JPH11100610A - Method for preheating iron source in preheating vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the trouble in an equipment caused by the combustion heat of unburnt gas in waste gas and to simultaneously improve the preheating efficiency of an iron source, at the time of preheating the iron source in a preheating vessel with exhaust gas from an electric furnace. SOLUTION: Plural nozzles 14, 15, 16, 17, 18 are arranged in the flowing direction of the exhaust gas in the preheating vessel 7, and oxygen-containing gas is blown into the preheating vessel from these nozzles to preheat the iron source 10 while burning the unburnt gas in the exhaust gas. At this time, the combustion of the unburnt gas is accurately controlled by individually controlling the blowing quantity of the oxygen-containing gas and the blowing angle of the nozzle for each nozzle, thereby the heat conductive efficiency is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preheating method for efficiently preheating an iron source such as iron scrap or direct reduced iron using a high-temperature exhaust gas discharged from an electric furnace. Things.

[0002]

2. Description of the Related Art In an electric furnace, an arc source generated from an electrode heats and melts an iron source such as iron scrap or directly reduced iron and refines it to produce molten steel. A preheating tank using high-temperature exhaust gas generated from a furnace has been provided to preheat an iron source, thereby reducing power consumption.

[0003] In recent years, as a measure for further reducing the amount of electric power consumption, a method in which a carbon material such as coke and oxygen are blown into molten steel or molten slag in an electric furnace to utilize heat generated by a reaction between the carbon material and oxygen. As a result, the exhaust gas has a high temperature and contains a large amount of unburned CO gas, and the exhaust gas has been introduced into the preheating tank. Therefore, since the exhaust gas discharged through the preheating tank contains a large amount of CO gas, unburned gas such as CO gas is burned and then released to the atmosphere.

[0004] Since a dedicated combustion device is required for this combustion and the CO gas in the exhaust gas is not used effectively, let's make effective use of the unburned gas such as the CO gas in the exhaust gas. Some methods have been proposed.

For example, Japanese Patent Application Laid-Open No. Hei 8-136163 (hereinafter referred to as "prior art 1") has a sensor for detecting the concentration of CO gas in exhaust gas in an exhaust gas passage of a preheating tank. The CO gas is burned by controlling the amount of air or oxygen introduced into the upper space in the electric furnace, that is, the free space surrounded by the furnace wall and the furnace lid, so as to keep the gas concentration below a certain value. A preheating method is disclosed.

[0006] Also, Japanese Patent Application Laid-Open No. 9-4987 (hereinafter referred to as
In "Prior art 2"), air is blown from at least two air nozzles toward a free space in an electric furnace below a center position of an exhaust gas supply duct to a preheating tank arranged above the electric furnace, A method is disclosed in which CO gas is burned in the free space (this combustion is also referred to as secondary combustion), and then introduced into a preheating tank for preheating.

[0007]

In the prior arts 1 and 2, since the unburned gas such as CO gas is secondarily burned at the entrance of the preheating tank, the CO gas concentration in the exhaust gas in the preheating tank is reduced to a predetermined value. Although it can be reduced, the secondary combustion occurs at once in the free space in the electric furnace supplied with oxygen or air. Therefore, the extremely high temperature exhaust gas is introduced into the preheating tank or the duct leading to the preheating tank, so that the heat load of the preheating tank or the duct leading to the preheating tank becomes extremely high, which causes equipment trouble. If the supply amount of oxygen or air is excessive, oxidation of the iron source immediately before charging into the electric furnace occurs, so reduction heat is required when melting in the electric furnace, and the power consumption deteriorates. Come.

[0008] The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a preheating method capable of preventing equipment trouble due to combustion heat of unburned gas in exhaust gas and increasing the preheating efficiency of an iron source.

[0009]

A method of preheating an iron source in a preheating tank according to a first aspect of the present invention is to preheat an iron source filled in the preheating tank by introducing exhaust gas discharged from an electric furnace into the preheating tank. At this time, a plurality of nozzles are arranged in the flow direction of the exhaust gas in the preheating tank, an oxygen-containing gas is blown into the preheating tank from these nozzles, and the iron source is preheated while burning unburned gas in the exhaust gas. It is characterized by the following.

[0010] A method for preheating an iron source in a preheating tank according to a second invention is characterized in that, in the first invention, the amount of oxygen-containing gas blown from a plurality of nozzles is blown while being controlled individually by each nozzle. Is what you do.

A method for preheating an iron source in a preheating tank according to a third aspect of the present invention is characterized in that, in the first or second aspect, the blowing angles of a plurality of nozzles are individually controlled and blown by each nozzle. It is.

According to a fourth aspect of the present invention, there is provided a method for preheating an iron source in a preheating tank according to the first aspect, wherein when an iron source is suspended inside the preheating tank, an oxygen-containing gas is blown in the vicinity of the position where the suspension occurs. The present invention is characterized in that the amount is increased to eliminate shelf hanging.

In the present invention, nozzles are arranged at a plurality of positions in the flow direction of the exhaust gas in the preheating tank, and an oxygen-containing gas is blown into the preheating tank from each nozzle. Then, the CO gas in the exhaust gas, H
The unburned gas such as the _two gases burns in an amount equal to the chemical equivalent of the injected oxygen. That is, the unburned gas in the exhaust gas is not burned at once, but is sequentially burned in the preheating tank while passing through the preheating tank according to the oxygen equivalent of the oxygen-containing gas blown from each nozzle. Then, when the fuel is completely burned in the preheating tank and discharged from the preheating tank, the unburned gas in the exhaust gas has disappeared. Therefore, the heat generated by the combustion of the unburned gas is generated in the entire preheating tank, and the generated combustion heat is used each time for preheating the iron source. Equipment troubles such as a duct leading to the tank and the preheating tank can be suppressed. Furthermore,
Since the fuel is burned while being filled with an iron source such as iron scrap or direct reduced iron, the combustion heat is efficiently transmitted to the iron source.

Since the amount of oxygen-containing gas to be blown and the blowing angle of the nozzles are individually controlled and blown by each nozzle, the combustion of the unburned gas in the exhaust gas in the preheating tank is controlled more accurately, and the temperature of the exhaust gas is controlled. The rise is suppressed and the heat transfer efficiency to the iron source is improved.

Further, when a shelf hanging occurs in the preheating tank during preheating, the iron source is softened or melted by intensively blowing an oxygen-containing gas near the position where the shelf hanging occurs to eliminate the shelf hanging. Thus, the preheating can be continued. The oxygen-containing gas of the present invention is oxygen, air, or a mixed gas of oxygen and air.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings.
FIG. 1 is a schematic sectional view of an electric furnace and a preheating tank showing an example of an embodiment of the present invention.

In the figure, a cylindrical furnace wall 3 is arranged on the upper part of a furnace body 2 having a furnace bottom electrode 5 at the bottom, the inside of which is constructed of a refractory material. The opening is covered with an openable and closable furnace lid 4, and an upper electrode 6 made of graphite is provided to penetrate through the furnace lid 4 and move up and down into the furnace main body 2, thereby constructing the DC electric furnace 1.

Above the DC electric furnace 1, a preheating tank 7 for storing an iron source 10 such as iron scrap or direct reduced iron is arranged. An exhaust duct 28 connected to a dust collector (not shown) is provided on an upper side wall of the preheating tank 7, and a duct 8 serving as a charging path of the iron source 10 to the DC electric furnace 1 is provided at the bottom of the preheating tank 7. And a pusher 9 that moves under the duct 8. The other end of the duct 8 is disposed in contact with the opening of the furnace lid 4, and thus the DC electric furnace 1 and the preheating tank 7
And are connected. Exhaust gas generated in the DC electric furnace 1 is sucked into the dust collector through the duct 8, the preheating tank 7, and the exhaust duct 28 in this order, and the iron source 10 filling the preheating tank 7 is preheated by the exhaust gas.

Gas sensors 29 and 30 are disposed in the duct 8 and the exhaust duct 28. The gas sensor 29 detects the temperature and flow rate of the exhaust gas flowing into the preheating tank 7 and the CO 2 in the exhaust gas.
And the gas sensor 30 detects the gas concentration.
Temperature and flow rate of exhaust gas discharged from CO2 and CO in exhaust gas
Gas concentration is detected.

An iron source supply port 25 is provided above the preheating tank 7, and the iron source supply port 25 is provided with a pair of movable shelves 26, 26.
a and the opening / closing lid 27 are also sealed when the iron source 10 is supplied to the preheating tank 7, so that the exhaust gas from the DC electric furnace 1 is always sucked into the dust collector.

A nozzle 14 for blowing an oxygen-containing gas into a plurality of locations from the upstream side to the downstream side in the flow direction of the exhaust gas in the preheating tank 7, that is, five places in FIG. , 15, 16, 17, and 18 are arranged. In FIG. 1, the nozzles 14 to 18 are arranged at equal intervals,
There is no need to make them evenly spaced. However, it is preferable that the arrangement interval is 3 m or less. If the interval is more than 3 m, the combustion of the unburned gas in the exhaust gas becomes non-uniform, which may cause an excessive rise in temperature, which may lead to equipment trouble. The nozzles 14 to 18 can independently control the gas blowing amount by individually provided flow rate control valves (not shown), and can raise and lower the blowing angle by nozzle driving devices (not shown) attached to the respective nozzles 14 to 18. It can be changed left and right.

The oxygen-containing gas to be used is appropriately selected from oxygen, air, or a mixed gas of oxygen and air. In the case of using air, there is a cooling effect by nitrogen in the air and the temperature rise of the exhaust gas is suppressed, but in the case of oxygen, there is no such cooling effect. Therefore, the oxygen-containing gas is selected according to the exhaust gas temperature detected by the gas sensor 29 and the CO gas concentration of the exhaust gas. That is, when the temperature of the exhaust gas and the CO gas concentration are both low, oxygen is used. On the contrary, when both are high, air is used. When both are intermediate or one of them is low, mixing of oxygen and air is performed. Gas may be used.

The preheating tank 7 has optical transmitters 19a, 20a, 2
1a, 22a and optical receivers 19b, 20b, 21b, 22
b, four shelf hanging detection sensors 19, 20, 2
1, 22 are arranged. For example, when the light receiver 19b detects the light transmitted from the optical transmitter 19a, the shelf hanging of the iron source 10 determines that the shelf hanging has occurred above the shelf hanging detection sensor 19.

The DC electric furnace 1 is provided with an oxygen blowing lance 23 and a carbon material blowing lance 24 which penetrate the furnace wall 3 and can be inserted into the furnace main body 2.
Oxygen is blown into the furnace main body 2, and a carbon material such as coke, char, and coal is blown into the furnace main body 2 from the carbon material blowing lance 24 using air, nitrogen or the like as a carrier gas.

The operation of the DC electric furnace 1 is as follows.
A predetermined amount of the iron source 10 preheated in the preheating tank 7 during the previous operation is initially charged into the furnace main body 2 via the pusher 9. still,
When the operation is started in the cold furnace, the furnace lid 4 may be opened and initially charged by a bucket or the like, or the initial charging may be performed from the preheating tank 7 via the pusher 9. After the initial charging into the furnace body 2 is completed, the iron source 10 is supplied from the iron source supply port 25 to the preheating tank 7.
And a predetermined amount of the iron source 10 is filled in the preheating tank 7.

Next, while supplying a direct current between the furnace bottom electrode 5 and the upper electrode 6, the upper electrode 6 is moved up and down to allow the upper electrode 6 to move between the furnace bottom electrode 5 and the inserted iron source 10. An arc 13 is generated. Then, the iron source 10 is melted by the generated arc heat, and the molten steel 11 is generated. Since the level of the iron source 10 in the furnace main body 2 decreases with the generation of the molten steel 11, the iron source 10 in the preheating tank 7 is additionally charged into the furnace main body 2 via the pusher 9, and the iron source supply port 25 The iron source 10 is supplied to the preheating tank 7 to secure a predetermined amount of the iron source 10 in the preheating tank 7. The iron source 10 in the preheating tank 7 is preheated by the generated high-temperature exhaust gas.

Along with the formation of the molten steel 11, a flux such as quicklime or fluorite is charged into the furnace main body 2 to form a molten slag 12 on the molten steel 11, thereby preventing oxidation of the molten steel 11 and keeping the molten steel 11 warm. Plan.

Also, from the time when the molten steel 11 is formed, oxygen and carbon material are blown into the surface of the molten steel 11 or into the molten slag 12 from the oxygen blowing lance 23 and the carbon material blowing lance 24. The carbon material dissolved in the molten steel 11 or the carbon material suspended in the molten slag 12 reacts with the blown oxygen to generate combustion heat, and the reaction product CO gas forms the molten slag 12. , Arc 13 is molten slag 1
2, the arc heating efficiency increases, and the melting of the iron source 10 is promoted. At the same time, the temperature of the exhaust gas rises and the amount of generated exhaust gas increases, and the exhaust gas contains a large amount of unburned CO gas. It should be noted that the amount of the carbon material to be blown is about the same as the chemical equivalent of the oxygen to be blown. If the amount of carbon material blown is smaller than the amount of oxygen blown, it is not preferable because the molten steel 11 is excessively oxidized.

Depending on the flow rate of the exhaust gas detected by the gas sensor 29 and the CO gas concentration of the exhaust gas, the nozzles 14 to
The blowing flow rate of the oxygen-containing gas is determined. Nozzle 1
In order to completely burn the CO gas, the total flow rate of the blown gas is 4 to 18.
The amount is equal to or slightly larger than the chemical equivalent of O gas. Then, the individual blowing flow rates of the nozzles 14 to 18 are determined from the total blowing flow rate.

The blowing flow rate may be equalized by the nozzles 14 to 18. However, it is preferable to increase the blowing flow rate at a position where the temperature of the iron source 10 becomes low, that is, near the middle of the gas flow in the preheating tank 7. However, increasing the blowing flow rate on the downstream side near the exhaust duct 28 is not preferable because only the temperature of the exhaust gas discharged from the preheating tank 7 increases, and the heat applied to the iron source 10 decreases. Further, the CO gas can be burned in order by shifting the blowing angle alternately left and right by the nozzles 14 to 18. Then, it is confirmed by the gas sensor 30 that the CO gas is completely burned.

When a shelf change is detected by the shelf change detection sensors 19 to 22 during preheating, the nozzles located immediately below and immediately above the detection sensor for detecting the shelf change, for example, the shelf change detection sensor 20 use the shelf change detection sensor 20. Is detected, the blowing flow rate of the nozzles 15 and 16 is increased to soften or melt the shelf hanging portion, thereby eliminating the shelf hanging. At this time, if the blowing angle of the nozzle 15 is set to be upward, it is easy to eliminate the hanging. When the hanging of the shelves has been resolved, the blowing flow rate is returned to the original, and the preheating is continued.

In this way, the furnace body 2 from the preheating tank 7
The addition of the iron source 10 to the furnace and the supply of the iron source 10 to the preheating tank 7 are continuously performed, and the molten steel 11 for one heat is
When the amount is secured, the additional charging to the furnace main body 2 and the supply to the preheating tank 7 are stopped, and then the temperature is adjusted to a temperature convenient for tapping the molten steel 11. Thereafter, the DC electric furnace 1 is tilted, and the molten steel 11 is tapped from a tapping port (not shown) to a molten steel storage / transport container (not shown). After tapping, the preheated iron source 10 is initially charged from the preheating tank 7 into the furnace main body 2 again, the arc heating is performed again, and the operation of the DC electric furnace 1 is continued.

By preheating the iron source 10 in this manner, the heat of combustion of the CO gas efficiently heats the iron source 10 to reduce the power consumption. Also, at the place where the iron source 10 is filled, C
Since the O gas is burned, the gas temperature does not rise excessively, and equipment troubles can be prevented.

FIG. 2 is a schematic sectional view of an electric furnace and a preheating tank showing another embodiment of the present invention. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

In the present embodiment, a preheating tank 7 and a furnace wall 3 are arranged at the upper part of the furnace main body 2 and the DC electric furnace 1 and the preheating tank 7 are directly connected. The preheated iron source 10 is charged into the furnace main body 2 by a natural amount falling in the preheating tank 7 in an amount corresponding to the iron source 10 melted in the furnace main body 2. Further, unlike FIG. 1, the case where three shelf hanging detection sensors 19, 20, and 21 are arranged is shown.

The operation in the DC electric furnace 1 and the preheating tank 7 is performed by supplying an iron source 10 for one heat into the preheating tank 7.
The supply of the iron source 10 to the preheating tank 7 is stopped, all the iron sources 10 in the preheating tank 7 are melted, and the molten steel 11 is tapped with no unmelted iron source 10 remaining in the preheating tank 7. This operation is repeated, but the other operation methods are the same as those of the DC electric furnace 1 shown in FIG. 1, and the present invention is implemented according to the above description.

In the above description, the case of the DC electric furnace 1 has been described. However, the present invention can be applied without any problem to the AC electric furnace, and furthermore, the difference in the number of the upper electrodes 6 and the structure of the furnace bottom electrode 5 and the like. Needless to say, the difference in the number of the gas sensors 29, 30 and the like does not hinder the present invention.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the DC electric furnace shown in FIG. 1 will be described below. The electric furnace has a furnace capacity of 120 tons, a preheating tank having a width of 3 m and a length of 5 m, and a rectangular parallelepiped shape having a height of 9 m from the center bottom of the preheating tank to an exhaust duct. Then, starting at a height of 0.5 m from the center of the preheating tank, 0.8
Ten nozzles were arranged at m intervals.

The temperature of the exhaust gas at the inlet of the preheating tank is 1600 ° C.
The exhaust gas flow rate was 280 Nm ³ / min, and the CO gas concentration in the exhaust gas was 80%. Air is used as blowing gas, and the total blowing flow rate of air is 560 Nm ³ /
min, and in Example 1, the blowing flow rate from each nozzle was 56 Nm ³ / min, and the nozzles were evenly blown. In Example 2, as shown in FIG. 3, 34 Nm ³ / min from the lower two preheating tanks and the uppermost nozzle. The value was set to 78 Nm ³ / min from the sixth to the eighth from the bottom, and the value was linearly increased and decreased between these. For comparison, a comparative example in which blowing into the preheating tank was stopped was also performed. The above operating conditions are those when the DC electric furnace is operated continuously and the preheating temperature of the iron scrap in the preheating tank is in a steady state.

Then, 20 pieces of iron scrap charged into the furnace main body from the preheating tank were collected and measured for each condition, and the average value of the temperatures of the 20 pieces was taken as the preheating temperature. The preheating temperature was 890 ° C. in Example 1 and 900 ° C. in Example 2, indicating that the preheating temperature was significantly increased as compared with 320 ° C. in Comparative Example. Table 1 collectively shows the preheating conditions and the preheating results of Example 1, Example 2, and Comparative Example.

[0041]

[Table 1]

In Examples 1 and 2, the temperature of the exhaust gas from the preheating tank was measured. In Example 1, the temperature reached 1700 ° C. in the vicinity of the lowermost nozzle, but thereafter decreased gradually. Was. In Example 2, the maximum temperature was 1600 ° C. at the entrance of the preheating tank.
It did not exceed 600 ° C. Therefore, Embodiment 1
In both Example 2 and Example 2, no equipment trouble occurred. In Examples 1 and 2, the power consumption was significantly reduced as compared with the comparative example.

[0043]

According to the present invention, since the exhaust gas generated in the electric furnace is gradually burned in the preheating tank filled with the iron source, the combustion heat of the exhaust gas efficiently heats the iron source to reduce the preheating temperature of the iron source. As a result, power consumption can be reduced. Furthermore, since it is possible to prevent the exhaust gas temperature from excessively rising due to combustion heat,
Equipment troubles caused by excessive temperature rise can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an electric furnace and a preheating tank showing an example of an embodiment of the present invention.

FIG. 2 is a schematic sectional view of an electric furnace and a preheating tank showing another example of the embodiment of the present invention.

FIG. 3 is a diagram showing an air blowing pattern in a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC electric furnace 2 Furnace main body 3 Furnace wall 4 Furnace lid 5 Furnace bottom electrode 6 Upper electrode 7 Preheating tank 8 Duct 9 Pusher 10 Iron source 11 Molten steel 12 Molten slag 13 Arc 14 Nozzle

Claims (4)

[Claims] A plurality of nozzles are arranged in a flow direction of the exhaust gas in the preheating tank when preheating the iron source filled in the preheating tank by introducing the exhaust gas discharged from the electric furnace into the preheating tank. A method for preheating an iron source in a preheating tank, wherein an oxygen-containing gas is blown into the preheating tank from these nozzles to preheat the iron source while burning unburned gas in the exhaust gas. 2. The method for preheating an iron source in a preheating tank according to claim 1, wherein the blowing amount of the oxygen-containing gas blown from the plurality of nozzles is controlled by each nozzle individually. 3. The method for preheating an iron source in a preheating tank according to claim 1, wherein the blowing angles of the plurality of nozzles are individually controlled and blown by each nozzle. 4. The apparatus according to claim 1, wherein when a shelf of the iron source is generated inside the preheating tank, the amount of the oxygen-containing gas blown in the vicinity of the position where the shelf is dropped is increased to eliminate the hanging.
A method for preheating an iron source in the preheating tank described in 1.