SE544240C2

SE544240C2 - Slurry treatment with adjusted feed rate of additional liquid

Info

Publication number: SE544240C2
Application number: SE1951082A
Authority: SE
Inventors: Paul Davies
Original assignee: Metso Sweden Ab
Priority date: 2019-09-25
Filing date: 2019-09-25
Publication date: 2022-03-15
Also published as: SE1951082A1; CN212941642U; WO2021058802A1; CN112546684A

Abstract

The invention relates to an arrangement (100) for determining properties of a slurry comprising solids suspended in liquid, the arrangement (100) comprising a treatment vessel (1) having a predefined volume, a first sensor (7) arranged at or near the treatment vessel (1) and arranged to determine a settling rate of solids of said slurry when contained in the treatment vessel (1) and a second sensor (6) arranged at or near the treatment vessel (1) and arranged to determine a density of the slurry contained in the treatment vessel (1). An output from said second sensor (6) can be used to determine the percent solids in the slurry.

Description

The present invention relates to the determination of properties of aslurry, for example within the mining industry.

BACKGROUND OF THE INVENTION When extracting minerals or other valuable materials from the earth,resource consumption, such as power and water, is coming more and moreinto focus. Thickeners, sometimes also called clarifiers, depending on theapplication, can be used to recover immediately reusable process water, aswell as to extract fines and other materials. Thickeners are applied in e.g. themineral and aggregate industry but also in wastewater management. Theadvantages vary between different applications. For example, thickeners canbe used in locations where water is in short supply such that reusableprocess water can be fed back to the plant. They can also be used to reducethe size of, or if combined with filtration of the underﬂow of the thickener,possibly eliminate, tailings dams and to remove minerals and fines fromwater. To improve settling properties of the thickener, additives comprisingchemicals such as coagulants and/or flocculants are used. ln order to obtainoptimum settling properties, it is known to use so-called turbidity sensorswhich intermittently measures the settling rate of particles suspended in theliquid. Based on the information provided by the turbidity sensor, the feed rateof the additives can be adjusted to maintain optimal settling properties.

SUMMARY OF THE INVENTION The invention is based on the realization that the previously usedsolution of adjusting an additive feed rate based on the output from a turbiditysensor has certain drawbacks. For example, it is known that flocculation isbest performed within a certain range of feed solids content measured forexample as percentage by weight. However, it is often the case that in a slurry transported to a thickener the feed solids content will vary over timeand it has also been determined that the optimal range will vary with differentsolids, e.g. varying particle size distribution; varying particle material, etc. Anobject of the invention is to overcome, or at least lessen the above-mentionedproblems, especially those related to feeding of thickeners.

A particular object is to provide an arrangement for determiningproperties of a slurry comprising solids suspended in liquid. To better addressthis concern, in a first aspect of the invention there is provided anarrangement comprising a treatment vessel having a predefined volume; afirst sensor arranged at or near the treatment vessel and arranged todetermine a settling rate of solids of the slurry when contained in thetreatment vessel; a second sensor arranged at or near the treatment vesseland arranged to determine a density of the slurry contained in the treatmentvessel and wherein an output from the second sensor can be used todetermine the percent solids in the slurry. Being able to monitor the settlingrate and the percent solids in the slurry makes it possible to continuouslyobtain relevant detailed information about the slurry. And arranging bothsensors at or near the treatment vessel creates a compact solution with allnecessary equipment conveniently located.

The arrangement further comprises a control unit arranged to receivesignals from at least the second sensor, wherein the control unit is arrangedto determine the percent solids in the slurry based on the output from thesecond sensor. By determining the density of the content in the treatmentvessel, i.e. the slurry, it is possible to determine the percent solids in theslurry. This can be achieved by knowing the density of the liquid phase of theslurry, usually water, and assuming that the density of the solids is the samefor all particles. Thereafter the percent solids in the slurry can easily becalculated. To have continuous updates about the percent solids in the slurrymakes it easier to decide feed rate of the additive.

The control unit is arranged to adjust a feed rate of additional liquid that may be added to the slurry based on information from the__;š*_š_ second sensor. Additional liquid, also called dilution liquid, can be added to the slurryto reduce the solids content in the slurry. This may for example be beneficialto increase the performance of the additive, such as ﬂocculants. ln accordance with an embodiment of the arrangement, the control unitis arranged to receive signals from at least the first and second sensor andthe control unit is arranged to adjust a feed rate of an additive to the slurrybased on the output from the first sensor. This allows for continuousadaptation of the additive feed rate.ln accordance with an embodiment of the arrangement, the feed rate ofadditional liquid that may be added to the slurry is based on information fromthe first and the second sensor. This is an especially convenient solutionsince it allows both the settling rate and the percent solids to influence thedilution water.ln accordance with an embodiment of the arrangement, the additivecomprises a chemical such as a coagulant or a flocculant.ln accordance with an embodiment of the arrangement, the control unit is arranged to adjust the feed rate of additional liquid that may be added tothe slurry based on information from first and the secondsensor as well as information about a feed rate of the additive. ln a givensituation, it may be predicted that optimal ﬂocculation will occur within acertain range of percent solids. And based on the information from the firstand the second sensors it may be the case that flocculation is taking placeaccording to plan. However, it is possible that in order to achieve thisflocculation, the flocculant pump is running at a very high rate or even at ornear its maximum, which would indicate that flocculation is indeed notperformed as intended. As an explanatory example only, a situation wherethe percent solids is within the intended range and the settling rate sensorindicates that ﬂocculation is taking place as planned but where the amount offlocculant required to achieve this is much higher than expected such that thepump is running at e.g. 100% instead of e.g. 65%. Assuming that theflocculant is at the correct strength, this could indicate that the presumedoptimal range of percent solids in the slurry is incorrect. ln response to this information, the control unit can be arranged to increase or decrease theamount ofdilution water fed to the slurry such that a new, more correct rangeof percent solids can be determined. Without monitoring the actual feed rateof the additive, in addition to the information provided by the first and secondsensors, this could go on undetected for a long time. ln accordance with an embodiment of the arrangement, the secondsensor comprises at least one load cell arranged to determine the weight ofthe slurry contained in the treatment vessel. Using a load cell is simple andreliable solution. Since the weight of the treatment vessel as such as well asany auxiliary equipment attached to the treatment vessel is known and sincethe volume of the treatment vessel is known, the output from the load cell caneasily be used to determine the density of the slurry in the treatment vessel.This could be done by for example a lookup table by means of which thedensity of the slurry can be determined. ln accordance with an embodiment of the arrangement, the first sensorcomprises a turbidity sensor. Turbidity sensors or turbidity probes are wellknown in the art and provide reliable function for determining settling rate ofparticles. ln accordance with an embodiment of the arrangement, thearrangement further comprises a third sensor arranged upstream thetreatment vessel and the first and the second sensor, wherein the third sensoris arranged to determine a density of the slurry upstream of the treatmentvessel and wherein an output from this third sensor can be used to determinethe percent solids in the slurry. ln accordance with an embodiment of the arrangement, the additionalliquid is added to the slurry downstream of the third sensor and upstream ofthe second sensor. This has the advantage that it is possible to determine thepercent solids of both the diluted and the undiluted slurry. This makes itpossible to add dilution liquid to the slurry based on the output from the thirdsensor only. For example, if it is determined that the undiluted slurry has toohigh solids content, it can be diluted to achieve a predefined percent solidscontent in the slurry. Further, with the information provided by the sensorsarranged downstream of the addition of dilution liquid, i.e. the first and second sensors and possibly also the information from the additive pump, it ispossible to fine tune the addition of dilution liquid.ln accordance with an embodiment of the arrangement, the third sensor is arranged at or near a second treatment vesse| having a predefinedvolume. Similar to how the first and second sensors are arranged, the thirdsensor is arranged at or near a treatment vesse| having a predefined volumewhich can be filled with slurry such that the density thereof can be determinedand thus the percent solids in the undiluted slurry.

According to a second aspect of the invention, there is provided amethod for determining properties of a slurry comprising solids suspended inliquid, the method comprising the steps of providing a treatment vesse| havinga predefined volume; determining a settling rate of solids of the slurrycontained in the treatment vesse| by means of a first sensor arranged at ornear the treatment vesse|; determining a density of the slurry contained in thetreatment vesse| by means of a second sensor arranged at or near thetreatment vesse|; determining the percent solids in the slurry using an outputfrom said second sensor. lt should be noted that the steps of the methodneed not be performed in the order they are mentioned above. For example,the determination of the settling rate can be done independently of thedetermination of the percent solids.

The method further comprises the step of determining the percentsolids in the slurry based on the output from the second sensor by means of acontrol unit which is arranged to receive signals from at least said secondsensor.

The method further comprises the step of adjusting a feed rate ofadditional liquid that may be added to the slurry based on information from :tayšuthe second sensor by means of the control unit. ln accordance with an embodiment of the method, wherein the control unit is arranged to receive signals from at least the first and second sensorsand wherein the method further comprises the step of adjusting a feed rate ofan additive to the slurry based on the output from the first sensor by means ofthe control unit.

N WN» :h »w WN” .- :NN. Å .ANA ln accordance with an embodiment of the method, wherein the additivecomprises a chemical such as a coagulant or a flocculant. ln accordance with an embodiment of the method, the method furthercomprises the step of adjusting the feed rate of additional liquid that may beadded to the slurry based on information from at least one of the first and thesecond sensor as well as information about the feed rate of the additive. ln accordance with an embodiment of the method, the method furthercomprises the step of providing a third sensor upstream of the treatmentvessel and the first and the second sensor and determining a density of theslurry upstream of the treatment vessel and wherein an output from the thirdsensor can be used to determine the percent solids in the slurry. ln accordance with an embodiment of the method, wherein theadditional liquid is added to the slurry downstream of the third sensor andupstream of the second sensor. ln accordance with an embodiment of the method, the method furthercomprises the step of arranging the third sensor at or near a secondtreatment vessel.

Similarly, and correspondingly to the arrangement disclosed above, theembodiments of this method in accordance with this second aspect willprovide substantial advantages over prior art solutions.

Other objectives, features, and advantages of the present invention willappear from the following detailed disclosure, from the attached claims, aswell as from the drawings. lt is noted that the invention relates to all possiblecombinations of features.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitly definedotherwise herein. All references to “a/an/the [element, device, component,means, step, etc.]” are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unlessexplicitly stated otherwise.

As used herein, the term “comprising” and variations of that term arenot intended to exclude other additives, components, integers or steps.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail and with reference to theappended drawings in which: Fig. 1 shows a schematic structure of the arrangement in accordancewith a first embodiment of the invention.

Fig. 2 shows a first embodiment of a treatment equipment inaccordance with the invention.

Fig. 3 shows a second embodiment of a treatment equipment inaccordance with the invention.

DESCRIPTION OF EMBODIMENTS The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplifying embodimentsof the invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limited tothe embodiments set forth herein; rather, these embodiments are provided forthoroughness and completeness, and to fully convey the scope of theinvention to the skilled addressee. Like reference characters refer to likeelements throughout.

Referring now to figure 1, it can be seen that the arrangement 100 maystart with a feed flow F intended to enter a thickener 20. The feed flow Ftypically comprises a slurry coming from a previous step in for example amineral processing facility. The thickener is arranged to separate water viathe overflow 21 and recover e.g. fines from the slurry at the underflow 22. Thewater can then be reused in the mineral processing or be otherwise takencare of in subsequent treatment steps. The underflow will typically betransported towards for example a tailings dam or further treated to recover valuable material therefrom. ln order to optimize the function of the thickener20, chemicals are often added to the slurry, such as flocculants which areintended to ﬂoc solid particles to each other in order to increase their settlingrate. Flocculants may for example comprise non-ionic, anionic or cationicflocculants. Such flocculant may in this embodiment added to the slurry at anearlier stage and be present in the feed flow F. A first treatment vessel 1 anda second treatment vessel 2 are arranged such that they may extract samplesat different locations along the feed towards the thickener or from thethickener. Also, to be seen is a dilution flow DF arranged to let water from theoverflow of the thickener flow back into the feed flow F when and if so isrequired.

Referring to figures 1-3, different embodiments of invention will be described.A first slurry sample may be pumped, or otherwise transported, into thetreatment vessel 2 through sample intake 3 from the feed flow F. Thetreatment vessel has a defined volume and may be arranged with an overflowor similar such that the treatment vessel 2 is always filed with the exact samevolume of slurry. When the treatment vessel 2 is filled a pinch valve 4 isactivated and closes the flow of slurry towards the treatment vessel 2.Arranged at or near the pinch valve 4 is also a vacuum relief valve 5, which,when activated, will drain the pipe system 3 leading to the treatment vessel 2.This has the advantage that the subsequent measurements are notnegatively influenced by any slurry remaining in the pipes 3. Located belowthe treatment vessel 2 is a load cell 6 which is arranged to measure theweight of the treatment vessel 2. The load cell 6 may of course be locatedanywhere suitable. For example, the treatment vessel 2 may be arranged tohang from the load cell 6. As long as the load cell 6 is able to determine theweight of the treatment vessel 2, the exact location thereof is less relevant.Since the weight of all equipment, treatment vessel 2 and any auxiliaryequipment, is known and since the volume of the treatment vessel is known, itis easy to deduct the exact weight of the slurry sample located within thetreatment vessel. And since the density of water is known and if it is assumedthat the solid particles of the slurry all have the same density, the weight percentage of solids TS in the slurry can easily be calculated from a simpleweight measurement of the sample. The treatment vessel 1, seen in figure 2,has the exact same configuration except that it further comprises a clarometerin the form of a turbidity sensor 7 which is arranged to determine the settlingrate SR of the particles in the treatment vessel 1. The settling rate is anindicator as to if the amount of f|occu|ant is correct and is therefore oftenmonitored. The integration of both clarometer 7 and load cell 6 into the sametreatment vessel provides a compact solution in one unit. The equipment alsoincludes a control unit 7 arranged in communication with the other parts of theequipment. As can be seen in figure 1, the treatment vessel 1 is locateddownstream of the entrance of any dilution water DF whereas treatmentvessel 2 is arranged upstream of the entrance of DF. This allows forcontinuous monitoring of undiluted slurry as well as diluted slurry and as willbe described below, this has several advantages.

One way of running the arrangement of the invention is to determine asetpoint for the total solids content TS in the diluted slurry and a setpoint forthe settling rate SR. ln this case the control unit will run the pump for dilutionwater based on information regarding the total solid content TS fromtreatment vessels 1, 2 only where the output from the sensor of treatmentvessel 2 can be used to provide information about the total solid content TS ofthe undiluted slurry which is then used to determine the amount of dilutionliquid necessary and the output from the sensor of treatment vessel 1 may beused to provide feedback as to the total solid content TS in the diluted slurry.ln this embodiment, the f|occu|ant pump will be run based on informationregarding the settling rate SR in treatment vessel 1 only. The measurementsof total solid content TS and the settling rate SR are done with the intention ofmaintaining their individual setpoints. However, it is also possible to operatethe system in a more integrated manner where the input from all sensors aretaken into consideration. lt is often is assumed that a certain range of totalsolids content TS should be optimal for the ﬂocculation to occur. However,sometimes this assumption turns out to be wrong. lt may be the case that theinformation from the load cell and the clarometer shows that flocculation is taking place according to plan at the intended total solids content TS,indicating that the assumption of optimal total solids content TS is correct.However, it is possible that in order to achieve this flocculation, the flocculantpump is running at or near its maximum, which would indicate thatflocculation is indeed not performed as intended. ln response to thisinformation about the flocculant pump, the control unit can be arranged toincrease or decrease the amount of dilution water fed to the slurry such that anew, more correct range of percent solids TS can be determined. lt is thuspossible to effectively search for a new, more correct range of optimal solidscontent TS by means of the arrangement in accordance with the invention. ltis also possible to add historical data to be used as a pre-warning system forprocess deviation. Without monitoring the actual feed rate of the additive, inaddition to the information provided by the sensors measuring settling rateand total solids content, this could go on undetected for a long time.

The skilled person realizes that a number of modifications of theembodiments described herein are possible without departing from the scopeof the invention, which is defined in the appended claims. For example, theskilled person realizes that the arrangement may not necessarily be usingload cells in order to determine the density of the slurry. Other solutions, suchas nuclear density sensors may be applied. The important thing is that thedensity of the slurry can be obtained. Further, the terms clarometer, turbiditysensor, turbidity probe are used herein. They all aim to determine the settlingrate of the particles in the treatment vessel and other equipment capable ofthis may be applied.

Claims

1. An arrangement (100) for determining properties of a slurry comprising solids suspended in liquid, the arrangement comprising - a treatment vesse| (1) having a predefined volume; - a first sensor arranged at or near said treatment vesse| (1) andarranged to determine a settling rate of solids of said slurry whencontained in the treatment vesse| (1 ); - a second sensor_3§§§§;:¿ arranged at or near said treatment vesse| (1)and arranged to determine a density of the slurry contained in thetreatment vesse| (1 ); the arrangement (100) further comprising a control unit (7) arranged to receive signals from at least said first and second sensor__;:§j.§~f_,__f§§_§, wherein said control unit (7) is arranged to determine the percentsolids in the slurry based on the output from the second sensorwherein the control unit (7) is arranged to adjust a feed rate ofadditional liquid that may be added to the slurry based on informationfrom the first and the second sensorijšjkgïig.

2. An arrangement (100) in accordance with claim 1, wherein the control unit (7) is arranged to receive signals from at least said first and second sensor “Nwand wherein the control unit (7) is arranged to adjust a feed rate of an additive to the slurry based on the output fromthe first sensor__=¿fj.{f§_.

3. An arrangement (100) in accordance with claim 2, wherein the additivecomprises a chemical such as a coagulant or a flocculant.

4. An arrangement (100) in accordance with claim 2, wherein the controlunit (7) is arranged to adjust the feed rate of additional liquid that maybe added to the slurry based on information from at least one of thefirst and the second sensor well as information about the feedrate of the additive.

5. An arrangement (100) in accordance with claim 1, wherein the secondsensor (íjlfggcomprises at least one load cell arranged to determine theweight of the slurry in the treatment vessel (1 ).

6. An arrangement (100) in accordance with claim 5, wherein the at leastone load cell is arranged to determine the weight of the treatmentvessel (1).

7. An arrangement (100) in accordance with claim 1, wherein the firstsensor §§§§°f\}wcomprises a turbidity sensor.

8. An arrangement (100) in accordance with claim 1, further comprising athird sensor arranged upstream the treatment vessel (1, 2) and the first and the second sensor g:=_,__wherein said third sensor is arranged to determine a density of the slurry upstream of the treatment vessel andwherein an output from said third sensor can be used to determine thepercent solids in the slurry.

9. An arrangement (100) in accordance with claim 8, wherein theadditional liquid is added to the slurry downstream of the third sensorand upstream of the second sensor__§§§¿_§.

10. )An arrangement (100) in accordance with claim 9, wherein the third sensor is arranged at or near a second treatment vessel (2).

11. )A method for determining properties of a slurry comprising solids suspended in liquid, the method comprising the steps of: - providing a treatment vessel (1) having a predefined volume; - determine a settling rate of solids of said slurry contained in thetreatment vessel (1) by means of a first sensor gsjgšflfggarranged at ornear said treatment vessel (1 ); - determine a density of the slurry contained in the treatment vessel(1) by means of a second sensor (=;f§§;=__arranged at or near saidtreatment vessel (1 ); - determine the percent solids in the slurry using an output from saidsecond sensor a control unit (7) which is arranged toreceive signals from at least said second sensor¿§§§§_§_; - adjusting a feed rate of additional liquid that may be added to theslurry using said control unit (7) based on information from the firstand the second sensor_¿;f.~} tf»

12. )A method in accordance with claim 11, wherein the method furthercomprises the step of adjusting a feed rate of an additive to the slurrybased on the output from the first sensor means of the controlunit (7).

13. )A method in accordance with claim 12, wherein the additive comprisesa chemical such as a coagulant or a flocculant.

14. )A method in accordance with claim 12, further comprising the step ofadjusting the feed rate of additional liquid that may be added to theslurry based on information from at least one of the first and thesecond sensor well as information about the feed rate of theadditive.

15. )A method in accordance with claim 11, further comprising the step ofproviding a third sensor upstream of the treatment vessel (1) and the ~' “v .vxw first and the second sensor determining a density of theslurry upstream of the treatment vessel and wherein an output fromsaid third sensor can be used to determine the percent solids in theslurry.

16. )A method in accordance with claim 15, wherein the additional liquid isadded to the slurry downstream of the third sensor and upstream of thesecond sensor_¿§§~§:¿_§.

17. )A method in accordance with claim 11, further comprising the step ofarranging the third sensor at or near a second treatment vessel (2).