Hydrogen Integration in Gas and Steam Turbine Combined Cycles for Maritime Applications: Design and Performance Assessment of Hybrid LNG/LH2 Fuel Systems

The global energy transition towards low-carbon technologies has prompted significant efforts into high-efficiency, low-emission propulsion systems capable of operating with alternative low- or zero-carbon fuels while complying with the stringent regulations imposed by policymakers. In this context, the uptake of hydrogen-based propulsion systems is regarded as a promising route towards the decarbonisation of passenger shipping. Nevertheless, the use of hydrogen alone on board as an energy carrier poses complex challenges in terms of technology, storage, operations and safety. Particularly, due to its physical characteristics, significant quantities of energy cannot be stored for the typical mission profiles of a cruise ship; this is true even when its densest form, i.e. liquefied hydrogen (LH2), is utilised. Therefore, in order to exploit hydrogen power onboard in a manner that is both effective and sustainable, it is recommended that a hybrid hydrogen-natural gas fuel system be conceived. This system would then be able to feed gas turbine generators in combined cycle (CCGT) configuration. In the first part of this dissertation, commercial data were used to build weight and volume functions of low-emission alternative propulsion system, and such functions have been employed to conduct an assessment of different alternative technologies to determine the actual suitability of liquid hydrogen onboard large ships from both logistic (weight and volume occupancy) and environmental perspectives. In the second part, the system design and thermodynamic performance analysis of a hybrid hydrogen–natural gas (H2–NG) fuel handling and delivery system for a CCGT power plant is presented, with a specific focus on maritime applications, and particular emphasis on cruise ship propulsion and onboard power generation. The complete design, component sizing, and performance simulation of the hybrid combined cycle were developed using AVEVA Pro/II thermodynamic modeling tool to assess steady-state energy balances for efficient shipboard integration. A novel concept of hydrogen heat exchanger, namely a pressurizing heat exchanger (PHEX), is also presented as possible innovation from standard design to improve energy consumption, and its integration in the fuel system is assessed. Moreover, the preliminary control logic to convey fuel at the proper conditions to the generators is also proposed, considering the aim of potentially feed them with any combination of H2 and NG, as well as with the fuels taken individually as it is currently done in dual fuel (DF) engines. Moreover, basic safety considerations are made and potential outcomes of a failure in the fuel system are evaluated. In the design process, starting from the vast knowledge and technological efforts on LNG for the maritime as a drop-in solution, the main differences with LH2 are assessed, and the extent to which its good practices are applicable to LH2 are considered, in order to give a comprehensive overview of large scale hydrogen uptake readiness. Finally, granted the availability of hydrogen onboard of ships and/or in the harbour and island context, the thesis also analysed two auxiliary systems connected to the hydrogen transportation economy: (i) small size power generation on board, using low temperature fuel cell solutions, aiming at the potential application of LH2 to small size ships or boats, and (ii) the possibility of integrating fresh water production basing on high temperature reversible fuel cells.