US3074553A - Method and apparatus for screening pulp - Google Patents

Method and apparatus for screening pulp Download PDF

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Publication number
US3074553A
US3074553A US22236A US2223660A US3074553A US 3074553 A US3074553 A US 3074553A US 22236 A US22236 A US 22236A US 2223660 A US2223660 A US 2223660A US 3074553 A US3074553 A US 3074553A
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United States
Prior art keywords
screen
stock
line
pulp
shell
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Expired - Lifetime
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US22236A
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English (en)
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Henry F Szepan
Guy E Sanford
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Individual
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Individual
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Priority to US22236A priority Critical patent/US3074553A/en
Priority to GB30947/60A priority patent/GB912021A/en
Priority to SE8595/60A priority patent/SE307889B/xx
Priority to FI1596/60A priority patent/FI42498B/fi
Application granted granted Critical
Publication of US3074553A publication Critical patent/US3074553A/en
Anticipated expiration legal-status Critical
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
    • D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
    • D21D5/02—Straining or screening the pulp
    • D21D5/06—Rotary screen-drums

Definitions

  • FIGURE 1 is a schematic diagram of a complete installation with the preferred instrumentation indicated:
  • FIGURE 2 is a central section through a preferred form of screen
  • FIGURE 3 is a sectional view of a preferred form of cover plate
  • FIGURE 4 is an isometric projection of the gasket as a whole
  • FIGURE 5 is a partial section of the tailings end of a modified machine.
  • FIGURE 6 is a partial end elevation of the machine of FIGURE 5, showing the joint and severa means of exit of the tailings.
  • the present invention is based on hermetically sealing pulp screens of the types mentioned so that the rotor will generate subatmospheric pressure on the interior of the screen, with the absolute pressure of the interior being less than the absolute pressure of the exterior.
  • the absolute interior pressure seems to be the controlling factor.
  • the absolute exterior pressure to say the least, is not critical. Within reasonable limits even a positive superatmospheric absolute exterior pressure may occur.
  • the exterior subat-mospheric absolute pressure is caused, in all probability, by leak-age across the screen plates, most probably at the rejects or tailings, end. Under such conditions, there is no foaming, and thus it is possible to handle pulps without the addition of antifoaming agents.
  • the vacuum principle of this invention has value (in addition to increased capacity, screen for screen) in the deaeration, or at minimum, non-increase of aeration of the slurry at any location between the chipbin and the paper reel.
  • rejects and tailings are sometimes used synonymously, but are not quite synonymous. Tailings would refer to the total discharge from the interior of a screen, while rejects would refer to the solids content of the tailings. Even the term rejects, as just defined, requires some qualification. Ordinarily, this term means such knots and shives as would be intolerable in the finished product plus, of course, some unavoidably entrapped good fibre. If, however, the infeed slurry is a mixture of reclaimed groundwood (newsprint) and kraft, for example, the rejects would be predominantly kraft fibres and the accepted stock would be predominantly groundwood. In such case the screen is acting as a fibre classifier.
  • FIGURE 1 is generally illustrative of a preferred installation. In an actual installation, the details will vary from plant to plant depending on the pulp and on the physical limitations imposed by the location.
  • a brown stock blow tank 10 at the bottom of which, optionally, is a mechanical attrition mill 12 which may be of any of several tor-ms presently available.
  • This mill 12 if used at all, receives pulp from the tank 10, reduces the oversize particles, and 'also acts as a pump to feed the treated pulp through a line 14 and through a flow meter 16 to a pair of lines 18 and 20, each of which feeds primary screens 22 and 24.
  • Accepted stock from screen 22 goes through line 26 to a line 28 while accepted stock from the screen 24 goes to line 30 through a line 28.
  • Rejects from screen 22 pass through a line 32 to a pump 34, while reject-s from screen 24 pass through a line 36- to the pump 34.
  • the pump 34 delivers the combined rejects of screens 22 and 24 through a line 38 to a line 40 which is connected to the original supply line 14 and which feeds a secondary screen 42.
  • Accepted stock from the secondary screen 42 passes through a line 44 to the line 28 which carries acceptable stock from all three screens to a conventional pulp washer 46.
  • Rejects from the secondary screen 42 go to a pump 48, thence through a line 50 to a rejects screen 52.
  • the rejects are deliquored and freed from substantially all good fibre.
  • the rejects from this screen 52 are returned to the chipbin through a line 53.
  • the liquor and good fibre pass through a line 54 back to the blow tank 10.
  • the pulp slurry comes to the blow tank direct from the digester at a temperature usually about F.
  • a consistency at which optimum performance is obtained This is attained by dilution in the individual feed line of each screen.
  • a consistency regulator 56 is connected to the line 14 through a line 58, and through a consistency controller 60 adjusts a valve 62 which is connected to a black liquor line 64 which in turn is supplied by a dilution pump 68 connected to a primary liquor tank 66.
  • the tank 66 receives its liquor from the washer v 46 through a line 67.
  • a recorder controller 70 responds to the flow meter 16 to control the total flow through the line 14 by means of a recirculation valve 71, which connects with the consistency regulator 56 to recirculate excessive flow.
  • the screen 24 is supplied with stock by a line 20.
  • a pump 72 draws black liquor from the. tank 66 and through a line 74 and a branch line 76 delivers the black liquor to the screens as redilution liquor and also, through a line 78 connects with the. stock feed line 20.
  • a valve 80 is placed in the line 78 and a valve 82 is placed in the line 20. The valve 80 and the valve 82 are actuated by a pressure controller 84 which responds through a line 86 to the absolute internal pressure within the screen 24.
  • the interior of the screen operates at a subatmospheric absolute pressure approximately 8" Hg. minimum absolute pressure depends on the temperature of the slurry. In general the lower the temperature, the lower the absolute pressure.
  • the 8" Hg absolute pressure in the interior of the screen 24 is believed to be optimum for hot stock, though this has to be determined empirically for each installation.
  • recorder controller 84 senses a decrease in absolute pressure, it will actuate the value 80 to reduce the rate of addition of black liquor diluent. If, on the other hand, the blow tank consistency swings heavy, there will be an increase in absolute pressure, and the valve 80 will be opened to increase the dilution. If for some reason the screen 24 should continue to plug even after the valve 80 is fully opened, the interior absolute pressure will continue to increase even to positive superatrnospheric presure.
  • the pressure recorder controller 84 is set to close the stock valve 82, while leaving the valve 80 wide open.
  • FIGURE 2 The machine for performing the subatmospheric screening of pulp is best shown in FIGURE 2. While the machine is. designed and intended to and almost always will operate at an internal subatmospheric absolute pressure, it is not inconceivable that, perhaps due to plugging or control failure of some sort, there may be attained, within the machine, a positive or superatrnospheric pressure. With the stock at or about room temperature, should such pressure burst the shell of the machine, the result would be unfortunate. In handling hot, brown'stock, however, at about 190 F., the
  • the shell of the machine is designed as a pressure vessel to resist internal pressure of at least 30 p.s.i. Fortunately, the same mechanical characteristics which enable the shell to withstand internal pressure equally enable it to withstand external pressure induced by the machine operating, as it must, when sealed oif from the atmosphere.
  • FIGURE 2 there is shown a screen generally designated as made up of a convex head end 102, a cylindrical shell portion 104 and a concave end portion 106. Adjacent the convex head portion 102 where it is welded at 108 to the shell portion 104 is a bafile 110.
  • the baffle 110 has one or more openings 112.
  • the convex head 102 has an opening 114 by which it joins an inflow pipe 116.
  • a rotor shaft 118 penetrates the convex head 102, the concave head 106 and extends generally axially of the shell 104. It has a bearing 120 adjacent the convex head 102 and a bearing 122 adjacent the concave head 106. Keyed to the shaft 118 is a two-part bafile plate 124 of the sort disclosed in the patents and application above noted.
  • Rotor bars 126 are welded to the baflie plate 124 and are further supported by rings 128 to which they are welded in the manner set forth in the two cited patents.
  • the portions of the bars 126 at the trailing side of the bafile 124 may or may not be pitched reversely, as noted in the pending application above identified.
  • a screen 130 surrounds the shaft 118 and is strengthened by ribs 132 which actually mark the joints between segmented sections of the screen.
  • the screen 130 is perforated, preferably by circular perforations. The diameter and center to center pattern of the perforations will depend entirely on the nature of the screening operation and the nature of the pulp.
  • Accepted pulp goes through the screen 130 and rejects (oversize) are retained and discharged at the concave end 106 through a rejects pipe 134.
  • the accepted stock goes through a passage 136, welded at 138 to the shell 104.
  • the screen 130 bears at each end on a gasket supported by annular rings 146 and 146' respectively welded to the bathe 110 and to the concave head 106.
  • a water seal 140 with an inlet 142 and an outlet 144 is placed adjacent the bearings 120' and 122 and is separated from the interior of the shell 104 and the screen 130 by a stufiing 141 and is sealed on the other side by a stufling 143.
  • the pressure outside the line 152 is an absolute of about 2" Hg below atmospheric pressure. This value is not at all critical. It will be realized that the rotor blades 126' act to pump the stock upstream from the 8" Hg absolute below atmospheric pressure of the screens interior to the 2" Hg absolute below atmospheric pressure of the screens exterior. These blades, as in the Bowen and Rich-Luthi patents, also act to feed the stock axially over the bafiie 124 after which the stock is subjected todilution through one or more pipes 156. This provides redilution of the pulp mass prior to rejection to give leaner rejects. In addition and as noted in the patcuts, the blades, on the trailing side, have a cavitation elfect tending to clean the screen perforations. The cleaning effect is enormously improved by the existence of the internal relative subatmospheric pressure.
  • FIGURES 3 and 4 There must, of course, be access to the interior of the shell 104. This is accomplished by means of the cover plate and gasket shown in FIGURES 3 and 4.
  • the cover plate like the shell itself, must be engineered to withstand from to Hg of vacuum, up to 30 P.S.I.G. Bolting or capscrewing such a plate would lead to so much down time for any servicing as to be prohibitive cost-wise.
  • a sliding bayonet type joint has been devised. The sliding has been set up generally parallel to the axis of the rotor and is accomplished by means of axially spaced lugs 200 welded to the shell 104 adjacent a cut 202 in the shell 104 as seen in FIGURE 3.
  • the cover plate 204- has its axial edges machined and cut away to form lugs 206 which mate with the lugs 200.
  • the lugs 200 have a base portion 208 and a flange 210 to form a channel 212.
  • the tube 214 is inflatable to the dotted line position 215 as shown in that FIGURE. To accomplish this the tube 214 will usually be inflated to from 50 to 100 P.S.I.G. from the usual mill pressure line. The inflation is done from a pressure line 216 operating, at least through the bending stage through a steel shell 218 which is welded to the shell 104 at 220.
  • the gasket as seen in FIGURE 4 is molded to the form shown and is inflatable as above noted.
  • FIGURES 5 and 6 show a modification in which the rejects are subjected to mechanical attrition for recirculation, or discard or both. So far as the parts are the same as FIGURE 2, the reference numerals are the same.
  • the rotor blades 126 are given an extra reinforcing ring 128 and have bolted extensions 129.
  • a hub 300 is keyed to the shaft 118.
  • a disc 302 is welded to the hub 300.
  • the disc 302 is dished to conform to the concave shell end 106 and is axially slidable for adjustment.
  • impeller blades 304 At intervals around the periphery of the disc 302 there are impeller blades 304.
  • the blades 304 are pitched at about 15 to the axis of the shaft 118.
  • the screen support ring 146 has welded thereto a baffle 306 dished to conform to the disc 302.
  • the baffle 306 has an annular flange 303 which is perforated at 309.
  • the baifle 306 loosely surrounds the hub 300.
  • the shell 106 has the usual dilution connection 156.
  • a ring 314 is perforated at 316 with the same size and pattern of perforations as the flange 308.
  • the ring 314 is adjustable relative to the flange 308 by means of slots and bolts not shown. This permits a regulation of the rate of flow of the rejects through the perforated flange 308 of the disc 306.
  • the machine as above described take the rejected shives and knots and reduces or deflbres them between the bolted bars 129 and the perforated ring 308. Toothpick sized shives emerging from the rejects side of screens 22 and 24 of FIGURE 1 will undergo attrition between the blades 129 and the flange 308 (of FIGURE 5) and the remaining fragments will pass into the path of the impellers 304 on the disc 302.
  • rejects of course can be fed to a secondary screen which, in all probability would have smaller perforations than those of the screen from which the rejects come.
  • the rejects, of couse are returnable to the blow tank 10 or to the screen 52. In either of the cases, however, booster pumping almost always will'be required.
  • the blades 304 are pitched about 15 and, on the side facing the ring 308 are relieved about 5 to provide, in effect, a cutting edge to sever the shives of narrow, elongated dimensions which might penetrate the perforations 316, even though they are unacceptable by normal standards.
  • a preferred eight blades 304 and a preferred R.P.M. of from 300 to 350 it is quite clear that attrition over and above that occurring between the bars 129 and the flange 308 will occur between the flange 308 and the blades 304.
  • the tangential outlet 310 If recirculation is desired, use is made of the tangential outlet 310. If discard is desired, use is made of the axial outlet 312, normally covered by a plate 315 and sealed by a gasket 316.
  • the 15 pitch of the blades 304 feeds the rejects in such manner as to direct the rejects both axially and tangentially, henceeither or both of the exits 310 and 312 may be used.
  • the impeller blades 304 and the disc 302 depending on the nature of the rejects, or tailings, may not be required.
  • the attrition between the extensions 129 and the ring 314 may be suflicient and, for some end-use products, undoubtedly is.
  • a method of screening pulp comprising: advancing a slurry of pulp axially along the interior of a cylindrical screen formed of perforated sheet stock; forcing accepted stock outwardly through the perforations of said screen; and maintaining a cavity in the stock in said screen at a lower absolute pressure than that surrounding the exterior of said screen.
  • a method according to claim 1 in-Which the slurry includes washed pulp.
  • Apparatus for screening pulp comprising: a stationary cylindrical screen; a shell surrounding said screen, said shell having an inlet opening and outlet openings for accepted and rejected stock, said shell having pressure resistant ends; a multiple bladed rotor within said screen,
  • said rotor being secured to a shaft penetrating both ends of said shell and a vacuum sealed bearing at each end of said shaft, said bearings with said ends and said shell forming a sealed chamber at the interior of said screen, and means to maintain the interior of said screen at lower absolute pressure than the exterior of said screen.
  • Apparatus as set forth in claim 4 in which an annular, perforated bafile is placed adjacent the trailing end of said rotor and adjacent the blades thereof.
  • Apparatus as set forth in claim 7 in which the rej'ec't's end of the shell has an axial outlet adjacent the defibering elements.
  • a method of treating brown stock comprising: subjecting a slurry of freshly digested pulp in hot, spent cooking liquor to mechanical attrition; conducting the attritioned stock while in said liquor to a screen; maintaining a diflerential in absolute pressure on opposite sides of said screen; forcing acceptable stock through said screen against said pressure differential and thereafter subjecting said acceptable stock to a conventional brown 5 stock washing process.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
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US22236A 1960-04-14 1960-04-14 Method and apparatus for screening pulp Expired - Lifetime US3074553A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US22236A US3074553A (en) 1960-04-14 1960-04-14 Method and apparatus for screening pulp
GB30947/60A GB912021A (en) 1960-04-14 1960-09-08 Method and machine for screening pulp
SE8595/60A SE307889B (es) 1960-04-14 1960-09-08
FI1596/60A FI42498B (es) 1960-04-14 1960-09-27

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3229815A (en) * 1961-12-05 1966-01-18 Wilfred F Mathewson Pulp screen or filter
US3852191A (en) * 1971-04-23 1974-12-03 Supraton Bruchmann & Zucker Kg Process and apparatus for the production of a dispersion or solution from comminuted solid substances and a dispersion medium or solvent
US3874509A (en) * 1972-11-06 1975-04-01 Beloit Corp Pressure screen and surge tank
US4042503A (en) * 1973-12-10 1977-08-16 Beloit Corporation Classifier and process for recycled fiber separation
US4956102A (en) * 1986-09-08 1990-09-11 Allsing Karl J Method for operating rotating cylindrical filters and a rotatable cylindrical filter
WO2014098746A1 (en) * 2012-12-21 2014-06-26 Cassandra Oil Technology Ab Gastight reactor comprising rotating crushing means
CN104233896A (zh) * 2014-09-02 2014-12-24 郑州运达造纸设备有限公司 一种用于压力筛的稀释装置

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US833617A (en) * 1906-03-10 1906-10-16 Orville H Moore Pulp-screen.
US1225198A (en) * 1913-06-09 1917-05-08 Peder P Westby Pulp-screen.
US1260320A (en) * 1917-03-10 1918-03-26 George W Bulley Rubber-working machine.
US1320128A (en) * 1919-10-28 Bestjamibt s
US1722874A (en) * 1928-01-13 1929-07-30 Harold D Wells Pulp screen
US2363188A (en) * 1940-09-25 1944-11-21 Gen Motors Corp Chemistry
US2704604A (en) * 1955-03-22 rqlston
US2705562A (en) * 1953-12-18 1955-04-05 Floyd E Albertson Vacuum filter
US2845848A (en) * 1956-01-23 1958-08-05 North Carolina Pulp Company Apparatus for screening pulp
US2908390A (en) * 1958-01-28 1959-10-13 John P Rich Apparatus for screening pulp

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1320128A (en) * 1919-10-28 Bestjamibt s
US2704604A (en) * 1955-03-22 rqlston
US833617A (en) * 1906-03-10 1906-10-16 Orville H Moore Pulp-screen.
US1225198A (en) * 1913-06-09 1917-05-08 Peder P Westby Pulp-screen.
US1260320A (en) * 1917-03-10 1918-03-26 George W Bulley Rubber-working machine.
US1722874A (en) * 1928-01-13 1929-07-30 Harold D Wells Pulp screen
US2363188A (en) * 1940-09-25 1944-11-21 Gen Motors Corp Chemistry
US2705562A (en) * 1953-12-18 1955-04-05 Floyd E Albertson Vacuum filter
US2845848A (en) * 1956-01-23 1958-08-05 North Carolina Pulp Company Apparatus for screening pulp
US2908390A (en) * 1958-01-28 1959-10-13 John P Rich Apparatus for screening pulp

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3229815A (en) * 1961-12-05 1966-01-18 Wilfred F Mathewson Pulp screen or filter
US3852191A (en) * 1971-04-23 1974-12-03 Supraton Bruchmann & Zucker Kg Process and apparatus for the production of a dispersion or solution from comminuted solid substances and a dispersion medium or solvent
US3874509A (en) * 1972-11-06 1975-04-01 Beloit Corp Pressure screen and surge tank
US4042503A (en) * 1973-12-10 1977-08-16 Beloit Corporation Classifier and process for recycled fiber separation
US4956102A (en) * 1986-09-08 1990-09-11 Allsing Karl J Method for operating rotating cylindrical filters and a rotatable cylindrical filter
WO2014098746A1 (en) * 2012-12-21 2014-06-26 Cassandra Oil Technology Ab Gastight reactor comprising rotating crushing means
CN104233896A (zh) * 2014-09-02 2014-12-24 郑州运达造纸设备有限公司 一种用于压力筛的稀释装置
CN104233896B (zh) * 2014-09-02 2016-07-06 郑州运达造纸设备有限公司 一种用于压力筛的稀释装置

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Publication number Publication date
GB912021A (en) 1962-12-05
SE307889B (es) 1969-01-20
FI42498B (es) 1970-04-30

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