INTRODUCTION TO DRY GAS SEALS

Introduction to DGS

• Compressor shaft sealing

• Dry gas seal history
• Dry gas seal features and operation
• Operating principals
• Dry gas seal arrangements
Introduction to DGS

• T-28AT/XP/VL/ST seals
• Barrier seals
• Seal installation and removal
• Dry gas seal controls
• Oil seal retrofits
• Dry gas seal contamination and
troubleshooting
Compressor
shaft
sealing
Compressor shaft sealing
Compressor shaft sealing

• To isolate bearing cavity from the process

cavity:
– to prevent process gas from entering the
atmosphere
– to prevent bearing oil contamination of the
process
Compressor shaft sealing
Seal and Lube Oil System with Buffer Gas
Lube Oil Seal Oil Buffer Gas

Journal Carbon
Bearing Seal

Seal & Seal Oil

Lube Oil and
Buffer Gas
Compressor shaft sealing

• Power loss due to absence of oil shear

• Power loss due to seal oil pump and fans
• High seal gas decompression / venting and
booster blowdowns rates- environmental
considerations / loss of product
• Product contamination / pipe oil contamination
Compressor shaft sealing

• High cost of maintenance and downtime

• Fire hazards associated with wet oil systems
• High cost of oil disposal and spill cleanups -
environmental protection
Dry gas seal
history
Gas seal history
• 1968 First patent
• 1975 First field applications
Gas seal history
• 1968 First patent
• 1975 First field applications
• 1981 First beam type compressor
• 1985 First steam turbine
• 1985 First Mag brg / Dry seal
• 1991 Bi-directional seal
Gas seal history
• 1968 First patent
• 1975 First field applications
• 1981 First beam type compressor
• 1985 First steam turbine
• 1985 First Mag brg / Dry seal
• 1991 Bi-directional seal
• 1992 XP seal - 123 to 200 bar
Gas seal history
• 1968 First patent
• 1975 First field applications
• 1981 First beam type compressor
• 1985 First steam turbine
• 1985 First Mag brg / Dry seal
• 1991 Bi-directional seal
• 1992 XP seal - 123 to 200 bar
• 1994 Type 82 barrier seal
Worlds Largest Gas Seal (330mm)
Gas seal history
• 1968 First patent
• 1975 First field applications
• 1981 First beam type compressor
• 1985 First steam turbine
• 1985 First Mag brg / Dry seal
• 1991 Bi-directional seal
• 1992 XP seal - 123 to 200 bar
• 1994 Type 82 barrier seal introduced
• 1997 Worlds Largest 330mm Gas Seal
• 1997 Cranite 2000
• 1997 500 bar test rig
Gas seal history
• 1968 First patent
• 1975 First field applications
• 1981 First beam type compressor
• 1985 First steam turbine
• 1985 First Mag brg / Dry seal
• 1991 Bi-directional seal
• 1992 XP seal - 123 to 200 bar
• 1994 Type 82 barrier seal introduced
• 1997 Worlds Largest 330mm Gas Seal
• 1997 Cranite 2000
• 1997 500 bar test rig
• 1998 100,000,000 operating hours exceeded
• 2000 First 5000 psig balance piston seal
Features
and
operation
Dry gas seal features

• Reduces Capital Cost of New Installations

• Cartridge design simplifies installation and
protects critical seal components
• Proven and reliable technology
– Over…
• 180 Million Operation Hours
• 15,000 Cartridge Seals Installed
Dry gas seal features

• Extremely low process gas leakage

• Withstands rapid speed and pressure changes

• Theoretically, due to the non-contacting

design feature, seal life can be considered
unlimited
Dry gas seal features

• Allowance for axial shaft shifts

is normally + 0.125"

• Allowance for radial shaft shifts

is normally +.025"

• Capable of handling starts and stops

at full pressure
Dry gas seal features

• Eliminates Seal Oil Support System

• Reduces Maintenance Costs

• Saves Energy

• Prevents Oil Contamination

Dry gas seal features / operation
• Seal Reverse Rotation
– Short periods of reverse rotation can be
tolerated without damage but should be avoided
• Bi-directional seal designs are available
• Seal Reverse Pressurization
– Not recommended
• Seal Liquid Contamination
– Can tolerate small amounts of liquid
contamination, but should be avoided
Dry gas seal features / operation
• Slow Roll/Turning Gear
– Does not adversely affect seal performance
• Vibration
– Seal will withstand vibration allowances of
API 617
• Compressor Wash
– Compressor cleaning can be performed
provided seals are isolated by a buffer gas
Dry gas seal materials

• Mating Ring
– Tungsten/Silicon Carbide
• Primary Ring
– Carbon/Cranite 2000
• Hardware
– 410SS/316SS/Hasteloy/other
• Springs
– Hastelloy C
Operating
principals
Operating principals

Spiral Groove Comparison

UNIDIRECTIONAL BIDIRECTIONAL
SPIRAL GROOVE SPIRAL GROOVE
Operating principals
OUTER
LAND
DIAMETER

SPIRAL
GROOVE

GROOVE
DIAMETER

INNER
DIAMETER

ROTATION RELATIVE
TO PRIMARY RING
Operating principals
Direction of Rotation
Gas is induced
towards the
center.

Gas is Compressed &

Pressure increases to
Sealing Dam
set Gap.
Operating principals
Direction of Rotation Gas is induced
towards the
center.

Gas is Compressed &

Pressure increases to
Sealing Dam set Gap.
Operating principals
Normal Gap
FC = FO
FC FO

CLOSING FORCE OPENING FORCE

S P

Compression

Expansion

Gas Film
Spring Load Pressure
+ Hydrostatic Distribution
Operating principals
Increased Gap
FC >FO
FC FO
CLOSING FORCE OPENING FORCE

S P

Gas Film
Spring Load Pressure
+ Hydrostatic Distribution
Operating principals
Reduced Gap
FC < FO
FC FO
CLOSING FORCE OPENING FORCE

S P

Gas Film
Spring Load Pressure
+ Hydrostatic Distribution
Operating Principals

Non-Contacting Seal Hydrostatic

30 and Hydrodynamic Stiffness
Stiffness (GN/m)

20 Combined Stiffness
(Hydrostatic & Hydrodynamic)

10

Hydrostatic Stiffness Only

0 1 2 3 4 5 gap (µm)
Operating Principals

Thermal Balance of a Non-Contacting Seal

W Seal Temperature Seal Temperature
Higher Than Ambient Lower Than Ambient
.9

.8

.7
GAS EXPANSION
.6 HEAT REMOVAL

.5

.4

.3
VISCOUS SHEAR
HEAT GENERATION
.2

.1

0
0 1 2 3 4 5 6 gap µm
 Seal
arrangements
Dry gas seals: AT vs XP

28 AT SEAL 28 XP SEAL

PROCESS GAS SIDE

PROCESS GAS
SIDE
Polymer
Rings Carrier
Dry gas seal arrangements
SINGLE SEAL

Primary Vent Filtered Process Gas

Bearings Process Gas

Pressure: Up To 1800 PSIG Temperature: -4 To +400°F

Speed: Up To 660 Ft/Sec. Gases: All

SERVICE: PLANT AIR AND NITROGEN SERVICE

DGS Arrangements - XP Single Seal
BARRIER PRIMARY SEALING
GAS LEAKAGE GAS

PROCESS CAVITY
BEARING CAVITY

SERVICE: PLANT AIR AND NITROGEN SERVICE

Dry gas seal arrangements
TANDEM SEAL

N2 Purge Secondary Vent Primary Vent Filtered Process Gas

Bearings Process
Gas

Pressure: Up To 1800 PSIG Temperature: -4 To +400°F

Speed: Up To 660 Ft/Sec. Gases: All

SERVICE: Natural Gas Pipeline Compressors and Process Gas Compressors

 XP Tandem Seal
BARRIER SEALING
GAS GAS

SECONDARY PRIMARY
LEAKAGE LEAKAGE
BEARING CAVITY

PROCESS CAVITY
Dry gas seal arrangements
TANDEM SEAL WITH INTERMEDIATE LABYRINTH

N2 Purge Secondary Vent N2 Purge Primary Vent Filtered Process

Gas

Bearings Process
Gas

Pressure: Up To 1800 PSIG Temperature: -4 To +400°F

Speed: Up To 660 Ft/Sec. Gases: All

SERVICE: Applications Where Zero Process Leakage Is Required

 XP Tandem Seal w/ Int. Labyrinth

BARRIER SEPARATION SEALING

GAS (N2) GAS (N2) GAS

SECONDARY PRIMARY
LEAKAGE (N2) LEAKAGE
BEARING CAVITY

PROCESS CAVITY
DGS Arrangements - Double Seal
SEPARATION (N2) SEALING GAS (N2) BUFFER GAS
(PROCESS)
LEAKAGE
(N2)
BEARING CAVITY

PROCESS CAVITY
Pressure: Up To 400 PSIG Temperature: -4 To +400°F
Speed: Up To 660 Ft/Sec. Gases: HCL, Styrene,CO,…Etc.
SERVICE: Toxic and Corrosive Environments
Dry gas seals: AT vs. XP

• Resists seal hang-up due to O-Ring friction

• No explosive decompression problems

associated with O-Rings

• Provides long shelf life

• Applications are not compromised by chemical

compatibility of the O-Ring
Dry gas seal arrangements
• Pressure:
– AT: Up to 1800 PSIG
– XP: Up to 2900 PSIG
– EXP: Up to 6500 PSIG
• Temperature:
– AT: -70 to +400°F
– XP, EXP: -100 to +600°F
• Speed:
– Up to 660 Ft./Sec.
Type 28 ST
and
VL seals
Dry gas seals Type 28 ST
ST - Steam Seals

Pressure: Up To 400 PSIG Exhaust Temperature: Up To 750°F

Speed: Up To 590 Ft/Sec. Gases: Steam

SERVICE: Single and Multi Stage Steam Turbines

Dry gas seals Type 28 ST
• Low leakage rates
• Longer life compared to existing sealing
technology
• Eliminates steam cutting on shaft
• Eliminates shaft wear associated with
carbon bushings
• Low power consumption
Dry gas seals Type 28 ST - Limitations

• Dirty steam

• High pressures

• Difficult installations
Dry gas seals Type 28 VL

Filtered Process
Vent Fluid

Specialized Spiral
Groove Pattern

Process
Dry gas seals Type 28 VL
• Applications where process is extremely close to
flash point
– Methane
– Propane
– Ethane
– Ethylene
– CO2
• Typically on pumps where wet seals will not last
due to process flashing across seal faces
Barrier
seals
Barrier seals

• Seal selection

• Associated controls

• Operation
Barrier seals - Selection

• Carbon ring seal

• Split labyrinth

• Other
Barrier seals - Carbon ring
2ND STAGE BEARING
LEAKAGE BUFFER GAS VENT
GAS SEAL SIDE

BEARING SIDE
Barrier seals - Split labyrinth
BUFFER GAS
2ND STAGE BEARING
LEAKAGE VENT
Barrier seals - comparison

• Barrier Seal • Split Labyrinth

– N2 consumption < 1 – N2 consumption > 5
scfm per side scfm per side
– Seal life up to 5 years – Seal life indefinite
– Floating seal prevents (theoretically)
installation damage – Teeth can be damaged
during installation