RU2172304C2 - Method of preparing high-melting materials - Google Patents

Abstract

FIELD: metallurgy and chemical engineering. SUBSTANCE: method comprises using electrical arc forming current-conducting area in melt thickness on melting furnace bottom between unlike electrodes. Current-conducting area in melt thickness is adjusted at temperature of 1810-2200 C and surface area of its mirror is increased from fixed electrode-anode to point of pouring melt from furnace by reciprocating motion of electrode-cathode relative to electrode-anode in horizontal plane along furnace bottom. Method makes it possible to improve quality of material due to more intensive stirring of melt and efficiency becomes greater. EFFECT: more efficient preparation method. 2 cl, 3 dwg, 3 tbl

Description

 The invention relates to the production of refractory metallic and nonmetallic materials, mainly cement clinker, having a high degree of melt viscosity.

 A known method of producing Portland cement clinker by melting it in electric arc furnaces based on ferrochrome slag. The melt is purged with oxygen or air directly in the bath of an electric arc furnace (A.L. Mosset et al. Processing of dispersed materials in melting reactors, Minsk, 1980).

 The disadvantages of this method are the low productivity due to the frequent solidification of the viscous melt in the outlet notch, low quality due to insufficient mixing of the melt, high energy consumption.

There is also known a method of producing cement clinker, comprising melting the raw mixture using an electric arc, in which the raw mixture is mixed with a fraction of 0.05-20 mm with a moisture content of up to 2% at a temperature of 1600-1800 ^o C for 0.1-30 min a neutral gas environment or in a gas environment with up to 8% oxygen (RF patent N 2040497, C 04 B 7/44 from 07/27/95, bull. N 21).

 The disadvantages of this method are as follows.

 When the method is implemented, between the electrode-anode installed in the lining of the hearth of the electric arc furnace and the electrode-cathode installed in the arch of the furnace, an electric arc is ignited, which melts the raw material fed into the bath, forming a conductive section in the thickness of the melt. The surface mirror of a fluid melt is limited to a value equal to two electrode diameters, i.e. heating of the material is localized and located in the thickness of the melt layer around a common vertical axis between unlike electrodes.

 Productivity with this processing method, which depends in particular on the size of the melt pool, is limited, since in the peripheral zone of the bath, the viscous melt solidifies and does not pour out of the furnace. Forcing the arc power when it increases (stretching) vertically by moving (raising) the cathode leads to overheating of the walls and the arch of the furnace chamber, which in turn leads to fusion of the latter, an increase in heat loss to the environment, overheating and accelerated burnout of the graphite electrode-cathode .

In addition, melt mixing is also localized, which leads to a deterioration in the quality of the finished melt product, such as cement clinker. A temperature limited to 1800 ^° C is insufficient to give a fluid state to many types of refractory materials with high melt viscosity, in particular Portland cement clinker with high saturation coefficients, which are decisive in obtaining a high-quality product.

 The basis of the present invention is the task of improving the quality of the material by intensifying the mixing of the melt and increasing productivity by reducing stops on the elimination of frozen sections of the melt in the area of its discharge from the furnace.

According to the invention, the problem is solved in that the production of refractory materials with high melt viscosity is carried out using an electric arc forming a conductive section in the thickness of the melt on the hearth of the melting furnace between unlike electrodes. In this case, the conductive section in the thickness of the melt is brought to a temperature of 1810-2200 ^o C and its mirror is increased from a fixed electrode-anode to the place of discharge of the melt from the furnace by reciprocating movement of the electrode-cathode relative to the electrode-anode in a horizontal plane along the bottom of the furnace. Cement clinker is used as a refractory material with high melt viscosity.

 The essence of the proposed method for producing refractory materials is illustrated by the following examples.

 Examples of the method.

 From pre-crushed raw materials, by sieving and mixing them, raw mixes were prepared to produce cement clinkers. The compositions of the raw mixes and their dispersion are given in table. 1. The moisture content of the mixtures did not exceed 2-2.5%.

 To compare the proposed method with the prototype, the identical material and dispersed composition of the raw mixes was selected.

 The prepared mixtures were supplied by the dispenser to the electroplasma furnace both through the inner space of the cathode electrode and into the arc region along the outer surface of the cathode electrode through the furnace arch.

 In FIG. 1, 2, 3 schematically shows the operation of the furnace according to the proposed method, where three fragments of the electrodes relative to each other are shown on its fragments.

 1 indicates the furnace body equipped with a water-cooled jacket 2. The body inside the furnace is covered with a skull lining 3.

 An electrode anode 5 and a notch 6 are mounted under the furnace 4 to exit the melt from the furnace for further processing.

 The arch (conditionally not shown in the drawings) is included with the possibility of moving vertically and along the hearth 4 from the anode 5 to the recess 6 of the electrode-cathode 7. The melt has a different temperature depending on the distance from the electric arc 8 and, as a result, a different state from the fluid, located between the electrodes 9, to a more viscous, but conductive melt 10 outside the zone of fluid melt.

 The melting process is carried out by known methods (see Fig. 1 of the circuit) by installing the cathode 7 above the anode 5. In this case, the electrodes 5 and 7 are reduced to contact and, when an electric arc is formed, they are bent vertically to a certain height, providing a stable arc, the required current and voltage. The raw material supplied to the arc zone melts, gradually covering the surface of the hearth from the anode to the exit notch with a melt film.

In the area of the arc, the melt temperature can reach 1800-2200 ^o C. The melt boils and is in a liquid state (item 9). Depending on the composition of the raw material, the melt becomes conductive at temperatures exceeding 1400-1600 ^o C.

 Upon reaching such a temperature level throughout the bath from the anode to the notch, the electrode 7 is moved towards the notch horizontally, parallel to the hearth or the melt mirror. Moreover, as shown in FIG. 2 and 3 of the diagram, the zone of the fluid state (9) increases (as it stretches) as the cathode moves away from the anode, since the electric current flows through the arc and the melt enclosed between the electrodes at the moment of movement. When this occurs, the process of boiling and intensive mixing and flowing it from the zone of the anode 4 to the zone of the exit notch 6.

 When the melt layer is set above the upper edge of the notch 6 and when the cathode approaches close to the last, the liquid melt is poured out of the furnace for further processing, for example, cooling or granulation before cooling.

 When the cathode moves backward, the electric arc melts the crust frozen on the surface of the melt, turning the whole mass again into a fluid state (the area of the melt mirror increases).

 The cathode’s speed can control the output of the melt from the furnace, providing either periodic or constant output.

For reliable exit of Portland cement clinker from the furnace, it is necessary to have a local temperature in the current passage zone of at least 2000-2100 ^o C. In the total mass of the melt, a temperature of 1800 to 2000 ^o C is maintained depending on the composition of the raw material mixture.

For some refractory materials with a high melt viscosity, the temperature of the liquid state can reach 2200 ^o C.

 With the proposed method of melting, the output slots are not cooled and therefore they are made of heat-resistant materials that are corrosion-resistant with respect to the melt and oxygen, for example, silicon carbide that can withstand operating temperatures to the melting point. The adhesion of clinker melt to this material is practically negligible.

 The modes of firing raw mixes are presented in table 2.

 The resulting clinkers were characterized by the complete completion of clinker formation processes.

The combined content of alite and belite exceeded 80% and not less than 65% alite. Clinkers together with 5% gypsum were ground in a mill to a fineness of grinding, characterized by a residue on sieve N 008 within 10% and a specific surface within 300 m ² / kg.

 The prepared cements were tested according to GOST 310.1-310.4.

 Strength indicators of cements are presented in table. 3.

 Thus, the proposed method can significantly intensify the process of clinker formation, increase the yield of conditioned material, improve the quality of the clinker.

Claims (2)

1. A method of producing refractory materials with high melt viscosity, including the use of an electric arc forming a conductive section in the melt bulk on the hearth of the melting furnace between dissimilar electrodes, characterized in that the conductive section in the thickness of the melt is brought to a temperature of 1810 - 2200 ^o C and increase it a mirror from the fixed anode electrode to the place where the melt is drained from the furnace by reciprocating the cathode electrode relative to the anode electrode in a horizontal plane along the bottom of the furnace.  2. The method according to claim 1, characterized in that cement clinker is used as refractory materials with high melt viscosity.

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