Deep biogas cleaning through an innovative cryogenic system

The present work focuses its attention on the European project Waste2Watss, which aim to design and construct a large-scale biogas fed SOFC power plant. Biogas is produced from a large farm through anaerobic digestion, consisting mainly in methane and carbon dioxide, with a certain amount of contaminant to be removed. However, to ensure long-term SOFC operations, biogas feeding the cell should be ‘cleaned’ form sulphur compounds, siloxane and mercaptans. Up to now, many commercially available technologies aims to this purpose, even though for pure biomethane production. Therefore, the purpose of the present work is to design a proper biogas cleaning system based on cryogenics, avoiding the usage of chemicals or biological agents. The present work is based on what was done by the previous thesis writer, Falco Federico, who found a proper thermodynamic model describing the binary system CH4-CO2 and hence for the construction of the mixture phase diagrams. These data allow exploring different scenarios, aiming to the optimal one. The focus is paid on the P-x diagram at three different temperature: -100 °C, -90 °C and -80 °C. With these working conditions, a general system design is performed, under certain assumptions. Results were useful for Biokomp company, which is one of the eleven partners of Waste2Watts project, to have a clear picture of the overall system behaviour to be installed. Furthermore, once the thermodynamic behaviour is determined, an economic comparison between a traditional system and the analysed one is made, showing the advantages or disadvantages of making such a system.