Analysis of a Solid Oxide Fuel Cell System with Low Temperature Anode Off-Gas Recirculation

Abstract

At Forschungszentrum Jülich, an SOFC system with anode off-gas recirculation loop operating at temperatures up to 160 °C is simulated. To analyze the effect of anode off-gas recirculation, a dynamical system model was implemented in Matlab/Simulink®. The results show that the recirculation rate has a significant effect on the electrical efficiency. In principle, at constant current density high recirculation rates decrease the cell voltage and increase the power demand of the recirculation blower. Therefore, the highest electrical efficiency can be reached with high system fuel utilization, low recirculation rate and in consequence high stack fuel utilization. On the other hand less amount of steam is available for the reforming reaction at low recirculation rates. Therefore, the minimum recirculation rate is determined by the risk of carbon formation. An optimal operation range to avoid carbon formation and to ensure a high electrical efficiency requires recirculation rates between 65 and 70 % and system fuel utilizations above 90 %.

Techno-Economic Optimization of an Integrated Biomass Waste Gasifier–Solid Oxide Fuel Cell Plant

“…In addition, both the recirculated CO 2 and H 2 O mitigate the risk for carbon deposition at the SOFC stack inlet (Colpan et al, 2007). Another commonly mentioned reason for AOG recirculation is its potential to increase the electrical output of the stack by recirculating unreacted fuel back to the inlet, hence "increasing the overall fuel utilization" (Dietrich et al, 2011;Peters et al, 2013;Engelbracht et al, 2015;Torii et al, 2016). However, there is a trade-off, as recirculating the AOG can also lead to fuel dilution and thus negatively impact the stack performance, depending on the fuel type, system layout, and operating conditions (Lee et al, 2011;Rokni, 2017).…”

Modeling of a Novel Atmospheric SOFC/GT Hybrid Process and Comparison with State‐of‐the‐Art SOFC System Concepts

“…The basic approach of improving the efficiency of simple once-through SOFC systems is the increase of the global fuel utilization FU while maintaining a suitable local fuel utilization FU at stack level. Two different pathways have been discussed in literature: (i) single-stage SOFC module with anode off-gas recirculation [25][26][27], and (ii) two-stage SOFC module with a fuel regenerator between the modules [13][14][15]28].…”

“…After mixing, the fuel stream is fed to the external reformer, where the reforming reactions take place. Due to the recirculated anode off-gas containing electrochemically produced steam, the system does not depend on an external water supply [26]. However, because of the endothermicity of the reforming process, thermal energy has to be provided, which is realized via purge gas combustion.…”