Introduction of DRI SL/RN Rotary kiln Process (non-smelting method)
Sponge iron also known as "Direct Reduced Iron (DRI)" has emerged as prime feed stock in In duction Furn aces, Electric Arc Furnaces and in other steel making processes replacing steel scrap. The advantages of melting sponge iron over scrap are as follows:
• Fixed chemical composition of sponge iron improves charging efficiency of Induction Melting Furnaces and produces consistent quality of steel.
• Low content of residual elements makes possible production of clean and high quality steel.
• Helps in dilution of tramp elements entering from scrap into steel.
• Easier feeding to Induction Furnaces.
• Protection against widely varying scrap prices.
• Less pollution generation when compared with scrap
Sponge iron is the product of solid state reduction of iron ores or pellets. Its principal constituents are metallic iron, residual iron oxides, carbon & impurities such as phosphorous & sulfur and gangue (principally silica and alumina). The final product can be in the form of fines and lumps.
PROCESS DESCRIPTION:
Direct reduction is defined as the process by which metallic iron is produced by reduction of iron oxide (iron ore or pellets) below the melting point of any material involved in the process. The product of direct reduction process is called Direct Reduced Iron (DRI) or Sponge Iron. Direct reduction processes are gaining importance because the product from the process has proved to be better substitute of the scrap for the following reasons:
• The chemistry of the scrap is not consistent. The tramp elements vary widely, while sponge iron as a manufactured product has constant quality.
• Bulk density of the scrap also varies widely.
The main equipments used in the process are Rotary kiln, Rotary cooler and waste gas handling machinery, cooling and cleaning system. The rotary kiln serves the following functions:
• A conveyor of solids.
• A heat exchanger.
• A vessel for carrying out complex chemical reactions.
Iron ore, coal and lime stone or dolomite are introduced into the Kiln at controlled rates through a feed pipe fixed at the feed end. Because of the Kiln is inclined, its rotation causes the iron ore and coal to mix and travel downward towards the exit. The rotational speed of the Kiln can be adjusted to maintain the desired loading of the kiln and provide the required time to complete the reduction of the iron ore.
The quantity of coal feed is adjusted to get the required degree of production and to sustain the process. Adjustment of coal quantity can be done from the both ends of the Kiln. The size fraction of the discharge end coal can also be adjusted to ensure required distribution of coal along the length of the kiln as per requirement and optimize coal consumption without effecting the quality of the product. These flexibilities in the system help to get consistently good quality product and longer campaign life.
The air is supplied through the air piping system by fans mounted on the Kiln radially. The air piping system also con tains on/off valves which open and close to admit air above the charge bed to aid combustion of over bed gases and achieve desired temperature profile. The iron ore is converted to DRI as it traverses along the length of the kiln.
Hot product discharges from the Kiln through a transfer chute to the rotary drum cooler. The cooler is an inclined steel cylinder. Water is poured along its outside surface to provide a heat sink to cool the product as it moves from the feed end to the discharge end of the cooler.
