Analysis and techno-economic comparison of bio-hydrogen production processes

The objective of this thesis is to investigate two biological routes for hydrogen production, as hydrogen is considered a promising energy carrier for the future. The processes analysed are Dark Fermentation and Photofermentation: they require different type of microorganisms and distinct environmental conditions to operate efficiently. Biological processes, as the ones considered in the current study, present several challenges that make their applicability in larger scales difficult. In fact, they involve complex biological systems and are characterised by relatively low production yields compared to conventional chemical processes. In addition, these processes are highly sensitive to operating conditions and therefore require a precise control system to maintain an optimal environment, that can be complex and costly. In the current study, process simulation is used to address material and energy balances for the dark fermentation process. The simulation of the process relies on the results of the kinetic model employed for describing the kinetics of the reactions involved. For the photofermentation process, mass balances are computed based on the literature values for the specific hydrogen production. Then, process simulation outcomes and mass balances are used to perform an economic analysis both for the single dark fermentation process and for the combined processes. Moreover, the economic results are exploited to estimate a key indicator related to the economic performance of such processes. Different scenarios are considered in order to evaluate the optimal solution in terms of the levelized cost of hydrogen (LCOH). The research focuses on a techno-economic analysis of these processes, aimed at evaluating their potential for industrialization and small-medium scale production. The results obtained highlight, on one hand, the economic advantages of employing a single-stage dark fermentation process, while, on the other hand, they emphasize the limitations related to the implementation of the photofermentation, mainly due to technologies that should be optimized for this process.