A flue gas desulfurization and denitrification method for pricing oxidative coupling of nitrogen and sulfur synergistic absorption

Abstract

The present application relates to a kind of pricing oxidation coupling nitrogen sulfur synergic absorption flue gas desulfurization and denitrification method, it is related to flue gas desulfurization and denitrification technical field.The present application first after the catalytic oxidation of hydrogen peroxide and ozone with the pricing catalyst to flue gas, NO in flue gas is priced and oxidized into NO2, and oxidation flue gas is obtained;Afterwards, oxidation flue gas is absorbed slurry and is used to nitrogen sulfur synergic absorption, realizes flue gas desulfurization and denitrification;The catalyst used is Co x Mn 3‑x O4 Nano metal oxide.The present application solves the problem of low nitrogen oxide absorption efficiency at low cost, realizes final flue gas ultra-low emission.The absorbent of the present application can synergic absorption nitrogen sulfur flue gas mainly with nitrogen dioxide at normal temperature, can simultaneously meet the goal of low energy consumption and low emission.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flue gas desulfurization and denitrification, in particular to a flue gas desulfurization and denitrification method based on fixed-price oxidation and coupled nitrogen-sulfur absorption. BACKGROUND

[0002] For flue gas containing sulfur, many desulfurization technologies have been developed. According to the research results of Chen Guoqing et al., the flue gas desulfurization technology using calcium-based absorbent accounts for more than 95% of the market share. Among them, wet flue gas desulfurization (WFGD) is one of the most mainstream technologies, which has strong adaptability, simple operation, less equipment, low reaction energy consumption, and basically meets the requirements of flue gas desulfurization.

[0003] NO X The removal methods mainly include reduction method and oxidation method. The oxidation method can realize simultaneous removal of nitrogen and sulfur in flue gas in combination with desulfurization process, without the need for additional devices. However, the high-efficiency temperature range of desulfurization is in the low-temperature range (<180℃), and the high-efficiency temperature range of NO catalytic oxidation is (200℃-300℃), so they cannot achieve the purpose of efficient simultaneous removal of nitrogen and sulfur through simple superposition. In addition, the oxidation degree of NO is uncontrollable, which may produce multi-valence nitrogen oxides, affecting the subsequent synergistic removal efficiency. The commonly used catalytic reduction (SCR) technology of the reduction method can directly reduce nitrogen oxides to nitrogen, but it needs to increase a special catalytic device, and the reaction energy consumption is higher than that of catalytic oxidation, with a high-efficiency temperature range of (230℃-450℃) and significantly increased cost. The working temperature of the non-catalytic reduction (SNCR) technology is usually above 800℃, which is not widely applicable.

[0004] The common technical route of existing nitrogen-sulfur synergistic removal technology includes: the reduction synergistic method uses the addition of urea and other reducing agents to directly reduce NO to N2. However, the denitrification efficiency is generally lower than 50%, which is mainly due to the low solubility of NO, which is difficult to be fully reduced. The oxidation synergistic method adds NaClO2, H2O2, KMnO4 and other oxidizing agents to oxidize NO to NO2, which can improve the denitrification efficiency to about 65%. However, the molar ratio of oxidizing agent to NO is usually more than 5, which increases the economic cost and the oxidation products may exist in the form of N2O3 and N2O5, which is not conducive to the denitrification reaction in the low-temperature section. The common absorbents such as calcium-based wet method and semi-dry method also have low NOx absorption efficiency, which is mainly limited by the fact that the reaction products of calcium-based absorbent in the desulfurization process can mask the unreacted absorbent, affecting the overall denitrification efficiency.

[0005] Therefore, it is necessary to develop a SO2 and NO x The ideal process route of the synergistic removal technology can be based on a mature high-efficiency low-energy consumption pollutant (SO2) control technology for improvement and perfection, and try to improve another pollutant (NO xThe removal efficiency of NOx and SO2 is improved, and the removal of NOx and SO2 is realized in cooperation. SUMMARY

[0006] The application aims to provide a flue gas desulfurization and denitrification method of priced oxidation coupled with nitrogen-sulfur synergistic absorption, so as to solve the problems of the prior art, realize efficient and synergistic removal of nitrogen-sulfur flue gas, and realize upgrading emission by modification of the original WFGD process, or serve as an independent desulfurization and denitrification device to meet the tail gas treatment demand with low energy consumption and high standard.

[0007] To achieve the above-mentioned purpose, the application provides the following solutions.

[0008] The application provides a flue gas desulfurization and denitrification method of priced oxidation coupled with nitrogen-sulfur synergistic absorption, comprising the following steps.

[0009] Step 1, flue gas priced oxidation: after the flue gas is subjected to priced catalytic oxidation of hydrogen peroxide and ozone, NO in the flue gas is priced oxidized into NO2, and oxidized flue gas is obtained;

[0010] Step 2, nitrogen-sulfur synergistic absorption: the oxidized flue gas is subjected to nitrogen-sulfur synergistic absorption by using absorption slurry, so as to realize flue gas desulfurization and denitrification.

[0011] The catalyst is Co x Mn 3-x O4 nano metal oxide, wherein X is 3, 2, 1.5, 1 or 0.

[0012] Preferably, the preparation method of the catalyst in the application comprises the following steps: manganese carbonate and cobalt carbonate are configured into a mixed aqueous solution according to a stoichiometric ratio, then the system is adjusted to pH 9 by using sodium carbonate, and the obtained precipitate is collected, washed and calcined to obtain the Co x Mn 3-x O4 nano metal oxide. The calcination temperature is 400 DEG C, and the time is preferably 4 h.

[0013] According to the method of the application, preferably, the content of metal Co in the Co x Mn 3-x O4 nano metal oxide is 3, 2, 1.5, 1 or 0, and the corresponding content of metal Mn is 0, 1, 1.5, 2 or 3, wherein when the content of Co and Mn is 1:1, i.e. Co 1.5 Mn 1.5 O4, the oxidation rate of NO can reach 98% and the selectivity can reach 97% at a catalytic temperature of 140 DEG C.

[0014] The molar ratio of the sum of the molar amounts of hydrogen peroxide and ozone to the molar ratio of NO in the flue gas described in this invention is 1-5:1, preferably 1.2-3:1, and more preferably 1.2-1.5:1. In the prior art, a single oxidant such as hydrogen peroxide is used, and the molar ratio of the oxidant is usually above 5.

[0015] Preferably, the temperature for the pricing catalytic oxidation described in this invention is 120-200℃.

[0016] In the oxidized flue gas after oxidation by the present invention, nitrogen oxides are mainly nitrogen dioxide, while the content of nitric oxide and other high-valence nitrogen oxides such as dinitrogen pentoxide and nitric acid is less than 3%.

[0017] Preferably, the absorbent slurry of the present invention is a calcium-based solution containing sulfite. The sulfite is ammonium sulfite or calcium sulfite; the calcium-based solution is a calcium carbonate solution or a calcium hydroxide solution.

[0018] The molar ratio of sulfite in the absorbent slurry to nitrogen dioxide in the oxidizing flue gas is 1.5-3.0:1, preferably 2.0-2.7:1, and more preferably 2.2-2.4:1. This effectively reduces the amount of reducing agent while meeting the denitrification efficiency requirements. The molar ratio of calcium in the absorbent slurry to sulfur in the oxidizing flue gas is 0.5-2:1, preferably 0.5-1.5:1, more preferably 0.8-1.3:1, and most preferably 1-1.2:1. This improves the desulfurization and denitrification efficiency.

[0019] The solute content in the absorbent slurry of the present invention is 5-20 wt%, preferably 8-18 wt%, and more preferably 12 wt%. This can effectively save the amount of absorbent used, while the absorbent slurry has low mass transfer resistance and low conveying resistance, reducing the possibility of equipment blockage and facilitating daily use and maintenance.

[0020] According to the method of the present invention, preferably, the mass composition of calcium and sulfite in the absorbent slurry can be adjusted according to the flue gas composition. In this invention, when the nitrogen dioxide concentration changes, the adjustable range of sulfite content in the absorbent slurry is 4%–10%, and the corresponding adjustable range of calcium salt content is 2%–8%. High-efficiency absorption can be achieved within the given flue gas range and on the given absorption equipment.

[0021] In this invention, the ammonium sulfite in the absorbent can also absorb sulfur dioxide simultaneously, reducing the concentration of the calcium-based absorbent. At the same time, in a reaction system with excess sulfur dioxide, sulfur dioxide can also react with ammonia to generate ammonium sulfite, preventing ammonia escape while replenishing the ammonium sulfite consumed by the reaction system, further reducing the amount of absorbent used.

[0022] The mass composition of calcium and sulfite in the absorbent slurry can be adjusted according to the flue gas composition.

[0023] The reaction time of the absorption slurry and the oxidized flue gas in the nitrogen-sulfur synergistic absorption stage is 3-5 s.

[0024] The content of sulfur dioxide in the flue gas is 1000-6000 mg / Nm 3 The content of nitrogen oxide is 200-800 mg / Nm 3 The dust content is 100-200 mg / Nm 3 The moisture content is 5-12 wt%, and the oxygen content is 5-23 vol%. The concentration range of the nitrogen oxide and the sulfur dioxide basically covers the flue gas emitted by typical industries, such as petroleum cracking, sintering flue gas of the steel industry, coke oven flue gas, and coal-fired flue gas of thermal power plants.

[0025] Preferably, the process treatment method of the present application comprises the following steps:

[0026] (1) The flue gas flows through the catalytic oxidation device, and after being catalytically oxidized by the catalyst, hydrogen peroxide, and ozone, the NO in the flue gas is priced and oxidized to NO2 to obtain oxidized flue gas;

[0027] (2) The oxidized flue gas is transported into the spray tower by the induced draft fan and contacts the atomized liquid of the absorption slurry. After the reaction of the absorption slurry and the oxidized flue gas, the absorption slurry falls back to the bottom of the spray tower and is returned to the slurry tank by the circulating pump. The flue gas after desulfurization and denitrification leaves the spray tower through the screen.

[0028] In the preferred process treatment method of the present application: in the flue gas pricing and oxidation stage, the flue gas flows through the catalytic oxidation device and is catalytically oxidized by the catalyst, hydrogen peroxide, and ozone without additional heating. In a wide temperature range (120℃-200℃), the nitrogen monoxide in the flue gas is efficiently priced and oxidized to nitrogen dioxide to obtain oxidized flue gas. In the synergistic desulfurization and denitrification stage, the oxidized flue gas is transported into the spray tower by the induced draft fan and contacts the absorption slurry (calcium-based solution containing sulfite). The absorption slurry (calcium-based solution containing sulfite) in the slurry tank is lifted to the spiral nozzle in the tower by the liquid inlet pump to form absorption atomized liquid. After the reaction of the absorption slurry and the oxidized flue gas, the absorption slurry falls back to the bottom of the spray tower and is returned to the slurry tank by the circulating pump. The flue gas after desulfurization and denitrification leaves the spray tower through the screen.

[0029] The flow speed of the oxidized flue gas in the absorption tower is less than 1 m / s, preferably 0.2-0.5 m / s. The contact time of the sprayed slurry and the oxidized flue gas in the absorption tower is preferably 3 s-5 s. This absorption condition is basically consistent with the flue gas absorption condition in the conventional flue gas desulfurization tower, so it does not need to be excessively modified, which can meet the design requirements and maximize the economic cost savings.

[0030] The present application is based on the WFGD technology, aiming at realizing high-standard emission of nitration flue gas in perfect desulfurization facilities, the present application realizes high-efficiency (98%) and high-selectivity (97%) oxidation of NO into NO2 by using cobalt-manganese transition metal oxide catalyst, saves the amount of oxidant, and is also conducive to reduction of nitrogen oxides into nitrogen in the form of NO2 in the absorption stage, avoiding excessive oxidation of the consumption of reducing agent in the absorption slurry. Without affecting the desulfurization efficiency, in-situ low-cost modification can be carried out on the desulfurization device, and the denitration efficiency is improved to more than 85%, which basically meets the emission standard of NO x less than 150 mg / m 3 in the latest "Petroleum Chemical Industry Pollutant Discharge Standard" (GB 31571-2015) or "Coking Chemical Industry Pollutant Discharge Standard" (GB 16171-2012).

[0031] The present application discloses the following technical effects:

[0032] The present application has high NO oxidation efficiency, and the amount of oxidant is small, and only the flue gas waste heat in the low temperature zone is needed to realize the pricing oxidation, which has significant economic advantages.

[0033] The present application solves the problem of low nitrogen oxide absorption efficiency at low cost, and realizes the final flue gas ultra-low emission. The absorbent of the present application can efficiently and cooperatively absorb nitrogen and sulfur flue gas mainly containing nitrogen dioxide at normal temperature, and can meet the low energy consumption and low emission targets at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0035] Figure 1 The schematic diagram of the processing equipment used in embodiment 1 of the present application.

[0036] Figure 2 The XRD spectrum of the catalyst prepared in different embodiments of the pricing oxidation stage of the present application.

[0037] Figure 3 The oxidation efficiency of the catalyst prepared in embodiments 1-5 and comparative example 1 of the pricing oxidation stage of the present application.

[0038] Figure 4 The oxidation efficiency of the catalyst prepared in embodiments 1 and comparative examples 1-4 of the pricing oxidation stage of the present application.

[0039] Figure 5Absorption efficiency for flue gas absorption stage of the present application for Examples 6-10.

[0040] Figure 6 Absorption efficiency for flue gas absorption stage of the present application for Examples 6-10. DETAILED DESCRIPTION

[0041] Various exemplary embodiments of the present application will now be described in detail, which should be considered to be illustrative of the present application and should not be construed to limit the scope of the present application, and are understood to be a more detailed description of certain aspects, features and embodiments of the present application.

[0042] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values of a parameter, unless otherwise stated, each intervening value of the parameter is also specifically included within the scope of the present application. The intervening values of the parameter are combined with a stated value of the parameter in range form. These are only exemplary of the various preferred embodiments and are not intended to be limiting on the scope of the application. Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. Various embodiments of the present application will be described in detail, by reference to drawings, wherein:

[0043] Unless defined otherwise, 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 belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described. All patents, patent applications, publications, and descriptions mentioned herein are incorporated by reference to the extent allowed by law. Nothing herein is to be construed as an admission that the application is not entitled to antedate such disclosure by virtue of prior application.

[0044] Many modifications and variations of this application can be made in the light of the above teachings without departing from the spirit and scope thereof, and it is to be understood that all such modifications and variations warrant the patentable subject matter under the patent statutes. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. For example, the specification can be used to design methods and materials equivalent to those described herein, with the possession of ordinary skill in the art. The specification is to be considered to have generic and specific embodiments.

[0045] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", and the like are open-ended terms that are intended to permit but not to limit the description and / or claims hereafter. These terms encompass the terms "consisting of" and "consisting essentially of".

[0046] In the present application, the pricing oxidation coupled nitrogen and sulfur synergistic absorption method includes two stages: (1) the pricing oxidation stage of flue gas; (2) the synergistic desulfurization and denitrification stage. The present application realizes efficient synergistic desulfurization and denitrification under the conditions, which is different from the single desulfurization and denitrification method, different from the usual oxidation mode of NOx in flue gas, and different from the single oxidation and reduction method for denitrification. The following will be described in detail: x

[0047] ​<Flue gas pricing oxidation step>

[0048] The flue gas mainly containing NO is oxidized to NO2 by the oxidation device, and the flue gas passing through the oxidation device is called oxidized flue gas for distinction. The preferred nanometer transition metal oxide catalyst in the catalyst screen can be Co x Mn 3-x O4, preferably Co1Mn2O4, Co 1.5 Mn 1.5 O4, Co2Mn1O4, and more preferably Co 1.5 Mn 1.5 O4. The oxidation efficiency can reach 98% under the combined action of hydrogen peroxide and ozone, of which 95% is oxidized to NO2, which is beneficial to the reaction with the absorption liquid to improve the synergistic desulfurization and denitrification efficiency.

[0049] The residence time of the flue gas flowing through the catalyst layer in the catalytic device can be 0.1-0.4 s, more preferably 0.21 s. The molar ratio of the injected ozone and hydrogen peroxide to NO can be 1-5, preferably 1.2-3, and more preferably 1.2-1.5. The catalytic temperature of the catalytic device can be 120-200°C, preferably 120-160°C, and more preferably 140°C. According to the embodiment of the present application, NO can be oxidized to NO2 by the oxidant at low temperature under the catalysis of the catalyst. Since the waste heat of the flue gas can generally meet the catalytic requirements, additional heating is not required, which further reduces the oxidation cost and improves the oxidation efficiency. The directionally generated NO2 is also beneficial to the efficient absorption and reduction of the slurry liquid in the synergistic stage.

[0050] The content of sulfur dioxide in the oxidized flue gas is 1000-7000 mg / Nm 3 , preferably 1200-6000 mg / Nm 3 , and more preferably 2000-5500 mg / Nm 3 . The content of nitrogen dioxide is 100-800 mg / Nm 3 , preferably 150-600 mg / Nm 3 , and more preferably 200-500 mg / Nm 3 . The moisture content is 5-12 wt%, preferably 6-10 mg / Nm 3 , and more preferably 7-9 mg / Nm 3 . The oxygen content is 5-23 vol%, preferably 15-22 vol%, and more preferably 18-20 vol%.

[0051] <synergistic desulfurization and denitrification step>

[0052] The oxidized flue gas is sucked from the bottom end by a draft fan into the desulfurization tower of the WFGD process to contact with the sprayed slurry, to obtain clean flue gas and absorption slurry, and the absorption slurry is returned to the slurry tank by a circulating pump. The preferred sprayed slurry can form atomized liquid by a spiral nozzle to improve the spraying efficiency, and the more preferred sprayed slurry can be delivered to the spraying tower by a two-stage liquid feeding pump for secondary spraying. The removal efficiency can be effectively improved by sufficient contact mixing.

[0053] The sulfite in the calcium-based sulfite absorbent slurry in the application can be ammonium sulfite or calcium sulfite, and the calcium-based absorbent can be calcium carbonate or calcium hydroxide. More preferably, the solute of the absorbent slurry is composed of calcium carbonate and ammonium sulfite. The absorption efficiency can be met while the economic benefit is greatly improved.

[0054] The application will be described in more detail below with reference to the examples.

[0055] <Flue gas oxidation step>

[0056] Example 1

[0057] A Co x Mn 3-x O4 catalyst preparation method, comprising the following steps:

[0058] (1) 1.15 g of manganese carbonate and 1.19 g of cobalt carbonate are weighed and dissolved in 50 mL of deionized water to obtain solution A;

[0059] (2) While stirring, sodium carbonate is added dropwise to solution A until the pH is 9, so that the ions in the solution are precipitated, and the precipitate is collected;

[0060] (3) The precipitate is filtered, washed with deionized water, dried at 60℃, and then calcined at 400℃ for 4h to obtain a Co 1.5 Mn 1.5 O4 catalyst.

[0061] The catalyst is used to catalyze the directional oxidation of nitrogen monoxide by hydrogen peroxide and ozone, wherein the O3 concentration is 100 ppm, the NO concentration is 300 ppm, the hydrogen peroxide concentration is 300 ppm, the contact time is 0.21 s, and the catalytic temperature is 140℃. The NO conversion rate is 98%, and the NO2 selectivity is 97%.

[0062] Comparative Example 1

[0063] A Co x Mn 3-x O4 catalyst preparation method, comprising the following steps:

[0064] (1) 1.15 g of manganese nitrate and 1.19 g of cobalt nitrate were weighed and dissolved in 50 mL of deionized water to obtain solution A;

[0065] (2) Ammonia was added dropwise to solution A while stirring until the pH was 9, so that the ions in the solution were precipitated, and the precipitate was collected;

[0066] (3) The precipitate was filtered, washed with deionized water, dried at 60°C, and calcined at 400°C for 4 h to obtain a Co 1.5 Mn 1.5 O4catalyst.

[0067] The catalyst was used to catalyze the directional oxidation of nitrogen monoxide by hydrogen peroxide and ozone, wherein the O3concentration was 100 ppm, the NO concentration was 300 ppm, the hydrogen peroxide concentration was 300 ppm, the contact time was 0.21 s, and the catalytic temperature was 140°C. The NO conversion rate was 92%, and the NO2selectivity was 43%.

[0068] Example 2

[0069] The difference from Example 1 is only that the amount of cobalt carbonate is 2.38 g, and no manganese carbonate is added; the rest is the same as Example 1.

[0070] The obtained Co3O4catalyst obtained a NO conversion rate of 89%, and a NO2selectivity of 72%;

[0071] Example 3

[0072] The difference from Example 1 is only that the amount of cobalt carbonate is 1.59 g, and the amount of manganese carbonate is 0.77 g; the rest is the same as Example 1.

[0073] The obtained Co2Mn1O4catalyst obtained a NO conversion rate of 93%, and a NO2selectivity of 87%;

[0074] Example 4

[0075] The difference from Example 1 is only that the amount of cobalt carbonate is 0.80 g, and the amount of manganese carbonate is 1.54 g; the rest is the same as Example 1.

[0076] The obtained Co1Mn2O4catalyst obtained a NO conversion rate of 87%, and a NO2selectivity of 91%.

[0077] Example 5

[0078] The difference from Example 1 is only that the amount of manganese carbonate is 2.3 g, and no cobalt carbonate is added; the rest is the same as Example 1.

[0079] The obtained Mn3O4 catalyst obtains NO conversion rate of 76% and NO2 selectivity of 85%.

[0080] In combination with the difference in NO oxidation rate and NO2 selectivity in Examples 1-5, it can be seen that the mixed crystal state transition metal Co 1.5 Mn 1.5 The mixed crystal catalyst has a significant improvement in catalytic effect in the low-temperature working area compared with single Co3O4 and Mn3O4 nanometer transition metal oxides, and the NO2 selectivity of the mixed crystal catalyst is increased by 25% compared with pure Co3O4, and the NO oxidation of the mixed crystal catalyst is increased by 22% compared with pure Mn3O4. It can be seen that the mixed crystal state Co 1.5 Mn 1.5 O4 can efficiently and directionally oxidize NO to NO2, which is conducive to further synergistic absorption in the spray section. In combination with the nitric acid precursor cobalt manganese catalyst prepared in Comparative Example 1, it can be seen that the high selectivity of the catalyst to NO is affected by the precursor salt and the precipitating agent.

[0081] Comparative Example 1

[0082] The Co 1.5 Mn 1.5 O4 catalyst obtained in Example 1 is used to determine the working temperature of the catalyst, wherein the catalytic temperature is 120°C, and the NO conversion rate is 89% and the NO2 selectivity is 94%.

[0083] Comparative Example 2

[0084] The Co 1.5 Mn 1.5 O4 catalyst obtained in Example 1 is used to determine the working temperature of the catalyst, wherein the catalytic temperature is 160°C, and the NO conversion rate is 97% and the NO2 selectivity is 97%.

[0085] Comparative Example 3

[0086] The Co 1.5 Mn 1.5 O4 catalyst obtained in Example 1 is used to determine the working temperature of the catalyst, wherein the catalytic temperature is 180°C, and the NO conversion rate is 98% and the NO2 selectivity is 95%.

[0087] Comparative Example 4

[0088] The Co 1.5 Mn 1.5 O4 catalyst obtained in Example 1 is used to determine the working temperature of the catalyst, wherein the catalytic temperature is 200°C, and the NO conversion rate is 96% and the NO2 selectivity is 90%.

[0089] Figure 2 XRD spectra of the catalysts prepared in different embodiments of the present application.

[0090] As can be seen from Comparative Examples 1-4, the catalyst operates over a wide efficient temperature range (140℃-180℃). For most nitrogen and sulfur flue gases, no additional heating is required; only proper insulation is needed. In the low-temperature range of 120℃, the oxidation rate of NO is not high, but the selectivity of the catalyst remains relatively high. When the temperature reaches 200℃ and above, the conversion rate of NO does not decrease significantly, but the selectivity of NO2 decreases. Therefore, excessively high or low operating temperatures are detrimental to the directional oxidation of NO, thus affecting the subsequent reduction and removal efficiency.

[0091] <Collaborative Desulfurization and Denitrification Steps>

[0092] Example 6

[0093] Combination Figure 1 The simulated WFGD process for the synergistic removal of nitrogen and sulfur from flue gas is described. After oxidation, the nitrogen and sulfur flue gas enters the spray tower from below via an induced draft fan. The spray slurry is prepared and replenished in a slurry tank. Two-stage feed pumps deliver the spray slurry to the spray tower, and flow meters control the flow rates of the two stages separately. The spray slurry is atomized by spiral nozzles, increasing the gas-liquid contact area and improving absorption efficiency. After absorbing the flue gas, the spray slurry falls to the bottom of the spray tower and is returned to the slurry tank by a circulating pump. After oxidation and spray absorption, the flue gas becomes clean flue gas, which is then discharged after particle removal via a screen at the top of the spray tower. When the pH in the slurry tank drops below 5, new slurry needs to be added to maintain absorption efficiency.

[0094] The simulated low-temperature flue gas spray wet integrated desulfurization and denitrification reaction tower has an inner radius of 67 mm and a spray section length of 1400 mm. Sampling points are set at both the inlet and outlet of the spray tower to monitor the oxidation efficiency and flue gas desulfurization and denitrification efficiency in real time. Typical flue gas data after oxidation is 20 Nm³. 3 The empty tower velocity is 0.4 m / s, the residence time is about 3 seconds, the flue gas inlet temperature is 40℃, the oxygen content is 20 vol%, the flue gas moisture content is 10 wt%, and the sulfur dioxide content is 4000 mg / m³. 3 Nitrogen oxides were 400 mg / m³ 3 The desulfurization process primarily utilizes nitrogen dioxide. Absorption experiments were conducted using an absorbent slurry composed of 12% ammonium sulfite and calcium carbonate, with a Ca:S ratio of 1.2 and a molar ratio of ammonium sulfite to nitrogen dioxide of 2.2. The desulfurization efficiency reached over 98%, and the denitrification efficiency reached 86%–90%. Detailed data are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] Example 7

[0099] The only difference between Example 7 and Example 6 is that ammonium sulfite is replaced by calcium sulfite; the rest of the conditions are the same as in Example 6.

[0100] The results show that the desulfurization efficiency is reduced to 93%, and the denitration efficiency is reduced to 65%.

[0101] Example 8

[0102] The only difference between Example 8 and Example 6 is that ammonium sulfite is replaced by ascorbic acid; the rest of the conditions are the same as in Example 6.

[0103] The results show that the desulfurization efficiency is reduced to 88%, and the denitration efficiency is reduced to 53%.

[0104] Example 9

[0105] The only difference between Example 9 and Example 6 is that ammonium sulfite is replaced by urea; the rest of the conditions are the same as in Example 6.

[0106] The results show that the desulfurization efficiency is reduced to 90%, and the denitration efficiency is reduced to 15%.

[0107] Example 10

[0108] The only difference between Example 10 and Example 6 is that ammonium sulfite is replaced by sodium sulfite; the rest of the conditions are the same as in Example 6.

[0109] The results show that the desulfurization efficiency is reduced to 86%, and the denitration efficiency is reduced to 83%.

[0110] The absorption efficiency is shown in Table 1 Figure 3 Therefore, the absorption slurry composed of ammonium sulfite and calcium carbonate can efficiently and low-costly absorb the nitrogen and sulfur flue gas after oxidation. Compared with calcium sulfite, the concentration of sulfite ions in ammonium sulfite is high, which can efficiently react with nitrogen dioxide. At the same time, the generated calcium sulfate does not mask calcium sulfite, so that the reduction reaction can continue. More importantly, the cost of ammonium sulfite is much lower than that of calcium sulfite. Ascorbic acid is another commonly used industrial reducing agent, and its cost-effectiveness is lower than that of ammonium sulfite when used in the same molar ratio. It is speculated that ascorbic acid is too strong in reducing property and is easily oxidized by air, which is not conducive to its use as an absorbent. According to the literature, the efficient removal of nitrous acid produced by the dissolution of NO2 in urea solution occurs in an acidic environment with pH = 1. As the pH value increases, the removal efficiency will decrease rapidly. It is difficult to maintain a strong acid environment with pH = 1 for a long time. The price of sodium sulfite is higher than that of ammonium sulfite, and the reaction of sulfite with sulfur dioxide to obtain bisulfite is not conducive to the absorption of sulfur dioxide. More importantly, as the main reactant of NO2, sulfite not only cannot be supplemented but also will be consumed additionally, so its cost-effectiveness is also greater than that of ammonium sulfite.

[0111] Comparative Example 5

[0112] Based on Example 6, the transition metal catalyst in the catalytic oxidation section was removed, and the remaining conditions were the same as in Example 6. The desulfurization efficiency was reduced to 95%, and the denitration efficiency was reduced to 17%.

[0113] Comparative Example 6

[0114] In Example 6, all the solutes in the absorption solution were replaced with calcium hydroxide, and the remaining conditions were the same as in Example 6. The desulfurization efficiency was reduced to 91%, and the denitration efficiency was reduced to 9%.

[0115] Comparative Example 7

[0116] In Example 6, the mass fraction of ammonium sulfite in the absorption solution was further increased to 12%, and the total mass fraction was increased to 20%. The remaining conditions were the same as in Example 6. The desulfurization efficiency was increased to 99%, and the denitration efficiency remained at 90%.

[0117] Comparative Example 8

[0118] In Example 6, the residence time was shortened to 2.5s, and the denitration efficiency was reduced to 82%, while the desulfurization efficiency did not change significantly.

[0119] Further, the absorption slurry temperature, pH, and flue gas inlet temperature in Example 6 were adjusted within the preferred range, and the flue gas removal efficiency did not change significantly. The flue gas residence time was further extended to 5s, and the removal efficiency did not increase significantly.

[0120] The absorption efficiency is shown in Table 1 Figure 4 Based on the data in the comparative examples, targeted catalytic oxidation plays a decisive role in the overall nitrogen and sulfur co-removal. When the nitrogen-containing flue gas is mainly composed of NO, the overall removal efficiency is very low. However, when NO is oxidized to NO2 at a high price and low cost, the absorption slurry composed of calcium-based ammonium sulfite can efficiently achieve the co-removal of nitrogen and sulfur flue gas. Among them, ammonium sulfite plays a decisive role in denitration, and calcium-based absorption of sulfur dioxide is promoted. At the same time, part of the calcium sulfite generated by the calcium-based reaction can also promote denitration. The two can be dynamically adjusted according to the composition of the flue gas.

[0121] In the absorption working condition, the removal efficiency is less affected by pH and temperature. When the concentration of ammonium sulfite is further increased, the denitration efficiency improves to a limited extent. The change in residence time has no significant effect on the desulfurization process, but it has a more significant impact on denitration. Within the preferred residence time range, the spray liquid has excellent co-removal effect on nitrogen dioxide and sulfur dioxide in the flue gas.

[0122] Therefore, this invention is based on an improved and mature WFGD process, which can achieve efficient simultaneous desulfurization and denitrification. It can be used to upgrade existing equipment to meet energy conservation, emission reduction, and emission standard improvement requirements, or as a newly built independent flue gas treatment unit. Compared with other oxidation-reduction-absorption processes, this technology has a significant cost-effectiveness advantage. Its fixed-price oxidation technology effectively reduces the amount of oxidant and reductant used, lowering flue gas treatment costs and improving absorption efficiency. The selection of combined absorbents can effectively address changes in flue gas composition. Using ammonium sulfite as a reductant is not only cheaper than commonly used industrial reductants such as calcium sulfite, ascorbic acid, sodium sulfite, and sodium thiosulfate, but the ammonium ions can also synergistically remove sulfur dioxide gas, reducing the amount of calcium-based absorbent and further lowering costs. Simultaneously, due to the high sulfur dioxide content, ammonia escape is virtually eliminated.

[0123] The reaction principle is as follows:

[0124] 4(NH4)2SO3+2NO2→N2+4(NH4)2SO4

[0125] (NH4)2SO3 + SO2 + H2O → 2NH4HSO3

[0126] SO2 + 2NH 3. H₂O→(NH₄)₂SO₃+H₂O

[0127] Ca(OH)₂ + 2SO₂ → CaSO₃ + H₂O

[0128] 4CaSO3 + 2NO2 → N2 + 4CaSO4

[0129] 3NO₂ + Ca(OH)₂ → Ca(NO₃)₂ + NO + H₂O (weak)

[0130] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for flue gas desulfurization and denitrification involving pricing, oxidation, and synergistic nitrogen and sulfur absorption, characterized in that: Includes the following steps: Step 1, flue gas oxidation: After the flue gas is catalytically oxidized with a catalyst, hydrogen peroxide and ozone, the NO in the flue gas is oxidized to NO2, resulting in oxidized flue gas; Step 2, nitrogen and sulfur synergistic absorption: The oxidized flue gas is subjected to nitrogen and sulfur synergistic absorption using absorption slurry to achieve flue gas desulfurization and denitrification; The catalyst is Co. x Mn 3-x O4 nano-metal oxide, where X takes the value of 2, 1.5 or 1; The molar ratio of the sum of the molar amounts of hydrogen peroxide and ozone to the molar ratio of NO in the flue gas is 1.2 to 1.5:1; The temperature for the pricing catalytic oxidation is 120–200°C; The absorbent slurry is a calcium-based solution containing sulfites; The sulfite is ammonium sulfite or calcium sulfite; the calcium-based solution is calcium carbonate solution or calcium hydroxide solution; The molar ratio of sulfite in the absorbent slurry to nitrogen dioxide in the oxidizing flue gas is 1.5–3.0:1; the molar ratio of calcium in the absorbent slurry to sulfur in the oxidizing flue gas is 0.5–2:

1. The Co x Mn 3-x The preparation method of O4 nano-metal oxide includes the following steps: Manganese carbonate and cobalt carbonate were mixed in an aqueous solution according to a stoichiometric ratio. The pH of the system was then adjusted to 9 using sodium carbonate. The resulting precipitate was collected, washed, and calcined to obtain the Co. x Mn 3-x O4 nano-metal oxides; The solute content in the absorbent slurry is 5-20 wt%.

2. The flue gas desulfurization and denitrification method according to claim 1, characterized in that, The sulfur dioxide content in the flue gas is 1000–6000 mg / Nm³. 3 The nitrogen oxide content is 200–800 mg / Nm³. 3 Dust content is 100-200 mg / Nm³ 3 The moisture content is 5–12 wt%, and the oxygen content is 5–23 vol%.

3. The flue gas desulfurization and denitrification method according to claim 1, characterized in that, Includes the following steps: (1) Flue gas is passed through a catalytic oxidation device, and after being catalytically oxidized by the catalyst with hydrogen peroxide and ozone, NO in the flue gas is oxidized to NO2 to obtain oxidized flue gas; (2) The oxidizing flue gas is transported to the spray tower by the induced draft fan and comes into contact with the atomized liquid of the absorption slurry. After the absorption slurry reacts with the oxidizing flue gas, it falls back to the bottom of the spray tower and returns to the slurry tank by the circulating pump. The flue gas after desulfurization and denitrification leaves the spray tower through the screen and is discharged.

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