Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MULTI-STAGE AP MECHANICAL PULPING
WITH REFINER BLOW LINE TREATMENT
FIELD OF THE INVENTION
The present invention relates to a process for the production of
pulp from lignocellulosic material, such as wood chips or the like, by
-chemical-mechanical refining.
BACKGROUND OF THE INVENTION
Applying alkaline peroxide chemicals in a mechanical pulping
system (APMP) may be traced back as early as 1962. Since then,
there have been a number of different process ideas developed to
apply the chemicals before or during early stages of refiner pulping.
In recent years, an extensive and systematic investigation has been
reported on how different chemical treatments in refiner mechanical
pulping affect pulp property development and the process
consumption. For hardwoods, it was observed that alkaline peroxide
pretreatment in general gives, better optical properties, better
bleachability and higher pulp yield at similar strength properties when
compared to other conventional chemical pretreatment, such as
alkaline sulfite and cold caustic soda processes. When compared to a
peroxide post-bleaching process, applying alkaline peroxide before
refining has a tendency to give a higher bulk at a given tensile
strength for some-hardwood species, such as North. American aspen.
In a very broad sense, alkaline peroxide refiner mechanical
pulping is a type of pulping process where hydrogen peroxide and
alkali in various forms, together with various amounts of different
peroxide stabilizers, are applied to the lignocellulosic materials before
or during defiberization and fibrillation in a refiner. In the early stage
of development of this type of pulping process, two basic concepts
were tried. One was to apply alkaline peroxide treatment on chips,
to allow the bleaching reactions to complete or to approach
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completion before refining. The other basic concept was to apply all
the alkaline peroxide at the refiner, either with no pretreatment or
with stabilizers or other alkaline pretreatment prior to the alkaline
peroxide application at the refiner.
Conventionally the inclusion of chemicals' such as silicates prior to
the refiner leads to a situation where scale forms on the processing
equipment. The refiner area itself also can suffer due to the formation of
silicate precipitates, especially in processing softwoods, which can lead
to a glassing of the refiner plates.
The application of chemicals at a point downstream of the
refiner has also been proposed. However these proposals did not
encompass the use of chemical pretreatment or conditioning of the
chips. In addition such downstream chemical addition appeared
incompatible with high pressure refining conditions.
Summary Of The Invention
The present invention is directed to the introduction of chemicals
to lignocellulosic material immediately after refining in order to achieve,
among other things, a comparable bleaching efficiency as when applying
chemicals at locations upstream of and/or at the refiner.
The introduction of chemicals downstream of the refiner,
wherein the refiner may be a primary, secondary and/or tertiary
refiner, is utilized with the concept of applying chemicals such as
alkaline peroxide pre-treatment to lignocellulosic material before
refining. Preferably, the refiner has a highly pressurized case, for
achieving the known benefits of high pressure refining.
The introduction of chemicals downstream of the refiner
according to the invention may alternatively be utilized with the
process referred to herein as P-RC (Preconditioning followed by
Refiner Chemical treatment) for APMP, which combines the concept
of applying chemicals such as alkaline peroxide as a pretreatment to
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lignocellulosic feed material before primary refining with the concept
of applying chemicals such as alkaline peroxide at the primary refiner.
The preferred embodiment of the invention includes applying
more than one-third of total alkaline peroxide (and/or other chemicals
known in the art to bleach or otherwise process lignocellulosic
material into pulp or precursors of pulp) at or near the blow valve in
the post refiner intermediate line, in combination with chemical
addition at the refiner and chemical impregnation of the chips
upstream of the refiner, to yield a more energy efficient process and
to allow a more efficient bleaching than the application of all the
chemicals before discharge from the refiner.
A significant benefit of the invention is better chemical efficiency,
by moving a greater number of chemical reactions downstream relative to
conventional techniques, resulting from the relatively heavier or more
intense addition of chemicals and/or chemical stabilizers at the post
refiner blow line.
A further benefit of the invention is the reduction in the
detrimental effects of the high temperature and/or other conditions
prior to and during high pressure primary refining, which are known
to influence pulp brightness and development.
Another benefit of the invention as implemented in a high-
pressure system, is the recovery of more and higher quality of steam
and/or heat than in other types of P-RC APMP systems, where the
primary refiner is either completely atmospheric or atmospheric at the
inlet.
Brief Description Of The Drawings
The invention will be better understood by reference to the
accompanying drawings in which:
Figure 1 is a block diagram depicting the general P-RC APMP
process.
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Figure 1 A is a block diagram depicting steps of transferring lignocellulosic
material to a
refiner having a casing at atmospheric pressure, with discharge at atmospheric
pressure.
Figure 1 B is a block diagram depicting steps of transferring lignocellulosic
material to a
refiner having a pressurized casing withO pressurized discharge.
Figure 1 C is a block diagram depicting steps of transferring primary pulp
produced in the
refiner with a casing at atmospheric pressure, to a high consistency tower via
a transfer device.
Figure 1 D is a block diagram depicting steps of transferring primary pulp
produced in the
refiner with a casing at atmospheric pressure directly to a high consistency
tower.
Figure 1 E is a block diagram depicting steps of transferring primary pulp
produced in the
refiner with a pressurized casing, to a high consistency tower via a transport
device.
Figure 1 F is a block diagram consistent with an embodiment of the invention,
depicting
steps of transferring primary pulp produced in the refiner with a pressurized
casing to a high
consistency tower.
Figure 2 is a graph of freeness as related to energy consumption for P-RC and
two prior
art processes.
Figure 3 is a graph of density as related to energy consumption for P-RC and
two prior art
processes.
Figure 4 is a graph of the tensile of tensile development for P- RC and two
prior art
processes.
Figure 5 is a graph of burst development for P-RC and two prior art processes.
Figure 6 is a graph of brightness development for P-RC and two prior art
processes.
Figure 7 is a graph of the light scattering coefficient of the pulp as a
function of freeness
for P-RC and two prior art processes.
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Figure 8 is a block diagram consistent with an embodiment of the invention,
depicting
steps of transferring primary pulp produced in a refiner with a pressurized
casing to a
retention tower with a chemical addition in the intermediate line following
the control valve.
Figure 9 is a block diagram consistent with an embodiment of the invention,
depicting
steps of transferring primary pulp produced in the refiner with a pressurized
casing to a
retention tower with an alkaline peroxide chemical addition in the
intermediate line prior to
the inlet of the separator.
Figure 10 is a block diagram consistent with an embodiment of the invention,
depicting steps of transferring primary pulp produced in the refiner with a
pressurized casing
to a retention tower with an alkaline peroxide chemical addition in the
intermediate line at the
separator.
Figure 11 is a block diagram consistent with an embodiment of the invention,
depicting steps of transferring primary pulp produced in the refiner with a
pressurized casing
to a retention tower with an alkaline peroxide chemical addition in the
intermediate line at the
separator discharge.
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Figure 12 is a block diagram consistent with an embodiment of the invention,
depicting
steps of transferring pulp produced in a pressurized refiner via a
intermediate line to a tower.
Detailed Description Of The Invention
Figure 1 presents a simplified process flow diagram of the PRC alkaline
peroxide
mechanical pulping (APMP) process. The P-RC process generally applies alkaline
peroxide
chemicals at chip pretreatment/chip impregnation step (s) /stage (s) 1,2 and
as the material is fed
to the primary refiner 3.
The preconditioning step (s) as implemented in stages I and 2 of Figure 1,
preferably
include one or two atmospheric compression devices, such as screw presses.
Chip material is fed
through an inlet, and passes through at least one compression region and at
least one expansion
region, and is discharged. A chemically active solution (pretreatment
solution) is added to the
material, typically while decompressing or decompressed at or near the
discharge to facilitate
penetration of the solution into the material.
The refining step 3 may include a primary refiner of conventional size,
configuration, and
operating conditions as known for chemi-mechanical pulping. Depending on such
factors as
whether chemicals are to be added and what types of chemicals if any are to be
added the size,
configuration, and operating of the refiner can be tailored so as to not
expose the chemicals to
excessive temperature or time-temperature combination. In one embodiment of
the invention the
pressure can be within a range of about 15 psi to pressures greater than 45
psi. Any chemicals
added at the refiner will be referred to as the refiner solution.
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Steps implemented following the primary refining, may have a level of chemical
presence
carried downstream from the refiner or other upstream processing. In one
embodiment of the
invention, the post refining chemical environment is modified by an addition
or additions of a
intermediate line solution or solutions to the intermediate line. The
intermediate line is located
between the refiner and the retention tower. For instance, as shown in Figure
8, alkaline peroxide
solution is applied to pulp in the intermediate line, at the blow line 30,
after exposure to and discharge
from the refiner. The chemicals may be applied at a point or points along and
about the blow line 30.
The blow line 30 may extend between the blow valve and a separator of the
intermediate line. As
shown in Figure 12, the chemicals may also be applied in the intermediate line
immediately after the
blow valve 40, between the blow valve and the separator 42 immediately prior
to separator 44, at the
separator 46 and/or immediately after the separator 48. The separator, for
instance a cyclone, may
operate to separate steam/heat/liquid or combinations of those items from the
pulp. Prior to entry into
the separator the pulp may have a consistency of about 20% to about 60% and a
temperature of about
80 C to about 155 C.
Injection of the chemicals at a intermediate line location or locations may be
made through
simple orifices in the intermediate line and/or by the use of injectors, such
as nozzles, associated with
the line. The nozzles can be associated with the intermediate line in various
ways along and about the
intermediate line to desirably control the chemical addition. The control can
be dependent, for
example, on the effect that the additions have with regard to the bleaching
process and/or conditioning
process. Chemical profiles within the pulp flow can thus be modified or
maintained by, for example,
injection sequencing, flow rate, composition, and/or duration. Other variables
such as the depth of
injector intrusion into the flow path, injector angle, injector orifice
configuration, and other properties
of the injector installation may be modified to achieve a desired result.
Chemical introduction may be
modified by varying the introduction location based on the pressure used
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in refining. For instance, alkaline peroxide chemicals may be introduced
immediately (from less than a few inches to a few feet) after the blow
valve, especially in low pressure refining where the pressure is less than
about 45psi. The alkaline peroxide chemicals may also be introduced
immediately before the cyclone (from less than a few inches to a few
feet) after the blow valve, especially in high pressure refining where
pressures higher than 45psi are used. In other cases the alkaline
peroxide chemicals may be introduced intermediate the cyclone and the
blow valve, or even at the cyclone.
The refiner may be primary, secondary, and/or tertiary, with a
pressurized casing or fully pressurized from preheater to refiner
discharge. The pressure in the refiner aids in expelling the pulp from the
refiner during discharge. The discharge can be modified or controlled by,
e.g., the blow valve. The pressure assisted discharge of the pulp into the
intermediate line can result in the pulp having a residence time of a few
seconds to minutes in portions of the intermediate line. The pulp can
achieve high velocities and experience significant turbulence as it flows
through the intermediate line. These conditions enhance the mixing
between the chemicals and the pulp. The intensive turbulence and a high
temperature gradient in the pulp stream may also assist in transferring
the chemicals to individual pulp fibers as well into the fiber wall.
As an illustrative example, the pulp may be about 100 C or
higher, and the chemical liquor may be 40 C or lower. The intermediate
line solution may preferably be in the range of about 10 C to about 25 C
but can be up to 80 C. The application of alkaline peroxide chemicals at
the intermediate line reduces the exposure time of the alkaline peroxide
chemicals to high temperature, especially when elevated temperature
and/or pressure is present at refining. This post refining addition to the
pulp flow through injection proximity, facilitates an easier stabilization and
an increased efficacy of the peroxide. The use of the invention in an
intermediate line with a superatmopheric refiner system also can result in
the enhanced or modified recovery of steam/heat/liquid from the pulp.
Such steam may be diverted away through a steam pipe 36. These
features also allow for the production of high-freeness pulps with low
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shives content, since it is well known in the industry that the higher
refining pressure tends to produce lower shives, or cleaner pulp. In some
cases a press may be included in addition to or in place of the cyclone
32. The press could allow for an increase in steam/heat/liquid recovery
from the pulp.
In one embodiment of the invention the optimizing process to
influence peroxide efficiency and brightness development can be
accomplished when the primary refining is fully pressurized. In one
particular configuration this may be referred to as P-RC APTMP,
which differs from other P-RC APMP configurations where the
primary refiner is operated either under completely atmospheric
pressure, or with atmospheric pressure at the inlet and low pressure
at the casing.
Figures 1 A through 1F present various examples of a P-RC
process of the type generally shown in Figure 1. For example,
Figures 1 A and B show that after the material is pretreated at 1
and/or 2, addition of the solution to the lignocellulosic material may
more specifically occur at a cross conveyer 10, downstream of the
screw press and near refiner 3, or at the refiner itself, e.g., the ribbon
feeder 12, the inlet eye of the refiner disc 14, and/or at the inlet zone
of the plates on the refiner disc 16. As used herein, chemical
addition "as the material is fed to the refiner", encompasses the
locations 10, 12, 14, and 16. The refiner in a P-RC process may
have an atmospheric casing 3A or an overpressure casing 3B, but the
inlet to the refiner would normally be at atmospheric pressure. The
discharge from a pressurized casing 20a of primary pulp may be
through a blow valve or similar device, and discharge from an
atmospheric casing 20 may be by gravity drop or the like. The
discharge from the refiner will, in any event, directly or indirectly go
to a high consistency-bleaching tower 24 of any type known in the
art (but subject to temperature control).
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In one embodiment of the invention the pretreatment solutions, the refiner
solutions (if
present), and the intermediate line solutions act chemically on the
lignocellulosic material. It may be
advantageous, depending on the lignocellulosic material and the processing
equipment, to modify the
chemical exposure profile of the material to the chemical agents in order to
optimize the process,
and/or eliminate or reduce unwanted chemical effects or degradation. Such
chemical profile
modification may be accomplished by sequential chemical additions throughout
the process, and can
be combined with other variable conditions such as temperature, concentration,
pressure, and duration
to further enhance the desired effect.
Lignocellulosic material processed using the P-RC process can be discharged 4
from the
primary refiner casing (either atmospheric discharge 20 or overpressure
discharge 20a), as a primary
pulp having a measurable freeness and could properly be called a pulp able to
form a handsheet. As
shown in Figures 1 C and D, atmospheric discharge from the refiner could pass
via a transfer device
22 such as a transfer screw, to the tower 24, or more directly 28 via'a chute
or the like. As shown in
Figures 1 E and F, with a pressurized casing the refined pulp would typically
be discharged through a
blow valve and delivered either directly or indirectly to the tower.
Optionally, as shown in Figures 1 C
and E, the bleached pulp exiting the tower can be further processed in, e. g.
, a secondary refiner. The
high consistency retention tower 24 allows the chemical bleaching reactions
carried over from
upstream of the tower to continue.
In one embodiment of the invention, for example as shown in Figure 12, the
discharge from the blow
valve may be delivered indirectly to a retention tower through a seperator
and/or a press.
The presence of an ample amount of the alkaline peroxide chemicals in the
primary refiner
(e. g. , as by shifting a large proportion
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of the chemical reactions to the refiner chemical treatment stage)
improves efficiency. This is because variations in chip forms and
quality, in addition to the natural heterogeneity of wood chips and
fibers, often make it difficult, if not impossible, to achieve a good
chemical distribution in the chip pretreatment/impregnation stage(s).
In these situations, the mixing action at the primary refiner helps to
promote chemical distribution, and hence, improves the chemical
efficiency.
In accord with one embodiment of the invention, the addition
of chemicals into the post refining intermediate line allows, for
example, the use of a pressurized refiner and higher temperatures in
refining. Addition of chemicals to the intermediate line at, for
example, the blow line provides for a fast, and more direct,
distribution of chemicals such as peroxide to the chromophore sites
for efficient bleaching. This efficiency is achieved because the
targeted peroxide reactions are carried out at the reaction site of
interest quickly without lengthy exposure to the more heterogeneous
environment present in previous portions of the process.
Conventionally the temperature at the inlet between the plates of a
refiner pushes the chromophore removal and hemicellulose alkali
reactions so fast that that pH is lowered prematurely. Using the post
refiner intermediate line as the location for chemical mixing according
to an aspect of the present invention, distributes the chemicals fast
enough, to compete favorably against and counter to a significant
extent, the elevated temperature of the pulp. Such elevated
temperature can be, for example, from about 80 C to about 155 C.
In one embodiment of the invention, the pulp can be
maintained in an interstage high consistency retention tower. The
pulp in the high consistency retention tower may have a consistency
of about 20% to a consistency of about 40% consistency, with a
preferable consistency of about 30%. The temperature of the pulp in
the high consistency retention tower may be from about 600C to
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about 951C. The pulp can be held in the retention tower from about
30 minutes to more than 2 hours depending on the chemical reaction
needed for chemical treatment. The maintenance conditions include
but are not limited to temperature, pressure, pH, chemical
concentration, solids concentration, and time, that allow for
conditioning and/or bleaching of the pulp to continue and limit the
degradation of the bleaching agent through reactions that are
extraneous to the bleaching of the pulp. Such extraneous reactions
may be non-productive, inefficient, and/or harmful to the bleaching of
the pulp. Control of some and/or all of the conditions may or may not
be needed depending on e.g., the type and condition of the
lignocellulosic material used in the process, and the type, size and
operating environment of the equipment itself. For example,
conditions of temperature may be modified throughout the process
by the addition of the chemicals, pressurized gas, and other heating
or cooling methods. Temperature modifying means may be employed
during transfer of the primary pulp 22 by using a mixing screw with
water added while the pulp is mixed and transferred to the tower.
The temperature of the primary pulp may also be thermally adjusted
within the tower if the primary pulp is discharged directly to the
tower 28, by means known in the art. For example, the pulp may be
thermally adjusted through addition of liquids or gases, and/or
through use of heat transfer components such as tubing, tower
jacketing, etc.
As used herein, the term "control" should be understood as
including both active and passive techniques. Thus, control could be
implemented by a static hardware configuration or by continually
measuring one or more process parameters and controlling one or
more process variables.
The chemical conditions present anywhere in the inventive
process may be modified by additives to prevent extraneous
degradation. This modification may be made at, by way of example,
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the pretreatment step(s) 1 and/or 2, the cross conveyer 10, the
ribbon feeder 12, the inlet eye of the refiner disc 14, the plates of the
refiner disc 16, the blow valve 20a, the blow line 30, the separator,
32, and/or after the separator. An example of stabilizers would be
chelation agents. 'A chelation agent refers to a compound that has
an ability to form complexes, so called chelates, with metals
occurring in the lignocellulosic material, .and primary pulp. Such
metals may include monovalent metals sodium and potassium, earth-
alkali divalent metals calcium, magnesium and barium, and heavy
metals such as iron, copper and manganese. The metal ions retained
in the material as it is processed makes the bleaching by oxygen
chemicals (such as hydrogen peroxide) less effective, and results in
excess chemical consumption as well as other problems well known
in the art. In order to reduce or eliminate the effect of these metal
ions on the process, chelants such as for example diethylene triamine
pentaacetic acid (DTPA), ethylene diamine tetraacetic acid (EDTA)
and nitriletriacetic acid (NTA) may be used. These and other
chelation agents known in the art may be used alone or in
combination as needed or desired depending on process conditions. In
addition, silcates and sulfates as examples may also be used
advantageously as stabilizers as well as serving other functions well
known in the art.
Further embodiments and aspects of the invention will be
apparent from the examples and description set forth below.
ILLUSTRATIVE EXAMPLES
Example Set A
Several general series of pilot plant processes are illustrated in
the following examples. The materials and conditions for the
following examples, unless specified otherwise are:
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Wood: A blend of 50% aspen and 50% basswood was used in this study. The
aspen woods had rotten centers, which made it more difficult to bleach than
normally expected. The woods were all from Wisconsin USA, and debarked,
chipped and screened before further processing.
Chemical Impregnation: Chips were pre-steamed first for 10 minutes, and
then pressed using an AndritzTM 560GS Impressafiner at 4:1 compression
ratio before impregnated with alkaline peroxide chemical liquor. The chemical
liquor was introduced at the discharge of the press, and allowed for 30
minutes retention time before refining.
Refining: An AndritzTM 92 cm (36") Model 401 double disc atmospheric refiner
at a conventional speed of 1200 rpm was used for all the refining processes.
There was 15 minutes or more retention time between the primary and the
secondary, and no dilution after the primary and before the secondary. The
refining consistency was 20% at both the primary and the secondary.
Pulp Testing: Tappi Standards were used for all pulp testing except for
freeness, which follows Canadian Standard Freeness (CSF) test methods.
In the first of three processes compared, all of the alkaline chemicals
were applied, (3.3% total alkalinity, (TA), and 2.4% H202, together with 0.2%
DTPA, 0.07% MgSO4 and 3% Na2SiO3) at the chip impregnation
(preconditioning or pretreatment) stage, (only one stage chip impregnation
was applied), then refined at atmospheric pressure. This series was,
therefore, named "Chip". The second series used approximately two thirds of
the total alkaline peroxide chemicals, (or 2.4% TA, 1.6% H202, 0.08% DTPA,
0.04% MgSO4 and 2.4% Na2SiO3), at the chip impregnation stage, and
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approximately one third of the total chemicals, (1.0% TA, 1.0% H202, 0.19%
DTPA, 0.05%
MgS4, and 0.9% Na2SiO3), at the eye of the primary refiner. It is labeled as
"Chip +
Refiner", and represents the invention. In the third series, labeled
"Refiner", the chips were
first pressed using the same chip press as the first two series, and then all
the alkaline
peroxide chemicals, (4.2% TA, 3.3% H202, 0.36% DTPA, 0. 1 1% MgSO4, 4.3%
Na2SiO3),
were applied at the eye of the primary refiner. In all the series, the pulp
from the primary was
allowed 15 minutes retention under cover in drums, (which gave a temperature
about 80-90
C), before the second stage refining. There was no interstage washing.
Table 1 summarizes some of the process conditions and results from each
series. The
pulps are all from second stage refining. In peroxide bleaching of mechanical
pulps, a lower
TA/H202 ratio is in general preferred under higher temperature to prevent, or
to reduce the
possibility of alkali darkening reaction. For this reason, as shown in Table
1, the lowest
TA/HzOz ratio, 1.27, was use for "Refiner" series, the second lowest, 1.3 1,
for "Chip +
Refiner" series, and the highest, 1.37, for "Chip" series. In "Refiner"
series, a larger amount
of TA charge (4.2%) was used to prevent pH from dropping too fast and too low
during
refining because of the high temperature and the heat generated from refining
energy.
Reasonable amounts of residual peroxide and pH were maintained in each of the
series.
As to the chemistry, the main difference between "Chip" and "Chip+ Refiner"
series
is that the latter is more aggressive in moving more alkaline peroxide
chemicals to the refiner
chemical treatment stage.
Graphic presentation of the data gathered from pulp after secondary refining
after
different investigated processes are shown in Figures 2 through 7. Figure 2
shows effects of
the different chemical applications on pulp freeness development in relation
to specific
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CA 02533535 2006-01-23
WO 2005/042830 PCT/US2003/031341
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WO 2005/042830 PCTIUS2003/031341
energy consumption (SEC), which includes energy consumed during chip
pretreatment stage.
The "Chip + Refiner" series used slightly less SEC than the "Chip" series, but
both series
used, on average, approximately 200 kwh/odmt less SEC than the refiner
bleaching series,
"Refiner", even though the latter had more caustic chemicals applied than the
first two series
and has the same residual pH, 8. 2, as "Chip+Refiner" series. It appears that
adding the
alkaline chemical under high temperature, at refiner eye, causes more alkali
consumed on
nonproductive, or side reactions that have little to do with pulp property
development.
It should be pointed out that in a commercial operation, the SEC in general is
lower
than that observed at the lab for chemical mechanical pulping of hardwoods.
The SEC values
in Figure 2, therefore, are better used for comparison purpose than for their
absolute values.
Because many pulp properties, especially the strength properties, are
dependent on
handsheet density, this property was also analyzed under SEC, and results are
shown in
Figure 3. In this case, the more aggressive refiner chemical treatment P-RC
APMP
series,"Chip+Refiner" had the best efficiency for handsheet density
development, which was
followed by "Chip" and "Refiner" series. These results demonstrate that in
chemical
mechanical pulping, process energy efficiency depends not only on how much but
also on
how the chemicals are applied.
As for pulp intrinsic property development, there was however, little
difference
among the three series, as illustrated in Figures 4 and 5, suggesting that as
long as the
chemicals are added before refining, the mechanism involved in fiber strength
property
development remains the same.
As for pulp optical property development, in mechanical pulping, pulp
brightness is often
freeness-dependent. Figure 6 shows brightness at different freeness from each
series. Of
interest is that
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"Chip + Refiner" series had a similar brightness development as that of the
"Refiner" series,
even though the former used less amount of the bleaching chemicals, 2.6%
H202/3. 4% TA
versus 3.3% H202/4.2% TA. Adding all of the chemicals at the impregnation
stage, "Chip"
series, showed also a less bleaching efficiency, 2 or more points lower, than
that of "Chip +
Refiner" series. This suggests that the bleaching efficiency is sensitive to
how the chemicals
are distributed between the chip impregnation and refining in P-RC APMP
process. In this
case, a compromise between adding all of the chemicals at chip impregnation or
at eye of
refiner appears to be the most efficient in bleaching and peroxide
consumption.
Figure 7 shows that there was no difference in light scattering property
development
in all the series studied, suggest the pulp surface development mechanism also
remain the
same as long as the chemicals are added before refining.
Example Set B
The below examples illustrate a different refining configuration where the
primary refiner
was maintained at a negligible gauge pressure at the inlet and a low pressure
(approximately
140 kPa) at the casing. Advantages of this configuration include: 1) better
steam handling at
the refiner discharge, especially for high capacity refiners (300 t/d or
higher);
2) ease of transfer primary pulp from the refiner to the interstage high
consistency (HC)
tower;
3) a potential to use some of the steam generated from the primary refining
(by using a
cyclone to separate steam and pulp fiber);
4) ease of converting existing TMP systems into a P-RC
APMP process.
These examples show that running the primary refiner at a low pressure (140
kPa) in
the casing and atmospheric at the inlet can
17
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give similar bleaching efficiency as that of atmospheric at both the
inlet and the casing. Temperatures at the inlet and between the
plates in the primary refiner may push the chromophore removal and
hemicellulose alkali hydrolysis reactions fast enough that pH was
lowered considerably before the pulp reaches the casing out off the
refiner plates. The pulps at the cyclone discharge from the primary
refiner were measured in the examples below to have pH of 9.3-9.7,
at which peroxide is easy to stabilize even under the high
temperatures (80-90 C) observed.
The materials and conditions for the following examples below
were as follows:
Wood: Aspen and birch chips from a commercial pulp mill in eastern
Canada were used in this study.
Chip Impregnation: A conventional pilot chip impregnation system
was used in this study. In all the P-RC APMP runs studied, only DTPA
was used in the first stage of chip impregnation. The chips were
then impregnated with alkaline peroxide (AP) chemicals at second
stage impregnation. The AP treated chips were then allowed for 30
to 45 minutes' retention (without steaming) before being refined.
Atmospheric Refiner System: Andritz 36" diameter (92 cm) double
disc 401 system is typically used for conventional P-RC APMP
process investigations. This system consists of an open metering
belt, an incline twin-screw feeder, the refiner and an open belt
'discharge. The system is used for both primary and later stages of
refining. When used for the primary, the pulp discharged were
collected in drums and kept under cover to maintain a high
temperature (typically 80 to 90 C) for a certain period of time.
Pressurized Refiner System: An Andritz single disc 36" diameter (92
cm) pressurized system was modified for atmospheric
18
CA 02533535 2011-05-27
WO 2005/042830 PCTIUS2003/031341
inlet/pressurized casing configuration. The original refiner system has all
the standard features of
a conventional TMP system. In order to run the system with atmospheric
pressure at the inlet, a
valve was placed on top of the vertical steaming tube and was kept open during
refining. During
the trial, the plug screw feeder (PSF) was run at 50 rpm (normal speed for TMP
is 10 to 20 rpm)
to ensure the chemical impregnated chips were not compressed. The AP
impregnated chips were
placed in a chip bin, which discharged the chips into a blower.
The chips were then blown to a cyclone and discharged to a conveyor, which
feeds the PSF. The
chips were then dropped into a vertical steam tube before being fed into the
refiner. During
refining, the primary refiner was controlled to have zero pressure at the
inlet and 140 kPa in the
casing. From the casing, the primary pulp was blown to a cyclone and
discharged and collected in
drums, and then treated similarly as in the atmospheric refining runs.
Pulp Tests: TAPPI standard was used for brightness tests. Peroxide residuals
were measured
using standard iodometric titration.
Running the primary refiner with pressurized casing and atmospheric inlet was
compared
with conventional atmospheric refining in P-RC APMP pulping of aspen and birch
commercial
wood chips. The results showed that both refining configurations gave similar
bleaching
efficiency. For some installations, using pressurized casing can significantly
simplify the process,
engineering and operation of P-RC APMP process.
Table 2 presents the chemical conditions used for P-RC APMP pulping of aspen,
and
brightness results from atmospheric and casing pressurized runs with the
primary refiner.
Applying similar AP chemical strategies in both cases, and having similar
amounts of total
chemical consumption (5.2 to 5.4% total alkali, TA, and 3.7 to 3.9% H202),
both the atmospheric
and the casing pressurized gave a similar brightness, achieving 84. 2% ISO and
84. 7% ISO
respectively.
19
CA 02533535 2011-05-27
CA 02533535 2006-01-23
WO 2005/042830 PCT/US2003/031341
v
N
h M M M O ~, N N N Q 0~ O Vl M
a
N
N
P. CV t- c rt =-a oo d O N oo en N t~
p O M M c O O --+ N N oo hI in r)
ori
O C1 \ v
tj 110
Pi
O UI
yy a o ~ ;a ~ U
146) tz o N' N~ ~vI '~ L7 h O
q N 0 O ai qt :3
u -0 N C4 C)
t r9 0 U Abp C bo O V P4 O H W
C) 0
Q \ o 0 0 0 U Q
F, f
19a
CA 02533535 2011-05-27
WO 2005/042830 PCT/US2003/031341
The residual pH (8.8-9. 0) in both cases were slightly higher than ideal
(approximately 7.0-8. 5) and the HzOz residual (1.5 to 2.0% on o. d. pulp) was
also higher
than normal (0.5 to 1.0%), suggesting that in both cases the pulp property
could be further
developed had the chemical treatments been further optimized.
It is worth pointing out that the bleaching efficiency shown in Table 1 (3.7
to 3. 9%
llzOz and 5.2-5. 4% TA consumption to reach 84.2 to 84. 7% ISO brightness) is
comparable
to or better than bleaching efficiency normally observed in H202 bleaching of
TMP or CTMP
pulps from aspen.
Table 3 presents conditions and results from P-RC APMP pulping of the birch.
This
particular birch chips was slightly more difficult to, bleach than the aspen.
Using similar AP
chemical strategies, the atmospheric and the pressurizing casing again gave
similar bleaching
efficiency: 3.1-3. 2% TA and 3.4-3. 6% H202 to reach 82.4 to 82. 6% ISO
brightness. In this
case, the residual chemicals (0.1-0. 2% TA, 0.5-0. 6% Hz02 and pH of 8) were
within ideal
HaOa bleaching conditions.
Example Set C
This example set shows, among other things, that when the chemical recipe and
distributions
are optimized, the alkali peroxide chemicals at refiner chemical treatment
stage can be
applied at the intermediate line in a pressurized refiner system to achieve
similar bleaching
efficiency as P-RC APMP with conventional atmospheric inlet pressure. Because
the
residence time is very short in a intermediate line, the same process may also
be used in a
high pressure refining system, for example a refining system operating at 4
bar or higher.
Wood
All the hardwoods (birch and maple) were received in chip form and mixed
separately before
being further processed. All the softwoods
CA 02533535 2011-05-27
CA 02533535 2006-01-23
WO 20051042830 PCT1US2003/031341
N O r 1' O c i N b '-- "O O --~ %0 N
O O M M
y O N N N D .~ -+ O co
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cd
a
O. N O M 'qY - cn o0 00 ~+ O N v1 1-4 %0
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E
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20a
CA 02533535 2006-01-23
WO 2005/042830 PCT/US2003/031341
(spruce, pine and softwood blends) were received in log form, and
debarked, chipped and mixed prior to further processing.
Chip Impregnation
The wood chips, unless otherwise specified, were impregnated
twice with AP chemicals (consisting of sodium hydroxide (NaOH),
hydrogen peroxide (H202), DTPA, Magnesium Sulfate (MgSO4) and
sodium silicate (Na2SiO3), utilizing an Andritz 560GS Impressafiner
System. In some cases, the RT-Pressafiner was used at the first stage
impregnation (steamed at 1.4 bar for 20 seconds before being pressed).
Refining
An Andritz 36" diameter (91 cm) single disc 36-1 CP refiner system
was used for all pressurized and atmospheric inlet/casing pressurized
runs, and an Andritz 36" diameter (91 cm) double disc 401 system was
used for all atmospheric refining runs. Typically, except where stated
otherwise, the 401 refiner was used for all secondary and tertiary refining.
Process Description
The P-RC, (Preconditioning, following by Refiner Chemical
treatment, where AP chemicals are distributed between chip
pretreatment and refining stages), process was used in all trial'runs. For
the runs where AP chemicals were charged at the intermediate line, the
pulp discharged from the blow line was covered under a plastic bag in
drums to maintain a temperature of 85-95 C, depending specific refining
energy used at the refiner, the chemical charges, and the nature of the
raw materials.
Pulp Tests
Canadian Standard Freeness (CSF) was used for all freeness
tests and standard Tappi methods were used for all optical property tests
(brightness Tappi T218 OM-83, light scattering, and light absorption
coefficient Tappi T425 OM-86 (for handsheet Tappi 205 OM-88)).
21
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WO 2005/042830 PCT/US2003/031341
Table 4 shows the results obtained by applying AP chemicals at either the
refiner eye or
the intermediate line during the refiner chemical (RC) treatment stage. Birch
and maple woods
were used in this example. For each wood species, some chemical pretreatment,
(preconditioning), was applied on the chips. For birch the chips were treated
with 0.3% DTPA at
first stage impregnation, and then 0.2% MgSO4, 4.4% Silicate, 2.8% TA, and
2.8% H202 at the
second stage impregnation. For maple the chips were treated with 0.5% DTPA at
first stage
impregnation, and then 0.2% DTPA, 0. 1 % MgSO4, 2.0% Silicate, 1.6% TA and
2.6% H202 at
the second stage impregnation. The preconditioned chips then received a
similar amount of AP
chemicals during refiner chemical (RC) treatment stage, but at different
points: one at the refiner
eye before refining, and another at the intermediate line immediately after
refining.
For the birch, both series (Al and A2) used a total of 5.2% H202 and 4.6%
total alkali
(TA), and had a similar amount of H202 residuals (1.0%-1. 1%) and final pH
(8.9-9. 0). The
final pH's were relatively high, indicating that a higher brightness would be
achieved if a longer
retention time was used. The series from AP addition at the refiner eye (Al)
had a similar
brightness to samples where AP chemicals were added at the intermediate line,
A2, for example,
84.8 versus 84.2% ISO. The slight difference in the brightness was likely, at
least in part, due to
the slight difference in their freeness, 285 mL for the former case and 315 ml
for the latter. In
terms of chemistry, both series gave similar light absorption coefficients,
0.27 m2/kg from the
former and 0.25 m2/kg from the latter.
In the case of the maple wood, adding AP chemicals at intermediate line, A4,
actually
gave a higher brightness, 81. 9% ISO, than that, 79.2% ISO, from applying the
AP chemicals at
refiner eye, A3. The difference in this case was a combination of the lower
freeness, (295 vs.
320 mL), and the lower light absorption coefficient, (0.32 vs. 0.5 m2/kg), of
the former.
Softwoods, namely spruce and red pine, were also investigated in to examine
effects of
different AP chemical applications. Table 5
22
CA 02533535 2011-05-27
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WO 2005/042830 PCT/US2003/031341
4)
a ^^
3Q d v? vr o Mvi
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GQ -+ N
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22a
CA 02533535 2011-05-27
WO 2005/042830 PCT/US2003/031341
summarizes the results, and shows again that similar brightness was achieved
by applying AP
chemicals at either the refiner eye or the intermediate line. In the case of
spruce the chips were
first impregnated with 0.3% DTPA, 0.05% MgSO4, 0.7% Silicate, 0.2% TA and 0.5%
H202, and
then 0. 1% DTPA, 0. 08% MgSO4, 1.8% Silicate, 1. 4% TA and 1.9% H202 at second
stage
impregnation.. In the case of red pine the chips were treated with 0.4% TA,
0.5% H202, 0.2%
DTPA, 0.04% MgSO4 and 0.5% Silicate at first impregnation, and 0.4% TA, 0.6%
H202, 0.14%
DTPA, 0. 05% MgSO4, 0.4% Silicate at second stage impregnation. For spruce,
using similar
amounts of AP chemicals, for example see Figure 16, the blow line series, A6,
had a similar or
slightly higher brightness of, 78.8% ISO, than the, 78. 2% ISO, from the
series, A5, where the
last stage of AP chemicals were applied at the refiner eye. This slight
difference of brightness
again was likely a result of combined effects from their slightly different
freeness, 47 mL vs. 49
mL, and slightly different light absorption coefficient, 0.56 vs. 0.60 m2/kg.
In the case of red pine, the blow line series, A8, had a slightly higher
brightness, 71.8 vs.
71.2% ISO, lower light absorption coefficient, 0.84 vs. 1.01 m2/kg, but higher
freeness, 99 vs. 82
mL, compared to the refiner eye series, A7. As far as its effect on brightness
is concerned, in this
case, the difference in the light absorption coefficient was likely the
difference in their freeness.
The amounts of AP chemical treatment were the same for both series.
A softwood blend from spruce and pine was subjected to high pressure refining
at the
refiner chemical treatment stage as in Table 6. In this case, a RT-Pressafiner
was used at the first
stage impregnation, and Andritz Model 560GS Impressafiner at the second stage.
For this
chemical treatment 0.4% TA, 0. 6% H202, 0. 18 % DTPA, 0. 03 % MgSO4 and 0. 3%
Sodium
Silicate at 1't stage chip impregnation; 0.4% TA, 0. 7% H202, 0. 15% DTPA, 0.
05% MgSO4 and
0. 4% Sodium Silicate at 2nd stage chip impregnation; 0.9% TA, 1. 5% H202, 0.
18% DTPA, 0.
09% MgS04 and 1. 8% Sodium Silicate at refiner chemical treatment stage,
either at the refiner
eye as for A9, or the
23
CA 02533535 2011-05-27
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WO 2005/042830 PCT/US2003/031341
- o ri ri oo %0 09 C oo v
P n .1 O v v ..,. DD D\
GYa Q .. .. C o N 0 O n G O,
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CA 02533535 2011-05-27
CA 02533535 2006-01-23
WO 2005/042830 PCT/US2003/031341
d
O M KI I` v vl d. n
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42
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a G Q CV N . co t-- et
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23b
CA 02533535 2011-05-27
WO 2005/042830 PCT/US2003/031341
intermediate line as for A10 was used. Series, A9, A10, were performed, and
both had similar
chemical charges and recipe, but one (A9) had 2.1 bar pressure in the primary
refiner and the
other, A10,4. 2 bar. Table 6 presents results, and shows that the series with
the higher pressure,
A10, was able to achieve similar bleaching efficiency and brightness (using
1.7% TA and 2.8%
H202 and reached 73.7-73. 4% ISO). The samples had similar light absorption
coefficient (0.96-
1. 1 m2/kg). These results indicate that when the chemical strategies were
optimized, a similar
bleaching efficiency and brightness (at least in the range of 70- 75% ISO) can
be achieved at
even a very high pressure (4.2 bar, or 60 psi). The high pressure refining
would make it possible
to recover high quality steam with better efficiency than the lower pressures,
and provide an
opportunity to reduce shives (fiber bundles) for high freeness pulps.
24
