Running on emulsion in the Philippines20 November 2000
Four single-shaft combined-cycle units using V84.3A gas turbines have been successfully started up in the Philippines, initially using liquid fuels, including water/fuel-oil emulsion. Two more identical units are under construction at the same site.
As reported recently in Modern Power Systems (September 2000), Siemens 3A gas turbines are beginning to put their problems behind them and are now being successfully commissioned around the world.
A recent example is the Santa Rita plant at Batangas in the Philippines, where blocks 1 and 2 entered commercial operation in June and August respectively. This was some time after the original schedule, but the plants at Santa Rita incorporate all the lessons learned from 3A projects elsewhere and from extensive test bed programmes in Berlin. On arrival at site modifications were carried out to each of the four V84.3A gas turbines (the first arrived in December 1998). These modifications involved complete dismantling of all four turbines and included fitting of cylindrical burner outlet extensions to the burners to eliminate the phenomenon of “humming”, which results from pressure fluctuations caused by local variations in the combustion process (on a time scale of milliseconds).
However patience and persistence have paid off and so far the turbines have been performing well, with emissions well below the target levels (eg NOx emissions of 81.3 ng/J (47.8 ppm) and 75.1 ng/J (44.1 ppm) on condensate fuel and distillate oil fuel, respectively during reliability runs).
One relatively unusual feature of Santa Rita, at least as far as Siemens gas turbines are concerned, is that it is currently operating on a water/fuel-oil emulsion, which has the effect of reducing NOx emissions but is also beneficial when it comes to control of humming.
Apart from the Berlin test facility, Santa Rita is the first plant with a Siemens V-series turbine to run on emulsion. When running on fuel oil it is normal to inject water into the gas turbine combustion zone for NOx reduction. But use of emulsion results in a more even mixture of water and fuel than injecting water into an already combusting flame, leading to more even combustion and therefore less humming. The use of emulsion also provides more effective NOx control.
Each of the two blocks at Santa Rita consists of two 250 MWe single-shaft combined-cycle units, ie four units in all. Each of the four units (also called GUD 1S.84.3A modules) comprises a V84.3A gas turbine (the 60 Hz version of the 3A), an HP/IP/LP steam turbine, and a generator – all supplied by Siemens. There is an SSS synchronous clutch between steam turbine and generator. Each unit also has one heat-recovery steam generator (supplied by Samsung Heavy Industries), with a stack height of 60 m, and one generator transformer (supplied by Fuji Electric).
The plant, which features a high degree of modularisation, was intended for baseload, and no bypass stacks are provided, although it is not yet running in that mode and is essentially load following.
Although currently operating on Enron-supplied liquid fuel - gasoil (distillate), condensate and naptha - the plant will be switched to natural gas when gas from the Malampaya field becomes available, with the liquid fuels as back-up. Indeed, it was to exploit gas from the Malampaya field that prompted development of Santa Rita in the first place, together with its next door neighbour the 500 MWe San Lorenzo plant (see below), along with a third natural-gas-fired combined cycle plant. The Malampaya gas field, off the coast of the Philippine island of Palawan, was discovered in 1989. It is being developed by Shell, Texaco and the Philippine National Oil Company and has confirmed natural gas reserves of at least 2.5 trillion cubic feet and 85 million barrels of condensate.
The Santa Rita plant is owned by First Gas Power Corporation (FGPC), a wholly owned subsidiary of First Gas Holdings Corporation, which is a joint venture company owned by First Philippine Holdings Corporation (51 per cent), BG plc (40 per cent) and the pension fund of Meralco, Manila Electric Company, the utility serving the Manila conurbation and the off-taker of power from Santa Rita. The EPC contract was placed with Siemens in 1996, financial close was achieved in September 1997 and construction started in November 1997.
The project, on a site of 35 hectares, has included the building of a large jetty for unloading of liquid fuel and a tank farm consisting of: Untreated liquid fuel tanks – total capacity 141 300 m3 Treated liquid fuel tanks – total capacity 13 400 m3 Untreated start-up diesel tank – total capac ity 100 m3 Treated start up diesel tank – total capacity 500 m3.
The plant is directly cooled by seawater, unlike, for example, its near contemporary the V94.3A Otahuhu plant in New Zealand (see Modern Power Systems, January 2000), which uses a hybrid cooling system.
At Santa Rita the circulating cooling water is drawn from Batangas Bay by a pump through two 2.5 metre diameter fibreglass pipes at a rate of 19 m3/s.
The electrical concept
The plant also includes a 230 kV outdoor switchyard/substation and a 35 km long high-voltage overhead transmission line to the existing Calaca outdoor substation, which is operated by the Philippines National Power Company. From there the power is exported to Meralco.
Provision has already been made for the connection of a further two overhead transmission lines to accommodate plant extension.
Separate auxiliary power supply systems are provided for the turbine generators. While the gas turbine is being accelerated with the frequency converter motoring the generator and during plant stops, auxiliary power is imported from the grid. Both the 480 V switchgear and a battery-backed 220 V DC system with battery chargers are supplied by the respective independent 6.9 kV medium voltage switchboards. Static converters step this DC down to 24 V for I&C and other loads.
Separate switchgear and battery-backed 220 V DC systems are provided to supply higher level loads. This equipment is under normal operating conditions supplied via 6.9 kV connections from one or two turbine generators. The incoming feeder of the 6.9 kV black start and emergency diesel sets are also provided from this general switchgear, which ensure supply to the most important loads in the power plant. In cases of emergency a single shaft unit can be started up with the black-start diesel generator.
Although, somewhat bizarrely, it has a different name and a very slightly different project structure, the 500 MW San Lorenzo plant is basically units 5 and 6 of Santa Rita. San Lorenzo uses identical Siemens technology, ie two 250 MWe single shaft combined cycle units, and will use the same control room as Santa Rita, requiring just two more operational staff. Construction is currently underway on the two San Lorenzo units alongside the operating Santa Rita units, with operation scheduled for 2002.
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