Nano-porous transport membrane condenser for flue gas water recovery: Modeling and parametric membrane design analysis

Abstract

Water resources are becoming scarce and climate change is exacerbating the stress on traditional water supplies. Thus, it is important to identify viable solutions to resolve tensions in the water energy nexus. One example is the use of transport membrane condensers (TMCs) to recover water as well as waste heat from flue gases with the aim to improve economics and to reduce the environmental impact of the industrial sector. In this work, the authors present a detailed 1D+1D TMC model and investigate the impact of three key membrane design parameters upon the water recovery rate. Sensitivity analyses of pore radius, membrane porosity and contact angle reveal that pore radii of smaller than 10 nm can substantially improve condensation rates due to the exponential vapor pressure dependency described by the Kelvin equation. Reducing the pore radius from 15 nm to 1 nm increases water recovery by over 74% in some of the study scenarios. Additionally, a higher membrane porosity is shown to increase water condensation rates. A higher porosity increases the number of pores on the surface, and thus, the driving force for mass transport. The results show an increase in water recovery of up to 7.7% per 10% porosity increase. The contact angle, which is related to the hydrophilicity of the membrane material, influences the formation of the meniscus inside the pore. Changes in the contact angle from a flat surface (90°) to 30° are shown to have a strong impact upon the water condensation rate. Furthermore, condensation flux improvements through the above-mentioned membrane design modifications are more pronounced in environments with low mass transport driving force due to the nature of the suction effect, which is governed by diffusion and convection transport laws.