Energy-Optimal Control of RO Desalination

Abstract

A novel model-based control system for the operation of a spiral-wound RO membrane desalination system was developed with a focus on maintaining energy-optimal operation. The control scheme utilized an operational model for spiralwound RO desalting with a supervisory controller providing real-time updates of membrane permeability and the appropriate feed pressure set-points for maintaining the target permeate productivity at the lowest feasible specific energy consumption. System RO feed pressure and flow rates were controlled by a lower-level RO controller through adjustment of the RO high pressure feed pump, variable frequency drive, and RO concentrate valve. Seawater desalination tests with an RO plant, capable of permeate productivity up to 18 000 gallons/day, demonstrated effective self-adaptive energy-optimal operation, subject to feed salinity fluctuations, constraints imposed by the system's physical limitations (i.e., minimum and maximum feasible operational pressures and flow rates), and the thermodynamic restriction for cross-flow RO operation.

A perspective on reverse osmosis water desalination: Quest for sustainability

“…Improvements in membrane element design could also be beneficial to reducing pressure losses while possibly enabling reduction in concentration polarization, thereby allowing higher recovery operation per element and thus decreasing the plant footprint and possibly plant components. Operational considerations include optimal plant control that will ensure energy optimal operation while meeting the target permeate productivity …”

“…When the RO plant is incapable of operating close to the thermodynamic limit (due to design and equipment restrictions), one can drive the RO process toward the optimal operating condition via suitable model-based control. 49,91 In such an approach one must also consider constraints imposed by the target water production capacity and limitations placed on the operability of plants components (e.g., maximum allowable operating pressure for pumps and pressure vessels).…”

“…47 Right: a small mobile RO desalination plant (capacity of 45.4 m 3 /day). 48,49 The same size membrane elements (8 00 ) are used in both plant demonstrating the scalability of RO desalination.…”

Multi-criteria decision making on the energy supply configuration of autonomous desalination units

“…The main goals of testing several topologies of energy production for SWRO units is the minimization of power production and transmission losses, the minimization of the environmental impact of the system and the maximization of the socioeconomic benefits of the system. However, there are numerous other methods in literature that can further optimize the specific energy consumption of the RO units such as using a supervisory controller that provide real-time updates of membrane parameters set-points for maintaining the target permeate productivity and quality at the lowest feasible specific energy consumption [21]. Nonlinear optimization e based model, was also applied and verified against experimental data of an RO unit in order to minimize energy consumption of the desalination unit [22].…”

Computational Fluid Dynamics Simulation of Brine–Seawater Mixing in a Rotary Energy Recovery Device

“…15,16 However, the mixing does affect the salinity of the pressurized seawater and its osmotic pressure. The equation for the relationship between osmotic pressure and salinity of seawater can be represented as 4,17 …”