GAS BASED SPONGE IRON TECHNOLOGY
The gas based process works on counter current principle. The gases pass through the solid charge. The solid charge is rotated in a vertical kiln and gas passes through the charge.
Heat is provided for reduction reaction and carbon is converted into carbon monoxide.
In this process oxygen is separated from the iron ore. The exhaust gas is cleaned and reused.
The metallic content of sponge iron produced by gas based process may go up to 90%.The level of dust pollution is very less in this process. Both lumpy ores and ore fines are used
in this process.
FLUIDISED BED PROCESS
Iron ore fines and pellets are mostly used in this process for production of sponge iron. Natural gas and coal are reducing agent. The reduction is carried out in four fluidized bed
reactors. The first reactor preheats the ore. The reduction starts in the second reactor and continues in the third reactor. The reduction completes in the fourth reactor. The
temperature is maintained around 800'C. Hydrogen released from natural gas and steam helps in faster reduction. The quality in sponge iron produced in this process is also very good.
COAL BASED PROCESS
The coal based process uses non coking coal, iron ore and some amount of lime stone. Non coking coal is produced to provide heat and to produce carbon monoxide as the reducing gas.
The coal particle with iron ore and lime stone are heated by an oil burner inside a rotary kiln. When coal particles are heated, carbon monoxide is produced and acts as the reducing gas.
The iron ore is reduced and oxygen is separated to produce metallic iron ore concentrate. The metal content may go beyond 90 %. A long rotary kiln slightly inclined to the horizontal rotates slowly around its own axis.
The rotary kiln acts as the reactor for reduction reaction. The charge of iron ore, coal and lime stone is fed from the end which is at a higher level. The charge travels under gravity
and aided by rotary motion. The reduction is slow and continuous. It takes place over the full length of the kiln. In this process iron oxide gets heated to a maximum of 1100'C. The
temperature is maintained using auxiliary burners. The quality of sponge iron is dependent upon quality of raw materials used in the rotary kiln. The optimum size of the ore used in
the kiln is 8-20 mm. The ore fines are pelletized and used with lumpy ores. The sponge iron produced under the system is separated from the gangue materials by magnetic separator.
GASIFIED COAL BASED PROCESS
The coal is gasified and used along with steam for reduction reaction. The iron ore is reduced by the coal gas and steam. The reduction is fast and clean.
Rotary kiln and vertical kiln are used for producing sponge iron under this process. The saving of energy is high in comparison to other process. But the control mechanism is
comparatively complex.
The use of sponge iron for producing steel and foundry grade pig iron created new opportunities in the iron and steel sector. Use of coal, coal gas, natural gas and steam provided scope for use of fuel to produce sponge iron with reduced cost. Due to the short supply of quality iron ore, low grade iron ore is used to improve the metal content through the direct reduction process. Use of sponge iron in the electric arc furnace has created a new raw material base along with scrap for secondary steel units. Local requirements of steel and steel products are met by use of sponge iron as raw material in place of steel scrap.