A low-temperature desulfurization and denitrification flue gas purification device and purification method

Abstract

The present invention relates to the technical field of flue gas purification. Specifically, it relates to a low-temperature desulfurization and denitrification flue gas purification device and a purification method. The bottom of the reaction tower of the device is provided with a flue gas inlet, and the top is provided with a flue gas outlet; the bottom of the reaction tower is also provided with an ammonia inlet; the bottom of the reaction tower is also provided with an ammonium sulfite powder inlet, and the ammonium sulfite powder inlet is communicated with an ammonium sulfite grinding device. The method first crushes and grinds ammonium sulfite solid, and then simultaneously feeds the ammonium sulfite powder, ammonia, and the flue gas to be purified into the reaction tower and mixes them; the temperature of the flue gas is 50°C to 200°C, and the pressure is 500 Pa to 2000 Pa; after the reaction is completed, the purification is completed. This method has a low reaction temperature and does not require a catalyst; it can simultaneously purify nitrogen oxides and sulfur dioxide in the flue gas in the same reaction tower, with low operating costs, simple process flow, and by-products being easy to recycle and reuse.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas purification, and more particularly, to a low-temperature desulfurization and denitrification flue gas purification device and a purification method. Background Art

[0002] SO2 and nitrogen oxides (NOx) generated by coal combustion are the main causes of air pollution, which seriously affect the ecological environment and human health. To solve this problem, it is necessary to treat the waste gas, and it is imperative to fundamentally solve the pollution caused by SO2 and NOx.

[0003] With the development of the economy and the progress of technology, the requirements for flue gas treatment have gradually increased. In the 1990s, the treatment of sulfur oxides in flue gas began to be emphasized. Since this century, the treatment requirements for NOx in flue gas have gradually been put forward. In recent years, due to the increasing environmental protection requirements, the requirement for simultaneous desulfurization and denitrification of flue gas treatment has been put forward. To meet this demand, technicians in this field have continuously studied new technologies and equipment to simultaneously remove SO2 and NOx in the waste gas at one time. Currently, for simultaneous desulfurization and denitrification of flue gas, the main technology used in China is the combination process of wet desulfurization and SCR denitrification.

[0004] SCR refers to selective catalytic reduction technology. In the presence of a catalyst and oxygen, ammonia preferentially reacts with nitrogen oxides to undergo a reduction removal reaction, generating nitrogen and water, rather than undergoing an oxidation reaction with oxygen in the flue gas. The temperature required for this process is at least 300 - 400 °C.

[0005] Although the above process has good desulfurization and denitrification effects, it requires the use of a catalyst and has a high reaction temperature requirement, which results in a long process route for the purification equipment, a complex device, a large investment, and high operating costs. Moreover, due to the need to introduce oxygen, there are serious safety hazards in the purification process. In addition, this process requires the use of a catalyst and the desulfurization by-product calcium sulfate has a low value and cannot be effectively utilized, and a large amount of accumulation will also cause secondary pollution. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a low-temperature desulfurization and denitrification flue gas purification device and a purification method.

[0007] The technical solution of the present invention for solving the above technical problems is as follows:

[0008] A low-temperature desulfurization and denitrification flue gas purification device of the present invention includes a reaction tower, the bottom of the reaction tower is provided with a flue gas inlet, and the top is provided with a flue gas outlet;

[0009] The bottom of the reaction tower is also provided with an ammonia inlet;

[0010] The bottom of the reaction tower is also provided with an ammonium sulfite powder inlet, which is communicated with an ammonium sulfite grinding device.

[0011] The beneficial effects of the present invention are as follows: By providing an ammonium sulfite grinding device, solid ammonium sulfite can be crushed and ground, and ammonium sulfite powder, ammonia gas and flue gas are simultaneously introduced into the bottom of the reaction tower, so that the three can be mixed and fully reacted in the reaction tower. When the mixed gas rises to the flue gas outlet at the top of the reaction tower, the purification of nitrogen oxides and sulfur dioxide in the flue gas is completed.

[0012] On the basis of the above technical solution, the present invention can be further improved as follows.

[0013] Further, the flue gas inlet is communicated with a heat exchange device; the flue gas outlet of the reaction tower is communicated with an induced draft fan.

[0014] The beneficial effect of adopting the above further solution is that the flue gas to be purified has a certain temperature through the heat exchange device, and the flue gas to be purified has a certain pressure in the reaction tower through the induced draft fan, ensuring the smooth progress of the reaction in the reaction tower; the induced draft fan can also adjust the air volume.

[0015] Further, the heat exchange device is also communicated with a booster fan.

[0016] The beneficial effect of adopting the above further solution is that the flue gas to be purified is pressurized and then enters the heat exchange device through a pressurizing device, and the booster fan can adjust the air volume simultaneously with the induced draft fan and provide pressure for the flue gas to be purified.

[0017] Further, a cooling device is provided between the flue gas outlet of the reaction tower and the induced draft fan, and a dust removal device is provided between the cooling device and the induced draft fan.

[0018] The beneficial effect of adopting the above further solution is that the purified flue gas is cooled after passing through the cooling device, meeting the temperature condition for entering the dust removal device; the particulate matter contained in the flue gas can be removed through the dust removal device.

[0019] Further, the ammonium sulfite powder inlet and the flue gas inlet are arranged opposite to each other and are located on the same horizontal plane; the ammonium sulfite powder inlet and the flue gas inlet are respectively tangent to the side wall of the reaction tower.

[0020] The beneficial effect of adopting the above further solution is that the flue gas to be purified and ammonium sulfite powder can rotate clockwise or counterclockwise simultaneously after entering the reaction tower, so as to be fully mixed, enhancing the mixing effect and improving the reaction efficiency.

[0021] Further, a plurality of temperature sensors are installed on the reaction tower.

[0022] The beneficial effect of adopting the above further solution is that the temperature inside the reaction tower can be monitored.

[0023] The present invention also provides a low-temperature desulfurization and denitrification flue gas purification method using the above device, comprising the following steps:

[0024] S1. Crushing and grinding ammonium sulfite solid in the ammonium sulfite grinding equipment to obtain ammonium sulfite powder;

[0025] S2. Simultaneously introducing the ammonium sulfite powder, ammonia gas, and the flue gas to be purified into the reaction tower for mixing; wherein, the temperature of the flue gas to be purified is 50°C to 200°C, and the pressure is 500 Pa to 2000 Pa;

[0026] S3. The mixed flue gas rises from the bottom of the reaction tower to the top, and a reaction occurs during the rising process. After the reaction ends, the purified flue gas discharged from the flue gas outlet of the reaction tower is collected to complete the purification.

[0027] The beneficial effects of the present invention are: the reaction temperature is low and no catalyst is required; this method can achieve simultaneous purification of nitrogen oxides and sulfur dioxide in the flue gas in the same reaction tower, with low operating costs and a simple process flow.

[0028] Further, in step S1, the particle size of the ammonium sulfite powder is less than or equal to 75 μm.

[0029] The beneficial effect of adopting the above further solution is that the reaction is more complete.

[0030] Further, before performing step S2, first measure the contents of nitrogen oxides and sulfur dioxide in the flue gas to be purified.

[0031] The beneficial effect of adopting the above further solution is that the amounts of ammonium sulfite and ammonia gas introduced can be determined according to the measurement results.

[0032] Further, in step S2, determine the dosages of the ammonium sulfite powder and ammonia gas according to the reaction equation and the contents of nitrogen oxides and sulfur dioxide in the flue gas to be purified; wherein, the molar ratio of the ammonium sulfite powder to nitrogen oxides in the flue gas to be purified is 2 to 10:1; the molar ratio of ammonia gas to sulfur dioxide in the flue gas to be purified is 0.2 to 0.8:1. Description of the Drawings

[0033] Figure 1 is a schematic structural diagram of the low-temperature desulfurization and denitrification flue gas purification device of the present invention;

[0034] Figure 2 is a schematic structural diagram of the flue gas inlet and ammonium sulfite powder inlet of the reaction tower in the low-temperature desulfurization and denitrification flue gas purification device of the present invention.

[0035] In the attached drawings, the list of components represented by each reference numeral is as follows:

[0036] 1. Reaction tower; 11. Flue gas inlet; 12. Ammonium sulfite powder inlet;

[0037] 2. Ammonium sulfite grinding equipment; 3. Heat exchange equipment; 4. Booster fan; 5. Cooling equipment; 6. Dust removal equipment; 7. Induced draft fan; 8. Chimney; 9. Venturi device. Specific embodiments

[0038] The principles and features of the present invention will be described below in conjunction with the attached drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0039] As Figure 1 shown, the low-temperature desulfurization and denitrification flue gas purification device of the present invention includes a reaction tower 1. The bottom of the reaction tower 1 is provided with a flue gas inlet 11, and the top is provided with a flue gas outlet; the bottom of the reaction tower 1 is also provided with an ammonia inlet; the bottom of the reaction tower 1 is also provided with an ammonium sulfite powder inlet 12, and the ammonium sulfite powder inlet 12 is connected to the ammonium sulfite grinding equipment 2.

[0040] The low-temperature desulfurization and denitrification flue gas purification device of the present invention can crush and grind solid ammonium sulfite by setting the ammonium sulfite grinding equipment 2, and simultaneously introduce the ammonium sulfite powder, ammonia and flue gas into the bottom of the reaction tower 1, so that the three can be mixed and fully reacted in the reaction tower 1. The mixed gas rises to the flue gas outlet at the top of the reaction tower 1 and is discharged, completing the purification of nitrogen oxides and sulfur dioxide in the flue gas.

[0041] The low-temperature desulfurization and denitrification flue gas purification device of the present invention has a small floor area and is convenient for operation and maintenance.

[0042] The "low temperature" referred to in the present invention is lower in temperature compared with the SCR denitrification method; the temperature of SCR denitrification is generally 300 - 400 °C, while the temperature of the present invention is 50 - 200 °C.

[0043] Preferably, the flue gas inlet 11 is connected to the heat exchange equipment 3; the flue gas outlet of the reaction tower 1 is connected to the induced draft fan 7; the heat exchange equipment 3 can adjust the temperature of the flue gas, and the induced draft fan 7 can adjust the pressure of the flue gas; in this way, the flue gas to be purified entering the reaction tower 1 has a certain pressure and temperature through the heat exchange equipment 3 and the induced draft fan 7, ensuring the smooth progress of the reaction in the reaction tower 1.

[0044] Preferably, the heat exchange equipment 3 is also connected to the booster fan 4; the flue gas to be purified can obtain pressure through the booster fan 4 and then enter the heat exchange equipment 3; the booster fan 4 and the induced draft fan 7 can provide pressure and adjust the air volume for the flue gas at the same time.

[0045] Preferably, a cooling device 5 is further provided between the flue gas outlet of the reaction tower 1 and the induced draft fan 7, and a dust removal device 6 is provided between the cooling device 5 and the induced draft fan 7. The purified flue gas is cooled after passing through the cooling device 5 so that the flue gas meets the temperature condition for entering the dust removal device 6, and then the particulate matter contained in the flue gas is removed through the dust removal device 6 to achieve further purification.

[0046] Preferably, the outlet of the induced draft fan 7 is communicated with the chimney 8; the purified flue gas is discharged into the chimney 8.

[0047] As Figure 2 shown, preferably, the ammonium sulfite powder inlet 12 and the flue gas inlet 11 are arranged opposite to each other and are located on the same horizontal plane; the ammonium sulfite powder inlet 12 and the flue gas inlet 11 are respectively tangent to the side wall of the reaction tower 1; in this way, the flue gas to be purified and the ammonium sulfite powder can rotate clockwise or counterclockwise simultaneously after entering the reaction tower 1, so as to be fully mixed, enhance the mixing effect and improve the reaction efficiency.

[0048] Preferably, the ammonia inlet and the ammonium sulfite powder inlet 12 are located on the same side and above it.

[0049] Preferably, a plurality of temperature sensors are installed on the reaction tower 1. Generally, the temperature sensors are ordinary thermocouples; the plurality of temperature sensors can sense the real-time temperature of the reaction tower 1, which is convenient for adjusting the temperature inside the reaction tower 1 to ensure that ammonium sulfite, ammonia and flue gas can react.

[0050] Further preferably, at least one temperature sensor can be electrically connected to the heat exchange device 3, and the temperature sensor, the heat exchange device 3 and the control element are electrically connected; the temperature sensor transmits the sensed temperature signal to the control element, and the control element judges whether the temperature inside the reaction tower 1 meets the reaction requirement according to the temperature signal; when the temperature is too high, the control element can control the heat exchange device 3 to reduce the temperature of the incoming flue gas, and when the temperature is too low, the control element can control the heat exchange device 3 to heat the incoming flue gas; through the above control process, the dynamic balance of the temperature inside the reaction tower 1 can be achieved, so as to ensure that ammonium sulfite, ammonia and nitrogen oxides and sulfur dioxide in the flue gas to be purified can react fully.

[0051] Preferably, the ammonium sulfite grinding equipment 2 of the present invention can specifically be any one of Raymond mill, vertical mill and ball mill.

[0052] Preferably, the cooling device 5 of the present invention can be air cooling, water cooling or other devices that can reduce the flue gas temperature.

[0053] Preferably, the dust removal device 6 of the present invention can be one of a cyclone dust removal device, an electrostatic dust removal device and a bag dust removal device, or a device formed by connecting these devices in series.

[0054] Preferably, a Venturi device 9 is also installed in the reaction tower 1; the Venturi device 9 is located above the ammonia inlet and is arranged vertically; installing the Venturi device 9 can prevent the unreacted sulfurous acid powder from falling to the bottom of the tower, resulting in incomplete reaction.

[0055] Some internals are provided in the reaction tower 1, such as a deflector or a cyclone, etc. These internals can increase the gas-solid mixing effect and contact time, and improve the reaction efficiency again. These internals are not shown in the drawings of the present invention and can be arranged and installed according to actual needs during use.

[0056] The reaction tower 1 is generally cylindrical. To meet the process requirements, the height of the reaction tower 1 should be at least greater than 15 m.

[0057] The low-temperature desulfurization and denitrification flue gas purification method of the present invention includes the following steps:

[0058] S1. Crushing and grinding ammonium sulfite solid in the ammonium sulfite grinding equipment 2 to obtain ammonium sulfite powder;

[0059] S2. Simultaneously introducing the ammonium sulfite powder, ammonia, and the flue gas to be purified into the reaction tower 1 for mixing. The mixed flue gas rises from the bottom to the top of the reaction tower 1 and reacts simultaneously, so that the nitrogen oxides and sulfur dioxide in the flue gas are purified;

[0060] S3. Collecting the purified flue gas discharged from the flue gas outlet of the reaction tower 1 to complete the purification.

[0061] In the flue gas purification method of the present invention, ammonium sulfite powder and ammonia are used to react with nitrogen oxides and sulfur dioxide in the flue gas respectively. Compared with SCR, the reaction temperature is low and no catalyst is required; at the same time, the method of the present invention can realize the simultaneous purification of nitrogen oxides and sulfur dioxide in the flue gas in the same reaction tower 1, with low operating cost and simple process flow, making the method of the present invention have a wide application range, be environmentally friendly, and be easy to promote.

[0062] In addition, the by-products of the present invention are mainly ammonium sulfate solids, which can be recycled and utilized, avoiding the problems of waste of by-products and environmental pollution.

[0063] Specifically, after the ammonium sulfite in the reaction tower 1 removes the harmful gases in the flue gas, ammonium sulfate solids are generated. These ammonium sulfate solids enter the cooling equipment 5 or the dust removal equipment 6 together with the flue gas and are collected in the two equipment. If the cooling equipment 5 is a direct heat exchange water scrubber, most of the ammonium sulfate solids will be collected in the water scrubber, and a small part will be in the dust removal equipment 6. If the cooling equipment 5 is an indirect heat exchange equipment, a small part will remain in the cooling equipment 5, and most of them will be collected in the dust removal equipment 6.

[0064] Specifically, the ammonium sulfite of the present invention mainly removes nitrogen monoxide and nitrogen dioxide gases in the flue gas to be purified. The specific reaction equations are as follows:

[0065] 2(NH4)2SO3·H2O + 2NO = N2↑ + 2H2O + 2(NH4)2SO4

[0066] 4(NH4)2SO3·H2O + 2NO2 = N2↑ + 4H2O + 4(NH4)2SO4

[0067] In addition, ammonium sulfite will also undergo a decomposition reaction when heated. The specific reaction equation is as follows:

[0068] (NH4)2SO3 = 2NH3 + SO2 + H2O

[0069] The ammonia introduced into the reaction tower 1 and the ammonia generated by the thermal decomposition of part of the ammonium sulfite will react with SO2 in the flue gas to convert it into ammonium bisulfite and ammonium sulfite. The ammonium sulfite continues to participate in the denitrification reaction, and the ammonium bisulfite is finally converted into ammonium sulfate. The specific reaction equations are as follows:

[0070] 2(NH4)2SO3·H2O + SO2 = 2NH4HSO3 + 2H2O↑

[0071] 2NH3 + SO2 + H2O → (NH4)2SO3

[0072] NH3 + SO2 + H2O → NH4HSO3

[0073] 2NH4HSO3 + O2 → 2(NH4)2SO4

[0074] The ammonium bisulfite and ammonium sulfite generated after the reaction are solid particles, which are discharged from the reaction tower 1 together with the purified flue gas. These solid particles can be removed by setting up the dust removal device 6.

[0075] Preferably, in step S1, the particle size of the ammonium sulfite powder is less than or equal to 75 μm. During the actual crushing and abrasion process, it is necessary to ensure that 90% of the ammonium sulfite particle size is within 75 μm after grinding. This condition can be achieved by adjusting the ammonium sulfite grinding equipment 2.

[0076] Preferably, before step S2, the contents of nitrogen oxides and sulfur dioxide in the flue gas to be purified are measured first. In this way, the dosage of ammonium sulfite powder and ammonia can be controlled more accurately, which can not only save materials, but also ensure that the reaction occurs fully and make the flue gas purification reach the best efficiency.

[0077] Preferably, in step S2, the molar ratio of ammonium sulfite powder to nitrogen oxides in the flue gas to be purified is 2-10:1; the molar ratio of ammonia to sulfur dioxide in the flue gas to be purified is 0.2-0.8:1.

[0078] Preferably, in step S2, the reaction temperature in the reaction tower 1 is 50°C to 200°C, and the pressure is 500 Pa to 2000 Pa; during the process of the mixed flue gas rising from the bottom to the top of the reaction tower 1, the gas velocity is 4 m to 8 m, and the contact time between the ammonium sulfite powder and the flue gas is at least greater than 3 s.

[0079] The reaction temperature in the above reaction tower 1 is achieved by setting the heat exchange device 3; before the flue gas to be purified enters the reaction tower 1, it first passes through the heat exchange device 3, and the heat exchange device 3 can adjust the temperature of the flue gas to be purified between 50 and 200°C, and the specific temperature can also be adjusted according to the real-time temperature monitored in the reaction tower 1. This temperature can ensure that the flue gas to be purified can react with ammonium sulfite powder and ammonia after entering the reaction tower 1.

[0080] The pressure in the above reaction tower 1 is achieved by setting the booster fan 4 and the induced draft fan 7; before the temperature of the flue gas to be purified is adjusted, the air volume is first adjusted by the booster fan 4 and the induced draft fan 7 to make it have a pressure of 500 Pa to 2000 Pa, and then the temperature is adjusted by the heat exchange device 3, and finally it enters the reaction tower 1; in this way, the flue gas to be purified has a pressure that meets the reaction requirements.

[0081] The flue gas to be purified enters the reaction tower 1 from the bottom and is mixed with ammonium sulfite powder and ammonia; due to the certain gas velocity of the flue gas to be purified and ammonia, the mixed gas flows towards the top of the reaction tower 1 in the reaction tower 1 and fully reacts during the flowing process. In the actual reaction, the contact time between the ammonium sulfite powder, ammonia and the flue gas to be purified needs to be at least greater than 3 s to ensure full reaction. Therefore, the gas velocity in the present invention should be controlled between 4 m and 8 m. Too high or too low will result in poor mixing and reaction effects, and too fast speed will also increase the height of the reaction tower 1.

[0082] The following is an example of the present invention through specific examples.

[0083] Example

[0084] The flue gas purification device and purification method of the present invention are used to purify the flue gas to be purified with different flue gas volumes respectively.

[0085] After detection, the Nox concentration in the flue gas is about 300 mg / Nm 3 , and the SO2 concentration is about 2500 mg / Nm 3 , as shown in Table 1 specifically:

[0086] Table 1

[0087]

[0088] It can be seen that in Examples 1 to 5, the concentrations of sulfur dioxide and nitrogen oxides are both greatly reduced, indicating that the device and method of the present invention can effectively remove sulfur dioxide and nitrogen oxides in flue gas.

[0089] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0090] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "below" and "beneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0091] In the description of this specification, the descriptions with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0092] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0093] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A flue gas purification device for desulfurization and denitrification at low temperature, characterized in that, It includes a reaction tower (1). A flue gas inlet (11) is provided at the bottom of the reaction tower (1), and a flue gas outlet is provided at the top. An ammonia inlet is further provided at the bottom of the reaction tower (1). An ammonium sulfite powder inlet (12) is further provided at the bottom of the reaction tower (1), and the ammonium sulfite powder inlet (12) is communicated with an ammonium sulfite grinding device (2). The flue gas inlet (11) is communicated with a heat exchange device (3); the flue gas outlet of the reaction tower (1) is communicated with a draft fan (7). A cooling device (5) is further provided between the flue gas outlet of the reaction tower (1) and the draft fan (7), and a dust removal device (6) is provided between the cooling device (5) and the draft fan (7). The ammonium sulfite powder inlet (12) and the flue gas inlet (11) are arranged oppositely and are located on the same horizontal plane; the ammonium sulfite powder inlet (12) and the flue gas inlet (11) are respectively tangent to the side wall of the reaction tower (1). A Venturi device (9) is further installed in the reaction tower (1); the Venturi device (9) is located above the ammonia inlet and is arranged vertically.

2. The low-temperature desulfurization and denitrification flue gas purification device according to claim 1, characterized in that, The heat exchange device (3) is further communicated with a booster fan (4).

3. The low-temperature desulfurization and denitrification flue gas purification device according to claim 1 or 2, characterized in that, A plurality of temperature sensors are installed on the reaction tower (1).

4. A method for purifying flue gas by low-temperature desulfurization and denitrification using the device according to any one of claims 1 to 3, characterized in that, It includes the following steps: S1. Crush and grind ammonium sulfite solid in the ammonium sulfite grinding device (2) to obtain ammonium sulfite powder; the particle size of the ammonium sulfite powder is less than or equal to 75 μm. Before performing the step S2, first measure the contents of nitrogen oxides and sulfur dioxide in the flue gas to be purified. S2. Simultaneously introduce the ammonium sulfite powder, ammonia, and the flue gas to be purified into the reaction tower (1) for mixing; wherein, the temperature of the flue gas to be purified is 50°C to 200°C, and the pressure is 500 Pa to 2000 Pa. In the step S2, determine the dosages of the ammonium sulfite powder and ammonia according to the reaction equation and the contents of nitrogen oxides and sulfur dioxide in the flue gas to be purified; wherein, the molar ratio of the ammonium sulfite powder to nitrogen oxides in the flue gas to be purified is 2 to 10:1; the molar ratio of ammonia to sulfur dioxide in the flue gas to be purified is 0.2 to 0.8:

1. S3. The mixed flue gas rises from the bottom of the reaction tower (1) to the top, and a reaction occurs during the rising process. After the reaction ends, collect the purified flue gas discharged from the flue gas outlet of the reaction tower (1) to complete the purification.

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