Large-Scale Hydrogen Liquefaction Based on Brayton Cycle Concept

Abstract

The viability of hydrogen as a sustainable energy carrier is significantly affected by the costs linked to its transportation and storage. Transporting and storing hydrogen in its liquid form offers remarkable advantages, as liquid hydrogen has unique characteristics, including lower weight and volume, as well as a higher energy content compared to gaseous hydrogen. However, current industrial hydrogen liquefaction processes face significant challenges related to efficiency and cost, with a second-law efficiency of less than 25% and costs ranging from 2.5-3.0 US$/kgLH2.

Large energy storage systems can address the issue of energy demand fluctuations in renewable energy grids by storing excess energy produced and compensating for any energy shortfalls. The development of hydrogen energy storage systems will thus support the advancement and increased utilization of renewable energy sources. The demand for liquid hydrogen is expected to rise in the near future, driven by environmentally friendly applications and use in mobility sector. As a result, large-scale hydrogen liquefaction (LHL) plants will become increasingly important in the clean energy efficient hydrogen supply chain.

This thesis aims to develop a Large-scale Hydrogen Liquefaction (LHL) plant based on the Brayton cycle concept of 86 TPD. The plant is modeled using Aspen HYSYS, with preliminary designs for key equipment—such as compressors, turbines, and plate-fin heat exchangers, ensuring compatibility with current technological constraints. State properties of the fluid used in the design of compressors and turbine equipment were obtained from REFPROP software, utilizing the Peng-Robinson Equation of State (EOS). For the design of plate-fin heat exchangers, Aspen Exchanger Design and Rating (EDR) was employed. Subsequently, a techno-economic analysis was conducted using the Aspen Process Economic Analyzer (APEA) to estimate both capital and operating expenditures, based on the process simulation model and preliminary equipment designs.

The specific energy consumption (SEC) of the plant, accounting for power recovery from turbine shafts, is determined to be 6.9025 kWh/kgLH2. The plant’s exergy efficiency is calculated at 43.665%, and the specific liquefaction power is found to be 3.014 kWh/kgLH2. Assuming an electricity price of 0.1 €/kWh, modelled 86 TPD Brayton-cycle concept yielded specific liquefaction cost (SLC) of 1.57 €/kgLH2.

A sensitivity analysis was conducted to identify the parameters that influence the specific liquefaction cost (SLC) of the plant. The analysis focused on two key parameters: 1) electricity price and 2) feed pressure. The results reveal that fluctuations in electricity prices have a substantial impact on the plant’s economic performance. Additionally, the analysis indicates that the plant’s efficiency and economic viability are significantly sensitive to decreases in feed hydrogen pressure.