JPH029280B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to electric furnace steelmaking equipment, and more particularly to electric furnace steelmaking equipment that makes it possible to deodorize preheated gas with a foul odor after preheating scrap. It is something. This uses exhaust gas containing high thermal energy generated during the operation of the electric furnace to preheat the scrap charged into the electric furnace, reducing the melting power consumption rate and steelmaking time in the electric furnace. It is used in the field.

[Prior art]

Although the exhaust gas generated during the operation of an electric furnace contains a large amount of dust, the exhaust gas contains a large amount of thermal energy. By using this exhaust gas to preheat the scrap charged into the electric furnace, it is possible to save the melting power in the electric furnace and shorten the steelmaking time. However, scraps are often contaminated with oil, paint, rubber, plastic, etc. On the other hand, the exhaust gas that exchanged heat with the scrap while passing through the preheater containing the scrap,
The temperature will drop to around 100-300℃. For this purpose, the above-mentioned organic substances mixed in the scrap are thermally decomposed.
It becomes difficult to maintain a temperature of 650-700°C, and the scrap preheated gas has a bad odor.

In an attempt to remove the bad odor from the preheated gas and prevent pollution of the atmosphere and environment,
A scrap preheating device using electric steelmaking furnace exhaust gas described in Japanese Patent Application Laid-open No. 61-29686 and other similar devices have been proposed. This system guides the high-temperature exhaust gas containing a large amount of dust from the electric furnace to the combustion tube, burns the combustibles contained in the exhaust gas, such as CO gas, and then introduces the exhaust gas to the preheating device. The heat energy contained in the exhaust gas is then used to preheat the scrap that is charged into the electric furnace. Then, the preheated gas is introduced into the exhaust gas cleaning tower to wash the exhaust gas with a chemical solution, and the temperature of the exhaust gas is lowered with the chemical solution to generate desired saturated steam. Oil mist that cannot be cleaned with chemical liquid is attached to the saturated steam,
A wet electrostatic precipitator is used to collect oil mist along with water vapor and fine water droplets.

If a deodorizing device such as an exhaust gas cleaning tower or a wet electrostatic precipitator is adopted, the preheated gas discharged from the preheating device will be effectively deodorized when the exhaust gas temperature of the electric furnace is low, and the preheated gas will be combusted. This is a significant improvement over the deodorizing methods that have been proposed many times in the past, which involve returning the product to the tube and incinerating it. In other words, the exhaust gas of the electric furnace fluctuates greatly during one cycle of operation, as shown in FIG. In the initial melting state after scrap is charged, the temperature is generally low, and when the temperature rises to a certain extent, scrap is added, so outside air is mixed in and the exhaust gas temperature is lowered. Although the exhaust gas temperature will rise after the addition,
It decreases again during reloading, and after reloading, the exhaust gas with the highest temperature, which depends on the melting temperature, is discharged from the electric furnace. In such a one-cycle operation, the temperature of the exhaust gas fluctuates widely in the range of 400 to 1200°C. Low exhaust gas temperature e.g. 400℃~500℃
℃, the temperature inside the combustion tube is low, and even if the preheated gas is returned to the combustion tube, it cannot maintain the temperature above 650℃, which is sufficient for thermal decomposition to deodorize the gas. At that time, the preheated gas will be at a low temperature of, for example, 100°C to 150°C, so the extremely unpleasant odor will be released into the atmosphere as it is. Therefore, preheated gas is introduced into the deodorizing device described above, and desired deodorization can be achieved through chemical cleaning and collection of oil mist.

[Problem that the invention seeks to solve]

By the way, even when the temperature of the electric furnace exhaust gas is high, the preheated gas is accompanied by a certain degree of odor. This is because even though the exhaust gas temperature is high, if the scrap is preheated using a preheating device, the temperature of the preheated gas will be, for example, about 300°C. The preheated gas will be processed by the deodorizing device described above, but the odor is slightly different in composition from the preheated gas when the temperature of the electric furnace exhaust gas is low, so the ability of the deodorizing device is It is necessary to increase the operating load by increasing the That is, when the temperature of the preheated gas is high, there are many methane, hydrogen sulfide, ammonia, etc. in it, and the odor based on total hydrocarbon becomes strong, and it is necessary to remove it. Since these are flammable, they can be returned to the combustion tube, but if a large amount of preheated gas is returned to the combustion tube, the temperature inside the combustion tube will drop and the exhaust gas will be introduced into the preheating device. There is a problem that the temperature of the scrap becomes low and the scrap is not sufficiently preheated.

By the way, when the temperature of the electric furnace exhaust gas is high, the total amount of hydrocarbons contained in the preheated gas discharged from the preheating device is not always large, but according to the research of the present inventor, the temperature of the preheated gas is In other words, it was found that the amount increases significantly as the temperature inside the preheater increases. In other words, as shown by the solid line in the lower part of Fig. 3, the total hydrocarbon in the preheated gas increases as the temperature of one preheater (solid line) in the preheater increases as shown in the upper part in one cycle of electric furnace operation. It is most common in the period A shown in the diagram, which corresponds to a rising period, and there are also periods in which it is temporarily noticeable, such as period B. Except for period B, the deodorizing device described above can be processed normally, but during period B it is necessary to increase the operating load, and there is a problem in that the power consumption required for deodorizing processing increases at that time.

The present invention was made in view of the above-mentioned problems, and its purpose is to reduce the amount of total hydrocarbon introduced into the deodorizing device, which becomes extremely noticeable temporarily during periods when the exhaust gas temperature of the electric furnace is high. An electric furnace that reduces the operating load of the furnace, avoids a drop in exhaust gas temperature in the combustion tube, effectively preheats scrap using the electric furnace exhaust gas, and completely deodorizes the preheated gas. The purpose is to provide steel manufacturing equipment.

[Means for solving problems]

The electric furnace steelmaking equipment of the present invention is applied to an electric furnace steelmaking equipment having a preheating device 1 for preheating scrap 6 with electric furnace exhaust gas 4, and a deodorizing device 2 for cleaning the preheated gas 16 with a chemical solution and electrostatically collecting the dust. . Its characteristics will be described based on FIG. 1: an exhaust gas return passage 31 equipped with an induced blower 30 for returning preheated gas 16 discharged from the preheating device 1 to the combustion tube 5 immediately after the electric furnace 3; Branched from the exhaust gas return passage 31 and connected to the main exhaust gas passage 10 from the combustion tube 5 to the deodorizing device 2, with a switching valve 33 interposed, and installed in the exhaust gas passage 34 leading to the deodorizing device 2, A _THC detection device 35 detects the total amount of hydrocarbons in the exhaust gas sent to the deodorizing device 2. When the detected value of the _THC detection device 35 becomes higher than a set value, the switching valve 33 is closed and the induced blower 30 is closed. An exhaust gas feedback control means 37 for starting the operation is provided.

[Effect]

When the temperature of the electric furnace exhaust gas 4 is high, the temperature inside the combustion tube 5 into which the exhaust gas is introduced is also high. The exhaust gas is introduced into a preheating device 1 to preheat the scrap 6. The preheated gas 16 discharged at that time is introduced into a deodorizing device 2 that performs chemical cleaning and electrostatic precipitation, and total hydrocarbons in the preheated gas 16 are removed. In the deodorizing process, a _THC detection device 35 installed in the exhaust gas passage 34 leading to the deodorizing device 2 detects the total amount of hydrocarbons in the exhaust gas sent to the deodorizing device 2. If the detected value of the _THC detection device 35 is lower than the set value, the preheated gas 16 is deodorized by chemical cleaning and electrostatic precipitation.

On the other hand, when the detected value of the _THC detection device 35 becomes higher than the set value, the signal from the exhaust gas return control means 37 branches off from the exhaust gas return passage 31 while maintaining the deodorizing process by chemical cleaning and electrostatic precipitation. Then, the switching valve 33 of the branch passage 32 connected to the main exhaust gas passage 10 from the combustion tube 5 to the deodorizing device 2 is closed. Note that the degree of closure is adjusted by a command signal from the exhaust gas feedback control means 37 as necessary. At the same time, an induced blower 30 in the exhaust gas return path 31 returns the preheated gas 16 discharged from the preheating device 1 to the combustion tube 5 immediately after the electric furnace 3.
operation is started. As a result, preheated gas 1
All or part of the hydrocarbon 6 is returned to the combustion tube 5, and a part of the total hydrocarbon is incinerated. Therefore, the total amount of hydrocarbons introduced into the deodorizing device 2 is reduced, and the operating load for removing the total hydrocarbons in the deodorizing device 2 does not increase.

〔Effect of the invention〕

The present invention provides an exhaust gas return passage through which preheated gas is returned to the combustion tube immediately after the electric furnace, installs an induced blower in it, and connects it to the main exhaust gas passage that branches from the exhaust gas return passage and extends from the combustion tube to the deodorizing device. A switching valve is interposed in the branch passage, and a _THC detection device that detects the total amount of hydrocarbon in the exhaust gas is installed in the exhaust gas passage leading to the deodorizing device, and switching is performed based on the detected value of the _THC detection device. Since it is equipped with an exhaust gas return control means that closes the valve and starts the operation of the induced blower, the exhaust gas return control means controls all or part of the exhaust gas introduced into the deodorizing device based on the detection signal from the _THC detection device. It can be returned to the combustion tube. Therefore, when the total amount of hydrocarbons in the exhaust gas is extremely large, the operating load on the deodorizing device can be reduced by incineration in the combustion tube, and the deodorization can be performed as desired. In addition, the amount of exhaust gas returned to the combustion tube is not large, which prevents excessive temperature drop in the combustion tube and prevents preheating of the scrap from being inhibited.
It is possible to reduce the melting power unit in the electric furnace and shorten the steelmaking time.

〔Example〕

The present invention will be described in detail below based on examples thereof.

FIG. 1 is an overall system diagram of electric steelmaking equipment including a preheating device 1 and a deodorizing device 2, which can preheat scrap using electric furnace exhaust gas. In this equipment, high-temperature electric furnace exhaust gas 4 containing dust generated during operation of the electric furnace 3 is introduced into a combustion tube 5, where combustibles in the exhaust gas are combusted, and then all or A portion of the exhaust gas is led out to a preheating device 1, and the scrap 6 charged into the electric furnace 3 is preheated by the thermal energy of the exhaust gas.

The electric furnace 3 for melting scrap has a gas discharge port on the furnace wall, etc., and is connected to an exhaust gas passage 7 for leading out the electric furnace exhaust gas 4, to which a gap adjustment ring 8 and a combustion tube 5 are connected in sequence. ing.
A suitable amount of outside air 9 is sucked into the gap adjustment ring 8 and is supplied to the combustion tube 5 together with the electric furnace exhaust gas 4. The combustion tube 5 is capable of burning combustible substances such as CO gas by mixing the exhaust gas 4 and the outside air 9 and by spontaneous ignition, and is also capable of removing coarse dust. The structure is as follows. At the top of such a combustion tube 5, there is a main exhaust gas passage 1 that directly leads out part or all of the exhaust gas after combustion to a dust remover 17, which will be described later.
0 and a sub-exhaust gas passage 11 leading to the preheating device 1 are connected via a switching valve 12. For example, a plurality of preheaters 1a and 1b arranged in parallel are connected to the sub-exhaust gas passage 11 via switching valves 13a, 13b, 14a and 14b provided before and after each preheater. In addition, each preheater 1
A booster fan 15 is provided for introducing into the exhaust gases 1 and 1b, and preheated gas 16 containing odorous substances and oil mist and having a bad odor is led out to the main exhaust gas passage 10 described above.

Main exhaust gas passage 1 into which preheated gas 16 is introduced
A dry dust remover 17 such as a bag filter is installed downstream of the combustion tube 5 to remove dust from the exhaust gas 4 or preheated gas 16 or both exhaust gases 4 and 16 from the combustion tube 5. Immediately after that, a main induced blower 1 that sucks the exhaust gas in the main exhaust gas passage 10 into the dust remover 17 and leads out the preheated gas 16 to the deodorizing device 2 is installed.
8 is provided. The deodorizing device 2 includes an exhaust gas cleaning tower 19 and a wet electrostatic precipitator 20, which will be described next.

The exhaust gas cleaning tower 19 lowers the temperature of the exhaust gas 21 from the dust remover 17 to equalize the temperature, and at the same time removes odor substances in the exhaust gas by chemical cleaning, and also removes a large amount of odor substances by the heat contained in the gas. It generates saturated steam. In other words, even if the temperature of the electric furnace exhaust gas 4 fluctuates as shown in FIG.
Lower the temperature to 80℃. At this time, saturated steam corresponding to the exhaust gas temperature is generated from the cleaning liquid 22, and oil mist in the exhaust gas adheres to the steam and fine water droplets. At the same time, the exhaust gas 21 flowing inside is cleaned with a cleaning liquid 22 containing a neutralizing agent such as acids or alkalis, a solvent having a strong affinity for odor substances, and the like. Note that the exhaust gas temperature is detected by a temperature sensor (not shown), and the amount of cleaning liquid adjusted in response to the temperature signal is sprayed from the sprinkler 23.

The wet electrostatic precipitator 20 has a function of collecting fine oil mist adhering to saturated water vapor contained in the exhaust gas 24 from the exhaust gas cleaning tower 19 together with water vapor particles. This consists of a discharge electrode 25 and a dust collection electrode 26, and generates positive and negative ions very close to the discharge electrode 25 by corona discharge. When the negative ions move toward the cylindrical inner peripheral surface of the dust collection electrode 26, the water vapor particles to which the oil mist is attached are negatively charged, and the water vapor particles are attracted to the dust collection electrode 26 by the electric force. It is designed to collect fine oil mist, which is difficult to capture alone, together with water vapor particles. The exhaust gas cleaning tower 19 and the wet electrostatic precipitator 20 are equipped with a pump 27 that circulates the cleaning liquid 22 and a pump 29 that supplies cleaning water 28 that rinses the surface of the dust collecting electrode 26.
is provided. Incidentally, the deodorizing device 2 is not limited to the above-mentioned configuration, and may also include, for example, a temperature control tower and a deodorizing tower independently provided, and a wet electrostatic precipitator added thereto. In short, it is only necessary to be able to chemically clean the exhaust gas, generate desired water vapor particles, attach oil mist, and electrostatically collect the oil mist.

The preheated gas 16 discharged from the preheating device 1 described above is normally led out to the dust remover 17 from the main exhaust gas passage 10, but in addition, the preheated gas 16
An exhaust gas return passage 31 equipped with an induced blower 30 is provided so that the exhaust gas can be returned to the combustion tube 5 immediately after the electric furnace 3. The deodorizing device 1 branches from the exhaust gas return passage 31 and extends from the combustion tube 5.
A branch passage 3 connected to the main exhaust gas passage 10 leading to
2 is provided, and a switching valve 33 is interposed therebetween. The switching valve 33 is opened and closed by a drive signal from an exhaust gas feedback control means 37, which will be described later, and its opening degree is adjusted as necessary.

A _THC detection device 35 for detecting the total amount of hydrocarbons in the exhaust gas 21 is interposed in the exhaust gas passage 34 leading to the deodorizing device 2 described above. This _THC detection device 35 burns hydrogen in the exhaust gas, measures the extent to which it is ionized by the flame, and uses the detected value to send a signal of the total amount of hydrocarbons to the exhaust gas feedback control means 37.
This is what is output to. Therefore, since the _THC detection device 35 does not need to introduce all of the exhaust gas 21, the exhaust gas passage 3 on the downstream side of the dust remover 17
It is installed in the bypass passage 36 provided in 4.
Note that since it is preferable to introduce the exhaust gas from which dust has been removed into the _THC detection device 35, it is shown in the illustrated position, but it may be installed upstream of the dust remover 17.

When the detected value of the _THC detection device 35 becomes higher than the set value, an exhaust gas feedback control means 37 is provided which closes the above-mentioned switching valve 33 and starts operation of the induced blower 30. This is configured to receive a detection signal from the _THC detection device 35 and output a signal for driving the switching valve 33 and induced blower 30, and is composed of a microcomputer and the like. The fixed storage section stores, for example, the total hydrocarbons of the exhaust gas 21 introduced into the deodorizing device 2.
When it exceeds 250ppm, a drive signal is output.
The value is stored as a set value. Further, a control drive signal is outputted so as to adjust the degree of closure of the switching valve 33 or the amount of air blown by the induced fan 30 according to the total amount of hydrocarbons, if necessary. The set value is determined based on the change in the total amount of hydrocarbon and its magnitude in FIG.

In electric furnace steelmaking equipment with such a configuration,
The scrap 6 is preheated and the preheated gas 16 is deodorized in the following manner.

First, the scrap 6 preheated in the preheating device 1 is charged into the electric furnace 3 and is melted. In such refining, as shown in FIG. 2, scrap is added one after another to raise the melting temperature. Meanwhile, high-temperature electric furnace exhaust gas 4 containing a large amount of dust is led out from the electric furnace 3 to the exhaust gas passage 7, and even outside air 9 introduced through the gap adjustment ring 8 contains combustible substances such as CO gas. While being burned in the combustion tube 5, coarse dust 38
is removed. If preheating of the scrap 6 is not required now, the switching valve 12 is switched so that all of the exhaust gas 4 is led out to the main exhaust gas passage 10. Exhaust gas from the combustion tube 5 is transferred to the main induced blower 1
8 into the dust remover 17, where a predetermined amount of dust is collected.
released into the atmosphere via The electric furnace exhaust gas 4 is
This is because, since it is completely combusted in the combustion tube 5, unlike the preheated gas 16 after preheating the scrap 6, there is no foul odor.

When the scrap 6 is to be preheated by the thermal energy contained in the exhaust gas 4 during operation of the electric furnace 3, the opening degree of the switching valve 12 is changed and the switching valves 13a, 14a, etc. are opened. When the booster fan 15 installed downstream of the preheater, for example 1a, containing scraps such as dry powder, pig iron, rolling scraps, and iron scraps is driven, the suction force of the booster fan 15 moves from the combustion tube 5 to the sub-exhaust gas passage 11. A corresponding amount of gas is introduced and the remaining exhaust gas is led out from the main exhaust gas channel 10 directly to the dust remover 17 . 100 with foul odor cooled by preheating the scrap
The preheated gas 16 at about ~300°C is led out to the main exhaust gas passage 10 through the open switching valve 33, where it is combined with the exhaust gas led out directly from the combustion tube 5 for dust removal. The mixed exhaust gas is removed by a dust remover 17. Since this exhaust gas has an extremely disgusting odor, it cannot be immediately discharged from the stripping tower 40, but is introduced into the exhaust gas cleaning tower 19 by switching the switching valve 39.
Therein, a water sprinkler 23 sprays a cleaning liquid 22 in an amount adjusted according to temperature fluctuations of the exhaust gas 21 . Even if the temperature of the dust-containing high-temperature exhaust gas 2 fluctuates as shown in FIG.
It is also maintained at a temperature and concentration suitable for removing odorous substances. Therefore, the chemical removal treatment of the odor substances is carried out under certain conditions using a neutralizer or the like in the cleaning liquid 22. Furthermore, the heat given by the exhaust gas 21 and the heat received by the cleaning liquid 22 balance their temperatures, and the water in the cleaning liquid 22 evaporates to generate a substantially constant amount of saturated steam. The oil mist cannot be removed by the cleaning liquid 22, but it adheres to generated water vapor particles and fine water droplets. Exhaust gas 24 from which odor substances have been removed
Wet electrostatic precipitator 20 with water vapor particles, etc.
will be introduced in In the electric precipitator 20, the dust collecting electrode 26
A negative high voltage is applied to the discharge electrode 25 with the electrode 25 grounded, a strong electric field is formed around the discharge electrode 25, and corona discharge occurs. Positive and negative ions are generated in the vicinity of the discharge electrode 25, the positive ions are immediately neutralized by the negative discharge electrode 25, and the negative ions move toward the dust collecting electrode 26 in the electric field and generate water vapor. The particles and the like are negatively charged, and the oil mist and the water vapor particles are collected together with the dust collecting electrode 26. The purified exhaust gas is released into the atmosphere from the diffusion tower 40. Note that the switching valve 12 located downstream of the combustion cylinder 5
It goes without saying that if all of the exhaust gas 4 passing through is introduced into the preheater 1a, much of the thermal energy possessed by the exhaust gas 4 can be used for preheating the scrap 6.

By the way, the total amount of hydrocarbons contained in the preheated gas discharged from the preheating device 1 when the temperature of the electric furnace exhaust gas is high is as shown by the solid line in Figure 3. This is most common during the illustrated period A, which corresponds to the period when the temperature inside the device 1 rises, and there are also periods when it becomes noticeable temporarily, such as period B. Except for period B, the detection value of the _THC detection device 35 installed in the bypass passage 36 of the exhaust gas passage 34 leading to the deodorizing device 2 is lower than the set value, and the switching valve 3
3 is in a fully open state, the induced blower 30 is not operated, and the preheated gas 16 and the exhaust gas directly led out from the combustion tube 5 are introduced into the deodorizing device 2, where they are deodorized by chemical cleaning and electrostatic precipitation. The deodorizing device 2 is processed under normal load operation.

On the other hand, when the detected value of the _THC detection device 35 becomes higher than the set value, the signal from the exhaust gas return control means 37 branches off from the exhaust gas return passage 31 while maintaining the deodorizing process by chemical cleaning and electrostatic precipitation. Then, the switching valve 33 of the branch passage 32 connected to the main exhaust gas passage 10 from the combustion tube 5 to the deodorizing device 2 is closed. Note that the degree of closure is adjusted by a command signal from the exhaust gas feedback control means 37 as necessary. At the same time, the induced blower 30 in the exhaust gas return passage 31 that returns the preheated gas 16 discharged from the preheating device 1 to the combustion tube 5 immediately after the electric furnace 3 is started. As a result, all or a portion of the preheated gas 16 is returned to the combustion tube 5, and a portion of the total hydrocarbon is incinerated. Therefore, the total hydrocarbon introduced into the deodorizing device 2 is reduced from the amount shown by the solid line in FIG. 3 to the amount shown by the broken line, and the operation for removing the total hydrocarbon in the deodorizing device 2 is as follows: This is possible with almost the same load as in period A.

Incidentally, without adopting the exhaust gas feedback control means 37, the switching valve 33, and the induced blower 30 as in the present invention, it is possible to avoid increasing the operating load on the deodorizing device 2 even when the total hydrocarbon concentration is temporarily extremely high. As a means of completing
As shown by the imaginary line in the figure, an adsorption tower 41 containing activated carbon may be interposed in the downstream process of the electrostatic precipitator 20. Induced air blower 3 in the present invention
A comparison of the power required for 0 and the power consumption when the above-mentioned adsorption tower 41 is employed is as follows.

(1) [Comparative example] When using the adsorption tower 41 For example, as shown in Figure 3, in order to cope with the case where the peak value of total hydrocarbon exceeds 350 ppm, the pressure loss in the adsorption tower 41 must be It is necessary to expect 150mmAq, and if it is borne by the main induced blower 18,
For example, the power consumption will increase by 52KW.

(2) [Invention] When using the induced fan 30 If the induced fan 30 is operated only during the period B shown in FIG. 3, the increase in power at that time is, for example,
It will be 12KW.

As is obvious when comparing the two, when the present invention is employed, the power consumption is significantly reduced when performing the same deodorizing treatment. Moreover, when the adsorption tower 41 is employed, the cost of regenerating activated carbon is also incurred, and the running cost of deodorizing treatment increases significantly.Considering this, it can be said that the effects of the present invention are incomparable. As described above, according to the present invention, the operating load of the deodorizing device 2 is not increased, and increased power consumption can be kept to a minimum, and extremely excellent practical effects are exhibited.

[Brief explanation of drawings]

Figure 1 is an overall system diagram of electric steelmaking equipment to which the present invention is applied, Figure 2 is a graph showing fluctuations in exhaust gas temperature over time in one cycle of electric furnace operation, and Figure 3 is installed in a deodorizing device. It is a graph showing the fluctuation of the total amount of hydrocarbons. 1... Preheating device, 2... Deodorizing device, 3... Electric furnace, 4... Electric furnace exhaust gas, 5... Combustion tube, 6...
Scrap, 10... Main exhaust gas passage, 16... Preheated gas, 30... Induced blower, 31... Exhaust gas return passage, 32... Branch passage, 33... Switching valve, 34... Exhaust gas passage, 35... _THC detection device, 37...exhaust gas feedback control means.

Claims (1)

[Scope of Claims] 1. In an electric furnace steelmaking facility equipped with a preheating device for preheating scrap with electric furnace exhaust gas and a deodorizing device for cleaning the preheated gas with a chemical solution and electrostatically collecting the gas, the preheat discharged from the preheating device In order to return the waste gas to the combustion tube immediately after the electric furnace, an exhaust gas return passage equipped with an induced blower is provided, and the exhaust gas return passage branches off from the exhaust gas return passage and is connected to the main exhaust gas passage leading from the combustion tube to the deodorizing device. A branch passage with a switching valve interposed therebetween is provided, and a _THC detection device for detecting the total amount of hydrocarbon in the exhaust gas sent to the deodorization device is interposed in the exhaust gas passage leading to the deodorization device, and the _THC detection device An electric furnace steelmaking facility characterized in that an exhaust gas feedback control means is provided which closes the switching valve and starts operation of the induced blower when the detected value becomes higher than a set value.