JP5042203B2 - Production of granular metallic iron - Google Patents

Description

  When producing granular metallic iron by reducing and melting a raw material containing iron oxide such as iron ore and a carbonaceous reducing agent such as coke, the present invention is particularly suitable for transport and handling with high Fe purity and large particle size. The present invention relates to an improved method so that granular metallic iron having excellent properties can be produced with high yield and high productivity.

  For example, Japanese Patent Application Laid-Open No. 9-256017 discloses a method for producing a metallic iron by heating a raw material containing an iron oxide source such as iron ore and a carbonaceous reducing agent such as coke or coal powder, followed by solid reduction. Many proposals have already been made as seen in Japanese Patent Publication No. 11-335712. These publications also show that heating reduced iron produced by solid reduction, carburizing the reduced iron and lowering the melting point promotes melting and improves the productivity of metallic iron. Yes.

  However, in these publications, when the metallic iron produced by the solid reduction is melted, there is a description that the metallic iron having a high Fe content can be obtained by agglomerating while separating the slag produced as a by-product in the solid reduction process. However, it cannot be said that sufficient studies have been made on how to make it possible to manufacture the metallic iron as granular metallic iron having a particle size configuration that is easy to transport and handle. In addition, depending on the quality and composition of the raw materials, the metal iron is not sufficiently separated from the by-product slag in the melting step after solid reduction, and granulation does not proceed well, so that the slag is embraced or very fine granular The separation work becomes difficult, and the product having an appropriate particle size range may not be obtained with a good yield.

  JP-A 09-310111 discloses that when producing reduced iron pellets by heating and reducing carbonaceous material-containing pellets, the content of volatile components contained in the carbonaceous material is suppressed to a low level. A technique for preventing destruction (bursting) of pellets and stabilizing the quality and productivity of the obtained reduced iron is disclosed. However, the invention disclosed in this publication is to produce reduced iron by heat reduction without melting the iron oxide in the raw material pellet, and although the metallization rate itself is increased, the obtained reduced iron contains a large amount of slag. Incorporating components, Fe purity itself is quite low. Moreover, in the present invention, since it is a method for producing reduced molten iron in an unmolten state, it is different from the technique for obtaining high Fe purity granular metallic iron in which slag components are eliminated, and of course, the yield of granular metallic iron having a target particle size configuration is obtained. There is no problem of manufacturing well.

  In addition to the above, many methods have been proposed for producing reduced iron by heating and reducing a raw material containing an iron oxide source and a carbonaceous reducing agent, or by further melting after heating and reducing to produce granular metallic iron. However, in the manufacturing technology of granular metallic iron known so far including the method disclosed in the above publication, quality and handling properties as raw materials for iron making, steel making or alloy steel production are comprehensively considered. Thus, it is difficult to say that it has been established as a specific technique for producing granular metal iron having an appropriate particle size range with high yield.

  Further, for the carbonaceous reducing agent used as a raw material for producing metallic iron as described above, it is desirable to use a high quality carbonaceous material having a high fixed carbon content such as processed carbonaceous material such as coke and oil coke, anthracite and bituminous coal. However, recently, with the depletion of high-quality coal, low-quality coal such as lignite has often been used, and when these low-grade coal is used as a carbonaceous reducing agent, The quality and yield of the obtained granular metallic iron are lowered, and various unexpected problems arise especially when trying to obtain granular metallic iron having an appropriate particle size configuration.

  The present invention has been made paying attention to the circumstances as described above, and its purpose is not only when a high-quality carbon material is used as a carbonaceous reducing agent, but also when a low-quality carbon material is used, The object is to establish a method capable of producing granular metal iron having a high Fe purity and an appropriate particle size structure with high yield and high productivity.

  The production method of the present invention that has been able to solve the above-described problem is that a raw material containing a carbonaceous reducing agent and an iron oxide-containing substance is heated in a reduction melting furnace, and the iron oxide in the raw material is solid-reduced, and then the metal produced In the method of producing granular metallic iron by further heating and melting iron and aggregating it while separating it from the slag component, the gist is that a carbonaceous reducing agent having a high fixed carbon content is used.

  The carbonaceous reducing agent used in carrying out the present invention has a fixed carbon content of 73% (meaning mass%, hereinafter the same) or more, more preferably 74.5% or more. The amount of volatile components in the content is suppressed to 3.9% or less, more preferably 3.2% or less. Furthermore, the amount of carbonaceous reducing agent added to the metal oxide component contained in the iron oxide-containing material of the raw material If the temperature at which the metallic iron produced by solid reduction in the reduction melting furnace is melted is controlled to 1400 ° C. or higher, or 1460 ° C. or higher, the particle size is reduced to 45% or less, more preferably 44% or less. It is preferable because a relatively large granular metal iron can be obtained at a higher yield.

  As the carbonaceous reducing agent within the above-mentioned preferred fixed carbon amount range, a carbon material having a large amount of fixed carbon itself can be used alone, or a high quality carbon material having a relatively large amount of fixed carbon and a small amount of fixed carbon. It is preferable to use low-quality carbon materials in combination and adjust their blending ratio to ensure a predetermined amount of fixed carbon because even low-quality carbon materials can be used without any problem. In addition, if the powdered carbonaceous material is charged in the vicinity of the raw material before the metallic iron produced by the solid reduction in the reduction melting furnace is melted, the powdered carbonaceous material will change the atmosphere in the vicinity of the raw material at the end of the solid reduction. It can be kept highly reducible, and the reoxidation of the produced metallic iron is more reliably prevented, and the carbonaceous material becomes a source of carburizing into the metallic iron, and the melting and agglomeration of the metallic iron are performed at a lower temperature. It is preferable because it can contribute to the reduction of thermal deterioration of the reduction melting furnace, the reduction of thermal energy for operation, and the improvement of the productivity of granular iron.

  Further, the particle size of the granular metallic iron obtained in the present invention is not particularly limited, but it is preferable in consideration of the separation efficiency from the slag produced as a by-product during production, the ease of transportation and handling as a product, etc. Is in the range of 2-50 mm, more preferably 3-40 mm in particle size. Here, the granular metallic iron does not necessarily mean a true sphere, but is a general term for an oval shape, an egg shape, or a granular material including those slightly flattened. The diameter of an approximately true sphere is the average, the average of the major and minor axes for an oval and egg-shaped one, and the sum of the major and minor axes and the maximum thickness for a slightly flattened one. According to the present invention, granular metallic iron having a particle size in the range of 3 to 40 mm can be obtained with a yield of 80% or more, and further 90% or more.

The fixed carbon in the carbonaceous reducing agent means the carbon content according to the definition and measurement method defined in JIS M8812, and the volatile content is also defined in the same standard. The volatile content of lower hydrocarbons such as CH ₄ Organic substances, adsorbed H ₂ , CO, CO ₂ , moisture, and the like, and Zn, Pb, etc. are included when dusts are used as iron oxide-containing substances.

  Further, a part or all of the carbonaceous reducing agent or powdered carbonaceous substance in the raw material discharged from the reducing melting furnace together with the granular metallic iron to the outside of the furnace is reused as the carbonaceous reducing agent in the raw material. It is also recommended as a preferred form when practicing the present invention.

  The present invention is configured as described above, and when a raw material containing an iron oxide source and a carbonaceous reducing agent is heated and reduced to produce granular metallic iron, the amount of fixed carbon and the amount of volatile matter are specified as the raw material. By using carbonaceous materials, or by appropriately adjusting the amount of carbonaceous materials mixed with the iron oxide source, it is possible to produce granular metallic iron with a grain structure suitable for transportation and handling as products with high yield and high productivity. Decided to get.

  As described above, in the present invention, an iron oxide-containing substance such as iron ore, iron oxide or a partially reduced product thereof (hereinafter sometimes referred to as an iron oxide source or iron ore) and a carbonaceous reducing agent such as coke or coal. When reductively melting a raw material containing (hereinafter sometimes referred to as a carbonaceous material), further heating and melting the produced metal iron, and agglomerating while separating from the by-product slag component to produce granular metal iron In particular, the carbonaceous reducing agent that acts as a reducing agent for the iron oxide source in the raw material is selected and used with a high fixed carbon content, and further, the volatile content in the raw material and the iron oxide content in the raw material By appropriately adjusting the amount of carbonaceous reducing agent added to the metal oxide component contained in the substance, it promotes the melting and aggregation of metallic iron during reduction and melting, and the granular metal iron with an appropriate particle size configuration has a good yield. I tried to get it Than is.

  The raw material used here is not particularly limited as long as it contains the iron oxide source and the carbonaceous material, and a uniform mixture of these powders, or pellets using these in combination with an appropriate binder if necessary. However, in order to obtain the granular metal iron having a relatively large particle size intended in the present invention with high yield and high productivity, it may be converted into an average particle size of 3 It is desirable to use a thing of about ~ 30 mm.

  Hereinafter, the basic manufacturing method employed in the present invention will be described more specifically with reference to the drawings of the embodiments, and the reasons for defining the above requirements will be clarified.

  1-3 are schematic diagrams showing an example of a moving bed type reductive melting furnace developed by the present inventors to which the present invention is applied, and show a dome type structure having a donut-shaped rotating moving bed. 1 is a schematic sketch, FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, and FIG. 3 is a schematic cross-sectional view developed in the rotational movement direction of the rotary moving floor in FIG. In the figure, 1 is a rotary hearth, 2 is a furnace body covering the rotary hearth, and the rotary hearth 1 is configured to be rotationally driven at an appropriate speed by a driving device (not shown). .

A plurality of combustion burners 3 are provided at appropriate positions on the wall surface of the furnace body 2, and the heat of the raw material is reduced by transferring the combustion heat of the combustion burner 3 and its radiant heat to the raw material on the rotary hearth 1. . The furnace body 2 shown in the figure is a preferred example. The interior of the furnace body 2 is partitioned by a partition wall K into a reductive melting zone Z ₁ and a cooling zone Z _2. On the upstream side, the raw material and auxiliary raw material charging means 4 are arranged facing the rotary hearth 1, and at the most downstream side in the rotation direction (because of the rotating structure, the upstream side of the charging means 4 is also actually upstream. Is provided with a discharging means 6.

  As a heat source for the heat-reduction melting furnace, burner heating using gas, heavy oil, pulverized coal, waste plastic or the like as fuel, or by effectively using a combustible gas generated in the furnace, supplying oxygen or air It is also possible to use a combustion type or a heat storage burner. In addition, the generated granular metallic iron can be discharged by using an arbitrary discharging device such as a screw or a scraper, or a method of discharging by using gas blowing or suction.

  In operating the reduction melting furnace, the rotary hearth 1 is rotated at a predetermined speed, and the raw material is placed on the rotary hearth 1 with an appropriate thickness using the vibratory feeder 5 from the charging device 4. We will continue to supply. In charging the raw material, it is usually charged so that it is in a range of 10 to 40 mm, preferably 20 to 30 mm. When a molded body (pellet, briquette, etc.) is used as a raw material, Depending on the diameter, a single layer or 3 to 10 layers, preferably 3 to 6 layers, may be stacked and charged, and the raw material charge per unit hearth area may be increased to increase productivity.

  In addition, when the raw material is charged in layers, if the surface of the raw material layer is formed with irregularities of an arbitrary size, the effective heat transfer area on the surface is expanded, and the heating efficiency for the charged raw material is further increased. In addition, the heating efficiency with respect to the raw material on the lower layer side is improved, which is preferable. The unevenness is formed, for example, by changing the charging amount from a plurality of supply ports in the hearth width direction, or by changing the charging amount from an uneven hopper provided extending in the furnace width direction. For example, a method of forming irregularities by tracing with a surface shaping member having irregularities after being inserted almost horizontally may be employed.

The raw material charged on the hearth 1 receives combustion heat and radiant heat from the combustion burner 3 in the process of moving through the reductive melting zone Z ₁ and is generated by the reaction of iron oxide and carbonaceous reducing agent contained in the raw material. The iron oxide is reduced by the carbon monoxide that is produced, and the produced metallic iron is further heated in a carbon-rich atmosphere to be carburized and melted, and agglomerated while separating from the by-product slag to form granular molten metallic iron. After that, it is cooled and solidified by an arbitrary cooling means C in the cooling zone Z ₂ and is sequentially scraped by the discharge means 6 provided on the downstream side thereof. At this time, by-product slag is discharged at the same time, but after passing through the hopper H, the granular metal iron and slag are separated by any separation means (sieving, magnetic separator, etc.), and finally the iron content It can be obtained as granular metallic iron having a purity of about 95% or more, more preferably about 98% or more and a very low slag component content.

  In the above reduction / melting process, if the atmospheric temperature during the reduction (solid reduction phase) is too high, specifically, the atmospheric temperature is determined from the gangue component in the raw material, unreduced iron oxide, etc. When the temperature exceeds the melting point of the slag composition, the slag having a low melting point melts and reacts with the refractory constituting the moving hearth, so that the smooth hearth cannot be maintained. In addition, if more heat is applied than required for the reduction of iron oxide in the solid reduction phase, FeO, which is an iron oxide in the raw material, melts before being reduced, and the molten FeO becomes carbon ( So-called smelting reduction that reacts with C) (a phenomenon in which reduction proceeds in a molten state, which is different from solid reduction) proceeds rapidly. Metallic iron is also generated by the smelting reduction, but when the smelting reduction occurs, the highly fluid FeO-containing slag significantly melts down the hearth refractory, making continuous operation as a practical furnace difficult.

  Such a phenomenon varies depending on the composition of the slag forming component contained in the iron ore and carbonaceous material constituting the raw material, or the binder, etc., but if the atmospheric temperature during solid reduction exceeds about 1400 ° C., The melting of the hearth refractory occurs due to the exudation of the low melting point slag, and when the temperature exceeds 1500 ° C., the unfavorable smelting reduction reaction proceeds to dissolve the hearth refractory regardless of the brand name of the raw iron ore. Since the loss becomes remarkable, it is desirable to keep the temperature during the solid reduction period at 1500 ° C. or lower, more preferably at about 1450 ° C. or lower. Note that if the temperature of the solid reduction period is too low, solid reduction is difficult to proceed efficiently. Therefore, it is preferably 1200 ° C. or higher, more preferably 1300 ° C. or higher.

  After the solid reduction, the ambient temperature is preferably raised by about 50 to 200 ° C. and raised to 1400 to 1500 ° C. to melt the metallic iron produced by the solid reduction and agglomerate the molten metallic iron. At this time, the molten metal iron is agglomerated and coarsened, but during this time, the molten metal slag is agglomerated while being rejected, so the agglomerated metal iron has a high Fe purity that contains almost no slag. When this is cooled and solidified, and the granular metallic iron and slag are separated by sieving or magnetic separation, granular metallic iron with high Fe purity can be obtained.

  The melting of metallic iron produced by solid reduction proceeds by raising the ambient temperature above the melting point of metallic iron, but if C or CO is present in the vicinity of metallic iron at the start of melting, These are preferable because the metal iron is carburized to cause a melting point drop, and the melting of the metal iron can proceed at a lower temperature and in a shorter time. That is, in order to proceed with the melting quickly, it is preferable to leave a sufficient amount of carbon for the carburization in the raw material after the solid reduction, and this residual carbon amount is the same as the iron ore and carbonaceous material in the raw material. What is necessary is just to adjust with the mixture ratio of. As a result of experiments confirmed by the present inventors, in the state in which the final reduction rate in the solid reduction phase has reached almost 100%, that is, in the state in which the metallization rate has reached 100%, If the initial carbonaceous material blending amount is secured so that the carbon amount (ie surplus carbon amount) is 1.5% or more, the metal iron produced by solid reduction can be rapidly carburized to lower the melting point. It has been confirmed that it can be rapidly melted in the temperature range of 1300 to 1500 ° C.

  In addition, when the carburizing amount is zero, that is, the melting temperature of pure iron is 1537 ° C., the metal iron can be melted if heated to a temperature higher than this temperature, but in a practical furnace, the heat applied to the hearth refractory In order to reduce the load, it is desirable to keep the operating temperature as low as possible, and considering the melting point of by-product slag, it is desirable to keep the operating temperature below about 1500 ° C.

  In order to efficiently reduce the raw material charged in the furnace without causing partial melting of the iron oxide contained in the raw material while maintaining the solid state, the furnace temperature is set to 1200 to 1500. The solid reduction is performed while maintaining the temperature within a range of 1200 ° C., more preferably 1200 to 1400 ° C., and subsequently the furnace temperature is increased to 1400 to 1500 ° C. to reduce the remaining iron oxide and to melt the produced metallic iron It is desirable to adopt a two-stage heating method that causes them to agglomerate, and by setting these conditions, it is possible to produce granular metallic iron stably and with good yield, and solid reduction and melting of iron oxide usually takes about 10 to 13 minutes. And agglomeration can be completed.

  When producing granular metallic iron by adopting the method as described above, in the present invention, the carbonaceous reducing agent that acts as a reducing agent on the metal oxide component in the iron oxide-containing material has a high fixed carbon content. The yield as granular metallic iron can be reduced by using a low volatile content or by specifying the ratio of the carbonaceous reducing agent to the metal oxide component contained in the iron oxide-containing substance. Since it has the characteristic in the place to raise, those points are explained in full detail below.

  4 to 9 are graphs showing the effects of the above-mentioned requirements defined in the present invention on the yield of granular metallic iron as a product, based on experimental data obtained in examples described later. In these figures, the yield of granular metallic iron with a grain size of 3.35 mm or more (recovery rate: mass%) is used as a temporary standard to ensure a grain size configuration suitable for product transportation and handling. It was evaluated with. Here, since iron ore is used as the iron oxide-containing substance, the metal oxide component contained therein is iron oxide.

  4 and 5 are graphs showing the effects of the amount of fixed carbon in the carbonaceous material blended as a raw material on the yield of granular metallic iron. FIG. 4 is a diagram showing the melting of metallic iron that has undergone solid reduction. FIG. 5 shows the results when the temperature is set to 1460 ° C. when the temperature at the time of starting is set to 1400 ° C. As is apparent from these figures, the yield as granular metallic iron varies considerably depending on the temperature at the start of melting, and when the melting start temperature is set to 1400 ° C, the amount of fixed carbon in the carbonaceous material is around 74%. If the carbon material with a fixed carbon content of 74.5% or more is used, the yield of the granular metal iron having the target particle size configuration can be secured about 80% or more. When it is about 75% or more, a high yield of 90% or more can be secured. On the other hand, when the melting start temperature is set to 1460 ° C., as shown in FIG. 5, the yield rapidly rises from around 72% of the fixed carbon content in the carbonaceous material, and the carbonaceous material having the fixed carbon content of about 73% or higher. Can be used to secure a yield of about 80% or more of granular metallic iron having a target particle size configuration, and when the amount of fixed carbon is about 73.5% or more, a high yield of 90% or more can be secured. I understand. As is clear from these results, when a carbon material having a fixed carbon content of 73% or more is used, the temperature at the start of melting is set to about 1460 ° C. or more, so that the metallic iron having a suitable particle size is 80%. In the case of using a high quality carbon material with a fixed carbon amount of 74.5% or more, sufficient yield can be ensured even if the melting start temperature is lowered to about 1400 ° C. I understand that.

  In addition, what is necessary is just to use the said carbon material independently when the amount of fixed carbon of the said carbon material is about 73% or more, or 74.5% level or more. Moreover, even if it is a low-grade coal with a fixed carbon content of less than 73%, it can be used without any problem if it is used in combination with a high-grade coal with a high fixed carbon content to ensure the above suitable fixed carbon content as a total. As a result, even low-grade coal that is difficult to use alone can be used effectively.

  Next, FIGS. 6 and 7 are graphs showing the effect of the amount of volatile components in the raw material on the yield of granular metallic iron, and FIG. 6 shows the temperature at which the solid iron subjected to solid reduction starts melting. FIG. 7 shows the results when the temperature is set to 1460 ° C., respectively. As is apparent from these figures, the yield as granular metallic iron also varies considerably depending on the temperature at the start of melting. In this case, when the melting start temperature is set to 1400 ° C., the volatile content is about 3.2%. If the volatile content is 3.2% or less, a yield of 80% or more can be obtained, and if the volatile content is about 2.9% or less, the yield is 90% or higher. Can be secured. On the other hand, when the melting start temperature is set to 1460 ° C., the yield is remarkably reduced when the volatile content exceeds the 3.9% level as shown in FIG. It can be seen that the above yield can be obtained, and that a high yield of 90% level or higher can be secured if the amount of volatile matter is suppressed to a level of 3.7% or lower. As is clear from these results, when the volatile content is at a level of 3.8%, by setting the temperature at the start of melting to about 1460 ° C. or more, metallic iron having a suitable particle size is 80% or more. It can be seen that when it can be produced at a high yield and the volatile content is at or below the 3.2% level, a sufficient yield can be secured even if the melting start temperature is lowered to about 1400 ° C.

  Further, FIGS. 8 and 9 summarize the effects of the amount of carbonaceous material on the metal oxide component (iron oxide content: T.Fe) in the iron oxide-containing material (iron ore) blended as a raw material on the yield of granular metal iron. FIG. 8 shows the results when the solid iron subjected to solid reduction starts melting at 1460 ° C., and FIG. 9 shows the results when the temperature is set at 1400 ° C. Yes. As is apparent from these figures, the yield as granular metallic iron also varies considerably depending on the temperature at the start of melting. In this case, when the melting start temperature is set to 1400 ° C., the amount of the carbon material is approximately 44.2. If the carbon content is 44% or less, a yield of 80% or more can be obtained, and if the carbon content is suppressed to about 43.6% or less, the yield is 90%. High yield above the level can be secured. On the other hand, when the melting start temperature is set to 1460 ° C., as shown in FIG. 8, when the amount of the carbon material exceeds the 45% level, the yield is remarkably lowered. It can be seen that a yield can be obtained, and that a high yield of 90% or higher can be ensured if the amount of carbon material is suppressed to 44.8% or lower. As is clear from these results, when the amount of the carbon material is at the 45% level, by setting the temperature at the start of melting to about 1460 ° C. or higher, the metallic iron having a suitable particle size is increased to 80% or higher. It can be seen that when the amount of carbonaceous material is 44% or less, sufficient yield can be secured even if the melting start temperature is lowered to about 1400 ° C.

  By the way, in the reduction melting furnace used for carrying out the present invention, burner heating is often employed for heating the raw material. In this case, during the solid reduction period, a large amount of CO gas is generated due to the reaction between the iron oxide source in the raw material charged in the furnace and the carbonaceous material, so that the vicinity of the raw material is shielded from the CO gas released from itself. A sufficiently reducing atmosphere is maintained depending on the effect.

However, from the latter half to the end of the solid reduction period, the amount of generated CO gas rapidly decreases, so that the self-shielding action is reduced and combustion exhaust gas (oxidizing gas such as CO ₂ and H ₂ O) generated by burner heating. It becomes easy to receive the influence of the metal iron after the corner reduction. In addition, after the solid reduction is completed, the melting and agglomeration of the fine metallic iron proceed due to the melting point drop due to the carburization of the reduced iron due to the residual carbon in the raw material. It is susceptible to oxidation.

Therefore, it is desirable to appropriately control the atmospheric gas composition in the melting region in order to efficiently promote melting and aggregation after solid reduction while suppressing such reoxidation as much as possible. As a preferable means for that purpose, as described above, prior to charging the raw material onto the hearth, the powdery carbonaceous material is charged on the hearth, or the surface of the raw material in the case where the raw material is a molded body is previously carbonaceous. The method of making powder adhere is mentioned. That is, if the powdery carbonaceous material is charged to the hearth surface in this way, or the carbonaceous material is attached to the surface, these are generated by burner combustion at the start of melting after completion of solid reduction. Because it reacts immediately with the oxidized gas (CO ₂ and H ₂ O) and changes these gases into reducing gases such as CO and H ₂ , the vicinity of metallic iron produced by solid reduction is kept in a highly reducing atmosphere. And reoxidation of metallic iron can be prevented as much as possible. In addition, these powdery carbonaceous materials are preferable because they serve as a carburizing source for the produced metallic iron, and further exert an effect of promoting granulation by further reducing the time required for carburizing and melting the metallic iron.

  In order to effectively exert the effect of the carbonaceous material, the powdery carbonaceous material charged in advance on the hearth has a particle size of 3 mm or less, more preferably 2 mm or less, and particularly preferably 0.3 to A refined product having a range of 1.5 mm is used, which is preferably charged to a thickness of preferably about 2 to 7 mm, more preferably about 3 to 6 mm, and the raw material is molded and used. When it is made to adhere to the surface occasionally, it is desirable to set the adhesion amount to the range of 1-10 mass% with respect to this molded object, More preferably, it is the range of 3-7 mass%. However, it is also possible to charge the powdery carbonaceous material so as to descend from above before the melting start time at which the effect is most expected.

The granular metallic iron obtained by the above method is agglomerated while excluding by-product slag, and it contains almost no slag component and has very high Fe purity. Although it is used as a feed iron source to existing steel making facilities such as a furnace, it is desirable to reduce the content of sulfur [S] as much as possible in order to use these as steel making raw materials. Therefore, in the production process of metallic iron, a study was conducted to obtain as low as [S] granular metallic iron by removing as much as possible the S component contained in iron ore and carbonaceous materials. In a raw material that contains an appropriate amount of CaO source (including slaked lime and calcium carbonate in addition to quick lime) together with iron ore and charcoal, and that also incorporates slag forming components such as gangue components contained in iron ore If the components are adjusted so that the basicity (ie, CaO / SiO ₂ ratio) of all the slag forming components contained is in the range of 0.6 to 1.8, more preferably 0.9 to 1.5, finally It has been confirmed that the S content in the obtained granular metallic iron can be reduced to 0.10% or less, and further to about 0.05% or less.

  Incidentally, the coal most commonly used as a carbonaceous reducing agent usually contains about 0.2 to 1.0% of S, and most of these [S] is taken into metallic iron. On the other hand, when the basicity adjustment by positive addition of the CaO source is not performed, the basicity calculated from the slag-forming component contained in the raw material is 0.3 in most cases, although there is a considerable difference depending on the brand of iron ore. In such a low basicity slag, it is inevitable that S is mixed (vulcanized) into the granular metallic iron during solid reduction or subsequent melting / aggregation process, and all [S] contained in the raw material is contained. About 85% of the total amount is taken into the granular metallic iron. As a result, the amount of [S] of the granular metallic iron becomes a very high value of 0.1 to 0.2%, and the quality as the granular metallic iron is impaired.

  However, if the composition of the slag forming component is adjusted so that the basicity is in the range of 0.6 to 1.8 by positively adding a CaO source at the raw material preparation stage as described above, solid reduction and carburizing / melting / aggregation are performed. [S] is fixed in the slag by-produced at the time, and as a result, the amount of [S] of the granular metallic iron can be greatly reduced to, for example, 0.050 to 0.080% level. The mechanism for reducing S is considered to be that [S] contained in the raw material reacts with CaO (CaO + S = CaS) and is fixed as CaS.

  The raw materials used in the present invention are, as described above, a homogeneous mixture containing an iron oxide source and a carbonaceous material, and these agglomerated into particles of an appropriate size by using a small amount of binder (such as bentonite and starch) as necessary. Alternatively, it can be used as a molded body such as pellets and briquettes. When forming a molded body, for example, a normal molding method using a bread granulator, a disk granulator, a drum granulator or the like may be employed.

  Moreover, the iron oxide source used as a raw material is a broad concept including iron ore, mill scale, and the like, and may of course include blast furnace dust, electric furnace dust, steelmaking dust, and the like. Furthermore, depending on the iron ore production area, oxides of other metals such as Ni, Cr, Mn may be included in addition to iron oxide, but it is of course possible to include those other metal oxide components. . The kind of carbonaceous reducing agent is not particularly limited, and charcoal powder can be used in addition to the most common coal powder and coke powder. Examples of the binder that may be blended if necessary include bentonite and starch, but of course there is no reason to be limited thereto. Furthermore, if an appropriate amount of CaO source (quick lime, slaked lime, calcium carbonate, etc.) is contained in the raw material mixture for adjusting the basicity of the slag forming component, these act as a desulfurizing agent, and S contained in the raw material mixture Since it is fixed to the slag side as CaS and granular metallic iron with a low S content can be obtained, it is preferable.

  Furthermore, for adjusting the melting point of slag by-produced in the solid reduction process, an appropriate amount of limestone, slaked lime, calcium sources such as calcium carbonate, silica, alumina, etc. may be added depending on the composition of the slag-forming component contained in the raw material. It is valid.

  The supply of raw materials to the hearth surface is not necessarily a special method. For example, it is cut by a hopper, a vibration feeder, a drum feeder, etc., and supplied using a guide rod, pipe, or inclined plate. Should be adopted.

  Further, when the raw material is charged in layers, the surface of the raw material layer is formed into a concavo-convex shape by forming peaks and troughs of any shape in the vertical direction and / or side, and the surface area is increased by increasing the surface area. Increasing the heating efficiency by burner heating or radiant heat is preferable because the heating efficiency of the entire raw material can be increased and the heat transfer efficiency to the lower raw material layer can also be increased. The preferable shape, size, pitch, and the like of the unevenness cannot be uniformly defined because it varies depending on the laminated thickness, but preferably 5 to 30 mm in height (interval between the peak and valley bottom), More preferably, it is the range of 10-30 mm, It has confirmed that the preferable pitch (width | variety between adjacent peak parts) is the range of 10-100 mm, More preferably, it is the range of 10-70 mm. There is no particular limitation on the method of forming the unevenness, for example, a method of charging by changing charging amounts from a plurality of supply ports in the hearth width direction, charging from an uneven hopper provided extending in the furnace width direction. A method of charging by changing the thickness, a method of forming irregularities by tracing with a surface shaping member having irregularities after being charged almost horizontally, and the like can be selected and applied.

  In addition, when using a molded object as a raw material, the average particle size is preferably about 1 to 10 mm, more preferably 3 to 7 mm, because it may be crushed by the lamination load particularly when it is laminated and loaded on the hearth. It is desirable to use a molded body of a degree. With such a relatively small-diameter molded body, there is little possibility of crushing due to laminating pressure even when laminating, and heat transfer is fast, so it is dried quickly by initial heating, so it is not dried It can also be supplied on the hearth as it is. Moreover, in order to prevent more reliably the damage by the impact at the time of insertion or a lamination load, it is also recommended as a preferable embodiment that the charged body is dried after at least the surface layer side is dried in advance.

  Furthermore, when charging the raw material, the raw material is charged after laying a powdery carbonaceous material on the hearth, or when using a molded body, the carbonaceous material is attached to the surface of the molded body. If a method of charging on the hearth is adopted, for example, a) the carbonaceous material increases the reduction degree of the atmospheric gas in the vicinity of the raw material at the time of solid reduction, and the solid reduction proceeds more efficiently, b) the carbonaceous material Carburizes the metallic iron after solid reduction and lowers its melting point to promote melting and aggregation. C) The carbonaceous material suppresses adhesion of molten metallic iron to the hearth surface and promotes granulation. D) Insufficient reduction on the lower layer side, which tends to occur when the raw materials are stacked in layers, is compensated by the carbonaceous material to increase the overall solid reduction rate, and e) Insufficient reduction on the lower layer side Because it acts on FeO and tends to reduce it quickly The production of molten slag containing FeO that significantly melts down the hearth refractory is also suppressed, and the life of the hearth is extended. F) When using the raw material as a compact, the surface is coated with a carbonaceous material. If adhered, mutual adhesion and adhesion to the charging hopper and the like are prevented, so that the raw material molded body can be charged in an undried state.

  As the carbonaceous material used here, coal powder, coke powder, charcoal powder or the like is arbitrarily selected and used. In addition, the preferable particle diameter for exhibiting the said effect | action more effectively as a carbonaceous material spread | laid on an upper surface of a hearth is an average particle diameter of 2 mm or less, More preferably, it is a 1.5 mm or less thing. In addition, when attaching a carbonaceous material to the surface of a raw material molded body, a method of attaching a material having an average particle size of about 0.3 mm or less to the surface, and dispersing the carbonaceous material in a dispersion medium such as water. For example, a spraying method may be employed.

  In addition, carbonaceous reductant in the above-mentioned carbon material and raw materials together with granular metallic iron from the reductive melting furnace (what comes in as powder when charged into the furnace, generated when raw material pellets are pulverized in the furnace Etc.) may be emitted, but these can be reused as carbonaceous reducing agents. Since these materials are once exposed to high temperatures in the furnace to remove volatile components, they become high-quality raw materials.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited by the following examples, and is suitably within a range that can meet the purpose described above and below. It is also possible to change and implement, and all are included in the technical scope of the present invention.

Example 1
An iron oxide source and a carbonaceous material having the following component composition were used, and a production experiment of granular metallic iron was performed under the following conditions using a rotary hearth type reduction melting furnace as shown in FIGS.

[Iron oxide source]
Iron ore: main component; Fe; 68.1%, Al ₂ O ₃ ; 0.5%,
SiO ₂ ; 1.4%, average particle diameter; 50 μm
[Carbonaceous reducing agent]
Carbonaceous material (1): Fixed carbon content: 71.6%, volatile content: 19.6%,
Average particle size: 30 μm
Carbonaceous material (2): Fixed carbon content: 77.0%, volatile content: 9.4%
Average particle size: 30 μm

[Raw material preparation]
After blending the iron oxide source and the carbonaceous materials (1) and (2) in the mass ratio shown in Table 1 below and mixing them uniformly, a granular raw material having a particle size of 16 to 19 mm is obtained using a bread type granulator. Prepared.

[Experiment method]
The granular raw material is charged into a rotary hearth type reduction melting furnace to a thickness of about 20 mm, and the temperature is rapidly increased from raw material charging to 1100 ° C. in 4 minutes by burner heating, and solid reduction is performed at about 1350 ° C. After adjusting the temperature, adjust the temperature so that the temperature of the melting start part is about 1400 ° C or about 1460 ° C, and cool the molten and agglomerated metallic iron in the cooling part (using the water cooling jacket provided at the bottom of the hearth) To obtain granular metallic iron. The time from when the raw material is charged until the granular metallic iron is taken out of the furnace is about 10 to 12 minutes. The granular metallic iron taken out of the furnace is separated from the coagulated by-product slag discharged at the same time with a magnetic separator to make only the granular iron, and then the coarse metallic substance is further separated by using a sieve having a mesh size of 3.35 mm. The fine particles were separated and the yield of coarse particles having a particle size of 3.35 mm or more was determined.

  Table 1 shows the composition and composition of raw materials, the specifications including the fixed carbon content, the volatile content, and the yield. Based on the results in Table 1, “Effects of fixed carbon content in carbonaceous material on yield of granular metallic iron” are shown in Tables 3 and 2 and FIGS. 4 and 5, and “volatile content in raw material is granular metallic iron. Tables 5 and 4 and Figs. 6 and 7 show "Effects of Carbonaceous Materials on Iron Oxide (T.Fe) in Iron Ore on Yields of Granular Metal Iron" This is shown in FIGS.

The discussion from these results is as described above in the analysis of FIGS.
(1) When a carbon material with a fixed carbon content of 73% or more is used, the temperature at the start of melting is set to about 1460 ° C. or more, thereby producing metal iron having a suitable particle size with a high yield of 80% or more. If a high quality carbon material with a fixed carbon content of 74.5% or higher is used, a sufficient yield can be secured even if the melting start temperature is lowered to about 1400 ° C.,
(2) When the amount of volatile components in the raw material is at a level of 3.9%, the temperature at the start of melting is set to about 1460 ° C. or higher to produce metallic iron with a suitable particle size at a high yield of 80% or higher. If the volatile content is below the 3.2% level, a sufficient yield can be obtained even if the melting start temperature is lowered to about 1400 ° C.,
(3) When the amount of carbonaceous material with respect to the iron oxide content (T.Fe) in iron ore is at a level of 45%, the temperature at the start of melting is set to about 1460 ° C. or more, so that metallic iron having a suitable particle size is 80% It can be manufactured with the above high yield, and when the amount of the carbon material is 44% or less, it can be confirmed that a sufficient yield can be secured even if the melting start temperature is lowered to about 1400 ° C.

It is explanatory drawing which illustrates the reduction | restoration melting equipment used by this invention. It is an AA line cross-section equivalent figure in FIG. FIG. 2 is an explanatory cross-sectional view of FIG. 1 developed in the rotation direction of the rotary hearth. It is a graph which shows the influence which the amount of fixed carbon in a carbon material has on the yield of granular metallic iron when the temperature at the time of a melting start is set to 1400 degreeC. It is a graph which shows the influence which the amount of fixed carbon in a carbon material has on the yield of granular metallic iron when the temperature at the time of a melting start is set to 1460 degreeC. It is a graph which shows the influence which the amount of volatile matter in a raw material has on the yield of granular metallic iron when the temperature at the time of a melting start is set to 1400 degreeC. It is a graph which shows the influence which the amount of volatile matter in a raw material has on the yield of granular metallic iron when the temperature at the time of a melting start is set to 1460 degreeC. When the temperature at the start of melting is set to 1460 ° C., the T.I. It is a graph which shows the influence which the amount of carbon materials with respect to Fe amount has on the yield of granular metallic iron. When the temperature at the start of melting is set to 1400 ° C., T.I. It is a graph which shows the influence which the amount of carbon materials with respect to Fe amount has on the yield of granular metallic iron.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotary hearth 2 Furnace 3 Combustion burner 4 Raw material and auxiliary raw material charging means 5 Vibrating feeder 6 Discharge means K Partition wall C Cooling zone H Hopper

Claims (7)

The shaped body comprising a carbonaceous reducing agent and the iron oxide-containing materials are heated in a reducing melting furnace, after the iron oxide of the molded body and the solid reduced at a temperature of 1200 to 1500 ° C., further heating the metallic iron to produce In the method of producing granular metallic iron having a particle size in the range of 3 to 40 mm by being melted at a temperature of 1400 to 1500 ° C. and agglomerating while being separated from the slag component,
As the carbonaceous reducing agent, one or two or more carbonaceous reducing agents are selected and used so that the fixed carbon content is 73% (meaning mass%, hereinafter the same) or more,
When the fixed carbon content of the carbonaceous reducing agent is 73% or more, the lower limit of the melting start temperature of the metallic iron is set to 1460 ° C,
When the fixed carbon content of the carbonaceous reducing agent is 74.5% or more, the granular metallic iron can be obtained with a yield of 80% or more by setting the lower limit of the melting start temperature of the metallic iron to 1400 ° C. The manufacturing method of the granular metal iron characterized by these. When the fixed carbon content of the carbonaceous reducing agent is 73% or more , the volatile content in the molded body is 3.9% or less,
The process according to claim 1 , wherein when the fixed carbon content of the carbonaceous reducing agent is 74.5% or more, the amount of volatile components in the molded body is 3.2% or less . When the fixed carbon content of the carbonaceous reducing agent is 73% or more, the compounding amount of the carbonaceous reducing agent is suppressed to 45% or less with respect to the metal oxide component contained in the iron oxide-containing substance of the molded body,
When the fixed carbon content of the carbonaceous reducing agent is 74.5% or more, the blending amount of the carbonaceous reducing agent is 44% or less with respect to the metal oxide component contained in the iron oxide-containing substance of the molded body. The manufacturing method of Claim 1 or 2 to suppress. The manufacturing method according to any one of claims 1 to 3 , wherein a powdery carbonaceous material is charged in the vicinity of the molded body before the metallic iron produced by solid reduction in the reduction melting furnace is melted. The manufacturing method in any one of Claims 1-4 using the molded object whose average particle diameter is 3-30 mm. The manufacturing method in any one of Claims 1-5 which mix | blends a slag melting | fusing point modifier in the said molded object , and adjusts melting | fusing point of the slag produced | generated at a reductive melting process to 1400 degrees C or less. A part or all of the carbonaceous reducing agent or powdered carbonaceous substance in the molded body discharged from the reducing melting furnace together with the granular metal iron to the outside of the furnace is reused as the carbonaceous reducing agent in the molded body. The manufacturing method in any one of Claims 1-6 to do.

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