Thermodynamic analysis of syngas production and sulfur capturing from a mixture of methane and hydrogen sulfide using a solar thermochemical redox cycle

Abhishek Singh*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Scopus)

Abstract

Syngas production and sulfur capturing from a mixture of methane and H2S via a novel two-step solar thermochemical cycle based on metal oxide/metal sulfide redox reactions is thermodynamically analyzed. Fe2O3/FeS is used as a model metal oxide/metal sulfide pair for this study. During the reduction step, Fe2O3 is reduced to FeS using a mixture of CH4 and H2S. In this process, syngas (CO + H2) is produced in the gas phase. In the oxidation step, FeS is oxidized using air to obtain Fe2O3 in the solid phase and SO2 and unreacted N2 in the gas phase. The produced SO2 can be used to generate sulfuric acid. Favorable operating conditions for the redox cycle are determined using an open system, thermodynamic model. For the reduction step, T = 1200 K at 1 bar pressure provides complete conversion of Fe2O3 to FeS. At these conditions, gas phase products contain mainly H2 and CO. Carbon formation is also predicted by the model between 580 and 1150 K temperatures. Thermodynamic analysis shows complete conversion of FeS to Fe2O3 during the oxidation step at T ≥ 600 K and 1 bar pressure. Effect of higher system pressures over the Fe2O3 reduction process is also determined using the model. With the increase in system pressure, carbon formation decreases. At 10 bar system pressure, no carbon formation is predicted by the thermodynamic model. A thermodynamic process model is also developed to assess the energetic feasibility of the complete process. Concentrated solar power can be used to provide the necessary energy for the endothermic Fe2O3 reduction process. Effect of concentration ratio and heat recuperation from exhaust gases over solar to fuel energy efficiency is studied. Energy efficiencies of the complete process at various oxidation temperatures are also determined using the thermodynamic process model. An overall system efficiency of 46.9% can be achieved for heat exchanger effectiveness of 0.9 and concentration ratio of 1000 when reduction and oxidation reactions are performed at 1200 K temperature.

Original languageEnglish
Pages (from-to)11738-11746
Number of pages9
JournalIndustrial and engineering chemistry research
Volume57
Issue number34
DOIs
Publication statusPublished - 10 Aug 2018
Externally publishedYes

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