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 an 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:
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 form forming compounds in the 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 them 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 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 forming agent removal process. 
     Devices used in the past to detect the presence of foam forming chemicals 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 the solution in the reservoir has been diluted by a low concentration input stream 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 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. 
     SUMMARY OF THE INVENTION 
     A sample of the liquid to be tested enters the apparatus comprising the present invention through a fill valve at the top of a tubular column, flows down the sides of the column, and collects in a lower portion of the column. The liquid level in the column rises to the level of an outlet port. Excess liquid flows out of the column through a chamber exiting the apparatus through a discharge port. 
     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 ultrasonic distance measuring device. The measuring device measures the height of the foam 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 sample-and-hold circuit connected to the measuring device. 
     After a foam height measurement has been made, the fill valve closes, an sample drain valve opens, and a three-way valve is positioned to divert the 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; 
     FIG. 2 is an electrical schematic diagram of the 120 VAC control circuity for the apparatus of FIG. 1; 
     FIGS. 3A and 3B are an electrical schematic diagram of the 24 VDC control circuity for the apparatus of FIG. 1; and 
     FIG. 4 illustrates a series of plots which depict foam height as a function of time for solutions of aqueous fire fighting foam. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, there is shown an apparatus, designated generally by the reference numeral  20 , which measures the foam foaming capability of the solution with a time series of discrete tests. The apparatus  20  has detected fewer than ten parts per million of aqueous fire fighting foam (AFFF) in less than thirty seconds. 
     A sample of a liquid to be tested enters apparatus  20  (as indicated by arrow  22 ) through an inlet pipe  24  which includes an electrically operated fill valve  26 . When valve  26  is electrically de-activated, fill valve  26  is open allowing the liquid to pass through inlet pipe  24  and an opening  29  at the top of a tubular column  30  into tubular column  30 . The liquid then flows down the sides of tubular column  30 , and collects in the bottom or lower portion  31  of tubular column  30 . 
     The liquid level in the column rises to the level of an outlet port, which is designated generally by the reference numeral  32 . Outlet port  32  includes a chamber  34  and a pair of pair of weirs  36  and  38  positioned at each end of chamber  34 . Excess liquid flows out through chamber  34  from the lower portion  31  of tubular column  30 . The excess liquid then exits outlet port  32  through an opening/discharge port  40  (as indicated by arrow  42 ). The weirs  36  and  38  at each end of chamber  34  control the rate of outflow of excess liquid and dampen oscillations in foam column height. Dashed line  33  indicates the height of weirs  36  and  38  within chamber  34 . 
     After a sample of the liquid has collected in the lower portion  31  of column tubular  30 , an electrically operated air pump  44  is actuated providing compressed air which flows through a pipe  46 , a three-way electrically operated air valve  48 , and a pipe  50  into the sample through aeration stone  52 . The many small air bubbles produced 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 of tubular column  30 . 
     When apparatus  20  is not operational, float  66  rests on a support member  68  located within tubular column  30 . Support member  68  has a centrally located opening  70  which allows foam to pass through support member  68  lifting float  66  into the upper portion of tubular column  30 . 
     The float  68  serves as a solid target for an ultrasonic distance measuring device  67 . The ultrasonic distance measuring device  67 , which is positioned at the top of tubular column  30 , measures the height the column of foam and target  66  rises to within tubular column  30 . The ultrasonic 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 ultrasonic distance measuring device  67  is measured, sampled, and retained by a sample-and-hold circuit  69  connected to measuring device  67 . 
     At this time it should be noted that a laser distance-measuring device could be substituted for the ultrasonic distance measuring device  67  to perform the function of measuring the height of the foam column within tubular column  30 . 
     After a foam height measurement within tubular column  30  has been made, fill valve  26  closes and an electrically operated sample drain valve  60  opens. When electrically deactivated, drain valve  60 , which is connected to the bottom of tubular column  30  by a pipe  58 , allows liquid in tubular column  30  to exit tubular column  30  via connecting pipe  58  and a drain pipe  62  (as indicated by arrow  64 ). 
     Simultaneously, three way electrically operated air valve  48  is positioned to divert the compressed air from the aeration stone  52  to the top of column  30  via a connecting air pipe  54  through an opening  56  at the top of column  30 . This diversion of compressed air forces the sample of solution and foam out of tubular column  30  through drain valve  62  and drain pipe  64 . 
     After the solution and foam have been drained from tubular column  30 , valve  26  opens, valve  60  closes, and three-way air valve  48  redirects air to the aeration stone  52 . The entire sample acquisition and measurement cycle is repeated. 
     If the height of the column of foam rises too high in tubular column  30 , valve  26  is temporarily closed until the next drain cycle. Closing valve  26  precludes the introduction of excessive amounts of foam forming chemicals. 
     The accumulation of deposits of organic matter on the inside wall  74  of tubular column  30  may interfere with the free movement of the float/target  66 . To preclude the growth of algae and bacterial mats on the inside wall  74  of column  30  and remove deposits of oil and grease from the inside wall  74  of column  30 , apparatus  20  includes a cleaning cycle timer  120  (FIG. 3A) that allows for periodic flushing of the wall  74  of the column  30  with a biocide cleaning solution. The cleaning solution may be a solution of sodium hypochlorite or potassium permanganate. A cleaning solution pump  128  is activated periodically (about once a day) for a brief time period to flow the biocide cleaning solution over the wall  74  of column  30 . Energizing coil  122  of cleaning cycle timer  120  closes normally open contact  126  of relay  124  activating cleaning solution pump  128  whenever contact  118  of relay  88  is in the closed position, as shown in FIG.  3 A. 
     Referring now to FIGS. 1,  2 ,  3 A, and  3 B, a relay logic circuit controls the apparatus  20  in a typical process application. Included in the relay logic circuit is a latching relay  92  which is set when the foam height exceeds an input upper set point  73 . The relay  92  remains latched until the height of the foam column falls below an input lower set point  72  and remains below lower set point  72  for a time period set by a time delay relay  138 . 
     The latching relay  92  is used to control a process, such as diverting a contaminated flow stream from a wastewater treatment plant to storage tanks or a specialized treatment processing facility via diverter valve  96 . 
     The 120 VAC control circuity of FIG. 2 includes a 120 VAC power line  80 , a neutral power line  81 , a manual power switch  82  within power line  80  and a fuse  84  connected to switch  82 . Closure of switch  82  supplies 120 VAC to a 24 VDC power supply  86  which provides 24 VDC to the electrical components of FIGS. 3A and 3B. 
     When normally open contact  90  of relay  88  is closed 120 VAC is supplied to air pump  44  activating air pump  44 . Further, when normally open contact  94  of latching relay  92  is closed 120 VAC is also supplied to diverter valve  96  and an event counter  98 . The event counter  98  counts the number of times the concentration of foam producing chemicals in the wastewater has exceeded the set points  72  and  73  of apparatus  20 . 
     When a sample is diverted from the contaminated flow stream, normally open contact  100  of a flow switch (not illustrated) closes supplying 24 VDC to a relay coil  104  energizing coil  104 . Energizing coil  104  closes contact  90  of relay  88  activating air pump  44  which then supplies compressed air to tubular column  30 . Energizing coil  104  also closes normally open contact  106  of relay  88  supplying 24 VDC to control solid state relay  114 , control solid state relay  116 , and acoustic sensor  108 . Relays  114  and  116  operate to increase supply current respectively to coils  111  and  113  to activate coils  111  and  113  when normally open contacts  110  and  112  of acoustic sensor  108  are closed. 
     When spherical shaped lightweight float/target  66 , which is being lifted by a column of foam, reaches lower set point  72 , normally open contact  110  of acoustic sensor  108  closes which energizes coil  111  of relay  130 . Energizing coil  111  closes normally open contact  148  of relay  130 . When spherical shaped lightweight float/target  66  reaches upper set point  73 , normally open contact  112  of acoustic sensor  108  closes which energizes coil  113  of relay  132 . Energizing coil  113  closes normally open contact  150  of relay  132 . Closing contact  150  supplies 24 VDC to the latch coil  152  of latch relay  92  which results in the closure of contact  94  of latch relay  92 . Closing contact  94  of latch relay  92  activates diverter valve  96  and event counter  98 . 
     Energizing coil  111  of relay  130  opens normally closed contact  134  of relay  130 . Similarly, energizing coil  113  of relay  132  opens normally closed contact  136  of relay  132 . This insures that the unlatch coil  144  of latch relay  92  is not energized. 
     When spherical shaped lightweight float/target  66  drops below upper set point  73 , normally open contact  112  of acoustic sensor  108  opens which de-energizes coil  113  of relay  132 . De-energizing coil  113  of relay  132  closes contact  136  of relay  132 . When spherical shaped lightweight float/target  66  drops below lower set point  72 , normally open contact  110  of acoustic sensor  108  opens which de-energizes coil  111  of relay  130 . De-energizing coil  111  of relay  130  closes contact  134  of relay  130 , resulting in 24 VDC being supplied to the coil  140  of a time delay relay  138 . After a time delay of 120 seconds, contact  142  closes supplying 24 VDC to the unlatch coil  144  of latch relay  92 . Energizing the unlatch coil  144  of latch relay  92  opens contact  94  of latch relay  92 . The unlatch coil  144  of latch relay  92  is also energized by depressing momentary contact switch  146 . 
     Latch relay  92  is also connected to a blow down timer  154 . When latch coil  152  of latch relay  92  is energized, contact  153  of latch relay  92  closes supplying 24 VDC to the coil  156  of a blow down timer  154 . This closes normally open contact  158  of timer  154  resulting in 24 VDC being supplied to air valve  48 . Energizing air valve  48  diverts compressed air through pipe  54  to the top of column  30  to force foam and the wastewater sample through valve  60  and drain pipe  62 . Energizing coil  156  of a blow down timer  154  also moves two position contact  160  such that contact  160  opens the current path between terminal  162  and terminal  164  and closes the current path between terminals  162  and  166 . This results in fill valve  26  being electrically activated. Activating fill valve  26  shuts off the flow of liquid through inlet pipe  24  and opening  29  at the top of tubular column  30  into tubular column  30 . 
     When coil  156  of blow down timer  154  is energized, contact  160  opens de-energizing drain valve  60 . De-energizing drain valve  60  results in the foam and wastewater sample exiting tubular column  30  through pipe  58 , drain valve  60 , and drain pipe  62 . 
     When the unlatch coil  144  of relay  92  is energized contact  153  opens de-energizing coil  156  of blow down timer  154 . This results in contact  158  opening de-activating valve  48  which then diverts air flow through valve  48  and pipe  52  to aeration stone  52 . Activating valve  48  directs air through pipe  54  to the top of tubular column  30  so that the foam and wastewater within tubular column  30  is blown out of tubular column  30 . 
     Further, contact  160  returns to the position illustrated in FIG. 3B completing a current path between terminals  162  and  164  which activates drain valve  60  blocking the flow of wastewater and foam out of tubular column  30  through pipe  58  and drain valve  60 . 
     At this time it should be noted that the 24 VDC control circuit of FIGS. 3A and 3B includes a manual switch which has a normally open contact  102 . When the manual switch is activated closing contact  102  the circuit of FIGS. 3A and 3B operate in exactly the same manner as when contact  100  closes. The purpose of this switch is to provide the capability to manually unlatch relay  92  and reposition valve  96 . 
     It should be noted that the apparatus  20  is fabricated primarily from durable plastic allowing for a long life span. It should also be noted that a sample from the input stream may be collected, analyzed, and then discarded in about two minutes. This results in any error which occurs in measuring the change in composition of the input stream being no larger than the period required for the collect-analyze-discard cycle of about two minutes. 
     Referring to FIG. 4, FIG. 4 illustrates four plots  170 ,  172 ,  174 , and  176  in which foam height is depicted as a function of time for aqueous fire fighting foam (AFFF) having 40 ppm (plot  170 ), 20 ppm (plot  172 ), 10 ppm (plot  174 ), and 5 ppm (plot  176 ) for apparatus  20 . 
     From the foregoing, it may readily be seen that the present invention comprises a new, unique, and exceedingly useful system for detecting and measuring 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.