温度与氧气浓度对NH3还原NO特性耦合影响研究

为揭示烟气温度和氧浓度对NH₃还原NO过程的影响，通过对3种典型氮氧化物机理模型的对比与验证，选取Glarborg1998机理模型对不同温度(800～1 600℃)及O₂浓度下NH₃还原NO反应进行化学反应动力学研究.结果发现：在一定O₂浓度条件下，NH₃还原NO过程仅在一定温度窗口内才能获得较高的脱硝效率，这主要是由于H能与O₂反应生成O、OH以促进NH₃分解生成NH₂，保证NH₂还原NO；温度过高会促进NH₂氧化，导致脱硝效率降低.高温条件下O₂浓度降低时，虽然抑制了OH基团的形成，但H与CO₂、H₂O反应生成OH的反应速率明显增大，促进了NH₂的生成及其对NO的还原；同时，O₂浓度降低也抑制了NH₂氧化生成NO的反应，使得高温还原性气...     

柴油机排气组分对低温等离子体转化NO的影响

自制了介质阻挡放电型低温等离子体反应器,设计了低温等离子体柴油机模拟排气处理系统,研究了低温等离子体作用下O2、C3H6和水蒸气对NO氧化转化的影响及NO在N2中的还原转化.研究表明:NO在N2气氛中的还原转化率低,能耗大;模拟气中存在O2时,NO向N2的还原转化率降低,NO向NO2的氧化转化率大幅提高;排气中的H2O在低温等离子体作用下生成OH强氧化性粒子,促进NO向NO2的氧化转化;HC的存在可提高NO向NO2的氧化转化,并能有效降低NO向NO2的转化能耗.总之,在柴油机富氧排气环境中,低温等离子体很难直接将NO转化为N2,但可有效地将NO氧化为NO2及硝酸盐,为催化剂催化还原NOx创造条件.     

H2O2作添加剂对SNCR脱硝工艺的影响

为了改善选择性非催化还原(SNCR)脱硝工艺的反应特性,以H2O2为添加剂,对SNCR过程进行了实验研究。在小型SNCR实验台上进行实验,以N2作为载气,以纯NO模拟NOx气氛,初始NO浓度为360μL/L,O2=4%,H2O=8%,NSR=1.5。通过对实验结果进行分析,得到H2O2对低温下的脱硝率有促进作用,对最大脱硝率以及最佳脱硝温度没有影响,最大脱硝率依然为80%左右,最佳脱硝温度为925℃。另外还分析了H2O2对NH3浓度、HNCO浓度、NO2浓度、N2O浓度以及N2转化率的影响及其原因。     

分解炉内贫氧高CO2燃烧条件下挥发分NO生成机理

基于GRI3.0详细动力学反应机理数据库,采用生成速率分析方法,从化学反应动力学角度分析水泥分解炉内煤粉挥发分贫氧燃烧时低温、高浓度CO2条件下挥发分NO生成机理及挥发分中HCN转化生成NO的主要转化路径.分析结果表明,煤粉在过量空气系数为0.8的贫氧燃烧条件下,分解炉内高浓度CO2气氛会促进NO生成,增大NO的排放浓度;850～950℃温度范围内,CO2体积分数为0%～35%条件下挥发分NO生成的主要机理反应式为N+O2(→)NO+O、HNO+H(→)H2+NO和N+CO2(→)NO+CO;高体积分数CO2通过推进反应FINO+H(→)H2+NO和N+CO2(→)NO+CO促进NO生成;其中HNO是NO生成过程中最重要的活性含氮中间产物,对NO生成起主要的贡献作用;HCN氧化生成NO的主要反应路径为HCN先转化生成NHi,再进一步转化生成HNO活性含氮中间体,最终生成NO.     

Oxy-Steam燃烧方式下的NO生成特性

以甲烷掺混氨气为燃料对oxy-steam气氛下NO生成特性进行实验和模拟研究.在常压柱塞流反应器中开展了一系列O_2/N_2和O_2/H_2O气氛的对比实验,当量比从富燃至贫燃(1.6、1.0、0.2),温度范围为973~1,773,K.实验结果表明,O2/H_2O气氛下高浓度的水蒸气在当量和贫燃工况下抑制NO的生成,而在富燃工况下促进NO生成.更新并构建的详细化学机理能够很好地重现并解释实验中NO的生成特性.当量和贫燃工况下,极少的O基团抑制了反应NH_2+O H+HNO从而抑制了NH_2→HNO→NO反应路径,最终降低了NO的生成.富燃工况下,充足的OH基团显著促进了反应NH_2+OH=NH+H_2O从而促进了NH_2→NH→HNO→NO反应路径,最终增加了NO的生成.     

N2O在锰系低温催化剂上的生成途径

实验对比了由浸渍法、共沉淀法以及溶胶凝胶法制备的锰系低温催化剂在选择性催化还原(SCR)反应中的差异,发现溶胶凝胶法制备的催化剂在整个测试区间内都具有最高的脱硝效率,但是也有最多的 N2O 生成。针对溶胶凝胶法,进一步研究了N2O在SCR过程中的生成情况。发现N2O主要来源于NH3的直接氧化以及NH3和NO的反应,后者为N2O的主要生成途径。添加Ce、V后,随着反应温度升高,NH3的直接氧化逐步成为N2O主要来源。     

烟煤添加氮还原剂再燃脱硝过程中N2O的生成特性

在淮南烟煤中浸渍添加尿素和(NH4)2SO4,研究复合再燃脱硝过程中N2O的生成特性.再燃实验在石英固定床反应器上进行,温度范围为800～1 200 ℃.研究发现,复合再燃过程中,再燃和氮还原剂脱硝都会部分将NO转化成N2O,因此NO被还原的程度越大,N2O的排放浓度越高.氮还原剂的添加量越大,生成的N2O浓度越高,而添加尿素时的N2O排放量比添加硫酸铵时大得多.从NO转化成N2O的比例来说,使用氮还原剂添加量不大的情况下,与原煤再燃的N2O排放比例比较接近.随着反应器的温度的升高,N2O排放量迅速降低.低氧浓度亦有利于减少NO向N2O的转化.     

CO对NH3还原NO过程的影响与机理研究

为揭示CO对NH₃还原NO过程的影响,在不同CO体积分数下对NH₃还原NO过程进行了实验与模拟研究。实验结果表明：无氧气氛中存在CO时,对1 400℃以下NO还原率无显著影响;CO可提高1 400℃以上的NO还原率。在低氧体积分数条件下,CO的存在能扩展NH₃还原NO反应的温度窗口,使其在1 400℃以上仍保持高NO还原率。在高氧体积分数条件下,CO仅使最佳脱硝温度向低温移动,并使脱硝温度窗口变窄。模拟结果表明：在无氧及低氧体积分数条件下,1 400℃以上时CO可促进NH₂与CO反应生成HNCO,随后HNCO转化为NCO后将NO还原,增强了NO还原过程;高氧体积分数条件下,CO可在较低温度下促进OH、O等基团产生,保证NH₂生成及其还原NO过程进行;但温度升高会加快CO与OH反应产生H,H与O₂反应产生大量O,加速了NH₂氧化,导致NO还原率迅速降低。     

船舶尾气臭氧氧化-海水吸收的脱硫脱硝新工艺研究

通过模拟试验研究了臭氧氧化结合海水吸收同时脱除船用发动机排气中SO2和NO2的新工艺.在管式反应器内研究了反应温度、n(O3)/n(NO)(物质的量之比)、碳氢、SO2等对臭氧氧化NO的影响,并对模拟尾气进行了臭氧氧化结合海水吸收的脱硫脱硝试验.结果表明,n(O3)/n(NO)对臭氧氧化NO影响很大,NO氧化率随n(O3)/n(NO)呈线性增长,n(O3)/n(NO)为1,反应温度分别为常温、150℃和200℃时,NO氧化率分别达到99.0%、98.3%和98.1%;反应温度低于200℃时,温度对臭氧氧化NO影响很小,而当反应温度升至275℃时,NO氧化率明显下降,这与臭氧在较高温度下分解有关;SO2在O3/NO/SO2/N2/O2体系和O3/NO/C2H4/SO2/N2/O2体系中对臭氧氧化NO都没有影响;200℃以下,C2H4对臭氧氧化NO影响很小,而在275 ℃时,C2H4对臭氧氧化NO有一定促进作用;模拟尾气经臭氧氧化-海水吸收后,脱硫率为98.5%,n(O3)/n(NO)为1时的脱硝率为91.05,NO能耗为56.4 g、(kW·h).     

当量比天然气发动机氨排放特性研究

采用傅里叶变换红外线光谱仪研究了当量比天然气发动机的N H3排放,重点研究了不同工况下三元催化器(three-way catalyst,TWC)前的NOx、CO、CH4排放特性和TWC后的NH3排放特性.结果表明:当量比天然气发动机原始排气中无NH3排放,发动机原始排气经过TWC后的催化反应才是当量比天然气发动机NH3...     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

Contents in Volume 23,2014

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汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.