Improving Condensate Quality
By William F. Harfst
Historically, steam condensate has been viewed as the best quality water in the energy center. Pure condensed steam has all the characteristics of distilled water (i.e., low concentrations of dissolved and suspended solids) as reflected in very low specific conductance and filterable residue. By comparison, raw boiler makeup contains hardness, alkalinity, chlorides, sulfates, and metals that produce undesirable dissolved and suspended solids in the boiler. Because engineers and scientists recognize the benefits of removing impurities from the feedwater before they enter the boiler, considerable attention has been given to designing makeup water pretreatment systems that essentially remove these contaminants from the raw water before they can cause problems such as scale deposition and corrosion in the steam cycle. Sodium ion-exchange (IX) systems (water softeners) are capable of removing hardness before it reacts within the boiler to produce mineral scale deposits that adversely affect heat transfer. More sophisticated IX demineralizers and membrane separation arrays (such as reverse osmosis) are capable of complete deionization of boiler makeup. These systems produce make-up water that is of such exceptional purity that it often exceeds the quality of steam condensate.
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