U.S. patent number 3,895,998 [Application Number 05/273,280] was granted by the patent office on 1975-07-22 for production of shaped articles from paper sludge.
This patent grant is currently assigned to National Research Development Corporation. Invention is credited to George Robert Haywood, Alan David Plumstead.
United States Patent |
3,895,998 |
Haywood , et al. |
July 22, 1975 |
Production of shaped articles from paper sludge
Abstract
A process for the production of a shaped article from paper
sludge which comprises depositing a layer of an aqueous slurry of
the sludge and controlling the water content of the slurry by
applied pressure so as to produce a coherent agglomerated layer
having a degree of wet strength, and a water content of from 40 to
85% by weight based on the total weight of the layer and forming
the layer under pressure with drying to produce a shaped
article.
Inventors: |
Haywood; George Robert
(Tideswell, near Buxton, EN), Plumstead; Alan David
(London, EN) |
Assignee: |
National Research Development
Corporation (London, EN)
|
Family
ID: |
9803161 |
Appl.
No.: |
05/273,280 |
Filed: |
July 19, 1972 |
Foreign Application Priority Data
Current U.S.
Class: |
162/100;
162/DIG.9; 162/145; 162/149; 162/164.1; 162/164.7; 162/189;
162/231; 162/123; 162/159; 162/164.6; 162/165; 162/210 |
Current CPC
Class: |
B03B
7/00 (20130101); D21J 1/00 (20130101); Y10S
162/09 (20130101) |
Current International
Class: |
D21J
1/00 (20060101); B03B 7/00 (20060101); D21f
001/82 (); D21f 011/00 (); D21h 001/00 () |
Field of
Search: |
;162/189,190,4,231,210,211,312,313,314,123,164,165,159,100,145,149,205,206,DIG.
;264/86,119,120,174,280,294 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,275,042 |
|
May 1972 |
|
GB |
|
131,432 |
|
Mar 1969 |
|
CS |
|
Primary Examiner: Bashore; S. Leon
Assistant Examiner: Fisher; Richard V.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow and
Garrett
Claims
We claim:
1. A process for the production of a shaped article from paper
sludge which comprises depositing a layer of an aqueous slurry of
said sludge, controlling the water content of the slurry by applied
pressure so as to produce a coherent agglomerated layer having a
degree of wet strength and a water content of from 40 to 85% by
weight based on the total weight of the layer and then forming the
layer under pressure with drying to produce a shaped article.
2. The process according to claim 1 in which the aqueous slurry is
deposited on to a liquid permeable support.
3. The process according to claim 1 in which extra fibrous material
is added to the aqueous slurry before deposition to assist in
agglomeration of the sludge.
4. The process according to claim 1, in which the aqueous slurry
before deposition has a solids content of from 5 to 30% by
weight.
5. The process according to claim 4, in which the solids content
comprises 20 to 80% by weight of a fibrous component and 80 to 20%
by weight of a mineral component.
6. The process according to claim 2, in which the aqueous slurry is
deposited from the discharge orifice of an extruder at a
predetermined rate on to the liquid permeable support which is
movable relative to the discharge orifice.
7. The process according to claim 6, in which the liquid permeable
support comprises an endless moving belt of metal or plastic mesh
or gauze.
8. The process according to claim 2, in which the slurry is passed
through an extruder equipped with means for removing part of its
water content prior to deposition of the layer.
9. The process according to claim 2, in which the support carrying
the deposited slurry is passed through a series of pressure rolls
which progressively squeeze out water from the deposited slurry to
produce the coherent agglomerated layer.
10. The process according to claim 1, in which a cylindrical vacuum
filter is partly immersed in the slurry and rotated so as to
deposit a layer of slurry on its circumference and the layer of
agglomerated slurry is removed from the filter in a continuous
operation.
11. The process according to claim 1, in which the water content of
the layer is controlled so as to produce an agglomerated layer
having a wet strength sufficient to withstand bending to an angle
of 90.degree. without cracking.
12. The process according to claim 1, in which the water content of
the layer is controlled so as to produce an agglomerated layer
having a wet strength such that an 8 feet .times. 4 feet section
will maintain its integrity with minimal support over each 2 feet
of its running length and such that an area of at least 4 square
feet will maintain its integrity when supported only at its
edges.
13. The process according to claim 1, in which the water content of
the layer is controlled so as to produce an agglomerated layer
having a thickness of from one-eighth to one-half inch.
14. The process according to claim 1, in which the water content of
the layer is controlled so as to produce an agglomerated layer
having a density of from 0.8 to 2.0 grams per cc.
15. The process according to claim 1, in which the agglomerated
layer is molded under heat and pressure to form the shaped
article.
16. The process according to claim 15, in which the shaped article
is a board and the moulding pressure is up to 2,400 pounds per
square inch.
17. The process according to claim 15, in which the shaped article
is a moulded article and the moulding pressure is from 50 pounds
per square inch to 2 tons per square inch.
18. The process according to claim 1, in which the forming with
drying operation is carried out at a temperature of from
100.degree. to 190.degree.C.
19. The process according to claim 1, in which a plurality of
agglomerated layers are formed, superimposed one on the other, and
then laminated between pressure rollers.
20. The process according to claim 1, in which an agglomerated
layer is first formed and then a further layer of aqueous slurry of
paper sludge is deposited thereon, the water content of the
composite layer being controlled by passing it through pressure
rolls to obtain a laminated coherent agglomerated layer.
21. The process according to claim 1, in which there is added to
the slurry before deposition from 5 to 40% by weight of a synthetic
resin.
22. The process according to claim 21, in which the synthetic resin
is a styrene/butadiene resin, an acrylic resin, a vinyl acetate
resin, a vinyl chloride resin, a phenol formaldehyde resin, a
melamine formaldehyde resin, or a urea formaldehyde resin.
23. The process according to claim 1, in which there is added to
the slurry before deposition a flame retardant.
24. The process according to claim 23, in which the flame retardant
is a borate, boric acid, mono-ammonium phosphate, or aluminium
hydroxide.
25. The process according to claim 1, in which the slurry is
deposited over a reinforcing medium to form a reinforced
agglomerated layer.
26. The process according to claim 25, in which the medium is a
layer of fibres.
27. The process according to claim 25, in which the medium is a
fibrous mat.
28. The process according to claim 1, in which a mineral filler is
added to the slurry before deposition.
29. The process according to claim 1, wherein the coherent
agglomerated layer is dried to a water content of between 30 and
40% before the layer is formed into a shaped article.
30. A pressure-formable coherent agglomerated layer of paper sludge
having a thickness greater than one-sixteenth of an inch, a density
of from 0.8 to 2.0 grams per cubic centimeter, and a water content
of from 40 to 85% by weight based on a total weight of the layer,
the layer being sufficiently self-supporting to enable it to be
handled without disintegration.
31. The layer according to claim 30, having a wet strength
sufficient to withstand bending to an angle of 90.degree. without
cracking.
32. The layer according to claim 30, having a wet strength such
that an 8 foot by 4 foot section will maintain its integrity with
minimal support over each 2 feet of its running length and such
that an area of at last 4 square feet will maintain its integrity
when supported only at its edges.
33. The layer according to claim 30, having a thickness of from
one-eighth to one-half inch.
34. A laminate comprising a plurality of layers according to claim
30.
35. A process for the production of a pressure-formable coherent
agglomerated layer, which comprises depositing a layer of an
aqueous slurry of paper sludge and controlling the water content of
the slurry with applied pressure and drying so as to produce a
coherent agglomerated layer having a thickness greater than
one-sixteenth of an inch, a density of from 0.8 to 2.0 grams per
cubic centimeter, and a water content of from 40 to 85% by weight
based on the total weight of the layer, the layer being
sufficiently self-supporting to enable it to be handled without
disintegration.
36. The process according to claim 35, in which the aqueous slurry
is deposited onto a liquid permeable support to form the layer.
37. The process according to claim 35, in which the aqueous slurry
is deposited from an extruder at a predetermined rate onto a liquid
permeable support which is movable relative to the discharge
orifice of the extruder.
38. The process according to claim 35, in which the aqueous slurry
is deposited upon a liquid permeable support and the support
carrying the deposited slurry is passed through a series of
pressure rolls which progressively squeeze out water from the
deposited slurry.
Description
This invention relates to a process for the production of shaped
articles, and is more particularly concerned with the production of
shaped articles from industrial waste materials.
A variety of industrial waste materials comprise either fibrous or
mineral materials, and in many cases mixtures of both. Examples of
industrial waste materials include those obtained in paper
manufacture, asbestos slurry wastes, food wastes such as coffee
waste, tobacco waste and various quarry and mineral wastes. The
disposal of these materials represents a serious environmental
problem which is increasingly becoming one of national concern.
In British Pat. No. 1,275,042 there is described and claimed a
method of recovering the fibrous and mineral material in "paper
sludge" (the aqueous slurry obtained as a waste effluent in paper
manufacture) in which textile and/or mineral fibres with an average
fibre length of from 1/16th of an inch to 5 inches are added to the
slurry as individual fibres or as fragments of woven or like fabric
so as to assist in agglomerating together the fibre material of the
slurry together with at least part of any mineral content thereof,
and in which the agglomerated material is recovered as a board
product or as a moulding composition.
The present invention provides a process for the production of
shaped articles which may be broadly applied to a variety of
industrial waste materials.
According to the invention a process for the production of a shaped
article from fibrous and mineral industrial waste materials
comprises depositing a layer of an aqueous slurry comprising a
mixture of a fibrous component and a mineral component and
controlling the water content of the slurry so as to produce a
coherent agglomerated layer having a degree of wet strength, and
then forming the layer under pressure and drying to produce a
shaped article.
The invention also comprises an apparatus for the production of
shaped articles from fibrous and mineral industrial waste materials
comprising means for depositing a layer of an aqueous slurry
comprising a mixture of a fibrous component and a mineral
component, means for controlling the water content of the slurry so
as in operation to produce a coherent agglomerated layer having a
degree of wet strength, and means for forming the coherent
agglomerated layer under pressure, and for drying the layer so
formed.
According to one aspect of the invention an aqueous slurry
comprising a mixture of a fibrous component and a mineral component
is deposited on to a liquid permeable support to form a layer, and
the water content of the slurry is controlled by applied pressure
and/or drying so as to produce a coherent agglomerated layer having
a degree of wet strength. The layer may then be molded under the
action of heat and pressure to produce a shaped article.
The invention may be applied to a wide variety of industrial waste
materials and also to mixtures thereof. The fibrous component of
the mixture may be organic, for example cellulose fibres derived
from waste, paper, waste chopped rags, sisal, jute or hessian or
synthetic resin fibres for example nylon, terylene or polypropylene
fibers; or inorganic for example asbestos fibres or glass fibres.
The mineral component may be a clay, for example china clay or
micaceous china clay, an oxide, for example silica, titanium
dioxide, or antimony trioxide, and various inorganic salts for
example silicates and carbonates such as calcium carbonate or chalk
obtained as waste products from a wide variety of manufacturing
operations. The invention is particularly applicable to the
treatment of paper sludge which is an aqueous slurry comprising a
mixture of cellulose fibres of short fibre length, and minerals
such as clay, chalk or calcium carbonate, titanium dioxide and
antimony trioxide. The invention may also be applied to asbestos
slurry waste, food wastes, tobacco waste and quarry and mineral
wastes as previously mentioned.
In the case of industrial waste materials such as paper sludge, the
material is already in the form of an aqueous slurry when it is
discharged from the paper mill. It is also possible, however, to
make up an aqueous slurry suitable for use in the present invention
by dispersing the solid fibrous and mineral components in water.
For example shredded waste paper may be mixed with a suitable waste
mineral material such as micaceous china clay or fine granite dust
and water to form a useful aqueous slurry.
It is of course necessary for the aqueous slurry to contain
sufficient quantities of solids to enable it to be agglomerated.
Simple tests can be made first on filterability and on solids
content and from these tests it can be determined what particular
procedure in accordance with the invention can be employed and also
whether or not the application of the process of the invention to
the particular waste material is commercially practicable.
We have found that it is possible to use slurries containing fibres
having an average fibre length outside the range of 1/16th of an
inch to 5 inches. The nature of the slurry itself determines the
particular method of treatment which it is necessary to apply, and
addition of further fibrous material or mineral material may be
made as desired to give a slurry of the required consistency. We
have found that slurries containing a relatively large amount of
fibrous material frequently require no further additions, but
slurries with a very high mineral content for example certain kinds
of paper sludge do however appear to require the addition of extra
fibrous material or the like to assist in agglomeration of the
slurry and to obtain satisfactory products.
Although the exact proportions vary with the nature of the waste
material under consideration, we have found that it is preferable
to operate with a slurry having a solids content of from 5 to 30%
by weight. Industrially produced aqueous slurries frequently
contain only up to about 2% solids and in these cases the slurry
will usually need to be concentrated, for example by filtration, to
bring the solids content up to a usable value. Of this solids
content, the fibrous component preferably comprises from 5 to 95%
by weight particularly from 20 to 80% by weight and the mineral
component preferably comprises from 95% to 5% by weight
particularly from 80 to 20% by weight.
The aqueous slurry is preferably deposited upon a liquid permeable
support to form a layer, the solid materials remaining on the
support whilst the excess water is allowed to drain off. The slurry
may be deposited from a hopper, or preferably an extruder having
means for discharging the slurry at a predetermined rate. The
liquid permeable support may be a mesh or gauze of metal or plastic
material, for example stainless steel mesh or nylong mesh and is
preferably movable relative to the discharge orifice of the hopper
or extruder. For example the liquid permeable support may be in the
form of an endless moving belt of metal or plastic mesh or
gauze.
A number of methods of controlling the water content of the slurry
are available. For example the slurry may be passed through an
extruder equipped with means for removing part of the water content
of the slurry prior to deposition of the layer, so that the layer
of slurry leaving the extruder is of the desired composition.
However in a preferred embodiment of the invention, the liquid
permeable support carrying the deposited slurry is passed through a
series of pressure rolls producing a plurality of nip actions which
progressively squeeze out water from the deposited slurry and
control its thickness to produce a coherent agglomerated layer of
the desired water content and strength. The water content and
thickness of the deposited layer may be controlled by varying the
pressure applied by the pressure rolls and by nip setting
adjustment. The pressure rolls may be arranged above the deposited
layer so as to squeeze the layer between the rolls and the liquid
permeable support, or alternatively the rolls may be arranged in
pairs above and below the deposited layer. In an alternative method
of controlling the water content of the slurry there may be
employed a cylindrical vacuum filter which is partly immersed in
the slurry and rotated so as to deposit a layer of slurry on its
circumference. The layer of agglomerated slurry may be removed from
the filter in a continuous operation, for example with a take-off
knife.
The above treatments for reducing the water content of the layer by
applied pressure usually produce a layer having a water content of
about 45% by weight, i.e. having a solids content of substantially
55% by weight. In one embodiment of the invention after subjecting
the layer of slurry to applied pressure to reduce its water
content, a drying operation is performed to reduce the water
content of the layer to a preferred value. In its simplest form the
drying operation may merely consist of cutting the layer into
sheets of the desired length and stacking them to dry. Preferably
however the layer is passed through a drying oven to produce an
agglomerated layer of the desired water content. The layer should
not be completely dried since this will impair the subsequent
forming operation.
The water content of the slurry is controlled so as to produce a
coherent agglomerated layer having a degree of wet strength. The
degree of wet strength required of the layer is such that it can be
formed under pressure without tearing, and such that it is
sufficiently self-supporting to enable it to be handled without
disintegration. The layer should, for example, preferably be able
to withstand bending to an angle of 90.degree. without cracking.
Preferably also the layer should be capable of supporting its own
weight to such an extent that an 8 foot .times. 4 foot section will
maintain its integrity with minimal support over each 2 feet of its
running length and such that an area of at least about 4 square
feet will maintain its integrity when supported only at its
edges.
The wet strength of the agglomerated layer is dependent upon its
thickness, density and water content, but it has been found in
practice that the desired thickness and density can be attained by
an appropriate choice of the method of controlling the water
content. Thus if pressure is applied to the deposited layer of
slurry, the density will be increased and the thickness and water
content will be reduced. Alternatively if the water content is
reduced by heating, the thickness will be substantially unchanged
and the density will be reduced. A few simple experiments will
determine what conditions are necessary to achieve an agglomerated
layer having the desired thickness, density, water content and wet
strength.
It is found in general that the water content of the coherent
agglomerated layer of slurry may vary from less than 15 to about
85% by weight, based on the total weight of the layer. In choosing
an appropriate water content it is necessary to consider not only
the wet strength of the agglomerated layer but also the forming
operation which the layer is to undergo to produce the shaped
article. At the lower levels of water content say from 15 to 30% by
weight the agglomerated layer may be used to form flat products and
simple mouldings as described later. For more difficult mouldings,
and for a variety of general applications, the water content of the
layer should be somewhat higher, for example around 40 to 85% by
weight, particularly from 50 to 70% by weight. In this condition
the layer still surprisingly can possess the wet strength required
to permit it to be handled without disintegration.
The thickness of the agglomerated layer is dependent upon the
thickness of the final shaped article and the forming process, but
it is usually greater than one-sixteenth inch in order to obtain an
agglomerated layer having adequate wet strength. Preferably the
thickness of the layer is from one-eighth to one-half inch.
The process of the invention may also be modified to obtain shaped
articles of greater thickness.
Thus, for example:
i. A plurality of agglomerated layers may be formed and
superimposed one on the other. These are then laminated between
pressure rollers to obtain a multiple thickness, or slightly less
because of slight spread under lamination pressure.
ii. A single agglomerated layer is first formed in the usual way
and this is then followed by depositing a further layer of aqueous
slurry on to the first layer by means of one or more hoppers or
extruders situated after the first series of pressure rolls. The
composite layer is then passed through further pressure rolls to
obtain a laminated coherent agglomerated layer.
The density of the agglomerated layer is dependent upon the density
required in the final shaped article and the forming process, but
is usually from 0.8 to 2.0 grams per cc.
The coherent agglomerated layer is finally formed under pressure
and dried to produce the desired shaped article. Thus the forming
operation may comprise passing the layer through pressure rolls to
give a board product, or moulding the layer to produce a moulded
article. Preferably the forming and drying operations are carried
out together, and for example the layer may be moulded under heat
and pressure. Pressures varying from a few pounds per square inch
to several tons per square inch may be used in the forming
operation, depending on the desired physical properties of the
final shaped article. For boards, pressures of up to 2,400 pounds
per square inch have been found to give useful products, whilst for
moulded articles rather higher pressures are usually required,
preferably from 50 pounds per square inch to 2 tons per square
inch. When the forming and drying operations are carried out
together it is found that there is usually an optimum working
temperature which is generally in the range of from 100.degree. to
190.degree.C. In moulding operations the article is preferably left
in the heated mould for a few minutes to allow water to evaporate
though this time may be minimised by the use of a perforated mould
or by vacuum forming. In a preferred method of moulding the shaped
articles, there is inserted between a surface of the mould and a
surface of the layer a flexible permeable sheet material as
described in British Pat. No. 5820/72.
The process of the invention may be used to manufacture various
shaped articles:
a. Insulation fibre board
This is obtained by lightly pressing an agglomerated layer of
relatively low water content, say from 15 to 30% by weight to yield
a low-density board which has sound insulation properties,
comparable with those of existing commercial insulating board.
b. Hardboard-type board
An agglomerated layer or layers are pressed at a pressure of
substantially one-half ton per square inch and subjected at the
same time to heating at a temperature of substantially
150.degree.C, to obtain a consolidated product similar to hardboard
and with similar properties. This hardboard can be laminated to the
usual surface finishes including wallpaper, self-adhesive vinyl
film or paper of the kind common in home decoration. The layer or
board, may be sprayed with resin solution on one or both sides to
obtain a resin-rich surface of improved finish.
c. Decorative "formica"-type board product
This product is obtained by direct lamination of an agglomerated
layer or layers with melamine printed surface papers and phenolic
underlay. Pressures of up to one half of a ton per square inch and
temperatures of 110.degree. to 170.degree.C may be used depending
on the density required in the core of the laminate.
d. Packaging board
If the agglomerated layer is lightly pressed or rolled, the
resulting sheet is suitable for various types of packaging
materials and for box making. For instance, if a groove is routed
in the sheet, the material can be hinged at that point to form a
right-angled joint and a complete box can be made by forming the
necessary joints in this way. Boxes with a fair degree of strength
can also be made by using the hardboard-type board (b) and treating
it in the same manner.
e. Moulded decorative products
These products are an extension of the decorative formica type
product. A radiused or ribbed mould may be used and the product
takes on the shape of the mould together with a decorative effect.
The board may also be embossed. This cannot be done with usual
formica as such materials are not mouldable in commercial form.
Examples of articles which can be produced include moulded chair
seats and glove box compartments.
Other moulded articles without a decorative finish can also be
produced for particular applications, for example pallets can be
produced with a high load bearing capacity.
f. Construction sheets and boards
An agglomrated layer or layers pressed at a pressure of about
one-fourth ton per square inch and at a temperature of 165.degree.
to give products resembling plasterboard or asbestos board.
Products resembling stone or slate can also be produced by an
appropriate choice of composition. These are more fully described
in British Pat. No. b 23462/72.
A variety of additives may be incorporated into the slurry to
improve the properties of the final shaped articles. These include
synthetic resins which may be thermoplastic, for example
styrene/butadiene resins, acrylic resins, vinyl acetate resins and
vinyl chloride resins; or thermosetting, for example
phenolformaldehyde resins, melamine formaldehyde resins and urea
formaldehyde resins. The resins are preferably mixed with the
slurry in liquid form, for example as an emulsion or suspension in
water, and precipitated by the addition of a precipitating agent
such as alum. The resin content of the slurry may be from 5 to 40%
by weight. In the case of styrene-butadiene resin containing
formulations, thermoplastic boards may be obtained which can be
stamped out to shape after being plasticised by heating. A similar
result can be obtained with phenol-formaldehyde resin containing
formulations but a "cure-time dwell" is then needed. A preferred
resin content of the slurry is then 10 to 40% by weight. A further
group of useful additives are flame-retardants, particularly in the
production of boards and sections for the building industry.
Suitable flame retardants include borates, boric acid, monoammonium
phosphate, aluminium hydroxide and other commercially available
flame retardant materials. Excellent results have been obtained
using levels of up to about 8% by weight of the flame retardant. We
have found that boards made from a composition consisting of at
least 63.5% by weight cellulose fibres, 28.5% by weight minerals
and up to 8% by weight flame retardant compare favourably with
boards made from grade A60 asbestos. It is, of course, possible to
obtain boards having good flame retardant properties without the
addition of extra flame retardant materials by increasing the
proportion of minerals in the composition. Thus compositions
containing a minimum mineral content of 55% by weight and 45% by
weight fibres have been found to produce board exhibiting excellent
flame retardant properties.
If necessary the agglomerated layer may contain a reinforcing
medium. For example a layer of reinforcing fibres such as glass
fibres may be deposited upon the agglomerated layer if desired and
a light rolling action imparted to the layer to embed the fibres
therein. Alternatively reinforcing fibrous layers or "matts" may be
laminated on to one or both surfaces of the agglomerated layer or
deposited layer of slurry. Suitable reinforcing layers include
woven hessian backing or glass fibre matts. As a further
alternative the reinforcing medium may be sandwiched between two
agglomerated layers and the whole laminate integrated by passage
through pressure rolls.
Finally there may be added to the slurry mineral fillers for
example silica, quartz or limestone in finely divided form, or
pulverised fuel ash. This leads to harder, denser, more fire
resistant products.
The invention is illustrated by the following Examples:
EXAMPLE 1
This Example describes the production of boards from paper mill
sludge.
In determining the fibre and clay contents of various paper making
slurries so as to decide on whether or not either fibres or
minerals have to be added before the material is converted into
board the following analyses were made:
1. Dickinson Croxley Mill: fibre from 20 to 30% and clay from 80 to
70% by weight.
2. Bowater Thames Mill: fibre from 40 to 70% by weight and clay
from 60 to 30% by weight.
3. Bowater Mersey Mill: fibre from 66.6 to 50% by weight and clay
from 33.3 to 50% by weight.
4. Bowater Sittingbourne: substantially the same as in the case of
Bowater Mersey Mill.
5. Bowater Kelmsley Mill: fibre substantially 84% by weight and
clay substantially 16% by weight. The material was mainly from
hardboard making.
6. Reeds - Aylesford: the sludge was sampled daily and a composite
was tested weekly, over ten weeks, the results were as follows:
Solids content: Average 24% Range 17 - 35% Fibre content: Average
66% Range 53 - 76%
The only other major constituent was china clay.
Paper sludge from each individual mill is concentrated and if
necessary further fibre or mineral material added. The following
are examples of two formulations which are used in the manufacture
of various boards products:
A. Concentrated Sludge from Reeds Mill: Waste paper sludge
concentrated to 15% by weight solids content 67- lbs. Chopped rags
ground to 1/4" staple length 1- lb. *Phenolic resin CL-151/76 (76%
solids content) 11/2 lbs. 5% Alum solutions 600 ccs. B.
Concentrated Sludge from Bowater Thames Mill: Waste paper sludge
concentrated to 19% by weight solids content 45- lbs. Chopped rags
ground 1/4" staple length 1- lb. *Phenolic resin CL-151/76 (76%
solids content) 11/2- lbs. 5% Alum solutions 600 ccs. 3.6 Starch
solution 33- lbs. *CL-151/76 is a 76% solids phenolic resin
produced by Sterling Moulding Materials Ltd.
Both the above formulations contain added fibres in the form of
chopped rags. However, it is not always necessary to add fibres and
for example in the case of the Bowater Kelmsley Slurry (5), it is
usually necessary to add a quantity of clay or other minerals to
the slurry.
The formulations described above are processed in an apparatus
illustrated diagrammatically in FIGS. 1 to 4 of the accompanying
drawings in which:
FIG. 1 shows a flow line for the apparatus from the sludge
reservoir through filtering, mixing, the conveyor, dopple roller
and pressure rollers to cutting and pressing,
FIG. 2 shows a flow line of an alternative layout using extrusion,
ovens and a multi-daylight press,
FIG. 3 shows dewatering of the slurry between top and bottom belts
moving between fixed plates and conveying on one another, and
FIG. 4 shows an alternative arrangement to FIG. 3 in which the
plates are replaced by an array of pressure rolls acting on the
belts from the outside.
Referring now to FIG. 1, the apparatus comprises a container for
paper sludge which discharges into a rotary vacuum filter in which
the sludge is concentrated to a solids content of from 71/2 to 30%
by weight. From the filter the concentrated sludge is passed to a
mixer such as a Gardner Ribbon, Baker-Perkins dough type mixer or
alternatively a Hobart dough mixer. In the mixer the various
additives such as the phenolic resin are mixed with the sludge and
the resulting slurry is then pumped to a storage bin which acts as
a feed reservoir for the board manufacturing unit. From the storage
bin the slurry is deposited on to a vibrating conveyor in the form
of a continuous layer. The layer of slurry carried on the belt of
the vibrating conveyor is then passed through a dopple roller and
then through a dewatering device. The dewatering device may
comprise a pair of fixed plates forming a continuous nip as
illustrated in FIG. 3 in which the slurry is conveyed between top
and bottom belts thereby squeezing out excess water from the layer
of slurry. Alternatively the dewatering device may comprise a
series of pressure rolls as illustrated in FIG. 4, the layer of
slurry again being conveyed through the rolls by top and bottom
belts. The nip action of the dewatering device is arranged to be
such that the agglomerated layer of slurry leaving the device has
the desired thickness, density, and water content. The agglomerated
layer of slurry is then cut into boards and stacked to dry. Finally
the boards are pressed to form the desired shaped articles and sent
for dispatch.
An alternative arrangement is shown in FIG. 2 in which after mixing
of the additives with the paper sludge, the slurry is fed to an
extruder feeding mechanism which deposits a predetermined amount of
the mixture in the form of a continuous layer which is then
conveyed to the dewatering device. The dewatering device reduces
the water content of the layer, and when the layer emerges from the
device its water content is substantially 45% by weight, i.e. it
has a solids content of substantially 55% by weight. The
agglomerated layer is then passed to a drying oven where it is
dried to an extent sufficient to lower the moisture content to
around 15% by weight or less depending upon the properties required
of the final shaped article. The continuous agglomerated layer
emerging from the oven is then cut into boards and stored for
pressing. Finally the boards are pressed in a multi-daylight press
and sent for despatch.
EXAMPLE 2
This Example describes a further process for the production of
boards from paper sludge.
Analyses of a variety of paper sludge effluents from commercial
paper mills are given in Example 1. These effluents are processed
in the apparatus shown diagrammatically in section in FIG. 5 of the
accompanying drawings.
Referring to FIG. 5, the apparatus comprises a slurry hopper 1,
provided with an agitator 2, mounted upon and communicating with a
screw extruder 3. The extruder has a slit diehead 4 which
discharges on to the top surface of an endless stainless steel mesh
belt 5. The belt is carried on driven rollers 6 and passes beneath
chain driven pressure rolls 7. Water squeezed out of the slurry by
the pressure rolls is pumped to a large header tank (not shown)
from which any subsequent water demands of the process may be met,
or returned to filtration equipment to remove any solids content.
The endless belt is provided with cleaning water sprays 8 and
rotary brushes 9 on its lower surface. A take-off conveyor 10
adjacent the endless belt leads to pairs of nip rolls 11 and 12
positioned on either side of an automatic cutter 13. From the
cutter 13 a series of conveying rollers 14 leads to a power
operated loader 15 which feeds a multi-platen daylight press 16.
Each platen of the press has a high surface finish and is labyrinth
drilled to ensure even heat distribution. An unloader 17 receives
boards from the press, and the boards are then transferred to an
automatic stacking machine 18.
In operation sludge from the hopper 1 is metered into the screw
extruder 3 at a predetermined rate and emerges from the slit
diehead 4 as a continuous layer of slurry which is deposited on the
endless belt 5. The belt carrying the layer of slurry passes
beneath the pressure rolls 7 and water is squeezed out from the
layer. The progressive action of the pressure rolls is variable and
enables the water content of the layer to be reduced to the desired
value. At the same time the action of the rolls controls the
thickness and density of the layer. The layer leaves the endless
belt and is passed by the conveyor 10 to the nip rolls 11. The
cutter 13 automatically cuts the layer into boards of the desired
length which are removed by the nip rolls 12 and conveyed by the
conveying rollers 14 into the loader 15. The loader inserts the
boards into the press 16 where they are heated to a temperature of
160.degree.C and subjected to a pressure of 525 lbs. per square
inch. The dwell time in the press is of the order of 15 minutes.
From the press the unloader 17 removes the boards which are then
stacked by the automatic stacking machine 18.
It is found that excellent boards can be produced from slurries
having the following compositions:
1. Paper mill sludge (Reeds) 25% solids 40 lbs. Chopped rags (1/4
inch) 1 lb. Water (added) 40 lbs. 2. Paper mill sludge (Reeds) 25%
solids 40 lbs. Chopped rags (1/4 inch) 1 lb. Resin CL 164/50 22
lbs. Water (added) 40 lbs. Alum 600 ccs. 3. Paper mill sludge
(Reeds) 25% solids 40 lbs. Chopped rags (1/4 inch) 1 lb. Pulverised
fuel ash 10 lbs. Water (added) 40 lbs. 4. Paper mill sludge (Reeds)
25% solids 40 lbs. Chopped rags (1/4 inch) 1 lb. Mono ammonium
phosphate 40 lbs. Water (added) 40 lbs. 5. Paper mill sludge
(Reeds) 25% solids 40 lbs. Chopped rags (1/4 inch) 1 lb. Pulverised
fuel ash 20 lbs. Water 40 lbs.
Compositions 3, 4 and 5 have been found to give boards having an
excellent degree of flame retardance.
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