03-05-2014, 03:04 PM
SOLAR DESALINATION OF WATER BY MEMBRANE DESTILLATION
SOLAR DESALINATION.pptx (Size: 139.9 KB / Downloads: 12)
Freshwater, which man can use accounts for only one percent of abundant seawater
Currently implemented technology for converting seawater into freshwater, such as distillation, reverse osmosis and electric dialysis has problems of difficult maintenance such as pretreatment of seawater and the need for engineers with specialist knowledge.
Membrane Distillation, which is a simple and maintenance-free seawater Desalination system.
Membrane distillation uses a porous hydrophobic membrane, which means that water vapor can pass through it, but drops of water can’t. By passing hot seawater through one side of the membrane, only the water vapor generated from the seawater passes through. The cool water on the other side of the membrane, forming water drops, resulting in freshwater, then cools the water vapor.
Heat to warm the seawater is provided by solar collector, and photo voltaic panels power the pumps so that the system can been installed at sites without an electricity supply.
desalination :
Desalination is a process of that remove excess salt and other minerals from water. Water is desalinated in order to obtain fresh water suitable for animal consumption or irrigation, or, if almost all of the salt is removed, for human consumption.
solar desalination :
Solar Desalination is the desalination of water using solar energy. Although everybody recognizes the strong potential of solar thermal energy to seawater desalination in arid and semi–arid regions due to the usual coincidence of water shortage, good solar radiation and sea-water availability, the process is not yet developed at commercial level.
membrane distillation :
Membrane Distillation is the evaporation and subsequent collection of a liquid by condensation as a means of purification using a hydrophobic membrane.
Desalination using Sun as the energy source by distillation using a hydrophobic membrane as a separation medium.
Desalination: of ocean water is practiced in many regions that have scarce natural freshwater supplies; it is widespread in the Middle East and the Caribbean
ADVANTAGES OF MEMBRANE DISTILLATION:
It produces high-quality distillate. Water can be distilled at relatively low temperatures (0 to 100 °C).
Because of low process temperatures solar energy and waste energy can be used to run the plant.
The water does not require extensive pretreatment as in pressure-based membrane treatment. Membrane distillation may also be competitive in treating reverse osmosis (or nanofiltration) concentrate. Efficient and compact spiral-wound membrane distillation modules
Recovery of the heat of condensation is integrated in the module design Low system pressure Insensitive to dry-running and fouling, negligible scaling due to process temperatures below 80°C (176°F).
SUMMARY:
Small simple desalination plants operating independent from the electric grid are either not available or not economic at all. The process of membrane distillation allows the effective use of low temperature heat sources like solar energy or waste energy from engines for small to medium scale desalination.
Although the process of membrane distillation is known since over 30 years cost-effective desalination modules have not been available so far.
In order to achieve an effective membrane distillation process spiral wound modules have been developed and optimized during a 6-year R&D program. The modules are designed as compact units with integrated recovery of the heat of condensation, allowing a highly efficient use of low temperature heat sources.
In case there is a high amount of free waste energy available the heat recovery is not needed and flow rates 3-5 times higher can be obtained. Desalination modules without integrated recovery of latent heat have been developed, too and will be available soon.