Short-process ironmaking process

Abstract

The invention discloses a smelting process taking iron ore lump ore as a raw material, and belongs to the field of metallurgy and chemical industry. According to the iron ore lump ore, the mass percentage TFe of iron is 15-50%, and the smelting process of the raw material comprises the steps that the iron ore lump ore is subjected to roasting reduction, crushing and magnetic separation to obtain iron ore concentrate powder of zero-valent iron, and finally the iron ore concentrate powder is smelted through an electromagnetic induction furnace. The method has the advantages that the magnetism of DRI reduced iron is utilized, the DRI process is advanced to the beneficiation stage to be used for separating iron ore concentrate, the process of reducing iron is the process of producing sponge iron and the means of strengthening magnetic separation magnetization, the technological process is shortened through DRI preposition, and meanwhile quality improvement of refractory iron ore is facilitated; the gas base is used for reducing the iron ore lump ore, most gangue is removed through magnetic separation, non-metal impurities are further removed through electromagnetic smelting, multi-section ore grinding and grading, flotation, pelletizing or sintering and coking operation are omitted from the initial iron ore lump ore to iron making, and the method is an intensive iron making short-process technology.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical chemistry, and particularly relates to a short-process ironmaking process. Background Art

[0002] Currently, the steel smelting mainly adopts the carbon-based blast furnace-converter long process, including main production links such as mining → ore dressing → sintering / pelletizing → blast furnace ironmaking → converter steelmaking → continuous casting billet → hot rolling / cold rolling, etc. Among them, blast furnace ironmaking requires a large amount of coke and is accompanied by a large amount of carbon dioxide emissions. In order to achieve the transformation to a low-carbon economy, the steel industry urgently needs to change the production mode and transition from carbon metallurgy to hydrogen metallurgy. Energy structure adjustment is an important path. In steel smelting, hydrogen metallurgy generally refers to a non-blast furnace smelting process (DRI process) that uses a reducing gas with a hydrogen content greater than 55% and H 2 / CO higher than 1.5 to reduce high-grade iron ore lump ore or pellet ore or sinter ore to produce direct reduced iron. At present, hydrogen metallurgy in the whole steel smelting focuses on the ironmaking process, aiming to replace carbon with hydrogen. In the long process of steel smelting, ironmaking is an important link. On the one hand, it is necessary to provide the reduced iron that meets the needs of steelmaking, and on the other hand, it is necessary for the upstream process to provide high-purity raw materials. With the change of the process of replacing carbon with hydrogen, the ironmaking product produced is sponge iron. This process only completes the process of reducing iron ore to metallic iron, without removing the impurities in the ore itself and the impurities introduced when forming sinter ore or pellet ore. Therefore, strict requirements are imposed on the purity of the raw materials. For example, MIDREX and ENERGIRON gas-based shaft furnaces for direct reduced iron use lump ore or pellet as raw materials, and require their chemical composition to be TFe>67.0%, SiO 2 +Al 2 O 3 +TiO 2 <3%, S<0.008%, P<0.030%, Cu<0.010%. Therefore, at present, hydrogen reduction places higher requirements on the upstream process.

[0003] For refractory non-magnetic or weakly magnetic iron ores with fine disseminated particle size, close symbiotic relationship and complex composition, it is necessary to go through the processes of crushing, grinding, gravity separation, magnetic separation and flotation in sequence. Moreover, the finer the grinding particle size of iron ore powder, the more conducive it is to the enrichment and improvement of the grade of iron concentrate powder. However, the problem brought about at the same time is that once the ore powder particle size reaches -325 mesh, it is difficult to form pellets, and it is necessary to carry out multiple operations such as batching, wet grinding, pelletizing, drying and sintering on the iron ore powder. Obviously, currently refractory iron ores are difficult to meet the requirements of hydrogen metallurgy.

[0004] In fact, hydrogen metallurgy not only involves energy structure adjustment, but also involves the adjustment of the raw material purity of the process of replacing carbon with hydrogen and the adjustment of the subsequent smelting process of the process of replacing carbon with hydrogen. More precisely, it is a comprehensive adjustment of the production chain from ore dressing to ironmaking. Summary of the Invention

[0005] The object of the present invention is to achieve efficient hydrogen-substituted carbon smelting using iron ore lumps as raw materials. The present invention utilizes the magnetism of DRI reduced iron and advances the DRI process to the ore dressing stage for separating iron concentrate. The process of reducing iron is both a process of producing sponge iron and a means of enhancing magnetic separation magnetization. The front placement of DRI shortens the process flow and is conducive to improving the quality of refractory iron ore; combined with the eddy current motion, skin effect motion, and self-stirring motion of metallic iron during electromagnetic induction melting, an effective slag removal melting process is established. By making good slag, while smelting good iron, the requirements for raw materials are relaxed to match the front placement process of DRI.

[0006] The specific invention content is as follows: The raw material is iron ore lumps, and the smelting process of this raw material includes the following four processes: (1) Lump ore reduction: Roast and reduce the iron ore lumps to reduce the iron component in the iron ore lumps to zero-valent iron, obtaining lumps of zero-valent iron, that is, the reduced lumps. (2) Crushing: Crush and grind the reduced lumps in process (1) to obtain iron ore powder of zero-valent iron, that is, reduced iron ore powder. (3) Magnetic separation: Perform magnetic separation on the reduced iron ore powder in process (2) to remove gangue and obtain reduced iron concentrate powder. (4) Electromagnetic induction melting: Put the reduced iron concentrate powder in process (3) into the crucible of an electromagnetic induction furnace and quickly heat it with a water-cooled electromagnetic induction coil to melt the iron concentrate powder in the crucible; maintain the time when all the iron is in a molten state for 5 - 50 min; then, cool it; during the iron melting process and the molten state, iron and non-metallic impurities are gradually phase-separated, and the non-metallic impurities form a slag; after slag skimming, a purified ingot is obtained.

[0007] Further, for the iron ore lumps, the iron grade TFe, that is, the mass percentage content of iron, is 15 - 50%; in the lump ore reduction process, gas-based reduction is carried out in a roasting furnace, and the gas used is or H 2 or NH 3 or NH 3 + H 2 , or the above reduction gas + auxiliary gas N 2 , the reduction temperature is 850 - 1100 °C; in the crushing process, the reduced lumps are crushed and ground until the concentrate and gangue ore are monomer-dissociated; in the magnetic separation process, it is either dry magnetic separation, or wet magnetic separation, or a combination of dry magnetic separation and wet magnetic separation, and the magnet is an electromagnet or a permanent magnet; in the electromagnetic induction melting process, a medium-frequency alternating current is passed through the electromagnetic induction coil, and the highest temperature of the furnace charge is 1700 °C; for the purified ingot, TFe ≥ 96%.

[0008] Furthermore, the particle size of the iron ore is 8 - 25 mm; in the reducing mixed gas, the volume percentage of the reducing gas in the mixed gas is more than 20%; in the crushing process, the lumpy ore to be reduced is crushed and ground to a particle size of ≤75 μm; in the magnetic separation process, iron concentrate powder with TFe ≥ 80% is obtained and directly used as the furnace charge for electromagnetic induction melting; the heating rate of the electromagnetic induction heating is higher than 150 °C / min, the melting temperature is 1450 - 1650 °C, and the time for maintaining all the iron in a molten state does not exceed 30 min. After that, the heating of the furnace charge is stopped, the crucible is taken out from the induction coil, and the furnace charge cools with the crucible.

[0009] Furthermore, the melting temperature of the electromagnetic induction heating is controlled near the melting point of Fe.

[0010] Furthermore, the crucible is a three-layer concentric cylindrical crucible. The inner and outer crucibles are either magnesia crucibles, or calcium oxide crucibles, or corundum crucibles, and the middle crucible is a graphite crucible; the outer crucible supports the heating body, the middle crucible assists in heating, and the inner crucible loads the raw materials.

[0011] Compared with the existing process, the advantages of the present invention are as follows: 1. For lumpy iron ore, a process of lumpy ore reduction, crushing, magnetic separation and smelting is established. From the initial iron ore treatment to ironmaking, multiple stages of grinding and classification, flotation, pelletizing or sintering, and coking operations are omitted.

[0012] 2. When reducing lumpy iron ore, while the material undergoes chemical changes, its physical form becomes loose and porous. After one-stage grinding, a powder with a particle size of ≤75 μm can be obtained, reducing the crushing energy consumption; when the iron component in the lumpy iron ore is elemental iron, the magnetic difference from gangue is greatly increased, and the concentrate of zero-valent iron is more easily dissociated from gangue minerals. Therefore, iron concentrate powder with TFe ≥ 80% can also be obtained by dry magnetic separation, and the recovery rate is higher than 90%.

[0013] 3. Electromagnetic induction causes three separation methods for metallic iron and non-metallic impurities: (1) Melting separation: The zero-valent iron in reduced iron ore serves as a metal conductor. Its internal electrons move in a circular motion perpendicular to the magnetic field direction, generating heat through the resistance within the conductor, resulting in a rapid temperature increase. The metal quickly melts and separates from the non-conductive or poorly conductive and poorly fluid non-metallic impurities. The porosity of DRI sponge iron plays an important role in melting separation. The abundant pore channels in the sponge iron endow the raw material with a large gas-solid interface. When the present invention uses an electromagnetic induction furnace to rapidly melt the sponge iron, the large gas-solid interface is quickly transformed into a large slag-liquid interface, facilitating slag discharge; (2) Molten separation: After the metal forms a melt, the iron melt has a large density and sinks. At the same time, its viscosity decreases, and not only a large number of carriers are generated inside to form eddy currents, but also the skin effect causes the iron melt to move towards the periphery, forming a self-centrifugal movement and densifying at the edge. When the iron melt moves, the non-metallic impurities originally embedded in the iron powder particles experience a process of coalescence and growth and are extruded from the iron melt; (3) Stirring separation; The eddy current movement has a directionality, and the direction changes twice within one cycle, forming an internal stirring from the iron melt itself, making the composition and temperature of the molten steel uniform, and thus deeply removing non-metallic impurities. Electromagnetic induction provides an effective way for the separation of iron and non-metallic impurities at high temperatures.

[0014] 4. The melting process can effectively remove trace non-metallic impurities embedded or wrapped in the reduced iron, and has relatively loose requirements for the raw materials of reduced iron. For example, zero-valent iron concentrate with an iron grade of 80.05%, SiO 2 with a mass percentage of 7.73% and other impurities with a mass percentage of 12.22% can be directly used as the raw material for the electromagnetic induction smelting process, with high impurity removal efficiency, which not only reduces the burden on the front-end process of raw material preparation for ironmaking operations, but also makes full use of iron ore resources.

[0015] 5. The electromagnetic induction melting process is simple, can efficiently produce slag, and does not use any additives, such as deoxidizers and slag formers. It can remove harmful inclusion elements without relying on the metallurgical reaction at the slag-steel interface. The slag produced from treating natural ore lumps or powders is only the gangue minerals of the iron ore and their reaction products in the molten state.

[0016] 6. The present invention belongs to the combination of the beneficiation process and the smelting process, uses hydrogen / ammonia metallurgy to complete the magnetic separation of iron ore, and integrates the process into an intensive short process of beneficiation and smelting. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the process flow chart of the present invention.

[0018] Figure 2 is the SEM photograph of the reduced iron concentrate powder in Example 2 and its corresponding element distribution map.

[0019] Figure 3 SEM photograph of the ingot cross-section in Example 2 and the EDS spectrum of Region 1 Detailed implementation manners

[0020] The present invention will be described in detail with reference to the following examples. Example 1

[0021] The present invention provides a short-process ironmaking process. The process flow is shown in Figure 1 . The raw material is iron ore lump ore, and the smelting process of this raw material includes the following four processes: (1) Lump ore reduction: Roast and reduce the iron ore lump ore to reduce the iron component in the iron ore lump ore to zero-valent iron, obtaining a lump ore of zero-valent iron, that is, the reduced lump ore; (2) Crushing: Crush and grind the reduced lump ore in process (1) to obtain iron ore powder of zero-valent iron, that is, reduced iron ore powder; (3) Magnetic separation: Perform magnetic separation on the reduced iron ore powder in process (2) to remove gangue and obtain reduced iron concentrate powder; (4) Electromagnetic induction melting: Put the reduced iron concentrate powder in process (3) into the crucible of an electromagnetic induction furnace and quickly heat it with a water-cooled electromagnetic induction coil to melt the iron concentrate powder in the crucible; keep the time when all the iron is in a molten state for 5 - 50 min; then, cool it; during the iron melting process and the molten state, the iron and non-metallic impurities are gradually phase-separated, and the non-metallic impurities form a slag; after skimming the slag, a purified ingot is obtained. Example 2

[0022] On the basis of Example 1, the iron ore raw material used has a particle size of 10 - 15 mm and an iron grade of 35.46%. Roast and reduce 40 g of this raw material in a roasting furnace. The reducing gas used is NH 3 , which forms a mixed gas with the auxiliary gas N 2 . The volume percentage of NH 3 is 30%. When the furnace chamber temperature rises to 900 ± 10 °C, the mixed gas is introduced and the reaction lasts for 3 hours to reduce the iron component in the iron ore raw material to zero-valent iron; after cooling, crush and grind it to a content of -325 mesh accounting for 86.9% to obtain reduced iron ore powder. Precautions: Before reduction, the air in the furnace is replaced with N 2 and then the reducing gas is introduced. After the reaction, N 2 is used as the cooling protection gas.

[0023] Magnetic separation method: Two - stage dry magnetic separation. The dry magnetic separation is as follows: A closed separation space is constructed with a partition and a tailings receiver. The magnet is located outside the partition of the separation space, air is the separation medium, and the ore powder is placed in the tailings receiver. The magnet makes reciprocating motion outside the partition to carry the powder inside the partition for separating iron ore from gangue. After separation, the iron concentrate is adsorbed and retained on the partition by the magnet, the tailings enter the tailings receiver, the concentrate and the tailings are separated, and the tailings are discarded to obtain the dry - selected concentrate. The magnetic induction intensity generated by the magnet used in this embodiment on the other side of the partition is 200 - 800 mT, and the magnetic separation time for each time is 3 min. After the first dry magnetic separation of the reduced iron ore powder obtained in this embodiment, the first dry - selected concentrate is obtained. The first dry - selected concentrate is subjected to dry magnetic separation again to obtain the second dry - selected concentrate, which is the final concentrate of zero - valent iron, with an iron grade of 80.05%, SiO 2 The mass percentage is 7.73%, and the mass percentage of other impurities is 12.22%; the recovery rate of Fe in the final concentrate is 93.66%. The SEM photograph of the reduced iron concentrate powder and its corresponding element distribution map are shown in Figure 2 . Figure 2 It shows that non - metallic impurities containing C / O / Si / P / S / Mn are embedded or wrapped inside the reduced iron.

[0024] The crucible used in the electromagnetic induction heating furnace is a three - layer concentric cylindrical crucible. The inner and outer crucibles are corundum crucibles, the middle layer is a graphite crucible, the outer crucible supports the heating element, the middle crucible assists in heating, and the inner crucible loads the furnace charge. The reduced iron concentrate powder is loaded into the inner crucible, and the crucible is placed in the electromagnetic induction heating furnace. It is rapidly melted with a power of 4 KW, the heating rate is 200 °C / min, the maximum temperature is 1600 °C, all the iron powder is melted, and it is kept in the molten state for 10 min, and then cooled and slag is removed to obtain an ingot with TFe = 96.13%. Figure 3 For the SEM photograph of the cross - section of the ingot and the EDS energy spectrum of region 1, Figure 3 it shows that there is carbon precipitation at the marked 2 in region 1. The normalized mass percentage: C 18.48%, Fe 81.52%. Although it reduces the purity of iron in region 1, the normalized mass percentage in region 1: C 3.90%; Fe 96.10%, indicating that the iron content in region 1 is still relatively high and there are no other elements except C and Fe. Example 3

[0025] On the basis of Example 1, the iron ore raw material used has an iron grade of 34.23%, and the iron ore raw material is 8 - 12 mm. In the roasting furnace, 40 g of this raw material is subjected to hydrogen - based roasting reduction. The reducing gas used is H 2 , when the furnace cavity temperature is raised to 900 ± 10 °C, H 2, react for 2.5 hours to reduce the iron component in the iron ore raw material to zero-valent iron; after cooling, crush and grind to a -325 mesh content of 89.7% to obtain reduced iron ore powder. Precautions: Before reduction, replace the air in the furnace with N 2 After replacement, introduce hydrogen. After the reaction, N 2 is used as the cooling and protective gas.

[0026] Magnetic separation method: 2 times of dry magnetic separation + 4 times of wet magnetic separation. The wet magnetic separation is as follows: Use a partition and a tailings receiver to construct a closed separation space. The magnet is located outside the partition of the separation space. Tap water or distilled water or ethanol is used as the separation medium. The ore powder and the separation medium form a pulp. The pulp is placed in the tailings receiver, and the inner side of the partition touches the pulp. By making the magnet reciprocate outside the partition to carry the powder in the pulp on the inner side of the partition, the concentrate and gangue are separated. After separation, the iron concentrate is adsorbed and retained on the partition by the magnet, and the tailings enter the pulp in the tailings receiver. The concentrate and the tailings are separated, and the tailings are discarded to obtain the wet-separated concentrate. Discarding the tailings means discharging the pulp containing tailings and simultaneously recovering the solution by sedimentation. The magnetic induction intensity generated by the magnet used in this example on the other side of the partition is 200 - 800 mT, and the magnetic separation time for each time is 3 min. Perform 2 times of dry magnetic separation according to Example 1. After discarding the tailings, place the second dry-separated iron concentrate in the tailings receiver, add ethanol as the separation medium to form a pulp with the second dry-separated iron concentrate, and perform the above-mentioned wet magnetic separation, a total of 4 times of wet magnetic separation; after the tailings settle, recover the ethanol to obtain the final magnetic separation concentrate, whose iron grade is 89.68% and the recovery rate is 91.26%.

[0027] Load the reduced iron concentrate powder into a crucible (same as Example 2), place it in an electromagnetic induction heating furnace, quickly melt it with a power of 4.5 KW, the heating rate is 230 °C / min, the maximum temperature is 1600 °C, all the iron powder is melted, keep the molten state for 6 - 10 min, and then cool and remove the slag to obtain an ingot with TFe = 97.04%. Example 4

[0028] Based on Example 1, the iron ore raw material used has an iron grade of 24.05% and a particle size of 10 - 15 mm. Carry out gas-based roasting reduction on 55 g of this raw material in a roasting furnace. The reducing gas used is NH 3 , when the furnace cavity temperature rises to 900 ± 10 °C, introduce NH 3 , react for 3 hours to reduce the iron component in the iron ore raw material to zero-valent iron; after cooling, crush and grind to a -200 mesh content of 89.3% to obtain reduced iron ore powder. Precautions: Before reduction, replace the air in the furnace with N 2 After replacement, introduce ammonia. After the reaction, N 2 is used as the cooling and protective gas.

[0029] The magnetic separation method adopted is: 2 times of dry magnetic separation + 6 times of wet grinding magnetic separation. The dry magnetic separation is shown in Example 1. The wet grinding magnetic separation is as follows: the slurry of the previous wet concentrate is ground in a mortar for 1 minute to demagnetize the particles by friction, and then the next wet magnetic separation is carried out. The magnetic induction intensity generated by the magnet used in this example on the other side of the partition is 100 - 600 mT. The wet magnetic separation medium used is distilled water, and the magnetic separation time for each time is 3 minutes. Under this magnetic separation method, the magnetic separation concentrate of zero-valent Fe is obtained, with an iron grade of 86.03% and a recovery rate of 86.23%. After the tailings settle, ethanol is recovered.

[0030] Load the reduced iron concentrate powder into a crucible (the same as in Example 2), place it in an electromagnetic induction heating furnace, quickly melt it with a power of 4 KW, with a heating rate of 200 °C / min, a maximum temperature of 1600 °C. All the iron powder is melted, keep the molten state for 15 - 20 minutes, and then cool it and remove the slag to obtain an ingot with TFe = 96.04%.

[0031] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them.

Claims

1. A short-process ironmaking process, characterized in that, the raw material is iron ore lumps, and the smelting process of this raw material includes the following four processes: (1) Lump ore reduction: Roast and reduce the iron ore lumps to reduce the iron component in the iron ore lumps to zero-valent iron, obtaining lumps of zero-valent iron, that is, the reduced lumps; (2) Crushing: Crush and grind the reduced lumps in process (1) to obtain iron ore powder of zero-valent iron, that is, reduced iron ore powder; (3) Magnetic separation: Perform magnetic separation on the reduced iron ore powder in process (2) to remove gangue and obtain reduced iron concentrate powder; (4) Electromagnetic induction melting: Put the reduced iron concentrate powder in process (3) into the crucible of an electromagnetic induction furnace, quickly heat it with a water-cooled electromagnetic induction coil to melt the iron concentrate powder in the crucible; Keep the time when all the iron is in a molten state for 5 - 50 min; Then, cool it; During the iron melting process and the molten state, the iron and non-metallic impurities gradually separate and exist, and the non-metallic impurities form a slag; After slagging, a purified ingot is obtained.

2. A short-process ironmaking process according to claim 1, characterized in that: The iron ore lumpy ore has an iron grade TFe, i.e., the mass percentage of iron, of 15-50%; in the reduction process of the lumpy ore, hydrogen-based reduction is carried out in a roasting furnace, and the gas used is or H 2 or NH 3 or NH 3 +H 2 , or the above reduction gas + auxiliary gas N 2 , the reduction temperature is 850-1100°C; in the crushing process, the reduced lumpy ore is crushed and ground until the concentrate and gangue ore are monomer-dissociated; in the magnetic separation process, it is either dry magnetic separation, wet magnetic separation, or a combination of dry magnetic separation and wet magnetic separation, and the magnet is an electromagnet or a permanent magnet; in the electromagnetic induction melting process, a medium-frequency alternating current is passed through the electromagnetic induction coil, and the maximum temperature of the furnace charge is 1700°C; the purified ingot has TFe≥96%.

3. A short-process ironmaking process according to claims 1 and 2, characterized in that: the particle size of the iron ore is 8 - 25 mm; In the reducing mixed gas, the volume percentage of the reducing gas in the mixed gas is more than 20%; In the crushing process, the reduced lumps are crushed and ground to a particle size ≤ 75 μm; In the magnetic separation process, iron concentrate powder with TFe ≥ 80% is obtained and directly used as the furnace charge for electromagnetic induction melting; The heating rate of the electromagnetic induction heating is higher than 150 °C / min, the melting temperature is 1450 - 1650 °C, and the time when all the iron is in a molten state does not exceed 30 min. Then, stop heating the furnace charge, take out the crucible from the induction coil, and the furnace charge cools with the crucible.

4. A short-process ironmaking process according to claim 1, characterized in that: the melting temperature of the electromagnetic induction heating is controlled near the melting point of Fe.

5. A short-process ironmaking process according to claim 1, characterized in that: the crucible is a three-layer concentric cylindrical crucible. The inner and outer crucibles are either magnesia crucibles, or calcium oxide crucibles, or corundum crucibles, and the middle crucible is a graphite crucible; The outer crucible supports the heating body, the middle crucible assists in heating, and the inner crucible loads the raw materials.

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