Download - Water Technology 5
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8/2/2019 Water Technology 5
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Water used for industrial purposessufficiently pure.
The process of removing hardness producingsubstances from water is called softening ofwater.
1 . Lim e-Sod a pr ocess:
In this method soluble Ca & Mg salts in waterare converted in to insoluble compounds, byadding calculated amount of Lime and soda.
CaCO3 and Mg(OH)2, so precipitated, arefiltered off.
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Cold l im e soda p r ocess:
In this process calculated amount of chemicals(lime and soda) are mixed with water at RT
At RT the precipitates formed are finely divided,will not be settle down easily.
So, it is essential to add small amount of
coagulants (Alum, Sodium aluminate, Aluminiumsulphate).
These coagulants help in the fine precipitation.
Sodium aluminate also helps the removal of
silica and oil. This cold L-S process provides water-containing
50-60ppm.
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
NaAlO2 + H2O NaOH + Al(OH)3
Al2(SO4)-3+Ca(HCO3)2 Al(OH)3+ CaSO4+ CO2
HOT LI ME SODA PROSESS:It involves treating water with softening chemicals
at a temperature of 80-150oC
The reactions proceed faster
Softening capacity increased
Precipitates and sludge formed settle down rapidly
No coagulants are needed
Much of the dissolved gases driven out of the waterFiltration of softened water is fast
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Advan t ages o f Lim e Soda p r ocess:
Very economical. Lesser amount of coagulants is needed.
This process increases the pH of water andprotects from corrosion.
Mineral quantity is reduced.
Disadv ant ages o f L im e Soda p r ocess:
Careful operation and skilled supervision is
required. Disposal of large amount of sludge is difficult.
Removes hardness up to 15ppm.
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8/2/2019 Water Technology 5
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
2 .ZEOLI TE ( PERMUTI T) PROCESS:
Zeolite is hydrated sodium alumino silicate. It is also called as Permutits.
It capable of exchanging its sodium ions
Structure of sodium Zeolite is Na2O.Al2O3.xSiO2.yH2O.
Where x = 2-10, y = 2-6
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8/2/2019 Water Technology 5
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Zeolites are two types
1.Natural Zeolites: These arenon-porous.
Ex.: Na2O.Al2O3.4SiO2.2H2O
Synthetic Zeolites: These are porousand possess gel structure.
These have higher exchange capacity
Prepared by heating together chinaclay, faldspar and soda.
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
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8/2/2019 Water Technology 5
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Process:Na2Ze + Ca(HCO3)2 NaHCO3 + CaZeRegenera t ion : After some time the zeolite is converted in to Ca and
Mg Zeolites and it gets exhausted. At this stage the supply of this hard water is stopped
and the exhausted Zeolite is reclaimed by treating
with 10% NaClCaZe + NaCl CaCl2 + Na2ZeL im i ta t i ons : If the water is turbid, the suspended matter is to be
removed. Large quantity of iron and manganese should be
removed; otherwise they form Mn and Fe Zeolites. if mineral acids are present, they may destroy the
Zeolite bed.
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8/2/2019 Water Technology 5
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Advantages:It removes the hardness up to 10ppm.
The equipment used is very compact.No impurities are precipitated, so there is no formation
of sludge or scale.It requires less time.
It requires less skill.
Disadvantages: Treated water contains more sodium.
It removes only positive ions. High turbidity water cannot be treated.
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
I on Ex chan ge Pr ocess:
It is also called de-ionization or de-mineralisation.
Ion exchange resins are in soluble, long chain,cross-linked polymers with a micro porousstructure.
Resins containing acid groups (COOH, SO3H) arecapable of exchanging their H+ ions with othercations.
Resins containing acid groups (OH-, NH2-) arecapable of exchanging their OH- ions with otheranions.
Cation exchange resin
Anion exchange resin
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Dem ine ra l i za t ion o f B rack ish W ate r The process of removing common salt from the
water is known as desalination or
demineralization. The water containing dissolved salts with a
peculiar salty taste is called Brackish Water.Brackish water is demineralized by two methods:
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8/2/2019 Water Technology 5
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Electro dialysis:In this method ions are pulled out of the salt water by
passing direct currentIn this process electrodes and plastic membrane pair
are used.When direct current is passed through saline water,
Sodium ions start moving towards negative poleThe chloride ions start moving towards the positive pole
through the membrane.During this process the conc. of NaCl decreases in the
central component while it increases in two sidecomponents
Desalinated water is removed from the centralcomponent from time to time
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
For efficient separation ions-selectivemembranes are employed.
Ex. RCOO-, RSO3- and R4N+Cl-Elect r o d ia ly s is cel l consists of a large
number of paired sets of plastic membranes.
Advan tages : Most compact unit
Most economical
If electricity is easily available, it is bestsuited
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Rever se Osm osis : When two solutions of unequal concentrations
are separated by a *SPM, flow of solvent takes
place from dilute to concentrated sides, due toosmosis. If a hydrostatic pressure in excess of osmotic
pressure is applied on the concentrated side thesolvent flow reverses.
The membrane filtration is also called as Super-filtration or Hyper-filtration.
In this method 15-40 Kg/Cm2 is applied.
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
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EXTERNAL TREATMENT (SOFTENING METHODS)
WATER
Dr. E. LaxminarayanaMail: [email protected]
Advan tages :
It removes ionic, non-ionic, colloidal substances
etc. Cost is on the replacement of SPM (life time
2years)
Converts sea water into drinking water and
obtaining water for very high pressure boilers.