Reverse Osmosis &Thermal desalination

Desalination of water in arid regions, such as the Middle East, has become a common operation. The process can be based on distillation or membrane separation. Dequest phosphonates and polymers can be used as antiscalants and dispersants to prevent scale build up on heat transfer surfaces and reverse osmosis membranes.

Fouling of heat transfer surfaces in vapour compression systems, MSF’s (Multiple Stage Flash Evaporators) or MED’s (Multiple Effect Distillation) is a major problem. Scaling reduces heat transfer efficiency and decreases water production. Sulfuric acid fed to the evaporators to reduce carbonate scale formation, comibined with the inherent high temperatures of such systems, often leads to the formation of calcium sulphate scale.

Dequest polymers and phosphonates, being highly effective threshold scale inhibitors with excellent thermal stability, are a natural choice to control calcium sulphate scale in MSF’s, MED’s and vapour compression systems. Dequest phosphonates also bring the added benefit of reducing metal corrosion rates in the units.

Reverse osmosis is a process which is used to remove dissolved salts from water. It is used in the generation of potable water from salt, brakish, well or surface water, the manufacture of process water (eg ultrapure water for the power and electronic industries) and for re-use of waste water.

Reverse osmosis (RO) could be thought of as a very sophisticated type of filtering process (on a molecular level). In RO systems, pressure is applied across a membrane to force water from the “contaminated” side to flow through to the “clean” side. Very pure water is produced, as even low molecular weight ionic species and many organics do not pass through the membrane.

As you might imagine, the concentration of salt builds up on the membrane side where the pressure is applied. This can lead to loss of efficiency of the membrane. Dequest phosphonates can be used to prevent scale formation on the high pressure side of the membrane.