WO2010084822A1

WO2010084822A1 - Process for manufacturing granular iron

Info

Publication number: WO2010084822A1
Application number: PCT/JP2010/050373
Authority: WO
Inventors: 杉山　健; 修三伊東; 修津下; 晶一菊池
Original assignee: 株式会社神戸製鋼所
Priority date: 2009-01-23
Filing date: 2010-01-15
Publication date: 2010-07-29
Also published as: CA2745763A1; US20110265603A1; RU2484145C2; AU2010207300A1; RU2011135038A; AU2010207300B2; CN102272337A; JP2010189762A

Abstract

A process for manufacturing granular iron, which comprises introducing agglomerates formed from a raw material mixture comprising both an iron oxide-containing substance and a carbonaceous reducing agent onto a hearth with a coal-based material laid thereon, and heating the agglomerates to reduce and melt the iron oxide contained in the agglomerates, characterized in that: the temperature of the agglomerates in the furnace is controlled within a range of 1200 to 1500°C; the oxygen partial pressure of the atmospheric gas when heating the agglomerates is adjusted to 2.0 × 10^-13 atm or higher in terms of value at the standard state; and the linear velocity of the atmospheric gas in the furnace is adjusted to 4.5cm/s or higher.

Description

Production method of granular iron

The present invention introduces an agglomerate formed from a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent into a hearth laid with a carbonaceous material, and heats the agglomerate. The present invention relates to a method for producing granular iron by reducing and melting iron oxide in a chemical compound.

Direct reduction iron making methods have been developed to obtain granular metallic iron from a raw material mixture containing an iron oxide source such as iron ore or iron oxide (hereinafter sometimes referred to as iron oxide-containing substance) and a carbonaceous reducing agent. In this iron making method, the raw material mixture is charged onto the hearth of a heating furnace, and the iron oxide in the raw material mixture is reduced with a carbonaceous reducing agent by heating the raw material mixture with gas heat transfer or radiant heat in a furnace. It is reduced to iron, and this reduced iron is subsequently carburized and melted, then aggregated into granules while being separated from by-product slag, and then cooled and solidified to obtain granular metallic iron. Since this iron making method does not require large-scale facilities such as a blast furnace, and has high resource flexibility such as no coke, research on practical application has been actively conducted recently. However, in order to implement this iron manufacturing method on an industrial scale, there are many problems that must be further improved, including operational stability, safety, economic efficiency, quality of granular iron (product), and the like.

Since the granular iron obtained by the direct reduction iron making process is sent to existing steel making facilities such as electric furnaces and converters and used as an iron source, the content of impurity elements may be low. desired. Moreover, in order to improve the versatility as an iron source, it is desirable that the carbon content in the granular iron is as large as possible within a range that does not become excessive.

In order to improve the quality of granular metallic iron, the present applicant proposed in Patent Document 1 granular iron in which the Fe purity is increased to 94% by mass or more and the C content is adjusted to 1.0 to 4.5% by mass. ing. The granular iron is further adjusted to have an S content of 0.20 mass% or less, an Si content of 0.02 to 0.5 mass%, and an Mn content of less than 0.3 mass%. However, Patent Document 1 does not disclose the point of adjusting the P amount of granular iron. The reason for this is that the phosphorus behavior in the reduction process of iron oxide has already been clarified by the chemical reaction mechanism in the blast furnace. In order to reduce the amount of phosphorus in the granular iron obtained by the iron manufacturing method disclosed in Patent Document 1, since almost the entire amount remains in the reduced product (that is, metallic iron) and does not shift to by-product slag, This is because it is recognized that it is necessary to reduce the amount of phosphorus contained in the raw material and / or to further dephosphorize the granular iron.

In recent years, the quality of iron ore has been declining, and the amount of phosphorus contained in the iron ore to be mined has increased. Therefore, it will become increasingly difficult to procure raw materials with low phosphorus content. However, reducing the amount of phosphorus by subjecting the granular iron obtained by the iron-making method disclosed in Patent Document 1 to a further dephosphorization process causes an increase in cost.

JP 2002-339909 A

The present invention has been made in view of such a situation, and an agglomerate formed from a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is charged on a hearth laid with a carbonaceous material. An object of the present invention is to provide a method capable of producing granular iron with a low phosphorus content by reducing and melting iron oxide in the agglomerated material by heating the agglomerated material.

One aspect of the present invention is to charge an agglomerate formed from a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent onto a hearth laid with a carbonaceous material and heat the agglomerate. To produce granular iron by reducing and melting iron oxide in the agglomerated product, the temperature of the agglomerated product in the furnace is in the range from 1200 ° C. to 1500 ° C., and the agglomerated product The oxygen partial pressure in the standard state of the atmospheric gas when the gas is heated is 2.0 × 10 ⁻¹³ atm or more, and the linear velocity of the atmospheric gas in the furnace is 4.5 cm / second or more. It is a manufacturing method.

The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and drawings.

FIG. 1 is a graph showing the relationship between the gas linear velocity and the dephosphorization rate under different oxygen partial pressures. FIG. 2 is a graph showing the relationship between the gas linear velocity and the dephosphorization rate. FIG. 3 is a graph showing the relationship between the oxygen partial pressure and the dephosphorization rate. FIG. 4 is a graph showing the relationship between the time until removal and the dephosphorization rate. FIG. 5 is a graph showing the relationship between the amount of fixed carbon contained in the carbonaceous reducing agent blended in the raw material mixture and the dephosphorization rate.

An agglomerate formed from a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is placed on a hearth laid with a carbonaceous material, and the agglomerate is heated by heating the agglomerate. The metallurgical process for producing granular iron by reducing and melting iron oxide is usually performed in a reducing atmosphere. The reason is that when this process is performed in an oxidizing atmosphere, the reduction of iron oxide contained in the agglomerate is stagnant during heating of the agglomerate, and reduced iron cannot be obtained in a high yield. Because. On the other hand, when this process is performed in a reducing atmosphere, the reduction of iron oxide proceeds. However, when the reduced iron is melted in a reducing atmosphere, the phosphorus contained in the reduced iron hardly transfers to the slag produced as a by-product during the reduction, and remains in the granular iron obtained by melting the reduced iron. As a result, granular iron with a high phosphorus content is obtained. In order to reduce the phosphorus content of the granular iron, the obtained granular iron needs to be supplied to, for example, an electric furnace and further subjected to dephosphorization treatment.

When the agglomerated material is reduced and melted at a high temperature of 1200 to 1500 ° C., reducing gas from the carbonaceous reducing agent is actively generated from the inside of the agglomerated material while the iron oxide in the agglomerated material is reduced. Although it is released, almost no reducing gas is generated while the reduction of iron oxide is almost completed and the reduced iron melts and separates into granular iron and by-product slag. For this reason, the present inventors considered that the component composition of the granular iron while the reduced iron melts and separates into granular iron and by-product slag is greatly influenced by the component composition of the atmospheric gas. Therefore, the present inventors thought that the component composition of the granular iron could be adjusted by appropriately controlling the atmospheric gas while the reduced iron melts and separates into granular iron and by-product slag, and intensive studies are being conducted. Piled up. As a result, the inventors have
(I) The agglomerated material is charged on a hearth laid with a carbonaceous material and heated so that the agglomerated material is in a range from 1200 ° C to 1500 ° C.
(II) The oxygen partial pressure in the standard state of the atmospheric gas when heating the agglomerated material is 2.0 × 10 ⁻¹³ atm or more,
(III) If the linear velocity of the atmospheric gas in the furnace is 4.5 cm / second or more,
It has been found that phosphorus contained in reduced iron can be transferred to slag produced as a by-product during reduction during the melting of reduced iron, and granular iron with a low phosphorus content can be produced, thereby completing the present invention.

Hereinafter, the present invention will be described in accordance with the procedure for producing granular iron.

(I) As an agglomerated material, an agglomerated material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is prepared.

As the iron oxide-containing substance, for example, iron ore, iron sand, non-ferrous smelting residue and the like can be used. As the carbonaceous reducing agent, for example, a carbon-containing substance can be used, and specifically, coal, coke, or the like can be used.

Moreover, a binder, MgO supply substance, CaO supply substance, etc. can be mix | blended with the said raw material mixture as another component. As the binder, for example, a polysaccharide (for example, starch such as wheat flour) can be used. As the MgO supply substance, for example, an Mg-containing substance extracted from MgO powder, natural ore, seawater, or the like, or magnesium carbonate (MgCO ₃ ) can be used. For example, quick lime (CaO) or limestone (main component is CaCO ₃ ) can be used as the CaO supply substance.

The shape of the agglomerated material is not particularly limited. For example, a pellet form or a briquette form can be adopted. The size of the agglomerated material is not particularly limited. From the operational aspect, the particle size (maximum diameter) is preferably 50 mm or less, and preferably about 5 mm or more. If the particle size is large, the heat transfer to the lower part of the pellet is deteriorated, the productivity is lowered, and the granulation efficiency is also deteriorated. Therefore, it is preferable that it is 50 mm or less.

A charcoal material is laid on the hearth to reduce the agglomerates. This carbon material serves as a carbon supply source when the carbon contained in the agglomerated material is insufficient, and also acts as a hearth protective material.

It is recommended that the charcoal material laid on the hearth has a maximum particle size of 2 mm or less. By using a carbonaceous material having a maximum particle size of 2 mm or less, it is possible to prevent the molten slag from flowing down the gaps in the carbonaceous material. As a result, it is possible to prevent the molten slag from reaching the hearth surface and eroding the hearth. The lower limit value of the maximum particle size of the carbon material is preferably about 0.5 mm, for example. By using a carbon material having a lower limit of the maximum particle size of about 0.5 mm, it is possible to suppress the agglomerate from entering the carbon material layer. As a result, it is possible to prevent the heating rate from decreasing and the productivity from decreasing. The carbonaceous material is preferably laid on the hearth with a thickness of about 1 to 5 mm, for example.

Then, the prepared agglomerated material is placed on a hearth laid with a carbonaceous material and heated so that the temperature of the agglomerated material becomes 1200 to 1500 ° C., and iron oxide in the raw material mixture is reduced and melted. The temperature of the agglomerated material is preferably 1250 ° C. or higher. By setting it to 1250 degreeC or more, the fusion | melting time of granular iron and slag can be shortened, the isolation | separation of slag and granular iron can be accelerated | stimulated, and granular iron with high iron purity can be obtained. On the other hand, the temperature of the agglomerated material is preferably 1450 ° C. or lower. By setting the temperature to 1450 ° C. or lower, the structure of the heating furnace is not complicated, and a decrease in thermal efficiency can be suppressed. From the viewpoint of the structure of the heating furnace and the use of energy, it is preferable to produce the target metallic iron nugget at a low temperature. When a burner is used as the heating means in the furnace, the temperature of the agglomerated product can be adjusted by controlling the combustion conditions of the burner. The kind of furnace used by this invention is not specifically limited. For example, a heating furnace or a moving hearth furnace can be used. As the moving hearth furnace, for example, a rotary hearth furnace can be used.

(II and III) The oxygen partial pressure in the standard state of the atmospheric gas when the agglomerate is heated is set to 2.0 × 10 ⁻¹³ atm or more, and the gas linear velocity is set to 4.5 cm / second or more. As a result of various experiments conducted by the present inventors, the phosphorus contained in the reduced iron is oxidized by melting the reduced iron in a slightly oxidizing atmosphere, and this phosphorus migrates to the slag. This is because it has been found that the phosphorus content is reduced. Specifically, when the oxygen partial pressure of the atmosphere gas is less than 2.0 × 10 ⁻¹³ atm or the gas linear velocity is less than 4.5 cm / sec, the oxidation contained in the atmosphere gas in the vicinity of the surface of the agglomerated material. Since the amount of the reactive gas is insufficient, the dephosphorization of the granular iron cannot be promoted. Accordingly, the oxygen partial pressure in the standard state of the atmospheric gas when the agglomerate is heated is 2.0 × 10 ⁻¹³ atm or more, and the gas linear velocity is 4.5 cm / second or more.

The oxygen partial pressure in the standard state of the atmospheric gas is preferably 2.8 × 10 ⁻¹³ atm or more. The higher the oxygen partial pressure, the more the granular iron dephosphorization is promoted. However, if the oxygen partial pressure becomes too high, the granular iron is reoxidized and the iron purity (metalization rate) is lowered. Therefore, the oxygen partial pressure in the standard state is preferably 4.8 × 10 ⁻¹³ atm or less, and more preferably 4.0 × 10 ⁻¹³ atm or less.

The linear velocity of the atmospheric gas in the furnace is preferably 5 cm / second or more. As the gas linear velocity increases, the dephosphorization of granular iron is promoted. However, if the gas linear velocity becomes too high, the granular iron is re-oxidized and the iron yield is lowered. Therefore, the gas linear velocity is preferably 13.5 cm / second or less, and more preferably 9 cm / second or less.

The atmospheric gas when the agglomerated material is heated means an atmospheric gas near the surface of the agglomerated material. The vicinity of the surface of the agglomerated product means a region from the surface of the agglomerated product to a height of 50 mm. The oxygen partial pressure and gas linear velocity of the atmospheric gas in the furnace are often different below the furnace (near the hearth) and above (near the ceiling), so agglomerates that affect the redox reaction of the agglomerates. It is necessary to define the oxygen partial pressure and the gas linear velocity for the atmospheric gas in the vicinity of the surface.

The oxygen partial pressure of the atmospheric gas when the agglomerated material is heated can be calculated by collecting the atmospheric gas near the surface of the agglomerated material and analyzing the gas composition. The linear velocity of the atmospheric gas can be measured using a peat tube or the like.

The oxygen partial pressure of the atmospheric gas can be controlled, for example, by adjusting the amount of oxygen supplied to the burner, adjusting the amount of fuel supplied to the burner, the air ratio, etc., or adjusting the blowing of reducing gas. The linear velocity of the atmospheric gas can be controlled, for example, by adjusting the amount of gas supplied to the burner, adjusting the blowing angle of the burner, or changing the height of the ceiling.

The oxygen partial pressure and the gas linear velocity of the atmospheric gas are adjusted so that they are within the above ranges after the time when the reduced iron starts melting at the latest. This is because the component composition of granular iron is affected by the atmospheric gas composition at the time of melting rather than at the time of solid reduction.

Until the iron oxide contained in the raw material mixture starts to melt, the linear velocity of the atmospheric gas when the agglomerated material is heated is controlled to 5.4 cm / second or less (including 0 cm / second), and melting starts. After that, it is preferable to control the linear velocity of the atmospheric gas when the agglomerated material is heated to 4.5 cm / second or more. Until the iron oxide starts to melt, the reduction reaction takes place actively in the agglomerate, so even if the composition of the atmospheric gas in the furnace is changed, the agglomerate or near the surface of the agglomerate It is difficult to change the composition of the atmospheric gas. On the other hand, as solid reduction approaches completion, carburization into iron begins, the melting point of iron decreases, and melting begins. When iron starts to melt, little gas is generated from the agglomerated material, so the composition of iron is greatly influenced by the composition of the atmospheric gas in the furnace. Therefore, it is preferable to appropriately control the linear velocity of the atmospheric gas until the iron oxide starts melting and when the agglomerated material after the melting starts is heated. The oxygen partial pressure of the atmospheric gas until the iron oxide contained in the raw material mixture starts to melt is preferably 2.8 × 10 ⁻¹³ atm or less.

As described above, in the present invention, it is preferable to control the oxygen partial pressure and the gas linear velocity of the atmospheric gas after the iron oxide starts melting and after the melting starts, but a moving hearth furnace is used as a heating furnace. When used, for example, the partition plate may be suspended from the ceiling in the furnace to divide the furnace into a plurality of zones, and the oxygen partial pressure and gas linear velocity of the atmospheric gas may be controlled in each zone.

As described above, if the oxygen partial pressure and the gas linear velocity of the atmospheric gas during reductive melting are appropriately controlled, the dephosphorization of granular iron can be promoted more effectively than reductive melting in a reducing atmosphere. It is possible to produce granular iron with a low phosphorus content.

In the present invention, the fixed carbon amount contained in the carbonaceous reducing agent to be blended in the raw material mixture with respect to the fixed carbon amount necessary for reducing the iron oxide contained in the iron oxide-containing substance is 98% by mass to 102% by mass. It is preferable to set it as the range. The reason is that if the amount of fixed carbon contained in the carbonaceous reducing agent relative to the amount of fixed carbon necessary for reducing iron oxide is less than 98% by mass, the carbon is insufficient and, as will be described later, it is laid on the hearth. This is because even if reducing gas (CO gas) springs out from the carbonaceous material, the reduction of iron oxide is insufficient. The amount of fixed carbon contained in the carbonaceous reducing agent relative to the amount of fixed carbon necessary for reducing iron oxide is preferably 98% by mass or more, and more preferably 98.5% by mass or more. However, when the amount of fixed carbon contained in the carbonaceous reducing agent becomes excessive, the reducing gas (CO gas) continues to spring out from the agglomerated product by reacting with the atmospheric gas even after the reduction is completed. Therefore, as will be described later, the oxygen partial pressure when the reduced iron melts is lowered, and the dephosphorization rate of the reduced iron is lowered. Therefore, the fixed carbon amount contained in the carbonaceous reducing agent with respect to the fixed carbon amount required for reducing iron oxide is preferably 102% by mass or less, more preferably 101% by mass or less.

In the present invention, it is particularly recommended to adjust the amount of fixed carbon contained in the carbonaceous reducing agent to be slightly deficient with respect to the amount of fixed carbon necessary for reducing iron oxide. The reason is that when the amount of fixed carbon contained in the carbonaceous reducing agent is insufficient, the reduction of granular iron seems to be insufficient, but in the present invention, the agglomerate is located on the carbonaceous material, so This is because the unreduced portion of iron is reduced by the carbon material laid on the hearth.

That is, iron oxide (FeO _x ) contained in the agglomerated material is reduced by the following formulas (1) and (2) using carbon (C) contained in the carbonaceous reducing agent and carbon material laid on the hearth. Is reduced to form granular iron.
FeO _x + xCO → Fe + xCO ₂ (1)
FeO _x + xC → Fe + xCO (2)

As a result of various experiments conducted by the present inventors, when the FeO _{x of the} formula (1) undergoes a molar reaction and the FeO _{x of the} formula (2) undergoes b molar reaction, the proportion shown in the following formula (3) It was found that the reduction reaction proceeds. That is, the formula (3) indicates the number of oxygen atoms that one carbon atom can reduce. In the reduction of FeO _x , direct reduction with carbon (C) occurs about 38% of the whole, and indirect reduction with reducing gas (CO gas) occurs about 72% of the whole.
1.0 ≦ 1 + a / (a + b) ≦ 1.5 (3)

Therefore, the amount of carbon when calculated as one carbon atom necessary for reducing one oxygen atom contained in iron oxide is slightly insufficient because, for example, a carbonaceous reducing agent is blended in the raw material mixture in a small amount. Even if there is, the iron oxide in the agglomerates is sufficiently reduced.

In addition, the amount of fixed carbon contained in the carbonaceous reducing agent is adjusted to be deficient with respect to the amount of fixed carbon necessary for reducing iron oxide, so that iron oxide (FeO) contained in the by-product slag during reduction is reduced. ) Can be produced more, and the dephosphorization reaction when the reduced iron is melted can be promoted. Therefore, the amount of fixed carbon contained in the carbonaceous reducing agent with respect to the amount of fixed carbon necessary for reducing iron oxide is more preferably 100% by mass or less.

What is necessary is just to calculate the fixed carbon amount required in order to reduce | restore iron oxide based on the component composition of a raw material mixture.

In order to separate the molten granular iron and slag, it is necessary to carburize the granular iron to contain about 3% by mass of carbon in order to lower the melting point of the granular iron. However, if the amount of fixed carbon contained in the carbonaceous reducing agent to be blended in the raw material mixture is made insufficient relative to the amount of fixed carbon necessary for reducing iron oxide, the amount of fixed carbon contained in the granular iron is insufficient. Therefore, it becomes impossible to melt the granular iron. Therefore, if the carbon material is laid on the hearth and the amount of fixed carbon contained in the carbon material is made larger than the amount of fixed carbon necessary for reducing iron oxide, the amount of fixed carbon supplied to the granular iron is increased. The molten granular iron and slag can be separated.

It is preferable to adjust the amount of fixed carbon contained in the carbon material laid on the hearth to a range from 2% by mass to 5% by mass with respect to the amount of fixed carbon required for reducing iron oxide. . The kind of charcoal material laid on the hearth is not particularly limited. For example, a carbon-containing material used as the carbonaceous reducing agent can be used.

In the present invention, it is also preferable to adjust the composition of the raw material mixture so that the agglomerate has a basicity of slag by-produced during the reduction of iron oxide in the range of 1.0 to 1.6. The reason is that when the basicity of the slag is less than 1.0, the dephosphorization reaction does not proceed when the reduced iron melts, and the P content of the granular iron cannot be reduced. Accordingly, the basicity is preferably 1.3 or more, and more preferably 1.4 or more. However, if the basicity of the slag becomes too high, the melting point of the slag becomes too high, and when the reduced iron is melted, the slag is not melted, so that the separation between the granular iron and the slag is deteriorated. As a result, slag is caught in granular iron, and the quality of granular iron falls. Accordingly, the basicity is preferably 1.6 or less.

The basicity of slag is a value [(CaO) / (SiO ₂ )] calculated from the amount of CaO and the amount of SiO ₂ contained in the slag.

Hereinafter, the present invention will be described in more detail with reference to examples. The following examples are not intended to limit the present invention, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the preceding and following descriptions, all of which fall within the technical scope of the present invention. included.

In this example, each agglomerate formed from a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent was produced in a laboratory, and each agglomerate was heated in a furnace of a carbonaceous material. Each granular iron was manufactured by charging into the floor and heating the agglomerated material to reduce and melt the iron oxide in the agglomerated material. At this time, the composition of the agglomerated material and the reducing and melting conditions were variously changed. Specifically, it is as follows.

As the iron oxide-containing substance, two types of iron ore (n) having a low phosphorus content and iron ore (hpb) having a high phosphorus content were used. The component composition of iron ore (n) and iron ore (hpb) is shown in Table 1 below. As the carbonaceous reducing agent, two kinds of coal (p) having a low phosphorus content and coal (b) having a high phosphorus content were used. The component composition of coal (p) and coal (b) is shown in Table 2 below.

Additives were blended into the iron ore shown in Table 1 below and the coal shown in Table 2 below, and pelletized agglomerates (test materials) having a particle size of 18 to 20 mm were prepared. The blended additives are wheat flour added as a binder, MgO, CaO, and the like. Table 3 below shows the composition of the test material (percentage of the weighed value).

Table 3 below shows percentage target values of the amount of fixed carbon contained in the carbonaceous reducing agent blended in the raw material mixture with respect to the amount of fixed carbon necessary for reducing iron oxide. Table 3 below shows target values of basicity of slag produced as a by-product during reduction.

Table 4 below shows the component composition of the test materials. In Table 4 below, the test material (1) is a low phosphorus content pellet, and the test materials (2) to (5) are high phosphorus content pellets.

The test materials shown in Table 4 below are charged into the furnace of the hearth where each charcoal material is laid, and the iron oxide in the raw material mixture is reduced and melted by heating, and the granular iron and slag are completely The product was taken out into the cooling zone at the time when it was separated, and each granular iron was produced. The number of specimens charged into the furnace was 30. On the hearth, 130 g of anthracite having a maximum particle size of 2 mm or less was spread as a charcoal material. A large amount of charcoal was laid around to protect the hearth.

The test material charged in the furnace was heated so that the temperature of the test material became 1450 ° C. using a heater provided in the furnace.

In the furnace, the linear velocity of the atmospheric gas when the specimen is heated (the linear velocity of the atmospheric gas in the vicinity of the specimen) is controlled in the range of 1.35 to 20.27 cm / sec. The oxygen partial pressure of the atmospheric gas during heating (the oxygen partial pressure of the atmospheric gas in the vicinity of the specimen) was controlled in the range of 0 to 5.057 × 10 ⁻¹³ atm. The gas linear velocity and oxygen partial pressure are shown in Table 5 or Table 6 below. The gas linear velocity is a value in a standard state.

The gas linear velocity was calculated from the amount of gas supplied and the cross-sectional area at the sample installation part in the furnace. The oxygen partial pressure was calculated by the following procedure.

The combustion reaction of carbon is represented by the following equation (4), and the standard free energy of formation ΔF in this reaction is represented by the following equation (5).
C (graphite) + O ₂ (g) = CO ₂ (g) (4)
ΔF = −94640 + 0.05 × T (cal / mol) (5)

On the other hand, the standard free energy of formation ΔF for this reaction is expressed by the following equation (6) using the partial pressure P _{CO2 of} carbon dioxide gas in the atmospheric gas and the partial pressure P _{O2 of} oxygen gas in the atmospheric gas. .
ΔF = −RT × log (P _CO2 / P _O2 ) (6)

1450 ° C is the absolute temperature
1450 (° C.) + 273 = 1723 (K)
Therefore, the relationship between the partial pressure of carbon dioxide gas and the oxygen partial pressure of the atmospheric gas at 1450 ° C. is as follows from the above equations (5) and (6).

log (P _CO2 / P _O2 ) = 11.995
P _CO2 / P _O2 = 9.887 × 10 ¹¹

Here, by measuring the partial pressure of carbon dioxide gas in the atmospheric gas,
For example, when P _CO2 = 0.5 is measured, the partial pressure of oxygen gas in the atmospheric gas is
P _O2 = 5.0571 × 10 ⁻¹³
Is obtained.

The component composition of the obtained granular iron and the component composition of the slag produced as a by-product when the granular iron is generated are shown in Tables 5 and 6 below. In addition, among the component compositions of granular iron shown in Tables 5 and 6 below, the amount of Fe shows a calculated value obtained by subtracting the alloy elements and the amount of impurities from the whole (100% by mass).

In Table 6, No. No. 30 shows the result of taking out the granular iron 1 minute earlier than the time when separation of the slag and granular iron is completed. 31 shows the result of taking out granular iron from the furnace after hold | maintaining for 3 minutes from the time of completion | finish of isolation | separation of slag and granular iron. In Tables 5 and 6, no. 30 and no. Samples other than 31 show the results of taking out granular iron from the furnace when one minute has passed since the separation of slag and granular iron was completed.

When the center temperature of the test material is measured, it is about 1300 ° C. (No. 30) at a point one minute earlier than the separation of slag and granular iron, and 1 after the separation of slag and granular iron is completed. The temperature was about 1400 ° C. when a minute elapsed, and about 1450 ° C. (No. 31) when held for 3 minutes after the separation of slag and granular iron was completed.

In addition, the CO ₂ gas fraction in the vicinity of the specimen is from 1 minute earlier than the separation of slag and granular iron to the point of holding for 3 minutes after the separation of slag and granular iron is completed. Was almost constant. On the other hand, CO gas from the test material was slightly observed at one minute earlier than the separation of slag and granular iron, but after the separation of slag and granular iron was partially completed, No CO gas was detected from the specimen.

Based on the component composition of the test material and the component composition of the granular iron, the phosphorus removal rate was calculated by the following formula.

Based on the data in Tables 4 and 5, the relationship between the gas linear velocity and the dephosphorization rate under different oxygen partial pressures is shown in FIG. In FIG. 1, the symbol ◇ indicates the result when the oxygen partial pressure is 0 atm, the symbol ▲ indicates the result when the oxygen partial pressure is 1.011 × 10 ⁻¹³ atm, and the symbol × indicates the oxygen partial pressure is 1.517 × 10 ⁻¹³ atm. The symbol ◯ indicates the result when the oxygen partial pressure is 3.034 × 10 ⁻¹³ atm, and the symbol ■ indicates the result when the oxygen partial pressure is 5.057 × 10 ⁻¹³ atm.

As can be seen from FIG. 1, when the atmosphere gas contains oxygen, the dephosphorization rate increases as the linear velocity of the atmosphere gas when the specimen is heated is increased. Then, for example, in a gas linear velocity 5.41Cm / sec test material (3), increasing the partial pressure of oxygen in the atmosphere gas from 1.517 × ¹⁰ -13 atm to 3.034 × ¹⁰ -13 atm It can be seen that when the oxygen partial pressure of the atmospheric gas is increased, the phosphorus removal rate increases with the same specimen and the same gas linear velocity so that the phosphorus removal rate increases. When the oxygen partial pressure of the atmospheric gas is 0 atm (that is, in a nitrogen gas atmosphere), the phosphorus removal rate is not affected by the gas linear velocity. When the gas linear velocity is less than 5 cm / second, the result of the dephosphorization rate is reversed as compared with the case where the oxygen partial pressure of the atmospheric gas is 1.517 × 10 ⁻¹³ atm. It is considered that errors and sample variations have an effect.

From the above results, in order to increase the phosphorus removal rate, it is effective to increase the gas linear velocity and the oxygen partial pressure of the atmospheric gas to a predetermined value or more.

Next, among the results in which the oxygen partial pressure shown in Table 6 is 3.034 × 10 ⁻¹³ atm, No. For 24, 25 and 32, the relationship between the gas linear velocity and the dephosphorization rate is shown in FIG. Comparing FIG. 2 with FIG. 1 above, it can be seen that, even if the amount of phosphorus contained in the test material changes, when the oxygen partial pressure is constant, the dephosphorization rate increases as the gas linear velocity increases. Although not shown, for example, no. The same can be seen from 2, 4 and 6.

Next, among the results where the gas linear velocity shown in Table 6 is 5.41 cm / second, No. FIG. 3 shows the relationship between the oxygen partial pressure and the dephosphorization rate for 25, 27, 28, and 29. As can be seen from FIG. 3, when the gas linear velocity is constant, the dephosphorization rate increases as the oxygen partial pressure increases. It can also be seen that the dephosphorization rate hardly changes when the oxygen partial pressure is up to 1.517 × 10 ⁻¹³ atm. Although not shown, for example, no. From 3, 4 and 5, it can be seen that when the gas linear velocity is constant, the dephosphorization rate increases as the oxygen partial pressure increases.

Next, among the results shown in Table 6 where the oxygen partial pressure was 3.034 × 10 ⁻¹³ atm and the gas linear velocity was 5.41 cm / sec, No. For 25, 30, and 31, the relationship between the time until the granular iron is taken out and the dephosphorization rate is shown in FIG. FIG. 4 shows the time when the reduced iron is melted and the time when the slag and the granular iron are completely separated is 0 minute, and the time from when the granular iron separated from the slag is taken out of the furnace is changed. Shows the change in the dephosphorization rate. As is apparent from FIG. 4, it can be seen that the dephosphorization rate decreases when heating is continued as it is after the slag and granular iron are separated.

In FIG. 4, the highest dephosphorization rate is when the removal time is “−1 minute”. This “−1 minute” means that the slag and granular iron were removed from the furnace before they were separated. This is a condition that cannot be adopted in actual operation.

Next, of the results shown in Table 6, No. FIG. 5 shows the relationship between the amount of fixed carbon contained in the carbonaceous reducing agent blended in the raw material mixture and the dephosphorization rate for 21, 22, and 25. As is clear from FIG. 5, the amount of fixed carbon contained in the carbonaceous reductant blended in the raw material mixture is insufficient relative to the amount of fixed carbon necessary for reducing iron oxide. It can be seen that the phosphorus rate is higher.

On the other hand, when the amount of fixed carbon contained in the carbonaceous reducing agent blended in the raw material mixture with respect to the amount of fixed carbon necessary for reducing iron oxide is contained in excess of 102% by mass, the dephosphorization rate is lower. I understand that This is thought to be due to the fact that the amount of reducing gas flowing out increases in the process of melting reduced iron, so that the effect of increasing the gas linear velocity is impaired.

No. As is clear from the result of No. 22, the amount of fixed carbon contained in the carbonaceous reducing agent to be blended in the raw material mixture is insufficient with respect to the amount of fixed carbon necessary for reducing the iron oxide contained in the test material. However, after dephosphorization has progressed, the amount of carbon contained in the charcoal laid on the hearth is adjusted to a range of 2 to 5% by mass with respect to the amount of fixed carbon required to reduce iron oxide. It can be seen that the remaining iron oxide is stably reduced by the carbon material laid on the hearth.

As described above in detail, one aspect of the present invention is to charge an agglomerate formed from a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent onto a hearth laid with a carbonaceous material, A method of producing granular iron by reducing and melting iron oxide in the agglomerate by heating the agglomerate, wherein the temperature of the agglomerate in the furnace is from 1200 ° C. to 1500 ° C. The oxygen partial pressure in the standard state of the atmospheric gas when the agglomerated material is heated is 2.0 × 10 ⁻¹³ atm or more, and the linear velocity of the atmospheric gas in the furnace is 4.5 cm. It is the manufacturing method of the granular iron which makes it / second or more.

In the present invention, the agglomerated material after the reduction is melted in a state where the oxygen partial pressure and the gas linear velocity of the atmospheric gas are controlled to the above conditions, so that the phosphorus contained in the reduced iron is transferred to the slag produced as a by-product during the reduction. be able to. As a result, the amount of phosphorus contained in the granular iron obtained by melting reduced iron is reduced.

In the method for producing granular iron, the amount of fixed carbon contained in the carbonaceous reducing agent with respect to the amount of fixed carbon necessary for reducing the iron oxide is in a range from 98% by mass to 102% by mass. It is preferable to adjust the composition of the raw material mixture. Thereby, the reduction reaction of iron oxide proceeds more actively, and granular iron with less phosphorus content is obtained.

In the method for producing granular iron, it is preferable to adjust the composition of the raw material mixture so that the basicity of slag produced as a by-product during reduction of the iron oxide is in the range of 1.0 to 1.6. As a result, the dephosphorization reaction proceeds faster, and granular iron having a lower phosphorus content is obtained.

In the method for producing granular iron, the amount of fixed carbon contained in the carbonaceous reducing agent with respect to the amount of fixed carbon necessary for reducing the iron oxide is in a range from 98% by mass to 100% by mass. Is preferred. As a result, the amount of fixed carbon contained in the carbonaceous reducing agent becomes insufficient with respect to the amount of fixed carbon necessary for reducing iron oxide, and the amount of iron oxide (FeO) contained in the byproduct slag during reduction is reduced. Many can be generated. As a result, the dephosphorization reaction at the time of melting of the reduced iron is further promoted, so that the dephosphorization rate of the reduced iron can be further increased.

In the method for producing granular iron, until the iron oxide starts melting, the linear velocity of the atmospheric gas is set to 5.4 cm / second or less (including 0 cm / second), and the iron oxide starts melting. The linear velocity of the atmospheric gas is preferably 4.5 cm / second or more. By adjusting the linear velocity of the atmospheric gas when the agglomerate is heated, until the melting of iron oxide starts and after the melting starts, until the melting of iron oxide starts The reduction reaction in the agglomerated material proceeds actively, and on the other hand, after the melting has started, the melting of iron can proceed stably.

In the method for producing granular iron, the amount of fixed carbon contained in the carbonaceous material laid on the hearth with respect to the amount of fixed carbon necessary for reducing the iron oxide ranges from 2% by mass to 5% by mass. In addition, the maximum particle size of the carbon material is preferably 2 mm or less. Thereby, the amount of fixed carbon supplied to the granular iron can be increased, and the molten granular iron and slag can be separated, and the molten slag can be prevented from flowing down through the gap between the carbonaceous materials and eroding the hearth.

If the method for producing granular iron of the present invention is used, it is possible to stably produce granular iron with a low phosphorus content.

Claims

An agglomerate formed from a raw material mixture containing an iron oxide-containing substance and a carbonaceous reducing agent is placed on a hearth laid with a carbonaceous material, and the agglomerate is heated by heating the agglomerate. A method for producing granular iron by reducing and melting iron oxide,
The temperature of the agglomerate in the furnace is in the range of 1200 ° C. to 1500 ° C., and the oxygen partial pressure in the standard state of the atmospheric gas when the agglomerate is heated is 2.0 × 10 −13 atm. The method for producing granular iron is characterized in that the linear velocity of the atmospheric gas in the furnace is 4.5 cm / second or more.
The composition of the raw material mixture is adjusted so that the amount of fixed carbon contained in the carbonaceous reducing agent with respect to the amount of fixed carbon necessary for reducing the iron oxide is in the range from 98% by mass to 102% by mass. The manufacturing method according to claim 1.
The production method according to claim 1, wherein the composition of the raw material mixture is adjusted so that the basicity of the slag produced as a by-product during the reduction of the iron oxide is in the range of 1.0 to 1.6.
The production method according to claim 1, wherein the amount of fixed carbon contained in the carbonaceous reducing agent with respect to the amount of fixed carbon necessary for reducing the iron oxide is in a range from 98% by mass to 100% by mass.
Until the iron oxide starts to melt, the linear velocity of the atmospheric gas is set to 5.4 cm / second or less (including 0 cm / second), and after the iron oxide starts to melt, the linear velocity of the atmospheric gas is increased. The manufacturing method of Claim 1 which makes 4.5 or more cm / sec.
The amount of fixed carbon contained in the carbon material laid on the hearth with respect to the amount of fixed carbon necessary for reducing the iron oxide is in a range from 2% by mass to 5% by mass, and the maximum of the carbon material. The production method according to any one of claims 1 to 5, wherein the particle size is 2 mm or less.