System and method for determining concentration

Abstract

An apparatus to determine the concentration of a target component in a mixture, the apparatus including at least one acoustic transducer located within the mixture, a controller generating a signal for the at least one acoustic transducer that's generating an acoustic signal in the mixture and transmitting same toward the target component within the mixture, wherein the acoustic signal is generated with a known power level, and a processor for measuring change in the power level of the at least one acoustic transducer as the acoustic signal is transmitted through the mixture, wherein the magnitude of the change in signal power determines the concentration of the target component in the mixture.

Claims

1. A control system configured to dynamically determine the concentration of a target component within a mixture contained within a flotation vessel, the system including an apparatus comprising: at least one acoustic transducer located within the mixture; a controller for generating an acoustic signal for the at least one transducer operating at a fixed voltage and frequency and transmitting the acoustic signal for transmission towards the target component within the mixture, wherein the acoustic signal is generated at a known and fixed power level, and a processor for measuring a change in the power level of the at least one acoustic transducer that is required to maintain the at least one acoustic transducer at the fixed voltage and frequency as the acoustic signal is transmitted through the mixture wherein the magnitude of the change in power level of the at one acoustic transducer determines the concentration of the target component in the mixture; wherein the apparatus generates a control signal representative of the concentration of the target component, said control signal used to control one or more additional controllers to control either one or both of: a flow rate of a liquid into the flotation vessel; and a rate of aeration of the mixture.

2. A system according to claim 1 including two or more transducers located in a linear array.

3. A system according to claim 1 including three transducers located in a linear array.

4. A system according to claim 1 where the at least one array includes a plurality of arrays connectable with each other to form an extended array.

5. A system according to claim 1 wherein when two or more transducers are located in the mixture, the measured power level is the average power level of the two or more transducers.

6. A system according to claim 1 wherein the controller is programmed to control two or more transducers to generate the acoustic signal, wherein the power of the two or more acoustic signals is the calculated average power of the two or more acoustic signals.

7. A system according to claim 1 wherein the controller is programmed to generate the acoustic signal for the at least one transducer upon input of an external command which generates the acoustic signal for transmission into the mixture.

8. A system according to claim 1 wherein the controller is programmed to control the acoustic signal to generate a periodic acoustic signal.

9. A system according to claim 1 wherein the controller is programmed to control the acoustic signal to generate a continuous acoustic signal.

10. A system according to claim 1 wherein the apparatus utilizes high powered, low to medium frequency transducers.

11. A system according to claim 1 wherein the target component is suspended solids and the apparatus is configured to measure suspended solids concentration ranging from about 20% to about 65% (w/v).

12. A system according to claim 11 wherein a substantially linear relationship is observed between the suspended solids concentration and the measured power level.

13. A system according to claim 1, wherein the apparatus is used to determine a suspended solids concentration within the mixture, wherein the change in power level is substantially unaffected by the presence of a gaseous medium within the mixture.

14. A system according to claim 1 wherein the controller is adapted to control each transducer to operate in a cleaning mode for generating the acoustic signal which forms cavitation in the mixture.

15. A method for dynamically determining the concentration of a target component in a mixture contained within a flotation vessel, the method comprising the steps of: generating an acoustic signal for at least one acoustic transducer operating at a fixed voltage and frequency; measuring change in the power level of the at least one acoustic transducer that is required to maintain the at least one acoustic transducer at the fixed voltage and frequency as the acoustic signal is transmitted through the mixture; wherein the detection of a change in the power level of at least one acoustic transducer is indicative of the presence of the target component in the mixture; and wherein the magnitude of change in the power level of the at least one acoustic transducer determines the concentration of the target component in the mixture; wherein the method further includes generating a control signal representative of the concentration of the target component, and using said control signal to control one or more additional controllers to control either one or both of: a flow rate of a liquid into the flotation vessel; and a rate of aeration of the mixture.

16. A method according to claim 15, wherein the flotation vessel includes a bottom-most liquid layer, an intermediate froth layer and a top-most gaseous layer, and wherein the one or more transducers are submerged within the bottom-most liquid layer.

17. A method according to claim 15, wherein the mixture is a slurry or pulp containing at least one mineral.

18. A method according to claim 15, wherein the change in power level is substantially unaffected by the presence of gaseous medium within the mixture.

19. A method according to claim 15, wherein a substantially linear relationship is observed between the concentration of the target component in the mixture and the measured power level.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of a vessel and system in accordance with an embodiment of the present invention;

(2) FIG. 2 is a partially cut away perspective view of a flotation tank with transducer array in accordance with an embodiment of the invention;

(3) FIG. 3 is a perspective view of an alternative embodiment of an array having three (3) transducers in a linear configuration:

(4) FIG. 4 is a perspective view of a single array with eight (8) transducers in an array according to an alternative embodiment of the invention;

(5) FIG. 5 is a perspective view of an extended array of a plurality of arrays, in accordance with yet another embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION

(6) The system according to any embodiment of the invention and as shown in FIG. 1 will now be described. This figure shows flotation tank 32 with liquid layer 36, a froth layer 38 and an air layer 40 with interfaces 37, 39 therebetween. Liquid layer 36 also has solids 41 suspended therethrough.

(7) As is further shown in FIG. 1, extended array 30 is submerged within liquid layer 36 comprising suspended solids 41. FIG. 1 further shows controller 42 for controlling the operation of extended array 30. Also shown is monitoring apparatus 44 (which in embodiments may also include the processor for processing the power output from the transducer array). It will be understood that the monitor may be geographically proximal to the flotation tank, or remote.

(8) With reference to FIG. 2, further features of flotation tank 32 is shown, this time without the controller, processor or monitoring apparatus shown in FIG. 1. As shown in FIG. 2, tank 32 also has an aerator 110, including a motor 112, a shaft 114 and blades 116. Tank 32 also includes a submerged array of an extended array 30B of transducers 12 within liquid layer 36 which are used to conduct online sampling of the suspended solids 41 concentration within liquid layer 36. In this embodiment, extended array 30B includes two component arrays 10 each with eight transducers 12 arranged in a single line to form an extended array of a linear configuration. The array 30B is substantially vertically mounted in tank 32 and therefore spans the height of the liquid layer 36 so as to obtain a measurement of the suspended solids substantially throughout the entire liquid layer 36.

(9) Whilst the extended array 30B shown in FIG. 2 has 16 transducers in total (across the two array components 10 each with eight transducers 12 within the extended array 30B), it will be appreciated that any number of transducers may be adopted in the system of the invention ranging from a system with a single transducer to a system having an array of about 80 transducers for very large tanks where a total solids concentration profile of the entire flotation vessel is required.

(10) In an embodiment, the system includes three transducers 12 located in an array 10A as shown in FIG. 3. In certain embodiments, the measured power output of the transducers is the calculated average of the power output across the plurality of transducers and in the embodiment shown in FIG. 3, the measured power output is the average power output across all three transducers 12. FIG. 3 also shows transducers 12 arranged in housing 14.

(11) In another embodiment shown in FIG. 4, the system includes transducer array 10B including eight transducers 12, mounted in the transducer array housing 14B in a single line, and closely spaced (or abutting each other). The transducer array 10B may form an array component in an extended array 30B (see FIG. 2).

(12) FIG. 5 shows an embodiment wherein four transducer arrays 10B form transducer array components, and are connected together so as to form an extended array 30C. The array components 10B are connected together via bolt holes 22 and connecting bolts 24. However, it will be understood that there may be other means of connecting array components 10B together so as to form the extended array 30C. A bus (not shown) may data connect the array components together, so that data is transmitted between the arrays, the transducers of the arrays, the controller and the processor. However, an efficient design may include only one controller and one processor for the system and method of the invention.

(13) In embodiments, the aerator can be controlled by the system processor so as to set the speed of rotation, and thus the amount of aeration. This can control the amount of froth production and alter the suspended solids concentration within the slurry. In some other types of flotation tank, the aeration is provided via aeration tubes in which air is pumped into the liquid. These aeration tubes can also be controlled by the processor to regulate aeration in the tank.

(14) Referring once again to FIG. 1, froth layer 38 containing the mineral concentrate may be periodically removed from tank 32 through pipe 33 into a collection vessel such as a launder (not shown) where further processing of the mineral concentrate occurs. In embodiments, system 1, through the system processor, may also control the rate at which the mineral concentrate is removed from tank 32.

(15) The feed rate of water and/or mineral material to be processed into tank 32 may also be controlled by the system processor. It will be appreciated that in order to achieve optimum process efficiency and operation, the suspended solids concentration within a flotation tank is typically maintained at 30-40% (w/v) suspended solids. The ability to conduct continuous online sampling of the suspended solids concentration within the tank therefore allows continuous and rapid adjustment of the process conditions. For example, the feed rate of water and/or mineral material into the tank may be continuously adjusted in response to the online sample readings of the suspended solids concentration using system 1, so as to maintain the suspended solids concentration within tank 32 within an acceptable concentration range.

(16) In embodiments, transducers may be Commercial Off-The-Shelf (COTS) type products. Often such transducers have their own outer protection and/or casing, which may be suitable for mining applications. The system and method may provide additional protection by using an outer casing or housing, which also provides protection for any electronics, along with providing extra protection for the transducers. In some embodiments, spacers in the outer casing/housing may be filled with a substance, such as an epoxy resin, for reinforcement of the casing/housing in the high pressure conditions of the flotation cell/flotation tank.

(17) Where it is desired to provide an extended array, the array components (transducer arrays) are connected with each other so as to form an extended longitudinal array. In such an embodiment, there may be provided a bus connection between the array components (array modules). It will be understood that any such bus connections, along with all other electronic components situated in the flotation cell/flotation tank, must be protected against the conditions produced by substances in the flotation cell/flotation tank, and so must be enclosed in the array components, and must also be enclosed when the array components are connected together to form the extended array.

(18) In an embodiment, the system may include a housing for the array. The housing may be made from glass-reinforced propylene or ABS. It has been found that propylene assists in avoiding scale build-up, and is therefore easier for cleaning of the housing.

(19) In an embodiment, the transducer array, or extended array, may be pulsed so that all transducers in the array produce cavitation for self-cleaning at the same time. This facility may be useful for inter-operation cleaning purposes.

(20) It will be appreciated that improved efficiencies will be gained through the ability to continuously adjust and control the aeration rate in response to the measured concentration of suspended solids in a mineral flotation process. Such automatic and continuous control avoids overdosing with reagent which not only improves the froth structure, but also improves process economics.

(21) The system and method according to embodiments of the invention will now be further described with reference to the following experimental tests conducted to demonstrate the principle of operation of the system and method according to embodiments of the invention.

(22) Experimental Test 1—Measurement of Change in Acoustic Reflective Impedance (Transducer Power Output) with Change in Surface Area of Perforated Plates Simulating Varying Target Densities

(23) Test 1(a)—Small Scale Test in the Absence of Medium Aeration

(24) In order to demonstrate the change in acoustic impedance (transducer power output) with varying target densities, perforated plates of varying hole sizes (and hence varying surface areas) were adopted and placed in front of the operating diaphragm of transducers located within a transducer array immersed in an aqueous medium.

(25) It will be appreciated that the perforated plates with varying hole sizes were designed to simulate varying target densities as would be observed in situations where the system of the invention is used to determine the concentration (i.e., density) of solids suspended within an aqueous medium. A practical example of where such a system would find use is in froth flotation systems that are generally used in minerals processing, wherein the slurry is a dynamic system in which the suspended solids concentration (i.e., solids density) changes with time.

(26) The test was undertaken in a tank of dimensions H: 600 cm×W: 500 cm×D: 400 cm which was filled with water and fitted with a linear array of three transducers (as shown in, for example, FIG. 2). No aeration of the tank was performed.

(27) The acoustic transducers were calibrated to 90 W in clean water by adjusting the drive voltage level. Each test run was performed with a different perforated plate having a specific hole-size (and hence surface area/simulated solid density). Each plate was immersed in water and placed in front of the operating diaphragm of the acoustic transducers. In each test run, it was ensured that the perforated plate completely covered the operating diaphragm of each transducer.

(28) The following results were observed:

(29) TABLE-US-00001 % Surface area Measured change in Plate no. Closed Open average Power (W) 1 23 77 116 2 42 58 133 3 60 40 142 4 80 20 160

(30) As is demonstrated by the above results, an increase in transducer power output is observed as the % surface area of the perforated plate (i.e., simulated solids density) increases.

(31) Test 1(b)—Small Scale Test in the Presence of Medium Aeration

(32) Test 1(a) was repeated, this time, in the presence of aeration in order to determine the effect, if any, of the presence of gas bubbles on the power output level of the transducers with varying solids density. The aeration flow rate was initially lowered to the lowest possible flowrate and then progressively raised to the maximum flowrate.

(33) Each perforated plate (1 to 4—see Test 1(a)) was tested at each aeration level and similar results were obtained to those obtained in Test 1(a) with a ±1% change in average power output (W) observed from minimum aeration flowrate to maximum aeration flowrate for all plates 1 to 4. This demonstrates that the system and method of the present invention is independent of, or unaffected by, the presence of gas bubbles during aeration of the medium.

(34) Experimental Test 2—Measurement of Change in Acoustic Reflective Impedance (Transducer Power Output) with Change in Suspended Solids Density (Soil) within an Aqueous Medium

(35) The test was undertaken in an aeration tank of dimensions 3 m high and 1.5 m diameter which was filled with water and fitted with a linear array of three transducers. Medium aeration of the tank was performed. Aeration was performed using sintered filters that produced bubbles concentration of <3 mm. No air flow rates were measured.

(36) The acoustic transducers were calibrated to 90 Watts in clean water by adjusting the drive voltage level and with rates of aeration varying from minimum to maximum aeration, similar results with the perforated plates were obtained as compared with Experimental Test 1.

(37) As solids were gradually introduced into the liquid in the tank, changes to the power supplied to the transducers was measured and a similar correlation of the solid material in suspension as compared with the input power to the transducers operating at a fixed and known voltage and frequency.

(38) Solids (soil particles) progressively settle out of the suspension over time, the average input power to operate the transducers decreased thereby clearly providing further confirmation of a correlation between suspended solids density and transducer average power (W).

(39) Experimental Test 3: Measurement of Change in Power Level with Change in Suspended Solids Density

(40) Testing was performed in a vessel of dimensions (600×400×260 mm) using the apparatus of the present invention including three standard 20 kHz transducers.

(41) Testing was performed in 25 liters of water using a suspended solids concentration ranging between 0% to 46% (w/v) which covers the range of suspended solids concentration typically observed in industrial floatation cells (i.e., about 20% to 40% (w/v) with an optimal solids loading of about 30% to about 40% (w/v)).

(42) Uniform mixing of the contents was maintained throughout the vessel with the use of 2 high speed agitators controlled at an appropriate RPM in order to maintain the solids in suspension over the concentration ranged tested.

(43) Diatomaceous earth (food grade, 200 microns) was adopted as the suspended solids during testing (refer to Test 3(a) results). Further testing was conducted using food grade diatomaceous earth at 500 microns particle size (refer to Test 3(b) results).

(44) Food grade diatomaceous earth (200 and 500 microns) was chosen for testing as this material is free of impurities and its behaviour and characteristics approximate that of copper, gold and nickel particles that are typically observed in floatation cells of industrial mining processes. The selected particle sizes also cover the particle size range typically observed in floatation cells of industrial mining processes.

(45) Test 3(a) with Food Grade Diatomaceous Earth (200 Micron)

(46) Whilst agitating the vessel contents at a 0% (w/v) solids in suspension, the acoustic transducers were calibrated at an initial set point of 82 watts.

(47) One percent (250 g) increments of diatomaceous earth was tested by weighing each batch and measuring the average power output of three sample pulses of the transducers. The following results were observed:

(48) TABLE-US-00002 Measured Watts (Average of Solids % (w/v) three pulses) 0 82 1 93 2 96 3 98 4 99 5 101 6 103 7 104 8 105 9 107 10 110

(49) Test 3(b) with Food Grade Diatomaceous Earth (200 Micron)

(50) Further testing was conducted in which the suspended solids concentration within the vessel was progressively increased by 4% (w/v) increments (1000 g).

(51) Diatomaceous earth (food grade, 500 microns) was adopted as the suspended solids during this further testing. All other parameters were as for Test 3(a).

(52) The following results were observed with this further test (Test 3(b)):

(53) TABLE-US-00003 Measured Watts (Average of Solids % (w/v) three pulses) 14 117 18 126 22 133 26 144 30 152 34 159 38 167 42 171 46 176

(54) Accordingly, as the results of Tests 3(a) and 3(b) demonstrate, there is an observable and repeatable trend between the suspended solids concentration and the measured power (W) upon transmission of an acoustic, fixed frequency, acoustic pulse, through the slurry. In particular, as the suspended solids concentration of the slurry increases, a corresponding increase in the measured power (W) is observed.

(55) It will be appreciated that this method of measurement and the observable trend between suspended solids concentration and measured power (W) output may provide mining companies and the like with advantages in controlling their floatation cell operation, or any vessel in which the suspended solids concentration is to be measured.

(56) Accordingly, the system and method of the invention is not only able to provide results that are indicative of increased suspended solids concentration within a floatation vessel (or the like), but is also a self-cleaning system due to the ability to induce cavitation in the mixture (slurry) which is desirable from a processing and operating efficiency perspective.

(57) In embodiments, the system and method of the invention are substantially unaffected by the presence of gaseous medium within the slurry.

(58) In embodiments, system and method enables continuous sampling of the suspended solids and allows for automatic feedback to the reagent dosing tank for both water addition/subtraction to provide a constant desired average solids concentration (30-40% w/v).

(59) Embodiments of the system are suited for use in the harsh conditions that typically exist in mineral processing and is also suited for use in all Sulphides minerals in the flotation cell process.

(60) Any reference to prior art in this specification is not, and should not be taken as, an acknowledgement, or any suggestion, that the prior art forms part of the common general knowledge.

(61) It will be appreciated by persons skilled in the relevant field of technology that numerous variations and/or modifications may be made to the invention as detailed in the embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are therefore to be considered in all aspects as illustrative and not restrictive.