POWER April 2013 - 66

PLANT O&M
Clear theway
for quality air
the bottom of the cylinder while the top of
the cylinder remains relatively hot. As a
result, the cylinder will bend down while
the top of the casing will remain straight,
in most cases.
Also, poor clearances in the low-pressure
(LP) and intermediate-pressure (IP)
cylinder frames in multi-cylinder turbines
can occur when the distance bolts and
washers are incorrectly installed. Distance
bolts are used to secure the LP and IP casing
frames to the foundation. At the time
of operation and nominal load, if condenser
pressure (vacuum) and condensate
temperature are within normal range, then
the clearance should be as designed. But if
the condenser pressure (vacuum) is abnormal
and condensate temperature is high,
then the LP cylinder gets hotter than the
allowed limit, causing more volume expansion
in the condenser. The result is that
the distance bolt clearance is decreased or
goes to zero. If design clearances aren't
observed, turbine vibration may increase
and the turbine load must be reduced.
Next, don't forget the bolts, pins, and
140 years of history, and the present is yours
Optimizing air supply quality is a way of life at Atlas Copco. Our dryers, aftercoolers,
filters and oil-mist eliminators help ensure that your air is always clean, dry and ready
for the summer heat.
And it doesn't stop with quality air because the right air system components also save
energy. Atlas Copco knows you have challenging targets to reduce energy costs. We
know because we face those targets, too! With 14 production facilities in the United
States and dozens more globally, we never stop looking
for ways to help our manufacturing teams, and yours,
save energy and increase productivity.
In 2013 Atlas Copco celebrates our 140th
birthday. To celebrate this key milestone
we are offering a series of gifts: starting
with simple air studies for free. We'll log
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far into the future.
other casing joints. Casings for HP turbines
have thick walls, as well as big horizontal
joint flanges that require bolts and
pins. There are times when turbine loads
quickly change or the casing flange and
walls are heated unevenly during startup
or shutdown of a unit. A temperature difference
between the top and bottom of the
HP and IP casings (usually 50C to 70C)
and flange pins (maximum 15C to 25C)
can cause steam leakage through the casing
horizontal joint.
Finally, uncompensated movement of
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POWER | April 2013
steam pipes connected to the casing can
cause casing movements and rotor vibration.
This is particularly true for large-diameter
pipes with thick walls. When the turbine is
operating, the rotor has axial movement, as
does the turbine casing. Thermal expansion
of the system is accounted for in the turbine
design. The forces and moments that these
large pipes apply to the casing are also considered
during turbine design. Excessive
pipe connection loads may cause casing
deformation, and the bending moments applied
to the casing flanges may also cause
displacement and movement of the cylinder
within the casing, either of which can increase
rotor vibration. ■
-Farshad Shamoradi (fshamoradi@yahoo
.com) is manager of the instrument department,
Naser Mohammadi is manager of the
engineering department, and Mahdi
Heidari Kahkesh is manager of overall
maintenance at the Ramin Power
Plant, Ahwaz Power Generation
Management Co.
http://www.atlascopco.us/mboxusa http://www.powermag.com
POWER April 2013

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