U.S. patent application number 10/564373 was filed with the patent office on 2006-08-10 for batch process for preparing pulp.
This patent application is currently assigned to Metso Paper Inc.. Invention is credited to Seppo Martikainen, Mikael Svedman, Panu Tikka, Olli Timonen.
Application Number | 20060175029 10/564373 |
Document ID | / |
Family ID | 29763617 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060175029 |
Kind Code |
A1 |
Martikainen; Seppo ; et
al. |
August 10, 2006 |
Batch process for preparing pulp
Abstract
According to the invention, polysulfide is used in the
manufacture of kraft pulp in the initial stage of a displacement
batch process in order to improve the yield. Polysulfide-containing
white liquor is added inter-mixed with the first liquor charged to
the digester, or as a separate charge before the impregnation
liquor is introduced. Preferably, a cooking catalyst, e.g.
antraquinone, is added to the white liquor charge as the cooking
stage commences.
Inventors: |
Martikainen; Seppo;
(Kallaanvaara, FI) ; Tikka; Panu; (Espoo, FI)
; Timonen; Olli; (Rauma, FI) ; Svedman;
Mikael; (Vasa, FI) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,;KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Assignee: |
Metso Paper Inc.
Box 1220
Helsinki
FI
FIN-00101
|
Family ID: |
29763617 |
Appl. No.: |
10/564373 |
Filed: |
December 22, 2004 |
PCT Filed: |
December 22, 2004 |
PCT NO: |
PCT/FI04/50196 |
371 Date: |
January 12, 2006 |
Current U.S.
Class: |
162/37 ; 162/19;
162/39; 162/52 |
Current CPC
Class: |
D21C 3/222 20130101;
D21C 11/0021 20130101; D21C 3/02 20130101; D21C 1/06 20130101; D21C
3/26 20130101 |
Class at
Publication: |
162/037 ;
162/019; 162/039; 162/052 |
International
Class: |
D21C 3/02 20060101
D21C003/02; D21C 3/26 20060101 D21C003/26; D21C 1/06 20060101
D21C001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 31, 2003 |
FI |
20031929 |
Claims
1. A batch process for the preparation of kraft pulp with improved
yield from lignin-containing cellulosic material, comprising the
steps of filling and pressurizing a vessel containing cellulosic
material with impregnation liquor collected from a previous batch,
said impregnation liquor admixed with, or preceded by an addition
of, a volume of polysulfide white liquor; impregnating the
cellulosic material with the resulting mixture of impregnation
liquor; displacing the impregnation liquor with hot spent cooking
liquor; reacting the impregnated cellulosic material with said hot
spent liquor; displacing hot spent cooking liquor with a volume of
hot white liquor and cooking the cellulosic material with said
white liquor to a desired degree of delignification; displacing the
liquor used for cooking.
2. The process of claim 1, wherein the amount of polysulfide white
liquor added corresponds to 25-90% of the total active alkali
dosage for the batch.
3. The process of claim 1, wherein the amount of polysulfide white
liquor added corresponds to 50-75% of the total active alkali
dosage for the batch.
4. The process of claim 1, wherein the polysulfide dosage
corresponds to 0.5-5% relative to abs. dry wood.
5. The process of claim 1, wherein the volume of polysulfide white
liquor is added separately to the digester before the impregnation
liquor.
6. The process of claim 1, wherein an amount of cooking catalyst is
added to the hot white liquor.
7. The process of claim 6, wherein the cooking catalyst is
anthraquinone, anthraquinone sulfonate, hydroantraquinone or a
redox-catalyst derivative thereof.
8. The process of claim 1, wherein hot spent liquor displaced from
the digester is collected in a single hot liquor tank.
9. The process of claim 1, wherein after the cook is finished, a
volume of impregnation liquor is introduced into the digester as
the first volume of displacement liquor.
10. The process of claim 1, wherein a volume of impregnation liquor
is transferred from an impregnation liquor tank to a hot spent
cooking liquor tank.
11. The process of claim 10, wherein the digester system comprises
two hot spent liquor tanks.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process fir preparing
kraft pulp in which lignocellulosic material is treated with
recycled process liquors, polysulfide and fresh re-causticized
white liquor for removing lignin therefrom. More particularly, the
present invention relates to the use of polysulfide white liquor
(or another polysulfide source) in the early stages of modern
displacement kraft batch cooking, and the advantage thereof in
terms of improved pulp yield.
BACKGROUND OF THE INVENTION
[0002] In the various kraft pulping processes, lignocellulosic
material, most commonly wood chips, is generally treated at
elevated temperatures with alkaline cooking liquor containing
sodium hydroxide and sodium hydrogen sulfide, called white liquor.
In these processes a significant part of the cellulosic material,
especially hemicelluloses, are partly lost due to reactions with
the white liquor. In kraft pulping conditions hemicelluloses
undergo alkaline peeling reactions, de-polymerization, in which the
hemicelluloses are dissolved as organic acids into the cooking
liquor. A known fact is that by a polysulfide treatment,
hemicelluloses are stabilized and are thereafter more resistant to
cooking liquor in kraft cooking conditions, which leads to higher
yield from the processes lignocellulosic substance input.
[0003] In kraft pulping processes, fresh cooking liquor is obtained
from the recovery furnace's inorganic smelt, which is dissolved in
water and causticized to produce white liquor.
Polysulfide-containing white liquor is obtained from causticized
white liquor by various processes, which partially oxidize the
liquor's sodium sulfide into polysulfide. These processes typically
use oxidation catalysts to polymerize the white liquor's hydrogen
sulfide. Also, polysulfide can be produced directly by elemental
sulfur addition into white liquor. Polysulfide-containing white
liquor is called polysulfide white liquor or orange liquor.
[0004] The use of polysulfide white liquor has been quite
straightforward in conventional kraft cooking operations. The
normal white liquor has been converted to polysulfide white liquor,
and that liquor has been used in the same manner as normal white
liquor. After the impregnation into the wood chips in the digester
and during the temperature rise to above 100.degree. C., the
polysulfide has reacted with the carbohydrates making them less
vulnerable to alkaline degradation. Later during the cook, when
temperature has risen over 140.degree. C., the rest of the
polysulfide has rapidly broken down through thermal decomposition.
As all the conventional cooking systems have used cooking liquors
having initial temperatures well below 100.degree. C. and the
temperature in the digester has been elevated slowly or in steps,
the polysulfide has had the possibility to react and facilitate
higher pulp yield.
[0005] However, the development of the batch cooking systems has
caused a major deviation from the conventional cooking technology:
White liquor is introduced into the digester as "hot white liquor",
which has been heated up using the heat of the previously generated
spent liquor, and steam. For the purpose of this disclosure, "hot"
is meant to designate a liquor having a temperature above its
boiling point at ambient pressure, i.e. a liquor that must be
stored in a pressurized vessel.
[0006] The hot white liquor temperature in typical displacement
batch cooking is 140-180.degree. C. From the displacement batch
process point of view, polysulfide has been an impossible chemical.
Polysulfide is unstable at higher temperatures, for instance at
those used in kraft cooling; the chemical begins to break down at
temperatures above 100.degree. C., and it degrades completely in a
few minutes at 150.degree. C. Thus at the typical process
temperature of the hot white liquor, polysulfide white liquor is
not stable at all. This fact has disabled the use of polysulfide in
the modern displacement kraft pulping processes developed for
higher energy and chemical economy and improved pulp quality.
[0007] During the early 80's, new energy efficient kraft batch
processes using various liquor displacements emerged.
Characteristic for the displacement kraft batch process is to
recover hot black liquor from the end of the cooking by
displacement and then re-use the energy in the subsequent batches.
Partly this is done by using the hot spent cooking liquor as such,
and partly by heating the white liquor with the heat of the hot
spent liquor leaving the digester system or collected for re-use at
low temperature. This process arrangement leads to high
temperatures m the input liquor accumulators. A low temperature
white liquor, typically at 80.degree. C. in the storage tank after
re-causticization, cannot be used anymore, and the environment for
stable polysulfide in the white liquor does not exist anymore.
[0008] Good examples of the development of displacement batch
processes are given in, e.g., Fagerlund, U.S. Pat. No. 4,578,149
and Ostman, U.S. Pat. No. 4,764,251. A further characteristic
feature of a modern displacement batch process is to combine energy
efficiency and efficient use of residual and fresh cooking
chemicals to achieve, in addition to energy efficiency, high pulp
strength and good delignification through hydroxyl and hydrosulfide
concentration and temperature profiling at different stages of the
cooking cycle (Hiljanen, Tikka, EP-B 520 452, Tikka, U.S. Pat. No.
5,183,535).
[0009] The strive for higher pulp yield is easy to understand. It
is always more profitable to produce more pulp from a certain wood
amount. The pulping industry has faced increasing environmental
pressure to radically cut down environment-polluting effluents.
Reduction of the organic effluents from pulp bleaching requires
kraft cooking to be extended to yield much lower residual lignin
concentration in the pulp than before. Extended cooking means more
carbohydrate losses. In order to enable extended cooking while
improving energy economy and pulp quality, one popular option for
the industry has been to use modern displacement batch cooking
technology. In spite of all the advantages of this technology, it
has not been possible to take the pulp yield advantage by using
polysulfide white liquor. The present invention overcomes these
problems and enables an efficient use of polysulfide by a novel
displacement batch cooking process.
[0010] The use of anthraquinone (AQ) as a cooking catalyst is well
known. It acts by reducing carbohydrate end groups, stabilising
them against alkaline peeling and producing anthrahydroquinone,
which is alkali soluble. Anthrahydroquinone reduces lignin, making
it more reactive. In this process, anthraquinone is formed again
and may react with carbohydrates.
[0011] During operation of displacement batch cooking processes, it
has been observed that the properties of the black liquor
originating from the early stages of the cook differ from those of
black liquor from a traditional cook. Recycled black liquor
originating from the early stages of the cooking sequence may
complicate the evaporation of black liquor. A particular problem is
fouling of the surfaces of heat exchangers in the evaporation
plant, leading to a decrease in heat transfer. These evaporator
fouling problems are typically related to calcium. In the early
stage of alkaline cooking, calcium-containing material dissolves
into the black liquor from the lignocellulosic material. In a
traditional cook, the cook proceeds with heating, the temperature
increases and no essential liquor exchange occurs. Then, a major
part of the dissolved calcium-containing material in the cooking
liquor is broken down, calcium carbonate is formed and as a result,
a major part of the calcium is resorbed onto the lignocellulosic
material in the digester. Following such a cooking process,
evaporation of the black liquor can normally be carried out without
problems caused by precipitation of calcium. In contrast, the
evaporation problems with black liquors originating from the early
stages of cooking are typically related to calcium-containing
material dissolved in the early stages of a cook. The dissolved
calcium-containing material has not boon degraded, and the amount
of calcium bound to the dissolved material in the black liquor is
high As disclosed in publication EP 1 242 674, this problem may be
solved by re-introducing liquor having a high calcium precipitating
potential into the digester as a displacement liquor at the end of
a cook. At this point, the digester temperature is sufficiently
high to cause calcium liberation. The calcium is then removed
together with the pulp, and does not enter the evaporation and
regeneration cycle.
SUMMARY OF THE INVENTION
[0012] In accordance with the present invention, a method for
producing pulp using polysulfide white liquor has been provided.
The method involves a kraft batch process which comprises the
addition of polysulfide white liquor in the impregnation and
pretreatment in the very `front-end` of the cooking process, and a
finalizing delignification stage with white liquor and optional
cooking catalyst addition, which is facilitated by the modified
`front-end` process chemistry resulting in improved pulp yield. A
volume of polysulfide white liquor is added as the first portion of
liquor to enter the digester, or admixed with the impregnation
liquor prior to this being pumped into the digester. For the
purpose of this disclosure, "impregnation liquor" means a liquor
stored at a temperature below its atmospheric boiling point, used
for a first immersion of the lignocellulosic raw material in a
batch pulping process.
[0013] In the present invention, lignocellulosic material entering
a displacement batch process is thus pretreated with
polysulfide-containing process liquors in conditions favourable for
pre-treatment and polysulfide stability. A set of displacement
batch process arrangements, capable of taking advantage of the
polysulfide white liquor, are presented. The required dose of fresh
polysulfide white liquor is introduced in the initial stage of the
process. The impregnation stage provides for both impregnation and
polysulfide pretreatment reactions. An impregnation liquor
circulation collects the displaced impregnation liquor which is
re-used to fill and pressurize the digester after the first fresh
liquor fill. As a result, the polysulfide concentration and dosage
remain at a high level, and only the liquor balance excess is left
over to be sent to chemicals recovery or re-use later in the
cooking sequence. The displacement cooking process sequence then
continues with hot fills of black and white liquors, cooking and
final displacement
[0014] An optional feature in the present invention is a new way to
use a cooking catalyst, such as anthraquinone (AQ). As the
generation of polysulfide white liquor decreases the concentration
of hydrosulfide ions, the delignification rate is slower, reducing
cooking capacity. The cooking catalyst can be used to maintain a
normal kraft cooking rate and production level. In the present
invention, the catalyst may be introduced into the digester
together with the hot white liquor. By this means it will not
escape due to displacements, and on the other hand, it arrives in
the hot cooking stage where it is most needed. As a result, the
technical and economical benefits of the displacement batch cooking
are retained, while the advantages of polysulfide and cooking
catalyst can be fully exploited.
BRIEF DESCRIPTION OF THE FIGURES
[0015] FIG. 1 shows a block diagram of a kraft displacement batch
cooling system according to the invention. The top of the figure
defines the required tanks, leaving or entering streams denoted by
letters. The cooking stage sequence is displayed therebelow,
chronologically starting from the top and the vertically indicated
streams representing the liquors passing through the digester
during the various stages. The letters denoting the various
entering and leaving streams correspond to the source or
destination in the tank scheme.
[0016] FIG. 2 shows a further embodiment of a kraft displacement
batch cooking system according to the invention.
DISCLOSURE OF THE INVENTION
[0017] In the following, the method of the invention is disclosed
in detail with reference to the attached FIG. 1. It is understood,
that liquor is charged from the digester bottom and displaced gases
and liquor leave from the top.
[0018] The kraft batch cook is started by charging the digester
with wood chips, or with another lignocellulosic material. After
the lignocellulosic material charge, the digester is filled in a
stepwise sequence using a volume of fresh polysulfide white liquor
X1 from polysulfide white liquor tank 6, and impregnation liquor Al
from tank 4, topping the digester full of liquor. The volume of
polysulfide white liquor may be added as a separate first portion,
forming a raising pad of liquor as further liquor is pumped in from
below. Alternatively, the polysulfide white liquor is mixed into
the impregnation liquor.
[0019] An overflow, A2, conducted to the impregnation liquor tank
4, is preferred in order to remove air and the diluted first front
of liquor. After the flow A2 is stopped, the digester is
pressurized and impregnation is completed during an appropriate
period of time. The cooking process is then continued by pumping in
a volume of hot black liquor B1 from hot black liquor accumulator
1. The cooler impregnation liquor A3, displaced by hot black
liquor, is conducted to impregnation liquor tank 4 to be re-used in
subsequent batches. Pumping a volume C of hot white liquor from
tank 3 into the digester then continues the cooking sequence.
Together with white liquor C, an amount of cooking catalyst may be
dosed into the digester. The liquor D1, displaced by hot liquor
above about the atmospheric boiling point, in conducted to hot
black liquor accumulator 2.
[0020] At the end of the sequence described above, the digester is
close to the final cooking temperature. The final heating-up is
carried out using direct or indirect steam heating and digester
re-circulation. After the desired cooking time when the
delignification has proceeded to the desired final reaction degree,
the spent liquor is ready to be displaced with wash filtrate E1
from tank 5. A volume A4 from impregnation liquor tank 4 may be
used as a first portion of displacement liquor in order to
deactivate the potential scale-forming calcium therein, as
disclosed in EP 1 242 674.
[0021] In the final displacement, the first displaced volume B2
displaced by wash filtrate is conducted to black liquor accumulator
1. The second portion D2 of displaced black liquor, which is
diluted by the wash filtrate but is still above atmospheric boiling
point, is conducted to the hot black liquor accumulator 2. After
completed final displacement, the digester contents are discharged
for further processing of the pulp. The above cooking sequence may
then be repeated.
[0022] The hot black liquor from accumulator 2 is conducted to the
evaporation plant, first being used to heat white liquor due for
tank 3, and/or water, by means of heat exchange.
[0023] Tank 6 is provided for storage of polysulfide white liquor,
supplied from a plant for polysulfide generation.
DESCRIPTION OF PREFERABLE EMBODIMENTS
[0024] In the following, reference is made to the figure described
in the preceding section.
[0025] In the process of the present invention, a volume of
polysulfide white liquor, corresponding to 25-90% of the total
active alkali dosage and resulting in 0.5% to 5% polysulfide dosage
on abs. dry wood is added into the digester before the impregnation
fill is completed Impregnation is carried out using temperature
ofbetween 70.degree. C. and 120.degree. C., preferably between
85-95.degree. C., and a time of between about 20 to about 120
minutes, preferably between about 30 to about 60 minutes, more
preferably between about 25 to about 40 minutes.
[0026] In a preferable embodiment, the polysulfide white liquor is
added as a separate portion before the introduction of further
liquor.
[0027] In a preferable embodiment, the volume of polysulfide white
liquor corresponds to 50-75% of the total active alkali dosage for
the relevant batch.
[0028] In accordance with a particular embodiment of the process of
the present invention, a cooking catalyst is used. Preferable
catalysts are anthraquinone, anthraquinone sulfonate, and
hydroanthraquinone. Any other appropriate redox-catalyst as
anticipated by those skilled in the art may be used.
[0029] In accordance with an alternative embodiment of the process
of the present invention, the following fractions displaced from
the digester [0030] hot cooking spent liquor fraction B2 and [0031]
fractions D1 and D2, which are of lower temperature and poorer in
chemicals, are collected in a single accumulator to be used in the
hot black liquor pretreatment stage.
[0032] In this configuration, hot black liquor accumulators 1 and 2
of FIG. 1 are combined. The black liquor flow to the evaporation
plant is drawn from the single hot black liquor accumulator, the
stream being used to heat, by means of heat exchange, white liquor
heading for white liquor accumulator 3, and/or water, as shown for
tank 2 in FIG. 1.
[0033] If high dosages of polysulfide white liquor are used in the
impregnation stage of the process, longer impregnation times than
in the prior art and/or a two accumulator system and/or
impregnation liquor transfer to hot black liquor tank 1 maybe used
in order to avoid too high a residual alkali concentration in the
feed of the evaporation plant. Thus, in accordance with a further
embodiment of the process of the present invention, shown in FIG.
2, a volume of impregnation liquor from impregnation tank 4 is
conducted to hot black liquor tank 1 to be used in hot black liquor
treatment, B1. The stream from impregnation liquor tank 4 to hot
black liquor tank 1 may be heated by means of heat exchange with
the stream from hot black liquor accumulator 2 to the evaporation
plant In addition to the white liquor charge prior to the cooking
stage, one or more additional white liquor charges may be carried
out during the cook.
[0034] The principal advantage of the process of the present
invention is that the `front-end` of the kraft displacement batch
cooking system is rendered more effective from a chemical point of
view, and in regard to process arrangements. The polysulfide charge
used reflects the improvement in pulp yield from the digested
lignocellulosic material.
[0035] The following examples are illustrative of the invention.
The following abbreviations are used: [0036] WBL Warm impregnation
black liquor [0037] DWBL Displaced WBL (from the digester) [0038]
HBL Hot black liquor [0039] RHBL Displaced HBL (from the digester)
[0040] DCBL Displaced cooking black liquor [0041] WF Wash filtrate
[0042] PSWL Polysulfide white liquor
[0043] Production of a normal `reference` pine kraft pulp using the
displacement kraft batch technique:
[0044] 4.0 kg pine (Pinus sylvestris) chips (oven dry basis) were
metered into a chip basket positioned in a 20-litre jacketed
displacement batch digester. The lid of the digester was closed.
Impregnation black liquor, consisting of wash filtrate and white
liquor (WBL, 80-90.degree. C., 25 gEA/l) was pumped in during app.
10 minutes followed by impregnation at 90.degree. C. under 2.5 bar
overpressure. The duration of the impregnation stage was 40 minutes
(WBL-fill and impregnation in total). After impregnation, a hot
black liquor pre-treatment stage was commenced by introducing hot
black liquor (HBL 1, 150.degree. C., app. 20 gEA/l) to the bottom
of the digester, displacing the spent impregnation liquor (DWBL)
out from the top of the digester. The hot black liquor
pre-treatment stage duration was 30 minutes. After hot black liquor
pretreatment stage, hot white liquor (121 gEA (NaOH)/l, sulfidity
37%) charge was introduced into the digester bottom displacing the
corresponding volume of spent hot black liquor (RHBL) out of the
digester. A 45 minute heat-up sequence with cooking liquor
circulation raised the temperature from 150.degree. C. to the
cooking temperature of 167.degree. C. At 250 H-factors, a white
liquor charge was introduced into the digester bottom displacing
the corresponding volume of spent hot black liquor out of the
digester (DCBL 1). After the cooking time fulfilled the target
H-factor, terminal displacement was started by introducing cool
DWBL and wash filtrate (WF) in a sequence into the digester bottom
displacing the hot spent black liquor out of the digester top (DCBL
2). The fist displaced portion the hot black liquor with the hot
black liquor displaced earlier during the cooking sequence (DCBL
2+DCBL 1) covered the volume needed for the next cook's hot black
liquor (HBL 1). The terminal displacement stage duration was
approximately 40 minutes. After the terminal displacement, the pulp
was disintegrated, washed with deionised water, screened and
analysed. The cooking procedure was repeated and thus equilibrium
in the cooking process was obtained and the cooks started to repeat
themselves corresponding to the industrial batch cooking
system.
[0045] The experimental setup to produce pulp according to the
invention is described below.
[0046] 4.0 kg pine (Pinus sylvestris) chips (oven dry basis) were
metered into a chip basket positioned in a 20-litre jacketed
displacement batch digester. The lid of the digester was closed.
The chips were steamed until the digester temperature was
100.degree. C., approximately 5 minutes. Impregnation liquors were
introduced as sequence as follows: initially polysulfide white
liquor black liquor (PSWL, volume according to the charge, app.
4.5-5 l); subsequently re-circulated spent impregnation liquor
(DWBL) to hydraulically fill the digester. The impregnation fill
sequence took app. 11-13 minutes and was followed by impregnation
at 90.degree. C. under 2.5 bar overpressure. The duration of the
impregnation stage was 40 minutes (fill sequence and impregnation
in total). After impregnation, a hot black liquor pre-treatment
stage was carried out by introducing hot black liquor (HBL 1,
150.degree. C., app. 20 gFA/l) to the bottom of the digester of the
digester, displacing the spent impregnation liquor from the top of
the digester (DWBL). The hot black liquor pre-treatment stage
duration was 30 minutes. After the hot black liquor pre-treatment
stage, hot white liquor (121 gFA (NaOH)/l, sulfidity 37%) charge
was introduced, displacing the corresponding volume of spent hot
black liquor from the digester (RHBL). Together with the WL, a
cooking catalyst was charged mixed with a small volume of hot black
liquor. A 45 minute heat-u sequence with cooking liquor circulation
raised the temperature from 150.degree. C. to the cooling
temperature of 167.degree. C. At 250 H-factors, a further white
liquor charge was introduced into the digester bottom displacing
the corresponding volume of spent hot black liquor from the
digester (DCBL 1). After the cooking time fulfilled the target
H-factor, terminal displacement was started by introducing a volume
of cool DWBL and wash filtrate (WF) in a sequence into the digester
bottom displacing the hot spent black liquor out of the digester
top (DCBL 2). The first displaced portion of hot black liquor
together with the hot black liquor displaced earlier during the
cooking sequence (DCBL 2+DCBL 1) covered the 17 l volume needed for
the next cook's hot black liquor (HBL 1). After the terminal
displacement, the pulp was disintegrated, washed with deionised
water, screened and analysed. The cooking procedure was repeated,
equilibrium in the cooking process was reached and the cooks
started to repeat themselves corresponding to the industrial batch
cooking system.
EXAMPLE 1
Demonstration of Yield Improvement Using Polysulfide White Liquor
Addition
[0047] The reference cook follows the same addition and temperature
sequences as the cooks according to the invention. All cooks were
digested to the same target kappa number. A clear yield improvement
correlating with polysulfide addition can be observed
TABLE-US-00001 Cooking PS-charge, % Kappa Total yield, % Rejects, %
on model on wood number on wood wood Reference Nil 25.9 44.0 0.26
SB-PSAQ 1.21 25.9 45.8 0.36 SB-PSAQ 1.58 25.8 46.8 0.24
EXAMPLE 2
The Effect of Anthraquinone to Preserve the Rate of Delignification
During Cooking
[0048] It is seen, that the reference cook requires a significantly
higher H-factor to reach the target kappa number. TABLE-US-00002
Reject, PSWL PS, % Yield, % % on Method in imp, % on wood H-factor
EoC, g/l Kappa# on wood wood Reference -- -- 1285 16 26.9 43.6 1.01
PS pad, AQ 0% 70% 1.45 1106 19.1 27.1 44.3 0.15 PS pad, AQ 0.05%
70% 1.45 1030 19.9 26.7 44.5 0.16 PS pad, AQ 0.1% 70% 1.45 1096
18.1 27.3 45.8 0.1
* * * * *