Charcoal composition for steelmaking, slag foaming method in electric arc furnace steelmaking, and use of charcoal composition

Abstract

The present invention relates to a charcoal composition for steelmaking comprising 60 wt% to 90 wt% of fixed carbon, 13 wt% to 25 wt% of volatile material and 0.5 wt% to 5 wt% of ash wherein at least 98 vol% of the composition has a particle size of less than or equal to 40 mm. The invention also relates to a method for foaming slag in steelmaking in an electric arc furnace, and to the use of the charcoal composition in steelmaking.

Description

Technical Field

[0001] The present invention relates to charcoal compositions to be used as a replacement for coke in the process of foaming slag in electric arc furnace steelmaking. Background Art

[0002] The electric arc furnace steelmaking process is well known in the prior art. Iron scraps as raw materials are processed in the first stage (primary metallurgy) together with solid pig iron and / or liquid pig iron, and then the temperature and chemical composition are adjusted to solidify the steel, in this way producing steel products that can be applied in the fields of oil and gas, civil and automotive construction. One of the basic stages of primary metallurgy in electric steelworks is to foam the slag by injecting carbonaceous materials, usually using green petroleum coke, calcined coke and graphite (fossil fuels). At present, about 12 kg of coke is used per ton of molten steel. The foaming of the slag is fundamental because it provides a layer of insulation and protection to prevent the refractory material from being damaged due to the extreme heat radiation from the arc, and in addition ensures the thermal efficiency associated with the energy transfer from the arc to the metal bath.

[0003] However, the use of large amounts of fossil-derived carbonaceous materials, such as coke, emits large amounts of derived carbon dioxide gas, a greenhouse gas, into the atmosphere. Between 40% and 70% of carbon dioxide emissions from the electric furnace steelmaking process come from the stage of injecting carbon to foam the slag. Therefore, this process is a significant environmental impact factor that needs to be mitigated or prevented. In addition, the use of coke involves the input of sources of sulfur and phosphorus into the steelmaking process, which are largely undesirable.

[0004] Due to these problems, alternatives are sought to replace the use of coke in the slag foaming stage. Document CN101558170 discloses a method for manufacturing steel in an electric arc furnace, comprising feeding a mixture obtained by adding carbides obtained by dry distillation of coconut tree or oil palm coconut shells (palm kernel shell charcoal or PKS charcoal) and having a residual volatile material content of 12% or more to iron scraps, and a stage of producing molten steel by melting the iron scraps. According to the document, it is preferred that the residual volatile material content of this material injected into the electric arc furnace by a lance is less than 12%.

[0005] The coke substitute used in this document has a high carbon content and a maximum volatile material content of 12% for the application of the material by the lance. The limitation on the volatile material content is intended to ensure a satisfactory injection of the carbon source that penetrates the slag to continue its foaming, since the higher content of volatile materials associated with the low density compared to coke does not ensure the efficiency of such a process. Another problem with this coke substitute is the small scale of its production and the higher cost of its production, which hinders its continued use, which is more prominent due to the limitation on the volatile material content. Summary of the invention

[0006] Purpose of the Invention

[0007] The object of the present invention is to provide a substitute for coke used in electric furnace steelmaking which is less harmful to the environment by being suitable for use as charcoal in the slag foaming stage.

[0008] Brief description of the invention

[0009] The objects of the present invention are achieved by a method for foaming slag during steelmaking in an electric arc furnace, wherein charcoal is injected onto the surface to foam the slag.

[0010] The charcoal injected in the production process is a charcoal composition for steelmaking, which contains 60wt% to 90wt% fixed carbon, 13wt% to 25wt% volatile materials and 0.5wt% to 5wt% ash.

[0011] In a preferred composition, the charcoal used contains 70 to 85 wt% of fixed carbon, 13 to 23.5 wt% of volatile materials and 0.5 to 3 wt% of ash. In a preferred manner, the charcoal used has a particle size measurement of 100% less than 4 mm, said range having been determined in tests carried out so that no clogging of the injection line occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a better understanding, the features and advantages of the present invention will be presented and described in conjunction with the accompanying drawings of the present invention, which show:

[0013] Figure 1 A schematic design of an electric arc furnace is shown. DETAILED DESCRIPTION

[0014] The present invention is aimed at using a charcoal composition in a steelmaking process in an electric arc furnace 1, wherein scrap is used as the main raw material and solid pig iron and / or liquid pig iron may also be used for steelmaking.

[0015] As the raw material melts, its height within the furnace decreases, causing the arc 2 to radiate heat to the side walls and arches of the furnace, which are lined with refractory bricks. Excessive radiated heat is extremely destructive to the surface of the refractory bricks and can cause them to degrade faster, significantly increasing the maintenance costs of the furnace. This radiated heat also represents a considerable energy loss in the process, since heat that could have been used to help melt the raw material is dissipated into the environment.

[0016] At this point, the formation of foamed slag 3 is an important stage, as it forms a protective layer around the arc 2, retaining a large amount of energy that would otherwise be dissipated into the environment, which is then directed into the molten steel, resulting in higher energy efficiency and increased durability of the refractory lining. In addition to acoustic noise, the foaming of the slag 3 has the additional advantage of reducing current and voltage fluctuations. However, this practice produces a large amount of CO (carbon monoxide) gas.

[0017] To form foamed slag 3, (i) the availability of carbon and oxygen for the CO formation reaction, (ii) an increase in slag viscosity and (iii) a slag basicity greater than 2.5 are required. Typically, the carbon source used in this foaming process is coke, which is a fossil fuel and incorporates sulfur and phosphorus into the steel. These elements are undesirable in most applications of steel because they reduce the ductility, toughness and weldability of the material.

[0018] The charcoal composition according to the invention is used as a substitute for coke in a slag foaming process. The above charcoal contains 60 wt% to 90 wt% of fixed carbon, 13 wt% to 25 wt% of volatile materials and 0.5 wt% to 5 wt% of ash. Ash is an inherent pollutant in the process and has a minimum content of 0.5%. As a result of the charcoal production process, the minimum content of volatile materials is 13%, and production with lower values ​​is impossible. In addition, at least 98 vol% of the composition has a particle size measurement less than or equal to 4 mm.

[0019] Both the specified composition and the specified particle size measurement are fundamental for the method according to the present invention to work. In the tests performed, it was observed that the particle size measurement of the charcoal was a critical point in order to prevent clogging of the injection line. Five injection tests were performed, of which the first two were performed without particle size measurement control and there were injection line blockages. During the analysis of the occurrence of blockages, the presence of large pieces of charcoal was observed and the necessity of particle size measurement control was determined. Once the ideal particle size measurement range was defined as at least 98% less than or equal to 4 mm, no clogging events occurred in subsequent tests. The following Table 1 shows the progress of the particle size measurement refinement:

[0020]

[0021]

[0022] Table 1

[0023] Regarding the chemical composition, it was initially planned with a high fixed carbon target. Based on the results of the first two tests, the necessity of controlling the volatile materials and ash was demonstrated to ensure that the material was properly injected and that at the beginning of the injection of the material, it reached the slag as a carbon source without being burned, which was achieved by supersonic lance.

[0024] The refinement of the chemical composition of the charcoal tested in the 5 tests is shown in Table 2 below:

[0025]

[0026]

[0027] Table 2

[0028] The tests conducted allowed the development of a general charcoal composition that included a wide range of fixed carbon from 60% to 90%, including the maximum limit tested based on the inherent variables of the charcoal production process of ±5%. Volatile materials accounted for a wide range of 13% to 25%, and ash was in the range of 0.5% to 5%. The widest particle size measurement of the composition was 98 vol% less than or equal to 4 mm.

[0029] In tests conducted, satisfactory results included preferred charcoal compositions ranging from 70wt% to 85wt% fixed carbon, 13wt% to 23.5wt% volatile material and 0.5wt% to 3wt% ash. A satisfactory particle size measurement of the composition was 99vol% less than or equal to 4mm.

[0030] Finally, the best results obtained in the development allowed to define an even more preferred charcoal composition ranging from 70% to 85% fixed carbon, 13% to 18% volatile material and 0.5% to 1.5% ash. In this preferred composition, 100 vol% of the composition has a particle size measurement less than or equal to 4 mm. The combination of these defined limits of carbon, volatiles, ash and particle size measurements in the preferred composition allowed to obtain the best results in the test development conducted.

[0031] The use of charcoal in steelmaking is particularly advantageous compared to carbonaceous materials composed of fossil fuels, such as coke, because greenhouse gas emissions are theoretically considered neutral or neutralized. Carbon dioxide produced from biomass fuels is considered "neutral carbon" or "biogenic carbon" and is not included in the greenhouse gas category because its emissions are neutralized by the reforestation used in charcoal production. In addition, the sulfur and phosphorus content is lower when compared to coke, which is an additional advantage because these elements must be reduced in the first stage of the steelmaking process.

[0032] The above description shows the preferred embodiments of the present invention, however, its scope is not limited by the listed examples or the drawings accompanying this application. Those skilled in the art will recognize that various other configurations are entirely possible.

Claims

1. A charcoal composition for steelmaking, characterized in that: The composition comprises: 60wt% to 90wt% fixed carbon, 13wt% to 25wt% volatile materials, 0.5wt% to 5wt% ash, Wherein at least 98 vol% of said composition has a particle size measurement less than or equal to 4 mm.

2. The composition according to claim 1, characterized in that The composition comprises: 70wt% to 85wt% fixed carbon, 13wt% to 23.5wt% volatile materials, 0.5wt% to 3wt% ash, wherein at least 99 vol% of the composition has a particle size measurement less than or equal to 4 mm.

3. The composition according to claim 1 or 2, characterized in that The composition comprises: 70wt% to 85wt% fixed carbon, 13wt% to 18wt% volatile materials, 0.5wt% to 1.5wt% ash, wherein the composition has a particle size measurement of less than or equal to 4 mm.

4. A method for foaming slag in electric arc furnace steelmaking, characterized in that: The method comprises a stage of injecting a charcoal composition as claimed in any one of the preceding claims onto the surface of the slag to foam the slag.

5. The use of the charcoal composition according to any one of claims 1 to 3, characterized in that: The composition is used in steelmaking.

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