US2426804A - Liquid treatment tank with concentric compartments and with distributors below the bottom surface - Google Patents

Description

Sept. 2, 1947. R. WELTER 2,426,304

LIQUID TRBATIENT TANK .h'lli CONCEN'X'RIC COIPARTIBHTS AID IITB DISTRIBUTORS BE THE BOTTOI SURFACE F11 Jun: 1944 4 ShOOtE-Shflii 1 mmvmn. 1523 TVhlter,

'r, 3% may Sept. 2, 1947. R. WELTER 2,426,304

LIQUID TREAT-BN1 TANK 1TH CQNCBNTRIC COUPLRTIBNTS AND II'X'H DISTRIBUTORS BELOW THE BOT'IOI SURFACE Filed June 14, 1944 4 Shuts-Shut 2 mmvmn. E03 Welter,

Sept. 2, 1947. R. WELTER 2,426,804

LIQUID TREA'I'IBNT TANK WITH CONCENTRIC COIPAR'I'IBHTS AND II'I'H DISTRIBUTORS BE THE BOTTOI SURFACE Filed June 1944 4 Shun-Shout 3 LOW 14,

INVENTOR. flay Wclier',

SGPL 2, 1947. WELTER 2,426,804

LIQUID 'I'REATIENT TANK WITH coNcBm'RIc COIPARTIENTS AND WITH DISTRIBUTORS BELOW THE ao'r'roll SUHIAOI Filud June 14, 1944 4 Shanta-Shut 4 INVENTOR Roy Wan-n ATTORNEY Patented Sept. 2, 1947 LIQUID TREATMENT TANK WITH CONCEN- TRIC COMPARTMENTS AND WITH DIS- TRIBUTORS BELOW THE BOTTOM SUR- FACE Roy Welter, East hicago, Ind., assignor to Graver Tank & Mfg. 00., Inc., a corporation of Delaware Application June 14, 1944, Serial No. 540,256

11 Claims.

This invention relates to liquid treatment and particularly to sludge blanket clariflers and flow distributing means for the same.

It is an important object of this invention to provide improved flow distributing means, particularly for tanks of large area and capacity.

Another important object is to improve such tanks with respect to the power required for flow distribution.

Still other objects and advantages will appear from the detailed description which follows.

In the drawing:

Fig. 1 is a plan view of one embodiment hereof Fig. 2 is a partial section through the embodiment of Fig. 1, the section being taken along line 2-2 in Fig. 1 and showing outer parts of the apparatus, at a larger scale than Fig. 1;

Fig. 3 is a view generally similar to Fig. 2 but showing a modified embodiment;

Fig. 4 shows a detail in section along lines 4-! in Fig. 3;

Fig. 5 shows a similar detail in section along lines 5-5 in Fig. 3, and with a further-modification applied; and

Fig. 6 is a further, partial section through the embodiment of Fig. 1, the section being taken along line 8-6 in Fig. 1, and showing inner parts of the apparatus, at a larger scale than Fig. 1.

The treatment tank II is defined by a cylindrical concrete wall II and a substantially circular, flat concrete bottom i2, and is open at the top. Such tanks as considered herein are generally about 9 to feet deep, and may have a diameter of about 40 to 120 feet.

The raw liquid to be treated enters this tank,

through a pipe 13, adjacent the center of the bottom l2. Treated liquid is withdrawn through a launder ll, installed adjacent the top of the tank and drained by an outlet pipe IS. The sludge separated from the liquid settles on the bottom i2 and is scraped into a substantially central sump It by a slowly rotating scraper assembly ii; the sump being drained by pipe II. The scraper assembly ll may be rotated by conventional means, such as a traction device generally shown at Hill, in Fig. 1. Such a device may comprise a carriage Ilil having wheels I02 and running on top of the cylindrical concrete wall i2; one of the wheels being suitably actuated by a motor or engine ill and the carriage being connected with the scraper assembly IT by structural members I".

A substantially cylindrical partition I! is installed concentrically with the tank and extending from adjacent the bottom l2 upwards to a 2 point below the liquid level 20 determined by the overflow launder II. A narrow, annular, peripheral mixing channel 2i is formed by and between the wall it and partition iii. In many instances this channel will be about 12 to 18 inches wide.

A second annular and substantially cylindrical partition 22 is concentrically installed in the tank and extends from above the liquid level 20 downwards to a level below the top of the first partition I! and above the bottom I2. An inner, annular flocculation channel 23 is defined by and between the two annular partitions i8 and 22. This channel, generally, is at least a few feet wide, in tanks as contemplated herein. An annular, substantially unrestricted slot 23-A is l ft between the bottom i 2 and the lower edge 23-3 of the partition 22.

A clarification and sludge filtration zone 24 is defined by and within the inner annular partition 22. Generally, this zone occupies the whole balance of the tank area, and such balance, after deduction of the channels 2i and 23, amounts to the greater part, about to percent, of the total tank area.

In the center of the bottom I! there is a flow collector or pumping and distributing sump or pit 28, wherein a pumping impeller 26 is rotatably disposed, on a vertical shaft 26-A. This vertical shaft is driven by a motor 21, installed on a platform 28 on top of the tank, above the path of the traction device Hill for the sludge scrapers ll,

The side wall 25-A of the pit 25 is cylindrical, and a number of substantially horizontal pipes are secured thereto, communicating with said pit. These pipes radiate from this side wall towards the tank wall i I, below the top surface of the bottom i2. They include the raw water inlet pipe Ill, and a plurality of radial distributing pipes 29. These are preferably formed from vitrified pipe sections, and imbedded in concrete ribs an which are Integralwith the underside of the tank bottom i 2 andlying in trenches below this bottom. Vitrified pipe is not very expensive and has a smooth surface, conducive to a. low loss of head. Sometimes, however, preformed concrete pipe will be more economical, especially in very large tanks. Three distributing pipes 29 are shown, but in some instances there may be only one or two, or on the other hand there may be many more, as will be explained herein. With only three distributing pipes uniformly spaced from one another at degrees angular distance, a, large sludge sump I8 is conveniently placed in one of the 120 degree corners between two such distributing pipes, adi jacent the distributing sump 25, and the inlet pipe II can join the distributing sump between another pair of distributing pipes as shown.

The distributing pipes terminate in an annular duct 3| which is concentric with the tank, and disposed below the annular channel 2| adjacent the tank wall I l in an annular concrete foundation ring 32. This duct can be formed from similar materials as are used in the pipes 23, and vice versa. Preferably, however, this duct is formed with rectangular cross-section, andin-tegral with the concrete ring 32. The ipes can be formed in similar manner, for uniformity of construction, although preformed pipe sections are generally preferable for these pipes. The ring 32 is integral with the bottom i2, and supports the side wall ii on the outside of this annular duct 3|; a narrow ledge 33 being formed to provide an annular, horizontal ste between the inner surface 34 of the duct 3| in the foundation ring, and the inner surface 35 of the tank wall The opposite surface 36 of the inner wall of the annular duct 3| in the foundation ring extends to an upper surface 31 of said ring, on the same level with the ledge 33, which surface 31 may be identical with the top surface of the concrete bottom i2, and the bottom surface of a layer of cement grout 33. This grout forms part of the bottom l2. The outer end of each distributing pipe 23 is located below the surface 31 and above the bottom 39 of the duct 3|. This bottom 33 slopes upwardly from the point where a distributing pipe 25 enters the duct towards the next following distributing pipe, so as to make sure that the cross-sectional area of the duct adjacent the distributing pipe is substantially equal with that of the pipe, and the flow velocities in the pipes and duct are substantially equal and uniform. Ahead of the next following distributing pipe, adjacent the juncture between the low and high points of the bottom 39, a transverse concrete wall 40 extends across the duct 3|.

On top of the concrete duct 3|, a ring of concrete slabs 4| is installed, covering the top of this duct except for numerous, restricted distributing openings 42 in this ring of slabs. These distributing openings are uniformly inclined, preferably about 30-to 45 degrees from the horizontal, the slabs 4| being substantially parallelograms in longitudinal section. The several slots 42 are formed between the slabs, and have uniform area; the several slabs being spaced from one another by integral lugs 43 adjacent the edges on their lower sides, so that the distributing slots 42 in effect are nozzles expanding slightly in the direction of the flow. The total area of the nonzles 42 in a tank is slightly below, to approximately equal with, the total of the cross-sectional areas of the distributing pipes 23, to insure proper distribution.

The slabs 4| may be reinforced by steel wires 44, which may form loops 45 extending above the upper surfaces 45-A of the slabs, in order to facilitate installation of the slabs. The slabs can be loosely and removably placed .upon the ledge 33 and surface 31. to facilitate inspection and the cleaning out of the distributing system.

These slabs are preferably quite short so that a great many distributing openings 42 find place along the periphery of the tank. The slabs can be rectangular in plan view, in which eventlthe distributing slots 42 are slightly sector shaped. For all practical purposes, these slots are rectangular, if a sumcient number of slabs are used. Slabs of identical design and size can be used in tanks of very difl'erent sizes; in addition to the lugs 43, loose spacers (not shown) may be used in obvious manner, to insure slots 42 of proper width.

In the embodiment of Fig. 2, the outer annular partition |9 is made of redwood, which tends to float in the water, and is held against its buoyancy by chains 45 secured to the inside surface 35 of the tank wall ii by chain holding members 41; the chains being held to the outside of the partition i9 by generally similar holding membars 43. Additional chains 43 are installed between the latter holders 43 and additional holders 53 on the inner surface 35 of the tank wall H, to hold the partition i9 against gravity when the tank is drained. These latter chains are so adiusted as to prevent the partition I! from contacting the scraper assembly i'l at any time.

Similarly the inner partition 22, as shown, is constructed of redwood and held against buoyancy by chains 5| extending from holders 52 on the inside of the outer partition to holders 53 on the outside of the inner partition; and also held against gravity. to prevent injury to the scraper assembly, by chains 54 extending from the holders 52 to holders 55 on the inner partition Th buoyancy absorbing chains 45 and 5| can be lighter than the weight absorbing chains 45 and54, since the buoyancy of redwood amounts to less than the weight thereof in air, and this buoyancy is furthermore reduced by the chains and other parts mounted on the partitions. Even the heavier chains 43 and 54 will generally be very thin, all chains being entirely in the nature of tension members, so that these chains offer a minimum of obstruction to the flow passing through the channels 2| and 23. This is important, as will appear from the functional description hereina ter.

The aforementioned overflow launder I4 is preferably made from flat steel plates welded together to form troughs of rectangular cross section comprising horizontal bottom plates 53 and vertical side plates 51; the top edges of the side plates acting as overflow weirs 53. A series of rectangular troughs formed in this manner are readily assembled into an annular launder i4 forming a hexagon or other polygon concentric with the tank. This launder is preferably dimensionedso that the area of the clarification zone 24 is separated into two substantially equal parts by the same. This is quite important in large tanks for upward sludge filtration, as will appear from the following.

The launder i4 is secured to the inside of the inner partition 22 by a series of structural brackets 53. Such a structural bracket, particularly the compression part thereof, occupies considerably more area than do the chains 45, 43, 5| and 54. While such area might unduly obstruct the relatively rapid, spiral flows in the relatively small channels 2| and 23, it is quite unobjectionable, adjacent the launder l4, to use such area as the structural brackets inherently occupy. the clarification area being very large and the flow very slow.

Additional buoyancy of the assembly of the inner partition 22 and launder H can be provided by attaching a float 50 to the underside of the launder, this float being formed by straight plates 5| welded to the underside of the bottom plate 56 and inclined to form somewhat acuteangled isosceles triangles depending from this bottom, which at the same time is conducive to amasos a desirable type of upward flow in the clarification zone 2|.

In the modified embodiment of Fig. 3 the outer partition is formed by a cylindrical concrete wall 82 resting on the top surface 31 of the annular foundation ring 22, the outer channel 2| being separated from the inner channel 23 by a water stop 83 at the foot of this wall 02.

This construction has the advantage that a more positive flow through the channels is enforced, while in the embodiment of Fig. 2 some liquid may short-circuit from the duct Ii through the gap 64 adJacent the bottom edge of the outer partition l9. On the other hand, the construction of Fig. 2 has the advantage that the scraper assembly ll may carry a small scraper blade 85 projecting into the outermost channel 2| and removing sludge from the top surface 4 of the slabs ll, where it may have settled particularly after a shut-down of the tank. The amounts of liquid by-passing the channels through the gap 84 can be kept very small and unobjectionable, since the width of this gap, and the configuration thereof, can be restricted as compared with the slot 2IA; that is, it can be such as to force the vastly major portion of the liquid to pass upward through the outer channel 2i and then down through the inner channel 23. The outer channel It may have to be somewhat wider in the case of Fig. 2, in order to insure that most of the flow passes through this channel, and somewhat narrower in the case of Fig. 3, in order to counteract sedimentation. A wider channel has the final advantage that the slabs H are more easily installed.

Fig. 3 differs also in that structural concrete beams 66 are used, instead of the chains It and ii, to hold the inner partition ll. Accordingly, this inner partition can be formed of concrete rather than a floating material like redwood. The concrete beams 86 are preferably installed so as to leave the functional flocculation area ofthe channels 2i and 23 unobstructed; or in other words, so much of these channels as is required for proper flocculation, in the operation of the tank. is provided below these beams. In some instances, it is desirable that these beams should be installed entirely below the liquid level 20, as shown. whereby the beams act as baflles and a scum release zone 68 is formed between these beams. with a scum removal zone 88 above the same. The scum can be removed from the latter zone by hand or by automatic means (not shown) Of course, the inner partition 61, which hangs on the concrete beams 68, should be made as light as possible. Generally speaking, the thickness of this partition can be very slight. since it is not necessary that any appreciable liquid head be retained by this partition, and it is not even essential that the partition be absolutely liquid tight. If a scum release and removal zone is required, then ordinarily the baflies Bl required for the same are more than sufllcient to support the weight of this thin concrete partition 51.

The launder ll shouldalso be as light aspossible. The steel launder of Fig. 2 tends to be particularly light. However, in some instances. a somewhat heavier concrete construction is preferred, because it is more durable. Accordingly, Fig. 3 shows a launder it formed by concrete troughs Iii, which have the same approximate outer configuration as the launder and triangular float previously described. At the top of the concrete sidewalls of this trough Hi, weir supports may be provided by structural angles H, having weir plates 12 adustably secured thereto. The launders Il may be supported by concrete brackets 18 held by the inner partition II.

The basic elements of the apparatus are completed by a source of chemical reagents II, connected to the central distributing pit 25.

In operation, a variable flow of raw liquids enters the central sump 26 through the pipe II, while a proportional amount of chemicals is added from the source II. and continuous agitation and circulation is applied by the pumping impeller 28. This impeller is generally driven by the motor 21 at such a speed that liquid circulates at a considerable velocity through various parts of the tank, regardless whether the incoming flow from the pipe I3 is at a maximum or capacity rate, at an average rate, at a minimum or at zero. Continuous flows as obtained by such circulation are necessary to distribute the liquid under the sludge filter. bed or blanket I4 and to maintain the sludge bed in suspension above the bottom l2; but of course the circulation must not be so rapid, with or without a capacity throughput flow from the source II, as to raise this sludge bed, or part thereof, sufficiently to cause boil-ups of sludge and entrainment of liquid polluted thereby into the launder II, or to cause other damage. Thus the rate of rotation of the impeller 28 is quite critical and the motor 21 is preferably equipped with an adjustable speed reducer. Similarly it is most essential that the various parts of the tank should be dimensioned and proportioned so as to provide proper flow and circulation velocities in each of the several parts thereof. Finally, the direction as well as other characteristics of the various flows are important. The following data have been found important in this connection, aside from the major dimensions specified above.

The circulation induced and maintained by the pump 28 passes from the periphery of the pit 25 through the vitreous distributing pipes 29 and annular concrete duct 3|, then through the slots 42 at an angle of 30 to 45 degrees from the horizontal, in uniform directions, then spirally and upwardly through the outer channel 2| as a result of this method of injection, then continuing spirally and downwardly through the inner channel 23, then .continuing spirally and inwardly over the bottom l2, and finally back into the pit 25. It will be noted that this circulation is a closed one.

In the embodiment of Fig. 3, the flow in the pit 25, distributing pipes 29, annular duct 3!, slots 42 and outer channel 2| is properly designated as a mixing flow, and conducted at such mixing velocities as to produce considerable turbulence. for the purpose of initially mixing the circulating liquid with the raw liquid and chemicals added thereto, and subsequently causing collisions between solid particles. to promote their growth into large and heavy flocs. Of course, these constituents are roughly premixed in the pit 25 where desirably, the most rapid mixing velocities prevail, but in order to safely contact every molecule of impurities contained in the water with chemical and physical reagents, reliance is had on continued turbulence in the pipes 28, duct 3|, slots 42 and channel 2i. Accordingly, the sum total of these elements 25, 2!, ll, 42 and 2| is designated as a mixing zone and considerable, but decreasing mixing velocities are maintained therein. In the embodiment of Fig. 2, the mixing zone comprises only the elements 25, 29, 3i and 12.

asaasoc Referring further to the channel 23 in Fig, 3, this is identified as part of a fiocculating zone, and similarly the bottom part 24A of the sludge filtration and clarification zone 24 is properly called a part of the flocculation zone. The velocities maintained in this zone 23 and A are slower than the mixing fiows, and are called flocculating velocities. In the embodiment of Fig. 2, similar velocities may be maintained also in the outer channel 2|, or at least the velocities maintained in that channel may be intermediate between the mixing and fiocculating velocities, as a result of which some sludge may settle in this channel, which is removed by the scraper G5.

The spiral fiow over the bottom 12 serves the dual purpose of continuing flocculation, and substantially uniformly distributing the liquid below the whole of the large area of the sludge filter 14; it may be called a distributing flow. The effective depth of the zone A can be increased by well-known bafiles (not shown), if necessary.

In the bulk of the clarification and sludge filtration zone 2i, above the lower part 24A traversed by the circulation. a relatively quiescent clarification and sludge filtration is desired, and liquid passes through this zone at what is called a clarifying velocity, and in directions which at least comprise major vertical components by virtue of the aforementioned installation of the overflow weirs, in conjunction with the spiral distributing fiow. Of course, this upward flow, in the upper part of the clarification zone, comprises only the equivalent of so much liquid as is introduced through the pipe l3, at any time, and is not augmented by any appreciable circulation; moreover the area of the zone 24 is made very considerable, in order to insure a suitable low velocity.

Typical fiow rates in the various zones are as follows.

In order to produce such mixing velocities in the aforesaid mixing zone of a tank of large size and capacity, considerable power is required for the motor 21. It is important, for this reason, that no power should be wasted or mis-applied by functionally useless or objectionable hydraulic loads interposed on the mixing zone. Furthermore, it must be considered that all appreciable hydraulic loads, whether in the nature of restricted passages, sudden enlargements, contractions, or otherwise, have a tendency to create small but extremely rapid eddies, which not only consume hydraulic power for desirable mixing functions but also may, in some instances, reach linear velocities at which fiocculent particles in the liquid are broken up rather than built up.

In this connection, it is of course distinctly desirable to break up the raw liquid and chemicals into the finest possible particles; but there are limits to the permissible break-up of recirculated fiocs. In a tank of the present type. it

has also been found desirable to subject the fiocculent particles in the recirculated liquid to a succession of breaking up and building up influences, as a result of which, ultimately, more settleable fiocs are formed than otherwise. However, the breaking up of recirculated flocculent particles must not be excessive, because otherwise excessive time is required to rebuild fiocs of desired settleability.

Generally speaking, somewhat higher velocities are desirable and economical for the most rapid dispersion of raw chemicals, than are tolerable in view of the fact that this dispersion desirably takes place in the presence of recirculated liquid with flocculent particles therein. For the dispersion of raw chemicals, liquid velocities of about 6000 in./min. are quite economical, and even higher velocities would be desirable if it were not too expensive to provide them. Practically, the maximum mixing velocity must be limited to the amounts shown in the tabulation, in view of the fact that recirculated fiocs have to be present, and that newly formed flocs must largely agglomerate therewith.

For ordinary flocculation, liquid velocities about 1.5 ft./sec. or 1080 in./min. are generally considered most desirable, with considerable tolerances both above and below said velocity. Somewhat slower velocities were found to be desirable for flocculation in the presence of large amounts of recirculated sludge, as herein applied. This is particularly true where it is possible to remove sludge settling in the flocculating zone, and this, too, is possible herein.

'I'hus, both the mixing and the fiocculating velocities are preferably lower, herein, than in plants without sludge bed treatment. As a result, the clarifying velocities can be much higher. and the tanks smaller, with equal results.

The power required to obtain suitable flocculating and clarifying flows is practically the same herein as in other, comparable devices. However, in order to generate suitable mixing and spiral distributing fiows, less power is required in accordance herewith than otherwise, due to said relatively slow mixing velocities. Furthermore, power is saved and the results are improved by close attention to the following facts and figures.

Assuming a clarifier having a clarifying zone of 80 ft. diameter or about 5000 sq. ft. area. using filtration through a heavy lime sludge, the clarifying throughput flow, at a rising rate of zero to 5 in./m. or zero to 3.1 gal./sq. ft./min. is zero to 15,600 gal/min. or zero to 22 million gallons per day. In some instances, it may be possible to obtain fair clarification with such a flow, combined with a circulation which by itself varies between zero and 22 million gallons per day. Such a variable circulation would be used in order to compensate the throughput fiow; and the total mixing flow at all times would comprise about l5,600 gal./min., flowing at a velocity within the range of 500 to 3000 in./min., or about 1 to 4 ft./sec. In the preferred practice, even greater amounts of liquid are uniformly circulated, at such velocities, in order to insure better sludge suspension, to obtain better distribution in the spiral flow over the bottom i2, and to eliminate the necessity for adjustments of the circulating velocity, in normal operation, regardless of variable throughput fiows. In such practice, a continuous and uniform circulation of as much as 220 or at least million gallons per day may have to be maintained for best results, although, in some instances, a continuous and uniform circulation of about 66 million gallons per day is sufllcient. The total, maximum mixing flows, then, will amount to 242, 132 or 88 million gallons per day, respectively. A total mixing flow of about 144 million gallons per day,

or 100,000 gal/min, may be considered as an V average, for such practice.

This tremendous amount of liquid must be pumped through the mixing zone.

The total effective length of the distributing pipes and annular duct, with a clarifying zone of 80 ft. diameter, and a tank of about 92 ft. total diameter is about 330 feet, on the basis of a single 45 ft. distributing pipe for the complete circulation, lus annular duct of 285 it. length. Some loss of head is caused by this length of piping.

To this must be added, among other things, the entrance loss in the distributing pit, the interior loss oi the pumping device, and the losses due to all sudden contractions and sudden enlargements. In piping of the size as generally contemplated herein, each sudden contraction, entrance, and sudden enlargement causes a head loss equivalent to that of about, 45, 55 and 100 feet of pipe, respectively, at the flow rates generally considered for this piping. All this raises the loss of head in the tank to that which would be caused by 500 to 600 feet of pipe, at least.

Another most important, potential source of head losses consists in pipe turns, particularly close ones. The closed circulation, inherently, makes a succession of turns totalling at least 360 degrees. Every 90 degree turn, in such piping, is an equivalent of 200 feet of pipe when being close and sharp, and 60 feet of pipe when having a long sweep radius. It must be noted that potentially, this could more than double the inherent loss of head, equivalent to that of 500 feet of pipe. Thus it is a most important object hereof that only a minimum of turns should occur at mixing velocity, and such turns as unavoidably occur at mixing velocity should be smooth and have a long swee radius.

This is actually achieved. The mixing flow through and, from the radial distributing pipes, being one of the particular subjects hereof, is not only short but also devoid of all sharp turns. It makes only one turn, of about, 90 degrees, where the distributing pipe joins the peripheral duct.

The additional turns of the liquid, in approaching the small distributing slots 42, branching off from the peripheral duct at 30 to 45 degrees, are so gentle and gradual as to cause onl an almost negligible loss of head. This is the case by virtue of the arrangement involving the partitions 40 in the duct 3i, adjacent the pipes 29, as a result of which all of these numerous additional turns are made in uniform directions, and no liquid is forced to flow through a sharp return bend. Some appreciable head of course is lost in obtaining proper distribution of the flow, through the slots l2. Since distribution as mentioned is vital, some such loss is unavoidable,

The flow in, through and from the outer channel 2| takes place at a slower rate than that in the distributing pipes and peripheral duct, and is conducive to a much lower head loss. A still further, gradual dro of flow velocity, with resulting conservation of head, takes place at the top of this channel. By virtue of the slow flow rate at this point, where a 180 degree turn or return bend must be made, the additional loss of head is entirely negligible. The same thing is true of the further 90 degree turn at the bot- 10 tom of the inner channel 23, and the final degree turn adjacent the distributing pit 25.

It will be noted that due to the up-and-down flows in the two channels 2| and 23, the sum total of the successive turns in the circulation is greater than 360 degrees, actually being about 540 degrees. In some ,constructicns, known to the art, still further turns are used adjacent to the 'central distributing pit, raising this sum total to about 720 degrees. In some instances, the liquid flowing through such further turns adjacent this pit passes at considerable velocities, and considerable, additional head is lost as a result. The present arrangement eliminates such additional loss of head, by passing the liquid from the spiral distributing flow directly, downwardly, into the distributing pit.

In the modification shown by Fig. 5, the head conditions are additionally improved by providing a smooth and long-sweep turn from each distributing pipe 29 into the peripheral duct 3|. For this purpose there is provided, at the outer end of the distributing pipe and inlet of the duct, a transition duct or nozzle 15, having an inner wall 16 which gradually and smoothly merges into the cylindrical wall of the pipe, as well as into the rectangular wall of the duct, without a sudden contraction and expansion, according to wellknown principles of nozzle design. This inner wall 16 is conveniently formed by depositing an annular layer of grout H in a suitable recess 78 formed in the concrete oi the rib 30 and peripheral foundation 3!, and smoothly shaping said grout so as to form said inner wall.

The exact arrangement and dimensions of the distributing pipes 29 and duct 3| must be calculated from the amounts and velocities as specified above, and in doing so, turther consideration must 'be given to structural and functional problems. Particularly, the peripheral duct 3| must not be made too deep, in relation to the width thereof, in order to avoid an unfavorable cross-section which causes excessive liquid friction and requires costly excavations and foundations. The width of this duct, generally, can not be greater than that of the superimposed, peripheral channel 2|,

which as mentioned, may be about 12 to 18 inches wide, or possibly somewhat wider in case of Figure 2.

In order to pass said 144 million gallons per day at a mixin velocity of 3 ft./sec., through 10 distributing pipes 29, and continuing arcuate parts oi the duct 3|, each distributing pipe must have about 3 ft. inside diameter; and the rectangular duct 3|, when being 18 in. wide, must be about 5 ft. deep, adjacent the points where the pipes join this duct. Where lower mixing velocities are required, the duct would have to be deeper yet, which is undesirable; in order to compensate, there is required a greater number of pipes, and shorter arcuate duct continuing each pipe, which carries less water, and requires less depth.

The material as well as the labor required for the construction of a tank and equipment as described herein is relatively inexpensive, considering the efllciency, results, and relatively small overall size of the apparatus. It is true, of course, that some extra concrete form work is required for the concrete ribs 30 and duct 3|, but the forms required are simple, and of course the concrete or vitrified pipes 29 are most economical, as well as efficient, as compared with any other pipe materials that could be considered.

Reference was had, in the discussion of functional features, above, to "good clarification." It

has become usual, in sludge bed clariflers, to apply this term if the turbidity oi the eiiluent is safely kept below a certain limit, which generally is specified somewhere within the range of to 25 parts per million. Such an eflluent can be produced with the present device, within about 50 to 150 minutes overall detention time for a typical turbid or hard water, with minimum dosage of chemicals, and with shallow excavations for the tank, regardless of the size and capacity thereof. Earlier devices either were limited to greater depth or smaller diameter, or required longer detention or heavier chemical dosage or more power for mixing, or furnished eilluents of less than equal quality. All these factors are intimately inter-connected, and improvement as to one can affect all others.

I claim:

1. A liquid treatment tank comprising a substantially circular bottom; a substantially cylindrical wall surrounding said bottom; centrally located, annular wall means extending away from said bottom to form a flow collector, having location in and communication with a lower, central portion of the tank, at least a portion of said collector being located below the surface of said bottom; an outer, substantially cylindrical partition concentrically installed in the tank and extending from below the top thereof downwards to a lower level at least closely adjacent said bottom to define an outer, annular mixing channel between said wall and outer partition; an inner, substantially cylindrical partition concentrically installed in the tank and extending from the top of the tank to a level below the top of said outer partition but above said lower level, to define an inner, annular flocculation channel between said partitions and a clarification compartment within said inner partition; pipe means extending outward from said collector, below the surface of said bottom, and discharging into said mixing channel; means adapted to circulate liquid from said collector through said pipe means, outer and inner channels, over said bottom and back into said collector; means to introduce any newly incoming liquid to be treated and treating reagents into said flow collector; means to remove treated liquid from adjacent the top of said clariication compartment; rotatable means to collect sludge settled on said bottom; means to rotate said rotatable means; and means to remove collected sludge from said tank.

2. A liquid treatment tank as described in claim 1, additionally comprising an annular duct below said mixing channel; apertured division means interposed between said duct and mixing channel; said pipe means discharging into said mixing channel through said duct and the apertures in said division means.

3. A liquid treatment tank, according to claim 2, additionally comprising a plurality of wall members transversely extending across said annular duct, and spaced from one another, whereby said annular duct is subdivided into a plurality of portions; said pipe means comprising a plurality of pipes and each of said pipes communicating with one of the portions of said annular duct.

4. A liquid treatment tank according to claim 2 comprising a transition member interposed between said pipe means and duct, said transition member having smooth inner walls, shaped to avoid sudden contraction, expansion, sharp turns in the liquid flowing from the pipe means into the duct.

5. A liquid treatment tank according to claim 2, wherein said division means comprises individual slabs loosely inserted between said mixing channel and duct.

6. A liquid treatment tank according to claim 5, wherein said slabs are shaped substantially as parallelograms in longitudinal section; said slabs being longitudinally spaced from one another to provide the apertured division member.

7. A liquid treatment tank as described in claim 1, wherein at least one of said partitions is buoyant in the liquid under treatment, and which comprises tension means adapted to restrain said partition against buoyancy.

8. A liquid treatment tank comprising a substantially flat bottom; a wall surrounding said bottom; centrally located, annular wall means extending downwardly from said bottom to form a central pin in said bottom, for flow collection and distribution: annular partition means, concentrically installed in the tank and extending from adjacent the top thereof downwardly to above said bottom, to define an outer flocculation channel, and an inner clarification compartment communicating with said channel adjacent said bottom; distributor pipes extending outward from said central pit, below the surface of said bottom, and discharging into said flocculation channel; a centrifugal impeller disposed in said central pit to circulate liquid from said central pit through said distributor pipes and flocculating channel, over said bottom, back into said central pit; a vertical shaft carrying said impeller and upwardly extending therefrom; a motor mounted at the top of the tank and adapted to rotate said shaft; means to introduce any newly incoming liquid to be treated and treating reagents into said central pit; means to remove treated liquid from adJacent the top of said clarification compartment; rotatable means to collect sludge settled on said bottom; means to rotate said rotatable means; and means to remove collected sludge from said tank,

9. A liquid treatment tank according to claim 8 additionally comprising an annular duct, adjacent said wall surrounding said bottom; an apertured division means interposed between said annular duct and said outer flocculation channel; said distributing pipes discharging into said flocculation channel through said annular duct and through the apertures in said division means for further now distribution.

10. A liquid treatment tank according to claim 9 wherein said annular duct is located adjacent the lower part of said well surrounding said bottom.

11. A liquid treatment tank according to claim 10 wherein said annular duct, said distributor pipes and said central pit are completely incorporated in said bottom.

ROY WELTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATEN'lS Number Name Date 1,204,534 Andrews Nov, 14, 1916 1,529,019 Evans Mar. 10, 1925 2,135,860 Taysen Nov. 8, 1938 2,051,149 Nordell Aug. 18, 1936 2,233,792 Mallory Mar. 4, 1941 (Other references on following page) UNITED STATES PATENTS Number Number N Date g' i'g' l 1,108,864 mmbach W- 1929 2 108 021 1,950,841 Crawford Mar. 13. 1934 a 1, 2,314,917 Green 1943 a 23' 5: 2,330,059 welp Dee 14, 1943 {245289 2,353,355 Preset July 1944 {755585 1,678,788 Remick July 1928 a'ui'aeo ,239, 04 mm nr- ,1941

Certificate of Correction Patent No. 2,426,804.

this correction therein that t ROY WELTER Patent Ofiice. Signed and sealed this 11th day of November, A. D. 1947.

Name Date Zitkowskl Sept. 30, 1941 Talbot at .1. Aug. 4, 1942 Russell Feb, 8, 1938 Imhofl Feb. 19, 1929 Mallory Nov. 26, 1940 Hulhes June 17, 1941 Pearl June 10, 1930 Prager Nov. 19, 1946 September 2, 1947;

rinted specification of the above olumn 12, line 19, claim 8, for and that the said Letters Patent should be read with be same may conform to the record of the case in the THOMAS F. MURPHY,

Assistant Uommiasioner of Patents.

UNITED STATES PATENTS Number Number N Date g' i'g' l 1,108,864 mmbach W- 1929 2 108 021 1,950,841 Crawford Mar. 13. 1934 a 1, 2,314,917 Green 1943 a 23' 5: 2,330,059 welp Dee 14, 1943 {245289 2,353,355 Preset July 1944 {755585 1,678,788 Remick July 1928 a'ui'aeo ,239, 04 mm nr- ,1941

Certificate of Correction Patent No. 2,426,804.

this correction therein that t ROY WELTER Patent Ofiice. Signed and sealed this 11th day of November, A. D. 1947.

Name Date Zitkowskl Sept. 30, 1941 Talbot at .1. Aug. 4, 1942 Russell Feb, 8, 1938 Imhofl Feb. 19, 1929 Mallory Nov. 26, 1940 Hulhes June 17, 1941 Pearl June 10, 1930 Prager Nov. 19, 1946 September 2, 1947;

rinted specification of the above olumn 12, line 19, claim 8, for and that the said Letters Patent should be read with be same may conform to the record of the case in the THOMAS F. MURPHY,

Assistant Uommiasioner of Patents.

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