Method for analyzing sulfuric acid steam adsorbed by ash particles through experimental simulation

Abstract

The invention discloses a method for analyzing sulfuric acid vapor adsorbed by ash particles through experimental simulation, which comprises the following steps: (1) taking one part of fly ash from collected fly ash as a fly ash sample of a control group; (2) carrying out adsorption reaction on the fly ash sample of the control group and sulfuric acid steam; (3) respectively measuring the sulfur element content of the collected fly ash and the fly ash sample of the control group after the adsorption reaction, setting the sulfur element content of the collected fly ash as M0 and the sulfur element content of the fly ash sample of the control group after the adsorption reaction as M1, and describing the degree of the adsorption reaction by using the sulfur element content increment MD of the fly ash sample of the control group after the adsorption reaction, MD = M1-M0, the larger the MZ is, the stronger the adsorption effect of the fly ash on the sulfuric acid steam is. According to the method, theoretical basis and engineering guidance can be provided for selection of equipment parameters of the low-low-temperature electrostatic dust collector and optimization selection of fly ash particles, and the desulfurization and dust removal efficiency of a low-low-temperature electrostatic dust collection system can be further improved.

Description

Technical Field

[0001] This invention relates to the field of power plant energy-saving technology, and in particular to a method for experimentally simulating and analyzing the adsorption of sulfuric acid vapor by ash particles. Background Technology

[0002] Coal-fired power plants generate a large amount of air pollutants during operation, mainly sulfur oxides, nitrogen oxides, and particulate matter. As the main body of industrial carbon emission reduction, power plants face the challenge of ultra-low emission retrofitting. Low-temperature electrostatic precipitators are one of the key pieces of equipment for reducing particulate matter emissions in coal-fired power plants. They are an effective technology for achieving ultra-low emission standards for coal-fired power plants. Low-temperature electrostatic precipitators can simultaneously remove ash particles (fly ash) and sulfuric acid pollutants. By installing a low-temperature economizer or heat exchanger before the electrostatic precipitator, the temperature of the flue gas entering the electrostatic precipitator is reduced to below the acid dew point. When the temperature drops, gaseous SO3 will be adsorbed into the ash particles in the heat exchanger before the electrostatic precipitator in the form of H2SO4 droplets. When the flue gas enters the electrostatic precipitator, the SO3 carried by the ash is removed simultaneously.

[0003] Low-temperature electrostatic precipitators can efficiently remove dust and synergistically remove SO3. Ash particles are essentially porous media, and sulfuric acid vapor flows within their micro- and nano-scale pores, undergoing adsorption and desorption on their surfaces. The chemical composition of the ash particles affects the SO3 removal efficiency; however, currently, there is a lack of experimental methods to analyze the influence of the ash's chemical composition on particle agglomeration and SO3 adsorption. Summary of the Invention

[0004] The main objective of this invention is to provide an experimental simulation analysis method for the adsorption of sulfuric acid vapor by ash particles.

[0005] To achieve the above objectives, the present invention provides a method for experimentally simulating and analyzing the adsorption of sulfuric acid vapor by ash particles, comprising the following steps: (1) Sample preparation One sample of fly ash was taken from the collected fly ash and used as a control group fly ash sample. (2) Adsorption reaction The fly ash sample from the control group was subjected to an adsorption reaction with sulfuric acid vapor; (3) Conclusion Analysis The sulfur content of the collected fly ash and the control group fly ash samples after the adsorption reaction were determined. Let the sulfur content of the collected fly ash be M0, and the sulfur content of the control group fly ash samples after the adsorption reaction be M1. The increment of the sulfur content of the control group fly ash samples after the adsorption reaction, M... D M is used to describe the extent of the adsorption reaction. D =M1-M0,M Z The larger the value, the stronger the adsorption effect of fly ash on sulfuric acid vapor.

[0006] Furthermore, step (3) also includes: taking microscopic morphology photos of the collected fly ash and the control group fly ash samples after the adsorption reaction and observing the particle agglomeration phenomenon. The dust removal efficiency is described by the increase in the small particle agglomeration phenomenon in the control group fly ash samples after the adsorption reaction. Compared with the collected fly ash, the larger the increase in the small particle agglomeration phenomenon in the control group fly ash samples after the adsorption reaction, the easier it is for the fly ash to be electrostatically removed.

[0007] Furthermore, step (1) also includes: taking multiple portions of fly ash equal in amount to the control group fly ash sample from the collected fly ash, mixing them evenly with different additives, and using them as experimental group fly ash samples; Step (2) also includes: under the same adsorption reaction conditions as the control group fly ash samples, each experimental group fly ash sample is subjected to an adsorption reaction with sulfuric acid vapor; Step (3) also includes: determining the sulfur content of each experimental group of fly ash samples after the adsorption reaction, wherein the sulfur content of each experimental group of fly ash samples after the adsorption reaction is M. N N represents the group, and M represents the increase in sulfur content in the fly ash sample of the experimental group after the adsorption reaction. S M is used to describe the extent of the adsorption reaction. S =M N -M1,M S The larger the value, the stronger the promoting effect of the additives mixed into the fly ash samples of the corresponding experimental group on the adsorption of sulfuric acid vapor by fly ash.

[0008] Furthermore, step (3) also includes: taking microscopic morphology photos of each experimental group fly ash sample after the adsorption reaction and observing particle agglomeration. The dust removal efficiency is described by the increase in small particle agglomeration in the experimental group fly ash sample after the adsorption reaction. Compared with the control group fly ash sample after the adsorption reaction, the larger the increase in small particle agglomeration in the experimental group fly ash sample after the adsorption reaction, the stronger the promoting effect of the additive mixed in the corresponding experimental group fly ash sample on the electrostatic removal of fly ash.

[0009] Furthermore, in step (1), the different additives include equal amounts of different elements and / or different amounts of the same element.

[0010] Furthermore, in step (1), the particle size of the collected fly ash is less than 68 μm.

[0011] Furthermore, in step (2), the adsorption reaction is carried out at a temperature of 90°C for 20 minutes.

[0012] Furthermore, step (3) also includes measuring the distribution of sulfur on particles of different particle size ranges in the collected fly ash and the control group fly ash samples after the adsorption reaction. The more sulfur is distributed on the particles of the corresponding particle size range, the stronger the adsorption effect of the particles of that particle size range on sulfuric acid vapor.

[0013] The beneficial effects of this invention are reflected in: This invention provides an in-depth analysis of the removal of particulate matter and sulfuric acid pollutants from flue gas. By analyzing the effects of different additives on the adsorption of sulfuric acid vapor by particulate matter, and observing the morphological changes and agglomeration phenomena of fly ash samples before and after adsorption, it reveals the intrinsic performance of ash particles in adsorbing sulfuric acid vapor. The method of this invention can screen out: fly ash with better adsorption of sulfuric acid vapor, better additives that can promote the adsorption of sulfuric acid vapor by fly ash, fly ash that is easier to be electrostatically removed, better additives that can promote the electrostatic removal of fly ash, and a particle size range with better adsorption of sulfuric acid vapor.

[0014] This invention provides a theoretical basis and engineering guidance for the selection of parameters for low-temperature electrostatic precipitators and the optimization of fly ash particle selection, which helps to further improve the desulfurization and dust removal efficiency of low-temperature electrostatic precipitator systems and promotes the development of ultra-low emission retrofit technology for coal-fired power plants. Attached Figure Description

[0015] Figure 1 SEM images (400x magnification) of fly ash (a) collected in Example 2 and fly ash sample (b) of the control group after adsorption reaction.

[0016] Figure 2 The images show EDS diagrams (a) and S distribution diagrams (b) of the fly ash particle surface morphology collected in Example 2.

[0017] Figure 3 The images show the EDS diagram (a) and S distribution diagram (b) of the particle surface morphology of the fly ash sample from the control group after the adsorption reaction in Example 2. Detailed Implementation

[0018] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0019] Unless otherwise specified, the raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial sources or by existing known methods; unless otherwise specified, the methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0020] Example 1 Collection of fly ash The fly ash was collected from a 660MW boiler at a power plant in Fujian Province, specifically at the economizer ash hopper outlet, before the SCR denitrification system. Therefore, the fly ash collected from the economizer ash hopper outlet can be considered as the original sample that has not undergone an adsorption reaction with H2SO4 steam.

[0021] The industrial and elemental analyses of the bituminous coal used in the boiler are shown in Table 1. The ash samples were screened into four particle sizes: <68μm, 68–75μm, 75–91μm, and 91–125μm, with a mass ratio of approximately 6:1:2:1.

[0022] Table 1. Industrial and elemental analysis of coal from a power plant in Fujian Province (mass fraction / wt.%)

[0023] Note: ar indicates received base, O * The oxygen content is obtained by subtraction. The elemental analysis results of fly ash are shown in Table 2, determined by X-ray fluorescence spectrometry (XRF, S4 Pioneer, Bruker, Germany). Overall, the ash samples of all four particle sizes had the highest Fe content, with a mass fraction of over 4%, followed by Ca. The alkali metal content of the ash samples was lower than that of alkaline earth metals. For ash samples of different particle sizes, the mass fractions of Na, K, or Mg in ash samples <68 μm were less than 1%. As the particle size increased, the K content decreased monotonically, while the contents of other elements did not show a clear trend. Particles smaller than 68 μm constituted the main component of the ash samples and were selected as the experimental samples. Before the experiment, the fly ash was stored in a dry container to avoid the influence of air humidity.

[0024] Table 2. Elemental composition of fly ash samples (mass fraction / wt.%)

[0025] Example 2 Experimental simulation analysis of ash particles adsorbing sulfuric acid vapor The experiment was conducted in a three-stage fixed-bed system, which can simulate the adsorption process of fly ash particles under the operating conditions of a low-temperature electrostatic precipitator system.

[0026] (1) Sample preparation From the collected fly ash (particle size less than 68μm), one part of fly ash was taken as the control group fly ash sample, and multiple parts of fly ash with the same amount as the control group fly ash sample were taken, and then mixed evenly with different additives to serve as the experimental group fly ash samples. The composition of ash samples was altered by physically mixing and loading compounds to investigate the effects of chemical composition on sulfuric acid adsorption and particle agglomeration. Additives included Na₂CO₃, K₂CO₃, MgO, CaO, and Fe₂O₃, with NaCl and KCl selected for comparison. Then, by calculating the conversion between elemental and compound addition amounts, the ash particles were mixed with the added chemical reagents in a specific ratio (see Table 3).

[0027] Table 3. Compound addition amount (mass fraction / wt.%)

[0028] (2) Adsorption reaction Under the same adsorption reaction conditions, fly ash samples from the control group and each experimental group were subjected to adsorption reactions with sulfuric acid vapor; the specific operation was as follows: The sample was evenly spread in a thin layer inside the adsorption reactor, and a 20% sulfuric acid solution was injected at a rate of 0.15 mL / min. -1 After gaseous SO3 and H2O are generated in a pyrolysis furnace at 500℃, they are introduced into an adsorption reactor. SO3 and H2O condense into H2SO4 vapor in the adsorption reactor. Then, the fly ash particles undergo a surface adsorption reaction with sulfuric acid vapor. The temperature of the adsorption reactor is controlled at 90℃ and the adsorption reaction is set for 20 minutes. After the adsorption reaction is completed, the adsorbed fly ash sample is collected and further analyzed. All experiments were repeated three times to ensure accuracy and reproducibility.

[0029] (3) Conclusion Analysis 3.1): The sulfur content of the collected fly ash, the control group fly ash samples after the adsorption reaction, and the fly ash samples from each experimental group after the adsorption reaction were determined. Let the sulfur content of the collected fly ash be M0, the sulfur content of the control group fly ash samples after the adsorption reaction be M1, and the sulfur content of each experimental group fly ash samples after the adsorption reaction be M. N N represents the group; The increase in sulfur content M in the control group fly ash sample after the adsorption reaction D M is used to describe the extent of the adsorption reaction. D =M1-M0,M Z The larger the value, the stronger the adsorption effect of fly ash on sulfuric acid vapor; by conducting experiments on different fly ashes in this way, the best fly ash for adsorbing sulfuric acid vapor can be screened out.

[0030] The increase in sulfur content M in the fly ash samples of the experimental group after the adsorption reaction S M is used to describe the extent of the adsorption reaction. S =M N -M1,M SThe larger the value, the stronger the promoting effect of the additives mixed into the fly ash samples of the corresponding experimental group on the adsorption of sulfuric acid vapor by fly ash; by conducting experiments on different additives in this way, the best additives that can promote the adsorption of sulfuric acid vapor by fly ash can be screened out. 3.2): Microscopic morphology photos were taken of the collected fly ash, the control group fly ash samples after the adsorption reaction, and the fly ash samples of each experimental group after the adsorption reaction, and particle agglomeration was observed. The dust removal efficiency was described by the increase in small particle agglomeration in the control group fly ash samples after the adsorption reaction. Compared with the collected fly ash, the greater the increase in small particle agglomeration in the control group fly ash sample after the adsorption reaction, the easier the fly ash is to be electrostatically removed. By conducting experiments on different fly ash samples in this way, the fly ash that is most easily electrostatically removed can be screened out.

[0032] Compared to the control group fly ash samples after the adsorption reaction, the greater the increase in small particle agglomeration in the experimental group fly ash samples, the stronger the promoting effect of the additives mixed into the corresponding experimental group fly ash samples on the electrostatic removal of fly ash. Through experiments with different additives, the best additive for promoting the electrostatic removal of fly ash can be screened. 3.3): The distribution of sulfur on particles of different particle sizes was determined in the collected fly ash and the control group fly ash samples after the adsorption reaction. The greater the distribution of sulfur on particles of a certain particle size range, the stronger the adsorption effect of particles of that particle size range on sulfuric acid vapor.

[0034] Specifically, scanning electron microscopy (SEM) was used to capture microscopic images of fly ash samples to characterize the surface morphology of the fly ash samples, thereby describing the changes in fly ash morphology and the formation of agglomerates; X-ray diffraction was used to analyze the chemical composition of fly ash samples before and after adsorption, including the contents of Ca, Fe, Mg, Na, and K; elemental analysis was used for quantitative analysis of sulfur; and energy dispersive spectroscopy (EDS) was used to test the elemental composition of typical regions to analyze the influence of elements on the adsorption of sulfuric acid vapor by fly ash.

[0035] The specific experimental analysis results are as follows: Compared with the collected fly ash, the sulfur content in the control group fly ash sample after the adsorption reaction increased by 1.95 mg·g. -1 M D It is 1.95 mg·g -1 This is equivalent to an increase of 5.97 mg·g in sulfuric acid. -1 This indicates that fly ash particles have a significant adsorption effect on sulfuric acid. This is mainly attributed to the rough surface of the fly ash particles, their rich internal pore structure, and the presence of alkaline substances, which provide favorable conditions for the adsorption of sulfuric acid vapor.

[0036] SEM images of the collected fly ash and the control group fly ash samples after the adsorption reaction are shown below. Figure 1 As shown, Figure 1 (a) It can be seen that the fly ash particles before adsorption are in a loose state, which is conducive to the entry and diffusion of H2SO4 vapor into the pores of the ash particles. According to morphology, they can be divided into three categories: loose small particles, spherical large particles, and irregular block particles. Some small particles are adhered to the surface of the irregular block particles and large spherical particles, and there is agglomeration between the loose small particles, indicating that agglomeration already exists before the adsorption reaction. The degree of agglomeration is relatively light, which may be due to the collision between ash particles in the flue gas before sampling. Figure 4(b) shows that the fly ash particles have agglomerated with each other. Among them, the loose particles begin to agglomerate with each other, and the looseness of the fly ash particles decreases. This indicates that the originally loose particles have agglomerated after adsorbing H2SO4 vapor, filling the internal pores of the ash particles and reducing the porosity of the ash particles. The agglomeration of ash particles is mainly the agglomeration between small particles and the adhesion of loose small particles to large particles. The agglomeration between large particles is not obvious. Therefore, when fly ash particles with unchanged composition are used for adsorption reactions, particle agglomeration will still occur, even with a relatively low degree of agglomeration. Generally, power plant electrostatic precipitators cannot remove approximately 15% of ultrafine particles (0.1–1 μm). This demonstrates that the agglomeration of small particles is beneficial for improving the dust removal efficiency of low-temperature electrostatic precipitators, meaning that fly ash is more easily removed electrostatically.

[0037] Fly ash particles adsorb sulfuric acid and agglomerate during the condensation process. There are three types of agglomeration: agglomeration between small particles, loose particles adhering to large particles, and agglomeration between large particles.

[0038] Figure 2 (a) shows the EDS scan area of ​​the fly ash particle surface morphology collected before adsorption. Figure 2 (b) shows the distribution of sulfur in the fly ash collected before adsorption. Before adsorption, the sulfur in the fly ash particles was dispersed and only appeared on the surface of a small number of particles. Figure 3 (b) shows the distribution of sulfur (S) in the control group fly ash sample after the adsorption reaction. After adsorbing sulfuric acid vapor, S was present throughout the entire window and its distribution was uneven, indicating that the adsorption of sulfuric acid by fly ash particles was not uniform. Most small particles adsorbed S, but the distribution of S on large particles was very limited, less pronounced than on small particles. Since physical adsorption is prone to desorption, S must have diffused to the adsorption sites through external macropores and internal nanopores, and then been fixed in the form of chemisorption. Moreover, the liquid film and chemisorption reaction increased the adhesion of the particles, causing them to aggregate together. Figure 3 (a) shows that the surface of large particles is smooth, indicating that the surface pores are blocked. However, the surface of small particles is rough, and the specific surface area is increased, which is conducive to the diffusion and adsorption of steam into the ash particles.

[0039] Effect of alkaline compounds: When the addition amounts of MgO, CaO, Fe2O3, Na2CO3, and K2CO3 increased from 0% to 13.3%, 22.4%, 23.9%, 18.4%, and 14.2%, respectively, the sulfur content after adsorption increased from 1.95 mg·g⁻¹ to 13.3%, 22.4%, 23.9%, 18.4%, and 14.2%, respectively. - ¹Increased to 7.33, 7.71, 6.72, 5.10, and 5.44 mg·g - ¹. This indicates that adding these alkaline substances can increase the content of alkaline substances in fly ash samples, thereby enhancing their adsorption capacity. Simultaneously, the addition of these compounds has a significant impact on particle agglomeration, and the agglomeration phenomenon becomes more pronounced with increasing addition amounts, indicating that the adsorption and agglomeration processes of ash particles occur almost simultaneously, with the alkaline compounds playing a promoting role.

[0040] The inventors also used NaCl and KCl as additives, and the results showed that their addition had little effect on the adsorption of sulfuric acid by fly ash particles and almost no effect on particle agglomeration. This may be because NaCl and KCl are neutral salts, and their interaction with sulfuric acid vapor is weak, thus their promoting effect on the adsorption and agglomeration process is not significant.

[0041] This invention determines the total adsorption capacity of fly ash particles for H2SO4 vapor using a static weighing method and systematically analyzes the influence of SEM-EDS and XRF techniques on the adsorption process. The results show that the chemical composition, microstructure, and pore structure of fly ash particles significantly affect their adsorption of sulfuric acid vapor and their agglomeration characteristics. Based on experimental data, in-depth research into the adsorption mechanism of fly ash particles with different pore structures can provide theoretical basis and engineering guidance for the selection of parameters for low-temperature electrostatic precipitators and the optimization of fly ash particle selection. This will help further improve the desulfurization and dust removal efficiency of low-temperature electrostatic precipitator systems and promote the development of ultra-low emission retrofit technology for coal-fired power plants.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for experimentally simulating and analyzing the adsorption of sulfuric acid vapor by ash particles, characterized in that, Includes the following steps: (1) Sample preparation One sample of fly ash was taken from the collected fly ash and used as a control group fly ash sample. (2) Adsorption reaction The fly ash sample from the control group was subjected to an adsorption reaction with sulfuric acid vapor; (3) Conclusion Analysis The sulfur content of the collected fly ash and the control group fly ash samples after the adsorption reaction were determined. Let the sulfur content of the collected fly ash be M0, and the sulfur content of the control group fly ash samples after the adsorption reaction be M1. The increment of the sulfur content of the control group fly ash samples after the adsorption reaction, M... D M is used to describe the extent of the adsorption reaction. D =M1-M0,M Z The larger the value, the stronger the adsorption effect of fly ash on sulfuric acid vapor.

2. The method for experimentally simulating and analyzing the adsorption of sulfuric acid vapor by ash particles as described in claim 1, characterized in that, Step (3) also includes: taking microscopic morphology photos of the collected fly ash and the control group fly ash samples after the adsorption reaction and observing the particle agglomeration phenomenon. The dust removal efficiency is described by the increase in the small particle agglomeration phenomenon in the control group fly ash samples after the adsorption reaction. Compared with the collected fly ash, the larger the increase in the small particle agglomeration phenomenon in the control group fly ash samples after the adsorption reaction, the easier it is for the fly ash to be electrostatically removed.

3. The method for experimentally simulating and analyzing the adsorption of sulfuric acid vapor by ash particles as described in claim 2, characterized in that, Step (1) also includes: taking multiple portions of fly ash equal in amount to the control group fly ash sample from the collected fly ash, mixing them evenly with different additives, and using them as experimental group fly ash samples. Step (2) also includes: under the same adsorption reaction conditions as the control group fly ash samples, each experimental group fly ash sample is subjected to an adsorption reaction with sulfuric acid vapor; Step (3) also includes: determining the sulfur content of each experimental group of fly ash samples after the adsorption reaction, wherein the sulfur content of each experimental group of fly ash samples after the adsorption reaction is M. N N represents the group, and M represents the increase in sulfur content in the fly ash sample of the experimental group after the adsorption reaction. S M is used to describe the extent of the adsorption reaction. S =M N -M1,M S The larger the value, the stronger the promoting effect of the additives mixed into the fly ash samples of the corresponding experimental group on the adsorption of sulfuric acid vapor by fly ash.

4. The method for experimentally simulating and analyzing the adsorption of sulfuric acid vapor by ash particles as described in claim 3, characterized in that, Step (3) also includes: taking microscopic morphology photos of each experimental group fly ash sample after the adsorption reaction and observing particle agglomeration. The dust removal efficiency is described by the increase in small particle agglomeration in the experimental group fly ash sample after the adsorption reaction. Compared with the control group fly ash sample after the adsorption reaction, the larger the increase in small particle agglomeration in the experimental group fly ash sample after the adsorption reaction, the stronger the promoting effect of the additive mixed in the corresponding experimental group fly ash sample on the electrostatic removal of fly ash.

5. The method for experimentally simulating and analyzing the adsorption of sulfuric acid vapor by ash particles as described in claim 3, characterized in that, In step (1), different additives include equal amounts of different elements and / or different amounts of the same element.

6. The method for experimental simulation analysis of sulfuric acid vapor adsorption by ash particles as described in any one of claims 1 to 4, characterized in that, In step (1), the particle size of the collected fly ash is less than 68 μm.

7. The method for experimental simulation analysis of sulfuric acid vapor adsorption by ash particles as described in any one of claims 1 to 4, characterized in that, In step (2), the adsorption reaction is carried out at a temperature of 90°C for 20 minutes.

8. The method for experimental simulation analysis of sulfuric acid vapor adsorption by ash particles as described in any one of claims 1 to 4, characterized in that, Step (3) also includes measuring the distribution of sulfur on particles of different particle size ranges in the collected fly ash and the control group fly ash samples after the adsorption reaction. The more sulfur is distributed on the particles of the corresponding particle size range, the stronger the adsorption effect of the particles of that particle size range on sulfuric acid vapor.

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