Which chemical is often used to control scale in feedwater treatment?

Phosphate is a chemical commonly used in feedwater treatment specifically for scale control. In boiler systems, scale can form on the heat transfer surfaces, which reduces efficiency and can lead to equipment damage. Phosphates, when introduced into the boiler feedwater, work by reacting with calcium and magnesium ions, which are the primary culprits in scale formation.

When phosphates are present, they form soluble complexes with these ions, preventing them from precipitating out as scale. This solubilization of hardness ions effectively reduces the risk of scale deposits, ensuring that the boiler operates at optimal efficiency and prolonging the lifespan of the equipment. Additionally, phosphate treatment can also contribute to more complete boiler removal of impurities during blowdown, further enhancing overall system performance.

While other chemicals listed may play various roles in water treatment, such as adjusting pH or controlling corrosion, they do not specifically target scale control as effectively as phosphates do in this context.