Cyclic simulation and energy assessment of closed-circuit RO (CCRO) of brackish water
Mingheng Li
Abstract
A previously developed spatiotemporal model is enhanced to simulate detailed dynamic and cyclic behavior of closed-circuit RO (CCRO). The partial differential equation (PDE) model couples water balance, salt balance and momentum balance and explicitly accounts for pressure drop, concentration polarization and axial dispersion in both closed-circuit (CC) and flushing modes. Simulation case studies using conditions similar to those in a well-studied industrial brackish water plant were carried out and the specific energy consumption (SEC) in CCRO at the cyclic steady state (CSS) was analyzed from thermodynamic restriction, flux requirement, flow resistance, concentration polarization and salt retention. On the basis of the same flux used in industrial conditions, CCRO is not as energy efficient as state-of-the-art multi-stage RO for low-salinity brackish water desalination. Operating CCRO at a reduced flux can make it competitive.