Page 329 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Steam Turbine Best Practices Best Practice 5 .13

Trip valve is only as reliable as valve to move Most domestic vendors rely only on trip valve to shut off steam
Should periodically exercise valve to ensure movement supply (throttle valves remain open)
(minimum one per month for high pressure (40 bar) steam European vendors close both trip and automatic throttle valve
systems and daily for very high pressure (1000 bar + ) steam on trip signal
systems)
Exercises will not trip turbine
If valve does not move, must be remedied immediately Fig 5.12.7 Protection system philosophies

Fig 5.12.6 On-line manual exercise of trip valve

Best Practice 5.13Practice 5.13Practice 5.13
Best
Best
Accurately trend mechanical drive special purpose turbine Lessons Learned
efficiency, speed and flow rate using an installed torque- Condensing and extraction condensing steam turbine ef-
meter for condensing and extraction condensing steam ficiency calculations will be erroneous and non-conclusive
turbines. in determining maintenance requirements when torque-
Condensing and extraction steam turbine efficiency determination meters are not installed.
requires the calculation of the driven equipment power. This calcula-
tion can be inaccurate due to the many variables involved. Benchmarks
Installing a torquemeter during the project phase will ensure ac-
The installation of torquemeters has been recommended as part of
curate efficiency calculations for all condensing and extraction con-
project specifications since 1995. This has resulted in the accurate
densing steam turbines.
determination of critical (un-spared) steam turbine maintenance
Torquemeters can be installed in existing trains but will require:
to be carried out during turnarounds only and during planned
Rotor response study
operation.
Torsional study
Coupling and coupling guard modifications

B.P. 5.13. Supporting Material - Theoretical steam rate
- Actual steam rate
- Turbine efficiency
Steam turbine performance characteristics
An example will be presented for both non-condensing and
In this section we will discuss how energy is extracted from the condensing turbines. It should be noted that the exercises in this
vapor (steam) in a steam turbine. Power output is determined section will deal with overall steam turbine performance only. In
by the following factors in a steam turbine: the next section, we will discuss individual blade performance
and efficiencies, and determine, as an exercise, the number of
- The energy available from the vapor stages required for a given turbine application.
- The external efficiency of the turbine In this section we will also observe the effect of design steam
- The steam flow rate conditions on steam turbine performance and reliability. Finally,
typical turbine efficiencies and performance curves will be
Note: The external efficiency is equal to the internal effi- presented and discussed.
ciency (steam path efficiency) of the turbine factored by the
mechanical losses and steam leakage losses from the turbine.
The energy available from the vapor is determined by the Steam conditions
steam conditions of the particular application. That is, the
pressures and temperatures at the turbine inlet and exhaust Steam conditions determine the energy available per pound of
flanges. To determine the energy available from the vapor, steam steam. Figure 5.13.1 explains where they are measured and how
tables or a Mollier diagram are used. We have included a Mollier they determine the energy produced.
diagram for steam in this section. We will review in practical Frequently, proper attention is not paid to maintaining the
terms the use of a Mollier diagram to determine: proper steam conditions at the flanges of a steam turbine. Failure

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