JPS60177114A - Dephosphorizing method of molten iron - Google Patents

Abstract

PURPOSE:To progress satisfactorily a dephosphorization reaction with decreased fuel consumption by injecting a powder material for refining with a gas enriched with oxygen as a carrier to under the surface of a molten iron from a single pipe nozzle attached to a vessel body. CONSTITUTION:A single pipe nozzle made of refractories is attached to a vessel body in such a way that the nozzle port thereof is positioned at the level coinciding with the inside surface of the furnace bottom. A powder material for refining contg. >=50% in total calcium oxide and iron oxide is bottom-blown from said nozzle into the vessel with the gas enriched with oxygen having 50- 90vol% oxygen concn. as a carrier gas so that the material is injected to under the surface of the molten iron in the vessel. The bottom blowing is executed at a ratio of 4-50 solid-gas ratio (kg/Nm<3>) between the carrier gas and the powder material for refining. The rate of dephosphorization is increased with the amt. of the flux to be used decreased and the effect of obviating decrease in the temp. of the molten iron, etc. is attained according to the above-mentioned dephosphorizing method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dephosphorizing hot metal that allows the dephosphorization reaction to proceed favorably with a small flux unit.

Conventionally, when attempting to dephosphorize hot metal, it is important to form an oxidizing slag with a high degree of basicity that is suitable for dephosphorization, and for this purpose Franks material and an oxidizing agent (this is a solid material such as iron oxide) are used. (sometimes gaseous oxygen) has been used. In this case, conventional refining recipes include two methods: when using a powdered solid oxidant, the solid oxidant is injected into the vortex using an inert gas as a carrier gas; When oxygen or oxygen-enriched gas is used, a double-pipe submerged lance or a double-pipe nozzle (tuyere) is used to supply cooling gas, such as an inert gas or hydrocarbon gas, from the outer pipe. However, methods of supplying oxygen-enriched gas or pure oxygen to the inner tube are well known.

Although these methods have been effective to some extent, they are still not sufficient. This is because in both methods, a large amount of carrier gas and cooling gas are simultaneously blown in in addition to the oxidizing agent. The conventional general idea was that slag dephosphorization by oxidizing slag dominated the dephosphorization reaction.

It is thought that the use of such an inert carrier gas and the use of non-oxidizing cooling gas will not pose a major hindrance to the progress of the dephosphorization reaction, as long as the advantageous aspects such as stirring are emphasized. It's here.

Contrary to this common sense, the present inventors discovered that the dephosphorization reaction in hot metal depends on the oxidizing agent supplied to the hot metal, rather than how to make 1M slag, although the details will be described later. We obtained the knowledge that it is determined by the oxygen supply rate. The present invention has been made with the aim of developing a dephosphorization method that realizes this knowledge in actual operation. That is, the present invention provides a method for advantageously advancing the dephosphorization reaction by supplying gaseous oxygen and a solid oxygen source into hot metal while reducing the amount of inert gas and cooling gas as much as possible. As stated in the range,
A single refractory nozzle attached to the container body uses oxygen-enriched gas with an oxygen concentration of 50 to 90 Vo1% as a carrier gas, and the total amount of calcium oxide and iron oxide is 50M.
% or more of the powdered refining material at a solid-air ratio (kg/Nr+
? ) is injected into the container at a rate of 4 to 5 degrees.

The method of the present invention fundamentally differs from the conventional method in that, firstly, instead of an inert gas, a reactive oxygen-enriched gas, on the contrary, is used as the carrier gas.

Injecting powdered refining substances with a total content of calcium oxide and iron oxide of 50% or more by weight at a small solid-air ratio of 4 to 50, and secondly, injecting such extremely reactive fluids. It is possible to directly inject phosphor into the vortex from a refractory single-tube nozzle without cooling gas, and to achieve dephosphorization using a very small amount of refining flux, such as CaO or CaF2, and to use a carrier gas. One example of this is to prevent melting and damage of single pipe nozzles made of refractories by maintaining the oxygen concentration at a high level rather than lowering it.

The features of the present invention will be explained in detail below based on test results.

Figure 1 shows 40% Ca using pure oxygen as a carrier gas.
When a powder consisting of b-10% CaF2-50% mill scale or a powder consisting of 80% Cab-20% CaF2 is injected into hot metal with a P content of approximately 0.15% by changing the feeding rate. This figure shows the dephosphorization behavior of , organized by the basic unit of CaO supplied. The results shown in Figure 1 indicate that the dephosphorization rate does not necessarily increase even if the CaO basic unit increases, and that in order for dephosphorization to proceed most effectively, a slag with a large amount of Cavil should be formed. It is implied that it will not happen.

Figure 2 shows the test results in Figure 1 organized by the total amount of oxygen introduced into the hot metal (total amount of oxygen introduced as carrier gas and oxygen introduced as mill scale). . in this case.

The dephosphorization amounts show surprising agreement. Namely.

Even if the type and supply amount of the injected powder substance differ, in other words, the injected CaO
This shows that the amount of reactive oxygen supplied as a whole has a direct relationship with the amount of dephosphorization, regardless of the amount of reactive oxygen or the amount of CaF2. In other words, the rate of the dephosphorization reaction is determined by the total amount of oxygen supplied to the hot metal, that is, the total amount of oxygen gas and the amount of oxygen in the iron oxide in the mill scale. Therefore, it can be seen that the supply of an oxygen source is the most important requirement in order for the dephosphorization reaction of hot metal to proceed efficiently.

Figure 3 shows the same dephosphorization test as above except that nitrogen gas was used instead of pure oxygen as the carrier gas (this test was conducted using a powdered solid oxygen source and quicklime with the previously described inert gas as the carrier gas). (corresponding to the conventional method of supplying oxygen into hot metal), and the results are summarized in terms of the above-mentioned test results using the pure oxygen carrier gas and Franks basic unit.

As seen in the results in FIG. 3, it can be seen that when oxygen is used as the carrier gas, a remarkable dephosphorization effect can be obtained even if the Franks basic unit is very small. Also,
In actual operation when conventional nitrogen gas is used as a carrier gas, the temperature of the hot metal decreases, which also poses a problem. That is, there is also the problem that the temperature of the hot metal during treatment decreases due to the endothermic reaction due to the decomposition reaction of iron oxide and the absorption of sensible heat and latent heat of the flux. On the other hand, when oxygen gas is used as a carrier gas, the oxidation reaction (oxidation of Fe, St, P, C, etc.) by oxygen gas is an exothermic reaction, so it provides the effect of compensating for the aforementioned heat absorption. Become.

By the way, when oxygen gas is injected as a carrier gas, that is, when oxygen gas is supplied to hot metal without using a cooling gas as in the past, there is a concern that the nozzle that carries out this injection may be damaged by erosion. Whether or not permanent injection is possible is an extremely important issue in actual operation. However, the present inventors discovered an extremely interesting fact here. In other words, if a refractory single tube nozzle is attached to the container body below the scene and powder is injected from this refractory single tube nozzle using oxygen gas as a carrier gas, the oxygen concentration of this carrier gas may be lowered. (On the other hand, if you keep it high, the nozzle will melt and wear out.) (It turns out that permanent blowing is possible.In this case, if you do the same from the top blowing lance, the lance will melt quickly, but in the situation In the case of bottom blowing from the bottom single pipe nozzle made of refractory material, there is no erosion.The details are explained below.

FIG. 4 shows a state in which a refractory single tube nozzle that can be used in the method of the present invention is attached to the bottom body of a refining vessel. This single tube nozzle is made of a brick layer at the bottom of the furnace, such as MgO.
The nozzle is installed within the thickness of the brick layer 1 through two mortar layers 12 so that the inner surface 2 of the brick layer 1 and the nozzle tip surface 3 are aligned.

Therefore, the nozzle opening 4 is provided at a level that exactly coincides with the inner surface of the furnace bottom. The entire single tube nozzle is constructed by inserting a refractory cylinder 6 into a refractory stamp layer 5, and this refractory cylinder 6 forms a fluid passage 7. The refractory stamp layer 5 is made of, for example, a ^1203 Cr2O2-based refractory, and the refractory tube 6 is made of, for example, recrystallized AI20.
3 or MgO-based refractories. That is, this nozzle, including its tip, is made of a refractory material and has a single tube structure. Fluid passage 7
is connected to a vibrator 8 made of steel, for example stainless steel, and this pipe 8 is connected to a joint 9 outside the container,
The joint 9 is supplied with a mixed fluid in predetermined amounts from an oxygen-containing gas source 10 and a powdery solid material source 11, respectively.

Normally, when pure oxygen or oxygen-enriched gas is supplied through such a refractory single-tube nozzle, the nozzle immediately melts away, making it impossible to continue blowing. Therefore,
Conventionally, even in oxygen blowing, other inert gases such as nitrogen gas were supplied together with oxygen. The best example is air (nitrogen gas + oxygen gas) blowing into a converter. When supplying pure oxygen or oxygen-enriched gas from the bottom of the furnace, a nozzle with a single tube structure like this will melt and damage, so instead, a nozzle with a double tube structure as mentioned above is used. This was done while cooling the nozzle by blowing cooling gas such as nitrogen gas, argon gas, or even hydrocarbon gas through its outer tube.

However, according to experiments conducted by the present inventors, even if oxygen-rich gas is injected from such a refractory single-tube nozzle at the bottom of the furnace, if powdery solid substances are entrained in the gas, In fact, it was found that semi-permanent blowing was more advantageous when the oxygen concentration in the gas was increased.

Furthermore, this powdery solid substance may be a solid substance that serves as an oxygen source necessary for refining.

FIGS. 5 to 8 schematically show representative examples of tests conducted by the present inventors to investigate the behavior of melting loss of refractory single-pipe nozzles.

Test work (Results correspond to Fig. 5) A refractory single-tube nozzle with a nozzle diameter of 3IIIΦ and an inner nozzle made of recrystallized A1203 as shown by 6 in Fig. 4 was attached to the bottom of a 300 kg high-frequency furnace. C: 4.0% in this furnace from a refractory single tube nozzle.

Mn: ~0.55%, St: 0.42%, P
:0.135%, S double, 1350~ including 033%
Air (oxygen concentration? 21 V
o1%) as carrier gas, 40% CaO-1
A powdered material consisting of 0% CaF2-50% mill scale was bottom blown into the vortex at a feed rate of 600 g/min. The carrier gas flow rate was 8ONN/min. Approximately 5 minutes after starting this bottom-blowing injection, the pressure in the powder supply pipe began to rise, reached 6 kg/m2 after 12 minutes, and the supply of powder was cut off. Immediately stopping the test and observing the vicinity of this nozzle, we found that at the tip of this nozzle, a solidified shell 13 covered the top surface of the nozzle.
was generated, and the passage within this solidified shell 13 was 1 mm or less.

Test 2 (results correspond to Figure 6) Oxygen 80 Vo1% + Ar20 as carrier gas
The same test as Test 1 was conducted except that a gas with a Vo of 1% was used. That is, a similar experiment was conducted using a carrier gas with a higher oxygen concentration than in Test 1.

In this case, the pressure inside the pipe is 3.45 kg/cn
1, the blowing state was extremely stable, and the mixed fluid containing powder could be supplied without any problems. . This was considered to indicate that a steady state was achieved near the nozzle orifice.

FIG. 6 shows an observation of the vicinity of the nozzle after the bottom blow injection was stopped after 30 minutes. As shown in the figure, in this case, there is a height of about 25 mm from the nozzle tip into the furnace.
, a cylindrical solidified forging 4 having an outer diameter of 17 mm was produced.

And the nozzle was not damaged at all. When this solidified shell was collected and its cross section was observed under a microscope, a structure in which oxide-like substances were scattered here and there in the Fe metal was observed.

Test 3 (results correspond to Figure 7) Oxygen e; OVo1% + Ar40 as carrier gas
The same test as Test 2 was conducted except that a gas with a Vo of 1% was used. That is, a similar experiment was conducted using a carrier gas with a slightly lower oxygen concentration than in Test 2. In this case, there is no problem in supplying the mixed fluid containing powder.
I was able to implement it. FIG. 7 shows an observation of the vicinity of the nozzle after the bottom blow injection was stopped after 30 minutes.

As shown in the figure, in this case as well, a cylindrical solidified shell 14 was generated from the nozzle tip toward the inside of the furnace, and the nozzle was not damaged at all.

Test 4 (Results correspond to FIG. 8) The same test as Test 1 was conducted except that pure oxygen gas of 100 Vo 1% was used as the carrier gas. In this case, as 2 hours passed, the pressure in the supply piping tended to decrease more strongly. When the injection was stopped after 30 minutes and the condition of the nozzle was observed, as shown in FIG. 5, the vicinity of the nozzle eye was melted and damaged. That is, it was found that under these conditions, if pure oxygen with an oxygen concentration of 100% is injected, the refractory single pipe nozzle will be damaged by erosion.

In addition to the above tests, various tests were carried out, including various changes in the oxygen concentration in the carrier gas, changes in the blending ratio of powdered substances in the carrier gas, types of substances, and types of refractories constituting the nozzle. As a result of repeated numerous tests, the oxygen concentration in the carrier gas was 50 to 90 Vo.
1%, preferably in the range of 60 to 90 Vo1%, and the powdered material is the total gas INn? /min 4~50kg/
When the powder material is entrained in this carrier gas at a supply rate of sin, that is, when the powder material is entrained at a solid-air ratio (kg/Nrrr) of 4 to 50, a good tubular solidified shell is obtained. It was found that the dephosphorization reaction progressed well at the same time as the formation. If the oxygen concentration in the carrier gas is lower than this appropriate range, the nozzle clogging phenomenon will occur as in Test 1, and if the oxygen concentration exceeds 90 Vo1%, which is close to pure oxygen, the result of Test 4 will be In some cases, melting damage occurred. Powdered substances include iron ore, mill scale, iron oxide powder such as sintered ore powder, C
Franks materials such as ab, CaF2, etc. can be suitably used, and when these materials are properly supplied within the above range, good solidified shell formation has been observed.

On the other hand, A12 is the refractory material used to construct the nozzle.
Tests were conducted on 03 series, MgO series, ZrO2 series, etc., but no major differences were observed between them, and it was found that 2 batches of recrystallized A120'3 and MgO series refractories were sufficient.

As a comprehensive result of the above tests, the factor that shows a dramatic effect on preventing nozzle erosion is the oxygen concentration in the carrier gas. When used as a gas, it was confirmed that, contrary to expectations, even a refractory single-tube nozzle did not suffer from erosion. In other words, the heat-absorbing effect of sensible heat and latent heat of the powdery solid substance and the sudden amount of heat generated when the oxygen gas in the carrier gas collides with the hot metal are balanced, and the metal of the hot metal at the tip of the nozzle is balanced. There is a region in which a solidified shell of material containing particles is formed and does not grow excessively, and this steady state is maintained by continuous injection.

The present invention utilizes this solidified shell formation phenomenon to advantageously advance the dephosphorization reaction in actual operation, and the dephosphorization reaction, as seen in FIG. The fact that it is controlled by

However, such good results could not be obtained when the injection was top-blown instead of bottom-blown. Instead of the above-mentioned bottom blowing, the present inventors immersed a single pipe lance made of two types of refractories into the molten metal from above the surface of the molten metal,
A similar test was conducted by changing the oxygen concentration in the carrier gas, but even though the amount of powder was the same as in the case of bottom blowing, the lance was significantly eroded when the oxygen gas concentration was 80Vo1%. Namely.

Even if the injection substance and its amount are the same, top blowing does not give the same good results as bottom blowing. The reason for this is not necessarily clear, but the temperature distribution around the nozzle is fundamentally different between top blowing and bottom blowing.
In addition, in the case of bottom blowing, since the injection is upward from a fixed location, it is easier to maintain a steady state that is favorable for the formation of solidified shells.
This may be related to the fact that it is difficult to maintain such a steady state in top blowing.

Figure 9 shows an oxygen concentration of 50 Vo from a refractory single tube nozzle attached to the container body based on one or more test facts.
Using oxygen-enriched gas or pure oxygen gas changed to 1%, 80Vo1% or 100Vo1% as a carrier gas, the total amount of calcium oxide and iron oxide is 90fi amount% (4
0%CaO-10%CaF2 50% mill scale) powdered refining material with a Si concentration of 0.05%.

This figure shows the results of a typical example of the present invention in which three levels of hot metal, 0.20% and 0.45%, were injected into the scene, and in each case, the dephosphorization behavior was The horizontal axis shows the basic unit supply amount of powdery substances.

As is clear from the results shown in Figure 9, according to the two methods of the present invention,
When targeting hot metal with a low Si concentration of 0.05%, the Franks basic unit is only 20kg/)ton, which is extremely low ([%P) = 0.02 to 0.00].
Dephosphorization up to 5') was carried out. When the Si concentration is high, desiliconization occurs first and then dephosphorization proceeds. Therefore, although the overall Flux consumption rate has increased, if we look only at the dephosphorization period, the FRANXX consumption rate is about 20 kr/ton, the same as in the low Si concentration example, and good dephosphorization results can be achieved with a small amount of Flux. It is clear that this has been obtained.

As explained above, the method of the present invention performs dephosphorization using an oxygen-enriched gas as a carrier gas, instead of the conventional injection method using an inert gas or the dephosphorization method using a cooling gas and supplying oxygen gas. The dephosphorization method of the present invention provides a new method for dephosphorizing hot metal, and the dephosphorization method of the present invention has a high dephosphorization rate with a small amount of Franks used, does not involve a drop in hot metal temperature, and can reduce the amount of slag produced. It exhibits an extremely excellent effect in that it can dephosphorize with a small amount of oxidation.

[Brief explanation of the drawing]

Figure 1 shows 40% CaO using pure oxygen as a carrier gas.
- When a powder consisting of 10% CaF2-50% mill scale or a powder consisting of 80% Cab-20% CaF2 is injected into hot metal with a P content of approximately 0.15% by changing the feeding rate. A diagram illustrating dephosphorization behavior organized by CaO basic unit. Figure 2 shows the same tests as in Figure 1 organized by the total amount of oxygen introduced into the hot metal (total N of oxygen introduced as carrier gas and oxygen introduced as mill scale). . Figure 3 shows the results of the same dephosphorization test as in Figures 1 and 2, except that nitrogen gas was used instead of pure oxygen as the carrier gas. A diagram comparing the test results organized by Franks basic unit. FIG. 4 is a cross-sectional view showing an example of a refractory single-tube nozzle that can be used to implement the method of the present invention. FIGS. 5 to 8 are schematic cross-sectional views showing the state of the tip of a refractory single-tube nozzle when Tests 1 to 4 of the main text were conducted. FIG. 9 is a diagram showing the results of an example of the method of the present invention in terms of the relationship between the amount of phosphorization and the Franks basic unit. 1. Brick layer at the bottom of the hearth, 2. Inner surface of brick layer 1, 3. Nozzle tip surface, 4. Nozzle opening. 7. Fluid passage, 14. Solidified shell. Figure 1 CaO (kg/1nn) Figure 2 0 500 1000 1500 2000ΣO,CN
t) Fig. 3 0 20 40 60 80 100 Fulx basic unit (kg/ton -) DI Fig. 4 Fig. 5 Fig. 6 Fig. 7

Claims (1)

[Claims] Powdered clay with a total content of calcium oxide and iron oxide of 50% by weight or more is injected from a refractory single-tube nozzle attached to the container body using an oxygen-enriched gas with an oxygen concentration of 50 to 90 Vo1% as a carrier gas. The solid-gas ratio (kg/
A method for dephosphorizing hot metal, which comprises injecting hot metal below the surface of the hot metal in a container at a rate such that N rrr ) is 4 to 50.