Demineralisation Plants

What Demineralisation Plants Are and Why They are Important 

With the eventual realisation that infectious diseases were caused by microscopic organisms, and that water can sometimes provide these pathogens with an ideal breeding ground, the drive to develop new and improved methods to generate potable water, free from any biological, chemical, and physical contaminants, has never really ended. While relatively simple techniques, such as sedimentation and filtration through sand, have proved effective and are still employed today, their actions are most often supplemented by more advanced technologies, some of which, like that employed in demineralisation plants, can also be used on a standalone basis, and for quite different purposes.

The technology in question is not aimed at the removal of physical or biological contaminants from water, but is applied to sources already freed of these and, instead, its focus is on any chemical compounds that may be present. In addition, depending upon the nature of the compounds to be removed and the proposed use for the treated product, the choice of active components used in this type of water purification technology will vary. In essence, however, all demineralisation plants employ a process known as ion exchange and tend to be similar in their design. In general, that design will consist of a pair of pressure vessels, one of which is filled with a suitable cation exchange resin, and the other with an anion exchange resin. As their name implies, these resinous materials possess the ability to surrender their own ions, whether they be positively or negatively charged, and bind instead with any ions present in the water that bear an opposite charge.

Among the more common of the chemical contaminants encountered in water are the soluble salts of the metals sodium, calcium, and magnesium. In the first phase of treatment in demineralisation plants, the water is directed into the cationic chamber. In solution, the compounds dissociate into their ions and the cations (i.e. sodium etc.) become absorbed on to the resin, which then releases hydrogen ions in their place. The water continues on to the second pressure vessel where any anions present such as nitrate, sulphate, chloride, and bicarbonate will be absorbed in exchange for a release of hydroxyl ions. The released hydrogen and hydroxyl ions then combine naturally to form additional water molecules in an effluent now totally free of any mineral content that may make it unsuitable for its intended use.

Ion exchange technology is highly scalable, so demineralisation plants are to be found in all shapes and sizes, and expert advice invaluable when making a selection. Options range from the larger assemblies commonly employed in heavy industrial installations to units that are sufficiently compact for domestic use. One of the most common uses for demineralised water in heavy industry is to provide the feed water required to operate a high-pressure boiler. Unless it can be guaranteed to be free of calcium compounds in particular, its use could result in scaling and malfunction or serious damage requiring costly repairs and a subsequent loss of production.

Where water of exceptional purity may be required, a demineralisation plant is frequently the preferred solution. Some common activities in which this purification technology is indispensable include the manufacture of computer chips and other micro-electronic components, and the production of water suitable for the preparation of pharmaceuticals and specialised chemical reagents, as well as in many tests routinely performed in medical laboratories. Resins, of course, form the heart of these systems and there is a vast range, each with its particular properties from which to choose. These include products that are, for example, suitable for water containing organic matter, or when a demineralisation plant may be required to produce an effluent that contains an exceptionally low concentration of silica. With continued use, the ion exchange resins will eventually become exhausted. However, it is possible to restore their properties by washing the anionic and cationic components with either caustic soda or hydrochloric acid. In some models, this regeneration process may be triggered automatically when sensors detect that electrical conductivity has become significantly reduced.

Clearly, there are several factors that could prove crucial when selecting the most suitable demineralisation plant for a given job. As a leader in industrial water treatment solutions, few companies in South Africa are better able to provide the essential advice, the world-class products and the support services offered by the experts at WaterIcon.

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