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Power politics

Structures Abu Dhabi power station

Criss-crossing service lines, summer heat and tight security are all issues in the construction of a new power and desalination plant in Abu Dhabi, discovers Adrian Greeman.

Water is life to desert countries like the United Arab Emirates, and oil is wealth, so it is not surprising there is tight security around the Umm al Nar desalination plant and oil refinery complex just outside Abu Dhabi.

Anglo-Japanese-Arabic joint venture the Arabian Power Company (see box) is building a major 1,200MW power generating and water distillation plant at the site to extend and replace existing facilities.

'Police checks and passes have as much to do with the presence nearby of military facilities as anything else, ' believes Arabian Power Company business manager Junichi Yamada. But daily gate checks and clearance add to the normal logistical problems of a major project. The Umm al Nar scheme is among the biggest in the Middle East.

'We are installing five 240MW gas turbines, ' says Yamada, 'which will sit in a row along with a waste heat exchanger.'

From the boiler a 300MW steam turbine will be fed at high pressure. In turn its low pressure output will deliver heating to a five unit water distiller.

Technologically the plant will be at the cutting edge. New General Electric 9FA turbines, the first of their kind in the Middle East, and state of the art distillers from contractor Hitachi-Zosen have been specified. 'The waste heat exchange boiler is also pretty special, with a novel two stage firing system, ' adds Alan Rosewell from the owner's engineer, UK consultant Mott MacDonald, which is checking design and supervising construction.

But the project is complicated by the existence of older plant alongside. Not only must the various contractors take care not interfere with running plant and the all important power and water they are producing, but they must integrate new and old as they go.

'Our job is both to install and operate new plant and to take over operation of the older sections, ' says Yamada. Some of the oldest plant, 25 years old or more, will be phased out in the first three years of operations after 2005. Newer sections, the most recent being water desalinators brought on line only in 2002, will connect into the brand new systems.

These will come on line in 2005 and 2006.

Civil engineering contractor Toshiba Corporation is building foundations and support structures, and will later supply the waste heat steam generator and steam turbine.

'Their job is not so complex, ' says Yamada, ' because the substructures are very simple - just basic concrete plinths in the main. The ground is good here and although some piling is needed, it is not difficult.

We have hard limestone about 7m to 10m down.'

The Toshiba construction team agrees. 'Our main problem is the security aspect which can create problems for getting labour in and out of the site, ' says representative Mike Oda.

With 400 mainly Indian workers on site, rising to 700, obtaining visas and site permits can sometimes takes weeks. Permits are also needed for the trucks arriving and leaving with materials.

Construction itself is very straightforward, comprising mainly a series of pedestals for heavy turbines, the largest 6m high for the steam unit. Later there will be steelwork for the three main equipment buildings and reinforced concrete frames for ancillary buildings. Steel is being made in Sharjah.

Lateral thinking has enabled Toshiba to reduce excavation volumes for pad foundations and pile-caps. Quickly-built breezeblock walls are used as formwork, buttressed with polystyrene blocks to support them during pours. They are then simply integrated into the foundation.

Groundwater is a problem for the excavations, because the water table sits just 1.5m down.Dewatering is necessary for most pits even though few are more than 6m deep.

Groundwater derives from the sea nearby so has high sulphate and chloride content making it very aggressive - a universal problem on the Gulf.

'It means we have to protect all the concrete in the ground.

Piles have epoxy-coated reinforcement and for the most important structures there is a 3mm waterproof membrane.

We also use a very durable concrete mix with micro silica, PFA and admixtures, ' says Oda.

'We work to the international standard set in the CIRIA guide to concrete in the Middle East.

It has been well established and is usually available from ready-mix suppliers.' Concreting must usually be carried out at night, particularly in summer when temperatures reach 50infinityC plus around midday.

Suppliers of the new plant will have to cope with making phased connections into the existing systems, to allow old and new plant to work together. Connections will involve installation of some complex modern computer control systems to 'allow quite fancy rapid adjustments of the controls for maximum thermal efficiency', says Rosewell.

The client

International Power has expanded rapidly overseas since it was separated from UK generator Innogy in 2000.

Current projects are dispersed from the Czech Republic to Pakistan, Oman, Malaysia and Turkey. In Abu Dhabi the company is involved in a second project at Shuweihat and it recently announced international financing for the 1,075MW Saudi Aramco cogeneration projects in joint venture with Saudi Oger in Saudi Arabia.

For the Umm al Nar project, International Power has a 50% holding in a joint venture investment company with Mitsui Corporation and Tokyo Electric Power Company. This in turn has bought a 40% stake in the power and desalination plant from Abu Dhabi Electricity & Water Authority (ADWEA), via the Arabian Power Company.

International Power then has a 70%/30% venture with TEPCO in the long term maintenance company ITM.

The Abu Dhabi Water & Electricity Company will buy power and water for the 23 year operating period.

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