Design of an industrial multi-bed (V)PSA unit for argon concentration

Pressure swing adsorption systems have been devised to concentrate argon from a binary gas mixture of oxygen and argon (O₂:Ar = 95:5 mol%) that an industrial oxygen generation vacuum swing adsorption (VSA) unit produces from air. The kinetically-driven adsorption processes investigated in this study contain a self-purging step and up to two double-ended pressure equalization steps. Three adsorption cycle configurations, each of which has one, two and three beds, were simulated. The effects of pressure ranges of the adsorption cycle, either pressure swing adsorption (PSA, 1–3 bar) or vacuum swing adsorption (VSA, 0.1–1 bar), as well as adsorption step time were extensively assessed with respect to the following separation key performance indicators (KPIs): argon purity, argon recovery, bed productivity and specific energy consumption. It turned out that argon purity and recovery could be significantly improved in the VSA cycles at the expense of bed productivity and energy consumption. The single VSA unit could not concentrate argon up to a purity of 98+% which is typically required for certain applications such as steel production and inert gas welding. Thus, a second VSA unit was added to increase further the argon purity and it was found that the integrated two-stage VSA system is capable of achieving the following overall performances: argon purity of 98.1%, argon recovery of 20.3%, bed productivity of 0.011 mol_Ar kg_ads⁻¹h⁻¹ and specific energy consumption of 53.2 MJ kg_Ar⁻¹. Considering real efficiencies of turbomachinery the energy consumption of the proposed VSA unit resulted 75% higher than that of a conventional stand-alone cryogenic distillation system designed to achieve the same separation. However, the VSA technology is expected to be a more attractive option than the cryogenic process in terms of CAPEX.