PRE-TREATMENT OF HOT METAL
BATCH 7
WHAT IS PRE-TREATMENT ?
• Pre-treatment of hot metal is the adjustment of the
composition and temperature of blast furnace...
• To produce good quality steel, it is necessary to
lower the levels of sulphur and phosphorus to less
than 0.01% .
• Henc...
DESILICONISATION
• If silicon is on the higher side (1%) in the basic pig
iron, the lime consumption in a basic process wi...
• Silicon in hot metal can be removed by injecting an
oxidising agent like mill scale.
• It is accompanied by lime to help...
• Desiliconisation is not normally practised because of
problems in handling the highly siliceous slag .
• Such slags have...
DEPHOSPHORISATION
• It can only be done under oxidising conditions and in
the presence of a highly basic slag.
• It is pos...
DESULPHURISATION
 Sulphur is an unwanted element in most of the
applications of steel due to the following reasons:
• Sul...
Desulphurisation process
• Dip lance process is the most economical, effective
and reliable method of desulphurisation of ...
• The process allows the use of several
desulphurisation reagents, such as lime, calcium
carbide and magnesium, which remo...
DESULPHURISING REAGENTS
The most commonly used desulphurising reagents
are lime (CaO), calcium carbide and
magnesium (Mg)....
• Once in ladle, the magnesium vapour forms bubbles
which rise through the hot metal, dissolve and react
with sulphur in s...
• Complicated material handling procedures as well as
stringent environment requirements associated with
the disposal of s...
TORPEDO CAR HOT METAL
PRETREATMENT
CONCLUSION
• In the recent years, injection metallurgy has been
developed to such an extent that it is now widely
used to ...
THANK YOU !!!!
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Pretreatment of hot metal

desiliconisation, desulphurisation and dephosphorisation
Published on: Mar 4, 2016
Published in: Engineering      
Source: www.slideshare.net


Transcripts - Pretreatment of hot metal

  • 1. PRE-TREATMENT OF HOT METAL BATCH 7
  • 2. WHAT IS PRE-TREATMENT ? • Pre-treatment of hot metal is the adjustment of the composition and temperature of blast furnace produced hot metal for optimal operation of the oxygen converter process. • It is an extra step between the blast furnace and the BOF shop. • In most of the steelmaking practices hot metal is pre- treated to remove Si, P and S from hot metal to the extent it is possible.
  • 3. • To produce good quality steel, it is necessary to lower the levels of sulphur and phosphorus to less than 0.01% . • Hence, hot metal containing low levels of sulphur and phosphorus must be charged into the BOF. • It is not economical to produce these S and P levels in blast furnace. • Hence, pre-treatment of hot metal to remove excess sulphur and phosphorus prior to BOF steelmaking has gained worldwide acceptance as an intermediate operation . • It can be carried out either at blast furnace runner, or in transfer ladle or in torpedo car.
  • 4. DESILICONISATION • If silicon is on the higher side (1%) in the basic pig iron, the lime consumption in a basic process will increase in order to maintain the required basicity. • Hence, excess silicon must be removed. • Removal of excess silicon before the metal enters the steelmaking furnace is called external desiliconisation.
  • 5. • Silicon in hot metal can be removed by injecting an oxidising agent like mill scale. • It is accompanied by lime to help produce a neutral slag. • Soda ash can also be used to remove silicon: • When soda ash is added, dense fumes are generated, which can cause environmental problems. • Hence, it is not preferred in recent times. ][.][ 2232 CSiOONaSiCONa 
  • 6. • Desiliconisation is not normally practised because of problems in handling the highly siliceous slag . • Such slags have high temperature and are extremely fluid, causing aggressive attack on most refractories. • Instead, efforts have been made to produce low silicon(0.3-0.6 %) hot metal directly in blast furnace to the maximum possible extent.
  • 7. DEPHOSPHORISATION • It can only be done under oxidising conditions and in the presence of a highly basic slag. • It is possible only after the total removal of silicon. • If the basicity falls, phosphorus may soon revert back to the metal phase. • The activity of must be decreased using a strong and excess external basic flux like lime. 52OP ][5).3()(3)(5][2 52 FeOPCaOCaOFeOP 
  • 8. DESULPHURISATION  Sulphur is an unwanted element in most of the applications of steel due to the following reasons: • Sulphur affects both internal and surface quality of steel • Sulphur contributes to the steel brittleness. • It forms undesirable sulphides which promotes granular weakness and cracks in steel during solidification. • It lowers the melting point and intergranular strength.
  • 9. Desulphurisation process • Dip lance process is the most economical, effective and reliable method of desulphurisation of hot metal. • It consists of pneumatic injection of fine grained desulphurisation reagent into the hot metal. • Nitrogen gas is normally used as a carrier gas for the desulphurization reagent. • The injection of desulphurisation reagents through deeply submerged lance causes an intimate mixing of the desulphurisation reagent with the hot metal .
  • 10. • The process allows the use of several desulphurisation reagents, such as lime, calcium carbide and magnesium, which remove the sulphur in the hot metal by chemical reaction and convert it to the slag. • Sulphur rich slag generated during the process is removed immediately after completion of the reagent reaction. • The most common method is to tilt the ladle and rake the slag off with the help of a slag raking machine. • Dip lance method can reliably reduce the sulphur content of hot metal to figures as low as 0.001 %.
  • 11. DESULPHURISING REAGENTS The most commonly used desulphurising reagents are lime (CaO), calcium carbide and magnesium (Mg). • Lime – Its low cost and easy availability make it an attractive reagent. The grain size of the lime is to be restricted to 45 micrometer maximum. • Magnesium – Due to low boiling point (1090 deg C), magnesium vapourizes as it enters the hot metal. )( 2CaC 222)(2 OCaSSCaO 
  • 12. • Once in ladle, the magnesium vapour forms bubbles which rise through the hot metal, dissolve and react with sulphur in solution, forming magnesium sulphide (MgS). • This magnesium sulphide then floats on the top of the ladle and settles in the slag layer, which is skimmed off. • Calcium carbide - It was once most used desulphurizing reagent but now it is less prevalent. MgSSMg 
  • 13. • Complicated material handling procedures as well as stringent environment requirements associated with the disposal of slag have negatively influenced its use. • Sodium carbonate can also be used to remove sulphur. But, it is not preferred nowadays because of generation of harmful fumes. CCaSSCaC 22  COSNaSCCONa 3][][2 232 
  • 14. TORPEDO CAR HOT METAL PRETREATMENT
  • 15. CONCLUSION • In the recent years, injection metallurgy has been developed to such an extent that it is now widely used to pre-treat hot metal. • Hence, steelmaking is restricted to decarburisation alone. • Efficient removal of the slag after pre-treatment as well as the development of suitable refractories for the ladle are areas in which work is still continuing. • Nonetheless, it can be concluded that with ever- increasing demand for lower levels of impurities in steel, pre-treatment of hot metal will be adopted even more widely in the years to come.
  • 16. THANK YOU !!!!

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