Method and system for treating sulfur-containing flue gas

Abstract

The invention relates to a method and system for treating sulfur-containing flue gas, and the method comprises the following steps: S1, enabling the sulfur-containing flue gas, limestone slurry and an organic acid solution to be in contact and react to obtain a rich solution containing organic acid and Ca (HSO3) 2; s2, separating the pregnant solution through electrodialysis to obtain alkali chamber slurry, an acid chamber solution and a salt chamber solution; s3, the salt chamber solution is subjected to oxidation treatment, and gypsum is obtained. According to the method disclosed by the invention, part of sulfur elements in the sulfur-containing flue gas can be efficiently recovered in the form of SO2, and the crystal-form gypsum with relatively high use value is obtained.

Description

Technical Field

[0001] This disclosure relates to the field of flue gas desulfurization, and more specifically, to a method and system for treating sulfur-containing flue gas. Background Technology

[0002] Limestone-gypsum wet desulfurization is the most widely used process for flue gas purification in coal-fired power plants. This process typically generates a large amount of desulfurization byproduct—gypsum (CaSO4·2H2O). This gypsum product usually has a flaky or needle-like structure, has low economic value, and its large-scale storage occupies land and poses environmental risks. Therefore, providing a novel method for treating sulfur-containing flue gas to achieve high-value utilization of resources is an urgent problem to be solved in this field. Summary of the Invention

[0003] The purpose of this disclosure is to provide a method and system for treating sulfur-containing flue gas. The method of this disclosure can efficiently recover most of the sulfur elements in the sulfur-containing flue gas in the form of SO2 and obtain gypsum with high use value.

[0004] To achieve the above objectives, the first aspect of this disclosure provides a method for treating sulfur-containing flue gas, the method comprising the following steps: S1. Sulfur-containing flue gas and limestone slurry are contacted with organic acid solution and reacted to obtain a rich solution containing organic acid and Ca(HSO3)2. S2. The rich solution is separated by electrodialysis to obtain an alkaline slurry, an acidic solution, and a salt solution; S3. The salt chamber solution is oxidized to obtain gypsum.

[0005] Optionally, in step S1, the organic acid includes one or more of citric acid, adipic acid, and tartaric acid; In the organic acid solution, the concentration of the organic acid is 10-30% by weight. The concentration of the limestone slurry is 10-25% by weight. The pH value of the rich solution is 4-6.5.

[0006] Optionally, step S1 is carried out inside the desulfurization absorption tower, and step S1 includes: S11. The limestone slurry and the organic acid solution are introduced into the slurry tank of the desulfurization absorption tower according to the initial weight ratio for mixing; The initial weight ratio of the limestone slurry to the organic acid solution is (2-10):1; S12. The sulfur-containing flue gas is introduced into the desulfurization absorption tower, and the circulating slurry in the slurry tank is sprayed to contact the sulfur-containing flue gas and carry out the reaction. The resulting slurry is returned to the slurry tank. The liquid-to-gas ratio of the circulating slurry to the sulfur-containing flue gas is 10-20 L / m³. 3 ; Optionally, step S12 further includes: during the reaction, detecting the pH value of the circulating slurry in the slurry tank; when the pH value of the circulating slurry is greater than 6.5, adding the organic acid solution to the slurry tank; when the pH value of the circulating slurry is less than 4, adding the limestone slurry and / or the alkali chamber slurry obtained in step S2 to the slurry tank.

[0007] Optionally, in step S2, the voltage of the electrodialysis is 10-50V and the current density is 10-100A / m. 2 ; Optionally, in step S3, the oxidation treatment temperature is 50-80°C.

[0008] Optionally, the method further includes: pre-treating the rich liquid obtained in step S1 to remove solid particles, and then proceeding to step S2 with the pre-treated rich liquid.

[0009] Optionally, the method further includes: desorbing the acid chamber solution obtained in step S2 to obtain SO2; The desorption process includes heating at a temperature of 70-95°C.

[0010] A second aspect of this disclosure provides a system for treating sulfur-containing flue gas, the system comprising a desulfurization absorption tower, an electrodialysis unit, and a gypsum preparation unit; The desulfurization absorption tower is used for the contact and reaction of sulfur-containing flue gas, limestone slurry and organic acid solution; The desulfurization absorption tower is equipped with a rich liquid outlet and a slurry inlet. The electrodialysis unit includes an acid chamber, an alkali chamber, and a salt chamber. The acid chamber is provided with an acid chamber outlet, the alkali chamber is provided with an alkali chamber outlet, and the salt chamber is provided with a salt chamber outlet and a salt chamber inlet. The rich solution outlet is connected to the salt chamber inlet; The salt chamber outlet is connected to the inlet of the gypsum preparation unit.

[0011] Optionally, the system further includes an SO2 desorption unit, the inlet of which is connected to the outlet of the acid chamber.

[0012] Optionally, the system further includes a pretreatment unit, the inlet of which is connected to the rich liquid outlet, and the outlet of which is connected to the salt chamber inlet.

[0013] Optionally, the alkali chamber outlet is connected to the slurry inlet.

[0014] Through the above technical solution, the method disclosed herein adds an organic acid solution simultaneously during the contact reaction of sulfur-containing flue gas and limestone slurry. On the one hand, the organic acid solution can convert most of the sulfur element in the reaction slurry into HSO3. - This facilitates separation during subsequent electrodialysis to obtain SO2 products. Furthermore, the addition of organic acids allows the salt chamber solution containing organic acids and calcium bisulfite obtained through electrodialysis to produce gypsum crystals with a short columnar morphology, which enhances the gypsum's usability. Simultaneously, the organic acids also inhibit HSO3... - The oxidation effect reduces the content of insoluble calcium compounds in the slurry, protecting the electrodialysis membrane from clogging and failure, and effectively extending its service life. Furthermore, the method disclosed herein significantly reduces energy consumption and desulfurization costs. The entire process generates no solid waste, enabling the resource recovery and utilization of sulfur while reducing gypsum emissions and improving gypsum quality, thus achieving a high-value transformation of resources.

[0015] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of a system for treating sulfur-containing flue gas according to one embodiment of the present disclosure; Figure 2 This is a SEM image of the gypsum product prepared in Example 1 of this disclosure; Figure 3 This is a SEM image of the gypsum product prepared in Comparative Example 1 of this disclosure.

[0017] Explanation of reference numerals in the attached figures Detailed Implementation

[0018] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0019] The first aspect of this disclosure provides a method for treating sulfur-containing flue gas, the method comprising the following steps: S1. Sulfur-containing flue gas and limestone slurry are contacted with organic acid solution and reacted to obtain a rich solution containing organic acid and Ca(HSO3)2. S2. The rich solution is separated by electrodialysis to obtain an alkaline slurry, an acidic solution, and a salt solution; S3. The salt chamber solution is oxidized to obtain gypsum.

[0020] This disclosure achieves the separate recovery and recycling of sulfur and calcium, two core elements, by adding an organic acid solution during the reaction of sulfur-containing flue gas with limestone slurry and employing a "separation followed by desorption" process. The addition of organic acid promotes the conversion of sulfur in the reaction slurry into HSO3. - And it can inhibit HSO3 - Oxidation reduces the content of insoluble calcium compounds in the slurry, protecting the electrodialysis membrane from clogging and extending its lifespan. It also results in a final gypsum product with a desirable crystal morphology. The rich solution obtained from the reaction is primarily composed of calcium bisulfite, with a significant portion remaining unoxidized to calcium sulfate. The calcium bisulfite-rich solution is then separated in an electrodialysis unit to obtain an acid chamber solution containing sulfuric acid, an alkali chamber slurry containing calcium hydroxide, and a salt chamber solution containing calcium bisulfite and organic acids. The salt chamber solution is then used to prepare gypsum, resulting in a short columnar crystal structure, which has higher application value compared to other morphologies. Furthermore, the addition of organic acids addresses the structural issues of the desorption unit. This disclosed method significantly reduces energy consumption, generates no solid waste, and achieves high-value resource utilization.

[0021] According to one embodiment of this disclosure, in step S1, the organic acid includes one or more carboxylic acids with 4-8 carbon atoms, wherein the number of carbon atoms can be 4, 5, 6, 7, or 8. The organic acid is a polycarboxylic acid, such as a dicarboxylic acid, a tricarboxylic acid, etc. Preferably, the organic acid includes one or more of citric acid, adipic acid, and tartaric acid. The concentration of the limestone slurry is 10-25% by weight, including but not limited to 10%, 12%, 15%, 18%, 20%, 21%, 22%, 25%, or any combination thereof. In the organic acid solution, the concentration of the organic acid is 10-30% by weight, including but not limited to 10%, 12%, 15%, 18%, 20%, 22%, 25%, 27%, 30%, or any combination thereof.

[0022] According to one embodiment of this disclosure, step S1 is performed inside a desulfurization absorption tower, and step S1 includes: S11. The limestone slurry and the organic acid solution are introduced into the slurry tank of the desulfurization absorption tower according to the initial weight ratio for mixing; S12. The sulfur-containing flue gas is introduced into the desulfurization absorption tower, and the circulating slurry in the slurry tank is sprayed to contact the sulfur-containing flue gas and carry out the reaction. The resulting slurry is returned to the slurry tank. The mixed slurry in the slurry tank is the circulating slurry, which includes the slurry in the slurry tank that has not yet been reacted, as well as the slurry obtained from the reaction.

[0023] According to one embodiment of this disclosure, step S12 further includes: during the reaction, detecting the pH value of the circulating slurry in the slurry tank; when the pH value of the circulating slurry is greater than 6.5, adding the organic acid solution to the slurry tank; when the pH value of the circulating slurry is less than 4, adding the limestone slurry and / or the alkali chamber slurry obtained in step S2 to the slurry tank; preferably, adding the alkali chamber slurry first; when all the obtained alkali chamber slurry has been introduced into the slurry tank and the pH value is still less than 4, continuing to add limestone slurry; and returning the alkali chamber slurry containing calcium hydroxide to step S1 for continued use, which can improve the utilization efficiency of calcium and reduce production costs.

[0024] According to one embodiment of this disclosure, the specific gravity (relative to water) of the mixture in the slurry tank is detected, and when the specific gravity is 1.29 or higher, the reaction is considered complete.

[0025] According to one embodiment of this disclosure, the liquid-to-gas ratio of the circulating slurry to the sulfur-containing flue gas is 10-20 L / m³. 3 including but not limited to 10 L / m 3 12 L / m 3 15 L / m 3 17 L / m 3 18 L / m 3 20 L / m 3 The range of liquid-to-gas ratio, or any combination thereof, can be limited to the above range. This can increase the gas-liquid contact area and enhance the mass transfer driving force while avoiding excessive energy consumption, thereby improving the absorption efficiency of SO2.

[0026] According to one embodiment of this disclosure, the initial weight ratio of the limestone slurry to the organic acid solution is (2-10):1, including but not limited to 2:1, 2.5:1, 3:1, 3.2:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.3:1, 5.5:1, 5.7:1, 6:1, 6.2:1, 6.5:1, 7:1, 7.2:1, 7.5:1, 7.8:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, or any of the above. The "initial weight ratio" refers to the amount of limestone slurry and organic acid solution that are introduced into the slurry tank at one time before the reaction begins. Setting the ratio of limestone slurry to organic acid solution within the above range can control the slurry within a suitable acidity range, which can not only improve the desulfurization effect of flue gas, but also ensure that the sulfur element in the rich solution exists mainly in the form of bisulfite ions, while inhibiting the oxidation of bisulfite ions to sulfate ions. It can also make the crystals of the prepared gypsum product have a short columnar structure.

[0027] According to one embodiment of this disclosure, in step S1, the liquid-to-gas ratio of the limestone slurry to the sulfur-containing flue gas is 10-20 L / m³. 3 .

[0028] According to one embodiment of this disclosure, the pH value of the rich solution obtained in step S1 is 4-6.5.

[0029] According to one embodiment of this disclosure, the voltage for electrodialysis is 10-50V, including but not limited to 10V, 12V, 15V, 18V, 20V, 22V, 25V, 30V, 32V, 35V, 37V, 40V, 42V, 45V, 50V, or any combination thereof; the current density is 10-100A / m. 2 including but not limited to 10 A / m 2 12 A / m 2 15 A / m 2 18 A / m 2 20 A / m 2 22 A / m 2 25 A / m 2 30 A / m 2 35 A / m 2 37 A / m 2 40 A / m 2 42 A / m 2 45 A / m 2 50 A / m 2 53 A / m 2 55 A / m 257 A / m 2 60 A / m 2 65 A / m 2 70 A / m 2 72 A / m 2 75 A / m 2 80 A / m 2 85 A / m 2 90 A / m 2 95 A / m 2 100 A / m 2 Or any combination of the above; limiting the voltage and current density of electrodialysis within the above range can balance economy, equipment stability and separation efficiency, and achieve high separation efficiency while avoiding increased energy consumption and reduced equipment life.

[0030] According to one embodiment of this disclosure, in step S3, the oxidation treatment temperature is 50-80℃, including but not limited to 50℃, 52℃, 55℃, 58℃, 60℃, 63℃, 65℃, 67℃, 70℃, 72℃, 75℃, 79℃, 80℃, or any combination thereof; the above conditions can promote the gypsum product to have a short columnar crystal structure, thereby improving its utilization value.

[0031] According to one embodiment of this disclosure, the method further includes: pre-treating the rich solution obtained in step S1 to remove solid particles, and then proceeding to step S2 with the pre-treated rich solution; the rich solution obtained in step S1 may contain fine gypsum or other particulate matter, and this embodiment can reduce the content of insoluble calcium compounds therein, avoid particles clogging the ion exchange membrane of the electrodialysis device, and protect the ion exchange membrane.

[0032] According to one embodiment of this disclosure, the method further includes: desorbing the acid chamber solution obtained in step S2 to obtain SO2; the desorption treatment includes heating to decompose as much bisulfite as possible into SO2, further improving the resource utilization of sulfur; the heating temperature is 70-95℃, including but not limited to 70℃, 72℃, 75℃, 77℃, 80℃, 83℃, 85℃, 88℃, 90℃, 92℃, 95℃, or any combination thereof; the desorbed SO2 gas can be processed in a subsequent processing unit to obtain sulfur-derived products. The subsequent processing unit includes, but is not limited to, a sodium metabisulfite preparation unit and / or a sulfuric acid preparation unit. The remaining lean solution after desorption is oxidized and then discharged.

[0033] According to one embodiment of this disclosure, the method further includes: purifying the vapor obtained from the desorption treatment to obtain SO2 gas.

[0034] like Figure 1 As shown, a second aspect of this disclosure provides a system for treating sulfur-containing flue gas, the system comprising a desulfurization absorption tower 11, an electrodialysis unit 1, and a gypsum preparation unit; The desulfurization absorption tower 11 is equipped with a rich liquid outlet and a slurry inlet; The electrodialysis unit 1 includes an acid chamber A, an alkali chamber C, and a salt chamber B. The acid chamber A is provided with an acid chamber outlet, the alkali chamber C is provided with an alkali chamber outlet, and the salt chamber B is provided with a salt chamber outlet and a salt chamber inlet. The rich solution outlet is connected to the salt chamber inlet; The salt chamber outlet is connected to the inlet of the gypsum preparation unit.

[0035] In this disclosure, the salt chamber inlet of the electrodialysis unit is used to introduce sulfur-containing flue gas, limestone slurry, and organic acid solution into the electrodialysis unit for contact and reaction to obtain a rich solution for electrodialysis separation; the salt chamber outlet is used to discharge the salt chamber solution obtained by electrodialysis separation from the electrodialysis unit for subsequent gypsum preparation; the acid chamber outlet is used to discharge the acid chamber solution obtained by electrodialysis separation from the electrodialysis unit for subsequent processing; and the alkali chamber outlet is used to discharge the alkali chamber slurry obtained by electrodialysis separation from the electrodialysis unit.

[0036] In this disclosure, the rich liquid outlet of the desulfurization absorption tower is used to discharge the rich liquid obtained from the contact and reaction of sulfur-containing flue gas, limestone slurry and organic acid solution from the desulfurization absorption tower for further processing and separation; the slurry inlet is used to introduce limestone slurry and / or alkali chamber slurry into the desulfurization absorption tower.

[0037] According to one embodiment of this disclosure, the desulfurization absorption tower 11 has a conventional structure in the art, and this disclosure does not impose any special requirements. It should be noted that a spray layer is provided at the upper part of the desulfurization absorption tower 11 for spraying a mixed slurry of limestone slurry and organic acid downwards. The slurry inlet is located on the slurry pool of the desulfurization absorption tower 11 for introducing limestone slurry and / or alkali chamber slurry into the slurry pool; furthermore, a circulating slurry outlet is also provided on the slurry pool of the desulfurization absorption tower 11 for circulating the slurry in the slurry pool to the inlet of the spray layer, so that the circulating slurry is sprayed downwards.

[0038] According to one embodiment of this disclosure, the desulfurization absorption tower 11 has a sulfur-containing flue gas inlet in the middle and a desulfurization flue gas outlet at the top; the rich liquid outlet is located on the slurry pool of the desulfurization absorption tower 11. In this embodiment, before desulfurization treatment, the circulating slurry in the slurry pool of the desulfurization absorption tower 11 is circulated to the inlet of the spray layer through the circulating slurry outlet, so that the slurry is sprayed downwards; during desulfurization treatment, the sulfur-containing flue gas enters the middle of the desulfurization absorption tower 11 through the flue gas inlet and moves upwards, and comes into countercurrent contact with the sprayed slurry, which can remove sulfur dioxide from the sulfur-containing flue gas. The resulting desulfurized flue gas is discharged through the desulfurization flue gas outlet and enters the chimney. It should be noted that the desulfurization absorption tower 11 does not have an inlet for air entry, to avoid the oxidation of bisulfite ions caused by the introduction of air, thereby improving the desorption rate of sulfur dioxide.

[0039] According to one embodiment of this disclosure, the desulfurization absorption tower 11 is provided with an organic acid solution inlet. The organic acid solution enters the slurry tank of the desulfurization absorption tower through the organic acid solution inlet and mixes with the slurry in the slurry tank. For example, the organic acid solution inlet is located on the slurry tank of the desulfurization absorption tower. In this embodiment, adding organic acid solution to the slurry tank can, on the one hand, change the ionic form in the limestone slurry and inhibit oxidation, so that the rich solution mainly exists in the form of bisulfite ions; on the other hand, it can also inhibit the conversion of calcium bisulfite to gypsum, thereby improving the desorption rate of sulfur dioxide and improving the resource utilization rate of sulfur.

[0040] According to one embodiment of this disclosure, the electrodialysis unit is provided with a cation exchange membrane and an anion exchange membrane, and the arrangement is conventional in the art and can meet the separation requirements of this disclosure.

[0041] According to one embodiment of this disclosure, the system further includes an SO2 desorption unit 4, the inlet of which is connected to the outlet of the acid chamber; a heater can be installed in the SO2 desorption unit, with a heating temperature of 70-95℃, to desorb the acid chamber solution obtained from the electrodialysis unit to obtain SO2; SO2 desorption can be carried out under negative pressure conditions, the negative pressure can be 6-20 kPa, for example, 13 kPa, and the negative pressure is provided by a vacuum pump, wherein the location of the vacuum pump can be flexibly set according to the actual production situation.

[0042] According to one embodiment of this disclosure, the system further includes a purification unit, which includes a desorbed vapor cooler and a gas-liquid separator. The inlet of the desorbed vapor cooler is connected to the desorbed vapor outlet of the SO2 desorption unit, and the desorbed vapor containing SO2 obtained by desorption is passed into the desorbed vapor cooler for cooling to obtain cooled desorbed vapor. The cooled vapor outlet of the desorbed vapor cooler is connected to the inlet of the gas-liquid separator, so as to allow the cooled desorbed vapor to enter the gas-liquid separator for gas-liquid separation to obtain SO2 gas and condensate.

[0043] According to one embodiment of this disclosure, the desorption vapor cooler described in this disclosure is a conventional choice in the art, and this disclosure does not make any special requirements, as long as it can reduce the temperature of the material entering it.

[0044] According to one embodiment of this disclosure, the gas-liquid separator described in this disclosure is a conventional choice in the art, and this disclosure does not make any special requirements, as long as it can fully separate the condensate and desorbed sulfur dioxide gas in the cooling and desorbing gas.

[0045] According to one embodiment of this disclosure, the temperature for cooling the desorbed vapor is 40-60°C.

[0046] According to one embodiment of this disclosure, the system further includes an SO2 storage unit 5 for storing SO2 obtained from desorption and gas-liquid separation. The inlet of the SO2 storage unit is connected to the gas outlet of the SO2 desorption unit. If the system includes a purification unit, the gas outlet of the SO2 desorption unit is the gas outlet of the gas-liquid separator.

[0047] According to one embodiment of this disclosure, the system further includes a sulfurous acid oxidation unit 6, wherein the liquid outlet of the SO2 desorption unit is connected to the liquid inlet of the sulfurous acid oxidation unit for introducing the remaining lean liquid after desorption into the sulfurous acid oxidation unit for oxidation. Furthermore, the sulfurous acid oxidation unit is also provided with an air inlet for introducing air into the unit to oxidize the sulfurous acid into sulfuric acid. A stirring device may be provided in the sulfurous acid oxidation unit to promote the oxidation of sulfurous acid. This stirring device can be a conventional choice in the art, and this disclosure does not impose any special requirements.

[0048] According to one embodiment of this disclosure, the system further includes a pretreatment unit 2, the inlet of which is connected to the rich solution outlet, and the outlet of which is connected to the salt chamber inlet. The pretreatment unit is equipped with a filtration device. The pretreatment unit is used to treat the rich solution obtained by reacting sulfur-containing flue gas, limestone slurry, and organic acid solution. The rich solution may contain fine gypsum or other particulate matter. This embodiment can reduce the content of insoluble calcium compounds, prevent particles from clogging the ion exchange membrane of the electrodialysis unit, and protect the ion exchange membrane.

[0049] According to one embodiment of this disclosure, the alkali chamber outlet is connected to the slurry inlet to return the alkali chamber slurry separated by the electrodialysis unit to the adsorption desulfurization tower for continued use as a desulfurizing agent, thereby improving calcium utilization efficiency and reducing production costs; optionally, a return pump 3 may be provided between the alkali chamber outlet and the slurry inlet.

[0050] According to one embodiment of this disclosure, the gypsum preparation unit includes an oxidation blower 7, an oxidation tank 8, an oxidation tank discharge pump 9, and a centrifugal dewatering machine 10; the inlet of the oxidation blower is connected to an air source, and the outlet of the oxidation blower is connected to the air inlet of the oxidation tank; the slurry inlet of the oxidation tank is the inlet of the gypsum preparation unit, and is connected to the salt chamber outlet, so that the salt chamber solution containing calcium bisulfite and organic acid obtained from the salt chamber enters the oxidation tank and mixes with the air generated by the oxidation blower for oxidation treatment to obtain gypsum slurry; the operating temperature of the oxidation tank is 50-80℃; the outlet of the oxidation tank is connected to the inlet of the centrifugal dewatering machine through the oxidation tank discharge pump, so that the gypsum slurry is discharged from the oxidation tank and returned to the centrifugal dewatering machine for solid-liquid separation treatment to obtain gypsum.

[0051] According to one embodiment of this disclosure, the number of oxidation tanks can be one or more. When the number of oxidation tanks is two or more, the air inlet of each oxidation tank is connected to the outlet of the oxidation blower, the slurry inlet of each oxidation tank is connected to the salt chamber outlet of the electrodialysis unit, and the outlet of each oxidation tank is connected to the inlet of the centrifugal dewatering machine through an oxidation tank discharge pump.

[0052] According to one embodiment of this disclosure, the number of oxidation tanks is 2-10, wherein the multiple oxidation tanks can be arranged in series or in parallel, preferably in parallel.

[0053] According to one embodiment of this disclosure, taking two oxidation tanks as an example, denoted as the first oxidation tank and the second oxidation tank respectively, in the process of oxidizing and preparing gypsum, a portion of the salt chamber solution is first introduced into the first oxidation tank until the salt chamber solution occupies 50-70% of the volume of the first oxidation tank, allowing the first oxidation tank to undergo oxidation treatment. Then, the process switches to the second oxidation tank, i.e., the supply of slurry to the first oxidation tank is stopped, and the supply of slurry to the second oxidation tank is switched. When the solid content of the slurry in the first oxidation tank reaches 20% by weight, the oxidation reaction endpoint is reached. At this point, the slurry in the first oxidation tank is pumped to a centrifugal dewatering machine for solid-liquid separation via an oxidation tank discharge pump. When the salt chamber solution occupies 50-70% of the volume of the second oxidation tank, the second oxidation tank undergoes oxidation treatment, and the process switches back to the first oxidation tank, i.e., the supply of slurry to the second oxidation tank is stopped, and the supply of slurry to the first oxidation tank is switched. The endpoint of the oxidation reaction in the second oxidation tank is the same as that in the first oxidation tank. It should be noted that the time for oxidation treatment in the first oxidation tank and the time for all reaction products to be discharged are always shorter than the feeding time of the second oxidation tank. That is, during the oxidation treatment, one oxidation tank is always kept completely empty.

[0054] According to a specific embodiment of this disclosure, the following is adopted: Figure 1 The system shown includes the following methods for treating sulfur-containing flue gas: Before the reaction begins, an organic acid solution with a concentration of 10-30% by weight and a limestone slurry with a concentration of 10-25% by weight are introduced into the slurry tank of the desulfurization absorption tower 11 for mixing. The initial weight ratio of the limestone slurry to the organic acid solution is (2-10):1. The sulfur-containing flue gas enters the desulfurization absorption tower 11 and reacts with the circulating slurry in the slurry tank through countercurrent spraying. The liquid-to-gas ratio of the circulating slurry to the sulfur-containing flue gas is 10-20 L / m³. 3 The slurry obtained from the reaction flows downward to the slurry pool, while the desulfurized flue gas flows upward and is discharged from the desulfurization absorption tower. During the reaction, the pH value of the circulating slurry in the slurry tank is detected. When the pH value of the circulating slurry is greater than 6.5, an organic acid solution is added to the slurry tank. When the pH value of the circulating slurry is less than 4, limestone slurry and / or alkali chamber slurry is added to the slurry tank. When the specific gravity of the mixture in the slurry tank is above 1.29, the reaction ends. Then, the rich liquid (pH 4-6.5) in the desulfurization absorption tower 11 is introduced into the pretreatment unit 2 to remove particles and obtain the pretreated rich liquid. The pretreated rich solution is passed into electrodialysis unit 1 for electrodialysis separation. The electrodialysis unit is equipped with cation exchange membranes and anion exchange membranes. The voltage for electrodialysis is 10-50V, and the current density is 10-100A / m³. 2; The acid chamber A of the electrodialysis unit produces an acid solution containing sulfurous acid, the salt chamber B produces a salt solution containing organic acid and calcium bisulfite, and the alkali chamber C produces an alkali slurry containing calcium hydroxide. The acid chamber solution is passed into the SO2 desorption unit 4, where it is heated by a heater at a temperature of 70-95℃. The desorbed vapor is then cooled by a desorbed vapor cooler to obtain cooled desorbed vapor at a temperature of 40-60℃. The cooled desorbed vapor is then processed in a gas-liquid separator to obtain desorbed sulfur dioxide gas and condensate. The sulfur dioxide gas is then stored in the SO2 storage unit 5. The remaining lean liquid obtained from desorption is then oxidized in the sulfurous acid oxidation unit 6 to obtain dilute sulfuric acid product. The slurry from the alkali chamber is pumped to the slurry pool of the desulfurization absorption tower 11 via return pump 3 and used as a desulfurizing agent. The salt chamber solution is introduced into the oxidation tank 8 and mixed with the air generated by the oxidation blower 7 for oxidation treatment at a temperature of 50-80℃ to obtain gypsum slurry. The gypsum slurry is then discharged from the oxidation tank and returned to the pump 9 to be transported to the centrifugal dewatering machine 10 for solid-liquid separation treatment to obtain gypsum.

[0055] The present disclosure will be described in detail below through embodiments, but is not limited to the following embodiments.

[0056] Unless otherwise specified, the reagents and materials used in the following examples are all conventional reagents and materials that are already available in the prior art and can be purchased through legitimate commercial channels.

[0057] The original SO2 concentration of the sulfur-containing flue gas used in the examples and comparative examples was 2000 mg / Nm³. 3 .

[0058] The SEM testing method and instrument model were: Merlin model from Zeiss GmbH, Germany, with SE2 detector, resolution of 1.0 nm / 15 kV, and energy spectrum detection range of B4-U92.

[0059] Test method and instrument model for desulfurization efficiency: A flue gas analyzer is used to measure the SO2 concentration in the sulfur-containing flue gas entering the desulfurization absorption tower and the desulfurized flue gas obtained after treatment. The desulfurization efficiency is calculated as follows: Desulfurization efficiency = (SO2 concentration in sulfur-containing flue gas - SO2 concentration in desulfurized flue gas) ÷ SO2 concentration in sulfur-containing flue gas × 100%.

[0060] SO2 recovery rate = amount of SO2 obtained from SO2 desorption unit ÷ total SO2 absorption × 100%, where the total SO2 absorption is calculated based on the SO2 concentration in the sulfur-containing flue gas and the desulfurized flue gas obtained after treatment.

[0061] Example 1 Adopting such Figure 1The system shown and the following steps are used to treat sulfur-containing flue gas: (1) Before the reaction begins, a citric acid solution with a concentration of 20% by weight and a limestone slurry with a concentration of 20% by weight are introduced into the slurry tank of the desulfurization absorption tower 11 for mixing. The initial weight ratio of limestone slurry to citric acid solution is 5:1. The sulfur-containing flue gas enters the desulfurization absorption tower 11 and reacts with the circulating slurry in the slurry tank through countercurrent spraying. The liquid-to-gas ratio of the circulating slurry to the sulfur-containing flue gas is 12 L / m³. 3 The slurry obtained from the reaction flows downward to the slurry pool, while the desulfurized flue gas flows upward and is discharged from the desulfurization absorption tower. During the reaction, the pH value of the circulating slurry in the slurry tank is monitored. When the pH value of the circulating slurry is greater than 6.5, citric acid solution is added to the slurry tank; when the pH value of the circulating slurry is less than 4, alkali chamber slurry and limestone slurry are added to the slurry tank. (2) When the specific gravity of the mixture in the slurry tank is above 1.29, the reaction ends and the rich liquor (pH value is 4.8, Ca(HSO3)2 concentration is 2mol / L) enters the pretreatment unit to remove the particles and obtain the pretreated rich liquor. (3) The pretreated rich solution is passed into electrodialysis unit 1 for electrodialysis separation. The electrodialysis unit is equipped with cation exchange membrane and anion exchange membrane, and the effective membrane areas of the anion exchange membrane and the cation exchange membrane are 50 m² and 50 m², respectively. 2 The pore size is 1-4 nm; the operating voltage of the electrodialysis device is 30 V, and the current density is 40 A / m³. 2 ; The acid chamber A of the electrodialysis unit produces an acid solution containing sulfurous acid, the salt chamber B produces a salt solution containing citric acid and calcium bisulfite, and the alkali chamber C produces an alkali slurry containing calcium hydroxide. The acid chamber solution (H2SO3 concentration of 1.2 mol / L, pH of 2.0) is introduced into the SO2 desorption unit 4 and heated by a heater at a temperature of 75°C for desorption. The desorbed vapor is then cooled by a desorbed vapor cooler to obtain cooled desorbed vapor at 50°C. The cooled desorbed vapor is then processed in a gas-liquid separator to obtain desorbed sulfur dioxide gas and condensate. The sulfur dioxide gas is then stored in the SO2 storage unit 5. The remaining lean liquid obtained from SO2 desorption is introduced into the sulfurous acid oxidation unit 6, where oxygen is introduced for oxidation treatment to obtain dilute sulfuric acid product. The alkali chamber slurry (Ca) 2+ (At a concentration of 0.6 mol / L and a pH of 9.5) it is pumped to the slurry tank of the desulfurization absorption tower 11 via return pump 3 and used as a desulfurizing agent; A salt chamber solution containing citric acid and Ca(HSO3)2 (Ca(HSO3)2 concentration of 1.4 mol / L) is introduced into oxidation tank 8 and mixed with air generated by oxidation blower 7 for oxidation treatment at a temperature of 50°C to obtain gypsum slurry. The gypsum slurry is then discharged from the oxidation tank and returned to pump 9 to be transported to centrifugal dewatering machine 10 for solid-liquid separation treatment to obtain gypsum.

[0062] The obtained plaster product was subjected to SEM testing, and the results are as follows: Figure 2 As shown.

[0063] In Example 1, after 100 hours of operation, no scaling was observed in the desorption unit; the desulfurization efficiency of the flue gas was 95.4%, and the SO2 recovery rate was 30%.

[0064] Example 2 The method of Example 1 was used to treat sulfur-containing flue gas. The difference is that in step (1), the initial weight ratio of limestone slurry to citric acid solution was 2.5:1, the pH value of the rich solution obtained from the reaction was 4.2, and the concentration of Ca(HSO3)2 was 1.51 mol / L. The gypsum product was tested by SEM and found to have a similar crystal structure to the gypsum product of Example 1.

[0065] In Example 2, after 100 hours of operation, no scaling was observed in the desorption unit; the desulfurization efficiency of the flue gas was 92.5%, and the SO2 recovery rate was 23%.

[0066] Example 3 The method of Example 1 was used to treat sulfur-containing flue gas, except that in step (1), the initial weight ratio of limestone slurry to citric acid solution was 10:1, the pH of the resulting rich solution was 6.5, and the concentration of Ca(HSO3)2 was 1.62 mol / L. SEM testing of the gypsum product showed that it had a similar crystal structure to the gypsum product of Example 1.

[0067] In Example 3, the flue gas desulfurization efficiency was 93.2%, and the SO2 recovery rate was 25%.

[0068] Comparative Example 1 The method of Example 1 was used to treat sulfur-containing flue gas, the difference being that citric acid aqueous solution was not added in step (1). The SEM test results of the gypsum product are as follows: Figure 3 As shown.

[0069] In Comparative Example 1, the flue gas desulfurization efficiency was 92%, and the SO2 recovery rate was 12%.

[0070] according to Figure 2 and 3The comparison shows that the dihydrate gypsum crystals obtained in Comparative Example 1 mainly exhibit needle-like or plate-like structures with a large aspect ratio; the dihydrate gypsum crystals obtained in Example 1 are mostly short columnar crystals, with a greater crystal thickness than the gypsum obtained in Comparative Example 1. Due to their larger specific surface area and excellent dehydration properties, short columnar crystals are an ideal crystal form for desulfurization byproducts in limestone wet desulfurization processes. The method disclosed in this paper can prepare gypsum products with higher application value.

[0071] Based on the above data, it can be seen that the method disclosed herein can efficiently recover some of the sulfur elements in sulfur-containing flue gas in the form of SO2, and obtain gypsum with high crystalline form and high use value.

[0072] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0073] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0074] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method of treating a sulphur-containing flue gas, characterized in that, The method comprises the following steps: S1, contacting and reacting sulfur-containing flue gas, limestone slurry and organic acid solution to obtain a rich liquid containing organic acid and Ca(HSO3)2; S2, separating the rich liquid by electrodialysis to obtain alkali chamber slurry, acid chamber solution and salt chamber solution; S3, oxidizing the salt chamber solution to obtain gypsum.

2. The method of claim 1, wherein, In step S1, the organic acid includes one or more of citric acid, adipic acid and tartaric acid; In the organic acid solution, the concentration of organic acid is 10-30% by weight; The concentration of the limestone slurry is 10-25% by weight; The pH value of the rich liquid is 4-6.

5.

3. The method of claim 1, wherein, Step S1 is carried out in a desulfurization absorption tower, and step S1 comprises: S11, mixing the limestone slurry and the organic acid solution in the slurry pool of the desulfurization absorption tower according to an initial weight ratio; Optionally, the initial weight ratio of the limestone slurry to the organic acid solution is (2-10):1; S12, introducing the sulfur-containing flue gas into the desulfurization absorption tower, and making the circulating slurry in the slurry pool contact with the sulfur-containing flue gas by spraying to carry out the reaction, and returning the obtained slurry to the slurry pool; Optionally, the liquid-gas ratio of the circulating slurry to the sulfur-containing flue gas is 10-20 L / m 3 ; Optionally, step S12 further comprises: detecting the pH value of the circulating slurry in the slurry pool during the reaction, when the pH value of the circulating slurry is greater than 6.5, supplementing the organic acid solution into the slurry pool, and when the pH value of the circulating slurry is less than 4, supplementing the limestone slurry and / or the alkali chamber slurry obtained in step S2 into the slurry pool.

4. The method of claim 1, wherein, In step S2, the voltage for the electrodialysis is 10-50 V, and the current density is 10-100 A / m 2 ; Optionally, in step S3, the temperature of the oxidation treatment is 50-80℃.

5. The method of claim 1, wherein, The method further comprises: pretreating the rich liquid obtained in step S1 to remove solid particles, and then carrying out step S2 on the pretreated rich liquid.

6. The method of claim 1, wherein, The method further comprises: desorbing the acid chamber solution obtained in step S2 to obtain SO2; The desorption treatment method comprises heating, and the heating temperature is 70-95℃.

7. A system for treating a sulfur-containing flue gas, characterized by The system comprises a desulfurization absorption tower (11), an electrodialysis unit (1) and a gypsum preparation unit; The desulfurization absorption tower (11) is used for contacting and reacting sulfur-containing flue gas, limestone slurry and organic acid solution; The desulfurization absorption tower (11) is provided with a rich liquid outlet and a slurry inlet; The electrodialysis unit (1) comprises an acid chamber (A), an alkali chamber (C) and a salt chamber (B), the acid chamber (A) is provided with an acid chamber outlet, the alkali chamber (C) is provided with an alkali chamber outlet, and the salt chamber (B) is provided with a salt chamber outlet and a salt chamber inlet; The rich liquid outlet is in communication with the salt chamber inlet; The salt chamber outlet is in communication with the inlet of the gypsum preparation unit.

8. The system of claim 7, wherein, The system further comprises an SO2 desorption unit (4), and the inlet of the SO2 desorption unit (4) is in communication with the acid chamber outlet.

9. The system of claim 7, wherein, The system further comprises a pretreatment unit (2), and the inlet of the pretreatment unit (2) is in communication with the rich liquid outlet, and the outlet of the pretreatment unit (2) is in communication with the salt chamber inlet.

10. The system of claim 7, wherein, The alkali chamber outlet is in communication with the slurry inlet.

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