SEAL STEAM SYSTEM
Glands are used on turbine to prevent or reduce leakage
of
steam
or
air
between
rotating
and
stationary
components, which have a pressure difference across
them; this applies particularly where the turbine shaft
passes through the cylinder. If the cylinder pressure is
higher than atmospheric pressure, there will be a general
steam leakage outwards. If the cylinder is below
atmospheric pressure there will be a leakage of air
inwards, and some sort of sealing system must be used to
prevent air from entering the cylinder and the condenser.
SEAL STEAM SYSTEM
500MW turbine has got 6 sets of gland seals. One for
each side of HP, IP and LP. Each set has got number of
sectionalized gland. Each segment is supported by two
flat spring sections.
HP, IP AND LP TURBINE
HP, IP AND LP TURBINE
HP TURBINE
IP TURBINE
LP TURBINE
TURBINE SYSTEM
SEAL STEAM SYSTEM
The penultimate section of each gland is supplied with
steam from gland steam header, which is maintained
at a pressure of 1.03kg/sq cm to 1.05 kg/sq cm and
temperature between 130 deg C to 150 deg C in a 210
MW KWU Design Turbine. The last section of each
gland goes to Gland Steam Condenser which remains
at vacuum.
SEAL STEAM SYSTEM
Number of sections in each turbine front and rear glands:
HP front
: 3 sections
HP rear
: 4 sections
IP front
: 2 sections
IP rear
: 2 sections
LP front
: 2 sections
LP rear
: 2 sections
SEAL STEAM SYSTEM
SEAL STEAM SYSTEM
ROTOR
RADIAL CLEARANCE
AXIAL
CLEARANCE
STEAM
FLOW
RADIAL CLEARANCE
CASING
RADIAL CLEARANCE = 0.4 & 0.5 MM
SEAL STEAM SYSTEM
STEAM THROTTLING
When steam passes through the radial clearances
between the seal fins of the casing and rotor a
thermodynamic process known as throttling takes
place. As a result of passing through a small
aperture of fin clearance the steam tend to loose its
pressure and gain velocity. Thus the enthalpy of
the steam before and after remains constant.
The reduced pressure steam is connected to a
lower pressure header in steps.
SEAL STEAM SYSTEM
GLAND STEAM HEADER
HPT
LPT
IPT
CRH
GLAND STEAM CONDENSER
IP EXHAUST
GLAND STEAM HEADER TEMPERATURE
GLAND STEAM HEADER PRESSURE
:
:
280 0C
350 mmwc
SEAL STEAM SYSTEM
Spray from BFP discharge
S
Pressure Controller
From MS Line
To Atmosphere
To Interconnecting
Unit
DESUPERHEATER
Auxiliary Steam from
Interconnecting Unit
GSC
AUXILIARY
HPT
IPT
PRDS HEADER
LPT
S
For D/A
For
To
Pegging Atomizing SCAPH
For Turbine
Gland
Sealing
S
To Condenser
From CRH Line
S
S
Leak off Controller
S
Gland
Steam
Controller
To
Flash
Tank
Orifice
To
Flash
Tank
To Fuel
Oil Heating
SEAL STEAM SYSTEM
SEAL STEAM SYSTEM
SEAL STEAM SYSTEM
SEAL STEAM SYSTEM
SEAL STEAM SYSTEM
SEAL STEAM SYSTEM
ROTOR FINS
SEAL
SEGMENTS
SEAL STEAM SYSTEM
Labyrinth Seal
For labyrinth packing a relatively soft
metallic
material
packing
is
is
used.
segmented
The
and
assembled concentric to the turbine
shaft and held in place by multiple
coil springs. A labyrinth seal is a
Mechanical Seal that fits around an
axle to prevent the leakage of oil or
other fluids.
LABYRINTH SEAL
A labyrinth seal is composed of many straight grooves
that press tightly inside another axle, so that the fluid
has to pass through a long and difficult path to escape.
For labyrinth seals on a rotating shaft, a very small
clearance must exist between the tips of the labyrinth
threads and the running surface.
Labyrinth seals on rotating shafts provide non-contact
sealing action by controlling the passage of fluid through
a variety of chambers by centrifugal motion, as well as
by the formation of controlled fluid vortices.
LABYRINTH SEAL
At higher speeds, centrifugal motion forces the liquid
towards the outside and therefore away from any
passages. The labyrinth seals are non-contact type,
therefore the wearing out rate is much slower.
Turbines use labyrinth seals due to the lack of friction,
which is necessary for high rotational speeds.
GLAND STEAM CONDENSER
• Surface type.
• Horizontally pipe mounted cooler.
• single pass heat exchanger.
Numbers
:1 x 100%
Number of tubes
:799
Tube size (mm x mm)
:16.0 x 0.889
Overall length of shell (m)
:1.44
Shell outer diameter (mm)
:760
Shell thickness (mm)
:25.0
Condensate Flow,
:1133473.0 kg/hr
Condensate Inlet Temp, T1
:46.6 deg C
Condensate Outlet Temp, T2
:47.0 deg C
Heat Transfer Area provided, Aa :41.6 m2
PROBLEMS ASSOCIATED WITH
ABNORMAL SEAL STEAM PARAMETERS
• DAMAGE TO GLAND SEGMENTS
• BARRING GEAR JAMMING
• DISTORTION IN TURBINE CASING / ROTOR
• STEAM LEAKAGE
• POOR VACUUM
OTHER SEAL TYPES
OTHER SEAL TYPES
Felt Seals
Felt seals are mainly used as oil or grease seals for
retaining lubrication and at the same time preventing
dirt or dust entering the bearing.
Felt has long been used for sealing duties because of
numerous favourable properties such as wicking and
oil absorption properties, fine filtering and resilience.
This allows the felt to maintain a constant sealing
pressure and as the seal wears the felt surface
remains unchanged.
OTHER SEAL TYPES
Felt Seals
Felt seals are usually pre-saturated with lubricants of a
higher viscosity than the bearings offering positive
bearing protection. If the seal does run dry it will tend
to protect and polish the shaft rather than cause
damage.
Through normal operating temperatures
and conditions the felt seal is highly economical,
normally requiring replacement when the machine is
overhauled.
OTHER SEAL TYPES
Felt Seals
When the seal is correctly installed the seal is effective
over a variety of operating conditions and a wide
range of speeds. Normal maximum rubbing speed is
10 m/s but can be as high as 20m/s if the rubbing
surfaces are highly polished and lubricant is always
present.
Felt Seals are not suitable for oils with extremely low
viscosity or the lubricant is pressurised.
OTHER SEAL TYPES
FELT SEALS
OTHER SEAL TYPES
Lip Seals
This is an assembly consisting of a rubbing elastomer
ring seal element held in place by spring. The seal
friction is reduced as an oil film is generated between
the lip of the seal and the shaft. Any damage to the
shaft where the seal runs will cause leakage because
the optimum oil film thickness will be exceeded locally.
Therefore the shaft finish is especially important, as
leakage will occur if an irregular surface is present.
OTHER SEAL TYPES
Lip Seals
The lubricated rubbing provides the sealing action.
This sealing action cannot be maintained at high
speeds if the shaft is not running perfectly true. To
maintain oil film thickness the seal must follow any
shaft movement. This becomes difficult when the shaft
is subject to eccentric running or vibration at high
speeds. Typically these seals will operate in the region
of 18 m/s and the seals are affected by friction.
OTHER SEAL TYPES
LIP SEALS
OTHER SEAL TYPES
Ferrofluid Seals
This is a very specialised rotary seal type which has
superior theoretical benefits.
The seal is a fluid ring which is retained in place
between the rotating and fixed members under the
action of magnetic forces.
Ferrofluidic sealing technology takes advantage of the
response of a fluid, containing a uniform distribution of
magnetic particles, to an applied magnetic field.
OTHER SEAL TYPES
Ferrofluid Seals
It uses a magnet with magnetically permeable north
and south pole pieces and a magnetically permeable
shaft to create a permanent magnetic circuit. The
magnetic flux is concentrated in the gap under each
pole and when ferrofluid is applied to this gap it
assumes the shape of a liquid o-ring and produces a
hermetic seal.
OTHER SEAL TYPES
Ferrofluid Seals
Ferrofluidic seals offer provide hermetic sealing, long life,
virtually frictionless sealing and smooth operation. They
are non-contaminating, highly reliable and can operate at
high speeds. This type of seal can be used over a wide
temperature range, which can be increased by use of
cooling, or heating circuits. The seals have to be regularly
maintained as the fluid properties deteriorate over time.
These bearings are used for very specialised applications
OTHER SEAL TYPES
FERROFLUID SEALS
BRUSH SEALS
• Densely packed bristle pack welded to the front and
back plates that provide mechanical support for
sealed pressure.
BRUSH SEALS
• During rotor growth and excursions, bristle pack deflects
elastically and springs back to new positions to maintain
sealing contact– without little or no permanent damage.
• Current labyrinth seal will be permanently damaged
during a rotor contact
BRUSH SEALS
LABYRINTH SEAL VIS-ÀVIS BRUSH SEAL
BRUSH SEALS
LABYRINTH SEAL VIS-À-VIS BRUSH SEAL
Reduced leakage and parasitic loss compared
to current labyrinth seals, resulting from:
• Its ability to significantly reduce as-installed seal
clearance
• Its ability to withstand rotor growth and excursions
without enlarging seal clearance
BRUSH SEALS
LABYRINTH SEAL VIS-À-VIS BRUSH SEAL
• Large impact on efficiency gain with a relatively low
investment. Cost of energy savings is orders of
magnitude higher than incremental cost of seal