Page 362 - Steam Turbines Design, Applications, and Rerating

336 Chapter Sixteen

Figure 16.7 Reduction in leakage flow due to improved seal designs. (Advanced Tur-
bomachine, LLC)

16.1.2 Wavy face dry seals
Carbon rings are currently the most common way of sealing steam
turbines in the size range up to approximately 1500 kW. They are sim-
ple in design, but the sealing capability of these devices is very low.
This results in high steam losses, lower efficiency, and decreased equip-
ment reliability. New developments since 1980 have superseded the old
seal design and are worth considering in both new and retrofit situa-
tions.
The design, selection, and installation of a modern noncontacting
seal for operation in general-purpose steam turbines is discussed as
follows. The goals, objectives, and results of a specific project conducted
by a single user from 2000 through 2005 are referenced. The overall
project goal aimed to improve turbine efficiency, enhance the reliability
of the equipment, and reduce maintenance cost. The design has fea-
tures that include proper application along with shop fabrication, field
installation, and subsequent operation requirements. Details from
field application at the user’s plants and guidelines for installation are
included. The operation of steam turbine seals is discussed, along with
the cost justification for the use of dry seals in steam turbines.
Conventional carbon ring seals are made of a special form of
graphite. Special graphites have good self-lubricating properties that
allow for close operating clearances. Ideally, at final operating temper-
ature, the diametrical clearance between the shaft and the carbon ring