Achieving flexible baseload down under

Two gas fired combined-cycle power plants recently entered operation in Australia. The NewGen Kwinana and Tallawarra power stations are said to be amongst the most efficient in the country and have the added benefit of offering their operators the flexibility they need in a deregulated electricity market.

M. Chilcotte, L. Dawes & P. Krummenacher, Alstom Power, Australia

A combination of deregulation and the increasing need for new baseload and peaking capacity has prompted the recent start-up of two new combined-cycle plants in Australia. The NewGen Kwinana and Tallawara power plants are two projects, which were built by Alstom on a turnkey basis, that are now providing reliable baseload power to satisfy the country’s summer peaks.

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The first of the two projects to enter commercial operation was the NewGen Kwinana gas fired power station. The Kwinana project is located 30 km south of Perth in Western Australia, and is located on a site adjacent to the 240 MW Cockburn power station, which was built by Alstom back in 2003.

The contract for Kwinana was awarded to Alstom in September 2005 by NewGen Kwinana Power, with the Notice To Proceed given in March 2006. Under the turnkey EPC contract, Alstom’s responsibilities included overall plant engineering, global procurement and logistics, civil, electrical and mechanical construction and commissioning of the plant.

Alstom’s Plant Integrator approach allowed it to add value to NewGen Kwinana Power by integrating several of its advanced products to form a unique plant tuned for the specific needs of Western Australia’s South West Interconnected System, which is the state’s biggest interconnected network.

The scope of delivery included a GT13E2 gas turbine, an OCCTM heat recovery steam generator (HRSG), a COMAX 160 MW steam turbine, two TOPAIR generators, a seawater cooled condenser, the ALSPA plant control system, step-up transformers and a 330 kV switchyard.

With a maximum power output of 320 MW (at nominal ambient temperature of 32 à‚ºC) Kwinana is now the largest combined-cycle plant in Western Australia.

Taking Advantage of Peak Power Prices

To deal with the city of Perth’s daily load peaks NewGen Kwinana Power requested a baseload combined-cycle plant that would also allow it to take advantage of peak power prices in the wholesale power market.

To fulfil these requirements Alstom selected the KA13E2-1-SF standard design combined-cycle reference power plant. In order to provide further peaking power the plant was equipped with an additional gas burner located in the duct between the gas turbine and the HRSG, which results in an additional 80 MW of power.

In addition, by using the GT13E2’s short-term peak firing capability a further 20 MW of electricity can be produced for short periods of time making the plant versatile enough to deal with daily peaks, as well as baseload operation.

The plant is designed to perform ten hot starts per year, five warm starts and five cold starts, and is also capable of daily cycling by using the leading edge technology in the HRSG, which is ‘Optimized for Construction and Cycling’ (OCC). The plant is designed for high reliability with an equivalent availability factor more than 94 per cent.

With an efficiency of approximately 53 per cent, the power station represents the lowest cost baseload electricity for the South West Interconnected System, and is significantly more efficient that the equivalent coal plants in the region.

The GT13E2 gas turbine has an output of 160 MW and runs on natural gas with a nominal higher heating value of between 35.1 MJ/m3 and 42.3 MJ/m3. The turbine features an annular combustion chamber with low nitrogen oxides (NOx) EV burners, which keeps NOx emissions from the turbine between 25 and 28 ppmv.

Hot exhaust from the gas turbine at a temperature of about 510 à‚ºC enters the dual-pressure HRSG with reheat that generates HP steam at a temperature of 543 à‚ºC and a pressure of 126 bars, and LP steam at 282 à‚ºC/5.2 bar. Supplementary firing occurs in the horizontal gas path to increase the quantity of steam that can be fed to the steam turbine.

The steam turbine is a single-shaft, axial exhaust-condensing turbine, with a nominal capacity of 160 MW based on Alstom’s COMAX technology.

The plant’s steam bypass allows steam to be directed to the condenser, providing a faster start-up and shutdown, operation for short periods with the steam turbine out of service, reduced noise on start-up by avoiding venting steam to the atmosphere and reduced water losses.

When running in combined-cycle mode, flue gas is exhausted from a 60 m main stack that is located after the HRSG. The stack has sampling and access points to ensure that the local stringent environmental standards are maintained.

Although there is no shortage of seawater in Western Australia, fresh water is a precious commodity. In order to minimize its use a filtration system was deployed that recovers and recycles water from the HRSG blowdown, which traditionally is disposed as effluent.

Project Delivered On-time

Civil works began in October 2006, with the gas and steam turbines arriving on site in July 2007. The HRSG, which was delivered around the same time, was built as pre-fabricated modules that were tilted up on site.

But there were challenges, which the project managed to successfully recover from. A generator transformer à‚— a piece of equipment that normally has a lead-time of anywhere between 14-18 months à‚— was dropped and damaged during transport in March 2008. Fortunately, Alstom was able to replace the generator transformer within two months.

The NewGen Kwinana combined-cycle power plant near Pert, Western Australia. With a maximum power output of 320 MW, it is Western Australia’s largest combined-cycle plant.
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Further, a month was also lost towards the end of the project because of the Varanus Island gas incident, which resulted in the loss of gas supply for a month during the plant’s commissioning phase.

Nevertheless, despite having to acquire a new transformer and losing the gas supply all in the last six months of the project, the project was still delivered on time.

Lee Dawes, Alstom project director, states: “Alstom’s ability to integrate plants on a turnkey basis is a key differentiator in the Australian market place. Keeping the interfaces within a tight project team leads to a better overall product for our customers and a safe and efficient construction phase.”

This approach has produced an excellent track record for delivering plants on time in a market where meeting schedules can be a tremendous challenge.The gas turbine was first fired at the end of May 2008, with combined-cycle operation beginning in July 2008. Performance testing was completed in late September and the plant went into commercial operation on 9 October 2008.

NSW’s First Baseload Plant in 25 Years

The Tallawarra project was commissioned shortly after Kwinana, achieving handover to the owner TRUenergy in January of this year. Headquartered in Melbourne, TRUenergy has more than 1.2 million electricity and gas customers. In addition to Tallawarra, it owns the Yallourn power plant and the Hallett power station.

The plant is the first baseload plant to be built in New South Wales (NSW) in 25 years, and built on a 600 ha site where a coal fired plant was decommissioned in the 1990s. The new plant, however, has a much smaller footprint and blends in with the beautiful landscape around Lake Illawarra.

TRUenergy’s Tallawarra combined-cycle plant – claimed to be the most efficient in Australia
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The project was given the Notice To Proceed in June 2006. On site, there was a high level of involvement from local construction companies. During construction, one challenge was to ensure that a ‘green layer’, which covered rubble potentially containing asbestos from the old power station was not penetrated. Construction works had to closely follow a careful design of underground services, deep foundations and pump pits.

The plant is built on part of the original site and uses the existing cooling water structures of the old power station. This created further challenges in meeting, for example, the requirements of the Building Code of Australia in terms of safety distances and access. Nevertheless, high standards for health and safety were demonstrated during plant construction.

Environmental performance is a top priority for TRUenergy, which is committed to reducing its greenhouse gas emissions by 60 per cent by 2050. The company therefore wanted the most efficient combined-cycle gas fired power plant possible.

High Operational Flexibility, Availability and Fast-Start

Alstom was awarded a full EPC turnkey contract for the project. The contract covered the delivery of a KA26-1 single-shaft combined-cycle unit including: overall plant engineering; in-house design and manufacture of the gas turbine, steam turbine and generator, HRSG and the plant control system; procurement and logistics; civil, electrical and mechanical construction; and full commissioning responsibility.

Alstom was also awarded a long-term service contract to carry out scheduled maintenance and provide operational support. With requirements for high operational flexibility, availability and fast-start capability, the GT26 gas turbine, the heart of its KA26-1 combined cycle block, was selected.

Tallawarra uses the latest GT26 turbine rating. This unit has an improved compressor for increased mass flow and better seals for reduced leakage of air to deliver an additional 7 MW compared to the previous machine.

The GT26 is connected to a hydrogen-cooled generator and a steam turbine on a single shaft. The plant is connected to the local distribution 132 kV grid, which is interconnected to the NSW 330 kV grid via substations.

The gas turbine has a rated output of 288 MW. Exhaust gas leaving the gas turbine is fed into a triple pressure reheat HRSG, which generates the steam that is fed to a triple casing steam turbine to generate an additional 160 MW. The steam turbine is a three-casing design with HP, IP and LP sections that are connected to the generator via a self-synchronizing clutch. The steam turbine has a direct seawater cooled condenser, which uses water from Lake Illawarra à‚— the lake is a coastal lagoon.

Australia’s Most Efficient Power Plant?

Tallawarra is another example of a project where Alstom used its Plant Integrator capabilities to design a high efficiency baseload plant that is also able to take advantage of merchant market. With all components, including the plant distributed control system, being designed and delivered by Alstom, it was able to integrate the components in a manner to achieve a high electrical efficiency. The plant is now believed to be the most efficient in Australia.

Furthermore, the sequential combustion feature of the GT26 means that the plant has high part-load efficiency. Emissions are maintained at low levels when the turbine is run at low load. This also means that the plant has very high flexibility. The power station, although operating predominantly in baseload, is designed for daily start-stop operation. The latter operating regime will be more commonly used during the spring and autumn periods. The ability to reach full load from hot conditions in just one hour is a real benefit for TRUenergy.

During performance testing, which began in December 2008, the plant exceeded all of its guaranteed values. It achieved a net electrical efficiency of 58.5 per cent and a baseload net electrical power output of 410 MW at 25 à‚ºC ambient temperature.

Tallawarra also has power augmentation in the form of an evaporative cooling system located at the inlet of the gas turbine, as well as a high-fogging system. This enables TRUenergy to generate and more importantly sell an additional 20 MW at peak times.

The gas turbine was first fired in early October 2008 and the generator first synchronized in mid-October 2008. The performance testing and the reliability run were completed in December 2008, and the plant was handed over to TRUenergy in January 2009 in time for NSW’s summer peak.

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