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Exergy and Environmental Considerations in Gas Turbine Technology and Applications

Intailways5(14%9(25%328(28%)36201%85014%)29682pntFinal energy consumption 20by sector and transport modeSource: DG TREN 2007From: Rail Transport and Environment, page 5-Facts Figures, Nov 2008

Local air pollution二mSourcewwwecopassengeforg200From: Rail Transport and Environment, page 20- Facts Figures, Nov 2008

Exergy and Environmental Considerations in Gas Turbine Technology and ApplicationsFuel PropertiesMaxMinNoteser Heating Value, MJ/m3 None73-112054Absolute limitsFlammability Ratic22:1Rich: Lean Fuel/ Air RatioLimits, moleEthane, CHButane Chiohigherof reactant speciesparaffins(C++)of reactant specieCarbonof reactant speciesof reactant spTotal Inertsof total (reactants inertsAromatics (Benzene CaHee C7 Hs, etcReportTable 4 4 Range of typical heavy-duty gas turbine fuel specification(adapted from GErtems, Revised January 2002)Conventional and New Environmental-conscious Aero and Industrial Gas Turbine FuelsConventional aero gas turbine fuels are commonlyKerosene froldeumsing established refining pIdii synthetic kerosene from Fischer-Tropsch(FT) synthesis using coal, natural gas, orother hydrocarbon feedstock (e

g shale, tar sands, etc ) These are producegasifying the hydrocarbon resource followed by liquefaction to fepdate dateline 26 June 2009)New Environmentally-conscero gas turbine fuelsBio-fuels from bio-derived Fatty Acid Methyl Esters(FAME) mixed with conventionalii Bio-ethanol and bio-methanol neat or mixed in regulatedproduced from Fischer-Tropsch Synthesis(FTS)process using biomasunflower came lina, etc, as well as animaliv Bio-syngas produced by gasification of biomass, lignocellulosic biomass and otheragricultural wastes used as feed into the FIS (2nd generation biofuels) to produce liquidLNG, Methane and Hydrogen Both methane and hydrogen will have to be liquefied foras aircraftTable 45 below gives relative properties of conventionalLion kerosebiodiesel aircraft fuel (will vary with Fatty Acid Methyl Esters[FAME] type)

Gas TurbiHeat of combustioAirframe432[MJ/kg typicalpec, minDensity[kg/ ma] range75-840860-900792-852Wing tankProx Carbon lengtrace levels) C16-C22Flash point, Cmin5 to -10 with wing tankPoint°Cmaxlimits, Cold staand reSulfur [ppm)max300010001505ExcludedHd lifetrolled Not knowntionHydrocarbon FAMEo FAMEFrom: Ppt Presmpany Specialist-Fluids, Rolls Royce plc, titledA Gas Turbine manufacturersofuels2006reforming reactits with feedstock (hydrocarbmill sludge, black liquorderived fuel, agricultural biomass wastes and lignocellulosic plants) to produce biIt is a gas rich in carbon monoxide and hydrogen with typical composition shown in Tabl4

6 belowConstituentse(cozBenzene-Toluene-Xylene(BTX)Ethane(C2HsDthers(NH3, H2S, HCl, dust, ash, etcSource: M Balat et al Energy Conversion and Management 50(2009)3158-316846TypIcal comp

Exergy and Environmental Considerations in Gas Turbine Technology and Applicationsuseful reference for the thermo- conyersion of biomass into fuels and chemicals can beund in the above referenced paper by M Balat et alEthanol-powered gas turbines forelectricity generationcalled LPP Combive demonstrated that during gasNOx, CO, SO and PM(soot) from biofuel ethanol (ASTM Dme as natural gas-leveltechnology, Ialso claimed that the combustion of the bio-derived ethanol producedtually no net CO emissionsGas Turbines and biodieselsecent study by bolszo and McDonnell(2009) on emnization of a bodiesfired 30-kwthat biodiesel fthat the minimum nox emission levels achieved forcceeded the minimumttained for diesel, and that optimizing the fuel injection process will improve the biodieseltheoretical study was recentlyd out by Glaude et al (2009)the nox indexrefer diesels in gas turbines taking conventional petroleum gasoil and natural gas asof NOx emissions in gas turbines and used as a criterion for NOx emissionnecessitated by the conflicting results from a lab test on a microturbine and two recent gasturbine field testsrapeseed methyl ester(RME) and the otherbean methyl ester(SME), the lab test showing a higher NOx emission whiltthe two field tests showed slightlNOx emission relative tclear that biodiesels have reduced carbon-containing emissions and there isgreement also on experimental data from diesel engines which indicate a slight increase inNOx relative to petroleum diesel The five FAME's studied by Glaude et al were RME,The results showed that petroleum diesel fuels tend to genhile natural gas has the lowest, with biodiesel lying in-between

This rankingth the two field tests mentioned earlier It was also found out that themperature, while biofuels are less sensitive to composition variationsg gas turbine performanceThe Joule cycle (also popularly known as the Brayton cycle)is the ideal gas turbine cyclegainst which the performance (ie the thermal efficiency of the cycle ncr) of an actual gasturbine cycle is judgedWe prefer to restrict the use of JouleC D Bolszo and v G McDonell, Emissions optimization of a biodiesel fired gas turbine, Proceedingsrre A Glaude, Rene Fournet, Roda Bounaceur and Michel Moliere, (2009), Gas Turbines anddiesel: A clarification of the relative nox indices of FAME, Gasoil and Natural Gas

Gas Turbie to the idealpine cycle while the Brayton cycle is exclusively used for the actualgas turbine cycleeal gas turbine""cycle (or Joule cycle) consists of four idealhich appear as shown in Fig 5 1The thermal efficiencyhe Joule cycle in terms of the pressure ratio rp given bytio parameter Pp given by p=pF|=11)Hence, the thermal efncy of the ideal gas joule cycle is a function only of the pressuretio sincedependent of the isentropic terre ratios only, but independent of the compressor andthe turbine inlet temperatures separately without a knowledge of theis essentially the isentropic temperature ratio, the abscissa in Fig 51

If air is the workingfluid employed in the ideal Joule cycle, the cycle is referredhstandard jouleFig 5 1 Ideal Joule cycle(a)p-V and (b)T-Fixing the inlet temperature to the compressor Ta and the inlet temperature to the turbine Tautomatically sets a limit to there ratiohichafterisentropic compression from Ta is equal to the TIT Tb However, when this occurs, the netof the cycle on the T-s and p-v diagranindicateHaywood considers an interesting graphical representation of eq 5 1 above for T=15oCand Th=100° C as she

Exergy and Environmental Considerations in Gas Turbine Technology and Applicationsrati ferair cal4For Ta 15C and Tb= 100Cshows The limiting pressust-5)aMton ro=9982 approximated to 1005=he Joule cycle on the t-s diagraows that as rp approaches thiser used whensues of process irreversiblitieswhich thegraph pertainFi52cle efficth Isentropic temperature ratio p (ta=15C) From51 Effectes in the actual gas turbine cyclechangers andombustion chamberoduction of useful work the hFig

53, wherein the heat and work terms in each of the prere identifiedthe frictional effects in the heat exchangers, ductings and combustion chamber Wethan for the ideal Joule cycle, revealing the considerable effect of turbine and compressoinefficiencies on the cycle thermal efficiency An analytic expression for the Brayton cyclethermal efficiency can be shown to1-1/p)(a-P(52)(B-p)here a"nenre, B-1+nd(e-1)), and B-Tb/Te is depicted for turbine and compressorntropic efficiencies of 88%o and 85% respectively, t,- 15C for two values of tb- 800Cnd 500C respectively There ratioreduced fromto 112 for t"800C, and to only 48 at tb-500C This optimrealistically achievable in a single compressor Here also, we find thatdependent on e= To/Ta showing a drastic reduction from TIT=800C to TIT=500

Gas TurbinesThe corpressorunitworking fl1=13while4)Jawith a-ncnre and e- Tb/Ta as beforeFrom 5es whand wheAlso from differentiatingwe obtain that Wret is maximum when ppVa The variation of w with the adiabaticm hFig, 53 Enthalpy-erropy diagram for Actual Brayton cycle, with turbine and Compremaywood IHaywood n discusses the graphicalcawthorne and Davis[ for theth variation in Pp for fixed valuesf t and Th

The maximunefficiency is obtained at the valtsa1/, tangindicates tha-usnn the points of maximum thermalefficiency of thWarPw and popt are the values of pr frespectively,then Pw=V(1-nom)whereFig 54 Variation of heat supplied to the combustor QB, turbine work input Wc, and Wret with isentropic temperature ratio Pp From Haywood I

Exergy and Environmental Considerations in Gas Turbine Technology and ApplicationsFigs55 and 56 show the schematic of the simple-cycle, open-flow gas turbine with a singleelativeniform speed such as generator drives while in the dual shaftturbine rotor is mechanically separate from the high-pressureturbine and compressor rotor It is thus aerodynamically coupled, making it suitable fCombustorCompressor(43)GeneratorurbineInlet AirFig 5

5 Simple-cycle, open-flow, single-shaft gas turbineCombustorExhaustCompresLoadT

urbineInlet AirFig 56 Simpleopen-flow, dual-shaft gas turbine for mechanical drives52 Simple-cycle vs Combined-cycle gase power plant characteristicsthe simple-cycle top figure, at afiringefficiency and maximum output are a function of the firing temperature, the higher thepressure ratio, the greater the benefits from increased firing temperature At a give

Exergy and Environmental Considerations in Gas Turbine Technology and Applicationsand Inland Waterways(145%), Aviation (119%) From: Rail Transport and Envipage 5- Facts Figures, Nov, 2008 Rail Transport and Environment, page 5-Facts 8 Figures,Nou 2008]

The sectoral energy consumption for 2005 appears in the figure shown belofrom which the Transportation sector had the second largest share of 31% after theHouseholds Services sector, Aviations share of the Transportation sector energynsumption was 14 %, second to Road Transport A similar trend would be found in otherwhich accounts for the bulk of the global energySimilarly, local air pollution data for NOx and PM1o appears below for a journey of 545 kmby three modes of trarTransportation of 100 tons of cargo for a distance of 700 km between the Netherlands andSwitzerland generates the local pollution information as shown in the figure belFreight transport NOx and PMio comparisonThe table below compares the local air pollution from transporting100 tons of average goods from the port of Rotterdam, Netherlands, toLocal air pollution(100 tons cargo, Basel -Rotterdam, 7oo km)41425EURO4Sourcewwwecotransitorg200From: Rail Transport and Environment, page 19- Facts Figures, Nov 2008Energy efficiency is of utmost importance in addressing the climate problSomebeen made by some sub-sectors as the figure below indicate

In Germany, the consumption of specific energy for Deutsche Bahn,both for regional passenger trains and freight has decreased constantlysince 1990, due to the energy efficiency action plan of the companySpecific primary energy consumption(per pkm or tkm)1990-2007Deutsche bahn- Passenger regional199020002005urce: Deutsche BahnFrom: Rail Transport and Environment, page 11-Facts Figures, Nov 2008Finally, a look at the noise profile of sorPercentages of citizens who are "highly disturbedwhen exposed to rail, air and road traffic noise156668m:Rail Transport and Environment, page 22 -Facts Figures, Nov 2008

Exergy and Environmental Considerations in Gas Turbine Technology and ApplicationsFrom the above, it is clear that just as the other sectors are called upon to reduce their GHGemission, the same should hold for the transportation sector Gas turbines are employed industry generally It is claimed thaiWorkshop, Baltimore, USA, 12-13 October 2004] As of 2004 IPIECA Workshop, there wassubstitute envisioned for jet fuel neither was therniche alternative fuel on the horizonHowever, between 2008 and 2010jet fuel derived from natural gas /Airline Industry Informageneration biofuels from 50 50 blend of jathropha oil and standard Al jet fuel [The SeattleTimes, Dec 31, 2008 Similarly, the airline Industry Informationtion of 16 january2009 reported that the US Federal Aviation Administration(FAA) has announced the resultsof a commercial airline test flight using a mixture of jet fuel and biofuel derived from algaend jatropha plants early in January 2009 In June 2009, the aviation fuels subcommittee ofreported to have approved specifications for syntheticblend of synthetic Fischer-Tropsoeum-derivedGas turbinesloyed in the Energy, Industrial, and the Transporsectors which have been shown to be responsible for most of the carbon emissHence it is imperative to sustain the current drive for improvement in theexergy and environmental performance of gas turbines in general (land, aviation,gas turbine technology ) We shall consider some of thesein thise Brayton open-cycle components -simple cycle and combined cyclegas turbinesCombustion Chamber CombustorCompressed air from theer centrifur axial-flope)flows directlto the combustion chamber (such as that shown in Fig 21 below)in a Brayton opimple cycle gas turbine where part of it (< 1/3)is used in a direct-fired air heater to burnthe fuel after which themixed with the combustion products, all of whichto be carried out with minimum pressure loss Minimization of pitical at astages from inlet to the compressor to entry into the turbine to ensure optimal powerproduction from the gas turbine

The Turbine Chamber of a 3-stage gas turbine plant is shown in Fig 2 2 and Fig 23 showstypical turbine stage blades Substantial volumes of air and combustion gmachine, beitthrough a series of processes These processes follow thepic compression from the atmospheric inlet condof theto the isobaric (constant-pressure) combustion of the fuel in the combustchamber, and then followed by adiabatic (non-isentropic) expansion of the hot gases andfinally discharging thedprocess The energy transfer between the fluid and the rotor in the compression andnsion processes is achieved byof kinetic action rather thanin reciprocating machi

Gas TurbiFig 21 A Combustion Chamber Can [From Shepherd, D

G, Introduction to the GasTurbine d van nostrand co inc

Exergy and Environmental Considerations in Gas Turbine Technology and ApplicationsFiTypical turbine stage [Fherd, DG Introduction to the gas turbine dNostrand Co Inc4 Gas turbine fuels -conventional and new fuelsConventional gas turbine fuels currently indusually hydrocarbons, Solid gas turbine fuel technology is still in the research anddevelopmental stages

New gas turbine fuels, as mentioned earlier in the Introduction,include the synthetic Fischer-Tropsch aviation jet fuels and the second generation biofuelsne fuels- liquid and gaseous fuelsConventional gas turbine liquid fuels include the range of refined petroleum oils fromknd light diesel oil to a heavy residual oil ( BunkerC or No, 6 fuel oil), Table 4-1 gives the ultimate analysis of some liquid fuelsFuelCarbon Hydrogen Sulfur Ash,etcOctane petrolResidual fuel oilTable 41 Ultimate analfuels(From Applied Thermodynamics forEngineering Technologists, SI Units by Eastop &e McConkey, 2nd ed, 1970)also indicates some of the key properties of some of the many known

ergy and Environmental Considerations in Gas turbine Technology and Applicationsws typical distillation characteristics for military and commercial aircraftthe“pubstance single evapotemperatures of water and ethya mixture of liquid several hydrocarbons and its various componentstemperatures as can be seen in the graphsBP102030405060708090EPFig 41 Typical ASTM distillation characteristics for various types of fuels, DegreePower by Severns, Degler Miles, John Wiley Sons Inc

1964 om Steam, AirCentigrade scale supplied by Prof R ' Layi Fagbenle Abstracted from Steam, Air, and GasThe aviation gasoline graph at the bottom of the graph is for piston-engine powered aircraftts ignition characteristics It is usually a high-octanegasoline known as"avgas" Turbine engines on the other hand can operate with a widefuels with much higher flash points,Jet A specification fuel used in the USA anet A-l standard specification of most of thehave a relatively high flash point of 38C and a self-ignition temperaturesit)(or auto-ignition temperature) of 210 C, making them safer to handle than theditional avgas The open air burning temperatube compared with thetypical distillation characteristics for aircraft gas turbine fuel in Fig 4-1

Jet A-1

Range of typical heavy-duty gas turbine fuel classification(adapted from GEl41040G-GE Gas Power Systems, Revised January 2002)The feedstock for gasification fuelsbe coalkavy liquidGasification fuels generally have lower much lower heating values than other fuel gaseand they are produced byoxygen blown or air blown gasificationProcess gases are generated by many petrochemical and chemtablefor fuelling gas turbines, for example refinery gases) Constituents of process gases inclueH4, H2, CO, and CO Other process gases used as gas turbine fuels are byproducts of steelproduction such as blast furnace gases and coke oven gases Blast Furnace Gases(BFG)haveth other fuels suchas, natural gas or hydrocarbons such as propanebutaneifc gas turbine fuel specification ranges appear in Table 4-4 below In addition to sucheach turbine manufacturer allowableontaminant levels are also specifsuch trace metals as (Pb, v Ca, and me), alkalietals(Na and K)and particulates Sodium(Na)he only trace metal contaminantnormally found in natural gas, and it source is salt water in the ground gas wellsof contaminants in heavy-duty gas turbine applications include particulates arisingfrom corrosion chemicaltions in gas pipelines,hydrocarbon) condensates and lubricating oils from compressor stations; sulfur(as H2s orOS): trace metals; steam and water fection; alkali metals contained in compressordischarge; and the fuel