High-purity iron preparation method based on cooperation of hydrogen-rich gas-based shaft furnace and multi-stage refining

Abstract

The invention discloses a high-purity iron preparation method based on combination of a hydrogen-rich gas-based shaft furnace and a multi-stage refining process, aiming at common iron ore (TFe is 64-65%), the purity of molten iron is greater than or equal to 99.99% through full-flow cooperation of pelletizing, reduction, electric arc furnace melting separation, LF refining furnace and vacuum furnace. The core innovation comprises: 1) a high-porosity pellet roasting technology (the porosity is 25-32%) is adapted to efficient reduction of common-grade ore; 2) inhibiting carbon precipitation by a temperature control technology of the hydrogen-rich shaft furnace (H2 is greater than or equal to 85%); 3) directionally dephosphorizing and desulfurizing a CaO-SiO2-FeO-B2O3 slag system in an electric arc furnace and a CaO-SiO2-Al2O3-FeO slag system in a refining furnace (the content is less than or equal to 0.003); the metallization ratio is greater than or equal to 92%, and the method is suitable for the field of high-end special steel and electronic materials.

Description

Technical Field

[0001] This invention belongs to the field of green metallurgy technology, specifically involving a short-process technology for preparing ultra-high purity iron (≥99.99%) using ordinary grade iron ore as raw material through hydrogen-rich reduction and multi-stage refining. It is applicable to high-end materials fields such as aerospace and electronic devices. Background Technology

[0002] 1. Limitations of traditional techniques

[0003] Traditional blast furnace ironmaking relies on coke, resulting in high pollution and high impurity content in molten iron (carbon content >4%, and impurities such as silicon and manganese are difficult to control);

[0004] Coal-based direct reduction processes suffer from problems such as low reducing gas utilization, high energy consumption, and insufficient product purity, making it difficult to meet the demands of high-end steel materials.

[0005] 2. Advantages of hydrogen reduction

[0006] Hydrogen reduction can reduce emissions and carbon emissions, which is in line with the direction of green metallurgy;

[0007] Hydrogen molecules have a large diffusion coefficient and a fast reduction rate, which can improve production efficiency.

[0008] Hydrogen-based reduction can achieve selective reduction, preventing gangue impurities (such as silicon, aluminum, and titanium) from entering the iron phase, thus providing a raw material basis for the production of high-purity iron. Summary of the Invention

[0009] This invention provides a low-energy-consumption, high-purity, and environmentally friendly method for producing high-purity iron, breaking through the limitations of traditional processes and meeting the demand for high-end steel materials.

[0010] Technical solution

[0011] 1. Raw material pretreatment

[0012] 65% grade iron ore concentrate (containing ≥90% Fe2O3) is mixed with 2-3 wt% bentonite to form pellets, and 0.5% sodium carboxymethyl cellulose is added. After drying, the pellets are calcined at 1225-1275℃ for 10-15 minutes to form oxide pellets with a compressive strength ≥2500N.

[0013] 2. Hydrogen-rich vertical shaft furnace reduction

[0014] Reducing gas: Hydrogen purity ≥85%, temperature 950-1100℃, pressure 0.2-0.3MPa, gas flow rate 600-650Nm³ 3 / ton·hour;

[0015] Vertical shaft furnace segmented control: preheating section (800-900℃), reduction section (1050-1100℃), cooling section (≤150℃);

[0016] The reduction time is 2.5-3.5 hours, the metallization rate is ≥92%, and the residual carbon is ≤0.5%.

[0017] 3. Electric furnace melting and dephosphorization

[0018] The melting temperature is 1580-1650℃, the carbon content is 2-4%, and the slag basicity (CaO / SiO2) is controlled at 2.5-3.5.

[0019] Adding CaO-SiO2-FeO-B2O3 (3:4:2:1) adjusts the slag fluidity, and simultaneous dephosphorization is achieved by utilizing FeO in direct reduction of iron, reducing the phosphorus content to ≤0.008%.

[0020] The slag contains P2O5 ≥ 2.5%, which allows for further recovery of phosphorus resources.

[0021] 4. High-alkalinity slag refining

[0022] o Refining slag system: CaO 55-65wt%, SiO2 10-15wt%, Al2O3 15-20wt%, FeO≤1.0%;

[0023] The refining temperature is 1600-1650℃, the argon stirring intensity is 0.3-0.5 N·m / t, the oxygen content is reduced to ≤10ppm, and the sulfur and phosphorus content is ≤0.003%.

[0024] 5. Vacuum deep purification: RH vacuum treatment (≤10Pa) removes [H] and [N], resulting in high-purity iron with Fe greater than or equal to 99.99%, TO ≤5ppm, and H ≤1.5ppm.

[0025] Innovation

[0026] 1. Pellet porosity control technology: Calcination at 1200-1250℃ forms a porosity of 25-30%, enhancing H2 diffusion efficiency and enabling the metallization rate of 65% low-grade ore to exceed 92%.

[0027] 2. Carbon precipitation suppression technology: Control the reducing gas CH4 ≤ 3% and combine it with segmented temperature control (preheating zone 500℃ → reduction zone 1000℃ → cooling zone 150℃) to suppress the 2CO→C+CO2 reaction, and the carbon content ≤ 0.5%;

[0028] 3. Slag System Collaborative Design:

[0029] • An electric arc furnace using CaO-SiO2-FeO-B2O3 (3:4:2:1) achieves a phosphorus distribution ratio Lp≥230;

[0030] • LF furnace: CaO 55-65wt%, SiO2 10-15wt%, Al2O3 15-20wt%, FeO ≤1.0% directional adsorption of inclusions;

[0031] 4. Vacuum deep purification: Total oxygen content ≤5ppm, meeting the electronic grade pure iron standard (4N5). Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a high-purity iron preparation method based on a hydrogen-rich vertical shaft furnace and multi-stage refining. Detailed Implementation

[0033] Example 1:

[0034] Example 1 (Optimization of the entire process for ordinary iron ore)

[0035] Raw material and pellet preparation:

[0036] • Raw material composition: 65% grade iron ore concentrate (TFe 65.3%, SiO2 3.2%, Al2O3 3.0%, P 0.037%, S 0.022%), particle size distribution: -200 mesh ≥ 92%;

[0037] • Pelletizing process: Add 1.0% carboxymethyl cellulose (CMC) as a binder, press into green pellets with a diameter of Φ12-15mm, and the green pellet drop strength is ≥10 times / 0.5m;

[0038] • Oxidative roasting: Roasted in a chain grate rotary kiln (1250℃×10 minutes), resulting in pellets with a porosity of 32%, a compressive strength of 2700 N / pellet, and an Fe3O4 oxidation degree ≥98%.

[0039] Hydrogen-rich vertical shaft furnace reduction:

[0040] • Composition of reducing gas: H2 90%, CO 3%, CH4 4% (volume ratio), the gas is preheated to 800℃ and then introduced into the vertical furnace;

[0041] • Temperature control: Three-stage temperature control

[0042] o Upper preheating zone: 400-600℃, dwell time 30 minutes;

[0043] o Central reduction zone: 1000-1050℃, residence time 2.5 hours;

[0044] Lower cooling zone: 300-400℃, cooling hydrogen flow rate 10Nm 3 / ton·hour;

[0045] • Reduction effect: Metallization rate 91.5% (DRI composition: Fe 96.8%, C 0.4%, O 1.3%), hydrogen consumption per ton of iron 615 Nm³ 3 The unreacted H2 in the exhaust gas has a 93% recycling rate.

[0046] Electric arc furnace melting and impurity removal:

[0047] • Melting parameters: DRI is placed in a 100-ton electric arc furnace, heated to 1630℃, and stirred with argon gas (flow rate 0.6 Nm³). 3 / ton·minute);

[0048] • Slag system design: Add CaO-SiO2-FeO slag (CaO / SiO2 = 4.0, FeO 8%, MgO 5%), with the slag amount accounting for 12% of the weight of molten iron;

[0049] • Impurity removal effect: Phosphorus content decreased from the initial 0.037% to 0.0085%, sulfur content decreased from 0.022% to 0.0076%, and FeO content in the slag decreased to 6%.

[0050] LF furnace refining and deoxidation:

[0051] • Refining slag system: Al2O3 35%, CaO 58%, SiO2 7%, slag layer thickness 50mm;

[0052] Process parameters: Argon flow rate 1.2 Nm 3 / ton·minute, refining time 35 minutes;

[0053] • Impurity removal effect: Total oxygen content (TO) decreased from 40 ppm after melting to 8 ppm, inclusion size ≤ 5 μm, phosphorus content 0.0015%, sulfur content 0.0012%.

[0054] Vacuum furnace deep purification:

[0055] • Vacuum treatment: RH vacuum refining device is used, vacuum degree ≤5Pa, holding time 25 minutes;

[0056] • Degassing effect: Hydrogen content decreased from 2.5 ppm to 1.0 ppm, nitrogen content decreased from 25 ppm to 8 ppm, and the final molten iron purity was ≥99.993%.

[0057] Example 2 (Comparison of Process Parameter Adjustments):

[0058] Raw material and pellet adjustment:

[0059] • Raw material composition: 65% grade iron ore concentrate (TFe 64.9%, SiO2 3.1%, P 0.020%, S 0.032%), particle size distribution: -200 mesh ≥ 90%;

[0060] • Pelletizing optimization: A composite binder (1.0% bentonite + 0.5% carboxymethyl cellulose (CMC)) is used to improve the porosity of the pellets.

[0061] • Firing adjustment: Reduce the firing temperature to 1200℃ (time 15 minutes), compressive strength 2800N / ball, porosity 28%.

[0062] Vertical shaft furnace reduction parameter optimization:

[0063] • Reducing gas composition: H2 85%, CO 5%, CH4 0% (reduces the risk of carbon precipitation);

[0064] • Temperature control: Single-stage temperature control (1000℃ constant temperature reduction for 3 hours), hydrogen flow rate increased to 215 Nm 3 / ton·hour;

[0065] • Reduction effect: Metallization rate 92.2% (DRI composition: Fe 95.5%, C 0.2%, O 1.8%), hydrogen consumption per ton of iron 680 Nm³ 3 .

[0066] Electric arc furnace melting fraction enhanced desulfurization:

[0067] • Slag system adjustment: CaO / SiO2 = 3.8, FeO 10%, and 2% CaF2 added to improve slag fluidity;

[0068] • Desulfurization effect: Sulfur content reduced to 0.0083%, phosphorus content reduced to 0.0073%.

[0069] LF furnace and vacuum synergy:

[0070] • LF refining enhancement: Utilizing a dual-slag method (desulfurization slag first, then deoxidation slag), sulfur content is reduced to 0.0013%, phosphorus content to 0.001%, and total oxygen content to 5 ppm.

[0071] • Vacuum deep treatment: Extend the vacuum holding time to 30 minutes, hydrogen content ≤0.8ppm, final iron purity 99.992%.

[0072] Beneficial effects

[0073] High purity: Iron purity reaches over 99.99%, and the content of oxygen, sulfur, and phosphorus is lower than that of traditional processes;

[0074] Low carbon and environmentally friendly: CO2 emissions throughout the entire process are reduced by more than 80% compared to the furnace process;

[0075] Compatible with common iron ore: It can produce high-purity iron from 65% low-grade iron ore, reducing production costs;

[0076] Short-process, high-efficiency production: Integrating the four-step process of "reduction-melting-refining-vacuum", the time is shortened by more than 50% compared with the traditional long process of blast furnace-converter, and the energy consumption per ton of iron is reduced by 30%-40%.

Claims

1. A method for preparing high-purity iron, characterized in that... Includes the following steps: Step 1: Pelletize 65% grade iron ore concentrate (P≤0.05%, S≤0.05%) and oxidize and roast it (1225-1275℃×10-15min). The pellet porosity is 25-30% and the compressive strength is ≥2500N / pellet. Step 2: The pellets are reduced in a hydrogen-rich vertical shaft furnace. The reducing gas contains H2 ≥ 85%, CH4 ≤ 3%, and CO ≤ 12%. The reduction temperature is 950-1100℃, and the gas flow rate is 600-650 Nm³. 3 / ton·hour, metallization rate ≥92%; Step 3: The reduction product (DRI) is melted in an electric arc furnace (1600-1650℃), and a CaO-SiO2-FeO-B2O3 slag system (basicity 2.5-3.5, FeO 5-8%) is added, with sulfur and phosphorus content ≤0.008%. Step 4: The LF refining furnace uses an Al2O3-CaO-SiO2 slag system (Al2O3 35-40%, CaO 55-60%) combined with argon stirring (0.5-1.0 Nm). 3 / ton·min), total oxygen content decreased to ≤15ppm, sulfur and phosphorus content ≤0.003%; Step 5: Vacuum furnace (VD) treatment, vacuum degree ≤10Pa, holding time ≥20min, final molten iron TO≤5ppm, H≤1.5ppm, purity ≥99.99%.

2. According to claim 1, the characteristic is: Step one uses ≥0.5% of the organic binder sodium carboxymethyl cellulose and is calcined at a high temperature of 1200-1250℃.

3. According to claim 1, the characteristic is: The unique temperature control technology in step two reduces the temperature of the reduced metallized pellets to below 700℃ in 20-30 minutes, inhibiting carbon precipitation and ensuring that the carbon content of the metallized pellets is ≤0.5%.

4. According to claim 1, the characteristic is: Step 3: The unique slag system ratio of CaO-SiO2-FeO-B2O3 (3:4:2:1) in the melting and slag separation process can improve fluidity, resulting in high phosphorus removal rate and high iron recovery rate.

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