Studies of Air Dehydration by Using Hollow Fiber Modules.

摘要

Hollow fiber membrane module is widely used for commercial gas separation, such as production of high purity of nitrogen and enriched oxygen gas from air, carbon dioxide removal from methane, carbon dioxide sequestration from flue gas and hydrogen purification. Membrane gas separation for air dehydration (AD) differs from other commercial applications in several ways. First, the component to be removed (water) possesses a permeability that may be more than three orders of magnitude greater than the other components in the feed (oxygen and nitrogen). Second, the feed concentration is small, less than 1% in a molar basis. Third, the product concentration may be two orders of magnitude less than the feed concentration. This work seeks to study the hollow fiber gas separation modules for air dehydration.;The work evaluated potential module performance and the effect of the inefficiencies such as fiber property variability and deviation from ideal counter-current contacting.;This research investigated the effect of sweep uniformity on gas dehydration module performance by assuming the sweep around each fiber is Gaussian sweep distribution. In addition, this work explicitly calculated sweep distribution and presented the effect of sweep distribution, effect of fiber packing variation along case. Compared to fiber size variation, non-uniform sweep distribution has little effect on module performance.;Moreover, two fundamental issues for gas separation regarding the Hagen-Poiseuille law and boundary layer contributions on mass transfer coefficients were investigated.;This works investigated the of the Hagen-Poiseuille law for pressure drop calculations in hollow fiber gas separation modules. In this work a two dimensional (2D) computational fluid dynamics (CFD) mathematical modeling was used to obtain the numerical approximations to the solutions of the conservation of mass and momentum equations in a single fiber that is assumed to be representative of all fibers in the fiber bundle. Hagen-Poiseuille law is a good approximate solution of pressure drop for sufficiently low Reynolds number of the feed and permeation fraction for compressible flows.;For gas separations, concentration polarization can be significant when the fast gas permeance is greater than 1000 GPU. For air dehydration modules, the overall mass transfer coefficient is calculated by summing the lumen-side, membrane, and shell-side mass transfer resistances. In this work, effective mass transfer coefficients in the lumen and shell are calculated by using computational fluid dynamics (CFD) method and analytical method. The solutions will be obtained for a single fiber that is assumed to be representative of all fibers in the fiber bundle. The lumen mass transfer coefficient for constant wall permeance is 20% greater than that for constant wall concentration. The shell mass transfer coefficient in this research is 2–3 orders magnitude greater than the Donahue equation and the differences may arise from the complexity geometry of the shell fibers and the flows within it.;A commercial air dehydration hollow fiber module was evaluated. The module properties were obtained from experiment. Experimental results are in good agreement in simulation results-sweep increases product flow rate significantly.