Water Treatment Plant.ppt

8/13/2019 Water Treatment Plant.ppt

http://slidepdf.com/reader/full/water-treatment-plantppt 1/27

20 December 2013 1

Water Treatment

Plant



20 December 2013 PMI Revision 00 2

Why water treatment?

• Raw water contains many dissolved minerals and

organic materials.

• At high temperature certain minerals left scaling on the

tube metal of the boiler and cause permanent damage.

• Some dissolved minerals leads to corrosion of tube

metals. Some leads to foaming

• At high pressure and temperature an element, silica can

be carried away with steam causing damage to turbine

low pressure stage.

• A Thermal Power Station needs water of varying qualityfor different process and hence the requirement.

• The performance and life expectancy of the station

greatly depends on water chemistry compliance.




Type of water treatment

• the type of demineralization process chosen for a power

station depends on three main factors :

• The quality of the raw water.• The degree of deionization i.e. treated water quality

• Selectivity of resins.




Different water qualities in use at

NTPC StationsCondenser cooling…..Raw water/ Clarified &

post-chlorinated water.

BA flushing – Raw water.

Boiler feed water…..Conditioned DM water. ESP / Channel flushing…..Raw/ Clarified water. Other aux. cooling…..Clarified water.

H2 generation plant…..DM water. Drinking water…..Filtered & post-chlorinated

water.

DM plant operation…..Filtered water.




Steps of treatment process

• Aeration of raw water• Adding chemicals for bacteria removal

• Adding chemicals for sedimentation ofsuspended particles

• Flocculation

• Filtration

• Ion Exchange process

• water treatment process is generally made up oftwo sections :

– Pretreatment section

–Demineralization section




What is pre treatment process?• Pretreatment plant removes the suspended solids

• The coarse components, such as sand, silt etc, can be

removed from the water by simple sedimentation

• the non-separable solids (colloids) will not settle in any

reasonable time and must be floculated to produce the

large particles which are settle able.

• Flocculation is obtained by gentle and prolonged mixing

which converts the submicroscopic coagulated particle

into discrete, visible & suspended particles.

• This operation is done by flash mixer in the

clarifloculator.

• Proper pre treatment reduce loading on anion and cation

exchanger.




Raw water to Clarified waterRaw water bay

RW make up

pumps

Aerator

Pershall

flume

Cl2 dosing

Lime dosing

Alum dosing

Flash

mixer

Clarified

water

Clariflocculator



20 December 2013 8

A view of Clari flocculator

Flocculation zone

Clarification zone




Motion of water in a Clari-flocculator

Flocculation zoneClarification zone




Clarified water to Filtered waterClarified water

Clari-flocculator

To Township for

drinking water

Turbidity & Free Cl2 check

DM PLANT

Filtered water

DW

sump

FW

sump

FW

pumps

DW

pumps

DM water

for Plantpurpose

GF Bed

Sand filters

Cl2 Post-

chlorination

Cl2 House




Demineralization

plant




Demineralization Plant

Degasser

FW water

ACF WAC SAC

WBA SBA MB

CST




Activated carbon Filter (ACF)• Activated carbon acts on principle of adsorption which is a

surface active phenomenon

• It removes residual turbidity (<2 NTU) of water to its 1/10

level.• It removes organic molecules to control colour and odour.

• It removes free residual chlorine present in filtered water(0.5

ppmNil)




Ion exchange resin & its

functional group• An ion exchange resin consists of a cross-linked polymer

matrix (poly-styrene cross linked with 5-8% di-vinyl

benzene for srtuctural stability) to which chargedfunctional groups are attached.

• Common functional groups are : -SO3-H+ (SAC), -COO-

H+ (WAC), -NR4+OH- (SBA) and –NR2 (WBA).




Exchange Reactions

• CATION RESIN:

• 2R-H + Na2CO32R-Na+H2CO3

• ANION RESIN:

• 2R-OH + H2SO42R-SO4+2H2O




Working of WAC ion exchange

resins• WAC resin is capable to exchange cations of alkalinity

producing salts only ie, for carbonate hardness removal

purpose.

• 2 R-COOH + Ca(HCO3)2 (RCOO)2Ca2+ 2 H2CO3

• WAC resin can exchange ions only in neutral to alkaline

pH range.

• WAC results efficient TDS reduction in high carbonatehardness water.

• Efficient regeneration takes place even with very dilute

acid solution.




Working of SAC ion exchange

resins

• SAC resin works over wide pH range & is capable to

exchange any type of cations present in salts assulphonic acid group is strongly acidic.

• 2 R-SO3-H+ + CaCl2 (RSO3)2Ca2+ 2 (H+ + Cl- )




Working of Degasser

• Water from the ex-cation contains carbonic acid which is

very weak acid and difficult to be removed by strongly

basic anion resin and causing hindrance to remove silicate

ions from the bed.

• The ex-cation water is trickled in fine streams from top of a

tall tower packed with rasching rings, and compressed air

is passed from the bottom

• Carbonic acid break into CO^ and water. carbon dioxideescapes into the atmosphere. Water is pumped back to

anion exchanger bed




Working of WBA resins

• WBA resin works over acidic pH range only & is capable

to trap any strong type acid molecules present in cationeffluent, through protonation of secondary / tertiary

amine centre, as the amine group is weakly basic in

nature.

• ▓-NR2 + HCl ▓-NR2H+Cl-• WBA can be regenerated easily with very dilute alkali

(NaOH) solution




Working of SBA ion exchange

resins

• SBA resin works over wide pH range & is capable to

exchange any type of anions present in water asquarternary ammonium group is strongly basic.

• 2 ▓-NR3+OH- + SiO32- (▓-NR3+)2SiO32- + 2 OH-




Working of Mixed bed

• ex-anion water is fed to the mixed bed exchanger

containing both cationic resin and anionic resin.

• This bed not only takes care of sodium slip from cation but

also silica slip from anion exchanger very effectively

• The final output from the mixed bed is an extira-ordinarily

pure water having less than 0.2/Mho conductivity, H 7.0

and silica content less than 0.02 ppm.




Internal Treatment

• D.M.Water has a good affinity to absorb carbon dioxide

and oxygen, and both are extremely harmful to metal

surfaces for their destruction like corrosion,

• water is finally de-oxidized by a suitable doze of hydrazine,

at the point after deaerator.

• The pH of feed water is maintained at around 9.0




Regeneration of resin bed

•ACF is regenerated by backwashing the bed with

air-water.

•WAC and SAC are regenerated by counter

current regeneration with 4% Hydrochloric Acid

with a down flow of DM water.




•

WBA and SBA are regenerated by counter currentregeneration with 4% caustic with a down flow of DM

water.

•Resins of MB is first separated by air scouring.

•Individual resins are regenerated by acid and alkalirespectively.




Regeneration of ion exchanger

• After regeneration, the effluent comes out from the

system is treated in a neutralizing pit for

discharging through normal drain.




THANK YOU

Water Treatment Plant.ppt

Documents

Transcript of Water Treatment Plant.ppt