Thesis (D.Eng.)--Chulalongkorn University, 2007

The research focuses on the improvement of methane-fuelled solid oxide fuel cell system. Three improvements of the system were considered: 1) Operating under a non-uniform potential operation (SOFC-NUP), 2) Implementing a membrane reactor to the SOFC system (SOFC-MR) and 3) Integrating a CaO-CO₂ acceptor with the SOFC system (SOFC-CaO). For SOFC-NUP, the optimum split ratios of Sp,1 = 0.55 and Sp,2 = 0.45 was found to improve power density as high as 9.2%. In addition, the increase in the number of separated section (n) of the cell could increase the achieved maximum power density but less pronounced after n > 3. For SOFC-MR, an SOFC system integrated with a palladium membrane reactor operating at different modes; i.e., high pressure compressor (MR-HPC), vacuum pump (MR-V) and combined high pressure compressor and vacuum pump (MR-HPC-V) was considered. The power density of the SOFC was improved, depending on the increasing hydrogen recovery (). At high electrical efficiency, the SOFC-MR system became more attractive than the conventional system. It was found that the MR-HPC-V was the best operation mode among MR-SOFC systems. For the CaO-CO₂ acceptor SOFC systems, the CO₂ capture efficiency (Ec) depends on fresh feed CaO (F0), recycled CaO (FR) and amount of CO₂ ¬fed through. The CaO-CO₂ SOFC systems (i.e. CaO-After-Burner, CaO-After-SOFC and CaO-Before-SOFC) were compared with the conventional SOFC. Only CaO-Before-SOFC can improve SOFC performance which depends on both CO2 capture efficiency (Ec) and fuel utilization (Uf). The CaO-SOFC system can operate at lower cost than the conventional SOFC. The total added cost/reduced CO2 ($.mol-1) are in the sequence of the CaO-After-Burner > CaO-After-SOFC > CaO-Before-SOFC. Unfortunately, CaO-Before-SOFC can not reduce CO2 more than 40%. When the CO₂ reduction was required more than 40%, the CaO-After-SOFC was a suitable choice for the SOFC-CaO system.