# The Effect of Biogas Origin on the Electricity Production by Solid Oxide Fuel Cells
## 3 Simulation  
By considering the above presented theory, in the THERMAS computational tool, the designed simulated power plant is based on an SOFC device where the electricity is produced while a steam reformer is incorporated to the system in order to convert the biogas entering the system to a hydrogen reach gas, therefore being suitable for utilization in the fuel cell. In this research study, the simulated fuel for the power plant's operation is a \"model biogas\", consisting of two main components, CH\({}_{4}\) and CO\({}_{2}\), while inert impurities (less than 2%) are also contained. Such a feedstock can be produced from several organic raw materials [17]: anaerobic digestion of waste materials [18], urban organic waste [19], solid waste in landfill [20], organic fraction of municipal solid waste [21], lignocellulosic biomasses [22] and anaerobic co-digestion of multiple substrates [23]. Even if there are so many different sources for biogas production, the final product is a percentage of CH\({}_{4}\) and CO\({}_{2}\) over the whole amount of the inlet fuel (40-70% for CH\({}_{4}\) and 25-60% for CO\({}_{2}\)) according to the type of waste source utilized, while all mixtures present an insignificant amount of impurities (<2%), mainly H\({}_{2}\)S and H\({}_{2}\), which do not influence the process of biogas reforming, as previously stated. The above presented mixture leads to a specific ratio \"\(\lambda\)\" (concentration of methane over carbon dioxide), which represents in a unique manner the production source and route. During power plant operation, the impurities follow the main pipeline and are finally emitted to the environment through the flue gases [24]. Biogas reforming is nowadays a well-established technology and can be satisfactorily performed through several ways by using different catalysts during the reforming process, mainly named as dry reforming [25], bi-reforming (steam biogas reforming) [26] and tri-reforming [27]. In the present research study, by considering the simulated power plant, as presented in Figure 1, the essential amount of H\({}_{2}\) for the SOFC's feeding is exclusively produced through the steam biogas reforming process, which analytically presents by the first equation (see in Figure 1, Equation (1)) in the reformer device. Additionally, the present computational model embodies the electrochemical oxidization reaction of CO (see in Figure 1, Equation (2)) [27], and the extension can reach high levels in a low temperature range. It is essential to be mentioned that CH\({}_{4}\) reforming is not possible thermodynamically below 600 K [28], while the water-gas shift reaction is favored at lower temperatures (<800 K) [28]. In this respect, for the optimal simulated scenario of the present research project, the CH\({}_{4}\) reforming has been chosen to be finalized at 1100 K, which is around the low limit of the optimal temperature range for this process. At this temperature, by using the appropriate catalyst (Ni/MgAl\({}_{2}\)O\({}_{4}\)), the extension of the reforming reaction can reach the percentage of 98% [29]. Now, as concerns the SOFC modelling, the CO oxidization (see in Figure 1, Equation (4)) can approximately reach the 1/4 (0-15%) of the extension of the hydrogen reaction, positively contributing the overall efficiencies (energy and exergy) of the total power plant [30]. In general, throughout the literature, most computational models do not embody the hydrogen reaction due to its low impact on the general system's efficiency, contrary to THERMAS [11; 12], which approaches real life scenarios and is used here. Additionally, the operational temperature for the fuel cell device, for the optimal simulated scenario of the present project, has been chosen as 1060 K through thermodynamic analysis, which is near the low limit, but it absolutely meets the requirements of the (Intermediate Temperature Solid Oxide Fuel Cell) IT-SOFC technology [31].