700 mw plant descripion

Mitsubishi Heavy Industries, Ltd.Technical Review Vol.39 No.3 (Oct. 2002)

95

Design, Construction, and Com-missioning of the Nos.1 and 2 Unitsof the Ratchaburi Thermal PowerPlant for the EGAT of Thailand as aFull Turn-key EPC Contract

1. Introduction1. Introduction1. Introduction1. Introduction1. IntroductionThe Nos. 1 and 2 units of the Ratchaburi Power

Plant including two supercritical sliding pressureoperation once-through boilers began commercial op-eration in the year 2000.

MHI was assigned a broad scope in the construc-tion the Ratchaburi Power Plant ranging from thedesign, procurement, construction, and performancetesting, through commissioning of major machineryand plant equipment for the power plant, togetherwith the construction of the foundations and build-ings that house the equipment supplied by MHI. Thewide-ranging work of this project served to demon-strate the integrated capability of the Mitsubishigroup. This report introduces the features of themachinery and equipment delivered by MHI as wellas a brief description of the contents of the field con-struction work that was undertaken to erect andinstall the equipment.

2. Outline of project2. Outline of project2. Outline of project2. Outline of project2. Outline of projectThe Ratchaburi Power Plant is located about 100

km west of Bangkok, the capital of Thailand, in a ru-ral area of the country. For the electric supply systemin Thailand, the power plant is important as a majorsource of electric power that replaces the outdatedold thermal power plants in this area.

MHI was awarded the order in an international bidfor this power plant planned by the Electric Generat-ing Authority of Thailand (hereinafter referred to as

EGAT). The contract was agreed to as a so-called fullturnkey project, and came into effect on November 6,1996. Commissioning of the No. 1 unit began on June15, 2000 and on October 28, 2000 for the No. 2 unit.

A most notable aspect of this project is the fact thateach unit consists of the first supercritical slidingpressure operation once-through boiler in SoutheastAsia. Other special features include the combinationof a two-double low-pressure turbine/water-cooledgenerator and large capacity multiple pressure typecondenser to improve plant efficiency, and the adop-tion of a burner system that is capable of bothexclusive firing and mixed firing of oil and naturalgas. This project is also characterized by low NOxand low SOx operation through the application of lowNOx burner and high performance desulfurizationsystem. The power plant is also capable of meetingfrequent start-and-stop and quick load change re-quirements.

The major specifications of the power plant arelisted in TTTTTablablablablableeeee 11111. The overall layout of the power plantand equipment delivered by MHI are shown in FigFigFigFigFig..... 11111.A photograph of the power plant is shown at the topof this page.

3. Boilers3. Boilers3. Boilers3. Boilers3. Boilers3.13.13.13.13.1 Supercritical sliding pressure operation once-Supercritical sliding pressure operation once-Supercritical sliding pressure operation once-Supercritical sliding pressure operation once-Supercritical sliding pressure operation once-

through boilerthrough boilerthrough boilerthrough boilerthrough boilerThe boilers are the thirtieth and thirty-f irst

supercritical sliding pressure operation once-throughboilers (fourteenth and fifteenth as oil- and gas-fired

Power plants in Thailand, which has recently recovered from an economic crisis, are not only required to oper-ate stably at their base loads but also to respond flexibly to shifts in the balance of demand and supply for power.In order to meet this requirement, two supercritical sliding pressure operation once-through boilers were adoptedfor the first time in Southeast Asia. The units are highly efficient and environmentally friendly and have excellentfrequent start-and-stop and broad load change capabilities. They began commercial operation in the year 2000. Inconstructing the Ratchaburi Power Plant, Mitsubishi Heavy Industries, Ltd. (MHI) undertook the design, procure-ment, installation, and commissioning of most of the machinery and equipment in the power plant, such as theboilers, turbines, generators, cooling towers, flue gas desulfurization systems (FGD), and the foundations andbuildings that house the equipment delivered by MHI. This report introduces the main features of the varioustypes of machinery and equipment delivered by MHI together with a brief description of the field erection work.

Kenji AndoEisuke Asada

Kenjiro YamamotoToshihide Noguchi

Yasuo Sumiyoshi


96

boilers) to be delivered by MHI. Hence, they weredesigned and manufactured based on the extensiveexperience of MHI. The boilers have the same con-figuration as the Nos. 1 through 4 boilers of the 550MW power plant built at Qurayyah in Saudi Arabiathat have been in operation with an excellent perfor-mance record since 1989. Heavy oil, containing 3%sulfur, and natural gas were adopted as the designfuel. Full load operation is also possible with theexclusive firing of either fuel. FigFigFigFigFig..... 22222 shows a sche-matic side view of the boiler. The heat transferringsystem consists of a pendant type high-temperaturesuperheater / high temperature reheater, horizontaltype low-temperature reheater, and an economizer,which are provided in the order of the gas flow. In

order to cope with differences in the respective heatabsorption properties of gas and oil in the furnace,the temperature of the steam is adjusted by chang-ing the amount of gas recirculation (GR) that is done.A boiler circulation pump (BCP) system has been pro-vided in accordance with the requirements of thecustomer for heat recovery at the time of start-up andfor reduced load operation.

3.2 Low-NOx3.2 Low-NOx3.2 Low-NOx3.2 Low-NOx3.2 Low-NOx burner burner burner burner burnerA round type oil/gas dual firing, low-NOx burner

for circular firing, originally developed by MHI as oneof the features of the boiler, has been adopted to sat-isfy demands for strict environmental protection aswell as high efficiency. The burner has demonstratedsignificantly lower NOx emission levels than the

Feed water treatment

OutputSteam conditionFuel

Cooling systemCondenser vacuumFeed water heater

Type

Type

Type

CapacityExciter

Type

CWT

735 MW at generator terminal24.22 MPax538/566oC (at turbine inlet)Oil & gas (exclusive firing / mixed firing)

Mechanical draft wet cooling tower

Supercritical sliding pressure operation once-through boiler

8 stages

3000 rpm tandem compound quadruple exhaust condensing type reheat and regenerating turbine, LP (low pressure) end blade length: 35.4 inches

Totally enclosed, stator water cooled, rotor hydrogen cooled, complete with stationary armature and cylindrical rotor, directly coupled to the steam turbine990 MVAThyristor excitation system

Wet lime/lime stone gypsum process

Plant

Boiler

Turbine

Generator

Flue gasDesulfurization

Equipment Specification

Table 1 Major specifications of plant

Fig. 1 Layout of power station and equipment delivered by MHI


97

amount guaranteed. FigFigFigFigFig..... 33333 shows the respectivestates of oil and gas firing. As can be seen in thefigure, the light off is stable in both cases. Low NOxemissions are obtained by the fuel-rich/fuel-lean com-bined flame system based on the principle of the PM(Pollution Minimum) burner developed by MHI, aprinciple about which MHI has accumulated exten-sive experience. Thus, NOx emission levels as low as80 to 140 ppm (4% O2) have been achieved during thefiring of oil containing 0.45% N, and 20 to 40 ppm(5% O2) while firing natural gas.

3.3 Boiler performance3.3 Boiler performance3.3 Boiler performance3.3 Boiler performance3.3 Boiler performancePerformance tests were carried out for exclusive

oil firing, exclusive gas firing, and oil and gas mixedfiring. In the range from 25% load through full load,excellent performance levels higher than the designvalues were obtained in the firing of each fuel. Stableoperation was also demonstrated in the exclusive fir-ing of each fuel when a 15% load was specified as theminimum load.

4. Steam turbine4. Steam turbine4. Steam turbine4. Steam turbine4. Steam turbine4.1 Large-capacity tandem compound turbine4.1 Large-capacity tandem compound turbine4.1 Large-capacity tandem compound turbine4.1 Large-capacity tandem compound turbine4.1 Large-capacity tandem compound turbineFigFigFigFigFig..... 44444 shows a cross sectional schematic view of the

assembled steam turbine. The major specificationsof the steam turbine are listed in Table 1. Each tur-bine is a tandem compound type system consisting ofone high-pressure turbine, one intermediate-pressure(IP) turbine, and two low-pressure turbines. The

high-pressure turbine consists of a double-flow designwith four main steam inlets. Each flow consists ofone control stage and eleven reaction stages. Theintermediate- pressure turbine consists of a double-flow design with four reheated steam inlets. Eachflow consists of nine reaction stages. The low-pres-sure turbines also use a double-flow design, and eachflow consists of seven reaction stages, including a 35.4inch ISB LP (low-pressure) end blade. Each steamturbine has a capacity of 735 MW in rated output (841MW maximum possible output).

4.2 Design characteristics4.2 Design characteristics4.2 Design characteristics4.2 Design characteristics4.2 Design characteristics(1) Shaft line design to meet requirements for large

output, tandem type turbines for thermal powerplants

A thorough examination was made of the shaftline design taking into consideration a maximumoutput of 841 MW at a frequency of 50 Hz. As aresult, the diameter of the bearing between theturbine and generator becomes 535 mm, which isthe maximum diameter for a 3 000 rpm speed ma-chine.

(2) Adoption of advanced fully three-dimensional de-sign blade

In order to improve performance, advanced fullythree- dimensional design blades have beenadopted for the reaction stages in high-, interme-diate- , and low-pressure turbines. The fullythree-dimensional flow design is applied to all re-action blades, including the LP end blade.4.3 Performance4.3 Performance4.3 Performance4.3 Performance4.3 PerformancePerformance tests confirmed that each steam tur-

bine achieved higher levels of efficiency that exceededdesign values (guaranteed values) not only in 100%ECR (Economical Continuous Rating) and turbine-

Gas Heavy oil

Fig. 3 Burning states

Fig. 4 Cross sectional view of 735 MW steam turbine used in the Nos. 1 & 2 units of the Ratchaburi

Fig. 2 Schematic side view of boiler


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MCR (Maximum Continuous Rating), but also in thespecified full load range.

4.4 Shaft vibration4.4 Shaft vibration4.4 Shaft vibration4.4 Shaft vibration4.4 Shaft vibrationFigFigFigFigFig..... 55555 shows that shaft vibration measured at each

bearing during rated speed operation is as small as35μ or less. This demonstrates that very stable op-eration is obtained.

5. Generator5. Generator5. Generator5. Generator5. GeneratorThe results of studies aimed at the realization of a

1 000 MW class tandem generator that were conductedcontinuously since 1980s have been applied to thedesign of the generators. Fig 6Fig 6Fig 6Fig 6Fig 6 shows the structureof a generator. As generator capacity increases, thediameter of the rotor will invariably be increased andthe stator end supports will be strengthened. Accord-ingly, special material was developed for the rotor thatis capable of withstanding high centrifugal force.Verification tests of the system were conducted usinga mock-up. Shop tests and actual load tests on siteverified that the vibration in the rotor shaft and sta-tor coil ends as well as the temperatures in the coilwere all within design parameters.

6. Plant equipment6. Plant equipment6. Plant equipment6. Plant equipment6. Plant equipment6.1 Multi-stage pressure condenser6.1 Multi-stage pressure condenser6.1 Multi-stage pressure condenser6.1 Multi-stage pressure condenser6.1 Multi-stage pressure condenserA multi-stage pressure condensing system is em-

ployed which consists of two condensers. Thesecondensers have different internal vacuum levels fromeach other and are respectively installed under thecasing of each low-pressure steam turbine. A once-through water-cooling system is used in which coolingwater flows continuously through both condensers.

Thus, this water-cooling system is superior to singlestage condensers in the following points.(1) The turbine cycle efficiency is improved because

the extent of the average vacuum in the condens-ers is increased.

(2) The flow rate of the condenser cooling water isreduced because it flows once through both con-densers consecutively in series. As a result, thenumber of cells in the cooling tower can be reduced,thereby also serving to reduce construction costs.

(3) The condensate from the high vacuum condensertube bundles is reheated by the exhaust steam fromthe low vacuum condenser tube bundles (conden-sate preheating system). In addition, the reheatedcondensate is mixed with the condensate from thelow vacuum condenser tube bundles and sent tothe boiler system. Therefore, the amount of steamextracted from the low-pressure feed water heatercan be reduced, which means that an increase inoutput can be expected. As can be seen in FigFigFigFigFig..... 77777,reheating can be performed by having the conden-sate free-fall from the high vacuum condenser tubebundles into the steam from the low vacuum con-denser. The fallen condensate then generatesturbulence on the surface of the condenser hot well.The turbulence accelerates heat exchanging to re-heat the fallen condensate.Performance tests confirmed that the vacuum lev-

els in the condensers and the reheating efficiency ofthe condensate both equaled or surpassed the guar-anteed values.

6.2 Circulating water pump6.2 Circulating water pump6.2 Circulating water pump6.2 Circulating water pump6.2 Circulating water pumpEach set of Nos. 1 and 2 circulating water pumps

consists of three 50% capacity pull out type pumps(largest class in the world). In order to ensure smoothwater flow from the large pool provided under the

#1 #2 #3 #4 #5 #6 #7 #8 #9 #10

200

100

0

HP IP LP1 LP2 GEN

No. of bearing

Sha

ft vi

brat

ion

leve

l (a

mpl

itude

of b

oth

sid

e vi

brat

ion)

Fig. 5 Measured shaft vibration of turbine generator for the Ratchaburi No. 1 unit

Resin cone Stator coil

Stator core

Gas cooler

Rotor

Bearing

Bearing

Fig. 6 Construction of generator

LP-1 Turbine LP-2 Turbine

Low vacuum condenser

High vacuum condenser

Reheatingsteam

Perforatedplate

Tube bundle

Perforated plate

Tray

Tray

Fig. 7 Construction of multi-stage pressure type condenser


99

cooling tower, model tests were carried out to opti-mize the design of the intake pit.

6.3 Condensate pump6.3 Condensate pump6.3 Condensate pump6.3 Condensate pump6.3 Condensate pumpEach set of condensate pump consists of two 100%

capacity pumps. As a single condensate pump forthermal power plants, the condensate pump is char-acterized by being amongst the largest capacity classof pumps in the world. It is a vertical type pumpequipped with a large capacity fluid coupling in or-der to reduce auxiliary power consumption duringpartial load operation. Since these condensate pumpsabout seven meters in height from the installationfloor and are variable in speed, they are designedbased on vibration analysis that is carried out in or-der to reduce vibration and increase reliability.

7. Operating performance (load-following capability)7. Operating performance (load-following capability)7. Operating performance (load-following capability)7. Operating performance (load-following capability)7. Operating performance (load-following capability)The customer requested that the units be capable

of accommodating a wide range of load variations.Consequently, the equipment and controls were de-signed not only to meet this requirement but also toallow the application of precise adjustments duringoperation. As a result, the units are fully capable ofaccommodating the targeted load variations. Thisexcellent operating performance is comparable to thatof power plants used for utilities in Japan.

8. Water quality control (by CWT)8. Water quality control (by CWT)8. Water quality control (by CWT)8. Water quality control (by CWT)8. Water quality control (by CWT)The Ratchaburi Power Plant is equipped with a

combined water treatment (CWT) facility. The CWTfacility is superior to conventional AVT (AmmoniaVolatile Treatment) facilities because of the excellentenvironmental protect ion per formance that i sachieved through a reduction in the amount of chemi-c a l s u s e d , t h e a m o u n t w a s t e w a t e r t h a t i sre-generated from the condensate demineralizer, aswell as positive economic effects that result from re-duced furnace pressure loss and the frequency ofboiler acid-cleaning required. Accordingly, this CWTfacility is expected to be a model case for overseasplants.

9. Flue gas desulfurization (FGD) system9. Flue gas desulfurization (FGD) system9. Flue gas desulfurization (FGD) system9. Flue gas desulfurization (FGD) system9. Flue gas desulfurization (FGD) systemThis FGD system is not equipped with any electro-

static precipitator (ESP). Thus, in order to achieve ahigh dust removal efficiency (85%), a double-contact-flow scrubber (DCFS), which is operated by a highvelocity (10 m/s) gas flow, is employed as the firstabsorber. As an one-line desulfurizing capacity plant,the 2 224 000 Nm3/h gas treating capacity of this sys-tem is of a comparable scale to the FGDs used in 1 000MW class power p lants in Japan, such as theHaramachi No. 1 FGD of the Tohoku Electric PowerCo., Inc. and the Misumi No. 1 FGD of the ChugokuElectric Power Co., Inc. Desulfurizing performance

as high as 116 mg SO2/Nm3 by the No. 1 unit and 112mg SO2/Nm3 by the No. 2 unit have been obtained atthe outlet of the stack, when burning heavy oil con-taining 3% sulfur. Both are less than half of the 240mg SOx/Nm3 guaranteed value at 3% O2 dry at theoutlet of the stack. FigFigFigFigFig..... 88888 shows an outside view ofone of the flue gas desulfurization systems.

Excellent maintainability of the system is achievedby use of a compact layout in which the gas/gas heater(GGH) is installed on the absorber, and the gypsumdewatering system and the limestone slurry prepa-ration system are arranged close to the absorber.

10. Outline of construction work10. Outline of construction work10. Outline of construction work10. Outline of construction work10. Outline of construction workThe construction of the plant proceeded smoothly

from the start of the piling work through the columnlifting of the turbine building structures on Decem-ber 15, 1997. In July 1997, however, the Thai economyfell into disorder due in large part to transference toa floating exchanging rate system that was accompa-nied by a crisis in the value of the Thai baht.

Unprecedented events such as the transference ofthe EGAT to private management and the decision tosell the Ratchaburi Thermal Power Plant to a thirdparty occurred during this difficult period. Never-theless, both the Nos. 1 and 2 units could begincommercial operation without delaying the schedulefor selling the power plant.

10.1 Features of construction work of Ratchaburi10.1 Features of construction work of Ratchaburi10.1 Features of construction work of Ratchaburi10.1 Features of construction work of Ratchaburi10.1 Features of construction work of RatchaburiThermal Power PlantThermal Power PlantThermal Power PlantThermal Power PlantThermal Power Plant

In Thailand, construction work usually depends onhuman wave tactics based mainly on laborers fromthe east north area. Accordingly, massive manpower(1 850 000 man-days) was also needed for construc-tion of the Nos. 1 and 2 units. In spite of thiscondition, the construction work could be completedwithout any serious accident.

The site was a swamp zone where the ground wasso soft during the rainy season of 1998 that it wasdifficult to walk because one’s feet sank in the mud

Fig. 8 Absorber and auxiliary equipment of Ratchaburi Thermal Power Plant No.1 unit


100

up to the knees at certain places at both the construc-tion site and the material marshal yard, and themachine equipment erection work for the No. 1 unitwas peak. Under such conditions, it was useless topave the ground with temporary curing plates andeven crawler cranes were held up in the mud for along time. Therefore, it took a lot of time to trans-port heavy material and to assemble cranes andtransport equipment, as fights with the rain and mudcontinued for a long time.

10.1.1 Civil work10.1.1 Civil work10.1.1 Civil work10.1.1 Civil work10.1.1 Civil workGiven the large scale of the civil work involved,

several different contractors were chosen during theselection process of the local Thai contractors. Thebuilding and foundation work was divided among twocontractors, as was the piling work, and the stackconstruction work was undertaken by a specializedcontractor. MHI coordinated all work, including co-ordination of the erection work.

10.1.2 Boiler erection work10.1.2 Boiler erection work10.1.2 Boiler erection work10.1.2 Boiler erection work10.1.2 Boiler erection workBoth of the large and sophisticated supercritical

sliding pressure operation once-through boilers couldbe assembled to a superb degree of precision, thanksto the cooperation of the construction contractors andthe supervisors of MHI. No difficulties due to poorwelding work have yet been caused since completionof construction.

10.1.3 Turbine erection work10.1.3 Turbine erection work10.1.3 Turbine erection work10.1.3 Turbine erection work10.1.3 Turbine erection workIn erecting the turbines, 1500-ton cranes were used

because the turbines and generators were amongstthe largest in the world in terms of single capacity.Moreover, each generator stator in particular was asheavy as 400 tons, and other heavy equipment suchas the deaerators, heaters, and transformers were all

large and heavy items, as well.

11. Conclusion11. Conclusion11. Conclusion11. Conclusion11. ConclusionMHI completed this project on the basis of its broad

experience gained at Qurayyah in Saudi Arabia, LalPir, in Pakistan, Masinloc in the Philippines, and atZhuhai in China. Recent customer requirements havebecome increasingly complicated as most of overseaspower plant projects are shifted to IPPs (IndependentPower Producers). Accordingly, MHI intends to drawon these experiences in order to meet these variousfuture requirements, with superlative organizationthat is well accommodated to deal with such require-ments.

Kenji Ando

TakasagoMachineryWorks

EisukeAsada

NagasakiShipyard &MachineryWorks

KenjiroYamamoto

PowerSystemsHeadquarters

ToshihideNoguchi

PowerSystemsHeadquarters

YasuoSumiyoshi

NagasakiShipyard &Machinery

700 mw plant descripion

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