A problem faced by the primary metal and glass industries is their
intense energy usage. The secondary aluminum industry alone,
expends about 1,000 Btu per pound of aluminum to remove oil, paint,
plastics and other organics from the scrap. Another 3,000 Btu per
pound is used in melting the scrap for a total energy use of 4,000
Btu per pound. The glass industry uses about 4 MMBtu per ton of
batch and cullet to make glass bottles. Additionally, emissions and
generation of waste materials are also industry problems.
The de-coating is a thermal treatment applied on the aluminium
scrap, used to remove from the surface of the material all the
contaminants as paper, oil, links, paint, plastic.
The aluminium scrap is used as “raw material” to produce new
aluminium but before to be molten again has to be “cleaned”, i.e.
treated inside a de-coating unit, in order to reach the specific
characteristics requested. If the scrap is not cleaned (de-coated)
and is molten directly inside the furnace, the metal loss increases
and the presence of contaminants in the furnace might create
problems to the use of the regenerative burners, producing at the
same time an additional cost of the natural gas used in the
melting. The cleaning process is based on heating the aluminium
scraps in a controlled low oxygen atmosphere, through direct
convective exchange with exhaust fumes, which have been processed
into post-combustion chamber. The experience on existing pyrolysis
plants, allow to cover the following scraps: turning, cover,
ground, cans, tubes or caps, cables, sheets laminated with paper or
plastic, sheets coated.
The HENGYANG INDUSTRY has significant advantages over conventional
equipment: energy reduction, emissions reduction, production increase, and baghouse dust
reduction. Each is described.
Energy Reduction
Current dryers use 1,000 Btu/lbm. Most or all of this can be
eliminated with the HENGYANG INDUSTRY.
Emissions
The Clean Air Act effect on the secondary aluminum industry are now
being debated and will be settled shortly with the Best Demonstrable Technologies to
be mandated. It is not likely the current dryers will meet the new standards whereas the
HENGYANG INDUSTRY might. HENGYANG INDUSTRY emission measurements made by ERCo have shown low
values of NOx, SOx, VOC, and CO are achieved. CO2 emissions would also be reduced in
direct proportion to the reduction in firing rate.
Production Increase
Currently, conventional furnaces lose about 8 to 10% of their
furnace melt as dross. Some of this loss is attributable to the poor decoating process,
though how much is speculative. Further, dust creation in the current kiln of 6 to 7%
could be avoided with
the HENGYANG INDUSTRY.
Scrap Purchases
Aluminum smelters could possibly process lower grade scrap not
possible now. For instance, aluminum foil (such as candy wrappers) will undergo
significant oxidation in their current kiln since the foil is so
thin. Testing of Hengyang showed that foil could be readily
decoated with no oxidation.
