High ClO2 in Boiler Feedwater: Impacts

Excessive chlorine dioxide (ClO2) in boiler feedwater poses significant risks to boiler integrity and operation. Although (ClO2)  is valued as a disinfectant and oxidant in water pretreatment, overdosing leads to several adverse effects.

Firstly, (ClO2)  decomposes under high temperature and pressure inside the boiler. Its decomposition products include chlorite(ClO2) , chlorate(ClO2) , and chloride (ClO2) , along with oxygen and heat. These species lower the pH of the boiler water, creating an acidic environment. Acidic conditions accelerate corrosion of carbon steel and copper alloys commonly found in feedwater systems, economizers, and boiler tubes.

Secondly, chloride ions derived from(ClO2) breakdown promote pitting corrosion and stress corrosion cracking, particularly in stainless steel components. Pitting can rapidly penetrate tube walls, leading to leaks or catastrophic failures.

Thirdly, residual (ClO2)  itself is a strong oxidant. It can attack the protective magnetite layer on boiler internal surfaces, removing the passive film and exposing fresh metal to continuous corrosion. This process increases iron levels in boiler water, which may deposit on heat transfer surfaces, reducing thermal efficiency and causing localized overheating.

Moreover, excessive (ClO2)  may react with organic matter in makeup water to form harmful chlorinated byproducts. These byproducts can further contribute to corrosion or foaming, affecting steam purity.

To prevent these issues, (ClO2)  residual in boiler feedwater should be strictly controlled. Typical guidelines recommend less than 0.2 mg/L (ClO2)  entering the boiler system. Proper monitoring and dechlorination (e.g., using activated carbon or sodium sulfite) are essential when (ClO2)  is used upstream.

In summary, while ClO? is effective for biological control, its overdose deteriorates boiler water chemistry, accelerates corrosion, and compromises operational safety. Routine testing and chemical adjustment are critical to maintain optimal feedwater quality.