WO1995027551A1

WO1995027551A1 - Self-cleaning acoustic/screen filter system for solid/liquid separation

Info

Publication number: WO1995027551A1
Application number: PCT/US1995/004306
Authority: WO
Inventors: J. Robert Woolsey; Brian G. Noakes; Valery Yamshchikov; Semyon Shkundin
Original assignee: University of Mississippi
Current assignee: University of Mississippi
Priority date: 1994-04-07
Filing date: 1995-04-07
Publication date: 1995-10-19
Anticipated expiration: 1996-10-07
Also published as: AU2281095A

Abstract

A system which separates and filters fine, particulate, suspended solids from liquid. The system consists of a vessel (1) of appropriate design for solids/liquid mixture processing, with an inlet (2a) for mixture feed and outlets (3, 4) for processed/filtered liquid and solids concentrate; a means of inducing positive head pressure (10, 11) on the mixture feed; an acoustic energy source (8a) operating in an infrasonic or low frequency sonic range, and a fine mesh screen (7a) mounted so as to be hydraulically coupled with the acoustic energy. Acoustic energy transmitted via pressure wave promotes separation of the solids/liquid mixture fractions and induces an oscillatory field of flux acting on and through the screen (7a), the resultant effect of which serves to promote continuous separation, liquid filtration and self-cleaning of the screen. A beneficial side effect of the low frequency acoustic energy is the stressing and killing of bacteria contained in the liquid being processed.

Description

SELF CLEARING ACOUSTIC/SCREEN FILTER SYSTEM FOR SOLID/LIQUID SEPARATION

Background of the Invention

Traditional mechanical methods for the separation and removal of the fine solid particles from liquid suspensions and slurries typically involve cyclones, centrifuges, differential pressure filters, and vibrating screens. The former systems involving centrifugation, while effective, are typically high cost (capital and operating) relative to the separation of fine particles (<40 microns) per unit volume of liquid processed. The latter screening/filtration systems have the usual problems of blinding and blockage, of pore spaces by fine particles. This is typically countered with reverse flushing and changing of filter elements, which are both time and cost consuming.

U.S. Patent Nos. 3,864,249 and 4,028,232 to Wallis describe a particular arrangement involving the use of ultrasonic energy at 25,000 Hz acting normal to a flat screen to effect fine solids separation/filtration from liquid. U.S. Patent No. 4,747,920 to Muralidhara employs both ultrasonic and electric fields concurrently to effect similar solids/liquid separations, suggesting that sonic frequencies as low as possibly 5,000 Hz might be employed.

None of the aforementioned references suggest the use of acoustic energy in the low sonic (below 5,000 Hz) or subsonic (infrasonic) range or other methods, processes or apparatus arrangements for effecting solid/liquid separation. nιιιmιι»τ^»γ n fcha Invention

An object of the present invention is to provide an acoustic filter for separating solids from liquid in a liquid/solid mixture.

It is another object of the present invention to separate solids from liquid in a highly efficient manner, using a screen which is kept relatively clean using less energy compared to prior techniques.

It is another object of the present invention to separate solids from liquid in a continuous process.

According to one aspect of the invention, an apparatus for separating liquids from solids in a liquid/solid mixture is provided comprising a vessel having a top and bottom, an inlet to said vessel for providing a liquid/solid mixture generally at the top of the vessel, a screen in said vessel, disposed below the inlet, having a mesh size selected to allow liquid to pass through from one side of the mesh to the other while retaining solids having a particle size larger than the mesh, a solids outlet for removing solids retained by the screen from the vessel, a liquid outlet for removing liquid from the vessel, and vibrator means for creating acoustic pressure waves in the vessel which propagate toward the screen, said waves having a frequency in the infrasonic to low sonic range and having an amplitude sufficient for inducing the separation of solids from the liquid through the breakdown of surface tension, and sweeping the screen surface to prevent the buildup of solids on the screen surface.

According to another aspect of the invention, a process for separating liquids from solids in a liquid/solid mixture is provided comprising the steps of introducing the mixture into a vessel having a screen with a mesh size selected to allow liquid to pass through the screen while retaining passage of solids having a particle size larger than the mesh size, creating acoustic pressure waves in the vessel which propagate toward the screen, said waves having a frequency in the infrasonic to low sonic range and having an amplitude sufficient for inducing the separation of solids from the liquid through the breakdown of surface tension, and sweeping the screen surface to prevent buildup of solids on the screen surface, removing the liquid after it passes through the screen, and removing the solids retained from passage through the screen.

Description of the Drawings

Fig. 1 is an elevational view in cross-section of a first embodiment of the invention;

Figs. 2A and 2B are elevational views in cross-section of a second embodiment of the invention;

Fig. 3 is an elevational view in cross-section of a third embodiment of the invention;

Fig. 4A is an elevational view in cross-section of a fourth embodiment of the invention;

Fig. 4B is a cross-section of Fig. 4A taken along line B- B; and

Fig. 5 is an elevational view of the embodiment of Fig. 2A in more detail.

Detail Description of the Preferred Bmha-iiments

The acoustic pressure waves are preferably within the range of about 5 to 120 Hz.

The inlet may be through the vessel top wall, or through the vessel side wall to direct mixture tangentially into the vessel. A gravity tank, for holding liquid/solid mixture, connected to the inlet, may be used to provide a pressure head for the mixture into the vessel, and means may be provided for regulating the pressure differential between the inlet and at least one of the outlets.

The vessel may be shaped in many ways. For example, it may be shaped as a cylinder or have inwardly sloping walls, and may have a inner partition wall to divide the vessel into two chambers. The screen may also have different shapes, including planar panels, a cone, oriented with its apex up or apex down, or a cylinder. The screen may also rotate.

The vibrator means may comprise an energy source directly coupled with the liquid, such as a high voltage sparking device for producing a high voltage arc, or a water gun device having a vibrating shuttle bolt.

The vibrator means may comprise a diaphragm, oriented horizontally or vertically. The vibrator means may comprise first and second cam surfaces, and means for rotating the first cam surface relative to the second cam surface to cause the first cam surface to move axially relative to the second same surface, and diaphragm means coupled to said first cam surface. The vibrator means comprises a rotating impeller having oppositely oriented blades to create alternating positive and negative semipressure waves. The impeller blades rotate through a defined path adjacent the screen. The impeller and screen may both be cylindrical in shape. For example, the vibrator means preferably moves the diaphragm with displacement amplitudes from about 0.01 mm to about 5 mm. The screen preferably has a mesh size within the range of about 1 to 100 microns.

The apparatus may be used for various types of liquid/solid mixtures, including by way of example but not limitation an aqueous slurry having solid coal fines, an aqueous slurry having solid industrial minerals, processing water from foodstuff processing having organic particulate solids, an aqueous slurry having solid mineral products processed by hydrometallurgical mean sewage, or chemical or pharmaceutical product slurry.

The acoustic pressure waves preferably have a frequency within the range of about 5 to 120 Hz.

The mixture may be introduced into the vessel tangentially, and preferably, under pressure. The pressure at which the mixture is introduced may be maintained within a selected range.

The screen may be moved within the vessel, for example by rotation.

The acoustic pressure waves may be created by moving a diaphragm connected to an energy source.

The diaphragm may be located on the liquid side of the screen so that liquid is on both sides of the diaphragm.

The process can be used for many types of liquid/solid mixtures, including an aqueous slurry having solid coal fines, an aqueous slurry having solid industrial minerals, processing water from foodstuff processing having organic particulate solids, an aqueous slurry having solid mineral products processed by hydrometallurgical processes, sewage, pharmaceutical product slurry and chemical slurry.

Several embodiments of the invention will now be described with reference to the attached Figs., showing preferred embodiments. However, the invention is not limited to those preferred embodiments.

Referring to the drawings. Fig. 1 shows one embodiment of a system for separating and filtering fine, particulate, suspended solids from liquid according to the invention. In Fig. 1, a vessel 1 of rectangular or cylindrical shape is divided into two processing chambers by partition la. At the top is an inlet port 2a for receiving a liquid/solid mixture or slurry from gravity tank 6. A fine mesh screen 7a, having a mesh clearance size corresponding to the minimum size of solid particles to be retained or filtered from the host liquid, has rectangular or cone-shape, the latter with its vertex oriented upward. If the vessel is rectangular shaped, the screen may preferably be planar, and if the vessel is cylindrical, the screen may preferably be conical. A pair of outlet ports 3 are provided for processed/filtered liquid, and a pair of outlet ports 4 are provided for solids concentrated.

The gravity tank 6 provides a means for inducing hydrostatic head pressure on the solid/liquid slurry feed, so as to provide a sufficient and constant pressure differential to maintain continuous flow, from inlet port 2a to the respective outlet ports. Each of the outlet ports 3, 4 have adjustable cyclic valves 5 for flow rate/back pressure control.

A pressure controller 10 may be provided to the pressure at inlet 2a with sensor 11, and the pressure at the outlets 3 and 4 with sensors 12 and 13, respectively. The controller 11 regulates the amount of opening of inlet valve 15 in response to the pressure readings to help maintain the constant pressure differential.

An energy source 8a is coupled to a diaphragm 8b by suitable linkage or push rod 8C and the diaphragm generates acoustic pressure waves, the frequency of which may range from infrasonic (below 20 Hz) to the lower sonic (<500 Hz) , and preferably in the range of infrasonic to very low sonic (< 120 Hz) , with appropriate corresponding amplitudes. As used herein, the term "low sonic" means below about 500 Hz and "very low sonic" means about 120 Hz.

The diaphragm 8b is horizontally oriented (vertically mounted) and is attached to the partition la. The partition la and diaphragm 8b divide the vessel 1 into two processing chambers, with the diaphragm serving as a double acting diaphragm, interacting directly with liquid in each chamber. Thus when the diaphragm moves in one direction, a positive pressure wave will result in the direction of diaphragm movement, and a negative pressure wave will result on the other side of the diaphragm. Each chamber is in turn divided into an upper and lower section by the screen 7a.

This arrangement provides for utilizing infrasonic or sonic energy generated by an appropriate source, and transmitting the energy by hydraulic pressure waves through the entire volume of the solids/liquid mixture. A desired effect of this application of acoustic energy and resulting pressure waves is the inducement of separation of the particulate solids from the host liquid through the breakdown of surface tension. This acoustically induced deterioration of surface tension is primarily a result of acceleration forces, but is also influenced by the physical and chemical characteristics of the solids/liquid mixture to the extent that such variables affect factors like acoustic impedance and inertial/elastic forces which in turn effect critical processes such as vibra-agitation (threshold of cavitation) and avitation. Further, the pressure waves couple hydraulically with the screen, progressively and continually sweeping the screen surface. Along any given line on the screen the effect of the positive and negative semiperiod pressure wave sweep (which may or may not be equal in amplitude and/or period) may be described as an oscillatory force field acting on and through the screen. A means of supporting or stabilizing the screen may be provided so as to limit or control the degree of surface flex induced by the pressure waves to an appropriate level. Superimposed on the functioning system is a hydrostatic pressure head on the solids/liquid mixture feed sufficient to induce sustained flow through the screen to the processed liquid outlet ports 3.

The resultant effect of this complex interaction of infrasonic/flow frequency sonic energy and induced hydraulic pressure waves, solids/liquid mixture feed hydrostatic pressure, and fine mesh screen, is a process of continuous separation, continuous cleaning of screen via cyclic hydraulic backwash, screen surface boundary layer generation, net passage of processed and filtered liquid through the screen, and continuous take-off of solid concentrate.

An added benefit of this invention is that the particular frequency and amplitude of the acoustic pressure waves transmitting and permeating the solids/liquid (water) slurry has stressing and killing effect on some types of bacteria contained therein. The apparatus according to the invention may operate within a wide range of specifications with regard to applied acoustic energy and screen mesh size. For instance, the frequency of the acoustic pressure waves may range from infrasonic through low frequency sonic or approximately 1 through 500 Hz, but preferably 5 through 120 Hz for the more typical solids to liquid mixture ratios and types of materials/fluids processed in this embodiment. An appropriate average amplitude is chosen for a selected average frequency and as a rule should increase with corresponding decrease in frequency. A typical range of amplitudes corresponding with the frequency range of this embodiment, i.e. 1 through 500 Hz, would be 5mm through .01m.

Screen mesh size should correspond to the minimum size of particles to be retained or filtered from the host liquid. A typical mesh size range for an embodiment according to the invention might extend from < 1 to 200 microns, but with regard to efficiency and application relative to existing technology, 1.0 to 100 microns is preferred.

Fig. 2A show another embodiment according to the invention. In this embodiment, a vessel 1 of generally cylindrical shape has an inlet port 2a for receiving liquid/solid mixture from gravity tank 6, a screen 7b having a funnel shape with a bottom outlet whereby the liquids pass through the screen and the solids are retained to pass through a bottom outlet 4, regulated by valve 5. The liquids pass through outlet 3 regulated by valve 5. In this embodiment, a diaphragm 8b is arranged at the bottom of the vessel, and is coupled to energy source 8a to provide acoustic waves through the liquid which impact screen 7b. Fig. 2B shows a modification of the another embodiment of Fig. 2A according to the invention. Fig. 2B shows a similar arrangement to that of Fig. 2A with the exception that an appropriate energy source, 8, is coupled directly with the liquid without the use of a diaphragm. This direct coupled source may be electric in the form of a high voltage spark fired between electrodes in the liquid, or may be mechanical in the form of a shuttle bolt fired into the liquid at high velocity via high pressure air or hydraulic fluid. The vibrator means may comprise a water gun device which employs a vibrating shuttle bolt mounted in a guide frame open to the liquid of the lower filter chamber and fired into the liquid at high velocity via high pressure air or hydraulic fluid. The shuttle bolt (mounted singly or in multiples) is designed to rapidly displace a selectable volume of liquid varying from approximately 1 to 20 cubic inches and cycle at a selectable rate from 1 to 20 times per second, producing a desired repetitive energy pulse in the liquid of the lower filter chamber ranging from 50 to 1500 joules; the higher power settings corresponding to the lower firing rates and vice versa.

The vibrator means may comprise a high voltage sparking devices comprising a pair of electrodes mounted in the lower filter chamber such that a controlled high voltage arc is generated (across the electrodes in a permissive liquid) to produce a desired repetitive energy pulse in said lower chamber. The pulse may be fired at a selectable rate from 1 to 20 cycles per second and a selectable power range from about 50 to 1500 joules.

Although not shown in these embodiments, a pressure controller similar to that shown in Fig. 1 may also be used to sense pressure at various locations and control the pressure across the screen by adjusting one or more valves. The filter screen 7b is mounted centrally over the diaphragm or direct coupled energy source for efficient utilization of energy. Fig. 3 shows another embodiment according to the invention. In this embodiment, a vessel 1 of generally conical shape has a tangentially connected inlet port 2b for receiving liquid/solid mixture from gravity tank 6, a screen 7b having a cylindrical shape and adapted to rotate about its central axis by motor 9a. A pipe 9c is centrally disposed in the vessel 1 and screen 7b and has a plurality of holes 9d for receiving liquid for passage to liquid outlet 3, which has an associated valve 5. Solids outlet 4, regulated by an associated valve 5 allows the solids to be removed. A diaphragm 8b is arranged to provide acoustic waves through the liquid which waves impact the screen 7b. The bottom of the screen is fitted with a donut shaped diaphragm 8b encompassing the shaft and driven by a nesting pair of circular cams 8al and 8a2 centered on shaft. The upper part 8a2 of the cam fitted to the diaphragm 8b, is free to slide on the shaft with an up and down motion, driven by the fixed bottom half 8al, completing a full cycle in 360° of rotation. The tangential inlet arrangement promotes some separation of solid particles by centrifugal force. The rotation of the screen 7b may further enhance solids residue dispersal and cleaning of the screen by centrifugal force.

Figs. 4A and 4B show yet another embodiment according to the invention comprising a vessel 1 having downwardly depending walls which end at a solids outlet 4 regulated by an associated valve 5. Gravity tank 6 provides liquid/solid mixture to the vessel 1 through a tangentially connected inlet 2b. Here the screen 7b is cylindrical and stationary. An impeller 9b rotated by motor 9a provides the energy source to generate acoustic pressure waves against the screen. The impeller is a squirrel cage, modified vane, impeller. Fig. 4B shows the cross-section of the impeller 9b as having vane sections 9c, each section having a pair of oppositely oriented blades 9c-l and 9c-2. These blades when rotated generate cyclic alternations of positive and negative semiperiod pressure waves sweeping a given line on the surface of the cylindrical screen at a given time or a full sweep of 360° in unit time. The screen could be conical, with the impeller conical as well.

Fig. 5 shows the embodiment of Fig. 2 in somewhat greater detail. The vessel 1 has a vibrator energy source 8a at its bottom and is shock mounted with vibration damping rubber 15 and springs 16 at the base. The conical screen 7b is supported by a wire frame for increased strength and stability.

The mesh screen according to the invention may take several forms, as will occur to those skilled in the art. For example, it may be formed of planar panels of various shapes, mounted normal, or at an angle with the axis of the container. The panels may be triangular in shape, radially arranged in the form of a pyramid or continuous panels formed as cylinders or cones. The cone may be oriented with the vertex up or down so as to disperse to the radius, or concentrate to the vertex, respectively, the solids residue migrating down the screen surface under the influence of gravity. When the cone is oriented with the apex down, it may form a funnel with a solids outlet at the bottom so as to function as a means of filtering out particulate solids from the mixture feed, produce a filtrate liquid and concentrate the solids residue, directing it by gravity flow to the funnel outlet.

The energy sources can be any type of mechanical or electro-mechanical vibratory sources acting through one or more diaphragms that contact the liquid directly on one or both sides, below or above the screen, or as described above in connection with Fig. 2B. The efficiency of the solids/liquid separation process according to the invention may be enhanced by tuning the operating frequency of the energy source to the material resonance frequency of the system to effect mass oscillation of the liquid in sync with the diaphragm. In some cases such as high solids to liquid ratios, it may be necessary or desirable to arrange a second diaphragm above the screen to insure sufficient acoustic energy input for desired separation effect. The upper diaphragm should preferably be synchronized in order to assist and not interfere with the lower diaphragm, or be of a sufficiently different high or low frequency so as not to interfere.

The acoustic energy induces hydraulic pressure waves consisting of positive and negative semiperiods (which may or may not be equal in amplitude or period) which couple with the screen. This induces an oscillatory field of flux which acts on and through the screen surface, the resultant effect of which further serves to promote solids/liquid separation, through pressure squeezing of concentrated clouds of solid particles. The filtration of the solid/liquid mixture via the screen to produce a liquid filtrate solution, and solids residual fraction, is effected primarily by the negative semiperiod pressure waves and the superimposed hydrostatic head pressure. The screen is protected from binding of the solids thereto by the cyclic generation of a boundary layer ripple effect. The pressure waves also induce self-cleaning of the screen by cyclic hydraulic backwash effected by the sweep of the positive semiperiod pressure waves.

The present invention has application to separating and filtering organic particulate solids from processing or chiller water in the processing of chemical slurry, raw pharmaceutical products, produce, meat products (such as poultry, pork, beef and seafood) , so as to clean and promote purification of the processing or chiller water to industry standards for continuous recycling or return to the environment. The invention may also be used for separating and filtering coal fines from aqueous slurries, or may be used for separating and filtering industrial minerals such as sand, gravel, phosphorite and associated silts and clays for aqueous slurries. The invention may also be used for separating and filtering various mineral products from host aqueous solutions in hydrometallurgical processes. The invention may also be used for water treatment in industrial and municipal water systems in pre-cleaning and/or post cleaning operations for recycling or returning the water to the environment. The invention may also be used for cleaning and treating aqueous slurries for return to the environment. The invention may also be used for processing chemical slurry.

The unique characteristics and advantages of the invention are (1) simplicity of design, fabrication, installation, and operation with corresponding cost economy; (2) coupling of low frequency acoustic energy with solids/liquid mixtures and a variety of screen arrangements to effect a continuous process of separation of the solids/liquid fractions, liquid filtration, and screen self-cleaning; (3) stressing and killing effect on certain types of bacteria by low frequency acoustic energy; and (4) wide range of applications involving the separation and filtration of fine particulate solids from liquids, such as but not limited to, pre- and post¬ processing/cleaning of municipal industrial water; cleaning/recycling of meat, seafood and produce processing and chiller water; recovery of coal, phosphate and other mineral fines from aqueous slurries, sewage slurry processing, chemical slurry processing and pharmaceutical product processing. One test of the embodiment of Figs. 2 and 5 was conducted involving the cleaning of poultry chiller water. A batch of 100 gallons was cleaned having a temperature of 40° F (4.5*C) containing 5-10% by volume, particles and lumps of coagulated chicken fat and fine, sinuous, organic particles. A flow rate of 25 gallons/minute was used. A 1 cubic meter gravity tank was mounted to provide a positive pressure head of 0.5 to 1.5 meters.

The vessel was a rigid steel cylinder, 12" in diameter, and vertically mounted. The screen was funnel shaped and rigidly secured to the vessel body by a flange 17 welded to the screen, sealed and bolted in place. The screen was further secured by steel rods 18 fitted with rubber sleeves, mounted radially top and bottom, and spaced to provide a desired damping effect. The mesh size in the test ranged from 20 to 100 microns. The 100 micron screen used was a Tetco, Betamesh 20, stainless alloy with absolute filter rating of 18-22 microns and a nominal rating of 15 microns, similar to the 20-22 micron nominal industry standard.

The outlet valves 5 used were manually controlled. The bottom of the vessel body was fitted with a rubber diaphragm 8b with a 10" diameter steel backing disk, the diaphragm and disk was secured by bolting via peripheral, welded steel flanges, the backing disc was welded to a bracket, bolted in turn to the shaft of a piston type pneumatic vibrator (model "FEP", Cleveland Vibrator Company). The vibrator was rated at 35 Hz at 9.5 CFM/60 PSI (.27 m³/π»in at 414 KPa) , no load. The vibrator was acoustically isolated from the rigid vessel body by mounting separately on a 2.5 cm thick rubber damping pad 15 with spring filled bolts 16. The vibrator was operated at 15 Hz with corresponding amplitudes from 2.0 to 0.5 mm measured below and above the cone screen respectively.

The acoustic energy introduced to, and acting on and throughout, the whole volume of the solids/liquid mixture, within the vessel body at any given time induces hydraulic pressure waves, which may be further described in simplest form as positive and negative semiperiods (which may or may not be equal in amplitude or period) of the basic wave forms.

The processes involved may be considered in two phases. The first phase relates to the process of separation in which the acoustically induced force of acceleration manifests as vibra-agitation (threshold of cavitation) and possible cavitation is the primary factor in the breakdown of surface tension between the solid particles and suspending liquid, e.g. water. In the case of compressible organic solids, the separation of liquid by squeezing may also be a factor.

The second phase relates to a complex process of filtration whereby the separated solid particles are filtered out from the liquid fraction which passes through the pore spaces of the 20 micron screen (together with solid particles of sufficient fineness to pass through the mesh spaces, typically less than 15 microns for the test) . The acoustically driven hydraulic pressure waves serve to continuously clean the screen while enhancing the separation/filtration process. This may be most simply described as a process acting on a single point on the screen at a given time (and progressively and cyclicly effecting the entire screen in unit time) by which the negative pressure semiperiod assists the static pressure head in forcing liquid through the mesh spaces of the screen, followed in turn by the positive (back) pressure semiperiod which assists in the dislodging of particles that may become lodged in the screen mesh spaces. Further, this positive pressure semiperiod serves to force the increasing concentration of solids back from the screen surface and further deliquity the solids concentrate by squeezing, which continuously gravitates down the cone screen surface to the funnel exit port with the aid of redundant vibrations.

In unit time, the cyclic positive and negative semiperiod pressure waves tend to form a boundary layer ripple effect progressing sequentially from the lower to the upper section of the screen. This action further serves to provide a continuous cleaning effect assisting in the continuous flow of liquid filtrate through the screen.

In this poultry chiller water test, water was successfully filtered with solids passing mainly limited to less than 15 microns. The solids concentrate, consisting primarily of particles of chicken fat/tissue, and coagulated chicken oils in the form of grease lumps was successfully filtered out and concentrated in the funnel outlet plumbing for discharge. Examination of the cone screen, after passing 100 gallons of typical to worst-case chiller water, was found to be completely clean and free of any mesh blinding particles or any coating of grease or oily residues.

A subsequent test was conducted using an acoustic device rated at 3000 Hertz, with an amplitude of approximately 0.01mm, at a power rating comparable to that of the intial infrasonic run. All other elements of the test, including volume and composition of the batch, were similar as well. Inspection of the screen at the end of the test found it to be partially blinded over about 10% of the surface area. The results of this test (at 3000 Hz and 0.01mm), in comparison with the successful initial test (at 35 Hz and 2.0 to 0.5mm) described above, suggest that the low sonic frequency and greater amplitude resulted in an effective generation of the oscillatory field of flux (acting on and through the screen) . Since power is directly proportional to the squares of both frequency and amplitude, it follows, if power is held constant while frequency is increased, (as in the case of the latter test and with the higher frequencies of the prior art) then amplitude will be reduced correspondingly. With such a reduction in amplitude, the flux field and boundary layer effect is apparently diminished with attendant reduction of the desired continuous screen cleaning effect.

Thus the present invention provides an apparatus and method for effective solid/liquid separator with a screen while keeping the screen substantially free of blinding and blocking, making effective use of energy consumption compared to devices at 3000 Hz and upward.

Following the successful preliminary chiller water test, further experiments were initiated to evaluate the low frequency acoustic effects on a general spectrum of sewage related bacteria. In these preliminary tests, numbers of coliform type colonies were reduced to a minimum of one order of magnitude upon infrasonic treatment (kill approximately 90%) . The acoustic energy used (i.e. 15 Hertz, 2.0 - 0.5mm) was thus found to have a stressful and significant killing effect on certain types of bacteria, such as but not limited to coliform bacteria, and to the extent that those individual bacteria are not killed outright, they are rendered susceptible to standard bactericides or killing methods in lesser amounts and degrees. Although several preferred embodiments have been shown and described, the present invention is not limited to these preferred embodiments, as numerous variations and modifications to these embodiments will readily occur to those skilled in the art. The present invention is defined only by way of the appended claims and equivalents.

Claims

What is claimed is:

1. An apparatus for separating liquids from solids in a liquid/solid mixture comprising: a vessel having a top and bottom; an inlet to said vessel__for providing a liquid/solid mixture generally at the top of the vessel; a screen in said vessel, disposed below the inlet, having a mesh size selected to allow liquid to pass through from one side of the mesh to the other while retaining solids having a particle size larger than the mesh; a solids outlet for removing solids retained by the screen from the vessel; a liquid outlet for removing liquid from the vessel; and vibrator means for creating acoustic pressure waves in the vessel which propagate toward the screen, said waves having a frequency in the infrasonic to low sonic range and having an amplitude sufficient for inducing the separation of solids from the liquid through the breakdown of surface tension, and sweeping the screen surface to prevent the buildup of solids on the screen surface.

2. The apparatus according to claim 1, wherein the acoustic pressure waves are within the range of about 5 to 120 Hz.

3. The apparatus according to claim 1, wherein the vessel has a top wall and wherein the inlet is through the vessel top wall.

4. The apparatus according to claim 1, wherein the vessel has a side wall and wherein the inlet is through the vessel side wall to direct mixture tangentially into the vessel.

5. The apparatus according to claim 1, further comprising a gravity tank, for holding liquid/solid mixture, connected to the inlet, to provide a pressure head for the mixture into the vessel.

6. The apparatus according to claim 1, wherein the vessel has a cylindrical shape.

7. The apparatus according to claim 1, wherein the vessel has inwardly sloping walls.

8. The apparatus according to claim 1, wherein the screen has a cone shape.

9. The apparatus according to claim 1, wherein the screen is oriented with its cone apex up.

10. The apparatus according to claim 8, wherein the screen is oriented with is cone apex down, and has an opening in the bottom for passage of solids.

11. The apparatus according to claim 1, wherein the screen has a cylindrical shape.

12. The apparatus according to claim 1, wherein the screen has an axis, and further comprising means for rotating the screen about its axis.

13. The apparatus according to claim 1, wherein the vibrator means comprises a diaphragm.

14. The apparatus to claim 13, wherein the diaphragm is oriented horizontally in the vessel.

15. The apparatus according to claim 13, wherein the diaphragm in oriented vertically in the vessel.

16. The apparatus according to claim 1, wherein the vessel includes a partition wall which divides the vessel into two chambers.

17. The apparatus according to claim 1, wherein the vibrator means comprises first and second cam surfaces, and means for rotating the first cam surface relative to the second cam surface to cause the first cam surface to move axially relative to the second same surface, and diaphragm means coupled to said first cam surface.

18. The apparatus according to claim 1, wherein the vibrator means comprises a rotating impeller having oppositely oriented blades to create alternating positive and negative semiperiod pressure waves.

19. The apparatus according to claim 18, wherein the impeller blades rotate through a defined path adjacent the screen.

20. The apparatus according to claim 19, wherein the impeller and screen are both cylindrical in shape.

21. The apparatus according to claim 1 wherein the vibrator means comprises an energy source directly coupled with the liquid.

22. The apparatus according to claim 21, wherein the energy source is a high voltage sparking device for producing a high voltage arc.

23. The apparatus according to claim 21, wherein the energy source is a water gun device having a vibrating shuttle bolt.

24. The apparatus according to claim 1, further comprising means for regulating the pressure differential between the inlet and at least one of the outlets.

25. The apparatus according to claim 1, wherein the vibrator means comprises means for moving a diaphragm with displacement amplitudes from about 0.01 mm to about 5 mm.

26. The apparatus according to claim 1, wherein the screen has a mesh size within the range of about l to 100 microns.

27. The apparatus according to claim 1, wherein the liquid/solid mixture is an aqueous slurry having solid coal fines.

28. The apparatus according to claim 1, wherein the liquid/solid mixture is an aqueous slurry having solid industrial minerals.

29. The apparatus according to claim 1, wherein the liquid/solid mixture is processing water from foodstuff processing having organic particulate solids.

30. The apparatus according to claim 1 , wherein the liquid/solid mixture is an aqueous slurry having sol id mineral products processed by hydrometallurgical means .

31. The apparatus according to claim 1, wherein the liquid/solid mixture is sewage.

32. The apparatus according to claim 1, wherein the liquid/solid mixture is pharmaceutical product slurry.

33. The apparatus according to claim 1, wherein the liquid/solid mixture is chemical slurry.

34. A process for separating liquids from solids in a liquid/solid mixture, comprising the steps of: introducing the mixture into a vessel having a screen with a mesh size selected to allow liquid to pass through the screen while retaining passage of solids having a particle size larger than the mesh size; creating acoustic pressure waves in the vessel which propagate toward the screen, said waves having a frequency in the infrasonic to low sonic range and having an amplitude sufficient for inducing the separation of solids from the liquid through the breakdown of surface tension, and sweeping the screen surface to prevent buildup of solids on the screen surface; removing the liquid after it passes through the screen; and removing the solids retained from passage through the screen.

35. The process according to claim 34, wherein the step of creating acoustic pressure waves comprises creating acoustic pressure waves having a frequency within the range of about 5 to 120 Hz.

36. The process according to claim 34, wherein the step of introducing the mixture into a vessel comprises introducing the mixture tangentially into a vessel.

37. The process according to claim 34, wherein the step of introducing the mixture into a vessel comprises introducing the mixture under pressure.

38. The process according to claim 37, further including the step of regulating the pressure at which the mixture is introduced to maintain the pressure within a selected range.

39. The process according to claim 32, further including the step of moving the screen within the vessel.

40. The process according to claim 39, wherein the step of moving the screen comprises rotating the screen.

41. The process according to claim 34, wherein the step of creating acoustic pressure waves comprises moving a diaphragm connected to an energy source.

42. The process according to claim 41, including locating a diaphragm on the liquid side of the screen so that liquid is on both sides of the diaphragm, and moving the diaphragm.

43. The process according to claim 32, wherein the mixture is an aqueous slurry having solid coal fines.

44. The process according to claim 32, wherein the mixture is an aqueous slurry having solid industrial minerals.

45. The process according to claim 32, wherein the mixture is processing water from foodstuff processing having organic particulate solids.

46. The process according to claim 32, wherein the mixture is an aqueous slurry having solid mineral products processed by hydrometallurgical processes.

47. The process according to claim 32, wherein the mixture is sewage.

48. The process according to claim 32, wherein the mixture is pharmaceutical product slurry.

49. The process according to claim 32, wherein the mixture is chemical slurry.