JPH0118348B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bottom-blown arc furnace for steelmaking in which bath steel is stirred by blowing oxygen or the like from the bottom of the furnace.

In arc furnaces for steelmaking, scrap is melted by arc flare from the electrodes. Conventionally, oxygen has been blown into the arc furnace in order to increase the melting and stirring ability of the arc furnace and to perform refining work. There is.

A lance is used to blow in the oxygen, and the following oxygen blowing method has been adopted due to the structure of the lance itself.

(a) Consumable lance method In other words, this method uses a lance that burns and is consumed immediately when immersed in molten steel, as shown in Figure 1.

This method has been commonly practiced in steelmaking factories in the past, and a lance steel pipe b coated with ceramic or the like is inserted into the arc furnace a from a position above the hearth line of the arc furnace a. Oxygen is blown into the tank to prevent it from being immersed in water.

However, in this method, since the lance steel pipe b is located at a high position, the oxygen blown in is either guided to the boundary between the slag d and the molten steel c, or is slightly immersed in the molten steel, so the slag d is significantly oxidized. This results in For this reason, the iron oxide content of the slag is high, which has the disadvantage of increasing wear and tear on the refractory material e.Additionally, there is a large temperature difference between the molten steel and the slag due to insufficient stirring, and the composition of the molten steel. There are also drawbacks such as insufficient temperature uniformity.

(b) Cooling lance method In other words, this is a method in which the tip of the lance steel pipe is cooled using natural gas, etc., and oxygen is blown into the bath steel.

However, if the lance steel pipe is immersed in molten steel, it will be consumed in the same way as in the consumable lance method, so the immersion depth of the lance cannot be increased. Therefore, it has the same drawbacks as the consumable lance method described above.

(c) Refractory material coated immersion lance method In other words, as shown in Fig. 2, the immersion lance g is made by coating the tip of a lance steel pipe with a refractory material f.
is inserted into molten steel c from above, and oxygen is supplied into the molten steel while cooling the tip h of lance g using hydrocarbon such as kerosene as a coolant.

According to this method, compared to the methods (a) and (b) above,
The oxygen iron content in the slag is reduced and the stirring motion of the steel bath improves the uniformity of the molten steel. However, the coated refractory material f of the immersion lance g is mechanically
A high-quality material is required that has chemical strength and is resistant to temperature alterations.

When a refractory coated lance is immersed in molten steel, it floats up due to the large buoyant force. In order to push this into the molten steel, a powerful and large-sized external lance insertion device i is required, which is not only uneconomical but also significantly impedes the steelmaking workability around the arc furnace a.

During the work, the slag d adheres to the outer periphery of the refractory material f in a ring shape j as shown in the figure, so the lance g
More maintenance time is required to smoothly attach and detach the insertion port.

The mounting position of the lance g must be such that there is no risk of leakage when the steel is tipped, and the mounting position is regulated.

The lance may bend due to heat, and if the direction of oxygen blowing changes and the oxygen hits the refractory material e, the refractory material e will be significantly damaged.

There are drawbacks such as.

Therefore, it is possible to blow oxygen from the bottom of the arc furnace, but if leakage occurs from the fixed tuyeres at the bottom of the furnace, it will cause a major accident, and since the tuyere cannot be fitted with a stopper, - Refining - Bottom blowing operations have not been carried out in arc furnaces to date due to problems such as the need to carry out continuous bottom blowing throughout the entire period until the completion of steel tapping.

The present invention eliminates the drawbacks of the conventional method, quickly melts raw materials such as unmelted scrap or reduced iron in molten steel, and effectively equalizes the composition and temperature of molten steel, thereby shortening the melting time. This was done in an attempt to reduce the power consumption and to solve the problem of the lack of bottom blowing operation in arc furnaces. In a steelmaking arc furnace where an electrode is inserted and the scrap charged into the furnace is melted by the arc flare at the tip of the electrode and the surface of the molten steel is heated and stirred, the scrap is inserted into the bricks at the bottom of the furnace body. a blowing nozzle fixed to the tip of the lance toward the inside of the furnace; a nozzle having a large number of minute holes arranged inside the furnace of the blowing nozzle; a channel for supplying hydrocarbon to the porous nozzle at an early stage of reservoir formation to form a solidified layer of molten steel at the tip of the blowing nozzle;
a supply pipe connected to the lance and supplying refractory material powder to the blowing nozzle using an inert gas as a carrier gas during the early stage of tundish formation, and supplying oxygen gas to the blowing nozzle after the middle of the tundish forming stage; The present invention is characterized by having a device for forcing refractory material powder into the blowing nozzle instead of supplying inert gas.

Embodiments of the present invention will be described below with reference to the drawings.

3 to 5 show an embodiment of the present invention, in which a graphite electrode 4 held by an electrode holder 3 is inserted into the furnace lid 2 of an arc furnace 1, and the graphite electrode 4 is inserted into the furnace. In a steelmaking arc furnace in which scrap 5 is melted by an arc flare 6 at the tip of an electrode 4 and the surface of molten steel 7 is heated and stirred, a lance insertion tube 10 is inserted from above a working floor 8 into a brick 9 at the bottom of the furnace. is inserted, and the tip of the lance insertion tube 10 is communicated with an inspection hole 11 drilled in the bottom of the furnace, and inside the lance insertion tube 10 is a lance 13 having a throttle nozzle 12 as a blow nozzle at the tip. When inserted, the throttle nozzle 12 is directed toward the inside of the furnace, and the tip of the lance 13 is supported on the inner wall of the lance insertion tube 10 via the brick stand 14, so that the throttle nozzle 12 is fixed at a fixed position at the bottom of the furnace. . A nozzle (porous nozzle) 15 having a large number of minute holes is disposed on the tip side of the throttle nozzle 12, and an opening 16 for communicating the nozzle 15 with the inside of the furnace is provided in the furnace bottom brick 9. , porous nozzle 15, opening 1
6 into the furnace.

In addition, an oxygen supply hose 17 for supplying oxygen and a flexible hose 18 for supplying argon or nitrogen gas are connected to the rear end of the lance 13 that protrudes outside the furnace. Gas is at throttle nozzle 1
In addition to making it blow out from 2, lance 1
3 is taken out from the rear end of the lance and connected to a flexible hose 20 that supplies hydrocarbon such as kerosene or propane to be blown into the porous nozzle 15. A dam 21 of hydrocarbon and a plurality of small guide holes 22 for distribution are provided in the section, and the pipe 19 in the lance 13 is connected to the dam 21, so that the hydrocarbon is distributed as evenly as possible to the porous nozzle 15. be able to supply.

The inside of the lance insertion pipe 10 and the inspection opening 11 are filled with refractory material powder 23 such as silica sand in order to sinter the refractory material powder at the inserted portion and seal the molten steel in the event of insertion of molten steel. A bunker 24 is provided at a position outside the furnace of the lance insertion tube 10, and refractory material powder 23 supplied from a supply source (not shown) is charged and stored in the bunker 24, and is cut out when necessary. The damper 25 is opened so that the refractory material powder 23 can be charged into the lance insertion tube 10 and the inspection port 11.

The flexible hose 18 for argon or nitrogen gas is connected to the main pipe 26 as shown in FIG. A rotary feeder 29 that cuts out a fixed amount of material 28 when necessary.
By cutting it out, argon or nitrogen gas can be sent to the throttle nozzle 12 as a carrier.

Since the structure is as described above, the operation of each component will be explained below for each of the scrap melting period, the sump formation (scrap melting in molten steel) temperature rising period, and the oxygen blow stop period.

() After the completion of steel tapping before the scrap melting stage, the throttle nozzle 12 is not blown with oxygen, argon, nitrogen gas, etc. The solidified layer of molten steel grown by the endothermic decomposition reaction and the sintered layer of the refractory powder 28 fed with argon or nitrogen gas as a carrier are in a packed state as shown at 30 in FIG. This state remains until the next oxygen injection.

Even if the scrap 5 is introduced and begins to melt, hot water is prevented from leaking.

() Reservoir formation (dissolution of scrap in molten steel) Temperature rising period This period is when the scrap 5 begins to melt and the molten metal begins to form. , dam 21 , and guide hole 22 . As a result, the hydrocarbon decomposes and the molten steel is partially subcooled and solidified by an endothermic reaction, and at the same time, the sintering layer 30 of the refractory material powder is also cooled, and the molten steel 7 in the furnace is sealed. At this time, nitrogen gas is supplied to the lance 13 through the flexible hose 18, and the nitrogen gas is blown out from the gap that cannot be completely sealed by the molten steel solidification layer and the refractory powder sintering layer, and
If necessary (if a large amount of nitrogen gas is used), add refractory material powder 28 to nitrogen gas using rotary feeder 29.
The refractory powder 28 is fed to the throttle nozzle 12 and the porous nozzle 15 using nitrogen gas as a carrier gas to form a refractory powder sintering layer to more completely prevent hot water from leaking.

Next, when the sump reaches a suitable depth, the nitrogen blow is gradually switched to an oxygen blow. This is because melting and stirring is performed by blowing oxygen into the molten steel. First, when oxygen is sent into the lance 13, the solidified molten steel layer and the refractory powder sintering layer 30 fixed in the throttle nozzle 12 and porous nozzle 15 are gradually dissolved, and each nozzle 12, 15 is completely dissolved. When opened, oxygen is blown into the molten steel. Since oxygen is blown in from the bottom of the furnace, it burns the carbon and other components contained in the molten steel 7 and stirs it vigorously, removing the remaining scrap 5 in the molten steel.
Rapid melting, temperature rise, and homogenization of molten steel components are performed well. At this time, if necessary, carbon powder or the like is blown into the molten steel using a separate lance using nitrogen as a carrier, and if the carbon powder or the like is combusted with oxygen, the temperature of the molten steel can be further raised and the above-mentioned The effects of increasing the rapid dissolution rate of the scrap 5 and making the molten steel temperature and components uniform can be further enhanced.

() When oxygen blowing is stopped This is the time when scrap melting is complete and the melting temperature and components have been sufficiently homogenized.
Gradually replace oxygen with nitrogen. At the same time, the flow rate of hydrocarbon for cooling the throttle nozzle 12 and porous nozzle 15 with decomposition heat is increased to grow a solidified layer of molten steel flowing through the opening 16 of the furnace bottom brick 9, and argon and nitrogen gas are used as carrier gas. The throttle nozzle 12 and the porous nozzle 15 are closed by the cylinder layer 30 of the low melting point refractory material powder 28 such as silica sand, which prevents the occurrence of leakage from the bottom of the furnace. At this time, gas pressure such as argon is applied inside the throttle nozzle 12, and the molten steel solidification layer and refractory material powder sintering layer 30 are
Argon, etc. is constantly ejected from the gap to seal the molten steel.

In addition, in the currently practiced method of stirring molten steel by blowing argon gas, when the speed of argon blowing from the nozzle is increased, the nozzle is overcooled, the molten steel solidifies, and the nozzle is often clogged. However, in the present invention, when argon gas or the like is blown into the gap between the coagulation layer and sintering layer by taking advantage of this problem,
Solidification of molten steel can be expected due to supercooling.

This state is maintained until the completion of tapping, but since the seal can be brought completely close, the consumption of argon or nitrogen gas is extremely reduced.

At each of the above ()()(), oxygen or argon gas or the like is supplied to the bottom of the furnace to open and close the throttle nozzle 12 and the porous nozzle 15,
Stir the molten steel with oxygen and seal the molten steel with argon gas, etc.

It should be noted that the present invention is not limited to the above-mentioned embodiment, but may also be an embodiment shown in FIG.

Fig. 6 shows a method in which refractory powder is mechanically applied to a nozzle instead of the method described in the above embodiment in which molten steel is sealed by blowing argon or nitrogen gas or by feeding refractory powder using these gases as a carrier. It was designed to be pushed into the That is, the inspection port 1 at the bottom of the throttle nozzle 12
1, a pipe 31 communicating with the lance 13 is arranged,
A stopper 33 at the tip of the rod 32 is slidably housed in the tube 31, and the lower end of the rod 32 is connected to a rod 35 of a cylinder 34 fixed to the furnace body. 33 rises, and the refractory material powder 36 stored in advance above the stopper 33 is pushed up and pushed into the throttle nozzle 12, creating a sintering layer of refractory material in the part that comes into contact with the molten steel to seal the molten steel. It is something. In this case, the sealing gas such as argon or nitrogen can be stopped.

Furthermore, in the arc furnace of the present invention, in the case of solid injection of fuel or slag-forming agent such as carbon powder or limestone through the throttle nozzle 12, it is possible to inject an inert gas such as nitrogen gas as a carrier gas. You can also do it.

As described above, according to the bottom-blown arc furnace for steelmaking of the present invention, (i) rapid melting of raw materials such as undissolved scrap and reduced iron in the molten steel is achieved due to intense stirring motion of the molten steel, thereby shortening the melting time; .

(ii) Uniformity of molten steel composition and temperature is effectively achieved.

(iii) The temperature of molten steel can be rapidly raised by injecting other fuel such as carbon and burning it.

(iv) Through the above (i) to (iii), it is possible to shorten the melting time and significantly reduce the electric power consumption.

(v) Since the oxygen blowing part from the furnace bottom is closed when oxygen blowing is stopped to seal the molten steel, even if the furnace bottom tuyere melts, it completely prevents melt leakage from the furnace bottom. Furthermore, since the direction of oxygen blow is upward from the bottom of the furnace, there is no refractory material around, so there is less wear and tear on the refractory material, and the effect of stirring the molten steel is great.

(vi) Oxygen blowing can be started or stopped arbitrarily and safely, and the consumption of sealing gas such as nitrogen or argon used during this stopping can be minimized.

(vii) The nozzle can be reliably closed by mechanically closing it.

(viii) Also, compared to conventional refractory-coated lances, there is no need for lance refractory material, no insertion device for attaching and removing the lance, and maintenance such as repairing the lance insertion port, repairing the coated refractory material, and removing slag attached to the lance. is not necessary.

It can produce excellent effects such as

[Brief explanation of drawings]

1 and 2 are both schematic diagrams showing the entire conventional arc furnace for steelmaking, FIG. 3 is a schematic diagram showing the entire arc furnace of the present invention, and FIG. 4 is the furnace in the arc furnace of the present invention. FIG. 5 is a detailed view of the nozzle portion in FIG. 4, and FIG. 6 is a diagram corresponding to FIG. 5 showing another embodiment of the present invention. 1...furnace body, 5...scrap, 7...molten steel,
9... Hearth brick, 10... Lance insertion pipe, 11...
...Inspection port, 12...Throttle nozzle, 13...
Lance, 15... Porous nozzle, 16... Opening, 17... Oxidation hose, 18... Flexible hose, 19... Pipe, 20... Flexible hose, 21... Dam, 22... Guide hole, 23
... refractory material powder, 24 ... bunker, 27 ... refractory material powder feeding device, 28 ... refractory material powder, 33 ... stopper, 34 ... cylinder, 36 ... refractory material powder.

Claims (1)

[Claims] 1. A graphite electrode held by an electrode holder is inserted into the lid of an arc furnace, and the scrap charged into the furnace is melted by the arc flare at the tip of the electrode, and the molten steel is melted. In a steelmaking arc furnace that heats and stirs the surface, there is a lance inserted into a brick at the bottom of the furnace body, a blow nozzle fixed to the tip of the lance toward the inside of the furnace, and a blow nozzle placed inside the furnace of the blow nozzle. A nozzle with many tiny holes,
A channel is connected to the lance and is connected to the porous nozzle and supplies hydrocarbon to the porous nozzle during the scrap melting period and the early stage of the sump formation period to form a solidified layer of molten steel at the tip of the blowing nozzle. It is characterized by being equipped with a supply pipe that supplies refractory material powder to the blowing nozzle using an inert gas as a carrier gas at the early stage of the tundish formation stage, and supplies oxygen gas to the blowing nozzle after the middle stage of the tundish formation stage. A bottom-blown arc furnace for steelmaking. 2. A graphite electrode held by an electrode holder is inserted into the furnace lid of an arc furnace, and the scrap charged into the furnace is melted by the arc flare at the tip of the electrode, and the surface of the molten steel is heated and stirred. This steelmaking arc furnace has a lance inserted into the brick at the bottom of the furnace body, a blowing nozzle fixed to the tip of the lance toward the inside of the furnace, and a large number of minute holes arranged inside the furnace of the blowing nozzle. a nozzle and
A channel that communicates with the nozzle having the porous holes and supplies hydrocarbon to the nozzle having the porous holes during the scrap melting period and the early stage of the sump formation period to form a solidified layer of molten steel at the tip of the blow nozzle, and a flow path that communicates with the blow nozzle. a refractory powder storage section for storing refractory material; a device for forcing the refractory powder in the refractory powder storage section into the blowing nozzle during the scrap melting period and the early stage of the sump formation stage to form a sintered layer of refractory material; and a device connected to the lance. and a supply pipe for supplying oxygen gas to the blowing nozzle after the middle of the tundish formation stage.