US3563387A

US3563387A - Centrifugal thickener

Info

Publication number: US3563387A
Application number: US772253A
Authority: US
Inventors: Alf Torsten Okvist; Nils Olof Nilsmar
Original assignee: Eie Maskin Ab N A
Current assignee: MASKIN N A EIE AB
Priority date: 1967-11-02
Filing date: 1968-10-31
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16
Also published as: SE351372B

Abstract

A slurry thickener in which are employed both centrifugal force and an axial pressing force. The latter is made possible by the special conical configuration of the end portions of an otherwise cylindrical thickening cylinder.

Description

s21 U.S. Cl.

United States Patent [72] Inventors Alt'Torsten Okvist Skarblacka;

Nils Olof Nilsmar, Kallhall, Sweden [21] AppLNo. 772,253

[22] Filed Oct. 31,1968 [45] Patented Feb. 16, 1971 [73] Assignee Maskin AB N.A. Eie [32] Priority Nov. 2, 1967 [33] Sweden [31] 15,033/67 [54] CENTRIFUGAL THICKENER 5 Claims, 3 Drawing Figs.

[51] Int. Cl B0411 3/02 [50] Field of Search 210/376 [56] References Cited UNITED STATES PATENTS 1,944,391 1/1934 Altpeter 210/376 Primary Examiner-J. L. DeCesare Attorney-Pierce, Scheffler & Parker ABSTRACT: A slurry thickener in which are employed both centrifugal force and an axial pressing force. The latter is made possible by the special conical configuration of the end portions of an otherwise cylindrical thickening cylinder.

Patented Feb. 16, 1971 3,563,387

' Sheets-Sheet 1 v Fig.7

3 Sheets-Sheet 2 Patentd Feb. 15,1911

Patented Feb. 16, 1971 3 Sheets-Sheet 5 CENTRIFUGAL THICKENER This invention relates to thickening means for slurries of dif ferent types and particularly is concerned with the provision of a continuous thickener operating by assistance of centrifugal force and an axial pressing force.

In similar conventional thickeners the thickening is effected only by centrifugal force, while according to the present invention both centrifugal forceand a special axial pressing force are applied to the material to be thickened. Hereby it is possible to employ a means which is considerably simpler than heretofore, and at the same time to increase the throughput of the apparatus as well as the dry content of the product.

The centrifugal thickener according to the present invention comprises a machine housing, which includes a rotor, a rotor shaft and rigidly connected with said rotor, a perforated thickening cylinder feed means and discharge means in the cylinder the feed means being apipe projecting inwardly through one end of the rotor shaft, and the discharge means being a plate which is adapted to rotate with the thickening cylinder and is axially movable in relation to the same.

The present invention is characterized in that the thickening cylinder is provided with end cones inclined conically inwardly, the ends of which cones' 'are mounted within the cylinder and form a radial inwardly projecting edge, said cones being designed in two steps, viz. an inner step located closest to the cylinder and an outer, more remote step, said inner step having a mean diameter smaller than that of the step which is located outside thereof.

The invention will be described in greater detail in the following, and with reference to the accompanying drawing in which:

FIG. 1 shows a longitudinal section through a thickener according to the invention;

FIG. 2 shows in a schematic way a longitudinal section through one end of the thickening cylinder, the discharge plate in position to press slurry against the end; and

FIG. 3 shows in a schematic way a longitudinal section through. the lower half of a two-step centrifugal thickener according to the invention.

As appears from the drawing, the thickener according to a preferred embodiment comprises a machine stand with upwardly extending bearing brackets 2 which support a machine housing 3 and a rotor 4 mounted rotatably therein. Said rotor 4 has a relatively heavy tubular through shaft 5 with tubular shaft journals 8 and 9 at each end, said journals projecting outwardly each through the adjacentend wall of the machine housing 3 and being supported in the bearing brackets 2.

Within the rotor 4 and rigidly connected therewith there is mounted a thickening cylinder 31 with perforated wall. Said cylinder 31 is substantially straight, but it has end cones 32 inclined to the axis. The conicity, however, is small, for example approx. 12.

The end cones 32 are inserted into the thickening cylinder 31 proper in such a manner that the inner end of each cone forms a radially outwardly projecting edge 41, which is intended to prevent the watery slurry or'liquid to be pressed up in the end cones. Experience has shown that in thickness of the centrifugal type the tendency is for the liquid to continue to flow upwards closest to the cone wall and over its edge, thereby taking along already thickened slurry, while the already thickened slurry built up thereupon is discharged to a considerably reduced extent, at the same time as the moisture content of the slurry exceeds the desired value. It has also been found that the thickened slurry in the end cones at times tends to slide on the lowermost watery layer downwards (i.e., back) into the thickening cylinder.

For counteracting this tendency of the slurry to slide back, according to a further characterizing feature of the present invention we provide each of the end .cones with a shoulder or [which is located outside of said step, whereby the return motion of the slurry is stopped.

Approximately in the middle between the ends of the thickening cylinder the rotor shaft 5 is provided with a number of openings 33 through which material to be thickened is fed into the cylinder 31. The material is introduced through one of the tubular shaft journals 8 of the rotor 4. At the inner end of said journal there are mounted shovel-shaped discharge elements 34 for improving the radial distribution of the material when being fed into the cylinder. The material is fed axially along the inner periphery of the thickening cylinder and discharged through one or the other of its ends, by means of a reciprocating discharger in the form of an annular disc 35 extending radially between the rotor shaft 5 and the inner periphery of the thickening cylinder 31. At some distance from the outer edge of said disc ports 37 are provided uniformly distributed about the disc 35.

The discharge disc 35 is rigidly connected with a dampershaped bushing 38 mounted slidably on the rotor shaft 5 and guided axially by a control rod 21 projecting inwardly through the second tubular shaft journal 9 of the rotor 5 via a guide pin 39 shown in a cross section and extending upwards through a longitudinal slot 40 in the rotor shaft 5.

The thickener according to the present invention operates as follows. Material to be thickened, hereinafter called slurry, is fed in through the left-hand tubular shaft journal 8 to approximately the middle of the thickening cylinder 31 where the rotor shaft 5 is provided with peripheral openings 33 through which the slurry is fed centrifugally into the rotating thickening cylinder by assistance of the shovel-shaped feed elements 34. The discharge disc 35 is reciprocated between the ends of the cylinder 31 and, by scraping, takes along the slurry which has been fed in, which slurry on its travel to the end of the cylinder is pressed against the perforated cylinder wall by the centrifugal force and thereby partly thickened. The water pressed out falls down into an outflow funnel 26 and is discharged, while the slurry in its then relatively thickened state is advanced further to the end of the thickening cylinder where the slurry must :move upwards on the inclined plane formed by the conically inwardly inclined end extensions of the cylinder. The motion of the slurry is thereby braked, and the pressure from the discharge disc 35, which continues its motion, increases and thereby presses additional water out of the slurry. During the pressing operation against the end a dam of relatively dry slurry is built up ahead of the discharge disc and contributes to improving the pressing effect of the disc against the slurry. The watery slurry and the liquid will place themselves at the inner surface, radially seen, and can flow back through ports 37 in the discharge disc for being again thickened in the cylinder, while part of the more thickened slurry is fed out at each stroke of the discharge disc through the end of the cylinder and falls down into a discharge shaft 27 and transported away.

The present invention has rendered possible a substantially simpler and thereby less expensive thickening means. Owing to the double thickening action the capacity of the thickener is increased and at the same timeits effectiveness is improved, which results in a dryer slurry.

FIG. 3 shows a modification of the thickener according to FIGS. 1 and 2 for thickening in two steps.

The thickening cylinder 44 is divided by two locking rings 45 into an inner thickening zone in the middle and two outer thickening zones located between the locking rings and the end cones. The discharge plate 46 moves only within the inner thickening zone and is connected by axially extending rods 47 with two outer discharge members 48 adapted to be moved each in its zone of the outer thickening zones.

The locking rings 45 have a substantially triangular cross section, with a point 49 being directed to the inner thickening zone and a radial edge 50 being directed to the outer thickening zones. Thus, when the discharge plate 46 feeds slurry against one of the locking rings 45, the slurry is pressed upwards on the inclined side of the ring, whereby the uppermost watery slurry layer flows back to the inner thickening zone for again being thickened, while the dryer slurry at every stroke of the discharge plate is fed over the locking rings into the outer thickening zones where it is subjected to additional thickening. The outer discharge members are rings 48 with a triangular cross section having one point and one inclined side facing towards the locking rings, while an edge perpendicular to the wall of the thickening cylinder faces towards the end cones.

When one of the outer discharge rings 48 moves against one of the locking rings 45, the slurry in this thickening zone will be moved against the locking ring and thereby be fed upwards on the inclined side of the discharge ring 48 and be pressed by the locking ring 45 over the edge of the discharge ring down into the outer thickening zone. Already at this first pressing motion a certain thickening is effected. When the discharge ring 48 thereafter moves against its end cone 32, continuous thickening is effected, because the centrifugal force all the time acts upon the slurry. When the slurry thus thickened is pressed upward on the end cone, a certain additional thickening takes place at the same time as the watery slurry flows back to the thickening zone.

In conventional centrifugal thickening apparatus the thickened slurry must be dried or pressed subsequent to the thickening for arriving at a sufficiently low-moisture content to permit the slurry to be burnt.

By utilizing the centrifugal thickener according to the present invention, however, no extra thickening by pressing is required, because the slurry already in the centrifugal thickener is given a dry content of up to 40 percent, which is sufficient for allowing direct burning.

We claim:

1. in a horizontal, centrifugal thickener for pulp and other slurries, comprising a machine housing including a shaft-supported rotor with an open, perforated thickening cylinder, a feed means substantially comprising a pipe projecting inwardly through the rotor shaft, and a discharge means adapted to rotate with and to be moved axially in relation to the thickening cylinder, the end portions of said open thickening cylinder being provided with slightly inwardly inclined end cones, the improved construction according to which the cone ends form a low radial edge, and in which each of the end cones of the thickening cylinder includes two steps, the step located closest to the cylinder having a means diameter smaller than that of the step located outside thereof, and said discharge means comprising a plate provided with a plurality of axially extending ports spaced inwardly from the periphery thereof for allowing return flow of watery slurry.

2. Centrifugal thickener according to claim 1, in which the feed means comprises a feed pipe which is provided at its end with shovellike distribution members for throwing material, fed in centrifugally, out into the thickening cylinder through suitable openings in the rotor shaft.

3. Centrifugal thickener according to claim 1, in which the discharge means comprises a disc which is operated axially by assistance of a control rod projecting inwardly through the rotor shaft directly in front of the feed pipe, the disc being connected with said control rod byv a guide pin extending through a longitudinal slot in the rotor shaft.

4. Centrifugal thickener according to claim 1 for thickening in two steps, in which the thickening cylinder comprises a first inner thickening zone defined by l two locking rings having substantially triangular cross section, and (2) two outer thickening zones located between the locking rings and the end cones adjacent thereto, and in which said discharge means includes a plate which moves only within the inner zone and is connected by axially extending rods with a discharge member in each of the outer thickening zones.

5. Centrifugal thickener according to claim 4, in which each of the outer thickening zones comprises a ring, having substantially triangular cross section, of which ring one point faces towards the inner thickening zone and a radial edge faces towards the end cone.

Claims

1. In a horizontal, centrifugal thickener for pulp and other slurries, comprising a machine housing including a shaftsupported rotor with an open, perforated thickening cylinder, a feed means substantially comprising a pipe projecting inwardly through the rotor shaft, and a discharge means adapted to rotate with and to be moved axially in relation to the thickening cylinder, the end portions of said open thickening cylinder being provided with slightly inwardly inclined end cones, the improved construction according to which the cone ends form a low radial edge, and in which each of the end cones of the thickening cylinder includes two steps, the step located closest to the cylinder having a means diameter smaller than that of the step located outside thereof, and said discharge means comprising a plate provided with a plurality of axially extending ports spaced inwardly from the periphery thereof for allowing return flow of watery slurry.

3. Centrifugal thickener according to Claim 1, in which the discharge means comprises a disc which is operated axially by assistance of a control rod projecting inwardly through the rotor shaft directly in front of the feed pipe, the disc being connected with said control rod by a guide pin extending through a longitudinal slot in the rotor shaft.

4. Centrifugal thickener according to claim 1 for thickening in two steps, in which the thickening cylinder comprises a first inner thickening zone defined by (1) two locking rings having substantially triangular cross section, and (2) two outer thickening zones located between the locking rings and the end cones adjacent thereto, and in which said discharge means includes a plate which moves only within the inner zone and is connected by axially extending rods with a discharge member in each of the outer thickening zones.