Patent Application
20090078386
The present invention relates generally to sensing characteristics of a liquid. More particularly, the present invention relates to an apparatus and method for utilizing an electrode to sense characteristics of a liquid.
Paper mills produce paper through a wood pulping process that begins with wood chips as the raw material. The wood chips are initially broken down or digested into wood fibers, which are then passed on for further processing to produce a variety of paper-based products. During the process of “digesting” the wood chips, a caustic solution referred to as white liquor is added to the wood chips. The white liquor is typically composed of mainly sodium sulfide (Na2S) and sodium hydroxide (HaOH). At the end of the “digesting” process, chemical reactions, which have produced the desired wood fibers, have also produced a different caustic solution which is now referred to as black liquor. As a secondary process to minimize waste and optimize production, the black liquor may be recovered and chemically converted first to a green liquor and then back to a white liquor. The recycled white liquor may now be re-used in the digestion of another batch of wood chips.
The black liquor may be burned in a boiler, which leaves a smelt. This smelt is dissolved in water or “weak wash liquor” to produce green liquor. This conversion is often referred to as the “causticizing process” or the “causticizing reaction.” The causticizing process takes place in a “slaker” where “causticizing agents,” such as lime, are added during the conversion back to white liquor. The causticizing process can be optimized by proper control of the flow rate of the green liquor into the slaker and proper control of the quantity and frequency of the addition of the causticizing agent.
During the processing it is extremely beneficial to monitor the chemical composition of the changing liquor. One method of controlling the composition of the liquor during the causticizing process is to embed electrodes in the tank containing the liquor. This method is effective; however, the caustic solution that surrounds the electrodes can have adverse effects on the electrodes, such as fluctuations or inaccurate readings from the electrodes and physical deterioration of not only the electrode surfaces but also any seals around the electrodes. Both of these seals have short lifespans when exposed to the caustic pulp liquor. Any required maintenance and/or replacement of the electrodes may involve manual control of the liquor composition or a suspension of the paper mill processing. Accordingly, there exists a need to extend the usable life of the electrodes used to measure the characteristics of the highly caustic pulp liquor.
Some methods to isolate the electrodes from the liquor include the use of elastomeric or glass seals. Both of these seals may have short lifespans when exposed to the caustic pulp liquor. Any required maintenance and/or replacement of the electrodes may involve manual control of the liquor composition or a suspension of the paper mill processing. Accordingly, there exists a need to extend the usable life of the electrodes used to measure the characteristics of the highly caustic pulp liquor and provide for the replacement of the electrodes.
The present invention solves these and other needs by providing a method and apparatus for sensing characteristics of a liquid by using electrodes containing interior apertures. An exemplary embodiment may provide improved o-ring insulation to seal and isolate the electrodes from the liquid.
In an exemplary embodiment of the invention, a electrode is used for transmitting electrical signals associated with characteristics of a liquid to and from the liquid. The thin electrode has an aperture on the interior of the electrode, and the aperture surface is in contact with the liquid. An electrical coupling contained on an isolated outer surface of the electrode is used for communicating an electrical signal from the electrode.
In another embodiment where conditions require more than one electrode, the electrodes may be stacked alternately with o-rings. The electrodes and o-rings may be compressed together to seal the surfaces exposed to the liquid from the outer surfaces containing the electrical couplings. The apertures of the electrodes align to form a cavity where the liquid comes into contact with the electrodes. In another embodiment, a cleaning solvent supply orifice may direct cleaning solvent across the aperture surface of the electrodes and O-rings to remove any accumulations on this surface.
The above and other objectives and advantages of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference numbers refer to like parts throughout, and in which:
Referring to
The sensing end 106 of the electrode housing 100 extends into the tank 102. As shown in the cross-sectional view, electrodes or probes 104 may be mounted flush with a surface of the sensing end 106. The electrodes 104 are in direct contact with the liquid in the recausticizing tank 102. Wires 108 extend from the electrodes 104 through the electrode housing 100 and out of the tank 102 to transmit readings to receiving equipment outside of the tank. One possible electrode configuration is described in U.S. Pat. No. 6,235,123 issued May 22, 2001, entitled “Chemical Cleaning System for Electrodes Used in a Liquid Environment,” which is incorporated herein by reference.
Referring to
In an exemplary embodiment, the thickness of the electrode 200 may be about 4-8 mm although it is not limited to this range. The diameter of the electrode 200 may be about 25-50 mm although it is also not limited to this range. The electrode 200 has a circular outer shape; however, the outside shape of the electrode 200 is not limited to this shape. The electrode 200 may be composed of platinum or another inert conductive material, such as gold, graphite, iridium, palladium, or carbon. Other materials such as stainless steel and titanium are possible in certain situations.
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The liquid to be analyzed flows through a cavity 312 in the electrode housing 300 and comes into contact with the interior aperture surface 202. The electrical signal generated and/or received by the liquid is transmitted from the interior aperture surface 202 through the electrode 302 to wires 306. The electrode housing 300 allows the electrical signal to be transmitted from a harsh environment to the wires 306. The wires supply the electrical signal to receiving equipment. One possible example of receiving equipment is described in U.S. Pat. No. 6,416,651 issued Jul. 9, 2002, entitled “Multi-Electrode Composition Measuring Device And Method,” which is incorporated herein by reference.
In the exemplary embodiment, the electrodes 302 and the o-rings 304 are compressed together to isolate the outer surfaces of the electrodes 302 where the electrical couplings are located. This may be accomplished in a variety of ways. For example, the electrodes 302 and the o-rings 304 may be compressed between a top and a bottom plate (not shown). The electrodes 302 and the o-rings 304 may be fitted within cylindrical rings within a cylindrical housing. The electrodes 302 may rely on a compression fit to hold the electrodes 302 in place during operation. In another example, the electrodes 302 may have a threaded exterior surface that may be screwed into a cylindrical housing with a threaded interior surface. Embodiments are not limited to the above constructions. A variety of constructions will be apparent to an individual skilled in the art.
The o-rings 304 may contain urethane to help minimize the damaging effects of the caustic pulp liquor used in paper processing. The design and material of the O-rings 304 may be selected based on the desired operation environment and/or insulating need of the electrodes 302.
According to one exemplary embodiment, the electrode housing 300 contains a cleaning solvent supply orifice 308. The cleaning solvent supply orifice 308 directs a cleaning solvent across the interior aperture surface 202 to remove any accumulations on this surface. The cleaning solvent applied in this manner minimizes the damaging effects on the electrodes 302 due to caustic pulp liquor used in the Pulp and Paper Industry. The cleaning solvent supply orifice 308 allows the electrodes 302 to be cleaned periodically without needing to remove the electrodes 302. The method of cleaning the electrodes 302 may involve several different cleaning or rinsing cycles and/or purge cycles to remove the cleaning solvent from the electrodes 302.
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The tapered thread portion 602 may provide a tight seal to isolate the electrode sensing surface 604 from the electrical coupling 606. An assembly specification may provide a torque measurement to ensure that once assembled, there will be a suitable seal between the electrode sensing surface 604 and the electrical coupling 606. In another exemplary embodiment, the tapered thread portion 602 of the electrode 600 may be coated with urethane to further seal the electrical coupling 206 from the electrode sensing surface 204.
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The electrode housing assembly 700 may contain a threaded aperture 706 for receiving the tapered thread of the coupling portion of each electrode 702. Each threaded aperture 706 may also contain an electrical coupling for communicating the electrical signal from each electrode 702. The threaded apertures 706 are contained on a surface 704 of the electrode housing 708. The liquid to be analyzed flows over the electrode housing surface 704 and comes into contact with each electrode sensing surface 604. The electrical signal generated and/or received by the liquid is transmitted from the electrode sensing surface 604 through the electrode 702 and to the electrical coupling located in the threaded aperture 706 of the electrode housing 708.
The electrode housing assembly 700 allows the electrical signal to be transmitted from a harsh environment to the electrical coupling in the threaded aperture of the electrode housing 708. From the electrode housing 708, the electrical signal is then transmitted to receiving equipment external to the container of liquid that is being analyzed. One possible example of receiving equipment is described in U.S. Pat. No. 6,416,651 issued Jul. 9, 2002, entitled “Multi-Electrode Composition Measuring Device And Method,” which is incorporated herein by reference.
The o-rings 704 may contain urethane to help minimize the damaging effects of the caustic pulp liquor used in paper processing. The design and material of the O-rings 704 may be selected based on the desired operation environment and/or insulating need of the electrodes 702.
According to one exemplary embodiment, the electrode housing 700 contains a cleaning solvent supply orifice 708. The cleaning solvent supply orifice 708 directs a cleaning solvent across the interior aperture surface 602 to remove any accumulations on this surface. The cleaning solvent applied in this manner minimizes the damaging effects on the electrodes 702 due to caustic pulp liquor used in the pulp and paper industry. The cleaning solvent supply orifice 708 allows the electrodes 702 to be cleaned periodically without needing to remove the electrodes 702. The method of cleaning the electrodes 702 may involve several different cleaning or rinsing cycles and/or purge cycles to remove the cleaning solvent from the electrodes 702.
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It will be understood that the foregoing is only illustrative of the principles of the invention. The exemplary embodiments described herein have been illustrated for use in measuring liquor in the pulp making process; however, the embodiments are not limited to the pulp making process and may be used in a variety of industries. The embodiments are also not limited to measurement of liquid material. The electrodes may be used to measure, for example, semi-liquids or gases. Accordingly, such embodiments will be recognized as within the scope of the present invention.
Persons skilled in the art will also appreciate that the present invention can be practiced by other than the described embodiments, which are presented for purposes of illustration rather than of limitation and that the present invention is limited only by the claims that follow.
