Academia

Hydrogen, as a clean energy source, is recognized as a pivotal energy carrier in the global transition to sustainable energy systems and serves as a crucial pathway for energy storage and efficient utilization within cryogenic systems. Hydrogen liquefaction is one of the most promising methods for increasing its energy density, enabling more efficient storage, transportation, and utilization in large-scale energy systems. However, substantial challenges persist, particularly regarding the high energy consumption associated with the liquefaction process. This study addresses these challenges by proposing two designs for a triple-cascade mixed refrigerant cycle aimed explicitly at reducing energy consumption for high-density hydrogen storage: 66.7 kg/m3 at − 245 °C (Case 1) and 76 kg/m3 at − 249 °C (Case 2). The proposed systems utilize two mixed refrigerant cycles for the precooling and cryogenic stages. In Case 1, pure nitrogen is employed as the third refrigerant in the precooling stage, whereas Case 2 incorporates a regenerative cryogenic hydrogen cycle as the third refrigerant throughout the entire system, coupled with a carbon dioxide cycle for compressor cooling. Simulations were conducted using Aspen HYSYS, with optimization through the Aspen Optimizer algorithm. The results indicate that Case 1 achieves a specific energy consumption (SEC) of 6.98 kWh/kgH₂, representing a 17.4% reduction from the baseline, while Case 2 reduces SEC to 6.19 kWh/kgH₂, a 14.5% decrease. The exergy analysis of the heat exchangers shows a 37% reduction in exergy destruction in Case 2 compared to Case 1. Additionally, Case 2 demonstrates a 5.8% reduction in capital expenditure and a 22% reduction in carbon footprint (CFP). These findings highlight the potential of the proposed triple-cascade process to enhance energy efficiency, improve both thermodynamic and economic performance, and reduce environmental impact.
To view the article: Comparative study of advanced hydrogen liquefaction using triple cascade mixed refrigerant cycles with integrated energy exergy economic and environmental analysis | Scientific Reports 

Recommendations

1. Adopt TCMR cycles as benchmarks for next-generation hydrogen liquefaction plants The proposed triple-cascade mixed refrigerant (TCMR) configurations – particularly Case 2 with a specific energy consumption close to 6.2 kWh/kg H₂ – should be considered as benchmark designs in feasibility studies and FEED stages of medium- and large-scale hydrogen liquefaction projects.

2. Institutionalize integrated 4E assessments (Energy–Exergy–Economic–Environmental) Future hydrogen liquefaction and storage projects should systematically employ integrated 4E analysis instead of relying solely on conventional energy balances, ensuring that investment cost, operating cost, and carbon footprint are jointly optimized along with thermodynamic performance.

3. Incorporate CO₂-based decarbonization cycles and hydrogen refrigerant loops in new designs The study shows that adding a CO₂-based decarbonization loop for compressor cooling and using hydrogen as a tertiary refrigerant in TCMR Case 2 significantly reduces SEC, exergy destruction, and carbon footprint. Future plant designs should therefore consider such integrated configurations as strong candidates for high-efficiency LH₂ production. Nature+1.

4. Develop pilot and demonstration plants based on the proposed TCMR configurations Industrial stakeholders (oil, gas, and hydrogen producers) are encouraged to implement pilot- or demo-scale liquefaction units using the TCMR designs to validate performance under real operating conditions, generate reliable operating data, and de-risk full-scale deployment.

5. Integrate advanced liquefaction cycles with renewable power systems Considering hydrogen’s role in clean energy systems, future work should investigate the coupling of TCMR-based liquefaction plants with large-scale renewable power (solar, wind), exploring flexible operation strategies and optimal sizing to absorb excess renewable electricity.

6. Use the reported SEC and LH₂ density as reference values in national and corporate hydrogen roadmaps The achieved SEC of 6.19 kWh/kg H₂ and the high storage density of 76 kg/m³ at −249 °C can serve as realistic, yet ambitious, reference targets in hydrogen economy roadmap studies and levelized cost of hydrogen (LCOH) assessments. Nature+1

7. Expand sensitivity and uncertainty analyses in future research Further studies are recommended to investigate the sensitivity of the TCMR performance to variations in energy prices, carbon pricing, equipment costs, and off-design operation, as well as to perform dynamic simulations to assess start-up, shut-down, and load-following capabilities