presentation risk management and plant commissioning

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Supercritical Units: Efficiency AdvantageSupercritical Units: Efficiency AdvantageSupercritical Units: Efficiency AdvantageSupercritical Units: Efficiency Advantage

Improvements in the efficiency of pulverized coal (P.C.) fired boiler/steam

turbine power plants have been pursued since the introduction of P.C. firedboilers in the 1920s.

This led eventually in the late 1960s to the introduction of supercritical boilers

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Dr. Himadri Banerji:Conference onPlant Commissioning Kuala

Lumpur 1st and 2nd Nov 2010 1

operating at about 570 Deg C (1060qF) superheat/reheat temperatures and 24MPa (3400 psi) pressure for the steam.

Presently boilers with 300bar and 700 Deg C are being adopted for many of therecent power plants.

Since at these pressures and temperatures there is no distinct differencesbetween the water and steam phases, no drums are required in the same.


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Conventional steam

power plants operate at a

steam pressures in the

range of 170 bar and 565

Deg C.

These are Subcritical

power plants.

The new

generation of

power plants

operate atpressures higher

than the critical

pressure.

These are

Supercritical

power plants.

The operating

pressures are in

the range of 230

to 265 bar. And

TheTheTheThe next generationnext generationnext generationnext generation ofofofofpower plants willpower plants willpower plants willpower plants willoperate withoperate withoperate withoperate with SteamSteamSteamSteamPressuresPressuresPressuresPressures inininin the rangethe rangethe rangethe rangeof 300of 300of 300of 300 bar andbar andbar andbar andTemperatures 630Temperatures 630Temperatures 630Temperatures 630----700 Deg Centigrade.700 Deg Centigrade.700 Deg Centigrade.700 Deg Centigrade.

TheseTheseTheseThese are the Ultraare the Ultraare the Ultraare the Ultra

Super Critical PowerSuper Critical PowerSuper Critical PowerSuper Critical PowerPlantsPlantsPlantsPlants....

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The lower part of the boiler furnace is arranged in a spiralconfiguration such that the fluid path wraps around the boileras it travels up the furnace.

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Comparison of Allowable Stresses between Conventional and AdvancedStainless Steel Tubes, Advanced CrMo Steel Pipes

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The benefits from a once-through supercritical boiler on OT include:

Lowering overall corrosion rates by forming a protective, double-oxide layerwith a controlled amount of oxygen present in the condensate (This protective

layer is considered to be more stable than the oxide layer formed using AVT.)

Decreasing boiler chemical cleaning frequency due to reduced amounts ofiron transport and deposition

Advantages of Oxygenated Treatment OT of Supercritical Boilers

Allowing quicker, cleaner start ups and reduced corrosion product transportrates during cold and hot start ups

Allowing boiler operation at lower pH with overall objective of minimizingchemical costs

Eliminating feeding, handling, and storage of oxygen scavenger products


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Most once-through supercritical boilers have been converted frompreviously predominant AVT to OT, with new facilities almostexclusively using OT.

EPC Contractors Chemistry Challenges

This chemistry change requires allThis chemistry change requires allThis chemistry change requires allThis chemistry change requires all----ferrous metallurgy in the feedferrous metallurgy in the feedferrous metallurgy in the feedferrous metallurgy in the feedwater train, and precludes copper or copperwater train, and precludes copper or copperwater train, and precludes copper or copperwater train, and precludes copper or copper----based alloy feed waterbased alloy feed waterbased alloy feed waterbased alloy feed waterheat exchangers in system design and bronze impellers inheat exchangers in system design and bronze impellers inheat exchangers in system design and bronze impellers inheat exchangers in system design and bronze impellers incondensate pumps and valve trims in the condensate system.condensate pumps and valve trims in the condensate system.condensate pumps and valve trims in the condensate system.condensate pumps and valve trims in the condensate system. This isThis isThis isThis isprimarily the challenge to the engineering groupprimarily the challenge to the engineering groupprimarily the challenge to the engineering groupprimarily the challenge to the engineering group ogogogog the EPCthe EPCthe EPCthe EPC

contractor to ensure that this is strictly adhered..all steels containcontractor to ensure that this is strictly adhered..all steels containcontractor to ensure that this is strictly adhered..all steels containcontractor to ensure that this is strictly adhered..all steels containtraces of copper and zinc.traces of copper and zinc.traces of copper and zinc.traces of copper and zinc.

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ShowsShowsShowsShows the pressure drop history of a coalthe pressure drop history of a coalthe pressure drop history of a coalthe pressure drop history of a coal----fired supercritical plantfired supercritical plantfired supercritical plantfired supercritical plant in Japanin Japanin Japanin Japan that changed the waterthat changed the waterthat changed the waterthat changed the water

chemistry from AVT to OWT in 1996.chemistry from AVT to OWT in 1996.chemistry from AVT to OWT in 1996.chemistry from AVT to OWT in 1996.

AfterAfterAfterAfter 7777 years operationyears operationyears operationyears operation since the change, there has been no significant increase in pressuresince the change, there has been no significant increase in pressuresince the change, there has been no significant increase in pressuresince the change, there has been no significant increase in pressure drop.drop.drop.drop.

ThisThisThisThis plant has not required acid cleaning since the change, and no future cleaningplant has not required acid cleaning since the change, and no future cleaningplant has not required acid cleaning since the change, and no future cleaningplant has not required acid cleaning since the change, and no future cleaningis planned.is planned.is planned.is planned.

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SUPERCRITICAL UNITS: EPCSUPERCRITICAL UNITS: EPCSUPERCRITICAL UNITS: EPCSUPERCRITICAL UNITS: EPC CONTRACTORS CHEMISTRY CONTROLCONTRACTORS CHEMISTRY CONTROLCONTRACTORS CHEMISTRY CONTROLCONTRACTORS CHEMISTRY CONTROL PARADIGMPARADIGMPARADIGMPARADIGM

RISK MANAGEMENT

Plant Commissioning

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Some once-through supercritical boiler manufacturers have instituted penaltiesagainst the allowable pressure drop during initial boiler performance testing, an

additional complication that may impact start up and commissioning activities.

These penalties are based on extended operation on all volatile treatmentreducing (AVT[R]) during start up and commissioning.


The reducing environment (negative oxidation reduction potential [ORP])present when operating on AVT(R) may contribute to increased iron transport,subsequently increasing the pressure drop through the boiler.

These pressure drop correction penalties will be fervently debated by the EPCcontractor during commissioning and challenged by both owners and plantoperators.

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WARRANTY IMPLICATIONS

Steam turbine suppliers are also setting limits, in theequipment contract, on the number of hours a turbine can be

operated with out-of-specification chemistry. These limits aretypically listed in an action-level These limits are typicallylisted in an action-level format where minor chemistryexcursions are allowable for predetermined time

per o s w t out v o at ng t e equ pment warranty.

Steam Purity Limits DuringSteam Purity Limits DuringSteam Purity Limits DuringSteam Purity Limits During Start upStart upStart upStart up EPCEPCEPCEPCContractor Recommendation for OnceContractor Recommendation for OnceContractor Recommendation for OnceContractor Recommendation for Once----ThroughThroughThroughThroughBoilers...usually one weekBoilers...usually one weekBoilers...usually one weekBoilers...usually one week

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During steam-side start up and commissioning, the EPC contractor is mostly

interested in main and reheat steam chemistry.

Table below listsTable below listsTable below listsTable below lists EPRI recommendations for once-through boilers operating underOT, including normal target value and action levels 1, 2, and 3.

Although recommendations listed in TableAlthough recommendations listed in TableAlthough recommendations listed in TableAlthough recommendations listed in Table areareareareacceptable for targeted chemistry limits duringacceptable for targeted chemistry limits duringacceptable for targeted chemistry limits duringacceptable for targeted chemistry limits duringoperation, EPC contractors would like to see theoperation, EPC contractors would like to see theoperation, EPC contractors would like to see theoperation, EPC contractors would like to see thefollowing two columns added to this tablefollowing two columns added to this tablefollowing two columns added to this tablefollowing two columns added to this table::::

Allowable chemistry excursions during Allowable chemistry excursions during Allowable chemistry excursions during Allowable chemistry excursions duringhothothothot start ustart ustart ustart u


Allowable chemistry excursions during Allowable chemistry excursions during Allowable chemistry excursions during Allowable chemistry excursions duringcoldcoldcoldcold start upstart upstart upstart up

Feed WaterFeed WaterFeed WaterFeed Water

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Dr. Himadri Banerji:Conference on

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What Are Action Levels 1, 2, 3

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EPC CONTRACTORS CHEMISTRY CONTROL PROGRAMEPC CONTRACTORS CHEMISTRY CONTROL PROGRAMEPC CONTRACTORS CHEMISTRY CONTROL PROGRAMEPC CONTRACTORS CHEMISTRY CONTROL PROGRAM

Start up chemistry guidelines should primarily focus on main steam chemistrytargets, including

cation conductivity: it warns of salts and acids that may cause turbine corrosion

silica : silicate scaling may contribute to turbine capacity and efficiency losses.

sodium: critical for avoiding corrosion because uncontrolled sodium hydroxideconcentrations are known to cause corrosion damage failures in boilertubes.

Targets for chlorides, sulphates, and organic compounds should bedeferred until the end of the commissioning cycle.

Degassed cation conductivity is the preferred conductivity to bemeasured during commissioning since system air leaks are stillbeing discovered and sealed during the start up and commissioningphase. The measurement of degassed cation conductivity will aid indifferentiating between air leaks and other contamination sources

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The two most important parameters in Table are feed water cationconductivity and pH.

Cation conductivity should be maintained below 0.15 S/cm duringoperation on OT. Normal pH range for feed water under OT is 8.0 to 8.5.


The EPC contractor is challenged with controllingpH when feed water cation conductivity increasesto concentration levels listed in Table , action levels1, 2, and 3 (0.3 S/cm, 0.6 S/cm, >0.6 S/cm,respectively).

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The pH/conductivity relationship is crucial for once-through cycles on OT;thus, the EPC contractor implements the chemistry control at its own risk.

Important issues to be addressed when implementing OT include:


w a po n ur ng e s ar up an comm ss on ng process s ou e

chemistry regime be switched from AVT to OT to prevent frequent switching backand forth between a reducing and an oxidizing environment?

What would be the detrimental effects of going from an oxidizing atmosphere toa reducing (or close to reducing) atmosphere, for temporary periods?

How can these detrimental effects be quantified and addressed during designand equipment procurement?

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Comparison of Start-up Systems

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The turbine bypass system was designed to minimize the start-uptime by controlling the main steam pressure and temperature beforeturbine rolling, and enabling the steam to flow through the super

heater sections at a short time after light-off.

The low-load recirculation system was designed to recover residualheat during start-up by circulation of the un-evaporated water from

,

reducing start-up time.

As this system is automatically operated, the start-up process is assimple as with a natural circulation (NC) boiler.

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Start up Steam Chemistry Limits

Startup

EPC Contractor Guidelines on Feed Water Chemistry

Turbine Rolling Continued AVT(O)

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Turbine Rolling ContinuedBalance of Commissioning Period Chemistry Limits

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Operation Guidelines with AVT R and AVT O

AVT(R) Feed water Chemistry Control Guidelines

AVT(O) Feed water Chemistry Control Guidelines

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SuggestedSuggestedSuggestedSuggested Start up Feed waterStart up Feed waterStart up Feed waterStart up Feed water ChemistryChemistryChemistryChemistryGuidelines for OnceGuidelines for OnceGuidelines for OnceGuidelines for Once----Through Cycles Without DeaeratorsThrough Cycles Without DeaeratorsThrough Cycles Without DeaeratorsThrough Cycles Without Deaerators

Practical start up chemistry guidelines should be established by

consensus among the turbine manufacturer, boiler manufacturer,and EPC contractor early on in project development and outlinedin equipment contracts.

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ROLE OF CONDENSATE POLISHERS

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Once-through supercritical boilers are commonly installed withfull-flow

in condensate and feed water systems.The presence of impurities in feed water willsignificantly affect feed water chemistry, potentiallyexceeding boiler supplier feed water limits andturbine supplier steam purity specifications.

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Impurities shaken loose during start up may cause a chemistry hold, whereplant load increases are temporarily halted until these impurities areremoved from the system.

For a once-through supercritical boiler, impurities are removed exclusivelyby condensate polishers subsequent to chemical cleaning and boiler flush.

Once impurities are remove , t e c emistry o is i te an t e p ant is

allowed to continue to ramp up to full load without exceeding allowableboiler or turbine chemistry limits.

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Steam and Water Analysis System (SWAS) shall be furnished for continuousSteam and Water Analysis System (SWAS) shall be furnished for continuousSteam and Water Analysis System (SWAS) shall be furnished for continuousSteam and Water Analysis System (SWAS) shall be furnished for continuous

monitoring and control ofmonitoring and control ofmonitoring and control ofmonitoring and control of waterwaterwaterwater and steam purity in the plantand steam purity in the plantand steam purity in the plantand steam purity in the plant cyclecyclecyclecycle

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Control system component cleanliness during shop fabrication Control system component cleanliness during construction

EPC Contractor Responsibility includes that Chemistry limits are before, duringand after once-through supercritical boilers commissioning

us system components pr or to start-up

Implement stringent water quality requirements for hydro testing Perform boiler and feed water system chemical cleaning Flush system components thoroughly following chemical cleaning Perform steam blows to obtain steam cycle cleanliness Implement time-based, progressively improving feed water and steam

chemistry targets

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