Desalination units of the multiple-effect type use the distillation process to produce fresh water. This technique was developed for its reliability and greatly eliminates the problems of filtration, corrosion, pretreatment and scaling.

MED units are manufactured in a range of standard outputs from 2,500 gallons per day and larger.  These units are packaged up to 1,000,000 gallons per day depending on site transportation limitations.

Thus, multi-effect (MED) distillation offers a number of unparalleled advantages which will result in reduced investment as well as low operation and maintenance cost.
 

• Low operating temperature limits scaling and corrosion.
• Low energy consumption.
• Production of high purity distillate.
• Tolerance of high sea water salinity and temperature.
• Tolerance of sea water chlorination and the bacteria contained in sea water.
• Absence of sophisticated pretreatment of the incoming sea water, resulting in a low cost sea water intake.
• Compact design allowing a skid-mounted concept which minimizes associated civil and site erection work.
• Absence of brine recirculating pump.
• Excellent flexibility of operation.
• Resistance to hot and humid climate even in outdoor installations.
• Simplified procedure for preservation when the units are shutdown for extended periods.

 Heat input to the evaporator module can be achieved either by condensing low pressure-steam or by the circulation of hot water.  The latter can be - for example - the cooling water of an engine or of a chemical process.

The evaporator produces, on request, a distilled water with a particularly low salinity, suitable for any industrial process requiring high purity water.

If the product water is intended for domestic use, very simple remineralization equipment is added.

These units are designed to treat water with a high salt content without requiring complex chemical pretreatment, which is difficult to handle and costly.  The evaporator will operate well on any water to be treated - underground water, surface water, and sea water of medium (35 g/l) (35,000 ppm) or high salinity (55 g/l) (55,000 ppm).
 

Evaporator  Characteristics

The main features of the evaporator are:

1.  Compactness:

The evaporator is delivered as a packaged unit, is compact and mounted on a single frame support with the accessories (pipe work, pumps, electrical cubicle etc.) necessary for its operation.

Upon its arrival at the job site, this unit is ready to operate after being set on its foundation and connected to the utility.  For transport reasons, bigger units may be shipped in several blocks to be assembled on site.

2.  Low-Operating Temperatures:

The sea water is distilled in the evaporator at a very low temperature, around 40/60 degrees C.  (104/140 degrees F).

This minimizes the problem of scaling (which results in a drop of the heat exchanger efficiency) and of its eliminates frequent acid cleanings that over the long term result in materials corrosion.

3.  Reliability:

The plant is sturdily built and does not include any rotating parts except for the pumps.

4.  Simplified Water Intake:

Besides the generally necessary chlorination, the MED Unit does not require any pretreatment of the raw water.  The water intake facilities are thus simplified, and normally consist of a strainer and a pipeline.

It should be noted that the absence of any pretreatment procedure is thebasic advantage of the MED process.  The cost of the pretreatment plant and the chemicals required by any demineralization system will substantially increase the cost of the produced water.  Furthermore, pretreatment requires considerable equipment maintenance in the form of plugged filters, chemical handling, etc.

5.  Simple Operation and Maintenance:

The basic rules in designing MED evaporators has been to minimize erection work at the site, to simplify operation and to reduce required maintenance.  Thus the MED process is well adapted for use in remote areas where highly trained staff is not available.

6.  Flexible Operation:

The quantity of water produced can be adjusted to the customer’s actual needs.

MED units are particularly suitable for those cases where the heat input into the evaporator is recovered from another upstream process which can be operated at different loads.

Variation of the sea water temperature does not affect the production capacity or the purity of the distillate.