RU2352643C1 - Metal reduction method of iron group by natural gas and facility for its implementation - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metal production by means of its reduction from dispersed metallic oxide raw materials by natural gas in thermal-electric reactor. Natural gas and initial oxide raw material are fed to arc discharge area of electric furnace, there are implemented melting, reduction and it is utilised energy of effluent from furnace gas. Natural gas without the oxidant is fed into high-temperature - 2000°C and higher arc discharge area, and it is transferred carbon of natural gas by means of pyrolysis from gaseous compound - methane into condensed state - carbon-black. Effluent from furnace powder-gas mixture is subject to cooling with rate 10³-10⁵°C/s in facility for cooling, and from powder-gas mixture, effluent from the facility for cooling, it is extracted and stored nano-dispersed soot carbon.

EFFECT: essential reduction of atmospheric emission of carbon carbonic and greenhouse gases at manufacturing of metals of iron group from oxide raw materials with usage in the capacity of natural gas reducer, receiving during the process of reduction of iron group metals by natural gas of additional useful product, simplification of purification system of effluent gas from the furnace from CO and CO₂.

2 cl, 1 dwg

Description

The invention relates to non-coke metallurgy, in particular to the production of iron, cobalt, nickel by reducing these metals from oxide raw materials, such as dispersed ores, partially reduced ores, ore concentrates and metal-containing oxide waste, with a gaseous reducing agent being natural gas in a plasma chemical reactor, the main share energy into which is introduced using an arc discharge.

Known methods for the reduction of metals of the iron group and corresponding devices based on arc discharges (Electric industrial furnaces. Arc furnaces and special heating installations. Edited by A. Svenchansky, M., Energoizdat, 1981, p. 296; Plasma Physics and Chemistry metallurgical processes. Edited by B.E. Paton, M., Nauka, 1985, p. 1984; Blinov V.A., Konke G.Ya. et al. Reduction of nickel monoxide by natural gas during electric arc smelting, Physics and Chemistry of Processing Materials, 1988 No. 6 30-33 s).

Typically, the method and apparatus include an electric arc furnace and comprise a furnace chamber with a ceramic or metal crucible, a melt bath, metal and slag removal means, means for supplying an initial oxide feed and a reducing plasma-forming gas and a working electrode located on the central axis, usually made of graphite or tungsten. The working electrode is usually installed in the upper part of the device. In some cases, a hollow electrode is used to heat the reagents in the arc. Through it serves the source of oxide material and a reducing plasma-forming gas. The electrode is the cathode of the arc discharge, the role of the anode is played by the molten bath located on the bottom of the furnace, in contact with the bottom electrode. The energy of the exhaust gas from the furnace is disposed of in an energy unit that produces electrical and thermal energy.

The metal reduction process consists in the fact that reducing metal is supplied to the metal oxide melt, which includes carbon mainly in the form of CO and CH ₄ . Reductive synthesis gas is produced either by coal gasification, or by natural gas conversion (the interaction of coal or natural gas with oxidizing agents: oxygen, water vapor, etc.). During metal reduction, CO ₂ and water vapor are formed, which, together with unreacted CO, are removed from the reaction space of the furnace and emitted into the atmosphere. Thus, the carbon entering the furnace is emitted into the atmosphere in large quantities in the form of toxic and greenhouse gases.

A common disadvantage of the known methods and devices is that carbon is used as a reducing agent in the reduction of oxide raw materials in gaseous compounds (CO, CH ₄ ), and after interaction with metal oxide, carbon is released into the atmosphere in the form of toxic CO and greenhouse gas CO ₂ . The capture of carbon oxides or the so-called “washing” of the exhaust gas from the furnace from them with their high content is a complex and capital-intensive technical task.

The closest analogue to the present invention is a method and device for the reduction of metals of the iron group (iron, cobalt, nickel) with converted natural gas from dispersed oxide raw materials described in "Physics and Chemistry of Plasma Metallurgical Processes" / Edited by B.E. Paton, M ., Science, 1985 p. 184; Blinov V.A., Konke G.Ya. et al. “Recovery of Nickel Monoxide with Natural Gas during Electric Arc Smelting”, Physics and Chemistry of Materials Processing, 1988, No. 6, pp. 30-33. The device includes an electric arc furnace, the reduction reactor of which is formed by the working space of the furnace, electrodes: the upper one located above the bath of the ore melt, and the lower one located in the melt, between which an arc discharge is excited, a collector for diverting the products of the reduction reaction from the reduction reactor, and oxide feed sources raw materials, natural gas and oxidizing agent, device for collecting the finished product. In this device, the upper electrode is the cathode, and the melt pool is the anode of the arc discharge of the furnace connected to a constant current source.

A disadvantage of the known method and device is that natural gas is converted and carbon is used as a reducing agent in gaseous compounds — CO and CH ₄ . After the interaction of such a reducing gas with a metal oxide, carbon is removed from the furnace and released into the atmosphere in the form of toxic CO and greenhouse CO ₂ gases. Natural gas with an oxidizing agent (oxygen) is fed into the region of the arc discharge through the channel of the hollow graphite electrode, and the reaction products are directly discharged into the atmosphere through the furnace manifold.

In the known reduction method, as mentioned above, natural gas is subjected to conversion before metal reduction, i.e. mixed with an oxidizing agent - oxygen, which when heated leads to the formation of a synthesis gas consisting of carbon monoxide, hydrogen and methane. This gas is a metal reducing agent. Conversion of natural gas is used in order to avoid pyrolysis of natural gas and coking of the electrode cavity, through which reagents - oxide feed and reducing gas - are fed.

The use of converted natural gas for metal reduction leads to the fact that almost all the carbon of natural gas (about 250 kg / t of iron) is converted to carbon monoxide and emitted into the atmosphere in the form of carbon monoxide and greenhouse gases. The capture of large amounts of carbon monoxide is associated with the creation of a bulky and expensive separating device for exhaust gas. In addition, the conversion of natural gas lowers its reduction potential, which, in turn, requires an increased consumption of natural gas and an additional consumption of an oxidizing agent and, ultimately, complicates and increases the cost of the recovery process.

The problem to which the present invention is directed, is to create a method and device that allows you to restore the metals of the iron group by natural gas without harmful emissions into the atmosphere.

The technical result of the invention is to improve the environmental and economic indicators of production of metals of the iron group.

The technical result is achieved in that in a method for reducing metals of an iron group by natural gas, including supplying natural gas and an oxide feed to an arc discharge region of an electric furnace, excitation of an electric arc between an electrode and oxide feed, melting and reduction of an oxide feed, removal of reaction products from the furnace, removal of the finished metal product from the furnace and its collection, purification of the dust and gas mixture leaving the furnace from carbon dioxide, water vapor, dust particles, utilization of energy from the furnace according to the invention, natural gas without an oxidizing agent is fed into a high-temperature (2000 ° C and higher) region of the arc discharge, and carbon of natural gas is transferred by means of pyrolysis from a gaseous compound - methane to a condensed state - soot, the dust-gas mixture leaving the furnace is cooled at a speed of 10 ³ -10 ⁵ ° C / s in the device for cooling, and nanodispersed soot carbon is removed and stored from the dust-gas mixture leaving the device for cooling.

Device for the reduction of iron group metals by natural gas, including an electric arc furnace, electrodes: upper, located above the ore melt bath, and lower, located in the melt, to initiate an arc discharge between the upper electrode and the melt, a collector for removal of reduction reaction products from the furnace, feeders starting oxide raw materials and natural gas, a device for removing from a furnace and collecting finished metal products, a separating device for cleaning carbon dioxide exhaust from the furnace from carbon dioxide o gas, water vapor, dust particles, an energy unit that utilizes the energy of the gas leaving the furnace, according to the invention, the device further comprises a cooled pipeline for supplying raw natural gas to the arc discharge, located on the periphery of the electrode above its working end at a distance from the last 0.7 -1.2 diameter of the electrode, a device for cooling in the form of a heat exchanger, providing cooling of the reaction products of the reduction reactor, and the separating device further comprises a filter lement as a precipitator for collecting nanosized particles of black carbon.

Terms and definitions used.

A reduction reactor is a furnace space bounded by a hearth, side walls, and a vault in which oxide raw materials and natural gas interact, leading to metal reduction.

Arc discharge, electric arc, arc - gas electric discharge burning between solid and liquid electrodes and characterized by a low voltage of 10-10 ³ V and a high current of 10-10 ⁵ A.

Cooling device - a device designed to quickly cool the dust and gas stream in order to prevent reverse carbon oxidation reactions.

Separator, separating device - a device designed to separate fine particles, gases and liquids from a dust and gas stream.

Feeder - a device containing a hopper with an initial oxide feedstock or a gas source and means for supplying them at a given speed.

Oxide raw materials - mineral and industrial raw materials containing one or more oxides of iron, nickel, cobalt of various valencies.

An energy block is a device for converting the thermal and chemical energy of the gas leaving the furnace into electric and thermal energy.

Soot, carbon black, pyrocarbon - dispersed carbon with a particle size of 10-350 nm.

The drawing shows a schematic diagram of a device, including a longitudinal section of an arc furnace with a supply of natural gas and oxide raw materials around the periphery of the electrode.

The device comprises an electric arc furnace 10 with a top electrode 3 located along the axis of the furnace, a bottom hearth electrode 12, a cooled pipe 4 coaxial with respect to the electrode, and a metal drain device 13. A graphite solid electrode is used as the upper electrode. The cooled pipeline through which natural gas is supplied to the reduction reactor 8 is arranged on the periphery of the electrode and placed in relation to the arc discharge and the electrode so that the natural gas entering the melt mirror is heated to a mass-average temperature exceeding the pyrolysis temperature of natural gas, such as 1000 ° C is known. The drawing shows a section of a furnace with a coaxial in relation to the electrode arrangement of the pipeline.

An arc discharge 9 is excited between the melt 11 and the upper electrode 3. The mirror of the melt bath, the side walls and the arch of the furnace form a reduction reactor 8. The furnace arch is connected via pipelines 7 to a cooling device 6, which, in turn, is connected to the gas path via gas paths collector 5. The cooling device provides a high cooling rate of reaction products: 10 ³ -10 ⁵ ° C / s. At a cooling rate of less than 10 ³ ° C / s, reverse carbon oxidation reactions are not prevented. It is technically difficult to provide a cooling rate of more than 10 ⁵ ° C / s (only possible with supersonic flow rates and a Laval nozzle). As a device for cooling, a heat exchanger (slotted, tubular) is used.

The oxide raw material is supplied to the melt 11 through a feeder 2 and a pipe 4. Natural gas is supplied to the arc discharge region 9 through a feeder 1 and a coaxial pipe 4, where the temperature of the gas and electrode is 2000 ° C and higher. An electric power 20 is supplied to the furnace electrodes from the energy block 19. The energy block for utilizing the energy of the gas leaving the furnace may include a steam boiler for producing high-quality steam as a working fluid of a turboelectric generator, a gas turbine of a turboelectric generator and fuel cells. The energy block 19 generates electricity 20 to supply an electric arc arc discharge and commercial thermal energy 25 to external consumers by utilizing the thermal and chemical energy of the gas leaving the separator 18, to which the energy block is connected by a pipe 21.

The separator 18 includes filter elements 23. The separator extracts water 14, dust 15, soot 16 and carbon dioxide 17 from the gas. The separator is connected to the gas manifold of the furnace 5 by a gas line 24; a refrigerator is used to remove water from the gas; to remove dusty particles with a size of 1-100 microns or more (ore raw materials and metal), dust collectors of gravitational inertial action, bag filters are used; gas purification from CO _{2 is} carried out by chemisorption with an aqueous solution of monoethanolamine; to capture particles of pyrocarbon with a size of 10-350 nm, an electrostatic precipitator is additionally used.

The device operates as follows. Initially, a metal seed is charged into the reduction reactor 8. An arc discharge is excited between the “seed” and the electrode 3. The operating parameters of the installation are set: the value of the arc current, the value of the arc gap, the flow of natural reducing gas from the gas source 1 through a water-cooled coaxial pipe 4.

After the melt bath 11 is guided into the reactor 8 from the feeder 2, the initial oxide feed is fed to the mirror of the melt bath through a water-cooled pipe 4, which is mixed with the melt by gravitational, gas-dynamic and magnetic forces. Natural gas on the way to the oxide melt mirror as a result of its heating by an arc discharge to the pyrolysis temperature, as is known, 1000 ° C, forms soot carbon and hydrogen. The main reducing agent in this case is hydrogen. The carbon of natural gas, as a result of its transition to a condensed state and the formation of nanosized black carbon with a significant decrease in volume (the volume of carbon in the condensed phase is approximately 10,000 times less than the volume of CH ₄ gas), has a low probability of interaction with the oxide melt. This leads to the fact that an insignificant proportion of carbon is involved in the recovery process - about 10%, and its main share - up to 90%, is discharged from the reactor with exhaust gas to pipeline 7. The gas leaving the reactor includes, in addition to dispersed carbon, water vapor, methane, hydrogen , carbon dioxide, carbon monoxide and dust particles of oxide and metal.

To prevent the dispersed carbon from being oxidized by water vapor and carbon dioxide resulting from the reduction of the metal, the gas leaving the reduction reactor 8 is sent via pipelines 7 to a cooling device 6, which provides gas cooling at a rate of 10 ³ -10 ⁵ ° C / s. As a cooling device, well-known slotted or tubular heat exchangers are used. As noted above, at a cooling rate of less than 10 ³ ° C / s, a significant amount of carbon black will be oxidized by water vapor and carbon dioxide, it will be technically difficult to produce cooling at a rate above 10 ⁵ ° C / s (using a Laval nozzle, etc.).

The dust-gas mixture 24 leaving the cooling device enters the separating device 18. The separating device includes filtering elements 23 designed to separate from the gas and collect the corresponding components: water - 14, dust particles 1-100 μm in size and above - 15, soot with a size particles of 10-350 nm - 16 and carbon dioxide - 17.

The purified gas 21 leaving the separation device consists of hydrogen, methane and carbon monoxide. This gas enters the energy block 19 (steam boiler, gas turbine, fuel cell) to generate electrical and thermal energy. The generated electric energy 20 is supplied to the electrodes 3 and 12 of the electric furnace 10 to power the electric arc 9. Outgoing gas 22 from the energy block — water vapor and carbon dioxide enter the separator 18 to extract them.

The reduced metal as a heavier fraction of the melt accumulates in the lower part of the reduction reactor of the furnace and in the form of a metal melt, which periodically or constantly merges into the receiver of the finished product 13.

The value of the arc current is set such that thermodynamically necessary thermal conditions are provided in the reaction volume of the reduction reactor. For example, when reducing iron ore concentrate in a copper water-cooled crucible, the specific heat flux to the melt pool mirror should be about 5 MW / m, which, for example, for a crystallizer with a diameter of 100 mm corresponds to a current value of 1200 A. With a lower heat flux, iron does not recover, with a larger excessive evaporation of the metal occurs.

The consumption of natural gas is established on the basis of thermodynamic calculation and experimental data. For example, the consumption of natural gas, taking into account its pyrolysis, is 400-600 m ³ / t of reduced iron. In this case, the amount of carbon black produced is about 200 kg / t of iron.

To ensure the pyrolysis of natural gas, it is necessary, as mentioned above, to heat the gas due to its interaction with the arc to the mass-average temperature, as is known, 1000 ° C and lice. This is achieved by the fact that natural gas is supplied through a pipeline directly to the region of the arc, where the plasma temperature of the arc and electrode is 2000 ° C and higher. In this case, intense heat exchange of natural gas with the arc and electrode occurs, and the formation of pyrocarbon on the electrode surface is prevented (the deposition and sublimation rates of pyrocarbon are equal).

The pipeline for supplying natural gas is located above the working end of the upper electrode at a distance from the last 0.7-1.2 diameter of the electrode. At this distance, the electrode has the indicated temperature, i.e. 2000 ° C and above. When the distance of the pipeline from the end of the electrode is less than 0.7 diameter, there is a danger of arc transfer to the pipeline; at a distance of more than 1.2 diameters - the temperature of the electrode is below 2000 ° C and pyrocarbon is deposited on its surface.

In turn, the diameter of the electrode is determined by known methods, which are based on the permissible current density in the electrode and the working temperature of the electrode end, which provides the necessary thermionic current. This temperature is 3000-3500 ° С (see A.D. Svenchansky et al. Electric industrial furnaces, M., Energoizdat, 1981, p. 296).

Thus, the present invention due to the conversion of carbon of natural gas from a gaseous compound - methane to a condensed state - soot and its utilization allows:

1) significantly reduce the emission of carbon monoxide and greenhouse gases into the atmosphere during the production of iron group metals from oxide raw materials using natural gas as a reducing agent;

2) to receive in the process of reducing metals of the iron group by natural gas an additional useful product - soot;

3) reduce the cost of the metal obtained: when reducing iron, its cost is reduced by about 2 times due to the high price of an additional product - soot (the cost of soot is about 10 times higher than the cost of iron and is about 30,000 rubles / t);

4) to significantly simplify the system for purifying the exhaust gas from the furnace from CO and CO ₂ as a result of a sharp decrease in the content of carbon oxides in it, the extraction of which from gas in large volumes is a difficult technical task.

The invention can be used at the enterprises of metallurgy and mechanical engineering for environmentally friendly direct production of iron, nickel, cobalt from dispersed oxide raw materials using unconverted natural gas as a reducing agent. The resulting additional product, carbon black, is used in the rubber-driving and paint industry.

Industrial applicability of the invention is also determined by the widespread use in industry of individual elements of the invention, as follows from the description of the device for implementing the proposed method of metal recovery and the above analogues, but in other combinations and with other technical results.

Claims (2)

1. A method of reducing metals of an iron group by natural gas, including supplying natural gas and an oxide feed to an arc region of an electric furnace, exciting an electric arc between an electrode and an oxide feed, melting and reducing an oxide feed, withdrawing reaction products from the furnace, withdrawing the finished metal product from the furnace and its collection, cleaning the exhaust gas mixture from the furnace from carbon dioxide, water vapor, dust particles, utilizing the energy of the exhaust gas from the furnace, characterized in that natural gas without kislitelya fed into the high temperature - 2000 ° C and above the region of the arc discharge, and carbon gas is converted by pyrolysis of gaseous compounds - methane condensed state - carbon black, extending from the kiln dust and gas mixture is subjected to cooling at a rate of 10 ³ to 10 ⁵ ° C / s in the cooling device, and from the dust-gas mixture leaving the cooling device, nanodispersed carbon black is removed and stored. 2. Device for the reduction of metals of the iron group by natural gas, including an electric arc furnace, electrodes: the upper one located above the bath of the ore melt and the lower one located in the melt to initiate an arc discharge between the upper electrode and the melt, a collector for removing the products of the reduction reaction from the furnace , feeders with initial oxide raw materials and natural gas, a device for removing from a furnace and collecting finished metal products, a separating device for cleaning carbon-dioxide mixture leaving the furnace from carbon dioxide gas, water vapor, dust particles, an energy unit that utilizes the energy of the gas leaving the furnace, characterized in that the device further comprises a cooled pipeline for supplying raw natural gas to the arc discharge, located on the periphery of the electrode above its working end at a distance from the last 0 , 7-1.2 of the diameter of the electrode, a device for cooling in the form of a heat exchanger, providing cooling of the reaction products of the reduction reactor, and the separating device further comprises filtering th element in the form of an electrostatic precipitator for trapping nanosized particles of carbon black.