HYBAR Boiler Water Treatment

PRODUCT DATA

CH₂O's HYBAR products are formulated especially for use in high pressure boilers (Above 600 PSIA). Other applications include lower pressure boilers with deionized make up water and for those customers who desire a precipitation program. HYBAR products are robust and hold up under severe operating conditions. They consistently perform their intended function.

MINERAL CONTROL

Mineral control is provided by the well known coordinated phosphate program. This method is the tried and true technique used by water treatment chemists for over 30 years. The chief goal is to produce the precipitate calcium hydroxy phosphate (Hydroxy apatite) when calcium enters the boiler by a malfunction of feed water pretreatment.

Tremolite, another precipitate of calcium, magnesium and silica is produced as well.

These solids are then suspended in solution by temperature resistant synthetic organic dispersants. The coordination of sodium / phosphate ratios to boiler pressure prevents caustic corrosion and positively controls pH. The need for hydroxide (OH)- ions in the boiler water for the formation of Hydroxy Apatite and Tremolite is provided by the sodium. As the operating pressure increases the need for hydroxide is offset by concern for preventing free sodium hydroxide.

OXYGEN CONTROL

Oxygen appears in the high pressure boiler from incomplete mechanical deaeration and the decomposition of water at very high to critical pressures.

2H₂O 2H₂ + O₂

The use of an oxygen scavenger is necessary to remove oxygen. Sodium sulfite is not used in the HYBAR series for the reason that its sodium interferes with the precipitation program. Also, the residual sodium sulfate contributes to (undesirable) conductivity. HYBAR 6735 is a hydrazine based oxygen scavenger. The reaction products of oxygen and hydrazine are water and nitrogen gas.

N₂H₄ + O₂ 2H₂O + N₂

CARBONIC ACID CONTROL

Bicarbonate and carbonate alkalinities can enter the boiler through malfunction of feed water pretreatment. Carbonic acid is created as a result of carbonate and bicarbonate alkalinity decomposition. The decomposition product carbon dioxide exits the boiler as a gas with the steam. Then as the steam condenses it redissolves in the liquid condensate to form carbonic acid.

CO₂ + H₂O H₂CO₃

Volatile neutralizing amines are applied to either the feed water (after deaeration), the steam drum, or the steam header to prevent this corrosive attack.

2R-NH₄OH + H₂CO₃ (R-NH₄)₂CO₃ + H₂O

MAGNETITE FORMATION

The role of hydrazine in the treatment of boiler water is not limited to oxygen scavenging. A second reaction with ferric oxide on heat transfer surfaces produces a protective film of magnetite.

Magnetite

6Fe2O3 + N2H4 4Fe3O4 + 2H2O + N2

Magnetite adheres well to surfaces. There it works as a barrier protecting boiler metal from further oxygen attack.

VIVIANITE FORMATION

Phosphate in the treatment of boiler water is important for a reaction with iron metal surfaces. This produces vivianite which is similar to the protective film created when steel products are pickled in phosphoric acid.

rev:10/6/99