JPS6216243B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a cold material charge in a converter, that is, scrap iron.
Related to heating methods for ferroalloys, etc.

Traditionally, the commonly used steelmaking methods are pure oxygen top-blowing converter, pure oxygen bottom-blowing converter, and top-bottom blowing converter (combined blowing method), which has recently been developed and put into practical use.
This is a converter steel manufacturing method. A common functional problem with these various converter steelmaking methods is that compared to other steelmaking methods, such as open hearth or electric furnaces, the scrap iron melting capacity is limited to 25-30% at most, and the use of scrap iron is limited. There is a limit to the amount. Therefore, various proposals and attempts have been made to solve the basic functional problems of this converter steel manufacturing method. For example, a method has been widely adopted in which an auxiliary heat source such as ferrosilicon, carbide, metal aluminum, or even coke powder is charged into a converter and combusted with refining oxygen to increase heat input. Ta. Alternatively, the scrap iron charged to the converter may be heated using an oxyfuel burner or toroidal burner prior to smelting.
Methods such as preheating scrap iron using a burner have also been put into practical use under certain limited conditions.

However, these various methods of improving scrap iron melting capacity have a large cost burden on the heat source used, and the combustion products have a negative effect on the refining reaction of the converter, or the thermal efficiency is low and the preheating time is too long, making it difficult to make steel. There are various problems that prevent it from being widely adopted, such as a decrease in efficiency. Therefore, these various scrap iron melting capacity improvement methods have only found extremely limited application as a production measure in times of extreme hot metal shortage, such as when replacing the refractory lining of a blast furnace.

On the other hand, a method of preheating the charged scrap iron by blowing fuel such as kerosene and combustion oxygen using the bottom blowing tuyere for refining gas installed at the bottom of the converter has been known for a long time. (Patent Application Publication No. 53-28241 (Application: September 10, 1972)) It has been put into practical use in some bottom-blowing converters or top-bottom blowing converters.

In this method, during normal refining, refining oxygen is blown into the inner tube of a double-tube tuyere installed at the bottom of the converter.
Hydrocarbons such as methane and propane are injected from the outer tube to protect the tuyere, but when preheating the scrap metal, combustion oxygen is injected into the inner tube and fuel oil such as kerosene is injected into the outer tube. The high-temperature exhaust gas generated by the heating process is caused to escape and float upward from the bottom of the charged scrap metal layer, and in the process, heat is transferred to the scrap metal to be heated with high efficiency.

The present inventors have conducted detailed research on the industrialization of the above method, but as mentioned above, the known combustion method using tuyeres can only be applied to a very limited range of applications, depending on the type of material to be heated. It was discovered that there is a limit to the heating temperature, and that there is a problem with general-purpose industrialization.

Therefore, an object of the present invention is to provide a heating method for scrap iron or ferroalloy using the bottom-blowing tuyeres of a bottom-blowing converter or a top-bottom-blowing converter, and to
The heating temperature limit has been greatly improved, the thermal efficiency is high, and at the same time, there is very little loss of the heated material.
The aim is to provide highly versatile technical methods.

The basic problem with the previously mentioned method of heating scrap iron or ferroalloy by blowing combustion oxygen through the inner tube of the bottom-blowing tuyere and fuel such as kerosene through the outer tube is that the oxygen The combustion flame temperature of kerosene or other hydrocarbons or other carbon-containing substances is very high, and when the heated material reaches a certain temperature,
Detailed research by the inventors has revealed that the oxygen blown into the inner tube directly causes a violent oxidation reaction between the metal and oxygen (so-called oxygen-induced cutting phenomenon). It was also found that these two basic problems pose fatal obstacles in actual operation. The flame temperature of, for example, kerosene and oxygen injected from the bottom blowing tuyere has been confirmed by various theoretical calculations and experiments, including those of the present invention, as follows:
It becomes an extremely high temperature flame of approximately 3000℃, and as a result, the flame directly above the tuyere,
The area and its vicinity are locally heated by short-time heating, and the cutting phenomenon caused by oxygen occurs when the surface temperature of the heated object reaches approximately 1100 to 1250°C, although it also depends on the type of heated object. It has been confirmed that it will start. Due to this cutting of oxygen, which is a violent oxidative exothermic reaction of the metal of the object to be heated, such as iron, silicon, chromium, manganese, etc., the object to be heated, which is under the above-mentioned ultra-high temperature flame, rapidly melts. proceed. As a result, the area around the bottom blowing tuyere is locally heated to a high temperature, and a molten layer is partially formed, which forms a pool at the bottom of the furnace, but the oxygen gas blown from the inner pipe Even though the molten metal is formed in a pool under a pressure of
A portion of the molten layer is blown off as a spray by this oxygen jet. This splash scatters onto the packed bed of unmelted objects to be heated, fills the gaps between the individual objects to be heated in the packed bed, and finally locally becomes a large semi-molten lump. In other words, under the combustion conditions of kerosene and oxygen shown in the example, a pool of molten layer is formed around the tuyere, the area just above the tuyere is completely blown through by the blown gas, and the area around it is a semi-molten layer. A layer of lumps is formed. This phenomenon may be relatively slight if the object to be heated is a pig iron type that is relatively unlikely to be cut due to oxidation, and the heating temperature is low, but it may occur if the object to be heated contains a large amount of ordinary steel scrap, silicon, or chromium. It has been found that in the case of scrap iron or ferroalloys such as ferrochrome and ferronitkel, this occurs even when heated for an extremely short time.

Such an unavoidable phenomenon is a fatal hindrance to the heating method of scrap iron or ferroalloy, which utilizes the bottom blowing tuyere as a burner.

One of them is a decrease in thermal efficiency. A heating method using bottom-blowing tuyeres has the major advantage that high heat transfer efficiency can be obtained by allowing the high-temperature exhaust gas combusted at the tip of the tuyere to pass through the gap between the layers of the material to be heated upwards from the bottom. be. However, as mentioned above, the area directly above the tuyere melts to form a space through which most of the combustion gas blows through, resulting in a major problem in actual operation in which a significant drop in thermal efficiency is unavoidable. .

The next problem is that the pool of water formed around the tuyere at the bottom of the furnace is easily blown through by the oxygen jet blown through the inner pipe of the tuyere. This poses a serious problem in that a portion of the molten metal reaches the dust collector of the converter due to the splash, resulting in a significant drop in yield. moreover,
Due to the intense oxidation reaction caused by oxygen in the heated material,
Iron or valuable elements it contains, such as chromium,
This is the oxidation of manganese, etc. Particularly when heating alloyed iron alloys containing chromium, manganese, etc., oxidation of these elements becomes a major hindrance in the next refining process, and how to suppress these oxidations is an economic evaluation of the process. Very important.

The next big problem discovered was that the refractory material around the tuyere was exposed to extremely high temperatures due to the formation of ultra-high temperature flames above the tuyere tip, causing significant damage to the refractory material.

As described above, the conventional heating method of scrap iron or ferroalloy using a bottom blowing tuyere has the disadvantages of a decrease in thermal efficiency, a loss of the heated material to the dust collector (decreased yield rate), iron and chromium contained therein, There remain fundamental problems in industrialization, such as oxidation of valuable elements such as manganese, and damage to tuyeres and bottom refractories.

The present inventors have conducted various detailed studies and studies on heating methods that solve the above problems, and have found that these basic problems can be fundamentally solved by improving the combustion conditions at the tip of the tuyere. Obtained. The most fundamental problem with conventional heating methods using tuyeres is that the tip of the tuyere is required to completely burn fuel such as kerosene into CO ₂ and H ₂ O in a stoichiometric manner using oxygen. The flame temperature becomes extremely high, exceeding 3000℃, and the object to be heated near the tuyere is locally heated to a high temperature, and the locally heated object is cut (cutting) by the oxygen jet for combustion. It was discovered that a rapid oxidation reaction occurs, and that preventing this is a fundamental improvement measure.

First, as a solution to this problem, we changed the combustion conditions of kerosene and oxygen at the tip of the tuyere from the conventional stoichiometric complete combustion conditions to incomplete combustion conditions. Kerosene 1
The theoretical amount ^of oxygen required for the combustion of Local melting of the heated object as described in
The oxygen cutting phenomenon could not be prevented.

Through detailed consideration through this experiment,
As long as oxygen is blown into the inner tube of the tuyere, this oxygen is discharged from the tip of the tuyere as a jet flow close to the speed of sound.
This reminded us that the generation of ultra-high temperature flames and the cutting phenomenon of heated objects due to oxygen are unavoidable.

Therefore, after conducting small-scale off-line experiments and conducting various studies on the combustion conditions at the tip of the tuyere, we found that an inert gas such as nitrogen, argon, or carbon dioxide was mixed with the combustion oxygen blown from the inner tube. It was found that the cutting phenomenon of the heated object was significantly suppressed.

Based on this knowledge, we conducted various experiments on more detailed combustion conditions in a 150-ton converter, which is an actual operating furnace.

As shown in Figure 1, the converter used in the experiment had six tuyeres at the bottom of the furnace, and the inner tubes contained oxygen, nitrogen, and argon gases, either individually or mixed in arbitrary ratios. In addition to the propane that is normally flowed during blowing, nitrogen, argon, and kerosene used during heating can be flowed into the outer tube. Additionally, in addition to the normally flowing oxygen, nitrogen gas can be mixed with oxygen and flowed from the top-blown water cooling lance. Approximately 50 tons of scrap iron is charged into the top and bottom blowing converter in Figure 1, and kerosene is poured from 2,000 to 4,000/hour through the outer pipes of the six bottom blowing tuyeres.
/hour, the amount of gas blown into the inner tube was varied from pure oxygen to the mixing ratio of oxygen and nitrogen, and the flow ranged from 3000Nm ³ /hour to 10000Nm ³ /hour in various combinations, depending on the tuyere diameter. , test operations were conducted repeatedly. In this test operation, after heating the scrap iron, a predetermined amount of hot metal was additionally charged and normal decarburization refining was performed. The relationship between the mixing ratio of nitrogen to combustion oxygen, thermal efficiency during heating, and dust loss to the dust collector is
As shown in the figure. The thermal efficiency in the same figure is calculated from the average heating temperature after heating the scrap iron from the heat balance during refining after heating the scrap iron. Calculated from. As can be seen from Figure 2, when oxygen alone gas or nitrogen is mixed at about 10% from the inner tube, the basic problem mentioned above occurs.
In particular, 30 to 50% of the heated material was observed to be melted, and formation of metal oxide slag was observed on the surface. In such a state, the combustion flame blows through, resulting in poor heat transfer efficiency and low thermal efficiency of less than 40%, and the loss of dust from the heated material to the dust collector is extremely large.

On the other hand, when 20% nitrogen is mixed with oxygen, melting and cutting of the heated object is significantly prevented, and thermal efficiency and dust loss are also considerably improved. 30% is almost complete. As the nitrogen concentration is further increased, there is a tendency for thermal efficiency to decrease at a nitrogen mixing ratio of about 70%, and at 80%, this effect can no longer be ignored. However, at this time, the flame temperature was extremely low due to the cooling effect of nitrogen, and there was no dust loss or metal oxide formation. Therefore, considering the overall characteristics and efficiency of heating such as thermal efficiency, dust loss, and generation of metal iron oxide, it is recommended that the mixing ratio of nitrogen to oxygen be in the range of 20% to 70% under actual operating conditions. found. In addition, it was confirmed that when operating at this level of nitrogen mixing ratio, there was no major damage to the refractories around the tuyere, which was observed during conventional kerosene/oxygen combustion, and the life of the tuyere could be significantly extended. It was done.

We also conducted an experiment on a method of supplying oxygen from the top blowing lance shown in FIG. 1 and reducing the supply of bottom blowing gas by that amount to reduce the tuyere diameter. At this time, the combustion conditions using the bottom blowing tuyere are as follows.
Blow in the aforementioned mixed gas of oxygen and nitrogen,
Although this results in incomplete combustion with less oxygen than the theoretical amount, this method involves secondary combustion of the unburned decomposed gas with oxygen from the top blowing lance. When blowing oxygen for combustion from the top blowing lance, depending on the blowing conditions, the combustion may concentrate locally on the surface of the scrap metal, causing the same problem as the bottom blowing tuyere combustion mentioned earlier. At the same time, when the top blowing ratio is high, the temperature of the flame due to secondary combustion increases, and the atmospheric temperature inside the furnace reaches a high temperature of approximately 1800℃ according to actual measurements, leading to a phenomenon that promotes damage to the furnace refractories. It was discovered that Therefore, regarding the combustion conditions for this top-blown oxygen, we conducted the same study as the combustion conditions for the bottom-blown tuyere described above, and found that by mixing 20% to 70% nitrogen with the top-blown oxygen, It was confirmed that ideal heating conditions could be obtained in terms of thermal efficiency, dust loss, metal oxide formation, and damage to refractories. In particular, with regard to damage to the furnace refractories, a significant economic effect is that due to the drastic reduction in the atmospheric temperature within the furnace, damage hardly progresses compared to when no heating is performed. Although nitrogen was used as the gas to be mixed with oxygen in this experiment, other inert gases such as argon and carbon dioxide were used in the offline experiment in the small reactor mentioned above, which has the effect of cooling the combustion flame. It was also confirmed that if it has the effect of suppressing the cutting characteristics of metals due to oxygen, the original purpose can be achieved, and the selection range is wide.

The above is an example of a method for preheating ordinary steel scrap in converter blowing using ordinary hot metal and scrap iron as main raw materials to improve the scrap iron melting ability. FIG. 3 shows typical results when this result is applied, for example, to preheating ferrochrome alloy iron when producing high chromium alloy steel. The mixing ratio of nitrogen to combustion oxygen during heating is 0%, 15%,
Dust loss to converter dust collector in 50% case,
When evaluating the chromium concentration in the collected dust water, as shown in Figure 3, a very high concentration is detected up to a mixing ratio of nitrogen to oxygen of 15%;
At 50%, it is hardly detected. As a result, the overall chromium yield including the refining process after heating was less than 90% when the nitrogen mixing ratio was 0% and 15%, but when the nitrogen mixing ratio was 50%, it was 94.3%.
%, a significant improvement was achieved. Naturally, when the object to be heated contains chromium as shown in the above example, or an expensive element such as nickel or manganese, the effects of the present invention are greatly enhanced.

The embodiments described above do not represent all the constituent technologies of the present invention, and for example, as fuel injected from the bottom blowing tuyeres, other hydrocarbons or carbon-containing materials, or even as a top blowing method. Embodiments of the present invention include a method in which the water is blown through a tuyere installed at the upper part of the furnace wall, instead of using a top-blown water cooling lance.

By constructing and using the present invention as described above, it is possible to improve the heating efficiency of the object to be heated, and to significantly reduce heating loss, without any restrictions such as the type of object to be heated or the heating temperature. It greatly contributes to the heating of scrap iron, ferroalloy, etc. in converters.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of the present invention for heating scrap iron and ferroalloy in a top-bottom blowing converter, and Figure 2 is the relationship between the mixing ratio of nitrogen to combustion oxygen when heating scrap iron, thermal efficiency, and dust loss to the dust collector. Fig. 3 shows that when heating ferrochrome alloy iron, zero nitrogen is added to the combustion oxygen.
%, 15%, and 50% of the chromium concentration in the collected dust water. 1... Bottom-blown inner pipe gas piping, 2... Bottom-blown outer pipe gas pipe, 3... Top-blown lance, 4... Heated object, 5...
...Converter body, 6...Bottom-blown double pipe tuyere.

Claims (1)

[Claims] 1. A bottom-blowing converter equipped with bottom-blowing multi-tube tuyeres at the bottom of the furnace;
Alternatively, in the top-bottom blowing converter steelmaking method, fuel consisting of hydrocarbons or other carbon-containing substances is blown into one channel of the bottom blowing tuyere and oxygen for fuel combustion is blown into the other channel, then combusted, and then charged. In the method of heating scrap iron and/or ferroalloy, which is used in a converter, the converter is characterized in that 20% or more and less than 70% of an inert gas such as nitrogen, argon, or carbon dioxide is mixed with oxygen for combustion. Heating method for scrap iron and ferroalloy. 2. Claim 1, characterized in that, in addition to the bottom blowing tuyere, a part of the combustion oxygen is supplied from the top blowing water cooling lance or the tuyere provided through the furnace wall refractories. A method of heating scrap iron and ferroalloy in a converter. 3 Oxygen for combustion supplied from a water-cooled lance or a tuyere installed through the furnace wall refractories is mixed with an inert gas such as nitrogen, argon, or carbon dioxide by 20% or more and 70%.
3. A method for heating scrap iron and ferroalloy in a converter according to claim 2, wherein said scrap iron and ferroalloy are mixed in a converter.