Within the boiler Boiler water

1 within boiler

1.1 oxygen scavengers
1.2 coagulation
1.3 phosphates
1.4 chelants

within boiler

at elevated temperatures , pressures within boiler, water exhibits different physical , chemical properties observed @ room temperature , atmospheric pressure. chemicals may added maintain ph levels minimizing water solubility of boiler materials while allowing efficient action of other chemicals added prevent foaming, consume oxygen before corrodes boiler, precipitate dissolved solids before form scale on steam-generating surfaces, , remove precipitates vicinity of steam-generating surfaces.

oxygen scavengers

sodium sulphite or hydrazine may used maintain reducing conditions within boiler. sulphite less desirable in boilers operating @ pressures above 1,000 pounds per square inch (6,900 kpa); because sulfates formed combination oxygen may form sulfate scale or decompose corrosive sulfur dioxide or hydrogen sulfide @ elevated temperatures. excess hydrazine may evaporate steam provide corrosion protection neutralizing carbon dioxide in steam condensate system; may decompose ammonia attack copper alloys. products based on filming amines such helamin may preferred corrosion protection of condensate systems copper alloys.

coagulation

boilers operating @ pressures less 200 pounds per square inch (1,400 kpa) may use unsoftened feedwater addition of sodium carbonate or sodium hydroxide maintain alkaline conditions precipitate calcium carbonate, magnesium hydroxide , magnesium silicate. hard water treated way causes high concentration of suspended solid particles within boiler serve precipitation nuclei preventing later deposition of calcium sulfate scale. natural organic materials starches, tannins , lignins may added control crystal growth , disperse precipitates. soft sludge of precipitates , organic materials accumulates in quiescent portions of boiler removed during bottom blowdown.

phosphates

boiler sludge concentrations created coagulation treatment may avoided sodium phosphate treatment when water hardness less 60 mg/l. adequate alkalinity, addition of sodium phosphate produces insoluble precipitate of hydroxyapatite magnesium hydroxide , magnesium , calcium silicates. lignin may processed high temperature stability control calcium phosphate scale , magnetic iron oxide deposits. acceptable phosphate concentrations decrease 140 mg/l in low pressure boilers less 40 mg/l @ pressures above 1,500 pounds per square inch (10,000 kpa). recommended alkalinity decreases 700 mg/l 200 mg/l on same pressure range. foaming problems more common high alkalinity.

coordinated control of ph , phosphates attempts limit caustic corrosion occurring concentrations of hydroxyl ions under porous scale on steam generating surfaces within boiler. high pressure boilers using demineralized water vulnerable caustic corrosion. hydrolysis of trisodium phosphate ph buffer in equilibrium disodium phosphate , sodium hydroxide.

chelants

chelants ethylenediaminetetraacetic acid (edta) or nitrilotriacetic acid (nta) form complex ions calcium , magnesium. solubility of these complex ions may reduce blowdown requirements if anionic carboxylate polymers added control scale formation. potential decomposition @ high temperatures limits chelant use boilers operating @ pressures less 1,500 pounds per square inch (10,000 kpa). decomposition products may cause metal corrosion in areas of stress , high temperature.