| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | November 8, 1988 |
| PATENT TITLE |
Fluorescent tracers - chemical treatment monitors |
| PATENT ABSTRACT |
A method to determine performance of a treating agent (CA) added to a system body of liquid to enhance performance of the liquid body is determined by employing an inert fluorescent tracer (T) in a known T:CA dosage proportion, prepared on the basis of a concentration of CA (e.g. ppm) proposed for optimum performance in the liquid body. The system liquid is sampled and, on the basis of fluorescent emission, the sampled indicator is compared to a standard ppm concentration of T to determine the concentration and efficacy of CA and the physical characteristics and operating parameters of the liquid body. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | February 26, 1987 |
| PATENT CLAIMS |
We claim: 1. In an industrial or municipal water system involving equipment through which is a moving body of water containing impurities and containing a quantified dosage of a water treating component having the role of being consumed while removing or neutralizing impurities in the body of water, a method of monitoring the system to determine if the level of treating component subscribes to an acceptable parts-component: liquid volume proportion under operating conditions comprising the steps of: (A) adding to the body of water a water soluble fluorescent tracer in an amount proportioned to the amount of treating component in the system, the fluorescent tracer being inert to water, inert to the equipment and inert to the treating component; (B) withdrawing from the system a sample of the body of water containing both the component and tracer and subjecting the withdrawn sample to an analysis which consists essentially of the step of comparing the tracer concentration thereof to a standard on an emissivity basis to determine the concentration of tracer in the sample; and, if the operating concentration is outside an acceptable operating range, (C) changing the volume of water or the dosage of treating component until an acceptable operating range of concentration for the treating component is attained. 2. Method according to claim 1 in which step (B) is a step repeated at different locations in the body of water to analyze performance of the treating component at such different locations. 3. Method according to claim 1 in which the treating component is a scale inhibitor or corrosion inhibitor. 4. Method according to claim 1 in which step (B) is used with the step of conducting a separate quantitative analysis of the treating component level to verify the accuracy of step (B). 5. Method according to claim 1 in which step (B) indicates the need to change both the volume of water and the dosage of treating component and including the step of making both changes. 6. Method according to claim 1 in which the fluorescent tracer is either 2-napthalensulfonic acid or Acid Yellow 7. 7. Method according to claim 1 in which the water system is undergoing clarification resulting in a clarified body of water and in which the treating component is one which removes impurities to produce a clarified body of water. 8. Method according to claim 7 in which the system is an open system having both a flow inlet and flow outlet. 9. Method according to claim 8 in which the liquid body is a stream of water, into and out of a chamber, coupled with water in the chamber containing particulate solids to be removed therefrom, the treating component being one which aids removal of the particulate solids to increase the clarity of effluent water removed from the chamber. 10. Method according to claim 1 in which the system is a water cooling system. 11. Method according to claim 10 in which step (B) identifies an unknown loss or gain of water volume in the water system, and including the step of correspondingly increasing or decreasing the volume of water in the system. 12. Method according to claim 1 in which step (B) indicates a need to alter the dosage of component and including the step of altering that dosage. 13. Method according to claim 12 in which step (B) is repeated to determine the rate at which the system responds to the altered component dosage. 14. Method according to claim 1 including the step of employing at least two different treating components together with at least two different fluroescent tracers, the fluorescent tracers having recognizably different emissivity values, and the fluorescent tracers having emissivity values recognizably different from the emissivity value of any fluorescent background present. 15. Method according to claim 14 in which the fluorescent tracers are 2-napthalensulfonic acid and Acid Yellow 7. 16. Method according to claim 1 in which the system is a cooling water system, including the step of adding both a scale inhibitor and corrosion inhibitor to constitute the treating component. 17. Method according to claim 16 in which step (B) identifies an incorrect dosage of treating component and including the step of altering the dosage of treating component until an acceptable operating range therefore is achieved. 18. Method according to claim 16 in which step (B) identifies the need to correct a water loss in the system or a water gain in the system and including the step of undertaking such correction. |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION The present invention pertains to the utilization of compositions containing fluorescent agent(s) and particularly a method of utilizing the same to quantify and control feed rate(s) of treatment chemicals into liquid-containing systems. In addition, the fluorescent agent(s) provide a means of determining composition performance under static or changing operating conditions of the systems. Further, fluorescent agent(s) are used to quantify important characteristics of the system such as total volume and amount of a liquid entering and leaving the system. The singular form of terms such as agent, tracer, level, rate, component, compound, composition, treatment, formulation, liquid, fluid, and system will be used and are understood to describe both singular and multiple usage. The term liquid is entirely general and may be associated with aqueous, non-aqueous, and mixed aqueous/non-aqueous environments. BACKGROUND OF THE INVENTION In a system involving a body of liquid to which a treating agent is added, maintaining the proper feed level for the agent is essential for optimal performance. Improper feed rate of treating agent can lead to serious problems. For example, severe corrosion and/or deposit formation can rapidly occur on heat-exchange surfaces in cooling and boiler water systems when incorrect level of treating agent is used. One common method of estimating the concentration of a treating agent focuses on measuring the level of an active component in the treatment formulation (e.g. polymeric scale inhibitor, phosphate, or organophosphonate). That technique is often unsatisfactory due to one or more of the following problems: background interferences from the system liquid or materials contained in the liquid; analytical methods use bulky and costly equipment; time-consuming, labor-intensive analyses are not compatible with continuous monitoring; inaccurate readings result from degradation or deposition of active component within the system. An alternative method of determining treatment feed rates is to specifically add metal ions (e.g. Li.sup.+) to the formulation or system. That method helps circumvent the degradation/deposition and background interference problems. However, quantitation of low tracer levels commonly magnifies problems associated with expensive equipment and time-consuming test methods. Additional factors which must be considered are cost and environmental acceptability of the tracer. For example, radioactive tracers are detectable at very low levels, but are generally expensive and unacceptable due to environmental and health concerns. THE DRAWINGS FIG. 1 is calibration curve of fluorescein tracer concentration vs. fluorescent emission level; FIG. 2 is schematic view of a representative cooling tower system; FIG. 3 is molecular representation of fluorescent tracer used to accurately measure treatment concentration; FIG. 4 is performance comparison of dual fluorescent tracers vs. phosphorus analysis for product feed rate determination in pilot cooling tower; FIG. 5 is set of curves demonstrating that proper choice of analysis conditions allows determination of the concentration of more than one fluorescent tracer and circumvents interfering agents; FIG. 6 is performance comparison of fluorescent vs. Li.sup.+ tracers in "die-away" study of industrial cooling water system; FIG. 7 is use of fluorescent tracer(s) in system with stagnant and low fluid flow regions to determine effective working volume and treatment concentrations. DESCRIPTION OF THE INVENTION It is an object of the present invention to avoid all of the aforementioned problems and interferences by incorporating a fluorescent compound as a tracer into a treatment formulation to provide quantitative measurement/control of treatment feed rate and performance. By its very nature, fluorescence is a powerful and selective trace analysis technique, [refer to J. R. Lakowicz; "Principles of Fluorescence Spectroscopy" (1983)]. In general, the concentration of a fluorescent tracer is directly determined from a calibration curve of tracer concentration versus emission (FIG. 1). That comparison permits the determination of the concentration range over which linear emission response is observed. At higher tracer concentrations, a negative deviation from ideal behavior is observed. The concentration of the tracer can still be determined directly from the calibration curve or the sample can simply be diluted until the tracer concentration falls within the linear emission response range. For extremely dilute samples, techniques exist for increasing the concentration of the fluorescent tracer (e.g. liquid-liquid extraction) until it lies within a desirable concentration range. By properly choosing the fluorescing reagent, quantitative and in-situ measurement of tracer levels from parts per trillion (ppt) to parts per million (ppm) can be routinely accomplished on an instant or continuous basis with inexpensive portable equipment. In addition, multiple tracers may be used concurrently by choice of tracers with proper spectral characteristics. As such, various combinations of fluorescent tracers and treatment feeds can be quantified within a liquid system. For example, four individual treatments containing a single unique fluorescent tracer plus one additional treatment containing the two fluorescent tracers could be employed within a liquid system. In that case, each fluorescent tracer and the corresponding individual concentration of the five treatments can each be quantified. In addition to being able to quantify complex combinations of the treatment feeds, fluorescent compounds are available which environmentally acceptable, are not degraded by or deposited within the liquid systems, and are available at low cost. The invention can generally be applied in the following ways: (a) direct addition of from one or more fluorescent tracers to a liquid system; (b) incorporation of one to six (or even more) fluorescent tracers into chemical treatment composition containing other components and said treatment is applied to liquid system in order to maintain proper operation of that system; (c) addition of one to six chemical treatment agents (or even more) containing fluorescent tracer(s) directly into liquid system or into liquid feed leading into system; (d) addition of fluorescent tracers so that within the liquid system individual tracer concentrations ranging from 1 part per trillion to 100 parts per million (ppm), preferably from 1 part per billion (ppb) to 10 ppm, and most preferably from 10 ppb to 2 ppm are realized. The invention can be utilized in a broad range of aqueous, mixed aqueous/non-aqueous, or non-aqueous liquid systems (e.g. boilers, clarifiers, waste treatment, liquid-solid separations, down-hole oil field applications, etc.) where the level of chemical treating agent affects performance of the system. Two systems have been extensively evaluated: (1) pilot cooling towers (FIG. 2) used to simulate industrial systems; (2) field testing in an open-recirculating cooling water system of an industrial plant. The important differences between the pilot cooling tower (PCT) and industrial cooling water systems are that the latter are more complex with multiple water flow pathways through heat-exchangers, multiple sources of makeup and blowdown water and larger variations in operating control ranges (e.g. concentration of hardness ions, temperature, water quality, pH, etc.). In all systems, energy is extracted by the recirculating cooling water from the process-side of the system which is at a higher temperature. To maintain the efficiency of that heat transfer, energy is removed by evaporative cooling of the recirculating water in the cooling tower and the heat-exchanger surfaces need to remain clean. Evaporation (E) of the cooling water leads to concentration of the suspended and dissolved solids in the cooling system. The term concentration ratio (CR) is a measure of the increased level of dissolved and suspended matter in a system (eq 1). ##EQU1## Deposition of solids and corrosion of heat-exchanger surfaces are the problems most generally encountered. Cooling water systems commonly contain highly supersaturated levels of scaling salts and deposition of solids throughout the system (particularly at metal heat-exchangers) will occur unless chemical treatment(s) containing scale inhibitors is added. To prevent corrosion of metal heat-exchangers and water transfer lines, chemical treatment(s) commonly contains corrosion inhibitors. If the feed rate of the chemical treatment is too high or too low, severe scaling and corrosion can occur on the heat-exchangers and throughout the system. It is vital that the level of dissolved and suspended solids, total volume of system's liquid (V.sub.T) and concentration of chemical treatment be maintained between certain values in order to provide economical usage of water, efficient heat transfer, minimal fouling of entire cooling system, and low operating costs. To maintain the concentration ratio (CR) within an acceptable range, water containing a "high" concentration of impurity must be removed from the system [collectively defined as "blowdown" (B)] and replaced by water containing a "low" concentration of impurities [collectively defined as "makeup" (M)]. The values for E, B, M, and CR are variable due to changes in the weather, operating conditions of the industrial plant, and quality of the makeup water. Those factors are all interrelated (as shown below) and a change in any one of those factors must be counterbalanced by corresponding changes in other operating parameters. B+M=E (eq 2) CR=M/B (eq 3) In addition to the dynamic operating conditions of a cooling water system, other significant variables and unknown factors are commonly encountered. For example, blowdown water (B) can be removed from the cooling system through a variety of ways (eq 4), which unfortunately tend to be variable and ill-defined in nature. The rate at which water is specifically pumped from the cooling water system is defined as "recirculating water blowdown" (B.sub.R), and even that rate is not always accurately known due to practical difficulties in measuring large volumes of water. In addition, ill-defined amounts of recirculating water (un-accounted system losses) are commonly removed from the cooling water system to be used in other areas of the industrial plant, defined as "plant blowdown" (B.sub.R). Leakage of recirculating water (B.sub.L) and drift of liquid droplets from cooling tower (B.sub.D) also add to unaccounted system losses. A similar situation can occur with the makeup water, where the total makeup water rate (M) is the combined rate at which makeup water is specifically pumped into the recirculating system (M.sub.R) and liquid originating from other sources (M'). The complexity of the situation can be appreciated by considering equations 2-5. B=B.sub.R +B.sub.P +B.sub.L +B.sub.D (eq 4) M=M.sub.R +M' (eq 5) The feed rate of chemical treatment into the cooling water system is commonly based on estimated values for M.sub.R or B.sub.R, which means there can be considerable uncertainty regarding the concentration of the chemical treatment. When operating conditions of the cooling water system change, the feed rate of the chemical treatment should be adjusted. Those adjustments may or may not be made, depending on how carefully the cooling water system is monitored and controlled. Even when feed rates are adjusted, the concentration of chemical treatment within a cooling water system generally may respond slowly to the change (eq 6). t=(V.sub.T /B) 1n (2) (eq 6) where t=response time for 50% of concentration increase to occur. For example, consider a representative system containing one million gallons and total blowdown rate of 300 gal/min. If the treatment feed rate is increased from 50 to 100 ppm, 38.5 hours are required for only half of that change (25 ppm increase in treatment concentration) to be attained, assuming that no other fluctuations or changes have occurred within the system. For very large values of V.sub.T and small values of B, response time may be measured in days or weeks. In other cases, changes can occur rapidly, such as purposeful (or inadvertent) flushing of the system. Therefore, it is important that good control and accurate monitoring of the system be maintained. Another significant operating parameter which should be quantified is holding time index (HTI), a measurement of the half-life of a chemical species within the system (eq 7). HTI=0.693 (V.sub.T /B) (eq 7) Under severe operating conditions, it is important to optimize HTI in order to reduce possible degradation of components in the chemical treatment without greatly increasing operating costs. Due to all the operating limitations and uncertainties in cooling water systems, the need to rapidly determine and continuously monitor the concentration of chemical treatments is clearcut. The addition of a fluorescent tracer to the chemical treatment permits accurate detemination of all the unknown, imprecisely known and variable operating conditions previously described. FIGS. 3A-C demonstrate the operation of the water treatment program at the molecular level as a function of time. The concentrated chemical treatment (which contains one or more components) is slowly fed into the recirculating cooling water where the treatment is rapidly diluted and distributed throughout the system. If operating conditions of the cooling water system remained constant, the addition and removal of treatment (due to recirculating water blowdown and system losses) would equilibrate (FIG. 3A). The concentration of the chemical treatment and its components ideally should remain unchanged. However, that situation never occurs. As time progresses (FIGS. 3B-C), additional amounts of the Zn.sup.+2, polymer, and phosphorus-containing compounds can be lost from the recirculating water due to deposition and protective-film formation on metal surfaces and chemical/biological degradation processes. Also, changes in operating conditions (blowdown rate, concentration ratio, and product feed rate, and others) affects the concentration of the treatment components. Without a fluorescent tracer, analysis of the recirculating water may measure current concentrations of some of the treatment components (assuming an analysis method exists), but cannot directly indicate the original feed rate of the treatment program. Use of a fluorescent tracer to quantify and control the treatment feed rate is a valuable, if not essential, addition to current water treatment programs. FIGS. 3A-C also indicate how addition of an inert fluorescent tracer can provide accurate determination of treatment feed rate and treatment efficacy, in spite of deposition of other components in the chemical treatment. For example, assume the formulation feed rate was 100 ppm. If deposition occurred on the heat-exchangers, 40% of the phosphorus-containing species could be lost from the recirculating water, but none of the fluorescent tracer will be lost. The total phosphorus concentration would suggest only 60 ppm of the product was present. However, the fluorescent tracer would correctly indicate the formulation feed rate was 100 ppm and a loss of phosphorus-containing components equivalent to that supplied by 40 ppm feed of formulation was being deposited. Determination of loss rates of active component(s) of the treatment is a direct measurement of treatment efficacy. In summary, important system characteristics of many industrial systems (total volume, blowdown and makeup rates, holding time index, treatment feed rates and others) are imprecisely known, variable and sometimes unpredictable in nature. Lack of knowledge regarding those factors can lead to serious deposit and corrosion problems throughout the entire cooling water system. In particular, over/underfeeding of treatment program or improper operation of cooling water system can result in significant loss of treatment component(s) and adversely affect heat transfer within a cooling water system. In addition, water treatment programs commonly contain regulated or toxic materials (e.g. zinc ions, phosphate, or chromate). Overfeeding of treatments can be hazardous and makes it more difficult for industrial sites to meet government restrictions on effluent discharges. Use of a fluorescent tracer is a highly desirable means of accurately determining, continuously monitoring, and controlling cooling water system characteristics and treatment feed rates within desirable ranges. The successful use of a fluorescent tracer to accomplish the tasks described above has been accomplished in several systems. Pilot cooling tower tests (example 1) have clearly demonstrated the concept and feasibility of using fluorescent tracers in treatment formulations and field testing has proven applicability of fluorescent tracers in real-world systems (example 2). |
| PATENT EXAMPLES | available on request |
| PATENT PHOTOCOPY | available on request |
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