lectures%202007%20 ironmaking

Primary Metals Production 2007 Part 4: Ironmaking

Rob BoomMetals Production, Refining and Recycling (MPRR)Department of Materials Science and Engineering

Course contentsIronmaking and Steelmaking

• Steelmaking process flow• Coke making• Agglomeration• Ironmaking• Steelmaking• Secondary steelmaking• Casting

Steelmaking process flow

Steelmaking process flow

Coke plants Coke plants

coalgas

Ore agglomerationOre agglomeration

Gas

Oxygen

Steel sheet

Basic oxygen steel plantBasic oxygen steel plant

Steam

Air + Oxygen

Raw materials transport

oreSinter plant

Pellet plant

Power stationPower station Blast furnaceBlast furnace

Iron

Coal injection

Gas

Slag

Ironmaking process flow


• Steelmaking process flow• Cokemaking• Agglomeration• Ironmaking• Steelmaking• Secondary steelmaking• Casting

Coal stock area

Cross-section coke plant

In the coke ovens coal is being processed to get pure carbon fit for the BF

Coke battery

Charging

Level bar

Gas pressure

The ‘Plastic’ Layer

Pushing coke

Transport to quench tower

Transport screening

To Blast Furnace

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

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

Sintering Equipment: grate sintering

Iron ore sintering process

Layering

Principle Chevron method

Cross section

RakeBucket wheel

Reclaiming

Longitudinal section

Layering

Reclaiming

Reclaimer

Pellet Plant

• Dry grinding• Straight grate induration

strand 430 m2

• Acid, olivine doped• 4.6 million ton per year

Pellet plant lay-out

Grinding

Balling

Induration

Grinding and balling

Induration

Drying Drying Indurationcooling Cooling

gas Combustion air

To grinding section

Hot air

Cold airHot air

Stack

Stack

Green balls inFired pellets

out

Sinter Plant

• Suction Area 354 m2

• High Basicity• Screened at 4mm• 4.4 million ton per

year• EOS and Airfine

Sinter Strand with EOS System

sinter crusher

sinter to cooler

sinter mixhearthlayer

flame front

wind boxes sinter strand

flue gasto stack

Air for pO2ignitionhood

EOS 50 % of flue gas

Sinter Strand with EOS

Summary: ore preparations

Ironmaking

Why not put ore directly in the BF?• Size: < 1 mm• Variable composition• Calcination/dehydration are endothermic processes• Metallurgical quality:

reducibility/disintegration/swelling/softening

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)

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

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

Blast furnace plant

BF Development IJmuiden

Blast Furnace No.

Hearth diameter

Built

Initial productivity

Last renovation

Campaign overview

Production

Current/last production

Demolished

m

t/day

Mt

t/day

1

5.6

1924

280

800

1974

2

5.6

1926

280

800

1974

3

5.8

1930

360

1200

1991

4

8.5

1958

1380

3600

1997

5

9

1961

1700

3600

1997

6

11

1967

3000

2002

’86-’02

34.2

7000

7

13.8

1972

5000

1991

’91-pr.

36.3

10500


• 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

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


• Raw materials to Blast furnace• Coke: size 40 – 60 mm

• Fixed carbon, S content, volatile• Ash content

• Sinter and pellets, or lumpy ores• Strength, permeability

• Fluxes• Basic: limestone, dolomite (10-50

mm)• Acidic: silica (10-30 mm)

Lumpy ore10-30 mm

Pellets10-25 mm

Sinter5-50 mm

Coke25-70 mm

Blast furnace: Principle in-out

Raceway

Ore (Fe2O3) & coke (C) 25 °C

Cohesive zoneCoal (C) injection

Hot blast (N2+O2) 1200 °C

Hot metal (Fe) 1500 °C

dead man

2300°C

Slag

Top gas (N2,CO2,CO) 150 °C

Layered burden

14 m

35 m

Blast furnace: Basic reactions gas/solids

Fe2O3+ CO « Fe3O4 « ‘FeO’ «

Fe + CO2

Burden descent

Chemicalreaction

Heatexchange

Gas flowC + OC + O22 « COCO

C + CO2 « 2CO

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

oxide oxidealles Feox.

Fe3O4Fe2O3 FeO Fe

oxidealles Fe

Fe2O3 FeFe3O4 FeO

Reduction stages

oxide oxidealles Feox.

Fe3O4Fe2O3 FeO Fe

oxidealles Fe

Fe2O3 FeFe3O4 FeO

The Process

The Blast Furnace as a countercurrent mass and heat exchanger

Burdendescent

Gasascent

Dead Man

2300°C

BF as counter-current reactor

Dead Man

2300°C

Burden

Coke

Cohesive zone

Active coke zone

Raceway

Taphole

Top Gas

Hearth

Shaftzone

Belly

Throat

Bosh

Stack

Blast furnace zones

Reductions and temperatures

2300°C

1500 °C

1450 °C

1100 °C

150 °C>500 °C (wet zone):Fe2O3 + CO à Fe3O4 + CO2

Fe3O4 + CO à FeO + CO2

FeO + CO à Fe + CO2

>1100 °C (dry zone):CO2 + C à 2CO (Boudouard)FeO + C à CORaceway:C + O2 à COH2O + C à H2 + CO

PW CHUTE PW BELL

Moveable armour

Burdening

BF6 BF7

Smelting the burden: the tuyere flame

BlastBlast,CO, CO2

2200°C,CO, N2(+H2)

Coke (and coal):

C +1/2 O2 à CO

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 Boudouardreaction)

• 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, P2O5, SiO2 as impurities to liquid iron (Mn, P, Si, also S from coke) → “pig iron”

Blast furnace ironmaking

Products• Hot metal (pig iron)

• Temperature1450-1550 °C

• 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)

4.1 - 4.4%Carbon (C)

0.02 - 0.06%Titanium (Ti)

0.03 - 0.09%Phosphorus (P)

0.55 - 0.75%Manganese (Mn)

0.025 - 0.050%Sulphur (S)

0.30 - 0.90%Silicon (Si)

93.5 - 95.0%Iron (Fe)

Heat Balance

BlastFurnace

Heat in Hot MetalCooling Losses

Heat in SlagHeat in BF Gas

Loss

Heat of Formation

Heat fromgasification ofcoke, coal, oil

To Power Plant

Hot Metal

HBS

Heat in hot blast

Heat fromcombustion of BF Gas

Coke Oven Gas

BF Gas

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

Coal Injection

) Injection at Tuyeres(Gasification)

Tuyere injection arrangement

Pressure drop versus coke rate

Upper

Low

Middle

Hearth

To

tal

colu

mn

Low

Middle

400Coke rate [kg/tHM]

280 310 340 3700

400

800

1200dP

[mBa

r]

Upper

Total Column

World’s best performing blast furnace

BF6

Corus Strip Products IJmuiden

Data 100 BF’s

Period 2005

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.

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!

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

Midrex

Production of directly reduced iron (DRI) Midrex – dominating process

FIOR (+Circored/Circofer)

Cyclone Converter Furnace CCF

fine ore and

oxygen

stirring gas

coal

oxygen

hot metal

and slag

End of the lectureIronmaking

lectures%202007%20 ironmaking

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