Ammonia desulfurization system, process, absorption membrane and preparation method thereof

Abstract

The present application discloses an ammonia-based desulfurization system, process, absorption membrane, and preparation method thereof, belonging to the technical field of ammonia-based desulfurization. The ammonia-based desulfurization system includes a desulfurization tower, a concentration circulation tank, a crystallization tank, an ammonium sulfate product processing mechanism, and a circulating water tank. In the ammonia-based desulfurization system, based on membrane absorption and ammonia-based desulfurization, an absorption membrane composed of a first modified layer, a modified polypropylene fiber membrane, and a second modified layer is used. The first modified layer and the second modified layer are provided to improve the adhesion of the absorption membrane to the modified polypropylene fiber membrane, thereby avoiding delamination of the absorption membrane during use, thereby increasing the action time of the absorption membrane in the desulfurization tower, achieving long-term and efficient desulfurization and reducing ammonia escape.

Description

Technical Field

[0001] The present application relates to an ammonia desulfurization system, process, absorption membrane and preparation method thereof, and belongs to the technical field of ammonia desulfurization. Background Art

[0002] Ammonia desulfurization is currently the most commonly used flue gas desulfurization method. It has the advantages of high desulfurization efficiency and wide application range. In the desulfurization process, the ammonium sulfite generated chemically reacts with oxygen in the air in the oxidation section to form ammonium sulfate, which is then concentrated and crystallized to produce solid ammonium sulfate by-product. This by-product can also be used to prepare fertilizer, which can achieve effective utilization of resources.

[0003] However, current ammonia-based desulfurization technology suffers from the drawbacks of high ammonia escape and severe aerosol formation, hindering its widespread application. Researchers have found that ammonia escape is one of the main causes of aerosol formation. Therefore, if ammonia escape cannot be effectively reduced, the formation of aerosols cannot be completely avoided. Therefore, significantly reducing ammonia escape is the key to the successful application of ammonia-based desulfurization technology.

[0004] Prior art 202411719611.1 discloses an ammonia-based desulfurization method and its application that significantly reduces ammonia escape. It uses a first filler layer and a hollow absorption membrane in the absorption section of the desulfurization tower to combine membrane absorption and ammonia-based desulfurization methods. This method can greatly reduce the amount of ammonia water used, and therefore can also reduce ammonia escape from the source. The hollow absorption membrane used therein uses a modified polypropylene fiber membrane as the lower layer, and a copolymer of acrylamide, an olefin monomer with a piperazine group, and diethylaminoethyl methacrylate as the upper layer, which can promote the hollow absorption membrane to reabsorb the decomposed ammonia gas, reduce ammonia escape, and improve the temperature resistance and durability of the hollow absorption membrane. However, the adhesion of its modified layer to the modified polypropylene fiber membrane is not strong. When used for a long time in the desulfurization tower, there will be a problem of stratification under the impact of gas and the spraying of spray liquid, causing the gas to be retained between the separated layers, which will form bubbles. Over time, the hollow absorption membrane will be broken, making it difficult to play a long-term role. Summary of the Invention

[0005] In order to solve the above problems, an ammonia desulfurization system is provided. In this ammonia desulfurization system, on the basis of membrane absorption and ammonia desulfurization, an absorption membrane composed of a first modified layer, a modified polypropylene fiber membrane and a second modified layer is adopted. The arrangement of the first modified layer and the second modified layer can improve the adhesion of the absorption membrane to the modified polypropylene fiber membrane, avoid stratification of the absorption membrane during use, thereby increasing the action time of the absorption membrane in the desulfurization tower, and can achieve long-term and efficient desulfurization and reduce ammonia escape.

[0006] According to a first aspect of the present application, an ammonia desulfurization system is provided, comprising a desulfurization tower, a concentration circulation tank, a crystallization tank, an ammonium sulfate product processing mechanism, and a circulating water tank;

[0007] A desulfurization tower, wherein the desulfurization tower is divided into a demisting section, a purification section, an absorption section, a concentration and cooling section, and an oxidation section from top to bottom, wherein the concentration and cooling section and the absorption section are separated by a first partition, the absorption section and the purification section are separated by a second partition, and the oxidation section and the concentration and cooling section are separated by a third partition;

[0008] The oxidation section is provided with an air inlet, the side wall of the concentration and cooling section is provided with a flue gas inlet and a liquid discharge port, a first spray mechanism is provided above the concentration and cooling section, the first spray mechanism is connected to the concentration pump, the liquid discharge port is connected to the crystallization tank, and the bottom of the crystallization tank is connected to the ammonium sulfate product processing mechanism through the crystallization pump;

[0009] A plurality of evenly distributed air lift caps are provided on the first partition plate, and a first-stage demister, a second spray mechanism, an absorption membrane and a first packing layer are provided above the absorption section from top to bottom. The first packing layer is provided above the air lift cap, and the absorption membrane includes a first modified layer, a modified polypropylene fiber membrane and a second modified layer from top to bottom. The first modified layer and the second modified layer are prepared from at least acrylamide, an olefin monomer with a piperazine group, diethylaminoethyl methacrylate and modified dopamine. The second spray mechanism is connected to the oxidation section through a circulation pump, and the bottom of the absorption section is connected to the oxidation section through a reflux pipe.

[0010] A plurality of evenly distributed air lift caps are also provided on the second partition plate. A combined demister, a water washing spray mechanism, and a second packing layer are sequentially provided in the purification section from top to bottom. The second packing layer is arranged above the air lift cap. The water washing spray mechanism is connected to the circulating water tank through a water washing pump. The water washing liquid in the purification section is then returned to the circulating water tank through a water washing reflux pipe.

[0011] Optionally, the thickness of the first modified layer of the absorption membrane is 15-18 μm, the thickness of the modified polypropylene fiber membrane is 60-80 μm, and the thickness of the second modified layer is 15-18 μm.

[0012] Optionally, the absorption film has an average pore size of 70-75 nm and a porosity of 60-70%.

[0013] According to a second aspect of the present application, an ammonia desulfurization method is provided, which is performed using an ammonia desulfurization system as described above, comprising the steps of:

[0014] (1) The flue gas after dust removal enters the concentration and cooling section from the flue gas inlet, and is sprayed and cooled to below 60°C by the first spray mechanism. The concentrated liquid in the concentration section enters the crystallization tank through the drain port, and the upper concentrated liquid in the crystallization tank overflows into the concentration circulation tank. The concentration pump then sends the liquid in the concentration circulation tank into the concentration section for spraying. When the solid content in the crystallization tank reaches the first threshold, the material at the bottom of the crystallization tank is transported to the ammonium sulfate product processing mechanism;

[0015] (2) The flue gas then rises to the absorption section and passes through the first packing layer, absorption membrane, second spray mechanism and first-stage demister for defogger before entering the purification section. The liquid in the absorption section re-enters the oxidation section through the reflux pipe;

[0016] (3) In the purification section, the flue gas passes through the second packing layer and is washed by the water washing spray mechanism to capture ammonium sulfate and excess ammonia. After that, it is defogged by the combined demister in the demisting section and then discharged from the desulfurization tower into the chimney. The washing liquid in the purification section is then returned to the circulating water tank;

[0017] (4) Compressed air enters the oxidation section to oxidize the absorption liquid returned from the absorption section. The liquid formed after full oxidation is then sent to the absorption section for spraying. When the ammonium sulfate content in the oxidation section reaches the second threshold, a portion of the liquid is sent to the concentration circulation tank.

[0018] According to a third aspect of the present application, a method for preparing an absorption membrane for use with ammonia desulfurization is provided, comprising the steps of:

[0019] S1: Preparation of modified polypropylene fiber membrane: Polypropylene, polyacrylic acid, polyacrylonitrile and nanofiller are blended and extruded to obtain pellets, which are melt-spun to obtain spun fibers. The spun fibers are stretched to form pores and then treated at 100-110°C for 200 seconds to obtain a modified polypropylene fiber membrane;

[0020] S2: Preparation of the first modified layer: acrylamide, an olefin monomer having a piperazine group, diethylaminoethyl methacrylate, and a modified dopamine dispersion are mixed in a solvent, azobisisobutyronitrile and ammonium persulfate are added, and prepolymerization is performed to obtain a first prepolymer solution. The first prepolymer solution is coated on one side of the modified polypropylene fiber membrane, and then irradiated and dried to obtain the membrane.

[0021] S3: Preparation of the second modified layer: acrylamide, an olefin monomer with a piperazine group, diethylaminoethyl methacrylate, and a modified dopamine dispersion are placed in a solvent and mixed, azobisisobutyronitrile and ammonium persulfate are added, and prepolymerization is performed to obtain a second prepolymer liquid, and the second prepolymer liquid is coated on the other side of the modified polypropylene fiber membrane, and then irradiated and dried.

[0022] The modified polypropylene fiber membrane of the absorption membrane serves as the middle layer of the absorption membrane. Firstly, it can provide stable support force, and secondly, it can prolong the residence time of the flue gas entering the absorption membrane, thereby increasing the desulfurization amount of the absorption liquid. In addition, it can achieve a higher desulfurization rate based on a lower amount of ammonia water added, greatly saving desulfurization costs. The first modified layer and the second modified layer can selectively absorb sulfur dioxide in the flue gas, further improving the desulfurization rate, and can also reabsorb the decomposed ammonia, further reducing ammonia escape. The modified polypropylene fiber membrane is a blend of polyacrylic acid and polyacrylonitrile. Firstly, it can promote the reabsorption of decomposed ammonia by the absorption membrane, thereby reducing ammonia escape. Secondly, it can improve the temperature resistance and durability of the modified polypropylene fiber membrane, extending the service life of the absorption membrane.

[0023] The first modified layer and the second modified layer are arranged above and below the modified polypropylene fiber membrane. Compared with the design of only arranging one modified layer above the modified polypropylene fiber membrane in 202411719611.1, firstly, when the thickness of the modified layer is the same, the original modified layer is designed as two modified layers, which can reduce the thickness of the first modified layer and the second modified layer, thereby shortening the distance between the top surface of the first modified layer and the bottom surface of the second modified layer and the modified polypropylene fiber membrane, increasing the interaction force between the first modified layer and the second modified layer and the modified polypropylene fiber membrane, and thereby improving the adhesion between the layers; secondly, the absorption membrane with a three-layer sandwich design of the present application can achieve three-layer interception and absorption of flue gas, which can further improve the desulfurization rate, reduce ammonia escape, and save ammonia water consumption.

[0024] In the preparation method of the absorption membrane, the first modified layer and the second modified layer are bonded to the modified polypropylene fiber membrane by coating, and the added modified dopamine dispersion can, firstly, improve the adhesion between the first modified layer and the second modified layer, so that during the long-term operation of the desulfurization tower, the three-layer structure of the absorption membrane will not separate, and the gas will not be retained between the layers, thereby increasing the action time of the absorption membrane in the desulfurization tower, and achieving long-term and efficient desulfurization and reducing ammonia escape; secondly, it can synergistically improve the gas throughput of the first modified layer and the second modified layer with diethylaminoethyl methacrylate, and increase the flue gas throughput as much as possible on the basis of ensuring desulfurization efficiency and reducing ammonia escape, thereby improving the flue gas treatment efficiency.

[0025] Optionally, in step S1, based on weight, the polypropylene is 70-80 parts, the polyacrylic acid is 5-10 parts, the polyacrylonitrile is 10-25 parts, and the nanofiller is 4-5 parts.

[0026] Preferably, the nanofiller is selected from at least one of modified nano-silicon carbide, modified nano-calcium carbonate, modified nano-diamond, and modified dopamine.

[0027] Optionally, the particle size of the nanofiller is 50-80 nm.

[0028] When the nanofiller is selected from modified dopamine, since the same modified dopamine as in step S2 and step S2 is added in step S1, the compatibility of the first modified layer and the second modified layer with the modified polypropylene fiber membrane can be increased, thereby further increasing the adhesion of the modified polypropylene fiber membrane to the first modified layer and the second modified layer, thereby extending the service life of the absorption membrane.

[0029] When the nanofiller is selected from modified nano silicon carbide, modified nano calcium carbonate or modified nano diamond, the modified nano silicon carbide, modified nano calcium carbonate or modified nano diamond are all modified with 3-mercaptopropyltrimethoxysilane, and the specific modification method is:

[0030] Place nano-silicon carbide, nano-calcium carbonate or nano-diamond in an ethanol solution containing 3-mercaptopropyltrimethoxysilane, with the weight ratio of nano-silicon carbide, modified nano-calcium carbonate or modified nano-diamond to 3-mercaptopropyltrimethoxysilane being 1:(0.2-0.3), treat at a temperature of 50-70°C for 4-5 hours, filter and dry.

[0031] Preferably, the concentration of 3-mercaptopropyltrimethoxysilane in the ethanol solution containing 3-mercaptopropyltrimethoxysilane is 20-40 mg / ml.

[0032] The modification method mentioned above modifies nano-silicon carbide, nano-calcium carbonate or nano-diamond to obtain modified nano-silicon carbide, modified nano-calcium carbonate or modified nano-diamond, so that the surface of the nano-filler carries 3-mercaptopropyltrimethoxysilane, which has the following advantages:

[0033] Improve the strength of modified polypropylene fiber membrane:

[0034] The modified nanofiller has improved dispersibility in the modified polypropylene fiber membrane and increased compatibility with the modified polypropylene fiber membrane. Both of the above effects can further improve the strength of the absorption membrane, avoid degradation and rupture of the absorption membrane, and extend the service life of the absorption membrane.

[0035] Improving the adhesion between the modified polypropylene fiber membrane and the first modified layer and the second modified layer:

[0036] The first and second modified layers are formed by coating a first and second prepolymer liquid, respectively, on a modified polypropylene fiber membrane and drying them. During the drying process, the first and second prepolymer liquids further react to form a cross-linked network. Experimental verification has shown that modifying the nanofillers with 3-mercaptopropyltrimethoxysilane can also increase the adhesion of the modified polypropylene fiber membrane to the first and second modified layers. The analysis may be based on the following principle: the 3-mercaptopropyltrimethoxysilane carried on the surface of the nanofillers on the surface of the modified polypropylene fiber membrane contains mercapto groups, which can react with the double bonds remaining in the first and second prepolymer liquids, thereby improving the bonding between the nanofillers on the surface of the modified polypropylene fiber membrane and the first and second modified layers, thereby improving the adhesion of the modified polypropylene fiber membrane to the first and second modified layers.

[0037] Preferably, the nanofiller is selected from modified silicon carbide and modified dopamine in a 1:1 weight ratio. This nanofiller optimizes the adhesion of the first and second modified layers to the modified polypropylene fiber membrane, preventing separation of the absorbent membrane during long-term use. Furthermore, the two nanofillers promote mutual dispersion, optimizing the mechanical properties of the modified polypropylene fiber membrane.

[0038] Optionally, the prepolymerization in step (2) and step (3) is carried out at 50-70°C for 2-3 hours, and the drying is carried out at 30-40°C for 10-15 hours.

[0039] Optionally, in step (2) and step (3), the weight ratio of acrylamide, olefin monomer with piperazine group, diethylaminoethyl methacrylate and modified dopamine dispersion is 1: (0.1-0.15): (0.1-0.2): (0.05-0.08).

[0040] Optionally, the concentration of the modified dopamine dispersion is 10-20 mg / ml.

[0041] In this application, the first and second modified layers are primarily composed of acrylamide, which promotes the absorption of sulfur dioxide by the modified layers. The olefin monomers containing piperazine groups can enhance the function of acrylamide and increase the reabsorption rate of decomposed ammonia. However, an excessive amount of olefin monomers containing piperazine groups increases the density of the modified layers, hindering the passage of flue gas and reducing flue gas treatment efficiency. Therefore, diethylaminoethyl methacrylate is added to overcome this drawback. The addition of diethylaminoethyl methacrylate not only adjusts the gas flux of the modified layers, thereby increasing the amount of flue gas passing through, but also synergizes with the olefin monomers containing piperazine groups to increase the reabsorption rate of decomposed ammonia, thereby doubly reducing ammonia escape.

[0042] The amount of modified dopamine dispersion used can synergistically improve the adhesion of the three-layer interlayer structure of the absorption membrane, the gas throughput of the absorption membrane, the desulfurization efficiency of the absorption membrane, and the effect of ammonia escape, so that the above effects can synergistically reach the optimal level. If the amount of modified dopamine dispersion used is increased, the content of modified dopamine in the first modified layer and the second modified layer will increase. Although this can further improve the adhesion of the first modified layer and the second modified layer to the modified polypropylene fiber membrane and further reduce the probability of delamination of the absorption membrane, it will increase the density of the first modified layer and the second modified layer, increase the resistance to the passage of flue gas, thereby reducing the flue gas treatment efficiency, and also reduce the temperature resistance of the absorption membrane; if the amount of modified dopamine dispersion used is reduced, the effect of improving adhesion is not significant, and the production cost is increased, which is not conducive to industrial application.

[0043] Optionally, the preparation method of the modified dopamine is:

[0044] S10: adding dopamine hydrochloride to sodium borate and sodium bicarbonate and stirring to obtain a dopamine mixed solution;

[0045] S20: adding acrylic acid to tetrahydrofuran to obtain an acrylic acid solution;

[0046] S30: adding the acrylic acid solution to the dopamine mixed solution, and adding an alkaline solution to adjust the pH of the reaction solution to ≥8, and reacting for more than 12 hours;

[0047] S40: adding an acidic solution to adjust the pH of the reaction solution until the product precipitates, washing and drying, placing the dried product in a low-temperature plasma generator, ventilating, adjusting the discharge voltage, using radio frequency discharge, and performing plasma treatment to obtain modified dopamine.

[0048] The modified dopamine prepared above contains double bonds, allowing it to participate in reactions and form a cross-linked network with the remaining materials in the first and second modified layers, thereby improving the mechanical properties and temperature resistance of the first and second modified layers. Furthermore, the addition of modified dopamine further enhances the mechanical properties of the first and second modified layers. Therefore, even when bubbling occurs between the first or second modified layer and the modified polypropylene fiber membrane, rupture of the absorbent membrane is suppressed, maintaining the flue gas desulfurization effect.

[0049] According to a fourth aspect of the present application, there is provided an absorption membrane for use in conjunction with ammonia-based desulfurization, which is prepared by the method for preparing an absorption membrane for use in conjunction with ammonia-based desulfurization as described in any one of the above items.

[0050] The beneficial effects of this application include but are not limited to:

[0051] 1. The ammonia desulfurization system and method of the present application achieve efficient flue gas desulfurization through the synergy of membrane absorption and ammonia desulfurization, suppress ammonia escape, and can operate in a long-term cycle, thereby extending the operating time of the desulfurization system.

[0052] 2. The absorption membrane used in conjunction with ammonia-based desulfurization in this application, with its first and second modified layers, can enhance adhesion to the modified polypropylene fiber membrane and improve the interception and absorption of flue gas, further increasing the desulfurization rate, reducing ammonia escape, and saving ammonia consumption.

[0053] 3. The absorbent membrane used in conjunction with ammonia desulfurization in this application contains a modified dopamine substance in the first and second modified layers, which can significantly improve adhesion to the modified polypropylene fiber membrane, improve gas throughput, and enhance flue gas treatment efficiency.

[0054] 4. The absorbent membrane used in conjunction with ammonia desulfurization in this application uses a modified polypropylene fiber membrane prepared with modified nanofillers, which can improve the overall mechanical strength of the absorbent membrane, extend its service life, and also improve the adhesion between the three layers of the absorbent membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0056] Figure 1 This is a schematic structural diagram of the desulfurization system involved in Example 1 of the present application.

[0057] Figure 2 This is a schematic structural diagram of the desulfurization tower involved in Example 1 of the present application.

[0058] Figure 3 This is a schematic structural diagram of the absorption film involved in Example 1 of the present application.

[0059] List of parts and reference numerals:

[0060] 10. Desulfurization tower; 11. Purification section; 111. Combined demister; 112. Water washing spray mechanism; 113. Second packing layer; 114. Water washing pump; 12. Absorption section; 121. First packing layer; 122. Second spray mechanism; 123. First-stage demister; 124. Reflux pipe; 125. Second partition; 126. Circulation pump; 127. Absorption membrane; 1271. First modified layer; 1272. Modified polypropylene fiber membrane; 1273. Second modified layer; 13. Concentration Cooling section; 131. Flue gas inlet; 132. First spray mechanism; 133. Concentration pump; 134. First partition; 14. Oxidation section; 141. Air inlet; 142. Third partition; 20. Crystallization tank; 21. Crystallization pump; 30. Circulating water tank; 40. Ammonium sulfide product processing mechanism; 50. Air lift cap; 60. Three-layer spiral cone nozzle; 61. Volute nozzle; 70. Concentration circulation tank; 80. Liquid tank; 81. Liquid pump; 90. Water replenishment mechanism; 91. Ammonia replenishment mechanism. DETAILED DESCRIPTION

[0061] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0062] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0063] Unless otherwise specified, the methods used in the embodiments of the present application are conventional methods in the prior art.

[0064] Example 1

[0065] refer to Figure 1-3 This embodiment relates to an ammonia-based desulfurization system and method. The ammonia-based desulfurization system includes a desulfurization tower 10, a crystallization tank 20, a circulating water tank 30, and an ammonium sulfide product processing mechanism 40. The desulfurization tower 10 is divided into a demisting section, a purification section 11, an absorption section 12, a concentration and cooling section 13, and an oxidation section 14 from top to bottom.

[0066] The oxidation section 14 is provided with an air inlet 141. The air oxidizes the liquid in the oxidation section 14. The oxidized liquid is sprayed to the absorption section 12. When the ammonium sulfate content in the oxidation section 14 reaches a second threshold, a portion of the liquid is sent to the concentration circulation tank 70.

[0067] A flue gas inlet 131 and a drain port are provided on the side wall of the concentration and cooling section 13. A first spray mechanism 132 is provided above the concentration and cooling section 13. The first spray mechanism 132 is connected to a concentration pump 133. The concentration pump 133 is used to transport the concentrated liquid in the concentration circulation tank 70 to the first spray mechanism 132. The liquid after spraying flows back to the crystallization tank 20 through the drain port for crystallization. The upper concentrated liquid in the crystallization tank 20 overflows into the concentration circulation tank 70. When the solid content in the crystallization tank 20 is greater than the first threshold value, the material at the bottom of the crystallization tank 20 is transported to the ammonium sulfate product processing mechanism through the crystallization pump 21. The oxidation section and the concentration and cooling section are separated by a third partition 142. The third partition 142 has two types: an inclined partition and a ridge partition. The ridge is further divided into a positive ridge and an inverted ridge. The type of the third partition 142 is determined according to actual needs.

[0068] The oxidation section 14, concentration and cooling section 13, absorption section 12, and purification section 11 of the desulfurization tower are separated into four independent systems by the third partition 142, the first partition 134, and the second partition 125: oxidation system, concentration and cooling system, absorption system, and purification system.

[0069] The concentration and cooling section 13 and the absorption section 12 are separated by a first partition 134. A plurality of evenly distributed air lift caps 50 are provided on the first partition 134. A first-stage demister 123, a second spray mechanism 122, an absorption membrane 127 and a first packing layer 121 are provided above the absorption section 12 from top to bottom. The first packing layer 121 is provided above the air lift cap 50. The absorption membrane includes a first modified layer, a modified polypropylene fiber membrane and a second modified layer from top to bottom. The first modified layer and the second modified layer are prepared from at least acrylamide, an olefin monomer with a piperazine group, diethylaminoethyl methacrylate and modified dopamine. The circulation pump 126 transports the liquid in the oxidation section 14 to the second spray mechanism 122 for flue gas absorption. The liquid at the bottom of the absorption section 12 then re-enters the oxidation section 14 through the reflux pipe 124.

[0070] The absorption section 12 and the purification section 11 are separated by a second partition 125, and a plurality of evenly distributed air lifting caps 50 are also provided on the second partition 125. A combined demister 111, a water washing spray mechanism 112, and a second packing layer 113 are sequentially provided in the purification section 11 from top to bottom. The water washing pump 114 transports the water in the circulating water tank 30 to the water washing spray mechanism 112 for flue gas water washing, and the water washing liquid in the purification section 11 then flows back to the circulating water tank 30.

[0071] The method of using the desulfurization system is:

[0072] (1) The flue gas after dust removal enters the concentration and cooling section 13 from the flue gas inlet 131, and is sprayed and cooled to below 60°C by the first spraying mechanism 132. The concentrated liquid in the concentration section enters the crystallization tank 20 through the drain port. The upper concentrated liquid in the crystallization tank 20 overflows into the concentration circulation tank 70. The concentration pump 133 then sends the liquid in the concentration circulation tank into the concentration section for spraying. When the solid content in the crystallization tank 20 reaches a first threshold value (for example, above 20%), the material at the bottom of the crystallization tank 20 is transported to the ammonium sulfate product processing mechanism;

[0073] (2) The flue gas then rises to the absorption section 12 and passes through the first packing layer 121, the second spray mechanism 122 and the first-stage demister 123 for demisting before entering the purification section 11. The liquid in the absorption section 12 re-enters the oxidation section 14 through the reflux pipe 124;

[0074] (3) The flue gas passes through the second packing layer 113 in the purification section 11, and is washed with water to capture ammonium sulfate and excess ammonia. After that, the flue gas is defogged by the combined demister 111 in the demisting section and then discharged from the desulfurization tower 10 into the chimney. The washing liquid in the purification section 11 is then returned to the circulating water tank 30.

[0075] (4) Compressed air enters the oxidation section 14 to oxidize the absorption liquid refluxed from the absorption section 12. The liquid formed after sufficient oxidation is then sent to the absorption section 12 for spraying. When the ammonium sulfate content in the oxidation section 14 reaches a second threshold value (for example, above 95%), a portion of the liquid is sent to the concentration circulation tank 70.

[0076] Specifically, the uniform distribution of the rising air caps 50 on the first partition 134 and the second partition 125 includes both longitudinal uniform distribution and lateral uniform distribution. Those skilled in the art can set them to a suitable arrangement shape according to the needs of installation or production, such as a square arrangement, a polygonal arrangement, etc. The above arrangement does not constitute a limitation to the present application, as long as the flue gas can be evenly distributed so that the flue gas can be evenly contacted with the absorption liquid or the water washing liquid.

[0077] As an embodiment, it further includes a concentration circulation tank 70 and a feed liquid tank 80 , the concentration circulation tank 70 is connected to the crystallization tank 20 , the feed liquid tank 80 is connected to the ammonium sulfide product processing mechanism 40 and is connected to the crystallization tank 20 through a feed liquid pump 81 .

[0078] The upper concentrated liquid of the crystallization tank 20 first enters the concentration circulation tank 70, and then the liquid in the concentration circulation tank 70 is sent to the concentration section for spraying through the concentration pump 133. The liquid treated by the cyclone in the ammonium sulfide product processing mechanism 40 enters the feed liquid tank 80, and the liquid in the feed liquid tank 80 is then transported to the crystallization tank 20 through the feed liquid pump 81 to participate in circulation and crystallization.

[0079] The provision of the concentration circulation tank 70 can improve the component stability of the spray liquid in the concentration cooling section 13 , and the provision of the liquid tank 80 and the liquid pump 81 can improve the utilization rate of ammonia in the overall desulfurization system and reduce the flue gas treatment cost.

[0080] As an embodiment, it also includes a water replenishment mechanism 90 and an ammonia replenishment mechanism 91. The inlet of the water replenishment mechanism 90 is arranged above the desulfurization tower 10, and the ammonia water inlet of the ammonia replenishment mechanism 91 is arranged on the pipeline that transports the absorption liquid from the oxidation section 14 to the absorption section 12.

[0081] As an embodiment, the first spray mechanism 132 and the second spray mechanism 122 both include a plurality of circular brackets, and each circular bracket of the second spray mechanism 122 is provided with a plurality of three-layer spiral cone nozzles 60, and the three-layer spiral cone nozzles 60 are evenly distributed in the longitudinal and transverse directions. Each circular bracket of the first spray mechanism 132 is provided with a plurality of volute nozzles 61, and the volute nozzles 61 are also evenly distributed in the longitudinal and transverse directions.

[0082] The three-layer spiral cone nozzle 60, evenly distributed along the circular support, achieves uniform spraying of liquid within the concentration and cooling section 13 and the absorption section 12, thereby increasing the contact area between the flue gas and the liquid in both sections and improving absorption efficiency. The three-layer spiral cone nozzle 60 sprays three layers of liquid film, with a single-layer spray coverage rate of 150-200%. Flue gas passing through the three layers of liquid film ensures full gas-liquid contact, allowing for absorption reactions, significantly improving sulfur dioxide absorption efficiency. It also reabsorbs some of the decomposed ammonia, further preventing ammonia escape.

[0083] As an embodiment, the three-layer spiral cone nozzle 60 and the volute nozzle 61 on the outermost circular bracket are each 700-1200 mm away from the wall of the desulfurization tower 10. This arrangement not only improves spray coverage, but also facilitates installation and maintenance of the three-layer spiral cone nozzle 60 and the volute nozzle 61 by operators. Furthermore, it reduces the contact area between the spray liquid and the wall of the desulfurization tower 10, thereby reducing corrosion of the wall and improving the service life and safety of the desulfurization system.

[0084] As an embodiment, there is one first packing layer 121 , and the height of the first packing layer 121 is 400-600 mm; there is one second packing layer 113 , and the height is 400-450 mm.

[0085] As an embodiment, the first packing layer 121 and the second packing layer 113 are both formed by regular corrugated plates arranged in parallel. The regular corrugated plates have a thickness of 1-2 mm and a spacing of 10-30 mm. The regular corrugated plates are obtained by extrusion molding of polypropylene.

[0086] The arrangement of the regular corrugated plates can improve the uniformity of the redistribution of the flue gas, thereby achieving the best contact effect between the flue gas and the absorption liquid or the washing liquid.

[0087] As an embodiment, the thickness of the first modified layer 1271 of the absorption film 127 is 15-18 μm, the thickness of the modified polypropylene fiber film 1272 is 60-80 μm, and the thickness of the second modified layer 1273 is 15-18 μm.

[0088] As an embodiment, the distance between the absorption membrane 127 and the first packing layer 121 is 300-350 mm. This spacing can reserve a retention space for the smoke between the absorption membrane 127 and the first packing layer 121, acting as a buffer to prevent damage to the absorption membrane caused by excessive smoke volume. It can also stabilize the smoke volume when the smoke volume fluctuates, thereby improving the smoke treatment efficiency.

[0089] Example 2

[0090] This embodiment relates to an ammonia desulfurization method performed using the ammonia desulfurization system of Example 1, wherein the desulfurization system has one first packing layer with a height of 600 mm, and one second packing layer with a height of 400 mm. In the first packing layer and the second packing layer, the thickness of the regular corrugated plate is 2 mm and the spacing is 20 mm. The regular corrugated plate is obtained by extrusion molding of polypropylene, and the spacing between the absorption membrane 127 and the first packing layer is 300 mm.

[0091] The preparation method of modified dopamine in this embodiment refers to Example 1 in patent CN111171213B and will not be repeated here.

[0092] The preparation method of the absorption film comprises the steps of:

[0093] (1) Preparation of modified polypropylene fiber membrane: 70-80 parts of polypropylene, 5-10 parts of polyacrylic acid, 10-25 parts of polyacrylonitrile and 4-5 parts of nanofiller are blended and extruded to obtain pellets, which are melt-spun to obtain spun fibers. The spun fibers are stretched to form pores and then treated at 100-110°C for 200 seconds to obtain modified polypropylene fiber membrane;

[0094] (2) Preparation of the first modified layer: acrylamide, an olefin monomer with a piperazine group, diethylaminoethyl methacrylate and a modified dopamine dispersion in a weight ratio of 1: (0.1-0.15): (0.1-0.2): (0.05-0.08) are placed in a solvent and mixed, wherein the concentration of the modified dopamine dispersion is 10-20 mg / ml. After adding azobisisobutyronitrile, prepolymerization is carried out at 50-70°C for 2-3 hours to obtain a first prepolymer solution, and the first prepolymer solution is coated on one side of the modified polypropylene fiber membrane, and then dried at 30-40°C for 10-15 hours to obtain the first prepolymer solution;

[0095] (3) Preparation of the second modified layer: acrylamide, an olefin monomer with a piperazine group, diethylaminoethyl methacrylate, and a modified dopamine dispersion in a weight ratio of 1: (0.1-0.15): (0.1-0.2): (0.05-0.08) are placed in a solvent and mixed. The concentration of the modified dopamine dispersion is 10-20 mg / ml. After adding azobisisobutyronitrile, prepolymerize at 50-70°C for 2-3 hours to obtain a second prepolymer solution. The second prepolymer solution is coated on the other side of the modified polypropylene fiber membrane and then dried at 30-40°C for 10-15 hours.

[0096] Absorption films 1#-8# and comparative absorption films D1#-D4# were prepared according to the above preparation method. The specific differences are as follows:

[0097] Absorption film 1#

[0098] (1) Preparation of modified polypropylene fiber membrane: 80 parts of polypropylene, 10 parts of polyacrylic acid, 25 parts of polyacrylonitrile and 5 parts of nano-silicon carbide (particle size of 50 nm) were extruded to obtain pellets, and the pellets were melt-spun to obtain nascent fibers. The nascent fibers were stretched to form pores and then treated at 100°C for 200 s to obtain modified polypropylene fiber membrane. The modified polypropylene fiber membrane had a thickness of 60 μm, an average pore size of 70 nm and a porosity of 70%.

[0099] (2) Preparation of the first modified layer: acrylamide, 2-vinylpyrazine, diethylaminoethyl methacrylate, and modified dopamine dispersion in a weight ratio of 1:0.15:0.2:0.08 were placed in a solvent and mixed, and the concentration of the modified dopamine dispersion was 20 mg / ml. After adding 0.5 wt% of azobisisobutyronitrile and 0.5 wt% of ammonium persulfate as reactants, prepolymerization was carried out at 70°C for 2 h to obtain a first prepolymer solution, and the first prepolymer solution was coated on one side of the modified polypropylene fiber membrane, and then irradiated under a 150 W ultraviolet lamp for 30 min and dried at 40°C for 10 h to obtain a first modified layer with a thickness of 18 μm;

[0100] (3) Preparation of the second modified layer: acrylamide, 2-vinylpyrazine, diethylaminoethyl methacrylate, and modified dopamine dispersion in a weight ratio of 1:0.15:0.2:0.08 were placed in a solvent and mixed. The concentration of the modified dopamine dispersion was 20 mg / ml. After adding 0.5 wt% of azobisisobutyronitrile and 0.5 wt% of ammonium persulfate as reactants, prepolymerization was carried out at 70 ° C for 2 h to obtain a second prepolymer solution. The second prepolymer solution was coated on the other side of the modified polypropylene fiber membrane, and then irradiated under a 150 W ultraviolet lamp for 30 min and dried at 40 ° C for 10 h to obtain a second modified layer with a thickness of 18 μm.

[0101] Absorption film 2#

[0102] (1) Preparation of modified polypropylene fiber membrane: 70 parts of polypropylene, 5 parts of polyacrylic acid, 10 parts of polyacrylonitrile and 4 parts of nanodiamond (particle size 80 nm) were extruded to obtain pellets, which were melt-spun to obtain nascent fibers. The nascent fibers were stretched to form pores and then treated at 110 °C for 200 s to obtain modified polypropylene fiber membrane. The modified polypropylene fiber membrane had a thickness of 80 μm, an average pore size of 75 nm and a porosity of 60%.

[0103] (2) Preparation of the first modified layer: acrylamide, 2-vinylpyrazine, diethylaminoethyl methacrylate and modified dopamine dispersion in a weight ratio of 1:0.1:0.1:0.05 were placed in a solvent and mixed, the concentration of the modified dopamine dispersion was 10 mg / ml, 1 wt% of azobisisobutyronitrile was added as a reactant, and prepolymerized at 50°C for 3 h to obtain a first prepolymer solution, which was coated on one side of the modified polypropylene fiber membrane, and then irradiated under a 150W ultraviolet lamp for 30 min and dried at 30°C for 15 h to obtain a first modified layer with a thickness of 15 μm;

[0104] (3) Preparation of the second modified layer: acrylamide, 2-vinylpyrazine, diethylaminoethyl methacrylate and modified dopamine dispersion in a weight ratio of 1:0.1:0.1:0.05 were placed in a solvent and mixed. The concentration of the modified dopamine dispersion was 10 mg / ml. After adding 1 wt% of azobisisobutyronitrile as the reactant, prepolymerization was carried out at 50°C for 3 h to obtain a second prepolymer solution. The second prepolymer solution was coated on the other side of the modified polypropylene fiber membrane, and then irradiated under a 150W ultraviolet lamp for 30 min and dried at 30°C for 15 h to obtain a second modified layer with a thickness of 15 μm.

[0105] Absorption film 3#

[0106] The difference between this absorption film and absorption film 1# is that the following compound is used instead of 2-vinylpyrazine, and its specific structural formula is as follows:

[0107] .

[0108] The preparation method of the compound is:

[0109] S11: reacting glycidol and 1-tert-butyloxycarbonylpiperazine to obtain a dihydroxy-tert-butyloxycarbonylpiperazine compound;

[0110] S12: Then, dihydroxy tert-butyloxycarbonyl piperazine compound and acryloyl chloride are reacted at 30° C. for 6 h in the presence of a solvent and a catalyst pyridine. After washing and recrystallization, monomer 1 is obtained. The preparation formula is as follows:

[0111] ;

[0112] The rest is the same as absorption film 1#.

[0113] Absorption film 4#

[0114] The difference between this absorption film and absorption film 1# is that the weight ratio of acrylamide, 2-vinylpyrazine, diethylaminoethyl methacrylate and modified dopamine dispersion is 1:0.15:0.2:0.02, and the rest is the same as absorption film 1#.

[0115] Absorption film 5#

[0116] The difference between this absorption film and absorption film 1# is that the weight ratio of acrylamide, 2-vinylpyrazine, diethylaminoethyl methacrylate and modified dopamine dispersion is 1:0.15:0.2:0.1, and the rest is the same as absorption film 1#.

[0117] Absorption film 6#

[0118] The difference between this absorption film and absorption film 1# is that the concentration of the modified dopamine dispersion is 30 mg / ml, and the rest is the same as absorption film 1#.

[0119] Absorption film 7#

[0120] The difference between this absorption film and absorption film 1# is that nano-silicon carbide is replaced by modified dopamine, and the rest is the same as absorption film 1#.

[0121] Absorption film 8#

[0122] The difference between this absorption film and absorption film 1# is that nano-silicon carbide is replaced by modified dopamine and modified nano-silicon carbide in a weight ratio of 1:1. The specific modification method of modified nano-silicon carbide is:

[0123] Nano-silicon carbide is placed in an ethanol solution containing 3-mercaptopropyltrimethoxysilane. The weight ratio of nano-silicon carbide to 3-mercaptopropyltrimethoxysilane is 1:0.2. The concentration of 3-mercaptopropyltrimethoxysilane in the ethanol solution containing 3-mercaptopropyltrimethoxysilane is 20 mg / ml. The solution is treated at 50°C for 5 hours, filtered and dried. The rest is the same as the absorption film 1#.

[0124] Absorption film 9#

[0125] The difference between this absorption film and absorption film 1# is that the nano-silicon carbide is modified nano-silicon carbide. The specific modification method is:

[0126] Place nano-silicon carbide in an ethanol solution containing 3-mercaptopropyltrimethoxysilane, the weight ratio of nano-silicon carbide to 3-mercaptopropyltrimethoxysilane is 1:0.3, the concentration of modified dopamine in the ethanol solution containing 3-mercaptopropyltrimethoxysilane is 40 mg / ml, treat at a temperature of 70°C for 4 hours, filter and dry, and the rest is the same as absorption film 1#.

[0127] Comparative absorption film D1#

[0128] The difference between this comparative absorption film and absorption film 1# is that dopamine dispersion instead of modified dopamine dispersion is used in the preparation of the first modified layer, and the rest is the same as absorption film 1#.

[0129] Comparative absorption film D2#

[0130] The difference between this comparative absorption film and absorption film 1# is that the preparation of the second modified layer does not contain modified dopamine dispersion, and the rest is the same as absorption film 1#.

[0131] Comparative absorption film D3#

[0132] The difference between this comparative absorption film and absorption film 1# is that acrylic acid and dopamine with a weight ratio of 1:1 are used to replace the modified dopamine dispersion in the preparation of the first modified layer and the second modified layer, and the rest is the same as absorption film 1#.

[0133] Comparative absorption film D4#

[0134] It is prepared using the preparation method of hollow absorption membrane 1# in patent 202411719611.1.

[0135] Test Example 1

[0136] The ammonia desulfurization system of Example 1 was used to perform flue gas desulfurization operation under the same parameter conditions. The parameter conditions are shown in Table 1. The desulfurization rate and ammonia escape amount in the flue gas discharged from the desulfurization tower outlet were tested under the same ammonia water dosage. The test period was 1 week. The test results are shown in Table 2.

[0137] The ammonia desulfurization system and desulfurization method without an absorption membrane were named the control group. The absorption membrane prepared in Example 2 was added to the control group as the experimental group. The amount of ammonia water required when the desulfurization rate of the experimental group was the same as that of the control group (99%) was counted, and the ammonia water saving rate of each absorption membrane was calculated. The calculation formula was: (amount of ammonia water used in the control group - amount of ammonia water used in the experimental group) / amount of ammonia water used in the control group × 100.

[0138] Table 1

[0139]

[0140] Table 2

[0141]

[0142] The test results in Table 2 show that the above-mentioned absorber membrane can achieve a desulfurization rate of over 98%, and the ammonia savings rate is over 43.0% compared to the control group, significantly reducing desulfurization costs while maintaining the desulfurization rate. Furthermore, the amount of ammonia used in this test example is reduced, and the comparative absorber membrane D1# shows a decrease compared to the test data in Patent 202411719611.1.

[0143] Test Example 2

[0144] The absorption film prepared in Example 2 was placed in flue gas at 60°C for 60 days. The sulfur dioxide content in the flue gas was 5000 mg / Nm 3 During this period, the amount of ammonia used was 2.1m 3 / h, and then soak the absorption membrane in ammonia water at 130℃ for 30 days to observe whether the absorption membrane is stratified, and then perform the test of Test Example 1. After running for one week, check whether the absorption membrane has cracks or ruptures. The presence of ruptures indicates that the adhesion between the layers is weak during the desulfurization process, resulting in gas bubbling in the layers, causing cracks or ruptures. It is also tested whether the absorption membrane after the above-mentioned destructive high-temperature treatment has a reduced effect on desulfurization and reducing ammonia escape. The test results are shown in Table 3.

[0145] Table 3

[0146]

[0147] In Table 3 above, due to the delamination of the absorption membrane 4# and the comparative absorption membranes D1#-D4#, they were broken during operation and the desulfurization system could not continue to operate. Therefore, the desulfurization rate and ammonia escape amount could not be detected normally.

[0148] The foregoing is merely an embodiment of the present application, and the scope of protection of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the technical ideas and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing an absorption membrane for use with ammonia desulfurization, characterized in that: Including steps: S1: Preparation of modified polypropylene fiber membrane: 70-80 parts of polypropylene, 5-10 parts of polyacrylic acid, 10-25 parts of polyacrylonitrile and 4-5 parts of nanofiller are blended by weight, extruded to obtain pellets, and the pellets are melt-spun to obtain nascent fibers. The nascent fibers are stretched to form pores and then treated at 100-110°C for 200s to obtain a modified polypropylene fiber membrane. The nanofiller is selected from modified nano-silicon carbide and modified dopamine in a weight ratio of 1:

1. The modified nano-silicon carbide is modified with 3-mercaptopropyltrimethoxysilane. The nano-silicon carbide is placed in an ethanol solution of 3-mercaptopropyltrimethoxysilane with a concentration of 20-40 mg / ml, and the weight ratio of nano-silicon carbide to 3-mercaptopropyltrimethoxysilane is 1:(0.2-0.3). The fibers are treated at a temperature of 50-70°C for 4-5h, filtered, and dried. S2: Preparation of the first modified layer: acrylamide, an olefin monomer with a piperazine group, diethylaminoethyl methacrylate, and a modified dopamine dispersion are mixed in a solvent, azobisisobutyronitrile and ammonium persulfate are added, and prepolymerization is carried out at 50-70°C for 2-3 hours to obtain a first prepolymer solution, which is coated on one side of a modified polypropylene fiber membrane, followed by irradiation and drying at 30-40°C for 10-15 hours. S3: Preparation of the second modified layer: acrylamide, an olefin monomer with a piperazine group, diethylaminoethyl methacrylate, and a modified dopamine dispersion are mixed in a solvent, azobisisobutyronitrile and ammonium persulfate are added, and prepolymerization is carried out at 50-70°C for 2-3 hours to obtain a second prepolymer solution, which is then coated on the other side of the modified polypropylene fiber membrane, followed by irradiation and drying at 30-40°C for 10-15 hours. In steps S2 and S3, the weight ratio of acrylamide, an olefin monomer having a piperazine group, diethylaminoethyl methacrylate, and the modified dopamine dispersion is 1:(0.1-0.15):(0.1-0.2):(0.05-0.08), and the concentration of the modified dopamine dispersion is 10-20 mg / ml. The preparation method of the modified dopamine is: S10: adding dopamine hydrochloride to sodium borate and sodium bicarbonate and stirring to obtain a dopamine mixed solution; S20: adding acrylic acid to tetrahydrofuran to obtain an acrylic acid solution; S30: adding the acrylic acid solution to the dopamine mixed solution, and adding an alkaline solution to adjust the pH of the reaction solution to ≥8, and reacting for more than 12 hours; S40: adding an acidic solution to adjust the pH of the reaction solution until the product precipitates, washing and drying, placing the dried product in a low-temperature plasma generator, ventilating, adjusting the discharge voltage, using radio frequency discharge, and performing plasma treatment to obtain modified dopamine.

2. The absorption membrane for use in conjunction with ammonia-based desulfurization prepared by the preparation method of the absorption membrane for use in conjunction with ammonia-based desulfurization according to claim 1.

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