Water Technology - Questions and Answers

1. Define soft water and hard water.

Ans: Soft water : Water which forms lather easily and readily with soap is called soft water.

Hard Water : Water which does not produce lather with soap readily but forms an insoluble precipitate like scum is known as hard water.

2. Define hardness of water.

Ans: Soft water : Water which forms lather easily and readily with soap is called soft water.

Hardness is the characteristic property of which does not produce lather with soap, but on the other hand forms a white scum or precipitate.

3. Give the difference between temporary hardness and permanent hardness.

Ans:

S.No	Temporary hardness	Permanent hardness
1.	This is due the presence of bicarbonates of calcium and magnesium	This is due to the presence of chlorides and sulphates of calcium and magnesium.
2.	It can be removed by boiling.	It cannot be removed by boiling.

4. What is boiler feed water?

Ans: The water used to fed in boiler for the production of steam is called boiler fed water.

5. What are the disadvantages of using hard water in boilers?

Ans: When water from natural sources having hardness is fed directly to boilers, then the following problem or trouble may arise.

Scale and sludge formation
Priming and foaming
Caustic embrittlement
Boiler corrosion

6. What is a sludge? Give the substances responsible for sludge formation in boilers.

Ans: Sludge is a soft, loose and slimy precipitate formed in the boiler. Sludges are usually formed by substances which have greater solubilities in hot water than in cold water, e.g., MgCO₃, MgCl₂, CaCl₂, MgSO₄, etc. It is formed at comparatively colder portions of the boiler.

7. What are the disadvantages of sludge formation?

Ans: Disadvantages of sludge formation:

Sludges are the poor conductors of heat, So they waste a portion of heat generated.
Excess of sludge formation decreases the efficiency of boiler.

8. What are scales? Name the substances responsible for scale formation in boilers.

Ans: Scales are hard, adherent coating on the inner walls of the boiler during team generation. Scales are formed mainly by Ca(HCO₃)₂ and MgCl₂. In high pressure boiler, the scale forming substances are mainly CaSO₄, silica, etc.

9. What do you know about blow down operation?

Ans: Blow-down operation is the process in which a portion of concentrated water containing large amount of dissolved salt is replaced with fresh water frequently, during the production of steam.

10. Give any one method for the removal of dissolved oxygen.

Ans: By adding calculated quantity of sodium sulphite or sodium sulphide or hydrazine.

2Na 2 SO 3 +O 2 ⟶2Na 2 SO 4

Sodium sulphite

N 2 H 4 +O 2 ⟶N 2 +2H 2 O

Hydrazine

Na 2 S+2O 2 ⟶Na 2 SO 4

Sodium Sulphide

11. What is caustic embrittlement? How it can be prevented?

Ans: Caustic embrittlement is a type of boiler corrosion, caused by the use of highly alkaline water in the high pressure boiler.

Caustic embrittlement can be prevented by

(i) Using sodium phosphate as softening agent instead of sodium carbonate.

(ii) Adjusting the

pH

of the feed water carefully between 8 and 9 .

12. What are priming & foaming?

Ans: When a boiler is producing steam rapidly, some particles of the liquid water are carried along with the steam. This process of wet steam formation is called priming.

Foaming is the production of persistent foam or bubbles in boilers, which do not break easily. Foaming is due to the presence of substances like oils in boiler water.

13. What is boiler corrosion?

Ans: Boiler corrosion is due to the decay of boiler material by a chemical or electrochemical attack from its environment. It is caused by using the unsuitable water in the boilers.

14. What is softening of water?

Ans: The processes of removing hardness producing substances from the water is called ‘softening of water’.

15. What is ion-exchange method?

Ans: Ion – exchange methods for the purification of water help in the removal of all soluble minerals (both cations and anions) without distillation.

16. How will you regenerate the column in the demineralisation process?

Ans: After some time both the ion exchangers are exhausted by using their respective

H +

and

OH -

ions. The exhausted cation exchange column is regenerated by passing a solution of dilute

HCl

or dilute

H 2 SO 4

R 2 Ca 2+ + 2H + ⟶2RH + +Ca 2+

R 2 Mg 2+ + 2H + ⟶2RH + +Mg 2+

RNa + + H + ⟶RH + + Na +

The exhausted anion exchange column is regenerated by passing a solution of dilute

NaOH

R’ Cl + OH^– → R’OH^– + Cl^–

R’₂SO^2-+2OH^– → 2R’OH^–+SO^2-

17. What is internal treatment?

Ans: Treatment of water inside the boiler is called, Internal treatment or internal conditioning.

In this process, chemicals are added directly into the water in the boiler in order to remove the scale forming salts and corrosive chemicals in water.

18. What is desalination? Name any four methods of converting brackish water into fresh water.

Ans: The process of removing common salt

(NaCl)

from the sea water is known as desalination. The water containing dissolved salts with peculiar salty taste is called brackish water. The common method for the desalination of brackish water are,

(i) Reverse osmosis

(ii) Electrodialysis

(iii) Distillation

(iv) Freezing.

19. What is reverse osmosis?

Ans: The flow of solvent takes place from concentrated solution to diluted solution. This process is known as Reverse Osmosis.