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Remediation of Black Sea ecosystem and pure H2 generation via H2S-H2O co-electrolysis in a proton-conducting membrane cell stack reactor: a feasibility study of the integrated and autonomous approach

Ipsakis Dimitris, Kraia Tzouliana , Konsolakis Michail, Marnellos, Geōrgios E

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Summary

The present work explores the feasibility of an integrated and autonomous scaled up process towards the remediation of the Black Sea ecosystem with simultaneous H2 generation through the co-electrolysis of rich H2S/H2O seawater mixtures. The core unit of the proposed process is a proton-conducting membrane cell stack reactor (electrolyzer), where H2S in excess H2O mixtures are fed at the anode and co-electrolyzed to protons (H+), which are transferred through the electrolyte to the inert exposed cathode towards H2 generation. The proposed scaled-up process aims towards a Black Sea water intake of up to 2000 tn/hr and involves four distinct operating steps, i.e.: i) pumping Black Sea water from 1 km depth (H2S∼14 ppm) and H2S concentration enrichment up to 1 v/v% H2S-H2O, ii) Η2 production through H2S-H2O co-electrolysis at 850 °C and 2 bar, iii) purification and separation of the proton-conducting electrochemical membrane reactor effluent (H2 and SO2) and iv) H2SO4 production from off-gases. Overall heat management is accomplished through a natural gas high pressure burner along with flue gas power recovery (combined cycle) and the process system is assessed in terms of operating flexibility, electrical/heat requirements and economic perspectives. As was revealed, the decreased concentration of H2S/H2O mixtures (from 1 to 0.1 v/v%) results in a higher H2 and H2SO4 generation at the expense of higher heating/electrical demands, whereas the variation on the Black Sea water intake (from 650 to 1950 tn/hr) can be appropriately adjusted to regulate the corresponding operating costs. Based on a parametric sensitivity analysis, it was revealed that a H2S concentration of 1 v/v% and a water intake flow corresponding to a hydrogen production of >40 kg/h can promise favorable financial perspectives. The minimum products sale values that ensure the feasibility of the process along with a flexible heat and energy autonomy were identified at 9.85 €/kg of H2, 0.45 €/kg of H2SO4 and 0.277 €/kWh of produced electricity. Partial subsidy on the total fixed capital investment can further result in a substantial improvement of the investment's operating profitability.

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