37
IRONMAKING
DRI for low-emission steel production The topic of direct reduction ironmaking (DRI) has attracted much attention recently, especially in relation to the goal of reducing CO2 emissions in iron and steel production. By Dr. Joseph J. Poveromo* DRI is defined as the reduction of iron oxide to metallic iron without melting. Unreduced ore compounds remain as undesirable oxides. The iron oxide feedstock (Fe2O3) exits in the same form as it entered (pellets in, pellets out; lumps in, lumps out). Hot Briquetted Iron (HBI) refers to DRI that has been hot (1200°F, 650°C) briquetted to a high density pillow-shaped briquette, mainly to facilitate safe shipping and handling for merchant DRI production. DRI/ HBI is mainly used as a primary metallic feedstock in electric arc furnace (EAF) steelmaking in scrap-deficient regions such as the Middle East and North Africa (MENA) and as supplementary feed material in scrap-rich regions such as North America and Europe. HBI is also used selectively in blast furnaces and pneumatic steelmaking (BOF, LD) furnaces. DRI PROCESS FUNDAMENTALS – The reduction process itself proceeds in stepwise fashion: Fe2O3 + 3 CO = 2 Fe + 3CO2 2 Fe2O3 + 3 H2 = 2 Fe + 3H2O (Fe2O3 > Fe3O4 > FeO > Fe)
also be produced from coke oven gas, coal gasification, and Corex smelting top gases, as well as by self-reforming within the shaft. DRI process developers are now exploring switching to using H2 as the reductant, as part of the CO2 emissions reduction effort. The use of H2 is straightforward; the major
Prompt
pig hot
DRI/HBI
Scrap
iron
metal
Fe
98.0
94.5
93.0
Metallization, %
100
100
95
Metallic Fe
98.0
94.5
88.6
FeO
0
0
6.6
Carbon
0
4.5
1.5
Acidic gangue
1.0
1.0
2.2
Basic gangue, other
1.0
0
1.1
barrier is the current high cost of H2 gas; accordingly much research effort is being aimed at developing more economical methods of H2 gas production. Ore-based metallics DRI/HBI is one form of what are considered ore-based metallics (OBMs) that are used in EAFs. The other popular OBM is merchant pig iron, as produced in blast furnaces that produce hot metal, molten iron in liquid form, above 1370°C. Pig iron is simply solid hot metal. A comparison of the metallics charged to an EAF follows. It is clear that DRI/HBI is the disadvantaged relative to both scrap and pig iron with respect to total Fe, metallization, metallic Fe, and gangue levels; however DRI/HBI offers more potential for reduced CO2 emissions. Table 1.
Table 1.
Reductant:
coal-based
gas-based
Vessel: Iron Ore:
Rotary
Rotary
Fluid
Shaft
Fluid
Kiln
Hearth
Bed
Furnace
Bed
lump ore
fines
fines
pellets,
fines
fines
Midrex
FINMET
Flash Smelter
HyL
Iron Carbide
Primetals
fines
lump ore
For shaft furnace DRI processes, the above reducing gases, CO and H2, are most commonly produced from reforming (catalytic or steam) natural gas, but can
Process
SL/RN
Inmetco
Circofer
DRC Fastmet
others
Circored
Table 2. Direct Reduced Iron (DRI/HBI) processes
* Raw Materials & Ironmaking Global Consulting, Bethlehem, PA 18017, Tel: +1 (610) 442 3527 Email: joe.poveromo@rawmaterialsiron.com www.steeltimesint.com
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October 2020
20/10/2020 15:28:00