Lectures%202007%20 ironmaking
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    Lectures%202007%20 ironmaking Lectures%202007%20 ironmaking Presentation Transcript

    • Primary Metals Production 2007 Part 4: Ironmaking Rob Boom Metals Production, Refining and Recycling (MPRR) Department of Materials Science and Engineering
    • Course contents Ironmaking and Steelmaking • Steelmaking process flow • Coke making • Agglomeration • Ironmaking • Steelmaking • Secondary steelmaking • Casting
    • Steelmaking process flow
    • 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
    • Ironmaking process flow
    • Course contents Ironmaking and Steelmaking • 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
    • Course contents Ironmaking and Steelmaking • Steelmaking process flow • Coke making • Agglomeration • Ironmaking • Steelmaking • Secondary steelmaking • Casting
    • 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 Layering Reclaiming Rake Bucket wheel Longitudinal section
    • 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 Induratio Balling Grinding
    • Grinding and balling
    • 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
    • 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 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
    • Sinter Strand with EOS
    • Summary: ore preparations
    • Course contents Ironmaking and Steelmaking • Steelmaking process flow • Coke making • Agglomeration • Ironmaking • Steelmaking • Secondary steelmaking • Casting
    • Ironmaking
    • 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
    • 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
    • Blast furnace plant
    • BF Development IJmuiden Blast Furnace No. 1 2 3 4 5 6 7 Hearth diameter m 5.6 5.6 5.8 8.5 9 11 13.8 Built 1924 1926 1930 1958 1961 1967 1972 Initial productivity t/day 280 280 360 1380 1700 3000 5000 Last renovation 2002 1991 Campaign overview ’86-’02 ’91-pr. Production Mt 34.2 36.3 Current/last production t/day 800 800 1200 3600 3600 7000 10500 Demolished 1974 1974 1991 1997 1997
    • 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
    • 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
    • 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
    • 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
    • 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
    • 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
    • Reduction stages alles oxide oxide ox. Fe Fe2 O3 Fe3O4 FeO Fe alles oxide Fe Fe2O3 Fe3O4 FeO Fe
    • The Process The Blast Furnace as a countercurrent mass and heat exchanger Gas Burden ascent descent 2300°C Dead Man
    • BF as counter-current reactor
    • 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
    • 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
    • Burdening PW CHUTE PW BELL Moveable armour BF6 BF7
    • Smelting the burden: the tuyere flame 2200°C, CO, N2 (+H2) Blast, Blast CO, CO2 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 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”
    • 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)
    • 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
    • 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 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]
    • 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
    • Corex
    • FIOR (+Circored/Circofer)
    • Cyclone Converter Furnace CCF fine ore and oxygen oxygen coal hot metal and slag stirring gas
    • End of the lecture Ironmaking