Reduction of iron oxides in induction furnaces using graphite crucibles

Abstract

The present invention relates to an induction furnace containing a graphite crucible and a method for obtaining metallic iron from iron oxides.

Description

[0001] REDUCTION OF IRON OXIDES IN INDUCTION FURNACES USING GRAPHITE CRUCIBLES

[0002] Field of the Invention

[0003] The present invention is related to a method of recovering metallic iron from iron oxides with high efficiency and low economic cost.

[0004] The present invention relates to the reduction of iron oxides in induction furnaces using graphite crucibles.

[0005] State of the Art

[0006] Iron oxides are compounds that occur as a by-product in many industries. Since recycling and / or processing of iron oxide compounds is a long-term, inefficient and high economic cost process, iron oxide compounds are generally sold to the relevant sectors with very cheap prices. Iron oxide compounds (10.02.10 coded scale, 10.02.07 flue dust etc.) are classified as non-hazardous waste by the Ministry of Environment and Urbanization every year, millions of tons of scale (750000 - 2450000 tons) and 400000 tons of flue dust are disposed or sold. This amount corresponds to between 3 and 7% of the total annual iron and steel production. Basically, said scales can participate in processes in different areas. For example, scales with a very low content of undesirable material are added in very small quantities into the melt in iron melting furnaces for the purpose of reducing the amount of carbon or can be used in sintering processes. However, the usage rates are considerably lower than the resulting iron oxides. For this reason, recycle is not preferred; instead they are sold to the relevant sectors. In this sense, high amount of byproducts (generally iron oxide compounds) that do not pose a danger and that can be useful under appropriate conditions cannot be evaluated.

[0007] In the state of the art intensive studies are carried out to obtain iron by reduction of iron oxide compounds. Commonly studied methods use rotary furnaces, arc furnaces and induction furnaces. The most common of the above-mentioned studies is the use of carbon or hydrogen reducers for the reduction of iron oxides. However, hydrogen is a difficult and dangerous gas to obtain. Therefore, reduction with carbon rather than hydrogen is preferred. In the reduction method with carbon from chimney dusts containing zinc, called Waelz, zinc, lead and iron oxide are obtained from flue dust and filter cake or sludge obtained from electric arc furnaces in rotary kilns. In this way, it is possible to recover lead and zinc, which have higher unit prices than iron, as well as metallic iron. The by-product iron obtained here is recovered as sponge iron. Sponge iron can be reused in electric arc furnaces or blast furnaces. However, the recovery rate remains at very low levels. When the above-mentioned method is applied to scale, another source of iron oxide applied to flue dust, sponge iron is also obtained. When the same method is used for the purpose of obtaining iron with a low unit cost such as zinc, only sponge iron can be obtained and the cost of obtaining this type of iron is quite high.

[0008] In the final case, in the Waelz process applied in the rotary kiln, sponge iron is produced as the final product, partial metallization takes place and the electrical conductivity remains low. In addition, the reduction time is determined between 6 -10 hours. It is seen that slagging is high.

[0009] In the patent and literature search carried out for the state of the art, the patent application with the publication number US4494984 A was determined. Said patent application relates to a method for the direct reduction of iron oxide using induction heating. In the above-mentioned method, an iron oxide and carbon-based material is added to the multi-chamber induction furnace, the walls of the chambers are heated by means of induction coils to cause metallization of the iron oxide by the reducing agents contained in the carbonaceous material. Finally, the metallized iron is discharged from the outlet end of the plurality of chambers. However, the above-mentioned application does not mention the use of graphite crucibles.

[0010] As a result due to the abovementioned disadvantages and the insufficiency of the current solutions regarding the subject matter, a development is required to be made in the relevant technical field.

[0011] Brief Description of the Invention

[0012] The present invention relates to the reduction of iron oxides in induction furnaces using graphite crucibles which fulfills the abovementioned requirements, eliminates all disadvantages and brings some additional advantages.

[0013] The present invention aims to solve the abovementioned disadvantages by being inspired from the current conditions.

[0014] The main aim of the present invention is to develop a method of recovering iron from iron oxide in a much shorter time, with high efficiency and low economic cost, compared to the applications in the state of the art. In the invention, metallic iron is specifically obtained from iron oxide by induction.

[0015] Another aim of the present invention is to provide a method that provides the desired final product properties in the process of metallic iron recovery from iron oxide. It is possible to reduce the carbon emission caused by re-feedback by obtaining an iron alloy very similar to pig iron with the help of the inventive method. It is produced as an alternative to iron alloys with high iron content such as scrap and pig iron. With the Waelz method, which is used in the state of the art, 2 - 2.5 gr / cc density, 78 - 80% metallic iron is obtained, in the method of the present invention, the density is in the range of 7,5 - 7,8 gr / cc, and the metallic iron ratio is 95 - 97%.

[0016] Another aim of the present invention is to eliminate the disadvantages caused by the widely used Waelz method.

[0017] Another aim of the present invention is to evaluate the iron oxides produced as a by-product in many industries.

[0018] The structural and characteristic features of the present invention will be understood clearly by the following drawings and the detailed description made with reference to these drawings and therefore the evaluation shall be made by taking these figures and the detailed description into consideration.

[0019] Figures Clarifying the Invention

[0020] In Figure 1 , the general view of a conventional rotary kiln used in the state of the art is given.

[0021] In Figure 2, the general view of the induction furnace used in the method of the invention is given.

[0022] Detailed Description of the Invention

[0023] In this detailed description, the preferred embodiments of the present invention are described by means of examples only for clarifying the subject matter.

[0024] The present invention relates to the method of reduction of iron oxides in induction furnaces by means of graphite crucibles. In the invention, the reduction process can be performed in a much shorter time (45 - 50 minutes) in the induction furnace instead of the rotary furnace (Waelz method), which takes long hours (6 - 10 hours). The induction furnace used in the invention is different from a conventional induction furnace used in the technical field. Because a conventional rammed type lining crucible used in the state of the art will have difficulty in reducing iron oxides. Therefore, the reduction process will take long hours. This poses a risk to process efficiency. In order to solve this problem in the invention, a graphite (carbon) crucible is used in the induction furnace.

[0025] The final properties of the product obtained by the Waelz method, which is used in the state of the art, and the product obtained by the method subject to the invention are compared in the table below.

[0026] If the graphite crucible is not used in the induction furnace during the reduction process, as mentioned above, the processing time will be extended and this will not be economical. Even if carbon reducer is added to the process, the process will not be shortened. In this sense, the use of graphite crucible in said method constitutes the distinguishing feature of the invention.

[0027] In a preferred embodiment of the invention, metallurgical coke can be used in addition to the graphite crucible. The preferred proportion of metallurgical coke is about 10% by weight of iron oxide. Said ratio has been determined by numerous trials carried out within the scope of the invention and it has been found that this maximizes metallization. The stoichiometric efficiency of the coke used in the preferred embodiment cannot be calculated exactly because it gives carbon to the environment in the used crucible, and therefore an approximate result is given.

[0028] In a trial with iron oxide, approximately an efficency of 66% metallic ferrous alloy is recycled per tonne of scale in a typical billet mill scale, depending on the iron oxide distribution. At least 95% of the above-mentioned alloy is metallic iron. In this example, 66.6% (2 / 3) of iron alloy is recycled from approximately 1 ton of iron oxide (scale). When same conditions applied to blast furnace dust in a form of pressed powder or filter cake form than again 95% metallic iron is gained with an efficency of 55- 60%. In both cases, the iron alloys with high metallic iron content are 2,5 - 3 times denser than sponge iron. Therefore, the material does not need to be reprocessed to obtain iron. This saves melting costs and electricity consumption and reduces carbon emissions. In addition, since the obtained metallic alloy can be converted into any physical form, it reduces the volume of the material charged in the furnace for the second melting.

[0029] In addition to the method developed for the reduction of iron oxides to iron, the present invention also relates to the induction furnace in which said method is applied. Said induction furnace comprises at least one graphite crucible for reducing iron oxide to iron.

[0030] The product obtained with the induction furnace in the state of the art and the graphite crucible induction furnace used in the method of the present invention (as a result of melting 500 kg of iron oxide) are compared in the table below.

[0031] The experiment given above shows that the invention has advantages over the prior art in terms of melting time, electricity consumption and Induction Ability

Claims

CLAIMS1. A method of obtaining iron from iron oxides, characterized in that; it comprises the process step of reducing iron oxides to metallic iron in a graphite crucible in an induction furnace very economically compared to actual methods2. Method according to claim 1 , characterized in that; it comprises the process step of metallurgical coke addition.

3. Method according to claim 2, characterized in that; it comprises the process step of adding 10% metallurgical coke.

4. An induction furnace, characterized in that; it comprises at least one graphite crucible for reducing iron oxides to metallic iron.

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