Performance increase of membrane distillation pilot scale modules operating in vacuum-enhanced air-gap configuration

Authors: J.A. Andrés-Mañas, A. Ruiz-Aguirre, F.G. Acién, G. Zaragoza

Summary: This paper presents the first experimental evaluation at pilot scale of the operation of vacuum-enhanced air-gap membrane distillation (V-AGMD) using two commercial spiral-wound modules at Plataforma Solar de Almería's solar desalination test facilities. The main difference between the modules was the channel length (1.5 and 2.7 m) as a result of having different membrane surface area (7.2 m² and 25.9 m² respectively) and different number of envelopes. Suction of air from the gap improved the vapour transfer through the membrane pores and the performance of the modules was significantly increased in relation to common air-gap (AGMD) operational mode, especially in the treatment of high salinity feeds. Increases of up to 234% in permeate flux and decreases of 68% in specific thermal energy consumption were measured. Depending on the channel length of the modules, the effect of vacuum led to extreme permeate productivity (8.7 l h⁻¹ m⁻²) in the shortest, or to extreme energy efficiency (49 kWh_th m⁻³, equivalent to a GOR of 13.5) in the longest. These are the best experimental performances obtained so far with pilot scale modules in membrane distillation.

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