Time dependence of NOx removal rate by a corona radicalshower system

In this paper, the effects of flue gas flow rate and seed gas on the dynamics of corona discharge current-voltage characteristics and NO _x removal characteristics are experimentally investigated for a corona radical shower system. The corona discharge current-voltage characteristics have two operating modes which have a significant influence on NO_x removal characteristics, where the threshold value of the treatment gas to seed gas flow rate ratio is about 8. The hysteresis of corona current-voltage characteristics is observed in this system. For longer operational time, corona current and NO_x removal rate significantly changes with time. When the operation of the apparatus starts at relatively low applied voltage, the corona current under constant applied voltage increases with time to reach a maximum value, then decreasing with time to reach a steady state. At this condition, high NO_x removal efficiency can be achieved     

NOx removal process using pulsed discharge plasma

Nonequilibrium plasma can be used to promote chemical reactions that reduce the emission of gaseous pollutants, such as NO_x, produced by coal-burning power plants or by diesel engines. Laboratory experiments were carried out to study the decrease of NO_x in simulated flue gases (initial concentration of NO: 200-800 ppm, O₂ : 10%, N₂-balance gas) by means of a pulsed discharge plasma generated in a cylinder type reactor (outer electrode: 20-mm diameter). A rotating spark gap provided square wave high-voltages up to 25-kV, at a frequency of 250 Hz, to corona electrodes of 0.1-, 3.3-, and 6.4-mm diameter. The tests were performed at various temperatures (ambient to 220°C) and constant residence time (0.6 s). The removal performance depended on the size of the discharge electrode and was better at room temperature. The addition of C₂H₄ significantly enhanced the removal performance, concentration of NO_x decreased from 800 ppm to 300 ppm in the discharge. The by-products of this process were analyzed using infrared spectroscopy. No traces of toxic gases could be detected     

利用NaClO2/CaCO3浆液同时脱硫、脱硝的试验研究

在筛板式喷淋塔内,利用NaClO2/CaCO3浆液同时进行脱硫、脱硝试验.分析入口NO浓度、NaClO2加入量、浆液pH值、液气比、入口SO2浓度等因素对脱硫、脱硝效率的影响.结果表明,SO2的脱除效率随液气比的增大而升高,随入口SO2浓度的升高略有降低;入口NO浓度、NaClO2加入量、浆液pH值的变化对SO2的脱除效率影响甚微;NO的脱除效率随NaClO2加入量、液气比和入口SO2浓度的增大而升高,随入口NO浓度的增大而降低,浆液pH值的变化对脱硝效率影响甚微.     

SO2/NOx control compliance with environmentalregulations

The sources of SO₂ and NO_x in a Portland cement kiln system are identified. A brief discussion of several known and theoretical control methods for cement-plant SO₂ and NO _x emissions is presented. The US Portland cement industry is shown to be a minor contributor of SO₂ and NO_x to atmospheric contamination. The anticipated need and/or requirement for continuous monitoring of SO₂ and NO_x is discussed. The political climate for regulation of SO₂ and NO_x is examined. Consideration is given to an emerging environmental issue, the greenhouse effect, to which the carbon dioxide emissions of cement plants may contribute     

Low NOx thermophotovoltaic generator

Fiber matrix burners incorporating “superemissive” ceramic materials were tested to obtain the relationship between power generation and the pollutant emissions. The tested variables were the following: equivalence ratio, fuel input, and inlet air temperature. One important objective was to achieve maximum efficiency of electricity generation at the lowest level of NO_x emissions. It was found that NO_x emission under these specific conditions does not depend on inlet air temperature in the ranges from 20 to 200°C. This phenomena suggests that “thermal NO_x” is not a significant contributor of NO_x emission in these types of burners. The test data indicate that the thermophotovoltaic (TPV) power output increased by a factor of 2 by increasing the combustion temperature while the NO_x emissions were stable. The result of these findings is that high efficiency, low polluting TPV-power generation is feasible. The basic technology responsible for the low NO _x emission and the electric power generation is being further developed for use in high-efficiency appliances, generators, and total energy systems     

Industrial experiments on pulse corona simultaneous removal of NOx and SO2 from flue gas

The corona-induced simultaneous removal of NO_x and SO ₂ from flue gas is based on the application of narrow voltage pulses to an electrode structure similar to that of an electrostatic precipitator. The free electrons of the corona discharge, having energy up to 20 eV, originate active radicals which lead to the transformation of NO_x and SO₂ into their acids which can be neutralized to salt particulate by adding to the gas a basic compound such as ammonia and calcium hydroxide. The process has been investigated with a test rig installed in the slipstream of the flue gas duct of a coal-fired thermal power plant. The experiments were performed with three reactor modules of different geometries. Further experiments are necessary to assess the effect of different electrode geometries of the reactor, the efficiency of the process attainable with an improved coupling of narrow pulse power set to the reactor, and the practical ways for integrating the DeNO_x and DeSO₂ corona process with the solid particle collection system     

Control of NOx by positive and negative pulsed coronadischarges

The pulse-induced plasma chemical process (PPCP) is a novel means of processing with great potential in various applications including the removal of NO, SO₂, HCl, and Hg vapor and other gaseous pollutants from combustion gases, the composition of gaseous and solid substances, the production of ultrafine particulate materials, the treatment of surfaces, etc. An investigation of the DENOX and DESOX of combustion gas by PPCP was conducted, confirming that DENOX is possible by both positive and negative pulsings and DESOX only by positive pulsing. NO is oxidized by PPCP to NO₂, which is removed again by PPCP. The reaction speed for PPCP with positive pulsing is more than one order of magnitude higher than that with negative pulsing applicable to electrostatic precipitators. The reaction speed is greatly enhanced by raising the peak field intensity, which requires the use of a very sharp pulses. The speed is also enhanced by raising pulse frequency, lowering the gas temperature, and using sharp corona wires. The oxidation of NO and removal of NO₂ can proceed without O ₂ and moisture, but is greatly enhanced by them. The addition of NH₃ also enhances NO₂ removal, possibly by its NO₂-scavenging effect from the gas phase, while it does not enhance NO oxidation. The combination of PPCP with the electron-beam DENOX and DESOX does not produce a nonlinear enhancing effect beyond the independent effect of PPCP alone     

EXPERIMENTAL STUDY ON N2O AND NOx EMISSION

在一直径为Φ22mm的小型燃煤循环流化床内,通过调节给煤点的位置、分级燃烧以及注入二次风的高度,向床内注入碳氢燃料,研究N     

低NOx燃烧技术在高井发电厂的应用

根据燃煤锅炉煤粉燃烧过程中NOx生成的机理,高井发电厂锅炉燃烧设备的实际情况,着重阐述了高井发电厂1～4号炉低NOx燃烧器的设计、安装、使用及NOx排放达标情况.     

Reduction of NOx emissions from a dry process preheaterkiln with calciner through the use of the urea-based SNCR process

The post combustion reduction of NO_x using urea has proven to be an effective method in controlling NO_x from various combustion sources, such a reduction process has been successfully demonstrated in a week-long test at Ash Grove's dry process cement kiln system located in Seattle. This system is equipped with planetary coolers, a 5-stage preheater and an air-through-the-kiln calciner. Testing was done under ten different kiln/calciner operating conditions. Using three to four injectors, NO_x was efficiently reduced from 350-600 lb per hour lb/ton of clinker to less than 100 lb per hour. This calculates to a NO_x reduction of greater than 80% for most cases. Chemical utilization was greater than 50% percent. A high degree of mixing and a long residence time at an appropriate temperature present in the preheater tower contributed to these excellent results. An average ammonia slip was four ppm above a baseline level at a normalized stoichiometric ratio of 1. This demonstration confirms expectations that dry process cement kilns with 4+ preheater stages are an ideal application for the selective noncatalytic reduction of NO_x with urea. NO_x was efficiently and effectively reduced with minimal byproduct emissions and virtually no effect on plant operations     

A novel plasma reactor for NOx control usingphotocatalyst and hydrogen peroxide injection

The authors have developed a new type of plasma reactor combining discharge plasma with a photocatalyst (TiO₂) which improves the performance of NO_x removal. This reactor is designated as a plasma-driven catalyst (PDC) reactor. The authors found that hydrogen peroxide (H₂O₂) is a very effective additive in this PDC reactor and the formation of undesirable by-product (such as O ₃, N₂O) was reduced significantly. Comparative test results showed that the combination of discharge plasma with TiO ₂ catalyst is a very effective method in NO_x, removal over a conventional wire-cylinder reactor. NO_x was effectively oxidized to HNO₃ on the TiO₂ catalyst and trapped on the catalyst surface. Specific energy consumption of this de-NO_x process is significantly reduced, in particular, with the injection of H₂O₂     

Reduction of NOx from combustion flue gases bysuperimposed barrier discharge plasma reactors

NO_x reduction from combustion flue gases by superimposed barrier discharge plasma reactors is experimentally investigated. The experiments are conducted for applied voltages from 0 to 28 kV, flue gas rates from 0.5 to 2 L/min, ammonia mixture concentrations from 0.7 to 2.65 stoichiometry, and applied voltage phase differences from 0° to 180°, where two 60-Hz AC power supplies are used. The results show the following: (1) NO_x reduction rate decreases with increasing discharge power for surface discharge operations, however, NO_x reduction rate increases with increasing discharge power for silent and superimposing discharge operating modes; (2) NO_x reduction rate increases with increasing discharge power, gas flow rate and ammonia stoichiometry under in-phase operations; (3) NO_x reduction rate for out-of-phase operations is much higher compared with in-phase operations, however, NO_x reduction rate has an optimum condition on ammonia stoichiometry, discharge power, and gas flow rate; and (4) energy efficiency of NO_x reduction increases with increasing ammonia mixture and gas flow rate and decreases with increasing discharge power     

The effect of NOx regulations on emissions dispatch: aprobabilistic production costing analysis

The effect of NO_x emission restrictions on the cost of power generation is shown using the Bloom-Gallant model for production costing simulation. For this case study, it is found that tonnage caps provide a more cost-effective way to meet emission goals than lb/MBtu rate limiting policies. The inefficiency of rate limits is due to its encouragement of fuel use (“Btu dilution”) and to a reduction of cost-effective energy transactions. Emissions dispatch is confirmed as an economical technique for NO_x compliance. However, the cost-effective range of emissions dispatch is significantly reduced under lb/MBtu regulation, especially when the power system has large opportunities for trading energy     

Two-dimensional imaging of NO density profiles by LIF technique in a pipe with nozzles electrode during NO treatment

Two-dimensional NO concentration distribution was studied by a planar laser-induced fluorescence (PLIF) technique in nonthermal plasma during NO treatment. A pipe with a nozzles-to-plate electrode system, having an electrode gap of 50 mm, was used. A stable DC streamer corona discharge was generated in an NO/air mixture at atmospheric pressure. Laser pulses in the form of a sheet were shot between the electrodes during the discharge. LIF signal emitted at 90/spl deg/ to the laser sheet was imaged onto a gated-ICCD camera and two-dimensional distributions of NO concentration in the reactor were measured as a function of time during NO treatment. NO concentration was also monitored at the reactor outlet. The images of NO concentration covering almost the whole length of the reactor show that the density of NO molecule decreased not only in the plasma region formed by corona streamers but also in the upstream region of the reactor. This information is important for modeling and optimizing the plasma processes and designing the nonthermal plasma reactors.     

燃气轮机启动过程中减少NOx排放量的优化改造

针对9F燃气轮机在启动过程中,点火后普遍存在低负荷阶段NO_x排放量超标问题,分析其原因,对主蒸汽系统进行了技术改造,对GE S109FA-SS燃气轮机热态启动过程进行优化操作。结果表明:该操作方法优化后,燃气轮机在启动过程中NO x 排放量大幅下降,低负荷阶段冒黄烟的时间缩短了近30 min,由此改善了环保指标,进一步提升了企业在市场中的竞争力。     

华能大连电厂低NOx旋流燃烧器及燃烧优化

该文对安装在华能大连电厂二期工程2×350MW机组锅炉的三井巴布科克低NOx旋流燃烧器的设计特点进行了剖析,结合锅炉燃烧优化试验对低NOx旋流燃烧器的性能进行评价,对存在的问题进行了探讨.图2表2     

Negative corona in air using a point/cup electrode system

Calculations and simulations of potential and charged-particle distributions have been made by various workers for single pulses along the axis of point/plane electrode systems but not for the overall current. The difficult geometry makes this inevitable. In this paper the authors describe measurements of corona currents in air using a high-symmetry `point/cup' electrode system comprising a hemispherical-tipped point which is concentric with a concave hemispherical electrode; and simulations based on a spherically symmetric geometry. The simulations assumed avalanches to originate from the random release of electrons in the inter-electrode gap. The predicted onset voltages and the shape of the experimental curves for corona current vs. Voltage were in good agreement with the experimental results over a range of point-tip radii (0.5 to 3 mm) and pressures (0.02 to 0.10 MPa). Space charge effects were not included in the simulation so it follows that the accumulation of space charge is negligible at the onset voltage in air, although it is likely that it will have an increasing effect as the voltage increases     

Positive corona in air using a point/cup electrode system

The authors have previously published some measurements of negative corona currents in air using a spherically-symmetric point/cup electrode system, and also the related simulations. In this paper the corresponding current/voltage measurements and simulations for positive-point corona, again using the highly symmetric electrode system, are described. Although the corona onset voltages are again predicted with reasonable accuracy for different point radii and air pressures, the currents are very much lower, presumably due to the effect of positive space charge accumulating close to the point electrode (since the simulations assume the absence of space charges). In agreement with this assumption, the streamer pulses are only seen at or just above the onset voltage. Only avalanches occur from about 1 kV above the onset voltage.     

煤粉锅炉分级燃烧降低NOx排放的试验结果分析

通过对乌拉山电厂WGZ410/100-12型锅炉分级燃烧技术改造后的优化调整试验结果的分析,指明了燃尽风份额、二次风沿炉膛断面的分布、锅炉负荷、三次风投停等因素对炉内NO     

Influence of reactive SFx gases on electrode surfacesafter electrical discharges under SF6 atmosphere

A simulation of different electrical discharges under SF₆ atmosphere with subsequent surface and depth profile analysis is employed to investigate the effects that the formed corrosive byproducts have on gas-insulated system (GIS) electrodes. Cu, Al and Ag electrodes were treated with sparks (in the range of 0.15 J/spark) in an SF₆ discharge cell under various conditions at the Institut fur Spektrochemie und Angewandte Spektroskopie (ISAS) in Dortmund. The same materials were exposed to SF₆ in a GIS test compartment in which partial discharge (PD) occurred (Itaipu, Brazil). The treated materials were analyzed with energy dispersive X-ray (EDX) in a scanning electron microscope, X-ray photoelectron spectroscopy and high frequency (HF) plasma secondary neutral mass spectrometry (SNMS). The SNMS depth profiles were calibrated in order to quantify that part of the corrosive gaseous products having reacted with the solid material. The analysis of the electrodes exposed to the stressed SF₆ atmosphere show surface reaction only in the topmost nm, whereas with sparks, sulfur (S) and especially fluorine (F) compounds are detected to ~40 μm depths. A first comparison between surface analysis and Fourier transform infrared (FTIR) measurements of the reactive gaseous products indicates a correlation of SF₆ decomposition and the extent of electrode degradation