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TECHNICAL PAPERS

# Gas Turbine Assessment for Air Management of Pressurized SOFC/GT Hybrid Systems

[+] Author and Article Information
Alberto Traverso

Thermochemical Power Group, University of Genova, via Montallegro 1, 16145 Genova, Italyalberto.traverso@unige.it

Aristide Massardo

Thermochemical Power Group, University of Genova, via Montallegro 1, 16145 Genova, Italy

Rory A. Roberts, Scott Samuelsen

National Fuel Cell Research Center, University of California, Irvine, CA 92697-3550

Jack Brouwer

National Fuel Cell Research Center, University of California, Irvine, CA 92697-3550jb@nfcrc.uci.edu

J. Fuel Cell Sci. Technol 4(4), 373-383 (Jun 09, 2006) (11 pages) doi:10.1115/1.2714567 History: Received November 29, 2005; Revised June 09, 2006

## Abstract

This paper analyzes and compares transient and steady-state performance characteristics of different types of single-shaft turbo-machinery for controlling the air through a pressurized solid oxide fuel cell (SOFC) stack that is integrated into a SOFC/GT pressurized hybrid system. Analyses are focused on the bottoming part of the cycle, where the gas turbine (GT) has the role of properly managing airflow to the SOFC stack for various loads and at different ambient conditions. Analyses were accomplished using two disparate computer programs, which each modeled a similar SOFC/GT cycle using identical generic gas turbine performance maps. The models are shown to provide consistent results, and they are used to assess: (1) the influence of SOFC exhaust composition on expander behavior for on-design conditions, (2) the off-design performance of the bypass, bleed, and variable speed controls for various part-load conditions and for different ambient conditions; (3) the features of such controls during abrupt transients such as load trip and bypass/bleed valve failure. The results show that a variable speed microturbine is the best option for off-design operation of a SOFC/GT hybrid system. For safety measures a bleed valve provides adequate control of the system during load trip. General specifications for a radial GT engine for integration with a $550kW$ pressurized SOFC stack are identified, which allow operation under a wide range of ambient conditions as well as several different cycle configurations.

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## Figures

Figure 24

Air flow rate through the regulating valve (zero for the case of variable N) versus time

Figure 1

Basic schematic of a single shaft radial compressor and turbine

Figure 2

(a) Compressor pressure ratio versus corrected mass flow (nondimensional); and (b) compressor efficiency versus pressure ratio (nondimensional)

Figure 9

Surge margin for 1atm pressure and various ambient temperatures

Figure 10

Microturbine speed for 15°C and various pressures (atm)

Figure 11

Microturbine power for 15°C and various pressures (atm)

Figure 12

Bypassed percent mass flow for 1atm pressure and various ambient temperatures

Figure 13

Microturbine power for 1atm pressure and various ambient temperatures

Figure 14

High-pressure recuperator exit temperature for 1atm pressure and various ambient temperatures

Figure 15

Bypassed percent mass flow for 15°C and various pressures (atm)

Figure 16

Microturbine power for 15°C and various pressures (atm)

Figure 3

(a) Turbine expansion ratio versus corrected mass flow (nondimensional); and (b) turbine efficiency versus expansion ratio (nondimensional)

Figure 4

SOFC/GT hybrid system schematic

Figure 5

VI curve for the single-cell SOFC model

Figure 6

Speed of microturbine for 1atm pressure and various ambient temperatures

Figure 7

Microturbine power for 1atm pressure and various ambient temperatures

Figure 8

High-pressure recuperator exit temperature for 1atm pressure and various ambient temperatures

Figure 17

Bleed percent mass flow for 1atm pressure and various ambient temperatures

Figure 18

Microturbine power for 1atm pressure and various ambient temperatures

Figure 19

Bleed percent mass flow for 15°C and various pressures (atm)

Figure 20

Microturbine power for 15°C and various pressures (atm)

Figure 21

Delivery pressure at compressor exit for standard control cases (Tamb=15°C and Pamb=1atm)

Figure 22

Microturbine rotational speed versus time

Figure 23

Trace of the compressor operating point in the nondimensional mass flow–compression ratio map

Figure 25

Air flow rate in the recuperator cold side versus time

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