Desalination by Distillation

Cleaning Process Desalination plant components is essential on a regular basis in order to avoid scaling condition. In this condition salts get deposited on plant surfaces, such as pipes, tubing etc. Scaling can led to the corrosion in the pipes and effects plant efficiency. Scaling is directly proportional to temperature. Hence it is major cause of concern for the distillation plant. It is therefore necessary to remove scaling by various chemical or mechanical means.

Distillation is one of the preferred method for desalination. The product water is heated to such a high temperature that pure water rises in vapor whereas particulates remain behind in brine water. Condensation of the steam is done in separate container. However in this process less fresh water as a percentage of impure water is produced. The recovery rate as compare to reverse osmosis process is also low.

Input Water
The water for feeding desalination plant may come from sea water, brackish water or reclaimed water. Salt concentration in the brackish water is low therefore desalting brackish water incur lower cost as compared to seawater. However precaution must be taken to keep the intake pipes for desalination plants away from the sewage treatment plant to avoid intake of discharged effluent.

Product Water
The quality of the water produced by distillation is of high quality. It ranges from 1.0 to 50 ppm tds. Health and safety consideration is always kept in mind while producing water for domestic consumption. Desalinated product water can be used for various purposes like less pure water and used for drinking water, irrigation, or other uses. Since pure desalinated water is highly acidic it is corrosive to pipes hence it is necessary to mix it with other sources of water that are piped onsite.

Pretreatment Processes
For smooth desalting process it is necessary to remove substances that would interfere with the desalting process. Microorganism like, algae and bacteria can grow in distillation plants, hence it is necessary to clean the system using biocide. To prevent the corrosion problems some distillation plants may also need to remove metals.

Distillation Process
Saline water in distillation process is first heated and then condensed to produce freshwater. The processes involved in distillation are as follows:

• Multistage Flash (MSF) Distillation
• Multiple Effect Distillation
• Vapour Compression Distillation
• Membrane Distillation

In all the process vapor pressure of water is reduced to enable the boiling to occur at lower temperatures, without the use of additional heat.