Isothermal dehumidification or gas drying using vacuum sweep dehumidification

This article discusses a novel isothermal system for removing water vapor from gases using water selective membranes. Previous membrane systems for dehumidifying atmospheric pressure gases suffered from low driving forces across the membrane. The approach presented and tested here used a fraction of the dehumidified gas as “a dehumidifying working fluid” that passes through an expansion valve prior to re-entering the membrane unit. The combination of gas expansion and low absolute pressure sweep gas establishes a driving force strong enough to achieve dehumidification efficiencies >200%. The produced gas humidity is significantly reduced compared to the feed gas. It is even possible to produce gases with dew point's <0 °C. Experiments confirm these results using sweep gas pressures obtainable by rotary water-sealed or single stage reciprocating vacuum pumps. These evaluations encourages further research especially, but not limited to, those applications where the data indicated the technology is competitive with existing systems; such as, building ventilation dehumidification and dryers.

► Combined gas expansion with a vacuum to isothermally dehumidify gases. ► Achieved dehumidification efficiencies >200% or product dew pts <0 °C. ► Decoupled latent and sensible heats allowing independent humidity control. ► Matched existing system performances but with zero sensible heat ratios. ► High temperature tests mimicked drying applications for recycle dryers.