Ventilation and Leak Dispersion in CCGT Enclosures Patrick Phelps ( Flowsolve ) and Douglas Wylie (GEC Energy Services) IPUC 7 - Luxembourg - May 2000

Ventilation and Leak Ventilation and Leak Dispersion in CCGT Dispersion in CCGT EnclosuresEnclosures

Patrick PhelpsPatrick Phelps ( Flowsolve )( Flowsolve )

andand

Douglas WylieDouglas Wylie (GEC Energy (GEC Energy Services)Services)

IPUC 7 - Luxembourg - May 2000


Industrial ContextIndustrial Context Health and Safety IssuesHealth and Safety Issues Application to an Existing Power Application to an Existing Power

StationStation Application to New Enclosure Application to New Enclosure

DesignsDesigns ConclusionsConclusions Experimental VerificationExperimental Verification

Industrial Context - 1Industrial Context - 1

Combined Cycle Gas Turbine (CCGT) PlantsCombined Cycle Gas Turbine (CCGT) Plants

Gas turbines drive an electricity Gas turbines drive an electricity generatorgenerator

Engine exhaust waste heat recovered by Engine exhaust waste heat recovered by a boiler to produce steam. a boiler to produce steam.

Steam turbine generates further output. Steam turbine generates further output.


Turbines are fuelled by gas at Turbines are fuelled by gas at very high pressuresvery high pressures

Liquid fuel system as back-up Liquid fuel system as back-up Turbines are contained within Turbines are contained within

acoustic enclosures. acoustic enclosures. Enclosures tend to be Enclosures tend to be

installation-specific designsinstallation-specific designs

“ “ Frame 6” Turbine Frame 6” Turbine Generator Generator


Each enclosure is divided into a number of Each enclosure is divided into a number of compartments containing compartments containing

Auxiliary equipmentAuxiliary equipment Gas turbine and exhaust plenumGas turbine and exhaust plenum Reduction gearing and the generation Reduction gearing and the generation

equipment. equipment.

Auxiliary/GT/exhaust compartment is usually Auxiliary/GT/exhaust compartment is usually self-self-

contained, with a dedicated ventilation systemcontained, with a dedicated ventilation system


Health and Safety Issues Health and Safety Issues - 1 - 1

Enclosure ventilation system removes Enclosure ventilation system removes some heat from the turbine casingsome heat from the turbine casing

Enables operatives to carry out Enables operatives to carry out readings and routine maintenance readings and routine maintenance under operating conditions. under operating conditions.

However, enclosures remain a However, enclosures remain a “thermally hostile and noisome” “thermally hostile and noisome” environment .environment .

Health and Safety Issues Health and Safety Issues

- 2- 2

Gas from leakages can accumulate to Gas from leakages can accumulate to flammable proportions in poorly flammable proportions in poorly ventilated regions of the enclosures - ventilated regions of the enclosures - “dead zones”“dead zones”

OUTCOME - Big BangOUTCOME - Big Bang REMEDYREMEDY - Use the ventilating air to - Use the ventilating air to

safely dilute and disperse any gas safely dilute and disperse any gas leakage.leakage.

MOTIVATIONMOTIVATION - Legislation - Legislation

UK Safety Assessment of UK Safety Assessment of CCGT Enclosures - 1CCGT Enclosures - 1

Identify nature and potential sources of Identify nature and potential sources of hazardous material releaseshazardous material releases

Determine leak frequency and inventory Determine leak frequency and inventory of releasesof releases

Investigate airflow characteristicsInvestigate airflow characteristics identify "dead zones" identify "dead zones" Predict dispersion consequences safety-Predict dispersion consequences safety-

critical release scenarioscritical release scenarios Implement remedial measuresImplement remedial measures

UK Safety UK Safety Assessment of CCGT Assessment of CCGT Enclosures - 2Enclosures - 2

Experimental investigation of airflow Experimental investigation of airflow characteristics is difficult within the characteristics is difficult within the confines of a turbine generator confines of a turbine generator enclosure, especially under operational enclosure, especially under operational conditions.conditions.

HSE promote computer simulation as HSE promote computer simulation as the most appropriate technology in the most appropriate technology in this case.this case.

UK Safety UK Safety Assessment of CCGT Assessment of CCGT Enclosures - 3Enclosures - 3

CFD models canCFD models can simulate the dispersion simulate the dispersion

consequences of releases under a consequences of releases under a variety of operating conditionsvariety of operating conditions

compare the efficiency of compare the efficiency of alternative ventilation strategies, alternative ventilation strategies, to achieve the to achieve the desired dilution / desired dilution / dispersion resultdispersion result

““Safe” Dispersion Criteria Safe” Dispersion Criteria - 1 - 1

““Santon” CriterionSanton” Criterion““The ventilation arrangements within the turbine The ventilation arrangements within the turbine

enclosure must be such as to ensure the safe enclosure must be such as to ensure the safe dilution/dispersion of gas releases prior to dilution/dispersion of gas releases prior to activation of mitigation/shutdown systems by activation of mitigation/shutdown systems by the gas detection system. The criteria to be the gas detection system. The criteria to be applied are that the envelope of the 50% LEL applied are that the envelope of the 50% LEL concentration contour should not occupy more concentration contour should not occupy more than 0.1% of the free volume of the enclosure, than 0.1% of the free volume of the enclosure, for a gas leak of sufficient magnitude to trigger for a gas leak of sufficient magnitude to trigger the gas detection system.”the gas detection system.”


G = V * (0.01 * E) * (0.01 * S).G = V * (0.01 * E) * (0.01 * S).

Gas concentration level (S) detected by sensors for Gas concentration level (S) detected by sensors for activating emergency response systems (typically activating emergency response systems (typically 10%) 10%)

Lower Explosive Limit (E) for the turbine fuel gas is Lower Explosive Limit (E) for the turbine fuel gas is around 5%. around 5%.

Maximum undetected leak is thus of magnitude 10% of Maximum undetected leak is thus of magnitude 10% of LELLEL

For compliance, For compliance, ensuing flammable envelopeensuing flammable envelope (of the (of the 50% LEL surface) 50% LEL surface) must not exceed 0.1% of “the must not exceed 0.1% of “the compartment free volume”compartment free volume”..


“Compartment free volume”“Compartment free volume”

Reference Leak Reference Leak ScenarioScenario

Zero momentum leak source Zero momentum leak source corresponds to jet release corresponds to jet release

impinging immediately on an impinging immediately on an obstruction (casing, flange body}obstruction (casing, flange body}

No net directionality imparted to No net directionality imparted to release. release.

A directional release would require A directional release would require additional assumptionsadditional assumptions …..…..

Application to an Existing Application to an Existing Power Station - 1Power Station - 1

A CFD-based simulation study A CFD-based simulation study

commissioned by commissioned by

IVO Generation SystemsIVO Generation Systems

and and

Regional Power Generators LtdRegional Power Generators Ltd



Over 100 simulations performedOver 100 simulations performed

Studies to determine Studies to determine air flow distributionair flow distribution worst case operating condition (hot,cold);worst case operating condition (hot,cold); worst case leak location;worst case leak location; efficiency of alternative “retrofit” efficiency of alternative “retrofit”

ventilation strategies, to achieve HSE ventilation strategies, to achieve HSE compliancecompliance

Air flow Distribution at Air flow Distribution at inlet toinlet toTurbine CompartmentTurbine Compartment

Application to an Existing Application to an Existing Power StationPower Station

Application to an Existing Application to an Existing Power Station - Power Station - Parameter StudiesParameter Studies


Studies to determine Studies to determine air flow distributionair flow distribution worst case operating condition (hot,cold)worst case operating condition (hot,cold);; worst case leak location;worst case leak location; efficiency of alternative “retrofit” efficiency of alternative “retrofit”


Hot Operating Conditions:Hot Operating Conditions:Envelope volume - Envelope volume - 0.69%0.69%

Cold Operating Conditions:Cold Operating Conditions:Envelope volume - Envelope volume - 2.28%2.28%



Studies to determine Studies to determine air flow distributionair flow distribution worst case operating condition (hot,cold);worst case operating condition (hot,cold); worst case leak locationworst case leak location;; efficiency of alternative “retrofit” efficiency of alternative “retrofit”


““Worst Case” Leak Worst Case” Leak LocationLocation

Under both hot and cold conditions, Under both hot and cold conditions,

the worst case leak location was the worst case leak location was

found to be in the “pit” region, in found to be in the “pit” region, in

front of the lowest combustor flangesfront of the lowest combustor flanges



Studies to determine Studies to determine air flow distributionair flow distribution worst case operating condition (hot,cold);worst case operating condition (hot,cold); worst case leak location;worst case leak location; efficiency of alternative “retrofit” efficiency of alternative “retrofit”


Alternative Ventilation Alternative Ventilation Strategies :Strategies :

1 - Abject failures1 - Abject failures

Increasing ventilation rateIncreasing ventilation rate overhead pendant bafflesoverhead pendant baffles twin outletstwin outlets blowing air into the pit regionblowing air into the pit region sucking air from the pit regionsucking air from the pit region EGT “wavewall” ideaEGT “wavewall” idea


2 - Heroic failures2 - Heroic failures

Reversed flow systemReversed flow system• air supply through existing outletair supply through existing outlet• air extract to TG inlet plenumair extract to TG inlet plenum

Lateral side-gust systemLateral side-gust system• air supply through side doorair supply through side door• air extract through existing outletair extract through existing outlet• other inlets blocked off other inlets blocked off


3 - Final Success !3 - Final Success !

The “Corkscrew” StrategyThe “Corkscrew” Strategy Close all existing inlets Close all existing inlets plate over grated walkway topsplate over grated walkway tops Single non-symmetric outletSingle non-symmetric outlet Two inlet slots , one high, one low, Two inlet slots , one high, one low,

cut in connecting doorscut in connecting doors 30-degree deflector plates create 30-degree deflector plates create

corkscrew effect corkscrew effect

““Corkscrew” Ventilation Corkscrew” Ventilation SchemeScheme




And so . . . . . . . . . .And so . . . . . . . . . .

This led on to . . . . . . . .This led on to . . . . . . . .

Application to New Application to New Enclosure DesignsEnclosure Designs

A CFD-based simulation study A CFD-based simulation study

commissioned by commissioned by

the Thermal Power Division the Thermal Power Division

of Kvaerner Energy Ltdof Kvaerner Energy Ltd


Enclosure Geometry - Enclosure Geometry - ElevationElevation

Enclosure Geometry - End Enclosure Geometry - End ViewView


Turbine combustor flanges Turbine combustor flanges and associated pipeworkand associated pipework

Geometry Representation Geometry Representation - 1 - 1

Geometry Representation Geometry Representation - 2 - 2

Application to New Application to New Enclosure Designs - Enclosure Designs - WorkscopeWorkscope

Over 25 different simulations performedOver 25 different simulations performed

Studies to determine sensitivity to:Studies to determine sensitivity to: nodalisation level & distribution;nodalisation level & distribution; leak location;leak location; ventilating flowrate; ventilating flowrate; presence of internal geometric presence of internal geometric

features;features; inlet flow manipulation.inlet flow manipulation.

Findings - 1Findings - 1

The worst case leakage scenario, under cold The worst case leakage scenario, under cold start-up conditions, was a zero-momentum start-up conditions, was a zero-momentum leakage from the flanges in front of the leakage from the flanges in front of the lowest can combustorlowest can combustor

The flammable gas cloud with the The flammable gas cloud with the “reference” ventilation arrangement was “reference” ventilation arrangement was twenty five times larger than the target twenty five times larger than the target valuevalue (11 times larger if the accessory (11 times larger if the accessory compartment volume was included)compartment volume was included)

Reference ConfigurationReference Configuration{Flammable volume: 2.8% TC}{Flammable volume: 2.8% TC}







Studies to determine sensitivity to:Studies to determine sensitivity to: nodalisation level & distribution;nodalisation level & distribution; leak location;leak location; ventilating flowrateventilating flowrate; ; presence of internal geometric presence of internal geometric

features; features; inlet flow manipulation.inlet flow manipulation.

Findings - 2Findings - 2

Increasing the ventilating Increasing the ventilating air flow by 25% had little air flow by 25% had little effecteffect on ventilation on ventilation efficiency ( gas leak size efficiency ( gas leak size increased proportionately ).increased proportionately ).




features; features; inlet flow manipulation.inlet flow manipulation.

Atomising Air SystemAtomising Air System {Flammable volume: 1.9% TC}{Flammable volume: 1.9% TC}








features;features; inlet flow manipulation.inlet flow manipulation.

Findings - 3 :Findings - 3 :Inlet Flow ManipulationInlet Flow Manipulation

Improved resultsImproved results (decrease in (decrease in flammable cloud size) flammable cloud size) obtained byobtained by : :

adding a “scoop” diverter at inlet ;adding a “scoop” diverter at inlet ; ““throttling” - increasing the inlet velocity ;throttling” - increasing the inlet velocity ; concentrating the incoming flow towards concentrating the incoming flow towards

the axial centreline;the axial centreline; blocking off the outermost inlet hole(s) on blocking off the outermost inlet hole(s) on

each side; and each side; and biasing the massflow distribution.biasing the massflow distribution.

Final ConfigurationFinal Configuration{Flammable Volume: 0.2% TC}{Flammable Volume: 0.2% TC}





ConclusionsConclusions

Flammable cloud volumes of less than 0.1% Flammable cloud volumes of less than 0.1% of the free volume of the combined of the free volume of the combined compartments are attainable (at least compartments are attainable (at least conceptually) . conceptually) .

This would satisfy the current UK dispersion This would satisfy the current UK dispersion criterion. criterion.

Compliance achieved without major Compliance achieved without major structural changes to enclosure or to air structural changes to enclosure or to air delivery system.delivery system.

Future EffortsFuture Efforts

Confirm high velocities do not provoke Confirm high velocities do not provoke thermal shock problems in hot thermal shock problems in hot operation operation

Confirm required manipulation of inlet Confirm required manipulation of inlet air supply is technically feasible (!)air supply is technically feasible (!)

Use model to predict likely over-Use model to predict likely over-pressures arising from deflagration of pressures arising from deflagration of the confined gas plume.the confined gas plume.

Experimental Experimental VerificationVerification

No quantitative data available. No quantitative data available. Qualitative comparison - video footage Qualitative comparison - video footage

of smoke tests on installations with of smoke tests on installations with similar internal geometries.similar internal geometries.

Smoke trails confirm magnitude and Smoke trails confirm magnitude and direction of airflow in the region in front direction of airflow in the region in front of the can flanges and around the front of the can flanges and around the front upper part of the turbine barrelupper part of the turbine barrel


Thank you for your attention .Thank you for your attention .

“ “ When I count to three, When I count to three,

you will awake you will awake

and and

remember nothing …..”remember nothing …..”


Patrick PhelpsPatrick Phelps (Flowsolve Ltd)(Flowsolve Ltd)

andand

Douglas WylieDouglas Wylie (GEC Energy (GEC Energy Services)Services)

IPUC 7 - Luxembourg - May 2000

Documents

Ventilation and Leak Dispersion in CCGT Enclosures Patrick Phelps ( Flowsolve ) and Douglas Wylie (GEC Energy Services) IPUC 7 - Luxembourg - May 2000