Solar Desalination (2017)

Apunte Inglés
Universidad Universidad Politécnica de Valencia (UPV)
Grado Ingeniería de la Energía - 5º curso
Asignatura Tecnologías Avanzadas de Energía Solar Térmica
Año del apunte 2017
Páginas 2
Fecha de subida 10/06/2017
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Pau Carnero MUTEDS Si necesitas más apuntes puedes encontrarlos en Unybook.com buscando el usuario "pcarnero" Other Applications of Solar Thermal Power Solar Desalination In the water cycle, there’s only a 3% that is fresh water whereas up to a 97% is in the form of sea water. Then, there’s the idea of the desalination, in order to obtain fresh water from the sea water, however the process is very energy consuming, so the O&M costs represent a very high figure. Also, in the desalination process, there’s the outcome of the fresh water, but also the brine, which would need to be taken care of.
Technologies There are different technologies to perform the desalination process, and each one is able to reach a level of concentration of dissolved salts in the outlet fresh water.
• • • • • Ion Exchange. From 10 to 900 ppm.
Nanofiltration. From 50 to 1.300 ppm.
Reverse Osmosis. From 90 to 60.000 ppm.
Electrodyalisis. From 250 to 9.000 ppm.
Evaporation. From 10.000 to 900.000 ppm.
The most used technology is the Reverse Osmosis, which is a membrane technique based on filtration; followed by Multi-stage Flash, which is a thermal technique based on evaporation.
Reverse Osmosis The osmosis process is based on contrary to the natural process by which the thermodynamical potential, depending on temperatures, concentrations and pressures, of solutions tend to balance. This “anti-natural” technique is made by means of energy consumption in the pumping system. The plant works following some specific phases: • • • • • • Sea water intake.
Pre-treatment, with chlorination, filtration, sedimentation, etc.
Reverse osmosis, where the pumping takes place, and where the waste is generated.
It’s important to implement energy recovery systems in order to reduce the high net energy consumption.
The Energy Recovery Device is based on the recovery of the high pressure the water still has after the reverse osmosis process, so part of the flow is forced to give some of its energy to the incoming feed water.
Post-treatment, where there is the removal of certain chemical compounds, which vary depending on the final application.
Polishing steps, where depending on the final use for the water different sub-processes for purification purposes may be implemented.
Storage and distribution.
A typical osmosis plant is located in the sea, with an inlet of water to be treated and an outlet of the water with diluted brine. The outlet is a critical point in the design and operation of the plant, due to the fact that the brine is heavier that water it must be installed facing downwards and far away enough from the inlet. Very strict environmental control should be carried out in order to find out whether the increase of saltiness in the sea is acceptable or not.
Pau Carnero MUTEDS Si necesitas más apuntes puedes encontrarlos en Unybook.com buscando el usuario "pcarnero" The installation is very simple and easy to run, so the manpower needed is very reduced, representing only a 1% of the overall cost, being the highest consumption the one linked to the electricity consumption, 41%.
Multi-Stage Flash It’s based on a big quantity of evaporation-condensation processes, obtaining a high concentrated brine that does not evaporate and purified water, which it does evaporate. The consumption of this technology is not only the pumping power, but also the heating of the vapor.
Solar Desalination The different technologies of desalination could be powered by the Sun, for instance the electricity consumed in the Reverse Osmosis installations could be provided by a PV system.
However, the area of panels would be huge, since for each 1 m3/d of water desalinated there is a need of 10 m2. Also, the heat needed at the Multi-Stage Flash installation could be provided by solar collectors.
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