DEVICE AND METHOD FOR MEASURING A FILTER CAKE THICKNESS

Abstract

A rotary pressure filter, comprising a filter drum and a housing. A sensor is attached to the housing and emits light through a light-permeable section of the housing in the direction of a filter cake. The sensor receives light reflected from the filter cake through the light-permeable section of the housing. A processing unit compares properties of the emitted light with those of the received light and determines an absolute thickness of the filter cake and/or a change in the thickness of the filter cake over a pre-determined time. The invention further relates to a corresponding method.

Claims

1. A rotary pressure filter, comprising a filter drum for filtering material, wherein a filter cake is formed on a surface of the filter drum when the material is filtered; a housing that surrounds the filter drum and in which the filter drum is rotatably mounted; a sensor attached to the housing, wherein the sensor emits light through a light-permeable section of the housing in the direction of the filter cake and receives light reflected from the filter cake through the light-permeable section of the housing; and a processing unit configured to receiving information from the sensor representing properties of the emitted light and properties of the received light, wherein the processing unit is further configured to compare the properties of the emitted light with the properties of the received light and, based on the comparison, to determine a thickness of the filter cake.

2. The rotary pressure filter according to claim 1, wherein the rotary pressure filter further comprises a storage unit operatively connected to the processing unit, which the storage unit stores values of at least one of the properties of the emitted light or the properties of the received light.

3. The rotary pressure filter according to claim 1, wherein the sensor is arranged outside a process chamber of the rotary pressure filter.

4. The rotary pressure filter according to claim 1, wherein the sensor is arranged such that the emitted light strikes the surface of the filter cake substantially orthogonally.

5. The rotary pressure filter according to claim 1, wherein the sensor is a laser triangulation sensor.

6. The rotary pressure filter according to claim 1, wherein the sensor is a laser transit time measurement sensor.

7. The rotary pressure filter according to claim 1, wherein the sensor emits pulsed light.

8. The rotary pressure filter according to claim 1, wherein the sensor continuously emits light.

9. The rotary pressure filter according to claim 1, wherein the rotary pressure filter further comprises a control unit that is designed to set a rotational speed of the filter drum on the basis of the filter cake thickness determined by the processing unit.

10. A method for determining a thickness of a filter cake that is formed when filtering material on a surface of a filter drum of a rotary pressure filter, the method comprising: emitting, by a sensor, light in the direction of the filter cake; receiving, by the sensor, light reflected from the filter cake; providing, by the sensor, information representing properties of the emitted light and properties of the received light; comparing, by a processing unit, the properties of the emitted light with the properties of the received light so as to determine a thickness of the filter cake.

11. A method for determining a thickness of a filter cake according to claim 10, further comprising: outputting, by the processing unit, a signal to a control unit, wherein the signal indicates the filter cake thickness; and setting, by the control unit, a rotational speed of the filter drum based on the signal output by the processing unit.

12. A method for determining a thickness of a filter cake according to claim 9, wherein the filter drum is rotatably mounted in a housing and the sensor is attached to the housing.

13. A method for determining a thickness of a filter cake according to claim 12, wherein the sensor emits the light through a light-permeable section of the housing in the direction of the filter cake and receives light reflected from the filter cake through the light-permeable section of the housing.

14. A method for determining a thickness of a filter cake according to claim 10, further comprising storing, by a storage unit operatively connected to the processing unit, values of at least one of the properties of the emitted or the properties of the received light.

15. A method for determining a thickness of a filter cake according to claim 10, wherein the sensor is arranged such that the emitted light strikes the surface of the filter cake substantially orthogonally.

16. A method for determining a thickness of a filter cake according to claim 10, wherein the sensor comprises a laser triangulation sensor or a laser transit time measurement sensor.

17. A method for determining a thickness of a filter cake according to claim 10, wherein the sensor emits pulsed light.

18. A method for determining a thickness of a filter cake according to claim 10, wherein the sensor continuously emits light.

19. A method for determining a thickness of a filter cake according to claim 10, wherein the thickness of the filter cake represents at least one of an absolute thickness of the filter cake or a change in the thickness of the filter cake over a predetermined time.

20. The rotary pressure filter according to claim 1, wherein the thickness of the filter cake represents at least one of an absolute thickness of the filter cake or a change in the thickness of the filter cake over a predetermined time.

Description

[0025] In the drawings:

[0026] FIG. 1 is a schematic side cross-sectional view of a sensor arrangement on a section of a housing of the rotary pressure filter according to the invention.

[0027] A section of a rotary pressure filter 10 is shown in FIG. 1. In the section of the rotary pressure filter 10, a sensor 12 can be seen that emits a laser beam 14. The laser beam 14 extends from the sensor 12 through a sight glass 16 that arranged in a connecting piece 18. The connecting piece 18 is arranged at an opening 20 of a housing 22 of the rotary pressure filter 10 in such a way that it forms an airtight seal with the housing 22 and accommodates the sight glass 16 in an airtight manner with respect to an outer side of the housing 22. The sight glass 16 thus divides the laser beam 14 into a section 24 arranged outside a process chamber of the rotary pressure filter and a section 26 arranged inside the process chamber. Accordingly, it can be clearly seen in FIG. 1 that the sensor 12 is arranged outside the process chamber of the rotary pressure filter.

[0028] The laser beam 14 then strikes a surface of a filter cake 28 from which it is reflected. The filter cake 28 is formed when suspension is filtered on the surface of a filter drum 30. A portion of the reflected laser beam 14a (shown with the emitted laser beam 14 superimposed in FIG. 1) then re-enters through the sight glass 16 and into a receiving unit of the sensor 12.

[0029] According to a difference between properties of the light 14 emitted by the sensor 12 and properties of the light 14a reflected by the surface of the filter cake 28, such as a total transit time from emission to reception of the light or an angle between the emitted laser beam 14 and the laser beam 14a entering the receiving unit of the sensor 12, which has been reflected by the filter cake 28, a distance of the surface of the filter cake 28 relative to the sensor 12 and thus a thickness of the filter cake 28 can be determined.

[0030] In the embodiment shown in FIG. 1, the sensor 12 is based on a transit time measurement method. A pulse of a laser beam can be emitted by the sensor, which pulse is reflected by the surface of the filter cake 28 and then re-enters the receiving unit of the sensor 12. Either a change in the transit time can be recorded by means of a series of transit time measurements, and a change in the filter cake thickness can thus be concluded, or a transit time of the laser beam up to the bare filter drum, that is to say a filter drum without a filter cake formed thereon, can be known. Advantageously, transit times of the laser beam can also be known for pre-determined filter cake thicknesses, for example from 1 cm to 150 cm in 1 cm increments, such that a transit time of the laser beam can be compared directly with a known value to determine the thickness of the filter cake layer.