The previous blog described the alternative environment-friendly route to the conventional blast furnace known as the Corex process. It is a type of smelting reduction process which produces it by using non-coking coal instead of metallurgical coke, which is used by the Blast Furnace. The corex process consists of two parts namely Reduction stage and Melter-gasifier.
The Process Part-II
The iron ore with the additives is directly charged in the reduction stage to produce the DRI which is then discharged into the next stage called the Melter- Gasifier via speed controlled six discharge screw conveyors. The Melter gasifier stage mainly has three sections or zones which are namely:
- Gaseous freeboard zone
- Char bed zone
- Hearth zone
A fluidized bed exists between the char bed and the freeboard zone due to the continuous flow of gas through the char bed. It operates at a pressure range between 3- 5 kg/sq cm and consists an upper fluidized bed area at around 1500C and a lower melting and a liquid collection area at around 1550C. The first stage involves the creation of reduction gas by partial combustion of coal with oxygen which is injected through blast furnace type tuyeres gasifies the coal char which generates CO.
The heat of the gas is then transferred to the char bed, which is used for melting iron and slag. The hot metal and slag are collected in the hearth zone. The efficiency of the furnace depends mainly on the distribution of the gas in the char bed and utilization of heat of the gas. The dome temperature is maintained between 1000°C to 1100°C. The gas generated inside the melter-gasifier contains fine dust particles, which are separated using hot gas cyclones. The dust collected in the cyclones is recycled back to the melter-gasifier through the four dust burners which are located in the melter-gasifier above the char bed.
The gas from the melter-gasifier at the temperature range between 1,050-1,100 C is cooled to the reduction gas of temperature range between 800-850 C by the addition of cooling gas. The gas is then cleaned in a hot cyclone to recycle entrained fines. A portion of this clean gas is then introduced into the reduction shaft. The excess gas is mixed with the reduction shaft top gas and this mixture is called export fuel gas or Corex export gas, which is used for a range of applications like power generation, pressure control etc. The Corex gas has a calorific value around 2000 kcal/N cum.
Benefits in steel making
Compared to the conventional blast furnace, the advantages that make the corex process more beneficial are:
- Up to 20% lower CO2 emissions
- Lower production cost
- Higher calorific value of export gas
- Good operational flexibility