Abstract
This paper suggests a new method of predicting flux values at Reverse Osmosis (RO) desalination plants. The solution-diffusion model is utilized to determine the osmotic pressure drops for seawater sources. The same technique was applied to the groundwater source at the Abqaiq plant (500 RO plant) to calculate the osmotic pressure. The calculated osmotic pressures were utilized to determine the appropriate flux rates and membrane resistances of different BWRO Toray membranes and a performance comparison between various membranes has been established. The model results confirm an inverse relationship between membrane thickness and water flux rate. Also, a proportional linear relation between the overall water flux and the applied pressure is identified. Higher flux rates and lower salinity indicate lower membrane resistance yielding higher production. The modeled data predict that BWRO Toray TM720D-440 with an 8" membrane is the optimal choice for treating waters from the three water sources at the Abqaiq plant.
Highlights
The solution-diffusion model is a popular expression used to explain the transport in dialysis, reverse osmosis, gas permeation, and pervaporation
The osmotic pressure of the groundwater source is less than the Arabian Gulf and the Red Sea water sources which is related to the flux rates and water salinity
The required applied pressure drop must be larger in the case of seawater sources due to their higher determined osmotic pressure values
Summary
The solution-diffusion model is a popular expression used to explain the transport in dialysis, reverse osmosis, gas permeation, and pervaporation. Exclusion or filtration of larger permeant's pores is the separation technique explained via the pore-flow model [1, 2]. There is a major difference between the solution-diffusion model and the pore-flow model in expressing the chemical potential. In the solution-diffusion model, the pressure within a membrane is uniform and the chemical potential gradient is expressed only as a concentration gradient. Solution-diffusion membranes transmit pressure in the same way as liquids, which is the reason for expressing the pressure difference across the membrane as a concentration gradient only. The chemical potential gradient in the pore-flow model is expressed only as a pressure gradient since the concentrations of both solvent and solute within a membrane are uniform. Comparisons between the two models for a one-component solution in a pressure-driven permeation system were conducted in [1, 2]
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