Water Technology ECH By HB.pptx gassghahadhB

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1. Engineering Chemistry Water Technology PREPARED BY …...

2. Introduction Water is the most essential compound for all living matter on the earth. It plays an important role in human living, industrial and agricultural purposes. So there is no life in the earth without water. Uses : Industrial Coolant, solvent, reactant, Steam generation, fire fighting etc Domestic Bathing, drinking, washing, irrigation, sanitary etc.

3. Sources of water The two important sources of water are (1) surface water and (2) underground water. Surface water :The water available on the earth’s surface is called as surface water. Ex: rainwater, river water, lake water and sea water. Underground : water Underground water includes water present between the rocks in the earth crust. EX : spring water, well water etc.

4. Reason for Depletion of underground water The decrease in the quantum of underground water is depletion of water. Depletion of water is mainly caused by Modernization, industrialization and population growth Global warming causing excess evaporation of surface water Deforestation Decrease in rainfall caused by seasonal changes and Effluents from the industries spoiling the ground water

5. Types of water There are two types of water. 1. Hard water 2. Soft water Hardness of water : Hardness of water is the characteristic to prevent leather formation of water with soap. Generally salts like chlorides, bicarbonates and sulfates of Ca 2+ , Mg 2+ and Fe 2+ make water hard. This hard water on treatment with soap which is stearic or palmitic acid salt of sodium and potassium causes white precipitate formation of calcium or magnesium stearate or palmitate.

6. Hard water : water which does not give lather with soap is called hard water. Soft water : Water which readily gives lather with soap is called soft water. Types of hardness : There are two types of hardness in water Temporary Hardness(Carbonate hardness) Permanent Hardness(Non-Carbonate hardness)

7. Temporary Hardness: (Carbonate hardness) - It is due to the presence of calcium bicarbonate [Ca(HCO 3 ) 2 ] and magnesium bicarbonate [Mg(HCO 3 ) 2 ]. - Temporary Hardness can be removed by boiling. Permanent Hardness: - ( Non-Carbonate hardness) It is due to the presence of chloride and sulphates salts of calcium and Magnesium. (CaCl 2 , CaSO 4 , MgCl 2 , MgSO 4 ).Hence it is called as permanent hard water .

8. Units of hardness The hardness is expressed in terms of equivalent calcium carbonate. Equivalent of CaCO3 = (mass of hardness causing substance) (mw of CaCO3) (Mw of hardness causing substance) The reason for choosing CaCO3 as standard for report in hardness is ease in calculations on its molecular weight is exactly 100. 1. Parts Per Million : Parts of CaCO 3 equivalent hardness per 10 6 parts of water. OR 1 ppm = 1 part of CaCO 3 equivalent hardness in 10 6 parts of water.

9. 2. Milligrams per litre :- Number of milligrams of Calcium Carbonate equivalent hardness present in 1 litre of water. 1 mg / L = 1 mg of CaCO3 equivalent hardness present in 1 liter of water. 1 L = 1 Kg = 1000 g = 1000 x 1000 mg = 10 6 mg. 3. Degree French (°Fr) : It is in the parts of CaCo 3 eq hardness per 10 5 parts of water. 4. 1 °Clarke = 1 grain of CaCo 3 eq hardness per gallon of water. 1 part of CaCo 3 of hardness per 70,000 parts of water. Relation between various units o hardness: 1 ppm = 1 mg /L = 0.1 °Fr = 0.07 °CL

10. S.No Molecular formula of the hardness producing salt Molecular weight 1 Ca2+ 40 2 CaSO4 136 3 Ca(HCO3)2 162 4 CaCl2 111 5 CaCO3 100 6 Mg2+ 24 7 MgCO3 84 8 Mg(HCO3)2 146 9 MgCl2 95 10 MgSO4 120

11. Problems A sample of water contains 120mgs of MgSO4 per litre. Calculate the hardness in terms of CaCO3 equivalents. Ans : 100 ppm The analysis of three sample of water gives the following results. Sample 1 contains 10 mg/ litre of calcium sulphate, sample 2 contains 10 mg/ litre of magnesium bicarbonate, and sample 3 contains 10 mg/ litre of magnesium sulphate. Find which one of the sample is more hard. Ans : Sample 1: 7.35 mg/lit Sample 2: 6.85mg/lit Sample 3: 8.26mg/lit A sample of water on analysis contains 13.6 mg/ litre of calcium sulphate, 14.6 mg/ litre of magnesium bicarbonate, 12 mg/ litre of magnesium sulphate. Calculate the temporary hardness and total hardness of the sample. Ans : Temporary Hardness = 10 mg/ litre (Mg (HCO3) 2 alone) Permanent Hardness = 10+10 = 20 mg/ litre (CaSO4 +MgSO4)

12. Impurities of water The main impurities present in water are classified into three types. Physical impurities Chemical impurities Biological impurities Physical Impurities : Include suspended and colloidal impurities Suspended impurities - Clay, sand, decayed vegetable and animal matter. Causes - Makes the water turbid. Colloidal impurities - Finely divided clay and silica, coloring matter, complex proteins, amines etc., Causes - Impart color, odor and taste.

13. 2 . Chemical Impurities : Include dissolved salts and dissolved gases Dissolved salts Chlorides, sulphates, bicarbonates, carbonates of Ca, Mg, Na, etc., Causes: (i)CaCl 2 , CaSO 4 , Ca (HCO 3 ) 2 , MgCl 2 ,MgSO 4 , Mg (HCO 3 ) 2 make the water hard. (ii) Mg (HCO 3 ) 2 , Ca (HCO 3 ) 2 , Na 2 CO 3 ,NaHCO 3 , etc., make the water alkaline. (b) Dissolved gases Oxygen, carbon dioxide, hydrogen sulphide etc., Causes: (i) Oxygen accelerates the rate of corrosion. (ii) CO 2 and H 2 S makes the water acidic and corrosive

14. 3. Biological Impurities : Pathogenic microorganism like bacteria, algae, fungi etc. Causes – Spread various disease like typhoid, dysentery, hepatitis etc.,

15. Disadvantages of hard water In domestic uses Washing -It does not lather well. -It produces sticky precipitate of Ca and Mg soaps, which adheres on the cloth giving spots and wastage of soap. 2. Bathing - It does not lather well, but produces sticky scum on the body. thus cleaning quality decreases . Cooking - Boiling point of water increases hence more fuel and time required for cooking. - It produces unpleasant taste and muddy-looking extract. Drinking - Bad effect on our digestive system

16. In Industrial Use Textile & dyeing - They produce colored spots on fabrics. Sugar Industry - They cause difficulties in the crystallization of sugar from molasses. 3. Paper and pulp Industries - Affect color and brightness of the paper - Produces cracks in the paper. Beverage Industries - They will neutralize the fruit acids and destroy the tastes. Construction Industries - The hydration of cement and final hardening of cement are affected

17. Power Industries (boiler problems) - Scale and sludge formation - Priming and Foaming - Corrosion - Caustic embrittlement

18. Scale and Sludge formation : In boilers, water evaporates continuously and the concentration of the dissolved salts increases progressively. When the salts concentration reaches their saturation point, they are thrown out of water in the form of precipitates on the inner walls of the boiler. If the precipitated matter is soft and slimy, it is called sludge. While the precipitate forms an adherent coating on the inner walls of the boiler, it is called scale.

19. a) Sludge : - Sludge is a soft, loose and slimy precipitate forms inside the boiler during steam generation. - Sludge is generally formed at cooler portions of the boiler. - Sludges are formed by substances like CaCl 2 , MgCl 2 , MgSO 4 , MgCO 3 ,etc, - It can be easily scrapped off with a wire brush. Disadvantages of Sludge Formation - Sludges are poor conductors of heat, so they waste a portion of heat generated. - Excess of sludge formation decreases the efficiency of boiler.

20. Prevention of Sludge Formation - By using well softened water. - By frequent blow down operation. (Blow - down operation is a process in which a portion of concentrated water containing large amount of dissolved salts is replaced with fresh water frequently, during steam making). b) Scale : -Scale is a hard, adherent coating forms on the inner walls of the boiler during steam generation. - Scale is generally formed at hotter portions of the boiler. - Scales are formed by substances like CaSO4, Mg(OH)2 etc. Disadvantages of Scale Formation - Wastage of Fuel - Decrease in Efficiency - Danger of Explosion

21. Prevention of Scale Formation 1 . External treatment This method involves the removal of scale forming impurities from water before feeding to the boiler. Example o Lime soda process o Zeolite process o Demineralization process 2. Internal Treatment This method involves the addition of chemicals directly to the water in boilers to remove the scale forming substances which were not completely removed during external treatment. Example o Colloidal Conditioning o Carbonate Conditioning o Calgon Conditioning o Phosphate Conditioning

22. (ii) Priming and Foaming Priming : When boiler is steaming (producing steam) rapidly, some particle of the liquid water containing impurities are carried along with the steam The process ‘wet steam formation’ (steam containing droplets of water) is called Priming. Causes High steam velocity Very high water level in the boiler. Improper boiler design. Sudden boiling of water

23. Prevention Priming can be controlled by Controlling the velocity of steam. Keeping the water level lower. Good boiler design Foaming : The formation of stable bubbles above the surface of water is called foaming. These bubbles are carried along with steam leading to excessive priming. Causes Foaming may be caused by presence of oil, grease in water and finely divided sludge particles.

24. Prevention Foaming can be prevented by Adding coagulants like sodium aluminate, aluminium hydroxide, etc., Adding anti-foaming chemicals such as castor oil and synthetic polyamides.

25. (iii) Boiler Corrosion The decay of boiler material by its environment is termed as boiler corrosion. Corrosion in boilers is due to the presence of Dissolved oxygen Dissolved carbon dioxide Dissolved salts Dissolved Oxygen The presence of dissolved oxygen in water is the main cause of boiler corrosion. When water containing dissolved oxygen is heated in the boiler, the dissolved oxygen gets liberated and corrodes the boiler material as follows 2Fe + O 2 + 2H 2 O → 2Fe(OH) 2 4Fe(OH) 2 +O 2 → 2[Fe 2 O 3 .2H 2 O] Ferrous hydroxide Rust