Minimizing Dross

Recover, reduce, reuse: optimizing metal
recoveries from dross
Presented by Alan M Peel C.Eng
ALTEK Group
Recover, reduce, reuse: optimizing metal
recoveries from dross
Presented by Alan M Peel C.Eng
ALTEK Group
Agenda
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Dross management
Review basic principle of each technology
Information on the facility that sponsored trial
Testing procedure / protocol
Results of trial
Summary / Conclusion
Questions
The Dross process
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Process Route
Importance of logistics
Time
Labour
Environment
Initial Step
LOGISTICS
SKIM
COOL
TIME
or
LABOUR
HOT PROCESS
ENVIRONMENT
Two extremes !!
1% per minute Al loss
Capture the value at skimming
Dross Process - Which way ?
• Cooling
– Disconnects the dross
generation from
secondary recovery and
gives TIME
– Rapid sealing of
aluminium
– Easier logistics
– Less environmental
impact
• Hot Processing
– Logistics very important
– Continued Al burning if
dross bins left waiting
– Difficult if too many
furnaces
Prevalent Dross Cooling Technologies
Inert Gas Dross Cooler
Dross Press
Prevalent Hot Dross Processing
Techniques
Tilting Rotary Furnace
Dross Stirring
Dross Management
• Dross can account for 5% of
a facilities total production
• Dross can contain up to 80%
of aluminum
• 1% of aluminum can be lost
per minute through
oxidation
• The treatment of the dross after skimming is the
single most important factor influencing the metal
content and the value of the dross
Dross Management – In the Furnace
• Minimising dross in the furnace MUST be the
first priority
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Type of furnace
Burner set up
Pressure control
Door
Electromagnetic stirring
Bath surface temperature
782°C
The Temperature of the metal is the single most controllable factor that determines dross
generation in a furnace.
Dross Management
• Over the years a number of technologies have
been developed to address both economic and
environmental issues
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Dross Stirrers
Rotary Dross Coolers
Inert Gas Coolers
Hot Dross Processing in a Tilt Type Rotary
Dross Pressing Systems
• Many technologies have not gained universal
acceptance
Characteristics Required
• Needs to be safe.
• Minimal impact on the cast house and not interfere
with the day to day operations.
• Should be easy to use and require minimal
maintenance.
• Should be environmentally sound and meet all local
environmental standards.
• Should maximize the amount of Al recovery.
• Should be capable of handling a wide variety of dross
types including white, black and heavily thermiting
dross.
Inert Gas Dross Cooler
• Developed by Alcan in the
mid 1980’s
• Dross is skimmed into
compartmentalized pans
• Pan is transferred in a
cooling station
• Hood is lowered and the
chamber is purged with an
inert gas such as argon
• Pan is kept under the inert
atmosphere typically
between 4 to 7 hrs until
temp falls below 400 deg C
Dross Press
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Developed by ALTEK in the mid
1990’s
Consists of a steel frame,
hydraulic unit, press head and
dross pan set
Dross is skimmed into to the
dross pans
Pan is transferred into the dross
press
Head is slowly lowered into the
dross squeezing trapped metal
into the sow mold below
Head not only extracts metal but
also cools the dross preventing
further oxidation
Dross Stirrer
• More prevalent in
Japan and parts of
Asia
• Uses flux to increase
aluminium drain while
stirring
• Large real estate
• In house environmental
challenges
Trial Facility
• Pennex operate a very efficient billet re-melt
facility in Pennsylvania, USA
• 60 MT static melting/holding furnace that
generates approximately 2200 T of dross / year
• Facility successfully operated several inert gas
cooling hoods for many years
• At another facility in the group they also operated
a dross stirrer
• Had experience with operators recording the
weights of dross pans as part of standard working
practices
Dross Press
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Based on size of furnace and
dross generation, ALTEK selected
Tardis Generation II Model #500
Dross pans with an approximate
capacity of 700 Kg
Equipped with many latest
features:
– Air cooled press head
– Hydraulically operated guillotine
door
– Updated PLC and HMI
– Pressure feedback control
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Machine was fully assembled
and tested prior to shipment
Shipped preassembled to
minimize installation time and
costs
Testing Procedure
• Dross was skimmed simultaneously into the pans supplied for both
technologies.
• Inert Gas Cooler pan(s) were placed in the hood(s) and left to cool
under the inert atmosphere. Simultaneously, the Dross Press pan(s)
were processed through the dross press system.
• Once processed through each technology, every dross pan was
weighed to establish the weight of dross as well as the amount of
metal captured in the drain pan below.
• When cooled, the dross from each technology was placed in
separate dross bunkers.
• The dross was shipped to a separate facility where it was processed
in a Tilting Rotary Furnace.
• The secondary facility was aware that a comparative study was
being conducted and the loads of dross were segregated
accordingly.
Skimming Furnace
Pan being placed in Inert Gas Cooler
Pan being placed in Dross Press
In-house recovery – 16 weeks data
• In house recovery is
expressed as a percentage
of dross skimmed
• Data collated per week
• Dross Press consistently
provides a higher recovery
than the Inert Gas Cooler
In-house recovery
• Over the trial period
higher in house
recovery with press
technology
Secondary recovery – 16 weeks data
Similar results on the secondary recovery from a Tilt Type Rotary Salt Furnace
Total Recovery - 16 weeks data
• Higher combined
recovery ~ 3% from
press + Tilting Rotary
Salt Furnace
Summary Results – Press v Cooler
• Summary of Pennex Tests:– Higher recovery with Press + Tilt
Rotary Salt Furnace
– Lower transport cost due to less
shipped weight of dross
– Less space required at plant
(valuable undercover space)
– Quicker cycle times of dross to
secondary processor
– Less dross pan inventory
SAVINGS from using Dross Press v Dross Cooler > $250,000 per year
Secondary Dross Processing
• OPTIONS
– Tilting Rotary Salt Furnace
– Mechanical crushing/separation
• People say ‘remove the salt’ BUT there is more than
just the salt to consider
• You need to consider all the constituents of in dross !
The Dross Processor
Dross Skulls need to
be recycled in a Tilt
Type Rotary Furnace
ALTEK 16 MT Tilt
Type Rotary Furnace
Tilt Type Rotary Melting Furnace
The above 24 Tonne furnace currently being installed in large Middle East smelter
Tilt Type Rotary Melting Furnace
• Still the most effective way
to process dross:– Obtain the highest metal
yield
– Lowest emissions
– Smallest footprint
– Most flexible operation
• BUT requires further
processing of the salt slag
Typical solid components of dross
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Alumina Oxide (Al2O3)
Spinels (MgO.Al2O3)
Aluminium Nitride (2AlN)
Aluminium Carbides
Aluminium Sulphites (trace)
Aluminium Phosphates (trace)
Official Host:
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Possible Gaseous Components of Dross are:
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NH3
(Ammonia)
H2S
(Hydrogen Sulphide)
H2
(Hydrogen)
SO2
(Sulphur Dioxide)
CO2
(Carbon Dioxide)
CH4
(Methane)
NH4OH (Ammonium) Hydroxide)
Phosphine
Phosgene (possibly)
So its not just the salt slag you have to consider !
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NMP (Non Metallic Particulate)
• The key is to get the NMP ‘inert’
• Once safe it can then be used and transported
safely
• In Europe this is undertaken by salt wash systems
(large Salt Reclamation plants) to ensure the NMP
is safe for sale to down stream applications - and
will not release the gaseous emissions when wet.
Some end uses of NMP
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Cement clinker
Rock Wool
Refractory
Ceramics
Many companies are selling NMP into these
applications
Project - ALUSALT
• New development project
initiated in 2011
• Objective local salt recycling at
salt slag generation source
• Demonstration small capacity
pilot plant to be operational
Q1 2015
Summary
1. Consider dross skimming/cooling logistics
2. Rapid cooling and drain important – to maximise Al
3. Disconnect the dross generation process from the
secondary dross processing
4. Over 85% of the dross generated in Middle East today is
cooled using dross press technology
5. There are markets and uses for the NMP BUT it needs to
be inert
6. The Low Salt Tilting Rotary Furnace for secondary
recovery still is the most efficient route for highest
aluminium recovery