Transient analysis of solar-driven hydrogen and sulfur production from acid gas with thermal energy storage

Abstract

Acid gas, a byproduct of natural gas sweetening, mainly contains toxic hydrogen sulfide (H₂S) and carbon dioxide (CO₂). Decomposing H₂S reduces harmful emissions while producing valuable hydrogen and sulfur. This study presents a transient techno-economic analysis of a solar-driven system for co-producing carbon-free hydrogen and sulfur via thermal H₂S decomposition. The primary novelty of this work lies in the development of a transient framework for solar-powered thermal decomposition of H₂S, incorporating thermal energy storage to enable continuous, year-round production of hydrogen and sulfur under realistic solar intermittency conditions. The system comprises a heliostat field, a solar tower, a molten-salt thermal energy storage, a palladium–silver membrane for hydrogen separation, and a purification and compression unit. The thermal energy storage, with hot and cold tanks, enables continuous year-round operation. Designed for Bushehr, near major gas refineries with high solar potential, the system decomposes acid gas in a shell-and-tube reactor heated by molten salt at up to 1280 °C. A plug flow reactor model with a four-step kinetic mechanism predicts 30% H₂S conversion, yielding hydrogen and sulfur production efficiencies of 23% and 10.94%, respectively. Average annual outputs are 39 kg/h of hydrogen and 0.389 kg/s of sulfur, with 2.2 kg/s of superheated steam recovered from waste heat. The overall energy and exergy efficiencies are 69.66% and 25.35%, respectively. The total investment is $19.45 million, with a hydrogen cost of $10.1/kg, a 6.34-year payback, and a 20-year net present value of $17.1 million, confirming the system’s technical and economic viability.