Direct reduced iron
Direct reduced iron (DRI) or hot briquetted iron (HBI) has emerged as an important substitute of the scrap. DRI contain small amount( 0.02%)of tramp element; hence substituting DRI for scrap leads to dilution of tramp elements in steel.
DRI is produced by reduction of iron ore with carbon or gaseous reducing agent. The product of gaseous reductant is HBI.
DRI contains: Free iron +oxygen combined with iron+ free carbon+ gangue minerals  etc).
Quality of DRI is important. Quality of DRI can be judged in terms of metallization and oxygen remaining. Metallization (M) is defined as
 |
(1) |
Higher is the metallization, less oxygen would be required to remove oxygen from iron oxide of DRI during steelmaking.
Consider 1000kg iron ore of composition  and 20% gangue minerals. Reduction of iron ore produces DRI in which oxygen is present as  .
Metallization (%) |
Free iron (kg) |
Fe-FeO (kg) |
Gangue (kg) |
Oxygen with FeO(kg) |
80 |
448 |
112 |
200 |
32 |
85 |
476 |
84 |
200 |
24 |
90 |
504 |
56 |
200 |
16 |
95 |
532 |
28 |
200 |
08 |
|
We note from the table the following:
a) Increase in metallization increases free iron in DRI which is good.
b) Increase in metallization decreases iron which is combined with . Lower amount of heat and reductant would be required to recover iron of from DRI. Reduction of with C is endothermic. Energy is required to compensate for the endothermic reaction.
c) Increase in metallization decreases the gangue minerals in DRI. Gangue minerals would be recovered as slag; decrease in gangue minerals will decrease slag volume during production of steel using high metalized DRI as a charge material.
d) Because of b) and c), the overall effect would be decrease in electric consumption and reduced electrode wear.
|
