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Dubal prioritises energy efficiency

The GTX project and adoption of the chiller technology have helped enhance power generation efficiency and minimise energy consumption

August 2013

Primary aluminium smelting is an extremely energy-intensive industry as it involves an electrolytic process that reduces ore directly to metal.  At Dubai Aluminium (Dubal) – the corporation that owns and operates the world’s largest single-site primary aluminium smelter using pre-bake anode technology – more than one million tonnes of molten aluminium is produced per year, for which the total load demand for electrical power is approximately 1,900 MW.  With a generation capacity of 2,350 MW (at 30 degree C), the captive power plant at Dubal produces more than enough electricity to cater for the company’s electricity requirements. Despite this self-sufficiency, the company is committed to energy-efficiency and is a whole-hearted supporter of the Dubai Integrated Energy Strategy 2030 (DIES 2013), responsibility for which rests with the Dubai Supreme Council of Energy (DSCE), of which Dubal is a member entity.

Indeed, Dubal has adopted the DSCE directives regarding the measures which the Dubai Government is taking to minimise energy consumption in Dubai, in fulfilment of DIES 2030. By implementing the mandated directives, which were issued in April 2011, Dubal had achieved energy savings of 17,375,316 KWh by the end of 2012. Total energy savings in excess of 27 million KWh per year are targeted by the end of 2013.

Moreover, Dubal is providing corporate support for the DIES 2030 initiative to diversify energy sources. These include an investment of Dh20 million ($5.4 million) in the Sheikh Mohammed bin Rashid Solar Park, announced by the DSCE in February 2012, where Phase 1 will yield 10 MW by 2013 and the project is planned to be scaled-up in the future. In addition, Dubal is participating in a feasibility study relating to the establishment of clean coal-fired power stations in the UAE.

MINIMISING FUEL CONSUMPTION
Closer to home, Dubal has since its inception in 1979 adopted the policy of having either combined cycle power plants or co-generation power plants so as to benefit from fuel-free steam turbines (open cycle units have been strictly avoided). A recent case in point is Dubal’s GTX Project, which entailed the unique construction of a large cogeneration plant, comprising one gas turbine and one heat recovery steam generator (HRSG) that produces steam at dual pressure configuration.

The GTX Project entailed the unique
construction of a large cogeneration plant
comprising one gas turbine and one heat
recovery steam generator

The Dubal GTX Cogeneration Plant runs in cogeneration with three combined cycle blocks, each comprising two gas turbines and one steam turbine. By interconnecting the new plant with these existing combined cycle power plants an increase in generating output can be achieved on the respective steam turbines, especially during an outage of one of the gas turbines in these blocks. The additional output from the new plant can be supplied to the Dubal Desalination Plant and used for water production. Unlike conventional combined cycles, the GTX concept involved a very complex steam distribution network, allowing the finished GTX Cogeneration Plant to be operated in one of three modes:

• Add-on Mode – The steam generated by the GTX Cogeneration Plant’s HRSG is distributed to the three combined cycle blocks and to the Desalination Plant, so as to utilise the spare capacity of the latter’s steam turbines.

• Process Steam Mode – The steam generated by the GTX Cogeneration Plant’s HRSG is exported to the Dubal Desalination Plant.

• Replacement Mode – The GTX Cogeneration Plant fills-in for any of the existing HRSGs in the three combined cycle blocks during periodic maintenance procedures, thus maintaining power generation capacity.

Overall, the installation has enabled an increase in Dubal’s installed power generation capacity, without the need for a cooling water source. It has also improved the power station’s power generation efficiency: by integrating the new GTX Cogeneration Plant into the existing Dubal Power Plant infrastructure, better fuel utilisation has been achieved as evidenced by increased efficiency of electricity generation. An initial study has shown that the annual average generation efficiency of the Dubal Power Plant will improve from about 43 per cent to above 45 per cent. This means that Dubal’s annual fuel consumption can be reduced by about 3 per cent under gas-firing operations.

ABSORPTION CHILLER
Another example of Dubal’s commitment to minimising energy consumption is the innovative pilot energy-saving absorption chiller project built on the rooftop of the Dubal Desalination Plant Control Building. The absorption chiller has assumed the functions formerly fulfilled by the electrically-driven vapour compression air-conditioning chillers used for comfort cooling of the building.

The innovative pilot energy-saving
absorption chiller project

The installation is the UAE’s first-ever absorption chiller using waste heat and the first such application in a power plant. A nominal volume of the steam produced by the captive cogeneration and combined cycle Dubal power station is used (about 0.6 tonnes of steam per hour); and the absorption chiller process uses just 40 per cent of the electricity consumed by the conventional electrically-driven chillers to produce sufficient cooling for the same purpose. This means that the absorption chiller could reduce Dubal’s energy consumption by approximately 626,800 KWh per year, equating to a reduction in carbon dioxide (CO2) generation by about 350 tonnes per year (or an estimated 180 cars off the road per year). The concept can also be used for other applications where energy-efficient cooling is required – such as equipment cooling.

CUTTING ENERGY CONSUMPTION
Acknowledging the energy-intensive nature of the smelting process, Dubal has continuously striven to be a role model in terms of reducing kWh/kg of aluminium production since inception. Through extensive research, the Dubal Technology Development department has developed proprietary high amperage reduction cell technology that operates at benchmark specific energy levels. The 40 DX Technology cells at Dubal consume less than 13.2 kWh/kg aluminium (at 385 kA); while the five pilot DX+ Technology cells at Dubal consume less than 13.33 KWh/kg aluminium (at 420 kA). DX Technology has been installed in the 756-cell Emirates Aluminium (Emal) Phase I; and DX+ Technology has been licensed to Emal Phase II (444 cells, currently under construction).

In addition, a ground-breaking pilot project has confirmed Dubal’s expertise at retrofitting older potlines with modern technology, leading to greater energy-efficiency. The project, conducted in 2012, successfully reduced specific energy consumption – from approximately  15 KWh/kg aluminium to below 13 KWh/kg aluminium.

ONGOING UPGRADES
Dubal continuously upgrades and enhances its gas turbine fleet to achieve better energy-efficiency. The pace of change has accelerated in recent years, resulting in a complete upgrade of the company’s five main gas turbines.

The D18+ cell technology pilot line

Many other smaller projects to improve energy-efficiency have been implemented, or are in progress. This has led to a concomitant reduction in Dubal’s total greenhouse gas emissions, the total reduction between 2007 and 2012 amounting to 1.06 million tonnes of CO2eq emissions, thus simultaneously minimising Dubal’s carbon footprint and the overall impact of Dubal’s operations on the environment.

These initiatives and achievements clearly demonstrate Dubal’s contribution to the realisation of DIES 2030 goals to enhance both the demand- and supply-side management of the UAE energy sector. They also testify strongly to the company’s corporate commitment to minimising the impact of its operations on the environment, and its adherence to the principles of sustainability.




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