GB1584574A

GB1584574A - Method and apparatus for pulping and grading waste material

Info

Publication number: GB1584574A
Application number: GB48313/77A
Authority: GB
Original assignee: Beloit Corp
Current assignee: Beloit Corp
Priority date: 1977-01-03
Filing date: 1977-11-21
Publication date: 1981-02-11
Also published as: DE2757175A1; BR7708598A; MX146734A; DE2757175C2; ES465629A1; IT1088976B; CA1068959A; JPS5737719B2; JPS5386810A

Description

(54) METHOD AND APPARATUS FOR PULPING AND GRADING WASTE MATERIAL (71) We, BELOIT CORPORATION, a Corporation organised and existing under the laws of the state of Wisconsin, United States of America, of Beloit, Wisconsin 53511, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the pulping and grading of waste material and more particularly to the pulping and grading of waste stock intended for use in paper or board making machines.

In this specification and claims the term "accepts" will be used to mean particles of waste material sufficiently small to pass through a grading screen or perforate area, and the term "rejects" will be used to mean particles which are too large to pass therethrough.

In one known apparatus for pulping and grading waste stock, the stock to be pulped and graded is introduced through a tangential inlet into a generally cylindrical chamber. An impeller generally disposed in an end wall remote from the tangential inlet provides for pulping.and rotational movement of the stock within the chamber. Accepts pass through a screen in the wall behind the impeller. In an apparatus of this general type disclosed in United States Patent Specification No. 3,844,488, heavy rejects are removed from the chamber through an annular recess while light rejects are permitted to accumulate in the central core of the chamber near the wall opposite the impeller. Periodically the light rejects are tapped off through an axial outlet in the wall opposite the impeller.The apparatus is designed on the assumption that such a pulping and grading machine acts in the nature of a vortex separator.

The rotational movement of the stock within the chamber results in large centrifugal forces and a significant increase in pressure near the outer periphery or cylindrical wall of the chamber. As a result of the inlet being located at the outer periphery of the chamber, a significantly large pressure head is required to force the stock into the chamber for processing. Further, due to the fact that the exact rate of accumulation of light-weight rejects adjacent the central portion of the wall opposite the impeller is not known. and can vary throughout the operation of the apparatus, it is basically guesswork how often and how long the lightweight rejects outlet should be opened.

The applicants have discovered that pulping and grading units of the type generally described above act more in the nature of a low power, heavy duty defibring screen rather than a vortex separator. The stock is pulped within the chamber and the accepts pass through the screen behind the impeller. Lightweight rejects tend to concentrate near the radially outermost edge of the wall containing the screen. Heavy rejects follow the flow of the fluid of the stock radially outwardly and axially away from the impeller and tend to accumulate along the outer cylindrical wall and adjacent the end wall opposite the impeller.

The lightweight rejects, therefore, may be continuously tapped off through the cylindrical wall in an area near the end wall containing the screen while the heavy rejects may be tapped off through an outlet in the cylindrical chamber near the wall opposite the impeller.

The inlet, therefore, can be disposed in the wall opposite the impeller and located centrally thereof. With such an arrangement, since the inlet is disposed centrally of the wall and on the axis of rotation of the impeller, the pressure required to force the stock into the apparatus is reduced quite significantly compared with the known apparatus; in some cases to the extent that the stock can be introduced into the apparatus merely by gravity.

Applicants have also discovered that, quite surprisingly, efficiency of removal of waste material increases as the inlet flow increases.

It is an object, therefore, of the present invention to provide a pulping and grading method and apparatus with reduced power requirements without significant loss in pulping and separating efficiency.

According to the invention there is provided an apparatus for pulping and grading waste material comprising: a cylindrical chamber having a first end wall, a second end wall, a cylindrical wall, and a central axis extending through said chamber and both end walls thereof; a perforate area disposed in said first wall; an impeller in said chamber adjacent said perforate area and having its rotational axis coincident with said central axis; a stock inlet opening disposed centrally in said second end wall; an outlet in said chamber, for light rejects, disposed radially outwardly of said perforate area; an outlet, for heavy rejects, in said cylindrical wall; and means providing a takeoff chamber to receive a stream of stock passing through said perforate area.

The invention also provides a method of separating stock in a separator unit of the type comprising a cylindrical chamber having a cylindrical wall, a first end wall having a perforate area, a second end wall opposite said first end wall, a central axis extending through said chamber and both end walls thereof, and an impeller in said chamber adjacent said perforate area and having its rotational axis coincident with said central axis, the method comprising: introducing stock through an inlet in the axial centre of said second end wall; removing light rejects through an outlet in said chamber disposed radially outwardly of said perforate area; removing heavy rejects from an outlet in said cylindrical wall; and receiving in a takeoff chamber a stream of stock passing through said perforate area.

The following is a more detailed description of one embodiment of the invention reference being made to the accompanying drawings in which: Figure 1 is a side view of an apparatus constructed in accordance with the present invention with portions broken away; Figure 2 is a sectional view of the apparatus of Figure 1 taken substantially along line 2-2 of Figure 1 with portions broken away; Figure 3 is a graph illustrating the inlet pressure requirements of the method and apparatus of the present invention compared to a prior art method and apparatus; and Figure 4 is a graph illustrating the lightweight rejects removal efficiency of the method and apparatus of the present invention compared to a prior art method and apparatus.

With reference to the drawings, and in particular Figures 1 and 2, there is illustrated an apparatus 1 for pulping and grading waste material, particularly for pulping and grading waste paper. The apparatus 1 includes a generally cylindrical chamber 2 defined by a substantially cylindrical wall 3, a first end wall 4? and a second end wall 5. While the chamber is illustrated as being truly cylindrical with flat end walls, it will be appreciated that the cylindrical wall need not be perfectly flat. The ends walls 4 and 5 may, for example, merge with the cylindrical wall 3 through a smooth curve. For the purposes of describing the location and orientation of the various parts, an axis 6 extending perpendicularly through the centre of both end walls and through the centre of the cylindrical chamber will be referred to hereinafter as the central axis 6.

A generally circular or annular perforate area 7 is located centrally in the first end wall 4, the periphery of the perforate area being spaced from the cylindrical wall 3. This perforate area provides a screening arrangement for permitting accepts to pass through the end wall 4 and may have holes or perforations of whatever size and shape as is desired for most efficient screening of the particular type of stock being used, taking into consideration the specific quality and grade of accepts required.

An impeller 8 is disposed within the chamber in a known manner adjacent the perforate area 7, with its rotational axis coincident with the central axis 6 of the apparatus 1. A shaft 9, which is connected to a source of rotational power (not illustrated), extends through the end wall 4 and is operably connected to the impeller 8 to impart rotational motion thereto.

A supply pipe 10 is connected to an inlet nozzle 11 disposed centrally within the second wall 5. The inlet nozzle 11 has its centre coincident with the central axis 6 of the chamber 2 and provides for stock to enter the chamber 2 through the second end wall 5 and at a point directly opposite the impeller 8.

A light rejects outlet 12 is located in the apparatus 1 in an area disposed radially outwardly of the perforate area 7. More specifically, the light rejects outlet 12 is located in the cylindrical wall 3 and immediately adjacent the first end wall 4. Further, as best seen in Figure 2, the light rejects outlet 12 exits from the cylindrical wall 3 in a direction which is tangential to the cylindrical wall 3 and is connected to a light rejects pipe 13..Although it is not illustrated, it may be desirable to have a pump connected to the pipe 13 for assisting in transporting light rejects to the next point in the process.

A heavy rejects outlet 14 is disposed in the cylindrical wall 3 near the second end wall 5.

In the specific embodiment illustrated, the heavy rejects outlet 14 is disposed immediately adjacent the first wall 5. This provides the heavy rejects outlet at the point of last migration of heavy particles along the cylindrical wall 3, thus avoiding the build-up of heavy rejects adjacent the second wall 5, which rejects would continue to whirl around the chamber causing excessive wear. Also, as best seen in Figure 2, the heavy rejects outlet extends in a direction tangential to the cylindrical wall 3 and is connected to a rejects pipe 15.

An accepts chamber 16 is connected to the first wall 4 and encloses the area outside the chamber 2 adjacent the perforate area 7 for receiving accepts passing through the perforate area 7. An exit pipe is connected to the accepts chamber 16 and is in communication with an accepts pipeline 18.

In the particular embodiment illustrated, the direction of rotation of the impeller 8 is indicated by the arrow 19 (Figure 2). Thus, it can be seen that not only are the light rejects outlet 12 and heavy rejects outlet 14 disposed in directions tangential to the cylindrical wall 3, but they also are arranged to extend away from the wall in the general direction of rotation of the impeller 19. The impeller 19 imparts a pumping and whirling motion to the slurry or stock within the chamber, generally in the direction of the arrows 20. The stock enters the inlet nozzle 11 as generally indicated by the arrow 21. The inlet nozzle 11 extends in a direction along the central axis 6 to provide that the stock enters the chamber 2 in a direction along the central axis 6 and toward the impeller 8.The impeller 8 provides a pulping action and imparts the whirling motion described above which causes the stock to rotate through the chamber 2 in the direction of the arrows 20 illustrated in Figure 2. The whirling stock proceeds rearwardly from the first wall 4 toward the second wall 5,-as illustrated by the arrows 20 in Figure 1.

Accepts pass through the perforate area 7 into the accept chamber 16 and subsequently out through the exit pipe 17. Fine rejects become concentrated adjacent the first wall 4 and are continuously tapped off through the light rejects outlet 12. Heavy rejects are thrown radially outwardly by centrifugal force and migrate rearwardly toward the second wall 5 and are rejected through the heavy rejects outlet 14.

The apparatus of the present invention was compared with a known apparatus with respect to inlet pressure requirements and capability of separating light-weight rejects. i.e., rejects having a specific gravity less than 1. The known apparatus included a generally cylindrical chamber having a first end wall with a perforate area and an impeller immediately adjacent thereto. The second end wall was disposed opposite the first end wall with a light rejects outlet disposed at the axial centre thereof. The stock inlet was tangential to the cylindrical wall and located adjacent the second wall. The known apparatus, therefore, was similar to the apparatus of the present invention with the exception that the inlet df the known -apparatus was located in the cylindrical wall and the light rejects outlet was located centrally in the end wall opposite the impeller.

As illustrated in the following table and in Figures 3 and 4, the required inlet pressure for a given accepts flow was signifiantly less for the apparatus constructed in accordance with the present invention than for the known apparatus.

GPM ACCEPTS PSI INLET % OF LIGHT-WEIGHT FLOW PRESSURE REJECTS REMOVAL Prior Art 200 17 38.4 Separator 300 18.5 32.7 400 18.5 20.0 Separator of 100 7.75 41.7 Present 205 8.5 34.9 Invention 320 11 47.2 400 14 37.5 The efficiency in removing lightweight contaminates, or the percentage of lightweight rejects removed, was significantly greater with the apparatus constructed in accordance with the present invention, particularly at the higher flow rates. This is particularly valuable since heretofore known separators have decreased in efficiency of removal of lightweight rejects as the accepts flow rate increased. The apparatus of the present invention, however, provides essentially no decrease in efficiency of removal of lightweight rejects as the accepts flow increases.

It can be seen, therefore, that the present invention provides an apparatus and a method for pulping and separating waste material which can substantially reduce the inlet pressure required with no significant loss in efficiency of removal of lightweight rejects, and can provide improvements in the removal of lightweight rejects at higher flow rates. This permits an increase in flow and thus an increase in production. In addition, all this can be accomplished with a reduction of power requirements to get the stock into the pulper/separator and sometimes with the inlet pump eliminated altogether.

WHAT WE CLAIM IS: 1. An apparatus for pulping and grading waste material, comprising; a cylindrical chamber having a first end wall, a second end wall, a cylindrical wall, and a central axis extending through said chamber and both end walls thereof; a perforate area disposed in said- first wall; an impeller in said chamber adjacent said perforate area and having its rotational axis coincident with said central axis; a stock inlet opening disposed centrally in said second end wall; an outlet in said chamber, for light rejects, disposed radially outwardly of said perforate area; an outlet, for heavy rejects, in said cylindrical wall; and means providing a takeoff chamber to receive a stream of stock passing through said perforate area.

2. An apparatus as claimed in claim 1, wherein said perforate area is annular.

3. An apparatus as claimed in claim 1 or claim 2, wherein the periphery of said perforate area is spaced from said cylindrical wall.

4. An apparatus as claimed in any of claims 1 to 3, wherein the outlet for light rejects is located in said cylindrical wall adjacent said first wall.

5. An apparatus as claimed in claim 4, wherein the outlet for light rejects is tangential to said cylindrical wall and arranged to discharge the light rejects in the direction of rotation of said impeller.

6. An apparatus as claimed in any of claims 1 to 5, wherein the outlet for heavy rejects is located adjacent said second wall.

7. An apparatus as claimed in claim 6, wherein the outlet for heavy rejects is tangential to said cylindrical wall and is arranged to discharge the heavy rejects in the direction of rotation of said impeller.

8. An apparatus as claimed in any of claims i to 7, wherein a stock inlet pipe, leading to said stock inlet opening, has its axis coincident with said central axis for a sufficient length of said pipe such that the stock enters said cylindrical chamber in a direction along said central axis and toward said impeller.

9. A method of separating stock in a separator unit of the type comprising a cylindrical chamber having a cylindrical wall, a first end wall having a perforate area, a second end wall opposite said first end wall, a central axis extending through said chamber and both end walls thereof, and an impeller in said chamber adjacent said perforate area and having its rotational axis coincident with said central axis, the method comprising; introducing stock through an inlet in the axial centre of said second end wall; removing light rejects through an outlet in said chamber disposed radially outwardly of said perforate area; removing heavy rejects from an outlet in said cylindrical wall; and receiving in a takeoff chamber a stream of stock passing through said perforate area.

10. A method as claimed in claim 9, wherein said light rejects are removed from said chamber through an outlet located in said cylindrical wall and disposed adjacent said first end wall.

11. A method as claimed in claim 9 or claim 10, wherein the heavy rejects are removed through an outlet located in said cylindrical wall and disposed adjacent said second end wall.

12. A method as claimed in any of claims 9 to 11, wherein said light rejects and said heavy rejects are removed from said chamber respectively in directions which are tangential to said cylindrical wall and in the direction of rotation of said impeller.

13. A method as claimed in any of claims 9 to 12, wherein said stock is introduced into said chamber along the central axis thereof and in a direction toward the impeller.

14. An apparatus for pulping and grading waste material substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The efficiency in removing lightweight contaminates, or the percentage of lightweight rejects removed, was significantly greater with the apparatus constructed in accordance with the present invention, particularly at the higher flow rates. This is particularly valuable since heretofore known separators have decreased in efficiency of removal of lightweight rejects as the accepts flow rate increased. The apparatus of the present invention, however, provides essentially no decrease in efficiency of removal of lightweight rejects as the accepts flow increases. It can be seen, therefore, that the present invention provides an apparatus and a method for pulping and separating waste material which can substantially reduce the inlet pressure required with no significant loss in efficiency of removal of lightweight rejects, and can provide improvements in the removal of lightweight rejects at higher flow rates. This permits an increase in flow and thus an increase in production. In addition, all this can be accomplished with a reduction of power requirements to get the stock into the pulper/separator and sometimes with the inlet pump eliminated altogether. WHAT WE CLAIM IS:

1. An apparatus for pulping and grading waste material, comprising; a cylindrical chamber having a first end wall, a second end wall, a cylindrical wall, and a central axis extending through said chamber and both end walls thereof; a perforate area disposed in said- first wall; an impeller in said chamber adjacent said perforate area and having its rotational axis coincident with said central axis; a stock inlet opening disposed centrally in said second end wall; an outlet in said chamber, for light rejects, disposed radially outwardly of said perforate area; an outlet, for heavy rejects, in said cylindrical wall; and means providing a takeoff chamber to receive a stream of stock passing through said perforate area.

2. An apparatus as claimed in claim 1, wherein said perforate area is annular.

15. A method for pulping and grading waste material substantially as hereinbefore

described with reference to the accompanying drawings.