Flue gas ultralow emission system and method based on chemical looping combustion

Abstract

The invention relates to the technical field of flue gas treatment, in particular to a flue gas ultra-low emission system and method based on chemical looping combustion, and the flue gas ultra-low emission system comprises an in-furnace in-situ desulfurization unit, a cyclone separator, a nitrogen oxide removal unit, a dust removal unit, an out-furnace desulfurization unit and a recirculation unit which are connected in sequence in the flue gas flowing direction; wherein the nitrogen oxide removal unit is arranged in a flue between the cyclone separator and the dust removal unit; and part of recycled flue gas treated by the dust removal unit and / or the recycling unit is at least used for diluting or atomizing a denitration reducing agent in the nitrogen oxide removal unit, and / or returns to a chemical looping coal feeding system. According to the invention, through creative connection relations and medium circulation paths among the units, the beneficial effects of ensuring carbon capture advantages, efficiently purifying special pollutants, realizing internal circulation integration of the system, having good economy and the like are generated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flue gas treatment, in particular to a flue gas ultra-low emission system and method based on chemical looping combustion. BACKGROUND

[0002] Developing efficient and low-cost carbon capture, utilization and storage technology has become a key path for the energy field to achieve deep emission reduction. Among the many carbon capture technologies, chemical looping combustion technology is considered one of the most promising technology solutions due to its unique internal carbon enrichment mechanism. This technology realizes the directional transfer of oxygen through the circulation of metal oxides and other oxygen carriers between two reactors (air reactor and fuel reactor), thereby directly producing a high-concentration CO2 gas stream on the fuel reactor side. This process fundamentally avoids direct contact between fuel and air, eliminating the dilution effect of N2 in the air on the flue gas, so that the main components of the flue gas at the outlet of the fuel reactor are CO2 and H2O, greatly reducing the energy consumption and cost of subsequent CO2 capture.

[0003] However, the flue gas produced by chemical looping combustion technology is significantly different from the flue gas of traditional coal-fired boilers, which brings new challenges to the subsequent pollutant removal. Specifically, the chemical looping combustion flue gas has the following distinctive features: first, the water vapor content in the flue gas is extremely high, with a volume concentration usually between 40%-55%; second, due to the lack of mixing with a large amount of N2 during the combustion process, the SO2 concentration in the flue gas is highly concentrated, reaching 2%-4%, which is much higher than that of conventional coal-fired flue gas; third, during the flue gas pollutant removal process, air cannot be introduced, which would dilute the already enriched CO2 and affect the carbon capture efficiency. The unique flue gas characteristics of high humidity, high SO2 concentration, and high CO2 enrichment make the existing mature coal-fired power plant ultra-low emission technology system face serious inadaptability.

[0004] Currently, the engineering application of this technology mainly faces the following technical bottlenecks: 1. Current research on chemical looping combustion technology is mostly focused on the development of reactors, oxygen carriers, and cold and hot state experiments at pilot scale. The study of the special flue gas produced on the fuel reactor side is still insufficient, and there is a lack of a complete, efficient, and deeply coupled flue gas pollutant comprehensive treatment scheme for the chemical looping combustion process; 2. Due to the high SO2 content in the flue gas of chemical looping combustion, which is 4-5 times that of traditional thermal power industry flue gas, the existing limestone-gypsum wet desulfurization in the thermal power industry cannot achieve the standard emission after chemical looping flue gas desulfurization treatment; 3. The core advantage of chemical looping combustion is the internal enrichment of CO2 without additional energy consumption. If the conventional power plant introduces air (such as dilution gas, atomization gas, and oxidation air) into the flue gas for desulfurization and denitrification, a large amount of N2 will be introduced again, which will seriously dilute the enriched CO2 stream, destroy the low carbon capture cost advantage, and go against the original intention of the technology. The traditional flue gas desulfurization, selective catalytic reduction denitrification, and selective non-catalytic reduction technologies in the traditional thermal power industry cannot be directly applied to the treatment of chemical looping flue gas; 4. The existing exploratory technical solutions do not fully consider the cooperation with the air reactor flue gas treatment path in the main process system and the integrated integration of the entire power plant flue gas treatment system, which is likely to cause problems such as repeated construction of equipment, complex system, large occupied area, and high investment and operation cost; 5. Currently, SCR and SNCR are the mainstream denitrification technologies in the thermal power industry. The source of the denitrification reducing agent is usually urea hydrolysis for ammonia production in SCR denitrification, and urea pyrolysis for ammonia production in SNCR. Whether it is hydrolysis or pyrolysis, CO2 will be produced in the process of producing ammonia from urea as raw material and will be emitted with the flue gas, which is not captured. This increases the emission of carbon dioxide, which is contrary to the current carbon double control target.

[0005] Therefore, there is an urgent need in the art to develop a flue gas treatment method specially used for chemical looping combustion, which can efficiently treat special flue gas with high humidity and high sulfur, ensure that the pollutants meet the emission standard, and at the same time, the entire process does not introduce air or other dilution gas to protect the high purity of the CO2 stream, and a carbon dioxide compression and purification unit is provided to realize the recovery of carbon dioxide. And seamless connection and optimized integration with the main plant flue gas treatment system, facilitating industrial application.

[0006] In view of this, the present application is proposed. SUMMARY

[0007] The purpose of the present application is to provide a flue gas ultra-low emission system and method based on chemical looping combustion, which realizes efficient and stable removal of pollutants in high-concentration SO2 and high-humidity chemical looping combustion flue gas.

[0008] The present application provides a flue gas ultra-low emission system based on chemical looping combustion, which comprises, in the direction of flue gas flow, an in-situ desulfurization unit in the furnace, a cyclone separator, a nitrogen oxide removal unit, a dust removal unit, an off-site desulfurization unit, and a recirculation unit connected in sequence; The nitrogen oxide removal unit is arranged in the flue between the cyclone separator and the dust removal unit. Part of the recirculated flue gas after being treated by the dust removal unit and / or the recirculation unit is used at least for dilution or atomization of the denitrification reducing agent in the nitrogen oxide removal unit and / or returned to the chemical looping coal feeding system.

[0009] In a preferred embodiment of this technical solution, the in-situ desulfurization unit includes a fuel reactor body and an oxygen carrier addition pipeline disposed on the side wall of the fuel reactor body. The oxygen carrier addition pipeline is used to add desulfurization reducing agent to the fuel reactor body.

[0010] As a preferred embodiment of this technical solution, the desulfurization reducing agent includes any one of alkaline metal compounds and alkaline earth metal oxides.

[0011] In a preferred embodiment of this technical solution, the top of the fuel reactor body is connected to the cyclone separator, and the bottom of the cyclone separator is connected to the fuel reactor body in the opposite direction.

[0012] As a preferred embodiment of this technical solution, an economizer and an air preheater are sequentially arranged in the flue along the direction of flue gas flow.

[0013] As a preferred embodiment of this technical solution, the nitrogen oxide removal unit includes a first spray layer, a second spray layer, and a catalyst layer. The first spray layer is disposed at the inlet of the flue, and the second spray layer and the catalyst layer are disposed between the economizer and the air preheater. The first spray layer is used to spray urea solution atomized by recirculated flue gas into the flue gas, and the second spray layer is used to spray urea hydrolysis product gas diluted by recirculated flue gas into the flue gas.

[0014] The catalyst layer is filled with a selective catalytic reduction catalyst.

[0015] As a preferred embodiment of this technical solution, a condensation and dehydration device is provided between the dust removal unit and the external desulfurization unit.

[0016] As a preferred embodiment of this technical solution, the external desulfurization unit includes a desulfurization absorption tower, a slurry oxidation tank, a slurry circulation pump, and an oxidation fan. The desulfurization absorption tower is connected to the slurry oxidation tank, the slurry oxidation tank is connected to the desulfurization absorption tower in reverse through the slurry circulation pump, and the oxidation fan is connected to the slurry oxidation tank.

[0017] As a preferred embodiment of this technical solution, the recycling unit includes a dehydration device, a compression device, and a carbon dioxide purification device connected in sequence. Part of the recirculated flue gas after being processed by the compression device is used for dilution of the denitrification reducing agent in the nitrogen oxide removal unit and / or returned to the chemical loop feed system.

[0018] Secondly, this invention also discloses a method for treating chemical looping combustion flue gas using the aforementioned ultra-low emission system based on chemical looping combustion, which should also fall within the scope of protection of this invention. Specifically, it includes the following steps: S1. The high-temperature flue gas generated by the fuel reactor comes into contact with the desulfurization reducing agent in the in-situ removal unit inside the furnace for preliminary desulfurization. S2. The flue gas processed in step S1 enters the cyclone separator to remove the solid particles it carries, and the separated solid particles are returned to the in-situ removal unit inside the furnace. S3. The flue gas treated in step S2 enters the nitrogen oxide removal unit and is mixed with the denitrification reducing agent diluted by the recirculated flue gas to remove nitrogen oxides. S4. The flue gas treated in step S3 is then subjected to dust removal and external wet desulfurization in sequence. S5. Part of the flue gas after dust removal in step S3 is returned to the fuel reactor body. The flue gas treated in step S4 is dehydrated and compressed in sequence. Part of the compressed flue gas is drawn out as recirculated flue gas for dilution of the denitrification reducing agent in step S3 and / or returned to the chemical loop coal feeding system. The remaining part of the flue gas is purified to obtain high-purity carbon dioxide.

[0019] The ultra-low emission flue gas system based on chemical looping combustion of the present invention has at least the following beneficial effects: This invention relates to an ultra-low emission flue gas system based on chemical looping combustion. Along the flue gas flow direction, it includes, in sequence, an in-situ desulfurization unit, a cyclone separator, a nitrogen oxide removal unit, a dust removal unit, an external desulfurization unit, and a recirculation unit. Fuel and oxygen carrier burn in a fuel reactor to generate flue gas. First, in the in-situ desulfurization unit within the fuel reactor, sulfur dioxide is removed using a desulfurization reducing agent. After preliminary sulfur dioxide removal in the furnace, the flue gas carrying a large amount of solid particles is discharged from the top of the fuel reactor to the cyclone separator. In the cyclone separator, most of the solid particles are separated and captured. The separated solid particles return from the bottom of the cyclone separator to the fuel reactor to continue the desulfurization reaction. The flue gas then enters a flue between the cyclone separator and the dust removal unit. This flue is equipped with a nitrogen oxide removal unit, and the treated recirculated flue gas is used as dilution gas or atomized gas for the denitrification reducing agent in the nitrogen oxide removal unit. The flue gas, whose main components are CO2 and H2O, is used for dilution or as atomizing gas, which is equivalent to circulating the medium within the system without introducing any new impurity gases. This perfectly maintains the purity of the CO2 product gas, which is a prerequisite for achieving low carbon capture energy consumption. In addition, the waste heat of the flue gas itself can be cleverly utilized in the nitrogen oxide removal unit to provide an ideal reaction temperature for the denitrification reaction. After being treated by the nitrogen oxide removal unit, the flue gas is further treated by the dust removal unit and then enters the external desulfurization unit for wet fine desulfurization. Since the in-situ desulfurization unit can capture some SO2, it significantly reduces the SO2 load of the downstream external desulfurization unit. After being treated by the external desulfurization unit, the flue gas enters the recirculation unit for further dehydration, compression and purification. Part of the compressed flue gas is returned to the chemical chain coal feeding system as a transport and inerting gas for pulverized coal. This eliminates the risk of pulverized coal explosion and avoids the introduction of N2.

[0020] Therefore, the ultra-low emission flue gas system based on chemical looping combustion of the present invention completes the entire pollutant removal process in a CO2-rich atmosphere, effectively avoiding the introduction of external gases (such as air) and ensuring that high-purity, high-concentration CO2 product gas can be obtained in the end. Through the staged purification combination of "in-situ desulfurization in the furnace + wet desulfurization outside the furnace" and the nitrogen oxide removal unit set in the optimal temperature window, efficient and stable removal of pollutants from high-concentration SO2 and high-humidity flue gas is achieved. Through flue gas recirculation and energy cascade utilization, energy consumption, material consumption and operating costs are significantly reduced. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the ultra-low emission flue gas system based on chemical looping combustion of the present invention.

[0023] Figure label: 1: Fuel reactor body; 2: Oxygen carrier addition pipeline; 3: Cyclone separator; 4: Dust removal unit; 5: First spray layer; 6: Second spray layer; 7: Catalyst layer; 9: Condenser; 10: Desulfurization absorption tower; 11: Slurry oxidation tank; 12: Slurry circulation pump; 13: Oxidation blower; 14: Slurry discharge pump; 15: Gypsum discharge pump; 16: Dehydration device; 17: Compression device; 18: Carbon dioxide purification device. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1 like Figure 1As shown, this embodiment provides an ultra-low emission flue gas system based on chemical looping combustion. Along the direction of flue gas flow, it includes an in-situ desulfurization unit, a cyclone separator 3, a nitrogen oxide removal unit, a dust removal unit 4, an external desulfurization unit, and a recirculation unit connected in sequence. The nitrogen oxide removal unit is located in the flue between the cyclone separator 3 and the dust removal unit 4. Part of the recirculated flue gas after being treated by the dust removal unit 4 and / or the recirculation unit is used at least for the dilution or atomization of the denitrification reducing agent in the nitrogen oxide removal unit, and / or returned to the chemical looping coal feeding system.

[0028] In the ultra-low emission flue gas system based on chemical looping combustion of this invention, fuel and oxygen carrier are burned in a fuel reactor to generate flue gas. First, in the in-situ desulfurization unit within the fuel reactor, sulfur dioxide is removed using a desulfurization reducing agent. After preliminary sulfur dioxide removal in the furnace, the flue gas carrying a large amount of solid particles is discharged from the top of the fuel reactor to the cyclone separator 3. In the cyclone separator 3, most of the solid particles are separated and captured. The separated solid particles return from the bottom of the cyclone separator 3 to the fuel reactor to continue the desulfurization reaction. The flue gas then enters the flue between the cyclone separator 3 and the dust removal unit 4. This flue is equipped with a nitrogen oxide removal unit, and the treated recirculated flue gas is used as the dilution gas or atomizing gas for the denitrification reducing agent in the nitrogen oxide removal unit. The main components of this part of the flue gas are CO2 and H2O, which are used for dilution... The gas is released or used as atomizing gas, which is equivalent to circulating the medium within the system without introducing any new impurity gases. This perfectly maintains the purity of the CO2 product gas, which is a prerequisite for achieving low carbon capture energy consumption. In addition, the waste heat of the flue gas itself can be cleverly utilized in the nitrogen oxide removal unit to provide an ideal reaction temperature for the denitrification reaction. After being treated by the nitrogen oxide removal unit, the flue gas is further treated by the dust removal unit 4 and then enters the external desulfurization unit for wet fine desulfurization. Since the in-situ desulfurization unit can capture some SO2, it significantly reduces the SO2 load of the downstream external desulfurization unit. After being treated by the external desulfurization unit, the flue gas enters the recirculation unit for further dehydration, compression and purification. Part of the compressed flue gas is returned to the chemical chain coal feeding system as a conveying and inerting gas for pulverized coal. This eliminates the risk of pulverized coal explosion and avoids the introduction of N2.

[0029] In this embodiment, more preferably, a portion of the recirculated flue gas after treatment by the recirculation unit is used for the dilution or atomization of the denitrification reducing agent in the nitrogen oxide removal unit, and / or returned to the chemical chain coal feeding system. The flue gas treated by the recirculation unit has a lower sulfur content, which reduces the requirements for the corrosion resistance level of the pipeline.

[0030] Therefore, it can be seen that the flue gas ultra-low emission system based on chemical loop combustion of the present invention, through the creative connection relationship and medium circulation path between each unit, produces a multi-faceted synergistic amplification of beneficial effects such as "ensuring carbon capture advantages, efficiently purifying special pollutants, realizing system internal circulation integration, and possessing good economic efficiency".

[0031] Based on the above technical solution, and more preferably, the in-situ desulfurization unit includes a fuel reactor body 1 and an oxygen carrier addition pipeline 2 disposed on the side wall of the fuel reactor body 1, wherein the oxygen carrier addition pipeline 2 is used to add a desulfurization reducing agent to the fuel reactor body 1.

[0032] In a specific embodiment of the present invention, a desulfurization reducing agent can be added to the fuel reactor body 1 through the oxygen carrier addition pipeline 2 on the side wall of the fuel reactor body 1. The fuel reactor body 1 is the "source" of pulverized coal combustion and SO2 generation, and its interior has the highest temperature (usually 800-1000℃) and the most intense turbulent mixing environment. Injecting a desulfurization reducing agent (such as CaO) here provides optimal thermodynamic and kinetic conditions for the sulfur fixation reaction (e.g., CaO + SO2 + 1 / 2O2 → CaSO4), resulting in the fastest reaction rate and the highest desulfurization efficiency. The present invention precisely adds the desulfurization reducing agent to the "reaction core area," achieving true "in-situ" removal. The oxygen carrier addition pipeline 2 is an inherent and indispensable component of the chemical looping combustion system. The present invention utilizes this pipeline to simultaneously transport oxygen carrier and desulfurization reducing agent, significantly reducing the number of equipment, floor space, and initial investment. Furthermore, metal-based oxygen carriers (such as iron-based and copper-based ones) react with SO2 at high temperatures to form metal sulfates, leading to decreased activity or even permanent deactivation. This invention, by removing SO2 instantly and efficiently within the fuel reactor, significantly reduces the partial pressure of SO2 in the reaction zone, providing a "low-sulfur" environment for the oxygen carrier, thereby effectively alleviating sulfur poisoning and extending the service life of the oxygen carrier. Additionally, certain desulfurization reducing agents (such as CaO) or desulfurization products may also have a positive impact on the combustion or oxygen carrier reduction / oxidation process at high temperatures, forming a potential synergistic catalytic effect.

[0033] Based on the above technical solution, and further preferably, the desulfurization reducing agent includes any one of alkaline metal compounds and alkaline earth metal oxides, wherein the alkaline metal compounds include sodium carbonate, sodium bicarbonate and sodium hydroxide, etc., and the alkaline earth metal oxides include calcium oxide, calcium hydroxide, magnesium oxide and magnesium hydroxide, etc.

[0034] Based on the above technical solution, it is further preferred that the top of the fuel reactor body 1 is connected to the cyclone separator 3, and the bottom of the cyclone separator 3 is connected to the fuel reactor body 1 in the opposite direction.

[0035] The top of the fuel reactor body 1 is connected to the cyclone separator 3, whereby unreacted desulfurization reducing agent, reaction products (CaSO4), and oxygen carrier are carried by the flue gas to the cyclone separator 3. The bottom of the cyclone separator 3 is connected to the fuel reactor body 1 in the opposite direction. After capturing these components, the cyclone separator 3 returns them to the fuel reactor via a return system. The returned unreacted desulfurization reducing agent can continue to participate in the desulfurization reaction, effectively extending its residence time in the high-temperature zone. This allows the desulfurization reducing agent added each time to play a greater role, resulting in a significant improvement in calcium utilization. This not only reduces operating costs but also reduces solid waste emissions and the consumption of fresh desulfurization reducing agent.

[0036] Based on the above technical solution, and further preferably, along the direction of flue gas flow, an economizer and an air preheater are sequentially arranged in the flue. The economizer is used to recover the waste heat of the high-temperature flue gas at the outlet of the fuel reactor to heat the boiler feedwater, aiming to improve the thermal efficiency of the entire power generation cycle. The air preheater is used to use the waste heat of the flue gas to heat the combustion air sent into the air reactor, aiming to ensure the stability and efficiency of the oxygen carrier regeneration reaction in the air reactor, while further reducing exhaust losses.

[0037] Based on the above technical solution, and further preferably, the nitrogen oxide removal unit includes a first spray layer 5, a second spray layer 6, and a catalyst layer 7. The first spray layer 5 is disposed at the inlet of the flue gas duct. The first spray layer is used to spray a urea solution atomized from recirculated flue gas into the flue gas. The temperature at the flue gas inlet of the first spray layer 5 is 800-900℃. At this temperature, when the urea solution is sprayed into the flue gas, the NO in the flue gas... x Under conditions of 800-900℃, it reacts with the denitrification reducing agent to reduce to N2, thus removing it. That is, the SNCR of the first spray layer 5 acts as "coarse removal," and can first remove most of the NO in the most suitable temperature window (800-900℃). x Furthermore, when urea is used as a denitrification reducing agent, urea pyrolysis produces CO2, but this CO2 is captured by the system and does not cause additional carbon emissions. The second spray layer 6 and catalyst layer 7 are located between the economizer and the air preheater. Catalyst layer 7 is filled with a selective catalytic reduction catalyst. The second spray layer is used to inject urea hydrolysis product gas diluted by recirculated flue gas into the flue gas. The SCR of the second spray layer 6 and catalyst layer 7 acts as a "fine denitrification" process, removing the remaining, difficult-to-treat NO at a lower temperature (typically 300-400℃) under the action of the catalyst. xComplete restoration. The two processes work together to achieve a seamless transition between "coarse denitrification" and "fine denitrification," ultimately achieving a stable denitrification efficiency of over 95%, easily meeting "ultra-low emission" requirements. Furthermore, using a portion of the recirculated flue gas, treated by the dust removal unit and / or recirculation unit, instead of air as dilution or atomizing gas can maintain the purity of the CO2 stream.

[0038] The investment and operating costs of SCR systems (especially catalyst replacement) are very high. This invention uses a pre-installed SNCR unit to handle the main denitrification load, thus reducing the amount of NO entering the SCR unit. x The concentration has been significantly reduced.

[0039] The SCR reaction zone of the present invention does not require a separate reactor. Only a second spray layer 6 and a catalyst layer 7 need to be set between the economizer and the air preheater. The selection can be flexible according to the load. When the load is low, ammonia does not need to be sprayed in the SCR reaction zone. According to actual needs, SNCR or SCR or SNCR and SCR can be used simultaneously for denitrification.

[0040] For example, in another specific embodiment of the present invention, the first spray layer 5 (SNCR) in the high-temperature zone can be omitted, and only the second spray layer 6 and catalyst layer 7 (SCR) are provided after the economizer. The diluent gas used for this part of the ammonia injection can be a portion of the flue gas after dust removal or a portion of the recirculated flue gas after treatment by the recirculation unit. Using a portion of the flue gas after dust removal or the recirculated flue gas as the diluent gas instead of air can maintain the purity of the CO2 stream. Specifically, the NH3 / NO... x When the molar ratio is controlled at 1.4-1.6, the removal efficiency can reach 70%-80%.

[0041] For example, in another specific embodiment of the invention, urea solution atomized from recirculated flue gas can be sprayed only in the first spray layer of the high-temperature zone. Similarly, replacing air with a portion of the recirculated flue gas treated by the dust removal unit and / or recirculation unit as the atomizing gas can maintain the purity of the CO2 stream.

[0042] Based on the above technical solution, and further preferably, the dust removal unit 4 adopts a bag filter, and a recirculation fan is installed at the outlet of the bag filter. A portion of the flue gas, pressurized by the recirculation fan, enters the nitrogen oxide removal unit as dilution gas. A condensation and dehydration device is installed between the dust removal unit 4 and the external desulfurization unit. The condensation and dehydration device is preferably a condenser 9, such as a shell-and-tube condenser or a plate condenser. Another portion of the flue gas, after fly ash removal by the bag filter, enters the condenser 9, where the temperature is reduced to 120°C and condensate is removed, reducing corrosion to the external desulfurization unit. The cooled and dehydrated flue gas then enters the external desulfurization unit.

[0043] As a more preferred option, the condensation and dehydration device is a direct contact flue gas condensation tower to simultaneously achieve deep dehydration and synergistic purification.

[0044] As another preferred option, the condensation and dehydration device is a flue gas condensation-reheat system coupled with a heat pump, which can effectively eliminate white plumes and improve system energy efficiency while achieving dehydration.

[0045] Based on the above technical solution, and further preferably, the external desulfurization unit includes a desulfurization absorption tower 10, a slurry oxidation tank 11, a slurry circulation pump 12, and an oxidation fan 13. The desulfurization absorption tower 10 and the slurry oxidation tank 11 are equipped with agitators. The desulfurization absorption tower 10 is connected to the slurry oxidation tank 11 via a slurry discharge pump 14. The slurry oxidation tank 11 is connected to the desulfurization absorption tower 10 in reverse via the slurry circulation pump 12. The limestone slurry in the slurry oxidation tank 11 enters the desulfurization absorption tower 10 via the slurry circulation pump 12 and comes into contact with the flue gas. SO2 in the flue gas enters the slurry and reacts with it, thus removing SO2. The reacted flue gas enters the recirculation unit, and the slurry falls back into the desulfurization absorption tower 10. The oxidation fan 13 is connected to the slurry oxidation tank 11, providing oxidizing air to the slurry oxidation tank 11, causing the calcium carbonate in the limestone slurry to react with sulfur dioxide and oxygen, ultimately producing gypsum. This gypsum is then discharged by the gypsum discharge pump 15 and connected to the main plant's gypsum dewatering system. The specific number of slurry circulation pumps 12 and oxidation blowers 13 can be selected according to actual needs.

[0046] Based on the above technical solution, and further preferably, the recirculation unit includes a dehydration device 16, a compression device 17, and a carbon dioxide purification device 18 connected in sequence. The desulfurized flue gas first enters the dehydration device 16 to remove moisture, at which point the CO2 content in the flue gas is above 95%. Then it enters the compression device 17. After compression, the pressure of the flue gas is about 0.5-0.6 bar. About 10% of the flue gas (based on the requirements of the chemical chain) enters the chemical chain coal feeding system, or is used as dilution gas as a denitrification reducing agent in the nitrogen oxide removal unit. The remaining flue gas enters the carbon dioxide purification device 18, and after further compression and purification, it generates industrial-grade CO2. Specifically, the dehydration device 16 is preferably a condenser or a gas adsorption dryer, the compression device 17 is a compressor suitable for low-pressure boosting, and the carbon dioxide purification device 18 can be a cryogenic distillation device.

[0047] In this solution, the denitrification and desulfurization reducing agents are provided by the main plant, and the wastewater is connected to the main plant's wastewater treatment system. The gypsum slurry is connected to the main plant's treatment system, avoiding redundant arrangements and saving costs. The coupling of urea catalytic hydrolysis and chemical chain technology allows the large amount of carbon dioxide byproducts in the product gas to be compressed and purified together with the carbon dioxide enriched in the chemical chain, thus achieving the capture of this part of the carbon dioxide. This solves the problem that conventional catalytic hydrolysis technology products cannot be captured due to ultra-low emissions.

[0048] This invention is based on the characteristics of chemically chained flue gas having high SO2 content and multiple SO2 generation points. By combining dry and wet methods, it reduces the pressure of wet desulfurization, makes up for the shortcomings of in-furnace desulfurization in efficiency and the limitation of only removing SO2 from fuel reactors, and achieves full-process desulfurization and compliant emission of sulfur dioxide in flue gas. Furthermore, when operating at low load, in-furnace dry desulfurization can be omitted, saving operating costs.

[0049] The external desulfurization unit of the present invention adopts a dual-tower technology. The oxidation air is introduced into the slurry oxidation tank 11 and does not enter the absorption tower, thus avoiding the dilution of the flue gas enriched with carbon dioxide. The introduction of the heat exchange and dehydration device 16 in front of the desulfurization absorption tower 10 not only ensures the appropriate temperature for desulfurization, but also avoids high corrosion.

[0050] The first spray layer 5 (SNCR) of the nitrogen oxide removal unit of this invention is located at the outlet of the cyclone separator 3 and the inlet of the flue, where there is no NO downstream. x The nitrogen is generated at a temperature between 800-900℃, which facilitates improved denitrification efficiency. The second spray layer 6 and the catalyst layer 7 (SCR) are located between the economizer and the air preheater, allowing for flexible selection based on load. Under low load conditions, ammonia may not be sprayed in the SCR reaction zone. This invention employs a combined SNCR-SCR denitrification process, where some incompletely reacted ammonia gas can react with NO in the SCR zone under the action of the catalyst. x The reaction continues, reducing ammonia escape and further lowering the content of nitrogen oxides at the outlet, achieving ultra-low emissions.

[0051] Example 2 This embodiment discloses a method for treating chemical looping combustion flue gas using the most preferred ultra-low emission system based on chemical looping combustion, specifically including the following steps: S1. Using coal as fuel (sulfur content of 1.68%), CaO desulfurization reducing agent is added to the fuel reactor through the oxygen carrier pipeline at a Ca / S molar ratio of 1.9. The high-temperature flue gas generated by the fuel reactor comes into contact with the CaO desulfurization reducing agent in the in-situ removal unit inside the furnace for preliminary desulfurization. S2. The flue gas processed in step S1 enters the cyclone separator 3 to remove the solid particles carried therein, and the separated solid particles are returned to the in-situ removal unit inside the furnace. S3. The flue gas treated in step S2 enters the nitrogen oxide removal unit. A urea solution atomized from the recirculated flue gas is sprayed into the first spray layer 5 at the flue inlet. Urea hydrolysis product gas diluted with the recirculated flue gas is sprayed into the second spray layer. The urea hydrolysis product gas and the recirculated flue gas (dilution gas) are diluted at a volume ratio of 5:95, resulting in an NH3 / NO3 ratio. x The molar ratio is controlled at 1.4-1.6 to remove nitrogen oxides; S4. The flue gas treated in step S3 enters the bag filter for dust removal, is cooled by the condenser 9 to remove condensate, and then enters the external desulfurization unit. S5. The flue gas treated in step S4 is dehydrated and compressed sequentially. About 10% of the compressed flue gas is drawn out as recirculated flue gas for dilution of the denitrification reducing agent in step S3 and / or returned to the chemical loop coal feeding system. The remaining flue gas is purified to obtain high-purity carbon dioxide.

[0052] Compare with Example 1 This comparative example is basically the same as Example 2, except that: air is used as the atomized gas and dilution gas of the denitrification reducing agent, and the external desulfurization unit only includes the desulfurization absorption tower, and oxidizing air is blown into the desulfurization absorption tower by the oxidation fan.

[0053] Compare with Example 2 This comparative example is basically the same as Example 2, except that: in-situ desulfurization in the furnace is cancelled, and all SO2 is treated by the external desulfurization unit.

[0054] This invention relates to the concentrations of SO2 and NO at the final emission outlet of the system in Example 2 and Comparative Examples 1-2. x The concentrations of CO2 and CO2 at the inlet of the compression purification unit were measured to evaluate its desulfurization and denitrification efficiency. The results are shown in Table 1.

[0055] Table 1 Test Results

[0056] As shown in Table 1, the present invention can simultaneously achieve ultra-low emissions of pollutants (SO2 ≤ 35 mg / m³). 3 NO x ≤50mg / m 3 The core objective is to maintain a high CO2 concentration (≥95%). In contrast, the CO2 concentration at the inlet of the compression and purification unit in Control Example 1 decreased to 83%-85%, further demonstrating that using recirculated flue gas as atomizing and diluting gas, and not introducing oxidizing air into the desulfurization absorption tower, are key technical means to maintain a high CO2 concentration. Control Example 2 could not achieve the treatment of this SO2 concentration; therefore, the SO2 concentration at the system's final emission point was not tested.

[0057] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flue gas ultra-low emission system based on chemical looping combustion, characterized in that, Along the direction of flue gas flow, it includes an in-situ desulfurization unit, a cyclone separator, a nitrogen oxide removal unit, a dust removal unit, an external desulfurization unit, and a recirculation unit connected in sequence. The nitrogen oxide removal unit is located in the flue between the cyclone separator and the dust removal unit. Part of the recirculated flue gas after being processed by the dust removal unit and / or the recirculation unit is used at least for the dilution or atomization of the denitrification reducing agent in the nitrogen oxide removal unit, and / or returned to the chemical chain feed system.

2. The ultra-low emission flue gas system based on chemical looping combustion according to claim 1, characterized in that, The in-situ desulfurization unit includes a fuel reactor body and an oxygen carrier addition pipeline disposed on the side wall of the fuel reactor body. The oxygen carrier addition pipeline is used to add desulfurization reducing agent to the fuel reactor body.

3. The ultra-low emission flue gas system based on chemical looping combustion according to claim 2, characterized in that, The desulfurization reducing agent includes any one of alkali metal compounds and alkaline earth metal oxides.

4. The ultra-low emission flue gas system based on chemical looping combustion according to claim 2, characterized in that, The top of the fuel reactor body is connected to the cyclone separator, and the bottom of the cyclone separator is connected to the fuel reactor body in the opposite direction.

5. The ultra-low emission flue gas system based on chemical looping combustion according to claim 1, characterized in that, Along the direction of flue gas flow, an economizer and an air preheater are sequentially installed in the flue.

6. The ultra-low emission flue gas system based on chemical looping combustion according to claim 5, characterized in that, The nitrogen oxide removal unit includes a first spray layer, a second spray layer, and a catalyst layer. The first spray layer is disposed at the inlet of the flue, and the second spray layer and the catalyst layer are disposed between the economizer and the air preheater. The first spray layer is used to spray urea solution atomized from recirculated flue gas into the flue gas, and the second spray layer is used to spray urea hydrolysis product gas diluted from recirculated flue gas into the flue gas. The catalyst layer is filled with a selective catalytic reduction catalyst.

7. The ultra-low emission flue gas system based on chemical looping combustion according to claim 1, characterized in that, A condensation and dehydration device is provided between the dust removal unit and the external desulfurization unit.

8. The ultra-low emission flue gas system based on chemical looping combustion according to claim 1, characterized in that, The external desulfurization unit includes a desulfurization absorption tower, a slurry oxidation tank, a slurry circulation pump, and an oxidation fan. The desulfurization absorption tower is connected to the slurry oxidation tank, the slurry oxidation tank is connected to the desulfurization absorption tower in reverse through the slurry circulation pump, and the oxidation fan is connected to the slurry oxidation tank.

9. The ultra-low emission flue gas system based on chemical looping combustion according to claim 1, characterized in that, The recycling unit includes a dehydration unit, a compression unit, and a carbon dioxide purification unit connected in sequence. Part of the recirculated flue gas after being processed by the compression device is used for dilution of the denitrification reducing agent in the nitrogen oxide removal unit and / or returned to the chemical loop feed system.

10. A method for treating chemical looping combustion flue gas using the ultra-low emission system based on chemical looping combustion as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. The high-temperature flue gas generated by the fuel reactor comes into contact with the desulfurization reducing agent in the in-situ removal unit inside the furnace for preliminary desulfurization. S2. The flue gas processed in step S1 enters the cyclone separator to remove the solid particles it carries, and the separated solid particles are returned to the in-situ removal unit inside the furnace. S3. The flue gas treated in step S2 enters the nitrogen oxide removal unit and is mixed with the denitrification reducing agent diluted by the recirculated flue gas to remove nitrogen oxides. S4. The flue gas treated in step S3 is then subjected to dust removal and external wet desulfurization in sequence. S5. Part of the flue gas after dust removal in step S3 is returned to the fuel reactor body. The flue gas treated in step S4 is dehydrated and compressed in sequence. Part of the compressed flue gas is drawn out as recirculated flue gas for dilution of the denitrification reducing agent in step S3 and / or returned to the chemical loop coal feeding system. The remaining part of the flue gas is purified to obtain high-purity carbon dioxide.

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