RU2219245C2 - A method of production of liquid carbonaceous metal based on iron - Google Patents

Abstract

FIELD: metallurgy industry. SUBSTANCE: The invention presents a method of production of a liquid carbonaceous metal based on iron without application of an agglomeration of ores and coal carbonization. The method includes manufacture of pellets or cakes made of the fine-grained components of ore and coal materials, their feeding in the closed induction type electric crucible afterburning of the evolved gas by oxygen or air in the volume above the bath, transfer of the afterburning heat into the reaction zone by its emission by the furnace roof and liquid melt. The components for manufacture of the ore-coal materials and the metal additives are dosed counting upon production of the metal containing of no more than 3 % of carbon. Size of the ore and coal granules does not exceed 2.5 cm. EFFECT: the invention allows to intensify the process multiply higher, than one reached in industrial practice. 1 dwg

Description

 The method relates to metallurgy, and in particular to the production of liquid carbon-based metal based on iron without the use of ore agglomeration and coking of coal.

 The traditional aglocoxodomain cycle has significant and fundamentally unrecoverable disadvantages.

Blast-furnace smelting requires the production of a highly specific intermediate product - coke from special coals, whose reserves are limited. In South Africa, 6-8% of the total, in China - 6% with a complete absence of natural gas. The situation is not better in Korea, Australia, India. Japanese metallurgy works entirely on imported raw materials. In the CIS, coking coal is not deficient - 58% of the total reserves. However, in view of the natural discrepancy between the brand composition of the deposits and the composition of the charge for coking, an inter-basin charge is used, which includes unprofitable on-board transport of coal in long-distance communications [1]. The profitability of iron production is determined by the full use of the calorific value of carbon in the unit. Carbon has an unusual thermochemical property, emitting less than 40% of calorific value during initial oxidation (this feature of carbon affinity for oxygen has not been explained so far, although attempts have been made to interpret it [2]). The principle of blast-furnace smelting does not meet this property of carbon as an energy carrier: the transition of CO to CO ₂ in the mine, the main potential energy source, is limited by metal-oxide equilibria, and the furnace is heated in the least favorable way, by oxidation of C to CO. The burning of gas outside the furnace and the use of heat of combustion for heating the blast is limited by the fire resistance of the masonry of air heaters. In this way no more than 35% of blast furnace gas is used.

 The noted circumstance, on the one hand, explains the similarity of energy consumption in the sinter cycle and in processes using electricity: the conversion coefficient of the energy of primary fuel into electric energy is 0.31-0.37, and any fuel is suitable for its production.

 On the other hand, the circumstance under consideration stimulates the search for a rational method of iron production taking into account the noted anomaly.

There are known attempts to afterburn gas using double-row blasting in low-shaft furnaces. An unsuccessful attempt was to re-burn the gas leaving the electric arc furnace in the preparatory chamber, with heating the charge on an inclined (“glacier”) hearth. For the same purpose, it was also proposed to use the NIIITsement low-shaft furnace. Gas afterburning in the presence of free carbon in the system is not feasible due to the inevitable regeneration of CO during the interaction of CO ₂ with carbon.

 The development in recent years of the production of ore-coal materials (briquettes and pellets) from finely dispersed components opens up new possibilities. The purely quantitative differences of these materials from ore-coal blends (the degree of dispersion of the components, the contact surface area of the reagents) informed the system of new qualities. Here, intensive reduction in the volume of the briquette is compatible with a high oxidizing potential in the inter-cavity cavities, i.e. additional oxidation of gas in the recovery unit is possible, unattainable with separate loading. Both zones are separated by a protective gas shell around the briquette, arising and continuously renewing in the process.

 The production of ore-briquette briquettes or pellets is well mastered, and processes using them are obviously feasible.

 In the patented method, which is the closest analogue of the claimed one [3], briquettes are made from finely dispersed components, fed into a closed induction crucible electric furnace, the generated gas is burned with oxygen or air in a volume above the bath and the afterburning heat is transferred to the reaction zone by the radiation of the arch. This method involves immersing in a melt induction furnace a single large ore-briquette of unlimited length, manufactured using a screw (belt) press of the type used in the industry of refractories. A priori it was assumed that in a homogeneous mixture of finely divided components of the briquette, the process proceeds with the same speed throughout its volume. In practice, this means that the performance of the unit does not depend on the size of the briquettes and is determined only by the loading rate.

During the experimental melting, ore-briquette with a mass of 17 kg and a length of 0.8-1.2 m was melted in a crucible induction furnace with a capacity of 250 kg and a power of 320 kW. The process was conducted at a temperature of 1570-1690 ^o With a rate of immersion of the briquette of 0.5 mm / s. 50 briquettes were melted and about 300 kg of low-carbon (0.1%) iron were obtained. According to local conditions, the exhaust gas was not combusted. Therefore, as well as due to high heat losses, when using such a small tonnage unit, the slag did not melt and contained up to 45% FeO. These disadvantages are completely eliminated when using larger capacity furnaces, as demonstrated in a similar process [4].

 The objective of the invention and its essence is to create such conditions for the use of ore-coal materials (operating mode, selection of the unit), in which the process would proceed with an intensity many times higher than that achieved in industrial practice.

 The inventive method includes the manufacture of finely dispersed components of ore-coal materials - pellets or briquettes, supplying them to a closed induction crucible electric furnace, afterburning of the released gas with oxygen or air in a volume above the bath, transferring the afterburning heat to the reaction zone by arch radiation and melting. The components of the mixture for the manufacture of ore-coal materials and metal additives are dosed with the expectation of obtaining a metal containing not more than 3% C, when the size of the ore-coal materials is not more than 2.5 cm.

 The method involves the processing of ore-coal materials in an induction crucible furnace at an industrial frequency. Comparison with electric arc and induction channel furnaces testifies in favor of this choice.

 Induction furnaces in a number of parameters are preferable to arc furnaces. Their work is accompanied by smaller fluctuations in the electrical regime. For a given input power, the metal temperature is easily controlled by the feed rate. There are no high temperature zones, as under electric arcs, and it is easier to avoid overheating and burning metal. Intensive metal circulation in the induction furnace provides high heat transfer to the charge. Electric and thermal efficiency of powerful induction furnaces are comparable with arc coefficients: 0.87 and 0.81, respectively, which gives a through coefficient of 0.70 [5]. The capital and operating costs for steel production in induction and arc furnaces are close, but with the continuity of the process, the costs in the first case are lower due to the simplification of the construction of buildings and gas cleaning, elimination of the costs of noise control, refractories and maintenance.

 Channel induction furnaces have some advantages over crucible ones. Their electric efficiency in cast iron smelting reaches 95%, and the power factor is 0.8. The outlet without tilting the channel furnaces ensures the stability of the temperature regime of the lining and eliminates mechanical stresses in it during drains.

Nevertheless, channel furnaces lose significantly by crucibles due to the forced location of the inductor along the horizontal axis of the furnace to drive metal from the loading section to the reaction zone, or below the hearth for heating the bath using convection [6, 7]. There are no conditions for the excitation of Foucault eddy currents, which in the crucible furnaces cause intense metal circulation, which significantly accelerates the process: the density of the heat flux to the surface of the briquette reaches 2 GW / m ^{2 here} . It also implements the most advantageous combination of the state of aggregation of the reagents - the reduction of iron from solid oxides with carbon dissolved in the metal, as well as an unusually fast dissolution of iron in the bath. From reduction smelting, the process is distinguished by the development of carbothermic reduction to the melting of the oxide phase. The gas afterburning over the melt and the heat transfer by the radiation of the arch ensures the melting of the slag, which is immune to induction heating. Issues of slag removal during induction melting, selection of binders and others are discussed in [8].

Recent studies have made a significant contribution to understanding the mechanism of the process [9, 10]. Ore-coal briquettes with a particle size of 10-25 mm were heated in a laboratory tube furnace in a nitrogen stream, sequentially removing them for analysis. In the absence of a liquid metal solvent, the iron formed a shell, contained 1.7% C and was easily separated from the slag containing only 0.18% FeO. It turned out that due to the absorption of heat by the reaction
Fe ₂ O ₃ + 3C = 2Fe + 3CO-4.19 MJ / t Fe
the process in the briquette core is lagging, its speed is determined by the conductive heat supply to the briquette through porous intermediates, i.e. depends on the total surface area of the briquette and the intensity of heating.

 The use of a single large ore-briquette is irrational due to the small specific surface area of the reaction per unit mass. The proposed limitation of the size of the loaded material can significantly increase the intensity of the heat.

If, for example, a cylindrical briquette is replaced with spherical briquettes of the same density, then in order to maintain the loading rate of the briquettes, they will be required
n = 3HD ² / (2d ³ ),
where n is the number of spherical briquettes, pcs .;
N, D - respectively, the length and diameter of the replaced cylindrical briquette;
d is the diameter of the spherical briquette (pellet).

 At D = 0.12 m and H = 1 m (such as briquettes manufactured at the Makeevsky Metallurgical Plant) and replacing them with pellets with a grain size of 2.5 cm (usual in the production of disk granulators), their equivalent amount will be 1383 pcs. The surface area and the intensity of the heat will increase by more than 7 times.

No less significant factor in accelerating the process was the limitation of the carbon content in the bath. The work [11] showed that upon saturation of a metal with carbon, the reduction rate paradoxically decreases to the values inherent in free carbon reduction by a factor of ten. The rate of reduction of iron from a wustite melt by carbon dissolved in iron, depending on the activity of carbon in iron, is shown in the drawing. Apparently, nucleation plays a role here, the inhibitory effect of which is eliminated by dissolving the nuclei of reduced iron in the bath. Even a compact metal is dissolved in it at a rate 3 orders of magnitude higher than that arising from the theory of convective diffusion (established by the method of a rotating disk with an equally accessible surface [12]). The absence of a generally accepted explanation of these patterns does not prevent them from being used in processes involving the stages under consideration, for example, in the claimed one. Given the strong antibatical dependence of the process rate on the content (activity) of carbon in the liquid metal phase, this content is impractical to bring to saturation. Meanwhile, this was practiced in almost all analogues of the method. The initial components of the coal-bearing materials should be dosed based on the content of not more than 3% C in the bath (preferably 2-3% C). For example, at a melt temperature of 1570 ^{° C.} and a carbon activity in the bath of about 0.2, the reduction rate in the bath compared to the presence of free carbon will be about 7 times greater (see drawing). This, together with the factor of increasing the reaction surface by 7 times, gives an almost 50-fold acceleration of the process (49 times).

 When loading charged materials, one should also take into account the composition and quantity of metal additives, the remelting of which in this case is compatible with the main process. The invented method allows to utilize recycled scrap metal, for which neither blast furnaces nor converters are suitable, and reduce the scale of open-hearth production, which in the CIS is smelted up to 40% of steel. The country has accumulated more than 2 billion tons of metal. This allows us to process 60-70 million tons of secondary raw materials annually. The method extends the arsenal of tools for this purpose. Induction furnaces are currently used as remelters. It is proposed to use them for a new purpose.

Sources of information
1. Shchedrin V.M. Basics of alternative iron metallurgy: theoretical and experimental prerequisites. // Steel - 2001 - 12 - p. 8-13.

 2. Shchedrin V. M. Patterns of processes for producing iron. // Institute of Metallurgy, USSR Academy of Sciences - M.1991 - Dep. at VINITI 05.08.91, 3340 - B91.

 3. Shchedrin V. M., Orekhov A. P. The method of direct production of iron. RF patent 2080391, cl. 6 C 21 V 13/00. Publ. 05/27/97. Bull. fifteen.

 4. Elwander H.I., Edenwall L.A. et al. Boliden Inred process for smelting reduction of fine-grained iron oxides and concentrates. // Ironmaking and Steelinaking - 1979. - 5 - p. 236-244.

 5. Schwabe W. E., Robinson C.G. Report on ultrahigh power operation of electric steel furnaces. // Journal of Metals. - 1967 - v.19, - 4 - p. 67-75.

 6. Fourie L.F. Steelmaking process. US patent 5411570 C1, C 21 C 5/28, May 2, 1995.

 7. Fauri L.I. (SOUTH AFRICA). A method of producing steel and a device for its implementation. RF patent, 2127316, cl. 6 С 21 С 5/52, С 21 В 13/12, Decl. 06/15/94.

 8. Shchedrin V.M. Direct iron production: solutions to the problem. // Institute of Metallurgy, USSR Academy of Sciences. - M., 1992. - Dep. VINITI 10.30.92, 3150 - B92.

 9. Matsumura T., Takenaka Y. et al. Direct production of molten iron from carbon composite iron ore pellet. // La Revue de Metallurgie - CJT. - 1998 - 3 - p. 341-351.

 10. Sun S., Lu W.-K. A theoretical investigation of kinetics and mechanisms of iron ore reduction in an ore / coal composites. // ISIJ Intern. - 1999 - v. 39 - 2, - p. 123-129.

 11. Sato A., Aragane G. et al. Reducing rates of molten iron oxide by solid carbon or carbon in molten iron. // Transactions of the Iron a. Steel Institute of Japan. - 1987 - v.27 - p.789-796.

 12. Biletsky A.K., Verkhovlyuk A.M., Dolzhikov A.A. Kinetics of the dissolution of steel and ferroalloys in molten iron. // Adhesion of melts and soldering of materials. - 1986 - 17 - p. 66-69.

Claims (1)

A method for the production of iron-based liquid carbon metal, including the manufacture of fine-grained components of ore-carbon materials - pellets or briquettes, supplying them to a closed induction crucible electric furnace, afterburning of the released gas with oxygen or air in a volume above the bath, transferring the afterburning heat to the reaction zone by arch radiation and melting , characterized in that the components for the manufacture of coal-bearing materials and metal additives are dosed based on the production of metal containing not more than 3% C, and large st rudougolnyh materials does not exceed 2.5 cm.