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Defining Alkalinity

Alkalinity is a measurement of water's ability to neutralize acid. There are 3 types of alkalinity, depending on pH of the water: bicarbonate, carbonate and hydroxide. Bicarbonate (HCO3) has a pH ranging from 4.3 to 8.3. Bicarbonate is the most prevalent alkalinity in natural bodies of water. Carbonate (CO3) has a pH ranging from greater than 8.3 to 10. Hydroxide (OH) alkalinity exists when the pH is greater than 10.

How Alkalinity Affects Boiler Performance

Alkalinity is a significant factor in the production of many goods including food and beverages, and textile dyes, but it plays an even more significant role in boiler operations. Hydroxide (OH) and carbon dioxide (C02) are both produced from the breakdown of carbonate and bicarbonate ions during steam production. As the steam condenses, the carbon dioxide dissolves and forms carbonic acid (H2C03) – a highly corrosive compound that deteriorates condensate return lines. The presence of hydroxide with carbon dioxide and bicarbonate may also lead to further corrosion.

Certain amine compounds and other chemical additives are necessary to help protect the condensate return lines from corrosion. However, these chemicals are costly, and their effectiveness limited by the amount of carbonic acid they can control. For this reason, alkalinity is often the defining factor in determining the cycles at which a boiler can be operated safely. High alkalinity may require that a boiler operate at shorter cycles, wasting energy and chemicals due to high blowdown.


Generally, dealkalization can be used to treat water in boilers operating at less than 700 psi, with feedwater containing less than or equal to 50 ppm alkalinity, and with make-up of 1,000 gallons or more per day. Makeup water is the water added to the boiler to offset water lost due to steam and blowdown.

Raw water alkalinity may be reduced using several different methods:


A dealkalizer works similar to a water softener, in that it utilizes ion exchange to remove unwanted ions from a water supply. However, rather than removing calcium and magnesium ions, dealkalization removes carbonate ions, exchanging them for chloride ions. Like water softeners, dealkalizers make use of salt during the regeneration process. Unlike water softeners, a dealkalizer resin must also be treated with an additional caustic solution. This caustic solution boosts pH levels and enhances the resins efficiency.

Selection and Design:

Each dealkalization method described above has significant advantages and disadvantages. The WaterProfessionals® can evaluate your operation and, using raw water analysis and operating parameters for your boiler operation, model the most cost-effective method and provide important payback information.