Energy efficient water purification plant design techniques

Abstract

South Africa is facing regular water and energy shortages. The country is surrounded by two oceans consisting of sufficient seawater to solve its water shortage, however, seawater reverse osmosis (SWRO) processes are energy intensive. The investigation into energy efficient water purification techniques is therefore critical to ensure water supply, despite the energy constraints. Energy efficient water purification techniques can be applied through the integration of energy recovery techniques such as variable speed drives (VSDs), energy recovery devices (ERDs) and programmable logic controllers (PLCs). In order to investigate the impact of energy recovery techniques in SWRO plants, an existing 1 ML/day SWRO plant installed in South Africa was modelled using WAVE. The specific energy consumption (SEC) associated with the plant was therefore determined based on the equipment required. The actual SEC of the existing 1 ML/day SWRO plant was then compared to the theoretical SEC in order to quantify the effect of installing the energy recovery techniques. The theoretical SEC was found to be 4.79 kWh/m3, whilst the actual SEC was found to be 4.07 kWh/m3. Both the theoretical and actual SECs were within the typical ranges reported by previous studies. The difference of 0.72 kWh/m3 was attributed directly to the installation of energy recovery techniques. Previous studies quantify the effect of adding VSDs and ERDs to SWRO plants, however little information is available with respect to the quantifiable impact of installing PLCs. Future developments should include investigating the quantifiable impact of incorporating PLCs into SWRO plants. In addition, previous studies provide the actual SECs of SWRO plants to be expected with the integration of energy recovery techniques, but do not necessarily quantify the difference between the actual SECs and the theoretical SECs. Future developments should interrogate the difference between the theoretical and actual SECs such that the quantifiable impact of the energy recover techniques can be better understood.