Infoscience

Student project

Design of solar driven supercritical water desalination plant

The objective of this master project is to develop model for the solar driven supercritical desalination plant. Furthermore we propose a possible system integration and examination of its performance in terms of energy and cost effectiveness. The model simulations and calculations are performed using Belsim Vali and in-house LENI developed program OSMOSE. Supercritical salt separation model was created based on the solubility models proposed by Leusbrock and research conducted by Khan and Rogak on salt mixture solubility. This allowed the creation of a salt separation model as a function of pressure and temperature in supercritical conditions. The proposed model is validated in certain range of pure water density and is characterized by 86% water recovery ratio for salts inlet concentration of 4%. During the simulation, a reactor was operated in fixed temperature of 660 K and 221 bar in order to fulfill potable water requirements in terms of TDS value. The simulations results show that through integration of recompression and steam network, a significant improvement in terms of energy usage and cost incurred can be obtain. Steam network integration with double steam step allows to eliminate electricity requirements and increase the exergy efficiency to 3.16%. The majority cost of the system is caused by the investment in the solar system due to linear behavior of costing function for solar installations. It is shown that 75% of overall investment cost is intended for hot utility. However, it was found that profitability can be obtain when secondary products income are taken into account. By possibility of selling industry salts that are separated in the reactor, it is possible to obtain cost of 0.96 CHF per cubic meter of generated potable water. Moreover, to achieve higher economic performance and fresh water recovery ratio hybrid, the “Reverse Osmosis – Supercritical Desalination Plant” system was investigated. It was found that joining two technologies led to significant economic savings together with drastic increase in water recovery ratio up to 91%. This shows that proposed integration not only increased profitability of the installation, but also increased water recovery ratio. Thus showing promising perspectives for possible future desalination systems.

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