Ultralow-temperature denitration system for flue gas reuse and denitration enhancement
By adopting flue gas reuse technology in the flue gas denitrogenation system of small boiler, the problem that low-temperature flue gas is difficult to meet the catalyst reaction temperature is solved, efficient flue gas denitrogenation is achieved, the denitrification effect and efficiency are improved, and pollutant emissions are reduced.
Patent Information
- Application Number
- CN202421684394.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-17
- Publication Date
- 2025-05-30
- Estimated Expiration
- 2034-07-17
AI Technical Summary
The smoke exhaust temperature of existing small boilers is low, and the temperature of ammonia water is also low after vaporization, which makes it difficult for the mixed flue gas temperature to meet the reaction temperature required by the catalyst, resulting in poor denitrification effect and low denitrification efficiency.
The ultra-low temperature denitrification system is adopted to strengthen denitrification by mixing the reflux of flue gas after denitrification with the vaporized ammonia gas to increase the temperature of the vaporized ammonia gas to ensure that the mixed flue gas reaches the reaction temperature required by the catalyst (above 200℃), thereby improving the denitrification effect and efficiency.
Through the flue gas reuse technology, the denitrification reaction temperature is increased, the denitrification effect and efficiency are significantly improved, the emission of ammonia and NOx is reduced, the utilization rate of ammonia water is increased, and the use of ammonia water is reduced.
Smart Images
Figure CN222918456U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of flue gas denitrification, in particular to an ultra-low temperature denitrification system for enhancing denitrification by recycling flue gas. Background Art
[0002] In recent years, the environmental protection problems in the coal gasification industry have attracted more and more attention. Among them, the emission problem of flue gas, which is one of the main sources of air pollution, has always been the focus of research in the environmental protection field. NOx is a general term for a series of nitrogen oxides, including NO, N 2 O, N 2 O 5 、N 2 O 4 and N 2 O 3 。NOx can be divided into anthropogenic NOx and natural NOx according to its source. The emissions of NOx from coal-fired flue gas account for 70% of the anthropogenic emission sources of NOx. Therefore, the NOx emissions during the coal combustion process are the key objects we control. More than 95% of the NOx in coal-fired flue gas is in the form of NO, and among the remaining 5% of NOx, mainly NO 2 。The NOx (including SOx) emitted into the atmosphere is the main factor causing acid rain. In addition to acid rain, these acidic substances can also form "acid snow", "acid fog" and "acid frost" along with snowfall, fog and frost. Even in dry climates, these acidic substances can still settle in the form of dust and smoke. The acidic substances falling into rivers, lakes and seas change their pH values, which seriously affects the survival of animals and plants in the landing areas and destroys the ecological system.
[0003] There are many types of flue gas denitrification technologies, mainly including selective catalytic reduction (SCR), non-selective catalytic reduction (SNCR), wet methods, etc. Selective catalytic reduction and selective non-catalytic reduction are the two most commonly used NOx gas pollution control devices. Among them, the ammonia catalytic reduction method is the most widely used technology. It has no by-products, does not form secondary pollution, has a simple device structure, and has a high removal efficiency (up to more than 90%), reliable operation, and is easy to maintain. Nowadays, SCR technology and SNCR+SCR combined technology for post-combustion NOx treatment of coal combustion have become the standard configurations in the field of NOx treatment. However, SNCR and SCR denitrification technologies have high requirements for the reaction temperature. The SNCR denitrification technology requires the reaction temperature to be around 850-1100°C, and the SCR denitrification technology requires the reaction temperature to be around 320-420°C. Although there are individual catalysts in SCR denitrification technology whose reaction temperature can be reduced to around 200°C, for small gas boilers, their flue gas discharge temperature is relatively low (within the range of the reaction temperature required by the catalyst), and the temperature after ammonia vaporization is also low (less than 200°C). Therefore, after the vaporized ammonia gas is mixed with the flue gas, the temperature of the mixed flue gas before the catalyst reaction is greatly reduced, resulting in problems such as the difficulty of the mixed flue gas temperature to meet the reaction temperature required by the catalyst, poor denitrification effect, and low denitrification efficiency. Utility Model Content
[0004] The utility model provides an ultra-low temperature denitrification system for enhancing denitrification by recycling flue gas to solve the problems that the flue gas discharge temperature of existing small boilers is relatively low, and the temperature after ammonia vaporization is also low, resulting in the difficulty of the mixed flue gas temperature to meet the reaction temperature required by the catalyst, poor denitrification effect, and low denitrification efficiency.
[0005] The utility model provides an ultra-low temperature denitrification system for enhancing denitrification by recycling flue gas, including: a denitrification unit, an ammonia unit, and an emission unit; the denitrification unit includes a boiler, an ammonia injection mixer, a denitrification reactor, and an economizer connected in sequence through a flue gas pipeline; the flue gas outlet of the economizer is connected to the emission unit, and a flue gas on-line detection element is provided on the flue gas pipeline of the economizer; the ammonia unit includes an ammonia water storage tank, an ammonia distillation tower, a pipeline mixer, and a flue gas circulation fan. The inlet of the ammonia distillation tower is connected to the outlet of the ammonia water storage tank, and the outlet of the ammonia distillation tower is connected to the vaporized ammonia gas inlet of the pipeline mixer; the inlet of the flue gas circulation fan is connected to the flue gas pipeline between the denitrification reactor and the economizer, the outlet of the flue gas circulation fan is connected to the denitrification flue gas inlet of the pipeline mixer, and the ammonia-smoke mixed gas outlet of the pipeline mixer is connected to the inlet of the ammonia injection mixer.
[0006] Preferably, the emission unit includes a dust collector, a desulfurization device, a suction fan, and a chimney connected in sequence.
[0007] Preferably, the pipeline mixer includes a housing. The two ends of the housing are respectively connected with a vaporized ammonia inlet and an ammonia-smoke mixture outlet. A denitrification flue gas inlet is connected to the side wall of the housing near the vaporized ammonia inlet. The housing between the vaporized ammonia inlet and the ammonia-smoke mixture outlet is composed of a tapered pipe, a small-diameter pipe, a divergent pipe, and a large-diameter pipe connected in series. The tapered pipe and the divergent pipe are concentric reducers with the same shape and size. The diameters of the flared ends of the tapered pipe and the divergent pipe are the same as those of the large-diameter pipe, the vaporized ammonia inlet, and the ammonia-smoke mixture outlet. The diameters of the reduced ends of the tapered pipe and the divergent pipe are the same as the diameter of the small-diameter pipe.
[0008] Preferably, a mixing element is provided in the small-diameter pipe. The mixing element includes a bracket, a first impeller, a second impeller, and an impeller connecting shaft. The bracket is a three-pronged bracket. The end of the bracket is fixedly connected to the pipe wall of the small-diameter pipe. The center of the bracket has a through hole. Two impeller connecting shafts are respectively connected to the front and rear sides of the bracket. Each impeller connecting shaft is fixed in the through hole through a bearing. The first impeller is fixedly connected to the end of the front-side impeller connecting shaft, and the second impeller is fixedly connected to the end of the rear-side impeller connecting shaft.
[0009] Preferably, the installation directions of the first impeller and the second impeller are opposite; the diameter of the first impeller is smaller than that of the second impeller.
[0010] Preferably, a plurality of flow disturbing members are provided on the inner wall of the divergent pipe. The flow disturbing members are arranged at intervals along the axial direction of the divergent pipe.
[0011] Preferably, spiral blades are provided on the inner wall of the large-diameter pipe. The outer side wall of the spiral blades is connected to the inner wall of the large-diameter pipe. A plurality of ventilation holes are evenly formed in the spiral blades.
[0012] Preferably, the pitch of the spiral blades gradually decreases first and then gradually increases along the fluid flow direction.
[0013] The ultra-low temperature denitrification system for enhancing denitrification by flue gas recycling provided by the present utility model improves the temperature of the vaporized ammonia by using the denitrified flue gas for reflux and mixing it with the vaporized ammonia, ensuring that the mixed flue gas can reach the reaction temperature required by the catalyst (above 200 °C), and improving the denitrification effect and denitrification efficiency. At the same time, the recycled flue gas not only recovers the waste heat therein, but also enables the unreacted ammonia to be recycled, further reducing the total amount of ammonia and NOx discharged from the system, and also improving the utilization rate of ammonia water and reducing the consumption of ammonia water.
[0014] The pipeline mixer used for mixing the denitrification flue gas and the vaporized ammonia in this system can perform various mixing methods such as flow splitting, cross mixing, and reverse swirling in the pipeline to fully mix evenly and improve the mixing effect. Its structure is simple, the overall occupied space is small, it is convenient for installation and disassembly, improves the flow field mixing system, is applicable to various use occasions, and can also be used for the mixing of low-viscosity liquid fluids. Brief Description of the Drawings
[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.
[0016] Figure 1 It is a schematic structural diagram of an ultra-low temperature denitration system for enhanced denitration with flue gas recycling provided by an embodiment of the present invention;
[0017] Figure 2 It is a schematic structural diagram of a pipeline mixer provided by an embodiment of the present invention;
[0018] Figure 3 It is a schematic structural diagram of a mixing element provided by an embodiment of the present invention;
[0019] Figure 4 It is a schematic structural diagram of a spiral blade provided by an embodiment of the present invention.
[0020] Description of the Reference Numerals:
[0021] 11. Boiler, 12. Ammonia injection mixer, 13. Denitration reactor, 14. Economizer, 15. Flue gas on-line detection element, 21. Ammonia water storage tank, 22. Ammonia distillation tower, 23. Pipeline mixer, 24. Flue gas circulation fan, 31. Dust collector, 32. Desulfurization device, 33. Exhaust fan, 34. Chimney, 231. Shell, 232. Vaporized ammonia inlet, 233. Ammonia-smoke mixture outlet, 234. Denitrated flue gas inlet, 235. Converging pipe, 236. Small-diameter pipe, 237. Diverging pipe, 238. Large-diameter pipe, 2371. Turbulence element, 2361. Support, 2362. First impeller, 2363. Second impeller, 2364. Impeller connecting shaft, 2381. Spiral blade, 2382. Vent hole. Detailed Embodiments
[0022] In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts also belong to the scope of protection of the present invention.
[0023] Such as Figure 1, a cryogenic denitrification system for enhancing denitrification by recycling flue gas provided by the present utility model includes: a denitrification unit, an ammonia unit, and an emission unit; the denitrification unit includes a boiler 11, an ammonia injection mixer 12, a denitrification reactor 13, and an economizer 14 connected in sequence through a flue gas pipeline; the flue gas outlet of the economizer 14 is connected to the emission unit, and a flue gas on-line detection element 15 is provided on the flue gas pipeline of the economizer 14; the ammonia unit includes an ammonia water storage tank 21, an ammonia evaporation tower 22, a pipeline mixer 23, and a flue gas circulation fan 24. The inlet of the ammonia evaporation tower 22 is connected to the outlet of the ammonia water storage tank 21, and the outlet of the ammonia evaporation tower 22 is connected to the vaporized ammonia inlet 232 of the pipeline mixer 23; the inlet of the flue gas circulation fan 24 is connected to the flue gas pipeline between the denitrification reactor 13 and the economizer 14, the outlet of the flue gas circulation fan 24 is connected to the denitrified flue gas inlet 234 of the pipeline mixer 23, and the ammonia-smoke mixed gas outlet 233 of the pipeline mixer 23 is connected to the inlet of the ammonia injection mixer 12.
[0024] In this cryogenic denitrification system, low-pressure steam at 0.5 MPa is used in the ammonia evaporation tower 22 to vaporize the ammonia water with an ammonia content of 20% from the ammonia water storage tank 21. Then, in the pipeline mixer 23, the vaporized ammonia (about 150 °C) is mixed with the denitrified flue gas (mainly containing carbon dioxide, sulfur dioxide, ammonia, ammonium sulfate, etc., about 200 °C) extracted by the flue gas circulation fan 24 to obtain an ammonia-smoke mixed gas with a temperature not lower than 180 °C. Then, in the ammonia injection mixer 12, the ammonia-smoke mixed gas is mixed with the high-temperature flue gas (about 220 °C) from the boiler 11, and the obtained mixed flue gas is sent into the denitrification reactor 13 for denitrification, ensuring the denitrification reaction temperature and enabling the denitrification catalyst to react normally, thereby reducing the nitrogen oxide content in the high-temperature flue gas. Except for the recycled part of the denitrified flue gas, the rest is sent into the economizer 14 for waste heat recovery. After the nitrogen oxide content in it is monitored in real time by the flue gas on-line detection element 15, it is finally discharged through the emission unit. This system uses the denitrified flue gas for reflux and mixes it with the vaporized ammonia to increase the temperature of the vaporized ammonia, ensuring that the mixed flue gas can reach the reaction temperature required by the catalyst (above 200 °C), improving the denitrification effect and denitrification efficiency. At the same time, the recycled flue gas not only recovers the waste heat in it, but also enables the unreacted ammonia to be recycled, further reducing the total amount of ammonia and NOx discharged from the system, and also improving the utilization rate of ammonia water and reducing the consumption of ammonia water.
[0025] Preferably, the emission unit includes a dust collector 31, a desulfurization device 32, a suction fan 33, and a chimney 34 connected in sequence. After the denitrified flue gas is subjected to waste heat recovery by the economizer 14, it is sent into the dust collector 31 for dust removal, and the flue gas after dust removal is introduced into the desulfurization device 32 for desulfurization. The desulfurized flue gas is guided to the chimney 34 for emission by the suction fan 33. The whole system completes the steps of denitrification, dust removal, desulfurization, and emission of the flue gas of the boiler 11, and has obvious energy-saving, emission-reduction, and consumption-reduction effects.
[0026] As Figure 2 , preferably, the pipeline mixer 23 includes a housing 231. The two ends of the housing 231 are respectively connected with a vaporized ammonia inlet 232 and an ammonia-smoke mixed gas outlet 233. A denitrified flue gas inlet 234 is connected to the side wall of the housing 231 near the vaporized ammonia inlet 232. The housing 231 between the vaporized ammonia inlet 232 and the ammonia-smoke mixed gas outlet 233 is composed of a tapered pipe 235, a small-diameter pipe 236, a tapered expansion pipe 237 and a large-diameter pipe 238 connected in series. The tapered pipe 235 and the tapered expansion pipe 237 are concentric reducers with the same shape and size. The diameters of the flared ends of the tapered pipe 235 and the tapered expansion pipe 237 are the same as the diameters of the large-diameter pipe 238, the vaporized ammonia inlet 232 and the ammonia-smoke mixed gas outlet 233, and the diameters of the constricted ends of the tapered pipe 235 and the tapered expansion pipe 237 are the same as the diameter of the small-diameter pipe 236.
[0027] The vaporized ammonia enters the housing 231 from the vaporized ammonia inlet 232, and the denitrified flue gas enters the housing 231 from the denitrified flue gas inlet 234. The mixed fluid of the two passes through the tapered pipe 235, the small-diameter pipe 236, the tapered expansion pipe 237 and the large-diameter pipe 238 in sequence. The flow rate gradually increases in the tapered pipe 235, passes through the small-diameter pipe 236 at a relatively high flow rate, then enters the tapered expansion pipe 237, the flow rate decreases in the tapered expansion pipe 237, and passes through the large-diameter pipe 238 at a relatively low flow rate, and finally flows out through the ammonia-smoke mixed gas outlet 233. When the mixed fluid flows in the housing 231, the flow rate changes from small to large and then to small, forming a significant variable-speed flow, which is beneficial to promoting the mixing of the vaporized ammonia and the denitrified flue gas, and provides a longer mixing path and mixing time in the relatively long housing 231, strengthening the mixing effect of the two.
[0028] As Figure 2 and Figure 3 , preferably, a mixing element is provided in the small-diameter pipe 236. The mixing element includes a bracket 2361, a first impeller 2362, a second impeller 2363 and an impeller connecting shaft 2364. The bracket 2361 is a three-pronged bracket 2361. The end of the bracket 2361 is fixedly connected to the pipe wall of the small-diameter pipe 236, and the center of the bracket 2361 has a through hole. Two impeller connecting shafts 2364 are respectively connected to the front and rear sides of the bracket 2361, and each impeller connecting shaft 2364 is fixed in the through hole through a bearing. A first impeller 2362 is fixedly connected to the end of the front-side impeller connecting shaft 2364, and a second impeller 2363 is fixedly connected to the end of the rear-side impeller connecting shaft 2364.
[0029] The mixed fluid enters the small-diameter tube 236 through the tapered tube 235, and the flow velocity gradually increases. When flowing through the first impeller 2362 and the second impeller 2363 supported by the bracket 2361 and connected by the impeller connecting shaft 2364, part of the static pressure energy can be converted into kinetic energy. The mixed fluid converted into kinetic energy can drive the first impeller 2362 and the second impeller 2363 to rotate, and the rotation can also further promote more complete mixing of the mixed fluid.
[0030] Preferably, the first impeller 2362 and the second impeller 2363 are installed in opposite directions; the diameter of the first impeller 2362 is smaller than the diameter of the second impeller 2363. The first impeller 2362 has a smaller diameter, so its blades are also smaller, so its rotation speed is faster, and it can form a faster turbulence and mixing effect. The second impeller 2363 has a larger diameter and blades, and the relative resistance is also larger. At the same time, the installation and rotation directions of the first impeller 2362 are opposite, so that the second impeller 2363 can destroy the turbulence effect formed by the first impeller 2362 when rotating, thereby intensifying the mixing degree of the mixed fluid.
[0031] like Figure 2 Preferably, a plurality of spoilers 2371 are provided on the inner wall of the gradually expanding tube 237, and the spoilers 2371 are arranged at intervals along the axial direction of the gradually expanding tube 237. The spoilers 2371 provide a more complex fluid channel for the gradually expanding tube 237, and can increase the turbulence of the mixed fluid during the process of deceleration of the mixed fluid, and also play a role in strengthening the mixing. The spoilers 2371 can be in the shape of a plate or a fin commonly used in the art.
[0032] like Figure 2 and Figure 4 Preferably, a spiral blade 2381 is provided on the inner wall of the large-diameter tube 238, and the outer wall of the spiral blade 2381 is connected to the inner wall of the large-diameter tube 238; a plurality of vents 2382 are evenly provided on the spiral blade 2381. The spiral blade 2381 is provided in the large-diameter tube 238, so that the mixed fluid can be mixed in the process of flowing along the spiral blade 2381, thereby improving the mixing effect. The vents 2382 provided on the spiral blade 2381 allow a part of the mixed fluid to flow along the rotation direction of the spiral blade 2381, and a part of the mixed fluid flows through the vents 2382, forming two different flow directions, which helps to improve the mixing effect. At the same time, the vents 2382 can also reduce the impact force on the spiral blade 2381 during the flow of the mixed fluid, thereby ensuring the installation stability of the pipeline mixer 23.
[0033] Preferably, the pitch of the spiral blade 2381 gradually decreases and then increases along the fluid flow direction. The pitch of the spiral blade 2381 is small in the middle and large at both ends, which is also to change the flow rate and flow direction of the mixed fluid, which is more conducive to evenly mixing the two fluids.
[0034] The ultra-low temperature denitration system for enhanced denitration by flue gas recycling of the present utility model, during specific operation, uses low-pressure steam of 0.5 MPa in the ammonia distillation tower 22 to vaporize ammonia water with an ammonia content of 20% from the ammonia water storage tank 21. Then, in the pipeline mixer 23, the vaporized ammonia gas at about 150 °C is mixed with the denitrated flue gas at about 200 °C extracted by the flue gas circulation fan 24 to obtain an ammonia-smoke mixture with a temperature not lower than 180 °C. Then, in the ammonia injection mixer 12, the ammonia-smoke mixture is mixed with the high-temperature flue gas at about 220 °C from the boiler 11, and the obtained mixed flue gas is sent into the denitration reactor 13 for denitration, ensuring the denitration reaction temperature and enabling the denitration catalyst to react normally, thereby reducing the nitrogen oxide content in the high-temperature flue gas. Except for the recycled part of the denitrated flue gas, the rest is sent into the economizer 14 for waste heat recovery. After the nitrogen oxide content is real-time monitored by the flue gas on-line detection element 15, it is sent into the dust collector 31 for dust removal. The flue gas after dust removal is introduced into the desulfurization device 32 for desulfurization, and the desulfurized flue gas is guided to the chimney 34 for emission by the induced draft fan 33.
[0035] Among them, during the use of the pipeline mixer 23, the vaporized ammonia gas enters the housing 231 from the vaporized ammonia gas inlet 232, and the denitrated flue gas enters the housing 231 from the denitrated flue gas inlet 234. The mixed fluid of the two successively passes through the tapered pipe 235, the small-diameter pipe 236, the tapered expansion pipe 237, and the large-diameter pipe 238. The flow rate gradually increases in the tapered pipe 235 and passes through the small-diameter pipe 236 at a relatively high flow rate, and then enters the tapered expansion pipe 237. The flow rate decreases in the tapered expansion pipe 237 and passes through the large-diameter pipe 238 at a relatively low flow rate, and finally flows out through the ammonia-smoke mixture outlet 233.
[0036] The mixed fluid enters the small-diameter pipe 236 through the tapered pipe 235. At this time, the flow rate gradually increases. When flowing through the first impeller 2362 and the second impeller 2363, part of the static pressure energy can be converted into kinetic energy. The mixed fluid with the converted kinetic energy can push the first impeller 2362 and the second impeller 2363 to rotate in the reverse direction, thereby intensifying the mixing degree of the mixed fluid. When the mixed fluid enters the tapered expansion pipe 237, the flow disturbing member 2371 can also intensify the turbulence degree of the mixed fluid. When the mixed fluid flows through the large-diameter pipe 238, part of it flows along the spiral direction of the spiral blade 2381, and part of it flows through the ventilation holes 2382 on the spiral blade 2381, forming two different flow directions. Moreover, the pitch of the spiral blade 2381 is small in the middle and large at both ends, changing the flow rate and flow direction of the mixed fluid during flow, which helps to improve the mixing effect.
[0037] It should be noted that in the present utility model, the detailed structures of some devices are not described in detail, but they belong to the prior art known to those skilled in the art, so they will not be elaborated here. In addition, the parts not involved in this device are the same as or can be implemented by the prior art.
[0038] It should be noted that pressure sensors, flow meters or temperature sensors are provided on the conveying pipelines inside the system between different units, devices and equipment, and different valves are also provided, such as pressure relief valves, pressure regulating valves, safety valves, etc., which are used to adjust and stabilize the pressure of the whole system.
[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. An ultra-low temperature denitration system for flue gas reuse and enhanced denitration, characterized in that: include: A denitration unit, an ammonia unit and an emission unit; the denitration unit comprises a boiler, an ammonia injection mixer, a denitration reactor and an economizer which are sequentially connected through a smoke exhaust pipe; the smoke outlet of the economizer is connected to the emission unit, and a smoke online detection element is provided on the smoke exhaust pipe of the economizer; The ammonia unit includes an ammonia water storage tank, an ammonia evaporation tower, a pipeline mixer and a flue gas circulation fan. The inlet of the ammonia evaporation tower is connected to the outlet of the ammonia water storage tank, and the outlet of the ammonia evaporation tower is connected to the vaporized ammonia inlet of the pipeline mixer; the inlet of the flue gas circulation fan is connected to the smoke exhaust duct between the denitrification reactor and the economizer, the outlet of the flue gas circulation fan is connected to the denitrification smoke inlet of the pipeline mixer, and the ammonia-smoke mixed gas outlet of the pipeline mixer is connected to the inlet of the ammonia injection mixer.
2. The ultra-low temperature denitration system for flue gas reuse and enhanced denitration according to claim 1 is characterized in that: The emission unit comprises a dust collector, a desulfurization device, an exhaust fan and a chimney which are connected in sequence.
3. The ultra-low temperature denitration system for flue gas reuse and enhanced denitration according to claim 1 is characterized in that: The pipeline mixer comprises a shell, the two ends of the shell are respectively connected with the vaporized ammonia gas inlet and the ammonia smoke mixed gas outlet, and the side wall of the shell near the vaporized ammonia gas inlet is connected with the denitrification smoke gas inlet; The shell between the vaporized ammonia inlet and the ammonia smoke mixed gas outlet is composed of a tapered tube, a small-diameter tube, a gradually expanding tube and a large-diameter tube connected in series; the tapered tube and the gradually expanding tube are concentric reducing tubes with the same shape and size; the diameter of the expanded end of the tapered tube and the gradually expanding tube is the same as the diameter of the large-diameter tube, the vaporized ammonia inlet and the ammonia smoke mixed gas outlet, and the diameter of the reduced end of the tapered tube and the gradually expanding tube is the same as the diameter of the small-diameter tube.
4. The ultra-low temperature denitration system for flue gas reuse and enhanced denitration according to claim 3 is characterized in that: A mixing element is provided in the small-diameter tube, and the mixing element includes a bracket, a first impeller, a second impeller and an impeller connecting shaft. The bracket is a three-pronged bracket, and the end of the bracket is fixedly connected to the tube wall of the small-diameter tube, and the center of the bracket is provided with a through hole; two impeller connecting shafts are respectively connected to the front and rear sides of the bracket, and each of the impeller connecting shafts is fixed in the through hole through a bearing; the first impeller is fixedly connected to the end of the impeller connecting shaft on the front side, and the second impeller is fixedly connected to the end of the impeller connecting shaft on the rear side.
5. The ultra-low temperature denitration system for flue gas reuse and enhanced denitration according to claim 4 is characterized in that: The first impeller and the second impeller are installed in opposite directions; the diameter of the first impeller is smaller than the diameter of the second impeller.
6. The ultra-low temperature denitration system for flue gas reuse and enhanced denitration according to claim 3 is characterized in that: A plurality of spoilers are arranged on the inner wall of the gradually diverging tube, and the spoilers are arranged at intervals along the axial direction of the gradually diverging tube.
7. The ultra-low temperature denitration system for flue gas reuse and enhanced denitration according to claim 3 is characterized in that: A spiral blade is arranged on the inner wall of the large-diameter tube, and the outer wall of the spiral blade is connected to the inner wall of the large-diameter tube; a plurality of vent holes are evenly arranged on the spiral blade.
8. The ultra-low temperature denitration system for flue gas reuse and enhanced denitration according to claim 7 is characterized in that: The pitch of the spiral blade gradually decreases and then increases along the flow direction of the fluid.