Process for making granular material

A process is disclosed which utilizes the "non-papermaking" portion of waste paper to produce a highly absorbent, essentially fiber-free granule which can be used, for example, as an agricultural chemical carrier. The process maximizes the amount of long (papermaking) fiber sent to the paper machine. The waste paper is broken up in a hydropulper, and the pulp stock is screened so that papermaking fibers are retained and sent forward to the papermaking process, and the solid material in the reject stream, such as kaolin clay and inorganic materials pass through a flotation clarifier to separate the solids. The slurry is then dewatered by means of a belt press to form a filter cake. The filter cake then enters a pin mixer where it is broken up into individual granules. The granules are then dried to a solids content of greater than 95%.

FIELD OF THE INVENTION 
The present invention relates to recycling wastepaper, and more 
particularly to recycling processes for recovering papermaking fibers and 
for making absorbent granular materials from wastepaper. 
BACKGROUND OF THE INVENTION 
It has been common practice for many years to make paper, especially 
tissue, from recycled paper. Paper recycling has in recent years become an 
important and attractive alternative to disposal of wastepaper by 
deposition in landfills or by incineration. When the wastepaper source 
includes a significant amount of coated paper, as much as 30-45% of the 
original wastepaper will be reject material which is unusable for 
papermaking. This reject material has typically been discarded in 
landfills. Increasing costs and decreasing availability of landfill space 
makes it desirable to find beneficial uses for this reject material. 
In the process of recycling waste paper, such as newspapers, magazines, 
office paper waste, the paper fibers are separated from the other solid 
components by using large quantities of water. The printing materials, 
such as laser print, photocopier print and ink, are removed before the 
paper fibers are conducted to the papermaking machine. Usually, these 
rejected solid materials are discharged with the water into large settling 
basins. The solid materials that settle out in the basins are then dumped 
in a landfill, or otherwise discarded. The material that settles out in 
the basins is known as paper mill sludge. 
The increasing cost of wastepaper makes it desirable to capture as much of 
the papermaking fibers as practicable. In view of the large quantities of 
water required for papermaking, it is important to use a process that 
conserves water. There have been various proposals for systems for 
utilizing rejected solid materials such as paper mill sludge to produce 
absorbent granules and other products. Kaolin clay is one of the rejected 
solid materials that has been recognized as having good absorbent 
capabilities. 
Conventional absorbent granules are produced from naturally occurring clay 
and are commonly used as agricultural chemical carriers. However, some of 
the agricultural chemicals (e.g., Diazinon) react with clay carriers. 
Accordingly, it would be advantageous to develop an agricultural chemical 
carrier that contains clay, but does not react with agricultural 
chemicals. Also, naturally occurring clays tend to create dust during 
handling. This is potentially hazardous to workers. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an efficient and 
economical wastepaper recycling process for recovering fibers for use in 
papermaking and producing useful granular products from the reject stream. 
It is another object of this invention to produce a granular product that 
has high absorbency, is free flowing, substantially dust free and has high 
resistance to attrition. A further object is to produce a material of 
broad utility as a water and oil absorbent. 
The process of this invention utilizes wastepaper, preferably office waste 
that is printed with laser print, photocopier print, or other inks, as 
well as stationery and magazines that have a coated surface. The 
wastepaper is pulped with water, caustic and surfactants to produce a 
slurry containing cellulose fibers, cellulose fines and fillers. The 
slurry passes through wire washers which separate papermaking fibers from 
the fines and fillers. Papermaking fibers are a mixture of long and short 
fibers, although it is recognized that some of the short fibers will pass 
through the screens. For the purposes of this description, long fibers are 
greater than about 1 mm in length and short fibers are between about 1 mm 
and about 0.1 mm in length. The papermaking fiber stream, also referred to 
as the "accepts stream", is directed through a cleaning and deinking step 
and then to a conventional papermaking machine for processing into paper. 
Separately, various streams from the papermaking machine and other sources 
are passed through a fiber recovery system where a series of wire washers 
separate papermaking fibers from these streams, sending the papermaking 
fibers back to the cleaning and deinking stages. The rejects from this 
fiber recovery system contain essentially the same solid materials as the 
first reject stream mentioned above. These reject streams are combined and 
sent to a flotation clarifier where a flocculating polymer is added and 
air is injected to cause the suspended solids (fines and fillers) to be 
concentrated as a flotate. Clarified water is removed from the clarifier 
for reuse in the process. 
In order to sterilize the absorbent material, the flotate stream is 
pasteurized at a minimum temperature of 160 degrees F., and then a second 
flocculating polymer is added to the flotate stream. This flotate stream 
then passes through a belt press or similar dewatering device where the 
water content is further reduced. The filter cake from the belt press is 
in the form of a gray, wet cake. The wet cake then passes to a size 
reducer where the material is broken up. The wet granules are then sent 
through a conveyor dryer to produce dry granules of irregular shape and 
having good absorbent characteristics. 
The granules produced by this process have a high liquid holding capacity. 
The term granules is intended to include small particles and chunks that 
may be as large as 0.5 inches across. Their composition, by weight, is 
approximately 35-50% inorganic fillers (kaolin clay, calcium carbonate, 
titanium dioxide) and 50-65% organic (cellulose fines, starches, tannins, 
lignin, etc.). Less than 10% of the cellulosic material in the granules is 
in the form of fibers greater than 1 mm in length. The granules are free 
flowing and resistant to attrition. The bulk density of the granules is 
between about 28-38 lbs./cu.ft. These granules are useful as oil and water 
absorbents as well as carriers for agricultural chemicals.

DETAILED DESCRIPTION 
The process of this invention utilizes wastepaper that is collected from 
offices or other sources that contain primarily recyclable paper grades, 
including magazines (with clay and calcium carbonate based coatings) and 
printed paper such as paper used for laser printing, photocopying and 
other paper. 
Referring to FIG. 1, wastepaper is supplied to a hydropulper 2 along with 
water, caustic agents, such as sodium hydroxide, and dispersants to 
separate the fiber from the other components of the wastepaper. Plastics, 
debris and other foreign objects are removed by conventional means. The 
pulp slurry from the hydropulper, which contains more than 95% water, 
passes through a pipe 4 to a washer 6 where several conventional washing 
steps are performed. In the washer 6, the slurry flows over wire screens 
where fibers useful for papermaking pass across the screens and the reject 
stream passes through the screens and is conducted out of the washer 
through a pipe 16. The screens have slotted openings of about 100 to 300 
microns in width. Preferably, the screens are semi-cylindrical and the 
slurry is sprayed tangentially onto the screens. Fibers suitable for 
papermaking pass across the surface of the screens, while small particles, 
such as kaolin clay, cellulose fines and other suspended solids pass 
through the screens. Some of the fibers may also pass endwise through the 
screens. The papermaking fibers from the surface of the screen are 
included in the accepts stream that is pumped through the pipe 8 and are 
subject to further cleaning, deinking and processing, indicated at 10, 
before being supplied through a pipe 12 to a papermaking machine 14. 
The reject stream from the washer 6 is in the form of a slurry containing 
less than 1.5% solids. Typically, 50% by weight of the solids are fillers 
such as kaolin clay, calcium carbonate and titanium dioxide. The remaining 
50% is mostly sugars, tannins, lignins, and cellulose fiber or fines, 
which is referred to generally herein as cellulosic material. To the 
extent there are cellulose fibers in the reject stream, most of these 
fibers are less than 1 mm in length. This slurry, which contains at least 
98.5% water, is conducted through the pipe 16 to a dissolved air flotation 
clarifier 18. Suitable clarifiers are commercially available (e.g., 
Supracell from Krofta, or Deltafloat from Meri). A flocculating polymer, 
such as Drewfloc 441 from Drew Chemical Co., or Calgon TRP 945, is added 
to the reject stream in the pipe 16 before the slurry enters the 
clarifier. Air is injected into the feed stream of the clarifier 18. The 
slurry fills the clarifier 18, and the flocculated suspended solids float 
on the air bubbles to the surface of the clarifier. At this point, the mat 
of solids, which has a consistency of 3-9%, is skimmed or raked off the 
surface and removed from the clarifier through the pipe 20. The clarified 
water from the clarifier 18 is conducted back into the hydropulper 2 
through the pipe 22 to be reused and a portion of the clarified water is 
recycled via pipe 33 to other places in the mill. 
In accordance with this invention, nearly all unscreened mill process 
effluents that contain papermaking fibers are treated in a fiber recovery 
unit 26. Here the stream passes through screens that separate the 
papermaking fibers from fillers such as kaolin clay, cellulose material, 
sugars, lignins, tannins, etc., in a manner similar to the washer 6. This 
effluent includes some reject water streams, dumping or spills from pulp 
and paper chests, plant wash-ups, etc., indicated as stream 24 in FIG. 1. 
Previously, this effluent would have been discharged to a sewer. 
Papermaking fibers are returned through pipe 28 from the fiber recovery 
unit 26 to the washer 6. Pipe 30 conducts the reject stream from the fiber 
recovery unit 26 to the clarifier 18. 
The white water stream 25 from the papermaking machine is supplied to 
another flotation clarifier 27 where the flocculated suspended solids are 
removed in the same manner as in the clarifier 18. Process white water 
stream 23 is returned to the washer 6. 
The flotate from the clarifiers 18 and 27 is supplied to a heater 36 
through pipes 20 and 34 respectively. The heater 36 may be of any suitable 
type, such as a steam injection unit, or a heat exchanger. The flow rate 
of the stream and the heat applied should be sufficient to raise the 
temperature of the stream for sufficient time to achieve pasteurization of 
the stream. Preferably, the stream should be heated to a temperature of at 
least 160.degree. F. 
The stream passes out of the heat exchanger 36 through a pipe 38, and a 
second polymer (such as Drewfloc 453 from Drew Chemical Co.) is added to 
the slurry to cause the solids to dewater as the slurry enters a belt 
press 40. The belt press can be any one of the commercially available 
units (e.g., Kompress Belt Filter Press, Model GRS-S-2.0 from Komline 
Sanderson). At the outlet of the belt press, the filter cake contains 
35-40% solids. Process white water from the belt press is returned to the 
hydropulper 2 through the pipe 42. 
If a filter cake having a higher solids content is desired, a screw press 
may be used after the belt press, or instead of the belt press. 
Alternatively, a belt press with compressive rolls can be employed. The 
filter cake would pass through the nip between the rolls for additional 
dewatering. These arrangements can be used to produce a filter cake having 
a solids content of up to 45%. 
If small particles are desired as the final product, the filter cake from 
the belt press 40 is conveyed by a screw conveyor 44 to a pin mixer 46 
(such as the Turbulator from Ferro-Tech). The pin mixer has a cylindrical 
shell and a rotatable shaft mounted on the central axis of the shell. The 
shell is stationary and is supported on a frame so that the central axis 
of the shell is horizontal. The shaft has radial pins that are spaced 
about 1/8" from the interior wall of the shell. Pieces of the filter cake 
from the conveyor 44 are deposited in the shell at one end of the shell. 
The rate of filling of the shell should be adjusted so that the cake 
material occupies only about 2% of the volume of the shell. By maintaining 
a low density in the pin mixer 46, the filter cake is broken up by the 
rotating pins so that individual granules are separated as the material 
progresses from the inlet of the pin mixer to the outlet. It has been 
found that the pin mixer 46 produced optimum size particles for use as an 
agricultural carrier by running in the middle of its speed range, which is 
at 1500-4500 feet per minute tip speed of pins. Higher speeds give larger 
particles. Lower speeds yield a larger variability in sizes, with no net 
increase in smaller sized granules. It has been discovered that, when 
operating the mixer with a partially filled chamber in the middle of its 
speed range, the pin mixer 46 reduces the size of the particles as 
compared to the size of the particles that are discharged from the screw 
conveyor 44. 
The effect of the pin mixer 46 on the particle size is shown in FIG. 2, 
which compares the percent of particles retained on screens of 
progressively smaller openings (higher mesh numbers). As shown in FIG. 2, 
a substantially greater percentage of the particles that are discharged 
from the pin mixer 46 have a smaller size than the particles entering the 
pin mixer 46. Another way of stating this is that FIG. 2 shows that only 
8% of the particles discharged from the pin mixer 46 have a size large 
enough to be retained on a #8 mesh screen or larger (e.g., #4), while 25% 
of the particles supplied to the pin mixer have a size large enough to be 
retained on a #8 mesh screen or larger. Additives may be added at this 
point (e.g., to increase density or absorbency) but it is important not to 
increase the water content of the press cake since this would cause the 
particles to agglomerate, yielding a larger than desirable particle size 
and a less absorbent product. Operating the pin mixer in this fashion 
allows for uniform densification of the granules. It has been found that 
backmixing dried granules with the wet feed prior to the pin mixer also 
leads to a smaller, denser granule. Preferably, up to 50% by weight of the 
dried granules can be added. No additional binders are necessary since the 
matrix produced by the kaolin clay, along with the lignin, tannin, starch 
and short fibrils in the feedstock, serve as the binder for the granules. 
The resulting open pore structure yields an absorbent irregular particle. 
From the pin mixer 46, the granulated but still moist material moves, 
preferably under the force of gravity, onto a swing conveyor 48, to the 
belt of a conveyor dryer 50, such as a Proctor & Schwartz two-zone 
conveyor dryer. The belt is porous and a fan blows hot air through the 
belt to dry the granules. The velocity of the air flow is sufficiently low 
to avoid movement of the granules on the belt. At the outlet, the granules 
have a minimum solids content of 90% by weight, and preferably greater 
than 95%. 
Vibrating screens 52, such as manufactured by Sweco, are used to classify 
the material by size according to product specifications. 
Alternatively, instead of supplying filter cake to the pin mixer 46, the 
filter cake from the belt press 40 may be conveyed by a conveyor 54 to a 
dryer 56, such as a Komline Sanderson paddle-type dryer, as shown 
schematically in FIG. 1. In the dryer 56, the filter cake particles are 
further dried and may be ground into fine dry particles. The dried 
particles may have any desired solids content depending on the time and 
extent of drying. Preferably, the particles have a solids content of 90 to 
100% by weight. Even more preferably, the particles have a solids content 
of 96 to 99% by weight. Also, the particles desirably have a bulk density 
of from 45 lbs/ft.sup.3 to 50 lbs/ft.sup.3 and a size ranging from 4 to 
300 mesh. 
The particles from dryer 56 may be used directly as a product, or 
optionally mixed with wet filter cake particles at the dry/wet particle 
mixing stage 60. The dry particles from dryer 56 are conveyed through 62. 
The wet particles are conveyed through 58. Alternatively, the dried 
particles from dryer 56 may be returned to the main conveyor 44 and mixed 
with the filter cake particles to produce a final product. Preferably, the 
dry/wet particle mixing whether in a separate mixing stage 60 or in the 
main conveyor 44 provides a product having a solids content of from 40 to 
60% by weight, preferably 45 to 50% by weight. Alternatively, the wet 
particles from the belt press 40 may be used directly with little or no 
mixing of dry particles. The particles used as a final product either with 
or without addition of dry particles from the dryer 56 have a bulk density 
of from 50 lbs/ft.sup.3 to 60 lbs/ft.sup.3 and a size ranging from 4 to 
100 mesh. The mixing ratio of dry particles from dryer 56 to wet particles 
from belt press 40 ranges from 0 to 50% by weight, preferably 5 to 30% by 
weight. 
The purpose of the heater 36 is to prevent the growth of bacteria in the 
material produced by this process. If the filter cake or the granules from 
the pin mixer 46 are conducted through a dryer, as described above, the 
heater 36 may be omitted since any bacteria will be killed in the dryer. 
However, if coarse wet particles are produced, it is necessary to kill the 
bacteria. An alternative to the heater 36 would be the use of a stationary 
horizontal cylinder with a rotating auger that would advance the particles 
through the cylinder. Steam injected into the cylinder would heat the 
material sufficiently to cause the bacteria to be killed. 
The granules produced by this process contain approximately 50% by weight 
of organic materials, such as cellulosic fines, starches, tannins and 
lignins. The granules contain less than 10% fiber by weight over 1 mm in 
length. The inorganic fillers comprise about 50% by weight of the granules 
and are made up primarily of kaolin clay, calcium carbonate and titanium 
dioxide. The granules have an irregular, generally spherical shape. The 
granules from the conveyor dryer 50 vary in size. Typically, about 50% 
will be retained on an 8.times.16 mesh screen, i.e., 50% would pass 
through an U.S. Sieve No. 8 mesh screen but would be retained on a 16 mesh 
screen. Typically, the remaining portion would be about 40% in the 
16.times.30 mesh size range, and about 10% in the 20.times.60 mesh size 
range. The granules have a bulk density of about 30-40 lb./cu. ft. Bulk 
density can be increased by adding prior to the pin mixer a densifier such 
as Barium Sulfate. 
The granular material according to the present invention is able to 
withstand agitation such as might occur during shipment, handling, and 
storage. Resistance to attrition of the granules is between 90 and 95%. 
This percentage is based on the following test procedure. A weight of 75 
grams of sample is shaken on a limiting screen for ten minutes and 50 
grams of the material retained is then shaken in a pan for ten minutes 
with ten steel balls (5/8" in diameter). The entire sample is then shaken 
on the limiting screen for ten minutes. The percentage of the original 50 
grams retained on the limiting screen is the resistance to attrition cited 
above. Granular material according to the present invention has been found 
to generally have a pH between 8.5-9.4. 
Granular material according to the present invention is adapted to absorb 
various liquids to desired degrees as a function of percentage of weight 
of the granules. When the granular material according to the present 
invention is intended for use as an agricultural carrier, it has a liquid 
holding capacity (LHC) toward odorless kerosene of between 25-29%. The 
material for use as a floor absorbent, when tested with material retained 
on an 8.times.35 mesh, is able to absorb about 70-80% of its weight of 
water, and about 50-60% of its weight of oil. 
Since particles or granules used as an agricultural carrier are preferably 
small, the use of the pin mixer is an effective way to obtain smaller 
particles in an efficient manner. It has also been found that the 
particles produced using the pin mixer have less tendency to produce dust 
during the treatment and storage of the dry particles than naturally 
occurring clay. This is particularly important when the particles are used 
as an agricultural carrier because of the presence of herbicides or 
pesticides that may adversely affect workers if substantial amounts of 
dust are present. These granules are also useful as oil and grease 
absorbents and as pet litter. 
While this invention has been illustrated and described in accordance with 
preferred embodiments, it is recognized that variations and changes may be 
made therein without departing from the invention as set forth in the 
claims.