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Lec Smelting Of Iron


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Lec Smelting Of Iron

  2. 2. Outline <ul><li>Iron Ores </li></ul><ul><li>General view of Blast Furnace plant </li></ul><ul><li>Sketch of Blast Furnace </li></ul><ul><li>Construction and working of Blast Furnace </li></ul><ul><li>Blast Furnace Charge </li></ul><ul><li>Metallurgical Coke </li></ul><ul><ul><li>Coke Manufacturing & its Quality </li></ul></ul><ul><li>Flux </li></ul><ul><li>Charging Mechanism in Blast Furnace </li></ul><ul><li>Smelting operation </li></ul><ul><li>Chemical Reactions in Blast Furnace </li></ul><ul><li>Formation and tapping of slag </li></ul><ul><li>Pig Iron- Properties & uses </li></ul>
  3. 3. <ul><li>The most important variety of iron ore are: </li></ul>Iron Ores Nomenclature Composition Fe %age Location Magnetite (Black oxide) Fe 3 O 4 72.4 Makarwal, Swabi, Chitral (PAK), Land of midnight sun (Sweden), Pennsylvania(USA), Siberia(Russia) Hematite (red, brown & black) Fe 2 O 3 40-65 Kala bagh, Chnari, Chaghi, Chalghazi (PAK), Lake superior, Utah (USA), Lorraine (France), Amazon basin (Brazil) Limonite & other hydroxide types of ores 2Fe 2 O 3 . H 2 O to Fe 2 O 3 . 3H 2 O 20-55 Not found in PAK, Britain’s East coast Siderite FeCO 3 Low in Fe Hazara, Mardan (PAK), South Wales, Staffordshire &west York (UK) Iron Pyrite (yellow) FeS 42 Mardan, Chitral (PAK)
  4. 4. General view of Blast Furnace plant
  5. 5. Sketch of Blast Furnace Plant
  6. 6. Sketch of Blast Furnace
  7. 7. <ul><li>Construction and working of Blast Furnace </li></ul><ul><li>Blast furnace consists of a vertical steel shell ~ 100 ft high & ~ 21 ft dia and lined with refractory material. </li></ul><ul><li>It has a charging arrangement (Bell & Cone) at the top. Raw material is charged by a skip car through this charging mechanism into the blast furnace. </li></ul><ul><li>It has a means of running off Pig iron & Slag at the bottom. </li></ul><ul><li>Air is blown in near the bottom of the furnace. This forced draught increases the speed of combustion & maintains the necessary high temperature. </li></ul><ul><li>Cooling water is circulated around the Bosh area in order to protect the furnace from high temp. </li></ul>
  8. 9. Blast furnace diagram 1. Hot blast from Cowper stoves 2. Melting zone ( bosh ) 3. Reduction zone of ferrous oxide ( barrel ) 4. Reduction zone of ferric oxide ( stack ) 5. Pre-heating zone ( throat ) 6. Feed of ore , limestone , and coke 7. Exhaust gases 8. Column of ore, coke and limestone 9. Removal of slag 10. Tapping of molten pig iron 11. Collection of waste gases
  9. 10. Blast Furnace Charge <ul><li>BF charge consists of the following: </li></ul><ul><li>Iron ore ; iron oxide in lump or sinter form </li></ul><ul><li>Fuel ; coke </li></ul><ul><li>Flux ; limestone </li></ul><ul><li>In addition Hot air is admitted through the tuyeres </li></ul>
  10. 11. Metallurgical Coke <ul><li>Coke is a solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. </li></ul><ul><li>The volatile constituents of the coal—including water, coal-gas, and coal-tar—are driven off by baking in an airless oven at temperatures as high 1000° C. </li></ul><ul><li>Metallurgical coke is produced by carbonization of coal at high temperatures to produce a macroporous carbon material of high strength and relatively large lump size. </li></ul><ul><li>Notes: </li></ul><ul><li>Metallurgical cokes must have a high strength to support heavy loads in the blast furnace without disintegration. </li></ul>
  11. 12. Coke Manufacturing Process <ul><li>Bituminous coal is pulverized by ball mill into fine powder. </li></ul><ul><li>Fine coal is heated in coke oven battery at 700–900 ° C in absence of air. This process is called Carbonization. </li></ul><ul><li>After soaking at this temperature for about 7–8 hrs., it is allowed to cool in the furnace. </li></ul><ul><li>Due to coking property of bituminous coal powdered coal converts into lump size and becomes very hard and highly porous. </li></ul><ul><li>After cooling, the coke produced is crushed into desired size. </li></ul>
  12. 13. Coke Manufacturing Process <ul><li>Strength of the coke, </li></ul><ul><li>fixed Carbon (88-92%), </li></ul><ul><li>sulphur content and </li></ul><ul><li>ash content </li></ul><ul><li>is determined in the testing laboratory for justifying the quality of the coke. </li></ul><ul><li>By-products like tar may also be collected during carbonization process. </li></ul>
  13. 14. Quality Control and Standards <ul><li>Coking coal used should have </li></ul><ul><li>low ash content, </li></ul><ul><li>low sulphur and </li></ul><ul><li>should be highly coking in nature for better quality of coke. </li></ul><ul><li>Other properties like </li></ul><ul><li>porosity, </li></ul><ul><li>abrasive strength and </li></ul><ul><li>hardness </li></ul><ul><li>must be checked in the laboratory for maintaining the quality of Metallurgical coke. </li></ul>
  14. 15. Flux <ul><li>Flux is a material, which is added to the contents of a Blast furnace or a Cupola for the purpose of purging the metal of impurities, and of rendering the slag more liquid. </li></ul><ul><li>The flux most commonly used in iron and steel furnaces is limestone , which is charged in the proper proportions with the iron ore and fuel. </li></ul>
  15. 16. Charging Mechanism in Blast Furnace
  16. 17. Smelting operation <ul><li>Smelting consists of two operations : </li></ul><ul><li>a - Chemical reduction of iron from its oxides by CO , which is formed by the combustion of C in the coke with the O 2 of the air blast admitted through the tuyeres near the base. </li></ul><ul><li>b - The liquefaction of the gangue by means of flux (limestone) to form a fusible slag which will run from the furnace. </li></ul>
  17. 18. Smelting operation <ul><li>During the production of pig iron (smelting operation) large amount of gases are evolved , which contain about 30% CO having considerable calorific value. </li></ul><ul><li>The exit gases are collected, led through down-comer pipe to a cleaning chamber and electrostatic dust precipitator & then used as fuel gas in “Cowper Stoves” in order to pre-heat the air blast to the furnace. </li></ul>
  18. 19. Chemical Reactions in Blast Furnace <ul><li>The air , which is blown at the bottom of the furnace causes partial combustion of the coke : </li></ul><ul><li>2C + O 2 = 2CO + Heat 1 </li></ul><ul><li>As the CO , which is powerful reducing agent , rises through the charge, it chemically reduces the iron oxide :- </li></ul><ul><li>Fe 2 O 3 + 3CO = 2Fe +3CO 2 2 </li></ul>
  19. 20. <ul><li>Reduction sequence of iron oxide is as </li></ul><ul><li>Fe 2 O 3 Fe 3 O 4 FeO Fe , when temp is > 570 ˚ C </li></ul><ul><li>Fe 2 O 3 Fe 3 O 4 Fe, when temp is < 570 ˚ C </li></ul><ul><li>The equation # 2 takes place in the upper part of the furnace, where the temp is too low to melt the iron formed. </li></ul><ul><li>The iron therefore remains as a spongy mass until it moves down into the lower part of the furnace, where it melts & runs down over the hot coke, dissolving C, S, Mn, P & Si as it goes. </li></ul>
  20. 21. <ul><ul><li>SLAG: The slag is a liquid mixture of ash, flux, and other impurities . </li></ul></ul><ul><ul><li>Formation and tapping of Slag </li></ul></ul><ul><ul><li>At the time of the reduction of iron oxide, the gangue , which is composed of silica, combines with lime to produce slag as :- </li></ul></ul><ul><li>2CaO + SiO 2 = 2CaO.SiO 2 </li></ul><ul><li> (Calcium silicate slag) </li></ul><ul><li>Calcium silicate slag has much lower melting point than silica and can run from the furnace quite easily. </li></ul><ul><li>The furnace is tapped at regular intervals & the pig iron is run either into large ladles for transference, while still molten, to steel making plant, or alternatively, cast into pigs for subsequent use in the cupola or open hearth furnace. </li></ul>
  21. 22. <ul><li>Slag ……(Continue) </li></ul><ul><li>Limestone has an other function – </li></ul><ul><li>the removal of sulphur. </li></ul><ul><li>This entails having an excess of lime in the slag and is often impracticable with low grade ores, since they contain so much silica, which must be neutralized first. </li></ul><ul><li>In British practice the sulphur is removed at a later stage by adding soda-ash to molten pig iron as it runs from the blast furnace into the ladle:- </li></ul><ul><li>FeS + Na 2 CO 3 = FeO + Na 2 S + CO 2 </li></ul><ul><li>(Iron sulphide Soda ash joins the slag </li></ul><ul><li>in the pig iron) </li></ul>
  22. 23. Tapping of Slag
  23. 24. Pig Iron - Properties & uses <ul><li>Definition :- “It is a high-carbon iron made by reduction of iron ore in the blast furnace”. </li></ul><ul><li>Metallic iron, which is a product of reduction of of iron ore, appears in the lower part of ‘stack’ & in the ‘bosh’. </li></ul><ul><li>It contains ~ 1 % C and found to in spongy form. As this material sinks down in the B.F. and is heated further, iron dissolves C in increasing quantities. This reduces the melting temp & it melts and draws off to the ‘hearth’ in the form of drops. </li></ul>
  24. 25. <ul><ul><li>Pig Iron… (Continue) </li></ul></ul><ul><ul><li>Pig iron is really a complex alloy. In addition to Fe, it contains up to 10 % of other elements, mainly, C, Mn, Si, S & P. </li></ul></ul><ul><ul><li>Total amount of C in the pig iron is usually between 3 – 4% & is present either as compound, iron carbide (Fe 3 C) or as un-combined carbon in the form of graphite. </li></ul></ul><ul><ul><li>Pig iron low in S & high in P may be used in the manufacture of acid steel & high-duty iron castings. </li></ul></ul>
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