Pilot-Scale Experiment for Simultaneous Dioxin and NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Removal from Garbage Incinerator Emissions Using the Pulse Corona Induced Plasma Chemical Process

A pilot-scale pulse corona induced plasma chemical process (PPCP) reactor for controlling gas-phase dioxins and NO _x simultaneously is installed in a garbage incineration plant. The flow rate of the sampled flue gas is 5,000 Nm³/h (N: standard state) in maximum at the PPCP reactor, which consists of 22 wire-cylinder electrodes and is energized by a 50 kW nanosecond pulse high voltage generator. With an applied plasma energy density of 2.9–6.1 Wh/Nm³, the decomposition efficiency for dioxins is 75–84% based on TEQ (toxic equivalents); the conversion efficiency of NO to NO₂ is ~93% at maximum. The flue gas treated by the PPCP reactor is introduced at a rate of 50 Nm³/h to a wet-type chemical reactor, which uses an aqueous solution of sodium sulfite (Na₂SO₃). More than 90% of NO _x is reduced to nitrogen, with negligible byproducts such as NO₂ ⁻ or NO₃ ⁻ ions left in the solution.     

The Effect of Oxygen and Water Vapor on Nitric Oxide Conversion with a Dielectric Barrier Discharge Reactor

The effect of O₂ and H₂O vapor on the Nitric oxide (NO) removal rate, the NO₂ generation rate and the discharge characteristics were investigated using the dielectric barrier discharge (DBD) reactor at 1 atm pressure and at room temperature (20°). The results showed that the O₂ present in the flue gas always hampered the removal of NO and the generation of N₂O, but that the O₂ could enhance the generation of NO₂ in the NO/N₂/O₂ mixtures. Furthermore, with the increase of oxygen, the average discharge current gradually decreases in the reactor. The H₂O present in N₂/NO hindered the removal of NO and the generation of NO₂ but had no impact on the average discharge current in the reactor in the NO/N₂/H₂O mixtures in which the HNO₂ and HNO₃ was detected. The energy efficiency of the DBD used to remove the NO from the flue gas was also estimated.     

臭氧氧化结合湿法喷淋对玻璃窑炉烟气同时脱硫脱硝实验研究

采用臭氧氧化结合湿法喷淋对模拟玻璃窑炉烟气开展了同时脱硫脱硝实验研究.采用不同溶液(NaOH、Na₂S)进行了喷淋实验.结果表明,保证溶液pH值在10以上,NaOH浓度对NO_x脱除效率无影响,SO₂的存在促进了NO_x吸收.当O₃/NO物质的量比为1.6、溶液NaOH浓度为0.5%时,NO_x脱除效率可达70%,SO₂脱除效率在99%以上.往喷淋液中添加Na₂S,NO_x脱除效率随Na₂S浓度增加而提高,SO₂的存在对NO_x脱除效率无影响.当O₃/NO物质的量比为1.2、溶液中NaOH浓度为0.5%、添加剂Na₂S浓度为0.6%时,NO_x脱除效率可达70%,SO₂脱除效率在95%以上.60 min长时间运行实验证明,模拟烟气中的NO_x经碱液和添加剂吸收后主要以NO^-₂的形式存在于喷淋液中,且NO_x脱除效率不随溶液pH值的变化而变化.     

Dielectric Barrier Discharge for Ammonia Production

The leading after-treatment technology for NOx removal process in Diesel engines for stationary and mobile applications is the selective catalytic reduction of oxides of nitrogen [NOx] by ammonia [NH₃]. A novel non-thermal plasma electrode with a needle array in a dielectric barrier discharge reactor, powered by a high frequency neon transformer, is used for the thermal decomposition of solid urea [(NH₂)CO(NH₂)] to produce ammonia. The thermolysis of urea produces iso-cyanic acid [HNCO] as a byproduct, besides ammonia, which can react with water in the gas phase, thus giving carbon dioxide and more ammonia. The presence of water fed before and/or after the plasma reactor was studied to assess its effect on the amount of produced ammonia. Results clearly showed that water fed to the entrance of the reactor can efficiently promote the reaction of iso-cyanic acid to produce ammonia and this result can be improved when air is used as carrier gas for 115 V of input voltage to a neon transformer and with a gas flow rate of 4 L/min.     

尿素/H2O2溶液同时脱硫脱硝机理研究

在填料塔上对尿素/H₂O₂溶液同时脱硫脱硝进行了实验研究。结果表明,尿素溶液对SO₂具有很高的去除效率,但对NO_x的去除受到多种因素的影响。实验主要研究了H₂O₂浓度、吸收反应温度、溶液pH值等因素对脱硝效率的影响,并确定了最佳实验条件,在此条件下脱硫脱硝效率分别达到100%和52.6%。同时,采用化学分析法和气相色谱法对尿素溶液同时脱硫脱硝的反应产物进行分析,推导出尿素/H₂O₂溶液同时脱硫脱硝的反应机理和总化学反应方程式。该技术可用于对现有湿法脱硫技术的改造,使其同时具有脱硫脱硝功能。     

Simultaneous Removal of Nitrogen Oxides and Particulate Matters from Diesel Engine Exhaust using Dielectric Barrier Discharge and Catalysis Hybrid System

Dielectric barrier discharge (DBD) and catalysis hybrid process was used to remove nitrogen oxides and particulate matters from diesel engine exhaust. The DBD reactor converts a part of NO into NO₂, and then the exhaust gas containing the mixture of NO and NO₂ enters the catalytic reactor where both NO and NO₂ are reduced to N₂. The effect of energy density (power input divided by gas flow rate) and reaction temperature on the removal of nitrogen oxides was investigated with a stationary diesel engine. The hybrid process was able to remove about 80% of the initial nitrogen oxides at an energy density of 25 J/L and 150°C. The removal of particulate matters did not largely depend on the electrode structure, but it was a strong function of the energy density. On the basis of 80% removal efficiency, the energy yield for nitrogen oxides was 40 eV/molecule while that for particulate matters was 83 kJ/mg. The present study suggests that this kind of hybrid process can be applied to simultaneous removal of nitrogen oxides and particulate matters from diesel engine exhausts.     

Photocatalytic removal of nitrogen oxides from air on TiO<Subscript>2</Subscript> modified with bases and platinum

The efficiency of TiO₂ (Degussa P-25) modified with an alkaline admixture (urea, BaO), sulfuric acid, or platinum in the photocatalytic oxidation of NO (50 ppm) with a flowing 7% O₂ + N₂ mixture under UV irradiation in a flow reactor at room temperature and atmospheric pressure is reported. Because of the progressive blocking of active sites of the photocatalyst by the reaction products (NO₂, NO₃⁻), it is impossible to realize prolonged continuous removal of NO _x (NO + NO₂) from air without catalyst regeneration at elevated temperatures. The efficiency of the photocatalysts is characterized by specific photoadsorption capacity (SPC) calculated from the total amount of NO _x adsorbed during 2-h-long irradiation. Modification of TiO₂ with 5% BaO or 5% urea raises the SPC of the catalyst by a factor of 2–3. Presumably, this promoting effect is due to the basic properties of these dopants, which readily sorb NO₂ and NO₃⁻. A considerable favorable effect on SPC is also attained by adding 0.5% Pt to (5% BaO)/TiO₂. The SPC of the (0.5% Pt)/TiO₂ catalyst depends on the state of the platinum. The samples calcined in air at 500°C, which contain Pt⁺ and Pt²⁺, have an approximately 2 times higher SPC than unpromoted TiO₂ and ensure a much larger NO₂/NO ratio at the reactor outlet. Conversely, the samples reduced in an H₂ atmosphere at 200°C, whose platinum is in the Pt0 state, show a lower SPC than the initial TiO₂ and cause no significant change in the NO₂/NO ratio.     

Metal nitrate/fuel mixture reactivity and its influence on the solution combustion synthesis of γ-LiAlO<Subscript>2</Subscript>

The reactivity of LiNO₃ and Al(NO₃)₃ with respect to urea and β-alanine was investigated. Experimental results proved that β-alanine is a more suitable fuel for LiNO₃, whereas urea seems to be more adequate for Al(NO₃)₃. Based on the different metal nitrate/fuel mixture reactivity, nanocrystalline γ-LiAlO₂ powders were prepared by solution combustion synthesis using a fuel mixture of urea and β-alanine. This fuel mixture yielded single-phase nanocrystalline γ-LiAlO₂ (32.6 nm) directly from the combustion reaction. The resulted powder had a specific surface area of 3.2 m²/g and no supplementary annealing was required. On the other hand, pure γ-LiAlO₂ could not be obtained by using a single fuel (urea, β-alanine) unless annealing at 900 °C for 1 h was performed.     

多壁碳纳米管负载TiO2的光催化脱硝性能

采用溶胶凝胶法制备了多壁碳纳米管负载TiO₂ （MWCNTs/TiO₂）,并利用透射电镜、X射线光电子能谱、X射线衍射和紫外-可见漫反射光谱对样品进行了表征。结果表明,MWCNTs/TiO₂晶型以锐钛矿为主,MWCNTs的引入会限制TiO₂晶粒的生长。另外,MWCNTs/TiO₂的光吸收边向长波区域偏移。针对模拟烟气,在固定床光催化反应器中对采用涂覆处理的MWCNTs/TiO₂的光催化脱硝性能进行了实验研究。结果表明,NO初始浓度较低时,光催化脱硝效率较高,SO₂的存在可抑制光催化脱硝过程,而O₂及H₂O则有促进作用。在最佳实验条件（73 mg/m³ NO,8% O₂,5% H₂O）下,光催化脱硝效率可达46%。提出了光催化脱硝反应机理。     

The Effects of Gas Composition on Active Species and Byproducts Formation in Gas–Water Gliding Arc Discharge

The effects of gas composition on hybrid gas–water gliding arc discharge plasma reactor have been studied. The voltage cycles are characterized by a moderate increase in the tension which is represented by a peak followed by an abrupt decrease and a current peak in the half period (10 ms). Emission spectrum measurements revealed that ^•OH hydroxyl radicals are present in the discharge with feeding any gas. The H₂O₂ concentrations reach 38.0, 15.0, 10.0, and 8.0 mg/l after 25 min plasma treatment with oxygen, argon, air, and nitrogen, respectively. O₃ was produced when oxygen and air are used, but not when nitrogen and argon. The O₃ concentration reached the highest value 1.0 mg/l after 25 min plasma treatment with oxygen feeding gas, but gradually decreased to 0.2 mg/l after that. With feeding nitrogenous gas, NO₂ ⁻ and NO₃ ⁻ byproducts were formed by the plasma chemical process.     

By-Products NOx Control and Performance Improvement of a Packed-Bed Nonthermal Plasma Reactor

NO_x are main toxic by-products in the effluent gas whendecomposing volatile organic compounds in air by a packed-bed plasmareactor. Several types of materials such as 13X zeolite, BaTiO₃and Pd/Pt catalysts have been selected to be packed in the reactor, andmethane decomposition and NOx by-products in discharged gases areinvestigated at different range of reaction temperature and dischargeenergy density at atmospheric pressure. The ratios of methane decompositionpercentage/NO_x concentration are used to assess these packed bedmaterials and reaction conditions. The results show that usingPd/-Al₂O₃ with lower percentage Pd as packedbed, and discharging with lower discharge density at higher reactiontemperature can reduce NO_x output effectively and greatly improveperformance of the reactor.     

Removal of Model Pollutants in Aqueous Solution by Gliding Arc Discharge: Determination of Removal Mechanisms. Part I: Experimental Study

The respective roles of short and long-life oxidant species in the degradation of model organic pollutants in water have been investigated in a gas–liquid gliding arc plasma reactor. Three different model pollutants were treated in two configurations: direct discharge mode and spatial post discharge mode. In each case the pollutants were classified according to their ease of removal, from easier to more difficult to remove. The results were as follows: phenol >> 1-heptanol >> pCBA. The removal mechanisms also are different depending on the characteristics of the pollutant treated. Phenol (100 % of phenol was removed for energy density = 1.20 × 10⁵ J/L) was supposed to react strongly with NO₂° radicals produced by the dissociation of N₂O₄ in liquid phase. The degradation of 1-heptanol would proceed by desorption of the liquid phase to the gas phase, where oxidation occurs due to the plasma active short-lived species. In the case of pCBA, oxidation occurs in the liquid solution, but the degradation is low because of its low reactivity with species such as ozone and °NO₂ and insufficient production of OH° radicals in the solution.     

Chemical and Physical Characteristics of Pulsed Electrical Discharge Within Gas Bubbles in Aqueous Solutions

The chemical and physical characteristics of pulsed electrical discharge within gas bubbles immersed in an aqueous solution were investigated using a reactor with long protrusion length high voltage needle electrodes. Argon gas was introduced at the base of the needle electrode causing gas bubbles to flow upwards in contact with the needle. The effects of needle protrusion length were evaluated by using 2, 4, and 6 cm length needles under a wide range of power input (3–78 W). No significant differences in chemical or electrical characteristics were found among the different protrusion lengths. H₂ and H₂O₂ generation rates were proportional to input power and the energy yield efficiency for these species was not affected dramatically by input power. The results of discharge within bubbles in aqueous solution were also compared with those for direct liquid phase discharge and gas phase discharge above the liquid surface.     

The effect of Pt oxidation state and concentration on the photocatalytic removal of aqueous ammonia with Pt-modified titania

Platinum-modified titanium (IV) oxide (Pt-TiO₂) was used to photocatalytically oxidize aqueous ammonia selectively to nitrogen gas. The photocatalyst was solvent deposited on acrylic (PMMA) supports for use in simple distributive reactors. Pt was photodeposited on the titania surface within each reactor with concentrations ranging from 0.4% (w/w) to 5.1% (w/w) Pt. The oxidation state of the deposited Pt was subsequently modified using reduced phosphotungstic acid. Time-dependent kinetic studies were used to demonstrate the effect of oxidation state on the photocatalytic activity of the Pt-TiO₂. It was determined that treatment with reduced phosphotungstic acid enhanced the reaction rate and selectivity to nitrogen gas of the Pt-TiO₂ photocatalysts. Most significantly, treatment of Pt-TiO₂ with reduced phosphotungstic acid shifts the optimum Pt concentration to higher Pt loadings. The reactor containing 3.2% (w/w) post-treated Pt demonstrated the most favorable combination of NH₃ degradation rate and selectivity to N₂, resulting in the removal of 28.34% total nitrogen from 1.7 L of a 45.5 ppm NH₃-N solution within 72 h.     

Electron beam treatment of high NOx concentration off-gases

High concentration of NO_x removal from simulated off-gases was investigated using electron beam (EB) technology. Simulated off-gases were prepared by combusting Polish light oil or nature gas with addition of NO from a NO gas cylinder. Irradiation was carried out under a ILU-6 accelerator. It was found that removal efficiency of NO_x was influenced by inlet concentration of NO, temperature, SO₂ concentration, absorbed dose and irradiation dose rate. Methods of enhancing NO_x removal efficiency with additives using EB were also discussed.     

Photodegradation of humic acid using spherical activated carbon contained Zn in a fluidized bed system

In this study, a strong acid ion-exchange resin, as the starting material of spherical activated carbon contained Zn (Zn-SPAC), was treated by 0.1 N zinc solution. Ion-exchange treatment was performed from one to three times for controlling the zinc content. The ion-exchanged resins were activated under N₂/H₂O vapor atmosphere at 900°C for 0.5 h, followed by carbonization treatment at 700°C under N₂ atmosphere. The Zn-SPAC samples were measured for their physicochemical characteristics, such as X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) images, electron probe micro analyzer (EPMA) images, energy dispersive X-ray spectroscopy (EDXS), Brunauer–Emmett–Teller (BET) specific surface area, strength, and zinc content. Also, the samples were used in order to measure photochemical activities, such as the removal efficiency of humic acid (HA) in a fluidized batch reactor. The XRD patterns appeared as the ZnS type. The Zn-SPAC had a large BET specific surface area and their shape was spherical, with a diameter of about 350–400 μm. When the Zn-SPAC was dosed in a fluidized bed reactor with UV light, the HA removal efficiency increased by up to 60%. On the other hand, the HA removal efficiency by only UV-C (λ _max = 254 nm) irradiation was very low, about 15%. Therefore, we infer that Zn-SPAC has good photochemical activity and presented the possibility of being a useful photocatalyst for water purification.     

The Stability of Accumulating Nitrite from Swine Wastewater in a Sequencing Batch Reactor

Shortcut nitrification is the first step of shortcut nitrogen removal from swine wastewater. Stably obtaining an effluent with a significant amount of nitrite is the premise for the subsequent shortcut denitrification. In this paper, the stability of nitrite accumulation was investigated using a 1.5-day hydraulic retention time in a 10-L (working volume) activated sludge sequencing batch reactor (SBR) with an 8-h cycle consisted of 4 h 38 min aerobic feeding, 1 h 22 min aerobic reaction, 30 min settling, 24 min withdrawal, and 1 h 6 min idle. The nitrite production stability was tested using four different ammonium loading rates, 0.075, 0.062, 0.053, and 0.039 g NH₄-N/g (mixed liquid suspended solid, MLSS) day in a 2-month running period. The total inorganic nitrogen composition in the effluent was not affected when the ammonium load was between 0.053 and 0.075 g NH₄-N/g MLSS · day (64% NO₂-N, 16% NO₃-N, and 20% NH₄-N). Under 0.039 g NH₄-N/g MLSS · day, more NO₂-N was transformed to NO₃-N with an effluent of 60% NO₂-N, 20% NO₃-N, and 20% NH₄-N. The reducing load test was able to show the relationship between a declining free nitrous acid (FNA) concentration and the decreasing nitrite production, indicating that the inhibition of FNA on nitrite oxidizing bacteria depends on its levels and an ammonium loading rate around 0.035 g NH₄-N/g MLSS · day is the lower threshold for producing a nitrite dominance effluent in the activated sludge SBR under the current settings.     

High-capacity NO2 denuder systems operated at various temperatures (298–473?K)

In this study, we investigated several coatings for high-temperature, high-capacity, and high-efficiency denuder-based NO₂ removal, with the scope to face the harsh conditions and requirements of automotive exhaust gas sampling. As first coating, we propose a potassium iodide (KI)/polyethylene glycol coating with a high removal efficiency (ε?>?98?%) for about 2?h and 50?ppm NO₂ at room temperature (298?K). At elevated temperatures (423?K), the initial capacity (100?ppmh) is decreased to 15?ppmh. Furthermore, this is the first proposal of the ionic liquid methyl-butyl-imidazolium iodide ([BMIm⁺][I^?]) as denuder coating material. At room temperature, this ionic liquid exhibits far greater capacity (300?ppmh) and NO₂ removal efficiency (ε?>?99.9?%) than KI. Nevertheless, KI exhibits a slightly (~10?%) higher capacity at elevated temperatures than [BMIm⁺][I^?]. Both coatings presented are suitable for applications requiring selective denuding of NO₂ at temperatures up to 423?K.     

Posttreatment of Olive Mill Wastewater by Immobilized TiO2 Photocatalysis

A photocatalytic reactor with UV/TiO₂ was used for the posttreatment of olive mill wastewater after anaerobic digestion. A factorial experimental design was adopted to determine the statistical significance of each parameter tested, namely, initial chemical oxygen demand (COD), pH, treatment time and recirculation flow and possible interactions in three response variables: phenols, color and COD removals. Removal efficiencies of 90.8 ± 2.7%, 79.3 ± 1.9% and 50.3 ± 6.3% were obtained for total phenols (TPh), color and COD respectively. TPh and color were almost completely removed after 24 h of treatment, while the COD removal was partial. Because increasing the treatment time is economically unfeasible a recirculation to the anaerobic reactor should be considered. Regarding the most significant variables, the TPh removal efficiency is dependent of the initial COD concentration; the color removal efficiency decreased with increasing COD concentration and pH; and, the COD removal efficiency is directly linked with the treatment time. The interaction between the initial COD and treatment time affect negatively the response variables tested because of the inactivation of some active sites of the TiO₂ paper.     

Activated carbon prepared by physical activation of olive stones for the removal of NO2 at ambient temperature

Activated carbon was prepared from olive stones by physical activation using water vapor at 750 °C. Textural, morphology and surface chemistry characterizations were achieved (nitrogen adsorption, SEM, FTIR and TPD–MS). NO₂ adsorption was performed for different inlet gas compositions and temperatures. NO₂ may adsorb directly on the oxygenated surface groups, and can also be reduced to NO. Therefore, a second NO₂ molecule adsorbs on the oxygen left on the carbon surface. TPD performed after NO₂ adsorption showed the presence of various surface groups. The adsorption capacity was about 131 mg/g, which is higher than with several activated carbon prepared from classical lignocellulosic biomass. NO₂ reduction into NO decreased with increasing the inlet oxygen concentration. In contrast, a slight decrease in the NO₂ adsorption capacity was observed with increasing temperature. It seems that the activated carbons prepared from olive stones by steam activation could be used as efficient adsorbents for NO₂ removal.