Question

Outline the chemical reactions which occur in the iron blast furnace as the burden descends from the top of the furnace, until it reaches the top of the slag pool in the hearth. Refer to both direct and indirect reduction.

Explain in terms of chemistry and heat balances why the furnace is considered to consist of three distinct zones (Preheating zone, Indirect reduction zone, Direct reduction and melting zone).

Answer 1

The chemical reactions which occur in the iron blast furnace are,

C+O2→CO2

CO2+C⇌2 CO

In indirect reduction, indirect reduction of iron ores to iron by carbon monoxide takes place as follows(400 °C to 800 °C),

3 Fe2O3+ CO → 2 Fe3O4 + CO2

hematite magnetite

Fe3O4+ CO → 3 FeO + CO2

magnetite wustite)

FeO   + CO→ Fe+ CO2

wustite   iron

in direct reduction, direct reduction of iron ores to iron by carbon takes place as follows(800 °C to 1600 °C),

3Fe2O3 + C → 2 Fe3O4 + CO

hematite magnetite

Fe3O4 + C → 3 FeO + CO

magnetite wustite

FeO  + C → Fe + CO        

wustite iron

In carburisation, the enrichment of solid iron with carbon in a temperature range between 900 °C and 1200 °C happens as follows,

3Fe+ 2CO → Fe3C + CO2

3Fe   + C → Fe3C

The furnace is considered to consist of three distinct zones because of the heat required in each zones, according to the heat requirements temperature is maintained distinctly at three distinct zones. In the preheating zone the charge is preheated and dried. The functions of the indirect and direct heating zones are mentioned along with the chemical reactions. The temperature in the indirect reduction zone is of 400 °C to a maximum of 800 °C. The direct reduction takes place in the temperature zone between 800 °C to 1600 °C.