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(For Internal Circulation Only)

COS-ISO-00-OGN/OPS/CHEM/018Rev. No. : 0 April 2006

OPERATION GUIDANCE NOTE

Guidelines for

PerformanceOptimization of P.T.

Plant and Chlorination

System

CORPORATE OPERATION SERVICES

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NTPC Limited

NTPC LIMITED

OPERATION AND MAINTENANCE FORMAL DOCUMENTATION SYSTEM

OPERATION GUIDANCE NOTE : COS-ISO-00-OGN/OPS/CHEM/018

Rev. No.: 0 Date : April 2006

Guidelines for

PerformanceOptimization of P.T.

Plant and Chlorination

System

Approved for

Implementation by ..Director (O)

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Guidelines for Performance Optimization of P.T. Plant

and Chlorination System

INDEX

Sl. No. Con!n" P#$! No.

1.0 Introduction 1

2.0 Superseded Documents 1

3.0 Type of Clarifiers 1

4.0 Clarification 4

5.0 Operating Criteria

!.0 "aintenance Criteria #

.0 Trou$les%ooting Criteria 10

&.0 C%lorination C%emistry 12

#.0 'actors to $e considered (%ile installing a

c%lorination system 15

10.0 )e*ie( 1!

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+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem

Guidelie! "or Per"orma#e Optimi$atio o" P.T. Plat ad

C%loriatio &'!tem

(.0 INTRODUCTION

T%e $asic si+e of a clarifier is a function of flo(, t%e different configurations of

e-uipment, pumps, sludge remo*al mec%anism and ot%er miscellaneous apparatus

are usually at t%e discretion of t%e *endor or e-uipment manufacturer. Typically,

t%e four different types of clarifier designs are referred to as solids contact, sludge

$lanet, inclined/plate and adsorption types. "ost solid contact and sludge $lanet

clarifiers are of t%e up flo( design (%ere t%e (ater flo(s up (%ile t%e suspended

solids settle. Some of t%ese designs pro*ide for increased solids contact from

*arious types of internal sludge recirculation systems (%ic% pro*ides additional

opportunities for colloidal particle collisions / typically resulting in en%anced

effluent clarity.

2.0 &UPER&EDED DOCU)ENT&

il

*.0 T+PE O, CLARI,IER&

)etention time in clarification e-uipment is typically 1.5 to 3.0 %ours, $ased on

con*entional rise rates from 1.2/2.4 m%. lt%oug% t%is range is normal for mostclarification e-uipment, muc% s%orter retention times e.g., 1& minutes %a*e $een

utili+ed successfully.

*.( &lud-e la/et Clari"ier!

)eaction products, or precipitated solids, formed (%en t%e coagulant c%emicals and

ra( (ater impurities meet, settle slo(ly to(ard t%e $ottom of t%e unit due to t%e

influence of gra*ity. In a sludge $lanet clarifier t%e $ul of t%e precipitate does not

settle to t%e $ottom $ut rat%er is ept suspended $y a com$ination of gentle

mec%anical agitation and %ydraulic flo(. T%e *elocity of (ater flo(ing t%roug% t%e

clarifier unit is controlled to eep t%e precipitate in suspension forming a $lanet offinite dept%. 'locculated (ater from t%e miing +one passes up(ard t%roug% t%e

layer of suspended floc and precipitated particles sludge $lanet (%ic% en%ances

agglomeration and capture of floc. 'igure 2 depicts a typical up flo( sludge $lanet

clarifier. Operation of a sludge $lanet type clarifier is $ased on t%e principle t%at a

particle is supported $y an up(ard mo*ing stream of (ater if t%e *elocity is %ig%

enoug% so t%at t%e action of (ater on t%e particle eceeds t%e pull of gra*ity. s t%e

up(ard *elocity of a particle decreases due to decreased (ater *elocity as it

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ascends, a point is reac%ed at (%ic% t%e particle $ecomes too %ea*y to $e supported

$y t%e up flo(ing mo*ement of t%e (ater and it ceases to rise. s a result of t%ese

factors a (ell/defined sludgeli-uid interface is formed separating t%e sludge

$lanet from t%e clarified li-uid a$o*e. T%e center of t%e unit is s%aped lie an

in*erted cone allo(ing t%e outer +one of t%e clarifier to possess t%e desired flowc%aracteristics / decreasing rise rate (it% increasing ele*ation.

Control of t%e dept% and %eig%t of t%e sludge $lanet determines t%e efficiency of

t%e unit. 6ig%er sludge solids le*els increase t%e filtration efficiency. T%e top of t%e

sludge $lanet is carried at t%e %ig%est practical le*el so as to pre*ent floc

carryo*er7 also, ecessi*e sludge $lo( do(n s%ould $e a*oided as it may distur$

t%e $lanet. T%e sludge $lanet le*el is responsi*e to c%anges in flow, coagulant

addition and temperature.

8ariations of sludge $lanet clarifiers include types (%ic% feature s%ort inclined

plates lamella at t%e $ottom of t%e sludge $lanet layer or at t%e surface of t%e(ater 9ust prior to clarified li-uid egress from t%e *essel. Inclined plates possi$ly

e-uipped (it% deflectors are added in an attempt to augment t%e clarification

process, eit%er $y concentrating t%e sludge $lanet or limiting floc carryo*er as in

t%e t(o instances cited. Inclined/plate clarifiers are discussed later in t%is section.

One clarifier design utili+es a *acuum system to periodically apply a %ydraulic

pulse to t%e sludge $lanet layer in an attempt to maintain a sta$le sludge $lanet

layer under %ig%erflow loading conditions 14. m% depending on t%e application.

Inclined plates are present (it%in t%e sludge $lanet layer in t%at design 'igure 3.

'ig : 2 up flo( sludge $lanet clarifier

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i"re 1 -odified &l"de 3lan4et %larifier

*.2 &olid! Cota#t Clari"ier!

'igure 4 represents a typical solids contact clarifier design. )a( (ater and

coagulating c%emicals are introduced at t%e center of t%e unit (%ere primary miing

and reactions tae place. Sludge and %ea*ier particles settle to(ard t%e $ottom.;affles are employed for flo( direction and distri$ution.

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'ig : 4 Typical solid contact clarifier

.0 CLARI,ICATION

T%e clarification of (ater is a process applied mostly to surface (aters for t%e

remo*al of suspended solids, finely di*ided particles present as tur$idity or color,

and ot%er colloidal materials. Con*entionally t%e clarification process in*ol*es

coagulation, flocculation, and sedimentation=>. T%e primary function of t%eclarification process is li-uidssolids separation. Clarification occurs as a result of

increasing / t%roug% interparticle surface reactions / t%e si+e and density of particles

in t%e dispersed p%ase suc% t%at t%ey separate and settle from t%e $ul li-uid.

)emo*al of suspended particles (%ic% (ill not settle $y gra*ity alone re-uires t%eaddition of c%emical compounds commonly referred to as coagulants. ?articulate

materials comprising dispersions may range in si+e from 0.1 to 100 microns 0.004

to 4.0 mils. "aterials (it%in t%is particle si+e range are termed =colloids=. on

settlea$le suspended particles present in surface (ater e%i$it t%e properties ofcolloids. T%e small si+e of colloids coupled (it% t%eir surface c%arge is primarily

responsi$le for esta$lis%ing conditions fa*ora$le for t%e creation of dispersions.Sta$ili+ing factors associated (it% colloidal dispersions are electrostatic c%arge and%ydration. T%ese surface p%enomena are of greater relati*e importance due to t%e

large surface area to total *olume ratio of a dispersion of small particles. 'urt%er

miing of coagulant s%ould $e carried out in suc% a manner t%at t%e s%ear imposedon t%e (ater must not $rea up t%e floc it coagulates. In ot%er (ords it s%ould matc%

t%e floc strengt% at *arious stages of its formation.

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Se*eral factors tend to desta$ili+e colloids. T%ey are gra*itational and 8an der

@aals forces and ;ro(nian mo*ement. Ara*itational forces are relati*ely small dueto t%e small mass in*ol*ed in colloidal systems. 8an der @aals forces are attracti*e

forces $et(een particles t%at operate as molecular co%esi*e forces and can increase

in magnitude, as particles con*erge, at a rate t%ousands of times t%at of electrostaticforces. ;ro(nian mo*ement is t%e random motion imparted to colloidal particles

from impact (it% molecules of t%e suspending medium. Binetic energy of t%e

molecules increases as temperature increases, as does t%e intensity of t%e ;ro(nianmo*ement. T%is p%enomenon causes a desta$ili+ing effect on dispersions. If

collisions $et(een particles are stimulated, aggregation may result.

.( Coa-ulatio 1 ,lo##ulatio

T%e principal functions of c%emical coagulation are desta$ili+ation, aggregation and

$inding toget%er of particles. T%is in*ol*es neutrali+ation of c%arges to desta$ili+e

suspended solid particles. Once neutrali+ed particles no longer repel one anot%erand can $e $roug%t toget%er flocculation initiates (%en neutrali+ed or entrapped

particles $egin colliding and gro(ing in si+e. T%is process may occur naturally, or

t%e speed of reaction can $e increased $y t%e addition of coagulant c%emicals and

coagulant aids. T%e processes of coagulation and flocculation are usuallyaccomplis%ed $y t%e addition of one or more of floc/forming compounds (%ic% is

usually ferric alum.

cept for sodium aluminate, all common iron and aluminum coagulants are acid

salts (%ic% lo(er t%e p6 of treated (ater. Depending on initial ra( (ater alalinityand p6, an alali suc% as lime, soda as% or caustic may %a*e to $e added to ad9ust

for t%e p6 depression resulting from t%e addition of t%ese acidic coagulantmaterials.

Since p6 can affect $ot% particle surface c%arge and floc precipitation during t%e

coagulation process, it is an important *aria$le. Iron and aluminum %ydroide flocsare $est precipitated at p6 le*els (%ic% minimi+e t%e %ydroide solu$ility. @it%

aluminum sulfate alum, t%e optimum coagulation efficiency and minimum floc

solu$ility normally occur at p6 !.0/.0. Sodium aluminate is alaline and performs$est at ele*ated p6, #.5/11.0. Iron coagulants can $e used successfully o*er t%e

muc% $roader p6 range of 5.0/11.0. T%ey are most often applied at a p6 #.0 and

greater, %o(e*er, to minimi+e t%e solu$ility of iron in t%e treated (ater.

In t%e coagulation process, t%e c%emical coagulant is added (it% rapid miing to t%era( (ater to $e treated. s precipitation initiates, t%e floc consists of pinpoint si+edparticles. 'locculation follo(s coagulation, and t%e small floc particles are $roug%t

toget%er using gentle agitation or slo( miing, (%ic% forms large particles (%ic%

settle more rapidly. gitation must $e controlled so as to pro*ide a %ig% incidenceof collisions $et(een suspended particles and continued adsorption of suspended

matter on t%e large surface area pro*ided $y t%e floc. cessi*e agitation s%ould $e

a*oided since it tends to s%ear t%e floc.

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ar testing is t%e standard met%od $y (%ic% p6, temperature and c%emical additi*es

including order of addition and miing conditions are e*aluated eperimentallyfor application to clarification processes. ?l. refer ar test ?rocedure

Color in t%e ra( (ater typically imparts %ig%er le*els of $acterial and algalgro(t%, causes fouling of anion ec%ange resin, and interferes (it% t%e

coagulation and sta$ili+ation of iron and manganese. Color reduction can $e aprime o$9ecti*e of clarification. "ost organic color in surface (aters is colloidal,

negati*ely c%arged / usually classified as %umic or ful*ic acids / and> can $e

remo*ed $y a com$ination of c%lorination and coagulation (it% iron or

aluminum salts at lo( p6 *alues 4.5/5.5. Optimum p6 for tur$idity remo*al ismuc% %ig%er t%an t%at for color reduction. C%lorine (ill oidi+e some organic

color compounds and t%e inorganic coagulants (ill neutrali+e surface c%arges to

effect t%e remo*al of t%ose organic particles (%ic% produce t%e color. 6o(e*er,c%lorinated organic materials capa$le of passing t%roug% t%e maeup system

may also $e formed.Tips to ensure good floc E

1. lum (ors $est at p6 !/and ferric salts at p6 5/!.2. 'or eac% (ater and coagulant t%ere is a p6 range in (%ic% a (ide margin

$efore any ad*erse effect is seen, $ut floatation is more sensiti*e.

3. T%e coagulant dose may itself gi*e t%e correct p6 and if re-uired lime is$eneficial.

4. Colour i.e. %ig% %umic acid is $est remo*ed at lo( p6. 'urt%er %ig% %umic

concentration interferes (it% t%e gro(t% of floc and mae t%e (ater

difficult to treat.5. T%e ideal regime for miing consists of a flas% tan (it% *iolent stirring

follo(ed $y +ones of decreasing s%ear to promote t%e gro(t% of floc.!. ir $u$$les s%ould $e a*oided.. Constant silled super*ision is needed to eep a pre/treatment plant

perform as per design on regular $asis.

&. T%e follo(ing con*ersions come in %andy in *arious computations (it%respect to ?re/treatment plant E

1 ppm CaCO3 F 2.2.ppm as l2SO43 1& 62O

F 0.!& ppm as l2O3F 0.1& ppm as l

.2 &edimetatio

Sedimentation is t%e final step in t%e clarification process. 'locculated (ater from

t%e slo( > miing p%ase flo(s to t%e settling +one (%ere aggregated floc

particles settle out. s t%e aggregated or conglomerated floc settles, clarified clear(ater rises and is separated from t%e sediment. Settled floc particles are remo*ed

gra*itationally in a t%icened state i.e. sludge from t%e $ottom of t%e

sedimentation *essel. Clarified (ater typically o*erflo(s from t%e surface and is

treated furt%er t%roug% filtration e-uipment.

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.0 OPERATING CRITERIA

T%e successful operation of units for coagulation, flocculation and sedimentation is

dependent on a num$er of *aria$les discussed in ensuing su$sections / including

t%e follo(ing.

G Temperature.

G p6.

G )a( (ater composition.

G 'lo( rate.

G C%emical addition.

G ffect of miing and flocculation.

G Sludge $lanet maintenance.

G Sludge $lo( do(n.

.( E""e#t O" Temperature O Coa-ulatio

Coagulation and rate of floc formation are greatly influenced $y t%e temperature of

t%e inlet (ater. s temperature decreases, t%e c%emical dosage for effecti*ecoagulation must $e increased to ensure proper floc formation. T%e detrimental

effect of lo( temperature on floc formation can $e minimi+ed $y proper design of

e-uipment to pro*ide t%oroug% miing during flocculation. *en (it% optimum

design, more c%emicals are re-uired (it% colder (ater. Cold (ater slo(s $ot%coagulation and c%emical precipitation reactions. In addition, settling rates are

affected $y temperature c%anges. s temperature decreases, (ater density

increases, t%ere$y lo(ering t%e rate at (%ic% floc particles settle.

.2 E""e#t O" p3 O Coa-ulatio

T%e amount of coagulant re-uired to effect good clarification *aries (it% t%e nature

and amounts of suspended and solu$le solids present in t%e ra( (ater to $e treated.T%e p6 may affect t%e magnitude and c%arge on $ot% dispersed solids in t%e ra(

(ater and on t%e micro flocs of precipitated coagulant materials.

T%e solu$ility of precipitated material is usually a function of p6. Coagulation

processes operate (it%in a range of p6 *alues in (%ic% t%e solu$ility of t%e

coagulant is lo(. 'or some processes, optimum p6 range is narro(7 for ot%ers, it is

comparati*ely (ide7 and for still ot%ers, t%ere is more t%an one effecti*e range.Hnder controlled conditions, maimum flocculation (it% alum occurs at p6 5.5.

"aimum flocculation does not assure minimum solu$ility of residual ionsremaining in t%e treated (ater. T%e p6 can $e ad9usted (it% acid, lime, soda as%,

etc. / as needed / to o$tain optimum conditions for a specific coagulant and (ater

supply.

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.* E""e#t o" C%emi#al Additio &e4ue#e O Coa-ulatio

T%e order in (%ic% c%emicals are added (ill %a*e a profound impact on t%e success

or failure of a coagulation process. Hsually, a series of 9ar tests is conducted on

ra( (ater to determine t%e $est com$ination and se-uence of c%emicals to use toreduce suspended, colloidal and non/settlea$le matter from t%e ra( (ater.

?rocedures for conducting 9ar tests are a*aila$le from *arious sources. 'oradditional information, t%e reader is directed to )eference #.

@%en adding c%emicals, t%e preferred order s%ould $e alali or acid p6ad9ustment t%en coagulant, and lastly flocculant. T%e coagulation process is

sensiti*e to p6. 'or instance, aluminum %ydroide is least solu$le in t%e p6 range

of 5.&/.2. Outside t%is range, alum is a less efficient coagulant, and any residualaluminum may foul t%e media of su$se-uent treatment e-uipment. T%e critical p6

for coagulation of specific impurities and for different types of (ater may lie in a

muc% narro(er range t%an for aluminum %ydroide. 'or organic reduction color,it is typically p6 5.&/!.3. T%e coagulant dose and p6 employed in t%e treatment

plant may t%en $e ad9usted to approac% t%at (%ic% ga*e t%e $est results during 9ar

testing. @it% eperience, t%e operator (ill learn to interpret 9ar test data as a guide

to optimi+ing clarifier performance.

. E""e#t o" )i5i- Ad ,lo##ulatio

n important re-uisite for successful coagulation and settling of suspended solids is

t%e rapid, t%oroug% miing of t%e *arious c%emicals and t%e influent (ater. )apidmiing ensures uniform coagulant c%emical adsorption onto t%e suspended

particulate matter desta$ili+ing t%e colloids, t%us increasing t%e c%ances for

collision. To pre*ent floc particles from $reaing apart, any miing speeds (%ic%create ecessi*e s%ear forces s%ould $e a*oided. )apid miing time normally *aries

from t%ree to fi*e minutes. T%is is follo(ed $y slo( miing to permit t%e floc to

gro( in si+e and agglomerate into readily settlea$le particles. Slo( miing timeusually *aries from 15 to 30 minutes. S%ear forces s%ould again $e a*oided during

floc gro(t% periods to pre*ent ne(ly formed floc from $eing torn apart. S%eared

floc particles may not readily agglomerate.

. &lud-e la/et )aitea#e

In most con*entional clarifiers, it is a$solutely necessary to maintain an ade-uate

sludge $lanet. T%e sludge $lanet ser*es as a floating filter $ed. @ater containingfloc passes up(ard t%roug% t%e sludge $lanet or $ed (%ere t%e accumulated solids

tend to filter out t%e floc. dditionally, floc gro(t% is impro*ed (it%in t%e $lanet,

furt%er en%ancing suspended solids remo*al. T%e %eig%t of t%e sludge $lanet

depends on flo( rate t%roug% t%e plant and t%e etent of sludge $lo(do(n. It isimportant to maintain an ade-uate sludge $lanet to promote solids retention $ut it

is also necessary to maintain a clear +one a$o*e t%e $lanet to minimi+e suspended

solids carryo*er. clear or clarified +one of !.5/10 feet 2/3 m is preferred to limit

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carryo*er potential=. T%is is per%aps most important in sludge $lanet units, $ut

also a consideration (it% sludge contact type clarifiers. It is not of importance in aninclined/plate configuration, and is, in fact, a detriment.

.6 &lud-e lo do

Se*eral met%ods for sludge remo*al are a*aila$le, depending upon t%e e-uipment. proportion to >lo( type remo*al system is most popular. ac% time a fied

-uantity of (ater %as passed, an electric signal or pulse is transmitted to t%e $lo(

do(n counter, (%ic% results in one count. T%e counter is preset $y t%e operator to adesired num$er of counts. @%en t%e preset num$er is reac%ed, t%e $lo( do(n *al*e

opens and sludge is remo*ed. Sufficient $lo( do(n s%ould $e used to maintain

sludge in fluid condition to pre*ent plugging of t%e $lo( do(n lines or o*erloadingof t%e scraper dri*e. $ac flus% arrangement is employed on some designs to

$ac flus% t%e $lo( do(n lines, t%us minimi+ing $lo( do(n line pluggage.

Operating personnel s%ould maintain a log on t%e $lo( do(n $acflus% sc%eduleused and indicate on t%e log any c%anges made and t%e reasons for t%em.

.7 Clari"i#atio &'!tem )oitori- Re4uiremet!

*ariety of parameters s%ould $e monitored in any clarification system. ll of t%efollo(ing listed criteria s%ould $e recorded on appropriate log s%eets on t(o %ourly

$asis for flo( rate and p6 and ot%er parameters once per day and re*ie(ed to

assess plant operating efficiency.

G 'lo( rate.

G ?remi tan influent and clarifier effluent p6 *alues.

G Tur$idity of premi tan influent and clarifier effluent.

G Conditions and results of periodic 9ar testing to determine effecti*eness of

coagulant doses.

G C%emical dosages and feeder settings.

6.0 )AINTENANCE CRITERIA

6. ( Covetioal Clari"i#atio! E4uipmet

One pre*entati*e maintenance operation t%at %as pro*en $eneficial is periodicdraining of eac% clarifier. T%is affords an opportunity to c%ec under(ater parts,

%oppers, sludge scrapers, seals, $earings, orifices, etc. and remo*e accumulated

sludge and any scale $uildup. C%ec t%e e-uipment supplier>s Operations nd

"aintenance OJ" "anual for specific guidelines on draining fre-uencies.

Circular clarifiers %a*e a gaset seal $et(een t%e fied center column and t%erotating mec%anism t%at pre*ents s%ort/circuiting $et(een mied (ater and return

sludge areas. T%e unit needs to $e empty to c%ec t%e condition of t%is seal. Sludge

can $uild up in t%e corners of noncircular clarifiers (it% circular scrapers, leading to

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anaero$ic conditions (%ic% can lead to .gas generation and floating sludge, (%ic%

(ill carry o*er (it% t%e treated (ater. T%ese areas can only $e cleaned (%en t%eclarifier is emptied. lso, anaero$ic conditions can de*elop in t%e sludge layer

under t%e scraper arm, leading to t%e formation of sulfur/ric% deposits. 're-uently,

t%is area is missed during empty *essel inspection periods.

Since t%ere are a *ariety of %inges, springs, counter(eig%t systems, and ot%er%ard(are used $y different manufacturers, t%e manufacturer s%ould $e contacted to

de*elop t%e $est approac% to t%ese features. list s%ould $e composed indicating

t%e e-uipment and inspection fre-uency. Detailed maintenance logs s%ould $e

maintained.

Ot%er areas to include in t%e maintenance sc%edule are sludge $lanet le*elcontrols, return sludge flo( controls, scum remo*al, (eir le*els, coating integrity

and ot%ers as indicated in t%e OJ" "anual.

;ased on eperience, e-uipment operators (ill $e a$le to de*elop t%eir o(n list of

additional maintenance re-uirements.

7.0 TROULE&3OOTING CRITERIA

Improper operation of t%e clarifier system (ill produce an unaccepta$le -uality

treated (ater t%at (ill impact performance of all process e-uipment do(nstream.

Correction of out/of specification conditions in a timely manner is imperati*e.Ta$le 1 pro*ides a list of t%e common pro$lems associated (it% clarification and

flocculation systems and t%eir causes and solutions.

Ta$le 1

&'mptom! Cau!e! &olutio!

6ig% effluent

tur$idity, cloudy

appearance

Inade-uate c%emical

treatment.

Insufficient sludge in

recirculation +one.

C%ange in (ater -uality.

C%ec treated (ater analysis.

C%ec c%emical feeders.

C%ec mier speed rpm

C%ec recirculating sludge

concentration.

C%ec automatic $lo(do(n control and

*al*es for proper operation.

C%ec direction of recirculation7 rotation

s%ould $e cloc(ise.

?erform 9ar testing to determine proper

treatment program.

Continuous 'loc

Carryo*er (it%

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cessi*e recirculation speed

ir entrainment.

ir entrainment.

C%ec ra( (ater piping for air

introduction.

C%ec ra( (ater pumps for air leaage

t%roug% glands.

C%ec c%emical pumps for air leaaget%roug% glands.

C%ecing c%emical feed system for air

introduced $y *orteing.

Intermittent or

periodic floc

carryo*er (it% lo(

sludge le*el in

settling +one.

8aria$le ra( (ater

composition.

rratic feeder operation.

ir entrainment.

C%ec treated (ater analysis during

difficult period.

)un 9ar tests to optimi+e floc formation

and settlea$ility.

Continuously c%ee ra( (ater

temperature.

C%ec c%emical feeder cali$ration.

C%ec c%emical feeder for $ridging.

C%ec c%emical feeder cali$ration.

C%ec c%emical pump deli*ery.

C%ec ra( (ater piping for air

introduction.

C%ec ra( (ater pumps for air in

leaage t%roug% glands.

C%ec c%emical feed system for air

introduced $y *orteing.

"alfunctioning *aria$le

speed dri*e.

)epeated flo( surging.

8aria$le re/circulating

sludge concentration.

cessi*e $ac flus%.

C%ec re/circulator speed rpm.

C%ec *aria$le speed dri*e $elt tension.

C%ec inlet meter for flo( surging. C%ec le*el controller for proper

operation.

C%ec instrument air supply system and

pressure.

dd modulating inlet *al*e.

C%ec *olume/o*er :*olume ten

minutes at upper and lo(er draft tu$es.

C%ec $lo( do(n controller and *al*es

for proper operation.

C%ec $ac flus% (ater pressure.

C%ec $ac flus% timer setting. C%ec re/acti*ator operation (it%out

$ac flus%.

6ig% sludge le*el in

setting +one. cessi*e -uantities of

sludge in t%e unit.

C%ec $lo( do(n controller setting.

C%ec $lo( off *al*es and timer

operation.

C%ec re/circulating sludge

concentration at upper and lo(er draft

NTPC Limited

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S> @%ite states also t%at t%e %ypoc%lorite

ion OCl= =.... is a relati*ely poor disinfectant $ecause of its ina$ility to diffuse

t%roug% t%e cell (all of microorganisms due to t%e negati*e electrical p%arge.=

C%lorine is reported to induce a series of e*ents associated (it% cell en*elope

acti*ity and to damage nucleic acids.

@%en sodium %ypoc%lorite aOCI is dissol*ed in (ater to form a solution, t%esodium %ypoc%lorite ioni+es to form t%e %ypoc%lorite OCl/ ion $y t%e

follo(ing reaction -uation /2.

aOCI K 62O ////L a KK OCl /K 620 2

-uations 1 and 2 represent reactions (%ic% (ould predominate in relati*ely pure,

$uffered (aters. In practice, %o(e*er, t%ere is a dynamic e-uili$rium $et(een

NTPC Limited

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%ypoc%lorous acid and %ypoc%lorite ion. 'or disinfection purposes, t%e desired form

of c%lorine in (ater is as %ypoc%lorous acid. T%e form in (%ic% c%lorine is present

is a function of p6 and temperature of t%e c%lorinated (ater.

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8.2 Trou9le!%ooti- #%art "or Ga!eou! C%loriatio &'!tem!


?lugging Of Small

?orts

In C%lorinator

G Corrosion products resulting fromreaction of moist air, c%lorine, and

piping (%ile c%anging containers

and during long s%utdo(ns.Concentration of impurities in t%e

c%lorine gas as it cools.

S%ut *al*es leading to container$efore replacing containers. ?urge

c%lorine gas lines (it% dry air $efore

and after long outages.

Clean ports.

Do not allo( cylinders to sit in t%e %o

sun. ssure c%lorine containers are a

am$ient temperature $efore use. Cleanports. Install a gas filter a%ead of t%e

*acuum regulating *al*e.

C%lorinator @ill

ot 'eed

?roperly

G Insufficient In9ector *acuum.

G Inspect in9ector operating (ate

pressure.

G )emo*e t%e t%roat and tail(ay and

clean a replace t%e part, if necessary.

G C%ec for leas in c%lorinator

G Clogged *acuum regulator/c%ec

unit.

G Clean *acuum regulator c%ec unit a

per instruction manual.

G Clogged gas line.G Clean gas supply line, c%lorine inle

$loc and tu$e to %ead $loc.

G 'ailed in9ector diap%ragm c%ec

*al*e.

G Inspect O/rings and diap%ragms

replace if needed.

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G Outdoor storage (it% lo( outdoortemperature P50/!0Q', 10/

1!QC.

G Increase num$er of c%lorinecontainers in ser*ice (%en c%lorine

gas is (it%dra(n directly fromcylinders or ton containers.

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Ogn Ops Chem 018

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