CA2312281C - System for washing porous mat - Google Patents

Abstract

A shower for removing chemicals from a mat of porous material impregnated by the chemicals has an elongate housing defining a chamber. The housing has a longitudinal slot adapted to be positioned so that the slot opens toward the mat. A pressurized dispersion pipe extends through the elongate chamber above the longitudinal slot. The pipe has at least one inlet to receive cleaning liquid into the pipe and defines a plurality of spaced apart holes positioned along the length of the pipe within the housing through which the cleaning liquid can flow into the chamber. The holes are of varying size with the largest holes being located nearest the inlet and the smallest holes being located farthest from the inlet.

Description

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.

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.
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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 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.

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.

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.

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 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.

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 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 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.

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.

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 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 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 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.

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.

Claims (9)

Claims:

1. A shower for removing chemicals, impurities and dissolved solids from a mat of porous material impregnated by the chemicals, the shower comprising:

an elongate housing defining a chamber, the housing having a longitudinal slot adapted to be positioned so that the slot opens toward the mat; and a pressurized liquid dispersion conduit extending through the elongate chamber above the longitudinal slot, the conduit having at least one inlet to receive cleaning liquid into the conduit, the conduit defining a plurality of spaced apart holes positioned along the length of the conduit within the housing through which the cleaning liquid can flow into the chamber, the holes being of varying cross sectional dimension so as to enhance the uniformity of flow of cleaning liquid into the chamber and throughout the slot to the mat.

2. The shower of claim 1 wherein the cross sectional dimension of a plurality of holes a first distance from the inlet is larger than the cross sectional dimension of a plurality of holes a second distance from the inlet, the second distance being further from the inlet than the first distance.

3. The shower of claim 1 wherein the holes of the largest cross sectional dimension are located nearest to the inlet.

4. The shower of claim 1 wherein the holes in the conduit are formed in the upper half of the pipe so the cleaning liquid leaves the pipe in an upward and outward direction.

5. The shower of claim 1 wherein:

the conduit includes end portions, the conduit being secured to and extending through and beyond first and second ends of the housing; and wherein the housing is supported by the conduit.

6. The shower of claim 1 wherein the conduit has an inlet at only one end.

7. The shower of claim 1 wherein:

the conduit has inlets at both ends; and the largest holes are located nearest the two inlets and the smallest holes are located midway between the two inlets.

8. The shower of claim 1 where the holes have more than two sizes and hole size decreases progressively as a factor of distance from the inlet.

9. The shower of claim 1 including a slice assembly for directing the cleaning liquid from the slot to the mat, the slice assembly including a hinged slice portion.