A Brief Introduction of Rotary kiln
Rotary kiln is a commonly used production equipment in modern industrial production. It is widely used in chemical industry, building materials, non-ferrous metallurgy, ferrous metallurgy and other industries, such as: drying and oxidation roasting of materials in the chemical industry; drying of raw materials in the building materials industry and dolomite roasting; oxidative desulfurization of raw materials in the nonferrous industry, synthesis of reagents; drying of ore powder, preparation of smelting flux, production of oxidized pellets, production of direct reduced iron, and smelting of ferronickel in the steel industry.
The rotary kiln direct reduction method is to reduce the iron oxides to metallic iron by placing the raw materials in the rotary kiln without melting or slagging. The product basically maintains the form of the raw material and contains all the impurities of the raw material, with metallic iron as the main component. "Direct reduced iron (DRI)" is commonly known as "sponge iron" because of its "sponge"-like structure and body density <20g/cm3. The rotary kiln is one of the important reactors in "non-blast furnace ironmaking" technology. Among modern direct reduction technologies, the production capacity of the rotary kiln direct reduction method accounts for more than 20% of the world's total direct reduced iron (DRI) production capacity. Currently, there are hundreds of rotary kiln direct reduced iron production lines in operation in the world.
Classification of rotary kiln (based on the shape differences of materials)
1. Preheating and prereduction rotary kiln
The materials in the rotary kiln are preheated, dried, crystallized water removed, carbonate decomposed, and iron minerals partially reduced. The maximum temperature in the kiln is usually not greater than 1000C. Usually, the preheating and prereduction rotary kiln is a link in the entire process, such as: preheating and prereduction rotary kiln-ferro-nickel production by submerged arc furnace method.
2. Directly restore the rotary kiln
The highest temperature of the furnace charge in the kiln is 100~150C lower than the lowest "start softening temperature" of the material. The materials in the kiln are in a completely solid state, and the reduction process is completed without melting or slagging. The product basically retains the shape when it enters the furnace. It becomes "direct reduced iron" with metallic iron as the main component and impurities included.
3. Deep reduction kiln
The highest temperature of the charge in the kiln is slightly higher than the softening start temperature (the temperature when it shrinks by 3% under load reduction conditions) and the lowest softening start temperature value of the material, but lower than the softening temperature of the charge (when it shrinks by 30% under load reduction conditions) temperature). The material in the kiln undergoes a reduction reaction and at the same time produces a solid-phase slagging reaction, but does not melt. The material appears as a sintered block, similar to the shape of the material in the rotary kiln for cement clinker production. The iron in the materials discharged from the rotary kiln is in the form of metal particles >0.10mm distributed in the material clumps. The reduced briquettes are quenched with water and magnetically separated to obtain the product - fine granular metallic iron.
4. Granulated iron rotary kiln
After the charge enters the kiln, after drying, preheating, reduction of iron minerals, and slagging of the charge, the iron minerals are finally reduced to metallic iron, and are evenly suspended in the semi-molten slag in the form of 1.230mm iron particles. The semi-molten "clumps" wrapped in granular metallic iron particles are continuously discharged from the rotary kiln from the discharge end. Then, the product - granular metallic iron is obtained through water quenching, selective crushing and magnetic separation.
5. Molten state rotary kiln (pig iron cement method rotary kiln)
Using high alkalinity alkaline iron-containing materials as raw materials and coal as reducing agent, the raw materials are dried, preheated and iron minerals reduced in the kiln, and the charge finally forms molten iron and liquid slag in the rotary kiln. The molten iron is regularly discharged from the taphole at the lowest point of the rotary kiln, and the liquid slag is discharged from the discharge end of the rotary kiln. Because the slag can be used as cement clinker raw material after cooling, this method is called pig iron cement method (Baseet method). This method is suitable for processing alkaline ores, and the molten iron produced has extremely low S and P and can be used for casting. This method was eliminated due to the small production capacity of a single machine, high consumption of refractory materials, and difficulty in operation.
