Water treatment methods

easy to understand

1. Internal Treatment Methods
Can be achieved by adding certain chemicals to water in the
boiler
•Colloidal conditioning
•Carbonate conditioning
•Phosphate conditioning
•Calgonconditioning
1

2. External Treatment of water
•Lime Soda Process,
•ZeoliteProcess
•Ion Exchange Process
ZEOLITE PROCESS
Zeolites
•Naturally occuringhydrated, microporous, sodium aluminosilicate
minerals
•General formula Na
2O. Al
2O
3. xSiO
2· yH
2O
Zeolitesare Capable of exchanging their Na
+
ions with hardness
producing ions like Ca
2+
, Mg
2+
present in water
2

3. •Naturalzeolitesarenon-porous,e.g.Natrolite,Na
2O.
Al
2O
3.3SiO
2·2H
2O
•Syntheticzeolitesareporousandhaveagel
structure.
•Canbepreparedbyheatingtogethersod.Carbonate
(Na
2CO
3),alumina(Al
2O
3)andsilica(SiO
2)
•Syntheticzeoliteshavehigherionexchangecapacity
thanNaturalZeolites
3

4. Microporous
molecular
structure of a
zeolite
Structure of Zeolite
ZeolitecrystalconsistsofSiO
4tetrahedra
joinedtoeachotherandeachOxygenis
beingsharedwithanadjacentone.
Hasanopenstructurewithcavitiesin
whichNa
+
ionsarelooselyheldandcan
beexchangedwithhardnessproducing
ionsofwaterduringsoftening.
4

5. Processofwatertreatment
Hardwaterispassedataspecificratethroughabedof
zeoliteinacylindricalunit.
Ashardwaterpercolatesthroughzeolite,thehardness
producingionsi.e.Ca
2+
,Mg
2+
areexchangedwithNa
+
ionsof
zeolite
AzeolitewithgeneralformulaNa
2O.Al
2O
3.xSiO
2·yH
2Ois
convenientlyrepresentedasNa
2ZwhereZrepresents
aluminosilicatecomplex
5

6. Removal of Ca
2+
, Mg
2+
ions from hard water
Regeneration of Exhausted Zeolite
6

7. 7

8. 1.Hardness of water is removed almost completely and
softened water of about 10 ppmis obtained
2.The process requires much less time for completion and
operation is quite clean
3.The equipments used is compact and can be installed in a
limited space
4.No impurities are precipitated so there is no danger of sludge
formation in the treated water at later stage
5.The process automatically adjusts itself for variation in
hardnessof incoming water
6.Maintenance and operation is easy and requires less skills.
Advantages of ZeoliteProcess
8

9. Disadvantages of ZeoliteProcess
1.Watercontainingimpuritiesofmineralacidscandestroythe
ZeoliteBed.Somineralacidsmustbeneutralizedbefore
feedingwaterintoZeolitebed
2.Turbidwaterblockstheporesofzeolitebedanddecreases
theefficiency-Turbidity&suspendedmattermustbe
removedbeforefeeding
3.Watershouldnotbehot-(DissolvesZeolites)
4.CationsCa
2+
,Mg
2+
areremovedbutsulphates,bicarbonates
andchloridesarenotremoved.
9

10. Inindustrymainlythreeexternalmethodsareemployed
forsofteningofwater,theyare.
1.Lime-Sodaprocess
2.Zeoliteprocess
3.Ion-Exchangeprocess
WATER SOFTENING
“Processofremovalofhardnesscausingsaltsfromwater”
Itisveryimportantandessentialprocesssincehardwater
isunsuitablefordomesticandindustrialuse.
10

11. LIME-SODA PROCESS
Inthismethod,
•Thesolublecalciumandmagnesiumsaltsinwaterare
chemicallyconvertedintoinsolublecompounds(ppt),
byaddingcalculatedamountofLime(Ca(OH)
2)and
Soda(Na
2CO
3)
•PrecipitatesofCaCO
3andMg(OH)
2
theseprecipitatesarefilteredoff.
•Limesodaprocesshastwotypes
•ColdLime-sodaprocess
•HotLime-sodaprocess
11

12. •Inthismethod,calculatedquantityoflimeandsoda
aremixedwithwateratroomtemp.
•Atroomtemp.theprecipitatesformedarefinely
divided,sotheydonotsettledowneasilyand
cannotbefilteredeasily.
•Consequently,itisessentialtoaddsmallamountsof
coagulantslikealum,aluminiumsulphate,sodium
aluminate(NaAlO
2),etc.
COLD LIME SODA PROCESS
12

13. •Coagulantsformgelatinousprecipitatesofaluminum
hydroxideandentrapsfineprecipitates.
•Useofsodiumaluminate,NaAlO
2ascoagulantalso
helpstheremovalofsilicaaswellasoil,ifpresentin
water
•ColdL-Sprocessprovideswater,
containingaresidualhardnessof50to60ppm
NaAlO
2+2H
2O→NaOH+Al(OH)
3
Al
2(SO
4)
3+3Ca(HCO
3)
2→2Al(OH)
3+3CaSO
4+6CO
2
13

14. cellulosicelements that are extracted from trees, straw, bamboo, cottonseed, hemp, sugarcaneand other sources.
14

15. Rawwaterandcalculatedquantitiesofchemicals(Lime
+soda+Coagulants)arefedfromthetopintothe
innerverticalcircularchamber,fittedwithavertical
rotatingsystemcarryinganumberofpaddles.
Astherawwaterandchemicalsflowdown,thereisa
vigorousstirringandcontinuousmixing,whereby
softeningofwatertakesplace.
Thesoftenedwatercomesintotheouterco-axial
chamber,whereitrisesupwards.
METHOD OF TREATMENT
15

16. Theheavysludgeorprecipitatessettlesdowninthe
outerchamberbythetimethesoftenedwater
reachesup.
Thesoftenedwaterthenpassesthroughafiltering
mediathisisusuallymadeofwoodfibrestoensure
completeremovalofsludge.
Filteredsoftwaterfinallyflowsoutcontinuously
throughtheoutletatthetop.
Sludgesettlingatthebottomoftheouterchamberis
drawnofoccasionally.
METHOD OF TREATMENT
16

17. InHotlime-sodaprocesshardwateristreatedwith
sodaandlimeat94-100°C
Hotlime-sodaplantessentiallyconsistsofthreeparts
→A‘Reactiontank’inwhichrawwater,
chemicalsandsteamarethoroughlymixed.
→A‘Conicalsedimentationvessel’inwhich
sludgesettlesdown,and
→A‘sandfilter’whichensurescompleteremoval
ofsludgefromthesoftenedwater.
HOT LIME SODA PROCESS
17

18. •Thereactiontankhasthreeseparateinlets,oneeachforraw
water,lime-sodaandsteam
•Superheatedsteamisusedtoincreasethetemperature.
•Duetohightemp.,reactionsofwatersofteningproceedfaster
andsludgeiscollectedinconicalsedimentationtank.
•Thesoftenedwaterispassedthroughsandfilterwhichensures
completeremovalofsludgefromsoftenedwater.
•Duetohightemperature,thedissolvedgasesaredrivenoutof
water.
•Theresultingsoftenedwaterhasaresidualhardnessof15-30
ppm.
METHOD OF TREATMENT
18

19. METHOD OF TREATMENT
19

20. 1.Veryeconomical
2.Whencombinedwithsedimentation,lesser
amountsofcoagulantsshallbeneeded.
3.Thequantityofmineralsinthewaterisreduced.
4.Tocertainextent,ironandmanganesearealso
removed
ADVANTAGESOFLIME-SODAPROCESS
20

21. 1.Forefficientandeconomicalsoftening,careful
operationandskilledsupervisionisrequired.
2.Disposaloflargeamountsofsludgeorinsoluble
precipitatesposesaproblem.
3.Thiscanremovehardnessonlyupto15ppm,
whichisnotgoodforboilers.
DISADVANTAGESOFLIME-SODAPROCESS
21