A small-scale seawater reverse-osmosis system with excellent energy efficiency over a wide operating range

A small-scale seawater reverse-osmosis system with excellent energy efficiency is presented. The system promises to deliver up to 460 l/h of potable water, from seawater (at 40,000 ppm), while consuming less than 1600 W of electrical power. This represents a specific energy consumption of less than 3.5 kWh/m3. Moreover, the flow may be controlled in order to reduce the power consumption by a factor of four without any significant loss of efficiency — the specific energy consumption remains near to 3.5 kWh/m3. The keys to these impressive figures are the energy recovery provided by the Clark pump, from Spectra Watermakers Inc., and the use of a variable water recovery ratio control algorithm, developed by CREST. The significance of the system is that it may be operated from variable intermittent renewable-energy sources, such as wind and solar-photovoltaic (PV), without need of batteries. Results of laboratory testing and extensive modeling are presented.

The system presented in this paper promises to deliver excellent energy efficiency over a wide operating range. The performance predictions for the system as a whole are based on a detailed Matlab-Simulink model and the critical components of this model are based on laboratory measurements. CREST is now commissioning a fully instrumented prototype of the system, in order to verify its performance. Subsequently, field trials will be undertaken. Two further papers discussing PV-RO and small-scale wind-RO respectively are being presented in parallel with this one.