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A first approach study on the desalination of sea water using heat transformers powered by solar ponds

Salata, F., Coppi, M.
Applied energy 2014 v.136 pp. 611-618
absorption, desalination, developing countries, economic feasibility, energy, freshwater, heat transfer, ponds, seawater, solar collectors, solar energy, temperature
In many emerging countries over the past few years some phenomena, such as a better welfare state, industrial growth and a development in agriculture, led to a significant increasing of the demand concerning fresh water. In order to face this ever-growing demand, one of the possible solutions to counterbalance the lack of water resources, is the desalination of sea water. For this specific goal solar energy, as a resource, is the process which has more reliance since it allows a low-cost production of desalted water (without using any valuable energy resources such as fossil fuels) and in a complete respect of the environment.This first study has the purpose to analyze from an energetic perspective whether it is possible or not to reach process temperatures over 100°C, through the use of solar ponds and heat transformers, in order to produce desalinated water. The final aim of this work is to quantify the surface of solar ponds needed to a production (expressed in cubic meters) of desalinated water.An absorption heat transformer is a thermal machine that while extracting heat from a source (at an available temperature) is able to ennoble a portion of the heat collected/obtained, making it available at higher temperatures. This process occurs at the expenses of the remaining portion of heat whose temperature degrades by lowering its values. The portion of heat will be then transferred to a thermal well. Hence an absorption heat transformer can use the solar energy stored in solar ponds as an energy source at an average temperature.Process temperatures which are higher than 100°C for a whole year can take place only under certain chained conditions such as: source temperature with steady values during the entire season obtainable through solar ponds; condensation process occurring at sufficiently low temperatures through the use of sea water; exertion of heat transformers. The heat which is usually available at these temperatures could be used for common thermal processes during the desalination of seawater.In this work we want to demonstrate that it is possible, energetically speaking, to produce desalinated water by exploiting the solar energy stored in solar ponds and the technology of absorption heat transformers. We can notice how for every m3 of desalinated water produced in one day we need ponds with an area ranging between 1000 and 4000m2, this depends on the amount of heat flux drawn.The analysis we carried out represents a first attempt to face this kind of problem. In future studies we will examine both technical and economic feasibility.