Method for producing high-carbon ferrochrome through electric furnace smelting of chromite

Abstract

The invention relates to the technical field of a method for producing high-carbon ferro-chrome through chromite electric furnace smelting. The method comprises the following steps: mixing chromite subjected to ore grinding pretreatment, a binder, a calcium flux, a magnesium flux and a silicon-containing flux with water according to a ratio, pelletizing to obtain green pellets, and carrying out drying and high-temperature oxidation consolidation treatment on the green pellets to obtain fluxed oxidized pellets; and the fluxed oxidized pellets and a reducing agent are put into an electric furnace to be smelted, the smelting temperature ranges from 1600 DEG C to 1700 DEG C, and slag and alloy are separated to obtain the high-carbon ferrochrome. According to the method, the flux required by slagging of the electric furnace is added into the pellets, so that the problem of unstable furnace condition caused by non-uniform flux distribution due to direct addition of the flux into the electric furnace for smelting is solved, the difficulty of electric furnace smelting operation is reduced, and meanwhile, the flux can be subjected to solid-phase reaction with chromite to generate a low-melting-point compound during high-temperature oxidation and solidification of the pellets; the pre-slagging effect is achieved, the electric furnace smelting time can be shortened, and energy consumption is reduced. According to the process for producing the high-carbon ferrochrome through electric furnace smelting, the production efficiency can be remarkably improved, and the production cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization of chromite, specifically relating to a method for producing high-carbon ferrochrome by electric furnace smelting of chromite. Background Technology

[0002] Ferrochrome alloys are the main alloying additives used in the production of stainless steel and tool steel. They are classified according to carbon content into high-carbon ferrochrome, medium-carbon ferrochrome, low-carbon ferrochrome, and low-carbon ferrochrome. High-carbon ferrochrome alloys, with a chromium content of approximately 52%-60% and a carbon content of 4%-10%, are the main ferrochrome alloy products and can be used as raw materials for the production of other ferrochrome products such as medium, low, and low-carbon ferrochrome. Their production accounts for over 90% of the total ferrochrome output. With market and economic development, the demand for stainless steel is increasing, thus leading to a growing demand for high-carbon ferrochrome alloys.

[0003] The smelting methods for high-carbon ferrochrome include the electric arc furnace (EAF) method, the shaft furnace (blast furnace) method, the plasma method, and the smelting reduction method. Currently, the EAF method is the main method. The main charge structure for EAF smelting of high-carbon ferrochrome is "chromite + flux + reducing agent". The charge structure determines both the smelting effect and the smelting cost. The EAF smelting process for high-carbon ferrochrome requires high permeability, melting rate, and reducibility of the charge. Generally, chromite powder needs to be agglomerated. Common agglomeration methods include sintering, pelletizing, and briquetting. The pelletizing method has the advantages of low energy consumption, high single-unit capacity, and high production flexibility.

[0004] Currently, in the high-carbon ferrochrome smelting process, chromite agglomerates, slag-forming flux, and reducing agents are added at the electric furnace charging point. After a period of smelting, the high-carbon ferrochrome and slag are removed. Due to the significant differences in the properties of various furnace charges, local segregation of the charges, especially the flux, often occurs during smelting, leading to problems such as unstable furnace conditions, high operational difficulty, and high production costs. Furthermore, the slag currently used in high-carbon ferrochrome smelting is primarily a ternary slag system of MgO-Al2O3-SiO2, located in the magnesium-aluminum spinel phase region. This slag system has high viscosity and melting temperature, resulting in high smelting temperatures, high energy consumption, high carbon emissions, difficulty in slag-iron separation, and low recovery rates of valuable elements. Developing a new high-carbon ferrochrome production process that can improve the stability and efficiency of electric furnace production and reduce smelting energy consumption is of great significance for improving the economic and environmental benefits of high-carbon ferrochrome production enterprises. Summary of the Invention

[0005] This invention addresses the problems of poor stability, low production efficiency, high energy consumption, high carbon emissions, low recovery rate of valuable elements, and poor economic benefits in the production of high-carbon ferrochrome from chromite using electric arc furnaces. The aim of this invention is to provide a new process for producing high-carbon ferrochrome from chromite using electric arc furnaces. This process improves upon existing technologies, enhances the stability and efficiency of electric arc furnace production, reduces smelting energy consumption, and ultimately improves the economic and environmental benefits for high-carbon ferrochrome production enterprises.

[0006] This invention provides the following technical solution: a method for producing high-carbon ferrochrome by smelting ferrochrome ore in an electric furnace, comprising the following steps:

[0007] Step 1: Preparation of chromite flux pellets

[0008] Chromite pre-treated chromite, binder, calcium flux, and magnesium flux are mixed with water in a certain proportion and then pelletized to obtain chromite green pellets. The amount of calcium flux and magnesium flux added is based on the mass ratio of (CaO+MgO) / Al2O3 in the chromite pellet composition of 1.0-1.5:1, preferably 1.1-1.5:1. The amount of calcium flux added is based on the mass ratio of CaO to MgO in the chromite pellet composition of 0.2-0.5:1, preferably 0.3-0.5:1. The chromite green pellets are then dried and subjected to high-temperature oxidation and consolidation treatment to obtain chromite flux-oxidized pellets.

[0009] The chromite pellets contain 85-92% chromite and flux by mass, 1-3% binder by mass, and 7-12% water by mass; the mixture is composed of calcium-based flux and magnesium-based flux.

[0010] During implementation, the mass ratio of chromite to flux can be calculated based on the specific chemical composition of the chromite and flux according to the above ratio to determine the amount to be added.

[0011] Step Two: Electric Furnace Smelting

[0012] Chromite fluxing oxide pellets, siliceous flux, and reducing agent are charged into an electric furnace for smelting at a temperature of 1600-1700℃ for 1-1.5 hours. High-carbon ferrochrome and slag are obtained by separating the slag from the gold. The siliceous flux is added according to the SiO2 / Al2O3 mass ratio of 1.0 to 1.5:1 in the slag after smelting.

[0013] Furthermore, the grinding pretreatment method includes, but is not limited to, one or more of the following methods: ball milling, high-pressure roller milling, wet milling, vertical milling, etc.

[0014] Furthermore, the chromite particle size after the grinding pretreatment is ≥80% -200 mesh, and the flux particle size is ≥80% -200 mesh.

[0015] Furthermore, the binder is one or more of bentonite, organic binders, and composite binders.

[0016] Furthermore, the calcium flux includes, but is not limited to, one or more calcium-containing substances such as limestone, dolomite, quicklime, and high-calcium slag.

[0017] Furthermore, the magnesium flux includes, but is not limited to, one or more magnesium-containing substances such as dolomite, magnesite, magnesium silicate, serpentine, and magnesium-containing slag.

[0018] Furthermore, the chromite green pellet consolidation treatment method includes the chain grate-rotary kiln method, belt mill method, vertical shaft furnace method, etc. Drying temperature: 200–400℃, drying time: 5–10 min; preheating temperature: 800–1100℃, preheating time: 10–20 min; roasting temperature: 1200–1300℃, roasting time: 5–20 min.

[0019] Furthermore, the reducing agent in the electric furnace smelting process includes, but is not limited to, one or more of coke powder, anthracite, and semi-coke.

[0020] Furthermore, the silicon flux includes, but is not limited to, one or more silicon-containing substances such as silica, serpentine, quartz sand, and silicon-containing slag.

[0021] Chromite flux oxide pellets and reducing agent are smelted in an electric furnace at a mass ratio of 80-90:10-20.

[0022] The present invention can achieve a chromium recovery rate of over 97.5% by smelting at 1600-1650℃ for 60-90 minutes.

[0023] The advantages of this invention are:

[0024] This invention proposes a method for producing high-carbon ferrochrome from chromite ore using an electric arc furnace. It employs flux-modified pellets, incorporating a portion of the flux required for slag formation in the electric arc furnace into the pellets. This solves the problem of uneven flux distribution leading to unstable furnace conditions caused by directly adding flux into the electric arc furnace, thus reducing the difficulty of electric arc furnace smelting operations. Simultaneously, during the high-temperature oxidation and solidification of the pellets, the flux undergoes a solid-phase reaction with the chromite ore to generate low-melting-point compounds, effectively acting as a pre-slag-forming agent. This shortens the electric arc furnace smelting time and significantly reduces energy consumption and production costs. Detailed Implementation

[0025] The specific embodiments of the present invention will be further illustrated below, but the specific embodiments of the present invention are not limited to the following embodiments.

[0026] The main components of the chromite furnace charge used in this embodiment are shown in Table 1 below.

[0027] Table 1. Main chemical components of chromite (%)

[0028]

[0029] Example 1

[0030] A method for producing high-carbon ferrochrome by smelting ferrochrome ore in an electric furnace includes the following steps:

[0031] After crushing and grinding chromite and flux to -200 mesh (≥80%), bentonite (binder) and water are added and mixed evenly in a certain proportion to form chromite green pellets. The green pellets contain 2% binder and 8% water by mass, with the remainder being chromite and flux (chromite:flux = 1000:210 by mass). The flux consists of limestone and magnesite, added according to a (CaO+MgO) / Al2O3 mass ratio of 1.2:1, and limestone added according to a CaO:MgO mass ratio of 0.5:1. The qualified green pellets are then dried. The process involved drying at 300℃ for 8 minutes, preheating at 900℃ for 15 minutes, and oxidative roasting at 1250℃ for 15 minutes to obtain chromite flux pellets. These chromite flux oxide pellets were then loaded into an electric furnace, with coke powder added (the mass ratio of coke powder to the chromite flux oxide pellets was 88:12). Silica was added according to a SiO2 / Al2O3 mass ratio of 1.5:1 in the slag after smelting. The smelting temperature was 1600℃, and the smelting time was 90 minutes, yielding high-carbon ferrochrome and chromium-containing slag. The resulting chromium-containing molten iron contained 52.45% chromium, with a chromium recovery rate of 97.6%.

[0032] Example 2

[0033] A method for producing high-carbon ferrochrome by smelting ferrochrome ore in an electric furnace includes the following steps:

[0034] After crushing and grinding chromite and flux to -200 mesh (≥80%), bentonite (binder) and water are added and mixed evenly in a certain proportion to form chromite green pellets. The green pellets contain 1% binder and 9% water by mass, with the remainder being chromite and flux (chromite:flux = 1000:270 by mass). The flux consists of quicklime and dolomite, added according to a (CaO+MgO) / Al2O3 mass ratio of 1.3:1, and quicklime added according to a CaO:MgO mass ratio of 0.4:1. The qualified green pellets are then processed... The chromite flux pellets were obtained by drying (at 200℃ for 10 min), preheating (at 800℃ for 20 min), and roasting (at 1300℃ for 5 min). The chromite flux oxide pellets were then loaded into an electric furnace, and coke powder was added (the mass ratio of coke powder to the chromite flux oxide pellets was 85:15). Silica was added according to the SiO2 / Al2O3 mass ratio of 1.3:1 in the slag composition after smelting. The smelting temperature was 1650℃ and the smelting time was 80 min to obtain high-carbon ferrochrome and chromium-containing slag. The chromium content in the resulting ferrochrome molten metal was 52.46%, and the chromium recovery rate reached 98.5%.

[0035] Example 3

[0036] A method for producing high-carbon ferrochrome by smelting ferrochrome ore in an electric furnace includes the following steps:

[0037] After crushing and grinding chromite and flux to -200 mesh ≥80%, bentonite (binder) and water are added and mixed evenly in a certain proportion to form chromite green pellets. The raw chromite pellets contain 1% binder and 9% water by mass, with the remainder being chromite and flux (consistent with Example 2). The flux consists of hydrated lime and serpentine, added according to a (CaO+MgO) / Al2O3 mass ratio of 1.3:1, and hydrated lime added according to a (CaO:MgO) mass ratio of 0.3:1. The qualified green pellets are then dried (at a temperature of 40°C). The process involved heating at 0℃ for 5 minutes, preheating at 1000℃ for 15 minutes, and roasting at 1200℃ for 20 minutes to obtain flux-containing chromite pellets. These chromite pellets were then loaded into an electric furnace, with coke powder added (the mass ratio of coke powder to the chromite pellets was 85:15). Quartz sand was added according to a SiO2 / Al2O3 mass ratio of 1.3:1 in the slag after smelting. The smelting temperature was 1650℃, and the smelting time was 70 minutes, yielding high-carbon ferrochrome and chromium-containing slag. The chromium content in the resulting ferrochrome molten metal was 52.35%, and the chromium recovery rate reached 98.2%.

[0038] Example 4

[0039] A method for producing high-carbon ferrochrome by smelting ferrochrome ore in an electric furnace includes the following steps:

[0040] After crushing and grinding chromite and flux to -200 mesh ≥80%, bentonite (binder) and water are added and mixed evenly in proportion to form chromite green pellets. The raw chromite pellets contain 3% binder and 10% water by mass, with the remainder being chromite and flux (consistent with Example 2). The flux consists of limestone and dolomite, added according to a (CaO+MgO) / Al2O3 mass ratio of 1.3:1, and quicklime added according to a CaO to MgO mass ratio of 0.3:1. The qualified green pellets are then dried (at a temperature of 3°C). The process involves preheating (at 1100℃ for 10 minutes) and roasting (at 1300℃ for 10 minutes) to obtain chromite flux pellets. These chromite flux oxide pellets are then loaded into an electric furnace, with coke powder added (the mass ratio of coke powder to the chromite flux oxide pellets is 85:15). Silica is added according to a SiO2 / Al2O3 mass ratio of 1.0:1 in the slag composition after smelting. The smelting temperature is 1700℃, and the smelting time is 60 minutes, yielding high-carbon ferrochrome and chromium-containing slag. The chromium content in the resulting ferrochrome molten metal is 52.22%, and the chromium recovery rate reaches 98.1%.

[0041] Example 5

[0042] A method for producing high-carbon ferrochrome by smelting ferrochrome ore in an electric furnace includes the following steps:

[0043] After crushing and grinding chromite and flux to -200 mesh ≥80%, bentonite (binder) and water are added and mixed evenly in proportion to form chromite green pellets. The raw chromite pellets contain 1% binder and 9% water by mass, with the remainder being chromite and flux (consistent with Example 2). The flux consists of limestone and dolomite, added according to a (CaO+MgO) / Al2O3 mass ratio of 1.1:1, and quicklime added according to a CaO to MgO mass ratio of 0.4:1. The qualified green pellets are then dried (at a temperature of 3°C). The process involves heating at 1000℃ for 8 minutes, preheating at 1000℃ for 15 minutes, and roasting at 1250℃ for 15 minutes to obtain chromite flux pellets. These chromite flux oxide pellets are then loaded into an electric furnace, with coke powder added (the mass ratio of coke powder to the chromite flux oxide pellets is 85:15). Silica is added according to a SiO2 / Al2O3 mass ratio of 1.4:1 in the slag composition after smelting. The smelting temperature is 1630℃, and the smelting time is 60 minutes, yielding high-carbon ferrochrome and chromium-containing slag. The chromium content in the resulting ferrochrome molten metal is 52.12%, and the chromium recovery rate reaches 98.5%.

[0044] Comparative Example

[0045] A smelting test was conducted at a high-carbon ferrochrome smelter in the country to verify the effectiveness of the invention.

[0046] (1) Preparation of green chromite pellets: Chromite and coke powder are ground to -200 mesh ≥80%, then bentonite and water are added and mixed evenly in proportion to form green chromite pellets; wherein, by mass fraction, chromite accounts for 79.5%, coke powder accounts for 10%, bentonite accounts for 1.5%, and water accounts for 9.0%. Green chromite carbon-containing pellets are qualified with a drop strength greater than 3.0 times / 0.5m·p pellet and a compressive strength greater than 10N / p pellet.

[0047] (2) Oxidative roasting of chromite pellets: qualified carbon-containing chromite pellets are dried, preheated and oxidized, and then roasted in a rotary kiln. The drying temperature is 400℃ and the drying time is 8min. The preheating temperature is 1000℃ and the preheating time is 20min. The roasting temperature is 1250℃ and the reduction roasting time is 20min to obtain oxidized chromite pellets.

[0048] (3) Electric furnace smelting of chromite oxide pellets: The chromite oxide pellets are hot-charged into the electric furnace, and coke powder is added as a reducing agent. The particle size of the coke powder is 10mm~50mm>90%, and the amount of coke powder added is 10% of the mass of the pre-reduced pellets. Block silica, magnesite, and limestone (silica, magnesite, and limestone are all fluxes, and the flux particle size is 10-50mm) are added to the electric furnace to adjust the composition of the slag. The on-site electric furnace smelting parameters and effects are shown in Table 2.

[0049] Table 2 Results of a Smelting Test at a Certain Plant

[0050]

[0051]

[0052] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing high-carbon ferrochrome by smelting chromite in an electric furnace, characterized in that, Includes the following steps: Step 1: Preparation of chromite flux pellets Chromite pre-treated chromite, binder, calcium flux, and magnesium flux are mixed with water in a certain proportion and then pelletized to obtain chromite green pellets. The calcium flux and magnesium flux are added according to the mass ratio of (CaO+MgO) / Al2O3 in the chromite pellet composition of 1.0 to 1.5:1, and the calcium flux is added according to the mass ratio of CaO to MgO in the chromite pellet composition of 0.2 to 0.5:

1. After drying and high-temperature oxidation and consolidation treatment, chromite flux-oxidized pellets are obtained. The chromite pellets contain 85-92% chromite and flux by mass, 1-3% binder by mass, and 7-12% water by mass; the flux is composed of calcium-based and magnesium-based flux. Step Two: Electric Furnace Smelting Chromite fluxing oxide pellets, siliceous flux, and reducing agent are loaded into an electric furnace for smelting at a temperature of 1600-1700℃ for 60-90 minutes. High-carbon ferrochrome and slag can be obtained by separating the slag from the alloy.

2. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The grinding pretreatment methods include, but are not limited to, one or more of the following methods: ball milling, high-pressure roller milling, wet milling, vertical milling, etc.

3. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: After grinding pretreatment, the chromite particle size is ≥80% (-200 mesh) and the flux particle size is ≥80% (-200 mesh).

4. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The binder is one or more of bentonite, organic binders, and composite binders.

5. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The calcium-based flux includes, but is not limited to, one or more calcium-containing substances such as limestone, dolomite, quicklime, and high-calcium slag; The magnesium flux includes, but is not limited to, one or more magnesium-containing substances such as dolomite, magnesite, magnesium silicate, serpentine, and magnesium-containing slag.

6. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The methods for drying and high-temperature oxidation consolidation of chromite green pellets include chain grate-rotary kiln method, belt mill method, vertical furnace method, etc.; drying temperature: 200~400℃, drying time: 5~10min, preheating temperature: 800~1100℃, preheating time: 10~20min, roasting temperature: 1200~1300℃, roasting time: 5~20min.

7. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The reducing agent in the electric furnace smelting process includes, but is not limited to, one or more of coke powder, anthracite, and semi-coke.

8. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The silicon-based flux includes, but is not limited to, one or more silicon-containing substances such as silica, serpentine, quartz sand, and silicon-containing slag.

9. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The silicon-based flux is added according to a SiO2 / Al2O3 mass ratio of 1.0 to 1.5:1 in the slag composition after smelting.

10. A method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: Chromite flux oxide pellets and reducing agent are smelted in an electric furnace at a mass ratio of 80-90:10-20.

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