Condensate polishing systems are employed to purify the steam condensate returning from the process in order to minimise consumption of make-up water and meet the quality requirements of the steam generators and thermal cycles in general.
Polishing of the recovered condensate is implemented when the condensate is the major portion of the Boiler Feed Water and whenever there is a significant risk of contamination of the return condensate in particular by the cooling water.
Condensate Polishing deals with three specific types of impurities.
Corrosion products that are normally oxides of iron, copper and nickel either in form of particulate matter or in solution. The removal of such impurities is done by filtration. According to the capacity, size and concentration of particulate matter, filtration can be performed on pre-coat, media or cartridge filters.
Presence of dissolved salts in the steam condensate commonly arises from leakage of cooling water into the condensing steam or presence of soluble corrosion products. This is an issue in particular when high-salinity sea water is employed as cooling medium in the condenser. Even the smallest sea water inflow into the condensate stream is enough to affect the steam generators and the turbine. 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 levels 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 potentially affect the return condensate because of leakages into the heat exchangers from the organic phase into the steam-water one. The presence of oil in the boiler could form non-wettable films on the heat transfer surfaces so that steam bubbles adhere that could lead to severe corrosion or overheating failure because of the inadequate cooling of the surface. In presence of a significant amount of oil in the return condensate Cannon Artes is capable to provide the right solution: Coalescing Oleophilic Resin Separators or Walnutshell Filters. On the other hand, removal of traces of oil is normally done by means of adsorption processes on Granular Activated Carbon media filled into pressure-operated filters.
The Condensate Polishing system is often the “last chance” to prevent that contaminations of the steam circuit could affect the entire thermal circuit. Cannon Artes is familiar with the most challenging conditions considering various degree of contamination, high pressure and high temperature operation.