SPONGE IRON MANUFACTURING PROCESS
The reduction process is carried out in a rotary kiln (which is inclined and rotates at a pre-determined range of speeds) at a stipulated temperature (850oC – 1050oC). The inclination & the rotary motion of the kiln ensure that the raw materials move from feed-end to the discharge-end of the kiln and it is during this movement that the actual reduction of iron ore to iron takes place. The material discharged from the kiln is taken to a rotary cooler for cooling and the cooled product, after being discharged from the cooler moves on to the next step in the production process viz. product separation and handling system.
|For direct reduction of ore in the inclined rotary kiln, ore and coal normally pass through an inclined kiln in a counter current direction to the flue gases in the freeboard. The flat section, running nearly half the length of Kiln is called preheating Zone, where Iron Ore, Coal and Dolomite are heated up to reaction temperature. In this zone, moisture of the material is driven off. After material heating, ore reduction and carbon gasification takes place in close association with each other in the second half of the kiln, which is called reduction zone. The volatile constituents of the coal and carbon monoxide from the bed material are burnt, over the entire length of the kiln under controlled air supply, thereby providing necessary heat required for the metallization process. The basic reactions for the process are as follows:
The rotary kiln discharge is cooled in a rotary cooler connected to the kiln, screened and subjected to magnetic separation in order to remove the non magnetic material from the sponge iron,
Schematic line diagram / outlay indicating various sections including the positions of Kiln & WHRB boilers is as under
The overall process requires duration of approximately eight to ten hours inside the kiln, during which iron ore is optimally reduced and discharged to a rotary cooler for cooling below 120°C, before coming out into the finished product circuit, flowchart of the process is given below: