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Research Papers: Gas Turbines: Cycle Innovations

# Time Characterization of the Anodic Loop of a Pressurized Solid Oxide Fuel Cell System

[+] Author and Article Information
A. Traverso

Thermochemical Power Group, Dipartimento di Macchine Sistemi Energetici e Trasporti, via Montallegro 1,  Università di Genova, 1614S Genova, Italyalberto.traverso@unige.it

F. Trasino

Thermochemical Power Group, Dipartimento di Macchine Sistemi Energetici e Trasporti, via Montallegro 1,  Università di Genova, 1614S Genova, Italyfrancesco.trasino@unige.it

L. Magistri

Thermochemical Power Group, Dipartimento di Macchine Sistemi Energetici e Trasporti, via Montallegro 1,  Università di Genova, 1614S Genova, Italyloredana.magistri@unige.it

A. F. Massardo

Thermochemical Power Group, Dipartimento di Macchine Sistemi Energetici e Trasporti, via Montallegro 1,  Università di Genova, 1614S Genova, Italymassardo@unige.it

J. Eng. Gas Turbines Power 130(2), 021702 (Feb 29, 2008) (9 pages) doi:10.1115/1.2772638 History: Received May 05, 2007; Revised May 09, 2007; Published February 29, 2008

## Abstract

A dynamic solid oxide fuel cell (SOFC) model was integrated with other system components (i.e., reformer, anodic off-gas burner, anodic ejector) to build a system model that can simulate the time response of the anode side of an integrated $250kW$ pressurized SOFC hybrid system. After model description and data on previous validation work, this paper describes the results obtained for the dynamic analysis of the anodic loop, taking into account two different conditions for the fuel flow input: in the first case (I), the fuel flow follows with no delay the value provided by the control system, while in the second case (II), the flow is delayed by a volume between the regulating valve and the anode ejector, this being a more realistic case. The step analysis was used to obtain information about the time scales of the investigated phenomena: such characteristic times were successfully correlated to the results of the subsequent frequency analysis. This is expected to provide useful indications for designing robust anodic loop controllers. In the frequency analysis, most phase values remained in the $0–180deg$ range, thus showing the expected delay-dominated behavior in the anodic loop response to the input variations in the fuel and current. In Case I, a threshold frequency of $5Hz$ for the pressure and steam to carbon ratio and a threshold frequency of $31Hz$ for the anodic flow were obtained. In the more realistic Case II, natural gas pipe delay dominates, and a threshold frequency of $1.2Hz$ was identified, after which property oscillations start to decrease toward null values.

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## Figures

Figure 3

Reformate stream composition under part-load conditions

Figure 4

Figure 1

Layout of SOFC system anode loop

Figure 2

A block of RRFCS fuel cell strips (5)

Figure 5

Ejector scheme and TPG ejector test rig in open loop configuration (9)

Figure 6

Ejector model validation under unsteady conditions in closed loop configuration (10)

Figure 12

Anodic ejector recirculation factor (Case I)

Figure 17

Bode diagram of the mass flow at the anodic side inlet (amplitudes are nondimensionalized with the reference 100% value of 0.0695kg∕s)

Figure 18

Bode diagram of the fuel cell stack inlet pressure (amplitudes are nondimensionalized with the reference 100% value of the cathode-anode differential pressure of 3000Pa)

Figure 19

Bode diagram of the STCR (amplitudes are nondimensionalized with the reference 100% value of 2.4)

Figure 20

Bode diagram of the ejector recirculation factor (amplitudes are nondimensionalized with the reference 100% value of 6.9)

Figure 13

Anodic side inlet mass flow (Case II)

Figure 16

Anodic ejector recirculation factor (Case II)

Figure 14

Anodic side average operating pressure (Case II)

Figure 15

STCR at anodic ejector outlet (Case II)

Figure 7

Molar fraction of residual hydrogen at stack anodic outlet (Case I)

Figure 8

Molar fraction of residual hydrogen at stack anodic outlet (Case II)

Figure 11

STCR at anodic ejector outlet (Case I)

Figure 9

Anodic side inlet mass flow (Case I)

Figure 10

Anodic side average operating pressure (Case I)

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