A method for adsorbing and removing low-concentration sulfur dioxide and fine dust in flue gas

Abstract

The application is a method for adsorbing and removing low-concentration sulfur dioxide and dust in flue gas, which relates to the use of macroporous weak acid cation exchange resin which is transformed into weak base resin to adsorb and remove sulfur dioxide. The specific steps are as follows: after the flue gas is cooled and humidified by water washing, it is introduced into an adsorption column filled with macroporous weak acid cation exchange resin. The resin is packed in the form of bundled bags or scattered packing, or a combination of the two. During the adsorption process, the resin particles slowly shrink and discharge bisulfite solution, which can be used as a by-product or discharged harmlessly after oxidation. In addition, the resin layer can also intercept and capture small particles of dust in the flue gas, achieving the effect of dust removal. The resin can be regenerated by alkali leaching. The process of the application is simple, the desulfurization and dust removal efficiency is high, the equipment investment is small, and it has universality, which is suitable for the desulfurization needs of multiple industrial fields, especially for the capture and removal of low-concentration SO2 generated by small and medium-sized emission sources.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for adsorbing and removing low-concentration sulfur dioxide and dust in flue gas, and relates to the fields of industrial tail gas treatment, environmental protection, energy saving and emission reduction, etc. BACKGROUND

[0002] Large-scale acid rain has brought serious harm to ecological environment, human health and economic sustainable development, etc. Therefore, taking effective measures to control and govern sulfur dioxide in industrial flue gas has become a problem to be solved in air pollution prevention and control.

[0003] At present, the limestone-gypsum method is generally used for flue gas desulfurization in China. Although this method is very mature, it has technical defects, such as high construction cost, large power consumption, high operation cost, low effective utilization rate of limestone, serious consumption of limestone mineral resources, poor quality of by-product gypsum, which is difficult to effectively utilize and often can only be landfilled, high treatment cost for waste gas generated by small and medium-sized point emission sources, poor process applicability, etc. In summary, the limestone-gypsum desulfurization process is a high-consumption and high-cost technical route, which does not meet the development ideas and trends of current energy saving and emission reduction.

[0004] In addition to the limestone-gypsum method, industrial wet, semi-dry and dry desulfurization technologies such as seawater method, double-alkali method, ammonia water method, organic amine method, citrate method, magnesium method, phosphate ammonium fertilizer method, lime circulation fluidized bed method, in-furnace calcium injection method, charged method, pulse corona method, etc. have been developed. There are dozens of such technologies. These technologies generally focus on solving a certain aspect of the desulfurization process and compete with the limestone-gypsum method in technology, but due to the limitations of device investment, operation cost, resource consumption rate, and technical applicability, etc., they also have technical difficulties. In general, all of the above methods have been more or less applied in industry, but they still have a certain distance from the requirements of the era of energy saving and emission reduction.

[0005] In this context, various new desulfurization technologies are still being developed. Among them, the use of ion exchange resin as a desulfurization material provides us with a new solution. Cole et al. first reported the use of dry strong basic anion exchange resin (Amberlite IRA-400) for SO2 adsorption, with an adsorption capacity of 280 mg SO2 / g resin. Regeneration with 100°C dry air blowing can restore 68% of the adsorption capacity (Ind. Eng. Chem. Res., 1960, 52, p850). However, due to the gel type of the resin, there is not enough specific surface area and porosity, so it often takes several hours to reach adsorption equilibrium, which lacks practical application value. Since then, research on macroporous ion exchange resins has been carried out. Until the beginning of this century, a variety of macroporous ion exchange resins have been studied and tried, some of which have achieved good results. For example: Chen et al. used Dowex MWA-1 macroporous anion exchange resin for fixed bed adsorption study, the results showed that for the combustion tail gas of high sulfur coal (4 wt% sulfur content), the gas treatment capacity of Dowex MWA-1 can reach 1500 resin bed volume. In addition, Dowex MWA-1 shows very good selective adsorption of SO2, and the separation factor of SO2 / CO2 can reach 1000. However, a slight increase in tail gas temperature will cause a significant decrease in resin treatment capacity (Reactive Polymers, 1991, 14. p151). Patent CN108452777A discloses a kind of amino functionalized quaternary ammonium salt macroporous resin adsorbing SO2, which has poor thermal stability (less than 80°C), and the preparation process is more complicated. These research results have laid an important pre-stage foundation for the technical development of the present invention. SUMMARY

[0006] The purpose of the present invention is to overcome the shortcomings of traditional desulfurization methods such as limestone-gypsum method, and to provide a treatment method for adsorbing and separating sulfur dioxide in tail gas by using macroporous weak acid cation exchange resin transformed into weak base adsorbent by alkaline neutralization, and converting and producing value-added byproducts. At the same time, due to the small size of the resin material, the packing density is large, and it also has a rich microporous structure, so that the resin bed can effectively intercept the dust particles in the flue gas (especially PM2.5 particles), achieving the effect of further filtering and dedusting.

[0007] To achieve the above purpose, the following technical solutions are adopted in the present invention:

[0008] Step 1, purification, cooling and humidification of flue gas

[0009] As shown in the accompanying drawings Figure 1As shown, the flue gas introduced by the induced draft fan enters the bottom of the water scrubbing tower A, where it comes into counter-current contact with the atomized scrubbing water sprayed from the top of the tower. 80-90% (by mass) of the scrubbing wastewater from the water scrubbing tower is recycled, while the remaining 10-20% is sent to the settling tank B and neutralized with limestone to a pH of 6-9 for harmless discharge. The purified flue gas temperature drops to 40-70℃ and reaches water vapor saturation before being sent to adsorption towers C or D for desulfurization and further dust removal.

[0010] Step 2: Flue gas desulfurization and further dust removal

[0011] The low-temperature, water-saturated flue gas discharged from the top of the water washing tower enters the adsorption tower from the bottom. The tower is filled with macroporous, weakly acidic cation exchange resin, which has been neutralized and converted to alkali metal, alkaline earth metal, or ammonium form before use. The flue gas is then distributed into a uniformly distributed airflow via a flue gas distribution device.

[0012] Controls are attached. Figure 1 In the process shown, valves V1 and V3 are open, and the remaining valves are closed. At this time, adsorption tower 1 (C) is in the adsorption stage, and sulfur dioxide in the flue gas reacts with the neutralized and transformed macroporous weak acid cation exchange resin as follows:

[0013] R-COOM + SO2 + H2O = 2R-COOH + M2SO3

[0014] Or: (R-COO)2N + SO2 + H2O = 2R-COOH + NSO3

[0015] M₂SO₃ + SO₂ + H₂O = 2MHSO₃

[0016] Or: NSO3 + SO2 + H2O = N(HSO3)2

[0017] Since flue gas often contains a certain amount of oxygen, the main side reaction in this process is oxidation.

[0018] 2M₂SO₃ + O₂ = 2M₂SO₄

[0019] Alternatively: 2NSO3 + O2 = 2NSO4

[0020] Wherein, R refers to the resin skeleton, M is an alkali metal or ammonium ion, and N is an alkaline earth metal ion.

[0021] With the adsorption of SO2, the resin gradually changes from base form to hydrogen form. Because of the hydrogen bond between hydrogen ion and resin carboxyl, the combination between polymer chains is very tight, so the resin will gradually shrink and "squeeze out" the solution in its pores, forming a continuous liquid phase outside the resin and falling into the bottom of the tower. The shrinkage of resin of different base forms changing to hydrogen form is different, roughly as follows:

[0022] Na type <50%; Ca type <30%; NH4 type <20%.

[0023] At the same time, the dust particles in the flue gas are continuously physically adsorbed, deposited and coalesced on the surface of the resin through the interception of the resin. However, due to the slow shrinkage deformation and continuous solution discharge of the resin, it is difficult for the dust particles to form a firm adhesion layer on the surface of the resin, and they gradually fall off and enter the liquid phase with the solution discharged from the resin, so they will not block the contact and reaction of SO2 with the carboxyl groups of the resin. The liquid discharged from the resin is introduced into the centrifugal separation device through V5 from the bottom of the tower, and the filter residue is coal ash dust, which can be combined and treated with the sludge in the ash settling tank B in step 1. The filtrate is further treated as a product--for example, the ammonium bisulfite solution is oxidized by forced air and neutralized with ammonia gas to produce sulfur-containing fertilizer as a byproduct; the calcium bisulfite solution can be directly used as a pulp bleaching agent in papermaking enterprises; the sodium bisulfite solution can be used as a raw material for byproduct disinfecting water or bleaching water, etc. In order to handle excessive sodium bisulfite solution, a recommended method is to perform a regeneration treatment--for example, under the condition of forced air oxidation, the following reaction occurs between lime and sodium bisulfite to generate sodium hydroxide which can be used for resin regeneration, and gypsum as a byproduct:

[0024] Ca(OH)2 + 2NaHSO3 = Na2SO3 + CaSO3•1 / 2H2O↓ + 1 / 2H2O

[0025] Ca(OH)2 + Na2SO3 + 1 / 2H2O = 2NaOH + CaSO3•1 / 2H2O↓

[0026] CaSO3•1 / 2H2O + O2 + 3 / 2H2O = 2(CaSO4•2H2O)

[0027] In summary, there are many optional solutions for the treatment of filtrate, which can be selected according to local natural resources, industrial raw materials or market demand, so as to make full use of resources, produce valuable products and have no pollution emissions.

[0028] The purified flue gas after desulfurization and dust removal is sent to the chimney after the demister.

[0029] Step 3, resin cleaning and regeneration

[0030] When the concentration of SO2 in the flue gas discharged from the adsorption tower C reaches the set value, it is stopped, the valves V2 and V4 are opened, and the valves V1 and V3 are closed, and the adsorption is started by the adsorption tower 2 (D). At the same time, the water pump is opened to spray clean water from the top of the adsorption tower 1 (C) to wash the resin to be regenerated. The washing process is divided into two stages, the first stage of washing water is 0.1-0.5 times the volume of the resin bed, and the solution and dust particles remaining on the surface and inside of the resin are washed for 2-3 times, and the washing water in this stage is combined with the liquid at the bottom of step 2 for treatment; the second stage of washing water is 0.5-1.0 times the volume of the resin bed, and after 2-4 times of washing, the washing is stopped, and the pH of the solution is about 5-7 at this time. The washing water in the second stage is pumped into the silt pool in step 1 as the supplementary water for the water washing tower A. After the two-stage washing is completed, the valve V5 is closed, the alkali pump is opened, and the resin regeneration work is started, and the injected alkali solution reacts with the resin as follows:

[0031] RCOOH + MOH = R-COOM + H2O

[0032] Or: 2 RCOOH + N(OH)2= (R-COO)2N + 2H2O

[0033] The resin is converted from hydrogen type to alkali type, and the sulfur dioxide adsorption capacity is restored. The alkali solution is recycled until the pH is 8-10, and the resin is drained until no liquid is discharged, and the resin in the adsorption tower 1 (C) is regenerated, and a adsorption and regeneration cycle process is completed.

[0034] The above method for removing sulfur dioxide from flue gas, in step 1, the flue gas is generated from the sulfur dioxide generated in the power, steel, non-ferrous metal, chemical or building material industries. The concentration of sulfur dioxide in the flue gas is in the range of 100-6000 mg / m 3 .

[0035] The above method for removing sulfur dioxide from flue gas, in step 2, the functional group of the macroporous weak acid anion exchange resin is carboxyl (-COO - ), the skeleton is acrylic, and the pore structure is macroporous. The resin brands include D113 (equivalent to old brands: D131, D110, D111S, D152) in China, Amberlite IRC-84 in the United States, Lewatit CNP-80 in Germany, Diaion WK10 in Japan, Duolite C-476 in France, KB-3 in the Soviet Union, Ostion KM in the Czech Republic, etc.

[0036] The above method for removing sulfur dioxide from flue gas, in step 2, the adsorption tower at least includes: a flue gas inlet, a liquid spraying section, a resin filling section, a liquid storage section at the bottom of the tower, a demisting section and a flue gas outlet.

[0037] The method for removing sulfur dioxide from flue gas, in step 2, the macroporous weak acid ion exchange resin is packed in the adsorption tower in a bundled bag (as shown in Figure 2 ) or a loose packing bag (as shown in Figure 3 ) alone, or in a two-stage packing mixed with both. In the two-stage packing, the bundled bag is located at the lower end, with a height of 1 / 5 to 1 / 2 of the tower height; the loose packing section is located at the upper section, with a height of 4 / 5 to 1 / 2 of the tower height.

[0038] The method for removing sulfur dioxide from flue gas, in step 2, the bundled bag is made as follows: the resin before transformation is packed into a large bag made of glass cloth, the bag is sealed and the resin inside is spread into a flat layer with a thickness of 2-4 cm, and plastic or stainless steel wire is sewn in the longitudinal and transverse directions to form a large bag piece containing a plurality of long strip-shaped small bags arranged in order, then the front and back of the bag are covered with stainless steel wire mesh or plastic wire mesh, and then rolled into a cylindrical shape to form a bundled bag, as shown in Figure 2 . The length of each small bag on the cross section is ≤6 cm, the thickness is ≤4 cm, and the height is ≤10 cm, the height of the entire cylinder is 20-30 cm, and the diameter is determined according to the tower diameter. In the sewing of the bag, about 20-50% of the space of each small bag is left to facilitate the shrinkage and expansion of the resin during absorption and regeneration.

[0039] The method for removing sulfur dioxide from flue gas, in step 2, the resin bundled bag is packed in the tower as follows: when the tower diameter is ≤1 m, a single bundled bag is packed on the cross section of the adsorption tower; when the tower diameter is ≥2 m, a plurality of bundled bags are packed on the cross section of the adsorption tower, each with a diameter of 10-20 cm, arranged in a honeycomb pattern; when the tower diameter is greater than 1 m and less than 2 m, it is a transition zone, and both of the above methods can be applied. In addition, the wire mesh of the bundled bags of adjacent two layers of structure is staggered during installation to ensure uniform gas and liquid distribution.

[0040] The method for removing sulfur dioxide from flue gas, in step 2, the loose packing bag is made as follows: a single industrial commonly used open ring-shaped or spherical or garland-shaped bulk packing (as shown in Figure 3 ) is placed in a cloth bag made of glass cloth of appropriate size, resin particles before transformation are poured in, and 20-50% of free volume is reserved for shrinkage and expansion of the resin during absorption and regeneration, and the bag is tied tightly to become a loose packing bag containing resin.

[0041] The method for removing sulfur dioxide from flue gas, in step 2, the industrial commonly used bulk packing includes: Bauer ring, hollow multi-faced ball, Meller garland, eight-four inner arc ring (Meller ring), etc., with a nominal size of 38-100 mm, and the material is preferably stainless steel or plastic.

[0042] In step 2 of the method for removing sulfur dioxide from flue gas, the alkali metal ions include Na + and K + , and the alkaline earth metal ions include Ca 2+ , and NH4 + .

[0043] In step 3 of the method for removing sulfur dioxide from flue gas, the concentration of the alkali solution used for regeneration is 2-10% (mass percentage), the amount of alkali used is 0.8-1.2 times the total amount of carboxyl groups in the resin in the tower, and the alkali solution is sprayed in a cycle. When Ca(OH)2 is used as the alkali, because the solubility of Ca(OH)2 in water is limited, a milk lotion containing 1-5% Ca(OH)2 by mass can be used instead of the alkali solution. In addition, after the regeneration of the resin is completed, the alkali content in the alkali solution decreases, and fresh solid alkali can be repeatedly dissolved to increase the concentration, so as to be used as the alkali solution for the next regeneration of the resin. In this way, no waste water is generated in the regeneration process, so as to save resources and meet the requirements of environmental protection.

[0044] In step 3 of the method for removing sulfur dioxide from flue gas, the amount of the alkali solution used for regeneration that is sprayed in a cycle is controlled to be 0.1-1.0 BV / h (BV refers to the volume of the resin bed), so as to prevent the stress caused by the rapid expansion of the resin particles from causing the particles to be broken.

[0045] Compared with the prior art, the present application has the following advantages:

[0046] 1. The method of the present application is simple and universal, and is suitable for the desulfurization requirements of multiple industries, especially for the process treatment of flue gas desulfurization of small and scattered point emission sources.

[0047] 2. The desulfurization effect is remarkable, and valuable products can be by-produced, so as to reduce the pollution emission to the minimum.

[0048] 3. The dust removal effect is remarkable, and is integrated with the desulfurization process, so as to reduce the equipment investment.

[0049] 4. The desulfurization resin and the alkali used for the regeneration of the resin are cheap and easy to obtain, and the purity requirement of the alkali substance is low, so as to easily control the operation cost.

[0050] 5. The adsorption capacity of each gram of wet resin is as high as 4 mmol SO2 (when the volume content of SO2 is 0.15%), the flue gas treatment capacity is large, and the regeneration frequency is low. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 It is a process flow diagram of the sulfur dioxide adsorption method of the present application.

[0052] Figure 2 It is a schematic diagram of a baling bag provided by the present application for resin loading.

[0053] Figure 3 Optional bulk packing for packing resin in the present application.

[0054] Figure 1 The components in the figure are as follows: A is a pre-washing tower, B is a dust settling tank, C is an adsorption tower 1, D is an adsorption tower 2, E is a centrifuge, F and G are lye storage tanks; 1 is flue gas before purification, 2 is circulating washing water, 3 is slurry sewage, 4 is flue gas after cooling and humidification, 5 is flue gas after sulfur removal, 6 is a mixed solution of resin discharge and dust, 7 is a mixed solution of bisulfite and sulfate, 8 is dust solid, 9 is quicklime or limestone; V1-V6 are control valves. DETAILED DESCRIPTION

[0055] The technical solutions of the present application are described below with specific examples, but the protection scope of the present application is not limited thereto:

[0056] Example 1a: making a bale package

[0057] Put the D113 type resin in wet state before transformation (parameter P1) into a large pocket made of glass cloth, seal the pocket, spread the resin in it into a flat layer with a thickness of 2.5 cm, sew along the longitudinal and transverse directions with plastic or stainless steel wire, make a large cloth bag piece containing individual small cloth bags arranged in a long strip, then cover the front and back of the cloth bag with stainless steel wire mesh or plastic wire mesh respectively, and roll it into a cylinder to become a bale package, as shown in Figure 2 The length of each small cloth bag in the cross section is 5 cm, the height is 10 cm, the height of the entire cylinder is 30 cm, and the diameter is determined according to the diameter of the tower. During the sewing of the cloth bag, about 20-50% (parameter P2) of space should be left for each small pocket to facilitate the shrinkage and expansion of the resin during absorption and regeneration.

[0058] Example 1b: making a bulk packing package

[0059] Put a single 63 mm size Mellor ring (parameter P3) into a single small cloth bag made of glass cloth, then pour in the D113 type resin (parameter P1) in wet state, and the resin filling amount is 50% (parameter P2) of the pore volume of the Mellor ring (parameter P3). After filling, the bag opening is tied tightly to make a bulk packing package.

[0060] Example 1c: adsorption desulfurization and adsorbent regeneration

[0061] The flue gas from a 35 t / h low-pressure chain boiler has a flue gas temperature of 160°C, a working gas flow of 100000 m 3 / h, and a standard gas flow of 65000 m 3mg / m3, and the concentration of dust particles is 4120 mg / m3 3 mg / m3 (at standard state), 2520 mg / m3 3 (at standard state). The flue gas is introduced into the water washing tower A, and countercurrent washing is carried out in the water washing tower, 80-90% of the dust in the flue gas is preliminarily removed, the temperature of the flue gas is reduced to 60°C, and the water vapor is saturated. 90% (mass percentage) of the washing sewage of the water washing tower is used for recycling, and the other 10% is sent to the ash settling tank for neutralization to pH=6-9 by limestone. The supernatant of the ash settling tank is used for supplementing washing water, and the bottom layer is periodically discharged harmlessly.

[0062] The valves V1 and V3 are opened, and the other valves are closed, so that the adsorption tower 1 is in the adsorption state. The above flue gas is sent from the bottom of the tower to the adsorption tower 1 through the induced draft fan, and uniformly distributed flue gas flow is formed through the flue gas distribution device. The lower part of the adsorption tower is filled with the baling package prepared in Example 1a, and the upper part is filled with the loose packing, and the height ratio of the two is 1 / 4 (parameter P4). Regardless of the baling mode, the D113 type resin (parameter P1) in the packing is converted to weak base type by elution with sodium hydroxide (parameter P5) before adsorption. When the flue gas passes through the adsorption layer, the sulfur dioxide in the flue gas reacts with the carboxyl group on the resin, and the resin is slowly converted from weak base type to H type. The resin particles gradually shrink, and the discharged solution flows into the liquid storage section at the bottom of the tower. At the same time, the residual dust in the flue gas is further intercepted by the resin layer, and flows into the liquid storage section at the bottom of the tower together with the discharged solution. The flue gas passing through the adsorption tower has a dust particle concentration of 15 mg / m3 3 (result R1) and 50 mg / m3 3 (result R2), and the removal rates are 99.6% (result R3) and 98.0% (result R4), respectively. The purified flue gas is sent to the chimney through V3.

[0063] When the concentration of sulfur dioxide in the outlet flue gas rises to 100 mg / m3 3When the adsorption process is completed, the valve V1 and V3 are closed, and the valve V2 and V4 are opened, and the adsorption process is transferred from the column 1 to the column 2. At this time, the water pump of the column 1 is opened, and the resin layer is cleaned by spraying clean water from the top of the column, and the water consumption of the first cleaning stage is 0.25 times of the volume of the resin layer (parameter P6); the water consumption of the second cleaning stage is 1.0 times of the volume of the resin layer (parameter P7). The washing water of the first cleaning stage is combined with the liquid phase discharged from the resin in the adsorption process, and is sent into the centrifugal separator through V5. The solid phase after centrifugation is dust particles which enter the ash settling tank and are combined with the washing sewage for treatment. The liquid phase is sodium bisulfite aqueous solution (result R5), which is sent into the product tank and is used as disinfectant water (result R6) subsequently. After the cleaning is completed, the regeneration is started, the alkali pump is opened to spray alkali solution, the concentration of the alkali solution is 4% (parameter P8), the alkali consumption is 1.1 times of the total amount of the carboxyl groups in the resin, the regeneration liquid is sprayed circularly for 2-4 times, until the pH of the circulating liquid is reduced to about 8, and the regeneration is stopped. After the resin is drained, one adsorption and regeneration cycle is completed.

[0064] Examples 2-12: According to the processes in examples 1 (a, b, c), various different implementation results R1-R6 are obtained by changing the implementation parameters P1-P8 therein. Details are shown in the following table.

[0065] The present application proposes a modification method of ion exchange resin which is low in price, high in thermal stability, large in adsorption capacity of SO2, and can remove fine dust at the same time, and constructs corresponding process application technology and regeneration process method for the resin. The device construction cost of the present application is low, the operation cost is also low, and the SO2 can be resourceized into valuable by-products.

[0066]

Claims

1. A method for adsorption and removal of low-concentration sulfur dioxide from flue gas, characterized in that, Includes the following steps: Step 1: Purification, cooling, and humidification of flue gas The flue gas introduced by the induced draft fan enters the bottom of the water washing tower A, where it comes into countercurrent contact with the atomized washing water sprayed from the top of the tower. 80-90% of the washing wastewater from the water washing tower is recycled, while the remaining 10-20% is sent to the settling tank B to be neutralized with limestone to a pH of 6-9 for harmless discharge. The purified flue gas temperature drops to 40-70℃ and reaches water vapor saturation before being sent to the adsorption tower C or D for desulfurization and further dust removal. Step 2: Flue gas desulfurization and further dust removal The low-temperature, water-saturated flue gas discharged from the top of the water washing tower enters the adsorption tower C from the bottom. The tower is filled with macroporous weak acid cation exchange resin, which has been converted to alkali metal, alkaline earth metal, or ammonium form. The flue gas is distributed evenly by the flue gas distribution device. Control valves V1 and V3 are open, and the rest are closed. At this time, the adsorption tower C is in the adsorption stage. As sulfur dioxide is adsorbed, the resin gradually changes from the basic form to the hydrogen form and gradually shrinks, discharging the solution in its pores and forming a continuous liquid phase outside the resin, which falls into the bottom storage section of the tower. At the same time, dust particles in the flue gas are intercepted and captured by the resin and flow into the bottom of the tower with the resin discharge liquid. The bottom liquid is introduced into a centrifugal separation device, and the filter residue is coal ash particles, which are combined with the sludge in the settling tank in step 1 for treatment. The filtrate is further treated to produce products or regenerate. The flue gas after desulfurization and dust removal is sent to the chimney for emission after passing through a demister. Step 3: Resin Cleaning and Regeneration When the SO2 concentration in the flue gas discharged from adsorption tower C reaches the set value, it is stopped, control valves V2 and V4 are opened, and valves V1 and V3 are closed, and adsorption begins in adsorption tower D. Simultaneously, the water pump is turned on to spray clean water from the top of adsorption tower C for washing. The washing process is divided into two stages. In the first stage, the washing water volume is 0.1 to 0.5 times the resin bed volume, circulating 2-3 times to clean the resin surface and internal residual solution and dust particles. The washing water in this stage is combined with the liquid from the bottom of the tower in step 2 for treatment. In the second stage, the washing water volume is 0.5 times the resin bed volume. ~1.0 times, after 2-4 cycles of cyclic washing, the washing is stopped. At this time, the pH of the solution is between 5 and 7. During this stage, the washing water is pumped to the settling tank in step 1 as supplementary water for the washing tower A. After washing, valve V5 is closed and the alkali pump is turned on to start spraying alkali solution. The resin is converted from H type to alkali metal type, alkaline earth metal type or ammonium type, restoring the sulfur dioxide adsorption capacity. The alkali solution is circulated from the bottom of the tower until the pH is 8-10 and the circulation stops. The resin is drained until no liquid is discharged. The resin in the adsorption tower C completes the regeneration work and completes one adsorption regeneration cycle.

2. The adsorption and removal method for low-concentration sulfur dioxide in flue gas according to claim 1, wherein in step 1, the concentration of sulfur dioxide in the flue gas is between 100 and 6000 mg / m³. 3 Within the range.

3. The adsorption and removal method for low-concentration sulfur dioxide in flue gas according to claim 1, characterized in that: In step 2, the functional group of the macroporous weak acid anion exchange resin is a carboxyl group (-COO-), the backbone is acrylic, and the pore structure is macroporous. The resin grades included are: China: D113, USA: Amberlite IRC-84, Germany: Lewatit CNP-80, Japan: Diaion WK10, France: Duolite C-476, USSR: KB-3 or Czech Republic: Ostion KM.

4. The adsorption and removal method for low-concentration sulfur dioxide in flue gas according to claim 1, characterized in that: In step 2, the adsorption tower includes at least the following structures: flue gas inlet, liquid spray section, resin filling section, bottom liquid storage section, demister section, and flue gas outlet.

5. The adsorption and removal method for low-concentration sulfur dioxide in flue gas according to claim 1, characterized in that: In step 2, the macroporous weak acid ion exchange resin is individually packed in the adsorption tower using either a bundled packing method or a random packing method, or a two-stage packing method combining both. In the two-stage packing, the bundled packing is located at the lower end, with a height of 1 / 5 to 1 / 2 of the tower height; the random packing section is located at the upper end, with a height of 4 / 5 to 1 / 2 of the tower height.

6. The adsorption and removal method for low-concentration sulfur dioxide in flue gas according to claim 5, characterized in that: In step 2, the binding bag is made as follows: The resin before transformation is placed into a large bag made of glass cloth. After sealing the bag, the resin is spread out into a 2-4cm thick layer. This layer is then sewn together in both longitudinal and transverse directions with plastic or stainless steel wire to create a large bag containing neatly arranged long, narrow cloth bags. The front and back of the bag are then covered with stainless steel or plastic wire mesh, and finally rolled into a cylinder to form a binding bag. Each small cloth bag in the cross-section should be ≤6cm long, ≤4cm thick, and ≤10cm high. The overall cylinder height is 20-30cm, and the diameter is determined based on the tower diameter. During the sewing process, it is important to leave a 20-50% gap between each small bag to allow for resin absorption and shrinkage / expansion during the regeneration process.

7. The adsorption and removal method for low-concentration sulfur dioxide in flue gas according to claim 6, characterized in that: In step 2, the resin bundles are filled into the tower in the following way: when the tower diameter is ≤1 m, a single bundle is used to fill the cross-section of the adsorption tower; when the tower diameter is ≥2 m, multiple bundles are used to fill the cross-section of the adsorption tower, with each bundle having a diameter of 10~20 cm and arranged in a honeycomb pattern; when the tower diameter is greater than 1 m and less than 2 m, it is a transition zone, and both of the above resin bundle methods can be applied; in addition, during installation, the wire mesh bundles of adjacent two layers are staggered to ensure uniform gas-liquid distribution.

8. The adsorption and removal method for low-concentration sulfur dioxide in flue gas according to claim 5, characterized in that: In step 2, the random packing pack is made in the following way: a single industrial commonly used perforated annular, spherical or garland-shaped bulk packing is placed into a cloth bag made of glass cloth of appropriate size, resin particles before transformation are poured in, and 20-50% of the free volume is reserved for shrinkage and expansion during resin absorption and regeneration. The bag opening is tied tightly to become a random packing pack containing resin. In step 2, commonly used industrial bulk packing materials include: Pall rings, multifaceted hollow spheres, Myler rings, and 84 inner arc rings, with nominal sizes ranging from 38 to 100 mm, and made of stainless steel or plastic; In step 2, alkali metal ions include Na... + and K + Alkaline earth metal ions include Ca 2+ NH4 + .

9. The adsorption and removal method for low-concentration sulfur dioxide in flue gas according to claim 1, characterized in that: In step 3, the concentration of the alkali solution used for regeneration is 2-10% by mass, and the amount of alkali used is 0.8-1.2 times the total amount of carboxyl groups in the resin in the tower. The alkali solution is circulated and sprayed. When Ca(OH)2 is used as the alkali, since the solubility of Ca(OH)2 in water is limited, an emulsion containing 1-5% Ca(OH)2 by mass is used instead of the alkali solution. In addition, after the resin regeneration is completed, the alkali content in the alkali solution decreases. Fresh solid alkali can be repeatedly dissolved to increase the concentration so that it can be used as the alkali solution for the next resin regeneration.

10. The adsorption and removal method for low-concentration sulfur dioxide in flue gas according to claim 1, characterized in that: In step 3, the circulating spray rate of the alkali solution used for regeneration is controlled at 0.1~1.0 BV / h, where BV refers to the volume of the resin bed.

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