Electroflotation apparatus having an outlet pipe with a low turbulence orifice

Abstract

An electroflotation apparatus for removing impurities from waste water includes an electrolytic cell for treating the waste water and generating a flock containing the impurities and an outlet pipe having a linear central axis located co-axially with the electrolytic cell for passing the water and flock from the electrolytic cell to a separation area. The outlet pipe comprises a first end connected to the electrolytic cell and having a first diameter, and a second end through which the treated water and flock exit the outlet pipe, the second end having a second diameter. The outlet pipe reduces the turbulence of the treated water from the electrolytic cell before the treated water is passed to the separation area such that aggregation of the flock in the separation area is increased.

Claims

1. An electroflotation apparatus for removing impurities from waste water comprising: an electrolytic cell for treating the waste water and generating a flock containing the impurities; an outlet pipe having a linear central axis located co-axially with the electrolytic cell for passing the treated water and flock from the electrolytic cell to a separation area, the outlet pipe comprising: a first end connected to the electrolytic cell and having a first diameter; a second end through which the treated water and flock exit the outlet pipe, the second end having a second diameter; and a length extending between the first diameter and the second diameter; wherein the ratio of the second diameter to the first diameter is between 1.5:1 and 6:1; and wherein the ratio of the length to the first diameter is between 7:1 and 45:1; in order that the outlet pipe reduces the turbulence of the treated water from the electrolytic cell before the treated water is passed to the separation area such that aggregation of the flock in the separation area is increased.

2. The apparatus according to claim 1, wherein the ratio of the second diameter to the first diameter is between 2:1 and 5:1.

3. The apparatus according to claim 1, wherein the ratio of the length to the first diameter is between 10:1 and 30:1.

4. The apparatus according to claim 1, wherein the outlet pipe is a truncated cone or a truncated hyperbolic cone.

5. The apparatus according to claim 4, wherein the aperture of the truncated cone is less than 10.

6. The apparatus according to claim 4, wherein the aperture of the truncated cone is between 3 and 8.

7. The apparatus according to claim 1, wherein the separation area is a cylindrical tube extending above the outlet pipe.

8. The apparatus according to claim 7, wherein the cylindrical tube has a cylinder diameter and the ratio of the cylinder diameter to the second diameter is at least 1.5:1.

9. The apparatus according to claim 7, wherein the cylindrical tube has a cylinder diameter and the ratio of the cylinder diameter to the second diameter is between 2:1 and 30:1.

10. The apparatus according to claim 1, wherein the separation area is a pool or a basin located above the outlet pipe.

11. The apparatus according to claim 10, wherein a curved pipe extends between the outlet pipe and the pool or the basin for passing the treated water and flock from the outlet pipe to the pool or the basin.

12. The apparatus according to claim 10, further comprising a linear stabilizing zone between the curved pipe and the pool or the basin.

13. The apparatus according to claim 10, further comprising a conical outlet between the curved pipe and the pool or the basin.

14. The apparatus according to claim 10, wherein the ratio of the diameter of the curved pipe to the first diameter the outlet pipe is between 1.5:1 and 6:1.

15. The apparatus according to claim 10, wherein the ratio of the diameter of the curved pipe to the first diameter the outlet pipe is between 2:1 and 5:1.

16. The apparatus according to claim 1, wherein the first end of the outlet pipe further comprises a cylindrical portion connected to the electrolytic cell.

17. The apparatus according to claim 16, wherein the cylindrical portion is between about 30 mm to 70 mm long.

18. The apparatus according to claim 16, wherein the cylindrical portion is about 50 mm long.

19. The apparatus according to claim 1, wherein the ratio of the second diameter to the first diameter is between 2.5:1 and 4:1.

20. The apparatus according to claim 1, wherein the ratio of the length to the first diameter is between 14:1 and 22:1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects, features and advantages of which the invention is capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which

(2) FIG. 1 is a side view of an electroflotation apparatus according to one embodiment of the invention;

(3) FIG. 2 is a side view of a pool with a plurality of electroflotation apparatuses according to an embodiment of the invention;

(4) FIG. 3 is a side view of another pool with a plurality of electroflotation apparatuses according to an alternative embodiment of the invention;

(5) FIG. 4a is a side view of an electroflotation apparatus connected to the side of a pool according to an embodiment of the invention;

(6) FIG. 4b is a graph of bending radius (meters) versus pipe diameter (millimeters) of the curved pipe in FIG. 4a at flow rates of 500 litres/hour (dotted line . . . . . . . . ), 1000 litres/hour (dashed line - - - - - - - ), and 1500 litres/hour (solid line .sub.).

(7) FIG. 5 is a side view of two alternative outlet pipe designs for use with the electroflotation apparatus according to an embodiment of the invention; and

(8) FIG. 6 is a side view of yet another pool with a plurality of electroflotation apparatuses according to an alternative embodiment of the invention;

(9) FIG. 7 is a graph of water velocity (meters/second) versus position (meters) of the water along the linear central axis of the outlet pipe of an electroflotation apparatus according to one embodiment of the invention.

(10) FIGS. 1 to 4a, 5, and 6 are not drawn to scale.

DETAILED DESCRIPTION OF EMBODIMENTS

(11) The following description focuses on embodiments of the present invention applicable to an electroflotation apparatus. However, it will be appreciated that the invention is not limited to these applications but may be applied to other separation processes which involve generation of a solid and subsequent separation of the solid from a liquid.

(12) FIG. 1 illustrates an electroflotation apparatus 100. The apparatus broadly comprises an electrolytic cell 104, an outlet pipe 108, and a separation area in the form of a cylindrical tube 112. The outlet pipe 108 is connected to the electrolytic cell 104 and serves to pass the flock and treated water from the electrolytic cell 104 in a vertical direction to the separation area 112. A first end of the outlet pipe 108 has a cylindrical portion 116 that is connected to the top of the electrolytic cell 104. The flock and treated water enter the first end of the outlet pipe 108 and pass through the pipe before exiting a second end of the outlet pipe 108. The flock rises up to the surface of the water in cylindrical tube 112 where it is removed by a suitable mechanical mechanism (not shown). Sedimented material that is heavier than water sinks to the bottom and is removed from the apparatus 100 through sediment outlet 120. Treated water is removed from the apparatus 100 through water outlet 124 and may be either recycled to electrolytic cell 104 for further treatment or disposed of appropriately. More than one water outlet 124 may be included on the apparatus 100.

(13) The design of the outlet pipe 108 is an important feature of the invention. Outlet pipe 108 has a linear central axis (labeled A) located co-axially with the electrolytic call 104. The first and second ends of the outlet pipe 108 have first (d.sub.1) and second (d.sub.2) diameters respectively. A length (1) extends between the first (d.sub.1) and second (d.sub.2) diameters. The dimensions of the outlet pipe 108 are: d.sub.1: 50 mm d.sub.2: 155 mm d.sub.3: 400 mm l: 867 mm 2: 7

(14) The ratio of d.sub.2:d.sub.1 is 3.1:1, the ratio of 1:d.sub.1 is 17.3:1, and the ratio of d.sub.3:d.sub.2 is 2.6:1. The distance between the second end of the outlet pipe 108 and the surface of the water or flock (not shown) in the cylindrical tube 112 is 1190 mm.

(15) FIG. 2 illustrates a pool 204 with five electroflotation apparatuses 200 having their top portions located in the lower half of the pool 204 and their bottom portions located below the pool 204. Electroflotation apparatus 200 is similar in design and operation to electroflotation apparatus 100. Pool 204 provides a larger separation area than cylindrical tube 112 which allows for formation of a larger flock aggregate. There may be more or less than five electroflotation apparatuses 200 e.g. there may be one or more than one electroflotation apparatus 200, such as three to eight electroflotation apparatuses 200, expelling flock and treated water into the pool 200.

(16) FIG. 3 depicts a pool 304 with five electroflotation apparatuses 300 located below the pool 304. Electroflotation apparatus 300 is similar in design and operation to electroflotation apparatus 100. Like pool 204, pool 304 provides a larger separation area than cylindrical tube 112 and thus formation of a larger flock aggregate. Locating electroflotation apparatuses 300 below the pool 304 allows for an improved separation of the flock from the water at the surface of the pool 304. Again, there may be more or less than five electroflotation apparatuses 300 such as four or ten electroflotation apparatuses 300 all expelling flock and treated water into the pool 300.

(17) FIG. 4a shows an electroflotation apparatus 400 connected to the side of a pool 404 via a curved pipe 408, a linear stabilizing zone 412, and a conical outlet 416. The apparatus 400 has an electrolytic cell 401 and an outlet pipe 402. One end of the curved pipe 408 connects directly to the exit end (i.e. second end) of outlet pipe 402. In use the outlet pipe 402 reduces the turbulence of the treated water from the electrolytic cell 401 and creates a laminar flow of treated water that is preserved as the treated water passes from the outlet pipe 402 and through curved pipe 408 on the way to pool 404. The curved pipe 408 is made of a flexible material. The diameter and bending radius (R) of the curved pipe 408 are selected in order to preserve the laminar flow of the treated water. FIG. 4b illustrates the relationship between the bending radius (R) and the diameter of the curved pipe 408 at different flow rates as calculated by a computational fluid dynamics (CFD) analysis. Generally, as the pipe diameter increases the bending radius of the curved pipe 408 decreases for a given flow rate. Of course the diameter of the curved pipe 408 may be larger than 160 mm as shown on the horizontal axis of the graph in FIG. 4b. Although not illustrated, the diameter of the curved pipe 408 may be larger than the diameter of the exit of the outlet pipe 402. In that case one end of the curved pipe 408 extends over and/or below the exit of the outlet pipe 402 and is secured to the electrolytic cell 401 or below the exit of the outlet pipe 402 by any suitable method to prevent water leakage. Further, more than one electroflotation apparatus 400 and curved pipe 408 could be connected to different parts of the same pool 404. The linear zone 412 helps to preserve the laminar flow and avoid separation of the water and flock in the conical outlet 416. The linear zone 416 could be any suitable length. For instance, the length of linear zone 412 may be about four times the diameter of the curved pipe 408. The conical outlet 416 is connected to the pool 404 and helps to preserve the laminar flow of the treated water should the flow stagnate after entering the pool 404. However, it is not necessary to include both the linear stabilizing zone 412 and conical outlet 416. In one embodiment either the linear stabilizing zone 412 or the conical outlet 416 may be present. Alternatively, neither the linear stabilizing zone 412 nor the conical outlet 416 are present. In the latter case one end of the curved pipe 408 is connected directly to the outlet pipe 402 while the other end of the curved pipe 408 is connected directly to the pool 404. Moreover, the conical outlet 416, linear zone 412, or the curved pipe 408 need not be connected to the side of the pool 404 as shown in FIG. 4a. For example, the conical outlet 416, linear zone 412, or the curved pipe 408 may be connected to the bottom of the pool 404 in order that the treated water enters the pool 404 from underneath. Alternatively, the conical outlet 416, linear zone 412, or the curved pipe 408 could be suspended over the top of pool 404 in order that the treated water enters the pool 404 from above.

(18) Whether or not a pool 204, 304, 404 is utilized in place of cylindrical tube 112 as a separation area will depend on the volume of water to be treated. The relative location of electroflotation apparatuses 200, 300, 400 to the pools 204, 304, 404 will depend on the site space available and other engineering controls.

(19) FIG. 5 illustrates two alternative outlet pipe designs 508, 509 for use with the electroflotation apparatuses 100, 200, 300, and 400. Outlet pipe 508 is a truncated parabolic cone. Outlet pipe 509 is a truncated hyperbolic cone. The outlet pipe 509 is preferred. Thus in some embodiments the outlet pipe of the electroflotation apparatus is a truncated hyperbolic cone.

(20) The velocity of the water in and immediately external of the outlet pipe 108 of the electroflotation apparatus 100 was evaluated in a computational fluid dynamics (CFD) analysis. CFD is a branch of fluid mechanics that uses numerical analysis and algorithms to solve and analyze problems that involve fluid flows. The CFD analysis assumed a water temperature of 40 C. The turbulence model was realisable k- (two-layer) and a biphasic model (VOF) was used to model the flocking surface. Velocity is one aspect affecting the turbulence of the water.

(21) FIG. 6 illustrates a pool 604 with five electroflotation apparatuses 600 located upside down in the pool 604 so that their outlet pipes and top portions of their electrolytic cells are located in the upper half of the pool 604. Otherwise electroflotation apparatus 600 is similar in design to electroflotation apparatus 100. During operation the water will move downwards through the electrolytic cells as it is treated prior to exiting the outlet pipe into the pool 604. Like pools 204 and 304, pool 604 provides a larger separation area than cylindrical tube 112 which allows for formation of a relatively larger flock aggregate. There may be more or less than five electroflotation apparatuses 600 e.g. there may be one or more than one electroflotation apparatus 600, such as three to eight electroflotation apparatuses 600, expelling flock and treated water into the pool 600. The expelled flock floats to the surface of the pool 604 around the apparatuses 600.

(22) Use of a pool 204, 304, 404, or 604 allows for a simpler and less expensive construction as the weight of the treated water from one or more electroflotation apparatuses 200, 300, 400, 600 is carried by a single large pool.

(23) FIG. 7 shows a graph of the CFD results for outlet pipe 108 in comparison to a straight cylindrical pipe i.e. a pipe with a constant diameter (d.sub.1=d.sub.2=50 mm) and having the same length (l) as outlet pipe 108. Using the straight cylindrical pipe is known to result in disintegration of flock above the electrolytic cell.

(24) The key to FIG. 7 is:

(25) D=first end of the outlet pipe 108/straight cylinder pipe.

(26) E=second end of the outlet pipe 108/straight cylinder pipe.

(27) F=water surface in the separation area.

(28) P=straight cylinder pipe with a water throughput of 300 liters per hour.

(29) Q=straight cylinder pipe with a water throughput of 1000 liters per hour.

(30) R=outlet pipe 108 with a water throughput of 1000 liters per hour.

(31) S=outlet pipe 108 with a water throughput of 3500 liters per hour.

(32) FIG. 7 shows that the water has a much lower velocity while passing through, and just after exiting, outlet pipe 108 compared to the straight cylindrical pipe at the same water throughput (1000 liters per hour). Even at the higher water throughputs of 1000 and 3500 liters per hour, the outlet pipe 108 results in exiting water having a velocity similar to, or less than, the straight cylinder pipe at 300 liters per hour. The electroflotation apparatuses 100, 200, 300, 400 are expected to be capable of treating waste water at flow rates of up to 4000 l/h while simultaneously facilitating aggregation of flock formed during the treatment.

(33) The beneficial effect of the outlet pipe 108 was demonstrated by measuring the quality of treated water obtained from passage of municipal waste water through an electroflotation apparatus 100 fitted with outlet pipe 108 and a straight cylindrical pipe i.e. a pipe with a constant diameter (d.sub.1=d.sub.2=50 mm) and having the same length (1) as outlet pipe 108. All other experimental conditions were constant. The quality was determined by measuring the turbidity of the treated water using a nephelometer. A person skilled in the art will understand that turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye. The measurement of turbidity is a key test of water quality. The results are shown in Table 1.

(34) TABLE-US-00001 TABLE 1 Turbidity measurement of outgoing purified water from municipal waste water. Turbidity (NTU) Turbidity (NTU) of water after treatment with of water after treatment with Flow electroflotation apparatus 100 fitted electroflotation apparatus 100 (l/h) with a straight cylinder outlet pipe and outlet pipe 108 300 33.5 14 600 54.9 18 900 61.4 19.9 1100 41.6 22.1 1200 63.3 29.8 1500 59 35.4 1800 63.6 34.6 1900 56.5 34.1 2000 67.2 44.5 2100 82.9 42.6 NTU = Nephelometric Turbidity Units.

(35) As can be seen in Table 1, the turbidity of the treated water was significantly less (in fact often 2- to 3-fold less at most flow rates) when conical outlet pipe 108 was used instead of a straight cylinder pipe in the electroflotation apparatus 100. This shows the quality of the treated water is much higher after passage through an electroflotation apparatus 100 fitted with outlet pipe 108 rather than a straight cylindrical pipe.

(36) Although the present invention has been described above with reference to specific illustrative embodiments, it is not intended to be limited to the specific form set forth herein. Any combination of the above mentioned embodiments should be appreciated as being within the scope of the invention. Rather, the invention is limited only by the accompanying claims and other embodiments than the specific above are equally possible within the scope of these appended claims.

(37) In the claims, the term comprises/comprising does not exclude the presence of other species or steps. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. The terms a, an, first, second etc. do not preclude a plurality.