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Common Chemicals Used in Boiler Water Treatment

Nov. 20, 2021

If you want your boiler to remain in good condition and as efficient as possible, it is important that the water is free of impurities, which means that water treatment is required. Boiler water can be treated by both external and internal treatment.


Both processes rely on a conditioning process, which essentially counteracts the hardness in the water by introducing softening agents into the water. Whichever of these methods you use, there are many effective chemicals you can use to keep impurities out of your water, including everything from de-oxidants to anti-scaling agents.


Oxygen scavengers

Deaerators are specifically designed to reduce the amount of dissolved oxygen and oxides in water. If you use a DO sensor and find high levels of dissolved oxygen in your boiler water, deaerators such as hydrazine and sodium sulphite can be effective in reducing DO and oxides, resulting in purer water. Deaerators also usually passivate various metal surfaces, which helps prevent rust and other problems.


Carbohydrazide is a high-performance oxygen scavenger that can be used in all types of boilers. Carbohydrazide is a white water-soluble solid that decomposes at a melting point of about 153°C.


Carbohydrazide can be used as an oxygen scrubber to directly replace hydrazine in any boiler without related safety hazards and preventive measures. The product is based on volatile chemicals, so it does not leave dissolved solids and minimal ammonia in the boiler system. It does provide excellent oxygen corrosion protection as well as excellent feedwater and boiler system passivation.




The exact dose of scavenger you should use in your boiler depends on the type of deaerator you are using and whether the boiler is paired with a de-gas heater. For testing purposes, you should always keep 20 ppm of deaerator in the boiler feedwater. If you want to ensure that your boiler does not corrode, it is highly recommended that you use a deaerator.


Alkalinity additives

Alkalinity builders are specifically designed to raise the pH of the water in which they are placed. For steam boilers, it is essential to maintain a high pH to prevent corrosion, to minimise the amount of silica plating in high pressure boilers, and to maintain proper boiler efficiency. If you have a high alkalinity feed water, you do not always need to use an alkalinity additive, but if the water in the boiler becomes too acidic, you should consider using an alkalinity additive.


All you need to do to determine the pH of the boiler water is to test it with a pH sensor. If the pH drops too much, an alkalinity booster will help you to increase the alkalinity of the water. When you increase the alkalinity of the boiler feed water, you will be able to protect the feed lines and hot wells from acid corrosion. The amount of this chemical you need depends entirely on the pH level of the feed water.


The most common alkaline solutions for boiler water include sodium hydroxide and potassium hydroxide. You can usually purchase these products in 25% or 50% concentrations. If you need to significantly increase the alkalinity of the feed water, a 50% solution may be the most effective option. Some alkalinity additives come with sludge conditioning polymers, which are particularly beneficial for high temperature applications.

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