sello seco funcionamiento
DESCRIPTION
Seminario sobre funcionamiento del sistema de sello seco de compresores centrífugos de Dresser RandTRANSCRIPT
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);