Note: Descriptions are shown in the official language in which they were submitted.
TWIN BELT VACUUM WASHER
BACKGROUND OF THE INVENTION
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The present invention relates to machines for washing
paper stock pulp and other vacuum-filterable materials.
State of the Art
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According to various processes well-known in the
paper making industry, paper stock pulp is formed by
digesting wood chips in the presence of various chemicals
in a heated pressure vessel. After discharge from the
pressure vessel, the paper stock pulp must be washed and
filtered to separate ~he wood fibers from ~he digested
chemicals.
One system for washing paper stock pulp is taught in
U.S. Patent 2,3S5~243. According 1:o that patent9 paper
stock is diluted with water after digestion and then is
picked up by a large-diameter rotating cylinder whose
surface is formed o a wire mesh screen. A couch roll is
positioned to press downward onto the surface of the
screen-covered cylinder to express liquid from the stock
.
Case No. 798
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nd t]l~lS ~o -rorm a resiclual blanket or mat of dewatered
~ibers~ The systern described in the patent further includes
an a~3itation device wherein oncc-~-dewa-tered fibers are
repulped hy mixing with water. S-till further, the system
tau~ht in -the patent includes additional agitation devices,
screen-covered cylinders, and couch rolls to wash the
pulp in stages.
According to other processes well-known in the paper-
making industry, materials such as waste paper and ground-
wood, although not digested with chemicals, must neverthelessbe washed. Also, the preparation and manufacture of other
vacuum-filterable materials such as gold and uranium ores,
sugar and phosphoric acid includes washing the materials
with either water or chemicals. Conventional systems for
washing such vacuum-filterable materials are known. I
According to the presen-t invention there is provided
a machine Eor washing paper stock pulp and other vacuum-
filterable materials ! the machine having a horizontally-disposed
drum with a sidewall through which liquid can pass, the drum
beins mounted for rotation about its horizontal axis. A
tank is mounted to encompass at least the lower part of the
drum and the tank is constructed to contain liquid exterior
to the drum. Roller members are mounted for rotation at
spaced apart locations above and below the drum, and upper
and lower endless filter belts are trained around the drum
in face-to-face relationship with each other to hold a mat
of material to be washed. Feed means is located to deposit
the vacuurn-filterable material between the endless filter
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belts, alld drive means ls mounted to drive -the endless belts.
r~ uid inlet means is provided to introduce liquid into the
tank and vacuum means is connected in communication with the
sidewall oE the drum to produce a partial vacuum -to provîde
a pressure differen-tial between the mat of material and the
liquid contents of the tank thereby to force liquid from the
tank through the mat of material.
The primary object of the present invention is to
provide an improved machine to wash paper stock pulp and
other vacuum-filterable materials. As will be readily
understood in view of the following description~ the term
vacuum-filterable encompasses materials whlch, when covering
a filtering surface, allow liquid to pass therethrough
when a pressure differential is applied. The term pulp
is used herein as a synonym for vacuum-filterable materials.
A more specific object of the present invention is to
; provide an improved machine for washing pu]p which operates
without re-pulping of the pulp stock.
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BRIEF DESCRIPTION OE l'HE DRAWINGS
The above and other objects of the present invention
may be readily ascertained by consideration of the
following detailed description and appended drawings,
which are offered by way of illustration only and not in
limitation of the invention, the scope of which is defined
by the appended claims and equivalents.
In the drawings:
Figure 1 is a side elevation of a machine according
to the present invention shown schematically;
Figure 2 is a side elevation which schematically
illustrates a particular modification of a machine
according to the present invention; and
Figure 3 is a side elevation which schematically
illustrates another modification of a machine according to
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As shown in Figure 1, a machine according to this
invention includes a horizontally-d:isposed drum 10. The
drum 10 includes a cylindrical sidewall 12 and end walls
14. The cylindrical sidewall is perforated, say by small
spaced-apart apertures, not shown. Workers skilled in
this art will readily recognize that the sidewall of the
drum, instead of being perforated, could be comprised of a
2~ wedgewire grid or other conventional support means which
permit liquid flow communication with the interior of the
cylindrical sidewall 12. The illustrated end walls 14 are
nonforaminate; however, in practice they can be perforated
or the like to reduce their weight. Axle members~ not
shown, are fixed to the end walls 14, and are supported
for rotation outboard of the drum by stationary pillow
blocks or other journal means.
Case No. 79~
A rotary valve 20 with port 22 is formed in the axle
members of the drum 10 in fluid-flow communication With
radially-extending filtrate conduits 24 disposed within
the dru~ lQ. The conduits 24 are connected to the aper-
tures in the sidewall 12. Such a structure is conven-
tional. In operation, the rotary valve communicates with~he conduits 24 to permit liquid to flow through the
apertures in the sidewall 12 and thence from the drum via
the port 22. In operation the port 22 is coupled to a
vacuum means to apply vacuum to the apertures via conduits
24.
Referring still to Figure 1, open tank 30 is mounted
below the drum 10. The tank 30 is constructed and yosi-
tioned to encompass approximately the lower half of the
drum 10 and to contain a substantial quantity of liquid
exterior of the drum. A liquid inlet means, such as a
conduit 32 is connected in communication with the tank 30
to carry wash liquor thereinto. In some applications, the
wash liquor may simply be fresh water while in other
instances it may be aqueous solution of particular
chemicals or non-aqueous solvent.
The machine in Figure 1 further includes feed means
which, in the illustrated embodiment: by way of example,
comprises a horizontal vacuum pan 34 of conventional
construction which is mounted to the left of the drum 10.
A con~entional suction-producing device, not shown, i~
connected in communication with the interior of the vacuum
pan to draw liquid therefrvm via a conduit 36. Above the
vacuum pan 34 is mounted a distribution box 38, which also
can be understood to be of conventional construction. At
the opposite ends of the vacuum pan are rotatably mounted
support rollers 40 and 42. One ~killed in this art should
readily recognize that the feed means could, alternatively,
comprise other conventional means for forming a pulp mat
on a belt. For example, some forming means are illustrated
in Figures 2 and 3 and discussed below~
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Two endless filter belts 50 and 52, referred to
herein as the upper and low~r belts respectively, are
trained around the drum 10 as illustrated in Figure 1.
More particularly ! the endless bel~s are trained to pass
around part of the drum 10 in face-to-face relationship -to
each other and to pass around a plurality of roller
members. The endless belts should be understood to
comprise conventional porous belts of the type which are
well known in the filtration art, and the roller members
are rigid, hollow cylinder disposed on bearings to rotate
about their axes.
The upper belt 50 is trained around rollers 54 58;
and the lower bel~ 52 is trained around rollers 40, 42 and
60-68. Conventional drive means, not shown, are connected
to rotatably drive the drum 10 and, thus, to cause the two
endless belts 50 and 52 to travel together at equal speeds
in the directions indicated by the arrows in Figure 1.
Alternatively the drive means can be connected to drive a
selected roller such as roller 40. The rollers 56 and 64
are positioned to separate the upper and lower belts after
~he belts have passed around the drum 10 and, at the
opposite end of the machine, rollers 54 and 42 are located
to ~eunite the belts in face-to-face relationship after
the lower belt 52 travels between ~he distribu~ion box 38
and vacuum pan 34. It should be understood tha~ the
position of roller 60 relative ~o the drum 10 can be
adjusted to determine the extent to which the belts 50 and
52 wrap around the drum. In practice~ at least one roller
in both the upper and lower sets of bel~s is movably
mounted so that the tensions of the belts can be selec-
tively adjusted. Also, conventional means for laterally
aligning the belts are normally provided.
In certain applications where a relatively dry pulp
is desired, expression means are located between rollers
60 and 64 to express liquid from the pulp mat. In the
illustrated embodiment the expression means includes three
Case No. 798
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rollers 70 located in a triangular array adjacent roller
62. A tnird belt 72 is trained around the rollers 70
above the belts 50 and 52 where they traverse roller 62.
The uppermost roller 70 can be positioned vertically to
create a predetermined tension in the belt 72. This
expression means is conventional and known alternatives
can be employed to apply pressure to the pulp mat to
express liquid therefrom. Collection trough 74 is disposed
below roller 62 to collect liquid and carry it to disposal
via line 76.
Conventional spray means can be utilized to clean the
belts 50 and 52. The illustrated spray means include
spray nozzles 80 located adjacent the upper belt 50 between
rollers 54 and 58 and adjacent the lower belt 52 between
rollers 66 and 68. Collection means 82 are located
beneath the no~æles 80 to collect liquid.
Optionally, conventional spray means can also be
utilized to wash the pulp. In the illustrated embodiment
spray nozzles 81 are located adjacent the upper part of
th~ drum to spray liquid onto the belts and the pulp mat. ~.
The operation of the above~described machine can now
be understood. Initially a vacuum-filterable material,
such as paper stock containing digestion che~icals, is fed
into the distribution box 38 as indicated by the arrow.
That material is then discharged onto the belt 52 as it
travels across the vacuum pan 34. Suction applied through
the vacuum pan 34 draws liquid from the pulp, leaving a
sheet or mat of partially dewatered pulp lying on ~he belt
52. The withdrawn liquid, or filtrate, is discharged from
the machine. The lower belt 52, after passage across the
vacuum pan, meets the upper belt 50 in face-to-face rela-
tionship and, thus, the mat of pulp is held between the
two belts. Typically, the pulp mat is about one-quarter
to one inch in thickness.
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The two filter belts 50 and 52, with the pulp mat
between them, then meet the drum 10 and pass into the tank
30. Simultaneously the drum 10 is rota~ed by a drive
means, not shown. At this time vacwum is applied to the
port 22 to apply vacuum ko the interior of the pulp mat.
The vacuum induces liquid ~o flow from the wash tank 30,
through the pulp mat between the two belts, into ~he
interior of the drum 10 and thence from the drum 10 through
ports 22 and ~o a liquid receivin~ means. The flow of
liquid through the pulp mat serves to wash the pulp and,
in some instances, also increases the moisture content of
the pulp mat because some of the wash liquid is absorbed
by the pulp.
The two belts 50 and 52, after passing through the
liquid in the tank 30 remain next to the drum 10 for a
predetermined part of the rotation of the drum and exposed
to the air. During this time the vacuum inside the drum
pulls liquid from the pulp mat to dry the pulp. Option-
ally, additional liquid is sprayed onto the pulp mat at
this time. Thereafter the belts leave the drum and travel
over roller 60 and then between roller 62 and belt 70.
~uring this stage, the pulp mat is squeezed between the
belts due to the tension in the upper belt 70, and liquid
is expressed from the pulp. Next, the upper and lower
belts 50 and 52 are moved apart by the guide rollers 56
and 60 to expose the washed pulp mat. The pulp mat is
then discharged from ~he machine by suitable means, not
shown, such as a doctor blade or the like.
An embodiment of a particular modification of the
aforedescribed machine will now be described in conjunction
with Figures 2 and 3. In this embodiment, elements which
are common to the machine in Figure 1 are designated by
the same reference numerals. This ~mbodiment differs from
the one described earlier principally with respect to the
number and arrangement of the drums and tanks as well as
with respect to the piping of the machine.
Case No. 798
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As shown in Figure 2, a machine according to this
embodiment inc:ludes five horizontally-disposed drums 110,
112~ 114, 116 and 118 which are mounted in spaced-apart,
side-by-side relationship. The five illustrated drums
110-118 are essentially the same in construc$ion and
operation as drum 10 shown in Figure 1 and described
above.
A plurality open tanks 30 are mounted one below each
of the respective drums 110, 112 and 116. The tanks 30
associated with drums 112 and 116 are connected by an
inclined plate 119 located beneath drum 114 so that
liquid falling from drum 114 falls onto the plate and
flows into tank 30.
A liquid inlet means, such as a conduit 32 is
connected in communication with the tank 30 associated
with drum 116 to carry wash liquor into the tank. In some
applications, the wash liquor may simply be fresh water
while in other instances it may be a solution of particular
chemicals. As will be understood in view o~ the following
description, the flow of wash liquid is countercurrent to
the direction of travel of pulp material through the
; machine.
Liquid-carrying means are coupled to the drums 114-118
to convey liquid therefrom into tank 30 associated with
drum 112. In the illustrated embodiment the liquid-carrying
mPans includes a plurality of pipes 120 coupled to ~he
ports 22 of drums 114-118. The pipes 120 are coupled in
1uid-~low communication to the inlet of vacuum pump 122~
and the outlet of the vacuum pump is coupled via line 123
to tank 30 associated with drum 112. Liquid-carrying
- means including pipe 124 and vacuum pump 126 is coupled to
drum 112 to produce a vacuum in the drum and convey liquid
therefrom to disposal.
The rotary valve 20 of drum 110 includes two ports
127 and 128 coupled to pumps 129 and 130 respectively.
The port 127 communicates with the apertures in the wall
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of the drum which are beneath the liquid. The port 128
communicates with the apertures above the liquid which are
in contact with the pulp mat. Such a strucLure is a
~onventional means to permit the liquid from the tank to
be kep~ separate from the liquid and air removed from the
pulp above the liquid.
It should be understood that in certain applications
vacuum means other than pumps are substituted for pumps
122, 12~, 129 and 130. Some pulps contain chemicals which
contain soap-like chemicals which foam when pumped. When
such pulps are processed in the present system, conven-
tional vacuum receiving means are substituted for the
pumps. Conventional vacuum-receiving means for example,
comprise a tank with a vacuum pump connected to its top,
and liquid inlet means and discharge means connected near
the bottom. Thereby the liquid is removed from the lower
part of the $ank after it has settled, and foaming is
reduced or eliminated.
The machine in Figure 2 further includes feed means
which, in the illustrated embodiment by way of example,
comprises tank 30 associated with drum 110 and inlet
conduit 132 coupled to the tank.
According to Figure 2 the two endless belts 50 and 52
are trained around ~he drums in æig-zag fashion. ~lore
particularlyJ the endless belts are trained to pass under
the drums 112 and 116, and over drums 110, 114 and 118.
Above the rnachine, the upper belt 50 is trained
around a set of rollers 140; below the machine, the lower
belt 52 is trained around a set of rollers 142. Conven-
tional drive means, not shown, are connected to rotatablydrive at least one of the drums and, thus, to cause the
two endless belts 50 and 52 to travel together at equal
speeds in the directions indicated by the arrows in Figure
2. The upper and lower sets of rollers are positioned to
separate the upper and lower belts after the belts have
- passed under the drum 116 and, at the opposite end of the ~;
Case No. 798
machine, to reunite the belts in face-to-face relationship
against drum 110. It should be further observed that the
lower set of rollers 142 is positioned so tha~ the lower
belt 52 passes around the portion of the drum 110 beneath
the surface of the liquid in the tank 30 associated with
that drum. In practice, at least one roller in both the
upper and lower sets is movably mounted so that the
tensions of the belts can be selectively adjusted. The
tensions ~eed not be the same. In fact, the upper belt 50
0 i5 preferably at greater tension than the lower belt 52.This causes the compressive force on the pulp mat to be
greater when th~ mat passes over the drums 114 and 118
than when it passes under the drums 112 and 116. This is
advantageous because the pulp mat is "worked", i.e.~
compressed during its passage over the drum 114 and allowed
to expand and absorb wash liquid when passing under the
drums through the wash ]iquor. This working can be likened
to wringing a sponge and then allowing it to expand to
absorb more water.
The operation of the above-described machine can now
be understood. Initially a vacuum-filterable material is
fed into the tank 30 via conduit 132 as indicated by the
arrow. Suction is applied through the drum 110 to pull
the material onto the belt 52 and and remove liquid from
~he pulp, thereby forming a sheet or mat of pulp on the
belt 52. The withdrawn liquid, or filtrate, is discharged
from the machine via pump 130. The belt 52 moves wi~h the
drum 110 out of the liquid and vacuum is still applied to
the drum 110 to remove additional liquid from the pulp and
hold the mat on the belt 52. The lower belt 52, after
traversing a predetermined part of the drum 110, meets the
upper belt 50 in face-to-face relationship and, thus, the
mat of pulp fibers is gripped between the two belts.
The two belts 50 and 52, with the pulp mat between
them, then pass i~to the first tank 30 and under the first
drum 112. Simultaneously the drum 112 is rotated, say be
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frictional engagement with the upper belt 50. At this
time, liquid from the first wash tank 30 passes through
the pulp mat between the -two belts and then flows into the
interior of ~he first wash drum 112. This flow of liquid
through the pulp mat occurs because of ~he differential in
the pressure between the interior and exterior of the wash
drum 11; the differential head is provided and sustained
by the pump 126 which continuously draws liquid from the
interior of the drum 112 by vacuum. The flow of liquid
through the pulp mat serves to wash the pulp and, in some
instances, also increases the moisture content of the pulp
mat because some of the wash liquid is absorbed by the
pulp.
The two belts 50 and 52, after passing under the drum
112, then pass over the drum 114. During this stage,
vacuum is applied to the drum 114 by pump 122 to remove
liquid from the pulp. Optional sprays 80 spray wash water
onto the pulp to futher wash it. Liquid falling from drum
114 is collected on the plate 119 and flows into tank 30.
After passage over the drum 114 the two endless belts
50 and 52 carry the pulp mat in~o the second tank 30 and
then under the drl~ 116. During this stageg the pulp mat
undergoes a second wash like the one described above.
Next, the belts 50 and 52 are moved apart by the roller
140 and drum 118 $o expose the washed pulp mat. Vaccum
applied to drum 118 dries the pulp mat, which is then
discharged from the machine by suitable means, such as a
doctor blade 144 or the like.
It should now be apparent that a machine according to
this invention can include more than two tank and drum
combinations depending upon the number of stages of washing
which are required for a particular application.
Turning now to Figure 3, there is illustrated an
alternative means of forming the pulp mat. The illustrated
means includes a drum 10 which is the sa~e in construction
and operation as drum 10 shown in Figure 1 and described
Case No. 798
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above. Lower belt 52 is trained ~o cover approximately
the upper half of the drum 10, and the upper belt 50 is
located to meet the lower belt on the drum 10 about 90
degrees clockwise of the point of tangency of the lower
belt 52 with the drum. A feed means 150 is conventional
and is located adjacent the drum near the exposed surace
of the belt 52. In operation, vacuum-filterable material
is applied to the belt 52 through feed means 150 whi]e a
vacuum is maintained within the drum to remove water and
form a pulp mat.
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Case No. 798
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