water chemistry

Water Chemistry

  • Boiler Troubles:

    • Focus on scales and sludge formation, their causes, and effects.

Boiler Troubles

  • Usage of Water in Industries:

    • Water is used in boilers to produce steam.

    • Hard water can lead to significant issues in the functioning of boilers.

1. Scale and Sludge Formation

  • Sludge Formation:

    • When water evaporates in boilers, dissolved salts increase in concentration.

    • Upon reaching saturation, these salts are precipitated as sludge and scale.

    • Characteristics of Sludge:

      • Loose and slimy precipitate.

      • Formed by substances that are more soluble in hot water than in cold.

      • Salts causing sludge formation include MgCO3, MgSO4, MgCl2, CaCl2.

Disadvantages of Sludge Formation

  • Heat Conductivity:

    • Poor conductors of heat, leading to heat wastage.

  • Operational Issues:

    • Excessive sludge can disturb boiler operation by causing blockages, particularly in areas of poor water circulation such as pipes.

Scale Formation

  • Characteristics of Scale:

    • Hard, adherent coating on boiler walls.

    • Difficult to remove; requires significant effort.

  • Common Salts Causing Scale:

    • Examples include CaSO4, Ca(HCO3)2, Mg(OH)2.

Causes of Scale Formation

  1. Decomposition of Calcium Bicarbonate:

  • Heating leads to formation of CaCO3 as a precipitate.

  1. Deposition of Calcium Sulphate:

  • Soluble in cold water but precipitates in super-heated water, causing hard scale.

  1. Hydrolysis of Magnesium Salts:

  • Forms precipitate of magnesium hydroxide, which contributes to soft scale formation.

Disadvantages of Scale Formation

  1. Fuel Wastage:

  • Low thermal conductivity lowers heat transfer efficiency, increasing fuel consumption.

  1. Boiler Safety Risks:

  • Overheating due to scale makes boiler materials weaker, risking distortion and failure of the boiler under pressure.

  1. Decreased Efficiency:

  • Scales may block valves and condensers reducing overall efficiency.

  1. Explosive Danger:

  • Cracked scales can lead to rapid steam generation, risking explosions.

  • Impact of Scale Thickness on Fuel Wastage:

    • 0.325mm thick: 10% wastage

    • 2.5mm thick: 80% wastage

    • 12mm thick: 150% wastage

Comparison of Sludge and Scale

Aspect

Sludge

Scale

Nature

Soft, loose, slimy precipitate

Hard, adherent deposits

Removal

Easily removed

Difficult to remove

Heat Conductivity

Poor conductor of heat

Low thermal conductivity

Composition

CaCl2, MgCl2, MgSO4, MgCO3

CaSO4, Mg(OH)2, CaCO3, CaSiO3

Location of Formation

Colder portions of the boiler

Heated portions of the boiler

Boiler Efficiency Impact

Decreases efficiency but less risky

Decreases efficiency and more danger

Review Questions

  1. What are the disadvantages of hard water?

  2. Define scale and sludge formation in boilers.

  3. What salts cause scale and sludge formation in boilers?

  4. What are the disadvantages of scale and sludge formation in boilers?

  5. What are the differences between scales and sludge?

  • Thank you.