This work proposes a process simulation of high efficiency intermediate-temperature (660–730°C) SOFC systems for promising applications in the foreseeable future distributed power generation sector. Two case-studies have been considered: the kW-scale unit proposed by Ceramic Fuel Cell Limited (CFCL), which reaches up to 68% stack DC efficiency, and the FuelCell Energy (FCE) SOFC system, where a 65% DC efficiency has been verified on a 10 kW module. Both systems can be applied to distributed generation, yielding 60%+ net electric efficiency (LHV basis) from natural gas at small scale.
This study aims at calibrating the two considered SOFC balance of plants with the Politecnico di Milano in-house software GS. Throughout a zero-dimensional model of the complete system a validation of the manufacturer’s claimed performance is possible. The general module configuration is made up of a natural gas pre-treating processor, a SOFC stack, an anodic spent fuel combustor and a waste heat recovery system for CHP applications. A pre-reforming adiabatic reactor has been proven to be an efficient choice to reduce the higher hydrocarbon chains content in the fuel stream and therefore to lessen the burden on the anodic channel, especially in terms of solid carbon deposition. The fuel is then pre-heated and, in the FCE case-study, mixed with the anodic outlet recycle; this last solution is regarded as of utmost importance for the attainment of the high overall fuel utilisation (≈80–85%) factors necessary to reach the proposed high efficiency targets, as well as to provide the steam required by the internal reforming process.
Both the considered fuel cell systems performance have been verified and their extremely high efficient operation proven, according to those reported by their manufacturers.
In addition to the process simulation, the work lays the foundations for a more thorough SOFC stack modelling throughout a 2D in-house developed software. This analysis gives valuable insights on the geometry characterisation and on the flow arrangement, as well as on their effects on cell internal temperature and composition profiles. In particular, the proposed analysis focuses on the case of a planar cross-flow arrangement, representative of the latter of the two case-studies. The understanding of the internal behaviour of the systems provides useful information to optimise the cell performance and design.