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Dubai, United Arab Emirates:The innovative thinking and quest
for operating efficiency through continuous improvement at Dubai
Aluminium (DUBAL) has again been recognised on the international
stage. DUBAL's unique GTX project, which was presented by Tayeb M M
H Al Awadhi (Vice President: Power & Desalination) at Power-Gen
Asia, held in Singapore during 2010, has won the Project of the
Year 2011 "Honourable Mention Best Gas-Fired Project" at the
Power-Gen International 2011 conference, held recently in Las
Vegas, USA.
To appreciate the significance of the award requires an
understanding of the GTX project, its origins and the role it
plays. The project's setting is as important. In this regard, DUBAL
is one of the largest single-site aluminium smelters in the world
(producing more than 1 million metric tonnes of hot metal per
annum). The smelter complex includes a 2,350 megawatt (MW) power
station (at 30˚C), a water desalination plant and a large carbon
plant. The power station is designed to provide both electricity to
the smelter reduction process and saturated steam to the water
desalination plant. The present average aluminium smelting power
demand is about 1,900 MW, amply covered by the generation capacity
of the power plant.
Back in 2006 (i.e. prior to the GTX project), the DUBAL power
plant comprised 22 Gas Turbines and 7 Steam Turbines. The average
generation capacity of 2,115 MW met the 1,750 MW
average demand of the site at that stage. The plant configuration
fulfilled the continuous load supply requirement with sufficient
spare generation capacity to cover the loss of the highest
generating unit while one large unit was on planned maintenance
outage. The annual average station efficiency was 43 per cent, with
three to four Frame 9B Gas Turbines being required to meet the
plant's power and water demand.
An analysis of the planned extensions of DUBAL's existing
potlines indicated that the electricity generation requirements
within the DUBAL complex would rise to about 1,850 MW by 2010. A
feasibility study, conducted in 2006, showed that DUBAL's reserve
capacity would not be sufficient to cover the additional power
demand. Furthermore, the complex would have to rely on
less-efficient machines, which had already partially completed
their asset lifetime. It was clear that an increase in the
installed generation capacity of the DUBAL Power Plant complex was
needed.
The same feasibility study showed that the annual average
generation efficiency of the DUBAL Power Plant complex could be
improved by installing a GTX Cogeneration Plant; and that the
annual fuel consumption for power generation purposes could be
reduced by about 4 per cent. The expected partial operation of the
proposed GTX Cogeneration Plant on distillate oil due to possible
gas shortages in summer further improved the profitability of the
project.
Given these benefits, the project was given the go-ahead - with
the primary objective of implementing a GTX Cogeneration Plant
being to improve the power generation efficiency and decrease the
environmental impact of the DUBAL Power Plant complex. This would
be achieved by integrating the proposed GTX Cogeneration Plant into
the existing DUBAL Power Plant infrastructure, thus enabling better
fuel utilisation by increasing the efficiency of electricity
generation and water production within the complex; and minimising
industrial gas emissions, specifically oxides of nitrogen (NOx) and
carbon dioxide (CO2). A secondary objective was to
increase the total power generation capacity of the DUBAL Power
Plant by leveraging the ability of a GTX Cogeneration Plant to
raise the installed generation capacity.
Unlike a conventional Combined Cycle Power Plant (CCCP), DUBAL's
GTX project entailed installing one large state-of-the-art Gas
Turbine and one dual pressure Heat Recovery Steam Generator; and
then supplying the steam heat energy to three existing Frame 9E
Steam Turbines and the water desalination plant. The GTX
Co-generation Cycle is designed to work in three modes:
- Additional steam heat energy to operate the existing Steam
Turbines on peak load;
- Additional steam heat energy to replace one existing Heat
Recovery Steam Generator; or
- Steam heat energy to the water desalination plant.
- In essence, the new technology and new
process concept is not only capable of accommodating the increase
in power production and steam management, but is also more flexible
to accommodate the downtime and maintenance requirements resulting
from operating the existing Steam Turbines on peak load.
By enhancing the Steam Turbine output to peak operation, or
replacing an existing Steam Generator while on maintenance, the GTX
plant has enabled an annual average increase in overall fuel free
Steam Turbine output of over 50 MW while the surplus steam directed
to desalination plant produces additional water. Accordingly, the
annual average station efficiency rose from 43 per cent to 44.5 per
cent.
Moreover, the new GTX block has introduced 220 MW of reserve
capacity, which has been utilized to increase the load carrying
demand by 150 MW while the spare 70 MW has reduced demand for one
Frame 9B Gas Turbine. Switching-off one Frame 9B unit has resulted
in gas savings of about 15 mscfd, and a concomitant reduction in
CO2 emissions of 300,000 tonnes per annum.
The GTX project, which cost US$183 million, is the first of its
kind in scale and application, as integration with CCPP and
desalination has never been done before. It's also a first in the
aluminium industry, where no similar GTX projects are known.
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