Patent Application
20230266252
This invention relates to real-time analysis of moving slurries for industrial processes where slurries of solids particles suspended in liquids, are transported by pipe. The invention is particularly beneficial in the minerals processing industry.
A “slurry” typically contains solid particles (and some gas bubbles) suspended in a moving liquid like water and there is a basic, age-old need in industry to know, in real time, information about the contents of a slurry moving through a pipe. By knowing at least some information about the slurry contents in real time, action can also be taken quickly (preferably in real time) by industries to respond to changes in the slurry contents and maximise their operational benefits.
Typical information about slurry contents includes but is not limited to: elemental composition, mineral composition, particle size distribution, particle shapes, other particle characteristics, percentage solids and percentage gas.
Examples of the actions that could be taken in industry, if information about slurry contents were available quickly, include:
The typical benefits that such industries may reap from real time information about the contents of a slurry moving through a pipe, includes:
Current practices to determine slurry contents typically include analysing a sample of a flowing slurry, e.g. by conducting laboratory tests or by applying spectroscopic analysis to the sample. An example of current spectroscopic analysis conducted on a flowing slurry is represented in
Current practices to determine slurry contents all have one or more of the following disadvantages:
Even if measurements are taken in real time on samples diverted in sub-streams, the measurements are subject to sampling bias and the complexity of slurry manipulation. These disadvantages are unavoidable in all currently known techniques to take measurements on opaque process streams such as slurries that require light or other radiation to pass through the sample.
The present invention seeks to provide real time information about the contents of a bulk process stream in the form of a slurry flowing in a pipe, which overcomes at least to some extent, the disadvantages of current practices mentioned above.
According to a first aspect of the present invention there is provided a method for analysis of a moving slurry, said method comprising:
The term “smooth”, as used in this specification with reference to a pipe, means that the inside of the pipe is substantially free from disturbances such as surface anomalies, bends, changes in diameter, or the like.
The term “pipe” as used herein, includes a whole pipe, but also includes a part or section of a pipe.
The term “vertical” as used herein includes an orientation that is perfectly vertical, but also includes orientations that deviates from perfect vertical by a small degree.
The term “statistically significant” as used herein, means that the number of measurements evaluated is high enough to provide a predetermined degree of precision of the calculated characteristics with an uncertainty better than chance. By way of example, if 40,000 particles of the bulk are classified by individual measurement, then 1.0% of the bulk occurrence of a specific class of particle will result in 400 positive classifications, typically with a standard deviation of ±20 particles (an uncertainty of ±0.05%), meaning that 40,000 measurements provides an ability to differentiate statistically significantly between a 1.0% and a 0.9% occurrence of a particle class in the bulk.
The light source may be pulsed on for short enough periods of time so that the distance of movement of particles over said time period is less than the maximum expected diameter of said particles.
The light collection may be integrated for short periods of time so that the distance of movement of particles over said time period is less than the maximum expected diameter of said particles.
The light source may be directed at an acute angle relative to the axis of light collection to the examination zone.
A multiple of light sources, each with a different range of wavelengths, may be used to illuminate the examination zone, each from a different direction, so that the light of the different light sources overlaps in the examination zone.
The light source may be focused to an area in the examination zone that is smaller than the largest particles expected to be present.
The light source pulse energy may be high enough to cause light induced breakdown of particle surface to a state of plasma.
The light source may be directed through immersion oil instead of air to the transparent window in the wall of the pipe in order to minimise reflections from said window, light loss, and stray light.
The light source may be directed through an optical medium with high index of refraction, machined and polished to a shape to achieve close optical contact with the transparent window and with a machined second surface orthogonal to the light source direction, to minimise reflection.
Each light source may be directed through a prism with one surface that is in close optical contact with the transparent window and a second surface orthogonal to the light source direction, in order to minimise reflections from said window, light loss, and stray light.
The light source may be a coherent monochromatic beam size sufficiently large enough to cover the examination zone and be partially reflected from the window to serve as a reference beam for digital holography where the light reflected from both the examination zone and partially reflected from the window is collected by a 2-dimensional image sensor without lenses, to capture the interference patterns for further digital holography signal processing.
The light may be collected by a lens assembly and focused on a 2-dimensional image sensor with small enough pixels to differentiate between individual particles.
The two-dimensional image sensor may provide multispectral output.
The light may be collected by a lens assembly and focused on a one-dimensional hyper-spectral image sensor with small enough pixels to differentiate between individual particles, where a two-dimensional hyper-spectral image may be built up by recording a high number of line images from the slurry moving past the sensor, in the manner of a push-broom imager.
The method may include taking a plurality of consecutive digital images of the flowing slurry and analysing the digital images with digital image processing methods to identify the two-dimensional size of individual particles, and the results of enough particles from enough images may be combined to result in a statistically significant representation of the bulk slurry particle size distribution.
Digital image processing methods may be used to analyse the shape of individual particles, and the results of enough particles from enough images may be combined to provide in a statistically significant representation of the bulk slurry particle shape distribution.
A multi-spectral image may be obtained and digital image processing methods may be used to identify the spectral intensities of individual particles.
A multi-spectral image may be obtained and the spectral intensities of the light source may be determined from the specular reflectance off bubbles, to serve as reference spectral intensities and thus enable the calculation of relative diffuse spectral reflectance for individual particles.
The material of each particle may be identified according to the geometric distance between its relative diffuse spectral reflectance and the closest relative diffuse spectral reflectance of reference materials as stored in a table and a high enough number of results may be collated to provide a statistically significant representation of the bulk slurry solids content material composition.
The total particle surface summed over a large number of images may be calculated as a fraction of the sum of surface areas of all images and the results may then serve as a monotonically rising indicator of the fraction of solids in the slurry.
The total surface of identified bubbles summed over a large number of images may be calculated as a fraction of the sum of surface areas of all images and the results may then serve as a monotonically rising indicator of the fraction of gas in the slurry.
The light may be collected by a lens assembly and directed to a spectrometer with digital output.
The method may include directing the light from the light source and light returned from the examination zone co-axially in opposite directions and separating them by use of a partially reflecting mirror at an acute angle to the average light axis.
The method may include taking a plurality of consecutive digital spectrographs of an examination zone in the flowing slurry and analysing each digital spectrograph with chemometric methods to identify the most likely material that was in the examination zone during the time that the spectrograph was taken and then classifying the result as a solid particle type, gas bubble or transporting liquid for a high enough number of measurements to produce a statistically significant representation of the bulk slurry composition.
The total fraction of spectrographs classified as solids particles may be calculated and the result may then serve as a monotonically rising indicator of the fraction of solids in the slurry.
The method may include compensating by machine learning, by adjusting the results based on laboratory analysis of bulk samples taken during a multiple of measurements, in order to compensate for possible non-linear effects and presentation bias, when calculating the characteristic of the flowing slurry, as a whole.
The method may include using a wavelength area that is shorter than the primary light source wavelength in a Stokes Raman analyser, by adding a long pass dichroic mirror with a cut-on wavelength below that of the primary light source, into the primary light source path.
The method may include adding a lens camera behind said long pass dichroic mirror, said lens camera being configured to capture an image of the analysis area.
The method may include providing a polarised beam splitter and secondary collimated light source that are configured to emit wavelengths that include wavelengths that are shorter than the wavelengths of the primary light source, in order to illuminate the area of analysis.
The secondary light source may have an etendue that is lower than the primary light source, in order to increase its spot size at the examination zone.
The method may include using a secondary light source with a slightly unfocussed collimator in order to increase its spot size at the examination zone.
The pipe may be straight for a length of at least eight times the diameter of the pipe.
The slurry may flow upwards in the pipe.
The pipe may be straight, smooth and is free from disturbances.
The maximum expected dimensions of solid particles in the slurry may be less than 2% of the diameter of the pipe.
According to another aspect of the present invention there is provided apparatus for analysis of a moving slurry of solid particles in a liquid medium, said apparatus comprising:
The apparatus may be used in a method as described hereinabove.
For a better understanding of the present invention, and to show how it may be carried into effect, the invention will now be described by way of non-limiting example, with reference to the accompanying drawings in which:
Referring to
The present invention does not depend on a very precise and difficult quantification of a small number of measurements of the average of a high number of particles, as done in the prior art and as shown in
The present invention relies on the following assumptions, which have been supported by experimental data, that:
Referring to
The apparatus 10 is installed on a vertical pipe 12 in which a slurry 14 flows and the slurry preferably flows upwards, as shown by reference arrow 16. The slurry 14 comprises small solid particles suspended in a liquid and also includes some gas bubbles. The slurry 14 fills the entire cross-section of the pipe 12. The pipe 12 is straight and smooth and preferably has a straight length of at least eight times the diameter of the pipe. The flow rate of the slurry 14 is such that it flows in the pipe 12 with fully developed turbulence and the dimensions of the particles in the slurry are less than 2% of the pipe diameter. It has been found that if these conditions are met, characteristics of the part of the slurry 14 flowing past the apparatus (through an examination zone—see below) are representative of the slurry across the pipe 12.
The wall of the pipe 12 defines an opening 17 in which an instrument housing 18 of the apparatus 10, can be installed in a watertight manner. The instrument housing 18 supports a transparent window 20, preferably of an abrasion resistant material such as sapphire, such that the faces of the instrument housing and sapphire window are flush with the inside of the pipe 12, so as to cause no significant disturbance to the flow of the slurry 14 past the sapphire window.
The apparatus 10 further includes a monochrome camera 22, supported on a mounting 24 and an objective lens assembly 26, such that the camera can capture images of the slurry 14 flowing past the sapphire window 20 and store the images digitally for analysis by a computer. The mounting 24 allows the camera 22 and/or objective lens 26 to be moved to focus on the slurry flowing inside the pipe 12 past the face of the sapphire window 20.
The objective lens assembly 26 is configured to collect light from a very small region inside the slurry 14, in front of the sapphire window 20 (the examination zone) and projecting the light as an image into the imaging sensor of the camera 22.
The apparatus 10 further includes at least one light source 28 for illuminating the slurry 14 flowing past the face of the sapphire window 20. A light guide 30 such as an optical fibre, may be used to direct the light from the source to the slurry.
The light source 28 is preferably a flash illumination source, capable of generating a light pulse of short enough duration and adequate intensity to capture a stationary image of the moving solid particles in the slurry 14 in the examination zone. The light emitted by the light source 28 is of a suitable numerical aperture (NA) to illuminate the entire examination zone without obstructing the optical path of the camera and without projecting excessive light outside of the examination zone.
As shown more specifically in
Instead of using a monochrome camera 22, the camera can be a hyper-spectral line camera with small enough pixels to differentiate between individual particles, where a 2-dimensional hyper-spectral image is built up by recording a high number of line images from the slurry moving past the sensor, in the manner of a push-broom imager.
Instead of using a monochrome camera 22, the camera can be a multi-spectral camera with two or more wavelength ranges. The use of different wavelength ranges of light, emitted from different angles onto the solid particles 32 in the examination zone, which concurs with at least some of the wavelength ranges of the multispectral camera, can assist in showing the three-dimensional shapes of the particles, by use of colour photometric stereoscopy.
The angle between the optical axis of each illumination source, i.e. the angle at which light is emitted from each light guide 30 to the examination zone, and the common optical axis of the camera 22 and objective lens assembly 26, is preferably as large as possible to accentuate the colour photometric stereoscopy effect however not so large as to cause excessive reflection of light from the light source 28 off of the sapphire window 20 interfaces, either on the light source side 66 or the slurry side 64. Such reflections due to large angles are more pronounced for large differences between optical media indexes of refraction, as illustrated by reflected light 59.
The numerical aperture and f-stop of the objective lens assembly 26 and camera 22 are preferably used to restrict the depth of field in the part of the examination zone that is being photographed, i.e. the examination zone 34 for which a digital image is captured.
In embodiments where the camera 22 is either a multi-spectral camera or a hyper-spectral camera, the diffuse spectral intensities of individual particles can be identified with digital image processing methods. In addition, any bubbles can be identified by their circular shapes and strong specular reflections. The spectra of specular reflections are by their nature proportional to the spectrum of the light source and can therefore be used as reference to calculate the relative diffuse spectral reflectances of particles from their individual diffuse spectral intensities. During calibration, a library of reference materials can be built by storing their relative diffuse spectral reflectances in a table on a computer. Afterwards during operation, each spectrograph is identified according to the geometric distance between its relative diffuse spectral reflectance and the closest relative diffuse spectral reflectance of reference materials as stored in such a table. A high enough number of such results are then collated to a statistically significant representation of the bulk slurry solids content material composition.
Referring to
In a further preferred embodiment (
In a further preferred embodiment (
A further advantage of these methods illustrated in
The digital images of the examination zone 34 captured by either the camera 22 or produced from digital holograms captured by the sensor 71, are stored and are analysed on a computer, which identifies individual particles 32 from the slurry 14 in each digital image and determines the sizes of the individual particles from the images. The results of a statistically meaningful number of analysed particles 32 are used and the particle size distribution expressed as a percentage of total solids mass for each predetermined size fraction.
Similarly, the computer determines the shapes of the individual particles 32 from the stored digital images and the results of a statistically meaningful number of analysed particles are used and the particle shape distribution expressed as a percentage of total solids mass for each predetermined particle shape category.
The computer determines the sizes of particles 32 in the stored digital images, in relation to the total area of the examination zone 34 and uses these data to express slurry solids content as percentage solids in relation to total volume.
The computer can also identify and measure bubbles in the stored digital images, due to their spherical shape and specular reflectance, so that the gas contents can be expressed as a fraction or percentage in relation to the total volume of the slurry 14.
Referring to
The light source used for spectroscopy in the second embodiment is a pulsed light source 48 and the light emitted from the source is passed through a beam expander and collimator 50 and reflected off a mirror 52 and partially reflecting mirror 54, respectively, before being focused on the examination zone by an objective lens assembly 56. Light reflected off or emitted from the examination zone passes through the objective lens assembly 56, passes through the partially reflecting mirror 54 and a focusing lens 58 to the spectrometer 46, for analysis.
In a preferred embodiment, the pulsed light source 48 is a pulsed monochromatic laser, the partially reflecting mirror 54 is either a band pass or a long pass dichroic mirror and the returned light is due to laser induced fluorescence, the Raman Effect or due to light induced breakdown to a plasma state.
In a further preferred embodiment, the pulsed light source 48 is a non-monochromatic light source, for instance a Xenon flash light, the partially reflecting mirror 54 can be a semi-silvered mirror in order to reflect different wavelengths to an equal extent and the returned light is due to diffuse and specular reflectance.
The numerical aperture of the objective lens assembly 56 is preferably used to restrict the depth of field in the part of the examination zone that is being illuminated and measured, i.e. the region around particle 32.
Each resulting spectrograph from the spectrometer 46, whether due to laser induced fluorescence, Raman effect, light induced breakdown, diffuse or specular reflection, is analysed using chemometric methods to identify the most likely material that was in the examination zone of the moving slurry during the time that the spectrograph was taken and then classified as a solid particle type, gas bubble or transporting liquid. A high enough number of spectrographs are analysed to produce a statistically significant representation of the bulk slurry composition.
Referring to
This expansion shown in
Longer wavelengths than that of light source 48 from light source 84 are transmitted by long pass dichroic mirror 80 and absorbed by a dark absorber 85. Shorter wavelengths than that of light source 48 are reflected by long pass dichroic mirrors 80 and 54 and focused by lens 56 on particle 32. In a preferred embodiment, the light source 84 can be a broadband flash lamp with a lower etendue that of light source 48 which can be a laser, leading to a larger spot size of the short wavelengths from light source 84 than for light source 48. This larger spot size is then imaged through window 20, lens 56, dichroic mirrors 54 and 80, beam splitter 82 and lens 81 onto the photo-sensitive sensor of camera 82. The beam-splitter 82 can be a polarising beam splitter to reduce specular reflection from all optical surfaces in the imaging pathway.
Referring to all of
The present invention holds the following benefits over the prior art:
a) No sampling error is introduced as no sub-sample is extracted from the flowing slurry 14.
b) No waste produced as no sample is removed from production.
c) No sample handling, sample preparation, sample return or consumables are required.
d) No time delay, as the actual process slurry 14 is analysed in real time and no sub-samples need to be transported or prepared.
e) A low total cost of ownership due to the simplicity of the invention, with no moving parts.
f) No human intervention is required and very little if any maintenance is required.
g) Good detection limits due to measuring a number of small areas and using a robust statistical counting method instead of a sensitive averaging, bulk measure.
h) Smart evaluation of the effect of individual particles 32 in large numbers.
i) A very robust window 20 can be chosen, e.g. sapphire, capable of withstanding high temperature and pressure, chemical corrosion and mechanical abrasion.
j) Turbulent flow keeps the window 20 clean from static material build-up
k) Experimental results showed, contrary to expectations, that the slurry presenting against the window is a good representation of the bulk. Good mixing of the slurry 14 is therefore ensured if the requirements listed above are followed, since any particle 32 has an equal random chance of passing next to the transparent window 20, and presentation bias is removed.
The embodiment of the invention illustrated in
Next, 60 g mineral ore containing Zircon, with several Aluminium Silicates and Aluminium Oxide minerals as impurities, was added to 180 ml water and circulated as a slurry in front of the sapphire window as a turbulent flow. Using a prior art methodology as illustrated in
Though the typical Raman signatures for Zircon (1000 cy/cm), water (3700 cy/cm), various Aluminium Silicates and Oxides (4400 cy/cm) are visible, the nature of Raman spectroscopy means that signal intensity is highly variable. Depending on crystal orientation, its signal strength can vary more than an order of magnitude. Therefore, as can be seen in
However, when the present invention as depicted in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009498.3 | Jun 2020 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/055479 | 6/22/2021 | WO |
