Flue gas dust removal and denitrification system for medium and low temperature sulfur-containing and water-containing environments and filter bag manufacturing method

Abstract

The present invention proposes a flue gas dust removal and denitrification system and filter bag manufacturing method for medium- and low-temperature sulfur- and water-containing environments. The system includes a flue gas pretreatment device, an ammonia supply unit, a dust removal and denitrification reactor, and a purified flue gas emission device. The dust removal and denitrification reactor includes denitrification filter bags made of high-specific surface area and high-purity titanium dioxide. It uses a high-efficiency oxidant to selectively adjust the gases in the flue gas in advance to achieve the material ratio required for a rapid SCR reaction, significantly increasing the denitrification reaction rate. Titanium dioxide also has a high specific surface area, providing a high specific surface area for contact and adsorption of ammonia and nitrogen oxides, and is not highly oxidizing, significantly reducing the formation of ammonium bisulfate under low-temperature conditions and effectively increasing the service life of the filter bags. By utilizing a rapid SCR reaction mechanism and combining denitrification filter bags made of titanium dioxide, the system improves the filter bags' resistance to water and sulfur under low-temperature conditions, providing a method for dust removal and efficient denitrification of flue gas under medium- and low-temperature conditions containing water and sulfur.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas treatment, and in particular to a dust removal and denitrification system for flue gas in a medium-low temperature sulfur-containing and water-containing environment and a filter bag manufacturing method. Background Art

[0002] Currently, denitrification filter bags are widely used in flue gas simultaneous dust removal and denitrification systems in the chemical and environmental protection fields. Compared to traditional processes that treat dust and nitrogen oxides separately, using denitrification filter bags for simultaneous dust removal and denitrification offers advantages such as low system resistance, long catalyst life, and a small footprint. Denitrification filter bags primarily utilize the NH3-SCR method as their NOx removal mechanism. Specifically, at a certain temperature, NOx and oxygen in the flue gas react with injected ammonia in the presence of a powdered catalyst to produce nitrogen and water through a redox reaction.

[0003] Denitrification filter bags generally use PTFE and PPS as the base material. The maximum temperature resistance of these two base materials is around 260°C, and the normal operating temperature is limited to below 240°C. Therefore, the operating temperature of denitrification filter bags is generally between 150 and 240°C. Existing denitrification technologies mainly use vanadium-tungsten-titanium, manganese-iron, and manganese-cerium materials as catalysts. Such catalysts are very sensitive to water and sulfur dioxide in flue gas and are easily blocked and inactivated by ammonium bisulfate. It is difficult to maintain long-term and efficient catalytic activity in medium and low temperature (150-240°C) and water- and sulfur-containing working conditions, which seriously limits the application and promotion of denitrification filter bags. Therefore, it is now necessary to develop a method for using denitrification filter bags to simultaneously remove dust and denitrify flue gas under medium and low temperature (150-240°C) and water- and sulfur-containing working conditions.

[0004] Currently, existing technologies improve denitrification efficiency by introducing ozone into the flue gas treatment system to cause a rapid SCR reaction in the system, but further improvements to the dust removal and denitrification reactor are not considered. Summary of the Invention

[0005] In order to overcome the above-mentioned defects in the prior art, the first aspect of the present invention proposes a flue gas dust removal and denitrification system for a medium- and low-temperature sulfur- and water-containing environment, comprising: a flue gas pretreatment device, an ammonia supply unit, a dust removal and denitrification reactor and a purified flue gas emission device connected in sequence; the flue gas pretreatment device includes an oxidant supply unit, which is connected to the flue to prepare the oxidant and provide the oxidant to the flue; the dust removal and denitrification reactor is arranged on the flue, including a denitrification filter bag, and the denitrification filter bag only loads titanium dioxide, serving as a rapid SCR reaction site.

[0006] The above technical solution combines an oxidant supply unit with denitrification filter bags made of titanium dioxide, using a high-efficiency oxidant to selectively adjust the gases in the flue gas in advance to meet the material ratio required for a rapid SCR reaction, significantly improving the denitrification reaction rate. At the same time, titanium dioxide has a high specific surface area, providing a high specific surface area for contact and adsorption of ammonia and nitrogen oxides, and is not highly oxidizing, which can significantly reduce the oxidation of SO2 in the flue gas, thereby reducing the formation of ammonium bisulfate under low temperature conditions and effectively improving the service life of the filter bags. By utilizing the rapid SCR reaction mechanism and combining denitrification filter bags made of titanium dioxide, this system improves the water and sulfur resistance of the filter bags under low temperature conditions, providing a method for flue gas dust removal and efficient denitrification using denitrification filter bags under medium and low temperature (150-240°C) and water- and sulfur-containing conditions.

[0007] Furthermore, the oxidant supply unit includes an oxidant generating device and an oxidant dosing and distributing device, and the oxidant dosing and distributing device is arranged on the flue; the oxidant is ozone, sodium hypochlorite or hydrogen peroxide.

[0008] Through the above technical solution, different oxidants can be selected according to needs to perform pre-oxidation and conditioning on the flue gas.

[0009] Furthermore, the titanium dioxide has a D50≤2μm, a D90≤6μm, and a BET specific surface area>300m 2 / g, SO4≤1.4%, TiO2 purity≥98%.

[0010] Through the above technical solution, high specific surface area and high purity titanium dioxide is provided. The high specific surface area titanium dioxide can provide a higher specific surface area for contact and adsorption of ammonia and nitrogen oxides, thereby achieving a higher denitrification efficiency, improving the water and sulfur resistance of the filter bag under low temperature conditions, and increasing the service life of the filter bag.

[0011] Furthermore, the titanium dioxide loading of the denitrification filter bag is 15% to 50%, with 25% being the optimal situation.

[0012] Through the above technical solution, the denitrification filter bag is loaded with an appropriate amount of titanium dioxide, which provides a large amount of adsorption specific surface area. Under low temperature conditions, it provides a large amount of basic specific surface area for the competitive adsorption of H2O, SO2 and nitrogen oxides, thereby increasing NO xThe absolute amount of adsorption reaction under the same conditions slows the decline in denitrification efficiency, improves the filter bag's resistance to water and sulfur at low temperatures, and thus extends the bag's service life. Under appropriate gas distribution conditions, catalytic filter bags can achieve high denitrification efficiency by simply loading an appropriate amount of high-purity, high-specific surface area titanium dioxide, eliminating the need for expensive vanadium, tungsten, or manganese-cerium active ingredients required to enhance denitrification efficiency as with traditional catalysts. Denitrification filter bags with a titanium dioxide loading below 15% exhibit poor denitrification performance, while those with a loading above 50% exhibit low air permeability and high operating costs. A preferred embodiment is also provided, in which the denitrification filter bag has a titanium dioxide loading of 25%. Too low a titanium dioxide loading can result in reduced denitrification performance, while too high a loading can reduce air permeability and increase operating resistance. The 25% titanium dioxide loading achieves both good denitrification performance and excellent air permeability, achieving efficient denitrification while avoiding the excessive operating resistance associated with too low an air permeability, achieving a balanced denitrification efficiency and operating costs, resulting in excellent overall performance.

[0013] Furthermore, the flue includes a main flue and a circulating flue, one end of the circulating flue is connected to the main flue after the outlet of the dust removal and denitrification reactor, and the other end is connected to the main flue before the inlet of the dust removal and denitrification reactor, and the ammonia supply unit is connected to the circulating flue.

[0014] Through the above technical solution, part of the flue gas at the outlet of the dust removal and denitrification reactor is refluxed to be used for evaporation of ammonia water and input of ammonia gas.

[0015] Furthermore, the ammonia supply unit includes an ammonia water storage and supply device, a dual-fluid spray gun and a uniform mixer connected in sequence through pipelines. The nozzle of the dual-fluid spray gun is arranged in the flue. The ammonia water flows from the ammonia water storage and supply device into the dual-fluid spray gun, atomizes and evaporates to form ammonia gas, and is evenly mixed with the flue gas through the uniform mixer before entering the dust removal and denitrification reactor.

[0016] Through the above technical solution, the ammonia water in the ammonia water storage and supply device is sprayed into the clean flue gas above 150°C diverted from the outlet of the dust removal and denitrification reactor through a dual-fluid spray gun for atomization and evaporation to form ammonia gas, which is evenly mixed with the flue gas through the uniform mixer to ensure that the concentration distribution deviation of ammonia gas on the radial section of the denitrification filter bag in each chamber in the rear dust removal and denitrification reactor is no more than 5%.

[0017] Furthermore, the ammonia gas sprayed by the ammonia supply unit and the NO in the flue gas X The molar ratio is 1:1.

[0018] Through the above technical solution, the ammonia and NO X The molar ratio of 20% to 10% makes a rapid SCR reaction occur.

[0019] Furthermore, the oxidant supply unit is an ozone supply unit, and the ozone sprayed by the ozone supply unit is mixed with NO in the flue gas. X The molar ratio is 1:6 to 1:2, and the mass concentration of ozone is 5 to 10%.

[0020] Through the above technical solution, the advantages of ozone pre-oxidation denitrification technology compared with other pre-oxidation technologies are as follows: the amount of ozone can be flexibly controlled, the response is rapid, and the amount of ozone generated can be controlled according to the initial concentration of NO; ​​it has strong selectivity for the oxidation of target pollutant NO, while other substances in the flue gas such as SO2, CO and NO2 are not affected; the oxidation product is oxygen, which has no secondary pollution to the environment. X The molar ratio of NO to NO2 is 1:6 to 1:2, and the mass concentration of ozone is 5 to 10%. It can selectively oxidize part of the NO in the flue gas into NO2, so that the molar ratio of NO to NO2 in the flue gas is adjusted from the original 19:1 to the range of 3:1 to 1:1, meeting the NO and NO2 ratio required for the rapid SCR reaction.

[0021] Furthermore, the reaction occurring in the dust removal and denitrification reactor is:

[0022] NO+NO2+2NH3→2N2+3H2O.

[0023] Through the above technical solution, the reaction rate of the rapid SCR reaction is one order of magnitude greater than that of the conventional standard SCR reaction, and high-efficiency denitrification is achieved under high space velocity conditions and in the low temperature range of 150 to 240°C.

[0024] In summary, the flue gas dust removal and denitrification system for medium- and low-temperature sulfur- and water-containing environments proposed in this application has at least one of the following beneficial technical effects:

[0025] 1. The use of fast SCR reaction mechanism can significantly improve the denitrification reaction rate under medium and low temperature sulfur and water conditions.

[0026] 2. Use high-efficiency oxidants to selectively oxidize part of the nitrogen monoxide in the flue gas into nitrogen dioxide in advance, meeting the nitrogen monoxide and nitrogen dioxide ratio required for the rapid SCR reaction. Since the oxidant is not excessive and sulfur dioxide will not be oxidized into sulfur trioxide, the generation rate and amount of ammonium bisulfate are greatly reduced, which can effectively protect the catalyst on the denitrification filter bag.

[0027] 3. The catalyst loaded on the denitrification filter bags utilizes a pure titanium dioxide formula free of vanadium, manganese, and cerium. Its high surface area provides a reaction site for the adsorption of nitric oxide, nitrogen dioxide, and ammonia during the rapid SCR reaction, while the denitrification filter bags do not have an oxidizing effect. Because it no longer relies on active substances such as vanadium, manganese, and cerium, and the titanium dioxide catalyst surface does not oxidize sulfur dioxide in the flue gas, its catalytic activity is not easily affected or deactivated.

[0028] 4. Under the working conditions of low temperature, high sulfur dioxide and high water content, the denitrification filter bag can operate stably for a long time, expanding the application of the denitrification filter bag.

[0029] 5. The denitrification filter bag does not contain toxic substances and does not belong to hazardous waste after the expiration of its service life and can be directly disposed of harmlessly.

[0030] The second aspect of the present application provides a method for manufacturing a denitrification filter bag, which is used to manufacture the denitrification filter bag described in the first aspect, and the steps include:

[0031] S1: Particle size D50≤2μm, D90≤6μm, BET specific surface area>300m 2 / g, SO4≤1.4%, titanium dioxide with TiO2 purity ≥98% is dissolved in water, and additives are added to form a slurry with a solid content of 10-20%;

[0032] S2: Loading the bag with the slurry by spraying or dipping;

[0033] S3: Place the bag in a drying room and dry and activate it at a temperature of 200-250°C to make a denitrification filter bag.

[0034] The present invention proposes a method for manufacturing a denitrification filter bag, which is used to manufacture the denitrification filter bag described in the first aspect. Unlike existing vanadium-tungsten-titanium catalyst denitrification filter bags or manganese-cerium catalyst denitrification filter bags, this denitrification filter bag only carries modified high-specific surface area, high-purity titanium dioxide, and is used solely to provide the high-specific surface area required for the reaction of NO, NO2, and NH3 in the rapid SCR process. Because it no longer relies on active substances such as highly oxidizing metals or transition metal elements such as vanadium, manganese, and cerium, and the titanium dioxide surface does not oxidize SO2 in the flue gas, the catalytic activity of the denitrification filter bag is not easily affected or deactivated, and it can operate stably and long-term under medium-low temperature, high sulfur dioxide, and high water content conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings illustrate the embodiments and together with the description serve to explain the principles of the present application. The elements of the drawings are not necessarily to scale with each other. Like reference numerals designate corresponding similar parts.

[0036] Figure 1 Schematic diagram of a flue gas dust removal and denitrification system in a medium-low temperature sulfur-containing and water-containing environment according to a specific embodiment of the present invention;

[0037] Figure 2 The present invention is a flowchart of a method for manufacturing a denitrification filter bag in a specific embodiment of the present invention.

[0038] Figure 3 The present invention is a flowchart of a flue gas treatment method for dust removal and denitrification in a medium-low temperature sulfur-containing and water-containing environment in a specific embodiment of the present invention.

[0039] Explanation of the accompanying symbols: 1. Main flue; 2. Circulating flue; 3. Oxidant supply unit; 4. Ammonia storage and supply device; 5. Ammonia pump; 6. Ammonia gas dosing and distribution device; 7. Denitrification filter bag; 8. Induced draft fan; 9. Chimney; 10. SDA deacidification tower. DETAILED DESCRIPTION

[0040] The following describes examples of the present application to better understand the present application. Through the following detailed description, many expected advantages of other embodiments and embodiments can be recognized. It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device comprising a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device comprising the elements. It is understood that the use of directional terms for the purpose of illustration is by no means restrictive. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0041] The first aspect of the present invention provides a flue gas dust removal and denitrification system in a medium-low temperature sulfur-containing and water-containing environment. Figure 1 This is a schematic diagram of a flue gas dust removal and denitrification system for a medium- and low-temperature sulfur- and water-containing environment in a specific embodiment of the present invention, comprising: a flue gas pretreatment device, an ammonia supply unit, a dust removal and denitrification reactor, a purified flue gas discharge device, and a flue; the flue includes a main flue 1 and a circulating flue 2, one end of which is connected to the main flue 1 after the outlet of the dust removal and denitrification reactor and the other end is connected to the main flue 1 before the inlet of the dust removal and denitrification reactor, so that part of the flue gas at the outlet of the dust removal and denitrification reactor is recirculated. The flue gas pretreatment device includes an oxidant supply unit 3, which includes an oxidant generator and an oxidant dosing and distribution device connected to each other. The oxidant dosing and distribution device is disposed on the main flue 1; the ammonia supply unit includes an ammonia water storage and supply device 4, an ammonia water pump 5, and an ammonia gas dosing and distribution device 6 connected in sequence by pipelines; the dust removal and denitrification reactor includes a denitrification filter bag 7 loaded only with titanium dioxide; the flue gas temperature in the flue is 150°C to 240°C.

[0042] The oxidant supply unit 3 prepares the oxidant and supplies it to the main flue 1. In conventional boiler flue gas components, more than 95% of NO xExisting in the form of NO, the primary reaction in the SCR device is 4NH3+NO+O2→4N2+6H2O, the standard SCR reaction. When the ratio of NO to NO2 in the flue gas reaches 1:1, the reaction of NO+NO2+2NH3→2N2+3H2O occurs. This rapid SCR reaction has a reaction rate an order of magnitude greater than that of the conventional standard SCR reaction, demonstrating high denitrification efficiency under high space velocity conditions and within the low-temperature window (150-240°C). By supplying an oxidant to the main flue 1, some NO is converted into NO2, enabling a rapid SCR reaction in the subsequent dust removal and denitrification reactor. The oxidant can be ozone, sodium hypochlorite, or hydrogen peroxide, and different oxidants can be selected for pre-oxidation and conditioning of the flue gas according to requirements. Preferably, the oxidant generator is an ozone generator. The advantages of ozone pre-oxidation denitrification technology compared to other pre-oxidation technologies are: the amount of ozone can be flexibly controlled, the response is rapid, and the amount of ozone generated can be controlled according to the initial concentration of NO; ​​it has strong selectivity for the oxidation of target pollutant NO, while other substances in the flue gas such as SO2, CO and NO2 are not affected; the oxidation product is O2, which does not cause secondary pollution to the environment. X The molar ratio of NO to NO2 is 1:6 to 1:2, and the mass concentration of ozone is 5 to 10%. It can selectively oxidize part of the NO in the flue gas into NO2, so that the molar ratio of NO to NO2 in the flue gas is adjusted from the original 19:1 to the range of 3:1 to 1:1, meeting the NO and NO2 ratio required for the rapid SCR reaction.

[0043] The ammonia supply unit is connected to the circulating flue 2. The ammonia dosing and uniform distribution device 6 in the ammonia supply unit includes a dual-fluid spray gun and a uniform mixer. The ammonia storage and supply device 4, the ammonia pump 5, the dual-fluid spray gun and the uniform mixer are connected in sequence through pipelines. The nozzle of the dual-fluid spray gun is set in the circulating flue 2. The ammonia storage and supply device 4 stores ammonia with a concentration of 20%. Under the action of the ammonia pump 5, the ammonia is sprayed into the clean flue gas above 150°C diverted from the outlet of the dust removal and denitrification reactor through a dual-fluid spray gun for atomization and evaporation to form ammonia. The ammonia is evenly mixed with the flue gas through the uniform mixer and then enters the dust removal and denitrification reactor to ensure that the concentration distribution deviation of ammonia on the radial section of the denitrification filter bag 7 in each chamber of the rear dust removal and denitrification reactor is no more than 5%. The ammonia sprayed into the ammonia supply unit and the NO in the flue gas are X The molar ratio is 1:1.

[0044] The dust removal and denitration reactor is set on the main flue 1. The denitration filter bag 7 is only loaded with titanium dioxide, which serves as a fast SCR reaction site. The particle size of titanium dioxide is D50≤2μm, D90≤6μm, and the BET specific surface area is greater than 300m 2 / g, SO4 content ≤1.4%, Na2O ≤200mg / kg, K2O ≤200mg / kg, Fe ≤150mg / kg, TiO2 purity ≥98%. The titanium dioxide loading capacity of the denitrification filter bag 7 is between 15% and 50%, and the deviation of the same loading capacity bag is ≤5%. The denitrification filter bag 7 is loaded with an appropriate amount of titanium dioxide, which provides a large amount of adsorption specific surface area. Under low temperature conditions, it can absorb H2O, SO2 and NO x The competitive adsorption of NO provides a large amount of basic specific surface area, which increases the x Under the same conditions, the absolute amount of adsorption reaction is increased, thereby slowing the decline in denitrification efficiency, improving the filter bag's resistance to water and sulfur at low temperatures, and thus extending the bag's service life. Under appropriate gas distribution conditions, the catalytic filter bag only needs to be loaded with an appropriate amount of high-purity, high-specific surface area titanium dioxide, providing only the high-specific surface area required for the rapid SCR process to react with NO, NO2, and NH3, thereby achieving high denitrification efficiency. This eliminates the need to add expensive vanadium, tungsten, or manganese-cerium active ingredients, as is required with traditional catalysts, to improve denitrification efficiency. Denitrification filter bags 7 with a titanium dioxide loading of less than 15% exhibit poor denitrification performance, while those with a loading of more than 50% exhibit excessively low air permeability, increasing operating costs. In a preferred embodiment, the denitrification filter bag 7 has a titanium dioxide loading of 25%. This 25% titanium dioxide loading achieves both good denitrification performance and excellent air permeability, achieving efficient denitrification while avoiding the excessive operating resistance caused by low air permeability, achieving a balanced denitrification efficiency and operating costs, resulting in excellent overall performance.

[0045] The purified flue gas discharge device includes an induced draft fan 8 and a chimney 9, connected sequentially via a main flue 1. Flue gas flows from the flue through the various devices under the negative pressure of the induced draft fan 8. An SDA deacidification tower 10 is also installed before the oxidant supply unit 3 to protect the subsequent denitrification filter bags 7 from the effects of acidic substances such as SO2, HF, and HCl.

[0046] Reference Figure 2 The second aspect of the present application provides a method for manufacturing a denitrification filter bag, which is used to manufacture the denitrification filter bag described in the first aspect, and the steps include:

[0047] S1.1: Particle size D50≤2μm, D90≤6μm, BET specific surface area>300m 2 / g, SO4≤1.4%, titanium dioxide with TiO2 purity ≥98% is dissolved in water, and additives are added to form a slurry with a solid content of 10-20%;

[0048] S1.2: Loading the bag with the slurry by spraying or dipping;

[0049] S1.3: Place the bag in a drying room and dry and activate it at a temperature of 200-250°C to make a denitrification filter bag.

[0050] In a specific embodiment, the Na2O (mg / kg) of the titanium dioxide in S1.1 is ≤200, K2O (mg / kg) ≤200, and Fe (mg / kg) ≤150, the additives include dispersants and binders, etc., the denitrification filter bags prepared in S1.3 have uniform color, the titanium dioxide loading is between 15% and 50%, and the deviation of the bags at the same loading is ≤5%.

[0051] The present invention proposes a method for manufacturing a denitrification filter bag, which is used to manufacture the denitrification filter bag described in the first aspect. Unlike existing vanadium-tungsten-titanium catalyst denitrification filter bags or manganese-cerium catalyst denitrification filter bags, this denitrification filter bag only carries modified high-specific surface area, high-purity titanium dioxide, and is used solely to provide the high-specific surface area required for the reaction of NO, NO2, and NH3 in the rapid SCR process. Because it no longer relies on active substances such as highly oxidizing metals or transition metal elements such as vanadium, manganese, and cerium, and the titanium dioxide surface does not oxidize SO2 in the flue gas, the catalytic activity of the denitrification filter bag is not easily affected or deactivated, and it can operate stably and long-term under conditions of medium to low temperatures, high sulfur dioxide, and high water content.

[0052] Reference Figure 3 In order to treat flue gas using the flue gas dust removal and denitrification system and filter bag manufacturing method proposed in this application, a flue gas treatment method for dust removal and denitrification in a medium-low temperature, sulfur-containing, and water-containing environment is provided. This method uses a high-efficiency oxidant to selectively adjust the gases in the flue gas in advance to meet the material ratio required for a rapid SCR reaction, significantly improving the denitrification reaction rate; and a denitrification filter bag with a high specific surface area serves as a rapid SCR reaction site. The steps include:

[0053] S2.1: Flue gas enters the flue, the oxidant supply unit 3 sprays oxidant into the flue, and the ammonia supply unit sprays ammonia into the flue. After being evenly mixed, the mixture enters the dust removal and denitrification reactor;

[0054] S2.2: After the mixed gas enters the dust removal and denitrification reactor for reaction, it is discharged through the purified flue gas emission device.

[0055] In a specific embodiment, based on the specific embodiment of the flue gas dust removal and denitrification system in a medium-low temperature sulfur-containing aqueous environment proposed in the first aspect, the steps of the flue gas treatment method embodiment of the medium-low temperature sulfur-containing aqueous environment dust removal and denitrification include:

[0056] S102.1: Flue gas with a temperature of 150℃~240℃ enters the main flue 1. The ozone generator provides ozone with a mass concentration of 5~10%. The injected ozone reacts with NO in the flue gas. XThe molar ratio of NO to NO2 in the flue gas is 1:6 to 1:2, and is evenly mixed with the flue gas in the main flue 1 through the oxidant dosing and distribution device, so that the molar ratio of NO to NO2 in the flue gas is adjusted from the original 19:1 to the range of 3:1 to 1:1; 20% concentration ammonia water flows out from the ammonia water storage and supply device 4 under the action of the ammonia water pump 5, and is sprayed into the clean flue gas above 150°C diverted from the outlet of the dust removal and denitrification reactor by the circulating flue 2 through a dual-fluid spray gun for atomization and evaporation to form ammonia gas, which reacts with NO in the flue gas. X The molar ratio is 1:1, and then it is evenly mixed with the flue gas through a uniform mixer and then enters the dust removal and denitrification reactor.

[0057] S102.2: The mixed gas enters the denitrification filter bag 7 of the dust removal and denitrification reactor, and the reaction of NO+NO2+2NH3→2N2+3H2O occurs in the high surface area provided by the denitrification filter bag 7, completing the dust removal and denitrification. The gas is diverted at the outlet of the dust removal and denitrification reactor, and part of the flue gas flows back from the circulating flue 2 for the evaporation of ammonia water and the input of ammonia gas. Part of the flue gas is discharged from the chimney 9 after cooling.

[0058] The chemical reactions involved in this embodiment are mainly:

[0059] NO+O3→NO2+O2;

[0060] NO+NO2+2NH3→2N2+3H2O.

[0061] In another specific embodiment, based on the above-mentioned flue gas treatment method for dust removal and denitrification in a medium-low temperature sulfur-containing and water-containing environment, the performance of a flue gas dust removal and denitrification system for a medium-low temperature sulfur-containing and water-containing environment and a denitrification filter bag manufacturing method in this application are verified.

[0062] Filter bag ①: Catalytic bag made of conventional high-purity titanium dioxide, with a loading of 15%

[0063] Powder parameters: particle size D50 ≤ 2μm, D90 ≤ 6μm, BET specific surface area = 80~100m 2 / g, SO4(%)≤1.4, Na2O(mg / kg)≤200, K2O(mg / kg)≤200, Fe(mg / kg)≤150, TiO2 purity≥98%, bag powder loading capacity 15%.

[0064] Filter bag ②: Catalytic cloth bag made of high-purity medium-specification titanium dioxide, with a loading of 15%

[0065] Powder parameters: particle size D50 ≤ 2μm, D90 ≤ 6μm, BET specific surface area = 120~140m 2 / g, SO4(%)≤1.4, Na2O(mg / kg)≤200, K2O(mg / kg)≤200, Fe(mg / kg)≤150, TiO2 purity≥98%, bag powder loading capacity 15%.

[0066] Filter bag ③: Catalytic cloth bag made of high-purity and high-specific gravity titanium dioxide, with a loading of 15%

[0067] Powder parameters: particle size D50 ≤ 2μm, D90 ≤ 6μm, BET specific surface area ≥ 300m 2 / g, SO4(%)≤1.4, Na2O(mg / kg)≤200, K2O(mg / kg)≤200, Fe(mg / kg)≤150, TiO2 purity≥98%, bag powder loading capacity 15%.

[0068] Filter bag ④: Catalytic cloth bag made of high-purity and high-specification titanium dioxide, with a loading capacity of 25%

[0069] Powder parameters: particle size D50 ≤ 2μm, D90 ≤ 6μm, BET specific surface area > 300m 2 / g, SO4(%)≤1.4, Na2O(mg / kg)≤200, K2O(mg / kg)≤200, Fe(mg / kg)≤150, TiO2 purity≥98%, bag powder loading capacity 25%.

[0070] Filter bag ⑤: Catalytic cloth bag made of high-purity and high-specific gravity titanium dioxide, with a loading capacity of 50%

[0071] Powder parameters: particle size D50 ≤ 2μm, D90 ≤ 6μm, BET specific surface area > 300m 2 / g, SO4(%)≤1.4, Na2O(mg / kg)≤200, K2O(mg / kg)≤200, Fe(mg / kg)≤150, TiO2 purity≥98%, bag powder loading capacity 50%.

[0072] At 170℃, 0.8m / min flow rate, SO2=0, H2O=10%, O2=5%, NH3=400ppm, adjust NO:NO2 gas distribution conditions, and test the above filter bags respectively, and the NOx removal efficiency is as follows: (NOx removal efficiency=(NO in -NO out )+(NO 2in -NO 2out ) / (NO in +NO 2in ) x 100%, NO and NO2 are both in concentration units of ppm)

[0073] Table 1 Comparison of basic denitrification performance data of various application cases under different gas distribution conditions

[0074]

[0075] From the above data, it can be seen that at 170℃, 0.8m / min flow rate, SO2=0, H2O=10%, O2=5%, and NH3=400ppm, the denitrification efficiency of filter bags ①, ②, ③, ④, and ⑤ under pure NO gas distribution conditions is very low. As the proportion of NO2 in the flue gas increases, the denitrification efficiency is greatly improved. Among them, when the gas distribution condition NO:NO2=1:1, the denitrification efficiency reaches the highest value, and the denitrification efficiency of filter bags ③, ④, and ⑤ loaded with high-purity and high-specific surface area powders under the same gas distribution conditions is much higher than that of filter bags ① and ② loaded with high-purity, medium- and low-specific surface area powders. At the same time, the denitrification efficiency of filter bag ⑤ with a high loading capacity (50%) and filter bag ④ with a relatively high loading capacity (25%) is also much higher than that of filter bag ③ with a conventional loading capacity (15%). This proves that by increasing the specific surface area and dosage of loaded high-purity titanium dioxide, the denitrification efficiency of the filter bag can be greatly improved by relying on gas distribution without adding traditional vanadium-titanium-tungsten or manganese-cerium system catalysts.

[0076] At 170°C, 0.8m / min flow rate, O2=5%, NH3=400ppm, NO=200pm, NO2=200ppm, and the gas distribution condition is the optimal gas distribution ratio NO:NO2=1:1, the NOx removal efficiency of the above filter bag under the conditions of sulfur and water content is tested as follows:

[0077] Table 2 Comparison of water resistance, sulfur resistance and denitrification performance data of various application cases under the condition of NO:NO2=1:1 gas distribution

[0078]

[0079] From the above data, it can be seen that at 170℃, 0.8m / min flow rate, O2=5%,NH3=400ppm,NO=200pm,NO2=200ppm (optimal gas distribution ratio NO:NO2=1:1), under the condition of increasing the sulfur and water content of the inlet flue gas, the denitrification efficiency of filter bags ① and ② loaded with high-purity medium and low specific surface area titanium dioxide is greatly attenuated, while the denitrification efficiency of filter bags ③, ④ and ⑤ loaded with high-purity high specific surface area titanium dioxide is attenuated to a certain extent, and the denitrification attenuation efficiency of filter bag ④ with high loading (50%) and relatively high loading (25%) is also lower than that of filter bag ③ with conventional loading (15%). This proves that by increasing the specific surface area and dosage of loaded high-purity titanium dioxide, without the addition of traditional vanadium-titanium-tungsten or manganese-iron-copper catalysts, the anti-sulfur and anti-water denitrification efficiency of the filter bag can be greatly improved by gas distribution.

[0080] Take 50cm on the VDI test equipment 2The air permeability data of the above filter bags tested for samples of different sizes at a blowing pressure of 200Pa are as follows:

[0081] Table 3 Comparison of air permeability data for each application case under the same air distribution conditions

[0082]

[0083]

[0084] From the above data, we can see that under the same test conditions, the air permeability of filter bags ①, ②, ③, ④, and ⑤ has changed greatly. Among them, the air permeability of denitrification filter bags ①, ②, and ③ with a load of 15% is the highest, and the average air permeability is 38 (L / dm 2 ·min), while the air permeability of filter bags with high loading (50%) and relatively high loading (25%) decreased compared to filter bags ①, ②, and ③. Among them, the air permeability of filter bag ⑤ with high loading (50%) decreased by about 70% compared to filter bags ①, ②, and ③. This proves that increasing the amount of catalyst loaded on the bag will reduce the air permeability of the filter bag. In practical applications, this will result in increased system operating resistance and increased catalyst costs. Therefore, the higher the loading, the better. It is necessary to find the most appropriate catalyst loading to find the best balance between meeting denitrification efficiency requirements and reducing investment and operating costs. From the above experimental results, it can be seen that the denitrification filter bag with a titanium dioxide loading of less than 15% has poor denitrification performance, and the denitrification filter bag with a titanium dioxide loading of more than 50% has too low air permeability and too high operating costs. Considering the denitrification performance and air permeability of the filter bag, the denitrification filter bag with a titanium dioxide loading of 25% is the most preferred, taking into account both denitrification efficiency and operating costs. It can avoid excessive operating resistance caused by too low air permeability while achieving efficient denitrification, thus verifying its good overall performance.

[0085] The present application proposes a flue gas dust removal and denitrification system and filter bag manufacturing method for medium- and low-temperature sulfur- and water-containing environments, which combines a rapid SCR reaction with a denitrification filter bag made of high-specific surface area titanium dioxide, thereby improving the water and sulfur resistance of the denitrification filter bag under low-temperature conditions, without the need to add relatively expensive vanadium tungsten or manganese cerium active ingredients to improve the denitrification efficiency as with traditional catalysts. This provides a method for high-efficiency denitrification and dust removal of flue gas using a denitrification filter bag under medium- and low-temperature, water- and sulfur-containing conditions.

[0086] The above are preferred embodiments of the present application. Obviously, those skilled in the art can make various modifications and changes to the embodiments of the present application without departing from the spirit and scope of the present application. In this way, if these modifications and changes are within the scope of the claims of the present application and their equivalents, the present application is also intended to cover these modifications and changes.

Claims

1. Medium and low temperature sulfur and water containing environment flue gas dust removal and denitrification system, characterized by: include: A flue gas pretreatment device, an ammonia supply unit, a dust removal and denitrification reactor and a purified flue gas emission device connected in sequence; The flue gas pretreatment device includes an oxidant supply unit, which is connected to the flue, prepares an oxidant and supplies the oxidant to the flue; The flue comprises a main flue and a circulating flue; The dust removal and denitration reactor is arranged on the main flue, including a denitration filter bag, which is only loaded with titanium dioxide and serves as a fast SCR reaction site. The BET specific surface area of ​​the titanium dioxide is greater than 300m 2 / g; One end of the circulating flue is connected to the main flue after the outlet of the dust removal and denitration reactor, and the other end is connected to the main flue before the inlet of the dust removal and denitration reactor. The ammonia supply unit is connected to the circulating flue.

2. The flue gas dust removal and denitrification system for medium and low temperature sulfur-containing and water-containing environments according to claim 1 is characterized in that: The oxidant supply unit includes an oxidant generating device and an oxidant dosing and distributing device, and the oxidant dosing and distributing device is arranged on the flue; the oxidant is ozone, sodium hypochlorite or hydrogen peroxide.

3. The flue gas dust removal and denitrification system for medium and low temperature sulfur-containing and water-containing environments according to claim 1 is characterized in that: The titanium dioxide has D50≤2μm, D90≤6μm, SO4≤1.4%, and TiO2 purity≥98%.

4. The flue gas dust removal and denitrification system for medium and low temperature sulfur-containing and water-containing environments according to claim 1 is characterized in that: The titanium dioxide loading of the denitrification filter bag is 15% to 50%, with 25% being the best.

5. The flue gas dust removal and denitrification system for medium and low temperature sulfur-containing and water-containing environments according to claim 1 is characterized in that: The ammonia supply unit includes an ammonia water storage and supply device, a dual-fluid spray gun and a uniform mixer connected in sequence through pipelines. The nozzle of the dual-fluid spray gun is arranged in the flue. Ammonia water flows into the dual-fluid spray gun from the ammonia water storage and supply device, is atomized and evaporated into ammonia gas, and is sprayed out. It is evenly mixed with the flue gas through the uniform mixer and then enters the dust removal and denitrification reactor.

6. The flue gas dust removal and denitrification system for medium and low temperature sulfur-containing and water-containing environments according to claim 5 is characterized in that: The ammonia gas sprayed by the ammonia supply unit and the NO in the flue gas X The molar ratio is 1:

1.

7. The flue gas dust removal and denitrification system for medium and low temperature sulfur-containing and water-containing environments according to claim 1 is characterized in that: The oxidant supply unit is an ozone supply unit, and the ozone sprayed by the ozone supply unit is mixed with NO in the flue gas. X The molar ratio is 1:6 to 1:2, and the mass concentration of ozone is 5 to 10%.

8. The flue gas dust removal and denitrification system for medium and low temperature sulfur-containing and water-containing environments according to claim 1 is characterized in that: The reaction occurring in the dust removal and denitrification reactor is: NO+NO2+2NH3→2N2+3H2O.

9. A method for making a denitrification filter bag, characterized in that: For making the denitrification filter bag according to any one of claims 1 to 8, the steps include: S1: Particle size D50≤2μm, D90≤6μm, BET specific surface area>300m 2 / g, SO4≤1.4%, titanium dioxide with TiO2 purity ≥98% is dissolved in water, and additives are added to form a slurry with a solid content of 10-20%; S2: Loading the bag with the slurry by spraying or dipping; S3: Place the bag in a drying room and dry and activate it at a temperature of 200-250°C to make a denitrification filter bag.

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