Alkalinity Boost Chemistries

Where the alkaline constituents of the FW are low, or where simply raising BW cycles of concentration fails to provide adequate BW alkalinity without incurring risks of foaming, carryover, or similar problems, the use of an alkalinity booster (alkalinity builder) is recommended. 

Alkalinity boost chemistries typically are based on adjunct products containing primarily potassium hydroxide (for maximum solubility) or sodium hydroxide (for lowest cost), although sodium carbonate is still used in certain limited applications. These adjuncts may also contain (in almost any combination) smaller percentages of tannins, sodium ligonsulfonate, phosphate or polymers. 

Alkalinity content may be tested and reported in various ways, but for BW, the most important tests are methyl orange/total alkalinity (reported as M or T alkalinity, expressed as mg/1, mg/kg, or ppm CaC03), and caustic /hydroxide alkalinity (reported as OH alkalinity, expressed as mg/1, mg/kg, or ppm CaC03). 

NOTE With these types of programs, free sodium hydroxide is not formed, even in the event of complete evaporation thus the damage caused by localized concentration effects (dissolution of iron forming the soluble, nonprotective, sodium ferroate [sodium hypoferrite] salt, together with hydrogen liberation, tube wastage, and ultimate failure) does not occur. 

Free caustic alkalinity usually is not recommended for jet-type electrode, as foaming conditions may develop rapidly because of the high recirculation rate. Where high alkalinity is present and FW contamination from colloidal or organic matter takes place, the foaming that develops quickly causes the boiler to be shut down. 

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