koso turbine bypass systems_(sales training, march 10 2011)_rev a.ppt

KOSO Turbine Bypass Systems

2007 - KOSO. All rights reserved.

Typical turbine bypass problemsPipe/ components crackingWater hammerStuck valveHigh vibrationHigh noiseTrim erosion...The combination of high pressure drop and desuperheating requires special attention in turbine bypass systems*2007 - KOSO. All rights reserved.*


*2007 - KOSO. All rights reserved.*Kosos experience in turbine bypass and steam conditioning systems

Kosos strengths:Experience of over 25 years in desuperheatersturbine bypass systemsPRDSprocess steamThe most cost effective solutions resulting from a unique combination of:knowledge of systems, engineering expertise, and,customer support.


Turbine bypass Schematic (typical)

Current projects (recently completed or under construction - partial)


Turbine bypass systems for 600 MW supercritical units - Mo Chin*2007 - KOSO. All rights reserved.*Scope of supply for 600 MW supercritical x 2 Units:2 HP bypass systemssteam PRV - 8 x 16, 2795# SPCL, F91 bodySpray ring & probe desuperheatersFast-acting pneumatic actuator (< 2s trip)4 LP bypass systemssteam PRV - 10 x 18, 600# SPCL, F91 bodySpray ring desuperheaterFast-acting pneumatic actuator (< 2s trip)


LP bypass to condenser (Mo Chin)**

Turbine bypass systems for Sredneuralskaya (Ekaterinberg), RussiaScope of supply:1 HP bypass system2 inlets (6) for steam PRV, 24 outletJob-Rated 270 bar-a/ 545 C inlet, F91 bodySpray ring desuperheaterFast-stroking electric actuator*2007 - KOSO. All rights reserved.*

Turbine bypass systems Kharanorskaya, Russia*2007 - KOSO. All rights reserved.*Scope of supply (bypass to condenser):1 HP bypass system2 inlets (175 mm) for steam PRV, 630 mm outletJob-Rated 14 MPa-a/ 570 C inlet, F91 bodySpray ring desuperheaterFast-stroking electric actuator1 PRDS system (bypass to condenser)Globe steam PRV, (175 mm), 630 mm outletJob-Rated 14 MPa-a/ 570 C inlet, A216 C12A bodySpray ring desuperheaterFast-stroking electric actuator

Turbine bypass system for Iberdrola, Spain (400 MW Elektrenai CCGT, Lithuania)*2007 - KOSO. All rights reserved.*Scope of supply:1 HP bypass system (bypass to Cold Reheat)Job-Rated 142 barA/ 575 C inlet, F91 bodyMulti-Nozzle Ring desuperheaterFast-stroking pneumatic actuator1 IP bypass system (bypass to condenser)Job-Rated 31 barA/ 575 C inlet, F91 bodyMulti-Nozzle Ring desuperheaterFast-stroking pneumatic actuator1 LP bypass system (bypass to condenser)Job-Rated 7.5 barA/ 320 C inlet, A105 bodyPED certified

*2007 - KOSO. All rights reserved.*Size relationship: Plant MW & turbine bypassPower plant size has a major influence on sizing of major equipment in the station turbine, boiler etcSizing of turbine bypass systems depends on the design %-bypass and number of lines:1000 MW plant with 30% bypass through 1 line will be same size as for a 1000 MW plant with 60% bypass through 2 lines (and same as a 60% bypass through 1 line for 500 MW unit)


*2007 - KOSO. All rights reserved.*HP bypass experience

3 x 1 CCGT184 MW (ACC)Lithuania-Elektranai CCGTPulau SerayaMo ChinRiau Pulp & PaperANSIJob-ratedJob-Rated2500#2795# SPCL1500#Inlet size61010"ID 210 x 3810"Outlet size122012"OD 584 x 1912"Body MaterialWC9/F22F91WC9F91WC9Inlet pressure (barA)60 bar (873 psi )142185285186Temperature (oC)440 C (860 deg F)575544546544Flow rate (T/H)187 (420 kpph)317126678125


LP bypass experience*2007 - KOSO. All rights reserved.*

Example 3 x 1 CCGT 280 MWLithuania-Elektranai CCGTPoryongMo ChinWKC Heineken (ABB)ANSIJob-RatedJob-Rated300#600# SPCL900#Inlet size2424200 mmID 432 x 20150 mmOutlet size30321200 mmOD 863.6 x 12900 mmBody MaterialC12A/ F91F91F91Inlet pressure (barA)51 (791 psi)30.523.552.559Temperature (oC)594 (1102 deg F)575320574511Flow rate (T/H)385 (862 kpph)4088537339


Sizing & Selection of Turbine Bypass Systems


Sizing & Selection of Turbine Bypass SystemTurbine bypass system components:High Pressure (HP) bypass to Cold ReheatSometimes HP bypass to condenserHot Reheat (HRH) bypass (to condenser) also in the same general category Intermediate Pressure (IP) bypass (to condenser)Low Pressure (LP) bypass (to condenser)IP/LP bypass (to condenser)LLP bypass**

Turbine Bypass System ComponentsEach system consists of:Steam Pressure Reducing ValveSpraywater Control ValveDesuperheaterAdditional equipment:Spraywater isolation valve (for HP Bypass system)Steam isolation valves (sometimes)Dump deviceOnly for bypass to condenser**

9-pack of ChinaStandard configuration for coal-fired power stations in China:1 HP bypass line + 2 LP bypass linesHP system - HP steam valve (qty 1)HP spray control valve (qty 1)HP spray isolation valve (qty 1)LP system LP steam isolation valve (qty 2)LP steam valve (qty 2)LP spray control valve (qty 2)TOTAL number of valves = 9**

Steam Bypass Valve selectionTrim exit kinetic energy rules:Maximum 70 psi (480 kPa)General VectorTM applicationsContinuous operationMaximum 150 psi (1030 kPa)VectorTM Turbine bypass ONLYNormal turbine bypass ONLYStart-up, shutdown and Unit tripBase-loaded plant - only few start-up per yearNone (2 cages)VectorATM based on Cv,required ONLY**

Turbine bypass steam valve Flow-to-CloseFlow-to-close designCage trim for pressure reductionVectorTM is an optionDownstream flow distributor for noise controlSpray Ring desuperheater downstreamActuationPneumaticElectro-hydraulic

Design can be customized to meet specific system requirements*2007 - KOSO. All rights reserved.*


Turbine bypass steam valve Flow-to-OpenFlow-to-open designBalanced trimMore compactLess heavyLess structural support requirementsLower costMeets all performance requirements Design can be customized to meet specific system requirements*2007 - KOSO. All rights reserved.*


Spray valves for bypass systemsHP bypass spraywater valves - VectorTMLP bypass cage-guided/ top-guidedIsolation valves cage-guided/ top-guided

CalcCv is used for sizingGeneral service rules apply**

May 11, 2010*Desuperheating problemsBroken pipe supportsCracked pipes and jointsBroken/cracked internalsPoor temperature controlDrain valves open too longPlant trip due to condenser temperature


*2007 - KOSO. All rights reserved.*Desuperheating in turbine bypass systemsChallengingLarge amounts of spraywater injection15 20% of steam flow rate for HP bypass to Cold Reheat30 35% of steam flow rate for bypass to condenser


Solutions small dropletsSpraywater atomization is criticalThere is no industry standard for desuperheating applicationsStandard adopted by KOSO: Droplet size < 250 micronsDerived from physics-based analysisConfirmed by field experience*2007 - KOSO. All rights reserved.*

Size range micronsType

Primary atomizationPrimary atomization is initiated by shear between the liquid and gas streamsThe liquid stream to be unstable and eventually breaks up into droplets of different sizesMean droplet size after primary break-up from typical high capacity desuperheating nozzles is typically in 200 - 800 micron range.May 11, 2010*Primary break-up of a liquid jet

Small droplets (less than 250 microns):Faster evaporation,Faster mixing,Easily stay suspended in the steam flow,Less likely to impinge on (hot) metal pipeSecondary atomization


Solution - Cold water not hitting hot metalNo in-body desuperheatingSpray not hitting pipe wallsSpray penetration 18-85%


The fact that the control loop delays typically 30 seconds to 1 minute needs to be recognizedCorrect interlocks are required to ensure simultaneous flow of steam and spraywater

Feed-forward control based on enthalpy calculation is required when the final temperature set point is close to saturationSolution - Correct control logic


Steam piping layout should allow natural drainage of any condensate in the lineDrain lines must have sufficient capacitySolution - Stream pipe drains


Desuperheater selection rulesRULE #0: AVOID IN-BODY DESUPERHEATING The risk is high cold water coming in contact with hotmetallic valve body will lead to cracking at the pressure boundary.RULE #1: Average droplet size should be less than 250 m.Fixed area orifices/nozzlesSpring loaded nozzles, variable areaSteam assisted RULE #2: Eliminate direct spraywater hit on hot metalSpray penetration should be between 15% and 85%RULE #3: For control near saturation, feed-forward control logicRULE #4: Provide sufficient distances to bends & temp sensorsMay 11, 2010*

Actuation for turbine bypass service


Actuation for turbine bypass servicePneumaticElectro-hydraulicElectric

Choice is dictated by customer preferenceFunctional requirements must be metReliability must be high

KOSO can provide any of the actuation systems specified*2007 - KOSO. All rights reserved.*


Functional requirementsStroke speedModulation 10 s (typical)Trip .. 2 s (typical)ThrustModulationShutoff (seating)Failure modesSignal failurePower failureControllabilityPositioning accuracy to control upstream pressureAll these requirements are met in modern turbine bypass systems by pneumatic actuators*2007 - KOSO. All rights reserved.*


Double-acting, low-volume pneumatic actuator*Meets ALL functional requirementsBenefitsProven, mature technologyVery high reliability (simple construction)Maintenance is easySignificantly lower cost Very common for turbine bypass service2007 - KOSO. All rights reserved.*


Electro-Hydraulic actuation systemsSelf-contained electro-hydraulic actuation

*2007 - KOSO. All rights reserved.*


Electro-Hydraulic actuation systems

Comparison of actuator options*2007 - KOSO. All rights reserved.*

AttributePneumatic (Double-acting, Low-volume, Piston)Electro-HydraulicElectricStroke time< 2 seconds< 1 second< 10 secondsPositioning accuracy< 2%< 0.5%< 2%Step change response< 1 % overshootNo overshootNo overshootReliabilityVERY HIGHMODERATE to HIGHMODERATE to HIGHMaintenance requirementLowHIGHModerateHarsh environment capabilityHighModerateModerateCostLowHighModerate


Summary


SummaryIn summary:KOSO has a wide experience in turbine bypass systems for steam power plants.KOSO can meet turbine bypass system requirements for the Power industry with reliable equipment which is also economicalKOSO can provide strong follow-on engineering support this is critical in the proper commissioning of engineered systemsKOSO team is uniquely qualified to help their customers be competitive in markets of their interest.*2007 - KOSO. All rights reserved.*


Turbine bypass:FAQs Frequently Asked Questions


Turbine bypass systems Frequently Asked QuestionsBody type (steam PRV) - globe or angle valve?Body material (steam PRV) - forging or casting?Under-the-plug vs. over-the-plug geometry?Balanced plug or unbalanced plug?Desuperheater selection? Distances downstream?Actuator selection? - Pneumatic vs. Electro-Hydraulic vs. Electric. Piping layout, pre-warming requirements?Dump tube sizing and design?*2007 - KOSO. All rights reserved.*


Turbine bypass systems Frequently Asked QuestionsAllowable load on nozzles for By passMethod for atomizationTemperature Control Loop. Location of temperature sensor.TurndownActuator sizing and speed. Step change positioning / accuracyTurbine trip without losing boilerCV Sizing*2007 - KOSO. All rights reserved.*


FAQs - 1Body type (for steam PRV) globe or angle?Both will workUltimately, it is the designers design as to what best fits the piping systemAngle body is more economicalAngle body has higher capacity so it results in a smaller valve less weight, less cost, less demanding support requirements (all good)*2007 - KOSO. All rights reserved.*


FAQs - 2Body material (for steam PRV) forged or cast?Both work equally well (ASME code allows both)Stringent QA is necessary in either caseCastings are more economical*2007 - KOSO. All rights reserved.*


FAQs 3Under-the-plug (FTO) vs. over-the-plug (FTC) geometry?Both work equally wellFTO means higher steam density at the seat ring smaller trim size is required smaller valve less weight, less cost, less demanding support requirements (all good) (FTC means opposite of the above)FTC keeps the body gallery warmer FTO results in thinner sections (for body gallery), which react better to thermal transients*2007 - KOSO. All rights reserved.*


FAQs 4Balanced plug or unbalanced plug?Both will work; both can give tight shut-offUnbalanced plug in turbine bypass means Very high actuator forces are required electro-hydraulic actuator is a MUST (old thinking) More susceptible to vibration (no damping)Balanced plug in turbine bypass means Actuator forces required are moderate high performance pneumatic actuator works very well (used in most modern turbine bypass systems) Pressurized seat trim is an optionOnly Flow-to-Close (FTC) configuration.*2007 - KOSO. All rights reserved.*


FAQs 5Actuator selection? Pneumatic vs. Electro-Hydraulic vs. Electric. Any of the above is technically acceptable if it meets technical requirementsIn the old days, only Electro-hydraulic actuators met the system requirements but they also had significant maintenance problemsPneumatic actuator technology (double-acting, low-volume piston type) has now advanced to meet turbine bypass requirementsIt is highly reliable, low-cost and low maintenance*2007 - KOSO. All rights reserved.*


Comparison of actuator options*2007 - KOSO. All rights reserved.*

AttributePneumatic (Double-acting, Low-volume, Piston)Electro-HydraulicElectricStroke time< 2 seconds< 1 second< 10 secondsPositioning accuracy< 2%< 0.5%< 2%Step change response< 1 % overshootNo overshootNo overshootReliabilityVERY HIGHMODERATE to HIGHMODERATE to HIGHMaintenance requirementLowHIGHModerateHarsh environment capabilityHighModerateModerateCostLowHighModerate


FAQs 6Desuperheater selection? Key objectives are: (1) Small droplets, (2) no spray impingement on the pipe wallsMulti-Nozzle spray Ring DSH for HP bypass to CRHSpray Ring DSH for bypass to condenser*2007 - KOSO. All rights reserved.*


Fixed area Spray ring desuperheater layout(typical for turbine bypass to condenser)*2007 - KOSO. All rights reserved.*Simple, fixed-area spray nozzlesRelies on energy of the steam flow for atomizationBetter than 10:1 rangeability for good atomization for dump to condenser is possible


*2007 - KOSO. All rights reserved.*Spring-loaded, multi-nozzle spray ring typical for HP bypass to CRHSpring-loaded, variable area spray nozzlesRangeability for spray nozzles > 20:1Rangeability for steam flow rate > 10:1Commonly used for PRDS and process steam applications where pipe > 12 (300 mm)


FAQs 7Distances downstream?HP bypass to Cold Reheat:Distance to the first elbow > 6 meters Temperature probe > 15 metersBypass to condenser: a) when desuperheating is within a few metersto condenser with no tight bends in between: Enthalpy control only (Saturated steam, with small excess water) Temperature probe for alarm only Pressure 7-15 barA at full flow (depending on available water pressure)b) when desuperheater is far from condenser: Temp control, 25 OC superheat, Distance to the first elbow > 6 meters, Temperature probe > 20 meters, Pressure 7-15 barA at full flow (depending on available water pressure)*2007 - KOSO. All rights reserved.*


FAQs - 8Piping layout? Pre-warming requirement?Steam PRV take-off should be located near, and above, the main steam line.Long radius elbows downstream of DSH are preferredSteam PRVs should be well-insulated.Pre-warming is required when there is a risk of (steam) valve bodies cooling excessively below the main steam temperaturesPre-warming may be through a small continuous flow or via a natural convection line in the piping*2007 - KOSO. All rights reserved.*


FAQs - 9Dump tube sizing and design?Selection of dump tube pressure at maximum flow condition is importantDetermines the size of the upstream pipe & the dump tubeCorrect dump tube design is important for ensuring proper dispersal of steam into the condenser and to eliminate the potential for erosionMust be designed to fit in available space*2007 - KOSO. All rights reserved.*


FAQs 10Bolted bonnet or pressure seal bonnet?Both will workBolted bonnetWell-suited for compressed trim design Quick-change trim easier valve maintenance (desirable)Pressure seal bonnetWell-suited for hung cage or top-guided designs only Generally characterized by seat rings which are welded-in or screwed into the valve body difficult for maintenance of seats (not desirable)Smaller bonnet bolting requirement more economical than bolted bonnet in this respectPressure seal bonnet with compressed trim design drives up the overall cost*2007 - KOSO. All rights reserved.*


Air Cooled Condensers(ACCs)

Special requirements for ACCsTurbine bypass systems for plants with ACC require additional protection against:Excessive vibrationExcessive noiseThe requirements are special because of:thin duct downstream, and,lack of vibration/ noise attenuation as in the case of water-cooled condenser*2007 - KOSO. All rights reserved.*


Differences in noise considerations: Traditional versus ACC application (1/2)Traditional condenser (water cooled):ONLY CONTROL VALVE NOISE NEEDS TO BE ADDRESSED. Although valve aerodynamic noise prediction is complex, it is understood well enough to have an industry standard.Dump tube noise is not an issue. Dump tube is inside the condenser itself, which has thick concrete wall so very little of the noise from the dump tube transmits to the outside. Turbine bypass steam lines to the condenser is smaller dia and thick so noise transmission loss to outside is HIGH.The pipe resonant frequencies are high so the low frequency noise from valves is attenuated more effectively.Bypass lines to condenser have insulation which attenuates noise.*2007 - KOSO. All rights reserved.*


Differences in noise considerations: Traditional versus ACC application (2/2)Air Cooled Condenser:DUMP TUBE IS ALSO A MAJOR NOISE SOURCE IN BYPASS SYSTEMS (IN ADDITION TO THE CONTROL VALVE).Dump tube noise is not well understood in the industry.Steam bypass lines to the condenser are HUGE and thin so noise is transmission loss to outside is LOW, i.e. noise is easily transmitted to the outside.The pipe resonant frequencies are low so significant part of the low frequency noise from valve AND the steam dump element leaks through to the outside. In addition, the duct wall can get excited and vibrate.Steam dump element is inside the thin ACC duct which is outside of the condenser itself. So the noise is transmitted by the entire length of the ACC duct. *2007 - KOSO. All rights reserved.*


ACC source of high noiseLarge flow rates and high energy jets can be very noisyStrong shock waves and combination of high energy jets are additional sources*2007 - KOSO. All rights reserved.*Jet spacing-to-dia ratio = 1.44, Pressure ratio = 8Source: Noise Characteristics and Shock Structures of Under-expanded Jet Array Configurations, S. V. Sherikar, ASME FEDSM 2007-37290


Interaction of jetsThe noise contribution due to interaction of neighboring jets depends strongly on jet spacing-to-diameter ratio and pressure ratio across the jets*2007 - KOSO. All rights reserved.*Source: Noise Characteristics and Shock Structures of Under-expanded Jet Array Configurations, S. V. Sherikar, ASME FEDSM 2007-37290Conventional dump tube


ACC solution for low noiseControl of fluid kinetic energy and turbulence is required for steam PRVs in the bypass systemsDump tube has to be designed for low noiseEliminate/ minimize shock wave noiseMinimize noise contribution of recombining jetsOptimization of upstream pressure for economical sizeAll drains and vents must be checked for noise contributionAttention to all details flow discontinuities, elbows etc*2007 - KOSO. All rights reserved.*


koso turbine bypass systems_(sales training, march 10 2011)_rev a.ppt

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