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Oct 19, 2013 (3 years and 9 months ago)

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ALUMINIUM

DROSS PROCESSING
-
A C
ASE

S
TUDY

By:

Waheed Ahmed

General Manager

Cast Aluminium Industries

W
HAT

IS

A
LUMINIUM

D
ROSS



Aluminium dross is the mixture of metallic
aluminium and non metal part mostly Aluminium
oxide.


Dross is formed on the surface of molten Aluminum or
its alloys by oxidation.


Dross is a valuable by product of any Aluminium
Smelter or Aluminium Foundry.


Dross is recycled to recover the valuable Aluminium
Metal world wide.


Typical dross generation from a primary operation
can be from 0.8% to 1.3% of Aluminium output.


From the secondary smelters it can reach up to 10%.

TYPES OF A
LUMINIUM

D
ROSS



Broadly
there are two types of drosses


White Dross (Primary Dross)


Black Dross (Secondary Dross
)




The drosses are heterogeneous in nature because
of so many steps involved at generator’s site. The
recoverable metal content varies from 10% to
70%.




E
FFECT

OF

S
MELTER

S

P
RACTICE

ON

D
ROSS

Q
UALITY


Following key steps are involved


Drossing Temperature.


Fluxing Practice before drossing.


Skimming Practice.


Cooling of dross as soon as possible.


WAYS TO COOL THE DROSS.


Air Cooling.


Rotary Dross Cooler.


AROS Argon Cooler.


Dross Press (Most Widely used Practice)


A
LUMINIUM

DROSS

PROCESSING

TYPES


On site Processing



Off Site Processing

O
NSITE

PROCESSING



In this process the dross is skimmed from the molten
metal and is transferred directly to the Hot Dross
Processing Machine or furnace. The equipment uses
the hot dross thermitting reaction of Aluminium
Metal and the Al metal is separated from the oxides
by means of specific gravity and the agitation.


The metal is either cast into the ingots or the liquid
metal is fed directly to the smelters furnaces.


Following are the challenges associated with this
process,


Relatively low metal recovery as some metal is used as
fuel.


Unstable process encourages Al Metal thermiting.


Specialized Equipment requires more maintaince.


O
FF

SITE

PROCESSING


The off site processing of Al dross is the most
commonly done practice in the world. In this
practice the processor removes the dross from the
smelters premises and takes it to the processing
facility. The dross from the smelter is taken on
the following 2 basis.


The processor buys the dross


The processor takes the dross on tolling basis i.e.
the metal goes back to the smelter.


There are a number of challenges associated
with the off site processing of the Aluminium
dross specially when on tolling basis like,


Transportation of dross from Smelter in safe and
environment friendly manner.


The storage of dross at the processing facility in an
environment friendly manner.


The processing of dross with the BAT to maximize
the metal recovery.


The safe and sound disposal / usage of salt slag /
NMP with no liability towards the smelter.


The effective & efficient processes of
communication.


C
HALLENGES

IN

OFF

SITE

PROCESSING

S
TEPS

IN

OFF

SITE

PROCESSING

Segregation Process

Pressed Skull
Breaking
Process

Tapping Process



Enrichment of
aluminium
dross.

Smelting Process in
Tilting Rotary
Furnace.(TRF)


Chemical Analysis

Metal & Dross Mass Balance to Client
.


Aluminium Dross

Physical Quality
Check

Client

NMP

<1mm

Loose

Dross

DROSS STORAGE & ENRICHMENT


The dross is off loaded in covered shed /
designated bunker.


The quality inspection team keep record of
each delivery by visually inspecting the quality
of dross.


Any observation of foreign items and
un melted alloying metals is immediately
reported back to the generator.


The breaking of dross pressed lumps is done by
the JCB Jack Hammer.


The loose material is passed through a
enrichment process where by NMP is taken
out the process.

P
ROCESSING

OF

DROSS


There are many methods and technologies
available for the processing of dross. The key
criteria of selection should take into account the
local environmental laws, smelter’s vision and
industrial infrastructure of the country.

T
YPES

OF

OFFSITE

PROCESSING


The major types of off site processing are as
follows.


The Salt Process
. Most stable process, Maximizes
the waste thus requires more energy and down
stream handling of salt slag requires bigger plant.


The Low Salt process
. Stable process, does not
contribute much in increasing the waste but still
requires down stream recycling of salt slag


The No Salt process
. Unstable process, Can be
made stable and requires less work down stream to
recycle salt free waste.

S
ALT

PROCESS


The Salt Process uses between 20
-
30% of fluxes
that is the combination of sodium and potassium
chlorides with a small portion of cryolite.


The challenges associated are,


The washing of salts.


The inertization of oxides.


The reuse of oxides in other allied industries.


L
OW

SALT

PROCESS


The Low Salt process uses between 8
-
14 % of
fluxes having the same composition as of the
salt process.



The challenges associated are the same as that
of the salt process
.


The
washing of salts.


The inertization of oxides.


The reuse of oxides in other allied industries.





S
ALT

LESS

PROCESS


The Salt Less process uses no additional fluxes at
all.


The challenges associated are,


To achieve the maximum recoveries equivalent to the
more established salt processes.


The control of thermitting reaction during the
melting of the dross

is of utmost importance and
requires experience & special technology / tools.


Manageable environmental challenges.


No washing is required and relatively easy use of
oxides in other industrial sectors.


S
ALT

SLAG

/
NMP

HANDLING

,
STORAGE

&
DISPOSAL



Salt slag handling, storage and disposal should
be in accordance with the local authorities rules
& regulations. It should be kept in mind that the
smelter should not get any complaint for the salt
slag or NMP. A no liability must be provided to
the smelter.

REPORTING MECHANISM



Mass balance of the complete
incoming material
with
traceability
.


Chemical Analysis : The analysis of each heat to be
marked on the sows as per smelter’s requirement
along with the heat number for
tracebility
.


All
the steps involved in the dross processing must be
reported to the smelter on weekly, fortnightly
and
monthly basis.


The
visits between the smelters & the processor keeps
the relationship close and the
technological
collaboration
not only improves the benefits of both
the organizations to the maximum
but also
helps
to
develop
a trust between the organizations.


D
ISPATCH

OF

METAL

TO

SMELTER


Metal is weighed and the specific heat numbers
are marked along with the weighs on the metal
and is sent to the smelter in an safe and
environment friendly manner.


Before the dispatch of metal to the smelter the
metal is checked for the quality assurance so that
there is no complain in the final product from the
smelter and is safe for the use of smelter as well.

CONCLUSION


Dross is not a waste but a valuable by product of
the smelter.


Dross Handling at smelter is of utmost
importance.


Reporting mechanism and complete traceability
of the dross by the processor is key a factor for
smelter’s peace of mind.


Vision of the smelter / authorities is
the vital
factor in achieving the “Zero Waste Status”.


Down Stream handling of the waste is very
important in selecting the dross processing
process.

Thank

You