US2505513A - Method of and apparatus for screening paper pulp - Google Patents

Description

April 25, 1950 w, YOUNG ET AL 2,505,513

METHOD OF AND APPARATUS FOR SCREENING PAPER PULP Filed Feb. 1, 1944 INVENTOR. I FRANK W. YOU/VG 5y JVf/Y4F4HL6ZQf/Y fiTTOR/VEYS Patented Apr. 25, 1950 METHOD OF AND APPARATUS FOR SCREENING PAPER PULP Frank W. Young, Medfield, and Sven A. Fahi ren, Wrentham, Mass, assignors to Bird Machine Company, South Walpole, Mass, a corporation of Massachusetts Application February 1, 1944, Serial No. 520,608

3 Claims.

1 This invention relates broadly to the removal of chips and knots, of wood, from raw paper pulp stock, although not so limited. More particularly. the invention relates to the prevention of troublesome foam in the instrumentality utilized to remove or separate the chips and knots from the paper pulp.

* Paper pulp, manufactured from wood by any of the several chemical processes contains chips and knots. Such chips and knots are removed by various types of screens and so-called knotters. Most chemical pulps, such as those of the soda and sulphate types, as they come from the digesters, contain a foam producing liquor. It would be desirable, therefore, to wash the pulp free of such liquor before it is screened or knotted in-order to prevent the occurrence of foam in the knotter because such foam is often so troublesome that the operation of the knotter is difficult, if not impossible. On the other hand, the washing of the pulp is seriously hindered by the presence of chips and knots so that it would be of great advantage to screen and knot the stock be fore washing.

It is therefore an object of this invention to screen and knot the raw unwashed stock without producing foam. It is to be understood that bubbles or foam are produced when air becomes mixed with soapy liquor. Consequently, if air is eliminated or prevented from entering the soapy liquor, the foam is not formed. It is, therefore, a further object of the invention to so operate the knotter that air will not be mixed with the liquor flowing to and through the knotter. Accordingly the stock is introduced into the liqnor fed to the knotter below the level of such liquor.

Yet another object of the invention is a practical instrumentality by which to introduce the stock into the liquor in the knotter. To this end, the stock is introduced into the knotter box through a spout disposed below the level of liquid in the box.

The invention also seeks a method of an appsratus for screening unwashed stock without troublesome foam and at a relatively high consistency in the interest of relatively high capacity, relatively high pulp consistency, ease and convenience of operation and compactness of installation.

These and other objects of the invention and the means for their attainment will be more apparent from the following detailed description, taken in connection with the accompanying drawion, illustrating one embodiment by which the 2 invention may be realized and in which the annexed drawing is a somewhat diagrammatic view showing a blow tank from which the stock is delivered directly to the instrumentality in which tne knots and chips are separated from the raw s ock.

Referring to the drawing, it will be understood that the stock is blown from the digester (not shown) through the pipe 3 to the blow tank 5 at, say. about 12% consistency. It is diluted with black liquor entering from pipe I in the conical bottom 8 to about, say, 4% to 6% consistency. This consistency is regulated and maintained by the power input to the motor 9 which drives the agitator l l.

The stock, containing the chips and knots l2, and at, say, 5% consistency, is pumped by pump l3 from the blow tank 5 through pipe to a spout or nozzle I5 disposed above a screen 20 but with its open mouth submerged below the level is of the liquor, Thus no air is permitted to mix with the stock emerging from the spout l5 and the spout is shown as of progressively increasing diameter whereby turbulence is prevented and thus bubbles and foam are not formed.

In the illustrated embodiment, the screen box ill and trough l8 are illustrated as taking, generally, the form of the screen shown in United States Patents Nos. 2,222,146 and 2,293,978, although the method of this invention is not dependent for its utility upon the use of such screen box and trough since any screen serving the purpose is within the purview of the invention. In the illustrated embodiment, the screen 2|] is 1 formed with an upwardly inclined or otherwise exposed or unsubmerged screen portion 2i and is so mounted as to be capable of agitation or vibration. Spring suspension devices for the knotter box H may take the form shown in the patents and are schematically indicated at 23 and which are mounted in fixed position and connected as by pin 39 to the side wall of the box ill. The knotter box may be agitated by any convenient vibrating device, for instance, the eccentric connection indicated schematically at 25, which may be operated by motor means, not shown, as in the patents.

The chips and knots which enter the knotter box I] from the nozzle l5 travel along the unsubmerged portion of the screen and are here shown as travelling up the inclined portion 2| of the screen plate as the result of the vibratory action of the screen plate 20 and are discharged over the end of the screen 20 and into, say, the conduit 28 by which they are evacuated. The screened 3 stock, free of chips and knots (known as accepted stock), passes through the screen plate- 24 and falls into the lower portion of the trough II from which, contrary to the practice of the patents, it flows through the outlet 30 and pipe 32 into the compartment 33 where it is preferably diluted to about 1% consistency by liquor entering through pipe 35. The liquid level 34 in compartment 33, which regulates or controls the liquid level I9 in the knotter l1, I8 is maintained by controlling the flow of fluid in the outlet, here shown as by a float 38 controlling the outlet valve 35 in the conduit 31, by which the diluted stock is conducted to any type of pulp washer, not shown. Here, again, the outgoing accepted stock is conducted in a constant steady flow without the opportunity to become aerated and hence the formation of foam at this point is also avoided.

Various modifications will occur to those skilled in the art in the configuration and disposition of the component elements going to make up the invention as a whole as well as in the several features thereof capable of separate use and for other purposes, and no limitation is intended by the phraseology cf the foregoing description or illustrations in the accompanying drawings excent as indicated in the appended claims.

What is claimed is:

1. The method of screening knots and chips from paper pulp with freedom from troublesome foam which comprises feeding the pulp through a downwardly and outwardly inclined conduit formed with a bell-shaped submerged end disposed immediately above a vibrating submerged screen to thereby prevent the admission of air to the paper pulp fed to the screen.

2. The method of screening knots and chips of the soda and sulphate types with freedom from troublesome foam which comprises feeding the pulp through a downwardly and outwardly inclined conduit whereof the mouth is closely positioned to a curvilinear screen secured at its one end to an end of the knotter box and whereof its other end extends upwardly whereby 45 onthcvibrationofthescreentheknotaare caused to travel up the screen and are discharged over the end wall'of the knotter box.

3. Apparatus for treating paper pulp of a consistency in excess of 2%, comprising a screen, means to control the level of liquid to a predetermined elevation above the area of the screen and means to introduce stock into the liquid above the screen at a level below the level of the liquid.

- FRANK W. YOUNG.

BVEN A. FAHLGREN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Control of Beater Furnish to Eliminate Foaming on Paper Machines, Technical Association Papers, Series XI, pp. 57 and 58, (1928).

A Survey of Pitch Troubles in the Manufacture and Use of Sulphite Pulp. Technical Association Papers, Series XIX, p. 189, 1936.

The Manufacture of Pulp and Paper, v01 IV, section 7, p. 29, 1928.

Images