REFRACTORY COMPOSITION FOR CONSTRUCTING STRUCTURE IN FLUIDIZED BED REDUCTION FURNACE FOR REDUCTION OF IRON ORE Technical Field The present invention relates to refractories for constructing a structure in a fluidized bed reduction furnace for reduction of iron ore powder by fluidized reaction, and more particularly, to refractory composition for constructing a structure in a fluidized bed reduction furnace for use in the FINEX process, which is a new iron production 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 equipment for sintering and coke production, and causes a problem of discharging sulfur oxides SOx, nitrides NOx, carbon dioxide C02, and the like, which are environment pollution substances, from the sintered steel 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 a section of a key portion of the fluidized bed reduction furnace in FIG. 2 in detail. The FINEX process is a new iron production process for producing the molten iron economically, in which iron ore powder having a wide range of grain size distribution is reduced step by step through many stages of the fluidized bed reduction furnaces 1, and charges into a melting furnace 2 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.

In view of structure, the fluidized bed reduction furnace 1 is provided with a body 11 having a gas supply opening ll a in a lower portion for supplying a reductive gas, a plurality of vertical columns 12 in an inside space of the body, and a distribution plate 13 supported on the columns such that a plurality of portions of the distribution plate 13 are balanced and supported at the same time.

The column 12 simply supports the distribution plate 13, and the distribution plate 13 distributes the high temperature, high pressure reductive gas supplied to the inside space of the body 11 through the gas supply opening lla, to fluidize and reduce the iron ore, wherein, because the columns 12 and the distribution plate 13 can not, but

be exposed to the high temperature, high pressure reductive gas in the inside space of the body 11, the columns 12 and the distribution plate 13 are formed of a refractory material which has good chemical resistance, good thermal impact resistance, good mechanical strength, and good abrasion resistance, and the like.

In the meantime, the columns 12 and the distribution plate 13 have a plurality of pass through holes 12a and 13a respectively, for smooth flow and pass of the gas for fluidizing and reducing the iron ore powder.

Since the columns 12 and the distribution plate 13 are structures of a reaction furnace which is not for small sized experimental equipment, but for full scale commercial production equipment, the material of the columns 12 and the distribution plate 13 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 which is a main service temperature of the columns 12 and the distribution plate 13 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, since the columns 12 and the distribution plate 13 are required to be formed in various shapes of structures depending on design of the equipment, the material of the columns 12 and the distribution plate 13 is required to have no fixed form to enable formation to any shape, and, since most of the equipment is large sized construction, the material of the columns 12 and the distribution plate 13 is required to have no deformation of the structure during curing and drying even after formation, or explosion during formation.

For formation of the columns 12 and the distribution plate 13 of the fluidized bed reduction furnace 1 described thus, after preparing refractory composition for

formation of the same, the columns 12 and the distribution plate 13 are formed respectively, wherein, though the columns 12 and the distribution plate 13 may be formed by forming unit blocks of the refractory composition, and building up the blocks in the inside space of the body 11 in a fashion of general brick laying as shown in drawings of embodiments, different from this, after construction of molds in the inside space of the body 11, the refractory composition is mixed with bonding agent, and the like, the same as mixing general concrete, and filled, and cured in the molds, to form the columns 12 and the distribution plate 13.

It is apparent that the plurality of pass through holes 12a and 13a are provided at the time of formation of the columns 12 and the distribution plate 13 of the prepared refractory composition for, as described before, smooth flow and pass of the reductive gas.

Therefore, for formation of the columns 12 and the distribution plate 13 in the body 11 of the fluidized bed reduction furnace, the refractory composition is essential, wherein, since it can be foreseen that a service condition of the columns 12 and the distribution plate 13 is rigorous, the refractory composition is required to meet the following product design criteria; density of a structural body being 3.2 or higher, compression strength under service condition being 1500kg/cm2 or higher, good thermal impact resistance, abrasion resistance with an ASTM C704 wear rate of 3. 0cm3 or below, and the like.

However, taking that the equipment for the FINEX process itself is the first one in the world into account, there has been no related art refractory composition for formation of the columns and the distribution plate applied to the FINEX process in a commercial scale. Though a refractory (comparative example 1) with more than 90% alumina and around 1000kg/cm2 of compression strength, and without high strength silica component was applied to an experimental equipment, the refractory causes much

shrinkage and many cracks during service due to low thermal impact resistance, even if the refractory shows good resistance to CO gas.

Disclosure of Invention An object of the present invention is to provide refractory composition for constructing a structure in a fluidized bed reduction furnace for reduction of iron ore powder, which is different from related art experimental refractory composition, the structure being columns and a distribution plate, so that the columns and the distribution plate have good chemical resistance against reductive gas, good abrasion resistance under high temperature, high speed fluidized bed condition, and good thermal impact resistance enough to endure rapid temperature rise and drop following re-operation in an intermittent operation, when iron ore powder having a wide range of grain distribution is reduced step by step in many stages of fluidized bed reduction furnaces each having the columns and the distribution plate formed therein.

The object of the present invention can be achieved by providing a refractory composition for constructing a structure in a fluid bed reduction furnace for reduction of iron ore powder including 9-17wt% of calcined alumina, 3-6 wt% of superfine evaporated silica Si02, 5-lowt% of alumina cement, and balance of sintered or melted alumina to make up 100wt% of the refractory composition.

Preferably, the refractory composition further includes 0. 03-0. 3wt% of dispersing agent inclusive of setting retarder. The dispersing agent is selected from one or more than one kind of inorganic salt of hexameta-sodium phosphate, tripoly-sodium phosphate, tetrapoly-sodium phosphate, acidic hexameta-sodium phosphate, and sodium carbonate, sodium cirtate, tartarate, poly-acrylate-salts, sodium sulfonic acid, and naphthalene-sodium sulfonic acid, and the setting retarder is citric acid, gluconic acid, or boric acid.

Preferably, the refractory composition further includes 0. 03-0. 15wt% of one

or more than one kind of metal aluminum powder, or organic fiber. The refractory composition further includes 0. 01 # 0.05wt% of reaction retarder for adjusting a reaction speed of the aluminum metal powder if the metal aluminum powder is included. Preferably, the reaction retarder is inhibitor.

Preferably, the refractory composition includes 45-59wt% of 8mm # 1mm grain size, 14-20wt% of 1mm-75pm grain size, and 27 # 33wt% of 75µm and below grain size. Preferably, the calcined alumina includes 6-10wt% of average grain size 3 - 5µm, and 3-7wt% of 2-0. 5pm of average grain size. Preferably, the alumina cement includes 26 # 30wt% of CaO.

Brief Description of Drawings The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments. In the drawings; FIG. 1 illustrates a diagram for describing a method for producing iron by using a blast furnace method, schematically; FIG. 2 illustrates a diagram of the FINEX process having the present invention applied thereto schematically; FIG. 3 illustrates a section of a key portion of the fluidized bed reduction furnace in FIG. 2 in detail; FIG. 4 illustrates a section across a line I-I in FIG. 3; FIG. 5 illustrates a perspective view of columns in the fluidized bed reduction furnace in FIG 3; and FIG. 6 illustrates a perspective view of a distribution plate in the fluidized bed reduction furnace in FIG. 3.

Best Mode for Carrying Out the Invention It is preferable that final refractory composition of the present invention has 45 - 59wt% (weight percent) of 8 # 1mm grains, 14-20wt% of 1mm # 75µm grains, and

27-33wt% of 75, um or below grains, which is obtained as a result of repeated experiments in view of characteristics of construction and material. If the refractory composition has more than 59wt% of grains having a size equal to or greater than 8mm, stirring of the refractory composition in mixing with other materials for preparing material for forming the columns 12 and distribution plate 13 is difficult, and forming layers of the columns 12 and the distribution plate 13 closely without pores is difficult by pouring the refractory composition mixed with other materials into a mold.

The refractory composition is determined to have 45-59wt% of 8 ~ lmm grains, because, if the refractory composition has below 45wt% of 8 ~ lmm grains, spalling resistance becomes weak due to greater shrinkage at 1000°C, the main service temperature, even though fluidity increases owing to relative increase of fine dust, and if the refractory composition has above 59wt% of 8-1mm grains, formed state of the columns and the distribution plate become poor due to short of the fine dust that makes formability of the columns and the distribution plate poor.

With regard to the alumina as a main raw material, it is preferable that 95% or higher purity of lump of sintered alumina, melted white alumina, or melted brown alumina is used, and especially melted alumina with porosity below 10% for using raw material with density higher than 3.2 in view of design of the reaction furnace.

Alternatively, the lump may be refractory lump, such as high density zircon, zirconia, magnesia, which may meet the density requirement, but the characteristic requirements of thermal impact resistance, chemical resistance, workability, and the like.

Therefore, sintered or melted alumina formed to have density close to theoretical density is suitable, and preferably, the melted alumina having close texture with low porosity and low impurity.

The material of the columns 12 and the distribution plate 13 of the fluidized bed reduction furnace 1 are required to secure the least fluidity for smooth formation

thereof taking provision of many pipes in the columns 12 and the distribution plate 13 for pass of the high temperature reductive gas at a high speed into account.

Compression strength of the formed material is designed to be higher than 1500kg/cm2 after curing and drying, and for meeting the compression strength requirement, 9 # 17wt% of calcined alumina is used, composed of 6 ~ 10wt% of 3 ~ 511m average grain size, 3-7wt% of 0. 5 ~ 2, um average grain size, and 3-6wt% of superfine evaporated silica.

Thus, alumina with various grain sizes are used together, for securing required fluidity, and a close texture, and composition outside of above range can not provide satisfactory properties.

Of two kinds of superfine evaporated silica with purity of 94% and 97%, it is preferable to use 97% one because Fe, and Si components present therein as impurities cause reductive reaction to damage the texture. The evaporated silica is deflocculated to contain low moisture by assistance of the dispersing agent, to enable the construction.

The superfine evaporated silica starts reaction at a temperature higher than 800°C, and becomes mullite, to form a more stable texture, enabling to compensate for drop of strength caused by dewatering of cement at a high temperature, thereby permitting maintenance of a high strength without drop of strength, actually.

In order to secure the design strength of 1500kg/cm2 or higher of the structures (the columns and the distribution plate) of the present invention, 5-9wt% of alumina cement with 26 # 30% CaO content is used. If below 5wt% of alumina cement is used, the required strength can not be obtained, and if over 9wt% of alumina cement is used, the required strength can not be obtained, or even if obtained, spalling resistance becomes poor due to increased liquid phase material, and decreased amount of mullite formed.

Workable refractory composition can be prepared only when the dispersing

agent is used for having the required fluidity. The dispersing agent may be one selected from inorganic salt of hexameta-sodium phosphate, tripoly-sodium phosphate, tetrapoly-sodium phosphate, acidic hexameta-sodium phosphate, and sodium carbonate, sodium cirtate, tartarate, poly-acrylate-salts, sodium sulfonic acid, and naphthalene-sodium sulfonic acid.

Other than the dispersing agent, the refractory composition is added with setting retarder, preferably, such as citric acid, gluconic acid, and boric acid, for securing retarding of setting.

One or more than one kind of the dispersing agent added with the setting retarder with a content of total 0. 03-0. 3wt% may be used for 100wt% of refractory powder according to nature of construction.

Moreover, in order to secure dryness after construction, 0. 03-0. 15wt% of metal aluminum powder, or one or more than one kind of organic fiber may be used.

Below 0.03wt% of the same fails to provide a spalling prevention effect in the drying, and over 0. 15wt% of the same makes properties of the structure poor due to excessive porosity.

In a case metal aluminum powder is used for prevention of occurrence of spalling during drying, adjustment of a reaction rate of the metal aluminum powder is required, in which 0. 01-0. 05wt% of inhibitor is used as a metal component reaction retarder. If the reaction retarder is not used, the reaction rate varies with a temperature, to cause a difference of setting rates between a surface and an inside of the structure during curing, to fail in obtaining a uniform structure. Below 0. 01wt% of inhibitor is not effective, and over 0. 05wt% of the inhibitor makes the strength poor.

Mulling and construction of the refractory composition of the present invention is made possible by adding water thereto, and steel fiber may be added, as necessary.

Embodiments of the present invention will be described.

Table 1 Comparative examples Embodiments 2 3 1 2 3 4 8-lmm 40 Sintered alumina Below lmm 33 8-lmm 52 60 53 56 58 59 Melted alumina Below lmm 17 22 17 19.5 19.5 22 Do, 5=4jnm 12 10 6 10 8 7 6 Calcined alumina Do. s=2um I 8 3 7 5 4. 5 3 Superfine evaporated silica 97% 6 2 6 4.5 4 3 70% of alumina cement 13 7 7 7 7 7 7 1* 1. 0 Dispersing agent 2* 0. 07 0.07 0.07 0.07 0.07 0.07 0.07 3* 0.03 0.03 0.03 0.03 0.03 0.03 0.03 Total 100 100.1 100. 1 100. 1 100.1 100.1 100.1 Moisture (%) 7.0 4.0 4.0 4.0 4.0 4.0 4.0 Table flow test, 220 135 105 133 125 120 110 fluidity (mm) after 15 taps Evaluation of workability (Q) @ X 0 0 0 A Bulk specific gravity, 3.0 3.15 3.18 3.2 3.21 3.2 3.2 110°Cx24Hr 110°C 1000 1500 1000 1500 1500 1500 1500 Compression strength 1000°C 550 1750 1100 1750 1750 1750 1750 Linear change rate (%) 1000°C-0. 06-2.0-0. 03-0.13-0. 09-0.06-0. 03

Dispersing agent 1* : aluminaADS (Alcoa) Dispersing agent 1* : Sodium hexameta Phosphate Dispersing agent 3* : Sodium Pyro Phosphate In order to form the columns 12 and the distribution plate 13 in the fluidized bed reduction furnace, it is required to secure fluidity of the refractory composition enough to fill portions of the columns 12 and the distribution plate 13 excluding the pass through holes 12a, and 13a, for which the fluidity is measured by table flow test, for evaluation of the fluidity that is required to be minimum 110mm after 15 taps in the table flow test. As table 1 above shows fluidities of the refractory composition of the present invention after 15 taps in the table flow test being higher than 110mm, the fluidity is good.

Table 2 Comparative example Embodiments 4 5 6 5 6 7 8 9 8-lmm 57 57 57 57 57 56 57 57 Melted alumina Below lmm 19.5 19 18 19 19 19 19 19 Calcined Do. 5=4um 9 8 8 9 8 7.5 8 8 alumina Do. 5 = 2 im 5.5 4.5 4. 5 5.5 4. 5 4.5 4. 5 4.5 Superfine evaporated 4. 5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 silica 97% 70% of alumina cement 4.5 7 7 5 7 9 7 7 Total 100 100 100 100 100 100 100 100 Dispersing 2* 0.07 0.07 0.07 0.07 0.07 0.07 0.07 0.07 agent 3* 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 Metal A1 0.02 0.15 0.03 0.05 Organic Fiber 0.03 0. 05 Moisture (%) 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 Bulk specific 3. 25 3.20 3.08 3.22 3.21 3.18 3.20 3.20 gravity, 110°Cx24Hr Compression 110°C 1000 1500 1300 1500 1500 1500 1500 1300 strength 1000°C 1300 1750 1400 1500 1750 1500 1750 1400

Dry spalling occurrence 500°C yes no no No Wear rate (cm2) ASTMC704 2. 0 3. 0 2. 0 2. 0 * The spalling occurrence test is carried out for 5 hours at 500°C by a noncontact flame heating method with a cylindrical test piece with 100mm diameter x 200mm height cured for 24 hours.

Table 3 Embodiments ** 10 11 12 7 8 8-lmm 57 57 57 57 57 Melted alumina Below lmm 19 19 19 19 19 Calcined Do. 5 = 4 tm 8 8 8 8 8 alumina Do. 5 = 211m 4.5 4.5 4.5 4. 5 4.5 Superfine evaporated silica 97% 4.5 4.5 4.5 4.5 4.5 70% of alumina cement 7 7 7 7 7 Total 100 100 100 100 100 Dispersing 2* 0.07 0.07 0.07 0.07 0.07 agent 3* 0.03 0.03 0.03 0.03 0.03 Metal A1 0.05 0.05 0.05 0.05 0.05 Organic Fiber 0.03 0.03 0.03 0.03 0.03 Inhibitor 0 0.01 0.03 0.05 0.06 Moisture (%) 3.6 3.6 3.6 3.6 3.6 Swell after cure (mm) 5 2 0 25 0 Bulk specific gravity, 110°Cx24Hr 3.22 3.21 3.20 3.20 3.10 110°C 1500 1500 1500 1500 1500 Compression strength 1000°C 1750 1750 1750 1750 1750 ** Comparative examples * Swell: a surface height rise of a structure with a size of 350x350x500 (width x length x height) mm is measured at a curing temperature of 35°C.

Industrial Applicability As has been described, in formation of the columns 12 and the distribution plate 13 in the fluidized bed reduction furnace 1 of the refractory composition of the present invention, the present invention can provide a high strength, close textured refractory structure which enables to secure workability, having bulk specific gravity higher than 3.2 of a construction metal fibers can be added thereto, compression strength higher 1500kg/cm2, and 3 or lower ASTM C 708 wear rate, those are basic design criteria, to permit, in operation of the equipment, the columns 12 and the distribution plate 13 to have chemical endurance against reductive gas, good wear resistance under high speed fluidized condition, good thermal impact resistance enough to endure rapid temperature rise and drop, thereby enabling long time stable operation, and improvement of iron quality, to make industrial applicability very high.

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 inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.