4E assessment of a hybrid RO/MED-TVC desalination plant powered by CPV/T systems

Abstract

The growing demand for pure water and the challenges of energy transition encourage the use of renewable energies in desalination. This investigation aims to carry out an energy, exergy, economic and environmental analysis of a hybrid RO/MED-TVC desalination powered by CPV/T systems. The electrical and thermal needs of the hybrid desalination unit are supplied by a concentrated photovoltaic solar field. Computational models are elaborated and validated for the CPV/T, RO and MED-TVC units. Three reverse osmosis desalination configurations with two energy recovery strategies are studied: single stage-RO, double stage-RO and three stage-RO. The results showed that the conversion rate increased from 27 to 48 % and from 37 to 62 % and from 49 to 72 % by increasing the feed pressure from 5000 to 8000 kPa for the reverse osmosis units at one, two and three stages, respectively. The exergy destroyed in the whole system was less for Pelton turbine energy recovery than for a pressure heat exchanger. The number of RO membrane modules was minimum for double RO-stage and maximum for triple RO-stage. The results showed that the MED performance improved by 217 % and the specific thermal consumption was reduced by 68.5 % by increasing the number of effects from 4 to 12. The results highlighted that the production of electricity and thermal energy, electricity injected to the grid and the thermal energy storage are high for Sharm-el-Sheikh and low for Tripoli. The levelized costs of water were 0.424, 0.436, 0.448, 0.457, 0.463, 0.466 and 0.468 US$/m3 for Sharm-el-Sheikh, Nouakchott, Benghazi, Tangier, Doha, El Kuwait and Tripoli, respectively. The values of carbon intensity were also 0.67, 0.68, 0.71, 0.78, 0.84, 0.86 and 0.87 kg CO2/m3 for Sharm-el-Sheikh, Nouakchott, Benghazi, Tangier, Doha, El Kuwait and Tripoli, respectively. The overall results demonstrated that the double-stage-RO with energy recovery from the pressure exchanger combined with the ten-effect MED-TVC was the best solution to achieve efficient desalination using the electricity and heat produced by concentrated photovoltaic thermal systems.