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Research Papers

Experimental Modeling of Transients in Large SOFC Systems

[+] Author and Article Information
P. Leone

e-mail: pierluigi.leone@polito.it

A. Lanzini

e-mail: andrea.lanzini@polito.it
Dipartimento di Energia,
Politecnico di Torino,
Corso Duca degli Abruzzi 24,
10129 Torino, Italy

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF FUEL CELL SCIENCE AND TECHNOLOGY. Manuscript received January 31, 2012; final manuscript received October 23, 2012; published online January 15, 2013. Assoc. Editor: Ken Reifsnider.

J. Fuel Cell Sci. Technol 10(1), 011004 (Jan 15, 2013) (11 pages) Paper No: FC-12-1007; doi: 10.1115/1.4023217 History: Received January 31, 2012; Revised October 23, 2012

This work investigates the dynamic operation of a large solid oxide fuel cell (SOFC) system using the system identification modeling approach. Transient modeling can be of particular interest in order to describe and optimize start-up and shut-down procedures in SOFC systems; moreover, mathematical description of transients is helpful in the diagnostic of hazardous conditions during dynamic operation (i.e., load following). Physical based models—described by differential equations—are usually complex and need significant computing time. To achieve real-time capability, the focus is on empirical models. In this study, the transient operation of a large SOFC generator is reproduced by using the system identification approach that is based on the definition of a black-box model and on the identification of main model coefficients based on real experimental data. In particular, the start-up of the system and its dynamics under fuel sensitivity experiments are investigated. First, the work valuably shows some experimental results of a large SOFC generator under dynamic operation. In particular, modeling results show that the system identification approach is an effective tool for the description of the transient behavior of SOFC large systems. The simulation of the start-up of a 100 kWe (electric) SOFC system shows the possibility to save ∼20% of start-up time using an electric air heater rated a 30% in power than the nominal one. The increase of natural gas flow during the start-up operation is instead not beneficial in term of yielding a faster procedure; rather, it leads to an excessive cooling of the stack due to internal reforming of natural gas (the higher amount of fuel burnt in the combustion zone does not lead to a more efficient way to preheat the cathode air). The results of this work are fully supported by experimental data available from a real generator running in Italy through years 2006–2009 and thus believed to be a valuable contribution for the scientific and engineering community.

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References

Figures

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Fig. 6

Identification of a MISO model for the postcombustion chamber temperature during fuel utilization sensitivity experiments

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Fig. 1

A schematic diagram of the SOFC system with well-defined inputs and outputs of the system. (a) MISO structure for the analysis of dynamics during fuel utilization sensitivity experiments. (b) MIMO structure for the analysis of thermal dynamics during start-up. (c) MISO structure for the analysis of electrical dynamics during start-up.

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Fig. 2

Transients of the stack voltage during fuel utilization sensitivity experiments. Voltage is expressed in volts.

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Fig. 3

Transients of the postcombustion temperature during fuel utilization sensitivity experiments. Combustion temperature is expressed in  °C.

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Fig. 4

Identification of different structures of (a) SISO and (b) MISO linear models for stack voltage

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Fig. 14

Voltage behavior during start-up analyzed by means of an Hammerstein–Weiner model

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Fig. 5

Validation of the best MISO models for the simulation stack voltage transients due to fuel utilization sensitivity experiments

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Fig. 7

Validation of MISO models against different experimental data sets

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Fig. 8

Typical start-up operation of a SOFC large system

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Fig. 9

Simulation of SOFC system start-up by using an identified ARX model structure

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Fig. 10

Control strategy for reducing start-up time in SOFC systems: increasing the heaters' electrical power

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Fig. 11

Control strategy for reducing start-up time in SOFC systems: the variation of control parameters in the case of 2nd strategy

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Fig. 12

Control strategy for reducing start-up time in SOFC systems: increase of natural gas flow

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Fig. 13

Control strategy for reducing start-up time in SOFC systems: the variation of control parameters in the case of 3rd strategy

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