Continuous Casting of Asymmetric Tubular Reverse Osmosis Membranes
The advantages of tubular reverse osmosis module configurations for desalination primarily result from the large (typically 0.2 to 1 inch in diameter) characteristic fluid flow cross section and its uniformity in the flow direction. These inherent characteristics of the tubular module yield, with proper design, advantages of minimal fouling tendency, higher fractional recovery operation, and ease of physical in situ cleaning of the membrane surface in comparison with the performance of module geometries characterized by much smaller fluid flow cross sections and flow paths that are both exceedingly tortuous and contain many flow regions of stagnation and relative quiescence. From a cost-to-manufacture standpoint, full exploitation of the tubular module’s operational advantages will accrue as the cost for casting uniform, high performance tubular membrane is reduced to a level as close to the cost of polymer itself as is possible. Since, in the case of cellulose acetate, approximately 1/64 pound of polymer is required to produce one square foot of membrane 8 mils thick, then the cost of polymer is slightly greater than 1 cent per square foot of membrane or less than 1/10 of a cent per gallon/day of permeate flow capacity. The differential between this base cost, to which must be added the comparable cost of the other casting solution ingredients, and the cost of tubular membranes cast in the usual batch manner is significant.
KeywordsShear Rate Cellulose Acetate Continuous Casting Casting Solution Continuous Casting Process
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