Apparatus and Method for Detecting an Interface From a Remote Location

This invention relates to an apparatus and method for detecting an interface between two fluids, and more particularly to a method and apparatus for detecting the interface between the two fluids or liquids remote from the interface.

Heretofore various devices and methods have been provided for measuring the interface between two fluids or liquids using various conventional instruments which sense the differences between the two fluids forming the interface. The prior art devices and methods have required that such instrument or at least its probe's sample taking or detector portion be located at the interface in order to detect the interface. If such instrument or probe were permanently mounted in place, it had the disadvantage that the readings obtained were, not infrequently, distorted by material accummulating on the probe, if the fluids about the probe were stagnent as would be the case in a settling tank or pond. Such a permanent installation required frequent removal for cleaning of the probe's sample taking or detector portion. Such removal and cleaning could be cumbersome when the interface was located a few feet or more from or below the upper surface of the light fluid. In a large settling tank or pond, it was not unusual for the probe to be many feet in length in order to position the sample taking portion of the probe at the interface. Prior art portable instrument installations for such interface detection had their own deficiencies. The long length of the probe or the structure carrying the same made moving and using it to take readings very cumbersome. While the problem of distortion or improper measurement due to accummulations or contamination was somewhat less troublesome in a portable set up, the probe still needed to be cleaned frequently. Also, with a portable set up there was a tendency to take fewer readings because of the work involved in moving the instrument and setting it up. Further, the probability of the portable type probe being damaged was greater, a factor to be considered with an instrument costing several thousand dollars or more.

The disadvantages of the prior art devices and methods for use with conventional instruments or probes for detecting interfaces have been eliminated by the present invention.

The apparatus of the present invention is adapted to be used with a conventional interface detection instrument and comprises a elongated pipe like member having its one end opened to and adapted to be located adjacent the interface of the two fluids or liquids forming the interface, and its other end extending away from the interface and adapted to accommodate the sample taking or detector portion of the conventional interface detection instrument, intermediate the pipe's ends, and a means for injecting a drive fluid, such as air, into the elongated pipe member at a point further distance from the interface than the location of the sample taking portion. Thus, in the method of the present invention, the drive fluid, such as air, may be introduced into the elongated pipe member to draw fluid from the one or lower end of the pipe up past the sample taking portion of the conventional instrument wherein it may be sampled or detected, the fluid then being driven out the opposite or upper end of the elongated pipe.

The present invention eliminates the need for constantly cleaning the probe's sample taking or detector portion of the instrument, as the moving fluid in the elongated pipe keeps the probe clean. Further, as the light fluid, or air, to drive the fluids being sampled is introduced into the elongated pipe above the sample taking or detector portion, the reading of the probe is not disrupted or interferred with by the presence of the drive fluid, such as in the form of bubbles of air. As the sample taking portion no longer need be located at the interface, it can be located remotely, and the instrument need not have a probe several feet or more long.

It is one object of the interface detection apparatus and method of the present invention to provide a reliable apparatus and method for detecting the interface between two fluids with a sample taking or detector portion located remotely from the interface.

It is another object of the interface detection apparatus and method of the present invention to provide a continuous flow of fluids being sampled past a remotely located sample taking probe for keeping the probe free of distortion or error due to accummulations or contamination.

Yet another object of the interface detection apparatus and method of the present invention is the inducement of a cleaning flow by the introduction of a drive fluid, such as air, to cause the two fluids forming the interface and being sampled to flow past a sample taking or detector probe remotely located from the interface.

These and other objects and advantages of the interface detection apparatus and method of the present invention will become apparent from the following written description and the accompanying figures of the drawings wherein:

FIG. 1 is a cross-sectional view of a portion of a tank containing the interface detection apparatus of the present invention, with a portion thereof being broken away to better illustrate the invention; and

FIG. 2 is a cross-sectional view taken along lines 2--2 of FIG. 1.

Referring to FIGS. 1 and 2, a portion of a tank 10, such as a sedimentation or settlement tank or pond for a sewage treatment plant is shown and has a side wall 12 and a bottom 14 formed, in this instance, of concrete. The tank 10 is filled with a heavier fluid 16 (represented in the drawings by the line) and a lighter fluid 18 (represented by the lines). In the case of a sedimentation tank the heavier fluid 16 may be effluent containing water and lighter fluid 18 clear water. Between the fluids 16 and 18 an interface 20 (represented by the line) is formed. Of course, the interface need not be a clearly defined plane, but could be a zone of an inch or more in height, or fluids forming the interface could be a variation in concentration of an element. Tank 10 may be provided with inlet means, not shown, for adding fluid 16 to the tank. Normally in the operation of a tank 10, after tank effluent settles and drops out to the bottom of tank 10 (such not being shown), it is transformed into clear fluid 18 which may be removed from tank 10 by outlet means, not shown. For purposes of this discussion, and not by way of limitation, it will be assumed that in tank 10 it is desired to add fluid 16 and withdraw fluid 18 in a manner such that the interface 20 remains substantially stationary, or moves only a minimum amount. The apparatus and method of the present invention will be described in the environment of the above described tank 10, fluids 16 and 18 and interface 20.

The apparatus of the present invention comprises an elongated pipe like member or tube 26 having a first opening or its lower end 28 situated at about the interface 20 and a second opening or its upper end 30 extending above the upper surface 32 of liquid 18. In a conventional sedimentation or settling tank or pond the interface 20 may be located 12 feet or more below the surface 32 so that the pipe or tube 26 may be 12 feet or more in length. The tube 26 may, if desired, be secured in place to the tank by means such as a plurality of conventioanl brackets 34 and "U" clamps 36.

In this instance, schematically shown, mounted above the pipe or tube 26 at its upper end, is a sampling mechanism 39 of a remotely located, conventional interface detecting instrument 40 (such as a Monitek Model 53 suspended solids meter operating on a photocell principal or a similar Rexnord device, or a Monitek Model 55A or 156 sludge blanket detector). The mechanism 39 has a probe 42 extending therefrom. The instrument 40 has a sample taking or detecting portion 44 on probe 42, which samples the fluid from its adjacent environment or takes readings from the same which are analized by the remainder of the instrument 40, as is conventional. The sample taking or detecting portion 44 is connected to the instrument 40 by a cable 45. Of course the instrument 40 could be located adjacent mechanism 39, the important feature being that probe 42 and the sample taking or detection portion 44 be located within the tube 26 so that the fluid in the tube is sampled. The probe 42 is, by way of example in this instance, mounted to the wall 12 by means of a bracket 41 and "U" clamp 43. At the lower end of probe 42, the conventional sample taking or detection portion 44 is mounted within tube 26, mediate its ends, preferably only a short distance, say 24-26 inches below the surface 32 of fluid 18.

To cause fluid to move through the pipe or tube 26, it is intersected between the surface 32 and sample taking portion 44 by a supply line 46 for injecting a drive fluid 48 into tube 26. Generally, the intersection of line 46 with tube 26 should be about 20 inches below the surface 32 to provide sufficient drive forces to cause the flow in pipe 26. In many instances, compressed air may be used as the drive fluid. The intersection of line 46 with tube 26 is located sufficiently above the sample taking or detection portion 44 so that none of the air bubbles emanating from line 46 into the space between the tube 26 and probe 42, will interfere with the detecting or sample taking at the portion 44. Generally, a spacing of 4 to 6 vertical inches between the point of intersection with tube 46 and portion 44 should prove sufficient to drive the fluid in tube 26, but yet prevent any interference.

As is shown in FIG. 1, the introduction of the drive fluid or air from line 46 into the interior of tube or pipe 26 causes the air bubbles 50 to rise in the tube 26. The bubbles in turn induce a driving force in the fluid in the pipe 26 to draw fluid in from the lower end opening 28 of pipe 26 and expel the same out the upper end opening 30, the fluid then overflowing the upper end of pipe, as indicated at 52. More specifically, the fluids flow past the sampling portion 44 and upwardly out the top of the tube 26 because the hydrostatic head at the upper surface 32 is greater than that at the upper end 30, due to the introduction of the drive fluid, the compressed air and air bubbles, and the difference in the density or specific gravity thus created between the aerated and non-aerated fluids.

Of course the drive fluid selected should be compatible with the other fluids. In instances where the sample-taking portion 44 is located above the interface 20, the drive fluid should be lighter in density than either the fluids 16 and 18.

Thus in the method of the present invention, there is induced in the tube or pipe 26 a flow of fluid, which may be continuous, by the flow of air bubbles from line 46 to the top of pipe 26. Thus, the sampling-taking portion 44 of the probe 42 for the conventional interface detector 40 is provided with a continuous flow thereby from the lower end 28 of the pipe 26. Thus, depending upon whether fluid 16 or 18 is flowing into the pipe 26 and detected at the sample-taking portion 44, the instrument 40 can regulate the operation of the inlet or outlet flows of fluids 16 or 18 to or from tank 10, in a conventional manner, to maintain the interface 20 at the desired position, at or near the lower end 28 of pipe 26.

The continuous flow of fluid, even of the fluid 16, from the lower end 28 past the sample-taking portion 44 of the probe 42, and especially the flow of fluid 18, keeps the pipe 46 and probe 42 free and clear of accumulations and contaminates, which in the past effected readings. Further, as the installation can be made more or less permanent, it is more likely that frequent readings will be taken or the interface monitored continuously as reading or monitoring is more easily made or done and the likelihood of damage to the instrument 40 or its probe 42 is greatly reduced as it need not be moved, if installed permanently, or even if portable, for cleaning. Further, as the drive for the fluid in the pipe is provided by readily available compressed air, no costly pumps or piping need be used.

While the preferred apparatus and method have been illustrated and described, it will be appreciated that variations and modifications of the method steps and apparatus can be made. For example, the installation need not be permanently affixed to the wall of the tank. Other various forms of conventional interface detecting instrumentation could be adapted. The opening for the incoming fluid could be located at other than the lower end of the pipe. A drive fluid other than compressed air could be used. The sample-taking portion of the interface detection instrument could be located below the interface, in which case the drive fluid would be heavier than the fluids forming the interface with the drive fluid dropping downwardly and the upper opening of the pipe at the interface. The probe may be made smaller and need not extend down the center of the tube, but may merely be located remote from the interface. Such variations and modifications in the apparatus and method will still fall within the scope of the appended claims.