Fogdrop testing method for demister of wet desulphurization system

Abstract

The invention discloses a fog drop testing method for a demister of a wet desulphurization system. Compared with the prior art, the method has the advantages that the change of physical properties and chemical properties of the desulfurized slurry passing through the demister is considered, solid components in the fog drops are directly obtained through weighing, and the weight of water in the fog drops is calculated according to the tested magnesium ions, so that the specific weight and concentration of the fog drops are obtained. According to the improved fogdrop testing method, an ultrasonic or acid soaking cylinder and ultrasonic pretreatment mode and two-step weighing of solid components are adopted, the testing steps are more precise and detailed, and slurry data measurement is more accurate; meanwhile, the solid content of the slurry does not need to be measured, operation steps are reduced, influences caused by introduction of the solid content of the slurry into calculation are reduced, and the measured fog drop content is more accurate.

Description

Technical Field

[0001] This invention relates to a method for testing mist droplets that can be used in demisters of wet limestone-gypsum desulfurization systems. Compared with existing testing methods, the improved mist droplet testing steps result in more accurate mist droplet content, and the invention relates to the field of wet desulfurization. Background Technology

[0002] Demisters are an important component of wet desulfurization systems. They are desulfurization and environmental protection devices that capture mist and slurry droplets in flue gas using principles such as impact, inertia, Brownian motion, and centrifugal force. Currently, the term "demister" generally refers to traditional mechanical demisters such as plate, tubular, and ridge-type demisters. Electrostatic precipitators, also known as wet electrostatic precipitators, also have a demisting effect. Demisters are typically located at the top of the absorption tower. After flue gas enters the absorption tower and reacts counter-currently with the atomized slurry sprayed by the slurry circulation pump, the wet flue gas carrying slurry droplets flows through the demister at a certain speed. As the droplets pass through the demister blades of different shapes and sizes, they are captured on the blades due to the impact, inertia, Brownian motion, and centrifugal force generated by the droplet movement. The droplets converge to form a water flow, which falls into the slurry pool of the absorption tower under gravity, achieving gas-liquid separation. This ensures that the flue gas flowing through the demister meets the demisting requirements before being discharged. A typical demister's demisting effect is an outlet droplet concentration of <75 mg / m³. 3 The ultra-low efficiency demister, after modification, is designed to achieve an outlet droplet concentration of <20 mg / m³. 3Currently, the principle for testing the slurry droplet concentration in wet desulfurization flue gas is the magnesium ion tracer method. This involves collecting droplets from the flue gas using a droplet collector and collecting the slurry from the operating desulfurization tower. In the laboratory, the magnesium ion and solid content of the desulfurization slurry, as well as the magnesium ion content in the droplet collector, are measured. Using magnesium ions as tracer ions, the droplet content in the flue gas is calculated (Appendix A of DLT 1483-2015, Test Methods for Chemical and Physical Properties of Limestone-Gypsum Wet Flue Gas Desulfurization Systems, and Appendix D of GB / T 21508-2008, Test Methods for Performance of Coal-fired Flue Gas Desulfurization Equipment). However, the standard method assumes that the physical and chemical properties of the slurry in the desulfurization tower and the droplet collector remain unchanged. Furthermore, a review of relevant literature and industry discussions confirms that droplet testing is conducted according to the standard method, which implicitly assumes that the chemical and physical properties of the slurry droplets (mist) remain unchanged. This differs from the situation encountered in actual testing. After testing, visual observation showed that the moisture content in the droplet collector was significantly higher than the solid content. According to standards, this would generally be assumed to be caused by condensate in the flue gas, as the droplet and slurry components were still the same. However, our analysis revealed that this was also closely related to changes in the physicochemical properties of the droplets. We found that the chemical and physical properties of the desulfurization slurry droplets (mist) changed after passing through the demister. The main reasons are as follows: 1. Normally, after the desulfurization tower slurry is agitated, it foams. Part of this foam is discharged through the overflow pipe, while the other part, being lighter, is carried by the flue gas and becomes mist droplets. Compared to the desulfurization slurry, the foam contains a higher proportion of impurities such as silicon, aluminum, iron, and magnesium (Tables 1 and 2), leading to differences in the chemical composition of the slurry and mist droplets. Furthermore, the composition of the carried foam changes further after impact with the demister. 2. The demister collects mist droplets using principles such as impact, inertia, Brownian motion, and centrifugal force. Heavier and larger droplets are more easily collected. However, after the raw flue gas is sprayed with the desulfurization slurry, the flue gas temperature drops from 100℃ to 50℃, and some of the slurry... The moisture in the slurry evaporates and is carried away by the flue gas. Some of the slurry is also directly carried away by the flue gas. Compared to the water carried by evaporation, the directly carried slurry is heavier and easier to capture. This results in a difference in the composition of the droplets compared to the slurry. (Water has a lower density than slurry, and the evaporated water has a larger contact area with the flue gas, resulting in greater buoyancy and easier ascent. Therefore, water escapes more easily than slurry. When facing a demister, the escaping slurry, due to its larger mass, experiences greater inertial force, gravity, and centrifugal force, making it easier to capture. Water, with its smaller mass, experiences less inertial force, gravity, and centrifugal force, making it easier to escape. Therefore, the droplets contain more water than the slurry.) Furthermore, even without demister capture, the moisture content in the slurry carried by evaporation due to the decrease in flue gas temperature is much higher than that in the desulfurization slurry carried by the flue gas. This indicates that the composition of the droplets in the flue gas is different from that in the desulfurization slurry. Therefore, the default conditions in the standard test are biased, leading to inaccurate slurry droplet results from the standard test.Therefore, the purpose of this invention is to propose a new method for testing droplets in the demister of a wet desulfurization system.

[0003] Table 1. Composition Analysis of Desulfurization Slurry and Foam from Power Plant A

[0004] Testing items unit Desulfurization tower slurry Overflowing foam Loss on ignition ％ 21.53 29.35 <![CDATA[SO3]]> ％ 28.4 21.73 CaO ％ 20.51 13.16 <![CDATA[SiO2]]> ％ 13.98 11.29 MgO ％ 6.44 10.60 <![CDATA[Al2O3]]> ％ 5.39 2.37 <![CDATA[Fe2O3]]> ％ 1.83 7.57 <![CDATA[K2O]]> ％ 0.85 0.69 <![CDATA[Na2O]]> ％ 0.63 2.12 <![CDATA[P2O5]]> ％ 0.27 0.21 <![CDATA[TiO2]]> ％ 0.16 0.77

[0005] Table 2B: Composition Analysis of Power Plant Desulfurization Slurry and Foam

[0006] Testing items unit Desulfurization tower slurry Overflowing foam CaO ％ 39.06 12.59 MgO ％ 10.12 18.5 <![CDATA[SiO2]]> ％ 12.70 20.94 <![CDATA[Al2O3]]> ％ 3.33 5.47 <![CDATA[Fe2O3]]> ％ 1.26 28.52 Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a new method for testing mist droplets in demisters of wet desulfurization systems.

[0008] To achieve the above objectives, the technical solution of the present invention is to provide a method for testing mist droplets in a wet desulfurization system demister, comprising the following steps:

[0009] (1) Demister treatment:

[0010] Prepare a droplet collector, thoroughly clean and dry it, cool it, weigh it using a 0.01% balance, record it as M1, and store it in a sealed container for later use.

[0011] (2) On-site testing:

[0012] Secure the prepared droplet collector to the sampling head with the matching bayonet, and assemble the sampling smoke gun. Prepare a standard Pitot tube, hygrometer, and RTD or flue gas temperature probe. Connect the sampling smoke gun, standard Pitot tube, hygrometer, RTD or flue gas temperature probe to the main unit of the flue gas analyzer. Then, insert the sampling smoke gun, standard Pitot tube, hygrometer, and RTD or flue gas temperature probe into the flue to the same depth. Position the Pitot tube's positive pressure test port and the droplet collector directly in the direction of flue gas flow. The Pitot tube measures the flue gas velocity and pressure, the droplet collector collects droplets from the flue gas, the hygrometer measures the flue gas humidity, and the RTD or flue gas temperature probe measures the flue gas temperature. The flue gas analyzer ensures isokinetic sampling. The droplet collector sampling volume V is calculated based on the flow velocity measured by the Pitot tube. Using the measured flue gas pressure, humidity, and temperature, convert the actual operating condition wet basis sampling volume V to the standard operating condition dry basis sampling volume V. sd ; grid sampling was carried out on the flue gas cross section of the flue, and two parallel samples were collected from one flue; after sampling, the two ends of the droplet collector were sealed with sealing film, the outer wall was cleaned and dried, and the droplet collector was sealed and stored, and marked, which constitutes one droplet sample; when measuring droplets, the desulfurization tower slurry was sampled at the same time.

[0013] (3) Droplet sample preparation:

[0014] After the field test, remove the sealing films from both ends of the droplet collector, ensuring no droplets remain on the films. Rinse the inside of the sealing films with demineralized water, then rinse the inner wall of the collector with demineralized water. Filter all the rinsed solution with ashless filter paper and collect it in a volumetric flask, making up to volume. Record the volume of the volumetric flask as V1. Prepare a constant-weight crucible and record its weight before ignition. Place the filtered ashless filter paper into the crucible, then ignite and cool it. After constant weight in a desiccator, weigh it and record the mass increase (m) of the crucible before and after ignition, which is the mass of the rinsed droplets. Then, dry the droplet collector in an oven, and after drying, cool it in a desiccator. After cooling, weigh it using a 0.01% balance and record the weight as M2.

[0015] (4) Treatment of slurry samples and rinsing solutions:

[0016] The desulfurization tower slurry was filtered using filter paper, and the filtrate was diluted by a dilution factor of f. The magnesium ion concentration in the diluted filtrate and the rinse solution after volume adjustment in step (3) were determined by ICP-MS and denoted as C, respectively. 浆液 and C 雾滴 ;

[0017] (5) Data processing:

[0018] The specific droplet weight M and concentration C are calculated using the following formulas (1) and (2):

[0019]

[0020] In the formula:

[0021] M: Droplet weight, mg;

[0022] M2: Weight of the droplet collector after sampling and drying;

[0023] M1: Weight of the clean droplet collector after drying before sampling;

[0024] m: Crucible weight gain, i.e., the mass of solid components washed down inside the droplet collector;

[0025] C 雾滴 : Concentration of magnesium ions in the flushing solution of the droplet collector after volume adjustment;

[0026] V1: Volume of the volumetric flask containing the flushing solution for the droplet trap;

[0027] C 浆液 : Concentration of magnesium ions in the filtrate after dilution;

[0028] f: Dilution factor of slurry filtrate, dimensionless;

[0029] ρ: Droplet moisture density;

[0030]

[0031] In the formula:

[0032] C: Droplet concentration;

[0033] V sd : Standard sampling volume during droplet trap sampling.

[0034] The cleaning method in step (1) is as follows: use desalination water + ultrasonic cleaning until the surface of the mist collector is smooth, free of stains, and free of water droplets on the wall, and water does not flow down in streams; if the desalination water + ultrasonic cleaning is not clean, first soak it in a 10% to 20% HNO3 solution by mass, and then clean it by desalination water + ultrasonic cleaning.

[0035] In step (2), the sampling smoke gun, standard pitot tube, hygrometer, thermal resistor or smoke temperature probe are inserted into the flue, and the front ends are no more than 5 cm apart.

[0036] In step (2), the sampling time should be more than 1 hour or the amount of flue gas extracted should be such that the total weight of the droplets in the droplet collector is not less than 0.1g.

[0037] Before sampling the desulfurization tower slurry in step (2), the sampling bottle should be thoroughly rinsed with slurry, and the slurry sampling volume should be more than 500 mL.

[0038] In step (3), the burning temperature is 160-180℃ and the time is 4h.

[0039] In step (4), the diameter of the filter paper is 45 μm.

[0040] Beneficial effects:

[0041] The method of this invention has the following advantages: First, it considers the changes in the physical and chemical properties of the desulfurization slurry after passing through the demister, directly obtaining the solid components in the droplets by weighing, and calculating the water weight in the droplets from the tested magnesium ions, thereby obtaining the specific droplet weight and concentration; Second, it adopts an ultrasonic or acid soaking tank + ultrasonic pretreatment method and weighs the solid components in two steps, making the testing steps more precise and detailed, and the slurry data measurement more accurate; Third, it eliminates the need to determine the slurry solid content, which reduces the number of operation steps and eliminates the influence of the slurry solid content on the calculation. Attached Figure Description

[0042] Figure 1 This refers to the dimensions of the droplet collector. (Unit: mm) Detailed Implementation

[0043] The specific embodiments of the present invention will be further described in detail below with reference to examples.

[0044] Example 1: A method for testing droplets in a demister of a wet desulfurization system

[0045] (1) Cleaning of the droplet collector

[0046] First, prepare three droplet collectors. The droplet collectors should be the models specified in the standards (DLT 1483-2015 Test Methods for Chemical and Physical Properties of Limestone-Gypsum Wet Flue Gas Desulfurization Systems, Appendix A; and GBT 21508-2008 Test Methods for Performance of Coal-fired Flue Gas Desulfurization Equipment, Appendix D), with dimensions as shown. Figure 1 As shown. Use demineralized water and ultrasonic cleaning until the droplet collector surface is smooth, free of stains, and free of water droplets on the walls, with no water flowing down the inner walls. If demineralized water and ultrasonic cleaning are insufficient, soak in an acid bath (10%–20% HNO3 solution by mass) for 24 hours, then clean with demineralized water and ultrasonic cleaning. After cleaning, dry in an oven at 105℃ for 2 hours. During drying, place clean filter paper or padding under the droplet collector to prevent impurities from entering. After drying, place in a desiccator to cool. Once cooled to room temperature, weigh using a 0.01% balance and record as M1. Store in a clean, sealed self-sealing bag.

[0047] (2) Field test

[0048] When testing droplet content, the demister must be stopped from rinsing. The test should be conducted using a dust tester that has temperature, pressure, and flow rate testing functions as well as isokinetic sampling function. First, fix the prepared droplet collector to the sampling head with the matching bayonet, and assemble the sampling smoke gun. Simultaneously, prepare a standard Pitot tube, hygrometer, and RTD or smoke temperature probe. Connect the sampling smoke gun, standard Pitot tube, hygrometer, RTD or smoke temperature probe to the main unit of the smoke dust tester. Insert the sampling smoke gun, standard Pitot tube, hygrometer, RTD or smoke temperature probe into the flue to the same depth, ensuring that the distance between the tips of the Pitot tube, hygrometer, smoke gun, and RTD or smoke temperature probe does not exceed 5cm. The positive pressure test port of the Pitot tube and the droplet collector should face the direction of flue gas flow. The Pitot tube measures the flow velocity and flue gas pressure. The droplet collector collects droplets from the flue gas. The hygrometer measures the flue gas humidity, and the RTD or smoke temperature probe measures the flue gas temperature. The smoke dust tester ensures isokinetic sampling. The sampling volume V of the droplet collector is calculated based on the flow velocity measured by the Pitot tube. Using the measured flue gas pressure, humidity, and temperature, the actual sampling volume V under wet conditions is converted to the standard sampling volume V under dry conditions. sdGrid sampling should be conducted on the flue gas cross-section of the flue. The sampling time should be more than 1 hour, or the amount of flue gas extracted should ensure that the total weight of droplets in the droplet collector is not less than 0.1g. Two parallel samples should be collected from each flue. After sampling, seal both ends of the droplet collector with sealing film, rinse the outer wall with demineralized water, and dry it with clean cotton or cotton yarn. Seal the treated droplet collector in a self-sealing bag and label it; this constitutes one droplet sample. When measuring droplets, simultaneously sample the desulfurization tower slurry using a sampling bottle. Before sampling, thoroughly rinse the sampling bottle with slurry. The slurry sample volume should be more than 500mL.

[0049] (3) Droplet sample preparation

[0050] Remove the sealing films from both ends of the sealed droplet collector, ensuring no droplets remain on the films. Rinse the inside of the sealing films with demineralized water, then rinse the inner wall of the collector with demineralized water. Filter the rinse solution using ashless filter paper and collect it in a volumetric flask, making up to volume (V1). Prepare a constant-weight crucible and record its weight before ignition. Place the filtered ashless filter paper into the crucible, then place the crucible in a muffle furnace and ignite at 160–180°C for 4 hours. Cool the crucible, place it in a desiccator to maintain constant weight, and weigh it. Calculate the mass increase (m) of the crucible before and after ignition; this is the mass of the rinsed droplets. Note that the ignition temperature should not exceed 180°C to avoid affecting the solid components in the droplets, nor should it be too low, as this would prevent ignition of the ashless filter paper. Then, the droplet collector was placed in an oven at 105℃ for 2 hours. After drying, it was placed in a desiccator to cool. After cooling, it was weighed using a 0.01% balance and the weight was recorded as M2. This was to avoid any solid components adhering to the inner wall of the droplet collector and affecting the measurement.

[0051] (4) Treatment of slurry samples and rinsing solution

[0052] The desulfurization tower slurry was filtered using 45μm filter paper. The filtrate was then diluted by a dilution factor of f. The magnesium ion concentrations in the diluted filtrate and the rinse solution after volume adjustment in step (3) were determined using inductively coupled plasma mass spectrometry (ICP-MS) and denoted as C, respectively. 浆液 and C 雾滴 .

[0053] (5) Data processing

[0054] The weight of the droplets in the mist collector is mainly divided into three parts: condensate water in the flue gas, water content in the droplets, and solid components in the droplets. The original method used magnesium ions as tracers, subtracted the condensate water in the flue gas, and then directly calculated the droplet weight from the water content using the solids content of the desulfurization tower slurry. This assumed that the solid components in the droplets were the same as those in the slurry. However, after passing through the demister, the physical and chemical composition of the droplets changes compared to the slurry. Therefore, this invention considers not measuring the solids content of the slurry, but directly obtaining the solid components in the droplets by weighing, and calculating the water weight in the droplets from the measured magnesium ions, thus obtaining the specific droplet weight M and concentration C. Specific data processing is as follows:

[0055]

[0056] In the formula:

[0057] M: Droplet weight, mg;

[0058] M2: Weight of the droplet collector after sampling and drying, in mg;

[0059] M1: Weight of the clean droplet collector after drying before sampling, in mg;

[0060] m: Crucible weight gain, i.e., the mass of solid components washed down from the droplet collector, in mg;

[0061] C 雾滴 : Concentration of magnesium ions in the flushing solution of the droplet collector after volume adjustment, mg / L;

[0062] V1: Volume of the volumetric flask containing the flushing solution for the droplet trap, in L;

[0063] C 浆液 : Concentration of magnesium ions in the diluted slurry filtrate, mg / L;

[0064] f: Dilution factor of slurry filtrate, dimensionless;

[0065] ρ: Droplet moisture density, default value is 1 kg / L.

[0066]

[0067] In the formula:

[0068] C: Droplet concentration, mg / m³ 3 ;

[0069] V sd : Standard sampling volume (m³) during droplet trap sampling 3 .

[0070] Application examples:

[0071] A power plant has three 650MW supercritical coal-fired units. The outlet droplet concentration of these three units under high load was measured using both the method of this invention and the standard method. The test results are shown in Table 3. It can be seen that the concentration measured by the method of this invention is lower, reducing the concentration by 3 mg / m³ compared to the original standard method. 3 This is consistent with the previous analysis that the proportion of solid components in droplets is lower than that in slurry. The original standard method did not consider the changes in the chemical and physical properties of droplets and slurry, and analyzed droplets as slurry, ignoring the lower content of solid components in droplets, thus increasing the droplet mass and consequently increasing the droplet concentration. Therefore, the method of this invention is more accurate.

[0072] Table 3. Droplet measurement results of three units in a power plant.

[0073]

Claims

1. A method for testing droplets in a demister of a wet desulfurization system, characterized in that, Includes the following steps: (1) Demister treatment: Prepare a droplet collector, thoroughly clean and dry it, cool it, weigh it using a 0.01% balance, record it as M1, and store it in a sealed container for later use. (2) On-site testing: Fix the prepared droplet collector to the sampling head with the matching bayonet, assemble the sampling smoke gun, and prepare a standard Pitot tube, hygrometer, and thermal resistor or smoke temperature probe. Connect the sampling gun, standard Pitot tube, hygrometer, RTD or flue gas temperature probe, and the main unit of the flue gas dust tester. Then, insert the sampling gun, standard Pitot tube, hygrometer, RTD or flue gas temperature probe into the flue to the same depth. The Pitot tube's positive pressure test port and the droplet collector should be aligned with the flue gas flow direction. The Pitot tube measures the flue gas velocity and pressure, the droplet collector collects droplets from the flue gas, the hygrometer measures the flue gas humidity, and the RTD or flue gas temperature probe measures the flue gas temperature. The flue gas dust tester ensures isokinetic sampling. The droplet collector sampling volume V is calculated based on the flow velocity measured by the Pitot tube. Using the measured flue gas pressure, humidity, and temperature, the actual operating condition wet basis sampling volume V is converted to the standard operating condition dry basis sampling volume V. sd ; grid sampling was carried out on the flue gas cross section of the flue, and two parallel samples were collected from one flue; after sampling, the two ends of the droplet collector were sealed with sealing film, the outer wall was cleaned and dried, and the droplet collector was sealed and stored, and marked, which constitutes one droplet sample; when measuring droplets, the desulfurization tower slurry was sampled at the same time. (3) Droplet sample preparation: After the field test, the sealing films at both ends of the droplet collector were removed. The inside of the sealing films was rinsed with demineralized water, and then the inner wall of the collector was rinsed with demineralized water. All the rinsed solution was filtered with ashless filter paper and collected into a volumetric flask, which was then brought to a final volume. The volume of the volumetric flask was recorded as V1. A constant-weight crucible was prepared, and its weight before ignition was recorded. The filtered ashless filter paper was placed in the crucible, which was then ignited and cooled. After constant weight was achieved in a desiccator, the crucible was weighed, and the mass increase of the crucible before and after ignition, m, was recorded as the mass of the rinsed droplets. The droplet collector was then placed in an oven to dry. After drying, it was placed in a desiccator to cool. After cooling, it was weighed using a 0.01% balance, and the weight was recorded as M2. (4) Treatment of slurry samples and rinsing solutions: The desulfurization tower slurry was filtered using filter paper, and the filtrate was diluted by a dilution factor of f. The magnesium ion concentration in the diluted filtrate and the rinse solution after volume adjustment in step (3) were determined by ICP-MS and denoted as C, respectively. 浆液 and C 雾滴 ; (5) Data processing: The specific droplet weight M and concentration C are calculated using the following formulas (1) and (2): In the formula: M: Droplet weight, mg; M2: Weight of the droplet collector after sampling and drying; M1: Weight of the clean droplet collector after drying before sampling; m: Crucible weight gain, i.e., the mass of solid components washed down inside the droplet collector; C 雾滴 : Concentration of magnesium ions in the flushing solution of the droplet collector after volume adjustment; V1: Volume of the volumetric flask containing the flushing solution for the droplet trap; C 浆液 : Concentration of magnesium ions in the filtrate after dilution; f: Dilution factor of slurry filtrate, dimensionless; ρ: Droplet moisture density; In the formula: C: Droplet concentration; V sd : Standard sampling volume during droplet trap sampling.

2. The method for testing mist droplets in a wet desulfurization system demister according to claim 1, characterized in that, The cleaning method in step (1) is as follows: use desalination water + ultrasonic cleaning until the surface of the mist collector is smooth, free of stains, and free of water droplets on the wall, and water does not flow down in streams; if the desalination water + ultrasonic cleaning is not clean, first soak it in a 10% to 20% HNO3 solution by mass, and then clean it by desalination water + ultrasonic cleaning.

3. The method for testing mist droplets in a wet desulfurization system demister according to claim 1, characterized in that, In step (2), the sampling smoke gun, standard pitot tube, hygrometer, thermal resistor or smoke temperature probe are inserted into the flue, and the front ends are no more than 5 cm apart.

4. The method for testing mist droplets in a wet desulfurization system demister according to claim 1, characterized in that, In step (2), the sampling time should be more than 1 hour or the amount of flue gas extracted should be such that the total weight of the droplets in the droplet collector is not less than 0.1g.

5. The method for testing mist droplets in a wet desulfurization system demister according to claim 1, characterized in that, Before sampling the desulfurization tower slurry in step (2), the sampling bottle should be thoroughly rinsed with slurry, and the slurry sampling volume should be more than 500 mL.

6. The method for testing mist droplets in a wet desulfurization system demister according to claim 1, characterized in that, In step (3), the burning temperature is 160-180℃ and the time is 4h.

7. The method for testing mist droplets in a wet desulfurization system demister according to claim 1, characterized in that, In step (4), the diameter of the filter paper is 45 μm.

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