Holistic Approach to Design, Test, and Optimize Stand-Alone SOFC-Reformer Systems

Abstract

Reliable electrical and thermal energy supplies are basic requirements for modern societies and their food supply. Stand-alone stationary power generators based on solid oxide fuel cells (SOFC) represent an attractive solution to the problems of providing the energy required in both rural communities and in rurally-based industries such as those of the agricultural industry. The great advantages of SOFC-based systems are high efficiency and high fuel flexibility. A wide range of commercially available fuels can be used with no or low-effort pre-treatment. In this study, a design process for stand-alone system consisting of a reformer unit and an SOFC-based power generator is presented and tested. An adequate agreement between the measured and simulated values for the gas compositions after a reformer unit is observed with a maximum error of 3 vol% (volume percent). Theoretical degradation free operation conditions determined by employing equilibrium calculations are identified to be steam to carbon ratio (H2O/C) higher 0.6 for auto-thermal reformation and H2O/C higher 1 for internal reforming. The produced gas mixtures are used to fuel large planar electrolyte supported cells (ESC). Current densities up to 500 mA/cm2 at 0.75 V are reached under internal reforming conditions without degradation of the cells anode during the more than 500 h long-term test run. More detailed electrochemical analysis of SOFCs fed with different fuel mixtures showed that major losses are caused by gas diffusion processes.

Experimental Investigation of Electrochemical Reactions Along SOFCs for Internal and External Reformed Methane

“…Hence, the in situ identification of the degradation mechanism is essential to operate SOFCs under optimal operating conditions and without early degradation. One way of in situ detection of degradation mechanisms is to use electrochemical impedance spectroscopy (EIS) measurements in combination with the distribution of relaxation times (DRT) method (19)(20)(21)(22). The results of these measurement methods are interpreted by using studies of similar cells and similar gas compositions.…”

“…We tested two single cells, one with externally reformed methane and one at internal reforming conditions. External reformation of methane is conducted under auto thermal reforming (ATR) conditions within a reformer test rig (19). The measured off gas composition of the reforming tests are synthetically mixed at the single cell test rig and fed to the SOFC.…”