JP4828211B2 - Steelmaking method and refining equipment for steelmaking - Google Patents

Description

  The present invention relates to a steelmaking method in which scrap containing iron (hereinafter sometimes simply referred to as “scrap”) and hot metal are charged into a smelting furnace and blown in the smelting furnace, and the molten steel is smelted, and It relates to the refining equipment used for it.

  In the present invention, a refining furnace for producing steel is not particularly limited, but a converter or an electric furnace is preferred industrially.

  In the steelmaking process using the converter method, molten steel and scrap are charged as the main raw materials to produce molten steel. At the blast furnace integrated steelworks, waste generated in the lower process (= yield drop) is used as self-generated waste, and the ratio is less than 10% if the generated waste is not sold externally. Therefore, in the blast furnace integrated steelworks, the ratio of hot metal to the main raw material in the converter (hot metal ratio: HMR) is generally 90% or more.

On the other hand, in recent years, needs for CO ₂ gas emission reduction are increasing due to global environmental problems. In the steel industry, when the steel products to produce the molten iron by reducing iron ore, iron ore in the reduction in iron coke, since CO ₂ gas is generated, recycled steel products that have already been produced Recycling into a product can reduce the amount of hot metal used and greatly reduce CO ₂ gas emissions. For these reasons, attempts have also been made to actively use externally generated waste other than self-generated waste, such as city waste, in converters. However, since the amount of heat required for melting the scrap increases as the scrap ratio increases, there is a problem that the scrap usage ratio is set to a predetermined value or less, and generally about 15% is the limit.

  In response to such problems, it has been proposed to increase the scrap ratio by preheating the scrap in advance.

  For example, Patent Document 1 discloses a preheating device for a converter-charged iron source including a cover having a metallic floor plate and a burner on which the iron source is loaded.

  Further, in Patent Document 2, for the purpose of recycling used automobiles or used home appliances, when scrapping waste car press scraps and used home appliance scraps in a melting chamber (= electric furnace) having a heating furnace, An invention is disclosed that is directly connected to the melting chamber, preheats in the preheating chamber in which the exhaust gas from the melting chamber is introduced to preheat the raw material, gasifies and removes the gasification component, and then melts.

JP-A-2-240209 JP 2002-285225 A

  However, since the invention disclosed in Patent Document 1 directly preheats the scrap without processing, scrap oxidation due to the large specific surface area of the scrap cannot be ignored, and the effect of preheating is reduced. There's a problem. This is because when iron oxide is charged into a smelting furnace, the reaction when iron oxide is reduced to iron is an endothermic reaction, so that it acts rather as a coolant.

  It is known that the oxidation rate of iron is the rate of oxygen diffusion through the oxide layer, and the oxidation rate is proportional to the 1/2 power of time. Therefore, if the preheating conditions are the same, the thickness of the oxide layer generated per unit area is the same regardless of the shape of the scrap. Therefore, the larger the specific surface area of the scrap, the higher the mass ratio of the oxide layer, that is, the oxidation rate.

  Furthermore, when scraps such as shredder scraps, which have a small shape and a large specific surface area, are heated to high temperatures, in addition to the problem of iron oxide formation, partial melting occurs due to surface oxidation heat generation, causing the scraps to weld together. As a result, this method may make it impossible to handle scrap when preheated to a high temperature.

  The invention disclosed in Patent Document 2 is a method for preheating waste car press waste by introducing exhaust gas from a melting chamber into a preheating chamber directly connected to a melting chamber having a heating source. In general, it is a technology that can only be applied to electric furnaces.

  In addition, since preheating is performed with the exhaust gas generated in the melting chamber, the upper limit of the amount of scrap that can be preheated is determined by the amount of gas generated, and a large amount of scrap cannot be preheated.

  Furthermore, since the scrap is charged into the shaft furnace from above and preheated, the lower scrap is subjected to the heavy pressure of the upper scrap. Therefore, when heated in this state, scraps with reduced strength at high temperatures can be easily crimped. Therefore, especially when heated to high temperatures, the problem of welding of scraps cannot be avoided even if pressed scraps are used. .

  Furthermore, in a converter that generates a large amount of exhaust gas containing high-concentration CO, an OG (Oxygen Converter Gas Recovery System) facility that collects exhaust gas in an unburned state is installed for the purpose of reusing exhaust gas as fuel. Yes. In this OG facility, instead of sealing the converter furnace top and the exhaust gas recovery duct, the gas pressure loss is controlled to suppress atmospheric suction and exhaust gas leakage. In many cases, pressure loss is large and fluctuates, making it difficult to control pressure loss with high accuracy. Therefore, it is difficult to adopt this method in which the scrap preheating structure is provided on the exhaust gas duct.

On the other hand, the present invention can use a large amount of inferior and inexpensive scrap, can recover and treat exhaust gas, has no environmental problems, and contributes to CO ₂ emission reduction measures and It aims at providing the refining equipment used for it.

In order to solve the problem, the gist of the present invention is as follows.
(1) Preheating a scrap containing iron that has been processed to reduce a specific surface area by compression molding into a rectangular parallelepiped or a cube so that the temperature is 900 to 1200 ° C. when the smelting furnace is charged, A steelmaking process characterized by charging preheated scrap and hot metal into a refining furnace and refining molten steel while blowing oxygen .
(2 ) The scrap containing iron is one or more of used automobile scrap, waste household waste, HS scrap, H1 scrap, H2 scrap, H3 scrap, press scrap, shredder scrap, processed scrap, or return scrap. The steel making method according to (1 ) , characterized in that there is.
( 3 ) The steelmaking method according to (1) or (2) , wherein scrap scrap that has already been press-formed is used in combination as the scrap to be preheated.
( 4 ) The steelmaking method according to any one of (1) to ( 3 ), wherein heavy scrap is used as the scrap to be preheated.
( 5 ) When the temperature of the scrap at the time of charging into the smelting furnace is T ₂ with respect to the temperature T _{1 of the} scrap after preheating, T ₁ -T _{2 is set} to 200 ° C. or less. The steel making method according to any one of (1) to ( 4 ).
( 6 ) The Cu content in the molten steel is 0.10 mass% or less, the Ni content is 0.04 mass% or less, the Sn content is 0.02 mass% or less, and the Cr content is 0.00. The steelmaking method according to any one of (1) to ( 5 ), characterized in that melting is performed so that the content is 08 mass% or less and the Zn content is 0.25 mass% or less.
( 7 ) The amount of Cu, Ni, Sn, Cr, Zn is changed to a scrap mixing ratio so as to satisfy the following formulas, respectively, and is melted. (1) to ( 6 ) The steel making method described in any of the above.




( 8 ) The steelmaking according to any one of (1) to ( 7 ), wherein the scrap has a bulk specific gravity of 0.4 to 5.0 after being processed to reduce the specific surface area. Law .
(9 ) The steelmaking method according to any one of (1) to ( 8 ), wherein a thickness of the scrap after the processing for reducing the specific surface area is 80 to 1000 mm.
( 10 ) The steelmaking method according to any one of (1) to ( 9 ), wherein the smelting furnace is a converter.
( 11 ) The steelmaking method according to any one of (1) to ( 10 ), wherein the scrap is preheated using a tunnel furnace or a rotary hearth furnace.
( 12 ) The steelmaking method according to any one of (1) to ( 11 ), wherein the scrap is preheated in an atmosphere having a volume% and an oxygen concentration of 0 to 10%.
( 13 ) The steelmaking method according to any one of (1) to ( 12 ), wherein exhaust gas after preheating the scrap is collected and processed.
( 14 ) The steelmaking method according to ( 13 ), wherein the exhaust gas is treated at a temperature of 900 ° C or higher for 2 seconds or more and cooled to 300 ° C or lower.

According to the present invention, a large amount of scrap including inferior and inexpensive scrap can be used, preheated exhaust gas can be recovered and processed, and there is no environmental problem, and the amount of generated CO ₂ can be reduced.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 shows an example of a process flow targeted by the present invention. After some or all of the scrap is processed to reduce its specific surface area (for example, press molding), it is preheated in a preheating furnace, and the scrap is charged into the smelting furnace together with hot metal, and oxygen is blown into the smelting .

  Here, the scrap targeted by the present invention is not particularly limited, and as general municipal waste, in addition to heavy waste such as HS waste, H1 waste, H2 waste, H3 waste, press waste, shredder waste, processing It includes scraps, used automobile scraps, waste home appliance scraps, etc., and self-generated scraps such as return scraps and semi-finished scraps such as slabs and steel slabs that have a large thickness. Table 1 shows a simple explanation of these scrap types.

  As a refining furnace, a converter is usually used. As a form of refining, in the case of decarburization only, when dephosphorization is performed after dephosphorization, and further dephosphorization called MURC (Multi Refining Converter), the refining furnace is tilted to dephosphorize slag. There is a case where decarburization is continuously performed in the same furnace after only discharging.

  Furthermore, in the present invention, the molten iron is defined as mass% (hereinafter the same) of molten iron having a C of 2.0% or more, and molten steel is defined as molten iron having a C of less than 2.0%.

  First, the effect of preheating the scrap after it has been processed to reduce its specific surface area, such as press molding, will be described.

  Fig. 2 shows pre-heating in an atmosphere with an oxygen concentration of 1% by volume when using press waste as a method to reduce the specific surface area of scrap using the return scrap with a plate thickness of about 1 mm and without pressing. It is the figure which showed the relationship between scrap temperature and oxidation rate (mass ratio of iron oxide in scrap) at the time.

  The scrap temperature here is not the temperature immediately after preheating, but the temperature at the time of charging the refining furnace after transporting the preheated scrap to the refining furnace.

  This is because even if the temperature immediately after preheating is the same, the amount of heat that can be supplied from the preheated scrap to the smelting furnace depends on the shape of the scrap and the time until charging. This is because it is determined by temperature.

  Incidentally, in FIG. 2, the time for transporting the preheated scrap to the smelting furnace was about 4 to 6 minutes.

  As a result, in any case, it can be seen that the preheating time increases as the temperature increases and the oxidation rate increases as the temperature increases, so that the oxidation rate increases as the scrap temperature increases.

  However, in the case of no press molding, the oxidation rate is about 10% when the scrap temperature is 900 ° C, and the oxidation rate is 20% or more at 1100 ° C. It turns out that it can suppress to about 1/4.

  This is thought to be due to the fact that when press molding is performed, the specific surface area of the scrap is reduced, so that it is less likely to be oxidized.

  Furthermore, in the case of no press molding, since the scrap has a large specific surface area, the amount of heat dissipation increases, so the temperature drop from the preheating furnace to the refining furnace increases, and the same scrap In order to obtain the temperature, it is necessary to increase the preheating temperature. As a result, the preheating time increases, and it is considered that the oxidation rate further increased.

  Fig. 3 shows the results of calculating the effect on the temperature fluctuation of the smelting furnace when preheated scrap is put into the smelting furnace. In FIG. 3, the cooling ratio is expressed as a ratio when the temperature drop when the unpreheated scrap is added is 1, and is calculated by the following equation.

  Cooling ratio = (temperature drop when 1% by weight of preheated scrap is charged) / (temperature drop when 1% by weight of cold scrap is charged)

  From FIG. 3, it can be seen that in the case of no press forming, the heating effect starts to decrease when heated to about 500 ° C. or higher, and when heated to 800 ° C. or higher, the reverse effect is rather reversed. This is because scraps without press forming have a significantly higher oxidation rate as the preheating temperature increases, so the iron oxide content in the scrap increases, and this iron oxide is reduced to iron in the smelting furnace. This is because the endothermic reaction acts as a coolant.

The specific surface area is defined as the surface area per unit mass, and the unit is m ² / ton. The specific surface area can be easily calculated once the geometric shape is determined. In the case of a plate having a thickness t × width D × length L,
Surface area = 2LD + 2tL + 2tD
Mass = ρLDt
ρ: Density ton / m ³
Because
Specific surface area = 2 (1 / t + 1 / L + 1 / D) / ρ
It becomes.

  In the case of L, D >> t, such as a plate, sheet, etc., the non-surface area≈2 / ρt, which is determined only by the plate thickness. In the case of a cube, from t = L = D, the specific surface area = 6 / ρt.

  A general scrap is a board, a sheet, or a combination thereof, and can have a specific surface area ≈ 2 / ρt. On the other hand, in the case of pressed scrap, it can be calculated from the shape as a cube or a rectangular parallelepiped.

A normal scrap has a thickness of 1 to 6 mm and a specific surface area of 50 to 300 m ² / ton. On the other hand, when these are press-molded, the specific surface area can be significantly reduced to 5 to 6 m ² / ton.

  The oxidation rate refers to the mass% of iron oxide per unit mass, but it is difficult to measure directly. Therefore, it is calculated from the measured thickness value of the scrap surface after cooling using the following formula. Can do. The scale thickness can be measured by observing a cross section of the surface layer including the scale with an optical microscope.

Oxidation rate (%) = scale thickness ÷ (scrap volume) ^1/3 x 79.85 / 55.85 x 100
≒ Scale thickness ÷ Scrap thickness × 2 × 79.85 / 55.85 × 100
Here, 55.85 is the atomic weight of iron, and 79.85 is the molecular weight per mole of Fe ₂ O ₃ .

  From the above, in the invention relating to the above (1), a large amount of scrap is first produced by preheating a part or all of the scrap containing iron that has been processed to reduce the specific surface area to 600 to 1200 ° C. As will be described later, the resin and the like in the scrap can be removed.

  With regard to the scrap ratio, that is, (scrap mass) / ((molten metal mass) + (scrap mass)) × 100, the conventional technology is the refining form that can maximize the scrap ratio, only decarburization blowing without preliminary dephosphorization. Even in the case of carrying out, a scrap ratio of about 10% without the addition of an external heating material (for example, carbon material) and about 15% with the use of carbon material was the limit. However, according to the present invention, a scrap ratio of about 20% can be achieved without the use of charcoal, and a scrap ratio of 25% or more can be achieved with the use of charcoal.

  In addition, the effect of scrap preheating is the same as when performing hot metal dephosphorization, when the pre-heat treatment temperature is as low as 1450 ° C or less and the treatment time is as short as about 10 minutes, which is disadvantageous for scrap melting. , Especially bigger. Normally, the maximum scrap ratio at the time of dephosphorization is about 10%, but if the entire scrap is preheated to 900 ° C., the scrap ratio can be further increased by 10% or more.

Therefore, when molten steel having the same mass is produced, the scrap ratio can be increased as compared with the prior art, so that the amount of molten iron to be used can be reduced. Therefore, since the amount of tapping in the blast furnace can be reduced, as described above, the amount of CO ₂ generated in the blast furnace can be reduced. Incidentally, CO ₂ emission under blast furnace per ton of molten pig iron is about 2 tons CO ₂ generation amount due to the scrap preheating depending on the preheating temperature is for about 0.5 per ton scrap one ton present By replacing the hot metal with scrap by technology, it is possible to reduce CO ₂ of about 1.5 tons per ton of hot metal for each target smelting (charge), contributing to the global environment.

  On the other hand, reducing the amount of slag generated in the refining process is also required from the viewpoint of the global environment, and this is an effective means to improve the refining efficiency through the application of hot metal dephosphorization treatment. There was a problem of being restricted. However, the present invention can also solve the problem of reducing the amount of slag.

  Regarding the preheating temperature of scrap, if it is less than 600 ° C, the removal of volatile and combustion components such as resins will be insufficient, and if it exceeds 1200 ° C, the amount of oxidation will increase and scrap welding problems will occur. Since the temperature drop from preheating to charging the refining furnace becomes large and the effect of preheating decreases, it is specified in the above temperature range. Furthermore, the preheating temperature of scrap is more preferably 700 to 1100 ° C.

  Incidentally, the preheating temperature of scrap means the temperature at the time when the scrap is taken out from a preheating furnace such as a tunnel furnace or a rotary hearth furnace, that is, the temperature immediately after preheating. The temperature can be measured, for example, with a radiation thermometer.

  In addition, since the preheating time varies depending on the scrap thickness, the preheating time is not particularly specified and may be set as appropriate, but about 1 to 6 hours can be exemplified.

  Next, the preheat-treated scrap and hot metal are charged into the smelting furnace, and the molten steel is melted while blowing oxygen. Either the scrap or the hot metal can be charged first. When the smelting furnace is a converter, the converter is tilted and the scrap is charged. Therefore, it is preferable from the viewpoint of work that the scrap is charged first. On the other hand, when the smelting furnace is an electric furnace, pig iron or molten steel is left as seed water, so scrap may be charged later. In addition, when preheating a part of the scrap, after the normal temperature scrap is charged into the smelting furnace, the preheated scrap may be charged into the smelting furnace or in the reverse order.

  One of the important purposes of preheating scrap to the temperature range specified in the present invention is to burn and remove the resin, etc. contained in the scrap during preheating, and when the scrap is charged into the smelting furnace, it is flame and harmful. This is to prevent the generation of substances, etc. From the viewpoint of workability and environment, the resin and fats and oils in the mass of the entire scrap when charged into the smelting furnace are 0.5% by mass or less, preferably Is 0.1% or less, more preferably 0.01% or less.

  The smelting furnace is not limited in particular as an electric furnace in addition to a converter. The preheating of the scrap is not particularly limited, but it is preferable to use a horizontal furnace such as a tunnel furnace or a rotary hearth furnace in order to prevent scrap welding and pressure bonding.

  The invention related to (2) is characterized in that, in the invention related to (1), a process for reducing the specific surface area is performed by press molding. The purpose of press forming is to reduce the specific surface area, increase the bulk density of scrap, increase the heating efficiency, and make the shape constant to transport and charge to the preheating furnace and charge to the refining furnace. It is easy to handle. The shape of the press-molded scrap may be a cube or a rectangular parallelepiped.

  In the invention related to (3), the scrap containing iron is used automobile scrap, waste home appliance scrap, HS scrap, H1 scrap, H2 scrap, H3 scrap, press scrap, shredder scrap, processing scrap, return scrap. It is characterized by being one or more of.

  Since the return waste is self-generated waste (that is, scrap generated at the factory and returned for use at the same factory), its component value is known and there are few impurities. Processing scrap is generated from the processing plant of steel products, and there are few component variations.

  On the other hand, general municipal waste such as HS waste, H1 waste, etc., are high-grade waste that has been sorted to some extent by appearance, and there are many impurities, and unsorted inferior waste, scrapped vehicle waste, and household appliance waste cannot be recovered by single use. It contains impurities, especially Cu mixed from wiring and the like. Some impurity elements such as carbon, silicon, phosphorus, and sulfur can be removed using a refining reaction, but copper, nickel, tin, etc. cannot be removed. Therefore, for impurity elements that cannot be removed by these refining reactions, the only way to limit the amount of input to the refining furnace is. Therefore, it is necessary to adjust the components by mixing various scraps.

  Accordingly, scraps with few impurity elements can be used alone, but scraps containing impurity elements that cannot be removed by a refining reaction are preferably mixed with scraps with few impurity elements.

  As described above, scraps can be used alone or in combination with multiple types of scraps, so even a poor and cheap scrap can be used in large quantities. it can.

  The invention according to (4) above is characterized in that, in the steelmaking method according to any one of (1) to (3), scrap scraps that have already been press-molded are used in combination as preheated scrap. To do.

  When using scrap press-molded scrap press waste scrap press already formed, the same effect can be obtained, so press scrap scrap press already molded may be used in combination. .

  However, it is preferable to use the waste car press scrap used here, which is press-molded after removing motors, resins, waste oil / liquids from the waste car in advance.

  The invention according to (5) above is characterized in that heavy scrap is used together as scrap to be preheated.

  The heavy waste here refers to waste having a large cross section with a side of 100 mm or more. In general steel products, there are almost no scraps with a thickness of 100 mm or more, so there is almost no heavy scrap in the city scrap, but steel scrap and cast scrap that exist as semi-finished scrap in the steel manufacturing process are mainly heavy. Generated as scrap. Although this heavy dust is not press-molded, the specific surface area is already small, so that the same effect as that of press-molded waste can be obtained when preheating.

In the invention related to (6), ΔT = T ₁ −T _{2 is set} to 200 ° C. or less when the scrap temperature T ₂ when charging the refining furnace is set to the scrap temperature T ₁ after preheating. It is characterized by.

  The preheated scrap is transported using a chute and charged into the smelting furnace, but at that time, the heat from the preheated scrap reduces the scrap temperature. If this heat dissipation amount is excessive, the preheated process is wasted, so it is preferable to make the temperature drop (ΔT) as low as possible. From the experimental knowledge of the present inventors, it has been confirmed that if ΔT is 200 ° C. or lower, the effect of preheating the scrap is confirmed, and therefore it is preferable to operate so that ΔT is 200 ° C. or lower. .

  In the present invention, since the scrap is processed to reduce the specific surface area by press molding or the like, the heat radiation amount is suppressed. However, since ΔT can be made lower by implementing measures to reduce heat dissipation, such as shortening the time for transporting and charging the scrap after preheating, and installing heat insulating materials and heat insulating lids on the chute. Is preferred.

  The invention relating to the above (7) is characterized in that the molten steel is melted so that the contents of Cu, Ni, Sn, Cr, and Zn are not more than predetermined values, respectively.

  As described above, particularly inferior and inexpensive scrap contains an impurity element, and typical impurity elements include Cu, Ni, Sn, Cr, and Zn.

  Since Cu, Ni, and Sn are elements that cannot be removed in the refining process, it is important to make the value less than the upper limit that is acceptable in terms of required product characteristics. Therefore, it is important to set the scrap ratio in consideration of the content in the scrap so that the predetermined value within the range satisfying the required product characteristics is obtained.

  Although Cr can be removed by oxidation during the refining process, the chromium oxide generated at this time is transferred to slag, which causes a problem of Cr elution from slag. For this reason, it is important to set the scrap ratio in consideration of the content in the scrap so that the Cr also has a predetermined value in a range that satisfies the environmental standards.

  Furthermore, since Zn evaporates at the time of decarburization in the refining process and concentrates in steelmaking dust, it is contained in the scrap so that the predetermined value is within the allowable Zn content range from the upper limit of the Zn concentration in the dust. It is important to set the scrap ratio in consideration of the quantity.

  For the above reasons, in the present invention, it is preferable to melt so that the contents of Cu, Ni, Sn, Cr, and Zn are not more than the prescribed values specified respectively.

  The invention relating to the above (8) is characterized in that the amount of Cu, Ni, Sn, Cr, Zn is melted by changing the mixing ratio of scrap so that the following formulas are satisfied.

  The contents of Cu, Ni, Sn, Cr, and Zn were determined to be not more than the prescribed values in the invention relating to the above (7), but the present invention shows specific numerical values for that purpose. is there.

  In the above formula, the upper limit values related to Cu, Ni, and Sn are mainly based on experimental knowledge based on hot workability and material properties. The upper limit related to Cr is based on experimental knowledge for satisfying Cr elution characteristics from slag, and for Zn, it is based on operational knowledge about Zn concentration in dust collection dust recovered from exhaust gas by a wet dust collector. It is.

  Moreover, what is necessary is just to measure each component in the object scrap for the concentration of each component for each scrap type. However, since it is simple in actual operation, it is preferable to obtain an estimated value by regression analysis of past operation results. Then, the input amount of each impurity element component can be estimated from the charged amount of various scraps, and as a result, the content in steel can be estimated.

  In the invention according to (9), the bulk specific gravity of the scrap after processing to reduce the specific surface area is 0.4 to 5.0, preferably 1.0 to 5.0, more preferably 2.0 to 5.0.

  When press forming is performed as a process for reducing the specific surface area, it is desirable that the bulk specific gravity of the scrap after press forming is high in terms of preheating efficiency, oxidation suppression and handling. When the bulk specific gravity is 0.4 or more, the temperature drop of the scrap after preheating can be prevented, but preferably 1.0 or more, more preferably 2.0 or more. On the other hand, if the bulk specific gravity exceeds 5.0, a large load is required for press molding and it is not efficient, so the above range is preferable.

  The invention according to the above (10) is characterized in that scrap is processed into a rectangular parallelepiped or a cube to reduce the specific surface area.

  When press forming is performed as a process to reduce the specific surface area, by pressing the scrap into a rectangular parallelepiped or a cube, the heating efficiency in the preheating device is improved, and transport to the preheating device, subsequent unloading, and converter Since handling such as charging becomes easy, it is preferable to press-mold into a rectangular parallelepiped or a cube.

  The invention according to (11) above is characterized in that the thickness of the scrap after the processing for reducing the specific surface area is 80 to 1000 mm.

  As for the size of the rectangular parallelepiped or the cube, it is preferable that the length of each one side is in the range of 80 mm or more and 1000 mm or less from the viewpoint of oxidation inhibition, heating time, and handling properties.

  FIG. 4 shows various press thicknesses and preheating up to 900 ° C. in a tunnel furnace using scraps formed by mixing H1 scraps and return scraps when press forming is performed to reduce the specific surface area. It is the result of investigating the relationship with the oxidation rate at the time.

  From this result, it can be seen that the press thickness is preferably 80 mm or more because the oxidation rate of scrap is remarkably reduced by press forming. That is, when the length is less than 80 mm, the heating time can be shortened. However, as described above, the specific surface area becomes large, and oxidation of scrap cannot be ignored.

  On the other hand, even if the thickness of the press is large, the oxidation rate only slightly increases. However, if the thickness exceeds 1000 mm, a large amount of time is required for heating, and handling is also a problem. It is preferable that

  The invention according to (12) is characterized in that the refining furnace is a converter.

By blowing in the converter, scrap can be melted in large quantities to increase production and to reduce CO ₂ generation.

  The invention according to (13) is characterized in that scrap is preheated using a tunnel furnace or a rotary hearth furnace.

  If the tunnel furnace illustrated in FIG. 5 or the rotary hearth furnace illustrated in FIG. 6 is used, the atmosphere in the furnace can be easily controlled and no pressure higher than its own weight is applied. The scrap can be preheated to 600 ° C. or higher while suppressing the oxidation of.

  The invention according to (14) is characterized in that scrap is preheated in an atmosphere having a volume% and an oxygen concentration of 0 to 10%.

  If the atmosphere during scrap preheating is volume% and the oxygen concentration is 10% or less, oxidation of the scrap can be suppressed even if preheated to 600 ° C or higher, so the oxygen concentration should be 10% or less. preferable. Moreover, since oxidation can be suppressed as the oxygen concentration is lower, it is preferably 1% or less. Further, the lower limit value of the oxygen concentration includes 0%.

  The invention according to the above (15) is characterized in that the exhaust gas after preheating the scrap is recovered and processed.

  Since the exhaust gas after preheating the scrap contains dust, SOx, NOx, etc., these are collected with an electric dust collector, dry dust collector, wet dust collector, etc., and then treated with denitration, desulfurization, etc. as necessary. I decided to.

  The invention relating to the above (16) is characterized in that the exhaust gas treatment condition is maintained at 900 ° C. or more for 2 seconds or more and cooled to 300 ° C. or less.

  When inferior quality scrap such as scrap car scraps is used as preheating scrap, polymer resins containing chlorine such as vinyl chloride are often mixed in the scrap. These chlorine components are decomposed and vaporized when preheated, but they may produce very harmful dioxins in the process of cooling the exhaust gas. In order to prevent this formation, it is effective to raise the temperature to a temperature at which dioxins decompose and then rapidly cool to a temperature at which no resynthesis is performed.

For this purpose, the dioxins produced by holding the exhaust gas at 900 ° C. or higher for 2 seconds or more are decomposed, and then re-synthesis does not occur up to 300 ° C. or lower, preferably within 1 second, more preferably 0.5 seconds. by cooling within, can ensure no dioxin in the exhaust gas, can be satisfied 0.1ngTEQ / Nm ³ or less is a regulation value of the most stringent incinerator.

  The upper limit values of the temperature and time for decomposing dioxins in the exhaust gas are not particularly specified, but considering the size of the combustion tower, it is realistic to set the temperature to 1300 ° C. or less and 5 seconds or less.

  In addition, the lower limit of the temperature and time for preventing dioxin resynthesis afterwards is not particularly specified, but from the viewpoint of suppressing corrosion due to acid contained in the gas, The dew point temperature is preferable, and the shorter the time, the more effective the effect. Therefore, theoretically, the lower limit is over 0 seconds, but it is realistic to set it to 0.1 seconds or more. .

  As a specific method, water can be directly sprayed on the exhaust gas. As a result, even if vinyl chloride or the like causing dioxins is mixed, it can be preheated without any problem.

  The invention according to (17) is a steelmaking refining furnace characterized by having a tunnel furnace or a rotary hearth furnace for preheating iron-containing scrap.

  If the steelmaking refining furnace has a tunnel furnace or a rotary hearth furnace, the scrap can be melted in large quantities by continuously preheating the scrap, and the resin and oil components contained in the scrap can be tunneled. Can be burned and removed in the furnace. Therefore, the steelmaking smelting furnace can be smelted efficiently without the occurrence of flames of resin and oil components during scrap charging.

  The invention according to (18) above is characterized by having a press molding machine that presses the scrap in front of the tunnel furnace or rotary hearth furnace. If there is a press molding machine in the front stage of the preheating furnace, the scrap can be preheated in large quantities by continuously pressing the scrap.

  The invention according to (19) further includes an exhaust gas recovery treatment facility after preheating the scrap. If an exhaust gas recovery processing facility is provided, the resin and oil components generated during the preheating of the scrap can be recovered and processed.

  The invention according to (20) is further characterized in that the smelting furnace is a converter.

By blowing using a converter, it is possible to melt a large amount of scrap, expand production, and reduce CO ₂ generation.

  Examples of the present invention and comparative examples will be described below, but the present invention is not limited to the following examples.

(When decarburizing in the refining process)
Decarburization blowing of hot metal was performed using a 340-ton converter. The hot metal ratio, that is, (molten metal mass) / (molten metal mass + scrap mass) was 74 to 92%. Hereinafter, the hot metal ratio may be referred to as HMR (abbreviation of hot metal ratio).

Further, as scrap, in addition to H1 scrap, return scrap was in the form of a thin sheet and a coil, and heavy scrap was 250 mm thick × width-1000 mm × length-400 mm steel slab scrap. In the case of preheating, the heavy waste was used as it was, the H1 waste and the return waste were mixed and processed into a cuboid of 320 mm × 600 mm × 600 to 800 mm by press working. The return scrap and H1 scrap had a thickness of 6 mm and a specific surface area of 50-300 m ² / ton.

As a result of press molding these, the specific surface area was greatly reduced to 5 to 6 m ² / ton, and the bulk specific gravity was 2 to 3. On the other hand, the specific surface area of the weight waste was even smaller, in the range of 1.5 to ^2.5 m ² / ton.

  For the preheating of the scrap, a tunnel furnace type preheating furnace was used. The tunnel furnace temperature was controlled to 1100 ° C., and the furnace oxygen concentration was controlled to 1% by volume. In some cases, in order to see the effect of the oxygen concentration, combustion control was performed at an oxygen concentration of 3% by volume and 10% by volume. Furthermore, the scrap preheating time (that is, the residence time in the furnace) was 80 minutes. The preheated scrap was charged into the converter using a scrap chute with a heat insulating cover, and then molten metal was charged and then refined by blowing oxygen. The scrap temperature at the time of discharging the preheating furnace was 960 to 1000 ° C., and the scrap temperature before charging the converter was 900 to 940 ° C. as shown in Table 2.

The exhaust gas when the scrap was preheated in the tunnel furnace was led to the combustion tower and held at 950 ° C. for 2 seconds, and then water was sprayed from the spray nozzle to cool to 200 to 300 ° C. in 0.5 to 1 second. As a result, almost no dioxin in the exhaust gas was present, and 0.1 ngTEQ / Nm ³ or less could be satisfied.

  Further, the exhaust gas was subjected to denitration and desulfurization treatment using a wet desulfurization apparatus and a catalytic reduction denitration apparatus after dust was collected with a bag filter. Table 2 shows the results.

  Comparative Examples 1 to 4 are cases where preheated scrap is not used. Up to about 90% HMR was able to be blown without the addition of charcoal, but when the HMR was 86%, the amount of heat of melting of the scrap was insufficient, so it was necessary to add charcoal as a heating material.

  On the other hand, in Examples 1 to 5, the entire amount of scrap is preheated. HMR was able to be blown up to about 80% without adding carbonaceous material. That is, by preheating all the scraps up to 900 ° C., the HMR can be reduced by about 10% compared with the case of not preheating. Furthermore, even if the HMR was reduced to 75%, it was possible to blow with some charcoal.

  Further, in Examples 6 to 8, although the result was that a part of the scrap was preheated, even if part of the scrap was preheated, there was an effect corresponding to the ratio, and the HMR could be reduced.

  Examples 9 to 11 are examples in which scrap car scrap scraps that have been press-formed in advance are mixed and used. Although it is HMR comparable to Examples 3-5, it can be understood that the same effect can be obtained even if scraps that have been press-molded in advance are blown with the same basic carbon material unit.

  Further, Examples 12 to 13 are the results when the oxygen concentration in the preheating furnace is 3% and 10%, respectively. When the oxygen concentration is high, the oxidation rate increases and the preheating effect decreases. However, if the oxygen concentration is up to 10%, the HMR can be reduced by preheating.

  A similar experiment was performed using a rotary hearth furnace, but the same results as above were obtained.

  Table 3 shows the amount of scrap type used with the same charge as in Table 2 and Cu, Ni, and Sn component values after decarburization.

  Since Comparative Examples 1-4 uses only return scrap, Cu, Ni, and Sn are all low values.

  On the other hand, Examples 1-13 are the results of blending scraps according to the present invention. Compared with the comparative example, a larger amount of H1 scrap and scrap car press scrap are used, but Cu, Ni, and Sn are within the range defined in the present invention. That is, it was suggested that the present invention makes it possible to use a large amount of inferior scrap while suppressing the problem of impurities.

(When dephosphorization is performed in the refining process)
Table 4 shows the results of hot metal dephosphorization blowing in the same 340-ton converter. HMR was performed at 78-92%.

As scrap, in addition to H1 scrap, return scrap was thin sheet and coil, and heavy scrap was 250 mm thick × width˜1000 mm × length˜400 mm steel scrap. In the case of preheating, the heavy waste was used as it was, the H1 waste and the return waste were mixed and processed into a cuboid of 320 mm × 600 mm × 600 to 800 mm by press working. The return scrap and H1 scrap had a thickness of 6 mm and a specific surface area of 50-300 m ² / ton.

As a result of press molding these, the specific surface area was greatly reduced to 5 to 6 m ² / ton, and the bulk specific gravity was 2 to 3. On the other hand, the specific surface area of the weight waste was even smaller, in the range of 1.5 to ^2.5 m ² / ton.

  For the preheating of the scrap, a tunnel furnace type preheating furnace was used. The tunnel furnace temperature was controlled to 1100 ° C., and the furnace oxygen concentration was controlled to 1% by volume. The preheated scrap was charged into the converter using a scrap chute with a heat insulating cover, and then molten metal was charged and then refined by blowing oxygen.

  The exhaust gas when scrap was preheated in a tunnel furnace was treated in the same way as above.

  Comparative Examples 5 to 8 are cases where preheated scrap is not used. As in Comparative Examples 5-6, when the HMR was 90% or more, blowing was possible without any particular problem, but in Comparative Examples 7-8, where the HMR was less than 90%, the scrap was not completely melted and the furnace was not melted. Remained within.

  On the other hand, in Examples 14-19, although it was a case where the whole amount of scrap was preheated, HMR was able to be blown without becoming undissolved to 78.5%. Therefore, by preheating all scraps up to 900 ° C., it was possible to reduce the HMR by 10% or more compared with the case of not preheating.

  Further, Examples 20 to 22 are the results of preheating a part of the scrap, but even if part of the scrap was preheated, there was an effect corresponding to the ratio, and the HMR could be reduced.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  INDUSTRIAL APPLICABILITY The present invention is applicable to a steelmaking method in which scrap containing iron and molten iron are charged into a smelting furnace and blown in the smelting furnace to produce molten steel, and a smelting equipment used therefor.

It is a figure which shows an example of the whole process flow of the steel manufacturing method concerning this invention. It is a figure which shows an example of the relationship between the preheating temperature of a scrap, and an oxidation rate. It is a figure which shows an example of the relationship between the preheating temperature of a scrap, and a cooling ratio. It is a figure which shows an example of the relationship between the thickness of a scrap, and an oxidation rate. It is a schematic diagram which shows an example of the tunnel furnace used with the steel manufacturing method which concerns on this invention. It is a conceptual diagram which shows an example of the rotary hearth furnace used with the steel manufacturing method which concerns on this invention.

Claims (14)

A scrap containing iron that has been processed to reduce the specific surface area by compression molding into a rectangular parallelepiped or a cube is preheated to 900 to 1200 ° C. at the time of charging into the smelting furnace, and after the preheating, A steelmaking method characterized by charging scrap and hot metal into a refining furnace and refining molten steel while blowing oxygen. The scrap containing iron is at least one of used automobile waste, waste household waste, HS waste, H1 waste, H2 waste, H3 waste, press waste, shredder waste, processed waste, or return waste. The steelmaking method according to claim 1, characterized in that it is characterized. The steelmaking method according to claim 1 or 2 , wherein the scrap to be preheated is used in combination with scrap scraps that have already been press-formed. The steelmaking method according to any one of claims 1 to 3 , wherein heavy scrap is used in combination as the scrap to be preheated. When the temperature of the scrap at the time of charging into the smelting furnace is T ₂ with respect to the temperature T _{1 of the} scrap after preheating, T ₁ -T _{2 is set} to 200 ° C. or less, The steel manufacturing method of any one of Claims 1-4 . In the molten steel, the Cu content is 0.10% by mass or less, the Ni content is 0.04% by mass or less, the Sn content is 0.02% by mass or less, and the Cr content is 0.08% by mass. The steelmaking method according to any one of claims 1 to 5 , wherein the melting is performed so that the Zn content is 0.25 mass% or less. Cu, Ni, Sn, Cr, is charging amount of Zn, respectively by changing the compounding ratio of the scrap so as to satisfy the following formula, characterized in that melting, claim 1-6 1 The steel making method as described in the item.

The steelmaking method according to any one of claims 1 to 7 , wherein a bulk specific gravity of the scrap after the processing for reducing the specific surface area is 0.4 to 5.0. The steelmaking method according to any one of claims 1 to 8 , wherein a thickness of the scrap after the processing for reducing the specific surface area is 80 to 1000 mm. The steelmaking method according to any one of claims 1 to 9 , wherein the smelting furnace is a converter. The steelmaking method according to any one of claims 1 to 10 , wherein the scrap is preheated using a tunnel furnace or a rotary hearth furnace. The steelmaking method according to any one of claims 1 to 11 , wherein the scrap is preheated in an atmosphere having a volume% and an oxygen concentration of 0 to 10%. The steelmaking method according to any one of claims 1 to 12 , wherein the exhaust gas after preheating the scrap is collected and processed. The steelmaking method according to claim 13 , wherein the exhaust gas is treated at a temperature of 900 ° C or higher for 2 seconds or more and cooled to 300 ° C or lower.