Flowsolve Phelps Gas Leaks
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Transcript of Flowsolve Phelps Gas Leaks
7/27/2019 Flowsolve Phelps Gas Leaks
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Ventilation and Leak Dispersion
in CCGT Enclosures
Patrick Phelps ( Flowsolve )
andDouglas Wylie (GEC Energy Services)
I PUC 7 - Luxembourg - May 2000
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Ventilation and Leak Dispersion
in CCGT Enclosures
Industrial Context
Health and Safety Issues
Application to an Existing Power Station
Application to New Enclosure Designs
Conclusions Experimental Verification
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Industrial Context - 1
Combined Cycle Gas Turbine (CCGT) Plants
Gas turbines drive an electricity generator
Engine exhaust waste heat recovered by a
boiler to produce steam.
Steam turbine generates further output.
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Industrial Context - 2
Turbines are fuelled by gas at very
high pressures
Liquid fuel system as back-up
Turbines are contained within
acoustic enclosures.Enclosures tend to be installation-
specific designs
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“ Frame 6” Turbine Generator
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Industrial Context - 3
Each enclosure is divided into a number of
compartments containing
Auxiliary equipment Gas turbine and exhaust plenum
Reduction gearing and the generation equipment.
Auxiliary/GT/exhaust compartment is usually self-
contained, with a dedicated ventilation system
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Ventilation and Leak Dispersion
in CCGT Enclosures
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Health and Safety Issues - 1
Enclosure ventilation system removes
some heat from the turbine casing
Enables operatives to carry out readings
and routine maintenance under operating
conditions.
However, enclosures remain a “thermally hostile and noisome” environment .
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Health and Safety Issues - 2
Gas from leakages can accumulate to
flammable proportions in poorly ventilated
regions of the enclosures - “dead zones”
OUTCOME - Big Bang
REMEDY - Use the ventilating air to safely
dilute and disperse any gas leakage.
MOTIVATION - Legislation
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UK Safety Assessment of
CCGT Enclosures - 1
Identify nature and potential sources of
hazardous material releases
Determine leak frequency and inventory ofreleases
Investigate airflow characteristics
identify "dead zones" Predict dispersion consequences safety-critical
release scenarios
Implement remedial measures
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UK Safety Assessment of
CCGT Enclosures - 2
Experimental investigation of airflow
characteristics is difficult within the
confines of a turbine generator enclosure,especially under operational conditions.
HSE promote computer simulation as themost appropriate technology in this case.
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UK Safety Assessment of
CCGT Enclosures - 3
CFD models can
simulate the dispersion consequences of
releases under a variety of operating
conditions
compare the efficiency of alternative
ventilation strategies, to achieve thedesired dilution / dispersion result
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“Safe” Dispersion Criteria - 1
“Santon” Criterion “The ventilation arrangements within the turbine
enclosure must be such as to ensure the safedilution/dispersion of gas releases prior to
activation of mitigation/shutdown systems by the
gas detection system. The criteria to be applied
are that the envelope of the 50% LELconcentration contour should not occupy more
than 0.1% of the free volume of the enclosure, for
a gas leak of sufficient magnitude to trigger the
gas detection system.”
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“Safe” Dispersion Criteria - 2
G = V * (0.01 * E) * (0.01 * S).
Gas concentration level (S) detected by sensors foractivating emergency response systems (typically 10%)
Lower Explosive Limit (E) for the turbine fuel gas is around
5%.
Maximum undetected leak is thus of magnitude 10% of LEL For compliance, ensuing flammable envelope (of the 50%
LEL surface) must not exceed 0.1% of “the compartmentfree volume”.
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“Safe” Dispersion Criteria - 3“Compartment free volume”
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Reference Leak Scenario
Zero momentum leak source
corresponds to jet release impinging
immediately on an obstruction (casing,
flange body}
No net directionality imparted to release.
A directional release would require
additional assumptions …..
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Application to an Existing Power
Station - 1
A CFD-based simulation study
commissioned by
IVO Generation Systems
andRegional Power Generators Ltd
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Application to an Existing Power
Station - 2
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Application to an Existing Power
Station - 3
Over 100 simulations performed
Studies to determine
air flow distribution
worst case operating condition (hot,cold);
worst case leak location;efficiency of alternative “retrofit”
ventilation strategies, to achieve HSE
compliance
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Air flow Distribution at inlet to
Turbine Compartment
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Application to an Existing Power
Station
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Application to an Existing Power
Station - Parameter Studies
Over 100 simulations performed
Studies to determine
air flow distribution
worst case operating condition (hot,cold);
worst case leak location;efficiency of alternative “retrofit”
ventilation strategies, to achieve HSE
compliance
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Hot Operating Conditions:
Envelope volume - 0.69%
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Cold Operating Conditions:
Envelope volume - 2.28%
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Application to an Existing Power
Station - Parameter Studies
Over 100 simulations performed
Studies to determine
air flow distribution
worst case operating condition (hot,cold);
worst case leak location;efficiency of alternative “retrofit”
ventilation strategies, to achieve HSE
compliance
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“Worst Case” Leak Location
Under both hot and cold conditions,
the worst case leak location was
found to be in the “pit” region, in front
of the lowest combustor flanges
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Application to an Existing Power
Station - Parameter Studies
Over 100 simulations performed
Studies to determine
air flow distribution
worst case operating condition (hot,cold);
worst case leak location;efficiency of alternative “retrofit”
ventilation strategies, to achieve HSE
compliance
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Alternative Ventilation Strategies :
1 - Abject failures
Increasing ventilation rate
overhead pendant baffles
twin outlets
blowing air into the pit region
sucking air from the pit region EGT “wavewall” idea
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Alternative Ventilation Strategies :
2 - Heroic failures
Reversed flow system
• air supply through existing outlet
• air extract to TG inlet plenum
Lateral side-gust system
• air supply through side door
• air extract through existing outlet
• other inlets blocked off
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Alternative Ventilation Strategies :
3 - Final Success !
The “Corkscrew” Strategy
Close all existing inlets
plate over grated walkway tops
Single non-symmetric outlet
Two inlet slots , one high, one low, cut inconnecting doors
30-degree deflector plates create
corkscrew effect
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“Corkscrew” Ventilation Scheme
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“Corkscrew” Ventilation Scheme
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“Corkscrew” Ventilation Scheme
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“Corkscrew” Ventilation Scheme
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And so . . . . . . . . . .
This led on to . . . . . . . .
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Application to New Enclosure
Designs
A CFD-based simulation study
commissioned by
the Thermal Power Division
of Kvaerner Energy Ltd
A li i N E l
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Application to New Enclosure
Designs
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Enclosure Geometry - Elevation
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Enclosure Geometry - End View
A li ti t N E l
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Application to New Enclosure
Designs
T bi b t fl d
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Turbine combustor flanges and
associated pipework
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Geometry Representation - 1
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Geometry Representation - 2
A li ti t N E l
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Application to New Enclosure
Designs - Workscope
Over 25 different simulations performed
Studies to determine sensitivity to:
nodalisation level & distribution;
leak location;
ventilating flowrate;presence of internal geometric features;
inlet flow manipulation.
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Findings - 1
The worst case leakage scenario, under cold
start-up conditions, was a zero-momentum
leakage from the flanges in front of the lowestcan combustor
The flammable gas cloud with the “reference”
ventilation arrangement was twenty five timeslarger than the target value (11 times larger if the
accessory compartment volume was included)
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Reference Configuration{Flammable volume: 2.8% TC}
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Reference Configuration{Flammable volume: 2.8% TC}
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Reference Configuration{Flammable volume: 2.8% TC}
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Reference Configuration{Flammable volume: 2.8% TC}
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Reference Configuration{Flammable volume: 2.8% TC}
Application to New Enclosure
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Application to New Enclosure
Designs - Workscope
Over 25 different simulations performed
Studies to determine sensitivity to:
nodalisation level & distribution;
leak location;
ventilating flowrate;presence of internal geometric features;
inlet flow manipulation.
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Findings - 2
Increasing the ventilating air flowby 25% had little effect on
ventilation efficiency ( gas leak
size increased proportionately ).
Application to New Enclosure
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Application to New Enclosure
Designs - Workscope
Over 25 different simulations performed
Studies to determine sensitivity to:
nodalisation level & distribution;
leak location;
ventilating flowrate;presence of internal geometric features;
inlet flow manipulation.
Atomising Air System
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Atomising Air System
{Flammable volume: 1.9% TC}
Atomising Air System
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Atomising Air System
{Flammable volume: 1.9% TC}
Atomising Air System
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Atomising Air System
{Flammable volume: 1.9% TC}
Atomising Air System
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Atomising Air System
{Flammable volume: 1.9% TC}
Atomising Air System
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Atomising Air System
{Flammable volume: 1.9% TC}
Application to New Enclosure
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Application to New Enclosure
Designs - Workscope
Over 25 different simulations performed
Studies to determine sensitivity to:
nodalisation level & distribution;
leak location;
ventilating flowrate;presence of internal geometric features;
inlet flow manipulation.
Findings 3 :
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Findings - 3 :
Inlet Flow Manipulation
Improved results (decrease in flammable
cloud size) obtained by :
adding a “scoop” diverter at inlet ; “throttling” - increasing the inlet velocity ;
concentrating the incoming flow towards the
axial centreline; blocking off the outermost inlet hole(s) on each
side; and
biasing the massflow distribution.
Fi l C fi ti
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Final Configuration{Flammable Volume: 0.2% TC}
Fi l C fi ti
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Final Configuration{Flammable Volume: 0.2% TC}
Fi l C fi i
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Final Configuration{Flammable Volume: 0.2% TC}
Fi l C fi ti
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Final Configuration{Flammable Volume: 0.2% TC}
Fi l C fi ti
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Final Configuration{Flammable Volume: 0.2% TC}
C l i
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Conclusions
Flammable cloud volumes of less than 0.1% of the
free volume of the combined compartments are
attainable (at least conceptually) .
This would satisfy the current UK dispersion
criterion.
Compliance achieved without major structural
changes to enclosure or to air delivery system.
Future Efforts
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Future Efforts
Confirm high velocities do not provoke thermal
shock problems in hot operation
Confirm required manipulation of inlet air supply
is technically feasible (!)
Use model to predict likely over-pressures
arising from deflagration of the confined gas
plume.
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Experimental Verification
No quantitative data available.
Qualitative comparison - video footage of
smoke tests on installations with similarinternal geometries.
Smoke trails confirm magnitude and
direction of airflow in the region in front ofthe can flanges and around the front upper
part of the turbine barrel
Ventilation and Leak Dispersion
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Ventilation and Leak Dispersion
in CCGT Enclosures
Thank you for your attention .
“ When I count to three,
you will awake
and
remember nothing …..”
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Ventilation and Leak Dispersion
in CCGT Enclosures
Patrick Phelps (Flowsolve Ltd)
and Douglas Wylie (GEC Energy Services)