Comenius:Desaladora

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Proyecto de Jaume Lloret García, Rafael Bautista Yañez y Vicent Martínez Llorca


Desaladora Canarias


¿Cómo funciona una desaladora?



Given the large areas of the five continents that suffer water shortages, and that consumption in industrialized areas is growing by leaps and bounds, man has been forced to get drinking water in various ways. One of these is the desalination.

Desalination is a process whose end is to get fresh water by removing H2O from the mixture of salts and minerals present in seawater. The process is not very difficult to carry out nowadays but it usually involves a considerable energy expenditure and it can have significant environmental impacts.

It can be accomplished through various means, and the most used are:

  • Reverse osmosis: is performed by applying a pressure above the osmotic pressure that causes water to mix and salt. That pressure is performed through a permeable membrane that allows pure water to flow in one direction while the brackish do another.
  • Destillation: salt water evaporates and condenses into fresh water. The pressure and temperature are decreasing in each stage being achieved resulting concentration of the brine. The heat from condensation is used to reheat the water to be distilled.
  • Freezing: through this process, seawater is sprayed in a cold chamber and low pressure, thereby forming ice crystals on the brine. These crystals are separated and washed with fresh water.
  • Flash evaporation: water is introduced in the form of fine droplets in a low pressure chamber, below the saturation pressure. Some of these drops of water are immediately converted into steam, which are then condensed, obtaining desalinated water. The wastewater is introduced into another chamber at lower pressures than the first and using the same heating process, spray and flash evaporation desalinated water. This process is repeated until they reach desired values desalination. These plants can have more than 24 stages of flash desalination

Researchers have for years been trying to minimize the problem of high energy consumption of desalination plants. In fact, there is already a technology for energy based on brine itself: a device called a Pressure Exchanger transfers energy directly from the brine feed flow performance.

The resultant waste water of the desalted are saltier than the waters of origin and they present differences of temperature, of pH, of alkalinity and contain chemical substances used during the process of purification. In case of the plants that work for distillation the spillage represents from 8 to 10 times the water volume purified, whereas in plants of inverse osmosis the residual volume is minor that in the previous ones (2.5 to 3 times the polished volume) but the spillage has a content in you work out very much major. Countries wich top the list of the countries with largest number of desalination plants are Saudi Arabia and Kuwait followed by Spain, USA, Autralia and China. In Europe, the most big desalination plant is in Carboneras, Almería and it desalts more than 10000 litres per day.


What advantages and disadvantages has desalination?

Salmuera arrojada al mar en desaladora de Tenerife.jpg


Obtaining drinking water from the seawater is a possible solution to the lack of water but should not be introduced as a model for managing water resources.

The brine is pumped into the sea should increase the minimum possible level of salinity in the area where it is expelled. At the end of the whole represents a tiny brine drop when compared to the entire volume of seawater. Concern about the possible effects of discharges of brine desalination plants in the flora and fauna is relatively recent. Although there desalination plants operating for many years and had not observed any change in the flora and fauna in the dumping area, enough that the scientific community warned of possible negative effects, which was given to all means to study the problem and find a solution. First we studied the salinity tolerance of the most sensitive species and greater degree of protection in environmental directives and Spanish Europe, among which is the Posidonia oceanica, a plant that lives in the Mediterranean near the coast and forms a habitat of great value for the development of the fish, set the sandbanks and oxygenate the water, so we must be careful when the brine is returned to the sea. Tues It is therefore required to fully protect this species and prevent further minimum negative impact on it.

This study of salinity tolerance of the Posidonia oceanica has been out in the last 3 years, reaching maximum tolerable salinity set at 38.5 practical salinity units that are roughly equivalent to 39 grams per liter. Have participated in this study scientific bodies most prestigious Spanish in marine science. Once set the maximum tolerance of salinity, the solution must come from the hand technicians can always design a physical solution of the spill to achieve the natural dissolution of the brine in the very mass of seawater, to reach the tolerance limits set. There should be general recipes, but in each case study the best solution. Can always find the best way to completely avoid spillage any negative environmental effect. Different typologies as may be the dissolution of the brine before being discharged with more seawater (Carboneras and Javea), poured into the mouths of ravines where the Posidonia is far removed (Alicante, Palma Bay, etc.). and dumping at areas of heavy surf prove that in many cases the solution may be very simple. In more difficult cases by a few meters near the coast of the grass meadow (new projects for Murcia and the Balearic Islands) is designed too simple a solution but more elaborate, consisting of distributing brine for various broadcasters so that the brine coming out and running into the seawater itself produces an agitation that causes homogenise in whole mass salinity of sea water surrounding the diffuser. For simplicity, achieves the same effect as shaking the sugar in the bottom of the cup of coffee unifying flavor. With the application of the mathematical tools of calculus, already available, always reaches a perfectly viable solution, technically and economically.

It should be noted that the rigor with which Spain has been undertaken in both the tolerance study of protected species as the technical solution of each case, the subject of papers at various conferences, has been highly appreciated by the desalination community worldwide. From USA to Algeria, Morocco, Israel and others have requested information about our experience, in less than three years has analyzed the problem and has provided the solution.


Drawbacks

  • In the process of extracting salt from seawater it produces salt residues, once discharged into the sea, harming marine flora with increasing salinity.
  • Complex reverse osmosis plants require a large consumption of electricity.
  • The desalination would be installed in locations not occupied by tourism developments.
  • As factories are, have a limited life.
  • The desalinated water, it seems, could harm agriculture.
  • Would have to make costly new infrastructure to transport the desalinated water to areas where needed.

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