Method for controlling the operation of a continuously or periodically operating centrifuge and device for conducting the method

Abstract

A method for controlling the operation of a continuously or periodically operating centrifuge can be employed in the sugar industry for separating crystalline carbohydrates or sugar alcohols from a crystal suspension called a magma or a mother liquor. The magma has a varying content of fine grain that is dependent on the properties of the pretreatment and of the raw material. Variable control values are provided in a control device of the centrifuge. One or plurality of sensors are provided that carry out the measurements in electromagnetic, optical, acoustic, and/or conductive ways. These measurements that are conducted serve for determining the fine grain fraction of the magma. The measurements are supplied as measurement signals to the control device of the centrifuge. The control device automatically analyzes the measurement signals supplied to it and evaluates them with respect to the fine grain content of the magma. The control device changes the variable control values of the centrifuge as a function of this evaluation.

Claims

1. A method for controlling the operation of a continuously or periodically operating centrifuge, which is employed in the sugar industry for separating crystalline carbohydrates or sugar alcohols from a crystal suspension called a magma or a mother liquor, wherein the magma has a varying content of fine grain that is dependent on the properties of the pretreatment and of the raw material, with variable control values in a control device of the centrifuge, is hereby characterized in that one or a plurality of sensors are provided that carry out the measurements in electromagnetic, optical, acoustic, and/or conductive ways, in that these measurements that are conducted serve for determining the fine grain fraction of the magma, in that the measurements are supplied as measurement signals to the control device of the centrifuge, in that the control device automatically analyzes the measurement signals supplied to it and evaluates them with respect to the fine grain content of the magma, and in that the control device adjusts the variable control values of the centrifuge as a function of this evaluation, in that a regulation established in advance in the control routines is provided as follows: filling the centrifuge with more than 50% and less than 70% of a maximum filling load and at a predetermined first constant rotational speed (step V1); after filling the centrifuge, increasing the rotational speed (step V2) to a second constant rotational speed (step V3); maintaining the second constant rotational speed (step V3) for a predetermined period of time; and after maintaining the second constant rotational speed (step V3), increasing the rotational speed (step V4) to a third constant rotational speed (step V5).

2. The method according to claim 1, further characterized in that the measurement signals serving for determining the fine grain content of the magma are detected directly, or in that the measurement signals serving for determining the fine grain content of the magma are detected as the first time derivative, or in that the measurement signals serving for determining the fine grain content of the magma are detected as the second time derivative, or in that the detection is composed of a combination of a plurality of these alternatives.

3. The method according to claim 1, further characterized in that the measurement signal or one of the measurement signals is generated by interaction between sound waves and/or electromagnetic radiation and/or optical radiation and the elements of the magma, and in that, ultrasound-based, imaging, laser-based and/or scattered light-based methods are drawn on for extracting the measurement signal or the measurement signals.

4. The method according to claim 3, further characterized in that, in the case of using a scattered light-based method, a turbidity signal is extracted, which is detected as a transmittance signal and/or as a reflectance signal.

5. The method according to claim 4, further characterized in that a sensor or the sensor generating the measurement signal is arranged directly in a crystallizer at a bubble-free measurement position or at a measurement position along the transport path of the magma to the centrifuge.

6. The method according to claim 5, further characterized in that, in the case of levels of measurement signals that change over time and/or a changing rate of the measurement signals and/or a changing rate of the signaling speed outside of a tolerance region, control routines provided in the control device are triggered.

7. The method according to claim 1, further characterized in that the measurements for the measurement signal to be extracted are created by an interaction between electromagnetic radiation and the crystals of the magma or the magma itself, and in that the measurement signal is detected as a reflecting signal in the form of a distance signal by means of a laser sensor or radar sensor or ultrasonic sensor, or as a spectrophotometer signal by means of a spectrophotometer sensor, or as a dry-matter signal by means of microwaves.

8. The method according to claim 7, further characterized in that the sensor is found inside and/or outside the drum of the centrifuge and is aligned on the body of the drum and a crystal cake of the magma that is being built up thereon.

9. The method according to claim 7, further characterized in that when the level of a measurement signal over time exceeds or goes below a predefined threshold value, control routines established for this purpose are triggered, in particular during the filling and acceleration process.

10. The method according to claim 1, further characterized in that the measurements for establishing the measurement signal are extracted by means of an interaction between electromagnetic and/or acoustic fields and the mother liquor of the magma, and in that, the conductivity is determined as a measurement signal by means of a planar two-pole or four-pole electrode with predefined electrode geometry.

11. The method according to claim 10, further characterized in that the sensor or one of the sensors extracting the measurement signal is arranged flush in a spray casing of the centrifuge, in the lower third of the spray casing.

12. The method according to claim 10, further characterized in that when the level of a measurement signal over time exceeds or goes below a predefined threshold value, control routines established for this purpose are triggered during the filling and acceleration process.

13. The method according to claim 1, further characterized in that the sensors for conducting the measurements for extracting the measurement signals in the course of flow of the magma are arranged before the centrifuge, in the drum and/or in the cover of the centrifuge and in the spray casing of the centrifuge individually or in redundant combinations of two or three.

14. The method according to claim 1, further characterized in that the control routines contain a reduction of the inflow of magma, a reduction in the building up of the layer thickness, and/or a reduction or an increase in the rotational speed of the spinning centrifuge; moreover, there is also a regulating of the water blanket.

15. The method according to claim 1 wherein, after filling the centrifuge, linearly increasing the rotational speed (step V2) to a constant second rotational speed (step V3).

16. The method according to claim 15, further characterized by adding a first water blanket during the linear increase in the rotational speed (step V2).

17. The method according to claim 16, further characterized by adding a second water blanket during the second constant rotational speed (step V3).

18. The method according to claim 16, further characterized by adding a second water washing during the second constant rotational speed (step V3).

19. The method according to claim 15, further characterized by adding a first water washing during the linear increase in the rotational speed (step V2).

20. The method according to claim 1, further characterized by, after increasing the rotational speed to the third constant rotational speed (step V5); throttling the rotational speed in the case of an established imbalance; subsequent repeated increasing of the rotational speed and, optionally, several repetitions of this step; braking the centrifuge drum; emptying the centrifuge drum; and conducting a screen washing.

21. The method according to claim 1, further characterized by, after maintaining the third constant rotational speed for a predetermined period of time, decreasing the rotational speed (step V6), followed by an emptying step (step V7).

22. A method for controlling the operation of a continuously or periodically operating centrifuge, which is employed in the sugar industry for separating crystalline carbohydrates or sugar alcohols from a crystal suspension called a magma or a mother liquor, wherein the magma has a varying content of fine grain that is dependent on the properties of the pretreatment and of the raw material, with variable control values in a control device of the centrifuge, is hereby characterized in that one or a plurality of sensors are provided that carry out the measurements in electromagnetic, optical, acoustic, and/or conductive ways, in that these measurements that are conducted serve for determining the fine grain fraction of the magma, in that the measurements are supplied as measurement signals to the control device of the centrifuge, in that the control device automatically analyzes the measurement signals supplied to it and evaluates them with respect to the fine grain content of the magma, and in that the control device adjusts the variable control values of the centrifuge as a function of this evaluation, in that the measurements for establishing the measurement signal are extracted by means of an interaction between electromagnetic and/or acoustic fields and the mother liquor of the magma, in that the conductivity is determined as a measurement signal by means of a planar two-pole or four-pole electrode with predefined electrode geometry, in that the measurement used for establishing the measurement signal utilizes an interaction between electromagnetic radiation and the mother liquor of the magma, and in that the measurement signal is detected as a visual signal in the L*a*b or RGB color space or as a UV or IR/Raman or acoustic signal.

23. A method for controlling the operation of a continuously or periodically operating centrifuge, which is employed in the sugar industry for separating crystalline carbohydrates or sugar alcohols from a crystal suspension called a magma or a mother liquor, wherein the magma has a varying content of fine grain that is dependent on the properties of the pretreatment and of the raw material, with variable control values in a control device of the centrifuge, is hereby characterized in that one or a plurality of sensors are provided that carry out the measurements in electromagnetic, optical, acoustic, and/or conductive ways, in that these measurements that are conducted serve for determining the fine grain fraction of the magma, in that the measurements are supplied as measurement signals to the control device of the centrifuge, in that the control device automatically analyzes the measurement signals supplied to it and evaluates them with respect to the fine grain content of the magma, and in that the control device adjusts the variable control values of the centrifuge as a function of this evaluation, in that the sensors for conducting the measurements for extracting the measurement signals in the course of flow of the magma are arranged before the centrifuge, in the drum and/or in the cover of the centrifuge and in the spray casing of the centrifuge individually or in redundant combinations of two or three, in that a measurement signal is determined as a turbidity signal in front of a butterfly valve of the centrifuge, and in that another sensor is provided as a laser sensor or radar sensor or spectrophotometer sensor in the drum or on the cover of the centrifuge, and a third sensor is provided for the conductivity or the color in the spray casing of the centrifuge, and in that the sensor for the laser signal or the radar signal or the color signal and the sensor for the conductivity or the color are used as redundant secondary or tertiary measurement signals with a stepped, slight time delay.

24. A method for controlling the operation of a continuously or periodically operating centrifuge, which is employed in the sugar industry for separating crystalline carbohydrates or sugar alcohols from a crystal suspension called a magma or a mother liquor, wherein the magma has a varying content of fine grain that is dependent on the properties of the pretreatment and of the raw material, with variable control values in a control device of the centrifuge, is hereby characterized in that one or a plurality of sensors are provided that carry out the measurements in electromagnetic, optical, acoustic, and/or conductive ways, in that these measurements that are conducted serve for determining the fine grain fraction of the magma, in that the measurements are supplied as measurement signals to the control device of the centrifuge, in that the control device automatically analyzes the measurement signals supplied to it and evaluates them with respect to the fine grain content of the magma, and in that the control device adjusts the variable control values of the centrifuge as a function of this evaluation, in that a regulation established in advance in the control routines is provided as follows: filling the centrifuge with more than 50% and less than 70% of the maximum filling load; adjusting the rotational speed of the centrifuge during filling to 150 to 200 rpm; omitting the conventional syrup covering; after filling, increasing the rotational speed with adjustable acceleration curves dependent on the time course and/or dependent on the viscosity and/or dependent on the fine grain content of the magma up to a predetermined or defined rotational speed; adding a first water blanket (WB) or optionally a plurality of water blankets staggered in time during this increase in the rotational speed; optional conducting of an intermediate centrifuging step; in this case, adding another water blanket (WB); increasing the rotational speed to a predetermined or defined rotational speed; keeping this rotational speed constant for approximately 5 to 40 seconds; throttling the rotational speed in the case of an established imbalance; subsequent repeated increasing of the rotational speed and, optionally, several repetitions of this step; braking the centrifuge drum; emptying the centrifuge drum; and conducting a screen washing.

25. A method for controlling the operation of a continuously or periodically operating centrifuge, which is employed in the sugar industry for separating crystalline carbohydrates or sugar alcohols from a crystal suspension called a magma or a mother liquor, wherein the magma has a varying content of fine grain that is dependent on the properties of the pretreatment and of the raw material, with variable control values in a control device of the centrifuge, is hereby characterized in that one or a plurality of sensors are provided that carry out the measurements in electromagnetic, optical, acoustic, and/or conductive ways, in that these measurements that are conducted serve for determining the fine grain fraction of the magma, in that the measurements are supplied as measurement signals to the control device of the centrifuge, in that the control device automatically analyzes the measurement signals supplied to it and evaluates them with respect to the fine grain content of the magma, and in that the control device adjusts the variable control values of the centrifuge as a function of this evaluation, in that a regulation established in advance in the control routines is provided as follows: filling the centrifuge with more than 50% and less than 70% of the maximum filling load; adjusting the rotational speed of the centrifuge during filling to 150 to 200 rpm; omitting the conventional syrup covering; after filling, linearly increasing the rotational speed up to 700 rpm; adding a first water blanket (WB) during this linear increase in the rotational speed; conducting an intermediate centrifuging step; adding a second water blanket (WB); increasing the rotational speed to 1,000 to 1,200 rpm; keeping the rotational speed constant for approximately 15 to 40 seconds; throttling the rotational speed in the case of an established imbalance; subsequent repeated increase and, optionally, several repetitions of this step; braking the centrifuge drum; emptying the centrifuge drum; and conducting a screen washing.

Description

DESCRIPTION OF THE DRAWINGS

(1) Additional preferred features of the invention are characterized in the appended description of the figures and the dependent claims.

(2) Embodiment examples of the invention are explained in more detail in the following on the basis of the drawing. Herein:

(3) FIG. 1 shows a schematic arrangement of different elements used in the field of a sugar centrifuge according to different embodiments of the invention;

(4) FIG. 2 shows a lateral view of a sugar centrifuge; and

(5) FIG. 3 shows a schematic overview relating to a method run in a sugar centrifuge.

DETAILED DESCRIPTION

(6) Different elements in the surroundings of a sugar centrifuge are indicated in FIG. 1. The centrifuge itself is not shown in order to make clearer the details of the other elements.

(7) Therefore, one recognizes a slurry distributor 1 with an associated trough, wherein agitator shaft and motor are omitted. A connection piece 2, by way of which the product or the raw material is supplied, leads into the slurry distributor 1.

(8) Additional connection pieces 3 are provided, by which the quantity in the slurry distributor to be further processed is discharged to the centrifuge.

(9) Turbidity sensors 4 are indicated on the connection pieces 3 or at least on some of these connection pieces 3. Therefore, these turbidity sensors are found between the run-off from the slurry distributor and a butterfly valve 6 (can be better seen in FIG. 2) on the centrifuge. A measurement signal can now be generated by means of these turbidity sensors 4, with which conclusions can be made on the quality of the magma in the control device (not shown).

(10) This turbidity sensor 4 is continually wetted with magma, but it should not become encrusted. Therefore, a mounted position at the specified place on the connection piece 3 has been shown to be positive in tests.

(11) Not shown, but conceivable would be additionally providing a rinsing line or cleaning fitting for the turbidity sensors 4.

(12) The turbidity sensors 4 could also be accommodated at alternative mounting positions, roughly at the front or back of the slurry distributor 1, which is indicated by the reference number 5.

(13) Possible also is the introduction of the turbidity sensors 4 in the inlet for the product on the connection piece 2. This embodiment has the advantage that a plurality of centrifuges or machines could be correspondingly provided with connection to a turbidity sensor equally and can secure the advantages according to the invention.

(14) The turbidity sensor in this case is also better exposed to the fluid dynamic processes and any encrustation is improbable from the outset. Also, in this measurement position at the inlet with the connection piece 2, a warning time of approximately 12 minutes or 4 batches is sufficiently short, with which the arrival of possible fine grain in the centrifuge is announced and is fully effective, in that there is sufficient fine grain content added to the centrifuge to provoke an upswing. The centrifuges can also still be considered to be protected in such an embodiment.

(15) Alongside or in addition to the turbidity sensor, other forms of sensors can also be employed, for example acoustic sensors, in particular ultrasonic sensors. Also conceivable are imaging methods and the use of Koch microscopes or video microscopes. Of course, these imaging methods are more expensive and more complex, and are usually less compact when mounted in a constricted structural space on the slurry distributor.

(16) Possible also is the use of optical lasers according to the focused beam reflectance measurement (FBRM) principle, which are very expensive, of course, but which supply good measurement results.

(17) In addition to the turbidity sensor 4, a redundant system of sensors in the drum or on the cover of the centrifuge and on the spray casing of the centrifuge can provide additional safety. These redundant systems of sensors react to changes in the build-up and the color of the crystal cake or to changes in the properties of the separated mother liquor, in each case when compared to conventional data as are found in a standard operation of a centrifuge not embodied according to the invention.

(18) In this case, as indicated by reference number 9, fine grain can be recognized optically in a centrifuge drum by an absent or delayed color change. Recognizing fine grain due to the absence of a change in the layer covering or a delayed change is produced by means of radar, laser, or ultrasonic distance measurement. Unusually slow changes in the composition of the magma in the centrifuge drum can be detected by UV, IR/Raman and microwave signals and may also indicate fine grain as well as the reduced or suppressed separation of the mother liquor associated therewith.

(19) Fine grain can also be recognized optically by an absent or delayed change in color at the spray casing 7 of the centrifuge and at the position 8, whereas with a sensor for conductivity, an absent or a delayed conductivity signal is used for recognizing fine grain. No changes or unusually slow changes in the composition of the run-off can be detected by changed UV and IR/Raman signals and may also indicate fine grain as well as the reduced or suppressed separation of the mother liquor associated therewith.

(20) The measurement signals of all sensors employed can be continuously detected and evaluated by means of memory-programmable control (MPC). Each time depending on divergence, intensity and fine grain fraction, corresponding fail-safe control routines can be initiated.

(21) A method could appear overall as that shown schematically in FIG. 3 on the basis of an example.

(22) The time t is plotted toward the right and the rotational speed in revolutions per minute is plotted toward the top. The presentation, of course, is not shown at correct scale.

(23) Below the time axis is additionally plotted the phase in which a water blanket WB is applied, and finally the method step in which a screen washing is carried out.

(24) In a first step V1, the filling of the centrifuge is conducted. Unlike the case in conventional processes, the centrifuge is only filled to approximately 60% to 70%, but at least to 50%. With a smaller filling, an imbalance could arise. The rotational speed of the centrifuge amounts to approximately 150 to 200 rpm during the filling process.

(25) Unlike in the conventional case, a syrup covering is not provided from the outset and thus is turned off. It would only intensify problems that arise due to the fine grain content.

(26) In a second step V2, the rotational speed is increased and a first water blanket WB is supplied. The rotational speed is increased linearly up to the range of approximately 700 rpm, since otherwise too great a compacting of the crystal cake would occur.

(27) Simultaneously, in about the middle of this step a first water blanket WB is added in order to dissolve the fine grain contained and to partially dilute or replace the mother liquor before the crystal cake is added.

(28) This procedure can take place controlled by rotational speed or by time. The supplying of the water blanket WB will be carried out preferably 1 to 5 seconds after the end of the filling process; the duration of the water blanket is 1 second to 3 seconds.

(29) In a third step V3, an intermediate centrifuging and a second water blanket WB are carried out. The rotational speed is still maintained for approximately 10 seconds at 700 rpm. At the same time, at the end of this step, a second water blanket is supplied in order to completely replace the mother liquor.

(30) The water blanket WB can be supplied automatically, for example controlled by an optical sensor, wherein a measurement of color change is conducted.

(31) The duration of the second water blanket WB is set at a maximum that corresponds to the normal operation with a radar sensor or also a laser sensor and a 100% drum filling. In this case, 100% corresponds to approximately 12 seconds to 18 seconds.

(32) The layering of the water blanket should lie one-third to one-half in the next acceleration phase.

(33) In a fourth step V4, the rotational speed is increased linearly up to 1080 rpm.

(34) In a fifth step V5, the rotational speed is kept constant at 1080 rpm. The standard spin duration in this step is 20 seconds to 30 seconds. As long as an imbalance does not occur, the spin duration can be prolonged by 10% to 20% in order to reduce the greater moisture of the crystal cake.

(35) Depending on whether an imbalance occurs, which is determined by an oscillation measurement device, the rotational speed of the centrifuge is regulated downward under certain conditions and subsequently increased again. A multi-step centrifuging procedure results therefrom, which can be conducted approximately two or three times.

(36) Since the crystal cake is newly aligned during braking V6, it has been found in tests that the water can better penetrate the crystal cake in multi-step centrifuging. In this way, a quieter, stable run occurs.

(37) The rotational speed lies in the range of the intermediate centrifuging and of the centrifuging.

(38) The intrinsic resonance of the machine should be considered. In centrifuges commonly found on the market, it lies somewhat below 700 rpm. Beyond this rotational speed in the region of the intrinsic resonance, one should relatively quickly walk away from it.

(39) Further steps correspond to the standard process. Therefore, in conclusion to the braking V6, another method step of emptying V7 is provided, and subsequently thereto a screen washing SW.

LIST OF REFERENCE CHARACTERS

(40) 1. Slurry distributor 2. Connection piece for the product inlet 3. Connection piece to the centrifuge 4. Turbidity sensor 5. Alternative position of the turbidity sensors 6. Butterfly valve on the centrifuge 7. Spray casing of the centrifuge 8. Conductivity sensor or optical sensor 9. Laser sensor or optical sensor V1 First method step: Filling V2 Second method step: 1.sup.st acceleration V3 Third method step: Intermediate centrifuging V4 Fourth method step: 2.sup.nd acceleration V5 Fifth method step: Centrifuging V6 Sixth method step: Braking V7 Seventh method step: Emptying SW Screen washing WB Water blanket