SODIUM HYDROXIDE (Caustic Soda)
Application
Increases alkalinity, raises pH, precipitates magnesium, creates the proper conditions for fluid sludge
Comments
Contains no carbonate precluding formation of CO2 in steam; pH control improves form of calcium precipitate (See Phosphate)
Sodium Phosphate
Application
Precipitates calcium as hydroxyapatite.
Comments
Reaction requires sufficiently high alkalinity & pH.
Sodium Aluminate
Application
Precipitates calcium and magnesium.
Comments
Forms a flocculent sludge. Used in river water pretreatment.
Chelating Agents (EDTA,NTA)
Application
Control scale by forming heat-stable soluble complex with calcium and magnesium.
Comments
Prevents precipitation of scale forming compounds on metal surfaces. May break down at high pressure. Use oxygen free water.
Tannins, Starches, Lignin derivatives, Carboxymethyl-cellulose
Application
Prevent feedwater line deposits, coat scale crystals to produce sludge that does not adhere as readily to heat transfer surfaces.
Comments
Organic dispersants (often called protective colloids) used with phosphate. Also, distort scale. growth, inhibit caustic embrittlement. Rarely used due to high feed demand and poor results.
Polymers/Copolymers
Application
Disperse sludge, distort crystal structure of calcium and magnesium deposits; prevents fouling by corrosion byproducts.
Comments
Distortion of crystal structure of precipitates preventing their adherence to metal surfaces. May be used in with chelant, phosphate or carbonate program.
Sodium Sulfite
Application
Prevents oxygen corrosion
Comments
Neutralizes residual oxygen by forming sodium sulfate. May decompose at high temperatures and pressures, forming H2S in steam. Catalyzed form yields much more rapid reaction.
Hydrazine/Hydrazine
Application
Prevents oxygen corrosion
Comments
Reacts with residual oxygen to form Nitrogen and water. Hydrazine is a carcinogen.
Filming Amines (Octadecylamine, Soya Amine & Others)
Application
Control return-line corrosion by forming protective film on metal surfaces.
Comments
Protects against oxygen and CO2 attack. Low level of continuous feed maintains film. Feed based on steam production.
Neutralizing Amines (Cyclohexylamine)
Application
Control return-line corrosion by adjusting condensate pH up.
Comments
Protection given by neutralizing carbonic acid formed from CO2.
Sodium Nitrate
Application
Inhibits caustic embrittlement.
Comments
Used where water may have embrittling characteristics.
Antifoams
Application
Inhibits caustic embrittlement.
Comments
Usually added with other (Polyglycols, Silicones, chemicals used for scale control, sludge) Dispersant.