Problems caused by hard water in textile industry

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Hard water can create so many problems during wet processing from desizing to finishing in textile mills. Since every process is related to the next process, so all  processes should be done precisely to get best result. To do it first we have to know what problems hard water can create in different stage of wet processing.

In Boiler: 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 chesser or tessel. 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(HCO3)2 --> CaCO3 + CO2 + H2O

Mg(HCO3)2 --> Mg CO3 + CO2 + H2O

MgCO3 + 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%

Corrosion can be a 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 agent / component damage the boiler.

Fe + H2O + CO2 --> Fe CO3 + H2O

Fe CO3 + H2O     --> Fe(OH)2 + CO2

Desizing: Hard water de-active enzymes & insolubilize size materials such as starch, PVA etc.

Scouring: Hard react with soap during scouring. 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 and 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 which is deposited with the fabric. As a result, the surface of scoured fabric become harsh, hard & non-flexible which creates problem in the next process like produced uneven dyeing.

Bleaching: Hard water decompose bleach bath.

H2O2 --> H2O + [O]

Mercerizing: It forms insoluble metal acid, reduce absorbency and luster.

Dyeing: Ca2+ and Mg2+ ions of hard water react with dye molecules and precipitated the dye. As a result dyestuff are spoilt. Hence, uneven shade (depth of dyeing) of color is produced.

Printing: It break the emulsion, change it’s thickness and efficiency and it is also harmful for thickener. Hard water cause problems in printing process like dyeing.

Finishing: Hard water interfere with catalysts, cause resins and other additives to become non reactive, break emulsion and deactives soap.

From above, we saw that hard water causes problems in every process of wet processing. So, we have to use such water that is suitable for wet processing and don’t create any problem. Ideal quality of feed water for textile industry is :

• pH should be in the range of 7 – 8.
• Water should be odorless & colorless.
• Water hardness: maximum 5° dH.
• Solid content: < 50 mg/L.
• Dissolved solids : < 1 mg/L.
• Inorganic salts: < 500 mg/L.
• Organic salts: < 20 mg/L.
• Iron (Fe): < 0.1 mg/L.
• Mn : < 0.02 mg/L.
• Cu: < 0.005 mg/L.
• Nitrate: < 50 mg/L.
• Nitrite: < 5 mg/L.