Reducing wax content and enhancing quality of recycled pulp from OCC and waste paper

A system and method for treating a waxed fiber paper product with a high wax content to remove a substantial portion of the wax content includes the pulping of the wax paper fiber at an elevated temperature in excess of the melting temperature of the wax to separate a pulp fraction and to form an emulsion of water and molten wax. The pulp fraction is separated from the emulsion by filtering in a reverse pressure screen in which a finely perforated screen defines a high pressure side and a low pressure side, and a major portion of the water/emulsion is removed from the suspension through the screen perforations leading from the high pressure side to the low pressure side, in which a rotor and foil arrangement within the reverse screen is operated under such conditions that the suspension at the high pressure side of the screen is maintained in a constant fluidized condition.

BACKGROUND OF THE INVENTION 
This invention relates to the recycling of petroleum-based wax coated or 
impregnated waste paper and more particularly to the recycling of old 
corrugated cartons (OCC) which have been impregnated or coated with 
conventional petroleum-based wax. 
Wax saturated and wax coated cartons are particularly useful for shipping 
and storing food and produce, such as iced fresh produce, seafood, poultry 
and refrigerated meats. It is also useful as industrial packaging where a 
product is exposed to water and/or very high humidities and to packaging 
which require high stacking strengths and stiffness under dry conditions. 
The waxes which are most commonly used comply with U.S. Federal Drug 
Administration requirements and regulations for use as an indirect food 
additive and as a component of paperboard in contact with food products. 
Saturating waxes have also been approved by the United States Department 
of Agriculture (USDA) for use in packaging of meat, fish, and poultry 
under federal inspection, and are approved for packaging materials which 
come into direct contact with such poultry or food products. Such waxes 
are relatively easy to deploy since application temperatures run in the 
range of about 190-210.degree. F., depending on the particular wax grade 
and the product, and have relatively low melting points in the range of 
about 125-140.degree. , depending upon the wax formulation. 
The same moisture resistant characteristic of such carton material has 
formed an impediment to satisfactory use of repulped petroleum-based waxed 
paper products. Wax corrugated material or board packaging material is not 
generally considered to be an accepted source of secondary fiber. Small 
undispersed particles of wax can form dark spots on a sheet, often 
referred to as a wax spot, thereby providing an undesirable blemish. More 
importantly, only a small percentage of wax mixed within the cellulose 
fibers drastically reduces both the strength and the dry coefficient of 
friction, measured as a slide angle, of the finished carton product. A 
small percentage of residual wax in the furnish can reduce the coefficient 
of friction and the slide angle to the point where the resulting carton 
material is not acceptable. Existing OCC reclaiming systems, in most 
up-to-date paper and pulp mills, are state-of-the-art systems and function 
well on a furnish of traditional OCC. The introduction of varying amounts 
of wax material into such existing systems tends to upset that process, 
and contaminates the entire system. 
Also, a small amount of wax saturated OCC by volume or by weight, can add a 
significant amount of wax to mixed OCC and to a recycled paperboard 
furnish. Therefore, it is often necessary, in recycling, manually or by 
other means to separate out the heavily waxed cartons, to prevent an 
overloading of wax in the furnish. The principal obstacles to recycling 
waxed OCC is the resulting low paper-to-paper friction for packaging 
papers, the negative effect on strength, and generally reduced quality of 
the recycled product. Although cascade coated wax board products are 
beneficial and provide desirable moisture barrier and food compatible 
qualities at low costs, nevertheless this product carries with it the 
stigma that it is not considered to be recyclable, using presently known 
techniques. 
While petroleum wax coated or impregnated OCC represents approximately 5% 
of the U.S. production of corrugated carton material, only a small portion 
of this can be recycled and reclaimed, and then must be mixed with a very 
substantial portion of unwaxed OCC. Considerable efforts have been 
expended to improve the recyclability of petroleum waxed packaging 
products and improve the related processes. A major stumbling block has 
been the finding by leading researchers that waxed paper was not 
repulpable in a conventional hydra pulper. McEwen and Wang "OCC Recycling: 
Improving The Repulpability Of Wax Coated Corrugated Paperboard" Tappi 
1992 Pulping Conference Book 2, Nov. 1-15, 1992, pages 493-502 concluded 
that waxed corrugated carton is not an acceptable source of secondary 
fiber and that commercially available carton coatings (wax) are considered 
non-repulpable. In repulpability tests, the pulper was operated at a 
temperature below the melting point of the wax, for the purpose of 
allowing the wax to remain in pieces, for subsequent screening and 
cleaning. When the temperature in the pulper was raised from 49.degree. C. 
to 68.degree. C., close to the wax melting point, the paper became 
defibered but most of the wax softened and deposited on the pulper 
surface, an unsatisfactory result. McEwen and Wang went on then to test 
the effect of adding chemicals to the wax prior to the wax being applied 
for the purpose of promoting the release of the wax component, in 
repulping, of the paper fibers from the wax in order to maintain pulping 
temperatures far below the wax melting point. 
Back and Jousimaa, "Wax Removal After Alkaline Hot Dispersion On A Pilot 
Plant Scale, Autodispersible Waxes For Recyclable Packaging Of Papers," 
Progress in Paper Recycling, November 1955, pages 91-99, describe the 
results of using a wax coating which has been previously specially 
modified with fatty acids to facilitate subsequent removal from OCC. 
Pulping was accomplished in a chest at a temperature well below the 
congealing temperature of the wax, and hot dispersion was accomplished in 
a separate disk refiner at a pH of about 11.0 with wax removal taking 
place in one or more dewatering screws. Removal of such pre-treated wax 
using a low pitch screw press was observed as high as 90%. No data is 
given on the removal of unmodified petroleum waxes. 
Galland, Vernac, and Brun, "Recycling Of Wax Papers & Boards," Tappi, Mar. 
5-7, 1996, Tappi Recycling Symposium, pages 81-89 describes experimental 
efforts to remove conventional untreated wax from OCC. The wax coated 
paper was repulped at low temperature to avoid deposition of wax in the 
pulper pipes and chests. Subsequently, wax dispersion was accomplished in 
a separate kneader, and conventional screening was attempted to remove the 
wax. After two screening passes the total efficiency did not exceed 86%, 
and the 21/2% residual wax was considered as rendering the combination 
inefficient. Flotation using deinking flotation cells provided a higher 
efficiency of nearly 95%. Flotation appeared to be the most appropriate 
technique to remove wax although the flotation cell induced an additional 
loss of 15 to 20% of the pulp. This reject rate appeared to the authors to 
be too high for papermakers to economically produce corrugated paper. 
There accordingly exists a long felt need to provide a method and system by 
which unmodified wax content of waxed OCC or by which an excessive was 
content of a furnish may be efficiently and effectively removed or 
reduced, without wax buildup in the tanks and pipes, without unacceptable 
degradation of the pulp, with acceptable losses, to produce a dewaxed 
paper pulp having a wax content of 1% or less. There is likewise a need 
for an efficient process for pretreating a waxed furnish so that it may be 
introduced without detriment into an existing OCC system. 
SUMMARY OF THE INVENTION 
The invention is directed to a new an unobvious method and apparatus for 
removing wax from OCC and wax coated paper materials in which unmodified 
or conventional petroleum-based waxes are removed to a percentage of 1% or 
less in the resulting furnish using relatively low cost, conventional 
paper pulp defibering and washing equipment. 
Corrugated carton material may contain varying percentages of petroleum wax 
depending on the manner in which the wax has been added to the product. 
Generally, and commonly, the wax is applied by cascade applicators, by 
curtain coaters, or by dipping, in which the material of the carton is 
effectively submerged in the molten wax product. Typically, wax pickups by 
the untreated carton material may be as high as 45-50% or more by weight 
of the untreated material. Such material after treatment is considered to 
be saturated by the liquid wax. 
In the practice of the invention to disassociate and remove petroleum wax 
from waxboard or packaging materials (waxed OCC) the separate wax 
dispersion step, as practiced or attempted in prior art arrangements, 
identified above, is eliminated. This has the advantage of reducing the 
complexity of the system and correspondingly lowering the cost. 
The waxed OCC is pulped in a paper stock pulping machine including a bottom 
or side extraction bed plate and a driven impeller at the bed plate. A 
Hydrapulper.RTM. equipped with a Mid-Con screw flight mounted on the 
impeller as shown in U.S. Pat. No. 4,725,007 may be used, as supplied by 
Thermo Black Clawson, Inc., 605 Clark Street, Middletown, Ohio 45042 
(hereinafter "Black Clawson"). The Hydrapulper.RTM. machine both defibers 
the old carton material and disperses the wax content. Once the furnish 
has been defibered and the wax content dispersed at an elevated 
temperature in the Hydrapulper.RTM. machine, the defibered material is 
subject to the usual treatments of OCC fiber reclaiming including trash 
removal, course and fine screening, followed then by separation of the 
dispersed wax and water emulsion from the fibers. 
An important characteristic of the system is that all process steps from 
pulping through wax separation are carried out at a temperature above the 
melting temperature of the wax. All "cold" surfaces are eliminated, such 
as by preheating, and maintained at a temperature so that, at each stage, 
the fluid and all flow conduits, tanks and pressure vessels are maintained 
at a working temperature that exceeds the wax melting temperature, with 
the result that there is no tendency for wax to build up on walls of 
tanks, on pipes or in valves, thus permitting all system components to 
operate efficiently. 
The system may be batch operated or operated continuously. When batch 
operated, all parts should be preheated with hot water and/or steam. 
High efficiency pressure washing apparatus is used for separating the good 
fibers from the heated wax and water emulsion. This is accomplished by 
subjecting the suspension to thickening and separation pressure vessels, 
namely, high speed rotating reverse pressure screens as sold by Black 
Clawson. The reverse pressure screen contains a screen cylinder with a 
micro-perforated or micro-slotted electron beam or laser beam drilled 
openings. Each of such reverse screens removes wax substantially in 
accordance with its hydraulic split characteristic of about 90/10. The 
stock is provided at the inlet at relatively low consistency, and a 90/10 
split means that about 90% of the liquid content is removed in the 
screening apparatus. Thus, if the inlet consistency is 0.5%, the thickened 
pulp will have a theoretical consistency of 5%, and 90% of the wax/liquid 
content would have been removed. 
With a high wax content furnish, a plurality of such screens, such as two 
or three or as many as required to produce the desired result, may be 
connected in series or tandem relation and connected to have a counter 
current flow of cleaning liquid or filtrate from the last screen to the 
first. The freshest or cleanest liquid is applied to the last of the 
plurality of screens, and the liquid taken from the last screen is 
delivered to the inlet of the immediately preceding screen for stock 
dilution, and so forth back to the first of the screens. In this manner, a 
dispersed and emulsified wax content is effectively removed in the 
repeated thickening process through the screen perforations or slots and, 
at the same time, undesirable fines and water are removed along with the 
wax component. A certain amount of fines removal is beneficial, as fines 
generally do not have good papermaking qualities. An enhanced board 
furnish may thus be provided which has a substantially reduced residual 
wax content such as about 1% or less, and in any case less than the wax 
content now found in conventionally processed OCC with random and 
naturally occurring wax samples mixed in. 
The pressure screen used with this invention has been referred to as a 
"reverse" pressure cleaner because the "accepts" are collected at the 
inlet or high pressure side of the screen and the rejects are collected at 
the opposite or low pressure side of the screen. A drum-type rotor is 
positioned adjacent to the screen inlet surface. The rotor has on its 
surface impulse devices in the form of airfoil-shaped protuberances, known 
as "foils" and is rotated to maintain the fiber at the inlet surface of 
the screen in a continuously fluidized state, so that a fiber mat is 
prevented from forming on and blocking the screen inlet surface. The 
screen openings are of such dimensions that the heated wax emulsion is 
effectively separated from the fibers without blocking of the openings, 
since the heated wax emulsion freely flows through the small screen 
openings to the low pressure side of the screen. 
A certain amount of fines are also removed along with wax. The fines 
generally do not have good paper making qualities and tend to reduce the 
strength of the product. The enhanced furnish which is thus supplied has 
predominantly long fibers, and is essentially free of wax, i.e., about 1% 
or less and as low as 3/10 of 1% or less using a plurality serially 
connected reverse screens. The wax from the wastewater may be recovered in 
a clarifier by dissolved air flotation, and a particularly useful 
equipment for this purpose is the D-A-F "Supercell" manufactured by Krofta 
Engineering Corp., Lennox, Mass. 01240. Thereafter, the wax laden sludge 
may be used as a source of fuel or other wax by product uses. 
In another aspect of the invention, a reverse pressure screen is used in 
the method to reduce the wax content of conventionally repulped OCC. In 
this aspect, the process may be considered as "polishing" a paper pulp 
furnish which has an undesirable or unacceptably high wax content in 
excess of 1%. When it is considered that slide angle, in all grades of 
paperboard and paper carton material, is a significant problem, even a wax 
content as low as 2%, for example, may be undesirable. Since wax contents 
in this range seem to be pervasive, and tend to be recycled more than 
once, auxiliary means have been employed to increase the slip angle, such 
as by spraying the surface of the carton or board material with colloidal 
silica to increase its coefficient of friction. In some instances, further 
increase of the slip angle by more thorough reduction of wax content would 
permit the elimination of auxiliary treatments and systems for the purpose 
of increasing the friction between sheets of paper board material. Under 
these circumstances, and following the teachings of this invention, even a 
single reverse pressure screen, with a hydraulic split of 10:1, has the 
capability of reducing such wax content by about 90%. 
It is accordingly an important object of this invention to provide a method 
and apparatus by which petroleum or petroleum-based wax may be effectively 
removed from waxed OCC cartons or similar sources of paper fiber, for 
recycling such fiber and for providing a usable board furnish with a 
minimum wax content, and with a minimum decrease in friction 
characteristics of paperboard made from such stock. 
A further important object of the invention is the provision of a method, 
as outlined above, by which a petroleum wax constituent is separated from 
paper fibers in a hydrapulper at elevated temperature, and in which the 
wax laden liquid fraction is removed by screening in high pressure 
"reverse" screens having very small apertures or openings and in which the 
stock suspension is maintained in a fluidized condition with the wax and 
waste liquid component passing through the screen openings leaving a 
thickened and substantially de-waxed furnish. 
A still further object of the invention is the provision of a method, as 
outlined above, in which a plurality of such screens are arranged in 
serial or tandem fashion with counter current wastewater connections, in 
which the cleanest water is applied for dilution at the last of such 
screens and the wastewater from such screen is applied to the immediately 
proceeding screen as dilution water, etc. 
A still further object of the invention is the provision of a method in 
which waxed OCC material is pulped in a pulper at relatively high 
consistency and under elevated conditions of temperature and alkalinity, 
in which the resulting pulp is screened through conventional course and 
fine screenings, and in which the screened product having a dispersed wax 
emulsion is applied at low consistency serially to the inlets of revolving 
reverse pressure screens, in which the pulp component is maintained in a 
fluidized condition under pressure and in which a major portion of the 
liquid component is extracted through fine openings or slots in the 
screen, with a liquid wax component, along with a certain amount of fines 
and ash. It is preferably to employ a plurality of such pressure screens 
connected in serial arrangement with counter current flow of dilution 
liquid. 
Another object of the invention is the provision of a method, as outlined 
above, in which one or more reverse pressure screens are employed and 
operated to "polish" an existing recycled suspension of paper pulp, for 
making a further significant reduction in the wax content of such pulp. 
Other objects and advantages of the invention will be apparent from the 
following description, the accompanying drawings and the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1A and 1B represent the steps and the preferred apparatus used in 
performing a method of this invention. Beginning with the waxed OCC, it is 
applied to a high consistency stock pulper represented generally at 10 
with an impeller which operates over a perforated bed plate for extraction 
of pulped material from the pulper 10. The pulper may be a 
Hydrapulper.RTM. and shown in U.S. Pat. No. 3,339,851 issued Sep. 5, 1967 
and made by Black Clawson, previously identified. Preferably, the stock 
pulper is equipped with a Black Clawson MidCon screw 12 mounted on the 
impeller as shown in U.S. Pat. No. 4,725,007 issued Feb. 16, 1988. Such a 
configured pulper is particularly useful in defibering difficult furnishes 
such as those with a high wax content. 
Before pulping, all components in the system including the pulper 10 are 
heat preconditioned by being brought up to an operating temperature in 
excess of the melting point of the petroleum based wax. The systems 
operating temperature should be in excess of the wax melting temperature 
so that in instances where the wax melts at 120.degree., the system 
components should be preheated and conditioned to about 130.degree. F. or 
higher. This preconditioning is accomplished by running steam heated water 
through all of the conduits, valves, and apparatus to illuminate any cold 
walls or surfaces onto which wax may congeal. 
Following such preconditioning, the wax laden waste board and waste paper 
and old corrugated cartons, generically referred to here as "OCC", is 
added to the tank of the pulper 10 and heated water is added to provide a 
medium pulping consistency in the range of approximately 8 to 12%. In 
defibering this material, it has been found helpful to elevate the pH to a 
range of about 8.5 to 12, by adding sodium hydroxide or other pH elevating 
agents. The higher pH has the beneficial effect of promoting defibering of 
the components by assisting in breaking down difficult to defiber 
furnishes and preserving fiber strength. The swelling of the fiber under 
the influence of the alkaline conditions promotes separation of wax from 
the fiber and reduces fiber loss through the reverse pressure screens. 
The amount and extent of defibering can be monitored visually or by taking 
a grab sample and observing the results. The observation to determine the 
extent of defibering is no different from that which is made in the 
repulping of conventional OCC or mixed office wastes. The elevated 
temperature is maintained throughout. 
The pulper not only defibers the pulp but disperses the wax in liquid form 
throughout the mass and throughout the about 88 to 92% water content as an 
emulsion of liquid wax and water. At the elevated temperature, there is no 
tendency for wax to build up on the pulper tank walls or on the rotor. 
OCC, as well as other waxed papers, commonly contaminated with or 
accompanied with lightweight contaminants as well as heavy debris, which 
may be entrained with the wastepaper into the tank of the pulper. It is 
common to provide an auxiliary system for the purpose of relieving the 
pulper tank of such lightweight and heavyweight crude contaminants before 
they can be broken down by the impeller to sizes which are sufficiently 
small so as to pass through the holes of the extraction bed plate in the 
pulper. For this purpose, the pulper 10 may be equipped with a trash 
purging system such as the Hydrapurge detrashing system of Black Clawson. 
Such a detrashing system operates on a cycle basis and extracts stock 
directly from the pulper tub for a period of time where the fiber is 
accepted through a perforated bed plate and plastics and other lightweight 
debris build up inside where they are periodically purged to a dewatering 
drum. If such equipment is installed with the pulper, it is similarly 
important to assure that the operating components of the detrashing system 
are also brought up to or substantially to the previously defined system 
operating temperature. 
The defibered pulp suspension including the wax emulsion is then subjected 
to conventional waste paper cleaning steps which are diagrammed on FIG. 
1A. The particular steps and processes which are used to remove course 
undefibered clumps, heavy as well as lightweight contaminants and 
"stickies" including cyclone and screen cleaning steps, are not critical 
to the performance of this invention or the practice of the method, 
provided that all of the steps are performed at the previously-defined 
elevated temperature. 
FIG. 1A shows the output of the Hydrapulper.RTM. being applied to a high 
consistency free vortex cyclone separator 20. The cyclone separator 20 may 
be a Ruffclone separator having a top tangential inlet and accepts outlet, 
with a bottom rejects outlet for heavy contaminants, as made by Black 
Clawson. 
The accepts from the cyclone 20 is applied to one or more coarse screen 
separators designated at 22a and 22b. These are power driven paper pulp 
screening machines incorporating a generally cylindrical screen and having 
an internal rotating impeller. The screens 22 remove from the stock coarse 
contaminants which may be delivered on reject lines 23 to a reject sorter, 
while the screened accepts are directed to a medium consistency cleaning 
cyclone separator 24. The cyclone separator 24 is of the same general 
construction as the cyclone 20 and may be a Liquid Cyclone as sold by 
Black Clawson. The purpose of the medium consistency cyclone 24 is to 
remove lighter weight contaminants and "stickies". It is understood that 
the rejects from each of the cyclones 20 and 24 are conventionally 
processed and may also be sent to a reject sorter 21 as illustrated in 
FIG. 1A along with the rejects from the screens 22a and 22b. The reject 
sorter may be a Black Clawson ULTRASORTER reject processor which is a 
non-vibrating low attrition totally enclosed tailing screen that removes 
debris normally found in a coarse screening loop. After screening, the 
affluent may be returned to the pulper and the sorted rejects dumped to 
waste or landfill. 
The pulp is then conventionally processed with one or more fine pulp 
screens 25 which may be identical to the coarse screens 22 with the 
exception of the fact that the screening cylinder or screening basket is 
formed with finer perforations or slots. In the screens 25 as represented 
by a primary screen 25a, a secondary screen 25b and an optional tertiary 
screen 25c remove the smaller contaminants. In the setup as shown, the 
affluent reject from the first fine screen 25a is diluted and applied to 
the second fine screen 25b. If a further screening is required, this 
affluent from the screen 25b may be applied to the tertiary screen 25c. In 
the case of screens 25a and 25b, the accepts outlet will usually be joined 
for further processing while the accepts outlet of the tertiary screen may 
usually be re-applied as an input to the first screen 25a, while the final 
reject, from the last of the screens, may be sent to a rejects sorter. 
Up to this point, there has been no specific effort to remove the wax 
emulsion component or fraction from the pulp fraction of the furnish 
although a small part of the wax is inherently removed in the pulp washing 
and screening operations of FIG. 1A. The remaining wax emulsion fraction 
is removed in the reverse pressure screen stages represented in FIG. 1B 
and diagramed in FIG. 2. 
The pulped inlet furnish on line 28 is diluted by heated process water or 
heated fresh water to a relatively low consistency of about 1% or less 
through a conventional consistency controller 29 and is applied to the 
inlet of a high speed "reverse" pressure screen 30, comprising preferably 
one of three cascade connected identical, such pressure screens as shown 
in FIG. 3 with countercurrent washing, and described in greater detail 
below. 
The reverse pressure screen 30 closely resembles a conventional screen 
cylinder such as shown in U.S. Pat. No. 3,849,302 with a stationery 
cylindrical screen having an inner inlet high pressure surface and an 
outer outlet low pressure surface. Preferably a drum-type rotor is used 
with foils on its outer surface and within the interior of the screen 
adjacent the inlet or high pressure side of the screen. The principal 
difference between a conventional cylinder screen and a "reverse" screen 
cylinder is the fact that the openings of the reverse screen cylinder, as 
used in this invention, are much smaller than those of a conventional 
screen and act as a filter to prevent a major portion of the pulp from 
passing through. Preferably, the openings consist of electron beam drilled 
holes which may be as small as about 0.004", or smaller, but good results 
can be obtained with a cylindrical hole in the range of 0.006" to 0.016" 
diameter. Relatively high rotor speeds are employed such as about 5,000 
feet per minute or higher at the inner inlet screen surface to maintain a 
fully fluidized condition of the pulp suspension at the screen inlet 
surface. 
The stock and wax laden water emulsion are applied to the screen at the 
relatively low consistency as identified above, to the inner inlet side of 
the screen and is maintained in a constant fluidized condition to prevent 
a mat from forming on the screen surface. This fluidized condition is 
maintained by influence of the foils on the drum surface which move 
adjacent to the high pressure or inlet surface of the screen. The furnish 
is maintained at least at the previously defined elevated temperature, and 
the wax emulsion and water along with fine fiber particles are extracted 
through the small screen openings into the low pressure or outlet side of 
the screen. The thickened pulp is removed through an outlet. Thus, the 
screen may be considered as having a hydraulic split, such as 90/10, in 
which 90% of the mass entering is extracted from the high pressure side of 
the screen through the holes and 10%, the thickened pulp, is extracted 
through the screen outlet. Such a 90/10 hydraulic split by definition 
results in an increase in consistency by one decimal point so that if the 
inlet consistency is 0.5%, the outlet consistency will be 5%. 
The heated wax emulsion component, along with ash and some fines, are 
extracted together through the cylinder holes as "filtrate" in FIG. 2 and 
good fibers are retained as "fiber" in FIG. 2. If the wax component of the 
diluted suspension at the inlet represented 10% of the mass, following 
screening with theoretically clean dilution water, the resultant thickened 
suspension, i.e., "fiber" in FIG. 2 would have only 1% wax content. Due to 
the use of countercurrent washing, such theoretical efficiencies cannot be 
obtained but three washing stages, in tandem, are effective to remove the 
residual wax content to 1% or less of the thickened stock suspension and 
preferably less than 0.5% of the suspension by weight. 
Thus, in this manner, the thickened and washed stock suspension may be 
rediluted at a second consistency controller 33 and applied to a second 
tandem connected "reverse" screen 30b, and the process is repeated. The 
filtrate from the screen 30b is removed on line 34 and supplied to the 
controller 29 as dilution water for the screen 30a. 
If further washing is desired, the thickened and washed stock from the 
outlet of the screen 30b may be applied to a tertiary screen 30c after 
being diluted at a consistency controller 35, as previously described, 
using makeup water, and water from the clarifier 28 on line 36. The 
filtrate from the screen 30c is sent on line 37 for dilution at the input 
to screen 30b in a conventional countercurrent manner. The heavily wax 
laden affluent from the reverse screen 30A as the filtrate through the 
screen 45 is delivered by a line 38 to the clarifier 28 and is itself of 
relatively low consistency, while the thickened relatively high 
consistency fiber stock is delivered on line 38 for utilization or drying 
and storage, as the case may be. 
The countercurrent washing system in which the cleanest water is applied 
for dilution to the last cleaning stage, is most efficient for multiple 
stage washing from a conservation of water standpoint. The amount of fines 
that are removed depends to some extent upon the nature of the material 
which made up the furnish to begin with. Since fines generally do not have 
good papermaking qualities, the removal of some fines with the wax 
fraction is not considered to be undesirable. 
The clarifier 28, as previously described, may be a D-A-F Supercell 
dissolved air flotation unit as manufactured by Krofta Engineering Corp., 
previously defined, or other suitable apparatus by means of which the wax 
component is removed from the affluent. This equipment is operated below 
the melting temperature of the wax to take advantage of the congealing of 
the wax and its relatively lighter weight as compared to water. The 
reverse pressure screens 30, however, are operated at all times with the 
stock suspension above the melting temperature of the wax so that the wax 
passes through the screen openings as a liquid. 
As previously noted, the hole sizes in the cylindrical screen, in a 
practical range, would be from about 0.004" or less to about 0.016" in 
diameter with preferred ranges between about 0.006" and 0.010" in 
diameter. In such screens, the open area ranges from about 10% to about 
15%. Holes are preferred to slots, but a slotted screen could be used. 
The reverse pressure screen 30 is illustrated in partially cut-away view in 
FIG. 3 as having an outer housing 40 forming a pressure vessel. The 
housing 40 contains a stationary non-rotating screen cylinder 45 therein. 
The screen cylinder has an inner inlet or upstream surface 46 and an outer 
outlet or downstream surface 47 and is provided with a plurality of 
closely spaced perforations or slots of a dimension, as previously 
described. A rotating foil support member is positioned closely adjacent 
the inner inlet surface, and in the instance of the preferred embodiment, 
as shown in FIG. 3, the foil member is in the form of a rotating drum 50 
shown in partial elevation having foils 52 formed on the outer surface 
which foils rotate in close proximity to the inner filtering or inlet 
surface of the screen cylinder 45. Typically, the foils may be 2" high, 2" 
wide and 1/4"-3/16" thick at the point of maximum thickness. The drum is 
mounted for rotation by a drive shaft 53 and a drive motor 54 at a rate of 
about 5000 ft./minute or more surface speed. 
The spacing between the foils and the screen cylinder is maintained at a 
minimum so that, as the drum is rotated and driven by the motor 54, the 
stock suspension at the inlet surface 46 is maintained in fluidized 
condition. Thus, the spacing between the foils and the inside surface 46 
of the cylinder may be as little as 1/16 of an inch, and the outer surface 
of the drum in regions between the foils 52 may be spaced from the inside 
screen surface less than 1/2 an inch and in some instances less than 3/16 
of an inch. 
The heated stock suspension and the liquid wax emulsion is brought in, 
under pressure, to the inlet 48 and is delivered to an interior chamber 55 
and from there into the annular space between the outer surface of the 
drum 50 and the inside surface of the cylinder-shaped screen 45. There is 
thus created a substantial pressure differential between the inside 
(upstream) and the outside (downstream) surfaces of the screen, which 
differential is controlled by controlling inlet and outlet valves and, 
using these valves, the rate of flow through the reverse screen may also 
be controlled. Thus, in typical conditions, the inlet pressure may be in 
the range of about 30-50 psi or even higher. 
The thickened fiber, now with a major part of the free liquid and liquid 
wax component removed is collected in the dome 58 and exits the reverse 
pressure screen at the accepts outlet 60, while the separated heated water 
and emulsion is collected in an annular chamber 62 which surrounds the 
cylinder 45 and deliver to the outlet 65. In such a reverse pressure 
screen, with a screen basket approximately 43" high and 48" in diameter, 
500 gallons per minute of filtrate flow can be processed through a screen 
having perforated hole diameters of 0.006" and openness of between about 
10-15%. This provides a thickened stock accepts capacity of between about 
6-20 tons (dry) per 24 hour day. 
The preferred inlet consistency is about 0.5% or less, and a maximum inlet 
consistency, for most efficient operation of the reverse screen is about 
1%. The thickened stock would have a maximum of about 6% consistency to be 
flowable but dilution water may be added in the dome 58 to make the 
thickened stock more readily flowable from the accepts side. Under these 
operating conditions, an inlet pressure from the consistency controller 
29, 33 or 35 may be between 30 to 40 psi. The inlet pressure differential 
from feed to the accepts output 60 ranges from about 2 psi to 15 psi with 
4 to 8 psi differential as the normal operating range. 
With any given screen and given foil speed, the stock inlet and rejects 
outlet pressure may be controlled by valves in these lines to control the 
throughput of the screen and to prevent a fiber mat from forming, which 
could cause a sudden blockage of the screen holes or slots. 
For those instances where it is desired to "polish" an existing recycled 
pulp which may have or contain an unacceptably high wax content after 
having been processed by conventional OCC reclaiming procedures, a stock 
furnish may be diluted with heated water to bring the entire furnish above 
the melting point of its wax content, in the manner previously described, 
and applied to a pre-heated reverse pressure screen system for screening, 
preferably at an inlet consistency of about 1% or less, although higher 
consistencies may be used with somewhat lower efficiencies. The pressure 
screen is operated in the manner previously described, that is, the input 
energy to the rotor or to the rotating foils, taken with the through feed 
rate is more than sufficient to maintain a stock furnish in a fully 
fluidized condition at the inlet side of the screen. The emulsified and 
molten wax component will be removed concurrently with the excess water 
through the screen and the thickened pulp will be ejected through the 
accepts outlet, as previously described in connection with the description 
of the operation of the pressure screen 30. Thus, this aspect of the 
method of this invention, at low cost, permits the beneficiation of the 
output from conventional OCC processing systems. 
Laboratory tests were run for the purpose of evaluating the efficiency of 
wax removal from wax coated board material using the process and equipment 
of this invention. 
Two pulper batches were prepared. Both batches were run identically from 
pulping to fine screening. The first pulper batch was made to generate 
filtrate for dilution for the second batch to simulate the conditions of a 
commercial installation, with the thick stock from the first run being 
discarded. The filtrate was diluted to a 6:1 ratio of water to filtrate in 
the second run for dilution of pulping, and course and fine screening. 
Both pulper batches were made with about 1100 lb. of wax coated board 
material added to 1000 gallons of 150.degree. F. water (or filtrate) to 
obtain a pulping consistency of 10%. The hydrapulper was configured as 
previously described and the rotor was run at 290 rpm for 45 minutes on 
each batch. The temperatures were maintained to 150 degrees and 3.6 pounds 
of NaOH was added to each pulper batch to increase pH to 9.5. The pulper 
batches were extracted through 3/8" bed plate holes and pumped over to a 
screen supply tank. Both batch consistencies in the screen tank were 
adjusted to 2.5% to feed course screens 22. 
Thermo Black Clawson model 100 Ultra-V Pressure Screen is used a Black 
Clawson UP cylinder with 0.062" holes and a Black Clawson NS-II rotor 
running at 650 rpm. Accepts were collected in a holding tank and rejected 
material was recirculated back into the screen supply tank. The screen 
supply tank was emptied and the accepted material was then pumped back 
into the screen supply tank and the consistency adjusted to 1.5% for fine 
screening. The hydraulic reject rate was maintained to 15% on all runs. 
Fine screening by the screen 25 for both batches used a Black Clawson PSP 
cylinder 25 with 0.010" slots and a Black Clawson LP-1 rotor running at 
780 rpm. The holding tank received the accepted material and the rejects 
were recirculated back into the screen supply tank. The accepted material 
again was pumped back into the screen supply tank and consistency adjusted 
to 0.5% for reverse screening as in the case of the course screening. 
Reverse screening was accomplished on all runs with a reverse pressure 
cleaner 30 configured as described above using a cylinder with 0.006" 
holes and a 24" diameter rotor running at 900 rpm. The drive motor was 
rated at 100 hp and the consumed power measured between 35-38 hp. The unit 
was fed at approximately 500 gallons per minute for all runs and hydraulic 
splits were maintained to 10% (10-1). The first pulper batch run retained 
only the filtrate and the thick stock was sent to a second holding tank. 
Some of the filtrate was sent to the cleaner tank to hold for later 
dilution while the remainder was diluted to a 6:1 ratio of water to 
filtrate and used as dilution for the second pulper run pulper, course 
screen and fine screen. 
In the second run, the reverse screen 30 was run in four separate stages. 
The first stage used filtrate as dilution from the second holding tank 
that was diluted to 10:1 to adjust the feed consistency to 0.5%. The thick 
stock was collected in a dump tank and the filtrate collected in the first 
holding tank. The filtrate from this run was mixed with water to achieve a 
10:1 ratio to dilute the thick stock for stage two reverse cleaner feed at 
0.5%. Stage two was run in the same manner as stage one with the filtrate 
again diluted to 10:1 and used to dilute the thick stock to 0.5% for the 
third stage feed. The third stage dumped the filtrate to sewer and 
collected the thick stock; diluting it to 0.5% with fresh waster to feed 
the last stage of reverse cleaning. A fourth and final washing collected 
the thick stock in the dump tank and the filtrate went to sewer. 
Overall, the laboratory trial was considered to be a success, revealing the 
reverse screen apparatus to be very efficient for wax washing. The final 
result produced a fiber that physically was very clean in appearance and 
was essentially free of wax residue. The following table provides the wax 
content, as measured, in terms of grams per liter and in terms of % by 
weight of the feed to the reverse screen and the accepts from the reverse 
screen. The test results show that only three stages of cleaning was 
necessary to provide a very low wax content, in which the feed to the 
first stage exceeded 36% wax by weight and the accepts from the third 
stage was less than 0.3% by weight. If the criteria of wax content was 
acceptability at 1% or less, then two stages of reverse cleaning, using 
the method described, would have been sufficient since the accepts at the 
second stage were less than 1% by weight wax content. 
TABLE 
______________________________________ 
Wax Content 
% by Wt 
______________________________________ 
First Stage Feed 2.0g/L 36.56 
Accepts 2.4g/L 6.38 
Second Stage Feed 0.5g/L 9.98 
Accepts 0.4g/L 0.85 
Third Stage Feed 0.2g/L 6.17 
Accepts 0.1g/L 0.28 
Fourth Stage Feed 0.2g/L 6.38 
Accepts 0.1g/L 0.22 
______________________________________ 
It will therefore be seen that this invention provides a useful method and 
apparatus for the substantial removal of conventional and untreated 
petroleum wax components from a waxed furnish which results in a 
beneficiation of the pulp and a removal of wax loading, which may begin as 
high as 50%, and which may be reduced to about 1% or less, thereby 
providing a furnish which may be conventionally used as a reclaimed 
product in the manufacture of brown paper and board. 
While the methods herein described, and the forms of apparatus for carrying 
this method into effect, constitute preferred embodiments of this 
invention, it is to be understood that the invention is not limited to 
these precise methods and forms of apparatus, and that changes may be made 
in either without departing from the scope of the invention, which is 
defined in the appended claims.