Modeling, design, testing and analysis of biogas-fed SOFC power plants

The present work is related to the complete analysis of biogas-fed SOFC system. The first part of the work has been related to a review on the concept of polygeneration system and on the analysis of the current status of SOFC installations, especially when fed with biogas. The use of a renewable fuel, coupled with carbon capture, can lead to negative emissions plants, defined as key technologies for reaching the goals set in the Paris Agreement. Furthermore, biogas and SOFC show many affinities which have been discussed in the works: from the high efficiency at low sizes to the availability of already existing subsidy schemes for electricity production. An analysis of the potential biogas production in EU is proposed, with focus on wastewater treatment plants. In this particular area, the work tries to point out the numbers of potential installed power by using SOFCs. The experimental and modeling activities are then proposed. The PhD activity is linked to two European projects, SOFCOM and DEMOSOFC. The first project is related to the analysis of biogas fed SOFC system with carbon capture and re-use. In this context, a demonstration plant has been developed and tested in the SMAT Castiglione wastewater treatment plant. Results show an easy process for the CO2 capture from the SOFC exhaust, thus pointing SOFC as a key technology in the framework of negative carbon emissions plants. More criticalities have been found in the choice of CO2 utilization for production of algae in a photobioreactor: the unstable quality of the inlet wastewater coming from the plant, the fluctuating algae productivity as function of the weather conditions, and the algae attachment to the pipe, pointed out a need for improvements and research on this technology. The experimental activity has been coupled with a modeling activity on the same concept of biogas fed SOFC, with the possibility of a downstream carbon capture and use/ sequestration. Different plant layout and different system sizes have been analyzed from a technical and economical point of view. Finally, the analysis of a real industrial size SOFC system is proposed. This activity has been developed in the framework of the DEMOSOFC EU project, where the first industrial size biogas fed SOFC system will be installed. Being the first installation of its kind, many issued and improvements have been detected. The analysis is related to the system design and description, for what concerning plant integration (electrical and thermal), system operation, and biogas processing. Biogas processing has been especially pointed out as a key component in a biogas-fed SOFC system. Because of the low admissible contaminants levels for fuel cell, a new and dedicated cleaning unit is required, which is not currently available on the market. The processing unit design is proposed and ongoing experimental activity on the adsorption with activated carbons are proposed. The main harmful contaminants found in wastewater biogas are sulphur (in the form of H2S) and siloxanes (mainly D4 and D5).