JPH11190594A - Method and device for treating exhaust gas of electric furnace for steel manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent dioxins in dust being gathered inside a duct or the like when a high-temperature exhaust gas flows from being scattered again after a low- temperature exhaust gas flows. SOLUTION: Two groups of systems for treating a high-temperature gas being generated from an electric furnace 1 for steel manufacture are provided. When the temperature of the exhaust gas is equal to or more than a fixed value being predetermined based on the combustion decomposition temperature of dioxin, the exhaust gas is cooled by a cooling device 10 and is purified and treated by a dust collector 12. When the temperature of the exhaust gas is less than the fixed value, the exhaust gas is led to and is cooled by another cooling device 10' and is purified and treated by a dust collector 12' at the downstream of the cooling device 10'. In this case, the fixed temperature is 800 deg.C, thus satisfying the target value (for example, 0.5 ng-TEQ/ Nm<3> or less) of the concentration of dioxins in the exhaust gas being dissipated into air, at the same time, reducing the absolute value of exhaustion and the amount of the treatment of the dust containing dioxins, and, furthermore, eliminating the need for secondary burning facilities as in a conventional combustion decomposition method and the running costs.

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").

[0005]

The above prior art has the following problems. The prior art manages the operating conditions of the secondary combustion device in the combustion chamber even when the exhaust gas generated from the electric furnace contains dioxin, and maintains the temperature of the combustion chamber at a high temperature equal to or higher than a predetermined value. In this way, dioxin is burned and decomposed in the combustion chamber, dioxin in exhaust gas discharged from the combustion chamber is eliminated, and the exhaust gas not containing dioxin is cooled. During the cooling process, the exhaust gas is rapidly cooled from 350 ° C. or higher to 250 ° C. or lower in order to suppress the resynthesis of dioxin at a low temperature.

[0006] However, when the temperature of the exhaust gas generated from the electric furnace is considerably low, for example, in the first heat after the continuous operation is interrupted in the operation of the electric furnace or the like, 1
During the heat cycle, such as during the initial charging of raw materials or during the additional charging, in order to maintain the temperature of the combustion chamber outlet at 800 ° C or higher only by adding heat in the combustion chamber by the secondary combustion device, excessive capacity is required. A secondary combustion device is required. When the temperature of the exhaust gas from the electric furnace is low, the temperature of the exhaust gas at the outlet of the combustion chamber may be 800 ° C. or less. In such a case, the exhaust gas containing dioxin in the exhaust gas flows through the exhaust gas channel. Then, dioxin is adsorbed and contained in the dust accumulated in the duct and the like on the way.

As described above, when the temperature of the exhaust gas from the electric furnace is low, dust adsorbed by dioxin tends to accumulate in ducts and the like. However, after that, when high-temperature exhaust gas flows through a duct or the like, dioxin in the dust separates from the dust and re-scatters together with the exhaust gas. The re-scattered dioxin separates from the dust and enters the gas and scatters.

Accordingly, an object of the present invention is to solve the problem that dioxin contained in dust accumulated in a duct or the like after a relatively low temperature exhaust gas has flowed and a relatively high temperature exhaust gas subsequently flows. The phenomenon that dioxin re-scatters from the accumulated dust is prevented. It is another object of the present invention to efficiently treat dust containing dioxin accumulated in a dust collector such as a bag filter.

[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. Therefore, the temperature after the exhaust gas generated from the electric furnace burns in the combustion chamber,
The case where the temperature is equal to or higher than the temperature at which dioxin is decomposed by combustion is distinguished from the case where the temperature is lower than the temperature. The present invention has been made based on the above findings and ideas.

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 unburned exhaust gas in the exhaust gas. Gas components are burned in a combustion chamber and / or a duct, and 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. An exhaust gas treatment method for a steelmaking electric furnace to be treated is characterized in that an exhaust gas cooling process is divided into two main processes as follows.

When the temperature of the exhaust gas discharged from the combustion chamber and / or the duct is equal to or higher than a predetermined value in consideration of the combustion decomposition temperature of dioxin, the exhaust gas discharged from the combustion chamber and / or the duct is cooled. Then, the exhaust gas is guided to a dust collecting device disposed downstream of the cooling device, and is purified by the dust collecting device.

On the other hand, when the temperature of the exhaust gas discharged from the combustion chamber and / or the duct is lower than the above-mentioned fixed value, the exhaust gas discharged from the combustion chamber and / or the duct is discharged to another unit except the cooling device. The exhaust gas is guided to a cooling device, cooled by the cooling device, and then guided to a dust collecting device disposed downstream of the cooling device, and the exhaust gas is purified by the dust collecting device.

An exhaust gas treatment apparatus for a steelmaking electric furnace according to a second aspect of the present invention 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 an exhaust gas temperature discharged from the combustion chamber and / or the duct were measured. Based on the temperature information, an exhaust gas path from which the exhaust gas discharged from the combustion chamber and / or the duct is to be led to the next process is selected from a plurality of exhaust gas paths, and the exhaust gas is selected based on the selection result. An exhaust gas passage switching mechanism for guiding the exhaust gas to a flow passage, a cooling device for the exhaust gas arranged to communicate with each of the plurality of exhaust gas passages, and a dust collecting device arranged to a downstream side of the cooling device. And a plurality of cooling / dust collecting device systems.

According to a third aspect of the present invention, there is provided an exhaust gas treating method for a steelmaking electric furnace, wherein the number of systems comprising a combination of a plurality of exhaust gas passages and a plurality of cooling / dust collecting systems in the exhaust gas treating apparatus according to the second aspect. Using an exhaust gas treatment device of an electric furnace for steelmaking, wherein 800 ° C. is adopted as a predetermined value based on the combustion decomposition temperature of dioxin in the exhaust gas treatment method according to claim 1, and the combustion chamber and / or When the temperature of the exhaust gas discharged from the duct is 800 ° C. or higher, the exhaust gas is always led to one of the exhaust gas channels, and the temperature of the constant value is set to 8
When the temperature is lower than 00 ° C., it is always guided to the other exhaust gas flow path.

[0015]

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 device includes an electric furnace 1, a combustion chamber 2, an exhaust gas flow switching device 5, cooling devices 10, 10 ', dust collecting devices 12, 12', and transport, cooling, and combustion of exhaust gas among these devices. It consists of a group of ducts that are implemented as appropriate. The most significant feature of the exhaust gas treatment device of the present invention is that two cooling / dust collection systems including the cooling device and the dust collection device are provided.

The high-temperature exhaust gas 1a generated from the electric furnace 1 passes through the elbow pipe 1b and the sliding pipe 1c, is sucked into the smoke collection pipe 1d, then becomes the exhaust gas 1e, and enters the combustion chamber 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 measured value to the exhaust gas flow rate regulators 5a and 5b.
a to flow through the flow path A or flow path B. As the value of the constant temperature, for example, 800 ° C. is adopted.

When the temperature of the exhaust gas 4a is 800 ° C. or higher, the exhaust gas temperature instruction controller 4 instructs the exhaust gas flow controller 5a to open, and the exhaust gas flow controller 5b
Instruct to close. The exhaust gas 4a flows to the channel A,
The cooling / dust collection system of the cooling device 10 and the dust collection device 12 functions. When the temperature of the exhaust gas 4a is lower than 800 ° C., an instruction to open the exhaust gas flow controller 5b and an instruction to close the exhaust gas flow controller 5a are issued. The exhaust gas 4a flows to the stream B, and the cooling / dust collecting system of the cooling device 10 'and the dust collecting device 12' functions.

When the temperature of the exhaust gas 4a is high, dioxin is decomposed by combustion, but when the temperature of the exhaust gas 4a is low, dioxin is not decomposed by combustion.
This is included.

When the temperature of the exhaust gas 4a is high, the exhaust gas 4a is cooled to about 400 ° C. in the next step of the water cooling duct 3, and then rapidly cooled in the water spray cooling tower 9 from 350 ° C. or higher to 250 ° C. or lower. Dioxin is not resynthesized by this quenching, and dioxin is not originally contained. Therefore, it may be guided to the dust collecting device 12 at least at about 200 ° C. which is the heat-resistant temperature of the bag filter. Exhaust gas 14a purified by removing dust with a bag filter
From the chimney 14. In this case, the dust contains almost no dioxin.

On the other hand, when the temperature of the exhaust gas 4a is low, the exhaust gas 4a is
° C, and then in a water spray cooling tower 9 '
Rapid cooling from 350 ° C or higher to 250 ° C or lower. Dioxin is not newly resynthesized by this quenching, but dioxin is originally contained in the exhaust gas 4a. Therefore, the exhaust gas is cooled to about 80 ° C. or less, and the dioxin is adsorbed on the dust, and then treated with the bag filter of the dust collector 12 ′. In this case, the dust captured by the bag filter contains dioxin.

In the present invention, as described above, the combustion chamber 2
The following cooling / dust collection system is dedicated to the case where the dioxin is contained in the exhaust gas 4a after leaving the exhaust gas, and the case where the dioxin is not contained. It is possible to prevent dioxin from coming back from dust.

In the above case, the adsorbent blowing device 16 such as activated carbon or calcium hydroxide is installed on the downstream side of the cooling device 10 and in the middle of the duct on the upstream side of the dust collecting device 12 so as to adsorb the adsorbent. It is more desirable to inject the agent to adsorb the dioxin contained in the exhaust gas, and then treat the dioxin in the dust collector 12 '. Also, in the case of the above, a further clean exhaust gas 14a can be obtained.

FIG. 2 shows a schematic flow chart of another 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 apparatus is different from the apparatus shown in FIG. 1 in that a water spray cooling tower is first disposed as a cooling apparatus for exhaust gas, and then a rapid cooling is performed with a large amount of building dust gas. Other device configurations are the same as those in FIG.

Next, Table 1 shows that the conventional exhaust gas 4a treatment system after the combustion chamber is not divided according to the exhaust gas temperature, and that the present invention treats the exhaust gas 4a after the combustion chamber at 800 ° C. as a boundary. The behavior of dioxin was investigated when the system was divided into dedicated systems. Table 1 shows an example.

[0025]

[Table 1]

[0026]

As described above, according to the present invention,
In controlling the generation of dioxins contained in the gas generated from the electric furnace during the operation of the electric furnace for steelmaking, the cooling and dust collection system is not included when dioxin is contained in the exhaust gas (low-temperature exhaust gas) Since it is divided into cases (high-temperature exhaust gas), when the high-temperature exhaust gas is treated, dioxin does not come back from dust accumulated in a duct or the like due to the low-temperature exhaust gas treatment. Therefore, the concentration of dioxin in the exhaust gas emitted to the atmosphere is set to a target value (for example, 0.5 ng-TEQ / Nm ³
The following is satisfied, and the absolute emission is reduced. In addition, the processing amount of dioxin-containing dust is reduced. Further, secondary combustion equipment such as the conventional combustion decomposition method is not required, and the running cost is not required. 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 schematic flow chart showing another example of an exhaust gas treatment apparatus for carrying out the electric furnace exhaust gas treatment method of the present invention.

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 tube 1d Smoke collecting tube 1e Exhaust gas 2 Combustion chamber 2 'Secondary combustion facility 3 Water cooling duct 4 Exhaust gas temperature indication control device 4a Exhaust gas 5 Exhaust gas flow switching device 5a, 5b Flow rate control Device 7 Blower 8 Gas holder 8a Exhaust gas 8b Exhaust gas temperature indicator 9 Water spray cooling tower 9a Exhaust gas 10, 10 'Cooling device 11 Building dust collecting hood 11a Building dust collecting gas 12, 12' Dust collecting device 12a Exhaust gas 13 Exhaust gas 14 Chimney 14a Exhaust gas 16, 16 'Adsorbent injection device A, B Channel

Claims (3)

[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 a predetermined value based on the combustion decomposition temperature of dioxin, the exhaust gas discharged from the combustion chamber and / or the duct is cooled. The exhaust gas is guided to a device, cooled by the cooling device, and then the exhaust gas is guided to a dust collecting device disposed downstream of the cooling device, purified by the dust collecting device, When the temperature of the exhaust gas discharged from the duct is less than the predetermined value, the exhaust gas discharged from the combustion chamber and / or the duct is guided to another cooling device except the cooling device, and the cooling device uses the exhaust gas. A method for treating an exhaust gas in an electric furnace for steelmaking, comprising cooling, then guiding the exhaust gas to a dust collector disposed downstream of the cooling device, and purifying the exhaust gas with the dust collector. 2. An electric furnace for steelmaking, a combustion chamber and / or duct for burning unburned gas components in exhaust gas generated from the electric furnace, and a temperature of exhaust gas discharged from the combustion chamber and / or duct. Then, based on this temperature information, an exhaust gas flow path from which the exhaust gas discharged from the combustion chamber and / or the duct is to be led to the next process is selected from among a plurality of exhaust gas flow paths. An exhaust gas passage switching mechanism for leading to a selected exhaust gas passage, a cooling device for the exhaust gas arranged to communicate with each of the plurality of exhaust gas passages, and a cooling device for the exhaust gas arranged downstream of the cooling device. An exhaust gas treating apparatus for an electric furnace for steelmaking, comprising a plurality of cooling / dust collecting systems each including a dust collecting device. 3. The exhaust gas treatment apparatus for an electric furnace for steelmaking, wherein the number of systems comprising a combination of the plurality of exhaust gas passages and the plurality of cooling / dust collection systems in the exhaust gas treatment apparatus according to claim 2 is two. Wherein the predetermined value based on the combustion decomposition temperature of dioxin in the exhaust gas treatment method according to claim 1 is 800 ° C, and the temperature of the exhaust gas discharged from the combustion chamber and / or the duct is 800 ° C or higher. In such a case, the temperature is always led to one of the exhaust gas channels, and the temperature is set to 80.
2. The exhaust gas treatment method for an electric furnace for steelmaking according to claim 1, wherein when the temperature is lower than 0 [deg.] C., the exhaust gas is always led to the other exhaust gas channel.