A porous desulfurizer based on iron-containing clay and a method for preparing the same

Abstract

The application discloses a kind of porous desulfurizer based on iron-containing clay and its preparation method, belong to desulfurizer technical field.The desulfurizer stick is by calcium-based / sodium-based active component precursor and natural clay in situ composite by steam jet mill integrated process formation;Calcium-based / sodium-based active component precursor is one or several of calcium oxide, calcium acetate, calcium hydroxide, sodium bicarbonate.The specific surface area of the prepared desulfurizer is high, pore volume increases significantly and forms abundant mesoporous structure, greatly enhances the adsorption and reaction capacity to SO2;Wherein the Fe atom contained in clay can catalyze SO2 oxidation into SO3, promote the formation of stable sulfate, significantly improve desulfurization efficiency and sulfur capacity.The application solves the defects of traditional calcium-based / sodium-based desulfurizer, such as low specific surface area, few pores and insufficient reactivity, and has the advantages of simple process, low cost, good desulfurization performance, suitable for low-temperature flue gas and other advantages, which can be widely applied in flue gas purification in steel, electric power, building materials and other industries.

Description

Technical Field

[0001] This invention relates to the field of desulfurizing agent technology, and more specifically, to a porous desulfurizing agent based on iron-containing clay and its preparation method. Background Technology

[0002] Currently, industrial flue gas desulfurization technologies are mainly divided into three categories: wet, dry, and semi-dry. Among them, wet desulfurization (such as the limestone-gypsum method) is a mature technology with high desulfurization efficiency (>95%), and is the most widely used technology in coal-fired power plants. However, wet desulfurization systems are complex, have high investment and operating costs, require a large area, and face challenges in wastewater and waste residue treatment. Furthermore, they consume a large amount of water, limiting their application in water-scarce areas or in the retrofitting of small and medium-sized industrial boilers / kilns.

[0003] In contrast, dry and semi-dry desulfurization technologies, due to their simple process flow, no wastewater discharge, relatively low investment and operation and maintenance costs, and small footprint, have shown unique advantages and application prospects in fields such as steel sintering, waste incineration, industrial boilers, and small and medium-sized power plants. The core of this type of technology lies in the use of solid desulfurizing agents, which react with SO2 in flue gas in a dry or semi-dry state. Among them, calcium-based desulfurizing agents (mainly composed of CaO or Ca(OH)2) have become the mainstream choice due to their wide availability and low price. However, traditional calcium-based dry / semi-dry desulfurization technologies also face a series of severe challenges in practical applications, the fundamental reason being the limitations of the following physicochemical properties of the desulfurizing agent materials:

[0004] (1) Small specific surface area and poor pore structure: CaO obtained by calcination of natural limestone or Ca(OH)2 obtained by digestion often has dense original particles and a limited specific surface area (usually <20m). 2 The particle size is 0.5 g, and it lacks a well-developed mesoporous structure. This results in a severely insufficient gas-solid reaction contact area, high diffusion resistance of SO2 inside the particles, and a large number of active components unable to participate in the reaction.

[0005] (2) Low reactivity and calcium utilization: Due to mass transfer issues, desulfurization reactions mostly occur on the surface of particles, and the internal active components are wasted. In industrial applications, the calcium utilization rate of calcium-based desulfurizers is generally low (usually only 20%-40%), which means that excessive desulfurizer needs to be added, which not only increases raw material consumption and operating costs, but also generates more waste residue that needs to be treated.

[0006] (3) The reaction product layer is dense, which hinders further reaction: The CaSO3 / CaSO4 product layer generated by the reaction will form a dense coating layer on the particle surface, which further hinders the diffusion of SO2 into the interior, causing the reaction to terminate prematurely.

[0007] (4) Lack of low-temperature catalytic activity: At lower temperatures (especially in medium-low temperature dry desulfurization processes), the chemical reaction rate between SO2 and CaO is slow. There is a lack of effective catalytic components to activate the reaction molecules and lower the reaction energy barrier, which limits its efficient operation in a wide temperature window.

[0008] (5) Limitations of traditional improvement methods: To improve the performance of desulfurizers, researchers have tried methods such as ultrafine grinding, hydration activation, and the addition of organic acids. Although these methods have some effect, they often face problems such as increased cost, complex processes, or poor long-term stability. Developing new non-precious metal catalysts to improve low-temperature activity also often faces challenges in terms of cost, stability, or compatibility with desulfurizers.

[0009] Therefore, the key to overcoming the bottleneck of dry / semi-dry desulfurization technology and promoting its wider application lies in how to fundamentally design a new type of desulfurizing agent material that can significantly increase its specific surface area and porosity to enhance mass transfer while maintaining the low-cost advantage of calcium-based materials, and introduce inexpensive and efficient catalytic components to enhance intrinsic reactivity.

[0010] Natural clay minerals, particularly montmorillonite (whose main mineral form is bentonite) and attapulgite, have come into the research focus. However, how to efficiently, stably, and highly disperse calcium-based active components onto natural clay carriers, fully utilize their structural iron, and simultaneously achieve large-scale, low-cost material preparation through process design to form stable formulations suitable for dry / semi-dry processes, remains a technical challenge that has not yet been systematically solved by existing technologies. Existing loading methods (such as conventional impregnation and mechanical mixing) often fail to achieve uniform dispersion of active components at the nanoscale and effective coupling with the iron sites on the carrier, and the prepared powders exhibit poor flowability and wear resistance.

[0011] Based on this, this application aims to develop a porous desulfurizer based on iron-containing clay. Through innovative material design and preparation process, it comprehensively solves the core problems of traditional calcium-based desulfurizers, such as small specific surface area, few pores, low activity and utilization rate, and lack of low-temperature catalytic promotion, providing a high-performance and low-cost new solution for dry / semi-dry flue gas desulfurization. Summary of the Invention

[0012] The purpose of this application is to overcome the shortcomings of the prior art and provide a porous desulfurizing agent based on iron-containing clay and its preparation method. This desulfurizing agent uses natural and inexpensive clay as a carrier, and through a combination of structural design, active component loading, and advanced preparation processes, it significantly improves the specific surface area and mass transfer efficiency of the material while introducing and fully utilizing the iron element of the carrier itself as a catalytic active site, thus achieving a comprehensive improvement in desulfurization performance.

[0013] To achieve the above objectives, this application adopts the following technical solution:

[0014] A porous desulfurizing agent based on iron-containing clay, wherein the desulfurizing agent is formed by in-situ composite of calcium-based / sodium-based active component precursor and natural clay through an integrated steam jet milling process; the calcium-based / sodium-based active component precursor is one or more of calcium oxide, calcium acetate, calcium hydroxide, and sodium bicarbonate.

[0015] This application is further configured to,

[0016] The desulfurizing agent uses at least one of the following as active components: a mixture of CaO and Ca(OH)2, Ca(OH)2, and Na2CO3. The content of the active component in the desulfurizing agent is 20-40 wt%.

[0017] This application further specifies that the desulfurizing agent uses the iron element contained in the natural clay itself as the catalytic component, and the Fe2O3 content of the natural clay is 0.5-6wt%.

[0018] This application further specifies that the natural clay is one or more of bentonite and attapulgite.

[0019] This application further specifies that, when the natural clay is bentonite, the mass percentage of montmorillonite in the bentonite is 70-95%.

[0020] This application further specifies that the specific surface area of ​​the desulfurizing agent is greater than 150 m². 2 / g, median particle size d 50 Less than 3μm.

[0021] This application further specifies that, under conditions of 150°C and 0% relative humidity, the desulfurization efficiency of the desulfurizing agent for SO2 gas with a concentration of 2000ppm is not less than 90% within 90 minutes; and under conditions of 150°C and 20% relative humidity, the desulfurization efficiency of the desulfurizing agent for SO2 gas with a concentration of 2000ppm is maintained at 100% for more than 400 minutes.

[0022] A method for preparing a porous desulfurizing agent based on iron-containing clay includes the following steps:

[0023] S1. Premix the powdered calcium-based / sodium-based active component precursor with natural clay in a certain proportion;

[0024] S2. The premixed material is continuously fed into a steam jet mill, using superheated steam as the working medium, and the steam digestion of the active component precursor and the nanoscale composite with the bentonite carrier are completed simultaneously in the supersonic turbulent flow field to obtain composite powder.

[0025] S3. Collect and dry the composite powder to obtain a porous desulfurizer based on iron-containing clay.

[0026] The present application further specifies that, in step S2, the feeding rate of the premixed material is 40-80 kg / h; the pressure of the superheated steam is 0.4-0.8 MPa and the temperature is 250-300℃; and the classifier speed of the steam jet mill is 2500-3000 r / min.

[0027] This application further specifies that, in step S2, the airflow velocity generated by the Laval nozzle of the steam jet mill is supersonic, and the turbulent kinetic energy in the core region of the mill cavity is greater than 30,000 m³ / s. 2 / s 2 .

[0028] In summary, this application has the following beneficial effects:

[0029] (1) One-step high-efficiency preparation process: This application uses a steam jet mill as the core reactor to complete multiple key steps in a supersonic turbulent flow field, including ultrafine grinding and steam digestion of calcium-based / sodium-based active component precursors, exfoliation and dispersion of natural clay carriers, and nanoscale composite of calcium-based / sodium-based active component precursors and natural clay. This process replaces the complex multi-step process of "acid / alkali activation, liquid phase impregnation, long-term drying, and high-temperature calcination" required in the preparation of traditional composite desulfurizers, shortening the production cycle from several hours or even more than ten hours to minutes, achieving extreme simplification of the process and a leapfrog improvement in production efficiency.

[0030] (2) In the steam jet mill, superheated steam reacts instantaneously with the surface of the calcium-based active component precursor, achieving nearly 100% complete digestion of the calcium-based active component precursor and completely eliminating the inert "core-shell" structure present in traditional digestion methods; the sodium-based active component precursor can react violently with superheated steam, significantly increasing the reaction rate. Simultaneously, high-speed collisions and shear forces fully peel off the natural clay layers and allow them to recombine in situ with newly generated nano-active components, forming a tightly embedded structure. The specific surface area of ​​the resulting composite desulfurizer (100-300 m²) is... 2 The concentration of active components ( / g) is significantly higher than that of traditional digested lime, and the active components are highly dispersed at the nanoscale.

[0031] (3) Due to the nano-sized active components and their tight bonding with the porous carrier, the desulfurizer of this application can still maintain excellent initial desulfurization activity under low relative humidity (even 0% humidity) and low temperature (120-150℃) conditions. Experiments show that its desulfurization efficiency can still be greater than 90% within 90 minutes at 0% humidity, and its "penetration time" in the 5-20% low humidity range far exceeds that of traditional desulfurizers. This effectively solves the core bottleneck of dry desulfurization technology's excessive dependence on flue gas humidity and broadens its application range.

[0032] (4) This process directly uses inexpensive calcium-based / sodium-based active component precursors and natural clay as all raw materials, without the need for any chemical modification reagents (such as acid, alkali, and salt precursors), which greatly reduces the cost of raw materials from the source. The entire process uses superheated steam as the only medium, with no wastewater or waste acid generated. The waste gas is mainly low-temperature steam, which can realize waste heat recovery. It is a clean, low-carbon, and green manufacturing process with extremely high industrial economic and environmental value.

[0033] (5) The core product, desulfurizing agent, is an ultrafine, highly fluid powder that can be directly used in spray or circulating fluidized bed desulfurization systems. The desulfurizing agent can be quickly converted into high-strength granules through simple dry granulation, which is suitable for moving bed or fixed bed reactors and can be flexibly matched with various dry / semi-dry desulfurization process equipment.

[0034] (6) The intrinsic catalytic function of the carrier is utilized (the iron element widely present in natural clay (as an isomorphous substitution ion) is creatively used as a catalytic site). These iron sites can catalyze the oxidation of SO2 to SO3 in the desulfurization reaction, promote the formation of more stable sulfates, thereby breaking through the limitation of slow reaction kinetics of traditional calcium-based desulfurizers at low temperatures, and improving the overall reaction rate and desulfurization efficiency.

[0035] (7) A multi-level synergistic efficiency enhancement mechanism has been formed: the three elements of "high specific surface area carrier (physical adsorption and mass transfer channel)" + "highly dispersed calcium-based active center (chemical absorption host)" + "in-situ iron-based catalytic site (reaction promoter)" work together to form an efficient desulfurization process integrating "adsorption-catalysis-absorption".

[0036] (8) Significantly improves calcium utilization and desulfurization efficiency: Abundant pores and highly dispersed active centers allow more calcium atoms to participate in the reaction, effectively overcoming product layer obstacles. It is estimated that calcium utilization can be increased by more than 50% compared to traditional lime. Under the same dosage, higher and more stable desulfurization efficiency can be achieved. Attached Figure Description

[0037] Figure 1 SEM images of CaO and the desulfurizing agent prepared in Example 1 (a1 and a2 are SEM images of CaO, and b1 and b2 are SEM images of the desulfurizing agent in Example 1).

[0038] Figure 2 The EDS energy spectrum of CaO;

[0039] Figure 3 The image shows the EDS energy spectrum of the desulfurizing agent prepared in Example 1. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] This application is based on a porous desulfurizing agent containing iron clay, which is formed by in-situ compounding of calcium-based / sodium-based active component precursors (one or more of calcium oxide, calcium acetate, calcium hydroxide, and sodium bicarbonate) with natural clay (one or more of bentonite and attapulgite; when the natural clay is bentonite, the mass percentage of montmorillonite in the bentonite is 70-95%) through an integrated steam jet mill process.

[0042] This desulfurizing agent uses at least one of the following as its active component: a mixture of CaO and Ca(OH)2, Ca(OH)2, and NaCO3 (the content of the active component in the desulfurizing agent is 20-40 wt%). The catalytic component is the iron element contained in natural clay (the Fe2O3 content of natural clay is 0.5-6 wt%). The specific surface area of ​​the desulfurizing agent is greater than 150 m². 2 / g, median particle size d 50 The desulfurization agent has a particle size of less than 3μm. Under conditions of 150℃ and 0% relative humidity, the desulfurization efficiency of the desulfurizing agent for SO2 gas with a concentration of 2000ppm is not less than 90% within 90 minutes. Under conditions of 150℃ and 20% relative humidity, the desulfurization efficiency of the desulfurizing agent for SO2 gas with a concentration of 2000ppm is maintained at 100% for more than 400 minutes. It can be applied to dry or semi-dry desulfurization processes for flue gas in coal-fired boilers, steel sintering plants, and industrial kilns.

[0043] The preparation method includes the following steps:

[0044] S1. Premix the powdered calcium-based / sodium-based active component precursor with natural clay in a certain proportion;

[0045] S2. The premixed material is continuously fed into a steam jet mill (feed rate of 40-80 kg / h). Using superheated steam as the working medium, the steam digestion of the active component precursor and the nanoscale composite with the bentonite carrier are simultaneously completed in a supersonic turbulent flow field (superheated steam pressure 0.4-0.8 MPa, temperature 250-300℃; classifier speed of the steam jet mill 2500-3000 r / min; airflow velocity generated by the Laval nozzle of the steam jet mill is supersonic; turbulent kinetic energy in the core region of the mill cavity is greater than 30000 m³ / h). 2 / s 2 ), to obtain composite powder;

[0046] S3. Collect and dry the composite powder to obtain a porous desulfurizer based on iron-containing clay.

[0047] Example 1: Preparation of Ca(OH)2 / bentonite desulfurizer by in-situ digestion and integrated steam jet milling method

[0048] S1. Raw material preparation and premixing

[0049] Purchase industrial-grade high-purity powdered quicklime (CaO content ≥92%) and powdered natural bentonite ore (montmorillonite content ≥85%, Fe2O3 content approximately 5.0wt%). Based on a target Ca(OH)2 content of 30wt% in the final composite desulfurizer, weigh 700g of quicklime and 2138g of bentonite granules (dry basis), and physically premix them in a double cone mixer for 15 minutes to obtain the premixed raw material.

[0050] S2, Steam jet mill integrated digestion and compounding

[0051] The premixed raw materials were continuously fed into an LNGS-80 steam jet mill (feed rate 60 kg / h). After crushing, steam digestion, and compounding (in the mill chamber, the material is accelerated, collided, and crushed by the supersonic superheated steam flow generated by the Laval nozzle; simultaneously, the fresh surface of the quicklime particles undergoes an instantaneous digestion reaction with the high-temperature steam (CaO + H2O(g) → Ca(OH)2), and the generated nano-sized Ca(OH)2 collides, embeds, and compoundes with the simultaneously exfoliated bentonite nanosheets in highly turbulent flow), the material was classified and the fine powder product was collected by a cyclone separator to obtain a median particle size D. 50 It is a grayish-white, highly fluid ultrafine composite powder with a particle size of 1.0-2.5 μm. The waste gas generated during the processing (mainly cooled steam) is discharged after passing through a bag filter. The airflow velocity generated by the Laval nozzle of the steam jet mill is 1.5-2.5 Ma (approximately 510-850 m / s), and the turbulence in the core region of the grinding chamber is 30,000-50,000 m / s. 2 / s 2 The working medium is superheated steam, with a steam pressure of 0.6 MPa and a steam temperature of 280℃. The classifier speed is 2800 r / min, and the feeding speed is controlled by a screw feeder at 50 kg / h.

[0052] S3, Post-processing

[0053] The ultrafine composite powder was dried in an oven at 100℃ for 2 hours to remove trace amounts of physically adsorbed water. The resulting desulfurizing agent product was designated as Sample 1.

[0054] Comparative Example 1: Conventional grinding and mechanical mixing were used.

[0055] Using the same mass of quicklime and bentonite as in Example 1, the materials were mechanically mixed in a high-speed mixer for 1 hour at a mixing rate of 500 r / min, and then dried at 105°C for 12 hours. The resulting powder product was designated as Sample 2.

[0056] Comparative Example 2:

[0057] The quicklime powder was left untreated and designated as sample 3.

[0058] Comparative Example 3:

[0059] The baking soda powder was left untreated and was designated as sample 4.

[0060] Comparative Example 4: Quicklime digested by steam jet mill only (without carrier)

[0061] Using only 700g of quicklime granules, without adding bentonite, and processing with the exact same steam jet mill parameters as in Example 1, the resulting pure Ca(OH)₂ ultrafine powder was designated as Sample 5. This comparative example was used to verify the role of the bentonite carrier.

[0062] Comparative Example 5: Digestion of baking soda using only steam jet mill (without carrier)

[0063] Using only 700g of baking soda granules, without adding bentonite, the sample was processed using the exact same steam jet milling parameters as in Example 1. The resulting ultrafine powder was designated as Sample 6. This comparative example was used to verify the role of the pure active component and the bentonite carrier.

[0064] Example 2: Using attapulgite instead of bentonite

[0065] The bentonite in Example 1 was replaced with an equal mass of attapulgite powder (Fe2O3 content ≤ 0.5 wt%), and the remaining steps and process parameters were the same as in Example 1. The resulting Ca(OH)2 / attapulgite composite powder was designated as Sample 7. This comparative example was used to verify the structure of montmorillonite and the special role of its intrinsic iron element.

[0066] Example 3: Preparation of sodium bicarbonate / bentonite desulfurizer by in-situ combined steam jet milling method

[0067] 952g of baking soda (NaHCO3 content ≥99%) was used instead of quicklime and premixed with 1400g of bentonite granules, while other conditions remained the same as in Example 1. The resulting ultrafine powder was designated as Sample 8.

[0068] Simulated flue gas desulfurization tests were conducted on samples obtained from Examples 1-3 and Comparative Examples 1-5 using a fixed-bed reactor. Calcium utilization rate was calculated (calcium utilization rate = (total moles of SO2 actually removed) / (total moles of calcium in the desulfurizing agent) × 100%). The test method was as follows: 1.0 g of sample (40-60 mesh) was weighed. The reaction gas composition was: SO2 2000 ppm, O2 5%, N2 balance gas, and a total gas flow rate of 500 mL / min. The outlet SO2 concentration was monitored using an online flue gas analyzer. The reaction temperature was 150 ± 2℃, and the relative humidity was 0%, 20%, and 60%. The breakthrough point was defined as: when the outlet SO2 concentration reached 10% of the inlet concentration (CO), i.e., 200 ppm, breakthrough was considered; the time at which this occurred was recorded as the breakthrough time (t). B ).

[0069] The desulfurization efficiency and calcium utilization rate of each embodiment and comparative sample are shown in Table 1.

[0070] Table 1

[0071]

[0072] SEM images of the raw material quicklime and the desulfurizing agent prepared in Example 1 are shown below. Figure 1 As shown in Table 2, the specific surface area, average pore size, and pore volume of the samples prepared in each embodiment and comparative example are shown in Table 2.

[0073] Table 2

[0074]

[0075] The EDS spectrum of CaO is shown below. Figure 2 As shown, the elemental data of the CaO surface total spectrum are shown in Table 3. The EDS energy spectrum of the desulfurizing agent prepared in Example 1 is shown in [Table 3]. Figure 3 As shown.

[0076] Table 3

[0077]

[0078] The above description is merely a preferred embodiment of this application. The scope of protection of this application is not limited to the above embodiments. All technical solutions falling within the scope of this application's concept are within the scope of protection of this application. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of this application should also be considered within the scope of protection of this application.

Claims

1. A porous desulfurizing agent based on iron-containing clay, characterized in that, The desulfurizing agent is formed by in-situ compounding of calcium-based / sodium-based active component precursors and natural clay through an integrated steam jet mill process; the calcium-based / sodium-based active component precursors are one or more of calcium oxide, calcium acetate, calcium hydroxide, and sodium bicarbonate. The desulfurizing agent uses at least one of the following as active components: a mixture of CaO and Ca(OH)2, Ca(OH)2, and Na2CO3. The content of the active component in the desulfurizing agent is 20-40 wt%. The desulfurizing agent uses the iron element contained in natural clay as the catalytic component, and the Fe2O3 content of natural clay is 0.5-6wt%.

2. The porous desulfurizing agent based on iron-containing clay according to claim 1, characterized in that, Natural clay is one or more of bentonite and attapulgite.

3. The porous desulfurizing agent based on iron-containing clay according to claim 2, characterized in that, When the natural clay is bentonite, the mass percentage of montmorillonite in the bentonite is 70-95%.

4. The porous desulfurizing agent based on iron-containing clay according to claim 1, characterized in that, The specific surface area of ​​the desulfurizing agent is greater than 150m². 2 / g, median particle size d 50 Less than 3μm.

5. The porous desulfurizing agent based on iron-containing clay according to claim 1, characterized in that, Under conditions of 150℃ and 0% relative humidity, the desulfurizing agent has a desulfurization efficiency of no less than 90% for SO2 gas with a concentration of 2000ppm within 90 minutes; under conditions of 150℃ and 20% relative humidity, the desulfurizing agent maintains a desulfurization efficiency of 100% for SO2 gas with a concentration of 2000ppm for more than 400 minutes.

6. A method for preparing a porous desulfurizing agent based on iron-containing clay according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Powdered calcium-based / sodium-based active component precursors are premixed with natural clay to obtain premixed raw materials; S2. The premixed raw materials are continuously fed into a steam jet mill, and after crushing, steam digestion and compounding, they are classified and the fine powder products are collected by a cyclone separator to obtain composite powder. S3. Collect and dry the composite powder to obtain a porous desulfurizer based on iron-containing clay.

7. The method for preparing a porous desulfurizing agent based on iron-containing clay according to claim 6, characterized in that, In step S2, the feed rate of the premixed material is 40-80 kg / h; the pressure of the superheated steam is 0.4-0.8 MPa and the temperature is 250-300℃; the classifier speed of the steam jet mill is 2500-3000 r / min.

8. The method for preparing a porous desulfurizing agent based on iron-containing clay according to claim 6, characterized in that, In step S2, the airflow velocity generated by the Laval nozzle of the steam jet mill is supersonic, and the turbulent kinetic energy in the core region of the grinding chamber is greater than 30,000 m³ / s. 2 / s 2 .

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