Early warning method for instantaneous foaming of urea hydrolysate and application

Abstract

The invention discloses an early warning method for instantaneous foaming of urea hydrolysate. The early warning method comprises the following steps: S1, carrying out a catalytic hydrolysis reaction of a urea aqueous solution in a hydrolyzer; s2, in the hydrolysis reaction process, reaction liquid in the hydrolyzer is taken for biuret concentration detection; and S3, when the concentration of the biuret reaches the critical concentration, early warning is carried out, a valve is opened for pollution discharge, and when the concentration of the biuret is reduced to be lower than the critical concentration, the valve is closed for continuous reaction until the reaction is completed. According to the method, the concentration of the biuret is measured by adopting a liquid chromatography-mass spectrometry method, accurate detection of the concentration of the biuret can be realized, and effective early warning of instantaneous foaming is realized. The hydrolyzer solution can be continuously detected, when it is found that the content of polycondensate in the hydrolyzer solution is increased, early warning is conducted in time, pollution discharge is conducted in time, and the situation that the hydrolyzer solution is instantaneously and violently bubbled and uncontrollable is avoided.

Description

Technical Field

[0001] The invention relates to the field of testing by means of measuring the chemical or physical properties of materials, and in particular to an early warning method for instantaneous foaming of urea hydrolyzate and its application. Background Art

[0002] Most coal-fired power generation units use the selective catalytic reduction denitrification process. The urea aqueous solution decomposes in the hydrolyzer under a certain temperature and catalyst to generate carbon dioxide, water vapor and ammonia. During the reaction, the solution in the urea hydrolyzer foams violently and the liquid level rises rapidly. The foam overflows with the urea hydrolysis product gas, causing the product gas pipeline and the ammonia injection pipeline to be blocked. In severe cases, it will also affect the stable operation of the denitrification system, resulting in NO x Exceeding the emission standard. By analyzing the cause of violent foaming, an early warning can be given before the foaming occurs to avoid uncontrollable system reactions. Therefore, it is very important to develop an early warning method for instantaneous foaming of urea hydrolyzate.

[0003] Chinese invention patent CN117074445A discloses a method for determining the content of biuret in urea, which comprises mixing a urea sample with a known content of biuret and a pure phase biuret reagent, preparing multiple gradient reference samples, preparing a working curve, scanning the sample to be tested with an X-ray diffractometer and obtaining the X-ray diffraction spectrum of the sample to be tested, calculating the peak integral intensity of the strongest peak of biuret in the sample to be tested after deducting the background, and accurately determining the content of biuret in urea, without dissolving the sample and separating the compounds, but not being able to monitor the content of biuret in real time. Chinese invention patent CN118010717B discloses a method for detecting biuret in a urea aqueous solution of a nitrogen oxide reducing agent, preparing intercalated hydrotalcite, preparing an alkaline filler, preparing a reference color card, and testing. The detection reagent is resistant to storage, has low detection cost, short detection time, and is simple to operate. It can reduce the influence of the pH value of potassium sodium tartrate on the result, but the reference color card is used for control detection, and the accuracy is not high. Summary of the invention

[0004] In order to develop an early warning method for instantaneous foaming of urea hydrolyzate with high accuracy and sensitivity, the first aspect of the present invention provides an early warning method for instantaneous foaming of urea hydrolyzate, comprising the following steps:

[0005] S1 performs a catalytic hydrolysis reaction of urea aqueous solution in a hydrolyzer;

[0006] S2 takes the reaction liquid in the hydrolyzer to detect the biuret concentration during the hydrolysis reaction;

[0007] S3 When the concentration of biuret reaches the critical concentration, the valve is opened to discharge sewage as an early warning. When the concentration of biuret drops below the critical concentration, the valve is closed to continue the reaction until the reaction is completed.

[0008] The inventors found during the experiment that in the catalytic reduction denitrification process used in coal-fired power generation units, urea is catalytically hydrolyzed to produce ammonia, producing carbon dioxide, water vapor and ammonia. The urea in the hydrolyzer does not react completely, producing polycondensates, changing the surface tension and viscosity of the solution, and providing conditions for foaming. The catalyst phosphate generates pyrophosphate ions in the reaction, and the intermediate product of the hydrolysis reaction, ammonium carbamate, corrodes the equipment to produce metal ions. The pyrophosphate ions and metal ions are complexed to produce complexes that make the solution black. At the same time, the corrosion produces tiny metal oxide particles as the core to form a large number of bubbles and hinder the bubble rupture, which will cause the solution in the hydrolyzer to foam violently, affecting the stable operation of the denitrification system and causing NO x Emissions exceed the standard. Therefore, by monitoring the content of biuret, a byproduct of the urea catalytic reaction, early warning of severe foaming in the hydrolyzer can be achieved. In the denitration system, the monitoring of biuret content is affected by solid impurities such as urea, intermediate product ammonium carbamate, catalyst phosphate pyrophosphate ammonium, and metal oxides, so detection is somewhat difficult.

[0009] When urea is heated to a higher temperature, water molecules or ammonia molecules are lost between urea molecules, and condensation forms compounds with larger molecular weight. When these polymers with larger molecular weight accumulate to a certain extent in the urea solution, they will significantly change the physical properties of the solution such as surface tension and viscosity, thereby causing the solution to foam. Ammonium carbamate is an intermediate product of the urea catalytic reaction. Ammonium carbamate will corrode the heating coil and other parts, forming oxides of metals such as Fe and Cr. These metal oxides are tiny particles suspended in the solution, and as the reaction continues, these particles will continue to enrich. These particles can serve as the core for the formation of bubbles, making it easier for air or other gases to adhere to their surface and form bubbles. And prevent the bubbles from merging or bursting, thereby extending the life of the bubbles and making them easier to maintain.

[0010] As a preferred embodiment, the biuret concentration detection is to determine the biuret concentration by liquid chromatography-mass spectrometry.

[0011] As a preferred embodiment, the chromatographic column of the liquid chromatography is an ACQUITY UPLC BEH C18 chromatographic column, and the column temperature of the chromatographic column is 30-40°C.

[0012] As a preferred embodiment, the specifications of the chromatographic column are 2.1×150 mm, 1.7 μm; and the column temperature of the chromatographic column is 35° C.

[0013] As a preferred embodiment, the desolvation gas flow rate of the mass spectrometer is 700-100 L / h, and the desolvation gas temperature of the mass spectrometer is 300-500°C.

[0014] As a preferred implementation manner, the desolvation gas flow rate of the mass spectrometer is 800 L / h, and the desolvation gas temperature of the mass spectrometer is 400°C.

[0015] As a preferred implementation manner, the cone gas flow rate of the mass spectrometer is 50 L / Hr; the capillary voltage (ES+) of the mass spectrometer is 3 kV; and the ion source temperature of the mass spectrometer is 150°C.

[0016] As a preferred embodiment, the liquid chromatography comprises mobile phase A and mobile phase B, the mobile phase A is formic acid aqueous solution, and the mobile phase B is acetonitrile.

[0017] As a preferred embodiment, the mass concentration of the formic acid aqueous solution is 0.1-0.3%. Preferably, the mass concentration of the formic acid aqueous solution is 0.1%.

[0018] As a preferred embodiment, the flow rate of the mobile phase in the liquid chromatography is 0.1-0.5 mL / min.

[0019] As a preferred embodiment, the flow rate of the mobile phase in the liquid chromatography is 0.2 mL / min.

[0020] As a preferred embodiment, gradient elution is adopted in the liquid chromatography, and the conditions of the gradient elution are as follows: 0 min, 90 vol% mobile phase A, 10 vol% mobile phase B; 1 min, 90 vol% mobile phase A, 10 vol% mobile phase B; 1.5 min, 10 vol% mobile phase A, 90 vol% mobile phase B; 3.5 min, 10 vol% mobile phase A, 90 vol% mobile phase B; 4 min, 90 vol% mobile phase A, 10 vol% mobile phase B; 6 min, 90 vol% mobile phase A, 10 vol% mobile phase B.

[0021] Weigh 25 mg of biuret standard into a 25 mL volumetric flask, dilute to volume with ultrapure water, mix well, and prepare a 1000 mg / L standard solution.

[0022] Preparation of standard solution: Use the mixed standard stock solution as the mother solution, dilute it with ultrapure water to make 0.01mg / L, 0.02mg / L, 0.05mg / L, 0.1mg / L, 0.2mg / L, 0.5mg / L, 1mg / L, 2mg / L, 5mg / L, and 10mg / L standard solutions.

[0023] Establish a standard curve and calculate the biuret content in the sample according to formula (1). The blank value must be deducted from the calculation result:

[0024]

[0025] Where:

[0026] X i ——the content of biuret in the sample, in %;

[0027] C——The concentration of the target substance in the test solution obtained according to the standard curve, in mg / L;

[0028] C 0 ——The concentration of the target substance in the blank obtained according to the standard curve, in mg / L;

[0029] V——the volume of sample solution, in mL;

[0030] f——dilution multiple;

[0031] m – mass of the sample, in g.

[0032] As a preferred embodiment, the linear curve range of the biuret concentration detection is 0.00988 mg / L-9.884 mg / L.

[0033] As a preferred embodiment, the linear curve of biuret in the concentration range of 0.00988 mg / L-0.198 mg / L is Y=41246.5X+6.13408, R 2 =0.9994; the linear curve of biuret in the concentration range of 0.198mg / L-9.884mg / L is Y=-1197.5X 2 +37691.3X+1100.37,R 2 =0.9996.

[0034] Take 0.5g of the reaction solution in the hydrolyzer into a 25mL volumetric flask, add ultrapure water to dissolve, dilute to scale, and mix well. Then take 1mL of the mixed sample solution into a 100mL volumetric flask, add water to dilute to scale, mix well, and use it as the test solution.

[0035] As a preferred embodiment, the critical concentration of biuret is 50-500 mg / L.

[0036] A second aspect of the present invention provides an application of an early warning method for instantaneous foaming of a urea hydrolyzate, which is applied to a selective catalytic reduction denitrification process of a coal-fired power generation unit.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The method for early warning of instantaneous foaming of urea hydrolyzate of the present invention adopts liquid chromatography-mass spectrometry to determine the concentration of biuret, which can achieve accurate detection of the concentration of biuret and achieve effective early warning of instantaneous foaming.

[0039] (2) The early warning method for instantaneous foaming of urea hydrolyzate of the present invention adopts a spiked detection method during sample detection, subtracts background interference, has good separation, and has no obvious interference with the test of biuret.

[0040] (3) The early warning method for instantaneous foaming of urea hydrolyzate of the present invention has a high signal-to-noise ratio in a relatively low concentration of biuret standard solution, meeting the requirements of instrument detection limit and quantification limit.

[0041] (4) The early warning method for instantaneous foaming of urea hydrolyzate of the present invention has good precision in testing the content of biuret in the sample, with the RSD of the measurement result being less than 10% and high accuracy, and can be used to measure the content of biuret in the sample.

[0042] (5) The early warning method for instantaneous foaming of urea hydrolyzate of the present invention can continuously detect the hydrolyzer solution. When it is found that the content of polycondensate in the hydrolyzer solution increases, timely early warning and sewage discharge are carried out in time to avoid the situation where the hydrolyzer solution instantly foams violently and uncontrollably. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is the test spectrum of the process blank solution during the specificity verification process;

[0044] Figure 2 This is the test spectrum of 0.2 mg / L biuret standard solution during the specificity verification process;

[0045] Figure 3 This is the test spectrum of the sample spike solution during the specificity verification process;

[0046] Figure 4 This is the test spectrum of 0.01 mg / L biuret standard solution during the detection limit verification process;

[0047] Figure 5 This is the test spectrum of 0.05 mg / L biuret standard solution in the process of quantitative limit verification;

[0048] Figure 6 It is a linear curve of biuret in the concentration range of 0.00988mg / L-0.198mg / L;

[0049] Figure 7 It is a linear curve of biuret in the concentration range of 0.198 mg / L-9.884 mg / L. DETAILED DESCRIPTION

[0050] Example 1

[0051] A method for early warning of instantaneous foaming of urea hydrolyzate comprises the following steps:

[0052] S1 performs a catalytic hydrolysis reaction of urea aqueous solution in a hydrolyzer;

[0053] S2 takes the reaction liquid in the hydrolyzer to detect the biuret concentration during the hydrolysis reaction;

[0054] S3 When the concentration of biuret reaches the critical concentration, the valve is opened to discharge sewage as an early warning. When the concentration of biuret drops below the critical concentration, the valve is closed to continue the reaction until the reaction is completed.

[0055] The biuret concentration detection is to measure the biuret concentration by liquid chromatography-mass spectrometry.

[0056] The chromatographic column of the liquid chromatography is an ACQUITY UPLC BEH C18 chromatographic column, the specifications of the chromatographic column are 2.1×150 mm, 1.7 μm; the column temperature of the chromatographic column is 35° C.

[0057] The desolvation gas flow rate of the mass spectrometer is 800 L / h, and the desolvation gas temperature of the mass spectrometer is 400°C.

[0058] The cone gas flow rate of the mass spectrometer is 50 L / Hr; the capillary voltage (ES+) of the mass spectrometer is 3 kV; and the ion source temperature of the mass spectrometer is 150°C.

[0059] The liquid chromatography comprises a mobile phase A and a mobile phase B, wherein the mobile phase A is a formic acid aqueous solution, and the mobile phase B is acetonitrile, and the mass concentration of the formic acid aqueous solution is 0.1%.

[0060] The flow rate of the mobile phase in the liquid chromatography was 0.2 mL / min.

[0061] Gradient elution is adopted in the liquid chromatography, and the conditions of the gradient elution are as follows: 0 min, 90 vol% mobile phase A, 10 vol% mobile phase B; 1 min, 90 vol% mobile phase A, 10 vol% mobile phase B; 1.5 min, 10 vol% mobile phase A, 90 vol% mobile phase B; 3.5 min, 10 vol% mobile phase A, 90 vol% mobile phase B; 4 min, 90 vol% mobile phase A, 10 vol% mobile phase B; 6 min, 90 vol% mobile phase A, 10 vol% mobile phase B.

[0062] Weigh 25 mg of biuret standard into a 25 mL volumetric flask, dilute to volume with ultrapure water, mix well, and prepare a 1000 mg / L standard solution.

[0063] Preparation of standard solution: Use the mixed standard stock solution as the mother solution, dilute it with ultrapure water to make 0.01mg / L, 0.02mg / L, 0.05mg / L, 0.1mg / L, 0.2mg / L, 0.5mg / L, 1mg / L, 2mg / L, 5mg / L, and 10mg / L standard solutions.

[0064] Establish a standard curve and calculate the biuret content in the sample according to formula (1). The blank value must be deducted from the calculation result:

[0065]

[0066] Where:

[0067] X i ——the content of biuret in the sample, in %;

[0068] C——The concentration of the target substance in the test solution obtained according to the standard curve, in mg / L;

[0069] C 0 ——The concentration of the target substance in the blank obtained according to the standard curve, in mg / L;

[0070] V——the volume of sample solution, in mL;

[0071] f——dilution multiple;

[0072] m – mass of the sample, in g.

[0073] The linear curve of biuret in the concentration range of 0.00988mg / L-0.198mg / L is Y=41246.5X+6.13408, R 2 =0.9994, see Figure 6 The linear curve of biuret in the concentration range of 0.198mg / L-9.884mg / L is Y=-1197.5X 2 +37691.3X+1100.37,R 2 =0.9996, see Figure 7 .

[0074] Take 0.5g of the reaction solution in the hydrolyzer into a 25mL volumetric flask, add ultrapure water to dissolve, dilute to scale, and mix well. Then take 1mL of the mixed sample solution into a 100mL volumetric flask, add water to dilute to scale, mix well, and use it as the test solution for testing.

[0075] Performance Testing

[0076] 1. Specificity verification: Prepare a blank solution (ultrapure water), 0.2 mg / L biuret standard solution, the test solution + 0.2 mg / L biuret standard solution, and determine the concentration of biuret by liquid chromatography-mass spectrometry. The test spectrum is shown in Figure 1-3 .

[0077] The results showed that the target substances had good separation and the process blank had no obvious interference with the test of biuret, which met the method validation evaluation criteria.

[0078] 2. Detection limit and quantification limit verification: Prepare 0.01 mg / L biuret standard solution and 0.05 mg / L biuret standard solution, and determine the concentration of biuret by liquid chromatography-mass spectrometry. The test spectrum is shown in Figure 4-5 .

[0079] Results: The signal-to-noise ratio of the biuret chromatographic peak in the 0.01 mg / L standard solution was S / N=21.21, and the signal-to-noise ratio S / N>3, which met the instrument detection limit requirements.

[0080] The signal-to-noise ratio S / N of the biuret chromatographic peak in the 0.05 mg / L standard solution is 127.93, and the signal-to-noise ratio S / N>10, which meets the instrument quantification limit requirement.

[0081] The method detection limit was calculated by instrument detection limit × dilution factor (×50) to be 0.5 mg / kg, and the method quantification limit was calculated by instrument quantification limit × dilution factor (×50) to be 2.5 mg / kg.

[0082] 3. System suitability verification: Prepare 0.2 mg / L biuret standard solution, determine the concentration of biuret by liquid chromatography-mass spectrometry, repeat the determination 6 times, calculate the relative standard deviation of the concentration of 6 standards, and evaluate the system suitability. The test results are shown in Table 1.

[0083] Table 1

[0084]

[0085] Conclusion: This method can be used to test the content of biuret in samples. The relative standard deviation of 0.2 mg / L standard solution after repeated determination for 6 times is 1.49%, which meets the method validation evaluation criteria.

[0086] 4. Precision verification: Six 0.2 mg / L biuret standard solutions were prepared in parallel, and the concentration of biuret was determined by liquid chromatography-mass spectrometry. The relative standard deviation of the concentration of the six samples was calculated to evaluate the precision. The test results are shown in Table 2.

[0087] Table 2

[0088]

[0089] Conclusion: This method has good precision in testing the content of biuret in samples, and the RSD of the determination result is less than 10%, which meets the evaluation criteria for method validation.

[0090] 5. Accuracy verification: add three kinds of standard solutions of low, medium and high concentrations to the test solution respectively, that is, add 50%, 100% and 200% of the biuret standard solution relative to the concentration of the test solution to obtain the sample spiked solutions of low, medium and high concentration levels, and determine the concentration of biuret by liquid chromatography-mass spectrometry. Calculate the recovery rate of each concentration sample spiked solution and evaluate the accuracy. The test results are shown in Table 3.

[0091] Table 3

[0092]

[0093] Note: Recovery rate % = measured spiked amount / theoretical spiked amount × 100%

[0094] Actual spiked amount = actual measured value of spiked sample - sample value. The results show that this method has good accuracy in testing the biuret content in samples, with a recovery rate ranging from 80% to 120%, and a relative standard deviation of the recovery rate of <10%, which meets the method validation evaluation criteria.

[0095] The experimental conclusions are shown in Table 4.

[0096] Table 4

[0097]

[0098]

Claims

1. A method for early warning of instantaneous foaming of urea hydrolyzate, characterized in that: The following steps are involved: S1 performs a catalytic hydrolysis reaction of urea aqueous solution in a hydrolyzer; S2 takes the reaction liquid in the hydrolyzer to detect the biuret concentration during the hydrolysis reaction; S3 When the concentration of biuret reaches the critical concentration, an alarm is sounded and the valve is opened to discharge sewage. When the concentration of biuret drops below the critical concentration, the valve is closed and the reaction continues until the reaction is completed.

2. The early warning method for instantaneous foaming of urea hydrolyzate according to claim 1, characterized in that: The biuret concentration detection is to measure the biuret concentration by liquid chromatography-mass spectrometry.

3. The early warning method for instantaneous foaming of urea hydrolyzate according to claim 2, characterized in that: The chromatographic column of the liquid chromatography is an ACQUITY UPLC BEH C18 chromatographic column, and the column temperature of the chromatographic column is 30-40°C.

4. The early warning method for instantaneous foaming of urea hydrolyzate according to claim 2, characterized in that: The desolvation gas flow rate of the mass spectrometer is 700-100 L / h, and the desolvation gas temperature of the liquid chromatography is 300-500°C.

5. The early warning method for instantaneous foaming of urea hydrolyzate according to claim 2, characterized in that: The mobile phase in the liquid chromatography comprises a mobile phase A and a mobile phase B, wherein the mobile phase A is a formic acid aqueous solution and the mobile phase B is acetonitrile.

6. The early warning method for instantaneous foaming of urea hydrolyzate according to claim 5, characterized in that: The flow rate of the mobile phase in the liquid chromatography is 0.1-0.5 mL / min.

7. The early warning method for instantaneous foaming of urea hydrolyzate according to claim 5, characterized in that: Gradient elution is adopted in the liquid chromatography, and the conditions of the gradient elution are as follows: 0 min, 90 vol% mobile phase A, 10 vol% mobile phase B; 1 min, 90 vol% mobile phase A, 10 vol% mobile phase B; 1.5 min, 10 vol% mobile phase A, 90 vol% mobile phase B; 3.5 min, 10 vol% mobile phase A, 90 vol% mobile phase B; 4 min, 90 vol% mobile phase A, 10 vol% mobile phase B; 6 min, 90 vol% mobile phase A, 10 vol% mobile phase B.

8. The early warning method for instantaneous foaming of urea hydrolyzate according to claim 1, characterized in that: The linear curve range of the biuret concentration detection is 0.00988 mg / L-9.884 mg / L.

9. The early warning method for instantaneous foaming of urea hydrolyzate according to claim 1, characterized in that: The critical concentration of biuret is 50-500 mg / L.

10. An application of the early warning method for instantaneous foaming of urea hydrolyzate according to any one of claims 1 to 9, characterized in that: Applied to the selective catalytic reduction denitrification process of coal-fired power generation units.

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