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Research Papers: Energy Systems Analysis

Exergetic Performance Analysis of a Gas Turbine Cycle Integrated With Solid Oxide Fuel Cells

[+] Author and Article Information
Ibrahim Dincer1

Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canadaibrahim.dincer@uoit.ca

Marc A. Rosen

Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canadamarc.rosen@uoit.ca

Calin Zamfirescu

Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, ON, L1H 7K4, Canadacalin.zamfirescu@uoit.ca

1

Corresponding author.

J. Energy Resour. Technol 131(3), 032001 (Aug 04, 2009) (11 pages) doi:10.1115/1.3185348 History: Received December 17, 2007; Revised March 10, 2009; Published August 04, 2009

Energy and exergy assessments are reported of integrated power generation using solid oxide fuel cells (SOFCs) with internal reforming and a gas turbine cycle. The gas turbine inlet temperature is fixed at 1573 K and the high-temperature turbine exhaust heats the natural gas and air inputs, and generates pressurized steam. The steam mixes at the SOFC stack inlet with natural gas to facilitate the reformation process. The integration of solid oxide fuel cells with gas turbines increases significantly the power generation efficiency relative to separate processes and reduces greatly the exergy loss due to combustion, which is the most irreversible process in the system. The other main exergy destruction is attributable to electrochemical fuel oxidation in the SOFC. The energy and exergy efficiencies of the integrated system reach 70–80%, which compares well to the efficiencies of approximately 55% typical of conventional combined-cycle power generation systems. Variations in the energy and exergy efficiencies of the integrated system with operating conditions are provided, showing, for example, that SOFC efficiency is enhanced if the fuel cell active area is augmented. The SOFC stack efficiency can be maximized by reducing the steam generation while increasing the stack size, although such measures imply a significant and nonproportional cost rise. Such measures must be implemented cautiously, as a reduction in steam generation decreases the steam/methane ratio at the anode inlet, which may increase the risk of catalyst coking. A detailed assessment of an illustrative example highlights the main results.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

SOFC-gas turbine cycle with steam generation for methane conversion in the SOFC. Devices are identified as follows: SOFC stack (1), combustion chamber (2), turbine (3), compressors (4 and 5), heat exchangers (6–8), evaporator (9), condenser (10), pump (11), separator (12), mixers (13 and 14), and flow divider valves (15 and 16). The anode and cathode of the SOFC stack are identified by a and b, respectively.

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Figure 2

Block diagram of the analyzed system

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Figure 3

Variation with fuel cell stack energy efficiency ηs of operational-circuit fuel cell voltage Vs and number of moles of oxygen nO2 crossing the fuel cell electrolyte (per mole of methane input to the overall system)

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Figure 4

Variation with operational-circuit fuel cell voltage Vs of circulating water flow rate nO2 (per mole of methane input to the overall system)

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Figure 5

Variations in electrical energy We and net work WM (at turbine) per mole of methane consumed in the combined SOFC-gas turbine system, with operational-circuit fuel cell voltage Vs

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Figure 6

Variations with operational-circuit fuel cell voltage Vs of overall exergy destruction and the exergy destruction in the SOFC stack and combustion chamber per mole of methane consumed in the combined SOFC-gas turbine system

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Figure 7

Variation with operational-circuit fuel cell voltage Vs of thermal efficiency ηT and exergy efficiency ηe for the integrated SOFC-gas turbine system. The operating region is between Vs=0.4–0.7 V.

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Figure 8

Energy and exergy diagram for the overall plant showing flows of energy (values not in parentheses) and exergy (values in parentheses associated with flows). Also, exergy destruction for the overall plant is shown in parentheses in the box, which represents the plant. Flows are grouped into three categories: inputs, product outputs, and waste emissions. All values are in kJ/mole of methane input.

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Figure 9

Exergy destructions per mole of methane consumed for the devices in the integrated system for the illustrative example, where Vs=0.61 V (corresponding to ηs=20%). Column labels correspond to devices in Fig. 1.

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Figure 10

Energy and exergy diagram for the SOFC-gas turbine plant showing flows of energy (values not in parentheses) and exergy (values in parentheses associated with flows), as well as exergy destructions (values in parentheses in the boxes representing plant devices or sections). Devices are grouped into the three categories described in the text, to simplify the diagram. All values are in kJ/mole of methane input.

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