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S
i
BY J.T. WEARING, S. HUANG, A. PIGGOTT,
M.D.
OUCH1AND A. WONG
ew
strategies limit the
of paper
ne white-water
N A T Y P I C A L newsprint mill, large
amounts
of
effluent, rangin g from 10
I o
150
cubic metres per oven
dry
of
newsprint are dis-
a
la rge quant i ty
of
of
the effluent
riginates from points in the paper
iachine where fresh water
is
used
roue
It is. however, the pulping processes,
mecha nical o r chemica , which are mainly
responsible for the production
of
the
pollu tants . Du e to a
high
degree of overall
integration of pulp and white-water flows
in the newsprint mills, these poilutants
are typically dispersed throughout the
entire
mill
an d are eventually discharged
as
excess white-water, in dilute concentra-
tions.
A t these low concentrations, a ny form
of recovery of the dissolved material for
heat or chemical value is completely
impractical.
As a
result, pollution abate-
ment could be practised economically
membrane filtration and ot her mea ns for
ultimate disposal of dissolced mnterids.
Development of new white-water con-
figurations which are designed to niini-
mize dissolved solids concentrations at
the paper machine. Detailed computer
simulation of these new configurations.
For simplicity, this work was based on
a hypothetical integrated
mill
producing
newsprint from 100 TM P fu rn i sh .
Experimental
The behavior of dicsold
solids
in
nque-
ous pulp
slurric\: Primary- and second-
a r y - s t a g e t h e r m o m e c h a n i c a l p u l p s
only
by ex-plant bioIogical treatment
(Th lP) ,bb ta ined
from
various mill and
a t 60° .’. amples
or to tebting for
prop er opera tion of the paper machine. Technical Section methods wcre used.
By rcnroving some of the extraneous Eqidibritun
siztr l ) t
q f ’d i sdvcr l JoMs i u p d p
material
from
the system, it may be
slurries. A
study
of
a p p r e n i s o r p t i o n
possible to red uce effluent volume with- equilibria
was
done
o n
se\c ml samples of
out unacceptable buildup of dissolved pulp
to cxmiiiie
the effects of the
solids.
Such an approach is already Concentration
of
the liquor
on
the niate-
practised
in
chemical pulp processing. rial loss during dilution. TNO experimen-
Prior
todelivery to the paper machine, the tal techniques were used.
pu lp
is
thoroughly washed t o remove
and
In
method no
1
pulp
was
diluted with
recover val uab le dissolved materials. In deionized water
to
various consistencies
this report, we will demonstrate that this ranging from 1 to that prevailing at the
appronch m ight also
be
used for mrc han- refiner discharge. Th e sam ple\ \\ere
ical pulp of the newsprint furnish. placed in plastic bags, sealed an d held i n a
water bath at
60°C.
T h e
bags of
pulp were
ation, kneaded periodically and allowed to
e following equilibrate
for 24 or 48
hours. The
dewatering or pressing temperature was
In method
no.
2, the required pulp
sample was diluted
to
1% consistency and
mixed gently
60
rpm) using a large
To
assess
the likely effect
of
such
solids maintained at
60°C.
,
OT-
sfer
Further concentration of effluents by
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POLLUTION CONTROL
propeller. The pulp was maintained at a
temperature of 60°C for 30 minutes and
then dewatered. T he filtrate was sampled
for analysis, mixed with a small qu ant ity
of m akeup water, and then recycled to the
wash ing step together with the nex t fresh
batch of pulp.
Measuremenrs of rates mass transfer.
The moist pulp was very finely fluffed and
added to preheated, deionized water to
make a
IS
consistency slurry at 60°C.
Gentle stirring (60 rpm) was provided by
a large propeller. Sam ples were removed
at various intervals and dewatered at
60°C for subsequent liquor analysis.
Membrane filrrurion of
eflirents.
A 0.5-niZ
laboratory hyperfiltration module mem-
brane was supplied by the Danish Sugar
Company, Nakskov, Denmark. Samples
weie prefiltered using Reeve Angel 934
A H glass fibre filter paper
to
remove
suspend ed solids. Cellulose-acetate mem -
b r m z b (110.
66Sj
w i t h a noniiniii rooiwu-
lar
weight cutoff
of
50
2S°C and 3.6 MPa.
Th e concentra
until the conce
effluertt. Th e concentra te from the hyper-
filtration test was evaporated at 6OoC to
various concentrations using a Roto-
vap@ operating under vacuum .
The
resultant liquors were tested for viscosity
at various temperatures using Cannon-
Fenske viscometers. Heating value, and
carbon and ash contents were determined
on the oven-dried residue.
Results and
discussion
Equilibrium \tudy of dissolved
solids
in
W I durries: Dissolution
of wood
mate-
C = concentration
of
solute, kg/m'
k = empirical constant, m'/kg
The material balance for the present
experime ntal case, including the sorption
term, is:
Material dissolved in pulp washing =
total soluble material
-
sorbed material
The data shown in
Fig
1 were used in
the above material balance and, using a
non-linear regression technique,
values
for the constants T, Q; nd k were
obtained. Figure
2
illustrates the close
agreement of the CO D data to the
suggested form. Good fits were also
obtained
for
BOD and TDS. The behav-
ior of
U V
lignin could not be calculated
with Equation
(2).
The form of the curve
was quite different for UV lignin. It
is used here for empirical purposes only.
True
Langmuir
sorption
behavior, i.e.,
reversible, monolayer adsorption etc.,
may or may not exist.
Dissolution
of
w o o d material during
washing (at
1
consistency and
0.5
hour)
with successive recycling
of
the filtrate
be reduced
on in the
is shown in
Fig. 3
using COD data f rom the same
pulp processed above. Increased data
scatter is evident with me thod
no. 2
since
each result is found by subtracting the
larger inpqt and output COD values.
The Langmuir empirical data fit from
0
I
I
0 10 20 30
Consistency,
. .
rial during dilution of pulp to V SnO U S
o
nlethod
no,
I ~ was
Fig.
1.
W h en diluting TMP, more wood material is d isso lved at lower consistencies.
he greattr at lower stock consistency This
is shown in Fig. 1 for TIMP samp led a t an
eastern Canadian mill.
Th e effect of consistency appe ars unre-
lated to diffusion or reaction rate lim ita-
tions. as 24-h and 48-h equilibrations
produced similar results. I t seems likely
that f o r the parameters monitored,
a
conceiitration-dc.pendent sorption phc-
nomenon controls the amount of dissolu-
tioi;. This obscri e d effect dii be quan t i -
tati\ely dcscribcd.
a t
least
at
equilibration
times greater t h n n 24 hours. by n Lang-
muir-type sorption equation:
where
Q
= quaiitit , sorbed, kg/odt pulp
24 hour equiltbratlon
4 8
hour equtltbratlon
angmuir approxunatlon
Dissolved
Total-
Swbed
70
6
-
5 O -
-
D : T - k O s C / ( l + kC)
C
5
Concentration
'.
COD +-e,
d i s s o l v e d , 40 4-e-..
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ment evists betiveen the two me th o d s of
equilibration. Despite
large
variations in
washing time and consistency used. the
dissolution
of
ivood material during pulp
washing could bc characterized by a
single relationship.
In using the above procedure. sorption
constants were determined for nunierous
pulp samples.
A
pariial list is shoivn
in
Table I A \vide range in sorption
coefficicnts was found
for
the v:irioits
pulps tesred.
N o
consisicnt pattern relat-
ing sorption to
se;ison.
\vood species. pulp
type or ape. or relative proportion of
dissolved components was evident. One
pulp sample. a secondary-stage pulp from
Mill (not listed) has shown no sorpt ion
behavior at all.
Th e relationship between total dissolu-
tion of wood material and specific water
use was investigated recently by JSni ne n
et al
12)
using laboratory techniques
similar to our method
no. 2.
A mill scale
L , x G p k i w a l x ) conducted. Janqn-
e n et
a1
concluded tha t reduced water use
would result i n decreased dissolution
of
wood
materials.
Again,
UV
lignin (and dichlorome-
thane extractives) dissolution
was
noted
to show a much stronger depend ence on
concentration than
COD
and
BOD
Conclusions were not reached
as
to the
general controlling mechanism. The
observed phenomena might be explained
by an increase in concen tration at lower
water use and hence an increase in
quantity sorbed on the pulp.
The quantity could be a large fraction
.
,_._..-_.
COD
Dissolved,
k g l o d t pulp
6o
OD Concentration.
a/L
Fig.
3. Dissolut ion 01 COD dur ing d i lu t ion of TMP is reduced at high f i l t rate
concentrat ion.
I concentratlon.
400
TDS
8 I
i+
iquor
Washing
time, h
TOS COD
k
Standard
Mill PrOCeM kg l t
kg/t
“lkg emr ln
k g l t
kg/t
m’/kg error in
D kglt D kg/t
0.59
1.1 57.3 31 3 0 27 0 70
’
TMP spnrce/fir 38.4 15.1
o TMP spruce/hr/pine 428 16.0
5 3 2 24.9
spruce/ Rrlpine
61.1 234
f i t unsuccessful 66.6 223
0.49
2 1
1.8
1 9
1.2 1 4
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POLLUTION
CONTROL
*
pulps tested, to be very fast. Most
of
the
material is transferred in less than 0.25
hours.
effluent was concentrated using hyperfil-
tration membranes to establish dissolved
solids retention and permeate flux for
history
of
small fibre nodules and bun-
waF
obtained.
des. These appeared to
disintegrate,
in Gen erally, Cor mixed organ ic solutes ,
the early stages
of
the wash, at a rate
1301)
has a loner retention than COD in
similar to the increase of wash liquor mem brane filtration because BOD -con-
concentration. Therefore, if a cau wl tributing materials are mostly of low Assum ing 120'C to be th e maximum
relationship does indeed exist, the ratc of molecular weight. Nevertheless, BOD pract icable temp erature i n the product
their disintegration
may
repre sent a retention was nearly 93 n
our
tests. Th e end of the evaporator t ra in, the maximum
significant limitation
to
the ra te of fluu
of
permeate and the concentration of concentrations which m ay be obtained in
transfer of dissolvedmaterials
to
the wash dissolved
solids in the feed stream are com mon eq uipmen t types were calcu-
liquor.
shown
in Fig.
5 as
functions
of
time. lated. It
is
assumed
in
the extrapolations
In a separate experime nt, this hypothe- Similar flux dzta were reported
by
that chemical reactions leading t
sis
was
tested by im proving the degree
of
Clmssen [3] for
concentration of spent increased
or
decreased viscosity would
fibre separation prior to dilution.
The
sulphite liquor.
not occur.Thecon centrat ions aregicen i n
W
solids)
r = 0.9995
S.E.
= 0.0204 in log,, (visc.)
= 1.05 in visc.
is very fast and suggests tha t th c degree of
fiberization
of
the pulp would, for all
practical purposes, control the rate
of
transfer.
TABLE 11 Hyperfiltration
of
TMP wash
effluent.
the product end
of
multiple-effect
evapo-
rator systcmr. Because kiscosity measure-
ments at teniperatures near
or
above the
boiling point require specialized equip-
TABLE
l i l
~ ~ ~ ~ ~ ~ timits
f o r
TMP l iquor
in
two t ypes
o f
evaposa-
tor.
Maximum Maximum
viscosity
concentration
m's
'Y1O6 T O G
___ _____I___
DS
Natural circulation
BOD COD
Feed. mglL 2340 4613 3532 LTV 100 40
Concentrate. mg/L 44500 857
66400
Horizontal tube.
Permeate. mg/L
176 333 190
Retention
92 8 93 1 94 6 spray type 200 4 4
I 1 0
11
0
1
0 5 0 100
Time,
min.
1 2 0 ,
-
I
--__
0
Dissolved solids conc entration,
I
Fig. 5. Typical
f l ux
and disshlved solids concentration during
hyperfiltration of TMP wash liquor.
Fig.
6
Viscosity
of TMP
wash liquor inc rea ses dramatically abovc
30
to ta l
dissolved
solids.
T I
4 2
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Ca/or c
vahre. The
combustion proper-
ties of the dried liquor solids were
determined. Table 1V. For comparati\,e
purposes, typical values for other corn-
mon fuels are shoun .
Dried
TMP
liquor is a fuel of rathe r
loa,
heat value. comparable to bark. I t would
be available only
in small
qusnt i t ies
equivalent to the yield loss i n T M P
rkfining. ca..
20 to
40 kg/odt pulp.
I f
combustion is considered
for
ultiniate
disposal. integration
of
the liquor into
an
existing chemical recovery f urn ace
or
bark boiler would appear
to
be most
practical.
White-water management strategies
for
minimum contaminated effltrent volume:
Based on the equil ibriun~ nd ra te data
'POI-LUTION CONTROL
dissolved solids
machin e white-wa
developed for pulp-water intera ctions we
devise d models
for
white-water strategies.
aimed at reducing the concentration of
dissolved solids in the white-water, thus
allowing low effluent volumes. F or illus-
tration purposes, a newsprint mill usin
100 TMP
furnish was used
as
the stud
model.
The conventional white-water systerr
(A)
is shown in Fig. 7 The system is full)
integrated. White-water from dewatering
processes at the pulp mill and papel
machine enters a common white-water
storagechest. Dilution an d show er waters
in pulping and papermaking are drawn
from this common source.
As a
result of this integration, the
white-water concentration is very uni-
form
throughout the mill. It is desirable,
however, to have low concentrations
of
.. - -
5
e
{
paper machine, it would seem Gossible to
depress the
DS
concentration in the
white-water used at the pap er machine by
arranging for a counter-current flow of
pulp and effluent. Such a co unter-cu rrent
s js tem (B)
is
also shown in Fig. 7.
All paper machine dilution an d shower
needs
are met by
paper m achine and
save-all filtrates and some fresh water.
The
e x e s
paper machine white-water
is
i
routed
to
the
TMP
mill.
TMP
mill
effluent is removed from the pulp at the
thickeners but held back for reuse in the
T M P mill. Excess white-water is sewered
from the
TMP
mill, not the paper mill.
A
further refinement
of
this approach
may be the
use of
inter-stag e washing of
ThlP.
Earlier information developed by
Wong et
al [6] shows
that the majority of
pollutants
are
released in the primary
stage
of
refining. Thus. washing the pulp
a t this
stage
could provide effective
removal of dissolved materials while
taking advantage
of
the fast drainage
characteristics
of
high-freeness primary-
stage pulp.
To
maintain pulp quality in
refining, the washer mus t discharge pulp
to the secondary refiner a t
a
high
con.'stency. Figure
7 shoas
the inte-
g a te d . mill with im proved u.hite-\viiter
design and add ed inter-stage press w ash-
ing (System C ) .
A computerized process simulation
was developed to evaluate Lvater. pulp
and dissolved solids material balance5
and energy ba h c e s for these three cases.
A modular simulation technique
was
used. Called GEMS. this is
a
com pute r -
based proces s si m
i
I
a
ti
on
tech
ti
iq
ue
developed specifically
for
pulp
a n d
paper
manufacturing processes
by
Dr.
L.
Edwards and his associates
a i
the Univer-
sity of Idaho, Moscow, Idaho.
The design parameters for the
Th4P
mill
were derived from the material and
W -.tr.
Wood
ChlP.
I S.*..lI
Effluent
A .
Fully integrated white-water system.
1
I
I
P P 1
I
I
I
=
W.l
P M
W W c h e s l
3 .
Segregated,
counter-flow
system.
TABLE JV.
Characterization
of
TMP
liquor solids and selected
commer-
Fig.
7
TMP
white-water management methods.
T143
66
ood
IIpm
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L - - - A
I
I PY
W W
chest
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energy balances given by Azarn iouch et a1
80
at
an effluent volume
SI. Th e conventional p aper mach ine pulp. Lower effluent volu
white-water configuration c orrespon ds to considered. Wah ren
et
a1
[8
cur ren t Scandinavian opera t ion as out that the
effect
of
s
white-wa ters.
3.7
m'/odt in the
whitewater , the
atioii v effluent
0.06
60°C
white-water schemes. Substantial im-
provement could be achieved s imply by
KMW press washer
segregat ing the pulp and paper mill
white-waters. At constant headbox con-
centration, excess white-water may be
reduced from 10
to
3.7
m3/odt pulp. Th e
addi t ion of an efficient one-stage press
washing would allow
a
further reduct ion
of excess white-water to
1.7 m3/odt
discharge consistency:
t-bden E actor in wash zone:
Consistency in wash zone :
Genera,
-yield
IOSS:
l o
stage:
constants
40%
2.0
15.0%
4.0
3.2
0.8
Q. = 15.5 kg/od
pulp
k =
1
.O
m / k g
DU~D
L
The counter-current arrangement of
wh itew ater flows also results in reduced
t r a n s f a
af
.&axe
heat from rcfining into
the paper machine white-water. This
means that,
to
maintain a given headbo x
temperature (above that of the fresh water
input), niore heat would have to be added
directly to the paper machine white-
ivater.
This coiiiparison is drawn in Fig.
9
w
here heating rcc~uirements re
shown
as
a
funct ion of
excess white-water flow for
the
three
c:iscs
A t reduccd effluent
vnlunie
(;IS in
Systcni
C). there w u i d
he n
sninll s a t i n g in
s t c a ~ n
or
the
heat ing
of
mill \\
hitc-\rater
3s
compared
t o
the
con\ entional case
(Sys tem A).
Using
3 GEX1S
s imulat ion of ; I II
integr;rtcd refiner niechanical ptllp
( K h f
P) mill. Vcnkatesh et
a1 [7]
predicted
t1i:it the incorporation
of
a segrsgated,
countcr-ciirrcnt \vhi te-water arrang cnic nt
I 8 1 1
I \
6
Dissolved 5
solids
concentration
at
headbox
g/L
2
1
Fully
I n t e g ra t e d
(System A )
S e g r e g a t e d [ s y s t e m Sl
I n t e r s l a g s
washing
( S y s t e m C )
I
0
0
4 8 1 2 16 2 0
I_
xcess white water volume, m3/odt pulp
and P ( ~ ~ t - s ~ c ~ ~ ~ 1 ~ % '7cchanicd Pulp Fig. 8. T h e d i s s o l v e d s o l i d s c o n ce n t r a t io n at t h e i i e a d b o x
c a n
be great ly reduced by
u x h i n g \ \ . t T i i l d rcduce the concenlralion s e g r e g a t i n g the pulp mil l and paper mil l white-waters and by the incorporation
o f
of
di>sol\ed 5 c > l i d h
i n
thc pape r inill h y inter-stage washing .
PULP &
PAPER CANADA
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-
.-
-
-
-
~
-
f
the conventional
fu l ly
integrated sys-
I O
rn'/odt.
This means that \ - s l y small changes
i n
water input or production rate i n the
\vi11 result in large chnngcs i n
te-water concentrat ion,
affecting
uct quality and machine efficiency
i n
This would
be
volumes. Neverthe-
i t
is expected that a process control
water input
to maintain constant
The washing
of
the pulp
ivill
rcsult in a
of chrotnatographing
of
ap er m achine white-water relative to
h littleor nosorpiion. This might
of closure in th e white-
ter system after pulp washing in some
To
etermine theoptinium white-water
is
to specify the concentration of
aterial which can be tolerated
of the
been
developed [SI
to
on
product quality which can
to existing or projected mill
n economical alternative to
estcnial
With conventional
ons, the minimum
al excess white-water volume fro m
be
10
m3/odt
D U ~ D
ue to cons t raints
Piggott. contributed to
t h i s
nn rk u.liile on
co-oI)C'r;"i\,e-\vor~ ternis
f rom
the Uni-
versily of Waicrloo. 'The authors extend
their appreciation
to
J Kersch for
techni-
c d assistance and cxperiineni:il advice.
With such low volume of concentrated
other means
of
disposal of the
t hus
become
For
example, the excess white-
may
be concentrated further by
by
Since the amo unt of material
isvery s m d ,20kg/odt pulp,
might be can ied
out
in
an
or recovery boiler.
If all the mechanical pulping effluent
be
integrated in to an adjacent chem-
lacing fresh water,
sts might be effec-
White water
heating
requirements
GJ/odt pulp
2 0
-
Fully
Integrated
4
12
16
2 0
t : : ~&mtniig&s pour reduire d e facon significative
l es volumes
excddentaires d'eau
blanche tout en maintenant aussi basses que possible les concentration de matihres
so-
lides dissoutes durant le procede de fabrication d u papier.
La
rdduction
d e
ces volumes
peut permettre
d
de telles usines de liberer des effluents qui contiennent un tres fable
pourcentage d e matieres contaminantes, e t cela a des cod t s qui se comparent ceux des
I
installation conventionnelles de traitement biologique des effluents.
~ ~ ~
Reference:
WE ARING.
J.T.. HUANG. S..
PICXOTT.
A..
OUCIII .
A1.D.
i~ndN'OSC;.
A.
New u
hiie-watcr
management strategies
for
integrated new
sprint
mills. PI+ P U ~ W
LJII
O :
T139-145 (May 1985).
Paper
preserited at the 1983 Xlcchanical Pulping Coiifcrcncc
of
the
Tcclinic.al Section.
CPPA. co-sponsored
w i th EUCEPA and TAPPI
ai
Washington.
D.C..
Junc I 4
t o 17. 1983. Not to be reproduced without permission. Manuscript rcccivcd Junc 14.
19x3.
Approvcd
by
Review Panel. Scptcmbcr
20. 1984:
Abstract:
The white-water systcins in integrared
nrusprint m ilk
may bc re-organizctl with
niuch lo\vcr
excess
white-water
volunics
v, hile
still
maintaining low dissol\cd solids
concentrations in the papermaking operation. These lower volumes proniiw to niake i t posziblr
for such
inills
to
operate with effluent that
has a
very
low
degree
of
contaruination. at costs
comparable
to
the operation
of
conventional biological effluent
treatment
Keywords: WHITE-WATER, NEWSPRINT. INTEGRATED
MILLS.
TIIERMOME-
CHANICAL
PULPS,
V.OLUME,
POLLUTION
CONTROL.
T145
PULP
&
PAPER CANADA
86: 5 (1985)