Optimal Design of Gas Turbine Power Station P M V SubbaraoProfessorMechanical Engineering DepartmentMore Ideas for better fuel Economy.

1872, Dr Franz Stikzes Paradox

Chart4

00

0.10938867830.103630571

0.1796646440.1628007825

0.23033302060.2007915054

0.26940004440.2268265891

0.30087957990.2453842221

0.32704990370.2589308813

0.34931940790.2689481451

0.36861496440.2763844026

0.38557652110.2818770425

0.40066302530.2858712757

0.41421392860.288687963

0.42648680130.2905644157

0.4376813390.29168002

0.44795524320.2921729209

0.45743504890.2921512242

0.46622370480.2917007192

0.47440600040.2908903264

0.48205253210.2897760192

0.48922265210.2884036979

0.49596669670.28681133

0.5023276940.2850305668

0.50834268950.2830879808

0.51404378680.2810060231

0.51945897460.2788037738

0.52461278830.2764975339

0.52952684590.2741012981

0.5342202850.2716271348

0.5387101210.2690854932

0.54301154440.2664854555

0.54713816790.2638349424

0.55110223360.2611408839

0.55491478770.2584093612

0.55858582870.2556457249

0.56212443290.2528546947

0.56553886270.250040443

0.56883665920.2472066667

0.57202472220.244356647

0.57510937950.241493302

0.57809644720.2386192305

0.58099128240.2357367504

0.58379882960.232847932

0.58652366070.2299546262

0.58917001120.2270584897

0.59174181170.2241610065

0.59424271580.221263507

0.59667612510.2183671845

0.59904521150.2154731098

0.60135293690.2125822442

Pressure ratio

Sheet1

111010100

1.51.1228242621.50.10938867831.572.90410671021.50.10938867830.103630571

21.219013654220.1796646442114.530350469720.1796646440.1628007825

2.51.29926322262.50.23033302062.5141.25682407952.50.23033302060.2007915054

31.368738106630.26940004443159.572505425930.26940004440.2268265891

3.51.43036874793.50.30087957993.5172.62780026333.50.30087957990.2453842221

41.485994289140.32704990374182.157875027540.32704990370.2589308813

4.51.53685235454.50.34931940794.5189.20502004954.50.34931940790.2689481451

51.583819608850.36861496445194.436427220250.36861496440.2763844026

5.51.62754197125.50.38557652115.5198.30049938555.50.38557652110.2818770425

61.66851044160.40066302536201.110442445160.40066302530.2858712757

6.51.70710784856.50.41421392866.5203.09198193846.50.41421392860.288687963

71.743639034370.42648680137204.412066429370.42648680130.2905644157

7.51.77835108337.50.4376813397.5205.1968940527.50.4376813390.29168002

81.811447328580.44795524328205.543649827880.44795524320.2921729209

8.51.84309730678.50.45743504898.5205.52838621938.50.45743504890.2921512242

91.873444004690.46622370489205.21145595990.46622370480.2917007192

9.51.90260923989.50.47440600049.5204.64134461479.50.47440600040.2908903264

101.9306977289100.482052532110203.857429479100.48205253210.2897760192

10.51.957800211810.50.489222652110.5202.892001450710.50.48922265210.2884036979

111.9839958856110.495966696711201.7717706497110.49596669670.28681133

11.52.009354324111.50.50232769411.5200.519003776511.50.5023276940.2850305668

122.0339370098120.508342689512199.1523944757120.50834268950.2830879808

12.52.057798568912.50.514043786812.5197.687737244212.50.51404378680.2810060231

132.0809877766130.519458974613196.1384548373130.51945897460.2788037738

13.52.103548381813.50.524612788313.5194.516015079313.50.52461278830.2764975339

142.1255197908140.529526845914192.8302632427140.52952684590.2741012981

14.52.146937635614.50.53422028514.5191.089689303514.50.5342202850.2716271348

152.1678342526150.53871012115189.3016444833150.5387101210.2690854932

15.52.188239085215.50.543011544415.5187.4725179515.50.54301154440.2664854555

162.2081790273160.547138167916185.6078819621160.54713816790.2638349424

16.52.227678716116.50.551102233616.5183.71261182716.50.55110223360.2611408839

172.2467607829170.554914787717181.7909856149170.55491478770.2584093612

17.52.265446070717.50.558585828717.5179.846767489817.50.55858582870.2556457249

182.283753822180.562124432918177.8832777025180.56212443290.2528546947

18.52.301701841918.50.565538862718.5175.903451658518.50.56553886270.250040443

192.3193066419190.568836659219173.9098899893190.56883665920.2472066667

19.52.336583564419.50.572024722219.5171.904901174719.50.57202472220.244356647

202.3535468937200.575109379520169.89053797200.57510937950.241493302

20.52.370209952820.50.578096447220.5167.868628654620.50.57809644720.2386192305

212.3865851904210.580991282421165.8408039328210.58099128240.2357367504

21.52.402684257321.50.583798829621.5163.808520171421.50.58379882960.232847932

222.4185180745220.586523660722161.7730795355220.58652366070.2299546262

22.52.434096894822.50.589170011222.5159.735647490722.50.58917001120.2270584897

232.4494303572230.591741811723157.697268059230.59174181170.2241610065

23.52.464527536423.50.594242715823.5155.658877154123.50.59424271580.221263507

242.4793969867240.596676125124153.6213142681240.59667612510.2183671845

24.52.494046782324.50.599045211524.5151.585332739124.50.59904521150.2154731098

252.5084845531250.601352936925149.5516087929250.60135293690.2125822442

Sheet1

Pressure ratio

Efficiency

Efficiency Vs Pressure Ratio

Sheet2

Pressure Ratio

wnet

Specic Work Output Vs Pressure Ratio

Sheet3

Pressure ratio

Condition for Compact Gas Turbine Power Plant

At maximum power:

Important Comments:

What if I am not interested in Compactness.

Should I prefer high Pressure Ratio for Efficient Plant?

Why the plant is compact at this condition?

What else can be inferred form this condition?

The state-of-the-art The newer large industrial gas turbines size have increased and capable of generating as much as 200 MW at 50 Hz. The turbine entry temperature has increased to 12600C, and the pressure ratio is 16:1. Typical simple cycle efficiencies on natural gas are 35%. The ABB GT 13 E2 is rated at 164 MW gross output on natural gas, with an efficiency of 35.7%. The pressure ratio is 15:1. The combustion system is designed for low Nox production. The dry Nox is less than 25 ppm on natural gas. The turbine entry temperature is 11000C and the exhaust temperature is 5250C. The turbine has five stages, and the first two rotor stages and the first three stator stages are cooled; the roots of the last two stages are also cooled.

Siemens power corporation described their model V84.3. This is rated at 152 MW at an efficiency of 36.1%. The pressure ratio is 16:1. Six burners designed for low Nox emissions are installed in each chamber. The turbine entry temperature is 12900C and the exhaust temperature is 550 C. The turbine has four stages and the first three rotating stages are air cooled. The effectiveness of the cooling is improved by inter-cooling the cooling air after it is with drawn from the compressor.

General Electric and European Gas Turbines have jointly developed the MS9001F 50Hz engine. This unit generates 215 MW at an efficiency of 35%. The engine uses an 18 stage compressor with an overall compression ratio of order of 20:1. The gas turbine has three stages, with the first two stages cooled. Turbine entry temperature is 1288 C. These large high efficiency units can be used for peak lopping purposes. The research for more efficient gas turbine-based power generation cycles has been underway for some time. The aims are: - Higher turbine entry gas temperature, - Higher compressor efficiency and capability

The different manufactures participated and initiated the collaborative advanced gas turbine. The outcome of their effort include a variety of advanced cycle options, including intercooling, humid air turbine, steam injection, reheat combustor and chemical recuperation. The U.S. Department of Energy (DOE) has initiated a development program called the advanced turbine system (ATS). The aim of ATS is to achieve over 60% efficiency, with low Nox and suitable operating costs at the end of a 10-year program. They pictured the program with increasing in firing temperature up to over 1427 C and changes in cycle, as intercooling, reheat combustors, massive moisture injection and chemical recuperation.

9756 kJ/kWh

The Ideal Machine1824: Sadi Carnot, who founded the science of thermodynamics, identified several fundamental ideas that would be incorporated in later internal combustion engines: He noted that air compressed by a ratio of 15 to 1 would be hot enough (200C) to ignite dry wood. He recommended compressing the air before combustion. Fuel could then be added by "an easily invented injector". Carnot realized that the cylinder walls would require cooling to permit continuous operation. Later, Diesel thought he could avoid this, but found out the hard way. He noted that usable heat would be available in the exhaust, and recommended passing it under a water boiler.

Developments in Gas Turbine CyclesThe wet compression (WC) cycleThe steam injected gas turbine (STIG) cycleThe integrated WC & STIG (SWC) cycleThemo-chemical Recuperation cycles

Wet compressionOne of the most effective ways to increase the gas turbine power output is to reduce the amount of work required for its compressor.A gas turbine compressor consumes about 30 to 50% of work produced by the turbine.

The wet compression (WC) cycle

Representing wet compression process on P-V diagramW isothermal = f-1-2T-g-f (isothermal)Wwet compression = f-1-2K-g-f (wet compression)W isentropic = f-1-2S-g-f (isentropic)W polytropic = f-1-2n-g-f (polytropic)

12s2k2n2TP1P2fg0PV

The wet compression (WC) cycleThe wet compression cycle has the following benefits over the simple cycle.Lower compressor workHigher turbine workHigher cycle efficiency

ISENTROPIC INDEX OF WET COMPRESSION PROCESSIsentropic index of wet compression can be obtained from the equation

Where k=Isentropic index of wet compression, dw/dT = Evaporative rate kg/k, L= Latent heat kJ/kg, R=Gas constant of humid air kJ/kg k.

ACTUAL WET COMPRESSION INDEXActual wet compression index can be obtained from the equation

Wherem=polytropic index of actual wet compression process,n=polytropic index of actual dry air compression

Compressor work with wet compressionCompressor work with wet compression is a function of Pressure ratio ,Evaporative rate dw/dT andGeometry of the compressor.Wet compression work is much lower than that of dry air compression work.The higher is the pressure ratio, more the saving in compressor work.

Variation of wet compression work with pressure ratio(Evaporative rate dw/dT=7.5e-4 kg/k)

Pressure ratio = 7VARIATION OF WET COMPRESSION WORK WITH THE EVAPORATIVE RATE FOR A GIVEN PRESSURE RATIO

REAL WET COMPRESSION WORK CONSIDERING OFF DESIGN BEHAVIOURFor calculation purposes, if the design (dry) value of the polytropic efficiency is assumed to be maintained throughout the compression process, it is tantamount to the operation of the compressor at increased operating pressure ratio.

Comparison of Work Input For Wet and Dry Compression Considering Off-Design Behaviour

SlnoEvaporative rate, kg/kOperatingPr. ratioReal wet work kJ/kgDry workKJ/kg1010.2343.269343.26920.0001511.5597316.649370.41530.0003511.5737284.812370.68340.0007511.6017255.000371.218

ACTUAL WET COMPRESSION WORK CONSIDERING OFF DESIGN BEHAVIOUR

9756 kJ/kWh

WaterSuper Heated Steam

The steam injected gas turbine (STIG) cycle

The steam injected gas turbine (STIG) cycleSteam injection into the combustion chamber of a gas turbine is one of the ways to achieve power augmentation and efficiency gain. In a steam injected gas turbine (STIG), the heat of exhaust gasses of the gas turbine is used to produce steam in a heat recovery steam generator. The steam is injected into the combustion chamber or before entering the combustion chamber (i.e. in the compressor discharge). STIG cycle has higher cycle efficiency than the WC cycle.STIG cycle gives higher net work out put than the WC cycle up to a pressure ratio of 7.

The integrated WC & STIG (SWC) cycle

The integrated WC & STIG (SWC) cycle

It has the combined benefit of the advantage of higher efficiency of STIG cycle and higher net work output of WC cycle. But its cycle efficiency is less than that of the STIG cycle owing to the need for higher heat input.

COMPARISION BETWEEN SIMPLE, WC, STIG AND INTEGRATED WC & STIG CYCLES

Cycle efficiency versus pressure ratio

Net work output versus pressure ratio

Comparison of typical parameters of simple, WC,STIG and SWC cycles.

cyclePressure ratioPREvaporative rate, kg/kNet work output, MWCycle efficiency%Fuel mass flow rate, kg/secSteam mass flow rate, kg/secsimple110151.1331.2811.040WC117.5e-4232.7535.3515.040STIG110215.6539.6312.4354.49SWC117.5e-4303.1138.1618.1554.49

Future workThere are many areas and challenges which can be explored further to this work. They are: Economic feasibility of these cycles need to be studied.Compressor life reduction due to water injection. (because of the off design running conditions that prevail in reality).The difficulties involved in designing a turbine to handle large mass flow rates of combustion gasses and steam.The effect of steam injection in reducing NOX emissions.

A tree converts disorder to order with a little help from the Sun

Clues from Nature to get Better FuelOne of such clue is Thermo Chemical RecuperationThe major reactions involved in Steam-TCR are well known, and the overall reaction for a general hydrocarbon fuel, CnHm, is:

The formation of carbon must be minimized in the operation of the reformer to minimize fouling of heat transfer surfaces, blinding of catalyst particles, plugging of flow paths and carbon losses.

The theoretical merits of the Steam-TCR concept are based on the overall endothermic nature of the reforming chemical reactions, and the formation of a low-thermal-value fuel gas replacing the high-thermal-value turbine fuel, with both factors contributing to improved efficiency

Steam-TCR Power Plant Cycle Diagram

Flue Gas-TCR Power Plant Cycle Diagram

Model TCR Cycle

The chemical Reactions in Flue Gas TCR CycleCombustion of Methane with 100% theoretical air.Thermochemical recuperator: Reforming of Flue Gas Only Combustion of reformed flue gas :

Combustion of reformed flue gas and methane mixture:Thermochemical recuperator: Reforming of Flue gas with methaneThe chemical Reactions in Flue Gas & Methane TCR Cycle

First Law Analysis of Thermochemical RecuperatorNo work transfer, no heat transfer, change in kinetic and potential energies are negligible

Turbine ExhaustCooled exhustFuel & Flue gasReformed fuelEnergy lost by turbine exhaust = Increase in energy of reformed gas.

Generalized Recuperation Reaction

Analysis of Reformation Process

Study of Optimal TCR Cycle

ParameterSimple BraytonTCR BraytonFlue Gas Recirculation0%70%Mass flow rate of air 462 kg/s135 kg/sPower input to compressor155.2MW44.5MWFuel8.4kg/s7.35kg/sFlue gas compressor--114MWNet Power output134.7MW141.8MWEfficiency32.1%38.6%Steam generation252kg/s41kg/s

Reduction of CO2 EmissionsIncreasing CO2 content in atmosphere is one of the factor for Global Warming.Power Generated CO2 is responsible.Kayas Equation:WherePOP : Population that demands and consume energyGDP/POP: Per capita gross domestic product, reflecting standard of living.E/GDP: Energy generated per gross domestic product, the energy intensity. CO2/E : Emission per unit energy generation, the carbon intensityS: Natural and induced removal emission product from atmosphere into a sink.

Carbon dioxide Sinks Biosphere sinks : Natural ResourcesGeosphere Sinks: Natural Resources with anthropogenic intervention.Material Sinks: Anthropogenic Resoruces

Carbon Sequesterizaton

Partial Oxidation Cycles

Partial Oxidation Cycle