Page 358 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 6.3
Gas Turbine Best Practices Be st Practice 6.4

Best Practice 6.3Practice 6.3
Best
Size the gas turbine output power for a minimum of D10% at Insufficient driver power will restrict maximum possible flow rates or
rated site conditions (see B.P. 6.2 for site condition rating). generated power. The associated revenue losses can exceed over
Inaccurate site condition specifications, variances in fuel gas $100 MM for the life of the plant.
composition and fouling of the gas generator can significantly reduce
its output power and result in significant revenue losses. Benchmarks
Insufficient outputpower willdirectlyreduce maximum attainableflow This best practice has been used since 1990 to ensure that sufficient
rates, resulting in significant revenue losses for the life of the project. gas turbine power is available at site conditions. Project management
Perform a life cycle cost analysis, to determine possible lost reve- resistance will be initially encountered and will usually require a life
nue costs and to justify a larger power driver that is a minimum of cycle cost analysis to justify the additional revenue opportunity as
þ10% above rated power. compared to the additional capital and installation costs for a larger
gas turbine.
Lessons Learned
The majority of mechanical drive gas turbine installations
suffer revenue opportunity losses from insufficient site
power.

B.P. 6.3. Supporting Material

Please refer to material in B.P. 6.2.

Best
Best Practice 6.4Practice 6.4Practice 6.4
Best
Screen for proven model experience (including experience Start-up delays can result in significant revenue losses.
for all support systems) during the pre-FEED phase of the In addition, reliability issues resulting from unproven gas turbine
project to determine the acceptable vendors list. components and/or their support systems can add to revenue op-
Do not assume that a proven vendor’s gas turbine model will have portunity losses for the life of the process unit.
sufficient field operating experience. These issues can expose the end user to revenue losses in the
Model generations (higher operating temperatures, new control hundreds of millions of USD for the life of the process unit.
systems and modified support systems) can and will change.
Require vendor experience and references for review of the exact Benchmarks
turbine model quoted and all support systems during the pre-FEED This is a new best practice, added in 2010 as a result of the selection of
phase of the project. a proven gas turbine from a vendor that had recently combined forces
with a larger company. While the gas turbine design was maintained
Lessons Learned during the takeover, the proven control system was replaced by a ‘new
generation’ system that was used for the first time on our project. The
Failure to determine experience of gas turbine models and
result was a start-up delay of three months to correct the problems.
their support systems has led to significant start-up delays
and reliability issues that can last for the life of the oper-
ating plant.

B.P. 6.4. Supporting Material After each major type of support system is defined and
discussed, the accessory gearbox will be presented. The acces-
In this section, we will present and discuss the various gas tur- sory gearbox is a very critical piece of equipment, since it pro-
bine support systems. The gas turbine, at first glance, appears to vides power take-offs to the majority of support system pumps,
be a very complicated piece of rotating equipment. Part of the starters and blowers. Accessory gearboxes will be discussed for
reason for this perception is due to the complexity and number both industrial and aero-derivative type gas turbines.
of the various support systems involved. Figure 6.4.1 shows a sketch of the location and types of gas
The objective of this section will be to classify each type of turbine support systems along with the definition of a support
support system and present its particular function. It is felt that system.
this approach will make the reader realize that the support As can be seen in the figure 6.4.2, the availability of the gas
systems used for a gas turbine are very similar, in most cases, to turbine is a direct function of the support systems. Particular
those used by turbo-compressors and steam turbines. attention must be paid to the preventive maintenance (PM) and

329