JP2011219856A - Carbon-material-containing agglomerate, method for producing the same, and method for producing reduced iron using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon-material-containing iron oxide agglomerate which does not pulverize and is not accumulated in a movable furnace-type reduction furnace when it is heated in the reduction furnace to obtain reduced iron, and surely prevents a drop in yield due to the occurrence of the pulverization when the reduced iron thus obtained is conveyed; and to provide a method for producing the same and a method for producing the reduced iron using the same.SOLUTION: The carbon-material-containing iron oxide agglomerate contains pre-melt slag (for example, blast furnace slag and/or steelmaking slag) which is a ternary-system slag of AlO-CaO-SiOwhose solidus temperature, which is determined by an AlOcontent, a CaO content and an SiOcontent, is at most 1300°C, preferably at most 1200°C. More preferably, the solidus temperature of a ternary-system slag of AlO-CaO-SiOis also at most 1300°C, preferably at most 1200°C, the solidus temperature concerned being determined by the AlOcontent, CaO content and SiOcontent of the whole agglomerate, and, in addition, the liquefaction rate of the ternary-system slag of AlO-CaO-SiOin obtained reduced iron is 1-20%.

Description

  The present invention relates to a carbonaceous material agglomerate used as a raw material for a moving hearth type reduction furnace for producing reduced iron, a method for producing the same, and a method for producing reduced iron using the same.

  Contains powdered iron oxide-containing materials such as dust powder containing a large amount of iron oxide generated in iron ore and ironmaking and steelmaking processes, and carbon such as powder generated when producing coal and coke as a reducing material Add and mix the carbonaceous material, moisture and binder, form into pellets or briquettes, dry the compact (carbonized iron agglomerate), then heat in a rotary hearth furnace to reduce the reaction. A technique for producing reduced iron by causing oxidization is known. Since this molded body was originally composed of fine powder, if it was not reduced, the original powder was generated, and it contained carbon that was not used for reduction even when the reduction was completed. May be cracked by impact when discharged to the outside of the furnace, and the internal carbon, reduced iron particles and oxide components contained in the raw material may become powder and remain in the furnace. Further, when the discharged reduced iron is also transferred by a conveying device such as a belt conveyor, fine powder is generated due to friction between the reduced irons and drop collision at the time of transfer of the belt conveyor or the like.

  By the way, when manufacturing reduced iron, it is possible to adjust the formation of slag that affects the aggregation of reduced metallic iron simply by changing the heating temperature in the rotary bed type reduction furnace or adjusting the residence time. It is difficult and the crushing strength of reduced iron is weakened. For this reason, reduced iron is pulverized and damaged when discharged from the rotating bed type reducing furnace, making it difficult to discharge from the rotating bed type furnace, and reduced iron particles and slag that could not be discharged remain in the furnace. Reacts with hearth refractories and causes damage. In addition, some of the reduced iron that has been pulverized and destroyed at the time of discharge may float in the gas flow in the furnace and adhere to the inner wall of the rotary bed type reduction furnace and the exhaust gas equipment duct wall. Furthermore, if the discharged reduced iron is pulverized or damaged during transportation, it becomes a dust and needs to be used again as a raw material. In addition, the yield decreases in the process of melting reduced iron such as electric furnaces and blast furnaces to make pig iron. To do.

  For this reason, the technique which suppresses thru | or prevents generation | occurrence | production of a fine particle in the reduction | restoration process in a furnace, the time of carrying out outside a furnace, and conveyance is desired.

  On the other hand, since the produced reduced iron is used as an iron raw material for blast furnaces, converters, electric furnaces, etc., it is desired to have a carbon content as high as possible in order to improve the energy efficiency of the furnace. It is known that the strength of reduced iron decreases as the content increases.

  In order to solve the above problems, various measures for increasing the strength of the carbonaceous material-incorporated iron oxide agglomerates and the reduced iron have been studied.

For example, focusing on solidifying the reduced iron particles by melting and fixing the slag component so far, a basicity (CaO / SiO ₂ ) ratio of 0 is used by using a Ca-containing compound such as CaCO ₃ as a raw material for adjusting the basicity of slag. .3 or more and 0.6 or less, by improving the crushing strength of the reduced iron, the method and the basicity to suppress the pulverization is adjusted to 1.4 to 1.6, the carbon in the agglomerate is 10 A method of heating at 1250 ° C. to 1350 ° C. as ˜20% has been proposed (see Patent Documents 1 and 2). However, some iron sources such as iron ore and dust contain Al ₂ O ₃ and MgO in addition to CaO and SiO _{2. By} simply controlling the (CaO / SiO ₂ ) ratio, the slag melting temperature can be accurately controlled. The strength of reduced iron cannot be reliably increased.

Further, in order to suppress the generation of fine powder in the charging process to the furnace, adjusting the total amount of Al ₂ O ₃ and SiO ₂ in Konajotetsu material in the range of 4 to 10 wt% in the agglomerates And the technique which raises the intensity | strength of a molded object is proposed (refer patent document 3). However, the melting point of slag cannot be accurately controlled simply by defining the total of Al ₂ O ₃ and SiO _{2 in} the raw material, and it is not possible to increase the crushing strength and prevent pulverization.

Furthermore, a method for obtaining (XCaO + Al ₂ O ₃ + XMgO) / XSiO ₂ from the abundance of CaO, Al ₂ O ₃ , MgO and SiO ₂ and adjusting the value to 1 to 5 has been proposed. (See Patent Document 4). However, this focuses on the deposit component that can be easily cut when trying to remove the deposit attached to the hearth, and does not increase the strength of the reduced iron itself and prevent pulverization. .

In addition, a method in which a value calculated by (CaO + Al ₂ O ₃ ) / SiO ₂ is 1.6 or more, and a method of adding a hydrate containing calcium ions as a Ca-containing substance have been proposed (Patent Document 5). reference). However, in this method, it takes 3 days to form a hydrate, and a yard for holding the raw material for 3 days or more is required.

Moreover, with the addition of CaF ₂ component, (CaO / SiO ₂₎ method of 0.3 to 1.0 the ratio has been proposed (see Patent Document 6). However, in recent years, since CaF ₂ is concerned about the environmental impact, the disposal of slag containing CaF ₂ has been regulated, and the use of CaF ₂ is often limited.

For the purpose of preventing the generation of powder by bursting in the furnace, the (CaO / SiO ₂ ) ratio is set to 0.5 to 1.5, and the total amount of crystallization water and volatile matter is 10.5% by mass. A method has also been proposed in which the content of adhered moisture is 1.0% or less (see Patent Document 7). However, it cannot be applied to a raw material containing more than 10.5% by mass of crystal water in the oxide raw material, and much drying time is required to dry the water to 1% by mass or less.

(CaO-MgO) /T.Fe is 0.1 or less, and (CaO-MgO) / SiO ₂ is 2 or less, and the size of the iron oxide raw material is 50 μm or less. A method has also been proposed in which the ratio is 0.3 to 1, the metalization rate of reduced iron is 50 to 85%, and the residual carbon in the reduced iron is 2% by mass or less (see Patent Document 8). However, this method requires a pulverization step if the iron oxide raw material exceeds 50 microns, and the larger the particle size, the longer the time required for pulverization, and it is not possible to obtain reduced iron containing a large amount of carbon.

JP 2004-169140 A Japanese Patent Laid-Open No. 10-147806 Japanese Patent Laid-Open No. 11-12626 JP 2006-283136 A JP 2007-197783 A JP 2008-56986 A JP 2009-35820 A JP 2009-84688 A

  In view of this, the present invention provides a carbonaceous iron-incorporated iron oxide agglomerate that is heated in a moving hearth-type reducing furnace to obtain reduced iron, so that no powder is accumulated due to pulverization in the furnace. Provided with a carbonaceous material-containing iron oxide agglomerate that can reliably prevent yield reduction due to pulverization when the reduced iron is conveyed, and a method for producing the same, and a method for producing reduced iron using the same The purpose is to do.

The invention according to claim 1 is a carbonaceous material-containing iron oxide agglomerate used as a raw material of a moving hearth type reduction furnace for producing reduced iron, and contains Al ₂ O ₃ , CaO and SiO ₂ . Pre-melt slag having a solid phase temperature (hereinafter referred to as “pre-melt slag solid-phase temperature”) T _{S · P} of 1300 ° C. or less of Al ₂ O ₃ —CaO—SiO ₂ ternary slag determined from It is a carbonaceous material-incorporated iron oxide agglomerate characterized by being made.
The invention according to claim 2 is the carbonaceous material-incorporated iron oxide agglomerated product according to claim 1, wherein the premelt slag has a solidus temperature T _{S · P} of 1200 ° C or lower.

The invention according to claim 3 is the carbonized iron oxide agglomerate according to claim 1, wherein the premelt slag is blast furnace slag and / or steelmaking slag.
The invention according to claim 4 is the carbonized iron oxide agglomerated material according to claim 1, wherein the premelt slag is blast furnace slag and / or steelmaking slag.

The invention according to claim 5 is a method for producing the carbonaceous material-containing iron oxide agglomerated product according to claim 1 or 3, wherein the content of Al ₂ O ₃ , CaO and SiO _{2 in the} whole agglomerated material is included. The solidus temperature of Al ₂ O ₃ —CaO—SiO ₂ ternary slag determined from the following (hereinafter referred to as “total slag solidus temperature”) T _{S · S} is 1300 ° C. or less, and the agglomeration Al ₂ O ₃ —CaO determined from the content of Al ₂ O ₃ , CaO and SiO _{2 of the} whole agglomerated material in the moving hearth type reduction furnace, which is higher than the total slag solidus temperature T _{S · S.} The liquidus temperature of SiO ₂ ternary slag (hereinafter referred to as “total slag liquidus temperature”) Al ₂ O in reduced iron produced by heat treatment at a heat treatment temperature lower than _{TL · S} The melt rate of _3- CaO-SiO ₂ ternary slag is 1 It is a manufacturing method of the carbonaceous material internal iron oxide agglomerate characterized by adjusting the compounding ratio of the said premelt slag so that it may become -20%.
Here, the _{Al 2 O 3 -CaO-SiO 2} 3 ternary melt index of the slag during the reduction of iron, for the entire reduced iron, _{Al 2 O 3 -CaO-SiO 2} 3 -way system in reduced iron It is defined as the mass ratio of the portion of the slag that becomes a liquid phase at the heat treatment temperature (hereinafter the same).
The invention according to claim 6 is a method for producing the carbonaceous material-containing iron oxide agglomerated product according to claim 2 or 4, wherein the content of Al ₂ O ₃ , CaO and SiO _{2 in the} whole agglomerated material is included. The solidus temperature of Al ₂ O ₃ —CaO—SiO ₂ ternary slag determined from the following (hereinafter referred to as “total slag solidus temperature”) T _{S · S} is 1200 ° C. or lower, and the agglomeration Al ₂ O ₃ —CaO determined from the content of Al ₂ O ₃ , CaO and SiO _{2 of the} whole agglomerated material in the moving hearth type reduction furnace, which is higher than the total slag solidus temperature T _{S · S.} The liquidus temperature of SiO ₂ ternary slag (hereinafter referred to as “total slag liquidus temperature”) Al ₂ O in reduced iron produced by heat treatment at a heat treatment temperature lower than _{TL · S} The melt rate of _3- CaO-SiO ₂ ternary slag is 1 It is a manufacturing method of the carbonaceous material internal iron oxide agglomerate characterized by adjusting the compounding ratio of the said premelt slag so that it may become -20%.

The invention according to claim 7 is the carbonaceous material-containing iron oxide agglomerated product according to claim 1, 2, 3 or 4, or the carbonaceous material-oxidized oxide produced by the production method according to claim 5 or 6. An iron agglomerate, wherein the carbonaceous material-incorporated iron oxide agglomerated material whose carbon material blending amount is adjusted is a method for producing reduced iron by heat treatment in the moving hearth type reducing furnace, comprising: The heat treatment temperature is higher than the total slag solidus temperature T _{S · S} so that the carbon utilization efficiency η _C defined by the formula is in the range of 0.08 to 0.12, and the total slag liquidus It is a reduced iron production method characterized by obtaining reduced iron having a carbon content of 6% by mass or less by adjusting in a temperature range lower than the temperature T _{L · S.}
Formula η _C = N _{CO 2} / (N _CO + N _{CO 2} )
Here, N _CO and N _CO2, respectively, generated from the carbonaceous material furnished oxide TetsukatamariNaru in product during the heat treatment, the total molar amount of the total molar amount and CO ₂ in the CO.

According to the present invention, a premelt slag having a solidus temperature of Al ₂ O ₃ —CaO—SiO ₂ ternary slag of 1300 ° C. or less, more preferably 1200 ° C. or less, in the carbonaceous material-containing iron oxide agglomerated material. By blending, when the carbonaceous material-incorporated iron oxide agglomerate is heat-treated in a moving hearth type reducing furnace, a part of the premelt slag is easily melted, and the sintering reaction of metallic iron is promoted. It is now possible to produce reduced iron with higher crushing strength.

It is _{Al 2 O 3 -CaO-SiO 2} 3 ternary phase diagram for explaining a relationship between the slag composition and the solidus temperature of the carbonaceous material furnished oxide TetsukatamariNaru product. It is a longitudinal cross-sectional view which shows the apparatus outline | summary of the small high-frequency rapid heating furnace used for the reduction test. It is a figure which shows typically the heating pattern in a reduction test. Is _{Al 2 O 3 -CaO-SiO 2} 3 ternary phase diagram for explaining a relationship between the slag composition and the solidus temperature of the carbonaceous composite iron oxide pellets used for the reduction test.

  Hereinafter, the present invention will be described in more detail.

(Embodiment)
The present invention relates to the solidus temperature (pre-melt slag solids) of Al ₂ O ₃ —CaO—SiO ₂ ternary slag in a carbonaceous material-containing iron oxide agglomerate (hereinafter also simply referred to as “agglomerated product”). Preliminary slag having a phase line temperature (T _{S · P} ) of 1300 ° C. or lower, more preferably 1200 ° C. or lower, which is more suitable as an iron raw material for blast furnaces, electric furnaces, converters, etc. In this way, product reduced iron with further increased crushing strength is obtained.

  The basis for setting the above requirements will be described below.

First, pre-melt slag was used because, for example, limestone (CaO source) or silica (SiO ₂ ) as an auxiliary material was used to adjust the slag component in the carbonaceous material-incorporated iron oxide agglomerated material as in the prior art. Source), CaO alone and SiO ₂ alone have high melting temperature (melting point), so liquid phase is hardly generated from these auxiliary materials, and it takes time to slag, while premelt slag is already slag itself. This is because the melting temperature is low and the liquid phase is generated in a short time to further promote the sintering of metallic iron.

The reason for targeting the Al ₂ O ₃ —CaO—SiO ₂ ternary slag is that the components of the premelt slag are mainly composed of Al ₂ O ₃ , CaO and SiO ₂ .

  The reason why the solidus temperature, not the liquidus temperature, of the ternary slag is specified is as follows.

  That is, the liquidus temperature is a temperature at which the pre-melt slag is fully melted, whereas the solidus temperature is a temperature at which a partially molten slag begins to be generated. In other words, when the liquidus temperature of the premelt slag is defined and heated at a temperature higher than the liquidus temperature, the premelt slag melts all at once, creating a lot of voids in the agglomerate, and the metal Since the promotion of iron sintering is hindered, high strength reduced iron cannot be obtained. On the other hand, by prescribing the solidus temperature of the premelt slag and heating at a temperature higher than the solidus temperature, a solid-liquid coexistence state in which a part of the premelt slag is melted and not partially obtained is obtained Sintering of metallic iron can be promoted while suppressing formation of voids due to melting of the premelt slag. In short, the strength of reduced iron is not due to the formation of a slag phase, but due to the sintered structure of metallic iron.

The reason why the solidus temperature is set to 1300 ° C. or lower is that when reducing iron is produced in a rotary hearth type reducing furnace, the heating temperature is often 1300 ° C. or lower in many cases. Is.
Furthermore, the solidus temperature is more preferably set to 1200 ° C. or less because it has been found that the sintering of metallic iron can be promoted by creating a solid-liquid coexistence state at an early stage of the heat treatment.

Here, the solidus temperature (premelt slag solidus temperature) T _{S · P} of the Al ₂ O ₃ —CaO—SiO ₂ ternary slag can be determined as follows, for example.

1 is a phase equilibrium diagram of a commonly used CaO—SiO ₂ —Al ₂ O ₃ ternary composite oxide (SLAG ATLAS 2nd Edition (1995), Verlag Stahleisen GmbH, p. 105). Although the liquidus temperature (T _L ) is described in this figure, the solidus temperature (T _S ) is not described. Therefore, using the thermodynamic equilibrium calculation software “FactSage” (Thermact and GTT-Technologies), the solidus temperature (T _S ) in the ternary composite oxide is calculated, and the solidus A region where the temperature (T _S ) is 1300 ° C. or less (region surrounded by points P, Q, R, and S; each composition of the points P, Q, R, and S is as shown in Table 1 below), and Of these, the regions of 1200 ° C. or lower are indicated by hatching.

Therefore, what is necessary is just to select and mix the premelt slag so that the composition of the ternary slag in the premelt slag blended in the agglomerated product becomes a composition in the above region. Further, premelt slag having a plurality of different compositions having a premelt slag solidus temperature T _{S · P} of 1300 ° C. or lower, more preferably 1200 ° C. or lower, may be used in combination.

  As the premelt slag, for example, blast furnace slag and / or steelmaking slag can be used. Here, the steelmaking slag includes converter slag, hot metal pretreatment slag, electric furnace slag, and the like.

In the above, only the solidus temperature (premelt slag solidus temperature) TS _{/ P} of the premelt slag to be blended with the agglomerated material is specified, but the agglomerated material after blending the premelt slag. The solidus temperature (total slag solidus temperature) T _{S · S} of Al ₂ O ₃ —CaO—SiO ₂ ternary slag determined from the content of Al ₂ O ₃ , CaO and SiO _{2 in the} interior is also 1300 ° C. or less. More preferably 1200 ° C. or less, and the agglomerate is higher than the total slag solidus temperature T _{S · S in the} moving hearth type reducing furnace, and the entire agglomerated Al ₂ O ₃ , Manufactured by heat treatment at a heat treatment temperature lower than the liquidus temperature (total slag liquidus temperature) _{TL · S of} Al ₂ O ₃ —CaO—SiO ₂ ternary slag determined from CaO and SiO ₂ content In reduced iron As _{l 2 O 3 -CaO-SiO 2} 3 ternary melt index of the slag is 1-20%, and more preferable to adjust the mixing ratio of the pre-melt slag.

As described above, by limiting the total slag solidus temperature T _{S · S} to 1300 ° C. or less, more preferably 1200 ° C. or less, when the agglomerated material is heated in the furnace, first the premelt slag The liquid phase (molten slag) produced from the slag reacts with the gangue components in the iron oxide-containing raw material and the ash content of the carbonaceous material constituting the agglomerate, and the liquid phase state can be maintained even if the slag composition changes. Become.

The total slag solidus temperature T _{S · S} can be determined by the same method as the pre-melt slag solidus temperature T _{S · P} described above.

Furthermore, by controlling the melt rate of the Al ₂ O ₃ —CaO—SiO ₂ ternary slag in the reduced iron within a range of 1 to 20%, the slag can be melted in an appropriate amount so that the sintering reaction of metallic iron can be further performed. It is possible to proceed reliably. That is, if the melt rate is less than 1%, the slag melt is too small and the sintering of metallic iron does not proceed sufficiently. On the other hand, if the melt rate exceeds 20% and the slag melt becomes excessive, Since the strength development mechanism of reduced iron changes from the sintering-controlled rate of metallic iron to the slag bond-controlled rate, brittle fracture easily occurs at the slag bond site, and the yield of reduced iron decreases. The melt rate is more preferably in the range of 5 to 18%.

Here, the _{Al 2 O 3 -CaO-SiO 2} 3 ternary melt index of the slag during the reduction of iron, for the entire reduced iron, _{Al 2 O 3 -CaO-SiO 2} 3 ternary slag in reduced iron Is defined as a mass ratio of a portion that becomes a liquid (that is, a liquid phase) at the heat treatment temperature.

The carbonaceous material in the agglomerated material contains ash, and this ash composition also affects the determination of the composition of the whole agglomerated ternary slag below, but the blending amount of the carbonaceous material in the agglomerated material is: Al ₂ O ₃ —CaO—SiO ₂ ternary system determined from the content of Al ₂ O ₃ , CaO and SiO _{2 of the} entire agglomerated material because it is finally determined by the amount of residual carbon in the reduced iron described later. The composition of the slag (hereinafter abbreviated as “total agglomerated ternary slag”) is adjusted mainly by the blending amount of the iron oxide-containing raw material, the premelt slag and the auxiliary raw material. That is, the composition of the entire agglomerated ternary slag is the amount of premelt slag added according to the mixing ratio of iron dust or iron ore having a plurality of different slag component compositions, which is an iron oxide raw material. If necessary, it can be performed by adjusting the amount of addition of a calcium oxide-containing substance such as limestone or quicklime, or a silicon oxide-containing substance such as silica, which is an auxiliary material.

Moreover, the amount of carbonaceous material in the agglomerated material is such that the carbon utilization efficiency η _C defined by the following formula is within the range of 0.08 to 0.12, and the total slag solidus temperature T _{S · The} amount of carbon remaining in the reduced iron obtained by heat treatment at a heat treatment temperature that is higher than _{S and} lower than the total slag liquidus temperature _{TL · S} is 6% by mass or less. Is preferable.

  Here, the heat treatment temperature means the highest atmospheric temperature in the rotary hearth type reduction furnace.

The reason for adjusting the heat treatment temperature at a temperature higher than the total slag solidus temperature T _{S · S and} lower than the total slag liquidus temperature T _{L · S} is that the slag is partially liquid phased This is to promote sintering. Specifically, for example, when the heat treatment temperature is 1300 ° C., the slag composition may be selected such that the total slag liquidus temperature _{TL · S} exceeds 1300 ° C.

  Further, in the method described in Patent Document 8, the residual carbon in the reduced iron is limited to 2% by mass or less, but in the present invention, by appropriately controlling the melting of the slag component as described above, Furthermore, reduced iron strength can be secured even with a high carbon content. However, if it exceeds 6% by mass, the crushing strength of the reduced iron is lowered because the aggregation of metallic iron is inhibited. From the viewpoint of ensuring reduced iron strength, the less carbon that remains in the reduced iron is preferable, but as described above, from the viewpoint of improving the energy efficiency of blast furnaces, converters, electric furnaces, etc., as high C content as possible It is recommended that the amount of carbon remaining in the reduced iron be more than 2% by mass, further 3% by mass or more.

  The amount of residual carbon in the reduced iron can be adjusted by adjusting the amount of carbonaceous material (carbon content) in the carbonaceous material-incorporated iron oxide agglomerated material. Can be performed by adjusting the blending ratio of blast furnace dust having a high carbon content and the addition amount of coal such as coal and coke powder.

  The amount of carbonaceous material in the carbonaceous material-incorporated iron oxide agglomerate can be set based on the following concept.

  That is, when a material containing volatile matter such as coal and fixed carbon content is used as the carbon material, when the agglomerate is heated in the rotary hearth type reducing furnace, first, in the temperature raising process, 500 Volatiles are removed at ˜600 ° C., but these volatiles contribute little to the reduction of iron oxide. Further, it is known that when the temperature of the agglomerate further increases and reaches about 700 ° C., the reduction reaction of iron oxide is substantially initiated by the fixed carbon.

Therefore, the fixed carbon mass Xc in the agglomerated material is expressed by the following formula (2): the carbon mass Xc _T required to completely reduce iron oxide and zinc oxide to metal, and the reduced iron after reduction. It can be regarded as the total mass with the residual carbon mass Xc _{R in the} medium.

Xc = Xc _T + Xc _R Formula (2)

Wherein the carbon mass Xc _T required for complete reduction to metallic iron oxide and zinc oxide can be estimated by the following equation (3).

Xc _T = (12/16) · Xo / (1 + η _C ) ... Formula (3)
However, Xo is the total mass of oxygen of iron oxide and oxygen of zinc oxide in the carbonaceous material-incorporated iron oxide agglomerated material, and η _C is carbon utilization efficiency (details will be described later).

  In the above formula (3), the reduction of zinc oxide in addition to iron oxide is considered because when iron dust is used as a raw material, a considerable amount of zinc oxide is included, and a considerable amount of carbon mass is reduced for the reduction. This is necessary. However, the content of other non-ferrous metal oxides such as lead and alkali metals was negligible compared to iron oxide and zinc oxide.

Further, the term 1 / (1 + η _C ) in the above formula (3) indicates that iron oxide and zinc oxide are completely reduced to metal as the proportion of the CO ₂ gas component in the CO + CO ₂ gas generated by the reduction reaction increases. This means that the carbon mass required to do this is reduced.

Here, the carbon utilization efficiency η _C when the carbon material-containing iron oxide agglomerate is heat-treated in the rotary hearth type reduction furnace is the carbon material-containing iron oxide in the small high-frequency rapid heating furnace used in the examples described later. The agglomerate can be obtained by conducting a test for producing reduced iron by heat treatment in an inert gas atmosphere and analyzing the composition of CO and CO ₂ gas generated from the agglomerate. As a result, it was found that the carbon utilization efficiency η _C is in the range of 0.08 to 0.12, although it varies depending on the heat treatment temperature.

Therefore, first, the carbon utilization efficiency η _C is set between 0.08 and 0.12 according to the heat treatment temperature of the furnace actually used, and the carbon necessary for the reduction of iron oxide using the above formula (3). The amount Xc _T is calculated, and then the fixed carbon amount Xc in the agglomerated material is calculated using Equation (2). And based on this calculation result, the carbonaceous material compounding quantity in an agglomerate can be set.

When the carbonized iron oxide agglomerate produced as described above is heat-treated in a rotary hearth type reduction furnace, the carbon utilization efficiency η _C defined by the following re-expression (1) is 0. The heat treatment temperature is adjusted in a temperature range higher than the total slag solidus temperature T _{S · S and} lower than the total slag liquidus temperature T _{L · S} so that it falls within the range of 0.08 to 0.12. do it.

η _C = N _CO2 / (N _CO + N _CO2 ) ... Reprinting ceremony (1)
Here, N _CO and N _CO2, respectively, generated from the carbonaceous material furnished oxide TetsukatamariNaru in product during the heat treatment, the total molar amount of the total molar amount and CO ₂ in the CO.

The carbon utilization efficiency η _C can be changed by adjusting the heat treatment temperature between the solidus temperature and the liquidus temperature. For example, the higher the heat treatment temperature, the higher the heat treatment temperature in the agglomerate. Since the carbon solution reaction (C + CO ₂ → 2CO) is promoted, the carbon utilization efficiency η _C tends to decrease.

(Modification)
In the above embodiment, the rotary hearth furnace is exemplified as the furnace type of the moving hearth type reducing furnace, but a linear furnace may be used.

  In order to confirm the effect of the present invention, the following tests were conducted using the raw materials shown in Table 2 below.

〔experimental method〕
In this example, pellets were adopted as the form of the carbonaceous material-containing iron oxide agglomerated material.

1.5 mass of flour as a binder in the iron oxide-containing raw material (a), carbonaceous material (b), and premelt slag or auxiliary raw material (c) blended in various blending ratios as shown in Table 3 % (Constant) was added, and an appropriate amount of water was added, and the mixture was granulated into raw pellets having a diameter of 17 mm using a tire type granulator. The raw pellets were dried in a dryer at 105 ° C. for 20 hours to completely remove the attached water. The apparent density of the dried pellets (carbon material-containing iron oxide pellets) was in the range of 1800 to 2000 kg / m ³ .

The dried pellets (carbon material-containing iron oxide pellets) are heated in a small high-frequency rapid heating furnace (Sekisui Medical Electronics: oscillator type MU-1700, furnace type UD-250) whose outline is shown in FIG. Went. As the heating sleeve, a graphite tube coated with alumina was used in order to prevent the graphite from being consumed by the CO ₂ -containing gas generated when the pellet was heated.

As shown in FIG. 3, the heating pattern is as follows: room temperature to 1250 ° C. is heated at a heating rate of 150 ° C./min, and 1250 to 1300 ° C. is heated at a heating rate of 15 ° C./min. Stopped and performed rapid cooling. Note that N ₂ gas 3 NL / min was used as the atmosphere during heating, and He gas 3 NL / min was used as the atmosphere during cooling.

About the reduced iron obtained by heat-processing with the said heating pattern, carbon content and crushing strength were measured, and the result is shown in Table 4. The table shows the contents of SiO ₂ , CaO and Al ₂ O ₃ in the pellets before reduction (carbonaceous iron oxide pellets), and the solidus temperature T _{S · of the} agglomerated ternary slag as a whole. _S , the liquidus temperature _{TL · S, the} liquid phase ratio, and the melt ratio of the Al ₂ O ₃ —CaO—SiO ₂ ternary slag in the reduced iron are also shown.

The liquid phase ratio is defined as the mass ratio of the liquid in the solid + liquid (that is, solid phase + liquid phase) located between the solid phase line and the liquid phase line on the equilibrium diagram. (See paragraph [0036] of Japanese Patent Application Laid-Open No. 2005-48197), and in this example, using the thermodynamic equilibrium calculation software “FactSage” described above, the solid phase + at the heat treatment temperature (1300 ° C.) The mass ratio (%) of the liquid phase in the liquid phase was calculated.
Further, the melt rate (%) of the Al ₂ O ₃ —CaO—SiO ₂ ternary slag in the reduced iron is equal to the total mass% of the Al ₂ O ₃ —CaO—SiO ₂ 3 component in the reduced iron. Obtained by multiplying by liquid phase ratio (%) / 100.

  Moreover, the unit kgf of the crushing strength of reduced iron in the table corresponds to 9.80665N.

Also, a plot of the _{Al 2 O 3 -CaO-SiO 2} 3 ternary slag composition of the carbonaceous composite iron oxide pellets of the invention Examples 1 to 7 and Comparative Examples 1 to 5 on a ternary phase diagram of Figure 1 Is shown in FIG.

  In all the inventive examples and comparative examples, the carbon utilization efficiency was in the range of 0.08 to 0.12.

Both carbon composite iron oxide pellets of Inventive Example _1-7, Al ₂ O 3, CaO and SiO ₂ determined from the content of _{Al 2 O 3 -CaO-SiO 2} 3 ternary slag solidus temperature (pre-melt Premelt slag having a slag solidus temperature (T _{S · P} ) of 1300 ° C. or lower is blended.

In addition, the pellets of these inventive examples are the solidus temperature of the Al ₂ O ₃ —CaO—SiO ₂ ternary slag determined from the content of Al ₂ O ₃ , CaO and SiO _{2 of the} whole pellet (all slag solid phase (Line temperature) T _{S · S} is also 1300 ° C. or less, and the pellet is higher than the total slag solidus temperature T _{S · S} in the rotary hearth type reducing furnace, and Al ₂ O _{3 of the} whole pellet, Heated at 1320 ° C., which is a heat treatment temperature lower than the liquidus temperature (total slag liquidus temperature) _{TL · S of} Al ₂ O ₃ —CaO—SiO ₂ ternary slag determined from CaO and SiO ₂ content The melt rate of the Al ₂ O ₃ —CaO—SiO ₂ ternary slag in the reduced iron obtained by the treatment is in the range of 1 to 20%.

Furthermore, the pellets of these invention examples have a residual carbon content in reduced iron obtained by heat treatment at the same temperature of 6% by mass or less (also 3% by mass or more).
Therefore, all of the pellets of the inventive examples satisfy the requirements of the present invention, and the crushing strength of reduced iron has a high value exceeding 25 kgf / piece.
In particular, Invention Example 7 includes steelmaking slag having a solidus temperature T _{S · P} of 1200 ° C. or less, which is more preferably a premelt slag, a residual carbon content of 3% or more, and a total slag solidus temperature T _S. -As a result of _S becoming more preferable 1200 degrees C or less, the crushing strength of reduced iron obtained the highest value exceeding 40 kgf / piece.

On the other hand, all the carbonaceous iron-containing iron pellets of Comparative Examples 1 to 3 have a total slag solidus temperature T _{S · S} of 1300 ° C. or less and the melt ratio in the range of 1 to 20%. However, since the premelt slag is not blended, the requirements of the present invention are not satisfied, and the crushing strength of the obtained reduced iron remains at a low value of less than 15 kgf / piece.

Moreover, the carbonaceous material-containing iron oxide pellets of Comparative Example 4 contain a premelt slag having a premelt slag solidus temperature T _{S · P} of 1300 ° C. or lower and a total slag solidus temperature T _{S · S} of 1300. Although the melting rate is over 20%, it does not satisfy the requirements of the present invention, and the crushing strength of the obtained reduced iron remains at a very low value of about 4 kgf / piece. Yes.

Claims (7)

A carbonaceous material-containing iron oxide agglomerate used as a raw material for a moving hearth type reduction furnace for producing reduced iron, which is determined from the contents of Al ₂ O ₃ , CaO and SiO _2, Al ₂ O ₃ —CaO— A charcoal comprising a premelt slag having a solid phase temperature of SiO ₂ ternary slag (hereinafter referred to as “premelt slag solidus temperature”) T _{S · P} of 1300 ° C. or less. Material interior iron oxide agglomerates. The carbonaceous material-incorporated iron oxide agglomerated product according to claim 1, wherein the premelt slag has a solidus temperature T _{S · P} of 1200 ° C. or less.   The carbonized iron oxide agglomerate according to claim 1, wherein the premelt slag is blast furnace slag and / or steelmaking slag.   The carbonized iron oxide agglomerate according to claim 2, wherein the premelt slag is blast furnace slag and / or steelmaking slag. A method for producing a carbonaceous material-containing iron oxide agglomerated product according to claim 1 or 3, wherein Al ₂ O ₃ -CaO- is determined from the content of Al ₂ O ₃ , CaO and SiO _{2 of the} whole agglomerated product. The solidus temperature of SiO ₂ ternary slag (hereinafter referred to as “total slag solidus temperature”) T _{S · S} is 1300 ° C. or lower, and the agglomerated product is transferred to the moving hearth type reducing furnace. Liquid of Al ₂ O ₃ —CaO—SiO ₂ ternary slag that is higher than the total slag solidus temperature T _{S · S} and determined from the Al ₂ O ₃ , CaO and SiO ₂ contents of the whole agglomerated material. Phase wire temperature (hereinafter referred to as “total slag liquidus temperature”) Al ₂ O ₃ —CaO—SiO ₂ ternary system in reduced iron produced by heat treatment at a heat treatment temperature lower than _{TL · S} Before the slag melt rate becomes 1-20% The manufacturing method of the carbonaceous material interior iron oxide agglomerate characterized by adjusting the compounding ratio of the said premelt slag.
Here, the _{Al 2 O 3 -CaO-SiO 2} 3 ternary melt index of the slag during the reduction of iron, for the entire reduced iron, _{Al 2 O 3 -CaO-SiO 2} 3 -way system in reduced iron It is defined as the mass ratio of the portion of the slag that becomes a liquid phase at the heat treatment temperature (hereinafter the same). A method for producing a carbonaceous material-containing iron oxide agglomerated product according to claim 2 or 4, wherein Al ₂ O ₃ -CaO- is determined from the content of Al ₂ O ₃ , CaO and SiO _{2 of the} whole agglomerated material. The solidus temperature of SiO ₂ ternary slag (hereinafter referred to as “total slag solidus temperature”) T _{S · S} is 1200 ° C. or lower, and the agglomerated product is transferred to the moving hearth type reducing furnace. Liquid of Al ₂ O ₃ —CaO—SiO ₂ ternary slag that is higher than the total slag solidus temperature T _{S · S} and determined from the Al ₂ O ₃ , CaO and SiO ₂ contents of the whole agglomerated material. Phase wire temperature (hereinafter referred to as “total slag liquidus temperature”) Al ₂ O ₃ —CaO—SiO ₂ ternary system in reduced iron produced by heat treatment at a heat treatment temperature lower than _{TL · S} Before the slag melt rate becomes 1-20% The manufacturing method of the carbonaceous material interior iron oxide agglomerate characterized by adjusting the compounding ratio of the said premelt slag. A carbonaceous material-containing iron oxide agglomerated product according to claim 1, 2, 3, or 4, or a carbonaceous material-containing iron oxide agglomerated product produced by the production method according to claim 5 or 6, A method for producing reduced iron by heat-treating a carbonaceous material-containing iron oxide agglomerated material adjusted in the material blending amount in the moving hearth type reducing furnace, wherein the carbon utilization efficiency η defined by the following formula: _The heat treatment temperature is higher than the total slag solidus temperature T _{S · S and} lower than the total slag liquidus temperature T _{L · S} so that _C is in the range of 0.08 to 0.12. A reduced iron production method characterized by obtaining reduced iron having a carbon content of 6% by mass or less by adjusting in a range.
Formula η _C = N _{CO 2} / (N _CO + N _{CO 2} )
Here, N _CO and N _CO2, respectively, generated from the carbonaceous material furnished oxide TetsukatamariNaru in product during the heat treatment, the total molar amount of the total molar amount and CO ₂ in the CO.

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