Boilers

Elaborating how it creates problems in boilers

Sludge and Scale formation #

On continuous evaporation on hard water in boilers, the salts present in it get saturated and are finally deposited in the areas where the flow is slow.

• Sludge: When these precipitates are loose and slimy in nature.
  • Can be removed by scrapping with a brush
  • Disadvantages
    • Poor heat conduction
    • Efficiency
    • Difficult to remove if trapped with a scale
    • Clogging
• Scale: When they are hard and they adhere strongly to the inner surface
  • Disadvantages
    • Poor heat transfer
    • Overheating of boiler and development of high pressure.
    • Clogging and low efficiency

Removal and prevention #

Removal of Scales can be done by #

1. Wooden scraper or wire brush.
2. Blowdown operation with “make up” water replating hard water with softened water.
3. Thermal shocks
4. Chemical treatment

Prevention by Internal treatment #

1. Colloidal conditioning
2. Addition of sodium phosphates
3. Carbonate conditioning
4. Calgon conditioning
5. Sodium aluminate conditioning
6. Electrical conditioning
7. Radioactive conditioning

Caustic Embrittlement #

Boiler failure due to the development of certain types of crack resulting from excessive stress. Chemicals responsible: NaOH, silica

Prevention #

1. Sodium phosphate as softening agent instead of Na₂CO₃
2. Na₂SO₄/NaOH>2.5
3. Addition of organic agents
4. Crack resisting steels

Corrosion #

Occurs by chemical or electrochemical attack of the contents of water. chemicals like:

1. Oxygen; Can be removed by
   1. Mechanical deaeration
   2. Chemical treatment
   3. Ion exchange techniques
2. Dissolved CO2: Can be removed by
   1. Mechanical deaeration
   2. Adding lime/NH3
   3. Heating
3. Mineral Acids

Priming and Foaming #

During rapid steam production, some liquid water drops are also carried along with the steam. This wet-steam formation is called priming. Occurs due to:

• Dissolved solids
• High steam velocities
• Sudden boiling
• Sudden increase in steam production

Foaming is the production of bubbles and foams which do not break easily.