US 3391787 A
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July 9, 1968 s. M SALOMON POROUS CONE CLEANER Filed April 18, 1966 IN VENTOR. Sa/amcm A! a/amoxr ATTURNL'I Y-S' United States Patent 3,391,787 POROUS CONE CLEANER Salomon M. Salomon, Madison, Wis., assignor to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed Apr. 18, 1966, Ser. No. 543,272 3 Claims. (Cl. Z---84) ABSTRACT OF THE DISCLOSURE A cyclone separator including a porous wall forming a primary conically shaped chamber, a pipe for directing fluid having foreign particles therein tangentially into the larger end of the primary chamber to provide a vortical whirl, a clean-fluid outlet within the chamber between the inlet pipe and the smaller end of the primary chamher, a water jacket and a liquid inlet around the porous wall to force liquid therethrough and into the primary chamber and a conically shaped extension forming a secondary chamber connected to the smaller end of the pr mary chamber. The diameter of the primary chamber 18 smaller than the diameter of the secondary chamber at the junction of the two chambers.
This invention relates to a centrifugal separator for separating solids from a liquid suspension.
Centrifugal separators are generally used in the punfying of a liquid or a gas by the removal of particles entrained therein. An important field of use for centrifugal separators is in the purifying of paper stock where in wood pulp fibers are suspended in the water solution, an example of this type of general application of the centrifugal separator is shown in US. Patent 2,377,524, Sampson et al. It will be understood that the principles of the present invention will find application in many fields but for convenience of disclosure of preferred embodiments thereof reference will be made to the use of a centrifugal separator for purifying paper stock.
Considering the operation of a centrifugal separator or cleaner the carrier fluid and the particles are to be classified into categories as follows:
(a) The main fluid (gas or liquid) (b) The acceptable fraction (in this case wood pulp fiber) (c) The objectionable fraction which can be further grouped into:
(l) Particles of specific weight close the acceptable fraction similar in material but of different geo rnetric configuration and, therefore, of apparent greater density (in our case bark, shrves, nodules: etc.)
(2) Particles of other origin than the acceptable fraction but approaching in specific weight and size (3) Particles of other origin than the acceptable fraction and of substantially different specific weight or apparent density.
The bulk of the flow entering the tangential inlet of a centrifugal cleaner is immediately subjected to a centrifugal component, among other forces acting on the entering stream. This component is a function of the tangential velocity and the radius of the particular point and its action will immediately separate the c-3 fraction referred to above. This fraction will remain, during the interval of time present in the cone, in a helical path close to the wall until it is discharged at the apex of the cone.
The other force acting on the flow is the entrainment of the liquid created by the presence of central discharge orifice. As the liquid tries to exit through this opening it is immediately subjected to an increasingly larger centrifugal field. The intensity of this field depends on the size of this orifice, and it increases with decreasing of the orifice. (It is clear, then, that two units capable of identical discharge flows, pressure drop, geometric configuration, etc., the one which has a smaller discharge orifice will be superior in its final performance.) The probability that a particle, which passes through this field, will be accepted is extremely high since the retention time is extremely low.
Assume for the moment that separation has occurred and particles c-1 and c-2 will be rejected and, therefore, directed toward the periphery. In their path they will encounter other particles, collide and lose part of the energy they have been initially imparted. This energy loss is coupled with a concentrating effect of the entrained particle 1: present in the suspension between the core of the vortex and the periphery. In the operation of cyclone cleaners heretofore used the concentration at the wall increases rapidly until it reaches a maximum at the apex.
In accordance with the present invention fresh liquid is introduced through the Wall of the cone. The slowly difiusing liquid from the porous wall cleaner liberates the b fraction and entrains the same toward the center of the unit Where it will have again a chance to be accepted. The early introduction of the liquid through the porous wall increases, therefore, the number of chances the particles have to be selected since the flow continuously entrains also the dubious particles contained in the fraction c-l and 0-2 close to the periphery, toward the central discharge opening.
The liquid layer provided through the porous wall has, therefore, two possible exits:
(1) To fiow toward the apex with the reject fraction, (2) To flow radially toward the center of the cone and be accepted through the discharge opening.
I have found that both of these paths may be used by the injected liquid with the largest portion exiting through the apex, if the flow through the porous wall is maintained at a reasonably low level. It is thus apparent that the quantity of liquid injected through the wall will be another variable in the process and that ditference conditions of overall operation will be encountered by varying the flow and leaving all other variables constant.
It is accordingly an object of the present invention to provide an improved cyclone separator which operates in a more effective manner accomplishing better separation and which is particularly well suited for use for cleaning wood pulp stock.
A fu ther object of the invention is provided in an improved cyclone cleancr wherein a liquid layer is introduced throu h the porous outer wall cleaner for improved effects on the objectionable action of material which is to be separated from the acceptable fraction within the cleaner to obtain a more effective and elficient cleaning operation.
Yet another object of the invention is the reduction of the concentration of fiber at the wall of a conical separator and thereby providing a separator capable of efficiently handling suspensions having high or low consistencres.
Other objects, advantages and features will become more apparent with the teaching of the principles of the present invention in connection with the disclosure of the preferred embodiment thereof in the specification, claims and drawings, in which:
FIGURE 1 is a longitudinal sectional view of the centrifugal separator in accordance with the invention; and
FIGURE 2 is a detailed sectional view of a portion of the centrifugal separator shown in FIGURE 1.
As shown on the drawings:
Referring now to FIGURE 1, the water suspension and solid impurities are forced into the tangential input so that a vortical whirl is created along the inside wall of the conical primary chamber. Input flow may be controlled by a valve 11. The heavier solid particles move toward the tip 39 forming a secondary chamber and the liquid suspension, which is effected by centrifugal force to a lesser extent, is returned within the vertex of the vortical whirl to the outlet 4%.
. Water enters the water jacket 50 via the inlet connection ea. Since this fresh water is under pressure, the water flows through the wall 29, as it is constructed of porous material. It is significant to be able to control the quantity of water relative to the fluid entering through line 10, and a control valve 11 permits control of the liquid introduced. The water slowly diffuses inwardly through the porous wall and entrains the acceptable fraction of the paper pulp suspension toward the center of the vortrcal whirl. The rejectable particles which have not yet been removed from the suspension are also entrained so that the number of chances that have to be selected and removed is increased thereby increasing the effectiveness of the cleaning action of the cleaner.
It should be noted at this point that the cross-sectional area of the vortical whirl is less than the cross-sectional area of the conical chamber within the chamber due to the concentration effect. However, the effective diameter d of tip-section is greater than the diameter D of the cross-section of the porous wall 20. This enables the heavier particles to travel in a longer path which tends to keep these particles away from the central upwardly movin g vortex.
The apex of the tip-section 36 can also have a relatively smaller dimension, because the efiiciency of the centrifugal separator is correspondingly increased in accordance with a feature of this invention. The size of the discharge orifice of a centrifugal separator is controlled by the efficiency of the separator because dilution at the boundary of the wall of the chamber causes the desirable wood pulp or fibers to move radially toward the center of the vortical whirl and thence to the outlet 40 so that the suspension at the outlet has a greater percentage of desired particles. For a certain reject flow, normally a separator, due to the high consistency of the concentrated fibrous pulp at the apex outlet, must have an opening of a certain size to avoid clogging of the pulp in the outlet. This means that at higher consistency, due to a high tendency for clogging, the apex opening must be relatively larger. The increase in size of the opening is coupled with large reject flows and, therefore, lower efiiciencies due to the loss of desired fibrous pulp.
FIGURE 2 is a more detailed view of a portion of the porous wall 20 and a portion of the tip-section 30. It can be readily noted that a discontinuity exists between the inside of the Wall 20 and the inside of the tip-section 30 at the point at which the wall 29 joins the tip-section 30. The sudden enlargement lengthens the path of the particles thereby tending to keep the reject particles away from the central vortex so that reject particles are discouraged from becoming entrained in the upwardly moving vortex. Therefore, the water passing through the porous walls 29 causes the desired lighter particles to move radially toward the center of the vortex and thence become entrained in the upwardly moving central vortex; whereas, the larger tip-section 3% tends to keep the heavier undesirable particles way from the upwardly moving vortex and to continue on in a downward direction toward the apex orifice.
In summary, the invention involves the method and apparatus of cleaning a paper pulp suspension of foreign particles by passing the suspension into a conically shaped cyclone chamber provided with a layer oi fresh water on the wall and having a tip with the non-porous wall at the smaller end, having an opening for the removal of foreign particles. The tip has a diameter less than the smaller end of the chamber by an amount equal to the layers of water on the inner wall of the chamber. By providing the diluting thin wall within the chamber, a low concentration of fiber is provided. This layer of water provides a boundary lubrication which decreases frictional resistance. This layer of water also protects the wall of the chamber. By providing a diluting thin wall, the concentration of fiber is low, thereby increasing the efficiency. This arrangement permits a decrease in outlet orifice size with increased efficiency. Actually, the size of this orifice controls the eificiency and a smaller size is important. By decreasing the outlet orifice, an increase in angular velocity is achieved. It has been found that the size of the inlet orifice can be reduced with the same pressure differential it the shell surface is lubricated as is provided in accordance with the present invention. Also, with the same pressure differential, an increase in volume can be achieved.
It also can be seen that if the flow through the porous cone is for example 50% of the total flow, the flow density through the unit will change. This will force a greater portion of the particles referred to as c-l and c2 above through the discharge opening, making the unit more selective for the c-3 fraction only. The application of this flow distribution could arise in instances where very high consistency stock is introduced and low concentration of the rejects is imperative.
The other extreme is the application where the slurry consists of only the liquid carrier and the abrasive solid material referred to as c-3 above. In such case only a small amount of liquid injection becomes necessary to obtain the lubricating properties thereof.
As discussed the foregoing principles could be extended to gas cycle cleaners and the presence of the liquid on the wall will trap solid particles and discharge these through the apex. In other instances the liquid will function as a cooling and a wear reducing liquid barrier if the gases are extremely hot. It will be appreciated that other advantages and uses of the boundary control obtained by liquid injection are attainable in the various applications where cyclone cleaners are used.
Thus it will be seen that I have provided an improved centrifugal separator which meets the objectives and advantages above set forth and which provides a much greater efficiency by lowering the input pressure and protecting the wall with a boundary layer of water.
The reduction of frictional losses obtained by boundary lubrication of the wall permits the attainment of several important advantages. An increased capacity for the same pressure drop is obtained; i.e. up to 2530% more capacity as compared to a unit without boundary lubrication. Reduction in pressure drop results for the same capacity at higher efficiency and lower power consumption (lower pump pressure required). The efiiciency is greatly increased for the same pressure at the same capacity and power consumption by reducing the cross sectional area of the discharge orifice, as the smaller diameter permits higher angular velocities to be achieved at the outer core of the vortex with much sharper classification and separation capabilities. With all other variables being constant at no further increase in pressure drop or power, this invention enables considerable lengthening of the separator by changing the slope of the wall and, therefore, increasing the retention time which is a controlling factor where sharper classification is desired.
The drawing and specification present a detailed disclosure of the preferred embodiment of the invention, and it is to be understood that the invention is not limited to the specific forms disclosed, but covers all modifications, changes and alternative constructions and methods falling within the scope of the principles taught by the invention.
spar rat 6 I claim as my invention: directing a flow of pressurized fresh water radially into 1. An elongated cyclone separator for removing from the conical path to mix with the suspension and to a fluid foreign particles suspended therein comprising, urge lighter particles toward the center of the vortex,
a porous wall forming a conically shaped primary continually withdrawing a fraction of the mixture conchamber which extends substantially the entire length 5 taining heavier particles from a point adjacent the of the separator, smaller end of the conical path, means including awater jacket surrounding said porous returning the balance of the mixture constituting the wall for forcing a liquid through said porous wall, major fraction of the orignal stream of the suspension means including an inlet opening at the larger end adjacent the axis of the vortex toward the larger end of said chamber for directing the fluid with particles 10 of the conical path, and suspended therein tangentially into the primary chamcontinually withdrawing at least a portion of said balher in avortical whirl, ance from a point adjacent the larger end of the means forming an outlet for particle-removed fluid in conical path,
said primary chamber between said inlet opening and said fresh water being directed into said conical the smaller end of said primary chamber, path along a longitudinal portion thereof located a conically shaped fluid impervious wall connected to substantially centrally between the larger and the smaller end of said porous wall forming a secsmaller ends of the conical path and extending ondary conically shaped chamber in axial alignment from the point at which said balance is withwith the primary chamber with the larger end of the drawn to a point substantially axially spaced secondary chamber adjacent the smaller end of the from the smaller end of the conical path. primary chamber, and an outlet at the smaller end of the secondary chamber References Cited for removal of foreign particles from said separator. UNITED STATES PATENTS 2. The cyclone separator as defined in claim 1 wherein the smaller end of the primary chamber has a diameter g; a i '7 5? which is less than the diameter of the adjacent larger 00 m 1 1 end of the secondary chamber. FOREIGN PATENTS 3. A method of removing from a pulp suspension par- 1,184,373 2/1959 France. ticles of impurities having different weights comprising 971,939 10/1964 Great Britain the Steps of 270,811 12/1950 Switzerland.
introducing a continuous stream of the suspension tangentially into the larger end of a conical P REUBEN FRIEDMAN, Primary Examiner. to provide a vortical motion in the suspension leading in an axial direction toward the smaller end of SAMIH ZAHARNA Examme' the conical path and then freely in an opposite axial J, ADEE, D, M, RIESS, Assistant Examiners. direction within the path,