AU2017368919A1

AU2017368919A1 - Analysis of bubbles in a pulp phase of a flotation cell

Info

Publication number: AU2017368919A1
Application number: AU2017368919A
Authority: AU
Inventors: Adriaan Lodewicus HAASBROEK; Leendert VAN DER BIJL
Original assignee: Stone Three Digital Pty Ltd
Current assignee: Stone Three Digital Pty Ltd
Priority date: 2016-11-30
Filing date: 2017-11-30
Publication date: 2019-07-04
Anticipated expiration: 2037-11-30
Also published as: AU2017368919B2; WO2018100527A2; BR112019010829A2; ZA201903223B; PE20190833A1; WO2018100527A3; CL2019001450A1

Abstract

A method and system for measuring properties of the pulp phase of a flotation cell are disclosed and includes at least partially submerging a probe inside the pulp phase of the flotation cell. The probe includes a camera, a light source and a viewing pane at an operative end of the probe. The viewing pane is positioned at an angle to the vertical and the camera is used to obtain intermittent images of the pulp phase through the viewing pane and under illumination from the light source.

Description

ANALYSIS OF BUBBLES IN A PULP PHASE OF A FLOTATION CELL

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from South African provisional patent application number 2018/08265 filed on 30 November 2018, which is incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to a method, apparatus and system for analysing the pulp phase of a flotation ceil. More specifically, but not exclusively, the invention relates to measuring bubble size distribution (BSD), superficial gas velocity (Jg) and gas holdup in the pulp phase of such a flotation ceil.

BACKGROUND TO THE INVENTION

Froth flotation is a process for separating minerals from gangue by taking advantage of differences in their hydrophobicity. Hydrophobicity differences between valuable minerals and waste gangue are increased through the use of surfactants and wetting agents.

The process is used in several processing industries. Historically, this was first used in the mining industry, where it was one of the great enabling technologies of the 20th century. It has been described as the single most important operation used for the recovery and upgrading of sulphide ores. The development of froth flotation improved the recovery of valuable minerals such as copper- and lead-bearing minerals. Along with mechanized mining, it allowed the economic recovery of valuable metals at much lower head grades than before.

The flotation process typically takes place in an open ceil and consists of the pulp phase which can be described as the ‘reactor’ and the froth phase which can be termed the ‘separator’, in the pulp phase, hydrophobic particles preferentially attach to rising air bubbles which form a froth at the fop of the pulp phase and are recovered as concentrate. Sub-processes such as bubble-particle collision, attachment, detachment and entrainment dominate. These subprocesses have an overall effect of transporting particles, mostly hydrophobic particles to the froth phase. In the froth phase, the process of froth formation and transport determines the kind of sub-processes that take place. Froth phase sub-processes such as thinning of bubble films,

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PCT/IB2017/057533 bubble coalescence and froth drainage result in an increase in bubble sizes, particles detaching from bubbles and draining back into the pulp phase. Froth phase sub-processes may lead to cleaning/separating action if there is preferential re-attachment of the draining particles to the available bubble surface area. This cleaning action determines the overall grade and recovery of the flotation process. The initial separating action of the froth phase starts at the pulp-froth interface.

Important parameters for process control of such froths is the bubble size distribution (BSD), superficial gas velocity (Jg) and gas holdup in the pulp phase. Various methods for measurement of the BSD in the pulp phase have been developed. These methods, however, suffer from a variety of drawbacks. For example, available methods conduct offline or batch measurements of the pulp bubble properties. Most existing offline approaches also involve extracting bubbles from the flotation cell into a separate chamber, where the extracted matter is analysed through the use of camera imaging. The separate chamber is typically filled with clean water (using valve systems) to enable effective imaging of the bubbles. Mineral build-up also occurs in these chambers causing viewing ports to become fouled and necessitating regular cleaning, typically by way of flushing. The clean water inside the chamber gets displaced by the air contained in the bubbles and needs to be refilled after each measurement. Since the bubble collection or draw-off points of these offline devices are inside the ceil and the measurement points above or otherwise outside the cell, the pressure differences between the two environments need to be compensated for. This in turn complicates the calculation process to obtain accurate results.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with this disclosure there is provided a method of measuring properties of the pulp phase of a flotation cell, the method comprising the steps of:

at least partially submerging a probe inside the pulp phase of the flotation ceil, the probe comprising a camera, at least one light source and a viewing pane at an operative end thereof;

positioning the viewing pane at an angle to the vertical; and obtaining, with the camera, intermittent images of the pulp phase under illumination from the light source through the viewing pane.

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The camera, although not a strict requirement, will preferably be a digital camera that obtains digital images of the pulp phase under illumination.

Further features provide for the method to inciude the steps of transmitting the digitai images to a processor in data communication with the digitai camera; and processing the digitai images to provide near reai-time measurements of at ieast one property of the pulp phase. The property of the puip phase being measured may include one or more of a bubble size distribution, superficial gas velocity, pulp colour and a gas holdup in the pulp phase to name but a few. The measurements may be conducted using digitai image processing algorithms optimised for the analysis of one or more of the properties.

Still further features provide for the method to inciude steps of calculating an optimal angle to the vertical at which the viewing pane is to be positioned within the pulp phase, the calculation taking into consideration the reflection and refraction properties of light emitted by the light source, the angle at which light from the light source is omitted, material properties of the viewing pane and/or material properties of substances present in the puip phase; and of positioning the viewing pane at the optima! angle within the puip phase.

A yet further feature provides for the method to inciude the step of determining optimal angles at which one or both of the light source and a lens of the digital camera are to be directed to the viewing pane, the angles to be selected so as to take into consideration light reflection and refraction properties of the viewing pane and/or materials present sn the puip phase.

In accordance with a second aspect of this disclosure there is provided a probe for obtaining digitai images of a pulp phase of a flotation cell comprising:

a housing defining an internal cavity;

a digitai camera positioned at or near an operative end of the probe inside the cavity; a viewing pane at the operative end of the probe; and at ieast one light source positioned at or near the viewing pane inside the cavity, wherein the viewing pane is configured to be positioned inside the puip phase at an angle to the vertical and the digital camera is configured to obtain intermittent digitai images of the puip phase under illumination from the light source through the viewing pane.

Further features of the invention provide for the probe to inciude a communication module for transmitting the digital images to a processor; and for the processor to process the digital images to provide near real-time measurements of at least one property of the pulp phase. The property of the pulp phase being measured may inciude one or more of a bubble size distribution, superficial gas velocity, pulp colour and a gas holdup in the pulp phase to name but 3

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PCT/IB2017/057533 a few. The measurements may be conducted using digital image processing algorithms optimised for the analysis of one or more of the properties.

In one embodiment the processor may be incorporated in, and form part of, the probe and the processor may be configured to communicate processed image data and/or measured parameters to an external receiver utilising the communication module.

Still further features provide for a portion of the housing at the operative end of the probe to extend at an angle to a main portion thereof; for the viewing pane to effectively seal the camera and light source from its surrounding environment inside the cavity; for the light source to produce a focused light beam; and for one or both of the light source and a lens of the digital camera to be directed at predetermined angles to the viewing pane, preferable at angles relative to the viewing pane selected so as to take into consideration light reflection and refraction properties of the viewing pane and/or materials present in the pulp phase.

A yet further feature provides for the viewing pane to be positioned at an optimal angle to the vertical inside the pulp phase, the optimal angle having been calculated taking into consideration the reflection and refraction properties of light emitted by the light source, the material properties of the viewing pane and/or the material properties of materials present in the pulp.

The disclosure also provides a system for measuring properties of a pulp phase of a flotation cell comprising a probe as described above; and a processor in digital communication with the digital camera of the probe for receiving digital images taken by the digital camera and analysing the digital images to provide near realtime measurements of at least one property of the pulp phase. The at least one property of the pulp phase being measured may include one or more of a bubble size distribution, superficial gas velocity, pulp colour and a gas holdup in the pulp phase, to name but a few.

Further features provide for the system to include control circuitry configured to receive analysed pulp phase image data and issue control signals to electrically controlled components of the flotation ceil to make adjustments to the flotation ceil operation in an attempt to optimise bubble formation within the pulp phase.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings.

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BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a schematic illustration of a flotation ceil utilising a probe in accordance with this disclosure;

Figure 2 is a schematic diagram of a system for analysing bubbles in the pulp phase of a flotation ceil in accordance with the disclosure;

Figure 3 is an image taken with a test probe in accordance with this disclosure under laboratory conditions; and

Figure 4 is an image taken with a test probe in accordance with this disclosure under production, field conditions.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

In the embodiment of the invention shown in Figure 1, a probe (1) according to the current disclosure is provided and is submerged inside the pulp phase (3) of a flotation cell (5). The probe (1) comprises a digital camera (7) and a plurality of focused light sources (9) positioned at or near a forward extremity of the camera (7) and directed so as to focus visible light in the same general direction as the viewing lens of the camera (7). The probe (1) has a tubular housing (11) defining a cavity (13) inside which the camera (7) and light sources (9) are located. An operative end (15) of the probe (1) is covered with a transparent viewing pane (17) which effectively seals the interior of the probe (1) from the surrounding environment and more specifically the harsh conditions that may be prevalent inside the pulp. The material with which the viewing pane (17) is manufactured is selected so that its reflective and refractive properties enhance the image contrast of images of the pulp taken through it.

The probe (1), more specifically the camera (7) and light sources (9) are externally powered and are in digital communication with a digital processor (19), as shown in more detail in the schematic diagram shown in Figure 2, by means of digital communication infrastructure, in the present embodiment a power and communication cable (21). Communication between the camera (7) and processor (19) may, however, be established through any commonly available wired or wireless technologies. It is also foreseen that the probe (1) may include an on-board

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PCT/IB2017/057533 digital processor in communication with the camera and light sources, in which case on-board storage and external communication capabilities may be provided as well.

The probe (1) is further configured so that the operative end (15) extends at an angle to the main portion (23) thereof. The viewing pane (17) covers the operative end (15) of the probe and is positioned so that the viewing direction of the lens of the camera (7) and focus of the light sources (9) fall onto the viewing pane (17) at angles selected so as to take into consideration light reflection and refraction properties of the viewing pane (17) and/or materials present in the pulp phase, and thereby optimise contrast in resulting images taken through the viewing pane (17). It will also be appreciated that if the probe (1) is inserted substantially vertically into the pulp phase (3), the angled nature of the operative portion (15) of the probe will ensure that the viewing pane (17) is positioned at an angle to the vertical (25) inside the pulp phase (3).

The angle at which the viewing pane (17), and accordingly the angle of illumination of the pulp phase adjacent the viewing pane (17) as well as the viewing direction of the camera lens, is positioned relative to the vertical is calculated so that light refraction and reflection at the various material intersections and total internal reflection of the light causes the optimum contrast between the pulp slurry and the bubbles present therein. This so-called “optimal angle” is therefore calculated taking the various refraction and reflection properties of the various materials present in the path through which the light travels into consideration. It will be appreciated by those skilled in the art that the optimal angle may therefore differ depending on at least the wavelength of the light emitted by the light sources, the material properties of the viewing pane and the composition and material properties of the various materials present in the pulp phase.

In one embodiment of the invention it is foreseen that the angle at which the viewing pane is positioned relative to the vertical may be adjustable. Similarly the angle at which the light sources emit light and the viewing angle of the camera may be either manually or electronically adjustable to assist with obtaining optimal contrast in imaging.

The light sources utilised in the probe may include any number of available types. It is, however, foreseen that LED lights may be particularly suitable for use in the probe.

In use, and as shown in more detail in Figure 2 where like features to those described with reference to Figure 1 are indicated with like numerals, the probe (1) may be inserted inside the pulp phase (3) of the flotation ceil (5) and powered by an external power source via a power line in the communication cable (21) or a dedicated power line. Alternatively the probe may include a battery or other on-board power source. It will be appreciated that the probe (1) will be 6

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PCT/IB2017/057533 positioned inside the pulp phase so that the viewing pane (17) is at the optimum angle, the direction of light passing through the viewing pane and the camera viewing angle are all optimised to yield high contrast between bubble surfaces in the pulp and the pulp itself in the resulting images captured by the camera. The processor (19) is configured to issue instructions to the camera (7) to capture intermittent images of the pulp under illumination from the light sources through the viewing pane (17). Images may be captured at a high framerate, typically between 30 and 60 frames per second. The digital images are then communicated from the camera (7), over the communication cable, to an external processor (19) for image processing.

Once received at the processor (19), the images are processed using image processing algorithms and other software instructions operating on the processor which may be optimised to automatically detect bubbles present in the pulp phase from the images. Once detected, the sizes, volumes and other characteristics of the bubbles may be calculated as well as a number of other parameters relating to the pulp phase and, more specifically, the bubbles present therein. These parameters may include, but are not limited to, the gas holdup in the pulp which may be calculated from the total detected bubble volume in relation to the total volume of the pulp phase and the superficial gas velocity which may be calculated from bubble velocities and volume. If will be appreciated by those skilled in the art that calculation of bubble velocities inside the pulp is made possible by capturing numerous, consecutive images of the pulp phase in close succession and tracking targeted bubbles as they rise through the pulp.

In one embodiment of the disclosure if is foreseen that the probe may include a processor configured with the requisite software and algorithms to conduct image processing on-board the probe itself. In such an embodiment the probe may be configured to simply communicate the results of the parameters determined from the analysed digital images to an external source. By way of example, a probe according to such an embodiment may be configured to automatically determine the bubble size distribution, superficial gas velocity and gas holdup inside the pulp and simply communicate these parameters to the external source in an online, near real-time fashion.

It is also foreseen that the system may include, or be configured to communicate with, control systems configured to receive control signals generated in response to analysed pulp phase image data, and issue the control signals to electrically controlled components of the flotation cell to make adjustments to the flotation ceil operation in an attempt to optimise bubble formation within the pulp phase. In such an embodiment the probe according to the disclosure may form part of a close-loop control system by means of which the operation of a flotation cell may be continuously monitored, controlled and adjusted for optimal operation.

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The system may foreseeably also be configured with remote, wireless communication modules configured to supply analytic or diagnostic data regarding the flotation cell being measured to remote monitoring facilities. In this way a number of flotations cells may be simultaneously monitored from a remote location and warnings or other error conditions regarding individual cells may be flagged for manual intervention if required.

It will be appreciated by those skilled in the art that the disclosure provides a method and apparatus that enables in situ, continuous and real-time measurement of parameters relating to bubbles in the pulp phase of a flotation cell that were previously unavailable. While offline or batch measurements of such parameters have been conducted, to the applicant's knowledge no solutions for measuring these parameters in an online, continuous fashion in a production environment, as is set out in this disclosure, have been proposed.

The above disclosure is by way of example only and numerous changes and modifications may be made to the embodiments described without departing from the scope of the invention, in particular, it is foreseen that any number of different cameras and light sources may be used which will yield usable results. It is also anticipated that the exact angles at which light from the light sources fall onto the viewing pane may be adjusted to obtain optimum contrast between the pulp and the bubbles, while the viewing angle of the camera may be kept constant. Likewise, the viewing angle of the camera may be adjusted while the light inflection angles are kept constant to the same end.

During testing of the apparatus disclosed a power cable of the probe was connected to a portable battery unit and an Ethernet cable to a laptop for communication. In field conditions it is foreseen that the probe may be connected to a field cabinet which may contain the power supply for the probe. The cabinet may include a network switch. The probe may connect to the switch using Ethernet cable or WIFI. Processing may be done by a computer unit in the cabinet or alternatively by a computer unit housed in a server room. In this case the switch in the field cabinet may be connected to the switch in the plant’s server room using fibre optic cable. As referred to elsewhere in this specification it is also possible that processing may be done on the probe itself.

During a subsequent two-month testing period the probe was tested in a production flotation cell with the test results showing a satisfactory correlation with off-line laboratory test results of plant variables such as aeration rate. The probe showed no visible signs of wear and the lens required no cleaning during this test period. If will be appreciated that the housing should be designed to withstand the harsh conditions that may be found in the flotation cell which may, in turn, minimise required maintenance.

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The applicant envisages that the measurements would benefit from the use of high speed cameras in order to better track bubbles from frame to frame and more accurately calculate the bubble velocities. Subsequent build versions of the probe will therefore make use of a camera that can capture frames at framerates of 300 frames per second and higher.

In addition, the software employed by the processer to measure bubble size distribution, superficial gas velocity (Jg) and gas holdup, while not explicitly part of this disclosure, may be adapted and customised to yield optimum results given the specific characteristics of the components used. Such adaptations and modifications otherwise know methodologies and analysis tools may well fall within the scope of the invention.

Throughout the specification and claims unless the contents requires otherwise the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS:

1. A method of measuring properties of the pulp phase of a flotation ceil· the method comprising the steps of:

at least partially submerging a probe inside the pulp phase of the flotation ceil, the probe comprising a camera, at least one light source and a viewing pane at an operative end thereof;

positioning the viewing pane at an angle to the vertical; and obtaining, with the camera, intermittent images of the pulp phase under illumination from the light source through the viewing pane.
2. The method as claimed in claim 1, wherein the step of obtaining images includes obtaining images by means of a digital camera that obtains digital images of the pulp phase under illumination.
3. The method as claimed in claim 2, further including the steps of transmitting the digital images to a processor in data communication with the digital camera; and processing the digital images to provide near real-time measurements of at least one property of the pulp phase.
4. The method as claimed in claim 3, wherein the property of the pulp phase being measured is one or more of the group consisting of a bubble size distribution, superficial gas velocity, pulp colour and a gas holdup in the pulp phase.
5. The method as claimed in either claim 3 or claim 4, wherein the measurements are conducted using digital image processing algorithms optimised for the analysis of one or more of the properties.
6. The method as claimed in any one of claims 3 to claim 5, further including the steps of calculating an optimal angle to the vertical at which the viewing pane is to be positioned within the pulp phase, the calculation taking into consideration the reflection and refraction properties of light emitted by the light source, the angle at which light from the light source is omitted, material properties of the viewing pane and/or material properties of substances present in the pulp phase; and positioning the viewing pane at the optimal angle within the pulp phase.
7. The method as claimed in any one of claims 3 to claim 6, further including the step of determining optimal angles at which one or both of the light source and a lens of the

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PCT/IB2017/057533 digital camera are to be directed to the viewing pane, the angles being selected so as to take into consideration light reflection and refraction properties of the viewing pane and/or materials present in the pulp phase.
8. A probe for obtaining digital images of a pulp phase of a flotation ceil comprising: a housing defining an internal cavity;

a digital camera positioned at or near an operative end of the probe inside the cavity;

a viewing pane at the operative end of the probe; and at least one light source positioned at or near the viewing pane inside the cavity, wherein the viewing pane is configured to be positioned inside the pulp phase at an angle to the vertical and the digital camera is configured to obtain intermittent digital images of the pulp phase under illumination from the light source through the viewing pane.
9. The probe as claimed in claim 8, including a communication module for transmitting the digital images to a processor.
10. The probe as claimed in claim 9, wherein the processor is arranged to process the digital images to provide near real-time measurements of at least one property of the pulp phase.
11. The probe as claimed in claim 10, wherein the measured property of the pulp phase is one or more of the group consisting of a bubble size distribution, superficial gas velocity, pulp colour and a gas holdup in the pulp phase.
12. The probe as claimed in claim 10 or claim 11. wherein the measurements are conducted using digital image processing algorithms optimised for the analysis of one or more of the properties,
13. The probe as claimed in any one of claims 9 to claim 12, wherein the processor is incorporated in, and forms part of, the probe and wherein the processor is configured to communicate processed image data and/or measured parameters to an external receiver utilising the communication module.
14. The probe as claimed in any one of claims 8 to claim 13, wherein a portion of the housing at the operative end of the probe extends at an angle to a main portion thereof.

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15. The probe as claimed in any one of claims 8 to claim 14, wherein the viewing pane effectively seals the camera and light source from its surrounding environment inside the cavity.
16. The probe as claimed in any one of claims 8 to claim 15, wherein the light source produces a focused light beam.
17. The probe as claimed in anyone of claims 8 to claim 16, wherein one or both of the light source and a lens of the digital camera is directed at predetermined angles to the viewing pane.
18. The probe as claimed in claim 17, wherein the predetermined angles are selected so as to take into consideration light reflection and refraction properties of the viewing pane and/or materials present in the pulp phase.
19. The probe as claimed in any one of claims 8 to claim 18, wherein the viewing pane is positioned at an optimal angle to the vertical inside the pulp phase, the optimal angle having been calculated taking into consideration the reflection and refraction properties of light emitted by the light source, the material properties of the viewing pane and/or the material properties of materials present in the pulp.
20. A system for measuring properties of a pulp phase of a flotation cell comprising a probe as claimed in any one of claims 8 to claim 19; and a processor in digital communication with the digital camera of the probe for receiving digital images taken by the digital camera and analysing the digital images to provide near real-time measurements of at least one property of the pulp phase.
21. The system as claimed in claim 20, wherein the at least one measured property of the pulp phase includes one or more of a bubble size distribution, superficial gas velocity, pulp colour and a gas holdup in the pulp phase.
22. The system as claimed in either claim 20 or claim 21, further including control circuitry configured to receive analysed pulp phase image data and issue control signals to electrically controlled components of the flotation cell to make adjustments to the flotation cell operation in an attempt to optimise bubble formation within the pulp phase.