GB2040453A - Monitoring Mixing of Substances - Google Patents

Monitoring Mixing of Substances Download PDF

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Publication number
GB2040453A
GB2040453A GB7943325A GB7943325A GB2040453A GB 2040453 A GB2040453 A GB 2040453A GB 7943325 A GB7943325 A GB 7943325A GB 7943325 A GB7943325 A GB 7943325A GB 2040453 A GB2040453 A GB 2040453A
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United Kingdom
Prior art keywords
substances
admixture
volume
mixing
ultrasonic energy
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Application number
GB7943325A
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GB2040453B (en
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Priority to GB7943325A priority Critical patent/GB2040453B/en
Publication of GB2040453A publication Critical patent/GB2040453A/en
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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/032—Analysing fluids by measuring attenuation of acoustic waves
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
    • B01F35/20—Measuring; Control or regulation
    • B01F35/21—Measuring
    • B01F35/213—Measuring of the properties of the mixtures, e.g. temperature, density or colour
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
    • B01F35/20—Measuring; Control or regulation
    • B01F35/22—Control or regulation
    • B01F35/2201—Control or regulation characterised by the type of control technique used
    • B01F35/2208—Controlling using ultrasonic waves during the operation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/01—Indexing codes associated with the measuring variable
    • G01N2291/015—Attenuation, scattering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/022—Liquids
    • G01N2291/0222—Binary liquids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/022—Liquids
    • G01N2291/0224—Mixtures of three or more liquids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/024—Mixtures
    • G01N2291/02433—Gases in liquids, e.g. bubbles, foams
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/10—Number of transducers
    • G01N2291/101—Number of transducers one transducer

Abstract

In various processes, such as the mixing of two or more substances and the washing of substances, the state or degree of admixture of the substances is monitored by ultrasonic energy transmitted to and received from a volume (3), in which the admixture of substances is formed, by means of a transducer arrangement (2, 4). Means (8) responsive to the envelope of the received signal control (a) the mixing of the substances within the volume (3) and/or (b) the entry or exit of substances to or from the volume (3). <IMAGE>

Description

SPECIFIOATION An Apparatus for and a Method of Monitoring Substance Processing This invention relates to an apparatus for and a method of monitoring substance processing. In various processes such as the mixing of two or more substances, and the washing of substances the state or degree of admixture of the substances changes and it is frequently desired to interrupt, say, a mixing operation when a desired degree of mixing has occurred. The present invention is based on an appreciation of the fact that frequently in processes where the state or degree of admixture of substances changes, while the mixture is still non-uniform, variations in the distribution of the various substances through the mixture volume give rise to discontinuities or interfaces which tend to scatter or reflect ultrasonic energy.Various other acoustic properties of admixtures may be dependent upon the state or degree of admixture of the substances concerned.
Thus the present invention provides apparatus for processing substances comprising means defining a volume in which, in use, an admixture of substances is formed, monitoring means, including a transducer arrangement for transmitting ultrasonic energy to and receiving ultrasonic energy from the admixture to produce an electrical signal indicative of the state or degree of admixture of the substances, and means responsive to said signal for controlling (a) the mixing of substances within the volume and/or (b) the entry or exit of substances to or from the volume.
The present invention also provides a method for processing substances, which method comprises forming an admixture of substances in a volume, transmitting ultrasonic energy to and receiving ultrasonic energy from the admixture using a transducer arrangement thereby to produce an electrical signal indicative of the state or degree of admixture of the substances, and controlling (a) the mixing of substances within the volume and/or (b) entry or exit of substances to or from the volume in response to said signal.
The transducer arrangement can provide a signal indicating the uniformity of mixing of the substances. This can be achieved by arranging the monitoring means to detect changes in level of the received signal resulting from scattering or reflection of the ultrasonic energy by interfaces or scattering sources within the admixture.
Once an electrical signal indicative of the state or degree of admixture of the substances has been produced, means responsive to said signal can control the mixing of substances within the volume. The means may interrupt mixing when the signal indicates that a desired degree of uniformity of mixing has been achieved. The means responsive to the signal generated by the monitoring means can also control the entry or exit of substances to or from the volume. For example, the means may control the proportions ot substances added to the volume. Alternatively, when it has been detected that two or more substances have been completely mixed or mixed to a desired degree, the means may cause the mixture to exit from the volume, for example to pass on to a further stage in a multi-stage chemical or other process.
The present invention can be employed to process a wide variety of substances at least one of which is in the solid or liquid phase. It is possible to follow the course of the dissolution or dispersion of solids in a liquid, or the removal of solids from a liquid. The invention may therefore be employed to determine when a solid has become completely dissolved or uniformly dispersed in suspension in the liquid.
The volume in which an admixture of substances is formed can be monitored in a variety of ways. The volume may be a container provided with a sampling tube through which substances are circulated, for example from the bottom of the container to the top. Transducer means can be positioned to direct ultrasonic energy through the sampling tube. Further transducer means can be positioned to receive a proportion of the ultrasonic energy that is scattered and/or reflected by interfaces passing through the sampling tube. Whether the ultrasonic energy is scattered or reflected depends on the relationship between its wavelength and the sizes of the interfaces. The interfaces can be considered as discontinuities within the mix in the sampling tube.The transducer means receiving the ultrasonic energy can be connected to equipment designed to indicate the level of energy received from the reflecting and scattering interfaces. Alternatively, a container may be used without a sampling tube.
In such a case the admixture within the container should be circulated through the effective field of the monitoring means, for example by stirring.
Where continuous mixing occurs, it is of course preferable that the admixture is monitored near the outlet of the mixer.
When two or more substances are mixed together, the degree of uniformity of mixing may be measured in terms of the uniformity of the level of the signal produced by the monitoring means. This may either be monitored continuously or by sampling at predetermined intervals. In this embodiment, acoustically scattering and/or reflecting interfaces attributable to concentrations of an individual substance which have not been completely mixed are indicated by intermittent changes in the signal level as such unmixed material passes through the effective field of the ultrasonic energy. As mixing continues and becomes more complete, such signal changes become less frequent and less marked.
The eventual absence of such changes signifies completion of mixing. Consequently, the time at which substances have become uniformly mixed can be accurately determined and the mixture then passed on, for example, to another step in a chemical process. Thus the period of mixing can be minimised. This can be important in terms of the time taken for the operation of a process and other economic factors.
The present invention can also be used to determine when entrained gas bubbles have been removed from a liquid, for example by allowing the bubbles to rise to the surface of the liquid and thereby escape or are pressed into solution. This can be detected by the monitoring means. There will be progressive change in the level of the electrical signal received from the monitoring means as the bubbles of gas escape, because the liquid will contain fewer acoustically scattering or reflecting interfaces. Means responsive to the signal generated by the monitoring means can control the escape of gas, for example by controlling the pressure of gases above the liquid surface. Alternatively, such means can detect when the dissolved gas has been removed from solution and control the passage of the resultant liquid to a further treatment step.
In a further embodiment, the present invention may be employed to follow the course of a chemical reaction in the liquid phase in which gases are evolved. The course of the reaction can be monitored by the progressive change in the level of ultrasonic energy received from the liquid in which the reaction is taking place. When there is no further change in the signal level, evolution of gases will have stopped and the reaction will be complete. Alternatively, the apparatus in which the reaction is taking place may have been calibrated previously, and when predetermined signal level is reached this will be taken to correspond to the completion of the reaction.
Such measurements enable process times to be minimised or optimised. Means responsive to the signal generated by the monitoring means can perform similar functions to those mentioned above.
The present invention can also determine whether or not a substance, for example a poisonous contaminant which may not be expelled as waste, has been removed from a liquid. In such a method the liquid containing the substances to be removed may be first treated, for example by a filtration system. The liquid emerging can be analysed by the present apparatus and method with transducers being applied to container or connecting pipes as appropriate. The signal from the receiving transducer is monitored for a suitable interval of time. When a recognisable signal level is detected, the substance in question has been sufficiently removed from the liquid. Alternatively the signal may be monitored until a sufficiently smail rate of change related to the contaminant is detected, which indicates that the substance in question has been removed to a satisfactory degree for the desired purpose.Means responsive to the signal level can control the recirculation of the liquid to the treatment stage, or its exit as waste or to a further treatment stage.
The present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of one embodiment of apparatus according to the present invention; and Figure 2 is a somewhat schematic circuit diagram of part of one form of the embodiment of Figure 1.
The apparatus in Figure 1 includes an a.c.
generator 1 supplying a first transducer 2. The transducer 2 is positioned adjacent the wall of a container 3 in which mixing can take place to direct ultrasonic energy through the mixture of substances in container 3. A second transducer 4 positioned adjacent another wall of the container 3 receives ultrasonic energy scattered or reflected from the interfaces of any mixture in the container 3. The transducer 4 is connected in turn to an amplifier 5, an envelope detector 6 and a signal processing circuit 7.
Assume that a continuous H.F. waveform of unvarying electrical potential is applied to the ultrasonic transducer 2. If the substance(s) in the container 3 are stationary there will be present an electrical signal at the terminals of ultrasonic transducer 4 which has two principal components: (a) acoustic energy transmitted directly between the transducers where this is possible, e.g. where the transmitted ultrasonic energy is passed through the wall of the container 3; and (b) acoustic energy reflected and/or scattered from discontinuities in the liquid medium. The discontinuities may be interfaces between different liquid components and/or particulate discontinues in each liquid component where the liquid is not completely homogeneous with regard to the transmission of ultrasonic energy.
The sum of (a) and (b) is an alternating electrical waveform of substantially the same form as that applied to transducer 2 and the envelope of such waveform is unvarying with time if no changes are present in either the transmitted waveform or in the medium through which the acoustic energy passes (it being assumed that temperature and pressure remain constant throughout). The only major exception to the previous statement is due to the pressure of electrical noise generated or otherwise present in the transmitting or receiving apparatus which will result in a modulation of the waveform envelope where such noise is of frequency(s) which falls within the bandwidth of the receiving apparatus.
When the liquid medium is moving, two separate cases can be considered, (i) a liquid containing only particulate discontinuities, i.e. a single liquid or a completely mixed admixture, (ii) a liquid containing the discontinuities referred to in (i) together with interfaces between unmixed liquid/gaseous/solid components. In the former case (i) the received electrical waveform envelope at 4 will be modulated due to two principal effects: (1) the scattered or reflected energy will be contained within a bandwidth of frequencies differing by the (Doppler) shift in frequency, from the originally transmitted frequency due to the movement of the scattering sources within the liquid which have a range of velocities directly related to the bandwidth referred to above.The resulting modulation will contain a bandwidth of difference frequencies between the originally transmitted frequency and each component frequency in the bandwidth of scattered energy.
The second effect (2) mentioned above will be a form of modulation due to variations in the size, shape and concentration of scattering sources within the effective field of the necessary transducer 4.
In addition there will be local variations in the acoustic properties (principally absorption) of the liquid medium which will produce a modulation of scattered and reflected acoustic energy in combination with that referred to in (2) above.
These latter effects will combine to superimpose a substantially lower (random) variation in the modulation envelope due to (1) but nevertheless being also related in some degree to liquid velocity.
In the case (ii) mentioned above all the above effects will be present but in addition, periodic changes will occur due to the passage of interfaces between unmixed components of the mixture. Due to the substantially higher level of energy reflections from such interfaces, there will be an increase in the amplitude of the modulation envelope corresponding to the passage of each such interface and this will be recognisable in the detected response with a diminishing level as mixing continues.
The envelope detector 6 produces a smoothed output representative of the envelope of the output of amplifier 5. This output is delivered to the signal processing circuit 7 which comprises in its simplest form an averaging circuit having a time constant substantially longer than the period of the frequency difference signals from transducer 4, and a comparator for comparing the output of the averaging circuit with a reference value corresponding to a desired state or degree of admixture of the substances in container 3. In the case (ii) above one may be interested in the trend of periodic peaks in the receive envelope and in those circumstances the signal processing circuit may be appropriately designed to monitor the trend of these periodic peaks.
Figure 2 shows one possible form of part of the circuitry of Figure 1. The envelope detector 20 and buffer amplifier 21 are connected to the signal processing circuit which comprises an averaging circuit 22 having its input connected to the output of amplifier 21 and its output in turn connected to one input of a comparator 23. The other input of comparator 23 is connected to a potentiometer 24 to pick off a reference voltage representative of the desired degree of admixture of the substances in container 3.
The envelope of scattered ultrasonic energy can be displayed in any suitable form, e.g.
visually, by the signal processing circuit 7.
In addition, the circuit 7 is arranged to produce one or more signals for controlling parameters of the process which determine the state or degree of admixture of the substances in question via control element 8. For example in the case of a mixer having a rotary or other mixing element the circuit 7 could be arranged to produce a stop signal to interrupt operation of the mixing element. Signals from circuit 7 could of course operate other elements such as inlet and outlet valves.
The apparatus may be used to determine when, for example, a quantity of solid material has been dissolved or uniformly dispersed in suspension in a liquid. The solid and the liquid are introduced into the container 3 and are circulated within the container by a stirrer (not shown).
Whilst the solid and liquid are being stirred, ultrasonic energy is passed into the container by transducer 2. Some of the ultrasonic energy, scattered or reflected from solid-liquid interfaces within the container 3, is detected by the transducer 4 and processed to obtain a visual display of the signal level. When mixing of the solid and liquid first commences there are frequent changes in the signal level. As mixing continues, these decrease in number and are less marked; the circuit may be arranged so as to detect this effect and produce control signals when appropriate. When the solid had been completely dissolved or uniformly dispersed in the liquid, changes in the signal level will be minimal or recognisable as representing changes due to the mixing process. Means responsive to the signal level can control the proportions in which the solid and/or liquid is added to the container 3, the rate of stirring, or the exit of the resultant solution or dispersion to a further treatment step.

Claims (8)

Claims
1. Apparatus for processing substances comprising means defining a volume in which, in use, an admixture of substances is formed, monitoring means including a transducer arrangement for transmitting ultrasonic energy to and receiving ultrasonic energy from the admixture to produce an electrical signal indicative of the state or degree of admixture of the substances, and means responsive to said signal for controlling (a) the mixing of substances within the volume and/or (b) the entry or exit of substances to or from the volume.
2. Apparatus according to Claim 1 wherein the monitoring means is arranged to provide, in use, a signal indicating the uniformity of mixing of the substances.
3. Apparatus according to Claim 1 or 2 wherein the monitoring means is arranged to detect changes in received signal level resulting from scattering or reflection of ultrasonic energy from interfaces or scattering sources within the admixture.
4. Apparatus according to any one of the preceding claims wherein the means responsive to the electrical signal is arranged to interrupt, in use. mixing of substances when the signal indicates that a desired degree of uniformity of mixing has been achieved.
5. Apparatus according to any one of the preceding claims wherein means responsive to the electrical signal is arranged to control, in use, the proportions of substances added to the volume.
6. Apparatus for processing substances constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.
7. A method of processing substances, which method comprises forming an admixture of substances in a volume, transmitting ultrasonic energy to and receiving ultrasonic energy from the admixture using a tranducer arrangement thereby to produce an electrical signal indicative of the state or degree of admixture of the substances, and controlling either (a) the mixing of substances within the volume and/or (b) entry or exit of substances to or from the volume in response to said signal.
8. A method of processing substances substantially as hereinbefore described with reference to the accompanying drawing.
GB7943325A 1978-12-18 1979-12-17 Monitoring mixing of substances Expired GB2040453B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB7943325A GB2040453B (en) 1978-12-18 1979-12-17 Monitoring mixing of substances

Applications Claiming Priority (2)

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GB7848832 1978-12-18
GB7943325A GB2040453B (en) 1978-12-18 1979-12-17 Monitoring mixing of substances

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GB2040453A true GB2040453A (en) 1980-08-28
GB2040453B GB2040453B (en) 1983-01-06

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0108849A1 (en) * 1982-11-16 1984-05-23 General Signal Corporation Apparatus and method for controlling consistency
GB2155180A (en) * 1982-06-11 1985-09-18 Micro Pure Systems Inc Ultrasonic particulate sensing & identification
GB2192060B (en) * 1986-06-27 1990-08-01 Electricity Council Method of and apparatus for detecting interfaces
EP0493946A2 (en) * 1990-12-31 1992-07-08 Westinghouse Electric Corporation Method for monitoring the admixing of fluent materials
WO2009144209A1 (en) * 2008-05-27 2009-12-03 Alifax Holding Spa Mixing device and relative mixing method
WO2020064283A1 (en) * 2018-09-26 2020-04-02 Abb Schweiz Ag Non-invasive monitoring of a mixing process in a container

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2155180A (en) * 1982-06-11 1985-09-18 Micro Pure Systems Inc Ultrasonic particulate sensing & identification
EP0108849A1 (en) * 1982-11-16 1984-05-23 General Signal Corporation Apparatus and method for controlling consistency
GB2192060B (en) * 1986-06-27 1990-08-01 Electricity Council Method of and apparatus for detecting interfaces
EP0493946A2 (en) * 1990-12-31 1992-07-08 Westinghouse Electric Corporation Method for monitoring the admixing of fluent materials
EP0493946A3 (en) * 1990-12-31 1992-10-28 Westinghouse Electric Corporation Method for monitoring the admixing of fluent materials
WO2009144209A1 (en) * 2008-05-27 2009-12-03 Alifax Holding Spa Mixing device and relative mixing method
WO2020064283A1 (en) * 2018-09-26 2020-04-02 Abb Schweiz Ag Non-invasive monitoring of a mixing process in a container
CN112740027A (en) * 2018-09-26 2021-04-30 Abb瑞士股份有限公司 Non-invasive monitoring of a mixing process in a container

Also Published As

Publication number Publication date
GB2040453B (en) 1983-01-06

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Legal Events

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746 Register noted 'licences of right' (sect. 46/1977)
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19981217