GAS ASSISTED FLOTATION PROCESS AND APPARATUS

Abstract: This invention relates to a gas assisted flotation process and apparatus useful in the separation of solids from liquids in a slurry, such as treated waste waters, paper pulp solutions etc. The gas assisted flotation process may be operated on a continuous basis. The upper portion of the main chamber of the apparatus (36) is tapered inward to terminate in an apex (38) which has an opening through which the floated and compressed solids and gas are removed. The apparatus also has a fluid discharge line (50) through which the separated fluids may be removed which also contains a fluid discharge valve (54) which may be opened and constricted intermittently to control the flow of slurry through the system.

Description: This invention relates to a gas assisted flotation process and apparatus for continuously separating solid particles from liquids. The invention is useful in the treatment of industrial waste waters but may also be used in other applications, such as food processing, manufacturing and public and private water treatment systems. Gas assisted flotation (GAF) cells primarily in the form of dissolved air flotation (DAF) cells have been in use for years as a primary means of separating solids from liquids. In recent years, dissolved air flotation, has found wide acceptance in the treatment and pre-treatment of various waste waters prior to discharge or recycle. The advantages of a flotation process over a sedimentation process for liquid-solids separation are well known and some of them are set forth below. However, one disadvantage common to all dissolved air flotation cells currently in use is the inability to remove the sludge accumulation from the cell without taking significant amounts of the liquid with it. Dissolved air flotation cells such as described in U.S. patents 3,452,869 and 4,022,695 have competed with gravity sedimentation for the separation of precipitated or other suspended solids from liquids or solutions for a long time. Dissolved air flotation can have many advantages over gravity sedimentation. One of the greatest is space. Light coagulated-flocculated solids, such as various chemical precipitates, are slow to settle and thicken in their liquid media by gravity alone. It is therefore necessary to build relatively large settling tanks or thickeners to accomplish a good clean separation. On the other hand a DAF cell or unit that will handle the same flow rate can be much smaller because the rise rate of floc attached to air bubbles is typically four or five times greater than the settling rate of the same floc without air. Therefore, a DAF unit will always be much smaller than a sedimentation unit for the same volume throughput. DAF cells can be operated at high surface loading, thus small and quite shallow units are possible. Another advantage of DAF cells over sedimentation can be fast start-up with steady water quality being achieved quickly. Cost is also favorable in many cases. DE-B 663 960 discloses an apparatus for clearing liquids containing fibres resulting from the production of paper and other cellulosic materials. The apparatus disclosed in said document is characterized by a fluid discharge pipe which not only serves the discharge of clarified fluid but also contributes to a regulation of the liquid level in the main chamber of the apparatus. DE-A 3 412 217 discloses an apparatus for clarifying water by injecting air, together with a flocculating agent, into the water under pressure. The apparatus used for the process mainly consists of a reaction vessel into which the water containing air and a flocculating agent are fed by means of a pipe wherein the flocculating agent is reacted with contaminants in the water. The clarified water is discharged from the reaction vessel via the discharge pipe; any control of the flow discharge or control of the liquid level in the reaction vessel is missing in said apparatus. One major disadvantage of all existing DAF cell configuations, however, is the inability to separate the floating solids (floc) from their liquid media without removing an excess of liquid. This results in a very dilute sludge, often less than 0.2 percent solids. Such a dilute sludge is not an ideal feed for a filter or de-watering unit. This has been a major drawback to the DAF process for liquids-solids separation since its inception. Currently there are methods of removing floc from a DAF cell in use, such as an inclined continuous belt where the floc is picked up on the belt and excess water runs back into the cell. The floc can then be scraped off the belt into a receiver outside of the cell. Another available method is to use an inclined screw which is analogous to the a belt system. With the screw system, scoops of various design are in use to make the separation. Still another method involves a centrally-mounted revolving weir in a circular cell where the floc is carried off, but always with a significant amount of liquid. Sometimes rotary paddles or stationary scrapers are used to decrease the amount of solution carried away along with the true floating sludge. In recent years DAF has been used increasingly in the treatment or pre-treatment of many and varied waste waters, but always there has been a need for the production of a floc with a higher solids content which would create less sludge for disposal and make a more efficient feed for a filter or other de-watering device. In this invention floating solids are continuously separated from the host liquid by the process of claim 1. Preferred process embodiments are claimed in the subclaims 2 to 14. The apparatus suitable in such a process is claimed in claim 15. Preferred apparatus characteristics are claimed in the subclaims 16 to 20. The process according to the invention comprises concentrating the floating solids into a small area of a gas assisted flotation (GAF) cell and then removing the coagulated floating solids by a continuous process characterized by intermittently raising of the liquid level in the cell in such a manner as to force the floc out through a passage near the top of the cell, with only a negligible amount of the host liquid on which it has floated accompanying it. The present invention is based on the discovery that the floating solids in a GAF cell can be concentrated by various geometric shapes (such as an inverted funnel or pyramid) and continuous in-flow of solids-bearing liquid into the cell coupled with intermittently restricting the discharge of clarified liquid on a controlled basis which results in elevating the level of the host liquid and forcing the floc upward, toward the apex of the GAF cell. The thickened floc is then discharged out through an exit at or near the apex of the cell. The cell design incorporates a stilling chamber which allows time for floc formation and growth as well as the reduction of velocity and turbulence in the liquid to be clarified. Typically, a slurry containing dissolved or dispersed air enters the GAF unit after passing through a pressure relief valve. In normal operation the waste water and solids in the slurry have been chemically treated and saturated with dissolved or dispersed gas prior to being released into the GAF cell. Depending on the materials being separated, one or more polymers may be injected to improve the floatability of the precipitated or suspended solids. The slurry then enters the stilling chamber within the GAF cell. This chamber has a dual purpose. The first is to reduce the velocity to the point of a slow non-turbulent flow rate. The second is to provide enough retention time in the chamber to allow optimum coagulation, flocculation, gas bubble and air bubble adsorption and floc growth to take place. Under these parameters the average solids in a host liquid will be conditioned for a very effective separation by flotation. As the conditioned slurry rises within the GAP cell a rapid separation of liquids and solids takes place, the solids with bubbles attached rising into the progressively more constricted upper portion of the GAP cell and clarified liquid leaving the GAP cell via an outflow pipe typically located in the lower portion of the exterior wall of the cell. The height of liquids in an overflow pipe may determine the level in the GAF cell where the interface of floating solids and host liquid occurs prior to its being physically raised by increased volumes of liquid in the tank caused, in the preferred application, by the interruption of outflow via the closing or constricting of a valve in the overflow pipe or outflow line. The most efficient setting of this level will vary with different liquid-solids mixtures and must be determined for each application to produce optimum results. As the separated solids rise toward the top of the GAF cell as a result of gas assisted flotation, they are concentrated into a relatively small area by the progressively constricted upper portion of the cell. Depending on the retention time, the thickness of the bed of floating floc can also be varied. It is this design concept that makes it possible to have a clean separation of true floc from the liquid medium in which it is suspended or carried. This creates the production of a relatively dry and concentrated sludge which makes a greatly improved feed for de-watering as compared with the sludge produced by other known air or gas assisted flotation systems. Additionally, the solids further de-water by gravity above the level of the host liquid as excess gas channels upward through the floc. Maximum thickening and de-watering of the solids takes place through settlement out of liquids in the progressively more constricted upper portion of the cell above the host liquid. In the new GAF system described in this invention, thickening of the floc takes place above the host liquid as well as in it and produces a more concentrated sludge than is possible in any other known type of air or other gas flotation cell. For optimum operation of this GAF cell the overflow pipe should be sized so as to allow the solution flow to take place at essentially zero velocity head. Sludge removal from the GAF cell is typically accomplished on a generally continuous basis, controlled by intermittently opening and closing or constricting a liquid discharge valve. When this valve is fully or partially closed the liquid level in the GAF cell will rise as a result of continuing in-flow of solids-bearing liquid and the floating sludge (floc) will start to dischage via overflow into the sludge discharge pipe. When the solution level reaches a pre-set point near the apex of the GAF cell the liquid discharge valve is automatically opened again, thus dropping the liquid level in the GAF cell back to the normal level and thus momentarily stopping the discharge of sludge. This method of control and operation will insure that the removal of floating solids from the GAF cell is carried out with a minimum of liquid being removed with the solids. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a transverse section showing one embodiment of the gas assisted flotation apparatus of the invention. DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows a gas assisted flotation cell 10 containing main chamber 12. Liquid containing solids particles enters the gas assisted flotation cell 10 through entry pipe 14 and enters the stilling chamber 24 of main chamber 12 through opening 16. The liquid containing solids particles will generally enter the system under pressure. The pressure will be determined by the optimum operation of the system but the upstream pressure against pressure relief valve 18 will generally be about 4,14 bar (60 pounds per square inch) but may range from as low as 1,38 bar (20 pounds per square inch) to as high as 6,89 bar (100 pounds per square inch). In some cases a gas diffuser or diffusers may be used and the gas injected directly into the chamber at near 0 bar (zero pound per square inch) pressure. In a preferred practice of the invention, chemically treated waste water containing solids particles to be separated in the system will have had air or other gas induced under pressure whereby the gas has been dissolved in the liquid and small compressed bubbles of gas have become incorporated into the masses of solids particles and become attached to the surfaces of such solids particles. As the treated waste water containing solids particles enters entry pipe 14 under pressure, it passes through pressure relief valve 18 where the pressure is reduced to almost atmospheric pressure, resulting in the rapid formation of gas bubbles which expand, and physically elevate the solids particles to the surface of liquid in the cell. It is preferred to retain just enough pressure to keep the liquid containing solids moving in the system. An option in practicing the invention is the injection of a polymer system through polymer injection nipple 20 which feeds into entry pipe 14 between pressure relief valve 18 and opening 16. In a conventional application the polymer will be injected through polymer injection nipple 20 at a pressure only sufficent to overcome the residual pressure in entry pipe 14 and insure that the polymer mixes with the chemically treated waste water containing solids particles. Cut-off valve 22 is included in entry pipe 14 only as a means of bypassing cell 10 in case of malfunction but is otherwise closed to force the liquid into stilling chamber 24 through opening 16. The water or other liquid containing solids particles with expanding gas bubbles attached to their surfaces passes through opening 16 into a stilling chamber 24. Stilling chamber 24 is included to reduce the velocity of the liquid entering cell 10 to the point of a slow non-turbulant flow. Also, stilling chamber 24 is included to provide enough retention time to allow further coagulation, flocculation and gas bubble absorption as well as growth of the flocculants solids particles to take place. Optionally, the slurry will enter stilling chamber 24 through opening 16 at a velocity of approximately 0.76 m/min (2.5 feet per minute) with a flow rate of about 37,85 ℓ/min (10 gallons per minute) and retention time in stilling chamber 24 of approximately 24 seconds. These rates and times are not critical and will vary with the optimization of the system for each liquids/solids separation being treated and each particular cell 10. For example, the velocity may range from as low as 0.15 m/min (0.5 feet per minute) to as much as 1,52 m/min (5.0 feet per minute) or more. The flow rate may range from as low as 1,89 ℓ/min (0.5 gallons per minute) to as much as 378,5 ℓ/min (100 gallons per minute) or more. Retention time in stilling chamber 24 may range from as low as 10 seconds to as much as 60 seconds or more. These flow rates and retention times will depend on the size and configuration of the cell 10 and stilling chamber 24. The size of stilling chamber 24 may be varied considerably to optimize the operation of a particular cell 10. Stilling chamber 24 should be large enough to create the desirable coagulation and flocculation and air bubble absorption as the flocs of solids particles grows. Stilling chamber 24 may be cylindrical in shape or it may be any other cross-section configuration such as rectangular, square, or elliptical. The liquid, the bubbles and the forming floc exit stilling chamber 24 into main chamber 12 through stilling chamber opening 26. Stilling chamber opening 26 will generally be unrestricted so that the slurry containing solids particles with gas bubbles can over-flow in all directions to fill main chamber 12. The periphery of stilling chamber 24 may be any desired height but the top should be higher than fluid discharge exit 28 to minimize loss of solids particles. In the preferred embodiment of this invention treated waste water containing solids particles with gas bubbles attached to the surfaces of such particles and gas bubbles adhering thereto are flocculated together so that the bouyancy provided by the gas bubbles will cause the solids particles to move toward the top of the main chamber 12, whereby separation of the solids particles from the fluid is initiated. Bottom opening 32 in the bottom of main chamber 12 and exit valve 34 are provided only for the purpose of draining the system as, for example, for maintenance. The upper portion 36 of main chamber 12 slopes upward and inward to apex opening 38 and this is a critical component of the present invention although the angles of convergence and the precise physical configurations of such upper portion 36 are not critical. As the flocculated solids particles with gas bubbles attached move upward in the liquid toward the apex opening 38 the solids particles tend to congregate in the increasingly constricted upper portion 36 of main chamber 12 which effects further thickening of the rising solids particles which tends to produce a concentrated layer of floated solids. The concentrated solids (floc) will tend to form in a defined layer 40. The flocculated concentrated solids particles (floc) will typically exit from main chamber 12 through apex opening 38 into upper pipe 42 wherein the gas bubbles will tend to detach from the solids particles and exit from upper pipe 42 through upper pipe opening 44 where such gases may be vented or reclaimed for further use. Upper pipe 42 has a side opening 46 through which the solids will exit by force of gravity through sludge discharge pipe 48 into a sludge sump (not shown) for discharge or further treatment as appropriate. A critical element of this invention is a control system which provides for a continuous inward flow of liquid containing solids particles into the system and for the discharge of separated and thickened solids through a sludge discharge point, and for the discharge of clarified fluid through separate fluid discharge point. In the preferred embodiment referred to herein, as the separated fluid exits from main chamber 12 through fluid discharge exit 28 it enters fluid discharge pipe 50. Fluid discharge pipe 50 projects outward from the periphery of main chamber 12 in generally perpendicular relation thereto and is located generally near the bottom of main chamber 12 and generally horizontal with bottom 30 of main chamber 12. Fluid discharge pipe 50 extends outward from main chamber 12 for a short distance and then turns upward into upper fluid discharge pipe 52. Upper fluid discharge pipe 52 contains fluid discharge valve 54. Valve 54 is critical in the operation of the gas assisted flotation process of this invention because it is used to control the intermittent restriction of discharge of clarified fluid from the system which governs the level of liquid in the upper portion 36 of the cell 12 and thus the discharge of floated solids from the system in the form of relatively liquid-free sludge on a continuing basis. The opening and closing of fluid discharge valve 54 can be by manual operation based on visual observance of the formation of flocculated solids particles in defined layer 40. Preferably, fluid discharge valve 54 can be placed on a timing cycle. The timing cycle necessary to keep the system operating continuously will be dependent on the composition of the entering liquid containing solids particles. For a typical treatment system, the fluid discharge valve 54 may be operated on a cycle of about 1-5 seconds closed and about 59-115 seconds open. Also, it is possible to further control the cycle by only partially opening and closing fluid discharge valve 54. It is also an important part of this invention to operate the system on a continuing basis with an automatic timing device on the fluid discharge valve 54 which is actuated to open automatically when the fluid level reaches a pre-set point near the apex opening 38 of the gas assisted flotation cell 10, thus momentarily stopping the discharge of sludge and dropping the liquid level in the main chamber 12 of the cell 10 and dropping the liquid level back to the normal level. The pre-set points contain switches which will respectively actuate a motor (not shown) which will respectively open and close fluid discharge valve 54. These pre-set points will be selected and sequentially timed to optimize through-put and will depend on the nature of the original feed. Fluid discharge pipe 52 will be in mating relationship with overflow pipe 56 through which the clear fluid is discharged into a water sump for further treatment in accordance with established procedures. Overflow pipe 56 optionally works up and down inside upper fluid discharge pipe 52 in mating relationship and is held in position by overflow pipe collar and seal 58. Another preferred but optional component of gas assisted flotation cell 10 is level control pipe 60 which is connected to fluid discharge pipe 50 through opening 62. Thus, the level of fluid and slurry will rise and fall in the main chamber 12 at the same levels as those to which fluids rise and fall in level control pipe 60. Level control probes 62 and 64 may be inserted through level control collar 66 and respectively connected through switches to acutate the motor which opens and closes fluid discharge valve 54 to control the system. This is a preferred system for including automatic controls in the process because the level control probes 62 and 64 can be easily and quickly adjusted to maximize through-put of any particular chemically treated waste water containing solids particles. In operation a time cycle is chosen and fluid discharge valve 54 is opened and closed by these settings. Thus, the motor actuating fluid discharge valve 54 is opened by probes 62 and 64. This allows automatic adjustment and control for small changes in either the solids content or the flow into the system. This is an important feature of the invention. EXAMPLE 1 A laboratory apparatus was constructed and operated successfully with a metal hydroxide slurry containing about 0.032 percent by weight of dry solids particles in water. The flow rate was 1,89 ℓ/min (0.5 gallons per minute). The volume of the main chamber of the cell was 18,75 cm³ (1,144 cubic inches). The retention time in the main chamber was 9.9 minutes. The size of the apex opening was 5.06 cm² (0.785 square inches). Air was dissolved in the feed material at a pressure of 4.14 bar (60 pounds per square inch). After the feed passed through the pressure relief valve, the system operated at close to atmospheric pressure with just sufficient pump input pressure to maintain a constant flow of 1,89 ℓ/min (0.5 gallons per minute). The sludge volume was 1.6% of the feed volume and assayed 2.0% solids. This sludge was a good pressure filter feed and produced a "dry filter cake" which was very easy to handle and was acceptable for landfill. EXAMPLE 2 The same laboratory apparatus as described in example 1 was used to process treated laundry waters. These tests were also very successful in that the floating solids concentrated to an average of about 1.5% to 2.0% of the feed volume. The water was clear and suitable for recycle in a laundry operation. The sludge was thick and made a good feed for a vacuum drum filter. EXAMPLE 3 The same laboratory apparatus as described in example 1 was used to process car wash water. This test was also successful as the floating solids concentrated to about 2.0% of the feed volume. The water was grit and solid free and suitable for recycle in a high pressure car wash operation. Gases which are useful in the practice of this invention include air which is generally used for most purposes because it is available and inexpensive. Other gases which are useful in the practice of the invention are generally common gases which do not easily liquify under operating pressures in the system. Such gases include oxygen, nitrogen, carbon dioxide and other gases having similar characteristics. The gas is generally injected into the treated feed material prior to entering the gas assisted flotation cell. However, the gas may optionally be added at any point prior to the time the feed material enters the main chamber of the cell. For example, the gas could be injected through a diffuser or diffusers at any point along the entry pipe into the cell or located on the bottom of the cell. Although it is expected that the gas assisted flotation process of this invention will utilize the input pressure and regulated control of the pressure release valve to control throughput, it is also contemplated that the process may include an auxiliary pumping system which may be installed in the bottom of the main chamber, and it is also comtemplated that one or more auxiliary stirring devices may be incorporated into the main chamber to create additional bubbles. Although the upper portion of the main chamber is tapered to form an apex in the top, the angle of the taper is not particularly important and will depend on particular constructions. The angle of the taper from horizontal should always be sufficient to provide a funnel-like effect to move the contents towards the apex. The angle may range from as small as 45 degrees to as much as 75 degrees with about 60 degrees being preferred. The configuration of the gas assisted flotation cell of this invention will generally be cylindrical and the upper portion will generally be conical because such constructions are generally available in the tank construction industry. However, the invention may also be practical with other types of cell configurations. For example, the cell could be of rectangular configuration and the upper portion could be tapered in pyramidal fashion to form an elongated apex opening. Also, the cell construction could be hexagonal or any other configuration at the option of the installer. The optional conventional polymer may be catonic, anionic or non-ionic depending on the chemistry of the particular application. The gas assisted flotation process of this invention is continuous although it is controlled by intermittent opening and closing the fluid discharge valve which controls the fluid levels in the cell and which also thus controls the intermittent discharge of dewatered sludge.

Claims: A continuous process for separating solids particles from a liquid in a slurry comprising injecting a gas into said slurry under sufficient pressure to induce the formation of gas bubbles where the slurry is released to lower pressure, which gas bubbles tend to attach to said solids particles; passing said slurry into the lower portion of a gas assisted flotation cell (10) where sufficient retention time is provided for said solids particles to coagulate and flocculate by retaining said slurry in a stilling chamber (24) and thereafter passing said slurry through stilling chamber opening (26) into the main chamber (12) of said gas assisted flotation cell (10) whereby said solids particles with gas bubbles separate from said liquid and float upward in said slurry; floating said solids particles with gas bubbles upward into an upper portion (36) of said gas assisted flotation cell (10) as they separate from said liquid, thereby creating a greater concentration of solids particles with gas bubbles and tending to partially dry said solids particles as they are separated from said liquid, and passing said concentrated solids particles with gas bubbles through an opening (38) in the apex of said upper portion (36) of said gas assisted flotation cell (10) where the solids particles exit through a discharge pipe (48) and gas bubbles exit through a pipe opening (44) at the top of the flotation cell (10) while the liquid phase level is being regulated in said gas assisted flotation cell (10) by controlling the discharge of liquid by intermittently opening and closing or constricting a fluid discharge valve (54) while at the same time the liquid phase is being discharged from said gas assisted flotation cell (10) through a fluid discharge pipe (50) connected to said gas assisted flotation cell. Process according to claim 1, wherein said slurry containing solids particles, gas and liquid is passed under pressure through a pressure relief valve (18) whereby the pressure on the gas-containing slurry is reduced to a lower pressure sufficient only to keep the slurry system moving with the consequent formation of multiple gas bubbles which tend to attach to the solids particles. Process according to claims 1 or 2, wherein said slurry is passed into the lower chamber portion (24) of said gas assisted flotation cell (10) where it is retained temporarily in said stilling chamber (24) to reduce the flow velocity and reduce turbulance to provide sufficient retention time for said solids particles to coagulate and flocculate and to allow time for gas bubbles to attach to and be absorbed in and on said solids particles, and thereafter allowing said slurry to enter the main chamber (12) of said gas assisted flotation cell (10) whereby said solids particles with gas bubbles separate from said liquid and float upward in said slurry. Process according to any of claims 1 to 3 wherein said fluid discharge pipe (50) is supplied with means (54) whereby the discharge of liquid from said gas assisted flotation cell (10) may be periodically reduced or entirely interrupted while said incoming unclarified slurry continues to enter said gas assisted flotation cell (10) without reduction or interruption, thereby causing the liquid level in said cell to rise within said cell (10), forcing the separating solids particles and gas bubbles upward through the upper narrowing portion (36) of said main chamber (12) until they pass from the discharge points at or near the apex opening (38) of said cell (10) with minimum associated liquids, subsidence of the liquid level in said cell (10) being brought about by the periodic reopening of said fluid discharge pipe (50) controlled to take place prior to the time when said liquid rising in said cell (10) would otherwise flow out of the sludge discharge pipe (48) or the upper pipe opening (44). Process according to any of claims 1 to 4 wherein said means (54) in said fluid discharge pipe (50) is a fluid discharge valve (54) which may be closed intermittently to control the flow of said slurry through said gas assisted flotation cell (10). Process according to any of claims 1 to 5 wherein said gas assisted flotation includes a polymer injection. Process according to any of claims 1 to 6 wherein the fluid discharge flow in said fluid discharge pipe (50) is automatically controlled by a fluid level control pipe (60) having fluid level control probes (62, 64). Process according to any of claims 1 to 7 wherein said gas is air. Process according to any of claims 1 to 7 wherein said gas is oxygen. Process according to any of claims 1 to 9 wherein said gas is injected into said slurry by full steam pressurization, partial steam pressurization or recycle pressurization. Process according to any of claims 1 to 10 wherein said slurry is selected from treated metal bearing waters, laundry spent water, spent car wash water and food processing water. Process according to any of claims 1 to 11 wherein air is injected into said slurry at a pressure of 0 to 6.9 bar (0 to 100 pounds per square inch) to induce the formation of air bubbles which tend to attach to said solids particles, and said slurry containing solids particles in liquid under air pressure is passed through a pressure relief valve (18) whereby the gas pressure is reduced to a pressure sufficient only to keep the slurry system moving with the consequent formation of additional air bubbles which tend to attach to the solids particles. Process according to any of claims 1 to 12 wherein said slurry is passed at about atmospheric pressure into a stilling chamber portion (24) of a gas assisted flotation cell (10) where it is retained for a period of time sufficient to reduce the flow velocity and reduce turbulance so that said solids particles may coagulate and flocculate and the air bubbles attached to the surface of said solids particles may be absorbed in the forming flocs and adsorbed on the surface of said solids particles, and thereafter said slurry is allowed to enter the main chamber (12) of said gas assisted flotation cell (10) whereby said solids particles with gas bubbles separate from said liquid and float upward in said slurry. Process according to any of claims 1 to 13 which is controlled by a fluid discharge valve (54) which in turn is controlled by a pair of level control probes (62, 64) and timer which maintain the continuous flow by actuating the opening and closing of said fluid discharge valve (54) on a cycle ranging from about 1 second closed to 59 seconds open to about 5 seconds closed to about 115 seconds open. Gas assisted flotation apparatus (10) for gas assisted separation of solids from liquids in a slurry, said apparatus comprising a main chamber (12), said main chamber having a lower entry pipe (14) through which said slurry may enter a stilling chamber (24) and thereafter said main chamber (12), and said gas assisted flotation apparatus having an upper portion tapered to an apex opening (38) adapted to consolidate solids particles floated to the top portion of said apex opening (38) by gas bubbles attached to said solids particles, said gas assisted flotation apparatus having a fluid discharge pipe (50) extending outward from said main chamber (12) whereby separated fluids may be removed from said main chamber (12), said fluid discharge pipe (50) having a fluid discharge valve (54) included in said fluid discharge pipe (50) adapted to open and close said fluid discharge pipe (50) in order to control the level of slurry in said main chamber (12). The gas assisted flotation apparatus of claim 15, wherein the angle of the tapered portion of said main chamber (12) is about 45 to 75 degrees from horizontal so that the separating solids particles may float easily upward into said upper portion (36) of said gas assisted flotation cell (10) to create a greater concentration of solids particles. The gas assisted flotation apparatus of claim 16 wherein the taper of said upper portion (36) of said main chamber (12) is at an inside angle of about 60 to 65 degrees from the horizontal plane. The gas assisted flotation apparatus of any of claims 15 to 17 wherein said fluid discharge pipe (50) is in fluid communication with a level control pipe (60) wherein the levels of slurry, fluid and solids will be the same as in said main chamber (12) in order to facilitate the control of said fluid discharge valve (54) in said fluid discharge pipe (50). The gas assisted flotation apparatus of any of claims 15 to 18 wherein said fluid discharge pipe (50) is connected to said gas assisted flotation cell (10) via a fluid discharge exit (28) near the bottom (30) of said gas assisted flotation cell (10). The gas assisted flotation apparatus of any of claims 15 to 20 wherein said level control pipe (60) has level control probes (62, 64) inserted through a top collar (66) on said level control pipe (60) connected to said fluid discharge valve (54) and adapted for automatically controlling the flow of slurry through said main chamber (12).

Inventors: CARPENTER, ROBERT KENNETH, LYMAN, HARRISON FRANKLIN, JR.
Applicants: REDUX CORPORATION
Application year: 1989
Main classification: C02F1
IPC codes: C02F1