U.S. patent application number 10/122672 was filed with the patent office on 2002-10-03 for recovery of fibers from a fiber processing waste sludge.
Invention is credited to Hsu, Jay Chiehlung, Hu, Sheng-Hsin.
Application Number | 20020139494 10/122672 |
Document ID | / |
Family ID | 22806295 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020139494 |
Kind Code |
A1 |
Hsu, Jay Chiehlung ; et
al. |
October 3, 2002 |
Recovery of fibers from a fiber processing waste sludge
Abstract
A process of recovering a useful population of fibers and fines
from the waste stream of fiber processing facility is disclosed.
Steam explosion of the fiber-containing waste stream is used to
increase the separation efficiency of the fibers from the ash. The
steam explosion also enhances the quality of the recovered fibers
and fines, providing a population of recovered fibers which can be
incorporated into the fiber component of a tissue or absorbent
paper product.
Inventors: |
Hsu, Jay Chiehlung;
(Alpharetta, GA) ; Hu, Sheng-Hsin; (Appleton,
WI) |
Correspondence
Address: |
DORITY & MANNING, P.A.
POST OFFICE BOX 1449
GREENVILLE
SC
29602-1449
US
|
Family ID: |
22806295 |
Appl. No.: |
10/122672 |
Filed: |
April 15, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10122672 |
Apr 15, 2002 |
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09216235 |
Dec 18, 1998 |
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6372085 |
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Current U.S.
Class: |
162/4 ;
162/21 |
Current CPC
Class: |
D21B 1/36 20130101; D21C
5/02 20130101; Y02W 30/646 20150501; Y02W 30/64 20150501; Y02W
30/648 20150501; D21B 1/32 20130101 |
Class at
Publication: |
162/4 ;
162/21 |
International
Class: |
D21C 005/02 |
Claims
What is claimed is:
1. A process of recovering fibers from waste paper recycling sludge
comprising: providing a waste sludge stream comprising a plurality
of fibers and fines; placing said waste sludge in a first vessel;
bringing an interior of said vessel and said waste sludge to an
elevated temperature and pressure; maintaining said elevated
temperature and pressure for an effective time interval;
discharging said waste sludge from said first vessel to a second
vessel, said second vessel being sufficiently vented to maintain a
pressure drop during said discharge step, and to thereby provide a
treated sludge product comprising treated fibers and fines; passing
said treated sludge through a separator to separate and collect a
portion of said treated fibers and said treated fines from said
sludge.
2. The process according to claim 1, wherein said elevated
temperature is within the range of about 130.degree. C. to about
250.degree. C.
3. The process according to claim 1, wherein said effective time
interval is between about 0.5 minutes to about 30 minutes.
4. The process according to claim 1, wherein said elevated pressure
is about 100 to about 300 psi.
5. A process of converting waste fibers from a fiber process waste
stream to a recoverable fiber having improved fiber properties
comprising: providing a waste stream comprising a mixture of fibers
and ash from a fiber processing facility; exposing said waste
stream to an elevated temperature and pressure; releasing rapidly
said pressure from said waste stream, thereby providing a plurality
of treated fibers within a treated waste stream; and separating
said treated fibers from said waste stream.
6. The product according to the process of claim 5 wherein said
mixture of fibers further comprises a plurality of fines.
7. The process according to claim 5 wherein said elevated
temperature is within the range of about 130.degree. C. to about
250.degree. C.
8. The process according to claim 5 wherein said elevated pressure
is about 100 to about 300 psi.
9. The process according to claim 5 wherein said waste stream is
from a waste paper recycling operation.
10. The process according to claim 5 wherein said waste stream is
from a paper making operation.
11. A process of converting waste fibers from a fiber process waste
stream of a paper making facility to a recoverable fiber having
improved fiber properties comprising: providing a waste stream from
a papermaking facility comprising a mixture of a plurality of
fibers and ash; exposing said waste stream to an elevated
temperature and pressure; releasing rapidly said pressure from said
waste stream, thereby providing a plurality of treated fibers
within a treated waste stream; and separating said treated fibers
from said waste stream.
12. A process of improving the useful properties of fibers
comprising: providing a first supply of fibers, said fibers
contained within a portion of a waste stream from a paper fiber
processing operation; subjecting said fibers in said waste stream
to an elevated temperature; discharging said fibers and said waste
stream from a first pressure environment to a second pressure
environment, said first pressure being greater than said second
pressure; separating a portion of said fibers from said waste
stream, thereby providing a second supply of fibers, said second
supply of fibers having improved fiber qualities than untreated
fibers.
13. The process according to claim 12 wherein said portion of a
waste stream further comprises a first supply of fines.
14. The process according to claim 13 wherein said separating step
further comprises separating a supply of treated fines from said
treated waste stream.
15. The process according to claim 14 wherein said supply of fines
have improved fiber properties for paper product usage than said
first supply of fines.
16. The process according to claim 12 wherein said waste stream
further comprises a waste stream from a paper recycling
facility.
17. The process according to claim 11 wherein said separated
treated fibers are reintroduced into a paper making process
stream.
18. The process according to claim 12 wherein said waste stream is
from a waste paper recycling operation.
19. The process according to claim 12 wherein said waste stream is
from a paper making operation.
20. A modified cellulosic fiber that is prepared by a process
comprising steam explosion of fibers contained within a fiber
processing waste stream, said steam explosion occurring at a
pressure at super-atmosphere and at a temperature range of about
130.degree. C. to about 250.degree. C. to give a modified
cellulosic fiber having an altered morphology which increases the
separation efficiency of the modified fiber from the waste
stream.
21. The modified fiber of claim 20 wherein the modified fiber is in
the form of a fine.
22. The modified fiber of claim 20 wherein said altered morphology
includes a curl index greater than a curl index of fibers within
said unmodified waste stream.
23. An absorbent structure comprising modified cellulosic fibers
according to the process of claim 20.
24. An absorbent structure comprising treated fibers according to
the process of claim 5.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a process for recovering a useable
population of fibers and fines from the waste sludge of a fiber
production or fiber handling facility.
[0002] In particular, this invention provides a steam explosion
process and a resulting product which permits the separation of a
useful population of fibers and fines from the waste streams of
fiber production processes such as a waste paper recovery operation
or from the waste stream of a papermaking process. The process is
useful in fiber and fine recovery from white water waste streams
from paper making operations and waste sludge from the de-inking
and processing of waste paper. The present invention not only
increases the amount of usable fibers and fines recoverable from
the waste stream, but increases the fiber quality of the recovered
fibers. Additional benefits include a concomitant reduction in the
solid volume of the waste stream and increases the usable fiber
content available from the initial raw material. The process steps
of the present invention yield a fiber of improved quality suitable
for making tissue products such as toilet and facial tissues, paper
towels, and napkins.
DESCRIPTION OF THE PRIOR ART
[0003] Waste sludge from fiber production and papermaking
facilities typically contain numerous fibers and fines. In
particular, efforts to recover the fibers and fines from the waste
sludge streams of paper fiber recovery plants have been limited, in
part, by the high ash content of the sludge. Conventional fiber
screening techniques also retain the ash particulates. The high ash
content renders the recovered fibers and fines undesirable for
quality end products.
[0004] Paper is conventionally made by draining a low consistency
dispersion of cellulose fiber pulp, fillers, and additives through
a paper machine "wire" (essentially an endless mesh or sieve). A
certain amount of solid material passes through the wire with the
suspending water and is, thus, not retained in the wet paper web
formed on the wire. The drained liquid suspension, known generally
in the industry as "white water," carries entrained solid material.
White water from which the suspended particles have been removed is
reused in the papermaking process to the extent possible.
[0005] Obviously, wastepaper, if it can be recycled, is a much
cheaper and environmentally friendly source of wood pulp for making
paper. Before wastepaper can be reused as recycle material,
however, the wastepaper must be de-inked. De-inking processes
remove inks and coating materials from the wood fibers. Thus, when
recycled fibers, as opposed to virgin pulps, are used in the
papermaking process, the drained liquid suspension will contain
additional types of waste materials such as inks and hot melt
adhesives.
[0006] Unused white water and de-inking effluents must be treated
before being discharged from the paper mill. Treatment normally
involves passing the effluent through a clarifier, prior to which
flocculants are added to promote sedimentation of solid material
suspended in the water. A biological treatment with microorganisms
is also commonly performed to reduce the biological oxygen demand
(BOD) of the liquid effluent before it is discharged. As can be
expected, disposal of the unused white water and de-inked effluents
results in costs to the papermaking facility.
[0007] The sediment accumulated in the clarifier is a sludge
composed of pulp fibers, fiber particles or fines, fillers,
pigments, and other miscellaneous debris such as grit, sand,
plastic particles, general dirt. Many of the sludge components are
fillers, pigments and the like that were added to the pulp during
the sheet-forming process for the purpose of producing desired
properties in the finished paper. Such properties include proper
surface, opacity, strength and brightness. For example, finely
ground inorganic fillers, such as talc, certain clays, calcium
carbonate, blanc fixe, and titanium dioxide may be added to papers
to improve surface smoothness, whiteness, printability and opacity.
Sizing agents, such as soaps, gelatins, and rosins (with alum), wax
emulsions and starches, may be added to papers for improving
resistance to penetration by liquids. In addition, coloring agents,
such as acid, basic, direct and sulfur dyes and
[0008] natural and synthetic pigments may be added for coloring
purposes. Any of such products may ultimately end up in the
clarifier as part of the sludge. In addition, because the clarifier
is usually a large open air tank, other debris such as leaves,
branches, insects, etc. can also become part of paper sludge. The
major constituents of the sludge, however, are generally
fiber/fines and the inorganic fillers calcium carbonate and
clay.
[0009] Most de-inking processes involve the use of flotation and
washing. In de-inking processes, wastepaper is first washed and
then pulped with dilute sodium hydroxide or surfactants in a pulper
tank to cause the fibers to swell and loosen the ink and coating
material particles contained thereon. (These coating materials
include the previously mentioned clays, talc, etc.) After pulping,
the pulp stocks go through screening, cleaning, washing,
floatation, and bleaching to further remove trash, stickies, inks,
ash, and short fiber fines. During the washing and floatation
stages, most ash, stickies, and short fiber fines are separated
from the pulp stock. Thus, when the sludge comes from a mill using
recycled waste paper, this sludge may also have accumulations of
adhesives (otherwise known as "stickies"), foreign bodies (such as
pieces of plastic material or metal, otherwise known as
"contraries") in very small quantities, and other additives, such
as those described above, that are used in the papermaking
process.
[0010] Normally, the sludge is drawn off from the clarifier at
about 2.5 percent consistency (or "percent dry solids content") and
is then dewatered to a consistency of around 20 to 55 percent, for
example, by means of rotary vacuum filters, screw presses, or belt
presses. Dewatering reduces the weight of material going to the
landfill and reduces the charges for landfill disposal because
these are typically based on weight. Since the majority of the
weight in the sludge comes from water, it behooves the sludge
processor to remove as much water as possible. The dewatered sludge
is in a semi-solid state and usually contains about 40 percent to
about 80 percent by dry weight relatively fine wood fibers and from
about 20 percent to about 60 percent inorganics (also referred to
as "ash") and the additives mentioned above. The material typically
is a crumbly, not very cohesive material that appears to be dry. At
thirty percent consistency, most sludges are more like dry solids
as opposed to a suspension or dispersion. Because of the
non-cohesive character of sludge, the materials handling equipment
for moving, storing and transporting are generally the same as for
dry materials. Once in this state, the sludge is then capable of
being collected and transported for disposal in landfills.
[0011] According to some sources, it is estimated that the amount
of dry waste (waste sludge with substantially all of the residual
water removed) produced due to paper processing exceeds 4.6 million
tons per year. This sludge is produced by both papermaking from
virgin pulp and papermaking from recycled fibers. A typical
de-inking plant employing recycled fibers processes about 100 dry
tons of waste paper into about 65 to about 80 dry tons of recycled
(reusable) fiber. The remaining 20 to 35 tons of waste paper is
unusable, and becomes part of the sludge produced by the deinking
plant. After recycled fiber sludge is dewatered with various
suitable dewatering devices, including, for example, a belt press
or screw press, 100 dry tons of waste paper still produce from
about 70 to about 120 wet tons of sludge which must be
disposed.
[0012] Moreover, the sludge produced during the making of tissue
from an integrated mill with a recycled fiber plant produces 10
times the amount of sludge produced during the making of tissue
from virgin pulp. The typical virgin pulp tissue making process
with a 200 ton capacity produces 10 tons of sludge per day while
the typical tissue making with recycled fiber plant produces 100
tons of sludge per day.
[0013] Conventional methods for disposing of sludges include
landfill, land spreading, composting and incineration. Landfill and
land spreading sites are being depleted at an alarming rate, and
the establishment of new sites is difficult due to environmental
concerns. In addition, the cost associated with using landfills to
dispose of sludge is constantly increasing. For example, paper
manufacturers typically spend about $30/wet ton to send sludge to
the landfill. Composting and incineration of sludge also raise
environmental concerns. Some innovative sludge disposal techniques
include processing the sludge into pellets for fuel or into
lightweight aggregates for construction, pyrolysis, gasification,
and incorporation into cements. However, these techniques generally
require the use of complex methods and expensive equipment. In
addition, attempts to recycle sludge to make paper have been
unsuccessful because the process is inefficient due to drainage
problems resulting from the presence of slow drying fines which
tend to clog the wires and other equipment.
[0014] Due to the extremely large amounts of waste sludge generated
from both the virgin pulp papermaking and the recycled fiber
papermaking processes, new uses of sludge are needed in order to
curtail the disposal problems presently being encountered. Some
attempts have been made to create such uses.
[0015] The prior art sets forth basically five different approaches
for utilizing sludge in useful products:
[0016] (1) Pelletizing the sludge using high pressure and binders
where the sludge is dried before pelletizing. The pellets can be
used as absorbents or chemical carriers, e.g., fertilizer.
Alternatively, large diameter pellets or cylinders are used as
fuel.
[0017] (2) Extracting the fibers or fillers from sludge in various
ways to subsequently use the extracted material in a paper and/or
ceramic product. These are both wet and dry processes.
[0018] (3) Mixing the sludge with other construction ingredients
such as concrete or plastic to embody the sludge as reinforcing
fibers or filler. Again these are both wet and dry processes.
[0019] (4) Direct molding of sludge into large shapes (i.e., large
cross section) and drying. These products are construction blocks
or boards and can be made using both wet and dry processes. Some of
these can be fired to burn out the cellulosic and polymeric
materials, leaving a ceramic product.
[0020] (5) Some sludges are formed into particulates or briquettes
of various forms and sizes. These are subsequently carbonized to
make an activated carbon product.
[0021] U.S. Pat. No. 4,303,019 to Haataja discloses the making of
pellets by molding paper mill sludge blended with a fibrous
reinforcing material. U.S. Pat. No. 5,215,625 to Burton discloses
the making of products such as stepping stones, acoustic paneling,
flower pots and planters, sculptures, shipping containers and
packing materials, and the like, from waste products such as ink
and waste slurry from pulp manufacturing. The incorporation of
de-inking byproducts from wastepaper recycling operations and pulp
mill clarifier sludge into drywall and other gypsum-based building
products is disclosed in U.S. Pat. No. 5,496,441 to Tran.
[0022] Attempts have also been made to recover and re-use the raw
materials from paper mill waste sludge. For example, U.S. Pat. No.
5,478,441 to Hamilton, discloses a process for recovering such raw
materials. U.S. Pat. No. 5,332,474 to Maxham discloses a process
for producing a papermaking filler product from the fiber
fines/clay fraction of a pulp, paper, paperboard, or deinking mill
waste solids.
[0023] While considerable prior art exists with regard to methods
for handling, utilizing or recycling of sludge as outlined above,
in actual fact there has been little commercial implementation. The
majority of the materials classified as sludge from both deinking
operations as well as conventional pulp and paper mills ends up in
landfills or is discarded or disposed of in some other way. The
major reason is that few of the many procedures available to
convert sludges can produce products that have significant
value.
[0024] The need to develop methods and processes that would use
these waste materials, however, is growing. It is likely that
environmental and regulatory pressures to recycle paper and paper
products will increase. This will mean there will be more de-inking
and recycling operations in the future. In addition, it is likely
that the percentage of inorganic materials in recycled paper, such
as calcium carbonate and clay, will increase for a number of
reasons. For example, calcium carbonate improves the long term
stability of printing papers because the alkalinity of the calcium
carbonate reduces the rate of discoloration and embrittlement of
the paper. Additionally, both calcium carbonate and clay are used
to increase the opacity of paper. In printing items such as
magazines or advertising supplements, addition of inorganic
materials allows for reductions in the amount of fiber used for the
paper. The purpose for the added inorganic material is to provide
superior opacity. In addition to the improved opacity,
incorporation of clay as a coating or filler and calcium carbonate
as a filler also provide improvements to the surface of the paper
such that the quality of the printing is improved. Furthermore,
wood pulp, even though it is a renewable resource, is becoming more
expensive. The cost of wood pulp currently exceed the cost of
calcium carbonate or clay, and it, therefore, makes economic sense
to include considerable amounts of these fillers in paper.
[0025] Steam explosion has been used to defiber paper material as
described in U.S. Pat. No. 5,262,003 to Chupka et al. and in U.S.
Pat. No. 4,312,701, which are both incorporated herein by
reference. As further discussed in Chupka, non-fibrous contaminants
subjected to the steam explosions have a reduced particle size and
are more readily washed out of the fiber suspensions.
[0026] Steam explosion is also used in the defibration of wood
chips as taught in U.S. Pat. No. 4,798,651 to Kokta, incorporated
herein by reference. In Kokta, wood chips are chemically treated
followed by steaming and explosive decompression to defibrate the
chips.
[0027] In U.S. Pat. No. 4,163,687 to Mamers et al., a nozzle design
is disclosed which is used in cellulosic defibration which
increases usable fiber content from wood chips and results in less
fiber damage.
[0028] In U.S. Pat. No. 5,262,004 to Gilbert, incorporated herein
by reference, steam explosion is used as part of a chemical
separation and recovering process of chemical preservatives from
wood chips from previously treated wood.
[0029] U.S. Pat. No. 5,122,228 to Bouchette et al., incorporated
herein by reference, discloses a steam explosion process which is
used in the de-inking of waste paper. The temperature ranges used
by Bouchette are reported to decrease particle size of contaminants
and increase the ability to strip contaminants from the fibers.
[0030] Australian Patent Office Application AU-B-29615/92,
corresponding to U.S. application Ser. No. 840,370 filed Feb. 24,
1992, discloses a steam explosion of mixed grades of high and low
quality waste paper which have been delignified by alkaline
digestion.
[0031] As will be seen from the description and illustrations to
follow, none of the above-identified references discloses or
anticipates the present invention directed to the process of
treating waste sludge and waste liquor with steam explosion to
increase the recoverable yield of fibers and fines from the waste
stream. Further, none of the references teach or suggest that the
useful fiber characteristics of an individual fiber can be improved
for absorbent products by the steam explosion process.
SUMMARY OF THE INVENTION
[0032] The present invention recognizes and addresses some of the
limitations of prior art fiber production in papermaking processes
which discard a large percentage of fibers and fines as an
unsalvageable and/or non-useful waste material.
[0033] It is, therefore, a general object of the present invention
to provide a process for recovering a useful opulation of fibers
and fines from the waste stream of a fiber production, waste paper
recycling, or papermaking process. In carrying out the present
process, it has been found that a steam explosion process may alter
the morphology of fibers and fines contained within a waste stream,
the altered morphology facilitating not only the separation of the
fines from the waste stream, but improving their useful qualities
in a paper product or papermaking process.
[0034] The invention sets forth a process by which a supply of
treated, recovered fibers and fines have superior fiber quality
characteristics for absorbent products than similar untreated
fibers and fines. The present invention enables both the volume and
dry solid content of waste streams to be reduced by the recovery of
additional fibers and fines from the waste stream. As a result, it
is possible to increase the percentage of fibers and fines from the
starting material. It is further possible to incorporate the
increased percentage of fibers and fines into a finished paper
product without lowering the quality of the finished product.
[0035] These and other useful objects of this invention are
achieved by a process and resulting product which provides a waste
sludge stream containing uncaptured fibers and fines from a fiber
processing facility; subjecting the waste stream to an elevated
temperature and pressure; explosively releasing the pressure from
said waste stream; passing the now treated waste material through a
filter recovery apparatus; and, separating a population of
recovered fibers and a population of recovered fines from the waste
stream.
[0036] Another aspect of the present invention concerns an
absorbent structure comprising modified cellulosic fibers prepared
by the process disclosed herein.
[0037] One embodiment of such an absorbent structure is a handsheet
comprising the modified cellulosic fibers prepared by the process
disclosed herein, wherein the handsheet is prepared by a wet laid
process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a graphical depiction of data comparing the
screening efficiency of varying quantities of untreated waste
sludge.
[0039] FIG. 2 is a graphical depiction of data comparing the
screening efficiency with respect to ash content of varying amounts
of untreated waste sludge.
[0040] FIG. 3 is a graphical depiction of data comparing the
screening efficiency of fibers and fines from waste sludge
following treatment of the sludge by steam explosion.
[0041] FIG. 4 is a graphical depiction of data setting forth the
treated waste sludge retained ash content.
[0042] FIG. 5 is a graphical depiction of data comparing the
Canadian Standard Freeness values of handsheets with varying levels
of recovered fibers from treated sludge.
[0043] FIG. 6 is a graphical depiction of data comparing the burst
index of handsheets prepared with varying levels of incorporated
treated fibers.
[0044] FIG. 7 is a graphical depiction of data comparing the
tensile index for handsheets formed with varying levels of treated
fibers.
[0045] FIG. 8 is a graphical depiction of data comparing the
tensile stretch for handsheets formed with varying levels of
treated fibers.
[0046] FIG. 9 is a graphical depiction of data comparing the tear
index for handsheets formed with varying levels of treated
fibers.
[0047] FIG. 10 is a graphical depiction of data comparing the
effect on opacity of various fiber levels incorporated into
handsheets.
Detailed Description of A Preferred Embodiment
[0048] It is to be understood by one of ordinary skill in the art
that the present discussion is a description of exemplary
embodiments only, and is not intended as limiting the broader
aspects of the present invention, which broader aspects are
embodied in the exemplary construction.
[0049] The present invention addresses some of the objects and
needs discussed above by providing a process using steam explosion
to treat various fiber and fine containing waste streams. As used
herein, "waste stream" refers to the waste stream from a waste
paper recycling operation or the liquid waste stream (white water)
from a paper manufacturing process, all of which may contain
varying levels of fibers and fines within the waste.
[0050] The term "fiber" refers to natural fibers derived from
vegetable matter and that has a length usually many times greater
than its width, and that typically possesses tensile strength,
pliability, and resistance to mechanical abrasion. This term may
also encompasses similarly shaped man-made objects which may be
present in waste paper products.
[0051] The term "fines" refers to short, naturally occurring fibers
as well as fragments of fibers. Depending upon the underlying fiber
process involved, the term "fines" may refer to different lengths
of fibers. As broadly defined here, "fines" refers to the
population of fibers within a fiber processing stream having an
average length as determined by either a length average calculation
or a weight average calculation, which falls outside a desired,
useful range. Within a virgin paper-making operation which prefers
longer, intact fibers, the average length of the fines may be
greater than the fine population of a waste paper recycling
facility.
[0052] No matter how defined, the population of fines heretofore
considered as unsalvageable waste or of inferior quality can now be
recovered. In doing so, the recovery process enhances the
fiber-like qualities of the fines by increasing the curl value,
increasing the fiber diameter along a portion of the fiber, and by
increasing the wicking properties of the recovered, treated
fines.
[0053] By way of example, the Kajaani FS-200 average fiber length
present within the sludge utilized by the examples herein, fall
within the range of 0.60 to 0.85 mm and which corresponds to a
Kajaani FS-200 length weight average of between 1.75-2.00 mm.
Accordingly, the average fiber length present within the waste
sludge material is considered a "fine" for the purposes of this
invention. Further, the fiber material which is shorter than the
average range is also considered a fine. While the fiber material
which has a length equal to or less than the average fiber length
is considered a fine, it is recognized that longer fibers are also
present in the waste stream. Such longer fibers are also
recoverable and constitute a valuable recovered fiber product and
which also has improved absorptive fiber properties. It is the
longer population of fibers which are believed to be separated and
retained on the Bauer-McNett classifier screen of 200 mesh or
larger.
[0054] Heretofore, significant amounts of fibers and fines have
been considered a waste product in tissue and paper production. The
fibers and fines have historically proven difficult to isolate and
contain a high degree of contaminants such as ash.
[0055] The ash content of recycled fiber sludge is indicative of
the amount of additives which are incorporated in the waste paper.
The ash content of the recycled sludge is generally about 20 to
about 80%. Waste paper containing high filler and coating
materials, for example, magazines, provides a recycled sludge
having a high ash content. By way of comparison, newsprint
de-inking mills generally produce a lower ash content waste
sludge.
[0056] The ash content of the recycled fiber sludge employed in the
methods of the present invention can vary and depends, for example,
upon the source mill, the particular components of the recycled
source material, and the like. However, it is believed that the
beneficial effects of the present invention on the ash content,
renders the invention suitable with all varying levels of ash
content. Further, to the extent the present invention improves the
physical properties of the fibers within the waste stream, such
improvements occur irrespective of the ash content. Accordingly, a
fiber-containing waste stream having a negligible ash content would
provide a useful source of fibers for steam treatment.
[0057] In particular, fines have been considered a waste product in
the tissue and paper production industry since fines typically
retard water drainage, confer low air permeability to the formed
webs or sheets, exhibit a higher degree of chemical reactivity
which results in greater chemical cost, and tend to promote greater
fiber-fiber bonding which, while increasing product strength,
imparts an often undesired stiffness to the paper product. In
particular, the fiber component from paper recycling waste sludge
has heretofore been considered unsalvageable in that the reclaimed
fibers have had an unacceptably high ash content.
[0058] In accordance with one aspect of the present invention is
the discovery that the steam explosion of the waste sludge alters
the fine shape. As set forth in co-inventor Sheng-Hsin Hu U.S.
patent application Ser. No. 08/767,607 filed on Dec. 17, 1996
entitled "Treatment Process for Cellulosic Fibers" and incorporated
herein by reference, steam explosion can be used to increase the
curl value of individual fibers. Further, the steam explosion has
been found to increase the wicking properties of the resulting
product incorporating the steam exploded fibers, and increases the
separation efficiency of the fibers and fines from the waste
sludge. The steam explosion permits the separation of fibers and
fines from the waste sludge and does so in a manner which provides
a population of recovered fibers having a low ash content. This
recovered population of fibers has demonstrated improved burst
index, tear index, tensile index, and tensile strength compared to
handsheets incorporating a similar percentage of untreated sludge
fibers.
[0059] It is understood and appreciated by those having ordinary
skill in the art that the cellulosic fibers in the waste streams
described herein will be substantially in the form of individual
cellulosic fibers although some individual fibers may be in an
aggregate form. The current process, then, is in contrast to known
steam explosion processes that generally treat cellulosic fibers
that are typically in the form of virgin wood chips or the
like.
[0060] It is believed that the present steam treatment of the
sludge and sludge fibers brings about changes to the fiber and fine
properties which correspond closely with the results reported in
the co-pending application referenced above.
[0061] It is believed that any combination of high pressure, high
temperature, and time which is effective in achieving a desired
degree of fiber modification is suitable for use in the present
invention. Further, such combination of pressure, temperature and
time are believed to have beneficial effects on the ash content of
the sludge, thereby offering an improved quality of fiber while
increasing the efficiency of fiber separation from the sludge.
[0062] As a general rule, it is believed that the cellulosic fibers
in the waste material may be beneficially treated at a temperature
in the range from about 130.degree. C. to about 250.degree. C.,
suitably from about 150.degree. C. to about 225.degree. C., more
suitably from about 160.degree. C. to about 225.degree. C., and
most suitably from about 160.degree. C. to about 200.degree. C.
[0063] The elevated temperature and pressures are applied over a
time period within a range from about 0.1 minutes to about 30
minutes, beneficially from about 0.5 minutes to about 20 minutes,
and suitably from about 1 minute to about 10 minutes. In general,
the higher the temperature employed, the shorter the period of time
generally necessary to achieve a desired degree of modification of
the cellulosic fibers, fines, and ash present in the waste stream.
As such, it may be possible to achieve essentially equivalent
amounts of modification for different fiber-containing waste
streams by using different combinations of high temperatures and
times.
[0064] As a general rule, it is believed that the cellulosic fibers
in the waste stream would be treated at a pressure that is
super-atmospheric and within the range of about 40 to about 405
pounds per square inch, suitably from about 40 to about 230 pounds
per square inch, and more suitably from about 90 to about 230
pounds per square inch.
[0065] Without intending to be bound by theory, it is believed that
the steam explosion process causes the cellulosic fibers to undergo
a physical modification. The physical modification includes a
curling phenomenon which helps in the physical separation of the
fibers as well as alters other properties such as liquid absorption
or liquid handling capabilities.
[0066] The curl of a fiber may be quantified by a curl value which
measures the fractional shortening of a fiber due to kink, twist,
and/or bends in the fiber. As used in the present invention, a
fiber's curl value is measured in terms of a two-dimensional plane,
determined by viewing the fiber in a two-dimensional plane. To
determine the curl value of fiber, the projected length of a fiber
as the longest dimension of a two-dimensional rectangle
encompassing the fiber (I) and the actual length of the fiber (L)
are both measured. An image analysis method may then be used to
measure L and I. A suitable analysis method is described in U.S.
Pat. No. 4,898,642 incorporated herein in its entirety by
reference. The curl value of a fiber can then be calculated from
the following equation:
Curl value=(L.backslash.I)-1
[0067] It has been found in accordance with this invention that the
cellulosic fibers following steam treatment are suitable for use in
a wide variety of applications. One useful aspect of the recovered
fibers and fines are that they may be reintroduced into the
respective process stream associated with the initial waste stream
used to isolate the fibers. It is believed that the recovered
fibers and fines are suited for use in disposable absorbent
products such as diapers, adult incontinent products, bedpans,
sanitary napkins, tampons, and other absorbent products including
wipes, bibs, wound dressings, surgical capes, and tissue-based
products including facial or bathroom tissues, household towels,
wipes, and related products. Accordingly, the present invention
relates to a disposable absorbent product comprising the cellulosic
fibers treated according to the process of the present invention.
Further, in another aspect, the present invention relates to any
paper product comprising the recovered and treated cellulosic fiber
and fines treated in accordance with the present invention.
Test Procedures
[0068] Sludge Treatment
[0069] Approximately 100 grams of waste sludge at 45 percent
consistency was obtained from a waste paper fiber recycling
facility at Kimberly-Clark Corporation, Owensboro facility. The
waste sludge was placed into a two-liter reactor vessel (Stake
Technologies Ltd.) where high pressure steam was injected into the
reactor thereby achieving a temperature of 202.degree. C. and a
pressure of 200 psi. The sludge was retained for time intervals of
2 minutes and 5 minutes. Following the appropriate retention time,
a blow valve was opened and the sludge was blown into a collection
tank maintained at ambient conditions. The collection tank was
suitably vented so that transient pressure accumulations within the
collection tank during the sludge discharge were minimized so as to
achieve a rapid pressure drop of the sludge during the discharge
step. Three repetitive runs were conducted for each retention time
and the respective samples were combined for further analysis.
[0070] Fiber Collection
[0071] The two-minute and five-minute treated sludge samples along
with control (untreated sludge) samples were subsequently dispersed
in a British Disintegrator (Testing Machines, Inc.) for three
minutes, and then evaluated with a Bauer-McNett classifier (Testing
Machines, Inc.) for 20 minutes. The classifier comprises six
ten-liter cells separated by 14, 28, 48, 100, and 200-mesh screens.
All cells were filled with water and subjected to constant
agitation. 10 and 20-gram samples of oven dry weight of the treated
and control sludge were placed into respective first cells and
passed through each screen in sequential order from the lowest to
the highest mesh screen.
[0072] After 20 minutes, the water was drained from each cell and
the classified sludge samples were collected, weighed, and
evaluated for ash content using standard methods as established in
TAPPI Test Method T-211-OM-93.
[0073] The collected samples which were retained by the 200-mesh
screens or larger were combined and incorporated into wet-laid
handsheets. The remaining material smaller than the 200-mesh screen
was comprised largely of fines. While this population of fines was
not used in the present examples, it is believed that these fines
also show improvements in fiber quality similar to the results
reported below.
[0074] Preparation of Wet-Laid Handsheet
[0075] A standard 71/2 inch by 71/2 inch handsheet was prepared
using the desired fiber samples by using a 8 inch by 8 inch cast
bronze wet-laid handsheet former mold, available from Voith
Corporation. The handsheets had a basis weight of about 60 grams
per square meter.
[0076] The handsheets were made using ratios of 30, 70 and 100
percent steam exploded recovered fibers mixed, when applicable,
with the appropriate percentages of recycled fiber wet lap obtained
from the Kimberly-Clark Owensboro facility. The recycled fiber wet
lap is the recovered product, the production of which provided the
original waste sludge which was used in the steam explosion
treatment process.
[0077] A British Disintegrator mixer, available from Testing
Machines, Inc, was filled with about 2 liters of distilled water at
room temperature (23.degree. C.) and about 45.0 grams of the fiber
sample. The counter on the British Disintegrator was set to zero
and was turned on until the counter ran to about 600. The contents
of the British Disintegrator were then poured into a vessel filled
with about 8 liters of distilled water.
[0078] The handsheet former, having an approximate 12 inch deep
chamber, was filled with tap water to about 5 inches below the top
of the handsheet former chamber. The contents of the bucket were
then poured into the handsheet former chamber where a dedicated
stirrer was then used to mix the suspension in the handsheet former
chamber. The stirrer was moved slowly up and down 6 times to cause
small vortexes, but to avoid causing large vortexes, in the square
pattern of the handsheet former. The stirrer was then removed and
the suspension was drained through the forming screen of the
handsheet former. The handsheet former was then opened and two
layers of blotting paper were placed on top of the handsheet. A
roller, applying the equivalent of about 308 kiloPascals of
pressure inch, was moved back and forth one along each side and the
center of the formed handsheet. The blotting paper, with the formed
handsheet attached, was then lifted off the forming screen. The
blotting paper was then placed on a table such that the formed
handsheet faced upwards. An 18 inch, 4 mesh, stainless steel screen
was placed on top of the handsheet. The blotting paper, handsheet,
and screen were then flipped so that the screen was on the bottom
and the blotting paper was on top. The blotting paper was then
peeled off of the handsheet, leaving the handsheet on the screen.
The handsheet is transferred, wire side up, to the polished convex
surface of an 8 inch by 8 inch dryer hot plate. A canvas cover is
placed over the convex surface and handsheet and is weighted down
to prevent drying induced wrinkling. The handsheet is dried for 2
minutes and then removed for subsequent evaluation.
[0079] Recovered Fiber Properties
[0080] Set forth in Table 1, and as further discussed in reference
to the Figures, are various fiber properties as further discussed
in reference to the accompanying figures. As seen in FIG. 1, it was
initially determined that the loading concentration for control
(untreated) samples within the Bauer-McNeft classifier shows
similar efficiencies at 10 oven dried gram and 20 oven dried gram
loadings. As set forth in Table 1 and graphically represented in
FIG. 2, the ash separation efficiency of control (untreated) sludge
samples remain constant at the 10 and 20 gram loadings. Therein
after, 20 gram loading runs were used to increase the amount of
material collected and used in the remaining test. The data as
depicted in FIG. 2 confirms experience within the industry that it
is difficult to recover useful fibers from waste sludge since the
recovered product has a high ash content which limits the use of
the fibers.
[0081] As set forth in FIG. 4, the ash content associated with
recovered fibers from treated sludge is significantly reduced for
both the 2 minute and 5 minute treatment intervals. This finding is
further supported by the data set forth in FIG. 3 that indicates
the combined weight of the 200 mesh and larger control group of
recovered fibers from untreated sludge is higher than the weight of
treated sludge recovered fibers. The combined data indicates that
the untreated recovered fiber weight is greater as a result of the
increased levels of ash particles. Stated another way, the steam
treatment allows a fiber recovered product which has a
significantly lower ash content than is otherwise obtained.
EXAMPLE 1
[0082] Canadian Standard Freeness Measurements
[0083] The prepared handsheets were subjected to several tests,
namely Canadian Standard Freeness values, burst index, tensile
index, tensile stretch, tear index, and opacity.
[0084] As best seen in reference to Table 2 and FIG. 5, handsheets
prepared from the fibers recovered following steam explosion of the
sludge compare favorably at 30 percent, 70 percent and 100 percent
loading levels to the control sheet of zero percent treated fibers
with respect to the Canadian Standard Freeness values. Canadian
Standard Freeness values were determined according to protocols
established in TAPPI Test Methods T-227 OM-94.
[0085] Compared to untreated fibers, the treated 100 percent
recovered fiber improved the freeness values from a value of 300 to
between 470 to 490. It is believed that the improvement are the
results of a decrease in the fine and ash content in the reclaimed
fibers along with steam explosion induced changes in fiber
morphology.
EXAMPLE 2
[0086] Burst Index of Handsheets
[0087] The burst index of the handsheets were determined in
accordance with established protocols in TAPPI Test Method T 403
"Bursting Strength of Paper" and as further referenced in TAPPI
220-sp-96 procedure for Physical Testing of Pulp Handsheets.
[0088] As seen in Table 2 and in FIG. 6, the burst index of the
handsheet using reclaimed fibers from treated sludge consistently
exceeds the burst index of untreated sludge fibers.
EXAMPLE 3
[0089] Tensile Index Values of Handsheets
[0090] Tensile index of samples was calculated by dividing the
sample tensile strength by the sample basis weight. Tensile
strength refers to the maximum load or force (i.e., peak load)
encountered while elongating the sample to break. The tensile
strength was determined with an Instron Model 1122 Universal Test
Instrument in accordance with Test Method TAPPI T 404 cm-82. Each
sample was about 2.54 centimeters wide and the initial separation
between the tester jaws prior to elongation was about 12.7
centimeters.
[0091] The tensile index properties of sheets having reclaimed
fibers, as seen in FIG. 7, exceeds the values of the untreated
sludge fibers.
EXAMPLE 4
[0092] Tensile Stretch Values of Handsheets
[0093] The tensile stretch values are determined as a percentage of
the tensile index values as set forth above in Example 3. As seen
in reference to Table 2 and in FIG. 8, the tensile strength values
of treated recovered fibers is improved compared to the untreated
recovered fibers.
EXAMPLE 5
[0094] Tear Index of Handsheets
[0095] The tear index was calculated by dividing the tearing load
by the sample basis weight. The tearing load measures the toughness
of a material by measuring the work required to propagate a tear
when part of a specimen is held in a clamp and an adjacent part is
moved by the force of a pendulum freely falling in an arc.
[0096] The following method was used to determine the tearing load
of the handsheets. This method determined the average force
required to propagate a tear starting from a cut slit in the
material being tested. The higher the number, the greater the force
to tear the specimen.
[0097] This procedure is specific to a falling-pendulum
(Elmendorf-type) instrument. Desirably, the tester is equipped with
a pendulum that has a deep cutout (recessed area) on the pendulum
sector and pneumatically-activated clamps. The tester used was sold
under the trade designation Lorentzen and Wettre brand, Model 09ED.
This tester may be obtained from Lorentzen Wettre Canada Inc.,
Fairfield, N.J. 07004.
[0098] In addition to the tester, a specimen cutter was used
capable of providing 63.0.+-.0.15 mm (2.5.+-.0.006 in.) specimens.
It is recommended that the specimens be cut no closer than 15 mm
from the edge of the material and the specimens be taken only in
areas that are free from folds, creases, and crimp lines. The
handsheet specimens were cut to 63.+-.0.15 mm by 73.+-.1 mm and
placed facing up in the same direction. Additional equipment
included a 50 g weight.
[0099] Specimens were conditioned at laboratory conditions for 24
hours prior to testing. The tests were conducted in a standard
laboratory atmosphere of 23.+-.1.degree. C. (73.4.+-.1.8.degree.
F.) and 50.+-.2% relative humidity.
[0100] The number of plies needed for the test results to fall
between 20 to 60 on the linear range scale of the tear tester was
determined. The 63 mm length of the handsheet specimens was run
vertically on the tear tester.
[0101] The tester was placed a level surface free from noticeable
vibrations and leveled. Afterwards, testing of a specimen was begun
by verifying that the power was on. Next, the rotary dial was set
to the number of plies to be torn. That being done, the number
button was pushed and the cutting lever was pushed down.
Afterwards, the digital readout was verified as correct. Next, the
specimen was placed between the clamps with the edge of the
specimen aligned with the front edge of the clamp. If more than one
sheet was tested, the sheets were placed facing in the same
direction. That being done, the clamp button was pushed to close
the clamps. Afterwards, a slit was cut in the specimen by pushing
down on the cutting knife lever until it reaches its stop. The slit
was clean with no tears or nicks. Next, the pend button was pushed
to release the pendulum. That being done, the pendulum was caught
on the back swing and positioned to the starting position after the
pendulum traveled one full swing. Afterwards, the pend button was
depressed to raise the stop once the pendulum was behind it. The
value was recorded unless the tear line deviated more than 10
millimeters. If the deviation was more than 10 millimeters, the
specimen was discarded and a new specimen tested.
[0102] The results were recorded in grams centimeter. The values
were reported to the nearest whole number. The following conversion
factors were used with units which had a 1600-gram capacity and did
not automatically convert the test result:
1 # of sheets Multiply by # of sheets Multiply by 1 sheet 16 8
sheets 2 2 sheets 8 10 sheets 1.6 4 sheets 4 12 sheets 1.33 5
sheets 3.2 16 sheets 1
[0103] As seen in reference to Table 2 and in FIG. 9, improvements
are seen in the tear index values of the recovered fibers.
EXAMPLE 6
[0104] Opacity Determinations
[0105] The opacity coefficient was determined in accordance with
established protocols in TAPPI test method T 220 sp-96 and is set
forth in Table 2 and illustrated graphically in FIG. 10.
[0106] As recorded in Table 2, additional measurements of specific
volume, tensile energy absorption, scattering coefficient and
porosity determinations were evaluated and recorded. The
evaluations conform to TAPPI standards. The specific volume was
determined by measuring the thickness of the paper and dividing by
the measured papers' basis weight. The thickness of the paper was
determined in accordance with TAPPI standard T 411 om-89. The
procedure deviated from the TAPPI standard by measuring the
thickness of five specimens rather than the ten TAPPI specimens in
conducting three measurements rather than five TAPPI
measurements.
[0107] In reference to Table 2 and to FIG. 10, handsheets
incorporating recovered treated fibers have a lower opacity than
handsheets with untreated recovered fibers. Again, the lower
opacity of the treated recovered fibers is attributed to a lower
ash content of the source fibers.
[0108] While not wishing to be limited by theory, it is believed
that the above noted improvements to fiber separation and fiber
quality are indicative of several changes brought about by the
steam explosion treatment. One, it is seen that the treatment of
the waste sludge has a beneficial effect on the separation dynamics
of the particulate ash. The steam treatment may render a smaller
ash particle size, making the fiber/ash separation easier.
[0109] A second noted benefit of the steam explosion treatment
process is that the quality of the recovered population of fibers
has improved fiber characteristics as evaluated in the handsheet
properties. It is believed that the steam treatment process alters
the fiber morphology by increasing the curl index as well as
increasing the fiber diameter. As noted in the co-inventor's
application referred to and incorporated by reference above, the
steam explosion of isolated cellulosic fibers improves the fibers
liquid absorption and liquid handling properties.
[0110] Both the increase in curl index and the change in morphology
provide similar separation efficiency in fines. While the fine
population, as determined by the fiber/fine residue which passed
through #200 and larger mesh screen, was not separately evaluated,
the fines are believed to undergo similar changes. As noted above,
the separation efficiency of the fines from ash is increased. As
such, a recovered population of fines may be separated from the
waste, reducing the solid content of the waste stream. Further, it
is believed that the cellulosic fines, following steam treatment,
also have improved fiber qualities compared to untreated fines. As
such, the treated fines can be incorporated into certain paper
products.
[0111] To the extent the steam explosion treatment alters the
cellulosic fibers' morphology, it should be noted that the
population of recovered fibers likely contained material which,
untreated, would have been classified as a fine. In other words,
the curling and diameter changes seen in steam-treated fibers
likely produced altered fines having an increased curl index and/or
larger diameter. Either event increases the number of fines which
would be captured in the Bauer McNett classifier along with the
longer fiber population. As such, the data supports the conclusion
that increased loadings of fines and fibers from steam treated
sludge can be added to paper products.
[0112] The above embodiments are directed towards a recovered fiber
product from the waste sludge of a paper recycling facility.
However, the scope of the present invention is not limited to any
specific waste stream. Virgin chipping operations and paper making
operations all generate a waste stream which contains significant
levels of fibers and fines in the waste stream. The current
invention provides a process which can increase the recovery of
fibers and fines from the waste stream. Further, the steam
explosion improves the recovered fibers characteristics useful in
paper products.
[0113] Although desired embodiment of the invention has been
described using specific terms, devices, and methods, such
description is for illustrative purposes only. The words used are
words of description rather than of limitation. It is to be
understood that changes and variations may be made by those of
ordinary skill in the art without departing from the spirit and
scope of the present invention which is set forth in the following
claims. In addition, it should be understood that aspects of the
various embodiments may be interchanged, both in whole or in
part.
* * * * *