U.S. patent application number 09/186345 was filed with the patent office on 2001-09-27 for method for processing straw pulp.
This patent application is currently assigned to WEYERHAEUSER COMPANY. Invention is credited to FULLER, WILLIAM S., NAY, WAYNE H..
Application Number | 20010023749 09/186345 |
Document ID | / |
Family ID | 22684577 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010023749 |
Kind Code |
A1 |
NAY, WAYNE H. ; et
al. |
September 27, 2001 |
METHOD FOR PROCESSING STRAW PULP
Abstract
A method for processing straw pulp that includes caustic
treatment is provided. The caustic treated straw pulp can be
incorporated into a papermaking furnish to provide a paper product.
The caustic treated pulp imparts strength to papers incorporating
the pulp.
Inventors: |
NAY, WAYNE H.; (PLEASANT
HILL, OR) ; FULLER, WILLIAM S.; (FEDERAL WAY,
WA) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE
SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
WEYERHAEUSER COMPANY
|
Family ID: |
22684577 |
Appl. No.: |
09/186345 |
Filed: |
November 4, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09186345 |
Nov 4, 1998 |
|
|
|
08946497 |
Oct 7, 1997 |
|
|
|
Current U.S.
Class: |
162/21 ; 162/24;
162/90; 162/96; 162/97 |
Current CPC
Class: |
D21C 3/02 20130101; Y02P
60/877 20151101; A23K 10/37 20160501; D21C 5/00 20130101; D21B 1/36
20130101; Y02P 60/87 20151101; D21B 1/00 20130101 |
Class at
Publication: |
162/21 ; 162/24;
162/90; 162/96; 162/97 |
International
Class: |
D21B 001/12; D21B
001/36; D21B 001/16; D21C 003/02 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed defined as follows:
1. A method for pulping straw comprising: mixing straw chips with
steam and water to form a mixture; exposing the mixture to
temperatures and pressures sufficient to significantly soften the
straw chips to form straw pulp, lignins and hemicellulose when
exposed to a rapid decrease in pressure; passing the mixture
through a press to separate a portion of lignins and hemicellulose
from the straw pulp; passing the straw pulp through a defiberizer
to form fiberized straw pulp; and treating the fiberized straw pulp
with a caustic solution to provide caustic treated straw pulp.
2. The method of claim 1 wherein the straw chips are mixed with a
caustic before the mixture of straw chips, steam and water is
exposed to temperatures and pressures sufficient to significantly
soften the straw chips to form straw pulp, lignins and
hemicellulose in the mixture when exposed to a rapid decrease in
pressure.
3. The method of claim 2 wherein the caustic is present in the
mixture in about less than two percent (2%) by weight based upon
the dry straw chips.
4. The method of claim 2 wherein the caustic is selected from the
group consisting of sodium hydroxide, potassium hydroxide, and
mixtures thereof.
5. The method of claim 1 wherein the mixture is exposed to
temperatures and pressures sufficient to significantly softened the
mixture when exposed to a rapid decrease in pressure for between
about two and one half (21/2) minutes to about eight (8)
minutes.
6. The method of claim 1 wherein the straw chips are selected from
the group consisting of ryegrass, wheat, a mixture of grain and
cereal straws, and mixtures thereof.
7. The method of claim 1 wherein at least about seventy percent
(70%) by weight of the straw chips are formed into straw pulp.
8. The method of claim 1 wherein the pressures sufficient to
significantly soften the straw chips when exposed to a rapid
decrease in pressure from between about 140 psig and about 200 psig
to about atmospheric pressure.
9. The method of claim 1 wherein the straw chips are formed by
chopping straw to form a mixture of straw chips, meal, ash and grit
and screening said mixture to separate a substantial portion of the
straw chips from the meal, ash and grit.
10. The method of claim 1 wherein the straw pulp has a Canadian
Standard Freeness of between about 200 and about 700.
11. The method of claim 1 wherein treating the fiberized straw pulp
with a caustic solution comprises soaking the pulp in a caustic
solution.
12. The method of clam 1 wherein the caustic solution is an aqueous
solution comprising a caustic selected from the group consisting of
sodium hydroxide, potassium hydroxide and mixtures thereof.
13. The method of claim 1 wherein the caustic solution comprises a
caustic present in an amount from about 1 to about 5 percent by
weight of the solution.
14. The method of claim 1 wherein the caustic solution comprises a
caustic present in about 2 percent by weight of the solution.
15. The method of claim 11 wherein the straw pulp is soaked in the
caustic solution for a time from about 0.5 to about 2.0 hours.
16. The method of claim 11 wherein the straw pulp is soaked in a 2
percent by weight sodium hydroxide in water for about 0.5 hour.
17. The method of claim 9 wherein the separated meal, ash, and grit
is used as animal feed.
18. The method of claim 1 wherein passing the mixture through a
press to separate a portion of lignins and hemicellulose from the
straw pulp provides a usable byproduct comprising water, reacted
lignins, and hemicellulose.
19. The method of claim 18 wherein the byproduct is mixed with
meal, ash, and grit to form an animal feed.
20. Animal feed comprising meal, ash, and grit separated from straw
pulp according to the method of claim 9.
21. The animal feed of claim 20 further comprising the usable
byproduct formed by the method of claim 18.
22. Animal feed comprising the usable byproduct formed by the
method of claim 18.
23. Straw pulp produced by the method of claim 1.
24. Straw pulp produced by the method of claim 2.
25. A paper product comprising caustic treated straw pulp.
26. The paper product of claim 25 wherein the caustic treated straw
pulp is formed by: mixing straw chips with steam and water to form
a mixture; exposing the mixture to temperatures and pressures
sufficient to significantly soften the straw chips to form straw
pulp, lignins and hemicellulose when exposed to a rapid decrease in
pressure; passing the mixture through a press to separate a portion
of lignins and hemicellulose from the straw pulp; passing the straw
pulp through a defiberizer to form fiberized straw pulp; and
treating the fiberized straw pulp with a caustic solution to
provide caustic treated straw pulp.
27. A method for forming a paper product comprising forming a
papermaking furnish comprising caustic treated straw pulp and
forming a paper product from the papermaking furnish.
28. The method of claim 27 wherein the caustic treated straw pulp
is formed by: mixing straw chips with steam and water to form a
mixture; exposing the mixture to temperatures and pressures
sufficient to significantly soften the straw chips to form straw
pulp, lignins and hemicellulose when exposed to a rapid decrease in
pressure; passing the mixture through a press to separate a portion
of lignins and hemicellulose from the straw pulp; passing the straw
pulp through a defiberizer to form fiberized straw pulp; and
treating the fiberized straw pulp with a caustic solution to
provide caustic treated straw pulp.
29. A method for increasing the strength of a paper product
comprising: combining a papermaking furnish and caustic treated
straw pulp to provide a straw pulp furnish; and forming a paper
product from the straw pulp furnish to provide a paper product
having increased strength compared to a paper product formed the
papermaking furnish.
30. The method of claim 29 wherein the caustic treated straw pulp
is formed by: mixing straw chips with steam and water to form a
mixture; exposing the mixture to temperatures and pressures
sufficient to significantly soften the straw chips to form straw
pulp, lignins and hemicellulose when exposed to a rapid decrease in
pressure; passing the mixture through a press to separate a portion
of lignins and hemicellulose from the straw pulp; passing the straw
pulp through a defiberizer to form fiberized straw pulp; and
treating the fiberized straw pulp with a caustic solution to
provide caustic treated straw pulp.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation-in-part
application of copending application Serial No. 08/946,497, filed
Oct. 7, 1997, the benefit of the priority of the filing date of
which is hereby claimed under 35 U.S.C..sctn. 120.
FIELD OF THE INVENTION
[0002] This invention relates to a method for processing straw pulp
and, more particularly, to a method for processing straw pulp that
includes caustic treatment.
BACKGROUND OF THE INVENTION
[0003] There is increasing interest in the incorporation of nonwood
cellulosic fibers into paper products. There is a tremendous amount
of nonwood fibers available for pulp production. It has been
estimated that the world straw production is approximately
500,000,000 metric tons per year. Only about half of that amount is
used for low value purposes, such as building materials, fuel, and
cattle feed. Most of the remaining amount is wasted by burning,
without energy recovery, or plowing back into the ground. However,
among the limitations in making straw into paper is incorporating
the lower quality fiber derived from straw into a product with
sufficient strength, durability, and brightness for a marketable
end product.
[0004] U.S. Pat. No. 4,040,899, issued in 1977 to Emerson, attempts
to address the use of straw pulp in paper. Emerson teaches
intertwining and crimping fibers into a paper web.
[0005] According to Pulp and Paper, published 1952, 1960, by
Interscience Publishers, Inc.,
[0006] Straw is pulped by chemical processes and by a combination
mechanical and chemical process known as mechano-chemical process.
Among the different chemicals used for pulping straw are: (1)
sodium hydroxide, (2) lime alone or in combination with other
alkalies, (3) sodium sulfite plus other alkali, (4) chlorine, and
(5) sodium hydroxide plus sodium sulfide (sulfite process). Other
chemicals suggested for the pulping of straw are nitric acid and
sodium chlorite. Sodium carbonate plus sulfur has been suggested
for the preparation of a coarse pulp (straw Kraft) used for
corrugated papers. There are four principal processes for making
high grade bleachable straw pulp: (1) soda process, (2) sulfate
process, (3) monosulfite process, and (4) the Pomilio chlorine
process. The soda and sulfate processes produce good pulp, but in
rather low yield.
SUMMARY OF THE INVENTION
[0007] The present invention provides a method for pulping straw
chips and forming a usable byproduct. According to the method,
straw chips are mixed with steam and water to form a mixture. The
mixture is exposed to temperatures and pressures sufficient to
significantly soften the straw chips to form straw pulp, lignins,
and hemicellulose when exposed to a rapid decrease in pressure. The
mixture is washed to separate a portion of the lignins and
hemicellulose from the straw pulp such that a usable byproduct of
water, lignins and hemicellulose, referred to as black liquor, is
formed and passed through a mechanical refiner.
[0008] The straw chips may be mixed with a caustic before the
mixture of straw chips, steam and water is exposed to temperatures
and pressures sufficient to significantly soften the straw chips to
form straw pulp, lignins and hemicellulose in the mixture when
exposed to a rapid decrease in pressure. The caustic may be present
in the mixture in about less than two percent by weight. It is more
preferred that the caustic is present in the mixture in about less
than one-half percent by weight. The caustic may comprise sodium
hydroxide. Also, the caustic may comprise potassium hydroxide.
[0009] In one form of the method, the mixture may be exposed to
temperatures and pressures sufficient to significantly soften the
mixture when exposed to a rapid decrease in pressure for between
about two and one-half minutes to about eight minutes.
[0010] In yet another form of the invention, at least about seventy
percent by weight of the straw chips are formed into straw
pulp.
[0011] In yet another form of the invention, the pressure
sufficient to significantly soften the straw chips when exposed to
a rapid decrease in pressure is between about 140 psig and about
200 psig.
[0012] In another form of the invention, the fiber chips may be
selected from nonwood fibers such as ryegrass, wheat and a mixture
of grain and cereal straws.
[0013] Straw chips for use in the method may be formed by chopping
straw to form a mixture of straw chips, meal, ash and grit and
screening the mixture to separate a substantial portion of the
straw chips from the meal, ash and grit. The meal, ash, and grit
may be used as animal feed. In a preferred form of the invention,
the meal, ash, and grit may be mixed with the black liquor
byproduct to form animal feed.
[0014] The straw pulp formed by this method has a Canadian Standard
Freeness between about 200 and about 600.
[0015] The present invention also provides a paper product made
from wood pulp and straw pulp wherein the straw pulp is produced by
mixing straw chips with steam and water to form a mixture of straw
chips, steam and water. The mixture is exposed to temperatures and
pressures sufficient to significantly soften the straw chips into
straw pulp when exposed to decreased pressures. The mixture is then
refined and a substantial portion of the straw pulp is separated
from the mixture. A portion of the wood pulp and the paper product
may be derived from processed post-consumer waste.
[0016] The straw chips may be formed by chopping straw to form a
mixture of straw chips, meal, ash and grit and screening the
mixture to separate a substantial portion of the straw chips from
the meal, ash and grit.
[0017] In yet another form of the invention, the straw pulp has a
Canadian Standard Freeness (CSF) of between about 200 and about 600
and an STFI between about 14 and about 21.
[0018] In another embodiment, the present invention provides a
straw pulp product that, when incorporated into paper, imparts
increased strength to the paper. The straw pulp product is prepared
by a method that includes soaking the pulp in caustic. The method
also provides meal, ash, and grit that can be used as animal feed.
The meal, ash, and grit can also be mixed with the black liquor
byproduct of the method to form animal feed.
[0019] These and other advantages and features will become apparent
from the detailed description of the best mode for carrying out the
invention that follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated [as the same
becomes better understood] by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0021] FIG. 1 is an elevational view of a rye grass plant;
[0022] FIG. 2 is a flow diagram of a preprocessing plant
constructed according to the method of the present invention;
and
[0023] FIG. 3 is a flow diagram of a pulping plant constructed
according to the method of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] The present invention provides an improved method for
preprocessing and processing various lignocellulosic source
materials. Suitable lignocellulosic materials include nonwood
fibers such as grain and cereal straw, and corn stover. However,
the methods of the present invention have been found to be
particularly suited for lignocellulosic material derived from grass
and straw, such as annual ryegrass, fescue, and wheat. As used
herein, straw chips may refer to chips derived from any nonwood
fibers such as grain and cereal straw, grass and corn stover.
However, for simplicity, all such chips shall be referred to as
straw chips.
[0025] Referring first to FIG. 1, by way of example, a ryegrass
plant 10 is shown growing in soil 12. The ryegrass plant 10 has
seeds or kernels 14 held within ears 16, hollow stems or internodes
18 between joints or nodes 20, and an extensively branching fibrous
root system 22. Sheath portions 24 are formed on the stems 18 and
attach leaves 26 to the stems 18.
[0026] During harvest, the ryegrass plants 10 are cut or swathed
about three to six inches from the ground, generally below the
first of the joints or nodes 20. Then, the cut ryegrass plants are
left to cure in the fields for a few weeks. Seeds or kernels 14 may
be harvested from the cut plants by use of a combine. After the
combine has removed the seeds or kernels 14, the remainder of the
ryegrass plants, generally known as straw 30, is dropped to the
ground. The straw 30 may be recovered from the field and baled for
storage prior to further processing.
[0027] Referring to FIG. 2, for preprocessing, straw 30 is fed into
a tub grinder 28. The straw 30 may be fed into the tub grinder 28
in bales. The tub grinder 28 breaks up the bales and chops the
straw into pieces averaging roughly one inch in length. As the
chopped straw 32 exits the mill 34, the chopped straw 32 includes
nodes 20, leaves 26, sheath portion 24, and internodes 18, as well
as ash, silica, and grit.
[0028] After exiting the tub grinder 28, the chopped straw 32 is
sent into a mill 34 to reduce the chopped straw 32 to pieces
averaging roughly one-half inches in length. The mill 34 grinds
most of the nodes 20, leaves 26, and sheath portion 24 into
powder.
[0029] The chopped straw 32 may be stored in a storage tank 35
before being sent to the mill 34 if the capacity of the mill 34
does not permit the chopped straw 32 to be fed directly from the
tub 28 grinder to the mill 34.
[0030] After exiting the mill 34, milled mixture 36 is passed
through multilayer screens 37. Meal 38 is dislodged and removed
from straw chips 40 by passing the milled mixture 36 through the
multilayer screens 37. The meal 38 includes nonfibrous particles
and ash, enriched with silica and grit. The meal 38 may be used as
an agricultural byproduct for feeding livestock.
[0031] The straw chips 40 are then ready for processing into pulp.
The straw chips 40 may be stored before further processing. In
addition, if the pulp processing is to be carried out at a place
remote from where the straw chips 40 have been preprocessed, the
straw chips 40 may be transported by any manner used to transport
bulk materials, such as by the use of containers.
[0032] Referring to FIG. 3, for processing the straw chips 40 into
pulp, the straw chips 40 are fed into a mixer 42 where they are
mixed with steam and water 44 and any caustic or digestive
additives 46. Typically, the amount of digestive additives 46
utilized is calculated on a weight basis per amount of dry straw
chips entering the system. Scales may be incorporated into the
pulping process so that the straw chips 40 may be weighed as they
enter the system and the amount of digestive additives 46 may be
administered at the appropriate rate.
[0033] Preferably, the amount of digestive additives 46 mixed with
steam and water 44 and straw chips 40 is between about zero and
about 2.0 percent by weight. However, it is more preferable that
the amount of digestive additives 46 is between about zero and
about 0.5 percent by weight. Suitable digestive additives 46 for
use in the present invention include sodium hydroxide and potassium
hydroxide.
[0034] From mixer 42, a stream 48 composed of straw chips 40, steam
and water 44, and any digestive additives 46 is then fed into
reactor 50. In reactor 50, stream 48 is exposed to temperatures and
pressures sufficient for the steam 44 and any digestive additives
46 to penetrate the straw chips 40 such that when exposed to a
rapid decrease in pressure, a mixture of softened chips, cellulose,
lignins, hemicellulose and water is formed.
[0035] Suitable reactors for use in the present invention include
continuous feed reactors such as those manufactured by Stake
Technology, Ltd. of Oakville, Canada, and described in U.S. Pat.
Nos. 4,798,651 and 4,947,743, the contents of which are
incorporated herein by reference.
[0036] In the present invention, reactor products 52 may be exposed
to a rapid decrease in pressure by passing the reactor products 52
into a blow tank 56. The reactor products 52 may be metered from
the reactor 50 into the blow tank 56 by a blow valve 54. The
reactor products 52 include softened straw pulp mixed with lignins,
hemicellulose and water. In other words, straw chips are steam
exploded as they pass through the blow valve 54 when exiting the
reactor 50 to form straw pulp, lignins and hemicellulose.
[0037] Stream 58 from the blow tank 56 is sent into a screw press
59 where stream 126 of a straw pulp mixture is separated from the
steam exploded straw chips. Stream 126 is composed substantially of
black liquor and undissolved solids. Generally, stream 126 is
substantially composed of water, reacted lignins and hemicellulose.
Stream 126 is sent to a byproduct chest 142. Stream 144 from
byproduct chest 142 is passed through filtration system 128. Solids
130 removed at filtration system 128 are sent to blow tank 56.
Liquid stream 138 from filtration system 128 are collected in
storage tank 140.
[0038] The black liquor collected in storage tank 140 constitutes a
usable byproduct. This byproduct has usefulness as an animal feed
additive. In a preferred form of the invention, the byproduct may
be mixed with meal 38 from preprocessing to form animal feed. The
animal feed may be formed into a mash or pellets by methods known
in the art.
[0039] Stream 61 from screw press 59 is then defiberized. The
defiberization may be carried out by a mechanical refiner 60, such
as an Ahlstrom MDR (frotopulper).
[0040] The pulp is then ready to be washed. The pulp may be washed
by any method, such as dilution and extraction. For example, the
refined pulp mixture 62 may be sent to a dilution tank 64 where it
is diluted with water 73. Then, diluted pulp mixture 66 from tank
64 may be thickened by use of a wash press 68. Weak black liquor in
stream 69 from wash press 68 is sent to blow tank 56.
[0041] Thickened pulp 70 may then be screened to remove unwanted
particles. In preparation for the screening, the thickened pulp 70
may be sent to a prescreening dilution tank 72 where it is mixed
with water 73. Diluted pulp 74 from the dilution tank 72 may then
be passed into a primary screening 76. Accepts 78 from the primary
screening 76 may be collected in accepts tank 84.
[0042] Rejects 86 from primary screening 76 may be passed to a
primary screen rejects tank 90. Rejects 92 from rejects tank 90 may
be passed to a secondary screening 80. Accepts 82 from secondary
screening 80 may be collected in accepts tank 84. Rejects 88 from
secondary screening 80 are sent to drainer 146.
[0043] Drained stream 148 is sent to a secondary rejects tank 150.
Stream 152 from secondary rejects tank 150 is sent to a rejects
defiberizer 154. Stream 156 from the rejects defiberizer 154 is
collected in a tertiary screen feed tank 158. Stream 160 from the
tertiary screen feed tank 158 is passed through a tertiary
screening 162. Accepts 164 from tertiary screening 162 are
collected in the rejects tank 90. Rejects 166 from tertiary
screening 162 are sent to the drainer 146.
[0044] In another embodiment, the present invention provides a
straw pulp product that, when incorporated into paper, imparts
increased strength to the paper. In the method, straw pulp
processed as described above is further treated with caustic.
Preferably, the processed straw pulp is treated by soaking in
caustic. More specifically, after the thickened pulp has been
diluted and screened, the resultant pulp (i.e., accepts 78 from
primary screening 76) is treated with caustic. After caustic
treatment, the straw pulp product can then be collected (e.g., in
accept tank 84).
[0045] As noted above, meal, ash, and grit separated from the straw
chips in the method can be used as animal feed. The separated meal,
ash, and grit can also be mixed with the black liquor byproduct of
the method to form animal feed.
[0046] The caustic for pulp soaking is preferably an aqueous
solution that includes sodium hydroxide, potassium hydroxide, or
mixtures of sodium hydroxide and potassium hydroxide. Suitable
caustic solutions include from about 1 to about 5 percent by weight
sodium hydroxide or potassium hydroxide. Preferably, the caustic
contains about 2 percent by weight sodium hydroxide or potassium
hydroxide. Straw pulp caustic soaking is generally carried out at
ambient temperature for a period of time from about 0.5 to about 2
hour. In a preferred embodiment, straw pulp is soaked in 2 percent
by weight sodium hydroxide in water solution at ambient temperature
for about 0.5 hour.
[0047] Caustic treated straw pulp produced by the method of the
invention can be blended with other pulps or used as the sole pulp
component in a papermaking furnish to form a paper product. The
caustic soak can be performed in a tank that is a storage tank
supplying a furnish to a papermaking machine. The caustic treated
straw pulp can be the pulp furnish supplied to a papermaking
machine. Alternatively, other pulp can be added to the caustic
treated straw pulp and mixed to provide a blend that can be used as
a pulp furnish to a papermaking machine.
[0048] Caustic soaked straw pulp formed in accordance with the
present invention increases the density and advantageously imparts
strength to papers that incorporate the pulp. For example, soaking
in 2% caustic increased pulp density by about 9%. Burst (lbs.) and
strength as measured by STFI (Swedish Technical Forest Institute,
lbs./in.) for papers prepared from caustic soaked straw pulp were
determined to be greater than for papers prepared from straw pulped
processed as described above that were not subjected to caustic
soaking (i.e., Control in Table 1 below). Soaking in 2% caustic
increased the STFI value by about 25%. An increase in the STFI
value of about 9% was found for pulp soaked in caustic at about pH
9. Burst strength index increased about 9% for caustic soaked pulp,
whereas smaller increases were observed at pH 9 and 10.5. No
increase in burst strength index or STFI value was observed for
paper incorporating straw pulp soaked at neutral pH (i.e., pH
7).
[0049] The STFI index of papers prepared from caustic soaked straw
pulp approached, but did not meet, that of old corrugated
containers (OCC). The STFI index for papers prepared from caustic
soaked fibers was determined to be 0.48 (0.38 for paper prepared
from control straw pulp) and, for paper prepared from OCC, the STFI
index was determined to be 0.55. An increase in the STFI index for
paper prepared from caustic soaked OCC (0.61) was also found. Thus,
although caustic soaked straw pulp does not impart strength to
paper to the extent that OCC does, caustic soaked straw pulp
significantly improved the strength of papers that incorporated the
treated pulp.
[0050] The strength of papers prepared from the various caustic
soaked straw pulps is tabulated and compared to controls in Table 1
below. In Table 1,"Control" refers to straw pulp that has been
processed as described above, but not subjected to caustic soaking.
Table 1 also tabulates some properties of the fibers (e.g., CSF)
and papers made from these fibers (e.g., basis weight and density).
The papers in Table 1 are prepared from 100% of the noted pulp.
1TABLE 1 Paper Strength Comparison Basis STFI Weight Density Burst
Burst Burst STFI STFI 95% Conf. Pulp CSF lbs/ft.sup.2 lbs/ft.sup.3
lbs Stdev Index lbs/in Index Level Control (no soak) 610 27.16
23.96 30 1.77 1.105 10.25 0.377 0.0153 2% caustic soak 565 26.56
26.12 32 1.76 1.205 12.49 0.470 0.0140 pH 7 soak 605 26.52 23.40 29
1.41 1.094 10.01 0.377 0.0141 pH 9 soak 580 26.82 24.38 31 1.40
1.156 11.05 0.412 0.0226 pH 10.5 soak 580 27.08 24.81 31 1.57 1.145
11.50 0.425 0.0150 OCC Control 520 27.10 30.68 56 2.18 2.066 14.82
0.547 0.0091 OCC 2% caustic 520 27.53 32.07 65 2.98 2.361 16.87
0.613 0.0110
[0051] The nature and substance of the instant invention as well as
its objects and advantages will be more clearly understood by
referring to the following specific examples.
EXAMPLE 1
[0052] Annual rye grass straw is obtained. The protein level of the
straw is determined to be about three to four percent (3%-4%). The
moisture content of the rye grass straw is determined to be
approximately ten percent (10%). The annual rye grass straw is
preprocessed and pulped according to the method described in the
best mode of this application and as set forth herein.
[0053] Bales of the rye grass straw are fed into an agricultural
tub grinder where the bales are broken up and the straw chopped
into pieces averaging roughly one (1) inch in length. The
agricultural tub grinder has grate plates with round holes sized
between about one half (0.5) inches and about two (2) inches.
[0054] After exiting the agricultural tub grinder, the chopped
straw is sent into a disc mill. The disc mill is a United Milling
Systems mill which has milling gaps of between about 0.6 mm and
about 1.0 mm. In the disc mill, the chopped straw is reduced into
approximately one-half inch pieces. Also, the disc mill grinds most
of the hard node, leaf and sheath of the straw into a powder. Ash
and grit are determined to compose approximately two to five
percent (2%-5%) of the straw fed into the tub grinder.
[0055] After leaving the milling machine, the straw is passed into
a vibrating six-deck screen of 35 mesh. The screen is a gyratory
screen equipped with fine mesh and ball decks for cleaning fines
and dirt from the surfaces of the screen. Approximately eighteen
percent (18%) of the straw mixture is removed at the screen as
meal. Part of the meal removed is the powder formed in the disc
mill by the hard node, leaf and sheath of the straw. The remainder
of the straw chips leaving the screen averages approximately one
half (1/2) inch in size.
[0056] The meal has a protein level of about eight to thirteen
percent (8%-13%). The silica content is between about 8-15%. It is
determined that the meal removed at the screen is usable as animal
feed.
[0057] The preprocessed straw chips are then stored prior to
pulping. The straw chips are preprocessed at a site remote from the
pulping system. The preprocessed straw chips are transported to the
pulping system in container trucks.
[0058] The preprocessed straw chips are fed into a pulping system
at a rate consistent with the capacity of the pulping system. The
preprocessed straw chips are fed into a mixer where they are mixed
with steam and water to achieve a moisture content of about 40-50%
based on the charge of preprocessed straw chips to the mixer. The
preprocessed straw chips mixed with steam and water are fed into a
Stake Digester steam explosion reactor. In the reactor, the
preprocessed straw chips are exposed to pressure of about 160 psig
for about five and a half (5 1/2) minutes.
[0059] Pulp from the reactor is metered into a blow tank by a blow
valve. Pulp from the blow tank is passed through a screwpress where
black liquor is separated from the pulp. Then the pulp is
defiberized or refined in an Ahlstrom frotopulper mechanical
refiner. The refined pulp is sent to a dilution tank where it is
mixed with liquid at a dilution factor of about 2.5. The diluted
pulp is then thickened by use of a wash press. The thickened pulp
is screened in a two-stage pressure screen with about 0.010 inch
slotted plates.
[0060] It is determined that at least about seventy percent (70%)
by weight of the straw chips are formed into straw pulp.
[0061] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI (Swedish Technical Forestry Institute) between
about 14 and 21. As a comparison, OCC (pulp derived from recycled
corrugated cardboard) is determined to have a Canadian Standard
Freeness (CSF) of between about 200 and about 500 and STFI of
between about 15 and about 22. Kraft pulp is determined to have a
Canadian Standard Freeness (CSF) of between about 450 and about 750
and STFI of between about 21 and about 26.
[0062] Straw pulp with a Canadian Standard Freeness (CSF) between
about 200 and about 600 and STFI between about 14 and about 21 is
suitable to be blended with Kraft pulp and OCC to make liner board
in standard mill grades. The straw pulp comprises about less than
twenty percent (20%) of the liner board furnish.
EXAMPLE 2
[0063] Example 1 is repeated using about one-half percent (0.5%) by
weight sodium hydroxide in the mixer.
[0064] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 3
[0065] Example 1 is repeated using about one percent (1%) by weight
sodium hydroxide in the mixer.
[0066] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 4
[0067] Example 1 is repeated using two percent (2%) by weight
sodium hydroxide in the mixer.
[0068] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 5
[0069] Example 1 is repeated using about one-half percent (0.5%) by
weight potassium hydroxide in place of the sodium hydroxide in the
mixer.
[0070] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 6
[0071] Example 1 is repeated using about one percent (1%) by weight
potassium hydroxide in place of the sodium hydroxide in the
mixer.
[0072] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 7
[0073] Example 1 is repeated using about two percent (2%) by weight
potassium hydroxide in place of the sodium hydroxide in the
mixer.
[0074] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 8
[0075] Example 1 is repeated allowing the preprocessed straw chips
mixed water to remain in the reactor for about two and one-half
minutes.
[0076] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 9
[0077] Example 1 is repeated allowing the preprocessed straw chips
mixed water to remain in the reactor for about 4 minutes.
[0078] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 10
[0079] Example 1 is repeated allowing the preprocessed straw chips
mixed with water to remain in the reactor for about six (6)
minutes.
[0080] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 11
[0081] Example 1 is repeated allowing the preprocessed straw chips
mixed water to remain in the reactor for about eight (8)
minutes.
[0082] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 12
[0083] Example 1 is repeated with the preprocessed straw chips
mixed with water to be exposed to a pressure of about 140 psig in
the reactor.
[0084] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 13
[0085] Example 1 is repeated with the preprocessed straw chips
mixed with water to be exposed to a pressure of about 180 psig in
the reactor.
[0086] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
EXAMPLE 14
[0087] Example 1 is repeated with the preprocessed straw chips
mixed with water to be exposed to a pressure of about 200 psig in
the reactor.
[0088] After exiting the process, the straw pulp is determined to
have a Canadian Standard Freeness (CSF) of between about 200 and
about 600 and STFI between about 14 and about 21.
[0089] While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention.
* * * * *