NON-FIRED PELLETS FOR REDUCTION AND METHOD FOR PRODUCING SAME

Abstract

Non-fired pellets are used in a solid reduction furnace and are effective in preventing clustering by reducing the possibility of contact between low-melting-temperature slags and thus preventing the fusion therebetween. A method produces such non-fired pellets. Non-fired pellets for reduction, in which the proportion of high-viscosity slag components (Al.sub.2O.sub.3+MgO+SiO.sub.2) to the total Fe (T.Fe) satisfies an expression: (Al.sub.2O.sub.3+MgO+SiO.sub.2)/T.Fe0.12, and a method for producing the same. In the expression, Al.sub.2O.sub.3 represents the concentration (mass %) of Al.sub.2O.sub.3 in the non-fired pellets, MgO represents the concentration (mass %) of MgO in the non-fired pellets, SiO.sub.2 represents the concentration (mass %) of SiO.sub.2 in the non-fired pellets, and T.Fe represents the concentration (mass %) of T.Fe in the non-fired pellets.

Claims

1. Non-fired pellets for reduction, wherein a proportion of high-viscosity slag components (Al.sub.2O.sub.3+MgO+SiO.sub.2) to total Fe (T.Fe) satisfies the following Expression (1): $\begin{array}{cc}\left({\mathrm{Al}}_2{O}_3+\mathrm{MgO}+{\mathrm{SiO}}_2\right)/T.Math.\mathrm{Fe}0\text{.12},& \left(1\right)\end{array}$ where Al.sub.2O.sub.3 represents a concentration (mass %) of Al.sub.2O.sub.3 in the non-fired pellets, MgO represents a concentration (mass %) of MgO in the non-fired pellets, SiO.sub.2 represents a concentration (mass %) of SiO.sub.2 in the non-fired pellets, and T.Fe represents a concentration (mass %) of T.Fe in the non-fired pellets.

2. Non-fired pellets for reduction, wherein a proportion of high-viscosity slag components (Al.sub.2O.sub.3+MgO+SiO.sub.2) to total Fe (T.Fe) satisfies the following Expression (2): $\begin{array}{cc}\left({\mathrm{Al}}_2{O}_3+\mathrm{MgO}+{\mathrm{SiO}}_2\right)/T.Math.\mathrm{Fe}0\text{.15},& \left(2\right)\end{array}$ where Al.sub.2O.sub.3 represents a concentration (mass %) of Al.sub.2O.sub.3 in the non-fired pellets, MgO represents a concentration (mass %) of MgO in the non-fired pellets, SiO.sub.2 represents a concentration (mass %) of SiO.sub.2 in the non-fired pellets, and T.Fe represents a concentration (mass %) of T.Fe in the non-fired pellets.

3. A method for producing the non-fired pellets for reduction according to claim 1, further comprising using an iron-containing raw material formulated to achieve an average LOI (Loss on Ignition) of 5% or more.

4. The method for producing the non-fired pellets for reduction according to claim 3, wherein the iron-containing raw material has been pretreated for removal of crystal water in advance so as to achieve an average LOI (Loss on Ignition) of 2% or less.

5. The method for producing the non-fired pellets for reduction according to claim 3, wherein a mixed raw material containing 4 mass % to 24 mass % M.Fe is prepared by mixing a raw material containing M.Fe and is granulated.

6. The method for producing the non-fired pellets for reduction according to claim 5, wherein the raw material is reduced iron with a particle size of 3 mm or less that has been reduced in a solid reduction furnace.

7. The method for producing the non-fired pellets for reduction according to claim 6, wherein the reduced iron contains 79 mass % or more M.Fe.

8. A method for producing the non-fired pellets for reduction according to claim 2, further comprising using an iron-containing raw material formulated to achieve an average LOI (Loss on Ignition) of 5% or more.

9. The method for producing the non-fired pellets for reduction according to claim 8, wherein the iron-containing raw material has been pretreated for removal of crystal water in advance so as to achieve an average LOI (Loss on Ignition) of 2% or less.

10. The method for producing the non-fired pellets for reduction according to claim 4, wherein a mixed raw material containing 4 mass % to 24 mass % M.Fe is prepared by mixing a raw material containing M.Fe and is granulated.

11. The method for producing the non-fired pellets for reduction according to claim 8, wherein a mixed raw material containing 4 mass % to 24 mass % M.Fe is prepared by mixing a raw material containing M.Fe and is granulated.

12. The method for producing the non-fired pellets for reduction according to claim 9, wherein a mixed raw material containing 4 mass % to 24 mass % M.Fe is prepared by mixing a raw material containing M.Fe and is granulated.

13. The method for producing the non-fired pellets for reduction according to claim 10, wherein the raw material is reduced iron with a particle size of 3 mm or less that has been reduced in a solid reduction furnace.

14. The method for producing the non-fired pellets for reduction according to claim 11, wherein the raw material is reduced iron with a particle size of 3 mm or less that has been reduced in a solid reduction furnace.

15. The method for producing the non-fired pellets for reduction according to claim 12, wherein the raw material is reduced iron with a particle size of 3 mm or less that has been reduced in a solid reduction furnace.

16. The method for producing the non-fired pellets for reduction according to claim 13, wherein the reduced iron contains 79 mass % or more M.Fe.

17. The method for producing the non-fired pellets for reduction according to claim 14, wherein the reduced iron contains 79 mass % or more M.Fe.

18. The method for producing the non-fired pellets for reduction according to claim 15, wherein the reduced iron contains 79 mass % or more M.Fe.

Description

BRIEF DESCRIPTION OF DRAWING

[0030] FIG. 1 is a graph illustrating the relationship between (Al.sub.2O.sub.3+MgO+SiO.sub.2)/T.Fe and LOI of Australian iron ore that is an iron-containing raw material to be mixed.

DESCRIPTION OF EMBODIMENTS

[0031] A solid reduction furnace used in the present invention is a furnace for reducing fed non-fired pellets for reduction to Fe having a reduction degree of 90% or more by using a hydrogen gas, etc., as a reducing gas. In the operation of such a solid reduction furnace, the properties of raw material fed into the furnace, that is, the non-fired pellets are important.

[0032] What is most important for the non-fired pellets is whether the pellets can be prevented from contacting or fusing with each other, which would otherwise result in clustering, in a high-temperature zone (500 to 800 C.) of the solid reduction furnace as described above. In response to such demand, in the present invention, studies have been made on the relationship between an iron-containing raw material such as metallic iron, iron oxide such as iron ore, iron sulfide, or ironmaking dust and high-viscosity slag components, that is, viscous components. As a result, from the viewpoint of the fluidity of the various raw materials in the furnace, it is found preferable to appropriately manage the relationship particularly between the iron-containing raw material and high-viscosity slag components. That is, the high-viscosity slag is always controlled to be generated in the furnace so that an undesirable flow in the high-temperature zone is suppressed. This can prevent the fusion between slags, thereby preventing clustering.

[0033] As described previously, in the present invention, it has been found to be effective to include the high-viscosity slag components in a given ratio in an iron-containing raw material, iron ore, or an auxiliary material to be mixed.

[0034] As the components that can be the high-viscosity slag, focus is placed on (Al.sub.2O.sub.3, MgO, and SiO.sub.2), in particular. When the total content of such components is maintained at a predetermined ratio relative to the total iron (T.Fe), it becomes possible to effectively prevent the slag-to-slag fusion caused in the furnace.

[0035] This can be achieved when the non-fired pellets for reduction have a component composition such that the high-viscosity slag components (Al.sub.2O.sub.3+MgO+SiO.sub.2) are contained in a given ratio relative to the total iron (T.Fe) in the iron-containing raw material. That is, when the non-fired pellets satisfy the relationship of Expression (1) below.

[00003]$\begin{array}{cc}\left({\mathrm{Al}}_2{O}_3+\mathrm{MgO}+{\mathrm{SiO}}_2\right)/T.Math.\mathrm{Fe}0\text{.12}& \left(1\right)\end{array}$

[0036] In Expression (1) above, Al.sub.2O.sub.3 represents the concentration (mass %) of Al.sub.2O.sub.3 in the non-fired pellets for reduction. MgO represents the concentration (mass %) of MgO in the non-fired pellets for reduction. SiO.sub.2 represents the concentration (mass %) of SiO.sub.2 in the non-fired pellets for reduction. T.Fe represents the total Fe concentration (mass %) in the non-fired pellets for reduction.

[0037] In the present invention, there exists a more preferable relationship between the high-viscosity slag components (Al.sub.2O.sub.3+MgO+SiO.sub.2) and the total iron (T.Fe) from the viewpoint of preventing the contact or fusion between the slags in the high-temperature zone of the furnace, which is Expression (2) below. The relationship indicates that the high-viscosity slag components are contained in a higher amount.

[00004]$\begin{array}{cc}\left({\mathrm{Al}}_2{O}_3+\mathrm{MgO}+{\mathrm{SiO}}_2\right)/T.Math.\mathrm{Fe}0\text{.15}& \left(2\right)\end{array}$

[0038] In Expression (2) above, Al.sub.2O.sub.3 represents the concentration (mass %) of Al.sub.2O.sub.3 in the non-fired pellets for reduction. MgO represents the concentration (mass %) of MgO in the non-fired pellets for reduction. SiO.sub.2 represents the concentration (mass %) of SiO.sub.2 in the non-fired pellets for reduction. T.Fe represents the total Fe concentration (mass %) in the non-fired pellets for reduction.

[0039] Note that in the present invention, the total Fe in the iron-containing raw material refers to the total value of the iron concentrations including the concentrations of metallic iron (M.Fe) and iron compounds (iron oxide, iron sulfide, calcium ferrite, etc.). Meanwhile, the high-viscosity slag components refer to the total value of the concentrations of Al.sub.2O.sub.3, MgO, and SiO.sub.2 contained in the iron-containing raw material, such as iron ore or ironmaking dust; an auxiliary material (limestone, quicklime, dolomite, etc.); and a binder (bentonite, etc.).

[0040] The Al.sub.2O.sub.3, MgO, and SiO.sub.2 concentrations can be determined as follows. First, the Al concentration, Mg concentration, and Si concentration are measured by elemental analysis such as fluorescent X-ray analysis, for example. Then, each oxide concentration can be determined by multiplying the element concentration thus determined by (the molecular weight of the oxide per element/atomic weight). Specifically, for example, the Al.sub.2O.sub.3 concentration can be determined by multiplying the Al concentration measured by elemental analysis, such as fluorescent X-ray analysis, by (the Al.sub.2O.sub.3 molecular weight/2)/the Al atomic weight=50.98/26.98=1.890.

[0041] Next, the method for producing the non-fired pellets according to the present invention will be described. When producing the non-fired pellets for reduction according to the present invention, in order for the non-fired pellets to satisfy the above relationship between the high-viscosity slag components (Al.sub.2O.sub.3+MgO+SiO.sub.2) and the total iron (T.Fe), for example, it is possible to use an iron ore originally having a composition of components satisfying the above relationship, or to selectively use and mix a plurality of iron ores to satisfy the above relationship. For example, one or more of iron ores (A to Z) shown in FIG. 1, which are Australian iron ores, may be mixed, followed by granulation with a binder, such as bentonite, and an auxiliary material, such as quicklime, added thereto as appropriate.

[0042] When feeding the above non-fired pellets into the solid reduction furnace and reducing the pellets therein it is critical that these pellets do not have properties that would cause clustering in a high-temperature reducing atmosphere in the furnace. Therefore, in the present invention, focus is placed particularly on LOI (Loss on Ignition), the appropriate value of which has been studied. That is, in the production method according to the present invention, some of the types of iron ore (A to Z) shown in FIG. 1 are selectively used (mixed) to achieve a LOI (Loss on Ignition) value of 5% or more so that LOI5% is satisfied, thereby reducing clustering more effectively. This is because when volatile components, such as crystal water, in the pellets are heated in the reduction furnace to undergo disassociation and vaporization, and then dissipate to the outside of the pellets, the volume of the mineral phases remaining in the pellets is reduced, resulting in voids between the adjacent mineral phases.

[0043] Next, in the production method according to the present invention, in order for the iron-containing raw material to achieve the relation LOI5%, it is preferable to apply a pretreatment such as a process for removing crystal water to the iron ore to be used in advance so as to achieve LOI2%. This is because since many iron-containing raw materials such as raw material iron ore have a high crystal water content, pellets often burst during granulation due to water vapor generated from the crystal water. Thus, it would be unavoidable to increase the temperature slowly. This would reduce productivity.

EXAMPLES

Embodiment 1

[0044] The Examples (including Comparative Examples) show how the relationship between T.Fe and high-viscosity slag components (Al.sub.2O.sub.3+MgO+SiO.sub.2) in non-fired pellets for reduction affects the clustering in a solid reduction furnace.

[0045] As the iron-containing raw material, i.e., iron ore used herein, mainly one or more types of Australian iron ores shown in FIG. 1 were mixed with an auxiliary material and reagent (e.g., commercially available Al.sub.2O.sub.3 reagent) as appropriate. Table 1 shows examples of the component compositions of the mixtures.

[0046] Specifically, non-fired pellet were produced by adding 5 mass % cement to obtain predetermined components, grinding the mixture with a ball mill, granulating the resultant with a pelletizer while adding water to achieve a size of 9 to 16 mm, and then curing the resultant for two weeks.

[0047] All raw materials including one or more types of the Australian raw materials (A to Z shown in FIG. 1) described above and having the compositions shown in Table 1 were ground in a ball mill and granulated with a pelletizer while adding water to achieve a size of 9 to 16 mm. Then, the obtained non-fired pellets after granulation were cured for two weeks to produce the final non-fired pellets. Each of the obtained non-fired pellets shown in Table 1 was evaluated using a clustering index.

(Clustering Evaluation Test)

[0048] A sample weighing 500 g was fed into a vertical cylindrical furnace with a diameter of 100 mm and heated to 1000 C. in an N.sub.2 atmosphere. When the temperature of the sample reached 1000 C., a reducing gas was introduced into the furnace at a rate of 24 NL/min. The composition of the reducing gas was set to a volume ratio of H.sub.2:N.sub.2=20:80. The sample was then loaded at a rate of 1 kg/cm.sup.2 and held in this state for three hours, followed by cooling in an N.sub.2 atmosphere, so that reduced iron was produced. The reduced iron obtained was then sieved through a 16 mm sieve mesh, which is the maximum size of a single non-fired pellet, to measure the weight Wa (g) of the non-fired pellets remaining on the sieve. The non-fired pellets remaining on the sieve were put into a cylindrical shape vessel (132 mm700 mmL) of an I-type testing machine and were rotated at a rotational speed of 30 rpm for five minutes, to measure the weight Wb (g) of the non-fired pellets remaining on the sieve mesh of 16 mm. The non-fired pellets were evaluated based on a clustering index that is proportional to the non-crushing clustering proportion Wb/Wa.

[0049] The porosity of the non-fired pellets was evaluated by measuring the apparent density of the pellets and then measuring the real density of the pellets. As shown in Table 1, it is confirmed that each of the non-fired pellets of Examples 1 to 6 in which (Al.sub.2O.sub.3+MgO+SiO.sub.2)/T.Fe is 0.12 or more has a clustering index of 15 or less, and thus has excellent properties.

TABLE-US-00001 TABLE 1 LOI(%) of Iron (Al.sub.2O.sub.3 + MgO + Clustering Ore Before Firing SiO.sub.2)/T.Fe Index Comparative 0.3 0.06 43 Example 1 Comparative 0.4 0.09 21 Example 2 Example 1 5.1 0.12 4 Example 2 7.2 0.15 0 Example 3 8.8 0.21 0 Example 4 10.1 0.12 15 Example 5 3.8 0.12 0 Example 6 1.5 0.12 0

[0050] Note that Table 2 below shows the component composition of the non-fired pellets obtained in Examples 1 and 2 of Table 1.

TABLE-US-00002 TABLE 2 (mass %) T.Fe FeO SiO.sub.2 CaO Al.sub.2O.sub.3 MgO C/S Example 1 59.9 0.2 4.1 4.4 2.7 0.6 0.4 Example 2 57.7 0.4 5.8 6.0 2.3 0.5 0.6

Embodiment 2

[0051] Reduced iron (a sample when Wa was measured) obtained by the same method as the method of Comparative Example 2 shown in Table 1 (clustering evaluation test) of Embodiment 1 was ground into particles with a size of 3 mm or less. Then, the obtained particles were mixed with the unfired raw material of Comparative Example 2. The mixture was used to produce non-fired pellets by the method of Embodiment 1. Then, after the non-fired pellets were cured for two weeks, the crushing strength of the resulting non-fired pellets was measured.

[0052] The results are shown in Table 3 below. M.Fe in Table 3 below is derived from metallic iron (M.Fe) contained in the reduced iron. In Examples 10 to 12, reduced iron containing M.Fe=78 mass % was used. In Example 13, reduced iron containing M.Fe=80 mass % was used. As a result, it was found that mixing M.Fe with the raw material can increase the strength of the resulting pellets. Since clustering is promoted as the amount of powder increases, it is possible to suppress clustering by increasing the strength of the non-fired pellets. The reason why mixing M.Fe with the raw material can increase the strength of the resulting non-fired pellets is considered as follows. The reduced iron powder is exposed to air during the curing period, which in turn oxidizes the metallic iron and generates heat, thus promoting fusion between adjacent particles. Therefore, the effect of increasing the strength of the resulting non-fired pellets by mixing M.Fe with the raw material starts to show after two days from the start of granulation, and the increase in the strength almost stops after four weeks from the start of granulation.

TABLE-US-00003 TABLE 3 M.Fe (Al.sub.2O.sub.3 + MgO + Pellet Strength (%) SiO.sub.2)/T.Fe (kgf) Comparative 0 0.09 52 Example 2 Example 10 4 0.09 67 Example 11 8 0.09 88 Example 12 24 0.09 112 Example 13 8 0.12 91

[0053] In this specification, the unit L of volume represents 10.sup.3 m.sup.3. Symbol N added to the unit of the volume of a gas represents the volume of the gas in the standard state, that is, at a temperature of 0 C. and a pressure of 101325 Pa. The unit rpm of a rotational speed represents the number of rotations per min.

INDUSTRIAL APPLICABILITY

[0054] The non-fired pellets for solid reduction according to the present invention are the method that has been developed to be mainly applied to a hydrogen-based direct reduction process. However, as a matter of course, such non-fired pellets can also be used as a raw material for use in a blast furnace, etc.