(MERAF) for the Base Metals Smelting Sector - CCME

and is cut into shape using shears or by casting in special side dam blocs spaced
in defined intervals in the caster. The billets can be heated then extruded and
drawn into tubes. Slabs or cakes are preheated and rolled into sheets and strips.
Ingots are produced using a fixed mold casting process.
2.3.12. Process Off-Gas Conditioning
Off-gases from smelting facilities typically contain sulphur dioxide, particulate
matter, fume (e.g., volatile metals) and other pollutants of concern such as
carbon dioxide, nitrogen oxides and organics. Off-gases are treated to remove
sulphur dioxide, particulate matter and/or other pollutants before being released
to ambient air.
For removal of particulate matter and dust, cyclones are used to remove medium
to large sized particles. Cyclones are not considered sufficient control devices
on their own to remove particulate matter. Other control devices with greater
dust removal efficiencies include electrostatic precipitators (ESPs), either hot or
wet, and fabric filter baghouses. Hot ESPs can withstand higher off-gas
temperatures than fabric filter baghouses. However baghouses can achieve
greater dust collection efficiencies than hot ESPs 28 . Scrubbers are also used to
remove both dust and soluble or acidic gases from the off-gas stream.
Process off-gases with a minimum sulphur dioxide concentration of 5 to 7
percent can be used for the manufacture of sulphuric acid, and thus remove the
sulphur dioxide from the off-gas stream. Double contact acid plants are able to
achieve a higher conversion rate of sulphur dioxide in the process off-gas to
sulphuric acid, than single contact acid plants.
28
European Integrated Pollution Prevention and Control Bureau (EIPPCB), Reference
Document on Best Available Techniques in the Non Ferrous Metals Industries, Spain, May 2000.
http://eippcb.jrc.es
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