Why is boiler blowdown performed?

• A. To remove dissolved solids and prevent scale formation
• B. To vent air from the system
• C. To reduce boiler pressure
• D. To cool the boiler water

Answer: (A)

Blowdown is used to manage the concentration of dissolved solids in boiler water. As water is boiled, minerals and salts remain behind, so the remaining water becomes increasingly concentrated. When solids get too high, they form scale on heat transfer surfaces, which reduces heat transfer efficiency and can lead to overheating and tube damage. By discharging a portion of the boiler water and replacing it with fresh makeup, the overall solids level and conductivity stay within design limits, preserving efficiency and boiler life. This is different from venting air, which removes noncondensable gases and is not intended to control solids. It is not primarily used to reduce boiler pressure, nor to cool the water. Therefore, the main purpose is to remove dissolved solids to prevent scale formation.