Method for measuring total EDTA concentration in EDTA chemical cleaning solution and rinsing solution of power station boiler having high fe content

Abstract

Disclosed is a method for measuring total EDTA concentration in an EDTA chemical cleaning solution and a rinsing solution of a power station boiler having high Fe content, relating to the technical field of power station boiler chemical cleaning. The method comprises: adding an oxidizing agent to a power station boiler EDTA cleaning solution or rinsing solution having a total iron content ≥300 mg / L, heating to boiling, adding a masking agent, breaking down an original EDTA-Fe complex, and performing titration on the de-complexed EDTA using a Ca2+ standard solution, using a hydroxynaphthol blue indicator; and, on the basis of the titration result, obtaining the total concentration of EDTA in the chemical cleaning solution and the rinsing solution. The present invention solves the problems of complicated and time-consuming operation steps and poor result accuracy in conventional alkalization separation methods, and the method is characterized by high accuracy of detection results, simple operation, and high detection speed.

Description

Method for measuring total EDTA concentration in EDTA chemical cleaning fluid and rinse fluid of power plant boilers with high Fe content Technical Field

[0001] The invention relates to the technical field of chemical cleaning of power station boilers, in particular to an EDTA chemical cleaning liquid for power station boilers with a high Fe content and a method for measuring the total EDTA concentration in the rinsing liquid. Background Art

[0002] EDTA is a highly effective chelating agent that forms stable complexes with various metal ions, including iron, copper, calcium, and magnesium. It offers strong descaling capabilities, produces minimal sediment during cleaning, and exhibits minimal metal corrosion. It is widely used in chemical cleaning of high-parameter, high-capacity units. The total EDTA concentration in chemical cleaning fluids is a critical process parameter, and its accurate measurement is crucial for process control.

[0003] DL / T-794-2012 "Guidelines for Chemical Cleaning of Boilers in Thermal Power Plants" uses alkaline precipitation method to remove Fe 2+ 、Fe 3+ After separation, EDTA is titrated. 2+ 、Fe 3+ Separation efficiency requires boiling, repeated precipitation, filtration and other operations, which are tedious and time-consuming, and Fe 2+ 、Fe 3+ Incomplete separation results in a lower measured value of the total EDTA concentration.

[0004] Therefore, it is necessary to provide a method with high detection accuracy, simple operation and fast detection speed.

[0005] Summary of the Invention

[0006] In order to solve the problems existing in the above-mentioned existing detection methods, the purpose of the present invention is to provide a method for measuring the total EDTA concentration in EDTA chemical cleaning liquid and rinse liquid of high-Fe power plant boilers with high accuracy, simple operation and fast detection speed.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for measuring the total EDTA concentration in an EDTA chemical cleaning solution and a rinsing solution of a power station boiler with a high Fe content, comprising:

[0009] Add oxidant to the EDTA cleaning solution or rinse solution of power station boiler with total iron content ≥300mg / L and heat to boiling. Then add masking agent to destroy the original EDTA-Fe complex. The decomplexed EDTA is detected by CaCl2 solution with hydroxynaphthol blue as indicator. 2+The standard solution is titrated, and the total EDTA concentration in the chemical cleaning solution and the rinsing solution is obtained according to the titration results.

[0010] As a further improvement of the present invention, a dilution process is performed before adding the masking agent to the EDTA cleaning solution or rinsing solution of the power station boiler:

[0011] Take the EDTA cleaning solution or rinsing solution of the power station boiler and dilute it with desalted water. The volume ratio of the EDTA cleaning solution or rinsing solution of the power station boiler to the desalted water is 1:100.

[0012] As a further improvement of the present invention, the volume ratio of the oxidant to the masking agent is 1:10.

[0013] As a further improvement of the present invention, after adding the masking agent, the method further comprises:

[0014] Adjust the pH value to 12.5-13.0 with NaOH solution.

[0015] As a further improvement of the present invention, the Ca 2+ The standard solution is standard calcium acetate monohydrate solution, and the titration endpoint is when the solution changes from blue to red.

[0016] As a further improvement of the present invention, the total EDTA concentration in the chemical cleaning solution and the rinsing solution is obtained according to the titration results, including:

[0017] Record Ca at the end of titration 2+ The volume V of the standard solution can be used to calculate the total EDTA concentration in the cleaning solution.

[0018] As a further improvement of the present invention, the oxidant is ammonium persulfate solution, hydrogen peroxide or nitric acid solution.

[0019] As a further improvement of the present invention, the masking agent is a triethanolamine solution.

[0020] As a further improvement of the present invention, the hydroxynaphthol blue indicator comprises hydroxynaphthol blue and sodium chloride, and the mass ratio of hydroxynaphthol blue to sodium chloride is 1:100.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The present invention destroys the original EDTA-Fe complex by adding a masking agent, and the decomplexed EDTA is used as a hydroxy naphthol blue indicator and Ca 2+ The standard solution is titrated to obtain the total EDTA concentration in the cleaning solution and the rinsing solution. The present invention solves the problem of the traditional alkalinization separation method with complicated operation steps and poor accuracy of results, and has the characteristics of high accuracy of detection results, simple operation and fast detection speed. At the same time, it solves the problem of using acid chrome blue K as an indicator and using Zn 2+When titrating with the standard solution, the total Fe content in the cleaning solution and the rinsing solution is too high, which makes it difficult to judge the endpoint of the indicator and easy to recolor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0024] FIG1 is a flow chart of a method for measuring the total EDTA concentration in an EDTA chemical cleaning solution for a power station boiler provided by the present invention. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0026] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0027] 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 refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, c can be single or multiple.

[0028] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can 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 the present application.

[0029] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0030] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass described in the examples of this application may be a mass unit known in the chemical industry, such as μg, mg, g, kg, etc.

[0031] When measuring the total EDTA concentration in chemical cleaning solutions or rinse solutions with high Fe content, the following issues need to be addressed when using direct titration:

[0032] 1) Masking agents can mask a large amount of Fe in the solution 2+ 、Fe 3+ , and under the experimental conditions, Zn in the standard solution 2+ or Ca 2+ No masking effect;

[0033] 2) The selected oxidant has no effect on the indicator.

[0034] 3) Fe in solution 2+ 、Fe 3+ When the content is high, the acid chrome blue K indicator is prone to recolor when approaching the titration endpoint, and the recolor interval is long, which affects the judgment of the titration endpoint and the test speed.

[0035] 4) When EDTA is used for rinsing and passivation, although Fe 2+ 、Fe 3+ The content is not high, but due to the small total concentration of EDTA, when using acid chrome blue K indicator, there are still problems such as difficulty in judging the titration end point and easy color reversion.

[0036] The object of the present invention is to provide a method for measuring the total EDTA concentration in EDTA chemical cleaning solutions and rinse solutions for power station boilers with a high Fe content, comprising:

[0037] S1, adding an oxidant to the EDTA cleaning solution or rinse solution of the power plant boiler and heating it to boiling, and then adding a masking agent to destroy the original EDTA-Fe complex;

[0038] S2, decomplexed EDTA with hydroxynaphthol blue as indicator, and Ca 2+ The standard solution is titrated;

[0039] S3, obtaining the total EDTA concentration in the chemical cleaning solution and the rinsing solution according to the titration results.

[0040] The operation steps of the present invention have the characteristics of high detection result accuracy, simple operation and fast detection speed.

[0041] The principle is: by adding a masking agent, the original EDTA-Fe complex is destroyed, and the decomplexed EDTA is used as an indicator of hydroxynaphthol blue and Ca 2+ The standard solution is titrated to obtain the total EDTA concentration in the chemical cleaning solution and rinse solution.

[0042] At the same time, the solution was solved by using acid chrome blue K as indicator and Zn 2+ When titrating with the standard solution, the total Fe content in the cleaning solution and the rinsing solution is too high, which makes it difficult to judge the endpoint of the indicator and easy to recolor.

[0043] Exemplarily, a dilution process is performed before adding the masking agent to the EDTA cleaning solution or rinse solution of the power plant boiler:

[0044] Take a power plant boiler EDTA cleaning solution or rinse solution and dilute it with demineralized water. The volume ratio of the power plant boiler EDTA cleaning solution or rinse solution to demineralized water is 1:100. The dosage can be adjusted according to actual needs. For example, units such as mL or L can be used.

[0045] Wherein, as an optional solution, the masking agent is triethanolamine solution. The volume ratio of the oxidant to the masking agent is 1:10. 2+ The standard solution is standard calcium acetate monohydrate solution, and the titration endpoint is when the solution changes from blue to red.

[0046] Preferably, after adding the masking agent, the method further comprises: adjusting the pH value to 12.5-13.0 with a NaOH solution. The pH value may be 12.5, 12.6, 12.8, 13.0, etc.

[0047] Exemplarily, the total EDTA concentration in the chemical cleaning solution and the rinse solution is obtained according to the titration results, including:

[0048] Record Ca at the end of titration 2+ The volume V of the standard solution can be used to calculate the total EDTA concentration in the cleaning solution.

[0049] The oxidant is ammonium persulfate solution, hydrogen peroxide or nitric acid solution.

[0050] As an alternative, a method for measuring the total EDTA concentration in EDTA chemical cleaning solutions and rinse solutions for power plant boilers with high Fe content includes the following steps:

[0051] 1) Accurately measure 1 mL of EDTA cleaning solution or rinse solution for power plant boilers and inject it into a conical flask. Dilute it to 100 mL with deionized water.

[0052] 2) Add 1 mL of oxidant and 10 mL of masking agent, adjust the pH to 12.5-13.0 with NaOH solution, add 3-6 drops of hydroxynaphthol blue indicator, and titrate with standard calcium acetate monohydrate solution. The titration endpoint is when the solution changes from blue to red.

[0053] 3) Record the volume V of the calcium acetate monohydrate standard solution and calculate the total EDTA concentration in the cleaning solution.

[0054] The oxidant is a 10% by mass concentration ammonium persulfate solution, a 30% by mass concentration hydrogen peroxide solution, or a 20% by mass concentration nitric acid solution; the masking agent is a 30% by mass concentration triethanolamine solution, and the NaOH solution has a mass concentration of 50%; the hydroxynaphthol blue indicator is prepared by mixing and grinding hydroxynaphthol blue and sodium chloride in a ratio of 1:100.

[0055] The present invention will be further described in detail below with reference to specific embodiments.

[0056] Use disodium oxalate tetraacetate to accurately prepare an EDTA simulated cleaning solution with a total mass concentration of 8.0% and a total iron content of 6000mg / L, 8000mg / L, and 12000mg / L (add FeSO4·H2O), and use NaOH to adjust the pH value of the cleaning solution to about 9.0. At the same time, prepare an EDTA simulated rinse with a total mass concentration of 1.0% and a total iron content of 300mg / L, 500mg / L, and 1000mg / L (add FeSO4·H2O), and use NaOH to adjust the pH value of the cleaning solution to about 5.5. The above-mentioned simulated cleaning solution and rinse solution are respectively measured using the traditional alkaline precipitation method, the acid chrome blue K indicator method, and the method provided by the present invention. The specific operation method is as follows:

[0057] (1) Traditional alkaline precipitation method: Accurately measure 2 mL of EDTA cleaning solution or rinsing solution from a power plant boiler and inject it into a 250 mL conical flask. Dilute to 100 mL with deionized water. Adjust the pH value to 13.0-13.5 with 10 mol / L NaOH solution to precipitate iron. Heat to a boil and filter with medium-speed filter paper. Keep the filtrate. Wash the precipitate with deionized water 2-3 times and discard it. Adjust the pH value of the filtrate to below 2.0 with 1+1 HCl solution. Adjust the pH value to 13.0-13.5 with 10 mol / L NaOH solution. Repeat the precipitation and filtration operation 2-3 times until the filtrate is clear and transparent. Adjust the pH value of the remaining filtrate to about 10.0 with 1+1 HCl solution, add 5-10 mL of ammonia-ammonium chloride buffer solution, add 3-6 drops of chrome black T indicator, and use Zn2+ Titrate the standard solution until it turns red and record the Zn 2+ The volume V of the standard solution can be calculated to obtain the total EDTA concentration.

[0058] (2) Acid chrome blue K indicator method: Accurately measure 1 mL of EDTA cleaning solution or rinsing solution of power station boiler and inject it into a conical flask, dilute it to 100 mL with deionized water; add 1 mL of oxidant, heat to boiling, add 10 mL of masking agent, 20 mL of ammonia-ammonium chloride buffer solution (pH value about 10), add 3 to 6 drops of acid chrome blue K indicator, and use Zn 2+ The standard solution is titrated, and the solution changes from blue to purple-red and does not change color within 1 minute, which is the titration end point. Record the Zn 2+ The volume V of the standard solution can be calculated to obtain the total EDTA concentration in the cleaning solution. The oxidant is a 10% ammonium persulfate solution; the masking agent is a mixture of a 30% triethanolamine solution and a 20% ethylenediamine solution in a volume ratio of 1:1.

[0059] (3) The method provided by the present invention comprises the following steps: accurately measuring 1 mL of EDTA cleaning solution or rinse solution of a power plant boiler and injecting it into a conical flask, diluting it to 100 mL with deionized water; adding 1 mL of an oxidizing agent and 10 mL of a masking agent, adjusting the pH to 12.5-13.0 with a NaOH solution, adding 3-6 drops of a hydroxynaphthol blue indicator, and titrating with a standard calcium acetate monohydrate solution. The titration endpoint is when the solution changes from blue to red; recording the volume V of the calcium acetate monohydrate standard solution, and calculating the total EDTA concentration in the cleaning solution. The oxidizing agent is a 10% ammonium persulfate solution, a 30% hydrogen peroxide solution, or a 20% nitric acid solution; the masking agent is a 30% triethanolamine solution, and the concentration of the NaOH solution is 50%; the hydroxynaphthol blue indicator is prepared by mixing and grinding hydroxynaphthol blue and sodium chloride in a ratio of 1:100.

[0060] The measurement results and measurement errors of the above three methods are shown in Tables 1 and 2.

[0061] Table 1 Comparison of the accuracy of EDTA cleaning solution using different determination methods

[0062] Table 2 Comparison of the accuracy of EDTA rinse solution using different determination methods

[0063] Based on the above comparison, it can be concluded that the method of the present invention has the following advantages:

[0064] 1) The accuracy of the measurement results is higher than that of the alkaline precipitation method in DL / T-794-2012 "Guidelines for Chemical Cleaning of Boilers in Thermal Power Plants", and the detection time is significantly shortened.

[0065] 2) The selected masking agent has a great influence on Fe 2+ 、Fe 3+ Has a strong shielding effect on Ca 2+ No masking effect, solving the problem of low titration results.

[0066] 3) Hydroxynaphthol blue indicator can be used for Fe 2+ 、Fe 3+ The determination of total EDTA concentration in cleaning solutions and rinse solutions with high EDTA content is easy to determine with no color reversion, which improves the accuracy and speed of the determination.

[0067] All articles and references disclosed above, including patent applications and publications, are incorporated herein by reference for all purposes. The term "consisting essentially of..." when describing a combination should include the identified elements, ingredients, components or steps and other elements, ingredients, components or steps that do not materially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe a combination of elements, ingredients, components or steps herein also contemplates embodiments consisting essentially of these elements, ingredients, components or steps. By using the term "may", it is intended to indicate that any attribute described as "may" be optional.

[0068] Multiple elements, ingredients, parts or steps can be provided by a single integrated element, ingredient, part or step. Alternatively, a single integrated element, ingredient, part or step can be divided into separate multiple elements, ingredients, parts or steps. The disclosure of "a" or "an" to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

[0069] It should be understood that the above description is for illustrative purposes only and is not intended to be limiting. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but rather with reference to the preceding claims and the full scope of equivalents to which such claims are entitled. For the purpose of completeness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the preceding claims is not a disclaimer of such subject matter, nor should it be considered that the applicants did not consider such subject matter to be part of the disclosed inventive subject matter.

Claims

1. A method for measuring the total EDTA concentration in EDTA chemical cleaning liquid and rinsing liquid of a power plant boiler with high Fe content, characterized in that: include: Add an oxidant to the EDTA cleaning solution or rinse solution of a power plant boiler with a total iron content of ≥300 mg / L, heat it to boiling, then add a masking agent to destroy the original EDTA-Fe complex, and use hydroxynaphthol blue as an indicator to detect the decomplexed EDTA with Ca 2+ The standard solution is titrated, and the total EDTA concentration in the chemical cleaning solution and the rinsing solution is obtained according to the titration results.

2. The method for measuring the total EDTA concentration in the EDTA chemical cleaning liquid and the rinsing liquid of a power station boiler with a high Fe content according to claim 1, characterized in that: Before adding the masking agent to the EDTA cleaning solution or rinsing solution of the power station boiler, a dilution process is also carried out: Take EDTA cleaning solution or rinsing solution from power station boiler and dilute it with desalted water. The volume ratio of EDTA cleaning solution or rinsing solution to desalted water is 1:

100.

3. The method for measuring the total EDTA concentration in the EDTA chemical cleaning liquid and the rinsing liquid of a power station boiler with a high Fe content according to claim 1, characterized in that: The volume ratio of oxidant to masking agent is 1:

10.

4. The method for measuring the total EDTA concentration in the EDTA chemical cleaning liquid and the rinsing liquid of a power station boiler with a high Fe content according to claim 1, characterized in that: After adding the masking agent, it also includes: The pH value was adjusted to 12.5-13.0 with NaOH solution.

5. The method for measuring the total EDTA concentration in the EDTA chemical cleaning liquid and the rinsing liquid of a power station boiler with a high Fe content according to claim 1, characterized in that: The Ca 2+ The standard solution is standard calcium acetate monohydrate solution, and the titration endpoint is when the solution changes from blue to red.

6. The method for measuring the total EDTA concentration in the EDTA chemical cleaning liquid and the rinsing liquid of a power station boiler with a high Fe content according to claim 1, characterized in that: The total EDTA concentration in the chemical cleaning solution and the rinsing solution is obtained according to the titration results, including: Record Ca at the end of the titration 2+ The volume V of the standard solution can be used to calculate the total EDTA concentration in the cleaning solution.

7. The method for measuring the total EDTA concentration in the EDTA chemical cleaning liquid and rinsing liquid of a power station boiler with a high Fe content according to claim 1, characterized in that: The oxidant is ammonium persulfate solution, hydrogen peroxide or nitric acid solution.

8. The method for measuring the total EDTA concentration in the EDTA chemical cleaning liquid and the rinsing liquid of a power station boiler with a high Fe content according to claim 1, characterized in that: The masking agent is triethanolamine solution.

9. The method for measuring the total EDTA concentration in the EDTA chemical cleaning liquid and the rinsing liquid of a power station boiler with a high Fe content according to claim 1, characterized in that: The hydroxynaphthol blue indicator comprises hydroxynaphthol blue and sodium chloride, and the mass ratio of hydroxynaphthol blue to sodium chloride is 1:100.

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