Question

Inner layer of blast furnace is made of
A. Graphite
B. Silica bricks
C. Fire-clay bricks
D. Basic bricks

Answer 1

Hint: Blast furnace (metallurgical furnace) is used for smelting to form industrial metals such as pig iron, lead, or copper. Therefore the inner wall of a blast furnace is to be made of high-quality bricks to protect the furnace shell. The word ‘blast’ gives us an idea about the combustion of air that is forcefully happening at high atmospheric pressure.

Complete Step by Step Answer:
Metallurgical blast furnace produces pig iron from iron ore by the reducing action of carbon at a very high temperature and in the presence of a fluxing agent like limestone. It produces liquid metal form into the bottom of the furnace which consists of a mixture of coke, metallic ore, etc.

Generally, a blast furnace consists of several zones such as a crucible-shaped hearth at the bottom of the blast furnace, an intermediate zone between the hearth and stack, a vertical shaft that extends from the bosh to the top of the furnace, and the top of furnace consists of a mechanism for charging the furnace.

The furnace charge, Coke and flux descend through a shaft that is preheated and react with ascending reducing gases to produce liquid iron and slag which accumulate in the hearth. Also the preheated air reacts with preheated coke and thus produces carbon monoxide and a very high temperature (${{3000}^{{\mathrm O}}}F$).

The inner layer of the blast (stack) is made with high-quality fire-clay bricks to protect the furnace shell. Fire-clay can tolerate high temperatures and it has low thermal conductivity properties.
Thus, option (C) is correct.

Note: There is another brick named carbon brick used in the outside combustion chamber as it is capable of withstanding the internal heat of the combustion chamber and composite refractory material with more slag resistance capability and low expansibility of carbon.