Economic comparison of hydrogen production using sulfuric acid electrolysis and sulfur cycle water decomposition. Final report

Abstract

This final report discusses a technoeconomic comparison of the Westinghouse hybrid cycle with a water electrolysis process wherein the same electrolyzer concept was used for both processes and, in as far as possible, similar assumptions regarding energy source, fuel cost, etc. were employed in both cases. The objective was to better establish the economics of the two approaches and to establish the hydrogen production technology areas for R&D support. PROJECT OBJECTIVES The near-term objective of the EPRI hydrogen program is the identification of hydrogen applications and production technologies that can benefit the electric utility industry in the future. Under RP320 and RP467, EPRI assessed the technoeconomics of producing hydrogen by water electrolysis (using off-peak power) and thermochemical water-splitting cycles, respectively. Those results had indicated that water electrolysis would result in lower cost hydrogen than the pure thermochemical cycles assessed at that time. An alternative concept is a hybrid (thermochemical cycle with an electrolytic step) cycle being developed by Westinghouse. CONCLUSIONS AND RECOMMENDATIONS This report concludes that although the Westinghouse hybrid cycle has a better overall efficiency than water electrolysis (47% vs. 41°i), the costs of the hydrogen are essentially the same at $7.30-$7.80/10^ Btu (1976 dollars). Considering the major uncertainties that advanced thermochemical cycles face, such as the speculative nature of the high temperature heat source, as well as the kinetics of key reactions, EPRI does not recommend a large involvement in the thermochemical process area at this time. v It is possible that the General Electric solid polymer electrolyte (SPE) electrolyzer technology could be applied to the Westinghouse hybrid cycle with an improvement in both efficiency and cost. EPRI is now considering a oroject that would assess that possibility.

Materials-Related Aspects of Thermochemical Water and Carbon Dioxide Splitting: A Review

“…Ceramics such as silicon carbide, silicon nitrite, and cermet have an excellent resistance to H 2 SO 4 corrosion at ambient temperature and at low acid concentration [132]. …”

“…A number of conceptual process designs lead to overall thermal efficiencies of up to 40% [132]. The product gas separation is suggested to be carried out by already established and technically mature methods [6].…”