What is the Process of Smelting Ferro Alloys?

What is the Process of Smelting Ferro Alloys?

Ferrous Alloy Smelting Process

The ferroalloy production process by ferro alloy furnaces  is in which the charge, reducing agent, slag, and composition regulator undergo physical and chemical changes at high temperatures to generate alloy, slag, and furnace gas. To ensure that its changes proceed in the required direction, certain smelting ferro alloy furnace equipment, correct operations.

Ferroalloy Overview

Provide necessary heat. There are many varieties of ferroalloys, the raw materials are complex, and the physical and chemical properties of the extracted alloy elements vary greatly. Hence, the production methods used are also different.

Ferroalloy Production Methods

Sort By The Device Used

The different equipment used, can be divided into the blast furnace method, submerged arc furnace method, electric arc furnace method, outside furnace method, vacuum resistance furnace method and oxygen converter method.

(1) Blast furnace method. 

The blast furnace method is the most commonly used method for large-scale industrial production of ferroalloys. The blast furnace method for smelting ferroalloys has a high yield and low cost. Smelting is carried out using the heat generated by burning coke. Coke is not only a fuel but also a reducing agent.

The structure of the ferromanganese blast furnace is shown in Figure 1-1. During smelting, manganese ore, coke, and flux are loaded into the furnace from the top of the furnace. High-temperature air or oxygen-enriched air is blown in through the tuyeres to burn the coke at high temperatures for the reduction reaction. The molten metal and slag are concentrated in the furnace and pass through the slag. , the taphole is regularly discharged with slag and iron is tapped. As the charge melts and sinks, new materials are continuously added from the top of the furnace, and production is carried out continuously.

Because the furnace temperature is low and the alloy is carburized more, the blast furnace method is mainly used to produce high-carbon ferromanganese. In recent years, oxygen-rich high-temperature and other processes have been used to smelt low-grade silicon-manganese alloys in blast furnaces. This process can be used in areas with insufficient power.

(2) Submerged arc furnace method. 

Ore reduction furnaces (referred to as submerged arc furnaces) are commonly used in electric furnaces used to produce ferroalloys using carbon as a reducing agent. The submerged arc furnace method is the main method for ferroalloy production. About 72% of ferroalloy production is produced by this method. The source of heat during the smelting process is electrical energy, and carbon is used as the reducing agent. Figure 1-2 is a cross-sectional view of a submerged arc furnace.

During smelting, add the mixed raw materials from the furnace mouth. Three electrodes are buried in the furnace charge and rely on the resistance heat generated by the arc and current passing through the furnace charge for heating, and the iron and slag are regularly tapped through the tap hole. As the charge sinks, new materials are continuously added from the furnace's mouth, and production is carried out continuously.

Depending on the type of smelting, the furnace materials used are also different. For example. The raw materials used for smelting ferrosilicon mainly include silica, coke, and steel scraps; for smelting high carbon ferromanganese and other smelting processes, the raw materials used are not only ore and reducing agent coke but also need to add flux caO, etc. The varieties smelted include ferrosilicon, calcium silicon alloy, industrial silicon, high carbon ferromanganese, high carbon ferrochromium, silicon manganese alloy, etc.

(3) Electric arc furnace method. 

Electric arc furnaces are usually used to produce ferroalloys, using silicon (mainly silicon alloys) as a reducing agent. The heat source is electrical energy and chemical reaction heat.

Figure 3 is a simplified diagram of the tiltable refining furnace. The charge is loaded into the furnace from the top or door. The entire smelting process can be divided into five stages: arc ignition, charging, melting, refining, and tapping. The smelting process is completed by relying on the reaction heat of arc heat and silicon oxidation. After smelting is completed, the alloy and slag are poured into the bag together, and production is carried out intermittently.

The main raw materials used in electric arc furnace production include ores (including concentrates or relatively pure oxides), siliceous reducing agents, and fluxes. The main varieties currently produced include rare earth ferrosilicon alloys, medium and low carbon ferromanganese, medium and low carbon ferrochromium, ferrovanadium, and ferroniobium.

(4) Outside the furnace method. 

The outside-furnace method generally produces alloys or pure metals with high melting points, difficult to reduce, and extremely low carbon content. The smelting equipment used is

el furnace, the heat source is chemical reaction heat, and the production is intermittent. Figure 1-4 is a schematic diagram of a simple furnace using the external furnace method.

The raw materials used in smelting include concentrate or pure oxide, reducing agents (ferrosilicon, aluminum), flux (lime, fluorite), steel scraps, iron ore, and exothermic agent. Before smelting, the charge must be crushed, dried, mixed according to a certain proportion and sequence, and then loaded into the furnace. Use an igniting agent (composed of saltpeter, magnesium chips, and aluminum particles) to ignite the fire, and rely on the heat of the reaction to obtain a high temperature to complete the reduction process. Therefore, a certain calorific value must be achieved to

Ensure the high temperature required for the reduction process.

The varieties produced by the outside-furnace method mainly include ferromolybdenum, ferrotitanium, metallic chromium, ferroboron, ferroniobium, high ferrovanadium, etc.

(5) Vacuum resistance furnace method. 

Smelting is carried out in a vacuum resistance furnace, the heat source is mainly resistance heat, and production is intermittent. The cross-sectional view of the vacuum resistance furnace is shown in Figure 1-5.

During smelting, the mixture of high-carbon ferrochromium powder is pressed into a block shape and loaded into the furnace. The charge is heated by resistance heat when an electric current passes through the electrode, and gas is extracted at the same time. The decarburization reaction is carried out in a vacuum solid state at about 1300C. During smelting, the pressure in the furnace is generally 70O900 Pa. After smelting is completed, the alloy is taken out from the end furnace door of the horizontal cylindrical resistance furnace.

The varieties produced by vacuum resistance furnaces are mainly micro-carbon ferrochromium with extremely low carbon content (C content is less than 0.03%). It can also produce nitrogen-containing iron alloys, etc.

(6) Oxygen converter method. 

This is a newly developed ferroalloy production method with high productivity. Oxygen converters include side-blowing, top-blowing, and top-bottom combined-blowing converters according to oxygen supply methods. The production is intermittent. The oxygen top-blown converter is a cylindrical tiltable furnace built with refractory materials. Its structure is shown in Figure 6. The raw materials used in the converter are liquid high-carbon ferrochromium or high-carbon ferromanganese and a small amount of flux. During smelting, the liquid high-carbon alloy is mixed into the converter, and high-purity oxygen is blown into the furnace through the oxygen lance for smelting. The heat released by the silicon-carbon oxidation reaction is used for decarburization. The endpoint of the blowing is determined based on the changes in the flame emerging from the furnace. , after smelting is completed, pour the alloy and slag into the bag together. Smelting is intermittent.

The varieties produced include: medium and low carbon ferrochrome, medium and low carbon ferromanganese, etc.

Classification According To Process Characteristics

According to the different operating characteristics of the production process, it can be divided into flux-free method and flux method.

Ferroalloys produced by the flux-free method generally use carbonaceous materials as reducing agents. 

No slag-making materials are added during production to adjust the composition and properties of the slag. For example, ferrosilicon, calcium silicon alloy, industrial silicon, etc. are smelted by the slag-free method. 

The reducing agent used to produce ferroalloys by the flux method can be carbonaceous materials, silicon, or other metals. 

During production, flux must be added to make slag to adjust the composition and properties of the slag. 

Due to different production varieties, commonly used fluxes include lime, dolomite, and fluorite.  Ferrochromium, ferromanganese, etc. are commonly smelted by this method. Sometimes it can also be divided into slag method and micro-slag method according to the amount of slag produced during production.

Classification By Heat Source

Different heat sources can be divided into the carbothermal method, electrothermal method, electrosilicothermal method, and metal thermal method.

The heat source of the carbothermal method's smelting process is mainly the combustion heat of coke. Part of the coke is also used as a reducing agent to reduce oxides in the ore. Production is carried out in a blast furnace.

The heat source of the smelting process of the electrothermal method is mainly electric energy. Carbonaceous materials are used as reducing agents to reduce oxides in the ores. The production is mainly carried out in a submerged arc furnace in a continuous manner, such as ferrosilicon, ferromanganese, etc.

The electrosilicothermal method uses silicon or the silicide of the alloy element to be extracted.