Applicability of the common equations of state for modeling hydrogen liquefaction processes in Aspen HYSYS

Abstract

Liquid hydrogen will likely play a significant role in the future of energy as its applications are growing fast. Due to the low efficiency of the existing liquefaction plants, many studies are dedicated to the liquefaction processes. The accuracy of the simulations crucially depends on the fluid package and prediction of thermodynamic properties. Four common equations of state implemented in Aspen HYSYS used for hydrogen liquefaction, including PR, MBWR, SRK, and BWRS, are investigated to find their accuracy for estimating volumetric and calorimetric properties, that are essential for precise simulation of hydrogen liquefaction processes. Results show that MBWR is the best choice for hydrogen liquefaction processes, which are simulated by Aspen HYSYS. MBWR predicts thermodynamic properties of hydrogen and parahydrogen very well, in the whole range of temperature and pressure typically met in the liquefaction processes. The MBWR performs well in predicting enthalpy of ortho-para conversion too. Although PR performs better than SRK and BWRS, none of them yields reliable data in low temperatures, so they could not be applied for liquefaction processes. However, they may lead to desirable results for processes that experience higher temperatures range. An innovative, simplified hydrogen liquefaction cycle is developed to be able to capture the mere effect of EOS on essential performance parameters of the liquefaction cycles such as SEC and COP. Applying PR and MBWR to the developed cycle shows that PR compared to MBWR leads to 10% and 4% deviation in SEC and COP, respectively.