Developing a new hydrogen liquefaction process through configuration modification and parameter optimization

Abstract

A new concept for hydrogen liquefaction with a capacity of 300 tons per day is developed through the modification of an existing one. Pressure and temperature levels, mixed-refrigerant composition, and different configurations are explored to achieve a new concept with lower SEC and higher COP. Aspen HYSYS V9 is used to simulate the process. Exergy and energy analyses are employed for evaluating the process to capture the effect of changes. As different parameters of the liquefaction process are interlinked and depend on each other, optimization is done using a trial and error procedure. Modified-Benedict–Webb–Rubin and Peng-Robinson equations of state are utilized to simulate hydrogen and mixed refrigerant streams to increase the accuracy of the results, especially for the ortho-para conversion. Power consumption of the coolers is considered, and exergy destruction for all the components is calculated. It is found that ortho-para converters and separators could affect the total exergy destruction and efficiency of the process; however, their exergy efficiency is nearly 100%. The SEC of the new concept is 5.97 kWhr/kg, which shows an 18.8% improvement compared to the base concept. The COP and ε are improved by 14.4% and 15.5% too. The results show that the liquefaction section is responsible for 85% of the total SEC of the process, and it deserves to focus on this section for future studies.

Keywords

• hydrogen liquefaction
• exergy analysis
• aspen hysys
• mixed-refrigerant
• ortho-para conversion