Optimal Energy Consumption Design of Large Seawater Reverse Osmosis Systems

Abstract

The specific energy consumption SEC is the most determinant factor in operation cost of seawater reverse osmosis SWRO systems in desalination plants. This research aims to study the optimization of SWRO systems performance with minimal specific energy consumption by using the most an advanced technologies with respect to system configuration, pumping system, membrane assembly and energy recovery devices. This study focuses on both design and actual performance of the membranes by using FILMTEC™ in different stages. The energy consumption was measured in relation with other operating factors such as recovery, feed concentration, productivity, temperature, etc. ROSA 9.1 software used to investigate the performance of SWRO system, ERITM PXTM power Model used as supplementary tool to investigate SEC reduction after addition pressure exchanger PX to the system in first pass. Results of the analysis emphasized on the valuable contribution of the energy recovery devices ERD and high efficiency pumps for increasing water productivity and decreasing energy consumption per cubic meter of water produced. Results showed that using the available advanced technologies and new technical concepts, it is possible now to produce water with energy consumption of reverse osmosis processes close to 3 kWh/m3. The results showed that, for the first pass, the effect of using ERD leads to reduction in the SEC from 3.90 down to 2.04 kWh/m3. The resultant energy saving is 46% at recovery rate (40 - 50%). Finally, an acceptable agreement between actual (Perth case – Australia) and design results of the study has been noticed. The study concluded that Isobaric ERD such as the PX device can reduce the energy consumption of SWRO system by as much as 46% compared to systems with no ERD.Since energy consumption may comprise as much as 75% of the total operating costs of SWRO plant, it has become almost inconceivable to build SWRO system without using isobaric ERD. SWRO plants should be arranged in three centers: Pumping Center, Membrane Banks, and Energy Recovery Center to provide a significant reduction in overall water costs.