JNTU B.Tech III IRON MAKING Previous Question Paper (October - 2020 - R16)

In iron making, coke and limestone are essential raw materials charged into the blast furnace, each serving distinct chemical and physical functions critical to the reduction of iron ore.

Role of Coke: Coke serves as the primary fuel and the main reducing agent in the blast furnace. Its functions include:

• Fuel: Coke burns in the oxygen-rich blast at the tuyeres to produce heat through an exothermic reaction, maintaining the high temperatures required for melting iron and slag. The reaction is:
  C + O₂ → CO₂ + Heat
• Reducing Agent: The CO₂ produced reacts with more coke to form carbon monoxide (CO), which is the primary gas responsible for reducing iron oxides to metallic iron. The reaction is:
  CO₂ + C → 2CO
• Structural Support: Coke provides the necessary permeability in the furnace burden. As it is a strong, porous material, it maintains the bed structure, allowing the upward flow of hot gases and the downward flow of molten metal and slag.
• Carburization: Coke provides the carbon that dissolves into the molten iron, lowering its melting point and forming pig iron.

Role of Limestone: Limestone (CaCO₃) acts as a fluxing agent to manage the impurities present in the iron ore and coke ash. Its functions include:

• Slag Formation: Iron ore contains acidic gangue materials like silica (SiO₂) and alumina (Al₂O₃). Limestone decomposes at high temperatures to form calcium oxide (CaO), which reacts with these acidic impurities to form a liquid slag. The reaction is:
  CaCO₃ → CaO + CO₂
  CaO + SiO₂ → CaSiO₃ (Slag)
• Desulphurization: The basicity provided by CaO helps in removing sulfur from the molten iron, as sulfur has a higher affinity for the basic slag than for the molten metal.
• Viscosity Control: By forming a slag with a controlled melting point and fluidity, limestone ensures that the slag can be easily tapped from the furnace hearth, preventing the accumulation of solid impurities that could block the furnace.