Date post: | 03-Jun-2018 |
Category: |
Documents |
Upload: | premkumar-vasudevan |
View: | 220 times |
Download: | 0 times |
of 20
8/12/2019 Ogn Ops Chem 018
1/20
(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
8/12/2019 Ogn Ops Chem 018
2/20
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)
8/12/2019 Ogn Ops Chem 018
3/20
n!"irie# to: $ead of %orp. Operation &ervice#
8/12/2019 Ogn Ops Chem 018
4/20
Guidelines for Performance Optimization of P.T. Plant
and Chlorination System
INDEX
Sl. No. Con!n" P#$! 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2.0 Superseded Documents 1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 $e considered (%ile installing a
c%lorination system 15
10.0 )e*ie( 1!
8/12/2019 Ogn Ops Chem 018
5/20
'ae *%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"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 $y an up(ard mo*ing stream of (ater if t%e *elocity is %ig%
enoug% so t%at t%e action of (ater on t%e particle eceeds t%e pull of gra*ity. s t%e
up(ard *elocity of a particle decreases due to decreased (ater *elocity as it
NTPC Limited
8/12/2019 Ogn Ops Chem 018
6/20
'ae 2%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
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 $lanet clarifier
NTPC Limited
8/12/2019 Ogn Ops Chem 018
7/20
'ae 1%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
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.
8/12/2019 Ogn Ops Chem 018
8/20
'ae 5%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
'ig : 4 Typical solid contact clarifier
.0 CLARI,ICATION
T%e clarification of (ater is a process applied mostly to surface (aters for t%e
remo*al of suspended solids, finely di*ided particles present as tur$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 $rea up t%e floc it coagulates. In ot%er (ords it s%ould matc%
t%e floc strengt% at *arious stages of its formation.
NTPC Limited
8/12/2019 Ogn Ops Chem 018
9/20
'ae %O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
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 $e
a*oided since it tends to s%ear t%e floc.
NTPC Limited
8/12/2019 Ogn Ops Chem 018
10/20
'ae 6%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
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 $ottom of t%e
sedimentation *essel. Clarified (ater typically o*erflo(s from t%e surface and is
treated furt%er t%roug% filtration e-uipment.
NTPC Limited
8/12/2019 Ogn Ops Chem 018
11/20
'ae 7%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
.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.
NTPC Limited
8/12/2019 Ogn Ops Chem 018
12/20
'ae %O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
.* 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 $lanet to minimi+e suspended
solids carryo*er. clear or clarified +one of !.5/10 feet 2/3 m is preferred to limit
NTPC Limited
8/12/2019 Ogn Ops Chem 018
13/20
'ae 8%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
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 $uild up in t%e corners of noncircular clarifiers (it% circular scrapers, leading to
NTPC Limited
8/12/2019 Ogn Ops Chem 018
14/20
'ae *0%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
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 $e cloc(ise.
?erform 9ar testing to determine proper
treatment program.
Continuous 'loc
Carryo*er (it%
8/12/2019 Ogn Ops Chem 018
15/20
'ae **%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
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 $lo( off *al*es and timer
operation.
C%ec re/circulating sludge
concentration at upper and lo(er draft
NTPC Limited
8/12/2019 Ogn Ops Chem 018
16/20
'ae *2%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
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 $et(een
NTPC Limited
8/12/2019 Ogn Ops Chem 018
17/20
'ae *1%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
%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.
8/12/2019 Ogn Ops Chem 018
18/20
'ae *5%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
8.2 Trou9le!%ooti- #%art "or Ga!eou! C%loriatio &'!tem!
&'mptom! Cau!e! &olutio!
?lugging Of Small
?orts
In C%lorinator
G Corrosion products resulting fromreaction of moist air, c%lorine, and
piping (%ile c%anging containers
and during long s%utdo(ns.Concentration of impurities in t%e
c%lorine gas as it cools.
S%ut *al*es leading to container$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 $loc.
G 'ailed in9ector diap%ragm c%ec
*al*e.
G Inspect O/rings and diap%ragms
replace if needed.
8/12/2019 Ogn Ops Chem 018
19/20
'ae *%O&I&O00O+N,O'&,%$-,0* Rev. No.: 0
+"ideline# for 'erformance Optimi#ation of './. 'lant and %lorination &y#tem
&'mptom! Cau!e! &olutio!
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.
8/12/2019 Ogn Ops Chem 018
20/20