WO2024070135A1 - Iron ore pellet production method - Google Patents

Abstract

Provided is an iron ore pellet production method, whereby high-strength iron ore pellets can be obtained, and it is possible to contribute to carbon neutrality. This iron ore pellet production method comprises: a mixing step for mixing iron ore having a total Fe content of 63 mass% or less, solid carbon, a binder, and auxiliary raw materials to obtain a mixture; a granulation step for granulating the mixture to obtain green pellets; and a firing step for firing the green pellets by heating the green pellets from the inside by burning the solid carbon while heating the green pellets from the outside by burning CH₄ gas, to obtain iron ore pellets, wherein the solid carbon includes carbon generated from at least one selected from the group consisting of CO₂ gas, CO gas, and CH₄ gas.

Description

How iron ore pellets are made

The present invention relates to a method for producing iron ore pellets.

Iron ore pellets are produced by granulating iron ore powder to have properties (e.g., size, strength, reducibility, etc.) suitable for feeding into a blast furnace or a solid reduction furnace. Iron ore pellets are generally produced by the following steps: mixing iron ore powder, a binder, and any auxiliary material to obtain a mixture; granulating the mixture to obtain green pellets; and firing the green pellets to obtain iron ore pellets. In this specification, pellets as granulated before firing are referred to as "green pellets." Here, as described in Non-Patent Document 1, it is known to add a carbonaceous material such as anthracite to the mixture. In the firing step, natural gas containing _CH4 gas as a main component is burned to heat the green pellets, and the heat generated by this combustion is transferred from the surface of the green pellets to the inside. For this reason, the heating inside the pellets may be insufficient, leading to a decrease in strength. Therefore, in order to compensate for the heat inside the pellets, a carbonaceous material such as anthracite is added to the green pellets, and the carbonaceous material is burned in the firing step to heat the green pellets from the inside.

Volodymyr Shatokha, "Iron Ores and Iron Oxide Materials", IntechOpen, published July 11, 2018, pp. 41-59

Ensuring the strength of green pellets, and therefore the strength of iron ore pellets, is important to prevent the green pellets from powdering during handling before being placed in the sintering furnace, and the powder from adhering to the inside of the furnace, and there is a constant demand for improvements.

In addition, in response to the recent public opinion of reducing _CO2 emissions, a carbon-neutral ironmaking method is desired. In the production of iron ore pellets, the main cause of _CO2 emissions is the combustion of _CH4 gas and carbonaceous materials in the firing process. As a method for producing iron ore pellets without _CO2 emissions, it has been proposed to use non-fired green pellets as iron ore pellets by using organic and inorganic binders. However, non-fired green pellets have the following quality problems. When an organic binder is heated to a high temperature, carbonization or a gasification reaction with _CO2 accompanying carbonization (C + _CO2 → 2CO) occurs, so it cannot exist as a binder, and it is assumed that it is difficult to express the binder characteristics when the organic binder is used at a high temperature. In addition, silicates (sodium silicate, calcium silicate) are listed as inorganic binders, but silicate itself needs to be separated as slag from pig iron or molten steel in either the pig iron making or steel making process, and excess heat is required to melt the pig iron. In addition, there is also the problem that the inorganic binder is discharged as slag, i.e., excess material. Furthermore, while sodium in sodium silicate is solid at low temperatures, it vaporizes at 1000°C or less, so it is avoided as a substance that remains in a blast furnace. There has been no known technology aiming at carbon neutrality on the premise of producing iron ore pellets through a firing process.

In view of the above problems, the present invention aims to provide a method for producing iron ore pellets that can produce high-strength iron ore pellets and contribute to carbon neutrality.

In order to achieve this objective, the present inventors have focused on improving the carbonaceous material added to the green pellets. That is, they have come up with the idea of using solid carbon containing carbon generated from one or more selected from the group consisting of _CO2 gas, CO gas, and _CH4 gas as the carbonaceous material added to the green pellets. In this case, although _CO2 is generated by burning the carbonaceous material, the above-mentioned greenhouse gas is consumed as the raw material of the carbonaceous material, which contributes to carbon neutrality. In addition, according to the research of the present inventors, it has been found that the strength of iron ore pellets is unexpectedly increased by using solid carbon ( _carbonaceous material) containing carbon generated from one or more selected from the group consisting of _CO2 gas, CO gas, and CH4 gas.

The gist of the present invention, which was completed based on the above findings, is as follows:

[1] A mixing step of mixing iron ore having a total Fe content of 63% by mass or less, solid carbon, a binder, and auxiliary materials to obtain a mixture;
a granulation step of granulating the mixture to obtain green pellets;
a calcination step of calcining the green pellets by burning _CH4 gas to heat the green pellets from the outside and burning the solid carbon to heat the green pellets from the inside to obtain iron ore pellets;
having
The method for producing iron ore pellets, wherein the solid carbon comprises carbon generated from one or more selected from the group consisting of _CO2 gas, CO gas, and _CH4 gas.

[2] The method for producing iron ore pellets according to [1], wherein the solid carbon comprises carbon produced from one or both of _CO2 gas and CO gas.

[3] The method for producing iron ore pellets according to [1], wherein the _CH4 gas used in the production of the carbon includes _CH4 gas produced from one or both of _CO2 gas and CO gas.

[4] The method for producing iron ore pellets according to any one of [1] to [3], wherein the carbon includes carbon produced using iron as a catalyst.

[5] The method for producing iron ore pellets according to any one of [1] to [4], wherein the proportion of the carbon in the solid carbon is 10 mass% or more.

[6] The method for producing iron ore pellets according to any one of [1] to [5], wherein the CH ₄ gas used in the calcination step contains CH ₄ gas produced from one or both of CO ₂ gas and CO gas.

The method for producing iron ore pellets of the present invention makes it possible to obtain high-strength iron ore pellets and contributes to carbon neutrality.

1 shows a schematic diagram of a vertical reactor used in a carbon production test using CO gas as a raw material. Photographs showing the appearance of (a) sintered ore and (b) solid carbon after a carbon generation test are shown. 1(a) and (b) show schematic diagrams of an apparatus used in a carbon production test using _CH4 gas as a raw material. 6(a) to 6(c) show the results of TEM observation of the solid carbon obtained in each carbon production test.

Below, an embodiment of the method for producing iron ore pellets according to the present invention will be described. Note that the embodiment described below is one example of the present invention, and the configuration of the present invention is not limited to this specific example.

The method for producing iron ore pellets according to one embodiment of the present invention includes a mixing step of mixing iron ore, solid carbon (carbonaceous material), binder, and auxiliary materials to obtain a mixture, a granulation step of granulating the mixture to obtain green pellets, and a firing step of burning the solid carbon to heat the green pellets from the inside while burning _CH4 gas to heat the green pellets from the outside to obtain iron ore pellets. The solid carbon is characterized in that it contains carbon generated from one or more selected from the group consisting of _CO2 gas, CO gas, and _CH4 gas.

The mixture used to manufacture iron ore pellets consists of iron ore, solid carbon, binder, and auxiliary materials. In this embodiment, the iron ore contains iron with a total Fe content (T.Fe) of 63% by mass or less. Iron ore with a T.Fe content of 63% by mass or less is inexpensive and suitable for manufacturing.

The amount of solid carbon in the iron ore pellets is preferably 0.80% by mass or more relative to the amount of iron ore in the iron ore pellets in order to fully obtain the strength-improving effect of the green pellets. On the other hand, if an excessive amount of solid carbon is contained, excessive heat will be generated during the firing process, causing the iron ore pellets to melt. Therefore, the amount of solid carbon in the iron ore pellets is preferably 2.00% by mass or less relative to the amount of iron ore in the iron ore pellets.

The solid carbon includes carbon generated from one or more selected from the group consisting of _CO2 gas, CO gas, and _CH4 gas. That is, carbon generated from one or more selected from the group consisting of _CO2 gas, CO gas, and _CH4 gas is used as the carbonaceous material (solid carbon) to be added to the green pellets. In this case, although _CO2 is generated by burning the carbonaceous material, the greenhouse gas is consumed as the raw material of the carbonaceous material, which contributes to carbon neutrality. In addition, by adding carbon generated from one or more selected from the group consisting of _CO2 gas, CO gas, and _CH4 gas to the green pellets, the effect of increasing the strength of the green pellets and iron ore pellets can be obtained.

The proportion of the above carbon in the solid carbon added to the green pellets is preferably 10 mass% or more, more preferably 50 mass% or more, and most preferably 100 mass%. The greater the amount of the above carbon, the greater the effect of increasing strength and the greater the contribution to carbon neutrality. In addition, if the proportion of the above carbon in the solid carbon added to the green pellets is less than 100 mass%, the remainder of the solid carbon may be, for example, anthracite.

The solid carbon preferably contains carbon generated from one or both of _CO2 gas and CO gas. In addition, when the solid carbon contains carbon generated from _CH4 gas, the _CH4 gas used in generating the carbon preferably contains _CH4 gas generated from one or both of _CO2 gas and CO gas. The reaction for generating solid carbon from _CO2 gas, CO gas, or _CH4 gas is not particularly limited, but examples of the reaction include the following.

[Reaction to produce solid carbon from CO gas]
Solid carbon may be produced from CO gas by the Boudouard reaction shown in reaction formula (1). The Boudouard reaction makes it possible to produce solid carbon from CO gas at temperatures of about 700° C. or lower.
2CO=C+ _CO2 (1)

Solid carbon may be produced from CO gas by the reverse water-gasification reaction shown in reaction formula (2). The reverse water-gasification reaction makes it possible to produce solid carbon from CO gas at approximately 650° C. or lower.
CO + H ₂ = C + H ₂ O ... (2)

_CH4 gas may be produced from CO gas by the methanation reaction shown in reaction formula (3), and solid carbon may be produced from _CH4 gas by the thermal decomposition reaction shown in reaction formula (4). The methanation reaction can produce _CH4 gas from CO gas at approximately 650°C or lower, and the thermal decomposition reaction can produce solid carbon from _CH4 gas in air at approximately 500°C or higher.
CO+ _3H2 = _CH4 + _H2O ... (3)
_CH4 =C+ _2H2 ... (4)

Solid carbon may be produced from CO gas by the decomposition reaction shown in reaction formula (5). The decomposition reaction makes it possible to produce solid carbon from CO gas under low oxygen partial pressure.
2CO=2C+ _O2 (5)

[Reaction to produce solid carbon from _CO2 gas]
Solid carbon may be produced from _CO2 gas by the reverse water-gasification reaction shown in reaction formula (6). The reverse water-gasification reaction can produce solid carbon from _CO2 gas at approximately 650° C. or lower.
CO ₂ + 2H ₂ = C + 2H ₂ O ... (6)

CO gas may be produced from _CO2 gas by the reverse water gas shift reaction shown in reaction formula (7), and solid carbon may be produced from CO gas by the reverse water gasification reaction shown in reaction formula (2). The reverse water gas shift reaction can produce CO gas from _CO2 gas at about 850°C or higher.
CO ₂ + H ₂ = CO + H ₂ O ... (7)
CO + H ₂ = C + H ₂ O ... (2)

The methanation reaction shown in reaction formula (8) may generate _CH4 gas from _CO2 gas, and the thermal decomposition reaction shown in reaction formula (4) may generate solid carbon from _CH4 gas. The methanation reaction can generate _CH4 gas from _CO2 gas at approximately 600°C or lower.
_CO2 + _4H2 = _CH4 + _2H2O ... (8)
_CH4 =C+ _2H2 ... (4)

Solid carbon may be produced from _CO2 gas by the decomposition reaction shown in reaction formula (9). The decomposition reaction can produce solid carbon from _CO2 gas under low oxygen partial pressure.
_CO2 = C + _O2 ... (9)

[Reaction to produce solid carbon from _CH4 gas]
Solid carbon may be produced from _CH4 gas by the pyrolysis reaction shown in reaction formula (4).
_CH4 =C+ _2H2 ... (4)

The gas used in the carbon production reaction may be any one of _CO2 gas, CO gas, or _CH4 gas, a mixed gas of two or more of the above three types of gases, or a mixed gas of one or more of the above three types of gases with _H2 gas, _N2 gas, etc. For example, a mixed gas of CO: 31%, _H2 : 19%, and _N2 : 50% by volume may be used.

As the solid carbon to be added to the green pellets, any one of carbon produced from _CO2 gas, carbon produced from CO gas, and carbon produced from _CH4 gas may be used alone, or two or more of them may be mixed and used.

The solid carbon is preferably produced using iron as a catalyst. It is known that iron can be used as a catalyst in the Boudouard reaction shown in reaction formula (1) and the thermal decomposition reaction of _CH4 shown in reaction formula (4). It is also known that iron oxide can be used as a catalyst in the reverse water gas shift reaction shown in reaction formula (7). Therefore, when producing solid carbon, sintered ore or direct reduced iron may be charged into a furnace, and the iron or iron oxide contained in the sintered ore or direct reduced iron may be used as a catalyst. In addition, in a high-temperature reaction such as the thermal decomposition reaction of _CH4 shown in reaction formula (4), alumina may be charged into the furnace to maintain the temperature inside the furnace.

The solid carbon is preferably in a fibrous form, and preferably has an aspect ratio (length/diameter) of 10 or more. When the solid carbon is in a fibrous form, the strength of the iron ore pellets is preferably obtained. The solid carbon may also be in a spherical form. When the solid carbon is in a spherical form, the binder effect of the fine particles is obtained, and the strength of the iron ore pellets is preferably obtained. When the solid carbon is in a spherical form, the cumulative particle size D90 is preferably about 10 to 50 μm. The solid carbon (carbon material) generated from one or more selected from the group consisting of _CO2 gas, CO gas, and _CH4 gas preferably has a carbon content of 50 mass% or more, and the balance may contain Fe, FeO, etc.

Bentonite is preferred as a binder for iron ore pellets, but any known or arbitrary binder that provides a similar effect, such as organic or inorganic binders, may also be used. In order to fully obtain the effect of the binder, it is preferred that the binder be contained in an amount of 0.1 mass% or more relative to the amount of iron ore in the iron ore pellets. On the other hand, if an excessive amount of binder is contained, not only will the manufacturing cost increase, but the effect will decrease as the content increases. Therefore, it is preferred that the binder be contained in an amount of 4.0 mass% or less relative to the amount of iron ore in the iron ore pellets.

The iron ore pellets may be mixed with auxiliary materials such as quicklime, limestone (CaCO ₃ ), and dolomite (CaMg(CO ₃ ) ₂ ). The basicity of the iron ore pellets is adjusted by the auxiliary materials. The basicity of the iron ore pellets is calculated based on the weight ratio of CaO/SiO ₂ contained in the iron ore pellets. The basicity of the iron ore pellets is preferably 0.01 to 1.5.

The iron ore pellets are manufactured by the general crushing, mixing, granulation, and firing processes. The crushing process may use a crusher such as a general ball mill. The mixing process may use a general concrete mixer or high-speed agitating mixer. The granulation process may use a general pelletizer or drum mixer.

The Blaine index of the iron ore after pulverization is preferably about 2000 to 4000 ^cm2 /g. The Blaine index is measured using a Blaine air permeability device specified in JIS R 5201:2015 and represents the specific surface area of the powder. In the pellet manufacturing process, the Blaine index is used as a control index for the particle size of the ore, and the higher this value, the finer the powder.

The granulated green pellets preferably have a particle size of about 9.5 to 12 mm. If the particle size of the green pellets is less than 9.5 mm, the air permeability will be reduced when they are filled into a blast furnace as fired pellets. If the particle size of the green pellets exceeds 12 mm, the reducibility will decrease.

The firing step may be performed using a general rotary kiln or electric furnace. In the firing step, _CH4 gas is burned to heat the green pellets from the outside, while solid carbon is burned to heat the green pellets from the inside. The firing conditions are preferably a furnace temperature of 1200 to 1350°C and a holding time at the furnace temperature of 5 to 30 minutes.

From the viewpoint of carbon neutrality, the _CH4 gas used in the calcination step preferably contains _CH4 gas generated from one or both of _CO2 gas and CO gas. There are no particular limitations on the method for generating _CH4 gas, and it may be generated, for example, by the methanation reaction shown in reaction formulas (3) and (8).
_CO2 + _4H2 = _CH4 + _2H2O ... (8)
CO+ _3H2 = _CH4 + _H2O ... (3)

Iron ore, binder, and auxiliary materials were prepared as raw materials for iron ore pellets. The components of the iron ore used are shown in Table 1. The iron ore was dried at 105°C for 24 hours and then crushed to obtain iron ore powder with a Blaine index of 2560 ^cm2 /g and a volume average diameter of 95 µm. Bentonite was prepared as the binder, and limestone was prepared as the auxiliary material.

Next, a test was conducted to generate solid carbon from CO gas or _CH4 gas. Details are described below. In addition, anthracite was prepared as solid carbon that was not generated from any of CO gas, _CO2 gas, and _CH4 gas. The anthracite was prepared in particulate form with a particle size of 1 mm or less and a C content of 85 mass%.

[Carbon production test from CO gas]
Carbon was generated from CO gas using a vertical reactor. Figure 1 shows a schematic diagram of a vertical reactor. An alumina support 12, an alumina ball 14, and sintered ore 16 were charged in the order shown in the figure into a furnace core tube 10 with an inner diameter of φ80 mm. A gas containing 31% CO, 19% H ₂ , and 50% N ₂ (hereinafter referred to as CO mixed gas) was introduced from a gas inlet tube 18 at 550°C or 800°C (heated by a heater 20, measured by a thermocouple 22) for 3 hours at a gas flow rate of 17 L/min to generate solid carbon. The iron contained in the sintered ore was used as a catalyst for carbon generation.

The reduced sample was sieved through a 0.125 mm sieve to separate it into sintered ore and solid carbon. The reduced sample contained 1.5 wt% solid carbon. Figure 2 shows photographs of (a) sintered ore and (b) solid carbon after a carbon generation test from CO mixed gas at 800°C. The solid carbon is a fine powder, and the cumulative particle sizes were measured to be D10: 2.1 μm, D50: 6.61 μm, and D90: 14.8 μm. In other words, more than 90% of the cumulative number of powder particles had a particle size of 14.8 μm or less. Table 2 shows the results of the component analysis of the solid carbon.

[Carbon production test from _CH4 gas]
Carbon was generated from _CH4 gas using the apparatus shown in Figures 3(a) and (b). First, 30 g (about 20 to 30 pieces) of direct reduced iron (DRI) 32 obtained by reducing iron ore pellets having a diameter of 10 mm as a catalyst was charged into the electric furnace 30 shown in Figure 3(a), and 100% CH4 gas was flowed in from the gas inlet 34 under the conditions of 900 ° C. for 1 h and a gas flow rate of 1.0 L / min to generate solid carbon. Next, 500 g of alumina balls ₃₈ having a diameter of 6 mm were charged into the furnace core tube (alumina tube) 36 having a diameter of 80 mm shown in Figure 3(b), a uniform zone having a height of about 50 mm was formed, and 100% _CH4 gas was flowed in from the gas inlet 40 under the conditions of a gas temperature of 1400 (± 10) ° C. (heated by a heater 42) for 1 h and a gas flow rate of 1.0 L / min to generate solid carbon. The reduced samples obtained in each test were sieved through a 0.125 mm sieve to separate the DRI or alumina balls from the solid carbon.

Table 3 shows the morphology and carbon content of the solid carbon and anthracite produced under each condition. FIG. 4 shows the TEM observation results of (a) solid carbon produced from CO mixed gas at 550°C, (b) solid carbon produced from _CH4 gas at 900°C, and (c) solid carbon produced from _CH4 gas at 1400°C. The solid carbon obtained in the reaction at 900°C or less was fibrous and had an aspect ratio of 10 or more. The solid carbon obtained in the reaction at 1400°C was spherical and had a particle size of about 0.2 to 2.0 μm. This is thought to be because, at 1400°C, the reaction is high due to the high temperature, and carbon production in the gas phase occurs as the main reaction, but at 900°C or less, the thermal decomposition reaction of _CH4 gas is difficult to proceed, and the production reaction using iron as a catalyst occurs as the main reaction.

1000g of iron ore powder was prepared, and various solid carbons were added in the amounts shown in Table 4 relative to the amount of iron ore, and 1% by mass of bentonite was added relative to the amount of iron ore. In addition, limestone was added in an amount set so that the basicity of the iron ore pellets was 0.1, and the mixture was mixed for 3 minutes at 20 rpm using a concrete mixer. The amount of solid carbon in No. 2 to 7 was set so that the amount of carbon contained in the anthracite in No. 1 was the same as that contained in the anthracite. The ratio of carbon contained in the anthracite to carbon contained in solid carbon 1 to 4 is shown in the "carbon replacement rate" in Table 4. Next, the mixed raw materials were placed in a 1.2mφ pelletizer and granulated while adding water. Pellet particles with a particle size of 9.5 to 12 mm were collected and further rolled in the pelletizer for 10 minutes to obtain green pellets.

[Drop strength measurement of green pellets]
In each of the invention examples and comparative examples, ten green pellets were subjected to drop strength measurements, simulating transportation, charging, and the like during actual operation. The green pellets were repeatedly dropped from a height of 50 cm, and the test was terminated when cracks or breakage were confirmed in the green pellets. The number of times before the test was terminated (i.e., the number of times when cracks or breakage were confirmed) was taken as the drop strength, and the average drop strength of the ten pellets is shown in Table 3.

Green pellets not used in the above test were charged into an electric furnace and fired. In an air atmosphere, the temperature was raised at 10°C/min, held at 1300°C for 10 minutes, and then lowered at 10°C/min. After lowering the temperature, the sample was taken out to obtain iron ore pellets. In the firing process in actual operation, natural gas mainly composed of _CH4 gas is burned to heat the green pellets, but in this test, an electric furnace was used to simulate this heating.

[Measuring the crushing strength of iron ore pellets]
In each of the invention examples and comparative examples, the crushing strength (kgf) of 10 iron ore pellets was measured using an autograph. The displacement speed was 2 mm/min, and the average value for the 10 pellets is shown in Table 3.

From Table 4, it can be seen that the invention examples are superior to the comparative examples in both the drop strength of the green pellets and the crushing strength of the iron ore pellets. In addition to the above, by replacing the solid carbon from the conventional anthracite with carbon generated from one or more selected from the group consisting of _CO2 gas, CO gas, and _CH4 gas, it is possible to contribute to reducing _CO2 emissions, and the effect of the present invention is clear. Furthermore, it is clear that carbon neutrality can be achieved in the production of iron ore pellets by using _CH4 gas generated from one or both of _CO2 gas and CO gas in the carbon generation and firing process with the solid carbon replacement rate set to 100 mass%.

The present invention provides a method for producing iron ore pellets that can produce high-strength iron ore pellets and contribute to carbon neutrality.

REFERENCE SIGNS LIST 10 furnace core tube 12 alumina support 14 alumina ball 16 sintered ore 18 gas inlet tube 20 heater 22 thermocouple 30 electric furnace 32 DRI reduced from iron ore pellets
34 Gas inlet 36 Furnace core tube 38 Alumina ball 40 Gas inlet 42 Heater

Claims (6)

A mixing step of mixing iron ore having a total Fe content of 63 mass% or less, solid carbon, a binder, and auxiliary materials to obtain a mixture;
a granulation step of granulating the mixture to obtain green pellets;
a calcination step of calcining the green pellets by burning _CH4 gas to heat the green pellets from the outside and burning the solid carbon to heat the green pellets from the inside to obtain iron ore pellets;
having
The method for producing iron ore pellets, wherein the solid carbon comprises carbon generated from one or more selected from the group consisting of _CO2 gas, CO gas, and _CH4 gas. 2. The method of claim 1, wherein the solid carbon comprises carbon produced from one or both of _CO2 gas and CO gas. 2. The method of claim 1, wherein the _CH4 gas used in producing the carbon comprises _CH4 gas produced from one or both of _CO2 gas and CO gas. The method for producing iron ore pellets according to any one of claims 1 to 3, wherein the carbon includes carbon produced using iron as a catalyst. The method for producing iron ore pellets according to any one of claims 1 to 4, wherein the proportion of carbon in the solid carbon is 10 mass% or more. The method for producing iron ore pellets according to any one of claims 1 to 5, wherein the _CH4 gas used in the calcination step comprises _CH4 gas produced from one or both of _CO2 gas and CO gas.

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