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Computer-Aided Exergy Evaluation of Hydrothermal Liquefaction for Biocrude Production from Nannochloropsis sp.


Biomass (especially algae) is a renewable energy source that can be a great alternative to fossil fuels. Wet algal biomass converts into products such as solid, aqueous, and gaseous phases as well as biocrude in hydrothermal liquefaction (HTL). The aim of this work was to provide detailed exergy analyses of the production of biocrude from Nannochloropsis sp. by HTL. Physical and chemical exergy of the HTL products, exergy losses, exergy efficiency, and exergy distribution of the HTL process were determined in this research. The highest exergy loss and the lowest efficiency values obtained for the heat exchanger were 65,856.83 MJ/hr and 66.64%, respectively, which was mainly caused by the irreversibility of the heat transfer process. Moreover, the HTL reactor had high efficiency (99.9%) due to the complex reactions that occurred at high temperature and pressure. Also, the optimum operating conditions of the reactor were obtained at 350 °C and 20 MPa by using sensitivity analysis. The high overall exergy efficiency of the process (94.93%) indicated that HTL was the most effective process for the conversion of algae. In addition, the exergy recovery values of the overall exergy input values in the HTL process for biocrude, as well as the aqueous, solid, and gas phases, were nearly 74.88%, 18.42%, 0.86%, and 0.76%, respectively. Exergy assessment provides beneficial information for improving the thermodynamic performance of the HTL system.

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Data Availability

The data are available from the corresponding author upon request.



Percent of average absolute deviation


Aqueous phase


Exergy rate (kJ/hr)


Molar exergy (kJ/mol)


Gibbs energy (kJ/mol)


Enthalpy (kJ/hr)


Heat exchanger


Hydrothermal liquefaction


HTL reactor


Lower heating value (MJ/kg)


Mole flow rate (mol/hr)


Mass flow rate (kg/hr)




Gas constant (kJ/mol. K)


Entropy (kJ/hr k)


Solid separator


Temperature (K)




Work rate (kJ/hr)


Mole fraction (-)


Three-phase separator


Exergy coefficient (-)


Exergy efficiency (-)


Stoichiometric coefficient




Standard state







i, j:



Loss of exergy




Heat transfer


Reference state


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Author information




Ziba Borazjani: developing the concept and methodology, analyzing the data, writing the original draft, as well as reviewing and editing the final manuscript. Reza Azin: trial management, data acquisition, and reviewing the manuscript. Shahriar Osfouri: management, conceptualization, and acquisition of material used in the study, project initiation, reviewing, and editing. Markus Lehner: reviewing and editing the manuscript. Markus Ellersdorfer: reviewing, model validation, and editing the manuscript.

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Correspondence to Reza Azin.

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Borazjani, Z., Azin, R., Osfouri, S. et al. Computer-Aided Exergy Evaluation of Hydrothermal Liquefaction for Biocrude Production from Nannochloropsis sp.. Bioenerg. Res. (2021).

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  • Thermochemical process
  • Exergy analysis
  • Process simulation
  • Algae