Production of Direct Reduced Iron in Rotary Hearth Furnace

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Production of Direct Reduced Iron in Rotary Hearth Furnace

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Production of Direct Reduced Iron in Rotary Hearth Furnace

  1. 1. Production of Direct Reduced Iron in Rotary Hearth Furnace<br />
  2. 2. Direct Reduced Iron(DRI) <br />DRI: Iron produced by reducing an iron ore (65-70% iron) by reducing gas (H2+CO) at a temperature (approx. 800-1050 °C) high enough to burn off its carbon and oxygen content.<br />Reduction is done below the m.pt of iron cause the produced iron may react with water and air under the evolution of heat.<br />
  3. 3. Direct Reduced Iron(DRI) contd.<br />Output: In the form of pellets <br /> 90 to 97% pure iron & <br /> rest-carbon with other impurities.<br />Also called sponge iron due to its porous nature. [1]<br />
  4. 4. Advantages of DRI over Pig Iron<br />Rich in iron(up to 97%). <br />Uses pelletized iron ore or natural lump ore(no melting).<br />Used to produce Hot Briquetted Iron(HBI) at temp. >600 C, for ease of shipping, handling, and storage.<br />Not cooled before using in steel making electric arc furnaces thereby saving energy. [2]<br />
  5. 5. Rotary Hearth Furnace(RHF)<br />A donut-shaped refractory-lined vessel. <br />Contains rotating bottom or rotating hearth.<br />Uses ore and carbonaceous reductant in the form of a single or a multilayer bed.<br /> The temperature is controlled by means of burners positioned along the walls and on the roof of the furnace.<br />
  6. 6. Rotary Hearth Furnace contd.<br />Rotary Hearth Furnace for Iron Ore Reduction <br />American Iron and Steel Institute steeltrp.com/PDFs/9810.pdf [3*]<br />
  7. 7. Rotary Hearth Furnace contd.<br />Heat transportation by radiation.<br />Pellets are heated up to the reduction temperature.<br />Heat radiation to lower layers of the bed decreases because of shielding by the upper layers.<br />Motion of iron oxide ore bed in RHF<br />American Iron and Steel Institute<br />steeltrp.com/PDFs/9810.pdf [3*]<br />
  8. 8. Rotary Hearth Furnace contd.<br />The productivity of the RHF is limited by heat transport.<br />A number of stationary adjustable blades over the rotary table. <br />Hot solids are pushed toward the center of the table by one blade width by each blade.<br />Concentric path followed by removal through an opening at the centre of the hearth. [3]<br />
  9. 9. A typical RHF (Rotary Hearth Furnace) http://www.businessdictionary.com/definition/direct-reduced-iron-DRI.html [1*]<br />
  10. 10. Production of DRI in RHF<br />Feed: agglomerates made from a mixture of <br /> iron oxides (virgin ore or by-products)<br /> carbon source(coal or charcoal)<br />Hearth and reducing gas rotate in opposite directions.<br />Reactions: <br />Natural gas is partially oxidized (with heat and catalyst): <br />2 CH4 + O2 -> 2 CO + 4 H2<br />These gases are then treated with iron ore, producing solid sponge iron:<br />Fe2O3 + CO + 2 H2 -> 2 Fe + CO2 + 2 H2O<br />
  11. 11. Production of DRI in RHF contd.<br />Also Iron oxides are reduced by ’C’ producing ‘CO’<br />Heat transfer by convection to reduction zone is undesirable, since re-oxidation occurs by the arrival of oxidizing gas(from heating burners).<br />
  12. 12. Production of DRI in RHF contd.<br />Combustion of: CO provides 85% & fuel(burners) provides 15% of heat.<br />The iron oxides are reduced over a period of 6–12 min.<br />Waste gases are removed from the charging side, and their heat is used in heat exchangers.<br />The waste gases are subsequently burned in a steam boiler, cleaned of dust, and discharged through a smokestack.[4]<br />
  13. 13. Handling of DRI<br />Sponge iron reacts with water and air under evolution of H2 and heat.<br />If the heat generated can not be transferred to surroundings, self heating occurs which leads to complete oxidation.<br />So keep DRI in an inert atm. with O2 less than 5 vol%<br />Otherwise passivate it. <br />Example: decreasing the reactive surface by immersion in sodium silicate soln followed by drying.[6] <br />
  14. 14. Benefits<br />Energy-efficient feedstock for  steel manufacturers which rely upon scrap metal.<br />Reduced CO2 emission per ton compared to that produced by blast furnace.<br />Lowered capital investment and operating costs in Rotary Hearth Furnace iron ore reduction.<br />ZnO also undergoes reduction and zinc metal vapor - converted back to ZnO by waste gases.<br />The captured ZnO in filters is a raw material for use in nonferrous metallurgy. [2*]<br />
  15. 15. Current State in Iron Production<br />The world’s first commercial RHF, with a diameter of 16.7 m, was built by the company INMETCO in Elwood (in the U.S.) for recycling wastes containing nickel, chromium, and iron. The Direct Reduced Iron unit has a capacity of 200,000 tons a year and was built in 1997.[5]<br />The company Iron Dynamics Inc. (U.S.) began operation of an IDP (Iron Dynamics Process) unit in 1999. This furnace has a capacity of 500,000 tons of sponge iron a year and is the largest such furnace in the world.[5]<br />At present India is the largest producer of sponge iron at 17 million tones/annum.[4*] <br />
  16. 16. References<br />[1] S. Halder and R.J. Fruehan Reduction of Iron-Oxide-Carbon Composites: Part I. Estimation of the Rate Constants Metallurgical and Materials Transactions B, 2008, Volume 39, Number 6, Pages 784-795<br />[2] I. F. Kurunov Metallurgist, The Direct Production of Iron and Alternatives to the Blast Furnace in Iron Metallurgy for the 21st Century Vol. 54, Nos. 5–6, 2010<br />[3] Patent Weiss, Hans J. (Frankfurt am Main, DE) 1984 Rotary hearth furnace plant United States MetallgesellschaftAktiengesellschaft (Frankfurt am Main, DE) 4431406<br />[4] I. Sohn and R. J. Fruehan, The reduction of iron oxides by volatiles in a rotary hearth furnace process: Part II. The reduction of iron oxide/carbon composites Metallurgical and Materials Transactions B, 2006, Volume 37, Number 2, Pages 223-229<br />[5] Fu-ming Zhang, “Progress of rotary hearth furnace reduction technology, ibid” pp. 1347–1352<br />[6] Hattwig, Martin; Steen, Henrikus (2004), Handbook of explosion prevention and protection, Wiley-VCH, pp. 269–270, ISBN 9783527307180.<br />Bibliography<br />[1*]http://www.businessdictionary.com/definition/direct-reduced-iron-DRI.html<br />[2*]www.p2pays.org/ref/08/07543.pdf<br />[3*]American Iron and Steel Institute: steeltrp.com/PDFs/9810.pdf<br />[4*] http://www.spongeironindia.in/Sima%20April%20Issue%202010.pdf<br />

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