BLAST FURNACE

Extraction of Iron: Understanding the Blast Furnace Process

Introduction to Iron and Its Significance

• The module aims to explain the extraction process of iron and describe various parts of a blast furnace.

• Iron is the most widely used metal due to its strength and low cost; it is also the most abundant metal in Earth's crust.

• In nature, iron exists in chemical combinations with elements like oxygen, sulfur, and carbon, primarily found in minerals such as hematite and magnetite.

Overview of the Blast Furnace

• A blast furnace is a tall structure (30-40 meters high) designed for extracting metals from their compounds using reducing agents.

• It features a double cup-and-cone arrangement for introducing charge materials—coke, concentrated iron ore, and limestone.

• The furnace has three outlets: one for exhaust gases at the top and two at the base for molten metal and slag.

Functioning of the Blast Furnace

• Hot air is blown into the furnace through nozzles called tuyeres; this process is known as "blasting."

• Before entering the furnace, iron ore undergoes preliminary treatments like concentration (removing impurities known as gang).

Preparation of Iron Ore

• The ore is crushed into small pieces, powdered, washed to remove lighter impurities, then subjected to calcination.

• Calcination involves heating ores in air to convert non-oxide compounds into oxides while removing moisture and organic matter.

Smelting Process

• The roasted ore is mixed with coke (fuel that converts to carbon monoxide during reduction) and limestone (flux that forms slag).

• As hot air enters from below, coke burns producing heat; this region is termed "zone of combustion," reaching temperatures around 2000°C.

Chemical Reactions in Zones

• Carbon dioxide produced reacts with unburned coke to form carbon monoxide; limestone decomposes into quicklime.

• Quicklime combines with impurities forming liquid calcium silicate or molten slag that floats on top of molten iron.

Final Stages of Extraction

• In the "zone of fusion," molten slag collects at the bottom while iron descends through hotter regions where it melts.

Iron Production Process

Understanding Pig Iron

• The term "pig iron" refers to the brittle iron obtained from a blast furnace, which cools and solidifies in molds.

• The name originates from historical practices where molten iron was poured into a common runner, resembling a sow feeding piglets; the molds represented the piglets.

• Solidified iron ingots removed from these molds were thus called "pigs," highlighting the connection between production methods and terminology.

Gas Management in Iron Production

• Unused gases such as carbon monoxide, nitrogen, and carbon dioxide are expelled through an outlet at the top of the furnace.

• These gases pass through a dust catcher that removes particulates before being released or reused.