DRY GAS SEAL SYSTEMDRY GAS SEAL SYSTEMDesign Consideration & TroubleshootingDesign Consideration & Troubleshooting

Dresser-Rand Asia PacificDresser-Rand Asia Pacific Kuala Lumpur, April 07 Kuala Lumpur, April 07

2007Field Solutions Asia Pacific

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SummarySummary

Design Requirements Seal Gas Supply Seal Gas Supply Controls Dry Gas Seal Primary vent Dry Gas Seal Secondary vent Enrichment Line Alarm, S/D and Interlock Conditions Transient Operations / Start Up Gas Seal System Failures & Troubleshooting

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Design RequirementsDesign Requirements

The purpose of the gas seal system is:

To provide clean, dry sealing gas to the facesof the dry gas seals

To provide clean, dry separation gas to thebarrier seals

To monitor the "health" of the dry gas sealsand barrier seals

4•© 2000 by Dresser-Rand

Gas Seal System P&IDGas Seal System P&ID

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Seal Gas SupplySeal Gas Supply .. can be an inert gas, sweet gas, or process gas

coming from a steady and continuous source, whichmeets the cleanliness and temp requirements ( supplytemp shall be limited to a maximum of 250ºF /121 C) This gas should be filtered to 2 micron to remove solid

particles from the gas stream When moisture is present in the seal gas supply, a

coalescing element is recommended A duplex or stand-by filter assembly enables the

operator to change the dirty filter without system S/D.D-R's standard arrangement is duplex filter assembly witha stainless steel housing

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Seal Gas SupplySeal Gas Supply – Filter Arrangement – Filter Arrangement

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Seal Gas SupplySeal Gas Supply – Filter Arrangement – Filter Arrangement

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Seal Gas SupplySeal Gas Supply

To evaluate potential liquid condensation, a phase mapshall be used to look at all operating conditions (designpressure to atmospheric pressure) including pressurizedshutdowns and settle out conditions

Depending on the quality of the seal gas and the resultof the phase map analysis, it may be required to providespecial liquid separation and filtration equipment, andsupplemental heating of the sealing gas

If the ambient temperature can fall below the seal gasdew point, all seal gas supply piping shall be heat traced

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Seal Gas Supply – Phase EnvelopeSeal Gas Supply – Phase EnvelopePHASE ENVELOPE - SEAL GAS SUPPLY

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 20 40 60 80 100 120 140 160 180 200Temperature, F

Pres

sure

, PSI

ADEW POINTCritical PointSEAL GAS SUPPLY

C21983 New Gas

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 50 100 150 200 250

Temperature F

Pre

ssur

e P

sig

Dew PointsSeal GasSeal Gas fromDischarge

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Seal Gas Supply – Diff Press ControlSeal Gas Supply – Diff Press Control

D1A1

B1B1 C1C1

A2 A2

D1: Seal Ref. port A1: Seal gas injectionA2: Drain B1: Primary seal ventC1: Secondary seal vent C2: DrainE1: Separation gas injection FO: Seal inlet flow restriction orifice

E1E1

C2C2

FOFO

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Seal Gas SupplySeal Gas Supply – Flow Control – Flow Control

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Primary Vent LinePrimary Vent Line Monitoring the gas seal leakage through the primary

vent = method of assessment of the condition of the drygas seal. Monitoring the differential pressure across arestriction orifice in the primary vent piping fitted with anindicating, differential pressure transmitter

If the primary vent is connected to a flare system, acheck valve is required to prevent any potential reverseflow in the vent which could cause damage to the gasseal

The primary vent shall be provided with a low drainpoint valve to allow drainage of any potential liquid build-up, which could contaminate the primary seal. Periodicremoval of any accumulated liquids is required

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Primary leakage – Primary leakage – proper monitoringproper monitoringequip & safety devicesequip & safety devices

Rupture disc: unload the seal & release the pressure tovent / flare in case of a primary seal failure / PCV failure

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Rupture SensorRupture Sensor

The plastic film with the printed silver circuit lies between two armored graphite gaskets

There is no contact to the rupture disk

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Secondary VentSecondary Vent The secondary seal is intended to act as a backup in

case of primary seal damage, providing the necessaryshaft sealing until the unit can be safely SD anddepressurized

The compressor shall operate on the secondary sealonly for a controlled S/D

The secondary vent shall be provided with a low drainpoint valve to allow drainage of any potential liquid build-up, which could contaminate the secondary seal. Periodicremoval of any accumulated liquids is required

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Separation Gas SupplySeparation Gas Supply N2 source is recommended to be employed for

separation gas. Alternate solution, use of instrument airas the separation gas medium

The separation gas shall be free of solid particles 3microns and larger, 99.97 percent liquid free, and amaximum of 120 F (49 C) at the gas seal control panelconnection point

A separation gas filter is provided at the gas sealcontrol panel inlet. D-R's standard arrangement is toprovide a duplex filter with non-ferrous housing

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The supply of separation gas to the barrier seals is controlled using adifferential pressure control valve that regulates the separation gaspressure to a predetermined value [< 15 PSI (<103 KPa)] above thesecondary vent pressure

Separation Gas SupplySeparation Gas Supply

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Separation Gas Supply – Alarms &Separation Gas Supply – Alarms &S/DS/D

Note: If proper separation gas pressure is lost while thecompressor is S/D depressurized, lube oil pump shall bestopped except if the rotor system includes an activeturning gear

Alarm: is provided in the event the differential pressurebetween the separation gas supply and the secondaryvent falls below a predetermined level

S/D: If proper separation gas pressure is lost duringoperation of the compressor, S/D is initiated after 30minutes (After the compressor case has been vented, lube oilflow to the bearings shall be stopped)

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Permissive & Interlock ConditionsPermissive & Interlock Conditions

Proper separation gas differential pressureshall be confirmed before energizing the lube oilpumps

Permissive to start: provides an interlock forthe lube oil pump logic in the unit control panel

Permissive to start: provides an interlock forthe rupture sensor (hard wired to the unit controlpanel

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Explosive MixtureExplosive Mixture

If the primary vent is connected to a flare system, thesecondary vent is only permitted to employ a rich mixturedesign. Flame arrestors shall be provided (optionally byD-R) for secondary vents to atmosphere employingseparation air

When air is used as the separation gas medium, the gasseal system shall be evaluated for the possible occurrenceof explosive air / gas mixture in the secondary vent, underall operating and static conditions

The system can be designed to create a "lean" or "rich"environment in the secondary vent

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Explosive MixtureExplosive Mixture “lean” mode: a quantity of air is injected into the

secondary vent to insure that the gas to air mixtureis below the lower explosive level of the gas. (This isaccomplished by bypassing separation air from the supplypiping directly into the secondary vent piping)

“rich” mode: a quantity of process gas is injected intothe secondary vent such that the gas to air mixture isabove the upper explosive level of the gas. (This isaccomplished by bypassing process gas from the seal gas supplypiping directly into the secondary vent piping)

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Gas Seal Control PanelGas Seal Control PanelAlarm, S/D & Interlock ConditionsAlarm, S/D & Interlock Conditions

ClosedPrimary Vent Rupture Disc burst sensor

RequiredLow(30 minute

delay)

LowSeparation gas supply / secondary ventdifferential pressure

RequiredLow DPLow DP orHigh DP

Intermediate gas orifice DP

HighHighPrimary vent differential pressure

Note **Low DPSeal gas supply orifice DP or seal gas DP

HighFilter differential pressure (all)

PermissiveStart

ShutdownCondition

AlarmCondition

Parameter

Note **: A seal gas loss of supply shutdown is only required for toxicgas service

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Gas Seal Control Panel – Gas Seal Control Panel – Operator InterfaceOperator InterfaceMimic Screen (Flow Control)Mimic Screen (Flow Control)

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Gas Seal Control Panel – Gas Seal Control Panel – Operator InterfaceOperator InterfaceMimic Screen (DP control)Mimic Screen (DP control)

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Start Up - Start Up - ApliflowApliflowProvides pressure boost to seal supply gas to ensurefiltered gas to the seals during start-up or times of lowpressure differential

Manual Operation - Set by discharge pressure

Automatic Operationa) Begins operation at low differential pressureb) Continues operation until sufficient pressuredifferential re-established

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Start Up - Start Up - ApliflowApliflow (FLOWSERVE)(FLOWSERVE)

DRY SEALPANEL

Boosted Supply Gasto Dry Seals

CompressorDischarge Gas

Drive Air In

Drive Air Out

Vent

AMPLIFLOWSYSTEM

FilteredGas In Gas Out

Boost

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Ampliflow (Flowserve) P&ID

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Seal Supply Flow for Diameter 3/32" OrificeBased On Last TCPL Panel Design

Time (minutes)

Flow

rate

(SC

FM p

er S

eal)

-5.00

15.00

35.00

55.00

75.00

95.00

115.00

0 5 10 15 20 25 30 35 40 45 50

Dry Seal Supply Flow With AMPLIFLOW(Conservative Estimate)

Dry Seal Supply Flow Without AMPLIFLOW

Pressurization

Uni

t Ram

p-up

Normal Operation

Based on :Psuction=700psig

Pdischarge=880psigPseal=Psuction

AREA OF NOSEAL SUPPLY

Start

Idle

Example: How Flowserve Example: How Flowserve AmpliflowAmpliflowWorksWorks

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AmpliflowAmpliflow Benefits Benefits

Ensure positive flow of filtered gas to the drygas seal port (boost up the gas pressure)

Prevent contamination of the seals during start-up or times of recycle

Extend the dry gas seal life (less chance offailure due to contamination during start up /idle)

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DRY GAS SEALDRY GAS SEAL FAILURES & TROUBLESHOTING FAILURES & TROUBLESHOTING

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How does the contaminant enter the seal ?How does the contaminant enter the seal ?

Seal SupplyGas

INBOARD OUTBOARD

ProcessGas

BearingOil

SeparationGas

FlareSystem

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If foreign particles enter the sealIf foreign particles enter the seal

Consequences :

Erosion of the faces

Clogging of the grooves

Fretting / Seizing of seal sleeve

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Origin of particlesOrigin of particles

Unclean piping

Corrosion

Debris in the gas stream

Lack or poor filtration

Improper preservationprocedures

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Contamination with solid particlesContamination with solid particlesCompressor head seal gas supply port

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Erosion of the facesErosion of the faces

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Erosion of the facesErosion of the faces

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Clogging of the groovesClogging of the grooves

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Clogging of the groovesClogging of the grooves

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Fretting / Seizing of seal sleeve Fretting / Seizing of seal sleeve

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Fretting / Seizing of seal sleeve Fretting / Seizing of seal sleeve

pitting and fretting on the balancediameter and o'ring groove

pitting and fretting on the balance Ø)

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If liquid enters the sealIf liquid enters the seal

Consequences :

Blistering of the carbon ring face

Corrosion (ex: sea water)

Heat generation (partsdeformation, O ring extrusion)

Thermal shock (Tungsten ringrupture)

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Source of liquid ?Source of liquid ?

Lube oil (defective barrier)

Condensate (at operating conditions)

Liquid carry over in the gas stream

Improper filtration of the seal gas supply

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Primary Vent Line Piped to Flare WithoutPrimary Vent Line Piped to Flare WithoutCheck valveCheck valve

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Improper PreservationImproper Preservation

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Improper PreservationImproper Preservation

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Blistering of the carbon ring faceBlistering of the carbon ring face

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Blistering of the carbon ring faceBlistering of the carbon ring face

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CorrosionCorrosion

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CorrosionCorrosion

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CorrosionCorrosion

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Thermal shockThermal shock

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Thermal shockThermal shock

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Thermal shockThermal shock

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Thermal shockThermal shock

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Lube oil (defective barrier)Lube oil (defective barrier)

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Lube oil (defective barrier)Lube oil (defective barrier)

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Lube oil (defective barrier)Lube oil (defective barrier)

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Liquid ContaminationLiquid Contamination

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CondensateCondensate

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Improper filtration of the seal gasImproper filtration of the seal gassupplysupply

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Improper filtration of the seal gasImproper filtration of the seal gassupplysupply

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Improper filtration of the seal gasImproper filtration of the seal gassupplysupply

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Improper filtration of the seal gasImproper filtration of the seal gassupplysupply

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Other failure CausesOther failure Causes

Improper installation

Excessive Pressure

Excessive Temperature

Combination of the above factors

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Improper installationImproper installation

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Improper installationImproper installationHeadFond

SHAFTARBRE

HeadFond

SHAFTARBRE

Static Part

Rotating Part

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Typical list of questionsTypical list of questions

Operating data (rpm, pressure, temperature,gas composition, …)

No of running hours

No of Start/Stop

Sequence of events

Maintenance procedures (i.e. filters,secondary vent low drain point checks )

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Site Inspection (prior to seal removal)Site Inspection (prior to seal removal)

Check for liquid / particles at all drain points:

• Primary vent

• Secondary vent

• Casing

• Gas panel

Try and identify (color, aspect,.), take samples

Check gas seal filters

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Site Inspection (during seal removal)Site Inspection (during seal removal)

Record installation data ( Seal S/N, shimthickness, rotor S/N, shaft position, …)

Check for liquid / particles / debris /dirt. (Gasseal , barrier seal, inner laby, ports, …)

Inspect and identify (color, aspect,.), takesamples, take pictures

Visual inspect barrier seal

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Return the Seal to Manufacturer forReturn the Seal to Manufacturer forInspection & RepairInspection & Repair

Use initial boxing

Return complete set of parts with same S.N.

• Gas seal

• Setting plate

• Shear rings

• etc …

Return one pair of seals (not only one end)

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Gas Seal System – Operation &Gas Seal System – Operation &MaintenanceMaintenance

Seal gas supply shall be clean & dry and available atsufficient pressure to cover the entire operation range

PCV shall provide >10 psid diffpress across the gas seal labyrinth

Gas seal condition is determinedby the primary & sec leakage rate

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Gas Seal System – Operation &Gas Seal System – Operation &MaintenanceMaintenance

Inspect the secondary &primary low drain points

Monitor / service thebuffer gas supply filters

Monitor / service theseal gas supply filters

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Gas Seal System – On ConditionGas Seal System – On ConditionService StrategyService Strategy

Gas seal replacement is dictated by:

1) the primary vent leakage rate;2) secondary vent (primary) low drain point liquidaccumulations;3) vibration caused by unbalance (seal sleeve);

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