling duct 3, cooling it to about 400 ° C., and then guiding the exhaust gas 4 a to the water spray cooling tower 9.
Is directly cooled and rapidly cooled from 350 ° C. or higher to 250 ° C. or lower. Alternatively, the exhaust gas 4a is led to the water spray cooling tower 9 and the exhaust gas 4a
Is directly cooled, and then mixed with the exhaust gas coming out of the water spray cooling tower 9 at a high flow rate of almost room temperature without containing dioxin and the like sucked from the dust collecting hood 11. Quench.

As described above, the exhaust gas is heated from 350 ° C. or higher to 2 ° C.
By rapidly cooling to 50 ° C. or less, resynthesis of dioxin is suppressed. The thus cooled exhaust gas 12a substantially containing no dioxin is passed through a bag filter of the dust collector 12 to remove dust from the exhaust gas 12a. In this way, the exhaust gas 14a that does not contain dioxin and has been subjected to the dust removal processing and purified is sucked by the exhaust fan 13 and discharged from the chimney 14.

(B) When the temperature of the exhaust gas at the outlet of the combustion chamber is 8
As shown in FIG. 2, as shown in FIG. 2, the initial charging and melting of raw materials into the electric furnace, the initial charging and additional melting of the raw materials, and the start of tapping and the subsequent operation of the electric furnace exhaust gas 1a. Since the temperature is low, the temperature of the exhaust gas 4a at the outlet of the combustion chamber becomes less than 800 ° C. As described above, the time when the exhaust gas 4a becomes lower than 800 ° C. is usually about 15% as a proportion of about 60 minutes which is one heat cycle of the electric furnace operation. And
The generation speed (Q ₁ ) of the exhaust gas 1a at this time is about 40 times the generation speed (Q ₂ ) of the exhaust gas 1a at the time (a).
%. For example, in the case of electric arc furnace 100 t / heat, Q ₂ = a 1500 Nm ³ / min or so, _{thus, Q 1 = 1500 × 0.4 =} 600Nm 3 / min
About. Since the cycle time of one heat is usually about 60 minutes, the internal volume of the gas holder 8 for collecting and storing the exhaust gas 4a at a temperature lower than 800 ° C. does not become so large.

The temperature of the exhaust gas at the outlet of the combustion chamber is 800 ° C.
During the period below, since dioxin is contained in the exhaust gas 1e, the flow path of the exhaust gas 1e exiting from the combustion chamber 2 is changed by the exhaust gas flow switching device 5, and the entire amount is collected and stored in the gas holder 8. The exhaust gas 8a stored in the gas holder 8 is sent out by the following method and mixed with the exhaust gas 1e when the temperature of the exhaust gas 1e at the inlet of the combustion chamber 2 is 800 ° C. or more.

Exhaust gas temperature indicator 8 at the outlet of gas holder 8
b and an information signal from the exhaust gas temperature instruction control device 4 at the outlet of the combustion chamber 2 are transmitted to the recovered exhaust gas flow rate calculator 15.
The recovered exhaust gas flow calculator 15 calculates the exhaust gas 4 at the outlet of the combustion chamber 2.
a Flow controller 1 so that the temperature is maintained at 800 ° C. or higher.
The opening degree of the valve 7 is adjusted, and the exhaust gas 8a having an appropriate flow rate is mixed with the exhaust gas 1e and enters the combustion chamber.

As described above, since the exhaust gas 1e and the exhaust gas 4a are treated and then guided to the cooling device 10, the exhaust gas introduced into the cooling device 10 hardly contains dioxin. The cooling of the exhaust gas 4a by the cooling device 10 is performed in the same manner as in the method described in the above item (a), and the dust collection process is performed in the same manner as in the item (a). In this way, the exhaust gas 14a containing no dioxin and having been subjected to the dust removal processing and purified is sucked by the exhaust fan 13 and
Released from 4.

In the above description, when the temperature of the exhaust gas at the outlet of the combustion chamber is 800 ° C. or more, the entire amount of the exhaust gas 4a is always led to the cooling device 10 in the next process. May be flowed to the gas holder 8 line, and a correction operation may be performed to easily maintain the temperature of the exhaust gas 4a at 800 ° C. or higher.

In both cases (a) and (b), the adsorbent blowing device 16 such as activated carbon or calcium hydroxide is provided downstream of the cooling device 10 as a measure against abnormal operation or abnormal operation. Then, it is installed in the middle of the duct on the upstream side of the dust collecting device 12, and an adsorbent is blown in to adsorb dioxin contained in the exhaust gas. Thereafter, the dust is removed and the clean exhaust gas is diffused.

[0023]

As described above, according to the present invention,
In suppressing the generation of dioxin contained in the exhaust gas generated from the electric furnace during the operation of the electric furnace for steelmaking, secondary combustion equipment such as the conventional combustion decomposition method is not required, and the running cost is not required. The present invention can be applied to an operation mode such as a quasi-continuous furnace, which is a problem in a refuse incinerator. An exhaust gas treatment method and apparatus for a steelmaking electric furnace exhibiting such effects can be provided, and industrially useful effects can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic flow chart showing an example of an exhaust gas treatment apparatus for carrying out an electric furnace exhaust gas treatment method of the present invention.

FIG. 2 is a graph showing an example of a change over time in exhaust gas temperature at the outlet of an exhaust gas combustion chamber during one heat cycle under normal electric furnace operating conditions.

FIG. 3 is a schematic flowchart of an example of a conventional exhaust gas treatment apparatus for an electric furnace for steelmaking.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electric furnace for steel making 1a Exhaust gas 1b Elbow part 1c Sliding pipe 1d Smoke collecting pipe 1e Exhaust gas 2 Combustion chamber 2 'Secondary combustion equipment 3 Water cooling duct 4 Exhaust gas temperature instruction control device 5 Exhaust gas flow path switching device 5a, 5b Flow rate controller 6 Flow controller 7 Blower 8 Gas holder 8a Exhaust gas 8b Exhaust gas temperature indicator 9 Water spray device 9a Exhaust gas 10 Cooling device 11 Building dust collecting hood 11a Building dust collecting gas 12 Dust collecting device 12a Exhaust gas 13 Exhaust air 14 Chimney 14a Exhaust gas 15 Calculator 16 Adsorbent blowing device 17 Flow rate controller

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F27D 17/00 104 F23J 15/00 L

Claims (2)

[Claims] 1. A high-temperature exhaust gas generated from an electric furnace during operation of an electric furnace for steelmaking is guided to a combustion chamber and / or a duct, and an unburned gas component in the exhaust gas is burned in the combustion chamber and / or a duct. And a high-temperature exhaust gas discharged from the combustion chamber and / or the duct is cooled by a cooling device, then guided to a dust collector, and the exhaust gas is purified by the dust collector. In the above, when the temperature of the exhaust gas discharged from the combustion chamber and / or the duct is equal to or higher than 800 ° C., the exhaust gas is cooled by the cooling device, and then purified by a dust collecting device. When the temperature of the exhaust gas discharged from the duct is less than 800 ° C., the exhaust gas is collected in a gas holder, and then the exhaust gas discharged from the combustion chamber and / or the duct is discharged. When the temperature of the gas is 800 ° C. or more, the exhaust gas collected in the gas holder is burned in the combustion chamber and / or the duct together with the exhaust gas generated from the electric furnace, and the exhaust gas discharged from the combustion chamber and / or the duct The flow rate of the recovered exhaust gas is adjusted so that the temperature of the exhaust gas is maintained at 800 ° C. or higher, and
An exhaust gas treatment method for an electric furnace for steelmaking, wherein the exhaust gas maintained at 0 ° C. or higher is cooled by the cooling device, and then purified by the dust collecting device. 2. An electric furnace for steelmaking, a combustion chamber and / or a duct for burning unburned gas components in exhaust gas generated from the electric furnace, and an exhaust gas discharged from the combustion chamber and / or duct is cooled. A cooling device, a dust collector for purifying exhaust gas discharged from the cooling device, a blower for discharging exhaust gas from the dust collector, the electric furnace for steelmaking,
A mainstream duct connecting the combustion chamber and / or duct, a cooling device, a dust collector, and an exhaust fan, and exhaust gas discharged from the combustion chamber and / or duct,
An exhaust gas passage switching device for switching from a duct leading to the cooling device to another duct, a gas holder containing exhaust gas led to the another duct by the exhaust gas passage switching device, and the another duct And a recovery duct comprising: a duct for introducing exhaust gas in the gas holder into the combustion chamber; and exhaust gas in the gas holder according to the exhaust gas temperature at the combustion chamber and / or the duct outlet. Into the combustion chamber and / or
An exhaust gas treatment device for an electric furnace for steelmaking, comprising: an exhaust gas temperature / flow rate control mechanism for maintaining the temperature of exhaust gas at a duct outlet at 800 ° C. or higher.