Unit 1 water_technology


Published on

Published in: Education
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide
  • Platinum Cobalt Colour std: Dissolve 1.246 g of K2PtCl6 (equivalent to 0.5g of Pt) and 1 g of CoCl2.H2O in 1litre of distilled water containing 100 mL HCl. It corresponds to 500 colour units. Calibration range: 5 – 70 CPU (chloroplatinate unit). This method is used to measure the color of natural water and not industrial samples particularly colored ones.
  • Oil reduces the surface tension of the water greatly
  • Unit 1 water_technology

    1. 1. UNIT - IWATER TECHNOLOGY Dr. RupamSingh CY101 ENGG. CHEM. 1
    2. 2. “Without food, human can survive for number ofdays, but water is such an essential that without itone cannot survive”.“Although water is nature’s most wonderful,abundant and useful compound yet is also themost misused one”. 2
    3. 3. Distribution of water 3
    4. 4. Sources of WaterA) Surface Waters Rain Water - Pure but contaminated with gases River Water - High dissolved salts moderate organics Lake Water - Const. composition but high organics Sea Water - High salinity, pathogens, organicsB) Underground Waters Spring/Well Water - Crystal clear but high dissolved salts and high purity from organics 4
    5. 5. Classification of Impurities in water Physical Impurities - Dissolved Solids/Salts Chemical Impurities - Inorganic & Organic Chemicals Biological Impurities - Pathogens, algae, fungi,viruses... 1) Acidity (pH) 2) Gases (CO2-1) Colour2) Turbidity O2, NH3) 1) Microorganism3) Taste 3) Minerals 2) Water Bodies4) Odour 4) pH5) Conductivity 5) Salinity 6) Alkalinity 5 7) Hardness
    6. 6. Colour• Colour in water is due to metallic salts of Fe, Mn and due to organic substances like humus, peat, algae, weed …• Industrial activities such as textile, paper & pulp, dyeing, tanneries• Colour intensities of water sample can be measured using tintometer using Platinum cobalt standard colour complexTurbidity• It is due to colloidal, extremely fine suspension such as clay, slit, finely divided matters, sometimes microorganisms…• It reflects the optical properties of water in terms of light scattering ability instead of transmitting in straight lines.Conductivity• The ability of water to conduct electricity, indicates the amount of dissolved minerals and gases in water.• Conductivity measured in micro mhos/cm or MicroSiemns/cm3 6
    7. 7. Taste• Presence of dissolved salts and gases imparts bitter, soapy, brackish and palatable taste which normally co-related with odour but it is not applicable always the case• Bitter (Fe, Al, Mn, SO4, Ca(OH)2)• Soapy (NaHCO3)• Brackish (High salt content - NaCl)• Palatable (CO2 and NO3)Odour• Domestic and industries activities cause undesirable odour to water• Industrial effluent of organics, sewage discharge, presence of N, S and P contains compounds, metal ion pollution like Fe• Substances like algae, peat, bacterias• Grassy odour, peaty odour, offensive odour, tarry and faint odour 7
    8. 8. pH• pH a measure of hydrogen ion activity is used toexpress the intensity of acidic or alkaline condition of asolution.• The pH scale runs to 0 from 14 with 0 representingmaximum acidity and 14 maximum basicity pH = -log [H+] 8
    9. 9. Acidity of WaterAcidity is a measure of the effects of combination ofcompounds and conditions in water.It is the power of water to neutralize hydroxyl ions andis expressed in ppm interms of CaCO3 equivalence.• Acidity - - - - Free Mineral Acidity - - - - CO2 Acidity 9
    10. 10. MAJOR IMPURITIES OF WATER Ionic and dissolvedCationic Anionic Nonionic and undissolved Gases AlkalinityCalcium Bicarbonate Turbidity, silt, mud, dirt and CO2Magnesium Carbonate other suspended matter H 2S Hydroxide NH3Sodium Color, Plankton CH4Potassium Sulfate Organic matter, O2Ammonium Chloride Colloidal silica,Iron Nitrate Microorganisms,Manganese Phosphate Bacteria 10
    11. 11. Hard Water What’s hard water? Practically speaking, measurement of: •Calcium (Ca) ions •Magnesium (Mg) ionsHardness as calcium carbonate mg/L (ppm)Soft 0-17Moderately hard (Medium) 60-120Hard 120-180Very hard 180 & over 11
    12. 12. Why be concerned about Hard Water?• Originally, water hardness was defined as the measure of the capacity of the water to precipitate soap• Hard water does cause soap scum, clogs pipes and clogs boilers as lime scale 12
    13. 13. Hardness of Water• Hardness in Water is characteristic that prevents the‘lathering of soap’ thus water which does not produce latherwith soap solution readily, but forms a white curd is calledhard water.• Type of Hardness– Temporary or Carbonate Hardness– Permanent Hardness or non-carbonate Hardness. 13
    14. 14. Temporary Hardness– Temporary Hardness is caused by the presence of dissolved bicarbonateof calcium, magnesium and other heavy metals and the carbonate of iron.It is mostly destroyed by more boiling of water, when bicarbonates aredecomposed yielding insoluble carbonates.Ca(HCO 3 ) 2 Heat CaCO 3 + H2O + CO2Calcium bicarbonate Calcium CarbonateMg(HCO 3 ) 2 Heat Mg(OH) 2 + 2CO2Magnesium Bicarbonate Magnesium hydroxide– Calcium/Magnesium Carbonates thus formed being almost insoluble, aredeposited as a scale at the bottom of vessel, while carbon dioxide escapesout. 14
    15. 15. Permanent HardnessNon Carbonate Hardness is due to the presence ofchlorides, sulfates of calcium, Magnesium, iron and otherheavy metals 2C17H35COONa + CaCl2 (C17H35COO)2Ca + 2NaCl Sodium Hardness Calcium stearate stearate (Insoluble) (sodium soap) 2C17H35COONa + MgSO4 (C17H35COO)2Mg + 2Na2SO4 Sodium Hardness Magnesium stearate stearate (Insoluble) (sodium soap) 15
    16. 16. Units of HardnessMost Commonly used• Parts per million (ppm)1ppm=1 part of CaCO3 equivalence hardness causing substance present in 10 6parts of water• Milligrams per liter (mg/litre) 1mg/L=1mg of CaCO3 equivalence hardness causing substance present in oneliter of water1mg/L=1ppmRelationship; 1L water = 1Kg = 1000 g = 1000 X 1000 mg = 106 mg 1mg/L = 1mg of CaCO3 eq per 106 mg of water = 1 part of CaCO3 eq per 106 parts of water = 1ppm• Clares Degree(oCl)1o Clarke= 1part of CaCO3 equivalent hardness in 70000 parts of water• Degrees French (oFr) 161o Fr = 1 part of CaCO3 eq per 105 parts of water
    17. 17. CaCO3 equivalent hardness Mass of hardness Molecular weight producing X of CaCO 3Calcium carbonate equivalent = substance Molecular weight of hardness producing substancesProblem 1Calculate the calcium carbonate equivalent hardness of a water samplecontaining 204mg of CaSO4 per litre Solution : 204 X 100 Calcium carbonate equivalent hardness = = 150 mg of 136 CaCO 3 /L = 150 ppm Note : Mol. Weight of CaCO 3 = 100 Mol. Weight of CaSO 4 = 136 17
    18. 18. Calcium carbonate equivalence conversion during hardness calculation Hardness Molecular Multiplication factor producing weight (in terms of CaCO3 substance equivalence) Ca(HCO3)2 162 100/162 or 50/81 Mg(HCO3)2 146 100/146 or 50/73 CaSO4 136 100/136 or 50/68 CaCl2 111 100/111 or 50/55.5 120 100/120 or 50/60 MgSO4 95 100/95 or 50/47.5 MgCl2 100 100/100 or 50/50 CaCO3 84 100/84 or 50/42 MgCO3 44 100/44 or 50/22 CO2 61 100/61 or 50/61 HCO-3 17 100/17 or 50/17 OH- 60 100/60 or 50/30 CO32- 18
    19. 19. Problems 1. A water sample from an industry in Bombay had the following data Mg(HCO3)2 = 16.8mg/L, MgCl2 = 19 mg/L, CaCO3 = 20 ppm, MgSO4 =24.0mg/L and KOH = 1 ppm. Calculate the temporary, permanent and total hardness of the water sample. Solution Step 1 conversion in to CaCO 3 equivalent Constituent quantity Conversion Hardness present factorMg(HCO3)2 16.8 mg/L 100/146 16.8 *100/146 = 11.5ppm 19.0 mg/L 100/95 19.0*100/95 = 20ppmMgCl2 20.0*100/100 = 20 ppmCaCO3 20 ppm 100/100 24.0*100/120 = 20 ppmMgSO4 24.0 mg/L 100/120Calculation Temp. Hardness = 31.5 ppm P. Hardness = 40 ppm Tot. Hardness =71.5 ppm 19
    20. 20. Draw backs (or) Disadvantages of Hard WaterDomestic Use Industrial Use 1. Washing 1. Textile Industry 2. Bathing 2. Sugar Industry 3. Drinking 3. Dyeing Industry 4. Cooking 4. Paper Industry 5. Pharmaceutical IndustryThe sticky precipitate adhereson the fabric/cloth and givesspots and streaks. Fe salts stain 6. In Steam generation inthe cloths. BoilersProduces sticky scum on thebath tub and the bodyBad to the digestive systemand calcium oxalate formationis possible in urinary tracts Requires more fuel and time. Certains food don’t cook soft and also gives unpleasant taste 20
    21. 21. Boiler troubles due to Hard Water 1. Scale and 1. Sludge Sludge Slimy loose precipitate called sludge 2. Caustic suspended in water embitterment 3. Priming and Foaming 4. Boiler water corrosion Boiler wall Sludge is a soft, loose and slimy precipitate formed within the boiler. It can be easily scrapped off with a wire brush. It is formed at comparatively colder portions of the boiler and collects in areas of the system, where the flow rate is slow or at bends. It is formed by substances which have greater solubilitys in hot water than in cold water, e.g. MgCO 3 , MgCl 2 , CaCl 2 , MgSO 4 etc., 21Remedy: Sludges can be removed using wire brush or mild acid
    22. 22. 1. Scale Hard adherent coating on inner walls of boiler water Boiler wallScales are hard substances which sticks very firmly to theinner surfaces of the boiler wall.Scales are difficult to remove even with the help of a hammerand chisel.Examples: CaSO 4 , CaCO 3 , Mg(OH) 2 22
    23. 23. 23
    24. 24. Reasons for formation of scale 1. Presence of Ca(HCO 3 ) 2 in low pressure boilers Ca(HCO 3 ) 2 CaCO 3 + H2O + CO2 Low pressure boilers but in high pressure boilers it is soluble by Calcium bicarbonate Calcium Carbonate (scale) forming Ca(OH) 2 2. Presence of CaSO 4 in high pressure boilers T oC Solubility of CaSO 4 4. Presence of SiO 2 15 3200 ppm 230 15 ppm It forms insoluble hard adherent 320 27 ppm CaSiO 3 and MgSiO 3 as scales Cold water soluble Super heated water Insoluble (scale)3. Presence of MgCl 2 in high temperature boilers MgCl 2 + 2 H 2 O Mg (OH)2 + 2HCl Magnesium chloride scaleMg(OH) 2 can also be generated by thermally decomposing Mg(HCO 3 ) 2 24
    25. 25. Disadvantages of scale formation1. Fuel wastage – scales have low thermal conductivity2. Degradation of boiler material and increases of risk of accident3. Reduces the efficiency of the boiler and- deposit on the valves and condensers4. The boiler may explode – if crack occurs in scale Remedies: Removal of scale1. Using scrapper, wire brush often2. By thermal shock- heating and cooling suddenly with cold water3. Using chemicals – 5-10% HCl and by adding EDTA 25
    26. 26. Prevention of scale formation Scale formation can be prevented by two methods 1. Internal conditioning or Internal Treatment 2. External conditioning or External treatment- will be discussed later1. Internal conditioning methods - of boiler water to prevent scale formation 1. Phosphate conditioning – addition of phosphate compound 2. Carbonate conditioning – addition of carbonate compound 3. Calgon conditioning – addition of sodium hexa meta phosphate 4. Colloidal conditioning – spreading of organic compounds like tannin, agar gel 5. Sodium Aluminate – removes oil and silica 6. Complexometric method – using EDTA (refer expt. 1 chemistry lab manual)1. Phosphate conditioningScale formation can be prevented by adding sodium phosphate to the boiler water whichreacts with the hardness producing ions and forms easily removable phosphate salts ofrespective ions 3CaCl 2 (Boiler water) + 2 Na 3 PO 4 Ca 3 (PO 4 ) 2 + 6 NaCl Calcium Sodium calcium phosphate chloride phosphat (non adherent and e can be removed by 26 blow down method)
    27. 27. Selection of Phosphate compoundCalcium can not be precipitated below a pH = 9.5, hence the selection ofphosphate has to be based on the pH of the boiler feed water. NaH 2 PO 4 (acidic in nature) , Na 2 HPO 4 (weakly alkaline in nature), Na 3 PO 4 (Alkaline in nature)2. Carbonate conditioningCaSO 4 (Boiler water) + Na 2 CO 3 CaCO 3 +Na 2 SO 4Calcium Sodium calcium carbonate sulfate carbonate (non adherent loose sludge and can be removed by blow down method)Caution: Excess Na 2 CO 3 can result in caustic embrittlement 27
    28. 28. 3. Calgon conditioning Na 2 [Na 4 (PO 3 ) 6 2Na+ + [Na 4 P 6 O 18 ] 2- Calgon – sodium hexa meta phosphate2CaSO 4 (Boiler water) + [Na 4 P 6 O 18 ] 2- [Ca 2 P 6 O 18 ] 2- + 2Na 2 SO 4Calcium Soluble complex ionsulfate of calcium - can be removed easilyCalgon tablets are used in the cleaning of washing machinedrums 28
    29. 29. II. Caustic embitterment Excess sodium carbonate used up for removing hardness can alsoresult in the formation of NaOH in high pressure boilers.NaOH has better mobility and can percolate into fine cracks presentin boiler walls. Na2CO3 + H2O → 2 NaOH + CO2 NaOH gets concentrated in the fine cracks present in the boilerwalls. A concentration cell corrosion is established between the conc.NaOH and dilute NaOH solution in contact with boiler walls. Concentrated NaOH region behaves as anode thus resulting incorrosion of boiler leading to the formation of sodium ferroate.Remedies: (i) Use phosphate salts instead of sodium carbonate(ii) use Na 2 SO 4 or agar-agar gel compounds to fill the fine cracks. 29
    30. 30. III. Priming and foaming Foaming It is the production of continuous foam or hard bubblers in boilers. Foaming is due to the presence of substance like oil in boiling water. Priming Foamin It is the process in which some g Normal bubble particles in water are carried along with the steam. The resulting process is called as wet steam or carry over. The process of formation of wet steam in boilers is called as priming. Causes of Priming, 1. Presence of dissolved salts Priming 2. High velocity steam due to sudden Carry over boiling bubble 3. Improper boiler design Disadvantages of Priming and foaming – refer Jain and Jain Text 30 book
    31. 31. IV. Boiler corrosionDegradation or destruction of boiler materials (Fe) due to thechemical or electrochemical attack of dissolved gases or salts iscalled boiler corrosionBoiler corrosion is of three types1. Corrosion due to dissolved O 22. Corrosion due to dissolved CO 23. Corrosion due to acids formed by dissolved salts1. Corrosion due to dissolved oxygen(DO) 2 Fe + 2 H2O + O2 2 Fe(OH)2 4 Fe(OH)2 + O2 2 [Fe2O3.2H2O] Ferrous Rust hydroxide 31
    32. 32. Removal of Dissolved Oxygen (DO) 1. By the addition of chemicals The dissolved oxygen present in the boiler feed water can be removed by the addition of sodium sulphite or hydrazine and the reactions can be written as below 2 Na2SO3 + O2 2 Na2SO4 Sodium DO Sodium sulphite sulphate Water feed Na2S + 2O2 Na2SO4 N2H4 + O2 N2 + 2H2O O2 To vacuum Hydrazine Nitrogen Steam jacket 2. By mechanical deaerationIt comprises of a tall stainless tower with differentlayers capped with baffles to facilitate multiple Perforated plateequilibration.The entire chamber is vacuumized and also maintainedat high tempt using perforated heating plates on thewalls. Deaerate 32 d water
    33. 33. 2. Corrosion due to dissolvedCO 2Presence of bicarbonate salts of either magnesium or calcium also causes the releaseof CO 2 inside the boiler apart from the dissolved CO 2 Mg(HCO 3 ) 2 MgCO 3 + H 2 O + CO 2 CO 2 + H 2 O H 2 CO 3 (causes slow corrosion)Removal1. It can be removed by the addition of ammonia 2 NH 4 OH + CO 2 (NH 4 ) 2 CO 3 + H 2O 3. Corrosion due to dissolved salts MgCl2 + 2 H2O Mg(OH)2 + 2HCl Fe + 2 HCl FeCl2 + H2 FeCl2 + 2 H2O Fe(OH)2 + 2HCl 33
    34. 34. Softening of hard water – External treatment Attn: Part B Question 34
    35. 35. II External treatment of water – External Conditioning of water Softening of hard water can be done by the following methods 1. Lime soda process 2. Zeolite methods 3. Ion exchange resin method 4. Mixed bed deionizer method1. Lime soda processIt is a process in which Lime (Ca(OH) 2 ) and soda (Na 2 CO 3 ) are added to the hardwater to convert the soluble calcium and magnesium salts to insoluble compoundsby a chemical reaction. The CaCO 3 and Mg(OH) 2 so precipitated are filtered offand removed easily.It is further divided in to two types1. Cold lime soda process2. Hot lime soda process 35
    36. 36. 1. Cold lime soda processStep 1 In this process a calculated quantity of Ca(OH)2 (lime) and Na2CO3 (soda) are mixed with water at room temperature and added to the hard water. The following reactions takes place depending on the nature of hardness Chemical reactions If it is permanent hardness and due to calcium salt Ca2+ + Na2CO3 CaCO3 + 2Na+ (soda) slimy suspended precipitate If it is due to Magnesium salt Mg2+ + Ca(OH)2 Mg(OH)2 + Ca2+ (lime) slimy suspended precipitate Ca2+ + Na2CO3 CaCO3 + 2Na+ (soda) slimy suspended precipitate 36
    37. 37. Chemical reactions contd.. If it is Temporary hardness and due to calcium salt Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O slimy suspended precipitate If it is due to Magnesium salt Mg(HCO3)2 + 2Ca(OH)2 2CaCO3 + Mg(OH)2 + 2H2O slimy suspended precipitatesStep 2 The precipitates CaCO3 and Mg(OH)2 are very fine and forms sludge like precipitates in the boiler water and are difficult to remove because it does not settle easily making it difficult to filter and the removal process. Finally reduces the efficiency of the boiler. Therefore, it is essential to add small amount of coagulant (such as Alum, Aluminium sulfate, sodium aluminate etc) which hydrolyses to flocculent precipitate of Al(OH)3 which entraps the fine precipitates. NOTE: Particles finer than 0.1 µm (10-7m) in water remain continuously in motion due to electrostatic charge (often negative) which causes them to repel each other. Once their electrostatic charge is neutralized by the use of coagulant chemical, the finer particles start to collide and agglomerate (combine together) under the influence of 37 Van der Waalss forces. These larger and heavier particles are called flocs.
    38. 38. When coagulants are added flocculation takes place followed by theformation of flocculants.NaAlO2 + 2H2O NaOH + Al(OH)3Coagulant Flocculent- Gelatinous precipitate which entraps the fine precipitates of CaCO3 and Mg(OH)2 Al2(SO4)3 + 3 Ca(HCO3)2 2Al(OH)3 + CaSO4 + CO2 Aluminium Hard water sulfate sample Flocculent- Gelatinous precipitate which entraps the fine precipitates of CaCO3 and Mg(OH)2The Al(OH)3 formed by the addition of coagulants initiates the process offlocculation and entraps the fine precipitates and becomes heavy. Theheavier flocs then settles at the bottom and filtered off easily. 38
    39. 39. Continuous cold lime soda softener Chemicals Hard water (soda+lime feed +coagulant) feed Softened waterWood fiberfilter Stirrer paddles Sedimented sludge (CaCO3, Mg(OH)2 39
    40. 40. 2. Hot lime soda ProcessIn this process a calculated quantity of Ca(OH)2 (lime) and Na2CO3 (soda) aremixed with hot water at a temperature range of 80 to 150oC and added to the hardwater. The following reactions takes place depending on the nature of hardness Advantages of Hot Lime Soda Process1. The reaction between hardness producing substance and lime soda proceeds at a faster rate2. The precipitates and sludges formed are settled at the bottom easily and hence No coagulants are required3. The dissolved gases such as CO2 escapes and the water becomes free from dissolved gases4. It produces soft water with the residual hardness of 15-30ppm in contrast to the cold lime soda process which produces soft water with 50-60ppm of residual hardness Hot lime soda Plant consists of three parts 1. Reaction tank: water, chemicals and steam are mixed 2. Conical sedimentation tank : sludge settles down 3. Sand filter : complete removal of sludge from the soft water is ensured 40
    41. 41. Continuous Hot Lime soda Process Hard water feed Super heated steam Chemicals feed (lime and soda) Reaction tank Soft water r dl ayeConical sedimentation san Fine yertank a nd la r se s Coa n Precipitated sludge a tio Gravellayer (CaCO3, Mg(OH)2 ltr Sludge Fi nk ta outlet Filtered soft water 41
    42. 42. Advantages of Lime soda process1. It is very economical compared to other methods2. Iron and manganese salts are also removed by this process3. It increases the pH of the softened water hence corrosion is minimized also pathogenic bacteriaDisadvantages of Lime soda process1. Disposal of large amount of sludge (insoluble precipitates) poses a problem2. This can remove hardness to the extent of 15ppm which is not good for boilers 42
    43. 43. Calculation of lime and soda required for the softening of hard water bythe lime soda process Hardness producing Chemical reaction with lime and soda Need substance Permanent Hardness Ca Salts CaCl2 + Na2CO3 CaCO3 + 2NaCl S Mg salts MgSO4 + Ca(OH)2 Mg(OH)2 + CaSO4 L+S CaSO4 + Na2CO3 CaCO3 +Na2SO4 Temp. Hardness Ca(HCO3)2 Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O L Mg(HCO3)2 2L Mg(HCO3)2 + 2Ca(OH)2 2CaCO3 + Mg(OH)2 + 2H2O Acids HCl L+S 2H+ + Ca(OH)2 Ca2+ + 2H2O H2SO4 Ca2+ + Na2CO3 CaCO3 + 2Na+ L-S HCO3- HCO3- + Ca(OH)2 CaCO3 + H2O + CO32- L+S FeSO4 Fe2+ + Ca(OH)2 Fe(OH)2 + Ca2+ Ca2+ + Na2CO3 CaCO3 + 2Na+ L/2 43 NaAlO2 NaAlO2 + H2O Al(OH)3 + NaOH
    44. 44. Rules1. If Ca(HCO3)2 and Mg(HCO3)2 are considered as ions (Ca2+ + 2HCO3-) and (Mg2+ + 2HCO3-) respectively then the calculation result will be the same based on the ability of the ions to take up bicarbonate ions2. If treated water found to contain excess of OH - and CO32- ions these are formed from excess equivalent each of Ca(OH)2 and Na2CO3 and hence these excess amounts should be added to the calculation (in temp. hardness and perm. hardness)3. When the impurities are given as CaCO3 and MgCO3 present in water it should be considered as due to bicarbonates of calcium and magnesium respectively4. Substances like NaCl, KCl, Na2SO4, SiO2, Fe2O3 etc do not contribute to hardness and therefore, they do not consume any soda or lime and hence if these present need not be taken in to consideration during calculation.5. Soda (Na2CO3) neutralizes only permanent hardness Molecular weight of lime = 74 Molecular weight of soda = 106 Molecular weight of CaCO3 = 100 Therefore, 100 parts by mass of CaCO3 are equivalent to (i) 74 parts by mass of Ca(OH)2 44 (ii) 106 parts by mass of Na2CO3
    45. 45. Therefore, Lime requirement for softenening= 74 T.H of Ca2++ 2 x T.H of Mg2+ + P.H of (Mg2+ + Fe2+ + Al3+) + CO2 + H+ + 100 HCO3- - NaAlO2/2 X Vol .of water (L) T.H = temporary hardness P.H = Permanent HardnessllIly, Soda requirement for softenening= 106 P.H of (Ca2+ + Mg2+ + Fe2+ + Al3+) + H+ - HCO3- X Vol .of water (L) 100 Problem 1 Calculate the amount of lime required for softening 5,000 litres of hard water containing 72 ppm of MgSO4 (mol wt = 120) Ans = 222g 45
    46. 46. SolutionStep 1 List out the given dataGiven data : Hardness 72 ppm due to MgSO4; water qty = 5000 litres; mol. wt. MgSO4 = 120Step 2 calculate the CaCO3 equivalentHardness producing Quantity (ppm) Multiplication factor CaCO3 equivalentsubstance hardness (ppm or mg/L)MgSO4 72 100/120 72 X (100/120) = 60 Step 3 calculation of lime requirement Lime required = 74/100 (hardness due to MgSO4) x vol. of water = 74/100 (60 mg/L) x 5000 L = 222,000 mg = 222 g 46
    47. 47. Problem 2 Calculate the amount of lime and soda required for softening 50,000 litres of hard water containing: Mg(HCO3)2 = 144 ppm, CaCO3 = 25 ppm, MgCl2 = 95ppm, CaCl2 = 111ppm, Fe2O3 = 25ppm and Na2SO4 = 15ppm SolutionStep 1 List out the given dataGiven data : MgCO3 = 144 ppm, CaCO3 = 25 ppm, MgCl2 = 95ppm, CaCl2 = 111ppm, Fe2O3 = 25ppm and Na2SO4 = 15ppmStep 2 calculate the CaCO3 equivalent Hardness producing Quantity (ppm) Multiplication factor CaCO3 equivalent substance hardness (ppm or mg/L) Mg(HCO3)2 144 100/84 144 x(100/84) = 171.4 CaCO3 025 100/100 25 x (100/100) = 25.0 MgCl2 095 100/95 95 x (100/95) = 100.0 CaCl2 111 100/111 111 x (100/111) = 100.0 025 (does not cause hardness) Fe2O3 015 (does not cause hardness) Na2SO4Ca(HCO3)2 + Ca(OH)2 2CaCO3 + 2H2O; Mg(HCO3)2 + 2Ca(OH)2 2CaCO3 + Mg(OH)2 + 2H2O MgCl2 + Ca(OH)2 Mg(OH)2 + CaCl2 ; CaCl2 + Na2CO3 CaCO3 + Na2SO4 47What happens when lime is treated with CaCl 2?
    48. 48. Step 3 calculation of lime requirementLime required = 74/100 ( {2 x MgHCO3} + CaCO3 + MgCl2 in terms of CaCO3 eq) x vol. of water = 74/100 (2 x 171.4 + 25.0 +100.0) mg/L x 50,000 L = 74/100 (467.8) mg x 50,000 = 17, 309,000 mg Answer = 17. 31 kg Step 4 calculation of soda requirement soda required = 106/100 ( MgCl 2 + CaCl2 in terms of CaCO3 eq) x vol. of water = 106/100 (100 +100.0) mg/L x 50,000 L = 106/100 (200) mg x 50,000 = 10, 6,00,000 mg Answer = 10. 6 kg 48
    49. 49. II. Zeolite (Permutit) method of Softening of water Zeolite is a Hydrated Sodium Alumino Silicate (HSAS), capable of exchanging reversibly its sodium ions for hardness producing ions in water. The general chemical structure of zeolite is given below Na2O.Al2O3.xSiO2.yH2O (x = 2-10 and y = 2-6) Why synthetic zeolite is better than natural zeolite for the softening of water? Ans: Natural zeolites are non-porous Micro pores of Zeolite Porous Structure of zeolite Porosity or cavity size of synthetic zeolite structures can be controlled by varying the Si/Al ratio Ion-exchange process of zeolite structure is associated with sodium 49ions
    50. 50. Zeolite softener Hard water in Hard water spray Zeolite bed GravelInjector Softened waterNaCl storage To sink 50
    51. 51. Process of softening by Zeolite methodFor the purification of water by the zeolite softener, hard water is passed through the zeolitebed at a specified rate. The hardness causing ions such as Ca 2+, Mg2+ are retained by the zeolitebed as CaZe and MgZe respectively; while the outgoing water contains sodium salts. Thefollowing reactions takes place during softening process To remove temporary hardnessNa2Ze + Ca(HCO3)2 CaZe + 2NaHCO3 Scale formation HardnessNa2Ze + Mg(HCO3)2 MgZe + 2NaHCO3To remove permanent hardness water Na2Ze + CaCl2 CaZe + 2NaCl Na2Ze + MgSO4 MgZe + Na2SO4 Regeneration of Zeolite Bed CaZe (or) MgZe + 2NaCl Na2Ze + CaCl2 (MgSO4) Used 10% brine Regenerated Washings Zeolite solution Zeolite drained 51
    52. 52. Limitations of Zeolite process1. If the water is turbid ---- then the turbidity causing particles clogs the pores of the Zeolite and making it inactive2. The ions such as Mn2+ and Fe2+ forms stable complex Zeolite which can not be regenerated that easily as both metal ions bind strongly and irreversibly to the zeolite structure.3. Any acid present in water (acidic water) should be neutralized with soda before admitting the water to the plant, since acid will hydrolyze SiO 2 forming silicic acidAdvantages of Zeolite process1. Soft water of 10-15 ppm can be produced by this method2. The equipment occupies less space3. No impurities are precipitated, hence no danger of sludge formation in the treated water4. It does not require more time and more skillDisadvantages of Zeolite process1. Soft water contains more sodium salts than in lime soda process2. It replaces only Ca2+ and Mg2+ with Na+ but leaves all the other ions like HCO3- and CO32- in the softened water (then it may form NaHCO 3 and Na2CO3 which releases CO2 when the water is boiled and causes corrosion)3. It also causes caustic embitterment when sodium carbonate hydrolyses to give NaOH 52
    53. 53. How abo ut taking a few of th ese. Sorry- I’m Loaded –see the n ext guy Tak thes e eM &C g a as y ions ou g o 53
    54. 54. III. Ion-Exchange resin (or) deionization (or) demineralization process Ion exchange resin Ion exchange resins are insoluble, cross linked, long chain organic polymers with a microporous structure, and the functional groups attached to the chain is responsible for the “ion-exchange” properties.Cation Resin afterexchange Resin treatment 54
    55. 55. In general the resins containing acidic functional groups (-COOH, -SO 3H etc) are capable ofexchanging their H+ ions with other cations, which comes in their contact; whereas thosecontaining basic functional groups ( -NH 2, =NH as hydrochlorides) are capable of exchangingtheir anions with other ions, which comes in their contact.Based on the above fact the resins are classified into two types1. Cation exchange resin (RH+) – Strongly acidic (SO3-H+) and weakly acidic (COO-H+) cation exchange resins2. Anion Exchange resin (ROH-) – Strongly basic (R4N+OH-) and weakly basic (RNH2+OH-) anion exchange resins Continued… next slide 55
    56. 56. Structure of Cation and Anoin exchange resinsCation exchange resin Anion exchange resin R = CH3 56
    57. 57. Ion exchange purifier or softener Hard water Gravel Cation exchange Resin Anion exchange Resin bedInjector Injector Acid solution for Wastages to regeneratio sink Alkaline solution for n of resin Wastages to regeneration of resin sink pump 57 Soft water
    58. 58. Process or Ion-exchange mechanism involved in water softening Reactions occurring at Cation exchange resin 2 RH+ + Ca2+ (hard water) R2Ca2+ + 2 H+ 2 RH+ + Mg2+ (hard water) R2Mg2+ + 2 H+Reactions occurring at Anion exchange resin2 ROH- + SO42- (hard water) R2SO42+ + 2 OH-2 ROH- + Cl- (hard water) R 2Cl- + 2 OH-At the end of the processH+ + OH- H 2O 58
    59. 59. Regeneration of ion exchange resinsRegeneration of Cation exchange resinR2Ca2+ + 2H+ (dil. HCl (or) H2SO4) 2 RH+ + Ca2+ (CaCl2, washings)Regeneration of Anion exchange resinR2SO42- + 2OH- (dil. NaOH) 2 ROH- + SO42- (Na2SO4, washings)Advantages1. The process can be used to soften highly acidic or alkaline waters2. It produces water of very low hardness of 1-2ppm. So the treated waters by this method can be used in high pressure boilersDisadvantages1. The setup is costly and it uses costly chemicals2. The water should not be turbid and the turbidity level should not be more than 10ppm 59
    60. 60. IV. Softening of water by Mixed Bed deioniser Description and process of mixed bed deionizer 1. It is a single cylindrical chamber containing a mixture of anion and cation exchange resins bed 2. When the hard water is passed through this bed slowly the cations and anioins of the hard water comes in to contact with the two kind of resins many number of times 3. Hence, it is equivalent to passing the hard water many number of times through a series of cation and anion exchange resins. 4. The soft water from this method contains less than 1ppm of dissolved salts and hence more suitable for boilersHard water c a c a Anion exchange resin c Mixed bed Mixed a deionizer a resin bed a c a cc Cation exchange resin Demineralised water 60
    61. 61. Regeneration of mixed bed deionizer1. When the bed (resins) are exhausted or cease to soften the water, the mixed bed is back washed by forcing the water from the bottom in the upward direction2. Then the light weight anion exchanger move to the top and forms a upper layer above the heavier cation exchanger3. Then the anion exchanger is regenerated by passing caustic soda solution (NaOH) from the top and then rinsed with pure water4. The lower cation exchanger bed is then washed with dil.H 2SO4 solution and then rinsed.5. The two beds are then mixed again by forcing compressed air to mix both and the resins are now ready for use Low NaOH density resin c a c a c a c a c aa c aa a a a a cRegenerated a c Mixed bed c Exhausted a H2 Back washed a deionizer a a Mixed bed a Mixed bed SO a 4 deionizer a a ccccc c c a cc c a cc c a c c Back Compressed wash High air 61 water density resin
    62. 62. Treatment of Municipal Drinking Water• Screening – to remove floating matters• Aeration – to remove dissolved gas and improve taste of water• Sedimentation & Coagulation – this is done after chemical treatment (L-S)• Filtration – Gravity (or) Pressure sand filters• Sterilization and disinfection• Storage and distribution Attn: Part B Question 62
    63. 63. 63
    64. 64. Desalination of seawater• Desalination, refers to any process that removes some amount of salt and other minerals from water. Technologies for desalination process• Reverse Osmosis (Pressure membrane process)• Electrodialysis membrane process Attn: Part B Question 64
    65. 65. Pressure Membrane Processes• Microfiltration (MF), which can remove particles ranging in size from 10-100 μm. It is operated in the pressure range of 10 psig.• Ultrafiltration (UF), which can remove particles ranging in size from 0.01 to 10 μm. It is operated in the pressure range of 15 psig.• Nanofiltration (NF), which can remove particles size from 0.001 μm to 0.01 μm. It is operated in the pressure range of 75-250 psig.• Reverse osmosis (RO), which can remove particles in the size range of 0.1-1.0 nm. It operates in the pressure range of 200-1200 psig. 65
    66. 66. Principle - Reverse osmosis When two solutions of unequal concentration are separated by a semi-permeable membrane, flow of solvent takes place from dilute to concentration side, due to increase in osmostic pressure, which is termed as osmosis. However, when a hydrostatic pressure in excess of osmotic pressure is applied on the concentrated side, the solvent flow is reversed from concentrated side to dilute side, across the membrane. This principle is termed as reverse osmosis. The semi-permeable membrane (in reverse osmosis) is selective in not permitting the passage of dissolved solute particles such as molecules, ions, etc.) It permits only the flow of water molecules (solvent) from the concentrated to dilute side. Cellulose acetate, polyamide, etc., are used as membrane Reverse osmosis process requires only mechanical force to generate the required hydrostatic pressure. Hydrostatic pressure generated is in the order of 15-40 Kg m-266
    67. 67. Reverse Osmosis 67
    68. 68. Principle -Electrodialysis Electrodialysis is an electrochemical process whereby electrically charged particles, ions, are transported from a raw solution (retentate, diluate) into a more concentrated solution (permeate, concentrate) through ion-selective membranes by applying an electric field. 68
    69. 69. Theory of Electrodialysis• Electrodialysis chamber comprises of sheet like barriers made out of high-capacity, highly cross-linked ion exchange resins that allow passage of ions but not of water.• There are two types : (a) Cation exchange and (b) Anion exchange membranes• Cation exchange membranes consists of an insoluble matrix and mobile cation reside in the pore space that allows the pass through of only cations.• Anion exchange membranes consists of an insoluble matrix and mobile anion reside in the pore space that allows the pass through of only anions.• Cation- and Anion- exchange membranes are installed alternatively in the tank.• By impressing electricity on the electrodes, the positive anode attracts negative ions in solution, while the negative cathode attracts positive ions in the solution. 69