The Importance of Boiler Feed Water Chemical Treatment
Boilers are operated under high steam pressure, high steam temperature, and high steam capacity, which makes it crucial to use very pure water as feed water for boilers. Even pure water will contain some dissolved salts, also known as hardness salts.
(i) Some dissolved salts precipitate out of the water/solution when boiled. These salts adhere to the heating surfaces of the boiler and form a scale. Scales reduce heat transfer efficiency, cause local overheating, and can lead to tube failures.
(ii) Some dissolved salts remain in the water/solution. These salts can produce acids, which can corrode the metal of the boiler. Dissolved oxygen and carbon dioxide in the boiler feed water can also cause corrosion of the boiler and its feed system.
In addition, the boiler feed water may sometimes be contaminated by suspended matter, excess salts, or oil, leading to foaming. Foaming, in turn, leads to priming, which is the carryover of water with the steam. If the steam contains water, it can cause damage to steam turbines.
Boiler feed water chemical treatment is essential to prevent the boiler and its components from being affected by scale, corrosion-causing salts, and dissolved gases. The treatment is achieved through the following methods:
1. Keeping the hardness salts in suspension in the solution/water to prevent scale formation.
2. Preventing any suspended salts from sticking to the heat transfer surfaces.
3. Eliminating dissolved gases and providing some alkalinity to prevent corrosion.
Chemicals used for Auxiliary Boilers (Low-Pressure Boilers):
– Calcium hydroxide
– Sodium carbonate
– Sodium hydroxide
Chemicals used for Main Boilers (High-Pressure Boilers):
– Trisodium phosphate
– Disodium phosphate
– Sodium metaphosphate