Method and device for oil-in-water measurement

• US 6,614,242 B2
• Filed: 12/08/2000
• Issued: 09/02/2003
• Est. Priority Date: 12/08/1999
• Status: Expired due to Term

• Current Assignee: Mind Fusion, LLC (Ascend Innovation Management, LLC)
• Original Assignee: ABB Research Ltd. (ABB Limited)
• Inventors: Rüegg, Walter, Byatt, John Anthony, Matter, Daniel, Kleiner, Thomas
• Primary Examiner(s): Deb, Anjan K.
• Application Number:
  US09/732,009
• Publication Number:
  US 20010003426A1
• Time in Patent Office: 998 Days
• Field of Search: 324/698, 324/694, 324/686, 324/691, 324/71.1, 324/439, 324/601, 324/448, 204/406, 204/193, 204/400, 73/614.4, 73/10.2, 73/530.5
• US Class Current: 324/698
• CPC Class Codes: G01N 27/226 Construction of measuring vessels; Electrodes therefor
• CPC Class Codes: G01N 33/1833 Oil in water
• CPC Class Codes: Y02A 20/20 Controlling water pollution; Waste water treatment

Abstract

A method and a sensor (1) for oil-in-water measurement, in particular for the oil industry. In an electric measuring cell (7, 12) a capacitance is measured as a measure of an oil concentration in the water flowing through or in the accumulation filter (16, 16a, 16b). In order to reduce the maintenance requirement, the measuring cell (7, 12) is automatically calibrated at recurring time intervals with clean water (FIG. 1) and/or flushed with water, possibly oil-contaminated, in the back-flushing direction (FIG. 2). Advantages of the invention are reduced signal drift, improved long-term reliability and a long service life without monitoring or filter exchange. Important exemplary embodiments relate to: a measuring cell (7, 12) with a long measuring and short flushing/calibration cycle, a measuring cell (7, 12) with a plurality of accumulation filters (16a, 16b) whose measuring cycles supplement one another in time, a cross-flow filter (2) for oil enrichment upstream of the measuring cell (7, 12) and a compact, pressure-resistant cylindrical ring-type filter (13) made from porous ceramic (16, 16a, 16b) with measuring and flushing connections radially (17a, 17b, 18a, 18b) and axially (17c, 18c).

Claims

1. A method for oil-in-water measurement, comprising:

feeding oil-contaminated water to a measuring cell; and

measuring an electrical impedance signal of the measuring cell, wherein the measuring cell is calibrated and/or flushed automatically at periodic intervals, and wherein an interval comprises a longer measuring cycle and a shorter calibration and/or flushing cycle.

2. The method as claimed in claim 1, comprising:

permanently measuring an impedance signal of the measuring cell using a plurality of accumulation filters with alternating measuring and flushing cycles which supplement one another.

3. The method as claimed in claim 2, wherein at least one of the following steps is performed:

a) a capacitance signal is used in the measuring cell as a measure of the oil concentration in the water;

b) an oil concentration of the water flowing through, or an oil concentration accumulated in an accumulation filter of the measuring cell, is measured in the measuring cell; and

c) an oil concentration in the water is enriched in a separating filter connected upstream by a known factor.

4. The method as claimed in claim 1, wherein at least one of following steps is performed:

a) during calibration, the measuring cell is flowed through by clean water and a calibration signal is formed;

b) during flushing, the measuring cell is flowed through backward by water; and

c) during flushing, an accumulation filter of the measuring cell is cleaned by ultrasound.

5. The method as claimed in claim 1, wherein at least one of the following steps is performed:

a) a capacitance signal is used in the measuring cell as a measure of the oil concentration in the water;

b) an oil concentration of the water flowing through, or an oil concentration accumulated in an accumulation filter of the measuring cell, is measured in the measuring cell; and

c) an oil concentration in the water is enriched in a separating filter connected upstream by a known factor.

6. The method as claimed in claim 1, wherein, during flushing, the measuring cell is flowed through backward with at least one of oil-contaminated water and a solvent.

7. An oil-in-water sensor for carrying out the method recited in claim 1, the oil-in-water sensor comprising:

means for feeding oil-contaminated water to a measuring cell which is connected to measuring means for impedance measurement;

means for at least one of self-calibration and self-flushing of the measuring cell; and

control means for automatically activating the means for self-calibration and/or for self-flushing.

8. The method as claimed in claim 1, wherein at least one of the following steps is performed:

a) a capacitance signal is used in the measuring cell as a measure of the oil concentration in the water;

b) an oil concentration of the water flowing through, or an oil concentration accumulated in an accumulation filter of the measuring cell, is measured in the measuring cell; and

c) an oil concentration in the water is enriched in a separating filter connected upstream by a known factor.

9. A method for oil-in-water measurement, comprising:

feeding oil-contaminated water to a measuring cell; and

measuring an electrical impedance signal of the measuring cell, wherein the measuring cell is calibrated and/or flushed automatically at periodic intervals, and wherein;

a) the measuring cell has exactly two accumulation filters which are flowed through in series one behind another,

b) in a first work operation, a first of the two accumulation filters is operated in a measuring cycle and a second of the two accumulation filters is operated in at least one of a calibration cycle and a flushing cycle, and

c) in a second work operation, the first accumulation filter is operated in at least one of a calibration cycle and a flushing cycle, and the second accumulation filter is operated in a measuring cycle.

10. The method as claimed in claim 9, wherein to fix an offset signal, only one of the two accumulation filters is flowed through, and an offset measurement is carried out at the other of the two accumulation filters.

11. An oil-in-water sensor comprising:

means for feeding oil-contaminated water to a measuring cell which is connected to measuring means for impedance measurement;

means for at least one of self-calibration and self-flushing of the measuring cell; and

control means for automatically activating the means for self-calibration and/or for self-flushing, wherein the means for self-calibration comprise;

a cross-flow filter having a first outlet for oil-enriched water, and a second outlet for cleaned water, connected in an alternating fashion to the measuring cell via controllable valves.

12. The oil-in-water sensor as claimed in claim 11, comprising at least one of:

a) an accumulation filter of the measuring cell formed as a ceramic filter with a pore size which is water-pervious and oil-absorbing; and

b) an accumulation filter of the measuring cell formed as a polyethylene fibrid filter.

13. The oil-in-water sensor as claimed in claim 11, wherein for cleaning purposes the cross-flow filter has a second inlet for clean water.

14. The oil-in-water sensor as claimed in claim 11, comprising at least one of:

a) an accumulation filter of the measuring cell formed as a ceramic filter with a pore size which is water-pervious and oil-absorbing; and

b) an accumulation filter of the measuring cell formed as a polyethylene fibrid filter.

15. An oil-in-water sensor, comprising:

means for feeding oil-contaminated water to a measuring cell which is connected to measuring means for impedance measurement; and

means for self-flushing of the measuring cell, which means for self-flushing comprise two flushing lines parallel to the measuring cell, and wherein the measuring cell can be separated from a measuring line by first valves, and can be connected to the flushing lines in a back-flushing direction via second valves.

16. The oil-in-water sensor as claimed in claim 15, comprising:

control means for automatically activating the means for self-flushing.

17. The oil-in-water sensor as claimed in claim 15, comprising:

an electronic control system and control signal lines which are configured for automatic control of the valves.

18. The oil-in-water sensor as claimed in claim 15, wherein the measuring cell includes an accumulation filter configured as a cylindrical ring-type filter which has an outer electrode on an outer cylinder surface and an inner electrode on an inner cylinder surface and a radial connection and an axial connection.

19. The oil-in-water sensor as claimed in claim 15, comprising at least one of:

a) an accumulation filter of the measuring cell formed as a ceramic filter with a pore size which is water-pervious and oil-absorbing; and

b) an accumulation filter of the measuring cell formed as a polyethylene fibrid filter.

20. An oil-in-water sensor, comprising:

means for feeding oil-contaminated water to a measuring cell, which is connected to measuring means for impedance measurement; and

means for self-flushing and/or self-calibration of the measuring cell, wherein the measuring cell comprises a cylindrical ring-type accumulation filter, which accumulation filter has an outer electrode on an outer cylinder surface and an inner electrode on an inner cylinder surface and a radial connection and an axial connection.

21. The oil-in-water sensor as claimed in claim 20, wherein the cylindrical ring-type filter includes two half-shell outer electrodes and inner electrodes, as well as two separate radial connections.

22. The oil-in-water sensor as claimed in claim 20, wherein the means for self-calibration comprise:

a cross-flow filter having a first outlet for oil-enriched water, and a second outlet for cleaned water, connected in an alternating fashion to the measuring cell via controllable valves.

23. The oil-in-water sensor as claimed in claim 20, comprising:

control means for automatically activating the means for self-flushing and/or self-calibration.

24. A method for oil-in-water measurement, comprising:

feeding oil-contaminated water to a measuring cell;

measuring an electrical impedance signal of the measuring cell;

enriching an oil concentration in the water by a known factor in a separating filter connected upstream from the measuring cell, the separating filter comprising a first outlet for oil-enriched water and a second outlet for cleaned water; and

calibrating the measuring cell automatically at periodic intervals with water output from the second output of the separating filter.

25. A method for oil-in-water measurement, comprising:

feeding oil-contaminated water to a measuring cell, the measuring cell comprising a cylindrical ring-type accumulation filter, which accumulation filter has an outer electrode on an outer cylinder surface and an inner electrode on an inner cylinder surface and a radial connection and an axial connection; and

measuring an oil concentration accumulated in the accumulation filter through an electrical impedance signal of the measuring cell, the measuring cell being flushed and/or calibrated automatically at periodic intervals.

26. A method for oil-in-water measurement, comprising:

feeding oil-contaminated water to a measuring cell, an accumulation filter being arranged in the measuring cell, and

measuring oil concentration accumulated in the accumulation filter through an electrical impedance signal of the measuring cell, the measuring cell being flushed automatically at periodic intervals, and during flushing, the measuring cell being flowed through backward by water, wherein an oil concentration in the water is enriched in a separating filter connected upstream by a known factor.