Bottom electrode of direct-current electric arc furnace made of electric smelting refractory material

Abstract

The utility model belongs to the field of refractory material melting furnaces, and provides a bottom electrode of a direct current electric arc furnace for electrically melting refractory materials, the bottom electrode is a bottom anode and is used for melting refractory raw materials, and the bottom electrode comprises a lower material layer, a middle material layer and an upper material layer, a plurality of metal conductive elements distributed at intervals are arranged in the lower material layer and the middle material layer, the bottoms of the metal conductive elements are arranged on the bottom plate, the lower material layer comprises a heat-insulating refractory material filled among the metal conductive elements, and the middle material layer comprises a high-temperature-resistant material filled among the metal conductive elements. The upper material layer includes an ultra-high temperature resistant, electrically conductive material and electrically conductive bricks that are not eroded by a melt of refractory feedstock. The device is applied to the production of the submerged arc furnace, the power consumption of the product is reduced by 15-25%, the electrode consumption is reduced by about 50%, the environmental pollution caused by noise and the like is reduced by 30%, the production is more stable, the production efficiency is obviously improved, and contributions are made to energy conservation, emission reduction, cost reduction, efficiency improvement and dual-carbon economy.

Description

Technical Field

[0001] The utility model belongs to the field of refractory melting furnaces, in particular to a bottom electrode of a DC arc furnace for electrically melting refractory materials. Background Art

[0002] Fused corundum, fused magnesia, fused AZS, and fused mullite all use electric arc furnaces to convert electrical energy into heat, melting these high-temperature oxides. Melting temperatures reach over 2000°C, and some even exceed 3000°C. This places extremely high demands on the bottom electrode. It must not only withstand these ultra-high temperatures but also be stable at these temperatures, avoiding low-temperature reactions and redox reactions with the product. The bottom electrode of a single-electrode DC arc furnace must also possess excellent electrical conductivity. The equipment used to produce fused refractory raw materials is generally an AC arc furnace. Since the development of DC arc furnaces, they have seen significant progress in steelmaking and submerged arc furnaces. However, for fused refractory raw materials, there has been limited experimental development, but no real progress. This is likely due to the extremely high production temperatures of the melt, which increases the operational complexity of the equipment. Generally, steelmaking temperatures do not exceed 1700°C, and submerged arc furnaces also operate below 1700°C. However, fused magnesia temperatures reach 3000°C, and fused corundum temperatures reach 2200°C. At such ultra-high temperatures, many substances will vaporize, decompose, and melt, unable to withstand such high temperatures, let alone the requirement for good electrical conductivity. Therefore, the requirements for the bottom electrode of the DC arc furnace used to produce fused refractory raw materials are extremely high.

[0003] Existing patent CN212431784U discloses the electrode structure of a DC fused magnesium furnace, which uses a top-type positive and negative electrode method to produce fused magnesium. To date, DC arc furnaces have primarily focused on multiple top electrodes. Domestically, most cathodes and anodes are located in the upper portion of the arc furnace. There are no DC arc furnaces with bottom anodes used to produce refractory raw materials. The main reason for this is that the production temperature of fused refractory raw materials is too high, resulting in rapid reaction and erosion at the top of the bottom electrode at ultra-high temperatures. There are no advanced materials or structures to address this problem. However, if a bottom-electrode DC arc furnace could be used to produce refractory raw materials, the following advantages would be achieved: 1) Graphite electrode consumption would be significantly reduced; 2) the power factor would be further increased; and 3) the equipment would be simple and easy to maintain. Utility Model Content

[0004] The utility model aims at the technical problems existing in the bottom electrode of a DC electric arc furnace for producing refractory raw materials at ultra-high temperature, and proposes a bottom electrode of a DC electric arc furnace for melting refractory materials with reasonable design and simple structure.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is that the present invention provides a bottom electrode of a DC arc furnace for electric melting refractory materials, the bottom electrode being a bottom anode and being used to melt refractory raw materials, the bottom electrode comprising a lower material layer, a middle material layer and an upper material layer distributed from bottom to top, a plurality of spaced metal conductive elements being arranged inside the lower material layer and the middle material layer, the bottom of the metal conductive element being arranged on a bottom plate, the bottom plate being used to connect the power anode, the lower material layer comprising a thermal insulation refractory material filled between the metal conductive elements, the middle material layer comprising a high-temperature resistant material filled between the metal conductive elements, the high-temperature resistant material being a dry ramming material having the same composition as the refractory raw materials, the upper material layer comprising a material and a conductive brick that is resistant to ultra-high temperatures, conductive and not corroded by the melt of the refractory raw materials.

[0006] Preferably, the material that is resistant to ultra-high temperatures, electrically conductive and not corroded by the melt of the refractory raw material comprises carbon, carbide, nitride or boride.

[0007] Preferably, the refractory raw material is alumina, the material that is resistant to ultra-high temperatures, conductive and not corroded by the melt of the refractory raw material is titanium carbide, titanium nitride, silicon carbide, zirconium boride or titanium boride, and the high-temperature resistant material of the middle material layer is alumina dry ramming material.

[0008] Preferably, the refractory raw material is magnesium oxide, the ultrahigh temperature resistant, conductive material not corroded by the melt of the refractory raw material is titanium nitride or zirconium nitride, and the high temperature resistant material of the middle material layer is magnesium dry ramming material.

[0009] Preferably, the thermal insulation refractory material of the lower material layer includes closed pores and nano-micro pore materials.

[0010] Preferably, the closed pores and nano-micro pore materials are fumed silica, nano-alumina or nano-magnesia.

[0011] Preferably, the metal conductive element is a steel sheet or a steel needle with a width of ≤5 mm, and the cross-sectional area of ​​the steel sheet or the steel needle is ≥1.25×current intensity, wherein the cross-sectional area is measured in square millimeters and the current intensity is measured in amperes.

[0012] Preferably, the thickness of the lower material layer is ≤ 20% of the thickness of the entire DC arc furnace bottom, the thickness of the middle material layer is ≥ 25% of the thickness of the bottom electrode, and the remainder is the thickness of the upper material layer.

[0013] Preferably, the upper material layer includes a top section and a bottom section, the conductive brick is arranged in the top section, and the bottom section is embedded with the metal conductive element and the embedded area is ≥3.5×current intensity, where the cross-sectional area is measured in square millimeters and the current intensity is measured in amperes.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are:

[0015] 1. This utility model provides a bottom electrode for a DC arc furnace that produces fused refractory materials. Applied to the production of submerged arc furnaces, this product reduces power consumption by 15-25%, electrode consumption by approximately 50%, significantly reduces flickering effects on the power grid, and environmental pollution, such as noise, by 30%. This product also provides more stable production and significantly improves production efficiency through shortened melting times. This contributes to energy conservation and emission reduction, cost reduction and efficiency improvement, and the dual-carbon economy. Its rational design and simple structure make it suitable for large-scale deployment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, a brief introduction will be given below to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 A schematic structural diagram of a bottom electrode of a DC arc furnace for fused refractory materials provided in Examples 1 to 3;

[0018] In the above figures, 1. electric furnace shell; 2. corundum ramming material; 3. corundum brick; 4. bottom electrode; 5. lower material layer; 6. middle material layer; 7. upper material layer; 71. top section; 72. bottom section; 8. metal conductive element; 9. bottom plate; 10. conductive brick. DETAILED DESCRIPTION

[0019] To more clearly understand the above-mentioned objects, features, and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that the embodiments of the present application and the features therein may be combined with each other unless they conflict. For ease of description, the words "upper," "lower," "left," and "right" appearing below merely indicate the same directions as in the drawings themselves and do not limit the structure.

[0020] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed in the following specification.

[0021] like Figure 1As shown, the utility model provides a bottom electrode of a DC arc furnace for melting refractory materials, wherein the bottom electrode 4 is a bottom anode and is used to melt refractory raw materials, and the bottom electrode 4 includes a lower material layer 5, a middle material layer 6 and an upper material layer 7 distributed from bottom to top, and a plurality of spaced metal conductive elements 8 are arranged inside the lower material layer 5 and the middle material layer 6, and the bottom of the metal conductive element 8 is arranged on a bottom plate 9, and the bottom plate 9 is used to connect the power anode, the lower material layer 5 includes a heat-insulating refractory material filled between the metal conductive elements 8, the middle material layer 6 includes a high-temperature resistant material filled between the metal conductive elements 8, and the high-temperature resistant material is a dry ramming material with the same composition as the refractory raw material, and the upper material layer 7 includes a material that is resistant to ultra-high temperatures, conductive and not corroded by the melt of the refractory raw materials and a conductive brick 10.

[0022] More specifically, the present invention provides a bottom electrode 4 for a DC arc furnace of fused refractory material, which is used in the production of ore-bearing furnaces. The DC arc furnace includes a furnace shell 1, the inner wall of which is provided with corundum ramming material 2, and corundum bricks 3 are laid in the direction of the corundum ramming material 2 toward the bottom electrode 4. The bottom electrode 4 is composed of three sections from bottom to top: steel sheets or steel needles with a width of ≤5mm are erected on the bottom plate 9 close to the bottom of the DC arc furnace. The steel sheets or steel needles are distributed outward from the center and are set with equal current density. The cross-sectional area (mm2) of the entire steel sheet and steel needle is ≥1.25× the current intensity (A), and the gaps between the steel sheets or steel needles are formed by vibration ramming with high-temperature materials. From bottom to top, the first section is the lower material layer 5, whose thickness is ≤ 20% of the total furnace bottom thickness; the second section is the middle material layer 6, whose thickness is ≥ 25% of the thickness of the bottom electrode 4; and the third section is the upper material layer 7, which is constructed with conductive vibrating ramming materials such as ultra-high melting point carbides, nitrides, borides, carbides, and carbon graphite materials, as well as conductive bricks 10. This third section, or upper material layer 7, is further divided into two parts: a top section 71 and a bottom section 72. The bottom section 72 is composed of steel sheets or steel needles with conductive refractory fillings within the gaps; in other words, the bottom section 72 is embedded with the metal conductive elements 8; the top section 71 is made of conductive refractory without steel sheets or steel needles, and the conductive bricks 10 are set within the top section 71. The upper material layer 7 requires that the area (mm2) between the bottom section 72 and the steel sheet or steel needle is ≥3.5×current intensity (A). The material is preferably a conductive vibration ramming refractory such as dry carbon, titanium carbide, titanium nitride, etc.

[0023] Such a bottom electrode 4 has a low furnace bottom shell temperature, is energy-saving, safe and has a long service life. In particular, the furnace bottom electrode 4 can be hot-repaired or cold-repaired at any time during use, and has a service life of up to several years, which plays an important role in energy saving and cost reduction.

[0024] Example 1

[0025] A DC arc furnace for melting white corundum has an inner diameter of 3000mm, a transformer capacity of 2.4MVA, a maximum current intensity of 6KA, and a bottom anode made of stainless steel sheets and graphite ramming material as conductive materials. The graphite ramming material is the bottom section 72 of the upper material layer 7. The steel sheet thickness is 1mm and the cross-sectional area of ​​the metal sheet is 0.012m 2 =12000mm 2 The safe current density of the steel sheet is 500KA / m 2 The area of ​​the 4th zone of the small furnace bottom electrode is 0.012 / 1.6% = 0.75m 2 , that is, the diameter of the small furnace bottom is Φ1500mm. In order to prevent current concentration, the current density at the small furnace bottom is designed to be uniform, that is, it is designed to be 8KA / m 2 . This requires 4 turns, with diameters of 508, 823, 1103, and 1401 mm respectively. Weld the above-mentioned steel sheets to the bottom plate 9, and then connect them to the power anode. First, lay down the thermal insulation refractory material layer 5 in the gap between the metal sheets. The thermal insulation refractory material is made of Al2O3 nanomaterials and rammed 120 mm. Then, the middle material layer 6 is densely packed. The middle material layer 6 is a corundum ramming material of 600 mm. Then, the dry graphite ramming material is rammed until it is flush with the 1200 mm steel sheet. Then, lay 400 mm of conductive bricks upwards, and then ram 50 mm of TiN material for standby use. After the bottom anode is built, the thermal resistance of the bottom anode is 2+61+27+408+372=870 from top to bottom. Therefore, the bottom surface temperature is 184°C, and q=2317 w / m 2 The upward interface temperatures are 717°C, 1046°C, 1991°C, and 2200°C (temperature of alloy liquid in the furnace). Therefore, it can operate normally without air cooling or water cooling.

[0026] Example 2

[0027] A DC submerged arc furnace for smelting corundum has an inner diameter of 8000mm, a transformer capacity of 5MVA, a maximum current intensity of 12KA, and a bottom anode made of stainless steel sheets and graphite ramming material as conductive materials. The graphite ramming material is the bottom section 72 of the upper material layer 7. The steel sheet is 1.5mm thick and has a safe current density of 650KA / m 2 The cross-sectional area of ​​the metal sheet accounts for 0.0185m of the electrode area. 2 =18500mm 2 The area of ​​the 4th zone of the small furnace bottom electrode is 0.0185 / 1.6%=1.154m 2 , that is, the diameter of the small furnace bottom is 1500mm. In order to prevent current concentration, the current density at the small furnace bottom is designed to be uniform, that is, it is designed to be 10.4KA / m 2. This requires 5 circles, and the diameters of the steel sheet circles are 390, 631, 855, 1072, and 1495 mm respectively. Weld the above steel sheets to the bottom plate 9, and then connect them to the anode of the power supply. The small furnace bottom is fixed to the furnace bottom. First, lay down the thermal insulation refractory material layer 5 in the gap between the metal sheets. The thermal insulation refractory material uses 150 mm of alumina nanomaterials, then 600 mm of corundum ramming material, and then ram dry graphite ramming material until it is aligned with the 1500 mm steel sheet. Then lay 10 (8) 700 mm of conductive bricks upwards, and then ram 100 mm thick SiC ramming material for standby use. After the bottom anode is built, the thermal resistance from top to bottom is 6+108+112+266+465=957. Therefore, the bottom surface temperature is 175°C, and q=2116 w / m 2 The upward interface temperatures are 1159°C, 1722°C, 1959°C, and 2200°C (temperature of alloy liquid in the furnace). Therefore, it can operate normally without air cooling or water spraying.

[0028] Example 3

[0029] A DC submerged arc furnace for producing fused magnesium has an inner diameter of 1800mm and a height of 2500mm. The transformer capacity is 1.8MVA and the maximum current intensity is 5KA. The bottom anode uses stainless steel sheets and titanium nitride ramming material as the conductive material. The titanium nitride ramming material is the bottom layer 72 of the upper material layer 7. The steel sheet thickness is 1mm, and the cross-sectional area of ​​the metal sheet accounts for 0.0083m2 of the electrode area. 2 =8333mm 2 The safe current density of the steel sheet is 600KA / m 2 The area of ​​the 4th zone of the small furnace bottom electrode is 0.0083 / 1.6% = 0.5208m 2 , that is, the diameter of the small furnace bottom is 1000mm. In order to prevent current concentration, the current density at the small furnace bottom is designed to be uniform, that is, it is designed to be 9.6KA / m 2 . This requires 5 turns, with diameters of 250, 405, 548, 687.5, and 824 mm respectively. Weld the above to the base plate 9 (5), and then connect it to the anode of the power supply. The small furnace bottom is fixed to the furnace bottom. First, 150 mm of MgO nanomaterial (11) is beaten in the gap between the metal sheets, and then 2000 mm of dense magnesium dry ramming material is beaten to expose 20 mm of the metal steel sheet, and then a layer of TiN ramming material (12) of 50 mm (burying the steel sheet 30 mm) is beaten for standby use. The thermal resistance from top to bottom is 3+887+465=1355. Therefore, the bottom surface temperature is 164 ° C, q=2086 w / m 2 The upward interface temperatures are 1144°C and 3000°C (MgO liquid temperature in the furnace) respectively. Therefore, air cooling is unnecessary and water spraying is sufficient for normal operation.

[0030] Based on the results of Examples 1-3 and actual production experiments, the bottom electrode 4 of a DC arc furnace for fused refractory materials provided by the present invention, when applied to the production of submerged arc furnaces, reduces power consumption by 15-25%, electrode consumption by approximately 50%, significantly reduces flickering effects on the power grid, and environmental pollution such as noise by 30%. Furthermore, production is more stable, and smelting time is shortened, resulting in significantly improved production efficiency. This contributes to energy conservation and emission reduction, cost reduction and efficiency improvement, and the dual-carbon economy.

[0031] Furthermore, in the production of fused alumina, the refractory raw material is alumina, including white corundum, dense corundum, brown corundum, β-corundum, etc. The ultra-high temperature resistant, conductive material that is not corroded by the melt of the refractory raw material is titanium carbide, titanium nitride, silicon carbide, zirconium boride or titanium boride. These materials do not react with Al2O3 at ultra-high temperatures (melting temperature of about 2200°C), or react to form a high-temperature solid phase that will not corrode or contaminate the corundum. At the same time, the high-temperature resistant material of the middle material layer 6 is an alumina dry ramming mass. The basis for this design is:

[0032] For melting alumina, TiC, TiN and SiC are selected. They do not react with Al2O3 at ultra-high temperatures (melting temperature is about 2200℃), or react to form a high-temperature solid phase without corroding or contaminating the corundum.

[0033] 3TiC+2Al2O3=3TiO2+Al4C3 ΔG 0 =848320-66.35T

[0034] 4TiN+2Al2O3=2Ti2O3+4AlN ΔG 0 =442832-65.56T

[0035] 8SiC+7Al2O3=A3S2+6SiO+2CO+2Al4C3ΔG 0 =4069480-1132.37T

[0036] At the temperature of producing corundum, TiC, TiN and SiC are all suitable materials for the bottom electrode 4.

[0037] The situation is different for fused magnesium: the refractory material is magnesium oxide, and the material that is resistant to ultra-high temperatures, conductive, and not corroded by the molten refractory material is titanium nitride or zirconium nitride, which can meet the ultra-high temperature requirement of 3000°C. The high-temperature resistant material of the middle material layer 6 is alumina dry ramming material. The basis for this selection is:

[0038] The melting temperature of fused magnesium reaches 3000℃, which requires a conductive material that remains solid at 3000℃ and does not undergo gasification or liquefaction reaction with MgO. After analysis, TiN is suitable, but TiC and SiC are not.

[0039] TiN+MgO=TiO+Mg↑+0.5N2↑ΔG 0 =548220-104.01TReaction temperature is above 4626℃.

[0040] Similarly, when melting aluminum magnesium spinel material, the reaction TiN+MA=TiO+Mg↑+0.5N2↑+Al2O3

[0041] ΔG 0 =571824-198.1T, and the reaction temperature is above 2503°C. However, the actual production temperature of MA is only around 2300°C. That is, TiN can be used as the bottom electrode 4 material for smelting spinel raw materials.

[0042] In order to reduce the cost, the bottom electrode 4 can be made of composite materials. According to the reaction: TiN+C=TiC+0.5N2, ΔG 0 =151500-80.71T, and it can react when it exceeds 1604°C. However, TiC and C cannot react with MgO, etc. Instead, using TiN-coated graphite electrodes to form an isolation layer can achieve normal operation and reduce costs.

[0043] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any other form. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes for application in other fields. However, any simple modification, equivalent change and modification of the above embodiment made according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A bottom electrode of a DC arc furnace for melting refractory materials, the bottom electrode being a bottom anode and used for melting refractory raw materials, the bottom electrode comprising a lower material layer, a middle material layer, and an upper material layer arranged from bottom to top, a plurality of spaced metal conductive elements being arranged inside the lower material layer and the middle material layer, characterized in that: The bottom of the metal conductive element is set on the bottom plate, and the bottom plate is used to connect the power supply anode. The lower material layer includes a thermal insulation refractory material filled between the metal conductive elements. The middle material layer includes a high-temperature resistant material filled between the metal conductive elements. The high-temperature resistant material is a dry ramming material with the same composition as the refractory raw material. The upper material layer includes a material that is resistant to ultra-high temperatures, conductive and not corroded by the melt of the refractory raw material and a conductive brick.

2. The bottom electrode of a DC arc furnace for melting refractory materials according to claim 1, characterized in that: The material that is resistant to ultra-high temperatures, electrically conductive and not corroded by the melt of the refractory raw material includes carbon, carbide, nitride or boride.

3. The bottom electrode of a DC arc furnace for melting refractory materials according to claim 2, characterized in that: The refractory raw material is alumina, the material that is resistant to ultra-high temperatures, conductive and not corroded by the melt of the refractory raw material is titanium carbide, titanium nitride, silicon carbide, zirconium boride or titanium boride, and the high-temperature resistant material of the middle material layer is alumina dry ramming material.

4. The bottom electrode of a DC arc furnace for melting refractory materials according to claim 2, characterized in that: The refractory raw material is magnesium oxide, the ultrahigh temperature resistant, conductive material not corroded by the melt of the refractory raw material is titanium nitride or zirconium nitride, and the high temperature resistant material of the middle material layer is magnesium dry ramming material.

5. The bottom electrode of a DC arc furnace for melting refractory materials according to any one of claim 1, characterized in that: The thermal insulation refractory material of the lower material layer includes closed pores and nano-micro pore materials.

6. The bottom electrode of a DC arc furnace for melting refractory materials according to claim 5, characterized in that: The closed pores and nano-micro pore materials are fumed silica, nano-alumina or nano-magnesia.

7. The bottom electrode of a DC arc furnace for melting refractory materials according to any one of claims 1 to 6, characterized in that: The metal conductive element is a steel sheet or a steel needle with a width of ≤5 mm, and the cross-sectional area of ​​the steel sheet or the steel needle is ≥1.25×current intensity, wherein the cross-sectional area is measured in square millimeters and the current intensity is measured in amperes.

8. The bottom electrode of a DC arc furnace for melting refractory materials according to claim 1, characterized in that: The thickness of the lower material layer is ≤ 20% of the thickness of the entire DC arc furnace bottom, the thickness of the middle material layer is ≥ 25% of the thickness of the bottom electrode, and the remainder is the thickness of the upper material layer.

9. The bottom electrode of a DC arc furnace for melting refractory materials according to claim 1, characterized in that: The upper material layer includes a top section and a bottom section, the conductive brick is arranged in the top section, and the bottom section is embedded with the metal conductive element and the embedded area is ≥3.5×current intensity, where the cross-sectional area is measured in square millimeters and the current intensity is measured in amperes.

Images