Preamble

Blast furnace iron making is an example in which both unit processes that is reduction of iron oxide and smelting to separate liquid pig iron from slag is done simultaneously in a single reactor. Height of the blast furnace is around 25 to 30m. It must be mentioned that blast furnace is a very efficient reactor both in terms of heat and mass exchange between solids and gases.

Blast furnace operation

In the blast furnace burden (consists of iron ore sinter/pellets +coke +limestone/lime) at 298K is charged from top. During its descent, there occurs heat and mass exchange with the hot gases which are moving up. Hot gases comprise of  and . Thus blast furnace is a counter- current heat and mass exchange reactor.

In approximately 75% of the total height of the blast furnace (i.e. from top to bottom of stack), reduction of iron oxide to Fe and decomposition of limestone occur. Burden permeability is very important for the smooth operation. Figure 26.1 is a schematic sketch of blast furnace showing inputs of charge materials

and outputs of products, slag and metal.

Burden permeability is controlled essentially by coke, since coke is the only component of the burden which is fused at the tuyere level. Rest of the components says  and limestone loses oxygen and hence there occurrence changes in size and shape during decent.

Blast furnace cannot work without coke. Since coke is not a natural resource, coke making is an integral part of blast furnace iron making. In view of the importance of coke, let me discuss coke making.

Functions of coke

Strength reactivity, chemical composition etc. are the important properties
Coke consumption varies from  of hot metal. Modern blast furnaces with pulverized coal injection work with  of hot metal.