DE2624543A1 - FLOTATION PROCESS AND FLOTATION DEVICE - Google Patents

Description

PA Γ ENTAN WA LTE

SHIP v. FÜNER STREHL SCHÜBEL-HOPF EBBINGHAUS

MUNICH QO ₁ MARIAH1LFF ^J LATZ 2 & 3 POST ADDRESS: D-8 MÜNCHEN 95, POST BOX 95 O1 6O

ENVIROTECH CORP.

DIPL. CHEM. DR. OTMAR DITTMANN ( _T 107B) KARL LUDWIG SCHIFF DIPL. CHEM. DR. ALEXANDER V. FÜNER DIPL. ING. PETER STREHL

DIPL. CHEM. DR. URSULA SCHÜQEL-HOPF

DIPL. INa. DiETER 663INGHAUS

TELEPHONE (O89) 48 2O64

TELEX 6-23 505 AURO D TELEGRAMS AUROMARCPAT MUNICH

June 1, 1976 DA-K1550 (739/746) DE / bi

Priorities: June 2, 1975 U.S. No. 583 072 July 14, 1975 USA No. 595 906

E! L25ä £ i2 £ §Y§ £ i§ ^ £ ^en _ ^and · flotation device

The invention relates to a flotation process and a Flotation device.

It is known to distribute gas bubbles in a liquid to convert them into solid or liquid ones by flotation or suspension Separate components. Flotation is generally used to separate and concentrate valuable minerals and chemicals, for removing particulate matter from liquids and used to separate different liquids. In a typical flotation process used in mineral processing becomes an aqueous slurry of broken minerals with a chemical flotation agent processed. Then gas bubbles are dispersed in the slurry, so that a Foam that is relatively rich in the desired material is produced. Similar flooding is often used in oil production too.

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procedure applied to before the reintroduction of the water to separate crude oil from the same in a borehole or before it is discharged at the surface. When floating or It is important for flotation to be the contact surface between the foam-forming gas bubbles and the materials to be floated to make as large as possible and at the same time to keep the surface of the liquid as calm as possible, so that the foam is moved as little as possible. This allows the suspended materials to be separated from the gas bubbles, to which they adhered during flotation.

A number of other methods are also known in which gas bubbles must be distributed in a liquid. For this include, among other things, the saturation with carbon dioxide and the aeration of liquids for the flotation of bacteria, the removal of gases from liquids, accelerating fermentation and mixing gases and liquids. A common requirement of these processes, as well as flotation, is that the gas bubbles in the liquid be small and be well distributed.

The invention is based on the object of an improved foam flotation process for separating solids or Specify liquids from other liquids. In particular, a method and a device for injection are intended a two-phase fluid (e.g. an air-water mixture) into a liquid in a relatively non-turbulent manner Way are indicated by which an almost complete dispersion or distribution of the gas bubbles over the entire liquid and a calm, but foamy surface can be guaranteed.

In the flotation process according to the invention and the inventive A flotation device uses hydraulic effects to disperse the gas bubbles in a container liquid with free surface is exploited. According to the method according to the invention, a two-phase Fluid into the liquid with a density and a kinetic

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see energy related to the volume of that in the container Liquid introduced, which will be described in more detail below. The device according to the invention contains an ejection or ejection device which is arranged to have an air-liquid mixture in ejects the liquid. The ejection device contains a tubular expansion or calming chamber, whose one end is open as an outlet and the opposite end with a flat plate for receiving one Tube is provided through which the liquid is pumped under pressure into the chamber. The cross section of the chamber is opposite that of the pipe is relatively large. Gas to be mixed with the pumped liquid is passed through in the shallow Plate formed openings sucked.

The invention is explained in more detail with reference to the drawing. Show it:

1 shows the schematic perspective illustration of a flotation device according to the invention;

FIG. 2 shows a diagram of the conditions under which the device of FIG. 1 is performing the flotation is preferably operated;

3 shows the partially cut-away perspective view of an element of the device of FIG. 1; and

4 shows the partially cut-open plan view of the end an alternative embodiment of the element shown in FIG.

The flotation device of FIG. 1 contains a container 13 for receiving a liquid 16 with a free surface 16a and an injector 15 which is rigidly attached to the end of a tube 17, in the middle of the free surface of the liquid 16. The injection device 15 is used to introduce a two-phase fluid (usually an air-water mixture) into the liquid 16, from a point below its surface 16a in FIG Direction down. The liquid is by means of a no

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2 6 2 Λ 5 4 3

The conventional pump shown is pumped through the pipe 17 and then into the injector 15. The pumped liquid mixes with the gas in the injector 15 * whereby the two-phase fluid is created.

The container 13 is by upstanding side walls 20, 21, 22 and 23 and bounded by an overall flat base 24. At least one side wall of the container, in the present exemplary embodiment the wall 20, contains a weir 20a, about which the foam from the surface 16a of the liquid 16 is derived. A conventional auxiliary scraper, for example a paddle wheel, or the injection device 15 itself can support the foam removal be used. Slurry or other material to be treated is poured into a conventional feed container 26 or the like introduced into the container 13. The treated liquid is via a conventional one, not shown Underflow weir or other typical device, such as an outlet channel, derived. If necessary, the treated liquid can be pumped back into the container 13 via the pipe 17 for further treatment will.

Instead of downwards, the injection device 15 can be in the container 13 can also be arranged so that it injects the two-phase fluid horizontally or at an angle into the tank.

According to FIGS. 1 and 3, the injection device 15 contains a hollow straight pipe section 31 with a circular cross-section, which is connected to the end of the pipe 17 carrying the liquid and forms a calming chamber 32, the inner diameter of which is relatively large compared to that of the pipe 17. In practice, the ratio of the inner diameter of the calming chamber 32 to the inner diameter of the pipe 17 is between about 1.5 and 3.5, preferably at least 2. The outlet end 39 of the pipe section 31 is open and unobstructed, but its inlet end is circular by means of a flat Plate 33 tightly closed. From the-

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ORiOINAL INSPECTED

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stood between the plate 33 and the outlet end 39 determines the effective length of the pipe section 32. It is in in practice at least three times its diameter and can be twenty times or more the diameter, for example in the contact treatment of gases and liquids. Preferably the ratio is the length of the Calming chamber 32 to its inner diameter between approximately 2 and about 15- In the middle of the end plate 33 there is an opening 35 'through which the pumped liquid enters calming chamber 32 approximately axially. Around the central opening 35 are a number of small openings arranged in the plate 33, via which the interior of the calming chamber 32 with the atmosphere or, not shown, is in communication with a source of pressurized gas via a manifold or the like. Preferably the openings border exactly or approximately to the inner wall of the calming chamber 32 (Fig. 4), so that the gas along the inner wall of the chamber entry. The number of openings is arbitrary. For reasons that will be explained in the following, need they are not evenly distributed around the central opening 35.

To operate the injection device 15, the liquid is at a relatively high pressure (0.91 to 1.05 bar overpressure (13 to 15 psig)) through pipe 17. Upon entering the calming chamber 32, the pumped liquid forms on the inner surface of the end plate 33 of the chamber is a turbulent area of low pressure through which the gas is sucked through the openings 37 into the calming chamber 32. In most cases it is done by natural suction Sufficient gas is sucked into the injection device 15 from the atmosphere to achieve the working parameters described below to meet. If a larger amount of gas is required, a source of pressurized gas can be connected to the openings. to push the gas into the chamber. Inside the calming chamber The gaseous and liquid phases are carefully examined under the hydraulic conditions that prevail in them mixed. In view of this, it should be mentioned that the

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ORIOINAU INSPECTED

flat formation of the inner surface of the end plate 33 a cliff surface which creates hydraulic turbulence and shear effects in the fluid and in turn the mixing improved.

After your fiction according to the method, the device is the 1 preferably operated in such a way that certain energy-density ratios are maintained at the injection device 15 as shown in FIG. Fig. 2 shows a diagram, on the ordinate of which the kinetic energy of the two-phase medium flowing out of the injection device 15 based on the volume of the receptacle 13 each Second in ft lb / ft / s or rnkp / m ^ / s and on its abscissa the density of the two-phase medium flowing out of the injection device is plotted in Ib / ft or kp / m. The area I bounded by the solid curve ABC represents the preferred working area of the device. The area I is enclosed by a transition region II which is delimited by a dashed curve DEF. The outside Area III lying this limit represents an undesirable working area. If the device is in the area I operated, the liquid 16 in the container 13 is filled with gas bubbles, and the liquid surface 16a is relatively calm and frothy. If, on the other hand, the device is operated in region III, either the gas bubbles not distributed over the liquid 16, or the liquid surface is excessively turbulent and restless.

The abscissa of the diagram in FIG. 2 bears a linear scale with density values between 10 and 62.4 Ib / £ ir or 160 and 1,000 kp / m. These values are based on tests in which the outflowing medium consisted of an air-water mixture. Since the density of water is 62.4 lb / ft or 1,000 kp / nr, the density of the two-phase gas-water mixture is necessarily below this fourth. A logarithmic scale is plotted on the ordinate. The relative energy of the two-phase, outflowing medium is between 1/10 and 10 lb / ft / s or about 0.49 and about 49 mkp / m ³ / s. 609852/0673

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The curve AB represents the minimum energy limit because a Point on this curve with respect to a specific density of the outflowing medium determines the minimum energy that is expended can be made to achieve the desired conditions. In practice, it is preferred to work at an energy level above curve AB in order to be on the safe side Side to lie. The curve BC can accordingly be understood as the maximum energy limit, because there is a point on it Curve with regard to a certain density of the outflowing medium determines the maximum energy that is expended may »if the desired conditions are to be met. In practice, preference is given to energy levels worked well below the BC line to save power. For this reason the exact position of the curve is BC unimportant unless to show that the desired conditions are no longer given when the energy of the outflowing two-phase medium is too large.

It can also be seen from FIG. 2 that work should preferably be carried out at an energy-density point which lies within the hatched area at the top of curve ABC, if as little energy as possible is to be consumed. It has been found, however, that for reasons of reliability, work should not be carried out in this area, because small changes in the working parameters can easily lead to undesirable conditions in the container. If, for example, the working conditions are set to point b and the density of the outflowing medium shifts to point b ¹ (increase by about 10 %), the desired conditions no longer exist in the container. Such shifts in performance can result from clogging of the fluid or air supply, changes in pump speed, and normal mechanical wear and tear during operation. Therefore, work is normally carried out to the left and above the hatched area of the tip of the area I, for example at point b "in the non-hatched part of this area.

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The operating point b ″, which lies within the area I and is considerably shifted from the hatched part, is also preferable because for effective flotation a sufficient amount of gas is required to form a large number of bubbles which come into contact with the material to be floated In the device shown, the amount of gas introduced into the liquid is inversely dependent on the density of the two-phase medium emerging from the injection device 15, and since the number of bubbles generally increases with the amount of gas, operation at operating point b "(low density ) preferred over operating point b (high density) if the number of gas bubbles is a factor to be taken into account. The quantitative relationship of the density of the two-phase fluid, P? Gi> ^{to the gas diameter} "tz ° -δ ^{and the} liquid flow rate Qr can be represented by the following equation:

62.4 1,000

It should be noted that the relative number of bubbles and not the distribution of the bubbles is considered here will. The vesicles can, regardless of whether their number is relatively large or small, over the entire container be distributed.

The outlet end of the injection device is preferably arranged somewhat below the liquid surface i6a, so that the gas-liquid mixture emerging therefrom hits the container bottom 24 or passes over the same. The condition for impact depends on the depth of the container and on the energy of the two-phase medium. Observations give rise to the assumption that the impact or "near" impact with the container bottom 24 is important

609852/0673 ORIGINAL INSPECTED

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is to ensure a good distribution of the gas bubbles and a calm Achieve liquid surface with minimal power consumption.

In this context, a hysteresis effect was observed, which partially covers the transition area II in »Fig. 2 should explain. It has been observed that with increasing exit energy and constant density of the zv / egg-phase fluid, a critical value is reached at which the container suddenly moves with it. Bubbles fills and the free surface becomes calm. The observation of such a discontinuous phenomenon was extremely surprising. It was also found that after exceeding the critical energy value, the exit energy can be reduced while keeping the density of the medium flowing out of the nozzle constant and the container remains filled with bubbles until an energy value below the previous critical value is reached. In other words, the energy value at which the bubble distribution changes from the uniform to the non-uniform distribution depends on whether the energy is decreased from a point within the area I or the energy from a point in the area III is increased by one To reach point in area I. The boundary line AB of area I is the location of the energy values at which the preferred conditions occur when the exit energy is increased from a point in area III; the dashed boundary line DE of the transition area II is the location of the points at which the preferred conditions cease to exist when the exit energy is lowered from a point I. The hysteresis effect is likely to be closely related to the impact of the injected zv / egg-phase fluid on the container bottom. Using this effect, it is possible to work reliably at values that are slightly within the minimum energy limit line AB, because the preferred conditions in the container are maintained even if the density of the escaping medium decreases, for example when moving from point b ″ in area I to Point b " ¹ in area II.

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With regard to the hysteresis effect, the curve AB can be interpreted as a boundary line which represents the minimum energy level determined in which the preferred conditions with certainty be found in the liquid. In other words, those to safely maintain the preferred conditions necessary minimum energy is a function of the density of the emerging two-phase medium, and this function is determined by the curve AB.

During operation, the values can be on the abscissa and ordinate of the diagram of FIG. 2, in which the device operates, can be determined in various ways. For example the density of the exiting two-phase fluid can be calculated from the above-mentioned equation. The liquid and gas flow rates into the injector 15 (Q, respectively G.) can easily be measured, for example by means of a conventional venturi tube, a rotameter, a pitot tube or the like, or they can be determined from the operating condition of the pump. If you know the container volume, the gas and liquid flow rates and the density of the two-phase medium, so can the kinetic energy ■■ · of the two-phase fluid per unit volume of the container can be easily determined, where m is the mass flow rate of the two-phase fluid in weight units per second, determined by the density and the pipe geometry, ν the exit velocity of the two-phase mixture and g mean the gravitational constant.

It should again be pointed out that the abscissa values of FIG. 2 relate to the volume of the liquid in the container 13 refer. If, for example, the container volume is doubled and the density of the two-phase medium is constant held, its exit energy must also be doubled in order to maintain the preferred flotation conditions and to be able to maintain the same working point in the diagram of FIG. Usually the exit energy of the two-phase fluid is adjusted by changing the speed or the flow rate of the pump that supplies the liquid

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to the injection device 15 feeds. The setting can also be made by changing the dynamic pressure of the fluid at the injection device 15. The graph of FIG. 2 was determined from tests performed on container volumes between about 0.023 and about 14 nr ⁵ (0.83 to 500 ft ⁵ ). The range shown should be applicable to flotation cells in a volume range of 1,000: 1.

In the method according to the invention, a natural, hydraulically produced effect is used to carry out the flotation or, more precisely, to completely fill and mix a liquid with gas bubbles without excessive agitation and with a minimum of shear turbulence in the flotation tank. By completely filling the liquid With gas bubbles and the circulation of the bubbles, the contact between the bubbles and the material to be floated is established optimized. The natural hydraulic effect also allows the process to be carried out without guiding devices or other mechanical ones Carry out gas distribution facilities.

The two-phase fluid can also come from a middle position be introduced approximately horizontally into the lower area of the liquid in the container. From this it can be seen that the direction of injection in the container is not critical in order to achieve the desired hydraulic effects or To achieve properties in the liquid. However, it has been shown that the ejection direction of the two-phase Fluids in the liquid create a flow in the foam forming the liquid surface. More precisely, the one Foam located on the surface flows in a direction that is determined by the nozzle position. Small changes in the position of the injection device can therefore be used instead of the scraping devices mentioned at the beginning to create a foam stream.

The embodiment of FIG. 3 is preferably used for flotation, because it has been shown that here a Electricity is generated on the surface of the liquid in the container,

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which is determined by the position of the injection device, i.e. the injection direction. Small changes in position the injection device can therefore be used instead of the scraping devices mentioned above Generate foam stream. This phenomenon does not occur if the gas does not run along the inner wall of the calming chamber 32 is performed. Another effect of introducing the gas along the inner wall of the calming chamber 32 is in that the air forms a cushion-like boundary layer that protects the injector from impermissible mechanical Protects stress and wear from solids carried along with the pumped liquid.

In the embodiment of the injection device shown in FIG 15, a modified flat circular end plate 33a is attached to the end of the pipe section 31. The trained in it Central opening 35 serves to rigidly receive the pipe 17 leading to the liquid. As gas inlet openings are in the plate 33a large openings 37a with a relatively small distance from each other and smaller openings 37b provided at a greater distance from one another. All opening edges border on the inner wall of the pipe section 31, so that the boundary layer described above is created. It has been shown that in this non-symmetrical arrangement The openings also create a flow on the surface of the liquid, into which the two-phase fluid is expelled will. In other words, the surface flow can be increased by modifying the construction of the injector can also be generated as by the arrangement at an angle to the liquid surface.

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Claims (19)

1. A method for flotation by means of dispersed gas, in which hydraulic effects for dispersing the gas bubbles over liquid contained in a container with a free surface v / ground, characterized in that a two-phase fluid is injected into the liquid, its density and kinetic energy depending . Voluneneinheit the liquid through a point within the encompassed by the regions I and II of the diagram of Figure 2 is intended area v / ith (about 49m · kg-s / m ^{3 to} 146 kg / nr ^5; 0.093 m ^k P -s / cr ⁵ - 843 kp / m ⁵ ; 49m-kP: s / m ³ - 826 kp / m ³ ). 2. The method according to claim 1, characterized in that the kinetic energy and density of the two-phase fluid injected into the liquid is determined by a point within the area encompassed by area I in the diagram of FIG. 2 (49 m «Kp-s / m - 308 kp / nr ⁵ ; 0.19 m-kp.s / rir ⁵ - 790 kp / nr ⁵ ; 49 m'kp-s / m. - 665 kp / m ³ ). 3. The method according to claim 1, characterized in that the two-phase fluid in the downward direction is injected into the liquid. 4. The method according to claim 3, characterized in that the two-phase fluid from a point below the free surface of the liquid is introduced into the same. 5. The method according to claim 1, characterized in chn e t that the liquid is in a container without baffles or mechanical gas distribution devices is included. 6. The method according to claim 2, characterized in that after operation at a within the loading 609852/0673 area I of the diagram of FIG. 2 lying working point the kinetic energy dec injected two-phase Fluid is gradually lowered to a point within area II of the diagram of FIG. 2. 7. The method according to claim 1, characterized in that the two-phase fluid consists of a gas-water mixture consists. 8. The method according to claim 4, characterized in that kinetic energy and density of the two-phase Fluids are chosen so that it reaches the bottom of the container. 9- The method according to claim 1, characterized in that the liquid phase of the two-phase fluid consists of Water, which is pumped into a calming chamber, and that the other phase consists of gas that is drawn by suction is mixed into the water in the calming chamber. 10. The method according to claim 1, characterized in ch-. net that the kinetic energy per unit of the volume of the discharged two-phase fluid contained in the container is between about 0.98 and substantially above about 49 m-kp-s / m ³ (0.2 to 10 lb / ft ² / sec). 11. The method according to claim 2, characterized in that that the kinetic energy per unit of the in the container contained volume of the diverted two-phase fluid zv / ischen about 1.96 and substantially over about 49 m-kp's / m ³ (0.4 to 10 lb / ft ² / sec) is. 12. Flotation device, which takes advantage of hydraulic effects of gas bubbles over a liquid with a free Distributed surface, with a container (23) for receiving a liquid (16) with a free surface (i6a), with a device (26) which is effectively connected to the container and for introducing liquid to be processed 609852/0673 speed and for the discharge of the processed liquid from the container is used, and with a fluid injection device (15) »which is fixed in a position in which two-phase fluid enters that in the container Liquid is expelled, characterized in that that the fluid injection device (15) contains the following: a hollow tubular calming chamber (32) having an open end through which the two-phase mixed fluid into the liquid in the Container is ejected and the opposite end of which is connected to a tube (17) through which liquid is pumped under pressure into the interior of the calming chamber in the overall axial direction, the cross section of the pipe is small compared to the internal cross-section of the calming chamber, and a gas inlet device (37; 37a, 37b) for introducing gas into the interior of the calming chamber for mixing with the one located therein Liquid and to form the two-phase fluid that is ejected into the liquid and a dispersion formed by gas bubbles rising to the free surface. 13. The apparatus according to claim 12, characterized by a flat plate (33 »33a) which are tightly opposite End of the tubular calming chamber (32) is attached, and through a central opening (35) through the Plate for firmly holding the pipe (17) carrying the liquid. 14. The device according to claim 13, characterized in that the gas introduction device contains a plurality of relatively small openings (37; 37a, 37b) through the flat plate (33 _} 33a) which are in communication with the interior of the calming chamber (32). 15. The device according to claim 14, characterized in that that the openings (37; 37a, 37b) are arranged in the plate so that the gas along the 609852/0673 Inner wall of the calming chamber (32) is initiated. 16. The device according to claim 14, characterized in that g e k e η n- z e i chnet that the openings (37; 37a, 37b) rest on the inner wall of the calming chamber (32). 17. The device according to claim 15, characterized in that that the ratio of the inner diameter of the calming chamber (32) to the inner diameter of the Rohrs (17) is between about 1.5 and 3.5. 18. The device according to claim 17, characterized in that that the ratio of the length of the calming chamber (32) to its inner diameter between 2 and 15. 19. The device according to claim 15, characterized in that that some of the openings (37a) are relatively large and at a small distance from each other are arranged, and that the other openings (37b) relatively small and at a greater distance from each other are arranged. 609852/0673