Process-Level Techno-Economic Assessment of Thermodynamic Promoters for Hydrate-Based Solidified Natural Gas Production

Abstract

This study presents a process-level techno-economic analysis of solidified natural gas (SNG) production via clathrate hydrate formation, evaluating three configurations ─ pure methane (sI), methane-THF (sII), and methane-1,3-dioxolane (sII) ─ at a feed capacity of 0.13 MMTPA. Process simulations were developed in Aspen HYSYS V15 using the Twu–Peng–Robinson equation of state, with capital and operating costs estimated using the Towler and Sinnott framework. Sensitivity analyses examined methane inlet pressure (atmospheric vs 45 bar) and refrigerant choice (propane vs ammonia). Literature-derived methane conversions of 10.0% for the pure-methane case and 42.0% for the promoted cases were specified in the conversion-reactor model. The pure methane case yielded a process-cost levelized cost of storage (LCOS) of $0.794/kg under atmospheric conditions ─ uncompetitive against LNG ($0.169–$0.434/kg) and CNG ($0.175/kg). Promoter-assisted configurations achieved $0.107–$0.217/kg excluding raw material cost, competitive with LNG under favorable conditions. However, the promoter makeup requirement of 15209 kg/h ─ the stoichiometric quantity incorporated into the sII lattice and leaving with the solid product ─ generates an annual raw material cost of $184M, raising LCOS to $3.39–3.50/kg across all promoted cases regardless of operating conditions. Because this promoter is a structural constituent of the product rather than a recoverable stream, it cannot be reduced by in-process recovery. First-stage methane compression dominates capital and operating costs; colocation with high-pressure gas infrastructure reduces LCOS by 44–59%. These findings indicate that thermodynamic promoters confer no net economic benefit at industrial scale, and that the unpromoted pathway is the more tractable route to competitive SNG, contingent on improved conversion.