Methanol engine flue gas treatment system and method

Abstract

The invention relates to the technical field of engine flue gas purification, and discloses a methanol engine flue gas treatment system and method.The methanol engine flue gas treatment system is characterized in that a methanol SCR denitration catalyst and an oxidation catalyst are sequentially arranged in a reactor from bottom to top, an inlet horn is arranged at the bottom of the reactor and connected with an inlet flue gas pipe, and an outlet horn is arranged at the top of the reactor and connected with an outlet flue gas pipe; a first baffle plate and a second baffle plate are arranged in the inlet horn, a flow equalizing plate is arranged at the lower part of the methanol SCR denitration catalyst, the methanol storage tank is connected with a methanol delivery pump through an inlet pipeline, and an outlet pipeline of the methanol delivery pump is connected with a spray gun. According to the device, two stages of baffle plates are arranged in the inlet horn, and the flow equalizing plate is arranged at the lower part of the methanol SCR denitration catalyst, so that uniform distribution of a flue gas flow field is realized, the problem that the utilization rate of the catalyst is reduced due to over-high or over-low local flow velocity is avoided, and the surface flow velocity distribution standard deviation of a catalyst layer is controlled within 5%; the overall denitration efficiency is obviously improved.

Description

Technical Field

[0001] This invention relates to the field of engine exhaust purification, and in particular to a methanol engine exhaust treatment system and method. Background Technology

[0002] With increasingly stringent environmental regulations, methanol engines, as a clean alternative power system, are seeing a decline in nitrogen oxides (NOx) in their exhaust gases. x The synergistic purification of unburned methanol, formaldehyde, CO, and HC has become a research hotspot. Currently, there are already published patents related to flue gas treatment technologies for methanol engines.

[0003] Patent CN203009055U discloses an emission control system for an engine, including an alcohol fuel engine, a reducing catalyst, and an oxidizing catalyst. It utilizes the HC and CO generated in the engine from the alcohol fuel, and in the reducing catalyst, HC is converted into NO. x The system reduces pollutants, then treats the remaining contaminants using an oxidizing catalyst. The drawback of this system is that the reducing agent relies entirely on HC generated by engine combustion and cannot be adjusted based on NO. x The concentration changes actively adjust the supply of reducing agent. When the engine operating conditions fluctuate and the reducing agent in the flue gas is insufficient, the denitrification efficiency drops significantly. Furthermore, the flue gas flow field is not optimized, which can easily lead to a decrease in catalyst utilization due to uneven airflow distribution.

[0004] Patent CN116265113A discloses an integrally extruded molecular sieve-based methanol-SCR denitration catalyst, in which NO is disposed on the same matrix. x The reduction zone and CO oxidation zone exhibit high denitrification activity when methanol is used as the reducing agent. This patent focuses on improving the catalyst material but does not address the complete flue gas treatment system design. In particular, it fails to solve the problem of uniform mixing between methanol injection and flue gas, nor does it provide a solution for replenishing the reducing agent when it is insufficient. Therefore, it is difficult to guarantee stable denitrification performance in practical applications.

[0005] Patent CN03813986.3 discloses a catalyst and method for purifying waste gas, using protonated β-zeolite as a catalyst to reduce and remove NO from waste gas containing excess oxygen in the presence of methanol and / or dimethyl ether. x This patent also focuses on catalyst formulation, without addressing system integration and flow field optimization. Furthermore, it does not consider the deep oxidation of residual pollutants such as methanol, formaldehyde, HC, and CO in the flue gas after denitrification. Additionally, there is a risk of uneven mixing of methanol and flue gas leading to localized excess or deficiency of reducing agent.

[0006] The aforementioned existing technologies generally suffer from the following drawbacks: First, they lack a design for homogenizing the flue gas flow field within the reactor, resulting in low catalyst utilization and uneven local reactions; second, the supply method of the methanol reducing agent is singular, failing to consider the relationship between methanol and NO in the flue gas.x The following issues were identified: 1) The ratio was dynamically adjusted; 2) The problem of rapid and uniform mixing of methanol with flue gas after injection was not solved, affecting denitrification efficiency; 3) When using the NH3-SCR route, there is a risk of secondary pollution from ammonia escape and reaction with formaldehyde to generate highly toxic HCN.

[0007] Therefore, there is an urgent need to develop a methanol engine flue gas treatment system that features uniform flow field, adjustable reducing agent, high mixing efficiency, and no secondary pollution. Summary of the Invention

[0008] The purpose of this invention is to provide a methanol engine flue gas treatment system and method. This system achieves denitrification treatment of methanol flue gas by using waste to treat waste, while avoiding secondary pollution, through flow field optimization structure, adjustable methanol supplement injection device and high-efficiency mixer.

[0009] The technical solution adopted in this invention is: A methanol engine flue gas treatment system includes a reactor, an inlet flue, an inlet horn, an outlet horn, an outlet flue, a methanol storage tank, a methanol transfer pump, a spray gun, and a mixer. The reactor contains a methanol SCR denitrification catalyst and an oxidation catalyst arranged sequentially from bottom to top. The inlet horn is located at the bottom of the reactor and connected to the inlet flue. The outlet horn is located at the top of the reactor and connected to the outlet flue. The inlet horn contains a first baffle and a second baffle. The first and second baffles have identical structures, each consisting of an upper support, plates, and a lower support, and are welded to the inner wall of the inlet horn. The included angle α between the plates is [value missing]. At an angle of 30-45°, a flow equalization plate is provided at the bottom of the methanol SCR denitrification catalyst. The flow equalization plate has a porous plate structure with uniformly arranged round holes on the plate surface and an opening rate of 30%-50%. The methanol storage tank is connected to a methanol delivery pump through an inlet pipe. The outlet pipe of the methanol delivery pump is connected to a spray gun. The spray gun is set on the inlet flue pipe. A mixer is provided in the inlet flue pipe at the rear end of the spray gun. The mixer is composed of multiple Venturi tubes. Each Venturi tube includes an upper constriction, a throat, and a lower constriction. The Venturi tubes are welded to the first support plate and the second support plate. The first support plate and the second support plate are welded to the inner wall of the inlet flue pipe.

[0010] By adopting the above structure, the device achieves a uniform distribution of flue gas flow field by setting two-stage baffles in the inlet horn and a flow equalization plate under the methanol SCR denitrification catalyst. This avoids the problem of reduced catalyst utilization caused by excessively high or low local flow velocities, and controls the standard deviation of the flow velocity distribution on the catalyst layer surface to within 5%, thus significantly improving the overall denitrification efficiency.

[0011] Preferably, the methanol SCR denitration catalyst is a noble metal-based catalyst or a zeolite-based catalyst with an activity temperature window of 300~400℃, and the oxidation catalyst is a noble metal-based catalyst with an activity temperature window of 300~400℃.

[0012] By using methanol as a reducing agent, based on the methanol / NO ratio in the flue gas x The molar ratio dynamically determines whether methanol needs to be added. When the methanol in the flue gas is insufficient, it is actively added through the injection system, realizing a denitrification mode of treating waste with waste. There is no need to introduce a urea storage, dissolution and injection system, which simplifies the system structure and reduces operating costs.

[0013] Preferably, a regulating valve is provided on the outlet pipeline of the methanol transfer pump, and ball valves are provided in the pipelines before, after and in parallel with the regulating valve.

[0014] By adopting the above structure, it is easy to carry out online maintenance of the control valve.

[0015] Preferably, the spray gun consists of a liquid inlet, a gas inlet, and a nozzle.

[0016] By adopting the above structure, it is easy to spray methanol into divergent fine droplets.

[0017] Preferably, the mixer consists of 7 Venturi tubes arranged in a ring, with the ratio of the throat diameter to the inlet flue diameter being 1:3 to 1:5, the upper constriction angle being 20 to 30°, the lower constriction expansion angle being 8 to 15°, and the throat length-to-diameter ratio being 1 to 2.

[0018] By adopting the above structure, a mixer made of a venturi tube is set at the rear end of the spray gun. The local low-pressure zone formed by the high-speed airflow at the throat of the venturi tube causes the injected methanol droplets to be broken up in a secondary manner, forming fine droplets with a particle size D90 < 100 μm. This accelerates the vaporization of methanol and avoids the "wet wall" phenomenon and local overheating problem caused by the direct impact of liquid methanol on the catalyst surface. The mixing uniformity of methanol and flue gas is increased to more than 95%.

[0019] Preferably, a level gauge is installed on the upper part of the methanol storage tank, and a pressure transmitter and a flow meter are installed on the outlet pipeline of the methanol transfer pump.

[0020] Preferably, both the inlet and outlet flue pipes are equipped with temperature transmitters, pressure transmitters, and online monitoring; the methanol SCR denitrification catalyst and the oxidation catalyst are both equipped with temperature transmitters and pressure transmitters at their lower parts.

[0021] Preferably, the treatment method of the methanol engine flue gas treatment system includes the following steps: Step 1: The flue gas generated by the methanol engine enters the reactor through the inlet flue and the inlet horn. The flue gas flow field is evenly distributed through the guiding effect of the first baffle and the second baffle and the rectification effect of the flow equalization plate. Step 2: The homogenized flue gas enters the methanol SCR denitrification catalyst layer, where methanol is used as a reducing agent to react with NO in the flue gas. xA selective catalytic reduction reaction occurs, reducing NO... x It is reduced to N2, CO2 and H2O; Step 3: The denitrified flue gas enters the oxidation catalyst layer, where the remaining methanol, formaldehyde, HC, and CO in the flue gas are oxidized into CO2 and H2O under the action of the oxidation catalyst. Step 4: The purified flue gas is discharged through the outlet horn and outlet flue pipe; Among them, when the methanol / NO in the flue gas x When the molar ratio is higher than a set threshold, methanol in the flue gas is used directly as a reducing agent. x When the molar ratio is lower than the set threshold, the methanol delivery pump is started to draw methanol from the methanol storage tank and spray it into the inlet flue pipe through the spray gun. After being uniformly mixed with the flue gas by the mixer, it enters the reactor.

[0022] Preferably, the selective catalytic reduction reaction temperature in step 2 is 300~400℃, and the oxidation reaction temperature in step 3 is 300~400℃.

[0023] Preferably, the methanol injected by the spray gun is atomized into divergent fine droplets by compressed air, and then fully and evenly mixed with the flue gas by the turbulent effect of the Venturi mixer.

[0024] By adopting the above method, compared with the traditional NH3-SCR route, this invention uses methanol as a reducing agent, which avoids the introduction of ammonia at the source and completely eliminates the risk of secondary pollution from ammonia escape and reaction with formaldehyde in flue gas to produce highly toxic HCN, making it more environmentally friendly.

[0025] Compared with the prior art, the present invention has the following advantages: 1. The device of the present invention achieves uniform distribution of flue gas flow field by setting two-stage baffles in the inlet horn and setting a flow equalization plate under the methanol SCR denitrification catalyst, avoiding the problem of reduced catalyst utilization caused by excessively high or low local flow velocities, and controlling the standard deviation of the flow velocity distribution on the catalyst layer surface within 5%, which significantly improves the overall denitrification efficiency.

[0026] 2. The system of this invention uses methanol as a reducing agent, based on the methanol / NO content in the flue gas. x The molar ratio dynamically determines whether methanol needs to be added. When the methanol in the flue gas is insufficient, it is actively added through the injection system, realizing a denitrification mode of treating waste with waste. There is no need to introduce a urea storage, dissolution and injection system, which simplifies the system structure and reduces operating costs.

[0027] 3. The device of the present invention has a mixer made of a venturi tube at the rear end of the spray gun. The local low-pressure zone formed by the high-speed airflow at the throat of the venturi tube causes the injected methanol droplets to be broken up in a secondary manner, forming fine droplets with a particle size D90 < 100 μm. This accelerates the vaporization of methanol and avoids the "wet wall" phenomenon and local overheating problem caused by the direct impact of liquid methanol on the catalyst surface. The mixing uniformity of methanol and flue gas is increased to more than 95%.

[0028] 4. Compared with the traditional NH3-SCR route, the present invention uses methanol as a reducing agent, which avoids the introduction of ammonia at the source and completely eliminates the risk of secondary pollution from ammonia escape and reaction with formaldehyde in flue gas to produce highly toxic HCN, making it more environmentally friendly.

[0029] 5. The system of this invention is equipped with a complete detection and control unit, including a temperature transmitter, a pressure transmitter, online detection, a flow meter and a level gauge, which can monitor the temperature, pressure and pollutant concentration of each section in real time; at the same time, the design of the parallel bypass of the regulating valve realizes the online maintenance function, which significantly improves the system's operational reliability and maintenance convenience. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a schematic diagram of the mixer of the present invention; Figure 3 This is a schematic diagram of the Venturi tube structure of the present invention; Figure 4 This is a schematic diagram of the baffle structure of the present invention; Figure 5 This is a schematic diagram of the plate structure of the present invention; Figure 6 This is a schematic diagram of the flow equalization plate of the present invention.

[0031] The components include: 1. Reactor; 2. Inlet flue; 3. Inlet horn; 4. First baffle; 4-1. Upper support; 4-2. Plate; 4-3. Lower support; 5. Second baffle; 6. Flow equalization plate; 6-1. Circular hole; 7. Methanol SCR denitrification catalyst; 8. Oxidation catalyst; 9. Outlet horn; 10. Outlet flue; 11. Methanol storage tank; 12. Inlet pipe; 13. Ball valve; 14. Methanol transfer pump; 15. Outlet. 16. Pipeline; 17. Control valve; 18. Spray gun; 19. Liquid inlet; 10. Gas inlet; 11. Nozzle; 12. Mixer; 23. Level gauge; 24. Pressure transmitter; 25. Temperature transmitter; 26. Online monitoring; 27. Venturi tube; 28. Upper constriction; 29. ​​Throat; 20. Lower constriction; 21. First support plate; 22. Second support plate; 23. Flow meter. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0033] This invention optimizes the baffle angle, flow equalization plate opening ratio, and Venturi tube structural parameters through fluid dynamics (CFD) simulation. Simulation results show that when the plate angle α is 30~45°, eddies at the inlet horn can be effectively eliminated; when the flow equalization plate 6 opening ratio is 30%~50%, the standard deviation of the velocity distribution on the catalyst layer surface is less than 5%; when the ratio of the throat pipe 23-2 diameter to the inlet flue pipe 2 diameter is 1:3~1:5, the contraction angle is 20~30°, and the expansion angle is 8~15°, the mixing uniformity of methanol and flue gas reaches over 95%. The above parameter combination ensures the optimal performance of the system. Example 1

[0034] like Figure 1 As shown, this embodiment provides a methanol engine flue gas treatment system, including a reactor 1, an inlet flue pipe 2, an inlet horn 3, an outlet horn 9, an outlet flue pipe 10, a methanol storage tank 11, a methanol transfer pump 14, a spray gun 17, and a mixer 18.

[0035] Inside reactor 1, methanol SCR denitration catalyst 7 and oxidation catalyst 8 are arranged sequentially from bottom to top. In this embodiment, methanol SCR denitration catalyst 7 is a noble metal-based catalyst (Pd / Al2O3), and oxidation catalyst 8 is a noble metal-based catalyst (Pt / Al2O3), both with an activity temperature window of 300~400℃. An inlet horn 3 is located at the bottom of reactor 1 and connected to the inlet flue pipe 2, while an outlet horn 9 is located at the top of reactor 1 and connected to the outlet flue pipe 10.

[0036] To ensure a uniform flue gas flow field entering reactor 1, a first baffle 4 and a second baffle 5 are installed inside the inlet horn 3. Figure 4 , Figure 5 As shown, the first baffle plate 4 and the second baffle plate 5 have the same structure, both consisting of an upper support 4-1, plates 4-2, and a lower support 4-3, and are welded to the inner wall of the inlet horn 3. The included angle α of the plates 4-2 is 30~45°. A flow equalization plate 6 is provided at the bottom of the methanol SCR denitrification catalyst 7, as shown... Figure 6 As shown, the flow equalization plate 6 is a perforated plate structure with evenly distributed circular holes 6-1 on its surface, resulting in an opening rate of 40%. The flow equalization plate 6 is welded to the inner wall plate of the reactor 1. After being guided by two stages of baffles, the flue gas is then rectified by the flow equalization plate 6, which can effectively eliminate eddies and flow deviations, achieving uniform distribution.

[0037] A level gauge 19 is installed on the upper part of the methanol storage tank 11 to observe the methanol level inside the tank. The methanol storage tank 11 is connected to the methanol transfer pump 14 through the inlet pipe 12, which is equipped with a ball valve 13. The outlet pipe 15 of the methanol transfer pump 14 is equipped with a regulating valve 16, a pressure transmitter 20, and a flow meter 24 for detecting methanol pressure and flow rate. Ball valves 13 are installed before and after the regulating valve 16 and in its parallel pipes. When the regulating valve 16 fails, the ball valves 13 before and after the regulating valve 16 are closed, and the ball valves 13 in its parallel pipes are opened, enabling online maintenance of the regulating valve 16.

[0038] Methanol delivery pump 14 and outlet pipe 15 are connected to spray gun 17, which is installed on inlet flue pipe 2. Spray gun 17 consists of liquid inlet 17-1, gas inlet 17-2 and nozzle 17-3. Compressed air enters from gas inlet 17-2, mixes with methanol entering from liquid inlet 17-1 and atomizes it, and sprays it out from nozzle 17-3 to form divergent fine droplets, which is beneficial to the methanol SCR denitrification reaction.

[0039] A mixer 18 is installed inside the inlet flue 2 at the rear end of the spray gun 17. (Combined) Figure 2 , Figure 3 In this embodiment, the mixer 18 consists of a ring structure composed of seven Venturi tubes 23. Each Venturi tube 23 includes an upper constriction 23-1, a throat 23-2, and a lower constriction 23-3, which are welded to a first support plate 23-4 and a second support plate 23-5 to form the mixer 18. The first support plate 23-4 and the second support plate 23-5 are welded to the inner wall of the inlet flue pipe 2. The diameter of the throat 23-2 of the Venturi tube 23 is designed to be 1 / 3 to 1 / 5 of the inner diameter of the inlet flue pipe 2. The constriction angle of the upper constriction 23-1 is 25°, the expansion angle of the lower constriction 23-3 is 12°, and the ratio of the throat length to the throat diameter is 1.5 to achieve the best turbulent mixing effect. When the flue gas carrying the injected methanol droplets passes through the Venturi tube 23, the flow velocity and turbulence intensity increase at the throat 23-2, allowing the methanol and flue gas to mix thoroughly and evenly, which is beneficial for the subsequent denitrification reaction.

[0040] The Venturi mixer 18 of the present invention not only achieves physical mixing, but also the local low-pressure zone formed by the high-speed airflow in its throat helps to break up the injected methanol droplets into smaller droplets (particle size D90<100μm), which accelerates the vaporization of methanol and avoids the "wet wall" phenomenon and local overheating problem caused by the direct impact of liquid methanol on the catalyst surface.

[0041] Temperature transmitters 21 and pressure transmitters 20, as well as online detectors 22, are installed on both the reactor inlet flue 2 and outlet flue 10. These are used for temperature and pressure detection, respectively, while the online detectors primarily detect methanol, formaldehyde, and NO in the flue gas. xHCl, CO, H2O. Temperature transmitters 21 and pressure transmitters 20 are installed at the bottom of both the methanol SCR denitrification catalyst 7 and the oxidation catalyst 8. These transmitters can detect the temperature of flue gas in each section and calculate the operating resistance of each section based on the pressure difference.

[0042] The working process of this embodiment is as follows: The exhaust gas (temperature 300~400℃) produced by the methanol engine enters the system through inlet flue 2. Online detector 22 monitors the methanol and NO content in the exhaust gas in real time. x Concentration. When the methanol / NOx ratio in the flue gas... x When the molar ratio is higher than the set threshold, methanol in the flue gas is directly used as a reducing agent: the flue gas is guided by the first baffle 4 and the second baffle 5 inside the inlet horn 3, rectified by the flow equalization plate 6, and then uniformly enters the methanol SCR denitrification catalyst layer 7. Methanol and NO x A selective catalytic reduction reaction occurs, reducing NO... x The flue gas is reduced to N2, CO2 and H2O; after denitrification, the flue gas enters the oxidation catalyst layer 8, which oxidizes the remaining methanol, formaldehyde, HC and CO in the flue gas into CO2 and H2O; after purification, the flue gas is discharged through the outlet horn 9 and the outlet flue pipe 10.

[0043] When online detector 22 measured the methanol / NO in the flue gas x When the molar ratio is lower than the set threshold, the methanol delivery pump 14 is started to draw methanol from the methanol storage tank 11. After the flow rate is adjusted by the regulating valve 16, the methanol is sent to the spray gun 17 and sprayed into the inlet flue pipe 2. The injected methanol and flue gas are thoroughly mixed by the Venturi mixer 18 and then enter the reactor 1 for denitrification and oxidation treatment according to the above process.

[0044] During system operation in this embodiment, each temperature transmitter 21 monitors the temperature of each segment in real time to ensure that the reaction temperature is within the range of 300~400℃; the pressure transmitter 20 monitors the pressure at each point and calculates the resistance of each segment. When the resistance exceeds the set value, it prompts for system fault troubleshooting; the online detector 22 monitors the pollutant concentration at the emission outlet to ensure that the emission meets the standards. Example 2

[0045] This embodiment is basically the same as Example 1, except for the selection of catalyst and adjustment of porosity.

[0046] In this embodiment, the methanol SCR denitration catalyst 7 is a zeolite-based catalyst (Cu-SSZ-13), and the oxidation catalyst 8 is still a noble metal-based catalyst (Pt-Pd / CeO2-ZrO2), with an activity temperature window of 300~400℃ for both. The porosity of the flow equalization plate 6 is adjusted to 30%.

[0047] The mixer 18 still consists of 7 venturi tubes 23, but the diameter of the throat 23-2 of the venturi tube 23 is reduced by 10% compared with Example 1 to increase the turbulence intensity and make it suitable for conditions with a large methanol injection volume.

[0048] The working process in this embodiment is the same as in Example 1. Because zeolite-based catalysts have better hydrothermal stability, this embodiment is suitable for methanol engines operating under conditions of large load fluctuations and frequent flue gas temperature changes. Example 3

[0049] This embodiment is basically the same as Embodiment 1, except that the opening ratio of the flow equalization plate is adjusted and the mixer structure is optimized.

[0050] In this embodiment, the opening ratio of the flow equalization plate 6 is adjusted to 50%, which is suitable for scenarios with low dust content in flue gas and strict requirements for flow resistance.

[0051] The length of the throat 23-2 of the venturi tube 23 of the mixer 18 is increased by 20% compared with Example 1, so as to prolong the residence time of flue gas and methanol in the turbulent zone and further improve the mixing uniformity.

[0052] In this embodiment, the methanol SCR denitration catalyst 7 is a noble metal-based catalyst (Pt-Pd / Al2O3), and the oxidation catalyst 8 is a noble metal-based catalyst (Pt / CeO2-Al2O3), both with an activity temperature window of 300~400℃.

[0053] The working process of this embodiment is the same as that of Embodiment 1. By increasing the number of venturi tubes and extending the throat length, the mixing effect of methanol and flue gas is better, which is especially suitable for working conditions where the methanol injection volume fluctuates greatly and a rapid response is required.

[0054] This invention's device achieves a uniform distribution of the flue gas flow field by installing two-stage baffles inside the inlet horn 3 and a flow equalization plate below the methanol SCR denitrification catalyst. This avoids the problem of reduced catalyst utilization caused by excessively high or low local flow velocities, and controls the standard deviation of the flow velocity distribution on the catalyst layer surface to within 5%, significantly improving the overall denitrification efficiency. The system uses methanol as a reducing agent, based on the methanol / NO ratio in the flue gas... xThe system dynamically determines whether methanol needs to be added based on the molar ratio. When methanol in the flue gas is insufficient, it is actively added via an injection system, achieving a waste-to-waste denitrification mode. This eliminates the need for urea storage, dissolution, and injection systems, simplifying the system structure and reducing operating costs. A mixer 18, composed of a Venturi tube, is installed at the rear end of the spray gun 17. Utilizing the localized low-pressure zone created by the high-speed airflow at the throat of the Venturi tube, the injected methanol droplets undergo secondary breakage, forming fine droplets with a particle size D90 < 100 μm. This accelerates methanol vaporization and avoids the "wet wall" phenomenon and localized overheating problems caused by liquid methanol directly impacting the catalyst surface. The mixing uniformity of methanol and flue gas is increased to over 95%. Compared to the traditional NH3-SCR route, this invention uses methanol as a reducing agent, avoiding the introduction of ammonia at the source and completely eliminating the secondary pollution risk of ammonia escape reacting with formaldehyde in the flue gas to produce highly toxic HCN, resulting in superior environmental friendliness. The system is equipped with a complete detection and control unit, including a temperature transmitter 21, a pressure transmitter 20, an online detector 22, a flow meter 24, and a level gauge 19, which can monitor the temperature, pressure, and pollutant concentration of each section in real time. At the same time, the parallel bypass design of the regulating valve 16 enables online maintenance, which significantly improves the system's operational reliability and ease of maintenance.

[0055] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should be included within the scope of protection defined by the claims of the present invention.

Claims

1. A methanol engine flue gas treatment system, comprising a reactor, an inlet flue pipe, an inlet horn, an outlet horn, an outlet flue pipe, a methanol storage tank, a methanol transfer pump, a spray gun, and a mixer, characterized in that: The reactor contains a methanol SCR denitrification catalyst and an oxidation catalyst arranged sequentially from bottom to top. The inlet horn is located at the bottom of the reactor and connected to the inlet flue pipe, while the outlet horn is located at the top of the reactor and connected to the outlet flue pipe. The inlet horn contains a first baffle and a second baffle. The first and second baffles have identical structures, each consisting of an upper support, plates, and a lower support, and are welded to the inner wall of the inlet horn. The included angle α between the plates is 30° to 45°. A flow equalization plate is located below the methanol SCR denitrification catalyst. The flow equalization plate is a perforated plate structure with evenly distributed round holes on the plate surface, and the opening rate is 30%~50%. The methanol storage tank is connected to a methanol delivery pump through an inlet pipe, and the outlet pipe of the methanol delivery pump is connected to a spray gun. The spray gun is set on the inlet flue pipe, and a mixer is provided in the inlet flue pipe at the rear end of the spray gun. The mixer is composed of multiple venturi tubes, each venturi tube including an upper constriction, a throat, and a lower constriction. The venturi tubes are welded to the first support plate and the second support plate, and the first support plate and the second support plate are welded to the inner wall of the inlet flue pipe.

2. The methanol engine flue gas treatment system according to claim 1, characterized in that: The methanol SCR denitration catalyst is a noble metal-based catalyst or a zeolite-based catalyst with an activity temperature window of 300~400℃, and the oxidation catalyst is a noble metal-based catalyst with an activity temperature window of 300~400℃.

3. The methanol engine flue gas treatment system according to claim 1, characterized in that: A regulating valve is installed on the outlet pipeline of the methanol transfer pump, and ball valves are installed in the pipelines before, after and in parallel with the regulating valve.

4. The methanol engine flue gas treatment system according to claim 1, characterized in that: The spray gun consists of a liquid inlet, a gas inlet, and a nozzle.

5. The methanol engine flue gas treatment system according to claim 1, characterized in that: The mixer consists of 7 Venturi tubes, with the ratio of the throat diameter to the inlet flue diameter being 1:3 to 1:

5. The upper constriction angle is 20 to 30°, and the lower constriction expansion angle is 8 to 15°. The length-to-diameter ratio of the throat tubes, i.e., the length of the throat tube / the diameter of the throat tube, is 1 to 2.

6. The methanol engine flue gas treatment system according to claim 1, characterized in that: The methanol storage tank is equipped with a level gauge at the top, and the methanol transfer pump outlet pipeline is equipped with a pressure transmitter and a flow meter.

7. The methanol engine flue gas treatment system according to claim 1, characterized in that: Temperature transmitters, pressure transmitters, and online monitoring are installed on both the inlet and outlet flue pipes; temperature transmitters and pressure transmitters are installed at the bottom of both the methanol SCR denitrification catalyst and the oxidation catalyst.

8. The treatment method of the methanol engine flue gas treatment system according to any one of claims 1-7, characterized in that: Includes the following steps: Step 1: The flue gas generated by the methanol engine enters the reactor through the inlet flue and the inlet horn. The flue gas flow field is evenly distributed through the guiding effect of the first baffle and the second baffle and the rectification effect of the flow equalization plate. Step 2: The homogenized flue gas enters the methanol SCR denitrification catalyst layer, where methanol is used as a reducing agent to react with NO in the flue gas. x A selective catalytic reduction reaction occurs, reducing NO... x It is reduced to N2, CO2 and H2O; Step 3: The denitrified flue gas enters the oxidation catalyst layer, where the remaining methanol, formaldehyde, HC, and CO in the flue gas are oxidized into CO2 and H2O under the action of the oxidation catalyst. Step 4: The purified flue gas is discharged through the outlet horn and outlet flue pipe; Among them, when the methanol / NO in the flue gas x When the molar ratio is higher than a set threshold, methanol in the flue gas is used directly as a reducing agent. x When the molar ratio is lower than the set threshold, the methanol delivery pump is started to draw methanol from the methanol storage tank and spray it into the inlet flue pipe through the spray gun. After being uniformly mixed with the flue gas by the mixer, it enters the reactor.

9. The treatment method of a methanol engine flue gas treatment system according to claim 8, characterized in that: The selective catalytic reduction reaction temperature in step 2 is 300~400℃, and the oxidation reaction temperature in step 3 is 300~400℃.

10. The treatment method of a methanol engine flue gas treatment system according to claim 8, characterized in that: The methanol injected by the spray gun is atomized into divergent fine droplets by compressed air, and then fully and evenly mixed with the flue gas by the turbulent effect of the Venturi mixer.

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