Studies on scaling of membranes in desalination by DCMD

Membrane distillation whether of the DCMD (direct contact membrane distillation) or vacuum membrane distillation variety can have a role to play in desalting highly saline waters that have considerable osmotic pressures where reverse osmosis operation becomes more expensive and problematic. An analysis of the scaling potential in hollow fiber membrane-based crossflow DCMD is carried out in terms of the saturation index profiles throughout the hollow fiber membrane module as a function of the location in the module for the sparingly soluble salt, CaSO₄ and CaCO₃, individually or mixed together. The highest scaling potential is at the high temperature end of the module. Concentration effects are far more important than temperature. Even when the precipitation rate is fast in the mixed CaSO₄-CaCO₃ system at elevated temperatures or high concentrations, no significant loss in water vapor permeation is observed. This is an abstract of a paper presented at the 2007 AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).