Screening Apparatus

Abstract

Screening and defibering apparatus which includes a chamber which is preferably, but not necessarily, rectangular in cross section, and which is subdivided into a central intake section and outwardly disposed outlet sections by a pair of spaced, parallel, foraminous walls. A slurry of the material to be treated is passed through an intake line into the intake section where it is subjected to mechanical and hydraulic shear forces by a pair of rotors, each of which is rotatably mounted in the intake section in closely spaced relationship to one of the foraminous walls. Accepted portions of the slurry pass through perforations in the foraminous walls into the outlet sections for removal through outlet lines while rejected material is bled from the intake chamber, either periodically or continuously, through a reject line. A rinse line may also be utilized, feeding into the intake chamber, to assist in purging the system.

Description

BACKGROUND OF THE INVENTION

In the preparation of papermaking stock, whether from virgin fibers or waste paper, it is desirable to reduce the raw material to a slurry of individual fibers and screen out foreign objects and undefibered portions of the raw material. In conventional operations this is generally accomplished in two steps, a defibering operation followed by screening.

Additionally, although it is generally desirable to maintain the consistency of the papermaking stock relatively high and reduce it to normal papermaking consistency just prior to delivery of the stock to the papermachine headbox or the like, the capabilities of conventional stock preparation equipment have necessitated maintaining the consistency of the stock fairly low.

Conventional stock preparation equipment also places limitations on the quality of the stock being screened. Thus, the proportion of rejects must be kept fairly low to prevent overloading of the screening equipment and the presence of stringy materials must be reduced as much as possible, since they tend to hang up in the holes of vibrating screens and jam the foils in pressure type screens.

While the above discussion referes specifically to the preparation of papermaking stock it should be noted that the same general considerations apply to other processes which are, in fact, quite dissimilar to normal papermaking operations. For example, in a recently developed process for the treatment of solid waste materials of the class typified by municipal and industrial refuse, both of which are likely to contain a high proportion of fibrous material such as paper, reduction and screening of the solid wastes are essential.

Thus, as disclosed in application Ser. No. 861,778, filed Sept. 29, 1969, now U.S. Pat. No. 3,595,488, issued July 27, 1971, solid waste materials may be treated by depositing them in a waste treatment tub with an aqueous medium and subjecting them to mechanical and hydraulic shear forces through the rotation of a rotor having swinging flails or hammers mounted on some of its rotor arms. Relatively infrangible portions of the waste material are removed separately from the waste treatment tub while the remaining portions are degraded to a predetermined particulate size or smaller and removed in slurry form through perforations in the tub for further treatment.

For the purposes of the treatment which the slurry of waste material receives subsequent to its withdrawal from the waste treatment tub, it has been found desirable to provide equipment which is capable of operation on slurries of relatively high consistencies containing relatively large amounts of rejects. Additionally, it is preferable that such equipment exert a defibering as well as a screening effect so that undefibered material may be reduced sufficiently to pass therethrough. Since solid waste material will often contain a high proportion of stringy material it is also essential that such equipment be relatively insusceptible to jamming or blockage of the type experienced by conventional vibrating and pressure type screens.

SUMMARY OF THE INVENTION

The present invention provides screening and defibering apparatus which includes a chamber of substantially rectangular cross section divided by a pair of foraminous walls into an intake section and a pair of outwardly disposed outlet sections with a pair of opposed rotors rotatably mounted within the intake section in closely spaced relationship to the foraminous walls.

The material to be treated, whether a slurry of paper-making fibers, pulped solid wastes or other material, is fed into the intake section and those portions which have been reduced sufficiently prior to introduction into the intake section pass through the foraminous walls into the outlet sections. The remaining material is subjected to violent hydraulic and mechanical shear forces generated in the intake section which will defiber undefibered portions of the material, after which these portions may also pass through the perforations in the foraminous walls.

It should be noted that during this screening-defibering operation although undefibered portions of the slurry tend to be defibered by the above noted hydraulic and mechanical shear forces, those portions which are already of a size which permits them to pass through the perforations in the foraminous walls readily do so without further reduction in size. In this way, although a defibering action is created, it is done without the generation of an undue amount of fines and fibers of undesirably short lengths.

The rotors are so shaped that they exert a pulsating pressure on the foraminous walls, thereby preventing the obstruction of the perforations through these walls. Stringy, defiberable materials, rather than blocking the perforation as in the case of vibrating screens or jamming the rotors as in the case of rotating foils, are reduced in size by the rotors and then pass through the perforations in the foraminous walls. Non-defiberable materials, such as plastics, rubber, leather, textiles and the like, are accumulated in the inlet chamber and rejected. By forming the chamber, or at least the intake section thereof, of rectangular cross section the slurry is prevented from spinning in a regular pattern and instead, a highly turbulent condition is generated. While a rectangular cross section is the preferred configuration, other configurations such as cylinderical, properly baffled, may also be employed. It will also be seen that by mounting the rotors in opposition to each other balanced thrust forces are obtained which greatly enhance bearing design, facilitate construction and reduce cost.

Particularly where the screening apparatus is operated on an intermittent basis, it is desirable to have a rinse line communicating with the interior of the intake section of the chamber which can be turned on when the slurry feed to the intake section is discontinued to clean the system and wash the rejects that have been retained in the intake section.

Apparatus according to the present invention, therefore, is ideally suited for the screening and defibering of papermaking stock at a variety of points in the papermaking stock preparation system as well as in the treatment of slurries of pulped solid waste materials. In either case, apparatus according to the present invention is capable of handling slurries containing high proportions of rejects and at relatively high consistencies and of screening and defibering such slurries with little danger of malfunction through blocking, jamming or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of screening apparatus in accordance with the present invention;

FIG. 2 is an elevational view of the apparatus of FIG. 1 with portions broken away for clarity;

FIG. 3 is a view taken on line 3--3 of FIG. 2;

FIG. 4 is a somewhat diagrammatic view showing a typical installation of the screening apparatus of the present invention;

FIG. 5 is a view wimilar to FIG. 4 but showing a second installation in which the present invention may be used; and

FIG. 6 shows still a third installation of apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1-3 of the drawings, it will be seen that apparatus 10 in accordance with the present invention includes a substantially rectangularly cross sectioned chamber 12 which is subdivided into an intake section 14 and a pair of flanking outlet sections 16 by means of a pair of spaced, parallel, foraminous walls 18. A drive shaft 20 extends completely through the chamber 12 and has its end portions journaled outwardly of the chamber, as at 22. A pair of rotors 24 are fixed to the drive shaft 20 in opposed relationship to each other and in closely spaced relationship to the perforated central portion 25 of each of the foraminous walls 18. Means, such as the motor 26, sheaves 28 and 30, and the interconnecting pulley belt 32, serve to impart rotational movement to the drive shaft 20 and the rotors 24 attached thereto, and in this regard it will be seen that by mounting the rotors in opposed relationship the thrust forces generated by rotation of the rotor are balanced.

Each of the rotors 24, as best seen in FIG. 3 of the drawings, is of the type shown in U.S. Pat. No. 3,073,535 and includes a central hub portion 34 and a plurality of outwardly projecting rotor arms 36, each of which has a substantially planar leading edge 37 and a curved trailing edge 38. Deflecting bars 39 and 40 are also provided attached to opposed portions of the rotor 24 and perforated section 25, respectively, in angular relationship to each other. An inlet 42 delivers the slurry to the intake section 14 of the chamber 12 while a reject line 44 may be provided for withdrawing rejected material which does not pass through the perforated sections of the foraminous walls 18. It will be apparent, however, that it is within the scope of the present invention both to deliver slurry and to withdraw rejects through the same line. Entrance to the outlying outlet sections 16 of the apparatus 10 is, of course, through the perforated section 25 of each of the walls 18, and outlet lines 46 are provided for withdrawing accepted material from the outlet sections.

Turning now to FIG. 4 of the drawings, one system in which the screening apparatus of the present invention finds utility is shown. As seen in FIG. 4, raw material, such as waste paper which may contain such things as plastics and wet strength paper, is fed together with an aqueous medium into a pulper which may be of the same general type as that shown in the above noted U.S. Pat. No. 3,073,535. Pulper 50 may include upstanding sidewalls 52 and a perforated bed plate 54, above which is rotatably mounted a rotor 56, preferably of the type described above. Raw material deposited in the pulper is subjected to a defibering action by the rotor 56 so that a substantial portion thereof will pass from the pulper through the perforated bed plate 54 for further treatment, such as fine screening etc. Associated with the pulper may be a purging device, indicated diagrammatically at 58, which removes from the pulper materials such as plastics, wet strength papers, and other relatively undefiberable materials. Such materials may then be pumped by means of a pump 60 to a liquid cyclone 62 for the removal of high specific gravity materials such as grit and the like. The slurry of accepts from the liquid cyclone, which will contain, as noted above, plastic and high wet strength papers and other fibrous materials, may then be delivered to the screening-defibering apparatus 10 of the present invention.

In the apparatus 10, the rotors 24, turning, for example, at speeds of approximately 3,500 feet per minute at their outer ends, subject the slurry to violent mechanical and hydraulic shear and maintain the slurry in a highly turbulent condition. The deflecting bars 39 and 40 exert a scissors-like effect on any particles which might otherwise tend to lodge beneath the rotor, and with the rotor maintain the perforations in the wall 18 unobstructed. The rotors 24 impart a pumping or pulsating effect on the perforated walls 18 which not only serves to maintain the perforations unobstructed but also provides some defibering action on such materials as wet strength papers. Solid portions of the slurry of the proper size pass through the perforations in the walls 18 into the outlet sections 16 of the screening apparatus. From these sections the reduced and screened material is then continuously removed through the outlet lines 46 and recycled to the pulper 50 by means of a conduit 64 for futher treatment in the system.

Although there is preferably a continuous withdrawal of the accepted material from the screening apparatus, the feed into the system and the withdrawal of rejects therefrom may be accomplished either periodically or on an intermittent basis. If the feed and withdrawal of rejects are on a non-continuous basis, the rejects line 44 will ordinarily be maintained closed by a valve member 66 and a rinse line 68 is provided, normally maintained closed by means of valve member 70 as material is fed into the system. After some predetermined time, or when it has been determined that a certain amount of reject material has built up in the intake chamber, the feed line 42 may be closed by means of a valve 72 and the rinse line 68 and reject line 44 opened. This permits the system to be cleaned as the rejects are withdrawn and provides cleaner rejects from the intake chamber, particularly if the rinse line is open while the reject line remains closed, since this sequence provides for flushing of fiber to the outlet lines 46 for accepted material.

In the installation described above the apparatus of the present invention is utilized for processing material bled from the slurry being treated in the pulper. The screening-defibering apparatus 10, however also finds utility in other installations, as seen in FIG. 5 of the drawings. Thus, rejects from a primary screen 80 may be passed to holding tank 82 and thence, by means of a pump 84 through the feed line 42 into the intake section 14 for treatment as above. The accepts from the outlet sections 16 can of course be returned to the system with the accepts from the primary screen 80 while the rejects are then drained through line 44 and disposed of in a suitable manner.

In the above discussion the apparatus 10 is described in conjunction with the screening and defibering of fibrous materials such as papermaking stock. As noted above, however, apparatus of the present invention also finds utility in other processes, such as the treatment of solid waste materials. Thus, as seen in FIG. 6 of the drawings, solid waste materials, which may include such things as fibers, glass, ferrous and non-ferrous metals, plastics, food waste, and other organics and inorganics, may be dumped into a treatment vessel 90 having a rotor 92 of the type described above mounted in the bottom thereof, where the frangible portions of the solid waste materials are reduced in the presence of water or the like to a size sufficient to be extracted through a perforated bed plate 94.

A pump 96 then delivers the slurry of reduced solid materials and water to a liquid cyclone 98 where a major portion of the inorganics, such as metal, glass, stone, ceramics, etc., are removed and the remaining material, containing a high percentage of fibrous material, delivered through the line 42 into the intake section 14 of the screening and defibering apparatus 10. The rotors 24, turning at relatively high speeds in the preferably rectangularly cross sectioned intake section 14, create a highly turbulent condition which has a defibering effect on relatively undefibered materials in the section 14. At the same time, the flat leading edge of the rotors and the interreaction of the rotors and the surfaces of the intake section exert a mechanical reducing effect on the solid materials introduced into the intake section 14.

As a result of these hydraulic and mechanical shear forces a substantial portion of the material which is not initially of a size sufficiently small to pass through the perforations in the foraminous walls 18 is reduced to a point where it may do so. It will also be seen that the rotors exert a pulsating pressure on the foraminous walls 18 which serves to maintain the openings through the walls unobstructed and to prevent blockage of the system. As in the embodiments described above, operation of the apparatus 10 may be on either an intermittent or continuous basis and a rinse line 68 may be provided for purging the system. Again, as noted above, the apparatus 10 may handle relatively high consistency slurries of materials containing relatively high percentages of rejects and containing traditionally bothersome materials such as stringy materials and still provide trouble free, efficient operation.

While the forms of apparatus herein described constitutes preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention.

Claims

What is claimed is:

1. Apparatus of the type described comprising:

a. means defining a substantially enclosed chamber,

b. foraminous wall means mounted in said chamber and dividing said chamber into intake and outlet sections,

c. said intake and outlet sections communicating through said foraminous wall means,

d. rotor means rotatably mounted in said intake section in closely spaced relationship to said foraminous wall means,

e. inlet and accepts outlet defining means into and from said intake and outlet sections, respectively,

f. means defining a reject outlet from said intake section of said chambers, and

g. means for opening and closing said reject outlet.

2. The apparatus of claim 1 comprising:

a. a drive shaft extending through said chamber,

b. said rotor means being mounted on said drive shaft, and

c. means positioned outwardly of said chamber and journaling end portions of said drive shaft for rotation thereof.

3. The apparatus of claim 1 wherein each of said rotor means comprises:

a. a central hub portion, and

b. a plurality of rotor arms attached to and extending outwardly from said hub portion,

c. each of said rotor arms having a substantially planar leading edge.

4. The apparatus of claim 3 wherein:

a. said intake section is substantially rectangular in cross section.

5. Screening apparatus comprising:

a. a substantially enclosed chamber including pairs of opposed, parallel front and back, top and bottom and end walls,

b. a pair of foraminous walls extending in spaced parallel relationship to said end walls and defining therebetween a centrally disposed inlet section, and with said end walls, a pair of outlet sections communicating with said inlet sections through said foraminous walls,

c. a drive shaft extending through said end and foraminous walls and journalled outwardly of said outlet sections,

d. a pair of rotors each including a central hub and outwardly projecting arms have substantially planar leading edges mounted on said shaft within said inlet chamber and in overlying relationship to said foraminous walls,

e. an inlet line having a valve member therein communicating with said inlet chamber,

f. a rinse line having a valve member therein communicating with said inlet line intermediate said inlet chamber and said inlet line valve,

g. a reject line having a valve member therein communicating with said inlet chamber, and

h. an outlet line communicating with each of said outlet chambers.

6. The apparatus of claim 1 further comprising:

a. a rinse line including control means therefor connected with said inlet means.