Describe the effects of hard water in textile wet processing? | State the disadvantages of hard water?

1) SCALE FORMATION:

If hard water is used in boiler, then a layer is formed on the inner surface of the vessel or in the inner side of tube. This layer is very hard just like as stone which is not removed without hammer or chaser or tassel. This is called scale.

In boiler, temporary hard water produce CaCO3 & Mg (OH)2. The combination of CaCO3 & Mg(OH)2 is called scale.

Ca(H CO3)2 ∆→ CaCO3 ↓ + CO2 ↑ + H2O

Mg(H CO3)2 ∆→ Mg CO3 ↓  + CO2↑ + H2O

Mg CO3 + H2O ∆→ Mg(OH)2 + CO2↑

CaCO3 + Mg(OH)2 → Scale.

As a result, in boiler more heat will be needed &for that, more fuel will be required. For scale formation, equally heat transformation in boiler tube is not possible very often. As a result, for excess heat of a particular part of the tube, the tube may burst.Heat loss of tube up to 40% according to the diameter of the tube. Heat loss by pipe scaling up to 40% for 20 mm scale.

 

SCALE THICKNESS         HEAT LOSS

1 mm  → approximately 10%

3 mm →        „          17%

5 mm →        „          22%

10 mm           →        „          30%

20 mm           →        „          43%

2) REACTION WITH SOAP:

Soap is the Na & K salt of higher fatty acid (C17H35COONa). The Hard water does not easily form lather by reacting with soap. The Ca & Mg salt of hard water react with soap 7 produce insoluble organic salts which becomes the wastage of soap.

CaSO4 + 2 C17H35COONa → (C17H35COO)2Ca + Na2SO4

Insoluble organic salt If we use hard water in wet processing, then they produce insoluble salt.

3) DEPOSOTION OF INSOLUBLE SALT ON THE SURFACE OF FABRIC / TEXTILE GOOD DURING SCOURING:

Insoluble salt that is produced by reaction of soap & hard water is deposited with the fabric during scouring. As a result, the surface of scoured fabric become harsh, hard & non-flexible which creates problem in the next process.

4) REACTION WITH DYESTUFF:

If hard water is used in dyeing, then it react with dye molecules & reduce the tinctorial power of dyestuff. As a result, uneven shade (depth of dyeing0 of colour is produced. Sometimes, dyestuff are precipice & spoil.

5) CORROSION OF BOILER:

Corrosion can be serious problem in boiler, if hard water is used in it. Dissolved O2 in the presence of CO2 is the common cause of corrosion. Fe present in hard water reacts with CO2 to form Fe CO3, which is the main process of corrosion. This Fe CO3 is hydrolyzed & produce Fe(OH)2. this agents / components damage the boiler.

Fe + H2O + CO2 → Fe CO3 + H2O

Fe CO3 + H2O        →  Fe(OH)2 + CO2