JP2007177294A - Method for producing molten pig iron, and converter steelmaking method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing molten pig iron, which can melt a ferruginous cold charge which is partially or entirely composed of reduced iron containing unreduced iron oxides while adequately keeping unit consumptions of a carbonaceous material and oxygen, and to provide a condition of forming the optimal molten slag for melting the ferruginous cold charge with high productivity. <P>SOLUTION: This method for producing the molten pig iron by supplying the reduced iron, the carbonaceous material and oxygen to a melting furnace containing seed molten iron includes controlling an index Rsm to 0.6 to 0.85, which is determined by a relationship between the depth of a molten pig iron bath containing only the seed molten iron before the melting operation starts and the depth of the molten iron bath after the melting operation has been completed, expressed by depth of molten iron bath before melting operation/depth of molten pig iron bath after completion of melting operation. The method also includes controlling the quantity of slag existing in the melting furnace so that an index Rss can be in between 0.1 and 0.5, which is determined by a relationship between the quantity of remaining slag before the melting operation starts and the quantity of the slag after the melting operation has been finished, expressed by quantity of remaining slag before melting operation starts/quantity of slag after melting operation has been finished. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hot metal manufacturing method using reduced iron obtained by reducing dust containing iron as a main component, and a converter steelmaking method using the hot metal.

  As a converter steelmaking method using solid iron-containing cold materials such as granule, mold and scrap generated from steelworks, conventionally iron-containing cold materials, carbonaceous materials, and oxygen are supplied to a melting-only converter where seed water is present. The required amount is obtained by obtaining the total amount of high-carbon molten iron of the required amount of seed water in the converter dedicated to melting and the required amount of refining in another converter dedicated to refining, and oxygen refining in the converter dedicated to refining using this high-carbon molten iron as a raw material. The converter steelmaking method to obtain the molten steel of the component is known, and if the sulfur content of the carbon material used in the melting dedicated converter is high and the sulfur content of the high carbon molten iron is high, It is also known to desulfurize with a ladle before oxygen refining (Patent Document 1).

  In such a steelmaking method consisting of a melting-only converter and a refining-only converter using the entire iron-containing cold material as a raw material, the generation of dust containing iron as a main component cannot be completely eliminated in the melting-only converter and the refining-only converter. Therefore, it is necessary to efficiently recycle dust mainly composed of iron generated in a melting-dedicated converter and a refining-dedicated converter to solve the dust processing problem and improve the iron yield.

  In Patent Document 2, dust generated in a melting-dedicated converter and a refining-dedicated converter and lime content up to 15% or carbon material up to 35% are combined to form a lump by dish-type granulation method, compression molding method, etc. In order to prevent dissipation outside the converter due to the rising gas flow due to gas generation inside the converter when it is charged and reused by natural fall from the upper part of the converter, the particle size of 10 mm or more in the melting-only converter, In a refining converter, a method of reusing agglomerated dust having a particle size of 5 mm or more has been proposed. According to this method, the problem of processing the generated dust can be solved, and the generated dust can be efficiently recovered as iron, which is beneficial.

  Dust generated in a melting-only converter or a refining-only converter supplies pure oxygen, for example, by performing top blowing, so that most of iron is oxidized. In order to reduce and melt iron oxide, for example, ferrous oxide, a heat amount about four times that of pure iron is theoretically required. Therefore, when the agglomerated dust containing iron oxide is recycled to, for example, a melting-only converter, the amount of heat necessary for producing the molten iron is increased as compared with the case where the agglomerated dust is not recycled.

  On the other hand, the upper limit of the furnace heat supply rate (oxygen supply rate, carbon material supply rate) of the melting-dedicated converter is fixed by the oxygen supply facility capability, the carbon material supply facility capability, and the dust collection exhaust gas treatment facility capability. There is a problem that the production rate of molten iron decreases due to an increase in the amount of heat necessary to produce molten iron. In addition, since the heat of combustion of pure oxygen and a carbonaceous material, such as coal, is used as a heat source necessary for the above-described reduction, oxygen and the carbonaceous basic unit increase by that amount, and the manufactured molten iron by S in the carbonaceous material such as coal An increase in medium [S] is a problem.

  In Patent Document 3, as shown in the flow in FIG. 5, carbon material is agglomerated and agglomerated with dust generated in the melting converter 1 and the refining converter 3, and heated at a high temperature in the preliminary reduction furnace 8. A dust utilization method is disclosed in which after the internal carbonaceous material is preliminarily reduced as a reducing material, it is supplied to the melting-only converter 1 where seed hot water is present as a part of the iron-containing cold material at a high temperature and reused. As a result, after the agglomerated dust is preliminarily reduced and supplied to the melting-dedicated converter in a high temperature state, the supply amount of oxygen and carbon as a reduction heat source to the melting-dedicated converter 1 is reduced. Since a unit is reduced, the fall of the productivity of molten iron can be suppressed and the increase in [S] in manufactured molten iron can be suppressed.

In a melting method for melting scrap iron in a converter where seed water is present, Patent Document 4 discloses a preferable relationship between the amount of slag in the furnace during top blowing oxygen blowing and the slag dent depth by the oxygen jet. Yes. By controlling the ratio of slag depth L and slag thickness L _S0 by top blowing oxygen to 0.5-1 when scrap iron is melted, the secondary combustion rate is greatly improved while maintaining high heat receiving efficiency. , Remarkably reduce the carbon and oxygen consumption necessary for scrap iron dissolution.

Japanese Examined Patent Publication No. 4-11603 Japanese Patent Publication No. 4-38813 JP 2000-45012 A JP-A-8-260022

  In the method described in Patent Document 3, the metallization rate of the prereduced reduced iron is not 100%. Patent Document 3 describes that the metallization rate can be increased by increasing the reduction temperature or increasing the ratio of the amount of interior coal to dust, but increasing the reduction temperature reduces the productivity of the preliminary reduction furnace. As a result, the basic unit of energy required for pre-reduction is deteriorated and the ratio of the amount of coal in the interior increases, which leads to pulverization of the reduced iron lump, and further increases the scattering loss when reducing iron is fed into the melting furnace. In order to ensure both the productivity of the preliminary reduction furnace and the prevention of scattering loss when the reduced iron is charged into the melting furnace, it is preferable that the metallization rate is about 80 to 85%, although it depends on the raw material dust component. Then, even if it is said that it is metalized to 80-85%, when supplying reduced iron to a melting exclusive converter and melting it, the remaining 15-20% for the non-metallized part is reduced to a metal In order to achieve this, an excessive amount of heat is required. For this reason, when reduced iron is used as the charged iron-containing cold material, it is necessary to supply surplus oxygen and carbon material as compared with the case of using scrap.

  In melting the iron-containing cold material, the amount of heat necessary for melting and increasing the temperature is supplemented by the combustion heat of the supplied carbon material and oxygen. Moreover, since the melting of the iron-containing cold material proceeds mainly by carburization reaction, it is necessary to supply a carbon material to supplement the carbon concentration in the hot metal consumed by the melting. Furthermore, when using the reduced iron containing an unreduced iron oxide content, an excess carbon material is required as described above.

  Regarding the supply of the carbon material in the melting furnace, supply by bottom blowing is effective. Since the specific gravity of the carbon material is light, it is not possible to efficiently dissolve carbon in the hot metal if it is supplied to the hot metal from above, whereas if it is supplied by bottom blowing, there are many opportunities for contact with the hot metal bath and it is efficient. This is because it is possible to supply carbon.

  When iron-containing cold material is dissolved using reduced iron containing unreduced iron oxide as part or all of the iron-containing cold material, the carbon material basic unit and oxygen basic unit required to complete the dissolution are substances. It was found that the required amount exceeds the amount calculated from the balance and heat balance.

  In the present invention, when the iron-containing cold material is dissolved by using reduced iron containing unreduced iron oxide as a part or all of the iron-containing cold material, the carbon material basic unit and the oxygen basic unit are kept in good condition and are dissolved. It is a first object to provide a hot metal manufacturing method capable of manufacturing.

  When melting iron-containing cold material in a melting furnace in which seed water is present, as described in Patent Document 4, it is preferable to perform oxygen blowing in a range in which the fire point due to top blowing oxygen does not break through the molten slag layer. Therefore, a molten slag layer is formed on the hot metal in the melting furnace.

  By the way, when reducing iron is melted as an iron-containing cold material, after the melting of the pre-heat in the melting furnace is completed, the molten slag in the melting furnace is basically discharged after leaving the hot water and leaving the hot metal. After that, it was shifted to melting of the next heat. This is because if the molten slag is left, the operation becomes unstable due to forming or slopping, or reduced iron is wound around the slag and inhibits carburization and dissolution. When the reduced iron was melted as an iron-containing cold material based on such a concept, the time required for the dissolution increased, which caused a problem that the dissolution productivity was not sufficiently improved.

  The present invention provides optimum molten slag generation conditions for high-productivity melting when melting iron-containing cold material using reduced iron containing unreduced iron oxide as part or all of the iron-containing cold material. This is the second purpose.

  As described above, the metallization rate of reduced iron is at most 80 to 85%. When the reduced iron is supplied to the melting furnace and melted, it is necessary to metallize the remaining 15 to 20% which is not metallized and to supply surplus oxygen and carbonaceous material to ensure the necessary heat. This is a factor that reduces the production rate of molten iron.

  The present invention, when obtaining molten steel using a solid iron-containing cold material as a raw material using a melting-dedicated converter and a refining-dedicated converter, in a converter refining method in which dust generated in these converters is pre-reduced and used as a molten iron raw material, A third object is to provide a method capable of using reduced iron without reducing the production rate of molten iron.

  The first invention will be described.

  If the carbon material is supplied to the hot metal by bottom blowing, there are many contact opportunities between the carbon material and the hot metal bath as described above, and carbon can be efficiently supplied into the hot metal bath.

  When iron-containing cold material is charged into the melting furnace where the seed hot water is present, the specific gravity of the scrap is about 7.8, which is larger than the specific gravity of the hot metal 6.6 to 7.0. As a result, the hot metal bath is deepened. On the other hand, reduced iron contains a lot of slag, unreduced iron oxide, and pores, and therefore has a specific gravity of about 2 to 4 and smaller than hot metal. For this reason, the charged reduced iron floats on the surface of the hot metal bath, which is the seed hot water, and the depth of the hot metal bath does not increase even after the reduced iron is charged. That is, compared with the case where scrap is charged as the iron-containing cold material, the hot metal bath depth after charging becomes shallow when reduced iron is charged.

  Therefore, in the case of melting mainly using reduced iron as an iron-containing cold material, especially when the amount of the seed water is small, the hot metal bath depth becomes shallow at the initial stage of melting, and the charcoal and hot metal bath The contact opportunity is insufficient, and a part of the supplied charcoal is not dissolved in the hot metal and blows off from the hot metal bath surface. When iron-containing cold material is dissolved using reduced iron as part or all of the iron-containing cold material, a phenomenon that excessive carbon material unit and oxygen basic unit are required to complete the melting is observed. It was found that the hot metal bath depth at the initial stage of dissolution was too shallow.

A first aspect of the present invention is a method for obtaining molten iron by melting reduced iron containing iron as a main component and containing unreduced iron oxide, and a melting furnace containing seed hot water In order to obtain hot metal by supplying reduced iron, carbonaceous material and oxygen to the above, the relationship between the hot metal bath depth before melting, where only seed water exists, and the hot metal depth after melting at the time of melting is determined by the following formula (1) The hot metal production method is characterized in that Rsm is controlled to 0.6 to 0.85.
Rsm = depth of hot metal bath before melting / depth of hot metal bath after melting (1)

  In this way, the present invention can sufficiently maintain the hot metal bath depth from the beginning of dissolution, so that the carbon material supplied by bottom blowing can be stably dissolved in the hot metal, and the oxygen source required for dissolution is obtained. Units and carbon material basic units can be reduced. Moreover, when the amount of hot metal produced per heat increases, the ratio of occupying the furnace space increases, so the combustion space decreases and the secondary combustion rate decreases. Therefore, when melting in a 100 t scale furnace, the maximum amount of hot metal produced per heat is preferably about 30 t.

  Next, the second invention will be described.

  As described above, in the case of melting reduced iron as an iron-containing cold material, after the melting of the pre-heat in the melting furnace is completed, the molten slag in the melting furnace is basically left after leaving the hot metal and leaving the hot metal. And then moved to melting of the next heat. When the iron-containing cold material is charged and the top blowing acid is started, quick lime or dolomite is added as a slag modifier at the same time or thereafter. Molten slag is formed by hatching the slag contained in these slag modifier and reduced iron.

  However, it has been found that the hatching rate of these slag components is slow, and the slag component is not completely dissolved even when the time at which the melting of the iron-containing cold material is to be completed is reached. On the other hand, when a part of the molten slag existing in the melting furnace is left in the furnace at the end of the preheating, and this residual slag is used as the slag for the next heat, the amount of the newly added slag modifier is reduced. As a result, it has been found that hatching of slag proceeds rapidly, and as a result, the degree of wasteful consumption of supplied oxygen is reduced and productivity is improved.

In the second aspect of the present invention, in addition to the above first aspect, the relationship between the amount of residual slag before the start of melting and the amount of slag at the end of melting is expressed by the following equation (2). It is a hot metal manufacturing method characterized by controlling a fixed index Rss to 0.1 to 0.5.
Rss = residual slag amount before melting / slag amount at the end of melting (2)

  Accordingly, the present invention can maintain the molten state of the slag, that is, ensure the fluidity of the slag, and ensure the dissolution of the reduced iron and the reduction reaction of the unreduced iron oxide contained in the reduced iron.

  Finally, the third invention will be described.

  In the melting and refining method for obtaining molten steel using a solid iron-containing cold material as a raw material using a melting-dedicated converter and a refining-dedicated converter, when using a converter with the same furnace capacity as the melting-dedicated converter 1 and the refining-dedicated converter 3 Is common. In a converter plant having three converters of the same furnace capacity, when two of them are used as the converter 1 for melting and the other one is used as the converter 3 for refining, two converters dedicated for melting The production capacity of molten iron using 1 is insufficient to cover the required amount of molten iron when a single refining converter 3 is fully produced. Therefore, in the method described in Patent Document 3, the refining-only converter 3 is forced to be manufactured in a state where the production capacity remains. In such a case, if reduced iron containing unreduced iron oxide is used for the iron-containing cold material as the melting raw material, excess oxygen and carbonaceous materials are consumed to reduce the iron oxide. It causes the productivity of the entire refining to decrease.

  On the other hand, apart from a melting furnace for melting iron-containing cold materials such as scrap (hereinafter also referred to as “first melting exclusive converter”), a dedicated melting furnace for melting reduced iron (hereinafter referred to as “second melting dedicated converter”). )), The total molten iron production can be increased as compared with the case where the molten iron is produced only with the two first melting-only converters. By using the production capacity, it is possible to perform refining using all production molten iron as a raw material. As a result, it becomes possible to increase the molten steel production capacity by more effectively utilizing the three converters in the converter factory having the existing three converters.

  That is, the third of the present invention is provided with a first melting-dedicated converter, a reduced iron-dedicated converter (second melting-dedicated converter), a refining-dedicated converter, and a preliminary reduction furnace. Supplying iron-containing cold material, charcoal, and oxygen to the dedicated converter, obtaining the total amount of high-carbon molten iron of the required amount of seed water in the first melting dedicated converter and the amount of hot metal supplied to the refining dedicated converter, The reduced iron is melted in the melting-only converter to obtain the total amount of high-carbon molten iron required for the second melting-only converter and the amount of hot metal to be supplied to the refining-only converter. When obtaining molten steel of the required components by oxygen refining in a dedicated converter, the hot metal production method of the first and second inventions is used for melting reduced iron in the second melting dedicated converter. It is a furnace steelmaking method.

  First, the hot metal production method of the present invention is a method in which a hot metal is obtained by dissolving reduced iron, which contains iron as a main component, and which contains unreduced iron oxide. By adjusting the relationship between the hot metal bath depth and the post-melting hot metal depth at the completion of melting, the carbon material supplied by bottom blowing can be stably dissolved in the hot metal, and the oxygen source required for melting is reduced. Units and carbon material basic units can be reduced.

  Secondly, in addition to the first invention, the hot metal production method of the present invention ensures the fluidity of the slag by adjusting the relationship between the amount of residual slag before the start of melting and the amount of slag at the end of melting, It is possible to ensure the reduction reaction of the unreduced iron oxide contained in the reduced iron by dissolving the reduced iron.

  In the converter steelmaking method of the present invention, a dedicated melting furnace (second melting dedicated converter) for melting reduced iron is provided separately from a melting furnace (first melting dedicated converter) for melting iron-containing cold materials such as scrap. As a result, it is not necessary to use excessive oxygen / carbon material in order to completely metallize the reduced iron in the first melting converter, and it is possible to improve the molten iron production rate of the first melting converter. .

  The first invention will be described.

  Since the melting of the iron-containing cold material proceeds mainly by the carburization reaction, the carbon concentration in the hot metal decreases as the melting proceeds. It is important to supply a carbon material to supplement the carbon concentration in the hot metal and to efficiently dissolve the carbon material-containing carbon in the hot metal bath. Further, when dissolving reduced iron containing unreduced iron oxide as in the present invention, to increase the hot metal bath temperature lowered by the carbon supply for reducing the iron oxide content and the reduction reaction which is an endothermic reaction. Therefore, it is necessary to supply more carbonaceous material than when melting iron-containing cold material such as scrap.

  When supplying the carbonaceous material, in order for the supplied carbonaceous material to be efficiently dissolved in the hot metal, it is necessary to supply by bottom blowing. The specific gravity of the carbon material is light, and if it is supplied from above, it floats at the top of the hot metal bath, and there are few opportunities for contact with the hot metal bath and the efficiency is low. This is because it is possible to supply carbon efficiently.

  When supplying a large amount of carbonaceous material by bottom blowing, a large amount of carrier gas is required, and in order for the bottom blowing gas not to blow directly to the upper part of the hot metal bath, it depends on the amount of carbonaceous material supplied from the bottom blowing. A hot metal bath depth that does not blow through is necessary.

  However, as described above, when reducing iron is charged into a melting furnace in which seed hot water is present, the reduced iron contains a lot of slag, unreduced iron oxide, and pores, so the specific gravity is about 2 to 4 and smaller than the hot metal. . For this reason, the charged reduced iron floats on the surface of the hot metal bath, which is the seed hot water, and the depth of the hot metal bath does not increase even after the reduced iron is charged. That is, compared with the case where scrap is charged as the iron-containing cold material, the hot metal bath depth after charging becomes shallow when reduced iron is charged.

  In this way, the depth of the hot metal bath is optimized in order to efficiently supply carbonaceous material in the melting of reduced iron, which consumes a larger amount of charcoal than scrap, but is difficult to increase the hot metal bath depth. It is essential to do.

  If the amount of the seed hot water in the melting furnace before introducing the iron-containing cold material is small, the hot metal bath depth before melting becomes shallow, the hot metal bath depth immediately after the start of melting becomes insufficient, and the supplied charcoal material effectively becomes hot metal. The ratio of blowing through without charring increases. On the other hand, if the amount of the seed hot water is increased to deepen the hot metal bath depth before melting, the hot metal bath depth can be sufficiently secured immediately after the start of melting, and the supplied carbon material can be effectively dissolved in the hot metal. It becomes possible.

  On the other hand, if the amount of seed water is too large, the contact area between the melting furnace wall and the molten iron in the furnace increases, and the heat loss that escapes to the outside through the melting furnace wall increases. As a result, since the thermal efficiency of the melting operation is lowered, it is necessary to supply surplus carbon materials and oxygen.

In the present invention, the index Rsm determined by the following equation (1) is controlled to 0.6 to 0.85 for the relationship between the pre-melting hot metal bath depth in which only the seed hot water exists and the post-melting hot metal bath depth at the completion of the melting.
Rsm = depth of hot metal bath before melting / depth of hot metal bath after melting (1)

  To obtain molten iron by supplying reduced iron containing about 20% of unreduced iron oxide as FeO, carbonaceous material, and oxygen to a melting furnace where seed hot water is present, Oxygen and bottom blowing or carbon material supply from above were performed. While maintaining the ratio of the carbon material supply amount and the oxygen supply amount constant, changing the amount of seed hot water changed the Rsm in the formula (1) to various values and required to dissolve a certain amount of reduced iron. The amount of oxygen (oxygen basic unit) was compared. FIG. 1 shows the relationship between the value of Rsm and the oxygen intensity.

  In FIG. 1, the value of oxygen basic unit increases when Rsm is less than 0.6. This is because the hot metal bath depth at the initial stage of dissolution of the reduced iron was too shallow, and a part of the supplied carbon material was blown through and was not effectively dissolved in the hot metal. On the other hand, when Rsm exceeded 0.85, the amount of seed hot water was too large, resulting in an increase in heat loss from the furnace wall, resulting in an increase in oxygen intensity required for melting.

  On the other hand, if Rsm is 0.6 or more and 0.85 or less, there are few oxygen basic units, and efficient melt | dissolution can be performed. If Rsm is controlled within this range, the carbon content in the hot metal bath consumed by the reaction is quickly compensated, and sufficient carbon is supplied to the reduced iron floating on the hot metal bath, while the thermal efficiency is high and the productivity is high. Is possible. Since the oxygen basic unit is small, the carbonaceous basic unit can be reduced in conjunction with this. In addition, since the oxygen supply rate of the melting furnace is determined due to equipment restrictions, the fact that the oxygen basic unit is small can shorten the time required for melting and improve the melting productivity.

  Further, preferably, when Rsm is 0.6 to 0.80, the productivity is further increased. Rsm is more preferably about 0.62 to 0.75.

  The second invention will be described.

As described above, in the second aspect of the present invention, in addition to the first aspect, the relationship between the amount of residual slag before the start of melting and the amount of slag at the end of melting is as follows. 2) A hot metal production method characterized by controlling the index Rss determined by the equation to 0.1 to 0.5.
Rss = residual slag amount before melting / slag amount at the end of melting (2)

  After melting of the previous heat is completed and the hot metal is discharged while leaving the seed hot water, when a part of the molten slag of the previous heat is discharged, a part of the molten slag remains in the melting furnace. This residual slag is the amount of residual slag before the start of dissolution in the above equation (2). And in melting | dissolving of the said heat | fever, the slag content contained in the quicklime and dolomite input as slag modifier and reduced iron melt | dissolves, slag amount increases, and the slag amount at the time of completion | finish of melt | dissolution in (2) Formula Determined.

  To obtain molten iron by supplying reduced iron containing about 20% of unreduced iron oxide as FeO, carbonaceous material, and oxygen to a melting furnace where seed hot water is present, Oxygen and bottom blowing or carbon material supply from above were performed. The amount of residual slag before the start of melting was adjusted, and the amount of slag modifier added during melting was also adjusted, whereby the Rss in the above equation (2) was changed to various values to perform the melting treatment.

At this time, in order to evaluate the state of slag hatching at the end of dissolution, the ratio of “actual basicity / charging basicity” was evaluated. The actual basicity is the basicity (CaO / SiO ₂ ) obtained from the analysis value of the molten slag sampled at the end of dissolution. Charge basicity is the basicity calculated from the ingredients of raw materials and auxiliary materials charged during the melting operation. In order to take into account the effects of residual slag components, the slag components and residual slag amounts after pre-melting are calculated. It is a value obtained by considering it. The sampled slag is melted slag, and the closer the ratio of actual basicity / charging basicity is to 1, the more slag is melted (hatched).

At the same time, the secondary combustion rate was evaluated. The secondary combustion rate was defined by the equation (3), and was actually calculated by the following equation (4) subtracting the influence of combustion due to the intruding air at the furnace opening based on the analysis value of the flue gas. The flue gas was analyzed by gas chromatography for CO, CO ₂ , N ₂ , H ₂ and O ₂ , and H ₂ O by an absorption method (JIS Z8808).
_{PCR = [(CO 2%)} + (H 2 O%)] / [(CO 2%) + (CO%) + (H 2 O%) + (H 2%)] × 100 (%) (3)
PCR = [(CO ₂ %) _i + (H ₂ O%) _i -((O ₂ %) _a / (N ₂ %) _a × 2 ・ ((N ₂ %) _i -QN ₂ / Q _i × 100 )-2 ・ (O ₂ %) _i }] / [(CO ₂ %) _i + (CO%) _i + (H ₂ O%) i + (H ₂ %) _i ] × 100 (%) (4)
Q _i : Flue gas flow rate (Nm ³ / h)
QN ₂ : Amount of nitrogen gas blown into the furnace (Nm ³ / h)
(X%): Concentration of X component in furnace gas (vol%)
(X%) _a : Concentration of X component in air (vol%)
(X%) _i : Concentration of X component in flue gas (vol%)

  The results are shown in FIG. Rss is taken as an index on the horizontal axis, and the change in the value of the actual basicity / charging basicity and the secondary combustion rate is displayed.

  When Rss becomes small, particularly when Rss becomes less than 0.1, the ratio of actual basicity / charge basicity is visibly smaller than 1. It shows that the slag is not sufficiently hatched at the end of melting. When the index Rss is small, that is, when the amount of residual slag is small, the slag content contained in the reduced iron and the hatching (melting) rate of CaO and MgO added as a slag modifier are small, and the flow of slag The situation becomes low. As a result, the peelability of the slag contained in the reduced iron is inhibited, and the reduced rate of dissolution and reduction of the reduced iron occurs.

  On the other hand, when Rss becomes large, especially when Rss exceeds 0.5, the secondary combustion rate is lowered. This is because when the index Rss is large, the slag fluidity is ensured, but since the amount of slag in the furnace is large, the space for gas combustion is narrowed, resulting in a decrease in the secondary combustion ratio. A decrease in the secondary combustion rate results in a decrease in the amount of heat generated by the gas generated by the combustion of C in the hot metal, leading to an increase in the oxygen consumption rate accompanying an increase in the carbon material consumption rate, thereby reducing productivity.

  Therefore, by controlling the value of Rss within the range of 0.1 to 0.5, it is possible to maintain the molten state of the slag, that is, to ensure the fluidity of the slag, to dissolve the reduced iron and to prevent the slag from being contained in the reduced iron. It is possible to ensure the reduction reaction of the reduced iron oxide content. That is, in addition to controlling Rsm to about 0.65, by controlling Rss in the range of 0.1 to 0.5, high productivity hot metal production that maintains the molten state of the slag and the secondary combustion rate is achieved. Is possible. Further, the productivity is preferably further increased when Rss is 0.15 to 0.40.

  The third invention will be described.

  FIG. 3 shows a process flow showing an example of the embodiment of the present invention.

  Solid iron-containing cold material such as granule, mold, and steelworks generated scrap is supplied into the furnace for the first melting converter 1 where the molten iron and molten slag of the seed hot water exist. Then, oxygen is blown from the bottom blowing nozzle, and coal is blown from the bottom blowing nozzle using a non-oxidizing gas such as nitrogen gas as a carrier gas, thereby dissolving the supplied solid iron-containing cold material.

  The high-carbon molten iron produced in the first melting-only converter 1 leaves the seed hot water in the furnace and pours it into a ladle. Exclude part of the molten slag as needed. When the iron-containing cold material is not melted, such as when tilting for pouring and draining, or when the iron-containing cold material is charged all at once, non-oxidizing gas is blown from the bottom blowing nozzle to prevent the bottom blowing nozzle from being blocked.

  In the present invention, reduced iron, carbonaceous material, and oxygen are supplied to a reduced iron melting furnace (second melting dedicated converter 9) in which seed hot water exists, and the required amount of seed hot water and the refining dedicated conversion in the second melting dedicated converter 9 are supplied. The total amount of molten iron supplied to the furnace 3 is obtained. The second melting only converter 9 will be described in detail later.

  The high-carbon molten iron discharged from the first melting-only converter 1 to the ladle is desulfurized together with the high-carbon molten iron melted in the second melting-only converter 9 in the desulfurization equipment 2 such as KR and injection. The high-carbon molten iron after desulfurization is charged into the refining converter 3 and supplied with oxygen for decarburization. For example, a general top-bottom blowing converter is used as the refining converter 3.

  As shown in the process flow of FIG. 3, the dust generated in each of the first melting-dedicated converter 1, the second melting-dedicated converter 9, and the refining-dedicated converter 3 is OG type wet dust collector 4. In addition, after being dehydrated by the filter press 5, lime as a binder and coal as a reducing material are additionally mixed and supplied to an agglomeration device 6, for example, a pan pelletizer, and thereby pelletized. . At this time, after drying and heat reduction, which will be described later, when charging into a melting-dedicated converter in the hot state, the particle size is set to be 10 mm or more, for example, which is not lost due to scattering by the rising gas flow in the furnace. The production pellets are charged into the drying furnace 7. After drying, for example, a rotary hearth type prereduction furnace is used as the prereduction furnace 8, and heat reduction is performed using the internal coal as a reducing material in an air-LNG burner heating atmosphere to produce reduced iron. In the present invention, even if a plurality of prereduction furnaces 8 are provided, the production capacity of molten iron can be increased.

For example, the dust composition: T.I. Fe = 62%, M.I. Using dust of Fe = 21%, FeO = 34%, Fe ₂ O ₃ = 22%, coal interior amount is 10%, binder (lime) amount: 10%, particle size: 10-15mm, moisture: 1% or less If reduced to 1200 to 1300 ° C. in a rotary hearth type prereduction furnace, reduced iron preliminarily reduced to a metalization rate of about 80 to 85% can be produced.

  Consider the case where the reduced iron produced in this way is used as part of the raw material of the first melting-dedicated converter 1 as described in Patent Document 3.

  When the reduced iron use basic unit in the first melting-only converter 1 is 100 kg / ton and the reduced iron charging temperature is 1000 ° C., the metallization rate of the reduced iron and the oxygen source in the first melting-only converter 1 Fig. 4 shows the relationship between units and coal intensity. As apparent from FIG. 4, the oxygen unit and the coal unit in the first melting exclusive converter 1 increase as the metallization rate becomes lower than when the metallization rate of reduced iron is 100%. it is obvious. Since the time required for melting in the first melting-only converter 1 increases as the oxygen intensity and the coal intensity increase, the metallization rate of the reduced iron to be added is about 80 to 85%. As a result, it is understood that the oxygen unit and the coal unit of the first melting-only converter 1 are increased, and as a result, the time required for melting is increased and the productivity of the first melting-only converter 1 is deteriorated. .

  In the present invention, a reduced iron melting furnace (second melting dedicated converter 9) is prepared separately from the first melting dedicated converter 1, and the reduced iron is melted in the second melting dedicated converter 9. To do. Since the reduced iron is not melted in the first melting converter 1, it is possible to prevent an increase in oxygen intensity and coal intensity due to iron oxide contained in the reduced iron. This makes it possible to improve the productivity of molten iron.

  Furthermore, in the present invention, the production of molten iron is shared by the first melting-only converter 1 and the second melting-only converter 9, and the iron-containing cold material other than reduced iron is the first melting-only converter 1. Since the reduced iron is melted exclusively in the second melting converter 9, it is compared with the method described in Patent Document 3 in which all of the iron-containing cold material containing reduced iron is melted only in the first melting converter 1. The result of increasing the production capacity of molten iron can be obtained.

  In general, a converter having the same furnace capacity is used as the first melting-dedicated converter 1 and the refining-dedicated converter 3. In a converter factory having three converters of the same furnace capacity, when two of them are used as the first melting converter 1 and the remaining one is used as the refining converter 3, two first The molten iron production capacity using the melting-only converter 1 is insufficient to cover the required amount of molten iron when one full-scale refining converter 3 is produced. Therefore, in the method described in Patent Document 3, the refining-only converter 3 is forced to be manufactured in a state where the production capacity remains. In such a case, if the second melting-dedicated converter 9 is prepared as in the present invention and the melting of the reduced iron is left to the second melting-dedicated converter 9, only two first melting-dedicated converters are used. The total molten iron production can be increased as compared with the case of producing the smelting iron. However, the refining converter 3 can be smelted using all the produced molten iron as a raw material by using the production capacity. As a result, it becomes possible to increase the molten steel production capacity by more effectively utilizing the three converters in the converter factory having the existing three converters.

Example 1
Iron-containing cold material, carbonaceous material, and oxygen were supplied to the melting furnace in which seed hot water was present to produce hot metal. As the iron-containing cold material, the present invention example uses reduced iron that is reduced from dust containing iron as a main component and contains unreduced iron oxide, and scrap is used as a comparison.

  Reduced iron is mainly produced by mixing, kneading, and granulating dust generated from melting furnaces, converters, electric furnaces, etc. as the main raw material, carbon material containing C as the reducing material, and reducing and heating them in the reduction furnace. Processed and manufactured. As a main raw material, sludge may be mixed. The granulation was performed using a twin roll briquette machine, but pellet granulation by a rolling method may be used. The reduction furnace used was a rotary bed furnace having a furnace diameter of 20 m, and the reduction temperature was controlled to 1300 to 1400 ° C. with an LNG burner to carry out the reduction. The metallization rate of iron in the reduced iron is 78 to 83%.

In the melting operation, reduced iron is charged from the furnace, oxygen is supplied from the top blowing lance at 8000 Nm ³ / hr, the temperature after melting is 1390 to 1410 ° C., and the C concentration of the molten iron is 4.0 to 4.3. The carbonaceous material was supplied from the bottom blowing nozzle using N ₂ gas as a carrier gas. Slag adjusts the amount of slag discharged after completion of melting and adds lime and MgO to adjust the components of slag generated from coal and reduced iron so that the basicity of slag becomes 1.5 to 1.7. The amount of secondary material added was adjusted to control the slag weight ratio before and after dissolution to be constant. Moreover, in order to suppress the excessive forming state of slag and to promote the reduction of iron oxide in the slag, a certain amount of coal was added from the furnace.

  Table 1 shows the production results. No. in Table 1 Nos. 1 to 4 are comparative examples in which scraps are used as iron-containing cold materials. In Comparative Examples Nos. 5 to 7, in which reduced iron was used for the iron-containing cold material, the value of Rsm deviated from the scope of the present invention. 8 to 11 are examples of the present invention in which reduced iron is used as the iron-containing cold material. Rsm is outside the scope of the present invention with an underline.

  When the iron-containing cold material is scrap, even if the range of Rsm is outside the scope of the present application, a deep hot metal bath depth can be secured by sinking the hot metal bath into the hot metal bath, and high productivity can be maintained. When the iron-containing cold material is reduced iron, if the depth of the hot metal bath is controlled so that the index Rsm is in the range of 0.6 to 0.85, it is possible to ensure productivity while avoiding a decrease in dissolution rate. is there.

(Example 2)
The amount of dissolution was adjusted so that Rsm in the formula (1) was about 0.65, and hot metal was produced by dissolution and reduction of reduced iron. While supplying oxygen from the top blowing lance at 8000 Nm ³ / hr and supplying coal from the bottom blowing nozzle, reduced iron with a metallization rate of 78-83% was introduced into the hot metal bath from the furnace port, 29-31 ton hot metal dissolution / reduction operation was carried out. The operation was performed so that the hot metal temperature after melting was 1390 to 1410 ° C. while the hot metal C concentration after melting was maintained at 4.0 to 4.3% by mass.

  The amount of molten slag discharged after completion of pre-heat melting was adjusted, and Rss was changed in the range of 0.05 to 0.55. In order to adjust the components of slag generated from coal and reduced iron, lime and MgO were added to adjust the basicity of the slag to 1.5 to 1.7. Moreover, in order to suppress the excessive forming state of slag and to promote the reduction of iron oxide in the slag, a certain amount of coal was added from the furnace.

  Table 2 shows the results. The Rss is outside the scope of the present invention with an underline.

  No. In all of Nos. 1 to 7, Rsm is within the range of the first invention, and therefore, better productivity is realized as compared with the prior art. On the other hand, no. In Nos. 2 to 6, since Rss is also included in the range of the second invention, it was possible to achieve higher productivity and higher secondary combustion rate.

  No. in Table 2 No. 1, Rss deviates from the lower limit side of the present invention range. Compared with 2-6, dissolution time is long and productivity is low. Since Rss is 0.1 or less, as shown in FIG. 2, the slag is not sufficiently hatched even at the end of dissolution. Therefore, the fluidity of the slag is low, the peelability of the slag contained in the reduced iron is inhibited, and the dissolution / reduction rate of the reduced iron is lowered, resulting in an increase in the time required for dissolution.

  No. in Table 2 No. 7 had a large amount of residual slag before melting, so that the amount of slag in the furnace was large throughout the melting process, so that the gas combustion space in the furnace was narrowed, leading to a reduction in the secondary combustion rate. Therefore, as the carbon material basic unit required for dissolution increased, the oxygen basic unit also increased, resulting in a decrease in productivity.

(Example 3)
In the process of producing hot metal with two first melting converters and producing molten steel with one refining converter, dedicated melting of reduced iron was carried out using a new second melting converter. Table 3 shows the operating conditions of each melting furnace.

  In Comparative Example 1, as shown in FIG. 5, the iron-containing cold material containing reduced iron is supplied to the first melting-only converter 1 containing seed hot water without using the second melting-only converter, Coal is blown in and oxygen is supplied to melt the iron-containing cold material to obtain high-carbon molten iron. The reduced iron produced in the preliminary reduction furnace 8 is transported to the first melting exclusive converter by a ladle.

  For the present invention example and comparative example 2, as shown in FIG. 3, iron-containing cold material (scrap, etc.) excluding reduced iron is supplied to the first melting exclusive converter 1 in which seed hot water exists, and coal is supplied into the furnace. Blowing and supplying oxygen to melt iron-containing cold material to obtain high-carbon molten iron, supplying reduced iron to the second melting-only converter 9 where seed water is present, blowing coal into the furnace and supplying oxygen to iron-containing The cold material is melted to obtain high carbon molten iron. The obtained high carbon molten iron was subsequently desulfurized in the desulfurization facility 2 and decarburized in the refining converter 3.

  Table 4 shows the operating conditions and operating results of the inventive example, comparative example 1 and comparative example 2.

  In the example of the present invention, in the second melting only converter 9, Rsm and Rss were controlled to Rsm = 0.65 and Rss = 0.2, and the operation was performed. In Comparative Example 2, in the second melting-only converter 9, Rsm and Rss were controlled to Rsm = 0.58 and Rss = 0.55, and the operation was performed. As a result, the hot metal production capacity of the second melting-only converter 9 can be increased to 1.5 times that of the present invention example as compared with the comparative example 2, and the two first melting-only converters 1 The hot metal production capacity of 1.1 is added to the hot metal production capacity of 0.15 of the second melting exclusive converter 9 to enable the production of hot metal of 1.25 compared to the prior art, and the entire process from the prereduction furnace 8 to the continuous casting machine can be performed. Productivity can be increased 1.25 times. That is, it was possible to increase the capacity in the steelmaking process, and a 25% increase in productivity could be achieved.

  In Comparative Example 2, the introduction of the second melting-dedicated converter 9 avoids an increase in melting time due to an increase in the amount of oxygen used due to the use of reduced iron, and the two first melting-dedicated converters 1 By setting the hot metal production capacity to 1.1, the hot metal production of 1.2 compared with the conventional hot metal production capacity of the second melting exclusive converter 9 becomes possible, and the entire process from the prereduction furnace 8 to the continuous casting machine is possible. Productivity can be increased to 1.2 times that of Comparative Example 1.

It is a figure which shows the relationship between Rsm and oxygen basic unit. It is a figure which shows the relationship between Rss, real basicity / charge basicity, and a secondary combustion rate. It is a figure which shows the process flow of this invention. It is a figure which shows the relationship between the metallization rate of pre-reduction dust, and the oxygen basic unit, coal basic unit, and productivity in a converter only for melting. It is a figure which shows the conventional process flow.

Explanation of symbols

1 First melting-only converter (melting-only converter)
2 Desulfurization equipment 3 Refining converter 4 Wet dust collector 5 Filter press 6 Agglomeration device 7 Drying furnace 8 Prereduction furnace 9 Second melting dedicated converter

Claims (3)

It is a method of obtaining hot metal by dissolving reduced iron that contains iron-based dust and containing unreduced iron oxide,
When obtaining the hot metal by supplying the reduced iron, carbonaceous material and oxygen to the melting furnace where the seed hot water is present, the relationship between the hot metal bath depth before melting and the hot metal bath depth after melting when melting is complete is as follows. (1) The hot metal manufacturing method characterized by controlling the index Rsm determined by the equation to 0.6 to 0.85.
Rsm = depth of hot metal bath before melting / depth of hot metal bath after melting (1) For the amount of slag present in the melting furnace, the relationship between the amount of residual slag before the start of melting and the amount of slag at the end of melting is controlled to an index Rss determined by the following equation (2) to 0.1 to 0.5. The hot metal manufacturing method according to claim 1, wherein:
Rss = residual slag amount before melting / slag amount at the end of melting (2) The first melting converter, the reduced iron melting converter (hereinafter also referred to as the “second melting converter”), the refining converter, and the preliminary reduction furnace,
Supply iron-containing cold material, carbonaceous material, and oxygen to the first melting dedicated converter where seed hot water exists, and the total amount of the required seed hot water in the first melting dedicated converter and the amount of hot metal supplied to the refining dedicated converter Obtaining high-carbon molten iron, obtaining the total amount of high-carbon molten iron by melting the reduced iron in the second melting-dedicated converter and adding the required amount of hot water in the second melting-dedicated converter and the amount of hot metal supplied to the refining-dedicated converter, By using these high carbon molten iron as a raw material and oxygen refining in a special refining converter,
A converter steelmaking method, wherein the molten iron production method according to claim 1 or 2 is used for melting reduced iron in a second melting-dedicated converter.

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