Simulation and Validation of Small to LargeScale Hydrogen Liquefaction Cycles using Mixed and Normal-Hydrogen Refrigerant in MATLAB/Simscape Fluids

Kurzfassung

Hydrogen is emerging as one of the most promising energy carriers for a clean global energy system. It can address the issues facing the energy and transportation sectors with air pollution and climate change. Liquid hydrogen has sparked widespread interest due to its high energy storage density and potential for long-distance transportation. Delivering and storing hydrogen in its cryogenic liquid form is an economical method. The key factor for obtaining liquid hydrogen is an effective hydrogen liquefaction procedure, which cools down feed hydrogen gas at 300 K to liquid hydrogen at 20 K. However, compared to the straightforward compressionstorage approach, hydrogen liquefaction requires a greater infrastructure investment. Therefore, investigating energy-saving techniques for hydrogen liquefaction is crucial. This thesis work employed a physical modeling tool, Simscape Fluids, within the MATLAB/Simulink environment, which is used to model and simulate the energy-efficient hydrogen liquefaction process. This study evaluated the dynamic features of the hydrogen liquefaction process by creating a model of the unit module and performing simulation optimization based on the steady-state process and process parameters. In this study, hydrogen liquefaction systems are simulated at small, medium, and large-scale capacities of 5 TPD, 50 TPD, and 120 TPD, respectively. Each configuration employs different refrigerant arrangements with the objective of reducing the specific energy consumption (SEC) and improving overall thermodynamic performance. For the small-scale 5 TPD plant, a dual-pressure pre-cooling hydrogen liquefaction system is implemented. Normal hydrogen is used as the primary refrigerant, while liquid nitrogen provides the pre-cooling stage. The system achieves a specific energy consumption of 9.69 kWh⁄kgLH2, an exergy efficiency of 0.542, and a coefficient of performance (COP) of 0.118. In the medium-scale 50 TPD configuration, a Joule-Brayton cycle is adopted for the main liquefaction process. Helium serves as the refrigerant, and liquid nitrogen is utilized for precooling. This configuration demonstrates improved thermodynamic performance, with an SEC of 5.75 kWh⁄kgLH2, an exergy efficiency of 0.574, and a COP of 0.193. For the large-scale 120 TPD plant, the system is integrated with a liquefied natural gas (LNG)- based hydrogen production facility. The cold energy released during LNG regasification is effectively recovered to pre-cool the feed hydrogen from 300 K to 114 K, thereby significantly reducing the refrigeration load. A helium Brayton cycle is then employed for deep cryogenic cooling, with helium as the working refrigerant. This large-scale configuration achieves a reduced SEC of 7.56 kWh⁄kgLH2, an exergy efficiency of 0.432, and a COP of 0.144.