The document discusses the calculation of water hardness and its units of measurement. It defines hardness as the concentration of calcium carbonate (CaCO3) in water. The units used to measure hardness include parts per million (ppm), milligrams per liter (mg/L), degrees Clarke (°Cl), and degrees French (°Fr). The specification of water hardness for different industrial uses such as boilers, paper, and textiles is outlined. Scale and sludge formation in boilers from hard water is explained, including the disadvantages of each and methods for prevention and removal.

1. Hardness of any substance in equivalents of CaCO3
can be calculated as
Hardness=
[Mass of hardness producing substance in mg/L] X [Eqv. wt of CaCO3]
________________________________________________________
[Eqv. Wt of hardness producing substance]
[Mass of sub. in mg/L]x[Mol. Wt of CaCO3]
___________________________________
Mol. Wt of Subs.
Or=
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2. For e.g.
If a sample of hard water contains 10 mg/L of MgSO4,
then its CaCO3 equivalent is given by
Mass of MgSO4 (mg/L)X mol. Wt of CaCO3
__________________________________
Mol. wt of MgSO4
= 10x100/120 = 1000/120
= 8.33 mg/L (ppm)
CaCO3 equivalents of MgSO4 (Hardness)
2
=

3. DIFFERENT UNITS OF HARDNESS
1. PPM: May be defined as the no. of parts (by wt) of
CaCO3 equivalent hardness +nt per million parts (by
wt) of water
2. mg/L: It is the no of mg of CaCO3 equivalent hardness
present per liter of water
1mg/L=1mg of CaCO3 eq. hardness per liter of water
As mass of 1 L water = 1 Kg = 1000g = 1000x1000mg = 106 mg;
So, 1mg/L = 1mg of CaCO3 eq. hardness per 106 mg of
water=1ppm 1mg/L = 1ppm
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One litre of water has a mass of almost exactly one kilogram when
measured at its maximal density, which occurs at about 4 °C.

4. 3. Degree Clarke (°Cl): defined as the no. of parts of
CaCO3 equivalent hardness present per 70,000
parts of water. It is denoted by °Cl
1°Cl= 1 part of CaCO3 equivalent hardness present per
70,000 parts of water
4. Degree french (°Fr): defined as the no. of parts of
CaCO3 equivalent hardness in 105 parts of water.
Denoted by °Fr.
1°Fr= 1 part of CaCO3 equivalent hardness in 105 parts
of water
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5. Relationship between different units of hardness
1ppm=1part per 106 parts of water,
1°Fr = 1part per 105 parts of water
°Cl = 1part per 70,000 parts of water;
So, 106 ppm = 105 °Fr = 70,000 °Cl
Or 1ppm = 0.1 °Fr = 0.07 °Cl
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6. 6
SPECIFICATION OF WATER FOR DIFFERENT USE
• Boilers
• Paper Industry
• Textile Industry
• Sugar Industry
• Beverage Industry
• Laundries
• Cooling Systems
• Pharmaceutical Industries
• Cooking

7. Boilers:
• Water used in boilers should be free
from hardness because hard water
causes sludge and scale formation
which prevent efficient heat transfer
• Dissolved solids may cause caustic
embrittlement (material of boiler
becomes brittle due to accumulation
of caustic substances)
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8. 8
Paper Industry:
• Should be free from silica (produces
cracks in paper) and hardness (increases
ash content of paper)
• Fe & Mn can affect brightness & color of
the paper
• Water should be free from alkalinity as
alkaline water consume more alum and
increase cost of production.

9. 9
Textile Industry:
• Should be free from hardness as hard
water precipitates basic dyes and
decreases the solubility of acidic dyes
• Presence of Fe, Mn salts causes uneven
dyeing on fabrics
• Should be free from turbidity, colour and
organic matter

10. Sugar Industry:
• Should be free from sulphates, carbonates
and nitrates otherwise crystallization and
refining of sugar becomes difficult and sugar
obtained is deliquescent (absrob moisture
from air)
Laundries:
• Hard water increases consumption of soaps
Cooking:
• Hard water increases fuel consumption and
cooking time
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11. 11

12. 12

13. 13

14. SCALE & SLUDGE FORMATION
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In Boilers
Water is continuously converted into steam, resulting increase
in conc. of dissolved salts due to evap. of water.
When the conc. reaches to the saturation point, the dissolved
salts start precipitating out.

15. Sludge: If the pptes are soft, loose and slimly, these are called
sludges.
Scales: If the pptes are hard and adhering on the inner walls of
boiler, these are called scales.
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16. SLUDGE
Soft, loose and non-sticky precipitate formed
within the boiler
 It can be easily removed by a wire brush
 It is formed at the colder portion of a boiler due to substances
which have greater solubility in hot water than in cold water
(e.g. MgSO4 , MgCl2, CaCl2)
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17. 17
Disadvantages of sludge
1. Sludge is a poor conductor of heat, leads to increase in fuel
consumption
2. Decreases efficiency of boiler
3. Leads to blocking of pipes
(as sludge settles in the regions of poor water circulation)
Prevention of sludge formation
 by using soft water
 by removing a portion of water having conc. salts and
replacing it by fresh water (blow down operation)

18. SCALE
Hard deposits firmly adhering to the inner walls of boiler
(very difficult to remove)
Cause of formation:
1. At high temp, the bicarbonates +nt in water are converted into insoluble
carbonates (scales)
Ca(HCO3)2 → CaCO3 ↓ + H2O + CO2
scale
2. Magnesium salts get hydrolysed at high temperature formimg scales
MgCl2 + 2H2O → Mg(OH)2 ↓ + 2 HCl
Scale
3. Solubility of CaSO4 decreases with temperature, so CaSO4 is ppted as scale at
high temperature
Some Scale Constituents:
CaSO4, CaCO3, Mg(OH)2, Fe2O3, SiO2, Na2SO4
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19. Disadvantages of scales:
1. Scales are poor conductors of heat, so leads to the
wastage of fuel
2. Distortion of boiler material
Prevention: Internal treatment of boiler feed water
Removal of Scales:
• By wire brush or by blow down operation
• Sudden cooling
• By chemical dissolution-
CaCO3 by 5-10% HCl, CaSO4 by EDTA
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