(604b) Numericl Modeling of Scale Formation In Ro Memrbane Desalination

In membrane separation processes, rejection of solutes and solvent permeation lead to increased concentration of dissolved and suspended species in the retentate stream and at the membrane surface. In reverse osmosis (RO) desalination, this effect, known as concentration polarization, can result in salt concentrations exceeding saturation levels, thereby leading to mineral scale build-up on the membrane surface. This scale build-up leads to decreased module performance (e.g., flux decline) and shorter membrane lifetime. To better understand the effects of the integration of concentration polarization with mineral scale formation, 2-D and 3-D numerical models were developed to predict fluid dynamics and solute mass transfer within the feed flow channel of RO modules. This computational model was coupled with a surface crystallization kinetic model to provide a detailed description of the development of mineral scale on the membrane surface. Experimental results from a small RO module with an un-obstructed feed flow channel were used to calibrate and test the mineral scaling simulations, which were then extended to include the impact of channel spacers. The integrated scale formation model provides detailed information on the location and evolution of mineral salt scaling in the RO feed channel. Comparison with experimental scaling results from RO channels with and without spacer filaments will be presented and discussed with respect to the implications for RO module design and optimization of process conditions to reduce the propensity for scale formation.