A composite activated carbon fixed bed for catalytic flue gas desulfurization and a catalytic flue gas desulfurization device

Abstract

The application discloses a composite activated carbon fixed bed for catalytic flue gas desulfurization and a catalytic flue gas desulfurization device, and aims at solving the problem of how to improve the desulfurization efficiency, effectively reduce the cost and overcome the problems of activated carbon bed collapse and resistance. The composite activated carbon fixed bed comprises a first granular activated carbon layer, an activated carbon fiber layer and a second granular activated carbon layer arranged in sequence along the flue gas flow direction. The first granular activated carbon layer and the second granular activated carbon layer are both filled with granular activated carbon, and the activated carbon fiber layer is filled with activated carbon fiber. The activated carbon fiber layer is arranged between the first granular activated carbon layer and the second granular activated carbon layer to form a three-layer sandwich structure. The pore size distribution of the activated carbon fiber presents a single peak characteristic, and the single peak is composed of micropores with a pore size less than 2 nm. The pore size distribution of the granular activated carbon presents a multi-peak characteristic, and the multi-peak characteristic comprises a micropore peak and a macropore peak. The micropore peak is composed of micropores with a pore size less than 2 nm, and the macropore peak is composed of macropores with a pore size greater than 50 nm.

Description

Technical Field

[0001] This invention relates to the field of catalytic flue gas desulfurization technology, specifically to a composite activated carbon fixed bed and a catalytic flue gas desulfurization device for catalytic flue gas desulfurization. Background Technology

[0002] The basic principle of catalytic flue gas desulfurization technology is as follows: sulfur dioxide, water, and oxygen in the flue gas to be desulfurized are adsorbed on the desulfurization catalyst (specifically, an activated carbon bed) and react under the catalytic action of the active components to generate sulfuric acid; when the sulfuric acid attached to the desulfurization catalyst reaches a certain level, the desulfurization catalyst can be washed with a regeneration liquid (usually dilute sulfuric acid and / or water) to remove the attached sulfuric acid and release the active sites of the desulfurization catalyst; the regeneration liquid after use can be reused as a by-product (usually dilute sulfuric acid).

[0003] Current carbon-based flue gas desulfurization methods primarily utilize granular activated carbon (GAC) to form activated carbon beds. Granular activated carbon is widely available, relatively inexpensive, and possesses a certain level of mechanical strength. However, see... Figure 1 As shown, granular activated carbon has a complex and deep internal pore structure. During desulfurization, flue gas molecules often need to travel a long diffusion path to reach the deep effective adsorption sites, resulting in high mass transfer resistance and limited adsorption rate. Furthermore, granular activated carbon has a relatively low sulfur capacity (adsorption capacity). To maintain desulfurization efficiency, industrial applications often require large equipment volumes and frequent regeneration operations. During frequent regeneration, granular activated carbon is prone to oxidation loss and mechanical wear, leading to high carbon consumption.

[0004] Activated carbon fiber (ACF) has been introduced into the desulfurization field as a novel and highly efficient adsorption material. (See also...) Figure 2 As shown, compared with granular activated carbon, activated carbon fibers have a larger specific surface area, abundant micropores, and are mainly distributed on the fiber surface. This structure allows flue gas molecules to reach the adsorption sites more quickly, shortening the adsorption path. Therefore, activated carbon fibers have extremely fast adsorption kinetics and extremely high sulfur capacity. However, activated carbon fibers also face severe challenges in practical engineering applications: 1) The price of activated carbon fibers is much higher than that of granular activated carbon. 2) The bulk density of activated carbon fibers is relatively low, resulting in a low effective carbon content for the same volume. 3) Activated carbon fibers are usually in the form of felt or cloth, which can easily lead to excessive pressure drop (resistance) in the activated carbon bed; the activated carbon bed is prone to shrinkage and collapse, leading to flue gas short-circuiting (leakage). Summary of the Invention

[0005] The purpose of this invention is to provide a composite activated carbon fixed bed and a catalytic flue gas desulfurization device for catalytic flue gas desulfurization, so as to solve the problems of improving desulfurization efficiency, effectively reducing costs, and overcoming activated carbon bed collapse and resistance.

[0006] In the first aspect, a composite activated carbon fixed bed for catalytic flue gas desulfurization comprises a first granular activated carbon layer, an activated carbon fiber layer, and a second granular activated carbon layer arranged sequentially along the flue gas flow direction; both the first and second granular activated carbon layers are filled with granular activated carbon, and the activated carbon fiber layer is filled with activated carbon fiber; the activated carbon fiber layer is sandwiched between the first and second granular activated carbon layers, forming a three-layer sandwich structure; wherein the pore size distribution of the activated carbon fiber exhibits a single-peak characteristic, the single peak being composed of micropores with a pore size of less than 2 nm; the pore size distribution of the granular activated carbon exhibits a multi-peak characteristic, the multi-peak characteristic including micropore peaks and macropore peaks, the micropore peaks being composed of micropores with a pore size of less than 2 nm, and the macropore peaks being composed of macropores with a pore size of greater than 50 nm.

[0007] As an optimization and / or instance of the aforementioned composite activated carbon fixed bed for catalytic flue gas desulfurization, further: the volume ratio of the first granular activated carbon layer, the activated carbon fiber layer, and the second granular activated carbon layer is 1:(0.5-2.0):1; and it is configured to operate at a space velocity of 400 h⁻¹. -1 Up to 1000h -1 It operates under the following conditions.

[0008] As an optimization and / or instance of the above-mentioned composite activated carbon fixed bed for catalytic flue gas desulfurization, further: the volume ratio of the first granular activated carbon layer, the activated carbon fiber layer and the second granular activated carbon layer is 1:1:1.

[0009] As an optimization and / or instance of the aforementioned composite activated carbon fixed bed for catalytic flue gas desulfurization, further: the packing density of the activated carbon fiber layer is 0.3 g / cm³. 3 Up to 0.5g / cm 3 .

[0010] As an optimization and / or instance of the above-mentioned composite activated carbon fixed bed for catalytic flue gas desulfurization, further: the first granular activated carbon layer and the activated carbon fiber layer, and the second granular activated carbon layer and the activated carbon fiber layer are physically separated by a breathable separator.

[0011] As an optimization and / or instance of the above-mentioned composite activated carbon fixed bed for catalytic flue gas desulfurization, further: the permeable isolation element is made of glass fiber mesh.

[0012] As an optimization and / or instance of the above-mentioned composite activated carbon fixed bed for catalytic flue gas desulfurization, further: the activated carbon fiber is viscose-based activated carbon fiber.

[0013] As an optimization and / or instance of the above-mentioned composite activated carbon fixed bed for catalytic flue gas desulfurization, further: the granular activated carbon is columnar granular activated carbon with a diameter of 2 mm to 6 mm.

[0014] As an optimization and / or instantiation of the above-mentioned composite activated carbon fixed bed for catalytic flue gas desulfurization, further: the peak value of the single peak is between 0.7 nm and 1.5 nm; the peak value of the macropore peak is between 100 nm and 5000 nm.

[0015] Secondly, a catalytic flue gas desulfurization device includes at least one desulfurization reactor. The desulfurization reactor has an inlet, an outlet, a drain outlet, and an activated carbon bed located within the desulfurization reactor. The desulfurization reactor is equipped with a regeneration liquid spraying device for washing and regenerating the activated carbon bed. During operation, the flue gas to be desulfurized enters the desulfurization reactor through the inlet, passes through the activated carbon bed for desulfurization, and is then discharged from the outlet of the desulfurization reactor as desulfurized flue gas. The sulfur dioxide in the flue gas to be desulfurized reacts on the activated carbon bed to form sulfuric acid when passing through it. During the washing and regeneration of the activated carbon bed, the sulfuric acid enters the regeneration liquid sprayed on the activated carbon bed and is discharged from the drain outlet of the desulfurization reactor. The activated carbon bed is the composite activated carbon fixed bed for catalytic flue gas desulfurization described in the first aspect above.

[0016] The composite activated carbon fixed bed for catalytic flue gas desulfurization of the present invention, through the combination of a three-layer sandwich structure consisting of a first granular activated carbon layer, an activated carbon fiber layer, and a second granular activated carbon layer, and a specific pore size distribution, can produce the following technical effects:

[0017] First, it solves the problems of easy collapse and short circuit of activated carbon fiber layers, improving the mechanical stability of the composite activated carbon fixed bed. Using the first and second granular activated carbon layers as support and compaction layers, the activated carbon fiber layer is tightly sandwiched in the middle, forming a three-layer sandwich structure. This structure utilizes the high mechanical strength and bulk density of granular activated carbon, effectively limiting the volume shrinkage and displacement of the activated carbon fibers during airflow impact or washing regeneration processes, preventing the activated carbon fiber layer from collapsing or forming voids, thus avoiding flue gas short circuits and ensuring the long-term stability of desulfurization efficiency.

[0018] Secondly, by matching specific pore size distributions, synergistic optimization of mass transfer efficiency and adsorption kinetics is achieved. In this invention, the outer layer of granular activated carbon exhibits multi-peak characteristics, with its macropore peaks (composed of macropores with a pore size greater than 50 nm) providing rapid diffusion channels for flue gas molecules and reducing mass transfer resistance. Meanwhile, the middle layer of activated carbon fibers exhibits uni-peak characteristics (composed of micropores with a pore size less than 2 nm), providing a large specific surface area and abundant active sites, ensuring an extremely fast adsorption reaction rate. This gradient structure of "outer layer macropore diffusion, inner layer micropore reaction" overcomes the problem of low utilization rate of deep micropores in traditional granular activated carbon while fully leveraging the high sulfur capacity of activated carbon fibers, significantly improving the overall desulfurization efficiency.

[0019] Third, it effectively reduces operating resistance and controls costs. Compared to activated carbon beds that use activated carbon fibers entirely, this invention uses granular activated carbon to replace part of the volume, significantly reducing material costs. Simultaneously, the presence of the granular activated carbon layer improves airflow distribution, avoiding the problem of excessive pressure drop (resistance) in the activated carbon bed caused by overly tight packing of activated carbon fibers, thus reducing fan energy consumption. Furthermore, during the washing and regeneration process, the macroporous structure of the granular activated carbon facilitates the penetration of the regenerated liquid and the discharge of sulfuric acid, improving regeneration efficiency.

[0020] Fourth, the breathable insulating components ensure the independence of the interlayer structure. By setting breathable insulating components (especially fiberglass mesh) between the layers, a physical separation is achieved between the first granular activated carbon layer, the activated carbon fiber layer, and the second granular activated carbon layer. This not only prevents particles from embedding into the fiber layer and causing channel blockage, but also facilitates the layered replacement or treatment of activated carbon materials with different lifespans during maintenance, extending their service life.

[0021] Fifth, limiting the peak value of the single peak to between 0.7 nm and 1.5 nm, this range is highly matched with the space required for the adsorption and oxidation reaction of sulfur dioxide molecules, maximizing the effective adsorption capacity of activated carbon fibers; limiting the peak value of the macroporous peak to between 100 nm and 5000 nm further ensures the macroscopic transport efficiency of flue gas and regenerated liquid in the composite activated carbon fixed bed. Attached Figure Description

[0022] The accompanying drawings, which form part of this specification, are used to aid in understanding the invention. The contents provided in the drawings and their related descriptions in this specification can be used to explain the invention, but do not constitute an undue limitation of the invention.

[0023] Figure 1 This is a schematic diagram of the microstructure of granular activated carbon used in a composite activated carbon fixed bed according to an embodiment of the present invention.

[0024] Figure 2This is a schematic diagram of the microstructure of activated carbon fibers used in a composite activated carbon fixed bed according to an embodiment of the present invention.

[0025] Figure 3 This is a pore size distribution diagram of granular activated carbon and activated carbon fibers used in a composite activated carbon fixed bed according to an embodiment of the present invention.

[0026] Figure 4 To verify the effectiveness of a composite activated carbon fixed bed according to an embodiment of the present invention, a schematic diagram of a laboratory-scale catalytic flue gas desulfurization device was constructed.

[0027] Figure 5 For use Figure 4 The graph shows a comparison of the desulfurization performance of equal-mass activated carbon fibers and granular activated carbon obtained from experiments using a catalytic flue gas desulfurization device.

[0028] Figure 6 For use Figure 4 The curves shown represent a comparison of the desulfurization performance of equal masses of activated carbon fiber and granular activated carbon obtained from experiments using a catalytic flue gas desulfurization device.

[0029] Figure 7 For use Figure 4 The second curve shows the comparison of the desulfurization performance of equal-volume activated carbon fiber and granular activated carbon obtained from experiments using the catalytic flue gas desulfurization device.

[0030] Figure 8 For use Figure 4 The desulfurization performance curve of the catalytic flue gas desulfurization device shown is obtained from an experiment using steel wire mesh to fix activated carbon fibers.

[0031] Figure 9 For use Figure 4 The curves showing the desulfurization performance of the catalytic flue gas desulfurization device before and after activated carbon fiber regeneration are compared.

[0032] Figure 10 For use Figure 4 The diagram shows a comparison curve of the desulfurization performance of activated carbon fibers at different packing densities obtained from experiments using a catalytic flue gas desulfurization device.

[0033] Figure 11 For use Figure 4 The desulfurization performance curve of the catalytic flue gas desulfurization device shown is obtained from the experiment of the double-layer combination of activated carbon fiber and granular activated carbon.

[0034] Figure 12 For use Figure 4 The desulfurization performance curves of the catalytic flue gas desulfurization device with different densities of activated carbon fiber and granular activated carbon were obtained from experiments.

[0035] Figure 13 For use Figure 4 The desulfurization performance curves of the isolated double-layer combination of activated carbon fiber and granular activated carbon obtained from experiments using the catalytic flue gas desulfurization device are shown.

[0036] Figure 14 For use Figure 4 The desulfurization performance curve of the dual-reactor series combination obtained from the experiment of the catalytic flue gas desulfurization device is shown.

[0037] Figure 15 For use Figure 4 The catalytic flue gas desulfurization device shown in the figure has a series combined desulfurization performance curve obtained from experiments.

[0038] Figure 16 For use Figure 4 The desulfurization performance curve of the three-layer combination containing two layers of activated carbon fiber obtained from the experiment of the catalytic flue gas desulfurization device is shown.

[0039] Figure 17 For use Figure 4 The desulfurization performance curve of the three-layer combination containing two layers of granular activated carbon was obtained from the experiment of the catalytic flue gas desulfurization device shown.

[0040] Figure 18 For use Figure 4 The multi-layer combined desulfurization performance curves were obtained from experiments using the catalytic flue gas desulfurization device shown.

[0041] Figure 19 For use Figure 4 The catalytic flue gas desulfurization device shown in the figure has a three-layer combination multi-cycle desulfurization performance curve containing two layers of granular activated carbon, obtained from experiments.

[0042] Figure 20 For use Figure 4 The catalytic flue gas desulfurization device shown in the figure has a three-layer combination multi-cycle desulfurization performance curve containing two layers of activated carbon fiber obtained from experiments.

[0043] The markings in the diagram are as follows: 1-Mixed gas cylinder, 2-Pressure reducing valve, 3-Rotameter, 4-Buffer bottle, 5-Reactor jacket water circulation pump, 6-Super constant temperature water bath, 7-Saturated humidifier, 8-Thermometer, 9-Reactor, 10-Three-way valve, 11-Sampling bottle, 12-Tail gas absorption bottle, 13-Wet gas flow meter. Detailed Implementation

[0044] The present invention will now be clearly and completely described in conjunction with the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it should be particularly noted that:

[0045] The technical solutions and features provided in the various sections, including the following description, can be combined with each other without conflict. Furthermore, where possible, these technical solutions, features, and related combinations can be given specific technical subject matter and protected by relevant patents.

[0046] The embodiments of the present invention described below are generally only some embodiments and not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of patent protection.

[0047] The term "comprising" and any variations thereof in this specification, the corresponding claims, and related sections are intended to cover a non-exclusive inclusion. Other related terms and units can be reasonably interpreted based on the relevant content provided in this specification.

[0048] This invention proposes a composite activated carbon fixed bed for catalytic flue gas desulfurization. Its core design concept lies in resolving the contradiction between desulfurization efficiency and engineering application stability in single-material activated carbon beds by complementing the advantages of a three-layer sandwich structure in the macroscopic structure and the microscopic pore structure. Figures 1 to 3 As shown, this invention utilizes granular activated carbon (GAC) as a framework support, and its microstructure (such as...) Figure 1 (As shown) has well-developed internal pores and a certain mechanical strength, and its pore size distribution (as shown) Figure 3 As shown, the flue gas exhibits a multi-peak characteristic, with the large-pore peak (greater than 50 nm) providing a high-speed channel for flue gas diffusion. Simultaneously, this invention utilizes activated carbon fiber (ACF) as the core reaction layer, whose microstructure (as shown)... Figure 2 As shown, the micropores open directly onto the fiber surface, and the pore size distribution (as shown) Figure 3 As shown, the adsorbate exhibits a single-peak characteristic dominated by micropores (less than 2 nm), which greatly shortens the diffusion path of the adsorbate. By sandwiching the activated carbon fiber layer between two layers of granular activated carbon, the mechanical support and macroporous diffusion capacity of the granular activated carbon are utilized to prevent bed collapse and reduce resistance, while the rapid adsorption kinetics of the activated carbon fiber are fully leveraged, achieving a synergistic improvement in desulfurization performance.

[0049] To verify the design effect and performance advantages of the above-mentioned composite activated carbon fixed bed, this invention constructed a laboratory-scale experimental device for catalytic flue gas desulfurization. Figure 4 The structure of the experimental apparatus for catalytic flue gas desulfurization is shown. Figure 4As shown, the catalytic flue gas desulfurization experimental device consists of a mixed gas cylinder 1, a pressure reducing valve 2, a rotor flow meter 3, a buffer bottle 4, a reactor jacket water circulation pump 5, a super constant temperature water bath 6, a saturated humidifier 7, a reactor 9, a three-way valve 10, a sampling bottle 11, a tail gas absorption bottle 12, and a wet gas flow meter 13. The basic working principle of this catalytic flue gas desulfurization experimental device is as follows: Simulated flue gas is supplied by the mixed gas cylinder 1. After being metered by the pressure reducing valve 2 and the rotor flow meter 3, a portion of the gas enters the saturated humidifier 7 for humidification to simulate the moisture content in the flue gas. The humidified gas is mixed with dry gas in a pipeline, and after being uniformly mixed by the buffer bottle 4, it enters the reactor 9. The reactor 9 is equipped with a reactor jacket, and the bed temperature inside the reactor (e.g., 80°C) is maintained by the super constant temperature water bath 6 and the reactor jacket water circulation pump 5. The reactor 9 is filled with the activated carbon bed to be tested (i.e., the activated carbon bed of this invention or other activated carbon beds used as a control). When flue gas passes through the activated carbon bed, SO2, O2, and H2O undergo a catalytic oxidation reaction on the surface of the activated carbon bed to produce sulfuric acid. The resulting tail gas passes through a three-way valve 10; part of it enters a sampling bottle 11 for analysis, while the other part is treated by a tail gas absorption bottle 12 before being discharged into the atmosphere, with the total volume measured by a wet gas flow meter 13. This catalytic flue gas desulfurization experimental device can precisely control gas flow rate, temperature, humidity, and inlet concentration, providing a reliable experimental platform for evaluating the desulfurization performance of different bed structures.

[0050] Based on the aforementioned catalytic flue gas desulfurization experimental device, this invention adopts a progressive experimental verification approach to comprehensively reveal the performance characteristics of the composite activated carbon fixed bed. First, under the same experimental conditions, the desulfurization performance of single activated carbon fibers and granular activated carbon were compared using equal masses and volumes to establish benchmark performance differences. Second, addressing the issues of collapse and short circuits that easily occur with activated carbon fibers in fixed bed applications, the effects of different fixing methods and packing densities on performance were investigated. Subsequently, double-layer combinations and isolated double-layer combinations were gradually constructed to explore the interface effects between different materials. Finally, the three-layer sandwich structure proposed in this invention, comprising two layers of granular activated carbon sandwiching activated carbon fibers, was tested in detail, and its regeneration performance and stability under multi-cycle operation were thoroughly verified. Specific experimental data and analysis will be presented below. Figures 5 to 20 A detailed explanation is provided.

[0051] In the following series of experiments, the activated carbon fibers used were all viscose-based activated carbon fibers, whose pore size distribution exhibited a single-peak characteristic. This single peak consisted of micropores with a pore size of less than 2 nm, and the peak value was located around 1 nm. Granular activated carbon was uniformly columnar granular activated carbon with a diameter of 4 mm. Its pore size distribution exhibited a multi-peak characteristic, including micropore peaks and macropore peaks. The peak value range of the micropore peaks largely overlapped with the single-peak peak range, while the peak value of the macropore peaks was located around 1000 nm. The simulated flue gas used in the experiments was divided into two categories: first, a SO2-O2-N2 mixture prepared by precise gas mixing from liquid SO2 cylinders, nitrogen cylinders, and oxygen cylinders; second, a simulated flue gas of SO2-O2-H2O(gas)-N2 obtained by saturating and humidifying this mixture. All comparative and verification experiments were conducted under uniform operating conditions. The specific control parameters were as follows: the inlet SO2 concentration was maintained at around 2000 ppm, the total gas flow rate was set at 1 L / min, the oxygen concentration was controlled at 5%, and the reactor bed temperature and humidification temperature were maintained at 80℃ to ensure the comparability and accuracy of the experimental data.

[0052] I. Desulfurization of ACF and GAC separately.

[0053] 1.1 Desulfurization performance of ACF and GAC under the same mass.

[0054] Table 1 - Comparison of sulfur capacity of ACF and GAC of equal mass

[0055] Filling amount / g 22 35 ACF sulfur capacity (mg / g) 47 60 GAC sulfur capacity (mg / g) 20 30

[0056] from Figure 5 , Figure 6 As shown in Table 1, under the same mass, ACF has a better adsorption effect on SO2 than GAC. Under the same conditions, ACF has a significant advantage in 100% desulfurization time compared to GAC, and maintains a higher desulfurization rate for a longer period, achieving more stable adsorption desulfurization. Comparing desulfurization effects at 80%, from... Figure 5 It can be seen that ACF can reach 350 minutes, while GAC only reaches less than 200 minutes; from Figure 6 As can be seen, ACF can reach 230 min, while GAC only reaches less than 100 min. Table 1 shows that the sulfur capacity of ACF is twice that of GAC, indicating that the adsorption capacity of activated carbon fiber is significantly better than that of GAC, and the adsorption capacity of activated carbon fiber is much greater than that of GAC.

[0057] 1.2 Desulfurization performance of ACF and GAC under the same volume.

[0058] Table 2 - Comparison of sulfur capacity of ACF and GAC in equal volumes

[0059] ACF sulfur capacity (mg / g) 270 GAC sulfur capacity (mg / g) 72

[0060] from Figure 7 It can be seen that, under the same volume conditions, ACF and GAC have very similar desulfurization times to achieve 100% desulfurization and maintain a desulfurization efficiency of over 80%, indicating that their desulfurization performance is not significantly different. However, under the same volume conditions, the loading amount of GAC is ten times that of activated carbon fiber, while Table 2 shows that the sulfur capacity of ACF is four times that of GAC. Therefore, using activated carbon fiber for desulfurization can not only improve the desulfurization effect but also reduce the amount of desulfurizing agent required.

[0061] 1.3 Desulfurization performance of ACF fixed with wire mesh.

[0062] The dense structure of ACF results in a much larger pressure drop per unit volume compared to GAC. Therefore, it is necessary to study the optimal shape, structure, and packing method of ACF packing to reduce pressure loss and thus energy consumption. Economic viability is crucial for applying laboratory results to industrial production. Therefore, this experiment employed a wire fixation method to secure the ACF within the reactor. The experimental results are as follows... Figure 8 As shown in the figure. After desulfurization, regeneration was performed. It was found that the ACF did not collapse due to the support of the wire mesh, but it did shrink, resulting in air leakage and poor desulfurization effect.

[0063] 1.4 The effect of regeneration on the desulfurization performance of ACF.

[0064] In this experiment, the ACF loading was 10g, and the ACF was regenerated by washing with water. Figure 9 It can be seen that after regenerating ACF, the desulfurization time is slightly shortened with the same outlet SO2 concentration as the boundary, but the impact on its desulfurization effect is small.

[0065] 1.5 Desulfurization performance of ACF with different packing densities.

[0066] Table 3 - Comparison of sulfur capacity under different ACF packing densities

[0067] <![CDATA[ACF density (g / cm 3 )]]> 0.2 0.3 0.5 ACF loading amount (g) 4.8 15 20 ACF sulfur capacity (mg / g) 50 82 90

[0068] from Figure 10 As can be seen from Table 3, the ACF packing density is 0.2 g / cm³. 3 At that time, ACF could not achieve 100% desulfurization, and its sulfur capacity was only 50 mg / g; when the ACF packing density increased to 0.3 g / cm³, the desulfurization was further reduced. 3 At this stage, ACF can achieve 100% desulfurization time of approximately 50 minutes, with a sulfur capacity of 82 mg / g; when the ACF packing density increases to 0.5 g / cm³... 3 At this time, ACF can achieve 100% desulfurization time for up to 210 minutes, with a sulfur capacity of 90 mg / g. Therefore, the desulfurization performance of ACF gradually improves with the increase of activated carbon fiber packing density.

[0069] 1.6 Conclusion.

[0070] ACF has a significantly higher adsorption capacity than GAC, resulting in better SO2 removal. Fixing ACF with wire mesh is a good method, but its effectiveness needs further investigation, and other ACF fixation methods should be studied. Regeneration has a relatively small impact on the desulfurization effect of ACF. Increasing the ACF packing density gradually improves its desulfurization performance.

[0071] The SO2 removal process of ACF can be divided into three stages: adsorption, adsorption saturation, and stable removal. In the first stage, the outlet SO2 concentration is 0, and the removal efficiency is 100%. In the second stage, the outlet SO2 concentration gradually increases, and the removal efficiency decreases accordingly. In the third stage, the outlet concentration remains essentially constant, and the removal efficiency stabilizes at a certain value for a relatively long period. Further research shows that SO2 undergoes an oxidation reaction on ACF, and the reaction process does not alter the microporous pore structure of ACF. ACF can adsorb a certain amount of SO2 and enable the oxidation of SO2 to SO3, which would normally require heating, to occur at room temperature. This indicates that ACF not only has selective adsorption capacity, but its functional groups and surface potential field can also lower the activation energy required for the reaction, acting as a catalyst.

[0072] II. Dual-layer combined desulfurization

[0073] This section explores whether GAC and ACF can be combined in two layers in different ways to improve their desulfurization performance and the corresponding cost-effectiveness.

[0074] This experiment used two loading methods: ACF on top and GAC on the bottom. The ACF-on-top loading method had a loading amount of 2.7g ACF and 17g GAC, with a loading height of 12cm and a height ratio of 1:1. The ACF-on-top loading method had a loading amount of 2.4g ACF and 22g GAC. Figure 11 As shown in Table 4, the desulfurization effect is better with ACF on top than with ACF on the bottom. The overall desulfurization rate of the ACF-on-top combination is higher and more stable than that of the combination with ACF on the bottom. The loading amounts for the two combinations are 2.4g + 22g ACF on top and 17g + 2.4g ACF on the bottom; the sulfur capacities are 80mg / g and 78g / g, respectively, which is a certain improvement compared to the sulfur capacity of GAC alone (50mg / g). Although this combination reduces the loading weight, the improvement in desulfurization performance is not significant. Considering that activated carbon fiber is 10 times more expensive than GAC, the desulfurization cost-effectiveness of the double-layer combination is not high.

[0075] Table 4 - Sulfur Capacity of Bilayer Assemblies

[0076] Combination method Sulfur capacity (mg / g) ACF on 80 ACF below 78

[0077] One set of experiments combined ACF and GAC of different densities for desulfurization, and the results were as follows: Figure 12 As shown in the figure, with an 80% desulfurization rate as a comparison, the desulfurization time of low-density ACF is 6 hours, while that of high-density ACF is 10 hours. Therefore, we can see that high-density ACF has a better adsorption effect on SO2.

[0078] A set of experiments involved a combination that used glass springs to isolate ACF and GAC. The results were as follows... Figure 13 As shown. With Figure 11 This comparison demonstrates that this combination method has a certain effect on improving desulfurization efficiency.

[0079] A set of experiments tested desulfurization in series using two reactors packed with a double-layer assembly. The results are as follows: Figure 14 As shown. With Figure 11 , Figure 12 In comparison, this dual-reactor combined desulfurization method is a more ideal combined desulfurization method, which can greatly extend the desulfurization time and improve the desulfurization efficiency.

[0080] A series of experiments will be conducted to perform tandem desulfurization tests. The results are as follows: Figure 15 and Figure 9 As shown, by using two reactors in series for desulfurization, the addition of fiber reduces the loading amount and increases the overall sulfur capacity, but the increase is not significant.

[0081] Table 5 - Sulfur Capacity of Bilayer Assemblies

[0082] Combination method GAC+GAC ACF+ACF GAC+ACFGAC Sulfur capacity (mg / g) 137 149 145

[0083] Conclusion: The dual-layer combined desulfurization method can improve desulfurization performance, but the improvement is not significant and the cost-effectiveness is not high. Increasing the packing density of activated carbon fibers can improve its desulfurization efficiency and sulfur capacity. Both isolated combined and series desulfurization methods employ a dual-layer desulfurization approach, and while they show some improvement in overall desulfurization efficiency, the improvement is low and the cost-effectiveness is poor.

[0084] III. Three-layer and multi-layer combined desulfurization

[0085] The three-layer combined desulfurization experiments included two combinations: GAC+ACF+GAC and ACF+GAC+ACF. Each combination was tested with three different height ratios. The experiments explored whether different two-layer combinations of GAC and ACF improved desulfurization performance and cost-effectiveness.

[0086] One experiment used a combination of two layers of ACF and one layer of GAC (GAC being the middle layer). This combination increased the amount of fiber used but reduced the total mass. The loading amounts for the three methods (named 111, 121, and 212, where 111 indicates a volume ratio of 1:1:1, 121 indicates a volume ratio of 1:2:1, and 212 indicates a volume ratio of 2:1:2) were as follows: 111: 2.2g + 15g + 2.2g; 121: 1.05g + 25g + 1.05g; and 212: 3.4g + 10g + 3.4g. The results are as follows. Figure 16 As shown in Table 6.

[0087] Table 6 - Comparison of sulfur capacity of three-layer combinations with two-layer ACF

[0088] Three-layer combination with two-layer ACF (volume ratio) 111 121 212 Sulfur capacity (mg / g) 130 50 90

[0089] from Figure 16 As shown in Table 6, the desulfurization performance of the three-layer combination with two layers of activated carbon fiber, compared to GAC, is not improved at high desulfurization rates; in fact, it decreases. However, observations during the experiment revealed that this combination maintains its performance at lower desulfurization rates for a relatively long time. This phenomenon is due to the higher ACF loading, a characteristic of the fiber itself, resulting from its inherent structure. The outer surface of activated carbon fiber contains abundant micropores, while hollow and macropores are uniformly distributed within the molecules. It is this structure that allows for slow desorption during adsorption, thus enabling some desulfurization at lower rates. Table 6 shows that although the 111 combination can achieve a sulfur capacity of 130 mg / g, the increased fiber loading results in higher costs, therefore this project considers this combination not to be the optimal solution.

[0090] One experimental group used a combination of two layers of GAC and one layer of ACF (with ACF as the intermediate layer). The loading amounts for the three layers were: 111 with a loading of 20g + 2.5g + 20g, 121 with a loading of 15g + 3.8g + 15g, and 212 with a loading of 24g + 1.5g + 24g. The results are as follows. Figure 17 As shown in Table 7. Here, 111 also represents a volume ratio of 1:1:1, 121 represents a volume ratio of 1:2:1, and 212 also represents a volume ratio of 2:1:2.

[0091] Table 7 - Comparison of sulfur capacity of three-layer combinations of two-layer GAC

[0092] Three-layer combination with two-layer GAC (volume ratio) 111 121 212 Sulfur capacity (mg / g) 160 135 110

[0093] From such Figure 17As shown in Table 7, the desulfurization time is prolonged under the three different ratio combinations. Compared with the combination of two ACF layers and one GAC layer, as well as desulfurization using ACF or GAC alone, the desulfurization effect is significantly improved. In terms of cost, the best three-layer combination costs 38% more than the blank GAC, and the sulfur capacity is more than 3 times higher (GAC blank sulfur capacity is 50 mg / g, and the sulfur capacity of combination 111 is 160 mg / g). Therefore, this combination desulfurization method is very effective. Experiments show that when the ACF ratio is too high (121), although the active components increase, the utilization rate may decrease due to uneven distribution of bed resistance; when the ACF ratio is too low (212), there are insufficient core reaction sites. Therefore, a volume ratio of 1:1:1 is the best solution that balances performance and cost.

[0094] One set of experiments used a combination of five-layer ACF and four-layer GAC. The results are as follows: Figure 18 As shown. From Figure 18 It can be seen that the sulfur capacity for a desulfurization rate of over 90% is 79 mg / g. This indicates that the desulfurization efficiency has been improved to some extent, but the improvement is not the best seen in the experiments.

[0095] One set of experiments employed a desulfurization method using an equal volume (mass ratio: GAC:ACF:GAC = 20:2.5:20) combination of two layers of GAC and one layer of ACF. Three desulfurization cycles were completed through regeneration using water regeneration, followed by drying at 120℃ before desulfurization. The results are as follows: Figure 19 As shown in Table 8.

[0096] Table 8 - Comparison of sulfur capacity of three-layer combinations of two-layer GAC

[0097] Three-layer combination - two layers of GAC (equal volume) First cycle Second cycle Third cycle Sulfur capacity (mg / g) 140 74 56

[0098] from Figure 19 As shown in Table 7, the desulfurization times for the three cycles were 15.5 h, 8 h, and 6 h, respectively; the sulfur capacities were 140 mg / g, 74 mg / g, and 56 mg / g, respectively. This indicates that the desulfurization effect of the second cycle decreased to about 50% of that of the first cycle, while the desulfurization effect of the third cycle was similar to that of the second cycle, and the effect tended to stabilize.

[0099] One experiment involved filling two layers of ACF and one layer of GAC with equal volumes (the top and bottom layers were ACF, and the middle layer was GAC). ACF was used in larger quantities, and both were filled with equal volumes per layer (mass ratio:ACF:GAC:ACF=3.3:15:3.3). The total filling height was 12cm, with each layer 3cm high. The results are as follows: Figure 20 As shown in Table 9.

[0100] Table 9 Comparison of sulfur capacity of three-layer combinations with two-layer ACF

[0101] Three-layer combination - two layers of ACF (equal volume) First cycle Second cycle Sulfur capacity (mg / g) 137 75

[0102] from Figure 20 As shown in Table 9, the desulfurization times for the two cycles were 10 hours and 7 hours, respectively; the sulfur capacities were 137 mg / g and 75 mg / g, respectively. This indicates that the desulfurization effect of the second cycle decreased to about 50% of that of the first cycle. This is similar to the desulfurization effect of an equal-volume combination of two layers of GAC and one layer of ACF. This is because regeneration has a significant impact on the adsorption performance of GAC.

[0103] Conclusion: The three-layer combined desulfurization system (two layers of GAC and one layer of ACF) is the most ideal combined desulfurization method in this project, and it is most beneficial for SO2 removal. Multi-layer combined desulfurization has ideal effects but lower cost-effectiveness. Regeneration has a significant impact on the desulfurization effect of the three-layer combined desulfurization system.

[0104] IV. Economic Analysis.

[0105] ACF (Acrylic Acid Flue Gas) is an adsorbent with excellent selectivity for SO2, thus its adsorption performance far surpasses that of ordinary activated carbon. Due to the significantly improved adsorption capacity, the amount of adsorbent used in activated carbon-based flue gas desulfurization processes is significantly reduced compared to using GAC (Gas-Acrylic Acid). Currently, GAC costs 5-30 RMB / kg, while viscose-based ACF costs approximately 100-300 RMB / kg, about 10-20 times the price of ordinary activated carbon. However, as ACF becomes increasingly widely used in various industries, the inevitable large-scale production will lead to a continuous decrease in its price, making the overall cost comparable to that of GAC. Furthermore, the reduced adsorbent usage results in a significant reduction in equipment capacity, allowing for a substantial reduction in the size of the adsorption tower. Additionally, the reduced adsorbent usage leads to a thinner bed, greatly reducing the resistance of the flue gas during adsorption, thus eliminating the need for large-capacity fans to supplement pressure. Considering all these factors, using ACF desulfurization will reduce the initial investment of the system by more than 50% and operating costs by more than 30%. Therefore, from a techno-economic perspective, ACF desulfurization is significantly superior to GAC desulfurization. Combining ACF and GAC desulfurization is a highly worthwhile approach to promote, as it combines their respective advantages and greatly reduces investment and operating costs.

[0106] Based on the above experimental data and comparative analysis, the optimal operating parameter range for the composite activated carbon fixed bed used in catalytic flue gas desulfurization was determined. A comprehensive comparison of the desulfurization efficiency and economic cost of different combinations was conducted, and the experimental results (see [link to experimental data]) were presented. Figure 17As shown in Table 7, when the volume ratio of the first granular activated carbon layer, the activated carbon fiber layer, and the second granular activated carbon layer is controlled within the range of 1:(0.5-2.0):1, the composite activated carbon fixed bed can fully utilize the advantages of the large adsorption capacity of granular activated carbon (GAC) and the fast reaction rate and abundant micropores of activated carbon fiber (ACF) to achieve synergistic effect. Within this range, if the ACF ratio is too low (e.g., below 0.5), the rapid catalytic oxidation capacity is insufficient, and the breakthrough time is significantly shortened; if the ACF ratio is too high (e.g., above 2.0), although the desulfurization performance is improved, the material cost increases significantly, and the economic efficiency decreases compared to the performance improvement. Therefore, 1:1:1 is identified as the optimal volume ratio that balances desulfurization performance (high sulfur capacity, long breakthrough time) and economic cost (moderate material dosage).

[0107] Regarding the packing density of the activated carbon fiber layer, experimental data (see...) Figure 10 Table 3 shows that it has a decisive impact on desulfurization performance. When the packing density is too low (e.g., 0.2 g / cm³), the bed voids are too large, and the airflow short-circuiting phenomenon is obvious, resulting in insufficient gas-solid contact, and the desulfurization efficiency and sulfur capacity cannot meet the requirements. When the packing density is in the range of 0.3 g / cm³ to 0.5 g / cm³, the bed structure is moderately dense, which ensures sufficient contact reaction time and maintains a high sulfur capacity (e.g., the sulfur capacity reaches 90 mg / g at 0.5 g / cm³). Therefore, the present invention preferably limits the packing density of the activated carbon fiber layer to 0.3 g / cm³ to 0.5 g / cm³.

[0108] Furthermore, in the embodiments of the present invention, the total gas flow rate was set to 1 L / min. Combined with the total volume of the composite activated carbon fixed bed in different experimental groups (approximately 60 cm³ to 150 cm³), the experimental run space velocity of the present invention covered 400 h. -1 Up to 1000h -1 Within this space velocity range, all preferred embodiments exhibited 100% desulfurization efficiency and a long duration, demonstrating that this space velocity range can ensure sufficient residence time of flue gas within the bed for adequate catalytic oxidation, while also meeting the throughput requirements of industrial applications.

[0109] The foregoing has described the relevant content of the present invention. Those skilled in the art will be able to implement the present invention based on these descriptions. All other embodiments obtained by those skilled in the art based on the foregoing content of this specification without inventive effort should fall within the scope of the present invention.

Claims

1. A composite activated carbon fixed bed for catalytic flue gas desulfurization, characterized in that: It consists of a first granular activated carbon layer, an activated carbon fiber layer, and a second granular activated carbon layer arranged sequentially along the flue gas flow direction. The first granular activated carbon layer and the second granular activated carbon layer are both filled with granular activated carbon, and the activated carbon fiber layer is filled with activated carbon fiber; The activated carbon fiber layer is sandwiched between the first granular activated carbon layer and the second granular activated carbon layer, forming a three-layer sandwich structure. The activated carbon fiber exhibits a single-peak pore size distribution, which is composed of micropores with a pore size of less than 2 nm; the granular activated carbon exhibits a multi-peak pore size distribution, which includes micropore peaks and macropore peaks, wherein the micropore peaks are composed of micropores with a pore size of less than 2 nm and the macropore peaks are composed of macropores with a pore size of greater than 50 nm. The volume ratio of the first granular activated carbon layer, the activated carbon fiber layer, and the second granular activated carbon layer is 1:(0.5-2.0):1; it is configured to operate at a space velocity of 400 h⁻¹. -1 Up to 1000h -1 The activated carbon fiber layer operates under the specified conditions; the packing density of the activated carbon fiber layer is 0.3 g / cm³. 3 Up to 0.5g / cm 3 .

2. The composite activated carbon fixed bed for catalytic flue gas desulfurization as described in claim 1, characterized in that: The volume ratio of the first granular activated carbon layer, the activated carbon fiber layer, and the second granular activated carbon layer is 1:1:

1.

3. The composite activated carbon fixed bed for catalytic flue gas desulfurization as described in claim 1, characterized in that: The first granular activated carbon layer and the activated carbon fiber layer, and the second granular activated carbon layer and the activated carbon fiber layer are physically separated by a breathable insulating element.

4. The composite activated carbon fixed bed for catalytic flue gas desulfurization as described in claim 3, characterized in that: The breathable insulating component is made of fiberglass mesh.

5. The composite activated carbon fixed bed for catalytic flue gas desulfurization as described in claim 1, characterized in that: The activated carbon fiber is a viscose-based activated carbon fiber.

6. The composite activated carbon fixed bed for catalytic flue gas desulfurization as described in claim 1, characterized in that: The granular activated carbon is columnar granular activated carbon with a diameter of 2 mm to 6 mm.

7. The composite activated carbon fixed bed for catalytic flue gas desulfurization as described in any one of claims 1-6, characterized in that: The peak value of the single peak is between 0.7 nm and 1.5 nm; the peak value of the large pore peak is between 100 nm and 5000 nm.

8. A catalytic flue gas desulfurization device, comprising at least one desulfurization reactor, the desulfurization reactor having an inlet, an outlet, a drain outlet, and an activated carbon bed located within the desulfurization reactor, wherein the desulfurization reactor is equipped with a regeneration liquid spraying device for washing and regenerating the activated carbon bed, wherein during operation, the flue gas to be desulfurized enters the desulfurization reactor through the inlet, passes through the activated carbon bed for desulfurization, and is then discharged from the outlet of the desulfurization reactor as desulfurized flue gas, wherein the sulfur dioxide in the flue gas to be desulfurized reacts on the activated carbon bed to form sulfuric acid, and during the washing and regeneration of the activated carbon bed, the sulfuric acid enters the regeneration liquid sprayed on the activated carbon bed and is discharged from the drain outlet of the desulfurization reactor; characterized in that: The activated carbon bed is a composite activated carbon fixed bed for catalytic flue gas desulfurization as described in any one of claims 1-7.

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