One such water technologies is to treat the water by external treatment.

What is an External Treatment?

Treatment of water that are done outside of the boiler is called pre-boiler or external treatment. The main physical methods for improving quality of water for boiler include flocculation, clarification, deaeration, oil removal, colour removal, suspended solids removal and blow down. When preparing water for boilers operated at less than 150 psi, all necessary chemical treatments can be accomplished in a clarifier, but as pressure increases; the quality of feed water must improve. The purpose of external treatment is to reduce suspended solids, demineralize the feed water and remove silica. This purpose can be achieved by

• Coagulation with chemicals
  
• Demineralization/ Reverse osmosis/ Electrodialysis (cold lime, soda process, hotlime-soda process, mixed bed exchange)
  
• Silica removal (coagulation with chemical, Demineralization, Reverse Osmosis, Electrodialysis)

What is an Internal Treatment?

There are number of treatments that are made within the boiler to minimize the adverse effects of small concentration of components that remain in the feed water after the external treatment. In spite of various external treatments, it is not possible to attain an absolute perfect quality of boiler feed water. Chemical treatment or internal treatment of water inside the boiler is essential to take care of various impurities entering into the boiler such as hardness, dissolved solids, oxygen, and silica.

In many cases, external treatment of water supply is not necessary specifically in low or moderate pressure boilers or where large amount of condensed streams are used or when raw water available is of very good quality.

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