JP4329724B2 - Converter scrap increase method - Google Patents

Description

  The present invention relates to a converter scrap increasing method that enables an increase in the amount of scrap to be blended with hot metal in a furnace during converter blowing.

  Usually, when hot metal is blown in a converter, if there is a thermal margin, scrap is added to the hot metal in the furnace. This is because scrap that is already metallic iron does not need to be reduced, and can be made into molten steel with less energy than iron oxide such as iron ore. In other words, it is because the molten steel more than the amount of hot metal manufactured with a blast furnace can be smelted, and the production amount of molten steel can be increased.

  In particular, when there is a strong demand for iron, etc., an increase in production is expected, and even if the iron yield is somewhat low and the consumption of the ironmaking agent is large, the amount of scrap blended into the hot metal may increase. It may be desirable.

  Recently, hot metal removal P is often adopted because it is advantageous in terms of cost and quality. However, [Si], which is a heat source, has almost disappeared, and [C] concentration is also 0. There is a problem that there is almost no blendable amount of scrap because there is no heat margin because it is reduced by about 5% by mass. For this reason, when it is necessary to increase the production of molten steel, the operation method is temporarily changed to return to the previous converter blowing without demolition P and without demolition P and de-C at the converter. There was also.

  However, when there is so much demand for iron that the hot metal obtained in the blast furnace alone cannot be covered, the operating method is not changed, and the hot metal desorption P is performed as described above, and only the decarbonization is performed in the converter. At the same time, it is desirable to increase the amount of scrap.

As a method of increasing the amount of scrap in the converter, the CO gas generated by the de-C reaction at the time of converter blowing is subjected to secondary combustion in the furnace (2CO + O ₂ → 2CO ₂ ), and the heat generated by this combustion is applied to the molten steel. For example, Non-Patent Document 1 describes the influence of the jet angle of the oxygen blowing lance used for the secondary combustion on the scrap mixing ratio, and the secondary combustion. Detailed reports have been made on the effect of heat.

  However, in the secondary combustion method, there is a problem that the refractories constituting the converter are severely worn. For this reason, the secondary combustion rate is currently suppressed to, for example, 10% or less or 5% or less. Therefore, there is a limit to increasing the amount of scrap by this method.

  Also, a heat source such as ferrosilicon (Fe—Si), metal Al or carbon is added to the hot metal, oxygen is blown and reacted with these heat sources, and the heat of oxidation reaction (hereinafter also simply referred to as “oxidation heat”). There is also known a method of increasing the amount of scrap melt using the above.

  Table 1 shows the heat of oxidation per unit mass of these heat sources (that is, the calorific value) and the heat of oxidation converted per unit mass of oxygen required for oxidation of these heat sources.

As shown in Table 1, ferrosilicon and metal Al have a large calorific value during oxidation and are easy-to-use heat sources, but both are expensive because they require a large amount of power for production, and the production cost of molten steel increases. There is a problem. Further, when ferrosilicon or metal Al is used, a large amount of CaO is required to neutralize the generated SiO ₂ or Al ₂ O ₃ . That is, about 5 kg of CaO is required for 1 kg of ferrosilicon, and about 4 kg of CaO is required for 1 kg of Al. If this is taken into consideration, the cost is further increased.

  As carbon, coke and anthracite are often used, and these are relatively easy to use as a heat source. However, the calorific value per unit mass is smaller than that of ferrosilicon or metal Al. In addition, there is a limit to the amount of carbon that can be burned per unit time under the condition that the amount of blown oxygen is constant, so if a large amount of carbon is to be added, the converter blowing time must be significantly extended. On the contrary, there arises a problem that the productivity of the converter decreases. That is, although the amount of scrap blended per charge can be increased by adding a large amount of carbon, there is a problem that it does not lead to an increase in the production amount of molten steel.

  Furthermore, when coke and anthracite are used, the S pick-up of molten steel occurs due to the S contained therein. For this reason, especially when low-S steel is melted, it is necessary to desulfurize by secondary refining after converter blowing, and there is a disadvantage that the cost is increased.

  In addition to these, it is possible to use coal as carbon, but in the case of coal, there is about 30% volatile matter, and when added to molten steel, the hot metal is cooled by the endotherm associated with the decomposition reaction of this volatile matter. It does not function as a heat source.

  In order to cope with such a problem, Patent Document 1 discloses a method in which a carbon material such as coke is introduced into a converter and reacted with top-blown oxygen to increase the secondary combustion rate to 60% or more. Further, Patent Document 2 further takes measures such as introducing a slag agitation index and adjusting it appropriately to effectively heat the combustion heat of the carbonaceous material generated in the molten slag layer to the iron bath. Scrap melting methods that make maximum use of charcoal combustion have been proposed.

  However, in these methods, in order to increase the secondary combustion rate, the amount of slag in the furnace must be 100 kg / t or more, and the carbon material must be entrained therein. This means that the abundance ratio of forming slag in the furnace volume is increased, and it is difficult to increase the abundance of scrap and molten iron, so the melting efficiency of scrap must be reduced. There is.

  On the other hand, as an inexpensive heat source, Fe shown in Table 1 (that is, molten iron in the converter) itself can be considered. In particular, the calorific value converted to 1 kg of oxygen that reacts with Fe is close to that of ferrosilicon, and the blown oxygen can be used efficiently. However, when iron is oxidized, in the conventional method of reducing the [C] concentration in the hot metal by oxygen blowing (C blowing down method), the (FeO) concentration in the slag is as high as 35% by mass or more. There is a problem that the concentration of the refractory material is severely melted.

JP-A-8-260022 JP-A-10-265820 "Iron and Steel" 71st (1985) No. 15, pp. 1787-1794

  The present invention has been made in view of such a situation. The purpose of the present invention is to blow off de-P molten iron in a converter without greatly extending the blowing time and without requiring large facilities. An object of the present invention is to provide a method capable of increasing the amount of scrap mixing (that is, increasing the amount of scrap) without using an expensive heat source such as ferrosilicon or metal Al.

  The present inventors have made various studies on a heat source for increasing the amount of scrap in a converter. As a result, it has been found that using the oxidation heat of Fe (molten iron in the converter) is the cheapest and most effective.

  When utilizing this oxidation heat of Fe, if the amount of molten iron is oxidized by blowing oxygen while maintaining the amount of iron-forming agent used in the conventional furnace defoaming of de-P molten iron, oxidation in the slag The iron content (mainly FeO) increases, the (FeO) concentration increases, and the converter refractory is liable to melt. Therefore, conventionally, a hot metal heating method using Fe as a heat source has not been adopted.

  However, by adding scrap to the molten iron in the furnace and adding a slagging agent that matches the blending amount, the heat generated when oxidizing Fe to FeO (oxidation reaction heat) and the generated FeO are produced. The scraping heat generated when it reacts with the glaze is used to melt the scrap, and at the same time, the generated FeO is diluted with the glaze making agent, thus preventing the refractory from being noticeably melted. I found that it was possible.

  In addition, according to this method, expensive ferrosilicon, metal Al, etc. are not used, the blowing time is not extended so much, and special equipment is not required, so scrap addition is inexpensive. Can be implemented.

The present invention has been made on the basis of such knowledge, and the gist thereof is the converter scrap increasing method described in (2) below . The invention as a reference example of the present invention is a converter scrap increasing method described in (1) below.

  (1) When carrying out refining of de-P hot metal using a converter, scrape is added, and a fossilizing agent is added according to the amount of the additive, and the concentration of (FeO) in the slag produced is refractory. A converter scrap increase method in which molten iron is oxidized within a range that does not promote melting damage, and scrap is melted by the oxidation heat.

(2) When refining de-P hot metal using a converter, scrape is blended in an amount of 3% by mass or more, and a slagging agent is added so as to satisfy the following formula (i) according to the blending amount. In addition, the converter scrap increasing method in which molten iron is oxidized within a range that does not promote melting damage of the refractory with a concentration of (FeO) in the generated slag of less than 35%, and the scrap is melted by the oxidation heat .

(4.5 × S) <Z <(6.6 × S + 12) (i)
However, Z: addition amount of a faux former (kg / t)
S: Scrap content (%)
Note that the “addition amount Z of the iron making agent” is an addition amount (kg) per 1 ton of hot metal, and the “scrap compounding amount (%)” is a mass ratio of scrap to the hot metal in the converter in percentage. It is a representation.

  In the converter scrap increasing method according to the above (1) or (2), it is common to use one or more of quicklime, dolomite, magnesium oxide, silica and alumina-containing substances as a koji-forming agent. And desirable.

  According to the converter scrap augmentation method of the present invention, the oxidation heat of the molten iron (Fe) in the converter is used at the time of blowing in the converter, the blowing time is not so long, and the refractory is noticeable. It is possible to increase the amount of scrap blending at low cost without any loss.

The invention as a reference example of the present invention described in (1) and the converter scrap increasing method of the present invention described in (2) will be specifically described below. In addition, "%" of the element in hot metal, molten steel, or slag means "mass%".

  In the converter scrap increasing method according to the present invention described in (1) above, when refining de-P molten iron using a converter, scrap is added and a faux additive is added in accordance with the amount of addition. In this method, molten iron is oxidized within a range in which the concentration of (FeO) in the slag to be generated does not promote refractory erosion, and scrap is melted by the oxidation heat.

  The feature of the scrap increasing method described in the above (1) is that the heat necessary for melting the scrap is compensated by utilizing the oxidation heat of Fe. Added.

Specifically, at the time of the converter blowing, the scrap of the target blending amount is blended into the hot metal, and a slagging agent is added according to the blending amount, and oxygen is blown to react with the molten iron (Fe). Heat generated when FeO is generated [3767 × 10 ³ J / kg-FeO (900 kcal / kg-FeO)], that is, heat of oxidation reaction of Fe is used to heat the hot metal whose temperature has been lowered by the addition of scrap. It is. At this time, the heat of formation when the generated FeO reacts with the forming agent added according to the blending amount of the scrap to become slag [586 × 10 ³ J / kg-slag (140 kcal / kg-slag)] Can also be used.

  Therefore, the hot metal heating capacity is calculated based on the sum of the heat of formation of FeO and the heat of heat generated when the generated FeO reacts with the iron making agent to form molten slag. It is calculated as the amount of heat after subtracting the heat required to increase the temperature (in other words, the cooling capacity of the slagging agent).

  In the scrap increasing method described in the above (1), scraps are blended and a slagging agent is added according to the blending amount.

  The iron additive is added to the slag when the blowdown of C is performed while maintaining the amount of iron additive used at the time of the furnace blowing of hot metal, and the molten iron is subsequently oxidized in large quantities. This is because the (FeO) concentration in the converter increases and the refractory in the converter is easily melted, so that the generated FeO is diluted with a fossilizer to lower the (FeO) concentration.

  As described above, the amount of the iron making agent added according to the amount of scrap is determined by subtracting the cooling ability of the iron making agent from the sum of the oxidation heat of iron and the heat of iron making, and the scrap is molten iron. It is determined from the heat balance with the amount of heat required to become.

  Furthermore, in the scrap increasing method described in (1), the molten iron is oxidized within a range in which the concentration of (FeO) in the slag to be generated does not promote the refractory melting loss, and the scrap is melted by the oxidation heat.

  The above-mentioned “range that does not promote the refractory melting loss” means a range in which the degree of melting loss of the converter refractory does not greatly change compared to the conventional blowing. In other words, FeO produced by the oxidation of molten iron (oxygen blowing) reacts with the iron making agent to form molten slag and raises the (FeO) concentration of the slag. Oxygen is blown in such a way as to keep it within a certain range.

  In order to keep the oxidation of the molten iron within the range that does not promote the refractory erosion, for example, the (FeO) concentration in the slag is not blended with scrap, or at the time of normal blowing that keeps blending very little even if blended The concentration may be equal to or lower than the (FeO) concentration. This (FeO) concentration is determined by how much the degree of melting loss of the converter refractory is tolerated. If the Fe (total Fe) concentration is less than 27% (less than 34.7% in terms of FeO), it is possible to suppress severe melting of the refractory. Furthermore, if the (FeO) concentration is set to 27% or less, it is desirable because remarkable melting damage can be prevented.

  Then, the heat generated by the oxidation of the molten iron and the heat of forming the generated FeO are utilized for heating the hot metal whose temperature has been lowered by the mixing of scrap.

  The converter scrap increasing method described in (1) is applied when refining for de-P hot metal using a converter. As described above, the P-free soot hardly contains [Si] as a heat source, and the [C] concentration is also reduced by about 0.5% by mass. However, by applying the converter scrap distribution method of the present invention to the blowing of the dephosphorized hot metal, it is possible to carry out the hot metal dehumidifying P which is advantageous in terms of cost and quality, and to scrap the hot metal. The compounding amount of can be increased.

  Thus, when carrying out the refining of the de-P hot metal using the converter, the ironmaking agent is added according to the blending amount of the scrap, and the (FeO) concentration in the slag to be generated can cause the refractory to melt. It is possible to increase the amount of scrap blended into the hot metal by performing the operation of blowing so as to stay within the range not promoted, and the scrap blending amount is increased at a low cost because the blowing time is not so long. be able to.

In the converter scrap increasing method according to the present invention described in (2) above , when refining de-P hot metal using a converter, 3% by mass or more of scrap is blended, and depending on the blending amount, The agent is added so as to satisfy the following formula (i) , and the molten iron is oxidized within a range that does not promote the refractory melting loss in which the concentration of (FeO) in the slag to be generated is less than 35%. This is a method for melting scrap . In the formula (i), Z is an additive amount (kg / t), and S is a scrap blending amount (%).

(4.5 × S) <Z <(6.6 × S + 12) (i)
In general, in the case of converter blowing that blows oxygen into the hot metal, the molten iron (Fe) begins to be oxidized after the de-C rate decreases. At this time, if there is little slag, the (FeO) density | concentration in slag will increase rapidly with progress of de-C, and it will become slag in which the refractory of a converter refractory is easy to occur. On the other hand, since the absolute amount of FeO produced is small, not only the calorific value due to the oxidation of Fe is small, but also the heat of hatching caused by the reaction between the produced FeO and the slagging agent is reduced, which is necessary for scrap melting. I can't get heat.

  In addition, as the amount of the additive is increased and the amount of slag increases, the progress of de-C is slowed, the oxidation of Fe sufficiently proceeds, and the hatching reaction between the generated FeO and slag also proceeds. . Therefore, the calorific value is large, and the heat necessary for melting the scrap can be obtained, so that the extreme decrease in the [C] concentration is reduced, and it becomes easy to hit the blow at the desired (FeO) level.

  As mentioned above, the amount of scrap blended and the amount of iron making agent required are the amount of heat required by subtracting the cooling ability of the iron making agent from the sum of the oxidation heat of iron and the heat of iron making, and the scrap is molten iron It is determined from the heat balance with the amount of heat required to become. However, since the addition amount of the faux-forming agent is small, the (FeO) concentration in the slag becomes high due to the oxidation of Fe, and if the (total Fe) concentration exceeds 27%, for example, the melting loss of the converter refractory starts to stand out. It is desirable not to exceed this. On the other hand, if the addition amount of the slagging agent is too large and the (total Fe) concentration in the slag is 18% or less, the heating efficiency may be poor and scrap may not be melted.

  Formula (i) in the converter scrap increasing method described in (2) expresses desirable conditions determined by taking into account these points and taking into consideration the thermal conditions of the converter.

  Further, FIG. 1 is a diagram showing an appropriate range of the amount of addition of scraping agent and the amount of scrap blending determined by the equation (i).

  In FIG. 1, the hatched area below the straight line “Z = 6.6 × S + 12” and above the straight line “Z = 4.5 × S” (however, the two straight lines are not included). As long as the equation (i) is satisfied, the scrap blending amount can be increased in this region based on the heat balance described above.

  The straight line “Z = 4.5 × S” or a region below the straight line is a region where the additive amount of the slagging agent is small and the (FeO) concentration in the slag is high, and the melting damage of the converter refractory is promoted. The In addition, in the straight line “Z = 6.6 × S + 12” or in an area above the straight line, the amount of calorific agent added is large for the amount of heat generated, and the target scrap cannot be melted due to insufficient heat. .

  The scrap blending amount is not particularly limited, but is desirably 3% or more. If it is less than 3%, the amount of slag decreases, spitting and fume loss increase, and the iron yield deteriorates. In addition, in FIG. 1, the area | region whose scrap compounding amount is 3% or more is shaded.

  As described above, in the scrap increasing method described in (2), when carrying out the refining of de-P hot metal, it is possible to optimize the addition amount of the slagging agent numerically according to the above-mentioned formula (i). The increase in the amount can be more effectively performed.

In the invention as a reference example of the present invention described in the above (1) or the converter scrap increasing method of the present invention described in the above (2), the added slagging agent does not need to be special, quick lime, It is common to use one or more of dolomite, magnesium oxide (MgO), silica and alumina (Al ₂ O ₃ ) containing materials. These glazing agents are desirable not only for excellent performance but also for easy availability, handling, safety, and other various aspects. In addition to alumina, natural minerals such as bauxite can be used as the alumina-containing substance, and ladle slag after refining a ladle for clean steel melting performed by modifying slag can also be used.

  Usually, it is only necessary to adjust the mixing ratio (basicity) as appropriate based on quick lime and silica and considering the steel type to be melted and the operating conditions. However, dolomite or magnesium oxide (MgO) can be used when importance is attached to the reduction of the refractory melting loss. In particular, MgO is the same component as the furnace body brick, and is a desirable faux-making agent.

  On the other hand, it is important that the slagging agent becomes slag, that is, easily hatches. If hatching is poor, de-C is easy to proceed, the decrease in [C] concentration is accelerated, and heat generation is difficult, so the generated heat is wasted. To facilitate hatching, alumina and this are used. What is included is effective.

  The slag generated in the de-C furnace contains some P or the like in some cases, but contains useful components such as CaO, MgO and FeO, and can be recycled to the blast furnace.

  Using an up-and-down double-blowing converter with a capacity of 2 t, a test was conducted in which scrap was mixed and refined with de-P hot metal having the chemical composition shown in Table 2 to investigate the effect of the present invention.

(Comparative Example 1)
After the scrap was charged into the converter so that the mixing ratio was 3% (30 kg / t), the dephosphorized hot metal was poured, 6 kg / t of quicklime and 2 kg of silica were added, and a three-hole rubber nozzle was installed. Blowing was performed using an lance having a feed rate of 2.7 Nm ³ / min. On the way, the flame went down, but the blowing was continued until the molten steel temperature rose to 1650 ° C.

  At this time, the [C] concentration of the molten steel was 0.025%, the (FeO) concentration in the slag was as high as 40%, and the refractory erosion in the slag line was large. For this reason, it was impossible to mix more scraps without changing the addition amount of the koji-making agent.

  The required amount of addition of the slagging agent Z according to the formula (i) from the amount (3%) of scrap used in Comparative Example 1 is 13.5 to 31.8 kg / t. The added amount of the agent is 8 kg / t for quicklime and silica, which is out of the definition of the formula (i).

Example 1
After charging scrap into the converter so that the blending ratio is 7% (70 kg / t), the de-P molten iron is poured, 34 kg / t of quicklime and 8.5 kg of silica are added, and a three-hole rubber nozzle Blowing was performed using a lance with a feed rate of 2.7 Nm ³ / min.

  In the middle, blowing was controlled with an oxygen sensor (OXP), and the blowing was terminated at a [C] concentration of 0.05%. The molten steel temperature at that time was 1675 ° C., the (FeO) concentration in the slag was 29%, and the refractory melt loss was the same as in the conventional converter blowing, and there was no problem.

  The amount of scrap blending and the amount of addition of the faux agent used in Example 1 satisfy the condition of the above-mentioned formula (i).

(Example 2)
After the scrap was charged into the converter so that the blending ratio was 8% (80 kg / t), dephosphorized hot metal was charged, quick lime 25 kg / t, dolomite 4 kg / t, MgO 4 kg / t and silica 11 kg / t. t was added, and blowing was performed using a lance having a three-hole Laval nozzle at an acid feed rate of 2.7 Nm ³ / min.

  In the middle, the [C] concentration of the molten steel was confirmed by OXP, and the blowing was terminated when the [C] concentration reached 0.07%. At this time, the temperature of the steel bath was 1660 ° C., the (FeO) concentration in the slag was 30%, and the refractory melt was not different from that during conventional blowing, and there was no problem.

  The amount of scrap blending and the amount of addition of the faux agent used in Example 2 satisfy the condition of the above formula (i).

(Example 3)
After the scrap was charged into the converter so that the blending ratio was 10% (100 kg / t), de-P hot metal was poured into it, quick lime 45 kg / t, alumina (Al ₂ O ₃ ) 5 kg / t, and silica 10 kg / t was added, and blowing was performed at a feed rate of 2.7 Nm ³ / min using a lance with a three-hole rubber nozzle.

  In the middle, the [C] concentration of the molten steel was confirmed by OXP, and the blowing was terminated when the [C] concentration reached 0.07%. The steel bath temperature at this time was 1650 ° C., the (FeO) concentration in the slag was 25%, and the refractory erosion loss was not different from that during conventional blowing.

  The amount of scrap blending and the amount of addition of the faux-forming agent used in Example 3 satisfy the condition of the above formula (i).

  According to the converter scrap increasing method of the present invention, it is possible to increase the amount of scrap blending when blown de-P hot metal in the converter. This scrap increase method uses the heat of oxidation of the molten iron (Fe) in the converter, and the blowing time is not so long, and there is no noticeable refractory loss of refractories, so it can be carried out at a low cost. Therefore, it can be suitably used for blowing in a P-type hot metal converter that is difficult to remove.

It is a figure which shows the appropriate range of a faux-forming agent addition amount and a scrap compounding amount.

Claims (2)

When carrying out refining of de-P hot metal using a converter,
While adding 3% by mass or more of scrap, a faux additive is added according to the amount of the scrap so as to satisfy the following formula (i) ,
A converter scrap increasing method characterized in that molten iron is oxidized within a range in which the melting loss of a refractory is less than 35% in the concentration of (FeO) in the slag to be generated, and the scrap is melted by the oxidation reaction heat.
(4.5 × S) <Z <(6.6 × S + 12) (i)
However, Z: addition amount of a faux former (kg / t)
S: Scrap content (%) 2. The converter scrap increasing method according to claim 1, wherein one or more of quicklime, dolomite, magnesium oxide, silica, and alumina-containing material are used as a koji-forming agent.

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