JP5928329B2 - Smelting reduction smelting method - Google Patents

Description

  The present invention relates to a smelting reduction smelting method, and in particular, when adding a carbonaceous material to a chromium oxide-containing material, and melting and reducing the chromium oxide-containing material, while suppressing refractory erosion, It suppresses the generation of slopping and carbonaceous and metal dust, and further improves the yield of Cr.

  Ferrochrome, one of the main raw materials of stainless steel, has been manufactured by the electric furnace method that uses electric power as a heat source. However, since expensive electric power is used in large quantities, the cost of ferrochrome is high. The manufacturing cost was pushed up.

Therefore, in recent years, the use of a smelting reduction smelting method of chromium ore by a converter is increasing as a depowering type smelting method that does not use electric power.
The smelting reduction smelting method of chrome ore using this converter reduces the amount of ferrochrome used by reducing the amount of ferrochromium by using inexpensive chrome ore as the main raw material and reducing it with carbonaceous materials. The decarburization reaction (primary and secondary oxidation reaction) is caused by supplying by blowing or bottom blowing, etc., and the heat generated at that time is compensated for heat to compensate the reduction endotherm of the oxide, and the bath temperature required for smelting reduction Holding.

However, since this smelting reduction smelting method has a large reduction amount of chromium ore and a large endothermic amount, it is necessary to increase the amount of the top blown oxygen gas to increase the thermal compensation. Here, when the amount of the top blowing oxygen gas is increased, a large amount of dust is generated, and the following problems occur.
There are two types of dust generated in smelting reduction smelting: carbon-based dust and metal-based dust. The generation of carbon-based dust means that the carbon material supplied as the reducing material and the heat source is the reduction reaction or heat source. As a matter of course, the cost of the carbonaceous material increases because it escapes to the outside of the furnace without contributing. In addition, when metal dust is generated, the yield of Cr is reduced.

Here, the generation of metal dust is caused by the vaporization of the CO gas bubbles generated by the decarburization reaction and the evaporation of the metal from the reaction fire point (top blown oxygen fire point) on the bath surface by the top blown oxygen gas. It is thought to be the cause.
That is, in order to suppress the generation of dust, soft blowing is performed so that the top blowing oxygen gas is not strongly blown to the bath surface, or the top blowing oxygen fire point is generated, for example, on the upper surface of the molten metal. It is necessary to block the molten metal from the bath surface using
Moreover, since the carbonaceous dust is more easily accompanied by the gas generated in the furnace as the particle size of the carbonaceous material charged into the furnace is smaller, the amount of the carbonaceous dust generated increases. Therefore, the carbonaceous material put into the furnace needs to have a particle size of a certain size or more so that the falling speed overcomes the upward flow rate of the gas generated in the furnace. Increasing the value causes a problem that the specific surface area decreases and the reduction reaction of chromium ore is delayed, resulting in a decrease in the yield of Cr.

  In order to reduce the metal dust, the top blowing oxygen gas can be soft blown by increasing the height of the top blowing lance from the bath surface or by making the top blowing lance hole porous and the cross-sectional area of the lance hole. There is a method of decreasing the gas flow rate of the discharge hole by increasing the gas flow rate. However, in these methods, secondary combustion is promoted, and there is a problem that exhaust gas temperature rises and wear of the furnace refractory material becomes severe.

  On the other hand, as a method for shutting off the upper blown oxygen fire point from the bath surface with molten slag, for example, in Patent Document 1, generation of dust is caused by always having molten slag of 50 kg / t or more in a converter furnace. A method of suppressing this has been proposed. In this method, in order to always make slag exist in a furnace, the method of making the slag of a pre-charge remain in a furnace is taken.

  However, in the method described in Patent Document 1, when the scrap is charged into the furnace before the start of blowing, a part of the remaining slag is locally cooled and agglomerated by the scrap to dissolve the scrap. There was a problem of obstructing. In other words, in order to reduce costs, stainless steel smelting uses stainless steel scrap, especially stainless steel bullion generated in the refining and casting process of stainless steel as an inexpensive Cr and Ni source. If dissolution of these cold iron sources is hindered, the smelting efficiency will be greatly reduced.

  To solve this problem, a method of interrupting smelting and charging slag after melting the scrap is considered, but this method has a problem that the smelting time increases. Further, as a means for increasing the amount of slag without leaving slag, a method of increasing the amount of flux added during converter blowing is considered, but there is a problem that the cost increases.

In addition, as a method for reducing carbonaceous dust, a substance having a ratio of the number of hydrogen to carbon atoms, H / C of 0.5 or less and a fixed carbon content of 85% or more is used, and the bottom blown oxygen flow rate is set to 0.3. It is proposed in Patent Document 2 to be -0.8 Nm ³ / min · t. In this method, the carbonaceous material is thermally collapsed after being put into the furnace and refined to a particle size convenient for the reduction reaction or melting in the molten metal. The condition that the particle size is a certain size or more can be secured so as to overcome the upward flow rate of the internally generated gas.
However, if the property of the slag in the furnace is in an inappropriate condition such as insufficient forming or uneven distribution on the surface of the molten metal bath, the carbonaceous material collapses and atomizes, turning into dust. There was a problem of being discharged outside the furnace. Further, even if the carbonaceous dust is reduced by the above method, there is no effect of reducing the generation amount of the metal dust that occupies most of the generated dust.

Furthermore, the slag volume is increased by decreasing the apparent specific gravity of the slag without increasing the slag mass. That is, there has been proposed a method of blocking the top-blown oxygen jet from the molten metal bath surface by using slag forming. For example, as described in Patent Document 3, the basicity of slag ((mass% CaO) / (mass% SiO ₂ )) is set to 2.5 or less, and the residual carbonaceous material concentration in the slag is set to 20% or less. In this method, slag forming is promoted to reduce dust generation.

Japanese Unexamined Patent Publication No. 1-215949 Japanese Patent Laid-Open No. 10-251729 JP 10-317041 A

  However, it is extremely difficult to control the slag height by slag forming, and there is a high operational risk that the slag will slip and cause an operational failure. In addition, slopping occurred at the interface between molten metal and slag due to the reaction of slag containing a large amount of highly oxidizable components such as T.Fe and Cr oxide and molten metal with high carbon concentration during smelting. CO gas bubbles cannot easily pass through the slag, and after slag forming occurs to raise the slag level, the slag overflows from the furnace port at the top of the converter.

  In addition, the occurrence of slag foaming has a problem that the residual carbonaceous material concentration is lowered and the frequency of occurrence of poor reduction of chromium oxide is increased. Furthermore, the decrease in the residual carbon material concentration in the slag increases the concentration of highly oxidizable oxides such as iron oxide and chromium oxide in the slag, and increases the refractory wear of the portion in contact with the slag. There's a problem. This is because the converter furnace wall refractory usually uses mag-carbon bricks, so that the increase in the oxide concentration promotes the reaction between C and the oxide in the brick.

  Here, it is known that when the slag basicity is lowered, the MgO solubility in the slag is increased and the amount of magnesia eluted in the brick is increased. Therefore, although it is necessary to increase the basicity in order to suppress the refractory melting damage, when the basicity is increased, the slag viscosity is lowered and forming is difficult to occur. That is, it is extremely difficult to appropriately control the generation of forming while protecting the furnace refractory.

  The present invention has been developed in view of the above-described situation, and suppresses the generation of slopping, carbonaceous material and metal-based dust while suppressing refractory melting when chrome ore is melted and reduced. It aims at providing the method of improving the yield of Cr.

That is, the gist configuration of the present invention is as follows.
1. In the smelting reduction smelting method of the chromium oxide-containing material, the oxygen is supplied and the chromium oxide-containing material is melt-reduced while the chromium oxide-containing material is introduced into the smelting reaction vessel together with the carbonaceous material and the auxiliary material.
The ratio (mass% CaO) / (mass % SiO 2) between the amount of CaO and SiO ₂ content in the slag at the smelting reduction period, and 2.6 to 5.0, and a carbonaceous material concentration remaining in the slag, A smelting reduction smelting method of a chromium oxide-containing substance, characterized by smelting while controlling in a range of 20 mass% to 40 mass% (excluding 20 mass% to 30 mass%) .

2. 2. The smelting reduction smelting method according to 1 above, wherein the carbonaceous material is anthracite.

  According to the present invention, smelting of refractories during smelting reduction smelting of chromium oxide-containing materials in a converter, while suppressing the occurrence of slopping, carbonaceous and metal dust, and further Cr Yield can be improved.

It is a graph which shows the relationship between the residual carbonaceous material density | concentration in slag, and a metal type dust generation index. It is a graph which shows the relationship between the residual carbonaceous material density | concentration in slag, and a carbonaceous material type | system | group dust generation index. It is a graph which shows the relationship between the residual carbonaceous material density | concentration in slag, and a slopping generation | occurrence | production index. It is a graph which shows the relationship between the residual carbon material density | concentration in slag, and a furnace wall refractory wear index.

Hereinafter, the present invention will be specifically described. In addition, unless otherwise indicated, the% display shown below shall express mass%.
The present invention relates to a slag produced in a so-called smelting reduction period in which a chromium oxide-containing substance is introduced into a smelting reaction vessel (converter) together with a carbonaceous material and an auxiliary material to supply oxygen and perform smelting reduction. The ratio of CaO to SiO ₂ (% CaO) / (% SiO ₂ ), that is, the basicity of the slag is in the range of 2.6 to 5.0, and the residual carbon concentration in the slag is 20% to 40% Smelting while controlling to the range.

In smelting reduction blowing, a sufficient amount of carbonaceous material is supplied to prevent reduction defects. During the smelting reduction smelting operation, the carbon material is continuously or intermittently charged into the furnace from the furnace chute of the smelting reduction furnace. In a smelting reduction furnace, a large amount of gas mainly composed of CO produced by the reaction of oxygen from the lance and oxygen in the chromium oxide or iron oxide, which is the main component of chromium ore, and carbon in the carbonaceous material or hot metal. Has been attracted to the exhaust gas recovery system. The charged carbon material needs to overcome the upward flow of the generated gas and fall into the furnace, so a particle size of several mm to several tens of mm is required.
On the other hand, the carbonaceous material that has entered the slag in the furnace needs to quickly reduce chromium oxide and iron oxide or dissolve in the hot metal, so that a larger specific surface area, in other words, a smaller particle size is preferable.

  In order to meet these contradictory demands, in the present invention, the carbon material to be input uses a carbon material having heat disintegration property. The carbon material having the heat-disintegrating property becomes a fine powder preferable for reaction and dissolution by thermally disintegrating in a high-temperature slag while maintaining a large particle size until it falls in the furnace from the charging chute. Although it will not specifically limit if it is a carbon material which has heat disintegration property, coal is preferable. Coal contains volatile matter in addition to solid carbonaceous matter, and when it is exposed to high temperatures, the volatile matter volatilizes and expands, causing thermal collapse of the coal.

Here, the coal has a high degree of coalification in the order of lignite, lignite, subbituminous coal, bituminous coal, and anthracite, and the solid carbon content increases, and conversely, the volatile content decreases. The more the volatile matter in the coal, the more likely it will collapse due to heat transfer from the reaction gas or radiant heat from the refractory inside the furnace during the fall process in the furnace, and it will be more likely to be pulverized. In addition, the tendency to deviate outside the furnace as the carbonaceous dust is increased by riding the gas generated in the furnace. Therefore, the carbonaceous material used in the present invention is most preferably anthracite with the least amount of volatile matter among the coals.
In addition, you may replace a part with coke with a poor thermal disintegration, using the main carbon | charcoal materials which have the above heat disintegration. When coke with a size that does not deviate outside the furnace due to the gas flow generated in the furnace is used, the reduction reaction of chromium oxide and iron oxide in the slag and the dissolution in the hot metal are delayed. In other words, it means that it is convenient to suppress a sudden change in the carbonaceous material content in the slag and stably maintain a certain amount of the carbonaceous material content.

On the other hand, as the chromium oxide-containing material, in addition to chromium ore, stainless steel refining dust can be used in a powdered or agglomerated state, and various types of chromium ore are known. Among them, a so-called chromium sand produced in a sandy state can be particularly preferably used. In the smelting reduction method, since the chromium oxide-containing material put into the furnace needs to be quickly dissolved in the slag, it is desirable that the particle size is about several mm. Therefore, in the case of the chrome ore produced in a lump shape, a pulverization process is required in advance, but the chrome ore is extremely economical and requires a lot of energy for pulverization, which is not economical. On the other hand, chrome sand is already sandy with a particle size of several millimeters or less from the time of production, so that prior pulverization treatment is unnecessary. Chromium ores contain about 40 to 60% Cr ₂ O _{3 and} 10 to 25% FeO. In addition, MgO, Al ₂ O ₃ , SiO ₂ etc. are also included as gangue components. .

Further, as the auxiliary raw material, a substance containing CaO, SiO ₂ , MgO or Al ₂ O ₃ is used for the purpose of adjusting the melting point of slag, ensuring the desulfurization ability, and protecting the refractory inside the smelting reduction furnace. In addition to quick lime, limestone, and dolomite, the recovered steelmaking slag can be used as the CaO source. Silica stone, gravel or silica sand can be used as the SiO ₂ source, and magnesia refractory waste can be used as the MgO source in addition to magnesia, magnesite and dolomite. Al ₂ O ₃ can be ban shale or alumina refractory waste.

  In general, slag composition greatly affects refractory erosion, but if slag basicity is increased in an attempt to suppress refractory erosion, the slag viscosity decreases, making slag difficult to form, There is a problem that the bath surface cannot be blocked, and the dust reduction effect by slag cannot be expected.

  Therefore, the inventors diligently studied a method capable of reducing dust even under conditions where slag forming does not occur. As a result, in the case of high basicity conditions and conditions where slag forming does not occur, the higher the residual carbon concentration in the slag, the lower the dust generation rate. I found it.

  Although the details of the reason are not clear, the inventors believe that the reaction between the oxygen gas supplied from the top blowing lance and the C content in the slag increases.

The top blown oxygen in the smelting reduction smelting is intended to compensate for the reduction heat of the chromium oxide-containing material, so there is no problem even if it reacts with the carbonaceous material in the slag. This is because the amount of oxygen gas reaching the metal is reduced, and the amount of CO bubble generated from the molten metal is reduced.
In addition, the chromium concentration in the collected dust (referred to as Cr / (Cr + Fe) (%) in the present invention) is almost the same as the chromium concentration in the molten metal at the moment the dust is collected. Molten metal splashes due to CO bubbles generated in the occupy most of the generated dust. This also shows that it is important to suppress the maximum reaction between the oxygen blown oxygen and the carbon in the molten metal to suppress the generation of dust during smelting.

  Here, if the residual carbon material concentration in the slag is excessively increased, the amount of carbon material scattered increases, the amount of carbon material dust generated increases, and the carbon material cost increases. Therefore, in the present invention, the upper limit of the residual carbon material concentration is set to 40% or less. Further, if the basicity of the slag is increased too much, not only will the lime cost increase, but the amount of slag generated will increase, so the basicity needs to be 5.0 or less.

  On the other hand, the basicity of the slag is set to 2.6 or more from the viewpoint of suppressing refractory melt damage. Moreover, in order to prevent the reduction | restoration carbonaceous material density | concentration in slag from generating the reduction | restoration defect of chromium oxide, it is necessary to perform carbonaceous material injection | throwing so that it may maintain 20% or more.

The amount of residual carbon in the slag is the integrated value continuously from the start of converter blowing to the smelting, and the supply and discharge (dissolved amount of carbon in molten iron, exhaust gas such as CO and CO ₂₎ And the mass balance of the amount of C dissipated in the exhaust gas as dust). Based on the calculated amount of residual carbon material in the slag, the carbon material supply rate is controlled to maintain the residual carbon material concentration within the above-described appropriate range. The mass balance is the mass ratio of the amount of supplied carbon material minus the amount of dust scattered, the amount consumed in decarburization reaction and the amount dissolved in molten iron, and the mass of slag determined by the amount of raw material and flux. It is calculated by calculating | requiring.
The values necessary for calculating the above amounts are specifically, carbon material addition amount (yield), carbon material combustion amount (exhaust gas amount, exhaust gas composition) and slag amount (chromium ore supply amount, auxiliary raw material supply amount). It is.
In addition, in the case of anthracite, the carbon material to be used has characteristics of particle size: 10 to 25 mm, composition of FC: about 80 to 90%, VM: about 3 to 10% and SiO ₂ : about 1 to 7%. Is preferred.

Furthermore, if it is less than 30%, the carbon material having no heat collapse property can be made a part of the carbon material used in the present invention. For example, the coke has a particle size of 5 to 25 mm, and the component composition is FC: 75 to 90%, Ash: 5 to 15%, SiO ₂ : 2 to 10%, S: 0.2 to 1.0%, P: 0.01 It contains ~ 0.1%.

For example, a suitable temperature for smelting reduction of chromium ore is about 1550 ° C. Therefore, in order to supply the amount of heat necessary for melting the charged scrap and increasing the temperature of the hot metal, the carbon material is supplied and the acid is supplied. In addition, the basicity can be adjusted by introducing a CaO source and a SiO ₂ source for the sake making. In this case, it goes without saying that the amount contained as a gangue in the carbonaceous material and the ore is also taken into consideration when adjusting the basicity.
It should be noted that smelting methods other than those specifically defined above, that is, materials such as chromium oxide-containing substances, facilities used for smelting such as converters, and operating conditions thereof may be in accordance with ordinary methods.

Using a top-bottom converter (smelting reaction vessel), the chromium oxide-containing material was subjected to smelting reduction.
Specific implementation conditions were a heat size of 150 to 170 tons and a hot metal containing C: 4.3%, Si: 0.01%, Cr: 0.02%, P: 0.015% and S: 0.012% in the composition. While blowing top-blown oxygen gas (flow rate: 3.5 Nm ³ / min / ton-molten metal) and bottom-blown oxygen gas (flow rate: 0.8 Nm ³ / min / ton-molten metal), adding only charcoal from the top of the furnace The hot metal was heated to 1550 ° C. (heating phase). Next, while maintaining the hot metal temperature at 1550 ° C, chrome ore and stainless steel refining dust are added from the input lance, and carbonaceous materials and auxiliary materials are input from the upper part of the furnace, respectively, to perform smelting reduction of the chromium oxide-containing material ( In the smelting reduction period), the slag composition and the amount of residual carbon material in the slag were varied.
The input chromium ore has a composition of T.Cr: 32%, SiO ₂ : 2%, Al ₂ O ₃ + MgO: 25%, and the input carbon material is anthracite with a particle size of 10-25mm. The composition was FC: 88%, VM: 7%, SiO ₂ : 2%. Further, the anthracite had a property of being refined to 2 to 5 mm in advance by a thermal decay test using a small melting furnace.

Supply the carbon material by estimating the mass and concentration of C remaining in the slag in real time from the mass analysis value of the exhaust gas during the smelting process and the expected value of the input secondary material and the carbon material scattered as dust. The speed was adjusted to control the residual carbon concentration in the slag.
The basicity of the slag was adjusted by controlling the input of quick lime and gravel. In all conditions, the slag volume was in the range of 15 to 75 t. In addition, the slag generation amount index is a slag produced in each operation, after smelting reduction smelting is completed, and after the molten chromium-containing molten metal is discharged, it is discharged into a slag pan provided under the furnace and weighed later. The amount of slopping slag weighed together was added to form the amount of slag generated for each operation. It was calculated as a mass ratio to the amount of slag produced at 30 operations.
Here, the evaluation results of the metal dust generation rate index, the carbonaceous dust generation rate index, the slapping generation index, and the furnace wall refractory wear index obtained by the following procedure are shown in Table 1 and FIGS. Each is shown. In addition, these indices are No. 1 in Table 1. Indexed based on the operation of No. 3.

Carbonaceous dust generation index and metal dust generation index: Dust trapped in the wet dust collection water of the exhaust gas recovery equipment of the smelting reduction smelting furnace is sampled every minute over the entire period of smelting reduction smelting. Were classified by specific gravity, and the concentrations of carbonaceous dust and metal dust were quantified. From the flow rate of collected dust and these concentrations, the dust generation rate at each sampling time is obtained by calculation, and the average of all samplings is used to determine the carbon material dust generation rate and metal dust generation rate in the operation. did. As described above, No. 1 in Table 1 was obtained. A value obtained by dividing the carbon material dust generation rate obtained in each operation by the carbon material dust generation rate in operation No. 3 was defined as the carbon material dust generation rate.
Similarly, the metal dust generation index is No. 1 in Table 1. The value obtained by dividing the metal dust generation rate obtained in each operation by the metal dust generation rate in operation No. 3 was defined as the metal dust generation rate.

  Sloping generation index: A slag pan was placed in advance under the furnace, and slag overflowed from the smelting reduction furnace by slopping during smelting reduction smelting was accommodated. Some slopped slag sometimes dropped out of the slag pan, so the slag dropped out of the slag pan was recovered from the bottom of the furnace by a shovel loader at the end of the smelting reduction slag. Weighed together with the one contained in the slag pan. This was defined as the slapping slag mass. No. in Table 1 A value obtained by dividing the mass of the slapping slag obtained in each operation by the mass of the slapping slag in the operation of No. 3 was defined as a slipping generation index.

  Furnace wall refractory wear index: Using a laser-type refractory residual thickness measuring device, the refractory at a predetermined position in the smelting reduction furnace before and after smelting and refining The remaining thickness of the refractory was measured, and the amount of wear of the refractory in the smelting was calculated. No. in Table 1 A value obtained by dividing the refractory wear amount measured in each operation by the refractory wear amount in operation No. 3 was defined as a furnace wall refractory wear index.

As shown in Table 1 and FIGS. 1 to 4, when the slag basicity is 2.6 or more and the residual carbon material concentration in the slag in the smelting reduction period is 20% or less on average, the dust generation rate index Became high. On the other hand, when the slag basicity was 2.6 or more and the average residual carbon content in the slag was 20% or more, the dust generation rate index was relatively low.
At that time, the slapping occurrence index was low regardless of the residual carbonaceous material concentration. This is considered to be because if the basicity of the slag is high, the slag viscosity is low and forming does not easily occur.
Therefore, it can be seen that a decrease in the residual carbon material concentration increases the amount of metal dust generated and increases the wear index of the furnace wall refractory. At this time, poor reduction occurred, and the average steel output S concentration became high.

When the basicity is 2.5 or less and the residual carbon concentration in the slag during the smelting reduction period is 20% or more on average, the result is that the dust generation rate decreases as the residual carbon concentration in the slag increases. However, with the peak at 20%, even at 20% or less, the dust generation rate became low as the residual carbon material concentration decreased.
However, in the region where the basicity is 2.5 or less and the residual carbonaceous material concentration in the slag is 20% or less, along with the occurrence of slag forming, the occurrence index of slopping is high, and the concern about operational failure has become stronger. . Furthermore, the furnace wall refractory wear index increases regardless of the residual carbon material concentration.

  On the other hand, when the residual carbonaceous material concentration in the slag exceeded 40%, the amount of carbonaceous dust generated due to the scattering of the carbonaceous material in the slag increased. In addition, when the basicity was more than 5.0, increasing the basicity further not only reduced the metal dust generation rate but also increased the slag generation rate index.

In this example, under the smelting conditions according to the present invention, the metal dust generation rate index, the carbonaceous dust generation rate index, the slopping generation index, and the furnace wall refractory wear index are all as low as 1.2 or less. It was. This is a result of preventing an increase in the generation rate of dust while suppressing the refractory material melting loss without causing a risk of causing an operation hindrance due to slopping or the like.
In addition, the Cr yield was 93 to 97% in the condition according to the present invention, and 80 to 92% in the condition of the comparative example, and all of the inventive examples were improved in yield compared to the conventional smelting reduction smelting method. .

Claims (2)

In the smelting reduction smelting method of the chromium oxide-containing material, the oxygen is supplied and the chromium oxide-containing material is melt-reduced while the chromium oxide-containing material is introduced into the smelting reaction vessel together with the carbonaceous material and the auxiliary material.
The ratio (mass% CaO) / (mass % SiO 2) between the amount of CaO and SiO ₂ content in the slag at the smelting reduction period, and 2.6 to 5.0, and a carbonaceous material concentration remaining in the slag, A smelting reduction smelting method of a chromium oxide-containing substance, characterized by smelting while controlling in a range of 20 mass% to 40 mass% (excluding 20 mass% to 30 mass%) .   The smelting reduction smelting method according to claim 1, wherein the charcoal is anthracite.

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