MXPA99006896A - Production method of iron carbide - Google Patents

Abstract

A production method of iron carbide capable of efficiently producing an iron carbide in response to a grain size of an iron-containing material or to the progress of the reaction, comprising the steps of fluidizing a coarse ore in sections (8a to 8e) inside a fluidized bed type reactor (7), fluidizing a fine ore in sections (9a to 9d), and regulating a flow rate of a reaction gas to be supplied to the sections of the fine ore with a flow rate regulating valve (11).

Description

METHOD TO PRODUCE IRON CARBIDE FIELD OF THE INVENTION The present invention relates to a method for producing iron carbide suitable for a raw material for the production of iron and steelmaking comprising iron carbide (Fe3C) as the main component, for example, a raw material for the production of steel, which is used in an electric furnace and the like.

BACKGROUND OF THE INVENTION Steel production typically involves the steps of converting iron ore into pig iron using a blast furnace, and then converting pig iron to steel using a converter or open hearth furnace. Such a traditional method requires large amounts of energy and large-scale equipment, and has a high cost. Therefore, for the processing of small-scale steel, a method has been used that includes the steps of directly converting the iron ore into raw materials used in the steelmaking furnace, and converting the raw material into steel using a electric oven and similar. With regard to the direct steelmaking process, a direct reduction process has been used to convert iron ore into reduced iron. However, the reduced iron produced by the direct reduction process is highly reactive and reacts with the oxygen in the air to generate heat. Therefore, it is necessary to seal the reduced iron with an inert gas, or by any other measure, during transportation and storage of the reduced iron. According to this, iron carbide (Fe3C) which contains a comparatively high iron (Fe) content, and which has a low reaction activity and can be easily transported and stored, has recently been used as the material containing iron for the production of steel in an electric furnace and the like. Moreover, a material for steelmaking or for the manufacture of iron containing iron carbide as the main component is not only easy to transport and store, but also has the advantage that carbon combined with the element can be used iron as a source of energy in a steelmaking or ironmaking furnace, and can be used as a source to generate micro bubbles that reduce nitrogen in a steelmaking bath. Therefore, the raw materials containing iron carbide as the main component for the manufacture of steel and for the manufacture of iron have recently attracted special interest. According to a conventional method for producing iron carbide, a fine iron ore is charged into a fluidized bed reactor or the like, and is reacted with a gas mixture comprising a reducing gas (for example hydrogen gas) and a carburizing gas (for example methane gas and the like) at a predetermined temperature. In this way, iron oxides (for example hematite (Fe2O3), magnetite (Fe3O4), wustite (FeO)) in iron ore are reduced and carburized in a simple process (which means a process carried out by simultaneously introducing a reducing gas and a carburizing gas to a simple reactor). This reaction is performed by the following general reaction formula. 3Fe, O, + 5H, + 2CH, - * • 2 Fe, C + 9H, O The state of the art in the field of the present invention has been described, for example, in the publication of the Japanese translation of the Application Patent Number 6-501983, for example. In order to easily understand the present invention, an example of an apparatus for making iron carbide according to the state of the art will be described below. For example, an apparatus shown in Figure 1 has been known. With reference to Figure 1, the reference number 1 indicates a fluidized bed reactor. The fluidized-bed reactor 1 has an infector part to which a line 2 for the supply of reaction gases (a reducing gas and a carburizing gas) is connected., and an upper part to which a line 3 is connected for the discharge of the gas after the reaction. Reference number 4 denotes a preheating furnace. A fine iron ore fed to the preheating furnace 4 is subjected to a preheating treatment for a predetermined time in the preheating furnace 4. Then, the preheated iron ore is fed into the fluidized bed reactor 1 through a line 5, and is subjected to a carburization and reduction reaction for a predetermined time at a predetermined reaction temperature and reaction pressure within the fluidized bed reactor 1. Therefore, the iron carbide product is discharged from a line 6. In the case where a particle size distribution of the iron ore is wide, it is difficult for the reaction to proceed efficiently. The reaction is as follows. In order for the reaction to proceed efficiently, it is preferable that a velocity of a fluidized gas must be increased comparatively within the fluidized bed reactor 1 if the larger particle size of the iron ore is large (coarse) but the minerals fines should be expelled and that the velocity of the fluidized gas should be lowered comparatively in the fluidized bed reactor 1 if the larger particle size of the iron ore is small (fine) but the coarse minerals should not be fluidized. There are preferable process conditions that depend on the respective particle sizes. Moreover, a mobile bed reactor for iron ore having a large particle size is preferable. A gas to proceed in the reaction can easily be passed through a choke in the large uniform particle size. An increase in the flow rate of the fluidized gas for fluidization causes the generation of fine-sized iron ore by the additional particle friction and is disadvantageous for an iron ore yield. As indicated in the general reaction formula, a Fe203 particle is converted into a Fe3C particle that has about 3/4 of an original weight. In addition, the fine iron minerals rub against each other during the fluidization in such a way that their particle sizes are gradually reduced. Considering that the weight of the fluidized material (fine iron ore) is gradually reduced as the reaction proceeds, it is preferable that the velocity of the reaction gas supplied to the fluidized bed reactor should be increased comparatively in the previous half. of the reaction and be comparatively diminished in the later half of the reaction in order that the reaction proceeds efficiently. Due to the fact that there are proper process conditions according to the progress of the reaction, it is not preferable that the reduction reaction and the carburization reaction must be carried out under the same process conditions within the fluidized-bed reactor. In consideration of the above-mentioned problems of the prior art, an object of the present invention is to provide a method for efficiently producing iron carbide depending on the particle size of an iron-containing material or the progress of the reaction.

BRIEF DESCRIPTION OF THE INVENTION In order to achieve the objects mentioned above, the present invention provides a method for efficiently producing iron carbide by classifying a fine iron-containing material for the manufacture of iron in various grades according to a particle size, and reducing and carburizing the iron. iron-containing material corresponding to the respective particle sizes. A first aspect of the present invention is directed to a method for producing iron carbide comprising the steps of classifying a fine material containing iron for the manufacture of iron in various grades according to a particle size, and reducing and carburizing each material that contains iron belonging to each grade. According to the first aspect of the present invention, it is possible to treat a fine material containing iron for the manufacture of iron having a wide particle size distribution. By selecting the process conditions that depend on a particle size, iron carbide can be produced efficiently. A second aspect of the present invention is directed to the method for producing iron carbide according to the first aspect of the present invention, wherein the fine iron-containing material for the manufacture of iron is classified in various grades according to a size of particles after preheating. According to the second aspect of the present invention, the following effects can be obtained in addition to the above-mentioned effects. More specifically, if it is difficult to classify a wet material containing iron, a same sorting operation can be easily performed because the sorting is carried out in a dry state after preheating or a first step reaction process. Furthermore, the present invention is suitable for treating such iron-containing material as the fine iron ore generated from a raw material that is easily fragmented by heating and does not result in a by-product but in a product. A third aspect of the present invention is directed to the method for producing iron carbide according to the second aspect of the present invention, wherein the carburization and reduction reaction process comprises a first stepwise reaction process for carrying out an part of the reduction reaction and then a second step reaction process to perform the carburization reaction and further reduction. According to the third aspect of the present invention, the following effects can be obtained in addition to the above-mentioned effects. Several counter measures can be adopted for each process that can not be performed by the iron carbide production method in a simple reactor process according to the prior art. Therefore, a flexible process can be obtained. Consequently, a conversion rate and a reaction rate can be easily controlled. Moreover, the energy consumed in the generation of the by-product can be recovered efficiently. A fourth aspect of the present invention is directed to a method for producing iron carbide, comprising the steps of classifying a fine iron-containing material for the manufacture of iron in various grades according to a particle size after a first process of step reaction to reduce a portion of the iron-containing material, and to carry out a second stepwise reaction process to perform the further reduction and carburization reaction for each iron-containing material belonging to each grade. According to the fourth aspect of the present invention, the method of the present invention is suitable for treating the iron-containing material which is easily rendered finer by a reduction reaction. A fifth aspect of the present invention is directed to a method for converting a fine material containing iron for the manufacture of iron into iron carbide by a fluidized bed reactor having a part of the fluidized bed divided into several compartments by partition walls., comprising the steps of dividing the compartments into two portions for fine and coarse materials containing iron, respectively, and reducing and carburing the coarse materials containing iron in one part and the fine materials containing iron in the other part. According to the fifth aspect of the present invention, the supply of raw material can be treated in a reactor in which the fine and coarse minerals are reacted separately under their own conditions for each mineral. Therefore, the use of the reaction gas is optimized and an efficient process is achieved. In the present invention, the iron-containing material for the manufacture of iron is an iron ore or a powder or the like which is generated from an iron manufacturing process comprising at least one of the iron oxides such as iron. as hematite, megnetite and wustite and iron hydroxides such as ferrous hydroxide and ferric hydroxide or mixtures thereof of more than two as the main component. According to the present invention having the constitution mentioned above, the iron-containing fine material for the manufacture of iron which has a wide particle size distribution can be classified into several grades according to the size of the particles, and process conditions (reaction temperature, reaction time, gas flow rate and the like) corresponding to the respective particle sizes can be selected for an iron-containing material belonging to each grade. Consequently, iron carbide can be produced efficiently. Some materials that contain iron are easily fragmented by heat. Such materials are classified after preheating, and the process conditions that depend on each particle size are selected after sorting. Consequently, iron carbide can be produced efficiently. In addition, by applying a two-stage process to carry out a first stage reaction process that performs a part of the reduction reaction and then a second stepwise reaction process that performs the reduction reaction and additional carburization, a used gas in the first stepwise reaction process it may be an optimum composition only for the reduction reaction, and a gas used in the second step reaction process may be an optimum composition for the further reduction and carburization reaction. Applying the two-step process in the reduction and carburization (conversion to iron carbide) of the iron-containing material, a reaction rate can be increased and a reaction time (a time required to convert the iron-containing material into carbide iron) can be shortened as compared to a process to produce iron carbide in a simple process. Some iron-containing materials are easily converted into finer by a reduction reaction. Such materials are classified after the partial reduction, and the reduction and carburization reaction conditions corresponding to each particle size are selected after classification. Consequently, the reaction can be carried out efficiently. In the fluidized-bed reactor having a part of the fluidized bed divided into several partition walls of compartments, the compartments are classified into two portions for iron-containing materials comprising coarse and fine particles, and the separation is carried out separately. reduction and carburization of iron-containing materials comprising coarse and fine particles. Therefore, the supply of raw material and the discharge of the products can be carried out continuously, and the fluidization can be carried out uniformly for both the fine and coarse particles, and a contact area between the reaction gas and the raw material for the fine particles can be appropriately designed in such a way that the reaction time can be shortened.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a view showing a schematic flow according to the state of the art of an apparatus for producing iron carbide; Figure 2 (a) and 2 (b) are diagrams showing examples of the processes performed when iron carbide is produced according to the present invention, respectively; Figure 3 is a diagram showing another example of the process performed when iron carbide is produced according to the present invention; Figure 4 is a graph showing a fluidization range based on the particle size and a gas flow rate; and Figure 5 (a) is a side sectional view showing a fluidized bed reactor suitable for carrying out a method according to the present invention, and Figure 5 (b) is a sectional view taken along of the VV line in figure 5 (a).

BEST WAY TO CARRY OUT THE INVENTION The case where a method according to the present invention is applied to a fluidized bed reactor will be described below. (1) Classification Synchronization As described above, some iron-containing materials are easily fragmented by heat or easily converted into finer by a reduction reaction. For example, the rate of generation of a fine iron ore having a size of 70 μm or less is generally varied according to the type of raw material iron ore (from 0.1 mm to 1.0 mm) depending on the circumstances of the treatment to which the iron ore is subjected as shown in table 1.

TABLE 1 Mining type of steel A B C D After preheating 1% 8% 0% 12% After the reduction 12% 2% 5% 4% After carburization 5% 1% 2% 1% As will be described below, the optimal process conditions can be adopted by applying a classification synchronization suitable for the type of iron ore. (a) in the case where the iron ore (mineral "B" and "D") that is easily fragmented by heat, is used as a raw material, it is preferable that the process shown in figures 2 (a) should be applied and 2 (b). (b) in the case where the iron ore (ore "A") that is easily converted into thinner by a reduction reaction, is used as the raw material, it is preferable that the process shown in Figure 3 be applied. In Figures 2 (a) and 2 (b) and Figure 3, although the coarse and fine iron ores can be treated separately within the respective reactor, these can be treated simultaneously in a reactor if the reactor has the configuration described in (3). In addition, the classification can be set at two or more depending on the particle size distribution of the iron ore. (2) Sort Size Selection A classification size for the coarse and fine iron ore division based on the particle size distribution can be obtained as shown in Figure 4, for example. Figure 4 shows a range of fluidization, where a horizontal axis indicates a particle size (dp: logarithmic representation) and a vertical axis indicates a surface velocity (u: logarithmic representation). Line A indicates a lower limit of fluidization. Below line A, the speed is not sufficient to fluidize the iron ore inside the reactor. Line B indicates a limit of one ejection velocity (terminal velocity). Above line B, the velocity is very high so that the iron ore is expelled, and similarly, the iron ore may not be floated or fluidized. As shown in Figure 4, if the particle size distribution of the iron ore varies from 0.1 to 1.0 mm, the iron ore can be floated and fluidized under the same process conditions. Because the gas velocity in A1 is lower than in B1. However, if the particle size distribution of iron ore is wide, for example, the iron ore comprises a fine iron ore having a particle size of 0.05 to 0.5 mm and a coarse iron ore having a particle size of 0.5 to 5 mm, it is preferable that the reaction be carried out for the fine iron ore and the coarse iron ore separately in order to cause the reaction to proceed efficiently and that a borderline size for the division into "fine" and "coarse" should vary from 0.2 to 0.8 mm . If coarse iron ores having particle sizes of 5 to 7 mm or more is larger, it is preferable that a moving bed reactor be used. (3) Classification Equipment In the case where the iron ore is classified based on the particle size distribution, the coarse iron ore and the fine iron material can be treated in separate reactors to adopt the operating conditions that depend on the particle size. However, the coarse iron ore and the fine iron ore can be treated simultaneously in a reactor if the reactor has the configuration shown in Figure 5. More specifically, the fluidized bed reactor 7 is divided into compartments 8a to 8e for the coarse iron ore and compartments 9a to 9d for the fine iron ore, a flow regulating valve 11 is provided on a line 10 for a reaction gas to be supplied to the fine iron ore compartments, and the ore Fine iron in a gas discharged from the reactor is captured by a cyclone 12. The fine iron ore is returned to compartments 9a to 9d. According to the reactor having the configuration mentioned above, it is also possible to simultaneously treat the fine iron ore and the coarse iron ore using a simple reactor having the same composition of the incoming gas according to the following method . By adjusting the flow regulating valve 11, it is possible to control the flow rate of the reaction gas to have the best fluidization of the fine and coarse iron ore. In this case, it is preferable that the flow velocity (= surface velocity) of the reaction gas for the fine iron ore must be decreased to avoid the expulsion of the fine iron ore, and a bed height (Hff) of the ore Fine iron should be set lower than the bed height (Hfc) of the coarse iron ore to have the same contact time (gas and minerals). The fine iron ore tends to have a reaction rate that is slightly higher than the coarse iron ore as shown in Table 2. Table 2 indicates a reduction rate, where a Solid Vs. Gas ratio is established at 0.059 kg / LEM, a reaction temperature is set at 630 ° C, a reaction pressure is set at 4 to 5 atm, and a concentration of hydrogen in the reaction gas is set at 65 to 80%. The fine iron ore (Z) has a reduction rate that is slightly higher than that of the coarse iron ore (X, Y). LEM designates the Standard Liters per Minute (1 liter in a normal / minute condition). Therefore, in the case that the coarse and fine minerals are reacted in a reactor, the fine minerals act a lot to react the coarse minerals appropriately.

TABLE 2 In accordance with the present invention, the fine iron ore and the coarse iron ore are reacted separately in the same fluidized bed reactor. Accordingly, an amount of gas that is used per unit weight of iron ore can be reduced and the residence time within the reactor can be shortened. In this way, it is possible to produce iron carbide economically and efficiently. The iron ore classified as finest particles can not only be used to produce iron carbide, but also used as auxiliary material to produce cement or feed material after granulation.

INDUSTRIAL APPLICABILITY Since the present invention has the aforementioned constitution, the apparatus according to the present invention is suitable as the apparatus for efficiently producing iron carbide depending on a particle size of an iron-containing material or the progress of the reaction.

Claims (5)

1. A method for producing iron carbide comprising the steps of: classifying a fine material containing iron for the manufacture of iron in various grades according to the particle size; and reduce and carburize each material that contains iron belonging to each grade.

The method for producing iron carbide according to claim 1, wherein the iron-containing fine material for the manufacture of iron is classified into several grades according to a particle size after preheating.

The method for producing iron carbide according to claim 2, wherein the reduction and carburization reaction process comprises a first step reaction process to carry out a part of the reduction reaction and then a second reaction process by stages to execute the reduction reaction and additional carburization.

4. A method for producing iron carbide, comprising the steps of: classifying a fine material containing iron for the manufacture of iron in various grades according to a particle size after a first stepwise reaction process for the reduction partial of the material that contains iron; and carrying out a second stepwise reaction process to effect the further reduction and carburization reaction for each iron-containing material belonging to each grade.

5. A method for converting a fine iron-containing material for the manufacture of iron into iron carbide by a fluidized bed reactor having a part of the fluidized bed divided into several compartments by partition walls, comprising the steps of: dividing the compartments in two portions for the materials containing coarse and fine iron, respectively, and reducing and carburizing the coarse materials containing iron in one portion and fine materials containing iron in the other portion.