1. QUALITY OF CHARGE MATERIAL:
A blast furnace charge consists of coke, ore or sinter, and limestone. These materials must be in lumps of a certain size (40-60 mm). Larger lumps prolong the process of reduction and fluxing. Smaller lumps block the flue-gas passages and prevent a uniform descent of melting materials in the furnace.
2. IRON ORES:
Ore is a metal bearing mineral. The most important varieties of iron ore are:-
Magnetite or black iron ore.
Hematite or red iron ore.
Limonite or brown ore.
3. MANGANESE ORES:
Manganese ores are used for smelting ferromanganese, cast iron and pig iron containing about 1% Mn. Manganese is present in either of its following oxide and carbonites form:
Pyrosulite MnO2, braunite Mn2O3, hausmanniteMn3O4 and rhodochrosite MnCO3.
Fluxes are added to sinter or charged directly into the blast furnace in order to liquefy ore and sinter gangue and fuel ash, converting them to free flowing slag that can be run of the furnace. The flux is decided by the gangue and ash analysis.
The limestone is the most popular flux in blast furnace and sintering process. The limestone charged in the blast furnace must be in lumps (25-60 mm across), firm, not prone to fines and most important, free from harmful sulphur, phosphorus and silica.
5. UTILIZABLE WASTE:
Various metallurgical wastes high in iron or manganese are often utilized in a blast furnace burden. Some of important wastes are:
a. Blast furnace flue dust, which contains upto 45% Fe. It is therefore an important product for sintering plants where it is mixed with the charge to produce agglomerate.
b. Hearth cinder, is a rolling production waste from heating up steel billets in furnace. It contains about 50% Fe and is very low in sulphur and phosphorus.
c. Scale, it forms in rolling production and is removed from ingots and billets as they pass through roll stands.
Sometimes blast furnace operators utilize steel making mill slags, blast furnace waste, foundry scrap and machine building refuse such as metal chips, swarf, and fine scrap.