Method and apparatus for inline electrochemical monitoring and automated control of oxidizing or reducing agents in water systems

• US 5,382,331 A
• Filed: 07/26/1993
• Issued: 01/17/1995
• Est. Priority Date: 07/26/1993
• Status: Expired due to Fees

• Current Assignee: Ecolab USA Incorporated (Ecolab, Inc.)
• Original Assignee: Nalco Chemical Company (Ecolab, Inc.)
• Inventors: Banks, Rodney H.
• Primary Examiner(s): Niebling, John
• Assistant Examiner(s): Bell, Bruce F.
• Application Number:
  US08/097,654
• Time in Patent Office: 540 Days
• Field of Search: 204/402, 204/406, 204/407, 204/408, 204/409, 204/412, 204/153.11, 204/153.14, 204/153.22, 204/232, 204/267, 204/269
• US Class Current: 205/781
• CPC Class Codes: G01N 27/38 Cleaning of electrodes
• CPC Class Codes: G01N 27/4045 for gases other than oxygen
• CPC Class Codes: G01N 27/49 Systems involving the determination of the current at a single specific value, or small range of values, of applied voltage for producing selective measurement of one or more particular ionic species

Abstract

Method and apparatus for electrochemical monitoring of oxidizing agents, such as nitrite, or reducing agents in a water system and for controlling concentration levels for protecting surfaces exposed to the water. The apparatus includes a probe for selective exposure to fresh water samples of the system. The probe is connected to an analyzer that operates the probe and measures agent concentration by a chronoamperometry technique. A controller selectively feeds an agent to the water system in accordance with a set point to maintain a desired concentration level.

Claims

1. An apparatus for electrochemically monitoring and controlling oxidizing or reducing agent concentrations in a water system comprising:

an inline mounted probe exposed to a water sample of the system, said probe including a plurality of current measuring cells each of which includes a working electrode, a counter electrode and a reference electrode,

a source of oxidizing or reducing agent, means for selectively feeding the agent to the system,

and an analyzer and controller connected to the probe for operating the probe and measuring agent concentration by processing the current measured during a measurement cycle, said analyzer being connected to the feeding means for operating the feeding means.

2. The apparatus of claim 1, wherein said analyzer and controller includes means for switching the probe between cleaning and measuring modes and causing said feeding means to operate between feed and non-feed modes in relation to a set point of agent concentration.

3. The apparatus of claim 2, which further includes means selectively maintaining the water sample isolated from said water system at least during the measuring mode.

4. The apparatus of claim 3, wherein said isolation means includes a remotely operated valve driven by the analyzer and controller.

5. The apparatus of claim 4, wherein said means for selectively feeding the agent includes a feed pump, and said analyzer and controller having means to turn the pump on or off depending on the agent concentration in said water system.

6. The apparatus of claim 5, wherein said probe includes two cells, and said analyzer and controller operates the cells to each, takes a measurement and average, the measurements thereby providing a reliable agent concentration measurement for controlling the feed pump.

7. The apparatus of claim 3, wherein said isolation means includes a solenoid valve driven by the analyzer and controller.

8. The apparatus of claim 5, wherein said analyzer and controller includes a microprocessor programmed to operate the probe, the solenoid valve and the feed pump to maintain the optimum agent concentration in the water system.

9. The apparatus of claim 8, wherein said analyzer and controller further includes means to measure and compensate for the temperature of the sample.

10. The apparatus of claim 9, wherein said analyzer and controller further includes means for checking conductivity of the sample to determine if it is reasonably related to the agent concentration.

11. The apparatus of claim 10, wherein said analyzer and controller further includes means for making a reference electrode check.

12. The apparatus of claim 1, wherein the water system is closed.

13. The apparatus of claim 1, wherein the water system is open.

14. In a recirculating water system having a concentration of nitrite, an apparatus for electrochemically measuring and controlling the concentration of nitrite in said recirculating water cooling system to minimize corrosion of steel surfaces of lines and recirculating equipment, said apparatus comprising:

a sample line connected to a system line for receiving a water sample,

a probe mounted in the sample line,

valve means between the probe and the system line for statically conditioning a sample during the measuring of the concentration in the sample,

a feed pump connected to a supply of nitrite and the system line for selectively feeding nitrite to the water cooling system,

and analyzer means connected to the probe for operating the probe, the valve means and the feed pump to maintain the nitrite concentration within a set range.

15. The apparatus of claim 14, wherein said probe includes a steel casing, a plurality of electrodes mounted in the casing and electrically insulated from each other, and a temperature sensor.

16. The apparatus of claim 15, wherein said electrodes include a plurality of electrodes of non-reactive electrically conductive material and a plurality of silver-based reference electrodes.

17. The apparatus of claim 16, wherein said electrodes of non-reactive electrically conductive material are glassy carbon.

18. The apparatus of claim 16, wherein said electrodes of non-reactive electrically conductive material are a noble metal.

19. The apparatus of claim 16, wherein said silver-based electrodes include a silver base coated with silver chloride.

20. The apparatus of claim 16, wherein said silver-based electrodes include a silver base coated with a mixture of silver sulphide and silver chloride.

21. The apparatus of claim 16, wherein said electrodes are connected to said analyzer means and operated as a plurality of measuring cells.

22. The apparatus of claim 21, wherein each cell includes a working electrode, a counter electrode and a reference electrode.

23. The apparatus of claim 22, wherein said electrodes include a pair of glassy carbon electrodes and a pair of silver-based electrodes, each glassy carbon electrode being proximate to a silver-based electrode.

24. The apparatus of claim 23, wherein said analyzer means includes means operating said electrodes as a pair of nitrite concentration measuring cells, each cell consisting of a working electrode, a counter electrode and a reference electrode, said glassy carbon electrodes operating as working and counter electrodes, and said silver-based electrodes operating as reference electrodes.

25. The apparatus of claim 24, wherein said analyzer means further includes means for driving said probe in a cleaning mode by cycling the glassy carbon electrodes between positive and negative voltage potentials to cause cleaning of the electrodes, and in a nitrite concentration measuring mode by applying a positive potential to a cell to oxidize the nitrite in the sample and measure the current in the cell and convert the current measurement to a ppm nitrite concentration level.

26. The apparatus of claim 25, wherein said analyzer means further includes means for driving said probe in a physical cleaning mode on at least a daily basis by applying a potential between the steel casing and the glassy carbon electrodes.

27. The apparatus of claim 25, wherein said means for driving the electrodes in said measuring mode further includes opening said valve means to allow sample to flow past the probe to drain, subjecting the cells to a cleaning operation, closing said valve means to statically condition the sample, checking the power supply, checking the conductivity of the sample, conducting a reference electrode check, and making a temperature measurement, all prior to measuring the current in the cells.

28. The apparatus of claim 27, wherein said analyzer means further includes means for averaging the concentration measurements of each cell, and means for turning the feed pump on or off depending on the set point for the nitrite concentration.

29. The apparatus of claim 28, wherein said analyzer means further includes means for discontinuing the measuring mode if the conductivity measurement of the sample is outside a set range.

30. The apparatus of claim 21, wherein said glassy carbon electrodes include a circularly shaped flat surface exposed to the sample, and said silver-based electrodes include a semi-tubular shaped flat surface exposed to the sample, one each arranged in closely spaced concentric relation to a glassy carbon electrode.

31. A method of electrochemically measuring and controlling the concentration of nitrite in a recirculating water cooling system to minimize corrosion of steel surfaces of lines and/or recirculating equipment which comprises the steps of:

providing a sample line to receive a water sample from the system to measure the nitrite concentration,

providing means for selectively supplying nitrite to the system,

providing a probe in the sample line, wherein the probe includes a plurality of nitrite concentration electrochemical measuring cells, each of which includes a plurality of electrodes,

providing a power supply for said cells,

operating the probe to maintain the electrodes clean for taking optimum concentration measurements,

statically conditioning the sample,

supplying a voltage potential to the cells,

measuring the current through the cell,

converting the current measurement to a nitrite concentration,

and driving the nitrite supplying means in accordance with a set point of the measured concentration of nitrite.

32. The method of claim 31, which prior to the current measurement step further includes the steps of providing a fresh sample of cooling water to the probe during the current measuring step of each cell.

33. The method of claim 32, wherein said probe includes a pair of glassy carbon electrodes, a pair of silver-based electrodes and a temperature sensor, and said method further includes the steps of operating said electrodes as a pair of nitrite concentration measuring cells, each cell consisting of a working electrode, a counter electrode and a reference electrode, said glassy carbon electrodes operating as working and counter electrodes, and said silver-based electrodes operating as reference electrodes.

34. The method of claim 33, which further includes ramping up the voltage potential of each cell to oxidize nitrite and measuring current across the working and counter electrodes just prior to dropping the potential.

35. The method of claim 34, which prior to the current measurement step of each cell further includes the steps of providing a fresh sample to the probe, subjecting the cells to a cleaning operation, checking the power supply, checking the conductivity of the sample, conducting a reference electrode check, and taking a temperature measurement of the sample through the sensor in the probe.

36. The method of claim 35, which further includes the step of physically cleaning the electrodes at least once daily by applying a potential between the probe casing and the glassy carbon electrodes.

37. The method of claim 36, which further includes the step of discontinuing the operation of the probe to make a nitrite concentration current measurement if the conductivity check is outside a set range.

38. An apparatus for electrochemically monitoring oxidizing or reducing agent concentrations in a water system comprising:

an inline mounted probe exposed to a water sample of the system, said probe including a plurality of current measuring cells each of which includes a working electrode, a counter electrode and a reference electrode,

and an analyzer connected to the probe for operating the probe and measuring agent concentration by processing the current measured during a measurement cycle.

39. The apparatus of claim 38, wherein said analyzer further including means for switching the probe between cleaning and measuring modes.

40. A method of electrochemically measuring and controlling the concentration of nitrite in a recirculating water cooling system to minimize corrosion of steel surfaces of lines and/or recirculating equipment which comprises the steps of:

providing a sample line to receive a water sample from the system to measure the nitrite concentration,

providing a probe in the sample line, wherein the probe includes a plurality of nitrite concentration electrochemical measuring cells, each of which includes a plurality of electrodes,

operating the probe to maintain the electrodes clean for taking optimum concentration measurements,

statically conditioning the sample,

measuring the current through the cell,

converting the current measurement to a nitrite concentration.