Boilers Maintenance
Importance of Boiler Feed Water Chemical Treatment
- Boilers are operated at High Steam Pressure, High Steam Temperature and High Steam Capacity
- So Boilers require Very Pure Water as Feed Water
- Even Pure Water will contain some Dissolved Salts (Hardness Salts)
(i) Some Dissolved Salts come out of Water/Solution on Boiling
These Salts adhere to the Heating Surfaces as a Scale
Scales reduce Heat Transfer, cause local overheating and failure of Tubes
(ii) Some Dissolved Salts remain in Water/Solution
These Salts produce Acids
Acids will attack the metal of the Boiler
Dissolved Oxygen and Carbon-di-oxide in Boiler Feed Water causes corrosion of Boiler and Feed system
- Sometimes Feed Water / Boiler Water may be contaminated by suspended matter, an excess salts or oil
This causes Foaming
Foaming Leads to Priming
Priming is the carryover of Water with the Steam
If the Steam contains Water – Steam Turbine may get damaged
Boiler Feed Water Chemical Treatment
It is done to prevent boiler / boiler parts from getting affected by scale & corrosion causing salts and dissolved gases
It is achieved as follows:
- By keeping the hardness salts in a suspension in the solution/water to prevent scale formation
- By stopping any suspended salts from sticking to the heat transfer surfaces
- By eliminating dissolved gases and providing some degree of alkalinity which will prevent corrosion
Chemicals used/added for Auxiliary Boilers (Low Pressure Boilers) – Calcium hydroxide, Sodium carbonate, Sodium hydroxide
Chemicals used/added for Main Boilers (High Pressure Boilers) – Trisodium phosphate, Disodium phosphate, Sodium metaphospate