Energy analysis of an SOFC system fed by syngas

Abstract

The solid oxide fuel cells (SOFC) system fed by alternative fuels such as syngas, i.e. the gas produced by woody biomass gasification, can produce electric energy with high conversion efficiency and thermal energy. A part of carbon monoxide (CO) in syngas is directly converted into electric energy in the fuel cell anode and the remaining part with steam can be converted into hydrogen by the Water Gas Shift (WGS) chemical reaction. The WGS chemical reaction is set up according to the direct internal mode (Direct Internal Water Gas Shift, DIWGS). A part of the anode exhaust gas, consisting mainly of steam and carbon dioxide, can be recirculated at the fuel cell anode inlet. The syngas composition, the part of CO in syngas directly converted into electric energy in the fuel cell anode and the percentage of recirculated anode exhaust gas influence the SOFC system performances. In this article a zero-dimensional and stationary simulation model of an SOFC system fed by syngas in cogenerative arrangement is formulated and implemented in the Matlab environment by which the SOFC system performances were evaluated. Furthermore, the simulation model also considers the anodic carbonation phenomenon and evaluates the amount of carbon that can be formed in the anode at chemical equilibrium. All the above-mentioned variables and in particular the fraction of CO in syngas directly converted into electric energy in the fuel cell anode affect the SOFC system performances and at the anode the increase of recirculation fraction reduces the carbonation risk.