Device To Dampen Fluctuations In The Concentration Of A Substance In A Flowing Stream Of Fluid

Abstract

A process for smoothing out or damping concentration fluctuations of a substance in a fluid stream comprising dividing the stream into a number of substreams, feeding each of the substreams to a common point while introducing different time delays of arrival of each substream at the common point and then recombining the substreams into the single larger stream again. An apparatus for performing the above process comprising a combination of means capable of dividing the influent stream into a number of substreams, means capable of imparting different time delays to each substream for arrival at some common point and means for recombining the substreams.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device, termed an equalization basin or equalization tank, designed to smooth out or dampen fluctuations in concentration of a substance in a fluid system. In addition, the present invention also relates to a process for accomplishing the same result.

2. Description of the Prior Art

Obviously, in fluid systems where a constant concentration of a substance in a fluid is desired or necessary, fluctuations in the concentration of the substance in the fluid are undesirable or even potentially harmful. As an example, if the salt concentration in a liquid varied with time from 1 to 3 pounds per gallon with a mean value of 2 pounds per gallon over a long period of time, the perfect equalization device would accept this varying concentration as an input, and deliver liquid at a constant effluent concentration of 2 pounds per gallon. Such a perfect equalization device is not possible since it would have to be of infinite size. The best known and easiest to calculate practical equalization device for fluid systems is a "complete mix basin." This device consists of a pond or tank with a large, powerful mixer in it.

The term "complete mix" implies that the contents of the tank or pond are uniform at every point and equal to the effluent concentration. The influent enters through a pipe at one side and is instantly mixed with the entire contents of the tank or pond. It can be shown mathematically that the rate of change of concentration of the effluent with respect to time is slower than the rate of change of the influent concentration with respect to time, and that the magnitude of the change in the concentration of the effluent is proportionately less than the magnitude of the change of concentration of the influent by the amount that the rate of change of effluent concentration is slower than the rate of change of influent concentration. The ratio of the two rates of change and the two magnitudes of change is a function of the holding time of the complete mix equalization device.

U.S. Pat. No. 3,404,869 (Harder) discloses an interfacial surface generator, i.e., a mixing device, or static mixer which consists of a number of chambers having two or more inlets and two or more outlets, the inlets and outlets being noncoplanar and the planes intersecting an axis of flow. The device mixes the incoming fluid in such a manner that each of the outlet conduits contains a portion of the material from each of the inlet conduits.

Other known mixing devices are disclosed in the following U.S. Pat. Nos.: 3,291,456; 3,306,587, and 3,547,410.

The primary difficulty of the prior art devices and processes is that their efficiency is unacceptable while some, in addition, require complex apparatus and high energy inputs to achieve good results.

It is therefore a primary object of the present invention to provide a simple and efficient process for damping fluctuations in concentration of a substance in a fluid without the above disadvantages.

It is a further object of the present invention to provide a simple device by which such a process can be performed.

Other objects, features and advantages will become apparent from the ensuing description.

SUMMARY OF THE INVENTION

The process of the invention comprises:

1. dividing a stream of fluid containing a substance (whose concentration fluctuations in the fluid one wishes to dampen) into a number of substreams;

2. feeding each of the resulting substreams to a common point and introducing time delays of arrival of each substream at the point with each time delay of arrival being different for each substream; and

3. recombining the substreams into the single larger stream again.

The present invention also relates to an apparatus for performing the above process. Generally, the apparatus comprises a combination of means capable of dividing the influent stream into a number of substreams, means capable of imparting different time delays to each substream for arrival at some common point and means for recombining the substreams. Specific processes and apparatus will be discussed hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 represent simple devices which explain the theory of the present invention.

FIGS. 3 through 7 show possible shapes of devices which may be employed in the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is applicable to any fluid (gas and liquid) stream containing a foreign substance whose concentration gradient may vary with time or, generally, whose characteristic manifestations one wishes to equalize. Examples of the foreign substance are dissolved salt, dissolved alcohol, emulsified lubricating oil, fine suspended particles of ore, etc.; i.e., anything that may be dissolved in, suspended in, or generally "carried by" a fluid stream. Alternatively, the temperature of the fluid stream may vary with time, and the present invention is applicable to "equalizing" such a stream. Similar applications will become apparent to those skilled in the art.

Applying the above basic principle to a stream of blue water which suddenly turns red for a 2 minute period and then back to blue again, gives the following results. Assume that the main stream is divided into five substreams in the equalization device and that the time delay of arrival at the designated common point of the first substream is zero, of the second substream 2 minutes, of the third substream is 4 minutes, of the fourth is 6 minutes, and of the fifth is 8 minutes.

When the red slug comes along, the first substream will start to run red at once and will run red for 2 minutes (the length of the red pulse), but the other four streams will still be running blue because of the time delay. Since only one of five streams is red, the concentration of red in the effluent from the device will be only 20 percent of the concentration in the input stream.

At the end of the first two minutes, the first substream will start to flow blue again, but the second one (two minute time delay) will start to flow red. Substreams 3, 4 and 5 will still be blue because of their longer time delays so the concentration of red in the effluent will continue at 20 percent of the influent pulse value.

It can be seen that this situation will repeat itself across all five substreams. In this case, the device has taken an input pulse of 2 minutes duration and spread it out as an output pulse of only 20 percent of the initial concentration, but 5 times as long in duration.

The above example is simplistic in nature for purposes of illustration only. In actuality, the influent stream need not be divided into a discrete number of individual substreams and treated separately and finally recombined. Rather, the influent stream enters the device as a single stream, but the geometry of the device in effect divides the influent stream into what can be considered as a very large number of substreams with the difference in time delay of arrival at the common point becoming extremely small. To illustrate the point, refer to FIG. 1, which schematically shows a simple form of a device which accomplishes the desired results of the present invention. The flow of fluid through the device is indicated by the arrows. The fluid enters the device via pipe 1 and then flows into a manifold 2, from which it is divided into three separate streams designated 3, 4, and 5 in the Figure. These three streams are again recombined in exit manifold 6 and the fluid leaves the device via exit pipe 7. Assuming the concentration of a substance in the fluid stream reaches a peak value x periodically, the fluid stream exiting from the device as shown in FIG. 1 would have a concentration equal to some percentage of x depending on the ratio of the duration of the peak concentration value to the average of the delay time of the substreams. The lower this ratio is, the better the equalization.

The above theory forms the basis of the present invention, and a suitable apparatus for the practice of the present invention is schematically illustrated in FIG. 2. Inlet pipe 8, inlet manifold 9, exit manifold 11 and exit pipe 12 correspond respectively to the related means in FIG. 1. However, the three pipes (3, 4 and 5) of FIG. 1 have been replaced by a continuous flat tray 10 in FIG. 2. The fluid flows into the tray over a weir provided inlet manifold 9, which runs the width of the tray, and similarly, the fluid flows from the tray into exit manifold 11 over a similar weir in the latter. In effect, the device shown in FIG. 2 has divided the inlet stream into an infinite number of substreams, although the inlet stream is not actually divided into discrete substreams. Depending upon the width of the tray and the length and depth of the same, any desired degree of equalization can be obtained, and one skilled in the art can easily see how the device of the present invention functions to equalize or dampen fluctuations in concentration of a substance in the fluid flowing through the device.

In the present invention, equalization essentially equal to a complete mix basin of the prior art and the same size, is accomplished with no power input at all. It is simply the geometry of the device which makes it work.

The basin or tank can be made essentially into any size and shape, the size depending of course upon the volume of fluid flowing through the device, the degree of equalization or dampening desired, etc., and the shape of the device of course being such as to assure the delay times in the theoretical substreams necessary to achieve equalization.

FIG. 3 illustrates a typical tank or pond which can be employed to accomplish the purpose of the present invention. The flow of fluid through the device is indicated by the arrows in the Figure. The fluid enters the device along the hypotenuse of the triangle and flows outwardly therefrom toward one of the sides, where it is collected by suitable means and withdrawn from the device along that side. The particular configurations of the inlet and outlet manifolds is not critical. They may comprise a trough-like apparatus, wherein the fluid flows over the weir formed by the lower side of the trough (schematically illustrated in cross-section in FIG. 4). The edge over which the fluid flows may either be flat or may be rippled in order to achieve the effect which is more nearly alike a large number of small separate streams flowing over the edge of the inlet and exit manifolds. In addition, a plurality of pipes may be provided along the inlet manifold, each pipe being capable of discharging an equal volume of water into the tank.

Generally, any means which distributes the fluid uniformly over the length of the inlet, and any means which collects it uniformly at the outlet can be employed in the practice of the present invention.

A related arrangement is schematically shown in FIG. 5a wherein the inlet manifold is arranged along the diagonal of the substantially square or rectangular tank or pond, with the fluid flowing from the diagonally-disposed inlet manifold (see section A--A in FIG. 5b) to two adjacent sides of the pond or tank where it is collected by suitable means (e.g., the troughs shown in sections B--B and C--C in FIG. 5b).

Another alternative embodiment of the present invention is shown in FIGS. 6 and 7, FIG. 6 being a plan view and FIG. 7 being a cross-section along the line A--A of FIG. 6. The inlet may simply be a pipe which feeds the fluid to the tank at a point off-center thereof. The outlet shown in FIGS. 6 and 7 (a circular flat, level weir) surrounds the entire circumference of the tank as shown.

Generally, any shape, tank or pond (dug into the ground) is suitable for the present invention as long as the geometry of the device is such as to provide a series of delay times for travel of the fluid between the inlet and the outlet.

The only criteria for the design of the inlets and outlets is that the volume of water contained therein must be small relative to the volume contained in the tank or pond between them, that the flow of water be discharged (or collected, as the case may be) uniformly over the length of the inlet or outlet devices and that the number of discharge or collection points from or to the inlet or outlet devices to the pond or tank be large. This can generally be accomplished by providing relatively small inlet and outlet troughs of the type shown in FIG. 4, where the water flows uniformly over the lowermost edge thereof and wherein the number of discharge and collection points can be considered infinite.

The effectiveness of the equalization depends most importantly upon the volume of fluid which is contained in the pond or tank between the inlet and outlet, since the larger the volume, the longer the average retention time of the fluid in the pond or tank, of course, a longer retention time favoring a greater equalization or dampening of the fluctuations of the variable concentration which occurs in the inlet stream.

One skkilled in the art can apply the techniques described above to any system where it is desirable or necessary to eliminate great fluctuations in concentrations of a substance in a fluid stream, or similarly, to eliminate great fluctuations in temperature of a fluid stream, etc. For example, the present invention finds utility in the regeneration of zeolite softeners. Such softeners are normally regenerated with strong salt solutions, and usually on a batch basis resulting in periods of time where no waste salt solution is being discharged, and other times when it is being discharged at a high flow rate. Without equalizing the stream of waste salt leaving the plant, at times the concentration of salt in the plant effluent may be so high as to be potentially harmful. However, if the plant effluent is equalized using the present invention, the concentration of salt in the effluent would be essentially the average concentration over a long period of time which would of course be much lower than the peak values which would occur without equalization. As a result, the continuous lower concentration of salt would be much less harmful to the environment.

The present invention also finds utility in a process for treating liquid waste from a metallic plating plant. Normally, the metallic element is removed from the waste stream prior to discharging the stream to waste. If, however, at several times during the daily operation of the plant, large concentrations of concentrated metallic plating solutions are fed to the waste disposal operation, the entire system must be capable of removing this large concentration of the metallic element from the waste stream prior to discharging it. However, for those periods in the daily operation where a much lower concentration of metallic waste is fed to the waste treatment operation, the metallic removal system is greatly over-sized. By installing an equalization device according to the present invention in the waste treatment operation ahead of the metallic element removal system, the concentration of the metallic elements in the waste stream is reduced to an essentially continuous concentration which is substantially below the peak concentration normally encountered. The result of course is a considerable cost savings in the metallic element removing means, since it need only be designed to handle the equalized concentration instead of the peak concentration.

Another example, and very pertinent to the present invention, is in the design of a biological oxidation system to remove dissolved organic compounds from a flowing stream of water. Normally, a bio-oxidation system must be designed extremely accurately, since the system performs poorly if it is overloaded and equally poorly if it is underloaded. Thus, if there is any significant concentration variation at all of the organic in the stream which is the input to the biological oxidation system, it is essential to equalize the concentration of the organic in the water, and therefore the present invention finds particular utility in such an operation.

Although the present invention has been described above with reference to preferred embodiments, it is to be understood that variations may be made therefrom without departing from the spirit and scope of the invention, as is apparent to those skilled in the art.

Claims

What is claimed is:

1. An apparatus for damping variable concentrations of a substance in a liquid stream, said apparatus comprising:

a triangular-shaped liquid container,

means for feeding said liquid stream into said liquid container including a first, inlet manifold located along the hypotenuse of said triangle,

means including said first inlet manifold for dividing said stream into a plurality of substreams, and

mean for collecting said substreams at a common point comprising a second, liquid outlet manifold located along one of the opposite sides of said triangle;

whereby, said substreams dividing at said first inlet manifold and being collected by said outlet manifold at said hypotenuse and said side opposite thereto, respectively, imparts time delays to each substream for arrival at said common point to provide a single liquid stream which has a substantially constant concentration of said substreams which is substantially lower than the peak or highest concentration of said substreams in said stream prior to treatment with said apparatus.

2. An apparatus as claimed in claim 1, wherein said triangular shaped container comprises a basin, wherein said first, inlet manifold comprises a first trough along the hypotenuse of the triangular shaped basin, and said second, outlet manifold comprises a second trough located along one of the opposite sides of said triangular shaped basin; whereby, said basin imparts time delay to said liquid stream which divides into a plurality of substreams and moving from one trough to the other with said trough located along said opposite side acting to recombine said substreams at a common point to provide a single stream which has a substantially constant concentration of said substance which is substantially lower than the peak or highest concentration of said substance in said stream prior to treatment with said apparatus.

3. An apparatus for damping variable concentrations of a substance in a liquid stream, said apparatus comprising:

means capable of dividing said stream into a plurality of substreams;

means for feeding each of said substreams to a common point;

means for imparting time delays to each substream for arrival at said common point; and

means for recombining said substreams at said common point to provide a single stream which has a substantially constant concentration of said substance which is substantially lower than the peak or highest concentration of that substance in said stream prior to treatment with said apparatus,

said apparatus being rectangular in form and including a trough disposed along the diagonal of said rectangle, with said fluid flowing over both sides of said trough and toward the two sides of said rectangle opposite said diagonal,

and wherein means for collecting said substreams at said common point comprises troughs disposed along said two opposite sides and meeting at their intersection.

4. An apparatus for damping variable concentrations of a substance in a liquid stream, said apparatus comprising:

means capable of dividing said stream into a plurality of substreams;

means for feeding each of said substreams to a common point;

means capable of imparting time delays to each substream for arrival at said common point; and

means for recombining said substreams at said common point to provide a single stream which has a substantially constant concentration of said substance which is substantially lower than the peak or highest concentration of said substance in said stream prior to treatment with said apparatus;

and wherein, said apparatus is in the form of a circular tank and said means capable of dividing said liquid stream into a plurality of substreams comprises an inlet pipe for feeding said liquid stream into said circular tank at a point off-center thereof, and said means for collecting said plurality of substreams at said common point comprises a trough surrounding the circumference of said circular tank on the inside thereof such that the fluid flows from said inlet pipe outwardly toward the circumference of the circular tank and is collected within said trough.