Which forms of alkalinity typically exist in 150 psi boiler blowdown water?

In boiler blowdown water at 150 psi, the primary forms of alkalinity that typically exist are carbonate (CO3) and hydroxide (OH) ions. This is primarily due to the conditions found in a steam boiler system and how alkalinity behaves in different pressure and temperature ranges.

As the pressure increases, such as in a 150 psi boiler, the water doesn't carry as much bicarbonate (HCO3) because, at elevated temperatures and pressures, bicarbonate tends to decompose into carbonate and carbon dioxide. Therefore, bicarbonate is less prevalent in this scenario, leading to a reduction in its contribution to overall alkalinity.

The carbonate ions help in maintaining pH levels while the hydroxide ions contribute to increasing the alkalinity of the water. Maintaining appropriate alkalinity levels is crucial to prevent corrosion and scaling within the boiler system, as well as to ensure efficient operation.

It’s important to recognize that while bicarbonate ions may be present in very small amounts due to the chemistry of the system, the focus on the two primary alkaline species—carbonate and hydroxide—under higher pressure conditions of 150 psi supports the conclusion that carbonate and hydroxide are indeed the predominant forms of alkalinity in the blowdown water.