A method for monitoring or controlling the separation of particles suspended in a liquid and a particles separation apparatus

Abstract

A method (200) of determining a progress of separation of particles suspended in a liquid in a container (110) of a separation apparatus (100), wherein: said particles are separated from said liquid by sedimentation; said separation apparatus (100) compri- sing a container (110) with a feed inlet and a rotatable rake (120) at its bottom (114); a motor (126) for driving said rake (120); and a pressure measuring device (130), for measuring a hydrostatic pressure at or near the bottom of said container said method (200) comprising: measuring (210) said hydrostatic pressure; driving (220) said rake (120) by means of said motor; obtaining (230) at least one load parameter of said motor (126) during said driving of said rotation; determining (240), especially in real time, a status indicator relating to said separation process, as a function of said hydrostatic pressure and said load parameter, wherein said status indicator comprises: a sedi- mentation index, especially wherein the sedimentation index is indicative of the separation of said particles from said liquid, and / or a feed solid content index, wherein the feed solid content index is indicative of the solid content supplied by said feed.

Description

[0001] A method for monitoring or controlling the separation of particles suspended in a liquid and a particles separation apparatus

[0002] The present invention relates to a method and an apparatus for the separation of particles suspended in a liquid. More specifically, it pertains to a computer-implemented method for monitoring or controlling the progress of particle separation in a container of a separation apparatus, such as a thickener.

[0003] In various industrial processes, the separation of particles from a liquid suspension is a critical step. Traditional methods of monitoring the progress of sedimentation often rely on visual inspection or periodic sampling, which can be time-consuming and inaccurate. There is a need for a more efficient method to monitor and control the sedimentation process in real-time. WO 2021004748 A1 discloses a thickener and a method for monitoring the interface height between the particles and the liquid by means of a level sensor and additional instrumentation. While the above approach has its merits, it is the object of the present invention, to provide a method and an apparatus with an improved monitoring of the separation. The object is solved by the method according to claim 1 , the apparatus according to claim 11 . The method for building a model according to claim 12.

[0004] The method according to the invention serves to determine a progress of a separation process of particles suspended in a liquid comprised in a container of a separation apparatus, wherein: a medium, comprising said particles suspended in said liquid is supplied to said container; said particles are separated from said liquid by sedimentation; and wherein said separation apparatus comprises said container, a feed inlet for feeding said suspension into said container, a rake, mounted rotatably around a vertical axis in said container at the bottom of said container; a motor for driving a rotation of said rake; and a pressure measuring device, for measuring a hydrostatic pressure at or near the bottom of said container, wherein said method comprises: measuring said hydrostatic pressure at or near said bottom of said container; driving said rotation of said rake by means of said motor; obtaining at least one load parameter of said motor during said driving of said rotation; and determining a status indicator relating to said separation process; in real time, as a function of said hydrostatic pressure and said load parameter, wherein said status indicator comprises a sedimentation index, especially wherein the sedimentation index is indicative of the separation of said particles from said liquid, and / or a feed solid content index, wherein the feed solid content index is indicative of the solid content supplied by said feed.

[0005] In the context of the present invention, the term real time refers to a delay of preferably not more than 10 minutes, for example not more than 5 minutes, especially not more than 2 minutes between the availability of the input parameters, i.e. a measured hydrostatic pressure value and a load parameter value, and the availability of the output parameter, i.e. the sedimentation index.

[0006] According to an aspect of the invention, the method is a computer implemented method.

[0007] According to an aspect of the invention, said load parameter comprises a function of a torque of the motor, required to drive the rotation at a given angular velocity, or a function of the power required by the motor to drive the rotation and the angular velocity of said rotation.

[0008] According to an aspect of the invention, said status indicator, especially said sedimentation index further depends on a derivative of the hydrostatic pressure and or said load parameter with respect to time.

[0009] According to an aspect of the invention, said sedimentation index comprises a function of a ratio of the load parameter and the hydrostatic pressure.

[0010] According to an aspect of the invention, said sedimentation index comprises a function of a ratio of filtered measured values of the load parameter and / or the hydrostatic pressure.

[0011] According to an aspect of the invention, filter parameters for obtaining said filtered measured values are adaptive, and especially depend on the fluctuations of said measured values.

[0012] According to an aspect of the invention, filter parameters for obtaining said filtered measured values are adaptive, and especially depend on the fluctuations of said measured values. According to an aspect of the invention, said separation apparatus comprises a thickener, especially a radial thickener.

[0013] According to an aspect of the invention, said rake is a rake for pushing said sediment towards an underflow outlet located at a bottom of said container.

[0014] According to an aspect of the invention, said status indicator, especially said sedimentation index is indicative of the share of said particles that have sedimented to a bottom region of the container.

[0015] According to an aspect of the invention, the sedimentation of the particles can be stimulated by dosing flocculants to the suspension, wherein the dosing of said flocculants is controlled based on said status indicator, and / or wherein a flow rate of said suspension is controlled based on said status indicator, and / or wherein an angular velocity of said rake is controlled based on said status indicator, especially said sedimentation index.

[0016] The separation apparatus according to the invention comprises: a container; a feed inlet for feeding said suspension into said container a rake, mounted rotatably around a vertical axis in said container at the bottom of said container; a motor for driving a rotation of said rake; means for obtaining at least one load parameter of said motor during said driving of said rotation; a pressure measuring device, for measuring a hydrostatic pressure at or near the bottom of said container; and control circuitry, which is arranged for controlling the apparatus to execute the method according to the invention.

[0017] The method according to the invention for building a model used in a method according to the invention to determine a progress of separation of particles suspended in a liquid, wherein the model is used for determining a sedimentation index as a function of said hydrostatic pressure and said load parameter; wherein the method for building the model comprises: collecting initial data during an initial phase, said initial data comprising time series of tuples, said tuples comprising hydrostatic pressure values, values of load on the motor, at least one type of corresponding laboratory values selected from a list that comprises: a feed solid content based on samples taken from the feed of the suspen- sion into the container, an overflow solid content based on samples taken from an overflow of the suspension out of the container, and the concentration of solid particles measured in samples taken from the bottom of the container; and a corresponding time stamp; training a machine learning on this initial data; and providing the model to a computing unit, wherein said computing unit is arranged for determining by means of said model the sedimentation index as a function of the hydrostatic pressure and the load on the motor that drives the rake.

[0018] According to an aspect of the invention, the sedimentation index is indicative of the solid content at the bottom of the container.

[0019] According to an aspect of the invention the model enables said computing unit for determining by means of said model the sedimentation index as a function of only the hydrostatic pressure and the load on the motor that drives the rake.

[0020] According to an aspect of the invention, said tuples comprises two types of said corresponding laboratory values selected from said list, wherein said two types are said feed solid content based on samples taken from the feed of the suspension into the container, and said overflow solid content based on samples taken from an overflow of the suspension out of the container.

[0021] Said solid content may be obtained by measuring the concentration of suspended solid particles in said samples and by the corresponding flow rate at the time the samples were taken from the feed and overflow, respectively.

[0022] According to an aspect of the invention, said tuples further comprise the supply rate of flocculant into the container

[0023] The invention is presented in further detail with reference to the attached drawings, they show:

[0024] Fig. 1 shows a schematic drawing of a thickener according to an embodiment of an apparatus according to the present invention.

[0025] Fig. 2a shows a schematic diagram of vertical concentration distributions C(z) of particles suspended in a liquid at different times. Fig. 2b shows a corresponding schematic diagram of a plurality of time series of the concentration C(z) of particles suspended in a liquid at different vertical positions zi.

[0026] Fig. 2c shows a corresponding schematic diagram of the development over time of the total mass M of particles sedimented to a bottom region of a container and the corresponding torque T required to rotate a rake in said bottom region.

[0027] Fig. 2d shows a corresponding schematic diagram, of the corresponding time derivative of said torque.

[0028] Fig. 3 shows a schematic diagram of measuring or process parameters for monitoring a sedimentation process by the method according to the present invention.

[0029] Fig. 4 shows a flow chart of an embodiment of the method according to the present invention to determine a progress of separation of particles.

[0030] Fig. 5 shows a flow chart of an embodiment of the method according to the invention to build a model.

[0031] The embodiment of the separation apparatus 100 shown in Fig. 1 , is a radial thickener, it comprises a container 110, which essentially has cylindrical sidewalls 112 and a slightly conical bottom wall 114 which is inclined downward towards its center. The apparatus 100 further comprises a rake 120 which has a blade 122 near the bottom wall 114 of the container. The blade 122 is supported and driven by a shaft with a vertical axis 124, to rotate around said vertical axis. The rake is rotated in order facilitate the sedimented particles motion towards an underflow outlet B in the bottom wall 114 of the container 110. The outlet B may comprise a pump and / or a valve to control the outflow flow of material from the container. The apparatus 100 further comprises a pressure measuring device 130, mounted in an aperture in the bottom wall 114 of the container 100, preferably in proximity to the lowest point of the container 100. The separation apparatus further comprises a first inlet A for feeding a suspension of particles in a liquid to the container 110. The first inlet A may comprise a pump and / or a valve to control the flow of the suspension into the container. The separation apparatus further comprises a second inlet D for supplying a flocculant into suspension in the container 110 in order to stimulate the sedimentation. The second inlet D comprises a pump and / or a valve to control the supply of the flocculant into the suspension. The apparatus further comprises a second outlet C, which serves as an overflow outlet. The second outlet C may comprise a pump and / or a valve to control the outflow of material from the container 110. Moreover all inlets and outlets may comprise flow meters.

[0032] The apparatus 100 further comprises control circuitry 150, which is functionally connected to the motor 126 that drives the rake 120, the pressure measuring device 130 and, preferably, the valves and pumps of inlets and outlets, respectively. While the control circuitry 150 is presented as a single block the drawing in Fig. 1 , it may have a modular architecture with, e.g., remote computing capabilities.

[0033] With reference to Figs. 2a, 2b, 2c, and 2d, we discuss the impact of sedimentation on the load of the motor 126 driving the rake 120.

[0034] The diagram in Fig2a shows vertical concentration distributions C(z) of particles suspended in a liquid at different times. The presented development of concentration distributions from a starting time t1 to a final time t7 would occur in a batch process, wherein a suspension of particles is fed on top of a volume of pure liquid, above a height z1 . While this is not the most likely mode of operation, it illustrates the effects more clearly than other processes with a steady or intermittent feed of the suspension, into the empty container or on top of suspensions fed earlier into the container. The method according to the invention is not limited to any specific mode of operation. Turning to Fig. 2a and 2b, it can be seen, that the particles are moving downwards through the volume of liquid their initial position at the top above z1 , where they have a narrow vertical distribution. While the particles have fairly wide vertical distributions with correspondingly low concentrations at a specific altitude on their way down, they finally aggregate near the bottom z5, especially in the range indicated by the box r in Fig. 2a. This is the range which is reached by the blade 122 of the rake 120.

[0035] Fig. 2c shows the corresponding development over time of aggregated particle mass M(t) in the zone r near the bottom of the container and the resulting torque T(t) required to rotate the rake at a desired angular velocity. It clearly can be seen that the load on the motor, follows the aggregation of the particles near the bottom. Hence, it is an adequate measuring variable to assess the progress of sedimentation. Fig. 2d finally shows the derivative of the torque over time. This derivative is good parameter to identify the time when further sedimentation is not to be expected, l.e. when vertically higher portions of the material in the container are sufficiently depleted of the suspended particles. As is evident from Fig. 2c, the torque or any other type of load parameter is blind for the early stage of the batch process discussed above. However, if the hydrostatic pressure is considered as a second measured parameter a sufficiently detailed understanding of the sedimentation process can be obtained, as is discussed below with reference to Fig. 3.

[0036] Fig. 3 shows data for a situation, wherein an empty container of the apparatus according to the invention is filled completely with a suspension of particles. The dashed line shows the hydrostatic pressure at the bottom of the container, which increases until the filling is completed. It does not change during the sedimentation process. However, it implies an indication about the total mass of suspended particles, which in allows an estimate for the load or torque on the rake, when said mass of particles is sedimented sufficiently. The solid line shows that torque T, required to rotate the rake at a desired angular velocity. The corresponding mass S of suspended particles that have not yet sedimented to the bottom of the container is shown in the dash-dotted line in the diagram. Once the sedimentation is sufficiently completed, as indicated be the peaking torque. The container may be emptied through the underflow outlet, wherein the leading fraction comprises the desired particles. During operation, the mass S, and / or a corresponding degree of completion of the sedimentation process, can be calculated based on the hydrostatic pressure, the load on the motor for rotating the blade, e.g. the torque t, and, optionally, the derivative over time of the load and / or the pressure, e.g.

[0037] S = S(p,T, dp / dt, dT / dt).

[0038] According to a specific embodiment, the function S also depends on a ratio, comprising the load, divided by the hydrostatic pressure, e.g.:

[0039] S = S(p, T, T / p, dp / dt, dT / dt).

[0040] According to a further embodiment of the invention it is an option to supply some flocculant to the suspension in order to accelerate matters, when the sedimentation proceeds to slow.

[0041] The load, or torque data, may require averaging or other types of filtering, since agitating solids involve stick-slip motions that imply fluctuations in the torque.

[0042] Since pressure measurements may become challenging if the solid phase on the pressure sensitive element of the pressure sensor increases above a certain level, filtering techniques of pressure data can be helpful to improve the signal to noise ratio. According to a further embodiment of, the invention a pressure value p(f1 ) that is measured immediately after completion of the filling process as indicated in Fig. 3. At this stage early in the sedimentation process the pressure sensitive element is exposed to a large liquid portion of material. Hence, this early pressure value p(f1 ) is considered as the hydrostatic pressure until the total mass in the container or its composition is changed by adding or removing material. Then, a new pressure measurement is required to obtain a correct value of the hydrostatic pressure.

[0043] The method is implemented frequently in continuous processes, wherein a feed of the suspension with varying solid concentration is fed into the container. Especially in these situations, the status indicator may be indicative of the feed solid content. Which in turn provides a base for providing an adequate amount of flocculant to the suspension in the container.

[0044] An embodiment of the method according to the invention is discussed below with reference to Fig. 4. The method (200) for monitoring a sedimentation process, according to a preferred embodiment of the invention comprises measuring (210) a hydrostatic pressure at or near a bottom of a container, wherein according to this embodiment is a container of a radial thickener with a conical bottom wall.

[0045] The method further comprises driving (220) a rotation of a rake near the bottom by means of a motor, and obtaining (230) at least one load parameter of said motor during said driving of said rotation. According to this embodiment, said load parameter is the torque required to maintain the rotation at a desired angular velocity.

[0046] Once the above data are available, the method is completed by determining (240) a status indicator as a function of said hydrostatic pressure p and said torque T, wherein the status indicator is indicative of the separation of said particles from said liquid. Determining the status indicator can be done by calculating a function

[0047] S = S(p,T, dp / dt, dT / dt).

[0048] According to a specific embodiment, the function S also depends on a ratio, comprising the torque, divided by the hydrostatic pressure, e.g.:

[0049] S = S(p, T, T / p, dp / dt, dT / dt). The status indicator may be indicative of, which share of the particles is still suspended in the liquid, or of the complement, i.e. the share of particles that are already separated.

[0050] Based on the status indicator, supplying 250 a flocculant to the suspension, in order to accelerate the sedimentation process.

[0051] Once the status indicator indicate that the sedimentation is complete, harvesting 260 of the solid material may be initiated through and underflow outlet at the bottom of the container.

[0052] To build a model for monitoring a sedimentation process based on hydrostatic pressure measurements and load on the motor of a rotating rake, initial data are collected during an initial phase. These initial training data comprise time series of tuples, comprising hydrostatic pressure values, values of load on the motor, at least one type of corresponding laboratory values selected from a list that comprises: a feed solid content based on samples taken from the feed of the suspension into the container, an overflow solid content based on samples taken from an overflow of the suspension out of the container, and the concentration of solid particles measured in samples taken from the bottom of the container; and a corresponding time stamp.

[0053] Said solid content is preferably obtained by measuring the concentration of suspended solid particles in said samples and by the corresponding flow rate at the time the samples were taken from the feed and overflow, respectively. According to an aspect of the invention, said tuples comprises two types of said corresponding laboratory values selected from said list, wherein said two types are said feed solid content based on samples taken from the feed of the suspension into the container, and said overflow solid content based on samples taken from an overflow of the suspension out of the container. The laboratory values are usually provided with a delay of a day, but since the samples are associated with the corresponding pressure and load values, by means of their time stamp, they can be assigned easily to the appropriate tuples.

[0054] The initial data preferably cover the entire range of possible states that my occur during the operation of the sedimentation apparatus. Based on the initial data, a which may be split in different sets, a machine learning algorithm is trained and tested. Once the model is established, and tested, the progress of the sedimentation process, espe- cially the solid content at the bottom of the container can be determined in real time, from only the hydrostatic pressure and the load on the motor that drives the rake.

[0055] According to an aspect of the invention, said tuples comprise two types of said corresponding laboratory values selected from said list, wherein said two types are said feed solid content based on samples taken from the feed of the suspension into the container, and said overflow solid content based on samples taken from an overflow of the suspension out of the container.

[0056] Since the feed is the only source for the mass balance of solids, and sedimentation and overflow are the only sinks, the integrated balance between feed and overflow necessarily is attributable to sedimentation and to a residual small transient share in suspension.

[0057] According to an aspect of the invention, said tuples further comprise the supply rate of flocculant into the container

Claims

Claims1 . A method (200), in particular a computer implemented method of determining a progress of separation of particles suspended in a liquid comprised in a container (110) of a separation apparatus (100), wherein: a medium, comprising said particles suspended in said liquid is supplied to said container (100); said particles are separated from said liquid by sedimentation; and wherein said separation apparatus (100) comprises said container (110), a feed inlet (A) for feeding said suspension into said container (110) a rake (120), mounted rotatably around a vertical axis in said container at the bottom (114) of said container (110); a motor (126) for driving a rotation of said rake (120); and a pressure measuring device (130), for measuring a hydrostatic pressure at or near the bottom of said container said method (200) comprising: measuring (210) said hydrostatic pressure at or near said bottom (114) of said container (110); driving (220) said rotation of said rake (120) by means of said motor; obtaining (230) at least one load parameter of said motor (126) during said driving of said rotation; and determining (240), especially in real time, a status indicator relating to said separation process, as a function of said hydrostatic pressure and said load parameter, wherein said status indicator comprises: a sedimentation index, especially wherein the sedimentation index is indicative of the separation of said particles from said liquid, and / ora feed solid content index, wherein the feed solid content index is indicative of the solid content supplied by said feed.

2. The method according to claim 1 , wherein: said load parameter comprises a function of a torque of the motor, required to drive the rotation at a given angular velocity, or a function of the power required by the motor to drive the rotation and the angular velocity of said rotation.

3. The method according to claim 1 or 2, wherein: said status indicator, especially said sedimentation index further depends on a derivative of the hydrostatic pressure and / or said load parameter with respect to time.

4. The method according to any of claims claim 1 to 3, wherein: said status indicator, especially said sedimentation index comprises a function of a ratio of the load parameter and the hydrostatic pressure.

5. The method according to any of claims 1 to 4, wherein: said status indicator, especially said sedimentation index comprises a function of a ratio of filtered measured values of the load parameter and / or the hydrostatic pressure.

6. The method according to claim 5, wherein: filter parameters for obtaining said filtered measured values are adaptive, and especially depend on the fluctuations of said measured values.

7. The method according to any of claims 1 to 6, wherein: filter parameters for obtaining said filtered measured values are adaptive, and especially depend on the fluctuations of said measured values. wherein said rake (120) is a rake for pushing said sediment towards an underflow outlet (B) located at a bottom (114) of said container (100).

8. The method according to any of claims 1 to 7, wherein: said status indicator, especially said sedimentation index is indicative of the share of said particles that have sedimented to a bottom region of the container.

9. The method according to any of claims 1 to 8, wherein: the sedimentation of the particles can be stimulated by dosing flocculants to the suspension, wherein the dosing of said flocculants is controlled based on said status indicator, especially said feed solid content, and / or wherein a flow rate of said suspension is controlled based on said status indicator, and / or wherein an angular velocity of said rake is controlled based on status indicator, especially said sedimentation index.

10. The method according to any of claims 1 to 8, wherein: said separation apparatus comprises a thickener, especially a radial thickener.

11. A separation apparatus (100), comprising: a container (110); a rake (120), mounted rotatably around a vertical axis (124) in said container (110) at or near the bottom (112) of said container (110);a motor (126) for driving a rotation of said rake (120); means for obtaining at least one load parameter of said motor (126) during said driving of said rotation; a pressure measuring device (130), for measuring a hydrostatic pressure at or near the bottom (114) of said container; and control circuitry, for controlling the apparatus to execute the method according to any of the preceding claims.

12. A method (300) for building a model used in a method according to any of claims 1 to 10, wherein the model is used for determining (240) a status indicator as a function of said hydrostatic pressure and said load parameter; the method for building the model comprising: collecting (310) initial data during an initial phase, said initial data comprising time series of tuples, said tuples comprising: hydrostatic pressure values, values of load on the motor; at least one type of corresponding laboratory values selected from a list that comprises: a feed solid content based on samples taken from the feed of the suspension into the container, an overflow solid content based on samples taken from an overflow of the suspension out of the container, and the concentration of solid particles measured in samples taken from the bottom of the container; and a corresponding time stamp; training (320) a machine learning on this initial data; and providing (330) the model to a computing unit, wherein said computing unit is arranged for determining by means of said model the status indicator as a function of the hydrostatic pressure and the load on the motor that drives the rake.

13. The method according to claim 12, wherein said status indicator, especially said sedimentation index, is indicative of the solid content at the bottom of the container; and / or wherein the feed solid content index is indicative of the solid content supplied by said feed.

14. The method according to claim 12 or 13, wherein the model enables said computing unit for determining by means of said model the status indicator as a function of only the hydrostatic pressure and the load on the motor that drives the rake.

15. The method according to any of claims 12 to 14, wherein said tuples comprise: two types of said corresponding laboratory values selected from said list, wherein said two types are the concentration of solid particles measured in samples taken from a feed of the suspension into the container; and the concentration of solid particles measured in samples taken from an overflow of the suspension out of the container.

16. The method according to any of claims 12 to 15, wherein said tuples further comprise the supply rate of flocculant into the container.

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