Reflections on rapid construction at Shoaiba
Power demand in the Kingdom of Saudi Arabia has tripled over the last two decades in line with a fast growing population and fast expanding economy. With electricity demand growing at an average of 7% per annum, it is estimated that the country will need at least an additional 30 GW of generating capacity by 2023-25. This is twice the current installed base.
To meet this growing demand, in October 1998 Saudi Electricity Company (SEC) signed a contract to build stage 1 (5 x 400 MW) of the Shoaiba oil fired power project. Following completion of stage 1 in 2003, a further contract was signed in March 2004 for stage 2 (phases 1 and 2), consisting of a further six 400 MW units, bringing the total output of the plant to 4400 MW.
When completed in 2008 the plant, which will provide 32% of the western region’s current power requirements, will be a record breaker in terms of size for a conventional oil fired plant in the Middle East. As the project nears completion, stage 2 has broken records in terms of construction and commissioning time for a steam power plant.
Completed units at Shoaiba
Project overview
The Shoaiba plant is located on the coast of the Red Sea about 100 km south of Jeddah. The plant is in a flat coastal desert area that experiences extreme temperatures ranging between 11° C and 49° C and a relative humidity of 100% that can occur in any month.
In addition to providing power for the region, the plant also provides a small amount of desalinated water for the process and small community buildings that house the operation and maintenance team. There is no commercial export of water outside the plant.
The power station is being built under an EPC turnkey contract by Alstom Power with one external consortium member, Saudi Archirodon. As consortium leader, Alstom has delivered all the major components, such as the boilers, steam turbine generator sets, distributed control system, complete water steam cycle, instrumentation and control, electrical equipment, balance of plant and desalination. Saudi Archirodon is responsible for civil works.
Each of the eleven 400 MW units consists of a steam turbine and a reheat boiler capable of burning crude or heavy fuel oil. The controlled circulation boilers feature a reheater for the steam expanded in the HP turbine and an economiser, which heats the feedwater before it enters the steam drum and cools the flue gas before entering a regenerative air preheater.
The boilers also use tangential firing with over-fire air to reduce NOx. Each boiler generates 1100 t/h of steam at pressures of 172 and 40 bar, and temperatures of 541°C and 539°C. The high-pressure steam generated is expanded in a three-casing steam turbine and condensed in a seawater-cooled condenser at a pressure of 90 mbar. Extraction water is then heated through seven heaters (four LP, feedwater tank and two HP heaters).
The steam turbine is coupled to a generator that has a rating of 510 MVA and terminal voltage of 24 kV. This terminal voltage is transformed up to 400 kV for dispatch to the 60 Hz Saudi grid.
Flow diagram for Shoaiba, multiphased 400 MW class oil-fired steam power plant
Fast track
The project is separated into two stages and four phases. Stage 1 consists of phase 1, 3 x 400 MW, and phase 2, 2 x 400 MW. Stage 2 consists of phase 1, 3 x 400 MW, and phase 2, 3 x 400 MW.
The plant was built under market conditions that have in principle seen power plants taking longer to build. The general slow-down in construction times and delays has been caused by the ‘China effect’, where massive construction programmes underway in China have led to a global difficulty in securing material not to mention the attendant increase in material prices. Through its global long-term relationships with its partners and vendors, Alstom was able to overcome this challenge. This necessitated the acceleration of the procurement process to reserve in advance the structural steel and other materials in short supply such as titanium and copper.
But perhaps the major factor in making short lead-times possible has been Alstom’s ‘Plant Integrator’ approach. As a company with EPC expertise, which designs and manufactures all the major plant components in-house, Alstom was able to design and manufacture components to fit in with EPC tasks in order to produce the optimum overall time schedule. Typically, on Shoaiba, over 75% of the supply value is for Alstom supplied equipment. This meant manufacturing of the major items could be co-ordinated and controlled to suit the availability of material and to meet the needs of the schedule.
In terms of design, in any steam plant the boiler design and ordering of the boiler parts are critical to the completion schedule of the project. In constructing stage 2 of the project, Alstom was able to draw on the experience gained in stage 1 and the ‘repeat effect’ to optimise the schedule.
Units 10 and 11 were erected almost in parallel and this unprecedented feat presented a particular challenge. The construction of the steel structure for Unit 11 began on 1 August 2004 and Unit 10 just one month later.
All of the boiler foundations for Phase 1 were scheduled to be built at the outset so that the area would be accessible for the erection of the steel structure as early as possible. The foundations for all the boilers were progressed simultaneously and back-filled as soon as possible in order to provide the necessary access to the working platform for the subsequent erection of the steel structure. This approach saved around 5 months on the construction time.
The steam turbines, installed in the shadow of the boiler so to speak, were themselves not without challenges, namely the securing of the correct forged materials for the steam turbine. Whilst the “China effect” made it challenging to obtain the material for one steam turbine, to have sufficient for two required exceptional efforts assisted by the ‘Plant Integrator’ advantages.
Constructing this plant was a huge task.
It required around 7 000 000 m3 of backfilling, about 70 000 t of structural steel and almost 10 000 km of cable. At the peak of construction there were some 7000 workers on site. Nevertheless, 9 million man-hours were achieved without incident and without loss of productivity.
Construction underway at Shoaiba
Ahead of schedule
The letter of commitment for stage 2 phase 1 was signed on 22 January 2004 and that for stage 2 phase 2 on 26 February 2005.
The first units of both phases of stage 2 (units 11 and 8, respectively) were synchronised and providing power to the Saudi grid only 24.5 months after the client commitment date.
First firing of unit 11 took place on 9 November 2005 and it began its reliability test run just 28 months after the contract was awarded – a record for steam plant.
Equally impressive, unit 10 began its reliability test run just one month later. The completion of two successive units of a steam plant is usually separated by 5 – 6 months.
As of today, all units at Shoaiba are available for commercial operation.
The last unit (unit 6) successfully completed its reliability test run some 158 days in advance of the contract schedule.
Stage 2 features an Alstom distributed control system (DCS). The use of an in-house control system meant that Alstom was able to simulate operation of its own components and fine tune operation before the components were integrated into the power station. This allowed it to address potential problems at an early stage and thus streamline the commissioning process.
But it is important to note that Alstom would not have been able to meet these targets without full co-operation from the client, SEC, and the drive to secure a win-win situation. Developing a team approach with the common target of producing power as soon as possible remains an overriding key to success.
Panoramic view of Shoaiba showing cable racks between the power block and the GIS subsubstation
