CYCLONE WITH FLOW RATE CONTROL

Abstract: A cyclone (10) includes diametrically opposed inlets (14) and a lower outlet (22) for denser parts of the flow. Less dense parts of the flow pass upwardly through a take off tube (26). The flow rate to the inlets is varied periodically to increase the efficiency as compared to the use of a steady flow rate.

Description: CYCLONE WITH FLOW RATE CONTROL The present invention relates to a cyclone apparatus and to a method of operating cyclone apparatus. Cyclones are well known and are used for separating, for instance, particles from a liquid. However, their use could be more widespread if their efficiency were greater, particularly with small particles and/or when density differences are small. It is an object of the present invention to attempt to overcome at least some of the above or other disadvantages of cyclones. According to one aspect of the present invention cyclone apparatus includes inlet means arranged to receive flow including at least two different density portions and at least two outlets arranged to provide separate flows having different relative amounts of the different density portions than that arranged to be received at the inlet, and flow supply means arranged, in use, to supply flow to the inlet means and control means arranged, in use, to repeatedly vary the flow rate supplied to the inlet means. The control means may be arranged to vary the flow rate substantially continually either when increasing the flow rate or when reducing the flow rate or both. The control means may be arranged to alter the flow rate at a generally linear rate either when increasing or when decreasing the flow rate or both. The control means may be arranged to take longer to alter the flow rate in one direction as compared to the time taken to alter the flow rate in the other direction. For instance, the control means may be arranged to take longer to decrease the flow rate than it does to increase the flow rate. The control means may be arranged to provide a time taken to increase the flow rate as compared to a time taken to decrease the flow rate greater than or equal to 1:1.2 or greater than or equal to 1:1.5 or greater than or equal to 1:2. The control means may be arranged to vary the flow rate over a combined consecutive period comprising first reducing the flow rate and then increasing the flow rate of less than 20s or less than 10s or less than 5s or less than 2s or less than Is. Sequential combined periods may be of substantially the same duration. The supply means comprise a pump such as a centrifugal pump. Alternatively or additionally a variable restrictor may be used in the supply means. The flow rate may be arranged to be varied beyond the mean flow rate by more than 10 per cent or less than 50 per cent or less than 40 per cent or less than 30 per cent or in the region of 15 per cent either in relation to a flow rate that is greater than the mean flow rate or in a relation to a flow rate that is less than the mean flow rate or both. The flow rate may be arranged to vary beyond the mean flow rate by a greater amount when the flow rate is less. The cyclone may include collection means arranged to receive flow from at least one of the outlets. The collection means may be arranged to operate under a pressure greater than or less than atmospheric pressure. The collection means may be arranged to be emptied periodically. The collection means may include a bleed. The collection means may be arranged to include a fluid comprising one of the fluids that is arranged to be supplied to the inlet with that fluid being displaced from the collection means as a flow of a different density fluid enters the collection means. The volume of the cyclone and/or the orientation of the cyclone may vary. According to a further aspect of the present invention a method of operating a cyclone comprises supplying flow including at least two different density portions to at least one inlet of the cyclone and effecting at least a partial separation of the different density portions with the cyclone and repeatedly varying the flow rate of the flow supplied to the cyclone. The method may comprise varying the flow rate substantially continually when increasing the flow rate or when reducing the flow rate or both. The method may comprise altering the flow rate at a generally linear rate when increasing or when decreasing the flow rate or both. The method may comprise altering the flow rate in one direction over a different duration of time from that in which the flow rate is altered in the opposite direction. For instance, the method may comprise increasing the flow rate for a shorter duration than that which the flow rate is decreased by. The method may comprise varying the combined consecutive periods comprising first decreasing the flow rate and then increasing the flow rate for a duration of less than 20 or less than 10 or less than 5 or less than 2 seconds or less than 1 second. The method may comprise repeatedly varying the flow rates over combined sequential periods which periods are of substantially the same duration. The method may comprise increasing the variance as a percentage of the mean flow rate as the mean flow rate decreases . The present invention includes any combination of the herein referred to features or limitations. The present invention may be carried into practice in various ways but one embodiment will now be described, by way of example, and with reference to the accompanying drawings, in which :- Figure 1 is a schematic perspective view of a cyclone; Figure 2 is a graph showing the efficiency of separation achieved by the cyclone shown in Figure 1 under certain operating conditions; Figure 3 is a graph illustrating the inlet flow rate; Figure 4 is a graph showing the efficiency of separation for various flow rates; and Figure 5 is a graph showing efficiency separation under constant flow rates for variations in the time that a portion of fluid spends in the vortex divided by the time for a fluctuation in the flow cycle. As shown in Figure 1, the cyclone 10 includes a cone 12 that tapers inwardly and downwardly. The cone includes two diametrically opposed inlets 14 that supply flow tangentially in the direction of arrow 16 within the cyclone. That flow produces a vortex within the cyclone such that fluid flows downwardly in the directions of arrows 18 in the region of the outer portion of the cyclone and upwardly in the direction of arrow 20 in a central region of the cyclone. Whilst the cyclone is shown in the vertical position with flow being downwards, the cyclone may be located in any orientation. The cyclone may be of any size. The pressure gradient in the direction of arrows 18 is considerably smaller than the radial pressure gradient from the outside of the cyclone going inwardly. The vortex created may, for instance, cause fluid to circulate in the region of 10,000 revs per minute and the fluid may experience a force of, for instance, 1000 times gravity in the outwards direction. The cyclones are arranged to separate a denser part of the fluid from a less dense part of the flow. The denser part of the flow will be concentrated towards the outside of the cyclone and will consequently find itself in the region of the lower outlet 22 of the cyclone from which it will pass downwardly into the collection chamber 24. The less dense part of the flow passes upwardly in the direction as shown in arrow 20 and then outwardly through a take off tube 26. The part of the flow that is collected in the chamber 24 can be emptied periodically, for instance by opening the valve 28, for instance. Alternatively, the part of the flow in the chamber 24 could be continuously drained. The chamber 24 is sealed around the lower portion of the cyclone such that the outlet 22 of the cyclone projects inwardly into the chamber and such that a pressure is able to be created at greater or less than atmospheric pressure within the chamber 24. Liquid such as water may be present in the chamber 24 with the denser flow from the cyclone entering the chamber and displacing that liquid, for instance, where the chamber is sealed, by displacing that liquid through a small bleed 30. The flow supplied to the inlets 14 may comprise two liquids having different densities which are required to be separated, or liquids incorporating particles or a liquid and a gas or a gas with particles or any combination thereof. The cyclone can, for instance, be used to separate brine from oil or gas or for use with an etchant for silicone wafers (in which it is required to get small gas bubbles out of the liquid etchant) or for a fruit juice where it is desired to get the oxygen level in the juice reduced significantly in order to increase the shelf life or for petrol where it is required to get gas out or for liquids including very fine solids such as in the biological and pharmaceutical industries (where the small particles are required to be removed) or in the brewery industry where yeast is required to be removed from the brew. Liquid is supplied to the inlets 14 from a pump 32. Referring now to Figure 2, a graph is shown illustrating the efficiency of particle removal on the Y axis with the inlet flow rate on the X axis. Water including urea compound particles were used in the test, the urea having a mean diameter of 45 micron. The temperature of the mixture was 21 °C. The internal diameter of the take off tube 26 was 12 mm and it projected a distance of 50 mm into the top of the cyclone. The diameter of the outlet 22 of the cyclone was 10 mm. The cyclone used was a hydrocyclone which was PERSPEX (Registered Trade Mark) coded HC-12-1. The swirl number was 16. The chamber 24 was effectively a sealed chamber. No free gas was present. The four diamond plots 34 show how the efficiency was increased from approximately 37, then to 45, then to 60 and then to 71 as the flow rate increased from 20 to 40 to 60 and then to 80 litres per minute. The five square shaped plots 36 show the marked increase in efficiency when a periodically varied flow is provided to the inlets 14. This varied flow can be achieved by using a control 38 to act on the motor. The varied flow applied for the square plots, which may be sinusoidal was for a flow that decreased its rate for a period of 10 seconds before increasing its flow rate for a period of 10 seconds with the maximum and minimum flow rates being approximately plus or minus 15% of the average flow. The inlet flow rates shown on the X axis represent the mean flow. It can be seen that, at 20 litres per minute, the flow rate when a slowly varying flow is used as compared to when no flow rate variation is provided increases the efficiency from 37 to 48 per cent. This increase in efficiency as compared to a steady flow rate is more marked as the flow rate increases . The triangular plots 40 were made for a periodically varied flow rate that accelerated the rate of flow for a period of one second before decelerating the rate for a period of one second. Again the maximum and minimum flow rates varied by approximately 15 per cent from the mean flow rate. Even at a relatively low flow rate of 20 litres per minute an efficiency of 86 per cent was achieved with that efficiency approaching 100% when the flow rate was 80 litres per minute. Figure 3 shows a plot of the flow rates from which it can be seen that the variations in the flow rate that increased its flow rate and decreased its flow rate for a combined period of 2.5 seconds was not uniform for the increasing and decreasing periods. The pressure rise was rapid but brief with the flow rate increasing rapidly for a short period of 1 second or less and then decreasing more slowly over 1.25 seconds or more. The operating conditions were as described above. When the flow rate was averaging over 20 litres per minute, as shown by the trace 42, the flow rate increased from 20 litres per minute to 33 litres per minute in a period of less than one second with the flow rate then decreasing from 33 to 20 litres per minute in a period of well over one second. Lines 44, 46 and 48 represent flows in excess of 30, 40 and 60 litres per minute respectively. It can be seen that as the flow rate increases, although the variation between the maximum and minimum flow rates remains at approximately 13 or 14 litres per minute variation, the overall percentage variation from the mean flow rates decreases as the flow rate increases. As shown in the graph in Figure 4, particles having a mean cross-sectional dimension of 45μm at a concentration of 0.09% in water were fed to the vortex. The particles were plastic and are considered equivalent to sand particles having a mean cross-sectional dimension of 35μm. The x-axis 52 plots the efficiency of separation and the y-axis 52 plots the efficiency of separation. The line 54 plots a traditional vortex efficiency separation where there is no fluctuation in flow. It can be seen that this is less efficient than the other lines 56, 58 and 60 that undergo a flow variation as described above. The difference in the lines 56, 58 and 60 relate to the period that a particular point of the flow remains in the vortex when divided by the time period comprising a cycle of: greater pulse of supply to lesser pulse of supply to greater pulse of supply. For line 56 that figure is 0.1, for 58 the figure is 0.2 and for line 60 the figure is 0.3. This figure is known as t/T. Figure 5 is a graph showing the t/T figure on the x-axis and the efficiency of separation on the y-axis. The same particles and concentrations were used as described in relation to figure 4. Line 62 shows the efficiency increasing for a flow rate of 20 L/min as the t/T factor increased to 0.3. Lines 64, 66 and 67 show the efficiency increasing to a greater degree as the t/T factor increases for respective flow rates of 30, 40 and 50 L. in. It is thought that the additional pressure gradients consequent on the cycle of flow variation act in a non- linear manner to change the flow pattern within the cyclone to produce the improvement in separation. The control 38 and the pump 32 included a solid state power supply that controls the pump 32. The pump used was a centrifugal pump. If the increase in flow rate was to take 20 seconds with the decrease then taking 20 seconds then it is thought that not much benefit would be derived from varying the flow rate. It appears from the tests done so far that the flow rates where the combined time of the increase and decrease in the flow rate is less than 30 seconds or less than 20 seconds or less than 10 seconds or less than 5 seconds or less than 2 seconds or in the region of one second are likely to provide increasingly improved results. In an alternative embodiment a variable restrictor may be included downstream of the pump to produce the variation in flow rate. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment (s) . The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims: CLAIMS 1. Cyclone apparatus including inlet means arranged to receive flow including at least two different density portions and at least two outlets arranged to provide separate flows having different relative amounts of the different density portions than that arranged to be received at the inlet, and flow supply means arranged, in use, to supply flow to the inlet means and control means arranged, in use, to repeatedly vary the flow rate supplied to the inlet means. 2. Apparatus as claimed in Claim 1 in which the control means is arranged to vary the flow rate substantially continually when increasing the flow rate. 3. Apparatus as claimed in- Claim 1 or 2 in which the control means is arranged to vary the flow rate substantially continually when reducing the flow rate. . Apparatus as claimed in any preceding claim in which the control means are arranged to alter the flow rate at a generally linear rate when increasing the flow rate. 5. Apparatus as claimed in any preceding claim in which the control means are arranged to alter the flow rate at a generally linear rate when decreasing the flow rate. 6. Apparatus as claimed in any preceding claim in which the control means are arranged to take longer to alter the flow rate in one direction as compared to the time taken to alter the flow rate in the other direction. 7. Apparatus as claimed in Claim 6 in which the control means are arranged to take longer to decrease the flow rate than to increase the flow rate. " 8. Apparatus as claimed in any preceding claim in which the control means are arranged to vary the flow rate over a combined consecutive period comprising first reducing the flow rate and then increasing the flow rate of less than 20 seconds. 9. Apparatus as claimed in any preceding claim in which the average time that a portion of the flow takes to travel from the inlet means to the outlet means divided by the time for a complete fluctuation cycle is arranged to be equal to or greater than 0.05. 10. Apparatus as claimed in Claim 8 or 9 in which sequential combined periods are of substantially the same duration. 11. Apparatus as claimed in any preceding claim in which the supply means comprises a pump. 12. Apparatus as claimed in any preceding claim in which a variable restrictor is used in the supply means. 13. Apparatus as claimed in any preceding claim in which the flow rate is arranged to be varied beyond the mean flow rate by more than 5%. 14. Apparatus as claimed in any preceding claim in which the flow rate is arranged to be varied beyond the mean flow rate by less than 50%. 15. Apparatus as claimed in any preceding claim in which the flow rate is arranged to vary beyond the mean flow rate by a greater amount when the flow rate is less. 16. Apparatus as claimed in any preceding claim in which the cyclone includes collection means arranged to receive flow from at least one of the outlets. 17. Apparatus as claimed in Claim 16 in which the collection means are arranged to operate under a pressure greater than atmospheric pressure. 18. Apparatus as claimed in Claim 16 in which the collection means are arranged to operate under a pressure less than atmospheric pressure. 19. Apparatus as claimed in any of Claims 16 to 18 in which the collection means are arranged to be emptied periodically. 20. Apparatus as claimed in Claim 19 in which the collection means includes a bleed. 21. Apparatus as claimed in any of Claims 16 to 20 in which the collection means are arranged to include a fluid comprising one of the fluids that is arranged to be supplied to the inlet with that fluid being displaced from the collection means as a flow of a different density fluid enters the collection means. 22. Cyclone apparatus substantially as herein described with reference to, and as shown in any of the accompanying drawings or diagrams. 23. A method of operating a cyclone comprising supplying fluid including at least two different density portions to at least one inlet of the cyclone and effecting at least a partial separation of the different density portions with the cyclone and repeatedly varying the flow rate of the flow supplied to the cyclone. 24. A method as claimed in Claim 23 comprising varying the flow rate substantially continually when increasing the flow rate. 25. A method as claimed in Claim 23 or 24 comprising varying the flow rate substantially continually when reducing the flow rate. 26. A method as claimed in any of Claims 23 to 25 comprising altering the flow rate at a generally linear rate. 27. A method as claimed in any of Claims 23 to 26 comprising altering the flow rate in one direction over a different duration of time from that in which the flow rate is altered in the opposite direction. 28. A method as claimed in Claim 27 comprising increasing the flow rate for a shorter duration than that which the flow rate is decreased bv. 29. A method as claimed in any of Claims 23 to 28 comprising varying the combined consecutive periods comprising first decreasing the flow rate and then increasing the flow rate for a duration of less than 20 seconds . 30. A method as claimed in any of claims 23 to 29 comprising causing the average time that a portion of the flow resides in the cyclone, when divided by the time for a complete fluctuation cycle to be equal to or greater than 0.05. 31. A method as claimed in claim 30 comprising causing the efficiency to increase as the average time that a portion of the flow resides in the cyclone when divided by the time for a complete fluctuation increases . 32. A method as claimed in any of claims 23 to 31 in which the efficiency of separation is caused to increase as the flow rate increases. 33. A method as claimed in Claim 29 or any of claims 30 to 32 when dependent on claim 29 comprising repeatedly varying the flow rates over combined sequential periods which periods are of substantially the same duration. 34. A method as claimed in any of Claims 23 to 33 comprising increasing the variance as a percentage of the mean flow rate as the mean flow rate decreases . 35. A method of operating a cyclone substantially as herein described and with reference to any of the accompanying drawings or diagrams . 6. A method of operating a cyclone when using apparatus s claimed in any of Claims 1 to 22.

Inventors: FAGHMOUS ALI, THEW MARTIN THOMAS, FAGHMOUS, ALI, THEW, MARTIN, THOMAS
Applicants: FAGHMOUS ALI, THEW MARTIN THOMAS, UNIV BRADFORD, FAGHMOUS, ALI, THEW, MARTIN, THOMAS, UNIVERSITY OF BRADFORD
Application year: 2001
Main classification: B04C11
IPC codes: B04C11