Preparation method and application of acid-base indicator modified dry alkaline desulfurizer

Abstract

The invention belongs to the technical field of flue gas desulfurization, and particularly relates to a preparation method of an acid-base indicator modified dry-process alkaline absorbent and application of the acid-base indicator modified dry-process alkaline absorbent in dry-process desulfurization. In surface modification, an alkaline absorbent particle is used as an inner core, an alkaline absorbent and an absolute ethyl alcohol solution of an acid-base indicator (such as phenolphthalein and sulfophenolphthalein) are uniformly mixed, and after absolute ethyl alcohol is completely volatilized, a coating layer is formed on the surface layer of the particle. Through interaction of the modifier and the alkaline desulfurizer, modified desulfurizer particles are uniform in color such as purple red or blue. The modified dry desulfurization agent provided by the invention can significantly improve the SO2 capture capability, and experiments verify that under the same conditions, the SO2 absorption amount of the acid-base indicator modified sodium carbonate is 3-6 times that of unmodified sodium carbonate. In addition, the method is used for other dry alkaline desulfurizers (including but not limited to sodium bicarbonate, calcium hydroxide, calcium oxide, magnesium hydroxide and the like), and has the potential of improving the desulfurization performance under proper conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of flue gas desulfurization, and particularly relates to a preparation method of a dry alkaline absorbent modified by an acid-base indicator and an application thereof in dry desulfurization. Background Art

[0002] Sulfur dioxide (SO 2 ) emissions pose a significant environmental and health risk. Desulfurization agent technology in thermal power and coal power industries is relatively mature, mainly including wet, semi-dry and dry methods. Compared with wet methods in terms of initial investment, operation, maintenance and by-product treatment, dry flue gas desulfurization has the advantages of lower investment to obtain higher SO 2 The potential of removal efficiency is one of the hottest research directions in the field of flue gas purification in recent years. Due to the low demand for water, dry desulfurization technology is very attractive for drought-prone and drought-vulnerable regions or countries; and in the purification of industrial flue gas with low-temperature denitrification, it is particularly necessary to use technology that can complete desulfurization under dry conditions to reduce the flue gas temperature as little as possible.

[0003] Dry desulfurization processes mainly include fixed bed, moving bed and pipeline injection desulfurization. Compared with the high pressure drop of fixed bed or the complex process of moving bed, pipeline injection technology of slaked lime or baking soda is the most promising dry desulfurization process for industrial application. The particle size of the desulfurizer used in pipeline injection dry desulfurization process is mostly less than 20μm, and the main components are calcium-based (Ca(OH) 2 dominant) and sodium groups (such as NaHCO 3 There are two major categories.

[0004] Calcium-based desulfurizers have the characteristics of low cost and high availability, and have been widely used to control sulfur dioxide emissions from coal-fired power plants. However, their utilization rate is low, and the amount used to achieve the desulfurization target is large, and more desulfurization solid waste is generated. Existing research has proposed a modification method for calcium-based desulfurizers, such as the paper (R. Han, F. Sun, J. Gao, S. Wei, Y. Su, Y. Qin, Trace Na 2 CO 3 Addition to Limestone Inducing High-Capacity SO 2 Capture, Environ. Sci. Technol. 51 (2017) 12692–12698.) Studies have shown that trace Na 2 CO 3 Add to CaCO 3The surface of the slag can be effectively increased by calcining at 800°C and the pore size distribution can be optimized, which has a significant promoting effect on sulfation. In addition, the dry desulfurizer prepared by patent CN103752147A is a mixture of quicklime, modifier and wet carbide slag, which has a large specific surface area, a small particle size and a high efficiency desulfurization performance.

[0005] Sodium-based desulfurizers include natural alkali, soda ash, and sodium bicarbonate. Various reports and studies have shown that the use of NaHCO 3 As an adsorbent, it is superior to Na 2 CO 3 , mainly because NaHCO 3 After pyrolysis, the spatial pore structure is formed, which can significantly enhance its interaction with SO 2 Therefore, the modification of dry sodium-based desulfurization agents is mostly focused on NaHCO 3 The pore structure and desulfurization reaction process (temperature, sodium-sulfur ratio, SO 2 concentration, etc.), gas-solid mixed turbulence intensity, etc. There are relatively few studies involving the use of additives to modify sodium bicarbonate desulfurizers. A few patents have proposed methods to improve the dispersibility of sodium bicarbonate. For example, patent CN113233479A proposes physical mixing of silicon dioxide, talcum powder, magnesium hydroxide, magnesium oxide, calcium oxide, etc. with baking soda as dispersants and physical lubricants, thereby suppressing the hygroscopic properties of baking soda to a certain extent. Patent CN 116495757A proposes the use of water glass to form a silica protective film outside the sodium bicarbonate core to improve the fluidity and anti-caking properties of the desulfurizer.

[0006] Sodium carbonate (Na 2 CO 3 ), due to its almost no pore structure, its effect in dry desulfurization is very poor, and it is rarely used as a desulfurization agent in practical applications. 2 Capture Performance of Na 2 CO 3 / γ-Al 2 O 3 Sorbent Modified with Organic Acid, Energy Fuels 38 (2024) 7148–7157.) discloses a modified Na 2 CO 3The method forms an organic sodium compound by adding an organic acid, and then fully decomposes the organic acid sodium by calcining at 600°C. The acidification and decomposition process of the organic acid modification improves the Na 2 CO 3 The pore structure of this method has been shown to improve the absorption of carbon dioxide, but it has not been effective in removing SO 2 The patent CN 115253622 A proposed to use 0.1-1 μm primary particles to obtain coarse particles with a particle size of 1-10 mm through a rolling granulation device, and its microstructure sphericity is better than that of NaHCO 3 Moreover, more pore channels are formed in the process of fine particles agglomerating into particles.

[0007] In summary, the modification research on alkaline desulfurizers is mostly based on the regulation of specific surface area and pore structure. There are no reports on improving the application effect of alkaline desulfurizers in dry flue gas desulfurization by increasing reaction activity or adsorption sites through organic additives. This is an area to be explored. Summary of the invention

[0008] The present invention provides a preparation method of an acid-base indicator surface-modified dry alkaline desulfurizer based on experimental research and application of the dry alkaline desulfurizer as a dry desulfurizer, thereby improving the application effect of the alkaline desulfurizer in dry flue gas desulfurization.

[0009] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0010] A dry alkaline desulfurizer modified by an acid-base indicator, characterized in that the dry alkaline desulfurizer particles are used as the core, and the acid-base indicator compound is uniformly coated on the surface of the alkaline desulfurizer particles; the acid-base indicator on the surface forms a complex with the alkaline desulfurizer, so that the modified alkaline desulfurizer particles present different colors and have the ability to efficiently capture SO 2 ability.

[0011] Different from the method of enhancing performance by changing the specific surface area, the modification method provided by the present invention does not rely on increasing the specific surface area of ​​the material, but rather forms a complex by combining phenolphthalein or sulfonylphenolphthalein on the surface of the alkaline desulfurizer to increase the adsorption sites to significantly improve its SO 2 The modification method for enhancing adsorption performance through surface chemical reaction provided by the present invention is simple and effective, and has obvious innovation and advantages.

[0012] A dry alkaline desulfurization agent modified by an acid-base indicator, characterized in that:

[0013] (1) When the acid-base indicator is phenolphthalein and the alkaline desulfurizer is sodium carbonate, the amount of phenolphthalein added is preferably 0.3% by mass of the sodium carbonate, and the molar percentage is about 0.1%;

[0014] (2) Sodium carbonate particles are modified with phenolphthalein or sulfonephenolphthalein indicators, SO 2 The absorption capacity of SO 2 The absorption capacity is increased by about 3 to 6 times, and phenolphthalein is preferred.

[0015] The acid-base indicator modified dry alkaline desulfurization agent is characterized in that other dry alkaline desulfurization agents can be selected from calcium hydroxide, calcium oxide, sodium bicarbonate, etc.; in particular, sodium bicarbonate is preferably completely pyrolyzed at 150°C before modification.

[0016] The acid-base indicator modified dry alkaline desulfurizer is characterized in that the acid-base indicator is selected from triarylmethane compounds, preferably including thymolphthalein, bromophenol blue, bromothymol blue, etc. The added amount of the acid-base indicator is appropriately adjusted according to the specific process conditions, and the added solid content ranges from 0.3% to 1.2% of the mass of the alkaline absorbent, and the molar percentage is about 0.1%.

[0017] A method for preparing the acid-base indicator modified dry alkaline desulfurization agent, characterized in that it comprises the following steps:

[0018] Step ①: dissolving the acid-base indicator in anhydrous ethanol to form an indicator solution with a certain mass concentration;

[0019] Step ②: Evenly mix the anhydrous ethanol solution of the acid-base indicator with the alkaline desulfurizer particles;

[0020] Step ③: placing the mixture in a vacuum rotary evaporation device or a vacuum stirring evaporation device, evaporating and removing the anhydrous ethanol under vacuum and at a relatively low temperature, and condensing and recovering the evaporated anhydrous ethanol;

[0021] Step ④: After the anhydrous ethanol is completely evaporated, alkaline desulfurizer particles with an acid-base indicator coated on the surface and showing a certain color (purple, blue, cyan or brown, etc.) are obtained.

[0022] In order to facilitate the uniformity of the acid-base indicator coating on the surface of the particles, step ② of the preparation method further includes a mixed solid-liquid ratio of the acid-base indicator solution and the solid alkaline desulfurizer; for coarse-grained alkaline desulfurizer with a particle size >100μm, the ratio of solid mass to solution volume is 1g:(0.5~1)mL; for fine-grained or ultrafine-grained alkaline desulfurizer with a particle size <100μm, 2mm zirconium oxide balls are also required to be added, and the mass volume ratio of the alkaline desulfurizer, zirconium oxide balls and acid-base indicator solution is 1g:(15~25)g:(0.5~1)mL.

[0023] In order to facilitate the timeliness of the acid-base indicator coating on the surface of the particles, step ③ of the preparation method further includes placing the mixture in a container of a vacuum rotary evaporator or a vacuum stirring device, and evaporating anhydrous ethanol at a vacuum degree of about 0.01 to 0.02 MPa and a temperature of 50 to 60°C.

[0024] For the fine-particle modified alkaline desulfurizing agent, step ④ of the preparation method further comprises separating the fine-particle modified alkaline desulfurizing agent and zirconium oxide by sieving after drying.

[0025] An application of an acid-base indicator modified dry alkaline desulfurizer, characterized in that the desulfurizer can be used in different dry desulfurization processes, including:

[0026] (1) Pipeline injection desulfurization process: Ultrafine particles less than 20 μm are directly injected into the flue gas pipeline to fully contact with the sulfur-containing gas and cause desulfurization reaction;

[0027] (2) Fixed bed or moving bed desulfurization process: 100-250 μm coarse particles or ultrafine modified alkaline desulfurizers prepared by granulation molding equipment with 1-10 mm particles or strips are placed in a fixed bed device or a moving bed to make the sulfur-containing gas contact with the absorbent for desulfurization;

[0028] (3) Circulating fluidized bed desulfurization process: particles of 100 to 250 μm are used as the fluidizing medium, and desulfurization reaction occurs with the flue gas under fluidized state.

[0029] The preparation method of the acid-base indicator modified dry desulfurizer provided by the present invention has a simple process and is easy to operate; the energy consumption of drying is low; the anhydrous ethanol can be recycled and reused, and the loss is small. From the molar percentage value of 0.1%, the required amount of the acid-base indicator added belongs to the trace range. Experimental verification shows that when phenolphthalein is used as a dry desulfurizer, the desulfurization performance is excellent in a lower temperature range. Thymolphthalein, bromophenol blue and bromothymol blue can also enhance SO 2The other dry alkaline desulfurizers, such as calcium hydroxide, have a similar color state to sodium carbonate after adding an acid-base indicator. It is predicted that under appropriate conditions, after the acid-base indicator is modified, other dry alkaline desulfurizers will promote SO 2 There should be a similar effect in terms of capture capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The preparation process and particle color state diagram of phenolphthalein modified sodium carbonate in Example 1;

[0031] Figure 2 The SEM microstructure and specific surface area test results of Comparative Example 1 and Example 2 are compared;

[0032] Figure 3 This is a schematic diagram of the composition of the dry fixed bed desulfurization system used in Experimental Example 2 of the present invention;

[0033] Figure 4 It is a comparison chart of the desulfurization performance of Comparative Example 1 and Examples 1 to 6;

[0034] Figure 5 It is a comparison chart of the desulfurization performance of Comparative Example 1 and Examples 4, 7, 8 and 9;

[0035] Figure 6 It is a comparison chart of the desulfurization performance of Comparative Example 2 and Examples 10 to 16;

[0036] Figure 7 This is a comparison chart of the desulfurization performance of Example 1 at different temperatures;

[0037] Figure 8 This is a color comparison chart of sodium carbonate and calcium hydroxide raw materials and their modified acid-base indicators at 150°C. DETAILED DESCRIPTION

[0038] The acid-base indicator can be used to improve the reaction activity or catalytic reaction path of the dry alkaline desulfurization agent, significantly improving the SO 2 The capture efficiency is good for reducing the unit SO 2 Removing the required amount of alkaline desulfurization agent and the subsequent waste slag treatment volume can reduce operating costs and has important application value and practical significance.

[0039] The implementation process of the preparation method of the acid-base indicator surface modified alkaline desulfurizer of the present invention and the results in the dry flue gas desulfurization experiment are described in detail below in conjunction with specific examples.

[0040] Example 1

[0041] The surface modified dry alkaline desulfurizer of the acid-base indicator of this embodiment comprises sodium carbonate particles as the core, mixed with an anhydrous ethanol solution of phenolphthalein, and after the anhydrous ethanol is completely volatilized, the surface of the particles is coated with a complex formed by phenolphthalein and sodium carbonate, and the modified sodium carbonate particles are purple-red. In the following embodiments, the raw material used is industrial sodium carbonate, which is sieved through a sieve to obtain coarse sodium carbonate particles with a particle size of 60-80 mesh.

[0042] like Figure 1 As shown, the preparation of phenolphthalein surface-modified sodium carbonate of this embodiment comprises the following steps:

[0043] Step 1, dissolving phenolphthalein in anhydrous ethanol to form a phenolphthalein solution with a certain mass concentration;

[0044] Step 2, prepare 60-80 mesh sodium carbonate granules raw material, which are white granules, such as Figure 1 Take 50g of sodium carbonate and place it in the rotary evaporator, then add 25mL of phenolphthalein solution and stir to mix. Under the solid-liquid ratio of 1g:0.5mL, the particles are slightly wetted, and the material is purple-pink in the initial 2 to 3 minutes. Figure 1 As shown in state ②, this color can be used to judge the initial mixing state; if the mixing continues, the color of the material will gradually turn white, as shown in Figure 1 As shown in the middle state ③;

[0045] Step 3, fix the rotary evaporator to the rotary evaporator, set the speed to 30r / min, the vacuum degree to about 0.01-0.02Mpa, and the water bath temperature to 50-60°C. As the anhydrous ethanol evaporates further, the particles gradually turn purple-red. Figure 1 As shown in state ④, the uniform color indicates that phenolphthalein is uniformly attached to the sodium carbonate particles. The evaporated anhydrous ethanol can be reused after being condensed and collected;

[0046] Step 4: In order to completely volatilize the residual anhydrous ethanol, the modified sodium carbonate is placed in an oven at 120°C for 60 minutes. When the modified sodium carbonate is at a higher temperature, its color will change to dark purple. Figure 1 When the anhydrous ethanol is completely volatilized and at room temperature, the color of the modified sodium carbonate will become lighter than at a higher temperature, such as Figure 1 As shown in state ⑥.

[0047] Embodiments 2 to 6

[0048] The phenolphthalein surface-modified sodium carbonate of Examples 2 to 6 were all prepared according to the steps of Example 1, and the differences from Example 1 are listed in Table 1.

[0049] Table 1 Process formula of surface modified sodium carbonate with different phenolphthalein solid content in Examples 1 to 6

[0050]

[0051] Embodiments 7 to 9

[0052] The alkaline desulfurizer with acid-base indicator surface modification in this embodiment includes 60-80 mesh sodium carbonate particles as the core, respectively mixed with anhydrous ethanol solutions of thymolphthalein, bromophenol blue and bromothymol blue, and the solid content of the indicator is 0.3%. After the anhydrous ethanol is completely volatilized, a layer of complex formed by the acid-base indicator and sodium carbonate is coated on the surface of the particles, and the modified alkaline absorbent presents a specific color.

[0053] The acid-base indicator surface-modified sodium carbonate of Examples 7 to 9 were all prepared according to the steps of Example 1, and the differences from Example 1 are listed in Table 2.

[0054] Table 2 Process formula of surface modified sodium carbonate with different acid-base indicators in Example 1 and Examples 7, 8, and 9

[0055]

[0056] Example 10

[0057] The acid-base indicator surface modified alkaline desulfurizer of this embodiment comprises a sodium carbonate particle core, which is mixed with an anhydrous ethanol solution of phenolphthalein, and after the anhydrous ethanol is completely volatilized, a layer of complex formed by phenolphthalein and sodium carbonate is coated on the particle surface. The raw material used is ultrafine sodium carbonate obtained by jet milling industrial sodium carbonate.

[0058] The preparation of the phenolphthalein surface-modified carbonic acid of the present embodiment comprises the following steps:

[0059] Step 1, dissolving phenolphthalein in anhydrous ethanol to form an indicator solution with a certain mass concentration;

[0060] Step 2, take 20g of ultrafine sodium carbonate and 500g of 2mm zirconium oxide balls and place them in a rotary evaporator, then add 20mL of phenolphthalein solution and stir to mix.

[0061] Step 3, fix the rotary evaporator to the rotary evaporator, set the speed to 30r / min, the vacuum degree to about 0.01-0.02Mpa, and the water bath temperature to 50-60°C. As the anhydrous ethanol further evaporates, the particles gradually turn purple-red as a whole.

[0062] Step 4: In order to completely volatilize the residual anhydrous ethanol, the modified sodium carbonate is placed in an oven at 120° C. for 60 minutes. Finally, the dried ultrafine modified sodium carbonate and 2 mm zirconium oxide are sieved and separated using a sieve.

[0063] Examples 11 to 16

[0064] The phenolphthalein surface-modified ultrafine sodium carbonate of Examples 11 to 16 were all prepared according to the steps of Example 10, and the differences from Example 10 are listed in Table 3.

[0065] Table 3 Process formula of surface modified ultrafine sodium carbonate with different phenolphthalein solid content in Examples 10 to 16

[0066]

[0067] Comparative Examples 1-2

[0068] The comparative example is industrial sodium carbonate without any addition of any substance, and is screened on the particle size distribution. The coarse particles of industrial sodium carbonate screened by 60-80 mesh screen are compared with Examples 1-9. The ultrafine sodium bicarbonate is obtained by crushing by LNJ-6A type air flow mill under the conditions of air pressure 0.8MPa, classifier frequency 102Hz, and induced draft fan 30Hz. The particle size distribution of ultrafine particles is obtained by detection under dry conditions by LS13320 laser particle size analyzer produced by Beckman Coulter, Inc.USA. The particle size characteristics of the two comparative examples are shown in Table 4.

[0069] Table 4 Particle size characteristics of comparative examples

[0070]

[0071] Experimental Example 1 SEM and Specific Surface Area

[0072] The unmodified sodium carbonate of 60-80 mesh (Comparative Example 1) and the modified sodium carbonate with phenolphthalein solid content of 0.1% (Example 2) were selected for SEM characterization and specific surface area detection analysis. The results are as follows: Figure 2 As shown. From the SEM image with a magnification of 150, it can be clearly observed that the particle shape of sodium carbonate is not destroyed before and after phenolphthalein modification. From the local enlarged image marked by the yellow box, the surface morphology before and after phenolphthalein modification has not changed significantly. The morphology of industrial-grade sodium carbonate coarse particles presents a quasi-porous structure, which may be related to its forming process. The coarse particles obtained by rolling granulation equipment from ultrafine particles of 1 to 5 μm have more pore channels in their microstructure during the process of fine particle aggregation. This result is similar to the SEM image results in patent CN115253622 A. The specific surface areas before and after modification are 1.625m 2 / g and 2.398m 2 / g, a difference of 0.773m 2 / g, and the specific surface area changes very little. The results of SEM and specific surface area reflect that phenolphthalein modification has little effect on the microstructure and specific surface area of ​​sodium carbonate.

[0073] Experimental Example 2 Desulfurization Performance Evaluation

[0074] This experimental example evaluates the desulfurization performance of Examples 1 to 9 and Comparative Example 1 (60 to 80 mesh industrial sodium carbonate raw materials), Examples 10 to 16 and Comparative Example 2 (unmodified ultrafine sodium carbonate), and Example 1 at different temperatures.

[0075] Sulfur capacity is one of the important indicators to measure the desulfurization performance of desulfurizers. It refers to the amount of SO that a unit mass of desulfurizer can absorb under certain conditions. 2 The higher the sulfur capacity, the better the desulfurization performance of the desulfurizer.

[0076] The dry fixed-bed desulfurization system is the most commonly used experimental device for evaluating the performance of desulfurizers. By adjusting the sulfur dioxide concentration, water vapor content, flow rate and temperature at the gas-solid reaction position in the flue gas prepared on the laboratory platform, the ability of different desulfurizers to absorb sulfur dioxide is evaluated.

[0077] The composition and experimental steps of the dry fixed bed desulfurization system are as follows:

[0078] (1) Composition of dry fixed bed desulfurization system: Figure 3 As shown, it consists of air, nitrogen and sulfur dioxide standard gas cylinders, a pressure reducing valve, a flow valve, a gas mixer, a micro-injection pump, a steam generator, a micro-injection pump, a heating jacket and its temperature controller, a heating belt and its temperature controller, a resistance furnace and its temperature controller, a quartz tube, an exhaust gas absorption bottle and a flue gas analyzer.

[0079] (2) Experimental steps: ① Place the desulfurizer in the quartz tube and start the resistance furnace to preheat the quartz tube; ② Turn on the heating jacket and heating belt to heat and insulate the gas mixer and gas path; ③ Control the state of the three-way valve to allow the gas to flow directly to the tail gas absorption bottle through bypass A without passing through the quartz tube; ④ Open the main valve of the gas cylinder, control the gas pressure at the outlet of the gas cylinder through the pressure reducing valve, and control the flow rate of air, nitrogen and sulfur dioxide through the flow meter; ⑤ Turn on the injection pump and steam generator, and the generated steam is mixed evenly with air, nitrogen and sulfur dioxide in the gas mixer to obtain wet flue gas containing sulfur dioxide. The heating jacket and heating belt can maintain the temperature of the wet flue gas and ensure that water vapor does not condense; ⑥ The flue gas analyzer detects the sulfur dioxide content in the wet flue gas. After the concentration stabilizes to the target value, the three-way valve is controlled to switch the wet flue gas to the reaction gas path B to flow through the quartz tube for desulfurization gas-solid reaction. The gas after the reaction finally flows into the tail gas absorption bottle; ⑦ During the gas-solid reaction, the flue gas analyzer continuously monitors and records the sulfur dioxide concentration in the gas after the reaction.

[0080] (3) Graphical analysis: Process and analyze the experimental data to evaluate the desulfurization performance of modified sodium carbonate at different phenolphthalein solid contents, different acid-base indicator types and different temperatures.

[0081] 2.1 Comparison of desulfurization performance between Examples 1 to 6 and Comparative Example 1

[0082] The total flow rate of wet flue gas is 1.2L / min, the volume of water vapor accounts for about 20%, and the quartz tube imports SO 2 The target concentration is 2000 mg / m 3 The modified sodium carbonate of Comparative Example 1 and Examples 1 to 6 were subjected to desulfurization test evaluation at 150°C. The gas-solid contact reaction was performed at an outlet concentration of more than 200 mg / m 3 When it stops, the concentration at the outlet of the quartz tube is SO 2 The curve results of the change over time are as follows Figure 4 At the same time, Figure 4 The table shows the initial concentration of the inlet wet flue gas before the experiment in Comparative Example 1 and Examples 1 to 6, the actual desulfurization agent mass, and the outlet concentration not exceeding 200 mg / m 3 The sulfur capacity value within a time period. The initial concentration fluctuates inevitably due to the inherent errors of the control systems such as the pressure reducing valve, flow meter, and temperature in the dry fixed bed desulfurization evaluation system. The sulfur dioxide concentration is continuously monitored before the desulfurization experiment, and the experiment is started after the outlet concentration stabilizes. The average value is used to calculate the initial concentration of wet flue gas for sulfur capacity, which is close to 2000mg / m 3 .

[0083] From the export SO 2 The concentration variation curve over time shows that when the comparative example 1 and examples 1 to 6 react with the wet flue gas, the outlet SO 2 The concentration of SO2 can be close to zero within a certain period of time, and sulfur dioxide is effectively removed. 2 The time that the concentration is maintained close to zero is longer than that in comparative example 1. The desulfurization performance of the sodium carbonate prepared by the phenolphthalein surface modification method is significantly better than that of the unmodified sodium carbonate raw material. 2 The absorption of phenolphthalein will increase first and then stabilize with the increase of solid content of phenolphthalein. Figure 4 The outlet concentration listed in the table does not exceed 200 mg / m 3 Sulfur capacity value S in the time period 200 It can be seen that the sulfur capacity value of Example 4 (0.3% phenolphthalein solid content) is 422.585 mg / g, and the sulfur capacity value of sodium carbonate in Comparative Example 1 is 65.049 g, and the former is 6.48 times that of the latter. The sulfur capacity of Examples 5 and 6 is close, but both are slightly greater than that of Example 4, that is, after the solid content exceeds 0.3%, the degree to which the sulfur dioxide capture amount continues to increase with the increase in the amount of phenolphthalein added is very small. Considering the economic efficiency of the modification, the solid content of phenolphthalein is preferably 0.3% of that of Example 4.

[0084] 2.2 Comparison of desulfurization performance of Examples 4, 7, 8, 9 and Comparative Example 1

[0085] The total flow rate of wet flue gas is 1.2L / min, the volume of water vapor accounts for about 20%, and the quartz tube imports SO 2 The target concentration is 2000 mg / m 3 The modified sodium carbonate of Comparative Example 1 and Examples 4, 7, 8, and 9 were subjected to desulfurization test evaluation at 150°C. The gas-solid contact reaction was performed at an outlet concentration of more than 200 mg / m 3 When it stops, the concentration at the outlet of the quartz tube is SO 2 The curve results of the change over time are as follows Figure 5 At the same time, Figure 5 The table lists the initial concentration of wet flue gas before the experiment, the actual desulfurization agent mass and the outlet concentration of Comparative Example 1 and Examples 4, 7, 8 and 9. 3 Sulfur capacity values ​​over time.

[0086] Under the condition that the added solid content is 0.3%, the outlet SO 2 The time for the concentration to remain close to zero is longer than that in comparative example 1. Phenolphthalein (phenolphthalein, thymolphthalein) and sulfonylphenolphthalein (bromophenol blue, bromothymol blue) modified sodium carbonate can significantly increase SO 2 The sulfur capacities of Examples 4, 7, 8, and 9 were significantly higher than those of Comparative Example 1, but bromothymol blue and bromophenol blue had a higher capture capacity for SO 2 The degree of improvement in absorption capacity is worse than that of phenolphthalein; the effect of thymephthalein is similar to that of phenolphthalein, but the price of phenolphthalein is lower than that of thymephthalein. For sodium carbonate, phenolphthalein is the preferred choice.

[0087] 2.3 Comparison of desulfurization performance between Examples 10 to 16 and Comparative Example 2

[0088] The total flow rate of wet flue gas is 1.2L / min, the volume of water vapor accounts for about 20%, and the quartz tube imports SO 2 Concentration is 950mg / m 3 The ultrafine sodium carbonate of Examples 10 to 16 and Comparative Example 2 were subjected to a desulfurization test at 150°C. Direct accumulation of ultrafine sodium carbonate will form channel flow due to excessive pressure drop in the bed layer, especially in the state where the airflow direction in the quartz tube flows from top to bottom, and the airflow is even difficult to pass through the bed layer. Therefore, ultrafine sodium carbonate was mixed with 60-80 mesh quartz sand at a mass ratio of 1:50 and then placed in the quartz tube for desulfurization reaction. The gas-solid contact reaction stopped when the time reached 50 minutes, and the concentration SO at the outlet of the quartz tube was 1.3447 W / m. 2 The curve results of the change over time, the initial concentration value of the inlet wet flue gas before the experiment, the actual desulfurization agent mass and the sulfur capacity value within 50 minutes, such as Figure 6 shown.

[0089] From the export SO 2 The concentration variation curve over time shows that when the comparative example 2 and examples 10 to 16 react with the wet flue gas, the outlet SO 2 The concentration of SO2 can also be close to zero within a certain period of time, and sulfur dioxide is effectively removed. 2 The time for the concentration to approach 0 is about 5 minutes. In Examples 10 to 16, the outlet SO 2 The time for the concentration to maintain close to zero is longer than that of Comparative Example 2, up to about 31 minutes, which is 6 times that of Comparative Example 2; and the SO 2 The rising curve is much gentler than that of Comparative Example 2, and the desulfurization performance of the ultrafine sodium carbonate prepared by the phenolphthalein surface modification method is also significantly better than that of the unmodified ultrafine sodium carbonate.

[0090] from Figure 6 From the sulfur capacity values ​​listed in the table, the sulfur capacity value of Example 13 with a solid content of 0.3% is 444.56 mg / g, while the sulfur capacity value of Comparative Example 2 is 148.16 mg / g, the former being three times that of the latter. 2 The improvement in capture capacity is not as great as that of coarse particles, but in the stage where the gas-solid reaction rate is faster (export SO 2 The concentration of SO was close to zero in the period of time. After adding phenolphthalein to the ultrafine powder, 2 The improvement of the capture capacity is comparable to that of the coarse particles. The sulfur capacity of Example 14, Example 15 and Example 16 is close, and is slightly higher than that of Example 13. From Example 13 to Example 16, after the solid content exceeds 0.3%, the degree of further improvement of the sulfur dioxide capture amount with the increase of the phenolphthalein addition is also very small. Considering the economic efficiency of the modification, the phenolphthalein addition solid content of the ultrafine sodium carbonate is selected to be 0.3%.

[0091] 2.4 Comparison of desulfurization performance of modified sodium carbonate in Example 1 at different temperatures

[0092] The total flow rate of wet flue gas is 1.2L / min, the volume of water vapor accounts for about 20%, and the quartz tube imports SO 2 The target concentration is 2000 mg / m 3 The modified sodium carbonate of Example 1 was subjected to a desulfurization test at 110°C to 150°C. The gas-solid contact reaction was performed at an outlet concentration of more than 200 mg / m 3 When it stops, the concentration at the outlet of the quartz tube is SO 2 The curve results of the change over time show that the initial concentration of the inlet wet flue gas before the experiment, the actual desulfurization agent mass and the outlet concentration do not exceed 200 mg / m3 The sulfur capacity value within the time period is as follows Figure 7 shown.

[0093] From the export SO 2 The concentration variation curve over time shows that the high SO 2 The capture capacity is closely related to temperature. At 110 °C, the phenolphthalein-modified absorbent has a strong affinity for SO 2 Sulfur capacity S 200 The sulfur capacity is 74.562 mg / g, which is close to the sulfur capacity of 65.049 mg / g in Comparative Example 1. 2 The capture capacity is improved slightly. However, as the temperature increases, the sulfur capacity increases rapidly, and the desulfurization performance is optimal in the temperature range of 130-150°C. After exceeding 150°C, the capture capacity will be slightly reduced. The sulfur capacity at 120°C is 1.58 times that of Example 1, and the sulfur capacity at 165°C is 1.85 times that of Example 1, which is still quite obvious. Phenolphthalein-modified sodium carbonate has a significant effect on SO 2 The temperature range in which the absorption capacity is significantly improved is 120-165°C.

[0094] Figure 8 This is a comparison chart of the color states of sodium carbonate and calcium hydroxide raw materials and their modification with different acid-base indicators at 150°C. Sodium carbonate and calcium hydroxide will show specific colors after being modified with different acid-base indicators. At 150°C, sodium carbonate modified with phenolphthalein is purple-red, sodium carbonate modified with thymol blue is brown, sodium carbonate modified with bromothymol blue is cyan, and sodium carbonate modified with bromophenol blue is blue. The color of calcium hydroxide after being modified with the same acid-base indicator is similar to that of sodium hydrochloride, and the color is slightly darker.

[0095] In summary, after the surface of phenolphthalein and sulfaphenolphthalein acid-base indicators is modified with sodium carbonate, the microstructure and specific surface area of ​​the desulfurizer will not be changed. Moreover, when used for dry desulfurization, it can significantly increase the SO 2 Based on the experimental results of acid-base indicator modification of sodium carbonate and various phenolphthalein indicators modified calcium hydroxide Ca(OH) 2 The present invention further speculates that other dry alkaline desulfurizers can also significantly improve SO under appropriate conditions after being modified with acid-base indicators. 2 Capture the potential of capabilities.

[0096] Those skilled in the art should understand that, without departing from the core principles of the present invention, the alkaline adsorbent with similar chemical properties obtained by modifying the surface of the acid-base indicator with a dry alkaline absorbent (including but not limited to sodium carbonate, sodium bicarbonate, calcium hydroxide, calcium oxide, magnesium hydroxide, etc.), or by using other methods to combine the acid-base indicator with the alkaline absorbent, all fall within the scope of protection of this patent.

Claims

1. A dry alkaline desulfurization agent modified by an acid-base indicator, characterized in that: With dry alkaline desulfurizer particles as the core, the acid-base indicator compound is evenly coated on the surface of the alkaline desulfurizer particles; the complex formed by the acid-base indicator and the alkaline desulfurizer on the surface makes the modified alkaline desulfurizer particles present different colors while having the ability to efficiently capture SO2.

2. The acid-base indicator modified dry alkaline desulfurization agent according to claim 1, characterized in that: (1) When the acid-base indicator is phenolphthalein and the alkaline desulfurizer is sodium carbonate, the amount of phenolphthalein added is preferably 0.3% by mass of the sodium carbonate, and the molar percentage is about 0.1%; (2) After sodium carbonate particles are modified with phenolphthalein or sulfonephenolphthalein indicators, their SO2 absorption capacity is significantly improved; at the preferred addition amount and temperature, the SO2 absorption capacity is increased by about 3 to 6 times compared with unmodified sodium carbonate, with phenolphthalein being preferred.

3. The acid-base indicator modified dry alkaline desulfurization agent according to claim 1, characterized in that: Other alkaline desulfurizing agents can be selected from calcium hydroxide, calcium oxide, sodium bicarbonate, etc.; in particular, sodium bicarbonate is preferably completely pyrolyzed at 150°C before modification.

4. The acid-base indicator modified dry alkaline desulfurization agent according to claim 1, characterized in that: The acid-base indicator is selected from triarylmethane compounds, preferably including thymolphthalein, bromophenol blue, and bromothymol blue. The amount of the acid-base indicator added is appropriately adjusted according to specific process conditions, and the added solid content ranges from 0.3% to 1.2% of the mass of the alkaline absorbent, and the molar percentage is about 0.1%.

5. A method for preparing the acid-base indicator modified dry alkaline desulfurization agent according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step ①: dissolving the acid-base indicator in anhydrous ethanol to form an indicator solution with a certain mass concentration; Step ②: Mixing the anhydrous ethanol solution of the acid-base indicator with the alkaline desulfurization agent particles; Step ③: placing the mixture in a vacuum rotary evaporation device or a vacuum stirring evaporation device, evaporating and removing the anhydrous ethanol under vacuum and at a relatively low temperature, and recovering the evaporated anhydrous ethanol by condensation; Step ④: After the anhydrous ethanol is completely evaporated, alkaline desulfurizer particles with an acid-base indicator coated on the surface and showing a certain color (purple, blue, cyan or brown, etc.) are obtained.

6. The preparation method according to claim 5, characterized in that: Step ② further includes a mixed solid-liquid ratio of an acid-base indicator solution and an alkaline desulfurizer; for a coarse-grained alkaline desulfurizer with a particle size >100 μm, the ratio of solid mass to solution volume is 1 g: (0.5-1) mL; for a fine-grained or ultrafine-grained alkaline desulfurizer with a particle size <100 μm, 2 mm zirconium oxide balls are also added, and the mass-volume ratio of the alkaline desulfurizer, zirconium oxide balls and acid-base indicator solution is 1 g: (15-25) g: (0.5-1) mL.

7. The preparation method according to claim 5, characterized in that: Step ③ further comprises placing the mixture in a container of a vacuum rotary evaporator, and evaporating anhydrous ethanol at a vacuum degree of about 0.01 to 0.02 MPa and a temperature of 50 to 60°C.

8. The preparation method according to claim 5, characterized in that: Step ④ further comprises separating the fine particles of modified alkaline desulfurizing agent and zirconium oxide by sieving after drying.

9. The use of the dry alkaline desulfurization agent modified by the acid-base indicator according to any one of claims 1 to 4, characterized in that: The desulfurizer can be used in different dry desulfurization processes, including: (1) Pipeline injection desulfurization process: Ultrafine particles less than 20 μm are directly injected into the flue gas pipeline to fully contact with the sulfur-containing gas and cause desulfurization reaction; (2) Fixed bed or moving bed desulfurization process: 100-250 μm coarse particles or ultrafine modified alkaline desulfurizers prepared by granulation molding equipment with 1-10 mm particles or strips are placed in a fixed bed device or a moving bed to make the sulfur-containing gas contact with the absorbent for desulfurization; (3) Circulating fluidized bed desulfurization process: particles of 100 to 250 μm are used as the fluidizing medium, and desulfurization reaction occurs with the flue gas under fluidized state.

Images