(518p) Detailed Modelling and Simulation of Thermophysical Property Based Hydrogen Liquefaction Process with Exergy and Economic Analysis

Over the past few decades, many researchers in academia and industry have conducted to mitigate global warming. As the international convention for reducing greenhouse gas emissions was signed, the demand for hydrogen has been increasing with governments pursuing policies to solve fine dust and air quality problems [1]. In situations where large storages and transportation of hydrogen are required due to increase in demand, the development of highly efficient hydrogen liquefaction technology received much attentions [2].

In this study, a thermophyscial property based modeling and simulation approach for efficient hydrogen liquefaction with exergy and economic analysis was executed using Aspen HYSYS. For the design of the hydrogen liquefaction process, a suitable Equation of State (EOS) for accurate prediction of the hydrogen properties was investigated. Currently, NIST's REFPROP is considered as one of the most reliable EOSs [3], but seemed difficult to implement in simulation programs (e.g., Aspen HYSYS, PROâ…¡). Hence, three case studies were carried out to asssess the effect of several built-in EOSs (PR, SRK, MBWR) on the liquefaction process. The findings revealed that, MBWR was the most suitable EOS and hence was selected for this process.

In the hydrogen liquefaction process, ortho hydrogen is slowly converted to a more stable para hydrogen. To include this phenomenon in our modeling, an ortho-para conversion reactor was installed to convert the ortho hydrogen (75% of normal hydrogen) to more stable para hydrogen. Base on our modeling analsysis it was found that more than 40% of refrigerants were required when the ortho-para conversion reaction was included in the model. Furthermore, we adjusted the heat capacity parameters and equations to to take into account the conversion heat of ortho-para hydrogen so that it has the same effect as a continuous type heat exchanger that recent hydrogen liquefaction processes adopt [4]. Lastly, for the design of the heat exchanger, feasibility studies were carried out by comparing the implemented continuous type heat exchanger with the built-in batch type heat exchanger using equivalent amounts of hydrogen refrigerant in Aspen HYSYS. A minimal error of 1% was obtained confirming the possibility of using continuous heat exchangers in Aspen HYSYS with this newly developed approach. In addition, the exergy changes using different refrigerants in the pre-cooling cycle were examined and the process was validated through economic analysis.

Literature cited:

[1] K. Ohlig, L. Decker, “The Latest Development and Outlook for Hydrogen Liquefaction Technology,” Linde Kryotechnk AG., 2013.

[2] Alexander Alekseev, “Hydrogen Liquefaction,” Hydrogen Science and Engineering: Materials, Processes, Systems and Technology., Vol. 2, pp. 733–761, 2016.

[3] J.W. Leachman, R. T Jacobsen, S. G. Penoncello, and E. W. Lemmon, “Fundamental Equation of State for Parahydrogen, Normal Hydrogen, and Orthohydrogen,” J. Phys. Chem., Ref. Data 38, 721, 2009.

[4] Hamed Rezaie, Masoud Ziabasharhagh, Mostafa Mafi, “A review of Hydrogen Liquefaction, Current Situation and Its Future,” International Conference on Engineering&Applied Science., 2016