US3464272A - Continuous slurry sampler and deaerator - Google Patents

Description

Se t. 2, 1969 w. A. GRIFFITH ETAL 3,464,272

CONTINUOUS SLURRY SAMPLER AND DEAERATOR Filed May 13, 1968 4 Sheets-Sheet 1 Sept. 2, 1969 w. A. GRIFFITH ETAL 3,464,272

CONTINUOUS SLURRY SAMPLER AND DEAERATOR 4 Sheets-Sheet 2 Filed May 13, 1968 FIGZ.

Sept. 2, 1969 w. A. GRIFFITH ETAL 3,464,272

CONTINUOUS SLURRY SAMPLER AND DEAERATOR 4 Sheets-Sheet 5 Filed May 13, 1968 Sept. 2, 1969 Filed May 13. 1968 FIGS.

FEED

W. A. GRIFFITH ETAL PROCESS ANALYSIS CONTROLLER CONTINUOUS SLURRY SAMPLER AND DEAERATOR 4 Sheets-Sheet 4 7O 70 I PRIMARY PRIMARY SAMPLER METALLURGICAL PROCESS SAMPLER I I WASTE (TAILING) PRIMARY SAMPLE PRODUCT I (CONCENTRATE) I SAMPLE TRANSPORT EQUIPMENT I I I 7 SAMPLE CUTTER 78 I I I I 8O ANALVSIS 4 scREENs READOUT I I I I5 1 I DE-AERATORS t 82,

L. ?i 4 J L rm SAMPLE SELECTOR PROGRAMMER DENSITY ,-74- o DENSITY GAUGE I READOUT 8!- COMPUTING I DEVICE E X-RAY SIGNAL X-RAY ANALYZER INTEGRATOR I AND READOUT I 83 FLOW RESTRICTOR United States Patent 3,464,272 CONTINUOUS SLURRY SAMPLER AND DEAERATOR William Alexander Grifiith and Paul Eugene Link, Morenci, and Benny Ray Burns, Clifton, Ariz., assignors to Phelps Dodge Corporation, New York, N.Y., a corporation of New York Filed May 13, 1968, Ser. No. 728,670 Int. Cl. G01n 1/00 U.S. Cl. 73-423 Claims ABSTRACT OF THE DISCLOSURE In a system for the analysis of various sample streams, an apparatus for cutting a sample from :a fluid stream including an open ended conduit movable in a horizontal path and positioned above a stationary variable opening cutter during part of the path, a suspended deaerator tank through which the cut sample passes, a counterbalance for the deaerator and sample, and a linkage to open and close the cutter opening in response to vertical movement of the deaerator tank. A single sample analyzer incorporating one of the above apparatus for each stream to be analyzed wherein a manifold selects one stream at a time to be fed to the analyzer.

The present invention relates to an apparatus for forming a continuous fluid sample stream from a main stream with subsequent tank deaeration of the sample stream. More particularly, it involves utilizing variations in the weight of the fluid in the deaeration tank to adjust the flow rate of the sample stream.

Control of chemical and metallurgical processes is preferably based upon measurement of appropriate physical and chemical properties of the various process streams involved. Continuous automatic on-stream measurement of these characteristics is highly desirable, and progress has been made in developing such systems for application to fluid process streams. Most such systems cannot make measurements directly upon the main process stream when it is large but require a sample stream representative of it. This sample stream should be identical to the process stream in terms of the physical and chemical characteristics to be measured. In particular, it should be free of air bubbles which would reduce the apparent density of the stream and thereby pro duce errors in measurements. Because the sample flow chambers of the measuring systems must be kept full to exclude air, and because they are generally systems of fixed resistance to flow, they require a sample stream of nearly constant flow rate, whereas process streams generally have variable flow rates dictated by production requirements. As the analytical sample chambers used in connection with instruments such as the X-ray analyzer necessarily employ materials of construction which are of limited strength, the hydraulic head of pressure within the system must be controlled to prevent rupture of the chamber.

When the process stream is a homogeneous liquid, nearly any means employed to divert part of it as a sample stream will provide a sample of the same composition as the main stream. Any of a variety of known devices may then be used to remove air from the sample stream. A simple open surge tank with the bottom connected to the analytical system and an overflow return to the process or to waste is adequate for fiow rate adjustment and hydraulic head control.

But, when the process stream is a slurry of solid particles in a liquid, the problem becomes more complicated and such systems are not entirely satisfactory. Slurry 3,464,272 Patented Sept. 2, 1969 "Ice streams are notoriously non-homogeneous because each individual solid particle tends to settle in the liquid phase at a rate dependent upon its own size, shape, and specific gravity, as well as upon the slurry flow rate, solids concentration, and other hydrodynamic characteristics. As a result, samples taken from one part of the stream may have properties quite different from those taken from another part, and both may differ from the bulk of the stream. It is well known to those skilled in the art that, for these reasons, simple diversion of a portion of a slurry stream cannot be counted upon to produce a representative sample.

Many kinds of samplers have been devised to cut periodic batch samples from slurry streams and it is known that, if certain principles are adhered to, the sam ples will be representative. The basic principle in all of these devices is that a cutter of fixed dimensions be passed into, through, and out of the stream at a constant rate of speed in such a manner that each and every portion of the stream flows into the cutter for the same interval of time.

It is well known to use batch samplers of the above mentioned type, operating on a short time cycle, to produce practically continuous representative slurry sample streams for automatic on-stream analytical systems. Unfortunately, the design features necessary to produce a representative sample stream also produce one in which sample stream flow rate variations are in direct proportion to flow rate variations in the main process stream. In order to compensate for these flow rate variations, the sample stream flow rate has been adjusted to that accepted by the analytical system by using a head tank or deaeration tank with an overflow outlet for excess sample, similar to that which has proved satisfactory for homogeneous fluid streams. However, the use of such a tank results in distortion of the sample which tends to become nonhomogeneous in the head tank. Attempts have been made to maintain homogeneity in these tanks, and thus avoid sample distortion, by equipping them .with agitators and various kinds of baflles. But, these systems using a tank with an overflow have been found to be unsatisfactory for several reasons.

Firstly, sample distortion frequently results, with the material flowing out the bottom of the tank to the analytical system being different from either the overflow stream or the feed stream. These errors stem from the tendency of solid particles, particularly large or heavy ones, to settle and concentrate in the under'flow. In flotation process applications they also result from the tendency of some chemically treated mineral particles to stick to and rise to the surface with air bubbles. These kinds of errors are particularly great, for example, in the analysis of flotation process concentrates and have led to unsatisfactory results with such streams. See Fuller, M. L., et al., X-ray Assaying and Reagent Control at Friedensville, in the Mining Congress Journal for April 1967, at pp. 108-1 12.

Secondly, this overflow arrangement can cause errors in some analytical systems, such as X-ray fluorescence analysis, simply because the size of the particles in the two streams are different, even though the chemical compositions of the streams are identical. See Berstein, F., Particle Size and Mineralogical Effects in Mining Applications, a paper presented on Aug. 10, 1962, at the Eleventh Annual Conference, Applications of X-ray Analysis, University of Denver.

Thirdly, the tank overflow arrangement is unsatisfactory in that the strong agitation necessary to keep the solid particles in suspension is detrimental to effective deaeration, so that the final design is at best a compromise between the degree of sample distortion allowed and the completeness of deaeration achieved, without a completely satisfactory solution to either problem. In addition, the agitation requires large mechanical agitators and baffles with moving parts that wear out.

In accordance with the present invention, it has been discovered, in a system for cutting, deaerating, and analyzing a fluid sample, that the flow rate required by an analyzer being fed by a deaeration tank, can be adjusted by changing the opening dimension of a variable opening cutter, which feeds sample to the subsequent deaeration tank, dependent on the weight of sample in the tank.

Although the sampling and deaeration system of the present invention may be utilized for any fluid stream, including all liquid streams, it is particularly well adapted for use with slurries wherein sample distortion errors occur with a deaeration tank overflow system. Although not intended as limiting, the system will be described with respect to a slurry stream.

It is an object of the present invention to overcome the disadvantages of known sampling methods.

It is a further object of the present invention to cut a representative sample stream stream from a main stream.

It is also an object of the present invention to deaerate a sample stream before analysis in an improved manner.

It is another object of the present invention to adjust the flow rate of a sample stream, without changing the composition thereof, to the rate accepted by an analysis system.

In addition, it is an object of the present invention to control the hydraulic head on an analytical system for a sample stream taken from a main stream.

Other objects of the invention will be apparent to those skilled in the art from the present disclosure of a preferred embodiment of the invention taken in conjunction with the appended drawings, wherein:

FIGURE 1 is a schematic elevational view of one sample cutter and deaeration tank apparatus of the present invention.

FIGURE 2 is a diagrammatical elevational view, partly broken away, of the three-stream analysis system employing the sample cutter and deaeration tank shown in FIG- URE 1.

FIGURE 3 is an elevational view in perspective of the sample cutter of the present invention.

FIGURE 4 is an elevational view in perspective of the deaeration tank of the present invention.

FIGURE 5 is a schematic block diagram showing the functional relationships among the components of a system for taking samples at three stages of a metallurgical process and analyzing the samples wherein the double lines are process material flow lines and the single lines are mechancial, electrical or pneumatic signals.

As best shown in FIGURE 1 a conduit 1 is connected to a piece of flexible tubing 2 which tubing 2 is connected to nozzle 3 so as to form a continuous channel through conduit 1, tubing 2 and nozzle 3. The hose may be constructed of any suitable material, such as Tygon plastic, which is able to withstand flexing, corrosion, and abrasion. The nozzle 3 is mounted for movement in a horizontal path of travel controlled by a conventional sampler mechanism 4 for producing reciprocal horizontal motion at a substantially uniform rate of speed. Appended to mechanism 4 is a vertically depending arm 5 mounted for horizontal, reciprocal movement which is attached to one end of horizontal arm 6, which, in turn, is connected to nozzle 3.

A variable opening cutter housing 7 containing a cutter opening 8 and a cutter outlet 9 is vertically mounted with the opening 8 directly beneath the nozzle 3 during at least part of the path of travel of nozzle 3. The opening has a movable cutter blade 10 and a stationary cutter blade 11, both mounted on the cutter housing 7. A launder 12 with a discharge pipe 13 and an inlet opening 14 is mounted beneath the nozzle 3 so that the path of travel of the nozzle 3 is always directly above inlet opening 14. Cutter housing 7 is surrounded by launder 12 and projects therethrough in a sealing engagement.

A deaeration tank 15 is suspended by a flexible cable 16 which is supported by a series of free moving pulleys 17. From the opposite end of the cable is suspended a weight 18 adequate to counterbalance the deaeration tank and other components when the tank is filled to the desired level with slurry. One end of the linkage system 19 is connected to the cable with a bar 20 and the outlet end to the movable cutter blade 10 so that motion of the cable 16 resuiting from vertical motion of the tank 15 is converted into horizontal motion of the linkage 19 and the movable cutter blade 10, thus decreasing or increasing the cutter opening 8. The bottom discharge opening 21 of the tank 15 is connected by a flexible hose 22 to an analytical system described hereinafter.

As best shown in FIGURES l and 3, the central portion of the cutter housing is rectangular in shape bounded by pairs of sides 23 and 24. The two blades 10 and 11 are generally parallel to each other and perpendicular to the path of travel of nozzle 3. Blade 11 is rigidly mounted to one of sides 23 and blade 10 is hinged to the other of sides 23. Movable blade 10 is fastened to side 23 with a hinge 25, which is made leaktight by the addition of a strip of flexible material secured to both the movable blade 10 and side 23. A flexible sheet 26 connects the respective edges of blades 10 and 11 and is attached to a corresponding one of sides 24 for confinement of slurry flowing past the blades while allowing blade 10 to move relative to blade 11. The flexible sheet 26 and the flexible material covering the hinge 25 may be made of rubber in order to provide adequate resistance to abrasion and corrosion. The linkage system 19 connected to the cutter blade 10 comprises parallel bars 28 bolted to the outside edge of the top of cutter blade 10 at connection 29.

To insure that an accurate sample is obtained, the sampling device should include a cutter opening with almost perfectly parallel sides, a constant or uniform speed of passage of the sample stream in a straight line across the cutter, a cutter opening of size adequate to prevent stoppages in the opening, a cutter housing and opening large enough so that none of the sample stream will overflow or splash from it during operation, a cutter housing and opening designed to prevent entry of any part of the sample reject, an arrangement which cuts all of the stream part of the time and which takes the cutter entirely out of the stream after each cut, and a sampling frequency such that the sample reflects the true composition of the stream.

The deaeration tank, as shown in FIGURE 4, has a cylindrical wall 30 and a conical bottom section 31 of such a slope that solid particles in a slurry will not accumulate in it during operation or on cessation of operation. A feed entry pipe 32 is mounted at an upward angle to the horizontal in a direction tangential to cylindrical wall 30 to induce the deaeration of the slurry. A suitable up ward angle would be about 10 to 20 degrees. Flexible tubing 27 connects cutter outlet 9 and pipe 32. A small batfle 33 is supported in the lower portion of the tank 15 to control the swirling action of exiting slurry and to prevent the formation of a vortex which would introduce air into the slurry. The entire support for the tank 15 is provided by cable 16 which is attached to the upper edge of the tank by rings 34. A cover 35 is provided to protect the contents of the tank 15 from contamination. Small holes 36 in cover 35 allow air contained in the slurry sample to escape.

As shown in FIGURE 2, a trash screen assembly 40 may be interposed in tubing 27 between outlet 9 and pipe 32 containing screen cloth 41 and trash outlet 42. The optional screen 40 is used only when the trash content of the particular stream requires it. The screen cloth 41 normally has from 6 to 20 mesh openings per linear inch. Trash collected on the screen cloth 41 is discharged to waste through outlet 42.

In operation of one embodiment of a single sample cutter and deaerator assembly of the present invention, a

slurry sample stream cut from a process stream is directed through conduit 1, tube 2 and into nozzle 3. The nozzle is recipiocated in a horizontal path at a uniform rate of speed by mechanism 4 so that the sample stream falls into the cutter opening 8 during part of its path of travel and outside the opening 8 into the launder 12 during the remainder of the path of travel. The part of the primary sample stream flowing through the cutter forms a secondary sample stream which flows through outlet 9 and tubing 27, thence through pipe 32 into the deaerator tank 15. The remainder of the primary sample stream flows through launder 12 and out discharge pipe 13 from which it is returned to the main stream or directed to waste. It will be apparent that the proportion of the primary stream collected within the cutter to constitute the secondary sample stream will depend, inter alia, on the ratio of the cutter opening 8 to the distance that nozzle 3 traverses in its total path of travel.

That part of the slurry stream which enters the cutter 7 flows out of the cutter outlet 9, optionally via a screen assembly 40 for trash removal, and then enters the deaeration tank 15. The stream leave the deaeration tank 15 from its bottom opening 21, flowing in a closed system through the sample chamber of any suitable analytical or measuring instrumentation.

When the system is properly adjusted and the cutter opening 8 is correct, an equilibrium will develop in which the feed rate to the deaeration tank 15 is exactly equal to the discharge rate, and the selected slurry level in the tank i exactly that necessary to provide the static head to cause the then existing discharge flow rate. If, then, the feed to the tank 15 increases or the discharge rate decreases, slurry will accumulate in the deaeration tank 15, its weight will increase, it will overbalance its counterweight and move downward. This will cause the linkage 19 to move horizontally in such a way as to decrease the cutter opening 8; reducing the proportion of the primary sample stream collected as secondary sample and fed to the deaeration tank. Conversely, if the feed rate to the deaeration tank should become less than the discharge rate, the level in the tank will drop, the counterweight will overbalance the tank, the cutter will open, and a greater portion of the primary sample stream will be diverted to the deaeration tank to make up the deficiency. Thus the apparatus will seek and find an equilibrium condition for each combination of circumstances, always providing exactly the amount of truly representative sample stream necessary to maintain a uniform flow through the analytical sample chambers.

When the slurry exits pipe 32 and enters into the deaerator 15, the slurry travels tangentially to the cylindrical tank wall 30- just below the surface of the selected quantity of slurry in the tank and in an upward direction of about to 20 degrees from the horizontal. The momentum of the entering slurry imparts a mild swirling action to the slurry in the tank 15. Thi arrangement is conducive to the escape of air from the slurry. The small baffle 33 controls the swirling action and prevents the formation of a vortex which would introduce air into the slurry. Slurry exits through pipe 21 to be analyzed. Because the tank is open, and the amount of vertical motion is small, the hydraulic head on the subsequent analytical system is controlled within narrow limits.

FIGURE 2 shows an embodiment of the invention taking samples of a process at three different points. The three-stream system employs the same equipment as shown in FIGURE 1 for sampling and deaerating in three complete side by side assemblies through the three hoses 22 which flow to a sample selector 56. The sample selector 56 has a manifold 51 with a single outlet 58 and three inlets 52. There may be as many inlets 52 as there are streams to be analyzed in the system. Fitted to each inlet 52 a feed pipe 53 with two automatically operated valves 54 and 55. Feed valve 54 leads to manifold 51 and bypass valve 55 leads to a by-pass line 57 to sample return equipment These valves are so arranged that by closing the by-pass valve 55 and opening the feed valve 54, the entire stream of the corresponding hose 22 is directed into manifold 51. By closing the feed valve 54 and opening the by-pass valve 55 the entire sample stream in the corresponding hose 22 bypasses the manifold and flows into the bypass line 57.

The operation of the array of valves, two for each sample, is accomplished by electrical and pneumatic signals from a programmer as shown in FIGURE 5. Since it is important that each stream sequenced into the manifold 51 sweep the manifold chamber free of remnants of the previous stream, the feed valves 54 should be close coupled to the manifold 51. The by-pass valve 55 should be close coupled to the hoses 22 to avoid stagnant pools of slurry not flushed out by the new stream after each change of valve position.

In operation of the valves, only one stream enters the manifold and enters the analyzer. When measurement by the analyzer is complete, four simultaneous valve movements automatically occur. The open feed valve 54 closes, the closed by-pass valve 55 opens, one of the previously closed feed valves opens, and its corresponding by-pass valve closes. A new stream is then flowing through the analytical system,, and the previously analyzed stream is short-circuited to the sample equipment. In this sequential manner, each of the sample streams in turn flows through the analytical system. When all streams have been analyzed, the cycle automatically repeats. Of course, it is possible, through appropriate adjustment of the programmer, to set any desired sequence of stream analysis. For example, certain streams may be analyzed with greater frequency than other streams.

As best shown in FIGURE 2 after the slurry sample stream exits from the manifold 51 through a duct 58, it enters a density gauge 60. From the density gauge 60 the stream passes through a safety valve 63 and thence through sample cell '61 of an X-ray analyzer 62. Alternatively, the flow could first pass through the sample cell 61 of the analyzer 62 and then to the density gauge 60. The density gauge, which may be of any appropriate design, measures the concentration of solid particles in the slurry. The X-ray analyzer, also well known to the art, measures the concentration of a selected element in the slurry or of two or more selected elements. A flow restrictor 64 is employed to limit the slurry fiow and adjust pressures within the system.

The embodiment of the block diagram of FIGURE 5 shows the functional relationships among the elements of a control system for a simple metallurgical process. Three streams are chosen for analysis to provide a basis for control of the process: the feed stream, the concentrate stream and the tailings stream. There could, of course, be any number of process streams and a metallurgical process is chosen by way of example only. The apparatus could be employed to control any process in which the process streams are liquid or a slurry of solid particles in a liquid. In metallurgical processes, these slurries normally consist of mineral particles in water.

As further represented in FIGURE 5, there is one primary sampler 70, one assemblage of sample transport equipment 71, one trash screen assembly 40, one sample cutter 7 and one deaerator 15 for each of the process streams as part of the system. The number of assemblages of samples return equipment may vary from only one to as many as one for each process stream, depending on the value of the material and the requirements of the process.

Still referring to FIGURE 5, line represents the mechanical signal sent from the deaerators 15 to the sample cutter 7, caused by :a variance of slurry content from the desired level in the deaerator 15, which correspondingly increases and decreases the cutter opening 8.

While the signal through line 80 controls the sampler, the signal through line 81-87 enable the sampler to control and monitor the main process. The X-ray analyzer 62 measures the concentration of a selected element in the slurry or of two or more selected elements. A signal from the X-ray analyzer 62 is sent along line 81 to programmer 73 which operates to choose the sample stream to be analyzed. The thus formed selection signal is sent along line 82 to the sample selector 56 wherein the proper valves are opened and closed in response to the signal. The X-ray signal is also fed via line 83 to the integrator and readout 76 and then the generated electrical impulse is sent along line 84 to the computing device 75. The integrator and readout 76 also generate signals which instruct the programmer 73 and allow it to coordinate the performances of the sample selector 56 and the X-ray analyzer 62.

The density gauge measures the concentration of solid particles in the slurry. A signal from the density gauge 60 is sent along line 85 to readout 74 and the electrical impulse generated therein is sent to the computing device 75 along line 86. From the two input lines 84 and 86, device 75 computes the element concentration in the solids and relays this information along line 87 to remote analysis readout 78 and process analysis controller 77. Thus, in one embodiment, the results of analysis are used directly to control the process.

Regardless of the number of streams, within reasonable limits, only one each of the sample selector 56, density gauge 60, X-ray analyzer 62, flow restrictor 64, programmer 73, density readout 74, computing device 75, and X-ray signal integrator and readout 76 is required. The analysis readout 78 and process analysis readout or controller 77 may be simple as a single assemblage functioning to provide sequentially the analytical information on the several streams, or as complex as to include separate recorders and controllers for each stream sampled.

When the overflow system of the prior art is utilized, sample distortion results, with the material flowing out the bottom of the tank to the analytical system being different from the overflow stream. These errors stem from the tendency of solid particles, particularly large or heavy ones, to settle and concentrate in the underflow.

In flotation process applications, these errors also result from the tendency of some chemically treated mineral particles to stick and rise to the surface with air bubbles. The solids contained in the concentrates of a flotation process for copper were analyzed periodically in the underflow and the overflow from the deaeration tank. The variance between the percentage of copper contained in the underflow and in the overflow averaged over 4.5% based on the underflow. The apparatus of the present invention, in contrast to the overflow system heretofore used, only has one stream leaving the deaerator. In a flotation process for copper, an analysis of the sample reject stream (i.e. that portion of the stream falling outside the cutter into the launder) was compared to the underflow leaving the deaerator. The variance, based on the underflow, was under 0.1%. This is a striking contrast to the 4.5% variance in the overflow system heretofore used.

It is apparent that the system of the present invention avoids sample distortion errors which have been found to occur with the deaeration overflow system. These errors result from the difliculty of achieving both uniformity of dispersion of solid particles throughout the tank and simultaneously achieving deaeration. All solids and liquids of the present invention leave the deaeration via a single outlet. Therefore, all of the sample that enters the cutter is fed in the sample selector, and, thus, there is no concern about uniform dispersion. Also, mechanical agitators and associated battles are eliminated, reducing initial, operating, and maintenance costs.

The deaeration tank of the present invention need not be a comprise between the initially incompatible conditions best for deaeration and those best for solids dispersion. Hence, the present design of tangential feed entry unencumbered by factors of dispersion yields improved deaeration.

The terms and expressions which have been employed are used as terms of description not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention.

What is claimed is:

1. Apparatus for cutting a fluid sample from a fluid stream comprising:

(a) first conduit means for said fluid stream having an outlet movable in a horizontal direction;

(b) a cutter housing disposed below said movable outlet having a variable opening at the top thereof and an outlet at the bottom thereof, and being adapted to receive a sample from said fluid stream;

(c) a tank suspended for vertical movement having an inlet in the upper portion thereof and an outlet at the bottom portion thereof;

((1) second conduit means communicating between the outlet of said cutter housing and the inlet of said tank for the direction of said fluid sample from said cutter housing to said tank;

(e) a counterweight suspended for vertical movement;

(f) movable suspension means connected at one end thereof to said tank and at the other end thereof to said counterweight so that said counterweight balances the weight of said tank and a selected quantity of fluid sample in said tank;

(g) and means responsive to a change in the vertical position of said tank, caused by a fluctuation in amount of fluid sample from said selected quantity, for varying the size of said variable opening of said cutter housing.

2. Apparatus as described in claim 1 including means for reciprocating said movable outlet of said first conduit means in a substantially horizontal path at a substantially uniform speed.

3. Apparatus as described in claim 2 in which the length of the horizontal path of the movable outlet of the first conduit means is substantially greater than the variable opening of the cutter housing whereby during a portion of the travel of said movable outlet no fluid can enter said variable opening.

4. Apparatus as described in claim 1 in which the variable opening of said cutter housing comprises a fixed blade integral with said housing and a movable blade hinged to said housing at its lower edge.

5. Apparatus as described in claim 4 in which the lateral edges of said movable blade are connected to the respective lateral edges of said fixed blade by flexible sheet material.

6. Apparatus as described in claim 4 in which the means responsive to a change in the vertical position of said tank comprises a linkage means connected at one end to said movable suspension means and at the other end to said movable blade hinged to said cutter housing.

7. Apparatus as described in claim 6 in which the means responsive to a change in the vertical position of said tank moves the movable blade of the cutter housing toward the fixed blade as the tank descends.

8. Apparatus as described in claim 1 in which the inlet to said tank is arranged tangential to the wall of said tank so that a swirling motion will be induced in the fluid introduced into the tank.

9. Apparatus as described in claim 8 in which the inlet to said tank is inclined upwardly with respect to the vertical axis of the tank.

10. Apparatus as described in claim 8 in which a 9 10 stationary battle is positioned in the lower portion of said 3,252,328 5/ 1966 Huntington 73-423 tank. 3,279,260 10/1966 Huntington 73-423 References Cited 3,397,582 8/1968 Strand 73423 UNITED STATES PATENTS 3,387,497 6/1968 Huntington 73423 2,738,679 3/1956 Senkowski 73- 423 5 3397582 8/1968 Strand 3,110,183 11/1963 Logue 73423 3,175,402 3/1965 Higami et aL LOUIS R. PRINCE, Primary Examiner 3,198,017 8/ 1965 Taylor et a1. 73-421 HARRY C. POST III, Assistant Examiner

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