JPH11183046A - Method of treating exhaust gas in electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such a treading method for exhaust gas in an electric furnace that the dioxin adsorbed by an adsorber never returns into exhaust gas. SOLUTION: This system is provided with a temperature regulator 14 which detects the temperature before a bag filter 11, and keeps this temperature in fixed range. The adjustment of this temperature is performed by providing the system with a cooling water regulating valve 15 and regulating the opening of the cooling water regulating valve 15 by the output of the temperature regulator 14, and adjusting the quantity of water of the cooling water discharged from the spray nozzle 9 of an exhaust gas cooling tower 8. Moreover, this control method which detects the quantity of exhaust gas flow before a bag filter 11 and controls this within a fixed range, providing the system with an exhaust gas flow regulator 16 is performed by changing the quantity of air sucked in an exhaust gas pipe by regulating the opening, providing the system with an air flow rate regulating valve 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas in an electric furnace, and more particularly to a method for treating exhaust gas in which the amount of dioxin emission is reduced to the lowest possible range.

[0002]

2. Description of the Related Art Various methods have been proposed for reducing harmful substances, particularly dioxins, discharged from an electric furnace. A typical example is a method in which an adsorbent is blown into exhaust gas to adsorb harmful substances such as dioxin in front of a bag filter installed in an exhaust gas treatment system, and the adsorbent is captured by a bag filter. is there. FIG. 2 shows an example disclosed in Japanese Patent Application Laid-Open No. 6-117780.

The exhaust gas generated from the electric furnace 21 passes through a duct 22 and is introduced into a combustion mixer 25 by a blower 23. The combustion mixer 25 is supplied with kerosene, LP by a burner 24 by air supplied from a combustion air fan 26.
Fuel such as G is burned, the combustion gas is mixed with the exhaust gas, and aromatic chlorides and the like in the exhaust gas are decomposed. The heated exhaust gas is held in the holding chamber 27 at a high temperature for 0.5 to 5 seconds. During this holding period, 90% of aromatic chlorine compounds
The above is decomposed.

The exhaust gas that has left the holding chamber 27 is supplied to a gas cooler 2.
8 is introduced. Here, the exhaust gas is directly cooled by the fine particles of water sprayed by the spray nozzle 29. Aromatic chlorine compounds decomposed by combustion heating,
If the temperature is maintained at a temperature of about 300 ° C. for a certain period, the gas is regenerated. To prevent this, the gas cooler 28 rapidly cools the exhaust gas by direct cooling with water in a short time.

[0005] In order to further reduce the concentration of the aromatic chlorine compound, a powdery adsorbent is blown into the exhaust gas from the adsorbent supply device 30. Slaked lime, coal ash, activated carbon and the like are used as the adsorbent. The blown adsorbent is captured by the bag filter 31 together with the dust in the exhaust gas. Therefore, the aromatic chlorine compound in the exhaust gas discharged from the chimney 32 is at a very low level.

The dust and the adsorbent captured by the bag filter 31 are sent to a pelletizer 33 and granulated,
It is put into the electric furnace 21 again and melted. Therefore, it is not necessary to dispose of the adsorbent that has adsorbed the aromatic chlorine compound or the like, and secondary pollution can be prevented.

As described above, a method for adsorbing harmful substances such as dioxin by blowing an adsorbent such as pulverized coal or reduced slag into exhaust gas in front of a bag filter installed in an exhaust gas treatment system or the like is described in, for example, It is also disclosed in Japanese Unexamined Patent Publication No. 6-47237.

[0008]

The temperature inside the bag filter fluctuates by about 50 to 100 ° C. depending on the operation state of the electric furnace. That is, as shown in FIG. 3, the exhaust gas temperature at the outlet of the electric furnace rises with the start of the operation and temporarily stabilizes.
At the timing of scrap loading, it drops significantly, rises again, stabilizes, and begins tapping. The change in exhaust gas temperature at the outlet of the electric furnace reaches 800 ° C. Although this temperature change becomes smaller when the exhaust gas passes through the gas cooler, a temperature change of 50 to 100 ° C. is still inevitable.

[0009] On the other hand, dioxin has a high vapor pressure, and therefore has a high proportion in the gas phase even at low temperatures. The gaseous dioxin, once adsorbed by the adsorbent, separates from the adsorbent when the temperature rises. Therefore, dioxin may separate from the adsorbent, enter the exhaust gas, and be released to the atmosphere due to the temperature of the exhaust gas in the bag filter.

[0010] Further, since the ratio of dioxin present in the gas phase is high, if the amount of exhaust gas fluctuates, it is likely to be separated from the adsorbent and included again in the exhaust gas.

The present invention has been made in order to solve such problems, and an object of the present invention is to provide a method for treating exhaust gas in an electric furnace in which dioxin adsorbed by an adsorbent does not return to exhaust gas again. As an issue.

[0012]

The first means for solving the above-mentioned problems is that an adsorbent is charged in front of a dust collector in an exhaust gas treatment facility of an electric furnace to adsorb dioxin, and the adsorbent adsorbs dioxin. An exhaust gas treatment method for an electric furnace, wherein the temperature of the exhaust gas before the dust collector is controlled within a certain range in a method for treating exhaust gas in an electric furnace in which the agent is captured by a dust collector (claim 1).

In this means, since the temperature of the exhaust gas before the dust collector is controlled within a certain range, the dioxin once adsorbed by the adsorbent is not released into the exhaust gas again. Therefore, emission of dioxin to the atmosphere can be avoided.

[0014] A second means for solving the above-mentioned problems is as follows.
In a method of treating exhaust gas in an electric furnace, in which an adsorbent is introduced in front of a dust collector in an exhaust gas treatment facility of an electric furnace to adsorb dioxin, and the adsorbent adsorbing dioxin is captured by the dust collector, the flow rate of exhaust gas before the dust collector is reduced. A method for treating exhaust gas in an electric furnace, characterized in that the exhaust gas is controlled within a certain range.

In this means, since the flow rate of the exhaust gas before the dust collector is controlled within a certain range, the dioxin once adsorbed by the adsorbent is not released into the exhaust gas again. Therefore, the release of dioxin into the atmosphere can be avoided.

A third means for solving the above-mentioned problem is as follows.
In the method of treating exhaust gas in an electric furnace, in which an adsorbent is charged in front of a dust collector in an exhaust gas treatment facility of an electric furnace to adsorb dioxin, and the adsorbent that has absorbed the dioxin is captured by the dust collector, the temperature of the exhaust gas before the dust collector is reduced. An exhaust gas treatment method in an electric furnace, wherein a flow rate is controlled within a certain range.

In this means, since the temperature and the flow rate of the exhaust gas before the dust collector are respectively controlled within a certain range,
By the synergistic effect of the first means and the second means, it is possible to more reliably prevent the release of dioxin from the adsorbent. Therefore, emission of dioxin to the atmosphere can be avoided.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating an example of an embodiment of the present invention. In FIG. 1, 1 is an electric furnace, 2 is a duct, 3 is a blower, 4 is a burner, 5 is a combustion mixer, 6
Is a fan for combustion air, 7 is a holding chamber, 8 is an exhaust gas cooling tower,
9 is a spray nozzle, 10 is an adsorbent supply device, 11 is a bag filter, 12 is a chimney, 13 is a pelletizer, 14 is a temperature controller, 15 is a cooling water control valve, 16 is an exhaust gas amount controller, and 17 is an air flow rate controller. It is a valve.

Exhaust gas generated from the electric furnace 1 is supplied to a duct 2
And is introduced into the combustion mixing device 5 by the blower 3. In the combustion mixing device 5, fuel such as kerosene and LPG is burned by the burner 4 by air supplied from the combustion air fan 6, the combustion gas and exhaust gas are mixed, and dioxin and the like in the exhaust gas are decomposed. The heated exhaust gas is held in the holding chamber 7 at a high temperature for 0.5 to 5 seconds. During this holding period, more than 90% of the dioxin is degraded.

The exhaust gas leaving the holding chamber 7 is discharged to an exhaust gas cooling tower 8.
Will be introduced. Here, the exhaust gas is directly cooled by the fine particles of water sprayed by the spray nozzle 9. Dioxin decomposed by combustion heating is regenerated when it is kept at a temperature of about 300 ° C. for a certain period. To prevent this, the exhaust gas cooling tower 8 directly cools the exhaust gas in a short time by direct cooling with water. Cooling.

In order to further reduce the concentration of dioxin, a powder adsorbent is blown into the exhaust gas from the adsorbent supply device 10. As the adsorbent, a carbon-based adsorbent such as activated carbon and activated coke is used. The blown adsorbent is captured by the bag filter 11 together with the dust in the exhaust gas. Therefore, the dioxin in the exhaust gas discharged from the chimney 12 is at a very low level.

The dust and the adsorbent captured by the bag filter 11 are sent to a pelletizer 13 and granulated,
It is again put into the electric furnace 1 and melted. Therefore, disposal such as disposal of the adsorbent that has adsorbed dioxin becomes unnecessary, and secondary pollution can be prevented.

The above exhaust gas treatment process is the same as the prior art. In the present embodiment, a temperature controller 14 is newly provided to detect the temperature before the bag filter 11 and keep this temperature within a certain range. In the embodiment shown in FIG. 1, a cooling water control valve 15 is provided, and the opening of the cooling water control valve 15 is adjusted by the output of the temperature controller 14 to adjust the temperature of the spray nozzle of the exhaust gas cooling tower 8. Although the adjustment is performed by adjusting the amount of cooling water discharged from the nozzle 9, any other method that can adjust the temperature of the exhaust gas may be used.

The temperature range is 180 ° C or more of the dew point of water.
It is preferable that the temperature is set to not more than ° C. If the exhaust gas temperature is lower than the dew point, dew condensation easily occurs in the exhaust gas, which is not preferable. On the other hand, when the exhaust gas temperature exceeds 180 ° C., dioxin is easily separated from the adsorbent, which is not preferable.

In the embodiment shown in FIG. 1, in addition to this, an exhaust gas amount controller 16 is provided to detect the flow rate of exhaust gas before the bag filter 11 and to control the flow rate to a certain range. The control method is performed by providing an air flow control valve 17 and adjusting the opening thereof to change the amount of air blown into the exhaust gas pipe. In addition,
Since the temperature of the exhaust gas before the bag filter 11 also varies depending on the amount of blown air, the temperature detecting end of the temperature controller 11 needs to be provided downstream of the air blow port.

Temperature controller 14 and exhaust gas flow controller 16
Are preferably provided, but depending on the situation of temperature fluctuation and flow rate fluctuation of the exhaust gas from the electric furnace 1, only one of them may be provided.

In the embodiment shown in FIG. 1, the temperature and the flow rate of the exhaust gas at the inlet of the bag filter 11 are kept within a certain range. Therefore, the gaseous dioxin adsorbed by the adsorbent is not released from the adsorbent and released into the exhaust gas, so that the amount of dioxin released from the chimney 12 to the atmosphere can be reliably reduced.

[0028]

As described above, in the present invention, one or both of the temperature and the flow rate of the exhaust gas before the dust collector are controlled within a certain range, so that the dioxin adsorbed by the adsorbent can reduce the exhaust gas temperature and the exhaust gas temperature. It is possible to prevent the exhaust gas from being released again into the exhaust gas due to the change in the flow rate. Therefore, the amount of dioxin released into the atmosphere can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram showing a system of a conventional electric furnace exhaust gas treatment system.

FIG. 3 is a diagram showing a transition of exhaust gas temperature at an electric furnace outlet.

[Description of Signs] 1 Electric furnace 2 Duct 3 Blower 4 Burner 5 Combustion mixing device 6 Fan for combustion air 7 Holding chamber 8 Exhaust gas cooling tower 9 Spray nozzle 10 Adsorbent supply device 11 Bag filter 12 Chimney 13 Pelletizer 14 Temperature controller 15 Cooling water control valve 16 Exhaust gas amount controller 17 Air flow control valve

Claims (3)

[Claims] 1. A method for treating exhaust gas in an electric furnace in which an adsorbent is charged in front of a dust collector in an exhaust gas treatment facility of an electric furnace to adsorb dioxin, and the adsorbent having adsorbed dioxin is captured by the dust collector. A method for treating exhaust gas in an electric furnace, wherein the temperature of the exhaust gas is controlled within a certain range. 2. A method for treating exhaust gas in an electric furnace in which an adsorbent is charged in front of a dust collector in an exhaust gas treatment facility of an electric furnace to adsorb dioxin, and the adsorbent adsorbing dioxin is captured by the dust collector. A method for treating exhaust gas in an electric furnace, comprising controlling the flow rate of exhaust gas within a predetermined range. 3. A method for treating exhaust gas in an electric furnace in which an adsorbent is charged in front of a dust collector in an exhaust gas treatment facility of an electric furnace to adsorb dioxin, and the adsorbent having adsorbed dioxin is captured by the dust collector. A method for treating exhaust gas in an electric furnace, wherein the temperature and the flow rate of the exhaust gas are controlled within a certain range.