Method and system for deeply removing N2O in flue gas through low-temperature enhanced oxidation

Abstract

The invention belongs to the field of pollutant removal, and particularly discloses a low-temperature enhanced oxidation deep removal method and system for N2O in flue gas, and the method comprises the following steps: injecting an oxidizing agent into a flue to oxidize N2O into NO; flue gas is sequentially introduced into a gas-gas heat exchanger and a stepped cooling tower, and step-by-step cooling of the flue gas is achieved; introducing the cooled flue gas into a low-temperature adsorption tower to realize low-temperature oxidation, adsorption and removal of N2O and NO formed by oxidation; and finally, the purified flue gas is emptied after cold energy recycling through a gas-gas heat exchanger. According to the method, form directional regulation and deep removal of N2O in the flue gas can be realized under the condition of not introducing extra noble metal elements or high-value adsorption materials, and the method has the advantages of low cost, simple process, high removal rate, wide application range, no environmental safety risk and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of pollutant removal, and relates to a method and system for deep removal of N2O in flue gas by low-temperature enhanced oxidation. Background Art

[0002] N2O is a potent greenhouse gas with a global warming potential more than 260 times that of carbon dioxide (based on 100 years), and it also damages the ozone layer. In addition, N2O has a lifetime of more than 100 years in the atmosphere, posing a long-term and serious threat to the environment and climate. Therefore, it is necessary to strictly control the emission of N2O during the thermal conversion of solid fuels.

[0003] During the combustion / pyrolysis / gasification of solid fuels, the generation of N2O involves complex multiphase reaction processes such as oxidation of volatile nitrogen (NH3, HCN, etc.), direct oxidation of coke nitrogen, and heterogeneous reactions of surface nitrogen-containing active components. In a high-temperature furnace, N2O needs to go through a process from generation to decomposition. Since the generation rate of N2O is very fast, but the decomposition rate is relatively slow, the decomposition of N2O is hindered in low-temperature combustion scenarios, and the emission concentration increases sharply. For example, in a circulating fluidized bed combustion boiler (combustion temperature is 850-950℃), the N2O pollution problem needs to be paid special attention to.

[0004] At present, the mainstream control technologies for N2O in flue gas can be mainly divided into in-furnace control and tail treatment. In a high-temperature furnace, the generation of N2O can be effectively reduced by optimizing the thermal conversion conditions, such as adjusting the excess air coefficient, thermal conversion temperature, graded thermal conversion and optimizing the burner design, but the control effect is limited and it is difficult to meet the emission standards. Tail treatment technologies are mainly divided into high-temperature pyrolysis and catalytic decomposition. High-temperature pyrolysis refers to the direct decomposition of N2O at above 1000°C, which consumes a lot of energy. The catalytic decomposition method uses a catalyst to decompose N2O to form N2 and O2 at a relatively low temperature (400-800°C), but it requires expensive precious metal catalysts. At present, the control problem of N2O pollutants in flue gas is still severe and needs to be solved urgently.

[0005] In the existing technologies for controlling N2O emissions in flue gas, they mainly include: (1) CN116493018A discloses a composite oxide catalyst for catalytic decomposition of high-concentration N2O and its preparation method. By dissolving, mixing, aging, precipitating, drying, and calcining Ni, Nb, Co, alkali metal / alkaline earth metal-based salts, a composite catalyst is obtained. It still maintains good catalytic activity under high H2O and N2O concentrations. However, this method requires a large amount of consumption of precious metal elements such as Nb, Co, and Ni, with high costs, and the application conditions are harsh (above 400°C); (2) Improved N2O capture performance of chromium terephthalate MIL-101 via substituent engineering (Journal of Solid State Chemistry, 2022, 309: 122951) discloses an MTN-type metal-organic framework adsorbent. By loading different substituents (-H, -NH2, -Br, -NO2), the capture ability for N2O is improved, and the separation selectivity of N2O reaches 1.91. This method has a high efficiency for capturing N2O, but the preparation process of the adsorbent is complex and it is difficult to be applied on a large scale; (3) Feasibility of using red mud as bed material for treating N2O in fluidized bed combustion (Fuel, 2025, 379: 133068) discloses a technology for reducing N2O emissions in flue gas from fluidized bed combustion by using red mud. By replacing the traditional fluidized bed material with red mud and co-combusting with coal, the N2O concentration in the tail gas can be reduced by up to 50% at most. This method has low costs and can effectively utilize the solid waste red mud. However, the application is limited (only applicable to fluidized bed boilers), and it will cause an increase in NO emissions.

[0006] Through research, it is found that the existing technologies for controlling N2O emissions in flue gas mainly have the following problems: (1) Conventional adsorbents have poor adsorption ability for NO, and a large amount of precious metal elements are required for modification, resulting in high costs; (2) The process flow is complex and it is difficult to apply industrially; (3) The applicable range is limited, and it cannot handle various complex flue gas conditions, and it causes emissions of other pollutants. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a method and system for deep removal of N2O in flue gas through form-induced coupling and low-temperature enhanced oxidation, aiming to solve the problems such as the need to consume a large amount of precious metal elements, high costs, complex process flow, and limited applicable range in the existing control of N2O in flue gas.

[0008] The present invention is realized by the following technical solutions: A method for deeply removing N2O by low-temperature enhanced oxidation in flue gas, comprising the following steps: S1, injecting an oxidant into a specific position of the flue duct to partially oxidize N2O in the flue gas and convert it into NO; S2, passing the flue gas treated in S1 into the hot end of a gas-gas heat exchanger to preliminarily cool the flue gas; S3, passing the preliminarily cooled flue gas into a cascade cooling tower to cool the flue gas temperature to the target temperature; S4, passing the flue gas reaching the target temperature into a low-temperature adsorption tower, so that N2O and the formed NO in the flue gas are oxidized and adsorbed by activated carbon to form nitrogen-containing inorganic salts, thereby realizing the deep removal of N2O by low-temperature enhanced oxidation in the flue gas and obtaining purified flue gas; S5, passing the purified flue gas into the cold end of the gas-gas heat exchanger described in step S2 to heat the flue gas and then discharging it into the air.

[0009] Preferably, in S1, the oxidant is one or more of O2 gas, O3 gas, active O atoms, Cl2 gas, and active Cl atoms; the injection concentration of the oxidant is 50-1500 mg / m 3 .

[0010] Preferably, the specific position of the flue duct is one or more of the inlet of the dust collector, the inlet of the cascade cooling tower, the spray nozzle of the cascade cooling tower, the inlet of the low-temperature adsorption tower, and the inside of the low-temperature adsorption tower.

[0011] Preferably, in S3, the cascade cooling tower includes 1-3 stages of spraying, and the coolant is one or several of distilled water, brine, and organic solvents.

[0012] Preferably, in S3, the target temperature is -40 to 10 °C, preferably -20 to 0 °C.

[0013] Preferably, in S4, the gas hourly space velocity in the low-temperature adsorption tower is 500-2000 h -1 ; Preferably, in S4, the activated carbon is one or several of coal-based activated carbon, fruit shell activated carbon, wood-based activated carbon, and coconut shell activated carbon; the average particle size of the activated carbon is 1-30 mm, and the specific surface area of the activated carbon is 500-2000 m 2 / g.

[0014] Preferably, in S1, the flue gas includes one of entrained flow bed flue gas, circulating fluidized bed flue gas, grate furnace flue gas, sintering furnace flue gas, chain grate furnace flue gas, and coke oven flue gas.

[0015] Preferably, the source of the flue gas is one or more of coal, biomass, and solid waste combustion / pyrolysis / gasification.

[0016] A system for deep removal of N2O by low-temperature enhanced oxidation in flue gas, comprising a flue gas pretreatment device, a gas-gas heat exchanger, a cascade cooling tower and a low-temperature adsorption tower; The untreated flue gas is introduced into the inlet of the flue gas pretreatment device. The outlet of the flue gas pretreatment device is sequentially connected to the hot end of the gas-gas heat exchanger, the cascade cooling tower and the inlet of the low-temperature adsorption tower through pipelines. The outlet of the low-temperature adsorption tower is connected to the cold-end inlet of the gas-gas heat exchanger, and the cold-end outlet of the gas-gas heat exchanger is connected to the chimney to discharge the purified flue gas.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: The purpose of the present invention is to provide a method and system for deep removal of N2O by morphological induction coupling low-temperature enhanced oxidation in flue gas. Based on the basic properties of N2O in flue gas and the characteristics of flue gas, multi-channel means of oxidation-adsorption are used to realize the directional regulation and deep removal of the morphology of N2O. Through steps such as injecting oxidants, regulating flue gas temperature, and enhancing adsorption, the step-by-step conversion of N2O→NO→NO2→adsorbed NO3 - is achieved, so that N2O is finally separated from the flue gas without consuming precious metal elements or high-value adsorption materials. The process flow is simple and the cost is low. By setting a gas-gas heat exchanger, the present invention exchanges heat between the original hot flue gas and the purified cold flue gas in a non-contact form, realizes the preliminary cooling of the original flue gas and the heating of the purified flue gas, realizes the reuse of the cold energy of the purified flue gas, and reduces the system operation cost; Furthermore, the present invention controls N2O in the flue gas tail purification link. According to the properties of the flue gas itself (including components, temperature, concentration, etc.), various process parameters of the present invention can be optimized (such as the type of oxidant, the injection concentration of the oxidant, the target temperature, etc.) to make it applicable to the efficient removal of N2O in flue gas from various sources, and the application range is wide; Furthermore, the present invention uses O2 gas, O3 gas, active O atoms, Cl2 gas, active Cl atoms, etc. as the inducing oxidants for N2O. Among them, O2 gas is harmless to the environment, and other oxidants can be efficiently adsorbed and removed in the low-temperature adsorption tower without escape risk and is environmentally friendly. In addition, the present invention can realize the co-capture of other pollutants in the flue gas (such as NO / NO2, SO2, dust, heavy metals, VOCs), which can reduce the overall purification cost of the flue gas; Furthermore, by cooling the flue gas to -40~10°C, the present invention can condense and separate and recover the water vapor in the flue gas, and at the same time reduce the moisture content of the flue gas in the low-temperature adsorption tower, avoid the competitive interference effect of water vapor on the N2O adsorption process, and further improve the removal efficiency of pollutants in the low-temperature adsorption tower. Description of the Drawings

[0018] Figure 1 This is a schematic diagram provided by a preferred embodiment of the present invention. Among them, 1-5 are flue gas purification devices: 1-flue gas pretreatment device, 2-gas-gas heat exchanger, 3-staged cooling tower, 4-low-temperature adsorption tower, 5-chimney; a-g are oxidant injection sites: a-inlet of the dust collector, b-inlet of the staged cooling tower, c-primary spray port of the staged cooling tower, d-secondary spray port of the staged cooling tower (if any), e-tertiary spray port of the staged cooling tower (if any), f-inlet of the low-temperature adsorption tower, g-inside the low-temperature adsorption tower. Detailed implementation manners

[0019] The following further elaborates on the present invention with specific embodiments, which are explanations rather than limitations of the present invention.

[0020] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] The embodiment of the present invention provides a method and process for deeply removing N2O in flue gas by form-induced coupling with low-temperature enhanced oxidation, and the method includes the following steps: S1, injecting an oxidant into a specific site of the flue gas to partially oxidize N2O in the flue gas and convert it into NO; S2, passing the flue gas treated in S1 into the hot end of the gas-gas heat exchanger to preliminarily cool the flue gas; S3, passing the preliminarily cooled flue gas into the staged cooling tower to cool the flue gas temperature to the target temperature; S4, passing the flue gas reaching the target temperature into the low-temperature adsorption tower, so that N2O and the formed NO in the flue gas are oxidized and adsorbed by activated carbon to form nitrogen-containing inorganic salts, thereby realizing the deep removal of N2O in the flue gas by low-temperature enhanced oxidation and obtaining purified flue gas; S5, passing the purified flue gas into the cold end of the gas-gas heat exchanger described in step S2 to heat the flue gas and then discharge it.

[0022] Specifically, in step S1, due to the limited oxidation capacity of O2 contained in the flue gas itself, N2O, O2, and NO are in a state of chemical thermodynamic equilibrium, and N2O cannot be further oxidized. By injecting additional oxidants into specific locations in the flue to increase the overall content of oxidizing substances in the flue gas, the N2O oxidation rate can be increased, inducing more N2O to be converted into NO to be captured by the subsequent low-temperature adsorption tower. The oxidant added in step S1 is one or more of O2 gas, O3 gas, active O atoms, Cl2 gas, and active Cl atoms, and the chemical reaction formula involved is as follows: 2N2O+O2→4NO 3N2O+O3→6NO N2O+O→2NO N2O+Cl2→NO+NCl2 N2O+2Cl→NO+ NCl2 In step S2 and step S5, the flue gas (hereinafter referred to as the original flue gas) is introduced into the hot end of the gas-to-gas heat exchanger to initially cool the original flue gas; the purified flue gas is introduced into the cold end of the gas-to-gas heat exchanger in step S2 to heat the purified flue gas and then discharge it. This step allows the original flue gas to fully exchange heat with the purified flue gas. The temperature of the original flue gas is usually 100-200°C, and the temperature of the purified flue gas is usually -40-10°C. By exchanging heat between the two in the gas-to-gas heat exchanger, the original flue gas is initially cooled and the purified flue gas is heated. The cooling capacity of the purified flue gas can be utilized to avoid the waste of cooling capacity and potential ecological impact after being discharged into the atmospheric environment. At the same time, it can reduce the refrigeration energy consumption of the original flue gas and improve the overall economy of this process.

[0023] In step S3, the flue gas is passed into the cascade cooling tower, and the coolant in the cooling tower is injected by spraying, forming dispersed fine cooling droplets in the tower. The high-temperature flue gas contacts the cooling droplets, and completes heat exchange by heat conduction and heat convection, so that the flue gas temperature is cooled to the target temperature. Among them, the coolant is injected in a cycle by spraying-collecting-cooling-spraying, which can reduce the consumption of coolant and save process operation costs.

[0024] In step S4, the flue gas is passed into a low-temperature adsorption tower filled with multiple layers of activated carbon (AC) adsorbent. There are two main removal pathways for N2O in the flue gas. One is that N2O is converted into NO under the induction of the injected oxidant, and then NO (formed by oxidation of N2O) and O2 can continue to undergo oxidation reaction on the surface of activated carbon to form NO2. Since this reaction is an exothermic reaction, lowering the temperature can promote the forward reaction, so the rate and conversion rate of NO oxidation to form NO2 at low temperatures are greatly improved. The NO2 produced by oxidation has a stronger affinity with activated carbon and is more easily adsorbed by activated carbon and converted into NO3 -, so as to be separated from the flue gas. Second, N2O in the flue gas is directly captured by activated carbon through physical adsorption or chemical adsorption in the low-temperature adsorption tower. In addition, NO formed by the oxidation of N2O in the previous flue gas process can also be captured in the low-temperature adsorption tower after undergoing a similar process as described above. The chemical reaction equations involved in the low-temperature adsorption tower are as follows, 2N2O + O2 → 4NO 3N2O + O3 → 6NO N2O + O → 2NO N2O + Cl2 → NO + NCl2 N2O + 2Cl → NO + NCl2 NO + O2 → NO2 NO2 + O-AC → NO3 - (adsorbed state) + AC N2O + AC → N2O-AC (physical adsorption) N2O + 5O-AC → 2NO3 - (adsorbed state) + 5AC In addition, other pollutants in the flue gas (such as NO2, SO2, dust, heavy metals, VOCs) can be co-removed in the low-temperature adsorption tower.

[0025] Furthermore, in step S1, the oxidant is one or more of O2 gas, O3 gas, active O atoms, Cl2 gas, and active Cl atoms. The above gases all have strong oxidation ability for N2O. Among them, O2 gas, O3 gas, and Cl2 gas are common oxidizing gases with low cost; active O atoms and active Cl atoms can be formed by the ionization of O2 gas and Cl2 gas and then injected into the flue duct online, with stronger activity, which can reduce the injection amount of the oxidant. In addition, O2 gas is harmless to the environment, and other oxidants can be adsorbed and removed by activated carbon in the low-temperature adsorption tower without escape risk and are environmentally friendly.

[0026] Further, in step S3, the cascade cooling tower includes 1 to 3 stages of spraying. The spraying technology is determined according to the flue gas temperature and the target temperature. If the temperature difference between the flue gas temperature and the target temperature is 0 to 50 °C, preferably 1-stage spraying; if the temperature difference between the flue gas temperature and the target temperature is 50 to 120 °C, preferably 2-stage spraying; if the temperature difference between the flue gas temperature and the target temperature is 120 to 250 °C, preferably 3-stage spraying. The flue gas cooling capacity in the cascade cooling tower depends on the gas-liquid temperature difference, the spraying gas-liquid ratio, the relative flow rate, the spraying height, etc. Among them, the flue gas temperature depends on the configuration and working state of the front-end equipment and is difficult to be artificially regulated. In order to cool the flue gas to the target temperature, it is necessary to select an appropriate spraying stage according to the temperature difference between the flue gas temperature and the target temperature. Otherwise, it may lead to too high spraying gas-liquid ratio, relative flow rate, and spraying height, affecting the safe operation and operation economy of the system. In addition, the coolant is one or more of distilled water, brine, and organic solvents. If the target temperature is above 0 °C, preferably distilled water; if the target temperature is -40 to 0 °C, preferably brine or organic solvents. The difference between the above coolants lies in the freezing point. In order to reduce the flue gas below 0 °C, it is necessary to select brine or organic solvents with a freezing point below 0 °C. Select an appropriate coolant according to the target temperature, flue gas characteristics, and coolant cost.

[0027] Further, in step S1, the specific injection sites of the oxidant in the flue duct are one or more of the inlet of the dust collector, the inlet of the cascade cooling tower, the first-stage spraying port of the cascade cooling tower, the second-stage spraying port of the cascade cooling tower (if any), the third-stage spraying port of the cascade cooling tower (if any), the inlet of the low-temperature adsorption tower, and the inside of the low-temperature adsorption tower. The oxidation reaction of N2O is an endothermic reaction. Increasing the temperature is beneficial to the forward occurrence of the reaction and increases the reaction rate. The above injection sites are in the order of the inlet of the dust collector, the inlet of the cascade cooling tower, the first-stage spraying port of the cascade cooling tower, the second-stage spraying port of the cascade cooling tower (if any), the third-stage spraying port of the cascade cooling tower (if any), the inlet of the low-temperature adsorption tower, and the inside of the low-temperature adsorption tower along the flue gas flow direction. The flue gas temperature at each site gradually decreases along the flue gas flow direction. If the oxidant is injected at a high-temperature site, the reaction rate between the oxidant and N2O is fast, and the residence time of the oxidant in the flue duct is longer, and the oxidation rate of N2O is high. However, there are other impurity components in the flue gas at the high-temperature site, such as NO, SO2, H2S, etc., which can compete with N2O to consume the oxidant, resulting in an increase in the required injection amount of the oxidant. If the oxidant is injected at a low-temperature site, since other impurity components in the flue gas have been (partially) captured by the previous process (for example, inside the low-temperature adsorption tower, NO, SO2, and H2S have been basically completely removed), the oxidant has stronger targeting for the oxidation of N2O, and the injection amount of the oxidant can be saved. However, due to the low flue gas temperature and short residence time at the site, it is preferable to inject an oxidant with stronger oxidation activity to increase the oxidation rate of N2O.

[0028] Further, in step S3, the target temperature for the flue gas to condense in the cascade cooling tower is -40 to 10 °C, preferably -20 to 0 °C. The main function of the cascade cooling tower is to cool the flue gas, which then enters the low-temperature adsorption tower to achieve the removal of N2O. Since the removal of N2O involves two main reactions: the oxidation of N2O to NO and the oxidation of NO to NO2. Among them, the oxidation adsorption of N2O is an endothermic reaction, and the oxidation adsorption of NO is an exothermic reaction. Considering the concentrations of N2O and NO, the oxidation rate, and the adsorption capacity of activated carbon comprehensively, -40 to 10 °C is a suitable operating temperature range for the adsorption tower. Further considering the cooling energy consumption of the cascade cooling tower, the cost of the refrigeration medium, etc., it is preferably -20 to 0 °C.

[0029] Further, in step S1, the injection concentration of the oxidant is 5 to 500 mg / m 3 . The oxidation rate of N2O is affected by many factors such as flue gas temperature, flue gas impurity components, oxidant type, oxidation reaction time, etc. Appropriate excessive injection of the oxidant can increase the oxidation rate of N2O, while a large amount of excessive injection of the oxidant will cause waste of the oxidant and there is a risk of the oxidant penetrating the adsorption tower and escaping, causing additional pollution. Therefore, according to the N2O concentration, impurity components, injection temperature, oxidant type, oxidation reaction time, etc. in the flue gas to be treated, the injection concentration of the oxidant is preferably 50 to 1500 mg / m 3 .

[0030] Further, in step S4, the gas hourly space velocity in the low-temperature adsorption tower is 500 to 2000 h -1 . The hourly space velocity represents the size of the flue gas flow rate treated by a unit volume of adsorbent and reflects the residence time of the flue gas to be treated in the adsorption area. In the low-temperature adsorption tower, the oxidation / adsorption process of pollutants such as N2O and NO with activated carbon follows the heterogeneous gas-solid reaction mechanism, and the reaction rate is slow. If the hourly space velocity is too large (short residence time), some pollutants will not be able to fully contact and react with the activated carbon, resulting in a decrease in the removal rate; conversely, if the hourly space velocity is too small, the removal rate of pollutants such as N2O and NO in the low-temperature adsorption tower can be increased, but the required volume of activated carbon increases, resulting in an increase in the operating cost of the adsorption system and a decline in technical economy. Considering factors such as the concentrations of pollutants such as N2O and NO in the low-temperature adsorption tower, the removal rate, and the properties of activated carbon comprehensively, the gas hourly space velocity in the low-temperature adsorption tower is preferably 500 to 2000 h -1 .

[0031] Further, in step S4, the activated carbon is one or more of coal-based activated carbon, fruit shell activated carbon, wood-based activated carbon, and coconut shell activated carbon. The average particle size of the activated carbon is 1 to 30 mm, and the specific surface area of the activated carbon is 500 to 2000 m 2 / g. The adsorption capacity of activated carbon for pollutants such as N2O and NO is also affected by its own physical and chemical properties. For example, coconut shell activated carbon has well-developed physical pores, fruit shell activated carbon and wood activated carbon have rich surface active groups, and coal-based activated carbon is rich in catalytic metal elements. According to the pollutant components, flue gas conditions and operating costs in the flue gas to be treated, the preferred activated carbon is one or several of coal-based activated carbon, fruit shell activated carbon, wood activated carbon and coconut shell activated carbon. The particle size and specific surface area of activated carbon determine the diffusion and contact rate of flue gas pollutant components to the surface and pores of activated carbon. Generally speaking, reducing the particle size and increasing the specific surface area are beneficial to the adsorption and removal of pollutants by activated carbon. However, too small particle size will lead to a tight packing of the adsorption bed layer, a large flue gas flow resistance, and a high energy consumption loss of the booster fan. Too large specific surface area will lead to an increase in the production cost of activated carbon. Considering the performance of activated carbon and the operating energy consumption of the adsorption system, the average particle size of the preferred activated carbon is 1-30 mm, and the specific surface area of the activated carbon is 500-2000 m 2 / g.

[0032] Further, in step S1, the flue gas includes one of entrained flow bed flue gas, circulating fluidized bed flue gas, grate furnace flue gas, sintering furnace flue gas, chain grate furnace flue gas, and coke oven flue gas, and the source of the flue gas is one or more of coal, biomass, and solid waste combustion / pyrolysis / gasification. This method is used for purifying N2O in the flue gas after combustion, can operate independently and flexibly, and is not limited by the front-end thermal conversion equipment and fuel type. According to the upstream flue gas conditions (temperature, pressure, flow rate) and flue gas pollutant components (N2O, NO, NO2, SO2, dust, etc.), this method preferentially selects parameters such as the type of oxidant, the injection site of the oxidant, the injection concentration of the oxidant, the number of spray levels, the type of coolant, the cooling target temperature, the gas hourly space velocity of the low-temperature adsorption tower, and the type of activated carbon within the scope described above to achieve the efficient removal of N2O in the flue gas from different fuel sources and different thermal conversion equipment. Solid waste includes municipal solid waste; such as Figure 1As shown, the method and process for deep removal of N2O in flue gas by form-induced coupling with low-temperature enhanced oxidation provided by the present invention are applied to a flue gas purification process. The specific process is as follows: The N2O-containing flue gas generated by the upstream thermal conversion equipment successively passes through 1 - flue gas pretreatment device, 2 - gas-gas heat exchanger (hot end), 3 - cascade cooling tower, 4 - low-temperature adsorption tower, 2 - gas-gas heat exchanger (cold end), and then is discharged from 5 - chimney. Among them, an oxidant is injected at one or more of the a - dust collector inlet, b - cascade cooling tower inlet, c - first spray port of the cascade cooling tower, d - second spray port of the cascade cooling tower (if any), e - third spray port of the cascade cooling tower (if any), f - low-temperature adsorption tower inlet, and g - inside the low-temperature adsorption tower in the flue. The N2O in the flue gas undergoes an oxidation reaction under the induction of the oxidant to form NO. The flue gas is cooled to -40~10°C in the 2 - cascade cooling tower, and then the residual N2O and the NO formed by the above conversion in the low-temperature adsorption tower are captured by activated carbon through oxidation and adsorption, thereby realizing the deep removal of N2O in the flue gas by form-induced coupling with low-temperature enhanced oxidation. In the present invention, the flue gas pretreatment device can adopt a dust collector.

[0033] According to another aspect of the present invention, an application of the above method in a coal-fired power plant is provided to further elaborate on the present invention in detail.

[0034] The technical solution provided by the present invention will be further described below according to specific embodiments.

[0035] Example 1 Application object: Flue gas from the operation of a certain entrained flow bed, with coal as the raw material, N2O content in the flue gas of 30mg / m 3 , NO content of 285mg / m 3 , NO2 content of 54mg / m 3 , SO2 content of 1350mg / m 3 , O2 concentration of 6%, and the flue gas temperature at the dust collector outlet is 152°C.

[0036] Operation process: Inject oxidant O2 inside the low-temperature adsorption tower, with an injection concentration of 950mg / m 3 . Subsequently, the flue gas enters the cascade cooling tower (3 stages) and is cooled to -40°C. The coolant is brine. The cooled flue gas enters the low-temperature adsorption tower. The adsorbent in the low-temperature adsorption tower is coal-based activated carbon, with an average particle size of 15mm, a specific surface area of 1160m 2 / g, and an air velocity of 1600h -1 .

[0037] After the N2O form in the flue gas is induced to transform and deeply removed by enhanced oxidation at low temperature in this example, the N2O concentration at the chimney outlet is 2mg / m 3 , the removal rate is 93.33%, and the NO concentration is 1mg / m 3, the removal rate is 99.65%, and the NO2 concentration is 2 mg / m 3 , the removal rate is 96.30%, and the SO2 concentration is 8 mg / m 3 , the removal rate is 99.41%.

[0038] Example 2 Application object: Flue gas from a certain entrained-flow bed operation, with rice straw biomass as the raw material. The N2O content in the flue gas is 52 mg / m 3 , the NO content is 198 mg / m 3 , the NO2 content is 50 mg / m 3 , the SO2 content is 37 mg / m 3 , the O2 concentration is 6%, and the flue gas temperature at the outlet of the dust collector is 137 °C.

[0039] Operation process: Inject oxidant active Cl atoms at the inlet of the low-temperature adsorption tower, with an injection concentration of 150 mg / m 3 , and then the flue gas enters a cascade cooling tower (3 stages) to be cooled to -20 °C. The coolant is brine. The cooled flue gas enters the low-temperature adsorption tower. The adsorbent in the low-temperature adsorption tower is coal-based activated carbon, with an average particle size of 4 mm and a specific surface area of 880 m 2 / g, and the space velocity is 1800 h -1 .

[0040] After the N2O form in the flue gas is induced to transform and strongly oxidized and removed at low temperature in this example, the N2O concentration at the chimney outlet is 2 mg / m 3 , the removal rate is 96.15%, the NO concentration is 4 mg / m 3 , the removal rate is 97.98%, the NO2 concentration is 1 mg / m 3 , the removal rate is 98.00%, the SO2 concentration is 1 mg / m 3 , the removal rate is 97.30%.

[0041] Example 3 Application object: Flue gas from a certain circulating fluidized bed operation, with wood chip biomass as the raw material. The N2O content in the flue gas is 255 mg / m 3 , the NO content is 240 mg / m 3 , the NO2 content is 83 mg / m 3 , the SO2 content is 15 mg / m 3 , the O2 concentration is 5%, and the flue gas temperature at the outlet of the dust collector is 119 °C.

[0042] Operation process: Inject oxidant O3 at the inlet of the dust collector, with an injection concentration of 400 mg / m 3, Subsequently, the flue gas enters the cascade cooling tower (3-stage) and is cooled to 3 °C. The coolant is brine. The cooled flue gas enters the low-temperature adsorption tower. The adsorbent in the low-temperature adsorption tower is fruit shell activated carbon, with an average particle size of 6 mm and a specific surface area of 1750 m 2 / g, and the space velocity is 650 h -1 .

[0043] After the N2O form in the flue gas is induced to transform and intensively oxidized and removed at low temperature in this example, the N2O concentration at the chimney outlet is 8 mg / m 3 , the removal rate is 96.86%, the NO concentration is 3 mg / m 3 , the removal rate is 98.75%, the NO2 concentration is 3 mg / m 3 , the removal rate is 96.39%, the SO2 concentration is 1 mg / m 3 , and the removal rate is 93.33%.

[0044] Example 4 Application object: The flue gas from a circulating fluidized bed, with coal as the raw material. The N2O content in the flue gas is 327 mg / m 3 , the NO content is 138 mg / m 3 , the NO2 content is 35 mg / m 3 , the SO2 content is 1864 mg / m 3 , the O2 concentration is 6%, and the flue gas temperature at the outlet of the dust collector is 60 °C.

[0045] Operation process: Inject the oxidant O3 at the inlet of the cascade cooling tower, with an injection concentration of 1500 mg / m 3 , then the flue gas enters the cascade cooling tower (1-stage) and is cooled to 10 °C. The coolant is distilled water. The cooled flue gas enters the low-temperature adsorption tower. The adsorbent in the low-temperature adsorption tower is wood activated carbon, with an average particle size of 18 mm and a specific surface area of 525 m 2 / g, and the space velocity is 500 h -1 .

[0046] After the N2O form in the flue gas is induced to transform and intensively oxidized and removed at low temperature in this example, the N2O concentration at the chimney outlet is 7 mg / m 3 , the removal rate is 97.86%, the NO concentration is 2 mg / m 3 , the removal rate is 98.55%, the NO2 concentration is 1 mg / m 3 , the removal rate is 97.14%, the SO2 concentration is 6 mg / m 3 , and the removal rate is 99.68%.

[0047] Example 5 Application object: The flue gas from a grate furnace, with municipal solid waste as the raw material. The N2O content in the flue gas is 150 mg / m3 , with a NO content of 165 mg / m 3 , with a NO2 content of 35 mg / m 3 , with a SO2 content of 864 mg / m 3 , with an O2 concentration of 10%, and the flue gas temperature at the outlet of the dust collector is 123 °C.

[0048] Operation process: Inject the oxidant Cl2 at the secondary spray nozzle of the cascade cooling tower, with an injection concentration of 1200 mg / m 3 . Subsequently, the flue gas enters the cascade cooling tower (3 stages) and is cooled to -20 °C. The coolant is brine. The cooled flue gas enters the low-temperature adsorption tower. The adsorbent in the low-temperature adsorption tower is coconut shell activated carbon, with an average particle size of 1 mm and a specific surface area of 1950 m 2 / g, and the space velocity is 2000 h -1 .

[0049] After the N2O form in the flue gas is induced to transform and intensively oxidized and removed at low temperature in this example, the N2O concentration at the chimney outlet is 6 mg / m 3 , the removal rate is 96.00%, the NO concentration is 1 mg / m 3 , the removal rate is 99.39%, the NO2 concentration is 2 mg / m 3 , the removal rate is 94.29%, the SO2 concentration is 8 mg / m 3 , the removal rate is 99.07%.

[0050] Example 6 Application object: The flue gas from the operation of a certain sintering furnace, with coal as the raw material. The N2O content in the flue gas is 28 mg / m 3 , the NO content is 552 mg / m 3 , the NO2 content is 53 mg / m 3 , the SO2 content is 780 mg / m 3 , the O2 concentration is 6%, and the flue gas temperature at the outlet of the dust collector is 109 °C.

[0051] Operation process: Inject the oxidant active O atoms inside the low-temperature adsorption tower, with an injection concentration of 50 mg / m 3 . Subsequently, the flue gas enters the cascade cooling tower (2 stages) and is cooled to 0 °C. The coolant is an organic solvent. The cooled flue gas enters the low-temperature adsorption tower. The adsorbent in the low-temperature adsorption tower is coal-based activated carbon, with an average particle size of 30 mm and a specific surface area of 1280 m 2 / g, and the space velocity is 1800 h -1 .

[0052] After the N2O form in the flue gas is induced to transform and intensively oxidized and removed at low temperature in this example, the N2O concentration at the chimney outlet is 2 mg / m 3, the removal rate is 92.86%, and the NO concentration is 4 mg / m 3 , the removal rate is 99.28%, and the NO2 concentration is 1 mg / m 3 , the removal rate is 98.11%, and the SO2 concentration is 6 mg / m 3 , the removal rate is 99.23%.

[0053] Example 7 Application object: Flue gas from the operation of a chain grate boiler, with coal as the raw material. The N2O content in the flue gas is 121 mg / m 3 , the NO content is 234 mg / m 3 , the NO2 content is 135 mg / m 3 , the SO2 content is 1264 mg / m 3 , the O2 concentration is 6%, and the flue gas temperature at the outlet of the dust collector is 134 °C.

[0054] Operation process: Inject the oxidant O3 at the first-stage spray nozzle of the cascade cooling tower, with an injection concentration of 1200 mg / m 3 , and then the flue gas enters the cascade cooling tower (3 stages) to be cooled to -20 °C. The coolant is brine. The cooled flue gas enters the low-temperature adsorption tower. The adsorbent in the low-temperature adsorption tower is coconut shell activated carbon, with an average particle size of 25 mm and a specific surface area of 760 m 2 / g, and the space velocity is 1000 h -1 .

[0055] After the N2O form in the flue gas is induced to transform and intensively oxidized and removed at low temperature in this example, the N2O concentration at the chimney outlet is 5 mg / m 3 , the removal rate is 95.87%, and the NO concentration is 1 mg / m 3 , the removal rate is 99.57%, and the NO2 concentration is 4 mg / m 3 , the removal rate is 97.04%, and the SO2 concentration is 9 mg / m 3 , the removal rate is 99.29%.

[0056] Example 8 Application object: Flue gas from the operation of a coke oven, with coal as the raw material. The N2O content in the flue gas is 18 mg / m 3 , the NO content is 350 mg / m 3 , the NO2 content is 52 mg / m 3 , the SO2 content is 580 mg / m 3 , the O2 concentration is 7%, and the flue gas temperature at the outlet of the dust collector is 195 °C.

[0057] Operation process: Inject the oxidant O2 at the third-stage spray nozzle of the cascade cooling tower, with an injection concentration of 800 mg / m 3, and then the flue gas enters the cascade cooling tower (3 - stage) and is cooled to - 10°C. The coolant is brine. The cooled flue gas enters the low - temperature adsorption tower. The adsorbent in the low - temperature adsorption tower is coal - based activated carbon with an average particle size of 10 mm and a specific surface area of 1230 m 2 / g, and the space velocity is 1800 h -1 .

[0058] After the N2O form in the flue gas is induced to transform and intensively oxidized and removed at low temperature in this embodiment, the N2O concentration at the chimney outlet is 1 mg / m 3 , the removal rate is 94.44%, the NO concentration is 2 mg / m 3 , the removal rate is 99.43%, the NO2 concentration is 3 mg / m 3 , the removal rate is 94.23%, the SO2 concentration is 4 mg / m 3 , and the removal rate is 99.31%.

[0059] In this way, through the process of inducing coupling and low - temperature intensive oxidation for deep removal of N2O form in flue gas of the present invention, the directional regulation and deep removal of N2O form in flue gas can be realized without introducing additional precious metal elements or high - value adsorption materials, effectively reducing the emission of N2O in flue gas, and having the advantages of low cost, simple process, high removal rate, wide application range, no environmental safety risks and other negative impacts.

[0060] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above - mentioned drawings are intended to cover non - exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0061] In the present invention, unless otherwise clearly defined and limited, terms such as "installed", "connected", "joined", "fixed", etc. shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or a communication connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. When a component is referred to as "fixed to" another component, it can be directly on the other component or there may also be an intermediate component. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component at the same time. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component at the same time.

[0062] It should be understood that when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used in the specification of this invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0064] As described above, it is only the preferred embodiment of the present invention and does not impose any form of limitation on the present invention; any person skilled in the art can smoothly implement the present invention according to what is shown in the accompanying drawings of the specification and the above description; however, any equivalent changes such as slight modifications, evolutions made by those skilled in the art within the scope of the technical solution of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications, and evolutions made to the above embodiments based on the essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for deep removal of N2O by low-temperature enhanced oxidation in flue gas, characterized in that, It includes the following steps: S1. Inject an oxidant into a specific position of the flue duct to partially oxidize N2O in the flue gas and convert it into NO; S2. Pass the flue gas treated in S1 into the hot end of the gas-gas heat exchanger to preliminarily cool the flue gas; S3. Pass the preliminarily cooled flue gas into a cascade cooling tower to cool the temperature of the flue gas to the target temperature; S4. Pass the flue gas reaching the target temperature into a low-temperature adsorption tower, so that N2O and the formed NO in the flue gas are oxidized and adsorbed by activated carbon to form nitrogen-containing inorganic salts, thereby realizing the deep removal of N2O in the flue gas by low-temperature enhanced oxidation and obtaining purified flue gas; S5. Pass the purified flue gas into the cold end of the gas-gas heat exchanger described in step S2 to heat up the flue gas and then discharge it into the air.

2. The method for deep removal of N2O by low-temperature enhanced oxidation in flue gas according to claim 1, wherein In S1, the oxidant is one or more of O2 gas, O3 gas, active O atoms, Cl2 gas, and active Cl atoms; the injection concentration of the oxidant is 50~1500 mg / m 3 .

3. A method for deep removal of N2O by low-temperature enhanced oxidation in flue gas according to claim 1, characterized in that The specific position of the flue duct is one or more of the inlet of the dust collector, the inlet of the cascade cooling tower, the spray nozzle of the cascade cooling tower, the inlet of the low-temperature adsorption tower, and the inside of the low-temperature adsorption tower.

4. A method for deep removal of N2O by low-temperature enhanced oxidation in flue gas according to claim 1, characterized in that, In S3, the cascade cooling tower includes 1 to 3 stages of spraying, and the coolant is one or several of distilled water, brine, and organic solvents.

5. A method for deep removal of N2O by low-temperature enhanced oxidation in flue gas according to claim 1, characterized in that, In S3, the target temperature is -40 to 10 °C.

6. A method for deep removal of N2O in flue gas by low-temperature enhanced oxidation according to claim 1, characterized in that, In S4, the gas hourly space velocity in the low-temperature adsorption tower is 500 - 2000 h -1 .

7. A method for deep removal of N2O by low-temperature enhanced oxidation in flue gas according to claim 1, characterized in that, In S4, the activated carbon is one or more of coal-based activated carbon, fruit shell activated carbon, wood activated carbon, and coconut shell activated carbon; the average particle size of the activated carbon is 1 - 30 mm, and the specific surface area of the activated carbon is 500 - 2000 m 2 / g.

8. A method for deep removal of N2O by low-temperature enhanced oxidation in flue gas according to claim 1, characterized in that, In S1, the flue gas includes one of the flue gas from a entrained flow bed, the flue gas from a circulating fluidized bed, the flue gas from a grate furnace, the flue gas from a sintering furnace, the flue gas from a chain grate furnace, and the flue gas from a coke oven.

9. A method for deep removal of N2O in flue gas by low-temperature enhanced oxidation according to claim 1, characterized in that The source of the flue gas is one or several of the combustion / pyrolysis / gasification of coal, biomass, and solid waste.

10. A system for deep removal of N2O by low-temperature enhanced oxidation in flue gas, based on the method for deep removal of N2O by low-temperature enhanced oxidation in flue gas according to any one of claims 1-9, characterized in that, It includes a flue duct pretreatment device, a gas-gas heat exchanger, a cascade cooling tower, and a low-temperature adsorption tower; The untreated flue gas is passed into the inlet of the flue duct pretreatment device. The outlet of the flue duct pretreatment device is sequentially connected to the hot end of the gas-gas heat exchanger, the cascade cooling tower, and the inlet of the low-temperature adsorption tower through pipelines. The outlet of the low-temperature adsorption tower is connected to the cold end inlet of the gas-gas heat exchanger, and the cold end outlet of the gas-gas heat exchanger is connected to the chimney to discharge the purified flue gas into the air.

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