Page 303 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 5 .7 Steam Turbine Best Practices

Fig 5.6.6 Typical journal bearing selection curve (Courtesy of Kingsbury, Inc.)

Best
Best Practice 5.7Practice 5.7

Design audit thrust bearing loading for impulse and re- Lessons Learned
action turbines, to ensure that maximum encountered field Many impulse steam turbines designed in the 1980s and

thrust pad temperatures do not exceed 110 C and achieve 1990s have encountered high thrust bearing pad temper-
maximum MTBF. atures. This restricted turbine power and required multiple
Impulse bladed turbines, which historically did not produce signif-
icant thrust loads, have used reaction blades in the last three stages modifications to reduce thrust pad temperatures to an
since the 1980s for increased turbine efficiency. acceptable level.
The use of reaction blading in the last stages has significantly in- While vendor modifications helped reduce thrust loads in impulse
creased thrust loads e to the surprise of both end users and designers. turbines, it was not until rotor modifications were made that values

To avoid higher than expected thrust pad temperatures in impulse were reduced to acceptable levels (below 110 C [230 F] maximum).
turbines, consider undercutting the turbine shaft to act as a balance
drum, and reduce the load on the thrust bearing during the project pre- Benchmarks
bid phase (before vendor final priced proposals are submitted). This best practice has been used since the 1990s to finally reduce
In reaction turbine designs, where each blade row produces high impulse turbine thrust pad temperatures to acceptable levels without
thrust, the inlet end steam seal diameter is raised to function as the use of ‘band aid’ modifications (questionable fixes that may not
a balance drum. Vendor balance drum calculations should be audited last). This best practice has produced steam turbines with trouble-free
during the pre-bid project phase to ensure proper thrust balance under thrust bearing operation and thrust bearing MTBFs exceeding 100
all load and steam conditions. months.

278