Lectures%202007%20 ironmaking

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Lectures%202007%20 ironmaking

  1. 1. Primary Metals Production 2007 Part 4: Ironmaking Rob Boom Metals Production, Refining and Recycling (MPRR) Department of Materials Science and Engineering
  2. 2. Course contents Ironmaking and Steelmaking • Steelmaking process flow • Coke making • Agglomeration • Ironmaking • Steelmaking • Secondary steelmaking • Casting
  3. 3. Steelmaking process flow
  4. 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
  5. 5. Ironmaking process flow
  6. 6. Course contents Ironmaking and Steelmaking • Steelmaking process flow • Cokemaking • Agglomeration • Ironmaking • Steelmaking • Secondary steelmaking • Casting
  7. 7. Coal stock area
  8. 8. Cross-section coke plant In the coke ovens coal is being processed to get pure carbon fit for the BF
  9. 9. Coke battery
  10. 10. Charging
  11. 11. Level bar
  12. 12. Gas pressure
  13. 13. The ‘Plastic’ Layer
  14. 14. Pushing coke
  15. 15. Transport to quench tower
  16. 16. Transport screening
  17. 17. To Blast Furnace
  18. 18. Course contents Ironmaking and Steelmaking • Steelmaking process flow • Coke making • Agglomeration • Ironmaking • Steelmaking • Secondary steelmaking • Casting
  19. 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. 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
  21. 21. Sintering Equipment: grate sintering
  22. 22. Iron ore sintering process
  23. 23. Layering
  24. 24. Principle Chevron method Cross section Layering Reclaiming Rake Bucket wheel Longitudinal section
  25. 25. Reclaiming
  26. 26. Reclaimer
  27. 27. Pellet Plant • Dry grinding • Straight grate induration strand 430 m2 • Acid, olivine doped • 4.6 million ton per year
  28. 28. Pellet plant lay-out Induratio Balling Grinding
  29. 29. Grinding and balling
  30. 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. 31. Sinter Plant • Suction Area 354 m2 • High Basicity • Screened at 4mm • 4.4 million ton per year • EOS and Airfine
  32. 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
  33. 33. Sinter Strand with EOS
  34. 34. Summary: ore preparations
  35. 35. Course contents Ironmaking and Steelmaking • Steelmaking process flow • Coke making • Agglomeration • Ironmaking • Steelmaking • Secondary steelmaking • Casting
  36. 36. Ironmaking
  37. 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. 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. 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
  40. 40. Blast furnace plant
  41. 41. Blast furnace plant
  42. 42. 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
  43. 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. 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. 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. 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. 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. 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. 49. Reduction stages alles oxide oxide ox. Fe Fe2 O3 Fe3O4 FeO Fe alles oxide Fe Fe2O3 Fe3O4 FeO Fe
  50. 50. The Process The Blast Furnace as a countercurrent mass and heat exchanger Gas Burden ascent descent 2300°C Dead Man
  51. 51. BF as counter-current reactor
  52. 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. 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. 54. Burdening PW CHUTE PW BELL Moveable armour BF6 BF7
  55. 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. 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. 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. 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. 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
  60. 60. Coal Injection Injection at Tuyeres ) (Gasification)
  61. 61. Tuyere injection arrangement
  62. 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. 63. World’s best performing blast furnace BF6 Corus Strip Products IJmuiden Data 100 BF’s Period 2005
  64. 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. 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. 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
  67. 67. Midrex
  68. 68. Production of directly reduced iron (DRI) Midrex – dominating process
  69. 69. Corex
  70. 70. FIOR (+Circored/Circofer)
  71. 71. Cyclone Converter Furnace CCF fine ore and oxygen oxygen coal hot metal and slag stirring gas
  72. 72. End of the lecture Ironmaking

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