US3433362A - Cyclone purifier - Google Patents

Description

March 18, 1969 R. w. ROBINSON CYCLONE PURIFIER Sheet of 5 Filed Dec. 20, 1967 March 18, 1969 R. w. ROBINSON CYCLONE PURIFIER Sheet 2 of 5 Filed Dec. 20, 1967 M/t/EA/TOE ROBE/97' W/LUAM 6 05/4/30 March 1969 R. w. ROBINSON 3,433,352

CYCLONE PURIFIER Filed Dec. 20, 1967 Sheet 3 01* s om/n 14,086/65 US. Cl. 210-512 Int. Cl. B04c 3/06, 3/00, 1/00 3 Claims ABSTRACT 015 THE DISCLOSURE A cyclone separator for liquid suspensions comprising a conical container having a base portion and an apex portion at opposite ends thereof. A first outlet opening extends through the apex portion and a second outlet opening comprising a pipe positioned within the conical container extends axially outwardly through the base portion. A pressure chamber is mounted adjacent the base portion, which container is supplied with a pressurized liquid suspension. An opening between the base portion and the pressurized chamber is provided with a flow-d1- recting element for imparting a tangential velocity component to the suspension as it flows from the pressure chamber into the conical container to impart a rapid whirling motion to the suspension.

This application is a continuation-in-part of my copending application Ser. No. 538,493, filed Feb. 25, 1966, and now abandoned, and entitled Cyclone Purifier.

This invention relates to cyclone purifiers or cyclone separators by means of which impurities representing a heavier fraction of liquid suspension can be removed from the suspension, particularly particles in the form of sand, dirt, etc. Such purifiers, so-called hydrocycloues, have been used extensively within the paper and pulp industry for removing dirt particles and coarse and fine impurities from aqueous fibre pulp suspensions. These hydrocyclones possess a number of advantageous characteristics in that they lack moving mechanical components, are rather simple in construction, have high cleaning efiiciency and have a long working life if manufactured of suitable material and given a high surface finish.

A typical conventional hydrocyclone of the type in question consists of a rather long conical container positioned so that its widest portion or base is uppermost. A stock inlet is arranged at this portion directed tangentially in relation to the casing of the cone. The suspension to be treated is introduced into the cyclone at high speed wherein it is forced to enter into a rapid swirling motion, whereupon a vertical reversed conical column of rotating liquid is formed which, at the same time, is fed successively downward. Due to the centrifugal eflfeet, the majority of the dirt and heavier particles are propelled outward toward the peripheral layer and concentrated there. The conical shape of the cyclone causes the rapidly rotating outer layers to be drawn toward the apex of the cone where an outlet is arranged for the so-called reject containing the major portion of the impurities held in the suspension. The purified liquid collects in the quieter core zone of the rotating column, forming an upward flow toward a second outlet in the form of a central pipe introduced from the top through the upper side or the base of the cyclone and extending somewhat into the wider part of the cyclone. The cleaned suspension, the so-called accept, is removed by means of this pipe.

However, it has been found that introducing the fluid through the inlet in a direction substantially tangential to the conical casing causes the fluid to flow around the hyatent 3,433,362 Patented Mar. 18, 1969 drocyclone in a toroidal pattern whereby the fluid adjacent the conical casing has a downward velocity component while the fluid adjacent the central pipe has an upward velocity component. Thus, the fluid within the toroid develops a circular flow pattern similar to a vortex which thus greatly decreases the separating efiiciency of the hydrocyclone.

Attempts have been made to positively guide the fluid adjacent the inlet to the cyclone so that it will develop a swirling motion without developing the vortex motion which existed in the conventional hydrocyclone. One such cyclone separator utilizing a guide means therein for imposing a swirling motion on a gas is illustrated in United States Patent No. 2,667,944, issued to Crites. The separator illustrated in this patent comprises a conical housing having a helical vane member therein, which vane member extends for several revolutions and is preferably composed of at least two flights. However, this separator structure is designed for gaseous fluids, the low viscosity of which requires a helical vane extending for several revolutions to permit the necessary gripping of the gas to create suflicient swirling thereof to develop the desired centrifugal force.

Accordingly, an object of the present invention is to provide a hydrocyclone purifier having a helical guide vane adjacent the inlet thereof for imposing a swirling motion on a liquid, which guide vane preferably does not extend through more than one revolution whereby the liquid is quickly accelerated to the desired rotational velocity, while being subjected to a minimum of pressure drop due to friction between the liquid and the guide vane.

A further object of the invention is to provide a hydrocyclone purifier, as aforesaid, having clearance space adjacent at least one edge of the guide vane for permitting a quantity of pressurized liquid to bypass the vane through the purifier so as to create a flushing effect. A still further object of the present invention is the provision of a cyclone purifier, as aforesaid, which is of smaller size than conventional cyclone purifiers while etfecting eflicient separation of solids from liquids with only a minimal pressure drop occurring during the separation operation.

Other objects and purposes of this invention will be apaparent to persons acquainted with apparatuses of this general type upon reading the following specification and inspecting the accompanying drawings, in which:

FIGURE 1 is a sectional elevational view through a conventional hydrocyclone and illustrating, in dotted lines, how such a cyclone can be modified according to the present invention.

FIGURE 2 is a vertical section through the inlet portion of a hydrocyclone having a circulation initiating element therein according to the invention.

FIGURE 3 is a top view of the hydrocyclone taken along the line IIIIII of FIGURE 2.

FIGURE 4 is a perspective view of the inlet portion of a hydrocyclone according to the present invention.

FIGURE 5 is a partial perspective view of an alternate embodiment of the present invention.

FIGURE 6 is a partial perspective view of a further alternate embodiment of the present invention.

FIGURE 7 is a perspective view of a still further alternate embodiment of the present invention.

FIGURE 8 is a partial perspective view of another modification according to the present invention.

FIGURE 9 is a perspective view, partially in section, of a battery of cyclone separators according to the present invention.

FIGURE 1 illustrates a conventional hydrocyclone 10 comprising a conical casing 11 with the upper end or base of the casing being closed by means of an end wall 12. A stock inlet pipe 13 is positioned in a substantial tan gential relationship adjacent the upper end of the conical casing 11 and communicates with the interior of the casing by means of an inlet Opening 16 provided in the wall thereof whereby liquid flowing through the pipe 13 and the inlet opening 16 develops a substantially toroidal flow pattern as a swirling movement is imparted thereto.

The hydrocyclone is further provided with two central coaxial outlet openings therein, one of the openings comprising the reject outlet 14 located at the apex of the conical casing. The other outlet opening is axially spaced from the reject outlet 14 and is formed by means of a central pipe 17 which extends downwardly into the conical casing 11 through the end wall 12 thereof, which pipe 17 is open at the lower end thereof so as to define the accept outlet 18. A hydrocyclone of this type is common in the pulp industry and, when of a maximum length L of approximately 150 mm. and a cone angle (,0 of approximately degrees, has a capacity of about 250 liters per minute at a drop in pressure over the separator of approximately 2.5 kp./cm. This relatively large drop in pressure is in part caused by the fact that the liquid when injected into the separator assumes the shape of a toroid and further develops a vortex or circular flow pattern thereacross, as discussed above, which greatly decreases the efficiency of the separation function and increases the frictional losses within the cyclone, thus resulting in a greater pressure drop.

It has been found that a hydrocyclone of this type can be greatly simplified and reduced in size yet still retain its capacity and purifying efliciency if the conical casing is reduced to approximately half its original length and then secured to the underside of an inlet or pressure box 20. The central pipe 17 is arranged in the pressure box 20 in the form of a pipe extending somewhat into the mouth of the cyclone from the top of the pressure box as illustrated by dotted lines in FIGURE 1. An inlet 21 is arranged in some suitable position on one side of the pressure box 20, whereupon it should be noted that this inlet need not be directed tangentially in relation to the casing 11 connected to the pressure box. Further, the inlet 21 does not need to be as narrow as the inlet 16 of the conventional hydrocyclone wherein the liquid is introduced into the separator at a high initial velocity through the rather narrow inlet.

It has now been shown, and confirmed by exhaustive experiments, that when the liquid from the pressure box 20 gushes down into the cyclone cone 11 it tends spontaneously to set itself into a rotating or circulating mo tion, which is exactly the same as in conventional cyclones and has the same centrifugal effect on the liquid. Comparison tests on fiber suspensions have shown that if a truncated cyclone separator, as described above, is operated at the same output or through feed as a corresponding conventional cyclone, it is possible to attain a reduction in pressure drop while substantially retaining the cleaning or separation efliciency.

The tendency of a flowing liquid to set itself in rotation under conditions corresponding to those just described can be observed, for example, when emptying a vessel, e. g., a bathtub, through a bottom outlet where the liquid, at least during the final emptying stage, is without exception set into a strong whirling motion. In order to be absolutely certain that such a circular motion will occur, and remain stable, in the modified hydrocyclone according to the above, it is required that the flow of liquid through the cyclone be eflected under certain conditions; more precisely, the pressure drop over the cyclone and the flow velocity must lie within certain limits. Experiments have shown that these limits are rather broad and ';hat it is always possible, without undue difliculty, to adjust the flow so that the circulation is formed at full strength and then continues insensitive to slight variations in pressure and velocity. From the practical point of view, however, this limitation is seldom acceptable; naturally the purifier shall follow the system in which it is introduced without necessitating special adjustment after minimum requirements of pressure and velocity have been fulfilled.

However, it has been proven that the above-described truncated cyclone can be made absolutely start-safe, and to develop a completely stable circulation within the total working area without the risk of collapse, by adopting an extremely simple measure. It is only necessary to insert a circulation initiating element into the cyclone, preferably into, or in the proximity of the mouth of the cyclone, which element tangentially directs or deflects the liquid flowing down into the cyclone. An arrangement in its simplest form is illustrated in FIGURES 2 and 3. A conical cyclone casing 11 is secured to the bottom of a pressure box substantially as described above. In this case, however, a blade-like member 22, more specifically a guide vane, is mounted on the inside of the cyclone casing at or near the inlet opening 23 and projects out from the wall of the casing, possibly as far as the central pipe 17. As can be observed, this element forces passing liquid to move with a tangential component and such a tangential flow, developed within the restricting area of the element 22, is sufficient to set the complete liquid column into circulation. With such a guiding and initiating element inserted, the circulation is unavoidably created and remains stable. In fact, it is surprising how insignificant the required impulse need be in order to insure the course of circulation.

It is to be emphasized that FIGURES 2 and 3 are only intended to illustrate the principle of the circulation initiation applied by the simplest conceivable means. The preferred embodiments of the invention which result in the maximum separation efliciency while causing a minimum pressure drop across the separator, and further incorporating therein means for further increasing the etficiency by providing for axial flushing of the liquid through the separator, are illustrated in FIGURES 4-8 described hereinafter.

FIGURE 4 illustrates a modification of the invention which is substantially similar to the cyclone structure illustrated in FIGURE 2 and comprises a circulation initiating element 26 formed as a helical strip and inserted into the inlet opening of the cyclone between the casing 11 and the central pipe 17 so as to form a radial bridge between these members. As illustrated, the helical strip 26 is relatively short and extends for only a portion of a revolution relative to the central pipe 17.

FIGURE 5 illustrates another embodiment of the invention wherein the circulation initiating element comprises a helical strip 27 which is positioned between the casing 11 and the central pipe 17 and extends for a complete revolution around the central pipe 17. The helical strip 27 completely bridges the space between these members with the exception of the axial opening between the ends of tthe strip, which ends lie on different levels with the difference in height S between the ends corresponding to the pitch of the helical strip.

FIGURE 6 illustrates the preferred embodiment of the present invention wherein the circulation initiating element also comprises a helical strip 28 which is positioned between the conical casing 11 and the central pipe 17 and extends around the central pipe for substantially a complete revolution. Again, the ends of the strip 28 lie on different levels and are separated by a difference in height S substantially corresponding to the pitch of the helical strip. The strip 28 in the preferred embodiment of FIG- URE 6 is further provided with a clearance gap 5,, along the outer edge of the strip adjacent the wall of the cyclone casing 11. This clearance gap is preferably of a uniform width throughout the angular extent of the strip 28. In order to support the strip 28 within the cyclone, the strip 28 is preferably secured around its inner periphery to the central pipe 17. Further, if desired, the strip can be secured to the cyclone casing 11 by means of a plurality of small radial spokes (not shown) extending therefrom.

FIGURE 7 illustrates another preferred embodiment of the present invention, which embodiment is substantially similar to the embodiment of FIGURE 6. As illustrated in FIGURE 7, the circular initiating element again comprises a helical strip 29 which extends substantially one complete revolution about the central pipe 17. However, in this embodiment, the separator is provided with a gap 6 between the inner edge of the helical strip 29 and the periphery of the central pipe 17, in addition to the gap 6,, provided between the outer edge of the strip 29 and the periphery of the conical casing 11. The gap 6 as is true of the gap 6 is preferably of a uniform width throughout the circumferential length thereof. In this cyclone construction, the helical strip or bridge 29 is secured to the central pipe 17 or to the cyclone casing 11, or to both of these, by means of small radial spoke sections 29a.

FIGURE 8 illustrates still another modification of the present invention which is substantially similar to the embodiment illustrated in FIGURE 7 except that the helical strip 30 is provided only with a gap 6 between the inner edge thereof and the periphery of the central pipe 17. No gap is provided between the outer edge of the helical strip 30 and the periphery of the conical casing 11. The purpose of providing either or 'both of the gaps 6 or 6,, is discussed hereinafter.

Applicant has discovered that the hydrocyclone according to the present invention is particularly well adapted for use on liquids and results in the optimum separation efiiciency if the circulation initiating element or helical strip or vane does not substantially exceed 360 degrees. A helical strip of approximately one revolution, in conjunction with the relatively large viscosity of liquids, permits the cyclone to exert a sufiicient grip or guiding action on the liquid so as to impose thereon the desired swirling or rotational movement, thus resulting in the optimum centrifugal separation. On the other hand, if the helical strip substantially exceeds 360 degrees, then the optimum efliciency point is exceeded since any additional acceleration imposed on the liquid is more than off-set by the frictional losses caused by the extended length of the helical strip. More specifically, if the strip extends substantially beyond 360 degrees, portions of the strip overlap one another to define a relatively narrow duct or channel which severely restricts the liquid flow. This greatly increases the viscous friction throughout the cyclone separator, which causes a substantial and undesirable pressure drop thereacross.

Applicant has further discovered that provision of the edge gaps 6, and 5,, and, in particular, provision of the outer edge gap 6 substantially increases the separation efiiciency and reduces the pressure drop across the hydrocyclone. Considering the preferred embodiment as illustrated in FIGURE 6, the flow of liquid through the helix causes the liquid to possess a velocity component in correspondence with the pitch of the helix. Further, this velocity component generally increases in magnitude as the liquid becomes further radially spaced from the central pipe 17. However, as the liquid approaches the peripheral inner wall of the conical casing 11 in the region of the gap 5 the guiding action of the helix and its effect on the liquid decreases due to the presence of the gap. Further, the pressure of the liquid within the pressure box 20 located above the helix, which pressure is slightly greater than the pressure of the liquid as it moves through the helix, is transmitted downwardly through the gap and is exerted upon the liquid passing through the helix adjacent the gap, causing the liquid adjacent the gap to have a downward vertical velocity component which is greater than the downward vertical velocity component of the liquid spaced radially inwardly therefrom. Consequently, there will be a layer of rotating liquid adjacent the casing wall which passes through the gap and thus descends more rapidly downwardly through the hydrocyclone than does the remaining rotating liquid column confined by the helical strip.

Further, this layer of liquid adjacent the outer gap 8,, contains therein the heavy particles which have been centrifugally thrown outwardly due to the swirling motion of the liquid, which particles are thus drawn rapidly downwardly through the gap and conveyed to the reject outlet 14. Provision of the outer edge gap thus creates a flushing effect which permits the rejects to be more rapidly separated and withdrawn from the liquid with the remaining liquid or accept thus being conveyed to the accept opening 18. This flushing effect is highly desirable since, as will be apparent, it not only reduces the pos sibility of clogging of the device, but it also increases the flow capacity of the device and results in less pressure drop thereacross. Also, the edge gap should be of substantially uniform width throughout the axial and circumferential length thereof in order to permit the reject to be effectively flushed or separated from the liquid. Any narrowing of this gap in the direction of flow toward the reject outlet would tend to cause a stoppage or clogging of the hydrocyclone.

As an example of the improved efficiency which results from the cyclone separator or purifier of the present invention, a cyclone purifier according to the present invention was installed in a pulp mill alongside a conventional cyclone purifier, both cyclone purifiers being of the same flow capacity. Side-by-side operation of these two cyclone purifiers required a pumping pressure in the order of 40 psi. for the inlet liquid suspension to the conventional cyclone, while a pumping pressure in the order of only 20 p.s.i. was required for the liquid suspension supplied to the cyclone according to the present invention. Thus, this clearly points out that the pressure drop occurring in the cyclone according to the present invention is substantially less than the pressure drop or loss which occurs in the conventional cyclone separator. When one considers the enormous quantity or volume of fibrous suspensions which must be moved in pulp mills and must be separated by means of cyclone purifiers, it becomes readily apparent that such a pressure reduction results in a great improvement in economy and etliciency, especially in view of the enormous amount of energy required to pressurize the liquid to the desired level for supplying same to the inlet of the cyclone separators.

The cyclone purifier according to this invention also results in a further advantage since it permits the formation of a battery construction which, from the aspect of space and from the point of view of connecting or coupling, is much superior to conventional cyclone purifiers. FIGURE 9 shows a diagrammatical perspective view of such a battery arrangement.

The cyclone battery illustrated in FIGURE 9, indicated generally by the reference numeral 31, includes a pressure box 32 common to a plurality of cyclones, which box 32 includes a lower pressure chamber 34 and an upper outlet chamber 36 separated by an intermediate wall 38. In this instance, there are ten cyclone casings 11 suitably secured to the bottom of the pressure chamber, the cyclone casings 11 being arranged in two parallel rows, five in each row (other grouping methods can also be arranged). Corresponding accept outlet pipes 17 are secured to the intermediate wall 38 and extend down, in the usual manner, into the associated cyclone casing 11. An outlet 46 for the collected accept is arbitr-arily arranged in the top of the chamber 32. According to the invention, a suitably designed guide element 48 is inserted into each of the cyclones. The reject is emptied into a collecting box 40 through the reject openings 14, the two boxes 32 and 40 being connected with, or built into a common frame 42. An inlet 44 to the pressure chamber 34 is arranged in the one end wall of the chamber 32 and is directed conveniently, but not necessarily, in the very center of both of the rows of cyclones. The helical guide element 48 of one row is designed with a right-hand pitch, the other row with a left-hand pitch. Thus, the fiow entering between the rows of cyclones is divided into two branches which causes in a natural manner the column of liquid in the rows of purifiers to rotate in opposite directions. In this instance, the column of liquid in the most distant cyclones, as seen in FIG- URE 9, will rotate counterclockwise while those columns in the nearest cyclones will rotate clockwise.

A battery of this type forms a compact unit with a very high output capacity and cleaning efficiency. It requires but little space and is easy to connect, in a manner advantageous from the pipe coupling aspect. Several batteries can be connected together in parallel or in series, and such a unit can be extended to any desired degree.

As has previously been expressed, a plurality of variations of the above-described cyclones according to the invention are conceivable. It is thus contemplated that the guide elements can also be made movable within certain limits, it such should prove suitable.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A cyclone separator for a liquid suspension comprising:

a conically tapered container enclosing a cyclone chamber, said container having a conical sidewall with an apex portion and a base portion at opposite ends thereof, said base portion having a first inlet opening therein;

tubular outlet means substantially coaxial with said container and extending through said base portion;

second outlet means substantially coaxial with said container and opening through said apex portion;

wall means fixedly positioned adjacent said base portion and defining a pressure chamber communicating with the first inlet opening in said base portion, said wall means having a second inlet opening communicating with said pressure chamber;

liquid inlet means communicating with said second inlet opening for supplying a liquid suspension to said pressure chamber;

flow-directing means fixedly positioned relative to said container adjacent the first inlet opening for imparting a tangential velocity component to the liquid as it flows from the pressure chamber through the first inlet opening into said cyclone chamber, said flow-directing means comprising a single helical plate-like member positioned in an annular space between said tubul-ar outlet means and said conical sidewall;

said helical plate-like member extending angularly around said tubular outlet means a maximum of one revolution and having inlet and outlet edges which are axially spaced from one another by a maximum axial distance substantially equal to the pitch of said helical plate-like member;

said helical plate-like member further having an outer peripheral edge uniformly spaced throughout its entire circumferential and axial length from said con ical sidewall by a substantially uniform distance so as to define a uniform clearance gap between said conical sidewall and said outer peripheral edge throughout the complete length thereof through which a portion of said liquid can bypass the flowdirecting means.

2. A cyclone separator as defined in claim 1, wherein the inner edge of said helical plate-like member is substantially uniformly spaced from said tubular outlet means throughout the circumferential length thereof so as to define a further clearance gap therebetween.

3. A cyclone separator as defined in claim 1, wherein said flow-directing means consists of a single helical plate-like member angularly extending around said tubular outlet means through an angle of approximately 360 degrees with the inlet edge of said member being axially positioned directly above the outlet edge of said member, said inlet and outlet edges being axially spaced by a distance substantially equal to the pitch of said helical platelike member.

References Cited UNITED STATES PATENTS 2,667,944 2/1954 Crites -457 X REUBEN FRIEDMAN, Primary Examiner.

J. L. DE CESARE, Assistant Examiner.

US. Cl. X.R.

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