JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year INSTRUMENTATION PRACTICES IN INDUSTRIES Previous Question Paper (February - 2022 - R18)

A blast furnace is a massive, vertical, steel-shell structure lined with refractory bricks used to extract molten iron from iron ore through a continuous reduction process. The furnace operates on the principle of counter-current exchange, where solid raw materials move downward while hot gases move upward.

The primary components include:

• Charge: A mixture of iron ore (hematite or magnetite), coke (fuel and reducing agent), and limestone (flux to remove impurities as slag) fed from the top.
• Tuyeres: Water-cooled nozzles located at the base that inject preheated air (blast) into the furnace.
• Hearth: The bottom section where molten iron and slag collect.

The working process involves the following chemical and physical stages:

1. Combustion: At the tuyeres, coke reacts with the hot blast to produce carbon dioxide and intense heat, raising temperatures to approximately 2000°C. This reaction provides the energy required for the furnace operations.
2. Reduction: As the hot gases rise, carbon dioxide reacts with more coke to form carbon monoxide. This carbon monoxide acts as a reducing agent, stripping oxygen from the iron ore as it descends, converting iron oxides into metallic iron.
3. Slag Formation: Limestone decomposes to form calcium oxide, which reacts with silica and other impurities in the ore to form a molten slag. This prevents the iron from re-oxidizing and protects the hearth.
4. Tapping: The molten iron, being denser, settles at the bottom, while the lighter slag floats on top. These are periodically removed through tapholes at the base of the furnace.

The process is continuous; raw materials are added at the top through a bell-and-hopper mechanism, and the furnace runs 24/7 until a relining is required. The waste gases, primarily nitrogen and carbon dioxide, exit from the top and are cleaned for further use or heat recovery.