Performance analysis of solid oxide fuel cell system fueled by methanol

Abstract

This thesis investigates performance of Solid Oxide Fuel Cell (SOFC) system fed by methanol. Two types of solid electrolyte, i.e. oxygen-ion (SOFC-O[superscript 2-]) and proton-conducting (SOFC-H[superscript +]) electrolyte are considered. The thesis consists of three main parts, firstly, determination of inlet steam: methanol ratio at boundary of carbon formation, secondly, comparison of theoretical performance between two types of electrolyte and different of flow pattern (i.e. mixed flow (MF) and plug flow (PF)) and, lastly, investigation on benefit of application of palladium membrane reactor in SOFC-O[superscript 2-] system. It was found from the thermodynamic calculation that the minimum steam: methanol ratio for which carbon formation is thermodynamically unfavoured decreases with increasing temperature. Comparison between the two types of electrolyte reveals that the SOFC-O[superscript 2-] requires lower steam for the prevention for carbon formation due to the water formed by the electrochemical reaction at the anode side. In the efficiency point of view SOFC-H[superscript +] shows higher efficiency than SOFC-O[superscript 2-]. It is demonstrated that the maximum efficiencies decrease with increasing temperature and follow the sequence: SOFC-H[superscript +] (PF) > SOFC-O[superscript 2-] (PF) > SOFC-H[superscript +] (MF) > SOFC-O[superscript 2-] (MF). The corresponding inlet steam: methanol ratios are at the carbon formation boundary for the SOFC-O[superscript 2-] electrolyte, but are about 1.31.5 times the stoichiometric ratio for the SOFC-H[superscript +]. Although the benefit from the lower steam requirement is realized for the SOFC-O[superscript 2-], the use of the SOFC-H[superscript +] electrolyte in the SOFCs is more promising in the theoretical consideration. Finally, it was found that for the SOFC system equipped with Palladium membrane reactor, at the same electrical efficiency of the conventional SOFC system the system requires smallerSOFC stack; however, additional cost of the membrane is required.