1. ENGINEERING CHEMISTRY – II
Subject Code : CY 6251

2. Unit I – WATER TECHNOLOGY
Introduction – importance of water and its sources
Hard water and soft water - definition
Hardness of water – definition, types and its estimation
Boiler feed water – requirements, scale & sludge, priming & foaming,
Caustic embrittlement and Boiler corrosion
Softening / Conditioning Methods – Internal & External methods
Internal conditioning – carbonate, phosphate and calgon conditioning
External conditioning – ion exchange process and zeolite process
Desalination of Brackish water – reverse osmosis

3. UNIT I – WATER TECHNOLOGY

4. IMPORTANCE OF WATER Living things are indeed in need of water.
It cleanses our body.
It energizes us every day.
It keeps our body temperature at the right level.
It is one of the essential resources for our health.

6. Water is essential for the existence of human beings, animals and plants.
Though 80% of the earth’s surface is occupied with water, less than 1%
of water is available for ready use.

7. SOURCES OF WATER
Surface water : Rain, Rivers, Lakes and Sea
Ground water: Wells and Springs

8. Impurities in water
Dissolved impurities – inorganic salts of Na, K, Ca, Mg, Al, Fe and traces of other metals as chlorides, sulphates, bicarbonates,
etc.
Dissolved gases – oxygen, nitrogen, CO2, oxides of N and S, NH3, or H2S
Suspended impurities - sand or clay particles, decayed organic substances.
Microbial and biological impurities – pathogenic microorganisms, biological
matter of plant and animal origin.

9. Surface and ground water are normally used for industrial and domestic purposes.
Hence undesirable impurities should be removed from these water.
Water treatment / water technology - the process of removing all types of
impurities from water and make it suitable for industrial and domestic purposes.

10. Quality of water for different uses
Purpose
Quality requirements
Drinking
Palatable, clear and free from colour, odour, turbidity and pathogens.
Domestic washing
Soft water producing lather readily.
Textile dyeing
Free from colour, turbidity, organic matter, Fe and Mn.
Boiler feed water
Free from dissolved salts, suspended impurities, silica and dissolved gases.
Drugs and pharmaceuticals
Soft and clear. Free from pathogens, colour, odour and suspended impurities.
Construction
Not too hard, should contain less of chlorides.
Paper industry
Free from colour, turbidity, organic matter, Fe, Mn, silica and alkalinity

11. Analysis of water
Hardness, alkalinitym, total dissolved solids (TDS), dissolved oxygen (DO),
colour, iron, chloride and turbidity.
Fluoride, sulphate, nitrate, nitrite, biochemical oxygen demand (BOD), chemical
oxygen demand (COD) , metal ions – Mn, Pb, As.

12. HARD WATER and SOFT WATER
Hard water – does not produce lather with soap solution, but produces
white precipitate.
Soft water – produces lather readily with soap solution.

13. Soft water
Hard water
Soft water

14. Disadvantages of using hard water

15. HARDNESS OF WATER Detection of hardness
Hardness – the property or characteristics of water, which does not produce lather
with soap.
Detection of hardness
Hard water does not produce lather with soap solution and produces white scum.
Hard water gives wine red colour with Eriochrome Black-T indicator at pH 9 – 10.

16. TYPES OF HARDNESS Temporary hardness (or) Carbonate hardness:
- due to the presence of bicarbonates of Ca and Mg.
- removed by boiling the water; adding lime to the water.
Permanent hardness (or) Non-carbonate hardness:
- due to the presence of chlorides and sulphates of Ca and Mg.
- removed by i) lime soda process and ii) zeolite process.
Total hardness – the sum of temporary hardness and permanent hardness.

17. Units of hardness
ppm – the number of parts by weight of CaCO3 equivalent hardness per million
(106) parts of water.
mg/l – the number of milligrams of CaCO3 equivalent hardness per litre of water.
The concentration of hardness producing salts is calculated as
Mass of hardness producing salt x 50
amount of equivalent of CaCO3 =
Chemical equivalent of the hardness
producing substance

18. Determination of hardness Hohner’s alkali titration method
Soap titration method
Hohner’s alkali titration method
EDTA method

20. BOILER FEED WATER
In industry one of chief uses of water is generation of steam by boilers.
Boiler feed water – the water fed into the boiler for the production of steam.

21. Requirements of boiler feed water
It should have zero hardness.
It must be free from dissolved gases like O2, CO2, etc.
It should be free from suspended impurities.
It should be free from dissolved salts and alkalinity.
It should be free from turbidity and oil.
It should be free from hardness causing and scale forming constituents like
Ca and Mg salts.

22. Boiler troubles (or) Disadvantages of using hard water in boilers
Formation of deposits (scales and sludges).
Priming and foaming (carry over).
Caustic embrittlement.
Boiler corrosion.

23. Formation of deposits in boilers and heat exchangers
On continuous evaporation of water in boiler the concentration of soluble matters increases progressively which leads to the deposition of salts.

24. SLUDGE – the precipitate is loose and slimy
formed by the substances like MgCl2, MgCO3, MgSO4 and CaCl2.
have greater solubility in hot water than cold water.

25. SCALE - precipitate forms a hard and adherent coating on the inner walls.
- formed by the substances like Ca(HCO3)2, CaSO4 and Mg(OH)2.

26. Comparison of scales and sludges
S. No.
Sludge
Scale 1.
A loose, slimy and non-adherent precipitate
S hard and adherent coating 2.
MgCO3, MgCl2, MgSO4 and CaCl2
Ca(HCO3)2, CaSO4, Mg(OH)2 3.
Poor conductors of heat and decreases the efficiency of boiler
Decreases the efficiency of boiler, crack developed leads to explosion 4.
Prevention:
Using softened water
Using HCl, H2SO4
By blow-down operation
Internal and external treatment, by applying thermal shocks, scrapers, wire brush, etc.

27. Disadvantages of scales & sludges
1. Wastage of fuels
The heat transfer from boiler to inside water in not efficient because of the low thermal conductivity of scales.
Overheating is done to provide steady supply of heat to water which causes wastage of fuel.
The wastage of fuel depends on the thickness and nature of the
scale, which is shown in the table.

29. 2. Decrease in efficiency – due to the deposition of scales in the
valves and condensers of the boiler and choke.
3. Boiler explosion
Sometimes due to over heating the thick scales may crack and causes sudden contact of high heated boiler material with water.
This causes formation of a large amount of steam and high pressure is developed which may lead to explosion.

30. Prevention of scales
Scales can be removed using scraper, wire brush etc. at the initial stage.
If scales are brittle, they can be removed by thermal shocks.
By using suitable chemicals like dil. acids (for CaCO3 scale), EDTA (for CaSO4 scale) with which they form suitable complexes.
If the scales are loosely adhering, they can be removed by frequent blow down operation.

31. Priming and Foaming
Priming – the small droplets of liquid water associated with steam (wet steam).
Carry over - the droplets of water carry some suspended and dissolved solids.
It is caused by -
Improper boiler design
b. Very high water level in the boiler
c. Presence of finely divided particles in the water
Sudden increase in boiling rate
High steam velocity

32. Prevention of priming Priming can be prevented by
Controlling the velocity of steam.
Keeping the water level lower.
Using good boiler design.
Using soft water.
Priming can be minimized by placing a series of baffle plates or spiral baffles near the steam outlet to facilitate the condensation of water droplets carried over by the steam .

33. Foaming – the formation of stable bubbles over the surface of water.
These bubbles are carried over by steam leading to priming.
It is caused by
The presence of oil, grease, organic matter or finely divide solids.
Substances which decrease the surface tension of water and increase the
viscosity of the film.

34. Foaming can be prevented by
the addition of coagulants such as ferrous sulphate and sodium aluminate.
2. adding antifoaming agents such as castor oil or ployamides.

35. Caustic embrittlement
A form of corrosion caused by high concentration of NaOH in the boiler feed water.
It is a type of electrochemical corrosion occurs when the concentration of NaOH is
above 100 ppm. It occurs at the stressed parts like bends, joints, rivets, etc.

36. Caustic embrittlement

37. Prevention of caustic embrittlement
Caustic embrittlement can be prevented by
using sodium phosphate as the softening agent instead of Na2CO3.
adding chemicals such as tannin, lignin to the boiler water. They block the hairline cracks.
adjusting the pH of the feed water carefully between 8 and 9.

38. Boiler Corrosion Corrosion in boilers is due to the presence of
dissolved oxygen
dissolved carbon dioxide
dissolved salts like MgCl2

39. Dissolved carbon dioxide
Dissolved oxygen
Water containing dissolved oxygen when heated in a boiler, free oxygen is evolved, which corrodes the boiler material.
Dissolved carbon dioxide
When water containing bicarbonates is heated, CO2 is evolved which makes the water acidic (by forming carbonic acid). This leads to intense local corrosion called pitting corrosion.

40. Dissolved MgCl2
Hydrochloric acid, produced from MgCl2, attacks the boiler in a chain-like
reaction producing HCl again and again which corrodes boiler severely.
Corrosion by HCl can be avoided by the addition of alkali to the boiler water.

41. Prevention of boiler corrosion – chemical method or mechanical method
Removal of dissolved oxygen – sodium sulphite, hydarzine
Removal of dissolved CO2 – NH4OH

42. Mechanical method – dissolved oxygen and CO2 can be removed mechanically by
The de-aeration method.

43. Mechanical de-aerator

44. Softening or Conditioning Methods of Hard Water
It is mandatory to soften water to make it free from hardness producing
substances, suspended impurities and dissolved gases, etc.
Softening or conditioning of water - the process of removing hardness producing
salts from water.
Two methods – External treatment and Internal treatment

45. Distillation

46. External Treatment – the removal of hardness producing salts from the water
Before feeding it into the boiler.
Lime-soda process
Zeolite or Permutit process
Demineralisation or Iron exchange process

47. Zeolite (or) Permutit Process
Hydrated sodium aluminosilicate – Na2O.Al2O3.xSiO2.yH2O; x = 2 – 10, y = 2 – 6
Natrolite – Na2O.Al2O3.3SiO2.2H2O
Natural zeolites are green sand and are usually non-porous.
Permutit – artificial zeolite, porous.
Sodium zeolite – Na2Ze which exchange Na+ ions with the hardness producing
ions like Ca2+, Mg2+ in water.

48. Process

49. The sodium salts formed in the above reactions remain dissolved in the softened
water and do not impart any hardness.

50. Regeneration
Sodium zeolite gets exhausted due to its conversion into Ca and Mg zeolites.
Regeneration is done by percolating 10% brine solution through the exhausted
zeolite. The Ca and Mg zeolites are converted back into sodium zeolite.

51. Advantages of the process
Water obtained by this process will have a residual hardness between
7 and 15 ppm
The method is cheap, because the regenerated zeolite can be used again.
This process does not produce any sludge and hence a clean process.
The equipment is compact and occupies less space.

52. Disadvantages of the process
The process exchanges only calcium and magnesium ions with sodium ions and
hence the softened water contain more sodium and also more of dissolved salts.
It does not remove the acidic ions such as bicarbonate and carbonate and remain
as sodium salts contributing to the alkalinity and causes boiler corrosion.
The water containing turbidity and suspended impurities cannot be treated by this
method because turbidity clogs the pores of the zeolite bed.
The process cannot tolerate acidity or alkalinity as the zeolite disintegrates.
The process is not very efficient for treating water containing large quantities of
Fe2+ and Mn2+ ions as these ions convert sodium zeolite into their respective zeolites
which are difficult to be regenerated.

53. Demineralization or Ion Exchange Process
This process removes almost all the ions present in water.
Soft water does not contain hardness producing Ca2+ and Mg2+ ions but it may
contain other ions like Na+, K+, Cl-, SO42-.
Every soft water is not demineralized water whereas every demineralized water
is soft water.
Ion exchangers are resins with a long chain, cross-linked, insoluble organic
polymers with a microporous structure. The functional groups attached to the
chains are responsible for the ion exchanging properties.

54. The following two types of resins are used for demineralization process:
Cation exchange resins and Anion exchange resins
Cation exchange resins – possess acidic group such as –COOH or –SO3H groups.
Cations in hard water are exchanged with H+ ions of this resins. This resin may be
represented as RH2.
examples: sulphonated coal, sulphonated polystyrene
Anion exchange resins – possess basic groups such as OH- or NH2- group. Anions
in hard water are exchanged with –OH ions of this resins. It may be represented as
R’(OH)2.
examples – cross-linked quaternary ammonium salts, urea-formaldehyde resin.

55. A strongly acidic sulphonated polystyrene
Cation exchange resin
A strongly acidic sulphonated polystyrene cation exchange resin

56. A strongly basic quaternary ammonium
anion exchange resin

58. Process Demineralization or Ion Exchange Process

59. Hard water is first passed through the cation exchange resin
Hard water is first passed through the cation exchange resin. The cations like
Na+, K+, Ca2+, Mg2+, etc. in hard water get exchanged with H+ ions of the resin.
The water coming out from this column is acidic in nature.

60. The water is then passed through the anion exchange resin which exchanges the
anions like Cl-, SO42-, HCO3- with OH- ions of the resin.
The water coming out from this column is completely free from both cations and
anions. H+ and OH- ions combine to produce water molecule.
The water coming out from the second column is neutral and is free from all ions.
It is known as deionised or demineralised water.

61. Regeneration of resins
The exhausted cation exchange resin is regenerated by percolating a dilute HCl
solution through it.
The exhausted anion exchange resin is regenerated by percolating dilute NaOH

62. Advantages Limitations
The hardness of water can be reduced to about 2 ppm and hence it is suitable for
use in high pressure boilers.
Highly acidic or highly alkaline water can be softened by using this process.
Limitations
The resin used in the process are quite expensive.
If water contains turbidity, the efficiency of the process is reduced.
Water containing Fe and Mn cannot be treated because they form stable product
with the resins.

63. Demineralization process
Differences between zeolite and demineralization processes
S. No.
Zeolite Process
Demineralization process 1.
Only cations are exchanged.
Both cations and anions are exchanged. 2.
Since acidic water decomposes the zeolite it cannot be treated.
Acidic water can be treaated. 3.
Treated water contains more dissolved salts which causes priming, foaming and caustic embrittlement in boilers
Water treated by this process contains no dissolved salts and no priming or foaming is caused. 4.
Disadvantages
Water with Fe, Mn and turbidity cannot be treated.

64. Internal Treatment or Internal Conditioning
It involves adding chemicals directly to the water in the boilers for removing
dangerous scale forming salts.
This method is used to convert scale ro sludge which can be removed by
blow-down operation.

65. The following are the internal conditioning methods
Carbonate conditioning
Phosphate conditioning
Calgon conditioning
Colloidal conditioning
EDTA conditioning

66. Carbonate conditioning
Scale formation can be avoided by adding Na2CO3 to the boiler water.
It is used only in low pressure boilers.
The scale forming salt like CaSO4 is converted into CaCO3, which can be
removed easily.

67. Phosphate conditioning
Scale formation can be avoided by adding sodium phosphate.
It is used in high pressure boilers.
The phosphate reacts with calcium and magnesium salts to give soft
sludges of calcium and magnesium phosphates.

68. Generally 3 types of phosphates are employed
Trisodium phosphate – Na3PO4 (too alkaline) : used for too acidic water.
Disodium hydrogen phosphate – Na2HPO4 (weakly alkaline) : used for
weakly acidic water.
Monosodium dihydrogen phosphate – NaH2PO4 (acidic) : used for
alkaline water.

69. Calgon conditioning
Calgon is sodium hexa meta phosphate, Na2[Na4(PO3)6].
This interacts with calcium ions forming a highly soluble complex and thus
prevents the precipitation of scale forming salt.
The complex Na2[Ca2(PO)3]6 is soluble in water and there is no problem of sludge
disposal. So calgon conditioning is better than phosphate conditioning.

70. Colloidal conditioning
The colloidal conditioning agents are kerosene, agar-agar, gelatin, glue, etc.
They are used in low pressure boilers.
The colloidal substance convert scale forming substances like CaCO3, CaSO4
into a sludge which can be removed by blow-down operation.

71. Desalination or Desalting
Desalination – the process of removal of dissolved salts (NaCl) from water.
Brackish water – water containing high concentration of dissolved salts.
Water quality is usually graded as
Fresh water : less than 100 mg/l of dissolved salts
Brackish water : 1000 – mg/l of dissolved salts
Sea water : greater than mg/l of dissolved salts.

72. The following techniques are carried out for desalination of sea water
and brackish water
Reverse osmosis
Electrodialysis
Distillation

73. Reverse osmosis
Osmosis – when two solutions of different concentrations are separated by a
semi-permeable membrane, solvent flows from a region of lower concentration
to a region of higher concentration. This process is a natural process.

74. The reverse osmosis process is also known as super-filtration or hyper filtration.
Semi-permeable membranes (having pores in the range of mm in
diameter) used are
Cellulose acetate
Polyimide sulphone
Cellulose butyrate

75. Osmotic pressure - the excess pressure applied on the concentrated solution side
to prevent osmosis.
This natural process can be reversed by applying a pressure higher than the
osmotic pressure of the order 15 – 40 kg/cm2 on the high concentrated side.
The solvent flow is reversed ie. solvent flows from higher concentrated side to
lower concentrated side. This process is called reverse osmosis.

76. Advantages
The water obtained by this process is used for high pressure boilers
Due to low capital and operating cost and high reliability this process is
used for converting sea water into drinking water.
The life time of the membrane is high and it can be replaced within a short time.
It also removes ionic, non-ionic and colloidal impurities.

77. Water Purifier – RO & UV
Water Purifier – RO & UV

78. Semi-permeable membrane Filters

79. International Standards for water Water should be free from
Depends on purpose
Standards Set By:
WHO- World Health Organization
USPHD- United States Health Service
ICMR- Indian Council of Medical Research
Water should be free from
Turbidity, Colour
Taste, Odour
Microbes
Toxicity (Organic and Inorganic Metals)