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 NO and SO2 from Flue Gas by UV/H2O2/CaO

The effects of several influencing factors (CaO and H₂O₂ concentration, gas flow, solution temperature, NO, SO₂, O₂ and CO₂ concentration) on the simultaneous removal of NO and SO₂ from flue gas by using a UV/H₂O₂/CaO process were studied. In addition, the anions in the liquid phase were measured by ion chromatography and the material balances for NO and SO₂ were calculated. It was found that, under all experimental conditions, this process achieved a SO₂ removal efficiency of 100 %. With the increase in CaO concentration, NO removal efficiency first increased and then remained almost unchanged. With the increase in H₂O₂ concentration, NO removal efficiency increased but the changes gradually became smaller. NO removal efficiency greatly decreased with increasing gas flow, NO concentration and CO₂ concentration. Slightly increasing the solution temperature and SO₂ concentration reduced NO removal efficiency. Increasing O₂ concentration can promote the removal of NO. The anions in the liquid phase were mainly SO₄^2– and NO₃^–. Most of the low valence nitrogen elements in NO and the low valence sulfur elements in SO₂ transformed into the high valence nitrogen element in NO₃^– and the high sulfur element in SO₄^2–.     

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。     

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.     

甘氨酸合钴溶液脱除NO

结合乙二胺合钴具高效脱NO的特性,选取与乙二胺合钴配位结构相似的氨羧化合物——甘氨酸,替代乙二胺作钴配合物配体进行脱NO研究,以期解决乙二胺易挥发、难运输等问题.实验表明：甘氨酸合钴的初始浓度对NO脱除影响显著,随浓度的增大NO脱除率提高;吸收剂的pH值和吸收反应温度也对NO脱除率影响显著,最佳pH值为中性至弱碱性,最佳反应温度50℃左右;同时脱硫脱氮时,尿素的加入因其可促进SO^2-₃的氧化,从而提高甘氨酸合钴同时脱硫脱氮能力.     

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.     

NOx removal by selective noncatalytic reduction with urea solution in a fluidized bed reactor

A fluidized bed reactor has been developed to overcome the plugging problem of urea injection by employing a sparger rather than nozzles in the SNCR process for simultaneous removal of SO₂ and NO_x. In a developed fluidized bed reactor, the optimum temperature to remove NO_x is shifted to lower values, the reaction temperature window is widened with the presence of CO in flue gas, and NO conversion is higher than that in a flow reactor. The optimum amount of urea injection in the reactor is found to be above 1.2 based on the normalized stoichiometric molar ratio (NSR) with respect to NO conversion. In the simultaneous removal of SO₂/NO, conversions of SO₂ and NO reach 80–90%, nearly the same values for the individual removal of SO₂ and NO above 850 ‡C.     

Removal of nitric oxide and sulfur dioxide from flue gases using a FeII-ethylenediamineteraacetate solution

The combined absorption of NO and SO₂ into the Fe(II)-ethylenediamineteraacetate(EDTA) solution has been realized. Activated carbon is used to catalyze the reduction of Fe^III-EDTA to Fe^II-EDTA to maintain the ability to remove NO with the Fe-EDTA solution. The reductant is the sulfite/bisulfite ions produced by SO₂ dissolved into the aqueous solution. Experiments have been performed to determine the effects of activated carbon of coconut shell, pH value, temperature of absorption and regeneration, O₂ partial pressure, sulfite/bisulfite and chloride concentration on the combined elimination of NO and SO₂ with Fe^II-EDTA solution coupled with the Fe^II-EDTA regeneration catalyzed by activated carbon. The experimental results indicate that NO removal efficiency increases with activated carbon mass. There is an optimum pH of 7.5 for this process. The NO removal efficiency increases with the liquid flow rate but it is not necessary to increase the liquid flow rate beyond 25 ml min^?1. The NO removal efficiency decreases with the absorption temperature as the temperature is over 35 °C. The Fe²⁺ regeneration rate may be speeded up with temperature. The NO removal efficiency decreases with O₂ partial pressure in the gas streams. The NO removal efficiency is enhanced with the sulfite/bisulfite concentration. Chloride does not affect the NO removal. Ca(OH)₂ and MgO slurries have little influence on NO removal. High NO and SO₂ removal efficiencies can be maintained at a high level for a long period of time with this heterogeneous catalytic process.     

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。     

Removal of NO and SO2 by pulsed corona discharge process

Overall examination was made on the removal of NO and SO₂, by pulsed corona discharge process. The mechanism for the removal of NO was found to largely depend on the gas composition. In the absence of oxygen, most of the NO removed was reduced to N₂; on the other hand, oxidation of NO to NO₂ was dominant in the presence of oxygen even when the content was low. Water vapor was an important ingredient for the oxidation of NO₂, to nitric acid rather than that of NO to NO₂. The removal of NO only slightly increased with the concentration of ammonia while the effect of ammonia on the removal of SO₂ was very significant. The energy density (power delivered/feed gas flow rate) can be a measure for the degree of removal of NO. Regardless of the applied voltage and the flow rate of the feed gas stream, the amount of NO removed was identical at the same energy density. The production of N₂O increased with the pulse repetition rate, and the presence of NH₃ and SO₂ enhanced it. Byproducts generated from propene used as additive were identified and analyzed. The main byproducts other than carbon oxides were found to be ethane and formaldehyde, but their concentrations were negligibly small.     

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, NO and particulate by pilot-scale scrubber system

SO _x and NO _x have both previously been identified as primary precursors of acid rain, and thus the abatement of SO _x and NO _x emissions constitutes a major target in the field of air pollution control. In this study, the efficacy of a pilot-scale scrubber was evaluated with regard to the simultaneous removal of SO₂, NO and particulate with wet catalysts. The removal efficiencies of particulate were measured to be 83, 92 and 97% with catalyst flux of 0.5, 0.8 and 1.5 L/min, respectively. The average removal efficiencies of particulate with different nozzles were approximately 94 and 90% with FF6.5 (5/8 in.) and 14 W (1.0 in.) nozzles, respectively. At least 96–98% of particulate and SO₂ were removed, regardless of the stage number of reactor. In a one-stage scrubber, 83.3% removal efficiency of NO was achieved after 48 hours; however, the two-stage scrubber achieved an NO removal efficiency of 95.7%. Regardless of the liquid-gas ratio, SO₂ and particulate were removed effectively, whereas NO was removed about 84% and 74% under liquid-gas ratio conditions of 39.32 L/m³ and 27.52 L/m³, respectively. In experiments using STS and P.P. pall ring as packing material, particulate and SO₂ removal efficiency values in excess of 98% were achieved; however, NO removal was correlated with the different packing materials tested in this study. With the above optimum operation conditions, even after 20 hours, the removal efficiency for NO stayed at 95% or higher, the removal efficiency for SO₂ stayed at 97% or higher, and the removal efficiency for particulate stayed at 92% or higher. In accordance, then, with the above results, it appears that this process might be utilized in scrubber systems, as well as systems designed to simultaneously remove particulate, SO₂ and NO from flue gas.     

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.     

A sustainable mediated electrochemical process for the abatement of NOx from simulated flue gas by using Ag(I)/Ag(II) redox mediators

Electrochemical removal of NO and NO₂ by using Ag(I)/Ag(II) redox mediator system in nitric acid medium by two-stage scrubbing process was investigated. Experiments were carried out for the complete removal of NO and NO₂ from the stimulated flue gas at room temperature and atmospheric pressure. The process parameters like current density, Ag(I) concentration, HNO₃ concentration, initial concentration of NO, Ag(I) concentration and temperature were studied and optimized. A removal efficiency of >99% was achieved using this sustainable redox process. Ag(II)/Ag(I) can be regenerated and reused for the scrubbing of waste gases continuously and there is no other gases emission during scrubbing.     

Removal of NO by using Fenton reagent solution in a lab-scale bubbling reactor

Removal of NO was studied in a lab-scale bubbling reactor. Effects of operation parameters such as pH value, H₂O₂ concentration, NO inlet concentration and reaction temperature on NO removal efficiency were investigated. The operation parameters included 250–1000 ppm NO, 0.5–1.5 mol/L H₂O₂, FeSO₄ 0.05 mol/L, 2–6 pH, 25–70 °C. As can be seen from the experimental results, pH value had a great impact on NO removal efficiency. The experimental results indicated that the gas–liquid reaction between NO and Fenton reagent solution was liquid-film controlled as NO inlet concentration exceeded 600 ppm. And NO removal efficiency decreased with increasing reaction temperature.     

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。     

Performance,optimization, and mechanism of nitric oxide removal by thiourea dioxide/FeIIEDTA reaction systems

In this work, a new innovative absorption system containing both thiourea dioxide (TD) and Fe^IIEDTA was used to NO removal. The independently influences of O₂ volume concentration, TD concentration, original pH value and absorbent temperature on NO removal in bubbling device were examined preliminarily. The results revealed that the NO removal efficiency firstly increased and then decreased with the increasing of the three independent variables (O₂ volume concentration, TD concentration and temperature). However, the NO removal efficiency monotonously increased to some extent with pH value increasing from 6.5 to 10.5. In addition, the respective effects of the four variables and the interactive function of them on NO removal were checked with the response surface methodology (RSM) by central composite design (CCD). The calculative model showed that pH value possessed a main positive independent impact on NO removal. Furthermore, the interactive effects between any two factors were expounded by the 3D surface and counter plots. Finally, the optimum absorption conditions for the maximum NO removal at 94.3% experimentally and 95.8% statistically were obtained in O₂ volume content of 6.0%, TD concentration of 0.02 mol·L⁻¹, original pH value of 10.5 and absorption temperature of 42 °C.     

Calcium magnesium acetate and urea advanced reburning for NO control with simultaneous SO2 reduction

Calcium magnesium acetate (CMA) shows potential as a reductant for simultaneous NO_x and SO_x removal from coal-fired combustion plant. The performance of urea co-injection with CMA on NO reduction in an ‘advanced reburn’ (AR) configuration has been investigated with a view to optimization of the process in a pulverized coal-fired furnace operating at 80 kW. The impact on SO₂ reduction has also been investigated. Urea/CMA solution was sprayed into the reburn zone of the furnace using twin-fluid atomizers over a range of reductant/NO stoichiometric ratios (NSR). The influence on NO reductions of primary zone stoichiometry (λ₁) was investigated for a range of CMA reburn feed rates (Rff) and reburn zone stoichiometry (λ₂). In addition, the effect of temperature on the SNCR performance of urea was investigated. Optimum process conditions were categorized either by maximizing NO and SO₂ reductions (Modes A and B, respectively) or maximizing reductant utilization efficiencies (Modes C and D). NO control was best performed at λ₁=1.05, but SO₂ reductions were greatest at more fuel-lean primary zone conditions (λ₁=1.15). Highest NO reductions of 85% under AR-rich conditions were achieved under Mode A, but were only slightly higher compared with reductions of 79% under Mode B, where SO₂ reductions were optimized at 85%. N-utilization was also at an acceptable level of 25% compared to the maximum utilization efficiency which was obtained at NSR=1.5 of 30% for the same conditions of stoichiometry operating in Mode C. Operation at this lower level of reburn (9.6%) could significantly reduce the consumption of CMA with some impact on NO reduction (73%). SO₂ removal performance would be compromised severely with reductions lowered from 75% at Mode A to 35% at Mode C. Optimizing Ca utilization (Mode D) resulted in poor NO and SO₂ reductions, at 61 and 22%, respectively, and can be discounted as a viable option. The technique offers flexibility of operation depending on the emission control requirements.     

Simultaneous Removal of NOx and SOx from Flue Gas of a Glass Melting Furnace using a Combined Ozone Injection and Semi-dry Chemical Process

In this study, we propose a plasma-chemical hybrid NO_x removal process using nonthermal plasma for the treatment of flue gases emitted from glass melting furnaces; the process is demonstrated through a laboratory-scale model experiment conducted using a semi-dry desulfurization apparatus. The performance of the system for simultaneous removal of SO₂ and NO_x is investigated. As a result, NO is effectively oxidized to NO₂ by injecting ozone into the spray region and the removal efficiencies of 90% and 50% were obtained for NO and NO_x, respectively. In addition, the SO₂ removal efficiency of 84% was achieved.