Because of the synergistic effects (higher efficiencies, lower emissions) of combining a fuel cell and a gas turbine into a power generation system, many potential system configurations were studied. This work is focused on novel power plant systems by combining gas turbines, solid oxide fuel cells, and a high-temperature heat exchanger; these systems are ideal for the distributed power and on- site markets in the 1-5 MW size range

Lee, G. T.

Sudhoff, F. A.

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Paper Number:DOE/METC/C-97/7278Title:Fuel Cell/Gas Turbine System Performance STudiesAuthors:George T. Lee (METC)Frederick A. Sudhoff (METC)Conference:Fuel Cells ‘96 Review MeetingConference Location:Morgantown, West VirginiaConference Dates:August 20-21, 1996Conference Sponsor:U.S. DOE, Morgantown Energy Technology CenterDisclaimerThis report was prepared as an account of work sponsored by anagency of the United States Government.  Neither the United StatesGovernment nor any agency thereof, nor any of their employees,makes any warranty, express or implied, or assumes any legal liabilityor responsibility for the accuracy, completeness, or usefulness of anyinformation, apparatus, product, or process disclosed, or representsthat its use would not infringe privately owned rights.  Referenceherein to any specific commercial product, process, or service by tradename, trademark, manufacturer, or otherwise does not necessarilyconstitute or imply its endorsement, recommendation, or favoring bythe United States Government or any agency thereof.  The views andopinions of authors expressed herein do not necessarily state or reflectthose of the United States Government or any agency thereof.Fuel Cell/Gas Turbine System Performance StudiesGeorge T. Lee  (glee@.metc.doe.gov; 304-285-4824)Frederick A. Sudhoff  (fsudho@metc.doe.gov; 304-285-4560)U.S. Department of EnergyMorgantown Energy Technology CenterP.O. Box 880Morgantown, WV  26507-0880BackgroundBecause of the synergistic effects leadingto the higher efficiencies and lower emissionsachieved by combining a fuel cell and a gasturbine into a power generation system, manypotential system configurations were studied bythe Morgantown Energy Technology Center(METC) (1).  Natural gas, indirect-fired,carbonate fuel cell bottomed, combined cycle(NG-IFCFC) and the topping natural gas/solidoxide fuel cell combined cycle (NG-SOFCCC)novel power plant systems were earlierintroduced as high efficient systems.  METCdeveloped these systems for both the distributedpower and on-site markets in the 20-200megawatt (MW) size range.  Most of these largefuel cell/gas turbine systems utilize a steam cycleto achieve high thermal efficiency.  This work isfocused on novel power plant systems bycombining gas turbines, solid oxide fuel cells(SOFC), and a high temperature heat exchanger. These systems are ideal for the distributed powerand on-site markets in the 1-5 MW size range. The configuration, illustrated in Figure 2,Gas Turbine ConfigurationMETC developed a simple gascompressor-turbine (CT) system using theAdvanced System for Process Engineering(ASPEN) computer simulator.  This basicsystem consists of two gas turbines as shown inFigure 1.  The first turbine drives the air streamcompressors and the second turbine is used forpower production only.  For convenience, thefirst turbine is defined as a compressor-turbineand the second one a power-turbine.  Lowtemperature combustors 870°C (1,600EF) areconfigured as topping combustors for bothturbines.  A recuperated-heat exchangerrecovers waste heat from the power turbineexhaust.  This recuperated thermal energypartially heats the compressor turbine inletstream.  Typical small recuperative gas turbinesystem parameters and design results arepresented in Table 1.  One advantage possessedby this system is that the low operatingtemperatures allow the design of a low-temperature turbine without blade coolingrequirements and their associated costs.  Theelectrical conversion efficiency of the CT systemalone is greater than 40 percent on a net lowheating value (LHV) basis (2,3).Fuel Cell Configurationis a generic system of a fuel cell bottomed by aheat recovery steam generator (HRSG) and asteam cycle.  Fuel cells are electrochemicaldevices that oxidize fuel directly into electricalpower without causing an excessive temperaturerise, but oxidation of all the fuel is not completeinside the fuel cell.  The remaining fuel oxidationalso generates heat to raise the temperature offuel cell exhaust that is then recovered in theHRSG.Figure 1.  Gas Turbine Recuperative Cycle              (GTRC)Table 1.  Gas Turbine Power Plant                  Performance (GTRC)Compressor Air, lb/hr 40870Turbine Fuel, lb/hr 510CT Power, MW 1.3Power Out, MW 1.4System Efficiency, %LHV 42.9Compression Ratio 8.8Turbine Inlet, °F/°C 1580/860Turbine Outlet, °F/°C 1180/638Power Plant Exhaust,°F/°C 443/228Figure 2.  Fuel Cell — HRSGTable 2.  Fuel Cell Power Plant                     PerformanceFuel Cell Fuel, lb/hr 1165Fuel Cell Power, MW 4.2HRSG-Steam Cycle, MW 0.6Power Out, MW 4.8System Efficiency, %LHV 65Power Plant Exhaust °F/°C  200/95Thus, electrical energy and heat are bothgenerated from the fuel cell.  These large sys-tems can obtain efficiencies greater than65 percent (LHV) when coupled with anexpensive HRSG and a steam turbine-basedcycle.  Performance results are presented inTable 2.Fuel Cell/Gas Turbine SystemsRecently, development of small advancedgas turbines driven by low-inlet-temperature gasis underway (4).  The use of a low-inlet-temperature gas turbine is advantageous: first,the turbines are manufactured using inexpensiveconstruction materials and second, itsynergistically matches the operat-ing temperature of a fuel cell with the turbineinlet temperature.  These small low-inlet-temperature recuperatored gas turbinesFigure 3.  Gas Turbine/Fuel Cell                     (NG-GT/FC)can achieve high efficiency, greater than40 percent cycle efficiency, on an (LHV) basis. In general, a molten carbonate fuel cell (MCFC)or a SOFC can achieve approximately 50 percentoperating efficiency from fuel to electricity atatmospheric pressure.  Current development ofsolid oxide fuel cells allows operation atpressures of 10-15 bar (10-15 atmospheres). Among the benefits of pressurization includeimproved cell performance, (i.e., increasedpower output), smaller equipment size, andreduced heat loss and pressure drops.  Theelectric conversion efficiency increases severalpoints due to the higher fuel cell operatingpressure (5,6).  Fuel cell thermal exhaust at870EC serves as an excellent feed to the high-efficient, low-temperature gas turbine.  Thus, theconcept of a pressurized fuel cell topping asmaller gas turbine is born.High pressure operation was not used in efficiency of the system.  An ASPEN simulationearly fuel cells.  This restricted the fuel cell projects system efficiency for the above simpleoperation compatibility with the low pressure systems approaching 62-68 percent on an (LHV)power turbine.  Even with the low pressure basis.  These results are shown in Table 3.  Anrestrictions and inexpensive gas turbine com- alternative configuration is to move the singleponents, simulation results indicate that system fuel cell and locate it before the compressor-electrical conversion efficiencies can achieve 60 turbine and the ASPEN simulation indicatespercent or more (LHV).  Figure 3 shows a similar results.typical single fuel cell/gas turbine systemconfiguration.  The same shaft combustion As fuel cell research progresses, highturbine design provides a balance between pressure fuel cells are becoming available.  Theelectrical power output generated from the system efficiency can be increased further bycombustion turbine and the power requirement integrating a second fuel cell in front of theof the compressors.  Net electrical output is compressor-turbine.  Integrating the processes,generated from the low pressure (about three the fuel cell is used as a topping combustor tobar) fuel cell in series with the power turbine. the compressor turbine.  The topping fuel cellMost of the fuel is introduced into the SOFC. generates additional electrical power whileAbout 50 percent of the chemical energy providing a thermal exhaust at (870EC).  Theentering the fuel cell is converted to electrical calculated fuel to electricity efficiencies arepower.  Fuel cell exhaust gas expands through greater than 70 percent for the combined fuelthe second turbine in series with the fuel cell to cell/gas turbine system of 1-5 MW size (7,8). generate additional power.  Although the total Figure 4 shows the dual fuel cell/gas turbinefuel flow to the system increases, so does the system configuration.  System parameter total power output, therefore increasing theTable 3.  Low Pressure Fuel Cell Power               Plant Performance (NG-GT/FC)Compressor Air, lb/hr 40870Turbine Fuel, lb/hr 165LP Fuel Cell Fuel, lb/hr 979CT Power, MW 1.3Fuel Cell Power, MW 3.1Power Turbine, MW 1.5Power Out, MW 4.6System Efficiency, %LHV 64.4Compression Ratio 8.8Turbine Inlet, °F/°C 1580/860C. Turbine Outlet, °F/°C 1178/637P. Turbine Outlet, °F/°C 1204/651Power Plant Exhaust, °F/°C 350/177Figure 4.  Gas Turbine/Two Fuel Cells                   (NG-GT/FC2)Table 4.  Two Pressure Fuel Cell Power               Plant Performance               (NG-GT/FC2-5 MW)Compressor Air, lb/hr 40870LP Fuel Cell Fuel, lb/hr 630HP Fuel Cell Fuel, lb/hr  750CT Power, MW 1.3Power Turbine, MW 1.5LP Fuel Cell Power, MW 2.1HP Fuel Cell Power, MW 2.6Power Out, MW 6.2System Efficiency, %LHV 71.9 Compression Ratio 8.8Turbine Inlet, °F/°C 1580/860Turbine Outlet, °F/°C 1200/649Power Plant Exhaust, °F/°C 299/148values and ASPEN calculation results are shownin Table 4. Table 5 presents a summary of fuel toThe small (1-5 MW) fuel cell and the fuelcell/gas turbine systems are ideal for distributedpower generation.  Distributed locations inresidential areas are possible because of theenvironmentally clean and low noisecharacteristics of the fuel cell.  Furthermore, thecost of the system is potentially lower than thefuel cell-steam cycle system, since the expensivesteam cycle is replaced by a high efficiency gasturbine.  A lower total system cost is the primarybenefit obtained by coupling the fuel cell and gasturbine power generation systems.  Labor costsare also lower because an operator is constantlyrequired for steam turbines, while many states donot require an operator constantly on duty forgas turbines.  The integrated fuel cell and gasturbine are well suited to accomplish thisstrategy, allowing for an early introduction ofthe technology.electrical efficiencies for current advanced powergenerating systems calculated by the Table 5.  Comparison of Power Generating             TechnologiesEfficiencyTechnologyConfigurationLHV%HHV%NG-IFCFC GT-Fuel Cell-HRSG74 67NG-SOFCC GT-Fuel Cell-HRSG74 67NG-GT/FC2-5MWGT/2 Fuel Cell 72 65 NG-GT/FC GT/Fuel Cell 65 60MCFC-ST Fuel Cell-HRSG 65 60SOFC-ST Fuel Cell-HRSG 63 58ATS utility Adv. Gas Turb-HRSG62 56GTCC-200MWGas Turbine-HRSG56 51GTRC- 5MWGas Turbine/Recup C43 40PC/FGD PulverisedCoal/FGD-- 35Table 6.  Advantages of Fuel Cell/Gas                Turbine TechnologiesSystem has lower capital costs and life coststhan FC  +  ST.Near constant efficiency over a widetemperature range.Low temperature turbine operation results inno blade cooling.Ideal size for distributed power.Higher efficiency - reduced CO2 emission.Remains quiet operation.ASPEN simulator.  A quick comparison sug-gests that the fuel cell/gas turbine system is twiceas efficient as the baseline pulverized coal powerplant, reducing fuel consumption and CO2emissions by 50 percent. Summary ReferencesASPEN simulations of power generation (1) Rath, L.K., P.H. Le, and F.A. Sudhoff,systems indicate potential advantages of "Configuration and Performance of Fuel-developing a fuel cells/gas turbine system Cell Combined-Cycle Options,"without a steam cycle.  The synergistic effects Proceedings of the Workshop on Verycould improve electrical conversion efficiencies High Efficiency Fuel Cell/Gas Turbineto greater than 70 percent (LHV).  Also, it Power Cycles, DOE/METC-96/1024simultaneously reduces fuel consumption and (DE96000644), 21, Oct. (1995).environmental emissions by 50 percent whencompared to the baseline standard pulverizedcoal-fired power plant.The 5 MW system size is ideal for dis-tributed power generation.  Additionally, thecapital and life costs of the fuel cell/gas turbinesystem are potentially lower than a basic fuel cellor fuel cell-steam turbine system, because somepower is produced by a simple-cycle gas turbine.Further development and acceptance ofthis combined system allows a fuel cell to beintroduced to the market along with a gas tur-bine having a high response, low cost, and fuelflexibility.  The gas turbine is provided theopportunity to expand into environmental mar-kets in non-attainment areas and meet stringentemission regulations.  Table 6 summarizes theadvantages of the fuel cell/gas turbine powergeneration system.(2) Hendriks, R., Heron Turbine PrototypeTest Results, presented at 20thInternational Congress on CombustionEngines, (CIMAC), London (1993).(3) Stambler, I., "Recuperated 5 MW ATSgas turbine to be ready for field testing in1998," Gas Turbine World, Vol. 26 No.1, 30 (1996).(4) Williams, M.C., P.L. Micheli, and E.L.Parsons, Jr. Proceedings of the Fuel Cells'95 Review Meeting, DOE/METC-95/1020 (DE96000554), 30, Aug. (1995).(5) Bessette, N.F., and R.A. George,"Electrical Performance of Westing-house's Air Electrode Supported SolidOxide Fuel Cell," presented at 2ndInternational Fuel Cell Conference,February 5-7, 1996, Kobe, Japan.(6) Bevc, F.P., W.L. Lundberg, and D.M. Bachovchin, "SolidOxide Fuel Cell Combined Cycles," Presented at ASMETurbo EXPO '96, Birmingham, U.K., June 10-13, 1996.(7) Hendriks, R., H.J.Ankersmit, and L.J.M.J. Blomen,"Heron Turbine Integrated Systems with HydrogenTechnology and Fuel Cells," Presented at 21stInternational Congress of Combustion Engines, (CIMAC),InterLaken (1995).(8) Parker, W.G., and F.P. Bevc, "Surecell  Integrated SolidTMOxide Fuel Cell/Combustion Turbine Power Plants forDistributed Power Applications," Presented at 2ndInternational Fuel Cell Conference, Kobe, Japan,February (1996).

Fuel cell/gas turbine system performance studies

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Fuel cell/gas turbine system performance studies

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