Sello Seco Funcionamiento
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DRY GAS SEAL SYSTEM Design Consideration & Troubleshooting Dresser-Rand Asia Pacific Kuala Lumpur, April 07
Field Solutions Asia Pacific
2007
Summary 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
2
Design Requirements The purpose of the gas seal system is: To provide clean, dry sealing gas to the faces of the dry gas seals
To provide clean, dry separation gas to the barrier seals
To monitor the "health" of the dry gas seals and barrier seals
3
Gas Seal System P&ID
4 •© 2000 by Dresser-Rand
Seal Gas Supply .. can be an inert gas, sweet gas, or process gas coming from a steady and continuous source, which meets the cleanliness and temp requirements ( supply temp 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 with a stainless steel housing
5
Seal Gas Supply – Filter Arrangement
discharge
6
Seal Gas Supply – Filter Arrangement
discharge
7
Seal Gas Supply To evaluate potential liquid condensation, a phase map shall be used to look at all operating conditions (design pressure to atmospheric pressure) including pressurized shutdowns and settle out conditions
Depending on the quality of the seal gas and the result of the phase map analysis, it may be required to provide special liquid separation and filtration equipment, and supplemental heating of the sealing gas
discharge
If the ambient temperature can fall below the seal gas dew point, all seal gas supply piping shall be heat traced
supply
8
Seal Gas Supply – Phase Envelope DEW POINT Critical Point SEAL GAS SUPPLY
PHASE ENVELOPE - SEAL GAS SUPPLY 2000 1800 1600
1200 1000 800 600 400 200 0 0
20
40
60
80
100 Temperature, F
120
140
160
180
200
C21983 New Gas
2000 1800 1600 1400
discharge
Pressure Psig
Pressure, PSIA
1400
1200 Dew Points Seal Gas
1000
Seal Gas fromDischarge 800 600 400 200
supply
0 0
50
100
150 Temperature F
200
250
9
Seal Gas Supply – Diff Press Control A1 C1
D1
B1
E1 FO
C2
A2
D1: Seal Ref. port A2: Drain C1: Secondary seal vent E1: Separation gas injection
B1
C1 E1
FO
A2
C2
A1: Seal gas injection B1: Primary seal vent C2: Drain FO: Seal inlet flow restriction orifice 10
Seal Gas Supply – Flow Control
discharge
supply
11
Primary Vent Line Monitoring the gas seal leakage through the primary vent = method of assessment of the condition of the dry gas seal. Monitoring the differential pressure across a restriction orifice in the primary vent piping fitted with an indicating, differential pressure transmitter
If the primary vent is connected to a flare system, a check valve is required to prevent any potential reverse flow in the vent which could cause damage to the gas seal
The primary vent shall be provided with a low drain point valve to allow drainage of any potential liquid builddischarge up, which could contaminate the primary seal. Periodic removal of any accumulated liquids is required
supply
12
Primary leakage – proper monitoring equip & safety devices
Rupture disc: unload the seal & release the pressure to vent / flare in case of a primary seal failure / PCV failure
13
Rupture Sensor
The plastic film with the printed silver circuit lies between two armored graphite gaskets There is no contact to the rupture disk 14
Secondary Vent The secondary seal is intended to act as a backup in case of primary seal damage, providing the necessary shaft sealing until the unit can be safely SD and depressurized
The compressor shall operate on the secondary seal only for a controlled S/D
The secondary vent shall be provided with a low drain point valve to allow drainage of any potential liquid buildup, which could contaminate the secondary seal. Periodic discharge removal of any accumulated liquids is required
supply
15
Separation Gas Supply N2 source is recommended to be employed for separation gas. Alternate solution, use of instrument air as the separation gas medium
The separation gas shall be free of solid particles 3 microns and larger, 99.97 percent liquid free, and a maximum of 120 F (49 C) at the gas seal control panel connection point
A separation gas filter is provided at the gas seal control panel inlet. D-R's standard arrangement is to discharge provide a duplex filter with non-ferrous housing
supply
16
Separation Gas Supply
The supply of separation gas to the barrier seals is controlled using a differential discharge pressure control valve that regulates the separation gas pressure to a predetermined value [< 15 PSI (<103 KPa)] above the secondary vent pressure 17
Separation Gas Supply – Alarms & S/D Alarm: is provided in the event the differential pressure between the separation gas supply and the secondary vent falls below a predetermined level
S/D: If proper separation gas pressure is lost during operation of the compressor, S/D is initiated after 30 minutes (After the compressor case has been vented, lube oil flow to the bearings shall be stopped)
Note: If proper separation gas pressure is lost while the compressor is S/D depressurized, lube oil pump shall be discharge stopped except if the rotor system includes an active turning gear 18
Permissive & Interlock Conditions Proper separation gas differential pressure shall be confirmed before energizing the lube oil pumps
Permissive to start: provides an interlock for the lube oil pump logic in the unit control panel
Permissive to start: provides an interlock for the rupture sensor (hard wired to the unit control discharge panel
19
Explosive Mixture When air is used as the separation gas medium, the gas seal system shall be evaluated for the possible occurrence of explosive air / gas mixture in the secondary vent, under all operating and static conditions
The system can be designed to create a "lean" or "rich" environment in the secondary vent
If the primary vent is connected to a flare system, the secondary vent is only permitted to employ a rich mixture design. Flame arrestors shall be provided (optionally by discharge D-R) for secondary vents to atmosphere employing separation air
20
Explosive Mixture “lean” mode: a quantity of air is injected into the secondary vent to insure that the gas to air mixture is below the lower explosive level of the gas. (This is
accomplished by bypassing separation air from the supply piping directly into the secondary vent piping)
“rich” mode: a quantity of process gas is injected into the secondary vent such that the gas to air mixture is above the upper explosive level of the gas. (This is
accomplished by bypassing process gas from the seal gas supply piping directly into the secondary vent piping) discharge
21
Gas Seal Control Panel Alarm, S/D & Interlock Conditions Parameter Filter differential pressure (all) Seal gas supply orifice DP or seal gas DP Primary vent differential pressure Intermediate gas orifice DP Separation gas supply / secondary vent differential pressure Primary Vent Rupture Disc burst sensor
Alarm Condition
Shutdown Condition
Permissive Start
High Low DP
Note **
High
High
Low DP or High DP
Low DP
Required
Low
Low (30 minute delay)
Required
Closed
Note **: discharge
A seal gas loss of supply shutdown is only required for toxic gas service
22
Gas Seal Control Panel – Operator Interface Mimic Screen (Flow Control)
discharge
23
Gas Seal Control Panel – Operator Interface Mimic Screen (DP control)
discharge
24
Start Up - Apliflow Provides pressure boost to seal supply gas to ensure filtered gas to the seals during start-up or times of low pressure differential Manual Operation - Set by discharge pressure Automatic Operation a) Begins operation at low differential pressure b) Continues operation until sufficient pressure discharge differential re-established 25
Start Up - Apliflow (FLOWSERVE) Vent
Drive Air Out
DRY SEAL PANEL
AMPLIFLOW SYSTEM
Filtered Gas In
Drive Air In
Boost Gas Out
discharge Compressor Discharge Gas
Boosted Supply Gas to Dry Seals
26
Ampliflow (Flowserve) P&ID
27
Example: How Flowserve Ampliflow Works Seal Supply Flow for Diameter 3/32" Orifice Based On Last TCPL Panel Design 115.00
95.00
Pressurization
75.00
Normal Operation Idle
55.00 Unit Ramp-up
Flowrate (SCFM per Seal)
Based on : Psuction=700psig Pdischarge=880psig Pseal=Psuction
Start
35.00
Dry Seal Supply Flow With AMPLIFLOW (Conservative Estimate)
AREA OF NO SEAL SUPPLY
15.00
Dry Seal Supply Flow Without AMPLIFLOW
-5.00 0
5
10
15
20
25
30
35
40
45
50
Time (minutes)
28
Ampliflow Benefits
Ensure positive flow of filtered gas to the dry gas seal port (boost up the gas pressure)
Prevent contamination of the seals during startup or times of recycle
Extend the dry gas seal life (less chance of failure due to contamination during start up / idle) 29
DRY GAS SEAL FAILURES & TROUBLESHOTING
30
How does the contaminant enter the seal ? Seal Supply Gas
Process Gas
INBOARD
Flare System
Separation Gas
Bearing Oil
OUTBOARD
31
If foreign particles enter the seal Consequences :
Erosion of the faces
Clogging of the grooves
Fretting / Seizing of seal sleeve
32
Origin of particles
Unclean piping
Corrosion
Debris in the gas stream
Lack or poor filtration
Improper preservation procedures
33
Contamination with solid particles Compressor head seal gas supply port
34
Erosion of the faces
35
Erosion of the faces
36
Clogging of the grooves
37
Clogging of the grooves
38
Fretting / Seizing of seal sleeve
39
Fretting / Seizing of seal sleeve
pitting and fretting on the balance Ø)
pitting and fretting on the balance diameter and o'ring groove
40
If liquid enters the seal Consequences :
Blistering of the carbon ring face
Corrosion (ex: sea water)
Heat generation (parts deformation, O ring extrusion)
Thermal shock (Tungsten ring rupture)
41
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
42
Primary Vent Line Piped to Flare Without Check valve
43
Improper Preservation
44
Improper Preservation
45
Blistering of the carbon ring face
46
Blistering of the carbon ring face
47
Corrosion
48
Corrosion
49
Corrosion
50
Thermal shock
51
Thermal shock
52
Thermal shock
53
Thermal shock
54
Lube oil (defective barrier)
55
Lube oil (defective barrier)
56
Lube oil (defective barrier)
57
Liquid Contamination
58
Condensate
59
Improper filtration of the seal gas supply
60
Improper filtration of the seal gas supply
61
Improper filtration of the seal gas supply
62
Improper filtration of the seal gas supply
63
Other failure Causes
Improper installation
Excessive Pressure
Excessive Temperature
Combination of the above factors
64
Improper installation
65
Improper installation Head Fond
Head Fond
SHAFT
ARBRE
Static Part
Rotating Part
SHAFT
ARBRE
66
Typical 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 ) 67
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 68
Site Inspection (during seal removal)
Record installation data ( Seal S/N, shim thickness, rotor S/N, shaft position, …)
Check for liquid / particles / debris /dirt. (Gas seal , barrier seal, inner laby, ports, …)
Inspect and identify (color, aspect,.), take samples, take pictures
Visual inspect barrier seal 69
Return the Seal to Manufacturer for Inspection & 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) 70
Gas Seal System – Operation & Maintenance Seal gas supply shall be clean & dry and available at sufficient pressure to cover the entire operation range PCV shall provide >10 psid diff press across the gas seal labyrinth
Gas seal condition is determined by the primary & sec leakage rate
71
Gas Seal System – Operation & Maintenance
Monitor / service the seal gas supply filters
Monitor / service the buffer gas supply filters Inspect the secondary & primary low drain points 72
Gas Seal System – On Condition Service Strategy Gas seal replacement is dictated by: 1) the primary vent leakage rate; 2) secondary vent (primary) low drain point liquid accumulations; 3) vibration caused by unbalance (seal sleeve);
73
www.dresser-rand.com [email protected] 74
Field Solutions Asia Pacific
2007
Summary 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
2
Design Requirements The purpose of the gas seal system is: To provide clean, dry sealing gas to the faces of the dry gas seals
To provide clean, dry separation gas to the barrier seals
To monitor the "health" of the dry gas seals and barrier seals
3
Gas Seal System P&ID
4 •© 2000 by Dresser-Rand
Seal Gas Supply .. can be an inert gas, sweet gas, or process gas coming from a steady and continuous source, which meets the cleanliness and temp requirements ( supply temp 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 with a stainless steel housing
5
Seal Gas Supply – Filter Arrangement
discharge
6
Seal Gas Supply – Filter Arrangement
discharge
7
Seal Gas Supply To evaluate potential liquid condensation, a phase map shall be used to look at all operating conditions (design pressure to atmospheric pressure) including pressurized shutdowns and settle out conditions
Depending on the quality of the seal gas and the result of the phase map analysis, it may be required to provide special liquid separation and filtration equipment, and supplemental heating of the sealing gas
discharge
If the ambient temperature can fall below the seal gas dew point, all seal gas supply piping shall be heat traced
supply
8
Seal Gas Supply – Phase Envelope DEW POINT Critical Point SEAL GAS SUPPLY
PHASE ENVELOPE - SEAL GAS SUPPLY 2000 1800 1600
1200 1000 800 600 400 200 0 0
20
40
60
80
100 Temperature, F
120
140
160
180
200
C21983 New Gas
2000 1800 1600 1400
discharge
Pressure Psig
Pressure, PSIA
1400
1200 Dew Points Seal Gas
1000
Seal Gas fromDischarge 800 600 400 200
supply
0 0
50
100
150 Temperature F
200
250
9
Seal Gas Supply – Diff Press Control A1 C1
D1
B1
E1 FO
C2
A2
D1: Seal Ref. port A2: Drain C1: Secondary seal vent E1: Separation gas injection
B1
C1 E1
FO
A2
C2
A1: Seal gas injection B1: Primary seal vent C2: Drain FO: Seal inlet flow restriction orifice 10
Seal Gas Supply – Flow Control
discharge
supply
11
Primary Vent Line Monitoring the gas seal leakage through the primary vent = method of assessment of the condition of the dry gas seal. Monitoring the differential pressure across a restriction orifice in the primary vent piping fitted with an indicating, differential pressure transmitter
If the primary vent is connected to a flare system, a check valve is required to prevent any potential reverse flow in the vent which could cause damage to the gas seal
The primary vent shall be provided with a low drain point valve to allow drainage of any potential liquid builddischarge up, which could contaminate the primary seal. Periodic removal of any accumulated liquids is required
supply
12
Primary leakage – proper monitoring equip & safety devices
Rupture disc: unload the seal & release the pressure to vent / flare in case of a primary seal failure / PCV failure
13
Rupture Sensor
The plastic film with the printed silver circuit lies between two armored graphite gaskets There is no contact to the rupture disk 14
Secondary Vent The secondary seal is intended to act as a backup in case of primary seal damage, providing the necessary shaft sealing until the unit can be safely SD and depressurized
The compressor shall operate on the secondary seal only for a controlled S/D
The secondary vent shall be provided with a low drain point valve to allow drainage of any potential liquid buildup, which could contaminate the secondary seal. Periodic discharge removal of any accumulated liquids is required
supply
15
Separation Gas Supply N2 source is recommended to be employed for separation gas. Alternate solution, use of instrument air as the separation gas medium
The separation gas shall be free of solid particles 3 microns and larger, 99.97 percent liquid free, and a maximum of 120 F (49 C) at the gas seal control panel connection point
A separation gas filter is provided at the gas seal control panel inlet. D-R's standard arrangement is to discharge provide a duplex filter with non-ferrous housing
supply
16
Separation Gas Supply
The supply of separation gas to the barrier seals is controlled using a differential discharge pressure control valve that regulates the separation gas pressure to a predetermined value [< 15 PSI (<103 KPa)] above the secondary vent pressure 17
Separation Gas Supply – Alarms & S/D Alarm: is provided in the event the differential pressure between the separation gas supply and the secondary vent falls below a predetermined level
S/D: If proper separation gas pressure is lost during operation of the compressor, S/D is initiated after 30 minutes (After the compressor case has been vented, lube oil flow to the bearings shall be stopped)
Note: If proper separation gas pressure is lost while the compressor is S/D depressurized, lube oil pump shall be discharge stopped except if the rotor system includes an active turning gear 18
Permissive & Interlock Conditions Proper separation gas differential pressure shall be confirmed before energizing the lube oil pumps
Permissive to start: provides an interlock for the lube oil pump logic in the unit control panel
Permissive to start: provides an interlock for the rupture sensor (hard wired to the unit control discharge panel
19
Explosive Mixture When air is used as the separation gas medium, the gas seal system shall be evaluated for the possible occurrence of explosive air / gas mixture in the secondary vent, under all operating and static conditions
The system can be designed to create a "lean" or "rich" environment in the secondary vent
If the primary vent is connected to a flare system, the secondary vent is only permitted to employ a rich mixture design. Flame arrestors shall be provided (optionally by discharge D-R) for secondary vents to atmosphere employing separation air
20
Explosive Mixture “lean” mode: a quantity of air is injected into the secondary vent to insure that the gas to air mixture is below the lower explosive level of the gas. (This is
accomplished by bypassing separation air from the supply piping directly into the secondary vent piping)
“rich” mode: a quantity of process gas is injected into the secondary vent such that the gas to air mixture is above the upper explosive level of the gas. (This is
accomplished by bypassing process gas from the seal gas supply piping directly into the secondary vent piping) discharge
21
Gas Seal Control Panel Alarm, S/D & Interlock Conditions Parameter Filter differential pressure (all) Seal gas supply orifice DP or seal gas DP Primary vent differential pressure Intermediate gas orifice DP Separation gas supply / secondary vent differential pressure Primary Vent Rupture Disc burst sensor
Alarm Condition
Shutdown Condition
Permissive Start
High Low DP
Note **
High
High
Low DP or High DP
Low DP
Required
Low
Low (30 minute delay)
Required
Closed
Note **: discharge
A seal gas loss of supply shutdown is only required for toxic gas service
22
Gas Seal Control Panel – Operator Interface Mimic Screen (Flow Control)
discharge
23
Gas Seal Control Panel – Operator Interface Mimic Screen (DP control)
discharge
24
Start Up - Apliflow Provides pressure boost to seal supply gas to ensure filtered gas to the seals during start-up or times of low pressure differential Manual Operation - Set by discharge pressure Automatic Operation a) Begins operation at low differential pressure b) Continues operation until sufficient pressure discharge differential re-established 25
Start Up - Apliflow (FLOWSERVE) Vent
Drive Air Out
DRY SEAL PANEL
AMPLIFLOW SYSTEM
Filtered Gas In
Drive Air In
Boost Gas Out
discharge Compressor Discharge Gas
Boosted Supply Gas to Dry Seals
26
Ampliflow (Flowserve) P&ID
27
Example: How Flowserve Ampliflow Works Seal Supply Flow for Diameter 3/32" Orifice Based On Last TCPL Panel Design 115.00
95.00
Pressurization
75.00
Normal Operation Idle
55.00 Unit Ramp-up
Flowrate (SCFM per Seal)
Based on : Psuction=700psig Pdischarge=880psig Pseal=Psuction
Start
35.00
Dry Seal Supply Flow With AMPLIFLOW (Conservative Estimate)
AREA OF NO SEAL SUPPLY
15.00
Dry Seal Supply Flow Without AMPLIFLOW
-5.00 0
5
10
15
20
25
30
35
40
45
50
Time (minutes)
28
Ampliflow Benefits
Ensure positive flow of filtered gas to the dry gas seal port (boost up the gas pressure)
Prevent contamination of the seals during startup or times of recycle
Extend the dry gas seal life (less chance of failure due to contamination during start up / idle) 29
DRY GAS SEAL FAILURES & TROUBLESHOTING
30
How does the contaminant enter the seal ? Seal Supply Gas
Process Gas
INBOARD
Flare System
Separation Gas
Bearing Oil
OUTBOARD
31
If foreign particles enter the seal Consequences :
Erosion of the faces
Clogging of the grooves
Fretting / Seizing of seal sleeve
32
Origin of particles
Unclean piping
Corrosion
Debris in the gas stream
Lack or poor filtration
Improper preservation procedures
33
Contamination with solid particles Compressor head seal gas supply port
34
Erosion of the faces
35
Erosion of the faces
36
Clogging of the grooves
37
Clogging of the grooves
38
Fretting / Seizing of seal sleeve
39
Fretting / Seizing of seal sleeve
pitting and fretting on the balance Ø)
pitting and fretting on the balance diameter and o'ring groove
40
If liquid enters the seal Consequences :
Blistering of the carbon ring face
Corrosion (ex: sea water)
Heat generation (parts deformation, O ring extrusion)
Thermal shock (Tungsten ring rupture)
41
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
42
Primary Vent Line Piped to Flare Without Check valve
43
Improper Preservation
44
Improper Preservation
45
Blistering of the carbon ring face
46
Blistering of the carbon ring face
47
Corrosion
48
Corrosion
49
Corrosion
50
Thermal shock
51
Thermal shock
52
Thermal shock
53
Thermal shock
54
Lube oil (defective barrier)
55
Lube oil (defective barrier)
56
Lube oil (defective barrier)
57
Liquid Contamination
58
Condensate
59
Improper filtration of the seal gas supply
60
Improper filtration of the seal gas supply
61
Improper filtration of the seal gas supply
62
Improper filtration of the seal gas supply
63
Other failure Causes
Improper installation
Excessive Pressure
Excessive Temperature
Combination of the above factors
64
Improper installation
65
Improper installation Head Fond
Head Fond
SHAFT
ARBRE
Static Part
Rotating Part
SHAFT
ARBRE
66
Typical 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 ) 67
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 68
Site Inspection (during seal removal)
Record installation data ( Seal S/N, shim thickness, rotor S/N, shaft position, …)
Check for liquid / particles / debris /dirt. (Gas seal , barrier seal, inner laby, ports, …)
Inspect and identify (color, aspect,.), take samples, take pictures
Visual inspect barrier seal 69
Return the Seal to Manufacturer for Inspection & 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) 70
Gas Seal System – Operation & Maintenance Seal gas supply shall be clean & dry and available at sufficient pressure to cover the entire operation range PCV shall provide >10 psid diff press across the gas seal labyrinth
Gas seal condition is determined by the primary & sec leakage rate
71
Gas Seal System – Operation & Maintenance
Monitor / service the seal gas supply filters
Monitor / service the buffer gas supply filters Inspect the secondary & primary low drain points 72
Gas Seal System – On Condition Service Strategy Gas seal replacement is dictated by: 1) the primary vent leakage rate; 2) secondary vent (primary) low drain point liquid accumulations; 3) vibration caused by unbalance (seal sleeve);
73
www.dresser-rand.com [email protected] 74
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