US3863559A

US3863559A - Method and apparatus for dewatering fibrous materials

Info

Publication number: US3863559A
Application number: US281114A
Authority: US
Inventors: Edgar M Pierce
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-08-16
Filing date: 1972-08-16
Publication date: 1975-02-04
Anticipated expiration: 1992-02-04

Abstract

Disclosed herein is a method and apparatus for dewatering materials. The method includes the steps of applying a predetermined pressure, at a predetermined press rate, in a direction parallel to a screen, reducing the press rate so as to press the material being dewatered against itself as it is being forced through a 1/2 to 3/4 inch orifice. The apparatus includes as its primary elements a barrel having a longitudinal slot through which extends a blade, and a circular screen positioned below the barrel and blade. The apparatus has two cycles, clockwise and counterclockwise, and dewaters the material during each cycle. The barrel is positioned above the screen by about 1/2 to 3/4 inch by rims carried on the former. The 1/2 to 3/4 inch defines the orifice through which the material is pressed.

Description

baited States Patent 1 Pierce 1 Feb.4,l975

[ 4] METHOD AND APPARATUS FOR DEWATERING FIBROUS MATERIALS 22 Filed: Aug. 16, 1972 21 Appl. N0.;2s1,114

[52] U.S. CI ..100/37,100/127,100/l77, 100/186, lOO/DIG. 5, l00/DIG. 6, 425/84 [51] Int. Cl. A47j 19/02, B30b 9/06, 1330b l/OO [58] Field of Search 100/185, 186,37, 35, 41, 100/126,116,DIG.39,177,178,179,127,

[56] References Cited UNITED STATES PATENTS 500,490 6/1893 Grimm 100/186 X 711,938 10/1902 Casper I 100/177 947,013 l/19l0 Dowd 100/177 X 1,550,045 8/1925 Power.. lOO/DIG. 8 2,587,997 3/1952 Guettler 100/126 X 2,717,420 9/1955 Roy l00/D1G. 8 3,021,254 2/1962 1 Helversen et a1. 100/127 X 3,073,239 l/1963 Cowan et al 100/126 X 3,134,321 5/1964 Loehnert 100/185 X 3,279,357 10/1966 Farmer IOU/I77 X FOREIGN PATENTS OR APPLICATIONS 993,082 5/1965 Great Britain 100/126 Primary Examiner- Peter Feldnian Attorney, Agent, or Firm-Wood, Herron & Evans [57] ABSTRACT Disclosed herein is a method and apparatus for dewatering materials. The method includes the steps of applying a predetermined pressure, at a predetermined press rate, in a direction parallel to a screen, reducing the press rate so as to press the material being dewatered against itself as it is being forced through a /z to inch orifice. The apparatus includes as its primary elements a barrel having' a longitudinal slot through which extends a blade, and a circular screen positioned below the barrel and blade. The apparatus has two cycles, clockwise and counterclockwise, and dewaters the material during each cycle. The barrel is positioned above the screen by about to 9 inch by rims carried on the former. The ie to i inch defines the orifice through which the material is pressed.

14 Claims, 6 Drawing Figures PATENTED FEB 41975 SHEET 10F 4 I HIV/K PATENIEU 3. 863 559 SHEET 2 OF 4 BACKGROUND or THE INVENTION The dewatering of fibrous materials is commonplace in industry. For example, in the art of paper making, fibrous pulp must be dewatered before it is processed into its final form. In many instances the dewatered pulp is shipped after dewatering and stored until such time as it is used. The degree of moisture retention in the dewatered pulp affects the utility as well as the economics of the process. In storage, the pulp is subject to bacterial degradation. The rate of such degradation increases with increased moisture content. And, an increase in moisture content increases the cost of shipping the dewatered material.

For these reasons and others, it has been the objective of prior art inventors to provide dewatering methods and apparatus that will reduce the water content to the greatest extent possible. Whereas, commonly used methods such as screw presses, revolving discs, V- presses or roll type presses can dewater to a presscake with 60 to 70 percent moisture, it is possible to obtain presscake with 30 to 40 percent moisture by the method of my invention described here. I have found that the dewatering of fibrous materials can be accomplished to a high degree and a low moisture presscake can be the result if the characteristics of moisture release of the particular fibrous material are correctly interpreted by the dewatering method.

The characteristics of moisture release from fibrous materials are not like granular material because of the matting action of the fibers and because of the resilience of the mat formed, the retention of moisture in the soft porous structure of the fibers themselves and the trapping of fines and material other than fibers in the mat.

While I do not necessarily means to be bound by any theory as to why the herein described method and ap' paratus are successful, it is believed that the following theories explain such success.

I believe the general factors which affect the degree of moisture released are: (1) pressure must be applied sufficient to reduce volume of the matted material to the necessary degree; (2) pressure must be applied in a manner to avoid or reduce thrust on screens; (3) the travel path of moisture must be reduced by thin crosssection of material and close spacing of openings in screen; and (4) sufficient time for moisture travel must result from press action.

The failure of other and commonly used methods to produce low moisture presscake are due to the inherent mechanical problems of those designs. For instance:

A. Screw presses can meet the moisture release requirements of the fibrous material but in so doing the presscake binds and plugs the press.

B. Revolving disc or V-presses depending upon pressing between screens in a wedging action with too great a travel path for liquids. Also the application of pressure is limited by the structure or construction of the revolving discs.

C. Roll presses have a line contact of pressure, poor removal and insufficient sealing against moisture return. Also there is a feeding or flow problem into the rolls.

Other various type presses are disclosed in U.S. Pat.

Nos. 2,631,527. 2,337,261, 2,l2|,932, and 2,088,657.

LII

Not only is the extent to which a material may be dewatered an important consideration, but so is the cost of the apparatus used in such process an important consideration. Likewise, operating cost of the apparatus and process are important considerationssince obviously the dewatering must be effected in an economical manner.

SUMMARY OF THE INVENTION 1 have empirically found and discovered that the foregoing objectives, never before to my knowledge having been obtained, can be obtained through the practice of and use ofthe hereinafter described method and apparatus.

Briefly, as to my method, I have found that observing and following the foregoing four factors, and using a method wherein a predetermined pressure is applied at a predetermined rate, so that the material is forced through a V2 to /1 inch orifice, an excellent dewatering of the material may be obtained (i.e., 30-40 percent moisture). More particularly, pressures in the range of 300-3,000 psi are applied depending on the material being'dewatered. The rate, press rate, at which the material is forced through the orifice varies between about I to 8 feet per minute and is reduced at the end of the dewatering cycle. The size of the orifice has been found to be especially important and should be between /2 to inch. The force is applied in such a manner that the wet material is compressed against the dewatered material so that the components of the apparatus are not subjected to the pressure. In fact, the pressure is applied in a direction parallel to the surface ofthe screen through which the water escapes and is separated from the pulp or other material.

In practicing the above described process I have found that the hereinafter described apparatus is especially useful. However, those skilled in the art will recognize that other apparatus may also be adapted for use to practice the process. Those skilled in the art will likewise recognize that the moisture content of the dewatered material can be varied. In fact, the apparatus disclosed herein can also be used as a self-cleaning screen.

In its generic form, the hereinafter dewatering presses consist of a generally circular shaped, hollow barrel that includes in one wall a longitudinal slot. A blade extends about /2 to /1 inch through the slot in the barrel. Suitable means are provided for rotation of the barrel and the blade. In use, the blade and barrel rotate through a distance of about the middle of the cycle being in almost a vertical plane. Positionedbelow the barrel is a screen. The screen is bent in a circular manner so as to be spaced/apart from the barrel, throughout the distance the barrel rotates, an equal distance. As has been previously mentioned, this distance must be about /2 to inch in order to obtain the low moisture contents disclosed herein. Spaced above the screen in a scraper blade that, in addition to cleaning the barrel, also, in combination with the screen and the barrel, forms a chamber to contain the pulp during the dewatering or pressing step. During operation the barrel and blade are rotated in first one direction and then in the opposite direction. Pulp is dewatered in each operation. This mode of operation increases the capacity of the apparatus since while the barrel rotates in one direction and material is being pressed on one side of the blade, pulp slurry is received in the chamber formed on the opposite side of the barrel. Upon the change in direction of the barrel and blade, the pulp that has been just introduced into the chamber is pressed and dewatered.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of my dewatering method and my dewatering presses will now be described in connection with the drawings wherein:

FIG. 1 is an end elevation view showing in general the drive elements of my press and showing schematically the hydraulic circuit that may be employed;

FIG. 2 is a longitudinal section taken along the lines 22 of FIG. 1;

FIGS. 35 are cross-sectional views serving to illustrate complete cycle of operation including two pressing steps; and

FIG. 6 is charts which contain process data.

Referring to the drawings and especially FIG. 6, my process will first be described since an appreciation of it is especially useful in understanding the operation of my dewatering presses.

I have discovered a number of factors that must be taken into consideration in order to substantially reduce the moisture content of various materials. Empirically, I have determined that the successful dewatering of various materials requires the application of different pressures. Such a phenomena is shown in the bottom ,graph of FIG. 6 wherein on the horizontal axis is plotted pressures and on the vertical axis are plotted moisture contents. Various curves are presented showing pressures required to dewater, to various extents,

spent grain, citrus pulp, pulp fines, sulfite and kraft pulp, and groundwood fines. Also presented are lines indicating the dewatering capabilities of various types of prior art devices.

The top graph of FIG. 6 contains the same information plotted vertically but plots on the horizontal axis the speed of the press during the pressing cycle for the various materials at the various pressures selected to dewater the material.

Each graph is plotted on the assumptions that the material is compressed against itself to achieve the dewatering and also that the material is pressed through a chamber whose height is about /2 to inch.

The graphs of FIG. 6 illustrate the pressures and the press rate for the various materials. Other materials not shown will have similar characteristics for pressure and rate. For example, if kraft pulp is desired to be dewatered, to an extent not thought to be possible heretofore, a pressure of 3,000 psi is applied at a press rate which begins at about feet per minute and reduces as the moisture content is reduced to about two feet per minute. The wet kraft is pressed against dewatered kraft in a direction that is parallel to the press screen. The press chamber is between /2 to inch.

Empirical evidence has demonstrated the criticality of the following factors in my process: (l) pressure must be applied normal to the screen surface; (2) a press rate that begins at about 1 to 8 feet per minute and which is reduced toward the end of the cycle; (3) 300-3,000 psi pressure; (4) /2 to 1 inch pressing chamber; and (5) pressure applied parallel to the screen surface. The foregoing requirements may be obtained in the following presses.

The press includes as one element a circular, hollow barrel 1 which forms a slurry chamber for the material to be dewatered. At each end of the barrel are rims 2 whose diameters are greater than the diameter of the barrel 1 by a distance of about /2 to inch. The rims may be secured to the barrel in any suitable manner. For ease of assembly and disassembly, the rim may include holes therein, not shown, through which a rod 3, threaded at each end may be inserted. A plurality of rods 3, each in combination with two nuts 4, are used to secure the two rims 2 to the barrel 1. Each rim includes a hub portion 5 whose function is to receive a bearing 6.

Each of'the rims 2 contains a hole in the middle thereof, not shown, whose purpose is to receive a hollow drive shaft 7.

On the interior of the barrel 1, and removeably connected to the drive shaft 7, is a rotor shaft 8. The connection is made by making the diameter of the rotor shaft 8 larger than the diameter of the drive shaft 7 and using a key 9 for the connection. The rotor shaft 8 com tains slots 10 for introducing the slurry into the barrel 1.

A blade guide or holder 11 is connected to the rotor shaft 8 and contains the blade 12. The holder 11 as shown includes dependingwalls 13 forming a channel for receiving the blade 12, and support members 14 for bracing the walls 13. Walls 13 and support members 14 may be welded to each other and to the rotor shaft 8. An elastomeric material 15, having a thickness slightly less than the distance between the walls 13 is used as a positioning member for the blade 12. The width of the material 15 is selected so that the blade 12 is received between the walls 13 and extends therebeyond a distance about equal to the thickness of the barrel 1 plus /2 to inch.

Positioned below the barrel 1 such that the rims of the barrel ride thereon is a screen 16. The screen 16 contains holes 17 therein through which the water or other effluent, separated from the pulp, may pass. The screen 16 has a semicircular contour that corresponds generally to that of the rims 2. This may be done by providing screen retaining braces 18 that are carried by a screen retaining wall 19. The screen 16 is forced downwardly by the rims 2 into contact with the braces 18. The screen retaining walls 19 limit the travel of the screen 16 in a downward direction. FIG. 3 shows the screen being forced downwardly against the walls 19 by the dewatered plug 20 being pressed out of the apparatus FIG. 3 also shows the screen in position A where it is before the plug 20 depresses the screen 16 downwardly.

Two scraper blades 21 are held in place by scraper holders 22. Each scraper blade 21 is welded to the holder 22 at one end 23 and bent downwardly adjacent to its other end by a depending flange 24. The holder 22 is secured to the screen retaining walls 19. A spacer bar 25 separates the two so that a space is provided for the inclusion of an elastomeric spring member 26 which helps to force the screen 16 upwardly.

Connected to the drive shaft 7 at each end is a bell crank driving arm 27. The connection is made through the use of a connecting shaft 27a and a key 28. Attached to each bell crank driving arm 27 are two hydraulic cylinders 29. Suitable hydraulic system means 30, conventional in the art, are provided to operate conventional hydraulic cylinders 29 so that the bell crank may be moved clockwise and counterclockwise. The system means and hydraulic cylinders 29 are designed such that the bell crank 27 can be rotated about in a clockwise and counterclockwise direction or a total in all of about 90. It is also designed such that the hydraulic cylinders 29 carry the bell crank 27 to its full travel in one direction and then reverse it to travel a full path in the other direction. The system 30 and bell crank 27 are also designed so that the speed of travel toward the end of each path is slowed.

A suitable stand, designated generally by the number 31, is provided. In FIG. 2 it can be seen that the frame includes two vertical hub supporting members 32 on which hub 5 rides. Secured to the stand 31 is a formed support 33 for the screen 16. The support has the contour of the screen 16 when it is in place. In some instances it might be necessary to have formed supports 33 along the entire length ofthc screen 16. For simplicity, formed support 33 can be made integral with screen retaining wall 19.

The frame also includes two other vertical huh supporting members 34 that support bearings 35 which receive connecting shaft 27a.

At one side of the apparatus, and through the drive shaft 7 is introduced the slurry to be dewatered. The other end of the drive shaft 7 carries a cap 36 that prevents the slurry from leaking out.

As heretofore mentioned, the apparatus may be modified from the foregoing embodiment and the method still practiced. For example, the blade 12 may be secured to the rims 2 rather than to the rotor shaft 8. In such an embodiment the barrel is no longer secured to the rims 2 but instead discs are provided and attached to the rotor shaft 8 to position the barrel on the shaft. The discs are secured to the shaft 8 but not to the barrel 1 so that the latter is free to rotate independently of the rims 2 when the blade 12 contacts barrel 1.

In operation my press works as follows. The correct pressusre for the slurry to be dewatered is selected. The press rate is likewise determined. The slurry is fed through the rotor shaft 8 and discharged into the barrel 1 through the slots 10. Referring to FIG. 3 a part of the slurry will form in the bottom of the barrel 1 adjacent to the screen 16 and will also be received between the barrel 1 and the screen 16, an area designated generally by the number 37. The rims 2 prevent the slurry from escaping at the ends of the apparatus.

The rotor shaft 8 is caused, through the drive shaft 7 to move, as in FIG. 3, counterclockwise. The blade 12 forces the slurry clockwise, between the barrel 1 and the screen 16. In the start-up cycle the screen 16 will be in the A position and the force necessary to force it downwardly is such that the correct pressure for dewatering the slurry is obtained. Thereafter, the pressing of the slurry will be against the plug. The water or other liquid to be separated escapes through the screen 16 through holes 17. As used herein, the word water is meant to encompass water and other liquids.

As the blade rotates, it abuts the barrel 1, as shown in FIG. 4, and carries it along in the manner shown in FIG. 4. At this point the slurry is totally confined and a press chamber has been established. As the barrel 1 continues to rotate, slurry is introduced onto the screen behind the blade. Finally, the counterclockwise movement is stopped when the scraper blade 21 is contacted. The clockwise cycle is then commenced and proceeds in the same manner.

As heretofore set forth, moisture contents of 30-40 percent are possible using the foregoing method and apparatus. lnorder to do so the steps previously discussed must be followed. However, if one wants to use the apparatus for another purpose, as for example, an automatic self-cleaning screen, the criteria set forth as being critical for obtaining a 3040 percent water con tent need not be followed. For example, the V2 to inch width is no longer required. Also, the decreased press rate may be eliminated.

Having thusdesc'ribed my invention, I claim:

1. A method for dewatering materials comprising confining the material to be dewatered between two surfaces one constituting a perforated screen, the two surfaces being spaced apart a distance of about /2 to 1 of an inch whereby the dewatered material has a thickness ofbetween /2 to A of an inch, and pressing the material against itself in adirection parallel to the perforated screen at a press rate which decreases as the pressing continues, the pressure asserted on the material being about 300-3,000 psi, the water content of said dewatered material being reduced to below about 60 percent at a pressure of about 3,000 psi.

2. The method of claim 1 wherein the material is selected from the group consisting of spent grain, citrus pulp, pulp fines, groundwood, sulfite pulp, or kraft pulp.

3. The method of claim 2 wherein the initial press rate is about 7 feet per minute and the final press rate is below about 5 feet per minute.

4. The method of claim 3 wherein said material is sul- I fite pulp or kraft pulp, said pressure is about 3,000 psi, and said press rate is reduced to about 3 feet per minute during the latter part of the pressing cycle.

5. The method of claim 3 wherein the pressure at which the material is compressed against itself, the initial press rate, and the final press rate are selected from the charts in FIG. 6, whereby the moisture content of said material is reduced to below 50 percent.

6. A dewatering apparatus comprising a generally circular slurry chamber, said chamber having a longitudinal slot therein,

means for rotating said slurry chamber in a clockwise and a counterclockwise direction,

a blade, said blade extending through said clot,

means for rotating said blade in a slot, and counterclockwise direction,

a perforated screen, said screen positioned below said slurry chamber and spaced about /z to of an inch therefrom.

7. The apparatus of claim 6 wherein said means for rotating said slurry chamber and said blade includes a shaft extending through said chamber.

8. The apparatus of claim 7 wherein said blade is connected to said shaft and rotates said slurry chamber.

9. The apparatus of claim 7 wherein said chamber includes rims positioned at the ends thereof.

10. The apparatus of claim 9 wherein said blade is secured to said rims.

11. The apparatus of claim 7 wherein said chamber includes rims positioned at the ends thereof.

12. The apparatus of claim 11 wherein said rims ride on said screen, said rims are generally circular in diameter, and have a diameter that is V2 to inch greater than the diameter of said chamber.

13. The apparatus of claim 8 wherein said rims ride on said screen, said rims are generally circular in diameter, and have a diameter that is "/2 to 74 inch greater than the diameter of said chamber.

14. The apparatus of claim 10 wherein said rims ride on said screen, said rims are generally circular in diam eter, and have a diameter that is a to inch greater than the diameter of said chamber.

PATENT NO.

DATED INVENTOR(S) 1 UNITED STATES PATENT OFFICE February 4, 1.975

Edgar M. Pierce it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column Column Column insert Column Column Column Column 1, line 1, line line 5, line 6, line 6, line 6, line Arrest:v

RUTH C. MASON Arresting Officer 50, after "apparatus" and before "Fig. 3"

41, "pressusre" should be --pressure-.

36, "below" should be ---about--.

42, "clot" should be slot--.

"slot" should be --clockwise-.

Signed and Sealed this Thirty-first I 0f v August 1976 p C. MARSHALL DANN Commissioner oj'larents and Trademarks

Claims

1. A method for dewatering materials comprising confining the material to be dewatered between two surfaces one constituting a perforated screen, the two surfaces being spaced apart a distance of about 1/2 to 3/4 of an inch whereby the dewatered material has a thickness of between 1/2 to 3/4 of an inch, and pressing the material against itself in a direction parallel to the perforated screen at a press rate which decreases as the pressing continues, the pressure asserted on the material Being about 300-3,000 psi, the water content of said dewatered material being reduced to below about 60 percent at a pressure of about 3,000 psi.

4. The method of claim 3 wherein said material is sulfite pulp or kraft pulp, said pressure is about 3,000 psi, and said press rate is reduced to about 3 feet per minute during the latter part of the pressing cycle.

6. A dewatering apparatus comprising a generally circular slurry chamber, said chamber having a longitudinal slot therein, means for rotating said slurry chamber in a clockwise and a counterclockwise direction, a blade, said blade extending through said clot, means for rotating said blade in a slot, and counterclockwise direction, a perforated screen, said screen positioned below said slurry chamber and spaced about 1/2 to 3/4 of an inch therefrom.

10. The apparatus of claim 9 wherein said blade is secured to said rims.

12. The apparatus of claim 11 wherein said rims ride on said screen, said rims are generally circular in diameter, and have a diameter that is 1/2 to 3/4 inch greater than the diameter of said chamber.

13. The apparatus of claim 8 wherein said rims ride on said screen, said rims are generally circular in diameter, and have a diameter that is 1/2 to 3/4 inch greater than the diameter of said chamber.

14. The apparatus of claim 10 wherein said rims ride on said screen, said rims are generally circular in diameter, and have a diameter that is 1/2 to 3/4 inch greater than the diameter of said chamber.