US3507397A - Hydrocyclone unit - Google Patents

Description

Api-i l 2l, 1970 w. R. ROBINSON I 3,507,397

HYDROCYGLONE UNIT Filed April 9, 1969 2 Sheets-Sheet l ATTORN S April 21, 1970 w. R. ROBINSON 3,507,397

HYDROCYCLONE UNIT Filed April 9, 1969 2 Sheets-Sheet 2 MZL MW ATTORNE 5 United States Patent 3,507,397 HYDROCYCLONE UNIT William R. Robinson, 58 Parkvagen, 183 51 Taby, Sweden Filed Apr. 9, 1969, Ser. No. 814,589 Int. Cl. 1304c 3/06 US. Cl. 210512 3 Claims ABSTRACT OF THE DISCLOSURE A hydrocyclone unit for use in purifying aqueous sus pensions of fibrous pulp and comprising a container having one inlet for the suspension and two outlets, one for purified liquid and the other for rejected matter. The suspension is introduced tangentially into the container so as to be provided with a rotative motion and is engaged by a medium introduced at right angles to said rotative motion and being urged towards the rotative suspension by the pressure difference between the static pressure under which said medium is introduced and the pressure in a chamber into which said one inlet discharges. As a result, a substantial quantity of impurities is removed from the suspension and discharged through said outlet for rejected matter, whereas the remainder of the suspension is discharged through said outlet for purified liquid.

BACKGROUND OF THE INVENTION Field of the invention This invention refers to hydrocyclone units and particularly to such hydrocyclone units that are intended for use in the paper and pulp industry for purifying aqueous suspensions of fibrous pulp from coarse and fine impurities and dirt particles.

Description of the prior art The hydrocyclone has attained extensive use in the mentioned industry as the result of several extremely advantageous qualities. It lacks mechanically movable parts, is not particularly complicated, has surprisingly high purifying efiiciency, and, if it is manufactured of appropriate materials and with care in fabrication and has a high grade surface finish etc., it will have a long life. Hydrocyclones may also readily be combined to form batteries of small bulk and having extremely high handling capacities.

A modern hydrocyclone consists of a rather long conical container having its widest portion or base facing upwards. This portion is provided with an inlet in tangential direction with respect to the envelope surface of the cone. The suspension to be handled is introduced into the hydrocyclone at high speed (7-10 meters per second) and is forced into a rapid swirling motion, hence forming a vertical column of rotating liquid in the shape of an inverted cone, said liquid simultaneously being conveyed gradually downwards. Dirt and heavier particles in general are propelled outwards towards the peripheral layers and concentrated there as the result of the centrifugal force. Due to the conical form of the hydrocyclone the rapidly rotating outer layers are pinched together towards the apex of the cone which is provided with an outlet for the so-called reject containing the greater part of the impurities of the suspension. The purified liquid is collected in the quieter core zone of the rotating column, and here a flow upwards is developed towards a second outlet having the form of a central pipe introduced from above through the top or base end of the hydrocyclone and protruding to some extent into the widest portion of the latter. The purified suspension, i.e. the so-called accept, is removed by means of this pipe. The achieved degree of purification is in the vicinity of 90%.

In a hydrocyclone of given dimensions the velocity of the passing liquid is of decisive importance. The higher the velocity is, the stronger will the field of the separating centrifugal force become and the greater will the capacity of the hydrocyclone be, i.e. the quantity of the suspension handled per time unit. However, increased velocity results in increased pressure losses, and this may make the pressure drop over the hydrocyclone considerable. A compromise or determination of the optimum qualities must be made, and as a representative example of an effective modern hydrocyclone for the pulp industry the following data of such a hydrocyclone may be mentioned: length 0.9 meters, base diameter millimeters, cone angle 56, capacity approximately 80 liters per minute, pressure drop approximately 2 kilopounds per square centimeter and purification degree To a great extent, the pressure losses arising in the hydrocyclone are derived from inevitable internal friction in the liquid and boundary layer sliding against the walls of the hydrocyclone. However, pure impact losses also occur, and these may become substantial. The liquid is introduced into the hydrocyclone at high velocity along a linear path directed tangentially to the base of the hydrocyclone and is immediately deflected into a relatively restricted circular path. Particularly during the first revolution, substantial impact losses occur, together with associ ated pressure drops, as the result of this rapid change of direction in the motion of the liquid.

SUMMARY OF THE INVENTION The present invention has the object of decreasing these impact losses that occur when a liquid or a suspension enters a hydrocyclone so as to facilitate an increase of the flow-through velocity and thus of the capacity without increasing the pressure drop over the purifier and hence without increasing the pumping power necessary for operating the purifier. This purpose is achieved and certain other advantages are also attained by the hydrocyclone of the invention being provided with the features indicated in the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS As an example, the invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic illustration of the base portion of a hydrocyclone in accordance with the invention, with a series of velocity triangles having been introduced in order to illustrate the changes in velocity and direction of the liquid gushing into the hydrocyclone during the first revolution in the hydrocyclone.

FIGURE 2 is a spread-out view of the interior of the chamber of the hydrocyclone schematically shown in FIGURE 1, as seen from line 11-11 in FIGURE 1.

FIGURE 3 is a sectional horizontal projection (along the plane IIIIII in FIGURE 4) through the base or inlet portion of a practical embodiment of the hydrocyclone in accordance with the invention.

FIGURE 4 is a sectional elevational projection through the hydrocyclone illustrated in FIGURE 3, with the lower conical portion thereof having been omitted.

In accordance with the invention, the liquid flowing into the hydrocyclone chamber is subjected to a series of impact pulses directed radially inwards towards the center of the chamber, with said impact pulses tending to deflect the flow of liquid. The deflection of the latter, which normally occurs as the result of the flow striking the inside of the wall of the hydrocyclone chamber and being forced into its rotative path thereby, will, in accordance with the invention, be effected to a certain extent by the incoming liquid flow being struck at even intervals by jets of liquid coming from the side and directed at right angles to the flow, with said jets of liquid materially contributing to the deflection of said incoming liquid. Hence, as the result of said deflection being caused by dynamic pulse interaction between two flows or currents encountering each other instead of exclusively by static deflection by means of a solid wall, the impact losses during the inflow phase decrease substantially, which has been confirmed by practical tests to be accounted for below.

FIGURE 1 schematically illustrates a base portion or an inlet chamber 12 of a hydrocyclone 10 designed in accordance with the invention and having a tangential inlet 14. A number of narrow vertical slits or nozzles 18 are provided in the wall 16 of said chamber and are distributed at even intervals along the circumference of the chamber. The base portion 12, 16 of the hydrocyclone is surrounded by a jacket having its exterior wall at a predetermined distance from the hydrocyclone chamber wall 16 so as to form an annular chamber 22 around the base of the hydrocyclone, with this chamber communicating with the interior of the hydrocyclone by means of the slits or nozzles 18. Inflowing liquid is introduced into the annular chamber 22 at a predetermined pressure through an inlet 2-4 and flows from said chamber through the slits 18 into the hydrocyclone chamber 12 in the form of radial jets of velocitay V These jets meet the tangentially directed main flow coming from the inlet at velocity V, and subject the latter to repeated, radially inwardly directed pulses that contribute to the deflection of the main flow.

As has been mentioned, the liquid flowing into the hydrocyclone chamber 12 has high velocity, which results in it being subjected to a considerable static pressure reduction, of the order of magnitude of 0.30.5 kilopounds per square centimeter at flow velocities of 7-10 meters per second. The liquid in the annular chamber 22 is located in a stagnation region having full static pressure, and if this chamber and hydrocyclone chamber 12 are fed in common, for instance simply by the separate inlet 24 being omitted and the annular chamber being fed through a branch-off from inlet 14, as indicated at 26 in FIGURE 1, the pressure in annular chamber 22 will be 0.3-0.5 kilopounds per square centimeter higher than in chamber 12. Hence, comparatively strong radial liquid jets will be urged into hydrocyclone chamber 12 from the annular chamber so as to engage the incoming main flow. In FIG- URE l the velocity triangles for the combined flow are drawn at each radial inlet 18 1 under the assumption that the individual flows engage each other at right angles. If the inflow velocity of the liquid through main inlet 14 is designated V, and the radial inflow velocity through nozzles 18, which increases gradually as the result of the static pressure decreasing in the chamber in response to the increase in velocity, is designated V V etc., the corresponding velocity vectors will be added to each other so as to first form V as indicated at 18 in FIGURE 1. The pulse coming from the radial jet through 18 towards the incoming tangential jet will thus result in a change of direction and a velocity increase of the main jet from V to V During the continuation the main jet is deflected additionally by chamber wall 16 so as to engage a new, somewhat stronger radial jet, having the velocity V at right angles. By pulse action redirecting is now efiected together with a velocity increase from V to V In this manner the inflowing liquid is continuously redirected dynamically (concurrently with being deflected statically by the curved hydrocyclone wall between the nozzles 18) in combination with a continuous velocity increase from V to V which may become quite substantial.

A comparison between the velocity distribution in a conventional hydrocyclone and the corresponding distribution in a hydrocyclone in accordance with the invention is of interest for estimating the purifying capacity. A curve illustrating the velocity distribution from the wall of the hydrocyclone chamber to its center will start out as half a parabola and will then turn off linearly towards the center. In the hydrocyclone of the invention this curve will have a smaller radius of curvature in the parabola portion than in the case of the conventional hydrocyclone, which means that the maximum point of the velocity distribution will occur closer to the chamber wall. In a conventional hydrocyclone the result of this is that a dirt particle of a certain size located between the wall and the maximum point of the velocity will not with certainty be intercepted and removed through the apex of the cone but that it may pass out through the accept pipe in the base of the cone. In the hydrocyclone of the invention said particle will achieve higher velocity at an unchanged distance from the hydrocyclone wall so as to follow the conical wall downwards and to be ejected through the discharge opening. Hence, the removal of dirt will be more effective. In a conventional hydrocyclone, generally speaking, the liquid flow will have a tendency to be deflected quickly and to pass out through the accept pipe as the result of the lower velocity at the chamber wall. Due to the liquid in the hydrocyclone of the invention having greater velocity at the wall, deflection will occur later, i.e. further down towards the apex of the cone, thereby increasing the probability of the dirt particles accompanying the reject and hence contributing to improving the separation. In response to the accelerating effect of the radial jets flowing in through the nozzles the same separating capacity may be achieved in a hydrocyclone in accordance with the invention having lower velocity of the inflowing liquid that is achieved for a conventional hydrocyclone having higher velocity. In other words, it is possible to operate with a lower pressure in the hydrocyclone of the invention and still to achieve the same dirt removal.

FIGURES 3 and 4 illustrate a practical embodiment of a hydrocyclone in accordance with the invention. It consists of a conical container 30 having a tangential inlet 32 and a central outlet for accept in the form of a pipe 34 introduced into the base portion of the container and coaxial therewith. In reality, the container 30 with its inlet 32 and outlet 34 for accept conform with a conventional hydrocyclone of the type utilized in the paper and pulp industry for purifying fibrous suspensions, and with respect to a comparison following below a conventional hydrocyclone of this type will be designated type A. In order to provide a hydrocyclone in accordance with this invention the upper portion or base of container 30 is provided with a cylindrical jacket 35 so as to form an annular chamber 38 around the base portion of the hydrocyclone. This annular chamber is provided with a tangential inlet 40 which is wider than inlet 32 and is positioned in front of the latter as indicated in FIG- URE 3. Beginning somewhat to the right of the connection of the tangential inlet 32 to the hydrocyclone proper, as illustrated in FIGURE 3, there are disposed a series of slits 36 at an annular pitch of 60. Thus, the in flowing suspension will flow through the inlet 40 and further on through the inlet 32 tangentially into the hydrocyclone chamber so as to engage a radial jet there from the slit or nozzle 36 in the surrounding annular chamber, which latter, as may be seen, also communicates with the main inlet 40. Because of the relative smallness of the nozzles 36 with respect to the volume of the annular chamber the liquid in this chamber will be in a state of stagnation, i.e., in comparatively slow motion, and for this reason the static pressure is developed to its full extent in annular chamber 38. Hence, the process described above occurs under operation, and the liquid gushing into the hydrocyclone chamber at high velocity is exposed to a series of pulses which materially contribute to its deflection and to its introduction into the fast rotative motion that is characteristic of the hydrocyclone.

Table I given below shows a compilation of the results of comparison tests carried out at a paper mill with a TABLE 1 Type (according to the Type A Type B invention) Inlet pressure (kp./em. 2. 9 2. 9 2. 9 Counterpressure (kp./em. 0.6 0.6 0.6 Pressure drop (kp./em. 2.3 2. 3 2. 3 Quantity of accept (kpjcmfl) 75 265 240 Quantity of reject (kp./cm. 5 10 Total capacity 80 275 250 Degree of purification, percent 92 67 89 The comparison shows that under conditions that otherwise are identical with respect to inlet pressure, counterpressure and pressure drop, the velocity and hence the capacity of a conventional hydrocyclone is more than tripled if it is designed in accordance with the invention and with retained dimensions, while the degree of purification becomes the same or merely insignificantly smaller. A conventional hydrocyclone of larger type and having a capacity corresponding to that of the hydrocyclone of the invention has substantially lower purifying capacity, as illustrated in the table under Type B.

The connection of the annular chamber 36, 38 may naturally be modified in different ways with respect to practical experience and structural requirements. Specifically, in certain cases it may be desirable to regulate the pressure of chamber 38, and this may be done in different ways. For instance, the annular chamber may be provided with a separate inlet, as indicated in FIGURE 1, under the control of appropriate valve means. With a design in accordance with FIGURE 3 the annular chamber 38 may be shielded outwards, for instance by means of a closed wall 42 and a flap valve 44, as indicated by dashed lines in FIGURE 3, thereby also making it possible to control the inflow into the annular chamber. Furthermore, the openings between the annular chamber and the hydrocyclone chamber may be mutually different, for instance having a flow-through area decreasing from the inlet. The number of openings may be arbitrary and selected with respect to the circumstances, and in this connection it is emphasized that the invention also contemplates extending the series of openings to the area below the plane through the inlet, for instance so that said series, beginning at said inlet, extends helically around the entire hydrocyclone chamber and continues downwards along the tapering portion thereof. Finally, it is also possible to convey a medium that is different from the suspension to be treated through said openings, for

instance saturated steam, and measures for supplying such may be taken within the scope of the invention.

Under certain circumstances the annular jackets 20 and 35, respectively, around each individual hydrocyclone may be omitted, viz. in the case of a plurality of hydrocyclones being assembled into a battery, wherein the hydrocyclones may be disposed with their base portions positioned in a collective box having an outlet common to all the hydrocyclones. From the interior of this box the suspension will then pass through a main inlet to each individual hydrocyclone simultaneously with the suspension being ihtroduced into the hydrocyclones by means of openings surrounding the same, as is described above.

Modifications may be carried out within the scope of the invention in other respects than those mentioned above in accordance with the basic concept of the invention.

What I claim is:

1. A hydrocyclone unit, particularly for purifying aqueous suspensions of fibrous pulp, comprising a conically tapered container having a tangential inlet for the liquid or suspension lying in a plane at right angles to the longitudinal axis of the container, said inlet being positioned at the widest portion of the container, said container also having two outlets coaxial thereto, firstly a reject outlet at the tip end of the container and secondly an accept outlet at the base of the container, the container also having a series of openings formed in the wall thereof beginning at said inlet and located at intervals along the wall, an annular chamber being disposed along the outside of said wall and having means for introducing a medium therein .under a static pressure exceeding the pressure prevailing in the interior of the container, so that the radial inflow of the medium through the openings developed by the pressure difference is superimposed on the flow of the liquid entering through the inlet.

2. A hydrocyclone unit in accordance with claim 1, wherein said openings are disposed in a helical path extending along the wall of the container and having its starting point at said inlet, said path continuing downwards along the tapering portion of the container.

3. A hydrocyclone unit in accordance with claim 1, wherein a jacket is positioned around the widest portion of the container on the same level as said inlet and outside of said openings in such manner as to form said annular chamber around the container.

References Cited UNITED STATES PATENTS 2,890,929 6/1959 Rummert 2105l2 X 3,034,647 5/1962 Giesse 2l0512 X 3,064,811 11/1962 Mumper -459 X 3,091,334 5/1963 Morton 209144- JAMES L. DECESARE, Primary Examiner US. Cl. X.R. 209211

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