Note: Descriptions are shown in the official language in which they were submitted.
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System for Washing Porous Mat
Background of the Invention
This invention relates to washing systems wherein liquid is passed through a
porous
mat disposed on a screen over a vacuum head.
Various industrial processes require that a mass of porous material be washed
in order
to remove chemical or other impurities. For example, this need appears in the
sugar
industry, where sugar is washed from bagasse; in the textile industry where
excess
dyes are washed from fabric; in mining where impurities are washed from ore;
and in
the paper industry.
In a standard paper production line, wood chips are cooked with chemicals in
aqueous
solution, the precise composition of the cooking chemicals depending on the
particular
process and desired paper product. This step, normally carried out in a
digester under
heat and pressure, breaks down the wood by dissolving the organic compounds
that
hold the cellulose fibers together.
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The mixture of pulp, spent cooking chemicals, and organic materials,
collectively
known as stock, is then fed to a series of washers. The most common type of
washing system includes a rotary vacuum drum onto which the stock is spread as
a
mat. The drum has a cylindrical, porous outer surface, most commonly a screen.
A
negative pressure is maintained inside the drum, such that liquid in the mat
is pulled
into the interior of the drum and thereby separated from the pulp. A shower,
that is
disposed above the mat and extends axially along the drum, directs relatively
clean
liquid at and through the pulp mat to wash out chemical substances, dirt and
organic
solids. Typically in the brown stock area, there are three drums in sequence
with wash
liquid flowing from drum to drum countercurrently to the direction of the pulp
movement. Each drum can have multiple showers to direct wash liquid at its
pulp mat.
The final effluent from the drum washing operation is black liquor containing
water,
spent cooking chemicals, dirt and organic materials. Such liquor typically
contains
approximately 15% solid material, which must be separated from the water to
allow
reuse of the inorganic pulping chemicals in the liquor. Separation of the
water and
solids also reduces environmental problems when disposing of the liquor.
The solids and water are typically separated by an evaporation process in
which the
liquor passes through a series of evaporators. Within the evaporators, steam
moves
countercurrent to the liquor flow until the liquor is concentrated to a 60%
solids
content, at which point the liquor is burned in a boiler. The solid organic
materials
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provide the fuel to generate steam for the evaporators, and inorganic
chemicals smelt
out the bottom of the boiler to be reused. The steam from the liquor recovery
part of
the cycle supplies most of the mill's steam needs.
It is apparent that the more dilute the liquor, the more energy must be
expended in
evaporating the water to recover the solids. At the same time, it is necessary
to
efficiently remove the chemicals from the pulp to provide a satisfactorily
clean pulp.
Thoroughly washing the mat improves the efficiency of chemical removal, but
the
large quantity of water typically required for thorough washing with existing
showers
forms a dilute liquor that requires a high expenditure of energy to separate
water and
solids.
Water typically is supplied to a pulp mat by showers that direct a stream of
washing
liquid towards a rotating mat. But such showers are often unable to evenly
distribute
water across the drum. This is because in elongated showers, typically there
is a high
liquid flow at one end of the shower adjacent to the liquid inlet to the
shower,
gradually decreasing to a low flow at the opposite end spaced from the inlet,
or
furthest from the inlets if plural inlets are used. Pressure is also lower at
the high flow
areas of the shower. The mat is therefore washed unevenly across its width.
This is
wasteful because, when sufficient cleaning liquid is supplied to adequately
treat or
wash the whole mat, an excessive amount is applied in some areas.
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Accordingly, there remains a need for a mat washing system that will more
evenly
distribute washing fluid over the width of a pulp mat.
SUMMARY OF THE INVENTION
It has now been discovered that the uniformity of distribution of a washing
liquid is
enhanced by supplying the liquid via an improved shower. The shower is
generally of
the type shown in U.S. Patent Nos. 4,616,489 and 4,907,426, the disclosures of
which are incorporated by reference. Water is delivered to the mat from an
elongated
housing. A pipe, having a series of holes along the side of the pipe, extends
through
the chamber allowing water or other cleaning liquid to be forced through the
pipe and
through the holes in the pipe into the chamber. The cross-sectional area of
the
openings is varied and arranged along the pipe in such an order that cleaning
liquid
flows more evenly to all regions of the chamber. For example, a plurality of
holes of
varying cross-sectional dimensions may be positioned along the pipe with holes
of the
largest dimension positioned in relatively high fluid flow areas of the pipe
(e.g.,
adjacent to one or more fluid inlets) and holes of the smallest dimension
positioned in
relatively low fluid flow areas of the pipe (e.g., farther from the inlet or
inlets).
This shower distributes liquid more evenly across the entire width of the mat
than has
heretofore been possible.
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Brief Description Of The Drawings
FIG. 1 is an oblique view showing the exterior of a shower of the present
invention
above a rotating drum in a pulp washing line;
FIG. 2 is an enlarged, sectional view of a shower of the type shown in FIG. 1;
FIG. 3 is an enlarged, partial sectional view of a shower of the type shown in
FIG. 1,
showing an alternate attachment of a slice or sluiceway;
FIGS. 4 and 5 are side elevational views of a hinged slice suitable for use
with the
showers of FIGS. 2 and 3;
FIG. 6 is a top plan view of a manifold pipe shown in FIG. 2; and
FIG. 7 is a vertical, sectional view taken along line 7-7 of FIG. 6;
FIG. 8 is a vertical, sectional view taken along line 8-8 of FIG. 6;
FIG. 9 is a vertical, sectional view taken along line 9-9 of FIG. 6.
FIG. 10 is a vertical sectional view of an alternative embodiment of a shower.
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Detailed Description
The present invention aids in the washing of chemicals and other substances
out of a
mat by maintaining a uniform body of washing liquid in contact with the
outside
surface of the mat. The mat is typically disposed on a porous moving surface,
such as
a screen, over a vacuum head, such as provided by a rotary vacuum drum.
FIG. 1 shows one form of a shower 10 positioned above a wood pulp mat 12 that
is
formed on a rotary vacuum drum 14 that rotates about a horizontal axis in the
direction of arrow 16. Stock, that includes pulp, spent cooking chemicals,
dirt and
water, is continuously fed from a digester (not shown) into a vat (not shown)
where it
forms a pool in which drum 14 is partially submerged. Drum 14 has a perforated
outer
shell through which a partial vacuum inside the drum is communicated to the
outside.
As drum 14 rotates, pulp mat 12 forms on the outside of the drum and liquid is
withdrawn by the vacuum into the drum. It is not unusual for drums of this
type to be
from ten to thirty-six feet long.
At a position generally near the top of the drum, the mat passes under one or
more
showers 10 that remove chemical impurities by displacement washing. To
simplify the
description, only one shower 10 is illustrated and described; but, in
practice, a
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plurality of showers are included in a washer. These other showers may be
structurally similar to shower 10.
The vacuum between mat 12 and drum 14 is released at a position that is
approximately ten degrees past top center. Subsequently, the pulp mat
separates from
the rotating drum. The separation of the mat from the drum is typically
accomplished
by a doctor blade (not shown) that may either be a mechanical device or a
linear array
of nozzles directing pressurized air upwardly underneath the mat.
Shower 10 in the form shown includes an elongated chamber defined by sidewalls
32,
34 that extend axially with respect to drum 14, end walls 36, inwardly sloping
top
panels 38,40, and inwardly sloping bottom panels 42, 44. The illustrated
chamber is
thus of a generally hexagonal cross-section, but may assume other
configurations.
The sidewalls and panels are typically made of a durable corrosion resistant
material,
such as of 12 gauge stainless steel. Sloping panels 42, 44 are angled toward
one
another but terminate before they meet, thereby defining an elongated slot 48
extending axially along the bottom of the chamber. Each of sloping panels 42,
44 is
provided with a respective neck section 50, 52 (FIGS. 2 and 3) that extends
along the
length of the sloping panel and depends downwardly towards mat 12. The
respective
neck sections 50,52 terminate in outwardly directed supporting flanges 53,55.
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A gap adjustment mechanism 54 is provided at the base of the flanges 50,52.
The
illustrated adjustment mechanism is an elongated flow adjuster bar 56 that
bolts to the
outturned portion 55 of the neck section 52. The bar 56 may comprise multiple
pieces aligned end-to-end. In this approach, either the flange 55 or bar 56
typically
contains bolt-receiving slots so the bar 56 can be moved to the left or right
as viewed
in FIG. 2, and then secured in a desired position, such as by bolts 58 and
nuts 60.
A pipe 98, such as a 3-inch schedule 40 pipe, extends through chamber 11 and
end
walls 36 and 40. Pipe 98 is mounted on a pair of end mounts (not shown). An
inlet
hose 86 (FIG. 6) is attached to one end of pipe 98, with the other end being
capped in
this example. For long showers, inlet hoses can be attached at multiple
locations,
such as to both ends of the pipe 98.
The pipe 98 has fluid delivery openings along its length such as a plurality
of apertures
102 spaced along its length. The illustrated apertures are shown located above
the
horizontal axis 104 of pipe 98 and positioned along the length of the pipe
between the
end walls 36. A shower support such as a radial fin 106 is welded or otherwise
secured to the pipe 98 and extends upwardly and outwardly of the casing
between
the top panels 38,40. The circular section of pipe 98 together with the other
aspects
of shower 10 create a strong structure and allows the pipe to easily support
the
shower assembly. For example, it has been found that a standard 3-inch
schedule 40
pipe may be used in showers 10. The components surrounding the pipe and
defining
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the channel within which pipe 98 is positioned may be unreinforced planar or
flat
components or of other simplified constructions as the pipe 98 and shower
support
provide primary support for the structure.
As seen in FIGS. 2 and 6-8, the apertures 102 may be circular holes aligned
with short
tubes 110 (more specifically tubes 1 10A through 1 10C) that serve as upwardly
directed nozzles which direct the flow of liquid toward the panels 32, 38, and
34, 40.
The respective tubes 1 10A, 1 10B and 1 10C may be of a durable material such
as
1.25 inch schedule 40 pipe; 1.0 inch schedule 40 pipe and 0.75 inch schedule
40 or
80 pipe. The nozzles in the illustrated construction are arranged in two rows.
Although variable, as seen in FIG. 2 the nozzles of the two rows in the
illustrated form
are separated by an angle 0 which is, in the illustrated example, one hundred
and
twenty degrees. Each row of nozzles is thus inclined at an angle of sixty
degrees from
the plane of the pipe supporting fin 106 which extends vertically upwardly
from the
pipe 98. The angle of the openings may be altered, but upwardly directed
openings
are advantageous.
The illustrated nozzles and holes are not of uniform size, but vary in cross-
sectional
area, such as in diameter in the case of circular holes, as a factor of
distance from the
pipe inlet to enhance the uniformity of washing fluid flow toward the mat.
Thus, the
cross-sectional dimension of the fluid delivery openings is varied to increase
the fluid
flow through the openings at locations where fluid flow would tend to be
reduced due
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to pressure and flow variations in the pipe and to decrease the fluid flow
through the
openings at locations where fluid flow would tend to be increased. This may be
accomplished by increasing the cross-sectional area of fluid flow openings
adjacent to
the fluid inlet or inlets (where fluid flow tends to be at a higher velocity
and pressure
lower) than openings further from the fluid inlet or inlets (where fluid flow
would tend
to be lower and pressure would tend to be higher). Typical fluid pressures in
pipe 98
would be on the order of five to six psi.
In the illustrated embodiment, nozzles of three different diameters are
located in three
different portions or zones of the pipe 98. In a zone A, nearest the single
inlet 86 in
the FIG. 6 example, the nozzles 1 10A have the greatest cross-sectional area.
In a
central zone B, the nozzles 1 10B have a cross sectional area of intermediate
size.
And, in a zone C, furthest from the inlet, the nozzles 1 10C have orifices 1
02C of the
least cross sectional area. Although variable, as a specific example, the
cross
sectional area of openings 1 10A may be 1.25 inches, the area of openings 1
10B may
be 1.0 inch, and the area of openings 1 10C may be 0.75 inch.
As seen best in FIG. 1, the shower 10 has a slice or sluiceway device or
assembly 70
that extends the width of mat 12. Figs. 2 and 3 show a one-piece slice device
that
collects water in a pool 126 for delivery to the mat 12. The device 70 is
typically
made of a corrosion resistant material, such as stainless steel or fiberglass.
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In the embodiments of FIG. 4 and 5, the slice assembly 70 has multiple parts
including
a top member 72, a hinge mechanism 78 and a concave fiberglass slice portion
88.
The slice portion 88 is hingedly mounted so that it can pivot between various
positions, such as shown in solid and broken lines in FIGS. 4 and 5.
The top member 72 may have a flange 82 (see FIGS. 2 and 4) that can be used to
bolt
or otherwise secure the slice device to the shower body (e.g. to flange 53),
as shown
in FIGS. 2. Alternatively, as shown in the embodiments of FIGS. 3 and 5, the
member
72 may have an enlarged portion, such as a square cross section upper lip 74
that
slides into a bracket 66 to hold member 72 in place. Other mounting approaches
may
also be used.
The distal edge 92 of slice portion 88 rests on mat 12 and forms a floating
seal that
deters liquid from flowing backwardly between distal edge 92 and mat 12. The
illustrated slice portion 88 is generally concave, merging with the mat 12 in
the
direction of drum rotation. Radially extending dams 94 (FIG. 1) are provided
at the
ends of the slice device to inhibit washing fluid from flowing out from the
ends of the
slice device from a body of standing fluid located in the concave lower
portion of the
slice device. Intermediate dams 96 may also be used as dividers to create
several
pools of water along the slice device or to inhibit or prevent flow along some
sections
of the slice. For example, fluid flow into the space between dams 96 may be
blocked
such that no fluid is delivered to the drum at this location.
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The illustrated hinge mechanism 78 is a flexible joint that may be a piece of
fabric-like
material (such as of Kynar) that pivotally interconnects member 72 with slice
portion
88. The web 78 may be attached to the slice portion 88 between a proximal edge
90
and a distal edge 92 of the slice portion 88. The fabric may also be a sheet
of woven
glass fabric coated with Teflon (polytetrafluoroethylene) polymer. Any other
corrosion
resistant flexible material may be used for the hinge.
Water entering chamber 11 of shower 10 through pipe 98 flows through apertures
110, through slot 48 and into contact with the outer surface of pulp mat 12.
The
cleaning liquid collects behind slice portion 88 and forms a body of standing
liquid 126
that is sufficiently deep to rise above distal edge 92 and contact the outside
surface of
mat 12 across its width. The flow of liquid from shower 10 is regulated such
that the
vacuum in drum 14 draws liquid 126 through mat 12 at a rate sufficient to
maintain
the depth of the body of liquid 126 at a substantially constant level above
distal edge
92. The prolonged contact between body of liquid 126 and mat 12 and enhanced
uniformity of fluid delivery from pipe 98 as explained above increases the
efficiency of
washing by improving the even distribution of washing liquid across mat 12.
Liquid is
constantly drawn through the mat to wash chemicals and dissolved solids out of
it.
If mat 12 is uneven, slice portion 88 pivots about hinge fabric 78 to
accommodate
irregularities in thickness of mat 12 while retaining the body of liquid 126
at a
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substantially constant depth. If clumps of material are present on mat 12,
distal edge
92 of slice portion 88 rides over and smoothes the clumps into the surface of
mat 12.
If all the nozzles and fluid delivery openings were of uniform cross-sectional
area and
spacing, there would be an uneven distribution of water inside the casing.
This is due
to fluid flow and pressure variations that exists along the length of the
interior of the
pipe or other conduit. By selecting nozzles or openings of plural sizes and
appropriately positioning them in along the pipe such as in the illustrated
example,
variations in fluid delivery is compensated for and substantially equal liquid
flow
occurs through all the nozzles.
It will be appreciated that, with only three nozzle sizes, the flow will not
be perfectly
uniform. If more nozzle sizes are used, flow uniformity can be further
improved. But
for most operations, it is cost effective to use three sizes of nozzles. Some
improvement is achieved when nozzles of only two cross sectional areas are
used.
But three or more is superior to two. Other orifice configurations which
enhance fluid
flow uniformity may also be used, but a series of plural discrete openings of
varying
sizes has proven effective.
Having illustrated and described the principles of the invention in preferred
embodiments, it should be apparent to those skilled in the art that the
invention may
be modified in arrangement and detail without departing from such principles.
For
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example, the showers for a particularly wide washer may be fed by more than a
single
inlet hose 86. In such washers, a conduit, or plural conduits joined end-to-
end inside
the casing, may be fed from plural locations, such as fed by two inlet hoses
each
attached to a respective end of the pipe or conduit. In such an embodiment, if
openings having a uniform cross sectional area and spacing were used, the
liquid
pressure gradient inside the combined pipes is not a continuous progression.
Instead,
in this case, the pressure is greater midway between the ends of the joined
pipes and
progressively decreases toward the free ends where the fluid supply inlets are
located.
To compensate for this inverted, V-shaped pressure gradient pattern, nozzles
of the
greatest size may be placed near both free ends of the pipe and nozzles of
smaller
orifice size may be placed near the center of the joined pipes. This means
that for a
system having nozzles in three sizes, the nozzle zones would be arranged, for
example, in an A-B-C-C-B-A order. As another example, the openings may be of a
constant size with extra openings being provided in areas nearest the inlet or
inlets to
thereby increase the cross-sectional area available for fluid flow at these
otherwise
low flow areas. Other approaches may also be used to provide a fluid flow
passageway with an increased cross sectional area available for fluid flow
from the
pipe at locations where (e.g. near inlets) fluid delivery is to be increased
and with a
decreased cross sectional area available for fluid flow at locations (e.g.
spaced from
inlets) where fluid delivery is to be reduced.
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Also, although the illustrated embodiments show showers equipped with slice
devices
70, it should be understood that the multi-sized nozzle or aperture
arrangement shown
and described in relation to FIGS. 2 and 6-10, can be advantageously employed
in
showers that deliver washing liquid to a mat by means other than a slice
device.
The embodiment of FIG. 10 includes a double wall chamber surrounding the fluid
delivery pipe 98. The wall sections are indicated at 32, 32'; 34, 34'; 38,
38'; 40,
40'; 42, 42'; and 44, 44'. The space 130 is filled with a reinforcing
material, such as
balsa wood. In this construction, the wall sections are, for example, made of
fiberglass. Also, the flange 106 in this example terminates in an arcuate pipe
supporting portion 200 which engages and supports the upper portion of the
pipe. In
this case, the fluid delivery openings 102B (for example) pass through the
pipe and the
pipe supporting portion. Nozzle extensions may be associated with these
openings.
Also, the lower slice assemblies 70 may assume different configurations, and
may lack
a hinge element. A number of these configurations are shown in dashed lines in
FIG.
10.
All modifications which fall within the spirit and scope of the following
claims form a
part of the present invention.
