U.S. patent application number 10/677545 was filed with the patent office on 2004-04-15 for multi-stage ap mechanical pulping with refiner blow line treatment.
Invention is credited to Xu, Eric Chao.
Application Number | 20040069427 10/677545 |
Document ID | / |
Family ID | 23187705 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040069427 |
Kind Code |
A1 |
Xu, Eric Chao |
April 15, 2004 |
Multi-stage AP mechanical pulping with refiner blow line
treatment
Abstract
The invention combines the step of adding chemicals such as
alkaline peroxide to an intermediate line after refining, with the
step of applying chemicals such as alkaline peroxide as a
pre-treatment before primary refining and/or applying chemicals
such as alkaline peroxide at the primary refiner. This is
implemented in the preferred embodiment, by pre-treating feed
material, refining the materials into a pulp in a superatmospheric
refiner, and adding chemicals in the post refining blow-line.
Inventors: |
Xu, Eric Chao; (Miamisburg,
OH) |
Correspondence
Address: |
ALIX YALE & RISTAS LLP
750 MAIN STREET
SUITE 1400
HARTFORD
CT
06103
US
|
Family ID: |
23187705 |
Appl. No.: |
10/677545 |
Filed: |
October 2, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10677545 |
Oct 2, 2003 |
|
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PCT/US02/23078 |
Jul 19, 2002 |
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60306974 |
Jul 19, 2001 |
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Current U.S.
Class: |
162/78 |
Current CPC
Class: |
D21C 9/163 20130101 |
Class at
Publication: |
162/078 |
International
Class: |
D21C 003/00 |
Claims
What is claimed is:
1. An alkaline peroxide mechanical pulping process comprising the
steps of: feeding a lignocellulosic material into a first press;
pressing the lignocellulosic material; discharging the
lignocellulosic material from the first press; impregnating the
lignocellulosic material discharged from the first press with a
first alkaline peroxide pretreatment solution and maintaining the
impregnation for a first reaction time; feeding the impregnated
lignocellulosic material to a refiner having an inlet and a
rotating disc within a superatmospheric casing; refining the
impregnated lignocellulosic material to form a primary pulp having
a temperature of at least about 80 C; delivering a stream of
primary pulp from the superatmospheric casing to an intermediate
line while the primary pulp temperature is at least about 80 C;
adding an alkaline peroxide intermediate line solution to the
stream of primary pulp within the intermediate line while the
primary pulp temperature is at least about 80 C; mixing the
intermediate line solution and the stream of primary pulp to form a
reaction mixture in the intermediate line; discharging the reaction
mixture having a temperature of at least about 80 C into a
retention vessel; retaining the reaction mixture in the retention
vessel to produce a bleached material.
2. The alkaline peroxide mechanical pulping process of claim 1
further comprising; feeding the lignocellulosic material that has
been impregnated with the first pretreatment solution for a first
reaction time, into a second press; pressing and discharging the
lignocellulosic material from the second press; impregnating the
lignocellulosic material discharged from the second press with a
second alkaline peroxide pretreatment solution and maintaining the
second impregnation for a second reaction time.
3. The alkaline peroxide mechanical pulping process of claim 1
further comprising adding an alkaline peroxide refiner solution to
the lignocellulosic material at the refiner.
4. The alkaline peroxide mechanical pulping process of claim 1,
wherein the step of feeding the impregnated lignocellulosic
material to a refiner having an inlet and a rotating disc within a
superatmospheric casing includes maintaining the superatmospheric
casing at a pressure of at least about 240 kPa.
5. The alkaline peroxide mechanical pulping process of claim 1,
wherein the step of mixing is immediately followed by introducing
the mixture into a separator and the separated pulp is then
discharged into said retention vessel.
6. The alkaline peroxide mechanical pulping process of claim 1,
wherein the step of adding an alkaline peroxide intermediate line
solution to the stream of primary pulp within the intermediate line
includes adding the intermediate line solution immediately after a
blow valve.
7. The alkaline peroxide mechanical pulping process of claim 5,
wherein the step of adding an alkaline peroxide intermediate line
solution to the stream of primary pulp within the intermediate line
includes adding the intermediate line solution immediately prior to
the separator.
8. The alkaline peroxide mechanical pulping process of claim 1,
wherein the step of delivering a stream of primary pulp from the
superatmospheric casing to a intermediate line further includes the
primary pulp having a temperature in the range of about 90 C to
about 155 C and a consistency of about 20 to about 60%.
9. The alkaline peroxide mechanical pulping process of claim 1,
wherein the reaction mixture is retained in the retention vessel at
a temperature of about 60 C to about 95 C and a consistency of
about 20% to about 40%.
10. The alkaline peroxide mechanical pulping process of claim 1,
wherein the reaction mixture is retained in the retention vessel at
a temperature of about 85 C to about 95 C, and a consistency of
about 30%.
11. The alkaline peroxide mechanical pulping process of claim 1,
wherein the impregnation solution contains alkali, peroxide, and
stabilizer; the intermediate line solution contains alkali,
peroxide, and stabilizer; and said intermediate line solution has a
temperature less than about 80 C.
12. The alkaline peroxide mechanical pulping process of claim 2,
wherein the first impregnation solution contains 0.3% DTPA; the
second impregnation solution contains 0.2% MgSO.sub.4, 4.4%
silicate, 2.8% TA, and 2.8% H2O2; and the intermediate line
solution contains 0.16% DTPA, 0.16% MgSO4, 2.3% silicate, 1.8% TA
with 0.5% being residual, 2.4% H2O2 with 1.1% being residual.
13. The alkaline peroxide mechanical pulping process of claim 2,
wherein the first impregnation solution contains 0.5% DTPA; the
second impregnation solution contains 0.2% DTPA, 0.1% MgSO4, 2.0%
silicate, 1.6% TA, and 2.6% H2O2; and the intermediate line
solution contains 0.13% DTPA, 0.13% MgSO4, 2.5% silicate, 1.2% TA
with 0.1% being residual, 2.1% H2O2 with 2.1% being residual.
14. The alkaline peroxide mechanical pulping process of claim 2,
wherein the first impregnation solution contains 0.3% DTPA, 0.05%
MgSO4, 0.7% silicate, 0.2% TA, and 0.5% H2O2; the second
impregnation solution contains 0.1% DTPA, 0.08% MgSO4, 1.8%
silicate, 1.4% TA, and 1.9% H2O2; and the intermediate line
solution contains 0.22% DTPA, 0.11% MgSO4, 1.1% silicate, 0.9% TA
with 0.2% being residual, 1.2% H2O2 with 1.7% being residual.
15. The alkaline peroxide mechanical pulping process of claim 2,
wherein the first impregnation solution contains 0.4% TA, 0.5%
H2O2,0.2% DTPA, 0.04% MgSO4, 0.5% silicate; the second impregnation
solution contains 0.14% DTPA, 0.05% MgSO4, 0.5% silicate, 0.4% TA,
and 0.6% H2O2; and the intermediate line solution contains 0.18%
DTPA, 0.06% MgSO4, 1.8% silicate, 1.2% TA with 0.1% being residual,
1.8% H2O2 with 1.1% being residual.
16. The alkaline peroxide mechanical pulping process of claim 2,
wherein the first impregnation solution contains 0.4% TA, 0.6%
H2O2,0.18% DTPA, 0.03% MgSO4, 0.3% silicate; the second
impregnation solution contains 0.15% DTPA, 0.05% MgSO4, 0.4%
silicate, 0.4% TA, and 0.7% H2O2; and the intermediate line
solution contains 1.7% TA, and 2.8% H2O2 with 1.1% being
residual.
17. A chemimechanical pulping process comprising the steps of:
feeding a lignocellulosic material into a first press; pressing the
lignocellulosic material; discharging the lignocellulosic material
from the first press; impregnating the lignocellulosic material
discharged from the first press with a first chemical bleaching
pretreatment solution and maintaining the impregnation for a first
reaction time; feeding the lignocellulosic material impregnated
with the first pretreatment solution to a refiner having an inlet
and a rotating disc within a superatmospheric casing; refining the
lignocellulosic material to form a primary pulp having a
temperature of at least 80 C; while the primary pulp temperature is
at least about 80 C, discharging the primary pulp from the casing
to an intermediate line; while the primary pulp temperature is at
least about 80 C, adding an alkaline peroxide intermediate line
solution at the intermediate line which contains the primary pulp;
mixing the intermediate line solution with the primary pulp; while
the intermediate line solution and primary pulp mixture are at a
temperature of at least about 80 C discharging the intermediate
line solution and primary pulp mixture into a retention tower;
retaining the mixture in the retention tower; and processing the
primary pulp further to a secondary pulp.
18. An alkaline peroxide mechanical pulping process comprising the
steps of: in a primary refiner having a superatmoshperic casing,
refining a lignocellulosic material that has been pretreated and
impregnated with at least a first alkaline peroxide pretreatment
solution; discharging the lignocellulosic material at temperature
of at least about 80 C into intermediate line having at least one
solution inlet port; injecting an alkaline peroxide intermediate
line solution through the at least one solution inlet port; mixing
the intermediate line solution and the lignocellulosic material in
the intermediate line; discharging the lignocellulosic material
from the intermediate line at a temperature of at least about 80 C;
and maintaining the discharged lignocellulosic material for a
reaction period.
19. The alkaline peroxide mechanical pulping process of claim 18,
wherein the step of refining further includes adding a refiner
solution of alkaline peroxide at the primary refiner.
20. The alkaline peroxide mechanical pulping process of claim 18,
wherein the step of injecting an alkaline peroxide intermediate
line solution through the at least one solution inlet port and into
the intermediate line containing the lignocellulosic material
includes injecting an alkaline peroxide intermediate line solution
through, at least, one solution inlet port located immediately
after the blow valve.
21. An alkaline peroxide mechanical pulping process comprising the
steps of: feeding a lignocellulosic material into a first press;
pressing the lignocellulosic material; discharging the
lignocellulosic material from the first press; impregnating the
lignocellulosic material discharged from the first press with a
first alkaline peroxide pretreatment solution and maintaining the
impregnation for a first reaction time; feeding the impregnated
lignocellulosic material to a refiner having an inlet and a
rotating disc within a superatmospheric casing; refining the
impregnated lignocellulosic material to form a primary pulp;
discharging the stream of primary pulp from the superatmospheric
casing to an intermediate line; adding an alkaline peroxide
intermediate line solution to the stream of primary pulp within the
intermediate line; mixing the intermediate line solution and the
stream of primary pulp to form a reaction mixture; discharging the
reaction mixture into a retention vessel; retaining the reaction
mixture in the retention vessel to produce a bleached material.
22. The alkaline peroxide mechanical pulping process of claim 21,
further comprising; feeding the lignocellulosic material that has
been impregnated with the first pretreatment solution for a first
reaction time, into a second press; pressing and discharging the
lignocellulosic material from the second press; impregnating the
lignocellulosic material discharged from the second press with a
second alkaline peroxide pretreatment solution and maintaining the
second impregnation for a second reaction time.
23. The alkaline peroxide mechanical pulping process of claim 21
further comprising adding an alkaline peroxide refiner solution to
the lignocellulosic material at the refiner.
24. The alkaline peroxide mechanical pulping process of claim 21,
wherein the step of discharging the stream of primary pulp from the
superatmospheric casing to an intermediate line includes the
intermediate line having a blow valve and adding the alkaline
intermediate line solution immediately after the blow valve.
25. The alkaline peroxide mechanical pulping process of claim 21,
wherein discharging the stream of primary pulp from the
superatmospheric casing includes the intermediate line having a
blow valve followed by a separator and the step of adding an
alkaline peroxide intermediate line solution to the stream of
primary pulp within the intermediate line includes adding the
alkaline peroxide intermediate line solution immediately prior to
the separator.
26. The alkaline peroxide mechanical pulping process of claim 21,
wherein discharging the stream of primary pulp from the
superatmospheric casing includes the intermediate line having a
blow valve followed by a separator and the step of adding an
alkaline peroxide intermediate line solution to the stream of
primary pulp within the intermediate line includes adding the
alkaline peroxide intermediate line solution at the separator.
27. The alkaline peroxide mechanical pulping process of claim 24,
wherein discharging the stream of primary pulp from the
superatmospheric casing includes the intermediate line having a
blow valve followed by a separator and the step of adding an
alkaline peroxide intermediate line solution to the stream of
primary pulp within the intermediate line includes adding the
alkaline peroxide intermediate line solution immediately after the
separator.
28. The alkaline peroxide mechanical pulping process of claim 21,
wherein the step of feeding the impregnated lignocellulosic
material to a refiner having an inlet and a rotating disc within a
superatmospheric casing includes maintaining the superatmospheric
casing at a pressure of at least about 240 kPa.
29. The alkaline peroxide mechanical pulping process of claim 21,
wherein the impregnation solution contains alkali, peroxide, and
stabilizer; the intermediate line solution contains alkali,
peroxide and stabilizer; and said intermediate line solution is at
a temperature less than the stream of primary pulp.
30. The alkaline peroxide mechanical pulping process of claim 22,
wherein the first impregnation solution contains 0.3% DTPA; the
second impregnation solution contains 0.2% MgSO4, 4.4% silicate,
2.8% TA, and 2.8% H2O2; and the intermediate line solution contains
0.16% DTPA, 0.16% MgSO4, 2.3% silicate, 1.8% TA with 0.5% being
residual, 2.4% H2O2 with 1.1% being residual.
31. The alkaline peroxide mechanical pulping process of claim 22,
wherein the first impregnation solution contains 0.5% DTPA; the
second impregnation solution contains 0.2% DTPA, 0.1% MgSO4, 2.0%
silicate, 1.6% TA, and 2.6% H2O2; and the intermediate line
solution contains 0.13% DTPA, 0.13% MgSO4, 2.5% silicate, 1.2% TA
with 0.1% being residual, 2.1% H2O2 with 2.1% being residual.
32. The alkaline peroxide mechanical pulping process of claim 22,
wherein the first impregnation solution contains 0.3% DTPA, 0.05%
MgSO4, 0.7% silicate, 0.2% TA, and 0.5% H2O2; the second
impregnation solution contains 0.1% DTPA, 0.08% MgSO4, 1.8%
silicate, 1.4% TA, and 1.9% H2O2; and the intermediate line
solution contains 0.22% DTPA, 0.11% MgSO4, 1.1% silicate, 0.9% TA
with 0.2% being residual, 1.2% H2O2 with 1.7% being residual.
33. The alkaline peroxide mechanical pulping process of claim 22,
wherein the first impregnation solution contains 0.4% TA, 0.5%
H2O2,0.2% DTPA, 0.04% MgSO4, 0.5% silicate; the second impregnation
solution contains 0.14% DTPA, 0.05% MgSO4, 0.5% silicate, 0.4% TA,
and 0.6% H2O2; and the intermediate line solution contains 0.18%
DTPA, 0.06% MgSO4, 1.8% silicate, 1.2% TA with 0.1% being residual,
1.8% H2O2 with 1.1% being residual.
34. The alkaline peroxide mechanical pulping process of claim 22,
wherein the first impregnation solution contains 0.4% TA, 0.6%
H2O2,0.18% DTPA, 0.03% MgSO4, 0.3% silicate; the second
impregnation solution contains 0.15% DTPA, 0.05% MgSO4, 0.4%
silicate, 0.4% TA, and 0.7% H2O2; and the intermediate line
solution contains 1.7% TA, and 2.8% H2O2 with 1.1% being
residual.
35. A chemimechanical pulping process comprising the steps of:
feeding a lignocellulosic material into a press; pressing the
lignocellulosic material; discharging the lignocellulosic material
from the press; impregnating the lignocellulosic material
discharged from the press with a chemical bleaching pretreatment
solution; feeding the lignocellulosic material impregnated with the
pretreatment solution to a refiner having an inlet and a rotating
disc within a superatmospheric casing; refining the lignocellulosic
material to form a primary pulp; discharging the primary pulp from
the casing through an intermediate line; adding an alkaline
peroxide solution at the intermediate line to the primary pulp;
mixing the intermediate line solution with the primary pulp;
delivering the intermediate line solution and primary pulp mixture
to a retention tower; processing the primary pulp from the
retention tower, into a secondary pulp.
36. An alkaline peroxide mechanical pulping process comprising the
steps of: in a primary refiner having a superatmoshperic casing,
refining a lignocellulosic material that has been pretreated and
impregnated with at least a first alkaline peroxide pretreatment
solution; discharging the lignocellulosic material into an
intermediate line having at least one solution inlet port;
injecting an alkaline peroxide intermediate line solution through
the at least one solution inlet port; mixing the intermediate line
solution and the lignocellulosic material; discharging the
lignocellulosic material from the intermediate line; and retaining
the discharged lignocellulosic material for a reaction period.
37. The alkaline peroxide mechanical pulping process of claim 36,
wherein the step of refining further includes adding a refiner
solution of alkaline peroxide at the primary refiner.
38. The alkaline peroxide mechanical pulping process of claim 36,
wherein the step of injecting an alkaline peroxide intermediate
line solution through the, at least one, solution inlet port and
into the intermediate line containing the lignocellulosic material
includes injecting an alkaline peroxide intermediate line solution
through, at least, one solution inlet port located immediately
after a blow valve.
39. The alkaline peroxide mechanical pulping process of claim 36,
wherein the step of injecting an alkaline peroxide intermediate
line solution through the, at least one, solution inlet port and
into the intermediate line containing the lignocellulosic material
includes injecting an alkaline peroxide intermediate line solution
through, at least, one solution inlet port located immediately
prior to a separator.
40. The alkaline peroxide mechanical pulping process of claim 36,
wherein the step of injecting an alkaline peroxide intermediate
line solution through the, at least one, solution inlet port and
into the intermediate line containing the lignocellulosic material
includes injecting an alkaline peroxide intermediate line solution
through, at least, one solution inlet port located at a
separator.
41. The alkaline peroxide mechanical pulping process of claim 36,
wherein the step of injecting an alkaline peroxide intermediate
line solution through the, at least one, solution inlet port and
into the intermediate line containing the lignocellulosic material
includes injecting an alkaline peroxide intermediate line solution
through, at least, one solution inlet port located at a discharge
portion of a separator.
42. An alkaline peroxide mechanical pulping process comprises the
steps of: in a refiner having a casing, additionally refining a
lignocellulosic based material that has been previously pretreated
and impregnated with at least a first alkaline peroxide
pretreatment solution and which has been previously refined;
discharging the lignocellulosic based material into an intermediate
line having at least one solution inlet port; injecting an alkaline
peroxide intermediate line solution through the at least one
solution port; mixing the intermediate line solution and the
lignocellulosic based material; discharging the lignocellulosic
based material from the intermediate line; and retaining the
discharged lignocellusic based material for a reaction period.
43. The alkaline peroxide mechanical pulping process of claim 42,
wherein the refiner casing is superatmospheric.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of
International Application No. PCT/US0223078 under 35 U.S.C.
.sctn.365(c) filed Jul. 19, 2002 (designating the U.S.) which
claims benefit under 35 U.S.C. .sctn. 119(e) of U.S. Provisional
Application No. 60/306,974 filed Jul. 19, 2001.
FIELD OF THE INVENTION
[0002] 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
[0003] 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.
[0004] 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 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.
[0005] 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.
[0006] 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
[0007] 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.
[0008] 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.
[0009] 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
lignocellulosic feed material before primary refining with the
concept of applying chemicals such as alkaline peroxide at the
primary refiner.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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
[0014] The invention will be better understood by reference to the
accompanying drawings in which:
[0015] FIG. 1 is a block diagram depicting the general P-RC APMP
process.
[0016] FIG. 1A is a block diagram depicting steps of transferring
lignocellulosic material to a refiner having a casing at
atmospheric pressure, with discharge at atmospheric pressure.
[0017] FIG. 1B is a block diagram depicting steps of transferring
lignocellulosic material to a refiner having a pressurized casing
with pressurized discharge.
[0018] FIG. 1C 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.
[0019] FIG. 1D 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.
[0020] FIG. 1E 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.
[0021] FIG. 1F 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.
[0022] FIG. 2 is a table comparing P-RC with two prior art
processes.
[0023] FIG. 3 is a graph of freeness as related to energy
consumption for P-RC and two prior art processes.
[0024] FIG. 4 is a graph of density as related to energy
consumption for P-RC and two prior art processes.
[0025] FIG. 5 is a graph of the tensile of tensile development for
P-RC and two prior art processes.
[0026] FIG. 6 is a graph of burst development for P-RC and two
prior art processes.
[0027] FIG. 7 is a graph of brightness development for P-RC and two
prior art processes.
[0028] FIG. 8 is a graph of the light scattering coefficient of the
pulp as a function of freeness for P-RC and two prior art
processes.
[0029] FIG. 9 is a comparative table of atmospheric versus
pressurized casing processing of aspen wood chips according to
P-RC.
[0030] FIG. 10 is a comparative table of atmospheric versus
pressurized casing processing of birch wood chips according to
P-RC.
[0031] FIG. 11 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.
[0032] FIG. 12 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.
[0033] FIG. 13 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.
[0034] FIG. 14 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.
[0035] FIG. 15 is a comparative table of refiner eye versus blow
line chemical addition processing of birch and maple wood chips
according to the invention.
[0036] FIG. 16 is a comparative table of refiner eye versus blow
line chemical addition processing of spruce and red pine wood chips
according to the invention.
[0037] FIG. 17 is a comparative table of refiner eye versus blow
line chemical addition processing wood chips at higher pressure
according to the invention.
[0038] FIG. 18 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
[0039] FIG. 1 presents a simplified process flow diagram of the
P-RC 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.
[0040] The preconditioning step(s) as implemented in stages 1 and 2
of FIG. 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.
[0041] 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.
[0042] 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 FIG. 11,
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
FIG. 18, 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.degree. C. to about 155.degree.
C.
[0043] 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 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 45 psi. 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 45 psi are used. In other cases the alkaline
peroxide chemicals may be introduced intermediate the cyclone and
the blow valve, or even at the cyclone.
[0044] 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.
[0045] As an illustrative example, the pulp may be about
100.degree. C. or higher, and the chemical liquor may be 40.degree.
C. or lower. The intermediate line solution may preferably be in
the range of about 10.degree. C. to about 25.degree. C. but can be
up to 80.degree. 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 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.
[0046] 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.
[0047] FIGS. 1A through 1F present various examples of a P-RC 20
process of the type generally shown in FIG. 1. For example, FIGS.
1A 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).
[0048] 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.
[0049] 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 FIGS. 1C 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 FIGS. 1E 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 FIGS. 1C 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.
[0050] In one embodiment of the invention, for example as shown in
FIG. 18, the discharge from the blow valve may be delivered
indirectly to a retention tower through a seperator and/or a
press.
[0051] The presence of an ample amount of the alkaline peroxide
chemicals in the primary refiner (e.g., as by shifting a large
proportion 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.
[0052] 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.degree. C.
to about 155.degree. C.
[0053] 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 60.degree.
C. to about 95.degree. C. 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.
[0054] 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.
[0055] 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,
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.
[0056] Further embodiments and aspects of the invention will be
apparent from the examples and description set forth below.
ILLUSTRATIVE EXAMPLES
EXAMPLE SET A
[0057] 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:
[0058] 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.
[0059] Chemical Impregnation: Chips were pre-steamed first for 10
minutes, and then pressed using an Andritz 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.
[0060] Refining: An Andritz 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.
[0061] Pulp Testing: Tappi Standards were used for all pulp testing
except for freeness, which follows Canadian Standard Freeness (CSF)
test methods.
[0062] In the first of three processes compared, all of the
alkaline chemicals were applied, (3.3% total alkalinity, (TA), and
2.4% H.sub.2O.sub.2, together with 0.2% DTPA, 0.07% MgSO.sub.4 and
3% Na.sub.2SiO.sub.3) 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%
H.sub.2O.sub.2, 0.08% DTPA, 0.04% MgSO.sub.4 and 2.4%
Na.sub.2SiO.sub.3), at the chip impregnation stage, and
approximately one third of the total chemicals, (1.0% TA, 1.0%
H.sub.2O.sub.2, 0.19% DTPA, 0.05% MgSO.sub.4, and 0.9%
Na.sub.2SiO.sub.3), 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% H.sub.2O.sub.2, 0.36%
DTPA, 0.11% MgSO.sub.4, 4.3% Na.sub.2SiO.sub.3), 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.degree. C.), before the
second stage refining. There was no interstage washing.
[0063] FIG. 2 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/H.sub.2O.sub.2
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/H.sub.2O.sub.2 ratio,
1.27, was use for "Refiner" series, the second lowest, 1.31, 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, FIG. 2.
[0064] 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.
[0065] Graphic presentation of the data gathered from pulp after
secondary refining after different investigated processes are shown
in FIGS. 3 through 8. FIG. 3 shows effects of the different
chemical applications on pulp freeness development in relation to
specific 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.
[0066] 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 FIG. 3,
therefore, are better used for comparison purpose than for their
absolute values.
[0067] 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 FIG. 4. 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.
[0068] As for pulp intrinsic property development, there was
however, little difference among the three series, as illustrated
in FIGS. 5 and 6, suggesting that as long as the chemicals are
added before refining, the mechanism involved in fiber strength
property development remains the same.
[0069] As for pulp optical property development, in mechanical
pulping, pulp brightness is often freeness-dependent. FIG. 7 shows
brightness at different freeness from each series. Of interest is
that "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% H.sub.2O.sub.2/3.4% TA
versus 3.3% H.sub.2O.sub.2/4.2% 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.
[0070] FIG. 8 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
[0071] 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:
[0072] 1) better steam handling at the refiner discharge,
especially for high capacity refiners (300 t/d or higher);
[0073] 2) ease of transfer primary pulp from the refiner to the
interstage high consistency (HC) tower;
[0074] 3) a potential to use some of the steam generated from the
primary refining (by using a cyclone to separate steam and pulp
fiber);
[0075] 4) ease of converting existing TMP systems into a P-RC APMP
process.
[0076] These examples show that running the primary refiner at a
low pressure (140 kPa) in the casing and atmospheric at the inlet
can 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.degree. C.) observed.
[0077] The materials and conditions for the following examples
below were as follows:
[0078] Wood: Aspen and birch chips from a commercial pulp mill in
eastern Canada were used in this study.
[0079] 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.
[0080] 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.degree. C.) for a certain period of
time.
[0081] Pressurized Refiner System: An Andritz single disc 36"
diameter (92 cm) pressurized system was modified for atmospheric
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.
[0082] Pulp Tests: TAPPI standard was used for brightness tests.
Peroxide residuals were measured using standard iodometric
titration.
[0083] 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.
[0084] FIG. 9 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% H.sub.2O.sub.2), both the atmospheric and the casing
pressurized gave a similar brightness, achieving 84.2% ISO and
84.7% ISO respectively.
[0085] The residual pH (8.8-9.0) in both cases were slightly higher
than ideal (approximately 7.0-8.5) and the H.sub.2O.sub.2 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.
[0086] It is worth pointing out that the bleaching efficiency shown
in Table 1 (3.7 to 3.9% H.sub.2O.sub.2 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 H.sub.2O.sub.2
bleaching of TMP or CTMP pulps from aspen.
[0087] 20 FIG. 10 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%
H.sub.2O.sub.2 to reach 82.4 to 82.6% ISO brightness. In this case,
the residual chemicals (0.1-0.2% TA, 0.5-0.6% H.sub.2O.sub.2 and pH
of 8) were within ideal H.sub.2O.sub.2 bleaching conditions.
EXAMPLE SET C
[0088] 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
[0089] All the hardwoods (birch and maple) were received in chip
form and mixed separately before being further processed. All the
softwoods (spruce, pine and softwood blends) were received in log
form, and debarked, chipped and mixed prior to further
processing.
Chip Impregnation
[0090] The wood chips, unless otherwise specified, were impregnated
twice with AP chemicals (consisting of sodium hydroxide (NaOH),
hydrogen peroxide (H.sub.2O.sub.2), DTPA, Magnesium Sulfate
(MgSO.sub.4) and sodium silicate (Na.sub.2SiO.sub.3), 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
[0091] An Andritz 36" diameter (91 cm) single disc 36-1CP 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
[0092] 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.degree. C., depending specific refining energy used at the
refiner, the chemical charges, and the nature of the raw
materials.
Pulp Tests
[0093] 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)).
[0094] FIG. 15 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% MgSO.sub.4, 4.4% Silicate, 2.8% TA, and
2.8% H.sub.2O.sub.2 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% MgSO.sub.4, 2.0% Silicate, 1.6% TA and 2.6%
H.sub.2O.sub.2 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.
[0095] For the birch, both series (A1 and A2) used a total of 5.2%
H.sub.2O.sub.2 and 4.6% total alkali (TA), and had a similar amount
of H.sub.2O.sub.2 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 (A1) 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 m.sup.2/kg
from the former and 0.25 m.sup.2/kg from the latter.
[0096] 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 m.sup.2/kg), of the
former.
[0097] Softwoods, namely spruce and red pine, were also
investigated in to examine effects of different AP chemical
applications. FIG. 16 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% MgSO.sub.4, 0.7%
Silicate, 0.2% TA and 0.5% H.sub.2O.sub.2, and then 0.1% DTPA,
0.08% MgSO.sub.4, 1.8% Silicate, 1.4% TA and 1.9% H.sub.2O.sub.2 at
second stage impregnation.. In the case of red pine the chips were
treated with 0.4% TA, 0.5% H.sub.2O.sub.2, 0.2% DTPA, 0.04%
MgSO.sub.4 and 0.5% Silicate at first impregnation, and 0.4% TA,
0.6% H.sub.2O.sub.2, 0.14% DTPA, 0.05% MgSO.sub.4, 0.4% Silicate at
second stage impregnation. For spruce, using similar amounts of AP
chemicals, for example see FIG. 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
m.sup.2/kg.
[0098] 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 m.sup.2/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.
[0099] A softwood blend from spruce and pine was subjected to high
pressure refining at the refiner chemical treatment stage as in
FIG. 17.
[0100] 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% H.sub.2O.sub.2,
0.18% DTPA, 0.03% MgSO.sub.4 and 0.3% Sodium Silicate at 1.sup.st
stage chip impregnation; 0.4% TA, 0.7% H.sub.2O.sub.2, 0.15% DTPA,
0.05% MgSO.sub.4 and 0.4% Sodium Silicate at 2.sup.nd stage chip
impregnation; 0.9% TA, 1.5% H.sub.2O.sub.2, 0.18% DTPA, 0.09%
MgSO.sub.4 and 1.8% Sodium Silicate at refiner chemical treatment
stage, either at the refiner eye as for A9, or the 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. FIG.
17 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% H.sub.2O.sub.2 and reached
73.7-73.4% ISO). The samples had similar light absorption
coefficient (0.96-1.1 m.sup.2/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.
* * * * *