JPH0435524B2 - - Google Patents

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 has been considered important to form an oxidizing slag with a high degree of basicity, which is suitable for dephosphorization. (sometimes gaseous oxygen) has been used. In this case, the conventional refining recipe is to inject the solid oxidant into hot water using an inert gas as a carrier gas when using a powdered solid oxidant, and to use a gaseous oxidant such as pure When using oxygen or oxygen-enriched gas, an immersion lance with a double pipe structure (for example,
126910) or a nozzle with a double tube structure (for example, Q
A well-known method is to supply oxygen-enriched gas or pure oxygen gas to the inner tube while supplying a cooling gas, such as an inert gas or hydrocarbon gas, from the outer tube using a tuyere (BOP method). ing. Also, JP-A-58-
Publication No. 147506 proposes a method of supplying oxygen and powdered dephosphorizing agent to the surface of the hot water from a top blowing lance while stirring by injecting inert gas from the tuyeres at the bottom of the furnace.

Although these methods have been effective to some extent, they are still not sufficient. This is because, in addition to the oxidizing agent, a large amount of carrier gas, cooling gas, and stirring gas are simultaneously blown into the system. Conventionally, the general idea was that slag dephosphorization by oxidizing slag dominated the dephosphorization reaction, so the use of such inert carrier gas and non-oxidizing cooling gas was not recommended due to stirring, etc. It has been thought that once the advantageous aspects are emphasized, there will be no major hindrance to the progress of the dephosphorization reaction.

Contrary to this common sense, the present inventors discovered that, although the details will be described later, the dephosphorization reaction in hot metal depends on the oxidizing agent supplied to the hot metal, rather than on how to make oxidizing slag. 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, oxygen-enriched gas with an oxygen concentration of 50 to 90 Vol% is used as a carrier gas from a single refractory nozzle attached to the container body, and the total amount of calcium oxide and iron oxide is 50% by weight or more. This method is characterized by injecting a powdered refining substance under the surface of hot metal in a container at a solid-gas ratio (Kg/Nm ³ ) of 4 to 50.

The method of the present invention is fundamentally different from the conventional method in that, first, a reactive oxygen-enriched gas is used as a carrier gas instead of an inert gas;
Injection of powdered refining materials with a total content of calcium oxide and iron oxide of more than 50% by weight at a low solid-air ratio of 4 to 50, and secondly, the use of highly reactive fluids such as Direct injection into hot water from a refractory single-tube nozzle without cooling gas, and even refining fluxes such as
By attempting to dephosphorize using very small amounts of CaO and CaF ₂ , and by maintaining the oxygen concentration of the carrier gas at a high level rather than lowering it, we are able to prevent erosion of the refractory single-tube nozzle. prevention, etc.

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

Figure 1 shows 40% pure oxygen carrier gas.
When a powder consisting of CaO - 10% CaF ₂ - 50% mill scale or a powder consisting of 80% CaO - 20% CaF ₂ 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 rate of dephosphorization does not necessarily increase even if the basic unit of CaO increases, and that in order for dephosphorization to proceed most effectively, a slag with a large amount of CaO should be formed. It is implied that this is not the case.

Figure 2 shows the test results in Figure 1 organized by the total amount of oxygen introduced into the hot metal (the total amount of oxygen introduced as carrier gas and oxygen introduced as mill scale). in this case,
The dephosphorization amounts show surprising agreement. That is,
Even if the type and amount of injected powdery material differs, in other words, regardless of the amount of CaO or _CaF2 injected, the amount of reactive oxygen supplied as a whole is determined. This shows that there is a direct relationship with the amount of phosphorus. In other words, the rate of the dephosphorization reaction is determined by the total amount of oxygen supplied into the hot metal, that is, the total amount of oxygen gas and the amount of oxygen in the iron oxide in the mill scale. It can be seen that the supply of an oxygen source is the most important requirement for the process to proceed efficiently.

Figure 3 shows a dephosphorization test similar to the above except that nitrogen gas was used instead of pure oxygen as the carrier gas (this test was performed using a powdered solid oxygen source and quicklime as the carrier gas, using the previously described inert gas as the carrier gas). The results are summarized in terms of the test results using the pure oxygen carrier gas mentioned above and the flux consumption rate.
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 flux consumption rate is very small. Further, in actual operation when conventional nitrogen gas is used as the 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, since the oxidation reaction (oxidation of Fe, Si, P, C, etc.) by oxygen gas is an exothermic reaction, it also has the effect of compensating for the heat absorption mentioned above. Become.

By the way, when injecting oxygen gas 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 can be achieved 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 hot water level, and powder is injected from this refractory single-tube nozzle using oxygen gas as a carrier gas, instead of lowering the oxygen concentration of the carrier gas, On the other hand, it was found that if the temperature was maintained at a high temperature, permanent blowing could be performed without the nozzle melting or being damaged. In this case, if the same procedure is carried out from the top blowing lance, the lance will immediately be eroded, but if it is bottom blown from a refractory single pipe nozzle below the surface of the molten metal, it will not be eroded. The contents will be 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 installed through a mortar layer 12 within the thickness of a brick layer, for example, an MgO-based brick layer 1 at the bottom of the furnace, so that the inner surface 2 of this brick layer 1 and the nozzle tip surface 3 are aligned. Therefore, its 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, an _{Al2O3 - Cr2O3 -} based refractory, and the refractory cylinder 6 is made of, for example, _{recrystallized Al2O2} or MgO-based refractory. 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 pipe 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 powdered 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, other inert gases such as nitrogen gas have been supplied together with oxygen even in oxygen blowing. 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 single-tube structure nozzle like this would be damaged by melting, so instead, a double-structure nozzle as described 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 the 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. Moreover, 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 erosion of refractory single-pipe nozzles.

Test 1 (Results correspond to Fig. 5) A refractory single tube nozzle with a nozzle diameter of 3 mmφ and whose nozzle inner surface was made of recrystallized Al ₂ O ₃ as shown by 6 in Fig. 4 was attached to the bottom of a 300 Kg high frequency furnace. , C: 4.0%, Mn in this furnace from this refractory single tube nozzle
~0.55%, Si: 0.42%, P: 0.135%, S: 0.033%
Using air (oxygen concentration ≒ 21 Vol%) as a carrier gas, 40
A powdered material consisting of %CaO-10% _CaF2-50 % mill scale was bottom blown into the hot water at a feed rate of 600 g/min. The carrier gas flow rate was 80N/min. About 5 minutes after starting this bottom blowing injection
After a few minutes, the pressure inside the powder supply pipe began to rise, reaching 6 kg/mm ² after 12 minutes, and the powder supply was cut off.
Immediately stopping the test and observing the vicinity of this nozzle, as shown in FIG. The passageway was less than 1mm thick.

Test 2 (results correspond to Figure 6) Oxygen 80Vol% + Ar20Vol as carrier gas
A test identical to Test 1 was conducted except that % gas 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 was kept constant at 3.45 Kg/cm ² , resulting in an extremely stable blowing condition, 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. Figure 6 shows the bottom blowing injection stopped after 30 minutes and the vicinity of the nozzle observed. As shown in the figure, in this case, a cylindrical solidified shell 14 having a height of about 25 mm and an outer diameter of about 17 mm was generated in the furnace from the nozzle tip. And the nozzle was not damaged at all. When we collected this solidified shell and observed its cross section under a microscope, we observed a structure in which oxide-like substances were scattered here and there within the Fe metal.

Test 3 (results correspond to Figure 7) Oxygen 60Vol% + Ar40Vol as carrier gas
A test identical to Test 2 was conducted except that % gas 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 as well, the mixed fluid containing powder could be supplied without any problems. Figure 7 shows a view of the vicinity of the nozzle after the low 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 containing 100 Vol% oxygen was used as the carrier gas. In this case, the pressure within the supply piping tended to decrease as time progressed. When the injection injection was stopped after 30 minutes and the condition of the nozzle was observed, as shown in FIG. 5, the vicinity of the nozzle opening was found to be melted and damaged. In other words, it was found that under these conditions, a refractory single-pipe nozzle would be eroded if it was injected with pure oxygen with an oxygen concentration of 100%.

In addition to the above tests, we varied the oxygen concentration in the carrier gas, changed the blending ratio of powdered substances in the carrier gas, changed the type of substance, and changed the type of refractory material constituting the nozzle. As a result of repeated numerous tests, the oxygen concentration in the carrier gas is 50 to 90 Vol% in the total gas, preferably 60 to 90 Vol%.
The range is 90Vol%, and the powder material is 1Nm ³ /
Good results are obtained when powdered materials are entrained in this carrier gas at a feed rate of 4 to 50 kg/min, that is, when powdered materials are entrained to a solid-air ratio (Kg/Nm ³ ) of 4 to 50. It was found that the dephosphorization reaction progressed well at the same time as a tubular solidified shell was formed. If the oxygen concentration in the carrier gas is lower than this appropriate range, nozzle clogging will occur as in Test 1, and if the oxygen concentration exceeds 90 Vol%, which is close to pure oxygen, as in Test 4, In some cases, melting and damage occurred. In addition, as the powdery substance, iron oxide powder such as iron ore, mill scale, and sintered ore powder, and flux materials such as CaO and _CaF2 can be suitably used. Good solidified shell formation was observed. On the other hand, we tested Al ₂ O ₃ -based, MgO-based, ZrO ₂ -based refractories for constructing the nozzle, but no major differences were found between them, and ordinary recrystallized Al ₂ O ₃ and MgO-based refractories were found to be 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, it was confirmed that, contrary to expectations, even a refractory single-tube nozzle did not suffer from erosion. In other words, the heat absorption effect of the sensible heat and latent heat of the powdery solid substance and the rapid calorific value generated when the oxygen gas in the carrier gas collides with the hot metal are balanced, and the metal content of the hot metal is absorbed at the tip of the nozzle. There is a region in which a solidified shell of material containing ions occurs 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. The fact that oxygen is controlled by the amount of oxygen has been realized without any operational problems.

However, such good results could not be obtained when the injector was top blown instead of bottom blown. Instead of the bottom blowing described above, the inventors conducted similar tests by immersing single-pipe lances made of various refractories into the molten metal from above the molten metal and varying the oxygen concentration in the carrier gas. , even if the amount of powder is the same as in the case of bottom blowing, the oxygen gas concentration is
At 80Vol%, the lance was significantly eroded. That is, even if the substance and the amount of injection are the same, top blowing does not give the same good results as bottom blowing. The reason for this is not necessarily clear, but it is because the temperature distribution around the nozzle is fundamentally different between top blowing and bottom blowing, and in the case of bottom blowing, there is upward injection from a fixed location. This may be related to the fact that while it is easy to maintain a steady state that is favorable for the formation of solidified shells, it is difficult to maintain such a steady state in top blowing.

Figure 9 shows that, based on the above test facts, oxygen-enriched gas or pure oxygen gas with varying oxygen concentrations of 50 Vol%, 80 Vol%, or 100 Vol% is injected from a refractory single-tube nozzle attached to the container body. As a carrier gas, the total amount of calcium oxide and iron oxide is 90% by weight (40% CaO − 10% OaF ₂ − 50% mill scale)
Si concentration is 0.05%, 0.20%,
This figure shows the results of a typical example of the present invention in which three levels of 0.45% hot metal were injected below the hot metal surface. In each case, the dephosphorization behavior was determined by the amount of powdered material supplied. The basic unit is summarized on the horizontal axis.

As is clear from the results shown in Figure 9, according to the method of the present invention, when hot metal with a low Si concentration of 0.05% is targeted, the flux consumption rate is extremely low at only 20 kg/ton ( [%P] = 0.02~
Dephosphorization to 0.05) was carried out. When the Si concentration is high, desiliconization occurs first, followed by dephosphorization. Therefore, although the overall flux intensity has increased, if we look only at the dephosphorization period, the flux intensity is approximately 20 kg/kg, the same as in the low Si concentration example.
It is clear that good dephosphorization results can be obtained with a small amount of flux.

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

[Brief explanation of drawings]

Figure 1 shows 40% pure oxygen as a carrier gas.
When a powder consisting of CaO - 10% CaF ₂ - 50% mill scale or a powder consisting of 80% CaO - 20% CaF ₂ is injected into hot metal with a P content of approximately 0.15% by changing the feeding rate. The dephosphorization behavior of
Figure 2, a diagram organized by CaO basic unit, is
Figure 3 shows the same test as shown in the figure, 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). The results of the same dephosphorization test as in Figures 1 and 2, except that nitrogen gas was used instead of , are summarized by the test results using pure oxygen carrier gas in Figures 1 and 2, and the flux consumption rate. A comparative diagram, FIG. 4 is a cross-sectional view showing an example of a refractory single pipe nozzle that can be used to carry out the method of the present invention, and FIGS. FIG. 9 is a schematic cross-sectional view showing the state of the tip of a refractory single-tube nozzle in the case of the above, and is a diagram showing the results of an example of the present invention in terms of the relationship between the amount of phosphorous removed and the flux consumption rate. 1... Brick layer at the bottom of the furnace, 2... Inner surface of brick layer 1, 3... Nozzle tip surface, 4... Nozzle opening, 7...
...Fluid passage, 14...Coagulation shell.

Claims (1)

[Claims] 1. Powdered refining substances with a total content of calcium oxide and iron oxide of 50% by weight or more are produced using oxygen-enriched gas with an oxygen concentration of 50 to 90 Vol% as a carrier gas from a refractory single-tube nozzle attached to the container body. A method for dephosphorizing hot metal, which consists of injecting molten pig iron into the surface of hot metal in a container at a rate such that the solid-gas ratio (Kg/Nm ³ ) is 4 to 50.