Dessalement de l'eau de mer (document en anglais)

Desalination of sea Water

INTRODUCTION

I/ VARIOUS DESALINATION PROCESSES

1/ Presentation

2/ Comparison between this processes

II/ SOME FACTORIES OF DESALINATION IN THE WORLD

1/ Localization of this factories

2/ Some examples

III/ INCONVENIENCES OF DESALINATION

CONCLUSION

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INTRODUCTION

Bryan

The water is plentiful on earth it represents 1380 million of km3. There are 97% of sea water and 3% of drinking water. But, some people have no access to the drinking water. So, an interesting solution is to desalinate sea water . The desalination of the sea water developed during the fifties and sixty. In a first stage, fourteen processes considered as promising were analyzed, but finally only two of them survived the test(event) of the industrial development: the distillation and the reverse osmosis.

From then on, the purpose of our argumentation is to present you the desalination of the sea water, the various used processes, where as it is found them in the world and the various inconveniences .

I/ VARIOUS DESALINATION PROCESSES

Claude

1/ Presentation

There are two main processes of desalination . It’s the reverse osmosis and the distillation .

REVERSE OSMOSIS

The reverse osmosis is an effective industrial process of desalination. There are three steps .

1. Filters remove suspended solids

And others particles that would interfere with the desalting process

2. Reverse osmosis membranes separate dissolved minerals (including salts) and other impurities from the water.

3. Mineral and/or chemicals are added to ensure produced water meets health , aesthetic and anti-corrosion standards .

DISTILLATION

Bryan

Distillation is a process of separating the component substances from a liquid mixture by selective evaporation and condensation. There are Two main processes of distillation :

Multi Stage Flash

Multi effect distillation

Vapor compression

But we will talk about the two main processes in distillation : MSF and MED.

MULTI STAGE FLASH Distillation

The distillation by successive relaxations or flash ( MSF). The cold salt water is introduced into the successive cells(units) in serpentines. She(it) condenses the vapor which is by warming itself there gradually. After heating she(it) is introduced on the base(basis) of cells(units) or she(it) vaporizes the salt water. Condensed water and brine are got back. The energy cost is lower(weaker), of the order of 10kWh by m3.

MULTI EFFECT DISTILLATION

The distillation with multiple effect ( MED) contains a series of cells(units) working in pressures and decreasing temperatures. The heat losses are lower and the better yield(efficiency). He can be increased if there is compression of the vapor. The important energy costs are of the order of 15 kWh by m3.

COMPARISON BETWEEN THIS PROCESSES

Claude

Reverse osmosis is the lower energy consumer (3 to 4 Kilowatt per cubic meter) and between this processes. It’s an low cost process and it can filtrate chemical products into water . But his membrane has limited life Cycle and the water quality is very poor .

This technique has the advantage to produce a very pure water but the inconvenience to consume a great deal of energy (15kWh / m3 of handled water) and thus to be very expensive

II/ SOME FACTORIES OF DESALINATION IN THE WORLD

1/ Localization of this factories

In 2008, the main producing countries of fresh water by desalination are: - Saudi Arabia, - the United Arab Emirates, - the United States, - Spain, - Kuwait. These countries being then followed by Algeria, China, Qatar, Japan and Australia, which(who) produce between 2 % and 4 % of the water desalinated in the world

2/ Some examples

Bryan

In Saudi Arabia, 86 % of the water is desalinated by distillation Flash by successive relaxations ( MSF).

In the United States, 84 % of the water is desalinated by membranaires technologies (reverse osmosis and électrodialyse). In Spain, 69 % of the water is desalinated by reverse osmosis ( Oi)

For examples , The Jebel Ali desalination plant in Dubai , a dual-purpose facility, uses multistage flash distillation and is capable of producing 300 million cubic meters of water per year.

With a drinking water output of 200,000m³/day, Barcelona desalination plant is the largest reverse osmosis-based desalination plant in Europe. It was awarded the "Desalination Plant of the Year" award by the Global Water Awards 2010.

In this picture , we can see a project of the Saline Water Conversion Corporation , whose the objectives is to build the world largest solar powered desalination plant in Saudi Arabia .

III/ INCONVENIENCES OF DESALINATION

The main characteristic of waters of discharges of desalination plants is its strong salinity. This water is called brine. When she(it) is rejected without treatment(processing), this water leads(infers) an increase of the salinity of the environment(middle), what is a brake for the development of the marine ecosystem.

So, the brine rejected at high temperature leads(drives) to an environment(middle) impoverished there oxygene that is in the eutrophication.

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