Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INV~NTION
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The use of a hydrophobic foam fllter to separa-te
solid material from a stream has been described in U.S.
Patent Nos. 4,310~424 and 4,303,533. See also, U.S. Patent
No. 4,212,737 whlch relies on and teaches hydrophobic foam
rather than hydrophilic. In previous descriptions of the
assignees' teachings, a couch roll, shower, or other
mechanical means was used to retrieve the solid material
from the foam surface. Such mechanical me-thods have the
potential for causing compaction of the solid material
within the reticulated foam structure due to the pressure
exerted on the surface. The ultimate result can be a
reduction in flow through the filtering medium.
BRIEF DESCRIPTION OF THE INVENTION
This invention describes methods of fiber re-
trieval which minimize the build-up of solid material on
the surface and within the reticulated foam structure and,
therefore, maintain the volumetric ra-te through the fiber.
In accordance with the invent:ion there is pro-
vided an efficient method of treating suspensions of solid
material in liquid to separate a substantial portion of
said solid material from said liquid which includes
maximizing volumetric flow of the liquid through an open-
celled reticulated hydrophobic foam separation medium and
maximizing said separation for a sustained period, said
method comprising: providing on a revolving drum an open-
celled reticulated hydrophobic ioam separation medium of a
thickness of from one-eighth inch to two inches and a
porosity in the range of 40 (+10~) pores per lineal inch to
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80 (~10~) pores per lineal inch; subjecting said foam
separating medium to a lo~ gravi-ty created pressure
differential by submersion of a portion thereof mounted on
stream of said suspens
create a flow of liquid into and through said medium, a
deposit of a major part of the solid material on the sur-
face of sald medium and a deposit of at least some of the
rema.ining part of the solid material in the reticulated
t re and the rest, includi g
through the reticulated foam structure in the flow; util-
i id vacuum nozzle spaced fr
carrying a flexible shroud; retrieving the major portion of '
said solid material from the foam surface and from the
reticulated structure by entraining solid materlal in an
i ted fluid moving transver y
withl within and through the open-celled reticulated
hydrophobic foam medium.
The invention consists of a rotating drum, bel-t
i il r device covered witb a y
~0 celled hydrophobic foam. The thickness of the foam is
greater than l/8-inch and the porosity is in excess of 40
pores per lineal inch. Other characteristics of the foam
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are described in U.S. Patent Nos. ~,303,533 and 4,310,424.
Typically, the liquid feed stream containing suspen-
ded solid material is introduced into a tank containing a
rotary drum covered with an open-celled hydrophobic foam.
Regardless of the specific foam medium moving support appa-
ratus, the stream is filtered as it passes through the
foam, leaving some or all of the solid material on the
surface, and any remainder trapped within the reticulated
foam structure. The clean filtrate is withdrawn from the
interior of the drum or belt structure and either reused
or discarded. Any material trapped within the foam can be
retrieved by expressing methods described in U.S. Patent
Nos. 4,303,533 and 4,310,424.
The novel method of this invention for retrieving
the ~;olid material from the foam surface and reticulated
foam structure includes entraining at least some of the
solitl mate!rial in a fluid passed through the foam medium.
Emodiments of the method include: ~1) vacuuming the mater-
ial from the foam surface and reticulated foam structure by
entrainment in a transversely directed lEluid, (2) using a
couch roll to remove the majority of fiber from the foam
surface and then vacuuming the surface and reticulated
structure to remove the remainder of the solids, (3) using
a vacuum nozzle or vacuum couch roll to remove solids from
the surface anld the reticulated foam structure, (4) using
a water or air~spray from inside the foam medium moving
support apparatus to loosen and entrain remaining solids
after first removing the major part of the solid material
by means of a vacuum nozzle or couch roll.
In each case, it is important that the mechanical
element, at least with regard to its rigidly fixed parts,
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be spaced so as to have only minimum contact, if any, with
the foam medium. The moving and loaded foam medium inher-
ently resists geometric integrity and may have areas which
are variably spaced from the retrieving apparatus. If the
foam medium has significant regular contact with the
rigidly fixed parts of the retrieving apparatus, it will
unduly abrade, distort and otherwise impair its structural
integrity.
In the case of couch roll or vacuum couch roll the
moving fiber mat on the foam surface provides spacing, even
if there is some minimal foam compression under the roll.
In the case of a vacuum nozzle, for instance, a flexible
shroud may extend from the nozzle and contact the foam to
enhance entrainment.
An advantage of this invention is that the high cap-
acity~ of the filter, i.e., maxiumum volumetric flow rate,
can be maiotained through efficient, continuous, and
thorough retrieval of solid material from the filtration
surface and reticulated structure, thus minimizing any
tend~ncy for build-up or "plugging" of ~;olid material
which would reduce capacity.
Another advantage of the invention is that selection
of various combinations of the novel retrieval methods
allows the solids consistency to be tailored to meet the
needs of the specific application. For example, solids
can be retrieved from the foam at 1-4% consistency using
vacuum only and up to 19% consistency using a couch roll/
vacuum combination in accordance with the principals of
the invention.
BRIEF DESCRIPTON OF THE DRAWINGS
Figure 1 is a schematic elevational view of a drum
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type of foam separation device of the invention with a
vacuum nozzle for retrieving the solid material Erom the
foam surface and reticulated foam structure.
Figure 1a is an enlarged fragmentary view of a
portion of Figure 1 showing a flexible shroud on the
vacuum nozzle.
Figure 2 is a view similar to Figure 1 of a belt
type of foam separation device of the invention with a
couch roll followed by an air spray from inside the drum.
Figu~e 3 is a view similar to Figure 1 of a drum
type of foam separation device.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Figures 1 to 3 illustrate foam media separation
devices or filters for use on a pulp or paper process
stream. The devices can advantageously be utilized to
recl~im and thicken fiber in streams with either occa-
sion~31 or continuous high fiber loading in a manner to
be described hereinafter. Like numerals identify like
parts and elements in various views.
~he separation and thickening de~ice 10 of Figure 1
includes a rotary drum 12 having a thin layer of open-
celled resilient hydrophobic foam 14 in a thickness range
of from 1/8-inch to 2 inches (1/8" to 2n), preferably
approximately 1 inch (1"), and a porosity in the range of
from 40 pores per lineal inch to 80 pores per lineal inch
(40 ppi to 80 ppi), preferably in the range from 65ppi to
80ppi. Other characteristics of~ the foam are as described
in U.S. Patent Nos. 4,303,533 and 4,310,424.
The feed stream or pulp slurry is a aqueous solu-
tion of cellulosic pulp which routinely flows from thepulpmaking or papermaking processes and which contains
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desirable fiber, small contaminants and small undesirable
fiber parts. The feed stream is introduced into a tank
16 containing the rotary drum 12 by means of inlet pipe
18. The stream is filtered as it passes through the foam
14, leaving the majority of the larger desirable fiber 20
on the foam surface. The foam passes the marjority of the
contaminants and small fiber parts with the liquid filtrate
22 which flows from the drum interior through outlet pipe
24. The difference in height between the outer liquid
level in tank 16 and the inner liquid level of filtrate 22
produces a pressure differential h P-
The drum type separation device of Figure 1 is pro-
vided with a vacuum nozzle retrieval device 26 which
removes the fiber mat or major part of the solids from the
foam surface and remaining fiber particles from the reticu-
lated foam structure as fluid air and residual water in the
foam pass transversely through the foam and entrain the
particles in their flow stream for movement outwardly toward
and into the vacuum nozzle. Showers can be used subse-
quently to clean the foam surface, if desired.
The vacuum nozzle retrieval device 26 deposits thesolids and residual liquid associated therewith in a sep-
arator 27 connected by means of pipe 28 to blower 29 and air
outlet 29a. The solids, which are typically fiber of a con-
sistency of from 1-4% (1% equals 10,000 ppm) in the embodi-
ment of Figure 1, is removed from separator 27 through out-
let pipe 30. The blower 29 typically provides approxi-
mately 8 to 12 inches (water) of vacuum at the nozzle.
In comparison with other drum filters, the separa-
tion device of Figure 1 offers the following advantages:
1. Significantly higher sustained area flow rates
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of the nature of 15 to 30 gal./ft.2/min.
compared to the 10 -to 20 gal./f-t. /min.
achievable wi-th a s-tandard or typical wire
or perforated plate gravity decker or
vacuum thickener;
2. The potential for sustained fiber
consistencies of the nature of 12 to 19
percent compared to 12 percent maximum
obtained with typical wire or perforated
plate deckers or thickeners, when multiple
retrieving devices are used.
The inherent resistance flow of the typical
thickener wire is higher than that of the foam within the
. ~
disclosed porosity and thickness ranges, and these ranges
due to their porosity and their vold volume provide
incr~ased fluid takeaway and driving force -throughout the
proce!ss over that obtained in wire covered thickeners. The
prese~nt invention permits this flow to be sustained.
Figure la illustrates a portion of the Figure 1
apparatus with the attachment oE a flexible shroud 26a
attached to the rigid vacuum nozzle. This prevents the
rigid nozzle structure from damaging contact with the foam
but permits an enhanced vacuum entrainment by minimizing
extraneous fluid flow and directing the major fluid flow
transversely through the foam. The flexible shroud 26a
does little, If any, damage to the foam.
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Figure 2 illus-trates a foam bel-t filter device
110 which utilizes a foam separation medium 114 having -the
proper porosity and thickness. The foam medium 114 rota-
tionally driven about rotating members 112a and 112b. The
schematic drawing of device 110 shows that a feed
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stream tank 116 deposits a feed stream on foam belt 114
and a vacuum draws filtrate 122 into a reservoir 223 for
removal through outlet pipe 124. The fiber mat 120 is
retrieved by a doctor 226 from the surface of a couch
roll 125. Vacuum nozzle 128 is provided to clean the foam
belt surface and reticulated structure after retrieval.
Separator 127, air outlet 128a and outlet pipe 130 for
the fiber complete the illustrated combination. A blower
tnot shown) is connected as shown in Figure 1 to provide
the vacuum at nozzle 128.
Figure 3 illustrates an apparatus 210 similar to
the Figùre 1, apparatus 10, with tank 216, drum 212 and Eoam
214. The apparatus 210 includes a vacuum couch roll 226
from which the doctor 226a removes the fiber for a gravity
drop onto chute 231 and into tank 232 with fiber outlet
pipe 230. A fluid nozzle 240 directs a fluid, which is
air, water or both, transversely through the rotating foam
medium 214 to entrain the solids on the surface and in the
reticulated structure not picked up by the vacuum couch
roll 226 and to deposit them on chute 231.
By use of the retrieval apparatus of the embodiments
of the invention, the advantages of foam filtration can
be obtained for substantial periods of time with minimal
loading or "plugging" of the reticulate structure of the
foam.
A typical foam filtration test run on an alkaline
bleach sewer, ~sing a vacuum nozzle apparatus of the type
illustrated in Figure 1, with one inch 65 ppi stiff foam,
on a drum turning 2.5 RPM, produced the following data:
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Elapsed time: 47 hours (foam use)
Flow (rate in): 63 GPM (gal./min.)
Flow (rate through): 27.9 GFM (effective area yal./ft.
2/min. )
5 Vacuum: 8 in. (water ~ P)
Stream: TSS ASH TS T PH
(PPM) (%) (PPM) (F.)
Feed: 294 14 5,092 116 9.6
Filtrate: 80 40 4,812 116 9.6
Fiber: 15,558 2 19,636 116 9.6
Legend: TSS = total suspended solids
TS - total solids
T ~= temperature (F.)
Running the foam filtration apparatus with couch
roll retrieval only can obtain fiber consistency up to 19%
but this cannot be sustained easily without the use of
vacuum or other fluid entrainment to remove material from
the reticulated foam structure and thereby prevent loading
or "plugging."
Another test run on paper machine white water using
a vacuum nozzle similar to the apparatus of Figure 1 as a
"saveall," with 1" 80ppi stiff foam and a drum turning at
3.5 RPM, produced the following data.
Elapsed time: 43 hours (foam use)
Flow (rate in): 87 GPM (gal./min.) 2
Flow (rate through): 2.8 GFM (effective area gal./ft. /
min.)
Va,cuum: 6 in. (water ~ P)
Stream: TSS ASH TS T PH
(PPM) (~) ~PPM) (F.)
Feed: 3,353 23 4,670 100 5.8
Filtrate: 27 29 1,369 100 5.8
Fiber: 38,084 20 39,950 --- 6.0
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This was the highest fiber recovery of the tests
using only a vacuum nozzle and approached 4~. The fiber
at this consistency can be directly recycled to the
paper machine system. Obviously, the couch roll and
vacuum combination would be the most effective way to
retrieve and thicken fiber from the foam medium up to 19%
consistency for storage or disposal.
A more typical run as a "saveall" using the same
white water feed stream and foam medium, with the drum
turning at 2.0 RPM, produced the following data~
Elapsled time: 24 hours (foam use)
Flow ~rate in): 178 GPM (gal./min.)
Flow ~rate through): 6.0 GFM (effective area gal./ft.2/
min.)
Vacuum: 8 in. (water ~ P)
Stream: TSS ASH TS T PH
(PPM) (%) (PPM) (F.)
Feed: 2,594 15 3,574 82 5.3
Filtrate: 67 63 1,537 82 5.4
Fiber: 24,912 13 26,37~ 81 5.1
Recovery of suspended solids from pulp mill process
streams using the foam filter fiber retrieval apparatus of
the invention can be sustained rnany hours. This is sig-
nificant because these systems typically handle between
6.5 and 20.5 tons of fiber per day. Analysis of the recov-
ered fiber, including freeness, viscosity, permanganate
number, and fis)er length, shows they are all typically in
the normal range for desirable asld useable fiber.
