JPH068447B2 - Method for melting iron-containing cold material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for melting an iron-containing cold material.

(Prior Art) In Japanese Patent Laid-Open No. 60-174812, iron-containing cold material, carbonaceous material, and oxygen are supplied into a converter in which seed hot water is present, and the iron-containing cold material is melted to obtain high carbon molten iron. A converter steelmaking method comprising a step and a second step in which the above-mentioned high carbon molten iron as a raw material is blown with oxygen in another converter to obtain molten steel having a required temperature and composition is known.

The temperature of the molten iron in the first step is preferably 1450 ° C. or lower in order to suppress melting loss of refractory in the melting process, and when the temperature of the molten iron at the completion of melting of the iron-containing cold material is 1450 ° C. or lower,
From the viewpoint of securing a heat source in the second step, [C] is 3.0% or more,
Preferably 3.5% or more is required.

A method for melting an iron-containing cold material that can be used as the first step in the converter steelmaking method is known from Japanese Patent Publication No. Sho 56-8085. The method of melting the iron-containing cold material disclosed in the publication is:
As shown in FIG. 1, a triple pipe nozzle 1 having an upper blown oxygen lance 14 and having a structure as shown in FIGS.
2, the iron-containing cold material 17 such as scrap, sponge iron, pellets, solid pig iron, iron ore, etc. is fed into the converter 15 in which the molten iron 16 such as molten pig iron is present. Non-oxidizing gas such as nitrogen gas from the inner tube 2 of the triple tube nozzle 1 of FIG. 3 is used for carbonaceous materials such as coal powder, coke powder, etc., middle tube 3 for oxygen, and outer tube 4 for non-oxidizing cooling such as LPG. Injecting a volatile gas to dissolve the carbonaceous material in the bath and burn the carbon in the bath to the primary combustion (C +
(1/2) O ₂ → CO) and oxygen is supplied from the above-mentioned blown oxygen lance 14, and the above carbon monoxide is secondarily burned (CO + (1/2) O ₂
→ CO ₂ ) and heat is supplied to the bath to melt the iron-containing cold material and obtain molten pig iron.

In FIGS. 2 and 3, reference numeral 7 denotes a protrusion extending on the outer circumference of the inner pipe 2 at equal intervals in the axial direction of the inner pipe, and the outer surface thereof contacts the inner surface of the middle pipe 3 to form a gap 5. ing. Reference numeral 8 is a protrusion extending on the outer periphery of the middle tube 3 at equal intervals in the middle tube axial direction, and the outer surface thereof contacts the inner surface of the outer tube 4 to form a gap 6. Reference numeral 9 is a furnace shell, and 10 is a refractory material inside the furnace.

Secondary combustion is important in the above-described method for melting iron-containing cold material, and the basic unit of carbonaceous material and the basic unit of oxygen in the method for melting iron-containing cold material such as steel scrap are determined by the secondary combustion rate as shown in FIG. The higher the secondary combustion rate, the less the carbonaceous material and the iron-containing cold material can be melted with the carbon consumption rate.

According to Japanese Patent Publication No. 56-8085, the height of the oxygen top blowing lance 14 is set to 2 m or more above the molten metal surface, and the top blowing oxygen is supplied by a free jet from a height of 2 m or more above the molten metal surface while bottom blowing oxygen is supplied. The ratio is 20 to 80% (the upper blowing oxygen ratio is 80 to 20).
%), It is said that a high secondary combustion rate will be obtained.
If the bottom blown oxygen ratio is less than 20%, the slag will home and the space for forming free jets on the surface of the molten metal will decrease, which is high.
It is said that the secondary combustion rate cannot be obtained.

The above-mentioned bottom blown oxygen ratio is important both in terms of equipment and operating costs. The lower the bottom blown oxygen ratio, the easier the bottom blown equipment (the number of nozzles is reduced), the lower the bottom blown equipment cost, and the bottom blown oxygen. The non-oxidizing gas for cooling such as LPG and the protective gas such as N ₂ and Ar which are supplied to prevent the oxygen nozzle from clogging when it is not dissolved will decrease as the bottom blowing oxygen ratio decreases and the operating cost will decrease. To do.

Further, in general, the higher the stirring power of the bath, the easier the furnace bottom refractory is to melt, so it is desirable that the bottom blown oxygen ratio is low in order to prevent furnace bottom refractory melt damage.

(Problems to be Solved by the Invention) The present invention secures a secondary combustion rate equivalent to that of the conventional method with a lower bottom blowing oxygen ratio than that of the above-mentioned conventional method, and a carbonaceous material and oxygen-containing unit equivalent to those of the conventional method are used. Disclosed is a method for melting iron-containing cold material, which is capable of melting the cold material and reducing the bottom blowing equipment cost, non-oxidizing gas for cooling, the amount of protective gas used, and the rate of refractory wear of the furnace bottom, as compared with the conventional method. It is a thing.

(Means for Solving the Problems) The gist of the present invention is as follows.

Using a converter having an upper blown oxygen lance and a triple tube nozzle at the bottom of the furnace, an iron-containing cold material is supplied into the converter in which molten iron is present, and a non-oxidizing gas is supplied from the inner tube of the triple tube nozzle. Carbon material, oxygen from the middle tube, while blowing a non-oxidizing gas for cooling from the outer tube and supplying oxygen from the above-mentioned blowing oxygen lance to melt the iron-containing cold material to obtain molten iron, in the method for melting the iron-containing cold material, The temperature of the molten iron in the melting process is 1
Maintaining [C] at 3% or higher at 450 ° C. or lower, making the bottom blown oxygen ratio 10% or more and less than 20% of the total amount of upper bottom blown oxygen, and imparting a twist to the bottom blown oxygen, the triple pipe A method for melting an iron-containing cold material, characterized in that the molten iron is put into a molten iron bath after leaving the nozzle.

Hereinafter, the present invention will be described in detail.

The inventors of the present invention have a triple tube nozzle 1 shown in FIGS. 2 and 3 at the bottom of the furnace, and a converter 15 having an upward blowing oxygen lance 14 as shown in FIG. C] 3.0 to 3.5
% Of 70% of molten iron, 30 t of scrap, and 1.5 t of quick lime as a slag material are charged to produce about 100 t of molten iron at [C] 3.7% or more and a temperature of 1400 to 1450 ° C. Change the blown oxygen ratio to 15 to 30% (upper blown oxygen ratio 70 to 85%) (fix the oxygen supply rate per nozzle to 5% to the bottom blown oxygen ratio and change the number of nozzles installed on the furnace bottom) Then, the secondary combustion rate during the melting period was measured by exhaust gas analysis.

The acid transfer rate is 13000 to 20000 Nm ³ / hr,
As the carbonaceous material, finely powdered anthracite is 1.4 per unit volume of oxygen.
Blows at a set speed of Kg / Nm ³ . The target secondary combustion rate at this time was 30%, and the lance height of the upper blowing oxygen lance 14 was adjusted to control the target value. When the secondary combustion rate does not reach the target value, the [C] in the bath decreases, so to compensate for this, the carbonaceous material blowing speed is increased above the set value to increase the [C] in the molten iron to 3.0-3. It was maintained at 0.5%. The temperature of the molten iron decreased at the same time as the charging of scrap, increased as the melting progressed, and finally increased to 1400 to 1450 ° C to complete the melting. Fig. 5 shows an example of changes in the secondary combustion rate. In the case of the oxygen bottom blowing ratio of 30%, the secondary combustion rate remains stable at around 30% over the entire period, but at 20%, the fluctuation is large, and at 15%, the secondary combustion occurs especially in the first half of the melting period. The rate did not rise to the target value. When a high secondary combustion rate such as an oxygen bottom blowing ratio of 30% is obtained stably, it is indicated by ○, when it is slightly unstable, it is indicated by △, and when it is not obtained, it is indicated by ×. Graphically showing the above test results,
It became like the broken line in FIG.

As a result of investigating the reason why a high secondary combustion rate cannot be obtained when the bottom blowing oxygen ratio is less than 20%, the carbonaceous material is not completely dissolved in the iron bath while floating in the iron bath and floats on the bath surface. Then, this rises in the furnace together with the exhaust gas, and for example, CO ₂ burned according to the reaction of the equation (1) is reduced to CO and an endothermic reaction occurs,
It was found that the secondary combustion rate (CO ₂ / (CO + CO ₂ )) decreases.

CO ₂ + <C> Carbonaceous material = 2CO (1) Since it was found that the carbonaceous material could not be completely dissolved in the iron bath and the secondary combustion rate decreased when the bottom blowing oxygen ratio was less than 20%. The present inventors have diligently studied a method of completely dissolving carbonaceous material at a bottom blowing oxygen ratio of less than 20%. The bottom blowing oxygen is twisted to leave the triple pipe nozzle, and the temperature is 1450 ° C. or lower, [C ] It is made to enter into a molten iron bath of 3.0% or more.

9 and 10 show an embodiment of a triple tube nozzle in which bottom blown oxygen is twisted to leave the triple tube nozzle and enter the molten iron bath. The tube nozzles 13 are provided in the outer circumference of the inner tube 2 of the conventional triple tube nozzle 1 shown in FIGS. 2 and 3 at equal intervals in the axial direction of the inner tube, and the outer surface thereof contacts the inner surface of the middle tube 3. By spirally forming the protruding portion 7 in the axial direction of the inner pipe, the spiral guide element 12 is provided in the gap 5 between the inner pipe 2 and the middle pipe 3 of the nozzle, and melts from the gap 5 between the inner pipe 2 and the middle pipe 3. It is designed to give a twist to the oxygen blown into the iron bath.

The twist angle α (inclination angle in the vertical direction) of the spiral guide element 12 is 10 to 40 ° because if the angle α becomes too large, the pressure loss becomes large, and if the angle α becomes too small, the oxygen dispersion region becomes small. Is desirable.

1390 to 1420 ° C., [C] 3.2 in a converter 15 having a triple tube nozzle 13 shown in FIGS. 9 and 10 at the bottom of the furnace and an upper blowing oxygen lance 14 as shown in FIG. 1. 30t of scrap and 70t of molten iron of 3.6% and 1.5t of quick lime as a slag material are inserted to produce about 100t of molten iron of 1400-1450 ° C [C] 3.7% or more. Change the blown oxygen ratio to 5-20% (top blown oxygen ratio 95-80%) (fix the oxygen supply rate per nozzle to 5% for bottom blown oxygen and change the number of nozzles installed on the furnace bottom) Then, the behavior of the secondary combustion rate during the melting period was investigated. The acid transfer rate is 13000
It was up to 20000 Nm ³ / hr, and as the carbonaceous material, fine powder of anthracite was blown at a set rate of 1.4 kg / Nm ³ per unit volume of oxygen. The target secondary combustion rate at this time was 30%, and the lance height of the upper blowing oxygen lance 14 was adjusted to control the target value.
When the secondary combustion rate does not reach the target value, the [C] in the bath decreases, so to compensate for this, the carbonaceous material blowing speed is increased above the set value to increase the [C] in the molten iron to 3.0-3. It was maintained at 0.5%. The temperature of molten iron decreases at the same time as the charging of scrap, and rises as the melting progresses, and finally 1400-1450 ° C.
The temperature was raised to 0 to complete the dissolution. Sixth example of change in secondary combustion rate
In the figure and in FIG. 7, the solid line shows the relationship between the stability evaluation of the secondary combustion rate and the bottom blown oxygen ratio.

As is clear from comparing FIG. 6 and FIG. 5, the bottom blown oxygen ratio using the triple tube nozzle 13 of FIGS. 9 and 10 (hereinafter referred to as spiral triple tube nozzle) is 15% (10%).
The secondary combustion rate of the pattern is almost the same as the secondary combustion rate of the bottom blown oxygen ratio of 30% (20%) using the triple tube nozzle 1 (hereinafter referred to as a straight triple tube nozzle) of FIGS. 2 and 3. Has become.

In Fig. 6, the transition of the secondary combustion rate when molten iron [C] is less than 3.0% during melting is also shown by a broken line. When [C] becomes less than 3.0% ( At the melting time of 10 minutes), the homing phenomenon of the molten slag was recognized from the furnace mouth, and the secondary combustion rate drastically decreased, and after several minutes (5 minutes), the operation was stopped by sloping. The molten iron [C] at that time was 2.7.
It had fallen to%.

FIG. 8 shows the relationship between the [C] concentration of molten iron and the sloping occurrence frequency at the bottom blown oxygen ratio of 5 to 30%, and when the molten iron [C] is less than 3.0%, sloping occurs. Occurs, and the frequency of occurrence increases as the [C] of molten iron decreases. 3.0% of molten iron [C] in the melting process
[C] causes slag homing when turned off.
When it falls below 0%, FeO in slag increases, which is slag-
CO due to the reaction of (FeO) + [C] = Fe + CO at the metal interface
This is considered to be due to the fact that many air cells are generated and homing is likely to occur. Further, when the slag is homing, the secondary combustion rate lowers because the free jet is formed by the oxygen supplied from the oxygen top blowing lance, but the molten iron is formed by the homing as described in Japanese Patent Publication No. 56-8085. This is probably because the space for forming free jets on the bath surface is reduced.

As is clear from FIGS. 5 to 8, the bottom blown oxygen ratio is 20%.
If less than 10%, the bottom blown oxygen is twisted to leave the triple tube nozzle 13 and enter the molten iron bath, and [C] in the molten iron is maintained at 3.0% or more. By doing so, the secondary combustion rate as high as that of the conventional method and stable over the melting period can be obtained without slag homing.

Thus, in the present invention, the oxygen bottom blowing ratio is less than 20% and 10%.
Even with the above low bottom blown oxygen ratio, the mechanism that the secondary combustion rate at the initial stage of melting and the unstable behavior are eliminated, and the secondary combustion rate is as high and stable as the conventional method, is obtained. It can be considered as follows.

Since the bottom-blown oxygen is twisted to leave the triple tube nozzle 13 and enter the molten iron bath, the conventional bottom-blown oxygen is not twisted as shown in the schematic diagram of FIG. As compared with the triple tube nozzle 1 which is separated from the triple tube nozzle 1 , the area 18 for dispersing the bottom-blown oxygen gas in the bath becomes wider. It is desirable that the temperature of the carbonaceous material rapidly dissolves in the bath and that the surrounding [C] be low. As the dispersed area of oxygen expands, the melting area of the carbonaceous material during floating increases, and this area is decarburized by oxygen and the temperature rises, forming a lower carbon high temperature area than the surrounding molten iron. Gives the condition that dissolves quickly. Further, the carbonaceous material that enters the molten iron bath from the inner pipe 2 is also entrained in the above-mentioned twisting flow, and is uniformly and widely dispersed in the molten iron bath to promote the melting of the carbonaceous material and prevent the carbonaceous material from floating on the bath surface. It is thought that this is because it is done.

On the other hand, in the case of the conventional triple tube nozzle 1 , since the dispersion region 19 is narrow, it is necessary to increase the amount of oxygen, and the bottom blowing oxygen ratio is 20%.
The above is considered necessary.

Further, since the [C] of the molten iron is maintained at 3.0% or more in the melting process, the slag 20 is added in the melting process.
It is thought that this is because homing is prevented and a sufficient space for forming the free jet 21 on the molten iron bath surface is secured as described in Japanese Patent Publication No. 56-8085.

For example, according to the method of the present invention having a bottom-blown oxygen ratio of 15% (10%) using a spiral triple-tube nozzle, the same method as the conventional method having a bottom-blown oxygen ratio of 30% (20%) using a straight triple-tube nozzle is used. Since the subsequent combustion rate pattern can be obtained, the method of the present invention can dissolve the iron-containing cold material with the same oxygen and carbonaceous material unit as the above-mentioned conventional method even with a low bottom blowing oxygen ratio. For example, when using a triple tube nozzle that secures a bottom blown oxygen ratio of 5%, 6 (4) are used in the conventional method.
No. of nozzles is required, but in the method of the present invention, the number of nozzles required is three (two), and the equipment cost including the bottom can be reduced by half.

Since the number of required nozzles is halved in this way, the amounts of non-oxidizing gas for cooling and protective gas used can also be halved.

Since the method of the present invention has a lower bottom blowing oxygen ratio than the conventional method, the method of the present invention can further reduce the melting rate of the furnace bottom refractory as compared with the conventional method.

(Example) Seed water of pre-heat ([C] = 3.5%, temperature 1350 ° C.) 70
30 t of steel scrap and quick lime as a slag forming agent in a converter (equipped with a top-blown oxygen lance and three spiral triple-tube nozzles (twisting angle of spiral guide element: 30 °)) where t exists.
Steel scrap was melted by charging 5t.

At that time, from the inner pipes of the three triple pipe nozzles
Blowing N ₂ gas as a carrier gas at an average of 1.4 kg / Nm ³ (set value) per unit volume of oxygen, and blowing 15% of the total oxygen amount by twisting between the inner tube and the middle tube,
Furthermore, LPG is blown from between the middle pipe and the outer pipe to the bottom blown oxygen amount of about 10 vol.
% Blown. The total acid flow rate is 16,000 Nm ³ / hr.

The target secondary combustion rate at this time was 30%, and the lance height of the upper blowing oxygen lance was adjusted to control the target value.

If the secondary combustion rate does not reach the target value, the [C] in the bath decreases, so to compensate for this, the anthracite blowing rate is increased above the set value to increase the [C] in the molten iron to 3.0 to 3.5. Maintained at%. In the latter half of the melting, the carbonaceous material blowing rate was increased to 3.8%.

Also, the temperature of the molten iron decreases at the same time as the steel scrap charging,
The temperature increased as the dissolution progressed, and finally the temperature was raised to 1400 ° C to complete the dissolution.

Fig. 12 shows the transitions of the secondary combustion rate, carbonaceous material injection speed, and lance height during the melting process.

(Comparative example) Preheated seed water ([C] = 3.4%, temperature 1380 ° C.) 70
30 t of steel scrap and 1.5 of quick lime as a slag-making agent were charged into a converter (equipped with an immediate lance of acid and three straight triple-tube nozzles) where t was present to carry out melting.

At that time, fine powder of anthracite was blown from the inner pipes of the three straight triple pipe nozzles with N ₂ gas as a carrier gas at an average of 1.4 kg / Nm ³ per unit volume of oxygen, and the total oxygen was fed between the inner pipe and the middle pipe. Blow straight 15% of the amount of oxygen,
Furthermore, LPG is blown from between the middle pipe and the outer pipe to the bottom blown oxygen amount of about 10 vol.
% Blown in. The total acid flow rate is 16,000 Nm ³ / hr.

The target secondary combustion rate at this time was 30%, and the lance height of the upper blowing oxygen lance was adjusted to control the target value.

When the secondary combustion rate does not reach the target value, the [C] in the bath decreases, so to compensate for this, the carbonaceous material blowing speed is increased above the set value to increase the [C] in the molten iron to 3.0-3. It was maintained at 0.5%.

In the latter half of the melting, the carbonaceous material blowing rate was increased to 3.8%. The temperature of molten iron decreased at the same time as the charging of steel scrap, increased as the melting progressed, and finally increased to 1410 ° C to complete the melting.

Fig. 13 shows changes in the secondary combustion rate, carbonaceous material injection speed, and lance height during the melting process.

(Conventional example) Preheated seed water ([C] = 3.5%, temperature 1370 ° C) 70
30 t of steel scrap and 1.5 t of quick lime as a slag-making agent were charged into a converter (equipped with a top-blown oxygen lance and 6 straight triple tube nozzles) where t was present to melt the steel scrap.

At that time, fine anthracite coal was blown from the inner tubes of the six straight triple tube nozzles with N ₂ gas as a carrier gas at an average of 1.4 kg / Nm ³ per unit volume of oxygen, and the total amount of gas was fed between the inner tube and the middle tube. Blow straight 30% of the oxygen amount,
Furthermore, LPG is blown from between the middle pipe and the outer pipe to the bottom blown oxygen amount of about 10 vol.
% Blown. The total acid flow rate is 16,000 Nm ³ / hr.

The target secondary combustion rate at this time was 30%, and the lance height of the upper blowing oxygen lance was adjusted to control the target value.

When the secondary combustion rate does not reach the target value, the [C] in the bath decreases, so to compensate for this, the carbonaceous material blowing speed is increased above the set value to increase the [C] in the molten iron to 3.0-3. It was maintained at 0.5%. In the latter half of melting, the carbonaceous material blowing rate was increased to carburize to 3.9%.

The temperature of molten iron decreased at the same time as the charging of steel scrap, increased as the melting progressed, and finally increased the temperature to 1400 ° C to complete the melting.

FIG. 14 shows changes in the secondary combustion rate, carbonaceous material injection speed, and top blowing lance height during the melting process.

Average secondary combustion rates in the above-mentioned examples, comparative examples, and conventional examples,
The following table shows the carbon material consumption rate, oxygen consumption rate, LPG consumption rate, and furnace bottom refractory wear rate.

(Effects of the Invention) As described in detail above, according to the method of the present invention, a secondary combustion rate equivalent to that of the conventional method is ensured with a lower bottom blowing oxygen ratio than that of the conventional method.
The iron-containing cold material is melted with the same carbon material and oxygen consumption rate as the conventional method,
And, compared with the conventional method, the equipment cost including bottom, non-oxidizing gas for cooling,
It is possible to reduce the amount of protective gas used and the rate of wear of refractory bottoms.

[Brief description of drawings]

FIG. 1 is an explanatory view of a melting method of iron-containing cold material, FIGS. 2 and 3 are explanatory views of a structure of a triple pipe nozzle (straight triple pipe nozzle) used in a conventional method, and FIG. Explanatory diagram of the relationship between secondary combustion rate, carbonaceous material, and oxygen consumption rate in the melting method,
FIG. 5 is an explanatory diagram of a transition example of the secondary combustion rate of the conventional method, FIG. 6 is an explanatory diagram of an transition example of the secondary combustion rate of the present invention method, and FIG. 7 is a bottom blow in the present invention method and the conventional method. FIG. 8 is an explanatory view of the relationship between the oxygen ratio and the stability of the secondary combustion rate, FIG. 8 is an explanatory view of the relationship between the [C] concentration of molten iron and the sloping occurrence frequency, and FIGS. 9 and 10 are the present invention. Fig. 11 is an explanatory view of an example of a triple pipe nozzle used in the method, and Fig. 11 shows a bottom blown oxygen ratio of less than 20% and 10%.
It is explanatory drawing of the presumed mechanism by which the secondary combustion rate which is as high and stable as the conventional method is obtained even if the above-mentioned low bottom blown oxygen ratio. FIG. 12, FIG. 13, and FIG. 14 are transition charts of the secondary combustion rate, the carbonaceous material injection speed, and the top blowing lance height in the melting process in Examples, Comparative Examples, and Conventional Examples. 1 ... Triple tube nozzle (straight triple tube nozzle), 2 ... Inner tube, 3 ... Medium tube, 4 ... Outer tube, 5 ... Gap, 6 ... Gap, 7 ... Projection part, 8 ... Projection part, 9 ... Furnace iron Leather, 10 ... Refractory in the furnace, 12 ... Helical guide element, 13 ... Triple tube nozzle (spiral triple tube nozzle), 14 ... Oxygen top blowing lance, 15 ...
Converter, 16 ... Molten iron, 17 ... Iron-containing cold material, 18 ... Dispersion region, 19 ... Dispersion region, 20 ... Slag, 21 ... Free jet.

Claims (1)

[Claims] 1. A converter having a top-blown oxygen lance and a triple-tube nozzle at the bottom of the furnace is used to supply iron-containing cold material into the converter in which molten iron is present. Carbon-containing material with non-oxidizing gas, oxygen from the middle tube, non-oxidizing gas for cooling from the outer tube, and oxygen from the above-mentioned oxygen blowing lance to melt the iron-containing cold material to obtain molten iron. In the melting method, the temperature of the molten iron in the melting process is maintained at 1450 ° C. or lower, [C] is maintained at 3% or higher, and the bottom blown oxygen ratio is 10% or more of the upper bottom blown total oxygen amount.
A method for melting an iron-containing cold material, characterized in that it is less than 20% and the bottom-blown oxygen is twisted to leave the triple-tube nozzle and enter the molten iron bath.