The document provides an overview of the ironmaking process, including:
- Coke making to produce pure carbon for the blast furnace
- Ore agglomeration through sintering or pelletizing to prepare the iron ore for the blast furnace
- The blast furnace which uses coke, iron ore, and flux to produce liquid iron through countercurrent reduction reactions at high temperatures
It describes the basic zones and reactions within the blast furnace to chemically reduce and physically convert iron oxides into liquid iron.
1. Primary Metals Production 2007
Part 4:
Ironmaking
Rob Boom
Metals Production, Refining and Recycling (MPRR)
Department of Materials Science and Engineering
2. Course contents
Ironmaking and Steelmaking
• Steelmaking process flow
• Coke making
• Agglomeration
• Ironmaking
• Steelmaking
• Secondary steelmaking
• Casting
4. Steelmaking process flow
gas coal ore
Sinter plant
Pellet plant
Raw materials transport
Coke plants Ore agglomeration
Gas Oxygen
Gas
Coal injection
Steam
Steel sheet
Air + Oxygen Slag
Iron
Power station Blast furnace Basic oxygen steel plant
18. Course contents
Ironmaking and Steelmaking
• Steelmaking process flow
• Coke making
• Agglomeration
• Ironmaking
• Steelmaking
• Secondary steelmaking
• Casting
19. Feed preparation: iron ore sintering
• Agglomeration techniques
• Pelletising: drum or pan (disk) pelletiser, with water, drying
and firing often needed, very popular
• Sintering: partial melting and re-solidification
• Why sintering?
• An agglomeration process
• Gases going thorough a charge of solids
• Permeability (packed bed)
• Why pelletising?
• An agglomeration process
• Fine ore (dust) not suited for direct charge to BF
• Transport and storage possible
• Additions to iron ore in pellet feed for metallurgical purposes
20. Feed preparation: sintering
• The Nature of Sintering
• Physical nature: partial melting, bridges vis-a-vis porosity.
• Strength and porosity, influenced by particle size, water content, coke
quality (size, reactivity)
• Chemical nature: self-fluxing, reduction (partial, oxides e.g. iron
ores)
• Heat source
• Coke particles for oxide ores (coke breeze)
• Sintering Capacity
• Suction duty (0.1-0.2 atm), ignition length, band speed, bed
permeability
• Sintering Equipment
• Grate sintering: Dwight-Lloyd sintering machine, most popular
30. Induration
To grinding section
Hot air
Stack
gas
Combustion air
Green balls in Drying cooling Cooling
Drying Induration Fired pelle
out
Hot air
Cold air
Stack
31. Sinter Plant
• Suction Area 354
m2
• High Basicity
• Screened at 4mm
• 4.4 million ton per
year
• EOS and Airfine
32. Sinter Strand with EOS System
EOS 50 % of flue gas
hearth sinter mix
layer ignition
Air for pO2
hood
flame front
sinter strand wind boxes
sinter crusher
flue gas sinter to cooler
to stack
37. Aim of the blast furnace process
• Reduce the iron oxide (30 wt% oxygen)
• Separate iron from waste rock (10 wt%)
• Remove the impurities
• Continuously produce liquid iron (hot metal)
Why not put ore directly in the BF?
• Size: < 1 mm
• Variable composition
• Calcination/dehydration are endothermic processes
• Metallurgical quality:
reducibility/disintegration/swelling/softening
38. Ironmaking blast furnace
• General information
• Dominant iron production process for steelmaking
• Oxygen steelmaking 60% (70% liquid iron + 30% scrap)
• EAF steelmaking 40% (100% scrap)
• Requiring sinter or pellets of ore, fluxing agent
(lime), high quality coke, compressed hot air
• Complex plant
39. Ironmaking blast furnace: How it works
• The purpose of a blast furnace is to chemically reduce and physically
convert iron oxides into liquid iron called "hot metal“
• The blast furnace is a huge, steel stack lined with refractory brick,
where iron ore, coke and limestone are dumped into the top, and
preheated air is blown into the bottom
• The raw materials require 6 to 8 hours to descend to the bottom of
the furnace where they become liquid slag and liquid iron
• The liquid products are drained from the furnace at regular intervals
• The hot air blown into the bottom of the furnace ascends to the top
in 6 to 8 seconds after going through numerous chemical reactions
• Once a blast furnace is started it will continuously run years with only
short stops to perform planned maintenance
• BF campaigns last 15-17 years, future 30 years
Source: http://www.thepotteries.org/shelton/blast_furnace.htm
43. Ironmaking blast furnace
• Daily consumption of a blast
furnace (10,000 ton/day hot metal)
• 16,000 – 20,000 ton iron ore
• 4,000 – 6,000 ton coke
• 2,000 – 4,000 ton flux
• 11,000 kNm3 compressed air
• Generating
• 4,000 – 5,000 ton slag
• 15,000 kNm3 top gas
Production of 1 ton hot metal
• 1.6 – 2.0 ton iron ore
• 0.4 – 0.6 ton coke
• 0.2 – 0.4 ton flux
• generate 0.4 – 0.5 ton slag
44. The ironmaking blast furnace
• How large a blast furnace
(c.a. 10000 t/d hot metal)
• Hearth diameter 14 m
• Height 46 m
• Volume 4450 m3
• Hot blast 1250 oC
6800 Nm3/h
45. Ironmaking blast furnace
Coke
• Raw materials to Blast furnace 25-70 mm
• Coke: size 40 – 60 mm Sinter
• Fixed carbon, S content, volatile 5-50 mm
• Ash content
• Sinter and pellets, or lumpy ores
• Strength, permeability
Pellets
• Fluxes 10-25 mm
• Basic: limestone, dolomite (10-50
mm)
• Acidic: silica (10-30 mm)
Lumpy ore
10-30 mm
46. Blast furnace: Principle in-out
Ore (Fe2O3) & coke (C) 25 °C Top gas (N2,CO2,CO) 150 °C
Layered burden
Cohesive zone
Coal (C) injection 35 m
Hot blast (N2+O2) 1200 °
2300°C
Raceway
dead man
Slag
Hot metal (Fe) 1500 °C
14 m
47. Blast furnace: Basic reactions gas/solids
Burden descent
Fe2O3+ CO « Fe3O4 « ‘FeO’ «
Fe + CO2
Heat
Chemical
exchange
reaction
C + CO2 « 2CO
Gas flow
C + O2 « CO
48. The ironmaking blast furnace
• Zones in BF
• Stack: 400 – 1000oC
• Preliminary reduction
• Thermal reserve zone
• Bosh: 1800oC
• Fusion
• Reduction
• Slag – metal equilibrium
• Tuyere: coke/coal combustion
• Hearth: 1400oC
• Slag – metal separation
• C-saturation
• Consumption of dead-man
• Stage-wise reductions:
• Fe2O3 → Fe
alles alles
oxide oxide ox. Fe oxide Fe
49. Reduction stages
alles
oxide oxide ox. Fe
Fe2 O3 Fe3O4 FeO Fe
alles
oxide Fe
Fe2O3 Fe3O4 FeO Fe
50. The Process
The Blast Furnace as a countercurrent mass and heat
exchanger
Gas Burden
ascent descent
2300°C
Dead Man
52. Blast furnace zones
Top
Gas Throat
Burden
Coke
Stack Shaft
zone
Cohesive zone
Active coke zone Belly
2300°C
Bosh
Raceway
Dead Man
Hearth
Taphole
53. Reductions and temperatures
>500 °C (wet zone): 150 °C
Fe2O3 + CO à Fe3O4 + CO2
Fe3O4 + CO à FeO + CO2
FeO + CO à Fe + CO2
>1100 °C (dry zone):
1100 °C
CO2 + C à 2CO
(Boudouard)
1450 °C
FeO + C à CO
Raceway: 2300°C
C + O2 à CO
H2O + C à H2 + CO
1500 °C
54. Burdening
PW CHUTE PW BELL
Moveable
armour
BF6 BF7
55. Smelting the burden: the tuyere
flame
2200°C,
CO, N2
(+H2)
Blast,
Blast CO, CO2
Coke (and coal):
C +1/2 O2 à CO
56. Blast furnace ironmaking
• The furnace gas: RTD~ 6-8 seconds
• Hot blast: via tuyere, preheated at 1000oC (hot stove)
• Generation CO: raceway, combustion of coke, pulverized
coal (coal injection): C+O2=2CO (due to Boudouard
reaction)
• Reduction of FexOy by CO, generating CO2 in the stack
• Top gas composition: 500oC, 26%CO+CO2+62%N2, 3
MJ/m3
• The solid charge: RTD 6-8 hours
• Primary reduction zone: higher oxides reduction,
• Thermal reserve zone: 1000-1200oC, only wustite stable!
• Fusion zone: 1200-1800oC, reduction to Fe metal,
melting, slag formation
• Coke is consumed in the raceway, but will stay in the
hearth (dead-man) for a very long time (many days)
• The liquid phases
• Liquid metal (Fe): from fusion/dripping zone
• Liquid slag phase: from fusion/dripping zone
• Other reactions: C-saturation (~4% via dead-man);
reduction of MnO, P 2O5, SiO2 as impurities to liquid iron
(Mn, P, Si, also S from coke) → “pig iron”
57. Blast furnace ironmaking
Iron (Fe) 93.5 - 95.0%
Products Silicon (Si) 0.30 - 0.90%
• Hot metal (pig iron) Sulphur (S) 0.025 - 0.050%
Manganese (Mn) 0.55 - 0.75%
• Temperature Phosphorus (P) 0.03 - 0.09%
1450-1550 °C Titanium (Ti) 0.02 - 0.06%
Carbon (C) 4.1 - 4.4%
• Liquid slag: SiO2-CaO-Al2O3 system
• Basic type and acidic type
• 25-35% SiO2
• 35-50% CaO
• 6-17% Al2O3
• Important for hot metal quality (e.g. S content)
58. Heat Balance
Loss
Coke Oven Gas
HBS
Heat from
combustion of BF Gas
Heat in hot blast
To Power Plant
Blast BF Heat in BF Gas
Heat in S
Furnace Gas
Heat from
gasification of
coke, coal, oil
Cooling Lo
Hot Metal Heat in Hot Metal
Heat of Formation
59. Pulverised coal injection
• Pulverised coal injection (PCI) to replace coke
• Grinding of suitable coal types
• Transport and injection by nitrogen carrier gas
• Oxygen enrichment to assist process
• PCI partial solution for coke batteries end-of-
life problem
• Corus IJmuiden leading in daily practice
62. Pressure drop versus coke rate
1200
Total
Column Upper
Total column
800
dP [mBar]
Upper
400
Middle
Middle
Low
Low
0
280 310 340 370 400 Hearth
Coke rate [kg/tHM]
63. World’s best performing blast furnace
BF6
Corus Strip
Products IJmuiden
Data 100 BF’s
Period 2005
64. Future trends in ironmaking
• The issues facing the blast furnace are
• external such as coke supply
• internal such as limitations on coal injection and
hearth life,
• influenced by phenomena in the various furnace
zones.
• The challenges to the blast furnace process
• Alternative steel production routes such as the integrated
DRI/scrap/EAF mode
• Alternative hot metal processes.
65. Alternative ironmaking
• Direction reduction
• Using solid fuels:
• SL-RN process, coal and rotary kiln
• Using gaseous fuels:
• Midrex, CO+H2 reductant, shaft furnace
(commercially popular)!
• Product: sponge iron (DRI), EAF steelmaking!
• Commercial processes
• Main problem: corrosion of sponge iron
• Smelting reduction
• Many process options
• not yet commercialized!
66. Pre-reduction and direct reduction
• Alternative ironmaking for steel production
• Nature of pre-reduction
• Iron (800oC): partial or complete reduction
• 3Fe2O3 + CO = 2Fe3O4 + CO2
• Fe3O4 + CO = 3FeO + CO2
• FeO + CO = Fe + CO2
• Chromite (FeCr2O4): at 1500oC, only partial reduction
• Sponge Iron: directly used for steelmaking
• Directly reduced iron (DRI)
• Increasing portion in total primary iron supply
• Solid Fuels:
• SL-RN Kiln: 7/3Fe2O3 + 6C =14/3Fe + CO+CO2
• Gaseous Fuels: CO and H2
• Midrex: shaft furnace, using CO+H2 mixture