Efficiency Enhancement of a Gas Turbine in Hot climate conditions. Design strategies and technology varieties. Detailed Case Studies of TIAC equipped power plants, economic and performance analysis. Study of Climate effect on GT Performance in three different locations.

2. Topics
Gas Turbine
Climate Study
Plant Case
Study
Advantages
Efficiency
Optimization Methods to Optimize GT
Phoenix (AZ-USA)
New Orleans (LA-USA)
Abu Dhabi (UAE)
Westinghouse GT
Union Electric Company
Essex Unit No. 9
Pesanggaran Power Plant
Conclusion

3. The gas turbine is the engine at the heart of the power plant that produces electric current.
A gas turbine is a combustion engine that can convert natural gas or other liquid fuels to mechanical energy.
This energy then drives a generator that produces electrical energy. It is electrical energy that moves along
power lines to homes and businesses.
- General Electric
A gas turbine, also called a combustion turbine, is a
type of internal combustion engine. It has an
upstream rotating compressor coupled to a
downstream turbine, and a combustion chamber or
area, called a combustor, in between.

4. 1899: Charles Gordon Curtis patented the first
gas turbine engine in the USA ("Apparatus for
generating mechanical power", Patent No.
US635,919).

5. Gas
Turbine
High Power
to Weight
Ratio
Less Moving
parts
High
Reliability
High
availability
Low
Maintenance
cost
Low Fuel
Economy
Low Emission
Cogeneration
Compatibility

6. Fast Fact: The GE 7F.05 gas turbine generates
225 MW, equivalent to 644,000 horsepower, or
the power of 644 Formula One cars.

8. Optimizing
Efficiency
of GT
Reducing
Internal
Losses
Waste Heat
Recovery
Decreasing
Ambient
Temperature

9. Turbine
Inlet Air
Cooling
Fogging
Evaporative
Cooling
Vapor
Compression
Refrigeration
Absorption
Chiller
Liquid Air
Injection
Thermal
Energy
Storage

10. Fogging is the spraying of droplets of demineralised water, 5-20 microns in diameter, into air inlet ducts at
1000-3000 psia . As the fog droplets evaporate,100% relative humidity is produced and the air is cooled to
the wet-bulb temperature (the lowest possible temperature obtainable without refrigeration.)

11. • Low capital cost
• Excess fogging evaporates in compressor reducing turbine
compressor work and increasing turbine power
• No limitation on time or duration of inlet air-cooling operation
• Low annual maintenance time
• Low parasitic power consumption
• Quick delivery and installation
• Limited power gain due to the ambient wet-bulb
limitation on inlet air temperature
• Higher water consumption than evaporative cooling
• Requires demineralised water
• Additional filters and drainage systems required
• Limited capacity improvement
Benefits
Drawbacks

12. Evaporative cooling is most suited to hot dry areas as it uses the latent heat of vaporization to cool ambient
temperature from the dry-bulb to the wet-bulb temperature.

13. • Very low unit capital cost
• Simple and reliable design and operation
• No limitation on time or duration of inlet
air-cooling operation
• Low parasitic power consumption
• Low operational costs
• Quick delivery and installation
• Limited power gain due to the
ambient wet-bulb
• Limitation on inlet air temperature
• High consumption of large amounts
of purified water
• High maintenance costs due to
scaling and water treatment
• Limited capacity improvement
Benefits
Drawbacks

14. Absorption chiller cooling recovers heat from turbine exhaust gases, which it uses to produce chilled water in
a double effect Lithium-bromide absorption chiller. The chilled water is passed through a heat exchanger to
cool the ambient air temperature.

15. • Not sensitive to ambient-air wet-bulb temperature
• Potential use of recovered energy from the CT
• No limitation on time or duration of inlet air-cooling operation
• Minimum parasitic electric power losses
• Greater performance increase than evaporative or fogging
• High capital cost
• High O&M costs
• Limited inlet air temperature by CT manufacturer
• Complex system requiring expertise to operate and maintain
• Not suitable for open-cycle turbines
• Requires larger heat rejection (and cooling tower water) than
other reference systems
• Longer delivery and installation time
Benefits
Drawbacks

16. Thermal energy storage stores cooling energy using either the sensible heat capacity of chilled water, or the
latent heat capacity of ice. Typically, chillers run during off-peak times, and the cooled media is used to cool
ambient air during peak load times.

17. • Inlet air temperature can be brought
down to 4 C
• Requires low electric power during peak
times
• Can utilize low night-time tariff to
produce and store ice for peak hours
operation
• Greater performance increase than
evaporative or fogging
• Limited power gain due to the
ambient wet-bulb
• Limitation on inlet air temperature
• High consumption of large amounts
of purified water
• High maintenance costs due to
scaling and water treatment
• Limited capacity improvement
• Low capital cost
• Requires low electric power during peak
times
• Relatively simple and reliable design and
operation
• Greater performance increase than
evaporative or fogging
• Limitation of inlet air temperature
(7 C)
• Requires a very large storage
volume (physical space as well as
water requirement)
• Limited hours of inlet air-cooling
per day
IceThermalEnergyStorage
ChilledWaterThermalEnergyStorage
Benefits
Drawbacks
Benefits
Drawbacks

18. Refrigerative cooling uses mechanical or electrical vapor compression refrigeration equipment. Equipment
and O&M costs are less than absorption chillers, but capital costs are higher and parasitic power
requirements can be 30% of the power gain.

19. • Not sensitive to ambient-air wet-bulb temperature
• No practical limitation on achievable inlet air temperature
• No limitation on time or duration of inlet air-cooling operation
• Relatively simple and reliable design and operation
• Greater performance increase than evaporative or fogging
• High capital cost
• Very large electric power demand during peak times
• High O&M costs
• Higher level of O&M expertise required
• Long delivery and installation time
• Requires additional chilled-water cooling circuit
• Higher parasitic load than evaporative or fogging
Benefits
Drawbacks

20. The gas turbine inlet air cooling system with
injecting liquid air consists of an air liquefaction
unit, storage tanks and an liquid air injection unit.
The liquid air injection unit will spray liquid air
uniformly into the compressor inlet through a
number of swirl nozzles. Swirl nozzles can atomize
liquid air into fine grains which vaporize
instantaneously after injection and mix with the
air. Fine drops of liquid air have the property of
self-diffusing and condensing vapor into water
drops which is very fine and harmless to the
compressor blades.

21. Phoenix (AZ-USA) – Hot and dry climate
New Orleans (LA-USA) – Warm and Wet climate
Abu Dhabi (UAE) – A Wet and very Hot climate

22. The reference power plant of the present study is a 55.5 MW combined cycle based on GE LM6000PF GT and
a two-level pressure bottoming steam cycle coupled with an air cooled condenser. The cycle is rated with an
efficiency of about 54%. Steam is produced at two pressure levels: 12.1 kg/s at 400 C/60 bar and 3.6 kg/s at
220 C/10 bar. With a design condenser pressure of 0.034 bar at ISO condition the steam turbine gross power
is rated 13.77MW. Chilled water is produced by using centrifugal compressor chillers driven by AC motors.
Chiller COP (Coefficient of Performance) at nominal ISO conditions was assumed equal to 5.5. COP then
varies depending on ambient condition.

28. An optimization routine provides indeed the inlet air
temperature set-point that maximizes daily revenues.
Typically, during the hottest day, an increment of inlet air
temperature grants the inlet air cooling system to remain
operational all along the peak period. If a lower inlet air
temperature had been chosen, the thermal storage
would have been exhausted in advance, obliging the inlet
air cooling system to be turned off.

29. Power output augmentation for the two selected typical days and the considered site locations. When IC
system goes into operation CC power output undergoes an increase of 7-9 MW(about 15%) in July while only
of 2 MW in January, whatever the site location. Power augmentation progressively increases along the day
hours up to about 10 MW for New Orleans and 14-15 MW for the two other locations.

30. The high data dispersion at high ambient temperature is due to the variation of relative humidity. Power
augmentation at high ambient temperatures (thus for Phoenix and Abu Dhabi locations) reaches 14-15 MW,
corresponding to roughly 25-27% of the Combined Cycle power at ISO conditions. The power increase
reduces down to about 9 MW (corresponding to 16% of PCC,ISO) for the case of New Orleans. When IC is
off, power output decrease is never larger than 1.8 MW and for Phoenix (dry climate) it is always less that
for the two other cases.

31. Incremental efficiency for the three locations, as a function of ambient temperature. Also reported is the
reference CC efficiency at ISO condition (dotted red (in the web version) line). When ambient temperature is
low (i.e. below 15-20 C), power output increment is small.

32. Finally, even the techno-economical analysis presented
in this paper refers to three specific site locations, at
least the technical results can be extended to any other
location worldwide with similar climatic condition. For
example, a desert location like Riyadh is expected to
give results similar to Phoenix, making inlet air cooling
systems with cold thermal storage an attractive
solution also for this region.
Results

33. Westinghouse 501D5 Gas Turbine
Union Electric Company’s Gas Turbine
Essex Unit No. 9
Pesanggaran Power Plant

34. This new power enhancing technique is investigated and modeled on
a Dallas, Texas site and based on the American Society of Heating,
Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) and U. S.
International Station Meteorological Climate Summary (US ISMCS)
ambient temperature data.
Westinghouse 501D5 Gas Turbine has a nominal ISO base rating of
118.5 mW at a heat rate of 10,023 btu/kWh(10,568KJ). The
comparison will be based on an uncooled turbine, an evaporative
cooled GT and a refrigerated GTIAC system with the inlet air cooled to
40F(8C).

36. Evaporative Cooling
Refrigerated Air Washer
Refrigerated Cooling Coils

37. Evaporative cooler consisting of recirculated water
spray over a saturating extended surface media which
is mounted downstream from the air filter System.
The heat transfer efficiency of this commonly
available media provides a dry bulb "depression“ or
cooling "approach" to the ambient wet bulb
temperature in the range of 80-90% of the difference
between the dry bulb air temperatures. The level and
efficiency of the evaporative cooling stream is limited
to this approach to the wet bulb temperature of the
site area.
• Low Cost
• Low Efficiency
• Bad for high ambient conditions
• High cooling load requirement

38. Finned coils are replaced by direct spray air/coil air washers which use chilled water sprayed onto
saturating media through which the air is passed, much like the evaporative units. In a similar fashion,
this media increases the heat transfer efficiency and reduces the size of the air washers.
This method is used to reduce cooling load. The Psychometric Process Chart is shown

39. One major method of inlet air cooling is through the use
of primary refrigerants circulated through extended
surface (finned) coils mounted in the air stream of the
GTG inlet. This inlet air cooling system, consists of a free
standing central refrigeration system to cool the inlet air
using direct evaporation of refrigerant within the finned
air cooling coils located in the inlet air stream.
This inlet air cooling system, consists of a
free standing central refrigeration system
to cool the inlet air using direct
evaporation of refrigerant within the
finned air cooling coils located in the inlet
air stream.
Using the Dallas 501D5 example for a 6,000
ton(75.9mmKJ) GTIAC system, the following
refrigerant charge quantities and relative costs
are estimated.
Ammonia: 80,000 lbs(36,364Kg) /$25,000;
Propane: 150,000 lbs(68,182Kg) / $75,000;
R22: 200,000lbs (90,909Kg) /$500,000;
R134a: 500,000 lbs(227,273Kg) /$3,000,000.
• High Cost
• High Efficiency
• Good for high ambient conditions
• Minimum cooling load requirement

43. Choosing Refrigerated coils will have the following benefits
• Consistent 40F Air Supply
• Low Heat Rate
• Low Maintenance
• Low Operating Cost
• High overall net Plant Output
• High Efficiency
• High Revenue

48. Union Electric Company is a summer peaking utility,
experiencing peak electrical load demands during the hot
summer months. Combustion turbine generators are often
used to meet the summer peak demands. However, the
generating capability of a combustion turbine decreases as the
ambient air temperature increases. When system peak
demands are at their highest levels on the hottest days of the
year, the generating capacity of the combustion turbines are at
their lowest values. This lost generating capacity can be
recovered by cooling the air entering the combustion turbines.

50. The ISO ratings for the machine are as follows:
o Base Load Rating ......................59,000 kW
o Peak Load Rating ......................65,200 kW
o Base Load Heat Rate (LHV).......1 1,120 Btu/kWhr
o Peak Load Heat Rate (LHV).......11,010 Btu/kWhr
o Base ISO Airflow ......................1,896,000 lb/hr
o Peak ISO Airflow ......................1,896,000 lb/hr
o Base Load Generator Rating...... 68,889 kVA
o Peak Load Generator Rating...... 75,889 kVA
The design conditions that were used in developing and evaluating
each air cooling alternative were:
o Site Elevation - 418 feet msl
o Ambient Air Temperature - 100 °F, Dry Bulb - 76 °F, Wet Bulb
o Combustion Turbine Operating Cycle - 15 hrs/wk

51. Evaporative Cooling
Thermal Energy Storage
Mechanical Chiller
Absorption Chiller
Absorption/HRSG Chiller
Well Water Cooling

52. Assuming a cooler efficiency of 90% and an air velocity of 400 fpm.
The system includes two evaporative cooler compartments with
two heat transfer media packs per compartment (four total). The
total heat transfer media would be approximately 918 square feet.
Based on the design ambient air conditions, the inlet air
temperature would be cooled to 78°F dry bulb and 76°F wet bulb.
Water would be circulated by four - 25 percent capacity circulating
water pumps from the basin to the top of the cooling media. The
total circulating water flow rate would be 1,200 gpm. Make-up
water flow to the basin would be 23 gpm to account for
evaporative and blowdown losses. See the evaporative cooling
system process on a psychometric chart.
Significance of Evaporative Cooling System
The advantages of evaporative cooling include relatively low capital and
operating costs, small space requirements, simple design and operation,
and reduction of dust loading on the inlet filtration system. The main
disadvantages include a limited increase in combustion turbine output,
and reduced effectiveness in humid climates.

54. Ice was selected for the storage media since the volume required to
store chilled water would be on the order of 7 times greater than ice
(ice latent heat of fusion - 144 Btu/lb).
Conceptual design for the air cooling portion of the thermal energy
storage system for the G.E. 7B. Chilled water would be taken from the
bottom of the ice storage tank at 33 OF and circulated by two (2) 50
percent capacity chilled water pumps through the air cooling coils and
back to the top of the tank. The cooled air temperature would be
maintained at 40 OF by chilled water flow control valves at the inlet of
the air cooling coils. The chilled water flow rate would be
approximately 6,575 gpm at maximum turbine output.
Psychometric Chart is Shown

56. Mechanical chillers would be considered an on-line
system utilizing a refrigeration cycle to provide chilled
water for cooling the air. The chilled water portion of
the system would be a closed-loop system utilizing a
head tank for system expansion, chilled water
evaporator, water pumps, and air cooling coils. A
mechanical chiller system would use electricity
produced by the combustion turbine to power an
electrical refrigeration motor/compressor.
As with the thermal energy storage system, the air cooling process used in the
mechanical chiller system involves sensible cooling and dehumidification. The
wet and dry bulb temperatures as well as the specific humidity and enthalpy of
the air decrease during the cooling process. See the mechanical chiller system
air cooling process on a psychometric chart.

58. An absorption chiller system, like a mechanical chiller
system, is an on-line system. A refrigeration cycle is
utilized to provide chilled water to cool the air while
the gas turbine is operating. An absorption chiller is
different from a mechanical chiller because it utilizes
waste heat directly from the combustion turbine
exhaust gas as the driving energy source for the system.
There are no large electric drive motors required.
Because less electrical energy is required, the operating
cost of this system would be less than either the
thermal energy storage or mechanical chiller systems.
The range of chilled water temperatures that can be achieved with a lithium bromide cycle, typically used in
absorption chiller systems, is 40 to 45 °F. Manufacturer's rate their equipment at a chilled water temperature
of 45 OF much like an mechanical chiller. A chilled water temperature of 45 OF was used in the study.

60. An absorption/HRSG chiller system is very similar to an
absorption chiller system. However, the absorption/HRSG
chiller system utilizes steam from a waste heat recovery steam
generator (HRSG) as the driving energy source for the system.
Exhaust gas from the combustion turbine is used as the heat
source for the HRSG. Other than the steam production system,
the process for producing chilled water and cooling the
combustion turbine inlet air is similar to the absorption chiller
system.
Exhaust gas from the combustion turbine would be routed through a duct
directly to the heat recovery steam generator. The required exhaust gas flow
would be 210,000 pounds per hour at a temperature of 947 °F. The exhaust
gas would exit the HRSG at approximately 350 °F.

61. The well water cooling system utilizes the cooler
temperature of ground water to cool the air to the
combustion turbine. Well water is pumped through
air cooling coils located in the turbine air inlet.
Energy for well water pumping is the only external
energy required by the system.
The advantage of well water cooling like evaporative cooling includes relatively low capital and operating costs.
The disadvantage of well cooling involves the flow rate of well water required for the cooling process,
extraction and disposal. The flow of water needed for effective cooling of the inlet air flow ranges from 6,000
to 10,000 gpm. This flow rate would require the construction of several wells and a substantial piping network.
Discharge or disposal of the heated well water leaving the air cooling coils may also be a problem. Another
disadvantage is the potential of the well water to be corrosive or to cause deposits on piping and equipment.

66. Based on the inlet air cooling study for the G.E. 7B gas
turbine, the following conclusions are presented:
• The evaporative cooler system is the least expensive
capital cost alternative. However, capacity improvement is
limited to approximately 4.1 MW due to thermodynamics.
• The thermal energy storage system provides the greatest
incremental capacity improvement of about 12.6 MW.
• The mechanical chiller and absorption chiller systems are
estimated to high very high installed capital costs.
• The well water cooling system provides limited but
economical incremental capacity improvement. However,
the once through system requires large well water flow
rates and may present a environmental disposal problem.
Results

67. To achieve the desired cooling of the inlet air to the
turbine's compressor, it is proposed to use indirect
cooling from a mechanical-vapor compression-type
chiller in combination with cool storage.
Two types of cool storage are examined, including
chilled water storage and ice storage.
A sizing methodology for the chiller and storage
capacity was formulated by PSE&G to maximize the
economic attractiveness which a cooling capability
can achieve under the power-pool rules.

68. Chilled Water Storage
Ice Storage
Mechanical Chiller + Thermal Energy Storage

70. The existing demineralized water-injection tank for Essex Unit No. 9
was proposed for use as the chilled-water storage-tank for inlet-air
cooling. Cooling medium for this option is chilled demineralized water
suitable for both water injection and inlet-air cooling. This tank was
originally dedicated to fuel-oil storage for the old station; however, it
was converted to its current use when the gas turbine was installed.
When converted, the tank's interior surface was sandblasted and
painted with an epoxy coating to prevent rusting. The tank measures
50 feet high and 120 feet in diameter. Storage volume is specified as
100,000 barrels or 4,200,000 gallons.

71. Two ice-storage options are examined in this study. Both options use an ethylene glycol solution which
circulates in the cooling loop.
One option offers a coil-in-tank design where a tightly wound coil is immersed in a tank of water. During
charging of the coil-in-tank modules, the glycol solution is chilled to approximately 26°F in the chiller. The
solution flows to the ice storage modules through the coils where it freezes the tank of water. During storage
discharge, the glycol solution flows through the cooling coil, where it is warmed in cooling the inlet air and
then returns to the ice modules through the coils to be chilled by the melting ice.
The other option offers a bottle-in-tank configuration where water-filled bottles are stacked within a closed
storage vessel. During charging of the bottle-in-tank modules, the glycol solution is chilled to approximately
26°F in the chiller. The solution flows to the ice storage modules through the voids between the bottles
where it freezes the bottles of water. During storage discharge, the glycol solution flows through the cooling
coil, where it is warmed in cooling the inlet air and then returns to the ice modules through the voids
between bottles to be chilled by the melting ice.

72. Chilled Water Storage
The available charging time was 20 or 68 hours,
depending on the selected sizing option, to store
sufficient cooling for 4 continuous hours of
turbine cooling at a constant 94°F (peak
conditions). This criteria enabled calculation of
chiller and storage-tank size. An "efficiency
factor" of 80% was assumed for both chiller-and
tank-size calculations to account for thermal
losses from the tank and any mixing which occurs
in the tank at the thermocline. Chiller size ranges
from 635 tons for a 20-hour charge time to 322
tons for a 68-hour charge time. Tank size ranges
from 1,828,614 gallons for a 20-hour charge time
and 3,154,359 gallons for a 68-hour charge time.
Under these criteria, the existing water-injection
tank (4,000,000 gallons) appears to have
sufficient capacity.
Ice Storage
The glycol-temperature differential across the cooling
coil was assumed to be 15°F. The available charging
time was 20 or 68 hours, depending on the selected
sizing option, to store sufficient cooling for 4
continuous hours of turbine cooling at a constant 94°F.
This criteria enabled calculation of chiller and storage-
tank size. An "efficiency factor" of 70% was applied in
the chiller-sizing calculation to account for decreased
chiller capacity in the ice-making mode. Chiller size
ranges from 725 tons for a 20-hour charge time to 368
tons for a 68-hour charge time.

76. Based on the results, it is evident that chilled water
storage provides a faster payback than a comparable
ice-storage system and within an acceptable time frame
recognizing the availability of the existing water
injection tank. The study has demonstrated the
feasibility of installing inlet-air cooling to an existing
gas-turbine installation and has confirmed the benefits
of inlet-air cooling to the utility.
Results

77. Evaporative cooling system had been applied to improve
the performance of gas turbine in Pesanggaran power
plant in southern Bali Island, Indonesia. Moreover, the
economic analysis was conducted to determine the
capacity cost, operating cost and payback period due to
the investment cost of the system. Based on the
evaluation results, the power improvement for the three
gas turbine units (GT1, GT2 and GT3) are 2.09%, 1.38%,
and 1.28%, respectively.
Site Ambient Conditions
Before Cooling
Pressure = 14.69 psia
Temperature = 80.6F
Relative humidity = 83%.
After Evaporative Cooling System
Relative humidity = 98.04%
Temperature = 76.61F (dropped 4.95%)
Pressure = 14.51 psia (dropped 1.23%).

78. Evaporative Cooling
In the evaporative cooling system, a wet media is
installed in the cross-section of the gas turbine filter
house. The media is kept wet using high quality water,
such as that from a reverse osmosis unit. The air
entering the filter house passes over the saturated
media, and the water contained in the media
evaporates into the air stream on its way to the gas
turbine. This results in Decrease in Dry Bulb
Temperature but also increase in Relative Humidity.

83. These results are not very significant compared to the
previous studies with the enhancement of power
ranges between 5-13.3%. These apply also to the SFC,
heat rate and thermal efficiency, where the influence of
evaporative cooling system does not have a significant
impact to the performance of the gas turbine. This
could be caused by the high relative humidity in
Pesanggaran site so that a decrease in turbine inlet
temperature from the existing conditions is less
effective only around 4.95%, whereas in previous
studies could reach between 30-35%.
Results

84. By conditioning the compressor inlet air at high
ambients and increasing its density, the GT is driven to
a more efficient, higher output mode of operation. This
is a key factor for the competitiveness for power plants
servicing summer peaking grids. It is no secret that gas
turbine based combined cycles are the most cost
effective and environmentally accepted form of new
generation option available today. However, all gas
turbines, being mass flow machines, will suffer output
degradation during summer base load and specific
peak conditions. Inlet conditioning enhances the
performance of modern combined cycles, recovering a
potential lost revenue, both in terms of energy sales
and capacity sales.
Conclusion