Efficiency increase in thermal desalination plants by matching thermal and solar distillation: theoretical analysis

The effluent streams from MSF and MED plants retain substantial thermal and mechanical energy which is usually wasted as the streams are rejected into the environment. Recent environmental studies pose the question of environmental sustainability of desalination due to the large amount of heat and brine dissipated into the sea. Moreover the use of renewable energy so far have been confined to experimental studies or to the use in remote areas and no studies have been carried out on the coupling of a solar still plant with an existing thermal desalination installation in order to take advantage of the heat streams generated by the thermal plants. The combination of a solar desalination system utilizing the heat reject or the brine from MED or MSF as feed water to the solar plant could mitigate the environmental impact and dramatically increase the efficiency and cost effectiveness of solar plant. This paper presents a number of theoretical solutions to couple a thermal plant and a solar distiller. The possibility of further increasing the 'economical' efficiency of the process by a batch/continuous crystalliser for producing different sea-salts has also been considered.