De-Alkanization
The removal of alkalinity from a water supply by neutralization or ion exchange.
Alkalinity
Alkalinity means the buffering capacity of water; the capacity of the water to neutralize itself. It prevents the water pH levels from becoming too basic or acid. It also adds carbon to water. Alkalinity stabilizes water at pH levels around 7. However, when the acidity is high in water the alkalinity decreases, which can cause harmful conditions for aquatic life.
In water chemistry alkalinity is expressed in ppm or mg/L of equivalent calcium carbonate. Total alkalinity of water is the sum of all four sorts of alkalinity; Dissolved carbon dioxide (CO2), Bicarbonate (HCO3), Carbonate (CO3) and Hydroxyl (OH).
Why De-Alkanization?
Dealkalizers are most often used as pre-treatment to a boiler and are usually preceded by a water softener if required. Alkalinity is a factor that most often dictates the amount of boiler blowdown.
High alkalinity promotes boiler foaming and carryover and causes high amounts of boiler blowoff. When alkalinity is the limiting factor affecting the amount of blowdown, a dealkalizer will increase the cycles of concentrations and reduce blowdown and operating costs.
The reduction of blowdown by dealkalization keeps the water treatment chemicals in the boiler longer, thus minimizing the amount of chemicals required for efficient, noncorrosive operation.
Carbonate and bicarbonate alkalinities are decomposed by heat in boiler water releasing carbon dioxide into the steam. This gas combines with the condensed steam in process equipment and return lines to form carbonic acid. This depresses the pH value of the condensate returns and results in corrosive attack on the equipment and piping.
In general, a dealkalizer is best applied to boilers operating below 700 psi (48 bar). In order to justify installation of a dealkalizer on low-pressure boilers, the alkalinity content should be above 50 ppm with the amount of make-up water exceeding 4,000 litres per day.
Cooling system make-up will also benefit from reduced alkalinity. The addition of a dealkalizer to a cooling water system will substantially reduce the amount of acid required to treat the same amount of water.
Alkalinity needs to be removed and monitored to prevent scale and corrosion to minimize total operating costs.
De-Alkalizer
Dealkalization with Weak Acid Cation (WAC) Exchange Resin
When for the influent water, total hardness is high and equal to alkalinity, dealkalization using Weak Acid Cation Exchanger in H+ form becomes extremely efficient and cost effective.
The cations associated with alkalinity are exchanged for H+ ions. The carbonic acid formed is removed by degasser giving alkalinity free soft water. Salts of mineral acids or neutral salts are not exchanged.