Note: Descriptions are shown in the official language in which they were submitted.
WO 95123891 PCTIUS95I02719
TITLE:
"IMPACT OF TEMPERATURE AND ALKALI CHARGE
ON PULP BRIGHTNESS"
BACKGROUND OF THE INVENTION
The present invention relates to a process for improving the final
brightness of pulp. More particularly, the present invention relates to
modifications in both the cooking temperature and white liquor charge for a
rapid displacement heating cooking system.
Rapid Displacement Heating ("RDH") is a low energy batch cooking
process for producing kraft pulp. Combining the inherent advantages of batch
cooking with the energy efficiencies of a continuous digester, RDH reuses the
spent black liquors that are displaced from a cooked digester to pretreat the
wood chips in a consequent cook. Thus, both the chemicals and the heat in
these spent liquors are recycled to a consequent cook. The pretreatment of
fresh wood chips in a consequent cook begins with lower temperature liquors
(approximately 80 ~ 130°C), and is followed by high temperature liquors
(approximately 130° to 165°C) which heat the digester to the
highest possible
temperature before raising the temperatures to the final cooking temperature
(3170°C) with steam.
RDH and other alkaline cooking processes produce pulp that is relatively
dark in color. Greater contrast is usually needed for the many uses of pulp
and
paper, so pulp is usually bleached to a high brightness in order to make white
pulp for writing and printing papers and paperboard. Pulp color arises from
changes in the lignin component of the raw material which occur in the pulping
process. Unfortunately, with the use of high cooking temperatures and low
black liquor strength in the RDH process, low bleachability problems have
WO 95/23891 2 ~ g q. 7 Q ~ PCTIUS9SI02719
2
occurred following the use of conventional, ECF and TCF bleaching processes.
High cooking temperatures and low black liquor strer~th seem to accelerate
condensation reactions, resulting in the condensation of lignin with lignin
and
other wood extractives. As a result, the bleachability of pulp decreased.
An alternative method is, therefore, needed in the RDH cooking process
to eliminate such adverse side reactions and improve pulp bleachability.
SUMMARY OF THE INVENTION
The present invention provides a method for improving pulp brightness.
Based on modifications to a batch cooking process utilizing rapid displacement
heating, the method of the present invention combines the steps of adding
white
liquor solution (% active alkalinity (AA) or effective alkalinity (EA)) or
NaOH to
both the warm fill and initial hot fill stages and cooking wood chips at lower
temperatures than previously used in a batch type operation to produce pulp
that has improved bleachability. In this regard, a total white liquor charge
ranging from 15% AA ~ 35% AA is distributed over the warm, hot and cooking
stages in a predetermined amount. If a cool pad is used in practicing the
invention, cool white liquor is also added to the black liquor that is
released from
the cool liquor accumulator. Essentially, white liquor is added to every stage
of
the batch cooking process prior to the actual cook.
During the cooking of the chips, white and black liquors are present in
the digester. Cooking temperatures are low, ranging from 150° ~
167°C. With
the combination of a high AA or EA white liquor charge and low cooking
temperatures, final brightness of pulp is improved. As a result, pollutants
and
bleaching chemical usage are decreased in pulp mill operations.
WO 95!23891 PCT/US95/p2719
3
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a schematic view of a digested, and its associated
equipment used in the current RDH cooking system.
FIGS. 2A, 2B and 2C each illustrate white liquor profiling or the addition
of white liquor at various stages of the RDH cooking process. In FIG. 2A, plot
A
represents the addition of a small amount of white liquor at the beginning of
the
warm fill mode. Plot B represents the cooking stage and illustrates the
presence of white liquor in the digester during the actual cooking of the
chips.
FIG. 2B illustrates the continuous addition of white liquor to the black
liquor at each stage of the RDH cooking process, beginning with the warm fill
and continuing through the end of the hot fill. White liquor, as shown, is
also
present in the digester during the actual cook.
FIG. 2C illustrates the continuous addition of white liquor at each RDH
stage including the addition of white liquor to the washer filtrate from the
displacement tank.
FIG. 3 illustrates a Stage 3 RDH system without white liquor addition
during the warm and hot fill modes.
FIG. 4 illustrates a Stage 3 RDH system with the addition of white liquor
during the warm and hot fill modes.
FIG. 5 illustrates a plot of D1-brightness versus total (D100 + D1)
available chlorine charge for the best case and baseline case RDH pulps. Plot
A represents RDH pulp R3 (0.225 Kappa factor). Plot B represents RDH pulp
R4 (0.27 Kappa factor). Plot C represents RDH pulp R7 (0.225 Kappa factor).
Plot D represents RDH pulp R8 (0.27 Kappa factor).
WO 95/23891 PCT/US95102719
4
FIG. 5A illustrates a plot of D1-brightness verses D1-chlorine dioxide
charge. Plot A represents RDH pulp R3 (0.225 Kappa factor). Plot B
represents RDH pulp R4 (0.27 Kappa factor). Plot C represents RDH pulp R7
{0.225 Kappa factor). Plot D represents RDH pulp R8 (0.27 Kappa factor).
FIG. 6 illustrates the D1-brightness versus the total available chlorine
charge in the D100- and D1-stages far all 0.225 Kappa factor bleaches. Plot A
represents RDH pulp R3. Plot B represents RDH pulp R12. Plot C represents
RDH pulp R7.
FIG. 6A illustrates the D1-brightness versus the D1-stage chlorine
dioxide charges. Plot A represents RDH pulp R3 (0.225 Kappa factor). Plot B
represents RDH pulp R12 (0.225 Kappa factor). Plot C represents RDH pulp
R7 (0.225 Kappa factor).
FIG. 7 illustrates the D1-brightness versus the total available chlorine
charge in the D100- and D1-stages for all 0.27 Kappa factor bleaches. Plot A
represents RDH pulp R4. Plot B represents RDH pulp R12. Plot C represents
RDH pulp R8.
FIG. 7A illustrates the D1-brightness versus the D1-stage chlorine
dioxide charges. Plot A represents RDH pulp R4 (0.27 Kappa factor). Plot B
represents RDH pulp R12 (0.27 Kappa factor). Plot C represents RDH pulp R8
(0.27 Kappa factor).
yFTOU Fn r~ESCRIPTION OF
IHE PRESENTLY PREFERRED EMBODIMENTS
The present invention provides a method for improving pulp bleachability,
which is based on modifications to the existing RDH Cooking System for the
.~_ 2184706
- 5 -
digestion of wood chips. More specifically, the method
involves the addition of a white liquor charge commencing
at the start of the RDH cooking cycle and continuing
until the time to temperature stage of the process, at
which time the actual cook begins. The method of the
present invention is also predicated on the use of
somewhat lower cooking temperatures for the actual cook
as compared to cooking temperatures commonly used in the
RDH pulping process.
In accordance with the present invention, a total
white liquor charge ranging between approximately 15%AA
35%AA is distributed over the warm black liquor,
initial hot black liquor and cooking stages. When used,
the cool pad or cool liquor accumulator also receives a
white liquor charge. In addition to the use of a
distributed white liquor charge, the present invention
utilizes lower cooking temperatures ranging between
approximately 150°C ~~ 167°C. As a result, pulp is
produced which, upon bleaching with any combination of
bleaching chemicals, is improved in final brightness.
The operational stages for a typical RDH Cooking
System are as follows: (1) chip fill; (2) cool black
liquor fill; (3) warm black liquor fill; (4) hot black
liquor fill; (5) time to temperature; (6) time at
temperature; (7) displacement; and (8) pump out. The
basic principles of RDH operation are described in U.S.
Patent No. 4,578,149 (issued March 25, 1986).
Accordingly, details of RDH operations will be discussed
only to the extent necessary for one of ordinary skill in
the art to appreciate the modifications in the RDH
cooking system, which produce the bleachable grade pulp
described herein.
FIG. 1 schematically illustrates the type of apparatus
for RDH that is used for the digestion of pulp. It should
be understood that this figure illustrates very general
features of the cooking apparatus, and modifications and
WO 95/23891 PCTIUS95I02719 ..r..
6
variations in this system are indeed made as will be discussed in greater
detail
below. Many instrumentalities such as gauges, pressure vents, pumps and
valves have been eliminated from the figures disclosed herein for reasons of
simplicity. FIG. 1 is used to illustrate the existing RDH cooking process and
to
facilitate an understanding of the improvements to the process in accordance
with the principles of the present invention.
Referring to FIG. 1, a digester is illustrated at 10 of the type generally
used in the chemical digestion of wood chips. The digester 10 has a truncated
bottom 12. An inlet valve 14 controls the entry of various reactive liquors
into
digester 10. Although not shown, the contents of digester 10 can be heated to
a final cooking temperature by pumping cooking liquor through a heat
exchanger or steam sparger which is connected to digester 10 by a
valve-controlled line.
After the wood chips are added to digester 10, cool black liquor
(temperature around 70°-95°C) from the cool liquor accumulator
(A tank) 16 is
pumped by means of pump 18 through line 20 which is controlled by a valve 22
into the bottom of the digester 10 through an inlet valve 14. Next, warm black
liquor (temperature between approximately 90°-150°C) from the
warm liquor
accumulator 24 is pumped out by means of a pump 18 through a valve 22 and
through valve 14 into the bottom of digester 10. During this warm liquor fill,
some black liquor is displaced from the digester 10 and then returned by a
line
26 to the cool liquor accumulator 16. Hot black liquor (temperature between
150°-168°C) is then pumped from the hot liquor accumulator (C
tank) 28 by
means of a pump 30 which is controlled by a valve 32 into the bottom of the
digester 10 utilizing valve 14. During the hot fill, black liquor is displaced
from
the digester 10 and returned to the warm liquor accumulator 24 and hot liquor
accumulator 28 through lines 34 and 36, respectively. During the middle of the
hot fill, hot white liquor stored in the hot white liquor accumulator 38 is
pumped
WO 95/23891 PCT/LTS95102719
7
out by means of a pump 30 where it combines with the hot black liquor leaving
the hot liquor accumulator 28, the combined liquors thin passing through a
valve 32 and into the base of the digester 10.
After the hot fill is completed, the inlet and outlet valves to the digester
are closed as the time to temperature stage commences. Steam is injected
into the digester 10 and the temperature is increased to the cooking
temperature, which averages approximately 170°C. The temperature of the
digester is maintained at about this temperature until the wood chips are
digested, depending on white liquor charge and H-factor.
Upon completion of the cooking stage, washer filtrate (temperature
approximately 70 ~ 85°C) stored in a displacement tank (D tank) 40 is
pumped
into the digester 10, utilizing pump 42 and valve 44. The contents are washed
and the digester 10 is cooled. As the washer filtrate is added to the digester
10,
the spent liquors are displaced and returned to the warm liquor accumulator 24
and the hot liquor accumulator 28 by lines 46 and 48, respectively. The
displacement mode is concluded when all washer filtrate is used, which is
based on the dilution factor of the washer. After displacement is completed,
the
digested pulp is then pumped out of the digester 10 to a discharge tank using
pump 50.
With the current RDH cooking system, cooking temperatures of greater
than 170°C are used for rapid cooking, resulting in the acceleration of
condensation reactions. As a result, bleachability problems occurred when the
pulp was subjected to conventional, ECF and TCF bleaching processes. The
present invention overcomes these problems and improves pulp bleachability
by modifying the cooking process for wood chips. This improved RDH process
utilizes a combination of higher alkalinity (or white liquor charge) and lower
cooking temperatures. More specifically, white liquor is added during the warm
WO 95123891 PCT/US95/Q2719
and initial hot fill stages. This is in contrast to the existing RDH cooking
process, wherein white liquor is added only during thecmiddle of the hot fill
mode. Further, when a cool pad is used in the present invention, white liquor
is
added to the cool black liquor leaving the cool liquor accumulator (or A
tank).
Thus, from the beginning of the RDH cooking process until the time to
temperature stage, white liquor is added during each stage to the black
liquor.
The addition of white liquor at every stage, also called white liquor
profiling, is
illustrated in greater detail below in FIGS. 2A, 2B and 2C.
In FIG. 2A, plot A illustrates the addition of a small amount of white liquor
at the beginning of the warm fill mode when warm black liquor leaves the B
tank
or warm liquor accumulator and flows to the digester. White liquor can also be
added to the A tank or cool pad when used. At the end of the hot fill mode,
which utilizes two hot liquor accumulators C1 and C2, the mixture of white and
black liquors remains in the digester. Plot B represents the cooking stage and
illustrates the presence of white liquor in the digester during the actual
cooking
of the chips. Black liquor is also present during the cook.
F1G. 2B illustrates the continuous addition of white liquor to black liquor
at each stage of the cooking process, beginning with the warm fill through the
end of the hot fill mode.
FIG. 2C illustrates the continuous addition of white liquor throughout the
various stages, including the addition of white liquor to the washer filtrate
from
the displacement tank.
The concentration of dissolved organic material in the initial hot fill
operation (C1 and C2 tanks containing black liquor) was compared with and
without white liquor addition during the warm and hot fill operations. FIG. 3
illustrates a Stage 3 RDH system where no white liquor is added during the
. M WO 95123891 PCT/US95/02719
s 2184706
warm and hot fill modes. Only warm black liquor is leaving the warm liquor
accumulator (B tank) 24 to flow through line 56 during~the warm fill mode and
into line 20, which then empties into the digester 10. Although this RDH
system
contains two hot liquor accumulators 28 (C1 tank) and 58 (C2 tank),
respectively, there are RDH pulping processes which utilize only one hot
liquor
accumulator. In practicing the present invention, it is contemplated that the
process of white liquor profiling can be applied to systems having any number
of black liquor accumulators.
As shown in FIG. 3, during the initial hot fill mode, hot black liquor leaves
the hot liquor accumulators 28 and 58 by lines 60 and 62, respectively, and
flows to the digester 10 through lines 64 and 20. During the middle of the hot
fill, hot white liquor from the hot white liquor accumulator 38 mixes with the
hot
black liquor leaving hot liquor accumulator 58 by line 66. The mixture then
flows through lines 64 and 20 and into the digester 10.
FIG. 4 illustrates a Stage 3 RDH System with the addition of white liquor
during the warm and hot fill modes. First, during the warm fill, white liquor
is
added to the warm black liquor leaving the warm liquor accumulator 24 by line
70. The warm fill flows through lines 56 and 20 into the digester 10. Either
cool
or hot white liquor may be used during the warm fill mode. During the initial
hot
fill mode, hot white liquor from the hot white liquor accumulator 38 is mixed
with
black liquor leaving hot liquor accumulator 28 by line 72, and is further
mixed
with the black liquor exiting 'the second hot liquor accumulator 58 by lines
62
and 66. The mixture of hot white and black liquors flows from the two hot
liquor
accumulators 28 and 58 through lines 64 and 20 into the digester 10.
The results of the comparison are as follows:
WO 95!23891 PCT/US95102719
21 ~4~lOb
Without White Liquor Addition at Warm and Hot Fill Operations (FIG. 3)
Initial Hot Fill Operation Total Flow. aallcook Dissolved Organic.
C1 black liquor 20799 13.1
C2 black liquor 8709 14.9
With White Liquor Addition at Warm and Hot Fill Operations (FIG. 4)
White Liquor charges: 1.5% AA at C1 black liquor
1.5% AA at C2 black liquor
Initial Hot Fill eration Total Flow. gallcook Dissolved Organic.
C1 Black liquor 19877 10.1
C2 black liquor 7971 9.8
This case study clearly demonstrates that the concentration of dissolved
organic compounds at initial hot fill operation can be adjusted by adding
white
liquor to the hot fill line. The concentration of dissolved organic compounds
in
the C1 black liquor and in the C2 black liquor decreases from 13.1 % to 10.1
and 14.9% to 9.8%, respectively.
In order to maximize bleachability benefits and extend delignification for
the RDH process, warm black liquor (temperatures between approximately
70°
and 150°C and its strength between 3 and 20 gll AA) and hot black
liquor
(temperatures between approximately 100° and 168°C and its
strength between
8 and 30 gll AA) should be reinforced with any combination of white liquor or
NaOH solution.
As shown in the figures presented above, warm and hot black liquor can
be modified using white liquor profiling. These liquors can also be modified
by
sodium hydroxide (NaOH) profiling. The addition of white liquor or NaOH
W O 95123891 21 ~ 4 7 0 ~ PCTIUS95J02719
11
controls the total dissolved solids (TDS) concentration and black liquor
strength
using any combination of black liquor, white liquor anc~ NaOH. The washer
filtrate displacement stage, in which the black liquor temperature is held
between approximately 50° and 105°C and black liquor strength
between 1 and
18 g/l AA, can be reinforced with any combination of white liquor or NaOH
solution.
By way of example, and not limitation, the following examples serve to
further illustrate the present invention in its preferred embodiments.
As shown below, Tables 1, 1A, 2, 2A, 3 and 3A provide the pulping
results and conditions for a number of cooks used in preparing the RDH pulps
for subsequent bleaching studies. A summary of the pulping results is provided
in Table 3B.
TABLE 1
RDH Pulp i~gi Conditions and Results - "Best Case"
Post Post Post Post
Cook NumberR1 R1 R2 R2 R3 R3 R4 R4
H factor 937 532 475 452
(TAPPI) 16.0 16.0 ' 16.0 16
to Hot
Fill, a
Sulfidity 30.4 30 30.3 30.
(TAPPI),% 2
on AA
aximum 160 160 160 160
temp, C
Time to 16 20 17 19
max, min
Time at 130 37 60 57
max, min
WO 95123891 PCTItJS95/02719
12
Kappa, 7.2 8.9 9.2 9.8
unscreened
Kappa, 7.1 8.2 8.8 a 9.3
screened
Total 46.3 47.3 48.2 1.7
yield,%
Total 0.9 1.2 1.4 1.7
rejects,%
Screened 45.4 46.1 46.8 46.
vield,%
iscosity,0 26 39 40.7 44.
.5% CED,
cp
End of Cook
Residual:
AA(Na20), 28.2 31.6 32.9 31.
g/L 6
EA (Na20), 21.1 24.2 24.2 24.
g/L 2
14.
Na2S 14.3 14.9 17.4 9
(Na20),
g/L
TTA(Na20),g
/L
Solids,% 14.8 15.9 16.7 16.
8
Solids.g/L 161 ~ 173 183 185
Sulfidity 51 47.1 52.9 47.
%
on A.A. 1
Hot liquor 18 18 18 18
charge,
L
Charge 13 14 13 13
time, min
Temperature
C
Top 130 127 127 128
Bottom 145 141 141 141
~K,. WO 95123891 PCT/US95102719
13
Chemical
Coaditions
in Accumulator:
(Na20), 22.9 20.6 25.7 21.7 29.2 e24.627. 23.6
g/L 3
EA (Na20),16.1 15.1 1B.1 16.1 20.2 18.3 19. 17.9
g/L 8
Na2S 13.7 11 15.2 11.2 18 12.7 14. 11.4
(Na20), 9
g/L
TTA (Na20),- - - - - - - -
g/L
Sulfidity,59.4 53.4 59.1 51.6 61.6 51.2 54. 48.3
on A.A. 9
Solids,% 9.5 10.5 11.1 11.9 11.9 13.6 12. 13.6
7
Solids, 99.8 111 118 127 127 146 137 146
g/L
Total 45 43 41 42
elapsed
time, min*
* includes heating time to 145C and time at 145C after initial hot black
liquor injection and final hot
BIL with WIL mix.
TABLE 1A
RDH Pulging Conditions and Results - "Best Case"
Cook Post Post Post Post
Number R1 R1 R2 R2 R3 R3 R4 R4
White 6.04 5.65 5.53 5.52
liquor
charge,L
Hot B/L,L 5 4.13 5.5 5.8
Charge 11 11 9 9
time, min
Temperatur
e, C
Top 140 139 140 139
Bottom 141 141 144 143
WO 95123891 ~, 8 4 7 0 b PCTIUS95102719
14
Chemical in (TAPPI)
conditions accumulator:
(Na2o) 98 99.2 10~. 101.
, 2 ~ 5
g/L
EA(Na20) 83.1 84.3 85.8 86.2
g/L
Na2S - - - -
(Na20)
,
g/L
TTA
(Na20),
g/L
Sulfidity,30.4 30 30.3 30.2
%on AA
Chip 3,700 3,500 3,50 3,50
charge, 0 0
g
Chip 37.3 37.3 37.3 37.3
oisture,
O.D. 62.7 62.7 62.7 62.7
Solids,
warm
Liquor
charge, 24.7 24 24 24
L
Exit pH, 12.8 13.5 13.3 13.3
initial
Charge 15 15 15 15
time,
min
Temperatur
e, C
Top 100 104 102 100
Bottom 113 112 111 112
Chemical in
conditions Accumulator:
(Na20), 23.6 16.4 26.4 17.7 25.719.2 28.5 21.1
g/L
EA (Na20),16.4 10.5 17.4 11.5 18 12.4 18.6 13.6
g/L
Na2S 14.3 11.8 18 12.4 15.513.6 19.8 14.9
(Na20),
g/L
TTA - - - - -
(Na20),
g/L
Sulfidity,60.8 71.7 68.3 70.2 60.371 69.5 70.6
on A.A.
WO 95/23891 PCTIUS95102719
Solids,% 9 9.25 13.6 12.4 14.3 13.1 14.1 13.1
Solids, 94.3 96.4 147 131 155 141 152 141
g/L
Total 40 31 34 33
elapsed
time, min*
Displaceme32 32 32 32
nt Volume,
L
Charge 26 26 26 26
time, min
Chemical
Coaditioas
in accumulator:
(TAPPI)
(Na20), 9.5 10.1 9 10.1
g/L
EA (Na20),9.5 10.1 9 10.1
g/L
Na2S - - - -
(Na20),
g/L
TTA
(Na20),
g/L _ _ _ _
Sulfidity,0 0 0 0
% on A.A.
includes fill time, heating time to 120C and time at 120C after warm fill.
TABLE 2
RDH Pul~g Conditions and Results - "Baseline Case"
Cook Post Post Post Post
Number R5 R5 R6 R6 R7 R7 R8 R8
H factor 1 765 831 832
16
1
AA 10. 10.0 10.0 10.0
(TAPPI) 0
to
Hot Fill,
Sulfidity 30. 30.3 30.3 30.2
(TAPPI),% 2
on AA
WO 95/23891 PCT/US95102719
16
Maximum 170 170 170 170
temp, C
Time to 23 27 21 ' 21
max, min
Time at 62 35 41 42
max, min
Kappa, 7.6 9.7 9.5 8.9
unscreene
d
Kappa, 7.2 9.1 8.9 8.8
screened
Total 47. 48.3 48.6 49.1
yield, 3
%
Total 1.1 1.6 1.7 1.4
rejects,
Screened 46. 46.7 46.9 47.7
yield, 2
%
Viscosity,19. 33.2 33.3 32.2
0.5% 5
CED, cp
End of
Cook Residual:
AA(Na20) 27. 25.4 26 25.4
9IL 9
EA 19. 18 17.4 17.4
(Na20), 2
g/L
Na2S 17. 14.9 ~ 17.4 16
(Na20), 4
g/L
TTA(Na20
), g/L
Solids,% 19 19.1 19.2 19.1
Solids,g/L210 211 213 210
Sulfidity 62. 58.3 66.2 63
on A.A. 4
WO 95/23891 PCTIUS95I02719
~1~4706
Hot liquor18 18 18 18
charge,
L
Charge 12 13 12 13
time, min
Temperatu
re, C
Top 135 137 137 135
Bottom 153 153 154 155
Chemical
conditions
in Accumulator:
AA(Na20) 30. 23.6 26 21.1 26.7 20.5 26.4 20.5
g/L 4
EA 22. 16.2 18.6 14.3 18 13.6 18.3 13.6
(Na20), 3
g/L
Na2S 16. 14.9 14.9 13.6 17.4 13.6 16.1 13.6
(Na20), 1
g/L
_ _ _ _ _ _ _ _
(Na20),
g/L
Sulfidity,53. 63.6 56.9 64.5 65.2 67.3 61.4 67.3
on A.A. 3
Solids, 16. 17 17.2 17,1 17 17.3 17 16.9
%
7
Solids, 183 185 189 187 187 189 186 184
g/L
Total 46 44 45 44
elapsed
time, min
~"
* includes heating time to 155C and time at 155C after initial hot black
liquor injection and final hot
B/L. with WIL mix.
WO 95/23891 PCTIUS95/02719
18
TABLE 2A
RDH Purina Conditions and Results - "Baseline Case"
Cook Post Post Post Post
Number R5 R5 R6 R6 R7 R7 R8 R8
ite 3.47 3.45 3.46 3.47
liquor
charge,L
Hot 5.4 7 5.6 5
B/L,L
Charge 9 9
time,
min
Tempera-
ture,
C
Top 151 152 151 151
Bottom 149 147 145 144
Chemicalconditions in (TAPPI)
accumulator:
100.8 101.4 101.2 100.
(Na20), 8
g/L
EA(Na20) 85.6 86 85.9 85.6
g/L
Na2S - - - -
(Na20),
g/L
TTA 121.6 122.8 123.1 120.
(Na20), 6
g/L
Sulfidit 30.2 30.3 30.3 30.2
y, %
on
cuTV Rf:E & R RIHS~:
f'HA LIQUO PA~
Chip 3,500 3,500 3,500 3,50
charge,
0
g
Chip 37.3 37.3 37.3 37.3
Moisture
O.D. 62.7 62.7 62.7 62.7
Solids,
WO 95123891 PCTIUS95102719
21$x.7 pb
19
arln 24.4 25 25.2 24
Liquor
charge,
L
Exit 13.1 13.3 13.5 13.3
pH,
initial
Charge 15 15 15 15
time,
min
Temper-a
ture,
C
Top 109 109 106 106
Bottom 121 120 118 116
Chemical PPI)
conditions
is Accumulator:
(TA
(Na20) 28.1 19.2 27.9 18.6 26.7 19.2 26.7 19.7
g/L
EA 18.3 12.4 18 11.2 18 11.8 18.6 12.1
(Na20),
g/L
Na2S 19.6 13.6 19.8 14.9 17.4 14.9 16.1 15.1
(Na20),
g/L
Sulfidit69.8 70.8 71 79.6 65.2 77.1 60.7 77.2
y, %
on
.A.
Solids, 14.5 15,.4 15 16 14.7 15.5 14.6 15.9
Solids, 157 167 164 173 159 168 158 172
g/L
Total 35 33 31 30
elapsed
time,
min*
Displace32 32 32 32
-ment
olume,
L
Charge 26 26 26 26
time,
min
Chemical
Conditions
in accumulator:
4.3 4.31 4.3 4.3
(Na20),
g/L
EA 3.7 3.7 3.7 3.5
(Na20),
g/L
WO 95123891 PCTIUS95102719
2~
Na2S 1.24 1.24 1.24 1.74
a
(Na20),
g/L
Sulfidit27.9 27.9 27.9 27.9
y, %
on
.A.
Solids, 9.7 10.6 10.4 10.3
Solids, 102 112 109 108
g/L
* includes fill time, heating time to 120C and time at 120C after wane fill.
TABLE 3
RDH Pulping ~'~~''~'+~nnc anti RPCnItS - "Best Do-able Case"
Cook Number Post Post Post Post
R9 R9 R10 R10 R11 R11 R12 R12
H factor 484 558 483 494
(TAPPI) 18.9 16.0 16.0 16
to Hot
Fill,
Sulfidity 30.6 30.2 29.8 30.4
(TAPPI),%
on AA
i 160 160 160 160
mum
ax
temp, C
Time to 20 20 18 16
ax, min
Time at 60 72 62 63
max, min
Kappa, 9.1 8.9 9.6 10
unscreened
Kappa, 8.1 8.5 9.2 9.3
screened
Total 48.1 48.1 49.1 49.1
yield,%
Total 1.1 1.2 1.5 1.3
rejects,%
Screened 47 46.9 47.6 47'8
yield,%
Viscosity,033.5 33 39.3 32.1
.5% CED,
cp
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21
End of
Cook Residual:
(Na20), 37.6 32.8 34.1 ~ 33.5
g/L
EA (Na20),28.6 25.3 25.9 25.3
g/L
Na2S 17.9 15.2 16.4 16.4
(Na20),
g/L
Solids,% 18.8 19.1 19.2 19.3
Solids, 210 212 215 214
g/L
Sulfidity 47.9 45.7 , 48.1 49
%
on A.A.
Hot liquor18 18 18 18.7
charge,
L
Charge 13 13 13 13
time, min
Temperature
C
Top 129 132 132 132
Bottom 145 147 147 145
Chemical
conditions
in Accumulator:
(Na20), 27.8 25.9 27.3 25.3 27.1 24.6 26.5 23.4
g/L
EA (Na20),19.9 18.9 19.9 18.3 20.2 18.3 19.5 17
g/L 7
Na2S 15.8 13.4 14.9 13.9 13.9 12.6 13.9 12.6
(Na20),
g/L
TTA (Na20),- - - - - - - -
g/L
Sulfidity,56.8 54.1 54.2 55.3 50.9 51.2 52.3 54.7
on A.A.
Solids,% 16.2 16.1 16.7 16.7 1? 17.2 17.3 17
Solids, 177 176 182 183 187 189 190 186
g/L
Total 42 42 42 39
elapsed
time, min*
* includes heating time to 145C and time at 145C after initial hot black
liquor injection and final hot
BIL with WIL mix.
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22
TABLE 3A
F3DH P~~i_na Conditions and Results - "Best Do-able Case"
Cook Post Post Post Post
Number R9 R9 R10 R10 R11 R11 R12 R12
White 6.17 5.81 5.79 5.6
liquor
charge,L
Hot 4.8 5.2 5.0 6.4
B/L, L
Charge l0 10 10
time,
in
Tempera-
ture,
C
Top 139 140 139 141
Bottom 139 145 140 144
Chemical
conditions
in accumulator:
(TAPPI)
107.3 96.4 96.7 100
(Na20),
g/L
EA(Na20) 90.8 81.8 82.3 84.8
g/L
TTA 125.8 115.6 117.8 120.
(Na20),
g/L
Sulfidit 30.6 30.2 29.8 30.4
y, % on
Chip 3,500 3,500 3,500 3,50
charge, 0
g
Chip 37.3 37.3 37.3 37.3
oisture
%
O.D. 62.7 62.7 62.7 62.7
Solids,
WO 95/23891 PCTIUS95/02719
2184706
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arm 24.5 24.3 23.9 24.2
Liquor
charge,
L
Exit 13.3 13.2 13.2 13
pH,
initial
Charge 15 15 15 15
time,
min
Tempera-
ture
, C
Top 108 106 104 108
Bottom 121 117 116 118
Chemical
conditions
in Accumulator:
(TAPPI)
(Na20) 27.1 21.1 26.5 21.1 26.5 20.8 25.9 20.8
g/L
EA 20.5 14.5 18.9 14.1 18.3 13.3 17.7 13.3
(Na20),
g/L
Na2S 13.3 13.3 15.2 14.1 16.4 15.2 16.4 15.2
(Na20~,
g/L
Sulfidit48.7 62.6 57.4 66.4 61.9 72.1 63.3 72.1
y, %
on
.A.
Solids, 14.3 14.9 14.8 15.8 15.6 16.1 15 15.6
Solids, 155 161 162 171 170 176 163 170
g/L
Total 30 30 31 30
elapsed
time,
min*
Displace32 32 32 32
-ment
Volume,
L
Charge 26 26 26 26
time,
min
WO 95/23891 PCT/US95/02719
24
Chemical
Conditions
in accumulator:
(TAPPI)
-.
9.5 9.8 8.B 11.4
(Na20),
g/L
EA 8.2 9.2 8.2 10.7
(Na20),
g/L
Na2S 2.5 1.3 1.3 1.3
(Na20),
g/L
Sulfidit 31.7 13 14.6 13.1
y, % on
.A.
Solids, 10.3 10.6 11.2 -
%
Solids, 109 112 118 -
g/L
' includes fill time, heating time to 120C and time at 120C after warm fill.
TABLE 3B
PULPING STUDY SUMMARY
COOK NUMBER
BEST COOK: NEW RDH COOKING PROCEDURE R3 R4
BASELINE COOK: OLD RDH COOKING PROCEDURER7 R8
BEST DO-ABLE COOK: MODIFIED NEW RDH R12
COOKING
PROCEDURE
COOKING CONDITIONS
WO 95/23891 PCTIUS95102719
R3 R4 R7 R8 R12
WARM FILL
EA (g/1) as 18 18.6 18 18.6 Q17.7
Na20
Solids, % 14.3 14.1 14.7 14.6 15
HOT FILL
EA (g/1) Na2020 19.8 18 18.3 19.6
Solids, % 11.9 12.7 17 17 17.3
COOKING STAGE
Charge, 'k 16 16 10 10 16
H-FACTOR 475 452 831 832 494
MAXIMUM TEMP.160 160 170 170 160
DEGREE C
DISPLACEMENT
EA (g/1) as 9 10.1 3.7 3.5 10.7
a20
[Solids, % 0 [ 0 10.4 10.3 10
I
The following definitive pulps were produced for the bleaching study:
Case Cook No. Kappa Brightness, TAPPI
"Best" R3 8.8 45.3
R4 9.3 45.0
"Baseline" R7 8.9 40.6
R8 8.8 41.3
"Best Do-able"R 10 8.5 41.5
R1 1 9.2 40.8
R12 9.3 41.5
Five RDH pulps (R3, R4, R7, R8 and R12) were bleached using an
(O)(D100)(EO)(D) sequence. However, each of the five RDH pulps were first
oxygen delignified in stirred reactors using the conditions shown below in
Table
4.
WO 95123891 PCT/US95/02719
26
TABLE 4
OXYGEN DELIGNIFICATION CONDITIONS
"Do-able
;gPSt Basel,'-ne "
Case Case Best
Case
Sample R3 R4 R7 RB R12
identification
Species Aspen Aspen Aspen Aspen Aspen
Cook type RDH RDH RDH RDH RDH
Kappa g.8 9.2 8.9 8.8 9.3
Viscosity, mPa.s40.7 44.9 33.3 32.2 32.1
Until. 45.3 45 40.6 41.3 41.5
brightness,
O-Staae~ 95
~sig, 99C.
12% cons.
NaOH, % 2 2 2 2 2
02 time, min 60 60 60 60 60
Final pH 12.8 12.9 12.5 12.5 12.3
Kappa 4.7 5.2 4.7 4.5 5
Viscosity, mPa.s14.4 13.8 12.6 13.6 12.5
Kappa reduction,46.6 43.5 47.2 48.9 50
Yield on raw 95.2 95.8 94.3 98.8 94.4
stock, %
For the bleaching studies, a 0.225 kappa factor was used in calculating
the chlorine dioxide charge in the D100-stage for pulps R3, R7 and R12. A 0.27
kappa factor was used for pulps R4, R8 and R12. Tables 5 through 10 below
show the (D100) (Eo)(D) bleaching conditions and results on the oxygen
delignified pulps from these cooks. The chlorine dioxide solution
concentration
was adjusted by a 0.92 factor to compensate for losses of chlorine dioxide in
charging the reactors and polyethylene bags during bleaching.
WO 95/23891 PCT/LTS95/02719
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TABLE 5
Kappa factor = 0.225
Sample identification R3
Species Aspen
Cook type RDH
02 Pulp Kappa 4.7
iscosity, 14.4
mPa.s
0 0
Chlorination 0.23
factor
C102, % as 1.06
available
C12*
ctual C102, 1.15
% as avail.
C1,
Substitution, 100
%
H2S04. % 1.5
Final pH 2
Residual, 0.14
g/L avail.
C1,
0 0
NaOH, % 0.8
02 pressure, 25
psig
02 time, 15
minutes
Final pH 12.4
K No. (25 2.3
M1)
iscosity, 13.7
mPa.s
Yield on 93.5
raw stock,
%
0 0
Sample number#1 #2 #3 #4 #5 #6 #7 #B
C102 as C102,0.1 0.3 0.5 0.7 0.9 1.1 0.9 1.1
%*
ctual C102, 0.11 0.33 0.54 0.76 0.98 1.2 0.98 1.2
% C102
NaOH, % 0 0 0.09 0.16 0.25 0.3 0.33 0.42
H2S04, % 0.1 0.05 0 0 0 0 0 0
Final pH 4 3 3 . 3 2 . 2 ~ 3 ~ 3
. . 3 9 . . .
1 4 6 6 '7
l
WO 95/23891 PCTIUS95102719
28
Residual 0.02 0.01 0.01 0.02 0.02 0.02 0 0
as
C102,
Brightness, 89.7 90.4 91.2 91.5 91.6 ~ 91.1 91.3
92
%ISO
Viscosity, 13.1 - - 11.~ - - - 9.2
mPa.s
' Actual C102 concentration x 0.92
TABLE 6
Em~~~~~o ~~,~+h (Y;;D100y(Eo)(~) on Optimal RDH Pulp
Ka~oa factor = 0.27
Sample identification R4
Species Aspen
Cook type ~H
02 Pulp Kappa 5.2
iscosity, mPa.s 13.8
0 0
Chlorination factor 0.27
C102, % as available 1.4
Clz*
ctual C102, % as avail.1.53
Clz
Substitution, % 100
H2S04, % 2
Final pH 1.9
Residual, g/L avail. 0.09
C12
0 0
NaOH, % 0.8
02 pressure, psig 25
02 time, minutes 15
Final pH 12.5
K No. (25 M1) 2
iscosity, mPa.s 13.3
Yield on raw stock, 92.8
%
WO 95123891 PCTIUS95102719
29
0 0
Sample #1 #2 #3 #4 #5 #6 #7 #8
number o
C102 as 0.1 0.3 0.5 0.7 0.9 1.1 0.9 1.1
C102, %*
ctual C102,0.11 0.33 0.54 0.76 0.98 1.2 0.98 1.2
C102
NaOH, % 0 0 0.09 0.16 0.25 0.3 0.33 0.42
H2S04, % 0.1 0.05 0 0 0 0 0 0
Final pH 4.3 3.4 3.4 3.2 2.8 2.7 3.7 3.5
Residual 0.01 0.01 0.01 0.02 0.01 0.01 0 0
as
C102,
Brightness,89.8 90.5 91.2 91.5 91.8 91.8 91.4 91.5
%ISO
iscosity, 12.5 - - 11.6 - - - 9.8
mPa.s
' Actual C102 concentration x 0.92
TABLE T
Kappa factor = 0.225
Sample identification R7
Species Aspen
Cook type RDH
02 Pulp Kappa 4.5
iscosity, mPa.s 13.6
0 0
Chlorination factor 0.23
C102, % as available Clz* 1.01
ctual C102, % as avail. C1, 1.1
Substitution, % 100
H2S04, % 2
Final pH 2.7
Residual, g/L avail. C12 0.01
WO 95/23891 PCTJUS95102719
P' fi0 min. 74C.
10% cons.
NaOH, % 0.8 c'
02 pressure, 25
psig
02 time, minutes 15
Final pH 12.3
K No. (25 M1) 2.3
iscosity, mPa.s 13.3
Yield on raw 97
stock, %
0 0
Sample number #1 #2 #3 #4 #5 #6
C102 as C102, 0.1 0.3 0.5 0.7 0.9 1.1
%*
ctual C102, % 0.11 0.33 0.54 0.76 0.98 1.2
C102
NaOH, % 0 0 0.08 0.2 0.33 0.42
H2S04, % 0.1 0.05 0 0 0 0
Final pH 4 3.5 3.4 3.4 3.4 3.8
Residual as C102,0 0 0 0 0 0
Brightness, %ISO87.6 88.7 89.7 90.3 90.3 90.6
Viscosity, mPa.s12.6 - - 11.4 - 9.6
' Actual C102 concentration x 0.92
TABLE 8
Bleaching ~rs ith (.Ol(D1 Q~~(Eo~(D_)~ on Baseline RDH Pulp
Kappa factor = 0.27
Sample identification R8
Species Aspen
Cook type ~H
02 Pulp Kappa 4.7
Viscosity, mPa.s 12.6
0 0
Chlorination factor 0.27
C102, % as available C12* 1.27
ctual C102, % as avail. 1.38
C12
WO 95!23891 PCTIUS95/02719
21 gq~~70g
31
Substitution, 100
%
H2S04, % 2
Final pH 1.9
Residual, g/L 0.07
avail. C1~
0 0
aOH, % 0.8
02 pressure, 25
psig
02 time, minutes 15
Final pH 12.2
K No. (25 M1) 2.1
iscosity, mPa.s 12.6
Yield on raw 94.2
stock, %
0 0
Sample number #1 #2 #3 #4 #5 #6
C102 as C102, 0.1 0.3 0.5 0.7 0.9 1.1
%*
ctual C102, 0.11 0.33 0.54 0.76 0.98 1.2
%
C102
NaOH, % 0 0 0.08 0.2 0.33 0.42
H2S04, % 0.1 0.05 0 0 0 0
Final pH 3.6 3.1 3.1 3.1 3.2 3.6
Residual as 0 0 0 0 0 0
C102,
Brightness, 87 88.7 89:3 90.1 90.5 90.5
%ISO
iscosity, mPa.s12.2 - - 11.2 - 9.5
' Actual C102 concentration x 0.92)
WO 95123891 PCT/US95/02719
32
TABLE 9
Blea~hing with~0)(D100)lEo~(D) on Best "Do-able" R~'JH Puln
Kappa factor = 0.225
Sample identification R12
~
Species Aspen
Cook type ~H
02 Pulp Kappa 5
iscosity, mPa.s 12.5
0 0
Chlorination 0.03
factor
C102, % as available 1.13
Clz*
ctual C1O2, % 1.22
as avail. C12
Substitution, 100
%
H2S04, % 1.5
Final pH 2
Residual, g/L 0.04
avail. C1z
0 0
NaOH, % 0.8
02 pressure, 25
psig
02 time, minutes 15
Final pH 12.7
K No. (25 M1) 2.3
Viscosity, mPa.s 11.9
Yield on raw -
stock, %
o i o
Sample number #1 #2 #3 #4 #5 #6
C102 as C102, 0.1 0.3 0.5 0.7 0.9 1.1
%*
ctual C102, % 0.11 0.33 0.54 0.76 0.98 1.2
C102
NaOH, % 0 0 0.08 0.2 0.33 0.42
H2S04, % 0.1 0.05 0 4 0 0
Final pH 4.1 3.7 3.4 3.4 3.4 3.3
Residual as C102,0.01 0.01 0.01 0.01 0.01 0.01
Brightness, %ISOB8.9 90 90.8 91 91.6 91.8
Viscosity, mPa.s11.9 - - 10.5 - 9~4
" Actual C102 concentration x u.S~
WO 95123891 PCT/LTS95I02719
218 4706
33
TABLE 10
Bleaching with (O)(D100)(Eo)(D) on Best "Do-able" RDH PuIR
Kappa factor = 0.27
Sample identification R12
Species Aspen
Cook type RDH
02 Pulp Kappa 5
Viscosity, mPa.s 12.5
0 0
Chlorination 0.03
factor
C102, % as available 1.35
C12*
ctual C102, 1.47
% as avail.
ClZ
Substitution, 100
%
H2S04, % 2
Final pH 2.3
Residual, g/L 0.08
avail. C1,
0 0
NaOH, % 0.8
02 pressure, 25
psig
02 time, minutes 15
Final pH 12.6
K No. (25 M1) 2.2
iscosity, mPa.s 12.2
Yield on raw -
stock, %
0 0
Sample number #1 #2 #3 #4 #5 #6
C102 as C102, 0.1 0.3 0.5 0.7 0.9 1.1
%*
ctual C102, 0.11 0.33 0.54 0.76 0.98 1.2
%
C102
NaOH, % 0 0 0.08 0.2 0.33 0.42
H2S04, % 0.1 0.05 0 0 0 0
Final pH 3.9 3.4 3.3 3.3 3.3 3.2
Residual as 0.01 0.01 0.01 0.01 0 0.01
C102,
%
Brightness, 88.9 90 90.8 91.1 91.5 91.8
%ISO
Viscosity, mPa.s12.4 - - 10.7 - 9.5
Actual C102 concentration x 0.92
WO 95123891 PCT/US951G2719
34
As shown in FIGS. 5 and 5A, the use of a higher kappa factor did not
appear to reduce the D1-stage chlorine dioxide requirements. The best case
RDH pulps (R3 and R4) produced 1.5 to 2 points higher brightness than the
baseline case RDH pulps (R7 and R8) at equivalent chlorine dioxide charges.
From FIGS. 6 and 6A, it is shown that the best do-able case RDH pulp
(R12) produced intermediate brightness between the best case RDH pulp (R3)
and the baseline case RDH pulp (R7).
FIGS. 7 and 7A show that the best do-able case RDH pulp (R12) gave
intermediate brightness between the best case RDH pulp (R4) and the baseline
case RDH pulp (R8).
From the pulp bleaching studies, a summary of the results is shown
below in Table 11. The easiest pulps to bleach were the best case pulps. The
most difficult to bleach were the baseline case pulps with the bleachability
of the
best do-able case falling between the first two cases. Results indicated that
a
combination of high alkalinity (white liquor addition at the warm and hot fill
mode
plus cooking stage, AA charge between 15% AA and 35% AA) and a low
cooking temperature (approximately 150°C ~ 167°C) improves pulp
bleachability and, thus, final brightness of pulp. It should be noted that the
black liquor strength during the RDH cook should be maintained.
WO 95123891 PCTIUS95/02719
TABLE 11
BLEACHING STUDY SUMMARY
COOK NUMBER
BEST COOK: NEW RDH COOKING PROCEDURE R3 R4
BASELINE COOK: OLD RDH COOKING R7 R8
PROCEDURE
BEST DO ABLE COOK: MODIFIED NEW RDH R12
COOKING PROCEDURE
BLEACHING RESULTS
KAPPA 0.225 IN THE D (900% CI02 SUBSTITUTION)
FACTO
R
FINAL BRIGHTNESS, % lS0
CI02
CHARGES
IN THE
LAST
D STAGE,
0.1 0.3 0.5 0.7 0.9 1.1
R3 89.7 90.4 91.2 91.5 91.6 92
(BEST
COOK)
R12 88.9 90 90.8 91 91.6 91.8
(BEST
DO-
BLE)
R7 87.6 88.7 89.7 90.3 90.3 90.6
(BASE-
LINE)
KAPPA
FACTOR 0,27 IN THE D (700% CI02 SUBSTITUTION)
FINAL BRIGHTNESS, % ISO
WO 95/23891 PCTIUS95102719
36
C102
CHARGES
IN THE
LAST
D~,STAGE,
0.1 0.3 0.5 0.7 0.9 1.1
R4 89.8 90.5 91.2 91.5 91.8 91.8
(BEST
COOK)
R12 88.9 90 90.8 91.1 91.5 91.8
(BEST
DO-
BLE)
Rg 87 88.7 89.3 90.1 90.5 90.5
(BASE-
LINE)
It should be understood the various changes and modifications to the
presently preferred embodiments described herein will be apparent to those in
the art. Such changes and modifications can be made without departing from
the spirit and scope of the present invention and without diminishing its
attended advantages. It is, therefore, intended that such changes and
modifications be covered by the appended claims.
