RU2511419C2 - Method for liquid-phase obtaining of direct-reduced iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to obtaining of direct-reduced iron in electric-arc furnaces as per one-stage procedure. Molten metal bath is used as a reaction medium and a reduction zone, solid carbon-containing material and iron-ore raw material in the form of particles of maximum 6 mm and flux is supplied to the metal bath volume, and technical gaseous oxygen is blown. Heating of carbon-containing material and gasification of its organic part is performed; heating of particles of iron-ore raw material is performed till molten state so that transition of carbon to molten state and interaction of liquid iron oxides with carbon is provided and iron and CO is obtained. The molten bath is bubbled with gas obtained as a result of gasification and oxidation of carbon so that its boiling and mixing and rise of gas bubbles to the bath surface is provided. CO is additionally burnt above the surface with an oxidation gas, thus transmitting additional burning heat to the molten bath. Formed process gasses are removed, and liquid metal and slag is tapped.

EFFECT: reduction of power consumption and enlargement of a range of produced direct-reduced iron.

7 cl, 1 tbl

Description

The invention relates to ferrous metallurgy, and specifically to the production of direct reduction iron in electric arc furnaces and reduction units according to a one-stage technology using unexcited iron ore raw materials and carbon-containing material.

Known single-stage methods for direct production of iron direct reduction in the liquid state [1, 2]. In this case, the stages of heating, reduction, melting and refining of metal are combined in one unit. The reduction of iron ore materials in them proceeds at high temperatures, which increases the reaction rate and unit productivity.

Single-stage methods for the direct production of liquid metal are divided into two types [2]. The first type includes processes in which the reduction of iron ore materials proceeds in the solid phase, followed by melting and additional reduction of iron oxides according to the reduction-melting scheme.

The most typical example of such processes is the Corex process, which has already found industrial application. In this process, coal is the reducing agent and source of heat. The main structural element of this method is a reactor in which coal gasification is carried out by burning it in a stream of injected oxygen to obtain temperatures up to 2500 ° C. These temperatures provide a quick gasification of particles of carbon-containing material and the formation of synthesis gas, consisting mainly of CO and H ₂ . This gas then enters the charge, where it reduces iron ore pellets to produce solid iron. Then this iron is sent to the lower part of the gasifier, where it is melted and carbonized, forming liquid pig iron.

The disadvantage of the Korex process is the relatively slow rate of iron reduction, due to the very long metallization process, which takes a lot of time - 7-9 hours. The main reason for this is the solid-state state of iron ore materials during their reduction, which limits the rate of reduction reaction.

Another significant drawback of the Korex process is the narrow range of the resulting metal, limited to molten iron, and the impossibility of producing iron-carbon melts with a low carbon content such as crude iron. These fundamental shortcomings are also characteristic of other similar processes [3-8].

The second type of one-stage methods for the direct production of liquid metal, in contrast to the first, is based on the preliminary melting of iron ore materials with the subsequent reduction of iron from its oxides in the molten state by carbon according to the melting-reduction scheme. As a reducing agent, solid carbon injected into the melt or carbon dissolved in a metal bath, as well as gases (CO, H ₂ , CH ₄ ) can be used. The main advantage of such processes is the possibility of a significant increase in the rate of reduction of iron oxides due to their liquid state and, consequently, the productivity of the processes of direct production of liquid metal. These processes eliminate the need for preparation of raw materials, which reduces energy consumption, improves the ecological state of the natural environment, and reduces capital investments. Unfortunately, technological difficulties did not allow to bring these methods to wide industrial use and to provide them with a significant role in the production of direct reduction iron [2, 5].

Closest to the industrial implementation of the method of single-stage liquid-phase production of direct reduced iron from unskilled iron ore and coal came in the ROMELT process [6-8]. The process is based on the use of a liquid slag bath sparged with an oxygen-containing gas as a reaction medium and a recovery zone, located inside water-cooled caissons. Coal and iron ore are fed to the slag, where iron oxides are reduced by carbon. In this process, coal simultaneously plays the role of reducing agent and energy carrier. The main heat source in the ROMELT process is the burning of CO and H ₂ above the surface of the slag with an oxygen-containing gas. The oxidation of part of carbon to CO by an oxygen-containing gas plays a role in the heat balance. The heat of combustible gases partially returns to the slag and through it to the metal bath, providing energy requirements. A mixture of compressed air and gaseous oxygen is used as an oxidizing blast.

The reduction of iron oxides occurs in the slag layer. Further, liquid iron particles are carburized and lowered down through the slag layer to the bottom of the furnace, where a metal bath is formed from a high-carbon melt. Thanks to this reaction product between carbon and iron oxides in the slag is a solution of carbon in iron - cast iron. Another reaction product is flue gases, which have high reserves of physical and chemical heat and are suitable for the production of electric and thermal energy from them.

The liquid-phase method for producing ROMELT direct reduction iron involves the use of a liquid slag bath as a reaction medium and a reduction zone, blowing oxidizing gas into it from a mixture of air and gaseous oxygen, feeding particles of carbon-containing material, iron ore, flux, oxidizing (burning) carbon in the volume of slag baths to СО, transfer of heat of carbon oxidation from slag to metal, heating of carbon-containing material, gasification of its organic part, mainly to СО and Н ₂ , heating the iron ore particles to a molten state, the interaction of liquid iron oxides with carbon in a slag bath, the reduction of iron oxides with carbon to produce iron and CO, bubbling the molten bath with gas bubbles, its boiling and mixing, bubbling, in particular CO and H ₂ to the surface of the bath, afterburning them above the surface of the slag bath, transferring the heat of afterburning, first to the slag and then to the metal bath, melting and / or dissolving the carbon-containing mineral components in the slag its material, waste rock of iron ore raw materials, the removal of the resulting process gases from the furnace to the power plant, their subsequent use to generate electric and thermal energy, the release of liquid metal and slag.

The main disadvantages of this method are:

- use as a reaction medium and recovery zone of a liquid slag bath. When fed into it, the iron-containing raw material is melted and passes into slag. This reduces the activity of iron oxides, increases the temperature of their reduction and reduces the rate of reduction of iron;

- the use of slag also has a negative effect on the carbon-containing material. Unlike iron, slag does not have the ability to transfer carbon into an atomically dispersed state, that is, into a solution of carbon in iron. Therefore, coal particles in the slag, although they are reduced in size, however, retain the properties of a separate solid phase. From the point of view of kinetics, this factor reduces the rate of reduction of iron oxides by carbon in comparison with carbon that has passed into a dissolved state and is in the form of separate atoms in a liquid medium;

- liquid slag, which performs, in addition to other tasks, the coolant with respect to the direct reduction iron obtained, has a significantly higher Prandtl thermal criterion, which determines the rate of heat transfer from the slag to the metal bath, in comparison with the iron-carbon melt. This means that the slag melt acts as an effective heat-insulating layer, it is for this reason that the rate of heat transfer of slag with metal is lower than possible, causing a heat deficit;

- bubbling of the slag bath with oxygen-containing gas causes foaming of the upper layer of slag, leaving its lower part, adjacent directly to the metal bath, stationary. Both of these factors significantly reduce the intensity of heat transfer of oxidation of carbon to CO in the slag bath and the heat of afterburning of CO to CO ₂ above the surface of the slag into the volume of the metal bath. This increases the consumption of coal, which plays the role of the dominant energy carrier and, accordingly, increases the energy consumption for the reduction of iron;

- oxidation of carbon to CO by a mixture of air and oxygen sharply compared with pure oxygen reduces the amount of heat entering the slag and metal and negatively affects the energy intensity of the recovery process, causing the need to increase the consumption of coal;

- the use of a slag bath as a reduction zone instead of metal leads to the separation of the heat source, which is the upper part of the slag bath, from the place of energy consumption - the lower part of the slag bath and liquid metal. This, of course, reduces the degree of assimilation of the heat released during the oxidation (burning) of carbon to CO and afterburning of CO to CO ₂ , thereby also increasing the consumption of coal;

- reduction of iron from its oxides by carbon, contained in slag in superstoichiometric amounts, is inevitably accompanied by carburization of iron droplets and their transformation into cast iron. Therefore, this process limits the assortment of direct reduced iron to one material - cast iron, differing from the latter only in a lower content of silicon and manganese;

- limited possibilities of using blowing oxygen-containing gas into the slag bath both in quantity and in oxidation potential. With an excessive amount of oxygen in the blast, the process will be reverse to the reduction of iron, namely, the oxidation of FeO slag to Fe ₂ O ₃ , and freshly reduced iron to FeO. Limitations on the amount of oxygen injected, in turn, reduce the rate of carbon oxidation by blast oxygen and limit the flow of heat into the recovery process, which is endothermic in nature and is accompanied by high energy costs.

The factors noted above cause a significant increase in the specific heat consumption for iron reduction, which manifests itself in a high consumption of steam coal, reaching 1031 kg / t, according to the publication [9], and 1345-1375 kg / t according to the source [5].

In combination with a narrow range of smelted iron, limited only by cast iron, these factors are the reason for the decrease in the competitiveness of the known method and the similar one-stage processes for the production of primary metal raw materials, which have not yet allowed them to be widely used in ferrous metallurgy.

The problem solved by the present invention and the technical result achieved is to create an economical method for producing direct reduction iron in electric arc furnaces and reduction units using a single-stage technology using unrated iron ore and carbon-containing material, reducing energy consumption based on more efficient use of carbon potential as an energy carrier and expanding assortment of iron produced direct reduction, including the entire range of likely impacts of carbon content in the iron - 0.05% in the crude iron and up to 4.5% iron.

To solve the problem and achieve the claimed technical result in the method of liquid-phase obtaining direct reduced iron in an electric arc furnace, characterized in that it is used as a reaction medium and a reduction zone metal a bath, solid carbon-containing material and iron ore raw materials in the form of particles of not more than 6 mm are fed into the volume of the metal bath, the oxidizing gas is injected into the flux and the carbon-containing material is heated and the organic part is gasified, the iron ore particles are heated to the molten state to ensure the transition of carbon into the melt and the interaction of liquid iron oxides with carbon and the production of iron and CO, bubbling the molten bath with gas bubbles resulting from gasification and oxidation of carbon, both by boiling it, mixing and bubbling gas bubbles on the surface of the bath, burning CO over the surface with oxidizing gas to ensure heat transfer from the burning of the molten bath, melting and / or dissolving in the slag of the flux, mineral components of the carbon-containing material, waste rock of iron ore and ash of carbon-containing material, removal from the furnace of the resulting process gases, including the gasified organic part of the carbon-containing material, and the release of liquid metal and slag, while Particles of carbon-containing material and iron ore are injected directly into the volume of the metal bath and iron is reduced therefrom from the oxides with part of the incoming carbon to produce carbon monoxide, and technical gas is blown into the metal bath as an oxidizing gas simultaneously and simultaneously with the supply of starting materials and iron reduction oxygen with a specific intensity of 0.1-5m³/ (t · min) and carry out the oxidation of the rest of the input carbon, while the specific consumption of carbon and oxygen is selected from the ratio

=0,5-1,5,(m _C -321) / $$m_O{}_{{}_2}$$

= 0.5-1.5,

Where

m _C is the specific consumption of carbon introduced with the carbon-containing material per ton of iron, kg / t;

321 — specific carbon consumption for reduction from Fe ₂ O _{3 of} one ton of iron, kg / t;

- удельный расход газообразного кислорода, вводимого с дутьем на одну тонну железа, кг/т, $$m_O{}_{{}_2}$$

- specific consumption of gaseous oxygen introduced with blast per ton of iron, kg / t,

and 0.5-10.0 minutes before the direct reduction iron obtained from the furnace is removed, 5-95% of carbon is removed from it by additional oxidation, gaseous oxygen injected into the metal with a specific intensity of 0.1-5.0 nm ³ / ( caraway).

Besides:

- to restore iron, carbon is used simultaneously in dissolved and free states with its total concentration in the metal bath of 3-15%, while the ratio of the concentrations of dissolved and free carbon in the course of reduction smelting is maintained within the range of 1: (0.1 ÷ 3);

- in a metal bath maintain a temperature equal to or greater than 1400 ° C;

- to reduce iron, an electric arc furnace is used with a specific electric power equal to or greater than 0.8 mW per ton of furnace capacity;

- during the reduction of iron, an additional 30–200 mW per minute of electric energy is supplied to the electric furnace per ton of iron ore;

- combustible components of the process gases are sent to a power plant to generate electrical and / or thermal energy;

- combustible components of the process gases are burned above the surface of the molten metal bath with a degree of afterburning of not more than 20%.

Thus, the method of liquid-phase production of direct reduction iron in an electric arc furnace from un-bunched iron ore and carbon-containing material is characterized by using a molten metal bath as a reaction medium (or volume) and a further zone of carbon-containing material, iron ore, flux, injection into the bath volume in it oxidizing gas, which is used as technical gaseous oxygen with an oxygen content of 95% or less, oxidation m (burning) carbon in the bath volume to CO, transferring the released heat of decarburization of the molten bath, heating the carbon-containing material, gasifying its organic part, converting carbon into a solution with iron, heating the iron ore particles to a molten state, by the interaction (or reaction) of liquid iron oxides with carbon, to produce iron and CO, bubbling the molten bath with gas bubbles (CO, H ₂ , N ₂ ), boiling and stirring it, floating gas bubbles on the surface of the bath, afterburning CO and Н ₂ above the surface with oxidizing gas, transferring the heat of afterburning to the bath, melting and / or dissolving in the slag of flux, mineral components of carbon-containing material, waste rock of iron ore and ash of carbon-containing material, removal from the furnace of the resulting process gases - gasification products of the organic part of coal (СО, H ₂ , air, nitrogen), products of iron reduction by carbon (CO and CO ₂ ), products of direct oxidation by gaseous oxygen (CO and CO ₂ ), and the release of liquid metal and slag, with particles carbon-containing material or substance (various types of solid fossil fuels - steam coal, coke, graphite, anthracite, charcoal, their mixture and their waste) and iron ore raw materials (iron ore concentrate, ground iron ore, scale, partially reduced iron and mixtures thereof, and also iron-containing wastes (smelting dust, sludge, fines of sponge iron), etc.) are introduced directly into the volume of the metal bath and reduction of iron oxides by carbon is carried out in it to obtain carbon monoxide by endo thermal reaction 3 [C] + (Fe ₂ O ₃ ) = 2 [Fe] +3 {CO}, accompanied by oxidation of carbon, moreover, gaseous oxygen with an oxygen content of 50- is blown into the metal bath in parallel with the supply of starting materials and reduction of iron 95% of the specific intensity of 0.1-5 m ³ / ^(m. min) and carry out the oxidation (burning) of the introduced carbon by the exothermic reaction [C] +1/2 {O ₂ } = {CO}, with the exception of its part, which goes to the reduction of iron from Fe ₂ O ₃ , while the specific consumption of carbon and oxygen is selected from the ratio

(m _C -321) / m _O2 = 0.5 ÷ 1.5,

where m _C is the specific consumption of carbon introduced with the carbon-containing material per ton of iron, kg / t;

321 — specific carbon consumption for reduction from Fe ₂ O _{3 of} one ton of iron, kg / t;

m _O2 is the specific consumption of gaseous oxygen introduced with blast per ton of iron, kg / t,

and 0.5-10.0 minutes before the direct reduction iron obtained from the furnace is removed, 5% to 95% of carbon is removed from it by additional oxidation by gaseous oxygen injected into the metal with a specific intensity of 0.1-5.0 nm ³ / (t min).

To restore iron, carbon is used simultaneously in the dissolved and free states with its total concentration in the metal bath from 3% to 15%, while the ratio of the concentrations of dissolved and free carbon during the reduction smelting is maintained within the range of 1: (0.1 ÷ 3), and in a metal bath maintain a temperature equal to or greater than 1400 ° C.

To restore iron, an electric arc furnace is used with a specific electric power equal to or greater than 0.8 mW per ton of furnace capacity, and along with the reduction of iron, electric energy is additionally supplied to the electric furnace in an amount of 30-200 mW per minute per ton of iron ore.

Process gases, including their combustible components and the gasified organic part of the carbon-containing material, are sent outside the furnace to a power plant to generate electric and / or thermal energy or burned over the surface of a molten metal bath from an iron-carbon melt with the transfer of the released heat to it.

For the implementation of the proposed method, liquid-phase aggregates of various types can be used - from the ROMELT process to the DIOS and Haysmelt processes, as well as processes based on the use of an electric arc furnace (Elred, Extra-Wallak, Inred, Plazma-red, etc.).

The need to use an electric arc furnace for liquid-phase production of direct reduction iron is justified as follows. Electric arc processes provide the formation of a liquid metal bath from an iron-carbon melt before starting supply (injection) of iron ore and coal. Also, the use of an electric furnace makes it possible to meet the energy recovery needs of the process, since heat of oxidation of carbon by oxygen and heat of afterburning may not be enough for the recovery process. Additionally, electric arc heating allows you to create high-temperature local zones on the surface of the bath, accelerating the reduction of iron from oxides. Thus, for the implementation of the process, it is sufficient to have an electric arc furnace with a specific electric power equal to or greater than 0.8 mW per ton of furnace capacity.

The process is as follows. At the end of the production of part of the metal and part or all of the final slag, iron ore and carbon-containing material in the form of particles with a size of not more than 6 mm, as well as flux (limestone or lime) are continuously fed into the liquid metal left from the previous smelting. If necessary, the liquid metal is heated using electric arcs.

The carbon-containing material is heated in a metal bath, gasified with the formation of synthesis gas, consisting mainly of CO and H ₂ . Carbon dissolves in a metal bath, forming an iron-carbon melt. The carbon content in the melt is maintained at a level of at least 2%. The transition of carbon from solid to dissolved state and maintaining its concentration above 2% increases its rate of interaction with iron oxides compared to solid carbon [10], which is in the form of a separate phase.

Iron oxides, getting inside a liquid metal bath, heat up, dissociate into gaseous oxygen and iron monoxide. The latter forms a low-melting phase with an empty rock of iron ore raw materials, which, due to this, quickly passes into a molten state. The transition of the initial solid iron oxides to a liquid melt sharply increases their oxygen potential and oxygen affinity for carbon [11].

Due to these factors, the use of a metal bath from an iron-carbon melt instead of a slag bath creates the necessary and sufficient conditions for increasing the rate of interaction of carbon in a metal bath with liquid droplets of iron oxides and, in general, the reduction rate [10, 11]. This reaction in the general case has the form (Fe ₂ O ₃ ) + [C] = 2 [Fe] +3 {CO} and has a strongly pronounced endothermic character. The thermal effect of this reaction is 1570 kW · h / t of iron [11]. Taking into account the inevitable losses during the thermal efficiency of the furnace 0.7, the actual heat consumption will be 2242.80 kWh / t of iron.

In contrast to the method of one-stage liquid-phase production of direct reduction iron from unskulled iron ore and coal in the ROMELT process, the heat source for meeting the needs of the reduction process, simultaneously with the electricity obtained from the process gases in the proposed method, is the energy released during the oxidation of carbon coming from carbon-containing material with pure gaseous oxygen. In this regard, for energy recovery process in parallel and simultaneously with the supply of expendable components of the charge in the metal bath, instead of the mixture of air and oxygen is injected oxygen gas with a specific intensity of 0.1-5.0 m ³ / (min · m), and carried out the oxidation of carbon exothermic reaction [C] +1/2 {O ₂ } = {CO}. The specific consumption of oxygen and carbon is selected from the ratio

(m _C -321) / m _O2 = 0.5 ÷ 1.5,

where from

m _O2 = (m _C -321) / (0.5 ÷ 1.5).

Thus, complete oxidation of all injected carbon and reduction of all iron is achieved, as well as the simultaneous preservation of the concentration of carbon in the metal bath during recovery.

This reaction in the temperature range of 1400-1600 ° C provides heat transfer to the metal bath in an amount of about 3.07 kW · h per 1 kg of oxidized carbon [12,13]. This value is significantly - 1.56 times higher than the thermal effect during the oxidation of carbon with a mixture of air and oxygen in a ratio of 50:50 in the known process, equal to 1.97 kWh / kg of carbon. This significantly increases the heat gain from oxidation of carbon in the proposed method and improves the heat balance, thereby creating conditions for reducing the flow of heat carrier - coal.

The simultaneous occurrence of two reactions in a metal bath with opposite signs, namely, the endothermic reaction of the reduction of iron oxides with carbon, accompanied by the oxidation of part of the carbon entering the bath, on the one hand, and another reaction of an exothermic nature, namely, the oxidation of carbon dissolved in metal bath with oxygen blast can increase the heat input from the oxidation of carbon by oxygen, reduce heat shortages, reduce fuel consumption and, ultimately ie, to reduce the energy consumption for producing iron.

An additional and very significant advantage of the proposed method is a higher thermal efficiency in the oxidation of carbon by oxygen in a metal bath compared to a slag bath. As is known [11–13], the heat released in the volume of liquid metal during the oxidation of carbon by oxygen blasting is almost completely absorbed by the metal bath, since the heat release zone and the heat absorption zone are combined in time and space. Therefore, the value of thermal efficiency in this case approaches 100%.

In the known method of single-stage liquid-phase production of direct reduced iron in the ROMELT process, the oxidation (burning) of carbon occurs in a slag bath consisting of two parts - the upper layer of foamed slag and the lower layer of stationary slag. From the standpoint of heat transfer, both the foamed state of the liquid medium and the lack of mixing inside the liquid medium significantly limit the heat transfer through the slag layer to the metal bath. As a result of this, the thermal efficiency decreases and does not exceed 0.50.

A similar situation occurs with the process of transfer of heat generated during the afterburning of CO over a slag layer in a metal.

In the proposed method, the bubbles of CO arising from the oxidation of carbon in a metal bath float through a layer of metal and slag, actively sparging them and causing intense mixing. This facilitates the transfer of heat from the afterburning zone above the surface of the slag through a layer of bubbling slag into a metal bath. As a result of the better organization of heat transfer in the inventive method, the absorption coefficient of the afterburning heat is significantly increased compared to the known one. Accordingly, the efficiency of using the carbon energy potential is improved and energy consumption is reduced.

The ratio of the specific amount of carbon supplied to the bath in the form of a carbon-containing material and the specific amount of gaseous oxygen in the course of melting is maintained at a level of 0.5-1.5, which is close to the stoichiometric values of this parameter for the carbon-oxygen reaction, equal to 0.75. Since the exact value of the parameter is difficult to maintain, deviations in the direction of 0.5 and 1.5 are permissible. Due to this, a constant concentration of carbon in the metal is maintained in the metal bath and at the same time there is a continuous oxidation of carbon coming from the injected carbon-containing material. The oxidation reaction of carbon, dissolved in a metal bath with oxygen of the blast, is exothermic and allows you to heat the metal to a predetermined temperature with minimal energy consumption.

After depositing a certain amount of direct reduction iron and achieving a given furnace capacity for liquid metal, 5% to 99% of the carbon contained in the metal is removed before release, for which 0.5-10.0 minutes before the direct reduction iron obtained from the furnace is removed gaseous oxygen with a specific intensity of 0.1-5.0 nm ³ / (t ^. min.) is blown into the bath. The rate of carbon oxidation and the temperature of the metal at the outlet are regulated by changing the ratio of the amounts of carbon and oxygen supplied in the range (95 ÷ 5) :( 5 ÷ 95), respectively. This ratio ensures the production of direct reduction iron with any carbon content - from 0.05% in crude iron to 4.5% in cast iron, as well as the achievement of a given degree of overheating and the temperature of the final metal, depending on the carbon content. Next, produce metal and slag.

During the smelting process, partial — not more than 20% —– afterburning of the combustible components of the process gases is performed. The afterburning heat is partially transmitted through the slag to the metal bath. The overall degree of assimilation of that heat in comparison with the known process increases, since the coolant in the proposed method is a carbon melt in iron, which has better thermophysical properties compared to slag.

The above shows that the use of a metal bath of iron-carbon melt in the proposed method as a reaction medium and a reduction zone instead of a slag bath and the introduction of the starting components into the thickness of the metal bath fundamentally changes for the better the mechanism, kinetics and energy of the main carbothermal reduction of iron oxides by carbon.

The reduction of iron in this case occurs directly in the volume of the iron-carbon melt and proceeds at high speeds. This is due to the increased reduction potential of carbon dissolved in iron, on the one hand, and the increased oxygen potential of iron oxides that have transferred to the molten state, on the other hand [10]. As a result of this, the initial charge components — carbon and iron oxides — acquire significant chemical affinity for each other. In combination with a developed metal-iron oxide reaction surface and intensive mixing of the metal bath under the predominant influence of CO bubbles formed during carbon oxidation, this significantly increases the reduction rate and reduces energy consumption.

A significant role in accelerating the reduction of iron in the proposed method is played by the high thermophysical properties of the liquid metal, characterized by a very small value of the Prandtl thermal criterion [12]. This allows you to intensify the processes of heat and substance transfer compared to a slag bath. Thanks to this, an accelerated supply of heat to the reduction zone is achieved, in which the endothermic reaction of the interaction of carbon and iron oxides proceeds. Therefore, the use of a metal bath instead of slag accelerates heat transfer both from the zone of carbon oxidation by oxygen in the blast and from the afterburning zone of CO to CO ₂ above the surface of the slag.

The advantages of a metal bath are most fully manifested when metal carbon is oxidized by gaseous oxygen instead of a mixture of air and oxygen. In this case, two factors work simultaneously. Firstly, the amount of heat received by the metal from the oxidation of carbon to a value of 3.07 increases instead of 1.97 kWh / kg of carbon in the known method. Secondly, the coefficient of assimilation of heat of decarburization due to the volumetric nature of carbon oxidation and the combination in time and space of the zones of heat generation and heat absorption zones approaches the maximum possible value close to 100%. Therefore, the efficiency of using carbon as an energy source in the proposed method in comparison with the known one is obtained significantly more.

This is ensured by the creation of zones of carbon oxidation by oxygen in a metal bath instead of a mixture of air and oxygen, giving a greater amount of heat. The appearance of an additional heat source inside the metal bath increases the heat input, improves the recovery energy and helps to reduce energy and carbon consumption.

Another advantage of the proposed method is the possibility of changing over a wide range the amount of carbon introduced into the bath and oxidized by oxygen blasting. The carbon consumption for iron reduction is limited by the reaction stoichiometry - 321 kg of carbon per 1 ton of iron. Therefore, an increase in carbon consumption in excess of this value increases the absolute and relative amount of heat received by the bath from carbon oxidation. This opens up the possibility of simultaneously reducing the specific heat and carbon consumption for the production of direct reduction iron, and also increases the energy potential of the exhaust gases and the generation of energy from them, including electricity.

Thus, the conversion of the reaction of the interaction of carbon with iron oxides in a metal bath consisting of an iron-carbon melt, instead of slag, radically changes the mechanism, kinetics, thermodynamics and energy of the process of reduction of iron oxides by carbon in the dissolved state, accelerating the course of this reaction and reducing energy costs. A special role is played by the injection of gaseous oxygen into a metal bath and its replacement of oxidizing gas in the form of a mixture of air and oxygen. The supply of oxygen into the iron-carbon melt creates in the metal bath a new front of carbon oxidation by gaseous oxygen, which is distinguished by an exothermic character. This front complements the oxidation of carbon with oxygen from iron oxides, leading to the reduction of iron oxides and carbon removal and which has a pronounced endothermic character. The emergence of a new front of carbon oxidation by gaseous oxygen, which gives a significant amount of heat, radically improves the energy of the entire reduction process, creating an additional heat influx in the zone of this reaction. As a result of this, the thermal effect of the decarburization reaction significantly increases (from 1.97 to 3.07 kWh / kg of carbon) and, accordingly, the heat input to the metal bath increases. In addition, the combination of the heat liberation zone and the heat perception zone, achieved in this case, increases the absorption coefficient of carbon oxidation energy to the maximum possible value close to 100%.

At the same time, the use of a metal bath instead of a slag improves the conditions of afterburning of CO to CO ₂ , which occurs above the surface of the slag, which is intensively bubbled by CO bubbles, and also enhances the transfer of heat from the afterburning zone to the slag and through it to the metal bath. Due to this, the total absorption coefficient of the afterburning heat of the metal increases significantly. In turn, this reduces the energy consumption and consumption of carbon introduced by the carbon-containing material.

In the course of iron reduction, if necessary, in addition to decarburization energy, electric energy is supplied (injected) in an amount of 30-200 mW per minute per ton of iron ore. The real need for additional heat and closing the heat balance can be met, among other things, by recycling the electricity actually produced from process gases in the process of iron recovery.

Consider the possibility of practical implementation of the invention.

The specific intensity of the injection of gaseous oxygen into the metal bath is maintained equal to 0.1-5 m ³ / (t ^. Min ^. ), Which ensures the rate of carbon oxidation at the level of the oxygen-converter process in the range of 0.1-0.8% C / min. If this parameter decreases below the lower value of the indicated limit — 0.1 m ³ / (t ^. Min), the intensity of carbon oxidation decreases, which increases the duration of the reduction cycle and causes an increase in heat consumption and, accordingly, carbon.

Exceeding the upper value of the specific purge intensity of more than 5 m ³ / (t ^. Min ^. ) Increases the rate of CO formation as a product of the carbon oxidation reaction by oxygen blast. As a result of this, excessive foaming of the slag is observed and the total degree of absorption of the afterburning heat is worsened.

The ratio of the specific consumption of carbon and gaseous oxygen going to the oxidation (burning) of carbon is selected from the expression

(m _C -321) / m _O2 = 0.5 ÷ 1.5.

If this ratio is lower than 0.5, then the amount of oxygen is insufficient to oxidize all the carbon coming in with the injected carbon-containing material. As a result of this, excessive carburization of the metal occurs. If this ratio exceeds 1.5, then the flow rate of the incoming oxygen exceeds the amount of oxidizing agent required to oxidize the carbon introduced by the carbon-containing material. Due to the excess of oxygen with respect to carbon, additional oxidation of part of the carbon soluble in the metal bath occurs, which reduces the effectiveness of the proposed method. For this reason, the ratio of the consumption of carbon and gaseous oxygen in the range of 0.5-1.5 is the most rational. It provides the simultaneous oxidation of all carbon entering the bath and the complete reduction of iron oxides, as well as maintaining the concentration of carbon in the metal bath during recovery.

The amount injected into a metal oxygen bath is determined by the rate of oxidation of all carbon contributed to the bath carbonaceous material except the part of the carbon consumed in reduction of iron and equal to iron oxide Fe ₂ O ₃ 321 kg per tonne of iron, which meets the stoichiometry of the reaction of iron reduction from its oxide. If this figure turns out to be less than 321 kg / t, then part of the iron oxides will be unreduced due to the lack of a reducing agent. Therefore, a decrease in the value of this parameter below 321 kg / t of iron is undesirable. In the case when this indicator is higher than the stoichiometric value of 321 kg / t of iron, the part of the carbon exceeding the indicated value will pass into the metal and will not be oxidized by oxygen in the blast. The excess carbon generated during this will remain in the bath and will accumulate in it, increasing the concentration of carbon in the metal. In addition, the bath will not receive the corresponding amount of heat, which will worsen the heat balance of the heat and increase the consumption of carbon. As a result, an increase in the parameter above 321 kg / t of iron reduces the efficiency of the method.

Thus, in a generalized form, adjusted for the above specific technological parameters, the method of liquid-phase production of direct reduction iron is as follows.

In an electric arc furnace, for example, with a specific electric power equal to or greater than 0.8 mW per ton of capacity, a reaction medium (volume) is formed, it is also an iron reduction zone, in the form of a molten metal bath.

A carbon-containing material (substance), iron ore, flux are fed directly into the volume of the metal bath, oxidizing gas is blown. In parallel, gaseous oxygen is blown into the metal bath.

In this case, two reactions occur simultaneously in a metal bath. The first is the reduction of iron from its oxides with the formation of iron and CO, which is endothermic in nature and is accompanied by a consumption of carbon. The second is the oxidation (burning) of the introduced carbon by gaseous oxygen by an exothermic reaction, with the exception of its part, which is used to reduce iron from Fe ₂ O ₃ . The decarburization heat released during this is transferred to the molten bath, the carbon-containing material is heated and its organic part is gasified. Carbon passes into a solution with iron, particles of iron ore are heated to a molten state, liquid iron oxides react with carbon, resulting in the production of Fe and CO. Due to the intense formation of gas bubbles — CO, H _2, and N ₂ — bubbling of the molten bath occurs, it boils and mixes, while gas bubbles float to the surface of the bath. In the volume of boiling slag, flux melts and dissolves, the mineral components of the carbon-containing material, waste rock of iron ore and ash of the carbon-containing material. As a result of the ongoing metallurgical processes, reduced iron is collected in the lower part on the bottom of the furnace, from which excess carbon is removed almost immediately before the release, for which the required amount of gaseous oxygen is additionally blown into the metal bath.

Process gases are also diverted from the furnace, which are sent outside the furnace to a power plant to generate electrical and / or thermal energy. Part of them in an amount of not more than 20% is burned over the surface of the molten metal bath from the iron-carbon melt with the transfer of the generated heat to it.

The table shows real examples of the method of liquid-phase production of direct reduction iron in a reduction furnace with various technological parameters according to the proposed method and the well-known ROMELT method of single-stage liquid-phase production of direct reduction iron.

When analyzing the performance of the method we take them following values: a degree of afterburning of CO to CO ₂ - 0.55, a degree of afterburning heat transfer metal bath - 0.67, the total heat utilization afterburning - 0.37, the amount of heat produced in the oxidation bath ( burning) 1 kg of carbon by gaseous oxygen - 3.07 kWh, the coefficient of assimilation of heat of oxidation (burning) of carbon by gaseous oxygen - 1.0.

In determining the parameters of the known method of one-stage liquid-phase production of direct reduced iron from unrated musk ore and ROMELT coal, research materials were used [4-9]. The degree of afterburning of CO to CO _{2 was} taken equal to 0.55, the degree of transfer of heat to the afterburning to slag was 0.60, the degree of transfer of this heat from slag to metal was 0.8, the resulting utilization of heat from the afterburning of a metal bath was 0.26, and the thermal efficiency during natural combustion gas - 0.45, the heat obtained by the slag bath during the oxidation of 1 kg of carbon by oxidizing gas in the form of a mixture of air and oxygen in a ratio of 50:50 - 1.97 kWh. The coefficient of assimilation of heat of oxidation of carbon by oxidizing gas was conventionally assumed equal to the maximum value of 1.0. The indicators of the proposed and known method relate to the same temperature range of 1400-1600 ^about C.

In the optimal embodiments of Examples 3-7, by using a metal bath as a medium and a reaction zone, by injecting gaseous oxygen into the metal bath, and by oxidizing carbon of the liquid metal, this oxidizing agent provides the necessary amount of heat to recover iron over the entire range of coal consumption values exceeding 816.7 kg / t of iron. Thus, the proposed method provides a reduction in specific consumption compared with the known [9] from 1031.0 to 817.7 kg / t or 214.3 kg / t of iron. This corresponds to a decrease in carbon consumption from 742.3 to 588.0 kg / t or 154.3 kg / t of iron. The effect of reducing coal consumption increases if we use for comparison the data given in [4, 5, 7], according to which the specific coal consumption in the ROMELT process is 1345-1375 kg / t of iron. The reduction in energy consumption in the proposed process compared to the prototype reaches 443.7 kg / t The coal consumption indicators presented in [9, 5] are 1031 and 1360 kg / t of iron, respectively, are minimal. According to [14], the coal consumption in the ROMELT process is significantly higher than these figures. With the same specific consumption of coal and carbon, respectively 1031 and 742.3 kg / t in the proposed and known method (examples 6 and 8), the first provides additional heat, amounting to about 850 kW · h / t of iron. The achieved reduction in energy consumption shows the advantages of the proposed process over the known.

In addition to higher energy efficiency, the proposed process provides (examples 3-7) the production of direct reduced iron with a given carbon content in the range of 0.05-4.5%. This expands the range of smelted metal from crude iron to pig iron. Some deterioration in the process indicators in examples 1 and 2 is explained by the absence of carbon oxidation by gaseous oxygen (example 1) or the relatively low proportion of carbon oxidized by oxygen blasting (example 2). The consequence of this is the insufficient amount of heat entering the bath and the need to compensate for it by receiving heat from other sources.

As a result of the invention, the energy consumption for producing direct reduction iron in electric arc furnaces and reduction units using a single-stage technology using underexposed iron ore raw materials and carbon-containing material was reduced, the carbon potential as an energy carrier was used more efficiently, the range of direct reduction iron produced was expanded, including the entire range of possible carbon contents in iron - from 0.05% in draft, to 4.5% in cast iron.

List of documents cited in the description of the invention

1. Pokhvistnev AN, Kozhevnikov I.Yu., Spector A.N., Yarkho E.N. Instantaneous iron production abroad. - M.: Metallurgy. 1964 .-- 364 p.

2. Yusfin Yu.S., Gimmelfarb A.A., Pashkov N.F. New metal production processes (iron metallurgy). Textbook for high schools. - M.: Metallurgy. 1994 .-- 320 p.

3. Weber S., Nose D. Hismelt Process. International Meeting on Ironmaking. September 234 to 26, 2001, Belo Horizonte / MG - Brazil. - c. 319-322.

4. Abramenkov Yu.Ya., Strigunov N.A. On the issue of heat shortage of the liquid phase reduction process “ROMELT”. Metallurgy heating technology: A collection of science processes NMetAU Two books. - Friend's book. - Dnipropetrovsk: Thresholds. 2005 .-- 460 s.

5. Abramenkov Yu.Ya., Strigunov N.A. Comparison of technical and economic characteristics of the processes of liquid-phase reduction of iron // Metallurgyna teplotekhnika: Zb. Science. pr. National Academy of Ukraine. Dnepropetrovsk. 2008. - p. 3-21

6. Romenets V.A. New metal production processes. Status and prospects. Moscow, MISIS, publishing house "Study", 2001, p. 37.

7. Soloviev A.N., Levin M.Ya., Valavin V.S., Vandaryev S.V., Chaykin B.S. Engineering aspects of ROMELT plants // Steel. - 2001. - No. 2. - p. 60-64.

8. Romenets V.A. The process of liquid-phase reduction of iron: development and implementation // Steel. - 1990. - No. 8. - p.20-27.

9. Lisienko VG, Lapteva AV, Parenkov AE. Evaluation of the effectiveness of alternative cokeless metallurgical technologies // Steel. - No. 2. - 2009. - p. 72-77.

10. Shakhpazov E.Kh., Dorofeev G.A. New synthetic composite materials and steel smelting technology using them. - M .: Intercontact Science. 2008 .-- 272 p.

11..Medzhibozhsky M.Ya. Fundamentals of thermodynamics and kinetics of steelmaking processes. - Kiev; Donetsk: Vskha school Golovn. publishing house 1986.- 280 s.

12. Yavoysky V.I., Dorofeev G.A., Powkh I.L. Theory of purge steelmaking bath. - M.: Metallurgy. 1974.- 496 p.

13. Metallurgy of steel. Yavoysky V.I., Levin S.L., Baptismansky V.I. et al. - M.: Metallurgy. 1973.- 816 p.

14. Yusfin Yu.S., Chernousov PI, Travyanov A.Ya .. Fuel consumption for liquid-phase reduction of iron ore materials // Steel. - No. 5. - 1995. - p. 20-25.

Table. Examples of the method of liquid-phase production of direct reduced iron in a reduction furnace

No. Specific consumption, kg / t of iron The share of carbon oxidized (burned) by gaseous oxygen, of its total carbon consumption,% rel. The total specific amount of heat generated in the process of iron recovery by carbon, kW · h / t iron The specific heat input to the metal bath from various sources of energy generation, kW · h / t of iron The balance of heat input and consumption during the recovery of iron-carbon iron, kWh / t of iron “-” - heat deficiency “+” - excess heat The proportion of heat obtained from the oxidation (burning) of carbon by gaseous oxygen in the total heat consumption for the reduction of 1 ton of iron,% rel. The carbon concentration in the iron at the outlet,% mass. coal including carbon from afterburning of the process of iron reduction from oxidation (burning) of carbon to CO with gaseous oxygen from the afterburning of CO, which is formed during the oxidation (burning) of carbon by gaseous oxygen from burning natural gas Total one 445.8 321 - 777.90 777.90 - - - 777.90 -1464.90 35.5 3,1 2 648.6 467 32.1 3507.07 777.90 448.22 353.83 - 1579.95 -662.85 70.4 4.0 3 816.7 588 45.4 46-71.09 777.90 819.69 647.07 - 2244.67 +1.86 100.1 0.12 four 833.3 600 46.5 4786.63 777.90 894.00 676.16 - 2312.59 +69.79 103.1 3.5 5 972.2 700 54.1 5748.53 777.90 1163.52 918.51 - 2859.84 +617.14 127.5 0.9 6 1031.0 742.3 56.8 6025.59 777.90 1293.39 1021,02 - 3092.31 +849.51 137.9 2.1 7 1180.6 850 62,2 7191.53 777.90 1624.03 1282.03 - 3683.96 +1441.16 164.3 4.3 8
(process
ROMELT) 1031.0 742.3 56.8 6008,20 555.07 830.00 728.54 142.00 2213.61 2255.61 -12.92 +12.81 94.2 100.6 4.1-4.5

Note on example 8 - In fractional indicators, the numerator shows information excluding the heat of combustion of natural gas, and the denominator shows information taking into account this heat.

Claims (7)

1. The method of liquid-phase production of direct reduced iron in an electric arc furnace, characterized in that the molten metal is used as a reaction medium and a reduction zone metal a bath, solid carbon-containing material and iron ore raw materials in the form of particles of not more than 6 mm are fed into the volume of the metal bath, the oxidizing gas is injected into the flux and the carbon-containing material is heated and the organic part is gasified, the iron ore particles are heated to the molten state to ensure the transition of carbon into the melt and the interaction of liquid iron oxides with carbon and the production of iron and CO, bubbling the molten bath with gas bubbles resulting from gasification and oxidation of carbon, both by boiling it, mixing and bubbling gas bubbles on the surface of the bath, burning CO over the surface with oxidizing gas to ensure heat transfer from the burning of the molten bath, melting and / or dissolving in the slag of the flux, mineral components of the carbon-containing material, waste rock of iron ore and ash of carbon-containing material, removal from the furnace of the resulting process gases, including the gasified organic part of the carbon-containing material, and the release of liquid metal and slag, while Particles of carbon-containing material and iron ore are injected directly into the volume of the metal bath and iron is reduced therefrom from the oxides with part of the incoming carbon to produce carbon monoxide, and technical gas is blown into the metal bath as an oxidizing gas simultaneously and simultaneously with the supply of starting materials and iron reduction oxygen with a specific intensity of 0.1-5m³/ (t · min) and carry out the oxidation of the rest of the input carbon, while the specific consumption of carbon and oxygen is selected from the ratio
(m_C-321) / $$m_O{}_{{}_2}$$

= 0.5-1.5,
where m_C - specific consumption of carbon introduced with carbon-containing material per ton of iron, kg / t;
321 - specific carbon consumption for recovery from Fe₂ABOUT₃ one ton of iron, kg / t;
$$m_O{}_{{}_2}$$

 - specific consumption of gaseous oxygen introduced with the blast per ton of iron, kg / t,
and 0.5–10.0 min before the direct reduction iron obtained from the furnace is removed, 5–95% of carbon is removed from it by additional oxidation with gaseous oxygen injected into the metal with a specific intensity of 0.1–5.0 nm³/(caraway). 2. The method according to claim 1, characterized in that for the reduction of iron, carbon is used simultaneously in the dissolved and free states with its total concentration in the metal bath of 3-15%, while the ratio of the concentrations of dissolved and free carbon in the course of reduction smelting is maintained within 1: (0.1 ÷ 3). 3. The method according to claim 1, characterized in that in a metal bath maintain a temperature equal to or greater than 1400 ° C. 4. The method according to claim 1, characterized in that for the reduction of iron using an electric arc furnace with a specific electric power equal to or greater than 0.8 mW per ton of metal bath in the furnace. 5. The method according to claim 4, characterized in that, in the course of reducing iron, an additional electric power is supplied to the electric furnace in an amount of 30-200 mW per minute per ton of iron ore. 6. The method according to claim 1, characterized in that the combustible components of the process gases are sent outside the furnace to a power plant to generate electrical and / or thermal energy. 7. The method according to claim 1, characterized in that the combustible components of the process gases are burned above the surface of the molten metal bath with a degree of afterburning of not more than 20%.