Compositions and methods for measuring calcium hardness in industrial water

Abstract

An indicator composition may be used to measure calcium hardness within a water sample from an industrial water system. The indicator composition may include a calcium indicator, a range extender, and a buffer. The indicator composition can accurately measure the calcium concentration within the water sample at low, medium and high calcium levels, including at calcium concentrations greater than 50 ppm. The indicator composition can measure calcium hardness at a pH of less than about 7 without the use of a masking agent.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 414,632, filed Oct. 10, 2022, and U.S. Provisional Application No. 63 / 477,444, filed Dec. 28, 2022, both entitled "Composition and Method for Measuring Calcium Hardness in Process Water", the contents of which are hereby incorporated by reference in their entireties. Technical Field

[0003] The present disclosure relates to compositions, methods, and systems for measuring calcium hardness in industrial water (including but not limited to boiler water, cooling water, and wastewater systems). Background Art

[0004] In the water treatment industry, calcium is one of the main ions that form scale on water systems. Since calcium ions are naturally present in water, water treatment systems (such as but not limited to boiler water, cooling water, and wastewater systems) face challenges related to forming scale on surfaces, especially on surfaces with elevated temperatures. Fouling typically forms a hard and adherent layer, resulting in processing challenges due to the delay in heat transfer. In addition, scale within the transfer tubes can reduce water flow, which requires a higher head and can accelerate additional fouling. Although scale formation typically requires a temperature gradient, under some conditions scale formation can still occur without a temperature difference.

[0005] Common calcium scales in water systems include calcium carbonate, calcium phosphate, and calcium sulfate. Generally, scale formation occurs when water containing dissolved minerals becomes supersaturated due to exceeding the solubility of the minerals. There can be an induction period, which is defined as the time required from the supersaturation point to the initial formation of mineral scale particles. If there is a certain degree of supersaturation, crystallization of the scale will typically occur; however, in the absence of some solid sites, the supersaturated solution will not form scale. Thus, water treatment systems are highly susceptible to fouling.

[0006] As scale grows, water flow rate decreases and pumping backpressure increases. Because scale has a lower thermal conductivity than the metal heat exchanger surface, the presence of scale formation results in reduced heat transfer. As a result, reduced plant efficiency, reduced production capacity, schedule delays, increased energy costs, production losses due to downtime for maintenance, and increased costs for equipment repair and replacement may occur. These effects directly lead to higher operating costs and reduced profitability. Since the degree of supersaturation is the main factor used to control the deposition process, the concentration of scaling-causing minerals such as calcium should be monitored regularly to prevent scaling, thereby extending the life of the equipment and reducing the use of excess water, energy, and water treatment chemicals.

[0007] Currently, there are ways to measure calcium, including options for real-time calcium measurement to provide more insights and the possibility of controlling the scale stress on equipment. Online methods for measuring calcium hardness in water include ion-selective electrodes (ISEs), fluorescence, titration, and colorimetry. Although colorimetry provides a convenient option for measuring calcium, accuracy is often compromised because many components in the water system can interfere with calcium measurement. In addition, in many industrial water systems, the calcium concentration in the water can be as high as 1000 ppm (as CaCO3) or more. However, traditional dyes used to measure calcium, such as chlorophosphonazo-III used in the Hach method 8374, for example, can only measure trace amounts of calcium up to 1 ppm (as CaCO3).

[0008] Additional calcium indicators have been used; however, many calcium indicators are not thermally stable in liquid form. For example, U.S. Patent Publication 2015 / 0198540 discloses a method for using o-cresolphthalein complexone (OCPC) to measure calcium hardness in water. However, it was found that OCPC is only thermally stable in liquid form for two weeks, which is impractical for field and laboratory applications involving industrial water systems. Therefore, there is still a need for other compositions, methods, and systems that can accurately measure the calcium concentration in industrial water. SUMMARY OF THE INVENTION

[0009] Generally speaking, the present disclosure relates to compositions, methods, and systems for detecting, identifying, and measuring the calcium hardness in a water sample (i.e., water from an industrial water system). An indicator composition is provided and can advantageously measure calcium concentration over a much higher range than existing methods. The methods disclosed herein utilize colorimetry and the indicator composition to measure the calcium concentration in a water sample in a range up to 1400 ppm or higher.

[0010] The indicator composition of the present disclosure is formulated to be capable of measuring medium to high levels of calcium in a water source. The indicator composition includes a weak ligand as a range extender to compete with the calcium indicator such that most of the calcium ions within the water source complex with the weak ligand. A small amount of remaining calcium ions can then react with the calcium indicator. Advantageously, the measurement range of the calcium indicator is expanded. Additionally, a buffer can be included to maintain the pH at a level suitable for the calcium indicator to selectively chelate to calcium ions. This provides the benefit of not requiring an additional masking agent to prevent the calcium indicator from chelating to other ions (such as magnesium) present in the water source.

[0011] When measuring the calcium concentration in a water source, the absorbance, transmittance, or reflectance of a sample solution containing the water source and the indicator composition can be obtained at a specific wavelength or wavelength range. After obtaining the absorbance, transmittance, or reflectance, a linear calibration curve can be formed. The calibration curve using the indicator composition of the present disclosure can provide a linear calibration curve for determining the calcium concentration within the water source.

[0012] The indicator composition can exhibit excellent dimensional stability during the expected storage period under a range of storage conditions, including relatively high temperature conditions. Compared to current indicators, the indicator composition of the present disclosure can provide stability for a period greater than two weeks. In some cases, the indicator composition can remain stable for at least one month or at least one year.

[0013] In one example, a method for measuring calcium hardness is described. The method includes extracting a water sample containing calcium from an industrial water system and adding an indicator composition to the water sample to form an optical analysis solution. The example specifies that the indicator composition can include a calcium indicator, a range extender, and a buffer. The method further includes the steps of optically analyzing the optical analysis solution and determining the concentration of calcium in the water sample therefrom. As a result of determining the calcium concentration in the water sample, the addition of a calcium control agent to the industrial water system can be controlled or adjusted based on the determined calcium concentration in the water sample.

[0014] As another example, a system for measuring calcium is described. The system includes an optical sensor configured to receive a water sample containing an unknown concentration of calcium from an industrial water system. The indicator composition can include a calcium indicator, a range extender, and a buffer. The system further includes at least one pump fluidly coupled to the indicator composition. Additionally, a controller is communicatively coupled to the optical sensor and the pump. The controller is configured to perform a plurality of functions, including controlling the pump to produce an optical analysis solution by at least combining the water sample with the indicator composition, and controlling the optical sensor to optically analyze the optical analysis solution. Additionally, the controller can be configured to determine the calcium concentration in the water sample based on the optical analysis.

[0015] For another example, an indicator composition for measuring calcium concentration is described. The indicator composition includes a calcium indicator, a range extender, and a buffer, wherein the indicator composition has a working pH less than 7.0. This example specifies that the indicator composition includes a calcium indicator in an amount less than 0.5 wt%, a range extender in an amount of about 2 wt% to about 10 wt%, and a buffer in an amount of about 0.1 wt% to about 5 wt%. The composition can be provided in the form of a solid composition or can be diluted with water before addition to a calcium-containing water sample from an industrial water system to form a working solution.

[0016] Details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a graph illustrating the absorption spectrum of the complex of calcium and chlorophosphonazo III. The graph provides absorbance values at wavelengths between 300 nm and 750 nm.

[0018] Figure 2 is a graph illustrating the calibration curve of the reagent mixture of the indicator composition at room temperature. The calibration curve is shown as the ppm calcium concentration (as CaCO3) versus the absorbance ratio at 668 nm and 521 nm.

[0019] Figure 3 is a graph illustrating the thermal stability of the reagent mixture measured over a 40-week period at a wavelength of 668 nm and a temperature of 120°F.

[0020] Figure 4 is a graph illustrating the thermal stability of the reagent mixture measured over a 40-week period at a wavelength of 521 nm and a temperature of 120°F.

[0021] Various embodiments will be described in detail with reference to the accompanying drawings. The reference to various embodiments does not limit the scope of the disclosure. The drawings presented herein do not limit the various embodiments according to the disclosure but are presented for illustrative purposes. DETAILED DESCRIPTION

[0022] Embodiments of the present disclosure are not limited to specific compositions, methods, and systems that can vary and are understood by those skilled in the art. Further, it should be understood that all terms used herein are for the purpose of describing particular embodiments only and are not intended to limit in any way or scope. For example, unless the context clearly dictates otherwise, the singular forms "a" and "the" as used in this specification and the appended claims may include plural referents. Additionally, all units, prefixes, and symbols may be expressed in their SI accepted form.

[0023] The methods, compositions, and systems of the present disclosure may comprise, consist essentially of, or consist of: the components and ingredients of the present disclosure and other ingredients described herein. As used herein, "consisting essentially of" means that the methods, systems, and compositions may include additional steps, components, or ingredients, provided that the additional steps, components, or ingredients do not materially alter the basic and novel characteristics of the claimed methods, systems, and compositions.

[0024] The numerical ranges recited in the specification include the numbers defining the ranges and include every integer within the defined ranges. In the present disclosure, various aspects of the present disclosure may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the present disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges, fractions, and individual numerical values within that range. For example, a description of a range such as 1 to 6 should be considered to have specifically disclosed sub-ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., and the individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, as well as decimals and fractions, such as 1.2, 3.8, 1 1 / 2 and 4 3 / 4. This applies regardless of the width of the range.

[0025] As used herein, the term "about", when used in connection with the description of embodiments of the present disclosure, such as amounts, concentrations, and similar values and ranges thereof of ingredients in a composition, refers to variations in the numerical amounts that may occur, for example, as a result of typical measuring and processing procedures used in the preparation of compounds, compositions, concentrates, or use formulations; errors that occur due to negligence in these procedures; differences in the manufacture, source, or purity of starting materials or ingredients used in carrying out the methods, and similar considerations proximate thereto. The term "about" also encompasses amounts that differ due to the aging of a formulation or mixture having a particular starting concentration, and amounts that differ due to the mixing or handling of a formulation or mixture having a particular starting concentration.

[0026] As used herein, the term "absorbance" refers to a quantitative measure expressed as the logarithm of the ratio of the radiation incident on a material to the radiation transmitted through the material according to the following formula:

[0027]

[0028] where A λis the absorbance at a particular optical wavelength (λ), I1 is the intensity of the radiation (light) that has passed through the material (transmitted radiation), and I0 is the intensity of the radiation (incident radiation) before it passes through the material. The amount of light transmitted through the material decreases exponentially as it travels through the material. Since the absorbance of a sample is a logarithmic measurement, it is proportional to the thickness of the sample and the concentration of the absorbing material in the sample. Although absorbance is properly unitless, it is usually reported in "absorbance units" or AU. Any actual measurement instrument has a finite range within which it can accurately measure absorbance. If the readings are to be trusted, the instrument must be calibrated and checked against known standards. Many instruments will become non-linear (fail to follow the Beer-Lambert law) starting at about 2 AU (about 1% transmission). The theoretical best accuracy for most commercially available instruments is in the range close to 1 AU. Then, when possible, the path length or concentration should be adjusted to achieve readings close to that range. Additional meanings of this term are described in Compendium of Chemical Terminology, 2nd ed. ("Gold Book"), published by IUPAC, (1997).

[0029] As used herein, the term "water" for treatment according to the present disclosure includes a variety of sources such as fresh water, pond water, seawater, brine or saline sources, recycled water, and the like. The term "water" is also understood to optionally include both fresh and recycled water sources, and any combination of water for treatment with the compositions according to the present disclosure. In some embodiments, recycled water refers to a mixture of water that includes both recycled water from a previous use (e.g., a previous heat exchange cycle as a heat transfer medium) and water that has not been previously used (e.g., as a heat transfer medium in a heat exchange cycle), such as fresh water, pond water, seawater, etc.

[0030] As used herein, the terms "weight percentage", "wt%", "percentage by weight", "weight %", and variations thereof refer to the concentration of a substance in the form: the weight of the substance divided by the total weight of the composition and multiplied by 100. It should be understood that as used herein, "percentage", "%", etc. are intended to be synonymous with "weight percentage", "wt%".

[0031] The present disclosure generally relates to calcium indicator compositions for detecting and measuring calcium concentration in aqueous systems to ultimately control the formation of scale and corrosion deposits in the aqueous systems. The aqueous system to be treated with the calcium indicator composition can generally be a cooling water system that supplies water to one or more processes in which thermal energy from a relatively hot process stream is transferred to a relatively cold water stream via a separate heat exchange surface. In some specific embodiments, the indicator composition according to the present disclosure can be used in an open recirculating cooling water system, such as an open recirculating cooling water system including one or more cooling towers that cool water via evaporative cooling. In other specific embodiments, the aqueous system to be treated with the calcium indicator composition can be a wastewater treatment system, a boiler water system, or other industrial water systems.

[0032] In certain specific embodiments, the indicator composition generally can comprise a calcium indicator, a range extender, and a buffer. The range extender can be provided as a weak ligand to compete with the calcium indicator for calcium ions in the water sample. In some aspects, this competition results in most of the calcium ions in the water sample complexing with the range extender. This allows a small amount of calcium ions to react with the calcium indicator to form an resulting compound that alters the light absorption of the calcium indicator. The relationship among the calcium indicator, the range extender, and the calcium ions within the water sample allows for the detection of a wide range of calcium concentrations in the water sample. In a further aspect, at a pH less than 7 (including at a pH less than 6), the calcium indicator can be more selective for calcium ions than other ions within the water sample. To provide a more precise composition for measuring calcium concentration, a buffer can be provided to maintain the pH within a range less than 7. In a further embodiment, a buffer can be provided to maintain the pH within a range less than 6. In some aspects, maintaining the pH level less than 7 obviates the need for additional masking agents to mitigate interference from other ions (such as magnesium) in the water sample.

[0033] The indicator composition according to the present disclosure comprises at least one calcium indicator. In some aspects, the calcium indicator is a substance that exhibits a change in fluorescence properties upon binding to calcium. In certain specific embodiments, the calcium indicator may include dyes such as, but not limited to, chlorophosphonazo III (CPA III), chlorophosphonazo I (CPA I), o-cresolphthalein (CPC), o-cresolphthalein complexone (OCPC), methyl thymol blue, arsenazo III, xylenol blue, and Eriochrome Black T. In certain embodiments, the calcium indicator includes CPA III. In some aspects, CPA III has a higher selectivity for calcium ions over other ions in a pH range less than 7. The calcium indicator may be present in the indicator composition in an amount of about 0.001 wt% to about 1 wt%, about 0.005 wt% to about 0.9 wt%, about 0.01 wt% to about 0.8 wt%, or about 0.02 wt% to about 0.5 wt%. In further embodiments, the indicator is present in the indicator composition in an amount less than 1 wt%, less than 0.9 wt%, less than 0.8 wt%, less than 0.7 wt%, less than 0.6 wt%, or less than 0.5 wt%.

[0034] The range extender of the indicator composition may include at least one of the following: polycarboxylic acid, acrylate-based polymer, poly maleic anhydride (PMA), polyepoxysuccinic acid (PESA), maleic anhydride and sulfonated styrene copolymer (MA / SS), polyaspartic acid, chelating agent, or salts thereof. In some embodiments, the range extender includes a polycarboxylic acid selected from the group consisting of citric acid, 1,2,3-propane tricarboxylic acid, glucaric acid, their salts, and combinations thereof. In some aspects, the range extender includes an alkali metal citrate, such as sodium citrate. In some embodiments, the range extender includes a polymer selected from the group consisting of polyacrylate (PAA), poly maleic anhydride (PMA), polyepoxysuccinic acid (PESA), poly(acrylate-co-acrylamide) copolymer (AA / AM), acrylic acid and hydroxypropyl acrylate copolymer (AA / HPA), acrylic acid and 2-acrylamido-2-methylpropanesulfonate copolymer (AA / AMPS), maleic anhydride and sulfonated styrene copolymer (MA / SS), acrylic acid / acrylamide / tert-butylacrylamide copolymer (AA / AM / t-BAM), acrylic acid / 2-acrylamido-2-methylpropanesulfonate / tert-butylacrylamide (AA / AMPS / t-BAM), acrylic acid / sulfonated styrene / 2-acrylamido-2-methylpropanesulfonate (AA / SS / AMPS), acrylic acid / acrylamide / aminomethylsulfonic acid ester copolymer (AA / AM / AMS), polyaspartic acid, their salts, and combinations thereof. In further embodiments, the range extender includes a chelating agent selected from the group consisting of tetrasodium L-glutamate N,N-diacetate (GLDA), iminodisuccinic acid ((N-1,2-dicarboxyethyl)-D,L-aspartic acid), ethylenediamine-N,N'-disuccinic acid (EDDS), methylglycine diacetic acid (MGDA), ethylene glycol-O,O'-bis(2-aminoethyl)-N,N,N',N'-tetraacetic acid (EGTA), disodium ethylenediamine-tetraacetate (EDTA), ODS (oxydisuccinic acid), their salts, and combinations thereof.

[0035] The range extender may be present in the indicator composition in an amount of about 0.1 wt% to about 15 wt%, about 0.1 wt% to about 10 wt%, 0.2 wt% to about 9 wt%, or about 0.3 wt% to about 8 wt%. In some specific embodiments, the range extender may be present in the indicator composition in an amount less than 15 wt%, less than 12 wt%, less than 10 wt%, less than 9 wt%, or less than 8 wt%.

[0036] The indicator compositions according to the present disclosure can be pH-controlled, e.g., to provide a resulting solution when the indicator composition is dissolved in an aqueous sample. The pH of the indicator composition can be pH-controlled in a variety of ways, such as by selecting and incorporating one or more acidifying and / or base-forming components in the formulated indicator composition and / or by incorporating one or more pH-adjusting components in the composition, which serve to change the pH of the resulting solution formed by the indicator composition. In some aspects, the indicator composition includes at least one buffer. Suitable buffers used in the indicator compositions of the present disclosure can effectively form a resulting solution that achieves a target pH threshold and / or is within a target pH range. In some aspects, the buffer is capable of maintaining the pH at a level less than about 7. For example, the pH of the resulting solution can be at least 0.5, such as at least 1.0, at least 1.5, at least 2.0, at least 2.5, at least 3.0, at least 3.5, at least 4.0, or at least 4.5. Additionally or alternatively, the pH of the resulting solution can be less than 7.0, such as less than 6.0, less than 5.0, less than 4.5, less than 4.0, less than 3.5, less than 3.0, or less than 2.5. In some examples, the pH of the resulting solution is in the range of about 1.0 to about 7.0, such as about 1.5 to about 6.5, about 2.0 to about 6.0, or about 3.0 to about 6.0.

[0037] In some embodiments, the buffer can include at least one of the following: lactic acid, acetic acid, formic acid, uric acid, malic acid, tartaric acid, phthalic acid, citric acid, oxalic acid, phosphoric acid, MES (2-(N-morpholino)ethanesulfonic acid), 4-morpholineethanesulfonic acid, sulfamic acid, benzylsulfonic acid, methylbenzylsulfonic acid, glycine, and their salts. In some embodiments, the buffer includes citric acid. In further embodiments, the buffer includes citric acid and alkali metal citrate. The buffer can be present in the indicator composition in an amount of about 0.1 wt% to about 8 wt%, about 0.1 wt% to about 7 wt%, about 0.1 wt% to about 6 wt%, about 0.1 wt% to about 5 wt%, or about 0.2 wt% to about 4 wt%. In some embodiments, the buffer can be present in the indicator composition in an amount less than 8 wt%, less than 7 wt%, less than 6 wt%, or less than 5 wt%.

[0038] In some embodiments, the indicator composition includes a range extender (including alkali metal citrate) and / or includes a buffer (including citric acid and alkali metal citrate). In some embodiments, the indicator composition consists essentially of the calcium indicator CPA III, a range extender, an alkali metal citrate, the buffer citric acid and alkali metal citrate, and water to form an indicator solution. In further embodiments, alternative calcium indicators, range extenders, and buffers can be used as described herein.

[0039] The indicator composition may optionally include a masking reagent. In some embodiments, the masking reagent preferentially binds magnesium. Representative magnesium masking reagents include 8-hydroxyquinoline, 8-hydroxyquinoline-5-sulfonic acid, and any combination thereof. In a preferred embodiment, the indicator composition does not include a masking reagent, such as a magnesium masking reagent. The indicator composition may also include optional additives. The optional additives may include one or more of the following: carriers, biocides, surfactants, and fillers and / or binders.

[0040] An indicator composition comprising a calcium indicator, a range extender, and a buffer can be provided directly to a water source or a water sample. In some specific embodiments, the indicator composition is provided in the form of a solid composition. The term "solid" means that the hardened composition does not flow and will substantially retain its shape under moderate stress or pressure or merely gravity. Solids can take a variety of forms, such as powders, flakes, granules, pellets, tablets, rhomboid pieces, ice ball-shaped chunks, agglomerates, bricks, solid blocks, unit doses, or another solid form known to those skilled in the art.

[0041] Additionally, the term "solid" refers to the state of the composition under the conditions of intended storage and use of the solid composition. Many of the currently available calcium indicators are not thermally stable (i.e., are only thermally stable for about 2 weeks in liquid form). However, the indicator composition according to the present disclosure can remain dimensionally stable for a much longer period of time than 2 weeks under elevated temperature and humidity storage conditions. For example, the indicator composition can remain dimensionally stable for at least one month, such as at least two months, at least 6 months, or at least one year (e.g., a period of one month to one year) at a temperature of 50 °C (about 122 °F) and 70% relative humidity. The term "dimensionally stable" means that when exposed to the noted environmental conditions outside of packaging protection for the tested period of time, the solid composition does not change in size by more than 1% in any measured dimension.

[0042] The indicator composition can take forms including but not limited to the following: cast solid products; extruded, molded, or formed solid pellets, blocks, tablets, powders, granules, flakes; pressed solids v or the formed solids can subsequently be ground or formed into powders, granules, or flakes. In some specific embodiments, the calcium indicator, the range extender, the buffer, and the optional additives can be ground together into a homogeneous dry powder and pressed into a pressed solid form. In some specific embodiments, the solid composition is provided in the form of a cast solid, an extruded solid, a molded solid, or a formed solid or a pressed solid, which includes pellets, blocks, tablets, powders, granules, or flakes.

[0043] The indicator composition can be made by blending the dry components in appropriate ratios or coalescing the materials in a suitable coalescing system. The granulated material can be manufactured by compressing the solid granular or coalesced material in a suitable granulating device to produce a granulated material of appropriate size. The solid block and the cast solid block material can be prepared by introducing a pre-hardened material block or a castable liquid that hardens into a solid block within a container. Examples of containers include disposable plastic containers or water-soluble film containers. Other suitable packagings for the composition include flexible bags, sachets, shrink wraps, and water-soluble films such as polyvinyl alcohol.

[0044] The indicator composition can be formed using a batch or continuous mixing system. In one example, a single-screw or twin-screw extruder is used to combine and mix one or more components under high shear to form a homogeneous mixture. In some embodiments, the processing temperature is at or below the melting temperature of the components. The processed mixture can be dispensed from the mixer by shaping, casting, or other suitable means, whereby the composition hardens into a solid form. According to methods known in the art, the structure of the matrix can be characterized based on the hardness, melting point, material distribution, crystal structure, and other similar properties of the matrix. Generally, the solid composition processed according to the present disclosure is substantially homogeneous in terms of the distribution of components throughout its mass and is dimensionally stable.

[0045] In an extrusion method, one or more liquid and / or solid components are introduced into a final mixing system and continuously mixed until the components form a substantially homogeneous semi-solid mixture in which the components are distributed throughout its mass. The mixture is then discharged from the mixing system and into or through a die or other shaping device. The product is then packaged.

[0046] In a casting method, one or more liquid and / or solid components are introduced into a final mixing system and continuously mixed until the components form a substantially homogeneous liquid mixture in which the components are distributed throughout its mass. Once mixing is complete, the product is transferred to a packaging container where curing occurs.

[0047] In a method of pressing a solid, a flowable solid (such as a granular solid, powder, or other particulate solid) is combined under pressure. In the method of pressing a solid, the flowable solid of the composition is placed in a forming member (such as a mold or container). The method may include gently pressing the flowable solid in the forming member to produce an indicator composition. Pressure may be applied by a block machine or a rotary press, etc. The pressure may be applied at from about 1 psi to about 2000 psi, from about 1 psi to about 300 psi, from about 5 psi to about 200 psi, or from about 10 psi to about 100 psi. In certain embodiments, the method may employ a pressure as low as greater than or equal to about 1 psi, greater than or equal to about 2 psi, greater than or equal to about 5 psi, or greater than or equal to about 10 psi. As used herein, the term "psi" or "pounds per square inch" refers to the actual pressure applied to the flowable solid being pressed and not to the gauge pressure or hydraulic pressure measured at a point in the equipment in which the pressing is carried out. The method may include a curing step to produce an indicator composition. As mentioned herein, an uncured composition comprising a flowable solid is compressed to provide sufficient surface contact between the particles making up the flowable solid such that the uncured composition will cure into a stable composition. Sufficient numbers of fine particles (such as granules) contacting each other provide binding of the particles to effectively prepare a stable solid composition. Including a curing step may include allowing the pressed solid to cure for a period of time, such as several hours or about 1 day (or longer). In a further aspect, the method may include vibrating the flowable solid in the mold or die.

[0048] In some examples, the indicator composition is formed as a solid having a weight of at least 0.05 grams, at least 0.1 grams, at least 0.5 grams, at least 1 gram, at least 5 grams, or at least 10 grams (such as at least 100 grams, at least 1 kg, or at least 10 kg). For example, the composition may be formed as a solid having a weight of from 1 kilogram to 100 kilograms (such as from 1 kilogram to 25 kilograms). In alternative examples, the composition may be formed as a solid having a mass of from about 0.05 grams to about 100 grams (such as from about 0.1 grams to about 50 grams).

[0049] In some aspects, the solid composition may provide a stable source of functional material. In a further embodiment, the indicator composition may be dissolved in, for example, an aqueous medium to produce a concentrated reagent solution. The reagent solution may be directed to a storage reservoir for later use and / or dilution, or it may be applied directly to the point of use. For example, the indicator composition may be dissolved in water to form a use solution. The use solution / reagent solution may then be added to a water sample in a water treatment system. Alternatively, the indicator composition is provided in the form of a solid composition and is dissolved directly in the water sample of the water treatment system.

[0050] The indicator composition may be substantially completely soluble in the water to which the composition is added. For example, the composition may exhibit a solubility of about 100% in the water to which the composition is added. The composition may dissolve in the water to which the composition is added within a time period of 1 hour or less, such as 30 minutes or less, 15 minutes or less, 10 minutes or less, 5 minutes or less, 2 minutes or less, 1 minute or less, 30 seconds or less, 20 seconds or less, 10 seconds or less, or 5 seconds or less. The water to which the solid composition is added may optionally be mixed to aid and accelerate dissolution. The temperature of the water to which the solid composition is added may be varied and, in some examples, may be in the range of about 20°C to about 80°C, such as about 20°C to about 30°C, about 30°C to about 40°C, about 40°C to about 50°C, about 50°C to about 60°C, about 60°C to about 70°C, or about 70°C to about 80°C.

[0051] In one application, a method for measuring calcium hardness is disclosed. The method may include extracting a water sample containing calcium from an industrial water system (such as any of the industrial water systems disclosed herein). In some aspects, the method includes adding an indicator composition (such as any of those disclosed herein) to the water sample to form an optical analysis solution. In some embodiments, the indicator composition contains a calcium indicator, a range extender, and a buffer, as disclosed herein. The method further includes optically analyzing the optical analysis solution and determining the concentration of calcium in the water sample therefrom. Based on the calcium concentration in the water sample, the addition of a calcium control agent (e.g., an antiscalant) to the industrial water system can be controlled.

[0052] The indicator compositions disclosed herein can be used in industrial water systems, such as but not limited to boiler water systems, wastewater treatment systems, and cooling systems (e.g., cooling towers, radiators, heat pipes, etc.). In additional aspects, the methods disclosed herein can further be used in desalination systems, pipelines, drilling equipment (e.g., drill strings, drilling mud, etc.), tracing and fracturing equipment, paper or pulp processing systems, water purification systems, ware washing, evaporators, condensers, filtration, mining, water softening, pumps, storage containers, or any other system that uses a water source or contacts one or more surfaces thereof. During use, when the scale and / or corrosion-promoting contents of the water source become concentrated (e.g., by evaporation) and / or when thermal shock occurs, the corrosion conditions are enhanced, corrosion begins, and scale deposits on the surfaces of the water-containing system from the water source with which it is in contact. Such surfaces can include the interior of pipelines, storage containers, radiators, heat pipes, filters, digesters, condensers, the exterior of cooling towers, or any other surface that contacts the water source. The surfaces of the water-containing system can include metals, plastics, glass, rubber or latex, fiberglass, concrete or stone, or any other material suitable for containing, transporting, or filtering water.

[0053] In some specific embodiments, the source water using the indicator composition is a cooling system, which includes one or more of the following: water jacket, radiator, pipeline, heat pipe, pump, cooling tower, etc. In some specific embodiments, the indicator composition according to the present disclosure can be used in an open recirculating cooling water system, such as an open recirculating cooling water system including one or more cooling towers that cool water by evaporation. When the water source circulates through the water-containing system and evaporates on one or more of its parts, the total dissolved solids content gradually concentrates with each cycle through the system. If not treated, the corrosive / scaling materials therein (such as calcium ions) can reach concentrations at which they begin to corrode and / or scale the surfaces with which they come into contact. Since calcium is one of the main ions forming scale on the surfaces of water systems, the indicator composition of the present disclosure can be added to industrial water sources to measure the concentration / hardness of calcium in the water source. By accurately measuring the calcium concentration in the water source, subsequent treatment steps can be adjusted to inhibit or prevent corrosion (such as pitting or oxidation) and / or scaling caused by the composition of the water source (e.g., pH and / or dissolved solids).

[0054] The industrial water source to be measured using the indicator composition disclosed herein may contain one or more corrosion agents / scaling agents therein, where the one or more corrosion agents / scaling agents comprise, consist essentially of, or consist of the following: carbon dioxide, hydrogen sulfide, organic sulfur compounds, metal ions, metal complexes such as hydrated metal ions, metal chelates, and / or organometallic complexes, aluminum ions, ammonium ions, barium ions, chromium ions, cobalt ions, cuprous ions, copper ions, calcium ions, ferrous ions, iron ions, hydrogen ions, lead ions, magnesium ions, manganese ions, molybdenum ions, nickel ions, potassium ions, sodium ions, strontium ions, titanium ions, uranium ions, vanadium ions, zinc ions, bromide ions, carbonate ions, chlorate ions, chloride ions, chlorite ions, dithionate ions, fluoride ions, hypochlorite ions, iodide ions, nitrate ions, nitrite ions, oxide ions, perchlorate ions, peroxide ions, phosphate ions, phosphite ions, sulfate ions, sulfide ions, sulfite ions, bicarbonate ions, hydrogen phosphate ions, phosphite hydrogen ions, bisulfate ions, bisulfite ions, carbonic acid, hydrochloric acid, nitric acid, sulfuric acid, nitrous acid, sulfurous acid, peroxy acid, phosphoric acid, ammonia, bromine, carbon dioxide, chlorine, chlorine dioxide, fluorine, hydrogen chloride, hydrogen sulfide, iodine, nitrogen dioxide, nitric oxide, oxygen, ozone, sulfur dioxide, hydrogen peroxide, polysaccharides, or combinations thereof.

[0055] In some aspects, the industrial water source to be measured contains a corrosion / scale agent that includes calcium ions. For example, the calcium ions present in the industrial water source can come from at least one source of calcium carbonate, calcium phosphate, and calcium sulfate. In some aspects, the calcium source within the industrial water source comes from calcium-containing rocks and minerals such as, but not limited to, limestone, marble, calcite, dolomite, gypsum, fluorite, and apatite.

[0056] Measuring calcium ions in the water source (especially in a real-time manner) provides more insights and opportunities to control the scale stress on equipment in industrial water. Various online methods for measuring calcium hardness are available, including but not limited to ion-selective electrodes (ISEs), fluorescence, titration, and colorimetry.

[0057] The ion-selective electrode (ISE) method uses a transducer that converts the activity of a specific ion dissolved in a solution into an electrode potential. According to the Nernst equation, the voltage theoretically depends on the logarithm of the ion activity. The advantages of a calcium ISE probe include its small and compact body, linear response to calcium concentrations up to several thousand ppm, and short response time. However, the need for frequent calibration of the calcium ISE probe in this field limits its application.

[0058] The use of fluorescence is an alternative method for measuring calcium. Some calcium reagents can be used to complex calcium ions in the water source and then emit fluorescence. Then, the fluorescence signal can be used for the measurement of calcium because its intensity is proportional to the ionic concentration of calcium. However, the fluorescence method can generally only measure hardness in a low concentration range. An automated fluorescence method for measuring magnesium, calcium, and total hardness for boiler water applications has been described in U.S. Patent No. 8,956,875, which is hereby incorporated by reference in its entirety.

[0059] In an alternative method, the titration method for calcium measurement is well-known and is commonly applied in a laboratory environment. Some commercially available online calcium analyzers are based on the titration method through an automated titration procedure. In this method, the titrant is usually a standard solution of ethylenediaminetetraacetic acid (EDTA). The calcium indicator can be any calcium complexing agent that changes color when complexed with calcium ions, such as, for example, Black T. In some aspects, if only calcium needs to be measured, potassium hydroxide will be required to precipitate magnesium ions before titration. For online analyzers, the main challenges can include complex automated equipment and procedures, unclear endpoints, and interference from other ions with the indicator.

[0060] In a further embodiment, a colorimeter method is employed. Advantageously, colorimetric measurement is a convenient and inexpensive alternative to other methods of measuring calcium. A colorimeter is a device used to test the concentration of an analyte in a solution by measuring its absorbance of light at a specific wavelength. The device can be used to find the density and / or concentration of a solution only after the device has been calibrated. In some aspects, an optical filter is used in the colorimeter to eliminate any interference from absorbance at unwanted wavelengths. In a preferred embodiment, the colorimeter method is employed to measure the calcium concentration in an industrial water source.

[0061] Absorbance, transmittance, or reflectance at a specific wavelength or wavelength range can be obtained by a spectrophotometer. A calibration curve with a known calcium concentration is typically obtained, and then the calcium concentration is calculated from the calibration curve. In some embodiments, the method of the present disclosure includes optically analyzing a solution containing industrial water to be analyzed and an indicator composition as disclosed herein (also described herein as an optical analysis solution). Using a spectrophotometer, the optical analysis solution is analyzed to measure at least one of absorbance, transmittance, or reflectance of the optical analysis solution. In some embodiments, the optical analysis solution is optically analyzed to measure the absorbance of the optical analysis solution.

[0062] Once absorbance, transmittance, or reflectance at a specific wavelength or wavelength range is collected from a sample solution, a linear calibration curve is formed. In some embodiments, the calibration curve is plotted based on a calcium reagent at a calcium concentration of 0 ppm to about 1000 ppm (as CaCO3). In an alternative embodiment, the calibration curve is formed based on the square root of the calcium concentration. In a further embodiment, the calibration curve is formed based on the absorbance of the analyzed solution at a single wavelength. In an alternative embodiment, the calibration curve is formed based on the absorbance of the analyzed solution at the ratio of two different wavelengths. In some aspects, the optical analysis is performed at one or more wavelengths. For example, the absorbance, transmittance, or reflectance of the optical analysis solution is analyzed at wavelengths in the range of 300 nm to 800 nm, such as 350 nm to 750 nm, 400 nm to 700 nm, or 500 nm to 700 nm.

[0063] In a further embodiment, the correlation coefficient can be calculated from the calibration curve. In a preferred embodiment, in order to provide a suitable calibration curve for accurately measuring the calcium concentration in a water sample, the correlation coefficient shown should be at least 0.99, with a quadratic regression. In some aspects, the indicator composition of the present disclosure provides a calibration curve with a correlation coefficient of 0.99 or greater.

[0064] With current calcium measurement methods, test protocols are often ineffective for solving high concentrations of analytes. Since many measurement protocols are optical, once a specific threshold is exceeded (such as up to and exceeding 3 absorbance units), the readings are often "off the chart" (i.e., it is so dark that further measurement cannot be achieved). This requires adding cumbersome dilution steps during the measurement process. Therefore, the methods of the present disclosure in combination with the indicator compositions described herein advantageously reduce the amount of free calcium that interacts, such that colorimetry can be used to obtain an accurate measurement of calcium. In some aspects, the use of the indicator compositions described herein results in an absorbance of 3 AU or less, 2 AU or less, or 1 AU or less. In some specific embodiments, the indicator compositions described herein are used to measure high concentrations of calcium (i.e., from about 1 ppm to about 1400 ppm and higher) without additional dilution.

[0065] In some embodiments, the amount of calcium in a water source or water sample can be present in a concentration range of at least about 1 ppm, such as at least about 5 ppm, at least about 10 ppm, at least about 50 ppm, at least about 100 ppm, at least about 300 ppm, at least about 500 ppm, or at least about 1000 ppm. In further embodiments, calcium can be present in a water source or water sample in a concentration range of from about 1 ppm to about 2000 ppm, from about 1 ppm to about 1500 ppm, from about 1 ppm to about 1400 ppm, from about 1 ppm to about 1000 ppm, from about 1 ppm to about 750 ppm, from about 1 ppm to about 500 ppm, from about 1 ppm to about 100 ppm, or from about 1 ppm to about 50 ppm. In further embodiments, calcium can be present in a water source or water sample in a concentration range of from about 100 ppm to about 2000 ppm, from about 100 ppm to about 1500 ppm, from about 100 ppm to about 1000 ppm, from about 200 ppm to about 1000 ppm, or from about 250 ppm to about 1000 ppm.

[0066] In one application, the method for measuring calcium hardness further includes extracting a water sample from the industrial water system disclosed herein, including withdrawing a sidestream from the industrial water system. The indicator composition can be added to the water sample to form an optical analysis solution. Then, the optical analysis solution can be optically analyzed using an automated on-line analysis device. In some aspects, the on-line analysis device extracts the water sample and optically analyzes the optical analysis solution at least once a day. In further embodiments, the optical analysis solution is analyzed multiple times a day. In additional embodiments, the optical analysis solution is analyzed once or more a week, or once or more a month.

[0067] In some specific embodiments, the addition of a calcium control agent to an industrial water system can be controlled or adjusted based on the determined calcium concentration in a water sample. In some aspects, the determined calcium concentration is compared with at least one calcium threshold. Based on this comparison, multiple action steps can then be carried out. In some aspects, if the calcium concentration exceeds the threshold, at least one of the following action steps can occur: (1) activating at least one calcium control agent; and (2) increasing the addition rate of the calcium control agent. In a further aspect, if the calcium concentration is less than the threshold, at least one of the following action steps can occur: (1) stopping the addition of the calcium control agent; (2) decreasing the addition rate of the calcium control agent; and (3) maintaining the amount of the calcium control agent the same.

[0068] In some examples, the indicator compositions disclosed herein can be provided directly to a water source or water sample. In some specific embodiments, the indicator composition is provided in the form of a solid composition for direct dissolution into the water source or water sample. The solid composition can be mixed with the water source or water sample, for example, by placing the solid in the source water and / or spraying the source water onto the solid. In other examples, the indicator composition can be diluted with water prior to combination with the water source or water sample to form a use solution. The combination of the composition and the source water can be mixed. The mixing can include one or more of batch, continuous, or incremental (e.g., make-up, on-demand, or monitoring) feeding.

[0069] In some applications, the pH of the water source is from 7 to 14, such as from about 7 to about 10, from about 10 to 14, from about 9 to about 11, from about 7 to about 9, or from about 7 to about 8. In some other applications, the pH of the water source is from 0 to 7, such as from about 1 to about 6, from about 5 to 6, from about 4 to about 5, from about 3 to about 4, from about 2 to about 3, or from about 1 to about 2.

[0070] In a further specific embodiment, the indicator compositions disclosed herein can be maintained in a closed system or an open system, supplemented with additional water (e.g., make-up water) from outside the system, and / or can be cycled out of the system (e.g., blowdown water) and replaced with additional water and / or indicator composition from outside the system. Such maintenance, supplementation, and removal of the water source and / or indicator composition allow the user to selectively control the concentration of the composition in the water source and / or the amount or rate of the calcium control agent in the water-containing system.

[0071] In one application, the system includes an optical sensor configured to receive a water sample containing an unknown concentration of calcium from an industrial water system. In some embodiments, the industrial water system can be an open recirculating cooling water system, such as an open recirculating cooling water system including one or more cooling towers that cool water via evaporative cooling. In other specific embodiments, the industrial water system can be a wastewater treatment system, a boiler water system, or other industrial water systems.

[0072] The system may also include at least one pump fluidly coupled to an indicator composition as described herein. In some embodiments, the indicator composition comprises a calcium indicator, a range extender, and a buffer, as described herein.

[0073] In some aspects, the system further includes a controller communicatively coupled to the optical sensor and at least one pump. In certain embodiments, the controller is configured to perform a plurality of operational steps. The controller may be configured to control the pump to produce an optical analysis solution by at least combining a water sample with the indicator composition. In further embodiments, the controller is configured to control the optical sensor to perform an optical analysis of the optical analysis solution. The optical analysis of the solution may include at least measuring the absorbance of the optical analysis solution.

[0074] In still further embodiments, the controller is configured to determine the calcium concentration in the water sample based on the optical analysis. In some aspects, the amount of calcium in a water source or water sample may be present in a concentration range of at least about 1 ppm, such as at least about 5 ppm, at least about 10 ppm, at least about 50 ppm, at least about 100 ppm, at least about 300 ppm, at least about 500 ppm, or at least about 1000 ppm. In further embodiments, calcium may be present in a water source or water sample in a concentration range of about 1 ppm to about 2000 ppm, about 1 ppm to about 1500 ppm, about 1 ppm to about 1400 ppm, about 1 ppm to about 1000 ppm, about 1 ppm to about 750 ppm, about 1 ppm to about 500 ppm, about 1 ppm to about 100 ppm, or about 1 ppm to about 50 ppm. In further embodiments, calcium may be present in a water source or water sample in a concentration range of about 100 ppm to about 2000 ppm, about 100 ppm to about 1500 ppm, about 100 ppm to about 1000 ppm, about 200 ppm to about 1000 ppm, or about 250 ppm to about 1000 ppm.

[0075] The system of the present disclosure may optionally include a calcium control agent pump. In some embodiments, the controller is communicatively coupled to the calcium control agent pump and is configured to control the addition of the calcium control agent to the industrial water system based on the determined calcium concentration in the water sample. In some aspects, the determined calcium concentration is compared with at least one calcium threshold. Based on this comparison, multiple action steps may subsequently be taken. In some aspects, if the calcium concentration exceeds the threshold, the controller is configured to implement at least one of the following action steps: (1) activate at least one calcium control agent; and (2) increase the addition rate of the calcium control agent. In a further aspect, if the calcium concentration is less than the threshold, the controller is configured to implement at least one of the following action steps: (1) stop the addition of the calcium control agent; (2) decrease the addition rate of the calcium control agent; and (3) maintain the amount of the calcium control agent the same.

[0076] All of the disclosures and patent applications in this specification show the level of ordinary skilled artisans in the field to which the present invention pertains. All publications and patent applications are incorporated herein by reference to the extent as if each individual publication or patent application is specifically and individually indicated to be incorporated by reference.

[0077] Example

[0078] Embodiments of the present invention are further defined in the following non-limiting examples. It should be understood that these examples, while disclosing certain embodiments of the present invention, are given by way of illustration only. From the above discussion and these examples, those skilled in the art can identify the basic characteristics of the present invention, and without departing from its spirit and scope, various changes and modifications can be made to the embodiments of the present invention to adapt it to various uses and conditions. Therefore, various modifications to the embodiments of the present invention will be apparent to those skilled in the art based on the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.

[0079] Example 1

[0080] The calcium hardness in water is measured colorimetrically using various formulations. Table 1 illustrates a non-limiting example of a reagent mixture for measuring calcium in a water sample. Chlorophosphonazo III (CPA III) is used as a calcium indicator to prepare the formulations provided in Table 1. Sodium citrate is added as a weak ligand to compete with CPA III for calcium ions in the water sample. This allows a smaller amount of remaining calcium ions to be available for reaction with CPA III. Citric acid is further added to the formulation as a pH buffer to maintain the pH less than 7. Subsequently, the composition is diluted with water to form a reagent mixture.

[0081] The reagent mixture of Table 1 was introduced into the calcium-containing water sample. An absorption spectrum provided by the complex of calcium in the water sample with CPA III of the reagent mixture was generated and shown in Figure 1 . A linear calibration curve for calcium between 0 ppm and 1000 ppm (as CaCO3) was formed, where the correlation coefficient was 0.9990, as shown in Figure 2 . As shown in Figure 1 , a calibration curve was formed using the absorbance ratio at wavelengths of 668 nm and 521 nm.

[0082] Table 1

[0083]

[0084]

[0085] Additional reagent formulations were prepared as shown in Table 2. The reagent formulations in Table 2 were prepared using different concentrations of CPA III, citric acid, and sodium citrate.

[0086] Table 2

[0087]

[0088] The above formulations provided in Table 2 were used to further generate a linear calibration curve under specific conditions of the water sample or solution. In the various formulations provided in Table 3 below, the reagent mixture was further combined with the water sample or solution. The water sample or solution was prepared as follows:

[0089] (1) Preparation of a stock solution containing 10,000 ppm of calcium (as CaCO3): 14.70 grams of calcium chloride dihydrate (CaCl2·2H2O) powder was added to a 1.0-liter volumetric flask. Deionized (DI) water was added to the 1000 mL mark. The powder was completely dissolved.

[0090] (2) Preparation of a stock solution containing 10,000 ppm of magnesium (as CaCO3): 20.33 grams of magnesium chloride (MgCl2·6H2O) powder was added to a 1.0-liter volumetric flask. DI water was added to the 1000 mL mark. The powder was completely dissolved.

[0091] (3) Preparation of the water sample or solution: The following stock solutions were mixed in the amounts shown in Table 3.

[0092] Table 3

[0093]

[0094]

[0095] Table 4 provides the specified conditions and the resulting correlation coefficients for water samples or solutions. As shown in Table 4, linearization of each specified formulation was measured at the ratio of two wavelengths or at a single wavelength. The linearization was further generated as the calcium concentration (CaCO3) or the square root of the calcium concentration. The correlation coefficients were further determined based on the calibration curves generated for each formulation provided in Table 4. A correlation coefficient of at least 0.99 was considered to provide sufficient accuracy. Since the absorbances of formulations S-7 and D-3 both reached the detection limit, no results were available for analysis.

[0096] Table 4

[0097]

[0098]

[0099] Additional reagent compositions were evaluated to identify linearity. The formulations and results are shown in Table 5. The data in Table 5 are based on the ratio of the absorbance at 668 nm to the absorbance at 521 nm. The results are based on the ratio itself, or as an exponential function of the ratio of the absorbance at 668 nm to the absorbance at 521 nm. In embodiments where the exponential function of the ratio was measured, the calcium concentration was plotted against the exponential function of the ratio of the absorbance at 668 nm to the absorbance at 521 nm.

[0100] Table 5

[0101]

[0102]

[0103] Example 2

[0104] The thermal stability of the indicator compositions of the present disclosure was further evaluated. In one non-limiting example, the thermal stability of the reagent formulations provided in Table 1 was evaluated at two different wavelengths and three different calcium concentrations (as CaCO3). As Figure 3 shown, stability was observed at a wavelength of 668 nm, and as Figure 4 shown, stability was also observed at a wavelength of 521 nm. Stability was measured for calcium concentrations of 0 ppm, 400 ppm, and 1000 ppm, and the period of 40 weeks was observed at a temperature of 120°F. As can be seen from Figure 3 and Figure 4 the absorbance readings remained stable throughout the 40-week period. Thus, the formulations of the present disclosure advantageously provide thermally stable compositions.

[0105] Various embodiments have been described. These and other embodiments are within the scope of the appended claims.

Claims

1. A method for measuring calcium hardness, the method comprising: extracting a water sample containing calcium from an industrial water system; adding an indicator composition to the water sample to form an optical analysis solution, the indicator composition comprising a calcium indicator, a range extender, and a buffer; optically analyzing the optical analysis solution and determining the concentration of the calcium in the water sample therefrom; and controlling the addition of a calcium control agent to the industrial water system based on the determined calcium concentration in the water sample.

2. The method according to claim 1, wherein the calcium indicator comprises chlorophosphonazo III or chlorophosphonazo I.

3. The method according to claim 1 or 2, wherein the range extender comprises at least one of the following: polycarboxylic acid, acrylate-based polymer, polymaleic anhydride (PMA), polyepoxysuccinic acid (PESA), maleic anhydride and sulfonated styrene copolymer (MA / SS), polyaspartic acid, chelating agent, and salts thereof.

4. The method according to any one of claims 1 to 3, wherein the range extender comprises a polycarboxylic acid selected from the group consisting of citric acid, 1,2,3-propane tricarboxylic acid, glucaric acid, salts thereof, and combinations thereof.

5. The method according to any one of claims 1 to 4, wherein the range extender comprises an alkali metal citrate.

6. The method according to claim 1 or 2, wherein the range extender is a polymer selected from the group consisting of polyacrylate (PAA), polymaleic anhydride (PMA), polyepoxysuccinic acid (PESA), poly(acrylate-co-acrylamide) copolymer (AA / AM), acrylic acid and hydroxypropyl acrylate copolymer (AA / HPA), acrylic acid and 2-acrylamido-2-methylpropanesulfonate copolymer (AA / AMPS), maleic anhydride and sulfonated styrene copolymer (MA / SS), acrylic acid / acrylamide / tert-butylacrylamide copolymer (AA / AM / t-BAM), acrylic acid / 2-acrylamido-2-methylpropanesulfonate / tert-butylacrylamide (AA / AMPS / t-BAM), acrylic acid / sulfonated styrene / 2-acrylamido-2-methylpropanesulfonate (AA / SS / AMPS), acrylic acid / acrylamide / aminomethylsulfonate copolymer (AA / AM / AMS), polyaspartic acid, and combinations thereof.

7. The method according to any one of claims 1 to 3, wherein the range extender is a chelating agent selected from the group consisting of L-glutamic acid N,N-diacetic acid tetrasodium salt (GLDA), iminodisuccinic acid ((N-1,2-dicarboxyethyl)-D,L-aspartic acid), ethylenediamine-N,N'-disuccinic acid (EDDS), methylglycine diacetic acid (MGDA), ethylene glycol-O,O'-bis(2-aminoethyl)-N,N,N',N'-tetraacetic acid (EGTA), disodium ethylenediamine-tetraacetate (EDTA), ODS (oxydisuccinic acid), salts thereof, and combinations thereof.

8. The method according to any one of claims 1 to 7, wherein the buffer is at least one of the following: lactic acid, acetic acid, formic acid, uric acid, malic acid, tartaric acid, phthalic acid, citric acid, oxalic acid, phosphoric acid, MES (2-(N-morpholino)ethanesulfonic acid), 4-morpholineethanesulfonic acid, sulfamic acid, benzylsulfonic acid, methylbenzylsulfonic acid, glycine, and their salts.

9. The method according to any one of claims 1 to 8, wherein the buffer comprises citric acid and an alkali metal citrate.

10. The method according to any one of claims 1 to 9, wherein the indicator composition is provided in the form of a solid composition.

11. The method according to claim 10, wherein the solid composition is provided in the form of a cast solid, an extruded, molded or shaped solid, or a pressed solid, and the pressed solid comprises pellets, blocks, tablets, powders, granules or flakes.

12. The method according to any one of claims 1 to 9, wherein the indicator composition is diluted with water to form a use solution.

13. The method according to any one of claims 1 to 12, wherein the optical analysis solution has a pH of less than 7.

0.

14. The method according to any one of claims 1 to 5 and 8 to 13, wherein the indicator composition consists essentially of chlorophosphonazo III as a calcium indicator, the range extender alkali metal citrate, the buffer citric acid and alkali metal citrate, and water to form an indicator solution, and wherein the indicator solution has a pH of less than 7.

0.

15. The method according to any one of claims 1 to 14, wherein: the calcium indicator accounts for less than about 0.5 wt% of the indicator composition; the range extender accounts for about 0.1 wt% to about 10 wt% of the indicator composition; and the buffer accounts for about 0.1 wt% to about 5 wt% of the indicator composition.

16. The method according to any one of claims 1 to 15, wherein the calcium concentration in the water sample ranges from about 1 ppm to about 50 ppm.

17. The method according to any one of claims 1 to 15, wherein the calcium concentration in the water sample is greater than about 50 ppm.

18. The method according to any one of claims 1 to 15, wherein the calcium concentration in the water sample ranges from about 250 ppm to about 1000 ppm.

19. The method according to any one of claims 1 to 18, wherein the industrial water system comprises at least one of a boiler water system, a wastewater system, and a cooling water system, and the cooling water system comprises a cooling tower that reduces the temperature of the cooling water flow by evaporative cooling.

20. The method according to any one of claims 1 to 19, wherein the calcium is present in the water sample as at least one of calcium carbonate, calcium phosphate, and calcium sulfate.

21. The method according to any one of claims 1 to 20, wherein performing an optical analysis on the optical analysis solution comprises measuring at least one of the absorbance and transmittance of the optical analysis solution.

22. The method according to any one of claims 1 to 20, wherein optically analyzing the optical analysis solution includes measuring the absorbance of the optical analysis solution.

23. The method according to any one of claims 1 to 22, wherein optically analyzing the optical analysis solution includes optically analyzing the solution at one or more wavelengths in the range of 500 nm to 700 nm.

24. The method according to any one of claims 1 to 23, wherein: extracting the water sample includes withdrawing a side stream from the industrial water system; and adding the indicator composition to the water sample and optically analyzing the optical analysis solution includes adding the indicator composition to the water sample and optically analyzing the optical analysis solution using an automated on-line analysis device.

25. The method according to claim 24, wherein the automated on-line analysis device extracts the water sample, adds the indicator composition, and optically analyzes the optical analysis solution at least once a day.

26. The method according to claim 25, wherein controlling the addition of the calcium control agent to the industrial water system based on the determined calcium concentration in the water sample includes comparing the determined calcium concentration with at least one calcium threshold; and if the determined calcium concentration exceeds the threshold, then at least one of the following is performed: starting the addition of the calcium control agent and increasing the addition rate of the calcium control agent; and if the determined calcium concentration is less than the threshold, then one of the following is performed: stopping the addition of the calcium control agent, reducing the addition rate of the calcium control agent, or maintaining the amount of the calcium control agent the same.

27. A system, the system comprising: an optical sensor configured to receive a water sample containing calcium at an unknown concentration from an industrial water system; an indicator composition comprising a calcium indicator, a range extender, and a buffer; at least one pump fluidly coupled to the indicator composition; and a controller communicatively coupled to the optical sensor and the pump, wherein the controller is configured to: control the pump to produce an optical analysis solution by at least combining the water sample with the indicator composition; control the optical sensor to optically analyze the optical analysis solution; and determine the calcium concentration in the water sample based on the optical analysis.

28. The system according to claim 27, wherein the system further comprises a calcium control agent pump, wherein the controller is communicatively coupled to the calcium control agent pump and is configured to control the addition of the calcium control agent to the industrial water system based on the determined calcium concentration in the water sample.

29. The system according to claim 28, wherein the controller is configured to control the addition of the calcium control agent to the industrial water system based on the determined calcium concentration in the water sample by at least comparing the determined calcium concentration with at least one calcium threshold; and If the determined calcium concentration exceeds the threshold, then at least one of the following is performed: start adding the calcium control agent and increase the addition rate of the calcium control agent; And If the determined calcium concentration is less than the threshold, then at least one of the following is performed: stop adding the calcium control agent, reduce the addition rate of the calcium control agent, or maintain the amount of the calcium control agent the same.

30. The system according to any one of claims 27 to 29, wherein: The calcium indicator comprises chlorophosphonazo III or chlorophosphonazo I; The range extender comprises at least one of the following: polycarboxylic acid, acrylate-based polymer, polymaleic anhydride (PMA), polyepoxysuccinic acid (PESA), maleic anhydride and sulfonated styrene copolymer (MA / SS), polyaspartic acid, chelating agent, and salts thereof; and The buffer is at least one of the following: lactic acid, acetic acid, formic acid, uric acid, malic acid, tartaric acid, phthalic acid, citric acid, oxalic acid, phosphoric acid, MES (2-(N-morpholino)ethanesulfonic acid), 4-morpholineethanesulfonic acid, sulfamic acid, benzylsulfonic acid, methylbenzylsulfonic acid, glycine, and salts thereof.

31. The system according to any one of claims 27 to 30, wherein the indicator composition consists essentially of the calcium indicator chlorophosphonazo III, the range extender alkali metal citrate, the buffer citric acid and alkali metal citrate, and water to form an indicator solution, and wherein the indicator solution has a pH less than 7.

0.

32. The system according to any one of claims 27 to 31, wherein: The calcium indicator accounts for less than 0.5 wt% of the indicator composition; The range extender ranges from about 0.1 wt% to about 10 wt% of the indicator composition; and The buffer ranges from about 0.1 wt% to about 5 wt% of the indicator composition.

33. The system according to any one of claims 27 to 32, wherein the calcium concentration in the water sample is greater than 50 ppm, such as 100 ppm to 1000 ppm.

34. The system according to any one of claims 27 to 33, wherein the industrial water system comprises at least one of a boiler water system, a wastewater system, and a cooling water system, the cooling water system comprises a cooling tower, and the cooling tower reduces the temperature of the cooling water flow by evaporative cooling.

35. The system according to any one of claims 27 to 34, wherein the controller is configured to control the optical sensor to optically analyze the optical analysis solution by at least measuring the absorbance of the optical analysis solution.

36. An indicator composition for measuring calcium concentration, the indicator composition comprising: A calcium indicator; A range extender; and A buffer, wherein the indicator composition has a use pH less than 7.

0.

37. The indicator composition according to claim 36, wherein the calcium indicator comprises chlorophosphonazo III or chlorophosphonazo I.

38. The indicator composition according to claim 36 or 37, wherein the range extender comprises at least one of the following: polycarboxylic acids, acrylate-based polymers, poly(maleic anhydride) (PMA), poly(epoxysuccinic acid) (PESA), maleic anhydride and sulfonated styrene copolymer (MA / SS), polyaspartic acid, chelating agents, and salts thereof.

39. The indicator composition according to any one of claims 36 to 38, wherein the range extender comprises polycarboxylic acids selected from the group consisting of citric acid, 1,2,3 - propane tricarboxylic acid, glucaric acid, salts thereof, and combinations thereof.

40. The indicator composition according to any one of claims 36 to 38, wherein the range extender is a polymer selected from the group consisting of polyacrylate (PAA), poly(maleic anhydride) (PMA), poly(epoxysuccinic acid) (PESA), poly(acrylate - co - acrylamide) copolymer (AA / AM), acrylic acid and hydroxypropyl acrylate copolymer (AA / HPA), acrylic acid and 2 - acrylamido - 2 - methylpropanesulfonate copolymer (AA / AMPS), maleic anhydride and sulfonated styrene copolymer (MA / SS), acrylic acid / acrylamide / tert - butylacrylamide copolymer (AA / AM / t - BAM), acrylic acid / 2 - acrylamido - 2 - methylpropanesulfonate / tert - butylacrylamide (AA / AMPS / t - BAM), acrylic acid / sulfonated styrene / 2 - acrylamido - 2 - methylpropanesulfonate (AA / SS / AMPS), acrylic acid / acrylamide / aminomethylsulfonic acid ester copolymer (AA / AM / AMS), polyaspartic acid, salts thereof, and combinations thereof.

41. The indicator composition according to claim 36 or 37, wherein the range extender is a chelating agent selected from the group consisting of tetrasodium L - glutamate N,N - diacetate (GLDA), iminodisuccinic acid ((N - 1,2 - dicarboxyethyl) - D,L - aspartic acid), ethylenediamine - N,N'- disuccinic acid (EDDS), methylglycine diacetic acid (MGDA), ethylene glycol - O,O'- bis(2 - aminoethyl) - N,N,N′,N′ - tetraacetic acid (EGTA), disodium ethylenediamine - tetraacetate (EDTA), ODS (oxydisuccinic acid), salts thereof, and combinations thereof.

42. The indicator composition according to any one of claims 36 to 41, wherein the buffer is at least one of the following: lactic acid, acetic acid, formic acid, uric acid, malic acid, tartaric acid, phthalic acid, citric acid, oxalic acid, phosphoric acid, MES (2 - (N - morpholino)ethanesulfonic acid), 4 - morpholinoethanesulfonic acid, sulfamic acid, benzylsulfonic acid, methylbenzylsulfonic acid, glycine, and salts thereof.

43. The indicator composition according to any one of claims 36 to 42, wherein the range extender comprises alkali metal citrate, and / or wherein the buffer comprises citric acid and alkali metal citrate.

44. An indicator composition according to any one of claims 36 to 40 and 42 to 43, wherein the indicator composition consists essentially of the calcium indicator chlorophosphonazo III, the range extender alkali metal citrate, the buffer citric acid and alkali metal citrate, and water.

45. An indicator composition according to any one of claims 36 to 44, wherein: the calcium indicator accounts for less than 0.5 wt% of the indicator composition; the range extender ranges from about 0.1 wt% to about 10 wt% of the indicator composition; and the buffer ranges from about 0.1 wt% to about 5 wt% of the indicator composition.

46. An indicator composition according to claim 36, wherein the indicator composition is provided in the form of a solid composition.

47. An indicator composition according to any one of claims 36 to 46, wherein the solid composition is provided in the form of a cast solid, an extruded solid, a molded solid, or a shaped solid or a pressed solid, and the pressed solid includes pellets, blocks, tablets, powders, granules, or flakes.

48. An indicator composition according to any one of claims 36 to 47, wherein the indicator composition is diluted with water to form a use solution.

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