A method for measuring total iron content in EDTA chemical cleaning fluid for power plant boilers

Abstract

This invention discloses a method for measuring the total iron content in EDTA chemical cleaning solution for power plant boilers, relating to the field of chemical cleaning technology for power plant boilers. The method includes: injecting the EDTA cleaning solution into a UV reactor and diluting it with demineralized water; adjusting the pH of the solution in the UV reactor to acidic using hydrochloric acid and ammonia, then adding persulfate solution, heating the reaction, and allowing complete digestion; transferring the solution from the UV reactor to a reaction flask, adding sulfosalicylic acid as an indicator, and titrating with EDTA standard solution until the purple-red color changes to pale yellow as the endpoint, recording the volume of EDTA consumed, and calculating the total iron content in the chemical cleaning solution. This invention features high accuracy, simple operation, and fast detection speed.

Description

Technical Field

[0001] This invention relates to the field of chemical cleaning technology for power plant boilers, and in particular to a method for measuring the total iron content in EDTA chemical cleaning solution for power plant boilers. Background Technology

[0002] EDTA is a highly efficient complexing agent that can form stable complexes with various metal ions such as iron, copper, calcium, and magnesium. It has advantages such as strong descaling ability, low sludge production during cleaning, and minimal metal corrosion, and is widely used in the chemical cleaning of high-parameter, large-capacity units. During chemical cleaning, the cleaning endpoint is reached when the total iron content in the cleaning solution reaches equilibrium and the monitoring tube is thoroughly cleaned. DL / T-794-2012, "Guidelines for Chemical Cleaning of Boilers in Thermal Power Plants," stipulates that the total iron content in the cleaning solution should be measured every 30 minutes.

[0003] In volumetric analysis, total iron is typically determined using sulfosalicylic acid as an indicator and titrated with a standard EDTA solution. Therefore, the Fe in the EDTA washing solution... 2+ Fe 3+ Before testing, EDTA and Fe need to be mixed. 2+ Fe 3+ Based on the different separation methods, the methods for measuring the total iron content in EDTA chemical cleaning solutions can be divided into traditional pyrolysis method, acidification separation and detection method, and alkaliification separation and detection method.

[0004] Traditional pyrolysis methods use ammonium persulfate as an oxidant to oxidize EDTA in the cleaning solution to CO2. Then, sulfosalicylic acid is used as an indicator, and a standard EDTA titration solution is used to determine the Fe content in the chemical cleaning solution. 3+ Titration was performed to obtain the total iron content in the chemical cleaning solution. To ensure the EDTA oxidation rate, the solution needed to be heated to boiling for more than 5 minutes, but the EDTA oxidation rate was still low (40%–70%), resulting in a lower measured total iron content.

[0005] The acidification separation detection method utilizes the property that EDTA is sparingly soluble in acid. After acidifying the EDTA washing solution with concentrated sulfuric acid, EDTA precipitates out in crystal form, thus achieving separation of EDTA and Fe. 2+ Fe 3+ The complexation separation is performed. The total iron content can be obtained by subsequent titration of the supernatant of the acidified washing solution. The key to the acidification separation method is the control of the pH value, which requires the use of highly hazardous concentrated sulfuric acid. This method often results in incomplete EDTA separation (generally less than 50%), leading to lower total iron content results.

[0006] Alkali separation and detection method utilizes Fe 3+ The characteristic of easily forming Fe(OH)3 precipitate under alkaline conditions will cause Fe in the cleaning solution to be removed. 2+Oxidized to Fe 3+ Then, NaOH was added to adjust the pH of the cleaning solution to around 12, so that the Fe in the cleaning solution... 2+ Fe 3+ A precipitate is formed and separated from EDTA by decomposition. The total iron content can be obtained by subsequent Fe(OH)3 filtration, dissolution, and titration. This method has high accuracy, but it involves many steps and is difficult to implement rapidly on-site during cleaning, making it difficult to meet the requirement of DL / T-794-2012 "Guidelines for Chemical Cleaning of Boilers in Thermal Power Plants" to detect the total iron content in the cleaning solution every 30 minutes. Summary of the Invention

[0007] In order to solve the problems of the existing detection methods, the purpose of this invention is to provide a method for measuring the total iron content in EDTA chemical cleaning fluid of power plant boilers that is accurate, simple to operate, and fast to detect.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for measuring the total iron content in EDTA chemical cleaning fluid for power plant boilers, comprising:

[0010] EDTA cleaning solution from the power plant boiler is injected into the ultraviolet reactor and diluted with demineralized water.

[0011] The pH of the solution in the UV reactor was adjusted to acidic using hydrochloric acid and ammonia, then persulfate solution was added, and the reaction was heated to ensure complete digestion.

[0012] The solution in the UV reactor was transferred to a reaction flask, and sulfosalicylic acid was added as an indicator. The solution was titrated with EDTA standard until the purple-red color turned pale yellow, and the volume of EDTA consumed was recorded. The total iron content in the chemical cleaning solution was then calculated.

[0013] As a further improvement of the present invention, the total volume ratio of the EDTA cleaning solution for power plant boilers to the demineralized water solution is 1:20.

[0014] As a further improvement of the present invention, adjusting the pH value to acidic means adjusting the pH value to 2-3.

[0015] As a further improvement of the present invention, the pH value is adjusted using a 1:1 mixture of ammonia and a 1:4 mixture of HCl.

[0016] As a further improvement of the present invention, the heating reaction is carried out at 80°C to 90°C.

[0017] As a further improvement of the present invention, the volume percentage of sulfosalicylic acid is 10%.

[0018] As a further improvement of the present invention, the volume ratio of EDTA cleaning solution to sulfosalicylic acid for power plant boilers is 5:(1-3).

[0019] As a further improvement of the present invention, the ultraviolet reactor includes an ultraviolet lamp, a heating and temperature control module, and quartz glass, with the ultraviolet radiation source placed directly inside the reactor.

[0020] As a further improvement of the present invention, the wavelengths used in the ultraviolet lamp are 185nm and 254nm.

[0021] As a further improvement of the present invention, the persulfate is ammonium persulfate, potassium persulfate, or sodium persulfate.

[0022] As a further improvement of the present invention, the persulfate is 25% ammonium persulfate by mass.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] This invention replaces traditional pyrolysis, acidification separation and detection, and alkaliification separation and detection methods with ultraviolet (UV) wet (persulfate) oxidation. Through UV wet (persulfate) oxidation, EDTA in the EDTA chemical cleaning solution is fully oxidized to CO2, thus achieving the separation of EDTA and Fe in the cleaning solution. 2+ Fe 3+ The complex was dissolved, and then, using sulfosalicylic acid as an indicator, Fe in the chemical cleaning solution was titrated with EDTA standard solution. 3+ Titration was performed to obtain the total iron content in the chemical cleaning solution. This invention features high accuracy, simple operation, and fast detection speed. Specific advantages are as follows:

[0025] 1) The oxidation rate of EDTA is higher than that of traditional pyrolysis, reaching over 90%; the oxidation time and temperature of EDTA are lower than those of traditional pyrolysis, resulting in higher accuracy of test results and more convenient operation.

[0026] 2) The accuracy of the measurement results is higher than that of the acidification separation detection method, and it does not use concentrated sulfuric acid, thus improving operability and safety.

[0027] 3) The accuracy of the measurement results is close to that of the alkali separation detection method, but the detection time is significantly shortened. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a simplified flowchart of a method for measuring the total iron content in an EDTA chemical cleaning solution for power plant boilers according to the present invention. Detailed Implementation

[0030] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0031] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0032] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0033] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0034] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0035] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, and c can be single or multiple.

[0036] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0037] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0038] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0039] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0040] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0041] This invention provides a method with high accuracy, simple operation, and fast detection speed. For example... Figure 1 As shown, this invention specifically provides a method for measuring the total iron content in EDTA chemical cleaning fluid for power plant boilers, including:

[0042] EDTA cleaning solution from the power plant boiler is injected into the ultraviolet reactor and diluted with demineralized water.

[0043] The pH of the solution in the UV reactor was adjusted to acidic using hydrochloric acid and ammonia, then persulfate solution was added, and the reaction was heated to ensure complete digestion.

[0044] The solution in the UV reactor was transferred to a reaction flask, and sulfosalicylic acid was added as an indicator. The solution was titrated with EDTA standard until the purple-red color turned pale yellow, and the volume of EDTA consumed was recorded. The total iron content in the chemical cleaning solution was then calculated.

[0045] After fully oxidizing EDTA in the EDTA cleaning solution to CO2 using a UV-wet (persulfate) oxidation method, sulfosalicylic acid is used as an indicator, and a standard EDTA titration solution is used to titrate the Fe in the chemical cleaning solution. 3+ Titration was performed to obtain the total iron content in the chemical cleaning solution.

[0046] More specifically, the process includes: accurately measuring 5 mL of EDTA cleaning solution for power plant boilers and injecting it into a UV reactor, then diluting it with deionized water to 100 mL; adjusting the pH of the solution in the UV reactor to approximately 2-3 using hydrochloric acid and ammonia, then adding 3-5 mL of 25% persulfate solution, heating to 80-90°C, and digesting for 3 minutes. The solution in the UV reactor is then transferred to an Erlenmeyer flask, and while still hot, 1-3 mL of 10% sulfosalicylic acid is added as an indicator. The solution is titrated with EDTA standard solution until the purple-red color changes to pale yellow, and the volume of EDTA consumed is recorded. The total iron content in the chemical cleaning solution can then be calculated.

[0047] The aforementioned ultraviolet reactor mainly consists of ultraviolet lamps, heating and temperature control modules, and quartz glass. The ultraviolet radiation source is placed directly inside the reactor, and the wavelengths used for the ultraviolet lamps are 185nm and 254nm, ensuring that the ultraviolet reactor has high radiation density and effective decomposition capability.

[0048] The present invention will be further described in detail below with reference to specific embodiments.

[0049] Iron-containing (FeSO4·H2O added) simulated EDTA cleaning solutions were accurately prepared using disodium oxalate (DICO3) to achieve EDTA concentrations of 6.0% and total iron contents of 3000 mg / L, 5000 mg / L, and 10000 mg / L. The pH of the cleaning solution was adjusted to approximately 9.0 using NaOH. The total iron content in the simulated cleaning solutions was determined using conventional pyrolysis, alkaline separation and detection, acidification separation and detection, and ultraviolet (UV)-wet (persulfate) oxidation methods, respectively. The specific procedures are as follows:

[0050] Comparative Example 1

[0051] (1) Traditional pyrolysis method: Accurately measure 5 mL of EDTA cleaning solution for power plant boilers and inject it into a 250 mL Erlenmeyer flask. Dilute it to 100 mL with deionized water. Adjust the pH of the solution in the Erlenmeyer flask to 2.5 with hydrochloric acid. Then add 10 mL of ammonium persulfate with a mass percentage of 25%. Heat and boil for 5 minutes. While hot, add 1 mL of 10% sulfosalicylic acid as an indicator. Titrate the solution with EDTA standard solution until the purple-red color turns into a pale yellow color. Record the volume of EDTA consumed. The total iron content in the chemical cleaning solution can be calculated.

[0052] Comparative Example 2

[0053] (2) Alkali separation and detection method: Accurately measure 5 mL of EDTA cleaning solution from the power plant boiler and inject it into a 200 mL beaker. Add 30 mL of hot deionized water and 5 mL of 10% ammonium persulfate solution, then add 15 mL of 10% NaOH solution. Heat to boiling, then add 2 mL of H2O2 dropwise. After slightly cooling, filter using quantitative filter paper by tilting, and rinse the beaker with a small amount of deionized water, also adding the water to the filter paper. After filtration, rinse the precipitate 2-3 times with a small amount of deionized water. Dissolve the precipitate with 1:1 HCl and then use hot water... Wash the filter paper alternately with deionized water and hydrochloric acid until it is completely free of yellow color. Transfer this solution to a 100mL volumetric flask, dilute to the mark, and transfer 20mL of the solution to a 250mL Erlenmeyer flask. Add 80mL of deionized water. Adjust the pH to 2-3 with 1:1 ammonia and 1:4 HCl. Add 1mL of 10% sulfosalicylic acid as an indicator. Titrate with EDTA standard solution until the purple-red color turns pale yellow. Record the volume of EDTA consumed. The total iron content in the chemical cleaning solution can be calculated.

[0054] Comparative Example 3

[0055] (3) Acidification separation detection method: Take 50-100 mL of the boiler EDTA cleaning solution and pour it into a 300 mL beaker. Adjust the pH value to 0.5-0.8 with concentrated sulfuric acid (measured with a pH meter), cool to room temperature, and allow it to precipitate completely. Accurately pipette 5 mL of the supernatant into a 250 mL conical flask, add 100 mL of deionized water, and then add 5 mL of 20% ammonium persulfate solution. Heat to boiling for 5 min and cool to room temperature. Adjust the pH value to 2-3 with 1:1 ammonia water and 1:4 HCl. Add 1 mL of 10% sulfosalicylic acid as an indicator. Titrate with EDTA standard solution until the purple-red color turns pale yellow as the endpoint. Record the volume of EDTA consumed. The total iron content in the chemical cleaning solution can be calculated.

[0056] Example 1

[0057] (4) Ultraviolet (UV) wet (persulfate) oxidation method: Accurately measure 5 mL of EDTA cleaning solution for power plant boilers and inject it into the UV reactor. Dilute it to 100 mL with deionized water. Adjust the pH of the solution in the UV reactor to 2.5 with hydrochloric acid. Then add 3 mL of 25% ammonium persulfate solution by mass. Heat to 80°C and digest for 3 minutes. Transfer the solution in the UV reactor to an Erlenmeyer flask. Add 1 mL of 10% sulfosalicylic acid as an indicator while hot. Titrate with EDTA standard solution until the purple-red color turns pale yellow as the endpoint. Record the volume of EDTA consumed. The total iron content in the chemical cleaning solution can be calculated.

[0058] The measurement results and measurement errors of the above four methods are shown in Table 1.

[0059] Table 1 Comparison of accuracy of different measurement methods

[0060]

[0061]

[0062] Example 2

[0063] Accurately measure 5 mL of EDTA cleaning solution for power plant boilers and inject it into the UV reactor. Dilute with deionized water to 100 mL. Adjust the pH of the solution in the UV reactor to about 2-3 using hydrochloric acid and ammonia. Then add 4 mL of 20% potassium persulfate solution (by mass). Heat to 85°C and digest for 4 minutes. Transfer the solution in the UV reactor to an Erlenmeyer flask. While hot, add 1.5 mL of 11% sulfosalicylic acid as an indicator. Titrate with EDTA standard solution until the purple-red color turns pale yellow. Record the volume of EDTA consumed. The total iron content in the chemical cleaning solution can be calculated.

[0064] Example 3

[0065] Accurately measure 5 mL of EDTA cleaning solution for power plant boilers and inject it into the UV reactor. Dilute with deionized water to 100 mL. Adjust the pH of the solution in the UV reactor to about 3 using hydrochloric acid and ammonia. Then add 5 mL of 23% sodium persulfate solution, heat to 90°C, and digest for 3.5 minutes. Transfer the solution in the UV reactor to an Erlenmeyer flask, and add 3 mL of 10% sulfosalicylic acid as an indicator while hot. Titrate with EDTA standard solution until the purple-red color turns pale yellow as the endpoint. Record the volume of EDTA consumed. The total iron content in the chemical cleaning solution can be calculated.

[0066] Example 4

[0067] Accurately measure 5 mL of EDTA cleaning solution for power plant boilers and inject it into the UV reactor. Dilute with deionized water to 100 mL. Adjust the pH of the solution in the UV reactor to about 2-3 using hydrochloric acid and ammonia. Then add 4.5 mL of 26% persulfate solution, heat to 88°C, and digest for 4 minutes. Transfer the solution in the UV reactor to an Erlenmeyer flask, and add 2.5 mL of 12% sulfosalicylic acid as an indicator while hot. Titrate with EDTA standard solution until the purple-red color turns pale yellow as the endpoint. Record the volume of EDTA consumed. The total iron content in the chemical cleaning solution can be calculated.

[0068] All articles and references disclosed above, including patent applications and publications, are incorporated herein by reference for various purposes. The term “substantially constitutes…” used to describe a combination should include the identified elements, components, parts, or steps, as well as other elements, components, parts, or steps that do not substantially affect the essential novelty of the combination. The use of the terms “comprising” or “including” to describe combinations of elements, components, parts, or steps herein also contemplates embodiments substantially constituted by such elements, components, parts, or steps. The use of the term “may” herein is intended to indicate that any described attribute included by “may” is optional.

[0069] Multiple elements, components, parts, or steps can be provided by a single integrated element, component, part, or step. Alternatively, a single integrated element, component, part, or step can be divided into multiple separate elements, components, parts, or steps. The use of "a" or "an" to describe an element, component, part, or step does not imply the exclusion of other elements, components, parts, or steps.

[0070] It should be understood that the above description is for illustrative purposes and not for limitation. Many embodiments and applications beyond the provided examples will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this teaching should not be determined by reference to the above description, but rather by reference to the foregoing claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the applicant has not considered that subject matter as part of the disclosed inventive subject matter.

Claims

1. A method for measuring the total iron content in an EDTA chemical cleaning solution for a power plant boiler, characterized by, The method comprises the following steps: The power station boiler EDTA cleaning solution is injected into a UV reactor, and desalted water is added for dilution; The pH value of the solution in the UV reactor is adjusted to be acidic by using hydrochloric acid and ammonia water, then a persulfate solution is added, and the solution is heated to be fully digested; The solution in the UV reactor is transferred into a reaction bottle, sulfosalicylic acid is added as an indicator, EDTA standard titration solution is added dropwise until the color changes from purple red to light yellow, the volume of the consumed EDTA is recorded, and the total iron content in the chemical cleaning solution is calculated; The heating is performed at 80-90 DEG C. The UV reactor comprises a UV lamp, a heating and temperature control module, and quartz glass, and the UV radiation source is directly placed in the reactor; the wavelength of the UV lamp is 185 nm and 254 nm.

2. The method for measuring the total iron content in the EDTA chemical cleaning solution for power plant boilers according to claim 1, characterized in that, The total volume ratio of the power station boiler EDTA cleaning solution to the desalted water after dilution is 1:

20.

3. The method for measuring the total iron content in the EDTA chemical cleaning solution for power plant boilers according to claim 1, characterized in that, The pH value is adjusted to be 2-3.

4. The method for measuring the total iron content in the EDTA chemical cleaning solution for power plant boilers according to claim 1, characterized in that, The pH value is adjusted by using 1:1 ammonia water and 1:4 HCl.

5. The method for measuring the total iron content in the EDTA chemical cleaning solution for power plant boilers according to claim 1, characterized in that, The volume percentage of the sulfosalicylic acid is 10%.

6. The method for measuring the total iron content in the EDTA chemical cleaning solution for power plant boilers according to claim 1, characterized in that, The volume ratio of the power station boiler EDTA cleaning solution to the sulfosalicylic acid is 5: (1-3).

7. The method for measuring the total iron content in the EDTA chemical cleaning solution for power plant boilers according to claim 1, characterized in that, The persulfate is ammonium persulfate, potassium persulfate or sodium persulfate.

8. The method for measuring the total iron content in the EDTA chemical cleaning solution for power plant boilers according to claim 1, characterized in that, The mass percentage of the ammonium persulfate is 25%.

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