Method for removing sulfur trioxide in flue gas by evaporation coupling of desulfurization wastewater bypass flue

Abstract

The invention provides a method for removing sulfur trioxide in flue gas by evaporation coupling of a desulfurization wastewater bypass flue, which comprises the following steps of: changing quenched and tempered desulfurization wastewater into solid particles by utilizing a bypass flue evaporation device, spraying the solid particles into the front side and the rear side of an SCR (Selective Catalytic Reduction) denitration device, absorbing SO3 in the original flue gas at a boiler outlet and SO3 newly added after SO2 is catalyzed by a catalyst, and removing sulfur trioxide in the flue gas by utilizing the desulfurization wastewater bypass flue evaporation coupling. The SO3 removal efficiency is improved, the problem that a liquid spraying type nozzle directly sprays high-salt desulfurization wastewater and is easy to block is solved, and the device is suitable for large-scale popularization and application.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas treatment, and in particular to a method for removing sulfur trioxide from flue gas by evaporation coupling of desulfurization wastewater bypass flue. Background Art

[0002] The unconventional pollutant SO3 in flue gas not only causes environmental pollution, but also causes blockage of the air preheater and corrosion of the tail flue. Environmental protection equipment in coal-fired power plants often only treats a single pollutant, and the SCR process is generally used for flue gas denitrification. The SCR catalyst will catalytically oxidize part of the SO2 in the flue gas into SO3. Conventional pollutant control equipment such as electrostatic precipitators and WFGD also have low efficiency in removing SO3 from flue gas. In recent years, many coal-fired power plants have carried out zero-emission transformation of wastewater. Among them, flue bypass evaporation technology is one of the current mainstream zero-emission wastewater solidification technologies. The environmental protection facilities of coal-fired power plants have various processes and complex equipment. How to use existing environmental protection equipment to synergistically remove SO3 is an important technical direction.

[0003] At present, most methods for removing SO3 are to directly spray alkaline powder or solution. CN105126561A discloses a method for removing PM from coal-fired flue gas based on evaporation treatment of desulfurization wastewater. 2.5 / SO3 / Hg combined removal method, CN103933838A discloses a device and method for the combined removal of pollutants by recycling chlorine elements in coal, both of which are methods of removing sulfur trioxide by spraying after conditioning desulfurization wastewater. However, the above method has the disadvantage that all desulfurization wastewater is sprayed into the main flue, such as affecting the entire flue system, and ash accumulation caused by incomplete atomization will affect the safe and stable operation of the boiler system. Therefore, the application of direct spraying in the above flue is rare. The above method also cannot reduce the oxidation of SO2 to SO3 in the SCR.

[0004] CN106630269A discloses a method and a removal system for removing SO3 from boiler flue gas by using desulfurization wastewater, wherein the desulfurization wastewater is conditioned and sprayed into the flue before SCR, air preheater or dust collector to remove SO3, but the method cannot avoid the toxic effects of heavy metals in the wastewater on the catalyst, and incomplete atomization will also cause the catalyst to accumulate dust, which will seriously affect the safety of the SCR catalyst. And since the removal of SO3 is a gas-solid two-phase reaction, the liquid phase absorbent needs to be dried to the solid phase before the liquid is sprayed into the SCR, which shortens the reaction time. In addition, the current bypass flue evaporation is generally concentrated first, and the wastewater is acidic. Spray evaporation under acidic conditions will cause the chlorine in the wastewater to be released and then washed by the desulfurization tower, resulting in the enrichment of chlorine in the desulfurization system, causing the desulfurization tower to increase the discharge volume, and increasing the operating pressure of the desulfurization wastewater zero-discharge treatment equipment. The above methods all spray liquid wastewater, and because the salt content in the wastewater is very high, it is very easy to clog the nozzle when spraying at high temperature.

[0005] In summary, it is of great significance to develop a safer and more efficient method to remove sulfur trioxide from flue gas. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for removing sulfur trioxide from flue gas by coupling evaporation of desulfurization wastewater through a bypass flue. Alkaline particulate matter is obtained by evaporating and tempering the desulfurization wastewater through a bypass flue. The particulate matter is then sprayed on the front and rear sides of an SCR denitrification device to remove SO3 from the flue gas, thus achieving waste treatment with waste and avoiding the problem of nozzle clogging and SCR catalyst poisoning caused by direct spraying of desulfurization wastewater.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for removing sulfur trioxide from flue gas by evaporation coupling of desulfurization wastewater bypass flue, the method comprising the following steps:

[0009] (1) After the desulfurization wastewater discharged from the desulfurization tower enters the conditioning separation device for treatment, it is injected into the bypass flue evaporation device to exchange heat with the flue gas to form flue gas carrying alkaline particulate matter;

[0010] (2) The flue gas carrying the alkaline particulate matter enters the first gas-solid separation device, the separated flue gas enters the boiler flue after the air preheater, and the separated alkaline particulate matter is sent to the solid storage device for storage;

[0011] (3) The particulate matter in the solid storage device is respectively injected into the front and rear sides of the SCR denitrification device arranged in the boiler flue to react with SO3 in the boiler flue gas and thereby remove SO3.

[0012] The method of removing sulfur trioxide from flue gas by coupling desulfurization wastewater bypass flue evaporation of the present invention first conditions the desulfurization wastewater to make the wastewater alkaline, and removes the suspended matter in the wastewater. The treated desulfurization wastewater enters the bypass flue evaporation device for heat exchange and evaporation, which can reduce the release of chloride ions in the wastewater and the enrichment of chloride ions in the bypass flue evaporation device. Then, the flue gas carrying alkaline particles formed after evaporation is separated by a first gas-solid separation device, and the solid alkaline particles are stored in a solid storage device. After that, the particles are injected into the front and rear sides of the SCR denitration device, which can avoid the problem of catalyst poisoning caused by the prior art directly using desulfurization wastewater to be injected into the SCR denitration device. Moreover, the particles in the solid storage device enter in the form of powder spray, which greatly reduces the risk of nozzle clogging.

[0013] The method of removing sulfur trioxide from flue gas by evaporating the desulfurized wastewater bypass flue coupled with SO3 removal of the desulfurized wastewater bypass flue is described in the present invention, which couples the desulfurized wastewater bypass flue evaporation with SO3 removal, thereby achieving waste treatment with waste, and avoiding the adverse effects of the main flue spray on the boiler exhaust system. In addition, the solid particles formed by the desulfurized wastewater are sprayed into the front and rear sides of the SCR denitrification device, absorbing the SO3 in the original flue gas at the boiler outlet and the newly added SO3 after the catalysis of the catalyst, thereby improving the SO3 removal efficiency and avoiding the problem of easy clogging of the liquid spray type nozzle spraying high-salt wastewater.

[0014] The "front side" and "rear side" mentioned in the present invention refer to the position along the flow direction of the smoke, where the position that the smoke passes first is the "front side" and the position that the smoke passes later is the "rear side".

[0015] The alkaline particles separated in step (2) of the present invention are pneumatically conveyed into a solid storage device for storage.

[0016] Preferably, the desulfurization wastewater in step (1) enters a concentration device for concentration treatment before entering the conditioning and separation device.

[0017] Preferably, the concentration device comprises any one of a low-temperature multiple-effect evaporation concentration device, a flue gas source direct contact evaporation concentration device or an air source direct contact evaporation concentration device.

[0018] Preferably, the treatment steps of step (1) include: first adding a first alkaline agent into a conditioning separation device to adjust the pH of the desulfurization wastewater to 9-11, for example, it can be 9, 9.5, 9.8, 10, 10.5 or 11, etc., but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable; and then separating the suspended matter.

[0019] The present invention suppresses the release of chlorine caused by spraying the desulfurization wastewater at high temperature by adjusting the pH of the desulfurization wastewater to 9-11, thereby avoiding the enrichment of chlorine in the SCR denitration device.

[0020] Preferably, the first alkaline agent comprises any one of sodium hydroxide powder, calcium hydroxide powder or sodium carbonate powder, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of sodium hydroxide powder and calcium hydroxide powder, a combination of sodium carbonate powder and sodium hydroxide powder, or a combination of calcium hydroxide powder and sodium carbonate powder.

[0021] Preferably, the particle size of the first alkali agent is 25-50 μm, for example, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the flue gas in step (1) includes the flue gas from before the air preheater, and the flue gas enters the boiler flue after the air preheater after heat and mass transfer with the desulfurization wastewater.

[0023] The present invention preferably uses the flue gas from before the air preheater and the desulfurization wastewater for heat and mass transfer, which has the advantages of high flue gas temperature and good evaporation effect.

[0024] Preferably, the flue gas before the air preheater first enters the second gas-solid separation device to separate the dust particles.

[0025] Preferably, the separated dust particles enter the dust collector ash hopper, slag bin or boiler flue before the dust collector.

[0026] Preferably, the bypass flue evaporation device in step (1) comprises a dual-fluid type flue evaporation device or a rotary atomization type flue evaporation device.

[0027] Preferably, in step (2), a fan is further provided between the first gas-solid separation device and the boiler flue to prevent excessive wind resistance of the flue gas in the bypass flue evaporation device.

[0028] Preferably, a second alkaline agent is added to the solid storage device in step (2) so that the chemical equivalence ratio of the alkaline substance sprayed into the flue gas to the sulfur-containing substance in the flue gas reaches 5:1 or above, for example, it can be 5:1, 5.3:1, 5.5:1, 5.8:1, 6:1, 7:1 or 8:1, which can improve the SO3 removal efficiency.

[0029] Preferably, the second alkaline agent comprises any one of sodium hydroxide powder, calcium hydroxide powder or sodium carbonate powder, or a combination of at least two thereof, wherein typical but non-limiting combinations include a combination of sodium hydroxide powder and calcium hydroxide powder, a combination of sodium carbonate powder and sodium hydroxide powder, or a combination of calcium hydroxide powder and sodium carbonate powder.

[0030] Preferably, before spraying the particles in the solid storage device in step (3), the particles in the solid storage device are ground to a particle size of 10 to 50 μm, for example, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 40 μm or 50 μm, etc., but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] As a preferred technical solution of the present invention, the method comprises the following steps:

[0032] (1) The desulfurization wastewater discharged from the desulfurization tower enters the concentration device for concentration treatment and then enters the conditioning separation device. The first alkaline agent is first added to the conditioning separation device to adjust the pH of the desulfurization wastewater to 9-11, and then the suspended matter is separated. After that, it is injected into the bypass flue evaporation device to exchange heat with the flue gas to form flue gas carrying alkaline particles;

[0033] The concentrator comprises any one of a low-temperature multiple-effect evaporation concentrator, a flue gas source direct contact evaporation concentrator or an air source direct contact evaporation concentrator; the first alkali agent comprises any one of sodium hydroxide powder, calcium hydroxide powder or sodium carbonate powder or a combination of at least two thereof; the particle size of the first alkali agent is 25 to 50 μm;

[0034] The flue gas includes the flue gas from before the air preheater; the flue gas enters the boiler flue after the air preheater after heat and mass transfer with the desulfurization wastewater;

[0035] The flue gas before the air preheater first enters the second gas-solid separation device to separate dust particles; the separated dust particles enter the dust collector ash hopper, slag bin or boiler flue before the dust collector;

[0036] The bypass flue evaporation device includes a dual-fluid type flue evaporation device or a rotary atomization type flue evaporation device;

[0037] (2) The flue gas carrying the alkaline particulate matter enters the first gas-solid separation device, and the separated flue gas enters the boiler flue after the air preheater through the fan, and the separated alkaline particulate matter is sent to the solid storage device for storage;

[0038] A second alkaline agent is added to the solid storage device so that the chemical equivalent ratio of the alkaline substance sprayed into the flue gas to the sulfur-containing substance in the flue gas reaches 5:1 or more; the second alkaline agent includes any one of sodium hydroxide powder, calcium hydroxide powder or sodium carbonate powder or a combination of at least two thereof;

[0039] (3) After the particulate matter in the solid storage device is ground to a particle size of 10 to 50 μm, it is injected into the front and rear sides of the SCR denitrification device arranged in the boiler flue, reacting with SO3 in the boiler flue gas to remove SO3.

[0040] Compared with the prior art, the present invention has at least the following beneficial effects:

[0041] The present invention provides a method for removing sulfur trioxide from flue gas by coupling evaporation of desulfurized wastewater through a flue bypass. The method utilizes a desulfurized wastewater through a flue bypass evaporation system to couple the removal of SO3 from flue gas. The system modification cost is low, and the problem of nozzle blockage and SCR catalyst poisoning caused by direct spraying of desulfurized wastewater is avoided. The method also suppresses the problem of increased discharge of desulfurized tower wastewater caused by re-precipitation of chlorine evaporated through a high-temperature bypass flue. The method is suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the device system used in the method for removing sulfur trioxide from flue gas by coupling the desulfurization wastewater bypass flue evaporation provided in Example 1 of the present invention.

[0043] In the figure: 1-dust collector; 2-desulfurization tower; 3-chimney; 4-concentration device; 5-tempering separation device; 6-bypass flue evaporation device; 7-first gas-solid separation device; 8-solid storage device; 9-combustion boiler; 10-SCR denitrification device; 11-air preheater; 12-second gas-solid separation device; 13-fan. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0045] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0046] It should be understood that, in the description of the present invention, the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are 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 cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0047] It should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" 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 a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0048] Those skilled in the art should understand that the present invention necessarily includes necessary pipelines, conventional valves and general pump equipment for realizing a complete process, but the above content does not belong to the main inventive point of the present invention. Those skilled in the art can add layouts on their own based on the process flow and equipment structure selection, and the present invention does not make special requirements and specific limitations on this.

[0049] Example 1

[0050] This embodiment provides a method for removing sulfur trioxide from flue gas by evaporating desulfurization wastewater bypass flue. The schematic diagram of the device system used is as follows: Figure 1 shown.

[0051] The device system includes a boiler unit, a dust collector 1, a desulfurization tower 2 and a chimney 3 which are connected in sequence; the device system also includes a concentration device 4, a conditioning separation device 5 and a bypass flue evaporation device 6 which are connected in sequence to the desulfurization tower 2.

[0052] The bypass flue evaporation device 6 is connected to the first gas-solid separation device 7 and the solid storage device 8 in sequence.

[0053] The boiler unit comprises a combustion boiler 9 and a boiler flue; an SCR denitration device 10 and an air preheater 11 are sequentially arranged in the boiler flue along the flue gas flow direction.

[0054] The boiler flue at the front side of the air preheater 11 is connected to the bypass flue evaporation device 6 via the second gas-solid separation device 12 .

[0055] The first gas-solid separation device 7 is connected to the boiler flue at the rear side of the air preheater 11 via the fan 13 .

[0056] The method comprises the following steps:

[0057] (1) The desulfurized wastewater discharged from the desulfurization tower 2 enters the concentration device 4 for concentration treatment and then enters the conditioning and separation device 5. The first alkaline agent is first added to the conditioning and separation device 5 to adjust the pH of the desulfurized wastewater to 10, and then the suspended matter is separated and then injected into the bypass flue evaporation device 6 to become the first alkaline particulate matter;

[0058] The concentrator is a low-temperature multiple-effect evaporator; the first alkali agent is calcium hydroxide powder; the particle size of the first alkali agent is 50 μm;

[0059] The flue gas is the flue gas from before the air preheater 11; the flue gas enters the boiler flue after the air preheater 11 after heat and mass transfer with the desulfurization wastewater;

[0060] The flue gas before the air preheater 11 first enters the second gas-solid separation device 12 to separate the dust particles; the separated dust particles enter the ash hopper of the dust collector 1;

[0061] The bypass flue evaporation device 6 is a dual-fluid type flue evaporation device;

[0062] (2) The first alkaline particulate matter enters the first gas-solid separation device 7, and the separated flue gas enters the boiler flue after the air preheater 11 through the fan 13, and the separated alkaline particulate matter is sent to the solid storage device 8 for storage;

[0063] A second alkaline agent is added to the solid storage device 8 so that the chemical equivalent ratio of the alkaline substance sprayed into the flue gas by the particulate matter in the solid storage device 8 to the sulfur-containing substance in the flue gas reaches 5.5:1; the second alkaline agent is sodium hydroxide powder;

[0064] (3) After the particulate matter in the solid storage device 8 is ground to a particle size of 50 μm, it is injected into the front and rear sides of the SCR denitrification device 10 arranged in the boiler flue, reacting with SO3 in the boiler flue gas to remove SO3.

[0065] Example 2

[0066] This embodiment provides a method for removing sulfur trioxide from flue gas by evaporating desulfurization wastewater through a flue bypass, the method comprising the following steps:

[0067] (1) The desulfurization wastewater discharged from the desulfurization tower enters the concentration device for concentration treatment and then enters the conditioning separation device. The first alkaline agent is first added to the conditioning separation device to adjust the pH of the desulfurization wastewater to 9, and then the suspended matter is separated, and then injected into the bypass flue evaporation device to become the first alkaline particles;

[0068] The concentration device is a flue gas source direct contact evaporation concentration device; the first alkali agent is sodium hydroxide powder; the particle size of the first alkali agent is 50 μm;

[0069] The flue gas is the flue gas from before the air preheater; the flue gas enters the boiler flue after the air preheater after heat and mass transfer with the desulfurization wastewater;

[0070] The flue gas before the air preheater first enters the second gas-solid separation device to separate dust particles; the separated dust particles enter the slag bin;

[0071] The bypass flue evaporation device is a rotary atomization type flue evaporation device;

[0072] (2) The first alkaline particulate matter enters the first gas-solid separation device, and the separated flue gas enters the boiler flue after the air preheater through the fan, and the separated alkaline particulate matter is sent to the solid storage device for storage;

[0073] A second alkaline agent is added to the solid storage device so that the chemical equivalent ratio of the alkaline substance sprayed into the flue gas by the particulate matter in the solid storage device to the sulfur-containing substance in the flue gas reaches 6:1; the second alkaline agent is sodium hydroxide powder;

[0074] (3) After the particulate matter in the solid storage device is ground to a particle size of 50 μm, it is injected into the front and rear sides of the SCR denitrification device arranged in the boiler flue, respectively, to react with SO3 in the boiler flue gas and thereby remove SO3.

[0075] In summary, the method for removing sulfur trioxide from flue gas by coupling desulfurization wastewater bypass flue evaporation provided by the present invention is simple to operate, reasonably designed, and realizes waste treatment with waste; and avoids the adverse effects of main flue spray on the boiler exhaust system; the bypass flue evaporation device forms solid particles from the tempered desulfurization wastewater and sprays them into the front and rear sides of the SCR denitrification device, absorbs SO3 in the original flue gas at the boiler outlet and the newly added SO3 after catalysis by the catalyst, improves the SO3 removal efficiency, avoids the problem of easy clogging of liquid spray type nozzles spraying high-salt wastewater, and is suitable for large-scale promotion and application.

[0076] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for removing sulfur trioxide from flue gas by evaporation coupling of desulfurization wastewater bypass flue, characterized in that: The method comprises the following steps: (1) After the desulfurization wastewater discharged from the desulfurization tower enters the conditioning separation device for treatment, it is injected into the bypass flue evaporation device to exchange heat with the flue gas to form flue gas carrying alkaline particulate matter; (2) The flue gas carrying the alkaline particulate matter enters the first gas-solid separation device, the separated flue gas enters the boiler flue after the air preheater, and the separated alkaline particulate matter is sent to the solid storage device for storage; (3) The particulate matter in the solid storage device is respectively injected into the front and rear sides of the SCR denitrification device arranged in the boiler flue to react with SO3 in the boiler flue gas and thereby remove SO3.

2. The method according to claim 1, characterized in that The desulfurization wastewater in step (1) enters a concentration device for concentration treatment before entering a conditioning and separation device; Preferably, the concentration device comprises any one of a low-temperature multiple-effect evaporation concentration device, a flue gas source direct contact evaporation concentration device or an air source direct contact evaporation concentration device.

3. The method according to claim 1 or 2, characterized in that: The treatment steps of step (1) include: firstly adding a first alkaline agent into a conditioning separation device to adjust the pH of the desulfurization wastewater to 9-11, and then separating the suspended matter; Preferably, the first alkaline agent comprises any one of sodium hydroxide powder, calcium hydroxide powder or sodium carbonate powder, or a combination of at least two thereof; Preferably, the particle size of the first alkali agent is 25-50 μm.

4. The method according to any one of claims 1 to 3, characterized in that: The flue gas in step (1) includes the flue gas from before the air preheater; Preferably, the flue gas enters the boiler flue after the air preheater after heat and mass transfer with the desulfurization wastewater.

5. The method according to claim 4, characterized in that The flue gas before the air preheater first enters the second gas-solid separation device to separate dust particles; Preferably, the separated dust particles enter the dust collector ash hopper, slag bin or boiler flue before the dust collector.

6. The method according to any one of claims 1 to 5, characterized in that: The bypass flue evaporation device in step (1) includes a dual-fluid type flue evaporation device or a rotary atomization type flue evaporation device.

7. The method according to any one of claims 1 to 6, characterized in that: In step (2), a fan is also provided between the first gas-solid separation device and the boiler flue.

8. The method according to any one of claims 1 to 7, characterized in that: Adding a second alkaline agent into the solid storage device in step (2) so that the chemical equivalent ratio of the alkaline substance sprayed into the flue gas to the sulfur-containing substance in the flue gas reaches 5:1 or more; Preferably, the second alkaline agent comprises any one of sodium hydroxide powder, calcium hydroxide powder or sodium carbonate powder, or a combination of at least two thereof.

9. The method according to any one of claims 1 to 8, characterized in that: Before the particles in the solid storage device are sprayed in step (3), the particles in the solid storage device are ground to a particle size of 10 to 50 μm.

10. The method according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) The desulfurization wastewater discharged from the desulfurization tower enters the concentration device for concentration treatment and then enters the conditioning separation device. The first alkaline agent is first added to the conditioning separation device to adjust the pH of the desulfurization wastewater to 9-11, and then the suspended matter is separated. After that, it is injected into the bypass flue evaporation device to exchange heat with the flue gas to form flue gas carrying alkaline particles; The concentrator comprises any one of a low-temperature multiple-effect evaporation concentrator, a flue gas source direct contact evaporation concentrator or an air source direct contact evaporation concentrator; the first alkali agent comprises any one of sodium hydroxide powder, calcium hydroxide powder or sodium carbonate powder or a combination of at least two thereof; the particle size of the first alkali agent is 25 to 50 μm; The flue gas includes the flue gas from before the air preheater; the flue gas enters the boiler flue after the air preheater after heat and mass transfer with the desulfurization wastewater; The flue gas before the air preheater first enters the second gas-solid separation device to separate dust particles; the separated dust particles enter the dust collector ash hopper, slag bin or boiler flue before the dust collector; The bypass flue evaporation device includes a dual-fluid type flue evaporation device or a rotary atomization type flue evaporation device; (2) The flue gas carrying the alkaline particulate matter enters the first gas-solid separation device, and the separated flue gas enters the boiler flue after the air preheater through the fan, and the separated alkaline particulate matter is sent to the solid storage device for storage; Adding a second alkaline agent into the solid storage device so that the chemical equivalent ratio of the alkaline substance sprayed into the flue gas to the sulfur-containing substance in the flue gas reaches 5:1 or more; the second alkaline agent includes any one of sodium hydroxide powder, calcium hydroxide powder or sodium carbonate powder, or a combination of at least two thereof; (3) After the particulate matter in the solid storage device is ground to a particle size of 10 to 50 μm, it is injected into the front and rear sides of the SCR denitrification device arranged in the boiler flue, reacting with SO3 in the boiler flue gas to remove SO3.

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