Difference between sludges and scales.

Solution-:

Sludges-:

1) Sludges are soft, loose and slimy precipitate.

2) They are non-adherent deposits and can be easily removed.

3) They are formed by substances like CaCl₂  , MgCl₂ , MgSO₄ , and MgCO₃ 

4) They are formed at comparatively colder portions of the boiler.

5) They decrease the efficiency of boiler but are less dangerous.

6) They can be removed by blow-down operation.

Scales-:

1) Scales are hard deposits.

2) They stick very firmly to the inner surface of boiler and very difficult to remove.

3) They are formed by substances like CaSO₄ , Mg(OH)₂ , CaCO₃ , and CaSiO_3­  

4) They are formed generally at heated portions of the boiler.

5) They decrease the efficiency of boiler and chances of explosions are also there.

6) They cannot be removed by blow-down operation.