Report on improved efficiency of gas turbine final

Improved Efficiency of
Gas turbine

Topic of the report: Improved Efficiency of Gas turbine
Course: ART-203
Submitted to:
Course Instructor: Arif Md. Shahed Iqubal
Faculty, Department of Mechanical Engineering.
Submitted by:
Name: Razin Sazzad Molla
ID No: 13107010
Program: BSME
Section: Eve
Date of Submission: 10/03/2017

Students Declaration: This review report on efficiency improvement of gas turbine
engine has been duly conducted as an integral part of the coursework of ART 203 in
order to meet the course requirements.
Acknowledgement: This review report was conducted with the help of all the researches
carried out by world’s gas turbine engine manufactures. I thank the researchers mostly
from “General Electric”, “Rolls-Royce”, “Siemens”, “Alstom” and “Mitsubishi Hitachi
Power Systems (MHPS)” who provided insight and expertise through their works that
greatly assisted the report.
I thank R.S. Bunkerof GE Global Research Center, USA for assistance with cooling
techniques of gas turbines components.
I would also like to show our gratitude to “Fern Engineering” for sharing their pearls of
wisdom with me during the course of this research, and we thank “Jeffrey Phillips and
Philip Levine” for their insights.
Abstract: The world we are living in today is pushing the technology harder and harder.
Which implies the products necessity to get better and better today they also need to be
friendlier to the environment. To get better products we need better analysis tools to
optimize them and to get closer to the limit what the material can withstand. Gas turbines
are important in producing power and electricity. Electricity is our most important
invention we have and most of the people are just taking electricity for
granted. One way to produce electricity is to use a gas turbine which is connected to a
generator and by combing the turbine with a steam turbine the efficiency can be up to 60
%.This article reviews some specific methods for boosting power and improving heat rate
− either by increasing inlet air density or by boosting specific power. While the
techniques mentioned here are by no means the only ones available to gas turbine
owners, they represent some of the most cost-effective upgrade options. While some of
the gas turbine upgrade options reviewed here are clearly less expensive than others,
there is no one “best” technique. The best option for a particular gas turbine will depend
on its age, location, and operating cycle.
Table of content: The report consists of 4 chapters:
Chapter 1: Introduction (Provides the introductory description relating to gas turbine
engines of various types)
Chapter 2: Body part (describes the mechanism of gas turbine engines)
Chapter 3: Analysis and problem findings. (Analysis of various methods.)
Chapter 4: Concludes the report with recommendations.

List of illustrations: The figures used throughout the report are as follows:
Fig 1: Schematic of turbine with cooling flows.
Fig 2: Corrosion-resistance tests conducted on high-pressure compressor vanes revealed
the significant benefit of coatings. The upper section has no coating; bottom section was
coated with SermeTel 5380DP.
Fig 3: A fogging nozzle array inside a GE 9FA filter house (right) and a high pressure
fogging pump skid (left). Photos: American Moistening Co., Pineville, NC.
Fig 4: Supercharging a gas turbine boosts power output in proportion to firing
temperature. Graph assumes a 40 in. H2O, fan-driven pressure increase, followed by fog
cooling back to ambient temperature.
Fig 5: NRG Energy’s El Segundo Energy Center near Los Angeles, a Siemens Flex-Plant
10, incorporates Clean-Ramp technology to meet the area’s stringent emissions controls.
Courtesy: NRG.
Fig 6: Alstom’s MXL2 turbine is designed to improve power and efficiency on legacy
systems. Courtesy: Alstom.
Fig 7: GE’s new 9HA air-cooled turbine offers up to 592 MW in combined cycle mode.
Courtesy: GE.
Fig 8: Mitsubishi Hitachi Power Systems is upgrading its J-series line of large-frame gas
turbines, like the one shown here, with the air-cooled M501JAC. Courtesy: MHPS.
Fig 9: Direct evaporative panel.
Fig 10: Schematic of evaporative air cooling with optional water treatment.
Fig 11: Gas turbine with mechanical chiller.

Chapter 1
Introduction
In the world of engines, the gas turbine is perhaps the simplest in principle. Compared to
conventional gas engines, like those currently used in automobiles that require at least 20
moving parts for a four-cylinder engine, elemental gas turbines might require only one
moving part. However, despite their relative simplicity, turbine engines have drawbacks
that have prevented their widespread use. For example, turbine blades burn up at the
temperature required for the engine to be as efficient as a modern reciprocating engine, so
present turbines must operate at lower temperatures, making them less efficient. In a new
innovation in turbine engines devised by FluidTherm Engineering, high-pressure air
leaving the compressor flows through hollow turbine blades to provide unusually
effective cooling. The cooling protects the blades so that the turbine inlet gas temperature
can be significantly increased. With the resulting increase in efficiency, this type of
turbine engine could, for the first time, compete with much bulkier diesel and gasoline
engines on the basis of fuel economy.[6][2]
Inventors and scientists have been fascinated by the concept of turbine engines to create
power even before Leonardo di Vinci sketched an early turbine idea in one of his famous
notebooks. But, it has only been in the last 80 years that the electricity-generating
potential of turbines has been realized. Now, with demands for energy rising along with
calls for reduced greenhouse gas emissions, the need for cleaner more efficient next
generation turbine technology is critical. With a robust research portfolio, productive
partnerships, and a mandate to increase power-producing efficiencies and improve the
environment for future generations, the National Energy Technology Laboratory (NETL)
is shepherding innovations for improved gas turbine productivity. [5]
Several options to improve the operating characteristics of gas turbines do exist and,
given that those few extra percentage points of operating efficiency are essential to
maximizing the value of an installation, they should be taken up. Michael Gabriel reports.
Many things can be done to keep a turbine operating at peak efficiency. Attention to
detail when observing and trending operating parameters can identify degrading turbine
performance. Various types of monitoring packages exist to assist in this endeavor. Some
are designed to warn of impending failures (i.e. bearing vibration), thereby averting
costly forced outages. Other products are aimed at analyzing turbine or plant performance
over time. Remote monitoring centers can do either or both.

Objective of the study:
Broad objectives: Learning overview and methodology of writing review reports as
required by the respective faculty of ART 203
Specific objectives: Investigating the possible ways of increasing efficiencies of gas
turbine engines by various methods including inlet fire temperature, ceramic coatings and
refrigeration methods for inlet air cooling.
Outline of the report:
Chapter 1: Provides the introductory description relating to gas turbine engines of various
types.
Chapter 2: Chapter 2 describes the mechanism of gas turbine engines, various procedures
relating to it, scopes of improvements, introduction to various engineering methods of
efficiency improvement.
Chapter 3: This section analyzes various present methods its improvement, firing
temperature management, ceramic coatings and so on.
Chapter 4: Concludes the presentation of arguments with possible recommendations.

Chapter 2
Body part
A gas turbine, also called a combustion turbine, [1] is a type of internal combustion
engine. It has an upstream rotating compressor coupled to a downstream turbine, and a
combustion chamber in between.
This article reviews some specific methods for boosting power and improving heat rate −
either by increasing inlet air density or by boosting specific power. While the techniques
mentioned here are by no means the only ones available to gas turbine owners, they
represent some of the most cost-effective upgrade options. [2]
The basic operation of the gas turbine is similar to that of the steam power plant except
that air is used instead of water. Fresh atmospheric air flows through a compressor that
brings it to higher pressure. Energy is then added by spraying fuel into the air and
igniting it so the combustion generates a high-temperature flow. This high-temperature
high-pressure gas enters a turbine, where it expands down to the exhaust pressure,
producing a shaft work output in the process. The turbine shaft work is used to drive the
compressor and other devices such as an electric generator that may be coupled to the
shaft. The energy that is not used for shaft work comes out in the exhaust gases, so these
have either a high temperature or a high velocity. The purpose of the gas turbine
determines the design so that the most desirable energy form is maximized. Gas turbines
are used to power aircraft, trains, ships, electrical generators, and tanks. Aero derivatives
are also used in electrical power generation due to their ability to be shut down, and
handle load changes more quickly than industrial machines. They are also used in the
marine industry to reduce weight. The General Electric LM2500 [3], General Electric
LM6000, Rolls-Royce RB211 and Rolls-Royce Avon are common models of this type of
machine. Industrial gas turbines differ from aeronautical designs in that the frames,
bearings, and blading are of heavier construction. They are also much more closely
integrated with the devices they power— often an electric generator—and the secondary-
energy equipment that is used to recover residual energy (largely heat).Air breathing jet
engines are gas turbines optimized to produce thrust from the exhaust gases, or from
ducted fans connected to the gas turbines. Jet engines that produce thrust from the direct
impulse of exhaust gases are often called turbojets, whereas those that generate thrust
with the addition of a ducted fan are often called turbofans or (rarely) fan-jets. [4]
Gas turbines are also used in many liquid propellant rockets, gas turbines are used to
power a turbo pump to permit the use of lightweight, low-pressure tanks, which reduce
the empty weight of the rocket.

The gas turbine engine design is fundamentally, taking the air flow into the compressing
stage then combustion stage to add energy, and finally extracting energy in the turbine
module. This journey of the flow in the engine is in serial connections. Posing the
problem of the limiting turbine inlet temperature, the number that all the turbomachinery
engineers desperately want to increase by tuning the inlet stages materials, or fine
changes onto the blades’ profile or the flow paths. But the significant increase to this
temperature lies under more fundamental and radical redesigns to the theory of the gas
turbine operation, and its thermodynamical cycle. These principles were considered for
long untouchable facts, and stayed lurking from the engineers examining eyes. This paper
introduces one of these possibilities by genuine redesign concepts. Backed with CFD [5]
analysis, and thermodynamical feasibility studies to address the potential problems of
these modifications. The redesigns include implementing the new concept of the contra-
rotating turbine more effectively to reduce the turbine module size, connecting
pressurized fluid streams of two counter-rotating compressors in parallel instead of the
serial connection, forming a protecting Pressurized shield for the entry turbine stages and,
Extracting the energy in the process flow using flows interactions instead of flow-blades
interactions.
Several options to improve the operating characteristics of gas turbines do exist and,
given that those few extra percentage points of operating efficiency are essential to
maximizing the value of an installation, they should be taken up. Michael Gabriel reports.
In the present economic environment, owners and operators are seeking cost effective
ways to expand gas turbine operability, improve efficiency, gain more output and extend
the life of their existing equipment. The regulatory process for permitting new generation
sources is slow and more demanding than ever before, making minor turbine
improvements to existing equipment a more attractive option.
GT performance is critical, especially now that the price of oil is unpredictable and
demand for power is soaring. For example, in the Kingdom of Saudi Arabia, the demand
for power generation fuel can exceed 400,000 barrels per day in summer [6]. The
situation becomes even trickier in such a hot environment because turbine power output
reduces with an increase in ambient temperature among other factors.
Many things can be done to keep a turbine operating at peak efficiency. Attention to
detail when observing and trending operating parameters can identify degrading turbine
performance. Various types of monitoring packages exist to assist in this endeavor. Some
are designed to warn of impending failures (i.e. bearing vibration), thereby averting
costly forced outages. Other products are aimed at analyzing turbine or plant performance
over time. Remote monitoring centers can do either or both.
Compressor inlet air cooling is one of the most well-known methods to improve gas
turbine power plant performance. In this study, pressure reduction valve in natural gas

pressure reduction station is replaced by a turbo-expander to use the potential energy of
the compressed gas. The turbo-expander shaft is connected to a mechanical chiller to
produce refrigeration; the produced refrigeration is used to decrease the compressor inlet
air temperature. Moreover, thermodynamic and exergetic analyses are carried out and the
effect of compressor air cooling on the performance of the plant is studied. To do so,
MontazerGhaem power plant is considered as the case study. Results showed that using
cooling system causes 3.2% temperature drop which leads to 1.138% increment in both
thermal efficiency and net output power in the warmest month. Exergetic analysis reveals
that using the cooling system leads to a higher exergy efficiency and hence lower exergy
destruction. Also combustion chamber with 81.26 MW has the highest amount of exergy
destruction which decreases to 77.36 MW after implementation of the cooling system. In
January, exergetic efficiency of total plant has 1.86% enhancement and exergy
destruction reduces about 3.8 MW. [7]
The development of ceramic materials for incorporation into the hot section of gas
turbine engines has been ongoing for about fifty years. Researchers have designed,
developed, and tested ceramic gas turbine components in rigs and engines for automotive,
aero-propulsion, industrial, and utility power applications. Today, primarily because of
materials limitations and/or economic factors, major challenges still remain for the
implementation of ceramic components in gas turbines. For example, because of low
fracture toughness, monolithic ceramics continue to suffer from the risk of failure due to
unknown extrinsic damage events during engine service. On the other hand, ceramic
matrix composites (CMC) with their ability to display much higher damage tolerance
appear to be the materials of choice for current and future engine components. The
objective of this paper is to briefly review the design and property status of CMC
materials for implementation within the combustor and turbine sections for gas turbine
engine applications. It is shown that although CMC systems have advanced significantly
in thermo-structural performance within recent years, certain challenges still exist in
terms of producibility, design, and affordability for commercial CMC turbine
components. Nevertheless, there exist some recent successful efforts for prototype CMC
components within different engine types.
Advanced heat transfer and cooling techniques form one of the major pillars supporting
the continuing development of high efficiency, high power output gas turbine engines.
Conventional gas turbine thermal management technology is composed of five main
elements including internal convective cooling, external surface film cooling, materials
selection, thermal-mechanical design at the component and system levels, and selection
and/or pre-treatment of the coolant fluid. The present summary will examine specific
cooling technologies representing cutting edge, innovative methods expected to further
enhance the aero-thermal-mechanical performance of turbine engines. The techniques
discussed will include forced convective cooling with unconventional turbulators and
concavity surface arrays, swirl-cooling chambers, latticework cooling networks,

augmentations of impingement heat transfer, synergistic approaches using mesh
networks, and film cooling.
Figure 1: Schematic of turbine with cooling flows.
The technology of cooling gas turbine components, primarily via internal convective
flows of single-phase gases and external surface film cooling with air, has developed over
the years into very complex geometries involving many differing surfaces, architectures,
and fluid-surface interactions. The fundamental aim of this technology area is to obtain
the highest overall cooling effectiveness with the lowest possible penalty on the
thermodynamic cycle performance. As a thermodynamic Brayton cycle, the efficiency of
the gas turbine engine can be raised substantially by increasing the firing temperature of
the turbine. Modern gas turbine systems are fired at temperatures far in excess of the
material melting temperature limits. This is made possible by the aggressive cooling of
the hot gas path components using a portion of the compressor discharge air, as depicted
in the following figure.[2]

Comprehensive Upgrades:
Comprehensive upgrades of gas turbine involve the replacement of “flange-to-flange”
parts with more advanced designs.[1] Because late-model gas turbines already
incorporate advanced technology, these comprehensive upgrades apply only to older gas
turbines that are part of a series or model line that the original equipment manufacturer
(OEM) has redesigned. Examples of these model lines include the Frame 7 and 9 series
supplied by GE Power Systems, Schenectady, NY, and the W251 and W501 series
supplied by Siemens Westinghouse Power Corp., Orlando, Florida[1]. An upgrade can be
applied to individual components or to the entire engine. Examples of components that
can be upgraded include:
• Inlet guide vanes, which allow more air flow
• Improved seals, tighter clearances
• Combustion liners and transition pieces, enabling higher firing temperatures
• Turbine blades and vanes, also enabling higher firing temperatures
The results of a comprehensive upgrade on performance depend, of course, on what is
included in the project. However, the upgrades of eight GE Frame 7Bs by Houston Light
& Power Co. (now Reliant Energy HL&P, Houston Texas)[2] in the 1990s provide a
good example of what can be accomplished.1 Reliant replaced the combustion liners,
transition pieces, 1st stage turbine vanes, and 2nd stage vanes and blades with Frame
7EA parts. This allowed operators to increase the firing temperature of the machines by
170 deg F. After the upgrades, the eight machines yielded power increases of 16 to 26%,
while the heat rate decreased by 4.5 to 11% − improvements that are approximately three
times greater than what could have been expected from a normal overhaul using new
Frame 7B parts. The cost for the upgrades divided by the increase in power output was
approximately $250/kW. This low figure actually overstates the incremental cost of the
additional capacity because it does not account for the expenses Reliant would have
incurred if it had performed a normal overhaul using 7B parts. One upgrade option
Reliant did not choose is high-flow inlet guide vanes (IGVs). This option can be very cost
effective. The thinner vanes of advanced designs allow more air flow to pass through the
turbine, compared to older IGVs. On a Frame 7B, you can expect a 4.5% boost in power
and a slight improvement in heat rate − approximately 1%. The cost of new IGVs
typically is less than $100/kW.
Hot Section Coatings [2]:
Another option for upgrading gas turbine performance is to apply ceramic coatings to
internal components. Thermal barrier coatings (TBCs) are applied to hot section parts in
advanced gas turbines. These same coatings can be applied to the hot sections of older

gas turbines in the field. The TBCs provide an insulating barrier between the hot
combustion gases and the metal parts. TBCs will provide longer parts life at the same
firing temperature, or will allow the user to increase firing temperature while maintaining
the original design life of the hot section. A recent analysis sponsored by the Combustion
Turbine Combine Cycle Users Organization showed that adding a 10 mil coating to the
1st stage blades and vanes of a GE Frame 7EA would allow an increase in firing
temperature from 2020 deg F to 2035 deg F. The report calculated that this small increase
could provide $4 million of net revenue over the life of the coating.
A similar study conducted by Fern Engineering, Inc., Pocasset, Mass., for the Electric
Power Research Institute, Palo Alto, Calif., concluded that the addition of TBCs to a GE
Frame 7B would provide an increase of 5.5 MW in power, at an incremental cost of
$140/kW. Note that this is cheaper than the cost of a comprehensive upgrade.
Compressor Coatings can also be applied to gas turbine compressor blades (the “cold
end” of the machine) to improve performance. Unlike hot section coatings, the purpose of
compressor blade coatings is not to insulate the metal blades from the compressed air.
Rather, the coatings are applied in order to provide smoother, more aerodynamic
surfaces, which increase compressor efficiency. In addition, smoother surfaces tend to
resist fouling because there are fewer “nooks and crannies” where dirt particles can
attach. Some coatings are also designed to resist corrosion, which can be a significant
source of performance degradation, particularly if a turbine is located near saltwater.
Corrosion resistance tests on the 3rd stage high-pressure compressor vanes of a Rolls
Royce Mainville, Ohio, RB211 revealed dramatic improvements with a coating. The
tests, conducted by Sermatech International, Limerick, Penn., subjected the vanes to five
cycles of exposure to salt-saturated fog followed by simulated full-load operation. One
compressor section had no coating; another was coated with a 1.3 mil layer of SermeTel
5380DP – an aluminum-filled ceramic primer (Figure 2).

Figure 2: Corrosion-resistance tests conducted on high-pressure compressor vanes
revealed the significant benefit of coatings. The upper section has no coating; bottom
section was coated with SermeTel 5380DP. [3]
Florida Power & Light (FP&L), Juno Beach, Fla., has evaluated the benefit of the same
Sermatech coating on the axial compressor of W501F gas turbine [4]. The utility coated
one of two units that were in combined cycle operation. Both machines were overhauled
at the same time, and the same maintenance was performed on each machine, except for
the smooth coating that was applied to the compressor of only one of the turbines. FP&L
then measured operating efficiencies at peak loads. The results of the tests showed that
the unit with the coated compressor had:
• Higher compressor efficiency of 0.64%
• Better heat rate, 0.58%
• Higher power output, 1.26%
While these improvements may not be as great as those that can be achieved with hot
section coatings, they are obtained at a relative low cost. The incremental capital cost of
the capacity boost was approximately $60/kW, and payback for the cost of applying the
coating occurred in just 6 months. [5]
Applying compressor coatings on much older gas turbines can provide much larger gains
than those achieved by FP&L. The compressor airfoils of older turbines tend to be
rougher than a newer model simply because of longer exposure to the environment. In
addition, the compressor of older models consumes a larger fraction of the power
produced by the turbine section. Therefore, improving the performance of the compressor
will have a proportionately greater impact on total engine performance. For example,
Turbine Resources Unlimited (TRU), West Winfield, NY, recently completed a
compressor overhaul of two W501AA gas turbines for a customer in New Jersey.
According to company president Bill Howard, TRU applied its compressor lubricity
coating, TRU-Flow 2000, to the compressor diaphragm sections and custom-fit the radial

seals to optimize clearances. The combination of these two actions allowed its customer
to produce 4 MW of additional power from each turbine − an increase of 6% over
previous power levels.[16]
Raising Air Flow Perhaps the simplest way to increase the power output of a gas turbine
is to increase the mass flow through the machine. And one of the most popular ways to
do this is to increase the density of the inlet air − by evaporative cooling, mechanical
chilling, or inlet fogging (Figure 3). [7]
Figure 3: A fogging nozzle array inside a GE 9FA filter house (right) and a high pressure
fogging pump skid (left). Photos: American Moistening Co., Pineville, NC
A more novel approach, but one that deserves more attention, is supercharging.
Supercharging of a gas turbine entails the addition of a fan to boost the pressure of the air

entering the inlet of the compressor by 40 to 80 in. H2O. In some ways, supercharging
mimics the upgrade tactic used by several OEMs of adding a “zero stage” to the
compressor. However, in the case of supercharging the additional stage of compression is
not driven by the main gas turbine shaft, but rather by an electric motor. The parasitic
power of the fan motor is less than the additional output of the gas turbine, so the net
result is a capacity boost.
The impact of supercharging is especially significant if it is coupled with inlet fogging
downstream of the fan. The fan stage increases the air temperature, which increases the
difference between the dry bulb and wet bulb temperatures. This allows more cooling to
be provided by the fogging system.
One application of supercharging was on a W301G combined cycle in San Angelo,
Texas, in the 1960s. However, analysis has shown that the net power boost from
supercharging increases with turbine firing temperature (Figure 3). As a result, the cost
per kilowatt of supercharging should be significantly less than it was for turbines built 40
years ago.
At least one company has recognized the potential impact supercharging could have on
advanced gas turbines. Enhanced Turbine Output, LLC (ETO), Washington, DC, has
patented a design of a supercharging system3 and is actively marketing the concept to
turbine owners. According to William Kopko, ETO’s VP of engineering, an ETO
variable supercharging and fogging system could increase the output of a GE 7FA by
20% beyond fogging alone in the Memphis, Tenn. climate while improving the heat rate
by 4%. The ETO system would achieve this improvement without entraining any water
into the turbine, despite the large increase in total fogging. The estimated cost for the
increased power is a low $200/kW.
Figure 4: Supercharging a gas turbine boosts power output in proportion to firing
temperature. Graph assumes a 40 in. H2O, fan-driven pressure increase, followed by fog
cooling back to ambient temperature.

Chapter 3
Problem finding, Analysis Solution and
Discussion
Reduced Emissions:
One of the challenges of backing up intermittent generation with gas is that this
operational mode can significantly increase emissions. This occurs for several reasons.
First, operating gas turbines at low loads produces higher levels of CO and NOx.
Conventional combined cycle plants typically need to be brought up to full power in
phases to allow the rest of the plant to heat up safely. Waiting out these low-load hold
points dramatically increases overall emissions.
Second, rapid changes in turbine output disrupt fuel and selective catalytic reduction
(SCR) equilibrium. The additional pilot fuel required during load changes causes
increased NOx production, and when turbine load is changing, maintaining accurate
ammonia injection in the SCR is more challenging: Too little means increased NOx out
the stack; too much means ammonia slip.
The major turbine manufacturers such as Siemens and General Electric (GE) have
recently introduced fast-starting plant technology that is designed to address the first
problem (such as the Siemens Flex-Plant used at the Lodi Energy Center in California, a
2012 POWER Top Plant). Improvements to heat recovery steam generator (HRSG)
design enable such plants to start up very quick and avoid low load holds that increase
emissions.
Addressing transient SCR emissions, however, requires operational changes in addition
to design adjustments. Siemens is introducing a solution it calls Clean-Ramp, which is
designed to be integrated into the Flex-Plant solution (Figure 1).

Figure 5: (Tight targets) NRG Energy’s El Segundo Energy Center near Los Angeles, a
Siemens Flex-Plant 10, incorporates Clean-Ramp technology to meet the area’s stringent
emissions controls. Courtesy: NRG
This technology changes how the gas turbine is controlled so that the emissions control
system can accurately predict changes in turbine exhaust when a load change is
requested. The exhaust molar flow rate is calculated based on factors such as combustion
airflow, fuel flow, historical performance, and so on. This information is used to predict
NOx emissions, and the system then adjusts the ammonia injection flow rate accordingly.
This allows the plant to stay at baseload emission levels even when the load is changing.
Siemens claims this allows a plant to ramp continuously at rates above 30 MW/minute
while keeping NOx emissions under 2 ppm. [2]
GE has developed a similar product in its GEN II SCR control. This solution pairs a
Rapid Response plant and GE’s OpFlex Startup Ammonia Control to reduce overall
startup emissions. GEN II measures specific equipment and emissions parameters and,
using model-based control technology, controls the ammonia to the SCR to reduce
emissions and ammonia slip.
Retrofits
New plants aren’t the only ones benefitting from new technology. With a large number of
older gas-fired plants seeing increased run time with the fall in gas prices, manufacturers
are offering upgrades that allow these projects to capture increases in output and
efficiency.

GE has been offering its Advanced Gas Path (AGP) upgrade solution for several years to
increase the output, efficiency, and availability of its workhorse 7F line. It recently
expanded this offering to its 9E and 9F turbines. The AGP solution involves improved
blade aerodynamics and better sealing, as well as advanced materials and improved
cooling technologies to allow higher operating temperatures. The physical improvements
are paired with OpFlex model-based control software to deliver additional performance
improvements.
Alstom recently rolled out its MXL2 upgrade package for its line of GT13 turbines. The
MXL2 upgrade consists of a completely new blade design to boost aerodynamic
efficiency in the compressor and turbine, optimized sealing and tighter clearances,
improvements to the combustor, and enhanced cooling design (Figure 2).[1]
Figure 6 :( Ready to roll) Alstom’s MXL2 turbine is designed to improve power and
efficiency on legacy systems. Courtesy: Alstom
Alstom says the upgrade will improve the power and efficiency of legacy turbines, as
well as stretch maintenance and inspection intervals. The upgrade offers two modes of
operation: M (for maximum output and efficiency) and XL (for extended life). Operating
modes can be switched with the press of a button, allowing generators to increase output
when market demand is high but reduce stress on components during periods of reduced
need. (For more on mitigating the effects of new operating modes, see “Managing the
Changing Profile of a Combined Cycle Plant” in this issue.)

GE introduced its steam-cooled H-class turbines more than 10 years ago, designs that
have become a staple in the company’s lineup. This year, GE is rolling out two new air-
cooled H-class turbines, the 9HA and 7HA. The 9HA.02 offers 592 MW of output at
better than 61% efficiency in 1 x 1 combined cycle mode, and can reach full output in
under 30 minutes (Figure 7). In simple cycle, it puts out 470 MW at 41% efficiency. The
9HA has a 14-stage compressor, a 16-chamber dry low-NOx combustor, and a four-stage
air-cooled hot gas path.
Figure 7: (Big air) GE’s new 9HA air-cooled turbine offers up to 592 MW in combined
cycle mode. Courtesy: GE
The smaller 60-hertz 7HA offers up to 486 MW at greater than 61% efficiency in 1 x 1
combined cycle mode and can reach full output in as little as 10 minutes. Both turbines

are designed to be installed considerably faster than previous models through the use of
modularized and preassembled components. [4]
Mitsubishi Hitachi Power Systems (MHPS) is also rolling out an air-cooled update to its
turbine line with the 60-hertz M501JAC (Figure 8). MHPS’s steam-cooled J-series
turbines, which operated at temperatures of 1,600C, were introduced in 2011 and have
been deployed mostly in Asia, with several plants coming online in 2013 and 2014.
Figure 8: (Evolution) Mitsubishi Hitachi Power Systems is upgrading its J-series line of
large-frame gas turbines, like the one shown here, with the air-cooled M501JAC.
Courtesy: MHPS

New Approaches to Simple Cycle:
Not all of the action is in combined cycle. MHPS is developing an approach to simple
cycle turbine generation that could potentially equal or exceed combined cycle generation
in efficiency. The technology, which is currently being commercialized for release later
this year, is called AHAT, or advanced humid air turbine. AHAT takes a simple cycle
turbine and uses humidified compressed air for combustion. The combustion air is cooled
by water atomization, compressed in the compressor, and then passed through a
humidification tower. The humidified air is then heated in a heat exchanger using the
turbine exhaust before entering the combustor. The water vapor in the exhaust is then
recovered and returned to the humidifier.
The method is similar to steam injection but adds far more water to the combustion
process. MHPS has been developing the technology since 2000. A pilot project using an
MHPS H-50 turbine was launched in 2010, and the company plans to commercialize it
this year. The H-50 turbine with AHAT outperformed the same turbine in combined
cycle mode, achieving 70 MW output at 50.6% efficiency. MHPS believes efficiencies
above 60% are achievable with larger turbines. [3]
MHPS is also developing a related retrofit product called Smart AHAT, which involves
adding significant steam injection to a combined cycle arrangement, with AHAT’s water
recovery system added to the exhaust.
Performance of a gas turbine is mainly depends on the inlet air temperature. The power
output of a gas turbine depends on the flow of mass through it. This is precisely the
reason why on hot days, when air is less dense, power output falls off. A rise of 1°C
temperature of inlet air decreases the power output by 1%. Gas turbine air cooling has
been studied recently to raise the performance to peak power level during hot seasons
when high atmospheric temperatures cause a significant reduction in its net power output.
Gas turbines are constant volume machines; at a given shaft speed, they always move the
same volume of air. In gas turbines, since the combustion air is taken directly from the
environment, their performance is strongly affected by weather conditions (Mahmoudi et
al., 2009). Power rating can drop by as much as 20 to 30%, with respect to international
standard organization (ISO) design conditions, when ambient temperature reaches, 35 to
45°C. One way of restoring, operating conditions is to add an air cooler at the compressor
inlet (Sadrameli and Goswami, 2007)[4]. The air cooling system serves to raise the
turbine performance to peak power levels during the warmer months when the high
atmospheric temperature cause the turbine to work at off-design conditions, with reduced
power output (Kakaras et al., 2004).The performance of a gas turbine power plant is
sensible to the ambient condition. As the ambient air temperature arises, less air can be
compressed by the compressor since the withdrawing capacity of compressor is given,
and so the gas turbine output is reduced at a given turbine entry temperature.

GAS TURBINE INLET AIR COOLING SYSTEM:
The gas turbine inlet air cooling methods can be divided into five categories including the
evaporative cooler, indirect mechanical refrigeration system, direct mechanical
refrigeration system, mechanical refrigeration system with chilled water storage and
absorption chiller inlet air cooling system (Kamal and Zuhairm, 2006).
Fig 9: Direct evaporative panel. (a) Schematic diagram panel (b)control volume
Evaporative cooler:
In an effort to boost the performance of gas turbine engine, the rigid media evaporative
coolers were used with gas turbine to increase the density of the combustion air; thereby
increasing the power output. Figure 1 shows the schematic diagram of rigid media
evaporative cooler. The evaporation surface is a saturated porous pad. Water introduced
through a header at the top of media and sprays into the top of an inverted half-pipe and
is deflected downward onto a distribution pad on top of the media (Johnson, 1989). Water
drains through the distribution pad into the media, by gravity action downward through it,
and wets enormous area of media surface contacted by air passing through the cooler
(Beshkani and Hosseini, 2006)[5].

.
Fig 10: Schematic of evaporative air cooling with optional water treatment.
Indirect mechanical refrigerationsystem:
Ondryas et al. (1991) investigated the various options for cooling the inlet air including
mechanical vapor compression and aqua-ammonia absorption refrigeration. Figure 4
shows a schematic diagram of gas turbine with mechanical chiller of centrifugal
compressor type. In this sort of inlet air cooling system, the air is cooled by a cooling coil
served by a mechanical compressor, which draws its electricity supply from the
generation unit itself.
Figure 11: Gas turbine with mechanical chiller.

Chapter 4
Conclusion with recommendations
From the forgoing review of literature, various available technologies of gas turbine inlet
air cooling system were studied including the evaporative coolers, mechanical chillers
with and without thermal energy storage systems. Furthermore, in cogeneration gas
turbine generators, aqua-ammonia and two-stage LiBr absorption system were explored
as booster for the gas turbine power output without affecting the thermal efficiency of the
cogeneration unit. All the aforementioned technologies can be used in conjunction with
gas turbine generators to boost the power output in hot months with various degrees of
effectiveness. The evaporative cooler is an old system used to cool down the gas turbine
inlet air temperature. However, it is simple in design, have a short installation time and
low capital and maintenance cost. Unfortunately, this technique is limited by the wet bulb
temperature of the inlet air and the gas turbine generator capacity may not be increased
by more than 12% in best cases even in dry climates. Water carry-over is another
problem associated with the use of evaporative coolers. Mechanical chillers increase the
capacity of gas turbine generators better than evaporative coolers because they can
produce any air temperature required by the designer. However, the main disadvantage of
this technique is not associated with high capital cost nor with the space required, but it is
associated with its high consumption of electricity which reduces the potential power
output increase of the gas turbine generator. Mechanical chillers with thermal energy
storage systems such as water and ice storage systems can be used as inlet air cooling
system to boost the gas turbine generator power in hot months in countries which adopts
variable price for selling electricity, off-peak and on-peak, and have no shortage of
electricity production. The exhaust gases of gas turbines carry a significant amount of
thermal energy which can be used as a heat source to drive the generator of a vapor
absorption chiller such as: aqua-ammonia absorption chiller, two-stage LiBr chiller and
single stage LiBr chiller that serves as a cooling system to cool the inlet air during hot
periods before admitting to the gas turbine compressor. However, the COP of aqua-
ammonia chiller is relatively lower than that of LiBr chiller for the same operating
conditions, requirehigh capital cost of refrigeration and large plot space while the two-
stage LiBr chiller is mainly used when high COP is required and boost the power output
in cogeneration gas turbines. The effort to boost the power output during hot periods for a
simple gas turbine unit without cogeneration, a single stage LiBr absorption chiller seems
a feasible solution to be investigated thermally and economically due to its relatively high
COP and low capital cost of refrigeration. As per author's knowledge, a very little work
has been undertaken in previous work.The development occurred in the inlet air cooling
system that is used to improve the performance of the gas turbine power plants had been
classified.

The following list summarizes the conclusion drawn:
1. The diversity used of system to achieve the cooling function reflects the necessity of
this technique in improving the performance of the gas turbine power plants.
2. The success of evaporative cooling in reducing the high air temperature depends on
relative humidity of the ambient air. These types of systems are economical and suitable
for hot and dry climates rather than hot and humid ones.
3. Absorption systems are similar to vapor-compression air conditioning systems except
the pressurization stage. The absorption cooling technique demonstrated a higher gain in
power output and efficiencythan evaporative cooling for a simple cycle gas turbine,
independent of the ambient conditions.
4. The absorption chiller system for inlet air cooling of the gas turbine increases the
peaking capacity of the gas turbines during the hot ambient operation.
Bibliography:
[1] International Journal of Physical Sciences Vol. 6(4), pp. 620-627, 18 February, 2011,
Available online at http://www.academicjournals.org/IJPS DOI: 10.5897/IJPS10.563
ISSN 1992 - 1950 ©2011 Academic Journals
[2] GAS TURBINE PERFORMANCE UPGRADE OPTIONS by Jeffrey Phillips and
Philip Levine
[3]Innovative gas turbine cooling techniques, R.S. Bunker &GE Global Research Center,
USA.
[4]http://www.decentralized-energy.com/articles/print/volume-11/issue-2/features/gas-
turbines-how-to-improve-operability-output-and-efficiency.html
[5]http://www.power-eng.com/articles/print/volume-120/issue-9/features/innovations-
for-improved-gas-turbine-productivity.html
[6]http://www.nrel.gov/docs/fy00osti/26738.pdf
[7]Sulzer technical review 2/2008, SulzerMetco (Canada) Inc.

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