US2407303A - Apparatus for reducing the fluid content of a fluid-solid intermixture - Google Patents

Description

Sept. 10, 1946. H. A. TEALE 2,407,303

APPARATUS FOR REDUCING THE FLUID CONTENT OF FLUID-SOLID INTERMIXTURES A Filed Aug. 15, 1943 3 Sheets-Sheet 1 I N V EN TOR. Harald fl. E a/e BY v Sept. 10, 1946. TEALE Y 2,407,303

APPARATUS FOR REDUCING THE FLUID CONTENT OF FLUID-SOLID INTERMIXTURES Filed Aug. 13, 1943 I 3 Sheets-Sheeti i0 v M I 65' 1m r j "H mun" i" .i v

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Patented Sept. 10, 1946 APPARATUS FOR REDUCING THE FLUID CONTENT OF A FLUID-SOLID INTERMIX- TUBE Harold A. Teale, Brooklyn, N. Y., assignor to Filter Irvington on Hudson, N. Y., a corporation of New York Application August 13, 1943, Serial No. 498,520 4 Claims. (01. 210-188) Media Corporation,

The invention relates to slurry separators, thickeners, clarifiers or the like and more particularly to a new and useful apparatus for continuously decreasing the fluid content of a solid and fluid intermixture.

Objects and advantages of the invention will be set forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the instrumentalities and combinations pointed out in the appended claims.

The invention consists in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.

The accompanying drawings, referred to herein and constituting a part hereof, illustrate one embodiment of the invention, and together with the description, serve to explain the principles of the invention.

Of the drawings:

Fig. 1 is perspective view of an apparatus embodying the invention;

Fig. 2 is an enlarged fragmentary vertical section, in expanded relation, of a plurality of typical elements comprising the thickener apparatus shown in Fig. 1;

Fig. 3 is an enlarged fragmentary section of the elements of Fig. 2 in assembled relation;

Fig. 4 is a fragmentary top plan view of a thickener plate taken on line 4--4 of Fig. 2;

Fig. 5 is a fragmentary bottom plan view of a filter plate taken on line 55 of Fig. 2; and

' Fig. 6 is a fragmentary vertical section through one element of the assembled apparatus, diagrammatically illustrating the nature of the slurry flow therethrough; and

Fig. '7 is an enlarged perspective view of a section of a plate ll showing the transverse nodes 44' and the transverse valleys 45 on one side and the longitudinal grooves 25 as Well as their adjacent lands 26;

Fig. 8 is an enlarged partial view similar to Fig. 6 but taken along the line 8-8 in Fig. 7, but with the filter medium 50 in place thereon, and this figure illustrates what seems to happen to the slurry particles in the channel 40;

Fig. 9 is a plan view of a portion of a channel 40 and shows a modified form of node; and

Fig. 10 is a partial perspective view of the modi fied arrangement of Fig. 9.

The invention is directed to providing novel and useful apparatus for reducing the fluid content of a fluid-solid intermixture (hereinafter called a slurry) by virtually continuous filtering or straining action wherein a clear fluid product is continuously removed from the slurry, thereby continuously increasing the proportion ofsolids remaining in the slurry which may be recirculated or passed several times through the apparatus, as required, to bring about the desired proportion of solids-to-fluid therein. The invention is of general application to practically any and all such slurries or intermixtures but is particularly useful in cases where thickening of the interm'ixture is impracticable or inefficient by usual means such as settling and decanting. Hence the invention is applicable to the thickening of many slurries where solids are very fine or in a state of colloidal suspension, which cannot be thickened by settling or gravity action.

Many of the novel principles of the invention are broadly and generally applicable to the separation or clarification orthickening of fluids containing intermixed solids, including gas and solid intermixtures. In the succeeding description, however, particular reference will be made to the treatment of liquid-solid intermixtures and for convenience of reference the action of the apparatus will be referred to as thickening and the apparatus itself as a thickener.

The invention employs exceedingly simple and inexpensive-means, but by means of novel principles, is enabled to produce very superior results in relatively short time and at a low expenditure of power and labor.

The thickening or liquid-removing action of the invention depends upon the movement of the slurry over or across the surface of a filter me dium while under pressure sufiicient to force liquid through said nledium, maintaining a state of motion in the slurry travelling over said medium such that no substantial amount of solid is deposited out of the slurry to form as cake on Said medium. In accordance with the invention the state of motion induced in the slurry to effect this desired action is brought about by exceedingly simple stationary means without the interposition of any mechanical agitation or pulsation from applied mechanical means or forces. In other words, the required motion and movement of the slurry over the filter medium and the maintenance of desired pressures and velocities therein are all effected by static and exceedingly simple devices within the chambers where the filtering action takes place.

One object of the invention is to prevent the deposition of solid particles onto the filter medium by maintaining a substantial continuous turbulence throughout the slurry as it travels in relatively high velocity streams across the surface of the filter medium thereby producing a substantial scouring action of the liquid against the surface of the filter cloth or other medium which prevents the formation of any substantial amount of cake or solid matter thereon. The invention also provides for recurrently actively forcing or urging the slurry against and into contact with the filter medium as it travels thereover, thus providing frequent surges or impulses in the slurry which cause the liquid in same to be driven against and through the medium.

Another principle employed in the invention, either as a concomitant of the foregoing or independently thereof, is the maintenance of a substantially constant velocity in the stream of Slurry passing over a length of filter cloth, This function is preferably efiected by causing the slurry to travel through channels of decreasing crosssection so that, as the amount of liquid therein decreases by the filtration effect, the loss in volume of the stream of slurry is compensated for by decrease in the size of the conduit, thereby effectively maintaining a generally continuous velocity which facilitates the maintenance of the flow of slurry over the filter medium, counteracting the tendency of the solid particles to settle out on the filter cloth, and, when used in combination with the turbulence-creating means above referred to, enhances the scouring and anti-precipitating action as well,

One feature of the invention which greatly facilitates the successful operation thereof is the maintenance of a proper balance of forces and fiuid movements so as to build up and maintain a relatively thin deposit or skin of solid matter on the face of the filter medium. This skin of cake is established at the beginning of the operation and, is maintained substantially constant throughout the continuous recirculation of the slurry through the apparatus. The maintenance of said skin of cake is effective in providing a clear solid-free liquid product delivered through the filter medium and the force employed are so regulated and balanced as to prevent the building up of said skin of cake beyond a predetermined very low maximum thickness, yet to establish and maintain same throughout the operation and in spite of a continuously increasing proportion of solid content in the slurry.

It will be understood that the foregoing general description and the following detailed description as well are exemplary and explanatory but are not restrictive of the invention. Referring now in detail to the present preferred embodiment of the invention, illustrated by way of example in the accompanying drawings, a general view of an apparatus embodying a preferred form of the invention is shown in Fig. 1. Same comprises in general a tank 8 for containing the supply of slurry which is drawn preferably from near the bottom thereof by conduit 2 on the intake side of a motor driven pump 3 and forced thereby through pipe 4 past pressure gauge 5 into the top of the thickening unit Ill by means of inlet pipe 6. The solid-free filtration product of the thickening unit l0, hereafter conveniently called filtrate, is delivered therefrom at one or more points by delivery pipes I5 into a suitable receptacle l6, while the thickened slurry, constituting the mixture which has passed through the unit Ill, is delivered therefrom by one or more outlet pipes l8 which, as shown, feed back into the tank In for re-mixture with the original batch and re-circulation through the unit ID as man times as may be required to reduce the slurry to the desired'liquid-solid ratio. With many products, however, a single pass of the slurry through the unit It may be sufficient to bring about the desired thickener action or on the other hand, the slurry delivered by the pipe I8 may be passed through a second unit similar to unit I 0 in series or tandem therewith so that sequential thickening actions on the progressively thickened slurry may thus be effected,

Referring superficially to the construction of unit Hi, same comprises a plurality of superposed rectangular plate members or elements I l which are relatively long and narrow and which are mounted to colliectively form a rectangular stack of inter-communicating elements or plates one above the other, as shown, A bottom supporting plate l2 and an overlying top plate l3 are provided, same being somewhat greater in area than the element plates II, and the entire stack is bound together by a plurality of vertical rods l'l. pairs of which at either side of the stack are tied by top and bottom cross-members I! and drawn together by nuts l9 at the threaded ends of the rods. Any other suitable means for compressing or drawing together the several superposed plates or elements of the unit Ill may be provided, it being understood that the hydraulic pressure for the thickening of most products is relatively low compared with that used in a typical filter press. Pressures of the order of about 15 lbs. per square inch have been used successfully and therefore an expensive and heavy duty clamping or pressure-maintaining means is not ordinarily required. However, for certain purposes and with some mixtures considerably higher pressures may be used and are sometimes desirable and in such cases the clamping or pressuremaintaining means may be adapted to the higher pressure operations without interfering with or changing the basic design of the apparatus nor its internal functioning.

The detailed construction of the several plates making up the unit l0 will be seen in Figs. 2-5.

As shown, th top plate or head stock I3 is provided near one end with the vertical port 20 for the reception of the inlet pipe 6, the lower portion of said port being counter-bored at 2|. The port 2ll2l is alined with a similar port 22 in the first or head plate 23 of the unit Ill, said head plate being smooth and flush on its top face to match with the bottom surface of the overlying head stock 13. The underface of head plate 23, however, is provided with a plurality of longitudinal grooves 25 and lands 26 which serve as channels for the filtrate after same has filtered through the filter medium 50 overlying said lands and grooves. As shown, each groove 25 begins adjacent the inlet slurry port 22, and terminates at 28 in a recessed cross-conduit 29. Said crossconduit thus communicates with all the discharge ends of the clearate grooves (Fig. 5) and in turn communicates with an upwardly inclined central duct 30 which directs the filtrate into a discharge channel which, in the head plate, begins with the enlarged socket portion 3| which is alined with similar capacity ports in the other plates just below.

The next plate or element II is typical of all those for making up the unit It], except for the head plate 23 and the tail plate 35 hereinafter described. That is, a plurality of said plates ll similar in construction thereto, will all be superposed to make up the unit It] and in practice a typical unit may include thirty of such plates combined as shown in Fig. l.

In the preferred construction, as shown, each.

rality of channels or conduits for the travel of the slurry therealong while in contact with the filter medium 50 lying against the lands of the filter grooves 25 of the plate just above. Preferably, in a unit of the general shape and dimensions shown, the plate will be provided with three parallel channels 40, the inlet ends of which communicate with the slurry port 22 of the plate just above. Each of said channels 40 extends from said inlet end to communicate with a down port 4| near the opposite end of the plate H so that liquid reaching said end travels downwardly through the port M to the next plate below. As will be apparent from Fig. 4 the three channels 4!] of the plate are separated by partitions or lands 43 which extend parallel for the length of said channels 40.

In accordance with the invention the course of the slurry travelling along a conduit 40 it continuously disrupted and changed in velocity so as to impart a disrupting turbulence therewithin as the liquid travels along said channel. For this purpose the bottom surface of the channel is preferably formed as a wavy surface comprising successive nodes 44 and valleys 45 which, as illustrated diagrammatically in Fig. 6, cause a constant turbulence and scouring activity within the stream of slurry flowing along said channel. The number, depth and spacing of the valleys 45 and node 44 do not appear to be especially critical although it is important to make frequent changes in the depth of the channel to thereby cause the slurry to be forced upwardly through narrow passages close to the overlying filter medium 5!] (Fig. 6) and then to quickly expand into zones of greater volume in the valley portions 45.

For example, in plates ll of the general shape shown, having an overall length of about 5' with grooves All of .8" in length, the approximate length from node to node is preferably about 4". However, it will be understood that the invention is not limited to any particular shape or number of elevations or depressions in the slurry guiding channels and that same may vary with different types of materials, with different hydraulic pressures and other factors. It will be found by practice with the invention that certain optimum arrangements of the general designs hereinbefore disclosed will obtain with various materials and mixtures of slurries but that a wide latitude may be had in the arrangement and number of the elevations and depressions in the grooves without departing from the essential principles of the invention.

Another feature which has been found helpful in facilitating the desired continuous thickening and prevention of solid precipitation, is the construction of the slurry flow channels 49 in such manner that they decrease in capacity or volume in the direction of flow of the slurry therealong, thereby to maintain substantially constant the general velocity of flow of the slurry in said channels and thus oppose any slowing down of the slurry flow which in tfirn would promote settling action of the solid particles. As shown in Fig. 2, for example, the channels 4|] in plate I l are of maximum depth at the inflow or righthand end and taper to a relatively shallow depth at the delivery or left-hand end thereof.

This feature of narrowing or tapering of the slurry channels has been found to be helpful in and by itself in preventing settling out all the solid material and consequent choking and blinding of the channels. The same is true to an even greater extent of the other features of the invention previously described, i. e. the provision of Wavy surfaces in the slurry channels to promote turbulence or ripples in said flow. That is, each of said features can be used independently of the other and when so independently used will improve the thickening action and efficiency of the unit. However, I prefer that they be used together, the combination of the two features contributing to the improved operation of the unit. Of the two such features, however, I regard the provision of the ripple or turbulence-creating elevations and depressions in the conduit as being more important and, with some materials, capable of efficient independent use, in which case the slurry channels 40 may be of uniform depth and width (except for the nodes and valleys) throughout their length.

In the preferred construction shown it will be noted that the slurry is caused to travel through relatively long and narrow passages 48 with reversals of flow direction at the end of each pass. The relatively sharp and. sudden reversals of direction have been found to contribute beneficially to the prevention of solid precipitation, in that said changes in direction assist in breaking up the continuity of flow and the maintenance of turbulence in the streams of slurry. The invention is not limited to use of relatively long passes of slurry in each compartment or section of the unit as, if desired, the pnitmay instead comprise a larger number of relatively short sections whereby the reversals of direction of slurry flow occur very frequently and thereby contribute of themselves in a relatively greater extent to the turbulencecreating action desired.

One important feature of the invention is to so regulate the turbulent or rippling flow of the slurry that a relatively thin skin or layer of solid matter is formed promptly on the adjacent surface of the filter cloth and thereafter no increase in the thickness thereof takes place. In practice, it has been found that with many substances a skin or cake thickness of about 2;" is the optimum, said skin acting as a filter-aid to increase the clarity of the filtrate while being sufficiently thin as not to interfere with the prompt passage of liquid through the filter medium at a relatively high and constant rate. In this connection it has been found that the construction and shape of the nodes 44 is of importance in creating a recurrent upward surging of the slurry or its bombardment against the overhead canopy of filter medium and its adherent skin of solid particles. That is, the upwardly-directed kinetic impact of the slurry passing over each rise or node in the channel imparts recurrent dashings of the slurry against the filter medium and thereby materially contributes to forcing liquid through the skin and the filter medium.

Such kinetic impact of particles of the slurry against the filter medium is illustrated in Fig. 8 of the drawings, wherein the horizontal arrows at the right hand of the figure indicate the infiowing slurry, while the V-shaped bent arrows indicate a defiective path taken by a slurry particle as it strikes a rise or node 44 in the channel 40. The A-shaped bent arrows indicate a defiective path taken by a slurry particle as it strikes the filter medium 50 and bounds away therefrom. The circular arrows indicate eddies and other disturbances created or set-up in the flowing slurry due to these: bounds and rebounds indicated by the bent arrows. This seems to be an explanation of the scouring action of the flowing slurry that keeps down the thickness of the filter cake on the filter medium 50 from growing thicker than that at which the cake normally stabilizes itself to the conditions of flow and kinetic impact.

The nodes or elevations 44 in the channels ea may be modified as shown in Fig. 9, which differs from the arrangement of Figs. 4 and 7, for instance. In those figures, the. crest or ridge of each node extends continuously transversely of the channel 40, whereas in the. arrangement of Fig. 9, each general node 44 maybe made up of a plurality of individual nodes culminating in crests 44a, Mb, 44c, 44d and so on, respectively, with these crests forming a broken or irregular line more or less transversely on the channel 40. These irregular crests create further scouring eddies or turbulence as indicated by the curved arrows shown in Fig. 9. Fig. 10 shows how these irregular crests appear.

For most purposes it will be found that wood is a suitable material for construction of the units especially because the pressures of operation are ordinarily not high or critical. However, the elements of the thickener unit may be made of molded or laminated Bakelite or other similar material, and such plastics are especially effective where chemicals corrosive to wood, metal or other materials are present, in the slurry to be thickened. Metal or any other available material may, of course, be used where called for.

The invention in its broader aspects is not limited to the specific mechanisms shown and described but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What I claim is:

1. In a slurry thickener in combination a filter plate having recesses on the lower side, means for removing filtrate from said recesses, a filter medium under said recesses and constituting therewith filtrate conduit means, and a slurry flow directing plate adjacent to the underside of said 8 filter medium and constituting therewith a conduit for the flow of slurry therethrough, said conduit having an undulating bottom surface presenting nodes and valleys for imparting turbulence to a stream of slurry passing through said conduit, and also having outlet means for passing slurry from said conduit.

2. In a slurry thickener comprising a stack of elements, a plate element, having on its lower side a downwardly open recess for the reception and flow therethrough of filtrate, a filtrate outlet passage, and having on the upper side a channel for the passage therethrough of slurry, said channel having an undulating bottom face presenting nodes and valleys, and slurry outlet means at the end of said channel.

In a slurry thickener a stack of plate elements, each plate element having on its lower side a downwardly open recess for the reception of filtrate, and on the upper side a channel for the passage therethrough of slurry, said channel having an undulating bottom face presenting nodes and valleys, a filter medium interposed between adjoining faces of any two such plate elements, and passage means in said plate elements whereby slurry passes from the end of a channel in one plate element into a corresponding channel of the next lower element and whereby the direction of flow of the slurry is reversed, a slurry inlet passage for the: first channel of said stack of plate elements, a slurry outlet passage for the last conduit of said stack of plate elements, and means for removing the filtrate from said recesses.

4. A slurry thickener including in combination a filter medium, flow conducting means constituting with the underside of said filter medium a conduit for passing therethrough a stream of slurry along and past said underside, said conduit having an undulating bottom surface presenting nodes and valleys for imparting turbulence to said stream passing through said conduit, inlet means for passing slurry into said conduit, outlet means for passing thickened slurry from said conduit, and conduit means for removing filtrate passing upwardly through said filter medium.

HAROLD A. TEALE.

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