JP3566868B2 - Exhaust gas detoxification equipment and method for detoxification of electric furnace or scrap preheating device for electric furnace - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is to remove harmful components contained in exhaust gas generated during melting, scouring and heating from an electric furnace for melting or refining metallic materials or exhaust gas generated when preheating an electric furnace scrap. More specifically, the present invention relates to a facility and a method for detoxifying exhaust gas by powder blown into an tower A through which exhaust gas flows upward from below.
[0002]
[Prior art]
When melting or scouring metal materials using an electric furnace, or when preheating electric furnace scrap with a preheating device, white smoke, foul odors, aromatic chlorine compounds, etc. are generated as harmful components in the exhaust gas. Various methods have been proposed as a method of removing these harmful components to make the exhaust gas harmless.
[0003]
For example, Japanese Patent Application Laid-Open No. 9-324990 discloses that powder is blown from below a tower A in which exhaust gas flows upward from below, and harmful components in the exhaust gas are adsorbed by the blown powder. A method for removal is disclosed. The flow rate of the exhaust gas in the tower A is set to a speed substantially equal to the free sedimentation speed of the blown powder falling in the exhaust gas, and is adjusted so that the powder floats in the tower A. Regarding the blowing amount of the powder, a sufficient amount is always supplied to remove the harmful components regardless of the increase or decrease of the harmful components in the exhaust gas.
[0004]
[Problems to be solved by the invention]
Exhaust gas from a steelmaking electric furnace greatly varies depending on the operation state, and the exhaust gas amount, the exhaust gas temperature, and the exhaust gas component fluctuate during each operation period (melting 1, melting 2, heating, etc.). The same applies to the exhaust gas from the electric furnace scrap preheating device. As the amount of exhaust gas and the content of harmful components in the exhaust gas change, the amount of harmful components to be removed also changes. During certain periods of operation, the amount of harmful components generated in the exhaust gas may be very small. In the conventional method, the amount of powder blown is set to a value that allows sufficient adsorption and removal even when the amount of harmful substances generated in the exhaust gas is large.
[0005]
However, in such a control method, even when the amount of the harmful substance in the exhaust gas is small, the amount of powder to be blown is the same as that in the time when the amount of the harmful substance in the exhaust gas is large. Even if the amount is small, a large amount of powder will be used. The amount of the powder used is not limited to the powder cost, but also leads to an increase in blowing power cost and a cost for treating dust finally discharged, which is inefficient and uneconomical.
[0006]
The present invention solves the above-described problems and reduces powder cost, blowing power cost, and dust processing cost by performing control to increase or decrease the amount of powder blown in accordance with the amount of harmful substances to be removed. An object of the present invention is to provide an exhaust gas detoxification facility and a detoxification method for an electric furnace or a scrap preheating device for an electric furnace.
[0007]
[Means for Solving the Problems]
That is, the gist of the present invention is:
(1) A tower 7, which flows exhaust gas upward from below, B tower 9, which is connected to the downstream side of A tower and flows exhaust gas downward from above, and supplies powder into the A tower from below the A tower. Of the exhaust gas of the electric furnace 1 or the scrap preheating device 3 for an electric furnace having the powder blowing device (14, 15) for upstream and downstream of the scrap preheating device 3 or downstream of the electric furnace 1. A detector 20 for measuring exhaust gas temperature is provided, and a control device 21 for controlling a powder blowing amount of the powder blowing device according to the exhaust gas temperature information from the detector 20 is provided. Equipment.
(2) A combination of the tower A 7, the tower B 8, and the powder blowing device is provided in at least two or more stages in the flow path of the exhaust gas, and a thermometer 16 for measuring the temperature of the exhaust gas is provided at the inlet of the tower A at each stage. 2. The exhaust gas detoxification equipment according to claim 1, further comprising an automatic selection device provided for selecting a tower for performing powder injection according to the measurement result of the thermometer.
(3) A method for detoxifying the exhaust gas in the electric furnace 1 or the scrap preheating device 3 for the electric furnace, in which the exhaust gas is caused to flow upward from below in the A tower 7 and the exhaust gas is rendered harmless by the powder blown into the A tower from below the A tower. Measuring the exhaust gas temperature upstream and downstream of the scrap preheating device or downstream of the electric furnace, and adjusting the amount of powder blown based on the exhaust gas flow rate and the exhaust gas temperature information. Method.
(4) The adjustment of the powder blowing amount based on the exhaust gas flow rate information is performed by increasing and decreasing the powder blowing amount based on the increase and decrease of the exhaust gas flow rate, and the powder blowing amount based on the exhaust gas temperature information. The adjustment of the amount is such that when the exhaust gas temperature is higher than a predetermined temperature T1, the powder blowing amount is reduced, and when the exhaust gas temperature is lower than a predetermined temperature T2, the powder blowing amount is reduced. The method for detoxifying exhaust gas (T1> T2) according to claim 3, wherein the method is performed.
It is.
[0008]
When the electric furnace 1 or the scrap preheating device 3 for the electric furnace is operated, the concentration of harmful components in the exhaust gas, particularly the concentration of the aromatic chlorine compound, is close to the temperature of the exhaust gas at the electric furnace or the temperature of the exhaust gas at the entrance or exit of the scrap preheating device. Turns out to be relevant. When the exhaust gas temperature is in the range of 300 ° C. to 600 ° C., the concentration of harmful components in the exhaust gas is high, and when the exhaust gas temperature is higher or lower than the above temperature range, the concentration of the harmful component in the exhaust gas decreases. The relationship between the concentration of harmful components in the exhaust gas and the exhaust gas temperature can be accurately grasped by measuring each electric furnace or scrap preheating device. The amount of harmful substances in exhaust gas is proportional to the product of the amount of exhaust gas and the concentration of harmful components in the exhaust gas.
[0009]
The harmful substances in the exhaust gas are adsorbed and removed by the powder blown in the tower A. When the amount of harmful substances generated per unit time is small, harmful substances can be removed even if the amount of powder blown is reduced, and the amount of harmful substances generated per unit time and the amount of powder blown can be approximately proportional. .
[0010]
In the present invention, the concentration of harmful components in the exhaust gas is estimated by measuring the exhaust gas temperature on the exit side of the electric furnace or the exhaust gas temperature on the entrance and exit sides of the scrap preheating device, and the product of the exhaust gas amount and the harmful component concentration estimated value is used. The amount of harmful substances generated per unit time is estimated, and control is performed such that the amount of powder blown is large when the amount of harmful substances is large, and the amount of powder blown is small when the amount of harmful substances is small. Accordingly, when the amount of harmful substances generated in the exhaust gas is small, the amount of powder blown can be reduced, and the power for blowing powder can be further reduced. Further, since the amount of powder to be blown is reduced, the amount of dust to be processed after collection is also reduced.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the exhaust gas flows upward from below in the tower A, and the powder is blown below the tower A 7. Normally, a B tower 9 in which exhaust gas flows downward from above is disposed, and the upper end of the A tower and the upper end of the B tower are connected. Dust boxes 6 and 10 are provided at the lower ends of the tower A and the tower B, respectively.
[0012]
In the exhaust gas treatment equipment, the exhaust gas is sucked in accordance with the amount of exhaust gas generated by the electric furnace or the scrap preheating device. The velocity at which the powder blown in the tower A does not reach the speed at which it floats and stops, and the residence time of the blown powder in the tower A also fluctuates according to the fluctuation of the exhaust gas velocity.
[0013]
In the tower A, the speed at which the powder rises is a speed obtained by subtracting the free sedimentation speed of the powder from the exhaust gas speed. In the tower A, the powder has a relative speed to the flue gas equal to the free sedimentation speed of the powder, so that the harmful components of the flue gas are adsorbed on the powder while the powder stays in the tower A. Since the powder stays in the tower A for a time necessary for adsorbing the harmful component to the harmful component adsorption capacity limit of the powder, the harmful component adsorption capability of the powder can be sufficiently utilized. The powder discharged together with the exhaust gas from the tower A usually descends in the tower B and is collected in the dust box 10 at the lower end of the tower B.
[0014]
The amount of exhaust gas generated is small, the exhaust gas speed is reduced, and the residence time of the powder in the tower A is prolonged. When the exhaust gas speed is lower than the free sedimentation speed of the powder, the powder is recovered in the dust box 6 below the tower A without rising. The height and the inner diameter of the tower A are within the normal fluctuation range of the exhaust gas flow rate, and even if the exhaust gas flow rate is high and the exhaust gas speed is high, the powder residence time in the tower A is a time sufficient for removing harmful substances, and The exhaust gas velocity is selected to be higher than the free sedimentation velocity of the powder even if the exhaust gas flow rate is small.
[0015]
As the blown powder, dust from an electric furnace which is collected by an electric furnace exhaust gas dust collector can be used. In addition, slaked lime, activated carbon, zeolite, or the like may be used.
[0016]
The concentration of harmful components, particularly aromatic chlorine compounds, in the exhaust gas is strongly affected by the exhaust gas temperature upstream and downstream of the scrap preheating device or downstream of the electric furnace, and the concentration of the harmful component varies depending on the temperature. More specifically, when the temperature is in the range of 300 ° C. to 600 ° C., the concentration of the harmful component increases, and when the temperature is higher or lower than the above temperature range, the concentration of the harmful component decreases. Therefore, if the relationship between the temperature and the concentration of the harmful component in the exhaust gas is measured in advance, the concentration of the harmful component in the exhaust gas can be estimated by measuring the temperature during operation.
[0017]
Since the amount of harmful components in the exhaust gas generated per unit time is proportional to the product of the amount of the exhaust gas and the concentration of the harmful component in the exhaust gas, the amount of powder blown into the tower A is estimated from the amount of the exhaust gas and the concentration of the harmful component in the exhaust gas. It can be blown in proportion to the product of the values. This makes it possible to reliably remove harmful components when the amount of harmful components generated in the exhaust gas is large, and to reduce the amount of powder blown when the amount of harmful components generated is small. The powder blowing amount according to the harmful component generation amount is determined in advance by experiments or the like.
[0018]
Control of the amount of powder blown based on the measurement results of the exhaust gas temperature upstream and downstream of the scrap preheating device or downstream of the electric furnace should be performed based on the relationship between the measured temperature and the concentration of harmful components in the exhaust gas in advance. Can be. At a temperature higher than the temperature T1 near 600 ° C., the concentration of the harmful component decreases, and at a temperature lower than the temperature T2 near 300 ° C., the concentration of the harmful component decreases. Therefore, the control of the amount of powder blown is performed by determining the temperatures T1 and T2 in advance by measurement or the like. When the temperature of the exhaust gas is higher than the predetermined temperature T1, the amount of powder blown is reduced, and the temperature of the exhaust gas is set in advance. When the temperature is lower than the temperature T2, it can be performed by reducing the powder blowing amount. For example, when the amount of powder blown when the exhaust gas temperature is between T1 and T2 is 1, control is performed such that the amount of powder blown when the exhaust gas temperature> T1 or when the exhaust gas temperature <T2 is 0.2. Is valid.
[0019]
The ability of the powder to absorb harmful substances is affected by the temperature of the exhaust gas in the tower A where the harmful substances are adsorbed to the powder. When the exhaust gas temperature is in the range of 100 ° C. to 150 ° C., the ability of the powder to absorb harmful components is maximized. When the exhaust gas temperature at the exit side of the electric furnace or the scrap preheating device is high, at the entrance side of the exhaust gas detoxification facility of the present invention, the exhaust gas temperature does not sufficiently decrease and becomes higher than the appropriate exhaust gas temperature range. There is. In the present invention, when a plurality of combinations of the tower A and the tower B are arranged in series, the tower A and the tower B exhibit the function of a vertical cooling tower, and can be arranged even in a small site. The exhaust gas temperature in the tower A on the downstream side of the column falls to a desirable temperature. Therefore, the exhaust gas temperature at the inlet of each tower A is measured, and the powder is blown into the stage where the exhaust gas temperature is the most preferable, whereby the exhaust gas can be detoxified most efficiently.
[0020]
【Example】
(Example 1)
FIG. 1 shows a first embodiment of the present invention. Exhaust gas generated from the electric furnace 1 passes through a water-cooled flue 2 and is introduced into a scrap preheating device 3. Thereafter, the gas is introduced into the header pipe 5 via the water-cooled flue 4, passes through the entrance dust box 6, is rendered harmless by the exhaust gas detoxification facility of the present invention, passes through the exit dust box 10, and passes to the duct 11. The stream is led to a dust collector (not shown) by the blower 12 and is finally released to the atmosphere. A temperature measuring device 19 is provided in the water-cooled flue 2 connecting the electric furnace 1 and the scrap preheating device 3, and a temperature measuring device 20 is provided in the water-cooled flue 4 connecting the scrap preheating device 3 and the header pipe 5. You. The temperature measuring devices 19 and 20 are connected to a control device 21, and the control device 21 controls the powder supply amount of the powder supply device 14 based on the temperature information from the temperature measuring devices 19 and 20.
[0021]
In the exhaust gas detoxification facility of the present invention, the exhaust gas flows upward from below in the tower A 7, and then flows downward from above in the tower B 9. The tower A and the tower B are connected via a 180-degree bent pipe 8. A powder supply device 14 is provided below the A tower 7, and supplies powder into the A tower via a pipe 15 and a powder supply port 13. The powder supply device 14 and the pipe 15 constitute a powder blowing device of the present invention. Electric furnace generated dust was used as the blown powder.
[0022]
The amount of powder blown was controlled by the following equation.
Z = β × α × Q
Here, Z is a powder blowing amount, Q is an exhaust gas flow rate per unit time, α is a proportional constant that determines a standard powder blowing amount per exhaust gas flow rate, and β is a coefficient to be changed based on the exhaust gas temperature measurement result. is there. In the present embodiment, β = 0.2 when the exhaust gas temperature> 600 ° C. or the exhaust gas temperature <300 ° C., and β = 1 in other cases.
[0023]
As a result, the effect of reducing the amount of powder blown by about 40% compared to the conventional example in which the amount of powder blown was not changed in accordance with the exhaust gas temperature could be obtained.
[0024]
(Example 2)
FIG. 2 shows a second embodiment of the present invention. The same combination of the tower A and the tower B as in the first embodiment is arranged in two stages, and the outlet side of the first stage and the inlet side of the second stage are connected by the connecting pipe 18. A thermometer (16a, 16b) is arranged on each side of the tower A, and the temperature of the exhaust gas on the side of the tower A is measured. Since the tower A and the tower B in each stage have the function of a vertical cooling tower, the exhaust gas temperature is lower in the latter stage than in the former stage. Therefore, of the exhaust gas temperatures on the inlet side of the tower A in each stage, a stage having a temperature (100 ° C. to 150 ° C.) having an excellent ability to adsorb harmful substances to the powder is selected, and the powder is blown in that stage. .
[0025]
【The invention's effect】
The exhaust gas detoxification facility of the present invention can reduce the amount of powder used, the power for blowing powder, and the amount of dust treatment while maintaining the amount of harmful components in the released exhaust gas at a low level. The running cost can be reduced.
[Brief description of the drawings]
FIG. 1 shows an embodiment of an exhaust gas detoxification facility according to the present invention. FIG. 2 shows another embodiment of an exhaust gas detoxification facility according to the present invention.
1 electric furnace (melting furnace)
2 Water-cooled flue 3 Scrap preheater 4 Water-cooled flue 5 Header pipe 6 Dust box 7 Tower A 8 Bent pipe 9 Tower B 10 Dust box 11 Duct 12 Blower 13 Powder supply port 14 Powder supply device 15 Pipe 16 Thermometer 17 Cable 18 Connection pipe 19 Temperature measuring device 20 Temperature measuring device 21 Control device

Claims (4)

Tower A, which flows exhaust gas upward from below, Tower B, which is connected to the downstream side of Tower A and flows exhaust gas downward from above, and powder injection for supplying powder into Tower A from below Tower A In the exhaust gas detoxification equipment of an electric furnace or a scrap preheating device for an electric furnace having a device,
A detector for measuring the exhaust gas temperature is disposed upstream and downstream of the scrap preheating device or downstream of the electric furnace, and the amount of powder blown by the powder blowing device is controlled according to the exhaust gas temperature information from the detector. Exhaust gas detoxification equipment characterized by disposing a control device. At least two or more stages comprising a combination of the tower A, the tower B, and the powder blowing device are provided in the exhaust gas flow path, and a thermometer for measuring the temperature of the exhaust gas is provided at the inlet of the tower A at each stage. 2. The exhaust gas detoxification equipment according to claim 1, further comprising an automatic selection device for selecting a tower for performing the powder injection according to the measurement result. An exhaust gas detoxification method for an electric furnace or a scrap preheating device for an electric furnace, in which exhaust gas is caused to flow upward from below in the tower A and the exhaust gas is rendered harmless by powder blown into the tower A from below the tower A,
An exhaust gas detoxification method characterized by measuring exhaust gas temperatures upstream and downstream of the scrap preheating device or downstream of an electric furnace, and adjusting the amount of powder blown based on the exhaust gas flow rate and the exhaust gas temperature information. The adjustment of the powder injection amount based on the exhaust gas flow rate information is performed by increasing or decreasing the powder injection amount based on the increase or decrease of the exhaust gas flow rate, and the adjustment of the powder injection amount based on the exhaust gas temperature information. Is performed by reducing the amount of powder blown when the exhaust gas temperature is higher than a predetermined temperature T1, and by reducing the amount of powder blown when the exhaust gas temperature is lower than a predetermined temperature T2. The exhaust gas detoxification method according to claim 3, characterized in that:
Note that T1> T2.

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