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

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 alongpower lines to homes and businesses.

- General Electric

A gas turbine, also called a combustion turbine, is atype of internal combustion engine. It has anupstream rotating compressor coupled to adownstream turbine, and a combustion chamber orarea, called a combustor, in between.

1899: Charles Gordon Curtis patented the firstgas turbine engine in the USA ("Apparatus forgenerating mechanical power", Patent No.US635,919).

Gas Turbine

High Power to Weight

Ratio

Less Moving parts

High Reliability

High availability

Low Maintenance

cost

Low Fuel Economy

Low Emission

Cogeneration Compatibility

Fast Fact: The GE 7F.05 gas turbine generates225 MW, equivalent to 644,000 horsepower, orthe power of 644 Formula One cars.

Optimizing Efficiency

of GT

Reducing Internal Losses

Waste Heat Recovery

Decreasing Ambient

Temperature

Turbine Inlet Air Cooling

Fogging

Evaporative Cooling

Vapor Compression Refrigeration

Absorption Chiller

Liquid Air Injection

Thermal Energy Storage

Fogging is the spraying of droplets of demineralised water, 5-20 microns in diameter, into air inlet ducts at1000-3000 psia . As the fog droplets evaporate,100% relative humidity is produced and the air is cooled tothe wet-bulb temperature (the lowest possible temperature obtainable without refrigeration.)

• 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

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.

• 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

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

• 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

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.

• 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

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Benefits

Drawbacks

Benefits

Drawbacks

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

• 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

The gas turbine inlet air cooling system withinjecting liquid air consists of an air liquefactionunit, storage tanks and an liquid air injection unit.The liquid air injection unit will spray liquid airuniformly into the compressor inlet through anumber of swirl nozzles. Swirl nozzles can atomizeliquid air into fine grains which vaporizeinstantaneously after injection and mix with theair. Fine drops of liquid air have the property ofself-diffusing and condensing vapor into waterdrops which is very fine and harmless to thecompressor blades.

Phoenix (AZ-USA) – Hot and dry climate

New Orleans (LA-USA) – Warm and Wet climate

Abu Dhabi (UAE) – A Wet and very Hot climate

The reference power plant of the present study is a 55.5 MW combined cycle based on GE LM6000PF GT anda two-level pressure bottoming steam cycle coupled with an air cooled condenser. The cycle is rated with anefficiency of about 54%. Steam is produced at two pressure levels: 12.1 kg/s at 400 C/60 bar and 3.6 kg/s at220 C/10 bar. With a design condenser pressure of 0.034 bar at ISO condition the steam turbine gross poweris 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 thenvaries depending on ambient condition.

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

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

The high data dispersion at high ambient temperature is due to the variation of relative humidity. Poweraugmentation 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 increasereduces down to about 9 MW (corresponding to 16% of PCC,ISO) for the case of New Orleans. When IC isoff, power output decrease is never larger than 1.8 MW and for Phoenix (dry climate) it is always less thatfor the two other cases.

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

Finally, even the techno-economical analysis presentedin this paper refers to three specific site locations, atleast the technical results can be extended to any otherlocation worldwide with similar climatic condition. Forexample, a desert location like Riyadh is expected togive results similar to Phoenix, making inlet air coolingsystems with cold thermal storage an attractivesolution also for this region.

Results

Westinghouse 501D5 Gas Turbine

Union Electric Company’s Gas Turbine

Essex Unit No. 9

Pesanggaran Power Plant

This new power enhancing technique is investigated and modeled ona 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 of118.5 mW at a heat rate of 10,023 btu/kWh(10,568KJ). Thecomparison will be based on an uncooled turbine, an evaporativecooled GT and a refrigerated GTIAC system with the inlet air cooled to40F(8C).

Evaporative Cooling

Refrigerated Air Washer

Refrigerated Cooling Coils

Evaporative cooler consisting of recirculated waterspray over a saturating extended surface media whichis mounted downstream from the air filter System.The heat transfer efficiency of this commonlyavailable media provides a dry bulb "depression“ orcooling "approach" to the ambient wet bulbtemperature in the range of 80-90% of the differencebetween the dry bulb air temperatures. The level andefficiency of the evaporative cooling stream is limitedto this approach to the wet bulb temperature of thesite area.

• Low Cost• Low Efficiency• Bad for high ambient conditions• High cooling load requirement

Finned coils are replaced by direct spray air/coil air washers which use chilled water sprayed ontosaturating 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

One major method of inlet air cooling is through the useof primary refrigerants circulated through extendedsurface (finned) coils mounted in the air stream of theGTG inlet. This inlet air cooling system, consists of a freestanding central refrigeration system to cool the inlet airusing direct evaporation of refrigerant within the finnedair cooling coils located in the inlet air stream.

This inlet air cooling system, consists of afree standing central refrigeration systemto cool the inlet air using directevaporation of refrigerant within thefinned air cooling coils located in the inletair stream.

Using the Dallas 501D5 example for a 6,000ton(75.9mmKJ) GTIAC system, the followingrefrigerant charge quantities and relative costsare 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

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

Union Electric Company is a summer peaking utility,experiencing peak electrical load demands during the hotsummer months. Combustion turbine generators are oftenused to meet the summer peak demands. However, thegenerating capability of a combustion turbine decreases as theambient air temperature increases. When system peakdemands are at their highest levels on the hottest days of theyear, the generating capacity of the combustion turbines are attheir lowest values. This lost generating capacity can berecovered by cooling the air entering the combustion turbines.

The ISO ratings for the machine are as follows:o Base Load Rating ......................59,000 kWo Peak Load Rating ......................65,200 kWo Base Load Heat Rate (LHV).......1 1,120 Btu/kWhro Peak Load Heat Rate (LHV).......11,010 Btu/kWhro Base ISO Airflow ......................1,896,000 lb/hro Peak ISO Airflow ......................1,896,000 lb/hro Base Load Generator Rating...... 68,889 kVAo 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 mslo Ambient Air Temperature - 100 °F, Dry Bulb - 76 °F, Wet Bulbo Combustion Turbine Operating Cycle - 15 hrs/wk

Evaporative Cooling

Thermal Energy Storage

Mechanical Chiller

Absorption Chiller

Absorption/HRSG Chiller

Well Water Cooling

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 SystemThe 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.

Ice was selected for the storage media since the volume required tostore 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 energystorage system for the G.E. 7B. Chilled water would be taken from thebottom of the ice storage tank at 33 OF and circulated by two (2) 50percent capacity chilled water pumps through the air cooling coils andback to the top of the tank. The cooled air temperature would bemaintained at 40 OF by chilled water flow control valves at the inlet ofthe air cooling coils. The chilled water flow rate would beapproximately 6,575 gpm at maximum turbine output.Psychometric Chart is Shown

Mechanical chillers would be considered an on-linesystem utilizing a refrigeration cycle to provide chilledwater for cooling the air. The chilled water portion ofthe system would be a closed-loop system utilizing ahead tank for system expansion, chilled waterevaporator, water pumps, and air cooling coils. Amechanical chiller system would use electricityproduced by the combustion turbine to power anelectrical refrigeration motor/compressor.

As with the thermal energy storage system, the air cooling process used in themechanical chiller system involves sensible cooling and dehumidification. Thewet and dry bulb temperatures as well as the specific humidity and enthalpy ofthe air decrease during the cooling process. See the mechanical chiller systemair cooling process on a psychometric chart.

An absorption chiller system, like a mechanical chillersystem, is an on-line system. A refrigeration cycle isutilized to provide chilled water to cool the air whilethe gas turbine is operating. An absorption chiller isdifferent from a mechanical chiller because it utilizeswaste heat directly from the combustion turbineexhaust gas as the driving energy source for the system.There are no large electric drive motors required.Because less electrical energy is required, the operatingcost of this system would be less than either thethermal energy storage or mechanical chiller systems.

The range of chilled water temperatures that can be achieved with a lithium bromide cycle, typically used inabsorption chiller systems, is 40 to 45 °F. Manufacturer's rate their equipment at a chilled water temperatureof 45 OF much like an mechanical chiller. A chilled water temperature of 45 OF was used in the study.

An absorption/HRSG chiller system is very similar to anabsorption chiller system. However, the absorption/HRSGchiller system utilizes steam from a waste heat recovery steamgenerator (HRSG) as the driving energy source for the system.Exhaust gas from the combustion turbine is used as the heatsource for the HRSG. Other than the steam production system,the process for producing chilled water and cooling thecombustion turbine inlet air is similar to the absorption chillersystem.

Exhaust gas from the combustion turbine would be routed through a ductdirectly to the heat recovery steam generator. The required exhaust gas flowwould be 210,000 pounds per hour at a temperature of 947 °F. The exhaustgas would exit the HRSG at approximately 350 °F.

The well water cooling system utilizes the coolertemperature of ground water to cool the air to thecombustion turbine. Well water is pumped throughair cooling coils located in the turbine air inlet.Energy for well water pumping is the only externalenergy 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 6,000to 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. Anotherdisadvantage is the potential of the well water to be corrosive or to cause deposits on piping and equipment.

Based on the inlet air cooling study for the G.E. 7B gasturbine, the following conclusions are presented:

• The evaporative cooler system is the least expensivecapital cost alternative. However, capacity improvement islimited to approximately 4.1 MW due to thermodynamics.

• The thermal energy storage system provides the greatestincremental capacity improvement of about 12.6 MW.

• The mechanical chiller and absorption chiller systems areestimated to high very high installed capital costs.

• The well water cooling system provides limited buteconomical incremental capacity improvement. However,the once through system requires large well water flowrates and may present a environmental disposal problem.

Results

To achieve the desired cooling of the inlet air to theturbine's compressor, it is proposed to use indirectcooling from a mechanical-vapor compression-typechiller in combination with cool storage.

Two types of cool storage are examined, includingchilled water storage and ice storage.

A sizing methodology for the chiller and storagecapacity was formulated by PSE&G to maximize theeconomic attractiveness which a cooling capabilitycan achieve under the power-pool rules.

Chilled Water Storage

Ice Storage

Mechanical Chiller + Thermal Energy Storage

The existing demineralized water-injection tank for Essex Unit No. 9was proposed for use as the chilled-water storage-tank for inlet-aircooling. Cooling medium for this option is chilled demineralized watersuitable for both water injection and inlet-air cooling. This tank wasoriginally dedicated to fuel-oil storage for the old station; however, itwas converted to its current use when the gas turbine was installed.When converted, the tank's interior surface was sandblasted andpainted with an epoxy coating to prevent rusting. The tank measures50 feet high and 120 feet in diameter. Storage volume is specified as100,000 barrels or 4,200,000 gallons.

Two ice-storage options are examined in this study. Both options use an ethylene glycol solution whichcirculates in the cooling loop.

One option offers a coil-in-tank design where a tightly wound coil is immersed in a tank of water. Duringcharging of the coil-in-tank modules, the glycol solution is chilled to approximately 26°F in the chiller. Thesolution flows to the ice storage modules through the coils where it freezes the tank of water. During storagedischarge, the glycol solution flows through the cooling coil, where it is warmed in cooling the inlet air andthen 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 closedstorage vessel. During charging of the bottle-in-tank modules, the glycol solution is chilled to approximately26°F in the chiller. The solution flows to the ice storage modules through the voids between the bottleswhere it freezes the bottles of water. During storage discharge, the glycol solution flows through the coolingcoil, where it is warmed in cooling the inlet air and then returns to the ice modules through the voidsbetween bottles to be chilled by the melting ice.

Chilled Water StorageThe available charging time was 20 or 68 hours,depending on the selected sizing option, to storesufficient cooling for 4 continuous hours ofturbine cooling at a constant 94°F (peakconditions). This criteria enabled calculation ofchiller and storage-tank size. An "efficiencyfactor" of 80% was assumed for both chiller-andtank-size calculations to account for thermallosses from the tank and any mixing which occursin the tank at the thermocline. Chiller size rangesfrom 635 tons for a 20-hour charge time to 322tons for a 68-hour charge time. Tank size rangesfrom 1,828,614 gallons for a 20-hour charge timeand 3,154,359 gallons for a 68-hour charge time.Under these criteria, the existing water-injectiontank (4,000,000 gallons) appears to havesufficient capacity.

Ice StorageThe glycol-temperature differential across the coolingcoil was assumed to be 15°F. The available chargingtime was 20 or 68 hours, depending on the selectedsizing option, to store sufficient cooling for 4continuous 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 inthe chiller-sizing calculation to account for decreasedchiller capacity in the ice-making mode. Chiller sizeranges from 725 tons for a 20-hour charge time to 368tons for a 68-hour charge time.

Based on the results, it is evident that chilled waterstorage provides a faster payback than a comparableice-storage system and within an acceptable time framerecognizing the availability of the existing waterinjection tank. The study has demonstrated thefeasibility of installing inlet-air cooling to an existinggas-turbine installation and has confirmed the benefitsof inlet-air cooling to the utility.

Results

Evaporative cooling system had been applied to improvethe performance of gas turbine in Pesanggaran powerplant in southern Bali Island, Indonesia. Moreover, theeconomic analysis was conducted to determine thecapacity cost, operating cost and payback period due tothe investment cost of the system. Based on theevaluation results, the power improvement for the threegas turbine units (GT1, GT2 and GT3) are 2.09%, 1.38%,and 1.28%, respectively.

Site Ambient ConditionsBefore CoolingPressure = 14.69 psiaTemperature = 80.6F Relative humidity = 83%. After Evaporative Cooling SystemRelative humidity = 98.04%Temperature = 76.61F (dropped 4.95%) Pressure = 14.51 psia (dropped 1.23%).

Evaporative Cooling

In the evaporative cooling system, a wet media isinstalled in the cross-section of the gas turbine filterhouse. The media is kept wet using high quality water,such as that from a reverse osmosis unit. The airentering the filter house passes over the saturatedmedia, and the water contained in the mediaevaporates into the air stream on its way to the gasturbine. This results in Decrease in Dry BulbTemperature but also increase in Relative Humidity.

These results are not very significant compared to theprevious studies with the enhancement of powerranges between 5-13.3%. These apply also to the SFC,heat rate and thermal efficiency, where the influence ofevaporative cooling system does not have a significantimpact to the performance of the gas turbine. Thiscould be caused by the high relative humidity inPesanggaran site so that a decrease in turbine inlettemperature from the existing conditions is lesseffective only around 4.95%, whereas in previousstudies could reach between 30-35%.

Results

By conditioning the compressor inlet air at highambients and increasing its density, the GT is driven toa more efficient, higher output mode of operation. Thisis a key factor for the competitiveness for power plantsservicing summer peaking grids. It is no secret that gasturbine based combined cycles are the most costeffective and environmentally accepted form of newgeneration option available today. However, all gasturbines, being mass flow machines, will suffer outputdegradation during summer base load and specificpeak conditions. Inlet conditioning enhances theperformance of modern combined cycles, recovering apotential lost revenue, both in terms of energy salesand capacity sales.

Conclusion