KR20060077424A - Nitrogen Blower for Arc Furnace - Google Patents

Abstract

The present invention relates to an apparatus for injecting nitrogen gas in an arc electric furnace having a furnace in which an arc generating electrode is installed and melting a charge to produce a molten metal, wherein a pair of sides of the furnace body inject oxygen gas into the molten metal. The oxygen injection lance and the oxygen gas supply pipe for supplying the oxygen gas to one oxygen injection lance are connected to a nitrogen gas branch pipe for supplying nitrogen gas, so that nitrogen gas is replaced to replace the oxygen agitation. The Cr oxide is reduced by stirring the molten metal through the molten metal to improve the yield of the molten metal and the recovery of the chromium and further improve the life of the furnace.

Molten metal stirring, nitrogen gas injection, chromium recovery rate, supply piping, branch pipe

Description

Apparatus for injecting nitrogen gas into an electric Arc furnace}             

1 is a view of a conventional arc electric furnace equipped with a nitrogen extraction facility;

2 is a view of an electric furnace in which a nitrogen gas blowing lance is installed at a side according to the present invention;

FIG. 3 is a graph showing comparison of the number of furnace bodies used in the electric furnace of FIG. 1 and the electric furnace of FIG.

4 is a graph showing the chromium recovery rate according to the nitrogen flow rate blown through the nitrogen gas blowing lance in the electric furnace according to the present invention;

Figure 5 is a graph showing the tapping temperature according to the nitrogen blowing amount in the electric furnace according to the present invention.

<Description of Symbols for Major Parts of Drawings>

20: arc furnace

22: electrode

24, 26: oxygen blowing lance

30: oxygen gas storage tank                 

32, 34: oxygen gas supply pipe

40: nitrogen gas storage tank

42: nitrogen gas supply pipe

34a, 42a: regulating valve

The present invention relates to a nitrogen blowing device for an arc furnace for blowing nitrogen gas to improve the recovery rate of chromium when melting stainless steel, and more specifically a pair of oxygen gas supply pipe for blowing oxygen gas into the molten metal in the furnace. By connecting nitrogen gas branch pipe supplying nitrogen gas to one of them and selectively blowing nitrogen gas, inducing reduction of chromium oxide from slag on the upper side of molten metal can improve the recovery rate of chromium and improve the life of the furnace. It relates to a nitrogen blowing device for an electric furnace.

In general, an electric arc furnace is widely used for steel making, and heats the molten material by flowing an electric current in the form of an arc between the molten material charged into the electric furnace and the three electrodes. Let's do it. Three-phase alternating current is used as the power source of the electrode.

Referring to FIG. 1, in the conventional arc electric furnace 10, three electrodes 12 are installed at an upper portion thereof, and a blowing nozzle (not shown) is installed at the bottom thereof to blow gas for stirring. The raw material charged in the electric furnace 10 is melted by passing an electric current through the three electrodes 12. At this time, an inert gas such as nitrogen or argon, which is blown into the electric furnace from the storage tank 22 through the blowing nozzle, is stirred from the slag located above the melt by agitating the melt in the electric furnace and Cr ₂ O ₃ , FeO, and MnO. The same metal oxide is reduced.

In this case, the blowing amount of the inert gas for stirring, for example, nitrogen gas, is small, and recovery of a metal oxide is inadequate. In addition, the blowing nozzle has a relatively weak corrosion resistance due to the melt compared to the furnace body in the case of carrying out the recovery operation of the metal oxide in a porous way to blow nitrogen gas through the blowing nozzle as described above. In the furnace body, the installation part of the blow nozzle was eroded, which caused a problem of shortening the life of the furnace body.

In addition, in order to reduce metal oxides such as Cr ₂ O ₃ , FeO, and MnO from slag, graphite is introduced into an electric furnace, and the injected graphite reacts with metal oxides in slag to recover metals such as Cr, Fe, and Mn. C-injection is known. Since the graphite injection method is carried out when 90% to 95% of the scrap is melted during the secondary melting operation of the furnace, slag-foaming occurs and overflow occurs during the tapping of the furnace. And problems such as the formation of holes in the graphite injection guide pipe were not possible for continuous use.

In addition, when the concentration of Cr ₂ O _{3 in} the metal oxide in the slag occupies 25% or more and the specific gravity is high, the reduction reaction rate due to graphite is slowed down, so that chromium is not easily reduced even by the graphite injection method. Brings about.

The present invention has been proposed in order to solve the conventional problems as described above, by connecting a branch pipe for supplying nitrogen gas to one blowing lance of a pair of oxygen gas blowing lances for blowing oxygen gas into the molten metal of the electric furnace selective It is an object of the present invention to provide a nitrogen injector for an arc electric furnace that can effectively reduce metal oxides from slag by blowing nitrogen gas into the furnace and improve furnace life.

In order to achieve the above object, according to the present invention, an arc electric furnace having a furnace body with an arc generating electrode rod and melting the charges to produce a molten metal, the side wall of the furnace body for blowing oxygen gas into the molten metal A pair of oxygen blowing lances are provided, and the supply pipe for supplying oxygen gas to the at least one oxygen injection lance is characterized in that the branch pipe for supplying nitrogen gas is connected.

The branch pipe is provided with a control valve for controlling the supply amount of nitrogen gas, the oxygen gas supply pipe connected to the branch pipe is preferably provided with a control valve for controlling the supply amount of oxygen gas.

Hereinafter, with reference to the accompanying drawings will be described the configuration of the nitrogen supply apparatus for an arc furnace according to the present invention.

Referring to FIG. 2, an arc generation electrode rod 22 is provided at an upper portion of the arc furnace 20, and an arc is generated by the electrode rod 22 to charge the charged matter in the arc furnace 20. Dissolution is carried out. In this melting operation, a pair of oxygen blowing lances 24 and 26 for blowing oxygen into the electric furnace 20 are installed on the side wall 20a of the arc electric furnace 20.

Oxygen gas supply pipes (32, 34) for supplying oxygen gas from the oxygen gas storage tank (30) are connected to each of the oxygen blowing lances (24, 26).

According to the present invention, at least one supply pipe of the oxygen gas supply pipes 32 and 34 is connected to a branch pipe 42 for supplying nitrogen gas from the nitrogen gas storage tank 40.

Preferably, the branch pipe 42 is provided with a control valve 42a for adjusting the supply amount of nitrogen gas, and also for adjusting the supply amount of oxygen gas to the oxygen gas supply pipe 34 to which the branch pipe 42 is connected. An adjustment valve 32a is provided. It is preferable that the control valves 32a and 42a serve to substantially block or open or close the supply of oxygen gas or nitrogen gas.

For example, in a state in which the control valve 42a provided in the branch pipe 42 is closed, the control valve 32a for oxygen gas is opened so that only the oxygen gas is provided to the supply pipe 34, whereas the branch pipe 42 is provided. When the control valve 42a provided at 42 is open, the oxygen gas control valve 32a is closed so that only nitrogen gas is supplied to the supply pipe 34.

Hereinafter, the melting operation for the charges in the arc electric furnace according to the present invention will be described.

Furnace operation is largely divided into igniter, main melting machine and heating device. In the igniter and the main melting machine, energization of the electrode rod 22 is started, and the charges charged in the arc electric furnace 20 are melted while blowing oxygen through the oxygen injection lances 24 and 26. In such an igniter and a main melting furnace, oxidation reactions and reduction reactions occur in an electric furnace, and in particular, oxidation and reduction reactions of Cr components having the largest specific gravity among the metal components in the electric furnace are expressed by the following equation.

Oxidation: [2Cr] + 3/2 O _2- > (Cr ₂ O ₃ ) + Heat

Reduction reaction: (Cr ₂ O ₃ ) + [3C]-> [2Cr] + 3 {CO} = -Heat

(Cr ₂ O ₃ ) + [2Al]-> [2Cr] + (Al ₂ O ₃ ) = + Heat

(Cr ₂ O ₃ ) + [3Si]-> [4Cr] + 3 (SiO ₂ ) = + Heat

At this time, according to the present invention, it is necessary to suppress the oxidation reaction in order to reduce Cr ₂ O ₃ having the largest specific gravity among the metal oxides in the electric furnace. It may be possible to lower the chromium (Cr) content as a method of inhibiting the oxidation reaction, but this is not preferable because it makes the post-processing work difficult.

Therefore, in order to reduce Cr ₂ O ₃ content in the oxidation reaction, it is possible to control the lowering of 0 ₂ so that the operation method can be changed and the temperature of the molten metal can be increased by changing the operation method such as input power or time.

In addition, in order to promote a reduction reaction for reducing Cr ₂ O ₃ , as can be seen from the above formula, the content of C, Al, and Si should be increased, and the content of CO, Al ₂ O ₃ , and SiO ₂ should be lowered. On the other hand, if a method of increasing the stirring force, securing the slag fluidity, and improving the temperature as a kinetic method besides the method of controlling the content of the components, it is possible to reduce the Cr ₂ O ₃ content by promoting the reduction reaction.

Therefore, after the above-described igniter and the main dissolving machine are finished, the oxygen blowing operation through one of the oxygen blowing lances 24 and 26 through the blowing lance (for example, 26) is terminated in the heat riser in which the redox reaction occurs violently. And blow nitrogen gas. In other words, after passing about 31000kwh ~ 32000kwh of electric power through the electric furnace, the molten metal is formed and nitrogen gas is blown until the melting is completed. At this time, the amount of nitrogen gas blown into the electric furnace is limited to about 300 ~ 500Nm3 / Ch, while the amount of oxygen gas is limited to 500Nm3 / Ch or less.

As a result, in the heater, nitrogen gas is blown into the molten metal to lower the O ₂ content, thereby inhibiting the oxidation reaction caused by O ₂ , and to replace the C-injection operation while improving the stirring power of the molten metal.

Then, the reducing agent is introduced into the molten metal through the reducing agent injecting member 28 to promote the reduction reaction. At this time, the reducing agent is a reducing agent of Fe-Si-C composition is used. This reducing agent is carried out immediately after starting the blowing of nitrogen gas. The blowing amount of the reducing agent is maintained at about 370 kg or more in the reducing agent of Fe-Si-C, for example.

EXAMPLE

Table 1 shows the conditions of the normal operation, the C-injection operation and the nitrogen injection operation according to the present invention, respectively, as shown below, when the electrode is energized after charging the charge into the arc electric furnace. , Table 2 shows the comparison of the results of each operation.

In a normal operation, electric current was started in the electrode rod to dissolve the electric charges, in particular, oxygen was blown during the main dissolving and heating of the electric furnace operation, and FeSi was added as a reducing agent. After the oxygen injection and energization were completed, the molten metal was tapped after the electric operation was completed.

In the C-injectiion operation, electricity was supplied to the electrode rod to dissolve the electric charges, and in particular, oxygen and graphite were blown during the main melting and heating of the electric furnace operation, and FeSiC was added as a reducing agent. Oxygen blowing, graphite injection, and energization were completed to complete the operation of the electric furnace, followed by tapping the molten metal.

According to the present invention, in another nitrogen blowing operation, electric current was started to the electrode rod to dissolve the charges with electricity, and oxygen was blown during the main melting period of the electric furnace operation. And nitrogen gas was blown in during a heat exchanger. At this time, FeSiC was added as a reducing agent. Nitrogen gas injection and energization were terminated and the molten metal was tapped after completion of the electric furnace operation.

TABLE 1

Operating conditions Nitrogen blowing operation C-injection Normal operation Amount of charge 100.271 tons 99.925 tons 100.331 t Melt amount 94.387 tons 93.863 tons 94.075 tons Amount of current 35,420 kwh 35,613kwh 35,609 kwh Oxygen injection 539 N㎥ 1,017 N㎥ 902N㎥ Nitrogen gas blowing amount 300 ~ 400 N㎥ - - Reductant input 370kg FeSiC 192kg FeSiC 258kg FeSi Graphite dosage - 423 kg -

TABLE 2

division Nitrogen blowing operation C-injection Normal operation Slag of Cr ₂ O ₃ 6.3% 8.4% 9.4% Cr real ratio (melting Cr amount / charged Cr amount) 97.5% 96.0% 93.9% Molten chamber yield (melt amount / charge amount) 94.1% 93.9% 93.8%

As shown in the table above, when the nitrogen blowing operation according to the present invention is carried out, the Cr ₂ O ₃ content in the slag is found to be relatively decreased compared with the conventional C-injecion operation and the conventional operation. The error rate is also improved.

Figure 3 is a graph comparing the number of times the use of the furnace when blowing the nitrogen gas through the nitrogen nozzle installed on the bottom of the furnace furnace when the nitrogen gas is blown through the nitrogen gas injection lance according to the present invention to be. As shown in Figure 3, it can be seen that the service life of the arc electric furnace according to the present invention significantly increased.

4 and 5 are graphs showing the Cr ₂ O ₃ content of the slag and the tapping temperature of the molten metal according to the nitrogen gas blowing flow rate. As the flow rate of nitrogen gas is increased, the content of Cr ₂ O _{3 in} the slag increases while the tapping temperature of the molten metal decreases.

When the nitrogen gas blowing flow rate is 500Nm3 / hr or more, the tapping temperature of the molten metal appears to be lower than 1500 ° C, which causes a problem that the subsequent process cannot be performed smoothly. In addition, when the nitrogen gas blowing flow rate is less than 200Nm 3 / hr, the content of Cr ₂ O ₃ in the slag is about 9% or more, which is similar to the operation result in the normal operation shown in the above table. In view of these results, it is preferable to limit the nitrogen gas blowing flow rate to 2000 to 400 Nm 3 / hr based on the charge of about 100 tons in the electric furnace operation.

The foregoing is merely illustrative of the preferred embodiments of the present invention and those skilled in the art to which the present invention pertains recognize that modifications and variations can be made to the present invention without departing from the spirit and gist of the invention as set forth in the appended claims. shall.

According to the present invention, in order to replace the oxygen agitation, the Cr oxide is reduced by the stirring of the molten metal through the nitrogen gas, thereby improving the molten metal yield and the chromium recovery rate and further improving the life of the furnace.

Claims (4)

An apparatus for injecting nitrogen gas into an arc electric furnace having a furnace body provided with an arc generating electrode rod and melting a charge to produce a molten metal, A sidewall of the furnace body is provided with a pair of oxygen blowing lances for blowing oxygen gas into the molten metal; And a branch pipe for supplying nitrogen gas is connected to a supply pipe for supplying oxygen gas to at least one oxygen injection lance. The method of claim 1, The branch pipe is provided with a control valve for controlling the supply amount of nitrogen gas, the oxygen gas supply pipe connected to the branch pipe is provided with a control valve for controlling the supply amount of oxygen gas nitrogen for arc furnace Blowing device. The method of claim 2, The nitrogen injection device for an arc furnace, characterized in that when the nitrogen gas is supplied through the branch pipe is added to the molten metal of the electric furnace. The method of claim 3, The reducing agent is a nitrogen blowing device for an arc furnace, characterized in that consisting of Fe-Si-C composition.

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