Electricity: measuring and testing – A material property using electrostatic phenomenon – In a liquid
Reexamination Certificate
2001-02-21
2003-02-04
Oda, Christine (Department: 2858)
Electricity: measuring and testing
A material property using electrostatic phenomenon
In a liquid
C324S071100, C073S863830
Reexamination Certificate
active
06515481
ABSTRACT:
BACKGROUND OF THE INVENTION
Streaming current detectors take advantage of physical phenomena in which an ionic flux is produced by rapid movement between a pair of spaced apart, but close-fitting dielectric elements, the surfaces of which carry electrical charges induced by a charge-bearing fluid which bathes both elements. Ions or charged colloids adsorbed on the dielectric walls—which may include remnants of an earlier test fluid—give this ionic flux its unique characteristics. In a typical streaming current detector, the spaced apart dielectric elements are fabricated of Teflon R and include a piston and a bore for slideably receiving the piston; clearances between them measure about 0.005 inch.
To transmit a “streaming current”, two electrodes, interconnected by an external circuit, are mounted proximate with the paired dielectric elements. A popular combination, taught by Bryant and Veal in U.S. Pat. No. 4,769,608, is to secure ring-like electrodes to the wall of the bore. An electrical signal is generated when the fluid attains a state of hydrodynamic shear as the close-fitting dielectric surfaces move past each other. The strength of this signal is dependent upon, among other things, the conductivity of the fluid, its velocity, the size of the fluid passageway, and the frequency of oscillation of the piston, as well as the presence of adsorbed species on the piston and bore surfaces.
While the usefulness of streaming current measurements for controlling the amount of chemicals needed to treat water, as well as various wastewater streams, is now widely recognized, operators trying to obtain such measurements, and have them be both continuous and reliable, still face daunting challenges. Not only does the buildup of contaminants on the electrodes or surfaces disposed proximate with them degrade the signal but also its strength can be reduced, with detrimental consequences, by numerous factors. Among them is an increase in the conductivity of the test fluid, a change which by itself can dramatically attenuate the streaming current signal. Indeed, if the conductivity goes high enough—to at least about 10,000 micromhos, the electrodes themselves short out. An operator could think, based on his streaming current observations, that he needs to add fewer chemicals or replace the dielectric elements and/or electrodes, when the real problem is that the process flow stream has experienced a sudden, unexpected increase in its electrolyte concentration.
Nor has a long-standing debate as to what the streaming current—sometimes referred to as the “streaming potential”—actually represents helped this situation. Getting beyond the basic assumption, i.e., the streaming current is related in some way to the surface charge or surface potential (zeta potential) of dispersed colloidal particles in a given system,.to an understanding of the zeta potential-streaming current detector response interrelationship remains an elusive goal. In view of this uncertainty, no one ventured to equip any of the prior art detectors with a compensating conductivity probe, even though the pronounced effects which changes in conductivity have on the streaming current are well known.
To circumvent conductivity-related distortions of the streaming current signal, prior art detectors have been relegated to a minor role in applications where the electrolyte concentration in a process flow stream varies widely. As part of an elaborate titration apparatus, the detector is used only to indicate when, as each discrete batch of test fluid is being titrated, the streaming current vanishes. The complexity of this apparatus introduces its own set of technical problems, as Krah discloses in U.S. Pat. No. 5,408,185.
On the other hand, progress towards eliminating streaming current aberrations caused by slow fouling is apparent in the prior art. Recognition came rather quickly that desorbing high molecular weight polymers once they are adsorbed on a Teflon R or similar dielectric material is virtually impossible in an on-line instrument. Instead, Bryant,and Veal invented an electrode holder which can be removed and replaced in less than one minute. As disclosed in U.S. Pat. No. 5,119,029, this holder included both the bore and the electrodes in a single unit. Problems with its use arose when operators seeking to rehabilitate holders soaked them in cleaning solution and inadvertently shorted out the electrical connections to the electrodes.
Attempts to provide reliable streaming current signals in situations where fouling occurs abruptly have been less successful. Problems with scaling in certain situations are so severe as to make the use of prior art detectors, including those equipped with removable electrode holders, cost prohibitive. In particular, lime scaling—which occurs wherever lime, a popular water treatment chemical, is used to coagulate/precipitate contaminants from a flow stream—has been inherently difficult to deal with.
Other conditions under which prior art remedies have proven inadequate involve the presence of grit or heavy silt in the test fluid. Not only do grit and heavy silt scratch less wear-resistant dielectric surfaces but also they introduce hairline crevasses along which charge-laden debris can accumulate. Jammed into the narrow fluid flow channels in a streaming current detector, grit can even cause a bore-mounted ring electrode to break or become dislodged. Pre-sample filters, strainers and hydrocyclone samplers have all been introduced to reduce grit, heavy silt and debris build-up within streaming current detectors but have failed to eliminate these troublesome impediments. dislodged. Pre-sample filters, strainers and hydrocyclone samplers have all been introduced to reduce grit, heavy silt and debris build-up within streaming current detectors but have failed to eliminate these troublesome impediments.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a streaming current detector in which the replacement of critical parts used to generate the test signal, such as the dielectric elements and the electrodes, can be accomplished quickly, easily and independently of each other, so that the detector can be used in situations in which the corrosive and/or abrasive nature of the test fluid formerly made any use of a streaming current detector cost prohibitive.
A further object of the present invention is to provide such a detector in which the dielectric elements and the electrodes can be replaced in the field in less than one minute, virtually eliminating downtime.
A still further object of the present invention is to provide an improved streaming current detector having a matched set of removable dielectric elements, respective matched sets being designed in the basis of their capacity to withstand abrasive environments, as well as their chemical compatibility with the test fluid and the operating temperature of the process flow stream.
A still further object of the present invention is to provide such a detector in which the matched set of dielectric elements can be selected to increase the strength of the test signal over that generated by a conventional piston and bore combination, a tight-fitting pair being used in applications where extra response is needed. Alternately, a “loose-fitting” pair can be selected for those situations in which large particles are present or the sensitivity needs to be reduced.
The intent of the present invention is also to provide for electrodes that are less vulnerable to breakage during ruse and can be easily inspected and removed for cleaning, so that the remaining components of the detector can be soaked in solution without simultaneously shorting out electrode connections.
Another object of this invention is to monitor the conductivity and streaming current of a test fluid simultaneously, so that sources of test signal variations can be better understood, especially in common applications such as municipal wastewater treatment where wide swings in conductivity often occur as a result of road salting, an event which has delayed, largely
Leon Harry I.
Oda Christine
Steadman Vivian L.
LandOfFree
Streaming current detector with easily removable matched... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Streaming current detector with easily removable matched..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Streaming current detector with easily removable matched... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3124262