Degasification module

Figure 13.16 Membrane degasification module. (Courtesy of Membrana.)...

Peterson PA, Runkle CJ, Sengupta A, and Wiesler EE, Shell-less hollow fiber membrane fluid contactor, US Patent 6,149,817, 20(30. Sengupta A, Runkle CJ, Vido TR, and Kitteringham BA, Economy of scale Large membrane modules for degasification and purification, International Water Conference, Pittsburgh, PA, October 2003. 

FIGURE 13.16 Experimental setup gas absorption and subsequent degasification using membrane modules. (From Bhaumik, D., Majumdar, S., Fan, O., and Sirkar, K.K., J. Mem. Sci., 235, 31, 2004. With permission.)... 

Figure 5.14 Experimental setup gas absorption and subsequent degasification using membrane modules. From Ref. [7] with permission.

Membrane degasification units generally use hydrophobic hollow-fiber polypropylene or polytetrafluoroethylene (PTFE) (Teflon) microporous membrane (Wiesler, 1996). Hollow-fiber modules are made by potting the desired number of fibers into an external shell. The potting compound may be polyurethane, epoxy, polyolefin, or fluorinated polymers. Since the membranes are hydrophobic and have small pores (Fig. 13.15), water will not easily pass through the pores. 

Extensive research both in industry and academia has resulted in the innovation of porous membranes, which are gas fiUed, with much smaller mass transfer resistance. Parallel research on microporous membranes has adjusted the pore size and membrane hydrophobicity, again yielding a much smaller mass transfer resistance. However, modules with different geometries perform differentiy. Flow outside of, but perpendicular to, the fiber bundle offers reasonably fast mass transfer. Not surprisingly, this geometry is chosen in most of the commercial membrane degasification units. 

Mass Transfer in Membrane Degasification Commercial membrane degasification units involve mass transfer in hollow-fiber modules where the vacuum and sweep gases are applied inside the fibers, and the water flows outside the flbers in cross flow perpendicular to the fiber axis. The mass transfer involves three sequential steps. First, dissolved gas diffuses out of the water to the membrane surface. Second, it diffuses into vapor pores in the walls of the hydrophobic hollow fibers. Third, when the dissolved gas reaches the other wall of the fibers, it diffuses into the surrounding nitrogen sweep gas in a high vacuum condition. 

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