\ 3
ICCBPE / SOMChE 2OO5
EES-36
Optimisation
of Regeneration
Unit to Achieve
Zero Discharge
in a Paper
Mill
Dominic C. Y. Fool arg Zainrddin A. Manan2
)
school a.f Chennat and Eneitunmentat Ensineerins, Uhitenirr of Nattihghatu (Maldrsia CMpus ) Jalah Btuga$5A0 Senen ih selanSor Dtrul Ehsaf, Malatsia.
Tet: +5A 3 3921'6130, FM: +60 3 892+8417, E-mait: Da"init:[email protected],h.n\, '1 Chetuical Engineenng Depantueat, Ltntuersiti Teknalo|i MaLalsid
81J 10 'lar.lai,
Johor, Mdloriia.
TeL +6a-7 553 5512, Fax: +6a-7-558 1163, E nail: .6ia@fkkktn utn n
The ddvent of tuater pinch ondl.rsis as 4 toal Jar the .lesish aJ aptiml wdtet recowtr nertork hN been one of fie mosl signilcont a&dntes in the area L,f wdtet consetuation orel the last deca.le. water Piach @a\"sn i d ,stematrc technique Ial nnplenenting str4tegies to mdinise water t r r , p a n r l 4 ) . L n I t h r c u p t : N p B a n o a o 1 ' w a t " - i n ? actirities at prccesses. Ia this Paper Possibni\ af dchieviv compl,ete elimindtion of ||1stewater, i.e. zera discharye is 6psed thtuu8h the use ofnatet teEenennnn units. Wdter tueeneratjon has been wideLt ac.ePte.l 6 an efedire nean to Jurther reduce \|ater tarsets in tuntPr pinch dnalysis. Warer rcSeaeration invoLres the pafint or totdt up|tadlns af water Puri1, rsins anr pulfication techniqu4- me rcEenerated warer can eithe/ be reused in other waterl^ihi processes ot rectcled to the sarc prcces b funhet tedoce water .ohlttuption nn . a pvr?. 8a1er t:a4. A Le , udt an a rnlet " t e n " i , P paper nill process is used to illustate how the water netv.rk can be opinned to achieve zero dis.harEe The tdBetins technique af wdt+ cascade analtsis k 6ed to Iacdte the various ketwork taryets Priot to the develPnenl , ! l e 0 4 ? 1 , "tu r'\ de ig" a aldianwht"a i ' r n capnaL Md annlal operdti4e costs was.btaned
K€ywordsr wirer nininisdtion, pirch edly$s, egeneration, ze.o dischffge, water cascade ealylis
Irtroduction
The curent drive towuds envi.onmenlal suslaioabilitl xnd rhe rising .osts ol lresh water and efi'luent Lratmeni hrve encouhsed the proca$ indusq !o find nea ways to reduce freshwaEr codsmptron and wastewater generano. Concurently, the delelopment of sys{ematic techniques lor water reducrio!, reuse dd recycling within a prcce$ Plet hd ser extenrive progress. The advent of wirer pinch lnrlyss (R"A) a! d rool lor |he design of optimal water recovery netrork has been ode of the mosr signacant ddvances ln rhe uea oi ware. conservatron over the last a " c a - L lol. $ " p:trh cr' -n i r Jqe- rc
technique for idplementlng strategies 1o haximise water r e u e d r d . . y r - g r ' r o u S h n e ! o I o n o l r o - r ' L J n 3 actiljties or prcce$os, Maimising wate! else aDd dcycliry can midmise freshwate. consumptiod and u d . r - u 1 e g e 1 b h o r . T r p . 1 W P A , o l r . o r c n - p l s e oftwo steps, i.e.. setting dinimum iiesh w^ter reqdrnent ud wastewarer generation (i.e. the ba€line water tdgets) followed by detwork design to achiele the baseline trgets. h setting bseljrc wate. trgets, the recent develoled vatel cB.ade ahdlrsh OVCA) rechlique [15] hd been proven to a t.omisins tool in locating dninun water a wastcwate. ta.sets in a mdimud w^te. reovery (MwR) ner*ork. Wat* cAscade' refers !o tbe reuse of a slent warei source ro satisfy a lower quality water demdd. In this laper, a waterinteffive pape. mill cdse study is used ro illust ate how WCA can b. effecrilely used to optimise
u o i r .
' o a c h i e \ e r r o d i r h r 8 e n a
Paper Mill Case
Study
Fisure 1 shows a lrelimilary water network for a !a!ef mill p.ocess thar was not designed based on the systemanc lechDique ol wPA. Old newspapes a!.1 nagazines as feedsiocks for the paper Eill ue blended wi$ dilution water and cbemiclls !o fom puh slu..! called stock. The stock is sent |o the lomhg secno! of the laper Mchine to fornr paper sh€et In the foming ard presing sections, fresh wate. (demand) is fed Io rerbee debris whlie wasbwater Golrceo de iemoved f.o'n rhe stoct dunng paper sheer fomation. Pdt of rhese water soolces de sent water stodge trnk Io be reused m otherplocesses. To remove printing lrk from the nain stock, the de inking pulper (DIP) Md iis asociated ?roceses (deloted as -DiP-Othes") receive a mixture of fresh water and sped valer frcm fie warer storage tank. The effltent water Aon Ue DIP main llocess is dixed slth freshwater to dllute the srock being punped to lhe deculalo. h the appro@h flow systen (AF) while lhe effluent from 'DIP-Otbe6" is seni ro water srorage tank. Tle chedical lrepdation unir (cP) also codsudes fesh watcr to dilute de-inkrng chemnrls tbr
use ddring ilk r@oval proce$ in the DIP udt. Pan of \rasiewate. from the foming secrior md the DIP unit N
Fof the paper miu warer network id FiSxre 1, the total fdsh water consdmptlon is 1989.06 ton/h dnd the lotal wstevater generatiotr is 1680.3 ton-&. At a fi.st glance. lhis paper mill seeDs to hale b@n designed wirh ^n extensive ilatef recolery scheme. However, it will be showr latel rhat there are aopLe rooms for tunher recovelv since the wrter and vastewaF! no{mtes 4e still far from rhe baseline w.te.talgets. Table 1 sbows the llmiting data for the paper milL cde study, ie. ihe naximum pemissible inlet (C,) and otrtler (C,) concentntions for the water demuds md the water souices iespectively. The nosr significani water quality faclor, i.e. total suspended stid (TSS) was chosen for the analysis.
l a b . e . . I n i ' 1 ? 1 ^ a t . " D n a f o P a P P U t l l ' ^ e < . n cj / Strean (kgt (PPm) 1 Ressing section 155.40 20 2 F o m i n g s e c t i o ! 8 3 1 . 1 2 8 0 J DIP Othels
2 0 1
8 4
i 0 0
,1 De inklng lulper (DIP) 1149 84 200 5 App.oach flow (AF) 34.68 20 h C n e o . - l o r e D d r a r 0 1 C P r 6 8 . - 0 2 0 u
water sources, SR, F,
sent fo. eifluetrt trearment beforc berng finaUy dischdged
Figure I - A Preliminalr Water NetvarkJor E Paper MillCLt Stullr
idelrlied d 828.12 ton/h and 539.36 ton^ respectively (1'able 2). The plnch poilt is ideniilied at the concertration level of 230 ppm. Fomxng sedion (SR,
r - . i d e r i ' i e d a , . h e p i n . h c a u J i n g \ r e l m i r L h ( c d e .
Tabk 2 - Taryeting for Papet MillCatr Stu.l!
,.
r,
1nl
F,
Nn
( um. au
" ,*.'
*?li
,ks<' ikvs,
'ke/s)
F.=848.121 0 0
8 4 8 . 1 2 1 6 . 9 6 2 2 A , 1 9 0 0 8
3 8 0 - 8 3 1 . 1 2
200
1 0 0
r70
T A
250
658.04 i9.48
, 1 7 3 . 0 8 3 . 4 6
1 6 . 9 6
56.1r1
(kg/s)
Ct
0.00 {PINCH)
t . l 9
53922J.42 ,219.52
2 0 1 . 8 4
- 1 7 . 6 8 , 1 2 1 8 . 5 4
-\236.22 1 t 0 5 . 7 8
6 9 5 6 469.80
5 2 . 9 3
- 1 5 . 3 7
37.62
,0.53
37.U)
-37.09
l . l 9 FD=539.36 5:,9226.03
2
1 DIP-Oihers De inking pulper (DIP)
Followine rhe \vCA apptuach t151, the mitrlmm fresh water {FF) Md wastewarer dischrge (,rD) flowrates ibr the cxse study, before any water rcgene.^tio. takes lldce are
Optimisation of Regeneration Unit to Achieve
Zero Discharge
A rcgeneiadon
unit is nolmly .ated ii terns of either
Iixed outlet cotrcenFatio! (C-) or fixed conrminet rcnovdl percentage (F). The fo@er .ates a reseneoror 1 5 5 . 4 0
1 3 0 5 . 7 8 2 0 1 . 8 4 469.80
9 1000000
1 0 0
ICCBPE / SOMChE 2OO5
based on a llxed outler water concent atio. (e.9.,20 ppm). On the other hdnd, Lhe latter is a nting based o. a nxed mouo! ol contamindt load removal and mry result m changing oudet conceftration. Fo! instance, a wdtewater flow at 100 ppm led (o a unit nted dr 9070 contmnot reftoval willproduce an orde!flow at 10Ppm.
The paper mill water nelsork consisrs of wo lndepeodent rhemodynmrc egions wbich exist abole dd belov the pinch concenffation. A iegene.ation unit can eithei be placed entlrely above the pinch or across it silce bo& olrions will ieduce the f€sh water and vdtewaler aowrates. Common regeneEtion udlts for the removal of suspended solids in Papef mill indusrry include the saveall disc filrer (SDF) and dissolved air noution (DAD udt. Forthis exmple, the use ofaDAF unit is consideftd. The DAF lras a conudinaot rcNoval pe.centage (,R) of 907, and an oleiatins cosr of $0.50^s of contMitrut load Gmoved. A DAF regenerales wastewafer to a hrgher purity by introdocing fine gar (usually aii) bubbtes to a*ach and llft pdticles to the watef sunice for removal. Any ol the four water sodrces of the Paper mlu can be purified betbE reuse within the warer netwo*. since the DAF unit is cap$le ol iegenerating th4e sources to the Egion abole the prnch (nole Lorn Figure 5 tbat tne Pinch occus at 230 ppm). For oltimal regeneration, lblee key f&oa dusr be considered:
i. Selection of rhe oplnnar seqBence to Punfy rhe avanabLe water sources
ij. Deciding the right mount to purify each oi rhe avdrlabl. ware. sour.es
iii. Fomulaling tbe mosl cost-effective regene.adon f h e r r . 0 1 l e r o v - . i r o - - vrler'ou|F i/An,l : n a regenerato. is gilen as follows:
Note also that, since the source flowrate (Fr.,) is invesely propo.tional to dCR, a smaller aRJ would be lequiied to regenerate a diitier water source ((ge. ACJ as conlaled ro that ibr a cleaner watei source (sna11e. AC foi a lixed mourt of Aft remoled. For insrmce, fo. n = 907d, a source at 250 ppm needed ro be punfied to 25 ppn (ACR = 2 l 5 p ! 1 q b i l e a . o u n e . r l0 0 t p m . o l 0 p p m ' ^ r p o 0 ppm). Herce, h order to achieve zero dischrse witb the diainun capital md olerarlng costj rhe followurg
PunI! watet sour.es oN b oae in desceadiry oftter oJ
. l - r h e u . : c n e . n \ . h a r . n o d p -
' o n r - . e c , p r . and opemtins costs, one shodd first punS' the vater source aI the hiShest concenbation Level (or the "diniesr") dd .ondnue wirh souoes at the next highest conceniraltron level util all have been puified lrd wasrew^ter eliminaled to achieve zero dischdge. Doing so will alwats lead to a smaller I.ir and hence, a smaller toml regereratio, flowrate (r-J and uumaoly a smaller and che^per eqdipmert.
For the papef mill pmcess. we begd by punfying soorce \ R , , o d 2 { 0 p l d . o 2 5 p p m A r , - l 0 ' . ' i \ g f t . f i 8 , R 2a). This reduced the Aesh waler ud waslewarer flowntes to 429.19 ionlt dd 120.63 tor^ ftspectilely, but tlis alone did nor lead to zero dischdge. We next proceeded with sou.ce S, dt 210 ppm. Purifying S, from 230 !!m to 23 ppm (Ane = 27.75 kg/h) finrlly led to zero
The WCA procedure revealed !ha! olly 134.05 ton/h of SR, (FRt needed Io be regenerated to lchieve zerc o { n f 8 e . K n o n . 1 3 r l - e e \ , d , e 8 r , e , d ' o n n o b e , , c r u . ' ! : n a\oidi, C e ( e . v e o v e ! d c . . 8 n . a n d h e n ". unnecesary caplal expendirure. A fresh water tdger of 308.76 toi./h genemted usitrg WCA matched tbe one computed lrcn rhe difieience beiveen fie slm of water sources dd lbe sum of {ater demands (Table 3). The &nual operaring cost a$ociated with th€ addilion of DAF is approiimately $533,E00, caLculated based on the total reSenerarion llowrate (rEJ of 603,85 io.'/h and totar
^u renoval o1133.45 k9,ft.
Fj6@l@'
B
E
i 5oo * E , " ^
z
Sa Md 134-05
- 603.90
ton/ir
ResdMl*lon flMnia (ld U
f.bk 3 TaryetnsJor Paper hiill Cae Studt
,
(.
1o,
F,
a,n
cum.au
' p p m r ,
L r r , k g / s r
' k g i ) r h g / s '
5 8 0 8 3 1 . 1 2 4 6 7 ' 1 5 . 8 5 - 1 0 8 . 5 9 , 2 1 7 1 . 8 0
6 100 -46.44 44604.05 r 5 5 . 0 3 -10852.i0
7 110 201_84 33751.95 46.81 1404.30
8 2 0 0 -1218.54 3 5 1 5 6 . 2 5 - 1 1 7 1 . 7 3 - 3 5 1 5 1 . 9 0
9 B A \ 1 7 1 . 1 3 4 . 3 5 lcD=0.00 4.35
101000000 0.00
(PINCH) L
2
3
0 0
20
190.08
2:l
84.05
25
469.8
liF=308.76
308.76 6175.24
6115.20 l r 8 . 6 8 3 5 6 . 0 4
6 5 3 1 . 2 4 252j3 505.46
7036.70 722.53 39139.15
'1@E
@,
Figure 2 ' Placenqt of a Regeneratian Unit ir the Cantett af tu OwrdLl Netvotk
ICCBPE / SOMChE 2OO5
Note that it one had srarred by purifylne the "clealest" water source, i.e., sRr, lollowed by sR3 and sR, (Figure r b . o , " !orld hr\e c.f e\"d r'F dm" 5-nual op-"rin' cost of $513,800 (for the same anount of A4 removed). However, in lhjs case, a ldser F.c v.lue of ?85.17 ton^, . n d 'en.e , luger DAf ri ro rld b" r e"dPd ,o rclie.F zero disch{ge Hence a nuch higher capiul cost is erpected for the purchase of a rew regenerntion unit. Figure 3 sirows a plot of rhe regeneotion flowrale ve6us fresh wate. dnd was€water flowrales for lhe DAF unil, r o . l o w i l g . - 1 c u | ' . ol punlir8 , ,er ou(e in descending order. Noie that fresh warer led ro the proces remdins constant at the regenerafion flowrale of 603.90 ro h. Thh js the tuming poirl lor the laper mill !rcca$ Lo achiev€ zerc liquid discharge.
One of the nary possible later retworks to achieve ze.o discbdge is shown in Flg!re 4. Apalr frcn the roral elmination of wastewater, the finrl network which includes reeeneratlon maD?ged to achieve 84.5% €duciton in liesh water. Tbis is an additional2T.l% reductior as compded to reuse/recycle alone (Table 2).
Condusior
A new merhod to optimise regenerarion onits into a maxinum water recovery (MwR) lelqork ro achieve zero liquid discharge has been deleloled. ware. cascade malysis (WCA) technique provides a quick and accuate deds in identirying a solution wirh rhe nininum captal and amual opeFting costs.
Fisure 4 -tuto \varte'/atet Discharye Netwo*Jotthe Paper Mi Cav Stu.It
Acknowledgement
The financial srploft of Minisiry of Scierce, Technology and EnvnoDmenr (MOSTE), Malaysia throush Irtensilied Resedch Priorirl Afa (IRPA) resedch giant od NationaL Science Fellowship NSF) schotdship is gratefully
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