Tutorial on roasting furnaces s.d.kahar
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The document provides an overview of different types of roasting furnaces used to oxidize or chemically treat mineral ores. It describes multiple hearth roasters, fluidized bed roasters, flash roasters, and sinter/blast roasters. Multiple hearth roasters slowly roast ore in a countercurrent design with multiple horizontally stacked hearths. Fluidized bed roasters suspend fine ore particles in an upward gas stream. Flash and sinter/blast roasters can roast larger throughputs of finer ore particles using combustion gases. The document outlines factors that influence roasting processes and furnace selection based on desired product characteristics.
Tutorial on roasting furnaces s.d.kahar
- 1. TUTORIAL on ROASTING FURNACES Prepared By Mr.. Sunil D. Kahar Assistant Professor Metallurgical & Materials Engineering Department Faculty of Technology & Engineering The M S University of Baroda, Vadodara
- 2. Roasting - Minerals or constituent of ore other chemical form Oxidizing Roasting - Metal sulphide Metal oxide MS + 3/2 O2 MO + SO2 Volatizing Roasting - Elimination of volatile oxide such as AS2O3, Sb2O3, ZnO Chloridizing Roasting - Metal compound chloride under oxidizing or reducing condition 2NaCl + MS +2O2 Na2SO4 + MCl2 2NaCl + 2MO +S2 + 3O2 Na2SO4 + 2 MCl2 - ( U, Be, Nb, Zr, Ti extracted from there oxides) O2 or heating
- 3. Sulphatizing Roasting - Sulphide sulphates prior to leaching Magnetic Roasting - Controlled reduction of hematite (Fe2O3 ) magnetite (Fe3O4) Reduction Roasting - Partial reduction of an oxide ore prior to actual reduction smelting Blast Roasting or Sinter Roasting - Partial oxidized as well as physical conditioned ore is charge.
- 4. Roasting depend upon 1. Time 2. Temperature 3. Avaibility of O2 or air 4. physical condition nature of the mechanical device Criteria of selection of roasting process 1. Physical condition of product blast furnace smelting – product should coarse or cellular reverberatory furnace – product should ne fine leaching - product should be porous 2. Chemical composition of product For copper – retain some sulphur For Lead & Zinc - complete elimination of sulphur
- 5. Multiple Hearth Roaster MacDougall in England (19th Centaury) Basic principle - Counter current flow of solid ore & the oxidizing gases - diameter = 25 ft, 6 to 12 hearth - Steel shell lined with cylindrical brick - Ore is charge from top - Revolving mechanical rabble attach to arm – continuously shifting the ore - Arm is attach with rotating shaft - Oxidizing gases move upward - External heating of charge is unnecessary except when charge content moisture Drawbacks: (1) Roasting is slow (2) Gases are unsuitable for production of H2SO4
- 6. Fluidizing Bed Roasting Principle- -Ore particles are roasted while it is suspended in an upward stream of gases -Gas is passes through the bottom of the bed - Behahaviour bed depend on the velocity of gas
- 7. Stage-1 • Bed is porous - gas easily flow • Pressure drop across the bed – proportional to flow rate • Factor influencing the flow rate 1. Void fraction 2. Particle size factor 3. Particle shape factor Stage-2 • Gas velocity is with expand of the bed in upward direction due to drag force exerted by gas stream Stage-3 • Continue to gas velocity • Presuure drop = wt. of the particle per unit area of bed So particle offer less resistance to gas flow
- 8. • Stage-4 • Further increase in gas velocity lead to continued expansion of the bed • Result in increase in inter particle distance • Pressure drop across bed is decrease with increase in gas velocity • Stage-5 • expansion of the bed is independent of gas velocity • Out coming gas appear as babble & bursting on the surface of the bed • Look like well stirred boiling liquid –said to be fluidized.
- 9. Flash Roaster • Preheated ore – free fall through body of hot air • Instantaneous oxidation of flashing of combustible constituent ore( S) • Hence called flash roasting • Ore should be in fine form • Capacity pf flash roaster > hearth roaster • Temp. pf combustion zone = 900-9500 C
- 10. Sinter Roasting OR Blast Roasting • Fine ore & concentrate have been agglomerated before charging • Use for Sulphides ore • Charge = (fine ore+ moisture) as layer of 15-50 cm thick on revolving belt • Combustion is done by burner • Speed is adjusted - roasting should be completed before it discharge • Produce porous cinder called sinter • Cooled sinter is sized ti give uniform product