INNOVATION AND OPTIMIZATION OF THE HYDROGEN TRANSPORT AND DISTRIBUTION CHAIN AS A GREEN AND RENEWABLE ENERGY VECTOR

Because of its enormous energy storage capacity, hydrogen appears to play a significant role in a world where fossil fuel depletion, global warming, and growing energy consumption are the main factors. However, issues with storage and transportation restrict its application. The aim of this thesis, titled “Innovation and Optimization of the Hydrogen Transport and Distribution Chain as a Green and Renewable Energy Vector”, is to investigate and address the technical challenges associated with the integration of hydrogen into the current energy infrastructure, with a particular focus on transportation, purification, and storage. In response to the growing interest in hydrogen as a clean energy carrier, this work emphasizes the potential of hydrogen blending with natural gas in existing pipeline networks, a strategy currently under exploration across Europe as a transitional solution. The study was carried out in collaboration with Regas S.p.A., a company based in Treviglio (BG) with longstanding expertise in the natural gas sector, particularly in the development of transmission and distribution stations, automatic odorization systems, and gas analysis technologies. Building on Regas’s ongoing initiatives in hydrogen blending, including the development of hydrogen production units and a dedicated blending station, this thesis focuses on one of the most critical post-injection challenges: the selective recovery of hydrogen from natural gas mixtures at the point of use. To address this, the research centres on the development and evaluation of the Electrochemical Hydrogen Compressor (EHC), a promising but still underdeveloped technology capable of selectively extracting and compressing hydrogen from gas mixtures. The dual functionality of purification and compression, coupled with the absence of moving mechanical parts, makes EHCs ideal candidates for decentralized applications and small-scale recovery units, such as on-site hydrogen recovery and use in hard-to-abate sectors, purification and compression for storage, and integration into hydrogen refuelling stations for sustainable mobility. The thesis first covers the design and optimization of a laboratory-scale pilot system, used to investigate the behaviour of EHCs under realistic conditions (Chapter 2). A complete experimental study was carried out to evaluate the influence of key parameters, such as membrane type, temperature, gas composition, flow rates, and current density, on EHC performance (Chapter 3). This study demonstrates the feasibility of using PEM based-EHC for purifying hydrogen from methane-rich mixtures, including natural gas. Three Nafion® membranes (N-115, N-117, and N-212) were compared in terms of ohmic resistance, efficiency and energy consumption. Among the Nafion® membranes tested, Nafion® 212 exhibited superior performance due to its lower thickness and higher ion-exchange capacity, resulting in reduced energy consumption. The system maintained high hydrogen purity (up to 99.45%) even with a 90:10 CH4:H2 feed, although methane crossover prevented meeting fuel cell-grade purity levels. Adjustments such as using thicker membranes or operating at lower humidity would affect CH4 permeation, as presented in more detailed in Chapter 4, but adversely affected energy efficiency. Elevated temperatures improved membrane conductivity but necessitated careful thermal and water management. Preliminary compression and stack-level tests confirmed the system's scalability and dual functionality in purification and compression. The experimental data were subsequently employed to validate a mathematical model developed in C++, specifically designed to simulate the performance of the EHC under a range of operating conditions (Chapter 5). The results highlight an average deviation of approximately 2.5% between the model predictions and the experimental measurements. Beyond validation, the model proved to be an insightful analytical tool. It enabled an in-depth investigation of hydrogen distribution along the anode flow field, highlighting how progressive hydrogen depletion along the serpentine contributes to non-uniform current distribution and rising overpotentials in downstream regions. The model was also used to evaluate the efficiency of the system considering the three membrane and different starting conditions. While the maximum total efficiency is comparable across all three membranes, its peak shifts towards higher current densities for thinner membranes, which exhibit superior energy efficiency but lower production efficiency. This suggests that the choice of membrane has a crucial impact on the trade-off between energy demand and hydrogen throughput. A tecno-economic analysis to assess the feasibility of using an electrochemical hydrogen compressor to separate and compress hydrogen from natural gas mixtures in pipelines was performed (Chapter 6). Two different approaches were adopted and compared. In the first approach, a constant current density of 1 A cm-2 was applied across all case studies, regardless of the operating conditions. In the second approach, the analysis was based on the optimization of energy consumption and operating parameters, discussed in Chapter 5. Starting from these optimized conditions, the total cost was then evaluated by balancing CAPEX and OPEX, in order to identify the configuration that minimizes the overall hydrogen cost for both purification and compression. The comparative analysis reveals that the model-based optimization strategy enables the customization of each system layout to achieve the lowest possible total hydrogen cost by tuning current density, particularly in low-pressure regimes where back-diffusion can be mitigated more efficiently. Indeed, in low-pressure purification scenarios, optimized operation with Nafion® 212 decreased OPEX by 81% (from 2.34 € to 0.44 € per kg H2), despite higher CAPEX. For high-pressure scenarios, this approach consistently delivered higher CAPEX but lower OPEX leading to lower normalized hydrogen costs, particularly for thicker membranes. Overall, optimization enables more efficient system configurations tailored to each membrane and application. The model has been successfully integrated into a process simulation environment using AVEVA Process Simulation (APS) (Chapter 7.1), allowing for process design, scale-up studies, and techno-economic assessments of different system configurations. The integration of the EHC model into APS enabled the creation of a fully configurable, custom unit capable of simulating real electrochemical behaviour within complex process environments. The model successfully captured key trends in energy consumption and hydrogen purity under varying operating conditions, validated against experimental data and the original C++ model. Case studies and optimization confirmed the system’s flexibility, highlighting trade-offs between performance parameters. This platform can be used in the future for system scale-up, integration with renewable energy sources, and the development of dynamic simulations within broader hydrogen network infrastructures. To conclude the work, since like natural gas, hydrogen is an odourless and colourless flammable gas, a safety-focused study on hydrogen odorization was carried out, investigating strategies to make hydrogen more detectable during distribution (Chapter 7.2). Starting from INGRID’s specification, on odorization machine developed by Regas S.p.A., it was possible to simulate a preliminary study on the odorization process of hydrogen and methane-hydrogen mixtures. The lapping odorization system was successfully simulated and the results demonstrated a variation in the secondary flow required, depending on the pure gas considered, namely hydrogen or methane, their ratio in the mixtures and the odorant taken into consideration. In conclusion, this work provides a detailed and structured investigation of PEM-based Electrochemical Hydrogen Compressors as a viable technology for hydrogen purification from natural gas blends. By integrating laboratory experimentation with process modelling and simulation, the study offers a realistic assessment of system performance under various operating conditions. While further development is needed to fully meet fuel cell-grade purity requirements and optimize efficiency at scale, the results presented contribute valuable insight toward the practical implementation of EHC in future hydrogen infrastructure.