Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Enhancement of the Electrical Efficiency of Commercial Fuel Cell Units by Means of an Organic Rankine Cycle: A Case Study

[+] Author and Article Information
Carlo De Servi

e-mail: carlo.deservi@polimi.it

Stefano Campanari

e-mail: stefano.campanari@polimi.it
Politecnico di Milano,
Department of Energy,
Via Lambruschini 4,
20156 Milano, Italy

Alessio Tizzanini

Enel Ingegneria e Ricerca SpA,
Via Mantova 24,
00198 Roma, Italy
e-mail: alessio.tizzanini@enel.com

Claudio Pietra

Turboden s.r.l.,
Via Cernaia 10,
25124 Brescia, Italy

The occupational exposure limit, the threshold below which a toxic substance has no effect on the health of the workers for an exposure period of 8 h per day, is 1 ppm for benzene, against 100 ppm of toluene and xylene, and 300 ppm of R245fa. Since toluene is currently employed in ORC systems and the toxicity level of the other considered aromatic hydrocarbons, when available, is comparable to that one of toluene (and also of some refrigerants), it is assumed that only benzene is affected by a level of toxicity incompatible with ORC applications.

The maximum allowable operating pressure of the turbine is calculated as the nominal operating pressure plus a safety margin of 3 bar.

1Corresponding author.

Contributed by the International Gas Turbine Institute of (IGTI) ASME for publication in the Journal of Engineering for Gas Turbines andPower. Manuscript received February 29, 2012; final manuscript received October 21, 2012; published online March 18, 2013. Assoc. Editor: Piero Colonna.

J. Eng. Gas Turbines Power 135(4), 042309 (Mar 18, 2013) (11 pages) Paper No: GTP-12-1063; doi: 10.1115/1.4023119 History: Received February 29, 2012; Revised October 21, 2012

Among the various fuel cell (FC) systems, molten carbonate fuel cells (MCFC) are nowadays one of the most promising technologies, thanks to the lower specific costs and a very high electrical efficiency (net low heating value (LHV) electric efficiency in the range 45%–50% at MWel scale using natural gas as fuel). Despite this high performance, MCFC rejects to the ambient almost half of the fuel energy at about 350–400 °C. Waste heat can be exploited in a recovery Rankine cycle unit, thereby enhancing the electric efficiency of the overall system. Due to the temperature of the heat source and the relatively small power capacity of MCFC plants (from few hundred kWel to 10 MWel), steam Rankine cycle technology is uneconomical and less efficient compared to that of the organic Rankine cycle (ORC). The objective of this work is to verify the practical feasibility of the integration between a MCFC system (topping unit) and an ORC turbogenerator (bottoming unit). The potential benefits of the combined plant are assessed in relation to a commercial MCFC stack. In order to identify the most suitable working fluids for the ORC system, organic substances are considered and compared. The figure of merit is the maximum net power of the overall system. Finally, the economical benefits of the integration are determined by evaluating the levelized cost of electricity (LCOE) of the combined plant, with respect to the standalone MCFC system. In order to assess the economic viability of the bottoming power unit, two cases are considered. In the first one, the ORC power output is approximately 500 kWel; in the latter, about 1 MWel. Results show that the proposed solution can increase the electrical power output and efficiency of the plant by more than 10%, well exceeding 50% overall electrical efficiency. In addition, the LCOE of the combined power plant is 8% lower than the standalone MCFC system.

Copyright © 2013 by ASME
Your Session has timed out. Please sign back in to continue.


Angelino, G., and Colonna di Paliano, P., 2000, “Organic Rankine Cycles (ORCs) for Energy Recovery From Molten Carbonate Fuel Cells,” Proceedings of the 35th Intersociety Energy Conversion Engineering Conference, Las Vegas, NV, July 24–28.
Angelino, G., and Colonna di Paliano, P., 2000, “Air Cooled Siloxane Bottoming Cycle for Molten Carbonate Fuel Cells,” Fuel Cell Seminar, Portland, OR, October 30–November 2.
Remick, R. J., Wheeler, D., and Singh, P., “MCFC and PAFC R&D Workshop Summary Report,” U. S. DOE, January 2010, http://www1.eere. energy.gov/
Campanari, S., Iora, P., Macchi, E., and Silva, P., 2007, “Thermodynamic Analysis of Integrated MCFC/Gas Turbine Cycles for Sub-MW and Multi-MW Scale Power Generation,” ASME J. Fuel Cell Sci. and Technol., 4, pp. 308–316. [CrossRef]
Di Pippo, R., 2005, Geothermal Power Plants: Principles, Applications and Case Studies, Elsevier, New York.
Aspen Technology Inc., 2011, Aspen Plus v. 7.3, Burlington, MA.
The MathWorks Inc., 2011, MATLAB 7.12, Natick, MA.
Moreno, A., McPhail, S., and Bove, R., 2008, “International Status of Molten Carbonate Fuel Cell (MCFC) Technology,” Joint Research Centre–Institute for Energy, JRC Scientific and Technical Report EUR 23373 EN, European Commission, Luxembourg.
FuelCell Energy, 2011, private communication.
FuelCell Energy, 2010, DFC3000: Direct FuelCell Power Plant Applications Guide, FuelCell Energy, Danbury, CT.
Lai, N. A., Wendland, M., and Fischer, J., 2011, “Working Fluids for High-Temperature Organic Rankine Cycles,” Energy, 36, pp. 199–211. [CrossRef]
Angelino, G., and Invernizzi, C. M., 1993, “Cyclic Methylsiloxanes as Working Fluids for Space Power Cycles,” ASME J. Sol. Energy Eng., 115, pp. 130–137. [CrossRef]
Drescher, U., and Brüggemann, D., 2007, “Fluid Selection for the Organic Rankine Cycle (ORC) in Biomass Power and Heat Plants,” Appl. Therm. Eng., 27, pp. 223–228. [CrossRef]
Angelino, G., and Invernizzi, C., 2003, “Experimental Investigation on the Thermal Stability of Some New Zero ODP Refrigerants,” Int. J. Refrig., 26(1), pp. 51–58. [CrossRef]
Zyhowski, G. J., “Honeywell Refrigerants Improving the Uptake of Heat Recovery Technologies,” http://www.honeywell-orc.com/wp-content/uploads/2011/09/Honeywell-Refrigerants-Improve-Uptake-Heat-Recovery-Technologies.pdf
Schroeder, D. J., and Leslie, N., 2010, “Organic Rankine Cycle Working Fluid Considerations for Waste Heat to Power Applications,” ASHRAE Trans., 116(Part 1), pp. 525–533.
Andersen, A., and Bruno, T., 2005, “Rapid Screening of Fluids for Chemical Stability in Organic Rankine Cycle Applications,” Ind. Eng. Chem. Res., 44, pp. 5560–5566. [CrossRef]
Havens, V. N., Ragaller, D. R., Silbert, L., and Miller, D., 1987, “Toluene Stability Space Station Rankine Power Systems,” Proceedings of the 22nd Intersociety Energy Conversion Engineering Conference (IECEC), Philadelphia, PA, August 10–14.
van Buijtenen, J. P., 2009, “The Tri-O-Gen Organic Rankine Cycle: Development and Perspectives,” Power Eng., 13(1), pp. 4–12.
Ginosar, D. M., Petkovic, L. M., and Guillen, D. P., 2011, “Thermal Stability of Cyclopentane as an Organic Rankine Cycle Working Fluid,” Energy Fuels, 25(9), pp. 4138–4144. [CrossRef]
Calderazzi, L., and Colonna, P., 1997, “Thermal Stability of R-134a, R-13I1, R-7146, R-125 Associated With Stainless Steel as a Containing Material,” Int. J. Refrig., 20, pp. 381–389. [CrossRef]
Colonna, P., Nannan, N. R., Gurdone, A., and Lemmon, E. W., 2006, “Multiparameter Equations of State for Selected Siloxanes,” Fluid Phase Equilib., 244, pp. 193–211. [CrossRef]
Colonna, P., Nannan, N. R., and Gurdone, A., 2008, “Multiparameter Equations of State for Siloxanes: [(CH3)3-Si-O1/2]2-[O-Si-(CH3)2]i=1,…,3, and [O-Si-(CH3)2]6,” Fluid Phase Equilib., 263(2), pp. 115–130. [CrossRef]
Prabhu, E., 2006, “Solar Trough Organic Rankine Electricity System. Stage 1: Power Plant Optimization and Economics,” Subcontract Report No. NREL/SR-550-39433.
Angelino, G., Invernizzi, C., and Macchi, E., 1991, “Organic Working Fluid Optimization for Space Power Cycles,” Modern Research Topics in Aerospace Propulsion, Springer-Verlag, New York.
Colonna di Paliano, P., 1996, “Fluidi di Lavoro Multi Componenti Per Cicli Termodinamici di Potenza (Multicomponent Working Fluids for Power Cycles),” Ph.D. thesis, Politecnico di Milano, Milano, Italy.
Leslie, N. P., Zimron, O., Sweetser, R. S., and Stovall, T. K., 2009, “Recovered Energy Generation Using an Organic Rankine Cycle System,” ASHRAE Trans., 115(Part I), pp. 220–230.
Lemmon, E. W., Huber, M. L., and McLinden, M. O., 2010, “NIST Standard Reference Database 23: Reference Fluid Thermodynamic and Transport Properties-REFPROP, Version 9.0”, National Institute of Standards and Technology, Standard Reference Data Program, Gaithersburg, MD.
“NIST Chemistry WebBook,” NIST, http://webbook.nist.gov/chemistry/
Calm, J. M., and Hourahan, G. C., 2011, “Physical, Safety and Environmental Data for Current and Alternative Refrigerants,” Proceedings of 23rd International Congress of Refrigeration (ICR2011), Prague, Czech Republic, August 21–26.
Papadopoulos, A. I., Stijepovic, M., and Linke, P., 2010, “On the Systematic Design and Selection of Optimal Working Fluids for Organic Rankine Cycles,” Appl. Therm. Eng., 30, pp. 760–769. [CrossRef]
Maizza, V., and Maizza, A., 1996, “Working Fluids in Non-Steady Flows for Waste Energy Recovery Systems,” Appl. Therm. Eng., 16(7), pp. 579–590. [CrossRef]
Chen, H., Goswami, D. Y., and Stefanakos, E. K., 2010, “A Review of Thermodynamic Cycles and Working Fluids for the Conversion of Low-Grade Heat,” Renewable Sustainable Energy Rev., 14, pp. 3059–3067. [CrossRef]
Marciniak, T. J., Krazinski, J. L., Bratis, J. C., Bushby, H. M., and Buyco, E. H., “Comparison of Rankine-Cycle Power Systems: Effects of Seven Working Fluids,” Argonne National Laboratory Report No. ANL/CNSV-TM—87.
Turboden s.r.l., http://www.turboden.eu
Martelli, E., Nord, L. O., and Bolland, O., 2012, “Design Criteria and Optimization of Heat Recovery Steam Cycles for Integrated Reforming Combined Cycles With CO2 Capture,” Appl. Energy, 92, pp. 255–268. [CrossRef]
Box, M. J., 1965, “A New Method for Constraint Optimization and a Comparison With Other Methods,” Comput. J., 8, pp. 42–52. [CrossRef]
Stijepovic, M. Z., Linke, P., Papadopoulos, A. I., and GrujicA. S., 2012, “On the Role of Working Fluid Properties in Organic Rankine Cycle Performance,” Appl. Therm. Eng., 36, pp. 406–413. [CrossRef]
Macchi, E., 1977, “Design Criteria for Turbines Operating With Fluids Having a Low Speed of Sound in Closed Cycle Gas Turbines,” Lecture Series 100 on Closed Cycle Gas Tubines, Von Karman Institute for Fluid-Dynamics, Bruxelles.
Lozza, G., Macchi, E., and Perdichizzi, A., 1982,“On the Influence of the Number of Stages on the Efficiency of Axial-Flow Turbines,” 27th International Gas Turbine Conference and Exhibition, London, April 18–22.
Craig, H. R. M., and Cox, H. J. A., 1970, “Performance Estimation of Axial Flow Turbines,” Proc. Inst. Mech. Eng., 185, pp. 407–424. [CrossRef]
Bronicki, L. Y., 1999, “Organic Rankine Cycle Power Plant, for Waste Heat Recovery,” 13th Symposium on Industrial Applications of Gas Turbines, Banff, Alberta, Canada, October.
“Costi di Produzione di Energia Elettrica da Fonti Rinnovabili,” Rapporto Commissionato da AEEG al Politecnico di Milano - Dipartimento di Energia, Dicembre 2010, http://www.autorita.energia.it/allegati/docs/11/103-11arg_rtalla.pdf


Grahic Jump Location
Fig. 1

Saturation curves of selected fluids

Grahic Jump Location
Fig. 2

Layout of the integrated plant

Grahic Jump Location
Fig. 3

The composite temperature thermal power curve (T-Q curve) of the exhaust gases and the working medium. Pinch point does not occur at the ends of PHE.

Grahic Jump Location
Fig. 4

Composite temperature thermal power curve (T-Q curve) of the exhaust gases and of the working medium. Pinch point occurs at the inlet of the working fluid in PHE.

Grahic Jump Location
Fig. 5

Temperature–entropy diagram for cyclohexane

Grahic Jump Location
Fig. 7

Temperature–entropy diagram for MM

Grahic Jump Location
Fig. 8

ORC capital cost (€/kW)

Grahic Jump Location
Fig. 10

LCOE reduction obtained by implementing the ORC unit



Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In