March/April 2000

Siemens on fast track tocommission Santa Rita

In the old days a steam plant with four250 MW sets might at best have beenbrought into operation over the spaceof two years, with one unit being putinto service every six months in accord-ance with the generation developmentplan of the utility concerned. Later,utilities faced with rapid growth inelectricity demand were attracted to thecombined cycle because a large multi-shaft block allowed the gas turbines tobe commissioned quickly and runsimple cycle for upwards of 12 monthswhile the steam cycle was completed.

The trend to install large single-shaft combined cycle blocks with, forthe 60 Hz market, gas turbines ofabout 180 MW has been accompaniedby a move to reduce the constructiontime by having a greater degree offactory assembly for what is effectivelya standardised plant design.

The electricity supply system in thePhilippines is in a process of change.The National Power Corporation(NAPOCOR) is no longer in thebusiness of building generating plant.That is left to IPP’s either alone or inpartnership with NAPOCOR, to buildnew plants or refurbish and repowerexisting stations. In effect the com-pany, which is still in the public sector,will become the market place for elec-tricity trade, with responsibility for thehigh-voltage grid and the HVDC linksbetween the major island networks.

Another factor which has broughtthe Santa Rita and other combinedcycles into being is the discovery ofthe Malampaya gas field offshoresouthwest Luzon in 1990. Shell, asdeveloper of the field saw that in theabsence of any gas market in Manilaand the other large cities, the only wayto exploit this field would be throughpower generation. 3000 MW was seenas the size of market that wouldenable the development to go ahead.

As development of the first com-bined cycle plants got under way, thecountry was seeing growth in demand

of 7.5% per year, then at the beginningof 1998, growth slowed down and isnow effectively at zero. In this situationnew construction is for plant replace-ment to benefit from improved effi-ciency and environmental quality ofpower generation.

Basically three large combinedcycle plants and a planned 300 MWCHP unit at the Caltex refinery inBatangas define the market thatenables the development of theMalampaya field. The first of these,Santa Rita, with four single-shaftblocks of Siemens Model V84.3A, isnearing completion. A second plant,San Lorenzo, on the neighbouring siteachieved financial closure February 15It will have two of the same combinedcycle units as Santa Rita and anumber of shared facilities includingthe control room. These two plantsaccount for half of the 3000 MW.

About 40 km north along the coast,at Ilijan, site preparation is in progress,pending financial closure, for a 1200MW combined cycle to be built for ajoint venture of NAPOCOR andKEPCO (Korea Electric Power Corp).Mitsubishi is reportedly the primecontractor. The plant is expected to becompleted just as the first gas arrives.

It was because of the prospect of

developing gas infrastructure in thePhilippines that British Gas holds 40%of First Gas Power Corporation, theowners of Santa Rita. The otherpartners are First Philippine Holdings,with 51%, and the Meralco PensionFund with 9%. For San Lorenzo, theowners are a joint venture of FirstPhilippine Holdings and British Gasalone. But Meralco, as the electricitydistributor in Manila will buy the netoutput of both stations which must bewheeled over the NAPOCOR 230 kVgrid. Indeed, Siemens’ turnkey contractfor Santa Rita includes construction ofa 35 km dual-circuit transmission linefrom the 230 kV switchyard on site toNAPOCOR’s Calaca substation, thecapacity of which is more than will bethe combined output of both plantswhen San Lorenzo comes into opera-tion in the second quarter of 2002.

Santa RitaIn December 1996, Siemens wereawarded a turnkey contract by FirstGas Power Corporation for the con-struction of a 1000 MW power plant.Preliminary access to site was grantedin July 1997 and financial closure wasachieved two months later on Septem-ber 4. Official ground breaking to signifythe start of works was performed two

Siemens on fast track tocommission Santa Rita

A 1000 MW combined cycle with four single-shaft blocks is nearing completion inthe Philippines. Through careful planning of the commissioning program on twofuels, Siemens are able to bring all four units into commercial operation within thespace of a few days.

Figure 1. Santa Rita power station viewed from the fuel unloading jetty. Unit 10, the firstto complete commissioning is at right of picture. The mobile crane at left is working onpreparation of the San Lorenzo site

months later on November 17.As originally planned the plant was

to be two 500 MW blocks and thisterminology has stuck even though thefour units are considered separate andnumbered 10, 20, 30 and 40. In anyevent the plan was to bring 10 and 20to completion in 24 months and 30 and40 after a further three months.Operational factors outside Siemenscontrol have led to some delays sothat the four units were due to behanded over in April, 2000.

Each unit is similar in its basicconfiguration of the power train, andthe steam cycle is similar to that of the50 Hz single shaft units with ModelV94.3A, as for instance at Otahuhu,New Zealand, (Jan/Feb 2000, p.34).The two gas turbines were developedas a common scaled design so thatalthough the mass flow is less, thetemperatures are the same.

Operating examples of ModelV84.3A in the United States exhibitedthe same humming at high loads thatwas observed on the larger ModelV94.3A. This was due to a circumfer-ential resonance being set up in thecombustion chamber which, as in thelarger 50 Hz machine was cured byfitting asymmetric collars to selectedburners to dampen out any tendencyto hum. The same modification hasbeen applied to the 60 Hz machines inthe field and subsequently on theproduction line. In the case of ModelV84.3A sixteen of the 24 hybridburners are fitted with these collars.

Siemens’ standard steam cycle forboth machines is tri-pressure reheat,with a 2-cylinder steam turbine ex-hausting to an axial condenser.Deaeration takes place in the con-denser hot well so that the condensateextraction pump doubles as the LPboiler feed pump. There is a singlepreheater stage in which the conden-

sate passes through a heat exchanger,which is supplied by a steam bleedfrom the LP turbine. The main concep-tual difference between this andOtahuhu is that it is directly cooled bysea water instead of having a hybridcooling tower; and that since the gasturbine will, for the first three years,burn liquid fuel, it has water injectionfor NOx control.

The initial fuel contracts for naph-tha and gas condensate have beenplaced with Enron and the first ship-ment of 50 000 m³ of gas condensatewas on site when TurbomachineryInternational visited on February 14. Inthe station’s tank farm there are five26 000 m³ tanks for storage of naphthaand gas condensate. In addition thereare two for storage of diesel fuel, anda further two day tanks for the dieselfuel used for start-up and shut-down.

The station will be operated onliquid fuel until Malampaya gas be-comes available, which is expected tobe in 2002. Shell are bringing it ashoreat their Batangas refinery, from whereFirst Gas Holdings will lay an 8 kmpipe to the Santa Rita site. Meanwhile

all four sets are being commissionedon diesel fuel, after which commission-ing will be carried out on whichever ofthe other liquid fuels is available. Incommercial operation the plant will bestarted on distillate and switched toeither naphtha or gas condensate, or amixture of both.

The original construction plan set aschedule to commission two 500 MWblocks three months apart. In practicethe delays in the first block havebrought the second block to the pointthat with careful planning commission-ing of two units within the block can beperformed at the same time.

Clutch aids testingFor this to be possible at all the genera-tor has to be in the middle of the powertrain with an SSS clutch separating itfrom the steam turbine. Besides itsnormal uses to facilitate rapid start up,and to enable early access to the gasturbine at a maintenance outage, atSanta Rita it plays an important role inthe commissioning of the combinedcycle units. With the clutch open, thegas turbine can be run to clean theboiler which discharges steam throughbypass valves to the condenser. Theclutch has only to be closed to commis-sion the steam turbine.

On February 14, three of the fourgas turbines had been synchronisedand boiler cleaning was about to starton unit 40. In the first block, work wasfocusing on the commissioning of unitGT10 to full load, and the commission-ing of ST20.

For cleaning the boilers the gasturbines can be operated with theirhybrid burners in diffusion mode. Thisis a high NOx mode of operation whichis permissible during commissioningwhen the plant is exempt from prevail-ing environmental rules. In any case, innormal operation, premix mode would

Figure 2: Steam cycle of Santa Rita and San Lorenzo combined cycles in their final configuration with gas firing, which is expe cted tostart in 3rd quarter of 2002. Until then Santa Rita will run on either gas condensate, naphtha, or a mixture of both.

Figure 3: Units 1 and 2 of the first Blockwere simultaneously commissioned ondiesel oil in mid February

Turbinebypass

28.4 bars 540ºC

110 bars, 540ºC

Fuel gas heater

250MW

Boosterpumps

HP

IP

4.8 bars, 235°C

Direct coolingby the sea

Liquid fuel feed

cut in at above the 80 MW output levelneeded to clean the boiler. With bothboilers cleaned and the clutch of theUnit 20 closed its steam turbine can betested up to full load and the controlsettings established with the gasturbine still firing in diffusion mode.While this is happening, the clutch ofGT10 is open with the gas turbinecommissioning, and the boiler dumpingsteam into the condenser.

Commissioning tests entail takingthe gas turbine output up to full load instages and checking out hardware andcontrol software to establish operatingsettings and eliminate any designanomalies. For this, the Telepermcontroller has a software editingdisplay which allows the commission-ing engineer to view, and if necessaryamend the section of the controlprogram code corresponding to theparticular condition of loading underwhich the gas turbine is testing. Usingthis facility, alarm signals can beverified and settings confirmed. Withcommissioning completed, the final-ised control software of unit GT10 cannow be transferred to the controller ofGT20. Similarly, control software forST20 can then be transferred to ST10.

The file transfers can be carried outovernight after which a final check ofGT20 and ST10 can proceed in

parallel so that both units can bebrought to completion of the entireblock of two gas turbines, and a steamturbine in about four days. While this isgoing on the defined control softwareroutines can be transferred to theother two units provided that cleaningof the boilers has been completed.

Running on naphtha or gas con-densate poses a problem of lubricity.This is not so severe in the Siemens

fuel system with an annular combustorarrangement as in some units withcannular combustors but it still meansthat without purging the system atshutdown there is a risk of sludgecollecting in fuel lines and pumps.

It is in India where naphtha firinghas really taken off and Siemens havetherefore carried out extensive tests onthe Paguthan combined cycle with twoModel V94.2 near Ahmedabad. Withnaphtha firing the gas turbine can bestarted on diesel fuel and switched tonaphtha when full load has beenreached. To shut down it is not neces-sary to switch back to diesel. The gasturbine is run down on naphtha andthen the whole fuel system can bepurged with demineralised water. Thismethod has been found to be effectivein Paguthan and will be applied also tothe four units at Santa Rita.

Commissioning on either naphthaor gas condensate followed commis-sioning on distillate, and using thesame methods to bring all four units upto commercial operation together. Atthe same time, work has started inearnest on the construction of the twosingle shaft blocks for San Lorenzo. Bythe time that this station is completednatural gas may be available, and thenSanta Rita will have to be taken out ofservice for commissioning on this fuel.

Figure 4: Siemens standard single shaft combined cycle hascentrally mounted generator and steam turbine exhausting toaxial condenser as can be seen here in left background.

Figure 5: Centrifuge fuel treatment system by Westfalia Separatorwill handle diesel , naphtha and condensate fuels in the first twoyears of operation until natural gas arrives.

Figure 6. Without an SSS clutch in eachunit simultaneous commissioning wouldnot have been possible

SSS Gears LimitedPark Road, Sunbury-on-ThamesMiddlesex, TW16 5BL, EnglandTelephone: +44 1932 780644Fax: +44 1932 780018

SSS Clutch Company Inc610 West Basin RoadNew Castle, DE 19720, USATelephone: +1 302 322 8080Fax: +1 302 322 8548

SSS Reference 0300/2

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