EA024335B1 - Carbon reducing agent and method for obtaining the same - Google Patents

Abstract

The invention relates to the field of metallurgy and chemical industry and concerns novel material rexil, suitable for conducting metallurgical and chemical reducing processes. The material represents carbon reducing agent, which possesses complex pore structure, consisting of fine-pored system, which includes nanopores with size smaller than 2 nm and transitive and communicating mesopores with size from 2 to 50 nm, and developed system of transport pores, which includes macropores with size from 50 to 1000 nm and tunnel pores with size from 1 to 1000 μm. The system of transport pores constitutes 5-85 vol.% counted per the total volume of the reducing agent material. The characteristics, which rexil material possesses (specific surface area, reaction ability, specific electric resistance, structural strength, gas permeability) make it possible to efficiently apply it for conducting metallurgical and chemical reducing processes, especially for smelting highly-pure crystalline silicon, achieving improved furnace productivity, reduced specific electric energy consumption and with essential reduction of silicon loss. Also proposed is the method for obtaining the said material by high-performance thermooxidising coal carbonisation, realised at high rate of coal heating in the range of its destruction temperature, using combined pulsing blast.

Description

The present invention relates to the field of ferrous metallurgy, non-ferrous metallurgy and the chemical industry. In more detail, the invention relates to a Rexyl material, which is a carbon reducing agent suitable for metallurgical and chemical reduction processes, in particular for the smelting of crystalline silicon and silicon-containing alloys by electrothermal or plasma melting.

State of the art

In the field of metallurgy and the chemical industry, a solid carbon reducing agent such as coke, obtained from sintering coal in a classical way in coke oven batteries without air access by external heat supply for heating a coal load, is well known. For example, blast furnace coke is known for smelting cast iron, ordinary grades of ferroalloys, containing, wt.%: Ash (L ⁴ ) 8.7-13.5%, volatiles (ν ^ ^{α £} ) 0.8-1.3%, sulfur 0.4-1.74%, phosphorus 0.015-0.050% (Volkov Yu.P., Shparber L.Ya., Gusarov A.K. Technologist-Domenshchik. - M .: Metallurgy, 1986, p. 263).

The disadvantage of the analogue is the high ash content, low reactivity of carbon coke, not exceeding 0.5-0.7 ml / g-s and low electrical resistivity, less than 4.0 Ohm-cm, the absence of a nanoscale finely porous structure characterized by the value of the iodine number ( iodine number is zero), which plays a decisive role in the processes of reduction of silicon and silicon-containing alloys occurring in a heterogeneous medium: solid-gas, which makes its use for these processes extremely inefficient and does not allow the smelting of metal s high purity, and also makes it difficult to achieve high technical and economic indicators of the technological process.

Solid carbon reducing agent is also known as special coke, obtained from non-sintering coals and containing, wt.%: Carbon 88.5-78%, ash (A ⁴ ) 7.0-10.0%, volatile substances (V ' ¹ ' ¹ ' ) 4.5-12%, sulfur 0.26-0.40%, phosphorus 0.017-0.023%. Such a special coke has a relatively developed finely porous structure (iodine number 1-10%); see Nurmukhambetov J.U. Research and development of technology for the production and use of special coke for smelting ferroalloys // Abstract of thesis. Cand. Sciences, Karaganda, 2005.

The disadvantage of this technical solution is the high ash content, insufficiently developed finely porous structure and relatively small specific surface area of 10-100 m ² / g (iodine number does not exceed 10%), a large amount of residual volatile substances (4.5-12%), which create excessive interstitial pressure of intrinsic pyrolysis gases that prevent the penetration of gaseous δίΘ into the interstitial space of the reducing agent when it is heated in the range of silicon reduction temperatures, as well as low structural strength awn special coke _from n = 45-55%, which in the aggregate does not allow, for example, by electrothermal smelting crystalline silicon containing more than 99.3% of silicon, and a low specific energy consumption less than 14.5 thousand KW / t, in the following ore-thermal furnace, as well as with a high degree of extraction of silicon from quartzite - more than 82%.

The closest in technical essence and the achieved result is the low ash solid carbon reducing agent previously proposed by the authors of this application, which they named Rexyl carbonizate. This product has a well-developed fine-pore structure (iodine number 12.5-50%) and a high specific surface area of 120-500 m ² / g, which provides a sufficiently high reactivity of the product - 7-12 ml / g-s. The product contains little ash (A ⁴ 1.0-5.0 wt.%), Has a high electrical resistivity (0.6-0.98) x10 ⁶ Ohm-cm and the structural strength of PS 70-85%. These characteristics make it possible to use it, in particular, as an effective base reducing agent for the smelting of crystalline silicon, which makes it possible to obtain crystalline silicon containing more than 99.3% of the base component, while improving the technical and economic indicators of the melting process, such as increasing the productivity of an electric furnace per unit time and reducing the specific energy consumption per unit of finished products (Schebentovsky V.D., Kim V.A., patent No. 23615, publ. 15.12.2010, bull. No. 12).

However, when using this product, a sufficiently noticeable amount of silicon is lost due to its entrainment from the reaction zone in the furnace in the form of gaseous silicon monoxide, or δ газа-gas (which can be about 7-8% or more of the mass of silicon in the feed), which to limit the possibility of increasing the productivity of the electric furnace and reduce the specific energy consumption per unit of finished product, as well as the overrun of high-quality quartzite raw materials used to obtain crystalline of silicon, and a solid carbon reductant itself.

Therefore, the task of the inventors was to develop an improved carbon reducing agent to overcome the above disadvantages.

- 1,024,335

SUMMARY OF THE INVENTION

To solve the problem, the authors of the present invention have developed new material for use in metallurgical and chemical reduction processes, called Rexyl and is a carbon-based reducing agent having a developed porous structure and consisting of carbon, ash and volatile substances. The specified material is characterized by the fact that it has a complex pore structure consisting of a finely porous system including nanopores smaller than 2 nm, and transitional and interconnected mesopores from 2 to 50 nm in size, and a developed transport pore system including macropores from 50 to 1000 nm and tunnel pores ranging in size from 1 to 1000 microns, moreover, the solid phase of the material accounts for 10-30 vol.%, the finely porous system - 5-65 vol.% and the transport pore system accounts for 5-85 vol. % based on the total amount of reducing agent material. Moreover, the specified Rexyl material is also characterized by the following properties:

specific surface area (§) - 105-600 m ² / g; reactivity - 7-13 ml / g-s; electrical resistivity - 0.1x10 ³ -0.98x10 ⁶ Ohm-cm; structural strength (P _s ) - 70-85%; bulk density - 0.18 to 0.45 t / m ³ ;

gas permeability, determined taking into account GOST 11573-98 and ISO 8841-91E, component 0.033.65 cm ³ / s for a sample with a cross section of 1 cm ² , length 1 cm, with a pressure drop of 0.1 MPa;

and the following composition: carbon (C) - 91.5-98.9 wt.%; ash (A ') - 1.0-5.0 wt% and the volatiles (V.' ^{1 '11)} - 0.1-3.5 wt.%.

The invention also relates to the use of such a carbon reducing agent in metallurgical and chemical reduction processes, including smelting of crystalline silicon and silicon-containing alloys by electrothermal or plasma melting, phosphorus production, production of silicon and calcium carbides, metallization and agglomeration of ore materials.

The use of the Rexyl material of the present invention allows the smelting of crystalline silicon and silicon-containing alloys with a high degree of extraction of silicon from quartzite raw materials (quartzite and / or quartz) - more than 93.5%, with reduced energy consumption and high productivity of the ore reduction furnace per unit time, which improves technical and economic indicators of smelting.

Brief Description of the Drawings

The drawings show micrographs of the Rexil material according to the present invention, made on a Mia high resolution scanning electron microscope from Texap (Czech Republic).

In FIG. 1 shows a photograph of a single grain of material with magnification x40.

In FIG. Figure 2 shows a photograph of a portion of the grain surface of a material with a magnification of x500.

In FIG. Figure 3 shows a photograph of a cross-section of a Rexil material with a magnification of x500.

In FIG. Figure 4 shows a photograph of a longitudinal section of a Rexil material with a magnification of x500.

In FIG. 5 shows a photograph of a cross-section of a Rexil material with a magnification of x2000.

In FIG. Figure 6 shows a photograph of a longitudinal section of a Rexil material with a magnification of x2000.

In FIG. Figure 7 shows a photograph of a slice of Rexyl material with magnification x 30,000.

In FIG. Figure 8 shows a photograph of a slice of Rexil material with a magnification of x50000.

In FIG. Figure 9 shows a photograph of a slice of Rexyl material with a magnification of x 100,000.

In FIG. 10 shows a photograph of a slice of Rexyl material with an increase of x170,000.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a new material called Rexyl, which is a carbon-based reducing agent having a developed porous structure and consisting of carbon, ash and volatile substances. This material can be used as an effective reducing agent in a wide range of metallurgical and chemical reduction processes occurring in heterogeneous solid-gas media. First of all, such processes include smelting of crystalline silicon and smelting of silicon-containing alloys (for example, FS-90 ferrosilicon) by electrothermal or plasma melting methods. The reducing agent is also applicable to other processes: production of phosphorus, silicon carbides and calcium, metallization and agglomeration of ore raw materials.

Rexyl material is characterized by the following composition of the main components: carbon (C) - 91.598.9 wt.%; ash (A ') - 1.0-5.0 wt.% and volatile substances (U ^s ) - 0.1-3.5 wt.%.

The low ash content in the material intensifies the reduction processes in which it is used, and provides a lower content of impurities in the final products of such processes. In turn, the low content of volatile substances during the smelting of silicon leads to a more efficient use of the original silicon-containing raw materials, to reduce losses of silicon and increase

- 2 024335 specific productivity of equipment (electric smelting furnaces) for the final product, as will be described in more detail below.

Preferably, the Rexyl material contains 94-96 wt.% Carbon (C), 2.5-3.7 wt.% Ash (L ⁴ ) and volatile substances (U ⁴¹ ) 0.7-1.5 wt.% On a dry weight .

Rexyl is a material with a well-developed porous structure. The total volume fraction of all pores in rexil is approximately 70 to 90% of the total volume of the material, and the volume fraction of the solid phase is from 10 to 30%. At the same time, an essential feature of the Rexil material is that its porous structure is complex and consists of a finely porous system and a developed system of transport pores.

In this case, the determination of the volume distribution of pores in rexil depending on their size, according to the present invention, was performed on a CPP-1100-ΑΜ-δΤ compression porometer.

The finely porous system (fine pore system) includes nanopores smaller than 2 nm in size and transitional and communicating mesopores ranging in size from 2 to 50 nm. The fine-porous system accounts for about 5 to 65 vol.%, Calculated on the total volume of the material. The role of the finely porous structure is to provide a high degree of development of the surface of the reducing agent, which, in turn, ensures its high reactivity in contact with the reduced δ-gas and other substances and thereby high efficiency of the recovery processes involving the inventive material, in particular, high process speed and a high degree of extraction of the target substance, such as silicon, from the feedstock.

The role of mesopores in the finely porous system is that they are transitional and interconnected pores in the finely porous system and contribute to the intensive development of nanoscale pores on their walls over the entire inner surface, as well as ensure the availability of nanopores for penetrating δίΘ gases and reagents, and timely removal gaseous reaction products (CO).

In FIG. 7-10, where microphotographs of slices of Rexyl material are performed using a Texap high resolution (2 nm) scanning electron microscope from Texap with an increase from x30000 to x170,000, the fine-porous structure with a pore size from about 10-20 to 50 nm is quite clearly distinguishable. As can be seen in these photographs, the structures presented on them (which are essentially the walls of the larger pores that form the transport pore system) have a rough surface covered with roughness-forming elements in the form of protrusions or grains, mainly about 20-200 nm in size. Pores related to the fine-pore structure essentially represent gaps and cracks between the indicated grains and / or protrusions, cracks in them themselves, as well as cracks and channels that go under these roughness elements between them and a layer of Rexil material (forming the wall of a large transport pore ) and in the material itself. Such cracks, gaps and channels, quite clearly visible in the photographs given, communicate with each other and have sizes (as can be estimated from the photographs) of the order of 10-20 to 50 nm, as already mentioned above. That is, the above photographs clearly illustrate the finely porous structure of rexyl with respect to the main part of the mesopores. As for the thinnest mesopores, as well as nanopores, which are already not sufficiently distinguishable with the available magnifications of photographs, their presence and quantity can be judged by other data, in particular, by determining the iodine number (where is the value obtained in the known method for determining the specific the surface area of micropores, in particular in sorbents, such as, for example, activated charcoal, according to GOST 6217-74). The iodine number for the Rexyl material is 10.5-60%, which corresponds to a surface area of 100-600 m ² / g, which is formed mainly by a finely porous structure.

At the same time, a significant feature of rexyl that distinguishes it from the prior art, including the prototype, is the presence of a highly developed large-porous system, or a system of transport pores, which may account for 5-85% by volume, based on the total volume material.

The transport pore system includes macropores from 50 to 1000 nm in size and tunnel pores from 1 to 1000 microns in size.

The system of transport pores in the rexyl reducing agent solves the problem of ensuring the effective reaction of the reduction of compounds in the gas phase in the melting furnaces to obtain crystalline silicon, ensuring the passage of hot δίΘ gas through the particles / pieces of the reducing agent and its entry to the developed surface of the finely porous material system, where target reduction reactions occur, as well as the effective removal of the volatile components of the reducing agent (in the initial stages of the process) and the products of ktsii.

In the series of microphotographs with magnifications from x40 to x2000 shown in FIG. 1-6, the developed system of rexyl transport pores is clearly illustrated. So in FIG. Figure 1 shows a single Rexil grain, where it can be seen that it is covered with a large number of cracks and pores of about tens and hundreds of micrometers in size. In FIG. 2, you can see a part of the surface of the indicated grain with a larger increase, where large transport pores opening to the surface are clearly visible. In the following FIG. 3 and 4, you can see the structure of the rexil slices made in the transverse and longitudinal

- 3,024,335 directions with the same x500 magnification as in FIG. 2, and in FIG. 5 and 6, respectively, with a larger magnification of x2000. These pictures clearly show that the entire internal volume of Rexyl material is penetrated through with a large number of transport pores of various sizes - from several hundred micrometers (about 100-500 microns) to units and tenths of a micrometer (about 0.1 microns (= 100 nm) - 5 μm). Moreover, these pores constitute a significant part of the volume of material, which essentially consists of these pores and the walls separating them with a thickness smaller than or close to the pore diameter. In these photographs, one can also see a transition with increasing magnification from the largest pores of the tunnel pores of the transport structure to smaller tunnel pores and macropores of the order of 1 μm or less in size and to sections of their walls on which meso and nanopores develop, forming a finely porous structure, as described above.

Due to the presence of the finely porous structure described above, the material has a high specific surface area (δ) of 105-600 m ² / g. More preferred is a specific surface area of from about 500 to 600 m ² / g. The determination of the specific surface area can be made by known methods. In particular, the specific surface was determined on a surface area and pore size analyzer δΑ 3100 from фирмы СОиЬТЕК (USA) with a relative error of the method of 2%.

In turn, the developed surface of the material contributes to its high reactivity. More specifically, the reactivity of rexyl, determined according to GOST 10089-89, is 7-13 ml / g-s.

At the same time, the presence of a developed rex system of transport pores in the claimed material ensures its high gas permeability, which plays a key role in the availability of effective pore space for δίΟ gas leaving the zone of the first stage of the main reactions at high speeds. The latter is from about 0.03 to about 3.65 cm ³ / s for a sample with a cross section of 1 cm ² , 1 cm long with a pressure drop of 0.1 MPa (when determined taking into account the methods in accordance with GOST 11573-98, as well as ISO 8841- 91E).

In addition to the above parameters, Rexil is characterized by a specific electrical resistance having a value in the range of about 0.1x10 ³ to 0.98x10 ⁶ Ohm-cm. The resistance value in this interval provides an optimally high heating rate of the pieces of rexyl in the electrically conductive part of the top and the zone of the main reactions of the electric melting furnace with minimal energy consumption. If the above values are exceeded, the heating rate in the specified zone becomes too high, which leads to premature melting and fluidity of quartzite / quartz and, as a result, to sintering of the charge, reduction of its gas permeability and freezing. At too low values of electrical resistance, the coefficient of conversion of electric energy into heat decreases, which increases the energy consumption by 1 ton of metal, and the speed of heating pieces of material in the electrically conductive part of the top and the main reaction zone decreases, resulting in a decrease in productivity per unit time and the degree of extraction. Preferably, the magnitude of the electrical resistance of Rexyl is (0.6-0.98) x 10 ⁶ Ohm-cm.

Rexil is also characterized by increased structural strength (P _s ) of 70-85%, determined by the method of N.S. Gryaznova for cokes, by destroying a portion of rexyl grains with a grain size of 3-6 mm in steel cylinders, where metal balls are placed, rotating at a frequency of 25 rpm for 40 minutes Structural strength is estimated by the number of pieces of rexil remaining on the sieve with a grain size of more than 1 mm (Big Encyclopedia of Oil and Gas).

Finally, Rexil has a bulk density of 0.18 to 0.45 t / m ³ . Moreover, in a preferred embodiment of the invention, Rexyl is a bulk material with a size of pieces ranging from 3-35 mm, more preferably from 3 to 25 mm, which, together with the friability and gas permeability of the top layer, provides the most complete adherence to a piece of quartzite / quartz by this reducing agent according to the entire surface, mainly part of the fine fraction - from 3 to 8 mm, while the larger fraction provides the overall gas permeability of the charge layer and reduces the pressure in the reaction gle.

The combination of the above characteristics makes Rexil an extremely suitable and convenient reducing agent for a number of metallurgical and chemical processes occurring in a heterogeneous solid-gas medium. To the greatest extent, the positive effects of the use of rexyl are achieved when it is used for the smelting of crystalline silicon and silicon-containing alloys, since the process of silicon reduction cannot proceed bypassing the gas phase, i.e. otherwise with the formation of a δίΟ gas.

Further consideration is intended to explain the possible causes and mechanisms of the effectiveness of using Rexil in the preparation of crystalline silicon. However, it is not intended to limit the invention to the stated general theoretical provisions and information.

As is known in the art, the chemical activity of a carbon reducing agent is mainly associated with the presence of nanopores (less than about 2 nm) and transition pores (about 2 to 50 nm), since the effective internal or reaction surface depends on them. Moreover, a large number of nanopores can be formed mainly on the walls of the communicating mesopores in the effective pore space. This can be evidenced by the high iodine number of Rexil material, which is 10.5-60% when determined according to GOST 6217-74.

On the other hand, the reaction rate is also determined by the rate of supply of reagents and removal of reaction products to / from the reactive surface, that is, the diffusion conditions of the gases reacting with it. The system of large transport pores (macropores and tunnel pores), penetrating particles or pieces of material and ensuring its fast supply of gases reacting with it to mesopores and further to the last nanopores developed on the surface, plays the main role in ensuring efficient diffusion mass transfer throughout the entire volume of the porous material. also the removal of products from a finely porous structure.

It is known that the preparation of crystalline silicon by electrothermal reduction is a rather complicated process. In general, in order to obtain crystalline silicon, a multi-component mixture is co-melted in a furnace, consisting of quartzite and / or quartz and a carbon reducing agent, and, as a rule, a mixture of various reducing agents of carbon: charcoal, petroleum coke, coal, wood chips and etc. (Gasik M.I., Lyakishev N.P. Theory and technology of electrothermal ferroalloys. - M .: SP Intermet Engineering, 1999).

The scheme of the main chemical reactions of silicon reduction is as follows:

3ίΟ ₂ + С = ЗУ + СО at 1300-1400 ° С and more ЗУ + 2С = 31С + СО at 1500-1550 ° С and more 31С + 5ίΟ = 231 + СО at 1650-1800 ° С

23YU + SiO ₂ = 35ΐ + 2CO at 1650-1800 ° C or more.

Crystalline silicon is formed in the reaction zone of the furnace (in particular, in the zone of an electric arc in an electrothermal furnace) at a temperature of 1650-1800 ° C. However, at lower temperatures of the order of 1300-1400 ° С and more, gaseous silicon monoxide δίΟ is formed, which, under these conditions, is a volatile gaseous product (δίΘ-gas), which tends to be carried away from the reaction zone together with other gases into the gas treatment system, which leads to a loss in productivity of the electric furnace and an increase in the specific consumption of electric energy and carbon of the reducing agent per 1 ton of finished products, as well as to a decrease in the degree of extraction of silicon from ore raw materials, environmental pollution E oxides of silicon and carbon and the like negative consequences.

At the same time, gaseous δίΘ heated to a temperature of 1600 ° С and more degrees, moving in an upward flow through the charge layer, moving down to the reaction zone, is able to interact with the charge reducing agents carbon at lower temperatures (up to 1500 ° С) with the formation of solid-phase carbide silicon δίΘ, which is an intermediate in the general mechanism for the reduction of silicon from quartzite and / or quartz δίθ ₂ and capable of further interacting with δίΘgas and δίθ = to metallic silicon in the main reaction zone. The absorption of gaseous silicon monoxide by the particles of the reducing agent with its subsequent chemical interaction with the carbon of the reducing agent is the mechanism that allows you to return to the main reaction zone the bulk of the flown off in the form of gaseous silicon δίΟ and then get it in the form of the final target product. Some part of δίΟ, which nevertheless did not have time to condense on the surface of the walls of the reducing agent and recover, will be carried away into the gas purification system, leading to the aforementioned negative consequences.

Since the rate of ascending gaseous flow δίΟ through the charge layer in the reaction zone is quite high, the time of its contact with the reducing agent in the charge is relatively small. Therefore, to reduce the entrainment of δίΟ gas from the reaction zone and increase its amount, which is reduced to solid-phase silicon carbide and then to the target product, crystalline silicon, the rate of interaction of δίΟ with the reducing agent material, which is determined by the rate of the chemical reaction of the reducing agent carbon with δίΟ, plays a decisive role also the total area and surface relief of the reducing agent, capable of interaction, and its accessibility to the reagents, that is, the availability of pore space.

These factors are mainly due to the pore structure of the reducing agent - the number of pores, their size distribution, their closure (open, closed, communicating, etc.), and, as shown above, the surface area is mainly associated with a finely porous structure (nano- and mesopores), while the availability of the entire reactive surface of a particle / lump of a reducing agent for gaseous reagents depends mainly on the presence and degree of development of the system of large transport pores penetrating it (macropores, tunnel pores) - see FIG. 2-6.

In addition, the presence of residual volatile substances in the reducing agent plays a significant role in the accessibility of the pore structure. The latter are released from the reducing agent during its heating in the course of advancement to the reaction zone and create excess pressure in the pore space for the time required for their complete evaporation and removal from the pore space, which prevents the effective penetration of gaseous δίΘ into the pore space. With a high content of volatile substances in the reducing agent, intense gas formation with their participation continues in the medium-temperature (middle) zone of the charge layer, so that the significant excess pressure created by them in the pore space makes it (the space) inaccessible to the penetration of gaseous δίΘ and thereby prevents capture in this zone of gaseous silicon monoxide from the ascending streams released from the lower (reaction) zone of the charge layer, thereby reducing the time of the possible interaction of the δίΘ gas with the surface of the reducing agent and the surface area itself, available for interaction, and accordingly reducing the height of the reactive charge layer.

Thus, the smaller the amount of residual volatile substances contained in the reducing agent, the faster the effective penetration of gaseous silicon monoxide to the working surfaces in the pore space of the reducing agent will begin, which will lead to an increase in the rate of the recovery process per unit time, as well as an increase in the height of the reactive charge layer and, as a result decrease in the fraction of ablation δίΘ from the reaction zone.

In addition, in the preparation of silicon in accordance with the above process, the conductivity of the reducing agent material is essential. The latter determines the rate of charge heating both in the electrical conductive and in the reaction zone, and, accordingly, the rate at which the required reduction temperature is reached. An increase in the electrical resistance of the reducing agent accelerates the heating of the material and makes it possible to quickly reach operating temperatures, which leads to an acceleration of the main process of silicon reduction and an increase in the volume of the zone of the main reactions (reaction crucible).

Finally, the particles / pieces of the reducing agent material must be of sufficient strength so that it does not grind to fine and dusty fractions during storage, transportation, loading into the furnace and moving the charge layer into the reaction zone, since the fine and dusty fractions that are formed can be easily carried away flue gases from the furnace and / or burn out near the open surface of the charge layer, which leads to an increase in the consumption of reducing agent per unit of the resulting product, as well as to reduce the gas permeability of the charge layer for flue gases, which disrupts the normal course of the process and contributes to the formation of increased pressure inside the reaction crucible, leading to the formation of fistulas, taking away δίΘ-gas, and heat and electric losses.

Thus, from the foregoing, it is understood that a number of requirements are imposed on the carbon reducing agent material used to produce crystalline silicon from quartzite and / or quartz, which may contradict each other. Therefore, to effectively carry out the process, which allows to obtain a high-purity final product with the most complete extraction of silicon from the feedstock, with increased specific productivity per unit volume of the furnace and the lowest possible energy costs, a very good balance of the properties of the reducing agent is required.

Thus, in order to increase the general reactivity of a reducing agent and, in particular, its ability to capture and chemically bind gaseous δίΘ released, it is necessary to increase the total fraction of the pore space, i.e. volume attributable to the porous structure, relative to the volume attributable to the solid phase. The thinner carbon walls forming partitions between pores in such a structure with a high fraction of pores also have a higher resistance, which increases the resistance of the entire piece of material, that is, it is also a positive factor.

In addition, the small wall thickness and their relief are extremely important due to the fact that they are heated to operating temperatures in the upper and middle part of the charge layer, mainly due to heat exchange with a gas stream passing through the charge layer containing hot δίΘ gas . The smaller the wall thickness and it is more prominent, the less heat is required to equalize the temperature of the wall and the δίΘ gas, and the higher will be the final local temperature of this wall and the volume of δίΘ gas in contact in this particular area as a result of heat exchange. Accordingly, on the whole, a larger volume of the top layer (charge) can be heated by the ascending flow of gaseous δίΘ to that temperature level (of the order of 1500 ° С or more) at which the reduction reaction δίΘ to silicon carbide δίΘ proceeds at a noticeable rate. This increases the available volume of the reaction space in which the binding reaction of gaseous δίΘ to solid δίΘ can occur, and as a result, the degree of extraction of silicon from the raw material increases at the same height of the charge layer.

At the same time, an excessively large fraction of pores and an excessive decrease in the fraction of the solid phase, i.e. thinning of the carbon walls leads to a decrease in the strength of pieces of material and to their easy destruction during transportation, loading into the furnace, etc., reducing the efficiency of the process, as described above. In addition, the density of such an excessively porous material will also be too low, so that it cannot be immersed at a sufficient speed in the charge layer from the top of the furnace up to the zone of the main reactions, and the ionized gas stream that arises in the reaction zone and electric arc zone creates an intense excess pressure, will prevent particles of material from entering the reaction zone due to the fact that light particles will be pushed out and carried away from it.

In turn, the presence in the total pore volume of a significant fraction of large pores is essential to ensure the availability of pore space inside the reducing agent material and to remove diffusion restrictions on the reaction rate on the inner surface of the pores. On the other hand, an excessive increase in the fraction of a large-pore system to the detriment of a fine-pore system will lead to a decrease in the total surface area of the system (determined mainly by thin pores), and, as a result, to a decrease in the reaction rate simply as a result of a reduction in the reaction surface.

Known, commonly used carbon reducing agents can have a high rate for any one parameter or group of parameters among the above, but none of them has an optimal set of the entire set of required properties, and the presence of improved indicators for one of the parameters is usually accompanied by unsatisfactory properties for other parameters.

For example, fossil fuels, at a fairly low cost, have a low content of solid carbon - within 50%, an unstable ash content, a sufficiently large amount of impurities, a high content of volatiles - up to 50%, etc., which ultimately is negative affects the electric and thermal operation of the furnace. Neftekoks carbon reducing agent has a high content of solid carbon (about 95%), however, its activity in the recovery process is close to zero, and the electrical resistance is very low, which leads to loss of power and attenuation of the electric arc and an increase in energy consumption per 1 ton of product. High chemical activity of carbon, with its content up to 70%, is characterized by such a reducing agent as charcoal. However, charcoal also has a number of disadvantages, including low structural strength, a sufficiently high content of volatile (average about 20%) and moisture (average 8-10%), as well as an ash content of 2%. Therefore, most often upon receipt of silicon, it is not individual carbon reducing agents that are loaded into the charge, but their particular mixtures selected so as to balance various parameters of the carbon reducing agent as much as possible. However, the preparation of mixtures in any case complicates the process, while the introduction of one or another component (for example, charcoal), improving some characteristics (reducing reactivity of the material), inevitably leads to a deterioration of its other characteristics (for example, structural strength and volatile content) .

A rather successful combination of properties was achieved in the technical solution disclosed in patent No. 23615 (owned by the authors of this application) and closest to the present invention, namely, for the material Rexyl carbonizate. The characteristics of this material given in the Prior art section make it possible to use it, in particular, as an effective base reducing agent for melting crystalline silicon, which is obtained with a purity of more than 99.3% of the target component (δί), while improving the technical and economic parameters of the melting process, in particular, increasing the productivity of the electric furnace per unit time. At the same time, silicon can be efficiently prepared using pure rexyl carbonate, without the addition of other types of carbon reducing agents.

At the same time, although rexyl carbonizate has a developed finely porous structure and its accompanying high specific pore surface (120-500 m ² / g, iodine number 12.5-50%), which contributes to a relatively higher heterogeneous reduction rate of silicon monoxide δίΟ in in the reaction space of the furnace, the degree of extraction of silicon from the initial quartzite raw material into the final target product does not exceed 92-93.5%.

This is due to the fact that the porous structure of this known material is predominantly finely porous, with a relatively small number of large transport pores, which limits the access of gaseous δίΟ to the developed internal reaction surface, and also slows down the evaporation and removal of residual volatile substances from the pores, thereby additionally inhibiting the entry of δίΟ into the pores. As a result, part of δίΟ does not have time to react with the reducing agent carbon when moving through the charge layer and is carried away to the gas purification system, which reduces the furnace productivity and increases the specific costs of electricity, reducing agent and silicon raw materials for smelting a unit of production.

In the present invention, the authors were able to eliminate this drawback and additionally provide the carbon reducing agent material with a developed system of large transport pores. As a result, the Rexyl material obtained according to the present invention is characterized by high gas permeability of 0.03-3.65 cm ³ / s (for a sample with a cross section of 1 cm ² , 1 cm long, with a pressure drop of 0.1 MPa).

Moreover, this improvement was carried out without any deterioration and / or with additional improvement of other significant characteristics of the material - specific surface area (105-600 m ² / g) and reactivity, electrical resistivity, as well as structural strength and content of non-combustible residue (ash) and volatile substances in the carbon material.

The preparation of Rexil material having properties in accordance with the present invention can be carried out by means of high-speed thermo-oxidative carbonization of coal with a grain size of 3-40 mm at a temperature of 1000-1500 ° C, providing a heating rate of coal in the region

- 7,024,335 temperatures of its destruction of more than 20 ° C / min, and preferably more than 400 ° C / min. At the same time, the conditions for heating particles (pieces) of coal with variable speed and acceleration are created in the reactor due to the use of a combined pulsating blast that creates alternating overpressure in the reactor. Preferably, the overpressure during pulsating blasting ranges from 0 to 10 atm (0 to 10x105 Pa).

Due to the different speeds and acceleration of heating of a single particle (piece) of coal in the reactor bed, which occurs in the temperature range of destruction, an uneven overpressure of intrinsic pyrolysis gases is generated that forms inside the body of the particle (piece), which directly depends on temperature (increases with its growth) , and to the greatest extent on the speed and acceleration of heating. These intrinsic pyrolysis gases at high temperatures form either a finely porous structure or, upon exiting it, a large-porous structure with open macro- and tunnel pores, i.e., a transport system of the present invention.

So, at a relatively low temperature, as well as the speed and acceleration of heating of the particle (piece), the rate of volume expansion is also relatively small, as a result of which a predominantly fine-pored rexyl structure with a high specific pore surface of 105-600 m ² / g is formed (iodine number 10.5 -60%), and the predominant formation of transitional interconnected pores, and micropores, contributing to the intensive development of nanoscale pores on their walls along the entire inner surface (see Figs. 9 and 10).

With an increase in the rate and acceleration of heating, due to a significant increase in the inter-pore pressure of the pyrolysis gases, a larger pore structure of rexyl is formed with the predominant formation of mesopores.

At the same time, the formation of macro- and tunnel pores included in the system of transport pores occurs at a very high rate of volume expansion of intrinsic pyrolysis gases generated in the inter-pore space, which is achieved only at very high speeds and heating accelerations of more than 400-500 ° / min

These intensely generated pyrolysis gases create a high burst pressure in the interstitial space, at which the pore (capsule) ruptures and exits outward at a tremendous speed through the body of the material, which is in a viscoplastic state, with the formation of macroholes and tunnels that retain their shape upon subsequent solidification (polymerization) due to an increase in temperature to 1000 ° C or more, which make up the main share in the system of transport pores penetrating the body of the Rexyl material (see Figs. 1-6).

High speed and acceleration of heating, contributing to the formation of a system of transport pores in a single particle (piece) of coal, is achieved due to the combined pulsed blasting.

In addition, the preliminary preparation of the initial coal raw material, for example, the beneficiation of lump coal and its fractionation according to the size class of 3–40 mm, makes it possible to reduce the ash content and obtain Rexil material with an ash content of not more than 5%.

The increased temperature of thermo-oxidative carbonization (more than 1000 ° C) promotes the production of a product with high structural strength (P _with more than 70%) and a low content of volatile substances (0.1-3.5%).

To further improve the characteristics of the obtained Rexil material, the above process of thermo-oxidative carbonization using a combined pulsating blast is carried out using water vapor. The introduction of water vapor into the charge, subjected to the specified process of carbonization of coal, can be carried out by wetting the coal used. In another embodiment, water vapor may be introduced by adding wet rexil to the charge. In yet another embodiment of the invention, water vapor is supplied to the charge in a pulsed mode by directly supplying humidified blast with a variable concentration of steam in air, i.e. using steam blast instead of air blast. The amount of steam used in the aforementioned embodiments of the invention can be up to 1 ton of water vapor per 1 ton of obtained rexyl. The use of water vapor in the process of thermal oxidative carbonization of coal, described above, allows to obtain rexil with a particularly favorable combination of properties, in particular, with the highest specific surface area of up to 600 m ² / g.

The resulting rexyl is best suited as a base reducing agent for silicon, characterized by a high content of active carbon (93-95%) and high chemical activity. Its use in a method for producing silicon by an electrothermal or plasma recovery process allows the following advantages to be provided.

1. Rexil has a high structural strength (P _from 70-85%), which ensures its resistance to mechanical stress and prevents grinding during storage, transportation, preparation of the charge and feeding it to the melting furnace. The absence of a fine fraction in the composition of rexyl (less than 3 mm) minimizes or completely eliminates its entrainment into the dust-gas removal system. This reduces the loss of active carbon and the need to load the excess (active carbon) of the reducing agent to compensate for this loss.

2) The low content of volatile compounds and moisture in rexil provides an actual absence

- 8 024335 ashing (burning out) rexylated at the top at relatively low temperatures (up to 750 ° C). The main heating of rexyl to its burning temperature (more than 1000 ° C) occurs in the anoxic middle zone of the top of the furnace as a result of heat exchange with heated gases, with the formation of silicon carbide, and in the lower high-temperature zone, i.e. directly in the reaction crucible, where a large amount of heat is released when exposed to electric current. It also reduces the loss of active carbon, which, in turn, prevents an increase in the amount of ash supplied with the reducing agent, and accordingly reduces the amount of impurities in the final product.

3) The high chemical activity of rexyl ensures its rapid heating and the occurrence of target reactions in the arc zone (at high temperatures above 1600 ° C), where silicon reduction reactions are actively taking place, and also in combination with the high availability of effective pore space for sorption and reduction of gaseous δίΘ at high and medium temperatures (10001600 ° С) it promotes accelerated carbide formation from δίΘ and, as a result, a significant increase in reactivity (reaction rate uu per unit time per gram carbon). It also reduces energy consumption and the time interval for heating rexil walls, and also allows for accelerated uniform heating of its entire internal part, since there is no need for volatile evaporation, and given its developed nanoporous structure and surface relief of the walls of the transport pores, it makes the whole reaction accessible specific surface, thereby increasing reactivity.

It should be borne in mind that rexyl can be used to obtain crystalline silicon in pure form, which is preferred from the point of view of simplifying the stages of delivery and preparation of the charge. However, if necessary, it can be used in combination with other carbon reducing agents, such as special coke, charcoal, Rexil carbonizate and other materials known to specialists. This use also allows you to improve the process parameters, although perhaps to a lesser extent than when using pure rexil.

In addition, rexyl can be used in other processes based on the occurrence of reduction reactions. Such processes are, in particular, the smelting of silicon-containing alloys, for example, the production of ferrosilicon FS-90, and other ferroalloys. Rexil can also be used for phosphorus production, production of silicon and calcium carbides, metallization and agglomeration of ore raw materials.

The invention is further demonstrated by the following examples.

Example 1. Obtaining a carbon reductant reducing agent.

Prepared coal charge fraction 3-30 mm was loaded into the reactor, after which it was launched. Air was supplied to the reactor in the mode of a combined pulsating blast with an overpressure of up to 10 atm and a pulsation frequency of 120 s. The process was carried out at an average temperature of 1100 ° C, with a local peak increase to 1350 ° C for 20 hours, with an average coal heating rate of more than 400 ° C / min. After that, the finished rexyl was discharged from the reactor into a metal cooler, where it was cooled to ambient temperature.

Hydroxyl rexyl was discharged from the cooler and packaged.

When determining the characteristics of the obtained product according to standard methods, the following results were obtained, which are shown below in table. 1 (in the column Rexil).

Example 2. Tests for the smelting of crystalline silicon with various reducing agents.

Crystalline silicon was smelted using various types of carbon reducing agents, including state-of-the-art reducing agents that used standard special coke (low-medium temperature carbonizate) from non-sintering coal, as well as a prototype Rexil carbonizate disclosed in patent No. 23615 and the material rexil of the present invention, obtained as described above in example 1. The properties of the used carbon reducing agents are shown in table. one.

- 9,024,335

Table 1

Solid carbon reducing agents for crystalline silicon smelting

Indicators Special Cox Carbonate Rexil Rexil Technical analysis, %: 5.15 3,50 3.20 14.40 1.20 one hundred _N r 3.8 3 b 3, 6 at 0, 58 0.35 0.33 Solid carbon content on a dry mass,% 79.87 94.05 95.47 Structural strength,% 62, 8 83.0 83.5 Reactivity with 1273 K ^- , ppm / s 9, 1 9, 6 11.6 Specific electrical resistance, Ohm * cm ^-1 0, 6410 ⁶ 0, 92 · 10 ^e 0.94-10 ‘ Surface Area m ³ / g 68 440 560

And ^a is the ash content;

V is the content of volatile substances;

No. ^p - moisture content;

8 / - sulfur content.

Smelting was carried out on a 200 kV-A ore-thermal furnace using quartzite and / or quartz from the Aktas deposit with a grain size of 10–25 mm of the following composition,%: δίθ ₂ - 99.8; A1 ₂ O ₃ - 0.17; CaO - 0.02. Three melting options were tested - standard (option I) using special coke in the charge, comparative (option II) using rexyl carbonate in the charge, and experimental, according to the present invention — using new rexyl material in the charge (option III).

Smelting conditions were the same throughout the study period. The test results are presented in table. 2.

table 2

Crystalline silicon electrofusion performance using various carbon reducing agents

Indicators Option I Option II Option III The composition of the mixture, in kg: quartzite and / or quartz one hundred one hundred 10.0 Special Cox 6.50 - - Rexil Carbonizate (prototype) - 6.24 - Rexyl (offered) - - 6.24 Low ash coal shubarkol 1.00 - one Silicon content in metal (final 99,20 99.52 99, 61 product)% Specific consumption electricity 14, 07 13,20 12.70 kWh / kg Performance in units time, kg / hour 2, 31 2.76 3.14 Degree of extraction 81, 62 93.48 94.52 silicon,%

From the above data it follows that the replacement of special coke with Rexil carbonizate increases the purity of the melted metal: the content of the base element in the melted crystalline silicon increased from 99.25 to 99.52%. In addition, there is an increase in smelting silicon furnace productivity - from 2.31 to 2.76 kg / h and a decrease in specific electric energy consumption from 14.07 to 13.2 kWh / kg.

Moreover, when using special coke, the degree of extraction of silicon is 81.62%. The use of Rexil carbonizate can increase it to 93.48%, however, more than 6.5% of silicon is still carried away from the furnace and is lost. With an average industrial productivity of 100 tons per day, the loss will be about 6.5 tons of silicon per day, which leads to both significant losses of the target product and significant damage to the environment.

At the same time, when using the new Rexil material, the content of the base element in smelted crystalline silicon is 99.61%, and the degree of silicon extraction is 94.52%. At the same time, the furnace productivity indicator improves to 3.14 kg / h and the specific energy consumption is reduced to 12.70 kWh / kg. At the same time, silicon losses at an average industrial productivity of 100 tons per day are about 5.5 tons per day.

Thus, the use of the Rexil material of the present invention allows, while maintaining the purity of the resulting product, to reduce its loss by more than 15%, which at an average industrial productivity of 100 tons per day is about 1.0 tons per day or 365 tons per year, the cost of which current prices is more than $ 1 million, to further increase furnace productivity per unit of time by more than 14.5% and reduce specific electricity consumption by 3.5% or more.

This shows that the proposed carbon rexyl reducing agent has a well-balanced combination of characteristics, which is especially advantageous for use as a carbon reducing agent for the smelting of crystalline silicon.

Claims (13)

CLAIM 1. Carbon reducing agent for the smelting of crystalline silicon, having a developed pore structure, consisting of carbon, ash, volatile substances, characterized in that it together: a) has a complex pore structure, consisting of a finely porous system, including nanopores less than 2 nm in size and transitional and communicating mesopores from 2 to 50 nm in size, and a developed system of transport pores, including macropores from 50 to 1000 nm in size and tunnel pores from 1 up to 1000 microns, moreover, the solid phase accounts for a share of 10-30 vol.%, the fine-porous system - 5-65 vol.% and the transport pore system accounts for 5-85 vol.% calculated on the total volume of the reducing material ; b) is characterized by the following properties and composition: specific surface area (8) - 105-600 m ² / g; reactivity - 7-13 ml / g-s; electrical resistivity - 0.1x10 ³ -0.98x10 ⁶ Ohm-cm; structural strength (C.) - 70-85%; bulk density - 0.18-0.45 t / m ³ ; gas permeability (determined taking into account GOST 11573-98 and ISO 8841-91E) - 0.03-3.65 cm ³ / s for a sample with a cross section of 1 cm ² , 1 cm long, with a pressure drop of 0.1 MPa; carbon (C) - 91.5-98.9 wt.%; ash (A ' ¹ ) - 1.0-5.0 wt.%; volatile substances (U **) - 0.1-3.5 wt.%. 2. The carbon reducing agent according to claim 1, characterized in that it is a loose bulk material with a size of pieces in the range of 3-35 mm 3. The carbon reducing agent according to claim 1, characterized in that it is obtained on the basis of coal raw materials, which is steam coal. 4. The use of the carbon reducing agent according to claim 1 as a reducing material during metallurgical and chemical reduction processes selected from the smelting of crystalline silicon and silicon-containing alloys by electrothermal or plasma melting, smelting of crystalline silicon and silicon-containing alloys, in particular FS-90 ferrosilicon, by electrothermics or by plasma melting, phosphorus production, calcium carbide production, metallization and agglomeration of ore raw materials. 5. A method of producing a carbon reducing agent in which high-speed thermo-oxidative carbonization of coal with a grain size of 3-40 mm is carried out at a temperature of 1000-1500 ° C, wherein said thermo-oxidative carbonization is carried out at a heating rate of coal in the region of its destruction temperatures of more than 20 ° C / min and s using a combined pulsating blast that creates a variable overpressure in the reactor, which provides heating of particles or pieces of coal with a variable speed and acceleration. 6. The method according to claim 5, in which the heating rate of coal in the temperature range of its destruction is more than 400 ° C / min. 7. The method according to claim 5 or 6, in which the change in excess pressure during a pulsating blast occurs in the range from 0 to 10 atm (from 0 to 10 x 10 ⁵ Pa). 8. The method according to any one of claims 5 to 7, in which the ripple period is from 0.01 to 150 s. 9. The method according to any one of claims 5 to 8, in which the thermally oxidizing carbonization of coal is carried out with the additional introduction of steam into the batch, at high temperatures. 10. The method according to claim 9, in which water vapor is introduced into the mixture by wetting the coal. 11. The method according to claim 9, in which water vapor is introduced into the mixture by adding the specified carbon reducing agent soaked in water. 12. The method according to claim 9, in which water vapor is introduced into the mixture by direct supply of humidified blast with a constant concentration of steam in the air. 13. The method according to any one of claims 9 to 12, in which the amount of water vapor used is up to 1 ton of steam per 1 ton of the resulting carbon reducing agent.