When treating steam boilers, ...

When treating steam boilers, the water quality of the make-up water needs to be taken into consideration and the steam usage as well as the condensate being returned as well as the type of boilers being used.  If the water has a low alkalinity and low dissolved solids, there is little point in using RO.  If the water has a moderate to high solids and alkalinity, then other forms such as de-alkalisation or reverse osmosis comes into its own.  The softening process removes the hardness but leaves dissolved solids and alkalinity.  This limits the concentration a boiler can run to without foaming because of high solids or high alkalinity.  The RO plant reduces the solids by 90% allowing the boiler to concentrate.  The second factor is the condensate corrosion.  If sodium bicarbonate enters a boiler, it breaks down and forms sodium hydroxide and carbon dioxide.  The latter flashes off in the steam and re-condenses with the water and forms carbonic acid.  This causes corrosion in the condensate and increases iron returning to the feed water.  It will even form grooving in stainless steel.  The use of the RO reduces the bicarbonate by 90 %, which in turn reduces the corrosion by reducing condensate pH.  In effect it should be close to neutral.