EP0767897A1 - Appareil de mesure pour un epaississeur de boues - Google Patents

Appareil de mesure pour un epaississeur de boues

Info

Publication number
EP0767897A1
EP0767897A1 EP95923124A EP95923124A EP0767897A1 EP 0767897 A1 EP0767897 A1 EP 0767897A1 EP 95923124 A EP95923124 A EP 95923124A EP 95923124 A EP95923124 A EP 95923124A EP 0767897 A1 EP0767897 A1 EP 0767897A1
Authority
EP
European Patent Office
Prior art keywords
vessel
liquid
solids
conductivity
resistivity
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP95923124A
Other languages
German (de)
English (en)
Other versions
EP0767897A4 (fr
Inventor
Vince Robert Dooley
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Alcoa of Australia Ltd
Original Assignee
Alcoa of Australia Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Alcoa of Australia Ltd filed Critical Alcoa of Australia Ltd
Publication of EP0767897A1 publication Critical patent/EP0767897A1/fr
Publication of EP0767897A4 publication Critical patent/EP0767897A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/24—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of resistance of resistors due to contact with conductor fluid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/0023—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm with a probe suspended by a wire or thread
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/06—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a liquid

Definitions

  • THIS INVENTION relates to a method and an apparatus for the determination of the concentration of solids in a liquid.
  • the method and apparatus are particularly useful in the alumina processing industry for determining the interface between red mud and green liquor.
  • Measurements based on turbidity are most common and give excellent results in clean liquids but have a limited application range in liquids commonly encountered in, for example, mineral processing.
  • One explanation for this is that they require frequent maintenance in processes where precipitate scales form on the detector.
  • a method of measuring the interface between a liquid and settled solids in a vessel comprising the steps of: (a) monitoring the electrical conductivity or resistivity of the liquid in the vessel at different levels therein;
  • an apparatus for determining the concentration of solids in a liquid in a vessel comprising in combination:
  • monitoring means associated with the electrical conductivity or resistivity measuring means the monitoring means being capable of recording electrical conductivity or resistance levels within the vessel and being capable of determining the concentration of solids from the electrical conductivity or resistivity results.
  • liquid used herein is intended to include, but is not limited to, any liquid solution, homogenised liquids, slurries and particulate material in gaseous suspension which behave as a liquid.
  • the method and apparatus of the invention may be employed in any process where it is important to monitor the solids content in a liquid in a vessel and where the solids exhibit some electrical conductive or resistive properties.
  • the method and apparatus may be applied to brine tanks, settling tanks, slurry tanks, any tank with a solid/liquid interface, calcium carbonate clarifiers and the like. It is convenient, therefore to explain the present invention, by way of example, in the context of its application to the alumina processing industry where it is used to determine the interface between red mud (i.e Bayer mud) and green liquor (i.e the alumina-bearing solution).
  • Alumina is typically produced from bauxite by the Bayer process.
  • aqueous caustic soda is used to treat bauxite under high temperature and pressure.
  • aluminium hydroxide present in the bauxite dissolves in the caustic solution forming a sodium aluminate.
  • the insoluble residues form red mud which is primarily composed of the oxides of iron, silica and clay.
  • sodium aluminate solution and caustic soda are separated from the red mud and other insoluble materials.
  • Coarse waste particles e.g sand etc.
  • red mud is then separated from the green liquor by a gravity sedimentation method in large diameter vessels known as thickeners.
  • the underflow from these vessels is known as "red mud” while the overflow is known as "green liquor”.
  • Red mud removed as underflow is washed in large washing tanks to remove valuable caustic soda for reuse.
  • Information concerning the interphase between red mud and the green liquor is important to improve efficiency and to institute process controls and automation.
  • Electrical conductivity or resistivity may be measured by any means known in the art. Preferably, that means is capable of withstanding high temperature and a caustic environment. Electrical conductivity may, for example, be measured using electrodes or toroidal sensors.
  • the concentration of solids in the liquid in a vessel has been found to be a function of the electrical conductivity or resistivity and of the temperature of the liquid in that vessel. Where the temperature of the liquid is consistent throughout the volume of the vessel, electrical conductivity or resistivity bares a direct inverse relationship to the concentration of solids in the liquid. Thus, temperature measurements are not generally required where temperature is constant. However, the temperature of the vessel is preferably monitored to ensure temperature consistency throughout the vessel whilst conductivity resistivity measurements are taken.
  • Process fluids encountered in the alumina industry are generally conductive but solids such as mud and sand behave as insulators.
  • the presence of dispersed solid particles reduce the fluid conductivity by a ratio which is dependent on the volumetric concentration of solids. This principle applies for any combination of solids and fluid where the ratio of their conductivities exceeds a value known as the Critical Conductivity Ratio (CCR).
  • CCR Critical Conductivity Ratio
  • the monitoring means is preferably connected to a temperature measuring device which is capable of determining temperatures of the liquid at different levels within the vessel.
  • a temperature measuring device that device should be capable of withstanding high temperatures and a caustic environment.
  • the temperature measuring device when present, is in communication with the monitoring means which in turn directs temperature data to be recorded at the same time that electrical conductivity or resistivity readings are taken.
  • the temperature measuring device may, for example, be a thermistor, a thermocouple, a resistance temperature device (RTD) or some other thermal detector. Further, the temperature measuring device may be positioned in combination with the conductivity or resistivity measuring means as a single sensor unit.
  • Figure 2 illustrates one form of the electrical conductivity measuring device of the present invention
  • Figure 3 is a graph showing the output data from 5 different liquid concentrations measured over varying electrical conductivity and temperature regimes; and Figure 4 illustrates an alternative form of the electrical conductivity measuring device of the present invention.
  • Figure 2 depicts an apparatus for determining the concentration of solids or for measuring the interface between a liquid and settled solids in a settling vessel, consisting of a conductivity sensor 1 which is in electrical communication with and suspended by a cable 2 from a winch 3.
  • the winch is controlled by the operation of a motor 4 which is controlled by a monitoring means 5.
  • the conductivity sensor signals are transferred from the cable 2 by sliprings 6 to a conductivity meter 7.
  • the conductivity data is then passed from the conductivity meter to the monitoring means 5 which measures positional data from a shaft encoder 8 and controls the position of the conductivity sensor by instructing the winch 3 to raise, lower or hold the sensor in any position inside the settlement vessel.
  • the monitoring means is adapted to continuously examine conductivity data from the sensor.
  • the conductivity sensor 1 is lowered at a predetermined speed into the settling vessel.
  • the monitoring means 5 records the position of the conductivity sensor 1 and the electroconductivity at different points. If a temperature sensor is present the monitoring means would also measure temperature at each point. From such data, the interface between green liquor and red mud may be identified as indicated by a substantial change (e.g decrease) in conductivity. The monitoring means 5 then indicates the position of the interface by any suitable means.
  • the present invention may also be used to control the level of red mud in a settling vessel.
  • the conductivity sensor 1 may be variably positioned within the settling vessel. The location of the conductivity sensor 1 will correspond to the maximum height that the red mud may rise to according to process control requirements.
  • the monitoring means 5 continuously examines electrical conductivity data from the conductivity sensor 1. When electrical conductivity reaches a predetermined value which corresponds to the maximum height to which the red mud may rise the monitoring means would produce a signal which automatically initiates withdrawal of red mud from an outlet in the bottom of the settling vessel.
  • the method of the present invention may also be used in rake- equipped tanks, for example to control the level of red mud in a liquid (i.e tanks equipped with automatic stirrers which are capable of maintaining solids liquid).
  • the monitoring means 5 is in electrical communication with the drive motor for the rake and is adapted to raise the conductivity sensor 1 when the rake approaches, and holds the output signal constant until the rake passes.
  • the monitoring means may then reposition the sensor at the last point of measurement prior to the rake approaching and resume recording data.
  • the monitoring means may reintroduce the sensor in to the liquid and commence continually recording data until it reaches the bottom of the vessel whereupon it returns to the surface.
  • the monitoring means When electrical conductivity reaches a pre- determined valve which corresponds to the maximum concentration of suspended solids in a liquid the monitoring means would signal that the pre-determined concentration was reached. In addition to or in the alternative the monitoring means would also direct an outlet means to open to release the liquid suspension. The same monitoring means may also direct the delivery of further liquid and or solid into the vessel.
  • the liquid in this instance preferably consists of one or more flocculants (ie. a settling and clarification aid). While the foregoing method is described for use in rake- equipped vessels it would be appreciated that the same method would be applicable to vessels devoid of a rake apparatus.
  • Figure 3 illustrates graphically test results showing the relationship between temperature, electrical conductivity, and solids concentration from a mud slurry in a sodium aluminate solution. The points on the graphs of Figure 3 show that at a constant temperature electrical conductivity decreases as solid concentration increases.
  • Figure 4 illustrates an alternative form of the invention wherein there is provided a doughnut style toroidal conductivity detector 10 suspended on a cable 12 which may be insulated with high temperature teflon, from a winch 14. The detector is connected to the cable by an underwater breakaway connector 16. The cable is connected to the winch and is in electrical communication with a conductivity transmitter 18. The conductivity transmitter is mounted in the winch drum 20 to avoid the need to pass low level detector signals across slip rings.
  • the conductivity signal wiring passes along the inside of the winch main shaft 22 to a rotary connector 24 mounted on the opposite end of the shaft. From there the signal is connected back to a small modular style controller (not shown) such as PLC, which is used to control the detector and record data from the detector.
  • a small modular style controller such as PLC, which is used to control the detector and record data from the detector.
  • the winch 14 is driven by a motor 26 having, an integral worm reduction gearbox 28 which serves to reduce the speed and prevent runaway of the winch under the weight of the detector. Further speed reduction is achieved through a timing belt and/or pulleys to give a winch speed of approximately 3m/min.
  • the present apparatus has a pulley on the motor output shaft which is mounted to a slip clutch 30 so that in the event of the detector being caught up on something inside the fluid containing vessel then the slip clutch will allow the cable to peel off the drum and disconnect therefrom.
  • a quick release socket (not shown) is used to wire the detector cable to the winch drum.
  • a secondary shaft 32 may be used to drive a rotary limit switch 34 with upper and lower winch settings. Also mounted on this shaft are gears which operate a proximity switch 36 for position measurement by the controller.
  • the conductivity transmitter 18 is mounted centrally in the winch drum on a flanged collar (after removing the terminal cover from the transmitter).
  • the conductivity transmitter is preferably a microprocessor based transmitter.
  • the detector is preferably able to operate reliably in caustic solution at 100- 120°C (eg 106°C).
  • the cable should also be able to withstand the same environment.
  • the present invention includes a wash system (not shown) to keep the winch cable clean and minimises scale build up on the detector.
  • the wash system may have two different types of wash nozzles. Straight nozzles should be used to wash the cable while deflection nozzles should be used to wash the detector.
  • the nozzles are mounted to the apparatus in close proximity to the cable and the detector to provide a washing thereof.
  • limit switches need to be mounted on the rake drive mechanism to provide an interlock so that the unit will operate in the safe zones between rake passes.
  • the apparatus initiates a scan each time the rake limits make a transition from an unsafe zone to a safe zone.
  • the winch lowers the detector into the vessel updating a reference position as the detector leaves the upper limit setting.
  • the controller records the fluid conductivity in that zone to use as a reference to calculate solids. Once in the scan range the controller continuously calculates the solids concentration from the conductivity readings and the reference reading. The controller calculates the position of the detector by counting the proximity pulses from the gear teeth. It counts on both positive and negative transitions so that each pulse represents 10mm or 1 cm.
  • the outputs are updated during the scan and are held until the next scan.
  • the output reaches a preset point the unit ceases scanning and returns to the upper limit position.
  • a wash system cleans the cable when the detector is being raised from the vessel and operates after each cycle to minimising scale growth on the detector.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Fluid Mechanics (AREA)
  • General Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • Electrochemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Thermal Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

L'invention concerne un appareil pour mesurer la concentration des matières solides ou pour localiser l'interface entre un liquide et des matières solides décantées dans une cuve de décantation comprenant (a) un dispositif de mesure de la conductivité électrique ou de la résistivité, agencé pour mesurer ces valeurs dans un liquide dans une cuve et (b) un dispositif de commande capable d'enregistrer la conductivité électrique ou la résistivité et de déduire à partir de ces valeurs la concentration en matières solides. L'appareil en question comprend une sonde (1) de mesure de la conductivité qui est connectée électriquement à un câble de support (2) accroché à un treuil (3). Le treuil est actionné par un moteur (4) commandé par un dispositif de commande (5). Les signaux de conductivité sont transmis par le câble (2) à une bague glissante (6) et ensuite à un dispositif de mesure de la conductivité (7). Les valeurs de conductivité sont transmises du dispositif de mesure de la conductivité au dispositif de commande (5). Ce dernier reçoit également des données de position à partir d'un capteur de position angulaire (8) et il commande la position de la sonde de mesure de la conductivité en ordonnant au treuil (3) de monter, descendre et tenir la sonde dans une position choisie à l'intérieur de la cuve de décantation. Le dispositif de commande permet d'analyser continuellement les données fournies par la sonde.
EP95923124A 1994-06-29 1995-06-27 Appareil de mesure pour un epaississeur de boues Withdrawn EP0767897A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
AUPM6540/94 1994-06-29
AUPM6540A AUPM654094A0 (en) 1994-06-29 1994-06-29 Thickener mud gauge (conductivity)
PCT/AU1995/000377 WO1996000885A1 (fr) 1994-06-29 1995-06-27 Appareil de mesure pour un epaississeur de boues

Publications (2)

Publication Number Publication Date
EP0767897A1 true EP0767897A1 (fr) 1997-04-16
EP0767897A4 EP0767897A4 (fr) 1998-08-19

Family

ID=3781109

Family Applications (1)

Application Number Title Priority Date Filing Date
EP95923124A Withdrawn EP0767897A4 (fr) 1994-06-29 1995-06-27 Appareil de mesure pour un epaississeur de boues

Country Status (5)

Country Link
EP (1) EP0767897A4 (fr)
AU (1) AUPM654094A0 (fr)
BR (1) BR9508193A (fr)
CA (1) CA2193360A1 (fr)
WO (1) WO1996000885A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110440871A (zh) * 2019-08-07 2019-11-12 深圳市建设工程质量检测中心 基于电位法的地下水位测量方法、装置和计算机设备

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4066211B2 (ja) * 1997-06-06 2008-03-26 財団法人国際科学振興財団 電荷転送増幅回路、電圧比較器及びセンスアンプ
AU776779B2 (en) * 1999-09-01 2004-09-23 De Beers Consolidated Mines Limited Apparatus and method for detecting the level of a mud bed
KR100449258B1 (ko) * 2002-11-25 2004-09-18 오상택 환경시험용 챔버 제조방법
FI20105197A7 (fi) 2010-03-01 2011-09-02 Outotec Oyj Aineiden välisiä rajapintoja ilmaiseva sondi
US9506850B2 (en) 2013-05-06 2016-11-29 Westech Engineering, Inc. Apparatus and method for determining one or more characteristics of a viscous material
CN103743650A (zh) * 2014-01-29 2014-04-23 长沙矿山研究院有限责任公司 一种尾砂浆最大沉降浓度和最大沉降容重的测试方法
CN109357725B (zh) * 2018-12-05 2020-10-09 飞翼股份有限公司 一种泥层高度自动测量装置及测量方法
CN109682729B (zh) * 2019-01-31 2021-08-20 广西壮族自治区环境监测中心站 一种用于土壤检测的数据采集系统及方法
CN112445136B (zh) * 2020-12-16 2022-02-22 北京科技大学 一种基于连续时间神经网络的浓密机预测控制方法及系统

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US2551983A (en) * 1944-05-19 1951-05-08 Phillips Petroleum Co Level indicator of interface between acid and hydrocarbon layers
JPS5780541A (en) * 1980-11-08 1982-05-20 Fuji Electric Co Ltd Measuring method for sludge concentration in condensing tank
JPS5926015A (ja) * 1982-08-03 1984-02-10 Sumitomo Jukikai Envirotec Kk 沈殿槽の汚泥界面検出方法
NO156305C (no) * 1982-09-17 1987-08-26 Tanksystem As Anordning for registrering av nivaa, overgangssoner og temperatur.
DD264296A1 (de) * 1987-08-28 1989-01-25 Berlin Ing Hochschule Verfahren und vorrichtung zur teilchengroessenanalyse
AU625347B2 (en) * 1989-05-08 1992-07-09 Australian Institute Of Marine Science Measurement of sediment level
AU6273190A (en) * 1989-08-25 1991-04-03 Europa International Manufacturing Pty Ltd Level sensing device
JPH0399280A (ja) * 1989-09-13 1991-04-24 Hioki Ee Corp 温度補正機能付き抵抗計
EP0422893B1 (fr) * 1989-10-13 1993-06-23 Alcan International Limited Procédé et appareil pour la décantation de suspensions
AU6093690A (en) * 1990-08-14 1992-06-04 Multotec Cyclones (Pty) Limited Device and method for determining the position of an interface between lower and upper fluid phases

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110440871A (zh) * 2019-08-07 2019-11-12 深圳市建设工程质量检测中心 基于电位法的地下水位测量方法、装置和计算机设备

Also Published As

Publication number Publication date
BR9508193A (pt) 1997-08-12
AUPM654094A0 (en) 1994-07-21
WO1996000885A1 (fr) 1996-01-11
EP0767897A4 (fr) 1998-08-19
CA2193360A1 (fr) 1996-01-11

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