CA2009328A1 - Pulp washing apparatus and process - Google Patents
Pulp washing apparatus and processInfo
- Publication number
- CA2009328A1 CA2009328A1 CA002009328A CA2009328A CA2009328A1 CA 2009328 A1 CA2009328 A1 CA 2009328A1 CA 002009328 A CA002009328 A CA 002009328A CA 2009328 A CA2009328 A CA 2009328A CA 2009328 A1 CA2009328 A1 CA 2009328A1
- Authority
- CA
- Canada
- Prior art keywords
- drum
- pulp
- mat
- washing
- plenum
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D1/00—Methods of beating or refining; Beaters of the Hollander type
- D21D1/20—Methods of refining
- D21D1/40—Washing the fibres
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
- D21C9/06—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents in filters ; Washing of concentrated pulp, e.g. pulp mats, on filtering surfaces
Abstract
Abstract of the Disclosure An improved pressure washer and process are disclosed for washing cellulose pulp, wherein a mat of pulp is provided on a rotating drum and moves through a washing zone and a dewatering zone between the mat formation zone and a mat removal zone.
A hood is provided over the drum, with appropriate seals, and a pressurized atmosphere is provided in the washing and dewatering zones. To relieve the pressure which normally builds up inside the washer drum, a conduit is connected between the drum interior and the inlet of the blower used for pressurizing the hood. In this way, foam generation is minimized as the drum interior is maintained at or below atmospheric pressure. A take-off roll, or doctor, is provided for removing the mat from the drum.
A hood is provided over the drum, with appropriate seals, and a pressurized atmosphere is provided in the washing and dewatering zones. To relieve the pressure which normally builds up inside the washer drum, a conduit is connected between the drum interior and the inlet of the blower used for pressurizing the hood. In this way, foam generation is minimized as the drum interior is maintained at or below atmospheric pressure. A take-off roll, or doctor, is provided for removing the mat from the drum.
Description
Ms258802104 -2;~
Patent Application E`or:
PULP WASHING APPARAT~S A~n PROCESS
Back~round of the Invention i. Techn l Field This invention relates generally to the field of papermaking, and more particularl~ to pulp production for ,capermaking. Specifically, this invention pertains to an apparatus and process for washing pulp.
ii. Prior Art In the papermaking process, wood chips, or other fiber source materials, are cooked with chemicals at elevated temperatures ana pressures to remove binders such as lignin, which hold the fibers together. During the cooking process, or digestion, various compounds and comple~es are ormed in the Cooking liquor. Large quantities of chemicals are used in the cooking process, and, even if inexpensive, chemical recovery is a cost-efficient measure. Evel more restrictive environmental standards necessitate proper handli.ng and treatment of all effluent components. Therefore, efficient pulp washing procedures are beneficial as well as necessary.
It is desirable, therefore, to separate the lisuor, as well as the compounds and complexes formed during the cooking process from the fi.bers after cooking is complete, so that each can be passed through proper disposal, reclamation, or other processes.
~ ~`8 The goa] of pulp washin(3 is to obtai.n pul~ essentially free from soluable impuriti.es. A preferred washing system would con-.pletely remove waste liquor and other impurities while using only a minima~ amount of wash liquid. For chemi.cal recovery and/or other subsequent waste li.quor processing any wash fluids added during the washing stage must also be treated, either by evaporation or other means. Therefore, it is desirable to minimize the amount of wash fluid added during the washing process. The papermaking industry has adopted the term dilution factor" in assessing the efficiency of wash systems with respect to the anmount of wash fluid used. The dilution factor can be described as the amount of water or other wash liquid put into the systen, and not taken out of the system with the washed pulp as the pulp is renmoved from the system. If the auantity of wash fluid added is equal to the quantity of washed fluid passing from the system with the pulp, the dilution factor is 2ero. Low dilution factors aLe therefore desi.rable.
Early processes for pulp washing can be described as dilution washing. This type of washing often was performed in digester blow pits or in separate vessels, and essentially consisted of successive stages wherein wash liquid was added to a drained volume of pulp to dilute the remaining liquor contained in the pulp, and the then-mixed liquor and wash liquid were drained from the pulp. Compacti.on was sometimes used to further assist the removal of diluted liquors, and several stages of successive dilution and draining were employed.
2 ~
Such diluti.on techniques were inherently inefficient, had high dilution factors, and became inappropriate as the need for efficient cher,~ical recovery grew, and as the environmental standards besan requiring treatment of all pulp mi.ll effluents.
A second, more effi.cient type of washing was pursued, generaliy characterized as di.splacement washins. In displacement washing techniques, diffusion of the wash liquid through the pulp material is controlled to avoid mixing, and the wash liquid merely replaces the liquor in the pulp. Early forms of displacement washing occurred as batch processes in large tanks separate from the digester known as diffusers.
E~.owever, because of the characteristics of pulp fibers, channelling, or tunnelli.ng, through a large pulp column often occurred, anà wash liquor would pass through a pulp column while bypassing entrapped liquor volumes held by fiber networks.
~ herefore, to increase washing efficiency and thorouyhness, apparatus to senerate pulp m.ats in washing devices were devised, which provided more uniform drainage and more consi.stent washing through smaller volumes of pulp at a tirne~ Operation was on a more-or-].ess conti.nuous basis, with pulp entering and leavi.ng the devi.ce conti.nuously as washing occurred.
~ arly pulp washers of thi.s type, sometimes referred to as gravity deckers, consisted of perforated drums rotating in large vats of stock. Because of the drainage resistance through the perforated rotatins drum, and the resulting ~93-~;$
differenti.al in fluid levels inside and outside the drum, hydraulic pressure differences between the stock and the interior of the arum, caused a mat to form on the drum as the drum rotates. The liqui.ds in the stock passed throush the mat alld the roll as the result o gravity as the roll rotated, and gravity deckers di.d not have high hydraulic capacity.
Drainage through the mat was the result o~ gravi.ty alone.
To increase drainage through the mat and drum of gravity deckers, the interior of the drum was partially evacuated b~
the use of a hydraulic drop leg to cLeate a parti.al vacuum, while the area above the mat remained at atmospheric pressure.
The increased pressure differerltial between the atmos~heric area outside the drum and the low pressure area inside the drum improved drainage through the mat and allowed showers to be used. r~ash li~uid sprayed through nozzles di.splaced the li.auid ill the mat.
~ significant difficulty encountered with vacuu~. washers of this type relates to flashing of hot fluids. Generally, drainage of liquor through a pulp mat improves wi.th elevated temperatures, and higher temperatures therefore improve washi.ng efficiency. However, vacuu~. washers, which opeLate with up to mi.nus five psi (-5 psi~ in the drum created lower equilibri.um temperature conditions. Therefore, it was not possible to significantly raise the operating temperature of vacuum washers to further i.mprove the drainage characteristics.
~1B258802 104 '2'~
Gravity deckers and vacuum washers, as described above, included outer housings and hoods to contain liquor and odors within a confined area. As an alternative to vacuum washers, and to improve drainage through the pulp mat while, at the same time, avoiding the problems of flashing which occurred in vacuum washers, it was discovered that the hood around the ~asher could be ~rovided with a seal, and a blower used to increase the air pressure above the mat within the sealed hood area The pressure washer operated with a positive pressure (i.e. above atmospheric pressure) in the hood, and a slightly higher than atmospheric pressure in the drum. Mat formation occurred as in previous washers in which the rotating drum picked up a fiber mat from a vat of slurr~. The pressure washers of this type also utilized showers in the wash zone, for displacing the liquor from the cellulose fibers. However, feed consistencies were limited on pressure washers, as in gravity deckers and vacuum washers, to about one to one and one-half percent (1 - 1~%). At higher feed consistencies clumpy mat formation occurred! and drainage characteristics varied significantly throughout the pulp mat, resulting in inconsistent washing.
A subsequent development in the art of pressure washers was the utilization of a headbox, or similar device, for distributing the stock on a foraminous drum, to replace the vat pick-up techniques used in gravity deckers and early vacuum and pressure washers. Headbox-like devices through the input of energy maintain the stock in a fluidized state, allowing the use of higher stock consistencies with impro~ed mat formation. A distinct separation could be created between the formation zone and the washing zone of such washers, allowing new washing techniques to be utilized. In one such technique, the mat forms the base of a pond of wash fluid thereabove, and ~he wash fluid drains through the pulp mat as the foraminous roll rotates.
In either this or earlier types of pressure washers, the air or other gas supplied to the hood to pressurize the hood permeates the mat and drum to cause an overpressure in the interior of the drum. Thus, both the hood and the drum operate at above-atmospheric pressure, with the hood being at a higher pressure, generally, than the drum interior.
At the end of the washing zone and a subsequent dewatering zone, the fiber mat paCses to a repulper, screw conveyor or other apparatus, which aenerally operate at atmospheric pressure. A seal is provided between the pressuriæed zones and the non-pressurized mat take-off area. Since the interior of the drum is at overpressure, a pressure di~ferential e~ists between the drum interior and the talce-off area, with the drum interior being at higher pressure. Thus, pressure from the drum attempts to escape from the drum, blowing the mat from the drum surface and into the repulper or screw conveyor.
This was generally considered to be advantageous for pulp removal, and, in fact, in some pressure washers bypass conduits have been provided from the washer hood to the drum interior to even further increase the overpressurization of the drum interior, to aid in blowing the mat from the drum.
~9~
In some circumstances, the escaping air from the drum has undesiLable effects. Because of the nature of washing, the interior surfaces of the washer become coated with a thin layer of black liquor. Air escaping from the drum and impinging on the liquor covered surfaces in the take-off area, generates a foam with the liquor, which entraps air bubbles. The foam becomes mixed with the pulp in the repulper and is passed with the pulp to subsequent washing stages or other treatment steps. Air in the pulp is generally undesirable, in that drainage is reduced and subsequent wash stages are, therefore, less efficient. In the past, this has been compensated for by the use of defoaming agents, or by the use of larger downstream washers to achieve the desired degree of washing in spite of the reduced drainage characteristics of the pulp.
However, with certain types of pulp, foaming becomes an even more significant problem, and the additional equipment cost for subsequent wash stages is economically undesirahle.
Additionally, large volumes of defoaming agents can be expensive, and their use may not be totally without hazard.
Summary of the Inventi~n It is, therefore, one of the primary objects of the present invention to provide an apparatus and process for washing papermaking pulp which is efficient in displacing liquor and impurities from the pulp, and which washes the pulp in a process having low dilution factors.
Another object of the present invention is to provide a pulp-washing apparatus and process which minimizes foam Ms258802104 2~ 2~
generation while washi.ng pulps with high foam generation characteristics.
Yet another object of the present invention i.s to provide a pulp-washing apparatus and process which operates as a continuous, flow-through pulp washing process.
Still another object of the present invention is to provide a pulp washer drum pressure relievi.ng system which can be added easily, quickly and inexpensively as a retrofit to exi.sting pressure washers.
These, and other objects, are achieved in the present invention by providi.ng in a pressure washer apparatus for removing the overpressure from the inside of the washer drum.
This can be achi.eved in a variety of structures. In a preferred embodiment, the intake for a blower supplying air to pressurize the washer hood is connected to the drum interior, thereby securing its flui.d supply, at least in part, from the drum interior. The i.nlets to the pressurizing blower can be controlled in such a manner as to provide vari.ous levels of negative pressuri.zation within the drum, thereby i.ncreasing the pressure di.fferential between the washer hood and drum i.nterior, to maximize fluid drainage through the pulp mat.
Since the hood area remains pressurized, drainage can be improved, and foami.ng reduced using only minimal negative pressures in the drum. Therefore, the pressure/vacuum washer of the present invention does not suffer signifi.cantly from the problems of flashi.ng experienced in other vacuum washers.
20~9328 High wash temperatuLes can be maintained to still further improve draining.
Relief of pressure in the drum can be achieved independently from the blower system used to pressurize the hood; however, economies of operation and installation costs can be achieved by combining the pressure relief system for the drum with the pressurizing system for the hood. In one such practical installation, a pipe with flow control means is provided between the drum interior and a plenum above the repulper in a pressure washer. The blower intake is connected to the plenum, and a common wall between the plenum and the repulper also includes a valve apparatus Lor controlling the flow of air therethrough. In this manner, the air provided to the plenum can be controlled between the supply from the repulper area, which is atmospheric, and the drum area, which is sealed and, but for relief through the present invention, would be at greater than atmospheric pressure. In this manner, the pressure in the drum can be maintained at atmospheric pressure, or at various levels of subatmospheric pressure.
Alternatively, the pressure relief system for the drum interior can be independently connected to the blower inlet apart ~rom the repulper plenum; or, as mentioned previously, a separate evacuation system with scrubbers discharging to atmosphere can be used to relieve pressure in the drum.
2~932~
Any of a number of apparatus may be utilized for removing the pulp mat from. the drum at the outlet si.de of the washing zone, including steam doctors, water doctors, or the like.
Additional objects and advantages of the present invention will become apparent from the detailed description and the accompanying drawings.
Brief Description of the Drawings Fi.gure 1 is a si.de-elevational view of a pulp washing apparatus employing drum pressure relief embodying the pLesent invention.
Figure 2 is an enlarged view of the mat formation zone of the pressure washer shown i.n Figure 1.
Figure 3 is an enlarged view of the mat removal zone in common pressure washers of the prior art.
Figure 4 is an end-elevati.onal view of a typical pressure washer with the end wall removed, exposing the internal regions of the washer.
Figure 5 is a si.de-elevational view of a suitable arrangement for the pressure relief apparatus of the present invention.
MB25~802104 2~09~28 Figure 6 is an end view of the pressure relief apparatus -~hown in Figure 5.
Detai.led Descripti.on of the Preferred E _odiment Referring no~ more specifically to the drawings, and to ~igure 1 i.n particular, numeral 10 designates a pressure pulp washer embodying the present invention, which employs the use of a drum pressure relieving apparatus 12.
Pulp washer 10 includes generally, as viewed externally, a housing 14 consisting of a vat 16 and a hood 18. Hood 18 i.ncludes a generally semi-cylindrical sidewall 20, and end walls 22 and 24. The vat and hood enclose the washer to allow pressurization and to contain the liquids and fumes within the washer. A variety of viewing ports 26 and manhole-type access ports 28 are provided at appropri.ate locations in the vat or hood for observation of the washing process and/or for performing minor adjustments or repairs.
It will be recogni.zed by those skilled in the art that the general arrangement, outside configuration, and ~iping to and from the washer may vary consi.derably, depending on the specific type of washer, and the installation in which the washer is provided. Therefore, the general washer embodiments described heretofore and subsequently are for illustrative purposes in explaining operation of the present invention, and do not, in and of themselves, limit the application of the pressure-relieving concept of the present invention.
MB258~302104 2~'9~8 r~eferring now with more particular reference to Figure 4, alld others of the drawings, the general washer apparatus will be described in ~.ore detail. A washing drum ~0 is disposed within the vat and hood, and is suitably journaled at its ends for rotation therein. Drum 40 includes a honeycomb-like support structure 42, and a foraminous surface material 44 disposed on the honeycomb support structure. A dri.ve means 46 is provided for rotating the drum 40 ~ithin the vat and hood, and rotates the drum in a clockwise direction, as viewed in ~i.gure 2 and indicated by the arrow indentified by numeral 47.
Drum 40 receives and supports a mat of pulp fibers, carrying the fibers between a mat formation zone 50 and a mat removal zone 52, while passi.ng through first a washing zone 54 and, second, a dewatering zone 56.
The mat formation zone 50, as best shown in ~igure 2, includes a formation plate 60 and suitable adjustment mechanisms such as a pivotal support 62 and a plurality of posi.tion control apparatus 64 for controlling the position and attitude of the format.ion plate with respect to drum 40. The position control apparatus 64 may be pneumatic or electri.cally operated cyli.nders, mechanical screw devices, or other suitable apparatus for controllably moving formation plate 60.
A headbox 66 receives a flow of pulp slurry, and deposits the p~lp in a generally uniform distribution along the drum surface at the inlet edge of formation plate 60. Generallyr formation plate 60 is controlled in position such that a region of convergence towards the drum 40 is defined between the drum and the formation plate, so that, as the stock mat Ms258802l04 2 ~
rotates from the formation end of the screen plate toward the was~iing zone 54, the mat is slightly com~acted.
Washing zone 54 extends from the formation plate 60, and includes a pond of wash liquid 70 to displace the liquor, or other liquid, in the pulp mat, which displaced liquid flows through the mat, the forarninous drum surf2ce and the honeycomb support structure, and is collected in the interior of drum 40 by ~o lection means not shown. The collected liquid, which may include some wash liquid, is then suitably collected and conducted from the washer. The pond extends generally from a sealed area at, or nc-ar, the elevation of headbox 66, upwardly through the upper left quadrant of the washer, as shown in Figure 2. Wash fluid supply is provided through an inlet 74.
When more than one wash stage is required, conventional wash showers may be included in the washing zone 54, and include shower pipes 76 and supply condui.ts 78, with appropriate valves 80. The wash showers spray additional displacing liquid on to the pulp mat as the mat leaves the pond 70.
The dewatering zone 56 extends generally along the upper half of the upper right quadrant of the washer, as seen in Figure 2, or generally from the last of the washing means, which may be the pond or last shower pipe 76, to a seal mechanism 82. In the dewatering zone 56, the stock is dewatered from a consistency of approximately eight percent (8%) upon leaving the pond, or last shower, to a consistency of from twelve to fourteen percent (12% - 14%) as the mat passes beneath the seal mechanism 82.
MB258802 lD4 2o0~328 In the mat removal zone 52, the pulp ma~ is separated from the drum and discharged into a repulper, screw conveyor or other ~uch device for further treatment or handling. A
repulper may be used to break-up the pulp mat and mix it with liquid to lower its consistency, if the pulp is to enter a second stage washer. A screw conveyor, on the other hand, mây be used if the pulp will be further processed or stored at the higher consistency ~resent following dewatering.
Drainage through the mat in the washing zone 54, and in the dewatering zone 56 is enhanced in that the area of hood 18 from the mat formation zone 50 up to the region of seal mechanism 82 is pressurized. A blower 84, having an inlet 86 and an outlet 88, is provided for pressuri%ing the hood.
Outlet 88 discharges into the hood in the was}iing zone 54, and, in the embodiment shown in Figure 1, inlet 86 is connected to a plenum 90 shown in Figures 4 and 5 above the mat removal zone 52.
The mat removal zone 52 following seal mechanism 82 is at atmospheric pressure, and air escaping from the above atmospheric pressure area of drum 40 through the foraminous surface material 44 to the atmospheric pressure area following seal 82 would blow the mat from the drum. This mat removal technique, utilizing air escaping from the drum, is used in prior art pressure washers and is illustrated for explanation purposes in Figure 3.
Seal mechanism 82 is provided to isolate the above-atmospheric pressure area within hood 40, along the 20~,~328 washing and dewatering zones, from the atmospheric pressure area Oî- mat removal zone 52. Seal mechanism ~2 includes a suppGr~ plate 100 which holds an inflatable bag 102 having a surface lining 104 of wear-resistant material. Inflatable bag 102 is inflated supplied and is forced against the surface material 104, to hold the material against the mat of pulp.
Water and air are provided to the inflatable bag through inlets 108, and is removed through a drain 110.
As thus far described, pulp washer 10 is a conventional pressure washer. As best seen in the enlarged view of Figure 3, in the conventional pressure washer, the drum interior designated by numeral 112 is pressurized by the air, or other pressurizing gas which permeates the mat 113 and foraminous drum surface 44 from the pressurized hood region 114.
~owever, as the mat 113 passes beneath seal mechanism 82, the mat 113 enters a region 116 of atmospheric pressure. As the mat 113 leaves the seal mechanism, a pressure differential exists, and the pressurized air in drum interior 112 escapes through the foraminous drum surface, as indicated by arrow 117 forcing the mat 113 off the drum 40 and into the mat removal zone. A receiving plate 118 may be provided for directing the mat toward the repulper, or other subsequent process apparatus.
To ensure separation of the mat from the drum, additional pressurization of the drum interior 112 was provided in some installations through conduits connecting the pressurized hood region 114 to the drum interior 112. While improving mat M~258802104 2~Q~8 separation from the drum the i.ncreased drurn pressure increased foam generation problems in the mat removal zone 54.
Drum 40 is seaied at its ends to the end walls 22 and 24 by conventional Lotating and nonrotating apparatus known to those knowledgeable in the art. According to the present in~ention a conduit 120 for evacuating the drunm e~tends through end wall 22 in a region within the sealed interior area 112 of drun) 40. At the end opposite that in conmunication with the drum interior 112 conduit 120 is connected to plenum 90 above the mat removal zone 52. Thus fluid pressuri.~ing drum interior 112 can flow through the cond~it 120 to the plenum 90. A valve mechanism 124 such as a sliding plate is provided to adjustably control the flow of flui.d through conduit 120. ~ithin plenum 90, a wall 126 includes a sliding gate 128 for controllably admitting air through an opening 130 from unsealed atmospheric regions of washer 10. If sliding gate 128 of wall 126 is closed, all inlet air to blower 84 is supplied through conduit 120 from drum interior 112. From the plenum 90, the air supplied from one or both of the conduit 120 or through the sliding gate 128 i.s drawn by blower 84 through its inlet 86 and discharged through its outlet 88 into the pressurized hood region 114. In this manner the pressure in drum interior 112 can be relieved.
Since i.nsufficient pressure remains in drum interior 112 to blow the sheet from the drum in the mat removal zone 52, a positive removal apparatus must be provided. Any of a number of such apparatus could be used, includi.ng a rotating roll for M~258~02104 2~ 9~
picki.ng the sheet from drum 40, water doctors, o~ steam doctoLs to separate the sheet from the drum.
In the use and operation of a pulp washer having a drum pressure reli.eving apparatus according to the present invention, a mat of pulp material is deposited on the foraminous surface material 44 of drum 40 in the mat formation zone 50. As the drum rotates, the mat i.s slightly compacted and enters the washing zone 54. Wash liquid from the pond 70 displace~ the fl~id in the mat, forcing the fluid through the foraminous surface material and i.nto the drum 40. Additional displacement type washing is provided from the shower pipes 76, and dewateri.ng of the mat occurs in known fashion throughout dewatering zone 56.
During operation, blower 84 draws air through its inlet 86 from the plenum 90. Discharge from blower 84 through its outlet 88 is into hood 18, thereby pressurizing the hood region 114, and improving drainage of the mat. By controlling the valve mechanism 124 and the sli.ding gate 128, the source of ai.r to plenum 122 can be controlled in desired fashion to control the pressure of drum interior 112. Only a slightly greater volume of air than that permeating the mat and drum from the pressuri2ed hood region 114 need be evacuated from the drum interior 112. Since the mat removal zone 52 is at atmospheric pressure, mai.ntaining drum interior 112 at only slightly less than atmospheric pressure wi.ll eliminate air escapiny from the drum and mixing with liquor to generate foam. In this manner, the advantages of pressure washers, including improved drainage and the availability of high Ms258802104 ~9~
washi.ng temperat.ures is maintained, while the disadvantages of foam generati.on are eliminated.
It should be understood that it i.s not necessary to relieve pressure frGm drum i.nterior 112 to the plenum 122, that structure being merely a preferred embodinment of the i.nvention. For example, a conduit with or without positive pumping apparatus can be provided, connected to the drum interior 110, and merely discharging to atmosphere.
Alternatively, the plenum in the mat removal zone 52 can be eliminated, and conduit 120 connected directly to inlet ~6 with an alternative atnmospheric inlet available for proper inlet mixing.
The drum pressure relievi.ng system of the present invention can be added quickly and easi.ly to existing pressure washers by adding a conduit which places the drum interior in flow communicat.i.on wi.th the blower inlet region, as then used.
Additionally, a valve in the conduit and one controlling flow from the original air source should be added. Normally, the blo~ler inlet receives air from the escaping washer ai.r, to mi.nimize the escape of fumes by recirculating the fumes.
Typically, this source is at or near the mat removal zone as described herein, maki.ng retrofit a si.mple undertaking.
While one embodiment and several modifications of a pressure pulp washing apparatus and process employing drum pressure relief have been shown and described in detail herein, various changes may be made without departing from the scope of the present invention.
Patent Application E`or:
PULP WASHING APPARAT~S A~n PROCESS
Back~round of the Invention i. Techn l Field This invention relates generally to the field of papermaking, and more particularl~ to pulp production for ,capermaking. Specifically, this invention pertains to an apparatus and process for washing pulp.
ii. Prior Art In the papermaking process, wood chips, or other fiber source materials, are cooked with chemicals at elevated temperatures ana pressures to remove binders such as lignin, which hold the fibers together. During the cooking process, or digestion, various compounds and comple~es are ormed in the Cooking liquor. Large quantities of chemicals are used in the cooking process, and, even if inexpensive, chemical recovery is a cost-efficient measure. Evel more restrictive environmental standards necessitate proper handli.ng and treatment of all effluent components. Therefore, efficient pulp washing procedures are beneficial as well as necessary.
It is desirable, therefore, to separate the lisuor, as well as the compounds and complexes formed during the cooking process from the fi.bers after cooking is complete, so that each can be passed through proper disposal, reclamation, or other processes.
~ ~`8 The goa] of pulp washin(3 is to obtai.n pul~ essentially free from soluable impuriti.es. A preferred washing system would con-.pletely remove waste liquor and other impurities while using only a minima~ amount of wash liquid. For chemi.cal recovery and/or other subsequent waste li.quor processing any wash fluids added during the washing stage must also be treated, either by evaporation or other means. Therefore, it is desirable to minimize the amount of wash fluid added during the washing process. The papermaking industry has adopted the term dilution factor" in assessing the efficiency of wash systems with respect to the anmount of wash fluid used. The dilution factor can be described as the amount of water or other wash liquid put into the systen, and not taken out of the system with the washed pulp as the pulp is renmoved from the system. If the auantity of wash fluid added is equal to the quantity of washed fluid passing from the system with the pulp, the dilution factor is 2ero. Low dilution factors aLe therefore desi.rable.
Early processes for pulp washing can be described as dilution washing. This type of washing often was performed in digester blow pits or in separate vessels, and essentially consisted of successive stages wherein wash liquid was added to a drained volume of pulp to dilute the remaining liquor contained in the pulp, and the then-mixed liquor and wash liquid were drained from the pulp. Compacti.on was sometimes used to further assist the removal of diluted liquors, and several stages of successive dilution and draining were employed.
2 ~
Such diluti.on techniques were inherently inefficient, had high dilution factors, and became inappropriate as the need for efficient cher,~ical recovery grew, and as the environmental standards besan requiring treatment of all pulp mi.ll effluents.
A second, more effi.cient type of washing was pursued, generaliy characterized as di.splacement washins. In displacement washing techniques, diffusion of the wash liquid through the pulp material is controlled to avoid mixing, and the wash liquid merely replaces the liquor in the pulp. Early forms of displacement washing occurred as batch processes in large tanks separate from the digester known as diffusers.
E~.owever, because of the characteristics of pulp fibers, channelling, or tunnelli.ng, through a large pulp column often occurred, anà wash liquor would pass through a pulp column while bypassing entrapped liquor volumes held by fiber networks.
~ herefore, to increase washing efficiency and thorouyhness, apparatus to senerate pulp m.ats in washing devices were devised, which provided more uniform drainage and more consi.stent washing through smaller volumes of pulp at a tirne~ Operation was on a more-or-].ess conti.nuous basis, with pulp entering and leavi.ng the devi.ce conti.nuously as washing occurred.
~ arly pulp washers of thi.s type, sometimes referred to as gravity deckers, consisted of perforated drums rotating in large vats of stock. Because of the drainage resistance through the perforated rotatins drum, and the resulting ~93-~;$
differenti.al in fluid levels inside and outside the drum, hydraulic pressure differences between the stock and the interior of the arum, caused a mat to form on the drum as the drum rotates. The liqui.ds in the stock passed throush the mat alld the roll as the result o gravity as the roll rotated, and gravity deckers di.d not have high hydraulic capacity.
Drainage through the mat was the result o~ gravi.ty alone.
To increase drainage through the mat and drum of gravity deckers, the interior of the drum was partially evacuated b~
the use of a hydraulic drop leg to cLeate a parti.al vacuum, while the area above the mat remained at atmospheric pressure.
The increased pressure differerltial between the atmos~heric area outside the drum and the low pressure area inside the drum improved drainage through the mat and allowed showers to be used. r~ash li~uid sprayed through nozzles di.splaced the li.auid ill the mat.
~ significant difficulty encountered with vacuu~. washers of this type relates to flashing of hot fluids. Generally, drainage of liquor through a pulp mat improves wi.th elevated temperatures, and higher temperatures therefore improve washi.ng efficiency. However, vacuu~. washers, which opeLate with up to mi.nus five psi (-5 psi~ in the drum created lower equilibri.um temperature conditions. Therefore, it was not possible to significantly raise the operating temperature of vacuum washers to further i.mprove the drainage characteristics.
~1B258802 104 '2'~
Gravity deckers and vacuum washers, as described above, included outer housings and hoods to contain liquor and odors within a confined area. As an alternative to vacuum washers, and to improve drainage through the pulp mat while, at the same time, avoiding the problems of flashing which occurred in vacuum washers, it was discovered that the hood around the ~asher could be ~rovided with a seal, and a blower used to increase the air pressure above the mat within the sealed hood area The pressure washer operated with a positive pressure (i.e. above atmospheric pressure) in the hood, and a slightly higher than atmospheric pressure in the drum. Mat formation occurred as in previous washers in which the rotating drum picked up a fiber mat from a vat of slurr~. The pressure washers of this type also utilized showers in the wash zone, for displacing the liquor from the cellulose fibers. However, feed consistencies were limited on pressure washers, as in gravity deckers and vacuum washers, to about one to one and one-half percent (1 - 1~%). At higher feed consistencies clumpy mat formation occurred! and drainage characteristics varied significantly throughout the pulp mat, resulting in inconsistent washing.
A subsequent development in the art of pressure washers was the utilization of a headbox, or similar device, for distributing the stock on a foraminous drum, to replace the vat pick-up techniques used in gravity deckers and early vacuum and pressure washers. Headbox-like devices through the input of energy maintain the stock in a fluidized state, allowing the use of higher stock consistencies with impro~ed mat formation. A distinct separation could be created between the formation zone and the washing zone of such washers, allowing new washing techniques to be utilized. In one such technique, the mat forms the base of a pond of wash fluid thereabove, and ~he wash fluid drains through the pulp mat as the foraminous roll rotates.
In either this or earlier types of pressure washers, the air or other gas supplied to the hood to pressurize the hood permeates the mat and drum to cause an overpressure in the interior of the drum. Thus, both the hood and the drum operate at above-atmospheric pressure, with the hood being at a higher pressure, generally, than the drum interior.
At the end of the washing zone and a subsequent dewatering zone, the fiber mat paCses to a repulper, screw conveyor or other apparatus, which aenerally operate at atmospheric pressure. A seal is provided between the pressuriæed zones and the non-pressurized mat take-off area. Since the interior of the drum is at overpressure, a pressure di~ferential e~ists between the drum interior and the talce-off area, with the drum interior being at higher pressure. Thus, pressure from the drum attempts to escape from the drum, blowing the mat from the drum surface and into the repulper or screw conveyor.
This was generally considered to be advantageous for pulp removal, and, in fact, in some pressure washers bypass conduits have been provided from the washer hood to the drum interior to even further increase the overpressurization of the drum interior, to aid in blowing the mat from the drum.
~9~
In some circumstances, the escaping air from the drum has undesiLable effects. Because of the nature of washing, the interior surfaces of the washer become coated with a thin layer of black liquor. Air escaping from the drum and impinging on the liquor covered surfaces in the take-off area, generates a foam with the liquor, which entraps air bubbles. The foam becomes mixed with the pulp in the repulper and is passed with the pulp to subsequent washing stages or other treatment steps. Air in the pulp is generally undesirable, in that drainage is reduced and subsequent wash stages are, therefore, less efficient. In the past, this has been compensated for by the use of defoaming agents, or by the use of larger downstream washers to achieve the desired degree of washing in spite of the reduced drainage characteristics of the pulp.
However, with certain types of pulp, foaming becomes an even more significant problem, and the additional equipment cost for subsequent wash stages is economically undesirahle.
Additionally, large volumes of defoaming agents can be expensive, and their use may not be totally without hazard.
Summary of the Inventi~n It is, therefore, one of the primary objects of the present invention to provide an apparatus and process for washing papermaking pulp which is efficient in displacing liquor and impurities from the pulp, and which washes the pulp in a process having low dilution factors.
Another object of the present invention is to provide a pulp-washing apparatus and process which minimizes foam Ms258802104 2~ 2~
generation while washi.ng pulps with high foam generation characteristics.
Yet another object of the present invention i.s to provide a pulp-washing apparatus and process which operates as a continuous, flow-through pulp washing process.
Still another object of the present invention is to provide a pulp washer drum pressure relievi.ng system which can be added easily, quickly and inexpensively as a retrofit to exi.sting pressure washers.
These, and other objects, are achieved in the present invention by providi.ng in a pressure washer apparatus for removing the overpressure from the inside of the washer drum.
This can be achi.eved in a variety of structures. In a preferred embodiment, the intake for a blower supplying air to pressurize the washer hood is connected to the drum interior, thereby securing its flui.d supply, at least in part, from the drum interior. The i.nlets to the pressurizing blower can be controlled in such a manner as to provide vari.ous levels of negative pressuri.zation within the drum, thereby i.ncreasing the pressure di.fferential between the washer hood and drum i.nterior, to maximize fluid drainage through the pulp mat.
Since the hood area remains pressurized, drainage can be improved, and foami.ng reduced using only minimal negative pressures in the drum. Therefore, the pressure/vacuum washer of the present invention does not suffer signifi.cantly from the problems of flashi.ng experienced in other vacuum washers.
20~9328 High wash temperatuLes can be maintained to still further improve draining.
Relief of pressure in the drum can be achieved independently from the blower system used to pressurize the hood; however, economies of operation and installation costs can be achieved by combining the pressure relief system for the drum with the pressurizing system for the hood. In one such practical installation, a pipe with flow control means is provided between the drum interior and a plenum above the repulper in a pressure washer. The blower intake is connected to the plenum, and a common wall between the plenum and the repulper also includes a valve apparatus Lor controlling the flow of air therethrough. In this manner, the air provided to the plenum can be controlled between the supply from the repulper area, which is atmospheric, and the drum area, which is sealed and, but for relief through the present invention, would be at greater than atmospheric pressure. In this manner, the pressure in the drum can be maintained at atmospheric pressure, or at various levels of subatmospheric pressure.
Alternatively, the pressure relief system for the drum interior can be independently connected to the blower inlet apart ~rom the repulper plenum; or, as mentioned previously, a separate evacuation system with scrubbers discharging to atmosphere can be used to relieve pressure in the drum.
2~932~
Any of a number of apparatus may be utilized for removing the pulp mat from. the drum at the outlet si.de of the washing zone, including steam doctors, water doctors, or the like.
Additional objects and advantages of the present invention will become apparent from the detailed description and the accompanying drawings.
Brief Description of the Drawings Fi.gure 1 is a si.de-elevational view of a pulp washing apparatus employing drum pressure relief embodying the pLesent invention.
Figure 2 is an enlarged view of the mat formation zone of the pressure washer shown i.n Figure 1.
Figure 3 is an enlarged view of the mat removal zone in common pressure washers of the prior art.
Figure 4 is an end-elevati.onal view of a typical pressure washer with the end wall removed, exposing the internal regions of the washer.
Figure 5 is a si.de-elevational view of a suitable arrangement for the pressure relief apparatus of the present invention.
MB25~802104 2~09~28 Figure 6 is an end view of the pressure relief apparatus -~hown in Figure 5.
Detai.led Descripti.on of the Preferred E _odiment Referring no~ more specifically to the drawings, and to ~igure 1 i.n particular, numeral 10 designates a pressure pulp washer embodying the present invention, which employs the use of a drum pressure relieving apparatus 12.
Pulp washer 10 includes generally, as viewed externally, a housing 14 consisting of a vat 16 and a hood 18. Hood 18 i.ncludes a generally semi-cylindrical sidewall 20, and end walls 22 and 24. The vat and hood enclose the washer to allow pressurization and to contain the liquids and fumes within the washer. A variety of viewing ports 26 and manhole-type access ports 28 are provided at appropri.ate locations in the vat or hood for observation of the washing process and/or for performing minor adjustments or repairs.
It will be recogni.zed by those skilled in the art that the general arrangement, outside configuration, and ~iping to and from the washer may vary consi.derably, depending on the specific type of washer, and the installation in which the washer is provided. Therefore, the general washer embodiments described heretofore and subsequently are for illustrative purposes in explaining operation of the present invention, and do not, in and of themselves, limit the application of the pressure-relieving concept of the present invention.
MB258~302104 2~'9~8 r~eferring now with more particular reference to Figure 4, alld others of the drawings, the general washer apparatus will be described in ~.ore detail. A washing drum ~0 is disposed within the vat and hood, and is suitably journaled at its ends for rotation therein. Drum 40 includes a honeycomb-like support structure 42, and a foraminous surface material 44 disposed on the honeycomb support structure. A dri.ve means 46 is provided for rotating the drum 40 ~ithin the vat and hood, and rotates the drum in a clockwise direction, as viewed in ~i.gure 2 and indicated by the arrow indentified by numeral 47.
Drum 40 receives and supports a mat of pulp fibers, carrying the fibers between a mat formation zone 50 and a mat removal zone 52, while passi.ng through first a washing zone 54 and, second, a dewatering zone 56.
The mat formation zone 50, as best shown in ~igure 2, includes a formation plate 60 and suitable adjustment mechanisms such as a pivotal support 62 and a plurality of posi.tion control apparatus 64 for controlling the position and attitude of the format.ion plate with respect to drum 40. The position control apparatus 64 may be pneumatic or electri.cally operated cyli.nders, mechanical screw devices, or other suitable apparatus for controllably moving formation plate 60.
A headbox 66 receives a flow of pulp slurry, and deposits the p~lp in a generally uniform distribution along the drum surface at the inlet edge of formation plate 60. Generallyr formation plate 60 is controlled in position such that a region of convergence towards the drum 40 is defined between the drum and the formation plate, so that, as the stock mat Ms258802l04 2 ~
rotates from the formation end of the screen plate toward the was~iing zone 54, the mat is slightly com~acted.
Washing zone 54 extends from the formation plate 60, and includes a pond of wash liquid 70 to displace the liquor, or other liquid, in the pulp mat, which displaced liquid flows through the mat, the forarninous drum surf2ce and the honeycomb support structure, and is collected in the interior of drum 40 by ~o lection means not shown. The collected liquid, which may include some wash liquid, is then suitably collected and conducted from the washer. The pond extends generally from a sealed area at, or nc-ar, the elevation of headbox 66, upwardly through the upper left quadrant of the washer, as shown in Figure 2. Wash fluid supply is provided through an inlet 74.
When more than one wash stage is required, conventional wash showers may be included in the washing zone 54, and include shower pipes 76 and supply condui.ts 78, with appropriate valves 80. The wash showers spray additional displacing liquid on to the pulp mat as the mat leaves the pond 70.
The dewatering zone 56 extends generally along the upper half of the upper right quadrant of the washer, as seen in Figure 2, or generally from the last of the washing means, which may be the pond or last shower pipe 76, to a seal mechanism 82. In the dewatering zone 56, the stock is dewatered from a consistency of approximately eight percent (8%) upon leaving the pond, or last shower, to a consistency of from twelve to fourteen percent (12% - 14%) as the mat passes beneath the seal mechanism 82.
MB258802 lD4 2o0~328 In the mat removal zone 52, the pulp ma~ is separated from the drum and discharged into a repulper, screw conveyor or other ~uch device for further treatment or handling. A
repulper may be used to break-up the pulp mat and mix it with liquid to lower its consistency, if the pulp is to enter a second stage washer. A screw conveyor, on the other hand, mây be used if the pulp will be further processed or stored at the higher consistency ~resent following dewatering.
Drainage through the mat in the washing zone 54, and in the dewatering zone 56 is enhanced in that the area of hood 18 from the mat formation zone 50 up to the region of seal mechanism 82 is pressurized. A blower 84, having an inlet 86 and an outlet 88, is provided for pressuri%ing the hood.
Outlet 88 discharges into the hood in the was}iing zone 54, and, in the embodiment shown in Figure 1, inlet 86 is connected to a plenum 90 shown in Figures 4 and 5 above the mat removal zone 52.
The mat removal zone 52 following seal mechanism 82 is at atmospheric pressure, and air escaping from the above atmospheric pressure area of drum 40 through the foraminous surface material 44 to the atmospheric pressure area following seal 82 would blow the mat from the drum. This mat removal technique, utilizing air escaping from the drum, is used in prior art pressure washers and is illustrated for explanation purposes in Figure 3.
Seal mechanism 82 is provided to isolate the above-atmospheric pressure area within hood 40, along the 20~,~328 washing and dewatering zones, from the atmospheric pressure area Oî- mat removal zone 52. Seal mechanism ~2 includes a suppGr~ plate 100 which holds an inflatable bag 102 having a surface lining 104 of wear-resistant material. Inflatable bag 102 is inflated supplied and is forced against the surface material 104, to hold the material against the mat of pulp.
Water and air are provided to the inflatable bag through inlets 108, and is removed through a drain 110.
As thus far described, pulp washer 10 is a conventional pressure washer. As best seen in the enlarged view of Figure 3, in the conventional pressure washer, the drum interior designated by numeral 112 is pressurized by the air, or other pressurizing gas which permeates the mat 113 and foraminous drum surface 44 from the pressurized hood region 114.
~owever, as the mat 113 passes beneath seal mechanism 82, the mat 113 enters a region 116 of atmospheric pressure. As the mat 113 leaves the seal mechanism, a pressure differential exists, and the pressurized air in drum interior 112 escapes through the foraminous drum surface, as indicated by arrow 117 forcing the mat 113 off the drum 40 and into the mat removal zone. A receiving plate 118 may be provided for directing the mat toward the repulper, or other subsequent process apparatus.
To ensure separation of the mat from the drum, additional pressurization of the drum interior 112 was provided in some installations through conduits connecting the pressurized hood region 114 to the drum interior 112. While improving mat M~258802104 2~Q~8 separation from the drum the i.ncreased drurn pressure increased foam generation problems in the mat removal zone 54.
Drum 40 is seaied at its ends to the end walls 22 and 24 by conventional Lotating and nonrotating apparatus known to those knowledgeable in the art. According to the present in~ention a conduit 120 for evacuating the drunm e~tends through end wall 22 in a region within the sealed interior area 112 of drun) 40. At the end opposite that in conmunication with the drum interior 112 conduit 120 is connected to plenum 90 above the mat removal zone 52. Thus fluid pressuri.~ing drum interior 112 can flow through the cond~it 120 to the plenum 90. A valve mechanism 124 such as a sliding plate is provided to adjustably control the flow of flui.d through conduit 120. ~ithin plenum 90, a wall 126 includes a sliding gate 128 for controllably admitting air through an opening 130 from unsealed atmospheric regions of washer 10. If sliding gate 128 of wall 126 is closed, all inlet air to blower 84 is supplied through conduit 120 from drum interior 112. From the plenum 90, the air supplied from one or both of the conduit 120 or through the sliding gate 128 i.s drawn by blower 84 through its inlet 86 and discharged through its outlet 88 into the pressurized hood region 114. In this manner the pressure in drum interior 112 can be relieved.
Since i.nsufficient pressure remains in drum interior 112 to blow the sheet from the drum in the mat removal zone 52, a positive removal apparatus must be provided. Any of a number of such apparatus could be used, includi.ng a rotating roll for M~258~02104 2~ 9~
picki.ng the sheet from drum 40, water doctors, o~ steam doctoLs to separate the sheet from the drum.
In the use and operation of a pulp washer having a drum pressure reli.eving apparatus according to the present invention, a mat of pulp material is deposited on the foraminous surface material 44 of drum 40 in the mat formation zone 50. As the drum rotates, the mat i.s slightly compacted and enters the washing zone 54. Wash liquid from the pond 70 displace~ the fl~id in the mat, forcing the fluid through the foraminous surface material and i.nto the drum 40. Additional displacement type washing is provided from the shower pipes 76, and dewateri.ng of the mat occurs in known fashion throughout dewatering zone 56.
During operation, blower 84 draws air through its inlet 86 from the plenum 90. Discharge from blower 84 through its outlet 88 is into hood 18, thereby pressurizing the hood region 114, and improving drainage of the mat. By controlling the valve mechanism 124 and the sli.ding gate 128, the source of ai.r to plenum 122 can be controlled in desired fashion to control the pressure of drum interior 112. Only a slightly greater volume of air than that permeating the mat and drum from the pressuri2ed hood region 114 need be evacuated from the drum interior 112. Since the mat removal zone 52 is at atmospheric pressure, mai.ntaining drum interior 112 at only slightly less than atmospheric pressure wi.ll eliminate air escapiny from the drum and mixing with liquor to generate foam. In this manner, the advantages of pressure washers, including improved drainage and the availability of high Ms258802104 ~9~
washi.ng temperat.ures is maintained, while the disadvantages of foam generati.on are eliminated.
It should be understood that it i.s not necessary to relieve pressure frGm drum i.nterior 112 to the plenum 122, that structure being merely a preferred embodinment of the i.nvention. For example, a conduit with or without positive pumping apparatus can be provided, connected to the drum interior 110, and merely discharging to atmosphere.
Alternatively, the plenum in the mat removal zone 52 can be eliminated, and conduit 120 connected directly to inlet ~6 with an alternative atnmospheric inlet available for proper inlet mixing.
The drum pressure relievi.ng system of the present invention can be added quickly and easi.ly to existing pressure washers by adding a conduit which places the drum interior in flow communicat.i.on wi.th the blower inlet region, as then used.
Additionally, a valve in the conduit and one controlling flow from the original air source should be added. Normally, the blo~ler inlet receives air from the escaping washer ai.r, to mi.nimize the escape of fumes by recirculating the fumes.
Typically, this source is at or near the mat removal zone as described herein, maki.ng retrofit a si.mple undertaking.
While one embodiment and several modifications of a pressure pulp washing apparatus and process employing drum pressure relief have been shown and described in detail herein, various changes may be made without departing from the scope of the present invention.
Claims (16)
1. In a pressurized pulp washer wherein a mat of pulp material is provided for washing on a rotating drum within a pressurized hood region, said mat being exposed to wash fluid in said hood, pressurizing apparatus being provided for supplying a gas for pressurizing said hood region, and a portion of said pressurizing fluid passes through said mat and said drum to an interior region of said drum; the improvement comprising:
conduit means connected to said drum interior region for evacuating pressurizing fluid from said drum; and control means connected to said conduit for maintaining a pressure not above atmospheric pressure in said drum.
conduit means connected to said drum interior region for evacuating pressurizing fluid from said drum; and control means connected to said conduit for maintaining a pressure not above atmospheric pressure in said drum.
2. The improvement defined in Claim 1 in which said conduit is connected to an inlet of a blower used for pressurizing said hood, and said pressurizing fluid evacuated from said drum interior is recirculated to pressurize said hood region.
3. In a method for washing pulp material wherein a mat of pulp is disposed on a rotating foraminous drum and exposed to wash liquid in a washing zone, and to dewatering in a dewatering zone, prior to removal from the drum in a mat removal zone, and wherein a hood and seals are provided around said washing zone and said dewatering zone, with blower means being provided for pressurizing the washing and dewatering zones above atmospheric pressure, the improvement comprising:
providing seals around the drum interior; and evacuating gas from said drum interior; thereby, maintaining pressure in said drum interior at or below atmospheric pressure while maintaining pressure above atmospheric pressure in said washing and dewatering zones outside said drum.
providing seals around the drum interior; and evacuating gas from said drum interior; thereby, maintaining pressure in said drum interior at or below atmospheric pressure while maintaining pressure above atmospheric pressure in said washing and dewatering zones outside said drum.
4. The improved method as defined in Claim 3 including the step of providing gas evacuated from said drum interior in said evacuating step to said blower means for use in pressurizing said washing and dewatering zones.
5. The improved method as defined in Claim 3 including the step of discharging to atmosphere gas obtained in said evacuating step.
6. A pulp washer comprising:
a rotatable washer drum having a foraminous surface for receiving pulp thereon and for passing liquids therethrough;
a housing surrounding said drum, and including a hood surrounding at least a portion of said drum;
stock supply means within said housing for depositing on said drum a mat of pulp material to be washed;
means defining a washing zone in said hood and including wash fluid supply apparatus for displacing liquid in said mat with wash liquid;
sealing means in said housing for separating a pressurized zone of said housing, including said wash zone, from nonpressurized areas of said housing;
blower means for supplying pressurizing gas to said pressurized regions of said housing;
second sealing means for separating a space defined by said drum and end walls thereof from said pressurized regions of said hood, to limit communication between said drum interior and said pressurized region to the openings in said foraminous surface;
receiving means in said drum interior for collecting and discharging liquids passing through said foraminous surface;
pulp mat removal apparatus for separating a mat of pulp from said drum outside of said pressurized region;
evacuation means connected to said drum interior for removing therefrom pressurizing gas entering said drum interior through said foraminous surface; and control means for maintaining said drum interior at a pressure not in excess of atmospheric pressure.
a rotatable washer drum having a foraminous surface for receiving pulp thereon and for passing liquids therethrough;
a housing surrounding said drum, and including a hood surrounding at least a portion of said drum;
stock supply means within said housing for depositing on said drum a mat of pulp material to be washed;
means defining a washing zone in said hood and including wash fluid supply apparatus for displacing liquid in said mat with wash liquid;
sealing means in said housing for separating a pressurized zone of said housing, including said wash zone, from nonpressurized areas of said housing;
blower means for supplying pressurizing gas to said pressurized regions of said housing;
second sealing means for separating a space defined by said drum and end walls thereof from said pressurized regions of said hood, to limit communication between said drum interior and said pressurized region to the openings in said foraminous surface;
receiving means in said drum interior for collecting and discharging liquids passing through said foraminous surface;
pulp mat removal apparatus for separating a mat of pulp from said drum outside of said pressurized region;
evacuation means connected to said drum interior for removing therefrom pressurizing gas entering said drum interior through said foraminous surface; and control means for maintaining said drum interior at a pressure not in excess of atmospheric pressure.
7. A pulp washer as defined in Claim 6 in which a pulp mat removal zone is provided open to the atmosphere, and a plenum in said pulp mat removal zone includes conduit means connected to said drum interior; control apparatus is provided in said plenum for controllably admitting ambient air to said plenum and said plenum is connected to an inlet conduit of said blower means for controllably supplying a mixture of ambient air and pressurizing fluid evacuated from said drum interior to said blower means.
8. A pulp washer as defined in Claim 6 in which said mat removal means includes a steam doctor.
9. A pulp washer as defined in Claim 8 in which a pulp mat removal zone is provided open to the atmosphere and a plenum in said pulp mat removal zone includes conduit means connected to said drum interior; control apparatus is provided in said plenum for controllably admitting ambient air to said plenum and said plenum is connected to an inlet conduit of said blower means for controllably supplying a mixture of ambient air and pressurizing fluid evacuated from said drum interior to said blower means.
10. A pulp washer as defined in Claim 6 in which said washing zone includes a pond of wash liquid exposed to said pulp mat.
11. A pulp washer as defined in Claim 10 in which a pulp mat removal zone is provided open to the atmosphere and a plenum in said pulp mat removal zone includes conduit means connected to said drum interior; control apparatus is provided in said plenum for controllably admitting ambient air to said plenum and said plenum is connected to an inlet conduit of said blower means for controllably supplying a mixture of ambient air and pressurizing fluid evacuated from said drum interior to said blower means.
12. A pulp washer as defined in Claim 6 in which said rotatable washer drum and said housing have a common end wall closing each to the atmosphere, and a conduit extends through said end wall to provide flow communication between said drum interior and said blower means.
13. A pulp washer as defined in Claim 12 in which a plenum is provided and said conduit is connected in flow communication with said plenum an adjustable opening is provided for admitting ambient air to said plenum, and an inlet pipe to said blower means is connected in flow communication with said plenum.
14. A process for washing pulp comprising:
distributing said pulp in a substantially even mat on a hollow foraminous drum rotating in a substantially enclosed housing;
exposing said mat on said hollow foraminous drum to the presence of a wash liquid for displacing liquid from the pulp mat;
pressurizing an area in said housing outside of said drum around said mat for increasing the drainage characteristics of said mat;
permitting fluid pressurizing said area in said housing to permeate said mat and said foraminous drum;
evacuating fluid permeating said mat and said foraminous drum; and maintaining the interior of said drum at below atmospheric pressure.
distributing said pulp in a substantially even mat on a hollow foraminous drum rotating in a substantially enclosed housing;
exposing said mat on said hollow foraminous drum to the presence of a wash liquid for displacing liquid from the pulp mat;
pressurizing an area in said housing outside of said drum around said mat for increasing the drainage characteristics of said mat;
permitting fluid pressurizing said area in said housing to permeate said mat and said foraminous drum;
evacuating fluid permeating said mat and said foraminous drum; and maintaining the interior of said drum at below atmospheric pressure.
15. A process for washing pulp as defined in Claim 14 further including the step of directing fluid evacuated in said evacuating step from said drum to means for performing said pressurizing step.
16. A method for washing pulp as defined in Claim 15 further including mixing fluid evacuated from said drum during said evacuating step with ambient air and supplying said mixed fluid and ambient air to said pressurizing step.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US31453389A | 1989-02-23 | 1989-02-23 | |
| US07/314,533 | 1989-02-23 |
Publications (1)
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|---|---|
| CA2009328A1 true CA2009328A1 (en) | 1990-08-23 |
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ID=23220332
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002009328A Abandoned CA2009328A1 (en) | 1989-02-23 | 1990-02-05 | Pulp washing apparatus and process |
Country Status (6)
| Country | Link |
|---|---|
| CN (1) | CN1046576A (en) |
| AU (1) | AU4848890A (en) |
| CA (1) | CA2009328A1 (en) |
| ES (1) | ES2020636A6 (en) |
| WO (1) | WO1990010109A1 (en) |
| ZA (1) | ZA901338B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106049155A (en) * | 2016-07-29 | 2016-10-26 | 无锡乐华自动化科技有限公司 | Paper pulp beater capable of self removing impurities |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI81020C (en) * | 1988-11-11 | 1992-03-24 | Sunds Defibrator Rauma Oy | Procedure for thickening suspension and treating with liquid drum filter |
| CA2161851C (en) * | 1995-10-31 | 1999-06-01 | Mark Tayler | Pressure washer drum |
| AT405420B (en) * | 1997-05-26 | 1999-08-25 | Andritz Patentverwaltung | DEVICE FOR DRAINING AND WASHING FIBER FIBER SUSPENSIONS |
| US6017416A (en) * | 1997-12-04 | 2000-01-25 | Bonded Fiberglass Co. | FRP hood for paper processing plant |
| SE528714C2 (en) * | 2005-06-03 | 2007-01-30 | Metso Paper Inc | Device for treating cellulose pulp in a washing device adapted to facilitate service and inspection of the device |
| SE528716C8 (en) * | 2005-06-03 | 2007-04-24 | Metso Paper Inc | Apparatus for treating cellulose pulp in a washing device |
| SE531847E (en) * | 2007-12-13 | 2012-06-01 | Metso Paper Inc | Apparatus for washing and dewatering of pulp |
| CN102877345A (en) * | 2012-10-31 | 2013-01-16 | 江苏大唐机械有限公司 | Paper-making raw material washing and dewatering equipment |
| CN104190598B (en) * | 2014-08-29 | 2017-02-08 | 山东天阳纸业有限公司 | Coating suction collector |
| CN104528413B (en) * | 2014-11-18 | 2016-09-07 | 南宁侨虹新材料有限责任公司 | Dust-free paper forming box rotary drum jetting type uniform distribution device |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1012815B (en) * | 1951-10-12 | 1957-07-25 | Rauma Repola Oy | Washing device for pulp suspensions |
| US2999785A (en) * | 1959-07-17 | 1961-09-12 | Kamyr Ab | Method and plant for washing of cellulosic pulp under overpressure |
| US3487941A (en) * | 1967-05-10 | 1970-01-06 | Pertti Olavi Haapamaki | Pressure washer |
| US4808265A (en) * | 1986-08-07 | 1989-02-28 | Ingersoll-Rand Company | Method of washing pulp in a pressure pulp washer adding two washing liquids |
-
1989
- 1989-12-07 WO PCT/US1989/005436 patent/WO1990010109A1/en unknown
- 1989-12-07 AU AU48488/90A patent/AU4848890A/en not_active Abandoned
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1990
- 1990-02-05 CA CA002009328A patent/CA2009328A1/en not_active Abandoned
- 1990-02-22 ES ES9000536A patent/ES2020636A6/en not_active Expired - Lifetime
- 1990-02-22 ZA ZA901338A patent/ZA901338B/en unknown
- 1990-02-23 CN CN90100872A patent/CN1046576A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106049155A (en) * | 2016-07-29 | 2016-10-26 | 无锡乐华自动化科技有限公司 | Paper pulp beater capable of self removing impurities |
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| Publication number | Publication date |
|---|---|
| AU4848890A (en) | 1990-09-26 |
| ZA901338B (en) | 1991-01-30 |
| CN1046576A (en) | 1990-10-31 |
| ES2020636A6 (en) | 1991-08-16 |
| WO1990010109A1 (en) | 1990-09-07 |
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