Hybrid photo-thermal sulfur-ammonia water splitting cycle: Thermodynamic analysis of the thermochemical steps

A. E. Kalyva, E. Ch Vagia, A. G. Konstandopoulos, A. R. Srinivasa, A. T-Raissi, N. Muradov, Konstantinos Kakosimos

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Solar driven hybrid sulfur-ammonia water splitting cycle (HySA) integrates a solar-photocatalytic hydrogen, H2, production step (H2 sub-cycle) with a high-temperature solar thermochemical oxygen, O2, evolution step (O2 sub-cycle), implementing efficient thermal energy storage as part of the cycle operation. Previous studies of the cycle omitted intermediate products, such as ammonium bisulfate, from the O2 sub-cycle and, thus, neglected their potential impact on the cycle's chemistry. Also, there are discrepancies in reported literature for the thermodynamic properties of ammonium sulfate, (NH4)2SO4 and ammonium bisulfate, NH4HSO4. In this study, thermal analysis experiments were conducted in order to determine the phase transition temperatures and enthalpies, and the heat capacity temperature dependence of the ammonium sulfate, (NH4)2SO4 and ammonium bisulfate, NH4HSO4. Our experimentally determined values for these parameters agree well with the data reported in DIPPR Project 801 database. Moreover, an exploratory thermodynamic analyses was performed using AspenPlus© and FactSage©, that included all potential reaction products, in order to identify critical parameters for an optimum O2 sub-cycle. A methodology is proposed and evaluated to mitigate AspenPlus©'s deficiency to handle solid phase changes. The thermodynamic analyses demonstrate that the NH4HSO4 inclusion in the O2 sub-cycle reduces the overall process energy requirements, and allows its use as an energy storage medium. Finally, we show that the use of molten salts, in combination with their interactions, significantly affects the efficiency and the operating conditions of the process, as well as the state of the mixtures.

Original languageEnglish
Pages (from-to)9533-9544
Number of pages12
JournalInternational Journal of Hydrogen Energy
Volume42
Issue number15
DOIs
Publication statusPublished - 13 Apr 2017

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Keywords

  • Ammonium bisulfate
  • Ammonium sulfate
  • FACTSAGE
  • Thermochemical steps
  • Thermodynamic analysis
  • Water splitting

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Fuel Technology
  • Condensed Matter Physics
  • Energy Engineering and Power Technology

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