Abstract:
An apparatus for detecting change in the foam forming characteristic of an input stream of an aqueous solution which continuously samples the input stream by taking a series of discrete, independent measurements. A sample of the input stream is collected, analyzed, then discarded. The collect-analyze-discard cycle is repeated. The apparatus relies on an acoustic sensor to measure foam height within a column. This allows the column containing the foam to be fabricated from any material, including durable plastics. A sample of the input stream is introduced into the apparatus. The sample is then aerated by a aeration stone to produce foam. The height of the column of foam produced is then measured using the acoustic sensor. The sample is then discarded and the process repeated. The height of the foam column is correlated with the concentration of foam forming chemical.

Description:
This application is continuation-in-part of patent application Ser. No. 09/566,888, filed May 8, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an apparatus for detecting the presence of foam forming compounds in aqueous solutions. More particularly, the present invention relates to an apparatus which detects the presence of specific foam forming compounds in an aqueous solution and, when calibrated, measures the concentration of the foam forming compounds present in the aqueous solution. 
     2. Description of the Prior Art 
     Foam forming compounds include cleaning compounds, such as detergents, fire-fighting chemicals, and naturally occurring surfactants, such as plant extractives. The presence of foam forming compounds can interfere with the operation of chemical plants, such as wastewater treatment plants, by causing inaccurate readings in flow and level sensing devices. 
     Foaming of wastewater tends to lift solid materials out of the liquid phase and suspend the materials in the foam. These solid materials may include metals or other hazardous materials. In open top tanks, pollutant-laden foams may be blown off the surface of the wastewater and onto the surrounding property. Hazards of this type often result in citations from public health offices and environmental protection officials. 
     Some foam forming chemical are also toxic to the microorganisms used in wastewater treatment plants. Early detection of foam forming chemicals permits process streams contaminated with these chemicals to be diverted from the main process flow. The diverted flow can be subsequently treated in a specialized foam forming agent removal process. 
     Foam detecting devices used in the past to detect the presence of foam forming chemicals in an aqueous solution cannot rapidly detect a change of state from a foaming input stream to a non-foaming input stream. For example, if a prior art device was measuring the foam forming characteristic of an input stream that contained a high concentration of a foam forming chemical, and then the input stream was changed to a stream that contained little or no foam forming chemical, the prior art device could not rapidly detect the change in input stream composition. This is because the prior art device has a fixed or static solution reservoir at the bottom of the device, and the concentration of the foam forming chemical in that reservoir is changed only by dilution from the input stream. It may take several minutes before a low concentration input stream dilutes the solution in the reservoir to a concentration that no longer forms a significant amount of foam. 
     Devices used in the past to detect the presence of foam forming chemicals are generally not automated. These devices are manually operated and are best suited to a laboratory environment. 
     Prior art devices for detecting the presence,-of foam forming chemicals are also fragile, generally consisting of a piece of custom blown glasswork. 
     In addition, prior art devices rely on photo-optical sensor pairs to detect and measure the presence of foam at discrete locations. This approach is expensive to implement and provides a limited number of foam height detection values. Also, reliance upon photo-optical pairs to detect the present of foam requires that the column containing the foam be transparent. In some foam sensing applications, a film of oil, algae, bacteria, and other deposits may eventually occlude a clear column. This renders the photo-optical sensors inoperable. 
     Further, at low concentrations of foam forming chemical, the foam can usually be characterized as being composed of a small number of large bubbles. The beam from a photo-optical sensor can intermittently pass through such loosely structured foam, resulting in intermittent false readings of foam height. 
     Accordingly, there is a need for an apparatus for detecting and measuring foam forming compounds in aqueous solutions which is accurate, relatively simple in design, sufficiently strong to avoid breakage, and low cost. 
     SUMMARY OF THE INVENTION 
     A sample of the liquid or wastewater to be tested enters the apparatus comprising the present invention from a fill valve through a column cap at the top of a tubular column, flows down the sides of the column, and collects in in a lower portion of the column. The liquid level in the column rises to a liquid level switch. Closing the liquid level switch prevents further flow of liquid into the tubular column. 
     After a sample of liquid has collected in the lower portion of the column, an air pump is actuated and compressed air flows into the sample through an aeration stone. The air bubbles produced by the aeration stone cause the foam forming compounds in the sample to produce foam. The foam rises in the column and lifts a float which functions as a solid target for an acoustic distance measuring device. The measuring device measures height within the column, generating a continuous analog electrical output signal which is a function of foam height. The value of voltage produced by the measuring device is measured and retained by a programmable logic controller connected to the measuring device. 
     As the float rises in the sensor tube, a beam of light between photo-optical sensors is encountered and is broken. As the float passes the beam of light, the beam then encounters the foam in the tubular column. If the foam is of sufficient density that it continues to interrupt the beam of light and it continues to lift the ball to a lower set point programmed into the measuring device, a red indicator light is illuminated. If the foam density is insufficient to block the beam of light generated by the optical sensors, the red indicator light does not illuminate and the system recognizes that the aqueous foam forming film concentration is below a predetermined threshold level. When the red indicator light remains illuminated, it indicates that the sample solution contains aqueous foam forming film at or above a predetermined threshold and the apparatus automatically sends a message to alert the user. 
     After a foam height measurement has been made, the fill valve closes, a sample drain valve opens, and a three-way valve is positioned to divert compressed air from the aeration stone to the top of the column. This forces the sample of solution and foam from the column through a drain valve. After the solution has been drained from the column, the fill valve opens, the drain valve closes, air is re-directed to the aeration stone, and the entire sample acquisition and measurement cycle is repeated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of an apparatus for detecting and measuring foam forming compounds in aqueous solutions comprising the present invention; 
     FIGS. 2A-2C is an electrical schematic diagram of the  120  VAC control circuity for the apparatus of FIG. 1; and 
     FIGS. 3A-3F is an electrical schematic diagram which illustrates the relay logic circuitry for the programmable logic controller of the apparatus of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, there is shown an apparatus, designated generally by the reference numeral  20 , which detects the presence of foam forming compounds in aqueous solutions. Apparatus  20 , when calibrated also will measure the concentration of specific foam forming. compounds in an aqueous solution. Foam forming compounds include cleaning compounds, such as detergents, fire fighting chemicals, and naturally occurring surfactants, such as plant extractives. 
     The apparatus  20  comprising the present invention, operates by measuring the foam forming capability of an aqueous solutions with a time series of discrete tests. A sample of an aqueous solution is introduced into apparatus  20 . The height of the column of foam is then measured by an apparatus  20  using an acoustic distance-measuring device. The sample of the aqueous solution is then discarded and the sampling process is repeated using apparatus  20 . The height of the column of foam is correlated with the concentration of foam forming chemical. The apparatus is capable of detecting fewer than fifteen parts per million of aqueous film forming foam in less than forty-five seconds. 
     A sample of a liquid or aqueous solutions to be tested enters apparatus  20  through an inlet supply line  24  (as indicated by arrow  22 ) which includes an electrically operated supply/fill valve  26 . When valve  26  is electrically energized, fill valve  26  is opened such that the liquid to pass through water supply line  27  and an opening  29  at the top of a tubular column  30  through a column cap  31  into the tubular column  30 . The liquid then flows down the inner wall/sides  35  of tubular column  30 , and collects in the bottom or lower portion  32  of tubular column  30 . 
     The liquid level in the lower portion  32  of column  30  rises to the level of a liquid level switch  34 . When liquid level switch  34  closes, fill valve  26  is deactivated and the flow of liquid is through fill valve  26  to a drain located on the backside of foam sensor housing  36 . 
     When the sample of the liquid has collected in the lower portion  32  of column tubular  30 , an electrically operated air pump  44  is actuated providing compressed air which flows through an air supply line  46  into a three-way electrically operated air valve  48 . The compressed air then passes through air valve  48  and an air line  50  into the liquid sample through a porous aeration stone  52  which forms bubbles. The aeration stone  52  is mounted horizontally in the lower portion  32  of tube  30  so that it generates small air bubbles within the sample. 
     The many small air bubbles generated by aeration stone  52  cause the foam forming compounds in the sample to produce foam. The foam rises in tubular column  30  lifting a spherical-shaped lightweight float/target  66  into the upper portion  54  of tubular column  30 . Spherical-shaped lightweight float/target  66  comprises a polystyrene ball. 
     As depicted in FIG.  1 . the upper portion  54  of tubular column  30  is larger in diameter than the lower portion  32  of tubular-shaped column  30 . Between the upper portion  54  and the lower portion  32  of tubular column  30  is a reducing collar  56 . When apparatus  20  is not operational, float  66  rest within the reducing collar  56  of tubular column  30 . Reducing collar  56  has a centrally located opening  70  which allows foam to pass through opening  70  to the upper portion of tubular column  30  lifting float  66  in a vertical direction upward within the upper portion  54  of tubular column  30 . 
     The float  66  serves as a solid target for an acoustic distance measuring device/acoustic sensor  67 . The acoustic distance measuring device  67 , which is positioned at the top of tubular column  30 , measures the height of the column of foam within tubular column  30  by bouncing ultrasonic sound waves off the target  66  and measuring time of travel of the ultrasonic waves to and from the target  66 . The acoustic distance measuring device  67  produces a continuous analog electrical output signal which is a function of foam height within tubular column  30 . The output signal&#39;s voltage value produced by the acoustic distance measuring device  67  is measured, sampled, and retained by a sample-and-hold circuit within a programmable logic controller  69  connected to measuring device  67 . 
     The programmable logic controller  69  used in the preferred embodiment is a Model Micro 3  Programmable Logic Controller commercially available from IDEC Corporation of San Jose, California. Programmable logic controller  69  is programmed using WINDLER software which is commercially available from IDEC Corporation. The WINDLER software includes a monitor mode which allows the user to monitor the logic control program currently running in the programmable logic controller in real time. 
     At this time it should be noted that a laser distance measuring device could be substituted for the acoustic distance measuring device  67  to perform the function of measuring the height of the foam column within tubular column  30 . 
     It should also be noted that the acoustic distance measuring device used in the present invention is a Model M-5000 Smart Ultrasonic Sensor commercially available from Massa Products Corporation of Hingham, Mass. The Current Loop Output Settings for device are as follows: 0 mA distance is 13 inches, the 20 mA distance is 4.5 inches, and the output span is 0-20 mA. The Set point Output Settings are as follows: the close set point distance is 7 inches and the far set point distance is 9 inches. The software for the M-5000 Smart Ultrasonic Sensor allows the user to monitor the performance of the sensor in real time. A status panel which appears on an external computer screen indicates the real time distance from the ultrasonic sensor to the target. 
     If float  66  rises above a predetermined set point within the portion  54  of tubular column  30 , an alarm is activated. The alarm that is activated comprises a red indicator light  71 . 
     After a foam height measurement within tubular column  30  has been made, an electrically operated sample drain valve  60  opens (i.e. is deactivated) and the sample drains from column  30  through valve  60  and a drain pipe  62  (as indicated by arrow  64 ). 
     Simultaneously, with the opening of valve  60 , valve  48  is deactivated which diverts compressed air provided by air pump  44  through an air supply line  47  to an opening positioned within the upper portion  54  of tubular column  30 . The opening  68  is positioned immediately below column cap  31  within tubular column  30 . Compressed air supplied through opening  68  forces the sample and foam out of tubular column  30  through drain valve  62  and drain pipe  64 . 
     After the foam forming solution has been drained from tubular column  30 , valve  60  is activated or closed; and valve  26  is again activated and the sample acquisition cycle is repeated. 
     There is also mounted within foam sensor housing  36  a pair of photo-optical sensors  77  and  79  which are in alignment on opposite sides of the upper portion  54  of tubular column  30 . The pair of photo-optical sensors  77  and  79  allow an operator of apparatus  20  to obtain supplementary measurements of foam density within tubular column  30 . When the foam within tubular column  30  has a low density, that is, the foam consists of a few large bubbles, the beam of light from the transmitter of the pair of photo-optical sensors  77  and  79  will pass through the foam to the receiver of the pair of photo-optical sensors  77  and  79 . 
     When, however, the foam within tubular column  30  has a high density, that is he foam consist of many small bubbles, the beam of light from the transmitter of the pair of photo-optical sensors  77  and  79  will not pass through the foam to the receiver of the pair of photo-optical sensors  77  and  79 . The data provided by the pair of photo-optical sensors  77  and  79  relative to foam density is then combined with data from acoustic distance measuring device  67  to provide an accurate and reliable measurement of foam quality. The data provided by optical sensor  79  to programmable logic controller  69  is in the form of direct current voltage signal. 
     Referring to FIGS.  1  and  2 A- 2 C, programmable logic controller  69  controls the operation of apparatus  20 . A power on switch SW 1  when set to the ON position supplies  120  VAC though fuse  3 A to programmable logic device  67 . Programmable logic device  67 , in turn, supplies  24  VDC to transmitter  77  and receive  79  illustrated in FIG.  2 B. Acoustic distance measuring device  67  and photo-optical receiver  79  are connected to programmable logic controller  69  to provide electrical signals to controller  69  indicative of foam quality in the upper portion  54  of tubular column  30 . 
     Programmable logic controller  69  provides electrical signals to coils C 0 , C 1 ,C 2 , and C 3  to activate coils. When, for example, coil C 0  is energized, contacts R 0A  and R 0B  are closed. This activates air pump  44  and a sample pump  80  which is used to supply samples of the liquid to apparatus  20  for testing for the presence of foam in the samples. 
     When programmable logic controller  69  energizes coil C 1 , contact R 1A  closes activating light  73 . Similarly, when programmable logic controller  69  energizes coil C 2 , contact R 2A  closes activating light  71 . Energizing coil C 3  closes contact R 3A  which activates an external sump pump  82 . Programmable logic controller  69  also provides activation signals to solenoid S 0 , solenoid S 1 , and solenoid S 2 . Solenoid S 0  is the solenoid for supply valve  26 , solenoid S 1  is the solenoid for air valve  48 , and solenoid S 2  is the solenoid for drain valve  60 . 
     Referring to FIG. 1, there is shown an oil water separator  84  which supplies water samples to apparatus  20  via inlet supply line  24  and electrically operated supply valve  25 . The oil water separator  84  comprises an inlet line  85  which includes a shut off valve  91  and a flow direction sensing switch SW 2 ; a backwash strainer  86  for removing large particulate matter; and a filter  88  equipped with an oleophilic element. The oil water separator  84  also has a pair of pressure gages  95  and  96  and a pressure gauge  98  operatively coupled to the backwash strainer  86 . 
     The filter  88  removes oil from the water samples. Oil water separator  84  also includes a backwash valve  90  which has a solenoid S 3  connected to programmable logic controller  69 . Periodic reversing the water flow through backwash strainer  86  is required to clean strainer  86 . The backwash interval and duration is controlled by programmable logic controller  69  which energizes the solenoid S 3  of backwash valve  90  to clean backwash strainer  86 . 
     The oleophilic element of filter  88  will eventually plug up and have to be replaced. A plugged filter results in an increase in pressure drop across filter  88 . When this occurs a differential pressure switch SW 4  sends an electrical signal to programmable logic controller  69  indicating that the oleophilic element of filter  88  needs replacement. Apparatus  20  is designed to automatically shut down and alert the user of apparatus that the oleophilic element of filter  88  needs replacement. The illumination of amber lamp  73  indicates that maintenance is required. 
     Referring to FIGS. 1 and 2A, electrical signals for a sump pump  82  and backwash valve  90  are provided by programmable logic device  69 . The sump pump  82  is connected to a holding tank  94  via a fluid flow line  81 . Holding tank  94  has mounted thereon an upper float switch SW 5  and a lower float switch SW 6 . The holding tank  94  is connected via a T shaped pipe connector  63  to drain pipe  62  to receive the samples of the aqueous solution, i.e. wastewater being tested. Backwash valve  90  is also connected to holding tank  94  via connector  63 . 
     When the holding tank  94  is full, switch SW 5  closes sending a signal to programmable logic device  69  which turns on sump pump  82 . When the liquid level in holding tank  94  reaches a low water level, switch SW 5  closes sending a signal to programmable logic device  69  which turns off sump pump  82 . 
     While apparatus  20  is operational many different events can occur. The sequence of events during normal operation of the apparatus  20  are illustrated by the following example. Bilge water is pumped from a ship to an oily-waste lift station. Assume for this example that the wastewater contains  50  ppm Aqueous Foam Forming Film (AFFF). As the sump in the lift station fills, large wastewater transfer pumps are energized to move the wastewater from a collection point to a wastewater treatment plant. 
     A small portion or sample of the waste stream is diverted to the apparatus  20 . Flow direction sensing switch SW 2  installed in the oil water separator  84  signals apparatus  20  to begin the wastewater sampling process. Fluid direction sensing switch SW 2  is adapted to detect the flow of liquid through separator  84 . Fluid direction sensing switch SW 2  is connected to programmable logic controller  69 . 
     The programmable logic controller  69  continuously loops through its set of instructions. Therefore, controller  69  is not necessarily at the beginning of the program cycle when the apparatus  20  receives the signal from the flow direction sensing switch SW 2 . However, for this example, we will assume the apparatus  20  starts at the beginning of a fill cycle. 
     With the fill valve  26  energized, flow is directed to the top of the tubular column  30 . The sample flows into the cap  31  on the top of the tubular column  30  and runs down the wall of the tubular column  30 . Water fills the chamber formed within the bottom portion  32  of the tubular  30  until the liquid level switch  34  in the chamber closes. When the chamber is full, fill valve  26  is de-energized and the wastewater flow is bypassed to the sump/holding tank  94  through valve  90  which is connected to sump  94 . 
     After an initial delay (to flush the pipes of the previous sample of wastewater), the air pump  44  is activated and air flows through the air valve  48  to the aeration stone  52 . Aeration occurs for a predetermined length of time and foam is generated in the tubular column  30 . As the foam rises in the tubular column  30 , the foam lifts a polystyrene ball  66 . The ball  66  provides a firm target for acoustic distance measuring device  67 , which measures the distance to the target ball  66 . Because the wastewater sample contains 50 ppm AFFF, sufficient foam will be generated in the column for the target  66  to reach a. sensor set point. 
     As the target  66  rises in the sensor tube, the beam of light between photo-optical sensors  77  and  79  is broken. As the target  66  passes the beam, the beam then encounters the foam in the tubular column  30 . If the foam is of sufficient density that it continues to interrupt the beam of light and it continues to lift the ball to a lower set point programmed into the acoustic sensor  67 , red indicator light  71  is illuminated. If the foam density is insufficient to block the beam from the optical sensors  77  and  79 , the red indicator light  71  does not illuminate and the system recognizes that the AFFF concentration is below a predetermined threshold level. When the red indicator light  71  is illuminated, it indicates that the sample solution contains AFFF at or above a predetermined threshold and apparatus  20  automatically sends a message to alert the user which may be, for example a plant operator. As soon as the red indicator light  71  is illuminated an internal timer in the control program for programmable logic controller  69  begins a count down. The target  66  must reach the lower set point during the next sample cycle before the timer expires or the red indicator light  71  will go out. If the ball continues to rise to a second high alarm programmed into the acoustic sensor  67 , air is diverted from the aeration stone  52  to the top of the tubular column through opening  68 . This prevents the target and foam from rising further and contacting the acoustic sensor  67 . 
     After a predetermined length of time, the apparatus  20  enters a wash-down cycle. The drain valve  60  is opened, sample flow is redirected to the top of the tubular column  30 , and air is redirected from the aeration stone  52  to the top of the column  30  through opening  68 . The sample is flushed out the drain valve  60  in the bottom of the tubular column  30  and flows into the sump  94 . Air pressure in the top of the column  30  helps expel the sample from apparatus  20 . When the wash-down cycle is finished, the drain valve  60  closes and a new wastewater sample fills tubular column  30 . 
     This process is repeated until the sample no longer contains a high enough concentration of AFFF in the wastewater to cause the target  66  to reach the low set point before the internal timer within programmable logic controller  69  expires. When this occurs, the red indicator light  71  no longer illuminates and a message is sent via an SCADA system interface that the foam event has ended. 
     The SCADA system (Supervisory Control and Data Acquisition) reports the presence of AFFF foam in the wastewater to a central monitoring facility, such as the wastewater treatment plant. 
     The foam concentration measuring process performed by apparatus  20  will also stop when the flow direction sensing switch SW 2  signals the apparatus  20  that fluid flow is no longer present in the wastewater transfer discharge line. When this occurs, the apparatus  20  is automatically switched off. 
     Referring to FIGS. 3A-3F, there is shown ladder logic diagram for programmable logic controller  69 . The programmable logic controller  69  activates and de-activates the mechanical and electrical elements of apparatus  20 . For example, to activate the air pump  44 , the flow switch SW 2  must be closed and an initial line flush must occur closing flow switch contact I 0000  and initial line flush contact T 009 . This results in activation of Air Pump Relay Q 0010  which turns on air pump  44 . The ladder logic on Rungs  1 ,  2 : and  3  must be activated to activate air pump  44 . 
     Rungs  4  and  5  turn on a maintenance alarm  83  if (1) there is a high filter delta pressure for filter  88  (2) the optical path is obscured for optical sensors  77  and  79 . Activation of maintenance alarm  83  requires closure of contact R 18  which is illustrated in FIG.  2 C. 
     Rungs  6  and  7  start aeration and blow down timers on the closure of switch  14 . Rung  8  closes fill valve  26  if apparatus  20  is in an aeration cycle and opens the valve  26  for a blow down or maintenance alarm. Rung  9  closes valve  48  during an aeration cycle and a bypass occurs during an initial line flush and a maintenance alarm. Rung  10  closes valve  60  during aeration. Rung  11  activates a blow down. Rung  12  delays the inputs from sensors  77  and  79  for a predetermined time period to minimize false signals. 
     Rungs  13  and  14  set foam alarm  87  when the float  66  is above a low set point and foam density is high. Activation of foam alarm  87  requires closure of contact R 28  which is illustrated in FIG.  2 C. Rung  15  and  16  reset foam alarm  87  wren float  66  fails below a low set point, a reset timer is started and float  66  fails to rise to the low set point before the reset timer expires. 
     Rung  17  sets an internal relay if a high set point has been reached. Compressed air is diverted to the top of column. 
     Rung  19  turns on sump pump  82  when upper float switch SW 5  closes, while rung  20  turns off sump pump  82  when lower float switch SW 6  closes. 
     Rungs  21 - 24  are used to control a backwash process. Programmable logic controllers  69  periodically actuates the solenoid S 3  of backwash valve  90 . Actuating the solenoid S 3  of backwash valve  90  results in wastewater inflow being diverted through valve  90  washing off accumulated dirt and other solid particles from backwash strainer  86 . The accumulated dirt and other solid particles then pass through backwash valve  90  into holding tank  94  where the wastewater can be pumped to a drain using pump  82 . 
     The apparatus  20  is capable of detecting the presence of concentrations of aqueous film forming foam in bilge water as low as fifteen parts per million in approximately, forty-five seconds. 
     From the foregoing, it may readily be seen that the present invention comprises a new, unique, and exceedingly useful system for detecting and measuring the concentration of foam forming compounds in aqueous solutions which constitutes a considerable improvement over the known prior art. Many modifications and variations of the present invention are possible in light of the above teachings. It is to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.