WO1987004521A1

WO1987004521A1 - Method and apparatus for monitoring deflocculated particles in suspension

Info

Publication number: WO1987004521A1
Application number: PCT/GB1987/000031
Authority: WO
Inventors: Barry Randall Jennings; Kevin Parslow; Terence Wilfred Webb
Original assignee: Ecc International Limited
Priority date: 1986-01-17
Filing date: 1987-01-19
Publication date: 1987-07-30
Also published as: GB2187278B; GB8601087D0; EP0253867A1; GB8701015D0; GB2187278A

Abstract

Method of monitoring and apparatus for monitoring the deflocculation of particles in a suspension, which particles, when deflocculated are such that they can become aligned in an applied field. The apparatus embodiments disclosed include a laser (3) for producing a beam of light incident on the surface area of said region, a detector (6) for detecting scattered light reflected in a particular direction from said surface area, means (8, 9, 10) for producing an electric field across said region and means (11) for detecting changes in detector output in the presence of an applied electric field as compared with the output in the absence of an electric field.

Description

METHOD AND APPARATUS FOR MONITORING DEFLOCCULATED PARTICLES IN SUSPENSION

The present invention relates to a method of and apparatus for monitoring deflocculated particles in a suspension, which particles, when de-flocculated are such that they can become aligned in an applied field, e.g. an electric, magnetic, ultrasonic, shock wave or shear field.

Our prior British Patent Application No. 8410730 discloses such methods and apparatus, each of which, in the specific embodiments disclosed, involves the use of a beam of light radiation transmitted through a sample of such a suspension. The beam of light is transmitted through a test cell having a narrow channel formed between transparent plates, the suspension in the channel having light transmitted therethrough and the change in scattered light output from the side of the channel opposite to the light source side being detected in the presence and in the absence of an electric field applied to the suspension in the channel in the path of the light beam.

Very successful results in monitoring defloccula- tion have been achieved with this apparatus for slurries having concentrations of solids of up to 30% in suspension. These results were achieved by monitor¬ ing the scattered light transmitted through the sample in a very narrow width (100um) channel.

There is, however, a great need for monitoring de-flocculation of the particles of suspensions with much higher solid concentration levels, e.g. concentra¬ tions 30% to 70% or more. To do this with the apparatus of British Patent Application 8410730 is not practicable since at higher concentrations, it is necessary to reduce the channel width below 100um and this results in problems of electrode design for the field producing means and also xn problems of obtaining satisfactory flow of such slurries through the narrow channel. Additionally, the channel becomes so narrow that its dimensions are comparable with the floes and can result in breaking down of the floes so that the sample is more deflocculated as a result of the slurry passing through the channel than is actually the case with the remainder of the slurry.

The present invention seeks to overcome these problems and to enable monitoring of deflocculation with slurries having a solid concentration of up to 70% or more.

According to one aspect of the present invention there is provided a method of monitoring deflocculated particles in a suspension, which particles, when deflocculated are such that they can become aligned in an applied field, the method comprising applying a beam of radiation to a region of the suspension, applying such a field to the region and detecting a change, if any, in the scattered radiation reflected from a surface area of said region as a result of the aligning in said field of deflocculated particles, if any, of the suspension.

According to a second aspect of the invention there is provided an apparatus for monitoring the deflocculation of particles in suspension, which particles, when deflocculated are such that they can become aligned in an applied field, the apparatus comprising a container for said suspension having a radiation transpaent wall portion and means for applying an incident beam of radiation at a region of said suspension, through said transparent wall portion, means for applying such a said field to said region, and means for detecting changes in the scattered radiation reflected from a surface area of said region as a result of the aligning in said field of defloccul¬ ated particles, if any, in the suspension. For a better understanding of the present invent¬ ion reference will now be made, by way of example, to the accompanying drawings, in which:

Figure 1 is a schematic diagram of one embodiment 5 of a monitoring apparatus in accordance with the invention,

Figure 2 is a perspective view of part of a second embodiment of an apparatus in accordance with the invention, -]__Q Figure 3 is a graphical representation of the results of monitoring one particular slurry by a method in accordance with the invention,

Figure 4 is a graphical representation of the results of monitoring a second slurry by a method in ^c accordance with the invention.

Figure 5 is graphical representation of the results of monitoring a third slurry by a method in accordance with the invention.

Figure 6 is a graphical representation of the __n results of monitoring a fourth slurry by a method in accordance with the invention.

Figure 7 is a graphical representation showing monitoring results for variations in the apparatus of Figure 1 , -- Figure 8 is a graphical representation showing the results of monitoring a slurry with different de- flocculant quantities added to the slurry and with variations of the apparatus of Figure 1 , and

Figure 9 is a graphical representation of the -- results of monitoring slurries of the same material but with different solids concentrations and with variation of the apparatus of Figure 1.

In Figure 1 , there is shown a container 1 , which may be a slurry test cell or an adapted part of 2 production apparatus containing the slurry to be monitored. Container 1 has a transparent wall 2, or a wall 2 with a transparent portion such that radiation in the form of a light beam from a helium/neon laser 3 or other high intensity light source can be directed therethrough so as to be incident on the surface area of a region of the slurry adjacent the wall 2.

The light beam from laser 3 passes through a polarising filter 4 between the laser 3 and the wall 2 Reflected scattered light passes through a second polarising filter 5 to a detector 6, which is position- ed in the same horizontal plane as laser 3. As indicated by the double-arrow-headed line 7 the detector 6 and polarising filter 5 may be moved so as to vary the angle between the incident beam from laser 3 and the reflected beam arriving at detector 6. Alternative positions for the second polarising filter and detector are shown referenced 5A and 6A in Figure 1. In this alternative arrangement detector 6A and filter 5A lie in the same vertical plane as laser 3 and polarising filter 4 and the angle represents the angle between the incident and reflected beams. Also, the double-arrow-headed line 7A indicates that the detector and second polarising filter may be moved to different vertical positions in the vertical plane so as to alter the angle Inside container 1 positioned at either side of the illuminated surface region and adjacent the side wall 2 are conductive plates 8 and 9, (e.g. of stain¬ less steel or other metal, or carbon) plate 8 being connected to earth, and plate 9 being connected to an output of a voltage generator 10. Voltage generator 10 is connected to receive signals from a processor unit 11, which itself receives the output of detector 6 (or 6A).

The method of monitoring de flocculated particles in accordance with the invention, using the apparatus of Figure 1 , is as follows. The suspension or slurry to be monitored is either stationary in the container 1 or is made to flow through the container/test cell 1. Light from laser 3 via polarising filter 4 is incident on a surface area of a region of the suspension through the transparent side wall 2 and reflected scattered light passes via filter 5 to detector 6. Output of the detector 6 is fed directly to a processing arrangment 11 which may be similar to the signal processing circuitry described in British Patent Application No. 84.0730. Voltage generator 10 is triggered in response to a signal from processor 11 to produce an AC voltage which is applied to plate 9 and produces an alternating electric field of suitable level between the plates 8 and 9. The electric field between the plates 8 and 9 results in the alignment of deflocculated particles at the surface region adjacent wall 2 and between the plates 8 and 9. This alignment in turn affects the level of the reflected scattered light passing via polarising filter 5 to detector 6 and the difference between the level of received scattered light by detector 6 before and during the application of the electric field is an indication of the level of deflocculation of the suspension in the container 1. Figure 3 shows in the upper curve the optical response level of detector 6 with the level at the left hand end of the curve being representative of the light level prior to application of a field pulse. On the same time scale the lower curve shows the envelope of the field pulse applied to the plates 8 and 9.

Although the field pulse 12 in figure 3 appears to be a simple rectangular pulse it is in fact an AC pulse which lasts for the duration of the rectangular pulse as shown. The optical pulse 13 shows a clear increase in the scattered light received by detector 6(6a) during the period of application of the electric field between plates 8 and 9. This increased reflection level drops sharply, initially, upon termination of the field pulse but thereafter the fall in level tails off as the level approaches the level it had prior to application of the field pulse. The curves shown in

Figure 3 were obtained with a one percent concentration of solids in a kaolinite suspension. The pre-field pulse response level was 6 volts with a 2 volt step occurring on application of the field which was a sinusoidal electric field at a_ frequency of 1kHz and with a field strength of SS m^"1 RMS.

Figure 4 shows corresponding curves for a suspens¬ ion containing 70% solids, the suspension being a Carbital 90 calcium carbonate suspension; Carbital is a registered trade mark of the applicant. In this case the pre-field pulse level was 2 volts and the increase in response was 40 millivolts for the application of a sinusoidal electric field at 50Hz and with a field strength of 40kVm^_'IRMS. It can be seen that return of the optical response to the pre-field pulse level is much slower in Figure 4. This is presumably caused by the very dense suspension which results in the particles taking a longer time to re-align after the removal of the field pulse. Additonally, the curves of Figure 3 and Figure 4 are for static suspensions whereas with a flowing suspension a new sample of the deflocculated suspension may quickly move in to the illuminated area and the optical response would drop to the pre-field pulse application level correspondingly quickly.

Although the apparatus of Figure 1 shows the use of polarising filters, it is also possible to detect significant changes in the optical response without using polarising filters. However, in tests so far carried out the optical response could be greatly enhanced by the use of polarising filters. Figures 5 and 6 show further output response curves for calcium carbonate and kaolin suspensions, respectively. In both cases the suspensions contained 1 % by weight of solids and the field pulse employed was

5 a 10 kilohertz burst pulse of 82 ms duration, and with a field strength of 150 kVm~¹rms between the plates 8 and 9. The duration of the burst is shown by a rectangle in each of Figures 5 and 6 on the same timescale as the optical response curve. The electric

10 field was applied horizontally with plates 8 and 9 vertical as shown in Figure 1 , the incident beam was vertically polarised and the detector was arranged to detect vertically polarised reflected light. Angle et between the incident and the detected reflected beams 5 was made as small as practically possible so as to correspond effectively to substantially 0°.

The arrangment in Figure 1 shows the possiblity of different positioning of the detector 6 (6a) relative to the laser 3. This allows for optimum positioning _n for maximum optical response with suspensions of different materials or concentrations. As shown the detector may be in a horizontal plane with the laser or in the same vertical plane as the laser. A position between the horizontal and vertical may also be

_- satisfactory.

Similarly the laser may be arranged to direct light at a different angle from that shown relative to the electric field. As shown the incident beam is at right angles to the electric field but it may be

-,- preferable for some suspensions or some arrangement to have the incident beam at an angle different from 90° or even in line with the electric field.

As indicated above the processing arrangement of the previous Patent application No. 8410730 (the

3- disclosure of which is, by reference, incorporated herein) may be used. Alternatively, it may with some suspensions be a better measure of the level of deflocculation to detect the RMS level of the AC voltage in the detector response rather than the overall increased pulse level output of the detector. Figure 7 shows detector output values for various angles of orientation of the polarisers 4 and 5 of Figure 1. Three pairs of curves are shown, each pair relating to a particular arrangement and field orientation of the electrodes 8 and 9. Three electrode orientations are shown diagram atically on the right- hand side of the figure and the directions of the light beam and electric field are indicated by arrow headed lines L and E respectively. Orientation (i) is similar to that shown in Figure 1 with vertical plates 8 and 9 and horizontal orientation for the electric field E which is transverse to the incident light beam. Two solid line curves correspond to this plate orientation. Orientation (ii) has horizontal plates 8 and 9 with a vertical direction of the field E which is transverse to the incident light beam L. Again two curves are shown for this orientation of the plates and these curves are represented by dashed lines. The third orientation (ii) is for transparent plate electrodes positioned transverse to the light beam L direction so as to produce a field direction E which is in line with the light beam direction. The two curves for this orientation are represented by dot-dash lines. The two curves for each orientation of the plates correspond to vertically polarised and horizontally polarised incident light beams respectively. The polarisation of the incident beam for the respective curve is shown by the H or V at the left-hand end of each curve and the subscript of the H or V corresponds to the polarisation of the detector filter at that point, i.e. -90° for angle φ . The position of 0° for angle φ corresponds to vertical polarisation for the detector polarising filter 5. From Figure 7 it can be seen from every test result curve that optimum output is obtained if the incident beam polarisation corresponds to the detected beam polarisation. Also it is preferable for the electric field to be transverse to the light beam direction for the kaolin suspension tested. In the particular case illustrated, the optimum arrangement is for horizontally polarised incident and detected light beams with a vertical electric field. . Figure 8 shows corresponding detector output curves for a 3% by weight kaolin suspension for different quantities of added de-flocculant. The de- flocculant was Dispex (Registered Trade Mark) and each curve represents a particular percentage of Dispex, as shown on the curves. The electric field was a horizontal field and vertical polarisation was used, i.e. the curves correspond to VJJ curves of Figure 7. It is clear from these curves that the detector output increases initially with the addition of de-flocculant and then after the addition of 0.25% (as shown) the output of the detector deteriorates for further edition of the de-flocculant. This shows that, for the percentage values of de-flocculant represented, 0.25% of de-flocculant is the level that corresponds most nearly to a fully de-flocculated suspension.

Figure 9 is a further set of detector response curves corresponding to those of Figure 8 with the same orientation of light polarisation and electric field. The different curves shown are for a calcium carbonate suspension varying in concentration of solids from 1% to 14%. The curves again emphasise the need for parallel polarisation of the input and output beams.

As will be understood from the foregoing descript¬ ion with reference to Figures 3 and 4 the AC frequency of the field pulse and the appropriate electric field strength should be chosen as appropriate in dependence upon the concentration and material of the suspension. In Figure 2 there is shown a probe unit which may be used as part of a monitoring apparatus for monitor¬ ing the deflocculation level of particles in a suspension in different parts of a container. In

Figure 2 a probe unit comprises a cyclindrical body 14 having channel 15 cut into the longitudinal side of the cyclinder. At the bottom of the channel a recess 16 is left clear and above this the channel is blocked by a transparent block 17. The facing side walls of the - recess 16 are provided with conductive plates to enable an electric field to be produced therebetween but for the sake of clarity these plates and the necessary electrical connectors are not illustrated. In the channel 15 above block 17 are two fibre-optic bundles 18 and 19 and these bundles are intended to be coupled one to a laser 3 and the other to a detector 6 as in Figure 1. The probe is intended to be lowered into a slurry such that slurry will fill the recess 16. Light from the laser is fed down one of the bundles, say 18, and reflected, scattered light from the surface of the area of the slurry passes via the other bundle of optical fibres 19 to the detector 6. Then, as with the apparatus of Figure 1 , electric field pulses are applied to produce a field across the slurry. Using this probe in different locations in a container enables checking as to whether deflocculation is the same throughout the suspension. Obviously, the processing circuitry can be similar to that used for Figure 1 and in the previous British Application.

Although two separate fibre optic bundles are shown in Figure 2 it may be possible in some applicat¬ ions to use a mixed fibre optic bundle containing both incident beam fibres and reflected beam fibres. Also, if necessary, it may be possible to provide for varying the position of the ends of the fibre optic bundles on the block 17 to optimise the position for different suspensions.

As indicated in the opening paragraph the field applied may be of any kind that causes an alignment of the deflocculated particles in the suspension to be monitored. Similarly, the radiation is chosen as one that will be reflectively scattered by the particles and it appears best for this to be radiation of a wavelength that corresponds approximately to the particle size, although, of course, useful results may be obtained with wavelengths that differ widely from this.

For slurries that have been tested frequencies of the applied field pulse in the range of 5Hz to 1KHz proved satisfactory with electric fields having field strengths of up to 200 kVm^-1.

Claims

1. A method of monitoring deflocculated particles in a suspension, which particles, when deflocculated are such that they can become aligned in an applied field, the method comprising applying a beam of radiation to a region of the suspension, applying such a said field to the region and detecting a change, if any, in the scattered radiation reflected from a surface area of said region as a result of the aligning in said field of deflocculated particles, if any, of the suspension.

2. A method according to claim 1 wherein said field is an electric field.

3. A method according to claim 1 or 2 wherein said radiation is light radiation.

4. A method according to claim 3 appended to claim2 wherein said electric field is transverse to said beam of light radiation.

5. A method according to claim 3 or 4 wherein said applied beam of light is polarised light.

6. A method according to claim 3, or 4, or

5,wherein only scattered light of one polarisation is detected.

7. A method according to any preceding claim wherein the applied field is an alternating field.

8. A method according to claim 7 wherein the amplitude of a corresponding alternating component of the reflected scattered radiation is detected as a measure of deflocculation.

9** Apparatus for monitoring the deflocculation of particles in suspension, which particles, when deflocc¬ ulated are such that they can become aligned in an applied field, the apparatus comprising a container for said suspension having a radiation transparent wall portion and means for applying an incident beam of radiation at a region of said suspension, through said transparent wall portion, means for applying such a said field to said region, and means for detecting changes in the scattered radiation reflected from a surface area of said region as a result of the aligning in said field of deflocculated particles, if any, in the suspension.

10. Apparatus according to claim 9 wherein said field is an electric field.

11. Apparatus according to claim 9 and 10 wherein said radiation is light radiation.

12. Apparatus according to claim 11 wherein said radiation is light radiation and said means for applying said radiation is a laser.

13. Apparatus according to claim 12 wherein a polarising filter is positioned in the path of the light beam between the laser and said region.

14. Apparatus according to claim 12 or 13 wherein a polarising filter is positioned in the reflected light path between the detecting means and said region.

15. Apparatus according to any of claims 9 to 14 wherein the axis of the beam of radiation and the axis of the detected reflected radiation path are in the same plane which passes through and is substantially parallel with the field direction.

16. Apparatus according to any of claims 9 to 14 wherein the axis of said beam of radiation and the axis of the detected reflected radiation path lie in the same plane which passes through and is substantially at right angles to the field direction.

17. Apparatus according to claim 15 or 16 wherein means are provided to enable variation of the angle between the detetected reflected path and said beam of radiation.