U.S. patent application number 10/383081 was filed with the patent office on 2003-11-27 for method for producing pulp and products from high silica content agricultural waste materials.
Invention is credited to Ong, Shaode, Zhu, Jie, Zhu, Xiaoping.
Application Number | 20030217823 10/383081 |
Document ID | / |
Family ID | 4777309 |
Filed Date | 2003-11-27 |
United States Patent
Application |
20030217823 |
Kind Code |
A1 |
Zhu, Jie ; et al. |
November 27, 2003 |
Method for producing pulp and products from high silica content
agricultural waste materials
Abstract
A method of producing a high quality paper pulp slurry from high
silica content lignocellulosic agricultural waste materials is
provided. The method includes combining the agricultural waste
materials with a chemical composition to form a mixture, sauting
the mixture, and grinding the sauted mixture to provide the pulp
slurry. The method results in greater than 55 percent solids
recovery in the pulp slurry relative to the starting
lignocellulosic agricultural waste materials, and removes
substantially none of the lignin from the agricultural waste
materials.
Inventors: |
Zhu, Jie; (Beijing, CN)
; Zhu, Xiaoping; (Beijing, CN) ; Ong, Shaode;
(Solon, OH) |
Correspondence
Address: |
PEARNE & GORDON LLP
526 SUPERIOR AVENUE EAST
SUITE 1200
CLEVELAND
OH
44114-1484
US
|
Family ID: |
4777309 |
Appl. No.: |
10/383081 |
Filed: |
March 6, 2003 |
Current U.S.
Class: |
162/20 ; 162/26;
162/76; 162/78; 162/80; 162/90 |
Current CPC
Class: |
D21B 1/16 20130101; D21C
5/00 20130101; D21C 3/02 20130101 |
Class at
Publication: |
162/20 ; 162/76;
162/78; 162/80; 162/90; 162/26 |
International
Class: |
D01B 001/14; D21C
003/20; D21C 003/02; D21C 009/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 9, 2002 |
CN |
02233439.4 |
Claims
What is claimed is:
1. A method for producing a pulp slurry comprising the steps of: a)
providing a lignocellulosic material having a silica content of at
least 1% by weight on a dry solids basis; b) combining said
lignocellulosic material with a chemical composition to form a
mixture, said chemical composition comprising 0.4-4.8 weight
percent base reckoned as alkali hydroxide, 0.2-4 weight percent
bleaching agent, 0.1-10 weight percent alkali metal silicate, and
0.001-10 weight percent chelating agent, all on a dry solids basis
relative to said lignocellulosic material; c) sauting said mixture;
and d) comminuting said sauted mixture to produce said pulp
slurry.
2. A method according to claim 1, further comprising adding water
to said mixture after said sauting step to provide said pulp slurry
with a total solids content of 0.02-5 weight percent.
3. A method according to claim 1, said bleaching agent being
hydrogen peroxide.
4. A method according to claim 1, said alkali metal silicate being
sodium silicate.
5. A method according to claim 1, said mixture being sauted at a
temperature of 100-300.degree. C.
6. A method according to claim 1, said mixture being sauted at a
temperature of about 200.degree. C.
7. A method according to claim 1, said pulp slurry having greater
than 55 percent solids recovery relative to said lignocellulosic
material.
8. A method according to claim 1, said pulp slurry having at least
a 60 percent solids recovery relative to said lignocellulosic
material.
9. A method according to claim 1, said lignocellulosic material
having an initial lignin content, wherein lignin is not
substantially removed from said lignocellulosic material to produce
said pulp slurry, said pulp slurry comprising substantially all of
said initial lignin content of said lignocellulosic material.
10. A method according to claim 1, being performed at substantially
atmospheric pressure.
11. A method according to claim 1, said lignocellulosic material
having a moisture content of 1-30 weight percent, balance solids,
said chemical composition being solvated in water supplied from
said moisture content of said lignocellulosic material.
12. A method according to claim 1, wherein no additional water is
supplied to said mixture during or prior to said sauting step
besides the water supplied from said moisture content of said
lignocellulosic material.
13. A method according to claim 1, said lignocellulosic material
having a moisture content of about 10 weight percent, balance
solids.
14. A method according to claim 1, further comprising adding water
to said mixture during or prior to said sauting step to provide a
total moisture content, relative to said lignocellulosic material,
of about 50 percent by weight.
15. A method according to claim 1, performed on a continuous basis
at steady-state.
16. A method according to claim 1, further comprising: a) providing
a pulping apparatus, said pulping apparatus comprising a cooker
unit and a milling unit, said cooker unit including an agricultural
waste material passage having an inlet and an outlet, and a
conveying device located within said agricultural waste material
passage, said milling unit having a first grinding plate and a
second grinding plate; b) providing said mixture into said inlet of
said agricultural waste material passage; c) conveying said mixture
through said agricultural waste material passage by operation of
said conveying device; d) sauting said mixture at a temperature of
100-300 degrees Celsius as said mixture is conveyed through said
agricultural waste material passage; and e) delivering said mixture
into said milling unit, said comminuting step being performed by
grinding between said first and second grinding plates to produce
said pulp slurry.
17. A method according to claim 16, said lignocellulosic material
being sauted in juices supplied from a moisture content of said
lignocellulosic material, said chemical composition being dissolved
or solvated at least in part in water from said moisture
content.
18. A method according to claim 16, further comprising moving or
shearing at least one of said first and second grinding plates
relative to the other grinding plate to provide a shearing grinding
force between adjacent surfaces of said first and second grinding
plates to comminute said mixture to produce said pulp slurry.
19. A method according to claim 1, said chelating agent being
selected from the group consisting of alkali earth sulfates.
20. A method according to claim 1, said chelating agent being
magnesium sulfate.
21. A method for producing a pulp slurry comprising the steps of:
a) providing a lignocellulosic material having an initial lignin
content and a silica content of at least 1% by weight on a dry
solids basis; b) combining said lignocellulosic material with a
chemical composition to form a mixture; c) sauting said mixture;
and d) comminuting said sauted mixture to produce said pulp slurry,
said pulp slurry comprising substantially all of said initial
lignin content of said lignocellulosic material.
22. A method according to claim 21, said pulp slurry having greater
than 55 percent solids recovery relative to said lignocellulosic
material.
23. A method according to claim 21, further comprising adding water
to said mixture after said sauting step to provide said pulp slurry
with a total solids content of 0.02-5 weight percent.
24. A method according to claim 21, further comprising adding water
to said mixture during or prior to said sauting step to provide a
total moisture content, relative to said lignocellulosic material,
of 30-70 percent by weight.
Description
This application claims priority from Chinese Patent Application
No. 02 2 33439.4 filed May 9, 2002.
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to producing useful products from
agricultural waste stocks. More particularly, it relates to
producing high quality paper pulp from annually renewable
agricultural residues or waste materials such as hay and straw,
having high silica content.
[0003] 2. Description of Related Art
[0004] Conventionally, paper pulp is produced via mechanical or
chemical pulping processes using wood chips as the starting
material. In mechanical pulping processes, the wood chips typically
are not chemically treated (except to add copious amounts of
water), and are ground into small pieces to form the pulp. Water is
added to the ground small pieces in order to provide the pulp with
the desired water content, typically above 90-95 percent by weight.
Pulp produced from wood chips via the conventional mechanical
pulping process generally has high recovery on a solid weight basis
(e.g. greater than 80 or 90 percent) of the original wood chips. In
other words, about 100 lbs of wood chips pulped via the
conventional mechanical pulping process typically produce greater
than 80 or 90 lbs (dry basis) of pulp.
[0005] In conventional chemical pulping processes, the wood chips
are treated chemically to remove lignin, a sticky glue like
substance that binds cellulose together in the living plants (e.g.
trees) from which the chips were harvested. Generally, the process
involves treating the chips in a highly alkaline solution (e.g.
10-30 weight percent NaOH based on dry weight of the chips) and
cooking the chips in this solution with high pressure steam in
order to remove or extract the lignin from the chips. This highly
caustic mixture of alkali and steam at high temperature and
pressure cannot be safely discharged to the environment. Therefore,
it is recycled in the process and used to treat subsequent batches
of wood chips in order to delignify them.
[0006] Following chemical treatment, the resulting delignified
chips must be rinsed, often several times, in order to wash away
excess or residual alkali. Any alkali residue in the chips that is
not washed away prior to producing the finished pulp will not only
have negative environmental impacts, but also could damage pulp or
paper processing equipment which uses the finished pulp to make
paper products. In addition, residual alkali represents a health
and safety hazard to consumers of finished paper products.
[0007] Once the lignin has been removed from the wood chips, the
chips must be smashed and combined with water in order to achieve
the appropriate consistency and water content for the finished pulp
(again typically greater than 90-95 weight percent). The
above-described rinsing step or steps can also be combined with
this step. Alternatively, the chips can be mixed and smashed into
pulp consistency during the alkaline delignification step described
above. The finished pulp is then used to produce paper products as
known in the art via conventional techniques.
[0008] The conventional chemical pulping process for pulping wood
chips as described above generally result in only about 50-55%
recovery on a solid weight basis of the original wood chips. In
other words, about 100 lbs of wood chips would produce about 50-55
lbs (dry basis) of pulp. The remaining 45-50 weight percent of the
wood chips is discarded as waste. This waste must be treated to
reduce or remove residual alkali before being discharged to the
environment.
[0009] In addition to the drawbacks noted in the preceding
paragraph for chemical pulping of wood chips, the production of
pulp from wood chips, whether by the conventional mechanical or
chemical process described above, contributes significantly to
global deforestation. The demand for paper products is growing
faster than the trees that are planted to replace those harvested.
Therefore, alternative sources of raw material for making paper
pulp (i.e. other than wood) are highly desirable.
[0010] Lignocellulosic materials other than wood can be used to
produce pulp. For example, pulp can be produced from agricultural
materials such as corn stalks and husks, rice straw, wheat straw,
bagasse and other grasses, and other cereal materials such as grain
materials and grain stalks. Unfortunately, neither the conventional
chemical nor mechanical pulping process described above is suitable
for producing pulp from the vast majority of these materials
(including corn stalks, rice straw, wheat straw, etc.). First, the
conventional mechanical pulping process used for pulping wood chips
results in grinding these materials to a fine powder, not useful
for pulp. This is because the cellulosic fibers in these materials
are not nearly as strong as those found in woods for which the
mechanical pulping processes were designed. The only exception is
sugar cane residue, whose fibers are sufficiently strong to
withstand pulping using the conventional mechanical pulping process
without being ground to powder.
[0011] Second, with regard to the conventional chemical pulping
process, the high silica content of such materials as stalks and
husks, straws, grasses and cereals make them highly unsuitable for
this process. Wheat straw contains 4-10% silica by weight as small
crystals embedded in the straw; rice straw has an even higher
silica content of 9-18% by weight; other cereals such as barley,
oat and rye straw have 1-6% silica by weight (all on a dry solids
basis). Wood on the other hand has a silica content of less than 1%
by weight (dry solids basis), making wood suitable for the
conventional chemical pulping process.
[0012] Silica is incompatible with the highly caustic alkaline
environment used in the chemical pulping process. In the chemical
pulping process described above, silica dissolves in the alkali
solution during the cooking step and remains in the cooking liquor
(black liquor). The black liquor contains inorganic material used
as the cooking chemicals, such as hydroxides to produce the
alkalinity, and both inorganic and organic materials removed from
the fibrous raw materials (wood or nonwood) during cooking. All
modern pulp mills include a chemical recovery process to treat the
black liquor and recover the pulping chemicals. In addition,
organic non-cellulose material from the black liquor is recovered
(up to 50% of the original material before cooking) to generate
energy for the pulp mill and to recycle process water. In
conventional chemical pulping processes, for every one ton of pulp
that is produced, approximately seven tons of black liquor are
produced which must be dealt with; i.e. recycled and/or abated.
[0013] A problem with cereal straw and other high silica content
materials is that the high silica content causes many problems in
the chemical recovery process for the black liquor, such as scaling
(coating equipment with a glass like substance) which reduces the
efficiency of some equipment due to increased viscosity, making it
difficult or impossible to pump the black liquor through portions
of the recovery system. The viscosity can be increased to so great
an extent as to effectively plug up the recovery equipment. These
problems make chemical recovery difficult, less efficient and more
costly compared to recovery for black liquor from wood which has
less than 1% silica by weight. If the silica content of the cereal
straw is not too high (less than 5-6%) it is possible to include a
modified wood-based recovery system, but at higher capital and
operating costs. But for higher silica content, especially for rice
straw, there is no presently available solution for producing pulp
that includes a waste recovery or recycling mechanism. Without
waste recovery, a pulping process is extremely polluting and less
energy efficient, which result in added operational costs for
pollution abatement and control and higher energy costs.
[0014] In particular, the silica in straws and cereals makes
recycling of the highly alkaline delignification solutions
impossible due to complex silicate-alkali chemical reactions.
Instead, they must be treated batchwise to neutral pH prior to
discharging to the environment. In addition, a fresh alkali
solution must be prepared for each new batch of the raw materials,
further compounding the complexity and the expense of making pulp.
For these reasons, high silica content materials such as cereals
and grasses generally are not used to produce paper pulp to any
significant degree, despite their virtually inexhaustible supply.
Furthermore, even when they are used (necessitating batchwise waste
stream abatement and substantially preventing any waste recovery),
cereals and grasses generally yield only about a 40% solids weight
recovery via conventional chemical pulping techniques; 10-15% lower
on average than for chemical pulping of wood chips, and 40-50%
lower than for mechanical pulping of wood chips. All these factors
combine to make high silica content lignocellulosics, such as
cereals and grasses, highly undesirable and underutilized in the
production of paper pulp, despite their vast supply. For this
reason, there is currently no commercially or economically
acceptable method for producing high quality paper pulp from annual
or renewable materials. Rather, present methods require wood chips
from trees that do not grow at nearly or even at a fraction of the
rate at which they must be cut down to provide the chips.
[0015] There is a need in the art for a method of producing paper
pulp from high silica content lignocellulosic raw materials, such
as cereals, straws and grasses, which are renewable on an annual
basis, that can be operated in a continuous process, and which does
not result in the generation of significant or substantial wastes.
Preferably, such a process will result in greater than 55% weight
recovery of the starting raw materials.
SUMMARY OF THE INVENTION
[0016] A method for producing a pulp slurry is provided having the
steps of: a) providing a lignocellulosic material having a silica
content of at least 1% by weight on a dry solids basis; b)
combining the lignocellulosic material with a chemical composition
to form a mixture, the chemical composition having 0.4-4.8 weight
percent base reckoned as alkali hydroxide, 0.2-4 weight percent
bleaching agent, 0.1-10 weight percent alkali metal silicate, and
0.001-10 weight percent chelating agent, all on a dry solids basis
relative to the lignocellulosic material; c) sauting the mixture;
and d) comminuting the sauted mixture to produce the pulp
slurry.
[0017] A further method for producing a pulp slurry is provided
having the steps of: a) providing a lignocellulosic material having
an initial lignin content and a silica content of at least 1% by
weight on a dry solids basis; b) combining the lignocellulosic
material with a chemical composition to form a mixture; c) sauting
the mixture; and d) comminuting the sauted mixture to produce the
pulp slurry, the pulp slurry having substantially all of the
initial lignin content of the lignocellulosic material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a side view of an apparatus for producing paper
pulp according to the invention, including a cooker unit and a
milling unit.
[0019] FIG. 2 is a side close-up view, partially broken away, of
the cooker unit of FIG. 1 for producing paper pulp according to the
invention.
[0020] FIG. 3 is a side close-up view, partially in section, of the
milling unit of FIG. 1 for producing paper pulp according to the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0021] As used herein, when a preferred range such as 5-25 (or 5 to
25) is given, this means preferably at least 5 and, separately and
independently, preferably not more than 25.
[0022] The invention includes a method for producing pulp from high
silica content agricultural waste materials. Agricultural waste
materials that can be used to produce pulp according to the
invention include straws (rice straw, corn straw, barley straw, oat
straw, and other straws), husks (e.g. corn husks), bagasse,
grasses, hay, as well as other lignocellulosic stalks or material
stocks that have a high silica content, e.g. greater than 1, 2, 3,
4, 5, 6, 7, 8, 9 or 10, percent by weight on a dry solids
basis.
[0023] The high silica content agricultural waste materials are
mixed and treated with a chemical composition according to the
invention and sauted at elevated temperature as will be more fully
described below. The resulting sauted mixture is then ground and
combined with water to produce a pulp slurry as will also be
described. The chemical composition preferably includes the
components listed below in table 1. In table 1, any preferred or
less preferred or more preferred weight percent or weight percent
range of any component can be combined with any preferred or less
preferred or more preferred weight percent or weight percent range
of any of the other components; it is not required or necessary
that all or any of the weight percents or ranges for all components
come from the same column. All values in table 1 are percentages by
weight of the high silica content waste materials (bone dry basis)
with which the composition is mixed. For example, a weight percent
of 4 listed in table 1 means that for 100 lbs of agricultural waste
material, 4 lbs of the component listed in table 1 are provided in
the composition that is mixed with the agricultural waste
material.
1TABLE 1 Composition for treating high silica content
lignocellulosics to produce pulp Component Most Preferred Less
Preferred Less Preferred Base (reckoned as 1.6-3.4 1-4 0.4-4.8
alkali hydroxide) 1.8-3.2 1.2-3.8 0.6-4.4 2-3 1.4-3.6 0.8-4.2
Bleaching agent 0.8-1.2 0.5-1.5 0.2-4 0.9-1.1 0.6-1.4 0.3-2 1
0.7-1.3 0.4-1.8 Alkali metal silicate 2.6-4.4 1.5-5.5 0.1-10
2.8-4.2 2-5 0.5-6.5 3-4 2.5-4.5 1-6 Chelating agent 0.02-0.06
0.006-1.5 0.001-10 0.03-0.05 0.008-1 .sup. 0.002-4 .sup. 0.04
0.01-0.7 0.004-2 .sup.
[0024] The above composition is preferably combined or mixed with
the high silica content lignocellulosic agricultural waste
materials just prior to being fed to a cooker unit to be sauted as
will be further described. The agricultural waste materials
typically contain about 10 weight percent water with the balance
(.about.90 weight percent) being solid material. However, depending
on environmental factors such as rain fall, humidity, harvesting
practices, etc., the waste materials may have a water content from
1-90 weight percent or more. It is important to consider the
relative moisture content of the waste materials when measuring the
amounts of the components listed in table 1, which are based on the
bone dry weight of the waste materials, excluding moisture content.
Preferably, the waste materials are supplied having a moisture
content of about 10, less preferably 8-12, less preferably 6-14,
less preferably 4-16, less preferably 2-20, less preferably 1-30,
weight percent, balance solids.
[0025] The base component from table 1 is provided to induce a
softening effect on the high silica containing agricultural waste
materials, such as rice stalks or hay. These stalks are generally
very rigid, tough fibrous materials and the base component is
supplied to make them more pliable and subject to more effective
sauting as will be explained below. The values listed in table 1
are for bases or hydroxides reckoned as alkali hydroxide. So, for
example, if some other hydroxide (such as Ca(OH).sub.2) or basic
(i.e. pH raising) agent is used instead of an alkali hydroxide,
then one must calculate or determine the amount of the substituted
hydroxide or basic agent required to supply an equivalent amount of
hydroxide or hydroxide reducing power as the amount reckoned as
alkali hydroxide listed in table 1. In the event another hydroxide
or basic agent is used, this calculated amount should be
substituted for the corresponding value in table 1 when preparing
the composition according to the invention. Most preferably the
base component is sodium hydroxide. Less preferably, other
hydroxides, such as other alkali hydroxides, alkali earth
hydroxides, heavy metal hydroxides, or other metallic hydroxides,
can be used. Less preferably, other bases and basic agents can be
used in appropriate amounts to supply equivalent hydroxide reducing
power as the amount of base reckoned as alkali hydroxide listed in
table 1.
[0026] The bleaching agent is provided to prevent the sauted waste
materials from becoming blackened or darkened in appearance as a
result of sauting, which is typical of sauted cellulosic materials.
The bleaching agent provides the sauted waste materials with a
light or tan coloring, that does not appear blacked or charred as a
result of being sauted, e.g. in a cooker unit. The bleaching agent
is preferably a peroxide bleaching agent, preferably hydrogen
peroxide. Less preferably, other peroxides can be used. Still less
preferably, other non-peroxide bleaching agents, such as
chlorinated bleaching agents can be used.
[0027] The alkali metal silicate component is provided to stabilize
the peroxide agent described in the preceding paragraph, which
otherwise may have a tendency to dissociate due to the relatively
weak peroxide bond and the highly reactive oxygen atoms which are
bound via the peroxide bond. Preferably, the alkali metal silicate
is sodium silicate. Sodium silicate functions as a rigidizer in the
finished pulp product. In addition, sodium silicate is abundantly
and inexpensively available. Perhaps most importantly, unlike most
silicates, sodium silicate is water soluble and hence is
effectively solvated in the water supplied by the moisture content
of the waste materials during the sauting step as explained
below.
[0028] The chelating agent can be an inorganic or organic chelating
agent, or a mixture of these. Preferably, the chelating agent is
inorganic, such as an inorganic salt, and preferably is selected
from alkali sulfates, alkali phosphates and alkali carbonates, more
preferably from alkali earth sulfates. Most preferably, the
chelating agent is magnesium sulfate. Less preferably, suitable
organic chelating agents include EDTA, NTA, and DTPA. The chelating
agent is supplied in a very low amount to bind heavy metal
impurities found in the agricultural waste materials. Magnesium
sulfate is most preferred because, in addition to binding heavy
metal impurities, magnesium sulfate acts as a further stabilizing
agent for the peroxide component described above. The inventors
herein have also found that the addition of magnesium sulfate to
the composition for treating high silica content agricultural waste
materials to produce pulp results in a surprising and significant
reduction in the presence of impurities, surprisingly higher
uniformity in appearance and color, and a minimization of dark
spots in the finished pulp product.
[0029] In practice the above-described chemical composition is
combined with the high silica content agricultural waste materials,
and together they are continuously fed into a cooker unit where the
composition is mixed with the agricultural waste materials and
becomes solvated in the water from the moisture content of the
agricultural waste materials. In one preferred embodiment, no
additional or excess water is supplied to the mixture in the cooker
unit, besides that which is supplied as the moisture content of the
waste material. Alternatively and preferably, additional water can
be added to bring the total moisture content within the cooker unit
(relative to the agricultural waste materials+water) to 10-90,
preferably 20-80, preferably 30-70, preferably 40-60, preferably
about 50, percent by weight. In the cooker unit, the chemical
composition-agricultural waste material mixture is sauted at a
temperature of 100-300, preferably 120-280, preferably 140-260,
preferably 160-240, preferably 180-220, preferably about 200,
.degree. C., for a period of time long enough to completely saut
the agricultural waste material solids in the water supplied from
their own moisture content and additional supplied water, if any,
in which the chemical composition described above is dissolved or
solvated. Most preferably, in the cooker unit the mixture of
agricultural waste materials, water and added chemical composition
being sauted comprises about 50 weight percent water. After
sauting, this mixture is discharged from the cooker unit into a
milling unit where the mixture is ground up to produce a slurry of
ground solid pieces suspended or mixed in a light colored aqueous
liquid. At this stage, additional water is added to bring the total
solids content of the slurry to 0.02-5, preferably 0.05-2, most
preferably about 0.1-0.2 weight percent. This slurry is discharged
from the milling unit as a pulp slurry, and is used to produce
paper products via conventional techniques.
[0030] Now with reference to FIGS. 1-3, a preferred embodiment for
a method of producing pulp according to the invention will now be
explained. A pulping apparatus 100 including a cooker unit 21 and a
milling unit 22 is provided. The cooker unit 21 includes a straight
tube 51 having an inlet 7 at one end and an outlet 16 at the other
end. A conveying device, such as an auger 25 or other rotating or
helical conveying device is provided within the straight tube 51 to
propel the waste materials from the inlet 7 toward the outlet 16.
The auger 25 has a shaft 11 and a helical blade 13. The shaft 11
extends axially outside of the straight tube 51 and is fixed at
either end to bearing seats 5 and 15 respectively. The axially
extending portions of the shaft 11 are fitted with sealing devices
6 and 14 respectively in order to ensure a fluid tight seal at the
point where the shaft 11 translates through the outer wall of the
straight tube 51 at either end thereof. The shaft 11 is driven in
rotation via a drive motor, with or without gears, belts, or other
transmission means in a conventional manner. In a preferred
embodiment, (seen in FIG. 2), the shaft 11 is connected via a speed
reducer 3 to a belt roller 2, and the belt roller 2 is driven in
rotation via a belt connected to a motor (not shown). The shaft 11
is connected to the speed reducer via a shaft coupling 4. The
rotational speed of the shaft 11 is regulated via the speed reducer
3 as known in the art. The direction of rotation of the shaft 11 is
selected so that the corresponding rotation of the helical blade 13
results in waste materials deposited into the straight tube 51
through inlet 7 being conveyed toward the outlet 16.
[0031] The straight tube 51 includes an inner, agricultural waste
material passage 52 where the auger 25 is located, and an outer
annular passage or heating jacket 9. In the preferred embodiment, a
heat transfer fluid, preferably a liquid, most preferably an
organic liquid or oil, is provided in the heating jacket 9, and
cycled therethrough co-current to the direction of travel of the
agricultural waste materials within the waste material passage 52.
Alternatively, the heat transfer fluid can be provided in a
countercurrent flow direction relative to the agricultural waste
materials. The heating jacket 9 is preferably part of a closed
system with spent or cooled oil exiting from valve assembly 12,
being reheated via conventional means (not shown in the drawings)
and then reintroduced through inlet 8. The heating jacket 9 is
preferably provided with a helical vane 10 so that the heat
transfer fluid or oil travels in a co-current (or countercurrent)
helical path relative to the straight tube 51, ensuring maximum
fluid-surface contact and effective heat exchange.
[0032] In the illustrated embodiment, the outlet 16 of the straight
tube 51 is arranged to deliver sauted agricultural wastes into the
milling unit 22. Though an elbow 24 is shown between the straight
tube 51 and the outlet 16, the elbow should not be considered an
essential feature of the pulping apparatus 100; e.g. a straight or
other suitable path for delivering materials from the straight tube
51 to the milling unit 22 may be employed.
[0033] The milling unit 22 includes an upper grinding plate 45 and
a lower grinding plate 47. The lower grinding plate 47 is driven in
rotation via drive shaft 32 which is in turn driven by a driving
motor. In a preferred embodiment, as shown in FIG. 3, the drive
shaft 32 can be coupled to a belt roller 31 which is driven via one
or a plurality of belts by a drive motor 46. Alternatively, other
driving or transmission means conventional in the art for rotating
the shaft 32, e.g., gears, speed reducing machinery, etc. can be
used. The upper grinding plate 45 is either fixed, or is rotated in
a direction opposite the direction of rotation of the lower
grinding plate 47. Alternatively, one of the grinding plates 45,47
is movable or shearable relative to the other such that a shearing
grinding force can be provided between adjacent surfaces of the
grinding plates.
[0034] A feed tube 43 is connected to the outlet 16 of the cooker
unit 21, to deliver the sauted agricultural wastes to the grinding
plates 45, 47. In the illustrated embodiment, the milling unit has
a casing that includes an underbody casing 48 that is butt-jointed
with an upper casing 44. The moving machinery of the milling unit
22 is provided within this casing. The drive shaft 32 is fixedly
connected to the lower grinding plate 47 and a lower tray 33. The
upper grinding plate 45 is located directly above and adjacent the
lower grinding plate 47, and has an associate upper tray 36 above
the upper grinding plate 45. The upper grinding plate 45 is spaced
some distance from the upper tray 36 to leave a gap therebetween,
and the lower grinding plate 47 is correspondingly spaced some
distance from the lower tray 33 to leave a corresponding gap
therebetween. The feed tube 43 passes through the upper casing 44
and the upper tray 36 which are preferably secured via bolts 38.
The nose or delivery end of the feed tube 43 is positioned adjacent
or within a central hole of the upper grinding plate 45. The
respective gaps between the upper grinding plate 45 and upper tray
36 and the lower grinding plate 47 and lower tray 33 are fluidly
connected with an outlet port 37 in the casing of the milling unit
22. A locking device is provided for securing the upper casing 44
to the underbody casing 48. The locking device includes a pair of
adjusting plates 41 and 42 and a pair of locking plates 39 and 40.
The adjusting plates and locking plates are screwed or secured
around an upward projecting section of the feed tube 43 to secure
the upper casing 44.
[0035] In operation, the method of the invention preferably
proceeds as follows. High silica content agricultural waste
materials are first harvested or obtained via conventional means.
These agricultural waste materials typically are comprised of about
90 weight percent solids and about 10 weight percent water. These
waste materials (solids and water content) are combined with the
chemical composition described above and the resulting mixture is
provided into the inlet 7 of the apparatus 100. Preferably,
additional water is added to bring the total water content of the
mixture in the waste material passage 52 to 40-60, most preferably
to about 50, percent by weight. From the inlet 7, the agricultural
waste materials-chemical composition mixture is conveyed through
the waste material passage 52 by operation of the auger 25. As it
is conveyed, the mixture is sauted at a temperature of 100-300,
most preferably about 200, .degree. C. via heat transfer from
heating oil passing through the heating jacket 9. In the waste
material passage 52, the high silica content waste materials are
sauted in their own juices, supplied by their own water content,
additional supplied water, if any, and the dissolved chemical
composition. The chemical composition treats the agricultural waste
materials as described above while they are being sauted; e.g.
preventing blackening or darkening of the agricultural waste
materials, binding heavy metals and other impurities, etc.
[0036] The rotational speed of the auger 25 is adjusted to provide
a suitable residence time within the cooker unit 21 (waste material
passage 52) for sauting of the agricultural waste materials. After
passing through the agricultural waste material passage 52, the
fully sauted agricultural waste materials are delivered into the
feed tube 43 of the milling unit 22 via elbow 24. The grinding
plates 45,47 comminute or grind up the or sauted agricultural waste
materials while at the same time (or upon entering the milling unit
22) water is added to these agricultural waste materials. The
ground up mixture may circulate between the grinding plates 45,47
and in the gaps between respective upper and lower grinding plates
and trays as described above, until the mixture ultimately is
eluted from the milling unit 22 via outlet port 37 as an aqueous
pulp liquid or slurry. Upon exiting the milling unit through the
port 37, the pulp has a solids content of 0.02-5, preferably
0.05-2, most preferably about 0.1-0.2 weight percent as mentioned
above. In addition, the pulp includes greater than 55, preferably
at least 60, preferably at least 70, preferably at least 80
preferably at least 90, preferably at least 93, preferably at least
95, preferably at least 97, preferably at least 99, percent of the
solid content of the original agricultural waste materials,
representing greater than 55, preferably at least a 60, 70, 80, 90,
93, 95, 97, or 99 percent solids recovery relative to the starting
agricultural waste materials. This is a dramatic and highly
significant and surprising advance over the state of the art which
uses wood chips as the starting material for producing pulp, where
solids recovers typically do not exceed 50-55 percent.
[0037] An important feature of the present invention is that the
chemical composition does not remove lignin from the waste
materials. In fact, by the present invention, lignin is not removed
at all from the agricultural waste materials before producing the
pulp. Instead, the pulp is produced having substantially all or
100% of the initial lignin content of the starting lignocellulosic
waste materials, and yet is still very useful and effective at
producing high quality, very strong paper products such as for
packaging applications, a highly surprising and unexpected result.
Without wishing to be bound to a particular theory, it is believed
that so significant and surprising a solids recovery for pulp
produced according to the present invention as stated in the
preceding paragraph is due at least in part to the fact that lignin
is not removed from the waste materials to produce the pulp.
Therefore, not only does the lignin not need to be abated or
cleaned up as a waste product, but the lignin mass remains with the
agricultural waste materials and is transferred into the finished
pulp, raising the solids recovery.
[0038] Another distinction from conventional chemical pulping
techniques is that in the present invention, the agricultural waste
materials are sauted in a relatively small amount of water. In the
conventional process, the material being pulped is not sauted, but
rather is fully cooked in a continuous or substantially continuous
bulk liquid phase of water present in an amount many times that of
the waste materials by weight, analogous to submersion in boiling
water as one might boil an egg. In the present invention, by
providing, in the most preferred embodiment, only about 50 weight
percent water in the cooker unit, the agricultural waste materials
are not submersed in a continuous water phase and cooked as by
boiling; instead the waste materials are sauted in a manner more
akin to a Chinese style of cooking or stir-fry. The inventors
herein have found that this method of sauting the waste materials
yields a finished pulp material that has surprisingly good and
strong qualities, particularly in the making and fabrication of
highly durable and strong packaging materials, having impact and
shear strength characteristics similar or superior to conventional
cardboards, yet having surface smoothness and writability
characteristics similar to writing paper.
[0039] The pulp produced according to the present invention has
been found to be very useful in making very strong, light colored
paper products, e.g. packaging materials, having strength
comparable to or better than conventional cardboards used in
packaging. That the pulp produced according to the invention would
be so strong and light colored compared to conventional cardboards
was also a surprising and unexpected result.
[0040] In sum, the invention includes a method for producing pulp
from high silica content agricultural waste materials
(lignocellulosics), that results in greater than 55 percent solids
recovery, and that does not remove any or substantially any of the
lignin from the starting agricultural waste materials, yet results
in a light colored pulp that is useful to make very strong paper
products having greater or comparable strength relative to
conventional cardboards used in packaging. The resulting paper
products (from pulp produced according to the invention) can be
produced having a very smooth surface, much smoother than
conventional cardboards.
[0041] From the above description it will be apparent that,
contrary to conventional pulp-making methods, which utilize
trees/wood as the raw materials, the invented method can be
performed on a continuous basis at steady-state to produce paper
pulp, as opposed to a batch process. The raw materials for the
present invention are not wood chips, but high silica content
lignocellulosic agricultural waste materials such as cereals and
straws, which are annually renewable sources that would otherwise
be burned as waste. Further, the method according to the invention
can be performed entirely at atmospheric pressure, and does not
need any special high-pressure handling equipment or piping, for
example to accommodate high pressure steam. In addition, the method
for producing pulp from high silica content lignocellulosic waste
materials according to the invention produces no or substantially
no waste (e.g. no solid, liquid or gaseous waste), and thereby
presents no or substantially no pollution control problems or
issues of any kind; unlike the conventional chemical pulping
processes that use wood chips as the raw material, which produce
about seven tons of black liquor waste for each ton (dry basis) of
pulp produced.
[0042] Although the hereinabove described embodiments of the
invention constitute the preferred embodiments, it should be
understood that modifications can be made thereto without departing
from the scope of the invention as set forth in the appended
claims.
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