US3280975A - Discharge control for hydraulic classification - Google Patents

Description

Oct. 25, 1966 R. D. EVANS 3,280,975

DISCHARGE CONTROL FOR HYDRAULIC CLASSIFICATION Filed March 29, 1963 1.: INVENTOR.

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Af/amey United States Patent 3,280,975 DISCHARGE CONTROL FOR HYDRAULIC CLASSIFICATION Robert D. Evans, Pierce, Fla, assignor, by mesne assignments, to Continental Oil Company, a corporation of Delaware Filed Mar. 29, 1963, Ser. No. 268,899 9 Claims. (Cl. 209-158) This invention relate-s to the hydraulic classification of particulate solids, and especially to methods and instrument-aities for effecting product discharge from a s-o-called hindered settling column wherein divided solid material is classified according to settling rate.

In hydraulic classifiers of the type including a hindered settling column, for classifying solid materials by particle size or settling rate, an eifective mode of withdrawal of accumulating, classified material from the column involves a siphon under control of a so-called hydrostatic column, i.e. as embraced in US. Patent No. 2,714,958 granted August 9, 1955 on an application of the present applicant. Essential features of an advantageous embodiment of the siphon discharge of the patent include siphon conduit means extending above the uppermost level of liquid in the classifier, arranged to discharge at an external locality below said level, together with a control device including a hydrostatic pipe opening in the classifier at a level adjacent the inlet opening of the siphon and extendin-g well above the classifier. The hydrostatic pipe comm-unicates with a control chamber at a selected elevation i.e. above the uppermost portion of the siphon, such control chamber including means for closing or opening a vent in the uppermost region of the siphon conduit, dependent on the presence or absence of liquid, e.g. water, in the hydrostatic column at a level corresponding to a desired pressure in the classifier, which pressure cor-responds, in turn, to a desired accumulation of solids in the hindered settling column.

An effective and simple control arrangement in the stated chamber comprises a float carrying a needle or cone-type valve element which may be raised by the float to close a tube leading to the siphon vent. Thus when -a pulp of accumulating solids of sufficient density is reached and maintained, say at the foot of the hinderedsettling column where the siphon opens, the increased pressure caused by such solids in a condition of so-called teeter raises the water in the hydrostatic column (which is essentially clear water, since there is no upward flow to carry solids) to a significantly high level, above the overflow level of the classifier. Under such circumstances, i.e. when a level of selected height is reached, the valve closes and siphon action is thereupon initiated, conducting a pulp or slurry of the desired, classified solid particles to the point of discharge. If insuflicient solid particles are accumulating, or solid particles of insufficient size (or settling rate), the pressure in the solids-containing body of water at the foot of the settling column falls, thereby lowering the level in the hydrostatic column. In consequence the float descends, opening the vent of the siphon and interrupting its discharge action.

Product discharge arrangements of the above character are more fully described in the cited patent, further instances of utilization of such siphon discharge means being shown with other hydraulic classifiers embodying hindered settling columns, i.e. in US. Patent No. 2,784,841 granted March 12, 1957 on the application of the present applicant, and likewise in US. Patent No. 2,967,167, granted January 10, 1961 and U.S. Patent No. 3,032,194 granted May 1, 1962, on applications of the present applicant and Harvie W. Breathitt, Jr. A still further arrangement of such siphon discharge control is disclosed and claimed 3,280,975 Patented Oct. 25, 1966 in the copending application of the present applicant and Harvie W. Breathitt, Jr., Serial No. 111,320, filed May 19, 1961, where the control chamber includes electrode means sensitive to the level of water in the hydrostatic pipe, with arrangements governed thereby for opening and closing the vent in the siphon.

Whereas the foregoing devices have been found to function very eifective'ly, with remarkable control of the nature of the product discharge, i.e. as to its limitation to desired characteristics of size (or more generically, settling rate) in such product, experience has indicated that with relatively light weight minerals or similar substances the actual elevation, or more accurately, the superelevation of the liquid in the hydrostatic column may sometimes be inconveniently low. No difiiculty has, in general, been encountered with substances such as phosphate rock, sand, and a variety of heavier minerals, but in the case of materials such as coal or equivalent solids having a specific gravity of not more than about 2.0, the valve control chamber (which may be adjusted in vertical position) may have to be located too close to the overflow level of the classifier, for convenience of operation, adjustment or servicing, and indeed for optimum, positive control of the siphon action. That is to say, if hindered settling classification is applied to particles of coal or similar material, e.g. having a specific gravity of not more than 1.2 to 1.5, the accumulation of such solids in teeter, as at the lower region of the classifier column, does not increase the pressure (above that of the normal head of water) by anything like as large an amount as occurs with phosphate rock, sand or heavier substances. Thus even under optimum conditions of product accumulation, the increase in density of the pulp in the settling column at the locality of product Withdrawal is relatively small, and the float box or equivalent chamber must then be situated unduly close to the overflow level of the classifier, for convenience of observation, servicing and use.

In accordance with the present invention, means and methods of operation are provided whereby an amplified or exaggerated level of super-elevation is achieved in the hydrostatic column, so that the control chamber may be situated at a correspondingly higher position, well above the top of the siphon. In this locality of greater elevation, the control instrumentalities are much more conveniently located and serve more positively and reliably for the desired function of governing the siphon discharge. In consequence the system functions in a thoroughly satisfactory manner, with proper regulation of the withdrawal of product particles, unaffected by the fact that such mineral may be of relatively low specific gravity.

Specifically, the method of the invention embraces supplying to the hydrostatic column a flow of water under considerable head, i.e. a constant pressure, of a suitable, selected value. That is to say, although the pipe extending from the control chamber to the locality of accumulating solids in teeter may conveniently be denoted as a hydrostatic column, a considerable part of its length is now traversed (i.e. according to the invention) by a continuous flow of water under the additional, constant pressure. The portion of the column which extends above the locality of introduction of water flow, then provides a control level (i.e. the liquid rises to such level) which is governed, in eifect, by the sum of the pressure of flowing water supply and the pressure contributed by the collecting solids. As explained above, the pressure in the hindered settling column is normally increased in accordance with the increase of apparent density of the solids-liquid suspension in teeter.

Hence, an example of effective embodiment of the invention embraces the supply of the hydrostatic column, ad-

vantageously at a region slightly above the tank overflow level, of water under a constant pressure. In order for this water to be driven downward through the hydrostatic column connection and out at the region at the foot of such column, there must be sufiicient head to effectu ate such flow out of the bottom opening of the hydrostatic column. The control point of level of water, e.g. clear water in the hydrostatic pipe, is thereby substantially raised above its otherwise normal locality. In all other respects the discharge-controlling function and operation are the same. With the control chamber or box located at an amplified super-elevation, operation proceeds as would be achieved (e.g. with substantially heavier minerals) with heavier feed. The control chamber is thus set at a correspondingly higher locality, i.e. as needed for the defined siphon control function.

Stated in another way, the control column portion (of the hydrostatic pipe) which extends above the point of entry of the supplemental water supply, constitutes a true hydrostatic column, where the liquid level for desired siphon action is greatly raised above the point where it would otherwise be placed. Although, as will be understood, other arrangements for supplying a flow of water at a constant pressure may be employed, an effective arrangement involves what might be described as a constant head water tank connected by a suitable pipe to the hydrostatic column or pipe (e.g. at the aforementioned locality) for example between the classifier overflow level and the point of normal super-elevation. With liquid flowing on downward through the control pipe into the hindered settling column, say at the foot thereof, the supplemental pressure of such flowing liquid (i.e. the pressure causing its flow) causes exaggerated or amplified super-elevation of water level in the hydrostatic pipe, so as to enable disposition of the control chamber or float box at the conveniently higher level.

In other words, the float box or its equivalent is then set at a substantially higher point, i.e. to control the siphon for initiation of discharge when desired accumulation of particles in teeter is reached at the bottom or other withdrawal locality of the hindered settling column. In other respects, the system functions as in previous embodiments, e.g. as in the cited patents. When pressure occasioned by the increased density of the solids-containing liquid reaches a desired point, the level in the hydrostatic column (now at an amplified place of super-elevation) effectuates closure of the vent in the siphon. The siphon, which heretofore had a tendency only to carry across clear liquid (in spurts or surges, as explained in the cited patents) now constitutes a functioning siphon and provides a discharge of the desired pulp of classified particles. That is to say, the pressure of liquid at the foot, filling the siphon first with clear water, promptly effectuates continuance of flow into the siphon, carrying particles of solid with it. The vent being closed, there is true siphon action, whereas with the vent open, the pressure at the foot is insuificient to carry the pulp as such above the tank overflow level.

It will be understood that the exaggerated condition in the hydrostatic column is directed solely to that column, the action of the siphon being dependent only on the condition of liquid and solids in the hindered settling column itself. Providing the uppermost turn of the siphon is above the tank overflow level, there is nevertheless efi'ective control of the siphon by opening and closing the vent, with the further provision that such uppermost part will be disposed below the level of normal or ordinary super-elevation in the hydrostatic column, i.e. the level that would be reached under desired conditions without the means and procedure of the present invention.

By way of simple further explanation of the function of the means providing exaggerated super-elevation, it might be stated that if the hydraulic classifier is filled only with water and water is then introduced into the hydrostatic pipe, there will be a flow into the classifier through such pipe. As the flow of water begins and is increased, the water in the hydrostatic pipe (e.g. in the upper portion thereof extending above the point of introduction of water) will rise so that for each rate of flow it reaches and maintains a corresponding level which represents sufficient head to force the water (flowing at the attained rate) through the lower part of the pipe and out into the classifier. As feed of solids is thereafter introduced into [the apparatus, and the classifying function, including establishment of a teeter column or hindered settling column, comes into play, the accumulating density of pulp at the foot of the hydrostatic pipe results in additional build-up of head in the clear water in the pipe; this head due'to hindered settling operation, being represented by further elevation of the level in the upper portion of the pipe, is as required in order to continue the downward flow of water through such pipe.

Thus for any given rate of water flow, as may be determined by setting of an appropriate valve, the superelevation or head (as last mentioned) corresponding to the increase of fluid density at the foot of the hydrostatic pipe is superimposed on the supplemental head or pressure necessary to force the water down and through. This supplemental or added head, occasioned by the flow of water under pressure to and through the hydrostatic pipe, produces an amplification of the operating super-elevation in the hydrostatic pipe, and thus provides the correspondingly higher locality for the control instrumentalities, in accordance with the present invention.

As will now be seen, the adjustment of a valve or other instrumentality for controlling the water flow provides a mode of adjusting the extent of super-elevation, the liquid upstream of such valve being advantageously supplied at a constant pressure. Indeed it will be understood that at any given setting of the valve, there will not only be a definite corresponding rate of water flow (because the pressure upstream of the valve is constant) but there will also be a correspondingly definite, and somewhat lower pressure immediately downstream of the valve, i.e. as occasioned by the drop across the orifice which the valve provides. Thus the last-mentioned pressure, at the downstream of the valve, in effect represents the extent of amplification of the super-elevation expected in the hy drostatic pipe. In other words, the valve adjustment determines the rate of flow of the supplied liquid and correspondingly determines, in accordance with the adjusted pressure at the downstream side of the valve, the amount by which the liquid level in the hydrostatic pipe is raised above the normal super-elevation which is imparted to it because of accumulating solids in teeter in the hindered settling column.

Further features and advantages of the invention will be apparent from the detailed description hereinbelow set forth, together with the accompanying drawing, which illustrates in schematic elevational view (partly in vertical section) a hydraulic classification system incorporating the apparatus of the present invention in an exem plifying embodiment.

There is shown in the drawing a hydraulic classifier of the hindered-settling type, represented by a tank 10 comprising an upright cylindrical tank section 11 opening downward into a wider cylindrical tank section or pocket 12. Means are provided for the continuous introduction of water in considerable quantity to a lower region of this pocket, e.g. a valved pipe 14 opening horizontally into the side wall of the pocket. Immediately above the locality of introduction of Water is a so-called constriction plate 17 separating the lower region 18 of the pocket from the upper region thereof; this plate has multiple perforations of suitable size, through which the water introduced by the pipe 14 flows with considerable velocity to rise in the column 11 and provide hinderedsettling conditions therein. For purposes of drainage at desired times, a valve pipe (normally closed) extends downwardly from the lower end of the pocket 12.

The classifier structure also includes a feed pipe 22, shown as opening into the upper portion of the tank section 11 at one side. Through this pipe, divided solid materials to be classified are advanced in the form of a pulp mixed with water. In addition, an annular launder 23 concentrically surrounds the upper extremity of the tank section 11 to receive overflow from the tank. The overflow is removed from the launder as through a downwardly extending outlet pipe 24.

In operation, the tank 10 is maintained filled with water by continuous supply of the aqueous pulp through the feed pipe 22 and continuous flow of so-called hydraulic water to the tank through the pipe 14. The solids to be classified, introduced in the pulp to the tank section 11, tend to settle downwardly through the tank. However, the upward flow of water from the pipe 14, as augmented in velocity by passage through the constriction plate 17, inhibits the settling of solids and creates in the tank section 1.1 a hindered-settling column wherein solid particles are maintained in a condition of suspension or teeter. Consequently, primarily only the largest or fastest-settling of the introduced particles can reach the pocket 12 in the lower portion of the tank, while the particles of slowest settling rate, e.'g. fines, are carried upwardly through the section '11 and away from the tank with the overflow to the launder 23. In other words, such hindered-settling operation separates the introduced solid particles according to settling rate, and provides in the pocket 12 an accumulating suspension of particles which are primarily of the largest or fastest-settling fraction, -i.e. that fraction of the introduced particles which it is ordinarily desired to separate and recover.

The apparatus of the present invention in the form shown is adapted to effect the controlled discharge of this classified product from the pocket 12 as an aqueous pulp containing particles chiefly of the desired large size or tast settling rate, and includes a siphon conduit system of the type disclosed in the aforementioned U.S. Patent No. 2,714,95 8. Thus there is provided an enlarged lower conduit section 25 opening downwardly into the pocket 12 and connected at its upper end with a long pipe section 26, of smaller diameter, extending upwardly to a locality above the tank overflow level. At this latter locality the pipe section 26 communicates as through a T-fit'ting chamber 28 with a further pipe section 29, which extends horizontally beyond the tank and thence downwardly' to a suitable external discharge location (not shown) at an elevation lower than the liquid level in the tank. To assist the siphon action, and in particular to facilitate its initiation or resumption, a supplemental flow of water is introduced to the lower section 25 as through a valved priming pipe 30. Desirably the pipe section 26 extends downwardly through the upper portion of the section 25 to open therein at a level lower than the opening of the printing pipe 30, as illustrated.

The discharge structure fiunther includes a pipe section 31, providing a hydrostatic column, opening downwardly in the pocket 12 at about the level of the opening of the siphon section '25 and extending upward for a considerable distance above the liquid level in the tank 10. This hydrostatic pipe 31 communicates through a section of flexible tubing 33 with a float valve chamber 34, shown as carried by a bracket which is mounted on the upper extension of the pipe 31 and is adjustable to vary the vertical position of the chamber 34 as desired. The latter chamber is positioned a predetermined distance above the tank [[0 and above the T-fitting chamber 28 of the siphon conduit system. At its top, this chamber 34 communicates with the atmosphere through a vent 37, and also with a flexible air vent tube 38 which opens into the siphon conduit system 25-29 at the T-fitting chamber 28. Within the chamber 34 is a needle valve float element which is adapted, on floating upward, to close the air vent tube 38.

As previously explained, the establishment of a condition of teeter in and above the pocket 12 increases the fluid pressure in the pocket to a value greater than normal liquid pressure at that region by an amount directly related to the density and size or settling rate of particles in teeter therein, with the result that water rises in the hydrostatic pipe '31 to a level of super-elevation, i.e. above the overflow level of the tank 10, representative of such increased pressure. The float valve chamber is positioned for closure of the air vent tube 38 by the element 40 when a predetermined increased pressure corresponding to a desired accumulation of solids in teeter is attained in the pocket 12, i.e. an increased pressure effective to raise water in the hydrostatic pipe to a predetermined level of super-elevation. The T-fitting chamber 28 of the siphon conduit system is located below the latter level.

With this arrangement of elements, product discharge through the siphon system can occur only if the pressure in the pocket is at or above the aforementioned predetermined value. When this pressure is less than such value, the float valve is open and hence the T fitting chamber 28 of the siphon system communicates with the atmosphere through the tube 38, preventing regular siphon action or withdrawal of product pulp from the pocket 12, although some water may pass through the siphon in spurts or surges. When the pressure in the pocket is at or above the selected minimum value, however, the element 40 of the float valve is buoyed up to close the tube 38, sealing the siphon system from the atmosphere and thereby enabling the development of a continuous, eflective siphon action in the system 254.9 to provide steady delivery of the classified product from the pocket. In other Words, the hydrostatic pipefloa't valve control regulates the functioning of the siphon system with respect to pressure in the pocket, permitting siphon action to occur only while a desired accumulation of solids in teeter (as represented by such pressure) is maintained in the pocket, to insure delivery of only a properly classified product pulp through the siphon.

According to prior practice, for such control the float valve chamber 34 would be disposed at the normal level of super-elevation to which water rises in the hydrostatic pipe when the desired pressure is attained in the pocket, so that such super-elevation of Water, communicated to the float valve chamber 34 by the tubing 33, will buoy up the element 40 to close the air vent tube 38. As further noted above, however, in the classification of mineral or other "solids (such as coal) having a specific gravity not more than about 2.0, the latter normal level even under optimum hindered-settling conditions is inconveniently colse to the overflow level of the tank 10. To obviate this difiiculty, and in particular to enable the positioning of the chamber 34 at an advantageously greater elevation relative to the tank overflow, the apparatus of the present invention in its illustrated form includes, in combination with the above-described elements of the siphon discharge and control system, structure for exaggerating or artificially raising this level of super-elevation to a substantially greater height above the tank.

This latter structure is specifically arranged to supply to the hydrostatic pipe 31 a continuous flow of water at a predetermined constant pressure, delivered through a horizontal conduit 42 (desirably of approximately the same diameter as the pipe 31) which communicates with the pipe 31 at a suitable locality below the level at which it is desired to position the float valve chamber 34, and conveniently slightly above the overflow level of the tank 10. As shown, the structure further includes a tank 43 disposed above the horizontal conduit 42 and surrounded at its upper extremity by an annular overflow-collecting launder 44 having a suitable drain outlet 45. This tank is maintained entirely filled with water supplied in continuous flow, eg through a conduit 47 opening downwardly above the tank 43 and controlled by a valve 49. At the lower end of the tank 43 a downwardly-tapering tank outlet funnel 50 communicates with a vertical pipe section 51 (also desirably of about the same diameter as the pipe 31) extending downward to and connecting with the horizontal conduit 42. A control valve 53 is connected in the pipe section 51. In addition, the conduit 42 may conveniently be connected to the conduit 47 at a point upstream of the valve 49 through a further pipe section 56 controlled by a normally closed valve 58, and the upper end of the funnel 50 may be covered with a screen 60 to prevent clogging of the narrow portion of the funnel or the pipe 51, e.g. by foreign matter.

In operation, with the valve 58 closed and the valve 49 open, the flow of water introduced by the conduit 47 flows through the tank 43 and pipe 51 to the horizontal conduit 42, and thence to the hydrostatic pipe 31. The tank 43 serves to provide a constant head of water at the valve 53, so that by appropriate setting of the latter valve to provide a given constant pressure drop across the valve, the water flowing to the hydrostatic pipe through the conduit 42 will be at a constant pressure, i.e. determined by the vertical distance between the overflow level of the tank 43 and the conduit 42, and the pressure drop across the valve 53.

Assuming that the tank 10 is filled with water only, so that there is no condition of hindered settling therein, this constant-pressure flow from the conduit 42 into the hydrostatic pipe 31 will continuously flow downward through and out of the latter pipe upon the development of a suificient head of water 'in the hydrostatic pipe. Accordingly, water rises in the hydrostatic pipe to a level, above the overflow level of the tank 10, representative of such head. The extent of elevation of this level (herein termed the control level) is dependent upon the pressure of the water introduced through the conduit 42, and the control level can therefore be readily positioned at a desired elevation by appropriate setting of the valve 53 which determines the pressure of the introduced water.

When a condition of teeter is established in and above the pocket 12, the resultant increase of pressure at the latter region requires development of a greater head in the hydrostatic pipe 31 to force the flow of introduced water from the conduit 42 down through and out of the pipe. Accordingly, water rises in the hydrostatic pipe, to provide such greater head, until it reaches a level which is higher than the aforementioned control level by an amount equal to the normal extent of super-elevation which the condition of teeter would otherwise produce in the hydrostatic pipe (i.e. in the absence of the supplemental flow from the conduit 42). In other words, with the constant-pressure flow from the conduit 42 supplied to the pipe 31, any given accumulation of solids in teeter in the tank 10 will raise the water in the pipe 31 to a level of super-elevation which is exaggerated, or raised above the normal level of super-elevation resulting from such accumulation, by the vertical distance of the control (or non-teeter) level above the overflow level of the tank 10. Thus, referring to the drawing, if the level 62 represents the normal extent of super-elevation for a given accumulation of solids at which it is desired to initiate siphon action by closure of the float valve, and the level 63 represents the exaggerated level of super-elevation produced by the supplemental flow from the conduit 42 (for the same accumulation of solids in the pocket 12), the distance between the levels 62, 63, i.e. the extent of exaggeration or raising of the level of super-elevation, is equal to the height of the control level (line 65) above the overflow level 64 of the tank 10.

As will therefore be appreciated, the continuous flow of water at constant pressure from the conduit 42 serves to raise the level of super-elevation by an amount which is dependent on the pressure of this flow and which can accordingly be fixed at a desired value by appropriate setting of the valve 53. With the degree of super-elevation in the hydrostatic pipe thus enhanced, the float valve chamber 34 is positioned above the normal level of superelevation at which it must otherwise be placed; specifically, and as illustrated in the drawing, its location is elevated above such normal level by a distance equal to the height of the control level above the tank overflow. As previously mentioned, this higher position of the float valve has particularly important advantages, from the standpoint of effective operation and convenience, in the classification of low-density solids or in other situations wherein the normal extent of super-elevation is of small magnitude.

In all other respects, the discharge of product pulp with the discharge system incorporating the foregoing structure for exaggerating the extent of super-elevation is essentially the same as that of the discharge system disclosed in the aforementioned US. Patent No. 2,714,958. Thus, the variations in the amount of super-elevation produced in the hydrostatic pipe 31 by variations in the accumulation of solids in the pocket 12 are of the same magnitude as if the supplemental flow to the pipe were not provided, but these variations occur at a higher level relative to the overflow level of the tank 10. The siphon action is entirely unaffected, the T-fitting chamber 28 being positioned (as before) below the normal level of super-elevation 62. Siphon action, and delivery of product from the pocket 12, can occur only when the exaggerated level of super-elevation in the pipe 31 is at or above :a predetermined level in the float valve chamber 34 (i.e. a level representative of a desired accumulation of solids in the pocket) so that the element 40 is buoyed up to seal the tube 38 from the atmosphere.

It will accordingly be understood that the product discharge method of the present invention, as performed with the described and illustrated apparatus, involves withdrawing product pulp from the pocket 12 by siphon action (viz. through the conduit system 25-29) under control of a hydrostatic column (i.e. in the pipe 31), and supplying to the latter column a continuous flow of water at constant pressure for raising the level of super-elevation therein by a constant amount; this column operates as through the float valve structure 34-40 to permit such siphon action to occur only when a predetermined accumulation of solids, as represented by a particular level of super-elevation, is maintained in the pocket.

For clarity of illustration the structure and operation of the apparatus are shown in the drawing in a schematic manner (rather than with precise dimensional accuracy) and indeed as functioning with a rather considerable addition to the head .in the hydrostatic pipe; the valve 53 may of course be adjusted to provide any desired (greater or less) exaggeration of the super-elevation, e.g. as by reducing the flow in the pipe 42 to bring the non-teeter head point (line 65) closer down toward the classifier overflow level 64 if less amplification in the hydrostatic pipe will suflice. For instance, in one system, where the opening of the funnel 50 was 10 /2 inches below the constant level of water in the tank 43 and inches above the horizontal pipe 42, the valve 53 was readily settable for a range of super-elevations (line 65) in the pipe 31, one instance of satisfactory operation providing a height of the level 65 of 12 inches above the classifier level 64,

to afford convenient further elevation of the hindered settling control level 63 as shown. In this example, the portion of the hydrostatic pipe 31 extending below the classifier level 64 had a diameter of 1 /2 inches, and the supplemental flow to this pipe from the horizontal pipe 42 was supplied at a flow rate of 5 gallons per minute. An equivalent extent of exaggeration of super-elevation can be attained with lower flow rates (i.e. a smaller supplemental flow) if the diameter of the hydrostatic pipe 31 is reduced.

Although in the drawing the extent of exaggeration of super-elevation shown is such that the horizontal pipe 42 enters the hydrostatic pipe 31 below the control level 65,

it will be appreciated that the pipe 42 can enter the pipe 31 at a higher point, i.e. above the latter control level.

It may further be noted that the structure illustrated may if desired be employed to effect the ordinary controlled discharge of product from the pocket 12 in the manner disclosed in the last-cited patent, i.e. without exaggerating the level of super-elevation, for the classification of higher-density solids as to which the normal level of super-elevation might approximate the level 63. This is accomplished simply by closing the valves 49, 53 in addition to the valve 58 so that there is no flow of water through the conduit 42 to the pipe 31 and hence no exaggeration of the level of super-elevation in the latter.

Again the supplemental fiow through the conduit 42 may be used to clear the hydrostatic pipe 31, e.g. when operation of the hydraulic classifier is resumed after an interruption which has left a settled deposit or bed of particles at the lower end of the hindered-settling colum. Sometimes, upon such resumption, the initial flow of hydraulic water from the pipe 14 may (due to back pressure created by the deposit of particles) temporarily have suflicient force to carry particles upward into the hydrostatic pipe, clogging it. By closing the valves 49 and 53, opening the valve 58, and directing through the then-connecting conduit 56, 42 to the pipe 31 a highpressure flow of Water from the source supplying the conduit 47, such particles can be elfectively dislodged. To prevent upward diversion of this high-pressure flow in the pipe 31, a valve 66 (normally open, but closed for such clearing operation) may be connected in the pipe 31 intermediate the level of the conduit 42 and the float valve chamber 34.

As will be appreciated, the method of the present invention may be practiced using other means for supply of a constant-pressure flow of water to the hydrostatic column, i.e. means alternative to the constant head tankcontrol valve arrangement illustrated. Moreover, while the procedures and apparatus of the present invention have been shown and described as used with a simplified form of hydraulic classifier, the same may be employed for provision of product discharge from other types of hindered-settling classifiers, and to deliver classified fractions of particulate material other tthan the fraction constituting the fastest-selling particles, to which reference has herein been made. In addition, the invention is of course adapted for use not only in connection with the classification of low-density solids, but also in other situations wherein hindered settling classification operation may produce an inconveniently slight pressure increase (represen-ted by a low level of super-elevation) at the locality from which discharge is to be effected.

It is to be understood that the present invention is not limited to the specific features and embodiments herein shown and set forth, but may be carried out in other ways without departure from its spirit.

I claim:

1. In the hydraulic classification of solid particles by hindered settling in a liquid filled classifier column wherein accumulating solids of desired character for separation create a liquid-solids mixture having an increased density relative to the liquid alone, in the classifier column at a predetermined region of such accumulation, the method of Withdrawing a pulp of said accumulating solids from said region which comprises establishing a hydrostatic column of liquid extending upwardly from said region, supplying additional liquid to an upper locality of said hydrostatic column under constant pressure for continuous flow of said liquid down the hydrostatic column into the liquid body in the classifier column, said increased density at said region being eflective to elevate liquid in the hydrostatic column to a corresponding distance above the upper level of liquid in the classifier column and said supply of water into the hydrostatic column being effective to provide additional elevation of said liquid in the hydrostatic column to a predetermined control region, and initiating and controlling discharge of pulp from said first-mentioned region of accumulation of solids in accordance with presence and absence, respectively, of liquid in the hydrostatic column at a predetermined level in said last-mentioned control region.

2. In the hydraulic classification of solid particles by hindered settling in a liquid filled classifier column where in accumulating solids of desired character for separation create a liquid-solids mixture having an increased density relative to the liquid alone, in the classifier column at a predetermined region of such accumulation, the method of withdrawing a pulp of said accumulating solids from said region by flow through a siphon extending from the region to and down from a locality above the upper level of liquid in said classifier column, which comprises establishing a hydrostatic column of liquid extending upwardly from said region, supplying additional liquid to said hydrostatic column under constant pressure for continuous flow of said liquid down the hydrostatic column into the liquid body in the classifier column, said increased density at said region being effective to elevate liquid in the hydrostatic column to a level of normal super-elevation spaced a corresponding distance above the aforesaid level of liquid in the classifier column and said supply of water into the hydrostatic column being effective to provide additional elevation of said liquid in the hydrostatic column to a predetermined control region, and initiating and controlling discharge of pulp through the siphon in accordance with presence and absence, respectively, of liquid in the hydrostatic column at a predetermined level in said last-mentioned control region, said locality to which said siphon extends being lower than a pre-selected level of normal superelevation in said hydrostatic column corresponding to a predetermined accumlation of solids in said first mentioned region in said classifier column.

3. A method according to claim 2, wherein said additional liquid is supplied to said hydrostatic column at a locality of said hydrostatic column above said upper level of liquid in said classifier column and below said control region.

4. A method according to claim 3, wherein said step of supplying additional liquid to said hydrostatic column comprises establishing above the level of said last-mentioned locality of said hydrostatic column a liquid-filled constant head region providing a predetermined constant head of liquid above said locality, and continuously conducting liquid from said constant head region to said hydrostatic column at said locality While decreasing the pressure of said liquid by a predetermined constant amount and while continuously supplying liquid to said constant head region to maintain said region filled with liquid as aforesaid.

5. In a hydraulic classifier, in combination, means providing a hindered settling column, including means supplying solid particles thereto for classification ac- .cording to settling rate and means supplying hydraulic liquid for efi ectuation of hindered settling, to produce a predetermined accumulation of solid particles having desired characteristics of settling rate, in teeter at a predetermined region of said column, said classifier including structure providing an upper level of liquid in the classifier, means for withdrawing pulp of accumulating solids from said region for discharge of said particles as product, a hydrostatic pipe opening into the column at said region and extending above the aforesaid liquid level of the classifier, whereby liquid from the column is caused to rise in said hydrostatic pipe above said level by reason of increased pressure occasioned by the aforesaid accumulating particles in teeter, means for supplying a supplemental flow of liquid into said hydrostatic pipe at a substantially constant pressure, said means being connected to said pipe to direct said flow therein at an intermediate locality thereof and being effective to create additional liquid-elevating pressure in the hydrostatic pipe, said hydrostatic pipe including a portion extending above the locality of said connection of the liquid supplying means, and means associated with said last-mentioned portion of the hydrostatic pipe at a locality space above the aforesaid liquid level of the classifier by a distance corresponding to the elevation of liquid due both to the pressure of solids in teeter and the aforesaid additional pressure, for controlling flow of pulp through the aforesaid discharge means to maintain said flow of pulp when the accumulating solids in teeter produce pressure corresponding to the predetermined accumulation of solids having desired characteristics of settling rate.

6. In a hydraulic classifier, in combination, means providing a hindered settling column, including means supplying solid particles thereto for classification according to settling rate and means supplying hydraulic liquid for etfectuation of hindered settling, to produce a predetermined accumulation of solid particles havling desired characteristics of settling rate, in teeter at a predetermined region of said column, said classifier including structure providing an upper level of liquid in the classifier, siphon means for conducting pulp of accumulating solids from said region up to and down from a locality above said las-t mentioned liquid level, for discharge of said particles as product; a hydrostatic pipe opening into the column at said region and extending above the aforesaid liquid level of the classifier, whereby liquid from the column is caused to rise in said hydrostatic pipe above said level by reason of increased pressure occasioned by the aforesaid accumulating particles in teeter, to a level of normal super-elevation spaced above said upper level of liquid by a distance corresponding to said increased pressure means for supplying a supplemental flow of liquid into said hydrostatic pipe at a substantially constant pressure, said means being connected to said pipe to direct said flow therein at an intermediate locality thereof and being effective to create additional liquid-elevating pressure in the hydrostatic pipe, said hydrostatic pipe including a portion extending above the locality of said connection of the liquid supplying means, and means associated with said last-mentioned portion of the hydrostatic pipe at a control locality spaced above the aforesaid liquid level of the classifier by a distance corresponding to the elevation of liquid due both to the pressure of solids in teeter and the through said siphon means to maintain said flow when the accumulating solids in teeter produce pressure corresponding to the predetermined accumulation of solids having desired characteristics of settling rate said locality up to and down from which said siphon means conducts said pulp being lower than a preselected level of normal super-elevation in said hydrostatic pipe corresponding to said predetermined accumulation of solids.

7. Apparatus as defined in claim 6, wherein said siphon means includes a vent at a locality above the said level of liquid in the classifier and wherein the control means in the hydrostatic pipe comprises a control chamber and liquid level responsive means therein for closing and opening said vent in accordance respectively with presence or absence "of liquid at said control locality in the hydrostatic pipe.

8. Apparatus as defined in claim 6, which includes constant-pressure liquid supply means connected to said means for supplying liquid into the hydrostatic pipe, and valve means intermediate said constant-pressure means and said means for supplying liquid into the pipe, for adjusting the rate of flow of said liquid and for thereby adjusting the extent to which liquid is elevated in the aforesaid portion of the hydrostatic pipe by reason of said supplemental liquid supply, the aforesaid connection of the liquid supplying means with the hydrostatic pipe being disposed at a locality of said pipe above the level of liquid in the classifier.

9. Apparatus as defined in claim 8, wherein said con-,

References Cited by the Examiner UNITED STATES PATENTS 8/1955 Evans 209-158 8/1955 Fit-ch 209-496 X FRANK W; LUTTER, Primary Examiner.

Claims (1)

1. IN THE HYDRAULIC CLASSIFICATION OF SOLID PARTICLES BY HINDERED SETTLING IN A LIQUID FILLED CLASSIFIER COLUMN WHEREIN ACCUMULATING SOLIDS OF DESIRED CHARACTER FOR SEPARATION CREATE A LIQUID-SOLIDS MIXTURE HAVING AN INCREASED DENSITY RELATIVE TO THE LIQUID ALONE, IN THE CLASSIFIER COLUMN AT A PREDETERMINED REGION OF SUCH ACCUMULATION, THE METHOD OF WITHDRAWING A PULP OF SAID ACCUMULATING SOLIDS FROM SAID REGION WHICH COMPRISES ESTABLISHING A HYDROSTATIC COLUMN OF LIQUID EXTENDIG UPWARDLY FROM SAID REGION, SUPPLYING ADDITIONAL LIQUID TO AN UPPER LOCALITY OF SAID HYDROSTATIC COLUMN UNDER CONSTANT PRESSURE FOR CONTINUOUS FLOW OF SAID LIQUID DOWN THE HYDROSTATIC COLUMN INTO THE LIQUID BODY IN THE CLASSIFIER COLUMN, SAID INCREASED DENSITY AT SAID REGION BEING EFFECTIVE TO ELEVATE LIQUID IN THE HYDROSTATIC COLUMN TO A CORRESPONDING DISTANCE ABOVE THE UPPER LEVEL OF LIQUID IN THE CLASSIFIER COLUMN AND SAID SUPPLY OF WATER INTO THE HYDROSTATIC COLUMN BEING EFFECTIVE TO PROVIDE ADDITIONAL ELEVATION OF SAID LIQUID IN THE HYDROSTATIC COLUMN TO A PREDETERMINED CONTROL REGION, AND INITIATING AND CONTROLLING DISCHARGE OF PULP FROM SAID FIRST-MENTIONED REGION OF ACCUMULATION OF SOLIDS IN ACCORDANCE WITH PRESENCE AND ABSENCE, RESPECTIVELY, OF LIQUID IN THE HYDROSTATIC COLUMN AT A PREDETERMINED LEVEL IN SAID LAST-MENTIONED CONTROL REGION.

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