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Condensate Polishing

Condensate polishing is employed to purify the return steam condensate in order to meet the quality requirements of high pressure thermal cycles and minimise consumption of make-up water. The polishing of the recovered condensate is implemented where the condensate is the major portion of the Boiler Feed Water and whenever there is a significant risk of contamination of the return condensate.

The Condensate Polishing is concerned with three specific types of impurities:

Corrosion products are normally oxides of iron, copper and nickel that could be either in the form of particulate matter or in solution, the removal of these products is done by filtration of the condensate and according to the capacity, size and concentration of particulate matter, filtration could be performed on pre-coat, media or cartridge filters

Presence of dissolved salts commonly arises from leakage of cooling water into the condensing steam or presence of soluble corrosion products. Removal of contaminants induced by condenser leaks requires the use of ion-exchange demineralisers. Mixed-bed ion exchangers are commonly used for low-contamination levels and high flow capacity, with internal or external regeneration facilities. In case of higher level of mineral contamination, separate cation and anion exchangers could be foreseen upstream the mixed bed polisher.

Particularly important for the Oil Refining and Petrochemical sectors, oils and hydrocarbons could be present in the return condensate because of leakage from steam-operated heat exchangers or process equipment. Oil in the boiler could form non-wettable films on the heat transfer surfaces so that steam bubbles adhere and severe corrosion or overheating failure could occur because of the inadequate cooling of the surface. Whilst a significant amount of oil from the return condensate can be removed by means of Coalescers or Walnutshell Filters, removal of traces of oil is normally done by means of adsorption processes on granular activated carbon media filled into pressure-operated filters.