Patent Publication Number: US-2004053415-A1

Title: Ozone-in-water decay rate analyzer

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to apparatus for determining the rate of decay of the ozone residual concentration in an ozone-in-water solution. More particularly, the present invention relates to a device for measuring an initial ozone residual concentration of an ozone-in-water solution, a time-delayed ozone residual concentration, and determining the first order ozone decay rate constant for a flow-through ozone contactor.  
       [0003] 2. Description of the Related Art  
       [0004] The effectiveness of ozone disinfection in flow-through contactors depends on the ozone concentration of the water being treated and the time interval during which the water to be treated is exposed to ozone. A suitable way to accurately assess the effectiveness of ozone disinfection is to monitor the initial ozone residual concentration (“C o ”) of the ozonated solution, and the final ozone residual concentration (“C”) of the solution at the end of a contact time interval (“T”), to arrive at the factors that enable the calculation of the so-called CT product for the ozonated water.  
       [0005] The initial and final ozone residual concentrations can be measured directly by wet chemistry using indigo trisulphonate—a calorimetric reagent, or by using a commercially available ozone-in-water on-line analyzer. The ozone decay rate constant for the water being treated can then be calculated based upon first order decay kinetics using the equation:  
         K   d =ln( C/C   o )/ T    
       [0006] where C is the final ozone residual in mg/L after a specified contact time, C o  is the initial ozone residual in mg/L at the start of a specified contact time, T is the contact time in minutes, and K d  is the decay rate constant in min −1 .  
       [0007] In operating ozone contactors the decay rate constant can be calculated by two methods. In the first method, a grab sample of ozonated water is collected in a beaker, the initial residual is measured using wet chemistry, the sample is held for a fixed time interval (say 1-5 minutes) at constant water temperature, the final residual is measured, and the first-order equation is used to compute the decay rate constant. In the second method, the ozone residual concentrations are measured at two fixed points along the ozone contactor using wet chemistry or two on-line ozone analyzers. A contact time value is assigned between the two sampling points and the first-order equation given above is utilized to compute the decay rate constant. The assigned contact time is based upon the measured flow rate through the contactor and the T 50  residence time distribution, which is determined from a tracer study of the contactor.  
       [0008] The first method has limited usefulness for disinfection compliance monitoring of ozone systems since it relies on grab sampling and wet chemistry analysis and cannot be automated. While the second method can be automated using two online ozone residual analyzers, the accuracy of the decay rate constant calculation is influenced by the magnitude and variability of flow short-circuiting through the contactor at different flow rates. Because flow short-circuiting results in changes in the residence time distribution at discrete sampling points along the contactor, it can result in uneven ozone residual concentrations across the width of the contactor at a given sample location. Consequently a single T 50  value determined from a tracer study may not be accurate where there are varying flow rates and varying hydraulic conditions in an operating ozone contactor.  
       [0009] It is an object of the present invention to overcome the problems and shortcomings noted above in connection with presently-utilized methods for determining the decay rate constant for an ozone-in-water solution.  
       SUMMARY OF THE INVENTION  
       [0010] Briefly stated, in accordance with one aspect of the present invention, apparatus is provided for enabling the determination of an ozone decay rate constant for an ozone-containing solution. The apparatus includes a sensor for measuring an ozone residual concentration value of an ozone-containing solution. A first flow conduit conveys the ozone-containing solution to the sensor for measuring an initial ozone residual concentration value for the solution. A second flow conduit is provided for conveying a time-delayed flow component of the solution to the sensor for measuring a time-delayed ozone residual concentration value for the solution. The second flow conduit branches from the first flow conduit to divert a portion of the solution through a time delay chamber for delaying the diverted solution for a time interval before measuring the ozone residual concentration of the diverted solution. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011] The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings in which:  
     [0012]FIG. 1 is a schematic diagram showing one embodiment of an ozone decay rate analyzer in accordance with the present invention in a first mode for measuring an initial ozone residual concentration;  
     [0013]FIG. 2 is a schematic diagram similar to that of FIG. 1 with the analyzer in a second mode for measuring a time-delayed ozone residual concentration;  
     [0014]FIG. 3 is an elevational view, in cross section, of a constant-temperature flow delay chamber for an ozone analyzer;  
     [0015]FIG. 4 is a cross-sectional view of the delay chamber shown in FIG. 3 taken along the line  4 - 4  thereof; and  
     [0016]FIG. 5 is a cross-sectional view of the delay chamber shown in FIG. 3 taken along the line  5 - 5  thereof. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0017] In the present invention there is provided apparatus for measuring the initial ozone residual concentration and for determining the first-order ozone decay rate constant for an ozone-in-water solution. The apparatus is suitable for use in flow-through ozone contactors. Precise contact times between two successive ozone residual measurements enable the accurate calculation of the ozone decay rate constant, thereby avoiding the inherent inaccuracies of the grab sample and twoanalyzer methods identified above. An analyzer in accordance with the present invention incorporates a single, standard, on-line ozone-in-water analyzer to provide an automatically operable, dual sampling arrangement for measuring ozone residual concentrations at the beginning (C 0 ) and at the end (C) of a variable contact time period (T).  
     [0018] Referring now to the drawings, and particularly to FIGS. 1 and 2 thereof, there is shown in schematic form an embodiment of one form of ozone decay rate analyzer  10  in accordance with the present invention. Components of analyzer  10  can be enclosed within a suitable housing  12 , which can be a NEMA 4X rated enclosure and can have dimensions of the order of about 16 inches in length, about 16 inches in width, and about 6 inches in depth. Housing  12  includes a sample inlet connection  14  and an outlet connection  16  for conveying the sampled ozone-in-water solution to a suitable disposal site, such as a drain, a sewer, or the like.  
     [0019] An inlet conduit  18  extends from inlet connection  14  to a tee  20 . Branching from tee  20  is a first sample line branch  22  containing a reducer fitting  24  and including a flow measurement device  26 , such as a rotameter, or the like. A flow control valve  28  is provided in branch  22  downstream of flow measurement device  26  to control the rate of flow of sample solution into a chamber  30  and into a coil of tubing (not shown) within the chamber. Inlet conduit  18  includes a flow control valve  19 . Valves  28  and  19  are adjusted to balance the split of flows to the two branches, but only branch  22  is utilized to measure the flow for calculating the lag time.  
     [0020] An outlet conduit  32  extends from chamber  30  and is connected with the inlet of a first three-way valve  34  that can be operated by a solenoid  36  that is operatively connected with a programmable logic controller  38  by a conductor  39 . One outlet of valve  34  communicates with a drain line  40  that extends to chamber  30  to conduct sample solution into the chamber to flow around the coil of tubing and to exit through outlet conduit  41  that communicates with outlet connection  16 . The second outlet of three-way valve  34  communicates with a sample conduit  44  through a reducer fitting  46  to join at a tee  48  with inlet conduit  18  through a second three-way valve  50 . Valve  50  controls flow through second branch  18 . A solenoid  52  operates valve  50  and is operatively connected with programmable logic controller  38  by conductor  54 . An outlet of tee  48  communicates with an ozone residual sensor  56  for sensing the ozone residual in the sample solution that passes through either of sample conduit  44  or conduit  18 .  
     [0021] Ozone residual sensors suitable for measuring the ozone residual in an ozone-in-water solution can be obtained from sources such as Orbisphere, of Geneva, Switzerland; GLI International, Inc., of Loveland, Colo.; INUSA Corporation of Needham, Mass.; and Rosemount Analytical, of Irvine, Calif. Sensor  56  has an outlet that communicates with drain line  40  that extends to and communicates with the interior of chamber  30 . A drain conduit  41  extends from chamber  30  to sample outlet  16 .  
     [0022] Programmable logic controller  38  is operatively connected with solenoids  36 ,  52  of first and second three-way valves  34 ,  50 , respectively, through respective conductors  39 ,  54  for transmitting electrical signals for controlling the operation of valves  34 ,  50 . Controller  38  is also operatively connected with ozone residual sensor  56  through a conductor  58  for receiving ozone-in-water residual concentration values measured by that sensor. Additionally, controller  38  can be in the form of a microprocessor that is suitably programmed, and it includes, or is connected with, a display device  60  for displaying ozone residual concentration values and also for displaying the value of a calculated ozone decay rate constant.  
     [0023] The structure of chamber  30  is shown in greater detail in FIGS. 3 through 5. Chamber  30  is a tubular component that includes a cylindrical sidewall  62 , a closed bottom end  64 , and an open top end  66 . An annular flange  68  extends outwardly from side wall  62  at top end  66  of chamber  30 , to which flange a top cover disc  70  is secured by a plurality of bolts  72  to completely close the interior of chamber  30 . An annular gasket  74  is positioned between cover disc  70  and flange  68  to provide a liquid-tight seal therebetween.  
     [0024] A tubular core member  76  is substantially centrally positioned within chamber  30 . Core member  76  has a smaller outer diameter than the inner diameter of chamber sidewall  62  to define therebetween an annular chamber  78 . At the lower end of center core  76  is a flow distributor plate  80  that is spaced from closed bottom end  64  of tubular chamber  30  to define an inlet plenum chamber  82 . Flow distributor plate  80  includes a plurality of spaced openings  84  to uniformly distribute a flow of drain solution that is introduced into chamber  30  through drain line  40 . The drain solution flows into plenum chamber  82  and through openings  84  into core member  76  and also into annular chamber  78 .  
     [0025] A sample-tubing coil  88  is carried within chamber  30 . Coil  88  is in fluid communication with a sample inlet line  22  and a sample outlet line  32 , each of which passes through cover disc  70 . Coil  88  is wrapped around core member  76  and is completely immersed within the drain solution that flows into chamber  30  through inlet line  40  and that exits therefrom through outlet line  41 . Coil  88  can be formed from any suitable material that is compatible with ozone, such as Teflon tubing. A coil formed from tubing having an inner diameter of ½ inch and an overall length of about 40 ft provides an effective flow delay time from entrance into the coil to exit from the coil of from about 1 to about 5 minutes at a sample solution flow rate range of from about 0.3 to about 1.5 lpm.  
     [0026] In operation, an ozone-in-water solution for which the ozone decay rate constant is to be determined is introduced into analyzer  10  at sample inlet connection  14 . To measure the initial ozone residual concentration of the solution, three-way valve  50  is set to allow flow of the solution from inlet conduit  18 , through tee  48 , and directly to ozone residual sensor  56 . The initial ozone-in-water residual concentration value C o  is measured by sensor  56 , in mg/L, and that value is provided to programmable logic controller  40  through conductor  58 , whereupon it can be displayed on display device  60 . After passing sensor  56 , the solution enters drain conduit  40  to flow to the inlet of chamber  30 , around tubing coil  88 , and then to exit from chamber  30  through drain line  41  to drain connection  16  for disposal.  
     [0027] While three-way valve  50  is in the position shown in FIG. 1 to allow sample solution to flow to sensor  56 , three-way valve  34  is in the position to allow flow from chamber outlet conduit  32  into drain line  40 , and to block flow into sample conduit  44 . Thus, a portion of the incoming solution flows into branch line  22  and into and through tubing coil  88  within chamber  30 . After exiting through outlet conduit  32 , the solution enters drain line  40  to bypass sensor  56  and to flow into and through the interior of chamber  30  to drain conduit  41  and sample outlet  16 .  
     [0028] In the flow configuration as represented in FIG. 1, the initial ozone residual concentration of the ozone-in-water solution is measured by sensor  56 . To measure the ozone residual concentration in the ozone-in-water solution at a later time, to assess the ozone residual decay rate, each of three-way valves  34 ,  50  is moved to the positions represented in FIG. 2, to cause the time-delayed solution that has passed through tubing coil  88  within chamber  30  to flow to ozone residual sensor  56  through sample conduit  44 .  
     [0029] Three-way valves  34 ,  50  can be operated by solenoids  36 ,  52 , respectively, in response to signals from programmable logic controller  38  transmitted over conductors  39 ,  54 , respectively. Thus, in the FIG. 2 flow configuration, the time-delayed sample solution flows to sensor  56  as the incoming sample solution is divided between inlet branch  22  and inlet conduit  18 . That portion of the sample solution flowing through branch  22  is time-delayed within chamber  30 , while the balance of the sample solution that flows through conduit  18  is diverted to drain line  40  by three-way valve  50 .  
     [0030] The time-delayed, final ozone-in-water residual concentration value C is determined, in mg/L, and can be displayed in display  60 . That value is provided to controller  38 , which then calculates the decay rate constant by suitable logic and computation circuitry, for example by utilizing the first-order decay rate equation given above, based upon the initial ozone residual concentration value, the time-delayed ozone residual concentration value, and the delay time. That constant can then be utilized in other computations, such as calculating a predicted outlet ozone residual concentration value in an ozone-in-water disinfection process.  
     [0031] In carrying out the method described above, the user can provide as input data a desired sample flow rate, which can be of the order of from about 0.3 to about 2 lpm. A selector switch  62  can be provided on controller  38  to enable any of several analyzer and display options: first, the initial ozone residual concentration value; second, a time-delayed ozone residual concentration value; and third the calculated ozone decay rate constant value. Also provided as input quantities are the sample flow cycle time for the initial ozone residual concentration determination C o , and for the time-delayed ozone residual concentration C, each of which times can be, for example, within the range of from about 1 to about 30 minutes, depending upon the sample flow rate through chamber  30 .  
     [0032] In addition to calculating the decay rate constant, controller  38  can also serve to determine the time-delayed sample contact time. That determination can be made by providing within the controller a lookup table relating sample flow rate to contact time for a particular configuration.  
     [0033] As will be apparent, chamber  30  serves to impose on the incoming sample stream entering analyzer  10  at inlet  14  a time delay before measurement of a second ozone residual concentration. The interval between an initial sample ozone residual concentration value and a time-delayed sample ozone residual concentration value permits the determination of the decrease over time of the ozone residual concentration in the sample stream. The time delay is a function of the sample stream flow rate, and that flow rate can be controlled by the operation of flow control valves  19  and  28 . Additionally, chamber  30  serves to maintain the time-delayed sample solution at the same temperature as that of the incoming sample solution, to permit a more accurate decay rate constant determination that is substantially independent of temperature changes that could otherwise occur in the sample solution between the respective ozone residual concentration determinations.  
     [0034] Although particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that changes and modifications can be made without departing from the spirit of the present invention. Accordingly, it is intended to encompass within the appended claims all such changes and modifications that fall with the scope of the present invention.