Title of Invention

REFRACTORY COMPOSITION FOR CONSTRUCTION DOME PORTION OF FLUIDIZED BED REDUCTION FURNACE FOR REDUCTION OF IRON ORE

Abstract

The present invention relates to refractory composition for construction of a dome portion of a fluidized bed reduction furnace for reduction of iron ore powder in a FINEX process which is a new iron production method, to provide castable refractory having properties of corrosion resistance so as to be chemically stable in a reductive gas environment, thermal impact resistance, and mechanical strength. For this, the refgractory composition includes 1.5 - 2.5wt% of silica SiO2, below 0.05wt% of Fe2O3, 8-11 wt% of CaO, and balance of alumina AI2O3, to make up 100wt% of the refractory composition.

Full Text

REFRACTORY COMPOSITION FOR CONSTRUCTING DOME PORTION OF FLUIDIZED BED REDUCTION FURNACE FOR REDUCTION OF IRON ORE Technical Field The present invention relates to refractories for constructing a dome portion of a fluidized bed reduction furnace for reduction of iron ore powder, and more particularly, to a refractory composition of castable refractories having high strength, good abrasion resistance, good chemical resistance against reductive gas, good thermal impact resistance, and good workability for constructing a dome portion of a fluidized bed reduction furnace for use in the FINEX process. Background Art In the modern steel production, an indirect method is used, in which molten iron prepared at first is subjected to decarbonization, to produce steel. The molten iron is produced by a blast furnace method, in which coke is used as fuel. FIG. 1 illustrates a diagram for describing a method for producing iron by using the blast furnace method schematically, wherein iron ore passes through a pretreatment process in which the iron ore is crushed, concentrated, briquetted of iron ore powder, sintered, to form hard pellets that are lumps of a predetermined size chargeable into the blast furnace, when coke from flaming coal is used as fuel. The pellets and the coke are charged into the blast furnace, and fired to produce the molten iron. Though the blast furnace method is used as the best iron production method for mass production of iron presently, the blast furnace method costs high due to complicated processes, and requirements for additional separate large sized facilities for sintering ore and cokes production, and causes a problem of discharging sulfur oxides SOx, nitrides NOx, carbon dioxide CO2, and the like, which are environment pollution substances, from the sintering ore and coke production. Equipment is developed by POSCO, a Korean steel production company, in which the production method of the blast furnace method is changed to reduce natural state iron ore powder directly by fluidized reaction without the pretreatment of the iron ore and coke, of which patent was filed with Korean patent application No. 10-1995- 41931, patented with a Korean Patent registration No. 10-236160, of which process is named as FINEX process, and the equipment is constructed and put into test operation, recently. FIG 2 illustrates a diagram of the FINEX process, an iron production process, having the present invention applied thereto schematically, and FIG 3 illustrates an enlarged view of the fluidized bed reduction furnace in FIG 2. The FINEX process is a new iron production process for producing the molten iron economically, in which iron ore powder is reduced step by step through many stages of the fluidized bed reduction furnaces 1, and charges into a melting furnace 3 together with 8~50mm sized briquette coal, to form molten iron, wherein iron ore powder with a grain size of about 8mm is passed through many stages of fluidized bed reduction furnaces 1, to change into reduced iron ore, formed into pellets(HCI ; Hot Compact Iron), and charged into the melting furnace. The fluidized bed reduction furnace with a closed dome portion 4 is provided with a distribution plate 2 supported on columns (not shown) inside of the fluidized bed reduction furnace. The distribution plate is a member provided for making uniform distribution of high pressure, high temperature reductive gas introduced into the inside of the fluidized bed reduction furnace to fluidize and reduce the iron ore powder, and has a plurality of pass through holes for pass of gas. The dome portion 4 of the fluidized bed reduction furnace can be formed by attachment of refractory to a dome frame, when, since the refractory can not be brought into the inside of the fluidized bed reduction furnace 1 directly, the refractory is required to be sprayed by means of a gunning machine of the fluidized bed reduction furnace. It is required that the refractory construction of the gunning machine is stable even in a high pressure, high temperature reductive gas environment, and endures even under rapid rise and drop of temperature. Therefore, the refractory sprayed by the gunning machine to construct the dome 4 of the fluidized bed reduction furnace 1 is a material having chemical resistance, particularly, corrosion resistance against CO gas, thermal impact resistance, and mechanical strength. Since the FINEX process equipment is the first one in the world, there has been no related art material for construction of the dome portion 4 yet. However, high alumina basis castable material was used in an experimental equipment, which causes a problem of shrinkage and cracking to break away during service due to poor CO gas resistance, and thermal impact resistance during service. Therefore, since the reaction furnace is not for small sized experimental equipment, but for full scale commercial production equipment for production of one million tones yearly, the material of the dome portion 4 is required to have no chemical reaction with the reductive gas and various components of the iron ore in the vicinity of 600 ~ 1000°C during service, good abrasion resistance in a high temperature, high speed fluidized condition of the iron ore powder, and good thermal impact resistance enough to endure fast temperature rise and drop following re-operation of the equipment because cracks occur, not in a continuous operation, but in an intermittent operation. Moreover, the dome portion 4 of the fluidized bed reduction furnace 1 can not be formed completely at a place outside of the furnace 1 in a refractory state, and mount it on the furnace 1 in view of structural nature of design, but be formed by attaching the refractory to a dome frame of the dome 4. Therefore, it is required that workability of the refractory is secured as a material of a non-fixed form that enables spraying by the gunning machine, and there is no deformation of the structure even during curing and drying process after construction or no burst of the structure during construction because the dome is a large sized construction. Since a more rigorous service condition, particularly, thermal impact caused by rapid rise and drop of a temperature of, not the experimental equipment, but commercial equipment, is foreseen, a material for the dome portion is required to meet product design criteria of a structural density of below 2.55, dry compression strength of 750kg/cm2 or higher at a service temperature, over 30% of porosity, CO gas resistance higher than A-B grade of ASTM C288. Disclosure of Invention An object of the present invention is to provide a refractory composition, which is different from related art experimental refractory composition, for constructing a dome portion of a fluidized bed reaction furnace, which has corrosion resistance so as to be chemically stable in a reductive gas environment, thermal impact resistance, and mechanical strength at the time iron ore powder having a wide range of grain size distribution is reduced in many steps by fluidized bed reduction furnaces. The object of the present invention can be achieved by providing refractory composition for constructing a dome portion of a fluidized bed reduction furnace for reduction of iron ore powder including 1.5 ~ 2.5wt% of silica SiO2, below 0.05wt% of Fe2O3, 8 ~ 11wt% of CaO, and balance of alumina Al2O3, to make up 100wt% of the refractory composition. Brief Description of the Accompanying Drawings The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings; FIG 1 illustrates a diagram for describing a method for producing iron by using the blast furnace method schematically; FIG 2 illustrates a diagram an iron production process of the FINEX process having the present invention applied thereto schematically; and FIG 3 illustrates an enlarged view of the fluidized bed reduction furnace in FIG. Best Mode for Carrying Out the Invention Final refractory composition of the present invention has 1.5 ~ 2.5wt% of silica SiO2, below 0.05wt% of Fe2O3, 8 ~ 11wt% of CaO, and balance of alumina A12O3, to make up 100wt% of the refractory composition, wherein contents of the silica SiO2, and Fe2O3 are defined for securing workability and the CO gas resistance because spray workability by using a spray gun becomes poor at a silica SiO2 content of below 1.5wt%, and CO gas resistance at high temperature, and high pressure becomes poor, or sintering shrinkage at a high temperature occurs due to free silica components at a silica content higher than 2.5wt%, to drop the thermal impact resistance. The Fe2O3 is for the CO gas resistance, and content below 0.05wt% is preferable. The CaO is CaO content in a material, for an example, in a case of using alumina cement. Below 8wt% of the CaO causes to fail in securing workability (i.e., regardless of kind of cement used or regardless of kind of CaO in a raw material used), resulting to drop attachment ratio in the construction, to increase rebound loss, to fail in securing a required strength. Over 11wt% of CaO content causes relative drop of the alumina A12O3 content to result in drop of strength at a high temperature, to make the thermal impact resistance poor, even if workability and strength can be secured. As a main component of alumina Al2O3, sintered or melted alumina may be used, and since the fluidized bed reduction furnace 1 having the present invention applied thereto is used in a strong reductive environment, it is preferable that the alumina content is higher than 95%. With reference to a whole composition of 100wt%, it is hot preferable that the alumina content, the main component, is too low, that increases contents of other sub- components (rest of components excluding the main component) to fail to obtain above described properties, and that increases the CaO content to drop the strength, and opposite to this, if the alumina content, the main component, is too high, that decreases contents of other sub-components relatively, to fail to meet required properties, and increases the density to drop the porosity below 30%. The refractory composition of the present invention, a material for constructing the dome portion 4-of the fluidized bed reduction furnace 1 for reduction of iron ore powder, is an alumina basis refractory composition having properties of a structural density of below 2.55, 30% or higher porosity at 1000°C, 750kg/cm2 or over dry compression strength, below 10% of dome construction rebound loss, and A ~ B grade or higher CO gas resistance with reference to ASTM C288. Table 1 below shows comparison of refractory composition for construction of a dome portion of the fluidized bed reduction furnace of a FINEX process applied to experimental equipment (comparative example), and a commercial equipment (embodiment). Table 1 The gunning machine used in spraying the refractory composition of the present invention in construction of the dome portion 4 of the fluidized bed reduction furnace 1 has an air discharge pressure 2kg/cm or higher, and a water discharge pressure 2kg/cm2 or higher. Industrial Applicability Since the alumina basis refractory obtained from the refractory composition of the present invention permits to secure workability required for basic design, and has properties of 30% or over of porosity at 1000°C, 750kg/cm2 or over of dry compression strength, 10% or below of dome construction rebound loss, and A ~ B grade of CO gas resistance with reference to ASTM C288, the dome portion of the fluidized bed reduction furnace of the refractory composition prevents deformation of the structure during curing or construction process or burst during construction, and has properties of a corrosion resistance so as to be chemically stable in a reductive gas environment, thermal impact resistance, and mechanical strength, thereby providing very high industrial applicability. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. What is Claimed is: 1. A refractory composition for constructing a dome portion of a fiuidized bed reduction furnace for reduction of iron ore powder comprising 1.5 ~ 2.5wt% of silica SiO2, below 0.05wt% of Fe2O3, 8 ~ 11wt% of CaO, and balance of alumina A12O3, to make up 100wt% of the refractory composition. The present invention relates to refractory composition for construction of a dome portion of a fluidized bed reduction furnace for reduction of iron ore powder in a FINEX process which is a new iron production method, to provide castable refractory having properties of corrosion resistance so as to be chemically stable in a reductive gas environment, thermal impact resistance, and mechanical strength. For this, the refgractory composition includes 1.5 - 2.5wt% of silica SiO2, below 0.05wt% of Fe2O3, 8-11 wt% of CaO, and balance of alumina AI2O3, to make up 100wt% of the refractory composition.

Documents:

249-KOLNP-2006-FORM-27.pdf

249-kolnp-2006-granted-abstract.pdf

249-kolnp-2006-granted-assignment.pdf

249-kolnp-2006-granted-claims.pdf

249-kolnp-2006-granted-correspondence.pdf

249-kolnp-2006-granted-description (complete).pdf

249-kolnp-2006-granted-drawings.pdf

249-kolnp-2006-granted-examination report.pdf

249-kolnp-2006-granted-form 1.pdf

249-kolnp-2006-granted-form 18.pdf

249-kolnp-2006-granted-form 3.pdf

249-kolnp-2006-granted-form 5.pdf

249-kolnp-2006-granted-gpa.pdf

249-kolnp-2006-granted-reply to examination report.pdf

249-kolnp-2006-granted-specification.pdf