Solar Organic Rankine Cycle coupled with Reverse Osmosis and mebrane distillation towards minimizing brine discharge
Abstract
The current research work is focused on the investigation, optimization and identification of key design parameters of a solar-Organic Rankine Cycle (ORC) power generation system coupled with Reverse Osmosis (RO) and Membrane Distillation (MD) desalination units for fresh water production. The core idea is to feed RO and MD units by exploiting both electricity generated by the ORC and the heat dissipated in the ORC condenser respectively. Electricity comes from the direct conversion of heat to power through ORC and is used to drive the system pumps, while heat for MD corresponds to that dissipated during condensation process (heat rejection of the power cycle). By combining RO with MD an increased water recovery ratio from both desalination processes can be achieved, resulting into reduction of the environmentally harmful brine. Further exploitation of the high concentrate is possible to extract sodium chloride crystals. The proposed system can be flexibly combined with other thermal sources (e.g. excess heat from industrial processes) and it is applicable for feed water treatment of different salinities (brackish, seawater etc.). Vacuum tube solar collectors operating at temperature in the order of 130 oC have been considered in the calculations. The condensation temperature where heat is supplied to MD is in the order of 90 oC, Some 90 kWth of heat are rejected in the full load operation, while net power generation from the ORC is about 3 kW with a thermal efficiency slightly above 3.5 %.