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ALUMINIUM MI DDL E EAST
Advancements in reduction technology improve specific energy
consumption and reduce greenhouse gas emissions at Dubal
© Dubal
Established to add value to the energy resources
of the Emirate, Dubai Aluminium
(Dubal) began operating in November
1979 and has since been a substantial
contributor to the national and regional
economy. Today, Dubal operates the
world’s largest single-site smelter using
pre-bake technology: 1,573 reduction
cells arranged in seven potlines produce
over one million tonnes of molten aluminium
a year (2012: 1,025,266 t), the
bulk of which (about 88%) is exported
to close on 300 customers in 57 countries
around the world.
The demand for electrical power to maintain
this production level is about 1,900 MW. This
is more than met through Dubal’s captive
combined cycle power station, which has an
installed power generation capacity of 2,350
MW (at 30 °C). While Dubal’s gas turbines
are fuelled primarily by natural gas, for which
DX+ pilot line
supply is available, the cogeneration and combined
cycle configuration of the Dubal Power
Plant means that approx. 36.8% of the power
generated at Dubal is fuel-free: a position that
reflects the company’s deep-seated awareness
of the energy-intensive nature of aluminium
smelting and its associated corporate commitment
to energy optimisation across its operations.
This commitment is evident in the inherently
responsible expansion of Dubal’s smelter
complex over the years. The fledgling smelter
complex, built on a 480 hectare site in Jebel
Ali, 35 km from the city of Dubai, comprised
360 Kaiser P69 cells arranged in three potlines.
An ongoing quest for sustainable, organic,
innovation-based growth, led to the cells in
these potlines being upgraded to D18 technology.
A fourth potline of 144 cells was built in
1990 and further cells were added in 2008 and
2010, bringing the total number of D18 cells
at Dubal to 520. At the same time, a series
of other expansion projects were completed
between 1998 and 2008 – each phase incorporating
more advanced reduction technologies
that operated at higher amperage levels and
thus produced more metal per unit of power
consumed.
Driven to achieve operating excellence
through continuous improvement, Dubal simultaneously
invested substantial resources
in advancing its aluminium smelting processes
and technologies with the aim of not only increasing
productivity, but also reducing the
impact of its smelter operations on the environment
– the latter through improved energy
efficiency and minimised emission of levels.
In essence, lower energy consumption would
mean reduced depletion of fossil fuels and an
associated decline in carbon dioxide (CO2)
produced during the combustion of these
fuels; while enhanced process control would
curtail emissions of other greenhouse gases –
specifically perfluorocarbons (PFCs).
This quest culminated in the development
in 2005 of Dubal’s proven in-house developed
DX technology – a UAE flagship technology
that has been installed in a dedicated 40-cell
potline at the Dubal smelter in Jebel Ali, Dubai;
and in the 756-cell first phase of Emirates
Aluminium (Emal) in Al Taweelah, Abu
Dhabi. The amperage of the DX cells at Dubal
was ramped up from 340 kA at start-up to
380 kA within the first two years of operation.
Operating stably at this level, these cells
produce 2.91 tonnes of aluminium per pot
per day at exceptionally high purity levels of
99.92%, with specific energy consumption
of 13.2 kWh/kg of aluminium produced and
current efficiency of 95.2%. These performance
parameters translate into measurable
energy conservation and associated operating
cost reductions, as well as reduced environmental
impact through lower fossil fuel
consumption. The DX cells at Emal
Phase I, which began operating at
350 kA, now also operate at 380 kA
– giving an production capacity of
800,000 tonnes a year.
While extremely proud of DX
technology, Dubal’s hunger for continuous
improvement has not been
satiated. To the contrary, ongoing
R&D activities at Dubal have resulted
in a re-design of the DX cells to
enable operating at even higher amperages.
Five new generation cells –
known as DX+ technology and
another UAE flagship innovation –
were built in a pilot line at Dubal’s
Jebel Ali smelter and began operating
at 420 kA at the end of August
2010. The amperage of these pilot
cells has since gradually increased
and reached 440 kA in February
2012, with stable results. Daily output
is 3.37 tonnes of aluminium per
pot, at purity levels of 99.93%, with specific
energy consumption of 13.27 kWh/kg of aluminium
produced. Ultimately, DX+ cells are
expected to operate at 460 kA.
Based on its demonstrated performance,
DX+ technology has been licensed to Emal
Phase II, where a single 444-cell potline is
currently under construction. At this industrial
scale, DX+ is targeted to achieve specific energy
consumption of less than 13.33 kWh/kg
34 ALUMINIUM · 3/2013