POWER June 2011 - 56

COMBUSTION TURBINES
Selecting Your Next Combustion
Turbine
With natural gas serving as the fuel de jour, many utilities and merchant generators
will be considering the purchase of new combustion turbines in
the near future. If you are in the market for a gas turbine, here are some
key design features you should discuss with turbine vendors prior to
your next purchase.
By Amin Almasi, WorleyParsons Services Pty Ltd.
T
he growth of the combustion turbine
(CT) market over the past two decades
has been facilitated by progress
in three technologies:
■ Metallurgical advances that have made
possible high temperatures in turbine
components (especially turbine blades)
and combustors.
■ The advancement of aerodynamic and
thermodynamic knowledge (especially
from aircraft and spacecraft industries).
■ Advanced computer technology used in
the design and simulation of turbine airfoils,
combustors, and turbine blade cooling
configurations.
Combined, these advances have made
possible CT designs with state-of-the-art
1,600C (2,912F) turbine inlet temperatures
and combined-cycle efficiency pushing the
60% thermal efficiency barrier.
The challenge for a purchaser of a new
CT is what questions to ask, given that
these design advances are not readily apparent.
The discussion that follows is not
meant to tell a manufacturer how to design
a CT, nor is it comprehensive. Rather, it is
intended to prompt some useful planning
before a potential buyer has the first technical
discussion with a potential supplier.
Turbine Configurations
CTs are usually categorized as either heavy
frame industrial or aero-derivative gas turbines,
although a few turbines have recently
adopted features of both design types.
One good example of a " hybrid " is General
Electric's LMS100; it has a Frame 6FA
low-pressure compressor and a CF6-80C2
high-pressure compressor.
In general, the differences between the
aero-derivative and industrial turbines are
weight, size, combustor and turbine design,
bearing design (antifriction bearings
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POWER | June 2011
for aero-derivative turbines and hydrodynamic
ones for industrial turbines), and
the lube oil system. Industrial turbines are
also field erected and maintained in place,
whereas aero-derivative turbine plants are
designed for a quick replacement of the entire
engine when maintenance is required.
Manufacturers of aero-derivative CTs
include General Electric, Rolls Royce
(Figure 1), and Pratt & Whitney. Manufacturers
of industrial CTs include Siemens
(Figure 2), Mitsubishi (see page 54), Alstom
(Figure 3), General Electric, and Solar
Turbines Inc. Each manufacturer's CT is
available in 50-Hz and 60-Hz models.
Selection of CT type is usually made
based on the nature and location of service
and a long list of site-specific design
2. Siemens SGT6-8000H. Siemens Energy introduced the 60-Hz version of its combustion
turbine in June 2010. The 274-MW turbine features a turbine inlet temperature of 1,500C.
This turbine can go from standby to start in 5 minutes and can reach full power in 15 minutes.
Courtesy: Siemens Energy
1. Rolls Royce RB211. The 44-MW engine
upgrade released by Rolls Royce in mid2010
boasts a 41.5% thermal efficiency. The
high-pressure turbine and much of the triplespool
compressor is based on aero engine
technology. Courtesy: Rolls Royce

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POWER June 2011

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