UV/H2O2氧化联合Ca(OH)2吸收同时脱硫脱硝

在小型紫外光-鼓泡床反应器中,对UV/H₂O₂氧化联合Ca(OH)₂吸收同时脱除燃煤烟气中NO与SO₂的主要影响因素[H₂O₂浓度、紫外光辐射强度、Ca(OH)₂浓度、NO浓度、溶液温度、烟气流量以及SO₂浓度]进行了考察。采用烟气分析仪和离子色谱仪分别对尾气中的NO₂和液相阴离子作了检测分析。结果显示:在本文所有实验条件下,SO₂均能实现完全脱除。随着H₂O₂浓度、紫外光辐射强度和Ca(OH)₂浓度的增加,NO的脱除效率均呈现先大幅度增加后轻微变化的趋势。NO脱除效率随烟气流量和NO浓度的增加均有大幅度下降。随着溶液温度和SO₂浓度的增加,NO脱除效率仅有微小的下降。离子色谱分析表明,反应产物主要是SO₄^2-和NO₃^-,同时有少量的NO₂^-产生。尾气中未能检测到有害气体NO₂。     

Removal of Hg0 from containing‐SO2/NO flue gas by ultraviolet/H2O2 process in a novel photochemical reactor

A novel photochemical spray reactor is first developed and is used to remove Hg⁰ and simultaneously remove Hg⁰/SO₂/NO from flue gas by ultraviolet (UV)/H₂O₂ process. The effects of several parameters (UV wavelength, UV power, H₂O₂ concentration, Hg⁰ inlet concentration, solution temperature, liquid–gas ratio, solution pH, SO₂ concentration, NO concentration, and O₂ concentration) on removal of Hg⁰ by UV/H₂O₂ process were investigated. Removal mechanism of Hg⁰ is proposed and simultaneous removal of Hg⁰, NO, and SO₂ is also studied. The results show that the parameters, UV wavelength, UV power, H₂O₂ concentration, liquid–gas ratio, solution pH, and O₂ concentration, have significant impact on removal of Hg⁰. However, the parameters, Hg⁰ inlet concentration, solution temperature, SO₂ concentration, and NO concentration, only have small effect on removal of Hg⁰. Hg²⁺ is the final product of Hg⁰ removal, and Hg⁰ is mainly removed by oxidations of H₂O₂, ·OH, · O, O₃, and photoexcitation of UV. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2275–2285, 2014     

Advanced Oxidative Removal of Nitric Oxide from Flue Gas by Homogeneous Photo‐Fenton in a Photochemical Reactor

In this work, advanced oxidation removal of nitric oxide (NO) from flue gas by homogeneous Photo‐Fenton was investigated in a photochemical reactor and the effects of several influencing factors on NO removal were evaluated. The gas‐liquid reaction products were determined. The reaction pathways of NO removal are also preliminarily discussed. It was found that with the increase of Fe²⁺ concentration, NO removal efficiency first increased and then decreased. Increasing H₂O₂ concentration and UV radiation intensity greatly increased NO removal efficiency, but the growth rates gradually became smaller. NO removal efficiency greatly reduced with the increase of gas flow and NO concentration, and only slightly decreased with the increase of solution temperature, but significantly increased with the increase of initial solution pH value. The main anion product in the liquid phase was NO₃^–. With respect to removal of NO using homogeneous Photo‐Fenton, ·OH oxidation was the main reaction pathway, and H₂O₂ oxidation was the secondary reaction pathway.     

Removal of NO from flue gas by wet scrubbing with NaClO2/(NH2)2CO solutions

The experiments were performed in a countercurrent packed column in a continuous mode to study the absorption of nitric oxide in sodium chlorite/urea solutions. Sodium chlorite mainly works as an agent to oxidize NO to NO₂. A combined SO₂/NO removal system was also tested. On the basis of high SO₂ removal efficiency, the NO removal efficiencies under various experimental conditions were emphatically measured. Among the operating variables such as initial NaClO₂ concentration, urea concentration, temperature and initial pH value, the pH value of the absorbing liquid was found to have a great impact on both NO removal efficiency and NO₂ concentration. NO removal efficiency was increased with increasing NaClO₂ concentration and temperature. Urea almost has no negative effect on NO removal efficiency, however it aids the abatement of NO₂ greatly. The anions in the spent scrubbing liquor were analyzed by ion chromatography.     

Elemental sulfur production through regeneration of a SO2-adsorbed V2O5-CoO/AC in H2

H₂ regeneration of an activated carbon supported vanadium and cobalt oxides (V₂O₅-CoO/AC) catalyst–sorbent used for flue gas SO₂ removal is studied in this paper. Elemental sulfur is produced during the H₂-regeneration when effluent gas of the regeneration is recycled back to the reactor. The regeneration conditions affect the regeneration efficiency and the elemental sulfur yield. The regeneration efficiency is the highest at 330 °C, with SO₂ as the product. The production of elemental sulfur occurs at 350 °C and higher with the highest elemental sulfur yield of 9.8 mg-S/g-Cat. at 380 °C. A lower effluent gas recycle rate is beneficial to elemental sulfur production. Intermittent H₂ feeding strategy can be used to control H₂S concentration in the gas phase and increase the elemental sulfur yield. Two types of reactions occur in the regeneration, reduction of sulfuric acid to SO₂ by AC and reduction of SO₂ to elemental sulfur through Claus reaction. H₂S is an intermediate, which is important for elemental sulfur formation and for conversion of CoO to CoS that catalyzes the Claus reaction. The catalyst–sorbent exhibits good stability in SO₂ removal capacity and in elemental sulfur yield.     

Basic rules of NO oxidation by Fe2+/H2O2/AA directional decomposition system

Basic rules of NO oxidation by a Fe²⁺/H₂O₂/AA directional decomposition system were researched based on the technical background of flue gas NO_x removal. Effects of gas‐liquid interfacial area, main gas, and solution parameters on NO oxidation efficiency (η) were analyzed. The results showed that adequate contact area was the precondition for high η by a Fe²⁺/H₂O₂/AA system. η decreased with the increase in NO concentration, which illustrated that this method would be efficient in oxidizing NO at a low concentration. η tended to decrease linearly with the growth in gas flow, however, the NO oxidation rate (v) rose with the increase in NO concentration and gas flow. η increased with the initial concentrations of H₂O₂ and Fe²⁺, but the amplitude decreased. Controlling the initial concentrations of H₂O₂ and Fe²⁺ to achieve reasonable synergies between generation rate and consumption rate of ·OH could weaken the invalid consumption of reactants. η increased with the increase in temperature in the range 30–60 °C, but it nearly did not change with temperature after 60 °C. This oxidation technology and the traditional wet flue gas desulphurization technology exhibited temperature synergy. Under typical pH of wet desulphurization, η and H₂O₂ consumption rate did not change obviously.     

SO_2对钙基吸收剂吸收NO的作用机理

针对低温条件下SO2对Ca(OH)2吸收NO的影响进行了实验研究,分析了烟气中O2和H2O对SO2促进Ca(OH)2吸收NO的影响。实验结果表明,当烟气不含SO2时,Ca(OH)2对NO基本无吸收作用;烟气中SO2的存在对NO吸收具有促进作用。H2O和O2对SO2促进NO吸收有显著影响;当烟气不含O2时,即使大量的SO2被吸收,NO吸收效率仍较低;只有SO2与O2和H2O共存才能促进NO吸收。脱硫产物CaSO3对NO无氧化作用;NO、H2O和SO2未在吸收剂表面产生可分解释放NO2的大分子中间配合物。分析认为在脱硫过程中产生了可以促进NO与O2反应的非稳定中间活性组分。     

Performance of a UV‐assisted Hydrogen‐peroxide‐fed Spray Tower for Sulfur Dioxide Abatement

Spray towers are widely used for controlling air pollution by gases such as SO₂, CO₂, NO_x, and HCl. Results of sulfur dioxide absorption in a spray tower using solutions of 1 g L^–1 and 2 g L^–1 of hydrogen peroxide are reported. For comparison, a water and sodium hydroxide solution was also used for SO₂ abatement. The results indicate that H₂O₂ may be an important alternative for SO₂ removal in spray towers. A set of experimental removal efficiency data was obtained as a function of gas and liquid flow rates. Volumetric mass transfer coefficients (k_ga) were calculated and an experimental relationship among k_ga, gas, and liquid flow rates was proposed. As a final experiment, an oxidation process assisted by UV radiation using a 1 g L^–1 solution of H₂O₂ was carried out to speed up the SO₂ removal rate. The results obtained in this condition are similar to those achieved with a solution of 2 g L^–1 H₂O₂.     

Simultaneous removal of SO2 and NO X with ammonia absorbent in a packed column

Catalytic oxidation of NO followed by simultaneous removal of SO₂ and NO _X with ammonia is a promising method for control of coal-fired flue gas pollutants. We investigated simultaneous absorption of SO₂ and NO _X in a packed column with ammonia, and found that SO₂ and NO _X could promote absorption with each other in the process of simultaneous removal SO₂ and NO _X . The removal efficiency of SO₂ and NO _X was, respectively, about 98% and 70.9% at pH 5.5, temperature 323.15 K, SO₂ concentration 1,800×10^?6, NO _X concentration 400×10^?6 and ${{m_{NO_2 } } \mathord{\left/ {\vphantom {{m_{NO_2 } } {m_{NO} }}} \right. \kern-0em} {m_{NO} }}$ in our experimental system. The experimental results also show that the formation of sulfite oxidized by reacting with dissolved NO₂ and the molar ratio of sulfite to total sulfur is more than 0.8 in the solution. Accordingly, the energy consumption for sulfite oxidation would be greatly reduced in the process of simultaneous desulfurization and denitrification with ammonia.     

UV/H2O2氧化联合CaO吸收脱除NO的传质-反应动力学

在实验室规模的光化学反应器中,基于实验研究﹑动力学理论以及双膜理论,研究了UV/H₂O₂氧化联合CaO吸收(UV/H₂O₂-CaO工艺)脱除燃煤烟气中NO的传质-反应动力学。分析了NO吸收的传质-反应过程,明确了NO吸收过程的主要控制步骤和强化措施,测定了关键的动力学参数,推导了NO吸收过程的理论模型。结果表明:在实验范围内,NO吸收速率随着NO浓度的增加几乎呈线性增加。随着H₂O₂浓度和CaO浓度的增加,NO的吸收速率均呈现先增加后变缓的趋势。UV/H₂O₂-CaO工艺脱除NO是一个拟一级快速反应过程,强化气相主体扰动﹑增加气液接触面积和提高NO分压可有效提高NO的吸收速率。NO吸收速率方程的计算值和实验值具有较好的一致性。     

Low cost coal-based carbons for combined SO2 and NO removal from exhaust gas

The aim of this paper is to show how a cheap carbonaceous material such as low rank coal-based carbon (or char) can be used in the combined SO₂/NO removal from exhaust gas at the linear gas velocity used in commercial systems (0.12 m s⁻¹). Char is produced from carbonization and optionally activated with steam. This char is used in a first step to abate the SO₂ concentration at the following conditions: 100 °C, space velocity of 3600 h⁻¹, 6% O₂, 10% H₂O, 1000 ppmv SO₂, 1000 ppmv NO and N₂ as remainder. In a second step, when the SO₂ concentration in the flue gas is low, NO is reduced to N₂ and steam at the following experimental conditions: 150 °C, space velocity of 900 h⁻¹, 6% O₂, 10% H₂O, 0-500 ppmv SO₂, 1000 ppmv NO, 1000 ppmv NH₃ and N₂ as remainder.It has been shown that the presence of NO has no effect on SO₂ abatement during the first step of combined SO₂/NO removal system and that low SO₂ inlet concentration has a negligible effect on NO reduction in the second step. Moreover, this char can be thermally regenerated after use for various cycles without loss of activity. On the other hand, this regenerated char shows the highest NO removal activity (compared to parent chars, either carbonized or steam activated) which can be attributed to the activating effect of the sulfuric acid formed during the first step of the combined SO₂/NO removal system.     

Effects of water vapor, CO2 and SO2 on the NO reduction by NH3 over sulfated CaO

Gas effects on NO reduction by NH₃ over sulfated CaO have been investigated in the presence of O₂ at 700–850 °C. CO₂ and SO₂ have reversible negative effects on the catalytic activity of sulfated CaO. Although H₂O alone has no obvious effect, it can depress the negative effects of CO₂ and SO₂. In the flue gas with CO₂, SO₂ and H₂O co-existing, the sulfated CaO still catalyzed the NO reduction by NH₃. The in situ DRTFTS of H₂O adsorption over sulfated CaO indicated that H₂O generated Br?nsted acid sites at high temperature, suggesting that CO₂ and SO₂ competed for only the molecularly adsorbed NH₃ over Lewis acid sites with NO, without influencing the ammonia ions adsorbed over Br?nsted acid sites. Lewis acid sites shifting to Br?nsted acid sites by H₂O adsorption at high temperature may explain the depression of the negative effect on NO reduction by CO₂ and SO₂.     

Removal of elemental mercury from simulated coal-combustion flue gas using a SiO2–TiO2 nanocomposite

A novel silica–titania (SiO₂–TiO₂) nanocomposite has been developed to effectively capture elemental mercury (Hg⁰) under UV irradiation. Previous studies under room conditions showed over 99% Hg⁰ removal efficiency using this nanocomposite. In this work, the performance of the nanocomposite on Hg⁰ removal was tested in simulated coal-fired power plant flue gas, where water vapor concentration is much higher and various acid gases, such as HCl, SO₂, and NO_x, are present. Experiments were carried out in a fix-bed reactor operated at 135 °C with a baseline gas mixture containing 4% O₂, 12% CO₂, and 8% H₂O balanced with N₂. Results of Hg speciation data at the reactor outlet demonstrated that Hg⁰ was photocatalytically oxidized and captured on the nanocomposite. The removal efficiency of Hg⁰ was found to be significantly affected by the flue gas components. Increased water vapor concentration inhibited Hg⁰ capture, due to the competitive adsorption of water vapor. Both HCl and SO₂ promoted the oxidation of Hg⁰ to Hg(II), resulting in higher removal efficiencies. NO was found to have a dramatic inhibitory effect on Hg⁰ removal, very likely due to the scavenging of hydroxyl radicals by NO. The effect of NO₂ was found to be insignificant. Hg removal in flue gases simulating low rank coal combustion products was found to be less than that from high rank coals, possibly due to the higher H₂O concentration and lower HCl and SO₂ concentrations of the low rank coals. It is essential, however, to minimize the adverse effect of NO to improve the overall performance of the SiO₂–TiO₂ nanocomposite.     

Simultaneous desulfurization and denitrification of flue gas by pre-ozonation combined with ammonia absorption

A process of simultaneous desulfurization and denitrification of flue gas was conducted in this study. The flue gas containing 200 mg·m⁻³ NO, 1000–4000 mg·m⁻³ SO₂, 3%–9% O₂, and 10%–20% CO₂ was first oxidized by O₃ and then absorbed by ammonia in a bubbling reactor. Increasing the ammonia concentration or the SO₂ content in flue gas can promote the absorption of NO_X and extend the effective absorption time. On the contrary, both increasing the absorbent temperature or the O₂ content shorten the effective absorption time of NO_X. The change of solution pH had substantial influence on NO_X absorption. In the presence of CO₂, the NO_X removal efficiency reached 89.2% when the absorbent temperature was raised to 60 °C, and the effective absorption time can be maintained for 8 h, which attribute to the buffering effect in the absorbent. Besides, both the addition of Na₂S₂O₃ and urea can promote the NO_X removal efficiency when the absorbent temperature is 25 °C, and the addition of Na₂S₂O₃ had achieved better results. The advantage of adding Na₂S₂O₃ became less evident at higher absorbent temperature and coexistence of CO₂. In all experiments, SO₂ removal efficiency was always above 99%, and it was basically not affected by the above factors.     

Simultaneous removal of SO2 and NO by low cost sorbent-catalysts prepared by lime, fly ash and industrial waste materials

The potential of the sorbent-catalysts prepared from three low cost materials, i.e., the lime, fly ash and some industrial waste material containing iron oxide, have been investigated for simultaneous removal of SO₂ and NO _x from flue gas in the temperature range 700–850 °C. NH₃ was chosen as the reducing agent for NO reduction in this study. Experimental results showed that SO₂ and NO could be simultaneously removed efficiently in the absence of O₂ at the temperature window of 700–800 °C. The effect of product layer generated from SO₂ removal on NO removal was not obvious. NO removal efficiency was strongly inhibited by O₂, which was attributed to the partial oxidation of NH₃ to NO over the sorbent-catalysts in the presence of oxygen. Neither NO₂ nor N₂O by-product was detected both in the absence and presence of O₂. Three routes were suggested to overcome the negative effect of O₂. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Characteristics of the mercury vapor removal from coal combustion flue gas by activated carbon using H2S

Removal of Hg⁰ vapor from the simulated coal combustion flue gases with a commercial activated carbon was investigated using H₂S. This method is based on the reaction of H₂S and Hg over the adsorbents. The Hg⁰ removal experiments were carried out in a conventional flow type packed bed reactor system in the temperature range of 80–150 °C using simulated flue gases having the composition of Hg⁰ (4.9 ppb), H₂S (0–20 ppm), SO₂ (0–487 ppm), CO₂ (10%), H₂O (0–15%), O₂ (0–5%), N₂ (balance gas). The following results were obtained: in the presence of both H₂S and SO₂, Hg removal was favored at lower temperatures (80–100 °C). At 150 °C, presence of O₂ was indispensable for Hg⁰ removal from H₂S–SO₂ flue gas system. It is suggested that the partial oxidation of H₂S with O₂ to elemental sulfur (H₂S+1/2O₂=S_ad+H₂O) and the Clause reaction (SO₂+2H₂S=3S_ad+2H₂O) may contribute to the Hg⁰ removal over activated carbon by the following reaction: S_ad+Hg=HgS. The formation of elemental sulfur on the activated carbon was confirmed by a visual observation.     

Simultaneous removal of SO2 and NO by sodium chlorite solution in wetted-wall column

The effect of feeding rate of NaClO₂ solution, inlet SO₂ and NO concentration, [NaClO₂]/[SO₂+NO] molar ratio (η), L/G ratio and, solution pH on the simultaneous removal of SO_x/NO_x has been investigated in a wetted-wall column. Both SO_x and NO_x removal efficiencies are enhanced with the increasing feeding rate of NaClO₂ solution and attain a steady state. NO_x removal efficiency increases with increasing SO₂ concentration, but SO_x removal remains unaffected with increasing NO concentration. In an acidic medium, DeSO_x and DeNO_x efficiency increased with increasing [NaClO₂]/[SO₂+NO_x] molar ratio and attained a steady state. NO_x removal starts only after the complete removal of SO_x. The excess of NaClO₂ does not enhance NO_x removal efficiency. Solution pH does not affect the DeSO_x and DeNO_x efficiency. The maximum SO_x and NO_x removal efficiencies achieved at the typical operating conditions of commercialized FGD processes are about 100 and 67%, respectively.     

Simultaneous removal of SO2 and NOx by microwave with potassium permanganate over zeolite

Simultaneous sulfur dioxide (SO₂) and nitrogen oxides (NO_x) removal from flue gas can be achieved with high efficiency by microwave with potassium permanganate (KMnO₄) over zeolite. The experimental results showed that the microwave reactor could be used to oxidation of SO₂ to sulfate with the best desulfurization efficiency of 96.8% and oxidize NO_x to nitrates with the best NO_x removal efficiency of 98.4%. Microwave accentuates catalytic oxidation treatment, and microwave addition can increase the SO₂ and NO_x removal efficiency by 7.2% and 12.2% separately. The addition of zeolite to microwave potassium permanganate increases from 16.5% to 43.5% the microwave removal efficiency for SO₂, and the NO_x removal efficiency from 85.6% to 98.2%. The additional use of potassium permanganate to the microwave zeolite leads to the enhancement of SO₂ removal efficiency up from 53.9% to 95%, and denitrification efficiency up from 85.6% to 98.2%. The optimal microwave power and empty bed residence time (EBRT) on simultaneous desulfurization and denitrification are 259 W and 0.357 s, respectively. SO₂ and NO_x were rapidly oxidized in microwave induced catalytic oxidation reaction using potassium permanganate with zeolite being the catalyst and microwave absorbent.     

介质阻挡放电中气体成分对NOx脱除的影响

利用介质阻挡放电(DBD)产生低温等离子体进行烟气的脱硝实验,研究了在乙烯存在的条件下,温度和其他烟气成分对NO_x脱除率的影响。结果表明:随着温度的升高,NO脱除速率增快;模拟烟气中加入CO₂,在能量密度较低时,CO₂作为电负性分子会降低自由基的生成,导致NO的脱除率降低,随着能量密度的升高,CO₂对NO脱除的影响减小;模拟烟气中加入水后可以产生更多的OH、HO₂等自由基,促进NO的氧化;SO₂的加入会与自由基O反应,使初始反应中O与C₂H₄的反应速率减弱,从而影响了NO的氧化速率,但O₃、HO₂等强氧化自由基会优先与NO反应,因此SO₂的加入不会影响NO最终的脱除率。